11,825 research outputs found
Single-shot electro-optic sampling of coherent transition radiation at the A0 Photoinjector
Future collider applications and present high-gradient laser plasma wakefield
accelerators operating with picosecond bunch durations place a higher demand on
the time resolution of bunch distribution diagnostics. This demand has led to
significant advancements in the field of electro-optic sampling over the past
ten years. These methods allow the probing of diagnostic light such as coherent
transition radiation or the bunch wakefields with sub-picosecond time
resolution. Potential applications in shot-to-shot, non-interceptive
diagnostics continue to be pursued for live beam monitoring of collider and
pump-probe experiments. Related to our developing work with electro-optic
imaging, we present results on single-shot electro-optic sampling of the
coherent transition radiation from bunches generated at the A0 photoinjector.Comment: 3 p
Formation and Acceleration of Uniformly-Filled Ellipsoidal Electron Bunches Obtained via Space-Charge-Driven Expansion from a Cesium-Telluride Photocathode
We report the experimental generation, acceleration and characterization of a
uniformly-filled electron bunch obtained via space-charge-driven expansion
(often referred to as "blow-out regime") in an L-band (1.3-GHz) radiofrequency
photoinjector. The beam is photoemitted from a Cesium-Telluride semiconductor
photocathode using a short ( fs) ultraviolet laser pulse. The produced
electron bunches are characterized with conventional diagnostics and the
signatures of their ellipsoidal character is observed. We especially
demonstrate the production of ellipsoidal bunches with charges up to
nC corresponding to a -fold increase compared to previous experiments
with metallic photocathodes.Comment: 9, pages, 13 figure
A hierarchical Bayesian model for predicting ecological interactions using scaled evolutionary relationships
Identifying undocumented or potential future interactions among species is a
challenge facing modern ecologists. Recent link prediction methods rely on
trait data, however large species interaction databases are typically sparse
and covariates are limited to only a fraction of species. On the other hand,
evolutionary relationships, encoded as phylogenetic trees, can act as proxies
for underlying traits and historical patterns of parasite sharing among hosts.
We show that using a network-based conditional model, phylogenetic information
provides strong predictive power in a recently published global database of
host-parasite interactions. By scaling the phylogeny using an evolutionary
model, our method allows for biological interpretation often missing from
latent variable models. To further improve on the phylogeny-only model, we
combine a hierarchical Bayesian latent score framework for bipartite graphs
that accounts for the number of interactions per species with the host
dependence informed by phylogeny. Combining the two information sources yields
significant improvement in predictive accuracy over each of the submodels
alone. As many interaction networks are constructed from presence-only data, we
extend the model by integrating a correction mechanism for missing
interactions, which proves valuable in reducing uncertainty in unobserved
interactions.Comment: To appear in the Annals of Applied Statistic
Tunable subpicosecond electron bunch train generation using a transverse-to-longitudinal phase space exchange technique
We report on the experimental generation of a train of subpicosecond electron
bunches. The bunch train generation is accomplished using a beamline capable of
exchanging the coordinates between the horizontal and longitudinal degrees of
freedom. An initial beam consisting of a set of horizontally-separated beamlets
is converted into a train of bunches temporally separated with tunable bunch
duration and separation. The experiment reported in this Letter unambiguously
demonstrates the conversion process and its versatility.Comment: 4 pages, 5 figures, 1 table; accepted for publication in PR
The exposure history of the Apollo 16 site: An assessment based on methane and hydrolysable carbon
Nineteen soils from eight stations at the Apollo 16 landing site have been analyzed for methane and hydrolysable carbon. These results, in conjunction with published data from photogeology, bulk chemistry, rare gases, primordial and cosmogenic radionuclides, and agglutinate abundances have been interpreted in terms of differing contributions from three components-North and South Ray Crater ejecta and Cayley Plains material
Gene therapy for B-cell lymphoma in a SCID mouse model using an immunoglobulin-regulated diphtheria toxin gene delivered by a novel adenovirus-polylysine conjugate
Generalized Jarzynski Equality under Nonequilibrium Feedback Control
The Jarzynski equality is generalized to situations in which nonequilibrium
systems are subject to a feedback control. The new terms that arise as a
consequence of the feedback describe the mutual information content obtained by
measurement and the efficacy of the feedback control. Our results lead to a
generalized fluctuation-dissipation theorem that reflects the readout
information, and can be experimentally tested using small thermodynamic
systems. We illustrate our general results by an introducing "information
ratchet," which can transport a Brownian particle in one direction and extract
a positive work from the particle
Effective Medium Theory of Filamentous Triangular Lattice
We present an effective medium theory that includes bending as well as
stretching forces, and we use it to calculate mechanical response of a diluted
filamentous triangular lattice. In this lattice, bonds are central-force
springs, and there are bending forces between neighboring bonds on the same
filament. We investigate the diluted lattice in which each bond is present with
a probability . We find a rigidity threshold which has the same value
for all positive bending rigidity and a crossover characterizing bending-,
stretching-, and bend-stretch coupled elastic regimes controlled by the
central-force rigidity percolation point at of the
lattice when fiber bending rigidity vanishes.Comment: 15 pages, 9 figure
Quantum discord and local demons
Quantum discord was proposed as a measure of the "quantumness" of
correlations. There are at least three different discord-like quantities, two
of which determine the difference between the efficiencies of a Szilard's
engine under different sets of restrictions. The three discord measures vanish
simulataneosly. We introduce an easy way to test for zero discord, relate it to
the Cerf-Adami conditional entropy and show that there is no relation between
the discord and the local disitnguishability.Comment: 7 pages, RevTeX. Some minor changes after comments from colleagues,
some references added. Similar to published versio
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