11,760 research outputs found
Photoperiodic influences on ultradian rhythms of male Siberian hamsters.
Seasonal changes in mammalian physiology and behavior are proximately controlled by the annual variation in day length. Long summer and short winter day lengths markedly alter the amplitude of endogenous circadian rhythms and may affect ultradian oscillations, but the threshold photoperiods for inducing these changes are not known. We assessed the effects of short and intermediate day lengths and changes in reproductive physiology on circadian and ultradian rhythms of locomotor activity in Siberian hamsters. Males were maintained in a long photoperiod from birth (15 h light/day; 15 L) and transferred in adulthood to 1 of 7 experimental photoperiods ranging from 14 L to 9 L. Decreases in circadian rhythm (CR) robustness, mesor and amplitude were evident in photoperiods ≤14 L, as were delays in the timing of CR acrophase and expansion of nocturnal activity duration. Nocturnal ultradian rhythms (URs) were comparably prevalent in all day lengths, but 15 L markedly inhibited the expression of light-phase URs. The period (τ), amplitude and complexity of URs increased in day lengths ≤13 L. Among hamsters that failed to undergo gonadal regression in short day lengths (nonresponders), τ of the dark-phase UR was longer than in photoresponsive hamsters; in 13 L the incidence and amplitude of light-phase URs were greater in hamsters that did not undergo testicular regression. Day lengths as long as 14 L were sufficient to trigger changes in the waveform of CRs without affecting UR waveform. The transition from a long- to a short-day ultradian phenotype occurred for most UR components at day lengths of 12 L-13 L, thereby establishing different thresholds for CR and UR responses to day length. At the UR-threshold photoperiod of 13 L, differences in gonadal status were largely without effect on most UR parameters
Selection and Oversight in the Public Sector, With the Los Angeles Police Department as an Example
I offer theoretical and empirical observations on the oversight of public sector employees. I argue that it is unreasonable to expect that the solutions typically considered in the literature will be effective with public sector employees, because bureaucrats are especially difficult to monitor. To offset this weakness, agencies tend to hire bureaucrats who are biased against consumers, where such bias increases incentives. I then address how bureaucrats should be overseen and offer a choice between internal monitoring of public agencies, with overseers who are biased against consumers, or external monitoring, where bureaucrats become excessively worried about the prospect of an investigation and may change their behavior to attain that goal. I provide evidence from the Los Angeles Police Department to show that officers appear to have responded to increased oversight by reducing crime-fighting activities in an attempt to avoid investigation.
Fano manifolds of index n-1 and the cone conjecture
The Morrison-Kawamata cone conjecture predicts that the actions of the
automorphism group on the effective nef cone and the pseudo-automorphism group
on the effective movable cone of a klt Calabi-Yau pair have
finite, rational polyhedral fundamental domains. Let be an -dimensional
Fano manifold of index such that for an ample divisor
. Let be the base locus of a general -dimensional linear
system . In this paper, we verify the Morrison-Kawamata cone
conjecture for the blow-up of along .Comment: 30 page
Time-Independent Gravitational Fields in the BGK Scheme for Hydrodynamics
We incorporate a time-independent gravitational field into the BGK scheme for
numerical hydrodynamics. In the BGK scheme the gas evolves via an approximation
to the collisional Boltzmann equation, namely the Bhatnagar-Gross-Krook (BGK)
equation. Time-dependent hydrodynamical fluxes are computed from local
solutions of the BGK equation. By accounting for particle collisions, the
fundamental mechanism for generating dissipation in gas flow, a scheme based on
the BGK equation gives solutions to the Navier-Stokes equations: the fluxes
carry both advective and dissipative terms. We perform numerical experiments in
both 1D Cartesian geometries and axisymmetric cylindrical coordinates.Comment: 31 pages including 19 figures (For higher resolution figs. see
http://www.mpia-hd.mpg.de/MPIA/Projects/THEORY/slyz), Accepted for
publication in Astronomy and Astrophysics, Supplement Serie
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