Physically consistent simulation of transport of inertial particles in porous media

A new numerical approach is presented for simulating the movement of test particles suspended in an incompressible fluid flowing through a porous matrix. This two-phase particle-laden flow is based on the Navier-Stokes equations for incompressible fluid flow and equations of motion for the individual particles in which Stokes drag is dominant. The Immersed Boundary method is applied to incorporate the geometric complexity of the porous medium. A symmetry-preserving finite volume discretization method in combination with a volume penalization method resolves the flow within the porous material. The new Lagrangian particle tracking is such that for mass-less test particles no (numerical) collision with the coarsely represented porous medium occurs at any spatial resolution

Immersed boundary method predictions of shear stresses for different flow topologies occuring in cerebral aneurysms

A volume-penalizing immersed boundary method is presented that facilitates the computation of incompressible fluid flow in complex flow domains. We apply this method to simulate the flow in cerebral aneurysms, and focus on the accuracy with which the flow field and the corresponding shear stress field are computed. The method is applied to laminar, incompressible flow in curved cylindrical vessels and in a model aneurysm. The time-dependent shear stress distributions over the vessel walls are visualized and interpreted in terms of the flow fields that develop. We compute shear stress levels at two different Reynolds numbers, corresponding to a steady and an unsteady flow. In the latter situation strong fluctuations in the shear stress are observed, that may be connected to raised risk-levels of aneurysm rupture

On the Birth of Isolas

Isolas are isolated, closed curves of solution branches of nonlinear problems. They have been observed to occur in the buckling of elastic shells, the equilibrium states of chemical reactors and other problems. In this paper we present a theory to describe analytically the structure of a class of isolas. Specifically, we consider isolas that shrink to a point as a parameter τ of the problem, approaches a critical value τ_0. The point is referred to as an isola center. Equations that characterize the isola centers are given. Then solutions are constructed in a neighborhood of the isola centers by perturbation expansions in a small parameter ε that is proportional to (τ-τo), with a appropriately determined. The theory is applied to a chemical reactor problem

A note on the power divergence in lattice calculations of ΔI=1/2\Delta I = 1/2 K→ππK\to\pi\pi amplitudes at MK=MπM_{K}=M_{\pi}

In this note, we clarify a point concerning the power divergence in lattice calculations of $\Delta I = 1/2$ $K\to\pi\pi$ decay amplitudes. There have been worries that this divergence might show up in the Minkowski amplitudes at $M_{K}=M_{\pi}$ with all the mesons at rest. Here we demonstrate, via an explicit calculation in leading-order Chiral Perturbation Theory, that the power divergence is absent at the above kinematic point, as predicted by CPS symmetry.Comment: 5 pages, 2 figure

Electromagnetic Chirps from Neutron Star-Black Hole Mergers

We calculate the electromagnetic signal of a gamma-ray flare coming from the surface of a neutron star shortly before merger with a black hole companion. Using a new version of the Monte Carlo radiation transport code Pandurata that incorporates dynamic spacetimes, we integrate photon geodesics from the neutron star surface until they reach a distant observer or are captured by the black hole. The gamma-ray light curve is modulated by a number of relativistic effects, including Doppler beaming and gravitational lensing. Because the photons originate from the inspiraling neutron star, the light curve closely resembles the corresponding gravitational waveform: a chirp signal characterized by a steadily increasing frequency and amplitude. We propose to search for these electromagnetic chirps using matched filtering algorithms similar to those used in LIGO data analysis.Comment: 13 pages, 5 figures, submitted to Ap

Modeling and visualizing uncertainty in gene expression clusters using Dirichlet process mixtures

Although the use of clustering methods has rapidly become one of the standard computational approaches in the literature of microarray gene expression data, little attention has been paid to uncertainty in the results obtained. Dirichlet process mixture (DPM) models provide a nonparametric Bayesian alternative to the bootstrap approach to modeling uncertainty in gene expression clustering. Most previously published applications of Bayesian model-based clustering methods have been to short time series data. In this paper, we present a case study of the application of nonparametric Bayesian clustering methods to the clustering of high-dimensional nontime series gene expression data using full Gaussian covariances. We use the probability that two genes belong to the same cluster in a DPM model as a measure of the similarity of these gene expression profiles. Conversely, this probability can be used to define a dissimilarity measure, which, for the purposes of visualization, can be input to one of the standard linkage algorithms used for hierarchical clustering. Biologically plausible results are obtained from the Rosetta compendium of expression profiles which extend previously published cluster analyses of this data

Electrocortical components of anticipation and consumption in a monetary incentive delay task

In order to improve our understanding of the components that reflect functionally important processes during reward anticipation and consumption, we used principle components analyses (PCA) to separate and quantify averaged ERP data obtained from each stage of a modified monetary incentive delay (MID) task. Although a small number of recent ERP studies have reported that reward and loss cues potentiate ERPs during anticipation, action preparation, and consummatory stages of reward processing, these findings are inconsistent due to temporal and spatial overlap between the relevant electrophysiological components. Our results show three components following cue presentation are sensitive to incentive cues (N1, P3a, P3b). In contrast to previous research, reward‐related enhancement occurred only in the P3b, with earlier components more sensitive to break‐even and loss cues. During feedback anticipation, we observed a lateralized centroparietal negativity that was sensitive to response hand but not cue type. We also show that use of PCA on ERPs reflecting reward consumption successfully separates the reward positivity from the independently modulated feedback‐P3. Last, we observe for the first time a new reward consumption component: a late negativity distributed over the left frontal pole. This component appears to be sensitive to response hand, especially in the context of monetary gain. These results illustrate that the time course and sensitivities of electrophysiological activity that follows incentive cues do not follow a simple heuristic in which reward incentive cues produce enhanced activity at all stages and substages

Technological Advances in Winery Wastewater Treatment: A Comprehensive Review

The commercial production of wine is directly linked to the use of large amounts of fresh water coupledwith the generation of copious amounts of wastewater containing significant amounts of organic andinorganic substances. The impact of this waste stream on the environment has required the wine industryto implement certain protocols in wastewater management to comply with respective effluent dischargeregulations as set out by local authorities. Reduced accessibility to good quality water resources in recentyears has forced wineries to consider more efficient wastewater management strategies to improve waterrecovery and re-use, thereby promoting more sustainable wine production and minimizing the impact onstressed water resources. This review presents a comprehensive overview of established and emerging,physicochemical, biological, advanced oxidation and hybrid wastewater treatment technologies specificallyapplicable to the wine producing industry. Herein, winery wastewater composition and treatmenttechniques, environmental implications, knowledge gaps, technological operational challenges, alternativedisposal and recycling options of treated winery wastewater are critically evaluated

Cooperatives for staple crop marketing: Evidence from Ethiopia

Rural producer organizations, such as farmers' organizations or rural cooperatives, offer a means for smallholder farmers in developing countries to sell their crops commercially. They hold particular promise for Sub-Saharan Africa, where small-scale farming is the primary livelihood but commercialization of foodcrops is very limited. Using the experience of smallholders in Ethiopia as a case study, this research monograph identifies the benefits of rural producer organizations for small farmers, as well as the conditions under which such organizations most successfully promote smallholder commercialization. The evidence from Ethiopia indicates that they do increase farmers' profits from crop sales, but that the beneficiaries do not tend to be the poorest smallholders. Moreover, a rural producer organization's marketing effectiveness is precarious: it can easily diminish if the number or diversity of its members increases or if it provides more nonmarketing services. The authors conclude that these organizations have a role to play in the agricultural development of Sub-Saharan Africa, but that role should be complemented by other programs that directly target the poorest farmers. Further, the effectiveness of rural producer organizations should be preserved by allowing them to follow their own agendas rather than being encouraged to take on nonmarketing activities. The assessment of rural producer organizations presented in this monograph should be a valuable resource for policymakers and researchers concerned with economic development and poverty reduction in Sub-Saharan Africa.Agricultural development, economic growth, Food security Africa, Poverty reduction, Rural poverty, Rural producer organizations (RPOs), Smallholders,

Government Preferences for Promoting Open-Source Software: A Solution in Search of a Problem

Governments around the world are making or considering efforts to promote open-source software (typically produced by cooperatives of individuals) at the expense of proprietary software (generally sold by for-profit software developers). This article examines the economic basis for these kinds of government interventions in the market. It first provides some background on the software industry. The article discusses the industrial organization and performance of the proprietary software business and describes how the open-source movement produces and distributes software. It then surveys current government proposals and initiatives to support open-source software and examines whether there is a significant market failure that would justify such intervention in the software industry. The article concludes that the software industry has performed remarkably well over the past 20 years in the absence of government intervention. There is no evidence of any significant market failures in the provision of commercial software and no evidence that the establishment of policy preferences in favor of open-source software on the part of governments would increase consumer welfare