1,430 research outputs found
An evaluation of electrochemical concentration Cell (ECC) sonde measurements of atmospheric ozone
Using Dobson spectrophotometer measurements of total ozone as a comparison, an analysis of the electrochemical concentration cell (ECC) ozonesonde's measurement accuracy is presented. Days of conjunctive ECC-Dobson observations (from 1970 to 1976 at Wallops Flight Center) provide a set of 123 pairs of total ozone values. Sample set statistics are generated with means and standard deviations of total ozone values and differences being noted. An in-depth study of factors such as time assumptions used in calculating residual ozone, and other possible sources of errors are examined. A study of ECC ozone profiles is also presented with an evaluation of sonde measurement of seasonal trends, altitude or peak ozone concentration, and other important ozone parameters. Short-period changes in total ozone using Dobson data during the observational period are also described
Improved constraints on non-Newtonian forces at 10 microns
Several recent theories suggest that light moduli or particles in "large"
extra dimensions could mediate macroscopic forces exceeding gravitational
strength at length scales below a millimeter. Such new forces can be
parameterized as a Yukawa-type correction to the Newtonian potential of
strength relative to gravity and range . To extend the search
for such new physics we have improved our apparatus utilizing cryogenic
micro-cantilevers capable of measuring attonewton forces, which now includes a
switchable magnetic force for calibration. Our most recent experimental
constraints on Yukawa-type deviations from Newtonian gravity are more than
three times as stringent as our previously published results, and represent the
best bound in the range of 5 - 15 microns, with a 95 percent confidence
exclusion of forces with at = 10 microns.Comment: 12 pages, 9 figures, accepted for publication in PRD. Minor changes,
replaced and corrected Figs 4,5,
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Common Short Selling and Excess Comovement
We show that common short sold capital can explain future four-factor excess return correlation one month ahead, controlling for many pair characteristics, including similarities in size, book-to-market, and momentum. We explore the possible explanations that could give rise to this result. Contrary to the predictions of price pressure, we find that the relationship weakens significantly with stock illiquidity. Instead, consistent with the informed trading hypothesis, the relationship is stronger when short positions originate from hedge funds, from active investors, and from short sellers with high past performance. Stocks connected by common short sellers are associated with non-transitory negative cumulative abnormal returns. Finally, we show that our results can be used to obtain diversifications benefits
New Experimental Constraints on Non-Newtonian Forces below 100 microns
We have searched for large deviations from Newtonian gravity by means of a
microcantilever-based Cavendish-style experiment. Our data eliminate from
consideration mechanisms of deviation that posit strengths ~10^4 times
Newtonian gravity at length scales of 20 microns. This measurement is 3 orders
of magnitude more sensitive than others that provide constraints at similar
length scales.Comment: 4 pages, 4 figure
First prototype of a silicon tracker using an artificial retina for fast track finding
We report on the R\&D for a first prototype of a silicon tracker based on an
alternative approach for fast track finding. The working principle is inspired
from neurobiology, in particular by the processing of visual images by the
brain as it happens in nature. It is based on extensive parallelisation of data
distribution and pattern recognition. In this work we present the design of a
practical device that consists of a telescope based on single-sided silicon
detectors; we describe the data acquisition system and the implementation of
the track finding algorithms using available digital logic of commercial FPGA
devices. Tracking performance and trigger capabilities of the device are
discussed along with perspectives for future applications.Comment: 9 pages, 7 figures, Technology and Instrumentation in Particle
Physics 2014 (TIPP 2014), conference proceeding
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