249 research outputs found
A Parameter Study of Classical Be Star Disk Models Constrained by Optical Interferometry
We have computed theoretical models of circumstellar disks for the classical
Be stars Dra, Psc, and Cyg. Models were constructed
using a non-LTE radiative transfer code developed by \citet{sig07} which
incorporates a number of improvements over previous treatments of the disk
thermal structure, including a realistic chemical composition. Our models are
constrained by direct comparison with long baseline optical interferometric
observations of the H emitting regions and by contemporaneous H
line profiles. Detailed comparisons of our predictions with H
interferometry and spectroscopy place very tight constraints on the density
distributions for these circumstellar disks.Comment: 10 figures,28 pages, accepted by Ap
Order parameter model for unstable multilane traffic flow
We discuss a phenomenological approach to the description of unstable vehicle
motion on multilane highways that explains in a simple way the observed
sequence of the phase transitions "free flow -> synchronized motion -> jam" as
well as the hysteresis in the transition "free flow synchronized motion".
We introduce a new variable called order parameter that accounts for possible
correlations in the vehicle motion at different lanes. So, it is principally
due to the "many-body" effects in the car interaction, which enables us to
regard it as an additional independent state variable of traffic flow. Basing
on the latest experimental data (cond-mat/9905216) we assume that these
correlations are due to a small group of "fast" drivers. Taking into account
the general properties of the driver behavior we write the governing equation
for the order parameter. In this context we analyze the instability of
homogeneous traffic flow manifesting itself in both of the mentioned above
phase transitions where, in addition, the transition "synchronized motion ->
jam" also exhibits a similar hysteresis. Besides, the jam is characterized by
the vehicle flows at different lanes being independent of one another. We
specify a certain simplified model in order to study the general features of
the car cluster self-formation under the phase transition "free flow
synchronized motion". In particular, we show that the main local parameters of
the developed cluster are determined by the state characteristics of vehicle
motion only.Comment: REVTeX 3.1, 10 pages with 10 PostScript figure
Effects of three-body interactions on the structure and thermodynamics of liquid krypton
Large-scale molecular dynamics simulations are performed to predict the
structural and thermodynamic properties of liquid krypton using a potential
energy function based on the two-body potential of Aziz and Slaman plus the
triple-dipole Axilrod-Teller (AT) potential. By varying the strength of the AT
potential we study the influence of three-body contribution beyond the
triple-dipole dispersion. It is seen that the AT potential gives an overall
good description of liquid Kr, though other contributions such as higher order
three-body dispersion and exchange terms cannot be ignored.Comment: 11 pages, 3 figures, LaTeX, to appear in J. Chem. Phy
The Synthesis and Characterization of LiFeAs and NaFeAs
The newest homologous series of superconducting As-pnictides, LiFeAs (Li111)
and NaFeAs (Na111) have been synthesized and investigated. Both crystallize
with the layered tetragonal anti-PbFCl-type structure in P4/nmm space group.
Polycrystalline samples and single-crystals of Li111 and Na111 display
superconducting transitions at ~ 18 K and 12-25 K, respectively. No magnetic
order has been found in either compound, although a weak magnetic background is
clearly in evidence. The origin of the carriers and the stoichiometric
compositions of Li111 and Na111 were explored.Comment: submitted for publication in Physica C special issue on Fe-pnictide
Environmental variablity in three major Mediterranean tuna spawning grounds.
We propose four different environmental indicators, three related to temperature variability in
three major spawning grounds of tuna species in the Mediterranean, and one related to the sea
surface salinity variability in the Balearic Sea. These oceanographic indicators show the
annual variability of environmental parameters affecting growth and survival of tuna eggs and
larval. The indicators are intended to provide quick access to assessment working groups and
fisheries scientist to identify potentially anomalous year
Long-Term Changes in the Water Mass Properties in the Balearic Channels Over the Period 1996–2019
The analysis of a 24-year time series of Conductivity-Temperature-Depth (CTD) casts collected in the Balearic Channels (1996–2019) has allowed detecting and quantifying long-term changes in water mass properties in the Western Mediterranean. For the complete period, the intermediate waters have experienced warming and salting at rates of 1.4°C/100yr and 0.3–0.6/100yr for the Western Intermediate Water, and 1°C/100yr and 0.3–0.4/100yr for the Levantine Intermediate Water. The density of these two water masses has not changed. The deep waters, defined as those denser than 29.1 kg/m3, showed positive trends in temperature, salinity, and density (0.8°C/100yr, 0.2/100yr, and 0.02 kg.m–3/100yr, respectively). The high temporal variability of the upper layer makes the detection of long-term changes more difficult. Nevertheless, combining CTD data with temperature data from the oceanographic station at L’Estartit and simulated data from the NCEP/NCAR reanalysis, it can be established that the Atlantic Water increased its temperature at a rate of 2.1–2.8°C/100yr and likely its salinity at a rate of 0.6/100yr. The water column absorbed heat at a rate equivalent to 1–1.2 W/m2. All these trends are much higher than those reported in previous works (more than double in some cases). The warming of the water column produced an increase in the thermosteric component of sea level. However, this increase was compensated by the decrease in the halosteric component. Besides these changes, other alterations related to the Western Mediterranean Transition have been observed over shorter periods. The temperature and salinity of the intermediate waters increased before the winter of 2004/2005 and then the temperature and salinity of the deep waters increased dramatically in 2005. The density of the deep water reached values unprecedented before 2005. Deep and intermediate waters were uplifted by the presence of such dense deep waters. The arrival of warmer and saltier intermediate waters from the Eastern Mediterranean is also observed, mainly after 2010.Postprin
New anti-perovskite-type Superconductor ZnNyNi3
We have synthesized a new superconductor ZnNyNi3 with Tc ~3 K. The crystal
structure has the same anti-perovskite-type such as MgCNi3 and CdCNi3. As far
as we know, this is the third superconducting material in Ni-based
anti-perovskite series. For this material, superconducting parameters,
lower-critical field Hc1(0), upper-critical field Hc2(0), coherence length
x(0), penetration depth l(0), and Gintzburg -Landau parameter k(0) have been
experimentally determined.Comment: 13 pages, 3 figures, 1 tabl
Li14Ln5[Si11N19O5]O2F2 with Ln = Ce, Nd-Representatives of a Family of Potential Lithium Ion Conductors
The isotypic layered oxonitridosilicates Li14Ln5[Si11N19O5]O2F2 (Ln = Ce, Nd) have been synthesized using Li as fluxing agent and crystallize in the orthorhombic space group Pmmn (Z = 2, Li14Ce5[Si11N19O5]O2F2: a = 17.178(3), b = 7.6500(15), c = 10.116(2) Å, R1 = 0.0409, wR2 = 0.0896; Li14Nd5 Si11N19O5]O2F2: a = 17.126(2), b = 7.6155 15), c = 10.123(2) Å, R1 = 0.0419, wR2 = 0.0929). The silicate layers consist of dreier and sechser rings interconnected via common corners, yielding an unprecedented silicate substructure. A topostructural analysis indicates possible 1D ion migration pathways between five crystallographic independent Li positions. The specific Li-ionic conductivity and its temperature dependence were determined by impedance spectroscopy as well as DC polarization/depolarization measurements. The ionic conductivity is on the order of 5 ×
10−5 S/cm at 300°C, while the activation energy is 0.69 eV. Further adjustments of the defect chemistry (e.g., through doping)can make these compounds interesting candidates for novel oxonitridosilicate based ion conductors
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