3,827 research outputs found
Hydrogen maser development at Laval University
The physical construction of two hydrogen masers is described and results of measurements made on one of the masers are given. These include: cavity Q, thermal time constant, line Q, signal power output, magnetic shielding factor. Preliminary results indicate that the frequency stability will be mainly affected by the thermal of the cavity. The magnetic field and the barometric fluctuations should not affect the maser at the stability level above a few parts in 10 to the 15th power, which is the goal for averaging times of several hours
Slow flows of yield stress fluids: complex spatio-temporal behaviour within a simple elasto-plastic model
A minimal athermal model for the flow of dense disordered materials is
proposed, based on two generic ingredients: local plastic events occuring above
a microscopic yield stress, and the non-local elastic release of the stress
these events induce in the material. A complex spatio-temporal rheological
behaviour results, with features in line with recent experimental observations.
At low shear rates, macroscopic flow actually originates from collective
correlated bursts of plastic events, taking place in dynamically generated
fragile zones. The related correlation length diverges algebraically at small
shear rates. In confined geometries bursts occur preferentially close to the
walls yielding an intermittent form of flow localization.Comment: 4 pages, 4 figure
The Rise and Expansion of Research in Media Economics
Media economics is the study of choices, what incentives and disincentives influence them, and how to make better choices to inform company decisions, public understanding, and policymaking. The present paper reviews the development of the field since the beginning in the 1970s with scholars such as Alfonso Nieto at the University of Navarra, Nadine Toussaint Desmoulins at the University of Paris 2, and Karl Erik Gustafsson at the University of Gothenburg to the emerging of the field with more scholars from different countries. Nowadays the field of media economics research has matured and become multifaceted, encompassing a wide variety of theories and approaches necessary to explore multiple developments and issues in media structures and operations. It is particularly relevant because media and communications are amid a massive transformation created by technology, social changes, and changes in demand. Expansion of commercial media and personal communications, new means of production and distribution, and new economic arrangements are altering well established relationship and interactions in media. This situation requires clear mindedness and knowledge to comprehend the developments and to develop the best individual, firm, and social responses to the challenges arising from the changes
Deep Radio Imaging of Globular Clusters and the Cluster Pulsar Population
We have obtained deep multifrequency radio observations of seven globular
clusters using the Very Large Array and the Australia Telescope Compact Array.
Five of these, NGC 6440, NGC 6539, NGC 6544, NGC 6624 and Terzan 5 had
previously been detected in a shallower survey for steep spectrum radio sources
in globular clusters (Fruchter and Goss 1990). The sixth, the rich globular
cluster, Liller 1, had heretofore been undetected in the radio, and the
seventh, 47 Tucanae, was not included in our original survey. High resolution 6
and 20 cm images of three of the clusters, NGC 6440, NGC 6539, NGC 6624 reveal
only point sources coincident with pulsars which have been discovered
subsequent to our first imaging survey. 21 and 18 cm images reveal several
point sources within a few core-radii of the center of 47 Tuc. Two of these are
identified pulsars, and a third, which is both variable and has a steep
spectrum, is also most likely a pulsar previously identified by a pulsed
survey. However, the 6, 20 and 90 cm images of NGC 6544, Liller 1 and Terzan 5
display strong steep-spectrum emission which cannot be associated with known
pulsars. The image of the rich cluster Terzan 5 displays numerous point sources
within , or 4 core radii of the cluster center. The density of these
objects rises rapidly toward the core, where an elongated region of emission is
found. The brightest individual sources, as well as the extended emission,
possess the steep spectra expected of pulsars. Furthermore, the flux
distribution of the sources agrees well with the standard pulsar luminosity
function. The total luminosity and number of objects observed suggest that
Terzan 5 contains more pulsars than any other Galactic globular cluster.Comment: 33 pages, 6 Postscript figures; Accepted for publication in the
Astrophysical Journal; abstract abridged. PDF version also available at
http://nemesis.stsci.edu/~fruchter/fg99/fg99.pd
Generating socially appropriate tutorial dialog
Analysis of student-tutor coaching dialogs suggest that good human tutors attend to and attempt to influence the motivational state of learners. Moreover, they are sensitive to the social face of the learner, and seek to mitigate the potential face threat of their comments. This paper describes a dialog generator for pedagogical agents that takes motivation and face threat factors into account. This enables the agent to interact with learners in a socially appropriate fashion, and foster intrinsic motivation on the part of the learner, which in turn may lead to more positive learner affective states
Global embedding of the Kerr black hole event horizon into hyperbolic 3-space
An explicit global and unique isometric embedding into hyperbolic 3-space,
H^3, of an axi-symmetric 2-surface with Gaussian curvature bounded below is
given. In particular, this allows the embedding into H^3 of surfaces of
revolution having negative, but finite, Gaussian curvature at smooth fixed
points of the U(1) isometry. As an example, we exhibit the global embedding of
the Kerr-Newman event horizon into H^3, for arbitrary values of the angular
momentum. For this example, considering a quotient of H^3 by the Picard group,
we show that the hyperbolic embedding fits in a fundamental domain of the group
up to a slightly larger value of the angular momentum than the limit for which
a global embedding into Euclidean 3-space is possible. An embedding of the
double-Kerr event horizon is also presented, as an example of an embedding
which cannot be made global.Comment: 16 pages, 13 figure
Ground-state behavior of the 3d +/-J random-bond Ising model
Large numbers of ground states of the three-dimensional random-bond
Ising model are calculated for sizes up to using a combination of a
genetic algorithm and Cluster-Exact Approximation. Several quantities are
calculated as function of the concentration of the antiferromagnetic bonds.
The critical concentration where the ferromagnetic order disappears is
determined using the Binder cumulant of the magnetization. A value of
is obtained. From the finite-size behavior of the Binder
cumulant and the magnetization critical exponents and
are calculated.Comment: 8 pages, 11 figures, revte
Multi-score Learning for Affect Recognition: the Case of Body Postures
An important challenge in building automatic affective state
recognition systems is establishing the ground truth. When the groundtruth
is not available, observers are often used to label training and testing
sets. Unfortunately, inter-rater reliability between observers tends to
vary from fair to moderate when dealing with naturalistic expressions.
Nevertheless, the most common approach used is to label each expression
with the most frequent label assigned by the observers to that expression.
In this paper, we propose a general pattern recognition framework
that takes into account the variability between observers for automatic
affect recognition. This leads to what we term a multi-score learning
problem in which a single expression is associated with multiple values
representing the scores of each available emotion label. We also propose
several performance measurements and pattern recognition methods for
this framework, and report the experimental results obtained when testing
and comparing these methods on two affective posture datasets
New Shortwave Infrared Albedo Measurements for Snow Specific Surface Area Retrieval
Snow grain-size characterization, its vertical and temporal evolution is a key parameter for the improvement and validation of snow and radiative transfer models (optical and microwave) as well as for remote-sensing retrieval methods. We describe two optical methods, one active and one passive shortwave infrared, for field determination of the specific surface area (SSA) of snow grains. We present a new shortwave infrared (SWIR) camera approach. This new method is compared with a SWIR laser- based system measuring snow albedo with an integrating sphere (InfraRed Integrating Sphere (IRIS)). Good accuracy (10%) and reproducibility in SSA measurements are obtained using the IRIS system on snow samples having densities greater than 200 kg m-3, validated against X-ray microtomography measurements. The SWIRcam approach shows improved sensitivity to snow SSA when compared to a near-infrared camera, giving a better contrast of the snow stratigraphy in a snow pit
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