549 research outputs found
The sensitivity of the calculation of ΔV to vehicle and impact parameters
AbstractΔV is frequently used to describe collision severity, and is often used by accident investigators to estimate speeds of vehicles prior to a collision, and by researchers looking for correlations between severity and outcome. This study identifies how ΔV varies over a wide range of input uncertainties allowing the direct comparison of different methods of input data collection in terms of their effect on uncertainty in the calculation of ΔV.Software was developed to implement this sensitivity analysis and was validated against examples presented in the CRASH3 manual. The findings are therefore representative of, and relevant to, commercially available tools such as CRASH3 and AIDamage.It is possible to measure the vehicle and collision parameters with sufficient accuracy to determine ΔV to a level of precision that is useful to predict occupant fatality. In many cases, ΔV is largely insensitive to the input parameter and category values or values determined from photographs may be used. A vehicle specific value of the stiffness parameter B should be used. Direct measurement of crush measurements and vehicle mass (including the best estimates of fluid loss) should be used. Similarly the mass of occupants and cargo should be measured directly rather than estimated from 50th centile values. Calculation of ΔV is sensitive to PDOF which should be measured with a precision of better than ±6°
Preprints and scholarly communication : an exploratory qualitative study of adoption, practices, drivers and barriers
Background: Since 2013, there has been a dramatic increase in the number of preprint servers. Little is known about the position of researchers, funders, research performing organisations and other stakeholders with respect to this fast-paced landscape. In this article, we explore the perceived benefits and challenges of preprint posting, alongside issues including infrastructure and financial sustainability. We also discuss the definition of a ‘preprint’ in different communities, and the impact this has on uptake.
Methods: This study is based on 38 semi-structured interviews of key stakeholders, based on a purposive heterogeneous sampling approach and undertaken between October 2018 and January 2019. Interviewees were primarily drawn from biology, chemistry and psychology, where use of preprints is growing. Interviews were recorded, transcribed and subjected to thematic analysis to identify trends. Interview questions were designed based on Innovation Diffusion Theory, which was also used to interpret our results.
Results: Participants were conscious of the rising prominence of preprints and cited early and fast dissemination as their most appealing feature. Preprints were also considered to enable broader access to scientific literature and increased opportunities for informal commenting. The main concerns related to the lack of quality assurance and the ‘Ingelfinger rule’. We identified trust as an essential factor in preprint posting, and highlight the enabling role of Twitter in showcasing preprints.
Conclusions: The preprints landscape is evolving fast, and disciplinary communities are at different stages in the innovation diffusion process. The landscape is characterised by experimentation, which leads to the conclusion that a one-size-fits-all approach to preprints is not feasible. Cooperation and active engagement between the stakeholders involved will play an important role going forward. We share questions for the further development of the preprints landscape, with the most important being whether preprint posting will develop as a publisher- or researcher-centric practice
Energy Level Quasi-Crossings: Accidental Degeneracies or Signature of Quantum Chaos?
In the field of quantum chaos, the study of energy levels plays an important
role. The aim of this review paper is to critically discuss some of the main
contributions regarding the connection between classical dynamics,
semi-classical quantization and spectral statistics of energy levels. In
particular, we analyze in detail degeneracies and quasi-crossings in the
eigenvalues of quantum Hamiltonians which are classically non-integrable.
Summary: 1. Introduction; 2. Quasi-Crossing and Chaos; 3. Molecular
Spectroscopy; 4. Nuclear Models; 4.1 Zirnbauer-Verbaashot-Weidenmuller Model;
4.2 Lipkin-Meshow-Glick Model; 5. Particle Physics and Field Theory; 6.
Conclusions.Comment: 26 pages, Latex, 9 figures, to be published in International Journal
of Modern Physics
Singular continuous spectra in a pseudo-integrable billiard
The pseudo-integrable barrier billiard invented by Hannay and McCraw [J.
Phys. A 23, 887 (1990)] -- rectangular billiard with line-segment barrier
placed on a symmetry axis -- is generalized. It is proven that the flow on
invariant surfaces of genus two exhibits a singular continuous spectral
component.Comment: 4 pages, 2 figure
Uniform approximations for pitchfork bifurcation sequences
In non-integrable Hamiltonian systems with mixed phase space and discrete
symmetries, sequences of pitchfork bifurcations of periodic orbits pave the way
from integrability to chaos. In extending the semiclassical trace formula for
the spectral density, we develop a uniform approximation for the combined
contribution of pitchfork bifurcation pairs. For a two-dimensional double-well
potential and the familiar H\'enon-Heiles potential, we obtain very good
agreement with exact quantum-mechanical calculations. We also consider the
integrable limit of the scenario which corresponds to the bifurcation of a
torus from an isolated periodic orbit. For the separable version of the
H\'enon-Heiles system we give an analytical uniform trace formula, which also
yields the correct harmonic-oscillator SU(2) limit at low energies, and obtain
excellent agreement with the slightly coarse-grained quantum-mechanical density
of states.Comment: LaTeX, 31 pp., 18 figs. Version (v3): correction of several misprint
Invariant varieties of periodic points for some higher dimensional integrable maps
By studying various rational integrable maps on with
invariants, we show that periodic points form an invariant variety of dimension
for each period, in contrast to the case of nonintegrable maps in which
they are isolated. We prove the theorem: {\it `If there is an invariant variety
of periodic points of some period, there is no set of isolated periodic points
of other period in the map.'}Comment: 24 page
A pseudointegrable Andreev billiard
A circular Andreev billiard in a uniform magnetic field is studied. It is
demonstrated that the classical dynamics is pseudointegrable in the same sense
as for rational polygonal billiards. The relation to a specific polygon, the
asymmetric barrier billiard, is discussed. Numerical evidence is presented
indicating that the Poincare map is typically weak mixing on the invariant
sets. This link between these different classes of dynamical systems throws
some light on the proximity effect in chaotic Andreev billiards.Comment: 5 pages, 5 figures, to appear in PR
Classical Dynamics of Anyons and the Quantum Spectrum
In this paper we show that (a) all the known exact solutions of the problem
of N-anyons in oscillator potential precisely arise from the collective degrees
of freedom, (b) the system is pseudo-integrable ala Richens and Berry. We
conclude that the exact solutions are trivial thermodynamically as well as
dynamically.Comment: 19 pages, ReVTeX, IMSc/93/0
Accelerating scholarly communication : the transformative role of preprints
The preprints landscape is evolving rapidly, and the full impact of sharing articles in pre-review form remains to be seen. After publishing our initial report ‘The evolving preprint landscape' in 2018 and a slide deck 'Practices, drivers and impediments in the use of preprints' in spring 2019, we are now able to share our final report 'Accelerating scholarly communication - The transformative role of preprints'.
Preprints (tentatively defined as versions of research papers typically prior to peer review and publication in a journal) have become more widespread in a number of disciplines over the last few years, partly to counter the slow pace of the traditional publishing process and partly to allow authors to reach a broader audience. Knowledge Exchange, in collaboration with Research Consulting, investigated this phenomenon in order to explore the current place of preprints in the scholarly communication process.
In this context, we interviewed 38 stakeholders, including researchers, research performing organisations, research funding organisations and preprint service providers, and reviewed over 60 literature sources.
Our key results include the benefits and challenges for researchers in using preprints as well as the establishment of trust without peer review including the role of twitter. Moreover, we reflect on the responsibilities for preprint posting in the future and the role of scholarly communities and commercial publishers.
In addition to our latest report you can find our detailed analysis in the preprint 'Preprints and Scholarly Communication: Adoption, Practices, Drivers and Barriers'Â by Research Consulting on F1000.Â
* Please note two corrections to Appendix A of the report 'Accelerating scholarly communication - The transformative role of preprints'. In table A2:
Thomas Lösch's affiliation is listed as Universität Bamberg. The correct affiliation is DIPF Leibniz Institute for Research and Information in Education
Zoe Ancion's affiliation is listed as DIPF Leibniz Institute for Research and Information in Education. The correct affiliation is AN
Semiclassical Inequivalence of Polygonalized Billiards
Polygonalization of any smooth billiard boundary can be carried out in
several ways. We show here that the semiclassical description depends on the
polygonalization process and the results can be inequivalent. We also establish
that generalized tangent-polygons are closest to the corresponding smooth
billiard and for de Broglie wavelengths larger than the average length of the
edges, the two are semiclassically equivalent.Comment: revtex, 4 ps figure
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