Urgency is a Non-monotonic Function of Pulse Rate

Magnitude estimation was used to assess the experience of urgency in pulse-train stimuli (pulsed white noise) ranging from 3.13 to 200 Hz. At low pulse rates, pulses were easily resolved. At high pulse rates, pulses fused together leading to a tonal sensation with a clear pitch level. Urgency ratings followed a nonmonotonic (polynomial) function with local maxima at 17.68 and 200 Hz. The same stimuli were also used in response time and pitch scaling experiments. Response times were negatively correlated with urgency ratings. Pitch scaling results indicated that urgency of pulse trains is mediated by the perceptual constructs of speed and pitch

Precessing Jets and Molecular Outflows: A 3-D Numerical Study

We present 3-D numerical hydrodynamical simulations of precessing supersonic heavy jets to explore how well they serve as a model for generating molecular outflows from Young Stellar Objects. The dynamics are studied with a number of high resolution simulations on a Cartesian grid (128x128x128 zones) using a high order finite difference method. A range of cone angles and precession rates were included in the study. Two higher resolution runs (256x256x256 zones) were made for comparison in order to confirm numerical convergence of global flow characteristics. Morphological, kinematical and dynamical characteristics of precessing jets are described and compared to important properties of straight jets and also to observations of YSOs. In order to examine the robustness of precessing jets as a mean to produce molecular outflows around Young Stellar Objects, ``synthetic observations'' of the momentum distributions of the simulated precessing jets are compared to observations of molecular outflows. It is found that precessing jets match better the morphology, highly forward driven momentum and momentum distributions along the long axis of molecular outflows than do wind-driven or straight jet-driven flow models.Comment: Accepted by ApJ, 31 pages, using aasms.sty, Also available in postscript with figures via a gzipped tar file at ftp://s1.msi.umn.edu/pub/afrank/3DJet/3DJet.tar.gz . For information contact [email protected]

Tolerable versus actual soil erosion rates in Europe

Erosion is a major threat to soil resources in Europe, and may impair their ability to deliver a range of ecosystem goods and services. This is reflected by the European Commission's Thematic Strategy for Soil Protection, which recommends an indicator-based approach for monitoring soil erosion. Defined baseline and threshold values are essential for the evaluation of soil monitoring data. Therefore, accurate spatial data on both soil loss and soil genesis are required, especially in the light of predicted changes in climate patterns, notably frequency, seasonal distribution and intensity of precipitation. Rates of soil loss are reported that have been measured, modelled or inferred for most types of soil erosion in a variety of landscapes, by studies across the spectrum of the Earth sciences. Natural rates of soil formation can be used as a basis for setting tolerable soil erosion rates, with soil formation consisting of mineral weathering as well as dust deposition. This paper reviews the concept of tolerable soil erosion and summarises current knowledge on rates of soil formation, which are then compared to rates of soil erosion by known erosion types, for assessment of soil erosion monitoring at the European scale

Low-temperature plasma technology as part of a closed-loop resource management system

The results of this testing indicate that the agitated low-temperature plasma reactor system successfully converted carbon, hydrogen, and nitrogen into gaseous products at residence times that were about ten times shorter than those achieved by stationary processing. The inorganic matrix present was virtually unchanged by the processing technique. It was concluded that this processing technique is feasible for use as part of a close-looped processing resource management system

The MHD Kelvin-Helmholtz Instability II: The Roles of Weak and Oblique Fields in Planar Flows

We have carried out high resolution MHD simulations of the nonlinear evolution of Kelvin-Helmholtz unstable flows in 2 1/2 dimensions. The modeled flows and fields were initially uniform except for a thin shear layer with a hyperbolic tangent velocity profile and a small, normal mode perturbation. The calculations consider periodic sections of flows containing magnetic fields parallel to the shear layer, but projecting over a full range of angles with respect to the flow vectors. They are intended as preparation for fully 3D calculations and to address two specific questions raised in earlier work: 1) What role, if any, does the orientation of the field play in nonlinear evolution of the MHD Kelvin-Helmholtz instability in 2 1/2 D. 2) Given that the field is too weak to stabilize against a linear perturbation of the flow, how does the nonlinear evolution of the instability depend on strength of the field. The magnetic field component in the third direction contributes only through minor pressure contributions, so the flows are essentially 2D. Even a very weak field can significantly enhance the rate of energy dissipation. In all of the cases we studied magnetic field amplification by stretching in the vortex is limited by tearing mode, ``fast'' reconnection events that isolate and then destroy magnetic flux islands within the vortex and relax the fields outside the vortex. If the magnetic tension developed prior to reconnection is comparable to Reynolds stresses in the flow, that flow is reorganized during reconnection. Otherwise, the primary influence on the plasma is generation of entropy. The effective expulsion of flux from the vortex is very similar to that shown by Weiss for passive fields in idealized vortices with large magnetic Reynolds numbers. We demonstrated that thisComment: 23 pages of ApJ Latex (aaspp4.sty) with 10 figures, high resolution postscript images for figs 4-9 available through anonymous at ftp://ftp.msi.umn.edu/pub/twj To appear in the June 10, 1997 Ap

The Density Spike in Cosmic-Ray-Modified Shocks: Formation, Evolution, and Instability

We examine the formation and evolution of the density enhancement (density spike) that appears downstream of strong, cosmic-ray-modified shocks. This feature results from temporary overcompression of the flow by the combined cosmic-ray shock precursor/gas subshock. Formation of the density spike is expected whenever shock modification by cosmic-ray pressure increases strongly. That occurence may be anticipated for newly generated strong shocks or for cosmic-ray-modified shocks encountering a region of higher external density, for example. The predicted mass density within the spike increases with the shock Mach number and with shocks more dominated by cosmic-ray pressure. We find this spike to be linearly unstable under a modified Rayleigh-Taylor instability criterion at the early stage of its formation. We confirm this instability numerically using two independent codes based on the two-fluid model for cosmic-ray transport. These two-dimensional simulations show that the instability grows impulsively at early stages and then slows down as the gradients of total pressure and gas density decrease. Observational discovery of this unstable density spike behind shocks, possibly through radio emission enhanced by the amplified magnetic fields would provide evidence for the existence of strongly cosmic-ray modified shock structures.Comment: 26 pages in Latex and 6 figures. Accepted to Ap

Acute military psychiatric casualties from the war in Iraq

Background: The view that most military personnel evacuated from war zones are suffering from combat stress reactions, or are otherwise traumatised by the horrors of war, has an impact on all aspects of military psychiatry. Aims: To delineate the reasons for psychiatric aeromedical evacuation from Iraq from the start of build-up of UK forces in January 2003 until the end of October that year, 6 months after the end of formal hostilities. Method: A retrospective study was conducted of field and in-patient psychiatric assessments of 116 military personnel evacuated to the UK military psychiatric in-patient facility in Catterick Garrison. Results: Evacuees were mainly non-combatants (69%). A significant proportion were in reserve service (21%) and had a history of contact with mental health services (37%). Only 3% had a combat stress reaction. In over 85% of cases evacuation was for low mood attributed to separation from friends or family, or difficulties adjusting to the environment. Conclusions: These findings have implications especially for screening for suitability for deployment, and for understanding any longer-term mental health problems arising in veterans from Iraq

The MHD Kelvin-Helmholtz Instability III: The Role of Sheared Magnetic Field in Planar Flows

We have carried out simulations of the nonlinear evolution of the magnetohydrodynamic (MHD) Kelvin-Helmholtz (KH) instability for compressible fluids in $2\frac{1}{2}$-dimensions, extending our previous work by Frank et al (1996) and Jones \etal (1997). In the present work we have simulated flows in the x-y plane in which a ``sheared'' magnetic field of uniform strength ``smoothly'' rotates across a thin velocity shear layer from the z direction to the x direction, aligned with the flow field. We focus on dynamical evolution of fluid features, kinetic energy dissipation, and mixing of the fluid between the two layers, considering their dependence on magnetic field strength for this geometry. The introduction of magnetic shear can allow a Cat's Eye-like vortex to form, even when the field is stronger than the nominal linear instability limit given above. For strong fields that vortex is asymmetric with respect to the preliminary shear layer, however, so the subsequent dissipation is enhanced over the uniform field cases of comparable field strength. In fact, so long as the magnetic field achieves some level of dynamical importance during an eddy turnover time, the asymmetries introduced through the magnetic shear will increase flow complexity, and, with that, dissipation and mixing. The degree of the fluid mixing between the two layers is strongly influenced by the magnetic field strength. Mixing of the fluid is most effective when the vortex is disrupted by magnetic tension during transient reconnection, through local chaotic behavior that follows.Comment: 14 pages including 9 figures (4 figures in degraded jpg format), full paper with original quality figures available via anonymous ftp at ftp://canopus.chungnam.ac.kr/ryu/mhdkh2d.uu, to appear in The Astrophysical Journa

Infrared interferometry to spatially and spectrally resolve jets in X-ray binaries

Infrared interferometry is a new frontier for precision ground based observing, with new instrumentation achieving milliarcsecond (mas) spatial resolutions for faint sources, along with astrometry on the order of 10 microarcseconds. This technique has already led to breakthroughs in the observations of the supermassive black hole at the Galactic centre and its orbiting stars, AGN, and exo-planets, and can be employed for studying X-ray binaries (XRBs), microquasars in particular. Beyond constraining the orbital parameters of the system using the centroid wobble and spatially resolving jet discrete ejections on mas scales, we also propose a novel method to discern between the various components contributing to the infrared bands: accretion disk, jets and companion star. We demonstrate that the GRAVITY instrument on the Very Large Telescope Interferometer (VLTI) should be able to detect a centroid shift in a number of sources, opening a new avenue of exploration for the myriad of transients expected to be discovered in the coming decade of radio all-sky surveys. We also present the first proof-of-concept GRAVITY observation of a low-mass X-ray binary transient, MAXI J1820+070, to search for extended jets on mas scales. We place the tightest constraints yet via direct imaging on the size of the infrared emitting region of the compact jet in a hard state XRB.Comment: 12 Pages, 3 figures, accepted for publication in MNRA