7,790 research outputs found
Exploratory wind tunnel tests of a shock-swallowing air data sensor at a Mach number of approximately 1.83
The test probe was designed to measure free-stream Mach number and could be incorporated into a conventional airspeed nose boom installation. Tests were conducted in the Langley 4-by 4-foot supersonic pressure tunnel with an approximate angle of attack test range of -5 deg to 15 deg and an approximate angle of sideslip test range of + or - 4 deg. The probe incorporated a variable exit area which permitted internal flow. The internal flow caused the bow shock to be swallowed. Mach number was determined with a small axially movable internal total pressure tube and a series of fixed internal static pressure orifices. Mach number error was at a minimum when the total pressure tube was close to the probe tip. For four of the five tips tested, the Mach number error derived by averaging two static pressures measured at horizontally opposed positions near the probe entrance were least sensitive to angle of attack changes. The same orifices were also used to derive parameters that gave indications of flow direction
The Euphrosyne family's contribution to the low albedo near-Earth asteroids
The Euphrosyne asteroid family is uniquely situated at high inclination in
the outer Main Belt, bisected by the nu_6 secular resonance. This large, low
albedo family may thus be an important contributor to specific subpopulations
of the near-Earth objects. We present simulations of the orbital evolution of
Euphrosyne family members from the time of breakup to the present day, focusing
on those members that move into near-Earth orbits. We find that family members
typically evolve into a specific region of orbital element-space, with
semimajor axes near ~3 AU, high inclinations, very large eccentricities, and
Tisserand parameters similar to Jupiter family comets. Filtering all known NEOs
with our derived orbital element limits, we find that the population of
candidate objects is significantly lower in albedo than the overall NEO
population, although many of our candidates are also darker than the Euphrosyne
family, and may have properties more similar to comet nuclei. Followup
characterization of these candidates will enable us to compare them to known
family properties, and confirm which ones originated with the breakup of (31)
Euphrosyne.Comment: Accepted for publication in Ap
Domains of invasion organelle proteins from apicomplexan parasites are homologous with the Apple domains of blood coagulation factor XI and plasma pre-kallikrein and are members of the PAN module superfamily
AbstractMicronemes are specialised organelles, found in all apicomplexan parasites, which secrete molecules that are essential for parasite attachment to and invasion of host cells. Regions of several microneme proteins have sequence similarity to the Apple domains (A-domains) of blood coagulation factor XI (FXI) and plasma pre-kallikrein (PK). We have used mass spectrometry on a recombinant-expressed, putative A-domain from the microneme protein EtMIC5 from Eimeria tenella, to demonstrate that three intramolecular disulphide bridges are formed. These bridges are analogous to those that stabilise A-domains in FXI and PK. The data confirm that the apicomplexan domains are structural homologues of A-domains and are therefore novel members of the PAN module superfamily, which also includes the N-terminal domains of members of the plasminogen/hepatocyte growth factor family. The role of A-domains/PAN modules in apicomplexan parasites is not known, but their presence in the microneme suggests that they may be important for mediating protein–protein or protein–carbohydrate interactions during parasite attachment and host cell invasion
Trapping Ultracold Atoms in a Time-Averaged Adiabatic Potential
We report the first experimental realization of ultracold atoms confined in a
time-averaged, adiabatic potential (TAAP). This novel trapping technique
involves using a slowly oscillating ( kHz) bias field to time-average the
instantaneous potential given by dressing a bare magnetic potential with a high
frequency ( MHz) magnetic field. The resultant potentials provide a
convenient route to a variety of trapping geometries with tunable parameters.
We demonstrate the TAAP trap in a standard time-averaged orbiting potential
trap with additional Helmholtz coils for the introduction of the radio
frequency dressing field. We have evaporatively cooled 5 atoms of
Rb to quantum degeneracy and observed condensate lifetimes of over
\unit[3]{s}.-Comment: 4 pages, 6 figure
MAESTRO, CASTRO, and SEDONA -- Petascale Codes for Astrophysical Applications
Performing high-resolution, high-fidelity, three-dimensional simulations of
Type Ia supernovae (SNe Ia) requires not only algorithms that accurately
represent the correct physics, but also codes that effectively harness the
resources of the most powerful supercomputers. We are developing a suite of
codes that provide the capability to perform end-to-end simulations of SNe Ia,
from the early convective phase leading up to ignition to the explosion phase
in which deflagration/detonation waves explode the star to the computation of
the light curves resulting from the explosion. In this paper we discuss these
codes with an emphasis on the techniques needed to scale them to petascale
architectures. We also demonstrate our ability to map data from a low Mach
number formulation to a compressible solver.Comment: submitted to the Proceedings of the SciDAC 2010 meetin
Asteroid family identification using the Hierarchical Clustering Method and WISE/NEOWISE physical properties
Using albedos from WISE/NEOWISE to separate distinct albedo groups within the
Main Belt asteroids, we apply the Hierarchical Clustering Method to these
subpopulations and identify dynamically associated clusters of asteroids. While
this survey is limited to the ~35% of known Main Belt asteroids that were
detected by NEOWISE, we present the families linked from these objects as
higher confidence associations than can be obtained from dynamical linking
alone. We find that over one-third of the observed population of the Main Belt
is represented in the high-confidence cores of dynamical families. The albedo
distribution of family members differs significantly from the albedo
distribution of background objects in the same region of the Main Belt, however
interpretation of this effect is complicated by the incomplete identification
of lower-confidence family members. In total we link 38,298 asteroids into 76
distinct families. This work represents a critical step necessary to debias the
albedo and size distributions of asteroids in the Main Belt and understand the
formation and history of small bodies in our Solar system.Comment: Accepted to ApJ. Full version of Table 3 to be published
electronically in Ap
Main Belt Asteroids with WISE/NEOWISE: Near-Infrared Albedos
We present revised near-infrared albedo fits of 2835 Main Belt asteroids
observed by WISE/NEOWISE over the course of its fully cryogenic survey in 2010.
These fits are derived from reflected-light near-infrared images taken
simultaneously with thermal emission measurements, allowing for more accurate
measurements of the near-infrared albedos than is possible for visible albedo
measurements. As our sample requires reflected light measurements, it
undersamples small, low albedo asteroids, as well as those with blue spectral
slopes across the wavelengths investigated. We find that the Main Belt
separates into three distinct groups of 6%, 16%, and 40% reflectance at 3.4 um.
Conversely, the 4.6 um albedo distribution spans the full range of possible
values with no clear grouping. Asteroid families show a narrow distribution of
3.4 um albedos within each family that map to one of the three observed
groupings, with the (221) Eos family being the sole family associated with the
16% reflectance 3.4 um albedo group. We show that near-infrared albedos derived
from simultaneous thermal emission and reflected light measurements are an
important indicator of asteroid taxonomy and can identify interesting targets
for spectroscopic followup.Comment: Accepted for publication in ApJ; full version of Table1 to be
published electronically in the journa
High Redshift Supernovae in the Hubble Deep Field
Two supernovae detected in the Hubble Deep Field using the original December
1995 epoch and data from a shorter (63000 s in F814W) December 1997 visit with
HST are discussed. The supernovae (SNe) are both associated with distinct
galaxies at redshifts of 0.95 (spectroscopic) from Cohen etal. (1996) and 1.32
(photometric) from the work of Fernandez-Soto, Lanzetta, and Yahil (1998).
These redshifts are near, in the case of 0.95, and well beyond for 1.32 the
greatest distance reported previously for SNe. We show that our observations
are sensitive to SNe to z < 1.8 in either epoch for an event near peak
brightness. Detailed simulations are discussed that quantify the level at which
false events from our search phase would start to to arise, and the
completeness of our search as a function of both SN brightness and host galaxy
redshift. The number of Type Ia and Type II SNe expected as a function of
redshift in the two HDF epochs are discussed in relation to several published
predictions and our own detailed calculations. A mean detection frequency of
one SN per epoch for the small HDF area is consistent with expectations from
current theory.Comment: 62 pages, 17 figures, ApJ 1999 in pres
Single-Shot Electron Diffraction using a Cold Atom Electron Source
Cold atom electron sources are a promising alternative to traditional
photocathode sources for use in ultrafast electron diffraction due to greatly
reduced electron temperature at creation, and the potential for a corresponding
increase in brightness. Here we demonstrate single-shot, nanosecond electron
diffraction from monocrystalline gold using cold electron bunches generated in
a cold atom electron source. The diffraction patterns have sufficient signal to
allow registration of multiple single-shot images, generating an averaged image
with significantly higher signal-to-noise ratio than obtained with unregistered
averaging. Reflection high-energy electron diffraction (RHEED) was also
demonstrated, showing that cold atom electron sources may be useful in
resolving nanosecond dynamics of nanometre scale near-surface structures.Comment: This is an author-created, un-copyedited version of an article
published in Journal of Physics B: Atomic, Molecular and Optical Physics. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The Version of Record is
available online at http://dx.doi.org/10.1088/0953-4075/48/21/21400
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