1,631 research outputs found
Le Royaume-Uni : Les conséquences de l’entrée dans la CEE
The brief historical review which opens the article shows that evolutions of the 70''s have les s affected agriculture - already very capitalistic and highly productive - than agricultural policies. The country's entry into the EEC and the need to adapt its agricultural policies to european norms are the main cause of his change. They are at the same time at the center of national debates and form the core of this article which also analyses land, fiscal and marketing policies
Assessing the Effects of Ownership Change on Women and Minority Employees: Evidence from Matched Employer-Employee Data
While there have been numerous papers on the employment and wage effects of mergers and acquisitions, there has been no direct analysis of the impact of such ownership changes on minority and female workers. This is an unexplored "equity" dimension of these transactions. We fill this gap by analyzing linked employer-employee data for the entire population of Swedish workers and approximately 16,000 manufacturing plants for the period 1985-1998. For each worker employed in these establishments (as well as the entire population of workers), we have data on gender, age, national origin, level of education, type of education, location, industrial sector, annual earnings, as well as each employee's complete work history during the period. We also have data on numerous plant and firm-level characteristics, which allows us to control for additional factors that might result in changes in labor composition and relative compensation. Our findings suggest that ownership change does not significantly alter the relative earnings and employment status of minority and female workers.
Joint entropy of continuously differentiable ultrasonic waveforms
This study is based on an extension of the concept of joint entropy of two random variables to continuous functions, such as backscattered ultrasound. For two continuous random variables, X and Y, the joint probability density p(x,y) is ordinarily a continuous function of x and y that takes on values in a two dimensional region of the real plane. However, in the case where X=f(t) and Y=g(t) are both continuously differentiable functions, X and Y are concentrated exclusively on a curve, Îł(t)=(f(t),g(t)), in the x,y plane. This concentration can only be represented using a mathematically singular object such as a (Schwartz) distribution. Its use for imaging requires a coarse-graining operation, which is described in this study. Subsequently, removal of the coarse-graining parameter is accomplished using the ergodic theorem. The resulting expression for joint entropy is applied to several data sets, showing the utility of the concept for both materials characterization and detection of targeted liquid nanoparticle ultrasonic contrast agents. In all cases, the sensitivity of these techniques matches or exceeds, sometimes by a factor of two, that demonstrated in previous studies that employed signal energy or alternate entropic quantities
High contrast ultrasonic imaging of resin-rich regions in graphite/epoxy composites using entropy
This study compares different approaches for imaging a near-surface resin-rich defect in a thin graphite/epoxy plate using backscattered ultrasound. The specimen was created by cutting a circular hole in the second ply; this region filled with excess resin from the graphite/epoxy sheets during the curing process. Backscat-tered waveforms were acquired using a 4 in. focal length, 5MHz center frequency broadband transducer, scanned on a 100 Ă— 100 grid of points that were 0.03 Ă— 0.03 in. apart. The specimen was scanned with the defect side closest to the transducer. Consequently, the reflection from the resin-rich region cannot be gated from the large front-wall echo. At each point in the grid 256 waveforms were averaged together and subsequently used to produce peak-to-peak, Signal Energy (sum of squared digitized waveform values), as well as entropy images of two different types (a Renyi entropy, and a joint entropy). As the figure shows, all of the entropy images exhibit better border delineation and defect contrast than the either the peak-to-peak or Signal Energy. The best results are obtained using the joint entropy of the backscattered waveforms with a reference function. Two different references are examined. The first is a reflection of the insonifying pulse from a stainless steel reflector. The second is an approximate optimum obtained from an iterative parametric search. The joint entropy images produced using this reference exhibit three times the contrast obtained in previous studies
Entropy vs. Energy Waveform Processing: A Comparison Based on the Heat Equation
Virtually all modern imaging devices collect electromagnetic or acoustic waves and use the energy carried by these waves to determine pixel values to create what is basically an “energy” picture. However, waves also carry “information,” as quantified by some form of entropy, and this may also be used to produce an “information” image. Numerous published studies have demonstrated the advantages of entropy, or “information imaging”, over conventional methods. The most sensitive information measure appears to be the joint entropy of the collected wave and a reference signal. The sensitivity of repeated experimental observations of a slowly-changing quantity may be defined as the mean variation (i.e., observed change) divided by mean variance (i.e., noise). Wiener integration permits computation of the required mean values and variances as solutions to the heat equation, permitting estimation of their relative magnitudes. There always exists a reference, such that joint entropy has larger variation and smaller variance than the corresponding quantities for signal energy, matching observations of several studies. Moreover, a general prescription for finding an “optimal” reference for the joint entropy emerges, which also has been validated in several studies
LS Peg: A Low-Inclination SW Sextantis-Type Cataclysmic Binary with High-Velocity Balmer Emission Line Wings
We present time-resolved spectroscopy and photometry of the bright
cataclysmic variable LS Peg (= S193). The Balmer lines exhibit broad,
asymmetric wings Doppler-shifted by about 2000 km/s at the edges, while the HeI
lines show phase-dependent absorption features strikingly similar to SW
Sextantis stars, as well as emission through most of the phase. The CIII/NIII
emission blend does not show any phase dependence. From velocities of Halpha
emission lines, we determine an orbital period of 0.174774 +/- 0.000003 d (=
4.1946 h), which agrees with Szkody's (1995) value of approximately 4.2 hours.
No stable photometric signal was found at the orbital period. A non-coherent
quasi-periodic photometric signal was seen at a period of 20.7 +/- 0.3 min.
The high-velocity Balmer wings most probably arise from a stream re-impact
point close to the white dwarf. We present simulated spectra based on a
kinematic model similar to the modified disk-overflow scenario of Hellier &
Robinson (1994). The models reproduce the broad line wings, though some other
details are unexplained.
Using an estimate of dynamical phase based on the model, we show that the
phasing of the emission- and absorption-line variations is consistent with that
in (eclipsing) SW Sex stars. We therefore identify LS Peg as a low-inclination
SW Sex star.
Our model suggests i = 30 deg, and the observed absence of any photometric
signal at the orbital frequency establishes i < 60 deg. This constraint puts a
severe strain on interpretations of the SW Sex phenomenon which rely on disk
structures lying slightly out of the orbital plane.Comment: 29 pages, 13 figures, to be published in PASP Feb. 199
FUSE Observations of a Full Orbit of Hercules X-1: Signatures of Disk, Star, and Wind
We observed an entire 1.7 day orbit of the X-ray binary Hercules X-1 with the
Far Ultraviolet Spectroscopic Explorer (FUSE). Changes in the O VI 1032,1037
line profiles through eclipse ingress and egress indicate a Keplerian accretion
disk spinning prograde with the orbit. These observations may show the first
double-peaked accretion disk line profile to be seen in the Hercules X-1
system. Doppler tomograms of the emission lines show a bright spot offset from
the Roche lobe of the companion star HZ Her, but no obvious signs of the
accretion disk. Simulations show that the bright spot is too far offset from
the Roche lobe to result from uneven X-ray heating of its surface. The absence
of disk signatures in the tomogram can be reproduced in simulations which
include absorption from a stellar wind. We attempt to diagnose the state of the
emitting gas from the C III 977, C III 1175, and N III 991 emission lines. The
latter may be enhanced through Bowen fluorescence.Comment: Accepted for publication in The Astrophysical Journa
Boundaries of Semantic Distraction: Dominance and Lexicality Act at Retrieval
Three experiments investigated memory for semantic information with the goal of determining boundary conditions for the manifestation of semantic auditory distraction. Irrelevant speech disrupted the free recall of semantic category-exemplars to an equal degree regardless of whether the speech coincided with presentation or test phases of the task (Experiment 1) and occurred regardless of whether it comprised random words or coherent sentences (Experiment 2). The effects of background speech were greater when the irrelevant speech was semantically related to the to-be-remembered material, but only when the irrelevant words were high in output dominance (Experiment 3). The implications of these findings in relation to the processing of task material and the processing of background speech is discussed
Spectroscopy and Component Masses of the Eclipsing Dwarf Nova HS0907+1902
HS0907+1902 was recently discovered to be one of a handful of deeply
eclipsing dwarf novae with periods longward of the 2 -- 3 hr `gap'. This paper
presents orbit-resolved spectra and time series photometry of an eclipse. The
apparent velocity amplitude of the M-dwarf secondary is K_2 = 297 +- 15 km/s.
The phase of the radial velocities of the H-alpha emission line wings agrees
accurately (for once) with the phase of the white-dwarf motion deduced from the
eclipse, and an estimate of the emission-line velocity amplitude yields K1 =
115 +- 7 km/s. The eclipse width is delta-phi = 0.060 +- 0.005. At face value,
these measurements yield mass estimates of M1 = 0.99 +- 0.12 solar masses for
the white dwarf and M2 = 0.38 +- 0.06 solar masses for the secondary. The
eclipse width and nominal mass ratio constrain the binary inclination to be
77.3 +- 0.9 degree. The influence of systematic uncertainties on these values
is discussed; the conclusion that the white dwarf is somewhat more massive than
typical field white dwarfs appears to be robust.
The H-alpha emission line profile out of eclipse is only slightly
double-peaked, but the line shows a strong rotational disturbance in eclipse.
Models of the line profile through eclipse using a flat, Keplerian disk do not
give a good quantitative match to the observations.Comment: One tex file, and 7 figures Replaced because of typo in abstract
(should be M2=0.38+-0.06
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