The pulsations and energy transfers in a double-orifice combustor

This work examines the effect of longitudinal oscillations on the heat transfer in a naturally-aspirating, propane-fuelled combustor. Previous investigations in the field have been predominantly experimental in nature, although theoretical studies of the effect of oscillations on local heat transfer coefficients have been made. In this work, a linearised wave equation, which governs the propagation of sound waves in a gas confined by a straight tube and exhibiting an axial temperature variation, is used to correlate local heat transfer coefficients by a quasi-steady-state method. An apparatus was . constructed, and measurements of the gas, wall and water temperatures and of the gas pressure amplitudes were taken in a concentric tube heat exchanger, which formed part of the resonating section

System integration report

Several areas that arise from the system integration issue were examined. Intersystem analysis is discussed as it relates to software development, shared data bases and interfaces between TEMPUS and PLAID, shaded graphics rendering systems, object design (BUILD), the TEMPUS animation system, anthropometric lab integration, ongoing TEMPUS support and maintenance, and the impact of UNIX and local workstations on the OSDS environment

Random-cluster multi-histogram sampling for the q-state Potts model

Using the random-cluster representation of the $q$-state Potts models we consider the pooling of data from cluster-update Monte Carlo simulations for different thermal couplings $K$ and number of states per spin $q$. Proper combination of histograms allows for the evaluation of thermal averages in a broad range of $K$ and $q$ values, including non-integer values of $q$. Due to restrictions in the sampling process proper normalization of the combined histogram data is non-trivial. We discuss the different possibilities and analyze their respective ranges of applicability.Comment: 12 pages, 9 figures, RevTeX

The geometry of nonlinear least squares with applications to sloppy models and optimization

Parameter estimation by nonlinear least squares minimization is a common problem with an elegant geometric interpretation: the possible parameter values of a model induce a manifold in the space of data predictions. The minimization problem is then to find the point on the manifold closest to the data. We show that the model manifolds of a large class of models, known as sloppy models, have many universal features; they are characterized by a geometric series of widths, extrinsic curvatures, and parameter-effects curvatures. A number of common difficulties in optimizing least squares problems are due to this common structure. First, algorithms tend to run into the boundaries of the model manifold, causing parameters to diverge or become unphysical. We introduce the model graph as an extension of the model manifold to remedy this problem. We argue that appropriate priors can remove the boundaries and improve convergence rates. We show that typical fits will have many evaporated parameters. Second, bare model parameters are usually ill-suited to describing model behavior; cost contours in parameter space tend to form hierarchies of plateaus and canyons. Geometrically, we understand this inconvenient parametrization as an extremely skewed coordinate basis and show that it induces a large parameter-effects curvature on the manifold. Using coordinates based on geodesic motion, these narrow canyons are transformed in many cases into a single quadratic, isotropic basin. We interpret the modified Gauss-Newton and Levenberg-Marquardt fitting algorithms as an Euler approximation to geodesic motion in these natural coordinates on the model manifold and the model graph respectively. By adding a geodesic acceleration adjustment to these algorithms, we alleviate the difficulties from parameter-effects curvature, improving both efficiency and success rates at finding good fits.Comment: 40 pages, 29 Figure

Combination of improved multibondic method and the Wang-Landau method

We propose a method for Monte Carlo simulation of statistical physical models with discretized energy. The method is based on several ideas including the cluster algorithm, the multicanonical Monte Carlo method and its acceleration proposed recently by Wang and Landau. As in the multibondic ensemble method proposed by Janke and Kappler, the present algorithm performs a random walk in the space of the bond population to yield the state density as a function of the bond number. A test on the Ising model shows that the number of Monte Carlo sweeps required of the present method for obtaining the density of state with a given accuracy is proportional to the system size, whereas it is proportional to the system size squared for other conventional methods. In addition, the new method shows a better performance than the original Wang-Landau method in measurement of physical quantities.Comment: 12 pages, 3 figure

Gallium scintigraphy in the diagnosis and total lymphoid irradiation of Takayasu's arteritis

Takayasu's arteritis (TA) in children causes appreciable morbidity and mortality, predominantly as a result of the complication of renovascular hypertension (RVH). Ten children with TA, complicated by RVH, were treated at our centre over the past decade. An initial raised erythrocyte sedimentation rate (ESR) and a purified protein derivative greater than 15 mm were present in every case. More recently, gallium scintigraphy has been used to demonstrate sites of active inflammation in affected vessels (3/4 patients) which became negative after total lymphoid irradiation (TU). The latter was used in the last 6 children, and appeared to be effective in controlling disease activity as evinced in the normalisation of their ESRs and negative findings on gallium scintigraphy (in all 3 patients with prior active inflammation). Because of vascular damage caused by the vasculitic process, surgical intervention is often required to improve organ perfusion, particularly of the kidney/so Renal autografting (or allografting) seems preferable (6/11 kidneys functional) to renal bypass grafting (5/5 kidneys clotted). Patient survival improved when TU was used in addition to standard surgical and medical therapy; this included steroids and antituberculous therapy with TU, and steroids and cyclophosphamide in the two relapses. Five of 6 patients treated with TU were alive after 32 - 54 months' follow-up, while 4 patients who received standard medical and surgical therapy but not TU all died within 18 months of diagnosis. Gallium scintigraphy is a helpful diagnostic tool in assessing vasculitic activity in TA; TU is an important mode of immunosuppression, but still needs to be compared with cyclophosphamide as the major immunosuppressive

Controlling magnetic order and quantum disorder in molecule-based magnets.

We investigate the structural and magnetic properties of two molecule-based magnets synthesized from the same starting components. Their different structural motifs promote contrasting exchange pathways and consequently lead to markedly different magnetic ground states. Through examination of their structural and magnetic properties we show that [Cu(pyz)(H 2 O)(gly) 2 ](ClO 4 ) 2 may be considered a quasi-one-dimensional quantum Heisenberg antiferromagnet whereas the related compound [Cu(pyz)(gly)](ClO 4 ) , which is formed from dimers of antiferromagnetically interacting Cu 2+ spins, remains disordered down to at least 0.03 K in zero field but shows a field-temperature phase diagram reminiscent of that seen in materials showing a Bose-Einstein condensation of magnons

Surface critical exponents at a uniaxial Lifshitz point

Using Monte Carlo techniques, the surface critical behaviour of three-dimensional semi-infinite ANNNI models with different surface orientations with respect to the axis of competing interactions is investigated. Special attention is thereby paid to the surface criticality at the bulk uniaxial Lifshitz point encountered in this model. The presented Monte Carlo results show that the mean-field description of semi-infinite ANNNI models is qualitatively correct. Lifshitz point surface critical exponents at the ordinary transition are found to depend on the surface orientation. At the special transition point, however, no clear dependency of the critical exponents on the surface orientation is revealed. The values of the surface critical exponents presented in this study are the first estimates available beyond mean-field theory.Comment: 10 pages, 7 figures include