17,245 research outputs found
Space Flight LiDARs, Navigation & Science Instrument Implementations: Lasers, Optoelectronics, Integrated Photonics, Fiber Optic Subsystems and Components
For the past 25 years, the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center's Photonics Group in the Engineering Directorate has been substantially contributing to the flight design, development, production, testing and integration of many science and navigational instruments. The Moon to Mars initiative will rely heavily upon utilizing commercial technologies for instrumentation with aggressive schedule deadlines. The group has an extensive background in screening, qualifying, development and integration of commercial components for spaceflight applications. By remaining adaptable and employing a rigorous approach to component and instrument development, they have forged and fostered relationships with industry partners. They have been willing to communicate lessons learned in packaging, part construction, materials selection, testing, and other facets of the design and production process critical to implementation for high-reliability systems. As a result, this successful collaboration with industry vendors and component suppliers has enabled a history of mission success from the Moon to Mars (and beyond) while balancing cost, schedule, and risk postures. In cases where no commercial components exist, the group works closely with other teams at Goddard Space Flight Center and other NASA field centers to fabricate and produce flight hardware for science, remote sensing, and navigation applications. Summarized here is the last ten years of instrumentation development lessons learned and data collected from the subsystems down to the optoelectronic component level
The Formation of Large Galactic Disks: Revival or Survival?
Using the deepest and the most complete set of observations of distant
galaxies, we investigate how extended disks could have formed. Observations
include spatially-resolved kinematics, detailed morphologies and photometry
from UV to mid-IR. Six billion years ago, half of the present-day spiral
progenitors had anomalous kinematics and morphologies, as well as relatively
high gas fractions. We argue that gas-rich major mergers, i.e., fusions between
gas-rich disk galaxies of similar mass, can be the likeliest driver for such
strong peculiarities. This suggests a new channel of disk formation, e.g. many
disks could be reformed after gas-rich mergers. This is found to be in perfect
agreement with predictions from the state-of-the-art LCDM semi-empirical
models: due to our sensitivity in detecting mergers at all phases, from pairs
to relaxed post-mergers, we find a more accurate merger rate. The scenario can
be finally confronted to properties of nearby galaxies, including M31 and
galaxies showing ultra-faint, gigantic structures in their haloes.Comment: Proceedings of the annual meeting of the French Astronomical Society,
2011, 6 pages, 1 Figur
Mesoscopic circuits with charge discreteness:quantum transmission lines
We propose a quantum Hamiltonian for a transmission line with charge
discreteness. The periodic line is composed of an inductance and a capacitance
per cell. In every cell the charge operator satisfies a nonlinear equation of
motion because of the discreteness of the charge. In the basis of one-energy
per site, the spectrum can be calculated explicitly. We consider briefly the
incorporation of electrical resistance in the line.Comment: 11 pages. 0 figures. Will be published in Phys.Rev.
Insectos plaga del arroz en Loreto, Amazonia peruana
The rice is extensively cultivated on the bank of the Ucayali River in the Peruvian Amazonia. Some plantations have been visited and sampled to make an inventory of the phytofagous insects of this crop. Fifteen species of pests of rice are reported. Three of them are considered as potentially dangerous for the rice in this region : #Diatraea saccharalis F., #Oebaleus poecilus Dallas and #Tibraca limbativentris$ Stal. (Résumé d'auteur
Law, Liberty and the Rule of Law (in a Constitutional Democracy)
In the hunt for a better--and more substantial--awareness of the “law,” The author intends to analyze the different notions related to the “rule of law” and to criticize the conceptions that equate it either to the sum of “law” and “rule” or to the formal assertion that “law rules,” regardless of its relationship to certain principles, including both “negative” and “positive” liberties. Instead, he pretends to scrutinize the principles of the “rule of law,” in general, and in a “constitutional democracy,” in particular, to conclude that the tendency to reduce the “democratic principle” to the “majority rule” (or “majority principle”), i.e. to whatever pleases the majority, as part of the “positive liberty,” is contrary both to the “negative liberty” and to the “rule of law” itself
Galaxy disks do not need to survive in the L-CDM paradigm: the galaxy merger rate out to z~1.5 from morpho-kinematic data
About two-thirds of present-day, large galaxies are spirals such as the Milky
Way or Andromeda, but the way their thin rotating disks formed remains
uncertain. Observations have revealed that half of their progenitors, six
billion years ago, had peculiar morphologies and/or kinematics, which exclude
them from the Hubble sequence. Major mergers, i.e., fusions between galaxies of
similar mass, are found to be the likeliest driver for such strong
peculiarities. However, thin disks are fragile and easily destroyed by such
violent collisions, which creates a critical tension between the observed
fraction of thin disks and their survival within the L-CDM paradigm. Here we
show that the observed high occurrence of mergers amongst their progenitors is
only apparent and is resolved when using morpho-kinematic observations which
are sensitive to all the phases of the merging process. This provides an
original way of narrowing down observational estimates of the galaxy merger
rate and leads to a perfect match with predictions by state-of-the-art L-CDM
semi-empirical models with no particular fine-tuning needed. These results
imply that half of local thin disks do not survive but are actually rebuilt
after a gas-rich major merger occurring in the past nine billion years, i.e.,
two-thirds of the lifetime of the Universe. This emphasizes the need to study
how thin disks can form in halos with a more active merger history than
previously considered, and to investigate what is the origin of the gas
reservoir from which local disks would reform.Comment: 19 pages, 7 figures, 2 tables. Accepted in ApJ. V2 to match proof
corrections and added reference
LSDA+U approximation-based analysis of the electronic estructure of CeFeGe3
We perform ab initio electronic structure calculations of the intermetallic
compound CeFeGe3 by means of the Tight Binding Linear Muffin-Tin
Orbitals-Atomic Sphere Approximation (TB-LMTO-ASA) within the Local Spin
Density Approximation containing the so-called Hubbard correction term
(LSDA+U^SIC), using the Sttutgart's TB (Tight Binding)-LMTO-ASA code in the
framework of the Density Funcional Theory (DFT).Comment: 12 pages 8 figures, submitted to Int. J. Modern Phys.
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