10,843 research outputs found
Detection of H-alpha emission from the Magellanic Stream: evidence for an extended gaseous Galactic halo
We have detected faint, diffuse H\alpha emission of surface brightness Rayleighs, R, and R respectively,
corresponding to emission measures of 1.0 to 0.5 \cmsixpc. We have observed
several positions near the MS IV concentration, and find that the strongest
emission is on the sharp leading-edge density gradient. There is less emission
at points away from the gradient, and halfway between MS III and MS IV the
H< 0.04\alpha emission at cloud leading edges to heating of the
Stream clouds by ram pressure from ionized gas in the halo of the Galaxy. These
observations suggest that ram pressure from halo gas plays a large role in
stripping the Stream out of the Magellanic Clouds. They also suggest the
presence of a relatively large density of gas, , in the Galactic halo at kpc radius, and far above the
Galactic plane, . This implies that the Galaxy has a very large
baryonic, gaseous extent, and supports models of Lyman-$\alpha and metal-line
QSO absorption lines in which the absorption systems reside in extended
galactic halos.Comment: 15 pages, aaspp latex, + 1 table & 3 figures. Accepted in A.J. Also
available from http://www.physics.rutgers.edu/~bweiner/astro/papers
Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance
We demonstrate control of the collapse and expansion of an 88Sr Bose-Einstein
condensate using an optical Feshbach resonance (OFR) near the 1S0-3P1
intercombination transition at 689 nm. Significant changes in dynamics are
caused by modifications of scattering length by up to +- ?10a_bg, where the
background scattering length of 88Sr is a_bg = -2a0 (1a0 = 0.053 nm). Changes
in scattering length are monitored through changes in the size of the
condensate after a time-of-flight measurement. Because the background
scattering length is close to zero, blue detuning of the OFR laser with respect
to a photoassociative resonance leads to increased interaction energy and a
faster condensate expansion, whereas red detuning triggers a collapse of the
condensate. The results are modeled with the time-dependent nonlinear
Gross-Pitaevskii equation.Comment: 5 pages, 3 figure
Thin-Film Personal Communications and Telemetry System /TFPCTS/ Third quarterly report, 21 Jun. - 21 Sep. 1965
Thin film triode fabrication, metal base transistor, and circuit design for thin film personal communications and telemetry syste
Fine-Structure FeII* Emission and Resonant MgII Emission in z = 1 Star-Forming Galaxies
We present a study of the prevalence, strength, and kinematics of ultraviolet
FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected
from the DEEP2 survey. We find FeII* emission in composite spectra assembled on
the basis of different galaxy properties, indicating that FeII* emission is
prevalent at z = 1. In these composites, FeII* emission is observed at roughly
the systemic velocity. At z = 1, we find that the strength of FeII* emission is
most strongly modulated by dust attenuation, and is additionally correlated
with redshift, star-formation rate, and [OII] equivalent width, such that
systems at higher redshifts with lower dust levels, lower star-formation rates,
and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII
emission in at least 15% of the individual spectra and we find that objects
showing stronger MgII emission have higher specific star-formation rates,
smaller [OII] linewidths, larger [OII] equivalent widths, lower dust
attenuations, and lower stellar masses than the sample as a whole. MgII
emission strength exhibits the strongest correlation with specific
star-formation rate, although we find evidence that dust attenuation and
stellar mass also play roles in the regulation of MgII emission. Future
integral field unit observations of the spatial extent of FeII* and MgII
emission in galaxies with high specific star-formation rates, low dust
attenuations, and low stellar masses will be important for probing the
morphology of circumgalactic gas.Comment: 29 pages, 22 figures, 2 tables; accepted to Ap
Control of Raman Lasing in the Nonimpulsive Regime
We explore coherent control of stimulated Raman scattering in the
nonimpulsive regime. Optical pulse shaping of the coherent pump field leads to
control over the stimulated Raman output. A model of the control mechanism is
investigated.Comment: 4 pages, 5 figure
Surface wave generation and propagation on metallic subwavelength structures measured by far-field interferometry
Transmission spectra of metallic films or membranes perforated by arrays of
subwavelength slits or holes have been widely interpreted as resonance
absorption by surface plasmon polaritons (SPPs). Alternative interpretations
involving evanescent waves diffracted on the surface have also been proposed.
These two approaches lead to divergent predictions for some surface wave
properties. Using far-field interferometry, we have carried out a series of
measurements on elementary one-dimensional (1-D) subwavelength structures with
the aim of testing key properties of the surface waves and comparing them to
predictions of these two points of view
Homophilic Protocadherin Cell-Cell Interactions Promote Dendrite Complexity
SummaryGrowth of a properly complex dendrite arbor is a key step in neuronal differentiation and a prerequisite for neural circuit formation. Diverse cell surface molecules, such as the clustered protocadherins (Pcdhs), have long been proposed to regulate circuit formation through specific cell-cell interactions. Here, using transgenic and conditional knockout mice to manipulate γ-Pcdh repertoire in the cerebral cortex, we show that the complexity of a neuron’s dendritic arbor is determined by homophilic interactions with other cells. Neurons expressing only one of the 22 γ-Pcdhs can exhibit either exuberant or minimal dendrite complexity, depending only on whether surrounding cells express the same isoform. Furthermore, loss of astrocytic γ-Pcdhs, or disruption of astrocyte-neuron homophilic matching, reduces dendrite complexity cell non-autonomously. Our data indicate that γ-Pcdhs act locally to promote dendrite arborization via homophilic matching, and they confirm that connectivity in vivo depends on molecular interactions between neurons and between neurons and astrocytes
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