5,107 research outputs found
Gauge Structure of Vacuum String Field Theory
We study the gauge structure of vacuum string field theory expanded around
the D-brane solution, namely, the gauge transformation and the transversality
condition of the massless vector fluctuation mode. We find that the gauge
transformation on massless vector field is induced as an anomaly; an infinity
multiplied by an infinitesimal factor. The infinity comes from the singularity
at the edge of the eigenvalue distribution of the Neumann matrix, while the
infinitesimal factor from the violation of the equation of motion of the
fluctuation modes due to the regularization for the infinity. However, the
transversality condition cannot be obtained even if we take into account the
anomaly contribution.Comment: 19 pages, LaTeX2
Baryons from instantons in holographic QCD
We consider aspects of dynamical baryons in a holographic dual of QCD that is
proposed on the basis of a D4/D8-brane configuration. We construct a soliton
solution carrying a unit baryon number and show that it is given by an
instanton solution of four-dimensional Yang-Mills theory with fixed size. The
Chern-Simons term on the flavor D8-branes plays a crucial role of protecting
the instanton from collapsing to zero size. By quantizing the collective
coordinates of the soliton, we work out the baryon spectra. Negative-parity
baryons as well as baryons with higher spins and isospins can be obtained in a
simple manner.Comment: 25 pages, v2: references added, minor changes, v3: PTP-style, minor
correction
Influence of heat input waveform on transient critical heat flux of subcooled water flow boiling in a short vertical tube
The transient critical heat fluxes (CHFs) of the subcooled water flow boiling for ramp-wise heat input [Q = αt, α = 6.21 × 108 to 1.63 × 1012 W/m3 s, (q 1.08 × 107 to 6.00 × 107 W/m2)] and stepwise one [Q = Qs, Qs = 0 W/m3 at t = 0 s and Qs = 2.95 × 1010 to 7.67 × 1010 W/m3 at t > 0 s, (q = 0 W/m2 at t = 0 s and q 1.61 × 107 to 3.87 × 107 W/m2 at t > 0 s)] with the flow velocities (u = 4.0–13.3 m/s), the inlet subcoolings (ΔTsub, in = 86.8–153.3 K) and the inlet pressures (Pin = 742.2–1293.4 kPa) are systematically measured by an experimental water loop comprised of a pressurizer. The SUS304 tubes of inner diameters (d = 3, 6 and 9 mm), heated lengths (L = 33.15, 59.5 and 49.3 mm), L/d (=11.05, 9.92 and 5.48), and wall thickness (δ = 0.5, 0.5 and 0.3 mm) respectively with the rough finished inner surface (surface roughness, Ra = 3.18 μm) are used in this work. The experimental errors in the subcooling measure and the pressure one are ±1 K and ±1 kPa, while in the heat flux it is ±2%. The transient CHF data for the ramp-wise heat input and the stepwise one are compared with those for the exponentially increasing heat input (Q = Q0 exp(t/τ), τ = 16.82 ms to 15.52 s) previously obtained and the dominant variables on transient CHF for heat input waveform difference are confirmed. The transient CHF data are compared with the values calculated by the steady state CHF correlations against inlet and outlet subcoolings, and the applicability of steady state CHF correlations is confirmed extending its possible validity for the reduced time, ωp, down to 800 ms. The transient CHF data are compared with the values calculated by the transient CHF correlations against inlet and outlet subcoolings, and the influence of heat input waveform on transient CHF is clarified based on the experimental data for the ramp-wise heat input, the stepwise one and the exponentially increasing one. The dominant mechanisms of the subcooled flow boiling critical heat flux for the ramp-wise heat input, the stepwise one and the exponentially increasing one are discussed
Semiconductor-enriched single wall carbon nanotube networks applied to field effect transistors
Substantial progress on field effect transistors "FETs" consisting of
semiconducting single wall carbon nanotubes "s-SWNTs" without detectable traces
of metallic nanotubes and impurities is reported. Nearly perfect removal of
metallic nanotubes is confirmed by optical absorption, Raman measurements, and
electrical measurements. This outstanding result was made possible in
particular by ultracentrifugation (150 000 g) of solutions prepared from SWNT
powders using polyfluorene as an extracting agent in toluene. Such s-SWNTs
processable solutions were applied to realize FET, embodying randomly or
preferentially oriented nanotube networks prepared by spin coating or
dielectrophoresis. Devices exhibit stable p-type semiconductor behavior in air
with very promising characteristics. The on-off current ratio is 10^5, the
on-current level is around 10 A, and the estimated hole mobility is larger
than 2 cm2 / V s
The Perturbative Spectrum of the Dressed Sliver
We analyze the fluctuations of the dressed sliver solution found in a
previous paper, hep-th/0311198, in the operator formulation of Vacuum String
Field Theory. We derive the tachyon wave function and then analyze the higher
level fluctuations. We show that the dressing is responsible for implementing
the transversality condition on the massless vector. In order to consistently
deal with the singular mode we introduce a string midpoint regulator and
we show that it is possible to accommodate all the open string states among the
solutions to the linearized equations of motion. We finally show how the
dressing can give rise to the correct ratio between the energy density of the
dressed sliver and the brane tension computed via the three-tachyons-coupling.Comment: 52 pages, v2: comment added in sec. 5, v3: one appendix added,
comments added in introduction and conclusion, to appear on PR
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