1,713 research outputs found
Theoretical research program to predict the properties of molecules and clusters containing transition metal atoms
The primary focus of this research has been the theoretical study of transition metal (TM) chemistry. A major goal of this work is to provide reliable information about the interaction of H atoms with iron metal. This information is needed to understand the effect of H atoms on the processes of embrittlement and crack propagation in iron. The method in the iron hydrogen studies is the cluster method in which the bulk metal is modelled by a finite number of iron atoms. There are several difficulties in the application of this approach to the hydrogen iron system. First the nature of TM-TM and TM-H bonding for even diatomic molecules was not well understood when these studies were started. Secondly relatively large iron clusters are needed to provide reasonable results
The impact of turbulence and magnetic field orientation on star forming filaments
We present simulations of collapsing filaments studying the impact of
turbulence and magnetic field morphologies on their evolution and star
formation properties. We vary the mass per unit length of the filaments as well
as the orientation of the magnetic field with respect to the major axis. We
find that the filaments, which have no or a perpendicular magnetic field,
typically reveal a smaller width than the universal width of 0.1 pc proposed by
e.g. Arzoumanian et al. 2011. We show that this also holds in the presence of
supersonic turbulence and that accretion driven turbulence is too weak to
stabilize the filaments along their radial direction. On the other hand, we
find that a magnetic field that is parallel to the major axis can stabilize the
filament against radial collapse resulting in widths of 0.1 pc. Furthermore,
depending on the filament mass and magnetic field configuration, gravitational
collapse and fragmentation in filaments occurs either in an edge-on way,
uniformly distributed across the entire length, or in a mixed way. In the
presence of initially moderate density perturbations, a centralized collapse
towards a common gravitational centre occurs. Our simulations can thus
reproduce different modes of fragmentation observed recently in star forming
filaments. Moreover, we find that turbulent motions influence the distance
between individual fragments along the filament, which does not always match
the results of a Jeans analysis.Comment: 14 pages, 8 figure, accepted for publication in MNRA
Book Review
Book review of "Dealing in Virtue: International Commercial Arbitration and the Construction of a Transnational Legal Order" by Yves Dezalay and Bryant G. Garth (Chicago: University of Chicago Press, 1996).Published in cooperation with the American Bar Association Section of Dispute Resolutio
Revealing the dynamics of Class 0 protostellar discs with ALMA
We present synthetic ALMA observations of Keplerian, protostellar discs in
the Class 0 stage studying the emission of molecular tracers like CO,
CO, HCO, HCO, NH, and HCO. We model the
emission of discs around low- and intermediate-mass protostars. We show that
under optimal observing conditions ALMA is able to detect the discs already in
the earliest stage of protostellar evolution, although the emission is often
concentrated to the innermost 50 AU. Therefore, a resolution of a few 0.1"
might be too low to detect Keplerian discs around Class 0 objects. We also
demonstrate that under optimal conditions for edge-on discs Keplerian rotation
signatures are recognisable, from which protostellar masses can be inferred.
For this we here introduce a new approach, which allows us to determine
protostellar masses with higher fidelity than before. Furthermore, we show that
it is possible to reveal Keplerian rotation even for strongly inclined discs
and that ALMA should be able to detect possible signs of fragmentation in
face-on discs. In order to give some guidance for future ALMA observations, we
investigate the influence of varying observing conditions and source distances.
We show that it is possible to probe Keplerian rotation in inclined discs with
an observing time of 2 h and a resolution of 0.1", even in the case of moderate
weather conditions. Furthermore, we demonstrate that under optimal conditions,
Keplerian discs around intermediate-mass protostars should be detectable up to
kpc-distances.Comment: 17 pages, 17 figures, accepted for publication by MNRA
Utah High School Sophomore Attitudes Toward Women\u27s Roles and Non-Traditional Vocational Career Choices
Role behaviors for men and women in our society are undergoing change. Research data to reveal student attitudes toward these role behaviors and choices were needed for the development of strategies to eliminate sex bias and sex stereotyping in our educational programs and ultimately in the socialization process.
The purpose of the study was to collect research data to determine Utah high school student attitudes toward women\u27s roles and non-traditional vocational career choices. The survey instrument used to collect the data was constructed, pilot tested, factor analyzed, and revised prior to its administration to the sample. The revised instrument contained 60 attitudinal statements regarding women\u27s roles and non-traditional vocational career chokes and demographic data requests.
Instrument reliability was determined on each of the factors using the Guttman Split-half. The Factor I coefficient of reliability was .91. The reliability coefficient on Factor II was .82, while the Factor III reliability coefficient was .81.
A total of 23 Utah public high schools and 1,454 sophomore students participated in the study. The data were analyzed using Five-way Analysis of Variance and Chi Square programs (Statistical Package for the Social Sciences). The Total Attitudinal Score, based on Women\u27s Roles and Non-Traditional Vocational Career Choices, and three factor scores were the dependent variables analyzed. The factor scores included: Factor I, Women\u27s Place--Women\u27s Roles; Factor II, Sex Role Equity--Equal Treatment; and Factor III, Leadership Roles. Comparisons were made on total score and three factor scores based on the five independent variables: Sex (male/female), Religious Commitment (high/low), Location of Family Residence (rural/metro), Mother\u27s Employment Status (employed/not employed), and Social Class (middle/working).
A significant difference was found between male and female student attitudes for each factor and the total score. On each comparison of the Sex variable, female attitudes toward women\u27s roles and choices were more non-traditional than male attitudes.
For comparisons on the Religious Commitment variable, a significant difference was found in attitudes between students of high and low religious commitment on total score and each of the factor scores. Students of low religious commitment held more non-traditional attitudes toward women\u27s roles and choices than students of high religious commitment.
A significant difference was found on the Location of Family Residence variable for Total Attitudinal Score. Students from metropolitan locations responded more non-traditionally toward women\u27s roles and non-traditional vocational career choices than students from rural locations. Differences in rural and metropolitan student attitudes were not found to be significant for Factor I, Factor II, and Factor III scores.
Significant differences in student attitudes were found on the Mother\u27s Employment Status variable on total score and each of the factor scores. Students whose mothers were employed outside the home held more non-traditional attitudes toward women\u27s roles and related career choices than students with homemaker mothers.
Findings on the Social Class variable were found to be significant for the Total Attitudinal Score and Factor scores II and III. A significant difference was found in attitudes between students from middle class families and students from working class families. Students from middle class families held more non-traditional attitudes toward roles and related career choices for women than students from working class families. No significant difference was found on the Social Class variable for Factor I
Theoretical research program to study transition metal trimers and embedded clusters
Small transition metal clusters were studied at a high level of approximation, including all the valence electrons in the calculation and extensive electron correlation, in order to understand the electronic structure of these small metal clusters. By comparison of dimers, trimers, and possibly higher clusters, the information obtained was used to provide insights into the electronic structure of bulk transition metals. Small metal clusters are currently of considerable experimental interest and some information is becomming available both from matrix electron spin resonance studies and from gas phase spectroscopy. Collaboration between theorists and experimentalists is thus expected to be especially profitable at this time since there is some experimental information which can serve to guide the theoretical work
Aluminum-26 Enrichment in the Surface of Protostellar Disks Due to Protostellar Cosmic Rays
The radioactive decay of aluminum-26 (Al) is an important heating
source in early planet formation. Since its discovery, there have been several
mechanisms proposed to introduce Al into protoplanetary disks, primarily
through contamination by external sources. We propose a local mechanism to
enrich protostellar disks with Al through irradiation of the
protostellar disk surface by cosmic rays accelerated in the protostellar
accretion shock. We calculate the Al enrichment, [Al/Al],
at the surface of the protostellar disk in the inner AU throughout the
evolution of low-mass stars, from M-dwarfs to proto-Suns. Assuming constant
mass accretion rates, , we find that irradiation by MeV cosmic rays
can provide significant enrichment on the disk surface if the cosmic rays are
not completely coupled to the gas in the accretion flow. Importantly, we find
that low accretion rates, M yr, are able
to produce canonical amounts of Al, . These accretion rates are experienced at the
transition from Class I- to Class II-type protostars, when it is assumed that
calcium-aluminum-rich inclusions condense in the inner disk. We conclude that
irradiation of the inner disk surface by cosmic ray protons accelerated in
accretion shocks at the protostellar surface may be an important mechanism to
produce Al. Our models show protostellar cosmic rays may be a viable
model to explain the enrichment of Al found in the Solar System.Comment: Accepted to ApJ, in pres
Probing 3D Density and Velocity Fields of ISM in Centers of Galaxies with Future X-Ray Observations
Observations of bright and variable "reflected" X-ray emission from molecular
clouds located within inner hundred parsec of our Galaxy have demonstrated that
the central supermassive black hole, Sgr A*, experienced short and powerful
flares in the past few hundred years. These flares offer a truly unique
opportunity to determine 3D location of the illuminated clouds (with ~10 pc
accuracy) and to reveal their internal structure (down to 0.1 pc scales). Short
duration of the flare(s), combined with X-rays high penetration power and
insensitivity of the reflection signal to thermo- and chemo-dynamical state of
the gas, ensures that the provided diagnostics of the density and velocity
fields is unbiased and almost free of the projection and opacity effects. Sharp
and sensitive snapshots of molecular gas accessible with aid of future X-ray
observatories featuring large collecting area and high angular (arcsec-level)
and spectral (eV-level) resolution cryogenic bolometers will present invaluable
information on properties of the supersonic turbulence inside the illuminated
clouds, map their shear velocity field and allow cross-matching between X-ray
data and velocity-resolved emission of various molecular species provided by
ALMA and other ground-based facilities. This will highlight large and
small-scale dynamics of the dense gas and help uncovering specifics of the ISM
lifecycle and high-mass star formation under very extreme conditions of
galactic centers. While the former is of particular importance for the SMBH
feeding and triggering AGN feedback, the latter might be an excellent test case
for star formation taking place in high-redshift galaxies.Comment: White paper submitted to the Astro2020 Decadal Surve
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