51 research outputs found
Recommended from our members
Generating strong shock waves with a supersonic peristaltic pump
An axially phased implosion of a cylindrical tube with a phase velocity exceeding the sound speed of the fill material acts as a peristaltic pump which drives a shock wave along the axis. The region behind the onset of the phased implosion forms a converging-diverging nozzle. When appropriately designed the flow approaches a steady state in which the shock is planar and propagates near the nozzle entrance. The steady-state flow and the approach toward it have been derived in a one-dimensional model. The steady-state nozzle flow is well characterized: uniform across the channel, simple and predictable in the axial direction. The flow in the converging section is very stable and not affected by the flow in the diverging section. These properties form the basis of an alternative shock tube design which is not limited in pressure by material strength of the tube wall. Experiments with a simple design have corroborated the theoretical predictions. A super-shock tube, in which the phased implosion is driven by high explosives, can reach extremely high pressures and energy densities. With a well characterized drive system, measurements of the steady-state shape of the nozzle can be used to determine the equation of state along an isentrope behind the axial shock. 5 refs., 4 figs
Transverse momentum spectra of charged particles in proton-proton collisions at GeV with ALICE at the LHC
The inclusive charged particle transverse momentum distribution is measured
in proton-proton collisions at GeV at the LHC using the ALICE
detector. The measurement is performed in the central pseudorapidity region
over the transverse momentum range GeV/.
The correlation between transverse momentum and particle multiplicity is also
studied. Results are presented for inelastic (INEL) and non-single-diffractive
(NSD) events. The average transverse momentum for is (stat.) (syst.) GeV/ and
\left_{\rm NSD}=0.489\pm0.001 (stat.) (syst.)
GeV/, respectively. The data exhibit a slightly larger than measurements in wider pseudorapidity intervals. The results are
compared to simulations with the Monte Carlo event generators PYTHIA and
PHOJET.Comment: 20 pages, 8 figures, 2 tables, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/390
Recommended from our members
Anomalous physical effects from artificial numerical length scales
Shock capturing algorithms are widely used for simulations of compressible fluid flow. Though these algorithms resolve a shock wave within a couple of grid points, the artificial length scale from the numerical shock profile can have side effects. The side effects are similar to physical effects that occur when a relaxation process gives rise to fully or partly dispersed shock waves. Two anomalies due to a non-zero shock width are discussed: (1) in one-dimension, a non-decaying entropy spike results from a transient when a shock profile is formed or changed; (2) in multi-dimensions, front curvature affects the propagation of a shock wave. The authors show that both the entropy anomaly and the curvature effect are a natural consequence of the conservation laws. The same analysis applies both to the continuum equations and to their finite difference approximations in conservation form. Consequently, the artificial length scale inherent in a shock capturing algorithm can mimic real physical effects that are associated with partly dispersed shock waves
Recommended from our members
A method for permanent disposal of CO{sub 2} in solid form
We describe a method for binding the greenhouse gas carbon dioxide as magnesium carbonate, a thermodynamically stable solid, for safe and permanent disposal, and with minimal environment impact. The technique is based on extracting magnesium hydroxide from common ultramafic rock for thermal carbonation and subsequent disposition. The economics of the method appear to be promising, however, many details of the proposed process have yet to be optimized. Initial estimates indicate that binding and disposal would impose a burden of approximately 3{cents}/kWH onto the cost of electricity. This cost could be reduced significantly in the short term by entering niche markets for various technologies for efficient extraction and thermal carbonation. In this paper, we describe some of the kinetic limitations and opportunities. The proposed disposal technique may be viewed as a sort of insurance policy in case global warming, or the perception of global warming causes severe restrictions on CO{sub 2} emissions
Recommended from our members
Magnesite disposal of carbon dioxide
In this paper we report our progress on developing a method for carbon dioxide disposal whose purpose it is to maintain coal energy competitive even is environmental and political pressures will require a drastic reduction in carbon dioxide emissions. In contrast to most other methods, our approach is not aiming at a partial solution of the problem, or at buying time for phasing out fossil energy. Instead, its purpose is to obtain a complete and economic solution of the problem, and thus maintain access to the vast fossil energy reservoir. A successful development of this technology would guarantee energy availability for many centuries even if world economic growth the most optimistic estimates that have been put forward. Our approach differs from all others in that we are developing an industrial process which chemically binds the carbon dioxide in an exothermic reaction into a mineral carbonate that is thermodynamically stable and environmentally benign
Recommended from our members
Binding carbon dioxide in mineral form: A critical step towards a zero-emission coal power plant
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors have successfully developed the foundation for sequestration of carbon dioxide in mineral form. The purpose of this technology is to maintain the competitiveness of coal energy, even when in the future environmental and political pressures will require a drastic reduction in carbon dioxide emissions. In contrast to most other sequestration methods, this is not aiming at a partial solution of the problem, or at buying time for phasing out fossil energy. Instead, the goal is to obtain a complete and economic solution of the problem, and thus maintain access to the vast fossil energy reservoir. Such a technology will guarantee energy availability for many centuries even if world economic growth exceeds the most optimistic estimates. The approach differs from all others in that the authors are developing an industrial process that chemically binds the carbon dioxide in an exothermic reaction into a mineral carbonate that is thermodynamically stable and environmentally benign
Recommended from our members
The need for carbon dioxide disposal: A threat and an opportunity
Ready energy is a cornerstone of modern society. The policies outlined at the recent Kyoto conference have put in question the largest, most readily available and most cost-effective energy resource available. Even if a doubling of atmospheric CO{sub 2} is deemed acceptable, emission reductions worldwide would have to be drastic. For 10 billion people to share equally into the 1990 emission level would allow a per capita emission of 10% of the current US level. Substantial reductions in CO{sub 2} emissions to the atmosphere are unavoidable. Uncertain is the time available to accomplish this reduction. There are also reasons to be optimistic about the future of coal and other fossil fuels. Barring a surprise technological breakthrough in alternative energies, fossil energy consumption is bound to grow. Political and economic drivers even stronger than the threat of climate change favor economic growth and therefore increased energy consumption. To resolve this apparent contradiction requires new technologies that prevent CO{sub 2} generated by combustion from entering the atmosphere. The authors will outline available technologies and show how the coal industry can adapt to them
- …