bluuebunny/crossref_metadata_2025 huggingface dataset:
THE OPTICAL CHARACTERISTICS OF NITROGEN-DOPED AMORPHOUS CARBON THIN-FILMS GROWN ON NOVEL HEAT-TOLERANT FLEXIBLE PLASTIC SUBSTRATES BY A NEWLY DEVELOPED MICROWAVE SURFACE WAVE PLASMA CHEMICAL VAPOR DEPOSITION METHOD
Authors: RUSOP M. , OMER A. M. M. , ADHIKARI S. , ADHIKARY S. , UCHIDA H. , SOGA T. , JIMBO T. , UMENO M.
Published: March 2005

Nitrogen-doped amorphous carbon ( a - C : N ) thin-films have been deposited on novel heat tolerant flexible plastic substrates by a newly developed microwave surface wave plasma chemical vapor deposition (MWSWP-CVD) method. Methane gas and also camphor dissolved with ethyl alcohol gas composition have been used as plasma source. Nitrogen gas has been used as a dopant material for a - C : N films. In this paper, the optical characteristics of absorption coefficients and band gaps for a - C : N are discussed. The optical band gap of a - C : N films was found to be approximately 1.7 eV, which is close to the suitable band gap for solar cell. The optical band gap of a - C : N was found to be dependent on the composition gas source pressures.
DESIGN AND SYNTHESIS OF CUTOFF FILTER USING PHOTONIC BANDGAP MATERIALS
Authors: MISHRA R. K. , MISRA K. D. , PANDEY R. P. , TIWARI R. P.
Published: March 2005

In this paper, the design of a long and short wavelength cutoff filter using three-component periodic structure is presented. It is predicted that the manipulation of layers to obtain maximum transmission in three-component periodic structures are more suitable than two-component periodic structures. It is demonstrated that periods up to 22 bring maximum transmission with less oscillation within the high transmission band. Calculation for bandwidth is presented using the transfer matrix approach. It is suggested that for making the ideal filter, the optimization of layers with the three-component base system should be the best option for obtaining a desired transmission.
EX SITU ATOMIC FORCE MICROSCOPY STUDIES OF GROWTH MECHANISMS OF MANGANESE MERCURY THIOCYANATE CRYSTALS
Authors: GENG Y. L. , XU D. , WANG X. Q. , DU W. , ZHANG G. H. , LIU H. Y. , WANG Y. L. , SUN D. L.
Published: March 2005

Growth mechanisms of the {110} planes of the manganese mercury thiocyanate, MnHg ( SCN )4 (MMTC), crystals have been investigated by using atomic force microscopy (AFM). The results show that spiral dislocation controlled mechanism and two-dimensional (2D) nucleation mechanism operate simultaneously during growth. 2D nuclei are found to cover up the outcrop of dislocation hillocks. Pairs of circular 2D nuclei appear on the wider steps terraces and the slope of 2D nucleation islands. Hillocks introduced by both simple spiral dislocation sources and 2D nucleation are elliptical in shape. It is determined the long sides orientate along the c-direction or the direction about 45° to the c-axis. Anisotropic growth hillocks and isotropic 2D nuclei coexist on the surface, which may be due to unequal supersaturations in the mother solution during the evaporation process.
MODELING OF Co/Cu ISLAND FORMATION ON A Cu(111) SURFACE
Authors: BOZZOLO GUILLERMO , FARÍAS DANIEL , VÁZQUEZ DE PARGA AMADEO L. , MIRANDA RODOLFO
Published: March 2005

The BFS method for alloys is applied to the study of Co growth on Cu (111). Atomistic simulations are performed to investigate the behavior of Co on Cu (111) as a function of temperature. Atom-by-atom analysis of the energy contributions of each atom in the island explain the observed features.
PLASTICITY-INSTABILITY COUPLING EFFECTS ON THE COLLAPSE OF THICK TUBES
Authors: CORRADI LEONE , LUZZI LELIO , TRUDI FULVIO
Published: March 2005

The imperfection sensitivity of cylindrical shells under external pressure is studied, focusing attention on tubes of considerable thickness, such as those to be employed for very deep water pipe lines or in some innovative nuclear power plant proposals. In such tubes collapse is dominated by yielding, but the decreasing nature of the post-collapse evolution makes the effects of interaction with instability significant enough to demand consideration. On the other hand, available theories assessing the imperfection sensitivity of thin shells do not apply in this context and empirical design formulas used for the medium-thick tubes typical of present oil industry applications are extremely conservative. The interaction phenomenon becomes inherently different as thickness increases, and its correct description appears a must in view of a rational assessment of the load bearing capacity. This paper is intended as a first step in this direction.
POST-BUCKLING BEHAVIOR AND IMPERFECTION SENSITIVITY OF L-FRAMES
Authors: GALVÃO ALEXANDRE S. , GONÇALVES PAULO B. , SILVEIRA RICARDO A. M.
Published: March 2005

In this paper, a detailed analysis is conducted to study the influence of the geometric parameters, boundary conditions as well as initial imperfections on the nonlinear response and imperfection sensitivity of L-frames. An efficient nonlinear finite element formulation for the analysis of planar elastic frames is used together with incremental-iterative strategies. This enables one to obtain the highly nonlinear equilibrium paths exhibited by L-frames under certain loading conditions and identify the bifurcation and limit points along these equilibrium paths. These results provide some insight as to the source and mechanism of asymmetric bifurcation and imperfection sensitivity in frames thus helping engineers to evaluate the importance of geometric nonlinearities in the analysis and design of slender elastic frames.
PROPORTIONATE DYNAMICALLY NON-SEPARABLE BUILDINGS: A CLASS OF BUILDINGS WITH HORIZONTAL SETBACK
Authors: BASU DHIMAN
Published: March 2005

This paper shows the existence of a class of horizontal setback buildings that exhibits (i) existence of two distinct types of mode, e.g., rigid floor mode and flexible floor mode, (ii) zero participation of flexible floor modes under spatially uniform ground motion, and (iii) zero participation of torsional modes. Such a class of buildings is referred herein as proportionate dynamically non-separable (PDNS) buildings. PDNS class differs from the existing concept of dynamically separable building in two respects. First, PDNS class does not impose any condition over the floor properties. Second, the eigen properties of the frames along one orthogonal direction may be different from that along other orthogonal directions. Therefore, PDNS class provides a wider latitude in modeling a building so as to minimize the effect of in-plane flexibility of the floor diaphragm. The existence of such buildings is shown in the form of horizontal setback buildings with all the wings oriented along the orthogonal directions (e.g., L, T, and + shapes).
POST-BUCKLING OF AN ELASTIC COLUMN WITH VARIOUS ROTATIONAL END RESTRAINTS
Authors: PHUNGPAINGAM B. , CHUCHEEPSAKUL S.
Published: March 2005

In this technical note, the post-buckling behavior of a simply supported elastic column with various rotational end conditions of the supports is investigated. The compressive force is applied at the tip of the column. The characteristic equation for solving the critical loads is obtained from the boundary value problem of linear systems. In the post-buckling state, a set of nonlinear differential equations with boundary conditions is established and numerically solved by the shooting method. The interesting features associated with this problem such as the limit load point, snap-through phenomenon and the secondary bifurcation point will be highlighted herein.
A NOTE ON POSSIBLE FLUTTER OF PIEZOELECTRIC LAYERS
Authors: WANG Q.
Published: March 2005

This technical note presents the solution for flutter instability of a piezoelectric layer subjected to an external voltage which can be modeled as a compressive follower force. The critical ratio of the length to the thickness of the piezoelectric layer for the possible flutter instability is derived given the endurable electric field of the piezoelectric material. The calculation is conducted for piezoelectric layers which are both free and surface bonded on a host structure. Numerical simulations are conducted for the possible flutter instability of different PZT (Lead Zirconium Titanate) materials. The findings in this study should serve as useful benchmarks for the stability analysis of piezoelectric materials.
ERRORS IN NUMERICAL SOLUTION OF EQUATION OF MOTION OF LIGHTLY DAMPED SDOF SYSTEM NEAR RESONANCE
Authors: PAVIC A. , ŽIVANOVIĆ S. , REYNOLDS P.
Published: March 2005

This study investigates the error which occurs when numerically integrating the equation of motion of a single degree of freedom system excited by a harmonic force near resonance. The Constant Average Acceleration method was considered in particular as it features in many finite element software packages. It was found that a considerable error in the calculated responses occurs in systems with low damping due to the well known phenomenon of period elongation. However, the error is reduced for systems with higher damping and/or when smaller time step is used. With regard to this, recommendations are given as to the time steps required to obtain solutions with a pre-defined level of accuracy.
THERMALLY INDUCED DISPLACEMENT IN SIMPLY-SUPPORTED LAMINATES
Authors: AKOUR SALIH N. , NAYFEH JAMAL F.
Published: March 2005

Thermally-induced transverse displacement of unidirectional ply, cross-ply and anti-symmetric angle-ply composite plate is investigated. The laminates are assumed to be simply supported along the four edges. The dynamic flexural response due to sudden surface heating is examined, with emphasis on the effects of plate thickness and stacking sequence on the maximum plate deflection of a graphite-epoxy composite. The total displacement is obtained by superposition of the first mode quasi-static and dynamic solutions. The quasi-static displacement is derived using a Levy-type solution while the dynamic displacement is formulated by utilizing the Classical Lamination Theory (CLT), Galerkin's Method and the Laplace Transform. The results show that thermally-induced displacements in unidirectional and cross-ply laminates for the same thickness are far less than those in angle-ply laminates.
LONGITUDINAL OSCILLATIONS OF BIMODULAR RODS
Authors: LUCCHESI MASSIMILIANO , PAGNI ANDREA
Published: March 2005

In this paper we consider the longitudinal vibrations of bimodular rods. After proving the equivalence between the entropy condition and Lax condition (whenever this latter is applicable), we go on to consider the Riemann problem and prove that a unique solution always exists except for the special case of no-tension materials. This procedure allows for easy determination of the explicit solution.
VIBRATION AND STABILITY BEHAVIOR OF LAMINATED COMPOSITE CURVED PANELS WITH CUTOUT UNDER PARTIAL IN-PLANE LOADS
Authors: RAVI KUMAR L. , DATTA P. K. , PRABHAKARA D. L.
Published: March 2005

The present paper is concerned with the vibration, buckling and dynamic instability behavior of laminated composite, cross-ply, doubly-curved panels with a central circular hole subjected to in-plane static and periodic compressive loads. A generalized shear deformable Sanders' theory is used to model the curved panels, considering the effects of transverse shear deformation and rotary inertia. Bolotin's approach is used for studying the dynamic instability regions of doubly-curved panels. The effects of non-uniform edge loads, curvature with different cutout ratios, static and dynamic load factors, and lamination parameters on curved panels are investigated with the results discussed.
Uncertainties and Risks in the Implementation of an E-Learning Information Systems Project in a Higher-Learning Environment: Viewpoints from Estonia
Authors: Ifinedo Princely
Published: March 2005

This paper investigates the sorts of risks and uncertainties inherent in implementing an e-learning information systems project in Estonia. The study uses a variation of the Delphi study in eliciting the risk factors or items from experienced top management professionals within the organisation. The main objective of the study is to identify the uncertainties or risks in the implementation of the systems, using the viewpoint of Estonia, which is an emerging economy. The findings of the work indicate that wrong development strategy, staff volatility, change in top management and lack of funding are amongst the top risk factors in implementing e-learning in Estonia. On the other hand, risks emanating from users' involvement and commitment seem to be viewed as less critical to the success of the project.
Adopting Competence Systems in Fast-Growing Knowledge-Intensive Organisations
Authors: Lindgren Rikard
Published: March 2005

Today, many organisations are reliant on the competence of individual knowledge workers. Information systems to support competence management are thus considered to be vital tools in order to gain competitive advantage. Competence systems are intended to support staff allocation and management of competence by providing firms with competence overviews. This paper presents a qualitative case study of the adoption of such systems in a fast-growing knowledge-intensive organisation. Applying a situated change perspective on organisational transformation, the paper analyses how different changes were managed in the process of competence systems adoption. Building on this analysis, this paper contributes a set of managerial implications for managing the situated nature of such changes in leveraging the use of competence systems. In addition, the paper also discusses how the implications generated apply to the management of knowledge management systems adoption.
Combining N-Grams and Stemming for Arabic Word-Based Inexact Matching and Term Conflation
Authors: Mustafa Suleiman H.
Published: March 2005

In this paper, the results of three N-gram techniques have been reported. Two of these techniques were based on the idea of combining N-grams and stemming. The first used first-order stemming, while the other used light stemming. The performance of the combined approach was then compared with that of pure conventional N-gram-based string matching. The results provide good evidence that combining N-grams with stemming improves the overall performance, as measured by word-match recall and word-match precision, using different similarity threshold values.
Three Consequences of Considering Innovation as a Collective Process and Knowledge as a Collective Good
Authors: Pénin Julien
Published: March 2005

Following the seminal work of Arrow (1962) and Nelson (1959) innovation is traditionally viewed as an individual process involving isolated agents connected only through market interactions and the outcome of this process, knowledge, is assumed to share the properties of a public good. Once produced, knowledge is supposed to spill over, i.e., to benefit other agents in the economy instantly. Departing from this approach we adopt here the view that innovation is a collective and interactive process and that knowledge is a collective good, in the sense that it flows only within networks or clubs. This shift of vision helps to improve our understanding of several points dealing with the innovation process. In this paper, we explore three of these points: the absorption of external knowledge, firms' strategies of knowledge management (secrecy versus disclosure) and innovation public policies.
Knowledge Documentation and Application in Egyptian Software Firms
Authors: Seleim Ahmed A. S. , Ashour Ahmed S. , Khalil Omar E. M.
Published: March 2005

Employing an in-depth qualitative analysis research method, this investigation explored knowledge documentation and application practices in 14 Egyptian software firms. Although they appear to document and apply knowledge variably, the firms generally have limited capabilities in documenting and applying their knowledge. Knowledge that is not captured and documented cannot be reused effectively. To cope with the knowledge documentation problems, the firms have adopted techniques such as having multiple developers possess the same project-related knowledge, using multiple-year appointment contracts, leveraging their emotional capital and improving loyalty. Also, the firms have no formal strategies that determine and guide knowledge application in software development, which may leave the firms with significant portions of their knowledge capital inactive. Software firms need to leverage the Egyptian culture, which is rich in social and emotional capital, and develop strategies and systems in order to tap the knowledge that is distributed, scattered and embedded within their routines and the skills of their software developers into organisational knowledge bases and active knowledge capitals.
ROBOTIC HANDWRITING
Authors: POTKONJAK VELJKO
Published: March 2005

Handwriting has always been considered an important human task, and accordingly it has attracted the attention of researchers working in biomechanics, physiology, and related fields. There exist a number of studies on this area. This paper considers the human–machine analogy and relates robots with handwriting. The work is two-fold: it improves the knowledge in biomechanics of handwriting, and introduces some new concepts in robot control. The idea is to find the biomechanical principles humans apply when resolving kinematic redundancy, express the principles by means of appropriate mathematical models, and then implement them in robots. This is a step forward in the generation of human-like motion of robots. Two approaches to redundancy resolution are described: (i) "Distributed Positioning" (DP) which is based on a model to represent arm motion in the absence of fatigue, and (ii) the "Robot Fatigue" approach, where robot movements similar to the movements of a human arm under muscle fatigue are generated. Both approaches are applied to a redundant anthropomorphic robot arm performing handwriting. The simulation study includes the issues of legibility and inclination of handwriting. The results demonstrate the suitability and effectiveness of both approaches.
DYNAMICS AND m-STABILITY OF LEGGED ROBOTS
Authors: FORET JEROME , BRUNEAU OLIVIER , FONTAINE JEAN-GUY
Published: March 2005

This article presents a theoretical approach for modeling and controlling the stability of legged robots. The new proposed concept is two-fold: (a) the definition of the (m-d)-stability and (b) the definition of the Virtual Generalized Stabilizer. These concepts are developed throughout a theoretical and general approach to the dynamics of legged robots. Numerical results are analyzed through the simulated behavior of a biped robot recovering a statically stable state under two conditions: an unstable initial posture and an impulsive external force.
GENERATING OPTIMAL WALKING CYCLES USING SPLINE-BASED STATE-PARAMETERIZATION
Authors: SEGUIN P. , BESSONNET G.
Published: March 2005

Optimal gait cycles are generated for a seven-link biped using a parametric optimization method. A sagittal walking pattern, including a double-support phase divided into two sub-phases, is considered. Generalized joint coordinates are approximated by three-time differentiable spline-functions. These are the concatenation of 4-order polynomials linked together up to their third derivatives at connecting points — or knots — distributed along the motion time of each phase. Optimization parameters are the values of joint coordinates at the knots, plus the joint velocities, and possibly the joint accelerations, at transitions between successive phases. An integral amount of driving torques is minimized throughout the walking cycle. During the double support, constraint forces in the kinematically closed locomotion system are dealt with as additional actuating forces. For this reason, these are also minimized. Using the above optimization parameters, this basic optimal control problem is transformed into an optimization problem of mathematical programming. The latter is efficiently solved using a Sequential Quadratic Programming algorithm. The only kinematic data required for generating a gait cycle is the walking speed. Postural configurations between successive phases, step length, and relative length of single and double supports are optimized with respect to a given walking speed.
FROM LAMPREY TO HUMANOID: THE DESIGN AND CONTROL OF A FLEXIBLE SPINE BELLY DANCING HUMANOID ROBOT WITH INSPIRATION FROM BIOLOGY
Authors: OR JIMMY , TAKANISHI ATSUO
Published: March 2005

Research on humanoid robotics has up to now been focused on the control of manipulators and walking machines. The contributions of body torso torwards daily activities have been neglected. To address this deficient area of humanoid robotics research, we developed a unique flexible spine biped humanoid robot. Inspired by the rhythmic and wave-like motions commonly seen in swimming lamprey and in belly dancing, we investigated the possibility of controlling the spine of our robot using the lamprey central pattern generator (CPG). Experimental results show that our robot is capable of mimicing both basic and complex spine motions with fewer actuators than the human spine and using only three input parameters (global and extra excitations from the brainstem, plane of actions). Our work suggests that the CPG is a suitable controller for humanoid spine motions because it can control a high degree of freedom mechanical spine with minimized control parameters. No complex computations of spine trajectories are involved. Furthermore, since our robot can move its upper body dynamically while standing and without external supports, it may be used as a prototype for the next generation of humanoid robots.
A GENERALIZED APPROACH TO MODELING DYNAMICS OF HUMAN AND HUMANOID MOTION
Authors: POTKONJAK VELJKO , VUKOBRATOVIĆ MIOMIR
Published: March 2005

This paper suggests a generalized approach to the modeling of human and humanoid motion. Instead of the usual inductive approach that starts from the analysis of different situations of real motion (like bipedal gait and running; playing tennis, soccer, or volleyball; gymnastics on the floor or by using some gymnastic apparatus; etc.) and tries to make a generalization, we suggest a deductive approach: one starts by considering a completely general problem. Once the general model is formulated, one may derive different real situations as being special cases. Such an approach require a serious effort in formulating the general model. This paper is an attempt in this direction. The general methodology is explained and the feasibility is supported by applying the general model to two illustrative examples: first, a well-known situation — the single-support phase of a biped motion — and second, a completely different problem — gymnastic exercise on a horizontal bar.
SPATIAL ORDER AND DIFFRACTION IN QUASICRYSTALS AND BEYOND
Authors: Gratias Denis , Bresson Lionel , Quiquandon Marianne
Published: March 2005

▪ Abstract  This review is an introduction to the problem of determining the nature of the diffraction spectra of ordered solids. After explicit computation examples of Bragg diffraction spectra of quasicrystals (bulk, surface) in kinematical and dynamical (high-resolution electron microscopy) situations, we show on simple toy models that long-range order does not necessarily lead to Bragg peaks which, in turn, are not necessarily the signature of the unique long-range periodic order.
The vitamin D receptor is not required for fetal mineral homeostasis or for the regulation of placental calcium transfer in mice
Authors: Kovacs Christopher S. , Woodland Mandy L. , Fudge Neva J. , Friel James K.
Published: March 2005

We utilized a vitamin D receptor (VDR) gene knockout model to study the effects of maternal and fetal absence of VDR on maternal fertility, fetal-placental calcium transfer, and fetal mineral homoeostasis. Vdr null mice were profoundly hypocalcemic, conceived infrequently, and had significantly fewer viable fetuses in utero that were also of lower body weight. Supplementation of a calcium-enriched diet increased the rate of conception in Vdr nulls but did not normalize the number or weight of viable fetuses. Among offspring of heterozygous ( Vdr+/−) mothers (wild type, Vdr+/−, and Vdr null fetuses), there was no alteration in serum Ca, P, or Mg, parathyroid hormone, placental45Ca transfer, Ca and Mg content of the fetal skeleton, and morphology and gene expression in the fetal growth plates. Vdr null fetuses did have threefold increased 1,25-dihydroxyvitamin D levels accompanied by increased 1α-hydroxylase mRNA in kidney but not placenta; a small increase was also noted in placental expression of parathyroid hormone-related protein (PTHrP). Among offspring of Vdr null mothers, Vdr+/−and Vdr null fetuses had normal ionized calcium levels and a skeletal ash weight that was appropriate to the lower body weight. Thus our findings indicate that VDR is not required by fetal mice to regulate placental calcium transfer, circulating mineral levels, and skeletal mineralization. Absence of maternal VDR has global effects on fetal growth that were partly dependent on maternal calcium intake, but absence of maternal VDR did not specifically affect fetal mineral homeostasis.
α-Ketoisocaproate-induced hypersecretion of insulin by islets from diabetes-susceptible mice
Authors: Rabaglia Mary E. , Gray-Keller Mark P. , Frey Brian L. , Shortreed Michael R. , Smith Lloyd M. , Attie Alan D.
Published: March 2005

Most patients at risk for developing type 2 diabetes are hyperinsulinemic. Hyperinsulinemia may be a response to insulin resistance, but another possible abnormality is insulin hypersecretion. BTBR mice are insulin resistant and hyperinsulinemic. When the leptinobmutation is introgressed into BTBR mice, they develop severe diabetes. We compared the responsiveness of lean B6 and BTBR mouse islets to various insulin secretagogues. The transamination product of leucine, α-ketoisocaproate (KIC), elicited a dramatic insulin secretory response in BTBR islets. The KIC response was blocked by methyl-leucine or aminooxyacetate, inhibitors of branched-chain amino transferase. When dimethylglutamate was combined with KIC, the fractional insulin secretion was identical in islets from both mouse strains, predicting that the amine donor is rate-limiting for KIC-induced insulin secretion. Consistent with this prediction, glutamate levels were higher in BTBR than in B6 islets. The transamination product of glutamate, α-ketoglutarate, elicited insulin secretion equally from B6 and BTBR islets. Thus formation of α-ketoglutarate is a requisite step in the response of mouse islets to KIC. α-Ketoglutarate can be oxidized to succinate. However, succinate does not stimulate insulin secretion in mouse islets. Our data suggest that α-ketoglutarate may directly stimulate insulin secretion and that increased formation of α-ketoglutarate leads to hyperinsulinemia.
Regulation by glucagon of the rat histidase gene promoter in cultured rat hepatocytes and human hepatoblastoma cells
Authors: Alemán Gabriela , Ortíz Victor , Langley Elizabeth , Tovar Armando R. , Torres Nimbe
Published: March 2005

Histidase (Hal), the amino acid-degrading enzyme of histidine, is regulated by the protein content of the diet and by hormones such as glucocorticoids and glucagon. However, glucagon can activate the following two possible transduction pathways: protein kinase A (PKA) and protein kinase C (PKC). The aim of this study was to isolate the 5′-flanking region of rat Hal gene to locate possible cAMP- and glucocorticoid-responsive elements and to identify whether the activation of the Hal promoter by glucagon occurs via PKA or PKC. The results showed that glucagon was able to induce Hal expression 1.5-fold in primary hepatocytes. The addition of phorbol 12-myristate,13-acetate (PMA) and forskolin to hepatocytes increased Hal mRNA concentration by 100 and 40%, respectively. To identify the Hal gene regulatory region, a 1248-bp fragment of the 5′-region was obtained. The transcription initiation site was located at 404 bp from ATG. The sequence did not show consensus TATA-like or CAAT-like boxes in the first 100 bp upstream from the transcription start site. The promoter contained six GC rich boxes, seven putative AP1 binding sites, and four glucocorticoid-responsive elements. The putative Hal promoter region was cloned into the pGL3basic vector and transfected into HepG2 cells. Luciferase expression was significantly stimulated by glucagon (0.9-fold), forskolin (0.9-fold), PMA (2.0-fold), and dexamethasone (2.9-fold). This evidence supports that the Hal gene is turned on by glucocorticoids and by glucagon either via PKC or PKA, but prefers the PKA pathway.
Contraction activates glucose uptake and glycogen synthase normally in muscles from dexamethasone-treated rats
Authors: Ruzzin Jérôme , Jensen Jørgen
Published: March 2005

Glucocorticoids cause insulin resistance in skeletal muscle. The aims of the present study were to investigate the effects of contraction on glucose uptake, insulin signaling, and regulation of glycogen synthesis in skeletal muscles from rats treated with the glucocorticoid analog dexamethasone (1 mg·kg−1·day−1ip for 12 days). Insulin resistance in dexamethasone-treated rats was confirmed by reduced insulin-stimulated glucose uptake (∼35%), glycogen synthesis (∼70%), glycogen synthase activation (∼80%), and PKB Ser473phosphorylation (∼40%). Chronic dexamethasone treatment did not impair glucose uptake during contraction in soleus or epitrochlearis muscles. In epitrochlearis (but not in soleus), the presence of insulin during contraction enhanced glucose uptake to similar levels in control and dexamethasone-treated rats. Contraction also increased glycogen synthase fractional activity and dephosphorylated glycogen synthase at Ser645, Ser649, Ser653, and Ser657normally in muscles from dexamethasone-treated rats. After contraction, insulin-stimulated glycogen synthesis was completely restored in epitrochlearis and improved in soleus from dexamethasone-treated rats. Contraction did not increase insulin-stimulated PKB Ser473or glycogen synthase kinase-3 (GSK-3) phosphorylation. Instead, contraction increased GSK-3β Ser9phosphorylation in epitrochlearis (but not in soleus) in muscles from control and dexamethasone-treated rats. In conclusion, contraction stimulates glucose uptake normally in dexamethasone-induced insulin resistant muscles. After contraction, insulin's ability to stimulate glycogen synthesis was completely restored in epitrochlearis and improved in soleus from dexamethasone-treated rats.
Regulation of leptin secretion from white adipocytes by insulin, glycolytic substrates, and amino acids
Authors: Cammisotto Philippe G. , Gélinas Yves , Deshaies Yves , Bukowiecki Ludwik J.
Published: March 2005

The aim of the present study was to determine the respective roles of energy substrates and insulin on leptin secretion from white adipocytes. Cells secreted leptin in the absence of glucose or other substrates, and addition of glucose (5 mM) increased this secretion. Insulin doubled leptin secretion in the presence of glucose (5 mM), but not in its absence. High concentrations of glucose (up to 25 mM) did not significantly enhance leptin secretion over that elicited by 5 mM glucose. Similar results were obtained when glucose was replaced by pyruvate or fructose (both 5 mM). l-Glycine or l-alanine mimicked the effect of glucose on basal leptin secretion but completely prevented stimulation by insulin. On the other hand, insulin stimulated leptin secretion when glucose was replaced by l-aspartate, l-valine, l-methionine, or l-phenylalanine, but not by l-leucine (all 5 mM). Interestingly, these five amino acids potently increased basal and insulin-stimulated leptin secretion in the presence of glucose. Unexpectedly, l-glutamate acutely stimulated leptin secretion in the absence of glucose or insulin. Finally, nonmetabolizable analogs of glucose or amino acids were without effects on leptin secretion. These results suggest that 1) energy substrates are necessary to maintain basal leptin secretion constant, 2) high availability of glycolysis substrates is not sufficient to enhance leptin secretion but is necessary for its stimulation by insulin, 3) amino acid precursors of tricarboxylic acid cycle intermediates potently stimulate basal leptin secretion per se, with insulin having an additive effect, and 4) substrates need to be metabolized to increase leptin secretion.
Repeated light-dark shifts speed up body weight gain in male F344 rats
Authors: Tsai Ling-Ling , Tsai Yu-Che , Hwang Kai , Huang Yu-Wen , Tzeng Jeh-En
Published: March 2005

This study is aimed at verifying the causal relationship of chronic circadian desynchronization and changes in body weight control. Eight male albino F344 rats aged between 12–15 wk were subjected to twice weekly 12-h shifts of the daily light-dark (LD) cycle for 13 wk (3 mo). Continuous circadian phase shifts consisting of intermittent phase delay and advance and reduced circadian amplitudes were consistently displayed in all five experimental rats implanted intraperitoneally with heart rate, body temperature, and activity transponders. The experimental rat maintained a greater body weight during LD shifts and even after 10 days of recovery than that of the age-matched control rat, which was maintained on a regular LD cycle. Body weight gain was greater in the first 2 mo of LD shifts in the experimental rat than in the control rat. Relative to the baseline, food intake and activity percentages were increased and reduced, respectively, for the experimental rats. Features of these results, such as increased body weight gain and food intake, and reduced activity, suggest a causal relationship of chronic circadian desynchronization and changes in body weight control in male albino F344 rats.
Isolation and characterization of theXenopusoocyte plasma membrane: a new method for studying activity of water and solute transporters
Authors: Hill Warren G. , Southern Nicole M. , MacIver Bryce , Potter Elizabeth , Apodaca Gerard , Smith Craig P. , Zeidel Mark L.
Published: March 2005

The intact Xenopus laevis oocyte is a useful model system for studying expressed water and solute transporters but suffers from a number of limitations, most notably large unstirred layers and other intracellular diffusion barriers. To overcome these, we have developed a method for isolating plasma membrane vesicles from oocytes. This approach facilitates more precise control of the intravesicular environment and virtually eliminates the problem of unstirred layers in kinetic experiments. The isolation procedure results in 50.6-fold enrichment of the plasma membrane marker alkaline phosphodiesterase compared with the homogenate. Markers of late endosomes/lysosomes and mitochondria were not enriched, and the endoplasmic reticulum was enriched only modestly. Permeabilities of native plasma membrane to water and urea were 8.1 × 10−4and 5.6 × 10−7cm/s, respectively, values that are sufficiently low to classify them as barrier membranes. Phospholipid analysis by mass spectrometry showed the membrane, not including cholesterol, to be rich in phosphatidylcholine (35.8 mole percent), sphingomyelin (25.8 mole percent), and phosphatidylinositol (6.8 mole percent). Cholesterol concentration was 20.7 mole percent. Membrane vesicles isolated from oocytes expressing aquaporin-1 exhibited fourfold higher water permeability in stopped-flow experiments. Oocytes expressing mouse urea transporter A3 (UT-A3) exhibited 7.5-fold faster phloretin-inhibitable urea transport compared with water-injected controls. There was no difference in water permeability between these membrane vesicles, suggesting that UT-A3 is not a water carrier. In conclusion, we describe an improved method for the isolation of the oocyte plasma membrane that will allow the study of water and solute transport kinetics as well as substrate selectivity in heterologously expressed proteins.
Defective expression of Tamm-Horsfall protein/uromodulin in COX-2-deficient mice increases their susceptibility to urinary tract infections
Authors: Dou Wenkai , Thompson-Jaeger Sandra , Laulederkind Stanley J. F. , Becker John W. , Montgomery Julia , Ruiz-Bustos Eduardo , Hasty David L. , Ballou Leslie R. , Eastman P. Scott , Srichai Betsy , Breyer Matthew D. , Raghow Rajendra
Published: March 2005

Mice lacking a functional cyclooxygenase-2 (COX-2) gene develop abnormal kidneys that contain hypoplastic glomeruli and reduced proximal tubular mass, and they often die of renal failure. A comparison of kidney-specific gene expression between wild-type and COX-2-deficient mice by cDNA microarrays revealed that although more than 500 mRNAs were differentially expressed between the two strains of mice depending on their ages, the genes encoding pre-pro-epidermal growth factor (pre-pro-EGF) and Tamm-Horsfall protein (THP)/uromodulin were aberrantly expressed in the kidneys of COX-2 −/− mice at all stages of their development. Downregulation of EGF could potentially affect renal development, and THP/uromodulin gene has been implicated in abnormal kidney development and end-stage renal failure in humans. We assessed in detail mechanism of defective THP/uromodulin gene expression and its potential consequences in COX-2-deficient mice. Consistent with the microarray data, the steady-state levels of THP/uromodulin mRNA were severely reduced in the COX-2 −/− kidney. Furthermore, reduced expression of renal THP/uromodulin, as assessed by Western blot and immunohistological methods, was closely corroborated by a corresponding decline in the urinary secretion of THP/uromodulin in COX-2 −/− mice. Finally, we demonstrate that the bladders of COX-2 −/− mice, in contrast to those of the wild-type mice, are highly susceptible to colonization by uropathogenic Escherichia coli.
Localization of the GLUT8 glucose transporter in murine kidney and regulation in vivo in nondiabetic and diabetic conditions
Authors: Schiffer Mario , Susztak Katalin , Ranalletta Mollie , Raff Amanda C. , Böttinger Erwin P. , Charron Maureen J.
Published: March 2005

Kidney disease is a major complication of diabetes, and poor glycemic control is associated with the development of diabetic nephropathy. The precise mechanisms that lead to diabetic kidney disease still remain largely unknown and are under current investigation. Because glucose transporters in the kidney play an important role in the local maintenance of intracellular glucose and plasma glucose homeostasis, the tissue distribution and regulation of glucose transporter GLUT8, a new member of the glucose transporter family with important functions in cellular survival, were examined. To understand the normal regulation of GLUT8 expression in response to metabolic signals, fasting and feeding conditions were studied. Additionally, GLUT8 expression was studied using two different models of insulin resistance, GLUT4−/− and db/db mice. GLUT8 was localized to glomerular podocytes and tubular epithelial cells in the distal portion of the nephron. Expression of GLUT8 in the kidney was influenced by plasma glucose levels in vivo. Podocytes in kidneys of diabetic db/db mice express higher levels of GLUT8 compared with nondiabetic db/m mice. Because podocytes play an important role in glomerulosclerosis development and high levels of glucose have been shown to induce apoptotic cell death in various kidney cells, these data may provide further insight into the pathogenesis of glomerulosclerosis and diabetic nephropathy.
The spiny mouse (Acomys cahirinus) completes nephrogenesis before birth
Authors: Dickinson Hayley , Walker David W. , Cullen-McEwen Luise , Wintour E. Marelyn , Moritz Karen
Published: March 2005

The spiny mouse is relatively mature at birth. We hypothesized that like other organs, the kidney may be more developed in the spiny mouse at birth, than in other rodents. If nephrogenesis is complete before birth, the spiny mouse may provide an excellent model with which to study the effects of an altered intrauterine environment on renal development. Due to its desert adaptation, the spiny mouse may have a reduced cortex-to-medulla ratio but an equivalent total nephron number to the C57/BL mouse. Kidneys were collected from fetal and neonatal spiny mice and sectioned for gross examination of metanephric development. Kidneys were collected from adult spiny mice (10 wk of age), and glomerular number, volume, and cortex-to-medulla ratios were determined using unbiased stereology. Nephrogenesis is complete in spiny mouse kidneys before birth. Metanephrogenesis begins at ∼ day 18, and by day 38 of a 40-day gestation, the nephrogenic zone is no longer present. Spiny mice have a significantly ( P < 0.001) lower total nephron number compared with C57/BL mice, although the total glomerular volume is similar. The cortex-to-medulla ratio of the spiny mouse is significantly ( P < 0.01) smaller. The spiny mouse is the first rodent species shown to complete nephrogenesis before birth. This makes it an attractive candidate for the study of fetal and neonatal kidney development and function. The reduced total nephron number and cortex-to-medulla ratio in the spiny mouse may contribute to its ability to highly concentrate its urine under stressful conditions (i.e., dehydration).
Molecular mechanisms of enhanced renal cell division in protection againstS-1,2-dichlorovinyl-l-cysteine-induced acute renal failure and death
Authors: Korrapati Midhun C. , Lock Edward A. , Mehendale Harihara M.
Published: March 2005

Sustained activation of ERK 1/2 by a low dose (15 mg/kg ip) of S-1,2-dichlorovinyl-l-cysteine (DCVC) 72 h before administration of a lethal dose of DCVC (75 mg/kg ip) enhances renal cell division and protects mice against acute renal failure (ARF) and death (autoprotection). The objective of this study was to determine correlation among extent of S-phase DNA synthesis, activation of transcription factors, expression of G1/S cyclins, cyclin-dependent kinases (CDKs), and CDK inhibitors downstream of ERK 1/2 following DCVC-induced ARF in autoprotection. Administration of the lethal dose alone caused a general downregulation or an unsustainable increase, in transcriptional and posttranscriptional events thereby preventing G1-S transition of renal cell cycle. Phosphorylation of IκBα was inhibited resulting in limited nuclear translocation of NF-κB. However, cyclin D1 expression was high probably due to transcriptional cooperation of AP-1. Cyclin D1/cyclin-dependent kinase 4 (cdk4)-cdk6 system-mediated phosphorylation of retinoblastoma protein was downregulated due to overexpression of p16 at 24 h after exposure to the lethal dose alone. Inhibition of S-phase stimulation was confirmed by proliferating cell nuclear antigen assay (PCNA). This inhibitory response was prevented if the lethal dose was administered 72 h after the low priming dose of DCVC due to promitogenic effect of the low dose. NF-κB-DNA binding is not limited if mice were pretreated with the priming dose. Cyclin D1/cdk4-cdk6 expression stimulated by the priming dose of DCVC was unaltered even after the lethal dose in the autoprotected group, explaining higher phosphorylated-pRB and S-phase stimulation found in this group. These results were corroborated with PCNA immunohistochemistry. These findings suggest that the priming dose relieves the block on compensatory tissue repair by upregulation of promitogenic mechanisms, normally blocked by the high dose when administered without the prior priming dose.
Stimulation of renal sulfate secretion by metabolic acidosis requires Na+/H+exchange induction and carbonic anhydrase
Authors: Pelis Ryan M. , Edwards Susan L. , Kunigelis Stan C. , Claiborne James B. , Renfro J. Larry
Published: March 2005

The acute effect of metabolic acidosis on SO42−secretion by the marine teleost renal proximal tubule was examined. Metabolic acidosis was mimicked in primary cultures of winter flounder renal proximal tubule epithelium (fPTCs) mounted in Ussing chambers by reducing interstitial pH to 7.1 (normally 7.7). fPTCs with metabolic acidosis secreted SO42−at a net rate that was 40% higher than in paired isohydric controls (pH 7.7 on interstitium). The stimulation was completely blocked by the carbonic anhydrase inhibitor methazolamide (100 μM). Although Na+/H+exchange (NHE) isoforms 1, 2, and 3 were identified in fPTCs by immunoblotting, administering EIPA (20 μM) to the interstitial and luminal bath solutions had no effect on net SO42−secretion by fPTCs with a normal interstitial pH of 7.7. However, EIPA (20 μM) blocked most of the stimulation caused by acidosis when applied to the lumen but not interstitium, demonstrating that induction of brush-border NHE activity is important. In the intact flounder, serum pH dropped 0.4 pH units (pH 7.7 to 7.3, at 2–3 h) when environmental pH was lowered from 7.8 to ∼4.3. Whereas serum [SO42−] was not altered by acidosis, renal tubular SO42−secretion rate was elevated 200%. Thus metabolic acidosis strongly stimulates renal sulfate excretion most likely by a direct effect on active renal proximal tubule SO42−secretion. This stimulation appears to be dependent on inducible brush-border NHE activity.
Contextual Masking of Oriented Lines: Interactions Between Surface Segmentation Cues
Authors: van der Smagt Maarten J. , Wehrhahn Christian , Albright Thomas D.
Published: March 2005

The ability of human observers to detect and discriminate a single feature of a visual image deteriorates markedly when the targeted feature is surrounded by others of a similar kind. This perceptual masking is mirrored by the suppressive effects of surround stimulation on the responses of neurons in primary visual cortex (area V1). Both perceptual and neuronal masking effects are partially relieved, however, if the targeted image feature is distinguished from surrounding features along some dimension, such as contour orientation. Masking relief is likely to play an important role in perceptual segmentation of complex images. Because dissimilar surfaces usually differ along multiple feature dimensions, we tested the possibility that those differences may influence segmentation in an invariant manner. As expected, we found that the presence of surrounding features resulted in perceptual masking and neuronal response suppression in area V1, but that either orientation or contrast polarity differences between the target and surrounding features was sufficient to partially relieve these effects. Simultaneous differences along both dimensions, however, yielded no greater relief from masking than did either difference alone. Although the averaged neuronal effects of orientation polarity cues were thus invariant, the time course over which these effects emerged after each stimulus appearance was different for the two cues. These findings refine our understanding of the functions of nonclassical receptive fields, and they support a key role for V1 neurons in surface segmentation.