11,581 research outputs found
Rayleigh-Brillouin light scattering spectroscopy of nitrous oxide (NO)
High signal-to-noise and high-resolution light scattering spectra are
measured for nitrous oxide (NO) gas at an incident wavelength of 403.00 nm,
at 90 scattering, at room temperature and at gas pressures in the range
bar. The resulting Rayleigh-Brillouin light scattering spectra are
compared to a number of models describing in an approximate manner the
collisional dynamics and energy transfer in this gaseous medium of this
polyatomic molecular species. The Tenti-S6 model, based on macroscopic gas
transport coefficients, reproduces the scattering profiles in the entire
pressure range at less than 2\% deviation at a similar level as does the
alternative kinetic Grad's 6-moment model, which is based on the internal
collisional relaxation as a decisive parameter. A hydrodynamic model fails to
reproduce experimental spectra for the low pressures of 0.5-1 bar, but yields
very good agreement (\%) in the pressure range bar. While these
three models have a different physical basis the internal molecular relaxation
derived can for all three be described in terms of a bulk viscosity of Pas. A 'rough-sphere' model, previously
shown to be effective to describe light scattering in SF gas, is not found
to be suitable, likely in view of the non-sphericity and asymmetry of the N-N-O
structured linear polyatomic molecule
pT distribution of hyperons in 200A GeV Au-Au by smoothed particle hydrodynamics
The transverse momentum distributions for hadrons in 200GeV Au-Au collision
at RHIC is calculated using a smoothed particle hydrodynamics code SPheRIO, and
are compared with the data from STAR and PHOBOS Collaborations. By employing
the equation of state which explicitly incorporate the strangeness conservation
and introducing strangeness chemical potential into the code, the transverse
spectrums give a reasonable description for the experimental data.Comment: 3 pages, 6 figure
Comparison of acoustic travel-time measurement of solar meridional circulation from SDO/HMI and SOHO/MDI
Time-distance helioseismology is one of the primary tools for studying the
solar meridional circulation. However, travel-time measurements of the
subsurface meridional flow suffer from a variety of systematic errors, such as
a center-to-limb variation and an offset due to the P-angle uncertainty of
solar images. Here we apply the time-distance technique to contemporaneous
medium-degree Dopplergrams produced by SOHO/MDI and SDO/HMI to obtain the
travel-time difference caused by meridional circulation throughout the solar
convection zone. The P-angle offset in MDI images is measured by
cross-correlating MDI and HMI images. The travel-time measurements in the
south-north and east-west directions are averaged over the same observation
period for the two data sets and then compared to examine the consistency of
MDI and HMI travel times after correcting the systematic errors.
The offsets in the south-north travel-time difference from MDI data induced
by the P-angle error gradually diminish with increasing travel distance.
However, these offsets become noisy for travel distances corresponding to waves
that reach the base of the convection zone. This suggests that a careful
treatment of the P-angle problem is required when studying a deep meridional
flow. After correcting the P-angle and the removal of the center-to-limb
effect, the travel-time measurements from MDI and HMI are consistent within the
error bars for meridional circulation covering the entire convection zone. The
fluctuations observed in both data sets are highly correlated and thus indicate
their solar origin rather than an instrumental origin. Although our results
demonstrate that the ad hoc correction is capable of reducing the wide
discrepancy in the travel-time measurements from MDI and HMI, we cannot exclude
the possibility that there exist other systematic effects acting on the two
data sets in the same way.Comment: accepted for publication in A&
Rayleigh-Brillouin scattering in SF in the kinetic regime
Rayleigh-Brillouin spectral profiles are measured with a laser-based
scatterometry setup for a 90 degrees scattering angle at a high signal-to-noise
ratio (r.m.s. noise below 0.15 \% w.r.t. peak intensity) in
sulphur-hexafluoride gas for pressures in the range 0.2 -- 5 bar and for a
wavelength of nm. The high quality data are compared to a
number of light scattering models in order to address the effects of rotational
and vibrational relaxation. While the vibrational relaxation rate is so slow
that vibration degrees of freedom remain frozen, rotations relax on time scales
comparable to those of the density fluctuations. Therefore, the heat capacity,
the thermal conductivity and the bulk viscosity are all frequency-dependent
transport coefficients. This is relevant for the Tenti model that depends on
the values chosen for these transport coefficients. This is not the case for
the other two models considered: a kinetic model based on rough-sphere
interactions, and a model based on fluctuating hydrodynamics. The deviations
with the experiment are similar between the three different models, except for
the hydrodynamic model at pressures . As all models
are in line with the ideal gas law, we hypothesize the presence of real gas
effects in the measured spectra.Comment: 8 pages, 3 figures, Chemical Physics Letters 201
Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations: Helioseismic travel times and forward modeling in the ray approximation
The south-north travel-time differences are measured by applying
time-distance helioseismology to the MDI and HMI medium-degree Dopplergrams
covering May 1996-April 2017. Our data analysis corrects for several sources of
systematic effects: P-angle error, surface magnetic field effects, and
center-to-limb variations. An interpretation of the travel-time measurements is
obtained using a forward-modeling approach in the ray approximation. The
travel-time differences are similar in the southern hemisphere for cycles 23
and 24. However, they differ in the northern hemisphere between cycles 23 and
24. Except for cycle 24's northern hemisphere, the measurements favor a
single-cell meridional circulation model where the poleward flows persist down
to 0.8 , accompanied by local inflows toward the activity belts
in the near-surface layers. Cycle 24's northern hemisphere is anomalous:
travel-time differences are significantly smaller when travel distances are
greater than 20. This asymmetry between northern and southern
hemispheres during cycle 24 was not present in previous measurements (e.g.,
Rajaguru & Antia 2015), which assumed a different P-angle error correction
where south-north travel-time differences are shifted to zero at the equator
for all travel distances. In our measurements, the travel-time differences at
the equator are zero for travel distances less than 30, but they
do not vanish for larger travel distances. This equatorial offset for large
travel distances need not be interpreted as a deep cross-equator flow; it could
be due to the presence of asymmetrical local flows at the surface near the end
points of the acoustic ray paths.Comment: accepted for publication in A&
CQESTR Simulation of Management Practice Effects on Long-Term Soil Organic Carbon
Management of soil organic matter (SOM) is important for soil productivity and responsible utilization of crop residues for additional uses. CQESTR, pronounced “sequester,” a contraction of “C sequestration” (meaning C storage), is a C balance model that relates organic residue additions, crop management, and soil tillage to SOM accretion or loss. Our objective was to simulate SOM changes in agricultural soils under a range of climate and management systems using the CQESTR model. Four long-term experiments (Champaign, IL, \u3e100 yr; Columbia, MO, \u3e100 yr; Lincoln, NE, 20 yr; Sidney, NE, 20 yr) in the United States under various crop rotations, tillage practices, organic amendments, and crop residue removal treatments were selected for their documented history of the long-term effects of management practice on SOM dynamics. CQESTR successfully simulated a substantial decline in SOM with 50 yr of crop residue removal under various rotations at Columbia and Champaign. The increase in SOM following addition of manure was simulated well; however, the model underestimated SOM for a fertilized treatment at Columbia. Predicted and observed values from the four sites were signifi cantly related (r2 = 0.94, n = 113, P \u3c 0.001), with slope not signifi cantly different from 1. Given the high correlation of simulated and observed SOM changes, CQESTR can be used as a reliable tool to predict SOM changes from management practices and offers the potential for estimating soil C storage required for C credits. It can also be an important tool to estimate the impacts of crop residue removal for bioenergy production on SOM level and soil production capacity
Moisture interaction and stability of ZOT (Zinc Orthotitanate) thermal control spacecraft coating
Two of the many performance requirements of the zinc orthotitanate (ZOT) ceramic thermal control paint covering parts of the Jupiter-bound Galileo spacecraft are that it be sufficiently electrically conductive so as to prevent electrostatic discharge (ESD) damage to onboard electronics and that it adhere to and protect the substrate from corrosion in terrestrial environments. The bulk electrical resistivity of ZOT on an aluminum substrate was measured over the ranges 22 C to 90 C and 0 percent RH to 100 percent RH, and also in soft (10 (minus 2) Torr) and hard (10 (minus 7) Torr) vacuums. No significant temperature dependence was evident, but measured resistivity values ranged over 9 orders of magnitude: 10 to the 5th power ohm-cm at 100 percent RH greater than 10 to the 12th power ohm-cm in a hard vacuum. The latter value violates the ESD criterion for a typical 0.019 cm thick coating. The corrosion study involved exposing typical ZOT substrate combinations to two moisture environments - 30 C/85 percent RH and 85 C/85 percent RH - for 2000 hours, during which time the samples were periodically removed for front-to-back electrical resistance and scratch/peel test measurements. It was determined that the ZOT/Al and ZOT/Mg systems are stable (no ZOT delamination), although some corrosion (oxide formation) and resistivity increases observed among the ZOT/Mg samples warrant that exposure of some parts to humid environments be minimized
- …