1,422 research outputs found
Electronic Structure and Dynamics of Higher-Lying Excited States in Light Harvesting Complex 1 from Rhodobacter sphaeroides
Light harvesting in photosynthetic organisms involves efficient transfer of energy from peripheral antenna complexes to core antenna complexes, and ultimately to the reaction center where charge separation drives downstream photosynthetic processes. Antenna complexes contain many strongly coupled chromophores, which complicates analysis of their electronic structure. Two-dimensional electronic spectroscopy (2DES) provides information on energetic coupling and ultrafast energy transfer dynamics, making the technique well suited for the study of photosynthetic antennae. Here, we present 2DES results on excited state properties and dynamics of a core antenna complex, light harvesting complex 1 (LH1), embedded in the photosynthetic membrane of Rhodobacter sphaeroides. The experiment reveals weakly allowed higher-lying excited states in LH1 at 770 nm, which transfer energy to the strongly allowed states at 875 nm with a lifetime of 40 fs. The presence of higher-lying excited states is in agreement with effective Hamiltonians constructed using parameters from crystal structures and atomic force microscopy (AFM) studies. The energy transfer dynamics between the higher- and lower-lying excited states agree with Redfield theory calculations
Quantum metastability in a class of moving potentials
In this paper we consider quantum metastability in a class of moving
potentials introduced by Berry and Klein. Potential in this class has its
height and width scaled in a specific way so that it can be transformed into a
stationary one. In deriving the non-decay probability of the system, we argue
that the appropriate technique to use is the less known method of scattering
states. This method is illustrated through two examples, namely, a moving
delta-potential and a moving barrier potential. For expanding potentials, one
finds that a small but finite non-decay probability persists at large times.
Generalization to scaling potentials of arbitrary shape is briefly indicated.Comment: 10 pages, 1 figure
Mass Flux of ZnSe by Physical Vapor Transport
Mass fluxes of ZnSe by physical vapor transport (PVT) were measured in the temperature range of 1050 to 1160 C using an in-situ dynamic technique. The starting materials were either baked out or distilled under vacuum to obtain near-congruently subliming compositions. Using an optical absorption technique Zn and Se, were found to be the dominant vapor species. Partial pressures of Zn and Se, over the starting materials at temperatures between 960 and 1140 C were obtained by measuring the optical densities of the vapor phase at the wavelengths of 2138, 3405, 3508, 3613, and 3792 A. The amount and composition of the residual gas inside the experimental ampoules were measured after the run using a total pressure gauge. For the first time, the experimentally determined partial pressures of Zn and Se, and the amount and composition of the residual gas were used in a one-dimensional diffusion limited analysis of the mass transport rates for a PVT system. Reasonable agreement between the experimental and theoretical results was observed
Abelian Gauge Fluxes and Local Models in F-Theory
We analyze the Abelian gauge fluxes in local F-theory models with G_S=SU(6)
and SO(10). For the case of G_S=SO(10), there is a no-go theorem which states
that for an exotic-free spectrum, there are no solutions for U(1)^2 gauge
fluxes. We explicitly construct the U(1)^2 gauge fluxes with an exotic-free
bulk spectrum for the case of G_S=SU(6). We also analyze the conditions for the
curves supporting the given field content and discuss non-minimal spectra of
the MSSM with doublet-triplet splitting.Comment: 43 pages, 15 tables; typos corrected, reference adde
Query-controllable Video Summarization
When video collections become huge, how to explore both within and across
videos efficiently is challenging. Video summarization is one of the ways to
tackle this issue. Traditional summarization approaches limit the effectiveness
of video exploration because they only generate one fixed video summary for a
given input video independent of the information need of the user. In this
work, we introduce a method which takes a text-based query as input and
generates a video summary corresponding to it. We do so by modeling video
summarization as a supervised learning problem and propose an end-to-end deep
learning based method for query-controllable video summarization to generate a
query-dependent video summary. Our proposed method consists of a video summary
controller, video summary generator, and video summary output module. To foster
the research of query-controllable video summarization and conduct our
experiments, we introduce a dataset that contains frame-based relevance score
labels. Based on our experimental result, it shows that the text-based query
helps control the video summary. It also shows the text-based query improves
our model performance. Our code and dataset:
https://github.com/Jhhuangkay/Query-controllable-Video-Summarization.Comment: This paper is accepted by ACM International Conference on Multimedia
Retrieval (ICMR), 202
Flipped SU(5) GUTs from E_8 Singularities in F-theory
In this paper we construct supersymmetric flipped SU(5) GUTs from E_8
singularities in F-theory. We start from an SO(10) singularity unfolded from an
E_8 singularity by using an SU(4) spectral cover. To obtain realistic models,
we consider (3,1) and (2,2) factorizations of the SU(4) cover. After turning on
the massless U(1)_X gauge flux, we obtain the SU(5) X U(1)_X gauge group. Based
on the well-studied geometric backgrounds in the literature, we demonstrate
several models and discuss their phenomenology.Comment: 46 pages, 23 tables, 1 figure, typos corrected, references added, and
new examples presente
On Global Flipped SU(5) GUTs in F-theory
We construct an SU(4) spectral divisor and its factorization of types (3,1)
and (2,2) based on the construction proposed in [1]. We calculate the chiral
spectra of flipped SU(5) GUTs by using the spectral divisor construction. The
results agree with those from the analysis of semi-local spectral covers. Our
computations provide an example for the validity of the spectral divisor
construction and suggest that the standard heterotic formulae are applicable to
the case of F-theory on an elliptically fibered Calabi-Yau fourfold with no
heterotic dual.Comment: 45 pages, 12 tables, 1 figure; typos corrected, footnotes added, and
a reference adde
Tutorial on Online Partial Evaluation
This paper is a short tutorial introduction to online partial evaluation. We
show how to write a simple online partial evaluator for a simple, pure,
first-order, functional programming language. In particular, we show that the
partial evaluator can be derived as a variation on a compositionally defined
interpreter. We demonstrate the use of the resulting partial evaluator for
program optimization in the context of model-driven development.Comment: In Proceedings DSL 2011, arXiv:1109.032
Changes in the expression of the Alzheimer's disease-associated presenilin gene in drosophila heart leads to cardiac dysfunction
Mutations in the presenilin genes cause the majority of early-onset familial Alzheimer’s disease.
Recently, presenilin mutations have been identified in patients with dilated cardiomyopathy
(DCM), a common cause of heart failure and the most prevalent diagnosis in cardiac
transplantation patients. However, the molecular mechanisms, by which presenilin mutations lead
to either AD or DCM, are not yet understood. We have employed transgenic Drosophila models
and optical coherence tomography imaging technology to analyze cardiac function in live adult
Drosophila. Silencing of Drosophila ortholog of presenilins (dPsn) led to significantly reduced
heart rate and remarkably age-dependent increase in end-diastolic vertical dimensions. In contrast,
overexpression of dPsn increased heart rate. Either overexpression or silencing of dPsn resulted in
irregular heartbeat rhythms accompanied by cardiomyofibril defects and mitochondrial
impairment. The calcium channel receptor activities in cardiac cells were quantitatively
determined via real-time RT-PCR. Silencing of dPsn elevated dIP[subscript 3]R expression, and reduced dSERCA expression; overexprerssion of dPsn led to reduced dRyR expression. Moreover,
overexpression of dPsn in wing disc resulted in loss of wing phenotype and reduced expression of
wingless. Our data provide novel evidence that changes in presenilin level leads to cardiac
dysfunction, owing to aberrant calcium channel receptor activities and disrupted Wnt signaling
transduction, indicating a pathogenic role for presenilin mutations in DCM pathogenesis.Cure Alzheimer’s FundNational Institutes of Health (U.S.) (Grant R01AG014713)National Institutes of Health (U.S.) (Grant R01MH60009)National Institutes of Health (U.S.) (Grant R01CA75289)National Institutes of Health (U.S.) (Grant R01HL095717)National Institutes of Health (U.S.) (Grant FA9550-07-1-0014
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