16,144 research outputs found
The hypersensitization of sixteen millimeter black and white motion picture film by pre-exposure to light.
Thesis (M.S.)--Boston Universit
Bistability and instability of dark-antidark solitons in the cubic-quintic nonlinear Schroedinger equation
We characterize the full family of soliton solutions sitting over a
background plane wave and ruled by the cubic-quintic nonlinear Schroedinger
equation in the regime where a quintic focusing term represents a saturation of
the cubic defocusing nonlinearity. We discuss existence and properties of
solitons in terms of catastrophe theory and fully characterize bistability and
instabilities of the dark-antidark pairs, revealing new mechanisms of decay of
antidark solitons.Comment: 8 pages, 10 figures, accepted in PR
HST Star Counts at High Galactic Latitudes
We use star counts from 13 deep HST fields imaged with the {\it Wide Field
Camera - 2} in order to constrain the amount of dark matter in the Galaxy that
can be in the form of low-mass main sequence stars or white-dwarfs. Based on
the number of red stars found in our fields, we exclude the possibility that
more than 25\% of the massive dark halo is made up of M dwarfs or subdwarfs;
fairly massive () and yet extremely faint ( \gtsima
) stellar candidates would have to be invoked in order to make the
observed number of stars compatible with that predicted by a stellar dark halo.
White dwarfs must also be intrinsically very faint ( \gtsima ) in
order to be consistent with the observed number of faint stars in the HST
fields. We also rule out an increasing or flat stellar luminosity function
beyond . The inferred slope of the disk luminosity function is
intermediary between local, volume-limited surveys and ground-based photometric
ones. Finally, the magnitude counts are well fitted by existing models for the
structure of the Galaxy, with only small changes in the fiducial values of the
model parameters. The colour distribution, however, is not well reproduced by
the models. It is unclear at present if this reflects inadequacies of the
available models or uncertainties in the colour-magnitude diagrams for low
metallicity stars and in the photometric calibration.Comment: 18 pages plus 6 figure
Connections of the Mesencephalic Locomotor Region (MLR) in the Cat
The cat entopeduncular nucleus (EN), which is the main output of the basal ganglia, is known to project to the mesencephalic tegmentum. We have been able to elicit antidromic responses in single EN neurons from the region of the mesencephalic locomotor region (MLR), then transect (precollicular-postmamillary) the brainstem and elicit rhythmic movements of the limbs by stimulation of the same site in the same animal. Injections of the fluorescent dye 2,4 diamidino phenylindole 2 HCL (DAPI) into this area induces retrograde labeling of cell bodies in EN and motor cortex. Injections of a tritiated amino acid (leucine) into the motor cortex induce terminal labeling in the area of the MLR. These studies describe convergent projections from EN and motor cortex to the MLR. These connections may be involved in the sequencing and ordering of voluntary movements in which locomotion is necessary
Generalized coherent states are unique Bell states of quantum systems with Lie group symmetries
We consider quantum systems, whose dynamical symmetry groups are semisimple
Lie groups, which can be split or decay into two subsystems of the same
symmetry. We prove that the only states of such a system that factorize upon
splitting are the generalized coherent states. Since Bell's inequality is never
violated by the direct product state, when the system prepared in the
generalized coherent state is split, no quantum correlations are created.
Therefore, the generalized coherent states are the unique Bell states, i.e.,
the pure quantum states preserving the fundamental classical property of
satisfying Bell's inequality upon splitting.Comment: 4 pages, REVTeX, amssymb style. More information on
http://www.technion.ac.il/~brif/science.htm
Eyeballs, soundbites and plings: understanding participation and engagement in the Cultural Olympiad
HST Observations of the Field Star Population in the Large Magellanic Cloud
We present and photometry, obtained with the Hubble Space Telescope,
for stars in a field in the inner disk of the Large Magellanic
Cloud. We confirm previous results indicating that an intense star formation
event, probably corresponding to the formation of the LMC disk, occurred a few
times years ago. We find a small but real difference between our field
and one further out in the disk observed by Gallagher et al (1996): either star
formation in the inner disk commenced slightly earlier, or the stars are
slightly more metal rich. We also find evidence for a later burst, around 1 Gyr
ago, which may correspond to the formation of the LMC bar. About 5% of the
stars in our field are substantially older than either burst, and are probably
members of an old disk or halo population with age Gyr.Comment: 18 pages, 7 figures: only 3 available ellectronically - complete
copies by request from [email protected]
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