11,719 research outputs found
Role of subclinical gut inflammation in the pathogenesis of spondyloarthritis
Subclinical gut inflammation occurring in patients affected by spondyloarthritis (SpA) is correlated with the severity of spine inflammation. Several evidences indicate that dysbiosis occurs in SpA, and that may modulate intestinal permeability and intestinal immune responses. The presence of intestinal dysbiosis is accompanied in SpA patients with the presence of zonulin-dependent alterations of gut-epithelial and gut-vascular barriers. The leakage of epithelial and endothelial surface layers is followed by the translocation of bacterial products, such as lipopolysaccharide and intestinal fatty acid binding protein, in the systemic circulation. These bacterial products may downregulate the expression of CD14 on circulating monocytes leading to an "anergic" phenotype. In the gut, IL-23 may induce the expansion of innate immune cells such as mucosal-associated invariant T cells, γΎ T cells, and innate lymphoid cells of group 3 that through the interaction with MAdCAM1 may recirculate form the gut to the sites of SpA active inflammation. On the basis of these findings, gut inflammation observed in SpA patient seems to be not only an epiphenomenon of the on going systemic inflammatory process but may also represent the base camp in which inflammatory cells are activated and from whom they shuttle
Histopathology of the gut in rheumatic diseases
The gastrointestinal tract regulates the trafficking of macromolecules between the environment and the host through an epithelial barrier mechanism and is an important part of the immune system controlling the equilibrium between tolerance and immunity to non-self-antigens. Various evidence indicates that intestinal inflammation occurs in patients with rheumatic diseases. In many rheumatic diseases intestinal inflammation appears to be linked to dysbiosis and possibly represents the common denominator in the pathogenesis of different rheumatic diseases. The continuative interaction between dysbiosis and the intestinal immune system may lead to the aberrant activation of immune cells that can re-circulate from the gut to the sites of extraintestinal inflammation as observed in patients with ankylosing spondylitis. The exact contribution of genetic factors in the development of intestinal inflammation in rheumatic diseases needs to be clarified
Transport properties in correlated systems: An analytical model
Several studies have so far investigated transport properties of strongly
correlated systems. Interesting features of these materials are the lack of
resistivity saturation well beyond the Mott-Ioffe-Regel limit and the scaling
of the resistivity with the hole density in underdoped cuprates. Due to the
strongly correlated nature of these materials, mainly numerical techniques have
been employed. A key role in this regards is thought to be played by the
continuous transfer of spectral weight from coherent to incoherent states. In
this paper we employ a simple analytical expression for the electronic Green's
function to evaluate both quasi-particle and transport properties in correlated
systems. Our analytical approach permits to enlighten the specific role of the
spectral transfer due to the correlation on different features. In particular
we investigate the dependence of both quasi-particle and transport scattering
rate on the correlation degree and the criterion for resistivity saturation.
systems.Comment: 11 pages, 8 figures. New version correcting a mistake of the previous
version and added figure
Bosonic Seesaw in the Unparticle Physics
Recently, conceptually new physics beyond the Standard Model has been
proposed by Georgi, where a new physics sector becomes conformal and provides
"unparticle" which couples to the Standard Model sector through higher
dimensional operators in low energy effective theory. Among several
possibilities, we focus on operators involving the (scalar) unparticle, Higgs
and the gauge bosons. Once the Higgs develops the vacuum expectation value
(VEV), the conformal symmetry is broken and as a result, the mixing between the
unparticle and the Higgs boson emerges. In this paper, we consider a natural
realization of bosonic seesaw in the context of unparticle physics. In this
framework, the negative mass squared or the electroweak symmetry breaking
vacuum is achieved as a result of mass matrix diagonalization. In the
diagonalization process, it is important to have zero value in the
(1,1)-element of the mass matrix. In fact, the conformal invariance in the
hidden sector can actually assure the zero of that element. So, the bosonic
seesaw mechanism for the electroweak symmetry breaking can naturally be
understood in the framework of unparticle physics.Comment: 5 pages, no figure; added one more referenc
Ammonia observations in the LBV nebula G79.29+0.46. Discovery of a cold ring and some warm spots
The surroundings of Luminous Blue Variable (LBV) stars are excellent
laboratories to study the effects of their high UV radiation, powerful winds,
and strong ejection events onto the surrounding gas and dust. The LBV
G79.29+0.46 powered two concentric infrared rings which may interact with the
infrared dark cloud (IRDC) G79.3+0.3. The Effelsberg 100m telescope was used to
observe the NH_3 (1,1), (2,2) emission surrounding G79.29+0.46 and the IRDC. In
addition, we observed particular positions in the (3,3) transition toward the
strongest region of the IRDC. We report here the first coherent shell-like
structure of dense NH_3 gas associated with an evolved massive star. The shell,
two or three orders of magnitude more tenuous than the IRDC, is well traced in
both ammonia lines, and surrounds the ionized nebula. The NH_3 emission in the
IRDC is characterized by a low and uniform rotational temperature (T_rot ~ 10
K) and moderately high opacities in the (1,1) line. The rest of the observed
field is spotted by warm or hot zones (T_rot > 30 K) and characterized by
optically thin emission of the (1,1) line. The NH_3 abundances are about
10^{-8} in the IRDC, and 10^{-10}-10^{-9} elsewhere. The warm temperatures and
low abundances of NH_3 in the shell suggest that the gas is being heated and
photo-dissociated by the intense UV field of the LBV star. An outstanding
region is found to the south-west (SW) of the LBV star within the IRDC. The
NH_3 (3,3) emission at the centre of the SW region reveals two velocity
components tracing gas at temperatures > 30K. The northern edge of the SW
region agrees with the border of the ring nebula and a region of continuum
enhancement; here, the opacity of the (1,1) line and the NH_3 abundance do not
decrease as expected in a typical clump of an isolated cold dark cloud. This
strongly suggests some kind of interaction between the ring nebula and the
IRDC.Comment: 15 pages, 13 figures, accepted by A&A. Note the change of title with
respect to previous versio
Chaos in temperature in the Sherrington-Kirkpatrick model
We prove the existence of chaos in temperature in the
Sherringhton-Kirkpatrick model. The effect is exceedingly small, namely of the
ninth order in perturbation theory. The equations describing two systems at
different temperatures constrained to have a fixed overlap are studied
analytically and numerically, yielding information about the behaviour of the
overlap distribution function in finite-size systems.Comment: REVTEX, 6 pages, 2 figure
Unique Identification of Lee-Wick Gauge Bosons at Linear Colliders
Grinstein, O'Connell and Wise have recently presented an extension of the
Standard Model (SM), based on the ideas of Lee and Wick (LW), which
demonstrates an interesting way to remove the quadratically divergent
contributions to the Higgs mass induced by radiative corrections. This model
predicts the existence of negative-norm copies of the usual SM fields at the
TeV scale with ghost-like propagators and negative decay widths, but with
otherwise SM-like couplings. In earlier work, it was demonstrated that the LW
states in the gauge boson sector of these models, though easy to observe,
cannot be uniquely identified as such at the LHC. In this paper, we address the
issue of whether or not this problem can be resolved at an collider
with a suitable center of mass energy range. We find that measurements of the
cross section and the left-right polarization asymmetry associated with Bhabha
scattering can lead to a unique identification of the neutral electroweak gauge
bosons of the Lee-Wick type.Comment: 16 pages, 6 figures; discussion and references adde
Single Production in Collisions at the NLC
Single production in collisions at the NLC can be used to
probe the Majorana nature of the heavy neutrinos present in the Left-Right
Symmetric Model below the kinematic threshold for their direct production. For
colliders in the TeV range, typical cross sections of order
are obtained, depending on the specific choice of model parameters.
Backgrounds arising from Standard Model processes are shown to be small. This
analysis greatly extends the kinematic range of previous studies wherein the
production of an on-shell, like-sign pair of 's at the NLC was considered.Comment: 13pp, 3 figures (available on request), LaTex, SLAC-PUB-647
A search for water maser emission toward obscured post-AGB star and planetary nebula candidates
Water maser emission at 22 GHz is a useful probe to study the transition
between the nearly spherical mass-loss in the AGB to a collimated one in the
post-AGB phase. In their turn, collimated jets in the post-AGB phase could
determine the shape of planetary nebulae (PNe) once photoionization starts. We
intend to find new cases of post-AGB stars and PNe with water maser emission,
including water fountains or water-maser-emitting PNe. We observed water maser
emission in a sample of 133 objects, with a significant fraction being post-AGB
and young PN candidate sources with strong obscuration. We detected this
emission in 15 of them, of which seven are reported here for the first time. We
identified three water fountain candidates: IRAS 17291-2147, with a total
velocity spread of ~96 km/s in its water maser components and two sources (IRAS
17021-3109 and IRAS 17348-2906) that show water maser emission outside the
velocity range covered by OH masers. We have also identified IRAS 17393-2727 as
a possible new water-maser-emitting PN. The detection rate is higher in
obscured objects (14%) than in those with optical counterparts (7%), consistent
with previous results. Water maser emission seems to be common in objects that
are bipolar in the near-IR (43% detection rate). The water maser spectra of
water fountain candidates like IRAS 17291-2147 show significantly less maser
components than others (e.g., IRAS 18113-2503). We speculate that most
post-AGBs may show water maser emission with wide enough velocity spread (> 100
km/s) when observed with enough sensitivity and/or for long enough periods of
time. Therefore, it may be necessary to single out a special group of "water
fountains", probably defined by their high maser luminosities. We also suggest
that the presence of both water and OH masers in a PN is a better tracer of its
youth, rather than the presence of just one of these species.Comment: To be published in Astronomy & Astrophysics. 16 pages, 1 figure
(spanning 5 pages). This version includes some minor language corrections and
fixes some errors in Table
No light shining through a wall : new results from a photoregeneration experiment
Recently, axion-like particle search has received renewed interest. In
particular, several groups have started ``light shining through a wall''
experiments based on magnetic field and laser both continuous, which is very
demanding in terms of detector background. We present here the 2 limits
obtained so far with our novel set-up consisting of a pulsed magnetic field and
a pulsed laser. In particular, we have found that the axion-like particle two
photons inverse coupling constant is GeV provided that the
particle mass 1 meV. Our results definitively invalidate
the axion interpretation of the original PVLAS optical measurements with a
confidence level greater than 99.9%.Comment: Version that will appear in Physical Review Letters, Vol. 99, n. 18,
(2 Nov 2007
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