10,931 research outputs found
Regional landform thresholds
Remote sensing technology allows us to recognize manifestations of regional thresholds, especially in the spatial characteristics of process agents. For example, a change in river channel pattern over a short distance reflects a threshold alteration in the physical controls of discharge and/or sediment. It is, therefore, a valuable indication of conditions as they exist. However, we probably will have difficulty determining whether the systemic parameters are now close to threshold conditions at which a different change will occur. This, of course, is a temporal and magnitude problem which is difficult to solve from the spatial characteristics
Formation of InAs Self-Assembled Quantum Rings on InP
Shape transformations of partially capped self-assembled InAs quantum dots
grown on InP are studied. Atomic force microscopy images show large anisotropic
redistribution of the island material after coverage by a 1 nm thick InP layer.
The anisotropic material redistribution occurs within a few minutes and leads
to a change from lens-like to elongated ring-like islands. The shape
transformation is not accompanied by dot material compositional change. The
formation of InAs/InP quantum rings disagrees with a previous model of
InAs/GaAs ring formation that assumes that the driving force for the dot to
ring transformation is the difference in surface diffusion velocity of indium
and gallium atoms.Comment: 13 pages, including 2 figures and 1 table. Submitted to Appl. Phys.
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A proof-theoretic analysis of the classical propositional matrix method
The matrix method, due to Bibel and Andrews, is a proof procedure designed for automated theorem-proving. We show that underlying this method is a fully structured combinatorial model of conventional classical proof theory. © 2012 The Author, 2012. Published by Oxford University Press
Towards More Data-Aware Application Integration (extended version)
Although most business application data is stored in relational databases,
programming languages and wire formats in integration middleware systems are
not table-centric. Due to costly format conversions, data-shipments and faster
computation, the trend is to "push-down" the integration operations closer to
the storage representation.
We address the alternative case of defining declarative, table-centric
integration semantics within standard integration systems. For that, we replace
the current operator implementations for the well-known Enterprise Integration
Patterns by equivalent "in-memory" table processing, and show a practical
realization in a conventional integration system for a non-reliable,
"data-intensive" messaging example. The results of the runtime analysis show
that table-centric processing is promising already in standard, "single-record"
message routing and transformations, and can potentially excel the message
throughput for "multi-record" table messages.Comment: 18 Pages, extended version of the contribution to British
International Conference on Databases (BICOD), 2015, Edinburgh, Scotlan
Strength, Width, and Pressure Shift Measurements of 54 Lines in the Oxygen A-Band
The absorption band of molecular oxygen, centered at 760]en1] nm, is the atmospheric absorber for the Differential Absorption Lidar (DIAL) systems used to measure atmospheric temperature, pressure, and density. To provide accurate line parameters for such systems, a careful spectroscopic study was made of the A-band, with measurements of line strengths, widths, pressure-induced frequency shifts, and collisional narrowing effects. The width and shift parameters were measured over a temperature range of -20 to 100 C so that the temperature dependence of these parameters can also be determined. To analyze the results, a least-squares fiting routine was written to fit standard line profiles to the observed profiles. These measurements, which include the first observations of pressure shifts and collisional narrowing in the band, are an important contribution to lidar system utilizing the A-band
Cygnus X-2, super-Eddington mass transfer, and pulsar binaries
We consider the unusual evolutionary state of the secondary star in Cygnus
X-2. Spectroscopic data give a low mass (M_2 \simeq 0.5 - 0.7\msun) and yet a
large radius (R_2 \simeq 7\rsun) and high luminosity (L_2 \simeq 150\lsun).
We show that this star closely resembles a remnant of early massive Case B
evolution, during which the neutron star ejected most of the \sim 3\msun
transferred from the donor (initial mass M_{\rm 2i}\sim 3.6\msun) on its
thermal time-scale yr. As the system is far too wide to result from
common-envelope evolution, this strongly supports the idea that a neutron star
efficiently ejects the excess inflow during super--Eddington mass transfer.
Cygnus X-2 is unusual in having had an initial mass ratio in a narrow critical range near . Smaller lead to long-period systems with the former donor near the Hayashi line,
and larger to pulsar binaries with shorter periods and relatively
massive white dwarf companions. The latter naturally explain the surprisingly
large companion masses in several millisecond pulsar binaries. Systems like
Cygnus X-2 may thus be an important channel for forming pulsar binaries.Comment: 9 pages, 4 encapsulated figures, LaTeX, revised version with a few
typos corrected and an appendix added, accepted by MNRA
Evolution of spin correlations in SrDy2O4 in an applied magnetic field
The development of short- and long-range magnetic order induced in a
frustrated zig-zag ladder compound SrDy2O4 by an applied field is studied using
neutron diffraction techniques. In zero field, SrDy2O4 lacks long-range
magnetic order down to temperatures as low as 60 mK, and the observed powder
neutron diffraction (PND) patterns are dominated by very broad diffuse
scattering peaks. Single crystal neutron diffraction reveals that the
zero-field magnetic structure consists of a collection of antiferromagnetic
chains running along the c axis and that there is very little correlation
between the chains in the ab plane. In an applied magnetic field, the broad
diffuse scattering features in PND are gradually replaced by much sharper
peaks, however, the pattern remains rather complex, reflecting the highly
anisotropic nature of SrDy2O4. Single crystal neutron diffraction shows that a
moderate field applied along the b axis induces an up-up-down magnetic order
associated with a 1/3-magnetisation plateau, in which magnetic correlation
length in the ab plane is significantly increased, but it nevertheless remains
finite. The resolution limited k = 0 peaks associated with a ferromagnetic
arrangement appear in powder and single crystal neutron diffraction patterns in
fields of 2.5 T and above.Comment: 10 pages, 11 figure
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