5,585 research outputs found
A 22 Degree Tidal Tail for Palomar 5
Using Data Release 4 of the Sloan Digital Sky Survey, we have applied an
optimal contrast, matched filter technique to trace the trailing tidal tail of
the globular cluster Palomar 5 to a distance of 18.5 degrees from the center of
the cluster. This more than doubles the total known length of the tail to some
22 degrees on the sky. Based on a simple model of the Galaxy, we find that the
stream's orientation on the sky is consistent at the 1.7 sigma level with
existing proper motion measurements. We find that a spherical Galactic halo is
adequate to model the stream over its currently known length, and we are able
to place new constraints on the current space motion of the cluster.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter
The First Report on the Molecular Identification of Fresh Water Microalgae from Waterfalls of Paracelis, Mountain Province, Philippines
Microalgae belong to diverse groups of complex unicellular photosynthetic microorganisms typically found in the freshwater and marine environment. Towards the isolation and an attempt to report the first molecular identification of freshwater microalgae from the waterfalls of Paracelis, Mountain Province, Philippines, two microalgae were successfully isolated independently, purified, and cultivated for DNA extraction, polymerase chain reaction, and sequencing using gene 16s rRNA and rbcL markers. Based on the 16s rRNA sequence, one of the isolates has a 92.05% sequence similarity to Oscillatoriales cyanobacterium (KJ611413). On the other hand, one isolate has 98.27% sequence similarity with Chlorella pyrenoidosa (AB240145) using the rbcL. The morphological features of two microalgae were described and the phylogenetic trees were constructed using the gene marker
Dynamics of Quintessence Models of Dark Energy with Exponential Coupling to the Dark Matter
We explore quintessence models of dark energy which exhibit non-minimal
coupling between the dark matter and the dark energy components of the cosmic
fluid. The kind of coupling chosen is inspired in scalar-tensor theories of
gravity. We impose a suitable dynamics of the expansion allowing to derive
exact Friedmann-Robertson-Walker solutions once the coupling function is given
as input. Self-interaction potentials of single and double exponential types
emerge as result of our choice of the coupling function. The stability and
existence of the solutions is discussed in some detail. Although, in general,
models with appropriated interaction between the components of the cosmic
mixture are useful to handle the coincidence problem, in the present study the
coincidence can not be evaded due to the choice of the solution generating
ansatz.Comment: 10 pages, 7 figure
On the Equivalence Between Type I Liouville Dynamical Systems in the Plane and the Sphere
Producción CientíficaSeparable Hamiltonian systems either in sphero-conical coordinates on an S2 sphere or in elliptic coordinates on a R2 plane are described in a unified way. A back and forth route connecting these Liouville Type I separable systems is unveiled. It is shown how the gnomonic projection and its inverse map allow us to pass from a Liouville Type I separable system with a spherical configuration space
to its Liouville Type I partners where the configuration space is a plane and back. Several selected spherical separable systems and their planar cousins are discussed in a classical context
Indium segregation and enrichment in coherent InxGa1-xAs/GaAs quantum dots
Significant differences in the image features of InxGa1-xAs quantum dots (QDs) grown on (001) and vicinal (001) GaAs were seen in [001] on-zone bright-held transmission electron microscope images. Simulated images were obtained by modeling the strain field distribution of the QDs with finite element analysis and then using this model in dynamical electron diffraction contrast simulations. Comparison of the experimental images and the simulated images shows that (i) In segregation exists in the QDs and (ii) the average In content of the QDs is higher than the average In content of the film
Classical Limit of Demagnetization in a Field Gradient
We calculate the rate of decrease of the expectation value of the transverse
component of spin for spin-1/2 particles in a magnetic field with a spatial
gradient, to determine the conditions under which a previous classical
description is valid. A density matrix treatment is required for two reasons.
The first arises because the particles initially are not in a pure state due to
thermal motion. The second reason is that each particle interacts with the
magnetic field and the other particles, with the latter taken to be via a
2-body central force. The equations for the 1-body Wigner distribution
functions are written in a general manner, and the places where quantum
mechanical effects can play a role are identified. One that may not have been
considered previously concerns the momentum associated with the magnetic field
gradient, which is proportional to the time integral of the gradient. Its
relative magnitude compared with the important momenta in the problem is a
significant parameter, and if their ratio is not small some non-classical
effects contribute to the solution.
Assuming the field gradient is sufficiently small, and a number of other
inequalities are satisfied involving the mean wavelength, range of the force,
and the mean separation between particles, we solve the integro- partial
differential equations for the Wigner functions to second order in the strength
of the gradient. When the same reasoning is applied to a different problem with
no field gradient, but having instead a gradient to the z-component of
polarization, the connection with the diffusion coefficient is established, and
we find agreement with the classical result for the rate of decrease of the
transverse component of magnetization.Comment: 22 pages, no figure
Induced inflation from a 5D purely kinetic scalar field formalism on warped product spaces
Considering a separable and purely kinetic 5D scalar field on a warped
product metric background we propose a new and more general approach for
inducing 4D scalar potentials on a 4D constant foliation of the 5D space-time.
We obtain an induced potential for a true 4D scalar field instead of a
potential for an effective 4D scalar field. In this formalism we can recover
the usual 4D inflationary formalism with a geometrically induced inflationary
potential. In addition the quantum confinement of the inflaton modes is
obtained naturally from the model for at least a class of warping factors.
Besides the 4D inflationary physics that results of this formalism is
independent of the 4D-hypersurface chosen.Comment: 8 pages Accepted for publication in European Physical Journal
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