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Exponential Decay (exponential + decay)
Terms modified by Exponential Decay Selected AbstractsA general model for predicting brown tree snake capture ratesENVIRONMETRICS, Issue 3 2003Richard M. Engeman Abstract The inadvertent introduction of the brown tree snake (Boiga irregularis) to Guam has resulted in the extirpation of most of the island's native terrestrial vertebrates, has presented a health hazard to small children, and also has produced economic problems. Trapping around ports and other cargo staging areas is central to a program designed to deter dispersal of the species. Sequential trapping of smaller plots is also being used to clear larger areas of snakes in preparation for endangered species reintroductions. Traps and trapping personnel are limited resources, which places a premium on the ability to plan the deployment of trapping efforts. In a series of previous trapping studies, data on brown tree snake removal from forested plots was found to be well modeled by exponential decay functions. For the present article, we considered a variety of model forms and estimation procedures, and used capture data from individual plots as random subjects to produce a general random coefficients model for making predictions of brown tree snake capture rates. The best model was an exponential decay with positive asymptote produced using nonlinear mixed model estimation where variability among plots was introduced through the scale and asymptote parameters. Practical predictive abilities were used in model evaluation so that a manager could project capture rates in a plot after a period of time, or project the amount of time required for trapping to reduce capture rates to a desired level. The model should provide managers with a tool for optimizing the allocation of limited trapping resources. Copyright © 2003 John Wiley & Sons, Ltd. [source] Land use affects the relationship between species diversity and productivity at the local scale in a semi-arid steppe ecosystemFUNCTIONAL ECOLOGY, Issue 5 2006Z. ZHOU Summary 1The accelerating extinction rate of plant species and its effect on ecosystem functioning is a hotly debated topic in ecological research. Most research projects concerning the relationship between species diversity and productivity have been conducted in artificial plant communities, with only a few in natural ecosystems. In this study we examined the relationship between species diversity and above-ground net primary productivity (ANPP) over two consecutive growth seasons (2004 and 2005) in a semi-arid steppe ecosystem of northern China, that were subjected to different land uses. 2Land use affected the relationship between species diversity and ANPP in this semi-arid steppe ecosystem. Exclusion of grazing without or with biomass removal by mowing increased ANPP, species richness and species diversity compared with free grazing; the effect was reflected mainly as enhanced importance of the perennial forbs functional group in terms of their relative contributions to ANPP, plant cover and plant abundance. 3Many mechanisms regulate the relationship between species diversity and productivity. Differential effects of anthropogenic activities on biodiversity and ecosystem functioning greatly complicate the analysis of such relationships. On grazing-exclusion sites the relationship between ANPP and species richness can be best described as an exponential growth function (R2 = 0·99, P < 0·001, n = 24); whereas on the free-grazing site the relationship takes the form of exponential decay (R2 = 0·96, P < 0·001, n = 24). Our study concludes that the mode and severity of disturbance are important factors for interpreting the relationship between species diversity and productivity in semi-arid steppe ecosystems. [source] Carbon dioxide exchange of a Russian boreal forest after disturbance by wind throwGLOBAL CHANGE BIOLOGY, Issue 3 2002Alexander Knohl Abstract The exchange of carbon dioxide (CO2) between the atmosphere and a forest after disturbance by wind throw in the western Russian taiga was investigated between July and October 1998 using the eddy covariance technique. The research area was a regenerating forest (400 m × 1000 m), in which all trees of the preceding generation were uplifted during a storm in 1996. All deadwood had remained on site after the storm and had not been extracted for commercial purposes. Because of the heterogeneity of the terrain, several micrometeorological quality tests were applied. In addition to the eddy covariance measurements, carbon pools of decaying wood in a chronosequence of three different wind throw areas were analysed and the decay rate of coarse woody debris was derived. During daytime, the average CO2 uptake flux was ,3 µmol m,2s,1, whereas during night-time characterised by a well-mixed atmosphere the rates of release were typically about 6 µmol m,2s,1. Suppression of turbulent fluxes was only observed under conditions with very low friction velocity (u* , 0.08 ms,1). On average, 164 mmol CO2 m,2d,1 was released from the wind throw to the atmosphere, giving a total of 14.9 mol CO2 m,2 (180 g CO2 m,2) released during the 3-month study period. The chronosequence of dead woody debris on three different wind throw areas suggested exponential decay with a decay coefficient of ,0.04 yr,1. From the magnitude of the carbon pools and the decay rate, it is estimated that the decomposition of coarse woody debris accounted for about a third of the total ecosystem respiration at the measurement site. Hence, coarse woody debris had a long-term influence on the net ecosystem exchange of this wind throw area. From the analysis performed in this work, a conclusion is drawn that it is necessary to include into flux networks the ecosystems that are subject to natural disturbances and that have been widely omitted into considerations of the global carbon budget. The half-life time of about 17 years for deadwood in the wind throw suggests a fairly long storage of carbon in the ecosystem, and indicates a very different long-term carbon budget for naturally disturbed vs. commercially managed forests. [source] CH3 + Cl = CH3Cl: RRKM/master equation modelingINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2009David M. GoldenArticle first published online: 30 DEC 200 Data for the title reaction have been fitted using an RRKM/master equation approach. Energy transfer was modeled using an exponential decay with downward step sizes, ,Ed, as a fitting parameter. The low temperature (200 < T (K) < 300) combination of CH3 with Cl atoms in He can be accommodated with ,Ed (cm,1) = 400. Higher temperature (1600 < T (K) < 2100) decomposition in Ar required ,Ed(T) (cm,1) = 694(T/300)0.46. Previous analysis of the analogous system CH4 = CH3 + H required ,Ed(T) (cm,1) = 100(T/300) for He and ,Ed(T) (cm,1) = 150(T/300) for Ar. Understanding of the magnitudes and temperature dependence of ,Ed remains the greatest detriment to quantitative calculation, extrapolation, and prediction of unimolecular rate constants. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 245,254, 2009 [source] Time asymmetry, nonexponential decay, and complex eigenvalues in the theory and computation of resonance statesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2002Cleanthes A. Nicolaides Abstract Stationary-state quantum mechanics presents no difficulties in defining and computing discrete excited states because they obey the rules established in the properties of Hilbert space. However, when this idealization has to be abandoned to formulate a theory of excited states dissipating into a continuous spectrum, the problem acquires additional interest in many fields of physics. In this article, the theory of resonances in the continuous spectrum is formulated as a problem of decaying states, whose treatment can entail time-dependent as well as energy-dependent theories. The author focuses on certain formal and computational issues and discusses their application to polyelectronic atomic states. It is argued that crucial to the theory is the understanding and computation of a multiparticle localized wavepacket, ,0, at t = 0, having a real energy E0. Assuming this as the origin, without memory of the excitation process, the author discusses aspects of time-dependent dynamics, for t , 0 as well as for t , ,, and the possible significance of nonexponential decay in the understanding of timeasymmetry. Also discussed is the origin of the complex eigenvalue Schrödinger equation (CESE) satisfied by resonance states and the state-specific methodology for its solution. The complex eigenvalue drives the decay exponentially, with a rate ,, to a good approximation. It is connected to E0 via analytic continuation of the complex self-energy function, A(z), (z is complex), into the second Riemann sheet, or, via the imposition of outgoing wave boundary conditions on the stationary state Schrödinger equation satisfied by the Fano standing wave superposition in the vicinity of E0. If the nondecay amplitude, G(t), is evaluated by inserting the unit operator I = ,dE|E> Unstructured model for seed cultures without pH control of Lactobacillus helveticus growing on supplemented whey permeateJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2002Abdeltif Amrane Abstract In cultures of Lactobacillus helveticus with pH controlled at 5.9, growth and lactic acid production were under the control of nutritional limitations (carbon and nitrogen). In the absence of pH control, as was the case for seed cultures, an inhibitory effect on growth of both pH and the undissociated lactic acid concentration were evident before nutritional limitations. The variations of the specific growth rate with the undissociated lactic acid concentration followed exponential decay. Then, the inhibitory effect of pH was also taken into account through the Henderson,Hasselbach equation. The specific growth rate history has been previously found to follow sigmoidal variation. Integration of these relationships gave the theoretical biomass and lactic acid production kinetics. The model fitted experimental kinetic data well and allowed fine analysis of the various growth phases, since the growth-associated, the deceleration and the stationary states can be characterized by means of the model parameters. © 2002 Society of Chemical Industry [source] Stabilization of penicillin V acylase from Streptomyces lavendulae by covalent immobilizationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2001Jesśs Torres-Bacete Abstract Penicillin,V acylase from the actinomycete Streptomyces lavendulae ATCC 13664 has been immobilized to epoxy-activated acrylic beads (Eupergit C®) by covalent binding. Further linkage of bovine serum albumin after enzyme immobilization was carried out in order to remove the remaining oxirane groups of the support. The obtained immobilized biocatalyst displayed double exponential deactivation kinetics at temperatures below 55,°C, while the native enzyme followed single exponential decay at the same temperatures. We concluded that soluble penicillin acylase was deactivated in one step, whereas the immobilized enzyme showed an enzymatic intermediate state which is highly thermostable. As a consequence of the immobilization process, the enzyme displayed a 10-fold increase in its half-life at 40,°C. At this temperature, the enzymatic intermediate state was progressively destabilized as the pH of the medium was increased. Thus, the optimum pH range for the immobilized enzyme preparation was established as being from 7.0 to 8.0. Higher pH values led to quicker enzyme deactivation. © 2001 Society of Chemical Industry [source] Linear scaling approaches to quantum macromolecular similarity: Evaluating the similarity functionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2002Pere Constans Abstract The evaluation of the electron density based similarity function scales quadratically with respect to the size of the molecules for simplified, atomic shell densities. Due to the exponential decay of the function's atom-atom terms most interatomic contributions are numerically negligible on large systems. An improved algorithm for the evaluation of the Quantum Molecular Similarity function is presented. This procedure identifies all non-negligible terms without computing unnecessary interatomic squared distances, thus effectively turning to linear scaling the similarity evaluation. Presented also is a minimalist dynamic electron density model. Approximate, single shell densities together with the proposed algorithm facilitate fast electron density based alignments on macromolecules. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 1305,1313, 2002 [source] Specimen charging in X-ray absorption spectroscopy: correction of total electron yield data from stabilized zirconia in the energy range 250,915,eVJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2005Dimitrios Vlachos The effects of specimen charging on X-ray absorption spectroscopy using total electron yield have been investigated using powder samples of zirconia stabilized by a range of oxides. The stabilized zirconia powder was mixed with graphite to minimize the charging but significant modifications of the intensities of features in the X-ray absorption near-edge fine structure (XANES) still occurred. The time dependence of the charging was measured experimentally using a time scan, and an algorithm was developed to use this measured time dependence to correct the effects of the charging. The algorithm assumes that the system approaches the equilibrium state by an exponential decay. The corrected XANES show improved agreement with the electron energy-loss near-edge fine structure obtained from the same samples. [source] Low magnetic fields behavior of photon echo in LuLiF4:Er3+LASER PHYSICS LETTERS, Issue 9 2006V. N. Lisin Abstract It is reported about the first observation and studying of the photon echo in LuLiF4:Er3+. The energy transition is 4I15/2 , 4F9/2 (, = 6536 Å). The density of ErF3 is 0.025 wt%. The operation temperature is 1.9 K. Measurements were spent at low (up to 1200 Oe) and even zero external magnetic fields. It was studied a behavior of the photon echo intensity versus the magnetic field magnitude and direction about the crystal axis C and versus the laser pulse separation t12. It was observed an exponential growth and then, after some plateau, an exponential decreasing of the photon echo intensity as a function of magnetic field with increasing of the magnetic field from zero value. The parameters describing the exponential growth and decreasing are not depended on direction of magnetic field. Value of a magnetic field at which the echo intensity accepts the maximum, and quantity of this maximum decrease with increased the pulse separation t12 and the angle , between the magnetic field and crystal axis. The echo intensity exponentially decreases with increased , . The parameter describing the exponential decreasing is not depended on the magnitude of the field. The echo intensity as a function of pulse separation shows exponential decay. The phase relaxation time is depended on the magnitude and direction of the magnetic field. T2 is equal to 202 ± 16 ns at zero magnetic field. Phenomenological formula is suggested, which qualitatively presents the mentioned dependencies. Polarization properties of the backward photon echo in this crystal are studied also. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Design and in vitro Biodegradation of Novel Hepatocyte-Targetable (Galactose Polycation/Hemoglobin) Multilayers and MicrocapsulesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 12 2009Fu Zhang Abstract The formation of novel hepatocyte-targetable and biodegradable polycation/protein multilayers and hollow microcapsules by LbL assembly is reported, in which galactose residues allow for targetability and Hb acts as a main degradable component. The in vitro biodegradability of multilayers via proteases was evaluated in detail on both planar substrates and CaCO3 particles followed by UV-Vis, SEM, and AFM characterizations. The degradation approximately follows an exponential decay, and the relation between the kinetic constant k and the number n of deposited bilayers is well approximated by a power equation. Sustained release of the encapsulated model drug was attained by using enzymatic degradation of hollow capsules. [source] Droplet Tailoring Using Evaporative Inkjet PrintingMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5 2009Jolke Perelaer Abstract An experimental study into the in-flight evaporation and impact of equally sized inkjet printed droplets that consist of a systematically varied polystyrene concentration in either toluene or butyl acetate is presented. At low polymer concentrations, a linear relationship that decreased was observed between dried droplet diameter and printing height. However, increased concentrations revealed an initial exponential decay in the dried droplet diameter, which stabilized at greater heights. At higher concentration and height, the polymer forms a skin on the surface of the inkjet printed droplet, which causes inhibition of the in-flight evaporation of the solvent. [source] On the transient phase of balanced SSFP sequencesMAGNETIC RESONANCE IN MEDICINE, Issue 4 2003Klaus Scheffler Abstract The signal intensity of balanced steady-state free precession (SSFP) imaging is a function of the proton density, T1, T2, flip angle (,), and repetition time (TR). The steady-state signal intensity that is established after about 5*T1/TR can be described analytically. The transient phase or the approach of the echo amplitudes to the steady state is an exponential decay from the initial amplitude after the first excitation pulse to the steady-state signal. An analytical expression of the decay rate of this transient phase is presented that is based on a simple analysis derived from the Bloch equations. The decay rate is a weighted average of the T1 and T2 relaxation times, where the weighting is determined by the flip angle of the excitation pulses. Thus, balanced SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k -space line. In addition, transient imaging of hyperpolarized nuclei, such as 3He, 129Xe, or 13C, can be optimized according to their T1 and T2 relaxation times. Magn Reson Med 49:781,783, 2003. © 2003 Wiley-Liss, Inc. [source] Asymptotic behaviour for a two-dimensional thermoelastic modelMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 5 2007M. Fabrizio Abstract In this paper we study a thermoelastic material with an internal structure which binds the materials fibres to a quadratic behaviour. Moreover, a hereditary constitutive law for heat flux is supposed. We prove results of asymptotic stability and exponential decay for the evolution problem in two-dimensional space domain. Copyright © 2006 John Wiley & Sons, Ltd. [source] A boundary condition with memory for the Kirchhoff plate equations with non-linear dissipationMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 3 2006Jong-Yeoul Park Abstract This paper is concerned with the existence of solutions for the Kirchhoff plate equation with a memory condition at the boundary. We show the exponential decay to the solution, provided the relaxation function also decays exponentially. Copyright © 2005 John Wiley & Sons, Ltd. [source] Blow up, decay bounds and continuous dependence inequalities for a class of quasilinear parabolic problemsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 3 2006L. E. Payne Abstract This paper deals with a class of semilinear parabolic problems. In particular, we establish conditions on the data sufficient to guarantee blow up of solution at some finite time, as well as conditions which will insure that the solution exists for all time with exponential decay of the solution and its spatial derivatives. In the case of global existence, we also investigate the continuous dependence of the solution with respect to some data of the problem. Copyright © 2005 John Wiley & Sons, Ltd. [source] Existence and uniform decay for Euler,Bernoulli beam equation with memory termMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 14 2004Jong Yeoul Park Abstract In this article we prove the existence of the solution to the mixed problem for Euler,Bernoulli beam equation with memory term. The existence is proved by means of the Faedo,Galerkin method and the exponential decay is obtained by making use of the multiplier technique combined with integral inequalities due to Komornik. Copyright © 2004 John Wiley & Sons, Ltd. [source] Selective activation of the sacral anterior roots for induction of bladder voidingNEUROUROLOGY AND URODYNAMICS, Issue 2 2006Narendra Bhadra Abstract Aim We investigated the efficacy of selective activation of the smaller diameter axons in the sacral anterior roots for electrically induced bladder voiding. Materials and Methods Acute experiments were conducted in five adult dogs. The anterior sacral roots S2 and S3 were implanted bilaterally with tripolar electrodes. Pressures were recorded from the bladder and from the proximal urethra and the external urethral sphincter. A detector and flow meter monitored fluid flow. A complete sacral dorsal rhizotomy was carried out. The effects of two types of pulse trains at 20 Hz were compared; quasitrapezoidal pulses (500 µsec with 500 µsec exponential decay) and interrupted rectangular (100 µsec, 2 sec on/2 sec off). Before rhizotomy, rectangular pulse trains (100 µsec) to activate all fibers were also applied. The experimental design was block randomized before and after rhizotomy. Results Quasitrapezoidal pulses showed block of sphincter activation with average minimum current for maximum suppression of 1.37 mA. All pulse types evoked average bladder pressures above the basal sphincter closure pressure. The pressure patterns in the proximal urethra closely followed the bladder pressures. Before dorsal rhizotomy, stimulation evoked a superadded increase in sphincter pressures with slow rise time. After rhizotomy, the sphincter pressure patterns followed the bladder pressures during selective activation and voiding occurred during stimulation with quasitrapezoidal trains and in between bursts with interrupted rectangular stimulation. Conclusions Selective activation of sacral ventral roots combined with dorsal rhizotomy may provide a viable means of low-pressure continuous voiding in neurological impairment. Neurourol. Urdynam. © 2005 Wiley-Liss, Inc. [source] Pharaonis Phoborhodopsin Binds to its Cognate Truncated Transducer Even in the Presence of a Detergent with a 1:1 Stoichiometry,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2001Yuki Sudo ABSTRACT Pharaonis phoborhodopsin (ppR) (also pharaonis sensory rhodopsin II) is a receptor of the negative phototaxis of Natronobacterium pharaonis.ppR forms a complex with its pharaonis halobacterial transducer (pHtrII), and this complex transmits the light signal to the sensory system in the cytoplasm. The expressed C-terminal-His tagged ppR and C-terminal-His tagged truncated pHtrII (t-Htr) in Escherichia coli (His means the 6× histidine tag) form a complex even in the presence of 0.1% of n -dodecyl-,- d -maltoside, and the M-decay of the complex became about twice slower than that of ppR alone. The photocycling rates under varying concentration ratios of ppR to t-Htr in the presence of detergent were measured. The data were analyzed on the following assumptions: (1) the M-decay of both ppR alone and the complex followed a single exponential decay with different time constants; and (2) the M-decay under varying concentration ratios of ppR to t-Htr, therefore, followed a biexponential decay function which combined the decay of the free ppR and that of the complex as photoreactive species. From these analyses we estimated the dissociation constant (15.2 ± 1.8 ,M) and the number of binding sites (1.2 ± 0.08). [source] Energy relaxation processes of photo-generated carriers in Mg doped (0001)GaN and (1-101)GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008J. Saida Abstract Energy relaxation processes of photo-generated excess carriers in Mg doped GaN epitaxial layers were investigated at room temperature, with photoluminescence intensity correlation method using femto-second pulse laser as the excitation source. The decay curve was well fitted by exponential decay with two time constants. The slow process of the order of 100 ps was attributed to the energy relaxation of electrons in the conduction band, while the fast process of the order of several pico-seconds was attributed to the capture process in the impurity band near the valence band. Little difference has been found out between the results for (0001)GaN and those for (1-101)GaN. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The determination of membrane transport parameters with the cell pressure probe: theory suggests that unstirred layers have significant impactPLANT CELL & ENVIRONMENT, Issue 12 2005MELVIN T. TYREE ABSTRACT A simulation model was written to compute the time-kinetics of turgor pressure, P, change in Chara corallina during cell pressure probe experiments. The model allowed for the contribution of a membrane plus zero, one, or two unstirred layers of any desired thickness. The hypothesis that a cell with an unstirred layer is a composite membrane that will follow the same kind of kinetics with or without unstirred layers was tested. Typical ,osmotic pulse' experiments yield biphasic curves with minimum or maximum pressures, Pmin(max), at time tmin(max) and a solute exponential decay with halftime . These observed data were then used to compute composite membrane properties, namely the parameters Lp = the hydraulic conductance, , = reflection coefficient and Ps = solute permeability using theoretical equations. Using the simulation model, it was possible to fit an experimental data set to the same values of Pmin(max), tmin(max) and incorporating different, likely values of unstirred layer thickness, where each thickness requires a unique set of plasmalemma membrane values of Lp, , and Ps. We conclude that it is not possible to compute plasmalemma membrane properties from cell pressure probe experiments without independent knowledge of the unstirred layer thickness. [source] New insight on ,-lactoglobulin binding sites by 1-anilinonaphthalene-8-sulfonate fluorescence decayPROTEIN SCIENCE, Issue 10 2000Maddalena Collini Abstract The fluorescence time decay parameters of the ,-lactoglobulin-1-anilinonaphthalene-8-sulfonate complex have been investigated under physical and chemical perturbations (2 < pH < 8 and added electrolyte 0 < NaCl < 0.5 M) to obtain new insight on the nature of the protein binding interactions. A double exponential decay of the bound probe lifetime has been confirmed by the presence of a longer component, 11 to 14.5 ns, and a shorter component, 2.5 to 3.5 ns. The two lifetimes are ascribed to different binding modes associated also with different exposure to the solvent; in particular, the longer component is attributed to binding inside the hydrophobic beta barrel, while a "surface" site is suggested for the shorter component. A detailed analysis of the lifetime fractional intensities correlates the binding constants with ionic strength and supports the presence of electrostatic effects at both sites. A Debye,Hückel approach, applied to extrapolate the electrostatic free energy contribution vs. pH at vanishing ionic strength, gives interesting clues on the effective charge felt by the ANS ligands in the proximity of each site. In particular, binding is found to parallel the aspartate and glutamate titrations between pH 3 and pH 4.5; the "surface" site mainly responds to the presence of these local titrating charges while the "internal" site more closely follows the overall protein net charge. [source] Mixing in time and space for lattice spin systems: A combinatorial viewRANDOM STRUCTURES AND ALGORITHMS, Issue 4 2004Martin Dyer The paper considers spin systems on the d -dimensional integer lattice ,d with nearest-neighbor interactions. A sharp equivalence is proved between decay with distance of spin correlations (a spatial property of the equilibrium state) and rapid mixing of the Glauber dynamics (a temporal property of a Markov chain Monte Carlo algorithm). Specifically, we show that if the mixing time of the Glauber dynamics is O(n log n) then spin correlations decay exponentially fast with distance. We also prove the converse implication for monotone systems, and for general systems we prove that exponential decay of correlations implies O(n log n) mixing time of a dynamics that updates sufficiently large blocks (rather than single sites). While the above equivalence was already known to hold in various forms, we give proofs that are purely combinatorial and avoid the functional analysis machinery employed in previous proofs. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004 [source] Ca2+ -dependent components of inactivation of unitary cardiac L-type Ca2+ channelsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2010Ira R. Josephson A Ca2+ ion-dependent inactivation (CDI) of L-type Ca2+ channels (LCC) is vital in limiting and shaping local Ca2+ ion signalling in a variety of excitable cell types. However, under physiological conditions the unitary LCC properties that underlie macroscopic inactivation are unclear. Towards this end, we have probed the gating kinetics of individual cardiac LCCs recorded with a physiological Ca2+ ion concentration (2 mm) permeating the channel, and in the absence of channel agonists. Upon depolarization the ensemble-averaged LCC current decayed with a fast and a slow exponential component. We analysed the unitary behaviour responsible for this biphasic decay by means of a novel kinetic dissection of LCC gating parameters. We found that inactivation was caused by a rapid decrease in the frequency of LCC reopening, and a slower decline in mean open time of the LCC. In contrast, with barium ions permeating the channel ensemble-averaged currents displayed only a single, slow exponential decay and little time dependence of the LCC open time. Our results demonstrate that the fast and slow phases of macroscopic inactivation reflect the distinct time courses for the decline in the frequency of LCC reopening and the open dwell time, both of which are modulated by Ca2+ influx. Analysis of the evolution of CDI in individual LCC episodes was employed to examine the stochastic nature of the underlying molecular switch, and revealed that influx on the order of a thousand Ca2+ ions may be sufficient to trigger CDI. This is the first study to characterize both the unitary kinetics and the stoichiometry of CDI of LCCs with a physiological Ca2+ concentration. These novel findings may provide a basis for understanding the mechanisms regulating unitary LCC gating, which is a pivotal element in the local control of Ca2+ -dependent signalling processes. [source] Evolution and modulation of intracellular calcium release during long-lasting, depleting depolarization in mouse muscleTHE JOURNAL OF PHYSIOLOGY, Issue 19 2008Leandro Royer Intracellular calcium signals regulate multiple cellular functions. They depend on release of Ca2+ from cellular stores into the cytosol, a process that in many types of cells appears to be tightly controlled by changes in [Ca2+] within the store. In contrast with cardiac muscle, where depletion of Ca2+ in the sarcoplasmic reticulum is a crucial determinant of termination of Ca2+ release, in skeletal muscle there is no agreement regarding the sign, or even the existence of an effect of SR Ca2+ level on Ca2+ release. To address this issue we measured Ca2+ transients in mouse flexor digitorum brevis (FDB) skeletal muscle fibres under voltage clamp, using confocal microscopy and the Ca2+ monitor rhod-2. The evolution of Ca2+ release flux was quantified during long-lasting depolarizations that reduced severely the Ca2+ content of the SR. As in all previous determinations in mammals and non-mammals, release flux consisted of an early peak, relaxing to a lower level from which it continued to decay more slowly. Decay of flux in this second stage, which has been attributed largely to depletion of SR Ca2+, was studied in detail. A simple depletion mechanism without change in release permeability predicts an exponential decay with time. In contrast, flux decreased non-exponentially, to a finite, measurable level that could be maintained for the longest pulses applied (1.8 s). An algorithm on the flux record allowed us to define a quantitative index, the normalized flux rate of change (NFRC), which was shown to be proportional to the ratio of release permeability P and inversely proportional to Ca2+ buffering power B of the SR, thus quantifying the ,evacuability' or ability of the SR to empty its content. When P and B were constant, flux then decayed exponentially, and NFRC was equal to the exponential rate constant. Instead, in most cases NFRC increased during the pulse, from a minimum reached immediately after the early peak in flux, to a time between 200 and 250 ms, when the index was no longer defined. NFRC increased by 111% on average (in 27 images from 18 cells), reaching 300% in some cases. The increase may reflect an increase in P, a decrease in B, or both. On experimental and theoretical grounds, both changes are to be expected upon SR depletion. A variable evacuability helps maintain a constant Ca2+ output under conditions of diminishing store Ca2+ load. [source] Degradation and effect of hydrogen peroxide in small-scale recirculation aquaculture system biofiltersAQUACULTURE RESEARCH, Issue 8 2010Martin Sune Mųller Abstract From an environmental point of view, hydrogen peroxide (HP) has beneficial attributes compared with other disinfectants in terms of its ready degradation and neutral by-products. The rapid degradation of HP can, however, cause difficulties with regard to safe and efficient water treatment when applied in different systems. In this study, we investigated the degradation kinetics of HP in biofilters from water recirculating aquaculture systems (RAS). The potential effect of HP on the nitrification process in the biofilters was also examined. Biofilter elements from two different pilot-scale RAS were exposed to various HP treatments in batch experiments, and the HP concentration was found to follow an exponential decay. The biofilter ammonia and nitrite oxidation processes showed quick recuperation after exposure to a single dose of HP up to 30 mg L,1. An average HP concentration of 10,13 mg L,1 maintained over 3 h had a moderate inhibitory effect on the biofilter elements from one of the RAS with relatively high organic loading, while the nitrification was severely inhibited in the pilot-scale biofilters from the other RAS with a relatively low organic loading. A pilot-scale RAS, equipped with two biofilter units, both a moving-bed (Biomedia) and a fixed-bed (BIO-BLOK®) biofilter, was subjected to an average HP concentration of ,12 mg L,1 for 3 h. The ammonium- and nitrite-degrading efficiencies of both the Biomedia and the BIO-BLOK® filters were drastically reduced. The filters had not reverted to pre-HP exposure efficiency after 24 h, suggesting a possible long-term impact on the biofilters. [source] Analytic smoothing effect for the Schrödinger equation with long-range perturbationCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 9 2006Andre Martinez We study the microlocal analytic singularity of solutions to the Schrödinger equation with analytic coefficients. Using microlocal weight estimates developed for estimating phase space tunneling, we prove microlocal smoothing estimates that generalize results by Robbiano and Zuily. We show that the exponential decay of the initial state in a cone in the phase space implies microlocal analytic regularity of the solution at a positive time. We suppose the Schrödinger operator is a long-range-type perturbation of the Laplacian, and we employ positive commutator-type estimates to prove the smoothing property. © 2005 Wiley Periodicals, Inc. [source] One-bit sigma-delta quantization with exponential accuracyCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 11 2003C. Si, nan Güntürk One-bit quantization is a method of representing bandlimited signals by ±1 sequences that are computed from regularly spaced samples of these signals; as the sampling density , , ,, convolving these one-bit sequences with appropriately chosen filters produces increasingly close approximations of the original signals. This method is widely used for analog-to-digital and digital-to-analog conversion, because it is less expensive and simpler to implement than the more familiar critical sampling followed by fine-resolution quantization. However, unlike fine-resolution quantization, the accuracy of one-bit quantization is not well-understood. A natural error lower bound that decreases like 2,, can easily be given using information theoretic arguments. Yet, no one-bit quantization algorithm was known with an error decay estimate even close to exponential decay. In this paper, we construct an infinite family of one-bit sigma-delta quantization schemes that achieves this goal. In particular, using this family, we prove that the error signal for ,-bandlimited signals is at most O(2,.07,). © 2003 Wiley Periodicals, Inc. [source]
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