The Universal Gaussian in Soliton Tails

We show that in a large class of equations, solitons formed from generic initial conditions do not have infinitely long exponential tails, but are truncated by a region of Gaussian decay. This phenomenon makes it possible to treat solitons as localized, individual objects. For the case of the KdV equation, we show how the Gaussian decay emerges in the inverse scattering formalism.Comment: 4 pages, 2 figures, revtex with eps

A Random Matrix Model of Adiabatic Quantum Computing

We present an analysis of the quantum adiabatic algorithm for solving hard instances of 3-SAT (an NP-complete problem) in terms of Random Matrix Theory (RMT). We determine the global regularity of the spectral fluctuations of the instantaneous Hamiltonians encountered during the interpolation between the starting Hamiltonians and the ones whose ground states encode the solutions to the computational problems of interest. At each interpolation point, we quantify the degree of regularity of the average spectral distribution via its Brody parameter, a measure that distinguishes regular (i.e., Poissonian) from chaotic (i.e., Wigner-type) distributions of normalized nearest-neighbor spacings. We find that for hard problem instances, i.e., those having a critical ratio of clauses to variables, the spectral fluctuations typically become irregular across a contiguous region of the interpolation parameter, while the spectrum is regular for easy instances. Within the hard region, RMT may be applied to obtain a mathematical model of the probability of avoided level crossings and concomitant failure rate of the adiabatic algorithm due to non-adiabatic Landau-Zener type transitions. Our model predicts that if the interpolation is performed at a uniform rate, the average failure rate of the quantum adiabatic algorithm, when averaged over hard problem instances, scales exponentially with increasing problem size.Comment: 9 pages, 7 figure

Spectrum of Neutral Helium in Strong Magnetic Fields

We present extensive and accurate calculations for the excited state spectrum of spin-polarized neutral helium in a range of magnetic field strengths up to $10^{12}$ G. Of considerable interest to models of magnetic white dwarf stellar atmospheres, we also present results for the dipole strengths of the low lying transitions among these states. Our methods rely on a systematically saturated basis set approach to solving the Hartree--Fock self-consistent field equations, combined with an ``exact'' stochastic method to estimate the residual basis set truncation error and electron correlation effects. We also discuss the applicability of the adiabatic approximation to strongly magnetized multi-electron atoms.Comment: 19 pages, 7 figures, 10 table

Restricted feedback control of one-dimensional maps

Dynamical control of biological systems is often restricted by the practical constraint of unidirectional parameter perturbations. We show that such a restriction introduces surprising complexity to the stability of one-dimensional map systems and can actually improve controllability. We present experimental cardiac control results that support these analyses. Finally, we develop new control algorithms that exploit the structure of the restricted-control stability zones to automatically adapt the control feedback parameter and thereby achieve improved robustness to noise and drifting system parameters.Comment: 29 pages, 9 embedded figure

Effects of type and level of training on variation in physician knowledge in the use and acquisition of blood cultures: a cross sectional survey

BACKGROUND: Blood culture (BCX) use is often sub-optimal, and is a user-dependent diagnostic test. Little is known about physician training and BCX-related knowledge. We sought to assess variations in caregiver BCX-related knowledge, and their relation to medical training. METHODS: We developed and piloted a self-administered BCX-related knowledge survey instrument. Expert opinion, literature review, focus groups, and mini-pilots reduced > 100 questions in multiple formats to a final questionnaire with 15 scored content items and 4 covariate identifiers. This questionnaire was used in a cross-sectional survey of physicians, fellows, residents and medical students at a large urban public teaching hospital. The responses were stratified by years/level of training, type of specialty training, self-reported practical and theoretical BCX-related instruction. Summary scores were derived from participant responses compared to a 95% consensus opinion of infectious diseases specialists that matched an evidence based reference standard. RESULTS: There were 291 respondents (Attendings = 72, Post-Graduate Year (PGY) = 3 = 84, PGY2 = 42, PGY1 = 41, medical students = 52). Mean scores differed by training level (Attending = 85.0, PGY3 = 81.1, PGY2 = 78.4, PGY1 = 75.4, students = 67.7) [p ≤ 0.001], and training type (Infectious Diseases = 96.1, Medicine = 81.7, Emergency Medicine = 79.6, Surgery = 78.5, Family Practice = 76.5, Obstetrics-Gynecology = 74.4, Pediatrics = 74.0) [p ≤ 0.001]. Higher summary scores were associated with self-reported theoretical [p ≤ 0.001] and practical [p = 0.001] BCX-related training. Linear regression showed level and type of training accounted for most of the score variation. CONCLUSION: Higher mean scores were associated with advancing level of training and greater subject-related training. Notably, house staff and medical students, who are most likely to order and/or obtain BCXs, lack key BCX-related knowledge. Targeted education may improve utilization of this important diagnostic tool

Excitability in autonomous Boolean networks

We demonstrate theoretically and experimentally that excitable systems can be built with autonomous Boolean networks. Their experimental implementation is realized with asynchronous logic gates on a reconfigurabe chip. When these excitable systems are assembled into time-delay networks, their dynamics display nanosecond time-scale spike synchronization patterns that are controllable in period and phase.Comment: 6 pages, 5 figures, accepted in Europhysics Letters (epljournal.edpsciences.org