Maximum Instantaneous Rate Research Articles

Phase Locking of Auditory Nerve Fibers: The Role of Lowpass Filtering by Hair Cells.

Phase locking of auditory-nerve-fiber (ANF) responses to the temporal fine structure of acoustic stimuli, a hallmark of the auditory system's temporal precision, is important for many aspects of hearing. Previous work has shown that phase-locked period histograms are often well described by exponential transfer functions relating instantaneous stimulus pressure to instantaneous spike rate, with no observed clipping of the histograms. The operating points and slopes of these functions change with stimulus level. The mechanism underlying this apparent gain control is unclear but is distinct from mechanical compression, is independent of refractoriness and spike-rate adaptation, and is apparently instantaneous. Here we show that these findings can be accounted for by a model consisting of a static Boltzmann transducer function yielding a clipped output, followed by a lowpass filter and a static exponential transfer function. Using responses to tones of ANFs from cats of both sexes, we show that, for a given ANF, the period histograms obtained at all stimulus levels for a given stimulus frequency can be described using one set of level-independent model parameters. The model also accounts for changes in the maximum and minimum instantaneous spike rates with changes in stimulus level. Notably, the estimated cutoff frequency is lower for low- than for high-spontaneous-rate ANFs, implying a synapse-specific contribution to lowpass filtering. These findings advance our understanding of ANF phase locking by highlighting the role of peripheral filtering mechanisms in shaping responses of individual ANFs.SIGNIFICANCE STATEMENT Phase locking of auditory-nerve-fiber responses to the temporal fine structure of acoustic stimuli is important for many aspects of hearing. Period histograms typically retain an approximately sinusoidal shape across stimulus levels, with the peripheral auditory system operating as though its overall transfer function is an exponential function whose slope decreases with increasing stimulus level. This apparent gain control can be accounted for by a static saturating transducer function followed by a lowpass filter. In addition to attenuating the AC component, the filter approximately recovers the sinusoidal waveform of the stimulus. The estimated cutoff frequency varies with spontaneous rate, revealing a synaptic contribution to lowpass filtering. These findings highlight the significant impact of peripheral filtering mechanisms on phase locking.

Imprint of magnetic flux expulsion at the core–mantle boundary on geomagnetic field intensity variations

SUMMARY During the last decade, rapid or extreme geomagnetic field intensity variations associated with rates greater than the maximum currently observed have been inferred from archeomagnetic data in the Near-East and in Western Europe. The most extreme events, termed geomagnetic spikes, are defined as intensity peaks occurring over a short time (a few decades), and are characterized by high variation rates, up to several μT yr–1. Magnetic flux expulsion from the Earth’s outer core has been suggested as one possible explanation for these peaks but has not yet been examined in detail. In this study, we develop a 2-D kinematic model for magnetic flux expulsion whose key control parameter is the magnetic Reynolds number Rm, the ratio of magnetic diffusion time to advection time. This model enables the tracking of magnetic field lines which are distorted and folded by a fixed flow pattern. Two processes govern the magnetic evolution of the system. The first is the expulsion of magnetic flux from closed streamlines, whereby flux gradually concentrates near the boundaries of the domain, which leads to an increase of the magnetic energy of the system. If the upper boundary separates the conducting fluid from an insulating medium, a second process then takes place, that of diffusion through this interface, which we can quantify by monitoring the evolution of the vertical component of magnetic induction along this boundary. It is the conjunction of these two processes that defines our model of magnetic flux expulsion through the core–mantle boundary. We analyse several configurations with varying flow patterns and magnetic boundary conditions. We first focus on flux expulsion from a single eddy. Since this specific configuration has been widely studied, we use it to benchmark our implementation against analytic solutions and previously published numerical results. We next turn our attention to a configuration which involves two counter-rotating eddies producing an upwelling at the centre of the domain, and comprises an upper boundary with an insulating medium. We find that the characteristic rise time and maximum instantaneous variation rate of the vertical component of the magnetic field that escapes the domain scale like $\sim R_m^{0.15}$ and $\sim R_m^{0.45}$, respectively. Extrapolation of these scaling laws to the Earth’s régime is compared with various purported archeointensity highs reported in the Near-East and in Western Europe. According to our numerical experiments magnetic flux expulsion is unlikely to produce geomagnetic spikes, while intensity peaks of longer duration (one century and more) and smaller variation rates appear to be compatible with this process.

Effects of Varying Tobacco Rod Circumference on Cigarette Combustion: An Experimental Investigation

Summary To study the effects of tobacco rod circumference on cigarette combustion status, cigarettes were made with three different circumferences of 24 mm, 20 mm, 17 mm and otherwise identical construction. Their combustion characteristics, including combustion coal volume, characteristic temperature distribution, heating rate, instantaneous burn rate, and yields of selected mainstream smoke chemicals, were systematically measured. The results indicated that the cigarettes with the lowest circumference of 17 mm showed higher combustion temperatures with a smaller coal volume. The maximum instantaneous burn rate was distinctly different for the three cigarettes, from 1.84 mm/s to 2.48 mm/s, when their circumference was reduced from 24 mm to 17 mm. The tobacco mass consumption per puff showed a negative trend when the circumference decreased. The majority of the chemical compounds (16 of 21) measured in mainstream smoke decreased when the circumference was reduced, except for formaldehyde, while the yields of the chemical compounds produced per weight of cut tobacco, consumed during puffing, showed an obverse trend.

In-depth study of desorption kinetics in adsorption process

In this paper, open-loop desorption experiments were carried out by hot gas sweeping. The effects of different concentrations of methylene chloride and temperatures in the sweeping gas on the desorption process were investigated from three perspectives: average desorption rate (, ), instantaneous desorption rate (Vmax) and desorption kinetics. It was concluded that the maximum instantaneous desorption rate could better represent the desorption rate required by the experiment at different sweeping concentrations and temperatures. The maximum instantaneous desorption rate Vmax increased with the rising temperature and decreased with the increasing concentration of inlet methylene chloride. The concluded law was the same as the average desorption rate () of 30 min. Thereinto, the temperature had a significant influence on Vmax. As the temperature increased, the concentration of inlet methylene chloride also inhibited the maximum instantaneous desorption rate Vmax more obviously. This provided important reference data for the optimization design of desorption equipment in the activated carbon adsorption process.

Extraction of Photosynthesis Parameters from Time Series Measurements of In Situ Production: Bermuda Atlantic Time-Series Study

Computing the vertical structure of primary production in ocean ecosystem models requires information about the vertical distribution of available light, chlorophyll concentration and photosynthesis response parameters. Conversely, given information on vertical structure of chlorophyll and light, we can extract photosynthesis parameters from vertical profiles of primary production measured at sea, as we illustrate here for the Bermuda Atlantic Time-Series Study. The procedure is based on a model of the production profile, which itself depends on the underwater light field. To model the light field, attenuation coefficients were estimated from measured optical profiles using a simple model of exponential decay of photosynthetically-available irradiance with depth, which accounted for 97% of the variance in the measured optical data. With the underwater light climate known, an analytical solution for the production profile was employed to recover photosynthesis parameters by minimizing the residual model error. The recovered parameters were used to model normalized production profiles and normalized watercolumn production. The model explained 95% of the variance in the measured normalized production at depth and 97% of the variance in measured normalized watercolumn production. A shifted Gaussian function was used to model biomass profiles and accounted for 93% of the variance in measured biomass at depth. An analytical solution for watercolumn production with the shifted Gaussian biomass was also tested. With the recovered photosynthesis parameters, maximum instantaneous growth rates were estimated by using a literature value for the carbon-to-chlorophyll ratio in this region of the Atlantic. An exact relationship between the maximum instantaneous growth rate and the daily growth rate in the ocean was derived. It was shown that calculating the growth rate by dividing the production by the carbon-to-chlorophyll ratio is equivalent to calculating it from the ratio of the final to the initial biomass, even when production is time dependent. Finally, the seasonal cycle of the recovered assimilation number at the Bermuda Station was constructed and analysed. The presented approach enables the estimation of photosynthesis parameters and growth rates from measured production profiles with only a few model assumptions, and increases the utility of in situ primary production measurements. The retrieved parameters have direct applications in satellite-based estimates of primary production from ocean-colour data, of which we give an example.

Avaliação do papel dos telhados verdes no desenho e desenvolvimento urbano de baixo impacto ambiental e no controle de enchentes na Cidade do Rio de Janeiro

Este trabalho discute o papel dos telhados verdes no desenho e desenvolvimento urbano de baixo impacto ambiental. São aprofundadas as questões relacionadas ao manejo das águas pluviais urbanas e é avaliado o desempenho dos telhados verdes como dispositivos nos sistemas de micro e macrodrenagem. A metodologia envolveu a aplicação de modelos computacionais hidrológicos-hidráulicos através de estudo de caso em bacia hidrográfica localizada em área de paisagem peri-urbana na cidade do Rio de Janeiro. O modelo computacional adotado, SWMM da US-EPA, permite que se insira de maneira hipotética estes dispositivos em edificações pré-existentes. Através do estudo de cenários sem e com inserção de telhados verdes, pode-se avaliar virtualmente o papel destes dispositivos na redução dos volumes escoados superficialmente e da vazão instantânea máxima, assim como das condições de extravasamento da calha fluvial sob chuva intensa real observada no local em abril de 2010. Os resultados permitiram verificar que apesar de não reverter o extravasamento da calha fluvial, os telhados verdes tiveram impacto na redução dos volumes escoados superficialmente, que agravam as enchentes urbanas, e da vazão máxima instantânea em até 10% aproximadamente. A partir destes resultados e da avaliação das outras sinergias dos telhados verdes com o desenho e desenvolvimento urbano de baixo impacto ambiental recomenda-se o incentivo de políticas públicas que possam viabilizar sua adoção nas cidades Brasileiras com vistas à melhoria da qualidade de vida da população que habita os aglomerados urbanos.

A modeling study of tidal energy extraction and the associated impact on tidal circulation in a multi-inlet bay system of Puget Sound

Previous tidal energy studies in Puget Sound have focused on major deep channels such as Admiralty Inlet that have a larger power potential. This paper focuses on the possibility of extracting tidal energy from minor tidal channels of Puget Sound by using a hydrodynamic model to quantify the power potential and the associated impact on tidal circulation. The study site is a multi-inlet bay system connected by two narrow inlets, Agate Pass and Rich Passage, to the Main Basin of Puget Sound. A three-dimensional hydrodynamic model was applied to the study site and validated for tidal elevations and currents. We examined three energy extraction scenarios in which turbines were deployed in each of the two passages and concurrently in both. Extracted power rates and associated changes in tidal elevation, current, tidal flux, and residence time were examined. Maximum instantaneous power rates reached 250 kW, 1550 kW, and 1800 kW, respectively, for the three energy extraction scenarios. Model results suggest that with the level of energy extraction in the three energy extraction scenarios, the impact on tidal circulation is very small. It is worth investigating the feasibility of harnessing tidal energy from minor tidal channels of Puget Sound.

Output power variation of different PV array configurations during irradiance transitions caused by moving clouds

This paper presents a study of the output power variation of different photovoltaic (PV) array configurations during irradiance transitions caused by moving clouds. The study was based on velocity and other characteristics of roughly 27,000 irradiance transitions identified in measured irradiance data and conducted using a mathematical model of irradiance transitions and an experimentally verified simulation model of a PV module. The studied electrical PV array configurations were series-parallel, total-cross-tied and multi-string. The different PV array orientations and layouts (physical shapes) of the configurations were also studied.The average rate of change of the power of these studied PV array configurations during the irradiance transitions was around 3%/s and the maximum instantaneous rates of change of the power were around 75%/s. Half of the time during the studied transitions, the rate of change in the power was over 1.2%/s, and most of the time during the transitions, it exceeded typical PV power ramp rate limits set by grid operators. The average rate of change of PV array power decreased with an increasing maximum array dimension and it was observed to be the largest when the shorter dimension of the array was parallel to the dominant movement direction of the shadow edges. The results of this study are relevant especially in terms of PV array design, maximum power point tracking algorithm development and energy storage systems sizing.

Daily growth patterns of juveniles and adults of the Peruvian anchovy (Engraulis ringens) in northern Chile

The Peruvian anchovy (Engraulis ringens) is a resource of considerable economic importance, whose stock unit is distributed between 16°00′S and 24°00′S and is shared between Chile and Peru. In the present study, daily growth patterns of juvenile and adult Peruvian anchovies in northern Chile were determined using micro-increments of sagittal otoliths for the recruitment and fishery seasons of 2009 and 2010. A characteristic feature was the existence of very distinctive daily micro-increments, through which a complete sequence of micro-increments was obtained from the primordium to otolith edge for juveniles (7.5–12-cm total length (TL)) and adults (12.5–18.0cm TL), whose ages were in the range 56–166 and 137–409 days respectively. Hatch dates extended from July 2009 to July 2010, where juveniles recruited to a fishery in a given month were the survivors of a spawning that had occurred approximately 3–4 months before. A Laird–Gompertz model fitted to length-at-age data for juveniles estimated maximum instantaneous growth rates that ranged from 0.98 to 1.57mm day–1, whereas overall mean individual growth rates back-calculated for the age range of juveniles ranged from 0.65 to 1.02mm day–1. The von Bertalanffy seasonal parameters estimated through the entire life history showed high growth, with a growth coefficient K=1.1 and mean length at the first year of 16.3cm TL. Consequently, E. ringens in northern Chile seems to maximize growth in the first year of life.

Evaluation of CaO-decorated Fe2O3/Al2O3 as an oxygen carrier for in-situ gasification chemical looping combustion of plastic wastes

The use of solid waste such as plastic waste in Chemical Looping Combustion (CLC) becomes interesting, with potential advantages of exploiting new energy sources, suppressing pollutants, and capturing carbon dioxide. However, the emission of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) which as toxic matter has aroused increasing attention during the utilization process of these solid wastes, especially for plastic waste which contains a high chlorine content. Through applying CaO decoration to Fe-based oxygen carrier (OC) is it possible to realize effective dechlorination during chemical looping processes. In this study, a 5wt.% CaO-decorated Fe2O3/Al2O3 as OC was used for in-situ gasification chemical looping combustion (iG-CLC) of plastic waste, and the reactivity of the decorated OC particles was tested in a batch fluidized-bed reactor, compared with that of raw Fe2O3/Al2O3 OCs. Operation conditions, including reaction atmosphere, supply oxygen ratio and reaction temperature, were investigated to explore their influence on carbon conversion, maximum instantaneous rate of fuel conversion and CO2 yield. Results indicated that CaO decoration results in a lower reactivity of OC particles. However, by optimizing these operation conditions the undesirable influence of CaO decoration can be mitigated. The stability of OC reactivity was evaluated through 10 redox cycles, where stable carbon conversion, maximum instantaneous rate of fuel conversion and CO2 yield were observed. These used OC particles were characterized by a surface area and porosity analyzer and an Environment Scanning Electron Microscope coupling with Energy Dispersive X-ray spectroscopy (ESEM–EDX). The specific surface area (BET) result indicated that CaO-decorated OC particles present lower BET and pore volume after 10 redox cycles, and the ESEM–EDX result also demonstrated little ash deposition on the surface of OC particles, which both contribute to the slight deterioration of OC reactivity. It was also observed from ESEM–EDX that there is the accumulation of Cl element on OC surface, providing sound evidence for dechlorination during the iG-CLC of plastic waste.

Radiation defect dynamics in Si at room temperature studied by pulsed ion beams

The evolution of radiation defects after the thermalization of collision cascades often plays the dominant role in the formation of stable radiation disorder in crystalline solids of interest to electronics and nuclear materials applications. Here, we explore a pulsed-ion-beam method to study defect interaction dynamics in Si crystals bombarded at room temperature with 500 keV Ne, Ar, Kr, and Xe ions. The effective time constant of defect interaction is measured directly by studying the dependence of lattice disorder, monitored by ion channeling, on the passive part of the beam duty cycle. The effective defect diffusion length is revealed by the dependence of damage on the active part of the beam duty cycle. Results show that the defect relaxation behavior obeys a second order kinetic process for all the cases studied, with a time constant in the range of ∼4–13 ms and a diffusion length of ∼15–50 nm. Both radiation dynamics parameters (the time constant and diffusion length) are essentially independent of the maximum instantaneous dose rate, total ion dose, and dopant concentration within the ranges studied. However, both the time constant and diffusion length increase with increasing ion mass. This demonstrates that the density of collision cascades influences not only defect production and annealing efficiencies but also the defect interaction dynamics.

Resolution Dependence of Future Tropical Cyclone Projections of CAM5.1 in the U.S. CLIVAR Hurricane Working Group Idealized Configurations

AbstractThe four idealized configurations of the U.S. CLIVAR Hurricane Working Group are integrated using the global Community Atmospheric Model version 5.1 at two different horizontal resolutions, approximately 100 and 25 km. The publicly released 0.9° × 1.3° configuration is a poor predictor of the sign of the 0.23° × 0.31° model configuration’s change in the total number of tropical storms in a warmer climate. However, it does predict the sign of the higher-resolution configuration’s change in the number of intense tropical cyclones in a warmer climate. In the 0.23° × 0.31° model configuration, both increased CO2 concentrations and elevated sea surface temperature (SST) independently lower the number of weak tropical storms and shorten their average duration. Conversely, increased SST causes more intense tropical cyclones and lengthens their average duration, resulting in a greater number of intense tropical cyclone days globally. Increased SST also increased maximum tropical storm instantaneous precipitation rates across all storm intensities. It was found that while a measure of maximum potential intensity based on climatological mean quantities adequately predicts the 0.23° × 0.31° model’s forced response in its most intense simulated tropical cyclones, a related measure of cyclogenesis potential fails to predict the model’s actual cyclogenesis response to warmer SSTs. These analyses lead to two broader conclusions: 1) Projections of future tropical storm activity obtained by a direct tracking of tropical storms simulated by coarse-resolution climate models must be interpreted with caution. 2) Projections of future tropical cyclogenesis obtained from metrics of model behavior that are based solely on changes in long-term climatological fields and tuned to historical records must also be interpreted with caution.

Instantaneous Rate of Loading During Manual High-Velocity, Low-Amplitude Spinal Manipulations

ObjectiveThe objective of this study was to determine the instantaneous rate of loading during manual high-velocity, low-amplitude spinal manipulations (HVLA SMs) in the lumbar and thoracic regions and compare to the average rates of loading. MethodsForce-time profiles were recorded using a hand force transducer placed between the hand of a doctor of chiropractic and the subject’s back during 14 HVLA SM thrusts on asymptomatic volunteers while 3 doctors of chiropractic delivered the spinal manipulations. Doctors also delivered 36 posterior to anterior thoracic manipulations on a mannequin. Data were collected at a sampling rate of 1000 Hz using Motion Monitor software. Force-time profile data were differentiated to obtain instantaneous rates of loading. The data were reduced using a custom-written MathCad program and analyzed descriptively. ResultsThe instantaneous rates of loading were 1.7 to 1.8 times higher than average rates of loading, and instantaneous rates of unloading were 2.1 to 2.6 times the average rates of unloading during HVLA SMs. Maximum instantaneous rates of loading occurred 102 to 111 milliseconds prior to peak load. Maximum instantaneous rates of unloading occurred 121 to 154 milliseconds after the peak load. These data may be useful for further understanding of HVLA SMs. ConclusionsThe instantaneous rates of loading and where they occurred may be useful data for understanding and describing HVLA SMs.

Reduction in ground reaction force variables with instructed barefoot running

BackgoundBarefoot (BF) running has recently increased in popularity with claims that it is more natural and may result in fewer injuries due to a reduction in impact loading. However, novice BF runners do not necessarily immediately switch to a forefoot strike pattern. This may increase mechanical parameters such as loading rate, which has been associated with certain running-related injuries, specifically, tibial stress fractures, patellofemoral pain, and plantar fasciitis. The purpose of this study was to examine changes in loading parameters between typical shod running and instructed BF running with real-time force feedback. MethodsForty-nine patients seeking treatment for a lower extremity injury ran on a force-sensing treadmill in their typical shod condition and then BF at the same speed. While BF they received verbal instruction and real-time feedback of vertical ground reaction forces. ResultsWhile 92% of subjects (n = 45) demonstrated a rearfoot strike pattern when shod, only 2% (n = 1) did during the instructed BF run. Additionally, while BF 47% (n = 23) eliminated the vertical impact transient in all eight steps analyzed. All loading variables of interest were significantly reduced from the shod to instructed BF condition. These included maximum instantaneous and average vertical loading rates of the ground reaction force (p < 0.0001), stiffness during initial loading (p < 0.0001), and peak medial (p = 0.001) and lateral (p < 0.0001) ground reaction forces and impulses in the vertical (p < 0.0001), medial (p = 0.047), and lateral (p < 0.0001) directions. ConclusionAs impact loading has been associated with certain running-related injuries, instruction and feedback on the proper forefoot strike pattern may help reduce the injury risk associated with transitioning to BF running.

南方小花蝽在不同空间及笼罩条件下对西花蓟马的控制作用

在室内研究了5种空间异质条件下南方小花蝽对西花蓟马的捕食作用，并研究了笼罩条件下4种比例释放南方小花蝽对西花蓟马的控制效果。结果表明，不同空间异质下，南方小花蝽对西花蓟马的功能反应均符合Holling Ⅱ圆盘方程；以瞬时攻击率和寻找效应为评价指标，发现南方小花蝽在小容器中的瞬时攻击率（<em>a</em>’）最高，为0.9204，寻找效应最好；在大容器且空间异质最复杂的处理中的瞬时攻击率（<em>a</em>’）最低，为0.6303，寻找效应最差。在笼罩条件下，以3：120和6：120比例释放南方小花蝽和西花蓟马，其控制效果差；以9：120的比例释放，5周后对西花蓟马成虫和若虫的控制效果分别达到74.70%和81.01%；以15：120比例释放，5周后对西花蓟马成虫和若虫的控制效果分别达到95.71%和89.02%。结果显示空间越小或异质性越简单，越利于南方小花蝽捕食西花蓟马。若实际生产中采用9：120的益害比例释放南方小花蝽，既可以达到对西花蓟马较好的控制效果，又相对节约成本。

Biomechanical and Anatomic Factors Associated with a History of Plantar Fasciitis in Female Runners

To compare selected structural and biomechanical factors between female runners with a history of plantar fasciitis and healthy control subjects. Cross-sectional. University of Delaware Motion Analysis Laboratory, Newark, Delaware; and University of Massachusetts Biomechanics Laboratory, Amherst, Massachusetts. Twenty-five female runners with a history of plantar fasciitis were recruited for this study. A group of 25 age- and mileage-matched runners with no history of plantar fasciitis served as control subjects. The independent variable was whether or not subjects had a history of plantar fasciitis. Subjects ran overground while kinematic and kinetic data were recorded using a motion capture system and force plate. Rearfoot kinematic variables of interest included peak dorsiflexion, peak eversion, time to peak eversion along with eversion excursion. Vertical ground reaction force variables included impact peak and the maximum instantaneous load rate. Structural measures were taken for calcaneal valgus and arch index during standing and passive ankle dorsiflexion range of motion. A significantly greater maximum instantaneous load rate was found in the plantar fasciitis group along with an increased ankle dorsiflexion range of motion compared with the control group. The plantar fasciitis group had a lower arch index compared with control subjects, but calcaneal valgus was similar between groups. No differences in rearfoot kinematics were found between groups. These data indicate that a history of plantar fasciitis in runners may be associated with greater vertical ground reaction force load rates and a lower medial longitudinal arch of the foot.

Sensing Single Base Incorporation with Nanopore Micromanipulation

Using single-molecule techniques, scientists can routinely investigate the action of a single enzyme. The goal of such studies is usually to gain accurate information unachievable in ensemble assays, such as the maximum instantaneous rate of reaction, the existence of pauses or backward steps, etc. In the article discussed here, the authors have increased their experimental sensitivity so that they can detect a single enzymatic cycle. This improvement makes possible the use of a polymerase enzyme to sequence a single DNA molecule.

Reference data for evaluating the growth of common riverine fishes in the UK

Summary Comparative assessments of population mean growth rates in length remain important aspects of stock assessment in river fisheries. To facilitate these assessments, for 15 fish species encountered in UK rivers reference data are provided on their expected lengths at age, maximum theoretical lengths (L∞), growth coefficient (K) and instantaneous mortality rate (Z). These data are also transferable to fish populations outside of the UK that experience a similar growth season (approximately April to October, mean water temperatures 12–22°C). Considerable plasticity was observed in the growth of all species examined, with length at age values revealing growth rates from very slow to very fast. Populations considered fast growing against reference data were coincident with a relatively low ultimate length, a high growth coefficient and a high instantaneous mortality rate, suggesting a trade-off exists between growth rate, ultimate length and life span.

The Spinal Contribution To Central Fatigue

Caffeine increases endurance time in sustained and intermittent isometric fatigue protocols. The drug also increases post-activation potentiation of the motor-evoked potential (MEP) in first dorsal interosseous and quadriceps femoris with single-pulse transcranial magnetic stimulation (TMS). If caffeine offsets central failure by enhancing central excitability, the effect may be spinal or supraspinal. PURPOSE To determine the spinal contribution to central fatigue using Hoffman reflex (H-reflex) recruitment curves to assess spinal excitability, and caffeine as a perturbation. METHODS We used a double-blind, repeated measures experimental design, with ten male subjects who attended two separate laboratory sessions one week apart. Only drug administration [caffeine (6mg/kg body weight) vs. placebo (all-purpose flour)] differed in the two sessions. Maximal contractile force (MVC), percent activation, and H-reflex recruitment curves were produced before, and one hour after drug administration, as well as immediately after completion of the fatigue protocol, and during recovery. The maximum instantaneous rate of rise (dH/dI:dM/dI) of the developmental slope of H-reflex recruitment curves was used to assess spinal excitability. RESULTS MVC declined from pre-fatigue to immediately post-fatigue in both placebo (26.9±4.0%) and caffeine (30.6±2.6%) trials, and did not recover within 15 minutes post-exercise. A decline in percent activation was observed from pre-fatigue to immediately post-fatigue in both placebo (4.8±1.0%) and caffeine (4.5±1.6%) trials, and a further decline in percent activation was observed at 5 minutes of recovery [placebo (8.2±1.8%), caffeine (8.5±4.5%)]. A decline in spinal excitability from pre-fatigue to immediately post-fatigue was observed in the placebo trial (33.1±11.1%), and recovered within 10 minutes post-fatigue. Caffeine attenuated the fatigue-induced decline in excitability, and potentiated spinal excitability during the recovery period. CONCLUSIONS These data suggest that the progressive decline in the ability to generate maximal force during a fatigue protocol is partially due to the loss of excitability at the level of the spinal cord. However, these data do not allow us to determine the relative contribution of the change in spinal excitability to the total loss of force. Supported by NSERC (EC) and an ACSM Foundation Grant (JMK).

The outbreak pattern of the SARS cases in Asia.

The severe acute respiratory syndrome (SARS) caused tremendous damage to many Asia countries, especially China. The transmission process and outbreak pattern of SARS is still not well understood. This study aims to find a simple model to describe the outbreak pattern of SARS cases by using SARS case data commonly released by governments. The outbreak pattern of cumulative SARS cases is expected to be a logistic type because the infection will be slowed down due to the increasing control effort by people and/or due to depletion of susceptible individuals. The increase rate of SARS cases is expected to decrease with the cumulative SARS cases, as described by the traditional logistical model, which is widely used in population dynamic studies. The instantaneous rate of increases were significantly and negatively correlated with the cumulative SARS cases in mainland of China (including Beijing, Hebei, Tianjin, Shanxi, the Autonomous Region of Inner Mongolia) and Singapore. The basic reproduction numberR 0 in Asia ranged from 2.0 to 5.6 (except for Taiwan, China). TheR 0 of Hebei and Tianjin were much higher than that of Singapore, Hongkong, Beijing, Shanxi, Inner Mongolia, indicating SARS virus might have originated differently or new mutations occurred during transmission. We demonstrated that the outbreaks of SARS in many regions of Asia were well described by the logistic model, and the control measures implemented by governments are effective. The maximum instantaneous rate of increase, basic reproductive number, and maximum cumulative SARS cases were also calculated by using the logistic model.