6,320 research outputs found
Side wire feed for welding apparatus
Coaxial electrode arrangement has solid central electrode, insulated outer electrode, and transverse channel for feeding wire through tip of electrode assembly. Polymeric insulation is thrust aside by pressure, which is provided by separately operated mechanism acting through central electrode
Recommended from our members
Evolution Of Galaxies .4. Highly Flattened Disks
NSF GP-18335, GP-32051Astronom
Recommended from our members
Evolution Of Galaxies .2. Chemical Evolution Coefficients
NSF GP-18355, GP-32051Astronom
Thermoelectric Outer Planets Spacecraft (TOPS) electronic packaging and cabling development summary report
Electronic packaging and cabling activities performed in support of the Thermoelectric Outer Planets Spacecraft (TOPS) Advanced Systems Technology (AST) project are detailed. It describes new electronic compartment, electronic assembly, and module concepts, and a new high-density, planar interconnection technique called discrete multilayer (DML). Development and qualification of high density cabling techniques, using small gage wire and microminiature connectors, are also reported
Two-Dimensional Hydrodynamics of Pre-Core Collapse: Oxygen Shell Burning
By direct hydrodynamic simulation, using the Piecewise Parabolic Method (PPM)
code PROMETHEUS, we study the properties of a convective oxygen burning shell
in a SN 1987A progenitor star prior to collapse. The convection is too
heterogeneous and dynamic to be well approximated by one-dimensional
diffusion-like algorithms which have previously been used for this epoch.
Qualitatively new phenomena are seen.
The simulations are two-dimensional, with good resolution in radius and
angle, and use a large (90-degree) slice centered at the equator. The
microphysics and the initial model were carefully treated. Many of the
qualitative features of previous multi-dimensional simulations of convection
are seen, including large kinetic and acoustic energy fluxes, which are not
accounted for by mixing length theory. Small but significant amounts of
carbon-12 are mixed non-uniformly into the oxygen burning convection zone,
resulting in hot spots of nuclear energy production which are more than an
order of magnitude more energetic than the oxygen flame itself. Density
perturbations (up to 8%) occur at the `edges' of the convective zone and are
the result of gravity waves generated by interaction of penetrating flows into
the stable region. Perturbations of temperature and electron fraction at the
base of the convective zone are of sufficient magnitude to create angular
inhomogeneities in explosive nucleosynthesis products, and need to be included
in quantitative estimates of yields. Combined with the plume-like velocity
structure arising from convection, the perturbations will contribute to the
mixing of nickel-56 throughout supernovae envelopes. Runs of different
resolution, and angular extent, were performed to test the robustness of theseComment: For mpeg movies of these simulations, see
http://www.astrophysics.arizona.edu/movies.html Submitted to the
Astrophysical Journa
Contestable adulthood: variability and disparity in markers for negotiating the transition to adulthood
Recent research has identified a discreet set of subjective markers that are seen as characterizing the transition to adulthood. The current study challenges this coherence by examining the disparity and variability in young peopleâs selection of such criteria. Four sentence-completion cues corresponding to four differentcontexts in which adult status might be contested were given to 156 British 16- to 17-year-olds. Their qualitative responses were analyzed to
explore patterns whilst capturing some of their richness and diversity. An astonishing amount of variability emerged, both within and between cued contexts.The implications of this variability for how the transition to adulthood is experienced are explored. The argument is made that markers of the transition to adulthood are not merely reflective of the bioâpsychoâsocial development of
young people. Rather, adulthood here is seen as an essentially contested concept,located within the discursive interactional environment in which young people participate
Stellar neutrino energy loss rates due to Mg suitable for O+Ne+Mg core simulations
Neutrino losses from proto-neutron stars play a pivotal role to decide if
these stars would be crushed into black holes or explode as supernovae. Recent
observations of subluminous Type II-P supernovae (e.g., 2005cs, 2003gd, 1999br,
1997D) were able to rejuvenate the interest in 8-10 M stars which
develop O+Ne+Mg cores. Simulation results of O+Ne+Mg cores show varying results
in converting the collapse into an explosion. The neutrino energy loss rates
are important input parameters in core collapse simulations. Proton-neutron
quasi-particle random phase approximation (pn-QRPA) theory has been used for
calculation of neutrino energy loss rates due to Mg in stellar matter.
The rates are presented on a detailed density-temperature grid suitable for
simulation purposes. The calculated neutrino energy loss rates are enhanced up
to more than one order of magnitude compared to the shell model calculations
and favor a lower entropy for the core of these massive stars.Comment: 20 pages, 4 figures, 2 table
Active Carbon and Oxygen Shell Burning Hydrodynamics
We have simulated 2.5 s of the late evolution of a star with full hydrodynamic behavior. We present the first simulations
of a multiple-shell burning epoch, including the concurrent evolution and
interaction of an oxygen and carbon burning shell. In addition, we have evolved
a 3D model of the oxygen burning shell to sufficiently long times (300 s) to
begin to assess the adequacy of the 2D approximation. We summarize striking new
results: (1) strong interactions occur between active carbon and oxygen burning
shells, (2) hydrodynamic wave motions in nonconvective regions, generated at
the convective-radiative boundaries, are energetically important in both 2D and
3D with important consequences for compositional mixing, and (3) a spectrum of
mixed p- and g-modes are unambiguously identified with corresponding adiabatic
waves in these computational domains. We find that 2D convective motions are
exaggerated relative to 3D because of vortex instability in 3D. We discuss the
implications for supernova progenitor evolution and symmetry breaking in core
collapse.Comment: 5 pages, 4 figures in emulateapj format. Accepted for publication in
ApJ Letters. High resolution figure version available at
http://spinach.as.arizona.ed
Activation of the P2Y2 receptor regulates bone cell function by enhancing ATP release
Bone cells constitutively release ATP into the extracellular environment where it acts locally via P2 receptors to regulate bone cell function. Whilst P2Y2 receptor stimulation regulates bone mineralisation, the functional effects of this receptor in osteoclasts remain unknown. This investigation used the P2Y2 receptor knockout (P2Y2Râ/â) mouse model to investigate the role of this receptor in bone. MicroCT analysis of P2Y2Râ/â mice demonstrated age-related increases in trabecular bone volume (â€48%), number (â€30%) and thickness (â€17%). In vitro P2Y2Râ/â osteoblasts displayed a 3-fold increase in bone formation and alkaline phosphatase activity, whilst P2Y2Râ/â osteoclasts exhibited a 65% reduction in resorptive activity. Serum cross-linked C-telopeptide levels (CTX, resorption marker) were also decreased (â€35%). The resorption defect in P2Y2Râ/â osteoclasts was rescued by the addition of exogenous ATP, suggesting that an ATP deficit could be a key factor in the reduced function of these cells. In agreement, we found that basal ATP release was reduced up to 53% in P2Y2Râ/â osteoclasts. The P2Y2 receptor agonists, UTP and 2-thioUTP, increased osteoclast activity and ATP release in wild-type but not in P2Y2Râ/â cells. This indicates that the P2Y2 receptor may regulate osteoclast function indirectly by promoting ATP release. UTP and 2-thioUTP also stimulate ATP release from osteoblasts suggesting that the P2Y2 receptor exerts a similar function in these cells. Taken together, our findings are consistent with the notion that the primary action of P2Y2 receptor signalling in bone is to regulate extracellular ATP levels
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