90 research outputs found
Transverse NMR relaxation in magnetically heterogeneous media
We consider the NMR signal from a permeable medium with a heterogeneous
Larmor frequency component that varies on a scale comparable to the
spin-carrier diffusion length. We focus on the mesoscopic part of the
transverse relaxation, that occurs due to dispersion of precession phases of
spins accumulated during diffusive motion. By relating the spectral lineshape
to correlation functions of the spatially varying Larmor frequency, we
demonstrate how the correlation length and the variance of the Larmor frequency
distribution can be determined from the NMR spectrum. We corroborate our
results by numerical simulations, and apply them to quantify human blood
spectra.Comment: 9 pages, 4 figure
What is the lightest excited state of the strongly selfcoupled Higgs field?
We argue for the existence of an upper bound on the Higgs mass at which
the lowest excited state of the Higgs field ceases to be the conventional plane
wave. An explicit construction of an alternative nonperturbative state is
discussed. This excitation is spatially localized. The field fluctuations
inside the localization region are large. The energy of the excitation is
smaller than the mass of the plane wave state at . An approximate
value of is found to be times the vacuum expectation
value. This is an upper bound at the tree level.Comment: 11 pages, Dortmund University Do-TH-94/19, LaTex, 7 figures appended
as uuencoded, tar-compressed .eps file
Investigation of structural perfection of SiC ingots grown by a sublimation method
Monocrystalline SiC ingots were grown by a modified Lely method using 6H-SiC seed crystals with (0001) base plane. The crystal growth was carried out in the temperature range 2200-2500 ⁰C at Ar pressure from 2 to 40 mbar. The rate of growth varied between 0.3 and 1.5 mm/hour in the C-axis direction. At growth time of about 15 hours we obtained the ingots with 35 mm useful diameter. To determine the polytype composition of SiC ingots the Raman scattering technique was used. The structural defects were investigated by means of reflection and transmission light microscopy and by selective etching. In the best ingots the dislocation density did not exceed 102 cm⁻², the micropipe density - 10-20 cm⁻², and blocks were absent
One-loop corrections to the metastable vacuum decay
We evaluate the one-loop prefactor in the false vacuum decay rate in a theory
of a self interacting scalar field in 3+1 dimensions. We use a numerical
method, established some time ago, which is based on a well-known theorem on
functional determinants. The proper handling of zero modes and of
renormalization is discussed. The numerical results in particular show that
quantum corrections become smaller away from the thin-wall case. In the
thin-wall limit the numerical results are found to join into those obtained by
a gradient expansion.Comment: 31 pages, 7 figure
Conoscopic patterns in photonic band gap of cholesteric liquid crystal cells with twist defects
We theoretically investigate into the effects of the incidence angles in
light transmission of cholesteric liquid crystal two-layer sandwich structures
with twist defects created by rotation of the one layer about the helical
axis.The conoscopic images and polarization resolved patterns are obtained for
thick layers by computing the intensity and the polarization parameters as a
function of the incidence angles.In addition to the defect angle induced
rotation of the pictures as a whole, the rings of defect mode resonances are
found to shrink to the origin and disappear as the defect twist angle varies
from zero to its limiting value and beyond.Comment: revtex4, 7 pages, 4 figure
spectroscopy
In the framework of potential models for heavy quarkonium the mass spectrum
for the system () is considered. Spin-dependent splittings, taking
into account a change of a constant for effective Coulomb interaction between
the quarks, and widths of radiative transitions between the () levels
are calculated. In the framework of QCD sum rules, masses of the lightest
vector and pseudoscalar states are estimated, scaling relation
for leptonic constants of heavy quarkonia is derived, and the leptonic constant
is evaluated.Comment: IHEP 94-51, LATEX, 39 page
Measurement of and between 3.12 and 3.72 GeV at the KEDR detector
Using the KEDR detector at the VEPP-4M collider, we have measured
the values of and at seven points of the center-of-mass
energy between 3.12 and 3.72 GeV. The total achieved accuracy is about or
better than at most of energy points with a systematic uncertainty of
about . At the moment it is the most accurate measurement of in
this energy range
New precise determination of the \tau lepton mass at KEDR detector
The status of the experiment on the precise lepton mass measurement
running at the VEPP-4M collider with the KEDR detector is reported. The mass
value is evaluated from the cross section behaviour around the
production threshold. The preliminary result based on 6.7 pb of data is
MeV. Using 0.8 pb of data
collected at the peak the preliminary result is also obtained:
eV.Comment: 6 pages, 8 figures; The 9th International Workshop on Tau-Lepton
Physics, Tau0
Measurement of \Gamma_{ee}(J/\psi)*Br(J/\psi->e^+e^-) and \Gamma_{ee}(J/\psi)*Br(J/\psi->\mu^+\mu^-)
The products of the electron width of the J/\psi meson and the branching
fraction of its decays to the lepton pairs were measured using data from the
KEDR experiment at the VEPP-4M electron-positron collider. The results are
\Gamma_{ee}(J/\psi)*Br(J/\psi->e^+e^-)=(0.3323\pm0.0064\pm0.0048) keV,
\Gamma_{ee}(J/\psi)*Br(J/\psi->\mu^+\mu^-)=(0.3318\pm0.0052\pm0.0063) keV.
Their combinations
\Gamma_{ee}\times(\Gamma_{ee}+\Gamma_{\mu\mu})/\Gamma=(0.6641\pm0.0082\pm0.0100)
keV,
\Gamma_{ee}/\Gamma_{\mu\mu}=1.002\pm0.021\pm0.013 can be used to improve
theaccuracy of the leptonic and full widths and test leptonic universality.
Assuming e\mu universality and using the world average value of the lepton
branching fraction, we also determine the leptonic \Gamma_{ll}=5.59\pm0.12 keV
and total \Gamma=94.1\pm2.7 keV widths of the J/\psi meson.Comment: 7 pages, 6 figure
Search for narrow resonances in e+ e- annihilation between 1.85 and 3.1 GeV with the KEDR Detector
We report results of a search for narrow resonances in e+ e- annihilation at
center-of-mass energies between 1.85 and 3.1 GeV performed with the KEDR
detector at the VEPP-4M e+ e- collider. The upper limit on the leptonic width
of a narrow resonance Gamma(R -> ee) Br(R -> hadr) < 120 eV has been obtained
(at 90 % C.L.)
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