7,796 research outputs found
Axial light emission and Ar metastable densities in a parallel plate dc micro discharge in steady state and transient regimes
Axial emission profiles in a parallel plate dc micro discharge (feedgas:
argon; discharge gap d=1mm; pressure p=10Torr) were studied by means of time
resolved imaging with a fast ICCD camera. Additionally, volt-ampere (V-A)
characteristics were recorded and Ar* metastable densities were measured by
tunable diode laser absorption spectroscopy (TDLAS). Axial emission profiles in
the steady state regime are similar to corresponding profiles in standard size
discharges (d=1cm, p=1Torr). For some discharge conditions relaxation
oscillations are present when the micro discharge switches periodically between
low current Townsend-like mode and normal glow. At the same time the axial
emission profile shows transient behavior, starting with peak distribution at
the anode, which gradually moves towards the cathode during the normal glow.
The development of argon metastable densities highly correlates with the
oscillating discharge current. Gas temperatures in the low current
Townsend-like mode (T= 320-400K) and the high current glow mode (T=469-526K)
were determined by the broadening of the recorded spectral profiles as a
function of the discharge current.Comment: submitted to Plasma Sources Sci. Techno
SO(10) GUT and Quark-Lepton Mass Matrices
The phenomenological model that all quark and lepton mass matrices have the
same zero texture, namely their (1,1), (1,3) and (3,1) components are zeros, is
discussed in the context of SO(10) Grand Unified Theories (GUTs). The mass
matrices of type I for quarks are consistent with the experimental data in the
quark sector. For the lepton sector, consistent fitting to the data of neutrino
oscillation experiments force us to use the mass matrix for the charged leptons
which is slightly deviated from type I. Given quark masses and charged lepton
masses, the model includes 19 free parameters, whereas the SO(10) GUTs gives 16
constrained equations. Changing the remaining three parameters freely, we can
fit all the entries of the CKM quark mixing matrix and the MNS lepton mixing
matrix, and three neutrino masses consistently with the present experimental
data.Comment: 32pp, REV TeX, 12 EPS Figure
g factor of Li-like ions with nonzero nuclear spin
The fully relativistic theory of the g factor of Li-like ions with nonzero
nuclear spin is considered for the (1s)^2 2s state. The magnetic-dipole
hyperfine-interaction correction to the atomic g factor is calculated including
the one-electron contributions as well as the interelectronic-interaction
effects of order 1/Z. This correction is combined with the
interelectronic-interaction, QED, nuclear recoil, and nuclear size corrections
to obtain high-precision theoretical values for the g factor of Li-like ions
with nonzero nuclear spin. The results can be used for a precise determination
of nuclear magnetic moments from g factor experiments.Comment: 20 pages, 5 figure
Atomic Transport in Dense, Multi-Component Metallic Liquids
Pd43Ni10Cu27P0 has been investigated in its equilibrium liquid state with
incoherent, inelastic neutron scattering. As compared to simple liquids, liquid
PdNiCuP is characterized by a dense packing with a packing fraction above 0.5.
The intermediate scattering function exhibits a fast relaxation process that
precedes structural relaxation. Structural relaxation obeys a time-temperature
superposition that extends over a temperature range of 540K. The mode-coupling
theory of the liquid to glass transition (MCT) gives a consistent description
of the dynamics which governs the mass transport in liquid PdNiCuP alloys. MCT
scaling laws extrapolate to a critical temperature Tc at about 20% below the
liquidus temperature. Diffusivities derived from the mean relaxation times
compare well with Co diffusivities from recent tracer diffusion measurements
and diffsuivities calculated from viscosity via the Stokes-Einstein relation.
In contrast to simple metallic liquids, the atomic transport in dense, liquid
PdNiCuP is characterized by a drastical slowing down of dynamics on cooling, a
q^{-2} dependence of the mean relaxation times at intermediate q and a
vanishing isotope effect as a result of a highly collective transport
mechanism. At temperatures as high as 2Tc diffusion in liquid PdNiCuP is as
fast as in simple liquids at the melting point. However, the difference in the
underlying atomic transport mechanism indicates that the diffusion mechanism in
liquids is not controlled by the value of the diffusivity but rather by that of
the packing fraction
Experimental results on strangeness production in proton-proton collisions at COSY
The production of K+ and K- mesons in elementary proton-proton collision has
been investigated at the Cooler Synchrotron COSY in Juelich. A high quality
proton beam with low emittance and small momentum spread permitted to study the
creation of these mesons very close to the kinematical threshold. The energy
dependence of the total cross section is investigated using internal beam
facilities providing a high accuracy particle momentum determination as well as
an external non-magnetic detection setup with a large geometrical acceptance.
The determination of the four-momentum vectors for all ejectiles of each
registered event gives the complete kinematical information allowing to study
the interaction of the outgoing particles. Results on the performed studies of
the pp --> pp K+ K-, pp --> p Lambda K+ and pp --> p Sigma0 K+ reactions will
be presented and their relevance to the interpretation of heavy ion collisions
will be discussed.Comment: 8 pages, 6 figures, plenary talk at 6th International Conference On
Strange Quarks in Matter: '2001 - A Flavorspace Odyssey' (SQM2001),
Frankfurt, Germany, September 25-29, 2001, to be published in J. Phys. G:
Nucl. Part. Phy
Paradoxes of neutrino oscillations
Despite the theory of neutrino oscillations being rather old, some of its
basic issues are still being debated in the literature. We discuss, in the
framework of the wave packet approach, a number of such issues, including the
relevance of the "same energy" and "same momentum" assumptions, the role of
quantum-mechanical uncertainty relations in neutrino oscillations, the
dependence of the production/detection and propagation coherence conditions
that ensure the observability of neutrino oscillations on neutrino energy and
momentum uncertainties, the question of (in)dependence of the oscillation
probabilities on the neutrino production and detection processes, the
applicability limits of the stationary source approximation, and Lorentz
invariance of the oscillation probability. We also develop a novel approach to
calculation of the oscillation probability in the wave packet picture, based on
the summation/integration conventions different from the standard one, which
gives a new insight into the oscillation phenomenology. We discuss a number of
apparently paradoxical features of the theory of neutrino oscillations.Comment: LaTeX, 45 pages, no figures. v2: references adde
Using biomarkers to predict TB treatment duration (Predict TB): a prospective, randomized, noninferiority, treatment shortening clinical trial
Background : By the early 1980s, tuberculosis treatment was shortened from 24 to 6 months, maintaining relapse rates of 1-2%. Subsequent trials attempting shorter durations have failed, with 4-month arms consistently having relapse rates of 15-20%. One trial shortened treatment only among those without baseline cavity on chest x-ray and whose month 2 sputum culture converted to negative. The 4-month arm relapse rate decreased to 7% but was still significantly worse than the 6-month arm (1.6%, P<0.01). We hypothesize that PET/CT characteristics at baseline, PET/CT changes at one month, and markers of residual bacterial load will identify patients with tuberculosis who can be cured with 4 months (16 weeks) of standard treatment.Methods: This is a prospective, multicenter, randomized, phase 2b, noninferiority clinical trial of pulmonary tuberculosis participants. Those eligible start standard of care treatment. PET/CT scans are done at weeks 0, 4, and 16 or 24. Participants who do not meet early treatment completion criteria (baseline radiologic severity, radiologic response at one month, and GeneXpert-detectable bacilli at four months) are placed in Arm A (24 weeks of standard therapy). Those who meet the early treatment completion criteria are randomized at week 16 to continue treatment to week 24 (Arm B) or complete treatment at week 16 (Arm C). The primary endpoint compares the treatment success rate at 18 months between Arms B and C.Discussion: Multiple biomarkers have been assessed to predict TB treatment outcomes. This study uses PET/CT scans and GeneXpert (Xpert) cycle threshold to risk stratify participants. PET/CT scans are not applicable to global public health but could be used in clinical trials to stratify participants and possibly become a surrogate endpoint. If the Predict TB trial is successful, other immunological biomarkers or transcriptional signatures that correlate with treatment outcome may be identified. TRIAL REGISTRATION: NCT02821832
A method to disentangle single- and multi-meson production in missing mass spectra from quasi-free pn --> pn X reactions
The separation of contributions from multi- and single-meson production in
the missing mass spectrum of the quasi-free pn --> pnX reaction constitutes
a~challenging task when the reaction is studied close to threshold. This is
especially true if the resolution of the mass determination is comparable with
the excess energy and if the investigated signal appears close to the
kinematical limit. In this article we outline a method which permits the
extraction of the signal originating from the creation of a single meson
without the necessity of conducting model-dependent simulations. For the pd -->
pnXp(spectator) reactions, the method allows one to combine events
corresponding to multi-meson production at various excess energies with respect
to the pn --> pn meson process, and hence leads to an increase of the
statistics needed for the determination of the shape of the multi-meson
background.
As an example of the application of the method, we demonstrate that the
evaluation of the data from the pd --> pnXp(sp) process according to the
described technique enables one to extract a signal of the pn --> pn eta
reaction whose shape is consistent with expectations, supporting the
correctness and usefulness of the method introduced.Comment: 14 pages, 10 figure
Far-infrared vibrational properties of linear C60 polymers: A comparison between neutral and charged materials
We report the far-infrared transmittance spectrum of a pure phase of the orthorhombic high-temperature and high-pressure C-60 polymer and compare the results with a previously published spectrum of the charged RbC60 orthorhombic polymer. Assignments for both spectra are made with the aid of first-principles quantum molecular dynamics simulations of the two materials. We find that the striking spectral differences between the neutral and charged linear fullerene polymers can be fully accounted for by charge effects on the C-60 ball
Inclusive Electron Scattering from Nuclei at
The inclusive A(e,e') cross section for was measured on H,
C, Fe, and Au for momentum transfers from 1-7 (GeV/c). The scaling
behavior of the data was examined in the region of transition from y-scaling to
x-scaling. Throughout this transitional region, the data exhibit -scaling,
reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.Comment: 4 pages, RevTeX; 4 figures (postscript in .tar.Z file
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