6,455 research outputs found
Nonparametric regression penalizing deviations from additivity
Due to the curse of dimensionality, estimation in a multidimensional
nonparametric regression model is in general not feasible. Hence, additional
restrictions are introduced, and the additive model takes a prominent place.
The restrictions imposed can lead to serious bias. Here, a new estimator is
proposed which allows penalizing the nonadditive part of a regression function.
This offers a smooth choice between the full and the additive model. As a
byproduct, this penalty leads to a regularization in sparse regions. If the
additive model does not hold, a small penalty introduces an additional bias
compared to the full model which is compensated by the reduced bias due to
using smaller bandwidths. For increasing penalties, this estimator converges to
the additive smooth backfitting estimator of Mammen, Linton and Nielsen [Ann.
Statist. 27 (1999) 1443-1490]. The structure of the estimator is investigated
and two algorithms are provided. A proposal for selection of tuning parameters
is made and the respective properties are studied. Finally, a finite sample
evaluation is performed for simulated and ozone data.Comment: Published at http://dx.doi.org/10.1214/009053604000001246 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Measurement of Gravitomagnetic and Acceleration Fields Around Rotating Superconductors
It is well known that a rotating superconductor produces a magnetic field
proportional to its angular velocity. The authors conjectured earlier, that in
addition to this so-called London moment, also a large gravitomagnetic field
should appear to explain an apparent mass increase of Niobium Cooper-pairs. A
similar field is predicted from Einstein's general relativity theory and the
presently observed amount of dark energy in the universe. An experimental
facility was designed and built to measure small acceleration fields as well as
gravitomagnetic fields in the vicinity of a fast rotating and accelerating
superconductor in order to detect this so-called gravitomagnetic London moment.
This paper summarizes the efforts and results that have been obtained so far.
Measurements with Niobium superconductors indeed show first signs which appear
to be within a factor of 2 of our theoretical prediction. Possible error
sources as well as the experimental difficulties are reviewed and discussed. If
the gravitomagnetic London moment indeed exists, acceleration fields could be
produced in a laboratory environment.Comment: To appear in the proceedings of the STAIF-2007 conference published
by AI
Some taste substances are direct activators of G-proteins
Amphiphilic substances may stimulate cellular events through direct activation of G-proteins. The present experiments indicate that several amphiphilic sweeteners and the bitter tastant, quinine, activate transducin and Gi/Go-proteins. Concentrations of taste substances required to activate G-proteins in vitro correlated with those used to elicit taste. These data support the hypothesis that amphiphilic taste substances may elicit taste through direct activation of G-proteins
Laser power stabilization for second-generation gravitational wave detectors
We present results on the power stabilization of a Nd:YAG laser in the frequency band from 1 Hz to 100 kHz. High-power, low-noise photodetectors are used in a dc-coupled control loop to achieve relative power fluctuations down to 5×10−9 Hz−1/2 at 10 Hz and 3.5×10−9 Hz−1/2 up to several kHz, which is very close to the shot-noise limit for 80 mA of detected photocurrent on each detector. We investigated and eliminated several noise sources such as ground loops and beam pointing. The achieved stability level is close to the requirements for the Advanced LIGO gravitational wave detector
Non-linear properties of supercooled liquids in the system Na2O---SiO2
The physical properties, viscosity, density, heat capacity and thermal expansivity, of relaxed supercooled liquids in the temperature range just above the glass transition have been determined for ten compositions along the compositional binary Na2O---SiO2, in the range of 2–45 mole% Na2O, by a combination of scanning calorimetry, dilatometry and micropenetration viscometry. The viscosity, density, heat capacity and thermal expansivity in the glassy state have also been determined.
The heat capacities illustrate a linear composition dependence for the glassy state and a smooth but strongly non-linear composition dependence for the supercooled liquid state. The thermal expansivities were determined by dilatometry up to the glass transition and, by a normalized comparison of relaxation behavior in the glass transition interval, to temperatures 50°C above the glass transition. The expansivity is a linear function of the molar composition in the glass but a strongly non-linear function of molar composition in the supercooled liquid.
The viscosity data just above the glass transition temperature, combined with data from high temperature using the concentric cylinder method, illustrate that the composition dependence of viscosity is strongly non-linear and exhibits an inflection as a function of composition. The glass transition temperature, taken as the peak temperature of the calorimetric measurements, is not in general an isokom in this system.
The data for these property determinations in the Na2O---SiO2 system provide much improved constraints on the partial molar properties of SiO2 liquid and partial molar properties of the SiO2 component in silicate melts. The complex behavior of the transport properties, i.e. the glass transition temperature and the viscosity, point to complexities in viscous flow beyond that of simple binary mixing of the Na2O and SiO2 components
Can the Tajmar effect be explained using a modification of inertia?
The Tajmar effect is an unexplained acceleration observed by accelerometers
and laser gyroscopes close to rotating supercooled rings. The observed ratio
between the gyroscope and ring accelerations was 3+/-1.2x10^-8. Here, a new
model for inertia which has been tested quite successfully on the Pioneer and
flyby anomalies is applied to this problem. The model assumes that the inertia
of the gyroscope is caused by Unruh radiation that appears as the ring and the
fixed stars accelerate relative to it, and that this radiation is subject to a
Hubble-scale Casimir effect. The model predicts that the sudden acceleration of
the nearby ring causes a slight increase in the inertial mass of the gyroscope,
and, to conserve momentum in the reference frame of the spinning Earth, the
gyroscope rotates clockwise with an acceleration ratio of 1.8+/-0.25x10^-8 in
agreement with the observed ratio. However, this model does not explain the
parity violation seen in some of the gyroscope data. To test these ideas the
Tajmar experiment (setup B) could be exactly reproduced in the southern
hemisphere, since the model predicts that the anomalous acceleration should
then be anticlockwise.Comment: 9 pages, 1 figure. Accepted by EPL on the 4th December, 200
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