767 research outputs found
Fouling Characteristics of a Light Australian Crude Oil
Australian crude oils, which generally contain little asphaltenes, nevertheless give rise to fouling in refinery pre-heat trains. In this research, fouling of a series of such crude oils and their blends is being assessed. The present work focuses on thermal fouling resulting from heating Gippsland crude oil at moderate temperatures. The oil is maintained under nitrogen at a pressure of 379 kPa, and re-circulated at bulk temperatures of 80-120°C through an electrically heated annular probe at velocities in the range 0.25 to 0.65 m/s with surface temperatures from 180-260°C. Experiments are run for periods up to 90 hours at constant heat flux. Fouling is detected by the increase of wall temperature of the probe. The oil is characterized by its filterable solids content, density and viscosity both before and after the fouling run. The trends in fouling rates are compared to predictions of the threshold-fouling model proposed by Ebert and Panchal (1995). Data on deposit composition are presented, and the fouling mechanism discussed
The phase diagram of twisted mass lattice QCD
We use the effective chiral Lagrangian to analyze the phase diagram of
two-flavor twisted mass lattice QCD as a function of the normal and twisted
masses, generalizing previous work for the untwisted theory. We first determine
the chiral Lagrangian including discretization effects up to next-to-leading
order (NLO) in a combined expansion in which m_\pi^2/(4\pi f_\pi)^2 ~ a \Lambda
(a being the lattice spacing, and \Lambda = \Lambda_{QCD}). We then focus on
the region where m_\pi^2/(4\pi f_\pi)^2 ~ (a \Lambda)^2, in which case
competition between leading and NLO terms can lead to phase transitions. As for
untwisted Wilson fermions, we find two possible phase diagrams, depending on
the sign of a coefficient in the chiral Lagrangian. For one sign, there is an
Aoki phase for pure Wilson fermions, with flavor and parity broken, but this is
washed out into a crossover if the twisted mass is non-vanishing. For the other
sign, there is a first order transition for pure Wilson fermions, and we find
that this transition extends into the twisted mass plane, ending with two
symmetrical second order points at which the mass of the neutral pion vanishes.
We provide graphs of the condensate and pion masses for both scenarios, and
note a simple mathematical relation between them. These results may be of
importance to numerical simulations.Comment: 13 pages, 5 figures, small clarifying comments added in introduction,
minor typos fixed. Version to be published in Phys. Rev.
Perturbative Renormalization of Improved Lattice Operators
We derive bases of improved operators for all bilinear quark currents up to
spin two (including the operators measuring the first moment of DIS Structure
Functions), and compute their one-loop renormalization constants for arbitrary
coefficients of the improvement terms. We have thus control over O(a)
corrections, and for a suitable choice of improvement coefficients we are only
left with errors of O(a^2).Comment: 4 pages, LaTeX + 1 eps file + epscrc2.sty (included). Talk given to
the Lattice 97 International Symposium, 22-26 July 1997, Edinburgh, UK. Minor
changes in notatio
Quenching Effects in the Hadron Spectrum
Lattice QCD has generated a wealth of data in hadronic physics over the last
two decades. Until relatively recently, most of this information has been
within the "quenched approximation" where virtual quark--anti-quark pairs are
neglected. This review presents a descriptive discussion of the effects of
removing this approximation in the calculation of hadronic masses.Comment: To appear in "Lattice Hadron Physics", ed. A.C. Kalloniatis, D.B.
Leinweber and A.G. William
Scaling Study of the Leptonic Decay Constants of Heavy-Light Mesons: A Consumers Report on Improvement Factors
A high statistics calculation, performed at and ,
enables us to study the variation of the leptonic decay constants of
heavy pseudoscalar mesons with the lattice spacing . We observe only a weak
dependence when the standard normalization is used for the
quark fields, whereas application of the Kronfeld-Mackenzie normalization
induces a stronger variation with . Increasing the meson mass from
to this situation becomes even more pronounced.Comment: Lattice 93, 3 pages Latex, 2 postscript figures (epsf style
B Meson Decay Constants From NRQCD
We present quenched results for B meson decay constants using NRQCD b quarks
and O(a) tadpole improved clover light quarks. For the first time, one-loop
matching factors between lattice and continuum currents are incorporated
through O(\alpha/M) taking operator mixing fully into account. This includes an
important O(\alpha a) discretization correction to the heavy-light axial vector
current. We find f_B = 0.147(11)(^{+8}_{-12})(9)(6) MeV and f_{B_s}/f_B =
1.20(4)(^{+4}_{-0}).
PACS numbers: 12.38.Gc, 12.39.Hg, 13.20.He, 14.40.NdComment: LaTeX file, 14 pages, typos corrected, to be published in Phys. Lett.
First results with non-perturbative fermion improvement
We present initial results for light hadron masses and nucleon structure
functions using a recent proposal for eliminating all effects from
Wilson fermion simulations in the quenched approximation. With initially
limited statistics, we find a much more linear APE plot and a value of the
axial coupling nearer to the experimental point than with comparable runs
using unimproved Wilson fermions.Comment: 3 pages, 2 PostScript figures, LaTeX 2.09 with espcrc2.sty v2.6,
amstex and epsf, talk presented at LATTICE96(phenomenology) by P. Stephenso
New geomorphic criteria on lateral propagation of blind thrust-related fold growth accommodating oblique convergence
International audienceThe aim of this contribution is to show the styles of growing anticlines and the ways in which they accommodate oblique convergence through proximal foreland basins and intramontane basins. The four natural examples of individual fault-related-folds are: the Chandigarh anticline in the Siwalik foothills of Himalaya (NW India), the Pakuashan anticline in the western foothills of Central Range (Taiwan), the J. Bou Dhar-Tamdafelt fold belt (Morocco) and the Marand anticline in the North-Tabriz Fault-Zone (NW Iran). The evolution of these geomorphic criteria and drainage patterns shows evidence of lateral propagation of folds accommodating oblique convergence. This paper focuses on the geomorphic indicators that could be used to provide information on the timing of fault-related folding and direction of lateral propagation. Several tectonic scenarios has been analysed and an attempt has been made to delineate the sequential evolution of anticlines accommodating oblique convergence
Generalised Spin Projection for Fermion Actions
The majority of compute time doing lattice QCD is spent inverting the fermion
matrix. The time that this takes increases with the condition number of the
matrix. The FLIC(Fat Link Irrelevant Clover) action displays, among other
properties, an improved condition number compared to standard actions and hence
is of interest due to potential compute time savings. However, due to its two
different link sets there is a factor of two cost in floating point
multiplications compared to the Wilson action. An additional factor of two has
been attributed due to the loss of the so-called spin projection trick. We show
that any split-link action may be written in terms of spin projectors, reducing
the additional cost to at most a factor of two. Also, we review an efficient
means of evaluating the clover term, which is additional expense not present in
the Wilson action.Comment: 4 page
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