403 research outputs found
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Preliminary Investigations of Eddy Current Effects on a Spinning Disk
The design of the positron source target for the International Linear Collider (ILC) envisions a Ti6Al4V wheel rotating in a large magnetic field (5-10 Tesla) being impacted by a photon beam to produce positrons. One of the many challenges for this system is determining how large a motor will be needed to spin the shaft. The wheel spinning in the magnetic field induces an eddy current in the wheel, which retards the spinning motion of the wheel. Earlier calculations by Mayhall [1] have shown that those eddy forces could be quite large, and resulted in the preliminary design being moved from a solid disk to a rim and spoke design, as shown in Figure 1. A series of experiments with a spinning metal disk were run at the Stanford Linear Accelerator Center (SLAC) to provide experimental validation of the Maxwell 3D simulations. This report will give a brief outline of the experimental setup and results. In addition, earlier work by Smythe [2] will be used to compare with the experimental results
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Fast Prediction of HCCI and PCCI Combustion with an Artificial Neural Network-Based Chemical Kinetic Model
We have added the capability to look at in-cylinder fuel distributions using a previously developed ignition model within a fluid mechanics code (KIVA3V) that uses an artificial neural network (ANN) to predict ignition (The combined code: KIVA3V-ANN). KIVA3V-ANN was originally developed and validated for analysis of Homogeneous Charge Compression Ignition (HCCI) combustion, but it is also applicable to the more difficult problem of Premixed Charge Compression Ignition (PCCI) combustion. PCCI combustion refers to cases where combustion occurs as a nonmixing controlled, chemical kinetics dominated, autoignition process, where the fuel, air, and residual gas mixtures are not necessarily as homogeneous as in HCCI combustion. This paper analyzes the effects of introducing charge non-uniformity into a KIVA3V-ANN simulation. The results are compared to experimental results, as well as simulation results using a more physically representative and computationally intensive code (KIVA3V-MPI-MZ), which links a fluid mechanics code to a multi-zone detailed chemical kinetics solver. The results indicate that KIVA3V-ANN produces reasonable approximations to the more accurate KIVA3V-MPI-MZ at a much reduced computational cost
Temperature dependence of the anomaly in the excitation spectrum of the 2D quantum Heisenberg antiferromagnet
It is well established that in the low-temperature limit, the two-dimensional
quantum Heisenberg antiferromagnet on a square lattice (2DQHAFSL) exhibits an
anomaly in its spectrum at short-wavelengths on the zone-boundary. In the
vicinity of the point the pole in the one-magnon response exhibits a
downward dispersion, is heavily damped and attenuated, giving way to an
isotropic continuum of excitations extending to high energies. The origin of
the anomaly and the presence of the continuum are of current theoretical
interest, with suggestions focused around the idea that the latter evidences
the existence of spinons in a two-dimensional system. Here we present the
results of neutron inelastic scattering experiments and Quantum Monte Carlo
calculations on the metallo-organic compound Cu(DCOO)DO (CFTD),
an excellent physical realisation of the 2DQHAFSL, designed to investigate how
the anomaly at evolves up to finite temperatures . Our
data reveal that on warming the anomaly survives the loss of long-range,
three-dimensional order, and is thus a robust feature of the two-dimensional
system. With further increase of temperature the zone-boundary response
gradually softens and broadens, washing out the anomaly. This is
confirmed by a comparison of our data with the results of finite-temperature
Quantum Monte Carlo simulations where the two are found to be in good accord.
At lower energies, in the vicinity of the antiferromagnetic zone centre, there
was no significant softening of the magnetic excitations over the range of
temperatures investigated.Comment: Dedicated to the life and work of Professor Roger Cowley. 22 pages, 8
figure
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Design of a Pulsed Flux Concentrator for the ILC Positron Source
The Positron Source for the International Linear Collider requires an optical matching device after the target to increase the capture efficiency for positrons. Pulsed flux concentrators have been used by previous machines to improve the capture efficiency but the ILC has a 1 ms long pulse train which is too long for a standard flux concentrator. A pulsed flux concentrator with a 40 ms flat top was created for a hyperon experiment in 1965 which used liquid nitrogen cooling to reduce the resistance of the concentrating plates and extend the lifetime of the pulse. We report on a design for a 1 ms device based on this concept
Eddy current studies from the undulator-based positron source target wheel prototype
The efficiency of future positron sources for the next generation of high-energy particle colliders (e.g. ILC, CLIC, LHeC) can be improved if the positron-production target is immersed in the magnetic field of adjacent capture optics. If the target is also rotating due to heat deposition considerations then eddy currents may be induced and lead to additional heating and stresses. In this paper we present data from a rotating target wheel prototype for the baseline ILC positron source. The wheel has been operated at revolution rates up to 1800rpm in fields of the order of 1 Tesla. Comparisons are made between torque data obtained from a transducer on the target drive shaft and the results of finite-element simulations. Rotordynamics issues are presented and future experiments on other aspects of the positron source target station are considered
Walking the walk: a phenomenological study of long distance walking
Evidence suggests that regular walking can elicit significant psychological benefits although little evidence exists concerning long distance walking. The purpose of this study was to provide detailed accounts of the experiences of long distance walkers. Phenomenological interviews were conducted with six long distance walkers. Data were transcribed verbatim before researchers independently analyzed the transcripts. Participants reported a cumulative effect with positive feelings increasing throughout the duration of the walk. Long distance walking elicited positive emotions, reduced the effects of life-stress, and promoted an increased sense of well-being and personal growth. Results are aligned to theories and concepts from positive psychology
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Hybridization and Selective Release of DNA Microarrays
DNA microarrays contain sequence specific probes arrayed in distinct spots numbering from 10,000 to over 1,000,000, depending on the platform. This tremendous degree of multiplexing gives microarrays great potential for environmental background sampling, broad-spectrum clinical monitoring, and continuous biological threat detection. In practice, their use in these applications is not common due to limited information content, long processing times, and high cost. The work focused on characterizing the phenomena of microarray hybridization and selective release that will allow these limitations to be addressed. This will revolutionize the ways that microarrays can be used for LLNL's Global Security missions. The goals of this project were two-fold: automated faster hybridizations and selective release of hybridized features. The first study area involves hybridization kinetics and mass-transfer effects. the standard hybridization protocol uses an overnight incubation to achieve the best possible signal for any sample type, as well as for convenience in manual processing. There is potential to significantly shorten this time based on better understanding and control of the rate-limiting processes and knowledge of the progress of the hybridization. In the hybridization work, a custom microarray flow cell was used to manipulate the chemical and thermal environment of the array and autonomously image the changes over time during hybridization. The second study area is selective release. Microarrays easily generate hybridization patterns and signatures, but there is still an unmet need for methodologies enabling rapid and selective analysis of these patterns and signatures. Detailed analysis of individual spots by subsequent sequencing could potentially yield significant information for rapidly mutating and emerging (or deliberately engineered) pathogens. In the selective release work, optical energy deposition with coherent light quickly provides the thermal energy to single spots to release hybridized DNA. This work leverages LLNL expertise in optics, microfluids, and bioinformatics
The makewaves tsunami tests and their relevance to tsunami engineering and risk management
MAKEWAVES is an international multi-partner collaborative project bringing together nine academic institutions and two commercial consultancies. The objective of the collaboration is to develop experimental data and associated numerical modelling on tsunami inundation and interaction with boulders, buildings, natural and engineered barriers, towards the development of new internationally accepted guidance for
structural codes and standards. Using a pneumatic tsunami simulator (TS) developed jointly by HR Wallingford and UCL the team conducted experiments between November 2022 and April 2023 within a highly instrumented 100m long flume. The TS is capable of simulating realistic trough and crest-led tsunami waves at 1:50, including traces from the The TS is capable of generating very long trough and crest-led waves, and can reproduce at 1:50 scale waves from real life events such as the Mercator trace from the 2004 Indian Ocean event and the and 2011 Tohoku tsunamis. The TS capability has been further extended to include bore-waves. The characteristics of the waves are controlled by adjusting the flow rate and total volume of water drawn in and discharged by the TS. The experimental campaign is was subdivided into discrete research areas, each aimed at furthering knowledge on how different tsunami wave characteristics affect their interaction with manmade and natural structures environments. These include tests aimed at understanding: (1) how roughness representative of coastal forests and mangroves affects tsunami inundation characteristics, (2) how tsunami interact with boulders (3) the effectiveness of offshore breakwaters as tsunami barriers (4) how structural loads and foundation scour are affected by building permeability. This paper presents an overview of the tests conducted and some of the important early observations made that are relevant to future
engineering standards and to tsunami disaster management
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