347 research outputs found
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
The Martian daytime convective boundary layer: Results from radio occultation measurements and a mesoscale model
We investigate the behavior of the Martian daytime convective boundary layer (CBL) through a combination of data analysis and modeling. This study relies on two subsets of Mars Express radio occultation (RO) measurements that sounded the atmosphere in north- ern spring of successive Mars years. Only the first year of observations has been examined previously (Hinson et al., 2008); the second year provides complementary spatial coverage and greatly increases the total number of observations. Analysis of the RO profiles yields basic characteristics of the CBL, such as its depth D and the average potential temperature of the mixed layer θm. We also combine RO retrievals of surface pressure with surface tem- peratures from infrared sounding to characterize the surface forcing, expressing the result as a potential temperature θs. These observations are at local times in early afternoon for θs and late afternoon for θm and D, when each parameter is near its diurnal maximum. We use measurements at mid-to-low latitudes, which sample a wide range of θs (227–294 K), to determine the response of the lower atmosphere to spatial variations in surface forcing. The depth of the CBL ranges from less than 3 km in the midlatitude topographic basins to more than 9 km above elevated terrain in the tropics. The dependence of θm on θs is linear, with a characteristic slope of about 0.7 in both years. We gain further insight by performing a simulation with the Oregon State University Mars Mesoscale Model in a region centered on Isidis Planitia, which includes two potential landing sites for the Mars 2020 Rover. As expected from previous modeling of much smaller craters, the arc of steep to- pography along the western and southern margins of Isidis produces a distinctive, diurnally varying, mesoscale circulation. The simulation captures key features of the observations, such as the wide variations in θm and D — by 34 K and 9 km, respectively — that occur within this region. The model also accounts for peculiar features of RO profiles on the rim of Isidis, where the wind field strongly influences the depth and diurnal evolution of the CBL. Detailed comparisons with the observations validate the general performance of the model and confirm several aspects of the simulated wind field
Streamer Wave Events Observed in Solar Cycle 23
In this paper we conduct a data survey searching for well-defined streamer
wave events observed by the Large Angle and Spectrometric Coronagraph (LASCO)
on-board the Solar and Heliospheric Observatory (SOHO) throughout Solar Cycle
23. As a result, 8 candidate events are found and presented here. We compare
different events and find that in most of them the driving CMEs ejecta are
characterized by a high speed and a wide angular span, and the CME-streamer
interactions occur generally along the flank of the streamer structure at an
altitude no higher than the bottom of the field of view of LASCO C2. In
addition, all front-side CMEs have accompanying flares. These common
observational features shed light on the excitation conditions of streamer wave
events.
We also conduct a further analysis on one specific streamer wave event on 5
June 2003. The heliocentric distances of 4 wave troughs/crests at various
exposure times are determined; they are then used to deduce the wave properties
like period, wavelength, and phase speeds. It is found that both the period and
wavelength increase gradually with the wave propagation along the streamer
plasma sheet, and the phase speed of the preceding wave is generally faster
than that of the trailing ones. The associated coronal seismological study
yields the radial profiles of the Alfv\'en speed and magnetic field strength in
the region surrounding the streamer plasma sheet. Both quantities show a
general declining trend with time. This is interpreted as an observational
manifestation of the recovering process of the CME-disturbed corona. It is also
found that the Alfv\'enic critical point is at about 10 R where the
flow speed, which equals the Alfv\'en speed, is 200 km s
Observation of strong final-state effects in pi+ production in pp collisions at 400 MeV
Differential cross sections of the reactions and have been measured at MeV by detecting the charged
ejectiles in the angular range . The
deduced total cross sections agree well with those published previously for
neighbouring energies. The invariant mass spectra are observed to be strongly
affected by production and final-state interaction. The data are
well described by Monte Carlo simulations including both these effects. The
ratio of and cross sections also compares
favourably to a recent theoretical prediction which suggests a dominance of
-production in the relative -state.Comment: 17 pages, 5 figure
Unique, non‐Earthlike, 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
Low Energy Analyzing Powers in Pion-Proton Elastic Scattering
Analyzing powers of pion-proton elastic scattering have been measured at PSI
with the Low Energy Pion Spectrometer LEPS as well as a novel polarized
scintillator target. Angular distributions between 40 and 120 deg (c.m.) were
taken at 45.2, 51.2, 57.2, 68.5, 77.2, and 87.2 MeV incoming pion kinetic
energy for pi+ p scattering, and at 67.3 and 87.2 MeV for pi- p scattering.
These new measurements constitute a substantial extension of the polarization
data base at low energies. Predictions from phase shift analyses are compared
with the experimental results, and deviations are observed at low energies.Comment: 15 pages, 4 figure
Study of the p p -> p p pi+ pi- Reaction in the Low-Energy Tail of the Roper Resonance
Exclusive measurements of the p p -> p p pi+ pi- reaction have been carried
out at Tp = 775 MeV at CELSIUS using the PROMICE/WASA setup. Together with data
obtained at lower energy they point to a dominance of the Roper excitation in
this process. From the observed interference of its decay routes N* -> N sigma
and N* -> Delta pi -> N sigma their energy-dependent relative branching ratio
is determined
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&
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