Path (un)predictability of two interacting cracks in polycarbonate sheets using Digital Image Correlation

Crack propagation is tracked here with Digital Image Correlation analysis in the test case of two cracks propagating in opposite directions in polycarbonate, a material with high ductility and a large Fracture Process Zone (FPZ). Depending on the initial distances between the two crack tips, one may observe different complex crack paths with in particular a regime where the two cracks repel each other prior to being attracted. We show by strain field analysis how this can be understood according to the principle of local symmetry: the propagation is to the direction where the local shear - mode K_II in fracture mechanics language - is zero. Thus the interactions exhibited by the cracks arise from symmetry, from the initial geometry, and from the material properties which induce the FPZ. This complexity makes any long-range prediction of the path(s) impossible.

Molecule-like photodynamics of Au102(pMBA)44 nanocluster

Photophysical properties of a water-soluble cluster Au102(pMBA)44 (pMBA = para-mercaptobenzoic acid) are studied by ultrafast time-resolved mid-IR spectroscopy and density functional theory calculations in order to distinguish between molecular and metallic behavior. In the mid-IR transient absorption studies, visible or near-infrared light is used to electronically excite the sample, and the subsequent relaxation is monitored by studying the transient absorption of a vibrational mode in the ligands. Based on these studies, a complete picture of energy relaxation dynamics is obtained: (1) 0.5-1.5 ps electronic relaxation, (2) 6.8 ps vibrational cooling, (3) intersystem crossing from the lowest triplet state to the ground state with a time constant 84 ps, and (4) internal conversion to the ground state with a time constant of ∼3.5 ns. A remarkable finding based on this work is that a large cluster containing 102 metal atoms behaves like a small molecule in a striking contrast to a previously studied slightly larger Au144(SC2H4Ph)60 cluster, which shows relaxation typical for metallic particles. These results therefore establish that the transition between molecular and metallic behavior occurs between Au102 and Au144 species.

Optical projection tomography as a tool for 3D imaging of hydrogels

An Optical Projection Tomography (OPT) system was developed and optimized to image 3D tissue engineered products based in hydrogels. We develop pre-reconstruction algorithms to get the best result from the reconstruction procedure, which include correction of the illumination and determination of sample center of rotation (CoR). Existing methods for CoR determination based on the detection of the maximum variance of reconstructed slices failed, so we develop a new CoR search method based in the detection of the variance sharpest local maximum. We show the capabilities of the system to give quantitative information of different types of hydrogels that may be useful in its characterization.

Nanoparticle imaging. Electron microscopy of gold nanoparticles at atomic resolution

Structure determination of gold nanoparticles (AuNPs) is necessary for understanding their physical and chemical properties, but only one AuNP larger than 1 nanometer in diameter [a 102-gold atom NP (Au102NP)] has been solved to atomic resolution. Whereas the Au102NP structure was determined by x-ray crystallography, other large AuNPs have proved refractory to this approach. Here, we report the structure determination of a Au68NP at atomic resolution by aberration-corrected transmission electron microscopy, performed with the use of a minimal electron dose, an approach that should prove applicable to metal NPs in general. The structure of the Au68NP was supported by small-angle x-ray scattering and by comparison of observed infrared absorption spectra with calculations by density functional theory.

Effective dose assessment in the maxillofacial region using thermoluminescent (TLD) and metal oxide semiconductor field-effect transistor (MOSFET) dosemeters: a comparative study

OBJECTIVES

The objective of this study was to compare the performance of metal oxide semiconductor field-effect transistor (MOSFET) technology dosemeters with thermoluminescent dosemeters (TLDs) (TLD 100; Thermo Fisher Scientific, Waltham, MA) in the maxillofacial area.

METHODS

Organ and effective dose measurements were performed using 40 TLD and 20 MOSFET dosemeters that were alternately placed in 20 different locations in 1 anthropomorphic RANDO(®) head phantom (the Phantom Laboratory, Salem, NY). The phantom was exposed to four different CBCT default maxillofacial protocols using small (4 × 5 cm) to full face (20 × 17 cm) fields of view (FOVs).

RESULTS

The TLD effective doses ranged between 7.0 and 158.0 µSv and the MOSFET doses between 6.1 and 175.0 µSv. The MOSFET and TLD effective doses acquired using four different (FOV) protocols were as follows: face maxillofacial (FOV 20 × 17 cm) (MOSFET, 83.4 µSv; TLD, 87.6 µSv; -5%); teeth, upper jaw (FOV, 8.5 × 5.0 cm) (MOSFET, 6.1 µSv; TLD, 7.0 µSv; -14%); tooth, mandible and left molar (FOV, 4 × 5 cm) (MOSFET, 10.3 µSv; TLD, 12.3 µSv; -16%) and teeth, both jaws (FOV, 10 × 10 cm) (MOSFET, 175 µSv; TLD, 158 µSv; +11%). The largest variation in organ and effective dose was recorded in the small FOV protocols.

CONCLUSIONS

Taking into account the uncertainties of both measurement methods and the results of the statistical analysis, the effective doses acquired using MOSFET dosemeters were found to be in good agreement with those obtained using TLD dosemeters. The MOSFET dosemeters constitute a feasible alternative for TLDs for the effective dose assessment of CBCT devices in the maxillofacial region.

Solvation chemistry of water-soluble thiol-protected gold nanocluster Au₁₀₂ from DOSY NMR spectroscopy and DFT calculations

The hydrodynamic diameter of Aum(pMBA)n [(m, n) = (102, 44) and (144, 60)] clusters in aqueous media was determined via DOSY NMR spectroscopy. The apparent size of the same (n, m) cluster depends on the counter ion of the deprotonated pMBA(-) ligand as explained by the competing ion-pair strength and hydrogen bonding interactions studied in DFT calculations. The choice of the counter ion affects the surface chemistry and molecular structure at the organic/water interface, which is relevant for biological applications.

Vibrational Perturbations and Ligand-Layer Coupling in a Single Crystal of Au144(SC2H4Ph)60 Nanocluster

We have determined vibrational signatures and optical gap of the Au144(PET)60 (PET: phenylethylthiol, SC2H4Ph) nanocluster solvated in deuterated dichloromethane (DCM-D2, CD2Cl2) and in a single crystal. For crystals, solid-state (13)C NMR and X-ray diffraction were also measured. A revised value of 2200 cm(-1) (0.27 eV) was obtained for the optical gap in both phases. The vibrational spectra of solvated AU144(PET)60 closely resembles that of neat PET, while the crystalline-state spectrum exhibits significant inhomogeneous spectral broadening, frequency shifts, intensity transfer between vibrational modes, and an increase in the overtone and combination transition intensities. Spectral broadening was also observed in the (13)C NMR spectrum. Changes in the intensity are explained due to vibrational coupling of the normal modes induced by the crystal packing, and the vibrational broadening is caused by ligand-environment inhomogeneity in the crystal. This indicates a pseudocrystalline state where the cluster cores are arranged in periodic fashion, while the ligand-layer molecules between the cores form amorphous structures.

Assessment of radiation exposure in dental cone-beam computerized tomography with the use of metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters and Monte Carlo simulations

OBJECTIVES

The aims of this study were to assess the organ and effective dose (International Commission on Radiological Protection (ICRP) 103) resulting from dental cone-beam computerized tomography (CBCT) imaging using a novel metal-oxide semiconductor field-effect transistor (MOSFET) dosimeter device, and to assess the reliability of the MOSFET measurements by comparing the results with Monte Carlo PCXMC simulations.

STUDY DESIGN

Organ dose measurements were performed using 20 MOSFET dosimeters that were embedded in the 8 most radiosensitive organs in the maxillofacial and neck area. The dose-area product (DAP) values attained from CBCT scans were used for PCXMC simulations. The acquired MOSFET doses were then compared with the Monte Carlo simulations.

RESULTS

The effective dose measurements using MOSFET dosimeters yielded, using 0.5-cm steps, a value of 153 μSv and the PCXMC simulations resulted in a value of 136 μSv.

CONCLUSIONS

The MOSFET dosimeters placed in a head phantom gave results similar to Monte Carlo simulations. Minor vertical changes in the positioning of the phantom had a substantial affect on the overall effective dose. Therefore, the MOSFET dosimeters constitute a feasible method for dose assessment of CBCT units in the maxillofacial region.

Experimental and Theoretical Determination of the Optical Gap of the Au144(SC2H4Ph)60 Cluster and the (Au/Ag)144(SC2H4Ph)60 Nanoalloys

Au144PET60 and Au144-xAgxPET60 (PET = SC2H4Ph, phenylethylthiolate, and 30 ≤ x ≤ 53) clusters were studied by optical spectroscopy and linear response time-dependent density functional theory. Spectra of thin dry films were measured in order to reveal the onset for electronic absorption. The optical gap of the Au144PET60 cluster was determined at 0.19 ± 0.01 eV, which agrees well with the computed energy for the first optical transition at 0.32 eV for a model cluster Au144(SH)60 when the line width of individual transitions is taken into account. The optical gaps for the Au144-xAgxPET60 alloy clusters were observed in a range of 0.12-0.26 eV, in good agreement with the calculations giving 0.16-0.36 eV for the lowest-energy optical transitions for corresponding Au144-xAgx(SH)60 models. This indicates that the gap is only moderately affected by doping Au with Ag. This work constitutes the first accurate determination of the fundamental spectroscopic gap of these compounds.

Facing the key workplace challenge: assessing and preventing exposure to nanoparticles at source

Nanomaterials present new challenges to understanding, predicting, and managing potential health risks in occupational environments. In this study, we characterize the key physical processes related to formation and growth of nanoparticles. The main focus is on various occupational environments, as these are known to be major environments with nanoparticles in indoor air. The protection of people potentially to be exposed to nanoparticles is one of the key issues in terms of risk assessment and prevention. Two of the main protection techniques that are discussed and characterized are ventilation and filtration, which are widely used in practical applications.

Creep of a fracture line in paper peeling

The slow motion of a crack line is studied via an experiment in which sheets of paper are split into two halves in a "peel-in-nip" (PIN) geometry under a constant load, in creep. The velocity-force relation is exponential. The dynamics of the fracture line exhibits intermittency, or avalanches, which are studied using acoustic emission. The energy statistics is a power law, with the exponent beta ~ 1.8 +/- 0.1. Both the waiting times between subsequent events and the displacement of the fracture line imply complicated stick-slip dynamics. We discuss the correspondence to tensile PIN tests and other similar experiments on in-plane fracture and the theory of creep for elastic manifolds.

Indoor air microbes and respiratory symptoms of children in moisture damaged and reference schools

Microbial indoor air quality and respiratory symptoms of children were studied in 24 schools with visible moisture and mold problems, and in eight non-damaged schools. School buildings of concrete/brick and wooden construction were included. The indoor environment investigations included technical building inspections for visible moisture signs and microbial sampling using six-stage impactor for viable airborne microbes. Children's health information was collected by questionnaires. The effect of moisture damage on concentrations of fungi was clearly seen in buildings of concrete/brick construction, but not in wooden school buildings. Occurrence of Cladosporium, Aspergillus versicolor, Stachybotrys, and actinobacteria showed some indicator value for moisture damage. Presence of moisture damage in school buildings was a significant risk factor for respiratory symptoms in schoolchildren. Association between moisture damage and respiratory symptoms of children was significant for buildings of concrete/brick construction but not for wooden school buildings. The highest symptom prevalence was found during spring seasons, after a long exposure period in damaged schools. The results emphasize the importance of the building frame as a determinant of exposure and symptoms.

A new potential toxaphene congener: synthesis, GC/EI-MS study, crystal structure, NMR analysis, and ab initio calculations of 3-endo,5-endo-dichloro-7,7-bis-chloromethyl-4-dichloromethyl-tricyclo[2.2.1.0(2,6)]heptane

A new potential toxaphene congener 3-endo,5-endo-dichloro-7,7-bis-chloromethyl-4-dichloromethyl-tricyclo[2.2.1.0(2,6)]heptane 2 has been isolated from reaction mixture obtained by the chlorination of 2-exo, 10,10-trichlorobornane 1. The X-ray structural analysis of 2 revealed an unusual tricyclic structure, where the two chlorine atoms occupying endo-positions are in close spatial proximity with each other and near to the neighbouring CHCl2 group. Further, it revealed that the symmetry of the molecule is distorted. The 1H and 13C NMR spectra of 2 have been assigned by means of 1H, 1H double-quantum filtered correlation spectroscopy (DQF COSY), PFG 1H, 13C HMQC (pulsed field gradient heteronuclear multiple-quantum coherence), 1H, 13C heteronuclear multiple bond correlation (HMBC) experiments, and computer aided 1H NMR spectral analysis. The asymmetry of 2 is also discernible on the 1H NMR parameters. In addition, gas chromatographic (GC) properties and electron impact (EI) mass spectrum of 2 has been studied. Ab initio Hartree-Fock (HF) method with the basis set 6-31G(d) has been used for the optimization of the equilibrium geometry and calculation of total energy for 2. The optimized geometry is in good agreement with the crystal structure. According to the rotation energy profile calculated at the HF/6-31G(d) level, rotation of the chloromethyl and dichloromethyl groups are highly unlikely at the room temperature.

Working memory of identification of emotional vocal expressions: an fMRI study

The distribution of brain activation during working memory processing of emotional vocal expressions was studied using functional magnetic resonance imaging (fMRI) in eight female subjects performing n-back tasks with three load levels (0-back, 1-back, and 2-back tasks). The stimuli in the n-back tasks were the Finnish female name [Saara] uttered in an astonished, angry, frightened, commanding, and scornful mode, and the subjects were instructed to memorize the emotional connotation of the stimuli. Subregions in the prefrontal, parietal, and visual association areas were load-dependently activated during the performance of the n-back tasks. The most consistently activated areas in the prefrontal region were detected in the inferior frontal gyrus corresponding to Brodmann's areas (BAs) 44 and 45 and in the middle and superior frontal gyri (BAs 6/8). Activation was also found in the inferior parietal lobe and intraparietal sulcus (BAs 40/7) and visual association areas including the lingual and fusiform gyri. The results suggest that a distributed neuronal network in occipital, parietal, and frontal areas is involved in working memory processing of emotional content of aurally presented information.

Analysis of moisture findings in the interior spaces of Finnish housing stock

A grading system was developed to rate the moisture damage profile of dwellings and to study the relationship between moisture-induced indoor air problems and occupant health. A total of 630 randomly selected houses and apartments, built between 1950 and 1989, were visually inspected. Moisture observations were standardized into three damage levels. Thus, a system to classify the homes into three grades was devised. The two grades of homes associated with the highest levels of damage were graded as index homes. Overall, 51% of the sample had some kind of moisture fault in them and one in every three homes (33%) was classified as an index home. The mean number of damage incidents in the index dwellings varied from 1.4 to 2.6. The mean number of damage incidents in the reference homes was 0.28. Prevalence of index dwellings was significantly higher (p < 0.01) in houses (38%) than in apartments (26%). There was no major difference in the prevalence of index buildings in houses built in any particular decade (30-35%). Moisture was observed in 28% of bathrooms, in 10% of kitchens, and in 17% of other spaces. Indoor relative humidity (RH) levels were low in most homes.

Three years in force: has the finnish Act on the Status and Rights of Patients materialized?

Finland enacted as the first country in Europe an Act on the Status and Rights of Patients. This report deals with the experiences gained in the course of the implementation of the patient law during the past three years it has been in force. Patients' rights to information and self-determination are considered as the most central matters. Also the right to good care, the status of minor patients and patients' right to privacy protection are important matters. Patient ombudsmen have tried to convey information to the field on the law and the obligations it imposes on health care personnel. The law is considered to already have influenced practical functions within health care. However, there is still much to improve in patients' access to information and in the treatment of patients; the attitudes and the care traditions change slowly. That living wills have become more general is a manifestation of people's willingness to use their right of self-determination even when they are no more able to express their will. Complaints that are processed at the local level are frequent, and each organization has a Patient Ombudsman. The principles of this system of complaints and patient ombudsmen are considered good, but there is much room for improvement.