3,739 research outputs found
Regulation of succinate-fuelled mitochondrial respiration in liver and skeletal muscle of hibernating thirteen-lined ground squirrels.
Hibernating ground squirrels (Ictidomys tridecemlineatus) alternate between two distinct metabolic states throughout winter: torpor, during which metabolic rate (MR) and body temperature (Tb) are considerably suppressed, and interbout euthermia (IBE), during which MR and Tb briefly return to euthermic levels. Previous studies showed suppression of succinate-fuelled respiration during torpor in liver and skeletal muscle mitochondria; however, these studies used only a single, saturating succinate concentration. Therefore, they could not address whether mitochondrial metabolic suppression occurs under physiological substrate concentrations or whether differences in the kinetics of mitochondrial responses to changing substrate concentration might also contribute to mitochondrial metabolic regulation during torpor. The present study confirmed that succinate oxidation is reduced during torpor in liver and skeletal muscle at 37 and 10°C over a 100-fold range of succinate concentrations. At 37°C, this suppression resulted from inhibition of succinate dehydrogenase (SDH), which had a greater affinity for oxaloacetate (an SDH inhibitor) during torpor. At 10°C, SDH was not inhibited, suggesting that SDH inhibition initiates but does not maintain mitochondrial suppression during torpor. Moreover, in both liver and skeletal muscle, mitochondria from torpid animals maintained relatively higher respiration rates at low succinate concentrations, which reduces the extent of energy savings that can be achieved during torpor, but may also maintain mitochondrial oxidative capacity above some lower critical threshold, thereby preventing cellular and/or mitochondrial injury during torpor and facilitating rapid recruitment of oxidative capacity during arousal
Kolmogorov Similarity Hypotheses for Scalar Fields: Sampling Intermittent Turbulent Mixing in the Ocean and Galaxy
Kolmogorov's three universal similarity hypotheses are extrapolated to
describe scalar fields like temperature mixed by turbulence. By the analogous
Kolmogorov third hypothesis for scalars, temperature dissipation rates chi
averaged over lengths r > L_K should be lognormally distributed with
intermittency factors I that increase with increasing turbulence energy length
scales L_O as I_chi-r = m_T ln(L_O/r). Tests of Kolmogorovian velocity and
scalar universal similarity hypotheses for very large ranges of turbulence
length and time scales are provided by data from the ocean and the Galactic
interstellar medium. The universal constant for turbulent mixing intermittency
m_T is estimated from oceanic data to be 0.44+-0.01, which is remarkably close
to estimates for Kolmogorov's turbulence intermittency constant m_u of
0.45+-0.05 from Galactic as well as atmospheric data. Extreme intermittency
complicates the oceanic sampling problem, and may lead to quantitative and
qualitative undersampling errors in estimates of mean oceanic dissipation rates
and fluxes. Intermittency of turbulence and mixing in the interstellar medium
may be a factor in the formation of stars.Comment: 23 pages original of Proc. Roy. Soc. article, 8 figures; in
"Turbulence and Stochastic Processes: Kolmogorov's ideas 50 years on", London
The Royal Society, 1991, J.C.R. Hunt, O.M. Phillips, D. Williams Eds., pages
1-240, vol. 434 (no. 1890) Proc. Roy. Soc. Lond. A, PDF fil
Cognitive function and mood at high altitude following acclimatization and use of supplemental oxygen and adaptive servoventilation sleep treatments.
Impairments in cognitive function, mood, and sleep quality occur following ascent to high altitude. Low oxygen (hypoxia) and poor sleep quality are both linked to impaired cognitive performance, but their independent contributions at high altitude remain unknown. Adaptive servoventilation (ASV) improves sleep quality by stabilizing breathing and preventing central apneas without supplemental oxygen. We compared the efficacy of ASV and supplemental oxygen sleep treatments for improving daytime cognitive function and mood in high-altitude visitors (N = 18) during acclimatization to 3,800 m. Each night, subjects were randomly provided with ASV, supplemental oxygen (SpO2 > 95%), or no treatment. Each morning subjects completed a series of cognitive function tests and questionnaires to assess mood and multiple aspects of cognitive performance. We found that both ASV and supplemental oxygen (O2) improved daytime feelings of confusion (ASV: p < 0.01; O2: p < 0.05) and fatigue (ASV: p < 0.01; O2: p < 0.01) but did not improve other measures of cognitive performance at high altitude. However, performance improved on the trail making tests (TMT) A and B (p < 0.001), the balloon analog risk test (p < 0.0001), and the psychomotor vigilance test (p < 0.01) over the course of three days at altitude after controlling for effects of sleep treatments. Compared to sea level, subjects reported higher levels of confusion (p < 0.01) and performed worse on the TMT A (p < 0.05) and the emotion recognition test (p < 0.05) on nights when they received no treatment at high altitude. These results suggest that stabilizing breathing (ASV) or increasing oxygenation (supplemental oxygen) during sleep can reduce feelings of fatigue and confusion, but that daytime hypoxia may play a larger role in other cognitive impairments reported at high altitude. Furthermore, this study provides evidence that some aspects of cognition (executive control, risk inhibition, sustained attention) improve with acclimatization
Bioeconomic Factors of Beef Heifer Maturity to Consider when Establishing Criteria to Optimally Select and/or Retain Herd Replacements
Understanding the biology of heifer maturity and its relationship to calving difficulty and subsequent breeding success is a vital step in building abioeconomic model to identify optimal production and profitability. A limited dependent variable probit model is used to quantify the responses among heifer maturities, measured by a maturity index (MI), on dystocia and second pregnancy. The MI account for heifer age, birth BW, prebreeding BW, nutrition level, and dam size and age and is found to be inversely related to dystocia occurrence. On average there is a 2.2% increase in the probability of dystocia with every 1 point drop in the MI between the MI scores of 50 and 70. Statistically, MI does not directly alter second pregnancy rate; however, dystocia does. The presence of dystocia reduced second pregnancy rates by 10.67%. Using the probability of dystocia predicted from the MI in the sample, it is found that on average, every 1 point increase in MI added 0.62% to the probability of the occurrence of second pregnancy over the range represented by the data. Relationships among MI, dystocia, and second pregnancy are nonlinear and exhibit diminishing marginal effects. These relationships indicate optimal production and profitability occur at varying maturities, which are altered by animal type, economic environment, production system, and management regime. With these captured relationships, any single group of heifers may be ranked by profitability given their physical characteristics and the applicable production, management, and economic conditions
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Relationships Between Chemoreflex Responses, Sleep Quality, and Hematocrit in Andean Men and Women.
Andean highlanders are challenged by chronic hypoxia and many exhibit elevated hematocrit (Hct) and blunted ventilation compared to other high-altitude populations. While many Andeans develop Chronic Mountain Sickness (CMS) and excessive erythrocytosis, Hct varies markedly within Andean men and women and may be driven by individual differences in ventilatory control and/or sleep events which exacerbate hypoxemia. To test this hypothesis, we quantified relationships between resting ventilation and ventilatory chemoreflexes, sleep desaturation, breathing disturbance, and Hct in Andean men and women. Ventilatory measures were made in 109 individuals (n = 63 men; n = 46 women), and sleep measures in 45 of these participants (n = 22 men; n = 23 women). In both men and women, high Hct was associated with low daytime SpO2 (p < 0.001 and p < 0.002, respectively) and decreased sleep SpO2 (mean, nadir, and time <80%; all p < 0.02). In men, high Hct was also associated with increased end-tidal PCO2 (p < 0.009). While ventilatory responses to hypoxia and hypercapnia did not predict Hct, decreased hypoxic ventilatory responses were associated with lower daytime SpO2 in men (p < 0.01) and women (p < 0.009) and with lower nadir sleep SpO2 in women (p < 0.02). Decreased ventilatory responses to CO2 were associated with more time below 80% SpO2 during sleep in men (p < 0.05). The obstructive apnea index and apnea-hypopnea index also predicted Hct and CMS scores in men after accounting for age, BMI, and SpO2 during sleep. Finally, heart rate response to hypoxia was lower in men with higher Hct (p < 0.0001). These data support the idea that hypoventilation and decreased ventilatory sensitivity to hypoxia are associated with decreased day time and nighttime SpO2 levels that may exacerbate the stimulus for erythropoiesis in Andean men and women. However, interventional and longitudinal studies are required to establish the causal relationships between these associations
Participation in contract farming and farm performance: Insights from cashew farmers in Ghana
The global demand for cashew nuts continues to increase steadily. However, many
African countries face difficulties in marketing and adding value to the product. Using
recent survey data of 391 cashew farmers in Ghana, this paper contributes to the grow-
ing evidence on the significance of contract farming (CF) in improving the welfare
of rural households in developing countries. Specifically, the paper analyzes the fac-
tors that influence cashew farmers’ decisions to participate in CF, and the impact
of participation on farmers’ performance. We employ a recently developed switch-
ing regression model with endogenous explanatory variables and endogenous switch-
ing to control for selection bias caused by observable and unobservable factors. The
empirical results show that participation in CF significantly increases labor produc-
tivity and price margins, as well as cashew yields, and net revenues. A disaggregated
analysis of the sample into farm size categories reveals that small-sized cashew farms
tend to benefit more through CF, compared to medium- and large-sized farms
What Next-Generation 21 cm Power Spectrum Measurements Can Teach Us About the Epoch of Reionization
A number of experiments are currently working towards a measurement of the 21
cm signal from the Epoch of Reionization. Whether or not these experiments
deliver a detection of cosmological emission, their limited sensitivity will
prevent them from providing detailed information about the astrophysics of
reionization. In this work, we consider what types of measurements will be
enabled by a next-generation of larger 21 cm EoR telescopes. To calculate the
type of constraints that will be possible with such arrays, we use simple
models for the instrument, foreground emission, and the reionization history.
We focus primarily on an instrument modeled after the
collecting area Hydrogen Epoch of Reionization Array (HERA) concept design, and
parameterize the uncertainties with regard to foreground emission by
considering different limits to the recently described "wedge" footprint in
k-space. Uncertainties in the reionization history are accounted for using a
series of simulations which vary the ionizing efficiency and minimum virial
temperature of the galaxies responsible for reionization, as well as the mean
free path of ionizing photons through the IGM. Given various combinations of
models, we consider the significance of the possible power spectrum detections,
the ability to trace the power spectrum evolution versus redshift, the
detectability of salient power spectrum features, and the achievable level of
quantitative constraints on astrophysical parameters. Ultimately, we find that
of collecting area is enough to ensure a very high significance
() detection of the reionization power spectrum in even the
most pessimistic scenarios. This sensitivity should allow for meaningful
constraints on the reionization history and astrophysical parameters,
especially if foreground subtraction techniques can be improved and
successfully implemented.Comment: 27 pages, 18 figures, updated SKA numbers in appendi
Effective field theory and the quark model
We analyze the connections between the quark model (QM) and the description
of hadrons in the low-momentum limit of heavy-baryon effective field theory in
QCD. By using a three-flavor-index representation for the effective baryon
fields, we show that the ``nonrelativistic'' constituent QM for baryon masses
and moments is completely equivalent through O(m_s) to a parametrization of the
relativistic field theory in a general spin--flavor basis. The flavor and spin
variables can be identified with those of effective valence quarks. Conversely,
the spin-flavor description clarifies the structure and dynamical
interpretation of the chiral expansion in effective field theory, and provides
a direct connection between the field theory and the semirelativistic models
for hadrons used in successful dynamical calculations. This allows dynamical
information to be incorporated directly into the chiral expansion. We find, for
example, that the striking success of the additive QM for baryon magnetic
moments is a consequence of the relative smallness of the non-additive
spin-dependent corrections.Comment: 25 pages, revtex, no figure
Analysis of dynamical corrections to baryon magnetic moments
We present and analyze QCD corrections to the baryon magnetic moments in
terms of the one-, two-, and three-body operators which appear in the effective
field theory developed in our recent papers. The main corrections are extended
Thomas-type corrections associated with the confining interactions in the
baryon. We investigate the contributions of low-lying angular excitations to
the moments quantitatively and show that they are completely negligible. When
the QCD corrections are combined with the non-quark model contributions of the
meson loops, we obtain a model which describes the moments within a mean
deviation of 0.04 . The nontrivial interplay of the two types of
corrections to the quark-model moments is analyzed in detail, and explains why
the quark model is so successful. In the course of these calculations, we
parametrize the general spin structure of the baryon wave functions
in a form which clearly displays the symmetry properties and the internal
angular momentum content of the wave functions, and allows us to use spin-trace
methods to calculate the many spin matrix elements which appear in the
expressions for the moments. This representation may be useful elsewhere.Comment: 32 pages, 3 figures, submitted to Phys. Rev.
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