7,889 research outputs found
Continuous Matrix Product Ansatz for the One-Dimensional Bose Gas with Point Interaction
We study a matrix product representation of the Bethe ansatz state for the
Lieb-Linger model describing the one-dimensional Bose gas with delta-function
interaction. We first construct eigenstates of the discretized model in the
form of matrix product states using the algebraic Bethe ansatz. Continuous
matrix product states are then exactly obtained in the continuum limit with a
finite number of particles. The factorizing -matrices in the lattice model
are indispensable for the continuous matrix product states and lead to a marked
reduction from the original bosonic system with infinite degrees of freedom to
the five-vertex model.Comment: 5 pages, 1 figur
Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful
tool for observing the Sun at high spatial, temporal, and spectral resolution.
These capabilities can address a broad range of fundamental scientific
questions in solar physics. The radiation observed by ALMA originates mostly
from the chromosphere - a complex and dynamic region between the photosphere
and corona, which plays a crucial role in the transport of energy and matter
and, ultimately, the heating of the outer layers of the solar atmosphere. Based
on first solar test observations, strategies for regular solar campaigns are
currently being developed. State-of-the-art numerical simulations of the solar
atmosphere and modeling of instrumental effects can help constrain and optimize
future observing modes for ALMA. Here we present a short technical description
of ALMA and an overview of past efforts and future possibilities for solar
observations at submillimeter and millimeter wavelengths. In addition, selected
numerical simulations and observations at other wavelengths demonstrate ALMA's
scientific potential for studying the Sun for a large range of science cases.Comment: 73 pages, 21 figures ; Space Science Reviews (accepted December 10th,
2015); accepted versio
Host galaxies of long gamma-ray bursts in the Millennium Simulation
(abridged) In this work, we investigate the nature of the host galaxies of
long Gamma-Ray bursts (LGRBs) using a galaxy catalogue constructed from the
Millennium Simulation. We developed an LGRB synthetic model based on the
hypothesis that these events originate at the end of the life of massive stars
following the collapsar model, with the possibility of including a constraint
on the metallicity of the progenitor star. A complete observability pipeline
was designed to calculate a probability estimation for a galaxy to be
observationally identified as a host for LGRBs detected by present
observational facilities. This new tool allows us to build an observable host
galaxy catalogue which is required to reproduce the current stellar mass
distribution of observed hosts. This observability pipeline predicts that the
minimum mass for the progenitor stars should be ~75 solar masses in order to be
able to reproduce BATSE observations. Systems in our observable catalogue are
able to reproduce the observed properties of host galaxies, namely stellar
masses, colours, luminosity, star formation activity and metallicities as a
function of redshift. At z>2, our model predicts that the observable host
galaxies would be very similar to the global galaxy population. We found that
~88 per cent of the observable host galaxies with mean gas metallicity lower
than 0.6 solar have stellar masses in the range 10^8.5-10^10.3 solar masses in
excellent agreement with observations. Interestingly, in our model observable
host galaxies remain mainly within this mass range regardless of redshift,
since lower stellar mass systems would have a low probability of being observed
while more massive ones would be too metal-rich. Observable host galaxies are
predicted to preferentially inhabit dark matter haloes in the range
10^11-10^11.5 solar masses, with a weak dependence on redshift.Comment: 11 pages, 10 figures, accepted for publication in MNRA
A search for debris disks in the Herschel-ATLAS
Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO)Aims. We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods. We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results. We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme.Peer reviewe
Thermal and thermo-oxidative characterisation of rice straw for its use in energy valorisation processes
[EN] The processes of pyrolysis and combustion of rice straw will be carried out in a spouted bed reactor. Both thermo-chemical processes were simulated in the first stage by multi-rate linear non-isothermal thermogravimetric (TGA) experiments using Ar and O-2 as carrier gas respectively. The results obtained from the TGA measurements, the kinetic methodology based on the combination of the iso-conversional methods Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Vyazovkin and the use of Master Plots assessed by Perez-Maqueda criterion have permitted to describe mathematically both thermo-chemical reactions. Lower operational temperatures and higher kinetic parameters (Ea, n, A) were required to carry out combustion reactions respect to those for pyrolysis. These results will be the initial parameters that will define both thermo-chemical processes in a spouted bed reactor. (C) 2016 Elsevier Ltd. All rights reserved.Moliner, C.; Bosio, B.; Arato, E.; Ribes-Greus, A. (2016). Thermal and thermo-oxidative characterisation of rice straw for its use in energy valorisation processes. Fuel. 180:71-79. https://doi.org/10.1016/j.fuel.2016.04.021S717918
Tensor network states and geometry
Tensor network states are used to approximate ground states of local
Hamiltonians on a lattice in D spatial dimensions. Different types of tensor
network states can be seen to generate different geometries. Matrix product
states (MPS) in D=1 dimensions, as well as projected entangled pair states
(PEPS) in D>1 dimensions, reproduce the D-dimensional physical geometry of the
lattice model; in contrast, the multi-scale entanglement renormalization ansatz
(MERA) generates a (D+1)-dimensional holographic geometry. Here we focus on
homogeneous tensor networks, where all the tensors in the network are copies of
the same tensor, and argue that certain structural properties of the resulting
many-body states are preconditioned by the geometry of the tensor network and
are therefore largely independent of the choice of variational parameters.
Indeed, the asymptotic decay of correlations in homogeneous MPS and MERA for
D=1 systems is seen to be determined by the structure of geodesics in the
physical and holographic geometries, respectively; whereas the asymptotic
scaling of entanglement entropy is seen to always obey a simple boundary law --
that is, again in the relevant geometry. This geometrical interpretation offers
a simple and unifying framework to understand the structural properties of, and
helps clarify the relation between, different tensor network states. In
addition, it has recently motivated the branching MERA, a generalization of the
MERA capable of reproducing violations of the entropic boundary law in D>1
dimensions.Comment: 18 pages, 18 figure
Alogliptin after acute coronary syndrome in patients with type 2 diabetes
Background - To assess potentially elevated cardiovascular risk related to new antihyperglycemic drugs in patients with type 2 diabetes, regulatory agencies require a comprehensive evaluation of the cardiovascular safety profile of new antidiabetic therapies. We assessed cardiovascular outcomes with alogliptin, a new inhibitor of dipeptidyl peptidase 4 (DPP-4), as compared with placebo in patients with type 2 diabetes who had had a recent acute coronary syndrome. Methods - We randomly assigned patients with type 2 diabetes and either an acute myocardial infarction or unstable angina requiring hospitalization within the previous 15 to 90 days to receive alogliptin or placebo in addition to existing antihyperglycemic and cardiovascular drug therapy. The study design was a double-blind, noninferiority trial with a prespecified noninferiority margin of 1.3 for the hazard ratio for the primary end point of a composite of death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke. Results - A total of 5380 patients underwent randomization and were followed for up to 40 months (median, 18 months). A primary end-point event occurred in 305 patients assigned to alogliptin (11.3%) and in 316 patients assigned to placebo (11.8%) (hazard ratio, 0.96; upper boundary of the one-sided repeated confidence interval, 1.16; P<0.001 for noninferiority). Glycated hemoglobin levels were significantly lower with alogliptin than with placebo (mean difference, -0.36 percentage points; P<0.001). Incidences of hypoglycemia, cancer, pancreatitis, and initiation of dialysis were similar with alogliptin and placebo. Conclusions - Among patients with type 2 diabetes who had had a recent acute coronary syndrome, the rates of major adverse cardiovascular events were not increased with the DPP-4 inhibitor alogliptin as compared with placebo. (Funded by Takeda Development Center Americas; EXAMINE ClinicalTrials.gov number, NCT00968708.
The VIMOS-VLT Deep Survey: Evolution in the Halo Occupation Number since z 1
We model the evolution of the mean galaxy occupation of dark-matter halos
over the range , using the data from the VIMOS-VLT Deep Survey
(VVDS). The galaxy projected correlation function was computed for a
set of luminosity-limited subsamples and fits to its shape were obtained using
two variants of Halo Occupation Distribution models. These provide us with a
set of best-fitting parameters, from which we obtain the average mass of a halo
and average number of galaxies per halo. We find that after accounting for the
evolution in luminosity and assuming that we are largely following the same
population, the underlying dark matter halo shows a growth in mass with
decreasing redshift as expected in a hierarchical structure formation scenario.
Using two different HOD models, we see that the halo mass grows by 90% over the
redshift interval z=[0.5,1.0]. This is the first time the evolution in halo
mass at high redshifts has been obtained from a single data survey and it
follows the simple form seen in N-body simulations with , and . This provides evidence for a rapid accretion
phase of massive halos having a present-day mass , with a merger event occuring between redshifts of 0.5
and 1.0. Futhermore, we find that more luminous galaxies are found to occupy
more massive halos irrespectively of the redshift. Finally, the average number
of galaxies per halo shows little increase from redshift z 1.0 to z
0.5, with a sharp increase by a factor 3 from z 0.5 to z 0.1,
likely due to the dynamical friction of subhalos within their host halos.Comment: 14 pages, 6 figures, 5 tables. MNRAS accepted
- âŚ