27,542 research outputs found
Action semantics in retrospect
This paper is a themed account of the action semantics project, which Peter Mosses has led since the 1980s. It explains his motivations for developing action semantics, the inspirations behind its design, and the foundations of action semantics based on unified algebras. It goes on to outline some applications of action semantics to describe real programming languages, and some efforts to implement programming languages using action semantics directed compiler generation. It concludes by outlining more recent developments and reflecting on the success of the action semantics project
Motion sickness and migraine: optokinetic stimulation increases scalp tenderness, pain sensitivity in the fingers and photophobia
The aim of this study was to determine whether scalp tenderness and photophobia, two well-recognized symptoms of migraine, develop during the motion sickness induced by optokinetic stimulation. To investigate whether motion sickness has a general influence on pain perception, pain was also assessed in the fingertips. After optokinetic stimulation, nausea increased more and headache persisted longer in 21 migraine sufferers than in 15 non-headache controls. Scalp tenderness increased during optokinetic stimulation in nauseated subjects, and pain in the fingertips increased more and photophobia persisted longer in migraine sufferers than controls. These findings suggest that the disturbance responsible for nausea also sensitizes trigeminal nociceptive neurones or releases inhibitory controls on their discharge. A low nausea threshold and a propensity for sensitization to develop rapidly in nociceptive pathways may increase susceptibility to migraine
Solution to the ghost problem in fourth order derivative theories
We present a solution to the ghost problem in fourth order derivative
theories. In particular we study the Pais-Uhlenbeck fourth order oscillator
model, a model which serves as a prototype for theories which are based on
second plus fourth order derivative actions. Via a Dirac constraint method
quantization we construct the appropriate quantum-mechanical Hamiltonian and
Hilbert space for the system. We find that while the second-quantized Fock
space of the general Pais-Uhlenbeck model does indeed contain the negative norm
energy eigenstates which are characteristic of higher derivative theories, in
the limit in which we switch off the second order action, such ghost states are
found to move off shell, with the spectrum of asymptotic in and out S-matrix
states of the pure fourth order theory which results being found to be
completely devoid of states with either negative energy or negative norm. We
confirm these results by quantizing the Pais-Uhlenbeck theory via path
integration and by constructing the associated first-quantized wave mechanics,
and show that the disappearance of the would-be ghosts from the energy
eigenspectrum in the pure fourth order limit is required by a hidden symmetry
that the pure fourth order theory is unexpectedly found to possess. The
occurrence of on-shell ghosts is thus seen not to be a shortcoming of pure
fourth order theories per se, but rather to be one which only arises when
fourth and second order theories are coupled to each other.Comment: 36 pages, revtex. Prepared for the proceedings of the 2006 Biennial
Meeting of the International Association for Relativistic Dynamics Version 2
contains an expanded discussion of the path integral quantization of the
Pais-Uhlenbeck fourth order oscillator theor
The potential of RIVPACS for predicting the effects of environmental change
RIVPACS has been used successfully for biological assessment of river water quality but its potential in forecasting the effects of environmental change has not been investigated. This study has shown that it is possible to simulate faunal changes in response to environmental disturbance, provided that the disturbance directly involves the environmental variables used in RIVPACS predictions. These variables relate to channel shape, discharge and substratum. Many impacts, particularly those associated with pollution, will not affect these variables and therefore RIVPACS cannot simulate the effects of pollution. RIVPACS was sensitive only to major changes in substratum. It was concluded that, because of the static nature of RIVPACS, it cannot respond to the dynamic effects and processes associated with environmental disturbance. Thus RIVPACS, while showing direction of change and indicating sensitive taxa, cannot be used to predict or forecast the effects of environmental impacts
Distribution of certain minor elements in Alaskan coals
Seventy-five samples of coal from Northern Alaska, Jarvis Creek, Nenana, Matanuska, Kenai and Bering River Coal Fields were analyzed by quantitative spectrochemical
procedures f o r lead, gallium, copper, barium, beryllium, nickel, titanium, vanadium, zirconium, cobalt, chromium,
germanium, and tin. Other elements, of significance, identified from the spectrograms were, gold and silver identified in certain Nenana coals and silver in coals from Chickaloon in the Matanuska field, in concentrations up to several parts per million of coal ash. Forty-one of the above samples were sink-floated to study the distribution of minor elements between the
organic and inorganic phases of the coals. Relative affinities of the minor of the minor elements to the organic matter in the coal is discussed
Thermogravimetric and distillation studies on mercury, antimony and arsenic sulfides
Thermogravimetric studies were made on naturally occurring sulfides of mercury,
antimony and arsenic to determine activation energies and Arrhenius rates of reaction
in vacuum and in atmospheres of air and nitrogen. Of the three sulfides only antimony
showed an appreciable change in rate of reaction for the different test conditions.
Distillation results on three flotation concentrates from Alaska mining operations showed that cinnabar (mercury sulfide) could be distilled in a closed system, with over 99 percent recovery of the mercury as metal when the sulfur was reacted with iron. Over 98 percent mercury recovery was obtained from a cinnabar-stibnite (antimony sulfide) concentrate, with less than 1 percent of the antimony distilled from the furnace charge. Cinnabarrealgar-orpiment (arsenic sulfides) could not be separated by distillation and large quantities of soot (condenser residue) formed with the metallic mercury in the condenser
Hydrometallurgy of the delta sulfide ores, second stage report
This report contains results of the Fluidized-Bed Leaching (FBL) initially adapted to improve Leaching-Flotation processing of Delta ores in sulfate solution. The research carried out in the continuous laboratory installation show, however, that the new, 3-phase (solid-liquid-gaseous) reactor also performs satisfactorily in other leaching systems. A new process of pyritic matrix destruction for precious metals recovery in the FBL reactor, and a new process for recovery of zinc and other metals in a chloride system are proposed on the basis of laboratory results.Submitted to:
Nerco Minerals Compan
Characterization and evaluation of washability of Alaskan coals
This report is a result of the second part of a continuing study to obtain washability data for Alaskan coals to supplement the efforts of the U.S. Department of Energy in their ongoing studies on washability of U.S. coals.Contract No. U.S.D.O.E. ET-78-G-01-8969 (formerly U.S.B.M. G0166212
Contribution of laser altimetry images to the geomorphology of the Late Holocene inland drift sands of the European Sand Belt
The paper explores the possibilities of applying the analysis of laser altimetry images to Dutch drift sands. All along the European Sand Belt, which stretches from Great Britain to the Ural Mountains, Late Glacial cover sands, river dunes and other iceāage deposits were reactivated as drift sand during the Holocene. New insights were obtained in three aspects of driftāsands geomorphology. First, the variety in forms of driftāsand landscapes is often described as chaotic. Laser altimetry images show that complex clusters are formed elongated in the direction of the prevailing SW wind and consisting of three zones which correspond to the successive aspects of the aeolian process: deflation, transport and deposition (dune formation). In densely populated areas, this structure has been ruined by human activities. Second, contrary to common belief, the driftāsand cells expanded against the prevailing SW wind whereas the characteristic comb dunes at the opposite NE edge remained fixed by vegetation. Third, the authors questioned the view that drift sands are due to anthropogenic activities. The origin of drift sands can best be explained by the climate with violent storms in the first part of the past millennium
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