2,015 research outputs found
Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. IV. The Variable UV Absorption Lines
We report the detection of variable UV absorption lines in NGC 4395, based on
UV observations with the HST STIS carried out in April and July, 2004, as part
of a reverberation-mapping campaign. Low-ionization lines of O I, N I, Si II, C
II, and Fe II, are present in the low-state spectra (April 2004) at a velocity
v_shift=-250 km/s (system A_l), and additional high-ionization lines of C IV
and N V appear in the high-state spectra (July 2004) at v_shift=-250 km/s
(system A_h) and at v_shift=-840 km/s (system B). The absence of absorption
from the low metastable levels of Si II implies a density <~10^3 cm^(-3) for
system A_l, indicating a location outside the narrow line region (NLR). System
A_h is peculiar as only N V absorption is clearly detected. A high N V/C IV
absorption ratio is expected for a high metallicity absorber, but this is
excluded here as the metallicity of the host galaxy and of the nuclear gas is
significantly subsolar. A simple acceptable model for systems A_h and B is an
absorber located between the broad line region (BLR) and the NLR, which absorbs
only the continuum and the BLR. At the low-state the strong narrow emission
lines of C IV and N V dominate the spectrum, making the absorption invisible.
At the high-state the absorbed continuum and BLR emission dominate the
spectrum. Thus, the change in the observed absorption does not reflect a change
in the absorber, but rather a change in the continuum and BLR emission from
behind the absorber, relative to the emission from the NLR in front of the
absorber. Studies of the absorption line variability in highly variable objects
can thus break the degeneracy in the absorber distance determination inherent
to single epoch studies.Comment: Accepted for publication in The Astrophysical Journa
OPserver: interactive online-computations of opacities and radiative accelerations
Codes to compute mean opacities and radiative accelerations for arbitrary
chemical mixtures using the Opacity Project recently revised data have been
restructured in a client--server architecture and transcribed as a subroutine
library. This implementation increases efficiency in stellar modelling where
element stratification due to diffusion processes is depth dependent, and thus
requires repeated fast opacity reestimates. Three user modes are provided to
fit different computing environments, namely a web browser, a local workstation
and a distributed grid.Comment: 5 pages, 1 figur
Comparing virtual patients with synthesized and natural speech
Virtual Patient (VP) simulations are often designed to use pre-recorded
speech in order to provide more realism and immersion. However, using actors for
recording these utterances has certain downsides. It can add to the cost during
implementation, can take considerable time especially when a large number of
VPs have to be created, and is not very flexible for example when sentences or
words have to be added frequently. This study aims to explore the use of
synthesized speech as an alternative to pre-recorded speech for VPs. Two medical
scenarios have been prepared for this study, and both have been implemented
using a VP with natural language or with synthesized speech. In a pilot study we
explored students' retention rates of the symptoms reported by the VP under both
conditions to investigate whether synthesized speech can serve as a good enough
alternative
A Look at the Canning Record
To have canned between 143 million and 160 million quarts of fruits and vegetables in a year is a pretty fair sized job. Iowa homemakers, assisted in some instances by their families, did just that last year, if a survey which we made shows the true picture of what happened in 1943.* The survey was made by Iowa State College and the State Nutrition Council
Updated opacities from the opacity project
Using the code autostructure, extensive calculations of inner-shell atomic data have been made for the chemical elements He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Cr, Mn, Fe and Ni. The results are used to obtain updated opacities from the Opacity Project (OP). A number of other improvements on earlier work have also been included. Rosseland-mean opacities from the OP are compared with those from OPAL. Differences of 5-10 per cent occur. The OP gives the 'Z-bump', at log(T) 5.2, to be shifted to slightly higher temperatures. The opacities from the OP, as functions of temperature and density, are smoother than those from OPAL. The accuracy of the integrations used to obtain mean opacities can depend on the frequency mesh used. Tests involving variation of the numbers of frequency points show that for typical chemical mixtures the OP integrations are numerically correct to within 0.1 per cent. The accuracy of the interpolations used to obtain mean opacities for any required values of temperature and density depends on the temperature-density meshes used. Extensive tests show that, for all cases of practical interest, the OP interpolations give results correct to better than 1 per cent. Prior to a number of recent investigations which have indicated a need for downward revisions in the solar abundances of oxygen and other elements, there was good agreement between properties of the Sun deduced from helioseismology and from stellar evolution models calculated using OPAL opacities. The revisions destroy that agreement. In a recent paper, Bahcall et al. argue that the agreement would be restored if opacities for the regions of the Sun with 2 Ă 106T 5 Ă 106 K (0.7-0.4 R) were larger than those given by OPAL by about 10 per cent. In the region concerned, the present results from the OP do not differ from those of OPAL by more than 2.5 per cent
Large-scale Breit-Pauli R-matrix calculations for transition probabilities of Fe V
Ab initio theoretical calculations are reported for the electric (E1) dipole
allowed and intercombination fine structure transitions in Fe V using the
Breit-Pauli R-matrix (BPRM) method. We obtain 3865 bound fine structure levels
of Fe V and oscillator strengths, Einstein A-coefficients and
line strengths. In addition to the relativistic effects, the intermediate
coupling calculations include extensive electron correlation effects that
represent the complex configuration interaction (CI). Fe V bound levels are
obtained with angular and spin symmetries and of the (e + Fe VI)
system such that = 5,3,1, 10, . The bound levels are
obtained as solutions of the Breit-Pauli (e + ion) Hamiltonian for each ,
and are designated according to the `collision' channel quantum numbers. A
major task has been the identification of these large number of bound fine
structure levels in terms of standard spectroscopic designations. A new scheme,
based on the analysis of quantum defects and channel wavefunctions, has been
developed. The identification scheme aims particularly to determine the
completeness of the results in terms of all possible bound levels for
applications to analysis of experimental measurements and plasma modeling. An
uncertainty of 10-20% for most transitions is estimated.Comment: 31 pages, 1 figure, Physica Scripta (in press
Microcanonical entropy inflection points: Key to systematic understanding of transitions in finite systems
We introduce a systematic classification method for the analogs of phase
transitions in finite systems. This completely general analysis, which is
applicable to any physical system and extends towards the thermodynamic limit,
is based on the microcanonical entropy and its energetic derivative, the
inverse caloric temperature. Inflection points of this quantity signal
cooperative activity and thus serve as distinct indicators of transitions. We
demonstrate the power of this method through application to the long-standing
problem of liquid-solid transitions in elastic, flexible homopolymers.Comment: 4 pages, 3 figure
An exact universal amplitude ratio for percolation
The universal amplitude ratio for percolation in two
dimensions is determined exactly using results for the dilute A model in regime
1, by way of a relationship with the q-state Potts model for q<4.Comment: 5 pages, LaTeX, submitted to J. Phys. A. One paragraph rewritten to
correct error
A Comprehensive and Cost-Effective Computer Infrastructure for K-12 Schools
Since 1993, NASA Langley Research Center has been developing and implementing a low-cost Internet connection model, including system architecture, training, and support, to provide Internet access for an entire network of computers. This infrastructure allows local area networks which exceed 50 machines per school to independently access the complete functionality of the Internet by connecting to a central site, using state-of-the-art commercial modem technology, through a single standard telephone line. By locating high-cost resources at this central site and sharing these resources and their costs among the school districts throughout a region, a practical, efficient, and affordable infrastructure for providing scale-able Internet connectivity has been developed. As the demand for faster Internet access grows, the model has a simple expansion path that eliminates the need to replace major system components and re-train personnel. Observations of optical Internet usage within an environment, particularly school classrooms, have shown that after an initial period of 'surfing,' the Internet traffic becomes repetitive. By automatically storing requested Internet information on a high-capacity networked disk drive at the local site (network based disk caching), then updating this information only when it changes, well over 80 percent of the Internet traffic that leaves a location can be eliminated by retrieving the information from the local disk cache
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