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Integrin α2ÎČ1 in nonactivated conformation can induce focal adhesion kinase signaling.
Conformational activation of integrins is generally required for ligand binding and cellular signalling. However, we have previously reported that the nonactivated conformation of α2ÎČ1 integrin can also bind to large ligands, such as human echovirus 1. In this study, we show that the interaction between the nonactivated integrin and a ligand resulted in the activation of focal adhesion kinase (FAK) in a protein kinase C dependent manner. A loss-of-function mutation, α2E336A, in the α2-integrin did not prevent the activation of FAK, nor did EDTA-mediated inactivation of the integrin. Full FAK activation was observed, since phosphorylation was not only confirmed in residue Y397, but also in residues Y576/7. Furthermore, initiation of downstream signaling by paxillin phosphorylation in residue Y118 was evident, even though this activation was transient by nature, probably due to the lack of talin involvement in FAK activation and the absence of vinculin in the adhesion complexes formed by the nonactivated integrins. Altogether these results indicate that the nonactivated integrins can induce cellular signaling, but the outcome of the signaling differs from conventional integrin signaling
Supergravity origin of the MSSM inflation
We consider the supergravity origin of the recently proposed MSSM
inflationary model, which relies on the existence of a saddle point along a
dimension six flat direction. We derive the conditions that the Kahler
potential has to satisfy for the saddle point to exist irrespective of the
hidden sector vevs. We show that these conditions are satisfied by a simple
class of Kahler potentials, which we find to have a similar form as in various
string theory compactifications. For these potentials, slow roll MSSM inflation
requires no fine tuning of the soft supersymmetry breaking parameters.Comment: v3: 10 pages, no figures; version accepted for publication. Typos
correcte
Non-Gaussianity from Instant and Tachyonic Preheating
We study non-Gaussianity in two distinct models of preheating: instant and
tachyonic. In instant preheating non-Gaussianity is sourced by the local terms
generated through the coupled perturbations of the two scalar fields. We find
that the non-Gaussianity parameter is given by ,
where is a coupling constant, so that instant preheating is unlikely to be
constrained by WMAP or Planck. In the case of tachyonic preheating
non-Gaussianity arises solely from the instability of the tachyon matter and is
found to be large. We find that for single field inflation the present WMAP
data implies a bound on the scale of tachyonic
instability. We argue that the tachyonic preheating limits are useful also for
string-motivated inflationary models.Comment: 12 pages, 1 figure, additional discussion, improved constraint on the
scale of tachyonic preheatin
Kahler potentials for the MSSM inflation and the spectral index
Recently it has been argued that some of the fine-tuning problems of the MSSM
inflation associated with the existence of a saddle point along a flat
direction may be solved naturally in a class of supergravity models. Here we
extend the analysis and show that the constraints on the Kahler potentials in
these models are considerably relaxed when the location of the saddle point is
treated as a free variable. We also examine the effect of supergravity
corrections on inflationary predictions and find that they can slightly alter
the value of the spectral index. As an example, for flat direction field values
we find while the
prediction of the MSSM inflation without any corrections is .Comment: 13 pages, one figure. Typos corrected and a reference adde
Dialogue based interfaces for universal access.
Conversation provides an excellent means of communication for almost all people. Consequently, a conversational interface is an excellent mechanism for allowing people to interact with systems. Conversational systems are an active research area, but a wide range of systems can be developed with current technology. More sophisticated interfaces can take considerable effort, but simple interfaces can be developed quite rapidly. This paper gives an introduction to the current state of the art of conversational systems and interfaces. It describes a methodology for developing conversational interfaces and gives an example of an interface for a state benefits web site. The paper discusses how this interface could improve access for a wide range of people, and how further development of this interface would allow a larger range of people to use the system and give them more functionality
Identifying the curvaton within MSSM
We consider inflaton couplings to MSSM flat directions and the thermalization
of the inflaton decay products, taking into account gauge symmetry breaking due
to flat direction condensates. We then search for a suitable curvaton candidate
among the flat directions, requiring an early thermally induced start for the
flat direction oscillations to facilitate the necessary curvaton energy density
dominance. We demonstrate that the supersymmetry breaking -term is crucial
for achieving a successful curvaton scenario. Among the many possible
candidates, we identify the flat direction as a viable MSSM
curvaton.Comment: 9 pages. Discussion on the evaporation of condensate added, final
version published in JCA
Precision mass measurements on neutron-rich rare-earth isotopes at JYFLTRAP - reduced neutron pairing and implications for the -process calculations
The rare-earth peak in the -process abundance pattern depends sensitively
on both the astrophysical conditions and subtle changes in nuclear structure in
the region. This work takes an important step elucidating the nuclear structure
and reducing the uncertainties in -process calculations via precise atomic
mass measurements at the JYFLTRAP double Penning trap. Nd, Pm,
Sm, and Gd have been measured for the first time and the
precisions for Nd, Pm, Eu, Gd, and
Tb have been improved considerably. Nuclear structure has been probed
via two-neutron separation energies and neutron pairing energy metrics
. The data do not support the existence of a subshell closure at .
Neutron pairing has been found to be weaker than predicted by theoretical mass
models. The impact on the calculated -process abundances has been studied.
Substantial changes resulting in a smoother abundance distribution and a better
agreement with the solar -process abundances are observed.Comment: 8 pages, 4 figures, accepted for publication in Physical Review
Letter
Supersymmetric Thermalization and Quasi-Thermal Universe: Consequences for Gravitinos and Leptogenesis
Motivated by our earlier paper \cite{am}, we discuss how the infamous
gravitino problem has a natural built in solution within supersymmetry.
Supersymmetry allows a large number of flat directions made up of {\it gauge
invariant} combinations of squarks and sleptons. Out of many at least {\it one}
generically obtains a large vacuum expectation value during inflation. Gauge
bosons and Gauginos then obtain large masses by virtue of the Higgs mechanism.
This makes the rate of thermalization after the end of inflation very small and
as a result the Universe enters a {\it quasi-thermal phase} after the inflaton
has completely decayed. A full thermal equilibrium is generically established
much later on when the flat direction expectation value has substantially
decareased. This results in low reheat temperatures, i.e., , which are compatible with the stringent bounds arising from the
big bang nucleosynthesis. There are two very important implications: the
production of gravitinos and generation of a baryonic asymmetry via
leptogenesis during the quasi-thermal phase. In both the cases the abundances
depend not only on an effective temperature of the quasi-thermal phase (which
could be higher, i.e., ), but also on the state of equilibrium
in the reheat plasma. We show that there is no ``thermal gravitino problem'' at
all within supersymmetry and we stress on a need of a new paradigm based on a
``quasi-thermal leptogenesis'', because in the bulk of the parameter space the
{\it old} thermal leptogenesis cannot account for the observed baryon
asymmetry.Comment: 53 pages. Final version published in JCA
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