30,108 research outputs found
Trial by Fire: Major-General Christopher Vokes at the Battles of the Moro River and Ortona, December 1943
During the month of December 1943, the 1st Canadian Infantry Division (1st Cdn Div) underwent the most severe trial yet experienced by Canadian troops in Italy, when it crossed the Moro River, engaged two German divisions in rapid succession and, after a week of vicious street fighting, took the town of Ortona. Hailed at the time as victories, these battles have since been the subject of considerable debate among soldiers and historians alike. Much of the controversy has revolved around the division’s commander, Major-General Christopher Vokes, who has been accused by some of mishandling his formation, and has been castigated by others for the heavy cost in lives that resulted.1 Are these verdicts too harsh? Was he solely to blame for the manner in which the battles of the Moro River and Ortona evolved, and for their tragic cost? In order to better understand Chris Vokes’ actions during his first divisional battle, it will be argued that he did indeed make mistakes but at the same time was forced to deal with an extremely difficult set of circumstances that largely dictated the course and outcome of the battle. These included a strategic situation that created the conditions for a war of attrition; an unrealistic Army Grouplevel plan; unfavourable terrain and weather; unexpected changes in German defensive tactics; the “fog of war”; and his own inexperience as a divisional commander. As a result Vokes faced the toughest challenge of his military career
On a recent proposal of faster than light quantum communication
In a recent paper, A.Y. Shiekh has discussed an experimental set-up which, in
his opinion, should make possible faster-than-light communication using the
collapse of the quantum wave function. Contrary to the many proposals which
have been presented in the past, he does not resort to an entangled state of
two systems but he works with a single particle in a superposition of two
states - corresponding to its propagation in opposite directions - one of which
goes through an appropriate interferometer. The possibility for an observer
near the interferometer to introduce or not, at his free will, a phase shifter
along one of the paths should allow to change instantaneously the probability
of finding the particle in the far-away region corresponding to the other state
of the superposition and, correspondingly, to change the intensity of a beam of
particles reaching a distant observer. In this paper we show a flaw in the
argument: once more, as it has been proved in full generality a long time ago,
the process of wave packet reduction cannot be used for superluminal
communication.Comment: 9 pages, LaTeX. Minor changes mad
Biological Carbon Sequestration and Carbon Trading Re-Visited
Biological activities that sequester carbon create CO2 offset credits that could obviate the need for reductions in fossil fuel use. Credits are earned by storing carbon in terrestrial ecosystems and wood products, although CO2 emissions are also mitigated by delaying deforestation, which accounts for one-quarter of anthropogenic CO2 emissions. However, non-permanent carbon offsets from biological activities are difficult to compare with each other and with emissions reduction because they differ in how long they prevent CO2 from entering the atmosphere. This is the duration problem. It results in uncertainty and makes it hard to determine the legitimacy of biological activities in mitigating climate change. Measuring, verifying and monitoring the carbon sequestered in sinks greatly increases transaction costs and leads to rent seeking by sellers of dubious sink credits. While biological sink activities undoubtedly help mitigate climate change and should not be neglected, it is shown that there are limits to the substitutability between temporary offset credits from these activities and emissions reduction, and that this has implications for carbon trading. A possible solution to inherent incommensurability between temporary and permanent credits is also suggested
Causality, particle localization and positivity of the energy
Positivity of the Hamiltonian alone is used to show that particles, if
initially localized in a finite region, immediately develop infinite tails.Comment: To appear in: Irreversibility and Causality in Quantum Theory --
Semigroups and Rigged Hilbert Spaces, edited by A. Bohm, H.-D. Doebner and P.
Kielanowski, Springer Lecture Notes in Physics, Vol. 504 (1998
Unsteady draining of a fluid from a circular tank
Three-dimensional draining flow of a two-fluid system from a circular tank is considered. The two fluids are inviscid and incompressible, and are separated by a sharp interface. There is a circular hole positioned centrally in the bottom of the tank, so that the flow is axially symmetric. The mean position of the interface moves downwards as time progresses, and eventually a portion of the interface is withdrawn into the drain. For narrow drain holes of small radius, the interface above the centre of the drain is pulled down towards the hole. However, for drains of larger radius the portion of the interface above the drain edge is drawn down first, rather than the central section. Non-linear results are obtained with a novel spectral technique, and are also compared against the predictions of linearized theory. Unstable Rayleigh-Taylor type flows, in which the upper fluid is heavier than the lower one, are also discussed
An intrusion layer in stationary incompressible fluids Part 2: A solitary wave
The propagation of a solitary wave in a horizontal fluid layer is studied. There is an interfacial free surface above and below this intrusion layer, which is moving at constant speed through a stationary density-stratified fluid system. A weakly nonlinear asymptotic theory is presented, leading to a Korteweg-de Vries equation in which the two fluid interfaces move oppositely. The intrusion layer solitary wave system thus forms a widening bulge that propagates without change of form. These results are confirmed and extended by a fully nonlinear solution, in which a boundary-integral formulation is used to solve the problem numerically. Limiting profiles are approached, for which a corner forms at the crest of the solitary wave, on one or both of the interfaces
An intrusion layer in stationary incompressible fluids Part 2: A solitary wave
The propagation of a solitary wave in a horizontal fluid layer is studied. There is an interfacial free surface above and below this intrusion layer, which is moving at constant speed through a stationary density-stratified fluid system. A weakly nonlinear asymptotic theory is presented, leading to a Korteweg-de Vries equation in which the two fluid interfaces move oppositely. The intrusion layer solitary wave system thus forms a widening bulge that propagates without change of form. These results are confirmed and extended by a fully nonlinear solution, in which a boundary-integral formulation is used to solve the problem numerically. Limiting profiles are approached, for which a corner forms at the crest of the solitary wave, on one or both of the interfaces
Does quantum nonlocality irremediably conflict with Special Relativity?
We reconsider the problem of the compatibility of quantum nonlocality and the
requests for a relativistically invariant theoretical scheme. We begin by
discussing a recent important paper by T. Norsen [arXiv:0808.2178] on this
problem and we enlarge our considerations to give a general picture of the
conceptually relevant issue to which this paper is devoted.Comment: 18 pages, 1 figur
Lie group classifications and exact solutions for time-fractional Burgers equation
Lie group method provides an efficient tool to solve nonlinear partial
differential equations. This paper suggests a fractional Lie group method for
fractional partial differential equations. A time-fractional Burgers equation
is used as an example to illustrate the effectiveness of the Lie group method
and some classes of exact solutions are obtained.Comment: 9 pp, accepte
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