4,631 research outputs found
Hadronization corrections to helicity components of the fragmentation function
In the hadronic decays of Z, gluon emission leads to the appearance of the
longitudinal component of the fragmentation function, F_L. Measurement of F_L
and the transverse component, F_T, could thus provide an insight into the gluon
fragmentation function. However, hadronization corrections at low x can be
significant. Here we present a method of accounting for such corrections, using
the JETSET event generator as illustration.Comment: 11 pages, 5 figure
Raman, infrared and optical spectra of the spin-Peierls compound NaV_2O_5
We have measured polarized spectra of Raman scattering, infrared and optical
transmission of NaV_2O_5 single crystals above the temperature of the
spin-Peierls transition Tsp=35 K. Some of the far-infrared (FIR) phonon lines
are strongly asymmetric, due to the spin-phonon interaction. In addition to the
phonon lines, a broad band was observed in the c(aa)c Raman spectrum and in the
E||a FIR transmission spectrum. A possible origin of these bands is discussed.
The absorption band at 10000 cm-1 1.25 eV is attributed to vanadium d-d
electronic transitions while the absorption edge above 3 eV is supposed to
correspond to the onset of charge-transfer transitions.Comment: 7 figures, 8 page
Puzzlement about thermal redshift
Discussed is the classical theoretical description of the experimentally
established thermal redshift of spectral lines. Straightforward calculation of
the observable spectrum from a canonical ensamble of monochromatic radiators
yileds overall blueshift rather than redshift. It is concluded that the
customary explanation of the thermal redshift as a second order Doppler effect
does not bear closer examination, and that in fact, the phenomenon ''thermal
redshift'' is not yet fully uderstood in classical terms.Comment: 4 pages RevTeX, 1 postscript figur
Effect of bonding of a CO molecule on the conductance of atomic metal wires
We have measured the effect of bonding of a CO molecule on the conductance of
Au, Cu, Pt, and Ni atomic contacts at 4.2 K. When CO gas is admitted to the
metal nano contacts, a conductance feature appears in the conductance histogram
near 0.5 of the quantum unit of conductance, for all metals. For Au, the
intensity of this fractional conductance feature can be tuned with the bias
voltage, and it disappears at high bias voltage (above 200 mV). The
bonding of CO to Au appears to be weakest, and associated with monotomic Au
wire formation.Comment: 6 figure
Surface and Bulk Structural Properties of Single Crystalline Sr3Ru2O7
We report temperature and thermal-cycling dependence of surface and bulk
structures of double-layered perovskite Sr3Ru2O7 single crystals. The surface
and bulk structures were investigated using low-energy electron diffraction
(LEED) and single-crystal X-ray diffraction (XRD) techniques, respectively.
Single-crystal XRD data is in good agreement with previous reports for the bulk
structure with RuO6 octahedral rotation, which increases with decreasing
temperature (~ 6.7(6)degrees at 300 K and ~ 8.1(2) degrees at 90 K). LEED
results reveal that the octahedra at the surface are much more distorted with a
higher rotation angle (~ 12 degrees between 300 and 80 K) and a slight tilt
((4.5\pm2.5) degrees at 300 K and (2.5\pm1.7) degrees at 80 K). While XRD data
confirms temperature dependence of the unit cell height/width ratio (i.e.
lattice parameter c divided by the average of parameters a and b) found in a
prior neutron powder diffraction investigation, both bulk and surface
structures display little change with thermal cycles between 300 and 80 K.Comment: 25 pages, 5 figures, 5 tables, to appear in Physical Review
Peculiarities in produced particles emission in 208Pb + Ag(Br) interactions at 158 A GeV/c
The angular structures of particles produced in 208Pb induced collisions with
Ag(Br) nuclei in an emulsion detector at 158 A GeV/c have been investigated.
Nonstatistical ring-like substructures in azimuthal plane of the collision have
been found and their parameters have been determined. The indication on the
formation of the ring-like substructures from two symmetrical emission cones -
one in the forward and other in the backward direction in the center-of mass
system have been obtained. The ring-like substructures parameters have been
determined. The experimental results are in an agreement with I.M. Dremin idea,
that mechanism of the ring-like substructures formation in nuclear collisions
is similar to that of Cherenkov electromagnetic radiation.Comment: 10 pages, 7 figures, Report at the HADRON STRUCTURE'04 Conference,
Smolenice, Slovakia, 30.8.-3.9.200
The fractality of the relaxation modes in deterministic reaction-diffusion systems
In chaotic reaction-diffusion systems with two degrees of freedom, the modes
governing the exponential relaxation to the thermodynamic equilibrium present a
fractal structure which can be characterized by a Hausdorff dimension. For long
wavelength modes, this dimension is related to the Lyapunov exponent and to a
reactive diffusion coefficient. This relationship is tested numerically on a
reactive multibaker model and on a two-dimensional periodic reactive Lorentz
gas. The agreement with the theory is excellent
Excitonic and vibronic spectra of Frenkel excitons in a two-dimensional simple latice
Excitonic and vibronic spectra of Frenkel excitons (FEs) in a two-dimensional
(2D) lattice with one molecule per unit cell have been studied and their
manifestation in the linear absorption is simulated. We use the Green function
formalism, the vibronic approach (see Lalov and Zhelyazkov [Phys. Rev. B
\textbf{75}, 245435 (2007)]), and the nearest-neighbor approximation to find
expressions of the linear absorption lineshape in closed form (in terms of the
elliptic integrals) for the following 2D models: (a) vibronic spectra of
polyacenes (naphthalene, anthracene, tetracene); (b) vibronic spectra of a
simple hexagonal lattice. The two 2D models include both linear and quadratic
FE--phonon coupling. Our simulations concern the excitonic density of state
(DOS), and also the position and lineshape of vibronic spectra (FE plus one
phonon, FE plus two phonons). The positions of many-particle (MP-unbound)
FE--phonon states, as well as the impact of the Van Hove singularities on the
linear absorption have been established by using typical values of the
excitonic and vibrational parameters. In the case of a simple hexagonal lattice
the following types of FEs have been considered: (i) non-degenerate FEs whose
transition dipole moment is perpendicular to the plane of the lattice, and (ii)
degenerate FEs with transition dipole moments parallel to the layer. We found a
cumulative impact of the linear and quadratic FE--phonon coupling on the
positions of vibronic maxima in the case (ii), and a compensating impact in the
case (i).Comment: 13 pages, 12 figure
Bias-assisted photoelectrochemical etching of p-GaN at 300 K
Photoelectrochemical (PEC)etching of p-type GaN has been realized in room temperature, 0.1 M KOH solutions. PECetching of GaN was achieved by applying a positive bias to the surface of the p-GaN layer through a deposited titanium mask. The applied bias reduces the field at the semiconductor surface, which induced the dissolution of the GaN. The effect of bias on etch rate and morphology was examined. It was found that insulating the Ti mask from the KOH solution with Si3N4 significantly increases the etch rate. The rms roughness of the etched region decreased as the bias voltage increased. Etch rates as high as 4.4 nm/min were recorded for films etched at 2 V
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