Inverse identification of hyperelastic constitutive parameters of skeletal muscles via optimization of AI techniques

Studies on the deformation characteristics and stress distribution in loaded skeletal muscles are of increasing importance. Reliable prediction of hyperelastic material parameters requires an inverse process, which possesses challenges. This work proposes two inverse procedures to identify the hyperelastic material parameters of skeletal muscles. The first one integrates nonlinear finite element method (FEM), random forest (RF) model, and Bayesian optimization (BO) algorithm. The other one integrates FEM, RF and hybrid Grid Search (GS), and Random Search (RS) algorithm. FEM models are first established to simulate nonlinear deformation of skeletal muscles subject to compression based on nonlinear mechanics principals. A dataset of nonlinear relationship between the nominal stress and principal stretch of skeletal muscles is created using our FEM models and the nonlinear relationship is learned through RF model. The BO, hybrid GS and RS algorithms are used to adjust the major model parameters in RF. Then the optimized RF is utilized to predict hyperelastic material parameters of skeletal muscles, with the help of uniaxial compression experiments. Intensive studies also have been carried out to compare the RF-BO approach with RF-Search approach, and the comparison results show that RF-BO approach is an effective and accurate approach to identify the hyperelastic material parameters of skeletal muscles. The present RF-BO model can be further extended for the predictions of constitutive parameters of other types of nonlinear soft materials.

Perfectly matched layer absorbing boundary conditions for Euler equations with oblique mean flows modeled with smoothed particle hydrodynamics

Absorbing boundary conditions (ABCs) play a critical role in the simulation of sound or wave propagation problems. This paper proposes a technique of space-time transformed perfectly matched layer (PML) boundary condition implemented in a widely used mesh-free method called smoothed particle hydrodynamic (SPH) method, to absorb the outgoing sound waves with oblique shear mean flow. Special consideration is given to the particle features of the SPH, and the PMLs are formulated to correct the truncation error of SPH and absorb the outgoing wave at the same time, aiming to reduce the storage and computational cost in the infinite computational domain. Because the group velocity and phase velocity of the outgoing sound waves in the PMLs may be in different directions, exponentially growing pseudo reflections can result. The authors thus employ space-time transformation to eliminate the reflections effectively in PML boundaries for stable solutions. Moreover, a uniform framework of PML absorbing boundary conditions for Euler equations in the cases of arbitrary oblique mean flow and static media is derived. Finally, the present PML-SPH method with this stable absorbing boundary is applied to simulate sound waves propagating with mean flow. The obtained numerical results agree very well with the reference results.

A compact perfectly matched layer algorithm for acoustic simulations in the time domain with smoothed particle hydrodynamic method

This paper focuses on the development of absorbing boundary conditions and their implementation in the smoothed particle hydrodynamics (SPH) method for wave propagation problems. A compact perfectly matched layer (C-PML) approach is formulated for transient acoustic problems in an infinite space using SPH models with a computational domain of finite dimensions. The proposed approach is based on the concept of fictitious physical damping acting within the additional perfectly matched layers (PMLs) to absorb outgoing waves to practically eliminate the reflection of waves from the boundary of the finite computational domain. To reduce the amount of computations resulting from the layers and improve the computational stability with respect to time, the C-PML algorithm uses the time exponential differencing scheme with small PML domains implemented in an SPH code for transient analyses of waves propagating in acoustic media. Tests of Gaussian pulse sound wave propagation are conducted to demonstrate the effectiveness of the proposed algorithm. The results show that the C-PML algorithm with SPH can absorb the outgoing wave with fewer layers than the conventional PML algorithm. The influence of the thickness of the PML layers, attenuation coefficient, and smoothing length on the C-PML algorithm are analyzed.

[Application and analysis of abdominal aortic branch malperfusion pattern in thoracic endovascular aortic repair for Stanford B aortic dissection]

OBJECTIVE

To evaluate the efficiency of thoracic endovascular aortic repair (TEVAR) in dealing with abdominal aortic branch malperfusion based on the analysis of aortic computed tomography angiography (CTA) images in pre- and post-TEVAR.

METHODS

Retrospective analysis from September 2015 to March 2016 in single institution to 32 patients, diagnosed as Stanford B aortic dissection with abdominal aortic branch malperfusion, CTA images in pre- and post-TEVAR were collected. Based on the aortic branch malperfusion pattern redefined by Nagamine, we identified and characterized branch malperfusion pattern for four abdominal aortic branches (celiac trunk, superior mesenteric artery, bilateral renal artery) in statistical analysis.

RESULTS

In the four abdominal aortic branches (total 128 branches), 86 branches (67.2%) expressed with Class I patterns, in which subtype I-b presented with 0.8%, subtype I-c with 5.5%; 14 branches (10.9%) expressed with Class II patterns, in which subtype II-b-1 with 3.9%, subtype II-b-2 with 3.1%; 16 branches (12.5%) expressed with Class III patterns, all with subtype III-a, no subtype III-b and III-c presented. The remaining 12 branches were normal. The 100% successful rate of TEVAR obtained in 32 patients performed. The mean following-up was 4 months. Aortic CTA showed that among the 14 "high-risk" abdominal aortic branch malperfusion, 13 (92.9%) with obvious branch malperfusion in post-TEVAR were observed to improve, and the remaining one branch malperfusion (7.1%) was observed to change from subtype I-b to I-c.

CONCLUSION

Few ratios in abdominal aortic branches suffered with obvious malperfusion complicated by Stanford B aortic dissection. For branches with "high-risk" malperfusion pattern, optimal changes were observed in abdominal aortic branch without revascularization in post-TEVAR, as well other branches with non-"high-risk" pattern perfusion were mostly stable in post-TEVAR. It could be of profound benefit to extend branch malperfusion patterns redefined by Nagamine in clinical practice to assess aortic dissection and in further guide for revascularization or not.

Levels and profiles of unintentionally produced persistent organic pollutants in surface soils from Shanxi province, China

Six species of unintentionally produced persistent organic pollutions comprised of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, polychlorinated biphenyls, polychlorinated naphthalenes, hexachlorobenzene and pentachlorobenzene in soils collected from Shanxi province, China were determined. The sum toxic equivalent ranged from 0.14 to 2.20 with an average of 0.94 pg TEQ/g. Polychlorinated dibenzo-p-dioxins/furans contributed the most toxic proportion to the total toxic equivalent. CB-126 was the most toxic contributor to polychlorinated biphenyls. CN66/67 and CN73 are the dominant toxic congeners to polychlorinated naphthalenes. From the patterns, it was speculated that thermal related industries were possible sources of unintentionally produced persistent organic pollutions.

Identification and validation of quantitative trait loci conferring tan spot resistance in the bread wheat variety Ernie

Tan spot, caused by Pyrenophora tritici-repentis, is a foliar disease of wheat, and it can inflict serious reduction in grain yield and quality. The bread wheat variety Ernie was found to be immune to this disease in Australia, and its genetic control was investigated by quantitative trait loci (QTL) analysis using a doubled haploid population. Eight QTL were identified in this population from three independent trials, and four of them were derived from the parent Ernie. The most significant QTL was located on chromosome arm 2BS, explaining 38.2, 29.8 and 36.2% of the phenotypic variance, respectively, in these trials. The effects of the 2BS QTL were further validated in four additional populations. The presence of this single QTL reduced disease severity by between 29.2 and 67.1% with an average of 50.5%. The significant effects of this QTL and its consistent detection across all the trials with different genetic backgrounds make it an ideal target for breeding programmes as well as for its further characterization. Data from this study also showed that neither plant height nor heading date significantly affects tan spot resistance.

Application of independent component analysis to dynamic contrast-enhanced imaging for assessment of cerebral blood perfusion

Dynamic contrast-enhanced (DCE) imaging is widely used for in vivo assessment of the cerebral blood perfusion. In this work, we investigate the use of independent component analysis (ICA) on DCE imaging data for assessment of cerebral blood perfusion, without any prior knowledge of the underlying tissue vasculature and arterial input function. The minimum description length (MDL) criterion and principle component analysis (PCA) were employed to reduce the dimension of the data. An oscillating index method was used to select the components of interest. Numerical simulation and patient case studies were carried out to investigate the performance of ICA. The results show that ICA is able to extract physiologically meaningful components from the DCE imaging data. The advantages of ICA include its efficiency of computation, clarity of obtained component maps, and no need of the manually selected input function. The obtained independent component maps can provide reliable reference to identify the arterial and venous structure, and allow better demarcation of the tumor territories. The potential of ICA to be a useful clinical tool for diagnosis of cerebral vascular disease and for the assessment of treatment response has been demonstrated.

Prediction of recovery from a post-traumatic coma state by diffusion-weighted imaging (DWI) in patients with diffuse axonal injury

INTRODUCTION

To determine whether diffusion-weighted magnetic resonance (MR) imaging findings combined with initial clinical factors indicate the depth of shearing lesions in the brain structure and therefore relate to coma duration in diffuse axonal injury (DAI).

METHODS

A total of 74 adult patients (48 male and 26 female) with DAI were examined with conventional MR imaging and diffusion-weighted MR imaging between 2 hours and 20 days after injury. Apparent diffusion coefficient (ADC) maps were obtained and the mean ADC values of each region of interest (ROI) were measured using MRI console software. The involvement of the brainstem, deep gray matter, and corpus callosum was determined for each sequence separately as well as for the combination of all sequences. The correlations between MR imaging findings indicating the presence of apparent brain injury combined with initial clinical factors were determined.

RESULTS

Clinical characteristics, such as initial score on the Glasgow coma scale (GCS), age and number of all lesions, and ADC scores were predictive of the duration of coma.

CONCLUSION

It was possible to predict post-traumatic coma duration in DAI from cerebral MR imaging findings combined with clinical prognostic factors in the acute to subacute stage after head injury. Age, ADC scores, GCS score and number of lesions were highly significant in predicting coma duration. The technique presented here might provide a tool for in vivo detection of DAI to allow the prediction of the coma duration during the early stages in patients with traumatic brain injury.

Relationships between the folding rate constant and the topological parameters of small two-state proteins based on general random walk model

In this paper, we propose an analytically tractable model of protein folding based on one-dimensional general random walk. A second-order differential equation for the mean folding time of a single protein is constructed which can be used to derive the observed relationship between the folding rate constant and the number of native contacts. The parameters appearing in the model can be determined by fitting the theoretical prediction to the experimental result. In addition, taking into account the fact that the number of native contacts is almost proportional to the relative contact order, we can also explain the observed relationship between the folding rate constant and the relative contact order.

Early diffusion weighted imaging and expression of heat shock protein 70 in newborn pigs with hypoxic ischaemic encephalopathy

OBJECTIVE

To establish a cerebral hypoxia ischaemic model in piglets and to explore the early diffusion weighted imaging (DWI) as well as the expression of heat shock protein 70 (HSP70) with hypoxic ischaemic encephalopathy (HIE).

METHODS

Twenty four 3 day old piglets were permanently ligated common carotid arteries bilaterally and ventilated with 3% oxygen for 30 minutes, and their brains were examined at three hours, six hours, and 24 hours after hypoxic ischaemia with T2 weighted images and diffusion weighted images. Apparent diffusion coefficient (ADC) values were measured and HSP70 expression was detected in the central and peripheral regions of lesions.

RESULTS

Abnormal signal intensity was detected on DWI and ADC maps in three hypoxic ischaemic groups. ADC values in the central lesions rapidly decreased, whereas ADC values in the peripheral regions reduced prominently at 24 hours after hypoxic ischaemia. There were significant differences (p<0.01) between ADC values of the central regions and the peripheral regions of lesions. The number of HSP70 positive cells was low at three hours, raised at the highest peak at six hours, and then rapidly decreased. There was statistical difference between HSP70 positive cells in the central regions and those in peripheral regions (p<0.01).

CONCLUSION

DWI may identify more early lesions, and improve conspicuity in the acute setting. ADC values can be used as an objective measure for hypoxic ischaemic injury. Tissue reversibility can be further reflected according to the information of ADC values and HSP70 immunohistochemical staining.

The brain mapping on reinforcement acupuncture stimulation at ST36 (zusanli) evidenced by fMRI

To characterize the brain mapping on reinforcement acupuncture stimulation at ST36 (zusanli), and to discuss the mechanisms of acupuncture to treat diseases. fMRI was performed on 26 healthy Chinese student volunteers. Sixteen subjects were acupunctured at the acupoint ST36, while 10 others at sham-acupoint (lateral from ST36 about 3 cm). The fMRI studies were performed using a gradient echo-EPI sequence. Brain mapping were generated using GE Functool program. Cerebral blood flow and correlation coefficient (CC) of ROl were analyzed. Stimulation at the right ST36 elicited 13 brain functional areas, and 10 of these areas were the same with the sham-acupoint group. However, only the temporal gyrus was specificity while by using reinforcement manual acupuncture (MA) at ST36 (Fisher's Exact test, P=0.022), and the contralateral hemisphere activation was prominent (McNemer test, P=0.020). Our results support the theory of acupuncture about meridian distribution overlapping on the whole body. The special transmission channel of meridian may exists, and it may be consist of spinal nerve and autonomic nerve. However, our results may oppose the theory concerning on stomach meridian walking lateral.

Coma duration prediction in diffuse axonal injury: analyses of apparent diffusion coefficient and clinical prognostic factors

The purpose of this paper is to evaluate the hypothesis that the Apparent Diffusion Coefficient (ADC) values combined with initial clinical factors indicates the depth of shearing lesions in the brain structure and therefore relates to coma duration of diffuse axonal injury (DAI). Seventy-four adult patients (48 male and 26 female patients) with diffuse axonal injury were examined with convention MR imaging and diffusion weighted MR imaging between 2 hours and 20 days after injury. Apparent diffusion coefficient (ADC) maps were obtained and the mean ADC values of each Region of Interest (ROI) were measured using MRI console software. The lesions involvement of brainstem, deep gray matter, and corpus callosum were determined for each sequence separately as well as for the combination of all sequences. The correlations between magnetic resonance (MR) imaging findings of presence of apparent brain injury combined with initial clinical factors were investigated. Clinical characteristics, such as initial score on the Glasgow Coma Scale (GCS), age, and the number of all lesions, ADC scores of the patient in MR findings were predictive of the duration of coma. Post-traumatic coma duration of DAI could be predicted by cerebral MRI findings in the acute to subacute stage after head injury combined with clinical prognostic factors. Age, ADC scores, GCS, number of lesions are highly significant in predicting coma duration. The technique presented herein might provide a tool for in vivo detection of DAI for the coma duration at the early stages in patients with traumatic brain injury.

Protein designability analysis in sequence principal component space using 2D lattice model

The number of proteins that fold into a certain structure differs drastically. The designability of a protein structure, which is defined as the number of sequences that have that structure as their unique lowest energy state, is studied in this paper using a simplified lattice model. The two-letter (HP) code and the pair-contact energy model are employed in the formulation of the relationship between the protein sequences and the compact structures. Due to the correlations between different dimensions, principal component analysis (PCA) is carried out to remove these correlations and develop reliable approximations of probability density functions of the protein sequences and the compact structures. An estimation of designability is derived using these probability density functions. Good correlation between estimated designabilities and those obtained through enumerative calculations is successfully achieved.

Finite Element Analysis of an Osseointegrated Stepped Screw Dental Implant

An osseointegrated stepped screw dental implant was evaluated using 2-dimensional finite element analysis (FEA). The implant was modeled in a cross section of the posterior human mandible digitized from a computed tomography (CT) generated patient data set. A 15-mm regular platform (RP) Branemark implant with equivalent length and neck diameter was used as a control. The study was performed under a number of clinically relevant parameters: loading at the top of the transmucosal abutment in vertical, horizontal, and 45° oblique 3 orientations. Elastic moduli of the mandible varied from a normal cortical bone level (13.4 GPa) to a trabecular bone level (1.37 GPa). The study indicated that an oblique load and elastic moduli of the cortical bone are important parameters to the implant design optimization. Compared with the cylindrical screw implant, the maximum von Mises stress of the stepped screw implant model was 17.9% lower in the trabecular bone-implant area. The study also showed that the stepped screw implant is suitable for the cortical bone modulus from 10 to 13.4 GPa, which is not necessarily as strict as the Branemark implant, for which a minimum 13.4 GPa cortical bone modulus is recommended.

Finite element analysis of four thread-form configurations in a stepped screw implant

The purpose of this study was to determine the optimal thread form configuration for an experimental stepped screw implant. Two-dimensional finite element analysis was applied to model the experimental stepped screw implant in a standard cross-section of the posterior human mandible digitized from a CT-generated patient data set. Four different thread form configurations: v-thread (V), thin-thread (T), and two square-thread forms of 0.24 mm (S1) and 0.36 mm (S2) thread width were compared under oblique load in normal cortical bone condition. The support-type constraint position changed from middle to the base of the bone segment. In middle support-type constraint position only the thin-thread (T) model demonstrated significantly different stress distribution from the other three models, however, in base support-type constraint position T and S1 models demonstrated significantly different stress distribution from the other two models. The results implies that v-thread (V) or large square-thread (S2) are optimal thread form for the experimental stepped screw implant. While, minimal support constraints allow clearer differentiation of the stress picture between the different stepped screw types at the trabecular bone-implant interface.

Shape identification of underwater objects using backscattered frequency signals

The inverse problems in the area of the acoustic scattering often concern the determination of the size, shape, and orientation of an object using the scattered field data. This paper presents a method to retrieve the shape information of an underwater object using illuminated lengths, which can be obtained from the ramp response signatures of the object. An ellipsoidal object submerged in water is considered. Both the low and high backscattered frequency data have been employed to calculate the illuminated lengths. The calculated results show that the illuminated lengths will be more accurate, if only the high-frequency-range data are employed. For ellipsoidal objects, any three illuminated lengths that are not of a same plane can in theory fully determine the shape of the ellipsoid. As the calculated illuminated lengths contain numerical errors, the calculated results of the three semiaxes of the ellipsoid will deteriorate and become unreliable, especially when the three incident directions of the illuminated lengths become close. The reason is that the condition number of the coefficient matrix becomes big in such situations, which leads to an increase of the relative error upper limit in the calculated results. To avoid such errors in close incident wave cases, it is found that the use of more than three incident waves works very well in the shape identification of an underwater object.

Application of finite element analysis in implant dentistry: a review of the literature

Finite element analysis (FEA) has been used extensively to predict the biomechanical performance of various dental implant designs as well as the effect of clinical factors on implant success. By understanding the basic theory, method, application, and limitations of FEA in implant dentistry, the clinician will be better equipped to interpret results of FEA studies and extrapolate these results to clinical situations. This article reviews the current status of FEA applications in implant dentistry and discusses findings from FEA studies in relation to the bone-implant interface, the implant-prosthesis connection, and multiple-implant prostheses.

Dispersion and characteristic surfaces of waves in laminated composite circular cylindrical shells

The dispersion behaviors and characteristic surfaces of waves in a laminated composite circular cylindrical shell are investigated using a semianalytical method based on the theory of three-dimensional elasticity. The radial displacement of the shell is modeled by finite elements, while the axial and circumferential displacements are expanded as the complex exponentials. The associated characteristic equation is developed by means of the Hamilton's principle. The eigenvalues are established in terms of the Rayleigh quotient. Six characteristic wave surfaces, viz., the phase velocity, phase slowness, and phase wave surfaces, as well as the group velocity, group slowness, and group wave surfaces, are introduced to visualize the effects of anisotropy on wave propagation. Numerical examples demonstrate that the ratio of the inner radius to the thickness of the shell has a stronger influence on the frequency spectra in the circumferential wave than on that in the axial wave; that negative group velocity appears at a range of smaller wave numbers and the range varies as the wave normal and the ratio of the inner radius to the thickness of the shell; and that the characteristic wave surfaces vary with the propagation modes of waves, the ratio of the inner radius to the thickness of the shell, and the lay-ups of the laminated shells.

A strip-element method for analyzing wave scattering by a crack in an immersed axisymmetric laminated composite cylinder

A strip-element method is presented for analyzing wave scattering by a crack in a laminated composite cylinder immersed in a fluid. In this approach, two-nodal-line and three-nodal-line axisymmetric strip elements are employed to model the fluid and laminated cylinder, respectively. Governing equations for the fluid and solid elements in the frequency domain are derived with a variational method and the Hamilton principle. The associated characteristic equations in the wave-number domain are obtained through Fourier transform techniques. Responses of the fluid-loaded cylinder to a line load are found by a modal-analysis method and inverse Fourier transform techniques. Numerical results are presented for cracked laminated composite cylinders submerged in water. Water is found to have strong influence on the scattered wave fields in a cracked laminated composite cylinder.

An investigation of adolescent health from China

In a senior high school in the Weicheng District of Weifang City, we studied the health of a total 445 students. The age of the first emission was 15.22 +/- 2.24 years, and the age of menarche was 13.56 +/- 2.26 years. Because 47.9% of boys and 63.8% of girls did not have previous knowledge about puberty, 39.9% of boys and 52.2% of girls felt puzzled and disgusted with the onset of puberty. About 18% of boys and about 2% of girls reported masturbation. The average frequency of masturbation was 3.5 times a month in the boys and two times monthly in girls. Adolescents acquired sexual knowledge and information predominantly from magazines (25.8% of boys and 28.0% of girls). About 64% of boys and 44% of girls wanted to be given educational programs on sex. About 43% of boys and 1% of girls smoked cigarettes and 83.5% of boys and 54.9% of girls drank alcohol. The survey suggested that it is essential to teach the senior high school students about the psychosocial and behavioral characteristics of adolescence and promote research on adolescent medicine.

[Lipid metabolism and pregnancy induced hypertension]

Lipid metabolism was studied in 30 healthy non-pregnant women, 35 normal pregnant women and 34 patients with pregnancy induced hypertension (PIH). Total cholesterol (TC), triglycerides (TG), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), LDL-C/HDL-C ratio, and athero-sclerosis index (AI) were determined. In comparison with the non-pregnant status, lipid levels did not increased during normal mid-trimester pregnancy, but significantly increased at late trimester of normal pregnancy (P < 0.05). There was no significant difference in lipid levels between normal late pregnancy and PIH of mild and moderate degree, but TG and AI were significantly higher in cases with severe PIH. It showed that: lipid profiles in severe PIH was characterized by type IV hyperlipidemia; high lipid levels during normal late pregnancy might be a physiological phenomenon which presents a risk factor for PIH; marked increase of TG and AI in severe PIH may result in a rise of lipid peroxide (LPO).

[Cytotoxicity of human lymphokine-activated killer cells against mitotic phase tumor cells]

To improve LAK/IL-2 efficiency in tumor immunotherapy, the cytotoxicity of human LAK cells against mitotic phase of human lung adenocarcinomas Anip 973 cells was studied in vitro. Anip 973 cells were synchronized by the specific mitotic phase antitumor drug vincristine (VCR). The differences in morphology between mitotic tumor cells and normal tumor cells were observed by light microscopy and transmission electronmicroscopy. The cytotoxicity of human LAK cells against mitotic phase Anip973 cells was significantly increased in standard 4-hour 51Cr release assay. In scanning and transmission electronmicroscopies, LAK cells were in close contact with target cells in the form of interdigitate of microvilli and protrusions structure. The form of death of mitotic phase tumor cells was lytic necrosis and apoptosis.

[Experimental method and clinical significance of hidden rheumatoid factors]

Hidden rheumatoid factor (HRF) was detected in rheumatoid arthritis (RA) serum with ELISA after separation and dissociation of immune complex (IC). It was found that 60% of the patients with active RA has positive latex fixation test, whereas 96% of them has been demonstrated to have IgM hidden rheumatoid factor (HIgMRF) and 70% of them IgG hidden rheumatoid factor (HIgGRF). When the disease was controlled, HIgMRF and HIgGRF was found in 24% and 12% respectively. The difference was significant with P < 0.01. Our results show that the presence of HRF in RA patients is related with the activity of the disease, but not with duration of disease, sex and age.