29,445 research outputs found
Spatial Control of Photoemitted Electron Beams using a Micro-Lens-Array Transverse-Shaping Technique
A common issue encountered in photoemission electron sources used in electron
accelerators is the transverse inhomogeneity of the laser distribution
resulting from the laser-amplification process and often use of frequency up
conversion in nonlinear crystals. A inhomogeneous laser distribution on the
photocathode produces charged beams with lower beam quality. In this paper, we
explore the possible use of microlens arrays (fly-eye light condensers) to
dramatically improve the transverse uniformity of the drive laser pulse on UV
photocathodes. We also demonstrate the use of such microlens arrays to generate
transversely-modulated electron beams and present a possible application to
diagnose the properties of a magnetized beam.Comment: arXiv admin note: text overlap with arXiv:1609.0166
Horizon Mass Theorem
A new theorem for black holes is found. It is called the horizon mass
theorem. The horizon mass is the mass which cannot escape from the horizon of a
black hole. For all black holes: neutral, charged or rotating, the horizon mass
is always twice the irreducible mass observed at infinity. Previous theorems on
black holes are: 1. the singularity theorem, 2. the area theorem, 3. the
uniqueness theorem, 4. the positive energy theorem. The horizon mass theorem is
possibly the last general theorem for classical black holes. It is crucial for
understanding Hawking radiation and for investigating processes occurring near
the horizon.Comment: A new theorem for black holes is establishe
Rotational energy term in the empirical formula for the yrast energies in even-even nuclei
We show that part of the empirical formula describing the gross features of
the measured yrast energies of the natural parity even multipole states for
even-even nuclei can be related to the rotational energy of nuclei. When the
first term of the empirical formula, , is regarded as the
otational energy, we can better understand the results of the previous analyses
of the excitation energies. We show that the values of the parameters
and newly obtained by considering the term as the
rotational energy of a rigid rotor are remarkably consistent with those values
extracted from the earlier `modified' analyses, in which we use the
logarithms of the excitation energies in defining the `modified'
values
Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation
We study the decuplet baryon magnetic moments in a QCD-based quark model
beyond quenched approximation. Our approach for unquenching the theory is based
on the heavy baryon perturbation theory in which the axial couplings for baryon
- meson and the meson-meson-photon couplings from the chiral perturbation
theory are used together with the QM moment couplings. It also involves the
introduction of a form factor characterizing the structure of baryons
considered as composite particles. Using the parameters obtained from fitting
the octet baryon magnetic moments, we predict the decuplet baryon magnetic
moments. The magnetic moment is found to be in good agreement with
experiment: is predicted to be compared to the
experimental result of (2.02 0.05) .Comment: 19 pages, 2 figure
Perturbation-minimized triangular bunch for high-transformer ratio using a double dogleg emittance exchange beam line
The longitudinal shape, i.e., the current profile, of an electron bunch determines the transformer ratio in a collinear wakefield accelerator and thus methods are sought to control the longitudinal bunch shape. The emittance exchange (EEX) appears to be promising for creating a precisely controlled longitudinal bunch shapes. The longitudinal shape is perturbed by two sources: higher-order terms in the beam line optics and collective effects and these perturbations can lead to a significant drop of the transformer ratio. In this paper, we analytically and numerically investigate the perturbation to an ideal triangular longitudinal bunch shape and propose methods to minimize it.1153Ysciescopu
Data reduction for the MIPS far-infrared arrays
Traditional photoconductive detectors are used at 70 and 160 microns in the Multiband Imaging Photometer for SIRTF. These devices are highly sensitivity to cosmic rays and have complex response characteristics, all of which must be anticipated in the data reduction pipeline. The pipeline is being developed by a team at the SIRTF Science Center, where the detailed design and coding are carried out, and at Steward Observatory, where the high level algorithms are developed and detector tests are conducted to provide data for pipeline experiments. A number of innovations have been introduced. Burger's model is used to extrapolate to asymptotic values for the response of the detectors. This approach permits rapid fitting of the complexities in the detector response. Examples of successful and unsuccessful fits to the laboratory test data are shown
Decoupling the coupled DGLAP evolution equations: an analytic solution to pQCD
Using Laplace transform techniques, along with newly-developed accurate
numerical inverse Laplace transform algorithms, we decouple the solutions for
the singlet structure function and of the two
leading-order coupled singlet DGLAP equations, allowing us to write fully
decoupled solutions: F_s(x,Q^2)={\cal F}_s(F_{s0}(x), G_0(x)), G(x,Q^2)={\cal
G}(F_{s0}(x), G_0(x)). Here and are known
functions---found using the DGLAP splitting functions---of the functions
and , the chosen
starting functions at the virtuality . As a proof of method, we compare
our numerical results from the above equations with the published MSTW LO gluon
and singlet distributions, starting from their initial values at . Our method completely decouples the two LO distributions, at the same
time guaranteeing that both distributions satisfy the singlet coupled DGLAP
equations. It furnishes us with a new tool for readily obtaining the effects of
the starting functions (independently) on the gluon and singlet structure
functions, as functions of both and . In addition, it can also be
used for non-singlet distributions, thus allowing one to solve analytically for
individual quark and gluon distributions values at a given and , with
typical numerical accuracies of about 1 part in , rather than having to
evolve numerically coupled integral-differential equations on a two-dimensional
grid in , as is currently done.Comment: 6 pages, 2 figure
Genomic basis and evolutionary potential for extreme drought adaptation in Arabidopsis thaliana
As Earth is currently experiencing dramatic climate change, it is of critical interest to understand how species will respond to it. The chance of a species withstanding climate change is likely to depend on the diversity within the species and, particularly, whether there are sub-populations that are already adapted to extreme environments. However, most predictive studies ignore that species comprise genetically diverse individuals. We have identified genetic variants in Arabidopsis thaliana that are associated with survival of an extreme drought event—a major consequence of global warming. Subsequently, we determined how these variants are distributed across the native range of the species. Genetic alleles conferring higher drought survival showed signatures of polygenic adaptation and were more frequently found in Mediterranean and Scandinavian regions. Using geo-environmental models, we predicted that Central European, but not Mediterranean, populations might lag behind in adaptation by the end of the twenty-first century. Further analyses showed that a population decline could nevertheless be compensated by natural selection acting efficiently over standing variation or by migration of adapted individuals from populations at the margins of the species’ distribution. These findings highlight the importance of within-species genetic heterogeneity in facilitating an evolutionary response to a changing climate
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