bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Nozzle Configuration and Coolant Flow Rate on Spray Evaporative Cooling in a Multi-Chip Module Using FC-72
Authors: Pautsch Adam G. , Shedd Timothy A.
Published: July 2013

With the power levels of computers constantly rising, the cooling of the die is becoming more challenging. One method of heat removal that can handle high heat fluxes and is still compact in size is Spray Evaporative Cooling (SEC). SEC, in this instance, uses arrays of nozzles to deliver a fluorinert cooling fluid, FC-72, to the die surface, and in the right conditions, a thin liquid film will form. This thin film allows for very high heat removal. Saturating the FC-72 with nitrogen enhances the effect. The characteristics of the spray greatly affect the behavior of the film. The critical heat flux (CHF), heat transfer coefficient of the system, and the variation in temperature on the die surface are important characteristics of an SEC system that must be considered. This study presents results of experiments performed to determine the effect of the number of spray nozzles on these quantities.
New Substrates for Use as Embedded Capacitors
Authors: Yamamoto Takuya , Andresakis John
Published: July 2013

As CPUs increase in performance, the number of passive components on the surface of the boards are increasing dramatically. To reduce the number of components, as well as improve the electrical performance (i.e. reduce inductance), designers are increasingly embedding capacitive layers in the PCB. The majority of the products in use today utilize reinforced epoxy laminates. These products are relatively easy to handle, but the thickness and Dk limit the effectiveness of the layer to perform as a capacitor. Other materials are being developed that are thinner (and thus increase capacitance), but either have problems with dielectric breakdown strength, handling or only marginal improvement over the existing material. This paper will describe new non-reinforced substrates for use as embedded capacitance layers that address these issues. The material selection process, substrate processing and electrical performance will be reviewed.
Analysis and Design of Liquid-Cooling Systems Using Flow Network Modeling (FNM)
Authors: Kelkar Kanchan M. , Patankar Suhas V.
Published: July 2013

Liquid cooling is used for thermal management of electronics in defense, power, medical, and computer applications due to the increasing power density and the desire for compact packaging. The objectives in the design of these systems are to create a sufficient amount of total flow and to appropriately distribute the flow so as to maintain the electronic component temperatures at the desired level. The technique of Flow Network Modeling (FNM) is ideally suited for the analysis of flow distribution and heat transfer in liquid-cooling systems. The FNM technique uses overall flow and thermal characteristics to represent the behavior of individual components. Therefore, solution of conservation equations over the network enables efficient prediction of the flow rates, pressures, and temperatures in a complete liquid-cooling system. This article describes the technical basis of the FNM technique and illustrates its application in the design of a distributed-flow cold plate and of a complete water-cooled system. The study demonstrates the utility of the FNM technique for rapid and accurate evaluation of different design options and the ensuing productivity benefits in the design of liquid cooling systems.
Thermofluid Design of Energy Efficient and Compact Heat Sinks
Authors: Yazawa Kazuaki , Solbrekken Gary L. , Bar-Cohen Avram
Published: July 2013

A compact, energy efficient heat sink design methodology is presented for shrouded, parallel plate fins in laminar flow. The analytic model accounts for the sensible temperature rise of the air flowing between fins, convective heat transfer to the flowing stream, and conduction in the fins. To evaluate the efficiency of the air cooling system, consideration is also given to the determination of the fan pumping power. This paper focuses on the optimization of the heat sink-fan combination for energy efficiency, subject to volumetric constraints. The design optimum is found by matching the most efficient operating point of the fan with the corresponding optimum fin geometry. A series of parametric studies was completed to identify the sensitivity of the cooling solution to parametric variations. This numerically validated model has been used to visualize the parametric impact of dealing with “real world” manufacturing limitation in the development of thermal packaging solutions for notebook computers and other electronic products.
Miniature Loop Heat Pipes for Electronic Cooling
Authors: Hoang Triem T. , O’Connell Tamara A. , Ku Jentung , Butler C. Dan , Swanson Theodore D.
Published: July 2013

Thermal management of modern electronics has become a problem of significant interest due to the demand for power and reduction in packaging size. Requirements of next-generation microprocessors in terms of power dissipation and heat flux will certainly outgrow the capability of today’s thermal control technology. LHPs, like conventional heat pipes, are capillary pumped heat transport devices. They contain no mechanical moving part to wear out or require electrical power to operate. But unlike heat pipes, LHPs possess much higher heat transport capabilities enabling them to transport large amounts of heat over long distances in small flexible lines for heat rejection. In fact, a miniature ammonia LHP developed for a NASA space program is capable of transporting 60W over a distance of 1 meter in 1/16”O.D. stainless steel tubing. Therefore, miniature LHPs using water as the working fluid are excellent candidates to replace heat pipes as heat transports in electronic cooling systems. However, a number of operational issues regarding system performance, cost, and integration/packaging must be resolved before water LHPs can become a viable option for commercial electronics.
Characterization of Vertical Interconnects in 3-D System in a Package
Authors: Kang Qinghua , Ferendeci Altan M.
Published: July 2013

A novel RF MEMS integration technology was developed to achieve the three-dimensional integration of microwave and millimeter-wave components and sub-circuits with improved performance using multilayer vertical interconnects. This technology, which allows planar circuits to be monolithically stacked vertically in three dimensions (3D), provides one of the major initial steps in the realization of a “system in a package.” To process high-aspect-ratio via interconnects in 3D MMIC multilayer circuitry, combination of unique microelectronic and traditional MEMS microfabrication technologies were used. Based on these techniques, a set of test structures were successfully fabricated to facilitate the vertical interconnect characterization. Experimental results revealed that at microwave frequencies, e.g. X band (8–12 GHz), the vertical interconnect discontinuities contributed significantly to the insertion loss and the phase change. With the available advanced conductor loss models, lumped-element equivalent circuit models were derived from the via module measurements. Using quarter wavelength T-junction resonator structures, polyimide was also characterized for its microwave properties over a wide frequency range. Multilayer vertically interconnected transmission line circuits were monolithically processed and used to verify the derived electrical models.
Microwave Module Thermal Considerations for Future Higher Powered MMICs in Phased Array Radars
Authors: Wilson James S.
Published: July 2013

Advances in RF power generation capability at the device level will soon force a change in phased array radar thermal management. The efficiency in converting electrical power into transmitted power is not increasing as rapidly which means that higher RF power generating devices also dissipate more heat. Removing this waste heat creates several thermal challenges including the topic of this paper, namely thermal issues at the die and package level. A comparison of the temperature differences between the junction and ambient shows that even at present heat dissipation levels, the temperature difference at the integrated circuit level is already a significant fraction of the total rise. Further increases in the device level heat dissipation will increase the temperature difference at the integrated circuit level to nearly unmanageable levels unless device-level design changes are made. Maintaining acceptable junction temperature levels will require lower device mounting surface temperatures or some thermally better method of die attachment and heat removal. Dividing the thermal management of a phased array radar into two portions (integrated circuit level and everything else) reveals that while thermal improvements at the system and packaging level are useful for near-future radar designs, thermal design and management at the device and package levels are crucial.
Analysis and Optimization of the Thermal Performance of Microchannel Heat Sinks
Authors: Liu Dong , Garimella Suresh V.
Published: July 2013

A number of modeling approaches of increasing levels of complexity for the analysis of convective heat transfer in microchannels are presented and compared. A detailed computational fluid dynamics (CFD) model is used to obtain baseline results against which the different approximate approaches are compared. These include a 1-D resistance model, a fin approach, two fin-liquid coupled models, and a porous medium approach, all of which are amenable to closed-form solutions for the temperature field. The good agreement between the exact and approximate methods indicates that with carefully chosen assumptions, these analytical results can lead to adequate descriptions of the thermal performance, while allowing easier manipulation of microchannel geometries for the purpose of optimization. Practical optimization procedures are developed to minimize the overall thermal resistance of microchannel heat sinks, using each of the five approaches.
Effective Thermophysical Properties of Thermal Interface Materials: Part II — Experiments and Data
Authors: Savija I. , Culham J. R. , Yovanovich M. M.
Published: July 2013

A new method for determining effective thermal conductivity and Young’s modulus in thermal interface materials is demonstrated. The method denoted as the Bulk Resistance Method (BRM) uses empircal thermal resistance data and analytical modeling to accurately predict thermophysical properties that account for insitu changes in material thickness due to external loading and thermal expansion. The BRM is demonstrated using commercially available sheets of Grafoil GTA. Tests were performed on thermal joints consisting of two Al 2024 machined surfaces with layers of Grafoil GTA in the interface. Test conditions included a vacuum environment, 0.2–6.5 MPa contact pressure, a nominal 50°C mean interface temperature and a continuous loading and unloading cycle. Test results indicated that the BRM consistently predicted thermal conductivity independent of the number of layers tested and that the predicted results were significantly lower than values reported using conventional ASTM test procedures.
Experiments and Modeling of the Thermal Resistance of In-Line Square Pin-Fin Heat Sinks With Top By-Pass Flow
Authors: Urdaneta Mario , Ortega Alfonso
Published: July 2013

The thermal resistance of in-line square-pin fin heat sinks was experimentally investigated. In a companion paper [1], extensive results for the hydraulic behavior of such heat sinks with and without top-bypass were reported. It was shown that the top-bypass, as well as pin pitch, strongly influence the fin flow available for cooling. Systematic measurements of the overall thermal resistance with a uniformly heated base were performed for the same set of twenty aluminum heat sinks. Pin height was varied from 12.5 mm to 22.5 mm, pin pitch was varied from 3.4 mm to 6.33 mm, and base dimensions were kept fixed at 25 × 25 mm. The overall base to ambient thermal resistance was measured as a function of heat sink geometry, approach velocity and by-pass height. Experimental results were compared with predictions based on a simple one-dimensional “two-branch bypass model”. It was found that the overall heat transfer is governed by the fin flow, hence, empirical data for the zero bypass case can be used to predict the decrease of heat sink performance with flow bypass.
On the Correlation Between Power Density Distribution and Junction-Case Thermal Resistance for Electronic Packages
Authors: Ankireddi Sai , Jung Henry H. , Jones James
Published: July 2013

When comparing two electronic packages identical in all respects except die plan dimensions and power, wherein the package with the smaller die is associated with a lower power, it is often hypothesized that the lower-powered package would have a lower junction-case thermal resistance. This hypothesis is generally based on the questionable argument that because the smaller package has lower power, its internal temperatures should be lower and hence a lower junction-case resistance should be ‘intuitively’ expected. In this article we show that drawing inferences about trends in junction-case resistance based merely on power trends, as outlined above, can be incorrect. In order to address this issue and provide better ‘indicators’ for comparing thermal performance across packages, we introduce the concept of the Power Density Distribution (PDD) and show how it relates with the junction-case thermal resistance. To illustrate its use in comparing thermal performance of packages we consider examples of several ICs with different die size/power combinations. Additionally, we also note the correlation between peaks in the spatial distribution of the power density and those of the die temperature distribution; in effect, this furnishes a simple way to identify candidate hot-spot locations on the die without resorting to extensive numerical thermal simulation/testing. We illustrate this intuitively anticipated concept for a variety of power distribution scenarios in some of our example IC packages.
Study of Electroplated Compliant G-Helix Chip-to-Substrate Interconnects
Authors: Zhu Qi , Ma Lunyu , Sitaraman Suresh K.
Published: July 2013

Microsystem packages continue to demand lower cost, higher reliability, better performance and smaller size. Compliant wafer-level interconnects show great potential for next-generation packaging. G-Helix, an electroplated compliant wafer-level chip-to-substrate interconnect can facilitate wafer-level probing as well as wafer-level packaging without the need for an underfill. The fabrication of the G-Helix interconnect is similar to conventional IC fabrication process and is based on electroplating and photolithography. G-Helix interconnect has good mechanical compliance in the three orthogonal directions and can accommodate the differential displacement induced by the coefficient of thermal expansion (CTE) mismatch between the silicon die and the organic substrate. In this paper, we report the wafer-level fabrication of an area-arrayed G-Helix interconnects. The geometry effect on the mechanical compliance and electrical parasitics of G-Helix interconnects have been studied. Thinner and narrower arcuate beams with larger radius and taller post are found to have better mechanical compliance. However, it is also found that structures with excellent mechanical compliance may not have good electrical performance. Therefore, a trade off is needed. Using response surface methodology (RSM), an optimization has been done, and the optimal compliant G-Helix interconnect will have a total standoff height of 64 μm, radius of 36 μm and cross-section area of 93 μm2.
Development of Reliable Electronic Packaging Solutions for Spacecraft Avionics Miniaturization Using Embedded Passive Devices
Authors: Schatzel Don
Published: July 2013

Miniaturization of electronic packages will play a key role in future space avionics systems. Smaller avionics packages will reduce payloads while providing greater functionality for information processing and mission instrumentation. Current surface mount technology discrete passive devices not only take up significant space but also add weight. To that end, the use of embedded passive devices, such as capacitors, inductors and resistors will be instrumental in allowing electronics to be made smaller and lighter. Embedded passive devices fabricated on silicon or like substrates using thin film technology, promise great savings in circuit volume, as well as potentially improving electrical performance by decreasing parasitic losses. These devices exhibit a low physical profile and allow the circuit footprint to be reduced by stacking passive elements within a substrate. Thin film technologies used to deposit embedded passive devices are improving and costs associated with the process are decreasing. There are still many challenges with regard to this approach that must be overcome. In order to become a viable approach these devices need to work in conjunction with other active devices such as bumped die (flip chip) that share the same substrate area. This dictates that the embedded passive devices are resistant to the subsequent assembly processes associated with die attach (temperature, pressure). Bare die will need to be mounted directly on top of one or more layers of embedded passive devices. Currently there is not an abundant amount of information available on the reliability of these devices when subjected to the high temperatures of die attach or environmental thermal cycling for space environments. Device performance must be consistent over time and temperature with minimal parasitic loss. Pretested and assembled silicon substrates with layers of embedded capacitors made with two different dielectric materials, Ta2O5 (Tantalum Oxide) and benzocyclobutene (BCB), were subjected to the die attach process and tested for performance in an ambient environment. These assemblies were subjected to environmental thermal cycling from −55°C to 100°C. Preliminary results indicate embedded passive capacitors and resistors can fulfill the performance and reliability requirements of space flight on future missions. Testing results are encouraging for continued development of integrating embedded passive devices to replace conventional electronic packaging methods.
Probabilistic Fracture Mechanics Analysis of Nuclear Piping Considering an Embedded Crack
Authors: Machida Hideo , Yoshimura Shinobu
Published: July 2013

This paper presents probabilistic fracture mechanics analyses of nuclear piping with an embedded crack. If the same crack depth and the same aspect ratio are supposed to both the surface and the embedded cracks, break and leak probabilities of the embedded crack case are much smaller than those of the surface crack case. This is because both of length and area of the embedded crack are one half of those of the surface crack, and when the center position of the embedded crack is close to the pipe surface, the crack comes out to the outside of the pipe partially. Consequently, an effective crack size is smaller than that given by probabilistic density function. Even when both of the area and aspect ratio of the embedded crack are the same as those of the surface crack, this tendency does not change. Although the embedded crack grows in the two directions of an inner and an outer surface of the pipe and the crack growth rate is higher than that of the surface crack, this effect does not appear in the failure probability clearly. The surface crack is effective for conservative evaluation, but it is not proper for a rational evaluation. Employing the realistic embedded crack model can lead to rational failure probability.
The Application of Reliability-Based Design Factors in Stress Corrosion Cracking Evaluations
Authors: Friedman Edward
Published: July 2013

First-order reliability methodology (FORM) is used to develop reliability-based design factors for deterministic analyses of stress corrosion cracking. The basic elements of FORM as applied to structural reliability problems are reviewed and then employed specifically to stress corrosion cracking evaluations. Failure due to stress corrosion cracking is defined as crack initiation followed by crack growth to a critical depth. The stress corrosion cracking process is thus represented in terms of a crack initiation time model and a crack growth rate model, with the crack growth rate integrated from the initiation time to the time at which the crack grows to its critical depth. Both models are described by log-normal statistical distribution functions. A procedure is developed to evaluate design factors that are applied to the mean values of the crack initiation time and the crack growth rate for specified temperature and stress conditions. The design factors, which depend on the standard deviations of the statistical distributions, are related to a target reliability, which is inversely related to an acceptable probability of failure. The design factors are not fixed, but are evaluated on a case-to-case basis for each application. The use of these design factors in a deterministic analysis assures that the target reliability will be attained and the corresponding acceptable probability of failure will not be exceeded. An example problem illustrates use of this procedure.
On the Design and Analysis of Fiber Reinforced Polymeric Composite Pipes and Vessels
Authors: Ellyin Fernand
Published: July 2013

Fiber reinforced plastic (FRP) composites offer a number of advantages over the conventional industrial materials. The reluctance of adopting composite materials in high pressure applications, is partly due to a limited understanding of their behavior under multiaxial loadings and lack of qualified design methodologies. Design and analysis issues concerning pressurized components made of fiber reinforced plastic composites, are discussed in this paper. Specifically, the optimum placement of reinforcement with respect to the applied loads, failure modes and failure analysis techniques, and a method of design based on long-term leakage envelope, are presented.
Improvements on a Newton-Krylov Based Solver for CFD Models Using Finite Rate NOx Chemistry
Authors: Tang Qing , Denison Martin , Maguire Mike , Bockelie Mike , Chen Jyh-Yuan
Published: July 2013

In this paper, we describe our progress on improving the performance of a newly developed Computational Fluid Dynamics (CFD) modeling tool, which uses reduced chemical kinetics mechanisms to model the finite rate chemistry effects and solves the resulting system of stiff partial differential equations with a matrix-free Newton-Krylov method. A multi-grid based preconditioner and a Newton iteration scheme have been implemented in the Newton-Krylov solver and the reduced mechanism module, respectively, to replace the original Picard based preconditioner and the point iteration scheme for steady state species evaluation. Preliminary tests of the improved modeling tool have been conducted using simple hotbox and a full-scale, coal fired electric utility boiler, and shown very promising results in terms of the accuracy, robustness, and efficiency of the new tool.
Near-Wall Turbulence Modeling Without Wall Distance
Authors: Rahman M. M. , Siikonen T.
Published: July 2013

A low-Reynolds number k-ε model is proposed in which the anisotropic production in near-wall regions is accounted for substantially by modifying the model constants Cε(1,2) and adding cross-diffusion terms in the ε equation. Hence, it reduces the kinetic energy and length scale magnitudes to improve prediction of adverse pressure gradient flows, involving flow separation and reattachment. Unlike the conventional k-ε model, it requires no wall function/distance parameter that bridges the near-wall integration. The model coefficients/functions depend nonlinearly on both the strain-rate and vorticity invariants. The model is validated against a few flow cases, yielding predictions in good agreement with the direct numerical simulation (DNS) and experimental data.
Analysis of Flow Field in an Ejector With Steam as Working Fluid
Authors: Li Haijun , Shen Shengqiang
Published: July 2013

Two-dimensional Navier-Stokes equations were solved to obtain local distributions of pressure, temperature and Mach number of the complex flow field in a steam ejector. From the computational results, we obtain that there is a critical discharging pressure for given motive pressure and suction pressure. The effects of motive fluid pressure, motive fluid overheat, suction fluid pressure and discharge fluid pressure on the entrainment ratio and critical discharging pressure were concluded in detail. Analysis was also done to comprehend the reason of shocks emerging, their positions, and their effects on ejector performance. Phase transition phenomenon occurred in the ejector when using steam as working fluid was obtained through calculating the percent of saturated water in the mixture. The effect of the ejector’s geometrical structure on its performance is further studied and high COP of the ejector is gained by optimizing its structure.
CFD, Thermal and Stress Analysis for daVinci X-Prize Manned Space Mission: Part 2 (Keynote)
Authors: Kudriavtsev Vladimir , Feeney Brian , Hsu Ta-Liang , Borovkov Alexei , Rooz Kalman , Klimshin Dimitriy
Published: July 2013

In the present article we review engineering and research efforts conducted by a group of volunteers with the help of advanced engineering commercial software (CFD-ACE+, ANSYS, CFD-FASTRAN, Matlab/Simulink, Autodesk Inventor, Maple) in support of the da Vinci Project, the first Canadian competitor in the International X Prize Competition. Full account of these activities was presented at the da Vinci Space Project Technical Conference Program [1]. Announced in 1996 to promote the development and flight of spacecraft for low-cost commercial transport of humans into space, the international X-Prize Foundation is providing a purse of US$10 million to the first competitor who can safely launch and land a manned spacecraft to an altitude of 100 kilometers (the international border of space), twice in a two-week period. The first Canadian entry in this competition, the fully volunteer da Vinci Project (a wholly owned by ORVA Space Corp.) has put years of engineering research, design and developmental testing into the vehicle design, propulsion and flight guidance system. A full-scale flight-engineering prototype of the manned rocket has been constructed. Detailed engineering and fabrication of the full-scaled manned rocket named Wild Fire Mk VI is currently underway. Flight-testing of the manned rocket and X-Prize competition flights are targeted to continue throughout 2004. For R&D efforts on the project, a wide range of engineering software was utilized for CAD, basic engineering calculations, trajectory analysis, dynamics and mission control, supersonic external aerodynamics, and internal heat flow. Part 1 of this lecture appearing in Volume 1 describes space mission, thermal and CFD analyses and CAD integration. This installment describes how ANSYS and LSDYNA software packages were utilized to perform stress analysis of the space capsule and the rocket block.
Modeling of Orthostatic Intolerance During Lower Body Negative Pressure
Authors: Etter Karen E. , Sharp M. Keith
Published: July 2013

Postflight orthostatic intolerance (POI) afflicts a significant fraction of male astronauts and nearly all female astronauts when they first stand on Earth after spaceflight. Symptoms include dizziness and fainting, which can impact their abilities to perform critical tasks during the post-landing period. On the Moon or Mars, poor performance or accidents resulting from POI may have potentially catastrophic consequences due to the more hazardous conditions and lack of medical facilities. In addition, the long duration flights necessary to reach Mars may elicit adaptations that increase the risk of POI. Of the many factors that may influence POI, one of the few that may explain the gradual decline in arterial blood pressure experienced by many subjects during stand tests is the loss of blood volume by capillary filtration. Previous simulations suggest that elevated capillary filtration rates distinguish nonfinishers from finishers of stand tests [1, 2]. In this investigation, further computer modeling was undertaken to compare modeled orthostatic response to that of volunteers during graded orthostatic stress (GOS) involving head up tilt (HUT) and lower body negative pressure (LBNP), which reliably produces presyncope and is a candidate training countermeasure for preventing POI.
Poroviscoelastic Modeling of Perfused Bovine Liver Tissue
Authors: Raghunathan Smitha , Evans Douglas , Sparks Jessica
Published: July 2013

Blunt and penetrating liver injuries make up one-third of all abdominal injuries, and 5% of all trauma admissions are due to injuries to this organ [1]. Additionally, the majority of blunt liver injuries stem from motor vehicle crashes (Moore 2004). Validated computational models of liver are useful for understanding injury to the liver from mechanical loading. It has been shown previously that the mechanical behavior of perfused ex vivo liver closely approximates the in vivo behavior, while unperfused ex vivo liver response differs significantly from the in vivo case [2]. Therefore, to achieve a realistic approximation of in vivo liver mechanics for injury prediction, it is beneficial to adopt a constitutive model for liver that incorporates both fluid and solid phases of the tissue, to reflect this perfusion effect.
Computational and In Vivo Analysis of the Role of Solid Biomechanics in the Development of Intimal Thickening Post-Stenting
Authors: Timmins Lucas H. , Miller Matthew W. , Clubb Fred J. , Moore James E.
Published: July 2013

Despite the tremendous success of vascular stents in treating occlusive artery disease, failure due to excessive neointimal hyperplasia resulting in the formation of a new blockage (termed restenosis) is still unacceptably high. While drug-eluting stents have reduced restenosis rates in coronary application, many problems (e.g. late term thrombosis, incomplete endothelialization, lack of success in peripheral arteries, hypersensitivity) and high cost still have raised concerns of their exclusive use. Regardless of the failure rates, vascular stenting is the standard treatment for occlusive artery disease, and as their use is likely to continually increase there is an imperative need to increase the success rate of this interventional therapy.
Role of IL-1 on Aggrecanase and COX-2 Gene Expression of Meniscal Explants Following Dynamic Compression
Authors: Killian Megan L. , Zielinska Barbara , Haut Donahue Tammy L.
Published: July 2013

The menisci within the knee likely respond to adverse loading conditions, leading to aggravated cartilage damage and fissuring [1]. Upregulation of catabolic molecules such as interleukin-1α (IL-1α), metalloproteinases (MMPs), aggrecanases (ADAMTS-4 and -5), and cyclooxygenase-2 (COX-2), as well as release of proteoglycans [2], have been shown in vitro for meniscal explants following dynamic loading [3]. A crucial event in matrix degradation is the loss of aggrecan, caused by the ADAMTS family [4]. In osteoarthritic cartilage, IL-1 has been shown to influence COX-2 activity, leading to increased synthesis of prostaglandin E2 and subsequent proteinase activity [5].
Assessment of Cancellous Bone Strength in the Lumbar Spine Using a “Smart” Ball-Tip Probe
Authors: Liddle Kate D. , Tufaga Michael A. , Diekmann Glenn , Buckley Jenni M. , Tai Viva , Mulligan Kathleen , Ames Christopher , McClellan Robert T.
Published: July 2013

Failure of the pedicle screw at the screw-bone interface is a common clinical problem, particularly in the setting of osteoporosis, and poses reconstructive challenges for all orthopaedic surgeons. Pedicle screw failure through screw loosing and pull-out is highly correlated with bone mineral density (BMD) and local bone quality [1]. Pre-operative assessment of BMD via dual x-ray absorptiometry (DEXA) has been shown to help determine the need for screw augmentation. However, patients frequently present without pre-operative DEXA scans. Furthermore, DEXA scans provide a measure of general bone quality, but do not necessarily reflect segmental and local variation in the spine [2]. The ability to assess BMD on a per-vertebrae basis intra-operatively would assist with surgical decisions regarding screw sizing, placement and augmentation.
Characterizing Flow in the Vertebro-Basilar System Using MR in Conjunction With Subject-Specific Computational Models
Authors: Wake Amanda K. , Gore John C. , Gatenby J. Christopher
Published: July 2013

Coronary artery bypass graft failure is often a consequence of intimal hyperplasia (IH), which correlates with hemodynamic factors (e.g., wall shear stress); this relationship has been used to evaluate arterial graft design [e.g., 1–4]. The vertebro-basilar system is a native arterial merge (i.e., two arteries, the vertebrals, converge into a single artery, the basilar artery); thus, characterizing the flow field of this system in healthy subjects could be useful for early detection of anomalies (e.g., aneurysms) or for vascular graft design improvements to ensure graft/vessel patency. This study uses high field MR and phase contrast MR (PCMR) to investigate the hemodynamics of the vertebro-basilar system in a healthy, adult subject for predicting pathophysiologically-relevant flow patterns (e.g., low wall shear stress) that are related to IH and subsequent graft failure.
Three-Dimensional Finite Volume Method of Triphasic Theory in Generalized Coordinates: Application to Human Intervertebral Disc During Compressive Stress Relaxation
Authors: Chen Xiangying , Gu Wei Yong , Huang Chun-Yuh , Zha Gecheng
Published: July 2013

The intervertebral disc is an avascular cartilaginous structure that plays an important role in supporting loads through the spine and providing flexibility to the spinal column. The triphasic theory [1,2] has been used successfully to describe many of the mechanical, chemical and electrical behaviors of cartilaginous tissues. As an example of applying the triphasic theory, Yao and Gu [3] conducted a finite element simulation of human intervertebral disc during compressive stress relaxation using commercial software (FEMLAB). Due to the limitation of the commercial software, in the simulation reported in [3], the computational grid (mesh) is fixed throughout the simulation and the mesh size was not optimized for the specific geometry of the disc.
Comparison of Biomechanics of Lumbar-Pelvis Segment With Posterior Screw-Rod Versus Interspinous Plate Fixation System
Authors: Kiapour A. , O’Donnell J. , Goel V. K. , Biyani A.
Published: July 2013

Spinal fusion is the traditional surgical option to improve the clinical outcome of patients with advanced lumbar degenerative disease. Various techniques including posterolateral arthrodesis, interbody arthrodesis, and circumferential arthrodesis are being pursued as fusion strategies to eliminate segmental instability, which is a recognized cause of low back pain [1]. There are several drawbacks associated with pedicle-screw fixation constructs including failure of implant components and back-out of the screws [2,3].
Design Optimization of a Wearable Artificial Pump-Lung Device With Computational Modeling
Authors: Taskin M. Ertan , Zhang Tao , Griffith Bartley P. , Wu Zhongjun J.
Published: July 2013

The heart-lung machine has been commonly used to replace or supplement the functions of both the heart and lung in the open heart surgery and extracorporeal membrane oxygenation (ECMO). Although ECMO devices are efficient on respiratory support, this traditional system consists of multiple components and is bulky. Furthermore, ECMO devices are associated with clinical complications as well as the necessity of being confined to the bed. To eliminate these, we aimed to design and develop a wearable artificial pump lung (APL) device.
Complete Solution Sets for Neuromuscular Models Reveal How Mechanical Constraints Limit Neural Control Options
Authors: Kutch Jason J. , Valero-Cuevas Francisco J.
Published: July 2013

One of the main goals of neuromuscular modeling is to establish the range of feasible muscle activations for a given mechanical output of the body. This is not a trivial problem because there are typically infinitely many combinations of muscle activations that will generate the same joint torques, as most joints are actuated by more muscles than rotational degrees of freedom. Here we show that well-established geometric methods easily provide a complete description of the set of muscle activations that generate a desired set of joint torques or endpoint forces. In contrast to iterative linear programming optimizations, geometric methods provide a set of solutions in muscle activation space simply by converting between the geometric representations of neural and mechanical constraints. As an example, we use geometric methods to find the feasible set of activations that produce fingertip forces in a set of directions. These results show that for a given set of fingertip forces, the range of feasible activation for each muscle can differ with the choice of mechanical constraints. Thus, the mechanical constraints of the task play an important role governing the options the nervous system has when controlling redundant muscles.
Microfibrillar Elastic Polymer Wrapping of Rat Vena Cava for the Study of Engineered Arterial Vein Grafts
Authors: Wang Qiang , He Wei , Hong Yi , Wagner William R. , Vorp David A.
Published: July 2013

The autologous saphenous vein graft remains the graft of choice for 95% of surgeons performing coronary artery or peripheral bypass procedures. Within the first 5 years after implantation, 20%–40% of arterial vein grafts (AVG) fail due to intimal hyperplasia (IH)1. This adverse pathological response by AVGs may be in part due to their abrupt exposure to the significantly elevated circumferential wall stress associated with the arterial system2. We believe that if an AVG is given an ample opportunity to adapt and remodel to the stresses of the arterial environment, cellular injury may be reduced, thus limiting the initiating mechanisms of IH.
Calcification of Trileaflet Polyurethane Heart Valve
Authors: Zadeh Parnian Boloori , N.-Hashemi Hamid , Corbett Scott C. , Coskun Ahmet U.
Published: July 2013

Heart valve disease is a common type of cardiac disease that causes a large number of mortalities worldwide. Patients with severe heart valve problems are required to undergo heart valve replacement surgeries. Mechanical and bioprosthetic heart valves are the current available prostheses for patients in need of a heart valve replacement surgery. Mechanical heart valves are susceptible to thromboembolism and thrombosis and bioprosthetic valves have a limited life-span because of leaflet wear and calcification. Different polyurethane valves were suggested as an alternative material. However, prior results indicated that tested polyurethanes failed due to calcification. The mechanism for polyurethane calcification is not yet completely understood. Kou Imachi et al. [2], suggested that the calcification is due to entrapment of blood proteins and/or phospholipids in microgaps in the polymer and subsequent attraction of Ca ion, leading to formation of calcium phosphate (Ca3(PO4)2). Bisphosphonates (BP), which are considered to enhance the calcification resistance of polymers once covalently bonded to the material, indicated promising results in some studies. Focus of the present study is the trileaflet polyurethane valve, originally developed in the design of the AbioCor® replacement heart, and has demonstrated excellent durability and hemocompatibility in clinical evaluation. Over the past three years, this valve has been modified and its potential as a replacement valve have been studied [1]. Valve hemodynamic analysis showed that it is comparable to bioprosthetic valve in terms of fluid flow, pressure drop and regurgitation [1]. In order to ensure the suitability of the trileaflet polyurethane valve as a replacement valve its fatigue and calcification resistance are studied. The purpose of this paper is to simulate calcification of trileaflet polyurethane valves in an in vitro accelerated test and compare that with that of tissue valves. Furthermore the effect of bisphosphonate modified polyurethane on calcification is studied.
Determination of the Diffusivity and Location and Pressure Dependent Permeability of Porcine Coronary Arteries
Authors: Keyes Joseph T. , Borowicz Stacy , Utzinger Urs , Simon Bruce , Vande Geest Jonathan P.
Published: July 2013

The modeling of drug delivery into tissues utilizes coupled convective and diffusive transport and therefore requires the experimental determination of the governing constants used in these models [1, 2]. The use of minimally destructive methods to determine these properties ensures increased accuracy [3]. Having the ability to test for strain or intraluminal pressure dependence also provides improved accuracy to the definitions of these properties.
Porcine Left Atrial Wall Stress After Ventricular Tachypacing Mimicking the Effects of Early Atrial Fibrillation
Authors: Di Martino Elena S. , Bellini Chiara , Ward Dale J. , Brown Nicolas , Schwartzman David
Published: July 2013

Atrial Fibrillation (AF) is the cardiac arrhythmia most commonly encountered in clinical practice. Current statistics referring to the US population indicate a prevalence of AF up to 2.2 million people, projected to increase to 2.66 million by the end of 2010. AF has a high impact on society in terms of human costs, with an annual mortality rate of 11,438 patients. AF also increases the risk of ischemic stroke at least by a factor of 4 and it is responsible for at least 15% of all ischemic strokes, which represent the main cause of long-term disability and one of the main contributors to health care costs [1]. AF results from the synergic action of electrophysiological, biochemical and structural remodeling. Ventricular tachypacing (VTP) has been successfully used in animal models to reproduce relevant features observed in patients suffering from AF, such as ion-channel alterations, fibrosis development and atrial dilatation [2] [3].
Development and Characterization of Tyramine Substituted-Hyaluronan (TS-HA) Enriched Fascia for Rotator Cuff Repair
Authors: Chin LiKang , Calabro Anthony , Derwin Kathleen A.
Published: July 2013

The failure rate of rotator cuff repair is reportedly as high as 70%. Several commercially available extracellular matrices are indicated for augmentation of rotator cuff repair. However, none has yet demonstrated both the appropriate biological milieu and mechanical properties for tendon healing. We are interested in fascia lata for its tendon-like mechanical properties. We propose modulating inflammation by enriching fascia lata with high molecular weight hyaluronan (HA), a molecule well known for its anti-inflammatory properties. Of particular interest is tyramine-substituted hyaluronan (TS-HA), i.e., HA substituted with tyramine adducts to allow cross-linking between chains. The extent to which TS-HA treatment affects the mechanical properties of fascia lata is not known. The objectives of this study are to develop and characterize TS-HA enriched fascia lata and to investigate the hypothesis that TS-HA treatment does not significantly decrease the mechanical properties of fascia.
Effect of Edge-to-Edge-Repair on Annulus Tension of Prolapsed Mitral Valve
Authors: Bhattacharya Shamik , He Zhaoming
Published: July 2013

The edge-to-edge repair (ETER) technique is a mitral valve (MV) repair procedure. It approximates the leading edges of the mitral leaflets by use of sutures, exhibits promising predictable repair results and offers the advantage of being performed pericutaneously without the need for open heart surgery. The technique is becoming a popular surgical procedure to correct MV prolapse caused by abnormal chordal elongation. MV prolapse leads to mitral regurgitation (MR). Generally the ETER technique is performed as a secondary procedure to ring annuloplasty. Although some groups have performed ETER without the ring annuloplasty, recent studies have shown that ETER technique alone leads to substandard results [1]. It is necessary to define the MV annulus mechanics in ETER condition during valve closure or mid-systole as it directly affects the annulus tension (AT) in the annulus plane. AT in the annulus plane is an important force component which balances the myocardium force and contributes to maintaining the annulus shape and size. This AT change caused by the ETER can lead to annulus dilation, reoccurrence of MR and impact reintervention. The objective of the current study is to understand this AT change in the MV annulus tension during the mid-systole in the ETER condition in order to improve the long term efficacy of the ETER procedure on MV annulus tension, after the technique has been applied with both anterior leaflet prolapse and posterior leaflet prolapse.
A First Optimal Control Solution for a Complex, Nonlinear, Tendon Driven Neuromuscular Finger Model
Authors: Theodorou Evangelos A. , Todorov Emo , Valero-Cuevas Francisco J.
Published: July 2013

In this work we present the first constrained stochastic optimal feedback controller applied to a fully nonlinear, tendon driven index finger model. Our model also takes into account an extensor mechanism, and muscle force-length and force-velocity properties. We show this feedback controller is robust to noise and perturbations to the dynamics, while successfully handling the nonlinearities and high dimensionality of the system. By extending prior methods, we are able to approximate physiological realism by ensuring positivity of neural commands and tendon tensions at all times.
Lentiviral Hematopoietic Stem Cell Gene Therapy Benefits Metachromatic Leukodystrophy
Authors: Biffi Alessandra , Montini Eugenio , Lorioli Laura , Cesani Martina , Fumagalli Francesca , Plati Tiziana , Baldoli Cristina , Martino Sabata , Calabria Andrea , Canale Sabrina , Benedicenti Fabrizio , Vallanti Giuliana , Biasco Luca , Leo Simone , Kabbara Nabil , Zanetti Gianluigi , Rizzo William B. , Mehta Nalini A. L. , Cicalese Maria Pia , Casiraghi Miriam , Boelens Jaap J. , Del Carro Ubaldo , Dow David J. , Schmidt Manfred , Assanelli Andrea , Neduva Victor , Di Serio Clelia , Stupka Elia , Gardner Jason , von Kalle Christof , Bordignon Claudio , Ciceri Fabio , Rovelli Attilio , Roncarolo Maria Grazia , Aiuti Alessandro , Sessa Maria , Naldini Luigi
Published: July 2013

Next-Generation Gene Therapy

Few disciplines in contemporary clinical research have experienced the high expectations directed at the gene therapy field. However, gene therapy has been challenging to translate to the clinic, often because the therapeutic gene is expressed at insufficient levels in the patient or because the gene delivery vector integrates near protooncogenes, which can cause leukemia (see the Perspective by

Verma

).

Biffi
et al.

(
1233158
, published online 11 July) and

Aiuti
et al.

(
1233151
; published online 11 July) report progress on both fronts in gene therapy trials of three patients with metachromatic leukodystrophy (MLD), a neurodegenerative disorder, and three patients with Wiskott-Aldrich syndrome (WAS), an immunodeficiency disorder. Optimized lentiviral vectors were used to introduce functional
MLD
or
WAS
genes into the patients' hematopoietic stem cells (HSCs) ex vivo, and the transduced cells were then infused back into the patients, who were then monitored for up to 2 years. In both trials, the patients showed stable engraftment of the transduced HSC and high expression levels of functional
MLD
or
WAS
genes. Encouragingly, there was no evidence of lentiviral vector integration near proto-oncogenes, and the gene therapy treatment halted disease progression in most patients. A longer follow-up period will be needed to further validate efficacy and safety.