2,029 research outputs found
Thermal distortion analysis of a deployable parabolic reflector
A thermal distortion analysis of the ATS-6 Satellite parabolic reflector was performed using NASTRAN level 15.1. The same NASTRAN finite element method was used to conduct a one g static load analysis and a dynamic analysis of the reflector. In addition, a parametric study was made to determine which parameters had the greatest effect on the thermal distortions. The method used to model the construction of the reflector is described and the results of the analyses are presented
Introduction to the special section on dependable network computing
Dependable network computing is becoming a key part of our daily economic and social life. Every day, millions of users and businesses are utilizing the Internet infrastructure for real-time electronic commerce transactions, scheduling important events, and building relationships. While network traffic and the number of users are rapidly growing, the mean-time between failures (MTTF) is surprisingly short; according to recent studies, in the majority of Internet backbone paths, the MTTF is 28 days. This leads to a strong requirement for highly dependable networks, servers, and software systems. The challenge is to build interconnected systems, based on available technology, that are inexpensive, accessible, scalable, and dependable. This special section provides insights into a number of these exciting challenges
Cosmological tensor perturbations in the Randall-Sundrum model: evolution in the near-brane limit
We discuss the evolution of cosmological tensor perturbations in the RSII
model. In Gaussian normal coordinates the wave equation is non-separable, so we
use the near-brane limit to perform the separation and study the evolution of
perturbations. Massive excitations, which may also mix, decay outside the
horizon which could lead to some novel cosmological signatures.Comment: 18 pages, 1 figur
Racetrack inflation with matter fields and cosmic strings
We consider the coupling of racetrack inflation to matter fields as realized in the D3/D7 brane system. In particular, we investigate the possibility of cosmic string formation in this system. We find that strings can form before or at the onset of racetrack inflation is possible, but they are then inflated away. Furthermore, string formation at the end of inflation is prevented by the presence of the moduli sector. As a consequence, no strings survive racetrack inflation
Information gap for classical and quantum communication in a Schwarzschild spacetime
Communication between a free-falling observer and an observer hovering above
the Schwarzschild horizon of a black hole suffers from Unruh-Hawking noise,
which degrades communication channels. Ignoring time dilation, which affects
all channels equally, we show that for bosonic communication using single and
dual rail encoding the classical channel capacity reaches a finite value and
the quantum coherent information tends to zero. We conclude that classical
correlations still exist at infinite acceleration, whereas the quantum
coherence is fully removed.Comment: 5 pages, 4 figure
Structure and functional motifs of GCR1, the only plant protein with a GPCR fold?
Whether GPCRs exist in plants is a fundamental biological question. Interest in deorphanizing new G
protein coupled receptors (GPCRs), arises because of their importance in signaling. Within plants, this
is controversial as genome analysis has identified 56 putative GPCRs, including GCR1 which is
reportedly a remote homologue to class A, B and E GPCRs. Of these, GCR2, is not a GPCR; more
recently it has been proposed that none are, not even GCR1. We have addressed this disparity
between genome analysis and biological evidence through a structural bioinformatics study, involving
fold recognition methods, from which only GCR1 emerges as a strong candidate. To further probe
GCR1, we have developed a novel helix alignment method, which has been benchmarked against the
the class A – class B - class F GPCR alignments. In addition, we have presented a mutually consistent
set of alignments of GCR1 homologues to class A, class B and class F GPCRs, and shown that GCR1
is closer to class A and /or class B GPCRs than class A, class B or class F GPCRs are to each other.
To further probe GCR1, we have aligned transmembrane helix 3 of GCR1 to each of the 6 GPCR
classes. Variability comparisons provide additional evidence that GCR1 homologues have the GPCR
fold. From the alignments and a GCR1 comparative model we have identified motifs that are common
to GCR1, class A, B and E GPCRs. We discuss the possibilities that emerge from this controversial
evidence that GCR1 has a GPCR fol
Position-dependent shear-induced austenite-martensite transformation in double-notched TRIP and dual-phase steel samples
While earlier studies on transformation-induced-plasticity (TRIP) steels focused on the determination of the austenite-to-martensite decomposition in uniform deformation or thermal fields, the current research focuses on the determination of the local retained austenite-to-martensite transformation behaviour in an inhomogeneous yet carefully controlled shear-loaded region of double-notched TRIP and dual-phase (DP) steel samples. A detailed powder analysis has been performed to simultaneously monitor the evolution of the phase fraction and the changes in average carbon concentration of metastable austenite together with the local strain components in the constituent phases as a function of the macroscopic stress and location with respect to the shear band. The metastable retained austenite shows a mechanically induced martensitic transformation in the localized shear zone, which is accompanied by an increase in average carbon concentration of the remaining austenite due to a preferred transformation of the austenite grains with the lowest carbon concentration. At the later deformation stages the geometry of the shear test samples results in the development of an additional tensile component. The experimental strain field within the probed sample area is in good agreement with finite element calculations. The strain development observed in the low-alloyed TRIP steel with metastable austenite is compared with that of steels with the same chemical composition containing either no austenite (a DP grade) or stable retained austenite (a TRIP grade produced at a long bainitic holding time). The transformation of metastable austenite under shear is a complex interplay between the local microstructure and the evolving strain fields
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