On the prospects of imaging Sagittarius A* from space

Very Long Baseline Interferometry (VLBI) at sub-millimeter waves has the potential to image the shadow of the black hole in the Galactic Center, Sagittarius A* (Sgr A*), and thereby test basic predictions of the theory of general relativity. We investigate the imaging prospects of a new Space VLBI mission concept. The setup consists of two satellites in polar or equatorial circular Medium-Earth Orbits with slightly different radii, resulting in a dense spiral-shaped uv-coverage with long baselines, allowing for extremely high-resolution and high-fidelity imaging of radio sources. We simulate observations of a general relativistic magnetohydrodynamics model of Sgr A* for this configuration with noise calculated from model system parameters. After gridding the $uv$-plane and averaging visibilities accumulated over multiple months of integration, images of Sgr A* with a resolution of up to 4 $\mu$as could be reconstructed, allowing for stronger tests of general relativity and accretion models than with ground-based VLBI.Comment: 4 pages, 4 figures, published in Proceedings IAU Symposium No. 342, 201

High Mass Star Formation. II. The Mass Function of Submillimeter Clumps in M17

We have mapped an approximately 5.5 by 5.5 pc portion of the M17 massive star-forming region in both 850 and 450 micron dust continuum emission using the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). The maps reveal more than 100 dusty clumps with deconvolved linear sizes of 0.05--0.2 pc and masses of 0.8--120 solar masses, most of which are not associated with known mid-infrared point sources. Fitting the clump mass function with a double power law gives a mean power law exponent of alpha_high = -2.4 +/- 0.3 for the high-mass power law, consistent with the exponent of the Salpeter stellar mass function. We show that a lognormal clump mass distribution with a peak at about 4 solar masses produces as good a fit to the clump mass function as does a double power law. This 4 solar mass peak mass is well above the peak masses of both the stellar initial mass function and the mass function of clumps in low-mass star-forming regions. Despite the difference in intrinsic mass scale, the shape of the M17 clump mass function appears to be consistent with the shape of the core mass function in low-mass star-forming regions. Thus, we suggest that the clump mass function in high-mass star-forming regions may be a scaled-up version of that in low-mass regions, instead of its extension to higher masses.Comment: 33 pages, 6 figures, 3 tables. Accepted for publication in the Astrophysical Journa

String Loop Corrections to Kahler Potentials in Orientifolds

We determine one-loop string corrections to Kahler potentials in type IIB orientifold compactifications with either N=1 or N=2 supersymmetry, including D-brane moduli, by evaluating string scattering amplitudes.Comment: 80 pages, 4 figure

Metastability and small eigenvalues in Markov chains

In this letter we announce rigorous results that elucidate the relation between metastable states and low-lying eigenvalues in Markov chains in a much more general setting and with considerable greater precision as was so far available. This includes a sharp uncertainty principle relating all low-lying eigenvalues to mean times of metastable transitions, a relation between the support of eigenfunctions and the attractor of a metastable state, and sharp estimates on the convergence of probability distribution of the metastable transition times to the exponential distribution.Comment: 5pp, AMSTe

Wigner Crystalline Edges in nu < 1 Quantum Dots

We investigate the edge reconstruction phenomenon believed to occur in quantum dots in the quantum Hall regime when the filling fraction is nu < 1. Our approach involves the examination of large dots (< 40 electrons) using a partial diagonalization technique in which the occupancies of the deep interior orbitals are frozen. To interpret the results of this calculation, we evaluate the overlap between the diagonalized ground state and a set of trial wavefunctions which we call projected necklace (PN) states. A PN state is simply the angular momentum projection of a maximum density droplet surrounded by a ring of localized electrons. Our calculations reveal that PN states have up to 99% overlap with the diagonalized ground states, and are lower in energy than the states identified in Chamon and Wen's study of the edge reconstruction.Comment: 8 pages, 8 figures, to be published in Phys. Rev.

Public-channel cryptography based on mutual chaos pass filters

We study the mutual coupling of chaotic lasers and observe both experimentally and in numeric simulations, that there exists a regime of parameters for which two mutually coupled chaotic lasers establish isochronal synchronization, while a third laser coupled unidirectionally to one of the pair, does not synchronize. We then propose a cryptographic scheme, based on the advantage of mutual-coupling over unidirectional coupling, where all the parameters of the system are public knowledge. We numerically demonstrate that in such a scheme the two communicating lasers can add a message signal (compressed binary message) to the transmitted coupling signal, and recover the message in both directions with high fidelity by using a mutual chaos pass filter procedure. An attacker however, fails to recover an errorless message even if he amplifies the coupling signal

Impact of Sleep and Circadian Disruption on Energy Balance and Diabetes: A Summary of Workshop Discussions

A workshop was held at the National Institute for Diabetes and Digestive and Kidney Diseases with a focus on the impact of sleep and circadian disruption on energy balance and diabetes. The workshop identified a number of key principles for research in this area and a number of specific opportunities. Studies in this area would be facilitated by active collaboration between investigators in sleep/circadian research and investigators in metabolism/diabetes. There is a need to translate the elegant findings from basic research into improving the metabolic health of the American public. There is also a need for investigators studying the impact of sleep/circadian disruption in humans to move beyond measurements of insulin and glucose and conduct more in-depth phenotyping. There is also a need for the assessments of sleep and circadian rhythms as well as assessments for sleep-disordered breathing to be incorporated into all ongoing cohort studies related to diabetes risk. Studies in humans need to complement the elegant short-term laboratory-based human studies of simulated short sleep and shift work etc. with studies in subjects in the general population with these disorders. It is conceivable that chronic adaptations occur, and if so, the mechanisms by which they occur needs to be identified and understood. Particular areas of opportunity that are ready for translation are studies to address whether CPAP treatment of patients with pre-diabetes and obstructive sleep apnea (OSA) prevents or delays the onset of diabetes and whether temporal restricted feeding has the same impact on obesity rates in humans as it does in mice

Honeybee Colony Vibrational Measurements to Highlight the Brood Cycle

Insect pollination is of great importance to crop production worldwide and honey bees are amongst its chief facilitators. Because of the decline of managed colonies, the use of sensor technology is growing in popularity and it is of interest to develop new methods which can more accurately and less invasively assess honey bee colony status. Our approach is to use accelerometers to measure vibrations in order to provide information on colony activity and development. The accelerometers provide amplitude and frequency information which is recorded every three minutes and analysed for night time only. Vibrational data were validated by comparison to visual inspection data, particularly the brood development. We show a strong correlation between vibrational amplitude data and the brood cycle in the vicinity of the sensor. We have further explored the minimum data that is required, when frequency information is also included, to accurately predict the current point in the brood cycle. Such a technique should enable beekeepers to reduce the frequency with which visual inspections are required, reducing the stress this places on the colony and saving the beekeeper time

Yang-Mills Theory as a Deformation of Topological Field Theory, Dimensional Reduction and Quark Confinement

We propose a reformulation of Yang-Mills theory as a perturbative deformation of a novel topological (quantum) field theory. We prove that this reformulation of the four-dimensional QCD leads to quark confinement in the sense of area law of the Wilson loop. First, Yang-Mills theory with a non-Abelian gauge group G is reformulated as a deformation of a novel topological field theory. Next, a special class of topological field theories is defined by both BRST and anti-BRST exact action corresponding to the maximal Abelian gauge leaving the maximal torus group H of G invariant. Then we find the topological field theory ($D>2$) has a hidden supersymmetry for a choice of maximal Abelian gauge. As a result, the D-dimensional topological field theory is equivalent to the (D-2)-dimensional coset G/H non-linear sigma model in the sense of Parisi and Sourlas dimensional reduction. After maximal Abelian gauge fixing, the topological property of magnetic monopole and anti-monopole of four-dimensional Yang-Mills theory is translated into that of instanton and anti-instanton in two-dimensional equivalent model. It is shown that the linear static potential in four-dimensions follows from the instanton--anti-instanton gas in the equivalent two-dimensional non-linear sigma model obtained from the four-dimensional topological field theory by dimensional reduction, while the remaining Coulomb potential comes from the perturbative part in four-dimensional Yang-Mills theory. The dimensional reduction opens a path for applying various exact methods developed in two-dimensional quantum field theory to study the non-perturbative problem in low-energy physics of four-dimensional quantum field theories.Comment: 58 pages, Latex, no figures, version accepted for publication in Phys. Rev. D (additions of Discussion, references and minor changes