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 $\beta =5.74,\;6.00$ and $6.26$, enables us to study the variation of the leptonic decay constants $f_P$ of heavy pseudoscalar mesons with the lattice spacing $a$. We observe only a weak $a$ dependence when the standard $\sqrt{2\kappa}$ normalization is used for the quark fields, whereas application of the Kronfeld-Mackenzie normalization induces a stronger variation with $a$. Increasing the meson mass from $1.1GeV$ to $2.3GeV$ 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 $O(a)$ 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 $g_A$ 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