Finite element modelling of radial shock wave therapy for chronic plantar fasciitis

Therapeutic use of high-amplitude pressure waves, or shock wave therapy (SWT), is emerging as a popular method for treating musculoskeletal disorders. However, the mechanism(s) through which this technique promotes healing are unclear. Finite element models of a shock wave source and the foot were constructed to gain a better understanding of the mechanical stimuli that SWT produces in the context of plantar fasciitis treatment. The model of the shock wave source was based on the geometry of an actual radial shock wave device, in which pressure waves are generated through the collision of two metallic objects: a projectile and an applicator. The foot model was based on the geometry reconstructed from magnetic resonance images of a volunteer and it comprised bones, cartilage, soft tissue, plantar fascia, and Achilles tendon. Dynamic simulations were conducted of a single and of two successive shock wave pulses administered to the foot. The collision between the projectile and the applicator resulted in a stress wave in the applicator. This wave was transmitted into the soft tissue in the form of compression–rarefaction pressure waves with an amplitude of the order of several MPa. The negative pressure at the plantar fascia reached values of over 1.5 MPa, which could be sufficient to generate cavitation in the tissue. The results also show that multiple shock wave pulses may have a cumulative effect in terms of strain energy accumulation in the foot.     

Investigation of the influence of reflection on the attenuation of cancellous bone

The model proposed in this paper is based on the fact that the reflection might have a significant contribution to the attenuation of the acoustic waves propagating through the cancellous bone. The numerical implementation of the mentioned effect is realized by the development of a new representative volume element that includes an infinitesimally thin ‘transient’ layer on the contact surface of the bone and the marrow. This layer serves to model the amplitude transformation of the incident wave by the transition through media with different acoustic impedances and to take into account the energy loss due to the reflection. The proposed representative volume element together with the multiscale finite element is used to simulate the wave propagation and to evaluate the attenuation coefficient for samples with different effective densities in the dependence of the applied excitation frequency. The obtained numerical values show a very good agreement with the experimental results. Moreover, the model enables the determination of the upper and the lower bound for the attenuation coefficient.     

Energy efficiency evaluation method based on multi-model fusion strategy

With the raise of “The Green Industrial Revolution” and the growing demand for low-carbon energy, determining the method for assessing energy usage has become an important problem. In this paper, an assessment method of energy is proposed based on the combination of several models. The study of energy efficiency in China is conducted. First, the data related to the energy efficiency in 24 provinces for the last 9 years is gathered. Meanwhile the key factors for ensuring effective energy utilization in two provinces is determined through feature recognition. Then, the comparative analysis on the categories-fusion model’s goodness of fit is performed, which was also used to predict the energy efficiency. Subsequently, the provinces with high and low energy efficiency based on the clustering strategies with multiple models merged are differentiated. Finally, corresponding recommendations for the development problem in China are presented based on the summary of the experimental results. The experimental results show that in comparison with the single-model approach, the merged multiple models has better performance than other methods. Therefore, this approach has a good engineering value.     

体外冲击波碎石焦点附近声压分布的时域有限差分法数值解析

泌尿系统结石症是一种多发病。体外冲击波碎石(Extracorporealshockwavelithotropisy,ESWL)法是应用人体外发射的高强度脉冲超声波在人体内的焦点附近形成的冲击波破碎结石,被破碎的结石碎片随尿液排出体外的治疗泌尿系统结石症方法。由于这种治疗方法具有非创伤等优点而被广泛地应用于泌尿系统结石症的治疗。但是,ESWL治疗过程中有时会引发尿血、肾血肿等并发症,影响其治疗效果的主要因素之一为ESWL焦点附近形成的声压分布。在这里,利用作者等以前提出的时域有限差分(finitedifferencetimedomain,FDTD)超声波非线性传播的仿真方法,数值仿真ESWL超声波非线性传播过程,研究ESWL焦点附近声压的分布、焦点区域(焦区)的大小形状、高强度超声波形成的实际焦点位置。     

Using a gel/plastic surrogate to study the biomechanical response of the head under air shock loading: a combined experimental and numerical investigation

A combined experimental and numerical study was conducted to determine a method to elucidate the biomechanical response of a head surrogate physical model under air shock loading. In the physical experiments, a gel-filled egg-shaped skull/brain surrogate was exposed to blast overpressure in a shock tube environment, and static pressures within the shock tube and the surrogate were recorded throughout the event. A numerical model of the shock tube was developed using the Eulerian approach and validated against experimental data. An arbitrary Lagrangian-Eulerian (ALE) fluid–structure coupling algorithm was then utilized to simulate the interaction of the shock wave and the head surrogate. After model validation, a comprehensive series of parametric studies was carried out on the egg-shaped surrogate FE model to assess the effect of several key factors, such as the elastic modulus of the shell, bulk modulus of the core, head orientation, and internal sensor location, on pressure and strain responses. Results indicate that increasing the elastic modulus of the shell within the range simulated in this study led to considerable rise of the overpressures. Varying the bulk modulus of the core from 0.5 to 2.0 GPa, the overpressure had an increase of 7.2%. The curvature of the surface facing the shock wave significantly affected both the peak positive and negative pressures. Simulations of the head surrogate with the blunt end facing the advancing shock front had a higher pressure compared to the simulations with the pointed end facing the shock front. The influence of an opening (possibly mimicking anatomical apertures) on the peak pressures was evaluated using a surrogate head with a hole on the shell of the blunt end. It was revealed that the presence of the opening had little influence on the positive pressures but could affect the negative pressure evidently.     

Role of helmet in the mechanics of shock wave propagation under blast loading conditions

The effectiveness of helmets in extenuating the primary shock waves generated by the explosions of improvised explosive devices is not clearly understood. In this work, the role of helmet on the overpressurisation and impulse experienced by the head were examined. The shock wave–head interactions were studied under three different cases: (i) unprotected head, (ii) head with helmet but with varying head–helmet gaps and (iii) head covered with helmet and tightly fitting foam pads. The intensification effect was discussed by examining the shock wave flow pattern and verified with experiments. A helmet with a better protection against shock wave is suggested.     

Generation of Alfvén waves by a plasma inhomogeneity moving in the Earth’s magnetosphere

The generation of an Alfvén wave by an azimuthally drifting cloud of high-energy particles injected in the Earth’s magnetosphere is studied analytically. In contrast to the previous studies where the generation mechanisms associated with the resonant wave-particle interaction were considered, a nonresonant mechanism is investigated in which the wave is excited by the alternating current produced by drifting particles. It is shown that, at a point with a given azimuthal coordinate, a poloidally polarized wave, in which the magnetic field lines oscillate predominantly in the radial direction, is excited immediately after the passage of the particle cloud through this point. As the cloud moves away from that point, the wave polarization becomes toroidal (the magnetic field lines oscillate predominantly in the azimuthal direction). The azimuthal wavenumber m is defined as the ratio of the wave eigenfrequency to the angular velocity of the cloud (the drift velocity of the particles). It is shown that the amplitudes of the waves so generated are close to those obtained under realistic assumptions about the density and energy of the particles.     

An integrated environmental and cost assessment method based on LCA and LCC for automobile interior and exterior trim design scheme optimization

Purpose

This paper provided an integrated method to evaluate environmental impact and life cycle cost (LCC) of various alternative design schemes in the early design and development stages of complex mechanical product; an optimization method of product design schemes based on life cycle assessment (LCA) and LCC is proposed as a supporting design tool to achieve optimal integration of environmental impact and cost of the design.

Methods

The applied research methods include product level deconstruction model, LCA/LCC integrated analysis model, and the product design scheme optimization method. In the life cycle environmental assessment, GaBi software and CML2001 evaluation method are used to evaluate product environmental impact. In terms of product design configuration scheme optimization, the TOPSIS method is used to optimize the design schemes generated. Taking the internal and external trim of automobile as an example, the specific implementation process of the method is illustrated.

Results and discussion

The case study indicates that, when comprehensively considering the environmental impact and cost, the composite indices of the optimal and worst schemes are 0.8667 and 0.3001, respectively; their costs are ¥164.87 and ¥179.68, respectively; and the eco points of environmental impact are 14.74 and 39.78, respectively. The cost of the two schemes are not much different, but the environmental impact of the optimal scheme is only 37.1% of the worst scheme’s; When cost is the only factor to be considered, the lowest cost design scheme is about 36.7% of the maximum scheme’s cost, and the environmental impact of the lowest cost design scheme is about 1.6 times of the maximum cost scheme’s. When environmental impact is the only factor to be considered, the least environmental impact of design scheme accounts about 31.7% of the largest; the cost of design scheme with the least environmental impact accounts for about 58.1% of the largest one’s. Integrating LCA and LCC, scientific suggestions can be provided from several perspectives.

Conclusions

By considering the environmental impact and LCC, this paper proposes a method of product design scheme optimization as a supporting design tool which could evaluate the design options of the product and identify the preferred option in the early stage of product design. It is helpful to realize the sustainability of the product. In order to improve the applicability of this method, the weighting factors of environmental impact and cost could be adjusted according to the requirements of energy saving and emission reduction of different enterprises.

     

基于能值理论的循环复合农业生态系统发展评价——以福建省福清星源循环农业产业示范基地为例

循环农业是当前农业可持续发展理念的具体运作模式。对能值分析方法优化,使其更适合循环复合生态系统的应用上进行优化,并以福建省福清星源循环农业产业示范基地为例验证,评价复合生态系统的可持续发展程度和经济效益。结果表明改进的能值分析方法对循环复合农业生态系统的可持续发展评价更科学,复合系统的可持续发展指数比单纯的生猪养殖提高23.44%—33.86%,在4种组合的循环模式中以"生猪养殖-沼气工程-有机肥生产-种植业"循环复合生态系统整体效益最佳,其可持续发展指数最高,环境负载率最低,净能值产出率仅略低于"生猪养殖-沼气工程-种植业"复合系统。     

Role of helmet in the mechanics of shock wave propagation under blast loading conditions

The effectiveness of helmets in extenuating the primary shock waves generated by the explosions of improvised explosive devices is not clearly understood. In this work, the role of helmet on the overpressurisation and impulse experienced by the head were examined. The shock wave-head interactions were studied under three different cases: (i) unprotected head, (ii) head with helmet but with varying head-helmet gaps and (iii) head covered with helmet and tightly fitting foam pads. The intensification effect was discussed by examining the shock wave flow pattern and verified with experiments. A helmet with a better protection against shock wave is suggested.     

Simulation of deformable models with the Poisson equation

In this paper, we present a new methodology for the deformation of soft objects by drawing an analogy between the Poisson equation and elastic deformation from the viewpoint of energy propagation. The potential energy stored due to a deformation caused by an external force is calculated and treated as the source injected into the Poisson system, as described by the law of conservation of energy. An improved Poisson model is developed for propagating the energy generated by the external force in a natural manner. An autonomous cellular neural network (CNN) model is established by using the analogy between the Poisson equation and CNN to solve the Poisson model for the real-time requirement of soft object deformation. A method is presented to derive the internal forces from the potential energy distribution. The proposed methodology models non-linear materials with the non-linear Poisson equation and thus non-linear CNN, rather than geometric non-linearity. It not only deals with large-range deformations, but also accommodates isotropic, anisotropic and inhomogeneous materials by simply modifying constitutive coefficients. A haptic virtual reality system has been developed for deformation simulation with force feedback. Examples are presented to demonstrate the efficiency of the proposed methodology.     

Simulation of deformable models with the Poisson equation

In this paper, we present a new methodology for the deformation of soft objects by drawing an analogy between the Poisson equation and elastic deformation from the viewpoint of energy propagation. The potential energy stored due to a deformation caused by an external force is calculated and treated as the source injected into the Poisson system, as described by the law of conservation of energy. An improved Poisson model is developed for propagating the energy generated by the external force in a natural manner. An autonomous cellular neural network (CNN) model is established by using the analogy between the Poisson equation and CNN to solve the Poisson model for the real-time requirement of soft object deformation. A method is presented to derive the internal forces from the potential energy distribution. The proposed methodology models non-linear materials with the non-linear Poisson equation and thus non-linear CNN, rather than geometric non-linearity. It not only deals with large-range deformations, but also accommodates isotropic, anisotropic and inhomogeneous materials by simply modifying constitutive coefficients. A haptic virtual reality system has been developed for deformation simulation with force feedback. Examples are presented to demonstrate the efficiency of the proposed methodology.     

Molecular dynamics analysis of the transient temperature increase at void locations in shocked materials: RDX and Cu

Molecular dynamics (MD) simulations of high velocity impact (1–6 km/s) of RDX crystal with a nanometer-sized void, has been carried out to understand the mechanism of increase in temperature at void locations under shock loading. Similar simulations are then carried out on single-crystal copper for better interpretation of the results. A reactive potential that can simulate chemical reactions (ReaxFF) has been used for RDX, whereas an EAM potential has been used for Cu. Increased temperature at the void locations are observed under shock loading. The atomic motion, temperature, average potential energy per atom (PE), and average kinetic energy per atom (KE) in and around the voids are closely monitored in order to understand the reason for temperature increase. We compare our results with existing proposed mechanisms and show that some of the proposed mechanisms are not necessary for increased temperature at a void location. It is shown that the directed particle velocity is efficiently is converted into randomized velocity due to the presence of voids thereby increasing the local temperature transiently. In this initial stage (few picoseconds) of the shock, chemical reactions of energetic materials do not play a part in the temperature rise.     

Nonparametric and semiparametric estimation with sequentially truncated survival data

In observational cohort studies with complex sampling schemes, truncation arises when the time to event of interest is observed only when it falls below or exceeds another random time, that is, the truncation time. In more complex settings, observation may require a particular ordering of event times; we refer to this as sequential truncation. Estimators of the event time distribution have been developed for simple left-truncated or right-truncated data. However, these estimators may be inconsistent under sequential truncation. We propose nonparametric and semiparametric maximum likelihood estimators for the distribution of the event time of interest in the presence of sequential truncation, under two truncation models. We show the equivalence of an inverse probability weighted estimator and a product limit estimator under one of these models. We study the large sample properties of the proposed estimators and derive their asymptotic variance estimators. We evaluate the proposed methods through simulation studies and apply the methods to an Alzheimer's disease study. We have developed an R package, seqTrun , for implementation of our method.     

Shape Similarity Measures for the Design of Small RNA Switches

Abstract

Conformational switching in the secondary structure of RNAs has recently attracted considerable attention, fostered by the discovery of ‘riboswitches’ in living organisms. These are genetic control elements that were found in bacteria and offer a unique regulation mechanism based on switching between two highly stable states, separated by an energy barrier between them. In riboswitches, the energy barrier is crossed by direct metabolite binding, which facilitates regulation by allosteric means. However, other event triggers can cause switching to occur, such as single-point mutations and slight variations in temperature. Examples of switches with these event triggers have already been reported experimentally in the past. Here, the goal is to computationally design small RNA switches that rely on these triggers. Towards this end, our computer simulations utilize a variety of different similarity measures to assess the distances between an initial state and triggered states, based on the topology of the secondary structure itself. We describe these combined similarity measures that rely on both coarse-grained and fine-grained graph representations of the RNA secondary structure. As a result of our simulations, we provide some candidate sequences of approximately 30–50 nt, along with the exact triggers that drive the switching. The event triggers under consideration can be modelled by Zuker's mfold or the Vienna package. The proposed methodology that rely on shape measures can further be used to computationally generate more candidates by simulating various event triggers and calculating their effect on the shape.     

In-between forest expansion and cropland decline: A revised USLE model for soil erosion risk under land-use change in a Mediterranean region

The present study illustrates an original approach for the long-term assessment of soil erosion risk under land-use changes in a Mediterranean region (Matera, southern Italy). The study has been focused on the implementation of a modified Universal Soil Loss Equation (USLE) model at three time points (1960, 1990, 2010) with the objective to evaluate the contribution of each component to model's performance and model outcomes’ reliability. A modified USLE model was proposed for the assessment of soil erosion risk, based on the simplification of model’s parameters and the use of high spatial resolution datasets. Spatio-temporal variability in the model's outcomes was analyzed for basic land-use classes. Our approach has improved model's flexibility with the use of high spatial resolution layers, producing reliable long-term estimates of soil loss for the study area.     

Attributable risk function in the proportional hazards model for censored time-to-event

Time-to-event endpoints are often used in clinical and epidemiological studies to evaluate disease association with hazardous exposures. In the statistical literature of time-to-event analysis, such association is usually measured by the hazard ratio in the proportional hazards model. In public health, it is also of important interest to assess the excess risk attributable to an exposure in a given population. In this article, we extend the notion of 'population attributable fraction' for the binary outcomes to the attributable risk function for the event times in prospective studies. A simple estimator of the time-varying attributable risk function is proposed under the proportional hazards model. Its inference procedures are established. Monte-Carlo simulation studies are conducted to evaluate its validity and performance. The proposed methodology is motivated and demonstrated by the data collected in a multicenter acquired immunodeficiency syndrome (AIDS) cohort study to estimate the attributable risk of human immunodeficiency virus type 1 (HIV-1) infections due to several potential risk factors.     

Testing Markovianity in the three‐state progressive model via future‐past association

The three‐state progressive model is a special multi‐state model with important applications in Survival Analysis. It provides a suitable representation of the individual’s history when an intermediate event (with a possible influence on the survival prognosis) is experienced before the main event of interest. Estimation of transition probabilities in this and other multi‐state models is usually performed through the Aalen–Johansen estimator. However, Aalen–Johansen may be biased when the underlying process is not Markov. In this paper, we provide a new approach for testing Markovianity in the three‐state progressive model. The new method is based on measuring the future‐past association along time. This results in a deep inspection of the process that often reveals a non‐Markovian behaviour with different trends in the association measure. A test of significance for zero future‐past association at each time point is introduced, and a significance trace is proposed accordingly. The finite sample performance of the test is investigated through simulations. We illustrate the new method through real data analysis.     

An ultrasound elastography method to determine the local stiffness of arteries with guided circumferential waves

Arterial stiffness is highly correlated with the functions of the artery and may serve as an important diagnostic criterion for some cardiovascular diseases. To date, it remains a challenge to quantitatively assess local arterial stiffness in a non-invasive manner. To address this challenge, we investigated the possibility of determining arterial stiffness using the guided circumferential wave (GCW) induced in the arterial wall by a focused acoustic radiation force. The theoretical model for the dispersion analysis of the GCW is presented, and a finite element model has been established to calculate the dispersion curve. Our results show that under described conditions, the dispersion relations of the GCW are basically independent of the curvature of the arterial wall and can be well-described using the Lamb wave (LW) model. Based on this conclusion, an inverse method is proposed to characterize the elastic modulus of artery. Both numerical experiments and phantom experiments had been performed to validate the proposed method. We show that our method can be applied to the cases in which the artery has local stenosis and/or the geometry of the artery cross-section is irregular; therefore, this method holds great potential for clinical use.