bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Impact of Shading Devices on Energy Consumption of Buildings in Tropical Regions
Authors: Samanta Akash , Saha Saibal , Biswas Jhumoor , Dutta Arindam
Published: March 2014

The aim of this paper is to demonstrate the role of shading devices in the improvement of energy efficiency of buildings in hot dusty and dry tropical regions. The effect of shading in reducing the energy consumption of buildings is investigated by considering a case study of a guest house chosen because of its logical design approach to reduce thermal loads. The building plan, measurements, and details on schedules of building usage activities have been used as input data to a simulation program of the building. Based on the inputs, a thermal building model is developed in trnsys 17 simulation program and the effect of external shading on the building has been explored. It is seen that building design and orientation determine the effectiveness of shading. Movable shading over windows has a significant impact reducing temperatures by about 1.5 °C in each thermal zone. The difference in thermal energy loads of the building calculated from modeling simulations of the base case and the control case utilizing movable shading devices is approximately 8%. A programmable logic controllers (PLC)-based movable shading device has been designed to facilitate optimal shading control. The results enable us to draw inferences regarding the additional contribution of the shading factor in energy saving techniques for buildings.
Noise Induced Loss of Tracking in Systems With Saturating Actuators and Antiwindup
Authors: Eun Yongsoon , Hamby Eric S.
Published: March 2014

This technical note is devoted to a recently discovered phenomenon that takes place in feedback systems with saturating actuators, proportional-integral (PI) control, and antiwindup. Namely, in such systems, measurement noise induces steady-state error in step tracking, which is incompatible with the standard error coefficients. We quantify this phenomenon using stochastic averaging theory and show that the noise induced loss of tracking occurs only if antiwindup is present. An indicator that predicts this phenomenon is derived, and a rule-of-thumb, based on this indicator, is formulated. An illustration using a digital printing device is provided.
Investigation of Local Stability Transitions in the Spectral Delay Space and Delay Space
Authors: Gao Qingbin , Zalluhoglu Umut , Olgac Nejat
Published: March 2014

The stability boundaries of LTI time-delayed systems with respect to the delays are studied in two different domains: (i) delay space (DS) and (ii) spectral delay space (SDS), which contains pointwise frequency information as well as the delay. SDS is the preferred domain due to its advantageous boundedness properties and simple construct of stability transition boundaries. These transitions at the mentioned boundaries, however, present some conceptual challenges in SDS. This transition property enables us to extract the corresponding local stability variation properties in the DS, while it does not have any implication in the preferred SDS. The novel aspect of the investigation is to introduce a comparison mechanism between these two domains, DS and SDS, from the stability transition perspective. Interestingly, we are able to prove their equivalency, which provides complementary insight to the parametric stability variations.
An Indirect Adaptive Velocity Controller for a Novel Steer-by-Wire System
Authors: Daher Naseem , Ivantysynova Monika
Published: March 2014

Increased environmental awareness and skyrocketing fuel prices have pressed researchers and engineers to find energy efficient alternatives to traditional approaches. A novel steer-by-wire technology, which is based on pump displacement control actuation, has been proposed by the authors and was shown to improve the fuel efficiency of a wheel loader steering system by 43.5%. Building on this realization, the work in this paper deals with designing an adaptive velocity controller, which takes the form of an indirect self-tuning regulator that has the facility to cope with parametric uncertainties and uncertain nonlinearities associated with hydraulically actuated systems. The indirect self-tuning regulator algorithm is selected given that the uncertain plant parameters are estimated in the process, which is a useful byproduct that gives insight into system properties that will be considered in future investigation. Furthermore, a discrete adaptive control law with low computational cost is required for the application on hand. The designed self-tuning regulator and the estimation algorithm were validated in numerical simulations as well as experimentally on a designated prototype test vehicle, demonstrating the effectiveness of the proposed adaptive scheme in the face of uncertainties. The controller was able to adapt to varying load mass and inertia, which correlate to varying operating conditions that influence the system dynamics. Hence, besides offering improved fuel efficiency, the new steering technology also results in smarter machines.
Seabed Interaction Modeling Effects on the Global Response of Catenary Pipeline: A Case Study
Authors: Elosta Hany , Huang Shan , Incecik Atilla
Published: March 2014

A steel catenary riser (SCR) attached to a floating platform at its upper end encounters oscillations in and near its touchdown zone (TDZ), which results in interaction with the seabed. Field observations and design analysis of SCRs show that the highest stress and greatest fatigue damage occurred near the touchdown point where the SCR first touches the seabed soil. The challenges regarding the fatigue damage assessment of an SCR in the TDZ are primarily because of the nonlinear behavior of SCR–seabed interaction and considerable uncertainty in seabed interaction modeling and geotechnical parameters. Analysis techniques have been developed in the two main areas: SCR–seabed interaction modeling and the influence of the uncertainty in the geotechnical parameters on the dynamic response and fatigue performance of SCRs in the TDZ. Initially, this study discusses the significance of SCR–seabed interaction on the response of an SCR for deepwater applications when subjected to random waves on soft clay using the commercial code OrcaFlex for nonlinear time domain simulation. In the next step, this study investigates the sensitivity of fatigue performance to geotechnical parameters through a parametric study. It is proven that employing the improved lateral SCR–seabed interaction model with accurate prediction of soil stiffness and riser penetration with cyclic loading enables us to obtain dynamic global riser performance in the TDZ with better accuracy. The fatigue analyses results prove that the confounding results indicated by the previous research studies on the SCR in the TDZ are due to different geotechnical parameters imposed with the seabed interaction model. The main benefit of employing nonlinear seabed approach is to capture the entity of realistic soil interaction behavior in modeling and analysis and to predict the likelihood of the fatigue damage of the SCR with seabed interaction, thereby minimizing the risk of the loss of the containment with the associated environmental impact.
Sensitivity of Hemodynamic Parameters to Waveform, Flow Division, and Head Rotation in the Human Carotid Bifurcation
Authors: Papaharilaou Yannis , Seimenis Ioannis , Ekaterinaris John , Georgiou Georgios , Eracleous Eleni , Brott Brigitta C. , Anayiotos Andreas
Published: March 2014

Hemodynamic parameters such as time averaged wall shear stress (TAWSS), wall shear stress temporal gradient (WSSTG) and Oscillatory Shear Index (OSI) have previously been cited as parameters associated with the development of atherosclerotic disease at the human carotid bifurcation [1,2]. The sensitivity of these important parameters however, with variations of driving flow waveform, flow division and posture changes are not well known. To investigate these changes, we have used image based CFD, to analyze the flowfield of the carotid bifurcation of a healthy volunteer for five different input waveforms, three flow division ratios and two head postures.
Dynamic Movement of Sub-Epiblastic ECM During Primitive Streak Formation
Authors: Zamir Evan A. , Rongish Brenda J. , Little Charles D.
Published: March 2014

A well known “Polonaise” pattern of epiblast cell movements accompanies formation of the amniote primitive streak (PS), which is the organizing center for gastrulation. Although the movements observed in classical (text book) and modern studies appear similar, the biophysical mechanisms driving these movements are unknown. In comparison to studies of dynamic cellular movements during PS formation, and more generally, gastrulation, there is a relative paucity of data regarding movement of the extracellular matrix (ECM) lying adjacent to the ventral surface of the epiblast. Electron microscopy and immunofluorescence studies demonstrated decades ago the presence of a nascent basement membrane-like structure, which we refer to as the sub-epiblastic ECM (SE ECM), containing, at least, fibronectin [1] and collagen [1]. Using ultrastructural markers, Sanders [2] found that the SE ECM is transported medially to the PS with the epiblast cells. Almost two decades later, Bortier et al. [3] grafted radiolabeled quail cells into the epiblasts of chicken blastoderms, and concluded that whole groups of epiblast cells slide across (move relative to) the SE ECM — thus, contradicting Sanders’ earlier findings.
Teaching Responsible Conduct of Research and Engineering to Bioengineering Graduate Students
Authors: Wilson Sara E.
Published: March 2014

Training in the responsible conduct of research (RCR) has become an increasing concern of federal funding agencies such as NIH and NSF. In 2000, the Office of Research Integrity published the policy of instruction in responsible conduct of research for NIH funded research. This policy mandates that all research staff participate in RCR instruction. In 2007, the COMPETES Act was signed by President Bush mandating RCR instruction of all NSF-funded undergraduate students, graduate students, and post-doctoral researchers. Such training can and does take many forms, from online tutorials and study guides to seminar series to semester long classes. Core instructional areas in such training include appropriate data management, mentor-trainee relationships, publication practices and authorship, peer review, human and animal subjects and conflict of interest.
Dynamic Simulation of Knee Motion Using Three-Dimensional Surrogate Contact Modeling
Authors: Lin Yi-Chung , Haftka Raphael T. , Queipo Nestor V. , Fregly Benjamin J.
Published: March 2014

Different types of computer models have been used to simulate contact conditions in human joints. One of the primary limitations of these models is computational speed. Even with simple elastic foundation (EF) contact models [1], CPU times on the order of 5 to 10 minutes for a one-cycle dynamic simulation can be prohibitively expensive for design sensitivity and optimization studies requiring thousands of simulations.
Using a Finite Element Model to Help Develop a Method to Test Knee Femoral Components
Authors: Kralovic Barbara J. , Wentorf Fred A. , Levine Dan L.
Published: March 2014

In total knee arthroplasty (TKA), the knee femoral component replaces the bone surfaces and cartilage on the distal femur (thigh bone) that have been damaged due to injury or disease. While success rates are high with TKA, some fractures of the femoral component have occurred clinically (Fig. 1 and 2) [1]. Understanding the nature of these fractures is critical since the industry is moving towards bone conserving designs, minimally invasive approaches, new materials and new technologies for TKA. At the same time patient requirements are changing as patients are heavier, younger, and more active.
Hemodynamic Phenotypes of Anatomically Realistic Terminal Aneurysms
Authors: Ford Matthew D. , Lee Sang-Wook , Piccinelli Marina , Antiga Luca , Steinman David A.
Published: March 2014

Intracranial aneurysms occur in approximately 4% of the population. While advances in medical imaging and surgical procedures have led to improved diagnosis and treatment, the decision of whether or not too treat an unruptured aneurysm is still largely subjective. The size of the aneurysm combined with its location and shape are the major determining factors, along with experience, when considering treatment. There is increasing recognition that hemodynamic forces play a key role in the life cycle of an aneurysm; however, it is difficult to provide this information in the clinic, owing to the need for time-consuming computational fluid dynamics (CFD) simulations. A more pragmatic solution, for now at least, may be to predict the gross flow patterns (“hemodynamic phenotype”) from simpler-to-measure geometric parameters.
Theoretical Evaluation of Tissue Damage Using Er,Cr:YSGG Laser for Root Canal Preparation
Authors: Zhu L. , Tolba M. , Arola D. , Salloum M. , Alvarez J. , Meza F. , Fouad A.
Published: March 2014

Lasers have been used in dentistry for removing hard tooth tissue for more than twenty years. In particular, the arbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) laser, which has a wavelength of 2.78 μm, has been shown to offer the advantages of straight, clean and precise hard tissue cuts [1]. Due to its long wavelength, the absorbed laser energy is limited within a very thin layer of the irradiated tissue and therefore, high temperature elevations (>100°C) at the surface results in hard tissue ablation. Recently, lasers have also been used to prepare a clean root canal surface as well as in disinfection and elimination of bacteria from the root canal system [2].
Quantifying the Motion of Murine Epicardial Coronary Arteries
Authors: Long David S. , Zhu Hui , Friedman Morton H.
Published: March 2014

Coronary artery atherosclerosis is a leading cause of morbidity and mortality in western societies. Atherosclerosis is a progressive fibroinflammatory disease identified by intimal thickening, the focal accumulation of lipids, fibrous elements, and cellular elements within the walls of large arteries. These lesions preferentially develop at arterial branches, the outer walls of bifurcations, and the inner walls of curved sections; the cause of this focal vasculopathy is not fully understood. It is, however, understood from epidemiological and clinical studies that individual susceptibility to the development and progression of atherosclerotic lesions is influenced by “traditional” systemic risk factors, including smoking, diabetes mellitus, obesity, hypertension, and high cholesterol. However, these risk factors cannot account for half of the variability in occurrence of this disease; this indicates additional risk factors have not been identified. One prevalent explanation of the focal nature of the disease is that the local fluid mechanical stresses at the walls of coronary arteries, as well as mechanical stresses within the vessel wall, may mediate the phenotype of endothelial cells thereby producing atherosusceptible sites. Therefore, it has been speculated [1] that certain aspects of arterial geometry and motion, which vary substantially among individuals, may increase an individual’s susceptibility to developing atherosclerosis — “geometric risk factors”.
Importance of Axial Stress in Arterial Growth and Remodeling
Authors: Humphrey J. D.
Published: March 2014

Since the mid-1970s, we have continued to understand better the fundamental importance of mechanotransduction in vascular biology. For example, beginning with Rosen and colleagues in 1974, we discovered that endothelial cells alter their production of vasoactive molecules in response to changes in flow-induced wall shear stress; beginning with Glagov and colleagues in 1976, we discovered that vascular smooth muscle cells alter their production of extracellular matrix proteins in response to changes in cyclic stretching comparable to that induced by pulsatile pressures [1]. Indeed, such findings are not surprising given the well know arterial adaptations that occur in response to sustained changes in blood flow or pressure. The caliber of an artery tends to increase (or decrease) in response to sustained increases (decreases) in blood flow and the thickness of the arterial wall tends to increase (or decrease) in response to sustained increases (decreases) in blood pressure. In both cases, it appears that the associated wall shear or intramural circumferential stresses are returned toward normal following the change in hemodynamics.
Modelling Dynamical Arterial Adaptations to Altered Chemo-Mechanical Environments
Authors: Cardamone Luca , Valentin Arturo , Humphrey Jay D.
Published: March 2014

Vascular smooth muscle cells (SMC), endothelial cells (EC), and fibroblasts exist in a dynamic mechanical environment and can sense and respond to mechanical stimuli in vivo (McKnight and Frangos [1]). It is becoming more and more clear that complex dynamics not only influences vascular tone but also SMC proliferation (see Dancu et al. [2]) and extracellular matrix turnover (Cummins et al. [3]) by stimulating cell activity.
How Concentration and Crowding Impact Protein Stability: Insights From a Coarse-Grained Model
Authors: Truskett Thomas M.
Published: March 2014

Much of the current understanding of the protein folding problem derives from studies of proteins in dilute solutions. However, in many systems of scientific and engineering interest, proteins must fold in concentrated, heterogeneous environments. Cells are crowded with many molecular species, and chaperones often sequester proteins and promote rapid folding. Proteins are also present in high concentrations in the manufacture, storage, and delivery of biotherapeutics. How does crowding generally affect the stability of the native state? Are all crowding agents created equal? If not, can generic structural or chemical features forecast their effects on protein stability?
Viscoelastic Properties of Genetically Engineered Silk-Elastin-Like Protein Polymers
Authors: Teng Weibing , Cappello Joseph , Wu Xiaoyi
Published: March 2014

Genetic engineering of protein-based materials provides material scientists with high levels of control in material microstructures, properties, and functions [1]. For example, multi-block protein copolymers in which individual block may possess distinct mechanical or biological properties have been biosynthesized [2, 3]. Polypeptide sequences derived from well-studied structural proteins (e.g., collagen, silk, elastin) are often used as motifs in the design and synthesis of new protein-based material, in which new functional groups may be incorporated. In this fashion, we have produced a series of silk-elastin-like proteins (SELPs) consisting of polypeptide sequences derived from silk of superior mechanical strength and elastin that is extremely durable and resilient [2, 4]. Notably, the silk-like blocks are capable of crystallizing to form virtual cross-links between elastin-mimetic sequences, which, in turn, lower the crystallinity of the silk-like blocks and thus enhance the solubility of SELPs. Consequently, SELPs may be fabricated into useful structures for biomedical applications, including drug delivery. In this study, we will characterize viscoelastic properties of SELPs, which are particularly relevant to tissue engineering applications.
Dispersion of the Drug in the Liquid Vitreous due to Saccadic Eye Movements
Authors: Balachandran Ram K. , Dorfman Kevin D. , Barocas Victor H.
Published: March 2014

The vitreous is a transparent gel that fills the posterior segment of the eye. With aging, the vitreous undergoes progressive liquefaction and thus more readily sloshes during eye motion [1]. In addition to its relevance to the problem of vitreous detachment [1], increased motion of the vitreous could have a profound effect on transport of drugs used to treat posterior segment eye diseases.
A Critical Distance Analysis of the Effect of Crack Length on Toughness and Fatigue in Compact Bone
Authors: Taylor David , Kasiri Saeid
Published: March 2014

The plane strain fracture toughness, KIC, has a constant value for long cracks, but when specimens containing short cracks are tested it is often found that the measured toughness is less than the long-crack value, and tends to decrease with decreasing crack length. A similar effect occurs when measuring the cyclic stress intensity range, ΔK, corresponding to a given rate of crack growth da/dN. Some experimental data are available in the published literature to show that cortical bone displays these short-crack effects for crack lengths of the order of millimeters or less. The hypothesis of the present work was that these effects can be predicted using an approach known as the Theory of Critical Distances. This is the first time that this approach has been used to predict short crack effects in bone.
Numerical Analysis of Brain Hypothermia Using a Vascular Model in the Neck
Authors: Xia Xiang , Cheng Shuxia , Zhao Gang , Hu Hanping , Zhu Liang
Published: March 2014

In recent years, mild or moderate hypothermia has been proposed for clinical use as an adjunct for achieving protection from cerebral ischemia and traumatic brain injury. Clinically feasible brain cooling methods include a head hood or helmet with chemical cooling, head immersion in ice water, nasophyaryngeal cooling after tracheal intubations, etc. Under normal conditions it has been shown that temperature along the common and internal carotid arteries does not change significantly due to relatively small heat exchange surface of the blood vessels and high flow velocity of the blood. However, when the neck and brain surfaces are cold due to wearing external cooling garments, heat loss from the common and internal carotid arteries may result in arterial blood cooling before the blood enters the Circle of Willis [Zhu 2000].
A Study of Intracellular Ice Formation in Jurkat Cells
Authors: Acharya Tathagata , Devireddy Ram V.
Published: March 2014

The objective of this study was to characterize the IIF behavior of Jurkat cells in isotonic conditions in the absence of any cryoprotective agents. The Jurkat cells were collected from culture and then washed and re-suspended in Dulbecco’s Phosphate Buffered Saline (PBS). The freezing experiments were carried out at defined freezing protocols and at various freezing rates of 5, 20, 30 and 50 °C/min. The results suggest there was no substantial evidence of intracellular ice formation at lower cooling rates of 5, 20 and 30° C/min. The first conspicuous indication of intracellular ice formation (IIF) was observed at a freezing rate of 50 °C/min. At this cooling rate, unlike the usual sudden blackening of cells, the cells suddenly grew and exploded suggesting the formation of intracellular ice, which was reminiscent of a prior observed phenomenon for IIF.
Relating Wall Shear Stress, Bleb Formation and Rupture of Cerebral Aneurysms: Image-Based Modeling and Clinical Observations
Authors: Cebral Juan R. , Putman Christopher M.
Published: March 2014

Cerebral aneurysms are widely believed to form and grow as a result of the interactions of hemodynamics and wall mechano-biology. Researchers have used a variety of tools to study these complex multi-factorial mechanisms including animal, in vitro, and computational models. The goal of these experiments has been to approximate the in vivo environment so that theories about the natural history of brain aneurysms can be developed and tested in realistic systems. Studying the link between hemodynamics and clinical observations of aneurysm progression is necessary to reach an understanding of the relative importance of the different mechanisms involved in these processes [1]. The objective of our research is to investigate the possible relationship between wall shear stress (WSS) — which is known to regulate mechano-biological processes at the arterial wall — produced by different blood flow patterns and the evolution and rupture of cerebral aneurysms.
Finite Element Modeling of Osmotic Swelling in Tissue-Engineered Cartilage
Authors: Bian Liming , Kelly Terri Ann N. , Lima Eric G. , Ateshian Gerard A. , Hung Clark T.
Published: March 2014

Proteoglycans and Type II collagen represent the two major biochemical constituents of articular cartilage. Collagen fibrils in cartilage resist the swelling pressure that arises from the fixed charges of the glycosaminoglycans (GAGs), and together they give rise to the tissue’s unique load bearing properties. As articular cartilage exhibits a poor intrinsic healing capacity, there is significant research in the development of cell-based therapies for cartilage repair. In some of our tissue engineering studies, we have observed a phenomenon where chondrocyte-seeded hydrogel constructs display cracking in their central regions after significant GAG content has been elaborated in culture. A theoretical analysis was performed to gain greater insights into the potential role that the spatial distribution of proteoglycan and collagen may play in this observed response.
Measuring Diffusion in Non-Sectioned Articular Cartilage: A FRAP Sensitivity Study
Authors: Docimo Jennifer E. , Novotny John E.
Published: March 2014

Measuring the diffusion of molecules within articular cartilage is essential in characterizing its behavior. Information about this important mechanism may be useful to understanding changes in cartilage during degeneration or osteoarthritis. One method used in quantifying diffusion is fluorescence recovery after photobleaching (FRAP). The FRAP technique has been used in previous studies for cartilage [1] and various tissues [2]. In FRAP, a small region of interest (ROI) is selected within the tissue and fluorescent molecules are bleached using a higher laser power than would be used for imaging. Immediately following the ROI bleaching, bleached molecules diffuse out of the ROI as unbleached molecules diffuse into it. The average intensity data within the ROI is collected as a function of time. This data is then fit to a diffusion model usually resulting in a calculation of the diffusion constant, D (μm2/second) [3].
Relation Between Wall Shear Stress and Plaque Necrotic Core in the Left Coronary Arteries of Patients Using Intravascular Ultrasound and Computational Fluid Dynamics
Authors: Suo Jin , McDaniel Michael , Samady Habib , Giddens Don
Published: March 2014

Atherosclerosis is a disease characterized by arterial plaques that include several components of which the necrotic core has been recognized as an important indicator of the likelihood of plaque rupture [1]. In the present study, the relation of hemodynamic wall shear stress (WSS) to necrotic core localization in the left coronary artery of patients was investigated using intravascular ultrasound (IVUS) and computational fluid dynamics (CFD). An innovative 3D measuring technique was developed and was successfully used to reconstruct coronary arteries in patients based on angiographic images and echo ultrasound slices from IVUS. The reconstruction includes lumen, external elastic membrane (EEM) and spatial distribution of plaque components such as fibrous tissue, necrotic core and calcium. WSS distribution in the vessel segment was computed by CFD, and the relative locations of necrotic core and WSS were determined. Results to date support the hypothesis that a greater necrotic core in coronary plaques is associated with areas of low WSS. The methodology developed has implications for the study of plaque progression and the prediction of likelihood of plaque rupture.
Ablation of Subsurface Tumors Using 1552 nm Ultra-Short Pulse Laser
Authors: Raje Shreya , Sajjadi Amir , Mitra Kunal , Grace Michael S.
Published: March 2014

Over last two decades lasers have been used for the treatment of subsurface tumors. Various techniques such as Laser-induced Hyperthermia, Laser Interstitial Thermal Therapy (LITT), and Laser Immunotherapy have been developed for the successful ablation of subsurface tumors by different researchers. All these techniques use photo-thermal mechanism for tumor ablation by delivering thermal energy at the tumor site. In all these existing techniques, either continuous wave (CW) or long pulse laser source has been used, which often produces larger heat affected zone as compared to that produced by short pulse laser. Moreover, the delivery of laser beam at the target site is achieved through fiber optic probes which often require perforation of the skin. These drawbacks can be eliminated if a converging laser beam from a short pulse laser source is directly focused at the subsurface location to ablate the tumor.
Analysis of Retrieved Surgical Implant Devices: Alternative Bearing Surfaces
Authors: Eberhardt Alan W. , Petersen Donald W. , Chowdhury Shafiul , Beck Preston R. , Lemons Jack E.
Published: March 2014

Analyses of orthopaedic devices and prostheses from surgical revisions (failures) have provided considerable and valuable information related to the causes of some unintended clinical outcomes. Thousands of explanted samples have been categorized and hundreds studied over past decades. Forensic approaches for determining cause-effect relationships specific to the prosthesis aspects of clinical performance could lead to recommendations of improvements of existing or design of new systems to further enhance clinical longevities. In the following we provide a summary of methodologies and example results from a series of recent retrieval studies aimed at the analysis of alternative bearing surfaces in orthopaedic implants.
Computation of Local Elastic and Torsional Properties of Soft Hydrogels
Authors: Chippada Uday , Georges Penelope , Jiang Xue , Li Lulu , Yurke Bernard , Langrana Noshir A.
Published: March 2014

Soft hydrogels serving as substrates for cell attachment are used to culture many types of cells. The mechanical properties of these gels influence the cell morphology, growth and differentiation. Young’s moduli of such hydrogels were calculated by our group using spherical beads of 400μm radius embedded in micro-liter samples [1]. This concept of inclusion-based measurement has also been utilized by other researchers to measure local viscoelastic responses [2, 3]. The present research involves scaling down the size of the inclusions to the level at which local inhomogeneties in the media become significant, thus allowing us to evaluate the local elastic behavior of the hydrogels.
Critical Buckling Pressure of Veins
Authors: Martinez Ricky , Fierro Cesar A. , Han Hai-Chao
Published: March 2014

Vein tortuosity is often seen as a consequence of venous hypertension and chronic venous disease. However, the underlying mechanism of vein tortuosity is unclear. The aim of this study was to test the hypothesis that hypertensive pressure causes vein buckling that leads to tortuous veins. We determined the buckling pressure of porcine jugular veins and tested the mechanical properties of these veins. Our results demonstrated that veins buckle when the transmural pressure exceeds a critical pressure that is not much higher than normal venous pressure. The critical pressure was found to be strongly related to the axial strain in the veins. Our results are useful in understanding the development of varicose veins.
Initial Observations in the Validation of a Hybrid Test Protocol for Motion Preservation Devices on a Biomechanical Spine Tester
Authors: Cheng Boyle C. , Welch William C.
Published: March 2014

Motion preservation of the cervical spine has been attractive from several vantage points. Clinically, the ability to limit adjacent level disease has been an important consideration. In addition, the cervical loading conditions may not be as demanding compared to other spinal segments, e.g., the lumbar region. Thus, devices that are designed to preserve motion for the cervical spine are widely perceived as promising technologies and require new methods of evaluation in order to more accurately predict clinical performance.
Optimal Control Solutions for a Simple Model of Human Jumping
Authors: Miller Ross H. , Umberger Brian R. , Caldwell Graham E.
Published: March 2014

Neuromuscular control of complex, multi-segment movements is often investigated with a modeling and computer simulation approach. Because a given movement can be completed using many different coordination choices, an optimization framework is often used to determine the muscle activity patterns that best accomplish the movement task. This framework is well suited to simulating movements whose performance objectives are easily specified by mathematical functions, such as vertical jumping for maximum height. However, these motion simulations tend to be difficult optimization problems because they contain many local optima that add complexity to the solution domain of the objective function [1–3].
Validation of Computational Knee Models Using a Dynamic Knee Simulator
Authors: Guess Trent M. , Kia Mohammad , Weimer Katherine , Dodd Kevin , Maletsky Lorin
Published: March 2014

Computational models of the knee provide valuable information on knee biomechanics, but validation of these models is challenging as in-vivo parameters such as muscle forces and tissue loading cannot be measured. Machines that simulate the dynamic loading and motion of physiological activities on cadaver knees can provide a means for validating computational knee models and modeling methods. In this approach, all forces applied to cadaver knees are known and can be replicated in computational simulations. The resulting experimental and computational kinematics can then be compared. Presented here is the development and use of a modeling platform comprised of a multi-body computational model of a cadaver knee and dynamic knee simulator and experimental measurements from the cadaver knee loaded in the machine. This modeling platform has been used to study: 1) patient specific reference lengths versus literature obtained reference lengths [1], 2) inclusion of ligament and tendon wrapping [2] and, 3) the development of a multi-body model of the meniscus [3].
Image-Based Modeling of Blood Flow in Human Coronary Arteries With and Without Bypass Grafts During Rest and Simulated Exercise
Authors: Shih Jessica , Kim Hyun Jin , Taylor Charles A.
Published: March 2014

The number of patients with coronary artery disease continues to rise, with approximately 469,000 coronary bypass procedures in 2005 alone [1]. A priori knowledge of the flow features within the coronary vascular system could prove useful in predicting flow changes due to coronary bypass surgery. Image-based modeling and 3-D computational simulations could be used to compute flow and pressure in a patient-specific manner. However, modeling coronary flow requires knowledge of the intramyocardial pressure that compresses coronary vessels, resulting in decreased flow in systole and increased flow in diastole. Left ventricular pressure can provide an estimate to intramyocardial pressure, but the aortic pressure and left ventricular pressure must be coupled in systole when the aortic valve is open. Previously, we have developed a method to couple a lumped-parameter heart model to the inlet of a 3-D model to compute aortic and ventricular pressure [2]. In this study, we use the lumped-parameter heart model and computational fluid dynamics to calculate flow dynamics in a patient model with coronary artery bypass grafts.
Biotransport to the Cerebral Tissues Related to the Vascular Diseases
Authors: Tanishita Kazuo , Masamoto Kazuto , Kanno Iwao , Kobayashi Hirosuke
Published: March 2014

Brain is a highly oxidative organ and its consumption rate of oxygen accounts for 20 percent of that of the whole body. This large consumption rate must be met by continuous supply of oxygen, because lack of oxygen rapidly causes irreversible damage to central nervous system. Acute hypoxic episodes cause a certain pattern of regional damage. Cerebral cortex (e.g., layers III, V, and VI) is one of the most susceptible regions to hypoxia, and damage to sensorimotor function is particularly severe in humans that survive hypoxic/ischemic episodes. However, little is known about whether oxygen transport in intracortical regions relates to such selective vulnerability to hypoxia.
Changes in Tibiofemoral Kinematics and Kinetics During Stair Ascent After Partial Medial Meniscectomy
Authors: Netravali Nathan A. , Andriacchi Thomas P.
Published: March 2014

Meniscectomy is a well-known risk factor for osteoarthritis (OA) in humans. It has been reported that total meniscectomy increases the risk of developing osteoarthritis radiographically by 14 times after 21 years [1] and that partial meniscectomy increases the risk of developing radiographic evidence of osteoarthritis within 16 years by a factor of four [2]. Two possible functional measures have been suggested as mechanisms for the development and progression of premature knee osteoarthritis: alterations in either kinematics or kinetics. Changes in kinematics, such as a shift in internal-external (IE) rotation after anterior cruciate ligament injury, have been suggested as a basis for an increased rate of cartilage thinning [3]. The other possible reason for the development of premature OA post-meniscectomy is a change in kinetics, the mechanical loading that occurs, particularly in the medial compartment [4]. The knee adduction moment has been associated with the rate of progression of osteoarthritis [5] and it has thus been suggested that the knee adduction moment is a good surrogate measure for in vivo load on the medial compartment osteoarthritis [6].
Proposal of a Mechano-Cell Model With Membrane, Cytoskeleton and Nucleus
Authors: Nakamura Masanori , Noguchi Ray , Ujihara Yoshihiro , Miyazaki Hiroshi , Wada Shigeo
Published: March 2014

The mechanical properties of cells have been of great interest to scientists from early studies which suggested that mechanical stress-induced alterations in cell shape and structure are critical for control of many cell functions. Although various loading tests of a cell have been designed to understand the cellular mechanical properties, the heterogeneous intracellular structure such as cytoskeletons brings about difficulties in interpreting experimental data.
A New Method of Blunt Cartilage Impact for a Model of Osteoarthritis
Authors: Fening Stephen , Jones Morgan , Moutzouros Vasilios , Miniaci Anthony
Published: March 2014

Impact injury to cartilage, a common consequence of joint trauma, is commonly thought to lead to degenerative osteoarthritis. Many pharmacologic agents have been developed to prevent or forestall this process. Development of a reliable model for the early stages of cartilage injury and osteoarthritis would enable the testing of novel treatments that could delay or even reverse the progression of this debilitating disease.
Relationship Between Obesity and Osteopenia in Lumbar Spines of Rats Using Mechanical and Morphological Studies
Authors: Woo D. G. , Lee Q. J. , Park W. P. , Ko C. Y. , Lim D. , Kim H. S. , Lee B. Y.
Published: March 2014

Obesity (OB) and osteopenia (OP), grave consequences for human health, quality of life, and even the efficiency of the labor force and economy, are two common complex diseases. Two public health problems have exploded in prevalence over the past decade [1]. OB, now a major epidemic in the developed world and frequent among elderly subjects, is a condition of excessive body fat that causes or exacerbates several risk of developing non-insulin dependent diabetes mellitus, cardiovascular disease, cancer and other diseases [2]. OP is defined as a systemic skeletal disease caused by low bone mass and microstructural deterioration of the bone.
Prediction of Muscle Forces and Joint Moments in Stroke Patients Using an EMG-Driven Model
Authors: Shao Qi , Bassett Daniel N. , Manal Kurt , Buchanan Thomas S.
Published: March 2014

Abnormal kinematic and kinetic patterns are associated with disability following stroke. The estimation of internal forces and moments during movements is important for developing better rehabilitation regimens for this population. In this study, we used an EMG-driven model to estimate muscle forces and joint moments for stroke patients, and analyzed the kinetics of these patients. Although such models have been used in healthy people, this is the first study to model post-stroke patients.
Kinematic Demands of Nucleus Replacement Technology
Authors: Sander Elizabeth J. , Zufelt Nephi A. , Kelly Brian P. , DiAngelo Denis J.
Published: March 2014

Recent advancements in biomaterial technologies have fostered growth in alternative surgical procedures to fusion surgery for treatment of early stages of degenerative disc disease. One application of immediate interest is that of nucleus replacement (NR). Novel materials are being developed to better match the nonlinear biomechanical properties of the native tissue [1]. The effects of changing the motion segment unit (MSU) properties via surgery (nucleotomy) or the placement of an NR material, changes the work required to move the altered spine condition through a prescribed kinematic path. The closer the loading mechanics of the altered spine are to the intact spine condition, the more likely the device will restore the native properties. The objective of this study was to use a kinematics based testing methodology to evaluate compliant materials being considered for NR devices.
Comparison Elbow Joint Angles for Male and Female Bat Swings
Authors: Gregory Elisha , Sheets Samantha , Witten Brent
Published: March 2014

Hitting has become one of the most studied aspects of the game of baseball. Many studies to date only focus on a specific group of players, like collegiate or major league players, but there have not been any studies comparing the male swing to the female swing. Additionally, most studies look at many different aspects of a swing at distinct times in the swing.
A Preliminary Investigation on the Grip Force Applied on a Cylindrical Handle
Authors: Wimer Bryan M. , Welcome Daniel E. , Warren Chris , McDowell Thomas W. , Dong Ren G.
Published: March 2014

Hand grip force is an important factor for risk assessment of hand musculoskeletal disorders. Grip strength is also one of the important indices for the diagnosis of hand disorders such as hand-arm vibration syndrome and carpel tunnel syndrome. Therefore, a considerable number of studies on grip force or strength have been reported. However, it remains an important issue how to quantify the grip force or strength. Conventionally, the grip force is measured using a handle that measures the applied force in two opposite directions in the grip action. However, it has been demonstrated that the grip force applied on a cylindrical handle is not uniformly distributed in each orientation of the hand [1]. Therefore, the grip force measured in a specific direction may not be an accurate measure of the grip effort. Alternatively, the total grip force has been proposed to serve as the grip measure [2]. The major objectives of this study are as follows: (i) to develop a cylindrical instrumented handle that can be used to perform the measurement of the total grip force and to characterize its distribution around the handle; (ii) to estimate the principle grip force and direction; and (iii) to investigate the relationship between the total grip force and that measured on a Jamar handle.
In-Vivo Evaluation of Severity of Microvascular Impairments and Epicardial Coronary Stenoses Using Fundamental Fluid Dynamics Endpoints
Authors: Ashtekar Koustubh D. , Kim Edward , Roy Abhijit S. , Helmy Tarek A. , Effat Mohamed A. , Schneeberger Eric W. , Gottliebson William M. , Back Lloyd H. , Banerjee Rupak K.
Published: March 2014

Coronary circulation is mainly regulated by two serial resistances, namely, epicardial stenosis and microvascular impairments, both causing abnormal coronary blood circulation [1]. Delineation of the true severities of these diseases is important to guide clinical decision-making processes for the selection of appropriate treatment procedures [2]. The presently used diagnostic parameters: FFR (fractional flow reserve defined as the ratio of distal to proximal hyperemic pressure) and CFR (coronary flow reserve defined as ratio of basal to hyperemic flow) [1], for the evaluation of severity of epicardial coronary stenosis are well established in clinical practice. On the other hand, current methods to evaluate the microcirculatory status are limited [3].
The Assessment of Loosely and Tightly Bound Water in Water Distribution Changes of Human Cortical Bone by NMR
Authors: Ni Qingwen , Leng Huijie , Nicolella Daniel P.
Published: March 2014

Bone quality in terms of water distribution, porosity, and pore size distributions in cortical bone and relate these measures can be used to correlate bone mechanical properties. The objective of this paper is to demonstrate that non-destructive low-field NMR technique can be used to determine the mobile and the bound water distribution, and further determine the loosely and the tightly bound water in cortical bone in vitro.
Mechanics of Individual-Specific Corneoscleral Shell Models
Authors: Norman Richard E. , Sigal Ian A. , Rausch Sophie M. K. , Tertinegg Inka , Eilaghi Armin , Portnoy Sharon , Sled John G. , Flanagan John G. , Ethier C. Ross
Published: March 2014

Glaucoma is a group of diseases involving a progressive optic neuropathy of unknown etiology. It is one of the leading causes of blindness worldwide. It has been postulated that glaucomatous optic neuropathy may result from mechanical stresses on the optic nerve fibers passing through the lamina cribrosa (LC), from ischemia in the LC region, or from a combination of these two.
Fluid Structure Interaction Analysis of Blood Flow Through a Mechanical Heart Valve
Authors: Roldán Alejandro , Sweitzer Nancy , Osswald Tim , Chesler Naomi
Published: March 2014

Modeling pulsatile flow past heart valves remains a relatively unexplored but critical area. Due to the geometric complexity and the interaction between the flowing blood and the heart valve leaflets, existing numerical techniques that require domain discretization, such as finite element methods or finite difference techniques, cannot fully represent the moving and deforming boundaries present in an operating valve. Our aim is to develop a technique to model the flow through heart valves which includes the interaction between the blood flow and the valve leaflets using the radial functions method (RFM). The RFM is a meshless technique that fully accounts for moving and deforming surfaces and thus is well suited to model the blood flow and its interaction with leaflet motion. Here we present a 2D fluid structure interaction (FSI) model of the blood flow through a bileaflet mechanical heart valve (MHV).
Vacuum Enhanced Heat Transfer Through Mammalian Radiator Structures
Authors: Grahn Dennis A. , Hall Christina L. , Heller H. Craig
Published: March 2014

Most mammals, including humans, maintain relatively constant internal temperatures despite changes in ambient conditions and fluctuations in internal heat production. To achieve this end, an individual must be able to: 1) protect the internal milieu from external thermal challenges and 2) dissipate excess internally produced heat. Heat is produced as a byproduct of cellular metabolism and is lost to the environment across the body surface. The thermoregulatory challenge is to dissipate excess internally produced heat despite the insulation layers that protect the internal milieu from external thermal influences.
Magnetic Resonance Detection of Inflammation in Elastase-Induced Aneurysms
Authors: DeLeo Michael J. , Gounis Matthew J. , Hong Bo , Walvick Ronn , Ford John Chetley , Wakhloo Ajay K. , Bogdanov Alexei A.
Published: March 2014

Intracranial aneurysm rupture is the leading cause of subarachnoid hemorrhage in the United States and is associated with higher fatality rates than ischemic stroke. There is currently no objective diagnostic means to identify aneurysms that are at high risk for rupture despite significant improvements in treatment. Often with no warning signs prior to aneurysm rupture such as the transient ischemic attack in ischemic stroke, the need to develop a method for detecting aneurysm instability is necessary.