Topological Phases in Neuberger-Dirac operator

The response of the Neuberger-Dirac fermion operator D=\Id + V in the topologically nontrivial background gauge field depends on the negative mass parameter $m_0$ in the Wilson-Dirac fermion operator $D_w$ which enters $D$ through the unitary operator $V = D_w (D_w^{\dagger} D_w)^{-1/2}$. We classify the topological phases of $D$ by comparing its index to the topological charge of the smooth background gauge field. An exact discrete symmetry in the topological phase diagram is proved for any gauge configurations. A formula for the index of D in each topological phase is derived by obtaining the total chiral charge of the zero modes in the exact solution of the free fermion propagator.Comment: 27 pages, Latex, 3 figures, appendix A has been revise

Analysis And Performance Of A Picosecond Dye Laser Amplifier Chain

Design considerations are discussed for a simple, easy to use and relatively efficient high gain dye laser amplifier chain for CW mode-locked dye lasers. The amplifier boosts the output of a synchronously mode-locked dye laser to obtain ≈005 mj, ≤ 1 psec pulses over a ≈ 400 Å bandwidth. These pulses are suitable for efficient Raman Shifting, frequency mixing and continuum generation to vastly extend the spectral range of the system. Our amplifier is pumped by a frequency doubled Nd:YAG oscillator only, which longitudinally pumps three identical brewster cells with the same flowing dye solution in each. Contrary to popular belief, high small signal gains (≥ 105) are easily attained in a single stage with longitudinal pumping, with better beam homogeneity and easier alignment than transverse pumping. Gain saturation measurements are presented which agree well with calculations. Factors which relax the pump timing sensitivity are examined. The importance of gain saturation for both efficient amplification and for amplitude stability is also discussed. The need for isolated amplifier stages is stressed and optimal amplifier cell areas for a given stage are calculated

Experimental and theoretical investigation for the suppression of the plasma arc drop in the thermionic converter

Ion generation and recombination mechanisms in the cesium plasma as they pertain to the advanced mode thermionic energy converter were studied. The decay of highly ionized cesium plasma was studied in the near afterglow to examine the recombination processes. Very low recombination in such a plasma may prove to be of considerable importance in practical converters. The approaches of external cesium generation were vibrationally excited nitrogen as an energy source of ionization of cesium ion, and microwave power as a means of resonant sustenance of the cesium plasma. Experimental data obtained so far show that all three techniques - i.e., the non-LTE high-voltage pulsing, the energy transfer from vibrationally excited diatomic gases, and the external pumping with a microwave resonant cavity - can produce plasmas with their densities significantly higher than the Richardson density. The implication of these findings as related to Lam's theory is discussed

Speed of light as measured by two terrestrial stable clocks

Despite the recent criticism within the special theory of relativity, there exists an arrangement of stable clocks rotating with the earth which predicts diurnal variations of the one-way speed of light, as suggested previously

Studies in upper and lower atmosphere coupling

The theoretical and data-analytic work on upper and lower atmosphere coupling performed under a NASA Headquarters contract during the period April 1978 to March 1979 are summarized. As such, this report is primarily devoted to an overview of various studies published and to be published under this contract. Individual study reports are collected as exhibits. Work performed under the subject contract are in the following four areas of upper-lower atmosphere coupling: (1) Magnetosphere-ionosphere electrodynamic coupling in the aurora; (2) Troposphere-thermosphere coupling; (3) Ionosphere-neutral-atmosphere coupling; and (4) Planetary wave dynamics in the middle atmosphere

A Measurement of the Absorption of Liquid Argon Scintillation Light by Dissolved Nitrogen at the Part-Per-Million Level

We report on a measurement of the absorption length of scintillation light in liquid argon due to dissolved nitrogen at the part-per-million (ppm) level. We inject controlled quantities of nitrogen into a high purity volume of liquid argon and monitor the light yield from an alpha source. The source is placed at different distances from a cryogenic photomultiplier tube assembly. By comparing the light yield from each position we extract the absorption cross section of nitrogen. We find that nitrogen absorbs argon scintillation light with strength of $(1.51\pm 0.15)\times10^{-4} \;\mathrm{cm^{-1} ppm^{-1}}$, corresponding to an absorption cross section of $(7.14 \pm 0.74)\times10^{-21}\;\mathrm{cm^{2} molecule^{-1}}$. We obtain the relationship between absorption length and nitrogen concentration over the 0 to 50 ppm range and discuss the implications for the design and data analysis of future large liquid argon time projection chamber (LArTPC) detectors. Our results indicate that for a current-generation LArTPC, where a concentration of 2 parts per million of nitrogen is expected, the attenuation length due to nitrogen will be $30 \pm 3$ meters.Comment: v2: Correct mistake in molecular absorption cross section calculation, and a minor typo in fig

ANKLE KINEMATICS OF CUTTING MOVEMENT DURING VOLLEY IN TENNIS

The purpose of this study was to investigate the ankle kinematics of cutting movement during volley in tennis. Three male tennis players performed three cutting angle movements (0°, 30° & 60°, represents by S0, F30, F60, respectively) to volley a dropping ball with racket. Kinematics of the ankle was recorded by three-dimensional (3D) motion analysis system. During the early stance (the first 30% from heel strike), the results showed difference in the kinematics parameters in the three cutting angle movements for each subject. During late stance (last 30% before foot off), the mean values of everison and plantarflexion angles with F60 are largest in three cutting angle movements, so are the angular velocities. Therefore, the subjects may select different strategies to avoid foot injuries after heel strike. Furthermore, movements of the foot in performing the F60 may increase Achilles tendon injuries and medial tibial stress syndrome before the foot leaves the ground during the tennis volley

InGaAsP/InP undercut mesa laser with planar polyimide passivation

An undercut mesa laser is fabricated on an n + -InP substrate using a single step liquid phase epitaxy growth process and a planar structure is obtained by using a polyimide filling layer. The lasers operate at fundamental transverse mode due to a scattering loss mechanism. Threshold currents of 18 mA and stable single transverse mode operating at high currents are obtained

Carrier leakage and temperature dependence of InGaAsP lasers

A direct measurement of electron and hole leakage in InGaAsP/InP lasers has been carried out. The effect of electron leakage on the temperature sensitivity of InGaAsP/InP lasers has been revealed