233 research outputs found
The Iron Unresolved Transition Array in Active Galactic Nuclei
The unresolved transition array (UTA) of iron M-shell ions is a prominent
absorption feature in the X-ray spectrum of many active galactic nuclei (AGNs).
Modeling photoionized plasmas in attempt to match the observed silicon and
oxygen lines fail to predict the level of ionization of iron as inferred by
this feature. It is suggested that the discrepancy is due to underestimation of
the low-temperature dielectronic recombination rates for iron M-shell ions.
Modified ionization balance calculations, based on new (guessed) atomic data,
support this idea. The results are shown and compared to the global properties
of several observed UTAs. Implications for AGN absorbing gas are discussed
including an analysis of the ionization parameter distribution in such sources.
The need for real calculations of such atomic data is stressed.Comment: 5 pages, 4 figures, accepted by Ap
Pengukuran Kesenjangan Kinerja Antara Supplier Dengan Customer Pada Rantai Pasokan Jasa Pendidikan Tinggi Menggunakan Metode Servqual
Performance is the key to measure the quality of service. On the other side an increase in the quality of service is one of the keys to winning the competition.The purpose of this study is measuring the service quality of services at the college using SERVQUAL. SERVQUAL method itself is a method to measure services through five dimensions namely Tangibels, Empathy, Reliability, Responsiveness and Assurance.The results of using SERVQUAL method from 25 variables obtained dimensions that has the biggest gap is Tangibels, Empathy, and Responsiveness
Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?
We compute the Milky Way potential in different cold dark matter (CDM) based
models, and compare these with the modified Newtonian dynamics (MOND)
framework. We calculate the axis ratio of the potential in various models, and
find that isopotentials are less spherical in MOND than in CDM potentials. As
an application of these models, we predict the escape velocity as a function of
the position in the Galaxy. This could be useful in comparing with future data
from planned or already-underway kinematic surveys (RAVE, SDSS, SEGUE, SIM,
GAIA or the hypervelocity stars survey). In addition, the predicted escape
velocity is compared with the recently measured high proper motion velocity of
the Large Magellanic Cloud (LMC). To bind the LMC to the Galaxy in a MOND
model, while still being compatible with the RAVE-measured local escape speed
at the Sun's position, we show that an external field modulus of less than
is needed.Comment: Accepted for publication in MNRAS, 13 pages, 7 figures, 3 table
Formation of molecular hydrogen on analogues of interstellar dust grains: experiments and modelling
Molecular hydrogen has an important role in the early stages of star
formation as well as in the production of many other molecules that have been
detected in the interstellar medium. In this review we show that it is now
possible to study the formation of molecular hydrogen in simulated
astrophysical environments. Since the formation of molecular hydrogen is
believed to take place on dust grains, we show that surface science techniques
such as thermal desorption and time-of-flight can be used to measure the
recombination efficiency, the kinetics of reaction and the dynamics of
desorption. The analysis of the experimental results using rate equations gives
useful insight on the mechanisms of reaction and yields values of parameters
that are used in theoretical models of interstellar cloud chemistry.Comment: 23 pages, 7 figs. Published in the J. Phys.: Conf. Se
Nucleation mechanism for the direct graphite-to-diamond phase transition
Graphite and diamond have comparable free energies, yet forming diamond from
graphite is far from easy. In the absence of a catalyst, pressures that are
significantly higher than the equilibrium coexistence pressures are required to
induce the graphite-to-diamond transition. Furthermore, the formation of the
metastable hexagonal polymorph of diamond instead of the more stable cubic
diamond is favored at lower temperatures. The concerted mechanism suggested in
previous theoretical studies cannot explain these phenomena. Using an ab initio
quality neural-network potential we performed a large-scale study of the
graphite-to-diamond transition assuming that it occurs via nucleation. The
nucleation mechanism accounts for the observed phenomenology and reveals its
microscopic origins. We demonstrated that the large lattice distortions that
accompany the formation of the diamond nuclei inhibit the phase transition at
low pressure and direct it towards the hexagonal diamond phase at higher
pressure. The nucleation mechanism proposed in this work is an important step
towards a better understanding of structural transformations in a wide range of
complex systems such as amorphous carbon and carbon nanomaterials
Voids in the Large-Scale Structure
Voids are the most prominent feature of the LSS of the universe. Still, they
have been generally ignored in quantitative analysis of it, essentially due to
the lack of an objective tool to identify and quantify the voids. To overcome
this, we present the Void-Finder algorithm, a novel tool for objectively
quantifying galaxy voids. The algorithm classifies galaxies as either wall- or
field-galaxies. Then it identifies voids in the wall-galaxy distribution. Voids
are defined as continuous volumes that do not contain any wall-galaxies. The
voids must be thicker than an adjustable limit, which is refined in successive
iterations. We test the algorithm using Voronoi tessellations. By appropriate
scaling of the parameters we apply it to the SSRS2 survey and to the IRAS 1.2
Jy. Both surveys show similar properties: ~50% of the volume is filled by the
voids, which have a scale of at least 40 Mpc, and a -0.9 under-density. Faint
galaxies populate the voids more than bright ones. These results suggest that
both optically and IRAS selected galaxies delineate the same LSS. Comparison
with the recovered mass distribution further suggests that the observed voids
in the galaxy distribution correspond well to under-dense regions in the mass
distribution. This confirms the gravitational origin of the voids.Comment: Submitted to ApJ; 33 pages, aaspp4 LaTeX file, using epsfig and
natbib, 1 table, 12 PS figures. Complete gzipped version is available at
http://shemesh.fiz.huji.ac.il/hagai/; uuencoded file is available at
http://shemesh.fiz.huji.ac.il/papers/ep3.uu or ftp://shemesh.fiz.huji.ac.i
Honey bee neurogenomic responses to affiliative and agonistic social interactions
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147835/1/gbb12509-sup-0003-FigureS3.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147835/2/gbb12509-sup-0002-FigureS2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147835/3/gbb12509-sup-0001-FigureS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147835/4/gbb12509.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147835/5/gbb12509_am.pd
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