3,047 research outputs found
Exact Casimir Interaction Between Semitransparent Spheres and Cylinders
A multiple scattering formulation is used to calculate the force, arising
from fluctuating scalar fields, between distinct bodies described by
-function potentials, so-called semitransparent bodies. (In the limit
of strong coupling, a semitransparent boundary becomes a Dirichlet one.) We
obtain expressions for the Casimir energies between disjoint parallel
semitransparent cylinders and between disjoint semitransparent spheres. In the
limit of weak coupling, we derive power series expansions for the energy, which
can be exactly summed, so that explicit, very simple, closed-form expressions
are obtained in both cases. The proximity force theorem holds when the objects
are almost touching, but is subject to large corrections as the bodies are
moved further apart.Comment: 5 pages, 4 eps figures; expanded discussion of previous work and
additional references added, minor typos correcte
Observing cirrus halos to constrain in-situ measurements of ice crystal size
International audienceIn this study, characteristic optical sizes of ice crystals in synoptic cirrus are determined using airborne measurements of ice crystal size distributions, optical extinction and water content. The measurements are compared with coincident visual observations of ice cloud optical phenomena, in particular the 22° and 46° halos. In general, the scattering profiles derived from the in-situ cloud probe measurements are consistent with the observed halo characteristics. It is argued that this implies that the measured ice crystals were small, probably with characteristic optical radii between 10 and 20 ?m. There is a current contention that in-situ measurements of high concentrations of small ice crystals reflect artifacts from the shattering of large ice crystals on instrument inlets. Significant shattering cannot be entirely excluded using this approximate technique, but it is not indicated. On the basis of the in-situ measurements, a parameterization is provided that relates the optical effective radius of ice crystals to the temperature in mid-latitude synoptic cirrus
Soybean: Evaluation of Inoculation
A soybean crop can obtain up to 50 to 75% of its nitrogen (N) requirements from the air when the biological fixation is effectively established (Pedersen, 2007). The overall objective of this project was to quantify the response to inoculation for soybean in a field without previous history of this crop. Following this rationale, a field study was conducted during the 2015 growing season at Ottawa (east central Kansas). The treatments consisted in five different N management approaches: non-inoculated, inoculated × 1, inoculated × 2, inoculated × 3 and non-inoculated but fertilized with 300 lb N per acre as the main N source. The study was planted in an area without soybean history, the grain yield ranged from 26 to 29 bushels per acre. Greater yields were recorded when a double inoculation rate was applied (× 2), while lowest yield was related to the non-inoculated scenario. However, statistically, treatments did not present any significant yield difference. In summary, further research will be performed to be more conclusive as related to the best management approach for N in soybeans when first planted in fields without previous history of this crop
Electromagnetic semitransparent -function plate: Casimir interaction energy between parallel infinitesimally thin plates
We derive boundary conditions for electromagnetic fields on a
-function plate. The optical properties of such a plate are shown to
necessarily be anisotropic in that they only depend on the transverse
properties of the plate. We unambiguously obtain the boundary conditions for a
perfectly conducting -function plate in the limit of infinite
dielectric response. We show that a material does not "optically vanish" in the
thin-plate limit. The thin-plate limit of a plasma slab of thickness with
plasma frequency reduces to a -function plate
for frequencies () satisfying . We show that the Casimir interaction energy between two parallel perfectly
conducting -function plates is the same as that for parallel perfectly
conducting slabs. Similarly, we show that the interaction energy between an
atom and a perfect electrically conducting -function plate is the usual
Casimir-Polder energy, which is verified by considering the thin-plate limit of
dielectric slabs. The "thick" and "thin" boundary conditions considered by
Bordag are found to be identical in the sense that they lead to the same
electromagnetic fields.Comment: 21 pages, 7 figures, references adde
How Does Casimir Energy Fall?
Doubt continues to linger over the reality of quantum vacuum energy. There is
some question whether fluctuating fields gravitate at all, or do so
anomalously. Here we show that for the simple case of parallel conducting
plates, the associated Casimir energy gravitates just as required by the
equivalence principle, and that therefore the inertial and gravitational masses
of a system possessing Casimir energy are both . This simple
result disproves recent claims in the literature. We clarify some pitfalls in
the calculation that can lead to spurious dependences on coordinate system.Comment: 5 pages, 1 figure, REVTeX. Minor revisions, including changes in
reference
SMAP Level 4 Surface and Root Zone Soil Moisture
The SMAP Level 4 soil moisture (L4_SM) product provides global estimates of surface and root zone soil moisture, along with other land surface variables and their error estimates. These estimates are obtained through assimilation of SMAP brightness temperature observations into the Goddard Earth Observing System (GEOS-5) land surface model. The L4_SM product is provided at 9 km spatial and 3-hourly temporal resolution and with about 2.5 day latency. The soil moisture and temperature estimates in the L4_SM product are validated against in situ observations. The L4_SM product meets the required target uncertainty of 0.04 m(exp. 3)m(exp. -3), measured in terms of unbiased root-mean-square-error, for both surface and root zone soil moisture
Investigation of microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells
Using laser optical pumping, widths and frequency shifts are determined for
microwave transitions between ground-state hyperfine components of Rb
and Rb atoms contained in vapor cells with alkane anti-relaxation
coatings. The results are compared with data on Zeeman relaxation obtained in
nonlinear magneto-optical rotation (NMOR) experiments, a comparison important
for quantitative understanding of spin-relaxation mechanisms in coated cells.
By comparing cells manufactured over a forty-year period we demonstrate the
long-term stability of coated cells, an important property for atomic clocks
and magnetometers
SAGA: A project to automate the management of software production systems
The project to automate the management of software production systems is described. The SAGA system is a software environment that is designed to support most of the software development activities that occur in a software lifecycle. The system can be configured to support specific software development applications using given programming languages, tools, and methodologies. Meta-tools are provided to ease configuration. Several major components of the SAGA system are completed to prototype form. The construction methods are described
Local and Global Casimir Energies for a Semitransparent Cylindrical Shell
The local Casimir energy density and the global Casimir energy for a massless
scalar field associated with a -function potential in a 3+1
dimensional circular cylindrical geometry are considered. The global energy is
examined for both weak and strong coupling, the latter being the well-studied
Dirichlet cylinder case. For weak-coupling,through ,
the total energy is shown to vanish by both analytic and numerical arguments,
based both on Green's-function and zeta-function techniques. Divergences
occurring in the calculation are shown to be absorbable by renormalization of
physical parameters of the model. The global energy may be obtained by
integrating the local energy density only when the latter is supplemented by an
energy term residing precisely on the surface of the cylinder. The latter is
identified as the integrated local energy density of the cylindrical shell when
the latter is physically expanded to have finite thickness. Inside and outside
the delta-function shell, the local energy density diverges as the surface of
the shell is approached; the divergence is weakest when the conformal stress
tensor is used to define the energy density. A real global divergence first
occurs in , as anticipated, but the proof is supplied
here for the first time; this divergence is entirely associated with the
surface energy, and does {\em not} reflect divergences in the local energy
density as the surface is approached.Comment: 28 pages, REVTeX, no figures. Appendix added on perturbative
divergence
H51W-1661 Water Balance in the SMAP Level-4 Soil Moisture Algorithm
No abstract availabl
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