2,640 research outputs found
A vertex algebra attached to the flag manifold and Lie algebra cohomology
Each flag manifold carries a unique algebra of chiral differential operators.
Continuing along the lines of arXiv:0903.1281 we compute the vertex algebra
structure on the cohomology of this algebra. The answer is: the tensor product
of the center and a subalgebra; the center is isomorphic, as a commutative
associative algebra, to the cohomology of the corresponding maximal nilpotent
Lie algebra; the subalgebra is the vacuum module over the corresponding affine
Lie algebra of critical level and 0 central character. We next find the
Friedan-Martinec-Shenker-Borisov bosonization of the cohomology algebra in case
of the projective line and show that this algebra vanishes nonperturbatively,
thus verifying a suggestion by Witten.Comment: a reference adde
Localization of affine W-algebras
We introduce the notion of an asymptotic algebra of chiral differential
operators. We then construct, via a chiral Hamiltonian reduction, one such
algebra over a resolution of the intersection of the Slodowy slice with the
nilpotent cone. We compute the space of global sections of this algebra thereby
proving a localization theorem for affine W-algebras at the critical level.Comment: 36 page
A chiral Borel-Weil-Bott theorem
We compute the cohomology of modules over the algebra of twisted chiral
differential operators over the flag manifold. This is applied to (1) finding
the character of -integrable irreducible highest weight modules over the
affine Lie algebra at the critical level, and (2) computing a certain elliptic
genus of the flag manifold. The main tool is a result that interprets the
Drinfeld-Sokolov reduction as a derived functor.Comment: Some considerable reworking. A final version to appear in Adv. in
Mat
New Tardigrade Opsins and Differential Expression Analyses Show Ontogenic Variation in Light Perception
Abstract
Opsins are light-sensitive proteins involved in many photoreceptive processes, including, but not limited to, vision and regulation of circadian rhythms. Arthropod (e.g., insects, spiders, centipedes, and crabs) opsins have been extensively researched, but the relationships and function of opsins found in lineages that are evolutionarily closely related to the arthropods remains unclear. Multiple, independent, opsin duplications are known in Tardigrada (the water bears), evidencing that protostome opsin duplications are not limited to the Arthropoda. However, the relationships, function, and expression of these new opsins are still unknown. Here, we use two tardigrade transcriptomes with deep coverage to greatly expand our knowledge of the diversity of tardigrade opsins. We reconstruct the phylogenetic relationships of the tardigrade opsins and investigate their ontogenetic expression. We found that while tardigrades have multiple opsins that evolved from lineage-specific duplications of well-understood arthropod opsins, their expression levels change during ontogeny such that most of these opsins are not co-temporally expressed. Co-temporal expression of multiple opsins underpins color vision in Arthropoda and Vertebrata. Our results clearly show duplications of both rhabdomeric and ciliary opsins within Tardigrada, forming clades specific to both the Heterotardigrada and Eutardigrada in addition to multiple independent duplications within genera. However, lack of co-temporal, ontogenetic, expression suggests that while tardigrades possess multiple opsins, they are unlikely to be able to distinguish color
Opportunities to demonstrate expertise and job satisfaction of community pharmacists in Japan and England
Background: In response to anticipated increased health needs as a consequence of aging populations, and associated rising co-morbidity and medicines use, in both Japan and the UK potential extended roles for community pharmacy are part of health policy agendas. It is widely perceived that community pharmacists do not fully utilize their expertise, which may limit their contribution to health care in their communities and also impact negatively on their own job satisfaction. Purpose: The aim of this qualitative study was to identify operations that are perceived as opportunities to demonstrate expertise (ODE) and/or sources of job satisfaction by pharmacists in Japan and England, and explore associated system and contextual factors. Methods: Data were gathered with purposively selected pharmacists in Japan and England. An initial questionnaire was forwarded which guided subsequent face-to-face semi-structured interviews. These were audio-recoded to enable qualitative analytical procedures. Results: There were 18 participants in England and 13 in Japan. There was a notable association between ODE and job satisfaction. However, ODE was not a sufficient condition for job satisfaction. Conclusion: In order for pharmacists to be satisfied with their jobs, not only ODE but also additional contextual factors, i.e. recognition of professionalism, autonomy and positive collaboration were also needed. The findings can inform initiatives in the development of pharmacy services that would be positive for pharmacists whilst potentially contributing to wider public health objectives
A Correlation between the Emission Intensity of Self-Assembled Germanium Islands and the Quality Factor of Silicon Photonic Crystal Nanocavities
We present a comparative micro-photoluminescence study of the emission
intensity of self-assembled germanium islands coupled to the resonator mode of
two-dimensional silicon photonic crystal defect nanocavities. The emission
intensity is investigated for cavity modes of L3 and Hexapole cavities with
different cavity quality factors. For each of these cavities many nominally
identical samples are probed to obtain reliable statistics. As the quality
factor increases we observe a clear decrease in the average mode emission
intensity recorded under comparable optical pumping conditions. This clear
experimentally observed trend is compared with simulations based on a
dissipative master equation approach that describes a cavity weakly coupled to
an ensemble of emitters. We obtain evidence that reabsorption of photons
emitted into the cavity mode is responsible for the observed trend. In
combination with the observation of cavity linewidth broadening in power
dependent measurements, we conclude that free carrier absorption is the
limiting effect for the cavity mediated light enhancement under conditions of
strong pumping.Comment: 8 pages, 5 figure
Calculation of pure dephasing for excitons in quantum dots
Pure dephasing of an exciton in a small quantum dot by optical and acoustic
phonons is calculated using the ``independent boson model''. Considering the
case of zero temperature the dephasing is shown to be only partial which
manifests itself in the polarization decaying to a finite value. Typical
dephasing times can be assigned even though the spectra exhibits strongly
non-Lorentzian line shapes. We show that the dephasing from LO phonon
scattering, occurs on a much larger time scale than that of dephasing due to
acoustic phonons which for low temperatures are also a more efficient dephasing
mechanism. The typical dephasing time is shown to strongly depend on the
quantum dot size whereas the electron phonon ``coupling strength'' and external
electric fields tend mostly to effect the residual coherence. The relevance of
the dephasing times for current quantum information processing implementation
schemes in quantum dots is discussed
P-shell carriers assisted dynamic nuclear spin polarization in single quantum dots at zero external magnetic field
Repeated injection of spin polarized carriers in a quantum dot leads to the
polarization of nuclear spins, a process known as dynamic nuclear spin
polarization (DNP). Here, we report the first observation of p-shell carrier
assisted DNP in single QDs at zero external magnetic field. The nuclear field -
measured by using the Overhauser shift of the singly charged exciton state of
the QDs - continues to increase, even after the carrier population in the
s-shell saturates. This is also accompanied by an abrupt increase in nuclear
spin buildup time as p-shell emission overtakes that of the s-shell. We
attribute the observation to p-shell electrons strongly altering the nuclear
spin dynamics in the QD, supported by numerical simulation results based on a
rate equation model of coupling between electron and nuclear spin system. DNP
with p-shell carriers could open up avenues for further control to increase the
degree of nuclear spin polarization in QDs.Comment: 23 pages, 6 figure
Duality in finite-dimensional spin glasses
We present an analysis leading to a conjecture on the exact location of the
multicritical point in the phase diagram of spin glasses in finite dimensions.
The conjecture, in satisfactory agreement with a number of numerical results,
was previously derived using an ansatz emerging from duality and the replica
method. In the present paper we carefully examine the ansatz and reduce it to a
hypothesis on analyticity of a function appearing in the duality relation. Thus
the problem is now clearer than before from a mathematical point of view: The
ansatz, somewhat arbitrarily introduced previously, has now been shown to be
closely related to the analyticity of a well-defined function.Comment: 12 pages, 3 figures; A reference added; to appear in J. Stat. Phy
Electron-hole correlation effects in the emission of light from quantum wires
We present a self-consistent treatment of the electron-hole correlations in
optically excited quantum wires within the ladder approximation, and using a
contact potential interaction. The limitations of the ladder approximation to
the excitonic low-density region are largely overcome by the introduction of
higher order correlations through self consistency. We show relevance of these
correlations in the low-temperature emission, even for high density relevant in
lasing, when large gain replaces excitonic absorption.Comment: 4 paes 3 figure
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