Information Flow in an R and D Laboratory

Statistical analysis of hypotheses concerning roles of technological gatekeeper and primary groups in flow of information in small research and development laborator

Large Magnetic Fields and Motions of OH Masers in W75 N

We report on a second epoch of VLBA observations of the 1665 and 1667 MHz OH masers in the massive star-forming region W75 N. We find evidence to confirm the existence of very strong (~40 mG) magnetic fields near source VLA 2. The masers near VLA 2 are dynamically distinct and include a very bright spot apparently moving at 50 km/s relative to those around VLA 1. This fast-moving spot may be an example of a rare class of OH masers seen in outflows in star-forming regions. Due to the variability of these masers and the rapidity of their motions, tracking these motions will require multiple observations over a significantly shorter time baseline than obtained here. Proper motions of the masers near VLA 1 are more suggestive of streaming along magnetized shocks rather than Keplerian rotation in a disk. The motions of the easternmost cluster of masers in W75 N (B) may be tracing slow expansion around an unseen exciting source.Comment: 7 pages including 4 figures (2 color) & 3 tables, to appear in Ap

Many-body theory of excitation dynamics in an ultracold Rydberg gas

We develop a theoretical approach for the dynamics of Rydberg excitations in ultracold gases, with a realistically large number of atoms. We rely on the reduction of the single-atom Bloch equations to rate equations, which is possible under various experimentally relevant conditions. Here, we explicitly refer to a two-step excitation-scheme. We discuss the conditions under which our approach is valid by comparing the results with the solution of the exact quantum master equation for two interacting atoms. Concerning the emergence of an excitation blockade in a Rydberg gas, our results are in qualitative agreement with experiment. Possible sources of quantitative discrepancy are carefully examined. Based on the two-step excitation scheme, we predict the occurrence of an antiblockade effect and propose possible ways to detect this excitation enhancement experimentally in an optical lattice as well as in the gas phase.Comment: 12 pages, 8 figure

Interactions Between Rydberg-Dressed Atoms

We examine interactions between atoms continuously and coherently driven between the ground state and a Rydberg state, producing "Rydberg-dressed atoms." Because of the large dipolar coupling between two Rydberg atoms, a small admixture of Rydberg character into a ground state can produce an atom with a dipole moment of a few Debye, the appropriate size to observe interesting dipolar physics effects in cold atom systems. We have calculated the interaction energies for atoms that interact via the dipole-dipole interaction and find that due to blockade effects, the R-dependent two-atom interaction terms are limited in size, and can be R-independent up until the dipolar energy is equal to the detuning. This produces R-dependent interactions different from the expected 1/R^3 dipolar form, which have no direct analogy in condensed matter physics, and could lead to new quantum phases in trapped Rydberg systems.Comment: 5 pages, 7 figures; Accepted to Phys. Rev. A, 18 Aug. 201

Model Independent Tests of Skyrmions and Their Holographic Cousins

We describe a new exact relation for large $N_c$ QCD for the long-distance behavior of baryon form factors in the chiral limit. This model-independent relation is used to test the consistency of the structure of several baryon models. All 4D semiclassical chiral soliton models satisfy the relation, as does the Pomarol-Wulzer holographic model of baryons as 5D Skyrmions. However, remarkably, we find that the holographic model treating baryons as instantons in the Sakai-Sugimoto model does not satisfy the relation.Comment: v2. Added references, corrected typo

One-year transitional programme increases knowledge to level sufficient for entry into the fourth year of the medical curriculum

BACKGROUND: To cope with a lack of doctors and in anticipation of the Bachelor-Master structure for Medicine, several Dutch universities offer graduate entry programmes for students with degrees in areas related to Medicine. The graduate entry programme is a four-year programme: after a transition period of one year students enroll in the fourth year of the regular six-year training programme. AIM: The research questions in this study were (1) whether and when graduate entry students' knowledge reached a level comparable to that of regular medical students and (2) whether there were differences in knowledge levels between graduate entry students with a university or HBO (college) degree. METHODS: The progress test results of ninety graduate entry students who were enrolled in the transitional programme between 2002 and 2004 were compared to those of regular third-year students. RESULTS: Initially, graduate entry students scored significantly lower on the progress tests, but differences disappeared within a year. No differences were found between graduate entry students with a university or HBO degree. CONCLUSIONS: The results of this study indicate that the increase in knowledge after a one-year transitional period is sufficient to enroll students with related degrees in the fourth year of the regular medical training programme

On The Importance Of The Interclump Medium For Superionization: O VI Formation In The Wind Of Zeta Puppis

We have studied superionization and X-ray line formation in the spectra of zeta Pup using our new stellar atmosphere code (XCMFGEN) that can be used to simultaneously analyze optical, UV, and X-ray observations. Here, we present results on the formation of the O VI lambda lambda 1032, 1038 doublet. Our simulations, supported by simple theoretical calculations, show that clumped wind models that assume void in the interclump space cannot reproduce the observed O vi profiles. However, enough O vi can be produced if the voids are filled by a low-density gas. The recombination of O vi is very efficient in the dense material, but in the tenuous interclump region an observable amount of O vi can be maintained. We also find that different UV resonance lines are sensitive to different density regimes in z Pup: C IV is almost exclusively formed within the densest regions, while the majority of O vi resides between clumps. N v is an intermediate case, with contributions from both the tenuous gas and clumps

Measurement of the ac Stark shift with a guided matter-wave interferometer

We demonstrate the effectiveness of a guided-wave Bose-Einstein condensate interferometer for practical measurements. Taking advantage of the large arm separations obtainable in our interferometer, the energy levels of the 87Rb atoms in one arm of the interferometer are shifted by a calibrated laser beam. The resulting phase shifts are used to determine the ac polarizability at a range of frequencies near and at the atomic resonance. The measured values are in good agreement with theoretical expectations. However, we observe a broadening of the transition near the resonance, an indication of collective light scattering effects. This nonlinearity may prove useful for the production and control of squeezed quantum states.Comment: 5 pages, three figure

High-precision Measurements of Ionospheric TEC Gradients with the Very Large Array VHF System

We have used a relatively long, contiguous VHF observation of a bright cosmic radio source (Cygnus A) with the Very Large Array (VLA) to demonstrate the capability of this instrument to study the ionosphere. This interferometer, and others like it, can observe ionospheric total electron content (TEC) fluctuations on a much wider range of scales than is possible with many other instruments. We have shown that with a bright source, the VLA can measure differential TEC values between pairs of antennas (delta-TEC) with an precision of 0.0003 TECU. Here, we detail the data reduction and processing techniques used to achieve this level of precision. In addition, we demonstrate techniques for exploiting these high-precision delta-TEC measurements to compute the TEC gradient observed by the array as well as small-scale fluctuations within the TEC gradient surface. A companion paper details specialized spectral analysis techniques used to characterize the properties of wave-like fluctuations within this data.Comment: accepted for publication in Radio Scienc