Adaptive Low-Complexity Sequential Inference for Dirichlet Process Mixture Models

We develop a sequential low-complexity inference procedure for Dirichlet process mixtures of Gaussians for online clustering and parameter estimation when the number of clusters are unknown a-priori. We present an easily computable, closed form parametric expression for the conditional likelihood, in which hyperparameters are recursively updated as a function of the streaming data assuming conjugate priors. Motivated by large-sample asymptotics, we propose a novel adaptive low-complexity design for the Dirichlet process concentration parameter and show that the number of classes grow at most at a logarithmic rate. We further prove that in the large-sample limit, the conditional likelihood and data predictive distribution become asymptotically Gaussian. We demonstrate through experiments on synthetic and real data sets that our approach is superior to other online state-of-the-art methods.Comment: 25 pages, To appear in Advances in Neural Information Processing Systems (NIPS) 201

Multi-physics ensemble snow modelling in the western Himalaya

Combining multiple data sources with multi-physics simulation frameworks offers new potential to extend snow model inter-comparison efforts to the Himalaya. As such, this study evaluates the sensitivity of simulated regional snow cover and runoff dynamics to different snowpack process representations. The evaluation is based on a spatially distributed version of the Factorial Snowpack Model (FSM) set up for the Astore catchment in the upper Indus basin. The FSM multi-physics model was driven by climate fields from the High Asia Refined Analysis (HAR) dynamical downscaling product. Ensemble performance was evaluated primarily using MODIS remote sensing of snow-covered area, albedo and land surface temperature. In line with previous snow model inter-comparisons, no single FSM configuration performs best in all of the years simulated. However, the results demonstrate that performance variation in this case is at least partly related to inaccuracies in the sequencing of inter-annual variation in HAR climate inputs, not just FSM model limitations. Ensemble spread is dominated by interactions between parameterisations of albedo, snowpack hydrology and atmospheric stability effects on turbulent heat fluxes. The resulting ensemble structure is similar in different years, which leads to systematic divergence in ablation and mass balance at high elevations. While ensemble spread and errors are notably lower when viewed as anomalies, FSM configurations show important differences in their absolute sensitivity to climate variation. Comparison with observations suggests that a subset of the ensemble should be retained for climate change projections, namely those members including prognostic albedo and liquid water retention, refreezing and drainage processes

Predictors of construction time in detached housing projects

Building on previous literature on construction time performance (CTP), this study looks at the extent to which Gross Floor Area (GFA) and Number of Levels (NoL) are important factors in determining the construction time in Australian detached housing projects. Using a dataset of 196 comparable detached housing projects the results show that while GFA and NoL correlate strongly with estimated construction time, they correlated weakly with actual construction time. Dynamically changing events during construction appear to be the reason for the difference. Analyses indicate that cost variations brought about by Design changes, Site management errors; Site workmanship problems and Unforeseen site problems are significant factors in explaining the difference between actual and estimated construction time. Further, these factors affect larger housing projects (>400m2) more significantly than they do smaller projects (<350m2). It would therefore seem that even though GFA on its own has a poor correlation with actual construction time, this improves when teamed with the above cost variations. These results open up avenues for future research to look more closely at the effects of project dynamics (e.g. using causes of cost increases as a proxy) when predicting CTP, rather than relying too heavily on static variables like GFA or NoL. It is important that such variables are taken into account as a basis for teaching and promulgating an analytical basis to predicting construction time

Eriophyid Mites New to Ohio

Author Institution: Department of Zoology and Entomology, Ohio Agricultural Experiment Station, Wooster, Ohi

NOSS altimeter algorithm specifications

A description of all algorithms required for altimeter processing is given. Each description includes title, description, inputs/outputs, general algebraic sequences and data volume. All required input/output data files are described and the computer resources required for the entire altimeter processing system were estimated. The majority of the data processing requirements for any radar altimeter of the Seasat-1 type are scoped. Additions and deletions could be made for the specific altimeter products required by other projects

Laboratory Growth, Reproduction and Life Span of the Pacific Pygmy Octopus, Octopus digueti

Octopus digueti Perrier and Rochebrune, 1894 was reared through its life cycle at 25°C in a closed seawater system using artificial sea water. Two field-collected females produced 231 hatchlings: 193 hatchlings were groupcultured while 24 were isolated at hatching and grown individually to allow precise analyses of growth in length and weight over the life cycle. All octopuses were fed primarily live shrimps. Maturing adults fed at a rate of 4.7% of body weight per day and had a gross growth efficiency of 48%. Growth in weight was exponential for the first 72 days and described best by the equation: WW(g) = .0405e•0646t. The mean growth rate over this period was 6.4% increase in body weight per day (%/d), with no significant difference between male and female growth. From 72 to 143 days, growth was logarithmic and described best by the equation: WW(g) = (6.78 x 1O- 6) t3 .13. Females grew slightly faster than males over this growth phase. During the exponential growth phase, mantle length increased at a mean rate of 2.1% per day, declining to 1.1% per day over the logarithmic phase. No attempt was made to describe mathematically the period of declining growth rate beyond day 143. The primary causes of early mortality in group culture were escapes and cannibalism. Survival was good despite high culture density: 73% survival to date of first egg laying (day 111). Survival was better among the isolated growth-study octopuses: 88% to the date of first egg laying (day 130). Mean life span was 199 days in group-reared octopuses and 221 days in the growth-study octopuses. There was no significant difference between male and female life span. Progeny of the group culture were reared at similar stocking densities and fed predominantly fresh dead shrimp and crab meat. This diet resulted in cannibalism, with only 6% survival to first egg laying on day 128. Fecundity in this group was lower. Octopus digueti is a good candidate for laboratory culture and biological experimentation because of its small size, rapid growth, short life span, and good survival in group culture

Dynamics of a liquid dielectric attracted by a cylindrical capacitor

The dynamics of a liquid dielectric attracted by a vertical cylindrical capacitor is studied. Contrary to what might be expected from the standard calculation of the force exerted by the capacitor, the motion of the dielectric is different depending on whether the charge or the voltage of the capacitor is held constant. The problem turns out to be an unconventional example of dynamics of a system with variable mass, whose velocity can, in certain circumstances, suffer abrupt changes. Under the hypothesis that the voltage remains constant the motion is described in qualitative and quantitative details, and a very brief qualitative discussion is made of the constant charge case.Comment: To appear in European Journal of Physic

Detection of positron-atom bound states through resonant annihilation

A method is proposed for detecting positron-atom bound states by observing enhanced positron annihilation due to electronic Feshbach resonances at electron-volt energies. The method is applicable to a range of open-shell transition metal atoms which are likely to bind the positron: Fe, Co, Ni, Tc, Ru, Rh, Sn, Sb, Ta, W, Os, Ir, and Pt. Estimates of their binding energies are provided.Comment: 5 pages, 1 figure; estimates of binding energies have been adde

Solving the radial Dirac equations: a numerical odyssey

We discuss, in a pedagogical way, how to solve for relativistic wave functions from the radial Dirac equations. After an brief introduction, in Section II we solve the equations for a linear Lorentz scalar potential, V_s(r), that provides for confinement of a quark. The case of massless u and d quarks is treated first, as these are necessarily quite relativistic. We use an iterative procedure to find the eigenenergies and the upper and lower component wave functions for the ground state and then, later, some excited states. Solutions for the massive quarks (s, c, and b) are also presented. In Section III we solve for the case of a Coulomb potential, which is a time-like component of a Lorentz vector potential, V_v(r). We re-derive, numerically, the (analytically well-known) relativistic hydrogen atom eigenenergies and wave functions, and later extend that to the cases of heavier one-electron atoms and muonic atoms. Finally, Section IV finds solutions for a combination of the V_s and V_v potentials. We treat two cases. The first is one in which V_s is the linear potential used in Sec. II and V_v is Coulombic, as in Sec. III. The other is when both V_s and V_v are linearly confining, and we establish when these potentials give a vanishing spin-orbit interaction (as has been shown to be the case in quark models of the hadronic spectrum).Comment: 39 pages (total), 23 figures, 2 table

A unified approach for the solution of the Fokker-Planck equation

This paper explores the use of a discrete singular convolution algorithm as a unified approach for numerical integration of the Fokker-Planck equation. The unified features of the discrete singular convolution algorithm are discussed. It is demonstrated that different implementations of the present algorithm, such as global, local, Galerkin, collocation, and finite difference, can be deduced from a single starting point. Three benchmark stochastic systems, the repulsive Wong process, the Black-Scholes equation and a genuine nonlinear model, are employed to illustrate the robustness and to test accuracy of the present approach for the solution of the Fokker-Planck equation via a time-dependent method. An additional example, the incompressible Euler equation, is used to further validate the present approach for more difficult problems. Numerical results indicate that the present unified approach is robust and accurate for solving the Fokker-Planck equation.Comment: 19 page