2,084 research outputs found
Functional design for operational earth resources ground data processing
The author has identified the following significant results. Study emphasis was on developing a unified concept for the required ground system, capable of handling data from all viable acquisition platforms and sensor groupings envisaged as supporting operational earth survey programs. The platforms considered include both manned and unmanned spacecraft in near earth orbit, and continued use of low and high altitude aircraft. The sensor systems include both imaging and nonimaging devices, operated both passively and actively, from the ultraviolet to the microwave regions of the electromagnetic spectrum
High-fidelity imaging of a band insulator in a three-dimensional optical lattice clock
We report on the observation of a high-density, band insulating state in a
three-dimensional optical lattice clock. Filled with a nuclear-spin polarized
degenerate Fermi gas of 87Sr, the 3D lattice has one atom per site in the
ground motional state, thus guarding against frequency shifts due to contact
interactions. At this high density where the average distance between atoms is
comparable to the probe wavelength, standard imaging techniques suffer from
large systematic errors. To spatially probe frequency shifts in the clock and
measure thermodynamic properties of this system, accurate imaging techniques at
high optical depths are required. Using a combination of highly saturated
fluorescence and absorption imaging, we confirm the density distribution in our
3D optical lattice in agreement with a single spin band insulating state.
Combining our clock platform with this high filling fraction opens the door to
studying new classes of long-lived, many-body states arising from dipolar
interactions.Comment: 10 pages, 8 figure
Ultracold + collisions in a magnetic field: on the role of the potential energy surface
The collision dynamics of in
the presence of a magnetic field is studied within the close-coupling formalism
in the range between 10 nK and 50 mK. A recent global {\em ab initio} potential
energy surface (PES) is employed and its effect on the dynamics is analyzed and
compared with previous calculations where an experimentally derived PES was
used [New J. Phys {\bf 11}, 055021 (2009)]. In contrast to the results using
the older PES, magnetic field dependence of the low-field-seeking state in the
ultracold regime is characterized by quite a large background scattering
length, , and, in addition, cross sections exhibit broad and pronounced
Feshbach resonances. The marked resonance structure is somewhat surprising
considering the influence of inelastic scattering, but it can be explained by
resorting to the analytical van der Waals theory, where the short range
amplitude of the entrance channel wave function is enhanced by the large
. This strong sensitivity to the short range of the {\em ab initio} PES
persists up to relatively high energies (10 mK). After this study and despite
quantitative predictions are very difficult, it can be concluded that the ratio
between elastic and spin relaxation scattering is generally small, except for
magnetic fields which are either low or close to an asymmetric Fano-type
resonance. Some general trends found here, such as a large density of
quasibound states and a propensity towards large scattering lengths, could be
also characteristic of other anisotropic molecule-molecule systems.Comment: 24 pages, 8 figure
Cold collisions of OH and Rb. I: the free collision
We have calculated elastic and state-resolved inelastic cross sections for
cold and ultracold collisions in the Rb() + OH() system,
including fine-structure and hyperfine effects. We have developed a new set of
five potential energy surfaces for Rb-OH() from high-level {\em ab
initio} electronic structure calculations, which exhibit conical intersections
between covalent and ion-pair states. The surfaces are transformed to a
quasidiabatic representation. The collision problem is expanded in a set of
channels suitable for handling the system in the presence of electric and/or
magnetic fields, although we consider the zero-field limit in this work.
Because of the large number of scattering channels involved, we propose and
make use of suitable approximations. To account for the hyperfine structure of
both collision partners in the short-range region we develop a
frame-transformation procedure which includes most of the hyperfine
Hamiltonian. Scattering cross sections on the order of cm are
predicted for temperatures typical of Stark decelerators. We also conclude that
spin orientation of the partners is completely disrupted during the collision.
Implications for both sympathetic cooling of OH molecules in an environment of
ultracold Rb atoms and experimental observability of the collisions are
discussed.Comment: 20 pages, 16 figure
Calculating energy levels of isomerizing tetra-atomic molecules. I. The rovibrational bound states of Ar2HF
A general, six-dimensional computational method for the accurate calculation of rotationally and vibrationally excited states of tetra-atomic molecules is developed. The resulting program is particularly appropriate for molecules executing wide-amplitude motions and isomerizations. An application to the Ar2HF van der Waals trimer is presented in which the HF intramolecular stretching coordinate is separated out adiabatically and is not treated explicitly. Vibrational term values up to about 100 cmā1 with absolute convergence to better than 0.1 cmā1 are reported. These calculations employ more extensive vibrational basis sets and hence consider a much higher density of states than hitherto. States that sample ArāArāHF linear configurations and approach ArāHFāAr linear configurations are characterized for the first time. Results for total angular momentumJ=0 and 1 provide the first accurate calculations of rotational constants for this system. The rotational constants for the HF bending states of Ar2HF in the ground and first vibrationally excited states of the HF monomer are in good agreement with experiment, confirming the accuracy of the potential used in this work
High-impact jumping mitigates the short-term effects of low energy availability on bone resorption but not formation in regularly menstruating females:A randomized control trial
Low energy availability (LEA) is prevalent in active individuals and negatively impacts bone turnover in young females. High-impact exercise can promote bone health in an energy efficient manner and may benefit bone during periods of LEA. Nineteen regularly menstruating females (aged 18ā31 years) participated in two three-day conditions providing 15 (LEA) and 45 kcals kg fat-free massā1 dayā1 (BAL) of energy availability, each beginning 3 Ā± 1 days following the self-reported onset of menses. Participants either did (LEA+J, n = 10) or did not (LEA, n = 9) perform 20 high-impact jumps twice per day during LEA, with P1NP, Ī²-CTx (circulating biomarkers of bone formation and resorption, respectively) and other markers of LEA measured pre and post in a resting and fasted state. Data are presented as estimated marginal mean Ā± 95% CI. P1NP was significantly reduced in LEA (71.8 Ā± 6.1ā60.4 Ā± 6.2 ng mLā1, p 0.999, d = 0.19), and these effects were significantly different (time by condition interaction: p = 0.007). Morning basal bone formation rate is reduced following 3 days LEA, induced via dietary restriction, with or without high-impact jumping in regularly menstruating young females. However, high-impact jumping can prevent an increase in morning basal bone resorption rate and may benefit long-term bone health in individuals repeatedly exposed to such bouts
Finite to infinite steady state solutions, bifurcations of an integro-differential equation
We consider a bistable integral equation which governs the stationary
solutions of a convolution model of solid--solid phase transitions on a circle.
We study the bifurcations of the set of the stationary solutions as the
diffusion coefficient is varied to examine the transition from an infinite
number of steady states to three for the continuum limit of the
semi--discretised system. We show how the symmetry of the problem is
responsible for the generation and stabilisation of equilibria and comment on
the puzzling connection between continuity and stability that exists in this
problem
Long beating wavelength in the Schwarz-Hora effect
Thirty years ago, H.Schwarz has attempted to modulate an electron beam with
optical frequency. When a 50-keV electron beam crossed a thin crystalline
dielectric film illuminated with laser light, electrons produced the
electron-diffraction pattern not only at a fluorescent target but also at a
nonfluorescent target. In the latter case the pattern was of the same color as
the laser light (the Schwarz-Hora effect). This effect was discussed
extensively in the early 1970s. However, since 1972 no reports on the results
of further attempts to repeat those experiments in other groups have appeared,
while the failures of the initial such attempts have been explained by Schwarz.
The analysis of the literature shows there are several unresolved up to now
contradictions between the theory and the Schwarz experiments. In this work we
consider the interpretation of the long-wavelength spatial beating of the
Schwarz-Hora radiation. A more accurate expression for the spatial period has
been obtained, taking into account the mode structure of the laser field within
the dielectric film. It is shown that the discrepancy of more than 10% between
the experimental and theoretical results for the spatial period cannot be
reduced by using the existing quantum models that consider a collimated
electron beam.Comment: 3 pages, RevTe
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