5,188 research outputs found
The "backdoor pathway" of androgen synthesis in human male sexual development.
Mammalian sex determination (male versus female) is largely controlled by genes, whereas sex differentiation (development of reproductive structures) is largely controlled by hormones. Work in the 20th century indicated that female external anatomy was a "default" pathway of development not requiring steroids, whereas male genital development required testicular testosterone plus dihydrotestosterone (DHT) made in genital skin according to a "classic" pathway. Recent work added the description of an alternative "backdoor" pathway of androgen synthesis discovered in marsupials. Unique "backdoor steroids" are found in human hyperandrogenic disorders, and genetic disruption of the pathway causes disordered male sexual development, suggesting it plays an essential role. O'Shaughnessy and colleagues now show that the principal human backdoor androgen is androsterone and provide strong evidence that it derives from placental progesterone that is metabolized to androsterone in nontesticular tissues. These studies are essential to understanding human sexual development and its disorders
Pismo clams and sea otters
Sea otter foraging along Monterey Bay beaches and at Atascadero State Beach has precluded recreational Pismo clam fisheries at six major clamming beaches. Outside the sea otter's foraging range Pismo clam stocks are yielding good catches; apparently the stringent controls on the recreational fishery is adequate to maintain the State's Pismo clam stocks. Clammer interviews at Orange and Los Angeles County beaches and at beaches near Pismo Beach and Morro Bay and in Monterey Bay revealed the clam stocks to be on a healthy, sustainable yield basis. Exceptionally
large numbers of small 1.5 to 3.5 inch Pismo clams were reported at all clam beaches surveyed north of Pt. Conception indicating good year class survival in recent years. Sea otters forage dense Pismo clam beds by moving along a "front", progressively foraging from one beach to the next, reducing the clams to low levels before moving on. Some sea otters continue to forage throughout the areas previously depleted by the larger aggregate moving northward, thus the large numbers of sublegal clams
in the 1.5 to 3.5 inch size group in these intertidal and shallow subtidal areas are not expected to reach legal size in numbers sufficient to develop a recreational fishery. In Monterey Bay about 60,000 Pismo clams were removed or killed by human activity in the April 1974 to March 1975 period. A rough estimate of the Pismo clams consumed by sea otters during this same period in Monterey Bay is over 500,000 clams. (51pp.
Atom chips on direct bonded copper substrates
We present the use of direct bonded copper (DBC) for the straightforward
fabrication of high power atom chips. Atom chips using DBC have several
benefits: excellent copper/substrate adhesion, high purity, thick (> 100
microns) copper layers, high substrate thermal conductivity, high aspect ratio
wires, the potential for rapid (< 8 hr) fabrication, and three dimensional atom
chip structures. Two mask options for DBC atom chip fabrication are presented,
as well as two methods for etching wire patterns into the copper layer. The
wire aspect ratio that optimizes the magnetic field gradient as a function of
power dissipation is determined to be 0.84:1 (height:width). The optimal wire
thickness as a function of magnetic trapping height is also determined. A test
chip, able to support 100 A of current for 2 s without failing, is used to
determine the thermal impedance of the DBC. An assembly using two DBC atom
chips to provide magnetic confinement is also shown.Comment: 8 pages, 5 figure
Adjustable microchip ring trap for cold atoms and molecules
We describe the design and function of a circular magnetic waveguide produced
from wires on a microchip for atom interferometry using deBroglie waves. The
guide is a two-dimensional magnetic minimum for trapping weak-field seeking
states of atoms or molecules with a magnetic dipole moment. The design consists
of seven circular wires sharing a common radius. We describe the design, the
time-dependent currents of the wires and show that it is possible to form a
circular waveguide with adjustable height and gradient while minimizing
perturbation resulting from leads or wire crossings. This maximal area geometry
is suited for rotation sensing with atom interferometry via the Sagnac effect
using either cold atoms, molecules and Bose-condensed systems
A Deep ROSAT HRI Observation of NGC 1313
We describe a series of observations of NGC 1313 using the ROSAT HRI with a
combined exposure time of 183.5 ksec. The observations span an interval between
1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray
flux of SN1978K, one of several luminous sources in the galaxy. No diffuse
emission is detected in the galaxy to a level of ~1-2x10^37 ergs/s/arcmin^-2. A
total of eight sources are detected in the summed image within the D_25
diameter of the galaxy. The luminosities of five of the eight range from
\~6x10^37 to ~6x10^38 erg/s; these sources are most likely accreting X-ray
binaries, similar to sources obseved in M31 and M33. The remaining three
sources all emit above 10^39 erg/s. We present light curves of the five
brightest sources. Variability is detected at the 99.9% level from four of
these. We identify one of the sources as an NGC 1313 counterpart of a Galactic
X-ray source. The light curve, though crudely sampled, most closely resembles
that of a Galactic black hole candidate such as GX339-4, but with considerably
higher peak X-ray luminosity. An additional seven sources lie outside of the
D_25 diameter and are either foreground stars or background AGN.Comment: 18 pages, 9 figures; accepted AJ, scheduled for November 200
Knowledge-Salvage Practices for Dormant R&D Projects
Most successful firms have an abundance of new and old knowledge in their research and development laboratories, and only a fraction is being put into use in new product development. This knowledge is left over from projects that have been killed at different development stages and may actually carry considerable value. In this article, we propose a knowledge bank as a possible solution to preserve and possibly grow this knowledge. It is a self-sustaining institute with minimal or no ongoing effort from the donor company, yet manages the knowledge in a way that protects proprietary interests and actively fosters communication and interchange among sponsoring companies wherever possible. The framework of this structure, as well as how it works, is described here. Specifically, a system dynamics modeling of the knowledge bank is developed, and a simulation study is conducted using VENSIM®. The results confirm the viability of creating such a system in a consortium of organizations
A Chandra observation of the long-duration X-ray transient KS 1731-260 in quiescence: too cold a neutron star?
After more than a decade of actively accreting at about a tenth of the
Eddington critical mass accretion rate, the neutron-star X-ray transient KS
1731-260 returned to quiescence in early 2001. We present a Chandra/ACIS-S
observation taken several months after this transition. We detected the source
at an unabsorbed flux of ~2 x 10^{-13} erg/cm^2/s (0.5-10 keV). For a distance
of 7 kpc, this results in a 0.5-10 keV luminosity of ~1 x 10^{33} erg/s and a
bolometric luminosity approximately twice that. This quiescent luminosity is
very similar to that of the other quiescent neutron star systems. However, if
this luminosity is due to the cooling of the neutron star, this low luminosity
may indicate that the source spends at least several hundreds of years in
quiescence in between outbursts for the neutron star to cool. If true, then it
might be the first such X-ray transient to be identified and a class of
hundreds of similar systems may be present in the Galaxy. Alternatively,
enhanced neutrino cooling could occur in the core of the neutron star which
would cool the star more rapidly. However, in that case the neutron star in KS
1731-260 would be more massive than those in the prototypical neutron star
transients (e.g., Aql X-1 or 4U 1608-52).Comment: Accepted for publicaton in ApJ letters, 13 September 200
Thermal radiation from magnetic neutron star surfaces
We investigate the thermal emission from magnetic neutron star surfaces in
which the cohesive effects of the magnetic field have produced the condensation
of the atmosphere and the external layers. This may happen for sufficiently
cool atmospheres with moderately intense magnetic fields. The thermal emission
from an isothermal bare surface of a neutron star shows no remarkable spectral
features, but it is significantly depressed at energies below some threshold
energy. However, since the thermal conductivity is very different in the normal
and parallel directions to the magnetic field lines, the presence of the
magnetic field is expected to produce a highly anisotropic temperature
distribution, depending on the magnetic field geometry. In this case, the
observed flux of such an object looks very similar to a BB spectrum, but
depressed in a nearly constant factor at all energies. This results in a
systematic underestimation of the area of the emitter (and therefore its size)
by a factor 5-10 (2-3).Comment: 10 pages, 9 figure
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