bluuebunny/crossref_metadata_2025 huggingface dataset:
Habitual exercise and vascular ageing
Authors: Seals Douglas R. , Walker Ashley E. , Pierce Gary L. , Lesniewski Lisa A.
Published: September 2009

Age is the major risk factor for cardiovascular diseases (CVD) and this is attributable in part to stiffening of large elastic arteries and development of vascular endothelial dysfunction (e.g. impaired endothelium‐dependent dilatation, EDD). In contrast, regular aerobic exercise is associated with reduced risk of CVD. Endurance exercise‐trained middle‐aged/older adults demonstrate lower large elastic artery stiffness and greater EDD than their sedentary peers. With daily brisk walking, previously sedentary middle‐aged/older adults show reduced stiffness and improved EDD. The mechanisms underlying the effects of regular aerobic exercise on large elastic artery stiffness with ageing are largely unknown, but are likely to include changes to the composition of the arterial wall. Enhanced EDD in older adults who exercise is mediated by increased nitric oxide (NO) bioavailability associated with reduced oxidative stress. Arteries from old rodents that perform regular aerobic exercise demonstrate increased expression and activity of endothelial NO synthase, reduced oxidative damage associated with reduced expression and activity of the oxidant enzyme NADPH oxidase, and increased activity of the antioxidant enzyme superoxide dismutase. Aerobic exercise also may protect arteries with ageing by increasing resistance to the effects of other CVD risk factors like LDL‐cholesterol. Habitual aerobic exercise is an effective strategy to combat arterial ageing.
Primary motor cortical metaplasticity induced by priming over the supplementary motor area
Authors: Hamada Masashi , Hanajima Ritsuko , Terao Yasuo , Okabe Shingo , Nakatani‐Enomoto Setsu , Furubayashi Toshiaki , Matsumoto Hideyuki , Shirota Yuichiro , Ohminami Shinya , Ugawa Yoshikazu
Published: September 2009

Motor cortical plasticity induced by repetitive transcranial magnetic stimulation (rTMS) sometimes depends on the prior history of neuronal activity. These effects of preceding stimulation on subsequent rTMS‐induced plasticity have been suggested to share a similar mechanism to that of metaplasticity, a homeostatic regulation of synaptic plasticity. To explore metaplasticity in humans, many investigations have used designs in which both priming and conditioning are applied over the primary motor cortex (M1), but the effects of priming stimulation over other motor‐related cortical areas have not been well documented. Since the supplementary motor area (SMA) has anatomical and functional cortico‐cortical connections with M1, here we studied the homeostatic effects of priming stimulation over the SMA on subsequent rTMS‐induced plasticity of M1. For priming and subsequent conditioning, we employed a new rTMS protocol, quadripulse stimulation (QPS), which produces a broad range of motor cortical plasticity depending on the interval of the pulses within a burst. The plastic changes induced by QPS at various intervals were altered by priming stimulation over the SMA, which did not change motor‐evoked potential sizes on its own but specifically modulated the excitatory I‐wave circuits. The data support the view that the homeostatic changes are mediated via mechanisms of metaplasticity and highlight an important interplay between M1 and SMA regarding homeostatic plasticity in humans.
Fuel Cell-Based Powertrain System Modeling and Simulation for Small Aircraft Propulsion Applications
Authors: Brinson Thomas E. , Ren Wei , Ordonez Juan C. , Luongo Cesar A. , Baldwin Thomas
Published: September 2009

A solid oxide fuel cell-based power system is modeled and simulated to investigate both power management and controllability issues experienced while subjecting the system to the typical power requirements of a small aircraft. Initially, the fuel cell stack is assumed to operate along one characteristic I-V curve, thus isolating the power management study to the system’s powertrain components. Electrical converters transfer dc power from the fuel cell to usable ac power for an electric motor-driven propeller. To avoid oversizing, the fuel cell stack is designed to operate near its maximum power limit during aircraft cruising, while a battery is employed as an alternative source to provide additional power beyond the cruising kilowatt requirement (e.g., takeoff or maneuvering).
Recent Advances in High Temperature Proton Exchange Membrane Fuel Cell Manufacturing
Authors: Puffer Raymond H. , Rock Stephen J.
Published: September 2009

Not enough attention has been devoted to developing the manufacturing processes required to transition fuel cell science into commercially viable products, despite clear recognition that cost and reliability are two key factors preventing more rapid introduction of the technology. Understandably, there is a natural reluctance of many companies to invest resources in manufacturing processes and systems for a product that is still evolving. Changes in materials, geometries, and even the basic fuel cell architecture can have profound effects on the viability of certain manufacturing processes and equipment. This situation suggests that modular flexible manufacturing processes be adopted to accommodate these uncertainties. Since 1999 researchers in the Center for Automation Technologies and Systems (CATS) at Rensselaer Polytechnic Institute have focused on developing flexible manufacturing processes and systems for the manufacture of high temperature proton exchange membrane (PEM) fuel cell components. One result has been a fully automated membrane and electrode assembly (MEA) pilot manufacturing line developed for BASF Fuel Cell, GmbH, formerly Pemeas, GmbH that has been operating since September of 2002. This pilot line has been designed as a highly flexible modular manufacturing system that is able to respond quickly and cost effectively to changes in product materials, geometries, and architectures. For example, the line has easily accommodated three generations of membrane materials and a broad range of MEA sizes and geometries. Because of this flexibility, short runs of prototype MEAs are feasible, and the pilot line is able to produce a high mix of a broad range of MEA sizes. The CATS research team continues to optimize manufacturing processes to provide increased capacity, consistency, reduced costs, and high product quality. This paper will describe the many challenges and risks associated with the development and implementation of an advanced manufacturing capability for high temperature PEM MEAs, and the continuing collaboration between the BASF Fuel Cell and the CATS. Specific examples of several technical challenges and the adopted solutions are presented, along with ongoing fuel cell manufacturing initiatives.
Fundamental Research Needs in Combined Water and Thermal Management Within a Proton Exchange Membrane Fuel Cell Stack Under Normal and Cold-Start Conditions
Authors: Kandlikar Satish G. , Lu Zijie
Published: September 2009

Each fuel cell component of a proton exchange membrane fuel cell (PEMFC) used in automotive application operates most effectively (from performance and durability standpoints) within specific ranges of water content and temperature. The water and heat transport processes are coupled and present a challenge in providing the right balance over the entire range of operating conditions. Another important related aspect is CO poisoning of the electrocatalyst, which adversely affects the fuel cell performance. Freezing and cold-start present additional challenges for automotive PEMFCs. A critical review of the recent developments on these topics is presented in this paper. The study covers both the microscopic and macroscopic aspects of the transport within membrane, catalyst layers, gas diffusion layers, and gas channels, and an overview of the current PEMFC cooling technology. After discussing the current status, suggestions for future work on the above topics are presented.
A Thermally Self-Sustaining Miniature Solid Oxide Fuel Cell
Authors: Ahn Jeongmin , Ronney Paul D. , Shao Zongping , Haile Sossina M.
Published: September 2009

A thermally self-sustaining miniature power generation device was developed utilizing a single-chamber solid oxide fuel cell (SOFC) placed in a controlled thermal environment provided by a spiral counterflow “Swiss roll” heat exchanger and combustor. With the single-chamber design, fuel/oxygen crossover due to cracking of seals via thermal cycling is irrelevant and coking on the anode is practically eliminated. Appropriate SOFC operating temperatures were maintained even at low Reynolds numbers (Re) via combustion of the fuel cell effluent at the center of the Swiss roll. Both propane and higher hydrocarbon fuels were examined. Extinction limits and thermal behavior of the integrated system were determined in equivalence ratio—Re parameter space and an optimal regime for SOFC operation were identified. SOFC power densities up to 420 mW/cm2 were observed at low Re. These results suggest that single-chamber SOFCs integrated with heat-recirculating combustors may be a viable approach for small-scale power generation devices.
Prediction of Assembly Variation During Early Design
Authors: Zhao Zuozhi , Bezdecny Michelle , Lee Byungwoo , Wu Yanyan , Robinson Dean , Bauer Lowell , Slagle Mark , Coleman Duke , Barnes John , Walls Steve
Published: September 2009

This paper presents the methods to move assembly variation analysis into early stages of aircraft development where critical partitioning, sourcing, and production decisions are often made for component parts that have not yet been designed. Our goal is to identify and develop variation prediction methods that can precede detailed geometric design and make estimates accurate enough to uncover major assembly risks. With this information in hand, design and/or manufacturing modifications can be made prior to major supplier and production commitments. In addition to estimation of the overall variation, the most significant contributors to assembly variation are also identified. In this paper, a generic framework for prediction of assembly variation has been developed. An efficient, top-down approach has been adopted. Instead of taking measurement everywhere, the variation analysis starts with airplane level requirements (e.g., load capabilities and orientation of horizontal/vertical stabilizers), and then assembly requirements (mainly geometric dimensioning and tolerancing callouts, quantifiable in quality control) are derived. Next the contributors to a particular assembly requirement are identified through data flow chain analysis. Finally, the major contributors are further characterized through a sensitivity study of metamodels or 3D variation analysis models. A case study of a vertical fin has been used to demonstrate the validity of the proposed framework. Multiple prediction methods have been studied and their applicability to variation analysis discussed. Simplified design simulation method and metamodel methods have been tested and the results are reported. Comparisons between methods have been made to demonstrate the flexibility of the analysis framework, as well as the utility of the prediction methods. The results of a demonstration test case study for vertical fin design were encouraging with modeling methods coming within 15% of deviation compared with the detailed design simulation.
Wavelet SDF-Reps: Solid Modeling With Volumetric Scans
Authors: Storti Duane , Ganter Mark A. , Ledoux William R. , Ching Randal P. , Hu Yangqiu Patrick , Haynor David
Published: September 2009

This paper describes a new formulation of solid modeling for treating parts derived from volumetric scans (computed tomography, magnetic resonance, etc.) along with parts from traditional computer-aided design operations. Recent advances in segmentation via level set methods produce voxel grids of signed distance values, and we interpolate the signed distance values using wavelets to produce an implicit or function-based representation called wavelet signed distance function representation that provides inherent support for data compression, multiscale modeling, and skeletal-based operations.
Linear and Nonlinear Dynamic Responses of Various Shaped Laminated Composite Plates
Authors: Tanveer Muhammad , Singh Anand V.
Published: September 2009

A unified approach to study the forced linear and geometrically nonlinear elastic vibrations of fiber-reinforced laminated composite plates subjected to uniform load on the entire plate as well as on a localized area is presented in this paper. To accommodate different shapes of the plate, the analytical procedure has two parts. The first part deals with the geometry which is interpolated by relatively low-order polynomials. In the second part, the displacement based p-type method is briefly presented where the displacement fields are defined by significantly higher-order polynomials than those used for the geometry. Simply supported square, rhombic, and annular circular sector plates are modeled. The equation of motion is obtained by the Hamilton’s principle and solved by beta-m method along with the Newton–Raphson iterative scheme. Numerical procedure presented herein is validated successfully by comparing present results with the previously published data, convergence study, and fast Fourier transforms of the linear and nonlinear transient responses. The geometric nonlinearity is seen to cause stiffening of the plates and in turn significantly lowers the values of displacements and stresses. Also as expected, the frequencies are increased for the nonlinear cases.
Flight Dynamics and Simulation of Laser Propelled Lightcraft
Authors: Ballard Christopher G. , Anderson Kurt S. , Myrabo Leik
Published: September 2009

A seven degree-of-freedom (7DOF) dynamic model was developed to provide insight into the flight behavior of Type 200 and other related lightcraft, and to serve as a research tool for developing future engine-vehicle configurations for laser launching of nanosatellites (1–10+kg). Accurate engine, beam, and aerodynamics models are included to improve the predictive capability of the 7DOF code. The aerodynamic forces of lift, drag, and aerodynamic pitching moment were derived from FLUENT® computational fluid dynamics predictions, and calibrated against limited existing wind tunnel data. To facilitate 7DOF model validation, simulation results are compared with video analysis of actual flights under comparable conditions. Despite current limitations of the 7DOF model, the results compared well with experimental flight trajectory data.
A van der Pol–Duffing Oscillator Model of Hydrodynamic Forces on Canonical Structures
Authors: Akhtar Imran , Marzouk Osama A. , Nayfeh Ali H.
Published: September 2009

Numerical simulations of the flow past elliptic cylinders with different eccentricities have been performed using a parallel incompressible computational fluid-dynamics (CFD) solver. The pressure is integrated over the surface to compute the lift and drag forces on the cylinders. The numerical results of different cases are then used to develop reduced-order models for the lift and drag coefficients. The lift coefficient is modeled with a generalized van der Pol–Duffing oscillator and the drag coefficient is expressed in terms of the lift coefficient. The parameters in the oscillator model are computed for each elliptic cylinder. The results of the model match the CFD results not only in the time domain but also in the spectral domain.
Lateral Load Transfer Effects on Bifurcation Behavior of Four-Wheel Vehicle System
Authors: Nguyen Vincent , Schultz Gregory , Balachandran Balakumar
Published: September 2009

In this article, vehicle handling behavior of a nonlinear four-wheel vehicle system is studied. Bifurcations with respect to vehicle speed and roll moment distribution are examined for innate understeering and oversteering models. Lateral load transfer effects are investigated, and these effects are shown to alter the bifurcation locations for oversteering vehicles when the roll moment distribution is adjusted. When the roll moment distribution is used as a control parameter, transitions between bifurcation behavior characteristic of oversteering systems and bifurcation behavior characteristic of understeering systems are observed. This effort provides a framework for developing a complete vehicle handling assessment in terms of nonlinear regions of performance, transient behavior, and lateral load effects.
Energy Transfer and Dissipation in a Duffing Oscillator Coupled to a Nonlinear Attachment
Authors: Viguié R. , Peeters M. , Kerschen G. , Golinval J.-C.
Published: September 2009

The dynamics of a two-degree-of-freedom nonlinear system consisting of a grounded Duffing oscillator coupled to an essentially nonlinear attachment is examined in the present study. The underlying Hamiltonian system is first considered, and its nonlinear normal modes are computed using numerical continuation and gathered in a frequency-energy plot. Based on these results, the damped system is then considered, and the basic mechanisms for energy transfer and dissipation are analyzed.
Shape Similarity Matching With Octree Representations
Authors: Zhang Jingsheng , Smith Shana
Published: September 2009

To achieve effective 3D shape retrieval, there is a crucial need for efficient shape matching methods. This paper introduces a new method for 3D shape matching, which uses a simplified octree representation of 3D mesh models. The simplified octree representation was developed to improve time and space efficiency over prior representations. The proposed method also stores octree information in extensible markup language format, rather than in a new proprietary data file type, to facilitate comparing models over the Internet.
The Modulus of Fibroblast-Populated Collagen Gels is not Determined by Final Collagen and Cell Concentration: Experiments and an Inclusion-Based Model
Authors: Evans Michael C. , Barocas Victor H.
Published: September 2009

The fibroblast-populated collagen lattice is an attractive model tissue for in vitro studies of cell behavior and as the basis for bioartificial tissues. In spite of its simplicity—containing only collagen and cells—the system is surprisingly difficult to describe mechanically because of the ability of the cells to remodel the matrix, including compaction at short times and synthesis and/or degradation (and cell proliferation) at longer times. The objectives of this work were to measure the equilibrium modulus of fibroblast-populated gels with different collagen and cell concentrations, and to use that characterization as the basis for a theoretical model that could be used to predict gel mechanics based on conditions. Although many observations were as expected (e.g., the gel compacts more when there are more cells in it, and the gel is stiffer when there is more collagen in it), an unexpected result arose: the final modulus of the gel was not dependent solely on the final composition. Even if it compacted more than a gel that was originally at a high collagen concentration, a gel that started at a low collagen concentration remained less stiff than the higher-concentration gel. In light of these results and experimental studies by others, we propose a model in which the gel compaction is not homogeneous but consists instead of extreme densification near the cells in an otherwise unchanged matrix. By treating the dense regions as spherical inclusions, we used classical composite material theory to develop an expression for the modulus of a compacted gel based on the initial collagen density and the final inclusion (i.e., cell) density. The new model fit the data for moderately compacted gels well but broke down, as expected, for larger volume fractions at which the underlying model assumptions did not apply.
Age Dependent Mechanical Properties of the Infant Porcine Parietal Bone and a Correlation to the Human
Authors: Baumer Timothy G. , Powell Brian J. , Fenton Todd W. , Haut Roger C.
Published: September 2009

An infant less than 18 months of age with a skull fracture has a one in three chance of abuse. Injury biomechanics are often used in the investigation of these cases. In addition to case-based investigations, computer modeling, and test dummies, animal model studies can aid in these investigations. This study documents age effects on the mechanical properties of parietal bone and coronal suture in porcine infants and correlates the bending properties of the bone to existing human infant data. Three beam specimens were cut from porcine specimens aged 3 days, 7 days, 10 days, 14 days, 18 days, and 21 days: one across the coronal suture and two from the parietal bone, one parallel to and one perpendicular to the coronal suture. An actuator-mounted probe applied four-point bending in displacement control at 25 mm/s until failure. Bending stiffness of bone specimens increased with age; bone-suture-bone specimens showed no change up to 14 days but increased from 14 days to 18 days. All three specimen types showed decreases in ultimate stress with age. Ultimate strain for the bone-suture-bone specimens was significantly higher than that for the bone specimens up to 14 days with no differences thereafter. There was no change in the bending modulus with age for any specimen type. Bone-suture-bone bending modulus was lower than that of the bone specimens up to 14 days with no differences thereafter. There was no change in strain energy to failure with age for the bone specimens; bone-suture-bone specimens showed no change up to 14 days but decreased from 14 days to 18 days. There was an increase in specimen porosity with age. Correlation analysis revealed a weak (−0.39) but significant and negative correlation between ultimate stress and porosity. While the mechanical properties of parietal bone and coronal suture did not change significantly with age, bone specimens showed an increase in bending stiffness with age. Bone-suture-bone specimens showed an increase in bending stiffness only between 14 days and 18 days of age. Correlation analyses using existing and new data to compute the bending rigidity of infant parietal bone specimens suggested that days of pig age may correlate with months of human age during the most common time frame of childhood abuse cases.
A Mechatronic Device for the Rehabilitation of Ankle Motor Function
Authors: Bucca Giuseppe , Bezzolato Alberto , Bruni Stefano , Molteni Franco
Published: September 2009

This paper presents the main results from a research aiming at the design of an electromechanical actuator for use in the rehabilitation of ankle motor function in patients suffering due to neurological diseases. Motivations for the research project are discussed within the framework of the application of mechatronic concepts for rehabilitation practice. The entire design process is then described, from the definition of project targets through the mechanical concept and control design steps until design validation by means of numerical simulations and tests on a prototype.
Ground Reaction Forces and Lower Extremity Kinematics When Running With Suppressed Arm Swing
Authors: Miller Ross H. , Caldwell Graham E. , Van Emmerik Richard E. A. , Umberger Brian R. , Hamill Joseph
Published: September 2009

The role of arm swing in running has been minimally described, and the contributions of arm motion to lower extremity joint kinematics and external force generation are unknown. These contributions may have implications in the design of musculoskeletal models for computer simulations of running, since previous models have usually not included articulating arm segments. 3D stance phase lower extremity joint angles and ground reaction forces (GRFs) were determined for seven subjects running normally, and running under two conditions of arm restraint. When arm swing was suppressed, the peak vertical GRF decreased by 10–13% bodyweight, and the peak lateral GRF increased by 4–6% bodyweight. Changes in peak joint angles on the order of 1–5 deg were observed for hip flexion, hip adduction, knee flexion, knee adduction, and ankle abduction. The effect sizes (ES) were small to moderate (ES<0.8) for most of the peak GRF differences, but large (ES>0.8) for most of the peak joint angle differences. These changes suggest that suppression of arm swing induces subtle but statistically significant changes in the kinetic and kinematic patterns of running. However, the salient features of the GRFs and the joint angles were present in all conditions, and arm swing did not introduce any major changes in the timing of these data, as indicated by cross correlations. The decision to include arm swing in a computer model will likely need to be made on a case-by-case basis, depending on the design of the study and the accuracy needed to answer the research question.
Spinal Subarachnoid Space Pressure Measurements in an In Vitro Spinal Stenosis Model: Implications on Syringomyelia Theories
Authors: Martin Bryn A. , Labuda Richard , Royston Thomas J. , Oshinski John N. , Iskandar Bermans , Loth Francis
Published: September 2009

Full explanation for the pathogenesis of syringomyelia (SM), a neuropathology characterized by the formation of a cystic cavity (syrinx) in the spinal cord (SC), has not yet been provided. It has been hypothesized that abnormal cerebrospinal fluid (CSF) pressure, caused by subarachnoid space (SAS) flow blockage (stenosis), is an underlying cause of syrinx formation and subsequent pain in the patient. However, paucity in detailed in vivo pressure data has made theoretical explanations for the syrinx difficult to reconcile. In order to understand the complex pressure environment, four simplified in vitro models were constructed to have anatomical similarities with post-traumatic SM and Chiari malformation related SM. Experimental geometry and properties were based on in vivo data and incorporated pertinent elements such as a realistic CSF flow waveform, spinal stenosis, syrinx, flexible SC, and flexible spinal column. The presence of a spinal stenosis in the SAS caused peak-to-peak cerebrospinal fluid CSF pressure fluctuations to increase rostral to the stenosis. Pressure with both stenosis and syrinx present was complex. Overall, the interaction of the syrinx and stenosis resulted in a diastolic valve mechanism and rostral tensioning of the SC. In all experiments, the blockage was shown to increase and dissociate SAS pressure, while the axial pressure distribution in the syrinx remained uniform. These results highlight the importance of the properties of the SC and spinal SAS, such as compliance and permeability, and provide data for comparison with computational models. Further research examining the influence of stenosis size and location, and the importance of tissue properties, is warranted.
A Steady-State Mass Transfer Model of Removing CPAs From Cryopreserved Blood With Hollow Fiber Modules
Authors: Ding Weiping , Zhou Xiaoming , Heimfeld Shelly , Reems Jo-Anna , Gao Dayong
Published: September 2009

Hollow fiber modules are commonly used to conveniently and efficiently remove cryoprotective agents (CPAs) from cryopreserved cell suspensions. In this paper, a steady-state model coupling mass transfers across cell and hollow fiber membranes is theoretically developed to evaluate the removal of CPAs from cryopreserved blood using hollow fiber modules. This steady-state model complements the unsteady-state model, which was presented in our previous study. The steady-state model, unlike the unsteady-state model, can be used to evaluate the effect of ultrafiltration flow rates on the clearance of CPAs. The steady-state model is validated by experimental results, and then is compared with the unsteady-state model. Using the steady-state model, the effects of ultrafiltration flow rates, NaCl concentrations in dialysate, blood flow rates and dialysate flow rates on CPA concentration variation and cell volume response are investigated in detail. According to the simulative results, the osmotic damage of red blood cells can easily be reduced by increasing ultrafiltration flow rates, increasing NaCl concentrations in dialysate, increasing blood flow rates, or decreasing dialysate flow rates.
In Vitro Stretches of the Mitral Valve Anterior Leaflet Under Edge-to-Edge Repair Condition
Authors: He Zhaoming , Gao Bo , Bhattacharya Shamik , Harrist Tyler , Mathew Sibi , Sun Wei
Published: September 2009

Mitral valve edge-to-edge repair (ETER) alters valve mechanics, which may impact efficacy and durability of the repair. The objective of this paper was to quantify stretches in the central region of the anterior leaflet of the mitral valve after ETER with a single suture and 6 mm suture. Sixteen markers, forming a 4×4 array, were attached onto the central region of the mitral valve anterior leaflet. The mitral valve was subjected to ETER with a single suture and 6 mm suture, and mounted in an in vitro flow loop simulating physiological conditions. Images of the marker array were used to calculate marker displacement and stretch. A total of 9 mitral valves were tested. Two peak stretches were observed during a cardiac cycle, one in systole and the other in diastole under mitral valve edge-to-edge repair condition. The major principal (radial) stretch during systole was significantly greater than that during diastole. However, there was no significant difference between the minor principal (circumferential) stretch during diastole and that during systole. In addition, there were no significant differences in the radial and circumferential, or areal stretches and stretch rates during diastole between the single suture and 6 mm suture. The ETER subjects the mitral valve leaflets to double frequency of loading and unloading. Minor change in suture length may not result in a significant load difference in the central region of the anterior leaflet during diastole.
Goldmann Tonometry Correction Factors Based on Numerical Analysis
Authors: Elsheikh Ahmed , Alhasso Daad , Pye David
Published: September 2009

With the world’s aging population, it is expected that the number of people affected by glaucoma, the second most common cause of irreversible blindness, will increase considerably. Current knowledge on glaucoma progression relates elevation of the intraocular pressure (IOP) to optic nerve damage and hence visual impairment. For this reason, IOP measurement in tonometry has become an essential part of routine eye examinations needed for the diagnosis and management of the disease. The accuracy of the current reference standard in tonometry, the Goldmann applanation tonometer, is known to be affected by the natural variations in corneal thickness, curvature, and material properties. Earlier studies attempted to quantify these effects and produced correction factors that considered the variations in each one of these parameters separately, and no guidance was given as to how to combine the effects of variations in more than one parameter. The present research attempted to address this gap by conducting a multidimensional numerical study that considered variations in thickness, curvature, material properties, and IOP, and used the results to develop a single correction equation that considered these parameters simultaneously. The results of the analysis and the correction equation were validated successfully against the outcome of earlier clinical and mathematical studies on the effect of individual parameters, and the correction equation was presented in a simple form suitable for clinical application.
Validation of a CFD Methodology for Positive Displacement LVAD Analysis Using PIV Data
Authors: Medvitz Richard B. , Reddy Varun , Deutsch Steve , Manning Keefe B. , Paterson Eric G.
Published: September 2009

Computational fluid dynamics (CFD) is used to asses the hydrodynamic performance of a positive displacement left ventricular assist device. The computational model uses implicit large eddy simulation direct resolution of the chamber compression and modeled valve closure to reproduce the in vitro results. The computations are validated through comparisons with experimental particle image velocimetry (PIV) data. Qualitative comparisons of flow patterns, velocity fields, and wall-shear rates demonstrate a high level of agreement between the computations and experiments. Quantitatively, the PIV and CFD show similar probed velocity histories, closely matching jet velocities and comparable wall-strain rates. Overall, it has been shown that CFD can provide detailed flow field and wall-strain rate data, which is important in evaluating blood pump performance.
ADAPTIVENESS IN MONOTONE PSEUDO-BOOLEAN OPTIMIZATION AND STOCHASTIC NEURAL COMPUTATION
Authors: GROSSI GIULIANO
Published: September 2009

Hopfield neural network (HNN) is a nonlinear computational model successfully applied in finding near-optimal solutions of several difficult combinatorial problems. In many cases, the network energy function is obtained through a learning procedure so that its minima are states falling into a proper subspace (feasible region) of the search space. However, because of the network nonlinearity, a number of undesirable local energy minima emerge from the learning procedure, significantly effecting the network performance.

In the neural model analyzed here, we combine both a penalty and a stochastic process in order to enhance the performance of a binary HNN. The penalty strategy allows us to gradually lead the search towards states representing feasible solutions, so avoiding oscillatory behaviors or asymptotically instable convergence. Presence of stochastic dynamics potentially prevents the network to fall into shallow local minima of the energy function, i.e., quite far from global optimum. Hence, for a given fixed network topology, the desired final distribution on the states can be reached by carefully modulating such process.

The model uses pseudo-Boolean functions both to express problem constraints and cost function; a combination of these two functions is then interpreted as energy of the neural network. A wide variety of NP-hard problems fall in the class of problems that can be solved by the model at hand, particularly those having a monotonic quadratic pseudo-Boolean function as constraint function. That is, functions easily derived by closed algebraic expressions representing the constraint structure and easy (polynomial time) to maximize.

We show the asymptotic convergence properties of this model characterizing its state space distribution at thermal equilibrium in terms of Markov chain and give evidence of its ability to find high quality solutions on benchmarks and randomly generated instances of two specific problems taken from the computational graph theory.
WOMEN ENTREPRENEURS IN THE GREEK COUNTRYSIDE: A TYPOLOGY ACCORDING TO MOTIVES AND BUSINESS CHARACTERISTICS
Authors: IAKOVIDOU OLGA , KOUTSOU STAVRIANI , PARTALIDOU MARIA
Published: September 2009

Differences between male and female entrepreneurs provide compelling reasons to study the latter separately. Especially in rural areas, research shows that women are a remarkable and unexplored source of the labor force. Nevertheless, few researchers have examined rural women and the issues pertaining to their entrepreneurship separately. The contribution of this study to the debate of women entrepreneurship is the closer examination of women in Greek rural areas. This research aims to examine factors that must be considered independently with recognition to the variances of rural areas with different geomorphologic and economic profiles. The characteristics of women entrepreneurship in Greek rural areas and the women's motives for the undertaking of the entrepreneurial activity are used to identify a typology of women entrepreneurs in the Greek countryside.
CHANGES IN LIVESTOCK PROJECTS ON THE BASIS OF ENVIRONMENTAL IMPACT ASSESSMENT SCREENING
Authors: KØRNØV LONE BOTIN , CHRISTENSEN PER
Published: September 2009

Growing pressures to increase animal production challenge the agricultural sector to identify technologies and solutions that will make livestock production environmentally sound. One mechanism which may assist the sector in meeting this challenge is Environmental Impact Assessment (EIA).

On the basis of an evaluation of EIA screenings of Danish livestock, this article presents and discusses how EIA responds to the environmental challenge of intensive livestock projects. The analysis and discussion focus on the changes introduced in livestock projects as a result of the EIA screening process. Screening is normally used for deciding whether or not a project proposal requires an EIA. The article shows how screening also functions as a tool for changing livestock projects, thus being a regulatory instrument in its own right.

The analysis of livestock EIA screenings shows that changes are initiated through a wide range of measures mitigating the environmental impacts of particular livestock projects. Fodder optimisation, cover crops, reduced animal pressure, change of crop rotation, repositioning of risk areas and changed design of animal houses are frequently applied measures. As a conclusion, EIA is identified as an important supplement to other regulatory instruments aiming at balancing the benefits and environmental costs of livestock production. However, the article also concludes that the systematic inspection of livestock projects needs to be improved in order to secure that the changes introduced through screening are also robust in character.
PARTICIPATIVE SEA APPROACH FOR DATA COLLECTION AND OBJECTIVE FORMULATION
Authors: AZCARATE JUAN , BALFORS BERIT
Published: September 2009

This paper analyses the interaction between data needs and objective formulation in Strategic Environmental Assessment (SEA). This topic is discussed from the experiences that were gained by designing and applying a participative SEA pre-study process in the developing region of the Sonso Lagoon, Colombia. Data collection and issue identification are described, as are the different purposes and similarities with objective-led and baseline-led SEAs. It is argued that the participative framework used in Sonso can be applied in similar developing country contexts where there is a lack of environmental data and clear development goals. Finally, it is stressed that the participative SEA pre-study process can be implemented in situations where different sector objectives conflict or in circumstances where there is a need to formulate regional or municipal development objectives.
EXPLORING THE POTENTIAL FAILURE OF THE REGULATORY FRAMEWORK AND MANAGEMENT TOOLS WHICH GOVERN THE CONSERVATION OF BIODIVERSITY: THE CASE OF ARTIFICIAL LAKE KERKINI IN GREECE
Authors: MANOU DIMITRA , PAPATHANASIOU JASON
Published: September 2009

This paper was developed in the context of the research project entitled GEMCONBIO (Governance and Ecosystems Management for the Conservation of Biodiversity), which is a European FP6-funded project under Priority 7 — Citizens and Governance in a Knowledge-Based Society. The projects strategic objective is, through the elaboration of certain case studies, to explore the interactions between governance modes and sustainable development objectives in view of identifying which governance processes and institutions can contribute best to the conservation of biodiversity.

The case study of Kerkini Lake was selected along with approximately 27 case studies across Europe, the United States and third countries because of the area's very important ecosystem. It is one of the 10 most important wetlands in Greece, a declared National Park and one of the most important wetlands for birds in Europe. There is a plethora of national, European and international laws and regulations as well as administrative decisions regarding the study area. However, problems of implementation and compliance appear to be very strong causing severe implications in the area's sustainable development.
Microbial Provinces in the Subseafloor
Authors: Schrenk Matthew O. , Huber Julie A. , Edwards Katrina J.
Published: September 2009

The rocks and sediments of the oceanic subsurface represent a diverse mosaic of environments potentially inhabited by microorganisms. Understanding microbial ecosystems in subseafloor environments confounds standard ecological descriptions in part because we have difficulty elucidating and describing the scale of relevant processes. Habitat characteristics impact microbial activities and growth, which in turn affect microbial diversity, net production, and global biogeochemical cycles. Herein we provide descriptions of subseafloor microbial provinces, broadly defined as geologically and geographically coherent regions of the subseafloor that may serve as potential microbial habitats. The purpose of this review is to summarize and refine criteria for the definition and delineation of distinct subseafloor microbial habitats to aid in their exploration. This review and the criteria we outline aim to develop a unified framework to improve our understanding of subseafloor microbial ecology, enable quantification of geomicrobial processes, and facilitate their accurate assimilation into biogeochemical models.
Evolution and Ecology of Species Range Limits
Authors: Sexton Jason P. , McIntyre Patrick J. , Angert Amy L. , Rice Kevin J.
Published: September 2009

Species range limits involve many aspects of evolution and ecology, from species distribution and abundance to the evolution of niches. Theory suggests myriad processes by which range limits arise, including competitive exclusion, Allee effects, and gene swamping; however, most models remain empirically untested. Range limits are correlated with a number of abiotic and biotic factors, but further experimentation is needed to understand underlying mechanisms. Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking. Evolution of range limits is understudied in natural systems; in particular, the role of gene flow in shaping range limits is unknown. Biological invasions and rapid distribution shifts caused by climate change represent large-scale experiments on the underlying dynamics of range limits. A better fusion of experimentation and theory will advance our understanding of the causes of range limits.
Treatment with SRT1720, a SIRT1 activator, ameliorates fatty liver with reduced expression of lipogenic enzymes in MSG mice
Authors: Yamazaki Yu , Usui Isao , Kanatani Yukiko , Matsuya Yuji , Tsuneyama Koichi , Fujisaka Shiho , Bukhari Agussalim , Suzuki Hikari , Senda Satoko , Imanishi Shingo , Hirata Kazuya , Ishiki Manabu , Hayashi Ryuji , Urakaze Masaharu , Nemoto Hideo , Kobayashi Masashi , Tobe Kazuyuki
Published: September 2009

Nonalcoholic fatty liver disease (NAFLD) is an abnormal liver metabolism often observed with insulin resistance and metabolic syndrome. Calorie restriction is a useful treatment for NAFLD and reportedly prolongs the life spans of several species in which sirtuin plays an important role. In this study, we examined whether the activation of SIRT1, a mammalian ortholog of sirtuin, may ameliorate the development of NAFLD. Monosodium glutamate (MSG) mice, which exhibited obesity and insulin resistance, were treated with SRT1720, a specific SIRT1 activator from the age of 6–16 wk. Sixteen-week-old MSG mice exhibited increased liver triglyceride content and elevated levels of aminotransferase. SRT1720 treatment significantly reduced these levels without affecting body weight or food intake. These results suggested that the administration of SRT1720 ameliorated the development of NAFLD in MSG mice. The expressions of lipogenic genes, such as sterol regulatory element-binding protein-1c, acetyl-CoA carboxylase, and fatty acid synthase, and the serum lipid profiles, including free fatty acids, were elevated in MSG mice and were reduced by SRT1720 treatment. SRT1720 treatment also reduced the expressions of lipogenic genes in cultured HepG2 cells. Furthermore, SRT1720 treatment decreased the expressions of marker genes for oxidative stress and inflammatory cytokines in the liver of MSG mice. Taken together, SRT1720 treatment may reduce liver lipid accumulation, at least in part, by directly reducing the expressions of lipogenic genes. The reduction of oxidative stress and inflammation may also be involved in the amelioration of NAFLD.
Intraventricular injection of antibodies to β1-integrins generates pressure gradients in the brain favoring hydrocephalus development in rats
Authors: Nagra Gurjit , Koh Lena , Aubert Isabelle , Kim Minhui , Johnston Miles
Published: September 2009

In some tissues, the injection of antibodies to the β1-integrins leads to a reduction in interstitial fluid pressure, indicating an active role for the extracellular matrix in tissue pressure regulation. If perturbations of the matrix occur in the periventricular area of the brain, a comparable lowering of interstitial pressures may induce transparenchymal pressure gradients favoring ventricular expansion. To examine this concept, we measured periventricular (parenchymal) and ventricular pressures with a servo-null micropipette system (2-μm tip) in adult Wistar rats before and after anti-integrin antibodies or IgG/IgM isotype controls were injected into a lateral ventricle. In a second group, the animals were kept for 2 wk after similar injections and after euthanization, the brains were removed and assessed for hydrocephalus. In experiments in which antibodies to β1-integrins ( n = 10) but not isotype control IgG/IgM ( n = 7) were injected, we observed a decline in periventricular pressures relative to the preinjection values. Under similar circumstances, ventricular pressures were elevated ( n = 10) and were significantly greater than those in the periventricular interstitium. We estimated ventricular to periventricular pressure gradients of up to 4.3 cmH2O. In the chronic preparations, we observed enlarged ventricles in many of the animals that received injections of anti-integrin antibodies (21 of 29 animals; 72%) but not in any animal receiving the isotype controls. We conclude that modulation/disruption of β1-integrin-matrix interactions in the brain generates pressure gradients favoring ventricular expansion, suggesting a novel mechanism for hydrocephalus development.
Intrinsic Neuronal Excitability Is Reversibly Altered by a Single Experience in Fear Conditioning
Authors: McKay Bridget M. , Matthews Elizabeth A. , Oliveira Fernando A. , Disterhoft John F.
Published: September 2009

Learning is known to cause alterations in intrinsic cellular excitability but, to date, these changes have been seen only after multiple training trials. A powerful learning task that can be quickly acquired and extinguished with a single trial is fear conditioning. Rats were trained and extinguished on a hippocampus-dependent form of fear conditioning to determine whether learning-related changes in intrinsic excitability could be observed after a few training trials and a single extinction trial. Following fear training, hippocampal slices were made and intrinsic excitability was assayed via whole cell recordings from CA1 neurons. Alterations in intrinsic excitability, assayed by the postburst afterhyperpolarization and firing frequency accommodation, were observed after only three trials of contextual or trace-cued fear conditioning. Animals that had been trained in contextual and trace-cued fear were then extinguished. Context fear-conditioned animals extinguished in a single trial and the changes in intrinsic excitability were reversed. Trace-cue conditioned animals only partially extinguished in a single trial and reductions in excitability remained. Thus a single learning experience is sufficient to alter intrinsic excitability. This dramatically extends observations of learning-specific changes in intrinsic neuronal excitability previously observed in paradigms requiring many training trials, suggesting the excitability changes have a basic role in acquiring new information.