400 research outputs found
Collision damping in the pi 3He -> d'N reaction near the threshold
We present a simple quantum mechanical model exploiting the optical potential
approach for the description of collision damping in the reaction pi 3He -> d'N
near the threshold, which recently has been measured at TRIUMF. The influence
of the open d'N -> NNN channel is taken into account. It leads to a suppression
factor of about ten in the d' survival probability. Applications of the method
to other reactions are outlined.Comment: RevTeX4, 14 pages, 3 Postscript figures, uses epsfig.sty, to appear
in Phys.Rev.
Search for Narrow NNpi Resonances in Exclusive p p -> p p pi+ pi- Measurements
Narrow structures in the range of a few MeV have been searched for in p p pi+
and p p pi- invariant mass spectra obtained from exclusive measurements of the
p p -> p p pi+ pi- reaction at Tp = 725, 750 and 775 MeV using the PROMICE/WASA
detector at CELSIUS. The selected reaction is particularily well suited for the
search for NN and / or N Delta decoupled dibaryon resonances. Except for a
possible fluctuation at 2087 MeV/c^2 in Mpppi- no narrow structures could be
identified neither in Mpppi+ nor in Mpppi- on the 3 sigma level of statistical
significance, giving an upper limit (95% C.L.) for dibaryon production in this
reaction of sigma < 20 nb for 2020 MeV/c^2 < m(dibaryon) < 2085 MeV/c^2Comment: 3 pages, 4 figure
Steady State of microemulsions in shear flow
Steady-state properties of microemulsions in shear flow are studied in the
context of a Ginzburg-Landau free-energy approach. Explicit expressions are
given for the structure factor and the time correlation function at the one
loop level of approximation. Our results predict a four-peak pattern for the
structure factor, implying the simultaneous presence of interfaces aligned with
two different orientations.
Due to the peculiar interface structure a non-monotonous relaxation of the
time correlator is also found.Comment: 5 pages, 3 figure
Ordering of the lamellar phase under a shear flow
The dynamics of a system quenched into a state with lamellar order and
subject to an uniform shear flow is solved in the large-N limit. The
description is based on the Brazovskii free-energy and the evolution follows a
convection-diffusion equation. Lamellae order preferentially with the normal
along the vorticity direction. Typical lengths grow as (with
logarithmic corrections) in the flow direction and logarithmically in the shear
direction. Dynamical scaling holds in the two-dimensional case while it is
violated in D=3
Nonequilibrium dynamics: a renormalized computation scheme
We present a regularized and renormalized version of the one-loop nonlinear
relaxation equations that determine the non-equilibrium time evolution of a
classical (constant) field coupled to its quantum fluctuations. We obtain a
computational method in which the evaluation of divergent fluctuation integrals
and the evaluation of the exact finite parts are cleanly separated so as to
allow for a wide freedom in the choice of regularization and renormalization
schemes. We use dimensional regularization here. Within the same formalism we
analyze also the regularization and renormalization of the energy-momentum
tensor. The energy density serves to monitor the reliability of our numerical
computation. The method is applied to the simple case of a scalar phi^4 theory;
the results are similar to the ones found previously by other groups.Comment: 15 pages, 9 postscript figures, revtex; version published in Phys.
Rev, with minor corrections; improves the first version of 1996 by including
the discussion of energy momentum tenso
Transiting exoplanets from the CoRoT space mission. XV. CoRoT-15b: a brown dwarf transiting companion
We report the discovery by the CoRoT space mission of a transiting brown
dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a
radius of 1.12 +0.30 -0.15 Rjup, a mass of 63.3 +- 4.1 Mjup, and is thus the
second transiting companion lying in the theoretical mass domain of brown
dwarfs. CoRoT-15b is either very young or inflated compared to standard
evolution models, a situation similar to that of M-dwarfs stars orbiting close
to solar-type stars. Spectroscopic constraints and an analysis of the
lightcurve favors a spin period between 2.9 and 3.1 days for the central star,
compatible with a double-synchronisation of the system.Comment: 7 pages, 6 figures, accepted in A&
Doppler follow-up of OGLE transiting companions in the Galactic bulge
Two years ago, the OGLE-III survey (Optical Gravitational Lensing Experiment)
announced the detection of 54 short period multi-transiting objects in the
Galactic bulge (Udalski et al., 2002a, 2002b). Some of these objects were
considered to be potential hot Jupiters. In order to determine the true nature
of these objects and to characterize their actual mass, we conducted a radial
velocity follow-up of 18 of the smallest transiting candidates. We describe
here our procedure and report the characterization of 8 low mass star
transiting companions, 2 grazing eclipsing binaries, 2 triple systems, 1
confirmed exoplanet (OGLE-TR-56b), 1 possible exoplanet (OGLE-TR-10b), 1 clear
false positive and 3 unsolved cases. The variety of cases encountered in our
follow-up covers a large part of the possible scenarii occuring in the search
for planetary transits. As a by-product, our program yields precise masses and
radii of low mass stars.Comment: accepted in A&
Lattice-gas simulations of Domain Growth, Saturation and Self-Assembly in Immiscible Fluids and Microemulsions
We investigate the dynamical behavior of both binary fluid and ternary
microemulsion systems in two dimensions using a recently introduced
hydrodynamic lattice-gas model of microemulsions. We find that the presence of
amphiphile in our simulations reduces the usual oil-water interfacial tension
in accord with experiment and consequently affects the non-equilibrium growth
of oil and water domains. As the density of surfactant is increased we observe
a crossover from the usual two-dimensional binary fluid scaling laws to a
growth that is {\it slow}, and we find that this slow growth can be
characterized by a logarithmic time scale. With sufficient surfactant in the
system we observe that the domains cease to grow beyond a certain point and we
find that this final characteristic domain size is inversely proportional to
the interfacial surfactant concentration in the system.Comment: 28 pages, latex, embedded .eps figures, one figure is in colour, all
in one uuencoded gzip compressed tar file, submitted to Physical Review
Unique, nonâEarthlike, meteoritic ion behavior in upper atmosphere of Mars
Interplanetary dust particles have long been expected to produce permanent ionospheric metal ion layers at Mars, as on Earth, but the two environments are so different that uncertainty existed as to whether terrestrial-established understanding would apply to Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission made the first in situ detection of the continuous presence of Na+, Mg+, and Fe+ at Mars and indeed revealed non-Earthlike features/processes. There is no separation of the light Mg+ and the heavy Fe+ with increasing altitude as expected for gravity control. The metal ions are well-mixed with the neutral atmosphere at altitudes where no mixing process is expected. Isolated metal ion layers mimicking Earth's sporadic E layers occur despite the lack of a strong magnetic field as required at Earth. Further, the metal ion distributions are coherent enough to always show atmospheric gravity wave signatures. All features and processes are unique to Mars
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