Structural and electronic properties of MgO nanotube clusters

Finite magnesium oxide nanotubes are investigated. Stacks of four parallel squares, hexagons, octagons, and decagons are constructed and studied by the pseudopotential density functional theory within the local-density approximation. Optimized structures are slightly distorted stacks of polygons. These clusters are insulators and the band gap of 8.5 eV is constant over an investigated range of the diameters of stacked polygonal rings. Using the L"owdin population analysis a charge transfer towards the oxygen atoms is estimated as 1.4, which indicates that the mixed ionocovalent bonding exists in investigated MgO nanotubes

An improved algorithm for evaluating trellis phase codes

A method is described for evaluating the minimum distance parameters of trellis phase codes, including CPFSK, partial response FM, and more importantly, coded CPM (continuous phase modulation) schemes. The algorithm provides dramatically faster execution times and lesser memory requirements than previous algorithms. Results of sample calculations and timing comparisons are included

Gauge invariant action at the ultraviolet cutoff

We show that it is possible to formulate a gauge theory starting from a local action at the ultraviolet (UV) momentum cutoff which is BRS invariant. One has to require that fields in the UV action and the fields in the effective action are not the same but related by a local field transformation. The few relevant parameters involved in this transformation (six for the $SU(2)$ gauge theory), are perturbatively fixed by the gauge symmetry.Comment: 5 pages, Latex, no figure

Saturn S-IB Stage assembly and test report, S-IB-1

Manufacture, assembly, and static tests of Saturn S-IB-1 stag

The Influence of Nuclear Composition on the Electron Fraction in the Post-Core-Bounce Supernova Environment

We study the early evolution of the electron fraction (or, alternatively, the neutron-to-proton ratio) in the region above the hot proto-neutron star formed after a supernova explosion. We study the way in which the electron fraction in this environment is set by a competition between lepton (electron, positron, neutrino, and antineutrino) capture processes on free neutrons and protons and nuclei. Our calculations take explicit account of the effect of nuclear composition changes, such as formation of alpha particles (the alpha effect) and the shifting of nuclear abundances in nuclear statistical equilibrium associated with cooling in near-adiabatic outflow. We take detailed account of the process of weak interaction freeze-out in conjunction with these nuclear composition changes. Our detailed treatment shows that the alpha effect can cause significant increases in the electron fraction, while neutrino and antineutrino capture on heavy nuclei tends to have a buffering effect on this quantity. We also examine the effect on weak rates and the electron fraction of fluctuations in time in the neutrino and antineutrino energy spectra arising from hydrodynamic waves. Our analysis is guided by the Mayle & Wilson supernova code numerical results for the neutrino energy spectra and density and velocity profiles.Comment: 38 pages, AAS LaTeX, 8 figure

High-frequency high-voltage high-power DC-to-DC converters

The current and voltage waveshapes associated with the power transitor and the power diode in an example current-or-voltage step-up (buck-boost) converter were analyzed to highlight the problems and possible tradeoffs involved in the design of high voltage high power converters operating at switching frequencies in the range of 100 Khz. Although the fast switching speeds of currently available power diodes and transistors permit converter operation at high switching frequencies, the resulting time rates of changes of current coupled with parasitic inductances in series with the semiconductor switches, produce large repetitive voltage transients across the semiconductor switches, potentially far in excess of the device voltage ratings. The need is established for semiconductor switch protection circuitry to control the peak voltages appearing across the semiconductor switches, as well as to provide the waveshaping action require for a given semiconductor device. The possible tradeoffs, as well as the factors affecting the tradeoffs that must be considered in order to maximize the efficiency of the converters are enumerated

Exact renormalization group equations and the field theoretical approach to critical phenomena

After a brief presentation of the exact renormalization group equation, we illustrate how the field theoretical (perturbative) approach to critical phenomena takes place in the more general Wilson (nonperturbative) approach. Notions such as the continuum limit and the renormalizability and the presence of singularities in the perturbative series are discussed.Comment: 15 pages, 7 figures, to appear in the Proceedings of the 2nd Conference on the Exact Renormalization Group, Rome 200

Analysis of transistor and snubber turn-off dynamics in high-frequency high-voltage high-power converters

Dc to dc converters which operate reliably and efficiently at switching frequencies high enough to effect substantial reductions in the size and weight of converter energy storage elements are studied. A two winding current or voltage stepup (buck boost) dc-to-dc converter power stage submodule designed to operate in the 2.5-kW range, with an input voltage range of 110 to 180 V dc, and an output voltage of 250 V dc is emphasized. In order to assess the limitations of present day component and circuit technologies, a design goal switching frequency of 10 kHz was maintained. The converter design requirements represent a unique combination of high frequency, high voltage, and high power operation. The turn off dynamics of the primary circuit power switching transistor and its associated turn off snubber circuitry are investigated

Axial anomalies in gauge theory by exact renormalization group method

The global chiral symmetry of a $SU(2)$ gauge theory is studied in the framework of renormalization group (RG). The theory is defined by the RG flow equations in the infrared cutoff \L and the boundary conditions for the relevant couplings. The physical theory is obtained at \L=0. In our approach the symmetry is implemented by choosing the boundary conditions for the relevant couplings not at the ultraviolet point \L=\L_0\to\infty but at the physical value \L=0. As an illustration, we compute the triangle axial anomalies.Comment: 11 pages + 1 appended EPS figure, LaTeX, UPRF 94-39

A simple extended-cavity diode laser

Operating a laser diode in an extended cavity which provides frequency-selective feedback is a very effective method of reducing the laser's linewidth and improving its tunability. We have developed an extremely simple laser of this type, built from inexpensive commercial components with only a few minor modifications, A 780 nm laser built to this design has an output power of 80 mW, a Linewidth of 350 kHz, and it has been continuously locked to a Doppler-free rubidium transition for several days