3,046 research outputs found
s/alpha/Fe Abundance Ratios in Halo Field Stars: Is there a Globular Cluster Connection?
We try to understand the s- and r-process elements vs Ti/Fe plots derived by
Jehin et al. (1999) for mildly metal-poor stars within the framework of the
analytical semi-empirical models for these elements by Pagel & Tautvaisiene
(1995, 1997). Jehin et al. distinguished two Pop II subgroups: IIa with
alpha/Fe and s-elements/Fe increasing together, which they attribute to pure
SNII activity, and IIb with constant alpha/Fe and a range in s/Fe which they
attribute to a prolonged accretion phase in parent globular clusters. However,
their sample consists mainly of thick-disk stars with only 4 clear halo
members, of which two are `anomalous' in the sense defined by Nissen & Schuster
(1997). Only the remaining two halo stars (and one in Nissen & Schuster's
sample) depart significantly from Y/Ti (or s/alpha) ratios predicted by our
model.Comment: 6 pages, 5 figures To appear in: Roma-Trieste Workshop 1999: `The
Chemical Evolution of the Milky Way: Stars vs Clusters', Vulcano Sept. 1999.
F. Giovanelli & F. Matteucci (eds), Kluwer, Dordrech
Letter to Sound Rules for Accented Lexicon Compression
This paper presents trainable methods for generating letter to sound rules
from a given lexicon for use in pronouncing out-of-vocabulary words and as a
method for lexicon compression.
As the relationship between a string of letters and a string of phonemes
representing its pronunciation for many languages is not trivial, we discuss
two alignment procedures, one fully automatic and one hand-seeded which produce
reasonable alignments of letters to phones.
Top Down Induction Tree models are trained on the aligned entries. We show
how combined phoneme/stress prediction is better than separate prediction
processes, and still better when including in the model the last phonemes
transcribed and part of speech information. For the lexicons we have tested,
our models have a word accuracy (including stress) of 78% for OALD, 62% for CMU
and 94% for BRULEX. The extremely high scores on the training sets allow
substantial size reductions (more than 1/20).
WWW site: http://tcts.fpms.ac.be/synthesis/mbrdicoComment: 4 pages 1 figur
Varying leptonic chemical potentials and spatial variation of primordial deuterium at high z
We try to explain the spatial variation of primordial deuterium suggested by
some observations by varying leptonic chemical potentials. The variation of the
latter may take place in some scenarios of leptogenesis. The model predicts a
large mass fraction of (35-60%) and (up to ) in
deuterium-rich regions. Because of lepton family symmetry, the angular
variations of cosmic microwave background radiation can be sufficiently small
although still observable in future measurements.Comment: 16 pages, late
Nonequilibrium quantum fluctuation relations for harmonic systems in nonthermal environments
We formulate exact generalized nonequilibrium fluctuation relations for the
quantum mechanical harmonic oscillator coupled to multiple harmonic baths. Each
of the different baths is prepared in its own individual (in general
nonthermal) state. Starting from the exact solution for the oscillator dynamics
we study fluctuations of the oscillator position as well as of the energy
current through the oscillator under general nonequilibrium conditions. In
particular, we formulate a fluctuation-dissipation relation for the oscillator
position autocorrelation function that generalizes the standard result for the
case of a single bath at thermal equilibrium. Moreover, we show that the
generating function for the position operator fullfills a generalized
Gallavotti-Cohen-like relation. For the energy transfer through the oscillator,
we determine the average energy current together with the current fluctuations.
Finally, we discuss the generalization of the cumulant generating function for
the energy transfer to nonthermal bath preparations.Comment: 21 page
Automated Virtual Machine Introspection for Host-Based Intrusion Detection
This thesis examines techniques to automate configuration of an intrusion detection system utilizing hardware-assisted virtualization. These techniques are used to detect the version of a running guest operating system, automatically configure version-specific operating system information needed by the introspection library, and to locate and monitor important operating system data structures. This research simplifies introspection library configuration and is a step toward operating system independent introspection. An operating system detection algorithm and Windows virtual machine system service dispatch table monitor are implemented using the Xen hypervisor and a modified version of the XenAccess library. All detection and monitoring is implemented from the Xen management domain. Results of the operating system detection are used to initialize the XenAccess library. Library initialization time and kernel symbol retrieval are compared to the standard library. The algorithm is evaluated using nine versions of the Windows operating system. The system service dispatch table monitor is evaluated using the Agony and ProAgent rootkits. The automation techniques successfully detect the operating system and system service dispatch table hooks for the nine Windows versions tested. The modified XenAccess library exhibits an average initialization speedup of 1.9. Kernel symbol lookup is 10 times faster, on average. The hook detector is able to detect all hooks used by both rookits
The Oxygen Abundance of Nearby Galaxies from Sloan Digital Sky Survey Spectra
We have derived the oxygen abundance for a sample of nearby galaxies in the
Data Release 5 of the Sloan Digital Sky Survey (SDSS) which possess at least
two independent spectra of one or several HII regions with a detected
[OIII]4363 auroral line. Since, for nearby galaxies, the [OII]3727 nebular line
is out of the observed wavelength range, we propose a method to derive (O/H)_ff
abundances using the classic Te method coupled with the ff relation. (O/H)_7325
abundances have also been determined, based on the [OII]7320,7330 line
intensities, and using a small modification of the standard Te method. The
(O/H)_ff and (O/H)_7325 abundances have been derived with both the one- and
two-dimensional t_2 - t_3 relations. It was found that the (O/H)_ff abundances
derived with the parametric two-dimensional t_2 - t_3 relation are most
reliable. Oxygen abundances have been determined in 29 nearby galaxies, based
on 84 individual abundance determinations in HII regions. Because of our
selection methods, the metallicity of our galaxies lies in the narrow range 8.2
< 12 + log (O/H) < 8.4. The radial distribution of oxygen abundances in the
disk of the spiral galaxy NGC 4490 is determined for the first time.Comment: 39 pages, 10 figures, 4 tables, accepted for publication in the
Astrophysical Journa
Design and fabrication of a radiative actively cooled honeycomb sandwich structural panel for a hypersonic aircraft
The panel assembly consisted of an external thermal protection system (metallic heat shields and insulation blankets) and an aluminum honeycomb structure. The structure was cooled to temperature 442K (300 F) by circulating a 60/40 mass solution of ethylene glycol and water through dee shaped coolant tubes nested in the honeycomb and adhesively bonded to the outer skin. Rene'41 heat shields were designed to sustain 5000 cycles of a uniform pressure of + or - 6.89kPa (+ or - 1.0 psi) and aerodynamic heating conditions equivalent to 136 kW sq m (12 Btu sq ft sec) to a 422K (300 F) surface temperature. High temperature flexible insulation blankets were encased in stainless steel foil to protect them from moisture and other potential contaminates. The aluminum actively cooled honeycomb sandwich structural panel was designed to sustain 5000 cycles of cyclic in-plane loading of + or - 210 kN/m (+ or - 1200 lbf/in.) combined with a uniform panel pressure of + or - 6.89 kPa (?1.0 psi)
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Ultraconserved words point to deep language ancestry across Eurasia
The search for ever deeper relationships among the Worldâs languages is bedeviled by the fact that most words evolve too rapidly to preserve evidence of their ancestry beyond 5,000 to 9,000 y. On the other hand, quantitative modeling indicates that some âultraconservedâ words exist that might be used to find evidence for deep linguistic relationships beyond that time barrier. Here we use a statistical model, which takes into account the frequency with which words are used in common everyday speech, to predict the existence of a set of such highly conserved words among seven language families of Eurasia postulated to form a linguistic superfamily that evolved from a common ancestor around 15,000 y ago. We derive a dated phylogenetic tree of this proposed superfamily with a time-depth of âŒ14,450 y, implying that some frequently used words have been retained in related forms since the end of the last ice age. Words used more than once per 1,000 in everyday speech were 7- to 10-times more likely to show deep ancestry on this tree. Our results suggest a remarkable fidelity in the transmission of some words and give theoretical justification to the search for features of language that might be preserved across wide spans of time and geography
A study of magnetic fluctuations and their anomalous scaling in the solar wind: the Ulysses fast-latitude scan
The solar wind is a highly turbulent and intermittent medium at frequencies between 10<sup>-4</sup> and 10<sup>-1</sup> Hz. Power spectra are used to look at fluctuations in the components of the magnetic field at high frequencies over a wide range of latitudes. Results show steady turbulence in the polar regions of the Sun and a more varied environment in the equatorial region. The magnetic field fluctuations exhibit anomalous scaling at high frequencies. Various models have been proposed in an attempt to better understand the scaling nature of such fluctuations in neutral fluid turbulence. We have used the Ulysses fast latitude scan data to perform a wide ranging comparison of three such models on the solar wind magnetic field data: the well-known P model, in both its Kolmogorov and Kraichnan forms, the lognormal cascade model and a model adapted from atmospheric physics, the G infinity model. They were tested by using fits to graphs of the structure function exponents g(q), by making a comparison with a non-linear measure of the deviation of g(q) from the non-intermittent straight line, and by using extended self similarity technique, over a large range of helio-latitudes. Tests of all three models indicated a high level of intermittency in the fast solar wind, and showed a varied structure in the slow wind, with regions of apparently little intermittency next to regions of high intermittency, implying that the slow wind has no uniform origin. All but one of the models performed well, with the lognormal and Kolmogorov P model performing the best over all the tests, indicating that inhomogeneous energy transfer in the cascade is a good description. The Kraichnan model performed relatively poorly, and the overall results show that the Kraichnan model of turbulence is not well supported over the frequency and distance ranges of our data set. The G infinity model fitted the results surprisingly well and showed that there may very well be important universal geometrical aspects of intermittency over many physical systems
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