356 research outputs found
Temperature compensation of NdFeB permanent magnets
Permanent magnet blocks of NdFeB have a relatively high maximum energy product. Because of its relatively low Curie temperature, however, NdFeB has a large temperature coefficient for its residual induction. The temperature coefficients of the relative magnetic fields ({Delta}B/B)/{Delta}T in the air gap of NdFeB dipole magnets were reduced from {minus}1.1 {times} 10{sup {minus}3}/c to less than 2 {times} 10{sup {minus}5}/{degree}C under operating temperatures of {+-} 6 C. This was achieved passively by using 1.25-mm-thick strips of 30%-Ni-Fe alloy as flux shunts for the NdFeB blocks. The magnets with soft-steel poles and flux-return yokes were assembled and measured in a temperature-controlled environment
Lunar maria and related deposits: Preliminary Galileo imaging results
During the Earth-Moon flyby the Galileo Solid State Imaging system obtained new information on lunar media. Imaging data in spectral bands from 0.4 to 1.0 micron wavelength provide color data for deposits on the western limb. General objectives were to determine the composition and stratigraphy of mare and related deposits for areas not previously seen well in color, and to compare the results with well-studied nearside maria. Initial results from images reduced with preliminary calibrations show that Galileo spectral reflectance data are consistent with previous earthbased observations
Dynamical fingerprints for probing individual relaxation processes in biomolecular dynamics with simulations and kinetic experiments
There is a gap between kinetic experiment and simulation in their views of the dynamics of complex biomolecular systems. Whereas experiments typically reveal only a few readily discernible exponential relaxations, simulations often indicate complex multistate behavior. Here, a theoretical framework is presented that reconciles these two approaches. The central concept is “dynamical fingerprints” which contain peaks at the time scales of the dynamical processes involved with amplitudes determined by the experimental observable. Fingerprints can be generated from both experimental and simulation data, and their comparison by matching peaks permits assignment of structural changes present in the simulation to experimentally observed relaxation processes. The approach is applied here to a test case interpreting single molecule fluorescence correlation spectroscopy experiments on a set of fluorescent peptides with molecular dynamics simulations. The peptides exhibit complex kinetics shown to be consistent with the apparent simplicity of the experimental data. Moreover, the fingerprint approach can be used to design new experiments with site-specific labels that optimally probe specific dynamical processes in the molecule under investigation
Representative Percentile Curves of Physical Fitness From Early Childhood to Early Adulthood: The MoMo Study
Introduction: Monitoring of physical fitness in youth is important because physical fitness is a summative indicator of health. From a developmental and preventive perspective, physical fitness levels are relatively stable from childhood to early adulthood. Thus, it is important to monitor physical fitness on a population based level being able to intervene at early stages (1). In order to reliably assess and evaluate the physical fitness of youth, a reliable system of standard values based on representative data is required. The aim of this analysis is to report sex- and age-specific physical fitness percentile curves from childhood to early adulthood in a nationwide sample in Germany.
Methods: We use data from the nationwide representative Motorik Modul (MoMo) Study in Germany (data collection wave 1: 2009–2012; age: 4–23 years; n = 3,742; 50.1% female). Physical fitness was assessed by means of the MoMo test profile covering four dimensions of physical fitness (strength, endurance, coordination, and flexibility) and including eight physical fitness items. Percentile curves were fitted using the LMS transformation method of Cole and Green.
Results: Standardized age- and sex-specific physical fitness percentiles were calculated for eight items: ergometric endurance testing, standing long jump, push-ups, sit-ups, jumping side-ways, balancing backwards, static stand, and stand and reach test. The physical fitness curves differ according to gender and the fitness dimension. Physical fitness improvements with age are linear (e.g., max. strength) or curvilinear (e.g., coordination) and have their stagnation points at different times over the course of adolescence.
Discussion: Our results provide for the first time sex- and age-specific physical fitness percentile curves for Germany from 4 to 17 years. Differences in curve-shapes indicating a timed and capacity-specific physical fitness development. Nationwide German physical fitness percentiles can be useful in comparing different populations (e.g., cross-country), reporting secular trends, comparing special groups, and to evaluate physical fitness interventions
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Investigation of open-loop beam motion at low frequencies at the APS
Sources of transverse beam motion in the APS storage ring have been investigated for ground-motion- and water-system-induced vibrations of the magnet and vacuum systems, and for power supply ripple. The displacement of magnets in a bandwidth of 4-30 Hz have been reduced significantly by inserting viscoelastic damping pads between the girder supports and pedestals, and by welding the magnet cooling headers to the ceiling of the storage ring tunnel. Current ripple on magnet power supplies was identified as a source of horizontal beam motion. Beam motion was measured without the closed-orbit feedback system activated. At {beta}{sub x} = 15.4 m and {beta}{sub y} = 10.4 m the rms beam motion in the 0.02-30 Hz band was 22.7 {mu}m and 6.3 {mu}m in the horizontal and verticle planes, respectively. A few narrow-band structures of the horizontal beam motion spectrum in the 1-4 Hz band have to be investigated further to identify the sources
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Alkenone sea-surface temperatures and carbon burial at site 846 (Eastern Equatorial Pacific Ocean) : the last 1.3 M.Y.
We analyzed the unsaturation ratio (U k/37 ) of long-chain ketones—a molecular sea-surface temperature (SST) indicator—concentrations of carbonate and organic carbon in sediments from Site 846 in the eastern equatorial Pacific Ocean. Based on an isotopic age model for the composite depth section of 0-46 m below seafloor and on estimates of sediment density, accumulation rates of these biogenic compounds were calculated. Our combined temperature and biogenic flux record traces conditions at the origin of the South Equatorial Current over the last 1.3 m.y. S STs have fluctuated considerably over the interval studied. A long trend of gradual decrease from 24°C at 1.3 Ma ends between 500 and 400 Ka, when lowest values of 19°C were reached. Since this time, the temperature data indicate a warming trend to the Holocene modulated by high-amplitude variation (19° to 27°C). The inversion of the trend between 400 and 500 Ka coincides with maximal accumulation rates of carbonate, which since then have decreased. In contrast, organic carbon accumulation since then has increased in variability and in absolute values. On shorter time scales, the records show a strong link to the global climatic background. Since 1.3 Ma, carbonate (0.2-3 g/cm² k.y.¯¹) and organic carbon accumulation rates (2-30 mg/cm² k.y¯¹) were consistently high (more than twice their modern values and those of interglacials) during glacial maxima in the benthic isotope record, when temperatures were low. However, cross-spectral analyses with the δ¹⁸O record suggest that variation in organic carbon flux is not linked directly to variations in SST. Temperature maxima in our record led interglacial events by 7 k.y. in the 100-k.y. eccentricity cycle and by 5 k.y. in the 41-k.y. obliquity cycle. In contrast, maxima in organic carbon accumulation lag behind glacial maxima and low temperatures by 14 k.y. in the eccentricity cycle. On glacial/interglacial time scales, a prominent influence on SST—but not on organic carbon burial—at Site 846 appears to be the advection of cold water into the South Equatorial Current
The Impact of COVID-19 on the Interrelation of Physical Activity, Screen Time and Health-Related Quality of Life in Children and Adolescents in Germany: Results of the Motorik-Modul Study
Reduced physical activity (PA) and prolonged screen time (ST) negatively influence health-related quality of life (HRQoL), a protective factor against illness and mortality. Studies addressing the relationship between PA, ST, and mental health in youth are scarce, especially in times with high mental health burdens like the COVID-19 pandemic. The purpose of this examination was to investigate whether PA, ST, and HRQoL before COVID-19 predict PA, ST, and HRQoL during the COVID-19 pandemic. Participants from the Motorik-Modul Study (MoMo; N = 1711; M = 10.36 (SD = 4.04) years, female = 49.8%; healthy weight = 76.8%) self-reported their PA and ST as well as HRQoL both before and during COVID-19. Relationships of all variables, from before to during COVID-19, were investigated through a path prediction model. Results showed all variables during COVID-19 were predicted by the respective levels before COVID-19, independent of gender and age. Cross-lags revealed a negative influence of before COVID-19 ST on during COVID-19 PA. HRQoL before COVID-19 was positively associated with during COVID-19 PA in children younger than 10 years and females, but not in adolescents and boys. As age- and gender-independent negative influence of before COVID-19 ST on during COVID-19 PA has been detected, health policy may be advised to focus on a general reduction in ST instead of PA enhancement to ensure high PA levels
Reply to Kersting et al. Comment on “Wunsch et al. The Impact of COVID-19 on the Interrelation of Physical Activity, Screen Time and Health-Related Quality of Life in Children and Adolescents in Germany: Results of the Motorik-Modul Study. Children 2021, 8, 98”
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A plan for the development of superconducting Undulator prototypes for LCLS-II and future FELs
Undulators serve as the primary source of radiation for modern storage rings, and more recently for the advent of Free-Electron Lasers (FELs). The performance of future FELs can be greatly enhanced using the much higher magnetic fields of superconducting undulators (SCU) [1]. For example, the LCLS-II hard x-ray undulator can be shortened by up to 70 m using an SCU in place of a PMU (permanent magnet undulator), or its spectral performance can be critically improved when using a similar length. In addition, SCUs are expected to be orders of magnitude less sensitive to radiation dose; a major issue at LCLS-II with its 1-MHz electron bunch rate. We present a funded R&D collaboration between SLAC, ANL, and LBNL, which aims to demonstrate the viability of superconducting undulators for FELs by building, testing, measuring, and tuning two 1.5-m long planar SCU prototypes using two different technologies: NbTi at ANL and Nb Sn at LBNL. Our goal is to review and reassess the LCLS-II HXR baseline plans (PMU) in July of 2015, after the development and evaluation of both prototypes, possibly in favor of an SCU for LCLS-II.
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