15,801 research outputs found
Application of Chiral Lanthanide-induced Shift Reagents to Optically Active Cations: the Use of Tris[3-(trifluoromethylhydroxymethylene)-( + )-camphorato]europium(III) to Determine the Enantiomeric Purity of Tris(phenanthroline)ruthenium(II) Dichloride
In non-polar solvents, chiral europium complexes provide attractive n. m. r. shift reagents to resolve spectra of optically active cations, and, in particular, for tris(phenanthroline)ruthenium dichloride,^1H n. m. r. shift differences of up to 0.7 p.p.m. between isomers easily permit the determination of absolute enantiomeric purity
Future mobile satellite communication concepts at 20/30 GHz
The outline of a design of a system using ultra small earth stations (picoterminals) for data traffic at 20/30 GHz is discussed. The picoterminals would be battery powered, have an RF transmitter power of 0.5 W, use a 10 cm square patch antenna, and have a receiver G/T of about -8 dB/K. Spread spectrum modulation would be required (due to interference consideration) to allow a telex type data link (less than 200 bit/s data rate) from the picoterminal to the hub station of the network and about 40 kbit/s on the outbound patch. An Olympus type transponder at 20/30 GHz could maintain several thousand simultaneous picoterminal circuits. The possibility of demonstrating a picoterminal network with voice traffic using Olympus is discussed together with fully mobile systems based on this concept
A small helium liquifier which provides continuous cooling based on cycled isentropic expansion
This simple cryocooler provides a small reservoir of liquid helium at a stable temperature of 4.2K. It uses a novel adaptation of the Simon expansion cryocooler to provide continuous cooling. Operation is in a four stage cycle: (1) A closed vessel of helium under high pressure is cooled to 12K using a conventional Gifford-McMahon closed-cycle cryocooler. (2) The pressure is released adiabatically providing cooling to 4.2K. (3) Liquid helium is collected in a second, well insulated, vessel. (4) The first vessel is repressurized. The cycle time is 15-30 minutes. In this manner, a pool of liquid helium is continuously maintained in the second vessel, with a temperature stability of 0.03 degrees. The continuous cooling power available is 3mW. This design provides simplicity and reliability through the absence of any orifices or moving parts at cryogenic temperatures except for the conventional Gifford-McMahon cryocooler
Local and Global Casimir Energies for a Semitransparent Cylindrical Shell
The local Casimir energy density and the global Casimir energy for a massless
scalar field associated with a -function potential in a 3+1
dimensional circular cylindrical geometry are considered. The global energy is
examined for both weak and strong coupling, the latter being the well-studied
Dirichlet cylinder case. For weak-coupling,through ,
the total energy is shown to vanish by both analytic and numerical arguments,
based both on Green's-function and zeta-function techniques. Divergences
occurring in the calculation are shown to be absorbable by renormalization of
physical parameters of the model. The global energy may be obtained by
integrating the local energy density only when the latter is supplemented by an
energy term residing precisely on the surface of the cylinder. The latter is
identified as the integrated local energy density of the cylindrical shell when
the latter is physically expanded to have finite thickness. Inside and outside
the delta-function shell, the local energy density diverges as the surface of
the shell is approached; the divergence is weakest when the conformal stress
tensor is used to define the energy density. A real global divergence first
occurs in , as anticipated, but the proof is supplied
here for the first time; this divergence is entirely associated with the
surface energy, and does {\em not} reflect divergences in the local energy
density as the surface is approached.Comment: 28 pages, REVTeX, no figures. Appendix added on perturbative
divergence
NMR evidence for specific intercalation of Î-rh(phen)_2phi^(3+) in [d(GTCGAC)_2]
The anchoring of metal complexes in the major groove of DNA through intercalation has been increasingly useful in the shape-selective design of novel metal complexes which bind DNA with high sequence-selectivity. Toward that goal, direct structural information regarding this intercalative interaction is essential. Phenanthrenequinone diimine (phi) complexes of Rh(III) bind avidly (K_b 1 â„ 10^7) to DNA by intercalation in the major groove. Here we report the first ^1H-NMR studies of Î-rh(phen)_2phi^(3+) bound to an oligonucleotide. These studies provide direct structural evidence for specific intercalation by this octahedral complex in the major groove of DNA
Experience and Assessment of the DOE/NASA Mod-1 2000 Kw Wind Turbine Generator at Boone, North Carolina
The Mod 1 program objectives are defined. The Mod 1 wind turbine is described. In addition to the steel blade operated on the wind turbine, a composite blade was designed and manufactured. During the early phase of the manufacturing cycle of Mod 1A configuration was designed that identified concepts such as partial span control, a soft tower, and upwind teetered rotors that were incorporated in second and third generation industry designs. The Mod 1 electrical system performed as designed, with voltage flicker characteristics within acceptable utility limits
Computer program to predict noise of general aviation aircraft: User's guide
Program NOISE predicts General Aviation Aircraft far-field noise levels at FAA FAR Part 36 certification conditions. It will also predict near-field and cabin noise levels for turboprop aircraft and static engine component far-field noise levels
Surface Divergences and Boundary Energies in the Casimir Effect
Although Casimir, or quantum vacuum, forces between distinct bodies, or
self-stresses of individual bodies, have been calculated by a variety of
different methods since 1948, they have always been plagued by divergences.
Some of these divergences are associated with the volume, and so may be more or
less unambiguously removed, while other divergences are associated with the
surface. The interpretation of these has been quite controversial. Particularly
mysterious is the contradiction between finite total self-energies and surface
divergences in the local energy density. In this paper we clarify the role of
surface divergences.Comment: 8 pages, 1 figure, submitted to proceedings of QFEXT0
Green's Dyadic Approach of the Self-Stress on a Dielectric-Diamagnetic Cylinder with Non-Uniform Speed of Light
We present a Green's dyadic formulation to calculate the Casimir energy for a
dielectric-diamagnetic cylinder with the speed of light differing on the inside
and outside. Although the result is in general divergent, special cases are
meaningful. It is pointed out how the self-stress on a purely dielectric
cylinder vanishes through second order in the deviation of the permittivity
from its vacuum value, in agreement with the result calculated from the sum of
van der Waals forces.Comment: 8 pages, submitted to proceedings of QFEXT0
Ultra-high-sensitivity two-dimensional bend sensor
A multicore fibre Fabry-Perot-based strain sensor interrogated with tandem interferometry for bend measurement is described. Curvature in two dimensions is obtained by measuring the difference in strain between three co-located low finesse Fabry-Perot interferometers formed in each core of the fibre by pairs of Bragg gratings. This sensor provides a responsivity enhancement of up to 30 times that of a previously reported fibre Bragg grating based sensor. Strain resolutions of 0.6 n epsilon/Hz(1/2) above 1 Hz are demonstrated, which corresponds to a curvature resolution of similar to 0.012 km(-1)/Hz(1/2)
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