522 research outputs found
Secondary Electron Yield Measurements of Fermilab's Main Injector Vacuum Vessel
We discuss the progress made on a new installation in Fermilab's Main
Injector that will help investigate the electron cloud phenomenon by making
direct measurements of the secondary electron yield (SEY) of samples irradiated
in the accelerator. In the Project X upgrade the Main Injector will have its
beam intensity increased by a factor of three compared to current operations.
This may result in the beam being subject to instabilities from the electron
cloud. Measured SEY values can be used to further constrain simulations and aid
our extrapolation to Project X intensities. The SEY test-stand, developed in
conjunction with Cornell and SLAC, is capable of measuring the SEY from samples
using an incident electron beam when the samples are biased at different
voltages. We present the design and manufacture of the test-stand and the
results of initial laboratory tests on samples prior to installation.Comment: 3 pp. 3rd International Particle Accelerator Conference (IPAC 2012)
20-25 May 2012, New Orleans, Louisian
Sputter-engineering a first-order magnetic phase transition in sub-15-nm-thick single-crystal FeRh films
Equiatomic FeRh alloys undergo a fascinating first-order metamagnetic phase transition (FOMPT) just above room temperature, which has attracted reinvigorated interest for applications in spintronics. Until now, all attempts to grow nanothin FeRh alloy films have consistently shown that FeRh layers tend to grow in the Volmer-Weber growth mode. Here we show that sputter-grown sub-15-nm-thick FeRh alloy films deposited at low sputter-gas pressure, typically
âŒ
0.1
~Pa, onto (001)-oriented MgO substrates, grow in a peening-induced Frank-van der Merwe growth mode for FeRh film thicknesses above 5 nm, circumventing this major drawback. The bombardment of high-energy sputtered atoms, the atom-peening effect, induces a re-balancing between adsorbate-surface and adsorbate-adsorbate interactions, leading to the formation of a smooth continuous nanothin FeRh film. Chemical order in the films increases with the FeRh thickness,
t
FeRh
, and varies monotonically from 0.75 up to 0.9. Specular x-ray diffraction scans around Bragg peaks show Pendell"{o}sung fringes for films with
t
FeRh
â„
5.2
~nm, which reflects in smooth well-ordered densified single-crystal FeRh layers. The nanothin filmâs roughness varies from 0.6 down to about 0.1 nm as
t
FeRh
increases, and scales linearly with the integral breadth of the rocking curve, proving its microstructured origin
Universal Continuous Variable Quantum Computation in the Micromaser
We present universal continuous variable quantum computation (CVQC) in the
micromaser. With a brief history as motivation we present the background theory
and define universal CVQC. We then show how to generate a set of operations in
the micromaser which can be used to achieve universal CVQC. It then follows
that the micromaser is a potential architecture for CVQC but our proof is
easily adaptable to other potential physical systems.Comment: 12 pages, 4 figures, accepted for a presentation at the 9th
International Conference on Unconventional Computation (UC10) and LNCS
proceedings
Particle Creation in the Marginally Bound, Self Similar Collapse of Inhomogeneous Dust
We consider the evaporation of the (shell focusing) naked singularity formed
during the self-similar collapse of a marginally bound inhomogeneous dust
cloud, in the geometric optics approximation. We show that, neglecting the back
reaction of the spacetime, the radiation on \scrip tends to infinity as the
Cauchy Horizon is approached. Two consequences can be expected from this
result: (a) that the back reaction of spacetime will be large and eventually
halt the formation of a naked singularity thus preserving the Cosmic Censorship
Hypothesis and (b) matter attempting to collapse into a naked singularity will
radiate away energy at an intense rate, thereby possibly providing experimental
signatures of quantum effects in curved spacetimes.Comment: 18 pages, 4 figures. Version to appear in Nucl. Phys.
Chaos in a double driven dissipative nonlinear oscillator
We propose an anharmonic oscillator driven by two periodic forces of
different frequencies as a new time-dependent model for investigating quantum
dissipative chaos. Our analysis is done in the frame of statistical ensemble of
quantum trajectories in quantum state diffusion approach. Quantum dynamical
manifestation of chaotic behavior, including the emergence of chaos, properties
of strange attractors, and quantum entanglement are studied by numerical
simulation of ensemble averaged Wigner function and von Neumann entropy.Comment: 9 pages, 18 figure
D-branes, Matrix Theory and K-homology
In this paper, we study a new matrix theory based on non-BPS D-instantons in
type IIA string theory and D-instanton - anti D-instanton system in type IIB
string theory, which we call K-matrix theory. The theory correctly incorporates
the creation and annihilation processes of D-branes. The configurations of the
theory are identified with spectral triples, which are the noncommutative
generalization of Riemannian geometry a la Connes, and they represent the
geometry on the world-volume of higher dimensional D-branes. Remarkably, the
configurations of D-branes in the K-matrix theory are naturally classified by a
K-theoretical version of homology group, called K-homology. Furthermore, we
argue that the K-homology correctly classifies the D-brane configurations from
a geometrical point of view. We also construct the boundary states
corresponding to the configurations of the K-matrix theory, and explicitly show
that they represent the higher dimensional D-branes.Comment: 53 pages, corrected a few typos, version published in JHE
Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator BiSe
We characterize the occupied and unoccupied electronic structure of the
topological insulator BiSe by one-photon and two-photon angle-resolved
photoemission spectroscopy and slab band structure calculations. We reveal a
second, unoccupied Dirac surface state with similar electronic structure and
physical origin to the well-known topological surface state. This state is
energetically located 1.5 eV above the conduction band, which permits it to be
directly excited by the output of a Ti:Sapphire laser. This discovery
demonstrates the feasibility of direct ultrafast optical coupling to a
topologically protected, spin-textured surface state.Comment: Accepted to Physical Review Letter
Feed supplementation with biochar may reduce poultry pathogens, including Campylobacter hepaticus, the causative agent of Spotty Liver Disease
Increased global regulation and restrictions on the non-therapeutic use of antibiotics in the poultry industry means that there is a need to identify alternatives that prevent infection while still conveying the growth and performance benefits afforded by their use. Biochars are produced by the incomplete pyrolysis of organic materials, with reports of use as a feed supplement and activity against pathogenic bacteria. In the current study the dose-dependent effects of biochar dietary inclusion in layer diets at 1%, 2% and 4% w/w were investigated to determine a) the efficacy of biochar as an anti-pathogenic additive on the intestinal microbiota and b) the optimal inclusion level. Biochar inclusion for anti-pathogenic effects was found to be most beneficial at 2% w/w. Poultry pathogens such as Gallibacterium anatis and campylobacters, including Campylobacter hepaticus, were found to be significantly lower in biochar fed birds. A shift in microbiota was also associated with the incorporation of 2% w/w biochar in the feed in two large scale trials on two commercial layer farms. Biochar inclusion for anti-pathogenic effects was found to be most beneficial at 2% w/w. Differential effects of the timing of biochar administration (supplementation beginning at hatch or at point of lay) were also evident, with greater impact on community microbial structure at 48 weeks of age when birds were fed from hatch rather than supplemented at point of lay.Nicky-Lee Willson, Thi T.H. Van, Surya P. Bhattarai, Jodi M. Courtice, Joshua R. McIntyre, Tanka P. Prasai, Robert J. Moore, Kerry Walsh, Dragana Stanle
Caustic avoidance in Horava-Lifshitz gravity
There are at least four versions of Horava-Lishitz gravity in the literature.
We consider the version without the detailed balance condition with the
projectability condition and address one aspect of the theory: avoidance of
caustics for constant time hypersurfaces. We show that there is no caustic with
plane symmetry in the absence of matter source if \lambda\ne 1. If \lambda=1 is
a stable IR fixed point of the renormalization group flow then \lambda is
expected to deviate from 1 near would-be caustics, where the extrinsic
curvature increases and high-energy corrections become important. Therefore,
the absence of caustics with \lambda\ne 1 implies that caustics cannot form
with this symmetry in the absence of matter source. We argue that inclusion of
matter source will not change the conclusion. We also argue that caustics with
codimension higher than one will not form because of repulsive gravity
generated by nonlinear higher curvature terms. These arguments support our
conjecture that there is no caustic for constant time hypersurfaces. Finally,
we discuss implications to the recently proposed scenario of ``dark matter as
integration constant''.Comment: 19 pages; extended to general z \geq 3, typos corrected (v2); version
accepted for publication in JCAP (v3
Framework for evaluating the health impact of the scale-up of malaria control interventions on all-cause child mortality in Sub-Saharan Africa
Concerted efforts from national and international partners have scaled up malaria control interventions, including insecticide-treated nets, indoor residual spraying, diagnostics, prompt and effective treatment of malaria cases, and intermittent preventive treatment during pregnancy in sub-Saharan Africa (SSA). This scale-up warrants an assessment of its health impact to guide future efforts and investments; however, measuring malaria-specific mortality and the overall impact of malaria control interventions remains challenging. In 2007, Roll Back Malaria's Monitoring and Evaluation Reference Group proposed a theoretical framework for evaluating the impact of full-coverage malaria control interventions on morbidity and mortality in high-burden SSA countries. Recently, several evaluations have contributed new ideas and lessons to strengthen this plausibility design. This paper harnesses that new evaluation experience to expand the framework, with additional features, such as stratification, to examine subgroups most likely to experience improvement if control programs are working; the use of a national platform framework; and analysis of complete birth histories from national household surveys. The refined framework has shown that, despite persisting data challenges, combining multiple sources of data, considering potential contributions from both fundamental and proximate contextual factors, and conducting subnational analyses allows identification of the plausible contributions of malaria control interventions on malaria morbidity and mortality
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