bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Contact Search Algorithms for Wheel/Rail Contact Problems
Authors: Sugiyama Hiroyuki , Suda Yoshihiro
Published: September 2009

In this investigation, contact search algorithms for the analysis of wheel/rail contact problems are discussed, and the on-line and off-line hybrid contact search method is developed for multibody railroad vehicle dynamics simulations using the elastic contact formulation. In the hybrid algorithm developed in this investigation, the off-line search that can be effectively used for the tread contact is switched to the on-line search when the contact point is jumped to the flange region. In the two-point contact scenarios encountered in curve negotiations, the on-line search is used for both tread and flange contacts to determine the two-point contact configuration. By so doing, contact points on the flange region given by the off-line tabular search are never used, but rather used as an initial estimate for the online iterative procedure for improving the numerical convergence. Furthermore, the continual on-line detection of the second point of contact is replaced with a simple table look-up. It is demonstrated by several numerical examples that include flange climb and curve negotiation scenarios that the proposed hybrid contact search algorithm can be effectively used for modeling wheel/rail contacts in the analysis of general multibody railroad vehicle dynamics.
Parameters Identification for Nonlinear Dynamic Systems Via Genetic Algorithm Optimization
Authors: Gondhalekar A. C. , Petrov E. P. , Imregun M.
Published: September 2009

This paper presents a frequency domain method for the location, characterization, and identification of localized nonlinearities in mechanical systems. The nonlinearities are determined by recovering nonlinear restoring forces, computed at each degree-of-freedom (DOF). Nonzero values of the nonlinear force indicate nonlinearity at the corresponding DOFs and the variation in the nonlinear force with frequency (force footprint) characterizes the type of nonlinearity. A library of nonlinear force footprints is obtained for various types of individual and combined nonlinearities. Once the location and the type of nonlinearity are determined, a genetic algorithm based optimization is used to extract the actual values of the nonlinear parameters. The method developed allows simultaneous identification of one or more types of nonlinearity at any given DOF. Parametric identification is possible even if the type of nonlinearity is not known in advance, a very useful feature when the type characterization is difficult. The proposed method is tested on simulated response data. Different combinations of localized cubic stiffness nonlinearity, clearance nonlinearity, and frictional nonlinearity are considered to explore the method’s capabilities. Finally, the response data are polluted with random noise to examine the performance of the method in the presence of measurement noise.
Discontinuity-Induced Bifurcations in Systems With Hysteretic Force Interactions
Authors: Dankowicz Harry , Paul Mark R.
Published: September 2009

This paper presents the application of the discontinuity-mapping technique to the analysis of discontinuity-induced bifurcations of periodic trajectories in an example hybrid dynamical system in which changes in the vector field associated with the crossing of a discontinuity-surface depend on the direction of crossing. The analysis is motivated by a hysteretic model of the capillary force interactions between an atomic-force-microscope cantilever probe tip and a nanoscale sample surface in the presence of a thin liquid film on the tip and the surface and operating in intermittent-contact mode. The analysis predicts the sudden termination of branches of periodic system responses at parameter values corresponding to grazing contact with the onset of the hysteretic force interactions. It further establishes the increase beyond all bounds of the magnitude of one of the eigenvalues of the linearization of a suitably defined Poincaré mapping, indicating the destabilizing influence of near-grazing contact.
Finite Element Modeling of Resurfacing Hip Prosthesis: Estimation of Accuracy Through Experimental Validation
Authors: Taddei Fulvia , Martelli Saulo , Gill Harinderjit Singh , Cristofolini Luca , Viceconti Marco
Published: September 2009

Metal-on-metal hip resurfacing is becoming increasingly popular, and a number of new devices have been recently introduced that, in the short term, appear to have satisfactory outcome but many questions are still open on the biomechanics of the resurfaced femur. This could be investigated by means of finite element analysis, but, in order to be effective in discerning potential critical conditions, the accuracy of the models’ predictions should be assessed. The major goal of this study was to validate, through a combined experimental-numerical study, a finite element modeling procedure for the simulation of resurfaced femurs. In addition, a preliminary biomechanical analysis of the changes induced in the femoral neck biomechanics by the presence of the device was performed, under a physiologic range of hip joint reaction directions. For this purpose, in vitro tests and a finite element model based on the same specimen were developed using a cadaver femur. The study focused on the Conserve Plus, one of the most common contemporary resurfacing designs. Five loading configurations were identified to correspond to the extremes of physiological directions for the hip joint. The agreement between experimental measurements and numerical predictions was good both in the prediction of the femoral strains (R2>0.9), and in the prosthesis micromotions (error<20 μm), giving confidence in the model predictions. The preliminary biomechanical analysis indicated that the strains in the femoral neck are moderately affected by the presence of the prosthesis, apart from localized strain increments that can be considerable, always predicted near the stem. Low micromotions and contact pressure were predicted, suggesting a good stability of the prosthesis. The model accuracy was good in the prediction of the femoral strains and moderately good in the prediction of the bone-prosthesis micromovements. Although the investigated loading conditions were not completely physiological, the preliminary biomechanical analysis showed relatively small changes for the proximal femur after implantation. This validated model can support realistic simulations to examine physiological load configurations and the effects of variations in prosthesis design and implantation technique.
The Effect of Flash Freezing on Variability in Spinal Cord Compression Behavior
Authors: Sparrey Carolyn J. , Keaveny Tony M.
Published: September 2009

The compression behavior of spinal cord tissue is important for understanding spinal cord injury mechanics but has not yet been established. Characterizing compression behavior assumes precise specimen geometry; however, preparing test specimens of spinal cord tissue is complicated by the extreme compliance of the tissue. The objectives of this study were to determine the effect of flash freezing on both specimen preparation and mechanical response and to quantify the effect of small deviations in specimen geometry on mechanical behavior. Specimens of porcine spinal cord white matter were harvested immediately following sacrifice. The tissue was divided into two groups: partially frozen specimens were flash frozen (60 s at −80°C) prior to cutting, while fresh specimens were kept at room temperature. Specimens were tested in unconfined compression at strain rates of 0.05 s−1 and 5.0 s−1 to 40% strain. Parametric finite element analyses were used to investigate the effect of specimen face angle, cross section, and interface friction on the mechanical response. Flash freezing did not affect the mean mechanical behavior of the tissue but did reduce the variability in the response across specimens (p<0.05). Freezing also reduced variability in the specimen geometry. Variations in specimen face angle (0–10 deg) resulted in a 34% coefficient of variation and a 60% underestimation of peak stress. The effect of geometry on variation and error was greater than that of interface friction. Taken together, these findings demonstrate the advantages of flash freezing in biomechanical studies of spine cord tissue.
The Theoretical Foundation for Artery Buckling Under Internal Pressure
Authors: Han Hai-Chao
Published: September 2009

The stability of blood vessels under the lumen blood pressure is essential to the maintenance of normal arterial function. Buckling equations have been established recently for linear and nonlinear elastic artery models with assumed sinusoidal mode shapes. However, the theoretical base for the assumption is not clear. This study established differential equations of artery buckling and then proved that straight arteries bifurcated into sinusoidal mode shapes when buckling occurs. These results set the buckling equation on a solid theoretical foundation.
Analytical Approach to Recovering Bone Porosity From Effective Complex Shear Modulus
Authors: Bonifasi-Lista Carlos , Cherkaev Elena , Yeni Yener N.
Published: September 2009

This work deals with the study of the analytical relations between porosity of cancellous bone and its mechanical properties. The Stieltjes representation of the effective shear complex modulus of cancellous bone is exploited to recover porosity. The microstructural information is contained in the spectral measure in this analytical representation. The spectral function can be recovered from the effective measurements over a range of frequencies. The problem of reconstruction of the spectral measure is very ill-posed. Regularized algorithm is derived to ensure stability of the results. The proposed method does not use any specific assumptions about the microgeometry of bone. The approach does not rely on correlation analysis, it uses analytical relationships. For validation purposes, complex shear modulus over a range of frequencies was calculated by the finite element method using micro-computed tomography (micro-CT) images of human cancellous bone. The calculated values were used in numerical algorithm to recover bone porosity. At the microlevel, bone was modeled as a heterogeneous medium composed of trabeculae tissue and bone marrow treated as transversely isotropic elastic and isotropic viscoelastic materials, respectively. Recovered porosity values are in excellent agreement with true porosity found from the corresponding micro-CT images.
Development of an Apparatus to Produce Fractures From Short-Duration High-Impulse Loading With an Application in the Lower Leg
Authors: Quenneville Cheryl E. , Fraser Gillian S. , Dunning Cynthia E.
Published: September 2009

Axial loading of the lower leg during impact events can cause significant fractures of the tibia. The magnitude of lower leg axial loading that occurs during short-duration high-impulse events, such as antivehicular landmine blasts, can lead to life-altering injuries. These events achieve higher forces over shorter durations than car crashes, the current standard used for protective measures. In order to determine appropriate injury limits for the lower limb, a testing apparatus has been designed that can simulate these types of events for testing of anthropomorphic test device (ATD) lower legs as well as cadaveric specimens. Moreover, the design allows for the velocity at which the specimen is struck to be varied independently of the force applied, thus allowing independent investigation into the effect of momentum or energy on fracture strength. Test specimens are supported on a low-friction bearing system, and receive the controlled impulse from a projectile of variable mass that is accelerated using pneumatics. The apparatus includes velocity sensors, a six-degree-of-freedom load cell, and an accelerometer to completely quantify the loading event. The apparatus’ performance was validated against an ATD lower leg. It was able to create impulse events with forces from 0.5 kN to 17.0 kN, and projectile speeds of 2.3–13.9 m/s. Various momenta could be achieved at a constant force level by varying the mass of the projectile, with a maximum difference of 65%, whereas kinetic energy was inherently linked to the impact force. This apparatus will be useful in future studies for determining the appropriateness of currently used injury limits for the lower limb to high-impulse events, as well as for quantifying the relationship between cadaveric fracture response and ATD measurements. This device can also be readily applied to other bones of the body, to create realistic fracture patterns for known injury mechanisms.
Increase in Opening Angle in Hypertension Off-Loads the Intimal Stress: A Simulation Study
Authors: Wang Chong , Kassab Ghassan S.
Published: September 2009

The stress distribution in the vessel wall has important bearing on vascular function including intima, media, and adventitia. The residual strain in the vessel wall has been thought to largely normalize the transmural stress distribution with slightly higher values at the intima. In hypertension, the compensatory increase in opening angle is thought to maintain a uniform stress distribution. We have recently shown that the circumferential stress at adventitia may exceed that at intima at physiological loading due to large opening angle (OA) in normal porcine coronary arteries. The objective of this study was to show that increases in opening angle subsequent hypertension can further shift the stress from the intima to the adventitia. The change in stress distribution during acute hypertension was calculated using available data on the changes in vessel geometry, material property, and internal pressure during hypertension. It was found that the increase in OA following acute hypertension off-loads the stress from intima to adventitia, therefore, relieving some of the stress increase in the intimal layer induced by the sudden pressure increase. This has important implications for hypertension where it may shift the excessive stress from the inner layer to the outer layer. This may be a protective mechanism for the intima layer in hypertension.
Accuracy of 3D Cartilage Models Generated From MR Images Is Dependent on Cartilage Thickness: Laser Scanner Based Validation of In Vivo Cartilage
Authors: Koo Seungbum , Giori Nicholas J. , Gold Garry E. , Dyrby Chris O. , Andriacchi Thomas P.
Published: September 2009

Cartilage morphology change is an important biomarker for the progression of osteoarthritis. The purpose of this study was to assess the accuracy of in vivo cartilage thickness measurements from MR image-based 3D cartilage models using a laser scanning method and to test if the accuracy changes with cartilage thickness. Three-dimensional tibial cartilage models were created from MR images (in-plane resolution of 0.55 mm and thickness of 1.5 mm) of osteoarthritic knees of ten patients prior to total knee replacement surgery using a semi-automated B-spline segmentation algorithm. Following surgery, the resected tibial plateaus were laser scanned and made into 3D models. The MR image and laser-scan based models were registered to each other using a shape matching technique. The thicknesses were compared point wise for the overall surface. The linear mixed-effects model was used for statistical test. On average, taking account of individual variations, the thickness measurements in MRI were overestimated in thinner (<2.5 mm) regions. The cartilage thicker than 2.5 mm was accurately predicted in MRI, though the thick cartilage in the central regions was underestimated. The accuracy of thickness measurements in the MRI-derived cartilage models systemically varied according to native cartilage thickness.
Accuracy of Inertial Motion Sensors in Static, Quasistatic, and Complex Dynamic Motion
Authors: Godwin Alison , Agnew Michael , Stevenson Joan
Published: September 2009

Inertial motion sensors (IMSs) combine three sensors to produce a reportedly stable and accurate orientation estimate in three dimensions. Although accuracy has been reported within the range of 2 deg of error by manufacturers, the sensors are rarely tested in the challenging motion present in human motion. Their accuracy was tested in static, quasistatic, and dynamic situations against gold-standard Vicon camera data. It was found that static and quasistatic rms error was even less than manufacturers’ technical specifications. Quasistatic rms error was minimal at 0.3 deg (±0.15 deg SD) on the roll axis, 0.29 deg (±0.20 deg SD) on the pitch axis, and 0.73 deg (±0.81 deg SD) on the yaw axis. The dynamic rms error was between 1.9 deg and 3.5 deg on the main axes of motion but it increased considerably on off-axis during planar pendulum motion. Complex arm motion in the forward reaching plane proved to be a greater challenge for the sensors to track but results are arguably better than previously reported studies considering the large range of motion used.
The Effect of the Shoe-Surface Interface in the Development of Anterior Cruciate Ligament Strain
Authors: Drakos Mark C. , Hillstrom Howard , Voos James E. , Miller Anna N. , Kraszewski Andrew P. , Wickiewicz Thomas L. , Warren Russell F. , Allen Answorth A. , O’Brien Stephen J.
Published: September 2009

The shoe-surface interface has been implicated as a possible risk factor for anterior cruciate ligament (ACL) injuries. The purpose of this study is to develop a biomechanical, cadaveric model to evaluate the effect of various shoe-surface interfaces on ACL strain. There will be a significant difference in ACL strain between different shoe-surface combinations when a standardized rotational moment (a simulated cutting movement) is applied to an axially loaded lower extremity. The study design was a controlled laboratory study. Eight fresh-frozen cadaveric lower extremities were thawed and the femurs were potted with the knee in 30 deg of flexion. Each specimen was placed in a custom-made testing apparatus, which allowed axial loading and tibial rotation but prevented femoral rotation. For each specimen, a 500 N axial load and a 1.5 Nm internal rotation moment were placed for four different shoe-surface combinations: group I (AstroTurf-turf shoes), group II (modern playing turf-turf shoes), group III (modern playing turf-cleats), and group IV (natural grass-cleats). Maximum strain, initial axial force and moment, and maximum axial force and moment were calculated by a strain gauge and a six component force plate. The preliminary trials confirmed a linear relationship between strain and both the moment and the axial force for our testing configuration. In the experimental trials, the average maximum strain was 3.90, 3.19, 3.14, and 2.16 for groups I–IV, respectively. Group IV had significantly less maximum strain (p<0.05) than each of the other groups. This model can reproducibly create a detectable strain in the anteromedial bundle of the ACL in response to a given axial load and internal rotation moment. Within the elastic range of the stress-strain curve, the natural grass and cleat combination produced less strain in the ACL than the other combinations. The favorable biomechanical properties of the cleat-grass interface may result in fewer noncontact ACL injuries.
Mechanical Stress Analysis of Microfluidic Environments Designed for Isolated Biological Cell Investigations
Authors: Kohles Sean S. , Nève Nathalie , Zimmerman Jeremiah D. , Tretheway Derek C.
Published: September 2009

Advancements in technologies for assessing biomechanics at the cellular level have led to discoveries in mechanotransduction and the investigation of cell mechanics as a biomarker for disease. With the recent development of an integrated optical tweezer with micron resolution particle image velocimetry, the opportunity to apply controlled multiaxial stresses to suspended single cells is available (Nève, N., Lingwood, J. K., Zimmerman, J., Kohles, S. S., and Tretheway, D. C., 2008, “The μPIVOT: An Integrated Particle Image Velocimetry and Optical Tweezers Instrument for Microenvironment Investigations,” Meas. Sci. Technol., 19(9), pp. 095403). A stress analysis was applied to experimental and theoretical flow velocity gradients of suspended cell-sized polystyrene microspheres demonstrating the relevant geometry of nonadhered spherical cells, as observed for osteoblasts, chondrocytes, and fibroblasts. Three flow conditions were assessed: a uniform flow field generated by moving the fluid sample with an automated translation stage, a gravity driven flow through a straight microchannel, and a gravity driven flow through a microchannel cross junction. The analysis showed that fluid-induced stresses on suspended cells (hydrodynamic shear, normal, and principal stresses in the range of 0.02–0.04 Pa) are generally at least an order of magnitude lower than adhered single cell studies for uniform and straight microchannel flows (0.5–1.0 Pa). In addition, hydrostatic pressures dominate (1–100 Pa) over hydrodynamic stresses. However, in a cross junction configuration, orders of magnitude larger hydrodynamic stresses are possible without the influence of physical contact and with minimal laser trapping power.
A NEURAL NETWORK MODEL FOR CREDIT RISK EVALUATION
Authors: KHASHMAN ADNAN
Published: September 2009

Credit scoring is one of the key analytical techniques in credit risk evaluation which has been an active research area in financial risk management. This paper presents a credit risk evaluation system that uses a neural network model based on the back propagation learning algorithm. We train and implement the neural network to decide whether to approve or reject a credit application, using seven learning schemes and real world credit applications from the Australian credit approval datasets. A comparison of the system performance under the different learning schemes is provided, furthermore, we compare the performance of two neural networks; with one and two hidden layers following the ideal learning scheme. Experimental results suggest that neural networks can be effectively used in automatic processing of credit applications.
A FULLY COMPLEX-VALUED RADIAL BASIS FUNCTION NETWORK AND ITS LEARNING ALGORITHM
Authors: SAVITHA R. , SURESH S. , SUNDARARAJAN N.
Published: September 2009

In this paper, a fully complex-valued radial basis function (FC-RBF) network with a fully complex-valued activation function has been proposed, and its complex-valued gradient descent learning algorithm has been developed. The fully complex activation function, sech(.) of the proposed network, satisfies all the properties needed for a complex-valued activation function and has Gaussian-like characteristics. It maps Cn → C, unlike the existing activation functions of complex-valued RBF network that maps Cn → R. Since the performance of the complex-RBF network depends on the number of neurons and initialization of network parameters, we propose a K-means clustering based neuron selection and center initialization scheme. First, we present a study on convergence using complex XOR problem. Next, we present a synthetic function approximation problem and the two-spiral classification problem. Finally, we present the results for two practical applications, viz., a non-minimum phase equalization and an adaptive beam-forming problem. The performance of the network was compared with other well-known complex-valued RBF networks available in literature, viz., split-complex CRBF, CMRAN and the CELM. The results indicate that the proposed fully complex-valued network has better convergence, approximation and classification ability.
NOVEL STABILITY CRITERIA ON DISCRETE-TIME NEURAL NETWORKS WITH BOTH TIME-VARYING AND DISTRIBUTED DELAYS
Authors: LI TAO , SONG AIGUO , FEI SHUMIN
Published: September 2009

This paper investigates robust exponential stability for discrete-time recurrent neural networks with both time-varying delay (0 ≤ τm ≤ τ(k) ≤ τM) and distributed one. Through partitioning delay intervals [0,τm] and [τm,τM], respectively, and choosing an augmented Lyapunov-Krasovskii functional, the delay-dependent sufficient conditions are obtained by using free-weighting matrix and convex combination methods. These criteria are presented in terms of linear matrix inequalities (LMIs) and their feasibility can be easily checked by resorting to LMI in Matlab Toolbox in Ref. 1. The activation functions are not required to be differentiable or strictly monotonic, which generalizes those earlier forms. As an extension, we further consider the robust stability of discrete-time delayed Cohen-Grossberg neural networks. Finally, the effectiveness of the proposed results is further illustrated by three numerical examples in comparison with the reported ones.
SOUTH-SOUTH TRADE AND APPROPRIATE TECHNOLOGY TRANSFERS AMONG AGRO-FOOD SMES: THE CASE OF SOUTHEAST ASIA AND WESTERN AFRICA
Authors: REGNIER PHILIPPE
Published: September 2009

This article reviews some results of a policy research project addressing agro-food SME trade promotion in Southeast Asian and Western African developing economies. The project was conducted by a group of scientific institutions based in Hanoi (Vietnam), Ouagadougou (Burkina Faso) and Geneva (Switzerland). The article documents the capacity of Southeast Asian and Western African agro-food SMEs to access domestic, regional and possibly global markets, as well as the role of international cooperation (public and private) to promote agro-food SME trade within and outside Southeast Asia, and Western Africa respectively. The article also calls for interested OECD and non-OECD partners to contribute to two types of South-South trade emerging innovations in the field of SME agro-business matching, namely, the promotion of existing and new business linkages between Southeast Asian and Western African agro-food SMEs (trade, finance and appropriate technology transfer), and the promotion of public-private partnerships to facilitate such agro-food SME business linkages between far distant Southeast Asia and Western Africa.
POLICY SUPPORT FOR INFORMAL SECTOR ENTREPRENEURSHIP: MICRO-ENTERPRISES IN INDIA
Authors: GURTOO ANJULA
Published: September 2009

This paper highlights the presence of a hidden enterprise culture in the Indian informal economy (versus a necessity driven view) and draws a developmental framework to harness micro-enterprise owners. Policy research has typically taken a welfare approach toward studying the informal sector in the developing countries. Therefore, the agenda has been to create a favorable environment for survival instead of cultivating entrepreneurship and facilitating their growth. Conversely, this paper explores a strategic orientation for the informal sector. The proposed framework balances entrepreneurial spirit of the individuals, market dynamics of the economy, and socio-economic imperatives of a developing nation. Implications for research and policy are also drawn.
AN ANALYSIS OF THE ROLE OF GENDER AND SELF-EFFICACY IN DEVELOPING FEMALE ENTREPRENEURIAL INTEREST AND BEHAVIOR
Authors: WILSON FIONA , KICKUL JILL , MARLINO DEBORAH , BARBOSA SAULO D. , GRIFFITHS MARK D.
Published: September 2009

To capture the talents of the next generations in new venture creation and to maintain the levels of entrepreneurship in our society, a vibrant "pipeline" of potential entrepreneurs is required. Previous research has shown this pipeline may still be weak, especially for women entrepreneurs. This paper explores the relationships between gender, entrepreneurial education, and entrepreneurial self-efficacy on entrepreneurial intentions and behaviors using the data from different sample groups in three different stages of education and career development: middle and high school students, MBA students, and early career adults. The results of our analyses underscore the importance of entrepreneurial self-efficacy as a key component in understanding entrepreneurship interest and actual career choice. The positive influence of entrepreneurship education on self-efficacy proved stronger for women than for men. Implications for entrepreneurship educators as well as study limitations and areas for future research are discussed.
STAKEHOLDERS, SPATIAL LOCATIONS AND TIME HORIZONS IN AN EXTENDED SOCIAL COST-BENEFIT ANALYSIS: A CASE OF PIPALPANKHA WATER RESOURCE PROJECT
Authors: RAM BABU P. , RAMAKRISHNA NALLATHIGA
Published: September 2009

Cost-Benefit Analysis (CBA) has been serving as an important tool for decision making with regard to the development projects involving large investments. The Social Cost-Benefit Analysis (SCBA) is an extension of the CBA to certain social impacts, which hitherto were not measured. As the impacts of development projects on ecology and environment assumed importance, measuring the corresponding costs and benefits also began to assume significance. With the advancement in economic valuation techniques over time, measurement could be done and the framework of SCBA has been extended to incorporate the same. Moreover, unlike the CBAs, which do not account for the distributional aspects, the SCBA can potentially account for these. This paper presents a case study of extending the SCBA framework to include social and environmental impacts of a large water resource development project in India. It emphasises the distribution of project benefits and costs over stakeholders, spatial locations and time horizons so as to demonstrate the utility of extended SCBA in project decision making. It is observed that both the numeraire measure i.e. cost-benefit ratio, as well as the distributional analysis present a favourable case for the project.
Insect Fat Body: Energy, Metabolism, and Regulation
Authors: Arrese Estela L. , Soulages Jose L.
Published: September 2009

The fat body plays major roles in the life of insects. It is a dynamic tissue involved in multiple metabolic functions. One of these functions is to store and release energy in response to the energy demands of the insect. Insects store energy reserves in the form of glycogen and triglycerides in the adipocytes, the main fat body cell. Insect adipocytes can store a great amount of lipid reserves as cytoplasmic lipid droplets. Lipid metabolism is essential for growth and reproduction and provides energy needed during extended nonfeeding periods. This review focuses on energy storage and release and summarizes current understanding of the mechanisms underlying these processes in insects.
Woody Plant Diversity, Evolution, and Ecology in the Tropics: Perspectives from Seasonally Dry Tropical Forests
Authors: Pennington R. Toby , Lavin Matt , Oliveira-Filho Ary
Published: September 2009

This review suggests that the ecology and patchy global distribution of seasonally dry tropical forest (SDTF) has distinctively structured the evolutionary history and biogeography of woody plant groups that are confined to it. SDTFs have few widespread woody plant species causing high β-diversity between separate areas of forests. These separate areas contain geologically old, monophyletic clades of endemic plant species that often have geographically structured intraspecific genetic variation. These patterns of diversity, endemism, and phylogeny indicate a stable, dispersal-limited SDTF system. SDTF species tend to belong to larger clades confined to this vegetation, exemplifying phylogenetic niche conservatism, and we argue that this is evidence that the SDTF is a metacommunity (biome) for woody plant clades. That phylogenetic, population genetic, biogeographic, and community ecological patterns differ in woody plants from tropical rain forests and savannas suggests a hypothesis that broad ecological settings strongly influence plant diversification in the tropics.
Small-Scale Properties of Turbulent Rayleigh-Bénard Convection
Authors: Lohse Detlef , Xia Ke-Qing
Published: September 2009

The properties of the structure functions and other small-scale quantities in turbulent Rayleigh-Bénard convection are reviewed, from an experimental, theoretical, and numerical point of view. In particular, we address the question of whether, and if so where in the flow, the so-called Bolgiano-Obukhov scaling exists, i.e., Sθ(r) ∼ r2/5 for the second-order temperature structure function and Su(r) ∼ r6/5 for the second-order velocity structure function. Apart from the anisotropy and inhomogeneity of the flow, insufficiently high Rayleigh numbers, and intermittency corrections (which all hinder the identification of such a potential regime), there are also reasons, as a matter of principle, why such a scaling regime may be limited to at most a decade, namely the lack of clear scale separation between the Bolgiano length scale LB and the height of the cell.
Recent advances in understanding leptin signaling and leptin resistance
Authors: Morris David L. , Rui Liangyou
Published: September 2009

The brain controls energy homeostasis and body weight by integrating various metabolic signals. Leptin, an adipose-derived hormone, conveys critical information about peripheral energy storage and availability to the brain. Leptin decreases body weight by both suppressing appetite and promoting energy expenditure. Leptin directly targets hypothalamic neurons, including AgRP and POMC neurons. These leptin-responsive neurons widely connect to other neurons in the brain, forming a sophisticated neurocircuitry that controls energy intake and expenditure. The anorexigenic actions of leptin are mediated by LEPRb, the long form of the leptin receptor, in the hypothalamus. LEPRb activates both JAK2-dependent and -independent pathways, including the STAT3, PI 3-kinase, MAPK, AMPK, and mTOR pathways. These pathways act coordinately to form a network that fully mediates leptin response. LEPRb signaling is regulated by both positive (e.g., SH2B1) and negative (e.g., SOCS3 and PTP1B) regulators and by endoplasmic reticulum stress. Leptin resistance, a primary risk factor for obesity, likely results from impairment in leptin transport, LEPRb signaling, and/or the neurocircuitry of energy balance.
Ontogeny of methionine utilization and splanchnic uptake in critically ill children
Authors: Verbruggen Sascha , Sy Jama , Gordon William E. , Hsu Jean , Wu Manhong , Chacko Shaji , Zurakowski David , Burrin Douglas , Castillo Leticia
Published: September 2009

To determine the rates of methionine splanchnic uptake and utilization in critically ill pediatric patients we used two kinetic models: the plasma methionine enrichment and the “intracellular” homocysteine enrichment. Twenty four patients, eight infants, eight children, and eight adolescents, were studied. They received simultaneous, primed, constant, intravenous infusions of l-[2H3]methylmethionine and enteral l-[1-13C]methionine. The ratio of [13C]homocysteine to [13C]methionine enrichment was 1.0 ± 0.15, 0.80 ± 0.20, and 0.66 ± 0.10, respectively, for the infants, children, and adolescents, and it was different between the infants and adolescents ( P < 0.01). Methionine splanchnic uptake was 63, 45, and 36%, respectively, in the infants, children, and adolescents, and it was higher ( P < 0.01) in the infants compared with the adolescents. The infants utilized 73% of methionine flux for nonoxidative disposal, while 27% was used for transulfuration ( P < 0.001). Conversely, in the adolescents, 40% was utilized for nonoxidative disposal, while 60% was used for transulfuration. There is ontogeny on the rates of methionine splanchnic uptake and on the fate of methionine utilization in critically ill children, with greater methionine utilization for synthesis of proteins and methionine-derived compounds ( P < 0.01) and decreased transulfuration rates in the infants ( P < 0.01), while the opposite was observed in the adolescents. The plasma model underestimated methionine kinetics in children and adolescents but not in the infants, suggesting lesser dilution and greater compartmentation of methionine metabolism in the infant population. All patients were in negative methionine balance, indicating that the current enteral nutritional support is inadequate in these patients.
Restoring AS160 phosphorylation rescues skeletal muscle insulin resistance and fatty acid oxidation while not reducing intramuscular lipids
Authors: Alkhateeb Hakam , Chabowski Adrian , Glatz Jan F. C. , Gurd Brendon , Luiken Joost J. F. P. , Bonen Arend
Published: September 2009

We examined whether AICAR or leptin rapidly rescued skeletal muscle insulin resistance via increased palmitate oxidation, reductions in intramuscular lipids, and/or restoration of insulin-stimulated AS60 phosphorylation. Incubation with palmitate (2 mM, 0–18 h) induced insulin resistance in soleus muscle. From 12–18 h, palmitate was removed or AICAR or leptin was provided while 2 mM palmitate was maintained. Palmitate oxidation, intramuscular triacylglycerol, diacylglycerol, ceramide, AMPK phosphorylation, basal and insulin-stimulated glucose transport, plasmalemmal GLUT4, and Akt and AS160 phosphorylation were examined at 0, 6, 12, and 18 h. Palmitate treatment (12 h) increased intramuscular lipids (triacylglycerol +54%, diacylglycerol +11%, total ceramide +18%, C16:0 ceramide +60%) and AMPK phosphorylation (+118%), whereas it reduced fatty acid oxidation (−60%) and insulin-stimulated glucose transport (−70%), GLUT4 translocation (−50%), and AS160 phosphorylation (−40%). Palmitate removal did not rescue insulin resistance or associated parameters. The AICAR and leptin treatments did not consistently reduce intramuscular lipids, but they did rescue palmitate oxidation and insulin-stimulated glucose transport, GLUT4 translocation, and AS160 phosphorylation. Increased AMPK phosphorylation was associated with these improvements only when AICAR and leptin were present. Hence, across all experiments, AMPK phosphorylation did not correlate with any parameters. In contrast, palmitate oxidation and insulin-stimulated AS160 phosphorylation were highly correlated ( r = 0.83). We speculate that AICAR and leptin activate both of these processes concomitantly, involving activation of unknown kinases in addition to AMPK. In conclusion, despite the maintenance of high concentrations of palmitate (2 mM), as well as increased concentrations of intramuscular lipids (triacylglycerol, diacylglycerol, and ceramide), the rapid AICAR- and leptin-mediated rescue of palmitate-induced insulin resistance is attributable to the restoration of insulin-stimulated AS160 phosphorylation and GLUT4 translocation.
Renal dopaminergic defect in C57Bl/6J mice
Authors: Escano Crisanto S. , Armando Ines , Wang Xiaoyan , Asico Laureano D. , Pascua Annabelle , Yang Yu , Wang Zheng , Lau Yuen-Sum , Jose Pedro A.
Published: September 2009

The C57Bl/6J mouse strain, the genetic background of many transgenic and gene knockout models, is salt sensitive and resistant to renal injury. We tested the hypothesis that renal dopaminergic function is defective in C57Bl/6J mice. On normal NaCl (0.8%, 1 wk) diet, anesthetized and conscious (telemetry) blood pressures were similar in C57Bl/6J and SJL/J mice. High NaCl (6%, 1 wk) increased blood pressure (≈30%) in C57Bl/6J but not in SJL/J mice and urinary dopamine to greater extent in SJL/J than in C57Bl/6J mice. Absolute and fractional sodium excretions were lower in SJL/J than in C57Bl/6J mice. The blood pressure-natriuresis plot was shifted to the right in C57Bl/6J mice. Renal expressions of D1-like (D1R and D5R) and angiotensin II AT1 receptors were similar on normal salt, but high salt increased D5R only in C57Bl/6J. GRK4 expression was lower on normal but higher on high salt in C57Bl/6J than in SJL/J mice. Salt increased the excretion of microalbumin and 8-isoprostane (oxidative stress marker) and the degree of renal injury to a greater extent in SJL/J than in C57Bl/6J mice. A D1-like receptor agonist increased sodium excretion whereas a D1-like receptor antagonist decreased sodium excretion in SJL/J but not in C57Bl/6J mice. In contrast, parathyroid hormone had a similar natriuretic effect in both strains. These results show that defective D1-like receptor function is a major cause of salt sensitivity in C57Bl/6J mice, decreased renal dopamine production might also contribute. The relative resistance to renal injury of C57Bl/6J may be a consequence of decreased production of reactive oxygen species.
Hindbrain leptin receptor stimulation enhances the anorexic response to cholecystokinin
Authors: Williams Diana L. , Baskin Denis G. , Schwartz Michael W.
Published: September 2009

Leptin is thought to reduce food intake, in part, by increasing sensitivity to satiation signals, including CCK. Leptin action in both forebrain and hindbrain reduces food intake, and forebrain leptin action augments both the anorexic and neuronal activation responses to CCK. Here, we asked whether leptin signaling in hindbrain also enhances these responses to CCK. We found that food intake was strongly inhibited at 30 min after a combination of 4th-intracerebroventricular (4th-icv) leptin injection and intraperitoneal CCK administration, whereas neither hormone affected intake during this period when given alone. Leptin injections targeted directly at the dorsal vagal complex (DVC) similarly enhanced the anorexic response to intraperitoneal CCK. Intra-DVC leptin injection also robustly increased the number of neurons positive for phospho-STAT3 staining in the area surrounding the site of injection, confirming local leptin receptor activation. Conversely, the anorexic response to 4th-icv leptin was completely blocked by IP devazepide, a CCKA-R antagonist, suggesting that hindbrain leptin reduces intake via a mechanism requiring endogenous CCK signaling. We then asked whether hindbrain leptin treatment enhances the dorsomedial hindbrain, hypothalamus, or amygdala c-Fos responses to IP CCK. We found that, in contrast to the effects of forebrain leptin administration, 4th-icv leptin injection had no effect on CCK-induced c-Fos in any structures examined. We conclude that leptin signaling in either forebrain or hindbrain areas can enhance the response to satiation signals and that multiple distinct neural circuits likely contribute to this interaction.
High-fat diets induce a rapid loss of the insulin anorectic response in the amygdala
Authors: Boghossian Stéphane , Lemmon Karalee , Park MieJung , York David A.
Published: September 2009

Intracerebroventricular insulin decreases food intake (FI) . The central bed nucleus of the amygdala (CeA), as other regions of the brain regulating feeding behavior, expresses insulin receptors. Our objectives were to show an insulin anorectic response in the amygdala, study the effect of high-fat diets on this response, and map the neural network activated by CeA insulin using c-Fos immunohistochemistry. Sprague-Dawley (SD) rats fitted with unilateral CeA cannulas were adapted to a low-fat (LFD) diet before they were fed a high-fat diet (HFD). Their feeding response to CeA saline or insulin (8 mU) was tested after 24 h, 72 h, or 7 days of being on a HFD. In a second experiment, SD rats were fed the HFD for 3, 7, or 49 days and were then refed with the LFD. They were tested for their insulin response before and after an HFD and every 3 days for the following weeks. Insulin tolerance tests were performed in a parallel group of rats. The CeA insulin stimulation c-Fos expression was studied to identify the distribution of activated neuronal populations. Feeding an HFD for 72 h or more induced a CeA, but not peripheral, insulin resistance, which was slowly reversed by LFD refeeding. The duration of HFD feeding determined the time frame for reversal of the insulin resistance. CeA insulin increased c-Fos in multiple brain regions, including the arcuate nucleus/paraventricular nucleus region of the hypothalamus. We conclude that the amygdala may be an important site for insulin regulation of food intake and may have a significant role in determining susceptibility to HFD-induced obesity.
Lack of periostin leads to suppression of Notch1 signaling and calcific aortic valve disease
Authors: Tkatchenko Tatiana V. , Moreno-Rodriguez Ricardo A. , Conway Simon J. , Molkentin Jeffery D. , Markwald Roger R. , Tkatchenko Andrei V.
Published: September 2009

The Postn gene encodes protein periostin. During embryonic development, it is highly expressed in the outflow tract (OFT) endocardial cushions of the developing heart, which give rise to several structures of the mature heart including the aortic valve. Periostin was previously implicated in osteoblast differentiation, cancer metastasis, and tooth and bone development, but its role in cardiac OFT development is unclear. To elucidate the role that periostin plays in the developing heart we analyzed cardiac OFT phenotype in mice after deletion of the Postn gene. We found that lack of periostin in the embryonic OFT leads to ectopic expression of the proosteogenic growth factor pleiotrophin ( Ptn) and overexpression of delta-like 1 homolog (Dlk1), a negative regulator of Notch1, in the distal (prevalvular) cushions of the OFT. This resulted in suppression of Notch1 signaling, strong induction of the central transcriptional regulator of osteoblast cell fate Runx2, upregulation of osteopontin and osteocalcin expression, and subsequent calcification of the aortic valve. Our data suggest that periostin represses a default osteogenic program in the OFT cushion mesenchyme and promotes differentiation along a fibrogenic lineage. Lack of periostin causes derepression of the osteogenic potential of OFT mesenchymal cells, calcium deposition, and calcific aortic valve disease. These results establish periostin as a key regulator of OFT endocardial cushion mesenchymal cell fate during embryonic development.
miR-290 acts as a physiological effector of senescence in mouse embryo fibroblasts
Authors: Pitto Letizia , Rizzo Milena , Simili Marcella , Colligiani Daria , Evangelista Monica , Mercatanti Alberto , Mariani Laura , Cremisi Federico , Rainaldi Giuseppe
Published: September 2009

The culture-induced senescence of mouse embryo fibroblasts (MEF) correlates with reduction of cell proliferation. In this work we found that the accumulation of cells with 4C DNA content and the transcriptional change of several microRNAs (miRNAs or miRs) are relevant events in culture senescence. By comparing the miRNA expression profiles of physiologically senescent MEF and that of senescent MEF induced by the downregulation of leukemia-related factor, we identified miR-290 as a common upregulated miRNA. When miR-290 was transfected in presenescent MEF, SA-β-gal+ cells and p16, two markers of culture senescence, increased compared with control, indicating that miR-290 is causally involved in senescence. Interestingly, nocodazole (NCZ), which induces G2/M block, increased the percentage of senescent cells as well as the expression of miR-290 and of the tumor suppressor p16, thus mimicking culture senescence. As miR-290 was overexpressed in NCZ-treated cells and it was able to induce senescence in proliferating MEF, we investigated whether miR-290 and NCZ could share common mechanisms of culture senescence. Whereas the induction of SA-β-gal+ by miR-290 was not strengthened by coupling its transfection with NCZ treatment, the transfection of the antagomir 290 (d-290) plus NCZ treatment, while blocking cells at G2/M, suppressed SA-β-gal+ and p16 induction. On the basis of these findings we conclude that miR-290 might act as a physiological effector of NCZ induced as well as culture senescence via p16 regulation expanding the role of this miRNA from embryonic stem to differentiated cells.