1,910 research outputs found
Simulations of Nonthermal Electron Transport in Multidimensional Flows: Synthetic Observations of Radio Galaxies
We have applied an effective numerical scheme for cosmic-ray transport to 3D
MHD simulations of jet flow in radio galaxies (see the companion paper by Jones
et al. 1999). The marriage of relativistic particle and 3D magnetic field
information allows us to construct a rich set of ``synthetic observations'' of
our simulated objects. The information is sufficient to calculate the ``true''
synchrotron emissivity at a given frequency using explicit information about
the relativistic electrons. This enables us to produce synchrotron
surface-brightness maps, including polarization. Inverse-Compton X-ray
surface-brightness maps may also be produced. First results intended to explore
the connection between jet dynamics and electron transport in radio lobes are
discussed. We infer lobe magnetic field values by comparison of synthetically
observed X-ray and synchrotron fluxes, and find these ``inverse-Compton''
fields to be quite consistent with the actual RMS field averaged over the lobe.
The simplest minimum energy calculation from the synthetic observations also
seems to agree with the actual simulated source properties.Comment: 7 pages, 1 figure; to appear in Life Cycles of Radio Galaxies, ed. J.
Biretta et al., New Astronomy Review
Simulations of Nonthermal Electron Transport in Multidimensional Flows: Application to Radio Galaxies
We have developed an economical, effective numerical scheme for cosmic-ray
transport suitable for treatment of electrons up to a few hundreds of GeV in
multidimensional simulations of radio galaxies. The method follows the electron
population in sufficient detail to allow computation of synthetic radio and
X-ray observations of the simulated sources, including spectral properties (see
the companion paper by Tregillis et al. 1999). The cosmic-ray particle
simulations can follow the effects of shock acceleration, second-order Fermi
acceleration as well as radiative and adiabatic energy losses. We have applied
this scheme to 2-D and 3-D MHD simulations of jet-driven flows and have begun
to explore links between dynamics and the properties of high energy electron
populations in radio lobes. The key initial discovery is the great importance
to the high energy particle population of the very unsteady and inhomogeneous
flows, especially near the end of the jet. Because of this, in particular, our
simulations show that a large fraction of the particle population flowing from
the jet into the cocoon never passes through strong shocks. The shock strengths
encountered are not simply predicted by 1-D models, and are quite varied.
Consequently, the emergent electron spectra are highly heterogeneous. Rates of
synchrotron aging in "hot-spots" seem similarly to be very uneven, enhancing
complexity in the spectral properties of electrons as they emerge into the
lobes and making more difficult the task of comparing dynamical and radiative
ages.Comment: 7 pages, 1 figure; to appear in Life Cycles of Radio Galaxies, ed. J.
Biretta et al., New Astronomy Review
Extracellular Protons Inhibit Charge Immobilization in the Cardiac Voltage-Gated Sodium Channel
AbstractLow pH depolarizes the voltage-dependence of cardiac voltage-gated sodium (NaV1.5) channel activation and fast inactivation and destabilizes the fast-inactivated state. The molecular basis for these changes in protein behavior has not been reported. We hypothesized that changes in the kinetics of voltage sensor movement may destabilize the fast-inactivated state in NaV1.5. To test this idea, we recorded NaV1.5 gating currents in Xenopus oocytes using a cut-open voltage-clamp with extracellular solution titrated to either pH 7.4 or pH 6.0. Reducing extracellular pH significantly depolarized the voltage-dependence of both the QON/V and QOFF/V curves, and reduced the total charge immobilized during depolarization. We conclude that destabilized fast-inactivation and reduced charge immobilization in NaV1.5 at low pH are functionally related effects
Ecological Modeling of Aedes aegypti (L.) Pupal Production in Rural Kamphaeng Phet, Thailand
Background - Aedes aegypti (L.) is the primary vector of dengue, the most important arboviral infection globally. Until an effective vaccine is licensed and rigorously administered, Ae. aegypti control remains the principal tool in preventing and curtailing dengue transmission. Accurate predictions of vector populations are required to assess control methods and develop effective population reduction strategies. Ae. aegypti develops primarily in artificial water holding containers. Release recapture studies indicate that most adult Ae. aegypti do not disperse over long distances. We expect, therefore, that containers in an area of high development site density are more likely to be oviposition sites and to be more frequently used as oviposition sites than containers that are relatively isolated from other development sites. After accounting for individual container characteristics, containers more frequently used as oviposition sites are likely to produce adult mosquitoes consistently and at a higher rate. To this point, most studies of Ae. aegypti populations ignore the spatial density of larval development sites. Methodology - Pupal surveys were carried out from 2004 to 2007 in rural Kamphaeng Phet, Thailand. In total, 84,840 samples of water holding containers were used to estimate model parameters. Regression modeling was used to assess the effect of larval development site density, access to piped water, and seasonal variation on container productivity. A varying-coefficients model was employed to account for the large differences in productivity between container types. A two-part modeling structure, called a hurdle model, accounts for the large number of zeroes and overdispersion present in pupal population counts. Findings - The number of suitable larval development sites and their density in the environment were the primary determinants of the distribution and abundance of Ae. aegypti pupae. The productivity of most container types increased significantly as habitat density increased. An ecological approach, accounting for development site density, is appropriate for predicting Ae. aegypti population levels and developing efficient vector control program
An Efficient Numerical Scheme for Simulating Particle Acceleration in Evolving Cosmic-Ray Modified Shocks
We have developed a new, very efficient numerical scheme to solve the CR
diffusion convection equation that can be applied to the study of the nonlinear
time evolution of CR modified shocks for arbitrary spatial diffusion
properties. The efficiency of the scheme derives from its use of coarse-grained
finite momentum volumes. This approach has enabled us, using
momentum bins spanning nine orders of magnitude in momentum, to carry out
simulations that agree well with results from simulations of modified shocks
carried out with our conventional finite difference scheme requiring more than
an order of magnitude more momentum points. The coarse-grained, CGMV scheme
reduces execution times by a factor approximately half the ratio of momentum
bins used in the two methods. Depending on the momentum dependence of the
diffusion, additional economies in required spatial and time resolution can be
utilized in the CGMV scheme, as well. These allow a computational speed-up of
at least an order of magnitude in some cases.Comment: Accepted for publication in Astroparticle Physics; 19 pages and 5
figure
`In pursuit of the Nazi mind?' the deployment of psychoanalysis in the allied struggle against Germany
This paper discusses how psychoanalytic ideas were brought to bear in the Allied struggle against the Third Reich and explores some of the claims that were made about this endeavour. It shows how a variety of studies of Fascist psychopathology, centred on the concept of superego, were mobilized in military intelligence, post-war planning and policy recommendations for ‘denazification’. Freud's ideas were sometimes championed by particular army doctors and government planners; at other times they were combined with, or displaced by, competing, psychiatric and psychological forms of treatment and diverse studies of the Fascist ‘personality’. This is illustrated through a discussion of the treatment and interpretation of the deputy leader of the Nazi Party, Rudolf Hess, after his arrival in Britain in 1941
Probing e-e interactions in a periodic array of GaAs quantum wires
We present the results of non-linear tunnelling spectroscopy between an array
of independent quantum wires and an adjacent two-dimensional electron gas
(2DEG) in a double-quantum-well structure. The two layers are separately
contacted using a surface-gate scheme, and the wires are all very regular, with
dimensions chosen carefully so that there is minimal modulation of the 2DEG by
the gates defining the wires. We have mapped the dispersion spectrum of the 1D
wires down to the depletion of the last 1D subband by measuring the conductance
\emph{G} as a function of the in-plane magnetic field \emph{B}, the interlayer
bias and the wire gate voltage. There is a strong suppression of
tunnelling at zero bias, with temperature and dc-bias dependences consistent
with power laws, as expected for a Tomonaga-Luttinger Liquid caused by
electron-electron interactions in the wires. In addition, the current peaks fit
the free-electron model quite well, but with just one 1D subband there is extra
structure that may indicate interactions.Comment: 3 pages, 3 figures; formatting correcte
Self-Similar Evolution of Cosmic-Ray-Modified Quasi-Parallel Plane Shocks
Using an improved version of the previously introduced CRASH (Cosmic Ray
Acceleration SHock) code, we have calculated the time evolution of cosmic-ray
(CR) modified quasi-parallel plane shocks for Bohm-like diffusion, including
self-consistent models of Alfven wave drift and dissipation, along with thermal
leakage injection of CRs. The new simulations follow evolution of the CR
distribution to much higher energies than our previous study, providing a
better examination of evolutionary and asymptotic behaviors. The postshock CR
pressure becomes constant after quick initial adjustment, since the evolution
of the CR partial pressure expressed in terms of a momentum similarity variable
is self-similar. The shock precursor, which scales as the diffusion length of
the highest energy CRs, subsequently broadens approximately linearly with time,
independent of diffusion model, so long as CRs continue to be accelerated to
ever-higher energies. This means the nonlinear shock structure can be described
approximately in terms of the similarity variable, x/(u_s t), where u_s is the
shock speed once the postshock pressure reaches an approximate time asymptotic
state. As before, the shock Mach number is the key parameter determining the
evolution and the CR acceleration efficiency, although finite Alfven wave drift
and wave energy dissipation in the shock precursor reduce the effective
velocity change experienced by CRs, so reduce acceleration efficiency
noticeably, thus, providing a second important parameter at low and moderate
Mach numbers.Comment: 29 pages, 8 figure
Disruption of marine habitats by artificial light at night from global coastal megacities
Half of globally significant megacities are situated near the coast, exposing urban marine ecosystems to multiple stressors such as waste-water discharge containing a host of organic and inorganic pollutants, air and noise pollution. In addition to these well recognized sources, artificial light at night (ALAN) pollution is inseparable from cities but poorly quantified in marine ecosystems to date. We have developed a time- and wavelength-resolving hydrological optical model that includes solar (daylight and twilight components), lunar and ALAN source terms and propagates these spectrally through a tidally varying water column using Beer’s Law. Our model shows that for 8 globally distributed cities surface ALAN dosages are up to a factor of 6 greater than moonlight, as ALAN intensities vary little throughout the night, over monthly or seasonal cycles. Moonlight only exceeds ALAN irradiances over the ±3-day period around full moon, and particularly during the brightest moons (mid-latitude winter, at zenith). Unlike the relatively stable surface ALAN, underwater ALAN varies spectrally and in magnitude throughout the night due to tidal cycles. The extent of ALAN in-water attenuation is location-specific, driven by the season, tidal range and cycle, and water clarity. This work highlights that marine ALAN ecosystem pollution is a particularly acute global change issue near some of the largest cities in the world
Interpreting complex fluvial channel and barform architecture: Carboniferous Central Pennine Province, northern England
The Bashkirian Lower Brimham Grit of North Yorkshire, England, is a fluvio-deltaic sandstone succession that crops out as a complex series of pinnacles, the three-dimensional arrangement of which allows high-resolution architectural analysis of genetically-related lithofacies assemblages. Combined analysis of sedimentary graphic log profiles, architectural panels and palaeocurrent data have enabled three-dimensional geometrical relationships to be established for a suite of architectural elements so as to develop a comprehensive depositional model. Small-scale observations of facies have been related to larger-scale architectural elements to facilitate interpretation of the palaeoenvironment of deposition to a level of detail that has rarely been attempted previously, thereby allowing interpretation of formative processes. Detailed architectural panels form the basis of a semi-quantitative technique for recording the variety and complexity of the sedimentary lithofacies present, their association within recognizable architectural elements and, thus, the inferred spatio-temporal relationship of neighbouring elements. Fluvial channel-fill elements bounded by erosional surfaces are characterized internally by a hierarchy of sets and cosets with subtly varying compositions, textures and structures. Simple, cross-bedded sets represent in-channel migration of isolated mesoforms (dunes); cosets of both trough and planar-tabular cross-bedded facies represent lateral-accreting and downstream-accreting macroforms (bars) characterized by highly variable, yet predictable, patterns of palaeocurrent indicators. Relationships between sandstone-dominated strata bounded by third-order and fifth-order surfaces, which represent in-channel bar deposits and incised channel bases respectively, chronicle the origin of the preserved succession in response to autocyclic barform development and abandonment, major episodes of incision probably influenced by episodic tectonic subsidence, differential tilting and fluvial incision associated with slip on the nearby North Craven Fault system. Overall, the succession represents the preserved product of an upper-delta plain system that was traversed by a migratory fluvial braid-belt system comprising a poorly-confined network of fluvial channels developed between major sandy barforms that evolved via combined lateral-accretion and downstream-accretion
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