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Kuva J, Sammaljärvi J, Parkkonen J, Siitari-Kauppi M, Lehtonen M, Turpeinen T, Timonen J, Voutilainen M. Imaging connected porosity of crystalline rock by contrast agent-aided X-ray microtomography and scanning electron microscopy. J Microsc 2017; 270:98-109. [PMID: 29071713 DOI: 10.1111/jmi.12661] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 09/27/2017] [Accepted: 10/02/2017] [Indexed: 11/28/2022]
Abstract
We set out to study connected porosity of crystalline rock using X-ray microtomography and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) with caesium chloride as a contrast agent. Caesium is an important radionuclide regarding the final deposition of nuclear waste and also forms dense phases that can be readily distinguished by X-ray microtomography and SEM-EDS. Six samples from two sites, Olkiluoto (Finland) and Grimsel (Switzerland), where transport properties of crystalline rock are being studied in situ, were investigated using X-ray microtomography and SEM-EDS. The samples were imaged with X-ray microtomography, immersed in a saturated caesium chloride (CsCl) solution for 141, 249 and 365 days and imaged again with X-ray microtomography. CsCl inside the samples was successfully detected with X-ray microtomography and it had completely penetrated all six samples. SEM-EDS elemental mapping was used to study the location of caesium in the samples in detail with quantitative mineral information. Precipitated CsCl was found in the connected pore space in Olkiluoto veined gneiss and in lesser amounts in Grimsel granodiorite. Only a very small amount of precipitated CsCl was observed in the Grimsel granodiorite samples. In Olkiluoto veined gneiss caesium was found in pinitised areas of cordierite grains. In the pinitised areas caesium was found in notable excess compared to chloride, possibly due to the combination of small pore size and negatively charged surfaces. In addition, elevated concentrations of caesium were found in kaolinite and sphalerite phases. The findings concerning the location of CsCl were congruent with X-ray microtomography.
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Affiliation(s)
- J Kuva
- Department of Physics, University of Jyväskylä, Jyväskylä, Finland.,Department of Chemistry, University of Helsinki, Helsinki, Finland
| | - J Sammaljärvi
- Department of Chemistry, University of Helsinki, Helsinki, Finland
| | - J Parkkonen
- Department of Physics, University of Jyväskylä, Jyväskylä, Finland
| | - M Siitari-Kauppi
- Department of Chemistry, University of Helsinki, Helsinki, Finland
| | - M Lehtonen
- Geological Survey of Finland, Espoo, Finland
| | - T Turpeinen
- VTT Technical Research Centre of Finland Ltd, Jyväskylä, Finland
| | - J Timonen
- Department of Physics, University of Jyväskylä, Jyväskylä, Finland
| | - M Voutilainen
- Department of Chemistry, University of Helsinki, Helsinki, Finland
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Ekman A, Miettinen A, Tallinen T, Timonen J. Contact formation in random networks of elongated objects. Phys Rev Lett 2014; 113:268001. [PMID: 25615387 DOI: 10.1103/physrevlett.113.268001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Indexed: 06/04/2023]
Abstract
The effect of steric hindrance is an important aspect of granular packings as it gives rise to, e.g., limitations on the densities of ordered and disordered packings, both of which are essentially defined by the geometry of the constituents. Here we focus on the random packing of rods via deposition and their distributions of contact number and segment length. Such statistical properties are relevant for mechanical properties of the structures, but the (quite large) steric effects on them have not been addressed in previous studies. We therefore develop a theory that describes the statistical properties of rod packings, while taking into account that the deposited rods cannot overlap and thus induce steric hindrances. The distributions derived from the theory are compared with experimental results and numerical simulations of networks constructed via deposition. The results explain the non-Poisson statistics observed in the experiments and show that the induced steric range of the rods can be large compared to their diameter and decreases with compactification of the pile, implying local orientational ordering of the structure.
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Affiliation(s)
- A Ekman
- Department of Physics and Nanoscience Center, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
| | - A Miettinen
- Department of Physics and Nanoscience Center, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
| | - T Tallinen
- Department of Physics and Nanoscience Center, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
| | - J Timonen
- Department of Physics and Nanoscience Center, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland and Saint-Petersburg State University of Information Technologies, Mechanics and Optics, 49 Kronverksky Avenue, 197101 St. Petersburg, Russia
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Heiskanen K, Ahonen R, Karttunen P, Kanerva R, Timonen J. Medicine shortages--a study of community pharmacies in Finland. Health Policy 2014; 119:232-8. [PMID: 25467285 DOI: 10.1016/j.healthpol.2014.11.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2014] [Revised: 10/29/2014] [Accepted: 11/03/2014] [Indexed: 11/24/2022]
Abstract
OBJECTIVES To explore the frequency, the reasons behind, and the consequences of medicine shortages in Finnish community pharmacies. METHODS During the 27-day study period in the autumn of 2013, randomly selected pharmacies reported on medicines that were in short supply from orders made to wholesalers. RESULTS Altogether 129 (66%, n=195) pharmacies participated in the study, and the study material consisted of 3311 report forms. Of the study pharmacies, 79.8% had medicine shortages daily or almost daily. Medicines in short supply were most commonly medicines that affect the nervous system (30.8%) and the cardiovascular system (17.5%). The reason behind the shortage was reported to the pharmacies in 11.2% of the shortage cases. The medicine shortages caused problems for the pharmacies in 33.0% of the cases. In most cases (67.0%) the medicine shortages did not cause problems for the pharmacies, usually because a substitutable product was available (48.5%). CONCLUSIONS Medicine shortages are common in Finnish community pharmacies. Medicines in short supply were commonly used medicines. The reason behind the shortage was rarely told to the pharmacies. Medicine shortages caused problems for the pharmacies in one-third of all the shortage cases. These shortages may be significant for the customers or the pharmacies, as they cause customer dissatisfaction and increase the workload of the pharmacy staff.
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Affiliation(s)
- K Heiskanen
- School of Pharmacy/Social Pharmacy, Faculty of Health Sciences, Kuopio Campus, University of Eastern Finland, Kuopio, Finland
| | - R Ahonen
- School of Pharmacy/Social Pharmacy, Faculty of Health Sciences, Kuopio Campus, University of Eastern Finland, Kuopio, Finland
| | | | - R Kanerva
- VI Pharmacy of Turku, Humalisto Pharmacy, Turku, Finland
| | - J Timonen
- School of Pharmacy/Social Pharmacy, Faculty of Health Sciences, Kuopio Campus, University of Eastern Finland, Kuopio, Finland.
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Kähärä T, Tallinen T, Timonen J. Numerical model for the shear rheology of two-dimensional wet foams with deformable bubbles. Phys Rev E Stat Nonlin Soft Matter Phys 2014; 90:032307. [PMID: 25314446 DOI: 10.1103/physreve.90.032307] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Indexed: 06/04/2023]
Abstract
Shearing of two-dimensional wet foam is simulated using an introduced numerical model, and results are compared to those of experiments. This model features realistically deformable bubbles, which distinguishes it from previously used models for wet foam. The internal bubble dynamics and their contact interactions are also separated in the model, making it possible to investigate the effects of the related microscale properties of the model on the macroscale phenomena. Validity of model assumptions was proved here by agreement between the simulated and measured Herschel-Bulkley rheology, and shear-induced relaxation times. This model also suggests a relationship between the shear stress and normal stress as well as between the average degree of bubble deformation and applied shear stress. It can also be used to analyze suspensions of bubbles and solid particles, an extension not considered in this work.
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Affiliation(s)
- T Kähärä
- Department of Physics, University of Jyväskylä, Finland
| | - T Tallinen
- Department of Physics, University of Jyväskylä, Finland
| | - J Timonen
- Department of Physics and Nanoscience Center, University of Jyväskylä, Finland and ITMO University, Kronverkskii ave. 49, 197101, Saint Petersburg, Russia
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Moilanen P, Määttä M, Kilappa V, Xu L, Nicholson PHF, Alén M, Timonen J, Jämsä T, Cheng S. Discrimination of fractures by low-frequency axial transmission ultrasound in postmenopausal females. Osteoporos Int 2013; 24:723-30. [PMID: 22638711 DOI: 10.1007/s00198-012-2022-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2011] [Accepted: 05/04/2012] [Indexed: 10/28/2022]
Abstract
SUMMARY In this cross-sectional study, 95 postmenopausal women, with and without fracture history, were measured by low-frequency axial transmission ultrasound. The measured ultrasound velocity discriminated the fractured subjects from the nonfractured ones equally or better than peripheral quantitative computed tomography (pQCT) and dual energy x-ray absorptiometry (DXA). These results suggest that low-frequency ultrasound is suitable for bone fragility assessment. INTRODUCTION Quantitative low-frequency axial transmission ultrasound is a promising modality for assessing mineral density and geometrical properties of long bones such as radius and tibia. The aim of the current study was to evaluate the ability of low-frequency axial transmission ultrasound to discriminate fractures retrospectively in postmenopausal women. METHODS A cross-sectional study involved 95 female subjects aged 45-88 years, whose fracture information was gathered retrospectively. The fracture group was defined as subjects with one or more low-/moderate-energy fractures. The radius and tibial shaft were measured with a custom-made ultrasonometer to assess the velocity of the low-frequency first-arriving signal (V (LF)). Site-matched pQCT was used to measure volumetric cortical and subcortical bone mineral density (sBMD), and cortical thickness (CTh). Areal BMD (aBMD) was measured using DXA for the whole body (WB), lumbar spine, and hip. RESULTS The majority (19/32; 59 %) of the fractures were in the upper limb. V (LF) in the radius, but not in the tibia, discriminated fractures with an age- and BMI-adjusted odds ratio (OR) of 2.06 (95 % CI 1.21-3.50, p < 0.01). In the radius, CTh and cortical BMD (CBMD) significantly discriminated fractures, as did the total, cortical, and sBMD in the tibia (adjusted OR 1.35-2.15, p < 0.05). Sensitivity and specificity were similar among all the measurements (area under the receiver operating characteristic curve 0.74-0.81, p < 0.001). CONCLUSIONS Low-frequency axial transmission ultrasound in the radius was able to discriminate fractured subjects from the nonfractured ones. This suggests that low-frequency axial transmission ultrasound has the potential to assess bone fragility in postmenopausal women.
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Affiliation(s)
- P Moilanen
- Department of Physics, University of Jyväskylä, P.O. Box 35, Jyväskylä, FI-40014, Finland.
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Åström JA, Timonen J. Spontaneous formation of densely packed shear bands of rotating fragments. Eur Phys J E Soft Matter 2012; 35:40. [PMID: 22644135 DOI: 10.1140/epje/i2012-12040-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Revised: 05/03/2012] [Accepted: 05/04/2012] [Indexed: 06/01/2023]
Abstract
Appearance of self-similar space-filling ball bearings has been suggested to provide the explanation for seismic gaps, shear weakness, and lack of detectable frictional heat formation in mature tectonic faults (shear zones). As the material in a shear zone fractures and grinds, it could be thought to eventually form a conformation that allows fragments to largely roll against each other without much sliding. This type of space-filling "ball bearing" can be constructed artificially, but so far how such delicate structures may appear spontaneously has remained unexplained. It is demonstrated here that first-principles simulations of granular packing with fragmenting grains indeed display spontaneous formation of shear bands with fragment conformations very similar to those of densely packed ball bearings.
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Affiliation(s)
- J A Åström
- CSC - IT centre for science, P.O. Box 405, FIN-02101 Esbo, Finland.
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Kilappa V, Moilanen P, Xu L, Nicholson PHF, Timonen J, Cheng S. Low-frequency axial ultrasound velocity correlates with bone mineral density and cortical thickness in the radius and tibia in pre- and postmenopausal women. Osteoporos Int 2011; 22:1103-13. [PMID: 20577874 DOI: 10.1007/s00198-010-1273-7] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2009] [Accepted: 04/08/2010] [Indexed: 01/28/2023]
Abstract
UNLABELLED Axial transmission velocity of a low-frequency first arriving signal (V (LF)) was assessed in the radius and tibia of 254 females, and compared to site-matched pQCT measurements. V (LF) best correlated with cortical BMD, but significantly also with subcortical BMD and cortical thickness. Correlations were strongest for the radius in postmenopausal females. INTRODUCTION Ultrasonic low-frequency (LF; 0.2-0.4 MHz) axial transmission, based on the first arriving signal (FAS), provides enhanced sensitivity to thickness and endosteal properties of cortical wall of the radius and tibia compared to using higher frequencies (e.g., 1 MHz). This improved sensitivity of the LF approach has not yet been clearly confirmed by an in vivo study on adult subjects. The aims of the present study were to evaluate the extent to which LF measurements reflect cortical thickness and bone mineral density, and to assess whether an individual LF measurement can provide a useful estimate for these bone properties. METHODS Velocity of the LF FAS (V (LF)) was assessed in the radius and tibia shaft by a new ultrasonometer (CV(RMS) = 0.5%) in a cross-sectional study involving 159 premenopausal (20-58 years) and 95 postmenopausal females (45-88 years). Site-matched volumetric total bone mineral density (BMD), cortical bone mineral density (CBMD), subcortical bone mineral density (ScBMD) and cortical thickness (CTh) were assessed using pQCT. RESULTS For the postmenopausal females, V (LF) correlated best with CBMD in the radius (R = 0.850, p < 0.001), but significantly also with ScBMD and CTh (R = 0.759 and R = 0.761, respectively; p < 0.001). Similar trends but weaker correlations were observed for the tibia and for the premenopausal women. CONCLUSIONS The LF assessment, with an optimal excitation frequency, thus provided good prediction of both cortical thickness and subcortical bone material properties. These results suggest that the LF approach does indeed have enhanced sensitivity for detecting osteoporotic changes that occur deep in the endosteal bone.
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Affiliation(s)
- V Kilappa
- Department of Physics, University of Jyväskylä, PO BOX 35 (YFL), 40014 Jyväskylä, Finland.
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Tallinen T, Ojajärvi J, Aström JA, Timonen J. Scaling behavior in non-Hookean compression of thin-walled structures. Phys Rev Lett 2010; 105:066102. [PMID: 20867989 DOI: 10.1103/physrevlett.105.066102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2010] [Indexed: 05/29/2023]
Abstract
The mechanics and stability of thin-walled structures is a challenging and important branch in structural mechanics. Under vertical compression the deformation of a thin-walled box differs from that of, e.g., a cylindrical shell. It is demonstrated here that compression of a box can be described by a set of generic scaling laws representing three successive regimes: a linear, wrinkled, and collapsed regime. The linear Hookean regime represents the normal behavior before any instability sets in, while the following wrinkled regime is shown to be analogous to compression of thin-film blisters. The compression force reaches its maximum at the onset of the final collapsed regime that has all the characteristics of membrane crumpling. The theoretical scaling laws were confirmed by numerical simulations.
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Affiliation(s)
- T Tallinen
- Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
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Tallinen T, Aström JA, Kekäläinen P, Timonen J. Mechanical and thermal stability of adhesive membranes with nonzero bending rigidity. Phys Rev Lett 2010; 105:026103. [PMID: 20867719 DOI: 10.1103/physrevlett.105.026103] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Indexed: 05/08/2023]
Abstract
Membranes at a microscopic scale are affected by thermal fluctuations and self-adhesion due to van der Waals forces. Methods to prepare membranes of even molecular scale, e.g., graphene, have recently been developed, and the question of their mechanical and thermal stability is of crucial importance. To this end we modeled microscopic membranes with an attractive interaction and applied Langevin dynamics. Their behavior was also analyzed under external loading. Even though these membranes folded during isotropic compression as a result of energy minimization, the process at high confinement was similar to crumpling of macroscopic nonadhesive sheets. The main difference appeared when the compression was released. In such cases, for membranes of sufficiently large size, folded or scrolled conformations emerged. At high temperature entropic effects made such conformations unfavorable, however.
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Affiliation(s)
- T Tallinen
- Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
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Folarin AA, Konerding MA, Timonen J, Nagl S, Pedley RB. Three-dimensional analysis of tumour vascular corrosion casts using stereoimaging and micro-computed tomography. Microvasc Res 2010; 80:89-98. [PMID: 20303995 DOI: 10.1016/j.mvr.2010.03.007] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Revised: 03/01/2010] [Accepted: 03/12/2010] [Indexed: 11/19/2022]
Abstract
OBJECTIVE In order to perform effective translational research for cancer therapy, we need to employ pre-clinical models which reflect the clinical situation. The purpose of this study was to quantitatively compare the vascular architecture of human colorectal cancer and experimental tumour models to determine the suitability of animal models for vascular studies and antivascular therapy. METHODS In this study we investigated the three-dimensional properties of colonic tumour vasculature in both human clinical tissues (normal mucosa control [n=20], carcinoma [n=20] and adenoma [n=6]) and murine colorectal xenografts (LS147T [n=6] and SW1222 [n=6]). Scanning Electron Microscope Stereoimaging (SEM) and X-ray Micro-Computed Tomography (Micro-CT) methods were employed for 3D analyses of the vascular corrosion casts from these tissues. RESULTS Morphological measurements showed that there were significant differences in the underlying morphology in the different tissues. Of the studied xenografts, LS147T is more consistently similar to the vascular architecture of the human carcinoma than SW1222. The only reversal of this is for the inter-vessel distance. CONCLUSION While SEM stereoimaging provided better surface detailed resolution of the corrosion casts, it was complimented by the fully 3D micro-CT method. Comparison made between the xenografts and clinical tumours showed that the LS147T xenografts shared many similarities with the clinical tumour vasculature. This study provides insight into how to select the most suitable pre-clinical models for translational studies of clinical cancer therapy.
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Affiliation(s)
- A A Folarin
- Department of Oncology, UCL Cancer Institute, London, UK.
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Järnström J, Väisänen M, Lehto R, Jäsberg A, Timonen J, Peltonen J. Effect of latex on surface structure and wetting of pigment coatings. Colloids Surf A Physicochem Eng Asp 2010. [DOI: 10.1016/j.colsurfa.2009.11.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Zheng A, Sakari R, Cheng SM, Hietikko A, Moilanen P, Timonen J, Fagerlund KM, Kärkkäinen M, Alèn M, Cheng S. Effects of a low-frequency sound wave therapy programme on functional capacity, blood circulation and bone metabolism in frail old men and women. Clin Rehabil 2009; 23:897-908. [DOI: 10.1177/0269215509337273] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Objective: To evaluate the effects of a low-frequency sound wave therapy programme on functional capacity, blood circulation and bone metabolism of the frail elderly. Design: Single-blind, randomized, controlled trial. Setting: Two senior service centres. Subjects: Forty-nine volunteers (14 males and 35 females) aged 62—93 years with up to 12 diagnosed diseases were allocated in either the intervention group (n = 30) or control group (n = 19). Intervention: The intervention group underwent sound wave therapy, 3—5 times a week for 30 minutes per session over a period of 6 months. The control group received no intervention. Main measurements: Blood pressure, functional capacity, mobility, bone density, biochemical markers, isometric muscle strength, balance, and skin surface temperature. Results: Compared with the control group, the intervention group’s mobility and the amount of self-reported kilometres walked per week increased by 3 km (P<0.05), while levels of cholesterol (4.97 (0.72) to 4.52 (0.65) mmol/L, P =0.019), low-density lipoprotein (2.82 (0.72) to 2.45 (0.61) mmol/L, P =0.022), bone markers of total osteocalcin (11.0 (6.5) to 10.3 (5.9) ng/mL, P =0.048)) and tartrate-resistant acid phosphatase isoform 5b (2.50 (1.0) to 2.41 (1.1) IU/L, P =0.021)) decreased. The average skin surface temperature was significantly higher during active sessions at the end of the intervention than in the beginning (P = 0.004). No change was found during placebo sessions. Conclusions: Low-frequency sound wave therapy may have the potential to promote well-being of frail elderly subjects via improved functional capacity, especially in subjects who are too frail to undertake exercise.
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Affiliation(s)
- A. Zheng
- Department of Health Sciences, University of Jyväskylä, Jyväskylä
| | - R. Sakari
- Department of Health Sciences, University of Jyväskylä, Jyväskylä
| | - SM Cheng
- Department of Health Sciences, University of Jyväskylä, Jyväskylä,
| | - A. Hietikko
- Department of Health Sciences, University of Jyväskylä, Jyväskylä
| | - P. Moilanen
- Department of Physics, University of Jyväskylä, Jyväskylä
| | - J. Timonen
- Department of Physics, University of Jyväskylä, Jyväskylä
| | - KM Fagerlund
- Department of Cell Biology and Anatomy, University of Turku, Turku
| | - M. Kärkkäinen
- Department of Health Sciences, University of Jyväskylä
| | - M. Alèn
- Department of Medical Rehabilitation, Oulu University Hospital and Institute of Health Sciences, University of Oulu, Oulu
| | - S. Cheng
- Department of Health Sciences, University of Jyväskylä, Jyväskylä, Department of Orthopaedics and Traumatology, Kuopio University Hospital, Kuopio, Finland
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Tallinen T, Aström JA, Timonen J. The effect of plasticity in crumpling of thin sheets. Nat Mater 2009; 8:25-29. [PMID: 19060887 DOI: 10.1038/nmat2343] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2008] [Accepted: 11/13/2008] [Indexed: 05/27/2023]
Abstract
Crumpling a thin sheet of material into a small volume requires energy for creating a network of deformations such as vertices and ridges. Scaling properties of a single elastic vertex or ridge have been analysed theoretically, and crumpling of a sheet by numerical simulations. Real materials are however elasto-plastic and large local strains induce irreversible plastic deformations. Hence, a numerical model that can be purely elastic or elasto-plastic is introduced. In crumpled elastic sheets, the ridge patterns are found to be similar, independent of the width to thickness (L/h) ratio of the sheet, and the fractal dimension of crumpled sheets is given by scaling properties of the energy and average length of ridges. In crumpled elasto-plastic sheets, such a similarity does not appear as the L/h ratio affects the deformations, and the fractal dimension (Dpl) is thereby reduced. Evidence is also found of Dpl not being universal but dependent on the plastic yield point of the material.
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Affiliation(s)
- T Tallinen
- Department of Physics, University of Jyväskylä, PO Box 35, FI-40014 University of Jyväskylä, Finland.
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Chinga-Carrasco G, Kauko H, Myllys M, Timonen J, Wang B, Zhou M, Fossum JO. New advances in the 3D characterization of mineral coating layers on paper. J Microsc 2008; 232:212-24. [PMID: 19017220 DOI: 10.1111/j.1365-2818.2008.02092.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The surface characteristics of a large set of commercial lightweight coated paper grades are explored. The quantification of the 3D structure is revealed by atomic force microscopy, laser profilometry and X-ray microtomography. This comprehensive study demonstrates the suitability of different and modern methods for assessing critical coating layer properties, thus identifying the right tools for specific structural analyses. Based on the assessment of the top and bottom surfaces of 25 commercial lightweight coated samples, three main conclusions can be drawn: (1) the facet orientation polar angle is a function of roughness, (2) skewness did not describe the surface details affecting the gloss of the commercial lightweight coated samples assessed in this study and (3) surface roughness at wavelengths below approximately 1.0 microm does not affect the paper gloss significantly. This is important knowledge for the understanding of lightweight coated paper surface structure and its properties.
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Abstract
Crumpled membranes have been found to be characterized by complex patterns of spatially seemingly random facets separated by narrow ridges of high elastic energy. We demonstrate by numerical simulations that compression of stiff elastic membranes with small randomness in their initial configurations leads to either random ridge configurations (high entropy) or nearly deterministic folds (low elastic energy). For folding with symmetric ridge configurations to appear in part of the crumpling processes, the crumpling rate must be slow enough. Folding stops when the thickness of the folded structure becomes important, and crumpling continues thereafter as a random process.
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Affiliation(s)
- T Tallinen
- Department of Physics, P.O. Box 35, FI-40014 University of Jyväskylä, Finland
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Kekäläinen P, Aström JA, Timonen J. Solution for the fragment-size distribution in a crack-branching model of fragmentation. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 76:026112. [PMID: 17930109 DOI: 10.1103/physreve.76.026112] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Indexed: 05/25/2023]
Abstract
It is well established that rapidly propagating cracks in brittle material are unstable such that they generate side branches. It is also known that cracks are attracted by free surfaces, which means that they attract each other. This information is used here to formulate a generic model of fragmentation in which the small-size part of the fragment-size distribution results from merged crack branches in the damage zones along the paths of the propagating cracks. This model is solved under rather general assumptions for the fragment-size distribution. The model leads to a generic distribution S(-gamma) exp(-S/S(0)) for fragment sizes S, where gamma = 2d-1/d with d the Euclidean dimension, and S(0) is a material dependent parameter.
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Affiliation(s)
- P Kekäläinen
- Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 University of Jyväskylä, Finland
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18
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Hyväluoma J, Koponen A, Raiskinmäki P, Timonen J. Droplets on inclined rough surfaces. Eur Phys J E Soft Matter 2007; 23:289-93. [PMID: 17646904 DOI: 10.1140/epje/i2007-10190-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2007] [Accepted: 06/08/2007] [Indexed: 05/16/2023]
Abstract
The behaviour of liquid droplets on inclined heterogeneous surfaces was simulated by the lattice-Boltzmann method using the Shan-Chen multiphase model. The effect of topography of the surface on the contact angle hysteresis was investigated. It is shown in particular, by using anisotropic rough surfaces, how surface topography and thereby the continuity of the three-phase contact line, affect this hysteresis. Our results clearly indicate that the superhydrophobicity of a surface cannot be judged by the contact angle alone.
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Affiliation(s)
- J Hyväluoma
- Department of Physics, University of Jyväskylä, FI-40014 Jyväskylä, Finland.
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19
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Hyväluoma J, Turpeinen T, Raiskinmäki P, Jäsberg A, Koponen A, Kataja M, Timonen J, Ramaswamy S. Intrusion of nonwetting liquid in paper. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 75:036301. [PMID: 17500785 DOI: 10.1103/physreve.75.036301] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2006] [Revised: 12/28/2006] [Indexed: 05/15/2023]
Abstract
The saturation curve of a sample of paper board was measured with mercury-intrusion porosimetry, and the three-dimensional structure of its pore space was determined by x-ray tomographic imaging. Ab initio numerical simulation of intrusion on the tomographic reconstruction, based on the lattice-Boltzmann method, was in excellent agreement with the measured saturation curve. A numerical invasion-percolation simulation in the same tomographic reconstruction showed good agreement with the lattice-Boltzmann simulation. The access function of the sample, determined from the saturation curve and the pore-throat distribution determined from the tomographic reconstruction, indicated that the ink-bottle effect is significant in paperlike materials.
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Affiliation(s)
- J Hyväluoma
- Department of Physics, University of Jyväskylä, FI-40014 Jyväskylä, Finland
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20
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Aström JA, Timonen J, Myllys M, Fellman J, LeBell J. Random networks of fibres display maximal heterogeneity in the distribution of elastic energy. Eur Phys J E Soft Matter 2007; 22:61-6. [PMID: 17318292 DOI: 10.1140/epje/e2007-00005-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Indexed: 05/14/2023]
Abstract
Above a small length scale, the distribution of local elastic energies in a material under an external load is typically Gaussian, and the dependence of the average elastic energy on strain defines the stiffness of the material. Some particular materials, such as granular packings, suspensions at the jamming transition, crumpled sheets and dense cellular aggregates, display under compression an exponential distribution of elastic energies, but also in this case the elastic properties are well defined. We demonstrate here that networks of fibres, which form uncorrelated non-fractal structures, have under external load a scale invariant distribution of elastic energy (epsilon) at the fibre-fibre contacts proportional to 1/epsilon. This distribution is much broader than any other distribution observed before for elastic energies in a material. We show that for small compressions it holds over 10 orders of magnitude in epsilon. In such a material a few 'hot spots' carry most of the elastic load. Consequently, these materials are highly susceptible to local irreversible deformations, and are thereby extremely efficient for damping vibrations.
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Affiliation(s)
- J A Aström
- CSC - IT-center for Science, P.O. Box 405, 02101 Esbo, Finland.
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21
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Moilanen P, Nicholson PHF, Kilappa V, Cheng S, Timonen J. Measuring guided waves in long bones: modeling and experiments in free and immersed plates. Ultrasound Med Biol 2006; 32:709-19. [PMID: 16677930 DOI: 10.1016/j.ultrasmedbio.2006.02.1402] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2005] [Revised: 01/26/2006] [Accepted: 02/07/2006] [Indexed: 05/09/2023]
Abstract
Guided waves, consistent with the A0 Lamb mode, have previously been observed in bone phantoms and human long bones. Reported velocity measurements relied on line fitting of the observed wave fronts. Such an approach has limited ability to assess dispersion and is affected by interference by other wave modes. For a more robust identification of modes and determination of phase velocities, signal processing techniques using the fast Fourier transform (FFT) were investigated. The limitations of FFT because of spatial resolution were addressed to improve the precision of the measured modes. An inversion scheme was developed for determining the plate thickness from the measured velocity. Experiments were performed on free and immersed plates, mimicking bone without and with an overlying tissue. With group velocity filtering, modes could be identified reliably with precise phase velocities and thicknesses. These methods were essential for the immersed plates and they should lead to more reliable in vivo measurements.
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Affiliation(s)
- P Moilanen
- Department of Physics, University of Jyväskylä, Jyväskylä, Finland.
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22
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Hyväluoma J, Raiskinmäki P, Jäsberg A, Koponen A, Kataja M, Timonen J. Simulation of liquid penetration in paper. Phys Rev E Stat Nonlin Soft Matter Phys 2006; 73:036705. [PMID: 16605696 DOI: 10.1103/physreve.73.036705] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2005] [Indexed: 05/08/2023]
Abstract
Capillary penetration of a wetting liquid in a microtomographic image of paper board, whose linear dimension was close to the average length of wood fibers, was simulated by the lattice-Boltzmann method. In spite of the size of the system not being large with respect to the size of structural inhomogeneities in the sample, for unidirectional penetration the simulated behavior was described well by that of the Lucas-Washburn equation, while for radial penetration a radial capillary equation described the behavior. In both cases the average penetration depth of the liquid front as a function of time followed a power law over many orders of magnitude. Capillary penetration of small droplets of liquid was also simulated in the same three-dimensional image of paper. In this case the simulation results could be described by a generalized form of the radial-penetration equation.
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Affiliation(s)
- J Hyväluoma
- Department of Physics, University of Jyväskylä, FI-40014 Jyväskylä, Finland
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23
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Hyväluoma J, Raiskinmäki P, Koponen A, Kataja M, Timonen J. Strain hardening in liquid-particle suspensions. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:061402. [PMID: 16485942 DOI: 10.1103/physreve.72.061402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2005] [Indexed: 05/06/2023]
Abstract
The behavior of a liquid-particle suspension induced to sheared motion was analyzed by numerical simulations. When the velocity (strain) of the suspension began to increase, its viscosity first stayed almost constant, but increased then rapidly to a clearly higher level. This increase in viscosity is shown to be related to formation of clusters of suspended particles. Clusters are shown to increase the viscosity by enhanced momentum transfer though clustered particles. This is the mechanism behind the strain-hardening phenomenon observed in small-strain experiments on liquid-particle suspensions.
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Affiliation(s)
- J Hyväluoma
- Department of Physics, University of Jyväskylä, FI-40014 Jyväskylä, Finland
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24
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Linna RP, Aström JA, Timonen J. Dimensional effects in dynamic fragmentation of brittle materials. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:015601. [PMID: 16090029 DOI: 10.1103/physreve.72.015601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2005] [Indexed: 05/03/2023]
Abstract
It has been shown previously that dynamic fragmentation of brittle D -dimensional objects in a D -dimensional space gives rise to a power-law contribution to the fragment-size distribution with a universal scaling exponent 2-1/D . We demonstrate that in fragmentation of two-dimensional brittle objects in three-dimensional space, an additional fragmentation mechanism appears, which causes scale-invariant secondary breaking of existing fragments. Due to this mechanism, the power law in the fragment-size distribution has now a scaling exponent of approximately 1.17 .
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Affiliation(s)
- R P Linna
- Department of Physics, University of Jyväskylä, P. O. Box 35, FIN-40351 Jyväskylä, Finland
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25
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Muller M, Moilanen P, Bossy E, Nicholson P, Kilappa V, Timonen J, Talmant M, Cheng S, Laugier P. Comparison of three ultrasonic axial transmission methods for bone assessment. Ultrasound Med Biol 2005; 31:633-42. [PMID: 15866413 DOI: 10.1016/j.ultrasmedbio.2005.02.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2004] [Revised: 01/29/2005] [Accepted: 02/03/2005] [Indexed: 05/02/2023]
Abstract
This study compared three approaches to bone assessment using ultrasonic axial transmission. In 41 fresh human radii, velocity of the first arriving signal was measured with a commercial device (Sunlight Omnisense) operating at 1.25 MHz, a prototype based on 1-MHz bidirectional axial transmission and a low-frequency (200 kHz) prototype, also measuring the velocity of a slower wave. Cortical and trabecular bone mineral density, cortical thickness and cross-sectional area were determined by peripheral quantitative computed tomography. Significant but modest correlation between velocities reflects differences in the nature of the propagating waves and methodological differences. Of the higher frequency devices, bidirectional measurements provided stronger correlations with bone properties than did conventional measurements. High-frequency devices were less sensitive to cortical thickness than was the low-frequency device, because higher frequency waves interrogate thinner cortical layers. The results suggest that different axial transmission approaches reflect different bone properties. Therefore, a multifrequency technique might be useful in probing different bone properties.
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Affiliation(s)
- M Muller
- Laboratoire d'Imagerie Paramétrique, UMR CNRS 7623, Université Paris 6, 15 rue de l'Ecole de Médecine, 75006 Paris, France.
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26
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Abstract
A first-principles numerical model for crumpling of a stiff tethered membrane is introduced. This model displays wrinkles, ridge formation, ridge collapse, and initiation of stiffness divergence. The amplitude and wavelength of the wrinkles and the scaling exponent of the stiffness divergence are consistent with both theory and experiment. Close to the stiffness divergence further buckling is hindered by the nonzero thickness of the membrane, and its elastic behavior becomes similar to that of dry granular media. No change in the distribution of contact forces can be observed at the crossover, implying that the network of ridges is then simultaneously a granular force-chain network.
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Affiliation(s)
- J A Aström
- Centre for Scientific Computing, P.O. Box 405, FIN-02101 Esbo, Finland
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27
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Aström JA, Linna RP, Timonen J, Møller PF, Oddershede L. Exponential and power-law mass distributions in brittle fragmentation. Phys Rev E Stat Nonlin Soft Matter Phys 2004; 70:026104. [PMID: 15447542 DOI: 10.1103/physreve.70.026104] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2004] [Indexed: 05/24/2023]
Abstract
Generic arguments, a minimal numerical model, and fragmentation experiments with gypsum disk are used to investigate the fragment-size distribution that results from dynamic brittle fragmentation. Fragmentation is initiated by random nucleation of cracks due to material inhomogeneities, and its dynamics are pictured as a process of propagating cracks that are unstable against side-branch formation. The initial cracks and side branches both merge mutually to form fragments. The side branches have a finite penetration depth as a result of inherent damping. Generic arguments imply that close to the minimum strain (or impact energy) required for fragmentation, the number of fragments of size s scales as s(-(2D-1)/D) f(1) (- (2/lambda)(D) s)+ f(2) (- s(-1 )(0 ) (lambda+ s(1/D) )(D) ), where D is the Euclidean dimension of the space, lambda is the penetration depth, and f(1) and f(2) can be approximated by exponential functions. Simulation results and experiments can both be described by this theoretical fragment-size distribution. The typical largest fragment size s(0) was found to diverge at the minimum strain required for fragmentation as it is inversely related to the density of initially formed cracks. Our results also indicate that scaling of s(0) close to this divergence depends on, e.g., loading conditions, and thus is not universal. At the same time, the density of fragment surface vanishes as L-1, L being the linear dimension of the brittle solid. The results obtained provide an explanation as to why the fragment-size distributions found in nature can have two components, an exponential as well as a power-law component, with varying relative weights.
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Affiliation(s)
- J A Aström
- Center for Scientific Computing, P. O. Box 405, FIN-02101 Esbo, Finland
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28
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Abstract
A generic model is introduced for brittle fragmentation in D dimensions, and this model is shown to lead to a fragment-size distribution with two distinct components. In the small fragment-size limit a scale-invariant size distribution results from a crack branching-merging process. At larger sizes the distribution becomes exponential as a result of a Poisson process, which introduces a large-scale cutoff. Numerical simulations are used to demonstrate the validity of the distribution for D=2. Data from laboratory-scale experiments and large-scale quarry blastings of granitic gneiss confirm its validity for D=3. In the experiments the nonzero grain size of rock causes deviation from the ideal model distribution in the small-size limit. The size of the cutoff seems to diverge at the minimum energy sufficient for fragmentation to occur, but the scaling exponent is not universal.
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Affiliation(s)
- J A Aström
- Centre for Scientific Computing, P.O. Box 405, FIN-02101 Esbo, Finland
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29
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Raiskinmäki P, Aström JA, Kataja M, Latva-Kokko M, Koponen A, Jäsberg A, Shakib-Manesh A, Timonen J. Clustering and viscosity in a shear flow of a particulate suspension. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 68:061403. [PMID: 14754200 DOI: 10.1103/physreve.68.061403] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2003] [Indexed: 05/24/2023]
Abstract
A shear flow of particulate suspension is analyzed for the qualitative effect of particle clustering on viscosity using a simple kinetic clustering model and direct numerical simulations. The clusters formed in a Couette flow can be divided into rotating chainlike clusters and layers of particles at the channel walls. The size distribution of the rotating clusters is scale invariant in the small-cluster regime and decreases rapidly above a characteristic length scale that diverges at a jamming transition. The behavior of the suspension can qualitatively be divided into three regimes. For particle Reynolds number Re(p) less than or approximately equal 0.1, viscosity is controlled by the characteristic cluster size deduced from the kinetic clustering model. For Re(p) approximately 1, clustering is maximal, but the simple kinetic model becomes inapplicable presumably due to onset of instabilities. In this transition regime viscosity begins to increase. For Re(p) greater than or approximately equal 10, inertial effects become important, clusters begin to breakup, and suspension displays shear thickening. This phenomenon may be attributed to enhanced contribution of solid phase in the total shear stress.
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Affiliation(s)
- P Raiskinmäki
- Department of Physics, P.O. Box 35, FIN-40014 University of Jyväskylä, Finland
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Moilanen P, Nicholson PHF, Kärkkäinen T, Wang Q, Timonen J, Cheng S. Assessment of the tibia using ultrasonic guided waves in pubertal girls. Osteoporos Int 2003; 14:1020-7. [PMID: 14564455 DOI: 10.1007/s00198-003-1528-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2002] [Accepted: 09/15/2003] [Indexed: 10/26/2022]
Abstract
The purpose of this study was to compare low frequency ultrasonic guided wave measurements with established ultrasound and bone density measurements in terms of their ability to characterize the tibia in pubertal girls. Subjects were 12-14-year-old girls ( n=106) who were participating in a calcium and vitamin D intervention study. A prototype low frequency pulse transmission device consisting of a uniaxial scanning mechanism and low frequency transducers orientated perpendicularly to the limb was used to measure two ultrasound velocities in the tibia. The first velocity, V1, was that of the first arriving signal, similar to that measured by existing commercial tibial ultrasound devices. The second velocity, V2, was that of a slower wave propagating at 1,500-2,000 m/s, which has been shown elsewhere to be consistent with the lowest order antisymmetric guided mode in the bone. In addition, commercial ultrasound devices (Omnisense, Sunlight Ltd.; QUS-2, Quidel Corp.) were used to measure the speed of sound (SOS) in the tibia and the radius and attenuation (BUA) in the calcaneus. Cortical bone cross-sectional area (CSA), mineral density (BMD) and cortical thickness (cTh) of the tibia were measured using pQCT, site-matched to the ultrasound measurements. Both V1 and V2 correlated significantly with cortical BMD and with cTh and CSA. On the other hand, tibial SOS correlated with BMD, but not with cTh and CSA. These results indicate that the prototype device using guided waves captures aspects of tibial cortical bone geometry in addition to bone density, thereby potentially offering increased diagnostic information compared to existing tibial ultrasound devices.
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Affiliation(s)
- P Moilanen
- Department of Physics, University of Jyväskylä, P.O. Box 35 (YFL), 40014, Jyväskylä, Finland.
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31
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Myllys M, Maunuksela J, Merikoski J, Timonen J, Horváth VK, Ha M, den Nijs M. Effect of a columnar defect on the shape of slow-combustion fronts. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 68:051103. [PMID: 14682784 DOI: 10.1103/physreve.68.051103] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2003] [Indexed: 05/24/2023]
Abstract
We report experimental results for the behavior of slow-combustion fronts in the presence of a columnar defect with enhanced or reduced driving, and compare them with those of mean-field theory. We also compare them with simulation results for an analogous problem of driven flow of particles with hard-core repulsion (ASEP) and a single defect bond with a different hopping probability. The difference in the shape of the front profiles for enhanced vs reduced driving in the defect clearly demonstrates the existence of a Kardar-Parisi-Zhang-type nonlinear term in the effective evolution equation for the slow-combustion fronts. We also find that slow-combustion fronts display a faceted form for large enough enhanced driving, and that there is a corresponding increase then in the average front speed. This increase in the average front speed disappears at a nonzero enhanced driving in agreement with the simulated behavior of the ASEP model.
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Affiliation(s)
- M Myllys
- Department of Physics, University of Jyväskylä, P.O. Box 35, Jyväskylä FIN-40014, Finland
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Merikoski J, Maunuksela J, Myllys M, Timonen J, Alava MJ. Temporal and spatial persistence of combustion fronts in paper. Phys Rev Lett 2003; 90:024501. [PMID: 12570549 DOI: 10.1103/physrevlett.90.024501] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2002] [Indexed: 05/24/2023]
Abstract
The spatial and temporal persistence, or first-return distributions are measured for slow-combustion fronts in paper. The stationary temporal and (perhaps less convincingly) spatial persistence exponents agree with the predictions based on the front dynamics, which asymptotically belongs to the Kardar-Parisi-Zhang universality class. The stationary short-range and the transient behavior of the fronts are non-Markovian, and the observed persistence properties thus do not agree with the predictions based on Markovian theory. This deviation is a consequence of additional time and length scales, related to the crossovers to the asymptotic coarse-grained behavior.
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Affiliation(s)
- J Merikoski
- Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland
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33
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Aström JA, Latva-Kokko M, Timonen J. Dynamic rigidity transition. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 67:016103. [PMID: 12636560 DOI: 10.1103/physreve.67.016103] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2002] [Revised: 10/23/2002] [Indexed: 05/24/2023]
Abstract
An inflated closed loop (or membrane) is used to demonstrate a dynamic rigidity transition that occurs when impact energy is added to the loop in static equilibrium at zero temperature. The only relevant parameter in this transition is the ratio of the energy needed to collapse the loop and the impact energy. When this ratio is below a threshold value close to unity, the loop collapses into a high-entropy floppy state, and it does not return to the rigid state unless the impact energy can escape. The internal oscillations are in the floppy state dominated by 1/f(2) noise. When the ratio is above the threshold, the loop does not collapse, and the internal oscillations resulting from the impact are dominated by the eigenfrequencies of the stretched membrane. In this state, the loop can bounce for a long time. It is still an open question whether bouncing will eventually vanish or whether a stationary bouncing state will be reached. The dynamic transition between the floppy and the rigid state is discontinuous.
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Affiliation(s)
- J A Aström
- Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland
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Abstract
A particle suspension flowing in a channel in which fouling layers are allowed to form on the channel walls is investigated by numerical simulation. A two-dimensional phase diagram with at least four different behaviors is constructed. The fouling is modeled by attachment during collision with the deposits and by detachment caused by large enough hydrodynamic drag. For fixed total number of particles and small Reynolds numbers, the relevant parameters governing the fouling dynamics are the solid volume fraction of the suspension and the detachment drag force threshold. Below a critical curve in this 2D phase space only transient fouling takes place when the suspension is accelerated from rest by a pressure gradient. Above the fouling transition line, persistent fouling layers are formed via ballistic deposition for low and via homogeneous deposition for large solid volume fractions. Close to the fouling transition line, the flow path between the deposited layers meanders, while necking appears for increasing distance from the transition. Finally, another transition to a fully blocked flow path takes place. As determined by the estimated amount of deposited particles at saturation, both transitions seem to be discontinuous. Large fluctuations and long saturation times are typical of the dynamics of the system.
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Affiliation(s)
- A Shakib-Manesh
- Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland
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35
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Manwart C, Aaltosalmi U, Koponen A, Hilfer R, Timonen J. Lattice-Boltzmann and finite-difference simulations for the permeability for three-dimensional porous media. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 66:016702. [PMID: 12241511 DOI: 10.1103/physreve.66.016702] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2001] [Indexed: 05/23/2023]
Abstract
Numerical micropermeametry is performed on three-dimensional porous samples having a linear size of approximately 3 mm and a resolution of 7.5 microm. One of the samples is a microtomographic image of Fontainebleau sandstone. Two of the samples are stochastic reconstructions with the same porosity, specific surface area, and two-point correlation function as the Fontainebleau sample. The fourth sample is a physical model that mimics the processes of sedimentation, compaction, and diagenesis of Fontainebleau sandstone. The permeabilities of these samples are determined by numerically solving at low Reynolds numbers the appropriate Stokes equations in the pore spaces of the samples. The physical diagenesis model appears to reproduce the permeability of the real sandstone sample quite accurately, while the permeabilities of the stochastic reconstructions deviate from the latter by at least an order of magnitude. This finding confirms earlier qualitative predictions based on local porosity theory. Two numerical algorithms were used in these simulations. One is based on the lattice-Boltzmann method, and the other on conventional finite-difference techniques. The accuracy of these two methods is discussed and compared, also with experiment.
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Affiliation(s)
- C Manwart
- ICA-1, Universität Stuttgart, 70569 Stuttgart, Germany
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36
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Aström JA, Linna RP, Timonen J. Comment on "Scaling behavior in explosive fragmentation". Phys Rev E Stat Nonlin Soft Matter Phys 2002; 65:048101-048102. [PMID: 12006085 DOI: 10.1103/physreve.65.048101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2000] [Indexed: 05/23/2023]
Abstract
We discuss the data analysis and the conclusions based upon the analysis given in the paper by Diehl et al. [Phys. Rev. E 62, 4742 (2000)].
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Affiliation(s)
- J A Aström
- Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland
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37
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Latva-Kokko M, Timonen J. Rigidity of random networks of stiff fibers in the low-density limit. Phys Rev E Stat Nonlin Soft Matter Phys 2001; 64:066117. [PMID: 11736246 DOI: 10.1103/physreve.64.066117] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2001] [Indexed: 05/23/2023]
Abstract
Rigidity percolation is analyzed in two-dimensional random networks of stiff fibers. As fibers are randomly added to the system there exists a density threshold q=q(min) above which a rigid stress-bearing percolation cluster appears. This threshold is found to be above the connectivity percolation threshold q=q(c) such that q(min)=(1.1698+/-0.0004)q(c). The transition is found to be continuous, and in the universality class of the two-dimensional central-force rigidity percolation on lattices. At percolation threshold the rigid backbone of the percolating cluster was found to break into rigid clusters, whose number diverges in the limit of infinite system size, when a critical bond is removed. The scaling with system size of the average size of these clusters was found to give a new scaling exponent delta=1.61+/-0.04.
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Affiliation(s)
- M Latva-Kokko
- Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland
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Myllys M, Maunuksela J, Alava M, Ala-Nissila T, Merikoski J, Timonen J. Kinetic roughening in slow combustion of paper. Phys Rev E Stat Nonlin Soft Matter Phys 2001; 64:036101. [PMID: 11580388 DOI: 10.1103/physreve.64.036101] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2001] [Indexed: 05/23/2023]
Abstract
Results of experiments on the dynamics and kinetic roughening of one-dimensional slow-combustion fronts in three grades of paper are reported. Extensive averaging of the data allows a detailed analysis of the spatial and temporal development of the interface fluctuations. The asymptotic scaling properties, on long length and time scales, are well described by the Kardar-Parisi-Zhang (KPZ) equation with short-range, uncorrelated noise. To obtain a more detailed picture of the strong-coupling fixed point, characteristic of the KPZ universality class, universal amplitude ratios, and the universal coupling constant are computed from the data and found to be in good agreement with theory. Below the spatial and temporal scales at which a crossover takes place to the standard KPZ behavior, the fronts display higher apparent exponents and apparent multiscaling. In this regime the interface velocities are spatially and temporally correlated, and the distribution of the magnitudes of the effective noise has a power-law tail. The relation of the observed short-range behavior and the noise as determined from the local velocity fluctuations is discussed.
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Affiliation(s)
- M Myllys
- Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland
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Abstract
Dense snow avalanches are analyzed by modeling the snow slab as an elastic and brittle plate, attached by static friction to the underlying ground. The grade of heterogeneity in the local fracture (slip) thresholds, and the ratio of the average substrate slip threshold to the average slab fracture threshold, are the decisive parameters for avalanche dynamics. For a strong pack of snow there appears a stable precursor of local slips when the frictional contacts are weakened (equivalent to rising temperature), which eventually trigger a catastrophic crack growth that suddenly releases the entire slab. In the opposite limit of very high slip thresholds, the slab simply melts when the temperature is increased. In the intermediate regime, and for a homogeneous slab, the model display features typical of real snow avalanches. The model also suggests an explanation to why avalanches are impossible to forecast reliably based on precursor observations. This explanation may as well be applicable to other catastrophic rupture phenomena such as earthquakes.
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Affiliation(s)
- J A Aström
- Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland
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Bogoliubov NM, Izergin AG, Kitanine NA, Pronko AG, Timonen J. Quantum dynamics of strongly interacting boson systems: atomic beam splitters and coupled Bose-Einstein condensates. Phys Rev Lett 2001; 86:4439-4442. [PMID: 11384254 DOI: 10.1103/physrevlett.86.4439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2000] [Indexed: 05/23/2023]
Abstract
An effective boson Hamiltonian applicable to atomic beam splitters, coupled Bose-Einstein condensates, and optical lattices can be made exactly solvable by including all n-body interactions. The model can include an arbitrary number of boson components. In the strong interaction limit the model becomes a quantum phase model, which also describes a tight-binding lattice particle. Through exact results for dynamic correlation functions, it is shown how the previous weak interaction dynamics of these systems are extended to strong interactions, now becoming relevant in the experiments. The effect of the number of boson components is also analyzed.
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Affiliation(s)
- N M Bogoliubov
- Steklov Istitute of Mathematics at St. Petersburg, Russia
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Timonen J, Kippo K, Glantz R, Pakkanen T. Combination of 3D MRI and connectivity analysis in structural evaluation of cancellous bone in rat proximal femur. J Mater Sci Mater Med 2001; 12:319-325. [PMID: 15348293 DOI: 10.1023/a:1011295020550] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Three dimensional (3-D) magnetic resonance (MR) microimaging combined with connectivity analysis was tested in the study of the structure of cancellous bone. MR microimaging was performed in vitro with an average resolution of 20*20*35 microm. A 3-D connectivity analysis was used to model the trabecular bone as a network consisting of nodes and struts. Size distribution curves of these two structural elements and the interconnectivity of nodes was used to estimate the cancellous structure. The analysis suggested the occurrence of two simultaneous network structures in cancellous bone differed by the size of details. The degradative effect of ostcopenia is found to be slightly different in these two subsystems. Interconnectivity is seen to increase with the size of a node and the expected loss of connectivity due to ostcopenia is observed. The method described offers a new way in the topological estimation of interconnected medium.
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Affiliation(s)
- J Timonen
- University of Joensuu, Department of Chemistry, P.O. Box 111, FIN-80140 Joensuu, Finland
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Latva-Kokko M, Mäkinen J, Timonen J. Rigidity transition in two-dimensional random fiber networks. Phys Rev E Stat Nonlin Soft Matter Phys 2001; 63:046113. [PMID: 11308918 DOI: 10.1103/physreve.63.046113] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2000] [Indexed: 05/23/2023]
Abstract
Rigidity percolation is analyzed in two-dimensional random fibrous networks. The model consists of central forces between the adjacent crossing points of the fibers. Two strategies are used to incorporate rigidity: adding extra constraints between second-nearest crossing points with a probability p(sn), and "welding" individual crossing points by adding there four additional constraints with a probability p(weld), and thus fixing the angles between the fibers. These additional constraints will make the model rigid at a critical probability p(sn)=p(sn)(c) and p(weld)=p(weld)(c), respectively. Accurate estimates are given for the transition thresholds and for some of the associated critical exponents. The transition is found in both cases to be in the same universality class as that of the two-dimensional central-force rigidity percolation in diluted lattices.
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Affiliation(s)
- M Latva-Kokko
- Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland
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Rybin AV, Varzugin GG, Lindberg M, Timonen J, Bullough RK. Similarity solutions and collapse in the attractive gross-pitaevskii equation. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 2000; 62:6224-8. [PMID: 11101953 DOI: 10.1103/physreve.62.6224] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2000] [Indexed: 11/07/2022]
Abstract
We analyze a generalized Gross-Pitaevskii (GP) equation involving a paraboloidal trap potential in D space dimensions and generalized to a nonlinearity of order 2n+1. For attractive coupling constants collapse of the particle density occurs for Dn>/=2 and typically to a delta function centered at the origin of the trap. By introducing a special variable for the spherically symmetric solutions, we show that all such solutions are self-similar close to the center of the trap. Exact self-similar solutions occur if, and only if, Dn=2, and for this case of Dn=2 we exhibit an exact but rather special D=1 analytical self-similar solution collapsing to a delta function which, however, recovers and collapses periodically, while the ordinary GP equation in two space dimensions also has a special solution with periodic delta function collapses and revivals of the density. The relevance of these various results to attractive Bose-Einstein condensation in spherically symmetric traps is discussed.
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Affiliation(s)
- AV Rybin
- Department of Physics, University of Jyvaskyla, P.O. Box 35, FIN-40351, Jyvaskyla, Finland
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Astrom JA, Alava MJ, Timonen J. Roughening of a propagating planar crack front. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 2000; 62:2878-2881. [PMID: 11088771 DOI: 10.1103/physreve.62.2878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2000] [Indexed: 05/23/2023]
Abstract
A numerical model of the front of a planar crack propagating between two connected elastic plates is investigated. The plates are modeled as square lattices of elastic beams. The plates are connected by similar but breakable beams with a randomly varying stiffness. The crack is driven by pulling both plates at one end in Mode I at a constant rate. We find zeta=1/3, z=4/3, and beta=1/4 for the roughness, dynamical, and growth exponents, respectively, that describe the front behavior. This is similar to continuum limit analyses based on a perturbative stress-intensity treatment of the front [H. Gao and J. R. Rice, J. Appl. Mech. 56, 828 (1989)]. We discuss the differences to recent experiments.
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Affiliation(s)
- JA Astrom
- Department of Physics, University of Jyvaskyla, P.O. Box 35, FIN-40351 Jyvaskyla, Finland
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Astrom JA, Makinen JP, Alava MJ, Timonen J. Elasticity of Poissonian fiber networks. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 2000; 61:5550-5556. [PMID: 11031609 DOI: 10.1103/physreve.61.5550] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/1999] [Indexed: 05/23/2023]
Abstract
An effective-medium model is introduced for the elasticity of two-dimensional random fiber networks. These networks are commonly used as basic models of heterogeneous fibrous structures such as paper. Using the exact Poissonian statistics to describe the microscopic geometry of the network, the tensile modulus can be expressed by a single-parameter function. This parameter depends on the network density and fiber dimensions, which relate the macroscopic modulus to the relative importance of axial and bending deformations of the fibers. The model agrees well with simulation results and experimental findings. We also discuss the possible generalizations of the model.
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Affiliation(s)
- JA Astrom
- Department of Physics, University of Jyvaskyla, Finland
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Abstract
Fragmentation of a two-dimensional brittle solid by impact and "explosion," and a fluid by "explosion" are all shown to become critical. The critical points appear at a nonzero impact velocity, and at infinite explosion duration, respectively. Within the critical regimes, the fragment-size distributions satisfy a scaling form qualitatively similar to that of the cluster-size distribution of percolation, but they belong to another universality class. Energy balance arguments give a correlation length exponent that is exactly one-half of its percolation value. A single crack dominates fragmentation in the slow-fracture limit, as expected.
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Affiliation(s)
- JA Astrom
- Department of Physics, University of Jyvaskyla, P.O. Box 35, FIN-40351 Jyvaskyla, Finland
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Myllys M, Maunuksela J, Alava MJ, Ala-Nissila T, Timonen J. Scaling and noise in slow combustion of paper. Phys Rev Lett 2000; 84:1946-1949. [PMID: 11017667 DOI: 10.1103/physrevlett.84.1946] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/1999] [Indexed: 05/23/2023]
Abstract
We present results of high resolution experiments on kinetic roughening of slow combustion fronts in paper, focusing on short length and time scales. Using three different grades of paper, we find that the combustion fronts show apparent spatial and temporal multiscaling at short scales. The scaling exponents decrease as a function of the order of the corresponding correlation functions. The noise affecting the fronts reveals short range temporal and spatial correlations, and non-Gaussian noise amplitudes. Our results imply that the overall behavior of slow combustion fronts cannot be explained by standard theories of kinetic roughening.
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Affiliation(s)
- M Myllys
- Department of Physics, University of Jyvaskyla, P.O. Box 35, FIN-40351 Jyvaskyla, Finland
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