1,447 research outputs found
Simulating Radiative Magnetohydrodynamical Flows with AstroBEAR: Implementation and Applications of Non-equilibrium Cooling
Radiative cooling plays a crucial role in the dynamics of many astrophysical
flows, and is particularly important in the dense shocked gas within
Herbig-Haro (HH) objects and stellar jets. Simulating cooling processes
accurately is necessary to compare numerical simulations with existing and
planned observations of HH objects, such as those from the Hubble Space
Telescope and the James Webb Space Telescope. In this paper we discuss a new,
non-equilibrium cooling scheme we have implemented into the 3-D
magnetohydrodynamic (MHD) code AstroBEAR. The new cooling function includes
ionization, recombination, and excitation of all the important atomic species
that cool below 10000 K. We tested the routine by comparing its predictions
with those from the well-tested 1-D Cox-Raymond shock code (Raymond 1979). The
results show thatAstroBEAR accurately tracks the ionization fraction,
temperature, and other MHD variables for all low-velocity (.90 km/s) magnetized
radiative shock waves. The new routine allows us to predict synthetic emission
maps in all the bright forbidden and permitted lines observed in stellar jets,
including H{\alpha}, [NII], [OI], and [SII]. We present an example as to how
these synthetic maps facilitate a direct comparison with narrowband images of
HH objects.Comment: 8 figure
Binary Biometrics: An Analytic Framework to Estimate the Performance Curves Under Gaussian Assumption
In recent years, the protection of biometric data has gained increased interest from the scientific community. Methods such as the fuzzy commitment scheme, helper-data system, fuzzy extractors, fuzzy vault, and cancelable biometrics have been proposed for protecting biometric data. Most of these methods use cryptographic primitives or error-correcting codes (ECCs) and use a binary representation of the real-valued biometric data. Hence, the difference between two biometric samples is given by the Hamming distance (HD) or bit errors between the binary vectors obtained from the enrollment and verification phases, respectively. If the HD is smaller (larger) than the decision threshold, then the subject is accepted (rejected) as genuine. Because of the use of ECCs, this decision threshold is limited to the maximum error-correcting capacity of the code, consequently limiting the false rejection rate (FRR) and false acceptance rate tradeoff. A method to improve the FRR consists of using multiple biometric samples in either the enrollment or verification phase. The noise is suppressed, hence reducing the number of bit errors and decreasing the HD. In practice, the number of samples is empirically chosen without fully considering its fundamental impact. In this paper, we present a Gaussian analytical framework for estimating the performance of a binary biometric system given the number of samples being used in the enrollment and the verification phase. The error-detection tradeoff curve that combines the false acceptance and false rejection rates is estimated to assess the system performance. The analytic expressions are validated using the Face Recognition Grand Challenge v2 and Fingerprint Verification Competition 2000 biometric databases
An alkylation route to carbo- and heteroaromatic amino acids
Amino acids carrying aromatic carbo- and heterocycles in the side chain, such as naphthyl-, biphenyl- and pyridylalanines, have been prepared by alkylation of a glycine enolate with a haloalkyl carbocycle or heterocycle, with enantiomeric excess up to 87% using the ephedrine amide protocol
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The EUV emission of cataclysmic variables
Approximately half the luminosity of a typical cataclysmic variable may emerge as an optically thick component peaking in the EUV. Observations of this component are important for understanding the energetics and accretion rates of CV's in general, as well as for understanding the physics of the accretion process. The nature of the turbulent boundary layers and winds of disk accretors and the heating of the white dwarfs by accretion are among the problems which can be addressed by observations in the EUV. 46 refs., 2 figs
Variability of nuclear and mitochondrial ribosomal DNA of a truffle species (Tuber aestivum)
The intraspecific genetic variability of #Tuber aestivum$ was studied using molecular markers at various geographical scales. We used the polymerase chain reaction (PCR) coupled with restriction fragment length polymorphism (RFLP) analysis to examine the variation of the nuclear and mitochondrial ribosomal DNA (rDNA). RFLPs were found in the nuclear internal transcribed spacer (ITS) and three alleles were detected in the six populations analysed. No variability was found in mitochondrial rDNA. We found, in a very few cases, that truffles sharing different ITS genotypes could be present within a single symbiotic tree. (Résumé d'auteur
Optical Imaging and Spectroscopic Observation of the Galactic Supernova Remnant G85.9-0.6
Optical CCD imaging with H and [SII] filters and spectroscopic
observations of the galactic supernova remnant G85.9-0.6 have been performed
for the first time. The CCD image data are taken with the 1.5m Russian-Turkish
Telescope (RTT150) at TUBITAK National Observatory (TUG) and spectral data are
taken with the Bok 2.3 m telescope on Kitt Peak, AZ.
The images are taken with narrow-band interference filters H, [SII]
and their continuum. [SII]/H ratio image is performed. The ratio
obtained from [SII]/H is found to be 0.42, indicating that the
remnant interacts with HII regions. G85.9-0.6 shows diffuse-shell morphology.
[SII] average flux ratio is calculated from the
spectra, and the electron density is obtained to be 395 . From
[OIII]/H ratio, shock velocity has been estimated, pre-shock density of
, explosion energy of ergs,
interstellar extinction of , and neutral hydrogen column density
of are reported.Comment: 20 pages, 4 tables, 4 figures. Accepted for publication in
Astrophysics & Space Scienc
The ecology of sexual dimorphism in size and shape of the freshwater blenny Salaria fluviatilis.
Sexual selection is considered the major cause of sexual dimorphism, but recent observations suggest that natural selection may play a more important role in the evolution of sex differentiation than previously recognized. Therefore, studying the trade-offs between natural selection and sexual selection is crucial to a better understanding of the ecology underlying the evolution of sexual dimorphism. The freshwater blenny Salaria fluviatilis, a fish inhabiting lakes and rivers around the Mediterranean Sea, displays strong sexual dimorphism in size, shape, and behavior (i.e., larger body and head size for males and higher swimming requirements for females during the reproductive period). We tested for differences in sexual dimorphism in size and shape between the populations from lake and river habitats with the goal of identifying the trade-offs between natural and sexual selection that underlie variations in sexual dimorphism in this species. Our results show i) differences in sexual size dimorphism (SSizeD) in accordance to Rensch's rule (i.e., larger individuals in rivers associated with higher SSizeD), and ii) a decrease in shape differentiation between males and females in lake populations. Together, this suggests that the different environmental conditions between lake and river habitats (e.g., resource limitations, predation pressure, water velocity) affect the relative importance of sexual selection in the display of sexual dimorphism within the species. This study highlights the importance of considering the environmental conditions to which populations are exposed to better understand the ecology underlying the evolution of sexual dimorphism
Galaxies in box: A simulated view of the interstellar medium
We review progress in the development of physically realistic three
dimensional simulated models of the galaxy.We consider the scales from star
forming molecular clouds to the full spiral disc. Models are computed using
hydrodynamic (HD) or magnetohydrodynamic (MHD) equations and may include cosmic
ray or tracer particles. The range of dynamical scales between the full galaxy
structure and the turbulent scales of supernova (SN) explosions and even cloud
collapse to form stars, make it impossible with current computing tools and
resources to resolve all of these in one model. We therefore consider a
hierarchy of models and how they can be related to enhance our understanding of
the complete galaxy.Comment: Chapter in Large Scale Magnetic Fields in the Univers
Thermal radiation processes
We discuss the different physical processes that are important to understand
the thermal X-ray emission and absorption spectra of the diffuse gas in
clusters of galaxies and the warm-hot intergalactic medium. The ionisation
balance, line and continuum emission and absorption properties are reviewed and
several practical examples are given that illustrate the most important
diagnostic features in the X-ray spectra.Comment: 37 pages, 16 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 9; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
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