396 research outputs found
Migratory flight imposes oxidative stress in bats
Many animal species migrate over long distances, but the physiological challenges of migration are poorly understood. It has recently been suggested that increased molecular oxidative damage might be one important challenge for migratory animals. We tested the hypothesis that autumn migration imposes an oxidative challenge to bats by comparing values of 4 blood-based markers of oxidative status (oxidative damage and both enzymatic and nonenzymatic antioxidants) between Nathusius’ bats Pipistrellus nathusii that were caught during migration flights with those measured in conspecifics after resting for 18 or 24 h. Experiments were carried out at Pape Ornithological Station in Pape (Latvia) in 2016 and 2017. Our results show that flying bats have a blood oxidative status different from that of resting bats due to higher oxidative damage and different expression of both nonenzymatic and enzymatic antioxidants (glutathione peroxidase). The differences in oxidative status markers varied between sampling years and were independent from individual body condition or sex. Our work provides evidence that migratory flight might impose acute oxidative stress to bats and that resting helps animals to recover from oxidative damage accrued en route. Our data suggest that migrating bats and birds might share similar strategies of mitigating and recovering from oxidative stress
Evaluación de la capacidad de rebrote en avena con distinta intensidad de defoliación y dos frecuencias de corte
La finalidad del presente trabajo fue estudiar el efecto de la frecuencia de corte y la intensidad de defoliación de la avena (Avena sativa), sobre la producción de materia seca y la persistencia. El ensayo se llevó a cabo en la Facultad de Agronomía de la UNLPam, durante el ciclo de cultivo en el año 1989. El diseño experimental empleado fue el de bloques completos al azar involucrando un arreglo de tratamiento factorial con cuatro repeticiones. En la experiencia se determinó producción de materia seca y stand de plantas. La comparación de las distintas frecuencias de corte dentro de una misma intensidad de defoliación, mostró diferencias altamente significativas en producción de materia seca en favor del intervalo entre cortes más prolongados y a su vez al comparar distintas intensidades de defoliación dentro de una misma frecuencia, se encontraron diferencias altamente significativas siendo mayor la producción de materia seca a mayor I.A.F. (índice de área foliar) remanente. En lo que respecta a stand de plantas se observó una pérdida muy importante en el corte más intenso, donde las pérdidas fueron del ochenta y cinco por ciento. Para lograr una alta producción de materia seca y buena persistencia se deben combinar una baja frecuencia con un elevado LA.F. remanente.Director: Ing. Agr. Oscar Hernández. Profesor Titular Cátedra de Forrajicultura y Manejó de pasturas
Non-equilibrium phase transition in a sheared granular mixture
The dynamics of an impurity (or tracer particle) immersed in a dilute
granular gas under uniform shear flow is investigated. A non-equilibrium phase
transition is identified from an exact solution of the inelastic Boltzmann
equation for a granular binary mixture in the tracer limit, where the impurity
carries either a vanishing (disordered phase) or a finite (ordered phase)
fraction of the total kinetic energy of the system. In the disordered phase,
the granular temperature ratio (impurity "temperature" over that of the host
fluid) is finite, while it diverges in the ordered phase. To correctly capture
this extreme violation of energy equipartition, we show that the picture of an
impurity enslaved to the host fluid is insufficient
Diffusion Process in a Flow
We establish circumstances under which the dispersion of passive contaminants
in a forced, deterministic or random, flow can be consistently interpreted as a
Markovian diffusion process. In case of conservative forcing the repulsive case
only, with bounded from below, is
unquestionably admitted by the compatibility conditions. A class of diffusion
processes is exemplified, such that the attractive forcing is allowed as well,
due to an appropriate compensation coming from the "pressure" term. The
compressible Euler flows form their subclass, when regarded as stochastic
processes. We establish circumstances under which the dispersion of passive
contaminants in a forced, deterministic or random, flow can be consistently
interpreted as a Markovian diffusion process. In case of conservative forcing
the repulsive case only, with bounded
from below, is unquestionably admitted by the compatibility conditions. A class
of diffusion processes is exemplified, such that the attractive forcing is
allowed as well, due to an appropriate compensation coming from the "pressure"
term. The compressible Euler flows form their subclass, when regarded as
stochastic processes.Comment: 10 pages, Late
Numerical Schemes for Multivalued Backward Stochastic Differential Systems
We define some approximation schemes for different kinds of generalized
backward stochastic differential systems, considered in the Markovian
framework. We propose a mixed approximation scheme for a decoupled system of
forward reflected SDE and backward stochastic variational inequality. We use an
Euler scheme type, combined with Yosida approximation techniques.Comment: 13 page
Ventilatory Responsiveness during Exercise and Performance Impairment in Acute Hypoxia
Introduction: An adequate increase in minute ventilation to defend arterial oxyhemoglobin saturation (SpO2) during hypoxic exercise is commonly viewed as an important factor contributing to large inter-individual variations in the degree of exercise performance impairment in hypoxia. Although the hypoxic ventilatory response (HVR) could provide insight into the underpinnings of such impairments, it is typically measured at rest under isocapnic conditions. Thus, we aimed to determine whether 1) HVR at rest and during exercise are similar and 2) exercise HVR is related to the degree of impairment in cycling time trial (TT) performance from normoxia to acute hypoxia (∆TT).
Methods: Sixteen endurance-trained men (V˙O2peak, 62.5 ± 5.8 mL·kg-1·min-1) performed two poikilocapnic HVR tests: one during seated rest (HVRREST) and another during submaximal cycling (HVREX). On two separate visits, subjects (n = 12) performed a 10-km cycling TT while breathing either room air (FiO2 = 0.21) or hypoxic gas mixture (FiO2 = 0.16) in a randomized order.
Results: HVREX was significantly (P < 0.001) greater than HVRREST (1.52 ± 0.47 and 0.22 ± 0.13 L·min-1·%SpO2-1, respectively), and these measures were not correlated (r = -0.16, P = 0.57). ∆TT was not correlated with HVRREST (P = 0.70) or HVREX (P = 0.54), but differences in ventilation and end-tidal CO2 between hypoxic and normoxic TT and the ventilatory equivalent for CO2 during normoxic TT explained ~85% of the variance in performance impairment in acute hypoxia (P < 0.01).
Conclusion: We conclude that 1) HVR is not an appropriate measure to predict the exercise ventilatory response or performance impairments in acute hypoxia and 2) an adequate and metabolically matched increase in exercise ventilation, but not the gain in the ventilatory response to hypoxia, is essential for mitigating hypoxia-induced impairments in endurance cycling performance
Diffusion and Current of Brownian Particles in Tilted Piecewise Linear Potentials: Amplification and Coherence
Overdamped motion of Brownian particles in tilted piecewise linear periodic
potentials is considered. Explicit algebraic expressions for the diffusion
coefficient, current, and coherence level of Brownian transport are derived.
Their dependencies on temperature, tilting force, and the shape of the
potential are analyzed. The necessary and sufficient conditions for the
non-monotonic behavior of the diffusion coefficient as a function of
temperature are determined. The diffusion coefficient and coherence level are
found to be extremely sensitive to the asymmetry of the potential. It is
established that at the values of the external force, for which the enhancement
of diffusion is most rapid, the level of coherence has a wide plateau at low
temperatures with the value of the Peclet factor 2. An interpretation of the
amplification of diffusion in comparison with free thermal diffusion in terms
of probability distribution is proposed.Comment: To appear in PR
Angiographic Findings of the Multicenter Randomized Study With the Sirolimus-Eluting Bx Velocity Balloon-Expandable Stent (RAVEL)
BACKGROUND: Restenosis remains the major limitation of coronary catheter-based intervention. In small vessels, the amount of neointimal tissue is disproportionately greater than the vessel caliber, resulting in higher restenosis rates. In the Randomized Study With the Sirolimus-Eluting Bx Velocity Balloon-Expandable Stent (RAVEL) trial, approximately 40% of the vessels were small (<2.5 mm). The present study evaluates the relationship between angiographic outcome and vessel diameter for sirolimus-eluting stents.
METHODS AND RESULTS: Patients were randomized to receive either an 18-mm bare metal Bx VELOCITY (BS group, n=118), or a sirolimus-eluting Bx VELOCITY stent (SES group, n=120). Subgroups were stratified into tertiles according to their reference diameter (RD; stratum I, RD 2.84 mm). At 6-month follow-up, the restenosis rate in the SES group was 0% in all strata (versus 35%, 26%, and 20%, respectively, in the BS group). In-stent late loss was 0.01+/-0.25 versus 0.80+/-0.43 mm in stratum I, 0.01+/-0.38 versus 0.88+/-0.57 mm in stratum II, and -0.06+/-0.35 versus 0.74+/-0.57 mm in stratum III (SES versus BS). In SES, the minimal lumen diameter (MLD) remained unchanged (Delta -0.72 to 0.72 mm) in 97% of the lesions and increased (=late gain, DeltaMLD <-0.72 mm) in 3% of the lesions. Multivariate predictors for late loss were treatment allocation (P<0.001) and postprocedural MLD (P= 0.008).
CONCLUSIONS: Sirolimus-eluting stents prevent neointimal proliferation and late lumen loss irrespective of the vessel diameter. The classic inverse relationship between vessel diameter and restenosis rate was seen in the bare stent group but not in the sirolimus-eluting stent group
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