bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model for Strongly Nonlinear Long Interfacial Waves with Background Shear
Authors: Boonkasame Anakewit , Milewski Paul A.
Published: January 2014

The Miyata–Choi–Camassa (MCC) system of equations describing long internal nonhydrostatic and nonlinear waves at the interface between two layers of inviscid fluids of different densities bounded by top and bottom walls is mathematically ill‐posed despite the fact that physically stable internal waves are observed matching closely those of MCC. A regularization to the MCC equations that yields a computationally simple well‐posed system for time‐dependent evolution is proposed here. The regularization is accomplished by keeping the full hyperbolic part of MCC and exchanging spatial and temporal derivatives in one of the linearized dispersive terms. Solitary waves of MCC over a wide range of parameters are used as a benchmark to check the accuracy of the model. Our model includes the possibility of a background shear, and we show that, contrary to the no shear case, solitary waves can cross the midlevel between the top and the bottom walls and may have different polarity from the case with no background shear. Time‐dependent solutions of the regularization stable model are presented, including interactions of its solitary waves, and classical and modified Korteweg‐de Vries equations for small amplitude waves with the inclusion of background shear are derived. Throughout the paper, the Boussinesq approximation is taken, although the results can be extended to the non‐Boussinesq case.
Sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice‐contact fan deposits: A Pleistocene example (Ireland)
Authors: Ravier Edouard , Buoncristiani Jean‐François , Clerc Sylvain , Guiraud Michel , Menzies John , Portier Eric
Published: January 2014

A pit located near Ballyhorsey, 28 km south of Dublin (eastern Ireland), displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice‐contact fan deposits. The coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies. The lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space, mainly controlled by the position of an overlying ice roof during ice‐bed decoupling. These sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments. The sorted sediments consist of fine‐grained laminated facies, cross‐laminated sand and channelized gravels, and are interpreted as subglaciofluvial sediments deposited within a subglacial de‐coupled space. The subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds, triggered by fluid overpressure and shear stress during episodes of ice/bed recoupling (clastic dykes and folds). The upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake, forming a thick sedimentary wedge erosively overlying the subglacial deposits. Gravel facies and large‐scale trough bedding sand are observed within this proximal wedge, while normally graded sand beds with developed bedforms are observed further downflow. The building of the prograding ice‐contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading (normal faults). This study facilitates the recognition of subglacial/submarginal depositional environments formed, in part, during localized ice/bed coupling episodes in the sedimentary record. The sedimentary sequence exposed in Ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation, the impact on the subglacial drainage system and the consequences on the Irish Sea Ice Stream flow mechanisms.
Climatic and eustatic signals in a global compilation of shallow marine carbonate accumulation rates
Authors: Kemp David B. , Sadler Peter M.
Published: January 2014

Two of the most important factors that control the accumulation rate of material in carbonate platform environments on geological time scales are climate and eustasy. Accurately assessing the importance of these inter‐related factors through the study of both modern and ancient carbonate facies, however, is problematic. These difficulties arise from both the complexities inherent in carbonate depositional systems and the demonstrable incompleteness of the stratigraphic record. Here, a new compilation of more than 19 000 global Phanerozoic shallow marine carbonate accumulation rates derived from nearly 300 individual stratigraphic sections is presented. These data provide the first global holistic view of changes in shallow marine carbonate production in response to climate and eustasy on geological time scales. Notably, a clear latitudinal dependence on carbonate accumulation rates is recognized in the data. Moreover, it can also be demonstrated that rates calculated across the last glacial maximum and Holocene track changes in sea‐level. In detail, the data show that globally averaged changes in carbonate accumulation rates lagged changes in sea‐level by ca 3 kyr, reflecting the commonly observed delay in the response of individual carbonate successions to sea‐level rise. Differences between the rates of carbonate accumulation and sea‐level change over the past 25 kyr ostensibly reflect changing accumulation mode, with platform drowning (give‐up mode) pervasive during peak Early Holocene sea‐level rise, followed by a switch to catch‐up mode accumulation from ca 9 ka to the present. Carbonate accumulation rates older than the Quaternary are typically calculated over time spans much greater than 100 kyr, and at these time spans, rates primarily reflect long‐term tectonically mediated accommodation space changes rather than shorter term changes in climate/eustasy. This finding, coupled with issues of stratigraphic incompleteness and data abundance, tempers the utility of this and other compilations for assessing accurately the role of climate and eustasy in mediating carbonate accumulation rates through geological time.
Musculoskeletal extremity injuries in a cohort of schoolchildren aged 6–12: A 2.5‐year prospective study
Authors: Jespersen E. , Rexen C. T. , Franz C. , Møller N. C. , Froberg K. , Wedderkopp N.
Published: January 2014

The objectives of this prospective school cohort study were to describe the epidemiology of diagnosed musculoskeletal extremity injuries and to estimate the injury incidence rates in relation to different settings, different body regions and injury types. In all, 1259 schoolchildren, aged 6–12, were surveyed weekly during 2.5 years using a new method of automated mobile phone text messaging asking questions on the presence of any musculoskeletal problems. All injuries were clinically diagnosed. Physical activity was measured from text messaging and accelerometers. A total number of 1229 injuries were diagnosed; 180 injuries in the upper extremity and 1049 in the lower extremity, with an overall rate of 1.59 injuries per 1000 physical activity units [95% confidence interval (CI) 1.50–1.68]. Upper extremities accounted for a rate of 0.23 (95% CI 0.20–0.27) and lower extremities accounted for 1.36 (95% CI 1.27–1.44). This study has added a wide overall perspective to the area concerning incidence and incidence rates of musculoskeletal extremity injuries in schoolchildren aged 6–12 years, including severe and less severe, traumatic, and overuse injuries. The understanding of injury epidemiology in children is fundamental to the acknowledgement and insurance of the appropriate prevention and treatment.
Deliberative Capacity in the Political and Civic Sphere
Authors: Pedrini Seraina
Published: January 2014

In an evolving deliberative system, a crucial question is how deliberation of ordinary citizens differs from that of professional politicians. This study compares the deliberative capacity of citizens and political elites on exactly the same issue, namely a direct democratic initiative in Switzerland on the expulsion of criminal immigrants. In concrete, I perform a quantitative content analysis of the quality of citizen deliberation in an online poll and compare this to the quality of deliberation in representative politics, namely in the non‐public committee and public floor debates in the Swiss parliament. The findings show that political elites reach much higher levels of justification rationality than ordinary citizens, but achieve lower levels in terms of respect. I conclude that citizen deliberation, while useful as an advisory tool, cannot replace serious deliberative scrutiny in representative politics.
Single‐copy gene‐based chromosome painting in cucumber and its application for chromosome rearrangement analysis in Cucumis
Authors: Lou Qunfeng , Zhang Yunxia , He Yuhua , Li Ji , Jia Li , Cheng Chunyan , Guan Wei , Yang Shuqiong , Chen Jinfeng
Published: January 2014

Chromosome painting based on fluorescence in situ hybridization (FISH) has played an important role in chromosome identification and research into chromosome rearrangements, diagnosis of chromosome abnormalities and evolution in human and animal species. However, it has not been applied widely in plants due to the large amounts of dispersed repetitive sequences in chromosomes. In the present work, a chromosome painting method for single‐copy gene pools in Cucumis sativus was successfully developed. Gene probes with sizes above 2 kb were detected consistently. A cucumber karyotype was constructed based on FISH using a cocktail containing chromosome‐specific gene probes. This single‐copy gene‐based chromosome painting (ScgCP) technique was performed by PCR amplification, purification, pooling, labeling and hybridization onto chromosome spreads. Gene pools containing sequential genes with an interval less than 300 kb yielded painting patterns on pachytene chromosomes. Seven gene pools corresponding to individual chromosomes unambiguously painted each chromosome pair of C. sativus. Three mis‐aligned regions on chromosome 4 were identified by the painting patterns. A probe pool comprising 133 genes covering the 8 Mb distal end of chromosome 4 was used to evaluate the potential utility of the ScgCP technique for chromosome rearrangement research through cross‐species FISH in the Cucumis genus. Distinct painting patterns of this region were observed in C. sativus, C. melo and C. metuliferus species. A comparative chromosome map of this region was constructed between cucumber and melon. With increasing sequence resources, this ScgCP technique may be applied on any other sequenced species for chromosome painting research.
Prevalence of fur mites (Chirodiscoides caviae) in pet guinea pigs (Cavia porcellus) in southern Italy
Authors: d'Ovidio Dario , Santoro Domenico
Published: January 2014

Background

Chirodiscoides caviae is the most common fur mite affecting guinea pigs; infestation is generally asymptomatic. No studies have been published on the prevalence of such mites in guinea pigs in southern Italy.

Hypothesis/Objectives

We sought to evaluate the prevalence and the clinical signs of C. caviae infestation in guinea pigs in southern Italy.

Animals

Clinical records of guinea pigs evaluated from August 2012 to July 2013 were retrospectively searched.

Methods

In this retrospective matched case–control study, records of guinea pigs with evidence of C. caviae infestation were selected. The prevalence of C. caviae infestation was evaluated and exposure variables were assessed among guinea pigs with and without infestation using stepwise conditional logistic regression. Guinea pigs seen during the same time period, but without a diagnosis of C. caviae, were included as control animals.

Results

The prevalence of C. caviae was 32% (42 of 131); 66.6% of affected guinea pigs (28 of 42) originated from pet shops, whereas 28% (14 of 42) were privately owned. Thirty‐one guinea pigs (73.8%) were asymptomatic, whereas 11 (26.1%) showed clinical signs (pruritus, alopecia, erythema and scaling). The most frequently affected area was the lumbosacral region (38 of 42). Guinea pigs in pet shops were more likely to be affected by C. caviae than owned guinea pigs (odds ratio, 5.12; 95% confidence interval, 2.32–11.29; P < 0.0001).

Conclusions and clinical importance

The results of this study indicate a high prevalence of C. caviae infestation in guinea pigs in southern Italy. Chirodiscoides mites should be sought in guinea pigs, particularly in animals coming from pet shops.
Unscented Kalman Filter for Real-Time Load Swing Estimation of Container Cranes Using Rope Forces
Authors: Kreuzer Edwin , Pick Marc-André , Rapp Christian , Theis Julian
Published: January 2014

The container crane represents the link between the containership and the port. It dictates the general conditions for the efficiency of container handling from the ship to the land and vice versa. While containers are handled by the crane, load swing reduces the rate of container turnover. In order to reduce load swing control systems are employed. Closed-loop control systems contain devices to track the position of the load with respect to the trolley's position. Accurate tracking of the load's motion during operation requires additionally installed sensors. Alternatively, the principle of state estimation can be employed. The observation of the motion of the container is carried out by a system model in parallel to the real system, taking into account the available rope force sensor information. Both, nonlinear system model and nonlinear sensor model are taken into consideration. An unscented Kalman filter is designed to estimate the states of the motion of the load. The observer is validated at the container crane test stand in order to provide accurate states for load swing control. Results are presented and discussed.
Modal Stability Theory
Authors: Juniper Matthew P. , Hanifi Ardeshir , Theofilis Vassilios
Published: January 2014

This article contains a review of modal stability theory. It covers local stability analysis of parallel flows including temporal stability, spatial stability, phase velocity, group velocity, spatio-temporal stability, the linearized Navier–Stokes equations, the Orr–Sommerfeld equation, the Rayleigh equation, the Briggs–Bers criterion, Poiseuille flow, free shear flows, and secondary modal instability. It also covers the parabolized stability equation (PSE), temporal and spatial biglobal theory, 2D eigenvalue problems, 3D eigenvalue problems, spectral collocation methods, and other numerical solution methods. Computer codes are provided for tutorials described in the article. These tutorials cover the main topics of the article and can be adapted to form the basis of research codes.
A Novel Flow Diverter for Direct Treatment of Cerebral Aneurysms
Authors: Ma Jiayao , You Zhong , Byrne James
Published: January 2014

Cerebral aneurysm (CA) is a localised dilatation in the wall of the brain vasculature which can cause it to swell out like a balloon. If not treated, it will continue to grow and eventually tear or rupture, resulting in severe disability from stroke and, in around 25% of cases, death [1]. CAs affect up to 5% of the adult population with 1% of detected aneurysms rupture every year [2].
Modal Characteristics of Self-Excited Oscillations in Collapsible Tube With Low Elastic Modulus
Authors: Wu Haijun , Jia Laibing , Wu Yanfeng , Yin Xiezhen
Published: January 2014

The flow through a flexible tube and the interactions between fluid- and wall-motion have been researched in recent forty years because they are involved in many physiological phenomena, such as clinically useful “Korotkoff sounds”, audible murmurs induced by the collapsed external jugular vein in the neck of upright subject (Grotberg and Jenson, 2004).
An Investigation Into the Molecular Pathways of Airway Smooth Muscle Relaxation
Authors: Al-Jumaily A. M. , Koumba N. , Avila M. J. , Roos K.
Published: January 2014

This paper investigates the effect of superimposed length oscillation (SILO) on tidal breathing on contracted airway smooth muscle (ASM) relaxation. The combined effect of SILO with each one of four inhibitors (Isoproterenol, Indomethacin, PD0980590 and SB 203580) is investigated to explore the molecular pathways involved in the tissue relaxation process.
Computational Modeling and Analysis of Hemodynamic Effects of Diastolic Heart Dysfunction During the Whole Cardiac Cycle
Authors: Zheng Xudong , Mittal Rajat , Xue Qian
Published: January 2014

Diastolic heart dysfunction (DHD) is a common finding in a variety of cardiac diseases including hypertension, coronary disease and cardiomyopathy. Its prevalence increases with age and it manifests as incomplete or/and delayed ventricular relaxation and a compensatory stronger atrial contraction. DHD is often associated with heart failure and contributes greatly to morbidity and hospitalizations especially in the elderly[3]. DHD is a very rich problem in fluid mechanics and it involves complex hemodynamic interactions among all of major cardiac phases during the whole cardiac cycle including ventricular filling, diastatsis, atrial filling, and systole[1]. Most studies to-date have, however, employed simple time varying volume-change profiles to model and examine the dynamics of ventricular filling[2]. Intercardiac flow effects i.e. interaction between filling and ejection have, however, not been investigated in detail. Also not studied in detail is the role of multiphasic filling which consists of early (E) filling, diastasis, and atrial (A) filling. In the current study, we will utilize three dimensional simulations to study the hemodynamics of DHD during the whole cardiac cycle. The vortex structure, filling velocity, intraventricular pressure gradient and energy budget will be analyzed to uncover the biomechanical effects and genesis of DHD.
Characterization of the Frequency and Muscle Response in the Lumbar and Thoracic Spines During Sinusoidal Vertical Whole Body Vibration
Authors: Baig Hassam A. , Dorman Daniel B. , Shivers Bethany L. , Breaux-Waltz Arlene , Chancey V. Carol , Winkelstein Beth A.
Published: January 2014

Vibration exposure has been linked to chronic neck and lower back pain [1,2]. For example, American male workers operating vibrating vehicles, such as industrial trucks and tractors, have been reported to have a higher prevalence of low back pain than workers whose occupations do not involve vibration exposures [1]. Also, military helicopter aviators report increased pain during deployment compared to pre-deployment, with between 22–37% reporting neck and 39–70% reporting low back pain [2]. It has been suggested that the cyclic muscle response to whole body vibration (WBV) can lead to muscle fatigue, further contributing to the development of low back pain [3]. Although several studies have measured the transmissibility response of the human spine [4,5], studies defining the mechanical effects of whole body vibration in a seated human are limited [4,5] and none have investigated the relationship between the biomechanical and muscle activity responses during such whole body vibration exposures.
Cost Effective Electrolarynx: A Feasibility Study
Authors: Amell Janine M. , Griffin Robert W. , Malfa Madison B. , Nycz Christopher J. , Osaheni Allen O. , Erath Byron D. , Fite Kevin , Kuxhaus Laurel
Published: January 2014

Speech is one of the most fundamental forms of self-expression and communication in humans [1]. Voiced speech is produced by fluid-structure interactions that drive vocal fold oscillations, creating a periodic pressure oscillation in the vocal tract. This excitation has a fundamental frequency, typically ranging between 100 and 200 Hz, depending on the individual. Thousands of people lose this ability each year when they are forced to undergo a total laryngectomy, which removes the entire larynx, usually to prevent the spread of cancer. The American Cancer Society predicts there will be about 3,000 laryngectomees in the United States alone during 2013 [2][3].
Solid and Fluid Simulations of Vertebral Artery Stenosis Treated With Stents With Different Shapes of Link
Authors: Qiao Aike , Zhang Zhanzhu
Published: January 2014

Stenting technology has emerged as an effective alternative for treating arterial stenosis, which recovers blood fluency through mechanical scaffold using struts. Different kinds of endovascular stents cause varying degrees of injury on the artery wall, inducing different ratios of post-operative in-stent restenosis (ISR). Therefore, the design of stent structure has a significant influence on the therapeutic effect of stent intervention. From the viewpoint of solid mechanics, the artery is subjected to long-term press by stent strut after intervention, leading to external mechanical force acting on artery. Straightening, mechanical stress, and stress concentration occurred, causing in-stent intimal hyperplasia extremely, which consequently induce ISR. From the viewpoint of hemodynamics, hemodynamic environment is changed to some extent after stenting. As a result, local blood flow is changed greatly. Vortex and low WSS occur, promoting thrombosis and intimal hyperplasia, which induce ISR more easily. To investigate the effect of stents with different links on treating stenotic vertebral artery and the relation between the shape of link and ISR, as well as provide scientific guidelines for designing stent structure and selecting stent in clinical procedure, numerical simulations of solid mechanics and hemodynamics were performed in this paper, which coupled the boundaries of stent, plaque and blood in the stented vertebral arteries using three kinds of stent with different links.
Evaluation of Temperature Transients at Various Body Temperature Measuring Sites Using a Fast Response Thermistor Bead Sensor
Authors: Vesnovsky Oleg , Topoleski L. D. Timmie , Grossman Laurence W. , Casamento Jon P. , Zhu Liang
Published: January 2014

Body temperature monitoring of humans has been an important tool for helping clinicians diagnose infections, detect fever, monitor thermoregulation functions during surgical procedures, and assess post-surgery recovery.1–3 Fever itself is typically not considered a disease. It is a response of the body to a disease, which is often inflammatory in nature. Elevation of the set point at the body temperature control center, the brain hypothalamus, is caused by circulating pyrogens produced by the immune system responding to diseases. Since the brain hypothalamus is not easily accessed by thermometers, other body locations have been identified as alternative measuring sites. Those sites include the pulmonary artery, rectum, bladder, distal esophagus and nasopharynx, sublingual surface of the tongue, under the armpit, tympanic membrane, and forehead.
Biomechanics of the Rat Vagina During Pregnancy and After Vaginal Delivery: A 3-Dimensional Ultrasound Approach
Authors: Feola Andrew , Endo Masayuki , Deprest Jan
Published: January 2014

The vagina plays a focal point in support by directly supporting the bladder, urethra, uterus, and rectum. The vagina also is a central location for connective tissue and muscle attachments. Failure in any component of this intricate support system can lead to the development of pelvic floor disorders, such as pelvic organ prolapse (POP), urinary and fecal incontinence and sexual dysfunction.
Influence of CO2 Blowing Agent on Porous Bioresorbable Stent Structure
Authors: Barker Gregory , Welch Tre , D’Souza Nandika , Nugent Alan , Eberhart Robert
Published: January 2014

Bioresorbable stents with limited functional lifetimes and with drug delivery capabilities are desired. Various methods have been investigated to induce porosity in bioresorbable polymeric stent fibers, thereby to permit increased drug reservoir capacity versus polymer-coated metal stents. We developed microporous surface layers on PLLA fibers to serve as the drug reservoir, but found that impurities, the use of chemicals, and multiple step procedures associated with our, and other published methods limited utility. Thus we investigated theoretically attractive CO 2 blowing methods, in which gas under pressure and temperature induces porosity. We report the results of initial studies of CO 2-induced porosity in PLLA stent fibers.
Shape Analysis for Automatic and Objective Visualization of Pathological Cardiovascular Remodeling From Cine Cardiac MRI
Authors: Menon Prahlad G. , Adhyapak Srilakshmi M.
Published: January 2014

Normal cardiovascular tissue structure and therefore shape is governed by an equilibrium existing between stimulator and inhibitor signals that regulate growth and remodeling [1]. Characterization of left ventricular (LV) remodeling following an insult or major adverse cardiac event that disturbs this balance (eg: transmural myocardial infarction) can provide crucial information to guide non-transplant therapeutic options for improving cardiac function or surgical restoration of ventricular shape. In this study, analysis of endocardial morphology and function in remodeled LV territories is presented in the context of front-line quantitative 4D (3D + time) assessment of an antero-apical LV aneurysm in a 42 year old male patient from cine cardiac MRI data. In this regard, two promising shape analysis techniques are discussed: a) Hausdorff distance; and b) weighted spherical harmonics (SPHARM).
Role of Hemodynamic Shear Stress Abnormalities in the Early Pathogenesis of Bicuspid Aortic Valve Calcification
Authors: Sun Ling , Chandra Santanu , Sucosky Philippe
Published: January 2014

With a prevalence of 1.3 million cases in the United States, the bicuspid aortic valve (BAV) is the most common congenital cardiac anomaly and is frequently associated with calcific aortic valve disease (CAVD) [1]. The most prevalent type-I morphology, which results from left-/right-coronary cusp fusion, generates different hemodynamics than a tricuspid aortic valve (TAV). While valvular calcification has been linked to genetic and atherogenic predispositions, hemodynamic abnormalities are increasingly pointed as potential pathogenic contributors [2–3]. In particular, the wall shear stress (WSS) produced by blood flow on the leaflets regulates homeostasis in the TAV. In contrast, WSS alterations cause valve dysfunction and disease [4]. While such observations support the existence of synergies between valvular hemodynamics and biology, the role played by BAV WSS in valvular calcification remains unknown. The objective of this study was to isolate the acute effects of native BAV WSS abnormalities on CAVD pathogenesis.
Articular Cartilage Biomechanics Modeled via an Intrinsically Compressible Biphasic Model: Implications and Deviations From an Incompressible Biphasic Approach
Authors: Travascio Francesco , Serpieri Roberto , Asfour Shihab
Published: January 2014

Biphasic continuum models have been extensively deployed for modeling macroscopic articular cartilage biomechanics [1,2]. This consolidated theoretical approach schematizes tissue as a mixture of an elastic solid matrix embedded in a fluid phase. In physiological conditions, intrinsic compressibility of each phase is very limited when compared to the whole tissue macroscopic counterpart. Based on such experimental evidence, intrinsic phase compressibility is generally reasonably neglected [3]. Hence, traditionally, cartilage biomechanics models have been developed on the basis of incompressible biphasic formulations [3–5], often referred to as Incompressible Theories of Mixtures (ITM). Alternatively, a more general biphasic model for cartilage biomechanics, accounting for full intrinsic compressibility of phases, may be considered. A consistent theoretical formulation of this type has been recently made available [6,7], hereby referred to as Theory of Microscopically Compressible Porous Media (TMCPM). In the present contribution, a new model for articular cartilage biomechanics, based on TMCPM, was developed. Predictions of this new model, and its deviations from a traditional ITM approach were studied. In particular, deviations between compressible and incompressible theoretical frameworks were investigated with a specific focus on the repercussions on models’ capability of characterizing fundamental tissue properties, such as hydraulic permeability, via established experimental testing procedures.
In Vitro Evaluation of Shear-Induced Platelet Activation in the MicroMed DeBakey Ventricular Assist Device With Antiplatelet Therapy
Authors: Sheriff Jawaad , Girdhar Gaurav , George Sheela , Chiu Wei-Che , Lynch Bryan E. , Jesty Jolyon , Slepian Marvin J. , Bluestein Danny
Published: January 2014

Mechanical circulatory support (MCS) devices, which include ventricular assist devices (VADs), offer an attractive solution to approximately 35,000 end-stage heart failure patients eligible for transplants, of which only 2,000–2,300 are performed annually [1]. These devices are employed to augment the function of the ailing left and/or right ventricle and serve as bridge-to-transplant or destination therapy, but are often accompanied by thrombotic complications. Pathologic flow patterns are characteristic of VADs and increase susceptibility to shear-induced platelet activation, which leads to thrombus formation [2]. Patients implanted with such devices are routinely prescribed antiplatelets to tackle these complications. Despite this concurrent therapy, thromboembolic incident rates of 0.9–13% are reported for the widely-implanted Thoratec HeartMate II and MicroMed DeBakey VADs [3, 4]. This has spurred the development of design optimization techniques to lower or eliminate the incidence of thrombosis and reduce the dependence on pharmacotherapy management.
Effect of Tumor Heterogeneity on Interstitial Pressure and Fluid Flow
Authors: Pyrz Matthew , Baish James
Published: January 2014

Delivery of drugs to solid tumors is often impeded by the elevation of the interstitial fluid pressure at the tumor core and the loss of plasma from the tumor to the surrounding normal tissue. Interstitial pressure in tumors is abnormally high because tumor blood vessels are highly permeable relative to their normal counterparts and tumors lack functional lymphatic vessels that can absorb the excess fluid loss [1]. As a result, there is a net outward flow of plasma-like fluid through the interstitial spaces of the tumor toward the exterior of the tumor where functional lymphatics may be found (Fig. 1).
Necking and Failure of Constrained Contractile 3D Microtissues: Role of Geometry and Stiffness
Authors: Wang Hailong , Svoronos Alexander A. , Boudou Thomas , Morgan Jeffrey R. , Chen Christopher S. , Shenoy Vivek B.
Published: January 2014

We report the discovery of a fundamental morphological instability of constrained 3D microtissues induced by a positive chemomechanical feedback between actomyosindriven contraction and the mechanical stresses arising from the constraints. Using a 3D model for mechanotransduction we find that perturbations in the shape of contractile tissues grow in an unstable manner leading to formation of “necks” where tensile stresses are sufficiently large to lead to the failure of the tissue by narrowing and subsequent elongation. The origin of the failure mechanism driven by active forces we report is distinct from the seemingly similar and well studied necking phenomena observed in “passive” materials due to elastic softening. Here the instability is caused by the active contraction (extension) of the regions of the tissue where the mechanical stresses are smaller (greater) than the characteristic actomyosin stall stress of the tissue. The magnitude of the instability is shown to be determined by the level of active contractile strain, the stiffness of the ECM and the stiffness of the boundaries that constrain the tissue. A phase diagram that demarcates stable and unstable behavior of 3D tissues as a function of these material parameters is derived. The predictions of our model are verified by analyzing the necking and failure of normal human fibroblast (NHF) tissue constrained in a loopended dogbone geometry and cardiac microtissues constrained between microcantilevers. In the former case, the tissue fails first by necking of the connecting rod of the dogbone followed by failure of the toroidal loops in agreement with our 3D finite element simulations. In the latter case we find that cardiac tissue is stable against necking when the density of the extra cellular matrix is increased and when the stiffness of the supporting cantilevers is decreased, also in excellent agreement with the predictions of our model. By analyzing the time evolution of the morphology of the constrained tissues we have quantitatively determined the chemomechanical coupling parameters that characterize the generation of active stresses in these tissues. More generally, the analytical and numerical methods we have developed provide a quantitative framework to study the biomechanics of cell to cellinteractions in complex 3D environments such as morphogenesis and organogenisis.
Effect of Boundary Stiffness on Contractility Profile of Valvular Interstitial Cells
Authors: Kural Mehmet H. , Billiar Kristen L.
Published: January 2014

Heart valve disease leads to approximately 300,000 heart valve replacement surgeries each year worldwide. Valvular interstitial cells (VICs) are believed to play a vital role in the repair of heart valves and also most disease processes. VICs synthesize, remodel, and repair the ECM; however, when VICs excessively differentiate to the highly contractile and synthetic myofibroblast phenotype, valvular fibrosis may ensue. Elevated mechanical stress triggers the differentiation of VICs into myofibroblasts. Transforming growth factor beta-1 (TGF-β1) is also critical for the formation of thicker stress fibers positive for α-smooth muscle actin (α-SMA), the defining characteristic of myofibroblasts.
Matrix Remodeling Accompanies In Vitro Articular Cartilage Shaping
Authors: Balcom Nathan T. , Grisafe Dominic J. , Gutierrez-Franco Juan D. , Crawford Daniel J. , Raub Chris B. , Cory Esther , Chen Albert C. , Hazelwood Scott J. , Klisch Stephen M. , Sah Robert L.
Published: January 2014

Articular cartilage (AC) supports and distributes loads in synovial joints while maintaining a nearly frictionless surface. Successful replacement of large AC defects with an osteochondral graft requires an appropriate geometrical match with the defect region. 1 In AC, collagen (COL) provides tensile support to the tissue, and glycosaminoglycans (GAG) provide a fixed negative charge that produce swelling and contribute to the compressive properties of the tissue. 2 Previous studies ( Fig. 1) have shown that 4 days of bending can reshape immature AC, but without a change in the total COL and GAG concentrations. 3 We hypothesized that more localized COL and/or GAG remodeling occurs during AC reshaping and may support the shape change. The objective of this study was to determine the presence, magnitude and depth-dependence of COL and GAG remodeling that accompany the shape change of AC.
Investigation of the Spatial Structure of the Microcirculation in a Capillary Bundle From Rat Spinotrapezius Muscle Tissue
Authors: Jacobitz Frank G. , Yamamura Niki L. , Schmid-Schönbein Geert W.
Published: January 2014

The microcirculation in the fascia of rat spinotrapezius muscle is studied using a computational approach that accounts for the shear- and hematocrit-dependent rheology of blood [1]. The simulations are based on a realistic network reconstruction derived from microscopic images of the fascia. The model includes fundamental aspects about passive properties of microvessels [5] as well as active myogenic constriction in arterioles [2]. We also present the development of a software tool to perform a spatial analysis of the hemodynamic results. This tool provides local information about the flow properties within a spatial microvessel network map in order to optimize the comparison with experiments. A review can be found in [4].
Intra-Aneurysmal Flow Complexity Quantification Using Flowlines Geometry
Authors: Hodis Simona , Kallmes David F. , Dragomir-Daescu Dan
Published: January 2014

We present a quantified description of the fluid flow and a novel flowline-based meshing technique to create adaptive grids for Computational Fluid Dynamics (CFD) simulations in patient-specific intracranial aneurysms. The adaptive grid density is obtained such that it captures the fine geometrical details of the flow with high grid density, while smoother flow characteristics are calculated with a coarser grid density. The correlation between the topological characteristics of the flow and the element size of the adaptive grid results in a practical mathematical formula for calculating the element size using only one uniform base mesh and a user defined implementation in CFD post processors.
Expression of Primary Cilia on Liver Stem and Progenitor Cells: Potential Role for Mechanosensing in Liver Development
Authors: Moran Emma C. , Baptista Pedro M. , Nishii Kenichiro , Wasnick David , Soker Shay , Sparks Jessica L.
Published: January 2014

The primary cilium is a non-motile organelle that projects out from the plasma membrane of many cell types in the body. It consists of an axoneme with microtubules arranged in a 9+0 arrangement that extends from the mother centriole contained within the basal body. Once thought to be a non-essential organelle, it is now known that primary cilia have an important role in embryonic and post-natal development, as well as maintenance of adult tissues. Mutations affecting primary ciliary development result in a class of serious diseases known as ciliopathies [1, 2]. Recent research suggests that the primary cilia/ centrosomes might play a role in embryonic stem cell differentiation through cell cycle regulation and their association with the Hedgehog signaling pathway [3, 4].
The Effects of Extracellular Matrix Protein Insufficiency and Treatment on the Stiffness of Arterial Smooth Muscle Cells
Authors: Espinosa Gabriela , Bennett Lisa , Gardner William , Wagenseil Jessica
Published: January 2014

Increased arterial stiffness is directly correlated with hypertension and cardiovascular disease. Stiffness of the conducting arteries is largely determined by the extracellular matrix (ECM) proteins in the wall, such as collagen and elastin, produced by the smooth muscle cells (SMCs) found in the medial layer. Elastin is deposited as soluble tropoelastin and is later crosslinked into elastin fibers. Newborn mice lacking the elastin protein ( Eln−/−) have increased arterial wall stiffness and SMCs with altered proliferation, migration and morphology [1]. Vessel elasticity is also mediated by other ECM proteins, such as fibulin-4. Elastic tissue, such as lung, skin, and arteries, from fibulin-4 deficient ( Fbln4−/−) mice show no decrease in elastin content, but have reduced elasticity due to disrupted elastin fibers [2]. Arteries from both elastin and fibulin-4 deficient mice have been previously studied, but the mechanical properties of their SMCs have not been investigated. Recent experiments comparing arterial SMCs from old and young animals suggest that mechanical properties of the SMCs themselves may contribute to changes in wall stiffness [3]. Hence, we investigated the stiffness of isolated arterial SMCs from elastin and fibulin-4 deficient mice using atomic force microscopy (AFM). In addition, we studied the effects of two elastin treatments on the mechanical properties of SMCs from Eln+/+ and Eln−/− mice. Differences between the treatments may elucidate the importance of soluble versus crosslinked elastin on single cell stiffness.
Effects of Cartilage Constitutive Model on Specimen-Specific Validation and Predictions of Cartilage Mechanics in the Human Hip
Authors: Henak Corinne R. , Kapron Ashley L. , Anderson Andrew E. , Ateshian Gerard A. , Ellis Benjamin J. , Maas Steve A. , Weiss Jeffrey A.
Published: January 2014

The initiation and progression of hip osteoarthritis (OA) may be predicted by mechanical factors [1]. Contact stress (CS), maximum shear stress (MSS) at the osteochondral interface and first principal strain (FPS) at the articular surface have been identified as parameters that alter the physical integrity and metabolism of cartilage [1]. Although these parameters are difficult to measure in-vivo, they can be predicted using finite element (FE) models. However, the reliability of model predictions and the effects of model assumptions are largely unknown. Direct validation of FE models against experimental measurements for a series of specimens shows the reliability of predictions across specimen geometry [1], although to date this has only been performed for a single hip [2].
Identification of True Knee Flexion Axis Despite Marker Misplacement Using Principal Component Analysis
Authors: Jensen Elisabeth , Lugade Vipul , Crenshaw Jeremy , Kaufman Kenton
Published: January 2014

Gait analysis is useful for revealing pathologic tibial rotation in children with cerebral palsy (CP), thus guiding interventions of de-rotational osteotomy [1]. Surface marker misplacement may cause an inaccurate definition of the knee flexion axis, which generates downstream artifacts such as cross talk between knee rotation angles and internal rotation errors, misleading these patients’ assessments and surgical interventions [2,3]. Therefore, the purpose of this study was to develop and evaluate a novel method for defining the true knee flexion axis from existing marker trajectories during gait. We hypothesized that the devised method would accurately quantify the offset in the flexion axis due to a systematically misplaced marker and correct the downstream crosstalk and rotation errors of the knee joint angles associated with the marker misplacement.
Design of Cardiopulmonary Assist Devices for Adult and Pediatric Patients: The Contribution of Robert Eberhart
Authors: Borovetz Harvey S.
Published: January 2014

Beginning in 1976 the University of Pittsburgh (UoP), initially through its Department of Surgery and later including the Swanson School of Engineering and McGowan Institute for Regenerative Medicine, has been actively engaged in the design and clinical utilization of cardiopulmonary assist devices for adult and pediatric patients. In launching these initiatives, the focus was on extracorporeal membrane oxygenation (ECMO) applied primarily to infants with respiratory distress, congenital and/or acquired cardiac disease. A leader in these early days of ECMO was Professor Robert Eberhart, who not only detailed the underlying bio-transport principles or oxygen and carbon dioxide exchange in ECMO devices, but who also participated in the early clinical utilization of ECMO. Professor Eberhart presented his path-finding results on an annual basis at the national meetings of the American Society for Artificial Internal Organs (ASAIO) with publication in Transactions ASAIO [1–3].
Understanding the Effects of Thermal Elevations Associated With Orthopedic Intervention: An Experimental and Computational Investigation
Authors: Dolan E. B. , Vaughan T. J. , Niebur G. L. , Tallon D. , McNamara L. M.
Published: January 2014

Specialized surgical cutting instruments are required to provide orthopedic surgeons with access to joints of the body, without causing extensive harm to native tissue, thus enhancing post-operative outcome. Orthopaedic intervention inevitably exposes bone tissue to elevated temperatures due to mechanical abrasion. Elevated temperatures lead to thermal necrosis and apoptosis of bone cells, surrounding soft tissue, bone marrow and stem cells crucial for postoperative healing (1–4). Thermally damaged bone tissue is subsequently resorbed and in severe cases replaced by connective tissue (2, 5) Bone thermal damage occurs when the local temperature exceeds a thermal threshold, largely recognised as ≥47°C (4, 6). Furthermore, it has been proposed that the area of bone to experience thermal damage is directly proportional to the duration of exposure to the heat source (7, 8). However, precise thermal elevations occurring throughout bone during surgical cutting are not well defined. It is also unclear whether temperatures generated in osteocytes in vivo are sufficient to induce cellular responses. Experimental analysis of temperature generation throughout bone is challenging due to its complex heterogeneous composition. There is a specific need for advanced 3D computational models that incorporate multi-scale variability in both bone tissue composition and thermal properties to predict how organ level thermal elevations are distributed throughout bone cells and tissue during orthopaedic cutting procedures.
Affect of Attachment Site on Medial Patellofemoral Ligament Reconstruction: A Finite Element Analysis
Authors: DeVries Nicole A. , Bollier Matthew J. , Grosland Nicole M.
Published: January 2014

Bony anatomy, soft tissue restraints, and the dynamic action of the quadriceps all play a role in maintaining patellar stability throughout knee motion. The medial patellofemoral ligament (MPFL) is the main soft tissue restraint to lateral translation of the patella, and helps guide the patella into the trochlear groove during the first 30° of knee flexion [1]. Studies have shown that the MPFL is the most consistently injured anatomical structure after acute lateral patellar dislocation [2]. Due to the high rate of recurrent episodes of instability following conservative management of acute lateral patellar dislocation, a number of bony and soft tissue procedures have been described to restore patellar stability, including MPFL reconstruction [2].
Patient Specific Modeling of a Stage II Flatfoot Population
Authors: Spratley Edward M. , Matheis Erika A. , Hayes Curtis W. , Adelaar Robert S. , Wayne Jennifer S.
Published: January 2014

Adult Acquired Flatfoot Deformity (AAFD) is a degenerative disease characterized by chronic changes in the joint alignment of the bones of the foot leading to significant pain and dysfunction. The hallmark of this disease is the functional loss in posterior tibialis tendon (PTT) strength though mechanical degradation of passive support structures of the foot have also been implicated, namely the spring ligament, talocalcaneal interosseous ligaments, fibers of the anterior deltoid, and the long and short plantar ligaments. [1] Clinically, AAFD patients present with midfoot collapse, forefoot abduction, and valgus tilting of the hindfoot and the magnitudes of these deformities are most often graded using plane radiographs in the mediolateral (ML), oblique anteroposterior (AP) and posteroanterior (PA) views. [1–3] The objective of this study was to develop a population of patient-matched rigid-body kinematic models using a standardized methodology that can be used to predict pathologic foot function with agreement between patient and model assessed through clinically relevant radiographic joint angles.
Synthesis of Poly (L-Lactic Acid) Scaffolds Under Controlled Freezing Conditions
Authors: Chinnasami Harish , Hayes Daniel , Devireddy Ram
Published: January 2014

Poly (l-lactic acid) (PLLA) scaffolds for bone grafts were prepared by using Thermally Induced Phase Separation (TIPS) method. Solutions of PLLA-dioxane was formed by dissolving a pre-determined value of PLLA in dioxane (3, 7 and 10% wt/vol) at 323K. These solutions were frozen at controlled cooling rates (1, 10 and 40°C/min) in cylindrical capsules. The frozen solutions were freeze-dried for a period of 48 hours for the frozen dioxane to completely sublimate, leaving the porous PLLA scaffold. The scaffolds which were formed under different processing conditions were characterized in terms of porosity, pore sizes and compressive moduli.