3,879 research outputs found
Npas4 is activated by melatonin, and drives the clock gene Cry1 in the ovine pars tuberalis
Seasonal mammalsintegrate changes in the duration of nocturnal melatonin secretion to drive annual physiologic cycles. Melatonin receptors within the proximal pituitary region, the pars tuberalis (PT), are essential in regulating seasonal neuroendocrine responses. In the ovine PT, melatonin is known to influence acute changes in transcriptional dynamics coupled to the onset (dusk) and offset (dawn) of melatonin secretion, leading to a potential interval-timing mechanism capable of decoding changes in day length (photoperiod). Melatonin offset at dawn is linked to cAMP accumulation, which directly induces transcription of the clock gene Per1. The rise of melatonin at dusk induces a separate and distinct cohort, including the clock-regulated genes Cry1 and Nampt, but little is known of the upstream mechanisms involved. Here, we used next-generation sequencing of the ovine PT transcriptome at melatonin onset and identified Npas4 as a rapidly induced basic helix-loop-helix Per-Arnt-Sim domain transcription factor. In vivo we show nuclear localization of NPAS4 protein in presumptive melatonin target cells of the PT (α-glycoprotein hormone-expressing cells), whereas in situ hybridization studies identified acute and transient expression in the PT of Npas4 in response to melatonin. In vitro, NPAS4 forms functional dimers with basic helix loop helix-PAS domain cofactors aryl hydrocarbon receptor nuclear translocator (ARNT), ARNT2, and ARNTL, transactivating both Cry1 and Nampt ovine promoter reporters. Using a combination of 5'-deletions and site-directed mutagenesis, we show NPAS4-ARNT transactivation to be codependent upon two conserved central midline elements within the Cry1 promoter. Our data thus reveal NPAS4 as a candidate immediate early-response gene in the ovine PT, driving molecular responses to melatonin
Tree-body loss of of trapped ultracold Rb atoms due to a Feshbach resonance
The loss of ultracold trapped atoms in the vicinity of a Feshbach resonance
is treated as a two-stage reaction, using the Breit-Wigner theory. The first
stage is the formation of a resonant diatomic molecule, and the second one is
its deactivation by inelastic collisions with other atoms. This model is
applied to the analysis of recent experiments on Rb, leading to an
estimated value of cms for the deactivation rate
coefficient.Comment: LaTeX, 4 pages with 1 figures, uses REVTeX4, uses improved
experimental dat
Testing quantum correlations in a confined atomic cloud by scattering fast atoms
We suggest measuring one-particle density matrix of a trapped ultracold
atomic cloud by scattering fast atoms in a pure momentum state off the cloud.
The lowest-order probability of the inelastic process, resulting in a pair of
outcoming fast atoms for each incoming one, turns out to be given by a Fourier
transform of the density matrix. Accordingly, important information about
quantum correlations can be deduced directly from the differential scattering
cross-section. A possible design of the atomic detector is also discussed.Comment: 5 RevTex pages, no figures, submitted to PR
On the stability of standing matter waves in a trap
We discuss excited Bose-condensed states and find the criterion of dynamical
stability of a kink-wise state, i.e., a standing matter wave with one nodal
plane perpendicular to the axis of a cylindrical trap. The dynamical stability
requires a strong radial confinement corresponding to the radial frequency
larger than the mean-field interparticle interaction. We address the question
of thermodynamic instability related to the presence of excitations with
negative energy.Comment: 4 pages, 3 figure
Power laws and collapsing dynamics of a trapped Bose-Einstein condensate with attractive interactions
The critical behavior of collective modes and the collapsing dynamics of
trapped Bose-Einstein condensates with attractive interactions are studied
analytically and numerically. The time scales of these dynamics both below and
above the critical point of the collapse are found to obey power laws with a
single parameter of N/N_c - 1, where N is the number of condensate atoms and
N_c is the critical number. The collapsing condensate eventually undergoes
rapid implosion, which occurs several times intermittently, and then the
implosion turns to an explosion. The release energy of the explosion is found
to be proportional to the square of the interaction strength, inversely
proportional to the three-body recombination rate, and independent of the
number of condensate atoms and the trap frequency.Comment: 9 pages, RevTeX, 7 figures, epsf.sty, corrected loss rate
Mean-field analysis of collapsing and exploding Bose-Einstein condensates
The dynamics of collapsing and exploding trapped Bose-Einstein condensat es
caused by a sudden switch of interactions from repulsive to attractive a re
studied by numerically integrating the Gross-Pitaevskii equation with atomic
loss for an axially symmetric trap. We investigate the decay rate of
condensates and the phenomena of bursts and jets of atoms, and compare our
results with those of the experiments performed by E. A. Donley {\it et al.}
[Nature {\bf 412}, 295 (2001)]. Our study suggests that the condensate decay
and the burst production is due to local intermittent implosions in the
condensate, and that atomic clouds of bursts and jets are coherent. We also
predict nonlinear pattern formation caused by the density instability of
attractive condensates.Comment: 7 pages, 8 figures, axi-symmetric results are adde
A TESS Dress Rehearsal: Planetary Candidates and Variables from K2 Campaign 17T
We produce light curves for all ∼34,000 targets observed with K2 in Campaign 17 (C17), identifying 34 planet candidates, 184 eclipsing binaries, and other 222 periodic variables. The forward-facing direction of the C17 field means follow-up can begin immediately now that the campaign has concluded and interesting targets have been identified. The C17 field has a large overlap with C6, so this latest campaign also offers an infrequent opportunity to study a large number of targets already observed in a previous K2 campaign. The timing of the C17 data release, shortly before science operations begin with the Transiting Exoplanet Survey Satellite (TESS), also lets us exercise some of the tools and methods developed for identification and dissemination of planet candidates from TESS. We find excellent agreement between these results and those identified using only K2-based tools. Among our planet candidates are several planet candidates with sizes <4 R[subscript ⊕] and orbiting stars with Kp ≲ 10 (indicating good RV targets of the sort TESS hopes to find) and a Jupiter-sized single-transit event around a star already hosting a 6 day planet candidate. Key words: methods, data analysis, planets and satellites, detection – techniques, photometricUnited States. National Aeronautics and Space Administration (K2GO Grant 80NSSC18K0308
Cryptic patterning of avian skin confers a developmental facility for loss of neck feathering
Vertebrate skin is characterized by its patterned array of appendages, whether feathers, hairs, or scales. In avian skin the distribution of feathers occurs on two distinct spatial levels. Grouping of feathers within discrete tracts, with bare skin lying between the tracts, is termed the macropattern, while the smaller scale periodic spacing between individual feathers is referred to as the micropattern. The degree of integration between the patterning mechanisms that operate on these two scales during development and the mechanisms underlying the remarkable evolvability of skin macropatterns are unknown. A striking example of macropattern variation is the convergent loss of neck feathering in multiple species, a trait associated with heat tolerance in both wild and domestic birds. In chicken, a mutation called Naked neck is characterized by a reduction of body feathering and completely bare neck. Here we perform genetic fine mapping of the causative region and identify a large insertion associated with the Naked neck trait. A strong candidate gene in the critical interval, BMP12/GDF7, displays markedly elevated expression in Naked neck embryonic skin due to a cis-regulatory effect of the causative mutation. BMP family members inhibit embryonic feather formation by acting in a reaction-diffusion mechanism, and we find that selective production of retinoic acid by neck skin potentiates BMP signaling, making neck skin more sensitive than body skin to suppression of feather development. This selective production of retinoic acid by neck skin constitutes a cryptic pattern as its effects on feathering are not revealed until gross BMP levels are altered. This developmental modularity of neck and body skin allows simple quantitative changes in BMP levels to produce a sparsely feathered or bare neck while maintaining robust feather patterning on the body. © 2011 Mou et al
Ordering ambiguity revisited via position dependent mass pseudo-momentum operators
Ordering ambiguity associated with the von Roos position dependent mass (PDM)
Hamiltonian is considered. An affine locally scaled first order differential
introduced, in Eq.(9), as a PDM-pseudo-momentum operator. Upon intertwining our
Hamiltonian, which is the sum of the square of this operator and the potential
function, with the von Roos d-dimensional PDM-Hamiltonian, we observed that the
so-called von Roos ambiguity parameters are strictly determined, but not
necessarily unique. Our new ambiguity parameters' setting is subjected to
Dutra's and Almeida's [11] reliability test and classified as good ordering.Comment: 10 pages, no figures, revised/expanded, mathematical presentations in
section 2 (Especially, the typological Errors in Eqs.(9)-(12))are now
corrected. To appear in the Int. J. Theor. Phy
Dense Antihydrogen: Its Production and Storage to Envision Antimatter Propulsion
We discuss the possibility that dense antihydrogen could provide a path
towards a mechanism for a deep space propulsion system. We concentrate at
first, as an example, on Bose-Einstein Condensate (BEC) antihydrogen. In a
Bose-Einstein Condensate, matter (or antimatter) is in a coherent state
analogous to photons in a laser beam, and individual atoms lose their
independent identity. This allows many atoms to be stored in a small volume. In
the context of recent advances in producing and controlling BECs, as well as in
making antihydrogen, this could potentially provide a revolutionary path
towards the efficient storage of large quantities of antimatter, perhaps
eventually as a cluster or solid.Comment: 12 pages, 3 figure
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