3,870 research outputs found
Time-dependent Photoionization of Gaseous Nebulae: the Pure Hydrogen Case
We study the problem of time-dependent photoionization of low density gaseous
nebulae subjected to sudden changes in the intensity of ionizing radiation. To
this end, we write a computer code that solves the full time-dependent energy
balance, ionization balance, and radiation transfer equations in a
self-consistent fashion for a simplified pure hydrogen case. It is shown that
changes in the ionizing radiation yield ionization/thermal fronts that
propagate through the cloud, but the propagation times and response times to
such fronts vary widely and non-linearly from the illuminated face of the cloud
to the ionization front (IF). Ionization/thermal fronts are often supersonic,
and in slabs initially in pressure equilibrium such fronts yield large pressure
imbalances that are likely to produce important dynamical effects in the cloud.
Further, we studied the case of periodic variations in the ionizing flux. It
is found that the physical conditions of the plasma have complex behaviors that
differ from any steady-state solutions. Moreover, even the time average
ionization and temperature is different from any steady-state case. This time
average is characterized by over-ionization and a broader IF with respect to
the steady-state solution for a mean value of the radiation flux. Around the
time average of physical conditions there is large dispersion in instantaneous
conditions, particularly across the IF, which increases with the period of
radiation flux variations. Moreover, the variations in physical conditions are
asynchronous along the slab due to the combination of non-linear propagation
times for thermal/ionization fronts and equilibration times.Comment: Accepted for publication in ApJ. 36 pages, 12 figure
Superconducting niobium thin film slow-wave structures
A superconducting comb structure as a slow-wave element in a traveling-wave maser will significantly improve maser noise temperature and gain by reducing the insertion loss. The results of the insertion loss measurements of superconducting niobium slow-wave structures subjected to maser operating conditions at X-Band frequencies are presented
Burt-Butler algebras of the bocs associated to a finite partially ordered set
Given an algebra and an -bimodule with co-algebra structure, a
bocs, the algebras of endomorphisms of as left or right module of the bocs
are known as Burt-Butler algebras (up to an appropriate opposite). Here we give
a description of these algebras for the bocs associated to a finite partially
ordered set in terms of incidence algebras and their balanced versions. We also
exhibit their quasi-hereditary structure, provide bound quiver presentations
for their Ringel duals, describe the embedding of as exact Borel subalgebra
and characterize the corresponding subcategories of induced and co-induced
modules
On the changes in the physical properties of the ionized region around the Weigelt structures in Eta Carinae over the 5.54-yr spectroscopic cycle
We present HST/STIS observations and analysis of two prominent nebular
structures around the central source of Eta Carinae, the knots C and D. The
former is brighter than the latter for emission lines from intermediate or high
ionization potential ions. The brightness of lines from intermediate and high
ionization potential ions significantly decreases at phases around periastron.
We do not see conspicuous changes in the brightness of lines from low
ionization potential (<13.6 eV) that the total extinction towards the Weigelt
structures is that the total extinction towards the Weigelt structures is AsubV
=2/0. that the total extinction towards the Weigelt structures is AV = 2.0.
Weigelt C and D are characterized by an electron density of that the total
extinction towards the Weigelt structures is AV = 2.0. Weigelt C and D are
characterized by an electron density of 10exp6.9 cm-3 that does not
significantly change throughout the orbital cycle. The electron temperature
varies from 5500 K (around periastron) to 7200 K (around apastron). The
relative changes in the brightness of He I lines are well reproduced by the
variations in the electron temperature alone. We found that, at phases around
periastron, the electron temperature seems to be higher for Weigelt C than that
of D. The Weigelt structures are located close to the Homunculus equatorial
plane, at a distance of about 1240 AU from the central source. From the
analysis of proper motion and age, the Weigelt complex can be associated with
the equatorial structure called the Butterfly Nebula surrounding the central
binary system.Comment: 19 pages, 18 figure
SACMAN automated canal control system
Presented during the Third international conference on irrigation and drainage held March 30 - April 2, 2005 in San Diego, California. The theme of the conference was "Water district management and governance."Includes bibliographical references.Many irrigation districts currently operate their main canals, pumping plants, etc. remotely with Supervisory Control and Data Acquisition (SCADA) software. This is usually manual operation with perhaps a few local automatic control features. SacMan (software for automated canal management) is a software package that adds canal automation logic to commercially-available, windows-based SCADA packages. It allows the user to implement a variety of automatic control features, including complete automatic control, where feasible. It was developed through research at the U.S. Water Conservation Laboratory in Phoenix, AZ. SacMan has several levels of implementation ranging from manual control to full automatic control, including upstream level control, flow rate control, routing of known demand changes, and full (distant) downstream level control. SacMan interfaces with commercial Supervisory Control and Data Acquisition (SCADA) software, currently iFix by GE Fanuc (formerly Intellution, Inc.), but potentially applicable to other SCADA packages. SacMan was field tested on the WM lateral canal at the Maricopa Stanfield Irrigation and Drainage District (MSIDD) in central Arizona. In July/August 2004, SacMan successfully operated the WM canal for a period of 30 days, nearly continuously. This paper describes the features of this canal automation software and some results from this long-term testing.Sponsored by USCID; co-sponsored by Association of California Water Agencies and International Network for Participatory Irrigation Management
Atomic Processes in Planetary Nebulae and H II Regions
Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have
driven much development in atomic physics. In the last few years the
combination of a generation of powerful observatories, the development of ever
more sophisticated spectral modeling codes, and large efforts on mass
production of high quality atomic data have led to important progress in our
understanding of the atomic spectra of such astronomical objects. In this paper
I review such progress, including evaluations of atomic data by comparisons
with nebular spectra, detection of spectral lines from most iron-peak elements
and n-capture elements, observations of hyperfine emission lines and analysis
of isotopic abundances, fluorescent processes, and new techniques for
diagnosing physical conditions based on recombination spectra. The review is
directed toward atomic physicists and spectroscopists trying to establish the
current status of the atomic data and models and to know the main standing
issues.Comment: 9 pages, 1 figur
Immigration Detention: Perspectives from Maine Law Students Working on the Ground at the Laredo Detention Center in Texas
Since 2017, students enrolled in the University of Maine School of Law Refugee and Human Rights Clinic have traveled to Laredo, Texas to participate in a program, sponsored and run by the law firm Jones Day in collaboration with Texas RioGrande Legal Aid, to provide representation for women in the Laredo Detention Center. Alongside Jones Day attorneys, the students conduct client intake interviews, draft memos detailing each woman’s experiences and any potential legal claims, and assist in the representation of clients. This article will provide a glimpse into the experiences of three Maine Law student attorneys during their time in Laredo, Texas, and will survey issues in the contemporary immigration landscape: first, an overview of the political climate surrounding the immigration debate, current immigration trends, and statistical figures; second, stories providing context for why people are seeking to immigrate to the U.S., and the persecution and challenges faced by immigrant women; third, the shortage of representation for immigrants, whether detained or non-detained; and finally, one of the most challenging and poignant issues encountered by student attorneys participating in the Laredo Project—the separation of immigrant mothers from their children
Radiative transition rates and collision strengths for Si II
Aims. This work reports radiative transition rates and electron impact
excitation collision strengths for levels of the 3s23p, 3s3p2, 3s24s, and 3s23d
configurations of Siii. Methods. The radiative data were computed using the
Thomas-Fermi-Dirac-Amaldi central potential, but with the modifications
introduced by Bautista (2008) that account for the effects of electron-electron
interactions. We also introduce new schemes for the optimization of the
variational parameters of the potential. Additional calculations were carried
out with the Relativistic Hartree-Fock and the multiconfiguration Dirac-Fock
methods. Collision strengths in LS-coupling were calculated in the close
coupling approximation with the R-matrix method. Then, fine structure collision
strengths were obtained by means of the intermediate-coupling frame
transformation (ICFT) method which accounts for spin-orbit coupling effects.
Results. We present extensive comparisons between the results of different
approximations and with the most recent calculations and experiment available
in the literature. From these comparisons we derive a recommended set of gf-
values and radiative transition rates with their corresponding estimated
uncertainties. We also study the effects of different approximations in the
representation of the target ion on the electron-impact collision strengths.
Our most accurate set of collision strengths were integrated over a Maxwellian
distribution of electron energies and the resulting effective collision
strengths are given for a wide range of temperatures. Our results present
significant differences from recent calculations with the B-spline
non-orthogonal R-matrix method. We discuss the sources of the differences.Comment: 6 figures, 5 tables within text, 2 electronic table
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