7,906 research outputs found
The accretion disk in the post period-minimum cataclysmic variable SDSS J080434.20+510349.2
This study of SDSS0804 is primarily concerned with the double-hump shape in
the light curve and its connection with the accretion disk in this bounce-back
system. Time-resolved photometric and spectroscopic observations were obtained
to analyze the behavior of the system between superoutbursts. A geometric model
of a binary system containing a disk with two outer annuli spiral density waves
was applied to explain the light curve and the Doppler tomography. Observations
were carried out during 2008-2009, after the object's magnitude decreased to
V~17.7(0.1) from the March 2006 eruption. The light curve clearly shows a
sinusoid-like variability with a 0.07 mag amplitude and a 42.48 min
periodicity, which is half of the orbital period of the system. In Sept. 2010,
the system underwent yet another superoutburst and returned to its quiescent
level by the beginning of 2012. This light curve once again showed a
double-humps, but with a significantly smaller ~0.01mag amplitude. Other types
of variability like a "mini-outburst" or SDSS1238-like features were not
detected. Doppler tomograms, obtained from spectroscopic data during the same
period of time, show a large accretion disk with uneven brightness, implying
the presence of spiral waves. We constructed a geometric model of a bounce-back
system containing two spiral density waves in the outer annuli of the disk to
reproduce the observed light curves. The Doppler tomograms and the
double-hump-shape light curves in quiescence can be explained by a model system
containing a massive >0.7Msun white dwarf with a surface temperature of
~12000K, a late-type brown dwarf, and an accretion disk with two outer annuli
spirals. According to this model, the accretion disk should be large, extending
to the 2:1 resonance radius, and cool (~2500K). The inner parts of the disk
should be optically thin in the continuum or totally void.Comment: 12 pages, 15 figures, accepted for publication in A&
Studying the evolution of galaxies in compact groups over the past 3 Gyr - II. The importance of environment in the suppression of star formation
We present an in depth study on the evolution of galaxy properties in compact
groups over the past 3 Gyr. We are using the largest multi-wavelength sample
to-date, comprised 1770 groups (containing 7417 galaxies), in the redshift
range of 0.01<z<0.23. To derive the physical properties of the galaxies we rely
on ultraviolet (UV)-to-infrared spectral energy distribution modeling, using
CIGALE. Our results suggest that during the 3 Gyr period covered by our sample,
the star formation activity of galaxies in our groups has been substantially
reduced (3-10 times). Moreover, their star formation histories as well as their
UV-optical and mid-infrared colors are significantly different from those of
field and cluster galaxies, indicating that compact group galaxies spend more
time transitioning through the green valley. The morphological transformation
from late-type spirals into early-type galaxies occurs in the mid-infrared
transition zone rather than in the UV-optical green valley. We find evidence of
shocks in the emission line ratios and gas velocity dispersions of the
late-type galaxies located below the star forming main sequence. Our results
suggest that in addition to gas stripping, turbulence and shocks might play an
important role in suppressing the star formation in compact group galaxies.Comment: (Accepted for publication in MNRAS, date of submission November 18,
2015
Getting Topological Information for a 80-Adjacency Doxel-Based 4D Volume through a Polytopal Cell Complex
Advanced homology computation of digital volumes via cell complexes
Given a 3D binary voxel-based digital object V, an algorithm for computing homological information for V via a polyhedral cell complex is designed. By homological information we understand not only Betti numbers, representative cycles of homology classes and homological classification of cycles but also the computation of homology numbers related additional algebraic structures defined on homology (coproduct in homology, product in cohomology, (co)homology operations,...). The algorithm is mainly based on the following facts: a) a local 3D-polyhedrization of any 2×2×2 configuration of mutually 26-adjacent black voxels providing a coherent cell complex at global level; b) a description of the homology of a digital volume as an algebraic-gradient vector field on the cell complex (see Discrete Morse Theory [5], AT-model method [7,5]). Saving this vector field, we go further obtaining homological information at no extra time processing cost
Modelling the behaviour of microbulk Micromegas in Xenon/trimethylamine gas
We model the response of a state of the art micro-hole single-stage charge
amplication device (`microbulk' Micromegas) in a gaseous atmosphere consisting
of Xenon/trimethylamine at various concentrations and pressures. The amplifying
structure, made with photo-lithographic techniques similar to those followed in
the fabrication of gas electron multipliers (GEMs), consisted of a 100 um-side
equilateral-triangle pattern with 50 um-diameter holes placed at its vertexes.
Once the primary electrons are guided into the holes by virtue of an optimized
field configuration, avalanches develop along the 50 um-height channels etched
out of the original doubly copper-clad polyimide foil. In order to properly
account for the strong field gradients at the holes' entrance as well as for
the fluctuations of the avalanche process (that ultimately determine the
achievable energy resolution), we abandoned the hydrodynamic framework,
resorting to a purely microscopic description of the electron trajectories as
obtained from elementary cross-sections. We show that achieving a satisfactory
description needs additional assumptions about atom-molecule (Penning) transfer
reactions and charge recombination to be made
Towards Minimal Barcodes
In the setting of persistent homology computation, a useful tool is the persistence barcode representation in which pairs of birth and death times of homology classes are encoded in the form of intervals. Starting from a polyhedral complex K (an object subdivided into cells which are polytopes) and an initial order of the set of vertices, we are concerned with the general problem of searching for filters (an order of the rest of the cells) that provide a minimal barcode representation in the sense of having minimal number of “k-significant” intervals, which correspond to homology classes with life-times longer than a fixed number k. As a first step, in this paper we provide an algorithm for computing such a filter for k = 1 on the Hasse diagram of the poset of faces of K
Analysis of transmitted HIV-1 drug resistance using 454 ultra-deep-sequencing and the DeepChek(®)-HIV system.
Introduction
Next-generation sequencing (NGS) is capable of detecting resistance-associated mutations (RAMs) present at frequencies of 1% or below. Several studies have found that baseline low-frequency RAMs are associated with failure to first-line HAART. One major limitation to the expansion of this technology in routine diagnostics is the complexity and laboriousness integral to bioinformatics analysis. DeepChek (ABL, TherapyEdge) is a CE-marked software that allows automated analysis and resistance interpretation of NGS data.
Objective
To evaluate the use of 454 ultra-deep-sequencing (Roche® 454, Life Sciences; 454-UDS) and DeepChek for routine baseline resistance testing in a clinical diagnostic laboratory.
Methods
107 newly diagnosed HIV-1-infected patients (subtypes: A, n=9; B, n=52; C, n=21; D, n=2; F, n=3; G, n=1; CRF01, n=7; CRF02, n=7; CRF06, n=1; CRF07, n=1; CRF10, n=1 and unassigned complex, n=2) with a median plasma viral load of 88,727 copies/mL (range: 1380–2,143,543) were tested by 454-UDS and Sanger sequencing for the detection of protease and reverse transcriptase RAMs. In addition, integrase RAMs were investigated in 57 of them. Sequence analysis and resistance interpretation were performed using DeepChek applying 1% and 20% thresholds for variant detections; filters applied were comparison between Sanger and 454-UDS, and Stanford and IAS list for resistance interpretation.
Results
The time elapsed from generation of raw 454 data (between 2,000–5,000 sequences/sample) to elaboration of a resistance report was approximately 10 minutes per sample, equivalent to the time required for the same process using Sanger sequencing. Four patients (3.7%) showed baseline resistance by Sanger and 454-UDS at frequencies above 20%, which affected both NRTIs (n=2) and NNRTIs (n=2). In addition, 12 patients (11.2%) showed transmitted drug resistance (TDR) by 454-UDS at frequencies below 20% affecting NRTIs (n=9), NNRTIs (n=7) and PIs (n=2). Integrase resistance was not detected at baseline by 454-UDS or Sanger sequencing.
Conclusions
DeepChek allowed easy and rapid analysis and interpretation of NGS data, thus facilitating the incorporation of this technology in routine diagnostics. The use of NGS considerably increased the detection rates of TDR to NRTI, NNRTIs and PIs. No transmitted resistance to integrase inhibitors was found in our population by Sanger sequencing or UDS
Thermodynamics of Chaplygin gas
We clarify thermodynamics of the Chaplygin gas by introducing the
integrability condition. All thermal quantities are derived as functions of
either volume or temperature. Importantly, we find a new general equation of
state, describing the Chaplygin gas completely. We confirm that the Chaplygin
gas could show a unified picture of dark matter and energy which cools down
through the universe expansion without any critical point (phase transition).Comment: 5 pages, 4 figures, version "Accepted for publication in Astrophysics
& Space Science
Steel heat treating: Mathematical modelling and numerical simulation of a problem arising in the automotive industry
We describe a mathematical model for the industrial heating and cooling processes of a steel workpiece representing the steering rack of an automobile. The goal of steel heat treating is to provide a hardened surface on critical parts of the workpiece while keeping the rest soft and ductile in order to reduce fatigue. The high hardness is due to the phase transformation of steel accompanying the rapid cooling. This work takes into account both heating-cooling stage and viscoplastic model. Once the general mathematical formulation is derived, we can perform some numerical simulations
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