265 research outputs found
Cold Nuclear Matter In Holographic QCD
We study the Sakai-Sugimoto model of holographic QCD at zero temperature and
finite chemical potential. We find that as the baryon chemical potential is
increased above a critical value, there is a phase transition to a nuclear
matter phase characterized by a condensate of instantons on the probe D-branes
in the string theory dual. As a result of electrostatic interactions between
the instantons, this condensate expands towards the UV when the chemical
potential is increased, giving a holographic version of the expansion of the
Fermi surface. We argue based on properties of instantons that the nuclear
matter phase is necessarily inhomogeneous to arbitrarily high density. This
suggests an explanation of the "chiral density wave" instability of the quark
Fermi surface in large N_c QCD at asymptotically large chemical potential. We
study properties of the nuclear matter phase as a function of chemical
potential beyond the transition and argue in particular that the model can be
used to make a semi-quantitative prediction of the binding energy per nucleon
for nuclear matter in ordinary QCD.Comment: 31 pages, LaTeX, 1 figure, v2: some formulae corrected, qualitative
results unchange
Interference effects in interacting quantum dots
In this paper we study the interplay between interference effects in quantum
dots (manifested through the appearance of Fano resonances in the conductance),
and interactions taken into account in the self-consistent Hartree-Fock
approximation. In the non-interacting case we find that interference may lead
to the observation of more than one conductance peak per dot level as a
function of an applied gate voltage. This may explain recent experimental
findings, which were thought to be caused by interaction effects. For the
interacting case we find a wide variety of different interesting phenomena.
These include both monotonous and non-monotonous filling of the dot levels as a
function of an applied gate voltage, which may occur continuously or even
discontinuously. In many cases a combination of the different effects can occur
in the same sample. The behavior of the population influences, in turn, the
conductance lineshape, causing broadening and asymmetry of narrow peaks, and
determining whether there will be a zero transmission point. We elucidate the
essential role of the interference between the dot levels in determining these
outcomes. The effects of finite temperatures on the results are also examined.Comment: 11 pages, 9 fugures, REVTeX
Critical behavior of a one-dimensional monomer-dimer reaction model with lateral interactions
A monomer-dimer reaction lattice model with lateral repulsion among the same
species is studied using a mean-field analysis and Monte Carlo simulations. For
weak repulsions, the model exhibits a first-order irreversible phase transition
between two absorbing states saturated by each different species. Increasing
the repulsion, a reactive stationary state appears in addition to the saturated
states. The irreversible phase transitions from the reactive phase to any of
the saturated states are continuous and belong to the directed percolation
universality class. However, a different critical behavior is found at the
point where the directed percolation phase boundaries meet. The values of the
critical exponents calculated at the bicritical point are in good agreement
with the exponents corresponding to the parity-conserving universality class.
Since the adsorption-reaction processes does not lead to a non-trivial local
parity-conserving dynamics, this result confirms that the twofold symmetry
between absorbing states plays a relevant role in determining the universality
class. The value of the exponent , which characterizes the
fluctuations of an interface at the bicritical point, supports the
Bassler-Brown's conjecture which states that this is a new exponent in the
parity-conserving universality class.Comment: 19 pages, 22 figures, to be published in Phys. Rev
Analytic representations based on SU(1,1) coherent states and their applications
We consider two analytic representations of the SU(1,1) Lie group: the
representation in the unit disk based on the SU(1,1) Perelomov coherent states
and the Barut-Girardello representation based on the eigenstates of the SU(1,1)
lowering generator. We show that these representations are related through a
Laplace transform. A ``weak'' resolution of the identity in terms of the
Perelomov SU(1,1) coherent states is presented which is valid even when the
Bargmann index is smaller than one half. Various applications of these
results in the context of the two-photon realization of SU(1,1) in quantum
optics are also discussed.Comment: LaTeX, 15 pages, no figures, to appear in J. Phys. A. More
information on http://www.technion.ac.il/~brif/science.htm
Renormalization Group Functions of the \phi^4 Theory in the Strong Coupling Limit: Analytical Results
The previous attempts of reconstructing the Gell-Mann-Low function \beta(g)
of the \phi^4 theory by summing perturbation series give the asymptotic
behavior \beta(g) = \beta_\infty g^\alpha in the limit g\to \infty, where
\alpha \approx 1 for the space dimensions d = 2,3,4. It can be hypothesized
that the asymptotic behavior is \beta(g) ~ g for all values of d. The
consideration of the zero-dimensional case supports this hypothesis and reveals
the mechanism of its appearance: it is associated with a zero of one of the
functional integrals. The generalization of the analysis confirms the
asymptotic behavior \beta(g)=\beta_\infty g in the general d-dimensional case.
The asymptotic behavior of other renormalization group functions is constant.
The connection with the zero-charge problem and triviality of the \phi^4 theory
is discussed.Comment: PDF, 17 page
SEPT9 occupies the terminal positions in septin octamers and mediates polymerization-dependent functions in abscission
Mammalian SEPT9 is positioned at the end of septin octamers and is necessary for octamer assembly into polymers necessary for abscission during cytokinesis
The effect of radio-adaptive doses on HT29 and GM637 cells
<p>Abstract</p> <p>Background</p> <p>The shape of the dose-response curve at low doses differs from the linear quadratic model. The effect of a radio-adaptive response is the centre of many studies and well known inspite that the clinical applications are still rarely considered.</p> <p>Methods</p> <p>We studied the effect of a low-dose pre-irradiation (0.03 Gy – 0.1 Gy) alone or followed by a 2.0 Gy challenging dose 4 h later on the survival of the HT29 cell line (human colorectal cancer cells) and on the GM637 cell line (human fibroblasts).</p> <p>Results</p> <p>0.03 Gy given alone did not have a significant effect on both cell lines, the other low doses alone significantly reduced the cell survival. Applied 4 h before the 2.0 Gy fraction, 0.03 Gy led to a significant induced radioresistance in GM637 cells, but not in HT29 cells, and 0.05 Gy led to a significant hyperradiosensitivity in HT29 cells, but not in GM637 cells.</p> <p>Conclusion</p> <p>A pre-irradiation with 0.03 Gy can protect normal fibroblasts, but not colorectal cancer cells, from damage induced by an irradiation of 2.0 Gy and the application of 0.05 Gy prior to the 2.0 Gy fraction can enhance the cell killing of colorectal cancer cells while not additionally damaging normal fibroblasts. If these findings prove to be true in vivo as well this may optimize the balance between local tumour control and injury to normal tissue in modern radiotherapy.</p
Young Aphids Avoid Erroneous Dropping when Evading Mammalian Herbivores by Combining Input from Two Sensory Modalities
Mammalian herbivores may incidentally ingest plant-dwelling insects while foraging. Adult pea aphids (Acyrthosiphon pisum) avoid this danger by dropping off their host plant after sensing the herbivore's warm and humid breath and the vibrations it causes while feeding. Aphid nymphs may also drop (to escape insect enemies), but because of their slow movement, have a lower chance of finding a new plant. We compared dropping rates of first-instar nymphs with those of adults, after exposing pea aphids to different combinations of simulated mammalian breath and vibrations. We hypothesized that nymphs would compensate for the greater risk they face on the ground by interpreting more conservatively the mammalian herbivore cues they perceive. Most adults dropped in response to breath alone, but nymphs rarely did so. Breath stimulus accompanied by one concurrent vibrational stimulus, caused a minor rise in adult dropping rates. Adding a second vibration during breath had no additional effect on adults. The nymphs, however, relied on a combination of the two types of stimuli, with a threefold increase in dropping rates when the breath was accompanied by one vibration, and a further doubling of dropping rates when the second vibration was added. The age-specificity of the aphids' herbivore detection mechanism is probably an adaptation to the different cost of dropping for the different age groups. Relying on a combination of stimuli from two sensory modalities enables the vulnerable nymphs to avoid costly mistakes. Our findings emphasize the importance of the direct trophic effect of mammalian herbivory for plant-dwelling insects
Systematic identification of abundant A-to-I editing sites in the human transcriptome
RNA editing by members of the double-stranded RNA-specific ADAR family leads
to site-specific conversion of adenosine to inosine (A-to-I) in precursor
messenger RNAs. Editing by ADARs is believed to occur in all metazoa, and is
essential for mammalian development. Currently, only a limited number of human
ADAR substrates are known, while indirect evidence suggests a substantial
fraction of all pre-mRNAs being affected. Here we describe a computational
search for ADAR editing sites in the human transcriptome, using millions of
available expressed sequences. 12,723 A-to-I editing sites were mapped in 1,637
different genes, with an estimated accuracy of 95%, raising the number of known
editing sites by two orders of magnitude. We experimentally validated our
method by verifying the occurrence of editing in 26 novel substrates. A-to-I
editing in humans primarily occurs in non-coding regions of the RNA, typically
in Alu repeats. Analysis of the large set of editing sites indicates the role
of editing in controlling dsRNA stability.Comment: Pre-print version. See http://dx.doi.org/10.1038/nbt996 for a reprin
Chlamydia pneumoniae Infection Induced Allergic Airway Sensitization Is Controlled by Regulatory T-Cells and Plasmacytoid Dendritic Cells
Chlamydia pneumoniae (CP) is associated with induction and exacerbation of asthma. CP infection can induce allergic airway sensitization in mice in a dose- and time-dependent manner. Allergen exposure 5 days after a low dose (mild-moderate), but not a high dose (severe) CP infection induces antigen sensitization in mice. Innate immune signals play a critical role in controlling CP infection induced allergic airway sensitization, however these mechanisms have not been fully elucidated. Wild-type, TLR2−/−, and TLR4−/− mice were infected intranasally (i.n.) with a low dose of CP, followed by i.n. exposure to human serum albumin (HSA) and challenged with HSA 2 weeks later. Airway inflammation, immunoglobulins, eosinophils, and goblet cells were measured. Low dose CP infection induced allergic sensitization in TLR2−/− mice, but not in TLR4−/− mice, due to differential Treg responses in these genotypes. TLR2−/− mice had reduced numbers of Tregs in the lung during CP infection while TLR4−/− mice had increased numbers. High dose CP infection resulted in an increase in Tregs and pDCs in lungs, which prevented antigen sensitization in WT mice. Depletion of Tregs or pDCs resulted in allergic airway sensitization. We conclude that Tregs and pDCs are critical determinants regulating CP infection-induced allergic sensitization. Furthermore, TLR2 and TLR4 signaling during CP infection may play a regulatory role through the modulation of Tregs
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