62,146 research outputs found
Method and means for providing an absolute power measurement capability Patent
Input radio frequency circuit for switching type absolute temperature measuring radiometer for noise source
Interquark Potential in Schrodinger Representation
Static charges are introduced in Yang-Mills theory via coupling to heavy
fermions. The states containing static color charges are constructed using
integration over gauge transformations. A functional representation for
interquark potential is obtained. This representation provides a simple
criterion for confinement.Comment: 9pp., Late
Heterocyst placement strategies to maximize growth of cyanobacterial filaments
Under conditions of limited fixed-nitrogen, some filamentous cyanobacteria
develop a regular pattern of heterocyst cells that fix nitrogen for the
remaining vegetative cells. We examine three different heterocyst placement
strategies by quantitatively modelling filament growth while varying both
external fixed-nitrogen and leakage from the filament. We find that there is an
optimum heterocyst frequency which maximizes the growth rate of the filament;
the optimum frequency decreases as the external fixed-nitrogen concentration
increases but increases as the leakage increases. In the presence of leakage,
filaments implementing a local heterocyst placement strategy grow significantly
faster than filaments implementing random heterocyst placement strategies. With
no extracellular fixed-nitrogen, consistent with recent experimental studies of
Anabaena sp. PCC 7120, the modelled heterocyst spacing distribution using our
local heterocyst placement strategy is qualitatively similar to experimentally
observed patterns. As external fixed-nitrogen is increased, the spacing
distribution for our local placement strategy retains the same shape while the
average spacing between heterocysts continuously increases.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Physical Biology. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher-authenticated version
will be available onlin
Growth, Characterization, and Electrochemical Properties of Doped n-Type KTaO_3 Photoanodes
The effects of compositionally induced changes on the semiconducting properties, optical response, chemical stability, and overall performance of KTaO_3 photoanodes in photoelectrochemical (PEC) cells have been investigated. Single crystals of n-type Ca- and Ba-doped KTaO_3 with carrier concentrations ranging from 0.45 to 11.5×10^(19) cm^(−3) were grown and characterized as photoanodes in basic aqueous electrolyte PEC cells. The PEC properties of the crystals, including the photocurrent, photovoltage, and flatband potential in contact with 8.5 M NaOH(aq) were relatively independent of whether Ca or Ba was used to produce the semiconducting form of KTaO_3. All of the Ca- or Ba-doped KTaO_3 single-crystal photoanodes were chemically stable in the electrolyte and, based on the open-circuit potential and the band-edge positions, were capable of unassisted photochemical H_2 and O_2 evolution from H_2O. The minority-carrier diffusion lengths values were small and comparable to the depletion region width. Photoanodic currents were only observed for photoanode illumination with light above the bandgap (i.e., λ<340 nm). The maximum external quantum yield occurred at λ=255 nm (4.85 eV), and the depletion width plus the minority-carrier diffusion length ranged from 20 to 65 nm for the various KTaO_3-based photoanode materials
The Instanton Molecule Liquid and "Sticky Molasses" Above T_c
The main objective of this work is to explore the evolution in the structure
of the quark-antiquark bound states in going down in the chirally restored
phase from the so-called "zero binding points" T_zb to the QCD critical
temperature T_c at which the Nambu-Goldstone and Wigner-Weyl modes meet. In
doing this, we adopt the idea recently introduced by Shuryak and Zahed for
charmed , light-quark mesons and
gluons that at T_zb, the quark-antiquark scattering length goes through
infinity at which conformal invariance is restored, thereby transforming the
matter into a near perfect fluid behaving hydrodynamically, as found at RHIC.
We show that the binding of these states is accomplished by the combination of
(i) the color Coulomb interaction, (ii) the relativistic effects, and (iii) the
interaction induced by the instanton-anti-instanton molecules. The spin-spin
forces turned out to be small. While near T_zb all mesons are large-size
nonrelativistic objects bound by Coulomb attraction, near T_c they get much
more tightly bound, with many-body collective interactions becoming important
and making the and masses approach zero (in the chiral limit).
The wave function at the origin grows strongly with binding, and the near-local
four-Fermi interactions induced by the instanton molecules play an increasingly
more important role as the temperature moves downward toward T_c.Comment: Contribution to QM2004 proceedings, 4 page
Sensitivity of exclusive proton knockout spin observables to different Lorentz invariant representations of the NN interaction
Within the framework of the relativistic plane wave impulse approximation, we
study the observable consequences of employing a complete Lorentz invariant
representation of the NN scattering matrix in terms of 44 independent
amplitudes, as opposed to the previously-employed, but ambiguous, five-term
Lorentz invariant parametrization of the NN scattering matrix, for the
prediction of complete sets of exclusive () polarization
transfer observables. Two kinematic conditions are considered, namely proton
knockout from the state of Pb at an incident energy of 202
MeV for coplanar scattering angles (), as well as
an incident energy of 392 MeV for the angle pair (). The results indicate that certain spin observables are ideal
for discriminating between the two representations.Comment: 19 pages, 5 figures, Revtex, To be published in Phys. Rev.
A new 1.6-micron map of Titan’s surface
We present a new map of Titan's surface obtained in the spectral 'window' at ∼1.6 μm between strong methane absorption. This pre-Cassini view of Titan's surface was created from images obtained using adaptive optics on the W.M. Keck II telescope and is the highest resolution map yet made of Titan's surface. Numerous surface features down to the limits of the spatial resolution (∼200–300 km) are apparent. No features are easily identifiable in terms of their geologic origin, although several are likely craters
Kaon Condensation in the Bound-State Approach to the Skyrme Model
We explore kaon condensation using the bound-state approach to the Skyrme
model on a 3-sphere. The condensation occurs when the energy required to
produce a falls below the electron fermi level. This happens at the
baryon number density on the order of 3--4 times nuclear density.Comment: LaTeX format, 15 pages. 3 Postscript figures, compressed and
uuencode
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