929 research outputs found
Modulations in Multi-Periodic Blue Variables in the LMC
As shown by Mennickent, et al(2003), a subset of the blue variable stars in
the Large Magellanic Cloud exhibit brightness variability of small amplitude in
the period range 2.4 to 16 days as well as larger amplitude variability with
periods of 140 to 600 days, with a remarkably tight relation between the long
and the short periods. Our re-examination of these objects has led to the
discovery of additional variability. The Fourier spectra of 11 of their 30
objects have 3 or 4 peaks above the noise level and a linear relation of the
form f_a = 2(f_b - f_L) among three of the frequencies. An explanation of this
relation requires an interplay between the binary motion and that of a third
object. The two frequency relations together with the Fourier amplitude ratios
pose a challenging modeling problem.Comment: 4 pages, 3 figures, Astrophysical Journal (in press
Nonlinear Analysis of Irregular Variables
The Fourier spectral techniques that are common in Astronomy for analyzing
periodic or multi-periodic light-curves lose their usefulness when they are
applied to unsteady light-curves. We review some of the novel techniques that
have been developed for analyzing irregular stellar light or radial velocity
variations, and we describe what useful physical and astronomical information
can be gained from their use.Comment: 31 pages, to appear as a chapter in `Nonlinear Stellar Pulsation' in
the Astrophysics and Space Science Library (ASSL), Editors: M. Takeuti & D.
Sasselo
Suppression of Classical and Quantum Radiation Pressure Noise via Electro-Optic Feedback
We present theoretical results that demonstrate a new technique to be used to
improve the sensitivity of thermal noise measurements: intra-cavity intensity
stabilisation. It is demonstrated that electro-optic feedback can be used to
reduce intra-cavity intensity fluctuations, and the consequent radiation
pressure fluctuations, by a factor of two below the quantum noise limit. We
show that this is achievable in the presence of large classical intensity
fluctuations on the incident laser beam. The benefits of this scheme are a
consequence of the sub-Poissonian intensity statistics of the field inside a
feedback loop, and the quantum non-demolition nature of radiation pressure
noise as a readout system for the intra-cavity intensity fluctuations.Comment: 4 pages, 1 figur
Surveying determinants of protein structure designability across different energy models and amino-acid alphabets: A consensus
A variety of analytical and computational models have been proposed to answer the question of why some protein structures are more “designable” (i.e., have more sequences folding into them) than others. One class of analytical and statistical-mechanical models has approached the designability problem from a thermodynamic viewpoint. These models highlighted specific structural features important for increased designability. Furthermore, designability was shown to be inherently related to thermodynamically relevant energetic measures of protein folding, such as the foldability F and energy gap Δ10.Δ10. However, many of these models have been done within a very narrow focus: Namely, pair–contact interactions and two-letter amino-acid alphabets. Recently, two-letter amino-acid alphabets for pair–contact models have been shown to contain designability artifacts which disappear for larger-letter amino-acid alphabets. In addition, a solvation model was demonstrated to give identical designability results to previous two-letter amino-acid alphabet pair–contact models. In light of these discordant results, this report synthesizes a broad consensus regarding the relationship between specific structural features, foldability F, energy gap Δ10,Δ10, and structure designability for different energy models (pair–contact vs solvation) across a wide range of amino-acid alphabets. We also propose a novel measure ZdkZdk which is shown to be well correlated to designability. Finally, we conclusively demonstrate that two-letter amino-acid alphabets for pair–contact models appear to be solvation models in disguise. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69591/2/JCPSA6-112-5-2533-1.pd
Kinetic and Cyber
We compare and contrast situation awareness in cyber warfare and in
conventional, kinetic warfare. Situation awareness (SA) has a far longer
history of study and applications in such areas as control of complex
enterprises and in conventional warfare, than in cyber warfare. Far more is
known about the SA in conventional military conflicts, or adversarial
engagements, than in cyber ones. By exploring what is known about SA in
conventional, also commonly referred to as kinetic, battles, we may gain
insights and research directions relevant to cyber conflicts. We discuss the
nature of SA in conventional (often called kinetic) conflict, review what is
known about this kinetic SA (KSA), and then offer a comparison with what is
currently understood regarding the cyber SA (CSA). We find that challenges and
opportunities of KSA and CSA are similar or at least parallel in several
important ways. With respect to similarities, in both kinetic and cyber worlds,
SA strongly impacts the outcome of the mission. Also similarly, cognitive
biases are found in both KSA and CSA. As an example of differences, KSA often
relies on commonly accepted, widely used organizing representation - map of the
physical terrain of the battlefield. No such common representation has emerged
in CSA, yet.Comment: A version of this paper appeared as a book chapter in Cyber Defense
and Situational Awareness, Springer, 2014. Prepared by US Government
employees in their official duties; approved for public release, distribution
unlimited. Cyber Defense and Situational Awareness. Springer International
Publishing, 2014. 29-4
Universal correlation between energy gap and foldability for the random energy model and lattice proteins
The random energy model, originally used to analyze the physics of spin glasses, has been employed to explore what makes a protein a good folder versus a bad folder. In earlier work, the ratio of the folding temperature over the glass–transition temperature was related to a statistical measure of protein energy landscapes denoted as the foldability F. It was posited and subsequently established by simulation that good folders had larger foldabilities, on average, than bad folders. An alternative hypothesis, equally verified by protein folding simulations, was that it is the energy gap Δ between the native state and the next highest energy that distinguishes good folders from bad folders. This duality of measures has led to some controversy and confusion with little done to reconcile the two. In this paper, we revisit the random energy model to derive the statistical distributions of the various energy gaps and foldability. The resulting joint distribution allows us to explicitly demonstrate the positive correlation between foldability and energy gap. In addition, we compare the results of this analytical theory with a variety of lattice models. Our simulations indicate that both the individual distributions and the joint distribution of foldability and energy gap agree qualitatively well with the random energy model. It is argued that the universal distribution of and the positive correlation between foldability and energy gap, both in lattice proteins and the random energy model, is simply a stochastic consequence of the “thermodynamic hypothesis.” © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70084/2/JCPSA6-111-14-6599-1.pd
Hydrodynamical Survey of First Overtone Cepheids
A hydrodynamical survey of the pulsational properties of first overtone
Galactic Cepheids is presented. The goal of this study is to reproduce their
observed light- and radial velocity curves. The comparison between the models
and the observations is made in a quantitative manner on the level of the
Fourier coefficients. Purely radiative models fail to reproduce the observed
features, but convective models give good agreement.
It is found that the sharp features in the Fourier coefficients are indeed
caused by the P1/P4 = 2 resonance, despite the very large damping of the 4th
overtone. For the adopted mass-luminosity relation the resonance center lies
near a period of 4.2d +/- 0.2 as indicated by the observed radial velocity
data, rather than near 3.2d as the light-curves suggest.Comment: ApJ, 12 pages, (slightly) revise
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