75,164 research outputs found
Internal electrostatic discharge hazard risk assessment to the Galileo orbiter
A worst case assessment was performed on the Command Data System (CDS) multilayer printed circuit board and an output power transformer module in the power subsystem. An estimate of the Jovian environment during the 35 hour orbit insertion was supplied by JPL and used as an input to calculate the electron transport into the Galileo components. A radiation shielding analysis computer code, CHARGE, calculated the electron transport deposition trapped in the anticipated sensitive areas of the multilayer board and transformer module. Based on these trapped charge calculations electric fields were calculated between the identified isolated areas and the spacecraft ground. The results of the assessment of electrostatic discharge (DSD) in the CDS multilayer printed circuit board indicate that the probability of ESD in the FR4 is low. The probability of ESD in the components attached to the multilayer board, however, is uncertain based on a lack of prior experimental data
Spin Effects in the Local Density of States of GaAs
We present spin-resolved measurements of the local density of states in Si
doped GaAs. Both spin components exhibit strong mesoscopic fluctuations. In the
magnetic quantum limit, the main features of the spin-up and spin-down
components of the local density of states are found to be identical apart from
Zeeman splitting. Based on this observation, we introduce a mesoscopic method
to measure the -factor in a material where macroscopic methods are severely
restricted by disorder. Differences between the spin-up and spin-down
components are discussed in terms of spin relaxation due to spin-orbit
coupling.Comment: 4 pages and 5 figure
Hourly Variability in Q0957+561
We have continued our effort to re-reduce archival Q0957+561 brightness
monitoring data and present results for 1629 R-band images using the methods
for galaxy subtraction and seeing correction reported previously. The new
dataset comes from 4 observing runs, several nights apiece, with sampling of
typically 5 minutes, which allows the first measurement of the structure
function for variations in the R-band from timescales of hours to years.
Comparison of our reductions to previous reductions of the same data, and to
r-band photometry produced at Apache Point Observatory shows good overall
agreement. Two of the data runs, separated by 417 days, permit a sharpened
value for the time delay of 417.4 days, valid only if the time delay is close
to the now-fashionable 417-day value; our data do not constrain a delay if it
is more than three days from this 417-day estimate. Our present results show no
unambiguous signature of the daily microlensing, though a suggestive feature is
found in the data. Both time delay measurement and microlensing searches suffer
from from the lack of sampling at half-day offsets, inevitable at a single
observatory, hence the need for round-the-clock monitoring with participation
by multiple observatories.Comment: AASTeX 4.0 preprint style, 21 pages, 8 EPS figure
Mobilities and Scattering Times in Decoupled Graphene Monolayers
Folded single layer graphene forms a system of two decoupled monolayers being
only a few Angstroms apart. Using magnetotransport measurements we investigate
the electronic properties of the two layers conducting in parallel. We show a
method to obtain the mobilities for the individual layers despite them being
jointly contacted. The mobilities in the upper layer are significantly larger
than in the bottom one indicating weaker substrate influence. This is confirmed
by larger transport and quantum scattering times in the top layer. Analyzing
the temperature dependence of the Shubnikov-de Haas oscillations effective
masses and corresponding Fermi velocities are obtained yielding reduced values
down to 66 percent in comparison to monolayers.Comment: 4 pages, 5 figure
Voltage-Controlled Spin Selection in a Magnetic Resonant Tunnelling Diode
We have fabricated all II-VI semiconductor resonant tunneling diodes based on
the (Zn,Mn,Be)Se material system, containing dilute magnetic material in the
quantum well, and studied their current-voltage characteristics. When subjected
to an external magnetic field the resulting spin splitting of the levels in the
quantum well leads to a splitting of the transmission resonance into two
separate peaks. This is interpreted as evidence of tunneling transport through
spin polarized levels, and could be the first step towards a voltage controlled
spin filter.Comment: To be published in Phys. Rev. Let
Observations of stratospheric source gas profiles during the Arctic winter
An international campaign was performed at ESRANGE rocket base, near Kiruna, Sweden (68 N) from January 4 to February 15 in order to investigate the Chemistry of Ozone in the Polar Stratosphere (CHEOPS). Within the framework of this campaign two sets of large stratospheric air samples were collected by means of a balloon borne cryogenic air sampler. The two balloons were launched on February 1, and February 10, 1988. At present the samples are analyzed in our laboratory for their contents of several long lived trace gases such as CH4, N2O, H2, CO2, CO and the major halocarbons CH3Cl, CFCl3, CF2Cl2, CCl4, CH3CCl3, and C2F3Cl3. The vertical profiles derived from these samples will be presented and compared with previous observations made in February 1987. The data will be discussed in view of the dynamical evolution of the Arctic polar vortex during this winter
Ionic polaron in a Bose-Einstein condensate
The ground state properties of a degenerate bosonic gas doped with an ion are
investigated by means of quantum Monte Carlo simulations in three dimensions.
The system features competing length and energy scales, which result in vastly
different polaronic properties compared to neutral quantum impurities.
Depending on whether a two-body bound state is supported or not by the atom-ion
potential, we identify a transition between a polaron regime amenable to a
perturbative treatment in the limit of weak atom-ion interactions and a
many-body bound state with vanishing quasi-particle residue composed of
hundreds of atoms. In order to analyze the structure of the corresponding
states we examine the atom-ion and atom-atom correlation functions. Our
findings are directly relevant to experiments using hybrid atom-ion setups that
have recently attained the ultracold regime.Comment: 11 pages, 6 figures, 1 tabl
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