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

The Repair and Return to Flight of Solid Rocket Booster Forward Skirt Serial Number 20022

On April 5, 1991, a solid rocket booster (SRB) forward skirt serial number (S/N) 20022 sustained buckling damage during water impact after the launch of Space Transportation System Flight 37 (STS-37). As of that date, five forward skirts had been lost during water impact. Repair attempts began with the least damaged skirt available (S/N 20022). Sp ecial hydraulic tooling was used to remove buckled areas of the skirt. Afterwards, its aft clevis pinholes were found to be out of alignment with the redesigned solid rocket motor (RSRM) check gauge, but weld passes were used to correct this condition. Meanwhile, USA Analytics generated mechanical property data for buckled and subsequently debuckled material. Their analysis suggested that structural integrity might be improved by adding stringer reinforcements, stiffeners, to the aft bay section of the skirt. This improvement was recommended as a fleet modification to be implemented on a case-by-case basis

Characteristic Temperatures of Folding of a Small Peptide

We perform a generalized-ensemble simulation of a small peptide taking the interactions among all atoms into account. From this simulation we obtain thermodynamic quantities over a wide range of temperatures. In particular, we show that the folding of a small peptide is a multi-stage process associated with two characteristic temperatures, the collapse temperature T_{\theta} and the folding temperature T_f. Our results give supporting evidence for the energy landscape picture and funnel concept. These ideas were previously developed in the context of studies of simplified protein models, and here for the first time checked in an all-atom Monte Carlo simulation.Comment: Latex, 6 Figure

Reply to Comment on "Criterion that Determines the Foldability of Proteins"

We point out that the correlation between folding times and $\sigma = (T_{\theta } - T_{f})/T_{\theta }$ in protein-like heteropolymer models where $T_{\theta }$ and $T_{f}$ are the collapse and folding transition temperatures was already established in 1993 before the other presumed equivalent criterion (folding times correlating with $T_{f}$ alone) was suggested. We argue that the folding times for these models show no useful correlation with the energy gap even if restricted to the ensemble of compact structures as suggested by Karplus and Shakhnovich (cond-mat/9606037).Comment: 6 pages, Latex, 2 Postscript figures. Plots explicitly showing the lack of correlation between folding time and energy gap are adde

Sequence Dependence of Self-Interacting Random Chains

We study the thermodynamic behavior of the random chain model proposed by Iori, Marinari and Parisi, and how this depends on the actual sequence of interactions along the chain. The properties of randomly chosen sequences are compared to those of designed ones, obtained through a simulated annealing procedure in sequence space. We show that the transition to the folded phase takes place at a smaller strength of the quenched disorder for designed sequences. As a result, folding can be relatively fast for these sequences.Comment: 14 pages, uuencoded compressed postscript fil

Cyclic brightening in the short-period WZ Sge-type cataclysmic variable SDSS J080434.20+510349.2

We have observed a new cataclysmic variable (CV) SDSS J080434.20+510349.2 and study the origin of a long-term variability found in its light curve. Multi-longitude time-resolved photometric observations were carried out to analyze the uncommon behavior also found recently in two newly discovered CVs. This study of SDSS J080434.20+510349.2 mainly concerns the understanding of the nature of the observed double-humped light curve and its relation to a cyclic brightening occurring during quiescence. The observations were obtained early in 2007, when the object was at about V~17.1, 0.4 mag brighter than the pre-outburst magnitude. The light curve shows a sinusoidal variability with an amplitude of about 0.07 mag and a periodicity of 42.48 min, which is half of the orbital period of the system. In addition, we have observed two "mini-outbursts" of the system up to 0.6 mag, with a duration of about 4 days each. The "mini-outburst" had a symmetric profile and repeated in about 32 days. Subsequent monitoring of the system shows a cyclical behaviour of such "mini-outbursts" with a similar recurrence period. The origin of the double-humped light curve and the periodic brightening is discussed in the light of the evolutionary state of SDSS J080434.20+510349.2.Comment: 7 pages, 6 figures, Accepted by A&A, typos added, figure correcte

Quantum open systems and turbulence

We show that the problem of non conservation of energy found in the spontaneous localization model developed by Ghirardi, Rimini and Weber is very similar to the inconsistency between the stochastic models for turbulence and the Navier-Stokes equation. This sort of analogy may be useful in the development of both areas.Comment: to appear in Physical Review

Photometric study of selected cataclysmic variables

We present time-resolved photometry of five relatively poorly-studied cataclysmic variables: V1193 Ori, LQ Peg, LD 317, V795 Her, and MCT 2347-3144. The observations were made using four 1m-class telescopes for a total of more than 250 h of observation and almost 16,000 data points. For LQ Peg WHT spectroscopic data have been analysed as well. The light curves show a wide range of variability on different time scales from minutes to months. We detect for the first time a brightness variation of 0.05 mag in amplitude in V1193 Ori on the same timescale as the orbital period, which we interpret as the result of the irradiation of the secondary. A 20-min quasi-periodic oscillation is also detected. The mean brightness of the system has changed by 0.5 mag on a three-month interval, while the flickering was halved. In LQ Peg a 0.05 mag modulation was revealed with a period of about 3 h. The flickering was much smaller, of the order of 0.025 mag. A possible quasi-periodic oscillation could exist near 30 min. For this object, the WHT spectra are single-peaked and do not show any radial-velocity variations. The data of LD 317 show a decrease in the mean magnitude of the system. No periodic signal was detected but this is certainly attributable to the very large flickering observed: between 0.07 and 0.1 mag. For V795 Her, the 2.8-hour modulation, thought to be a superhump arising from the precession of the disc, is present. We show that this modulation is not stable in terms of periodicity, amplitude, and phase. Finally, for MCT 2347-3144, a clear modulation is seen in a first dataset obtained in October 2002. This modulation is absent in August 2003, when the system was brighter and showed much more flickering.Comment: 19 pages, 15 figures, 7 tables. Accepted for pubication by A&

Generalized quantum Fokker-Planck, diffusion and Smoluchowski equations with true probability distribution functions

Traditionally, the quantum Brownian motion is described by Fokker-Planck or diffusion equations in terms of quasi-probability distribution functions, e.g., Wigner functions. These often become singular or negative in the full quantum regime. In this paper a simple approach to non-Markovian theory of quantum Brownian motion using {\it true probability distribution functions} is presented. Based on an initial coherent state representation of the bath oscillators and an equilibrium canonical distribution of the quantum mechanical mean values of their co-ordinates and momenta we derive a generalized quantum Langevin equation in $c$-numbers and show that the latter is amenable to a theoretical analysis in terms of the classical theory of non-Markovian dynamics. The corresponding Fokker-Planck, diffusion and the Smoluchowski equations are the {\it exact} quantum analogues of their classical counterparts. The present work is {\it independent} of path integral techniques. The theory as developed here is a natural extension of its classical version and is valid for arbitrary temperature and friction (Smoluchowski equation being considered in the overdamped limit).Comment: RevTex, 16 pages, 7 figures, To appear in Physical Review E (minor revision