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Perturbations
Kinds of Perturbations Terms modified by Perturbations Selected AbstractsGENERALIZED QUADRATIC STABILIZATION FOR DISCRETE-TIME SINGULAR SYSTEMS WITH TIME-DELAY AND NONLINEAR PERTURBATIONASIAN JOURNAL OF CONTROL, Issue 3 2005Guoping Lu ABSTRACT This paper discusses a generalized quadratic stabilization problem for a class of discrete-time singular systems with time-delay and nonlinear perturbation (DSSDP), which the satisfies Lipschitz condition. By means of the S-procedure approach, necessary and sufficient conditions are presented via a matrix inequality such that the control system is generalized quadratically stabilizable. An explicit expression of the static state feedback controllers is obtained via some free choices of parameters. It is shown in this paper that generalized quadratic stability also implies exponential stability for linear discrete-time singular systems or more generally, DSSDP. In addition, this new approach for discrete singular systems (DSS) is developed in order to cast the problem as a convex optimization involving linear matrix inequalities (LMIs), such that the controller can stabilize the overall system. This approach provides generalized quadratic stabilization for uncertain DSS and also extends the existing robust stabilization results for non-singular discrete systems with perturbation. The approach is illustrated here by means of numerical examples. [source] RAPID AMMONIUM- AND NITRATE-INDUCED PERTURBATIONS TO CHL a FLUORESCENCE IN NITROGEN-STRESSED DUNALIELLA TERTIOLECTA (CHLOROPHYTA),JOURNAL OF PHYCOLOGY, Issue 2 2003Erica B. Young When NH4+ or NO3, was supplied to NO3, -stressed cells of the microalga Dunaliella tertiolecta Butcher, immediate transient changes in chl a fluorescence were observed over several minutes that were not seen in N-replete cells. These changes were predominantly due to nonphotochemical fluorescence quenching. Fluorescence changes were accompanied by changes in photosynthetic oxygen evolution, indicating interactions between photosynthesis and N assimilation. The magnitude of the fluorescence change showed a Michaelis-Menten relationship with half-saturation concentration of 0.5 ,M for NO3, and 10 ,M for NH4+. Changes in fluorescence responses were characterized in D. tertiolecta both over 5 days of N starvation and in cells cultured at a range of NO3, -limited growth rates. Variation in responses was more marked in starved than in limited cells. During N starvation, the timing and onset of the fluorescence responses were different for NO3, versus NH4+ and were correlated with changes in maximum N uptake rate during N starvation. In severely N-starved cells, the major fluorescence response to NO3, disappeared, whereas the response to NH4+ persisted. N-starved cells previously grown with NH4+ alone showed fluorescence responses with NH4+ but not NO3, additions. The distinct responses to NO3, and NH4+ may be due to the differences between regulation of the uptake mechanisms for the two N sources during N starvation. This method offers potential for assessing the importance of NO3, or NH4+ as an N source to phytoplankton populations and as a diagnostic tool for N limitation. [source] AN INTRODUCTION TO SINGULAR PERTURBATIONSNATURAL RESOURCE MODELING, Issue 2 2000A.D. MACGILLIVRAY ABSTRACT. In this article we discuss the asymptotic analysis of so-called singularly perturbed differential equations. We begin by discussing some very simple nonmathematical examples, and then proceed to two mathematical examples, namely, the well-known example of Friedrichs and a problem of John Mahony's. The presentation is addressed primarily to those who may have had little or no previous experience with this particular type of problem. However, the author hopes others will find something of interest in the somewhat unusual approach we take. [source] Effect of elevated homocysteine on cardiac neural crest migration in vitroDEVELOPMENTAL DYNAMICS, Issue 2 2002Philip R. Brauer Abstract A positive correlation between elevated maternal homocysteine (Hcys) and an increased risk of neural tube, craniofacial, and cardiac defects is well known. Studies suggest Hcys perturbs neural crest (NC) development and may involve N-methyl-D-aspartate (NMDA) receptors (Rosenquist et al., 1999). However, there is no direct evidence that Hcys alters NC cell behavior. Here, we evaluated the effect of Hcys on cardiac NC cell migratory behavior in vitro. Neural tube segments from chick embryos treated in ovo with or without Hcys were placed in culture and the migratory behavior of emigrating NC cells was monitored. Hcys significantly increased in vitro NC cell motility at all embryonic stages examined. NC cell surface area and perimeter were also increased. However, the relative distance NC cells migrated from their original starting point only increased in NC cells treated in ovo at stage 6 or at the time neural tube segments were cultured. Cysteine had no effect. NMDA mimicked Hcys' effect on NC motility and migration distance but had no effect on cell area or perimeter. The noncompetitive inhibitor of NMDA receptors, MK801+, significantly inhibited NC cell motility, reduced migration distance, and also blocked the effects of NMDA and Hcys on NC motility and migratory distance in vitro. A monoclonal antibody directed against the NMDA receptor immunostained NC cells in vitro and, in western blots, bound a single protein with the appropriate molecular weight for the NMDA receptor in NC cell lysates. These data are consistent with the hypothesis that a Hcys-sensitive NMDA-like receptor is expressed by early emigrating NC cells or their precursors, which is important in mediating their migratory behavior. Perturbation of this receptor may be related to some of the teratogenic effects observed with elevated Hcys. © 2002 Wiley-Liss, Inc. [source] Boundary Perturbation Methods for Water WavesGAMM - MITTEILUNGEN, Issue 1 2007David P. Nicholls Abstract The most successful equations for the modeling of ocean wave phenomena are the free,surface Euler equations. Their solutions accurately approximate a wide range of physical problems from open,ocean transport of pollutants, to the forces exerted upon oil platforms by rogue waves, to shoaling and breaking of waves in nearshore regions. These equations provide numerous challenges for theoreticians and practitioners alike as they couple the difficulties of a free boundary problem with the subtle balancing of nonlinearity and dispersion in the absence of dissipation. In this paper we give an overview of, what we term, "Boundary Perturbation" methods for the analysis and numerical simulation of this "water wave problem". Due to our own research interests this review is focused upon the numerical simulation of traveling water waves, however, the extensive literature on the initial value problem and additional theoretical developments are also briefly discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Perturbation of mitochondrial complex V alters the response to dietary restriction in DrosophilaAGING CELL, Issue 1 2010Sepehr Bahadorani Summary Studies in a broad spectrum of model organisms have reported that dietary restriction (DR) is associated with an increase in mitochondrial electron transport chain (ETC) function. However, the question of whether ETC function is required for DR-mediated longevity remains controversial. Here, we report that genetic and pharmacological interventions that target mitochondrial complex V affect Drosophila lifespan in a nutrient-dependent manner. These findings support a requirement for mitochondrial complex V in DR-mediated longevity in flies. [source] Imbalance of plasma membrane ion leak and pump relationship as a new aetiological basis of certain disease statesJOURNAL OF INTERNAL MEDICINE, Issue 6 2003G. Ronquist Abstract. The basis for life is the ability of the cell to maintain ion gradients across biological membranes. Such gradients are created by specific membrane-bound ion pumps [adenosine triphosphatases (ATPases)]. According to physicochemical rules passive forces equilibrate (dissipate) ion gradients. The cholesterol/phospholipid ratio of the membrane and the degree of saturation of phospholipid fatty acids are important factors for membrane molecular order and herewith a determinant of the degree of non-specific membrane leakiness. Other operative principles, i.e. specific ion channels can be opened and closed according to mechanisms that are specific to the cell. Certain compounds called ionophores can be integrated in the plasma membrane and permit specific inorganic ions to pass. Irrespective of which mechanism ions leak across the plasma membrane the homeostasis may be kept by increasing ion pumping (ATPase activity) in an attempt to restore the physiological ion gradient. The energy source for this work seems to be glycolytically derived ATP formation. Thus an increase in ion pumping is reflected by increased ATP hydrolysis and rate of glycolysis. This can be measured as an accumulation of breakdown products of ATP and end-products of anaerobic glycolysis (lactate). In certain disease entities, the balance between ATP formation and ion pumping may be disordered resulting in a decrease in inter alia (i.a.) cellular energy charge, and an increase in lactate formation and catabolites of adenylates. Cardiac syndrome X is proposed to be due to an excessive leakage of potassium ions, leading to electrocardiographic (ECG) changes, abnormal Tl-scintigraphy of the heart and anginal pain (induced by adenosine). Cocksackie B3 infections, a common agent in myocarditis might also induce an ionophore-like effect. Moreover, Alzheimer's disease is characterized by the formation of extracellular amyloid deposits in the brain of patients. Perturbation of cellular membranes by the amyloid peptide during the development of Alzheimer's disease is one of several mechanisms proposed to account for the toxicity of this peptide on neuronal membranes. We have studied the effects of the peptide and fragments thereof on 45Ca2+ -uptake in human erythrocytes and the energetic consequences. Treatment of erythrocytes with the ,1,40 peptide, results in qualitatively similar nucleotide pattern and decrease of energy charge as the treatment with Ca2+ -ionophore A23187. Finally, in recent studies we have revealed and published in this journal that a rare condition, Tarui's disease or glycogenosis type VII, primarily associated with a defect M-subunit of phosphofructokinase, demonstrates as a cophenomenon an increased leak of Ca2+ into erythrocytes. [source] Constitutive high-affinity choline transporter endocytosis is determined by a carboxyl-terminal tail dileucine motifJOURNAL OF NEUROCHEMISTRY, Issue 1 2005Fabiola M. Ribeiro Abstract Maintenance of acetylcholine synthesis depends on the effective functioning of a high-affinity sodium-dependent choline transporter (CHT1). Recent studies have shown that this transporter is predominantly localized inside the cell, unlike other neurotransmitter transporters, suggesting that the trafficking of CHT1 to and from the plasma membrane may play a crucial role in regulating choline uptake. Here we found that CHT1 is rapidly and constitutively internalized in clathrin-coated vesicles to Rab5-positive early endosomes. CHT1 internalization is controlled by an atypical carboxyl-terminal dileucine-like motif (L531, V532) which, upon replacement by alanine residues, blocks CHT1 internalization in both human embryonic kidney 293 cells and primary cortical neurons and results in both increased CHT1 cell surface expression and choline transport activity. Perturbation of clathrin-mediated endocytosis with dynamin-I K44A increases cell surface expression and transport activity to a similar extent as mutating the dileucine motif, suggesting that we have identified the motif responsible for constitutive CHT1 internalization. Based on the observation that the localization of CHT1 to the plasma membrane is transient, we propose that acetylcholine synthesis may be influenced by processes that lead to the attenuation of constitutive CHT1 endocytosis. [source] Acute, Rapid, and Chronic Tolerance During Ontogeny: Observations When Equating Ethanol Perturbation Across AgeALCOHOLISM, Issue 9 2001Marisa M. Silveri Background: Sensitivity to the motor-impairing and hypnotic effects of ethanol (EtOH) increases notably during development. Less is known, however, about the ontogeny of EtOH tolerance and the ontogenetic relationship among different types of tolerance. Consequently, we compared the ontogenetic development of acute, rapid, and chronic tolerance to EtOH-induced motor impairment and hypothermia in a swim task. Methods: Preweanling, adolescent, and adult female and male Sprague-Dawley rats were given chronic saline (control group), five daily EtOH exposures before EtOH on test day (chronic group), one EtOH exposure before test day (rapid group), or EtOH exposure only on test day (acute groups). Separate groups of animals in the acute groups were tested at 15, 60, or 105 min after injection to estimate acute tolerance development via calculating slopes of the linear regression of impairment relative to brain alcohol levels at each postinjection interval. Initial EtOH perturbation of swim performance was equated across age by varying EtOH dose. Results: Acute tolerance was evident to the motor-impairing effects of EtOH at all ages. When impairment was indexed relative to brain alcohol levels, rapid and chronic tolerance to the motor-impairing effects of EtOH on latency to reach the start was seen across age, although this tolerance tended to be more pronounced in adults. Somewhat different ontogenetic patterns of tolerance development were observed with EtOH-induced hypothermia, a dependent measure for which EtOH perturbation was not equated across age. Conclusions: The degree of initial perturbation by EtOH seems to be an important predictor of tolerance expression during ontogeny. That is, ontogenetic profiles of tolerance development differ significantly when EtOH-induced motor impairment is equated across age rather than dose of EtOH administered . The role of target response measures and context stress should also be considered when exploring ontogenetic expression of EtOH tolerance. [source] Perturbation of complex polynomials and normal operatorsMATHEMATISCHE NACHRICHTEN, Issue 12 2009Armin Rainer Abstract We study the regularity of the roots of complex monic polynomials P (t) of fixed degree depending smoothly on a real parameter t. We prove that each continuous parameterization of the roots of a generic C, curve P (t) (which always exists) is locally absolutely continuous. Generic means that no two of the continuously chosen roots meet of infinite order of flatness. Simple examples show that one cannot expect a better regularity than absolute continuity. This result will follow from the proposition that for any t0 there exists a positive integer N such that t , P (t0 ± (t , t0)N) admits smooth parameterizations of its roots near t0. We show that Cn curves P (t) (where n = deg P) admit differentiable roots if and only if the order of contact of the roots is , 1. We give applications to the perturbation theory of normal matrices and unbounded normal operators with compact resolvents and common domain of definition: The eigenvalues and eigenvectors of a generic C, curve of such operators can be arranged locally in an absolutely continuous way (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Peritoneal mesothelial cells and the extracellular matrixNEPHROLOGY, Issue 6 2001Susan Yung SUMMARY: Continuous ambulatory peritoneal dialysis (CAPD) is an important treatment for patients with end-stage renal failure. Long-term success is dependent on the functional and structural integrity of the peritoneal membrane. Conventional peritoneal dialysis fluids are non-physiological. They contain glucose at high concentrations to provide the osmotic drive for ultrafiltration, lactate to correct the metabolic acidosis of renal failure, and a low pH to prevent caramelization of glucose during heat sterilization. These components, in isolation or acting together, exert adverse influences on both the resident cellular and extracellular elements of the peritoneal membrane, as well as phagocytic cells which infiltrate the peritoneum during inflammation, culminating in detrimental structural and functional effects, compromising the viability of the peritoneum during dialysis. Peritoneal biopsy studies of patients on long-term CAPD have demonstrated an intercellular space between adjacent mesothelial cells which allows the penetration of peritoneal dialysis fluid into the underlying submesothelium. This, together with episodes of peritonitis, can initiate a chronic inflammatory reaction within the peritoneum characterized by increased synthesis of matrix proteins. Perturbation of the regulatory mechanisms which govern the balance of synthesis and degradation of extracellular matrix can lead to progressive fibrosis. Human peritoneal mesothelial cells (HPMC) have been shown to synthesize fibronectin, laminin, collagens, proteoglycans and hyaluronan in vitro, and thus play a role in the pathogenesis of peritoneal fibrosis. This review will give an overview of extracellular matrix (ECM) synthesis by HPMC, how changes in the synthesis are affected by CAPD and postulate how these changes can compromise the dialytic properties of the peritoneum. [source] Control of Dkk-1 ameliorates chondrocyte apoptosis, cartilage destruction, and subchondral bone deterioration in osteoarthritic kneesARTHRITIS & RHEUMATISM, Issue 5 2010Lin-Hsiu Weng Objective Perturbation of Wnt signaling components reportedly regulates chondrocyte fate and joint disorders. The Wnt inhibitor Dkk-1 mediates remodeling of various tissue types. We undertook this study to examine whether control of Dkk-1 expression prevents joint deterioration in osteoarthritic (OA) knees. Methods Anterior cruciate ligament transection,and collagenase-induced OA in rat knees was treated with end-capped phosphorothioate Dkk-1 antisense oligonucleotide (Dkk-1,AS). Articular cartilage destruction, cartilage degradation markers, bone mineral density (BMD), and subchondral trabecular bone volume of injured knee joints were measured using Mankin scoring, enzyme-linked immunosorbent assay, dual x-ray absorptiometry, and histomorphometry. Dkk-1,responsive molecule expression and apoptotic cells in knee tissue were detected by quantitative reverse transcriptase,polymerase chain reaction, immunoblotting, and TUNEL staining. Results Up-regulated Dkk-1 expression was associated with increased Mankin score and with increased serum levels of cartilage oligomeric matrix protein and C-telopeptide of type II collagen (CTX-II) during OA development. Dkk-1,AS treatment alleviated OA-associated increases in Dkk-1 expression, Mankin score, cartilage fibrillation, and serum cartilage degradation markers. Dkk-1,AS also alleviated epiphyseal BMD loss and subchondral bone exposure associated with altered serum levels of osteocalcin and CTX-I. The treatment abrogated chondrocyte/osteoblast apoptosis and subchondral trabecular bone remodeling in OA. Dkk-1 knockdown increased levels of nuclear ,-catenin and phosphorylated Ser473 -Akt but attenuated expression of inflammatory factors (Toll-like receptor 4 [TLR-4], TLR-9, interleukin-1,, and tumor necrosis factor ,), the apoptosis regulator Bax, matrix metalloproteinase 3, and RANKL in OA knee joints. Conclusion Interference with the cartilage- and bone-deleterious actions of Dkk-1 provides therapeutic potential for alleviating cartilage destruction and subchondral bone damage in OA knee joints. [source] Overexpression of interleukin-23, but not interleukin-17, as an immunologic signature of subclinical intestinal inflammation in ankylosing spondylitisARTHRITIS & RHEUMATISM, Issue 4 2009Francesco Ciccia Objective Subclinical gut inflammation is common in spondylarthritis, but the immunologic abnormalities underlying this process are undefined. Perturbation of the interleukin-23 (IL-23)/Th17 axis has emerged as a fundamental trigger of chronic inflammation. This study was undertaken to investigate the expression and tissue distribution of IL-23/Th17,related molecules in Crohn's disease (CD) and in subclinical gut inflammation in ankylosing spondylitis (AS). Methods Quantitative gene expression analysis of Th1/Th2 and IL-23/Th17 responses was performed in intestinal biopsy samples obtained from 12 patients with CD, 15 patients with AS, and 13 controls. IL-23 tissue distribution and identification of IL-23,producing cells were evaluated by immunohistochemistry. Results We demonstrated a strong and significant up-regulation of IL-23p19 transcripts in the terminal ileum in patients with AS and patients with CD. IL-23 was abundantly produced by infiltrating monocyte-like cells in inflamed mucosa from AS and CD patients. Notably, we also identified Paneth cells as a major source of IL-23 in patients with AS, patients with CD, and normal controls. Unlike CD, in AS patients, IL-23 was not associated with up-regulation of IL-17 and the IL-17,inducing cytokines IL-6 and IL-1,. Finally, while the Th1-related cytokines interferon-,, IL-12p35, and IL-27p28 were overexpressed only in CD patients, IL-4, IL-5, and STAT-6 were also significantly increased in AS patients. Conclusion Our findings indicate that overexpression of IL-23, but not IL-17, is a pivotal feature of subclinical gut inflammation in AS. Identification of resident Paneth cells as a pivotal source of IL-23 in physiologic and pathologic conditions strongly suggests that IL-23 is a master regulator of gut mucosal immunity, providing a pathophysiologic significance to the reported association between IL-23 receptor polymorphisms and intestinal inflammation. [source] Adaptive L2 Disturbance Attenuation Of Hamiltonian Systems With Parametric Perturbation And Application To Power SystemsASIAN JOURNAL OF CONTROL, Issue 1 2003Tielong Shen ABSTRACT This paper deals with the problem of L2 disturbance attenuation for Hamiltonian systems. We first show that the L2 gain from the disturbance to a penalty signal may be reduced to any given level if the penalty signal is defined properly. Then, an adaptive version of the controller will be presented to compensate the parameter perturbation. When the perturbed parameters satisfy a suitable matching condition, it is easy to introduce the adaptive mechanism to the controller. Another contribution of this paper is to apply the proposed method to the excitation control problem for power systems. An adaptive L2 controller for the power system is designed using the proposed method and a simulation result with the proposed controller is given. [source] Perturbation of retinoic acid (RA)-mediated limb development suggests a role for diminished RA signaling in the teratogenesis of ethanol,,§BIRTH DEFECTS RESEARCH, Issue 9 2007Corey S. Johnson Abstract BACKGROUND: A proposed mechanism for ethanol teratogenicity entails ethanol-mediated reductions in retinoic acid (RA). This premise was investigated utilizing a mouse model, with limb reduction defects as the teratogenic end point. METHODS: Ethanol, Disulfiram, or BMS-189453 was administered to C57BL/6J mice on the 9th day of pregnancy. Forelimb morphology was assessed on gestation day 18 using Alcian blue and Alizarin red staining. Nile blue sulfate or LysoTracker Red (LTR) vital staining identified cell death in the limb bud. The ability of RA to prevent ethanol-induced cell death was assessed by coadministration followed by laser scanning confocal microscopic examination of LTR-staining. In situ hybridization and qPCR were used to examine gene expression in treated limb buds. RESULTS: Ethanol, Disulfiram, and BMS-189453 resulted in postaxial ectrodactyly, intermediate ectrodactyly, and other digital defects. Excessive Nile blue sulfate staining was evident in the presumptive AER following each of the three exposures. Ethanol-induced LTR staining was prevented by RA supplementation. Both in situ hybridization and qPCR illustrated decreases in Shh and Tbx5 in ethanol-exposed embryos as compared to control. CONCLUSIONS: Contrary to studies of prolonged RA deficiency, acute exposure to functional antagonists of RA results in limb defects that are morphologically similar to those caused by ethanol. The rescue of ethanol-induced cell death by RA and similar changes in Shh transcription further suggest that RA contributes to ethanol-induced limb dysmorphology. Moreover, the repression of key mediators of limb development soon after ethanol exposure adds to the existing knowledge of the pathogenic effects of ethanol. Birth Defects Research (Part A), 2007. © 2007 Wiley-Liss, Inc. [source] Oxidative Electrochemical Switching in Dithienylcyclopentenes, Part 1: Effect of Electronic Perturbation on the Efficiency and Direction of Molecular Switching,CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005Wesley R. Browne Dr. Abstract The electro- and spectroelectrochemical properties of dithienylhexahydro- and dithienyhexafluorocyclopentenes are reported. The large effect of variation in the central cyclopentene moieties on the redox properties of the dithienylcyclopentenes is in striking contrast to the minor effect on their photochemical properties. The electronic properties of the oxidised compounds in the +1 and +2 oxidation state are reported, and the possibility of electrochemical cyclisation and cycloreversion were explored by UV/Vis spectroelectrochemistry. The efficiency of electrochemical switching is found to be dependent both on the central cyclopentene unit and on the nature of the substituents at C5 of the thienyl rings. For the hexahydrocyclopentene-based compounds oxidative ring closure of the ring-open form is observed, while for the hexafluorocyclopentene-based compounds oxidative ring opening of the ring-closed form is observed. However, the introduction of electroactive groups such as methoxyphenyl allows oxidative ring closure to occur in the hexafluoro compounds. The effect of electrolyte, solvent and temperature on the spectroelectrochemical properties were examined, and the switching process was found to be sensitive to the donor properties of the solvent/electrolyte system employed. In addition, thermally activated reversible isomerisation of the dicationic closed form was observed. The driving force for electrochemical ring opening and closure appears to be dependent on the relative stabilisation of the dicationic ring-open and ring-closed states. This study provides insight into the factors which determine the direction of cyclisation. [source] Dispersion of Dust Acoustic Modes and Perturbations of Plasma Flux BalanceCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3 2007V. Tsytovich Abstract Previous considerations of dust acoustic waves is demonstrated to be inconsistent - the required equilibrium state for perturbations was not defined since balance of plasma fluxes was neglecting. The self-consistent treatment shows that plasma flux perturbations are accompanying any collective waves propagating in dusty plasmas and can play an important role in wave dispersion, wave damping and can create instabilities. This is illustrated by the derivation of dispersion relation for dust acoustic modes taking into account the plasma flux balances and plasma flux perturbations by waves. The result of this approach shows that the dust acoustic waves with linear dependence of wave frequency on the wave number exist only in restricted range of the wave numbers. Only for wave numbers larger than some critical wave number for low frequency modes the frequency can be have approximately a linear dependence on wave number and can be called as dust acoustic wave but the phase velocity of these waves is different from that which can be obtained neglecting the flux balance and depends on grain charge variations which are determined by the balance of fluxes. The presence of plasma fluxes previously neglected is the main typical feature of dusty plasmas. The dispersion relation in the range of small wave numbers is found to be mainly determined by the change of the plasma fluxes and is quite different from that of dust acoustic type, namely it is found to have the same form as the well known dispersion relation for the gravitational instability. This result proves in general way the existence of the collective grain attractions of negatively charged grains for for large distances between them and for any source of ionization. The attraction of grains found from dispersion relation of the dust acoustic branch coincides with that found previously for pair grain interactions using some models for the ionization source. For the existing experiments the effective Jeans length for such attraction is estimated to be about 8 , 10 times larger than the ion Debye length and the effective gravitational constant for the grain attraction is estimated to be several orders of magnitude larger than the usual gravitational constant. The grain attraction at large inter-grain distances described by the gravitationlike grain instability is considered as the simplest explanation for observed dust cloud clustering, formation of dust structures including the plasma crystals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Model of Declining StandardsINTERNATIONAL ECONOMIC REVIEW, Issue 2 2000Joel Sobel This paper presents a model in which relative standing determines standards. There are three kinds of agents in the model: candidates who wish to pass a test, members of the elite who have passed the test, and the judge who decides who passes. In order to pass, a candidate's performance must be at least as good as the performance of a representative member of the elite. Without perturbations in the underlying data, the model predicts that standards will not change. Perturbations in the preferences used to judge candidates lead to a reduction in standards. [source] General guidelines for invasive plant management based on comparative demography of invasive and native plant populationsJOURNAL OF APPLIED ECOLOGY, Issue 4 2008Satu Ramula Summary 1General guidelines for invasive plant management are currently lacking. Population declines may be achieved by focusing control on demographic processes (survival, growth, fecundity) with the greatest impact on population growth rate. However, we often have little demographic information on populations in the early stages of an invasion when control can be most effective. Here we determine whether synthesis of existing demographic data on invasive and native plant populations can address this knowledge problem. 2We compared population dynamics between invasive and native species using published matrix population models for 21 invasive and 179 native plant species. We examined whether the population growth rate responsiveness to survival, growth and fecundity perturbations varied between invasive and native species, and determined which demographic processes of invaders to target for reductions in population growth rate. 3Invaders had higher population growth rates (,) than natives, resulting in differences in demographic processes. Perturbations of growth and fecundity transitions (elasticities) were more important for population growth of invaders, whereas perturbations of survival had greater importance for population growth of natives. 4For both invasive and native species, elasticities of , to survival increased with life span and decreased with ,; while elasticities to growth and fecundity decreased with life span and increased with ,. 5For long-lived invaders, simulated reductions in either survival, growth or fecundity transitions were generally insufficient to produce population declines, whereas multiple reductions in either survival + growth or survival + fecundity were more effective. For short-lived invaders, simulated reductions in growth or fecundity and all pairwise multiple reductions produced population declines. 6Synthesis and applications. Life history and population growth rate of invasive species are important in the selection of control targets. For rapidly growing populations of short-lived invaders, growth and fecundity transitions should be prioritized as control targets over survival transitions. For long-lived invaders, simultaneous reductions in more than one demographic process, preferably survival and growth, are usually required to ensure population decline. These general guidelines can be applied to rapidly growing new plant invasions and at the invasion front where detailed demographic data on invasive species are lacking. [source] Nuclear microenvironments and cancerJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2008Gary S. Stein Nucleic acids and regulatory proteins are architecturally organized in nuclear microenvironments. The compartmentalization of regulatory machinery for gene expression, replication and repair, is obligatory for fidelity of biological control. Perturbations in the organization, assembly and integration of regulatory machinery have been functionally linked to the onset and progression of tumorigenesis. The combined application of cellular, molecular, biochemical and in vivo genetic approaches, together with structural biology, genomics, proteomics and bioinformatics, will likely lead to new approaches in cancer diagnostics and therapy. J. Cell. Biochem. 104: 1949,1952, 2008. © 2008 Wiley-Liss, Inc. [source] Resident bacteria in a mixed population of rhesus macaque (Macaca mulatta) monkeys: a prevalence studyJOURNAL OF MEDICAL PRIMATOLOGY, Issue 6 2009C.A. Carrier Abstract Background, Microflora populations residing in oropharyngeal and gastrointestinal sites defend against pathogenic bacterial colonization. Perturbations in these microbial communities may allow opportunistic pathogenic bacteria to establish themselves and cause morbidity and mortality from sepsis particularly after stressful experimental procedures. This study determined the prevalent facultative bacteria in a resident population of Macaca mulatta prior to use in experimentally induced immunosuppressive radiation studies. Methods, Standard microbiological methods were used to assess prevalent facultative bacteria in the oropharynx and rectum of 24 male M. mulatta. Results, The majority of the bacteria isolated from the oropharyngeal and rectal sites were gram-positive cocci. Species of Staphylococcus and Streptococcus predominated in all samples. Few gram-negative bacteria were isolated. Conclusions, Bacteriological assessment is recommended to identify predominant bacterial species to be prepared to provide appropriate antimicrobial therapy in non-human primates that are expected to undergo stressful immunocompromising procedures. [source] Molecular and Cellular Events in Alcohol-Induced Muscle DiseaseALCOHOLISM, Issue 12 2007Joaquim Fernandez-Solà Alcohol consumption induces a dose-dependent noxious effect on skeletal muscle, leading to progressive functional and structural damage of myocytes, with concomitant reductions in lean body mass. Nearly half of high-dose chronic alcohol consumers develop alcoholic skeletal myopathy. The pathogenic mechanisms that lie between alcohol intake and loss of muscle tissue involve multiple pathways, making the elucidation of the disease somewhat difficult. This review discusses the recent advances in basic and clinical research on the molecular and cellular events involved in the development of alcohol-induced muscle disease. The main areas of recent research interest on this field are as follows: (i) molecular mechanisms in alcohol exposed muscle in the rat model; (ii) gene expression changes in alcohol exposed muscle; (iii) the role of trace elements and oxidative stress in alcoholic myopathy; and (iv) the role of apoptosis and preapoptotic pathways in alcoholic myopathy. These aforementioned areas are crucial in understanding the pathogenesis of this disease. For example, there is overwhelming evidence that both chronic alcohol ingestion and acute alcohol intoxication impair the rate of protein synthesis of myofibrillar proteins, in particular, under both postabsorptive and postprandial conditions. Perturbations in gene expression are contributory factors to the development of alcoholic myopathy, as ethanol-induced alterations are detected in over 400 genes and the protein profile (i.e., the proteome) of muscle is also affected. There is supportive evidence that oxidative damage is involved in the pathogenesis of alcoholic myopathy. Increased lipid peroxidation is related to muscle fibre atrophy, and reduced serum levels of some antioxidants may be related to loss of muscle mass and muscle strength. Finally, ethanol induces skeletal muscle apoptosis and increases both pro- and antiapoptotic regulatory mechanisms. [source] The Price-Volatility Feedback Rate: An Implementable Mathematical Indicator of Market StabilityMATHEMATICAL FINANCE, Issue 1 2003Emilio Barucci Geometric analysis of iterated cross-volatilities of asset prices is adopted to assess the stability of the (risk-free) measure under infinitesimal perturbations. Perturbations of asset prices evolve through time according to an ordinary linear differential equation (hedged transfer). The decay (feedback) rate is explicitly computed through a Fourier series method implemented on high frequency time series. [source] Conservation implications of complex population structure: lessons from the loggerhead turtle (Caretta caretta)MOLECULAR ECOLOGY, Issue 8 2005B. W. BOWEN Abstract Complex population structure can result from either sex-biased gene flow or population overlap during migrations. Loggerhead turtles (Caretta caretta) have both traits, providing an instructive case history for wildlife management. Based on surveys of maternally inherited mtDNA, pelagic post-hatchlings show no population structure across the northern Atlantic (,ST < 0.001, P = 0.919), subadults in coastal habitat show low structure among locations (,ST = 0.01, P < 0.005), and nesting colonies along the southeastern coast of the United States have strong structure (,ST = 0.42, P < 0.001). Thus the level of population structure increases through progressive life history stages. In contrast, a survey of biparentally inherited microsatellite DNA shows no significant population structure: RST < 0.001; FST = 0.002 (P > 0.05) across the same nesting colonies. These results indicate that loggerhead females home faithfully to their natal nesting colony, but males provide an avenue of gene flow between regional nesting colonies, probably via opportunistic mating in migratory corridors. As a result, all breeding populations in the southeastern United States have similar levels of microsatellite diversity (HE = 0.70,0.89), whereas mtDNA haplotype diversity varies dramatically (h = 0.00,0.66). Under a conventional interpretation of the nuclear DNA data, the entire southeastern United States would be regarded as a single management unit, yet the mtDNA data indicate multiple isolated populations. This complex population structure mandates a different management strategy at each life stage. Perturbations to pelagic juveniles will have a diffuse impact on Atlantic nesting colonies, mortality of subadults will have a more focused impact on nearby breeding populations, and disturbances to adults will have pinpoint impact on corresponding breeding populations. These findings demonstrate that surveys of multiple life stages are desirable to resolve management units in migratory marine species. [source] Postural response of the pelvic floor and abdominal muscles in women with and without incontinence,NEUROUROLOGY AND URODYNAMICS, Issue 3 2007Michelle D. Smith Abstract Aims To determine whether activity of the pelvic floor (PF) and abdominal muscles differs between continent and incontinent women in response to a postural perturbation with a moderately full or empty bladder. Methods Electromyographic (EMG) activity of the PF and abdominal muscles was recorded with surface electrodes prior to and after a postural perturbation in which a 1 kg weight was dropped 30 cm into a bucket held by the subject. Perturbations were applied to the trunk in trials in which the timing of the weight drop was unknown (unexpected) or predictable (expected). Trials were performed with the bladder empty, and when the subject reported a sensation of moderate bladder fullness after drinking between 200 and 1,000 ml of water. Results Women with incontinence demonstrated increased PF EMG compared to continent women both prior to and during the postural response associated with unexpected loading. In addition, obliquus externus abdominis EMG was increased in incontinent women during these trials. When the bladder was moderately full, PF EMG decreased, whereas abdominal muscle EMG tended to increase. Conclusions These data suggest that women with incontinence have increased PF and abdominal muscle activity associated with postural perturbations. This finding challenges the clinical assumption that incontinence is associated with reduced PF muscle activity, and suggests that training control and coordination of abdominal muscle activity may be important in treatment of this condition. The contrasting effects of increased bladder volume on PF and abdominal muscle EMG are likely to present further challenges to the maintenance of continence. Neurourol. Urodynam. 26:377,385, 2007. © 2007 Wiley-Liss, Inc. [source] Growth perturbations in a phenotype with rapid fetal growth preceding preterm labor and term birthAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 6 2009Michelle Lampl The variability in fetal growth rates and gestation duration in humans is not well understood. Of interest are women presenting with an episode of preterm labor and subsequently delivering a term neonate, who is small relative to peers of similar gestational age. To further understand these relationships, fetal growth patterns predating an episode of preterm labor were investigated. Retrospective analysis of fetal biometry assessed by serial ultrasound in a prospectively studied sample of pregnancies in Santiago, Chile, tested the hypothesis that fetal growth patterns among uncomplicated pregnancies (n = 3,706) and those with an episode of preterm labor followed by term delivery (n = 184) were identical across the time intervals 16,22 weeks, 22,28 weeks, and 28,34 weeks in a multilevel mixed-effects regression. The hypothesis was not supported. Fetal weight growth rate was faster from 16 weeks among pregnancies with an episode of preterm labor (P < 0.05), declined across midgestation (22,28 weeks, P < 0.05), and rebounded between 28 and 34 weeks (P = 0.06). This was associated with perturbations in abdominal circumference growth and proportionately larger biparietal diameter from 22 gestational weeks (P = 0.03), greater femur (P = 0.01), biparietal diameter (P = 0.001) and head circumference (P = 0.02) dimensions relative to abdominal circumference across midgestation (22,28 weeks), followed by proportionately smaller femur diaphyseal length (P = 0.02) and biparietal diameter (P = 0.03) subsequently. A distinctive rapid growth phenotype characterized fetal growth preceding an episode of preterm labor among this sample of term-delivered neonates. Perturbations in abdominal circumference growth and patterns of proportionality suggest an altered growth strategy pre-dating the preterm labor episode. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] Perturbations produced by electrospray ionization mass spectrometry in the speciation of aluminium(III)/1,6-dimethyl-4-hydroxy-3-pyridinecarboxylate aqueous solutionsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2010Valerio B. Di Marco Electrospray ionization mass spectrometry (ESI-MS) is very often employed to study metal/ligand equilibria in aqueous solution. However, the ionization process can introduce perturbations which affect the speciation results in an unpredictable way. It is necessary to identify these perturbations in order to correctly interpret the ESI-MS speciation results. Aluminium(III)/1,6-dimethyl-4-hydroxy-3-pyridinecarboxylate (DQ716) aqueous solutions at various pH were analysed by ESI-MS, and speciation results were compared with those obtained by equilibrium techniques. Differences observed were both qualitative and quantitative. The ESI-MS spectral changes due to different settings of the following instrumental parameters were analyzed: the solution flow rate (FS), the nebulizer gas flow rate (FG), the potential applied at the entrance capillary (EC), and the temperature of the drying gas (TG). The effects produced by FS and EC on the spectra strongly suggest the key role of surface activity in determining the relative fraction of the ions reaching the detector. The experimental effects of FS and TG were interpreted considering the presence of at least two reactions in the gas phase and a dimerization occurring in the droplets. These perturbations cannot be generalized because they appear to be chemical system-related and instrument-dependent. Therefore, the identification of perturbations is a required task for any metal-ligand equilibrium study performed by ESI-MS. Our results indicate that perturbations can be identified by evaluating the effects produced in the spectra by a change of instrumental parameters. Copyright © 2010 John Wiley & Sons, Ltd. [source] Flow over a hill covered with a plant canopyTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 596 2004J. J. Finnigan Abstract We develop an analytical model for atmospheric boundary-layer flow over a hill that is covered with a vegetation canopy. The slope of the hill is assumed to be small enough that the flow above the canopy can be treated within the linear framework of Hunt. Perturbations to the flow within the canopy are driven by the pressure gradient associated with the flow over the hill. In the upper canopy this pressure gradient is balanced by downwards turbulent transport of momentum and the canopy drag. The flow there can be calculated from linearized dynamics, which show that the maximum streamwise winds are where the perturbation pressure is at a minimum, i.e. near the crest of the hill. Deep within the canopy the pressure gradient associated with the flow over the hill is balanced by the canopy drag, here the nonlinear canopy drag. This nonlinear balance shows how the streamwise winds are largest where the perturbation pressure gradient is largest, i.e. on the upwind slope of the hill. In the lee of the hill this nonlinear solution shows how the pressure gradient decelerates the wind deep within the canopy, leading to separation with a region of reversed flow when the canopy is sufficiently deep. Coupling between the out-of-phase flows within and above the canopy means that the maximum velocity is further upwind of the hill crest than in flow over a rough hill, while the extra turbulent mixing caused by the canopy significantly reduces the magnitude of the velocity speed-up over the hill. Finally, we find that there is no formal limit process where the solutions with a canopy yield the well-known solutions for flow over a rough hill. This finding calls into question the very use of a roughness length in accelerating or decelerating turbulent boundary layers. Copyright © 2004 Royal Meteorological Society [source] Homocysteine metabolism and its relation to health and diseaseBIOFACTORS, Issue 1 2010Kelly T. Williams Abstract Homocysteine is a metabolic intermediate in methyl group metabolism that is dependent on a number of nutritional B-vitamin cofactors. An emerging aspect of homocysteine metabolism is its relation to health and disease. Perturbations of homocysteine metabolism, particularly intracellular and subsequently circulating accumulation of homocysteine (i.e., hyperhomocysteinemia), are associated with vascular disease risk, as well as other pathologies. However, intervention with B-vitamin supplementation has been shown to successfully restore normal homocysteine concentrations, but without concomitant reductions in disease risk. Thus, the mechanistic relation between homocysteine balance and disease states, as well as the value of homocysteine management, remains an area of intense investigation. [source] Specific congenital heart defects in RSH/Smith-Lemli-Opitz syndrome: Postulated involvement of the Sonic Hedgehog pathway in syndromes with postaxial polydactyly or heterotaxiaBIRTH DEFECTS RESEARCH, Issue 3 2003Maria Cristina Digilio BACKGROUND RSH/Smith-Lemli-Opitz syndrome is an autosomal recessive syndrome due to an inborn error of cholesterol metabolism and is characterized by developmental delay, facial anomalies, hypospadias, congenital heart defect (CHD), postaxial polydactyly, and 2,3 toe syndactyly. CHD is found in half of the propositi, and a specific association with atrioventricular canal defect (AVCD) and anomalous pulmonary venous return has been demonstrated. METHODS We report on an additional patient with RSH/SLOS presenting with complete AVCD and anomalous pulmonary venous return, and discuss the possible relationship of the Sonic Hedgehog (SHH) pathway as causative factor of these CHDs and those in heterotaxia patients with postaxial polydactyly syndromes. RESULTS Anatomic similarities between heterotaxia and CHDs of several syndromes with postaxial polydactyly have been noted previously, considering the frequent association of AVCD with common atrium in these conditions. It is known that both CHDs of heterotaxia and postaxial polydactyly can be related to abnormalities of the SHH pathway. Cholesterol has a critical role in the formation of normally active hedgehog proteins. It could be hypothesized that specific types of CHDs in RSH/SLOS can be caused by modifications of the SHH protein related to the defect of cholesterol biosynthesis. CONCLUSIONS The specific association of AVCD and anomalous pulmonary venous return in patients with RSH/SLOS and the finding of AVCD ± common atrium in several syndromes with polydactyly leads to the hypothesis that heterotaxia due to SHH anomalies could be involved in a large spectrum of conditions. Perturbations in different components of the SHH pathway could lead to several developmental errors presenting with partially overlapping clinical manifestations. Birth Defects Research (Part A) 67149,153, 2003. © 2003 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||