379 research outputs found
Nonequilibrium brittle fracture propagation: Steady state, oscillations and intermittency
A minimal model is constructed for two-dimensional fracture propagation. The
heterogeneous process zone is presumed to suppress stress relaxation rate,
leading to non-quasistatic behavior. Using the Yoffe solution, I construct and
solve a dynamical equation for the tip stress. I discuss a generic tip velocity
response to local stress and find that noise-free propagation is either at
steady state or oscillatory, depending only on one material parameter. Noise
gives rise to intermittency and quasi-periodicity. The theory explains the
velocity oscillations and the complicated behavior seen in polymeric and
amorphous brittle materials. I suggest experimental verifications and new
connections between velocity measurements and material properties.Comment: To appear in Phys. Rev. Lett., 6 pages, self-contained TeX file, 3
postscript figures upon request from author at [email protected] or
[email protected], http://cnls-www.lanl.gov/homepages/rafi/rafindex.htm
The influence of coal particle and air jet momenta on MILD combustion in a recuperative furnace
The moderate or intense low-oxygen dilution (MILD) combustion regime is a promising technology that operates at high combustion efficiency and lessens pollutant emissions. This numerical study of a parallel jet recuperative MILD combustion furnace investigates the effects of coal particle size and inlet air momentum on furnace dynamics and global CO emissions. It is found that coal particle size affects the coal penetration depth within the furnace and the location of a particle stagnation point. The effects of air inlet momentum are tested in two ways, first by raising the inlet temperature at constant mass flow rate, and second by increasing the mass flow rate at constant temperature. In both cases, increasing the air jet momentum broadens the reaction zone and facilitates MILD combustion, but also increases CO emissions due to lowered reaction rates.Emmet M. Cleary, Paul R. Medwell, Bassam B. Dallyhttp://cfe.uwa.edu.au/news/acs2013http://www.anz-combustioninstitute.org
Pion and Kaon Vector Form Factors
We develop a unitarity approach to consider the final state interaction
corrections to the tree level graphs calculated from Chiral Perturbation Theory
() allowing the inclusion of explicit resonance fields. The method is
discussed considering the coupled channel pion and kaon vector form factors.
These form factors are then matched with the one loop results. A very
good description of experimental data is accomplished for the vector form
factors and for the P-wave phase shifts up to
GeV, beyond which multiparticle states play a non negligible role. In
particular the low and resonance energy regions are discussed in detail and for
the former a comparison with one and two loop is made showing a
remarkable coincidence with the two loop results.Comment: 20 pages, 7 figs, to appear in Phys. Rev.
Tau mesonic decays and strong anomaly of PCAC
Strong anomaly of the PCAC is found in and
in the chiral limit. It originates in WZW anomaly. Theoretical
result of agrees with data well and the
measurement of will confirm the strong anomaly
of PCAC. The strong anomaly of PCAC is studied.Comment: 27 page
Electromagnetic Meson Form Factors in the Salpeter Model
We present a covariant scheme to calculate mesonic transitions in the
framework of the Salpeter equation for -states. The full Bethe
Salpeter amplitudes are reconstructed from equal time amplitudes which were
obtained in a previous paper\cite{Mue} by solving the Salpeter equation for a
confining plus an instanton induced interaction. This method is applied to
calculate electromagnetic form factors and decay widths of low lying
pseudoscalar and vector mesons including predictions for CEBAF experiments. We
also describe the momentum transfer dependence for the processes
.Comment: 22 pages including 10 figure
A study of combustion characteristics of pulverised coal under MILD combustion conditions
In this experimental work, a laboratory-scale recuperative furnace has been used to investigate the sustainability of Moderate or Intense Low Oxygen Dilution (MILD) combustion with pulverised coal. Low-rank and high volatile Kingston brown coal and high-rank and low volatile Bowen Basin black coal with particle size in the range of 38-180 μm were injected into the furnace using either CO2 or N2 as a carrier gas. Operating conditions for stable MILD combustion of pulverised coal have been identified and evidencing MILD condition is achievable without any additional pre-heating of the air. The O2 and CO emissions were measured in parallel with NO emission. A water cooled sampling probe was used to conduct in-furnace gas sampling. Measurements of in-furnace gas concentration of CO and NO and in-furnace temperatures are presented. It was found that a significant reduction of NO emission owing to the strong NO reburning reaction inside the furnace. These findings, together with the potentiality of MILD conditions for soot depression and destruction, open the possibility of using high rank black and low rank brown coal with this technology.M. Saha, B. B. Dally, P. R. Medwell and E. M. Clearyhttp://cfe.uwa.edu.au/news/acs2013http://www.anz-combustioninstitute.org
Temperature and reaction zone imaging in turbulent swirling dual-fuel flames
Gaseous and liquid dual-fuel flames present both a practical approach to emissions reduction and a challenge to current state-of-the-art combustion modelling. This paper uses simultaneously imaged temperature and normalised OH signal fields to investigate flame structure and provide experimental data for model validation across a range of swirl-stabilised n-heptane spray flames. These data are obtained by non-linear excitation regime two-line atomic fluorescence (NTLAF) of indium, and planar laser-induced fluorescence (OH-PLIF), respectively. Swirling gas streams are varied by flowrate (63–88% of blow-off), premixed equivalence ratio (including air-only), and by type of gaseous fuel (natural gas and hydrogen). Results are used to describe how hot combustion products interact with the fuel spray: heating and diluting the region above the apex of the spray cone at low air flowrates but drawing fuel into outer branches of the flame with increasing air flowrates. Adding natural gas to the swirling air stream, at a concentration below the lean flammability limit, gives rise to a temperature increase in the outer branches with little effect on the hot region above the apex of the spray, along the burner centreline. The size of this region is significantly reduced; however, using hydrogen. As the concentration of gaseous fuel increases towards the lean flammability limit, peak temperatures shift towards the outer branch of the flame. Exceeding the lean flammability limit, an additional reaction zone begins to form in the premixed swirling stream, adjacent to the outer branch of the swirl flame. Stable outer branches of the swirl flame, however, become less prevalent and the peak temperatures of the spray flame return to burner centreline. This study provides insight into the complex behaviour of dual-fuel flames, a complementary dataset to related, PLIF-only studies and validation data for the development of numerical modelling tools.M.J.Evans, J.A.M.Sidey, J.Ye, P.R.Medwell, B.B.Dally, E.Mastorako
Form factors of pion and kaon
An addtional intrinsic form factors of pion and kaons have been studied.Comment: 14 pages and 10 figure
Pion-photon and photon-pion transition form factors in light-cone formalism
We derive the minimal Fock-state expansions of the pion and the photon wave
functions in light-cone formalism, then we calculate the pion-photon and the
photon-pion transition form factors of and
processes by employing these
quark-antiquark wave functions of the pion and the photon. We find that our
calculation for the transition form factor
agrees with the experimental data at low and moderately high energy scale.
Moreover, the physical differences and inherent connections between the
transition form factors of and have been illustrated, which indicate that these
two physical processes are intrinsically related. In addition, we also discuss
the form factor and the decay width at .Comment: 20 pages, 2 figure
Solar thermal hybrids for combustion power plant: A growing opportunity
The development of technologies to hybridise concentrating solar thermal energy (CST) and combustion technologies, is driven by the potential to provide both cost-effective CO2 mitigation and firm supply. Hybridisation, which involves combining the two energy sources within a single plant, offers these benefits over the stand-alone counterparts through the use of shared infrastructure and increased efficiency. In the near-term, hybrids between solar and fossil fuelled systems without carbon capture offer potential to lower the use of fossil fuels, while in the longer term they offer potential for low-cost carbon-neutral or carbon-negative energy. The integration of CST into CO2 capture technologies such as oxy-fuel combustion and chemical looping combustion is potentially attractive because the same components can be used for both CO2 capture and the storage of solar energy, to reduce total infrastructure and cost. The use of these hybrids with biomass and/or renewable fuels, offers the additional potential for carbon-negative energy with relatively low cost. In addition to reviewing these technologies, we propose a methodology for classifying solar-combustion hybrid technologies and assess the progress and challenges of each. Particular attention is paid to "direct hybrids", which harness the two energy sources in a common solar receiver or reactor to reduce total infrastructure and losses.G.J.Nathan, M.Jafarian, B.B.Dally, W.L.Saw, P.J.Ashman, E.Hu, A.Steinfel
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