6,349 research outputs found
Pressure tuning of light-induced superconductivity in K3C60
Optical excitation at terahertz frequencies has emerged as an effective means
to manipulate complex solids dynamically. In the molecular solid K3C60,
coherent excitation of intramolecular vibrations was shown to transform the
high temperature metal into a non-equilibrium state with the optical
conductivity of a superconductor. Here we tune this effect with hydrostatic
pressure, and we find it to disappear around 0.3 GPa. Reduction with pressure
underscores the similarity with the equilibrium superconducting phase of K3C60,
in which a larger electronic bandwidth is detrimental for pairing. Crucially,
our observation excludes alternative interpretations based on a high-mobility
metallic phase. The pressure dependence also suggests that transient, incipient
superconductivity occurs far above the 150 K hypothesised previously, and
rather extends all the way to room temperature.Comment: 33 pages, 17 figures, 2 table
Pancreatic cancer-derived S-100A8 N-terminal peptide: a diabetes cause?
BACKGROUND:
Our aim was to identify the pancreatic cancer diabetogenic peptide.
METHODS:
Pancreatic tumor samples from patients with (n=15) or without (n=7) diabetes were compared with 6 non-neoplastic pancreas samples using SDS-PAGE.
RESULTS:
A band measuring approximately 1500 Da was detected in tumors from diabetics, but not in neoplastic samples from non-diabetics or samples from non-neoplastic subjects. Sequence analysis revealed a 14 amino acid peptide (1589.88 Da), corresponding to the N-terminal of the S100A8. At 50 nmol/L and 2 mmol/L, this peptide significantly reduced glucose consumption and lactate production by cultured C(2)C(12) myoblasts. The 14 amino acid peptide caused a lack of myotubular differentiation, the presence of polynucleated cells and caspase-3 activation.
CONCLUSIONS:
The 14 amino acid peptide from S100A8 impairs the catabolism of glucose by myoblasts in vitro and may cause hyperglycemia in vivo. Its identification in biological fluids might be helpful in diagnosing pancreatic cancer in patients with recent onset diabetes mellitus
Pancreatic cancer-associated diabetes mellitus: an open field for proteomic applications.
Background: Diabetes mellitus is associated with pancreatic cancer in more than 80% of the cases. Clinical, epidemiological, and experimental data indicate that pancreatic cancer causes diabetes mellitus by releasing soluble mediators which interfere with both beta-cell function and liver and muscle glucose metabolism. Methods: We analysed, by matrix-assisted laser desorption ionization time of flight (MALDI-TOF), a series of pancreatic cancer cell lines conditioned media, pancreatic cancer patients' peripheral and portal sera, comparing them with controls and chronic pancreatitis patients' sera. Results: MALDI-TOF analysis of pancreatic cancer cells conditioned media and patients' sera indicated a low molecular weight peptide to be the putative pancreatic cancer-associated diabetogenic factor. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of tumor samples from diabetic and non-diabetic patients revealed the presence of a 1500 Da peptide only in diabetic patients. The amino acid sequence of this peptide corresponded to the N-terminal of an S-100 calcium binding protein, which was therefore suggested to be the pancreatic cancer-associated diabetogenic factor. Conclusions: We identified a tumor-derived peptide of 14 amino acids sharing a 100% homology with an S-100 calcium binding protein, which is probably the pancreatic cancer-associated diabetogenic facto
Quantum Effects in Friedmann-Robertson-Walker Cosmologies
Electrodynamics for self-interacting scalar fields in spatially flat
Friedmann-Robertson-Walker space-times is studied. The corresponding one-loop
field equation for the expectation value of the complex scalar field in the
conformal vacuum is derived. For exponentially expanding universes, the
equations for the Bogoliubov coefficients describing the coupling of the scalar
field to gravity are solved numerically. They yield a non-local correction to
the Coleman-Weinberg effective potential which does not modify the pattern of
minima found in static de Sitter space. Such a correction contains a
dissipative term which, accounting for the decay of the classical configuration
in scalar field quanta, may be relevant for the reheating stage. The physical
meaning of the non-local term in the semiclassical field equation is
investigated by evaluating this contribution for various background field
configurations.Comment: 17 pages, plain TeX + 5 uuencoded figure
Fermat hypersurfaces and Subcanonical curves
We extend the classical Enriques-Petri Theorem to -subcanonical
projectively normal curves, proving that such a curve is -gonal if and
only if it is contained in a surface of minimal degree. Moreover, we show that
any Fermat hypersurface of degree is apolar to an -subcanonical
-gonal projectively normal curve, and vice versa.Comment: 18 pages; AMS-LaTe
Gamma-ray polarization constraints on Planck scale violations of special relativity
Using recent polarimetric observations of the Crab Nebula in the hard X-ray
band by INTEGRAL, we show that the absence of vacuum birefringence effects
constrains O(E/M) Lorentz violation in QED to the level |\xi| < 9x10^{-10} at
three sigma CL, tightening by more than three orders of magnitude previous
constraints. We show that planned X-ray polarimeters have the potential the
potential to probe |\xi|~ 10^{-16} by detecting polarization in active galaxies
at red-shift ~1.Comment: 4 pages, 3 figure
O(d,d)-invariance in inhomogeneous string cosmologies with perfect fluid
In the first part of the present paper, we show that O(d,d)-invariance
usually known in a homogeneous cosmological background written in terms of
proper time can be extended to backgrounds depending on one or several
coordinates (which may be any space-like or time-like coordinate(s)). In all
cases, the presence of a perfect fluid is taken into account and the equivalent
duality transformation in Einstein frame is explicitly given. In the second
part, we present several concrete applications to some four-dimensional
metrics, including inhomogeneous ones, which illustrate the different duality
transformations discussed in the first part. Note that most of the dual
solutions given here do not seem to be known in the literature.Comment: 25 pages, no figures, Latex. Accepted for publication in General
Relativity and Gravitatio
Qualitative Properties of the Dirac Equation in a Central Potential
The Dirac equation for a massive spin-1/2 field in a central potential V in
three dimensions is studied without fixing a priori the functional form of V.
The second-order equations for the radial parts of the spinor wave function are
shown to involve a squared Dirac operator for the free case, whose essential
self-adjointness is proved by using the Weyl limit point-limit circle
criterion, and a `perturbation' resulting from the potential. One then finds
that a potential of Coulomb type in the Dirac equation leads to a potential
term in the above second-order equations which is not even infinitesimally
form-bounded with respect to the free operator. Moreover, the conditions
ensuring essential self-adjointness of the second-order operators in the
interacting case are changed with respect to the free case, i.e. they are
expressed by a majorization involving the parameter in the Coulomb potential
and the angular momentum quantum number. The same methods are applied to the
analysis of coupled eigenvalue equations when the anomalous magnetic moment of
the electron is not neglected.Comment: 22 pages, plain Tex. In the final version, a section has been added,
and the presentation has been improve
Polyhedra in loop quantum gravity
Interwiners are the building blocks of spin-network states. The space of
intertwiners is the quantization of a classical symplectic manifold introduced
by Kapovich and Millson. Here we show that a theorem by Minkowski allows us to
interpret generic configurations in this space as bounded convex polyhedra in
Euclidean space: a polyhedron is uniquely described by the areas and normals to
its faces. We provide a reconstruction of the geometry of the polyhedron: we
give formulas for the edge lengths, the volume and the adjacency of its faces.
At the quantum level, this correspondence allows us to identify an intertwiner
with the state of a quantum polyhedron, thus generalizing the notion of quantum
tetrahedron familiar in the loop quantum gravity literature. Moreover, coherent
intertwiners result to be peaked on the classical geometry of polyhedra. We
discuss the relevance of this result for loop quantum gravity. In particular,
coherent spin-network states with nodes of arbitrary valence represent a
collection of semiclassical polyhedra. Furthermore, we introduce an operator
that measures the volume of a quantum polyhedron and examine its relation with
the standard volume operator of loop quantum gravity. We also comment on the
semiclassical limit of spinfoams with non-simplicial graphs.Comment: 32 pages, many figures. v2 minor correction
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