An invariant in shock clustering and Burgers turbulence

1-D scalar conservation laws with convex flux and Markov initial data are now known to yield a completely integrable Hamiltonian system. In this article, we rederive the analogue of Loitsiansky's invariant in hydrodynamic turbulence from the perspective of integrable systems. Other relevant physical notions such as energy dissipation and spectrum are also discussed.Comment: 11 pages, no figures; v2: corrections mad

Clocked Atom Delivery to a Photonic Crystal Waveguide

Experiments and numerical simulations are described that develop quantitative understanding of atomic motion near the surfaces of nanoscopic photonic crystal waveguides (PCWs). Ultracold atoms are delivered from a moving optical lattice into the PCW. Synchronous with the moving lattice, transmission spectra for a guided-mode probe field are recorded as functions of lattice transport time and frequency detuning of the probe beam. By way of measurements such as these, we have been able to validate quantitatively our numerical simulations, which are based upon detailed understanding of atomic trajectories that pass around and through nanoscopic regions of the PCW under the influence of optical and surface forces. The resolution for mapping atomic motion is roughly 50 nm in space and 100 ns in time. By introducing auxiliary guided mode (GM) fields that provide spatially varying AC-Stark shifts, we have, to some degree, begun to control atomic trajectories, such as to enhance the flux into to the central vacuum gap of the PCW at predetermined times and with known AC-Stark shifts. Applications of these capabilities include enabling high fractional filling of optical trap sites within PCWs, calibration of optical fields within PCWs, and utilization of the time-dependent, optically dense atomic medium for novel nonlinear optical experiments

Pif1 Helicase Lengthens Some Okazaki Fragment Flaps Necessitating Dna2 Nuclease/Helicase Action in the Two-nuclease Processing Pathway

We have developed a system to reconstitute all of the proposed steps of Okazaki fragment processing using purified yeast proteins and model substrates. DNA polymerase δ was shown to extend an upstream fragment to displace a downstream fragment into a flap. In most cases, the flap was removed by flap endonuclease 1 (FEN1), in a reaction required to remove initiator RNA in vivo. The nick left after flap removal could be sealed by DNA ligase I to complete fragment joining. An alternative pathway involving FEN1 and the nuclease/helicase Dna2 has been proposed for flaps that become long enough to bind replication protein A (RPA). RPA binding can inhibit FEN1, but Dna2 can shorten RPA-bound flaps so that RPA dissociates. Recent reconstitution results indicated that Pif1 helicase, a known component of fragment processing, accelerated flap displacement, allowing the inhibitory action of RPA. In results presented here, Pif1 promoted DNA polymerase δ to displace strands that achieve a length to bind RPA, but also to be Dna2 substrates. Significantly, RPA binding to long flaps inhibited the formation of the final ligation products in the reconstituted system without Dna2. However, Dna2 reversed that inhibition to restore efficient ligation. These results suggest that the two-nuclease pathway is employed in cells to process long flap intermediates promoted by Pif1

Vision and Radar Steering Reduces Agricultural Sprayer Operator Stress without Compromising Steering Performance

Self-propelled agricultural sprayer operators work an average of 15 h d-1 in peak season, and steering is the task that causes the operator the most stress because of the large number of stimuli involved. Automatic guidance systems help reduce stress and fatigue for operators by allowing them to focus on tasks other than steering. Physiological signals like skin conductance (electrodermal activity, EDA) change with stress and can be used to identify stressful events. The objective of this study was to determine if using a commercially available vision and radar guidance system (VSN®, Raven Industries) reduces agricultural sprayer operators’ stress compared to when they are steering manually. Four male professional sprayer operators participated in this study. Each operator performed his job duties normally in GPS-guidance-planted fields, at his self-selected speed, except to drive some passes manually and others with VSN in the same field. EDA was measured with an Empatica E4 wristband, and stressful events were quantified. Machine data (e.g., speed, RTK-GPS, and VSN metrics) were collected from each sprayer via CAN logs. The steering type, stress rate (e.g., stressful events min-1), and steering performance (crosstrack error standard deviation, XTE SD) were determined for each pass. In total, 51 passes (23 manual, 28 VSN) in six fields were analyzed. Operators using VSN had a significant reduction (48% lower, p \u3c 0.001) in their stress rate compared to when they were steering manually. There was no significant difference in the XTE SD for the steering type. The use of an automatic guidance system such as VSN could have a dramatic positive effect on the health of sprayer operators, especially during the long workdays of the peak spraying season, and could reduce the negative effects that stress and fatigue have on steering performance, mistakes, and accidents

Hall drift of axisymmetric magnetic fields in solid neutron-star matter

Hall drift, i. e., transport of magnetic flux by the moving electrons giving rise to the electrical current, may be the dominant effect causing the evolution of the magnetic field in the solid crust of neutron stars. It is a nonlinear process that, despite a number of efforts, is still not fully understood. We use the Hall induction equation in axial symmetry to obtain some general properties of nonevolving fields, as well as analyzing the evolution of purely toroidal fields, their poloidal perturbations, and current-free, purely poloidal fields. We also analyze energy conservation in Hall instabilities and write down a variational principle for Hall equilibria. We show that the evolution of any toroidal magnetic field can be described by Burgers' equation, as previously found in plane-parallel geometry. It leads to sharp current sheets that dissipate on the Hall time scale, yielding a stationary field configuration that depends on a single, suitably defined coordinate. This field, however, is unstable to poloidal perturbations, which grow as their field lines are stretched by the background electron flow, as in instabilities earlier found numerically. On the other hand, current-free poloidal configurations are stable and could represent a long-lived crustal field supported by currents in the fluid stellar core.Comment: 8 pages, 5 figure panels; new version with very small correction; accepted by Astronomy & Astrophysic

Deterministic reaction models with power-law forces

We study a one-dimensional particles system, in the overdamped limit, where nearest particles attract with a force inversely proportional to a power of their distance and coalesce upon encounter. The detailed shape of the distribution function for the gap between neighbouring particles serves to discriminate between different laws of attraction. We develop an exact Fokker-Planck approach for the infinite hierarchy of distribution functions for multiple adjacent gaps and solve it exactly, at the mean-field level, where correlations are ignored. The crucial role of correlations and their effect on the gap distribution function is explored both numerically and analytically. Finally, we analyse a random input of particles, which results in a stationary state where the effect of correlations is largely diminished

Ellipticals at z=0 from Self-Consistent Hydrodynamical Simulations: Clues on Age Effects in their Stellar Populations

We present results of a study of the stellar age distributions in the sample of elliptical-like objects (ELOs) identified at z=0 in four simulations operating in the context of a concordance cosmological model. The simulations show that the formation of most stars in each ELO of the sample is a consequence of violent dynamical events, either fast multiclump collapse at high z, or mergers at lower z. This second way can explain the age spread as well as the dynamical peculiarities observed in some ellipticals, but its relative weight is never dominant and decreases as the ELO mass at the halo scale, $M_{vir}$, increases, to such an extent that some recent mergers contributing an important fraction to the total ELO mass can possibly contribute only a small fraction of new born stars. More massive objects have older means and narrower spreads in their stellar age distributions than less massive ones. The ELO sample shows also a tight correlation between $M_{vir}$ and the central stellar l.o.s. velocity dispersion, $\sigma_{los}$. This gives a trend of the means and spreads of ELO stellar populations with $\sigma_{los}$ that is consistent, even quantitatively, with the age effects observationally detected in the stellar populations of elliptical galaxies. Therefore, these effects can be explained as the observational manifestation of the intrinsic correlations found in the ELO sample between $M_{vir}$ and the properties of the stellar age distribution, on the one hand, and $M_{vir}$ and $\sigma_{los}$, on the other hand. These correlations hint, for the first time, at a possible way to reconcile age effects in ellipticals, and, particularly, the increase of $\alpha /$ ratios with $\sigma_{los}$, with the hierarchical clustering paradigm.Comment: 13 pages, 2 figures, accepted for publication in Astrophysical Journal Letter

Clinical practice guidelines: towards better quality guidelines and increased international collaboration

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Exact probability function for bulk density and current in the asymmetric exclusion process

We examine the asymmetric simple exclusion process with open boundaries, a paradigm of driven diffusive systems, having a nonequilibrium steady state transition. We provide a full derivation and expanded discussion and digression on results previously reported briefly in M. Depken and R. Stinchcombe, Phys. Rev. Lett. {\bf 93}, 040602, (2004). In particular we derive an exact form for the joint probability function for the bulk density and current, both for finite systems, and also in the thermodynamic limit. The resulting distribution is non-Gaussian, and while the fluctuations in the current are continuous at the continuous phase transitions, the density fluctuations are discontinuous. The derivations are done by using the standard operator algebraic techniques, and by introducing a modified version of the original operator algebra. As a byproduct of these considerations we also arrive at a novel and very simple way of calculating the normalization constant appearing in the standard treatment with the operator algebra. Like the partition function in equilibrium systems, this normalization constant is shown to completely characterize the fluctuations, albeit in a very different manner.Comment: 10 pages, 4 figure