4,199 research outputs found
Flux-density spectral analysis for several pulsars and two newly-identified gigahertz-peaked spectra
In this paper we present results from flux density measurements for 21
pulsars over a wide frequency range, using the Giant Metrewave Radio Telescope
(GMRT) and the Effelsberg telescope. Our sample was a set of mostly newly
discovered pulsars from the selection of candidates for gigahertz-peaked
spectra (GPS) pulsars. Using the results of our observations along with
previously published data, we identify two new GPS pulsars. One of them, PSR
J1740+1000, with dispersion measure of 24 pc cm, is the first GPS pulsar
with such a low DM value.We also selected several strong candidates for objects
with high frequency turnover in their spectra which require further
investigation.We also revisit our source selection criteria for future searches
for GPS pulsars.Comment: 10 pages, 2 tables, 9 figures, accepted for publication in MNRA
Quasi-local rotating black holes in higher dimension: geometry
With a help of a generalized Raychaudhuri equation non-expanding null
surfaces are studied in arbitrarily dimensional case. The definition and basic
properties of non-expanding and isolated horizons known in the literature in
the 4 and 3 dimensional cases are generalized. A local description of horizon's
geometry is provided. The Zeroth Law of black hole thermodynamics is derived.
The constraints have a similar structure to that of the 4 dimensional spacetime
case. The geometry of a vacuum isolated horizon is determined by the induced
metric and the rotation 1-form potential, local generalizations of the area and
the angular momentum typically used in the stationary black hole solutions
case.Comment: 32 pages, RevTex
Signal recognition particle RNA localization within the nucleolus differs from the classical sites of ribosome synthesis
The nucleolus is the site of ribosome biosynthesis, but is now known to have other functions as well. In the present study we have investigated how the distribution of signal recognition particle (SRP) RNA within the nucleolus relates to the known sites of ribosomal RNA synthesis, processing, and nascent ribosome assembly (i.e., the fibrillar centers, the dense fibrillar component (DFC), and the granular component). Very little SRP RNA was detected in fibrillar centers or the DFC of the nucleolus, as defined by the RNA polymerase Iâspecific upstream binding factor and the protein fibrillarin, respectively. Some SRP RNA was present in the granular component, as marked by the protein B23, indicating a possible interaction with ribosomal subunits at a later stage of maturation. However, a substantial portion of SRP RNA was also detected in regions of the nucleolus where neither B23, UBF, or fibrillarin were concentrated. Dual probe in situ hybridization experiments confirmed that a significant fraction of nucleolar SRP RNA was not spatially coincident with 28S ribosomal RNA. These results demonstrate that SRP RNA concentrates in an intranucleolar location other than the classical stations of ribosome biosynthesis, suggesting that there may be nucleolar regions that are specialized for other functions
The Wilsonian Renormalization Group in Randall-Sundrum 1
We find renormalization group transformations for the compactified
Randall-Sundrum scenario by integrating out an infinitesimal slice of
ultraviolet degrees of freedom near the Planck brane. Under these
transformations the coefficients of operators on the Planck brane experience RG
evolution. The extra-dimensional radius also scales, flowing to zero in the IR.
We find an attractive fixed point in the context of a bulk scalar field theory.
Calculations are simplified in the low energy effective theory as we
demonstrate with the computation of a loop diagram.Comment: 19 pages, typos adde
Background independent quantizations: the scalar field II
We are concerned with the issue of quantization of a scalar field in a
diffeomorphism invariant manner. We apply the method used in Loop Quantum
Gravity. It relies on the specific choice of scalar field variables referred to
as the polymer variables. The quantization, in our formulation, amounts to
introducing the `quantum' polymer *-star algebra and looking for positive
linear functionals, called states. Assumed in our paper homeomorphism
invariance allows to derive the complete class of the states. They are
determined by the homeomorphism invariant states defined on the CW-complex
*-algebra. The corresponding GNS representations of the polymer *-algebra and
their self-adjoint extensions are derived, the equivalence classes are found
and invariant subspaces characterized. In the preceding letter (the part I) we
outlined those results. Here, we present the technical details.Comment: 51 pages, LaTeX, no figures, revised versio
Real and complex connections for canonical gravity
Both real and complex connections have been used for canonical gravity: the
complex connection has SL(2,C) as gauge group, while the real connection has
SU(2) as gauge group. We show that there is an arbitrary parameter
which enters in the definition of the real connection, in the Poisson brackets,
and therefore in the scale of the discrete spectra one finds for areas and
volumes in the corresponding quantum theory. A value for could be could
be singled out in the quantum theory by the Hamiltonian constraint, or by the
rotation to the complex Ashtekar connection.Comment: 8 pages, RevTeX, no figure
Creating and Probing Electron Whispering Gallery Modes in Graphene
Designing high-finesse resonant cavities for electronic waves faces
challenges due to short electron coherence lengths in solids. Previous
approaches, e.g. the seminal nanometer-sized quantum corrals, depend on careful
positioning of adatoms at clean surfaces. Here we demonstrate an entirely
different approach, inspired by the peculiar acoustic phenomena in whispering
galleries. Taking advantage of graphene's unique properties, namely
gate-tunable light-like carriers, we create Whispering Gallery Mode (WGM)
resonators defined by circular pn-junctions, induced by a scanning tunneling
probe. We can tune the resonator size and the carrier concentration under the
probe in a back-gated graphene device over a wide range, independently and in
situ. The confined modes, revealed through characteristic resonances in the
tunneling spectrum, originate from Klein scattering at pn junction boundaries.
The WGM-type confinement and resonances are a new addition to the quantum
electron-optics toolbox, paving the way to real-world electronic lenses and
resonators
The status of Quantum Geometry in the dynamical sector of Loop Quantum Cosmology
This letter is motivated by the recent papers by Dittrich and Thiemann and,
respectively, by Rovelli discussing the status of Quantum Geometry in the
dynamical sector of Loop Quantum Gravity. Since the papers consider model
examples, we also study the issue in the case of an example, namely on the Loop
Quantum Cosmology model of space-isotropic universe. We derive the
Rovelli-Thiemann-Ditrich partial observables corresponding to the quantum
geometry operators of LQC in both Hilbert spaces: the kinematical one and,
respectively, the physical Hilbert space of solutions to the quantum
constraints. We find, that Quantum Geometry can be used to characterize the
physical solutions, and the operators of quantum geometry preserve many of
their kinematical properties.Comment: Latex, 12 page
Interaction Driven Quantum Hall Wedding cake-like Structures in Graphene Quantum Dots
Quantum-relativistic matter is ubiquitous in nature; however it is
notoriously difficult to probe. The ease with which external electric and
magnetic fields can be introduced in graphene opens a door to creating a
table-top prototype of strongly confined relativistic matter. Here, through a
detailed spectroscopic mapping, we provide a spatial visualization of the
interplay between spatial and magnetic confinement in a circular graphene
resonator. We directly observe the development of a multi-tiered "wedding
cake"-like structure of concentric regions of compressible/incompressible
quantum Hall states, a signature of electron interactions in the system.
Solid-state experiments can therefore yield insights into the behaviour of
quantum-relativistic matter under extreme conditions
- âŠ