Lasercooled RaF as a promising candidate to measure molecular parity violation

The parameter $W_\mathrm{a}$, which characterizes nuclear spin-dependent parity violation effects within the effective molecular spin-rotational Hamiltonian, was computed for the electronic ground state of radium fluoride (RaF) and found to be one of the largest absolute values predicted so far. These calculations were performed with the complex generalised Hartree-Fock method within a two-component (quasi-relativistic) zeroth-order regular approximation framework. Peculiarities of the molecular electronic structure of RaF lead to highly diagonal Franck-Condon matrices between vibrational states of the electronic ground and first excited states, which renders the molecule in principle suitable for direct laser cooling. As a trapped gas of cold molecules offers a superior coherence time, RaF can be considered a promising candidate for high-precision spectroscopic experiments aimed at the search of molecular parity-violation effects.Comment: 4.5 pages, 1 figure, 2 tables. Supplementary material can be requested from the authors. Minor changes to version

325 MHz VLA Observations of Ultracool Dwarfs TVLM 513-46546 and 2MASS J0036+1821104

We present 325 MHz (90 cm wavelength) radio observations of ultracool dwarfs TVLM 513-46546 and 2MASS J0036+1821104 using the Very Large Array (VLA) in June 2007. Ultracool dwarfs are expected to be undetectable at radio frequencies, yet observations at 8.5 GHz (3.5 cm) and 4.9 GHz (6 cm) of have revealed sources with > 100 {\mu}Jy quiescent radio flux and > 1 mJy pulses coincident with stellar rotation. The anomalous emission is likely a combination of gyrosynchrotron and cyclotron maser processes in a long-duration, large-scale magnetic field. Since the characteristic frequency for each process scales directly with the magnetic field magnitude, emission at lower frequencies may be detectable from regions with weaker field strength. We detect no significant radio emission at 325 MHz from TVLM 513-46546 or 2MASS J0036+1821104 over multiple stellar rotations, establishing 2.5{\sigma} total flux limits of 795 {\mu}Jy and 942 {\mu}Jy respectively. Analysis of an archival VLA 1.4 GHz observation of 2MASS J0036+1821104 from January 2005 also yields a non-detection at the level of < 130 {\mu}Jy . The combined radio observation history (0.3 GHz to 8.5 GHz) for these sources suggests a continuum emission spectrum for ultracool dwarfs which is either flat or inverted below 2-3 GHz. Further, if the cyclotron maser instability is responsible for the pulsed radio emission observed on some ultracool dwarfs, our low-frequency non-detections suggest that the active region responsible for the high-frequency bursts is confined within 2 stellar radii and driven by electron beams with energies less than 5 keV.Comment: 11 pages, 5 figures, submitted to A

Spatio-Temporal Scaling of Solar Surface Flows

The Sun provides an excellent natural laboratory for nonlinear phenomena. We use motions of magnetic bright points on the solar surface, at the smallest scales yet observed, to study the small scale dynamics of the photospheric plasma. The paths of the bright points are analyzed within a continuous time random walk framework. Their spatial and temporal scaling suggest that the observed motions are the walks of imperfectly correlated tracers on a turbulent fluid flow in the lanes between granular convection cells.Comment: Now Accepted by Physical Review Letter

Degree Distribution of Competition-Induced Preferential Attachment Graphs

We introduce a family of one-dimensional geometric growth models, constructed iteratively by locally optimizing the tradeoffs between two competing metrics, and show that this family is equivalent to a family of preferential attachment random graph models with upper cutoffs. This is the first explanation of how preferential attachment can arise from a more basic underlying mechanism of local competition. We rigorously determine the degree distribution for the family of random graph models, showing that it obeys a power law up to a finite threshold and decays exponentially above this threshold. We also rigorously analyze a generalized version of our graph process, with two natural parameters, one corresponding to the cutoff and the other a ``fertility'' parameter. We prove that the general model has a power-law degree distribution up to a cutoff, and establish monotonicity of the power as a function of the two parameters. Limiting cases of the general model include the standard preferential attachment model without cutoff and the uniform attachment model.Comment: 24 pages, one figure. To appear in the journal: Combinatorics, Probability and Computing. Note, this is a long version, with complete proofs, of the paper "Competition-Induced Preferential Attachment" (cond-mat/0402268

The Prompt Gamma-Ray and Afterglow Energies of Short-Duration Gamma-Ray Bursts

I present an analysis of the gamma-ray and afterglow energies of the complete sample of 17 short duration GRBs with prompt X-ray follow-up. I find that 80% of the bursts exhibit a linear correlation between their gamma-ray fluence and the afterglow X-ray flux normalized to t=1 d, a proxy for the kinetic energy of the blast wave ($F_{X,1}~F_{gamma}^1.01). An even tighter correlation is evident between E_{gamma,iso} and L_{X,1} for the subset of 13 bursts with measured or constrained redshifts. The remaining 20% of the bursts have values of F_{X,1}/F_{gamma} that are suppressed by about three orders of magnitude, likely because of low circumburst densities (Nakar 2007). These results have several important implications: (i) The X-ray luminosity is generally a robust proxy for the blast wave kinetic energy, indicating nu_X>nu_c and hence a circumburst density n>0.05 cm^{-3}; (ii) most short GRBs have a narrow range of gamma-ray efficiency, with ~0.85 and a spread of 0.14 dex; and (iii) the isotropic-equivalent energies span 10^{48}-10^{52} erg. Furthermore, I find tentative evidence for jet collimation in the two bursts with the highest E_{gamma,iso}, perhaps indicative of the same inverse correlation that leads to a narrow distribution of true energies in long GRBs. I find no clear evidence for a relation between the overall energy release and host galaxy type, but a positive correlation with duration may be present, albeit with a large scatter. Finally, I note that the outlier fraction of 20% is similar to the proposed fraction of short GRBs from dynamically-formed neutron star binaries in globular clusters. This scenario may naturally explain the bimodality of the F_{X,1}/F_{gamma} distribution and the low circumburst densities without invoking speculative kick velocities of several hundred km/s.Comment: Submitted to ApJ; 9 pages, 2 figures, 1 tabl

Conceptual design study of a Harrier V/STOL research aircraft

MCAIR recently completed a conceptual design study to define modification approaches to, and derive planning prices for the conversion of a two place Harrier to a V/STOL control, display and guidance research aircraft. Control concepts such as rate damping, attitude stabilization, velocity command, and cockpit controllers are to be demonstrated. Display formats will also be investigated, and landing, navigation and guidance systems flight tested. The rear cockpit is modified such that it can be quickly adapted to faithfully simulate the controls, displays and handling qualities of a Type A or Type B V/STOL. The safety pilot always has take command capability. The modifications studied fall into two categories: basic modifications and optional modifications. Technical descriptions of the basic modifications and of the optional modifications are presented. The modification plan and schedule as well as the test plan and schedule are presented. The failure mode and effects analysis, aircraft performance, aircraft weight, and aircraft support are discussed