11,864 research outputs found
Charged rotating noncommutative black holes
In this paper we complete the program of the noncomutative geometry inspired
black holes, providing the richest possible solution, endowed with mass, charge
and angular momentum. After providing a prescription for employing the
Newman-Janis algorithm in the case of nonvanishing stress tensors, we find
regular axisymmetric charged black holes in the presence of a minimal length.
We study also the new thermodynamics and we determine the corresponding
higher-dimensional solutions. As a conclusion we make some consideration about
possible applications.Comment: 13 pages, 3 figures, correction of a typesetting inattention, updated
reference list, version accepted for publication on Physical Review
Induced pluripotent stem cells, a giant leap for mankind therapeutic applications
Induced pluripotent stem cells (iPSC) technology has propelled the field of stem
cells biology, providing new cells to explore the molecular mechanisms of
pluripotency, cancer biology and aging. A major advantage of human iPSC,
compared to the pluripotent embryonic stem cells, is that they can be generated
from virtually any embryonic or adult somatic cell type without destruction of
human blastocysts. In addition, iPSC can be generated from somatic cells
harvested from normal individuals or patients, and used as a cellular tool to
unravel mechanisms of human development and to model diseases in a manner
not possible before. Besides these fundamental aspects of human biology and
physiology that are revealed using iPSC or iPSC-derived cells, these cells hold an
immense potential for cell-based therapies, and for the discovery of new or
personalized pharmacological treatments for many disorders. Here, we review
some of the current challenges and concerns about iPSC technology. We
introduce the potential held by iPSC for research and development of novel
health-related applications. We briefly present the efforts made by the scientific
and clinical communities to create the necessary guidelines and regulations to
achieve the highest quality standards in the procedures for iPSC generation,
characterization and long-term preservation. Finally, we present some of the
audacious and pioneer clinical trials in progress with iPSC-derived cells.info:eu-repo/semantics/publishedVersio
Spectral dimension of a quantum universe
In this paper, we calculate in a transparent way the spectral dimension of a
quantum spacetime, considering a diffusion process propagating on a fluctuating
manifold. To describe the erratic path of the diffusion, we implement a minimal
length by averaging the graininess of the quantum manifold in the flat space
case. As a result we obtain that, for large diffusion times, the quantum
spacetime behaves like a smooth differential manifold of discrete dimension. On
the other hand, for smaller diffusion times, the spacetime looks like a fractal
surface with a reduced effective dimension. For the specific case in which the
diffusion time has the size of the minimal length, the spacetime turns out to
have a spectral dimension equal to 2, suggesting a possible renormalizable
character of gravity in this regime. For smaller diffusion times, the spectral
dimension approaches zero, making any physical interpretation less reliable in
this extreme regime. We extend our result to the presence of a background field
and curvature. We show that in this case the spectral dimension has a more
complicated relation with the diffusion time, and conclusions about the
renormalizable character of gravity become less straightforward with respect to
what we found with the flat space analysis.Comment: 5 pages, 1 figure, references added, typos corrected, title changed,
final version published in Physical Review
Decoherence induced by a chaotic environment: A quantum walker with a complex coin
We study the differences between the process of decoherence induced by
chaotic and regular environments. For this we analyze a family of simple models
wich contain both regular and chaotic environments. In all cases the system of
interest is a "quantum walker", i.e. a quantum particle that can move on a
lattice with a finite number of sites. The walker interacts with an environment
wich has a D dimensional Hilbert space. The results we obtain suggest that
regular and chaotic environments are not distinguishable from each other in a
(short) timescale t*, wich scales with the dimensionality of the environment as
t*~log(D). Howeber, chaotic environments continue to be effective over
exponentially longer timescales while regular environments tend to reach
saturation much sooner. We present both numerical and analytical results
supporting this conclusion. The family of chaotic evolutions we consider
includes the so-called quantum multi-baker-map as a particular case.Comment: 7 pages, 8 figure
Long wavelength structural anomalies in jammed systems
The structural properties of static, jammed packings of monodisperse spheres
in the vicinity of the jamming transition are investigated using large-scale
computer simulations. At small wavenumber , we argue that the anomalous
behavior in the static structure factor, , is consequential of an
excess of low-frequency, collective excitations seen in the vibrational
spectrum. This anomalous feature becomes more pronounced closest to the jamming
transition, such that at the transition point. We introduce an
appropriate dispersion relation that accounts for these phenomena that leads us
to relate these structural features to characteristic length scales associated
with the low-frequency vibrational modes of these systems. When the particles
are frictional, this anomalous behavior is suppressed providing yet more
evidence that jamming transitions of frictional spheres lie at lower packing
fractions that that for frictionless spheres. These results suggest that the
mechanical properties of jammed and glassy media may therefore be inferred from
measurements of both the static and dynamical structure factors.Comment: 8 pages, 6 figure captions. Completely revised version to appear in
Phys. Rev.
Rheology and Contact Lifetime Distribution in Dense Granular Flows
We study the rheology and distribution of interparticle contact lifetimes for
gravity-driven, dense granular flows of non-cohesive particles down an inclined
plane using large-scale, three dimensional, granular dynamics simulations.
Rather than observing a large number of long-lived contacts as might be
expected for dense flows, brief binary collisions predominate. In the hard
particle limit, the rheology conforms to Bagnold scaling, where the shear
stress is quadratic in the strain rate. As the particles are made softer,
however, we find significant deviations from Bagnold rheology; the material
flows more like a viscous fluid. We attribute this change in the collective
rheology of the material to subtle changes in the contact lifetime distribution
involving the increasing lifetime and number of the long-lived contacts in the
softer particle systems.Comment: 4 page
invariant convex sets in polar representations
We study a compact invariant convex set E in a polar representation of a compact Lie group. Polar rapresentations are given by the adjoint action of K on p, where K is a maximal compact subgroup of a real semisimple Lie group G with Lie algebra g=k⊕p. If a⊂p is a maximal abelian subalgebra, then P=E∩a is a convex set in a. We prove that up to conjugacy the face structure of E is completely determined by that of P and that a face of E is exposed if and only if the corresponding face of P is exposed. We apply these results to the convex hull of the image of a restricted momentum map
Parametric Amplification in the Dynamic Radiation Force of Acoustic Waves in Fluids
We report on parametric amplification in dynamic radiation force produced by
a bichromatic acoustic beam in a fluid. To explain this effect we develop a
theory taking into account the nonlinearity of the fluid. The theory is
validated through an experiment to measure the dynamic radiation force on an
acrylic sphere. Results exhibit an amplification of 66 dB in water and 80 dB in
alcohol as the difference of the frequencies is increased from 10 Hz to 240
kHz
Signals of Warped Extra Dimensions at the LHC
We discuss the signatures of the spin-2 graviton excitations predicted by the
Randall-Sundrum model with one warped extra dimension, in dilepton and diphoton
production at LHC. By using a specific angular analysis, we assess the ranges
in mass and coupling constant where such gravitons can be discriminated against
competitor spin-1 and spin-0 objects, that potentially could manifest
themselves in these processes with the same mass and rate of events. Depending
on the value of the coupling constant to quarks and leptons, the numerical
results indicate graviton identification mass ranges up to 1.1-2.4 TeV and
1.6-3.2 TeV for LHC nominal energy of 14 TeV and time-integrated luminosity of
10 and 100~, respectively.Comment: 8 pages, Talk given at QCD@Work - International Workshop on QCD -
Theory and Experiment, 20 - 23 June, 2010, Martina Franca Ital
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