35,803 research outputs found
Local Spin-Gauge Symmetry of the Bose-Einstein Condensates in Atomic Gases
The Bose-Einstein condensates of alkali atomic gases are spinor fields with
local ``spin-gauge" symmetry. This symmetry is manifested by a superfluid
velocity (or gauge field) generated by the Berry phase of the
spin field. In ``static" traps, splits the degeneracy of the
harmonic energy levels, breaks the inversion symmetry of the vortex nucleation
frequency , and can lead to {\em vortex ground states}. The
inversion symmetry of , however, is not broken in ``dynamic"
traps. Rotations of the atom cloud can be generated by adiabatic effects
without physically rotating the entire trap.Comment: Typos in the previous version corrected, thanks to the careful
reading of Daniel L. Cox. 13 pages + 2 Figures in uuencode + gzip for
Remote measurement utilizing NASA's scanning laser Doppler systems. Volume 2: Laser Doppler dust devil velocity profile measurement program
The first detailed velocity profile data on thermally induced dust vortices are presented. These dust devils will be analyzed and studied to determine their flow fields and origin in an effort to correlate this phenomena with the generation and characteristics of tornadoes. A continuing effort to increase mankind's knowledge of vortex and other meteorological phenomena will hopefully allow the prediction of tornado occurrence, their path, and perhaps eventually even lead to some technique for their destruction
VLBA Polarization Observations of Markarian 421 After a Gamma-Ray High State
We present four high dynamic range, dual-circular polarization, Very Long
Baseline Array (VLBA) observations at 22 GHz of Markarian 421, taken throughout
the year following the source's unprecedented gamma-ray high state in early
2001. These four new VLBA observations are combined with data from our earlier
1999 paper and archival VLBA data-sets that have become available since 1999 to
produce a combined 28 epoch VLBA data-set on Mrk 421 spanning the years 1994 to
2002. No new component associated with the 2001 flares was seen on the total
intensity images, but the combined data-set allowed precise measurements of the
apparent speeds of the existing components. The peak measured apparent speed
was for component C5, which has an apparent speed of 0.1 +/- 0.02 c (H_0=71 km
s^{-1} Mpc^{-1}, Omega_m=0.27, and Omega_Lambda=0.73). No counterjet is seen
with a limit on the jet to counterjet brightness ratio J >~ 100. These observed
VLBI properties of Markarian 421 are consistent with a jet with a bulk Lorentz
factor of about 2 and an angle to the line-of-sight of about 1 degree,
suggesting a jet that decelerates between the gamma-ray producing region and
the parsec scale. The VLBI core and inner jet (component C7) have fractional
polarizations of about 5%, and an electric vector position angle (EVPA) aligned
with the jet axis. Component C5 (at 1.5 mas from the core) has a higher
fractional polarization of about 15%, and an EVPA nearly orthogonal to the jet
axis. Significant variability is detected in the EVPA of component C6, which at
two of the four epochs shows an EVPA aligned with the jet axis, possibly a sign
of propagating disturbances that are only visible on the polarization images.
If these propagating disturbances are linked to the 2001 gamma-ray high state,
then their inferred apparent speed is between 1 and 3 c.Comment: 11 pages, accepted to Ap
Remote measurement utilizing NASA's scanning laser Doppler systems. Volume 1. Laser Doppler wake vortex tracking at Kennedy Airport
Test operations of the Scanning Laser Doppler System (SLDS) at Kennedy International Airport (KIA) during August 1974 through June 1975 are reported. A total of 1,619 data runs was recorded with a totally operational system during normal landing operations at KIA. In addition, 53 data runs were made during cooperative flybys with the C880 for a grand total of 1672 recorded vortex tracks. Test crews were in attendance at KIA for 31 weeks, of which 25 weeks were considered operational and the other six were packing, unpacking, setup and check out. Although average activity equates to 67 recorded landing operations per week, two periods of complete runway inactivity spanned 20 days and 13 days, respectively. The operation frequency therefore averaged about 88 operations per week
End to end distance on contour loops of random gaussian surfaces
A self consistent field theory that describes a part of a contour loop of a
random Gaussian surface as a trajectory interacting with itself is constructed.
The exponent \nu characterizing the end to end distance is obtained by a Flory
argument. The result is compared with different previuos derivations and is
found to agree with that of Kondev and Henley over most of the range of the
roughening exponent of the random surface.Comment: 7 page
Designing a mobile augmented memory system for people with traumatic brain injuries
Augmented memory systems help people remember events in their lives. Individuals with Traumatic Brain Injury (TBI) often have memory impairments. We conducted a user study to learn about strategies individuals with TBI use to remember events in their lives. We explored what characteristics individuals with TBI expect of an augmented memory system. We then investigated these aspects in an initial mobile app design, and propose here a concept for a rehearsal application that addresses the issues found in our studies
Historical black carbon deposition in the Canadian High Arctic: a >250-year long ice-core record from Devon Island
Black carbon aerosol (BC), which is emitted from natural and anthropogenic sources (e.g., wildfires, coal burning), can contribute to magnify climate warming at high latitudes by darkening snow- and ice-covered surfaces, and subsequently lowering their albedo. Therefore, modeling the atmospheric transport and deposition of BC to the Arctic is important, and historical archives of BC accumulation in polar ice can help to validate such modeling efforts. Here we present a >250-year ice-core record of refractory BC (rBC) deposition on Devon ice cap, Canada, spanning the years from 1735 to 1992. This is the first such record ever developed from the Canadian Arctic. The estimated mean deposition flux of rBC on Devon ice cap for 1963-1990 is 0.2mg m-2a-1, which is at the low end of estimates from Greenland ice cores obtained using the same analytical method ( g1/4 0.1-4mg m-2a-1). The Devon ice cap rBC record also differs from the Greenland records in that it shows only a modest increase in rBC deposition during the 20th century. In the Greenland records a pronounced rise in rBC is observed from the 1880s to the 1910s, which is largely attributed to midlatitude coal burning emissions. The deposition of contaminants such as sulfate and lead increased on Devon ice cap in the 20th century but no concomitant rise in rBC is recorded in the ice. Part of the difference with Greenland could be due to local factors such as melt-freeze cycles on Devon ice cap that may limit the detection sensitivity of rBC analyses in melt-impacted core samples, and wind scouring of winter snow at the coring site. Air back-trajectory analyses also suggest that Devon ice cap receives BC from more distant North American and Eurasian sources than Greenland, and aerosol mixing and removal during long-range transport over the Arctic Ocean likely masks some of the specific BC source-receptor relationships. Findings from this study suggest that there could be a large variability in BC aerosol deposition across the Arctic region arising from different transport patterns. This variability needs to be accounted for when estimating the large-scale albedo lowering effect of BC deposition on Arctic snow/ice
Extraction efficiency of drifting electrons in a two-phase xenon time projection chamber
We present a measurement of the extraction efficiency of quasi-free electrons
from the liquid into the gas phase in a two-phase xenon time-projection
chamber. The measurements span a range of electric fields from 2.4 to 7.1 kV/cm
in the liquid xenon, corresponding to 4.5 to 13.1 kV/cm in the gaseous xenon.
Extraction efficiency continues to increase at the highest extraction fields,
implying that additional charge signal may be attained in two-phase xenon
detectors through careful high-voltage engineering of the gate-anode region
Edaq530: a transparent, open-end and open-source measurement solution in natural science education
We present Edaq530, a low-cost, compact and easy-to-use digital measurement
solution consisting of a thumb-sized USB-to-sensor interface and a measurement
software. The solution is fully open-source, our aim being to provide a viable
alternative to professional solutions. Our main focus in designing Edaq530 has
been versatility and transparency. In this paper, we shall introduce the
capabilities of Edaq530, complement it by showing a few sample experiments, and
discuss the feedback we have received in the course of a teacher training
workshop in which the participants received personal copies of Edaq530 and
later made reports on how they could utilise Edaq530 in their teaching
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