39,683 research outputs found
Optimization study of high power static inverters and converters Final report
Optimization study and basic performance characteristics for conceptual designs for high power static inverter
The bar PANDA focussing-lightguide disc DIRC
bar PANDA will be a fixed target experiment internal to the HESR antiproton storage ring at the future FAIR complex. The ANDA detector requires excellent particle-identification capabilities in order to achieve its scientific potential. Cherenkov counters employing the DIRC principle were chosen as PID detectors for the Target Spectrometer. The proposed Focussing-Lightguide Disc DIRC will cover the forward part of the Target Spectrometer acceptance in the angular range between 5° and 22°. Its design includes a novel approach to mitigate dispersion effects in the solid radiator of a DIRC counter using optical elements. The dispersion correction will enable the Focussing-Lightguide Disc DIRC to provide pion-kaon identification for momenta well above 3.5 GeV/c
Characterization of the second- and third-order nonlinear optical susceptibilities of monolayer MoS using multiphoton microscopy
We report second- and third-harmonic generation in monolayer MoS
as a tool for imaging and accurately characterizing the material's nonlinear
optical properties under 1560 nm excitation. Using a surface nonlinear optics
treatment, we derive expressions relating experimental measurements to second-
and third-order nonlinear sheet susceptibility magnitudes, obtaining values of
m V and for the first time for
monolayer MoS, m V.
These sheet susceptibilities correspond to effective bulk nonlinear
susceptibility values of m V and
m V, accounting for the sheet
thickness. Experimental comparisons between MoS and graphene are
also performed, demonstrating 3.4 times stronger third-order sheet
nonlinearity in monolayer MoS, highlighting the material's
potential for nonlinear photonics in the telecommunications C band.Comment: Accepted by 2D Materials, 28th Oct 201
Natural resources inventory and monitoring in Oregon with ERTS imagery
Multidiscipline team interpretation of ERTS satellite and highflight imagery is providing resource and land use information needed for land use planning in Oregon. A coordinated inventory of geology, soil-landscapes, forest and range vegetation, and land use for Crook County, illustrates the value of this approach for broad area and state planning. Other applications include mapping fault zones, inventory of forest clearcut areas, location of forest insect damage, and monitoring irrigation development. Computer classification is being developed for use in conjunction with visual interpretation
Endogenous Quasicycles and Stochastic Coherence in a Closed Endemic Model
We study the role of demographic fluctuations in typical endemics as
exemplified by the stochastic SIRS model. The birth-death master equation of
the model is simulated using exact numerics and analysed within the linear
noise approximation. The endemic fixed point is unstable to internal
demographic noise, and leads to sustained oscillations. This is ensured when
the eigenvalues () of the linearised drift matrix are complex, which
in turn, is possible only if detailed balance is violated. In the oscillatory
state, the phases decorrelate asymptotically, distinguishing such oscillations
from those produced by external periodic forcing. These so-called quasicycles
are of sufficient strength to be detected reliably only when the ratio
is of order unity. The coherence or regularity of
these oscillations show a maximum as a function of population size, an effect
known variously as stochastic coherence or coherence resonance. We find that
stochastic coherence can be simply understood as resulting from a non-monotonic
variation of with population size. Thus, within the
linear noise approximation, stochastic coherence can be predicted from a purely
deterministic analysis. The non-normality of the linearised drift matrix,
associated with the violation of detailed balance, leads to enhanced
fluctuations in the population amplitudes.Comment: 21 pages, 8 figure
The Accretion of Lyman Alplha Clouds onto Gas-Rech Protogalaxies; A Scenario for the Formation of Globular Star Clusters
A satisfactory theory for the formation of globular star clusters (GCs) has
long been elusive, perhaps because their true progenitors had not yet been
guessed. In this paper I propose a causal relationship between the strongly
decreasing densities of Lyman alpha (LyA) clouds at high redshift and the
formation of GCs - namely that GCs were created by the accretion of LyA clouds
onto protogalaxies. I describe a scenario which involves an inherently stable
and orderly cycling of compression and cooling in the central cores of clouds
during the extended period of dissipation in the outer regins of gas-rich proto
galaxies, culminating in a burst of efficient star formation. I demonstrate
that the comoving density of GCs is comparable to that of LyA clouds at high
redshift, that the energetic requirements for compression to core GC densities
can be met, and that the time-scale for cooling is within obvious limits
imposed by dynamical stability.
This dissipative process requires there to be a large column of dissipated
gas about the attractor in order to form GCs. In addition, the energy
requirements for compression requires attractor masses greater than that
capable of sustaining circular velocities of ~40 km/s. If this scenario is
supported by numerical simulations, then by implication, the GCs were formed at
modest redshifts of z~1-3. This knowledge could help to break the degeneracy
between lookback time and redshift. The model is consistent with a picture of
hierarchical galaxy growth over time scales of many billions of years.Comment: 7 pages. Accepted, 10 June 1999 Astrophysical Journa
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