Modeling the X-rays Resulting from High Velocity Clouds

With the goal of understanding why X-rays have been reported near some high velocity clouds, we perform detailed 3 dimensional hydrodynamic and magnetohydrodynamic simulations of clouds interacting with environmental gas like that in the Galaxy's thick disk/halo or the Magellanic Stream. We examine 2 scenarios. In the first, clouds travel fast enough to shock-heat warm environmental gas. In this scenario, the X-ray productivity depends strongly on the speed of the cloud and the radiative cooling rate. In order to shock-heat environmental gas to temperatures of > or = 10^6 K, cloud speeds of > or = 300 km/s are required. If cooling is quenched, then the shock-heated ambient gas is X-ray emissive, producing bright X-rays in the 1/4 keV band and some X-rays in the 3/4 keV band due to O VII and other ions. If, in contrast, the radiative cooling rate is similar to that of collisional ionizational equilibrium plasma with solar abundances, then the shocked gas is only mildly bright and for only about 1 Myr. The predicted count rates for the non-radiative case are bright enough to explain the count rate observed with XMM-Newton toward a Magellanic Stream cloud and some enhancement in the ROSAT 1/4 keV count rate toward Complex C, while the predicted count rates for the fully radiative case are not. In the second scenario, the clouds travel through and mix with hot ambient gas. The mixed zone can contain hot gas, but the hot portion of the mixed gas is not as bright as those from the shock-heating scenario.Comment: 15 pages, 9 figures, 1 table. Accepted for publication in the Astrophysical Journa

Driven Diffusive Systems: How Steady States Depend on Dynamics

In contrast to equilibrium systems, non-equilibrium steady states depend explicitly on the underlying dynamics. Using Monte Carlo simulations with Metropolis, Glauber and heat bath rates, we illustrate this expectation for an Ising lattice gas, driven far from equilibrium by an `electric' field. While heat bath and Glauber rates generate essentially identical data for structure factors and two-point correlations, Metropolis rates give noticeably weaker correlations, as if the `effective' temperature were higher in the latter case. We also measure energy histograms and define a simple ratio which is exactly known and closely related to the Boltzmann factor for the equilibrium case. For the driven system, the ratio probes a thermodynamic derivative which is found to be dependent on dynamics

Economical Valuation of Hypothetically Constructed Washland around a Wetland

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Monte Carlo Simulation of Sinusoidally Modulated Superlattice Growth

The fabrication of ZnSe/ZnTe superlattices grown by the process of rotating the substrate in the presence of an inhomogeneous flux distribution instead of successively closing and opening of source shutters is studied via Monte Carlo simulations. It is found that the concentration of each compound is sinusoidally modulated along the growth direction, caused by the uneven arrival of Se and Te atoms at a given point of the sample, and by the variation of the Te/Se ratio at that point due to the rotation of the substrate. In this way we obtain a ZnSe$_{1-x}$Te$_x$ alloy in which the composition $x$ varies sinusoidally along the growth direction. The period of the modulation is directly controlled by the rate of the substrate rotation. The amplitude of the compositional modulation is monotonous for small angular velocities of the substrate rotation, but is itself modulated for large angular velocities. The average amplitude of the modulation pattern decreases as the angular velocity of substrate rotation increases and the measurement position approaches the center of rotation. The simulation results are in good agreement with previously published experimental measurements on superlattices fabricated in this manner

A RISC-V Vector Processor With Simultaneous-Switching Switched-Capacitor DC-DC Converters in 28 nm FDSOI

This work demonstrates a RISC-V vector microprocessor implemented in 28 nm FDSOI with fully integrated simultaneous-switching switched-capacitor DC-DC (SC DC-DC) converters and adaptive clocking that generates four on-chip voltages between 0.45 and 1 V using only 1.0 V core and 1.8 V IO voltage inputs. The converters achieve high efficiency at the system level by switching simultaneously to avoid charge-sharing losses and by using an adaptive clock to maximize performance for the resulting voltage ripple. Details about the implementation of the DC-DC switches, DC-DC controller, and adaptive clock are provided, and the sources of conversion loss are analyzed based on measured results. This system pushes the capabilities of dynamic voltage scaling by enabling fast transitions (20 ns), simple packaging (no off-chip passives), low area overhead (16%), high conversion efficiency (80%-86%), and high energy efficiency (26.2 DP GFLOPS/W) for mobile devices

Bidirectional modulation of hyperalgesia via the specific control of excitatory and inhibitory neuronal activity in the ACC

Neurons in the anterior cingulate cortex (ACC) are assumed to play important roles in the perception of nociceptive signals and the associated emotional responses. However, the neuronal types within the ACC that mediate these functions are poorly understood. In the present study, we used optogenetic techniques to selectively modulate excitatory pyramidal neurons and inhibitory interneurons in the ACC and to assess their ability to modulate peripheral mechanical hypersensitivity in freely moving mice. We found that selective activation of pyramidal neurons rapidly and acutely reduced nociceptive thresholds and that this effect was occluded in animals made hypersensitive using Freund's Complete Adjuvant (CFA). Conversely, inhibition of ACC pyramidal neurons rapidly and acutely reduced hypersensitivity induced by CFA treatment. A similar analgesic effect was induced by activation of parvalbumin (PV) expressing interneurons, whereas activation of somatostatin (SOM) expressing interneurons had no effect on pain thresholds. Our results provide direct evidence of the pivotal role of ACC excitatory neurons, and their regulation by PV expressing interneurons, in nociception. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13041-015-0170-6) contains supplementary material, which is available to authorized users

Si IV COLUMN DENSITIES PREDICTED FROM NON-EQUILIBRIUM IONIZATION SIMULATIONS OF TURBULENT MIXING LAYERS AND HIGH-VELOCITY CLOUDS

We present predictions of the Si IV ions in turbulent mixing layers (TMLs) between hot and cool gas and in cool high-velocity clouds (HVCs) that travel through a hot halo, complementing the C IV, N V, and O VI predictions in Kwak & Shelton, Kwak et al., and Henley et al. We find that the Si IV ions are most abundant in regions where the hot and cool gases first begin to mix or where the mixed gas has cooled significantly. The predicted column densities of high velocity Si IV and the predicted ratios of Si IV to C IV and O VI found on individual sightlines in our HVC simulations are in good agreement with observations of high velocity gas. Low velocity Si IV is also seen in the simulations, as a result of decelerated gas in the case of the HVC simulations and when looking along directions that pass perpendicular to the direction of motion in the TML simulations. The ratios of low velocity Si IV to C IV and O VI in the TML simulations are in good agreement with those recorded for Milky Way halo gas, while the ratio of Si IV to O VI from the decelerated gas in the HVC simulations is lower than that observed at normal velocity in the Milky Way halo. We attribute the shortfall of normal velocity Si IV to not having modeled the effects of photoionization and, following Henley et al., consider a composite model that includes decelerated HVC gas, supernova remnants, galactic fountain gas, and the effect of photoionizationopen