104,429 research outputs found
New polymers for low-gravity purification of cells by phase partitioning
A potentially powerful technique for separating different biological cell types is based on the partitioning of these cells between the immiscible aqueous phases formed by solution of certain polymers in water. This process is gravity-limited because cells sediment rather than associate with the phase most favored on the basis of cell-phase interactions. In the present contract we have been involved in the synthesis of new polymers both to aid in understanding the partitioning process and to improve the quality of separations. The prime driving force behind the design of these polymers is to produce materials which will aid in space experiments to separate important cell types and to study the partitioning process in the absence of gravity (i.e., in an equilibrium state)
New polymers for phase partitioning
The synthesizing of several polyethylene glycols having crown ethers attached is reported. This work led to the identification of three new polymer types which promise to be more effective at selectively binding specific cell types. Work was completed on identification of chemical properties of the new polymer crowns and on development of new techniques for determination of polymer-phase composition
Improvements in micromanipulators
Design, operation, and application of micromanipulators in biological researc
On the Connection Between 2d Topological Gravity and the Reduced Hermitian Matrix Model
We discuss how concepts such as geodesic length and the volume of space-time
can appear in 2d topological gravity. We then construct a detailed mapping
between the reduced Hermitian matrix model and 2d topological gravity at genus
zero. This leads to a complete solution of the counting problem for planar
graphs with vertices of even coordination number. The connection between
multi-critical matrix models and multi-critical topological gravity at genus
zero is studied in some detail.Comment: 29 pages, LaTe
Dipole-Field Contributions to Geometric-Phase-Induced False Electric-Dipole Moment Signals for Particles in Traps
It has been shown in an earlier publication that magnetic field gradients
applied to particles in traps can induce Larmor frequency shifts that may
falsely be interpreted as electric-dipole moment (EDM) signals. This study has
now been extended to include nonuniform magnetic field gradients due to the
presence of a local magnetic dipole. It is found that, in the high
orbit-frequency regime, the magnitude of the shifts can be enhanced beyond the
simple expectation of proportionality to the volume-averaged magnetic-field
gradient.Comment: 2 pages, no figure
Fixed wing CCW aerodynamics with and without supplementary thrust deflection
The concept of circulation control was successfully demonstrated in flight using an A-6 aircraft. Circulation control can provide an aircraft with STOL performance of heavy lift capability. For ship based Naval aircraft the lower takeoff and landing velocities result in reduced deck gear and wind over the deck requirements. Circulation control airfoils can be mechanically less complex and lightweight compared to multi-element high lift airfoils
Computer program for solving compressible nonsimilar-boundary-layer equations for laminar, transitional, or turbulent flows of a perfect gas
A computer program is described which solves the compressible laminar, transitional, or turbulent boundary-layer equations for planar or axisymmetric flows. Three-point implicit difference relations are used to reduce the momentum and energy equations to finite-difference form. These equations are solved simultaneously without iteration. Turbulent flow is treated by the inclusion of either a two-layer eddy-viscosity model or a mixing-length formulation. The eddy conductivity is related to the eddy viscosity through a static turbulent Prandtl number which may be an arbitrary function of the distance from the wall boundary. The transitional boundary layer is treated by the inclusion of an intermittency function which modifies the fully turbulent model. The laminar-boundary-layer equations are recovered when the intermittency is zero, and the fully turbulent equations are solved when the intermittency is unity
Detailed Comparison of Next-to-Leading Order Predictions for Jet Photoproduction at HERA
The precision of new HERA data on jet photoproduction opens up the
possibility to discriminate between different models of the photon structure.
This requires equally precise theoretical predictions from perturbative QCD
calculations. In the past years, next-to-leading order calculations for the
photoproduction of jets at HERA have become available. Using the kinematic cuts
of recent ZEUS analyses, we compare the predictions of three calculations for
different dijet and three-jet distributions. We find that in general all three
calculations agree within the statistical accuracy of the Monte Carlo
integration yielding reliable theoretical predictions. In certain restricted
regions of phase space, the calculations differ by up to 5%.Comment: 10 pages, 7 eps-figures. To appear in the Proceedings of the Workshop
on ``Monte Carlo Generators for HERA Physics'', Hamburg 1998/9
X-ray Emission from the Radio Jet in 3C 120
We report the discovery of X-ray emission from a radio knot at a projected
distance of 25" from the nucleus of the Seyfert galaxy, 3C 120. The data were
obtained with the ROSAT High Resolution Imager (HRI). Optical upper limits for
the knot preclude a simple power law extension of the radio spectrum and we
calculate some of the physical parameters for thermal bremsstrahlung and
synchrotron self-Compton models. We conclude that no simple model is consistent
with the data but if the knot contains small regions with flat spectra, these
could produce the observed X-rays (via synchrotron emission) without being
detected at other wavebands.Comment: 6 pages latex plus 3 ps/eps figures. Uses 10pt.sty and
emulateapj.sty. Accepted for publication in the ApJ (6 Jan 99
The prompt gamma-ray emission of novae
Classical novae are potential gamma-ray emitters, because of the
disintegration of some radioactive nuclei synthesized during the explosion.
Some short-lived isotopes (such as 13N and 18F), as well as the medium-lived
22Na, decay emitting positrons, which annihilate with electrons and thus are
responsible for the prompt emission of gamma-rays from novae. This emission
consists of a 511 keV line plus a continuum between 20 and 511 keV, and is
released before the maximum in visual luminosity, i.e., before the discovery of
the nova. The main characteristics of this prompt emission, together with the
related uncertainties (both of nuclear and hydrodynamical origin, with a
particular emphasis on the influence of the envelope properties) and prospects
for detectability are analyzed in this paper.Comment: 6 pages, 3 figures (6 PS files), to appear in New Astronomy Reviews
(Proceedings of the Ringberg Workshop "Astronomy with Radioactivities III"
- …