2,340 research outputs found
Impact of observational uncertainties on universal scaling of MHD turbulence
Scaling exponents are the central quantitative prediction of theories of
turbulence and in-situ satellite observations of the high Reynolds number solar
wind flow have provided an extensive testbed of these. We propose a general,
instrument independent method to estimate the uncertainty of velocity field
fluctuations. We obtain the systematic shift that this uncertainty introduces
into the observed spectral exponent. This shift is essential for the correct
interpretation of observed scaling exponents. It is sufficient to explain the
contradiction between spectral features of the Elsasser fields observed in the
solar wind with both theoretical models and numerical simulations of
Magnetohydrodynamic turbulence
Dynamics of plasma blobs in a shear flow
The global dynamic of plasma blobs in a shear flow is investigated in a simple magnetized torus using
the spatial Fourier harmonics (k-space) framework. Direct experimental evidence of a linear drift in
k space of the density fluctuation energy synchronized with blob events is presented. During this drift, an
increase of the fluctuation energy and a production of the kinetic energy associated with blobs are observed.
The energy source of the blob is analyzed using an advection-dissipation-type equation that includes
blob-flow exchange energy, linear drift in k space, nonlinear processes, and viscous dissipations.
We show that blobs tap their energy from the dominant E B vertical background flow during the linear
drift stage. The exchange of energy is unidirectional as there is no evidence that blobs return energy to the
flow
The critical role of innate immunity in kidney transplantation
For a long time now, kidney transplant rejection has been considered the consequence of either cellular or antibody-mediated reaction as a part of adaptive immunity response. The role of innate immunity, on the other hand, had been unclear for many years and was thought to be only ancillary. There is now consistent evidence that innate immune response is a condition necessary to activate the machinery of rejection. In this setting, the communication between antigen-presenting cells and T lymphocytes is of major importance. Indeed, T cells are unable to cause rejection if innate immunity is not activated. This field is currently being explored and several experiments in animal models have proved that blocking innate immunity activation can promote tolerance of the graft instead of rejection. The aim of this review is to systematically describe all the steps of innate immunity response in kidney transplant rejection, from antigen recognition to T-cells activation, with a focus on clinical consequences and possible future perspectives
Amelioration of normothermic canine liver ischemia with prostacyclin.
A model of hepatic ischemia was developed in dogs using a pump-driven splanchnic-to-jugular vein bypass during crossclamping of the portal triad. An LD50 was established with three hours of ischemia. PGI2 given for one hour before the ischemic insult ameliorated the ischemic injury and increased survival
Nanotribological characterization of industrial Polytetrafluorethylene-based coatings by atomic force microscopy
We present the result of a systematic study of the tribological properties of
industrial Polytetrafluorethylene (PTFE)-based coatings carried out with an
atomic force microscope. A new characterization protocol allowed the reliable
and quantitative assessment of the friction coefficient and adhesion forces at
the sub-micrometer scale even for highly corrugated industrial samples. We have
studied and compared PTFE coatings charged with different additives in dry and
humid environment. The influence of additives and humidity on the friction
coefficient and on adhesion forces has been investigated using standard silicon
nitride tips as sliders in the low-load regime.Comment: to be published in Thin Solid Films 18 pages, 2 tables, 3 figure
Impact of displacement demand reliability for seismic vulnerability assessment at an urban scale
This paper addresses seismic vulnerability assessment at an urban scale by focusing on the displacement demand determination for building damage prediction. The study is based on the comparison of urban seismic damage distributions obtained by the displacement demand computed using non-linear time-history analysis (NLTHA) with three simplified methods. These methods include the N2 method, the Lin & Miranda proposal and an optimized version of the N2 method. Comparing the different damage distributions from the three simplified methods with the one obtained by time-history analysis helps understanding the reliability of displacement demand determination. The study is carried out on Sion and Martigny, two typical Swiss cities. For the case of Sion, results clearly show that using N2 method may lead to significant overestimation of damage grade distribution. The use of Lin & Miranda method and optimized version of N2 improves the damage prediction in both cases. For the other studied case of Martigny, N2 method and Lin & Miranda proposal are not accurate. The optimized version of N2 method provides stable and reliable results
Properties of Flares-Generated Seismic Waves on the Sun
The solar seismic waves excited by solar flares (``sunquakes'') are observed
as circular expanding waves on the Sun's surface. The first sunquake was
observed for a flare of July 9, 1996, from the Solar and Heliospheric
Observatory (SOHO) space mission. However, when the new solar cycle started in
1997, the observations of solar flares from SOHO did not show the seismic
waves, similar to the 1996 event, even for large X-class flares during the
solar maximum in 2000-2002. The first evidence of the seismic flare signal in
this solar cycle was obtained for the 2003 ``Halloween'' events, through
acoustic ``egression power'' by Donea and Lindsey. After these several other
strong sunquakes have been observed. Here, I present a detailed analysis of the
basic properties of the helioseismic waves generated by three solar flares in
2003-2005. For two of these flares, X17 flare of October 28, 2003, and X1.2
flare of January 15, 2005, the helioseismology observations are compared with
simultaneous observations of flare X-ray fluxes measured from the RHESSI
satellite. These observations show a close association between the flare
seismic waves and the hard X-ray source, indicating that high-energy electrons
accelerated during the flare impulsive phase produced strong compression waves
in the photosphere, causing the sunquake. The results also reveal new physical
properties such as strong anisotropy of the seismic waves, the amplitude of
which varies significantly with the direction of propagation. The waves travel
through surrounding sunspot regions to large distances, up to 120 Mm, without
significant decay. These observations open new perspectives for helioseismic
diagnostics of flaring active regions on the Sun and for understanding the
mechanisms of the energy release and transport in solar flares.Comment: 12 pages, 4 figures, submitted to Ap
Fairness Beyond Disparate Treatment & Disparate Impact: Learning Classification without Disparate Mistreatment
Automated data-driven decision making systems are increasingly being used to
assist, or even replace humans in many settings. These systems function by
learning from historical decisions, often taken by humans. In order to maximize
the utility of these systems (or, classifiers), their training involves
minimizing the errors (or, misclassifications) over the given historical data.
However, it is quite possible that the optimally trained classifier makes
decisions for people belonging to different social groups with different
misclassification rates (e.g., misclassification rates for females are higher
than for males), thereby placing these groups at an unfair disadvantage. To
account for and avoid such unfairness, in this paper, we introduce a new notion
of unfairness, disparate mistreatment, which is defined in terms of
misclassification rates. We then propose intuitive measures of disparate
mistreatment for decision boundary-based classifiers, which can be easily
incorporated into their formulation as convex-concave constraints. Experiments
on synthetic as well as real world datasets show that our methodology is
effective at avoiding disparate mistreatment, often at a small cost in terms of
accuracy.Comment: To appear in Proceedings of the 26th International World Wide Web
Conference (WWW), 2017. Code available at:
https://github.com/mbilalzafar/fair-classificatio
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
Progress towards an accurate determination of the Boltzmann constant by Doppler spectroscopy
In this paper, we present significant progress performed on an experiment
dedicated to the determination of the Boltzmann constant, k, by accurately
measuring the Doppler absorption profile of a line in a gas of ammonia at
thermal equilibrium. This optical method based on the first principles of
statistical mechanics is an alternative to the acoustical method which has led
to the unique determination of k published by the CODATA with a relative
accuracy of 1.7 ppm. We report on the first measurement of the Boltzmann
constant by laser spectroscopy with a statistical uncertainty below 10 ppm,
more specifically 6.4 ppm. This progress results from improvements in the
detection method and in the statistical treatment of the data. In addition, we
have recorded the hyperfine structure of the probed saQ(6,3) rovibrational line
of ammonia by saturation spectroscopy and thus determine very precisely the
induced 4.36 (2) ppm broadening of the absorption linewidth. We also show that,
in our well chosen experimental conditions, saturation effects have a
negligible impact on the linewidth. Finally, we draw the route to future
developments for an absolute determination of with an accuracy of a few ppm.Comment: 22 pages, 11 figure
- …