40,789 research outputs found
Simulations of an energy dechirper based on dielectric lined waveguides
Terahertz frequency wakefields can be excited by ultra-short relativistic
electron bunches travelling through dielectric lined waveguide (DLW)
structures. These wakefields can either accelerate a witness bunch with high
gradient, or modulate the energy of the driving bunch. In this paper, we study
a passive dechirper based on the DLW to compensate the correlated energy spread
of the bunches accelerated by the laser plasma wakefield accelerator (LWFA). A
rectangular waveguide structure was employed taking advantage of its
continuously tunable gap during operation. The assumed 200 MeV driving bunch
had a Gaussian distribution with a bunch length of 3.0 {\mu}m, a relative
correlated energy spread of 1%, and a total charge of 10 pC. Both of the CST
Wakefield Solver and PIC Solver were used to simulate and optimize such a
dechirper. Effect of the time-dependent self-wake on the driving bunch was
analyzed in terms of the energy modulation and the transverse phase space
Temperature control in continuous furnace by structural diagram method
The fundamentals of the structural diagram method for distributed parameter systems (DPSs) are presented and reviewed. An example is given to illustrate the application of this method for control design
ARE BASIC SCIENCE AND BIOTECHNOLOGY COMPLEMENTARY ACTIVITIES?
Enhancing agricultural productivity depends greatly on the management of information flows between basic and applied research. A framework is developed to examine the mutual relationship between molecular biological research and agricultural biotechnology innovations. Preliminary results provide a basis for university decision-making in both the short and long run.Research and Development/Tech Change/Emerging Technologies,
Adaptive confidence intervals for regression functions under shape constraints
Adaptive confidence intervals for regression functions are constructed under
shape constraints of monotonicity and convexity. A natural benchmark is
established for the minimum expected length of confidence intervals at a given
function in terms of an analytic quantity, the local modulus of continuity.
This bound depends not only on the function but also the assumed function
class. These benchmarks show that the constructed confidence intervals have
near minimum expected length for each individual function, while maintaining a
given coverage probability for functions within the class. Such adaptivity is
much stronger than adaptive minimaxity over a collection of large parameter
spaces.Comment: Published in at http://dx.doi.org/10.1214/12-AOS1068 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Coronal rain in magnetic arcades: Rebound shocks, Limit cycles, and Shear flows
We extend our earlier multidimensional, magnetohydrodynamic simulations of
coronal rain occurring in magnetic arcades with higher resolution,
grid-adaptive computations covering a much longer ( hour) timespan. We
quantify how in-situ forming blob-like condensations grow along and across
field lines and show that rain showers can occur in limit cycles, here
demonstrated for the first time in 2.5D setups. We discuss dynamical,
multi-dimensional aspects of the rebound shocks generated by the siphon inflows
and quantify the thermodynamics of a prominence-corona-transition-region like
structure surrounding the blobs. We point out the correlation between
condensation rates and the cross-sectional size of loop systems where
catastrophic cooling takes place. We also study the variations of the typical
number density, kinetic energy and temperature while blobs descend, impact and
sink into the transition region. In addition, we explain the mechanisms leading
to concurrent upflows while the blobs descend. As a result, there are plenty of
shear flows generated with relative velocity difference around 80 km s
in our simulations. These shear flows are siphon flows set up by multiple blob
dynamics and they in turn affect the deformation of the falling blobs. In
particular, we show how shear flows can break apart blobs into smaller
fragments, within minutes
Enhanced visibility of graphene: effect of one-dimensional photonic crystal
We investigate theoretically the light reflectance of a graphene layer
prepared on the top of one-dimensional Si/SiO2 photonic crystal (1DPC). It is
shown that the visibility of the graphene layers is enhanced greatly when 1DPC
is added, and the visibility can be tuned by changing the incident angle and
light wavelengths. This phenomenon is caused by the absorption of the graphene
layer and the enhanced reflectance of the 1DPC.Comment: 4 pages, 4 figures. published, ApplPhysLett_91_18190
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