69,285 research outputs found
SMSlingshot a shared encounter in urban space
Interaction design is increasingly situated beyond the desktop and demands new approaches, if it is made for Urban Space. Public and semi-public spaces add new challenges in terms of interaction theory, technology and sociology. SMSlingshot is an interactive unban installation (also named a Shared Encounter) and research vehicle that helps to explore these new challenges
Probing the gluon self-interaction in light mesons
We investigate masses and decay constants of light mesons from a coupled
system of Dyson--Schwinger and Bethe--Salpeter equations. We explicitly take
into account dominant non-Abelian contributions to the dressed quark-gluon
vertex stemming from the gluon self-interaction. We construct the corresponding
Bethe-Salpeter kernel that satisfies the axial-vector Ward-Takahashi identity.
Our numerical treatment fully includes all momentum dependencies with all
equations solved completely in the complex plane. This approach goes well
beyond the rainbow-ladder approximation and permits us to investigate the
influence of the gluon self-interaction on the properties of mesons. As a first
result we find indications of a nonperturbative cancellation of the gluon
self-interaction contributions and pion cloud effects in the mass of the
rho-meson.Comment: 4 pages, 5 figures. Matches published version in PR
Results of the second flight test of the Loran-C receiver/data collection system
The components of the Loran-C navigation system which were developed thus far are a phase-locked-loop receiver and a microcomputer development system. The microcomputer is being used as a means of testing and implementing software to handle sensor control and navigation calculations. Currently, the microcomputer is being used to collect and record data from the receiver in addition to development work. With these components, it was possible to record receiver data over a period of time and then reduce this data to obtain statistical information. It was particularly interesting to load the equipment developed in the laboratory into an aircraft and collect data while in flight. For initial flight tests, some important considerations were how well the entire system will perform in the field, signal strength levels while on the ground and in the air, the amount of noise present, changing of signal-to-noise ratio for various aircraft configurations and maneuvers, receiver overloading due to other equipment and antennas, and the overall usefulness of Loran-C as a navigation aid
Loran-C time difference calculations
Some of the simpler mathematical equations which may be used in Loran-C navigation calculations were examined. A technique is presented to allow Loran-C time differences to be predicted at a location. This is useful for receiver performance work, and a tool for more complex calculations, such as position fixing
Bi-directional communication interface for microprocessor-to-system/370
The design and operation of a bi-directional communication interface between a microcomputer and the IBM System/370 is documented. The hardware unit interconnects a modem to interface to the S/370, the microcomputer with an EIA I/O port, and a terminal for sending and receiving data from either the microcomputer or the S/370. Also described is the software necessary for the two-way interface. This interface is designed so that no modifications need to be made to the terminal, modem, or microcomputer
A discrete martingale model of pension fund guarantees in
In this paper we present a solution to the problem of pricing guarantees of minimum returns on pension fund contributions. These guarantees exist by law in Colombia and cover all pension fund contributions made to the country's private pension fund administration companies (AFPs). As of September 1997, the funds were collecting contributions of 2.5 million affiliates with an accumulated capital of 1.8 billion dollars starting from zero in 1994. Two types of guarantees exist: on obligatory contributions and on voluntary contributions. The solutions are based on a discrete martingale approach . We show that both guarantees are equivalent to an ''option to exchange.'' However, in the case of voluntary contributions a ceiling on the payoff s must be added. Using a discrete martingale framework and a binomial solution we develop all aspects of the model that are necessary for its practical application in the context of the pension fund guarantees. Binomial formulas are obtained for both forms of guarantees. Besides solving the problem of pricing the guarantees offered by insurance fund, the contributions in terms of options theory of this paper are: i) we adapt the binomila model of options to exchange to relate the relevant parameters of the same to a continuous-time lognormal process; ii) we provide a binomial solution to the problem of an option to exchange with a ceiling. We then investigate the incentives that the current fixed-price system introduces and propose possible systems of incentives that can be used to encourage higher-risk investment by the AFP's and a shift of the fund's portfolio to risky equity and debt. Given the country's effort to encourage capital markets development and the financing of the real sector via private financial markets, this strategy appears to be desirable from the social and economic point of view.Pension funds, guarantees, options pricing, Colombia, Latin America
Measurement of the Mass Profile of Abell 1689
In this letter we present calibrated mass and light profiles of the rich
cluster of galaxies Abell 1689 out to 1 Mpc from the center. The high
surface density of faint blue galaxies at high redshift, selected by their low
surface brightness, are unique tools for mapping the projected mass
distribution of foreground mass concentrations. The systematic gravitational
lens distortions of of these background galaxies in 15\arcmin\ fields
reveal detailed mass profiles for intervening clusters of galaxies, and are a
direct measure of the growth of mass inhomogeneity. The mass is measured
directly, avoiding uncertainties encountered in velocity or X-ray derived mass
estimates.
Mass in the rich cluster Abell 1689 follows smoothed light, outside 100
h kpc, with a rest-frame V band mass-to-light ratio of
. Near the cluster center, mass appears to be more
smoothly distributed than light. Out to a radius of 1 Mpc the total
mass follows a steeper than isothermal profile. Comparing with preliminary high
resolution N-body clustering simulations for various cosmogonies on these
scales, these data are incompatible with hot dark matter, a poor fit to most
mixed dark matter models, and favor open or cold dark matter.
Substructure is seen in both the mass and the light, but detailed
correspondence is erased on scales less than 100 kpc.Comment: 13 pages, uuencoded, compressed postscript file, 2 figures included
additional 1Mbyte figure available on request. Only change is that in
original errorbars on Fig. 5 were a factor of 2 too big
Optimal Addition of Images for Detection and Photometry
In this paper we describe weighting techniques used for the optimal
coaddition of CCD frames with differing characteristics. Optimal means maximum
signal-to-noise (s/n) for stellar objects. We derive formulae for four
applications: 1) object detection via matched filter, 2) object detection
identical to DAOFIND, 3) aperture photometry, and 4) ALLSTAR profile-fitting
photometry. We have included examples involving 21 frames for which either the
sky brightness or image resolution varied by a factor of three. The gains in
s/n were modest for most of the examples, except for DAOFIND detection with
varying image resolution which exhibited a substantial s/n increase. Even
though the only consideration was maximizing s/n, the image resolution was seen
to improve for most of the variable resolution examples. Also discussed are
empirical fits for the weighting and the availability of the program, WEIGHT,
used to generate the weighting for the individual frames. Finally, we include
appendices describing the effects of clipping algorithms and a scheme for
star/galaxy and cosmic ray/star discrimination.Comment: 27 pages (uuencoded compressed postscript), 199
Network dependence in multi-indexed data on international trade flows
Faced with the problem that conventional multidimensional fixed effects models only focus on unobserved heterogeneity, but ignore any potential cross-sectional dependence due to network interactions, we introduce a model of trade flows between countries over time that allows for network dependence in flows, based on sociocultural connectivity structures. We show that conventional multidimensional fixed effects model specifications exhibit cross-sectional dependence between countries that should be modeled to avoid simultaneity bias. Given that the source of network interaction is unknown, we propose a panel gravity model that examines multiplenetwork interaction structures, using Bayesian model probabilities to determine those most consistent with the sample data. This is accomplished with the use of computationally efficient Markov Chain Monte Carlo estimation methods that produce a Monte Carlo integration estimate of the log-marginal likelihood that can be used for model comparison. Application of the model to a panel of trade flows points to network spillover effects, suggesting the presence of network dependence and biased estimates from conventional trade flow specifications. The most important sources of network dependence were found to be membership in trade organizations, historical colonial ties, common currency, and spatial proximity of countries.Series: Working Papers in Regional Scienc
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