6,402 research outputs found
The Nullity of Bicyclic Signed Graphs
Let \Gamma be a signed graph and let A(\Gamma) be the adjacency matrix of
\Gamma. The nullity of \Gamma is the multiplicity of eigenvalue zero in the
spectrum of A(\Gamma). In this paper we characterize the signed graphs of order
n with nullity n-2 or n-3, and introduce a graph transformation which preserves
the nullity. As an application we determine the unbalanced bicyclic signed
graphs of order n with nullity n-3 or n-4, and signed bicyclic signed graphs
(including simple bicyclic graphs) of order n with nullity n-5
Charge Ordered RVB States in the Doped Cuprates
We study charge ordered d-wave resonating valence bond states (dRVB) in the
doped cuprates, and estimate the energies of these states in a generalized model by using a renormalized mean field theory. The long range Coulomb
potential tends to modulate the charge density in favor of the charge ordered
RVB state. The possible relevance to the recently observed
checkerboard patterns in tunnelling conductance in high cuprates is
discussed.Comment: 4 pages, 4 figures, 3 table
Photoreceptor Cell Differentiation Requires Regulated Proteolysis of the Transcriptional Repressor Tramtrack
AbstractThe transcription repressor Tramtrack (TTK) is found in cone cells but not photoreceptor cells of the Drosophila eye. We show that down-regulation of TTK expression occurs in photoreceptor cells and is required for their fate determination. Down-regulation requires the presence of Phyllopod (PHYL), which is induced by the RAS pathway, and Seven In Absentia (SINA). Loss of either gene causes accumulation of TTK in photoreceptor cells, and TTK does not accumulate in cone cells if both PHYL and SINA are present. We report that SINA and PHYL promote ubiquitination and rapid degradation of TTK by the proteasome pathway in cell culture, and both SINA and PHYL bind to the N-terminal domain of TTK. These results argue that photoreceptor differentiation is regulated by the RAS pathway through targeted proteolysis of the TTK repressor
Cavity QED treatment of scattering-induced efficient free-space excitation and collection in high-Q whispering-gallery microcavities
Whispering-gallery microcavity laser possesses ultralow threshold, whereas
convenient free-space optical excitation and collection suffer from low
efficiencies due to its rotational symmetry. Here we analytically study a
three-dimensional microsphere coupled to a nano-sized scatterer in the
framework of quantum optics. It is found that the scatterer is capable of
coupling light in and out of the whispering-gallery modes (WGMs) without
seriously degrading their high-Q properties, while the microsphere itself plays
the role of a lens to focus the input beam on the scatterer and vice versa. Our
analytical results show that (1) the high-Q WGMs can be excited in free space,
and (2) over 50% of the microcavity laser emission can be collected within less
than . This coupling system holds great potential for low
threshold microlasers free of external couplers.Comment: 10 pages, 8 figure
Strongly enhanced light-matter interaction in a hybrid photonic-plasmonic resonator
We propose a hybrid photonic-plasmonic resonant structure which consists of a
metal nanoparticle (MNP) and a whispering gallery mode (WGM) microcavity. It is
found that the hybrid mode enables a strong interaction between the light and
matter, and the single-atom cooperativity is enhanced by more than two orders
of magnitude compared to that in a bare WGM microcavity. This remarkable
improvement originates from two aspects: (1) the MNP offers a highly enhanced
local field in the vicinity of an emitter, and (2), surprisingly, the
high-\textit{Q} property of WGMs can be maintained in the presence of the MNP.
Thus the present system has great advantages over a single microcavity or a
single MNP, and holds great potential in quantum optics, nonlinear optics and
highly sensitive biosening.Comment: 5 pages, 4 figure
Angiotensin II directly regulates intestinal epithelial NHE3 in Caco2BBE cells
<p>Abstract</p> <p>Background</p> <p>Angiotensin II (AII) effects on intestinal Na<sup>+ </sup>transport may be multifactorial. To determine if AII might have a direct effect on intestinal epithelial Na<sup>+ </sup>transport, we investigated its actions on Na<sup>+ </sup>transport in human intestinal epithelial Caco2BBE cells.</p> <p>Results</p> <p>AII increased apical (brush border) sodium-hydrogen exchanger (NHE)-3, but not NHE2, activity within one hour. Similarly, only apical membrane NHE3 abundance increased at 1–2 hours without any change in total NHE3 protein abundance. From 4–48 hours, AII stimulated progressively larger increases in apical NHE3 activity and surface abundance, which was associated with increases in NHE3 protein expression. At 4–24 hours, NHE3 mRNA increases over baseline expression, suggesting increased gene transcription. This was supported by AII induced increases in rat NHE3 gene promoter-reporter activity. AII induction of NHE3 was blocked by the AII type I receptor antagonist losartan. Acute changes in AII-induced increases in NHE3 exocytosis were blocked by a phospholipase C inhibitor, an arachidonic acid cytochrome P450 epoxygenase inhibitor, as well as phosphatidylinositol 3 kinase (PI3K) inhibitors and Akt inhibitor, partially blocked by a metalloproteinase inhibitor and an EGF (epidermal growth factor) receptor kinase inhibitor, but not affected by an inhibitor of MEK-1 (MAPKK-1, mitogen activated protein kinase kinase-1).</p> <p>Conclusion</p> <p>We conclude that angiotensin II has a direct role in regulating intestinal fluid and electrolyte absorption which may contribute to its overall effects in regulation systemic volume and blood pressure. AII activates several key signaling pathways that induce acute and chronic changes in NHE3 membrane trafficking and gene transcription.</p
Quantum secure direct communication network with superdense coding and decoy photons
A quantum secure direct communication network scheme is proposed with quantum
superdense coding and decoy photons. The servers on a passive optical network
prepare and measure the quantum signal, i.e., a sequence of the -dimensional
Bell states. After confirming the security of the photons received from the
receiver, the sender codes his secret message on them directly. For preventing
a dishonest server from eavesdropping, some decoy photons prepared by measuring
one photon in the Bell states are used to replace some original photons. One of
the users on the network can communicate any other one. This scheme has the
advantage of high capacity, and it is more convenient than others as only a
sequence of photons is transmitted in quantum line.Comment: 6 pages, 2 figur
The formation of aromatic hydrocarbons during the pyrolysis of polyethylene
Plastics see very widespread use in modern society. The properties of many plastics can be modified relatively easily to fit a wide variety of applications. However, the disposal of waste plastics presents a significant environmental challenge. Recently, there has been considerable interest into tertiary recycling of waste plastics to produce liquid fuel. This project focuses on the formation of aromatic hydrocarbons during thermal pyrolysis of plastics. Several reactor configurations have been suggested for the pyrolysis of plastics. The reactor configuration used in this study consists of a stirrer tank reactor coupled with a reflux column and a condenser
Angular momentum of non-paraxial light beam: Dependence of orbital angular momentum on polarization
It is shown that the momentum density of free electromagnetic field splits
into two parts. One has no contribution to the net momentum due to the
transversality condition. The other yields all the momentum. The angular
momentum that is associated with the former part is spin, and the angular
momentum that is associated with the latter part is orbital angular momentum.
Expressions for the spin and orbital angular momentum are given in terms of the
electric vector in reciprocal space. The spin and orbital angular momentum
defined this way are used to investigate the angular momentum of nonparaxial
beams that are described in a recently published paper [Phys. Rev. A 78, 063831
(2008)]. It is found that the orbital angular momentum depends, apart from an
-dependent term, on two global quantities, the polarization represented by a
generalized Jones vector and a new characteristic represented by a unit vector
, though the spin depends only on the polarization. The
polarization dependence of orbital angular momentum through the impact of
is obtained and discussed. Some applications of the result
obtained here are also made. The fact that the spin originates from the
momentum density that has no contribution to the net momentum is used to show
that there does not exist the paradox on the spin of circularly polarized plane
wave. The polarization dependence of both spin and orbital angular momentum is
shown to be the origin of conversion from the spin of a paraxial
Laguerre-Gaussian beam into the orbital angular momentum of the focused beam
through a high numerical aperture.Comment: 21 pages including an appendi
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