bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Analysis of Transient Behavior of Polymer Electrolyte Membrane Fuel Cell Hybrid Vehicles
Authors: Arsie Ivan , Di Domenico Alfonso , Pianese Cesare , Sorrentino Marco
Published: August 2007

The paper focuses on the simulation of a hybrid vehicle with proton exchange membrane fuel cell as the main energy conversion system. A modeling structure has been developed to perform accurate analysis for powertrain and control system design. The models simulate the dynamics of the main powertrain elements and fuel cell system to give a sufficient description of the complex interaction between each component under real operating conditions. A control system based on a multilevel scheme has also been introduced and the complexity of control issues for hybrid powertrains have been discussed. This study has been performed to analyze the energy flows among powertrain components. The results highlight that optimizing these systems is not a trivial task and the use of precise models can improve the powertrain development process. Furthermore, the behavior of system state variables and the influence of control actions on fuel cell operation have also been analyzed. In particular, the effect of introducing a rate limiter on the stack power has been investigated, evidencing that a 2kW∕s rate limiter increased the system efficiency by 10% while reducing the dynamic performance of the powertrain in terms of speed error.
Molten Carbonate Fuel Cell Dynamical Modeling
Authors: Bittanti Sergio , Canevese Silvia , De Marco Antonio , Giuffrida Giorgio , Errigo Antonio , Prandoni Valter
Published: August 2007

The aim of this work is to build up a complete dynamical model of a molten carbonate fuel cell (MCFC) stack, describing both the thermo-fluid-dynamical and the electrochemical phenomena involved, i.e., both slow and (relatively) fast dynamics. Following a first-principle approach, a set of differential and algebraic equations is written, based on mass, momentum, energy, and charge balance referred to as small control volumes inside a cell. The outlined two-three-dimensional description takes into account the strong point-to-point anode and cathode reaction coupling due to gas crossflow. Simulations (carried out after suitable thermodynamical and electrochemical parameter tuning) highlight, for instance, the presence of dynamics, linked to the electrochemical behavior, with time constants on the order of a second; besides, rather fair matching to data which can be found in the literature is achieved, in terms of external potential difference and of electric power production. The obtained numerical results, therefore, support model correctness and reliability. This is useful in view of model-based cell operation analysis and control, both in stationary and in transient conditions.
Numerical Analysis of Thermal Behavior of Small Solid Oxide Fuel Cell Systems
Authors: Shimada Takanobu , Kato Tohru , Tanaka Yohei
Published: August 2007

Recently, small solid oxide fuel cell (SOFC) systems have been developed for various applications because of their high performance. In such small generation systems, quick and frequent start-stops are often required. However, it is generally considered that these start-stops with SOFC systems are not preferable because SOFC systems are operated at high temperature. Also, quantitative studies on the thermal behavior of small SOFC systems are limited. The purpose of this paper is to obtain insight into the possibility of using small SOFC systems with quick and frequent start-stops. A simple two-dimensional numerical model for 1kW-class SOFC systems was fabricated to study this problem. The model consists of a cylindrical SOFC stack, a prereformer on the stack, a heat exchanger for exhaust gas, and a thermal insulator that covers the stack and the prereformer. Using this model, first, the characteristics of the power generation efficiency were estimated under various operating conditions. In addition, the validity of the modeling was verified. Next, the start-up dependence on their structure and operating conditions was investigated. Finally, for the cyclic daily start-up and shutdown (DSS) procedure, the total efficiency during a day was calculated when the energy loss during start-stops is considered. As a result of the analysis, the following points were found. First, the validity and accuracy of the modeling was established, and their efficiency under the rated condition becomes 60% (DC/HHV) at a steam-carbon ratio=2.5 and an oxygen utilization=50%. Next, the thickness of the thermal insulator (0.03W∕m∕K) is required to be more than 6cm to reduce the heat loss from the outer surface of the thermal insulator to <5% of the provided fuel energy (2kW) under the rated condition. In this case, it takes ca. 150min to start, if the fuel (methane) flow rate is 3.02NL∕min, which is equivalent to 2kW of heat flow. Finally, for the DSS operation, consisting of repetition of a 16h operation and an 8h stop in a day, the total efficiency decreases by ca. 1.5% from the rated power generation efficiency. Therefore, it is clarified that 1kW-class SOFC systems can be quite suitable even in the case where quick and frequent start-stops are required.
Particle Image Velocimetry Measurements in a Model Proton Exchange Membrane Fuel Cell
Authors: Feser J. P. , Prasad A. K. , Advani S. G.
Published: August 2007

Particle image velocimetry was used to measure 2D velocity fields in representative regions of interest within flow channels of interdigitated and single-serpentine proton exchange membrane (PEM) fuel cell models. The model dimensions, gas diffusion layer (GDL) permeability, working fluid, and flow rates were selected to be geometrically and dynamically similar to the cathode-side airflow in a typical PEM fuel cell. The model was easily reconfigurable between parallel, single-serpentine, and interdigitated flow fields, and was constructed from transparent materials to enable optical imaging. Velocity maps were obtained of both the primary and secondary flow within the channels. Measurements of the secondary flows in interdigitated and single-serpentine flow fields indicate that significant portions of the flow travel between adjacent channels through the porous medium. Such convective bypass can enhance fuel cell performance by supplying fresh reactant to the lands regions and also by driving out product water from under the lands to the flow channels.
Innovative Flow-Field Combination Design on Direct Methanol Fuel Cell Performance
Authors: Jung Guo-Bin , Su Ay , Tu Cheng-Hsin , Weng Fang-Bor , Chan Shih-Hung
Published: August 2007

The flow-field design of direct methanol fuel cells (DMFCs) is an important subject about DMFC performance. Flow fields play an important role in the ability to transport fuel and drive out the products (H2O,CO2). In general, most fuel cells utilize the same structure of flow field for both anode and cathode. The popular flow fields used for DMFCs are parallel and grid designs. Nevertheless, the characteristics of reactants and products are entirely different in anode and cathode of DMFCs. Therefore, the influences of flow fields design on cell performance were investigated based on the same logic with respect to the catalyst used for cathode and anode nonsymmetrically. To get a better and more stable performance of DMFCs, three flow fields (parallel, grid, and serpentine) utilized with different combinations were studied in this research. As a consequence, by using parallel flow field in the anode side and serpentine flow-field in the cathode, the highest power output was obtained.
Investigation of Different Methods to Control a Small Variable-Speed Wind Turbine With PMSM Drives
Authors: Belhadj Jamel , Roboam Xavier
Published: August 2007

In this paper, a different control strategy of a small wind generator, including a permanent magnet synchronous machine (PMSM), has been studied. The objective is to analyze the produced power quality of small wind turbines connected to weak AC grids. The extraction of the electrical energy from the wind turbine is based on a maximum power point tracking (MPPT) algorithm to control a pulse width modulation (PWM) rectifier. The grid connection is realized by means of a PWM voltage source inverter via a filter. This inverter is controlled by three different methods based on current or active and reactive power control. These methods are applicable for different power ranges. The obtained results demonstrate the efficiency of the system and the energetic contribution, mainly for rural weak AC grids.
Effect of Fuel Moisture on Combustion in a Bagasse Fired Furnace
Authors: Shanmukharadhya K. S. , Sudhakar K. G.
Published: August 2007

Sugar cane bagasse, a biomass material that is readily available, has been used as a fuel for well over 4 decades. However, combustion of bagasse has its own special set of problems which appear to be due largely to the high moisture content of the fuel. In this present research work, in order to gain insight into the effect of moisture on the flame front, an experimental program is carried out on an operating, industrial size bagasse-fired furnace. The furnace is modeled by the three-dimensional CFD package FLUENT. The results of modeling show a considerable delay to ignition due to the drying of fuel. The effect of fuel moisture on drying and heating up of the fuel is the key feature for the investigation done in this work.
Development of a Novel Combined Absorption Cycle for Power Generation and Refrigeration
Authors: Zhang Na , Lior Noam
Published: August 2007

Cogeneration can improve energy utilization efficiency significantly. In this paper, a new ammonia-water system is proposed for the cogeneration of refrigeration and power. The plant operates in a parallel combined cycle mode with an ammonia-water Rankine cycle and an ammonia refrigeration cycle, interconnected by absorption, separation, and heat transfer processes. The performance was evaluated by both energy and exergy efficiencies, with the latter providing good guidance for system improvement. The influences of the key parameters, which include the basic working solution concentration, the cooling water temperature, and the Rankine cycle turbine inlet parameters on the cycle performance, have been investigated. It is found that the cycle has a good thermal performance, with energy and exergy efficiencies of 27.7% and 55.7%, respectively, for the base-case studied (having a maximum cycle temperature of 450°C). Comparison with the conventional separate generation of power and refrigeration having the same outputs shows that the energy consumption of the cogeneration cycle is markedly lower. A brief review of desirable properties of fluid pairs for such cogeneration cycles was made, and detailed studies for finding new fluid pairs and the impact of their properties on cogeneration system performance are absent and are very recommended.
Quantitative interpretation of gold nanoparticle-based bioassays designed for detection of immunocomplex formation
Authors: Zhou Ye , Xu Hongxing , Dahlin Andreas B. , Vallkil Jacob , Borrebaeck Carl A. K. , Wingren Christer , Liedberg Bo , Hööka Fredrik
Published: August 2007

The authors present in this paper how the extended Mie theory can be used to translate not only end-point data but also temporal variations of extinction peak-position changes, δλpeak(t), into absolute mass uptake, Γ(t), upon biomacromolecule binding to localized surface plasmon resonance (SPR) active nanoparticles (NPs). The theoretical analysis is applied on a novel sensor template composed of a three-layer surface architecture based on (i) a self-assembled monolayer of HS(CH2)15COOH, (ii) a 1:1 mixture of biotinylated and pure poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), and (iii) NeutrAvidin. Assisted by independent estimations of the thickness of the three-layer architecture using quartz crystal microbalance with dissipation (QCM-D) monitoring, excellent agreement with parallel mass-uptake estimations using planar SPR is obtained. Furthermore, unspecific binding of serum to PLL-g-PEG was shown to be below the detection limit, making the surface architecture ideally suited for label-free detection of immunoreactions. To ensure that the immunocomplex formation occurred within the limited sensing depth (∼10 nm) of the NPs, a compact model system composed of a biotinylated human recombinant single-chain antibody fragment (∅∼2 nm) directed against cholera toxin was selected. By tracking changes in the centroid (center of mass) of the extinction peak, rather than the actual peak position, signal-to-noise levels and long-term stability upon cholera toxin detection are demonstrated to be competitive with results obtained using conventional SPR and state-of-the-art QCM-D data.
Molecular-scale structural and functional characterization of sparsely tethered bilayer lipid membranes
Authors: McGillivray Duncan J. , Valincius Gintaras , Vanderah David J. , Febo-Ayala Wilma , Woodward John T. , Heinrich Frank , Kasianowicz John J. , Lösche Mathias
Published: August 2007

Surface-tethered biomimetic bilayer membranes (tethered bilayer lipid membranes (tBLMs)) were formed on gold surfaces from phospholipids and a synthetic 1-thiahexa(ethylene oxide) lipid, WC14. They were characterized using electrochemical impedance spectroscopy, neutron reflection (NR), and Fourier-transform infrared reflection-absorption spectroscopy (FT-IRRAS) to obtain functional and structural information. The authors found that electrically insulating membranes (conductance and capacitance as low as 1 μS cm−2 and 0.6 μF cm−2, respectively) with high surface coverage (>95% completion of the outer leaflet) can be formed from a range of lipids in a simple two-step process that consists of the formation of a self-assembled monolayer (SAM) and bilayer completion by “rapid solvent exchange.” NR provided a molecularly resolved characterization of the interface architecture and, in particular, the constitution of the space between the tBLM and the solid support. In tBLMs based on SAMs of pure WC14, the hexa(ethylene oxide) tether region had low hydration even though FT-IRRAS showed that this region is structurally disordered. However, on mixed SAMs made from the coadsorption of WC14 with a short-chain “backfiller,” ß-mercaptoethanol, the submembrane spaces between the tBLM and the substrates contained up to 60% exchangeable solvent by volume, as judged from NR and contrast variation of the solvent. Complete and stable “sparsely tethered” BLMs (stBLMs) can be readily prepared from SAMs chemisorbed from solutions with low WC14 proportions. Phospholipids with unsaturated or saturated, straight or branched chains all formed qualitatively similar stBLMs.
Characterization of protein resistant, grafted methacrylate polymer layers bearing oligo(ethylene glycol) and phosphorylcholine side chains by neutron reflectometry
Authors: Feng Wei , Nieh Mu-Ping , Zhu Shiping , Harroun Thad A. , Katsaras John , Brash John L.
Published: August 2007

Neutron reflectometry was used to investigate the structures of end-tethered protein resistant polymer layers based on poly(oligo(ethylene glycol) methyl ether methacrylate) [poly(OEGMA)] and poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)]. Layers having different graft densities were studied in both the dry and wet states. A stretched parabolic model was used to fit the neutron data, resulting in a one-dimensional scattering length density profile of the polymer volume fraction normal to the film. Measured in D2O, the cutoff thicknesses of OEGMA and MPC layers at high graft density (0.39 chains/nm2 for OEGMA and 0.30 chains/nm2 for MPC) and a chain length of 200 repeat units were 450 and 470 Å, respectively, close to their contour length of 500 Å, suggesting that the grafts become highly hydrated when exposed to water. It was also found that at similar graft density and chain length, the volume fraction profiles of poly(OEGMA) and poly(MPC) layers are similar, in line with the authors’ previous results showing that these surfaces have similar protein resistance [W. Feng et al., BioInterphases 1, 50 (2006)]. The possible correlation of protein resistance to water content as indicated by the average number of water molecules per ethylene oxide (Nw,EO) or phosphorylcholine (Nw,PC) moiety was investigated. Nw,EO and Nw,PC, estimated from the volume fraction data, increased with decreasing graft density, and when compared to the reported number of water molecules in the hydration layers of EO and PC residues, led to the conclusion that water content slightly greater than the water of hydration resulted in protein resistant surfaces, whereas water content either less than or greatly in excess of the water of hydration resulted in layers of reduced protein resistance.
Caught in the Draft
Authors: Edge Ron
Published: August 2007

We've all seen (in movies, newscasts, or perhaps in person) the violent effect of the downwash that occurs when a helicopter hovers over the ground. Leaves, grass, and debris are dramatically blown about. We've also sat in front of circulating room fans and felt a large draft, whereas there seems to be very little air movement behind the fan. The cause of this is a delightful manifestation of Bernoulli's principle. The fan blades, or helicopter rotor blades, produce a pressure differential as air passes through them—let us say p1 before and p2 after, as shown in Fig. 1, with p2 greater than p1. If p0 is the ambient pressure, Bernoulli's equation gives p0 = p1 +(1/2)ρv12, where v1 is the velocity of the air entering the fan. Continuity requires that v2 leaving the fan must equal v1 entering the fan for an incompressible fluid, approximately true here (Av1 = Av2, where A is the area swept out by the blades, the “rotor disk area”). However, some distance below the rotor (or in front of the fan) the velocity is vd (vdowndraft in the figure) and the pressure again p0, so Bernoulli gives us p2 + (1/2)ρv22 = (p1 + Δp) + (1/2) ρv12 = [p1 + (p2 − p1)] +(1/2) ρv12 = p2 + (1/2)ρv12 = p0 + (1/2) ρvd2.
Measuring the Forces Between Magnetic Dipoles
Authors: Gayetsky Lisa E. , Caylor Craig L.
Published: August 2007

We describe a simple undergraduate lab in which students determine how the force between two magnetic dipoles depends on their separation. We consider the case where both dipoles are permanent and the case where one of the dipoles is induced by the field of the other (permanent) dipole. Agreement with theoretically expected results is quite good.
Strong Little Magnets
Authors: Moloney Michael J.
Published: August 2007

Did you know that some strong little cylindrical magnets available in local hardware stores1 can have an effective circumferential current of 2500 A? This intriguing information can be obtained by hanging a pair of magnets at the center of a coil, as shown in Fig. 1, and measuring the oscillation frequency as a function of coil current.
Noise Doppler-Shift Measurement of Airplane Speed
Authors: Costa Ivan F. , Mocellin Alexandra
Published: August 2007

This paper illustrates a new and practical experimental technique for studying the Doppler effect1–3 where the pitch variation4 of noise from a passing aircraft is used to calculate its speed.
Introduction to Fourier Optics
Authors: Huggins Elisha
Published: August 2007

Much like a physical prism, which displays the frequency components of a light wave, Fourier analysis can be thought of as a mathematical prism that can tell us what harmonics or frequency components are contained in a recording of a sound wave. We wrote the MacScope II program1 so that the user could not only see a plot of the harmonic amplitudes but also see the harmonic waves and how these waves add together to recreate the original sound curve.
A Simple Experiment to Demonstrate the Effects of Greenhouse Gases
Authors: Keating C. F.
Published: August 2007

The role of greenhouse gases in our atmosphere is the subject of considerable discussion and debate. Global warming is well-documented, as is the continually increasing amount of greenhouse gases that human activity puts in the air. Is there a relationship between the two? The simple experiment described in this paper provides a good demonstration of the effect of greenhouse gases in the atmosphere. This experiment lends itself well to astronomy, physics, and Earth science classes at the high school and college levels.
MANY DROPLET PATTERN IN THE CYLINDRICAL PHASE OF DIBLOCK COPOLYMER MORPHOLOGY
Authors: REN XIAOFENG , WEI JUNCHENG
Published: August 2007

The Ohta–Kawasaki density functional theory of diblock copolymers gives rise to a nonlocal free boundary problem. In a proper range of the block composition parameter and the nonlocal interaction parameter, an equilibrium pattern of many droplets exists in a general planar domain. A sub-range of the parameters is identified where the multiple droplet pattern is stable. This stable droplet pattern models the cylindrical phase in the diblock copolymer morphology. Each droplet is close to a round disc. The boundaries of the droplets satisfy an equation that involves the curvature of the boundaries and a quantity that depends nonlocally on the whole pattern. The locations of the droplets are determined via a Green's function of the domain. In constructing the droplet pattern we overcome three obstacles: interface oscillation, droplet coarsening, and droplet translation.
ATTENTION AND VISUAL SEARCH
Authors: RODRIGUEZ-SANCHEZ ANTONIO J. , SIMINE EVGUENI , TSOTSOS JOHN K.
Published: August 2007

Selective Tuning (ST) presents a framework for modeling attention and in this work we show how it performs in covert visual search tasks by comparing its performance to human performance. Two implementations of ST have been developed. The Object Recognition Model recognizes and attends to simple objects formed by the conjunction of various features and the Motion Model recognizes and attends to motion patterns. The validity of the Object Recognition Model was first tested by successfully duplicating the results of Nagy and Sanchez. A second experiment was aimed at an evaluation of the model's performance against the observed continuum of search slopes for feature-conjunction searches of varying difficulty. The Motion Model was tested against two experiments dealing with searches in the visual motion domain. A simple odd-man-out search for counter-clockwise rotating octagons among identical clockwise rotating octagons produced linear increase in search time with the increase of set size. The second experiment was similar to one described by Thorton and Gilden. The results from both implementations agreed with the psychophysical data from the simulated experiments. We conclude that ST provides a valid explanatory mechanism for human covert visual search performance, an explanation going far beyond the conventional saliency map based explanations.
DOES ABNORMAL SPINAL RECIPROCAL INHIBITION LEAD TO CO-CONTRACTION OF ANTAGONIST MOTOR UNITS? A MODELING STUDY
Authors: CUTSURIDIS VASSILIS
Published: August 2007

It is suggested that co-contraction of antagonist motor units perhaps due to abnormal disynaptic Iareciprocal inhibition is responsible for Parkinsonian rigidity. A neural model of Parkinson's disease bradykinesia is extended to incorporate the effects of spindle feedback on key cortical cells and examine the effects of dopamine depletion on spinal activities. Simulation results show that although reciprocal inhibition is reduced in DA depleted case, it doesn't lead to co-contraction of antagonist motor neurons. Implications to Parkinsonian rigidity are discussed.
ON THE DEFINITIONS OF SOBOLEV AND BV SPACES INTO SINGULAR SPACES AND THE TRACE PROBLEM
Authors: CHIRON DAVID
Published: August 2007

The purpose of this paper is to relate two notions of Sobolev and BV spaces into metric spaces, due to Korevaar and Schoen on the one hand, and Jost on the other hand. We prove that these two notions coincide and define the same p-energies. We review also other definitions, due to Ambrosio (for BV maps into metric spaces), Reshetnyak and finally to the notion of Newtonian–Sobolev spaces. These last approaches define the same Sobolev (or BV) spaces, but with a different energy, which does not extend the standard Dirichlet energy. We also prove a characterization of Sobolev spaces in the spirit of Bourgain, Brezis and Mironescu in terms of "limit" of the space Ws,pas s → 1, 0 < s < 1, and finally following the approach proposed by Nguyen. We also establish the [Formula: see text] regularity of traces of maps in Ws,p(0 < s ≤ 1 < sp).
DIRICHLET PROBLEMS FOR THE 1-LAPLACE OPERATOR, INCLUDING THE EIGENVALUE PROBLEM
Authors: KAWOHL BERND , SCHURICHT FRIEDEMANN
Published: August 2007

We consider a number of problems that are associated with the 1-Laplace operator Div (Du/|Du|), the formal limit of the p-Laplace operator for p → 1, by investigating the underlying variational problem. Since corresponding solutions typically belong to BV and not to [Formula: see text], we have to study minimizers of functionals containing the total variation. In particular we look for constrained minimizers subject to a prescribed [Formula: see text]-norm which can be considered as an eigenvalue problem for the 1-Laplace operator. These variational problems are neither smooth nor convex. We discuss the meaning of Dirichlet boundary conditions and prove existence of minimizers. The lack of smoothness, both of the functional to be minimized and the side constraint, requires special care in the derivation of the associated Euler–Lagrange equation as necessary condition for minimizers. Here the degenerate expression Du/|Du| has to be replaced by a suitable vector field [Formula: see text] to give meaning to the highly singular 1-Laplace operator. For minimizers of a large class of problems containing the eigenvalue problem, we obtain the surprising and remarkable fact that in general infinitely many Euler–Lagrange equations have to be satisfied.
NON-BACKTRACKING RANDOM WALKS MIX FASTER
Authors: ALON NOGA , BENJAMINI ITAI , LUBETZKY EYAL , SODIN SASHA
Published: August 2007

We compute the mixing rate of a non-backtracking random walk on a regular expander. Using some properties of Chebyshev polynomials of the second kind, we show that this rate may be up to twice as fast as the mixing rate of the simple random walk. The closer the expander is to a Ramanujan graph, the higher the ratio between the above two mixing rates is.

As an application, we show that if G is a high-girth regular expander on n vertices, then a typical non-backtracking random walk of length n on G does not visit a vertex more than [Formula: see text] times, and this result is tight. In this sense, the multi-set of visited vertices is analogous to the result of throwing n balls to n bins uniformly, in contrast to the simple random walk on G, which almost surely visits some vertex Ω( log n) times.
EMERGENCE OF COMPLEX STRATEGIES IN THE EVOLUTION OF CHESS ENDGAME PLAYERS
Authors: HAUPTMAN AMI , SIPPER MOSHE
Published: August 2007

We examine a strong chess-endgame player, previously developed by us through genetic programming, focusing on the player's emergent capabilities and tactics in the context of a chess match. First, we provide a detailed description of the evolutionary approach by which our player was developed. Then, using a number of methods we analyze the evolved player's building blocks and their effect on play level. We conclude that evolution has found combinations of building blocks that are far from trivial and cannot be explained through simple combination — thereby indicating the possible emergence of complex strategies.
Lipoprotein receptor expression during luteinization of the ovarian follicle
Authors: Miranda-Jiménez Leonor , Murphy Bruce D.
Published: August 2007

Ovarian follicles luteinize after ovulation, requiring structural and molecular remodeling along with exponential increases in steroidogenesis. Cholesterol substrates for luteal steroidogenesis are imported via scavenger receptor-BI (SR-BI) and the low-density lipoprotein (LDL) receptor from circulating high-density lipoproteins and LDL. SR-BI mRNA is expressed in pig ovaries at all stages of folliculogenesis and in the corpus luteum (CL). An 82-kDa form of SR-BI predominates throughout, is weakly present in granulosa cells, and is robustly expressed in the CL, along with the less abundant 57-kDa form. Digestion of N-linked carbohydrates substantially reduced the SR-BI mass in luteal cells, indicating that differences between forms is attributable to glycosylation. Immunohistochemistry revealed SR-BI to be concentrated in the cytoplasm of follicular granulosa cells, although found mostly at the periphery of luteal cells. To examine receptor dynamics during gonadotropin-induced luteinization, pigs were treated with an ovulatory stimulus, and ovaries were collected at intervals to ovulation. SR-BI in granulosa cell cytoplasm increased through the periovulatory period, with migration to the cell periphery as the CL matured. In vitro culture of follicles with human chorionic gonadotropin induced time-dependent upregulation of 82-kDa SR-BI in granulosa cells. SR-BI and LDL receptor were reciprocally expressed, with the latter highest in follicular granulosa cells, declining precipitously with CL formation. We conclude that luteinization causes upregulation of SR-BI expression, its posttranslational maturation by glycosylation, and insertion into luteal cell membranes. Expression of the LDL receptor is extinguished during luteinization, indicating dynamic regulation of cholesterol importation to maintain elevated steroid output by the CL.
Integrin-mediated mechanotransduction in renal vascular smooth muscle cells: activation of calcium sparks
Authors: Balasubramanian Lavanya , Ahmed Abu , Lo Chun-Min , Sham James S. K. , Yip Kay-Pong
Published: August 2007

Integrins are transmembrane heterodimeric proteins that link extracellular matrix (ECM) to cytoskeleton and have been shown to function as mechanotransducers in nonmuscle cells. Synthetic integrin-binding peptide triggers Ca2+ mobilization and contraction in vascular smooth muscle cells (VSMCs) of rat afferent arteriole, indicating that interactions between the ECM and integrins modulate vascular tone. To examine whether integrins transduce extracellular mechanical stress into intracellular Ca2+ signaling events in VSMCs, unidirectional mechanical force was applied to freshly isolated renal VSMCs through paramagnetic beads coated with fibronectin (natural ligand of α5β1-integrin in VSMCs). Pulling of fibronectin-coated beads with an electromagnet triggered Ca2+ sparks, followed by global Ca2+ mobilization. Paramagnetic beads coated with low-density lipoprotein, whose receptors are not linked to cytoskeleton, were minimally effective in triggering Ca2+ sparks and global Ca2+ mobilization. Preincubation with ryanodine, cytochalasin-D, or colchicine substantially reduced the occurrence of Ca2+ sparks triggered by fibronectin-coated beads. Binding of VSMCs with antibodies specific to the extracellular domains of α5- and β1-integrins triggered Ca2+ sparks simulating the effects of fibronectin-coated beads. Preincubation of microperfused afferent arterioles with ryanodine or integrin-specific binding peptide inhibited pressure-induced myogenic constriction. In conclusion, integrins transduce mechanical force into intracellular Ca2+ signaling events in renal VSMCs. Integrin-mediated mechanotransduction is probably involved in myogenic response of afferent arterioles.
Adaptive Changes in Cortical Receptive Fields Induced by Attention to Complex Sounds
Authors: Fritz Jonathan B. , Elhilali Mounya , Shamma Shihab A.
Published: August 2007

Receptive fields in primary auditory cortex (A1) can be rapidly and adaptively reshaped to enhance responses to salient frequency cues when using single tones as targets. To explore receptive field changes to more complex spectral patterns, we trained ferrets to detect variable, multitone targets in the context of background, rippled noise. Recordings from A1 of behaving ferrets showed a consistent pattern of plasticity, at both the single-neuron level and the population level, with enhancement for each component tone frequency and suppression for intertone frequencies. Plasticity was strongest near neuronal best frequency, rapid in onset, and slow to fade. Although attention may trigger cortical plasticity, the receptive field changes persisted after the behavioral task was completed. The observed comb filter plasticity is an example of an adaptive contrast matched filter, which may generally improve discriminability between foreground and background sounds and, we conjecture, may predict A1 cortical plasticity for any complex spectral target.
Zn2+ Slows Down CaV3.3 Gating Kinetics: Implications for Thalamocortical Activity
Authors: Cataldi M. , Lariccia V. , Marzaioli V. , Cavaccini A. , Curia G. , Viggiano D. , Canzoniero L.M.T. , di Renzo G. , Avoli M. , Annunziato L.
Published: August 2007

We employed whole cell patch-clamp recordings to establish the effect of Zn2+ on the gating the brain specific, T-type channel isoform CaV3.3 expressed in HEK-293 cells. Zn2+ (300 μM) modified the gating kinetics of this channel without influencing its steady-state properties. When inward Ca2+ currents were elicited by step depolarizations at voltages above the threshold for channel opening, current inactivation was significantly slowed down while current activation was moderately affected. In addition, Zn2+ slowed down channel deactivation but channel recovery from inactivation was only modestly changed. Zn2+ also decreased whole cell Ca2+ permeability to 45% of control values. In the presence of Zn2+, Ca2+ currents evoked by mock action potentials were more persistent than in its absence. Furthermore, computer simulation of action potential generation in thalamic reticular cells performed to model the gating effect of Zn2+ on T-type channels (while leaving the kinetic parameters of voltage-gated Na+ and K+ unchanged) revealed that Zn2+ increased the frequency and the duration of burst firing, which is known to depend on T-type channel activity. In line with this finding, we discovered that chelation of endogenous Zn2+ decreased the frequency of occurrence of ictal-like epileptiform discharges in rat thalamocortical slices perfused with medium containing the convulsant 4-aminopyridine (50 μM). These data demonstrate that Zn2+ modulates CaV3.3 channel gating thus leading to increased neuronal excitability. We also propose that endogenous Zn2+ may have a role in controlling thalamocortical oscillations.
Optimization of Single-Photon Response Transmission at the Rod-to-Rod Bipolar Synapse
Authors: Okawa Haruhisa , Sampath Alapakkam P.
Published: August 2007

Our ability to see in dim light is limited by the statistics of light absorption in rod photoreceptors and the faithful transmission of the light-evoked signals through the retina. This article reviews the physiological mechanisms at the synapse between rods and rod bipolar cells, the first relay in a pathway that mediates vision near absolute threshold.
Keeping an “Ear” to the Ground: Seismic Communication in Elephants
Authors: O’Connell-Rodwell Caitlin E.
Published: August 2007

This review explores the mechanisms that elephants may use to send and receive seismic signals from a physical, anatomical, behavioral, and physiological perspective. The implications of the use of the vibration sense as a multimodal signal will be discussed in light of the elephant’s overall fitness and survival.
Activity-Dependent Signaling Pathways Controlling Muscle Diversity and Plasticity
Authors: Schiaffino Stefano , Sandri Marco , Murgia Marta
Published: August 2007

A variety of fiber types with different contractile and metabolic properties is present in mammalian skeletal muscle. The fiber-type profile is controlled by nerve activity via specific signaling pathways, whose identification may provide potential therapeutic targets for the prevention and treatment of metabolic and neuromuscular diseases.
Brain Glucose Sensing, Counterregulation, and Energy Homeostasis
Authors: Marty Nell , Dallaporta Michel , Thorens Bernard
Published: August 2007

Neuronal circuits in the central nervous system play a critical role in orchestrating the control of glucose and energy homeostasis. Glucose, beside being a nutrient, is also a signal detected by several glucose-sensing units that are located at different anatomical sites and converge to the hypothalamus to cooperate with leptin and insulin in controlling the melanocortin pathway.
Facilitated Hexose Transporters: New Perspectives on Form and Function
Authors: Manolescu Andrei R. , Witkowska Kate , Kinnaird Adam , Cessford Tara , Cheeseman Chris
Published: August 2007

The recent sequencing of the human genome has resulted in the addition of nine new hGLUT isoforms to the SLC2A family, many of which have widely varying substrate specificity, kinetic behavior, and tissue distribution. This review examines some new hypotheses related to the structure and function of these proteins.
Microvascular Dysfunction in Obesity: A Potential Mechanism in the Pathogenesis of Obesity-Associated Insulin Resistance and Hypertension
Authors: Jonk Amy M. , Houben Alfons J. H. M. , de Jongh Renate T. , Serné Erik H. , Schaper Nicoloaas C. , Stehouwer Coen D. A.
Published: August 2007

Obesity is an important risk factor for insulin resistance and hypertension and plays a central role in the metabolic syndrome. Insight into the pathophysiology of this syndrome may lead to new treatments. This paper has reviewed the evidence for an important role for the microcirculation as a possible link between obesity, insulin resistance and hypertension.
ER-Mitochondria Communication. How Privileged?
Authors: Franzini-Armstrong Clara
Published: August 2007

Mitochondria have a low affinity for Ca2+, but they take up these ions during normal cell activity because they are in close proximity to the sites of calcium entry into the cell and of internal Ca2+release. This gives mitochondria privileged access to cytoplasmic Ca2+without requiring a direct communication with the endoplasmic reticulum.
Macromolecule biosynthesis: a key function of sleep
Authors: Mackiewicz Miroslaw , Shockley Keith R. , Romer Micah A. , Galante Raymond J. , Zimmerman John E. , Naidoo Nirinjini , Baldwin Donald A. , Jensen Shane T. , Churchill Gary A. , Pack Allan I.
Published: August 2007

The function(s) of sleep remains a major unanswered question in biology. We assessed changes in gene expression in the mouse cerebral cortex and hypothalamus following different durations of sleep and periods of sleep deprivation. There were significant differences in gene expression between behavioral states; we identified 3,988 genes in the cerebral cortex and 823 genes in the hypothalamus with altered expression patterns between sleep and sleep deprivation. Changes in the steady-state level of transcripts for various genes are remarkably common during sleep, as 2,090 genes in the cerebral cortex and 409 genes in the hypothalamus were defined as sleep specific and changed (increased or decreased) their expression during sleep. The largest categories of overrepresented genes increasing expression with sleep were those involved in biosynthesis and transport. In both the cerebral cortex and hypothalamus, during sleep there was upregulation of multiple genes encoding various enzymes involved in cholesterol synthesis, as well as proteins for lipid transport. There was also upregulation during sleep of genes involved in synthesis of proteins, heme, and maintenance of vesicle pools, as well as antioxidant enzymes and genes encoding proteins of energy-regulating pathways. We postulate that during sleep there is a rebuilding of multiple key cellular components in preparation for subsequent wakefulness.
Estrogen Receptor α Inhibits p53-Mediated Transcriptional Repression: Implications for the Regulation of Apoptosis
Authors: Sayeed Aejaz , Konduri Santhi D. , Liu Wensheng , Bansal Sanjay , Li Fengzhi , Das Gokul M.
Published: August 2007

Estrogen receptor α (ERα) and tumor suppressor protein p53 exert opposing effects on cellular proliferation. As a transcriptional regulator, p53 is capable of activating or repressing various target genes. We have previously reported that ERα binds directly to p53, leading to down-regulation of transcriptional activation by p53. In addition to transcriptional activation, transcriptional repression of a subset of target genes by p53 plays important roles in diverse biological processes, such as apoptosis. Here, we report that ERα inhibits p53-mediated transcriptional repression. Chromatin immunoprecipitation assays reveal that ERα interacts in vivo with p53 bound to promoters of Survivin and multidrug resistance gene 1, both targets for transcriptional repression by p53. ERα binding to p53 leads to inhibition of p53-mediated transcriptional regulation of these genes in human cancer cells. Transcriptional derepression of Survivin by ERα is dependent on the p53-binding site on the Survivin promoter, consistent with our observation that p53 is necessary for ERα to access the promoters. Importantly, mutagenic conversion of this site to an activation element enabled ERα to repress p53-mediated transcriptional activation. Further, RNA interference–mediated knockdown of ERα resulted in reduced Survivin expression and enhanced the propensity of MCF-7 cells to undergo apoptosis in response to staurosporine treatment, an effect that was blocked by exogenous expression of Survivin. These results unravel a novel mechanism by which ERα opposes p53-mediated apoptosis in breast cancer cells. The findings could have translational implications in developing new therapeutic and prevention strategies against breast cancer. [Cancer Res 2007;67(16):7746–55]
Involvement of RNA Helicases p68 and p72 in Colon Cancer
Authors: Shin Sook , Rossow Kari L. , Grande Joseph P. , Janknecht Ralf
Published: August 2007

The homologous proteins p68 and p72 are members of the DEAD box family of RNA helicases. Here, we show that expression of both of these helicases strongly increases during the polyp→adenoma→adenocarcinoma transition in the colon. Furthermore, p68 and p72 form complexes with β-catenin and promote the ability of β-catenin to activate gene transcription. Conversely, simultaneous knockdown of p68 and p72 leads to reduced expression of the β-catenin–regulated genes, c-Myc, cyclin D1, c-jun, and fra-1, all of which are proto-oncogenes. Moreover, transcription of the cell cycle inhibitor p21WAF1/CIP1, whose expression is suppressed by c-Myc, is enhanced on p68/p72 knockdown. Thus, p68/p72 may contribute to colon cancer formation by directly up-regulating proto-oncogenes and indirectly by down-regulating the growth suppressor p21WAF1/CIP1. Accordingly, knockdown of p68 and p72 in colon cancer cells inhibits their proliferation and diminishes their ability to form tumors in vivo. Altogether, these results suggest that p68/p72 overexpression is not only a potential marker of colon cancer but is also causally linked to this disease. Therefore, p68 and p72 may be novel targets in the combat against colon cancer. [Cancer Res 2007;67(16):7572–8]
Caveolin-1 Reduces Osteosarcoma Metastases by Inhibiting c-Src Activity and Met Signaling
Authors: Cantiani Lara , Manara Maria Cristina , Zucchini Cinzia , De Sanctis Paola , Zuntini Monia , Valvassori Luisa , Serra Massimo , Olivero Martina , Di Renzo Maria Flavia , Colombo Mario Paolo , Picci Piero , Scotlandi Katia
Published: August 2007

Caveolin-1 (Cav-1) is highly expressed in normal osteoblasts. This article reports that Cav-1 down-regulation is part of osteoblast transformation and osteosarcoma progression and validates its role as oncosuppressor in human osteosarcoma. A survey of 6-year follow-up indicates a better overall survival for osteosarcoma expressing a level of Cav-1 similar to osteoblasts. However, the majority of primary osteosarcoma shows significantly lower levels of Cav-1 than normal osteoblasts. Accordingly, Met-induced osteoblast transformation is associated with Cav-1 down-regulation. In vitro, osteosarcoma cell lines forced to overexpress Cav-1 show reduced malignancy with inhibited anchorage-independent growth, migration, and invasion. In vivo, Cav-1 overexpression abrogates the metastatic ability of osteosarcoma cells. c-Src and c-Met tyrosine kinases, which are activated in osteosarcoma, colocalize with Cav-1 and are inhibited on Cav-1 overexpression. Thus, Cav-1 behaves as an oncosuppressor in osteosarcoma. Altogether, data suggest that Cav-1 down-modulation might function as a permissive mechanism, which, by unleashing c-Src and Met signaling, enables osteosarcoma cells to invade neighboring tissues. These data strengthen the rationale to target c-Src family kinases and/or Met receptor to improve the extremely poor prognosis of metastatic osteosarcoma. [Cancer Res 2007;67(16):7675–85]
Molecular Profiling of Matched Samples Identifies Biomarkers of Papillary Thyroid Carcinoma Lymph Node Metastasis
Authors: Cerutti Janete M. , Oler Gisele , Michaluart Pedro , Delcelo Rosana , Beaty Robert M. , Shoemaker Jennifer , Riggins Gregory J.
Published: August 2007

Biomarkers of papillary thyroid carcinoma (PTC) metastasis can accurately identify metastatic cells and aggressive tumor behavior. To find new markers, serial analysis of gene expression (SAGE) was done on three samples from the same patient: normal thyroid tissue, primary PTC, and a PTC lymph node metastasis. This genomewide expression analysis identified 31 genes expressed in lymph node metastasis, but not in the primary tumor. Eleven genes were evaluated by quantitative real-time reverse transcription-PCR (qPCR) on independent sets of matched samples to find genes that were consistently different between the tumor and metastatic samples. LIMD2 and PTPRC (CD45) showed a statistically significant difference in expression between tumor and metastatic samples (P < 0.0045), and an additional gene (LTB) had borderline significance. PTPRC and LTB were tested by immunohistochemistry in an independent set of paired samples, with both markers showing a difference in protein expression. All 20 metastases from 6 patients showed expression in both markers, with little or no expression in primary tumor. Some of these markers could provide an improved means to detect metastatic PTC cells during initial staging of a newly diagnosed carcinoma and/or to rule out recurrence. The functional role of these genes may also provide insight into mechanisms of thyroid cancer metastasis. [Cancer Res 2007;67(16):7885–92]