3,788 research outputs found
The high energy limit of the trajectory representation of quantum mechanics
The trajectory representation in the high energy limit (Bohr correspondence
principle) manifests a residual indeterminacy. This indeterminacy is compared
to the indeterminacy found in the classical limit (Planck's constant to 0)
[Int. J. Mod. Phys. A 15, 1363 (2000)] for particles in the classically allowed
region, the classically forbiden region, and near the WKB turning point. The
differences between Bohr's and Planck's principles for the trajectory
representation are compared with the differences between these correspondence
principles for the wave representation. The trajectory representation in the
high energy limit is shown to go to neither classical nor statistical
mechanics. The residual indeterminacy is contrasted to Heisenberg uncertainty.
The relationship between indeterminacy and 't Hooft's information loss and
equivalence classes is investigated.Comment: 12 pages of LaTeX. No figures. Incorporated into the "Proceedings of
the Seventh International Wigner Symposium" (ed. M. E. Noz), 24-29 August
2001, U. of Maryland. Proceedings available at
http://www.physics.umd.edu/robo
Welcher Weg? A trajectory representation of a quantum Young's diffraction experiment
The double slit problem is idealized by simplifying each slit by a point
source. A composite reduced action for the two correlated point sources is
developed. Contours of the reduced action, trajectories and loci of transit
times are developed in the region near the two point sources. The trajectory
through any point in Euclidian 3-space also passes simultaneously through both
point sources.Comment: 12 pages LaTeX2e, 9 figures. Typos corrected. Author's final
submission. A companion paper to "Interference, reduced action, and
trajectories", quant-ph/0605120. Keywords: interference, Young's experiment,
entanglement, nonlocality, trajectory representation, determinis
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‘Jugglers’, ‘copers’ and ‘strugglers’: academics’ perceptions of being a head of department in a post-1992 UK university and how it influences their future careers
This study investigates the experiences of academics who became department heads in a post-1992 UK university and explores the influence that being in the position has on their planned future academic career. Drawing on life history interviews undertaken with 17 male and female heads of department, the paper constitutes an in-depth study of their careers in the same university. The findings suggest that academics who become department heads not only need the capacity to assume a range of personal and professional identities, but need flexibility to regularly adopt and switch between them. Whether individuals can successfully balance and manage such multiple identities, or whether they experience major conflicts within or between them, greatly affects their experiences of being a head of department and seems to influence their subsequent career decisions. The paper concludes by proposing a conceptual framework and typology to interpret the career trajectories of academics that became department heads in the case university
The PAPAGENO Parallel-Parser Generator
The increasing use of multicore processors has deeply transformed
computing paradigms and applications. The wide availability of multicore systems had an impact also in the field of compiler technology, although the research on deterministic parsing did not prove to be effective in exploiting the architectural advantages, the main impediment being the inherent sequential nature of traditional LL and LR algorithms. We present PAPAGENO, an automated parser generator relying on operator precedence grammars. We complemented the PAPAGENO-generated parallel parsers with parallel lexing techniques, obtaining
near-linear speedups on multicore machines, and the same speed as Bison
parsers on sequential execution
The Cost of Stability in Coalitional Games
A key question in cooperative game theory is that of coalitional stability,
usually captured by the notion of the \emph{core}--the set of outcomes such
that no subgroup of players has an incentive to deviate. However, some
coalitional games have empty cores, and any outcome in such a game is unstable.
In this paper, we investigate the possibility of stabilizing a coalitional
game by using external payments. We consider a scenario where an external
party, which is interested in having the players work together, offers a
supplemental payment to the grand coalition (or, more generally, a particular
coalition structure). This payment is conditional on players not deviating from
their coalition(s). The sum of this payment plus the actual gains of the
coalition(s) may then be divided among the agents so as to promote stability.
We define the \emph{cost of stability (CoS)} as the minimal external payment
that stabilizes the game.
We provide general bounds on the cost of stability in several classes of
games, and explore its algorithmic properties. To develop a better intuition
for the concepts we introduce, we provide a detailed algorithmic study of the
cost of stability in weighted voting games, a simple but expressive class of
games which can model decision-making in political bodies, and cooperation in
multiagent settings. Finally, we extend our model and results to games with
coalition structures.Comment: 20 pages; will be presented at SAGT'0
Hidden Symmetry of Higher Dimensional Kerr-NUT-AdS Spacetimes
It is well known that 4-dimensional Kerr-NUT-AdS spacetime possesses the
hidden symmetry associated with the Killing-Yano tensor. This tensor is
"universal" in the sense that there exist coordinates where it does not depend
on any of the free parameters of the metric. Recently the general higher
dimensional Kerr-NUT-AdS solutions of the Einstein equations were obtained. We
demonstrate that all these metrics with arbitrary rotation and NUT parameters
admit a universal Killing-Yano tensor. We give an explicit presentation of the
Killing-Yano and Killing tensors and briefly discuss their properties.Comment: 4 pages, some discussion and references are adde
Coherent States and Modified de Broglie-Bohm Complex Quantum Trajectories
This paper examines the nature of classical correspondence in the case of
coherent states at the level of quantum trajectories. We first show that for a
harmonic oscillator, the coherent state complex quantum trajectories and the
complex classical trajectories are identical to each other. This congruence in
the complex plane, not restricted to high quantum numbers alone, illustrates
that the harmonic oscillator in a coherent state executes classical motion. The
quantum trajectories are those conceived in a modified de Broglie-Bohm scheme
and we note that identical classical and quantum trajectories for coherent
states are obtained only in the present approach. The study is extended to
Gazeau-Klauder and SUSY quantum mechanics-based coherent states of a particle
in an infinite potential well and that in a symmetric Poschl-Teller (PT)
potential by solving for the trajectories numerically. For the coherent state
of the infinite potential well, almost identical classical and quantum
trajectories are obtained whereas for the PT potential, though classical
trajectories are not regained, a periodic motion results as t --> \infty.Comment: More example
Reducing MCPA herbicide pollution at catchment scale using an agri-environmental scheme
Publication history: Accepted - 16 May 2022; Published online - 20 May 2022.In river catchments used as drinking water sources, high pesticide concentrations in abstracted waters require an expensive
treatment step prior to supply. The acid herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) is particularly
problematic as it is highly mobile in the soil-water environment following application. Here, an agri-environmental
scheme (AES) was introduced to a large-scale catchment (384 km2) to potentially reduce the burden of pesticides in
the water treatment process. The main measure offered was contractor application of glyphosate by weed wiping as
a substitute for boom spraying of MCPA, supported by educational and advisory activities. A combined innovation applied
in the assessment was, i) a full before-after-control-impact (BACI) framework over four peak application seasons
(April to October 2018 to 2021) where a neighbouring catchment (386 km2) did not have an AES and, ii) an enhanced
monitoring approach where river discharge and MCPA concentrations were measured synchronously in each catchment.
During peak application periods the sample resolution was every 7 h, and daily during quiescent winter periods.
This sampling approach enabled flow- and time-weighted concentrations to be established, and a detailed record of
export loads. These loads were up to 0.242 kg km−2 yr−1, and over an order of magnitude higher than previously reported
in the literature. Despite this, and accounting for inter-annual and seasonal variations in river discharges, the
AES catchment indicated a reduction in both flow- and time-weighted MCPA concentration of up to 21% and 24%, respectively,
compared to the control catchment. No pollution swapping was detected. Nevertheless, the percentage of
MCPA occurrences above a 0.1 μg L−1 threshold did not reduce and so the need for treatment was not fully resolved.
Although the work highlights the advantages of catchment management approaches for pollution reduction in source
water catchments, it also indicates that maximising participation will be essential for future AES.This work was carried out as part of Source to Tap (IVA5018), a project supported by the European Union's INTERREG VA Programme, managed by the Special EU Programmes Body (SEUPB)
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