2,274 research outputs found
A Kinetic Alfven wave cascade subject to collisionless damping cannot reach electron scales in the solar wind at 1 AU
(Abridged) Turbulence in the solar wind is believed to generate an energy
cascade that is supported primarily by Alfv\'en waves or Alfv\'enic
fluctuations at MHD scales and by kinetic Alfv\'en waves (KAWs) at kinetic
scales . Linear Landau damping of KAWs increases with
increasing wavenumber and at some point the damping becomes so strong that the
energy cascade is completely dissipated. A model of the energy cascade process
that includes the effects of linear collisionless damping of KAWs and the
associated compounding of this damping throughout the cascade process is used
to determine the wavenumber where the energy cascade terminates. It is found
that this wavenumber occurs approximately when ,
where and are, respectively, the real frequency and
damping rate of KAWs and the ratio is evaluated in the limit as
the propagation angle approaches 90 degrees relative to the direction of the
mean magnetic field.Comment: Submitted to Ap
Exploring the effect of current sheet thickness on the high‐frequency Fourier spectrum breakpoint of the solar wind
The magnetic power spectrum of the solar wind at 1 AU exhibits a breakpoint at a frequency of about 0.1–1 Hz, with the spectrum being steeper above the breakpoint than below the breakpoint. Because magnetic discontinuities contain much of the Fourier power in the solar wind, it is suspected that current sheet thicknesses (i.e., discontinuity thicknesses) may play a role in determining the frequency of this breakpoint. Using time series measurements of the solar wind magnetic field from the Wind spacecraft, the effect of current sheet thicknesses on the breakpoint is investigated by time stretching the solar wind time series at the locations of current sheets, effectively thickening the current sheets in the time series. This localized time stretching significantly affects the magnetic power spectral density of the solar wind in the vicinity of the high‐frequency breakpoint: a substantial fraction of the Fourier power at the breakpoint frequency is contained in current sheets that occupy a small fraction of the spatial volume of the solar wind. It is concluded that current sheet thickness appears to play a role in determining the frequency fB of the high‐frequency breakpoint of the magnetic power spectrum of the solar wind. This analysis of solar wind data is aided by comparisons with power spectra generated from artificial time series.Key PointsCurrent‐sheet thicknesses affect the high‐frequency breakpoint frequency of the solar windSolar‐wind current sheets contain substantial magnetic Fourier powerThere are outstanding questions about the solar‐wind current sheet origins and physicsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144299/1/jgra52192_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144299/2/jgra52192.pd
Public Pension Generosity and Old-Age Poverty in OECD countries
Pension adequacy is gaining importance as old-age poverty remains a pressing problem. In many advanced welfare states, the population is ageing rapidly and recent pension reforms have led to cuts in public pension provision. There are, however, few comparative longitudinal studies on the relationship between pension generosity and old-age poverty. This study provides a comparative empirical assessment of how the prevalence and depth of old-age poverty relates to generosity of public pension benefits in 14 advanced OECD welfare states from 1980-2010. We focus on the role of mandatory public pension provision of mainly first tier schemes that grant the major share of retirees’ income in most countries. We use data on theoretical pension replacement rates for retirees who had different working-age incomes. In order to address endogeneity issues, we adopt an instrumental-variable approach. Our main finding shows that pensions systems and earnings-related schemes, in particular, are quite efficient in reducing the risk of old-age poverty. Yet they still do very little to alleviate poverty among those pensioners in the most disadvantaged situations. We also found that redistribution within the pension system does not substantially contribute to poverty alleviation
Toxicity testing in environmental monitoring: The role of enzymatic biosensors
Biological toxicity testing is a rapidly expanding field involving numerous bioanalytical techniques. The enzymatic biosensors are valuable screening tools to identify pollutants and/or toxic agents in the environment and/or in food matrices, thus representing a valid alternative to animal testing in analytical toxicology. Inhibition based biosensors here presented have been proved to represent alternative assays for the toxicity evaluation of warfare agents and endocrine disrupting chemicals as well as algal toxins (phycotoxins) in the contamined sea foods (mainly clams and other mollusks). Results obtained by inhibition studies performed by means of several enzymatic biosensors indicate the reliability of the proposed method and the possibility to extend such an experimental approach to other toxicants as a simple, rapid and cheap biotest, to be used easily also "on the spot"
Orthotopic liver transplantation in dogs receiving FK-506.
Ten dogs that survived the perioperative events of liver transplantation were treated with 1 mg/kg/d oral FK. Eight of the recipients lived for at least 1 month postoperatively, and seven are still alive with normal hepatic function after 35 to 65 days. The consistency and good quality of results with this difficult transplant preparation using FK, in spite of its rumored great toxicity in dogs, have highlighted the importance of further developing the drug
Microwave apparatus for gravitational waves observation
In this report the theoretical and experimental activities for the
development of superconducting microwave cavities for the detection of
gravitational waves are presented.Comment: 42 pages, 28 figure
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