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

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 (π,0)(\pi,0) 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 $(\pi,0)$ 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)$_2\cdot 4$D$_2$O (CFTD), an excellent physical realisation of the 2DQHAFSL, designed to investigate how the anomaly at $(\pi,0)$ evolves up to finite temperatures $T/J\sim2/3$. 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 $(\pi,0)$ 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

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

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

Evaluating the use of the Child and Adolescent Intellectual Disability Screening Questionnaire (CAIDS-Q) to estimate IQ in children with low intellectual ability

In situations where completing a full intellectual assessment is not possible or desirable the clinician or researcher may require an alternative means of accurately estimating intellectual functioning. There has been limited research in the use of proxy IQ measures in children with an intellectual disability or low IQ. The present study aimed to provide a means of converting total scores from a screening tool (the Child and Adolescent Intellectual Disability Screening Questionnaire: CAIDS-Q) to an estimated IQ. A series of linear regression analyses were conducted on data from 428 children and young people referred to clinical services, where FSIQ was predicted from CAIDS-Q total scores. Analyses were conducted for three age groups between ages 6 and 18 years. The study presents a conversion table for converting CAIDS-Q total scores to estimates of FSIQ, with corresponding 95% prediction intervals to allow the clinician or researcher to estimate FSIQ scores from CAIDS-Q total scores. It is emphasised that, while this conversion may offer a quick means of estimating intellectual functioning in children with a below average IQ, it should be used with caution, especially in children aged between 6 and 8 years old