2,834 research outputs found
Conceptual design study Science and Application Space Platform SASP. Volume 1: Executive summary
The system design philosphy applied in the development of this platform concept is summarized. The system is to provide for simple, low cost, initial capability of accommodating Spacelab payloads that are modified for long duration flight. The supporting research and technology are also summarized
Customer and mission influence on space station architecture
Overall Space Station architecture is presented in schematic outlines and plans. How the customer and mission needs influence this design is studied. The uses, occupants, activities, interfaces, utilities, locomotion, environments, and technological costs are all factors which influence the architecture. User and system functions are profiled, interfaces are characterized and functions are grouped. These lead to packaging of functions into modules and the design of system and user accommodations
Conceptual design study Science and Applications Space Platform SASP. Volume 2: Technical report
The platform payload accommodations, configuration drivers, and power system are described in detail. The platform design was analyzed and is presented. Demonstration tests are described and the results are reported
Large Deployable Reflector (LDR) system concept and technology definition study. Analysis of space station requirements for LDR
A study was conducted to determine how the Large Deployable Reflector (LDR) might benefit from the use of the space station for assembly, checkout, deployment, servicing, refurbishment, and technology development. Requirements that must be met by the space station to supply benefits for a selected scenario are summarized. Quantitative and qualitative data are supplied. Space station requirements for LDR which may be utilized by other missions are identified. A technology development mission for LDR is outlined and requirements summarized. A preliminary experiment plan is included. Space Station Data Base SAA 0020 and TDM 2411 are updated
Distribution of Soils by Natural Drainage Class and by Slope Class for Iowa Counties
Natural drainage class (namely, poor, imperfect, and well drained) and slope class are estimated for Iowa counties through a 2% ¼-section sample soil survey. Estimate of soil drainage class is given also by slope class. Counties vary widely in the amount of poorly drained soils. Kossuth County has 56.4% of poorly drained soils, while Allamakee has less than 1%. Land use management and conservation considerations are discussed briefly
Phase Transitions in the Spin-Half J_1--J_2 Model
The coupled cluster method (CCM) is a well-known method of quantum many-body
theory, and here we present an application of the CCM to the spin-half J_1--J_2
quantum spin model with nearest- and next-nearest-neighbour interactions on the
linear chain and the square lattice. We present new results for ground-state
expectation values of such quantities as the energy and the sublattice
magnetisation. The presence of critical points in the solution of the CCM
equations, which are associated with phase transitions in the real system, is
investigated. Completely distinct from the investigation of the critical
points, we also make a link between the expansion coefficients of the
ground-state wave function in terms of an Ising basis and the CCM ket-state
correlation coefficients. We are thus able to present evidence of the
breakdown, at a given value of J_2/J_1, of the Marshall-Peierls sign rule which
is known to be satisfied at the pure Heisenberg point (J_2 = 0) on any
bipartite lattice. For the square lattice, our best estimates of the points at
which the sign rule breaks down and at which the phase transition from the
antiferromagnetic phase to the frustrated phase occurs are, respectively, given
(to two decimal places) by J_2/J_1 = 0.26 and J_2/J_1 = 0.61.Comment: 28 pages, Latex, 2 postscript figure
C in intense femtosecond laser pulses: nonlinear dipole response and ionization
We study the interaction of strong femtosecond laser pulses with the C
molecule employing time-dependent density functional theory with the ionic
background treated in a jellium approximation. The laser intensities considered
are below the threshold of strong fragmentation but too high for perturbative
treatments such as linear response. The nonlinear response of the model to
excitations by short pulses of frequencies up to 45eV is presented and analyzed
with the help of Kohn-Sham orbital resolved dipole spectra. In femtosecond
laser pulses of 800nm wavelength ionization is found to occur multiphoton-like
rather than via excitation of a ``giant'' resonance.Comment: 14 pages, including 1 table, 5 figure
Anomalous finite size spectrum in the S=1/2 two dimensional Heisenberg model
We study the low energy spectrum of the nearest neighbor Heisenberg model on
a square lattice as a function of the total spin S. By quantum Monte Carlo
simulation we compute this spectrum for the s=1/2, s=1 and s=3/2 Heisenberg
models. We conclude that the nonlinear sigma model prediction for the low
energy spectrum is always verified for large enough system size. However the
crossover to the correct scaling regime is particularly slow just for the s=1/2
Heisenberg model. The possibility to detect this unexpected anomaly with finite
temperature experiments on s=1/2 isotropic quantum antiferromagnets is also
discussed.Comment: 4 pages, RevTeX + 5 encapsulated postscript figure
The role of the North Atlantic overturning and deep ocean for multi-decadal global-mean-temperature variability
Earth's climate exhibits internal modes of variability on various
timescales. Here we investigate multi-decadal variability of the
Atlantic meridional overturning circulation (AMOC), Northern Hemisphere sea-ice extent
and global mean temperature (GMT) in an ensemble of CMIP5 models under control conditions.
We report an inter-annual GMT variability of about ±0.1° C
originating solely from natural variability in the model ensemble.
By decomposing the GMT variance into contributions of the
AMOC and Northern Hemisphere sea-ice extent using
a graph-theoretical statistical approach, we find the AMOC to
contribute 8% to GMT variability in the ensemble mean. Our
results highlight the importance of AMOC sea-ice feedbacks that
explain 5% of the GMT variance, while the contribution solely
related to the AMOC is found to be about 3%. As a consequence
of multi-decadal AMOC variability, we report substantial variations
in North Atlantic deep-ocean heat content with trends of up to
0.7 × 1022 J decade−1 that are of the order of
observed changes over the last decade and consistent with the
reduced GMT warming trend over this period. Although these
temperature anomalies are largely density-compensated by salinity
changes, we find a robust negative correlation between the AMOC and
North Atlantic deep-ocean density with density lagging the AMOC by 5
to 11 yr in most models. While this would in principle allow
for a self-sustained oscillatory behavior of the coupled AMOC–deep-ocean
system, our results are inconclusive about the role of
this feedback in the model ensemble
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