2,292 research outputs found
Photodarkening of amorphous selenium under high pressure
The photodarkening phenomena of amorphous Se have been studied by the optical absorption coefficient, sound velocity and attenuation measurements. The light illumination at low temperatures induces the photodarkening, and the photodarkened state is completely recovered by annealing near 306 K corresponding to the glass transition temperature. The photodarkening is enhanced by application of pressure. The sound velocity decreases and the sound attenuation increases by the illumination at low temperature. These suggest that a structural disorder increases in the photodarkened state. Three stages are observed for the recovery process of the photodarkened specimen. The photodarkening and the recovery process are discussed on the basis of VAP (valence alternative pair) model.<br /
Annual Performance Reviews Of, For and By Faculty: A Qualitative Analysis of One Department's Experiences
Purpose:
Although annual performance reviews and feedback are recommended for faculty development, best practices and faculty perceptions have not been documented. The authors sought to evaluate the process in one medical school department that established and has sustained an innovative review tradition for 25 years.
Method:
Content analysis of faculty reports and immersion/crystallization to analyze interviews.
Results:
Faculty reports described satisfaction and dissatisfaction; facilitators and barriers to goals; and requests for feedback, with community, collaboration and mentorship integral to all three. Interviewees emphasized practical challenges, the role of the mentor and the power of the review to establish community norms.
Conclusion:
Respondents generally found reviews constructive and supportive. The process informs departmental expectations and culture
Magnetorotational Instability around a Rotating Black Hole
The magnetorotational instability(MRI) in the Kerr spacetime is studied on a
3+1 viewpoint. The Maxwell's equations are expressed in a circularly orbiting
observer's frame that co-rotates with matter in Keplerian orbits. There exist
large proper growth rates in MRI around a rapidly rotating black hole. The
large "centrifugal force" and the rapid variations of magnetic fields are
caused by the rotation of spacetime geometry. As the result, in the extreme
Kerr case the maximum proper growth rate at becomes about twelve
times as large as that in Schwartzshield case.Comment: 18pages, 9figure
High frequency dynamics in liquid nickel: an IXS study
Owing to their large relatively thermal conductivity, peculiar,
non-hydrodynamic features are expected to characterize the acoustic-like
excitations observed in liquid metals. We report here an experimental study of
collective modes in molten nickel, a case of exceptional geophysical interest
for its relevance in Earth interior science. Our result shed light on
previously reported contrasting evidences: in the explored energy-momentum
region no deviation from the generalized hydrodynamic picture describing non
conductive fluids are observed. Implications for high frequency transport
properties in metallic fluids are discussed.Comment: 6 pages, 4 figures, to appear in "Journal of Chemical Physics
Many-spinon states and the secret significance of Young tableaux
We establish a one-to-one correspondence between the Young tableaux
classifying the total spin representations of N spins and the exact eigenstates
of the the Haldane-Shastry model for a chain with N sites classified by the
total spins and the fractionally spaced single-particle momenta of the spinons.Comment: 4 pages, 3 figure
Соотношение путей углеводного синтеза при введении свободных и фосфорилированных сахаров в листья картофеля
Показано, что регуляция путей биосинтеза углеводов может осуществляться через изменение концентрации промежуточных и конечных метаболитов. При этом одним из факторов, регулирующих направленность синтеза углеводов, является активность АДФГ- и УДФГ-пирофосфорилаз. По-видимому, регуляция работы этих ферментов может осуществляться низкомолекулярными метаболитами по принципу обратной связи
Flounder metamorphosis: its regulation by various hormones
The elongation and shortening of the flounder fin rays during its metamorphosis may be parallel to the appearance and resorption of the tadpole tail during amphibian metamorphosis. The dorsal fin rays of the Japanese flounder (Paralichthys olivaceus) elongate during the time when thyroid hormone levels are low and are resorbed during climax of metamorphosis when thyroid levels are elevated. Using an in vitro system for culture of isolated flounder fin rays, we examined how various hormones affect the process of resorption. Both T4 and T3 directly stimulated fin ray shortening, T3 being more potent than T4. Other hormones did not directly affect the resorption process but modified the tissue's response to thyroid hormones. Cortisol enhanced the stimulatory effects of both T4 and T3. On the other hand, estradiol and testosterone were inhibitory. Ovine prolactin (oPRL) also diminished the effect of T3 while ovine growth hormone (oGH) was without effect. Similar observations were observed from the in vivo studies.
Thyroid hormone levels, especially T4, were low during premetamorphosis, increased during prometamorphosis, to peak levels during metamorphic climax, and declined in the juveniles. The changes in whole body concentrations of Cortisol paralleled the changes in thyroid hormone concentrations. On the other hand, whole body estradiol and testosterone concentrations did not show significant change and remained low throughout the larval period. The expression of GH and PRLmRNA, as assessed by in situ hybridization using cDNA for flounder PRL and GH also increased during the metamorphosis. However, the increase in the expression of GH and PRL genes was observed later than the increases in tissue levels of thyroid hormones and Cortisol. At late climax, the flounder larvae have undergone considerable transformation, presumably triggered by both hormones, hence the increase in PRL could hardly be antimetamorphic but may have other physiological implications
Primordial black holes and gravitational waves induced by exponential-tailed perturbations
Primordial black holes (PBHs) whose masses are in
have been extensively studied as a
candidate of whole dark matter (DM). One of the probes to test such a PBH-DM
scenario is scalar-induced stochastic gravitational waves (GWs) accompanied
with the enhanced primordial fluctuations to form the PBHs with frequency
peaked in the mHz band being targeted by the LISA mission. In order to utilize
the stochastic GWs for checking the PBH-DM scenario, it needs to exactly relate
the PBH abundance and the amplitude of the GWs spectrum. Recently in Kitajima
et al., the impact of the non-Gaussianity of the enhanced primordial curvature
perturbations on the PBH abundance has been investigated based on the peak
theory, and they found that a specific non-Gaussian feature called the
exponential tail significantly increases the PBH abundance compared with the
Gaussian case. In this work, we investigate the spectrum of the induced
stochastic GWs associated with PBH DM in the exponential-tail case. In order to
take into account the non-Gaussianity properly, we employ the diagrammatic
approach for the calculation of the spectrum. We find that the amplitude of the
stochastic GW spectrum is slightly lower than the one for the Gaussian case,
but it can still be detectable with the LISA sensitivity. We also find that the
non-Gaussian contribution can appear on the high-frequency side through their
complicated momentum configurations. Although this feature emerges under the
LISA sensitivity, it might be possible to obtain information about the
non-Gaussianity from GW observation with a deeper sensitivity such as the
DECIGO mission.Comment: 33 pages, 19 figure
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