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Feedback Loop (feedback + loop)
Kinds of Feedback Loop Selected AbstractsIntegrated medical feedback systems for drug delivery,AICHE JOURNAL, Issue 4 2005Adam Heller Drugs are now administered at frequencies and doses based on averages optimized for large populations. Because the optimal frequency and dose for an individual differs, transiently or permanently, from that of a population's average, the dosing is necessarily suboptimal. Feedback loop-based individualized integrated medical systems, comprising an implanted sensor, battery, amplifier, processor, and actuator are now in use in cardiac pacemakers and defibrillators. Drug-delivering medical feedback loops, comprising miniature sensors and drug pumps, would individualize, and thereby improve the effectiveness and safety of drugs. Their sensor would continuously or frequently monitor the effect of the drug and adjust, through a medical control algorithm, its flow to the minimum necessary for effectiveness, reducing thereby side effects and improving the success rate of experimental drugs. The pace of integration of the drug delivering feedback loops depends on the availability of proven miniature components and of medical control algorithms. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] The role of soil community biodiversity in insect biodiversityINSECT CONSERVATION AND DIVERSITY, Issue 3 2010ALISON BENNETT Abstract., 1.,This study demonstrates that feedback loops between plants and insects contribute to both plant and insect diversity. Synthesis of several studies reveals that both bottom-up and top-down forces are important for plant and insect communities. 2.,Feedback loops between plants and soil organisms contribute to plant and soil diversity. An analysis of multiple systems reveals that pathogens, mutualists, and a wide variety of soil fauna directly influence, and are influenced by, plant diversity. 3.,The connection of plant,insect and soil,plant feedback loops leads to the maintenance of all three groups, and the maintenance of these feedback loops crucially affects insect diversity. Examples of the influence of soil community diversity on insect diversity, and the influence of insect diversity on soil community diversity, as well as feedbacks through all three trophic levels are provided. 4.,Finally, means of conserving and restoring soil communities to influence the conservation and restoration of insect communities are discussed. [source] EXTENDING SOCIAL DISORGANIZATION THEORY: MODELING THE RELATIONSHIPS BETWEEN COHESION, DISORDER, AND FEAR,CRIMINOLOGY, Issue 2 2001FRED E. MARKOWITZ In this study, we build on recent social disorganization research, estimating models of the relationships between disorder, burglary, cohesion, and fear of crime using a sample of neighborhoods from three waves of the British Crime Survey. The results indicate that disorder has an indirect effect on burglary through fear and neighborhood cohesion. Although cohesion reduces disorder, nonrecursive models show that disorder also reduces cohesion. Part of the effect of disorder on cohesion is mediated by fear. Similar results are obtained in nonrecursive burglary models. Together, the results suggest a feedback loop in which decreases in neighborhood cohesion increase crime and disorder, increasing fear, in turn, further decreasing cohesion. [source] The heel and toe of the cell's foot: A multifaceted approach for understanding the structure and dynamics of focal adhesionsCYTOSKELETON, Issue 11 2009Haguy Wolfenson Abstract Focal adhesions (FAs) are large clusters of transmembrane receptors of the integrin family and a multitude of associated cytoplasmic "plaque" proteins, which connect the extracellular matrix-bound receptors with the actin cytoskeleton. The formation of nearly stationary FAs defines a boundary between the dense and highly dynamic actin network in lamellipodium and the sparser and more diverse cytoskeletal organization in the lamella proper, creating a template for the organization of the entire actin network. The major "mechanical" and "sensory" functions of FAs; namely, the nucleation and regulation of the contractile, myosin-II-containing stress fibers and the mechanosensing of external surfaces depend, to a major extent, on the dynamics of molecular components within FAs. A central element in FA regulation concerns the positive feedback loop, based on the most intriguing feature of FAs; that is, their dependence on mechanical tension developing by the growing stress fibers. FAs grow in response to such tension, and rapidly disassemble upon its relaxation. In this article, we address the mechanistic relationships between the process of FA development, maturation and dissociation and the dynamic molecular events, which take place in different regions of the FA, primarily in the distal end of this structure (the "toe") and the proximal "heel," and discuss the central role of local mechanical forces in orchestrating the complex interplay between FAs and the actin system. Cell Motil. Cytoskeleton 66: 1017,1029, 2009. © 2009 Wiley-Liss, Inc. [source] Comparison of Endovenous Radiofrequency Versus 810 nm Diode Laser Occlusion of Large Veins in an Animal ModelDERMATOLOGIC SURGERY, Issue 1 2002Robert A. Weiss MDArticle first published online: 27 FEB 200 background. Endovenous occlusion using radiofrequency (RF) energy has been shown to be effective for the elimination of sapheno-femoral reflux and subsequent elimination of varicose veins. Recently, endovenous laser occlusion has been introduced with initial clinical reports indicating effective treatment for varicose veins. However, in our practice we note increased peri-operative hematoma and tenderness with the laser. Little is known regarding the mechanism of action of this new laser vein therapy. objective. To better understand the mechanism of action of endovenous laser vs. the endovenous RF procedure in the jugular vein of the goat model. methods. A bilateral comparison was performed using 810 nm diode laser transmitted by a bare-tipped optical fiber vs. the RF delivery by engineered electrodes with a temperature feedback loop using a thermocouple (Closure procedure) in three goat jugular veins. Immediate and one-week results were studied radiographically and histologically. Temperature measurements during laser treatment were performed by using an array of up to five thermocouples, spaced 2 mm apart, placed adjacent to a laser fiber tip during goat jugular vein treatment. results. Immediate findings showed that 100% of the laser-treated veins showed perforations by histologic examination and immediate contrast fluoroscopy. The RF-treated side showed immediate constriction with maintenance of contrast material within the vein lumen and no perforations. The difference in acute vein shrinkage was also dramatic as laser treatments resulted in vein shrinkage of 26%, while RF-treated veins showed a 77% acute reduction in diameter. At one week, extravasated blood that leaked into the surrounding tissue of laser treated veins acutely, continued to occupy space and impinge on surrounding structures including nerves. For the laser treatment, the highest average temperature was 729°C (peak temperature 1334°C) observed flush with the laser fiber tip, while the temperature feedback mechanism of the RF method maintains temperatures at the electrodes of 85°C. conclusion. Vein perforations, extremely high intravascular temperatures, failure to cause significant collagen shrinkage, and intact endothelium in an animal model justify a closer look at the human clinical application of the 810 nm endovenous laser technique. Extravasated blood impinging on adjacent structures may theoretically lead to increased peri-operative hematoma and tenderness. Further study and clinical investigation is warranted. [source] Zinc-finger paralogues tsh and tio are functionally equivalent during imaginal development in Drosophila and maintain their expression levels through auto- and cross-negative feedback loopsDEVELOPMENTAL DYNAMICS, Issue 1 2009José Bessa Abstract teashirt (tsh) and tiptop (tio) are two Drosophila gene paralogues encoding zinc-finger transcription factors. While tsh is an important developmental regulator, tio null individuals are viable and fertile. Here, we show that tio and tsh have coincident expression domains in the imaginal discs, the precursors of the adult body, and that both genes show similar functional properties when expressed ectopically. Furthermore, tio is able to rescue the development of tsh mutants, indicating that both genes are functionally equivalent during imaginal development. Of interest, the transcriptional regulation of tio and tsh is linked by a negative feedback loop. This mechanism might be required to maintain a tight control on the total levels of tio/tsh and could help explaining why Drosophila keeps an apparently dispensable gene. Developmental Dynamics 238:19,28, 2009. © 2008 Wiley-Liss, Inc. [source] Pax3 and Dach2 positive regulation in the developing somiteDEVELOPMENTAL DYNAMICS, Issue 3 2002G. Kardon Abstract In vertebrates, skeletal muscles of the body arise from cells of somitic origin. Recently, somite culture experiments have identified a set of genes, including Pax3, Six1, Eya2, and Dach2, that appear to play an important role in early myogenesis during somite development (Heanue et al. [1999] Genes Dev. 13:3231,3243). In somite culture Pax3, Six1, Eya2, and Dach2 not only function to activate myogenesis, but they form a complex network regulating each other's transcription. We sought to examine whether this putative Pax3/Six1/Eya2/Dach2 network of regulation actually functions in vivo. In particular, we tested whether Pax3 and Dach2 participate in a positive regulatory feedback loop in vivo as they do in culture. To test in vivo Pax3/Dach2 interregulation, we took advantage of the known dependence of both factors on ectodermal signals. Somites isolated from the overlying ectoderm lose expression of Pax3 and Dach2. Therefore, we attempted to rescue Pax3 or Dach2 expression in somites isolated from the ectoderm by retroviral misexpression of the complementary factor. Indeed misexpression of Pax3 or Dach2 resulted in rescue of Dach2 or Pax3, respectively. These rescue experiments demonstrate that Pax3 and Dach2 positively regulate each other's expression in vivo and support the validity of the Pax3/Six1/Eya2/Dach 2 network in regulating myogenesis. © 2002 Wiley-Liss, Inc. [source] Toward a better understanding of the pathophysiology of OCD SSRI responders: QEEG source localizationACTA PSYCHIATRICA SCANDINAVICA, Issue 3 2007T. G. Bolwig Objective:, To demonstrate the utility of three-dimensional source localization of the scalp-recorded electroencephalogram (EEG) for the identification of the most probable underlying brain dysfunction in patients with obsessive,compulsive disorder (OCD). Method:, Eyes-closed resting EEG data was recorded from the scalp locations of the International 10/20 System. Variable resolution electromagnetic tomography (VARETA) was applied to artifact-free EEG data. This mathematical algorithm estimates the source generators of EEG recorded from the scalp. Results:, An excess in the alpha range was found with sources in the corpus striatum, in the orbito-frontal and temporo-frontal regions in untreated OCD patients. This abnormality was seen to decrease following successful treatment with paroxetine. Conclusion:, The VARETA findings of an activation/deactivation pattern in cortical and subcortical structures in paroxetine-responsive patients are in good accordance with data obtained in previously published positron emission tomography studies related to current hypotheses of a thalamo-striatal-frontal feedback loop being relevant for understanding the pathophysiology of OCD. [source] The micro-topography of the wetlands of the Okavango Delta, BotswanaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2005T. Gumbricht Abstract The surface of the 40 000 km2 Okavango alluvial fan is remarkably smooth, and almost everywhere lies within two to three metres of a perfectly smooth theoretical surface. Deviations from this perfect surface give rise to islands in the Okavango wetlands. This micro-topography was mapped by assigning empirical elevations to remotely sensed vegetation community classes, based on the observation that vegetation is very sensitive to small, local differences in elevation. Even though empirical, the method produces fairly accurate results. The technique allows estimation of depths of inundation and therefore will be applicable even when high resolution radar altimetry becomes available. The micro-topography has arisen as a result of clastic sedimentation in distributary channels, which produces local relief of less than two metres, and more importantly as a result of chemical precipitation in island soils, which produces similar local relief. The micro-topography is, therefore, an expression of the non-random sedimentation taking place on the fan. Volume calculations of islands extracted from the micro-topography, combined with estimates of current sediment in,ux, suggest that the land surface of the wetland may only be a few tens of thousands of years old. Constant switching of water distribution, driven by local aggradation, has distributed sediment widely. Mass balance calculations suggest that over a period of c. 150 000 years all of the fan would at one time or other have been inundated, and thus subject to sedimentation. Coalescing of islands over time results in net aggradation of the fan surface. The amount of vertical aggradation on islands and in channels is restricted by the water depth. Restricted vertical relief, in turn, maximizes the distribution of water, limiting its average depth. Aggradation in the permanent swamps occurs predominantly by clastic sedimentation. Rates of aggradation here are very similar to those in the seasonal swamps, maintaining the overall gradient, possibly because of the operation of a feedback loop between the two. The limited amount of local aggradation arising from both clastic and chemical sedimentation, combined with constant changes in water distribution, has resulted in a near-perfect conical surface over the fan. In addition to providing information on sedimentary processes, the micro-topography has several useful hydrological applications. Copyright © 2004 John Wiley & Sons, Ltd. [source] Indirect effects of algae on coral: algae-mediated, microbe-induced coral mortalityECOLOGY LETTERS, Issue 7 2006Jennifer E. Smith Abstract Declines in coral cover are generally associated with increases in the abundance of fleshy algae. In many cases, it remains unclear whether algae are responsible, directly or indirectly, for coral death or whether they simply settle on dead coral surfaces. Here, we show that algae can indirectly cause coral mortality by enhancing microbial activity via the release of dissolved compounds. When coral and algae were placed in chambers together but separated by a 0.02 ,m filter, corals suffered 100% mortality. With the addition of the broad-spectrum antibiotic ampicillin, mortality was completely prevented. Physiological measurements showed complementary patterns of increasing coral stress with proximity to algae. Our results suggest that as human impacts increase and algae become more abundant on reefs a positive feedback loop may be created whereby compounds released by algae enhance microbial activity on live coral surfaces causing mortality of corals and further algal growth. [source] Regulation of erythropoietin productionEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 2005K.-U. Eckardt Abstract The glycoprotein hormone erythropoietin (EPO) is an essential growth and survival factor for erythroid progenitor cells, and the rate of red blood cell production is normally determined by the serum EPO concentration. EPO production is inversely related to oxygen availability, so that an effective feedback loop is established, which controls erythropoiesis. Since recombinant EPO became available as an effective therapeutic agent, significant progress has also been made in understanding the basis of this feedback control. The main determinant of EPO synthesis is the transcriptional activity of its gene in liver and kidneys, which is related to local oxygen tensions. This control is achieved by hypoxia-inducible transcription factors (HIF), consisting of a constitutive ,-subunit and one of two alternative oxygen-regulated HIF, subunits (HIF-1, and HIF-2,). In the presence of oxygen (normoxia) the HIF, subunits are hydroxylated, which targets them for proteasomal degradation. Under hypoxia, because of the lack of molecular oxygen, HIF cannot be hydroxylated and is thereby stabilized. Although HIF-1, was the first transcription factor identified through its ability to bind to an enhancer sequence of the EPO gene, more recent evidence suggests that HIF-2, is responsible for the regulation of EPO. Although EPO is a prime example for an oxygen- regulated gene, the role of the HIF system goes far beyond the regulation of EPO, because it operates widely in almost all cells and controls a broad transcriptional response to hypoxia, including genes involved in cell metabolism, angiogenesis and vascular tone. Further evidence suggests that apart from its effect as an erythropoietic hormone EPO acts as a paracrine, tissue-protective protein in the brain and possibly also in other organs. [source] Phospholipase,C, negatively regulates Rac/Cdc42 activation in antigen-stimulated mast cellsEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 1 2007Mirvat El-Sibai M.D. Abstract The Rho GTPases Rac and Cdc42 play a central role in the regulation of secretory and cytoskeletal responses in antigen-stimulated mast cells. In this study, we examine the kinetics and mechanism of Rac and Cdc42 activation in the rat basophilic leukemia RBL-2H3 cells. The activation kinetics of both Rac and Cdc42 show a biphasic profile, consisting of an early transient peak at 1,min and a late sustained activation phase at 20,40,min. The inhibition of phospholipase,C (PLC), causes a twofold increase in Rac and Cdc42 activation that coincides with a dramatic production of atypical filopodia-like structures. Inhibition of protein kinase,C using bisindolylmaleimide mimics the effect of PLC, inhibition on Rac activation, but not on Cdc42 activation. In contrast, depletion of intracellular calcium leads to a complete inhibition of the early activation peak of both Rac and Cdc42, without significant effects on the late sustained activation. These data suggest that PLC, is involved in a negative feedback loop that leads to the inhibition of Rac and Cdc42. They also suggest that the presence of intracellular calcium is a prerequisite for both Rac and Cdc42 activation. [source] Modulation by adenosine of both muscarinic M1 -facilitation and M2 -inhibition of [3H]-acetylcholine release from the rat motor nerve terminalsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2002Laura Oliveira Abstract The crosstalk between adenosine and muscarinic autoreceptors regulating evoked [3H]-acetylcholine ([3H]-ACh) release was investigated on rat phrenic nerve-hemidiaphragm preparations. Motor nerve terminals possess facilitatory M1 and inhibitory M2 autoreceptors that can be activated by McN-A-343 (1,30 µm) and oxotremorine (0.3,100 µm), respectively. The muscarinic receptor antagonist, dicyclomine (3 nm,10 µm), caused a biphasic (inhibitory/facilitatory) effect, indicating that M1 -facilitation prevails during 5 Hz stimulation trains. Concomitant activation of AF,DX 116-sensitive M2 receptors was partially attenuated, as pretreatment with M1 antagonists, muscarinic toxin 7 (MT-7, 0.1 nm) and pirenzepine (1 nm), significantly enhanced inhibition by oxotremorine. Activation of A2A -adenosine receptors with CGS 21680C (2 nm) (i) potentiated oxotremorine inhibition, and (ii) shifted McN-A-343-induced facilitation into a small inhibitory effect. Conversely, the A1 -receptor agonist, R- N6 -phenylisopropyl adenosine (R-PIA, 100 nm), attenuated the inhibitory effect of oxotremorine, without changing facilitation by McN-A-343. Synergism between A2A and M2 receptors is regulated by a reciprocal interaction with facilitatory M1 receptors, which may be prevented by pirenzepine (1 nm). During 50 Hz-bursts, facilitation (M1) of [3H]-ACh release by McN-A-343 disappeared, while the inhibitory (M2) effect of oxotremorine became predominant. This muscarinic shift results from the interplay with A2A receptors, as it was precluded by the selective A2A receptor antagonist, ZM 241385 (10 nm). In conclusion, when the muscarinic M1 positive feedback loop is fully operative, negative regulation of ACh release is mediated by adenosine A1 receptors. During high frequency bursts, tonic activation of A2A receptors promotes M2 autoinhibition by braking the M1 receptor operated counteraction. [source] Opposing actions of neuropeptide Y and light on the expression of circadian clock genes in the mouse suprachiasmatic nucleiEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2002Elizabeth S. Maywood Abstract The circadian clockwork of the hypothalamic suprachiasmatic nuclei (SCN) is synchronized by light and by nonphotic cues. The core timing mechanism is cell-autonomous, based on an autoregulatory transcriptional/translational feedback loop of circadian genes and their products. This study investigated the effects of neuropeptide Y (NPY), a potent nonphotic resetting cue, and its interaction with light in regulating clock gene expression in the SCN in vivo. Injection of NPY adjacent to the SCN and transfer to darkness 7 h before scheduled lights out, shifted the circadian activity,rest cycle. Exposure to light for 1 h immediately after NPY infusion blocked this behavioural response. NPY-induced shifts were accompanied by suppression of both mPer1 and mPer2 mRNA in the SCN, assessed 3 h after infusion. mPer mRNAs were not altered 1 h after infusion. Levels of mClock mRNA or mCLOCK immunoreactivity in the SCN were not affected by NPY at either time point. In parallel to the behavioural response, the NPY-induced suppression of mPer genes in the SCN was attenuated when a light pulse was delivered immediately after the infusion. These results identify mPer1 and mPer2 as molecular targets for both photic and nonphotic (NPY-induced) resetting of the clockwork, and support a synthetic model of circadian entrainment based upon convergent up- and downregulation of mPer expression. [source] EVOLUTIONARY PATHWAYS IN SHOREBIRD BREEDING SYSTEMS: SEXUAL CONFLICT, PARENTAL CARE, AND CHICK DEVELOPMENTEVOLUTION, Issue 10 2005Gavin H. Thomas Abstract Sexual selection, mating opportunities, and parental behavior are interrelated, although the specific nature of these relationships is controversial. Two major hypotheses have been suggested. The parental investment hypothesis states that the relative parental investment of the sexes drives the operation of sexual selection. Thus, the sex that invests less in offspring care competes more intensely and monopolizes access to mates. The sexual conflict hypothesis proposes that sexual selection (the competition among both males and females for mates), mating opportunities, and parental behavior are interrelated and predicts a feedback loop between mating systems and parental care. Here we test both hypotheses using a comprehensive dataset of shorebirds, a maximum-likelihood statistical technique, and a recent supertree of extant shorebirds and allies. Shorebirds are an excellent group for these analyses because they display unique variation in parental care and social mating system. First, we show that chick development constrains the evolution of both parental care and mate competition, because transitions toward more precocial offspring preceded transitions toward reduced parental care and social polygamy. Second, changes in care and mating systems respond to one another, most likely because both influenced and are influenced by mating opportunities. Taken together, our results are more consistent with the sexual conflict hypothesis than the parental investment hypothesis. [source] Seasonal dynamics of macrophytes and phytoplankton in shallow lakes: a eutrophication-driven pathway from plants to plankton?FRESHWATER BIOLOGY, Issue 3 2010CARL D. SAYER Summary 1. Seasonal relationships between macrophyte and phytoplankton populations may alter considerably as lakes undergo eutrophication. Understanding of these changes may be key to the interpretation of ecological processes operating over longer (decadal-centennial) timescales. 2. We explore the seasonal dynamics of macrophytes (measured twice in June and August) and phytoplankton (measured monthly May,September) populations in 39 shallow lakes (29 in the U.K. and 10 in Denmark) covering broad gradients for nutrients and plant abundance. 3. Three site groups were identified based on macrophyte seasonality; 16 lakes where macrophyte abundance was perennially low and the water generally turbid (,turbid lakes'); 7 where macrophyte abundance was high in June but low in August (,crashing' lakes); and 12 where macrophyte abundance was high in both June and August (,stable' lakes). The seasonal behaviour of the crashing and turbid lakes was extremely similar with a consistent increase in nutrient concentrations and chlorophyll- a over May,September. By contrast in the stable lakes, seasonal changes were dampened with chlorophyll- a consistently low (<10,15 ,g L,1) over the entire summer. The crashing lakes were dominated by one or a combination of Potamogeton pusillus, Potamogeton pectinatus and Zannichellia palustris, whereas Ceratophyllum demersum and Chara spp. were more abundant in the stable lakes. 4. A long-term loss of macrophyte species diversity has occurred in many shallow lakes affected by eutrophication. One common pathway is from a species-rich plant community with charophytes to a species-poor community dominated by P. pusillus, P. pectinatus and Z. palustris. Such compositional changes may often be accompanied by a substantial reduction in the seasonal duration of plant dominance and a greater tendency for incursions by phytoplankton. We hypothesise a slow-enacting (10,100 s years) feedback loop in nutrient-enriched shallow lakes whereby increases in algal abundance are associated with losses of macrophyte species and hence different plant seasonal strategies. In turn such changes may favour increased phytoplankton production thus placing further pressure on remaining macrophytes. This study blurs the distinction between so-called turbid phytoplankton-dominated and clear plant-dominated shallow lakes and suggests that plant loss from them may be a gradual process. [source] The evolution of gnathostome development: Insight from chondrichthyan embryologyGENESIS: THE JOURNAL OF GENETICS AND DEVELOPMENT, Issue 12 2009J. Andrew Gillis Alcian blue skeletal preparations of wild-type (front) and retinoic acid-treated (back) embryos of the little skate, Leucoraja erinacea. As in paired fins, the cartilaginous gill rays of L. erinacea are patterned by a retinoic acid-regulated Sonic hedghog (Shh)-Fibroblast growth factor 8 (Fgf8) feedback loop, and exposure to exogenous retinoic acid induces ectopic Shh expression and mirror-image gill ray duplications. (Cover design by Kalliopi Monoyios and Randy Dahn). See the review by Gillis and Shubin in this issue. [source] Nodal-related gene Xnr5 is amplified in the Xenopus genomeGENESIS: THE JOURNAL OF GENETICS AND DEVELOPMENT, Issue 7 2006Shuji Takahashi Abstract In Xenopus, six nodal-related genes (Xnrs) have been identified to date. We found numerous tandem duplications of Xnr5 in the Xenopus laevis and Xenopus tropicalis genomes that involve highly conserved copies of coding and regulatory regions. The duplicated versions of Xnr5 were expressed in both the superficial and deep layer of dorsal endoderm and in the deep layer of ventral endoderm, where the initial inducers of mesendoderm formation would be expected to be localized. Overexpression of secreted inhibitors of Xnrs led to a substantially enhanced transcription of the duplicated Xnr5 genes and Xnr6 in embryos. Therefore, Xnr5 and Xnr6 have a novel feedback loop to inhibit transcription of Xnr5 and Xnr6. These results suggest that the initialization of a strong Xnr5 and Xnr6 signal is enabled by the rapid transcription from multiple genes. The novel feedback loop may negatively regulate transcription of Xnr5s and Xnr6 to limit overproduction of these potent inducers, with the Xnr5/Xnr6 signal then activating positive (Xnrs) and negative (Xlefty) loops, which regulate the range of mesodermal tissues produced. genesis 44:309,321, 2006. [source] Elastin-derived peptides: Matrikines critical for glioblastoma cell aggressiveness in a 3-D systemGLIA, Issue 16 2009Bérénice Coquerel Abstract In the most common primary brain tumors, malignant glioma cells invade the extracellular matrix (ECM) and proliferate rapidly in the cerebral tissue, which is mainly composed of hyaluronan (HA) along with the elastin present in the basement membrane of blood vessels. To determine the role of ECM components in the invasive capacity of glioma cell lines, we developed a 3-D cell-culture system, based on a hydrogel in which HA can be coreticulated with kappa-elastin (HA-,E). Using this system, the invasiveness of cells from four glioma cell lines was dramatically increased by the presence of ,E and a related, specific peptide (VGVAPG)3. In addition, MMP-2 secretion increased and MMP-12 synthesis occurred. Extracellular injections of ,E or (VGVAPG)3 provoked a pronounced and dose-dependent increase in [Ca2+]i. ,E significantly enhanced the expression of the genes encoding elastin-receptor and tropoelastin. We propose the existence of a positive feedback loop in which degradation of elastin generates fragments that stimulate synthesis of tropoelastin followed by further degradation as well as migration and proliferation of the very cells responsible for degradation. All steps in this ECM-based loop could be blocked by the addition of either of the EBP antagonists, lactose, and V-14 peptide, suggesting that the loop itself should be considered as a new therapeutic target. © 2009 Wiley-Liss, Inc. [source] The effects of water table draw-down (as a surrogate for climate change) on the hydrology of a fen peatland, CanadaHYDROLOGICAL PROCESSES, Issue 17 2006Peter N. Whittington Abstract Hydrological response to climate change may alter the biogeochemical role that peatlands play in the global climate system, so an understanding of the nature and magnitude of this response is important. In 2002, the water table in a fen peatland near Quebec City was lowered by ,20 cm (Experimental site), and hydrological response was measured compared to Control (no manipulation) and Drained (previously drained c. 1994) sites. Because of the draw-down, the surface in the Experimental pool decreased 5, 15 and 20 cm in the ridge, lawn and mat, respectively, increasing bulk density by ,60% in the Experimental lawn. Hydraulic conductivity (K) generally decreased with depth and from Control (25,125 cm) 10,1 to 10,5 cm s,1 to Experimental (25,125 cm) 10,2 to 10,7 cm s,1 and to Drained (25,75 cm) 10,2 to 10,6 cm s,1. In similar topographic locations (ridge, lawn, mat), K trended Control > Experimental > Drained, usually by an order of magnitude at similar depths in similar topographic locations. Water table fluctuations in the Drained site averaged twice those of the Control site. The water table in the Control lawn remained at a stable depth relative to the surface (,, 1 cm) because the lawn peat floats with changes in water table position. However, the Drained lawn peat was more rigid because of the denser degraded peat, forcing the water to fluctuate relative to the surface and further enhancing peat decay and densification. This provides a positive feedback loop that could intensify further peat degradation, changing the carbon cycling dynamics. Copyright © 2006 John Wiley & Sons, Ltd. [source] The ancestral complement system in sea urchinsIMMUNOLOGICAL REVIEWS, Issue 1 2001L. Courtney Smith Summary: The origin of adaptive immunity in the vertebrates can be traced to the appearance of the ancestral RAG genes in the ancestral jawed vertebrate; however, the innate immune system is more ancient. A central subsystem within innate immunity is the complement system, which has been identified throughout and seems to be restricted to the deuterostomes. The evolutionary history of complement can be traced from the sea urchins (members of the echinoderm phylum), which have a simplified system homologous to the alternative pathway, through the agnathans (hagfish and lamprey) and the elasmobranchs (sharks and rays) to the teleosts (bony fish) and tetrapods, with increases in the numbers of complement components and duplications in complement pathways. Increasing complexity in the complement system parallels increasing complexity in the deuterostome animals. This review focuses on the simplest of the complement systems that is present in the sea urchin. Two components have been identified that show significant homology to vertebrate C3 and factor B (Bf), called SpC3 and SpBf, respectively. Sequence analysis from both molecules reveals their ancestral characteristics. Immune challenge of sea urchins indicates that SpC3 is inducible and is present in coelomic fluid (the body fluids) in relatively high concentrations, while SpBf expression is constitutive and is present in much lower concentrations. Opsonization of foreign cells and particles followed by augmented uptake by phagocytic coelomocytes appears to be a central function for this simpler complement system and important for host defense in the sea urchin. These activities are similar to some of the functions of the homologous proteins in the vertebrate complement system. The selective advantage for the ancestral deuterostome may have been the amplification feedback loop that is still of central importance in the alternative pathway of complement in higher vertebrates. Feedback loop functions would quickly coat pathogens with complement leading to phagocytosis and removal of foreign cells, a system that would be significantly more effective than an opsonin that binds upon contact as a result of simple diffusion. An understanding of the immune response of the sea urchin, an animal that is a good estimator of what the ancestral deuterostome immune system was like, will aid us in understanding how adaptive immunity might have been selected for during the early evolution of the vertebrates and how it might have been integrated into the pre-existing innate immune system that was already in place in those animals. The authors are grateful to Drs Sham Nair and Paul Gross for their critique of the manuscript and helpful suggestions. This work was supported by the National Science Foundation (MCB 9603086). [source] Manoeuvring and vibration reduction of a flexible spacecraft integrating optimal sliding mode controller and distributed piezoelectric sensors/actuatorsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 6 2007Qinglei Hu Abstract This investigation is to apply optimal sliding mode (OSM) control theory and distributed piezoelectric sensor/actuator technology to vibration control of a flexible spacecraft. An approximate analytical dynamic model of a slewing flexible spacecraft with surface-bonded piezoelectric sensors/actuators is developed using Hamilton's principle with discretization by assumed model method. To satisfy pointing requirements and simultaneously suppress vibration, two separate control loops are adopted. The first uses the piezoceramics as sensors and actuators to actively suppress certain flexible modes by designing a positive position feedback (PPF) compensators that add damping to the flexible structures in certain critical modes in the inner feedback loop; then a second feedback loop is designed using OSM control to slew the spacecraft. The OSM controller minimizes the expected value of a quadratic objective function consisting of only the states with the constraints that the error states always remain on the intersection of sliding surfaces. The advantage in this method is that the vibration reduction and attitude control are achieved separately in the two separate feedback loops, allowing the pointing requirements and simultaneous vibrations suppression to be satisfied independently of one another. An additional attraction of the design method is that the selection of PPF gain is determined by introducing a cost function to be minimized by the feedback gains which are subject to the stability criterion at the same time, such that the feedback gains are selected in a more systematical way to avoid the arbitrary selecting of feedback gains. The proposed control strategy has been implemented on a flexible spacecraft, which is a hub with a cantilever flexible beam appendage and can undergo a single axis rotation. Both analytical and numerical results are presented to show the theoretical and practical merits of this approach. Copyright © 2006 John Wiley & Sons, Ltd. [source] Convergence and synthesis issues in extremum seeking controlINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 10 2003R. N. Banavar Abstract Convergence and synthesis issues in an extremum seeking control scheme are addressed. The goal of an extremum seeking controller is to operate at a setpoint that represents the optimal value of a function being optimized in the feedback loop. The results presented here are based solely on assumptions on the curvature of the function being optimized in the loop. We present a class of generalized PI compensators and a set of strictly proper and stable compensators. Copyright © 2003 John Wiley & Sons, Ltd. [source] Designing predictors for MIMO switching supervisory controlINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 3 2001Edoardo Mosca Abstract The paper studies the problem of inferring the behaviour of a linear feedback loop made up by an uncertain MIMO plant and a given candidate controller from data taken from the plant possibly driven by a different controller. In such a context, it is shown here that a convenient tool to work with is a quantity called normalized discrepancy. This is a measure of mismatch between the loop made up by the unknown plant in feedback with the candidate controller and the nominal ,tuned-loop' related to the same candidate controller. It is shown that discrepancy can in principle be obtained by resorting to the concept of a virtual reference, and conveniently computed in real time by suitably filtering an output prediction error. The latter result is of relevant practical value for on-line implementation and of paramount importance in switching supervisory control of uncertain plants, particularly in the case of a coarse distribution of candidate models. Copyright © 2001 John Wiley & Sons, Ltd. [source] The hypothalamus-pituitary-testis axis in boys during the first six months of life: a comparison of cryptorchidism and hypospadias cases with controlsINTERNATIONAL JOURNAL OF ANDROLOGY, Issue 5 2009Frank H. Pierik Summary It is inconclusive whether the feedback mechanisms of the hypothalamus-pituitary-testis (HTP) axis are already established in the first 6 months of life, partly due to the dramatic changes in HPT-axis hormone levels over this period. Moreover, it is unclear whether these hormone levels are aberrant in boys with cryptorchidism or hypospadias, and therefore predictive for future fertility. We studied the regulation mechanisms of the HTP axis, and the effect of age, in boys 1,6 months of age. Secondly, we studied testicular function - as reflected by HPT hormones - in newborns with cryptorchidism or hypospadias. Sera from a population sample of infants with cryptorchidism (n = 43), hypospadias (n = 41) and controls (n = 113) were analyzed for inhibin B, anti-Müllerian hormone (AMH), testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH) and sex hormone binding globulin (SHBG). LH, testosterone, non-shbg-bound testosterone (NSBT), and AHM levels showed significant age-related trends. After age-correction, a negative correlation between FSH and inhibin B was observed (r = ,0.43). The only significant group-differences were lower testosterone and NSBT levels in cryptorchidism cases, with a mean testosterone of 1.8 and 2.6 nmol/L and a mean NSBT of 0.48 and 0.70 nmol/L for cryptorchidism cases and controls, respectively. The higher levels of LH, testosterone, and NSBT in boys born pre-term or with a low birthweight indicate that abnormal prenatal development may determine postnatal testis function. Our results support the hypothesis that the inhibin B , FSH feedback loop is already functional before puberty. The lower testosterone and NSBT levels indicate that disturbed Leydig cell function can already be detected early after birth in cryptorchid boys. [source] Modeling hippocampal theta oscillation: Applications in neuropharmacology and robot navigationINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 9 2006Tamás Kiss This article introduces a biologically realistic mathematical, computational model of theta (,5 Hz) rhythm generation in the hippocampal CA1 region and some of its possible further applications in drug discovery and in robotic/computational models of navigation. The model shown here uses the conductance-based description of nerve cells: Populations of basket cells, alveus/lacunosum-moleculare interneurons, and pyramidal cells are used to model the hippocampal CA1 and a fast-spiking GABAergic interneuron population for modeling the septal influence. Results of the model show that the septo-hippocampal feedback loop is capable of robust theta rhythm generation due to proper timing of pyramidal cells and synchronization within the basket cell network via recurrent connections. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 903,917, 2006. [source] H, feedback-control theory in biochemical systemsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2008E. Gershon Abstract In this paper we study the possible optimality of biochemical pathways in the H, sense. We start by presenting simple linearized models of single enzymatic reaction systems, where we apply classical and modern tools of feedback-control theory. We then apply the results obtained by our analysis to a linearly unbranched enzyme pathway system, where we explore the effect of a negative feedback loop internally exerted on the system by a self-product of the pathway. We then probe the sensitivity of the enzymatic system to variations in certain variables and we deal with the problem of assessing the optimality of the static-output feedback control, in the H, sense, inherent to the closed-loop system. In this point we demonstrate the applicability of our results via a theoretical example that provides an open-loop and closed-loop analysis of a four-block enzymatic system. We then apply the various tools we developed to the optimal analysis of the Threonine synthesis pathway which is regulated by three feedback loops. We demonstrate that this pathway is optimal in the H, sense, in the face of considerable uncertainties in the various enzyme concentrations of the pathway. Copyright © 2007 John Wiley & Sons, Ltd. [source] Inherent limitations and control design for camless engine idle speed dynamicsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 11 2001Yan Wang Abstract The idle speed control problem of a spark-ignited engine equipped with a camless valvetrain is considered. The camless valvetrain allows control of the individual intake and exhaust valves of each cylinder and can be used to achieve unthrottled operation, and consequently, optimize the engine performance. We formulate the speed control problem for this engine and show that it exhibits unstable open-loop behaviour with a significant delay in the feedback loop. The instability is intrinsic to the unthrottled operation and specific to the camless actuation used to achieve the unthrottled operation. The delay is caused by the discrete combustion process and the sensor/computer/actuator interface. We demonstrate the inherent system limitations associated with the unstable dynamics and the delay and provide insight on the structural (plant) design that can alleviate these limitations. Finally, stabilizing controllers using classical and modern robust design techniques are presented and tested on a nonlinear simulation model. Copyright © 2001 John Wiley & Sons, Ltd. [source] Social Representations Theory: A Progressive Research Programme for Social PsychologyJOURNAL FOR THE THEORY OF SOCIAL BEHAVIOUR, Issue 4 2008MARTIN W. BAUER ABSTRACT The study "Psychoanalysis,its image and its public" intimates that common sense is increasingly informed by science. But common sense asserts its autonomy and, in turn, may affect the trajectory of science. This is a process that leads to many differentiations,in common sense, in scientific innovation and in political and regulatory structures. Bauer and Gaskell's toblerone model of triangles of mediation provided a distillation of their reading of "La Psychanalyse." Here it was argued that representations are multi-modal phenomena necessitating the use of multiple methodologies (comparative and longitudinal; qualitative and quantitative). In this paper we briefly summarise these arguments and elaborate ways in which social representation theory can be considered a progressive research programme. "Progressive" because as the theory has developed it has extended the range and depth of its conceptual basis; it provides a new synthesis for the social scientific understanding of the phenomena of common sense and of representation; it acts as an antidote to the reductionism of public opinion and, finally, it is a stimulus to depart from disciplinary silos. However, there remain unresolved issues: how to segment the relevant social milieus and how to close the feedback loop from common sense to science? [source] Negative Regulation by p70 S6 Kinase of FGF-2,Stimulated VEGF Release Through Stress-Activated Protein Kinase/c- Jun N-Terminal Kinase in Osteoblasts,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 3 2007Shinji Takai Abstract To clarify the mechanism of VEGF release in osteoblasts, we studied whether p70 S6 kinase is involved in basic FGF-2,stimulated VEGF release in osteoblast-like MC3T3-E1 cells. In this study, we show that p70 S6 kinase activated by FGF-2 negatively regulates VEGF release through SAPK/JNK in osteoblasts. Introduction: Vascular endothelial growth factor (VEGF) plays an important role in bone metabolism. We have previously reported that fibroblast growth factor-2 (FGF-2) stimulates the release of VEGF through p44/p42 mitogen-activated protein (MAP) kinase and stress-activated protein kinase/c- Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells and that FGF-2,activated p38 MAP kinase negatively regulates VEGF release. However, the mechanism behind VEGF release in osteoblasts is not precisely known. Materials and Methods: The levels of VEGF released from MC3T3-E1 cells were measured by enzyme immunoassay. The phosphorylation of each protein kinase was analyzed by Western blotting. To knock down p70 S6 kinase in MC3T3-E1 cells, the cells were transfected with siRNA to target p70 S6 kinase. Results: FGF-2 time-dependently induced the phosphorylation of p70 S6 kinase. Rapamycin significantly enhanced the FGF-2,stimulated VEGF release and VEGF mRNA expression. The FGF-2,induced phosphorylation of p70 S6 kinase was suppressed by rapamycin. Rapamycin markedly enhanced the FGF-2,induced phosphorylation of SAPK/JNK without affecting the phosphorylation of p44/p42 MAP kinase or p38 MAP kinase. SP600125, a specific inhibitor of SAPK/JNK, suppressed the amplification by rapamycin of the FGF-2,stimulated VEGF release similar to the levels of FGF-2 with SP600125. Finally, downregulation of p70 S6 kinase by siRNA significantly enhanced the FGF-2,stimulated VEGF release and phosphorylation of SAPK/JNK. Conclusions: These results strongly suggest that p70 S6 kinase limits FGF-2,stimulated VEGF release through self-regulation of SAPK/JNK, composing a negative feedback loop, in osteoblasts. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||