30,846 research outputs found
Report on "Scheduling in a factory"
In order to carry out their orders of shoe soles, this company has a number of tasks T_1, ..., T_n of different lengths to be assigned to groups of machines.
Each group is operated by one worker (two in one case), and an operation cycle corresponds to injection, cooling, and removal of the sole. The time taken at each step varies from one order to another, and when starting a new task a machine needs to be tuned, which takes some extra time. Machines are working in parallel. At the moment the assignment is carried out empirically, and the problem proposed is to optimize the procedure
Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules
Dust grains in cold circumstellar regions and dark-cloud interiors at 10-20 K
are covered by ice mantles. A nonthermal desorption mechanism is invoked to
explain the presence of gas-phase molecules in these environments, such as the
photodesorption induced by irradiation of ice due to secondary ultraviolet
photons. To quantify the effects of ice photoprocessing, an estimate of the
photon absorption in ice mantles is required. In a recent work, we reported the
vacuum-ultraviolet (VUV) absorption cross sections of nonpolar molecules in the
solid phase. The aim was to estimate the VUV-absorption cross sections of
nonpolar molecular ice components, including CH4, CO2, N2, and O2. The column
densities of the ice samples deposited at 8 K were measured in situ by infrared
spectroscopy in transmittance. VUV spectra of the ice samples were collected in
the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged
hydrogen flow lamp. We found that, as expected, solid N2 has the lowest
VUV-absorption cross section, which about three orders of magnitude lower than
that of other species such as O2, which is also homonuclear. Methane (CH4) ice
presents a high absorption near Ly-alpha (121.6 nm) and does not absorb below
148 nm. Estimating the ice absorption cross sections is essential for models of
ice photoprocessing and allows estimating the ice photodesorption rates as the
number of photodesorbed molecules per absorbed photon in the ice.Comment: 9 pages, 6 figures, 7 table
Two-Dimensional Dilaton-Gravity Coupled to Massless Spinors
We apply a global and geometrically well-defined formalism for
spinor-dilaton-gravity to two-dimensional manifolds. We discuss the general
formalism and focus attention on some particular choices of the dilatonic
potential. For constant dilatonic potential the model turns out to be
completely solvable and the general solution is found. For linear and
exponential dilatonic potentials we present the class of exact solutions with a
Killing vector.Comment: 21 pages, LaTeX, minor changes in text and format, final version to
appear in Classical and Quantum Gravit
What communities have to say: using focus groups for SVP planning.
Presented at: 2015 National Sexual Assault Conference; September 2-4, 2015; Los Angeles, CA.https://digitalrepository.unm.edu/prc-posters-presentations/1038/thumbnail.jp
Chromospheric polarimetry through multi-line observations of the 850 nm spectral region
Future solar missions and ground-based telescopes aim to understand the
magnetism of the solar chromosphere. We performed a supporting study in
Quintero Noda et al. (2016) focused on the infrared Ca II 8542 A line and we
concluded that is one of the best candidates because it is sensitive to a large
range of atmospheric heights, from the photosphere to the middle chromosphere.
However, we believe that it is worth to try improving the results produced by
this line observing additional spectral lines. In that regard, we examined the
neighbour solar spectrum looking for spectral lines that could increase the
sensitivity to the atmospheric parameters. Interestingly, we discovered several
photospheric lines that greatly improve the photospheric sensitivity to the
magnetic field vector. Moreover, they are located close to a second
chromospheric line that also belongs to the Ca II infrared triplet, i.e. the Ca
II 8498 A line, and enhances the sensitivity to the atmospheric parameters at
chromospheric layers. We conclude that the lines in the vicinity of the Ca II
8542 A line not only increase its sensitivity to the atmospheric parameters at
all layers, but also they constitute an excellent spectral window for
chromospheric polarimetry.Comment: 11 pages, 8 figures, 1 tabl
Constraining reionization using the thermal history of the baryons
The thermal evolution of the intergalactic medium (IGM) depends on the
reionization history of the universe. Numerical simulations indicate that the
low density IGM, which is responsible for the low column density Ly-alpha
forest, follows a well defined temperature-density relation. This results in a
cut-off in the distribution of line widths as a function of column density. We
use hydrodynamic simulations to calibrate the relation between the cut-off and
the temperature-density relation and apply this relation to Keck spectra
spanning a redshift range z=2-4.5. We find that the temperature peaks at z~3
and interpret this as evidence for reheating due to the reionization of helium.Comment: 4 pages, 2 figures, to appear in "Cosmic evolution and galaxy
formation: Structure, interactions, and feedback", eds. J. Franco et a
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