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Time Constant (time + constant)
Kinds of Time Constant Selected AbstractsCardiac function during mild hypothermia in pigs: increased inotropy at the expense of diastolic dysfunctionACTA PHYSIOLOGICA, Issue 1 2010H. Post Abstract Aim:, The induction of mild hypothermia (MH; 33 °C) has become the guideline therapy to attenuate hypoxic brain injury after out-of-hospital cardiopulmonary resuscitation. While MH exerts a positive inotropic effect in vitro, MH reduces cardiac output in vivo and is thus discussed critically when severe cardiac dysfunction is present in patients. We thus assessed the effect of MH on the function of the normal heart in an in vivo model closely mimicking the clinical setting. Methods:, Ten anaesthetized, female human-sized pigs were acutely catheterized for measurement of pressure,volume loops (conductance catheter), cardiac output (Swan-Ganz catheter) and for vena cava inferior occlusion. Controlled MH (from 37 to 33 °C) was induced by a vena cava inferior cooling catheter. Results:, With MH, heart rate (HR) and whole body oxygen consumption decreased, while lactate levels remained normal. Cardiac output, left ventricular (LV) volumes, peak systolic and end-diastolic pressure and dP/dtmax did not change significantly. Changes in dP/dtmin and the time constant of isovolumetric relaxation demonstrated impaired active relaxation. In addition, MH prolonged the systolic and shortened the diastolic time interval. Pressure,volume analysis revealed increased end-systolic and end-diastolic stiffness, indicating positive inotropy and reduced end-diastolic distensibility. Positive inotropy was preserved during pacing, while LV end-diastolic pressure increased and diastolic filling was substantially impaired due to delayed LV relaxation. Conclusion:, MH negatively affects diastolic function, which, however, is compensated for by decreased spontaneous HR. Positive inotropy and a decrease in whole body oxygen consumption warrant further studies addressing the potential benefit of MH on the acutely failing heart. [source] Low-volume muscle endurance training prevents decrease in muscle oxidative and endurance function during 21-day forearm immobilizationACTA PHYSIOLOGICA, Issue 4 2009T. Homma Abstract Aim:, To examine the effects of low-volume muscle endurance training on muscle oxidative capacity, endurance and strength of the forearm muscle during 21-day forearm immobilization (IMM-21d). Methods:, The non-dominant arm (n = 15) was immobilized for 21 days with a cast and assigned to an immobilization-only group (Imm-group; n = 7) or an immobilization with training group (Imm+Tr-group; n = 8). Training comprised dynamic handgrip exercise at 30% of pre-intervention maximal voluntary contraction (MVC) at 1 Hz until exhaustion, twice a week during the immobilization period. The duration of each exercise session was 51.7 ± 3.4 s (mean ± SE). Muscle oxidative capacity was evaluated by the time constant for phosphocreatine recovery (,offPCr) after a submaximal handgrip exercise using 31phosphorus-magnetic resonance spectroscopy. An endurance test was performed at 30% of pre-intervention MVC, at 1 Hz, until exhaustion. Results:,,offPCr was significantly prolonged in the Imm-group after 21 days (42.0 ± 2.8 and 64.2 ± 5.1 s, pre- and post-intervention respectively; P < 0.01) but did not change for the Imm+Tr-group (50.3 ± 3.0 and 48.8 ± 5.0 s, ns). Endurance decreased significantly for the Imm-group (55.1 ± 5.1 and 44.7 ± 4.6 s, P < 0.05) but did not change for the Imm+Tr-group (47.9 ± 3.0 and 51.7 ± 4.0 s, ns). MVC decreased similarly in both groups (P < 0.01). Conclusions:, Twice-weekly muscle endurance training sessions, each lasting approx. 50 s, effectively prevented a decrease in muscle oxidative capacity and endurance; however, there was no effect on MVC decline with IMM-21d. [source] Impaired oxygen kinetics in beta-thalassaemia major patientsACTA PHYSIOLOGICA, Issue 3 2009I. Vasileiadis Abstract Aim:, Beta-thalassaemia major (TM) affects oxygen flow and utilization and reduces patients' exercise capacity. The aim of this study was to assess phase I and phase II oxygen kinetics during submaximal exercise test in thalassaemics and make possible considerations about the pathophysiology of the energy-producing mechanisms and their expected exercise limitation. Methods:, Twelve TM patients with no clinical evidence of cardiac or respiratory disease and 10 healthy subjects performed incremental, symptom-limited cardiopulmonary exercise testing (CPET) and submaximal, constant workload CPET. Oxygen uptake (Vo2), carbon dioxide output and ventilation were measured breath-by-breath. Results:, Peak Vo2 was reduced in TM patients (22.3 ± 7.4 vs. 28.8 ± 4.8 mL kg,1 min,1, P < 0.05) as was anaerobic threshold (13.1 ± 2.7 vs. 17.4 ± 2.6 mL kg,1 min,1, P = 0.002). There was no difference in oxygen cost of work at peak exercise (11.7 ± 1.9 vs. 12.6 ± 1.9 mL min,1 W,1 for patients and controls respectively, P = ns). Phase I duration was similar in TM patients and controls (24.6 ± 7.3 vs. 23.3 ± 6.6 s respectively, P = ns) whereas phase II time constant in patients was significantly prolonged (42.8 ± 12.0 vs. 32.0 ± 9.8 s, P < 0.05). Conclusion:, TM patients present prolonged phase II on-transient oxygen kinetics during submaximal, constant workload exercise, compared with healthy controls, possibly suggesting a slower rate of high energy phosphate production and utilization and reduced oxidative capacity of myocytes; the latter could also account for their significantly limited exercise tolerance. [source] Gating of the expressed T-type Cav3.1 calcium channels is modulated by Ca2+ACTA PHYSIOLOGICA, Issue 4 2006L. Lacinová Abstract Aim:, We have investigated the influence of Ca2+ ions on the basic biophysical properties of T-type calcium channels. Methods:, The Cav3.1 calcium channel was transiently expressed in HEK 293 cells. Current was measured using the whole cell patch clamp technique. Ca2+ or Na+ ions were used as charge carriers. The intracellular Ca2+ was either decreased by the addition of 10 mm ethyleneglycoltetraacetic acid (EGTA) or increased by the addition of 200 ,m Ca2+ into the non-buffered intracellular solution. Various combinations of extra- and intracellular solutions yielded high, intermediate or low intracellular Ca2+ levels. Results:, The amplitude of the calcium current was independent of intracellular Ca2+ concentrations. High levels of intracellular Ca2+ accelerated significantly both the inactivation and the activation time constants of the current. The replacement of extracellular Ca2+ by Na+ as charge carrier did not affect the absolute value of the activation and inactivation time constants, but significantly enhanced the slope factor of the voltage dependence of the inactivation time constant. Slope factors of voltage dependencies of channel activation and inactivation were significantly enhanced. The recovery from inactivation was faster when Ca2+ was a charge carrier. The number of available channels saturated for membrane voltages more negative than ,100 mV for the Ca2+ current, but did not reach steady state even at ,150 mV for the Na+ current. Conclusions:, Ca2+ ions facilitate transitions of Cav3.1 channel from open into closed and inactivated states as well as backwards transition from inactivated into closed state, possibly by interacting with its voltage sensor. [source] Impact of Left Ventricular Function on the Pulmonary Vein Doppler Spectrum:ECHOCARDIOGRAPHY, Issue 1 2003Nonsimultaneous Assessment with Load-Insensitive Indices Pulmonary vein Doppler spectrum is highly load-dependent and thus has been used to estimate left ventricular (LV) filling pressure. However, the impact of LV function on pulmonary vein Doppler spectrum remains obscure because only load-sensitive indices were studied previously. In the present study, measurements of the pulmonary vein Doppler spectrum were correlated with load-insensitive LV systolic (end-systolic elastance [Ees]) and diastolic (relaxation time constant [tau] and beta coefficient of the end-diastolic pressure volume relationship) function indices obtained from an invasive catheterization study nonsimultaneously. The peak velocity, velocity time integral, and duration of systolic forward spectrum were significantly correlated with Ees (r = 0.35, r = 0.36, andr = 0.41, respectively;P < 0.05). The pulmonary vein diastolic velocity time integral (PVDVTI) and duration of the diastolic forward spectrum were significantly correlated with Ees (r = 0.51andr = 0.57, respectively;P < 0.01). PVDVTI was correlated with tau and the end-diastolic pressure-volume relationship (EDPVR) (r = 0.42andr = 0.40respectively,P < 0.05). On the other hand, the systolic fraction of the forward spectrum was significantly correlated with ejection fraction (for peak velocity,r = 0.63, P < 0.01; for velocity time integral,r = 0.37, P < 0.05) but not with Ees, and the diastolic fraction of the forward spectrum was significantly correlated with minimum pressure derivative over time (for peak velocity,r = 0.48, P < 0.05; for velocity time integral,r = 0.44, P < 0.05, respectively) but not with tau or EDPVR. In summary, the systolic and diastolic components of the pulmonary vein Doppler spectrum are affected variably by LV systolic and diastolic function, independent of the loading condition. The systolic and diastolic fraction of pulmonary vein Doppler spectrum appears to depend more on the loading condition than the LV systolic or diastolic function. (ECHOCARDIOGRAPHY, Volume 20, January 2003) [source] Construction of Lyapunov function for power system based on solving linear matrix inequalityELECTRICAL ENGINEERING IN JAPAN, Issue 4 2007Atsushi Ishigame Abstract This paper presents construction of Lyapunov functions for power systems based on solving the Linear Matrix Inequality (LMI) derived from the Lyapunov stability theorem considering the dynamics of load characteristic and AVR control system. The proposed Lyapunov function is constructed as a quadratic form of state variables and an integral term which satisfies the curl equation and the sector condition. An induction machine and a synchronous machine are considered as load characteristics. One-machine one-load infinite bus system is considered taking into account the flux decay effects and AVR with one time constant of the generator. To verify the proposed Lyapunov function, the transient stability assessment is shown. The critical clearing times given by the proposed Lyapunov function are compared with those obtained by the numerical integration method, and they are shown to be practical. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 42, 50, 2007; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20328 [source] Detection of metastable excited molecules N2(A3,u+) in an atmospheric pressure nitrogen discharge by Raman scatteringELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 6 2010Tetsuo Fukuchi Abstract Raman scattering from metastable excited nitrogen molecules N2(A3,u+) created by an impulse discharge in nitrogen at atmospheric pressure was detected. A pulsed Nd:YAG laser at a wavelength of 266 nm was used as the light source, and Raman scattering from N2(A3,u+) at a wavelength of 277 nm was detected using an interference filter and photomultiplier tube. The filter had sufficient rejection of Rayleigh scattering of laser light at a wavelength of 266 nm and of Raman scattering from ground-state nitrogen molecules N2(X1,g+) at a wavelength of 284 nm. The temporal variation of the signal intensity of Raman scattering from N2(A3,u+) was measured by transmitting the laser light at different time delays relative to sparkover. The results showed that the signal intensity decayed with a time constant of about 200µs. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(6): 34,40, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10205 [source] Atorvastatin therapy improves exercise oxygen uptake kinetics in post-myocardial infarction patientsEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 6 2007M. Guazzi Abstract Background Statins represent a modern mainstay of the drug treatment of coronary artery disease and acute coronary syndromes. Reduced aerobic work performance and slowed VO2 kinetics are established features of the clinical picture of post-myocardial infarction (MI) patients. We tested the hypothesis that statin therapy improves VO2 exercise performance in normocholesterolaemic post-MI patients. Materials and methods, According to a double-blinded, randomized, crossover and placebo-controlled study design, in 18 patients with uncomplicated recent (3 days) MI we investigated the effects of atorvastatin (20 mg day,1) on gas exchange kinetics by calculating VO2 effective time constant (tau) during a 50-watt constant workload exercise, brachial artery flow-mediated dilatation (FMD) as an index of endothelial function, left ventricular function (echocardiography) and C-reactive protein (CRP, as an index of inflammation). Atorvastatin or placebo was given for 3 months each. Results, Atorvastatin therapy significantly improved exercise VO2 tau and FMD, and reduced CRP levels. We did not observe changes in cardiac contractile function and relaxation properties during all study periods in either group. Conclusions, In post-MI patients exercise performance is a potential additional target of benefits related to statin therapy. Endothelial function improvement is very likely implicated in this newly described therapeutic property. [source] Odour-evoked [Ca2+] transients in mitral cell dendrites of frog olfactory glomeruliEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2001Kerry Delaney Abstract We measured Ca2+ concentration, [Ca2+], transients in mitral cell distal apical dendritic tufts produced by physiological odour stimulation of the olfactory epithelium and electrical stimulation of the olfactory nerve (ON) using two-photon scanning and conventional wide-field microscopy of Ca2+ -Green-1 dextran in an in vitro frog nose,brain preparation. Weak or strong ON shock-evoked fluorescence transients always had short latency with an onset 0,10 ms after the onset of the bulb local field potential, rapidly increasing to a peak of up to 25% fractional fluorescence change (,F/F) in 10,30 ms, were blocked by 10 µm CNQX, decaying with a time constant of about 1 s. With stronger ON shocks that activated many receptor axons, an additional, delayed, sustained AP5-sensitive component (peak at ,,0.5 s, up to 40% ,F/F maximum) could usually be produced. Odour-evoked [Ca2+] transients sometimes displayed a rapid onset phase that peaked within 50 ms but always had a sustained phase that peaked 0.5,1.5 s after onset, regardless of the strength of the odour or the amplitude of the response. These were considerably larger (up to 150% ,F/F) than those evoked by ON shock. Odour-evoked [Ca2+] transients were also distinguished from ON shock-evoked transients by tufts in different glomeruli responding with different delays (time to onset differed by up to 1.5 s between different tufts for the same odour). Odour-evoked [Ca2+] transients were increased by AMPA-kainate receptor blockade, but substantially blocked by AP5. Electrical stimulation of the lateral olfactory tract (5,6 stimuli at 10 Hz) that evoked granule cell feedback inhibition, blocked 60,100% of the odour-evoked [Ca2+] transient in tufts when delivered within about 0.5 s of the odour. LOT-mediated inhibition was blocked by 10 µm bicuculline. [source] Two-dimensional finite element thermal modeling of an oil-immersed transformerEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 6 2008Jawad Faiz Abstract Finite element (FE) modeling of a typical transformer indicates that the hot spot position is always on the top most part of the transformer. The hot spot temperature of winding depends on the load and the type of loading and is changed by loading. A number of the generated magnetic flux lines of windings close to their paths perpendicular to the internal channel of the windings and therefore the flux density in the middle of the channel is considerably larger than the beginning and ending of the winding. Two models of windings are employed and different temperature distributions are obtained. The computation results show that the time constant of high voltage (HV) winding is lower than that of the low voltage (LV) winding. A good agreement between the test and computed results has been achieved. Copyright © 2007 John Wiley & Sons, Ltd. [source] The action of high K+ and aglycaemia on the electrical properties and synaptic transmission in rat intracardiac ganglion neurones in vitroEXPERIMENTAL PHYSIOLOGY, Issue 2 2009Jhansi Dyavanapalli We have investigated the action of two elements of acute ischaemia, high potassium and aglycaemia, on the electrophysiological properties and ganglionic transmission of adult rat intracardiac ganglion (ICG) neurones. We used a whole-mount ganglion preparation of the right atrial ganglion plexus and sharp microelectrode recording techniques. Increasing extracellular K+ from its normal value of 4.7 mm to 10 mm decreased membrane potential and action potential after-hyperpolarization amplitude but otherwise had no effect on postganglionic membrane properties. It did, however, reduce the ability of synaptically evoked action potentials to follow high-frequency (100 Hz) repetitive stimulation. A further increase in K+ changed both the passive and the active membrane properties of the postganglionic neurone: time constant, membrane resistance and action potential overshoot were all decreased in high K+ (20 mm). The ICG neurones display a predominantly phasic discharge in response to prolonged depolarizing current pulses. High K+ had no impact on this behaviour but reduced the time-dependent rectification response to hyperpolarizing currents. At 20 mm, K+ practically blocked ganglionic transmission in most neurones at all frequencies tested. Aglycaemia, nominally glucose-free physiological saline solution (PSS), increased the time constant and membrane resistance of ICG neurones but otherwise had no action on their passive or active properties or ganglionic transmission. However, the combination of aglycaemia and 20 mm K+ displayed an improvement in passive properties and ganglionic transmission when compared with 20 mm K+ PSS. These data indicate that the presynaptic terminal is the primary target of high extracellular potassium and that aglycaemia may have protective actions against this challenge. [source] Effects of Ischaemia on Subsequent Exercise-Induced Oxygen Uptake Kinetics in Healthy Adult HumansEXPERIMENTAL PHYSIOLOGY, Issue 2 2002Michael L. Walsh Leg muscles were occluded (33 kPa) prior to exercise to determine whether the induced metabolic changes, and reactive hyperaemia upon occlusion release just prior to the exercise, would accelerate the subsequent oxygen consumption (V,O2) response. Eight subjects performed double bouts (6 min duration, 6 min rest in-between) of square wave leg cycle ergometry both below and above their lactate threshold (LT). Prior to exercise, large blood pressure cuffs were put around the upper thighs. Occlusion durations were 0 min (control), 5 min and 10 min. Ischaemia was terminated within 5 s prior to exercise onset. Heart rate, V,O2, ventilatory rate (V,E), electromyogram (EMG) and haemoglobin/myoglobin (Hb/Mb) saturation were recorded continuously. Single exponential modelling demonstrated that, compared to control (time constant = 53.9 ± 13.9 s), ischaemia quickened the V,O2 response (P < 0.05) for the first bout of exercise above LT (time constant = 48.3 ± 14.5 s) but not to any other exercise bout below or above LT. The 3-6 min integrated EMG (iEMG) slope was correlated to the 3-6 min V,O2 slope (r = 0.73). Hb/Mb saturation verified the ischaemia but did not show a consistent relation to the V,O2 time course. Reactive hyperaemia induced a faster V,O2 response for work rates above LT. The effect, while significant, was not large considering the expected favourable metabolic and circulatory changes induced by ischaemia. [source] On the kinetics of voltage formation in purple membranes of Halobacterium salinariumFEBS JOURNAL, Issue 19 2000Richard W. Hendler The kinetics of the bacteriorhodopsin photocycle, measured by voltage changes in a closed membrane system using the direct electrometrical method (DEM) of Drachev, L.A., Jasaitus, A.A., Kaulen, A.D., Kondrashin, A.A., Liberman, E.A., Nemecek, I.B., Ostroumov, S.A., Semenov, Yu, A. & Skulachev, V.P. (1974) Nature249, 321,324 are sixfold slower than the kinetics obtained in optical studies with suspensions of purple membrane patches. In this study, we have investigated the reasons for this discrepancy. In the presence of the uncouplers carbonyl cyanide m -chlorophenylhydrazone or valinomycin, the rates in the DEM system are similar to the rates in suspensions of purple membrane. Two alternative explanations for the effects of uncouplers were evaluated: (a) the ,back-pressure' of the ,µ,H+ slows the kinetic steps leading to its formation, and (b) the apparent difference between the two systems is due to slow major electrogenic events that produce little or no change in optical absorbance. In the latter case, the uncouplers would decrease the RC time constant for membrane capacitance leading to a quicker discharge of voltage and concomitant decrease in photocycle turnover time. The experimental results show that the primary cause for the slower kinetics of voltage changes in the DEM system is thermodynamic back-pressure as described by Westerhoff, H.V. & Dancshazy, Z. (1984) Trends Biochem. Sci.9, 112,117. [source] Cavity pressure control during cooling in plastic injection moldingADVANCES IN POLYMER TECHNOLOGY, Issue 3 2006B. Pramujati Abstract Cavity pressure control during filling, packing, and cooling phases is imperative for maintaining product quality in injection molding process. This paper presents the design and implementation of a strategy to control cavity pressure profile during the cooling phase. In order to do this, a controlled variable parameter was defined to be the time constant , of the pressure profile. This parameter can be used effectively to control the shape of the cavity pressure over the cooling cycle. The coolant flow rate through the mold was used as the manipulated variable. A predictive control system was designed and implemented successfully to allow monitoring and control of , at several setpoints ,sp resulting in good and effective cavity pressure control. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25:170,181, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20068 [source] Regulatory volume decrease is actively modulated during the cell cycleJOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2002Liwei Wang Nasopharyngeal carcinoma cells, CNE-2Z, when swollen by 47% hypotonic solution, exhibited a regulatory volume decrease (RVD). The RVD was inhibited by extracellular applications of the chloride channel blockers tamoxifen (30 ,M; 61% inhibition), 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, 100 ,M; 60% inhibition), and ATP (10 mM; 91% inhibition). The level and time constant of RVD varied greatly between cells. Most cells conducted an incomplete RVD, but a few had the ability to recover their volume completely. There was no obvious correlation between cell volume and RVD capacity. Flow cytometric analysis showed that highly synchronous cells were obtained by the mitotic shake-off technique and that the cells progressed through the cell cycle synchronously when incubated in culture medium. Combined application of DNA synthesis inhibitors, thymidine and hydroxyurea arrested cells at the G1/S boundary and 87% of the cells reached S phase 4 h after being released. RVD capacity changed significantly during the cell cycle progression in cells synchronized by shake-off technique. RVD capacity being at its highest in G1 phase and lowest in S phase. The RVD capacity in G1 (shake-off cells sampled after 4 h of incubation), S (obtained by chemical arrest), and M cells (selected under microscope) was 73, 33, and 58%, respectively, and the time constants were 435, 769, and 2,000 sec, respectively. We conclude that RVD capacity is actively modulated in the cell cycle and RVD may play an important role in cell cycle progress. J. Cell. Physiol. 193: 110,119, 2002. © 2002 Wiley-Liss, Inc. [source] A structured model for the simulation of bioreactors under transient conditionsAICHE JOURNAL, Issue 11 2009Jérôme Morchain Abstract Modeling the transient behavior of continuous culture is of primary importance for the scale-up of biological processes. Spatial heterogeneities increase with the reactor size and micro-organisms have to cope with a fluctuating environment along their trajectories within the bioreactor. In this article, a structured model for bioreactions expressed in terms of biological extensive variables is proposed. A biological variable is introduced to calculate the growth rate of the population. The value is updated on the basis of the difference between the composition in the liquid and biotic phase. The structured model is able to predict the transient behavior of different continuous cultures subject to various drastic perturbations. This performance is obtained with a minimum increase in the standard unstructured model complexity (one additional time constant). In the final part, the consequences of decoupling the growth rate from the substrate uptake rate are discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Dependence of Hyperpolarisation-Activated Cyclic Nucleotide-Gated Channel Activity on Basal Cyclic Adenosine Monophosphate Production in Spontaneously Firing GH3 CellsJOURNAL OF NEUROENDOCRINOLOGY, Issue 7 2006K. Kretschmannova Abstract The hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels play a distinct role in the control of membrane excitability in spontaneously active cardiac and neuronal cells. Here, we studied the expression and role of HCN channels in pacemaking activity, Ca2+ signalling, and prolactin secretion in GH3 immortalised pituitary cells. Reverse transcriptase-polymerase chain reaction analysis revealed the presence of mRNA transcripts for HCN2, HCN3 and HCN4 subunits in these cells. A hyperpolarisation of the membrane potential below ,,60 mV elicited a slowly activating voltage-dependent inward current (Ih) in the majority of tested cells, with a half-maximal activation voltage of ,89.9 ± 4.2 mV and with a time constant of 1.4 ± 0.2 s at ,120 mV. The bath application of 1 mM Cs+, a commonly used inorganic blocker of Ih, and 100 µM ZD7288, a specific organic blocker of Ih, inhibited Ih by 90 ± 4.1% and 84.3 ± 1.8%, respectively. Receptor- and nonreceptor-mediated activation of adenylyl and soluble guanylyl cyclase and the addition of a membrane permeable cyclic adenosine monophosphate (cAMP) analogue, 8-Br-cAMP, did not affect Ih. Inhibition of basal adenylyl cyclase activity, but not basal soluble guanylyl cyclase activity, led to a reduction in the peak amplitude and a leftward shift in the activation curve of Ih by 23.7 mV. The inhibition of the current was reversed by stimulation of adenylyl cyclase with forskolin and by the addition of 8-Br-cAMP, but not 8-Br-cGMP. Application of Cs+ had no significant effect on the resting membrane potential or electrical activity, whereas ZD7288 exhibited complex and Ih -independent effects on spontaneous electrical activity, Ca2+ signalling, and prolactin release. These results indicate that HCN channels in GH3 cells are under tonic activation by basal level of cAMP and are not critical for spontaneous firing of action potentials. [source] Rapid lightoff of syngas production from methane: A transient product analysisAICHE JOURNAL, Issue 1 2005Kenneth A. Williams Abstract Steady-state production of syngas (CO and H2) can be attained within 10 s from room-temperature mixtures of methane and air fed to a short-contact-time reactor by initially operating at combustion stoichiometry (CH4/O2 = 0.5) and then quickly switching to syngas stoichiometry (CH4/O2 = 2.0). The methane/air mixture is first ignited, forming a premixed flame upstream of the catalyst that heats the Rh-impregnated ,-alumina foam monolith to catalytic lightoff (T > 500°C) in a few seconds. The methane/oxygen ratio is then increased to partial oxidation stoichiometry, which extinguishes the flame and effects immediate autothermal syngas production. Transient species profiles are measured with a rapid-response mass spectrometer (response time constant , 0.5 s), and catalyst temperature is measured with a thermocouple at the catalyst back face. Because the monolith thermal response time (, 1 s) is several orders of magnitude larger than the reaction timescales (, 10,12 to 10,3 s), chemistry and flow should be mathematically decoupled from local transient variations in catalyst temperature. Using this assumption, a transient temperature profile is combined with detailed surface chemistry for methane on Rh in a numerical plug-flow model. This approach accurately reproduces the transient species profiles measured during experimental lightoff for short combustion time experiments and lends insight into how the monolith temperature develops with time. The combined experimental and numerical efforts supply useful information on the transient reactor behavior for various combustion times and identify a combustion time to avoid undershoot or overshoot in catalyst temperature and minimize start-up time. © 2004 American Institute of Chemical Engineers AIChE J, 51: 247,260, 2005 [source] Mesomixing in semi-batch reaction crystallization and influence of reactor sizeAICHE JOURNAL, Issue 12 2004Marika Torbacke Abstract Experiments on semibatch reaction crystallization of benzoic acid are reported, in which hydrochloric acid was fed into an agitated solution of sodium benzoate. The influence of mixing and the influence of reactor size are examined on the product crystal mean size. The product mean size increases with increasing stirring rate and with decreasing feed rate. At low feed rates, the mean size increases at decreasing feed pipe diameter. At high feed rates the influence of the feed pipe diameter is more complex. Micromixing is of some importance in most experiments, but the rate of mesomixing especially governs the process. Mesomixing seems to be adequately described by the inertial-convective disintegration mechanism. In many aspects experimental results cannot be described by the turbulent-dispersion mechanism. The product mean size does not exhibit a clear dependence on reactor size, but depends more strongly on other parameters. Results from experiments from 1 L scale to 200 L scale can be correlated fairly well against a dimensionless number defined as the ratio of the total time of reactant feeding to the time constant of mixing. The best representation of the mixing time constant is obtained by making it directly proportional to the ratio of the feed pipe diameter and the linear velocity of the bulk flow passing the feed pipe. The proportionality constant can be calculated from turbulence data over the bulk flow at the feed point. © 2004 American Institute of Chemical Engineers AIChE J, 50: 3107,3119, 2004 [source] Nucleus pulposus glycosaminoglycan content is correlated with axial mechanics in rat lumbar motion segmentsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 9 2006John I. Boxberger Abstract The unique biochemical composition and structure of the intervertebral disc allow it to support load, permit motion, and dissipate energy. With degeneration, both the biochemical composition and mechanical behavior of the disc are drastically altered, yet quantitative relationships between the biochemical changes and overall motion segment mechanics are lacking. The objective of this study was to determine the contribution of nucleus pulposus glycosaminoglycan content, which decreases with degeneration, to mechanical function of a rat lumbar spine motion segment in axial loading. Motion segments were treated with varying doses of Chondroitinase-ABC (to degrade glycosaminoglycans) and loaded in axial cyclic compression-tension, followed by compressive creep. Nucleus glycosaminoglycan content was significantly correlated (p,<,0.05) with neutral zone mechanical behavior, which occurs in low load transition between tension and compression (stiffness: r,=,0.59; displacement: r,=,,0.59), and with creep behavior (viscous parameter ,1: r,=,0.34; short time constant ,1: r,=,0.46). These results indicate that moderate decreases in nucleus glycosaminoglycan content consistent with early human degeneration affect overall mechanical function of the disc. These decreases may expose the disc to altered internal stress and strain patterns, thus contributing through mechanical or biological mechanisms to the degenerative cascade. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [source] Hydrophobic ion pairing of isoniazid using a prodrug approachJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2002Huiyu Zhou Abstract Inhalation therapy for infectious lung diseases, such as tuberculosis, is currently being explored, with microspheres being used to target alveolar macrophages. One method of drug encapsulation into polymeric microspheres to form hydrophobic ion-paired (HIP) complexes, and then coprecipitate the complex and polymer using supercritical fluid methodology. For the potent antituberculosis drug, isoniazid (isonicotinic acid hydrazide, INH), to be used in this fashion, it was modified into an ionizable form suitable for HIP. The charged prodrug, sodium isoniazid methanesulfonate (Na,INHMS), was then ion paired with hydrophobic cations, such as alkyltrimethylammonium or tetraalkylammonium. The logarithms of the apparent partition coefficients (log P,) of various HIP complexes of INHMS display a roughly linear relationship with the numbers of carbon atoms in the organic counterions. The water solubility of the tetraheptylammonium,INHMS complex is about 220-fold lower than that of Na,INHMS, while the solubility in dichloromethane exceeds 10 mg/mL, which is sufficient for microencapsulation of the drug into poly(lactide) microspheres. The actual logarithm of the dichloromethane/water partition coefficient (log P) for tetraheptylammonium,INHMS is 1.55, compared to a value of ,,1.8 for the sodium salt of INHMS. The dissolution kinetics of the tetraheptylammonium,INHMS complex in 0.9% aqueous solutions of NaCl was also investigated. Dissolution of tetraheptylammonium,INHMS exhibited a first-order time constant of about 0.28 min,1, followed by a slower reverse ion exchange process to form Na,INHMS. The half-life of this HIP complex is on the order of 30 min, making the enhanced transport of the drug across biological barriers possible. This work represents the first use of a prodrug approach to introduce functionality that would allow HIP complex formation for a neutral molecule. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1502,1511, 2002 [source] Synthesis and photochemistry of a carotene,porphyrin,fullerene model photosynthetic reaction centerJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2004Gerdenis Kodis Abstract A new photosynthetic reaction center mimic consisting of a porphyrin (P) linked to both a fullerene electron acceptor (C60) and a carotenoid secondary electron donor (C) was synthesized and studied in 2-methyltetrahydrofuran using transient spectroscopic methods. Excitation of the porphyrin is followed by photoinduced electron transfer to the fullerene (,,=,32,ps) to yield C,P·+,C60·,. Electron transfer from the carotene to the porphyrin radical cation (,,=,125,ps) gives a final C·+,P,C60·, state with an overall yield of 0.95. This state decays to give the carotenoid triplet state with a time constant of 57,ns. The molecular triad is highly soluble in organic solvents and readily synthesized. These qualities make the molecule a useful artificial photosynthetic reaction center for a variety of spectroscopic and photochemical investigations. Copyright © 2004 John Wiley & Sons, Ltd. [source] Synthesis and photorefractivity of poly[methyl-3-(7-dibenzo[a,g]carbazolyl)-propylsiloxane]JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2008In Kyu Moon Abstract 7H -Dibenzo[a,g]carbazole-substituted polysiloxane (PSX-[a,g]BCz) has been synthesized by hexachloroplatinate (IV) hydrate polymerization from poly(methylhydrosiloxane) and 7-ally-7H -dibenzo[a,g]carbazole. PSX-[a,g]BCz composite showed large orientational birefringences because of both large dipole moments and high-polarizability anisotropies of P-IP-DC chromophore associated with the effective conjugation along the polyene. The 50-,m thick photorefractive material containing 30 wt % 2-[3-[(E)-2(piperidino)-1-ethenyl]-5,5-dimethyl]-2-cyclohexenyliden]malononitrile showed a diffraction efficiency of 51% at 55 V/,m, which corresponded to a ,n of 3.45 × 10,3. PSX-[a,g]BCz composite shows a fast time constant of 0.42 s at 34 °C and 55 V/,m, which corresponded to the space-charge field of 12 V/,m under 70 V/,m. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1783,1791, 2008 [source] Photoinduced electron transfer in glucose oxidase: a picosecond time-resolved ultraviolet resonance Raman studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2008Akiko Fujiwara Abstract Picosecond time-resolved ultraviolet resonance Raman (UVRR) spectroscopy has been applied to photoinduced electron transfer (ET) of glucose oxidase (GOD). In this study, we succeeded in directly observing changes in the aromatic amino acid residues in the photoinduced ET of GOD for the first time. UVRR spectra excited at 226 nm showed bands from Trp and Tyr residues. An intensity decrease of the Trp UVRR bands and the appearance of the UVRR bands attributable to Trp,+ were observed in the time-resolved spectra. In the time-resolved UVRR spectra excited at 240 nm, the intensity decrease of the flavin adenine dinucleotide (FAD) bands was also observed on the same time scale. These results showed that the Trp residue(s) serves as an electron donor to excited-state FAD in the photoinduced ET of GOD. The comparison of the temporal changes of the Trp and FAD band intensities suggested that the ET from the Trp residue(s) to the FAD occurs with a time constant of ,1.5 ps. Copyright © 2008 John Wiley & Sons, Ltd. [source] Electrochemical Behavior of Gel-Derived Lanthanum Calcium Cobalt Ferrite Cathode in Contact with LAMOX ElectrolyteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Tsu-Yung Jin The electrochemical performance and structural features of (La1,yCay)(CoxFe1,x)O3 cathode prepared via a citrate acid gel route are studied when it is interfaced with the (La1.8Dy0.2)(Mo2,zWz)O9 electrolyte. The resistance and chemical capacitance of a low-frequency arc are extracted from the impedance results to evaluate its catalytic activity in oxygen reduction reaction (ORR). (La0.75Ca0.25)(Co0.8Fe0.2)O3 cathode exhibits the minimum area-specific resistance of 0.9 , cm2 and maximum capacitance of 5.7 mF/cm2 at 800°C among the compositions of x=0.1,0.9 and y=0.25. As the Co content increases, the decrease in resistance outweighs the increase in capacitance so that the product of resistance and capacitance (RC time constant) decreases. In contrast, when varying the Ca content of the A-site, the changes in resistance and the capacitance compensate each other; hence the RC time constant is virtually unchanged with respect to the calcium content. Thus, Co is a more influential element than Ca on the ORR catalytic activity. The pore structure study reveals a small amount of Mo diffuses from the electrolyte into the cathode, and its quantity is reduced when interfaced to an electrolyte of high W content. [source] Effect of gluten content on recrystallisation kinetics and water mobility in wheat starch gelsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 4 2004Xin Wang Abstract The effect of gluten on starch retrogradation at 5 °C was studied using 1H NMR relaxometry. Gels were made from gluten and starch at 27.8 and 38.5% total solids and with gluten comprising either 10, 15 or 20% of the solids. Changes in the transverse relaxation time constant (T2) were related to water mobility. Mono-exponential analysis of relaxation curves showed that, in general, gluten retarded starch retrogradation. T2 values in gluten gels also decreased during storage, but to a much lesser extent. Distributed exponential analysis showed that two distinct regions of T2 were observed in all samples. During aging, the peak values of both regions shifted to lower values for all gels. Starch gel samples showed the most significant shift, and gluten gels showed the least. The three levels of gluten addition in starch/gluten gels produced similar shifts. For all samples the signal intensity of the less mobile region decreased more dramatically than that of the more mobile region during storage. It was suggested that gluten retards water loss in the granule remnants. Copyright © 2004 Society of Chemical Industry [source] Parahydrogen induced polarization of barbituric acid derivatives: 1H hyperpolarization studiesMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2008Meike Roth Abstract Homogeneous hydrogenation of barbituric acid derivatives with parahydrogen yields a substantial increase of the 1H NMR signals of the reaction products. These physiologically relevant compounds were hydrogenated at both ambient and elevated temperatures and pressures using a standard cationic rhodium catalyst. The resulting nonthermal nuclear spin polarization (hyperpolarization) is limited by the spin,lattice relaxation time T1 of the corresponding nuclei in the products, being shorter than the time constant of the hydrogenation. The signal-to-noise ratio of the NMR spectra could be further increased upon signal averaging the antiphase PHIP signals of 25 successive scans following 30° pulse experiments and a delay of 10 s. Copyright © 2008 John Wiley & Sons, Ltd. [source] Proton T2 relaxation study of water, N-acetylaspartate, and creatine in human brain using Hahn and Carr-Purcell spin echoes at 4T and 7TMAGNETIC RESONANCE IN MEDICINE, Issue 4 2002Shalom Michaeli Abstract Carr-Purcell and Hahn spin-echo (SE) measurements were used to estimate the apparent transverse relaxation time constant (T) of water and metabolites in human brain at 4T and 7T. A significant reduction in the T values of proton resonances (water, N-acetylaspartate, and creatine/phosphocreatine) was observed with increasing magnetic field strength and was attributed mainly to increased dynamic dephasing due to increased local susceptibility gradients. At high field, signal loss resulting from T decay can be substantially reduced using a Carr-Purcell-type SE sequence. Magn Reson Med 47:629,633, 2002. © 2002 Wiley-Liss, Inc. [source] A modified HICUM model for GaInP/GaAs HBT devicesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2006S.-C. Tseng Abstract A compact physics-based transit-time model is established for the GaInP/GaAs HBT device. The VBIC model fails to describe the transit-time frequency versus bias (IC, VCE), especially at low- and medium-current regimes. Starting with the HICUM model, we introduce a new time constant to describe the transit-time frequency versus bias (IC, VCE) more precisely. This model has obvious advantages over the VBIC model for showing the relation of ft versus bias (IC, VCE) in the low and medium current regimes for GaInP/GaAs HBT devices. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 780,783, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21474 [source] Resistive load of laryngeal mask airway and proseal laryngeal mask airway in mechanically ventilated patientsACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 6 2003G. Natalini Background:, The ProSeal Laryngeal Mask Airway (PLMA) ventilation tube is narrower and shorter than the standard Laryngeal Mask Airway (LMA) and is without the vertical bars at the end of the tube. In this randomized, crossover study, PLMA and LMA resistances were compared. Methods:, Respiratory mechanics was calculated in 26 anesthetized, mechanically ventilated patients with both LMA and PLMA. The laryngeal mask positioning was fiberoptically evaluated. Differences in the respiratory mechanics of the LMA and the PLMA were attributed to the differences between the laryngeal masks. Results:, In the total study population the airway resistance was 1.5 ± 2.6 hPa.l,1.s,1 (P = 0.005) higher with the PLMA than with the LMA. During the PLMA use, the peak expiratory flow reduced by 0.02 ± 0.05 l min,1 (P = 0.046), the expiratory resistance increased by 0.6 ± 1.3 hPa.l,1.s,1 (P = 0.022), and the time constant of respiratory system lengthened by 0.09 ± 0.18 s (P = 0.023). These differences doubled when the LMA was better positioned than the PLMA, whereas they disappeared when the PLMA was positioned better than the LMA. Conclusions:, The standard LMA offers a lower resistive load than the PLMA. Moreover, the fitting between the laryngeal masks and the larynx, as fiberoptically evaluated, plays a major role in determining the resistive properties of these devices. [source] | ||||||||||||||||||||||||||||||||||||||||