1,638 research outputs found
Crossed-boson exchange contribution and Bethe-Salpeter equation
The contribution to the binding energy of a two-body system due to the
crossed two-boson exchange contribution is calculated, using the Bethe-Salpeter
equation. This is done for distinguishable, scalar particles interacting via
the exchange of scalar massive bosons. The sensitivity of the results to the
off-shell behavior of the operator accounting for this contribution is
discussed. Large corrections to the Bethe-Salpeter results in the ladder
approximation are found. For neutral scalar bosons, the mass obtained for the
two-body system is close to what has been calculated with various forms of the
instantaneous approximation, including the standard non-relativistic approach.
The specific character of this result is demonstrated by a calculation
involving charged bosons, which evidences a quite different pattern. Our
results explain for some part those obtained by Nieuwenhuis and Tjon on a
different basis. Some discrepancy appears with increasing coupling constants,
suggesting the existence of sizeable contributions involving more than
two-boson exchanges.Comment: 13 pages, 5 .eps figures, submitted to 'Few Body Systems
Oh, the education (you think) you’ll have! Relative deprivation and students’ academic expectations, aspirations, and attainment
Scholars generally agree that financial deprivation negatively affects students’ educational outcomes. However, while absolute levels of resources are important, individuals’ perceived relative economic wellbeing also shape their educational outcomes. This article asks whether attending school with peers from comparably richer families is related to adolescents’ educational expectations, aspirations, university plans, and university attainment. We test the relative deprivation theory by comparing three different forms of the Yitzhaki Index. Data for this study comes from the Taiwan Youth Project, which consists of two cohorts of adolescents (N = 5098) from 162 middle school classrooms. The results show that relative deprivation in the classroom is negatively related to students’ educational expectations, aspirations, and plans to attend university. Yet, relatively deprivation is not associated with higher educational attainment when controlling for absolute measures of family background. These results highlight the need for a more nuanced understanding of perceived relative economic disadvantages in shaping student outcomes
Application rates to undergraduate programs in Information Technology in Australian universities
Over the past decade, there has been much discussion regarding both the supply and the current and potential demand for information technology-oriented graduates in Australia with numerous surveys and market analyses being undertaken. Some surveys have focussed on the supply of graduates from the tertiary and VET sectors and their demand in Australian industry, while others discuss enrolment statistics into IT based University and VET sector courses. Few, however, investigate application rates to IT courses. At the same time, there has been a general, and in some cases significant, decline in the application rates for some science and engineering courses prompting universities to review their awards with a view to making them more attractive to students and industry. Although this study takes advantage of the centralised admissions systems used in Australia, data available elsewhere shows that the results may be applicable more broadly
An analysis of application rates to programs in information technology, science, and engineering
A shift away from generic undergraduate degrees toward an emphasis on vocationally oriented qualifications has been evident in the awards offered by higher education institutions in Australia over the past few years. This has included those in information technology, science and engineering, where the growth in the number of, and variation in, awards has been particularly evident. The past few years have also seen a general, and in some cases significant, decline in the application rates for some forms of science and engineering. This has prompted many institutions to look at their awards with a view to making them more attractive, both to students and industry, often through the development of more highly specialized awards. In this paper, the authors investigate application trends for information technology, science and engineering awards from a number of perspectives, including the market perceptions of the institution offering the degree. Although the paper focuses on three broad categories of awards - information technology, science and engineering - some lessons may be appropriate for other disciplines. Moreover, although this study takes advantage of the centralized admissions systems used in Australia, available indicators show that the results may well be applicable in the United States and the U.K. and possibly elsewhere
First-Order Logic Theorem Proving and Model Building via Approximation and Instantiation
In this paper we consider first-order logic theorem proving and model
building via approximation and instantiation. Given a clause set we propose its
approximation into a simplified clause set where satisfiability is decidable.
The approximation extends the signature and preserves unsatisfiability: if the
simplified clause set is satisfiable in some model, so is the original clause
set in the same model interpreted in the original signature. A refutation
generated by a decision procedure on the simplified clause set can then either
be lifted to a refutation in the original clause set, or it guides a refinement
excluding the previously found unliftable refutation. This way the approach is
refutationally complete. We do not step-wise lift refutations but conflicting
cores, finite unsatisfiable clause sets representing at least one refutation.
The approach is dual to many existing approaches in the literature because our
approximation preserves unsatisfiability
Sensorimotor Alpha Activity is Modulated in Response to the Observation of Pain in Others
The perception–action account of empathy states that observation of another person's state automatically activates a similar state in the observer. It is still unclear in what way ongoing sensorimotor alpha oscillations are involved in this process. Although they have been repeatedly implicated in (biological) action observation and understanding communicative gestures, less is known about their role in vicarious pain observation. Their role is understood as providing a graded inhibition through functional inhibition, thereby streamlining information flow through the cortex. Although alpha oscillations have been shown to have at least visual and sensorimotor origins, only the latter are expected to be involved in the empathetic response. Here, we used magnetoencephalography, allowing us to spatially distinguish and localize oscillatory components using beamformer source reconstruction. Subjects observed realistic pictures of limbs in painful and no-pain (control) conditions. As predicted, time–frequency analysis indeed showed increased alpha suppression in the pain condition compared to the no-pain condition. Although both pain and no-pain conditions suppressed alpha- and beta-band activity at both posterior and central sensors, the pain condition suppressed alpha more only at central sensors. Source reconstruction localized these differences along the central sulcus. Our results could not be accounted for by differences in the evoked fields, suggesting a unique role of oscillatory activity in empathetic responses. We argue that alpha oscillations provide a unique measure of the underlying functional architecture of the brain, suggesting an automatic disinhibition of the sensorimotor cortices in response to the observation of pain in others
Abstract Canonical Inference
An abstract framework of canonical inference is used to explore how different
proof orderings induce different variants of saturation and completeness.
Notions like completion, paramodulation, saturation, redundancy elimination,
and rewrite-system reduction are connected to proof orderings. Fairness of
deductive mechanisms is defined in terms of proof orderings, distinguishing
between (ordinary) "fairness," which yields completeness, and "uniform
fairness," which yields saturation.Comment: 28 pages, no figures, to appear in ACM Trans. on Computational Logi
Hierarchic Superposition Revisited
Many applications of automated deduction require reasoning in first-order
logic modulo background theories, in particular some form of integer
arithmetic. A major unsolved research challenge is to design theorem provers
that are "reasonably complete" even in the presence of free function symbols
ranging into a background theory sort. The hierarchic superposition calculus of
Bachmair, Ganzinger, and Waldmann already supports such symbols, but, as we
demonstrate, not optimally. This paper aims to rectify the situation by
introducing a novel form of clause abstraction, a core component in the
hierarchic superposition calculus for transforming clauses into a form needed
for internal operation. We argue for the benefits of the resulting calculus and
provide two new completeness results: one for the fragment where all
background-sorted terms are ground and another one for a special case of linear
(integer or rational) arithmetic as a background theory
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