5,036 research outputs found
Asymmetric Dual Axis Energy Recovery Linac for Ultra-High Flux sources of coherent X-ray/THz radiation: Investigations Towards its Ultimate Performance
In order for sources of coherent high brightness and intensity THz and X-Ray
radiation to be accepted by university or industrial R&D laboratories, truly
compact, high current and efficient particle accelerators are required. The
demand for compactness and efficiency can be satisfied by superconducting RF
energy recovery linear accelerators (SRF ERL) allowing effectively minimising
the footprint and maximising the efficiency of the system. However such set-ups
are affected by regenerative beam-break up (BBU) instabilities which limit the
beam current and may terminate the beam transport as well as energy
recuperation. In this paper we suggest and discuss a SRF ERL with asymmetric
configuration of resonantly coupled accelerating and decelerating cavities. In
this type of SRF ERL an electron bunch is passing through accelerating and
decelerating cavities once and, as we show in this case, the regenerative BBU
instability can be minimised allowing high currents to be achieved. We study
the BBU start current in such an asymmetric ERL via analytical and numerical
models and discuss the properties of such a system
Optimizing the tuning range of the Fermilab Recycler 53MHz RF cavities by exploiting the avoided crossing of the tuner and cavity modes
The electromagnetic eigenmodes of the Fermilab Recycler RF cavities were
simulated with ACE3P running on NERSC's 'Perlmutter' supercomputer in an
attempt to optimize their tuning range to comfortably support slip-stacking. A
theory, based on coupled circuits and avoided crossings, was developed to
explain the origins of the tuning range for tuner-cavity waveguide systems.
This provided a logical, rigorous method to carry out this optimization,
although engineering problems due to high voltages in the tuner and the
operational range of the garnet had to be carefully implemented. It was
shown that the desired goal of 10kHz of tuning was not attainable with the
current cavity specifications. The maximum tuning range obtained was 5.59kHz
for a single tuner with a coaxial line of length 63in. A double tuner cavity
was also studied using the simulation software, although with little
improvement in the tuning range. A promising technique to improve the tuning
range involving the desynchronization of the garnets' magnetic permeabilities
is proposed
The bench scientist\u27s guide to statistical analysis of RNA-Seq data
RNA sequencing (RNA-Seq) is emerging as a highly accurate method to quantify transcript abundance. However, analyses of the large data sets obtained by sequencing the entire transcriptome of organisms have generally been performed by bioinformatics specialists. Here we provide a step-by-step guide and outline a strategy using currently available statistical tools that results in a conservative list of differentially expressed genes. We also discuss potential sources of error in RNA-Seq analysis that could alter interpretation of global changes in gene expression
On stability of discretizations of the Helmholtz equation (extended version)
We review the stability properties of several discretizations of the
Helmholtz equation at large wavenumbers. For a model problem in a polygon, a
complete -explicit stability (including -explicit stability of the
continuous problem) and convergence theory for high order finite element
methods is developed. In particular, quasi-optimality is shown for a fixed
number of degrees of freedom per wavelength if the mesh size and the
approximation order are selected such that is sufficiently small and
, and, additionally, appropriate mesh refinement is used near
the vertices. We also review the stability properties of two classes of
numerical schemes that use piecewise solutions of the homogeneous Helmholtz
equation, namely, Least Squares methods and Discontinuous Galerkin (DG)
methods. The latter includes the Ultra Weak Variational Formulation
Linking the High-Resolution Architecture of Modern and Ancient Wave-Dominated Deltas : Processes, Products and Forcing Factors
Many thoughts and concepts used in this paper were initially developed as a result of work conducted with funding provided to the WAVE Consortium at the Australian School of Petroleum, University of Adelaide (RBA, BKV and JB). The consortium sponsors (Apache, BAPETCO, BHPBP, BG, BP, Chevron, ConocoPhillips, Nexen, OMV, Shell, Statoil, Todd Energy, and Woodside Energy) are thus thanked for making this work possible. We are indebted to journal reviewers Cornel Olariu and Howard Feldman, and to Associate Editor Janok Bhattacharya for numerous comments and suggestions that improved the clarity of the manuscript.Peer reviewedPostprin
2024 Wheelchair Compendium of Physical Activities: An Update of Activity Codes and Energy Expenditure Values
Purpose: This paper presents an update of the 2011 Wheelchair Compendium of Physical Activities designed for wheelchair users and is referred to as the 2024 Wheelchair Compendium. The Wheelchair Compendium aims to curate existing knowledge of the energy expenditure for wheelchair physical activities (PAs).
Methods: A systematic review of the published energy expenditure of PA for wheelchair users was completed between 2011 and May 2023. We added these data to the 2011 Wheelchair Compendium data that was compiled previously in a systematic review through 2011.
Results: A total of 47 studies were included, and 124 different wheelchair PA reported energy expenditure values ranging from 0.8 metabolic equivalents for wheelchair users (filing papers, light effort) to 11.8 metabolic equivalents for wheelchair users (Nordic sit skiing).
Conclusion: In introducing the updated 2024 Wheelchair Compendium, we hope to bridge the resource gap and challenge the prevailing narratives that inadvertently exclude wheelchair users from physical fitness and health PAs
The Dynamic Characteristics of a High Pressure Turbine Stage in a Transient Wind Tunnel
ABSTRACT A new transient facility for the study of time averaged and unsteady aerodynamics and heat transfer in a high pressure turbine was recently commissioned. During the facility design a high priority was placed on ease of access to the turbine blading to facilitate the development of blade mounted instrumentation. The turbine disc was cantilevered on a shaft by a thin annular link, with the shaft passing back through the disc to a single row and matched pair of relatively closely spaced bearings. The bearings were originally designed for use in a marine gas turbine. Due to the facility's novel mode of operation the bearings were working well beyond some of their original design limits, primarily due to the high turbine acceleration and the high speed/low load condition at the end of facility operation. During the facility design a programme of work was undertaken to predict its dynamic performance. This was continued during commissioning to measure actual facility performance. In this paper the predicted dynamic performance of the disc/shaft assembly and its bearing system are presented. The programme of work undertaken during the facility commissioning phase to ascertain actual dynamic performance is described, and the results discussed. Finally, the technique developed to field balance the rotating assembly following changes to blade instrumentation is described
Pairing in low-density Fermi gases
We consider pairing in a dilute system of Fermions with a short-range
interaction. While the theory is ill-defined for a contact interaction, the BCS
equations can be solved in the leading order of low-energy effective field
theory. The integrals are evaluated with the dimensional regularization
technique, giving analytic formulas relating the pairing gap, the density, and
the energy density to the two-particle scattering length.Comment: 12 pages, 2 EPS-figures, uses psfig.sty, eq.(9) correcte
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