4,958 research outputs found
Electrode current distributions in MGD CHANNELS
Current distribution to and electric field behavior of segmented electrodes in linear magnetogasdynamic generato
Nonlinearity arising from noncooperative transcription factor binding enhances negative feedback and promotes genetic oscillations
We study the effects of multiple binding sites in the promoter of a genetic
oscillator. We evaluate the regulatory function of a promoter with multiple
binding sites in the absence of cooperative binding, and consider different
hypotheses for how the number of bound repressors affects transcription rate.
Effective Hill exponents of the resulting regulatory functions reveal an
increase in the nonlinearity of the feedback with the number of binding sites.
We identify optimal configurations that maximize the nonlinearity of the
feedback. We use a generic model of a biochemical oscillator to show that this
increased nonlinearity is reflected in enhanced oscillations, with larger
amplitudes over wider oscillatory ranges. Although the study is motivated by
genetic oscillations in the zebrafish segmentation clock, our findings may
reveal a general principle for gene regulation.Comment: 11 pages, 8 figure
A Correlation Between the Intrinsic Brightness and Average Decay Rate of Gamma-ray Burst X-ray Afterglow Light Curves
We present a correlation between the average temporal decay
({\alpha}X,avg,>200s) and early-time luminosity (LX,200s) of X-ray afterglows
of gamma-ray bursts as observed by Swift-XRT. Both quantities are measured
relative to a rest frame time of 200 s after the {\gamma}-ray trigger. The
luminosity average decay correlation does not depend on specific temporal
behavior and contains one scale independent quantity minimizing the role of
selection effects. This is a complementary correlation to that discovered by
Oates et al. (2012) in the optical light curves observed by Swift-UVOT. The
correlation indicates that on average, more luminous X-ray afterglows decay
faster than less luminous ones, indicating some relative mechanism for energy
dissipation. The X-ray and optical correlations are entirely consistent once
corrections are applied and contamination is removed. We explore the possible
biases introduced by different light curve morphologies and observational
selection effects, and how either geometrical effects or intrinsic properties
of the central engine and jet could explain the observed correlation.Comment: Accepted for Publication in ApJ; 16 pages, 15 figures, 2 table
Human consumption of agricultural toxicants from organic and conventional food
Over the past 60 years both the number of agricultural toxicants in use and rates of toxin-related diseases have increased dramatically, and countless studies attest to a link between the two. While data from residue surveys confirms higher levels of toxicants in conventionally farmed produce, few studies directly assess whether consuming organic produce results in a reduction in pesticide exposure in humans or confers any health benefits. Future research needs to confirm whether and to what extent agricultural toxicant levels vary between consumers of organic and conventional produce before attempting to draw any conclusions about the potential health implications of such differences
Physiological demands of fencing: A narrative review
Background and Aim
Fencers compete over long competition days (9-11 hours) wearing full body protective clothing whilst performing high-intensity explosive movements interspersed with low intensity preparatory or recovery movements. Therefore the aim of this review is to provide contemporary perspectives of the literature discussing the physiological and thermoregulatory demands of fencing to inform training, competition, and recovery practices.
Methods
Research articles were searched through three online databases (Pubmed, SPORTDiscus, and Google Scholar; 1985-2022) and included results discussing physiological demands for all three weapons (epée, foil, and sabre).
Results
The physiological demands of fencing performance are high and increase as fencers move from Poule fights to knockout Direct Elimination fights. Fencers compete at 75-100% of maximum heart rate, and ~75% maximal oxygen consumption in Direct Elimination fights. Fencing performance is reliant on the phosphocreatine and aerobic energy systems as shown through low blood lactate concentrations. Considerable variation in distance covered during competition is generally reported (i.e., 435 to 1652m in Direct Elimination fights). Despite fencers competing in full body protective clothing with a potentially large thermoregulatory challenge only one study has examined thermoregulatory responses during fencing whereby fencers’ gastrointestinal temperature can peak at >39°C.
Conclusions
Future research highlighted by the findings of this review includes studies of all weapon types especially foil and sabre, during actual competitive environments. Thermoregulatory responses of fencing need to be determined including measures of skin temperature, mask temperature (as a measure of micro-climates) and thermal sensation, allowing for appropriate cooling strategies to be applied between fights to maintain or improve performance.
Practical Applications
A greater understanding of the physiological demands of fencing performance will allow athletes, coaches, and practitioners to design training to prepare athletes for competition and allow fencing specific protocols to be developed to determine recovery strategies within fencing
GRB Flares: UV/Optical Flaring (Paper I)
We present a new algorithm for the detection of flares in gamma-ray burst
(GRB) light curves and use this algorithm to detect flares in the UV/optical.
The algorithm makes use of the Bayesian Information Criterion (BIC) to analyze
the residuals of the fitted light curve, removing all major features, and to
determine the statistically best fit to the data by iteratively adding
additional `breaks' to the light curve. These additional breaks represent the
individual components of the detected flares: T_start, T_stop, and T_peak. We
present the detection of 119 unique flaring periods detected by applying this
algorithm to light curves taken from the Second Swift Ultraviolet/Optical
Telescope (UVOT) GRB Afterglow Catalog. We analyzed 201 UVOT GRB light curves
and found episodes of flaring in 68 of the light curves. For those light curves
with flares, we find an average number of ~2 flares per GRB. Flaring is
generally restricted to the first 1000 seconds of the afterglow, but can be
observed and detected beyond 10^5 seconds. More than 80% of the flares detected
are short in duration with Delta t/t of < 0.5. Flares were observed with flux
ratios relative to the underlying light curve of between 0.04 to 55.42. Many of
the strongest flares were also seen at greater than 1000 seconds after the
burst.Comment: Submitted to ApJ. 20 pages (including 8 figures and 1 table
Control functionals for quasi-Monte Carlo integration
Quasi-Monte Carlo (QMC) methods are being adopted in statistical applications due to the increasingly challenging nature of numerical integrals that are now routinely encountered. For integrands with d-dimensions and derivatives of order α, an optimal QMC rule converges at a best-possible rate O(N^-α/d). However, in applications the value of αcan be unknown and/or a rate-optimal QMC rule can be unavailable. Standard practice is to employ \alpha_L-optimal QMC where the lower bound \alpha_L ≤αis known, but in general this does not exploit the full power of QMC. One solution is to trade-off numerical integration with functional approximation. This strategy is explored herein and shown to be well-suited to modern statistical computation. A challenging application to robotic arm data demonstrates a substantial variance reduction in predictions for mechanical torques
Comparison of Power Dependence of Microwave Surface Resistance of Unpatterned and Patterned YBCO Thin Film
The effect of the patterning process on the nonlinearity of the microwave
surface resistance of YBCO thin films is investigated. With the use of a
sapphire dielectric resonator and a stripline resonator, the microwave of
YBCO thin films was measured before and after the patterning process, as a
function of temperature and the rf peak magnetic field in the film. The
microwave loss was also modeled, assuming a dependence of
on current density . Experimental and modeled results
show that the patterning has no observable effect on the microwave residual
or on the power dependence of .Comment: Submitted to IEEE Trans. MT
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