3,450 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
Classical correlations of defects in lattices with geometrical frustration in the motion of a particle
We map certain highly correlated electron systems on lattices with
geometrical frustration in the motion of added particles or holes to the
spatial defect-defect correlations of dimer models in different geometries.
These models are studied analytically and numerically. We consider different
coverings for four different lattices: square, honeycomb, triangular, and
diamond. In the case of hard-core dimer covering, we verify the existed results
for the square and triangular lattice and obtain new ones for the honeycomb and
the diamond lattices while in the case of loop covering we obtain new numerical
results for all the lattices and use the existing analytical Liouville field
theory for the case of square lattice.The results show power-law correlations
for the square and honeycomb lattice, while exponential decay with distance is
found for the triangular and exponential decay with the inverse distance on the
diamond lattice. We relate this fact with the lack of bipartiteness of the
triangular lattice and in the latter case with the three-dimensionality of the
diamond. The connection of our findings to the problem of fractionalized charge
in such lattices is pointed out.Comment: 6 pages, 6 figures, 1 tabl
Charge degrees in the quarter-filled checkerboard lattice
For a systematic study of charge degrees of freedom in lattices with
geometric frustration, we consider spinless fermions on the checkerboard
lattice with nearest-neighbor hopping and nearest-neighbor repulsion at
quarter-filling. An effective Hamiltonian for the limit is given to
lowest non-vanishing order by the ring exchange (). We show
that the system can equivalently be described by hard-core bosons and map the
model to a confining U(1) lattice gauge theory.Comment: Proceedings of ICM200
Observation of soliton explosions in a passively mode-locked fiber laser
Soliton explosions are among the most exotic dissipative phenomena studied in
mode-locked lasers. In this regime, a dissipative soliton circulating in the
laser cavity experiences an abrupt structural collapse, but within a few
roundtrips returns to its original quasi-stable state. In this work we report
on the first observation of such events in a fiber laser. Specifically, we
identify clear explosion signatures in measurements of shot-to-shot spectra of
an Yb-doped mode-locked fiber laser that is operating in a transition regime
between stable and noise-like emission. The comparatively long,
all-normal-dispersion cavity used in our experiments also permits direct
time-domain measurements, and we show that the explosions manifest themselves
as abrupt temporal shifts in the output pulse train. Our experimental results
are in good agreement with realistic numerical simulations based on an
iterative cavity map.Comment: 5 pages, 5 figures, submitte
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
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
Spectral functions and optical conductivity of spinless fermions on a checkerboard lattice
We study the dynamical properties of spinless fermions on the checkerboard
lattice. Our main interest is the limit of large nearest-neighbor repulsion
as compared with hopping . The spectral functions show broad low-energy
excitation which are due to the dynamics of fractionally charged excitations.
Furthermore, it is shown that the fractional charges contribute to the
electrical current density.Comment: 9 Pages, 9 Figure
Disentangling different types of El Ni\~no episodes by evolving climate network analysis
Complex network theory provides a powerful toolbox for studying the structure
of statistical interrelationships between multiple time series in various
scientific disciplines. In this work, we apply the recently proposed climate
network approach for characterizing the evolving correlation structure of the
Earth's climate system based on reanalysis data of surface air temperatures. We
provide a detailed study on the temporal variability of several global climate
network characteristics. Based on a simple conceptual view on red climate
networks (i.e., networks with a comparably low number of edges), we give a
thorough interpretation of our evolving climate network characteristics, which
allows a functional discrimination between recently recognized different types
of El Ni\~no episodes. Our analysis provides deep insights into the Earth's
climate system, particularly its global response to strong volcanic eruptions
and large-scale impacts of different phases of the El Ni\~no Southern
Oscillation (ENSO).Comment: 20 pages, 12 figure
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
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