1,301 research outputs found
The Universe after inflation: the wide resonance case
We study numerically the decay of massive and massless inflatons into massive
excitations, via a coupling, in the expanding Universe. We find
that a wide enough resonance can survive the Universe expansion, though account
for the expansion is very important for determining precisely how wide it
should be. For a massive inflaton, the effective production of particles with
mass ten times that of the inflaton requires very large values of the resonance
parameter , q\gsim 10^8. For these large , the maximal size of produced
fluctuations is significantly suppressed by the back reaction, but at least
within the Hartree approximation they are still not negligible. For the
massless inflaton with a potential, the Universe expansion
completely prevents a resonance production of particles with masses larger than
for up to .Comment: LaTeX, 12 pages including 3 figure
23Na NMR study of non-superconducting double-layer hydrate NaxCoO2.yH2O
We report 23Na NMR studies of the polycrystalline samples of double-layer
hydrated cobalt oxides NaxCoO2.yH2O (x ~ 0.35 and y ~ 1.3) with the
superconducting transition temperatures Tc < 1.8K and ~4.5K, and the dehydrated
NaxCoO2 (x ~ 0.35). The hyperfine field and the electric field gradient at the
Na sites in the non-hydrated Na0.7CoO2 and the dehydrated Na0.35CoO2 are found
to be significantly reduced by the hydration, which indicates a strong
shielding effect of the intercalated water molecules on the Na sites. The
temperature dependence of 23 Na nuclear spin-lattice relaxation rate 1/23T1 of
the non-superconducting double-layer hydrate NaxCoO2.yH2O is found to be
similar to that of the non-hydrated Na0.7CoO2, whose spin dynamics is
understood by A-type (intra-layer ferromagnetic and inter-layer
antiferromagnetic) spin fluctuations. The superconducting phase is located
close to the quantum critical point with the A-type magnetic instability.Comment: 4 pages, 4 figure
Universality in heavy-fermion systems with general degeneracy
We discuss the relation between the T^{2}-coefficient of electrical
resistivity and the T-linear specific-heat coefficient for
heavy-fermion systems with general , where is the degeneracy of
quasi-particles. A set of experimental data reveals that the Kadowaki-Woods
relation; , collapses
remarkably for large-N systems, although this relation has been regarded to be
commonly applicable to the Fermi-liquids. Instead, based on the Fermi-liquid
theory we propose a new relation;
with and .
This new relation exhibits an excellent agreement with the data for whole the
range of degenerate heavy-fermions.Comment: 2 figures, to appear in Phys. Rev. Let
Cosmological Reheating and Self-Interacting Final State Bosons
We consider inflaton decay to final state bosons with self-interactions of
moderate strength. We find that such final state self-interactions
qualitatively alter the reheat dynamics. In the case of narrow-band resonance
decay, where a quantitative analysis is possible, we show that these final
state interactions regulate the decay rate. The phenomenon of parametric
amplification is then effectively suppressed, and does not drastically enhance
the decay rate and reheat temperature. Detailed applications of our results to
realistic classes of inflationary models will be considered elsewhere.Comment: 17 pages LaTeX, accepted for publication in Physics Letters B,
extended discussion of broad-band resonance regime, and references adde
Expert consensus ratings of job categories from the Third National Health and Nutrition Examination Survey (NHANES III)
Background A method of occupational physical exposure assessment is needed to improve analyses using large data sets (e.g., national surveys) that provide only job title/category information as a proxy for exposure. Methods Five ergonomic experts rated and arrived at consensus ratings for job categories used in the Third National Health and Nutrition Examination Survey. Interrater agreement was examined for initial (pre-consensus) ratings. Correlation between consensus ratings and an independent source of ratings (US Department of Labor (DOL)) was used as a basis of comparison. Results Interrater agreements for the initial ratings were weak. Highest interrater agreement was for sitting (weighted kappa (Κ w ) = 0.56). Lowest agreement was for standing (Κ w = 0.07). Consensus ratings were well correlated with DOL ratings (correlation coefficients ≥0.6). Conclusions The correlation between consensus ratings and DOL ratings support the use of expert consensus to assess physical exposures in national data sets. However, validation of expert consensus ratings is required. Am. J. Ind. Med. 50:608–616, 2007. © 2007 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56129/1/20487_ftp.pd
Stellarator microinstabilities and turbulence at low magnetic shear
[EN] Gyrokinetic simulations of drift waves in low-magnetic-shear stellarators reveal that simulation domains comprised of multiple turns can be required to properly resolve critical mode structures important in saturation dynamics. Marginally stable eigenmodes important in saturation of ion temperature gradient modes and trapped electron modes in the Helically Symmetric Experiment (HSX) stellarator are observed to have two scales, with the envelope scale determined by the properties of the local magnetic shear and an inner scale determined by the interplay between the local shear and magnetic field-line curvature. Properly resolving these modes removes spurious growth rates that arise for extended modes in zero-magnetic-shear approximations, enabling use of a zero-magnetic-shear technique with smaller simulation domains and attendant cost savings. Analysis of subdominant modes in trapped electron mode (TEM)-driven turbulence reveals that the extended marginally stable modes play an important role in the nonlinear dynamics, and suggests that the properties induced by low magnetic shear may be exploited to provide another route for turbulence saturation.The authors would like to thank F. Jenko for insightful questions that motivated this research and J. Smoniewski and J. H. E. Proll for engaging discussions. This work was supported by US DoE grant nos. DE-FG02-99ER54546, DE-FG02-93ER54222 and DE-FG02-89ER53291. J.E.R. was supported by Agencia Estatal de Investigacion (AEI) under grant TIN2016-75985-P, which includes European Commission ERDF funds. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a US Department of Energy Office of Science User Facility operated under contract no. DE-AC02-05CH11231. This research was performed using the compute resources and assistance of the UW-Madison Center For High Throughput Computing (CHTC) in the Department of Computer Sciences. The CHTC is supported by UW-Madison, the Advanced Computing Initiative, the Wisconsin Alumni Research Foundation, the Wisconsin Institutes for Discovery and the National Science Foundation, and is an active member of the Open Science Grid, which is supported by the National Science Foundation and the US Department of Energy's Office of Science.Faber, BJ.; Pueschel, MJ.; Terry, PW.; Hegna, CC.; Roman, JE. (2018). Stellarator microinstabilities and turbulence at low magnetic shear. Journal of Plasma Physics. 84(5). https://doi.org/10.1017/S0022377818001022S845Connor, J. W., & Hastie, R. J. (2004). Microstability in tokamaks with low magnetic shear. Plasma Physics and Controlled Fusion, 46(10), 1501-1535. doi:10.1088/0741-3335/46/10/001Terry, P. W., Faber, B. J., Hegna, C. C., Mirnov, V. V., Pueschel, M. J., & Whelan, G. G. (2018). Saturation scalings of toroidal ion temperature gradient turbulence. Physics of Plasmas, 25(1), 012308. doi:10.1063/1.5007062Hernandez, V., Roman, J. E., & Vidal, V. (2005). SLEPc. ACM Transactions on Mathematical Software, 31(3), 351-362. doi:10.1145/1089014.1089019Friedman, B., Carter, T. A., Umansky, M. V., Schaffner, D., & Joseph, I. (2013). Nonlinear instability in simulations of Large Plasma Device turbulence. Physics of Plasmas, 20(5), 055704. doi:10.1063/1.4805084Eiermann, M., & Ernst, O. G. (2006). A Restarted Krylov Subspace Method for the Evaluation of Matrix Functions. SIAM Journal on Numerical Analysis, 44(6), 2481-2504. doi:10.1137/050633846Connor, J. W., Hastie, R. J., & Taylor, J. B. (1978). Shear, Periodicity, and Plasma Ballooning Modes. Physical Review Letters, 40(6), 396-399. doi:10.1103/physrevlett.40.396Xanthopoulos, P., & Jenko, F. (2007). Gyrokinetic analysis of linear microinstabilities for the stellarator Wendelstein 7-X. Physics of Plasmas, 14(4), 042501. doi:10.1063/1.2714328Hegna, C. C., & Hudson, S. R. (2001). Loss of Second-Ballooning Stability in Three-Dimensional Equilibria. Physical Review Letters, 87(3). doi:10.1103/physrevlett.87.035001Hatch, D. R., Terry, P. W., Jenko, F., Merz, F., Pueschel, M. J., Nevins, W. M., & Wang, E. (2011). Role of subdominant stable modes in plasma microturbulence. Physics of Plasmas, 18(5), 055706. doi:10.1063/1.3563536Faber, B. J., Pueschel, M. J., Proll, J. H. E., Xanthopoulos, P., Terry, P. W., Hegna, C. C., … Talmadge, J. N. (2015). Gyrokinetic studies of trapped electron mode turbulence in the Helically Symmetric eXperiment stellarator. Physics of Plasmas, 22(7), 072305. doi:10.1063/1.4926510Sugama, H., & Watanabe, T.-H. (2006). Collisionless damping of zonal flows in helical systems. Physics of Plasmas, 13(1), 012501. doi:10.1063/1.2149311Hegna, C. C., Terry, P. W., & Faber, B. J. (2018). Theory of ITG turbulent saturation in stellarators: Identifying mechanisms to reduce turbulent transport. Physics of Plasmas, 25(2), 022511. doi:10.1063/1.5018198Zocco, A., Xanthopoulos, P., Doerk, H., Connor, J. W., & Helander, P. (2018). Threshold for the destabilisation of the ion-temperature-gradient mode in magnetically confined toroidal plasmas. Journal of Plasma Physics, 84(1). doi:10.1017/s0022377817000988Merz, F. 2008 Gyrokinetic simulation of multimode plasma turbulence. PhD thesis.Dorland, W., Jenko, F., Kotschenreuther, M., & Rogers, B. N. (2000). Electron Temperature Gradient Turbulence. Physical Review Letters, 85(26), 5579-5582. doi:10.1103/physrevlett.85.5579Xanthopoulos, P., Cooper, W. A., Jenko, F., Turkin, Y., Runov, A., & Geiger, J. (2009). A geometry interface for gyrokinetic microturbulence investigations in toroidal configurations. Physics of Plasmas, 16(8), 082303. doi:10.1063/1.3187907Dinklage, A., Beidler, C. D., Helander, P., Fuchert, G., Maaßberg, H., … Zhang, D. (2018). Magnetic configuration effects on the Wendelstein 7-X stellarator. Nature Physics, 14(8), 855-860. doi:10.1038/s41567-018-0141-9Hatch, D. R., Kotschenreuther, M., Mahajan, S., Valanju, P., Jenko, F., Told, D., … Saarelma, S. (2016). Microtearing turbulence limiting the JET-ILW pedestal. Nuclear Fusion, 56(10), 104003. doi:10.1088/0029-5515/56/10/104003Hatch, D. R., Terry, P. W., Jenko, F., Merz, F., & Nevins, W. M. (2011). Saturation of Gyrokinetic Turbulence through Damped Eigenmodes. Physical Review Letters, 106(11). doi:10.1103/physrevlett.106.115003Proll, J. H. E., Xanthopoulos, P., & Helander, P. (2013). Collisionless microinstabilities in stellarators. II. Numerical simulations. Physics of Plasmas, 20(12), 122506. doi:10.1063/1.4846835Whelan, G. G., Pueschel, M. J., & Terry, P. W. (2018). Nonlinear Electromagnetic Stabilization of Plasma Microturbulence. Physical Review Letters, 120(17). doi:10.1103/physrevlett.120.175002Friedman, B., & Carter, T. A. (2014). Linear Technique to Understand Non-Normal Turbulence Applied to a Magnetized Plasma. Physical Review Letters, 113(2). doi:10.1103/physrevlett.113.025003High mode number stability of an axisymmetric toroidal plasma. (1979). Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences, 365(1720), 1-17. doi:10.1098/rspa.1979.0001Boozer, A. H. (1998). What is a stellarator? Physics of Plasmas, 5(5), 1647-1655. doi:10.1063/1.872833Boozer, A. H. (1981). Plasma equilibrium with rational magnetic surfaces. Physics of Fluids, 24(11), 1999. doi:10.1063/1.863297Dewar, R. L. (1983). Ballooning mode spectrum in general toroidal systems. Physics of Fluids, 26(10), 3038. doi:10.1063/1.864028Anderson, F. S. B., Almagri, A. F., Anderson, D. T., Matthews, P. G., Talmadge, J. N., & Shohet, J. L. (1995). The Helically Symmetric Experiment, (HSX) Goals, Design and Status. 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(1995). Field‐aligned coordinates for nonlinear simulations of tokamak turbulence. Physics of Plasmas, 2(7), 2687-2700. doi:10.1063/1.871232Gates, D. A., Anderson, D., Anderson, S., Zarnstorff, M., Spong, D. A., Weitzner, H., … Glasser, A. H. (2018). Stellarator Research Opportunities: A Report of the National Stellarator Coordinating Committee. Journal of Fusion Energy, 37(1), 51-94. doi:10.1007/s10894-018-0152-7Helander, P. (2014). Theory of plasma confinement in non-axisymmetric magnetic fields. Reports on Progress in Physics, 77(8), 087001. doi:10.1088/0034-4885/77/8/087001Peeters, A. G., Camenen, Y., Casson, F. J., Hornsby, W. A., Snodin, A. P., Strintzi, D., & Szepesi, G. (2009). The nonlinear gyro-kinetic flux tube code GKW. Computer Physics Communications, 180(12), 2650-2672. doi:10.1016/j.cpc.2009.07.001Jenko, F., Dorland, W., Kotschenreuther, M., & Rogers, B. N. (2000). Electron temperature gradient driven turbulence. 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Effect of dose and duration of reduction in dietary sodium on blood pressure levels: systematic review and meta-analysis of randomised trials.
OBJECTIVE: To examine the dose-response relation between reduction in dietary sodium and blood pressure change and to explore the impact of intervention duration. DESIGN: Systematic review and meta-analysis following PRISMA guidelines. DATA SOURCES: Ovid MEDLINE(R), EMBASE, and Cochrane Central Register of Controlled Trials (Wiley) and reference lists of relevant articles up to 21 January 2019. INCLUSION CRITERIA: Randomised trials comparing different levels of sodium intake undertaken among adult populations with estimates of intake made using 24 hour urinary sodium excretion. DATA EXTRACTION AND ANALYSIS: Two of three reviewers screened the records independently for eligibility. One reviewer extracted all data and the other two reviewed the data for accuracy. Reviewers performed random effects meta-analyses, subgroup analyses, and meta-regression. RESULTS: 133 studies with 12 197 participants were included. The mean reductions (reduced sodium v usual sodium) of 24 hour urinary sodium, systolic blood pressure (SBP), and diastolic blood pressure (DBP) were 130 mmol (95% confidence interval 115 to 145, P<0.001), 4.26 mm Hg (3.62 to 4.89, P<0.001), and 2.07 mm Hg (1.67 to 2.48, P<0.001), respectively. Each 50 mmol reduction in 24 hour sodium excretion was associated with a 1.10 mm Hg (0.66 to 1.54; P<0.001) reduction in SBP and a 0.33 mm Hg (0.04 to 0.63; P=0.03) reduction in DBP. Reductions in blood pressure were observed in diverse population subsets examined, including hypertensive and non-hypertensive individuals. For the same reduction in 24 hour urinary sodium there was greater SBP reduction in older people, non-white populations, and those with higher baseline SBP levels. In trials of less than 15 days' duration, each 50 mmol reduction in 24 hour urinary sodium excretion was associated with a 1.05 mm Hg (0.40 to 1.70; P=0.002) SBP fall, less than half the effect observed in studies of longer duration (2.13 mm Hg; 0.85 to 3.40; P=0.002). Otherwise, there was no association between trial duration and SBP reduction. CONCLUSIONS: The magnitude of blood pressure lowering achieved with sodium reduction showed a dose-response relation and was greater for older populations, non-white populations, and those with higher blood pressure. Short term studies underestimate the effect of sodium reduction on blood pressure. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42019140812
Metric preheating and limitations of linearized gravity
Recently it has become clear that the resonant amplification of quantum field
fluctuations at preheating must be accompanied by resonant amplification of
scalar metric perturbations, since the two are united by Einstein's equations.
Furthermore, this "metric preheating" enhances particle production and leads to
gravitational rescattering effects even at linear order. In multi-field models
with strong preheating (q \gg 1), metric perturbations are driven nonlinear,
with the strongest amplification typically on super-Hubble scales (k \to 0).
This amplification is causal, being due to the super- Hubble coherence of the
inflaton condensate, and is accompanied by resonant growth of entropy
perturbations. The amplification invalidates the use of the linearized Einstein
field equations, irrespective of the amount of fine-tuning of the initial
conditions. This has serious implications at all scales - from the large-angle
cosmic microwave background (CMB) anisotropies to primordial black holes. We
investigate the (q,k) parameter space in a two-field model, and introduce the
time to nonlinearity, t_{nl}, as the timescale for the breakdown of the
linearized Einstein equations. Backreaction effects are expected to shut down
the linear resonances, but cannot remove the existing amplification, which
threatens the viability of strong preheating when confronted with the CMB. We
discuss ways to escape the above conclusions, including secondary phases of
inflation and preheating solely to fermions. Finally we rank known classes of
inflation from strongest (chaotic and strongly coupled hybrid inflation) to
weakest (hidden sector, warm inflation) in terms of the distortion of the
primordial spectrum due to these resonances in preheating.Comment: 31 pages, 16 figures, Revtex. Final version. Nuclear Physics B (in
press
Neutrino Beams From Electron Capture at High Gamma
We investigate the potential of a flavor pure high gamma electron capture
electron neutrino beam directed towards a large water cherenkov detector with
500 kt fiducial mass. The energy of the neutrinos is reconstructed by the
position measurement within the detector and superb energy resolution
capabilities could be achieved. We estimate the requirements for such a
scenario to be competitive to a neutrino/anti-neutrino running at a neutrino
factory with less accurate energy resolution. Although the requirements turn
out to be extreme, in principle such a scenario could achieve as good abilities
to resolve correlations and degeneracies in the search for sin^2(2 theta_13)
and delta_CP as a standard neutrino factory experiment.Comment: 21 pages, 7 figures, revised version, to appear in JHEP, Fig.7
extended, minnor changes, results unchange
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