540 research outputs found
Structure, Stresses and Local Dynamics in Glasses
The interrelations between short range structural and elastic aspects in
glasses and glass forming liquids pose important and yet unresolved questions.
In this paper these relations are analyzed for mono-atomic glasses and stressed
liquids with a short range repulsive-attractive pair potentials. Strong
variations of the local pressure are found even in a zero temperature glass,
whereas the largest values of pressure are the same in both glasses and
liquids. The coordination number z(J) and the effective first peak radius
depend on the local pressures J's. A linear relation was found between
components of site stress tensor and the local elastic constants. A linear
relation was also found between the trace of the squares of the local
frequencies and the local pressures. Those relations hold for glasses at zero
temperature and for liquids. We explain this by a relation between the
structure and the potential terms. A structural similarity between liquids and
solids is manifested by similar dependencies of the coordination number on the
pressures.Comment: 7 pages, 11 figure
The Inverse Scattering Method, Lie-Backlund Transformations and Solitons for Low-energy Effective Field Equations of 5D String Theory
In the framework of the 5D low-energy effective field theory of the heterotic
string with no vector fields excited, we combine two non-linear methods in
order to construct a solitonic field configuration. We first apply the inverse
scattering method on a trivial vacuum solution and obtain an stationary
axisymmetric two-soliton configuration consisting of a massless gravitational
field coupled to a non-trivial chargeless dilaton and to an axion field endowed
with charge. The implementation of this method was done following a scheme
previously proposed by Yurova. We also show that within this scheme, is not
possible to get massive gravitational solitons at all. We then apply a
non-linear Lie-Backlund matrix transformation of Ehlers type on this massless
solution and get a massive rotating axisymmetric gravitational soliton coupled
to axion and dilaton fields endowed with charges. We study as well some
physical properties of the constructed massless and massive solitons and
discuss on the effect of the generalized solution generating technique on the
seed solution and its further generalizations.Comment: 17 pages in latex, changed title, improved text, added reference
BRAF mutation-specific promoter methylation of FOX genes in colorectal cancer
Background: Cancer-specific hypermethylation of (promoter) CpG islands is common during the tumorigenesis of colon cancer. Although associations between certain genetic aberrations, such as BRAF mutation and microsatellite instability, and the CpG island methylator phenotype (CIMP), have been found, the mechanisms by which these associations are established are still unclear. We studied genome-wide DNA methylation differences between
On Synchronization in a Lattice Model of Pulse-Coupled Oscillators
We analyze the collective behavior of a lattice model of pulse-coupled
oscillators. By means of computer simulations we find the relation between the
intrinsic dynamics of each member of the population and their mutual
interaction that ensures, in a general context, the existence of a fully
synchronized regime. This condition turns out to be the same than the obtained
for the globally coupled population. When the condition is not completely
satisfied we find different spatial structures. This also gives some hints
about self-organized criticality.Comment: 4 pages, RevTex, 1 PostScript available upon request, To appear in
Phys. Rev. Let
Superconducting thin rings with finite penetration depth
Recently Babaei Brojeny and Clem [Phys. Rev. B 68, 174514 (2003)] considered
superconducting thin-film rings in perpendicular magnetic fields in the ideal
Meissner state with negligibly small magnetic penetration depth and presented
useful analytical limiting expressions and numerical results for the
magnetic-field and sheet-current profiles, trapped magnetic flux,
self-inductance, magnetic moment, and focusing of magnetic flux into the hole
when no net current flows in the ring. The present paper generalizes all these
results to rings with arbitrary values of the two-dimensional effective
penetration depth \Lambda = \lambda^2 /d (\lambda is the London depth and d <
\lambda/2 the film thickness) using a straightforward matrix inversion method.
We also present results for the energy of a superconducting ring as a function
of the applied magnetic induction B_a and the quantum number N defining the
size of the fluxoid N \phi_0 trapped in the hole.Comment: with 19 figures, gives 11.5 page
Role of the rdxA and frxA genes in oxygen-dependent metronidazole resistance of Helicobacter pylori
Almost 50 % of all Helicobacter pylori isolates are resistant to
metronidazole, which reduces the efficacy of metronidazole-containing
regimens, but does not make them completely ineffective. This discrepancy
between in vitro metronidazole resistance and treatment outcome may
partially be explained by changes in oxygen pressure in the gastric
environment, as metronidazole-resistant (MtzR) H. pylori isolates become
metronidazole-susceptible (MtzS) under low oxygen conditions in vitro. In
H. pylori the rdxA and frxA genes encode reductases which are required for
the activation of metronidazole, and inactivation of these genes results
in metronidazole resistance. Here the role of inactivating mutations in
these genes on the reversibility of metronidazole resistance under low
oxygen conditions is established. Clinical H. pylori isolates containing
mutations resulting in a truncated RdxA and/or FrxA protein were selected
and incubated under anaerobic conditions, and the effect of these
conditions on the MICs of metronidazole, amoxycillin, clarithromycin and
tetracycline, and cell viability were determined. While anaerobiosis had
no effect on amoxycillin, clarithromycin and tetracycline resistance, all
isolates lost their metronidazole resistance when cultured under anaerobic
conditions. This loss of metronidazole resistance also occurred in the
presence of the protein synthesis inhibitor chloramphenicol. Thus,
factor(s) that activate metronidazole under low oxygen tension are not
specifically induced by low oxygen conditions, but are already present
under microaerophilic conditions. As there were no significant differences
in cell viability between the clinical isolates, it is likely that neither
the rdxA nor the frxA gene participates in the reversibility of
metronidazole resistance
Properties of the Ideal Ginzburg-Landau Vortex Lattice
The magnetization curves M(H) for ideal type-II superconductors and the
maximum, minimum, and saddle point magnetic fields of the vortex lattice are
calculated from Ginzburg-Landau theory for the entire ranges of applied
magnetic fields Hc1 <= H < Hc2 or inductions 0 <= B < Hc2 and Ginzburg-Landau
parameters sqrt(1/2) <= kappa <= 1000. Results for the triangular and square
flux-line lattices are compared with the results of the circular cell
approximation. The exact magnetic field B(x,y) and magnetization M(H, kappa)
are compared with often used approximate expressions, some of which deviate
considerably or have limited validity. Useful limiting expressions and
analytical interpolation formulas are presented.Comment: 11 pages, 8 figure
3D heterotic string theory: new approach and extremal solutions
We develop a new formalism for the bosonic sector of low-energy heterotic
string theory toroidally compactified to three dimensions. This formalism is
based on the use of some single non-quadratic real matrix potential which
transforms linearly under the action of subgroup of the three-dimensional
charging symmetries. We formulate a new charging symmetry invariant approach
for the symmetry generation and straightforward construction of asymptotically
flat solutions. Finally, using the developed approach and the established
formal analogy between the heterotic and Einstein-Maxwell theories, we
construct a general class of the heterotic string theory extremal solutions of
the Israel-Wilson-Perjes type. This class is asymptotically flat and charging
symmetry complete; it includes the extremal solutions constructed before and
possesses the non-trivial bosonic string theory limit.Comment: 20 pages in Late
Cortical iron accumulation in MAPT- and C9orf 72-associated frontotemporal lobar degeneration
Neuroinflammation has been implicated in frontotemporal lobar degeneration (FTLD) pathophysiology, including in genetic forms with microtubule-associated protein tau (MAPT) mutations (FTLD-MAPT) or chromosome 9 open reading frame 72 (C9orf72) repeat expansions (FTLD-C9orf72). Iron accumulation as a marker of neuroinflammation has, however, been understudied in genetic FTLD to date. To investigate the occurrence of cortical iron accumulation in FTLD-MAPT and FTLD-C9orf72, iron histopathology was performed on the frontal and temporal cortex of 22 cases (11 FTLD-MAPT and 11 FTLD-C9orf72). We studied patterns of cortical iron accumulation and its colocalization with the corresponding underlying pathologies (tau and TDP-43), brain cells (microglia and astrocytes), and myelination. Further, with ultrahigh field ex vivo MRI on a subset (four FTLD-MAPT and two FTLD-C9orf72), we examined the sensitivity of T2*-weighted MRI for iron in FTLD. Histopathology showed that cortical iron accumulation occurs in both FTLD-MAPT and FTLD-C9orf72 in frontal and temporal cortices, characterized by a diffuse mid-cortical iron-rich band, and by a superficial cortical iron band in some cases. Cortical iron accumulation was associated with the severity of proteinopathy (tau or TDP-43) and neuronal degeneration, in part with clinical severity, and with the presence of activated microglia, reactive astrocytes and myelin loss. Ultra-high field T2*-weighted MRI showed a good correspondence between hypointense changes on MRI and cortical iron observed on histology. We conclude that iron accumulation is a feature of both FTLD-MAPT and FTLD-C9orf72 and is associated with pathological severity. Therefore, in vivo iron imaging using T2*-weighted MRI or quantitative susceptibility mapping may potentially be used as a noninvasive imaging marker to localize pathology in FTLD.</p
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