85 research outputs found
The Pursuit of Truth to Make Men Free
https://epublications.marquette.edu/mupress-book/1021/thumbnail.jp
Photon Propagation in Space-Time with a Compactified Spatial Dimension
The one-loop effects of vacuum polarization induced by untwisted fermions in
QED in a nonsimply connected space-time with topology are
investigated. It is found that photon propagation in this system is
anisotropic, appearing several massive photon modes and a superluminal
transverse mode. For small compactification radius , the superluminal
velocity increases logarithmically with . At low energies the photon masses
lead to an effective confinement of the gauge fields into a (2+1)-dimensional
manifold transverse to the compactified direction. The system shows a
topologically induced directional superconductivity.Comment: 5 pages, to appear in PL
Neutrino Propagation in a Strongly Magnetized Medium
We derive general expressions at the one-loop level for the coefficients of
the covariant structure of the neutrino self-energy in the presence of a
constant magnetic field. The neutrino energy spectrum and index of refraction
are obtained for neutral and charged media in the strong-field limit () using the lowest Landau level
approximation. The results found within the lowest Landau level approximation
are numerically validated, summing in all Landau levels, for strong and weakly-strong fields. The neutrino energy in
leading order of the Fermi coupling constant is expressed as the sum of three
terms: a kinetic-energy term, a term of interaction between the magnetic field
and an induced neutrino magnetic moment, and a rest-energy term. The leading
radiative correction to the kinetic-energy term depends linearly on the
magnetic field strength and is independent of the chemical potential. The other
two terms are only present in a charged medium. For strong and weakly-strong
fields, it is found that the field-dependent correction to the neutrino energy
in a neutral medium is much larger than the thermal one. Possible applications
to cosmology and astrophysics are considered.Comment: 23 pages, 4 figures. Corrected misprints in reference
Modulation control and spectral shaping of optical fiber supercontinuum generation in the picosecond regime
Numerical simulations are used to study how fiber supercontinuum generation
seeded by picosecond pulses can be actively controlled through the use of input
pulse modulation. By carrying out multiple simulations in the presence of
noise, we show how tailored supercontinuum Spectra with increased bandwidth and
improved stability can be generated using an input envelope modulation of
appropriate frequency and depth. The results are discussed in terms of the
non-linear propagation dynamics and pump depletion.Comment: Aspects of this work were presented in Paper ThJ2 at OECC/ACOFT 2008,
Sydney Australia 7-10 July (2008). Journal paper submitted for publication 30
July 200
Comparison of NITAG policies and working processes in selected developed countries
BACKGROUND: Vaccines are specific medicines characterized by two country-specific market access processes: (1) a recommendation by National Immunization Technical Advisory Group (NITAG), and (2) a funding policy decision. OBJECTIVES: The objective of this study was to compare and analyze NITAGs of 13 developed countries by describing vaccination committees' bodies and working processes. METHODS: Information about NITAGs bodies and working processes was searched from official sources from June 2011 to November 2012. Retrieved information was completed from relevant articles identified through a systematic literature review and by information provided by direct contact with NITAGs or parent organizations. An expert panel was also conducted to discuss, validate, and provide additional input on obtained results. RESULTS: While complete information, defined as 100%, was retrieved only for the UK, at least 80% of data was retrieved for 9 countries out of the 13 selected countries. Terms of references were identified in 7 countries, and the main mission for all NITAGs was to provide advice for National immunization programs. However, these terms of references did not fully encompass all the actual missions of the NITAGs. Decision analysis frameworks were identified for 10 out of the 13, and all NITAGs considered at least four criteria for decision-making: disease burden, efficacy/effectiveness, safety and cost-effectiveness. Advices were published by most NITAGs, but few NITAGs published meeting agendas and minutes. Only the United States had open meetings. CONCLUSIONS: This study supports previous findings about the disparities in NITAGs processes which could potentially explain the disparity in access to vaccinations and immunization programs across Europe. With NITAGs recommendations being used by policy decision makers for implementation and funding of vaccine programs, guidances should be well-informed and transparent to ensure National Immunization Programs' (NIP) credibility among the public and health care professionals
How does the electromagnetic field couple to gravity, in particular to metric, nonmetricity, torsion, and curvature?
The coupling of the electromagnetic field to gravity is an age-old problem.
Presently, there is a resurgence of interest in it, mainly for two reasons: (i)
Experimental investigations are under way with ever increasing precision, be it
in the laboratory or by observing outer space. (ii) One desires to test out
alternatives to Einstein's gravitational theory, in particular those of a
gauge-theoretical nature, like Einstein-Cartan theory or metric-affine gravity.
A clean discussion requires a reflection on the foundations of electrodynamics.
If one bases electrodynamics on the conservation laws of electric charge and
magnetic flux, one finds Maxwell's equations expressed in terms of the
excitation H=(D,H) and the field strength F=(E,B) without any intervention of
the metric or the linear connection of spacetime. In other words, there is
still no coupling to gravity. Only the constitutive law H= functional(F)
mediates such a coupling. We discuss the different ways of how metric,
nonmetricity, torsion, and curvature can come into play here. Along the way, we
touch on non-local laws (Mashhoon), non-linear ones (Born-Infeld,
Heisenberg-Euler, Plebanski), linear ones, including the Abelian axion (Ni),
and find a method for deriving the metric from linear electrodynamics (Toupin,
Schoenberg). Finally, we discuss possible non-minimal coupling schemes.Comment: Latex2e, 26 pages. Contribution to "Testing Relativistic Gravity in
Space: Gyroscopes, Clocks, Interferometers ...", Proceedings of the 220th
Heraeus-Seminar, 22 - 27 August 1999 in Bad Honnef, C. Laemmerzahl et al.
(eds.). Springer, Berlin (2000) to be published (Revised version uses
Springer Latex macros; Sec. 6 substantially rewritten; appendices removed;
the list of references updated
Should science educators deal with the science/religion issue?
I begin by examining the natures of science and religion before looking at the ways in which they relate to one another. I then look at a number of case studies that centre on the relationships between science and religion, including attempts to find mechanisms for divine action in quantum theory and chaos theory, creationism, genetic engineering and the writings of Richard Dawkins. Finally, I consider some of the pedagogical issues that would need to be considered if the science/religion issue is to be addressed in the classroom. I conclude that there are increasing arguments in favour of science educators teaching about the science/religion issue. The principal reason for this is to help students better to learn science. However, such teaching makes greater demands on science educators than has generally been the case. Certain of these demands are identified and some specific suggestions are made as to how a science educator might deal with the science/religion issue. © 2008 Taylor & Francis
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