10,203 research outputs found
Absorption Line Studies in the Halo
Significant progress has been made over the last few years to explore the
gaseous halo of the Milky Way by way of absorption spectroscopy. I review
recent results on absorption line studies in the halo using various
instruments, such as the Far Ultraviolet Spectroscopic Explorer, the Space
Telescope Imaging Spectrograph, and others. The new studies imply that the
infall of low-metallicity gas, the interaction with the Magellanic Clouds, and
the Galactic Fountain are responsible for the phenomenon of the intermediate-
and high-velocity clouds in the halo. New measurements of highly-ionized gas in
the vicinity of the Milky Way indicate that these clouds are embedded in a
corona of hot gas that extends deep into the intergalactic space.Comment: 7 pages, 1 figure; Invited review at the conference "How does the
Galaxy work ?", Granada/Spain, June 200
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TLR induces reorganization of the IgM-BCR complex regulating murine B-1 cell responses to infections.
In mice, neonatally-developing, self-reactive B-1 cells generate steady levels of natural antibodies throughout life. B-1 cells can, however, also rapidly respond to infections with increased local antibody production. The mechanisms regulating these two seemingly very distinct functions are poorly understood, but have been linked to expression of CD5, an inhibitor of BCR-signaling. Here we demonstrate that TLR-mediated activation of CD5+ B-1 cells induced the rapid reorganization of the IgM-BCR complex, leading to the eventual loss of CD5 expression, and a concomitant increase in BCR-downstream signaling, both in vitro and in vivo after infections of mice with influenza virus and Salmonella typhimurium. Both, initial CD5 expression and TLR-mediated stimulation, were required for the differentiation of B-1 cells to IgM-producing plasmablasts after infections. Thus, TLR-mediated signals support participation of B-1 cells in immune defense via BCR-complex reorganization
Calibration of the LIGO displacement actuators via laser frequency modulation
We present a frequency modulation technique for calibration of the
displacement actuators of the LIGO 4-km-long interferometric gravitational-wave
detectors. With the interferometer locked in a single-arm configuration, we
modulate the frequency of the laser light, creating an effective length
variation that we calibrate by measuring the amplitude of the frequency
modulation. By simultaneously driving the voice coil actuators that control the
length of the arm cavity, we calibrate the voice coil actuation coefficient
with an estimated 1-sigma uncertainty of less than one percent. This technique
enables a force-free, single-step actuator calibration using a displacement
fiducial that is fundamentally different from those employed in other
calibration methods.Comment: 10 pages, 5 figures, submitted to Classical and Quantum Gravit
O cenário da licenciatura nos Estados Unidos: implicações potenciais para a arte-educação no Brasil
Two scholars from the United States that work in art education programs speak to current issues resulting from the recent policies that have had direct impact on undergraduate courses, fieldwork, licensure and teacher retention. The study is informed by one author’s understanding of Brazilian art education through both experiential learning and focused research via comparative studies. The authors provide a contextual framing of the current educational landscape in the states with the intent of informing readers of trends that could have similar negative effects on licensure in Brazil. Finally, the authors will share some strategies they have implemented to respond to these challenges.Dois professores dos Estados Unidos que trabalham em programas de arte educação falam de questões atuais decorrentes das recentes polÃticas que tiveram impacto direto sobre cursos de graduação, trabalho de campo, licenciatura e retenção de professores. O estudo é apresentado a partir da compreensão de um dos autores sobre a arte educação brasileira, através da aprendizagem experiencial e da pesquisa por meio de estudos comparativos. Os autores fornecem um enquadramento contextual do cenário educacional atual nos Estados com a intenção de informar os leitores de tendências que podem ter efeitos negativos semelhantes nas licenciaturas no Brasil. Por fim, os autores compartilham algumas estratégias que implementaram para responder aos desafios pontuados
GHRS and ORFEUS-II Observations of the Highly Ionized Interstellar Medium Toward ESO141-055
We present Goddard High Resolution Spectrograph and ORFEUS-II measurements of
Si IV, CIV, N V, and O VI absorption in the interstellar medium of the Galactic
disk and halo toward the nucleus of the Seyfert galaxy ESO141-055. The high
ionization absorption is strong, with line strengths consistent with the
spectral signature expected for hot (log T = 5-6) collisionally ionized gas in
either a ``Galactic fountain'' or an inhomogeneous medium containing a mixture
of conductive interfaces and turbulent mixing layers. The total O VI column
density of log N ~ 15 suggests that the scale height of O VI is large (>3 kpc)
in this direction. Comparison of the high ion column densities with
measurements for other sight lines indicates that the highly ionized gas
distribution is patchy. The amount of O VI perpendicular to the Galactic plane
varies by at least a factor of ~4 among the complete halo sight lines thus far
studied. In addition to the high ion absorption, lines of low ionization
species are also present in the spectra. With the possible exception of Ar I,
which may have a lower than expected abundance resulting from partial
photoionization of gas along the sight line, the absorption strengths are
typical of those expected for the warm, neutral interstellar medium. The sight
line intercepts a cold molecular cloud with log N(H2) ~ 19. The cloud has an
identifiable counterpart in IRAS 100-micron emission maps of this region of the
sky. We detect a Ly-alpha absorber associated with ESO141-055 at z = 0.03492.
This study presents an enticing glimpse into the interstellar and intergalactic
absorption patterns that will be observed at high spectral resolution by the
Far Ultraviolet Spectroscopic Explorer.Comment: 24 pages + 8 figures, uses aaspp4.sty. Accepted for publication in
Ap
Tooth Contact Shift in Loaded Spiral Bevel Gears
An analytical method is presented to predict the shifts of the contact ellipses of spiral bevel gear teeth under load. The contact ellipse shift is the motion of the tooth contact position from the ideal pitch point to its location under load. The shifts are due to the elastic motions of the gear and pinion supporting shafts and bearings. The calculations include the elastic deflections of the gear shafts and the deflections of the four shaft bearings. The method assumes that the surface curvature of each tooth is constant near the unloaded pitch point. Results from these calculations will help designers reduce transmission weight without seriously reducing transmission performance
Spatial and temporal filtering of a 10-W Nd:YAG laser with a Fabry-Perot ring-cavity premode cleaner
We report on the use of a fixed-spacer Fabry–Perot ring cavity to filter spatially and temporally a 10-W laser-diode-pumped Nd:YAG master-oscillator power amplifier. The spatial filtering leads to a 7.6-W TEMinfinity beam with 0.1% higher-order transverse mode content. The temporal filtering reduces the relative power fluctuations at 10 MHz to 2.8 x 10^-/sqrtHz, which is 1 dB above the shot-noise limit for 50 mA of detected photocurrent
Stabilized high-power laser system for the gravitational wave detector advanced LIGO
An ultra-stable, high-power cw Nd:YAG laser system, developed for the ground-based gravitational wave detector Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory), was comprehensively characterized. Laser power, frequency, beam pointing and beam quality were simultaneously stabilized using different active and passive schemes. The output beam, the performance of the stabilization, and the cross-coupling between different stabilization feedback control loops were characterized and found to fulfill most design requirements. The employed stabilization schemes and the achieved performance are of relevance to many high-precision optical experiments
Flavor changing interactions mediated by scalars at the weak scale
The quark and lepton mass matrices possess approximate flavor symmetries.
Several results follow if the interactions of new scalars possess these
approximate symmetries. Present experimental bounds allow these exotic scalars
to have a weak scale mass. The Glashow-Weinberg criterion is rendered
unnecessary. Finally, rare leptonic B meson decays provide powerful probes of
these scalars, especially if they are leptoquarks.Comment: 13 pages, report LBL-3234
Stabilized lasers for advanced gravitational wave detectors
Second generation gravitational wave detectors require high power lasers with more than 100 W of output power and with very low temporal and spatial fluctuations. To achieve the demanding stability levels required, low noise techniques and adequate control actuators have to be part of the high power laser design. In addition feedback control and passive noise filtering is used to reduce the fluctuations in the so-called prestabilized laser system (PSL). In this paper, we discuss the design of a 200 W PSL which is under development for the Advanced LIGO gravitational wave detector and will present the first results. The PSL noise requirements for advanced gravitational wave detectors will be discussed in general and the stabilization scheme proposed for the Advanced LIGO PSL will be described
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