17,837 research outputs found
The Pierre Auger Observatory: Results on Ultra-High Energy Cosmic Rays
The focus of this article is on recent results on ultra-high energy cosmic
rays obtained with the Pierre Auger Observatory. The world's largest instrument
of this type and its performance are described. The observations presented here
include the energy spectrum, the primary particle composition, limits on the
fluxes of photons and neutrinos and a discussion of the anisotropic
distribution of the arrival directions of the most energetic particles.
Finally, plans for the construction of a Northern Auger Observatory in
Colorado, USA, are discussed.Comment: Proceedings of the International Workshop on Advances in Cosmic Ray
Science, Waseda University, Shinjuku, Tokyo, Japan, March 2008; to be
published in the Journal of the Physical Society of Japan (JPSJ) supplemen
Janis-Newman-Winicour and Wyman solutions are the same
We show that the well-known most general static and spherically symmetric
exact solution to the Einstein-massless scalar equations given by Wyman is the
same as one found by Janis, Newman and Winicour several years ago. We obtain
the energy associated with this spacetime and find that the total energy for
the case of the purely scalar field is zero.Comment: 9 pages, LaTex, no figures, misprints corrected, to appear in Int. J.
Mod. Phys.
Understanding the role of estrogen in the development of benign prostatic hyperplasia
Introduction: Benign prostatic hyperplasia (BPH) is a non-malignant enlargement of the prostate that affects ageing men. As the number of men affected by this condition will only continue to grow with the aging population, finding new strategies and new therapeutic options for its treatment is crucial. Androgenic hormones have been known to play an important role in the development of BPH and they have been a target in its medical treatment. Estrogens have also been implicated in BPH but in contrast to androgens, the functions of estrogens in the prostate are still obscure.Objective: This review aims to highlight the roles of estrogen in the development of BPH.Methods: Authors reviewed the literature covering the past forty years to highlight the roles of estrogen in the prostate and BPH. Data from authors’ experimental work in this field was also referenced.Results: The effects of estrogen in the prostate are mediated by estrogen receptors alpha and beta (ERα and ERβ). These two receptors have different expression and functions in the prostate, thereby presenting a window of opportunity to selectively target them for therapeutic purposes in BPH. The actions of estrogens, as mediated by estrogen receptors, appear to contribute to the development of BPH in men through an intricate molecular process that is yet to be fully elucidated. Although surgery remains the gold standard in the treatment of BPH, understanding the elusive role of estrogen in BPH, in addition to the established role of androgens, would enhance the current therapeutic options and perhaps lead to the development of new therapies. There are indications that phytoestrogens might be beneficial in the management of BPH.Conclusion: This review highlights the roles of estrogen as well as the therapeutic use of phytoestrogens in the prevention and management of BPH.Keywords: Benign prostatic hyperplasia (BPH); Estrogen; Estrogen receptors; Phytoestrogen; Androgen
The Visibility of Galactic Bars and Spiral Structure At High Redshifts
We investigate the visibility of galactic bars and spiral structure in the
distant Universe by artificially redshifting 101 B-band CCD images of local
spiral galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our
artificially redshifted images correspond to Hubble Space Telescope I-band
observations of the local galaxy sample seen at z=0.7, with integration times
matching those of both the very deep Northern Hubble Deep Field data, and the
much shallower Flanking Field observations. The expected visibility of galactic
bars is probed in two ways: (1) using traditional visual classification, and
(2) by charting the changing shape of the galaxy distribution in "Hubble
space", a quantitative two-parameter description of galactic structure that
maps closely on to Hubble's original tuning fork. Both analyses suggest that
over 2/3 of strongly barred luminous local spirals i.e. objects classified as
SB in the Third Reference Catalog) would still be classified as strongly barred
at z=0.7 in the Hubble Deep Field data. Under the same conditions, most weakly
barred spirals (classified SAB in the Third Reference Catalog) would be
classified as regular spirals. The corresponding visibility of spiral structure
is assessed visually, by comparing luminosity classifications for the
artificially redshifted sample with the corresponding luminosity
classifications from the Revised Shapley Ames Catalog. We find that for
exposures times similar to that of the Hubble Deep Field spiral structure
should be detectable in most luminous low-inclination spiral galaxies at z=0.7
in which it is present. [ABRIDGED]Comment: Accepted for publication in The Astronomical Journa
Collective Effects in Linear Spectroscopy of Dipole-Coupled Molecular Arrays
We present a consistent analysis of linear spectroscopy for arrays of nearest
neighbor dipole-coupled two-level molecules that reveals distinct signatures of
weak and strong coupling regimes separated for infinite size arrays by a
quantum critical point. In the weak coupling regime, the ground state of the
molecular array is disordered, but in the strong coupling regime it has
(anti)ferroelectric ordering. We show that multiple molecular excitations
(odd/even in weak/strong coupling regime) can be accessed directly from the
ground state. We analyze the scaling of absorption and emission with system
size and find that the oscillator strengths show enhanced superradiant behavior
in both ordered and disordered phases. As the coupling increases, the single
excitation oscillator strength rapidly exceeds the well known Heitler-London
value. In the strong coupling regime we show the existence of a unique spectral
transition with excitation energy that can be tuned by varying the system size
and that asymptotically approaches zero for large systems. The oscillator
strength for this transition scales quadratically with system size, showing an
anomalous one-photon superradiance. For systems of infinite size, we find a
novel, singular spectroscopic signature of the quantum phase transition between
disordered and ordered ground states. We outline how arrays of ultra cold
dipolar molecules trapped in an optical lattice can be used to access the
strong coupling regime and observe the anomalous superradiant effects
associated with this regime.Comment: 12 pages, 7 figures main tex
The Star Formation History of the Hubble Sequence: Spatially Resolved Colour Distributions of Intermediate Redshift Galaxies in the Hubble Deep Field
We analyse the spatially resolved colours of distant galaxies of known
redshift in the Hubble Deep Field, using a new technique based on matching
resolved four-band internal colour data to the predictions of evolutionary
synthesis models. We quantify the relative age, dispersion in age, ongoing
star-formation rate, star-formation history, and dust content of these
galaxies. To demonstrate the potential of the method, we study the
near-complete sample of 32 I ~ 0.5 studied by
Bouwens et al (1997). The dispersion of the internal colours of a sample of
0.4<z<1 early-type field galaxies in the HDF indicates that ~40% [4/11] show
evidence of star formation which must have occurred within the past third of
their ages at the epoch of observation. For a sample of well-defined spirals,
we similarly exploit the dispersion in colour to analyse the relative histories
of bulge and disc stars, in order to resolve the current controversy regarding
the ages of galactic bulges. Dust and metallicity gradients are ruled out as
major contributors to the colour dispersions we observe in these systems. The
median ages of bulge stars are found to be signicantly older than those in
galactic discs, and exhibit markedly different star-formation histories. This
result is inconsistent with a secular growth of bulges from disc instabilities,
but consistent with gradual disc formation by accretion of gas onto bulges, as
predicted by hierarchical theories. We extend our technique in order to discuss
the star formation history of the entire Bouwens et al sample in the context of
earlier studies concerned with global star formation histories.Comment: 8 colour postscript figures plus LaTeX source; submitted to MNRAS.
Uses the mnras.sty LaTeX style fil
Non-LTE, Relativistic Accretion Disk Fits to 3C~273 and the Origin of the Lyman Limit Spectral Break
We fit general relativistic, geometrically thin accretion disk models with
non-LTE atmospheres to near simultaneous multiwavelength data of 3C~273,
extending from the optical to the far ultraviolet. Our model fits show no flux
discontinuity associated with a hydrogen Lyman edge, but they do exhibit a
spectral break which qualitatively resembles that seen in the data. This break
arises from relativistic smearing of Lyman emission edges which are produced
locally at tens of gravitational radii in the disk. We discuss the possible
effects of metal line blanketing on the model spectra, as well as the
substantial Comptonization required to explain the observed soft X-ray excess.
Our best fit accretion disk model underpredicts the near ultraviolet emission
in this source, and also has an optical spectrum which is too red. We discuss
some of the remaining physical uncertainties, and suggest in particular that an
extension of our models to the slim disk regime and/or including nonzero
magnetic torques across the innermost stable circular orbit may help resolve
these discrepancies.Comment: Accepted for publication in Ap
Directional solidification of aluminum-nickel eutectic alloys using electroslag remelting
Attempts were made to produce directionally solidified, specifically grain aligned Al-6 wt pct Ni eutectic alloy using a laboratory scale ESR unit. For this purpose sand cast alloy electrodes were electroslag remelted under different mold conditions. The grain structure of the ingots obtained from these meltings showed that insulated silica molds gave the best vertical alignment of grains along the length of the ingot. The NiAl3 fibers within the grains tended to fan out and there was only a preferred alignment of fibers along the growth direction under the conditions of our experiments. The ESR parameters most suitable for vertical alignment of eutectic grains have been identified. In some electroslag remelting trials ingots were grown on a seed ingot. This resulted in a fewer vertical grains compared to the case when no seed ingot was used. The sand cast specimen of the eutectic exhibited a maximum tensile strength of around 88.2 MN/m2 (9.0 kg/mm2) whereas conventional ESR using water cooled mold gave strength value of 98.0 MN/m2 (10 kg/mm2). The directionally solidified ESR material showed longitudinal tensile strength as high as 213.7 MN/m2 (21.8 kg/mm2) which could be further increased to 220.6 MN/m2 (22.5 kg/mm2) by using the seed ingot. The average growth rate was varied between 5 to 25 mm/min during electroslag remelting in this study. The flow stresses, tangent modulus and ultimate tensile strength of directionally solidified eutectic increased with increasing growth rates
Rank Maximal Matchings -- Structure and Algorithms
Let G = (A U P, E) be a bipartite graph where A denotes a set of agents, P
denotes a set of posts and ranks on the edges denote preferences of the agents
over posts. A matching M in G is rank-maximal if it matches the maximum number
of applicants to their top-rank post, subject to this, the maximum number of
applicants to their second rank post and so on.
In this paper, we develop a switching graph characterization of rank-maximal
matchings, which is a useful tool that encodes all rank-maximal matchings in an
instance. The characterization leads to simple and efficient algorithms for
several interesting problems. In particular, we give an efficient algorithm to
compute the set of rank-maximal pairs in an instance. We show that the problem
of counting the number of rank-maximal matchings is #P-Complete and also give
an FPRAS for the problem. Finally, we consider the problem of deciding whether
a rank-maximal matching is popular among all the rank-maximal matchings in a
given instance, and give an efficient algorithm for the problem
Dimensionality reduction, and function approximation of poly (lactic-co-glycolic acid) micro-and nanoparticle dissolution rate
Prediction of poly(lactic-co-glycolic acid) (PLGA) micro- and nanoparticles’ dissolution rates plays a significant role in pharmaceutical and medical industries. The prediction of PLGA dissolution rate is crucial for drug manufacturing. Therefore, a model that predicts the PLGA dissolution rate could be beneficial. PLGA dissolution is influenced by numerous factors (features), and counting the known features leads to a dataset with 300 features. This large number of features and high redundancy within the dataset makes the prediction task very difficult and inaccurate. In this study, dimensionality reduction techniques were applied in order to simplify the task and eliminate irrelevant and redundant features. A heterogeneous pool of several regression algorithms were independently tested and evaluated. In addition, several ensemble methods were tested in order to improve the accuracy of prediction. The empirical results revealed that the proposed evolutionary weighted ensemble method offered the lowest margin of error and significantly outperformed the individual algorithms and the other ensemble techniques
- …