5,975 research outputs found
Proposed magneto-electrostatic ring trap for neutral atoms
We propose a novel trap for confining cold neutral atoms in a microscopic
ring using a magneto-electrostatic potential. The trapping potential is derived
from a combination of a repulsive magnetic field from a hard drive atom mirror
and the attractive potential produced by a charged disk patterned on the hard
drive surface. We calculate a trap frequency of [29.7, 42.6, 62.8] kHz and a
depth of [16.1, 21.8, 21.8] MHz for [133Cs, 87Rb, 40K], and discuss a simple
loading scheme and a method for fabrication. This device provides a
one-dimensional potential in a ring geometry that may be of interest to the
study of trapped quantum degenerate one-dimensional gases.Comment: 4 pages, 2 figures; revised, including new calculations and further
discussio
Analytical and experimental studies of acoustic performance of segmented liners in a compressor inlet
The performance of axially segmented (phased) acoustic treatment liners in the inlet of a compressor was investigated. Topics discussed include: (1) the validation of a theoretical procedure to predict propagation and suppression characteristics of duct liners; (2) the in-duct measurement of spinning modes; (3) investigation of phased treatment designs; (4) high Mach inlet acoustic tests; and (5) an experimental investigation of inlet turbulence. The analytical prediction for the multi-segmented treatment was found to provide the correct order of magnitude of suppression and was generally within 50% of that determined experimentally. Refinements required to improve the correlation are identified. Suppression due to high subsonic Mach number flow effects was found to become significant above an average throat Mach number of 0.65 to 0.7 and 20 PNdB was achieved with an average throat Mach number in the range of 0.80 to 0.85. For the measured turbulence in the inlet, including the axial and circumferential turbulence intensities and the axial integral length scale, data are presented with and without an inlet screen showing that the screen reduced the turbulence intensities and that the BPF noise was reduced as a consequence
Resonant enhancement of ultracold photoassociation rate by electric field induced anisotropic interaction
We study the effects of a static electric field on the photoassociation of a
heteronuclear atom-pair into a polar molecule. The interaction of permanent
dipole moment with a static electric field largely affects the ground state
continuum wave function of the atom-pair at short separations where
photoassociation transitions occur according to Franck-Condon principle.
Electric field induced anisotropic interaction between two heteronuclear ground
state atoms leads to scattering resonances at some specific electric fields.
Near such resonances the amplitude of scattering wave function at short
separation increases by several orders of magnitude. As a result,
photoaasociation rate is enhanced by several orders of magnitude near the
resonances. We discuss in detail electric field modified atom-atom scattering
properties and resonances. We calculate photoassociation rate that shows giant
enhancement due to electric field tunable anisotropic resonances. We present
selected results among which particularly important are the excitations of
higher rotational levels in ultracold photoassociation due to electric field
tunable resonances.Comment: 14 pages,9 figure
The Effects of Choice on Assignment Completion and Percent Correct by a High School Student with a Learning Disability
The effects of choosing between two academic assignments on task completion and percent correct by a ninth grade student with a learning disability was investigated. This case study extended the efficacy of antecedent based intervention as an instructional modification. Further, the study extends previous research by investigating the effect of choice on academic achievement. The withdrawal design showed that percent completed and correct were highest when the participant was given a choice between two assignments when compared to baseline conditions. Results are discussed in term of efficacy of choice as an antecedent intervention, choice selection, and future research directions
Design point study of auxiliary airbreathing engines for a space shuttle
Design analysis of auxiliary air breathing engines for space shuttle
Correlative Microscopy of Morphology and Luminescence of Cu porphyrin aggregates
Transfer of energy and information through molecule aggregates requires as
one important building block anisotropic, cable-like structures. Knowledge on
the spatial correlation of luminescence and morphology represents a
prerequisite in the understanding of internal processes and will be important
for architecting suitable landscapes. In this context we study the morphology,
fluorescence and phosphorescence of molecule aggregate structures on surfaces
in a spatially correlative way. We consider as two morphologies, lengthy
strands and isotropic islands. It turns out that phosphorescence is quite
strong compared to fluorescence and the spatial variation of the observed
intensities is largely in line with the amount of dye. However in proportion,
the strands exhibit more fluorescence than the isotropic islands suggesting
weaker non-radiative channels. The ratio fluorescence to phosphorescence
appears to be correlated with the degree of aggregation or internal order. The
heights at which luminescence saturates is explained in the context of
attenuation and emission multireflection, inside the dye. This is supported by
correlative photoemission electron microscopy which is more sensitive to the
surface region. The lengthy structures exhibit a pronounced polarization
dependence of the luminescence with a relative dichroism up to about 60%,
revealing substantial perpendicular orientation preference of the molecules
with respect to the substrate and parallel with respect to the strands
VLT Observations of Turnoff stars in the Globular Cluster NGC 6397
VLT-UVES high resolution spectra of seven turnoff stars in the metal-poor
globular cluster NGC 6397 have been obtained. Atmospheric parameters and
abundances of several elements (Li, Na, Mg, Ca, Sc, Ti, Cr, Fe, Ni, Zn and Ba)
were derived for program stars. The mean iron abundance is [Fe/H] = -2.02, with
no star-to-star variation. The mean abundances of the alpha-elements (Ca, Ti)
and of the iron-peak elements (Sc, Cr, Ni) are consistent with abundances
derived for field stars of similar metallicity. Magnesium is also almost solar,
consistent with the values found by Idiart & Th\'evenin (2000) when non-LTE
effects (NLTE hereafter) are taken into account. The sodium abundance derived
for five stars is essentially solar, but one object (A447) is clearly Na
deficient. These results are compatible with the expected abundance range
estimated from the stochastic evolutionary halo model by Argast et al. (2000)
when at the epoch of [Fe/H] -2 the interstellar medium is supposed to
become well-mixed.Comment: to appear in A&
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The Abundances Of Neutron-Capture Species In The Very Metal-Poor Globular Cluster M15: A Uniform Analysis Of Red Giant Branch And Red Horizontal Branch Stars
The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Delta(RHB-RGB) approximate to 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.National Science Foundation AST 07-07447, AST 09-08978Astronom
Hot Gas Structure in the Elliptical Galaxy NGC 4472
We present X-ray spectroscopic and morphological analyses using Chandra ACIS
and ROSAT observations of the giant elliptical galaxy NGC 4472 in the Virgo
cluster. We discuss previously unobserved X-ray structures within the extended
galactic corona. In the inner 2' of the galaxy, we find X-ray holes or cavities
with radii of ~2 kpc, corresponding to the position of radio lobes. These holes
were produced during a period of nuclear activity that began 1.2 x 10^7 years
ago and may be ongoing. We also find an asymmetrical edge in the galaxy X-ray
emission 3' (14 kpc) northeast of the core and an ~8' tail (36 kpc) extending
southwest of the galaxy. These two features probably result from the
interaction of NGC 4472 gas with the Virgo gas, which produces compression in
the direction of NGC 4472's infall and an extended tail from ram pressure
stripping. Assuming the tail is in pressure equilibrium with the surrounding
gas, we compute its angle to our line of sight and estimate that its true
extent exceeds 100 kpc. Finally, in addition to emission from the nucleus
(first detected by Soldatenkov, Vikhlinin & Pavlinsky), we detect two small
extended sources within 10'' of the nucleus of the galaxy, both of which have
luminosities of ~7 x 10^38 erg/s.Comment: 25 pages, 11 figures, accepted by Ap
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