3,598 research outputs found
Exact and Scaling Form of the Bipartite Fidelity of the Infinite XXZ Chain
We find an exact expression for the bipartite fidelity f=|'|^2,
where |vac> is the vacuum eigenstate of an infinite-size antiferromagnetic XXZ
chain and |vac>' is the vacuum eigenstate of an infinite-size XXZ chain which
is split in two. We consider the quantity -ln(f) which has been put forward as
a measure of quantum entanglement, and show that the large correlation length
xi behaviour is consistent with a general conjecture -ln(f) ~ c/8 ln(xi), where
c is the central charge of the UV conformal field theory (with c=1 for the XXZ
chain). This behaviour is a natural extension of the existing conformal field
theory prediction of -ln(f) ~ c/8 ln(L) for a length L bipartite system with
0<< L <<xi.Comment: 6 page
Bi-partite entanglement entropy in integrable models with backscattering
In this paper we generalise the main result of a recent work by J. L. Cardy
and the present authors concerning the bi-partite entanglement entropy between
a connected region and its complement. There the expression of the leading
order correction to saturation in the large distance regime was obtained for
integrable quantum field theories possessing diagonal scattering matrices. It
was observed to depend only on the mass spectrum of the model and not on the
specific structure of the diagonal scattering matrix. Here we extend that
result to integrable models with backscattering (i.e. with non-diagonal
scattering matrices). We use again the replica method, which connects the
entanglement entropy to partition functions on Riemann surfaces with two branch
points. Our main conclusion is that the mentioned infrared correction takes
exactly the same form for theories with and without backscattering. In order to
give further support to this result, we provide a detailed analysis in the
sine-Gordon model in the coupling regime in which no bound states (breathers)
occur. As a consequence, we obtain the leading correction to the sine-Gordon
partition function on a Riemann surface in the large distance regime.
Observations are made concerning the limit of large number of sheets.Comment: 22 pages, 2 figure
Interleukin-1 Receptor antagonist Production by Human Keratinocytes
Human keratinocytes produce biologically active pro–IL-Iα and inactive pro-IL-1β with most protein remaining intracellular. IL-1 receptor antagonist (IL-1ra) is a newly described member of the IL-1 family that is secreted by stimulated monocytes and binds competitively to IL-1 receptors without stimulating target cells. We examined the characteristics of IL-1ra production by cultured human keratinocytes. By ELISA, keratinocyte lysates contained 390 ng IL-1ra/mg total protein with little IL-1ra detected in supernatants. In contrast, monocytes produced 297 ng IL- 1ra/mg total protein during 24 h of culture on adherent IgG with about half of the IL-1ra detected in supernatants. By Western blot analysis, keratinocyte IL-1ra was ≈ 20 kD in size and was slightly larger than recombinant monocyte IL- 1ra. In contrast to monocytes, human keratinocyte IL-1ra was not secreted in 22- 25-kD molecular weight glycosylated forms. Affinity-purified keratinocyte IL-1ra exhibited identical biologic activity to recombinant monocyte IL-1ra, each inhibiting IL-1 -dependent augmentation of murint thymocyte proliferation to the same degree per amount protein. An IL-1ra mRNA of 1.8 kb was detected by Northern blot analysis in RNA extracted from keratinocytes. in order to determine the effect of differentiation on IL-1 and IL-1ra production, human keratinocytes were cultured for 72 h in low (0.03 mM), medium (0.15 mM), or high (1.0 mM) -calcium concentrations. The absolute amounts of IL-1ra increased twofold and the ratio of IL-1ra to IL-1ra in keratinocyte lysates increased from ≈ 12: 1 to 25: 1 during differentiation. These results indicate that keratinocytes constitutively produce large amounts of a biologically active intracellular variant of IL-1ra that increase with differentiation. IL-1ra released during keratinocyte damage may be important in modifying the inflammatory effects of IL-1α in human skin
The Radio Light Curve of the Gamma-Ray Nova in V407 Cyg: Thermal Emission from the Ionized Symbiotic Envelope, Devoured from Within by the Nova Blast
We present multi-frequency radio observations of the 2010 nova event in the
symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array
and spanning 1-45 GHz and 17-770 days following discovery. This nova---the
first ever detected in gamma rays---shows a radio light curve dominated by the
wind of the Mira giant companion, rather than the nova ejecta themselves. The
radio luminosity grew as the wind became increasingly ionized by the nova
outburst, and faded as the wind was violently heated from within by the nova
shock. This study marks the first time that this physical mechanism has been
shown to dominate the radio light curve of an astrophysical transient. We do
not observe a thermal signature from the nova ejecta or synchrotron emission
from the shock, due to the fact that these components were hidden behind the
absorbing screen of the Mira wind.
We estimate a mass loss rate for the Mira wind of Mdot_w ~ 10^-6 M_sun/yr. We
also present the only radio detection of V407 Cyg before the 2010 nova, gleaned
from unpublished 1993 archival VLA data, which shows that the radio luminosity
of the Mira wind varies by a factor of >~20 even in quiescence. Although V407
Cyg likely hosts a massive accreting white dwarf, making it a candidate
progenitor system for a Type Ia supernova, the dense and radially continuous
circumbinary material surrounding V407 Cyg is inconsistent with observational
constraints on the environments of most Type Ia supernovae.Comment: Resubmitted to ApJ after incorporating referee's comment
Radio studies of novae: a current status report and highlights of new results
Novae, which are the sudden visual brightening triggered by runaway
thermonuclear burning on the surface of an accreting white dwarf, are fairly
common and bright events. Despite their astronomical significance as nearby
laboratories for the study of nuclear burning and accretion phenomena, many
aspects of these common stellar explosions are observationally not
well-constrained and remain poorly understood. Radio observations, modeling and
interpretation can potentially play a crucial role in addressing some of these
puzzling issues. In this review on radio studies of novae, we focus on the
possibility of testing and improving the nova models with radio observations,
and present a current status report on the progress in both the observational
front and theoretical developments. We specifically address the issues of
accurate estimation of ejecta mass, multi-phase and complex ejection phenomena,
and the effect of a dense environment around novae. With highlights of new
observational results, we illustrate how radio observations can shed light on
some of these long-standing puzzles.Comment: 19 pages, 4 figures. Review article published in the Bulletin of the
Astronomical Society of India (BASI) special issue on nova
The Peculiar Multi-Wavelength Evolution Of V1535 Sco
We present multi-wavelength observations of the unusual nova V1535 Sco
throughout its outburst in 2015. Early radio observations were consistent with
synchrotron emission, and early X-ray observations revealed the presence of
high-energy (>1 keV) photons. These indicated that strong shocks were present
during the first ~2 weeks of the nova's evolution. The radio spectral energy
distribution was consistent with thermal emission from week 2 to week 6.
Starting in week 7, the radio emission again showed evidence of synchrotron
emission and there was an increase in X-ray emission, indicating a second shock
event. The optical spectra show evidence for at least two separate outflows,
with the faster outflow possibly having a bipolar morphology. The optical and
near infrared light curves and the X-ray measurements of the hydrogen column
density indicated that the companion star is likely a K giant.Comment: 20 pages, 13 figures, under review at ApJ, updated to match the most
recent version submitted to the refere
Metric trees of generalized roundness one
Every finite metric tree has generalized roundness strictly greater than one.
On the other hand, some countable metric trees have generalized roundness
precisely one. The purpose of this paper is to identify some large classes of
countable metric trees that have generalized roundness precisely one.
At the outset we consider spherically symmetric trees endowed with the usual
combinatorial metric (SSTs). Using a simple geometric argument we show how to
determine decent upper bounds on the generalized roundness of finite SSTs that
depend only on the downward degree sequence of the tree in question. By
considering limits it follows that if the downward degree sequence of a SST satisfies , then has generalized roundness one. Included among the
trees that satisfy this condition are all complete -ary trees of depth
(), all -regular trees () and inductive limits
of Cantor trees.
The remainder of the paper deals with two classes of countable metric trees
of generalized roundness one whose members are not, in general, spherically
symmetric. The first such class of trees are merely required to spread out at a
sufficient rate (with a restriction on the number of leaves) and the second
such class of trees resemble infinite combs.Comment: 14 pages, 2 figures, 2 table
OA02.02. Effect of MBSR and psychological state on inflammatory markers in HIV positive adults
Hippocampal neurons with stable excitatory connectivity become part of neuronal representations
Experiences are represented in the brain by patterns of neuronal activity. Ensembles of neurons representing experience undergo activity-dependent plasticity and are important for learning and recall. They are thus considered cellular engrams of memory. Yet, the cellular events that bias neurons to become part of a neuronal representation are largely unknown. In rodents, turnover of structural connectivity has been proposed to underlie the turnover of neuronal representations and also to be a cellular mechanism defining the time duration for which memories are stored in the hippocampus. If these hypotheses are true, structural dynamics of connectivity should be involved in the formation of neuronal representations and concurrently important for learning and recall. To tackle these questions, we used deep-brain 2-photon (2P) time-lapse imaging in transgenic mice in which neurons expressing the Immediate Early Gene (IEG) Arc (activity-regulated cytoskeleton-associated protein) could be permanently labeled during a specific time window. This enabled us to investigate the dynamics of excitatory synaptic connectivity-using dendritic spines as proxies-of hippocampal CA1 (cornu ammonis 1) pyramidal neurons (PNs) becoming part of neuronal representations exploiting Arc as an indicator of being part of neuronal representations. We discovered that neurons that will prospectively express Arc have slower turnover of synaptic connectivity, thus suggesting that synaptic stability prior to experience can bias neurons to become part of representations or possibly engrams. We also found a negative correlation between stability of structural synaptic connectivity and the ability to recall features of a hippocampal-dependent memory, which suggests that faster structural turnover in hippocampal CA1 might be functional for memory
Bi-partite entanglement entropy in massive (1+1)-dimensional quantum field theories
This paper is a review of the main results obtained in a series of papers involving the present authors and their collaborator J L Cardy over the last 2 years. In our work, we have developed and applied a new approach for the computation of the bi-partite entanglement entropy in massive (1+1)-dimensional quantum field theories. In most of our work we have also considered these theories to be integrable. Our approach combines two main ingredients: the 'replica trick' and form factors for integrable models and more generally for massive quantum field theory. Our basic idea for combining fruitfully these two ingredients is that of the branch-point twist field. By the replica trick, we obtained an alternative way of expressing the entanglement entropy as a function of the correlation functions of branch-point twist fields. On the other hand, a generalization of the form factor program has allowed us to study, and in integrable cases to obtain exact expressions for, form factors of such twist fields. By the usual decomposition of correlation functions in an infinite series involving form factors, we obtained exact results for the infrared behaviours of the bi-partite entanglement entropy, and studied both its infrared and ultraviolet behaviours for different kinds of models: with and without boundaries and backscattering, at and out of integrability
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