Inferring Latent States and Refining Force Estimates via Hierarchical Dirichlet Process Modeling in Single Particle Tracking Experiments

Optical microscopy provides rich spatio-temporal information characterizing in vivo molecular motion. However, effective forces and other parameters used to summarize molecular motion change over time in live cells due to latent state changes, e.g., changes induced by dynamic micro-environments, photobleaching, and other heterogeneity inherent in biological processes. This study focuses on techniques for analyzing Single Particle Tracking (SPT) data experiencing abrupt state changes. We demonstrate the approach on GFP tagged chromatids experiencing metaphase in yeast cells and probe the effective forces resulting from dynamic interactions that reflect the sum of a number of physical phenomena. State changes are induced by factors such as microtubule dynamics exerting force through the centromere, thermal polymer fluctuations, etc. Simulations are used to demonstrate the relevance of the approach in more general SPT data analyses. Refined force estimates are obtained by adopting and modifying a nonparametric Bayesian modeling technique, the Hierarchical Dirichlet Process Switching Linear Dynamical System (HDP-SLDS), for SPT applications. The HDP-SLDS method shows promise in systematically identifying dynamical regime changes induced by unobserved state changes when the number of underlying states is unknown in advance (a common problem in SPT applications). We expand on the relevance of the HDP-SLDS approach, review the relevant background of Hierarchical Dirichlet Processes, show how to map discrete time HDP-SLDS models to classic SPT models, and discuss limitations of the approach. In addition, we demonstrate new computational techniques for tuning hyperparameters and for checking the statistical consistency of model assumptions directly against individual experimental trajectories; the techniques circumvent the need for "ground-truth" and subjective information.Comment: 25 pages, 6 figures. Differs only typographically from PLoS One publication available freely as an open-access article at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.013763

Valley interference effects on a donor electron close to a Si/SiO2 interface

We analyze the effects of valley interference on the quantum control and manipulation of an electron bound to a donor close to a Si/SiO2 interface as a function of the valley-orbit coupling at the interface. We find that, for finite valley-orbit coupling, the tunneling times involved in shuttling the electron between the donor and the interface oscillate with the interface/donor distance in much the same way as the exchange coupling oscillates with the interdonor distance. These oscillations disappear when the ground state at the interface is degenerate (corresponding to zero valley-orbit coupling).Comment: 7 pages, 5 figure

Can the Philippines' Human Resource Base Meet the Challenge of a Liberalized Financial Sector?

Is the Philippines ready to face foreign competition in the financial sector? Does it have enough supply of professionals who are capable of meeting the human resource requirements of domestic and foreign financial corporations in this kind of liberalized environment? Professor Tullao seeks to provide the answers in this Policy Notes.financial sector, financial liberalization, human resource development

Functional properties of ceramic-Ag nanocomposite coatings produced by magnetron sputtering

In recent years, the use of nanocomposite materials to functionalize surfaces has been investigated, taking advantage of the complementary properties of the nanocomposite constituents. Among this family of materials, ceramic-Ag coatings have been widely studied due to the large variety of functionalities that silver possesses and the possibility of tuning the coating’s practical features by selecting the proper matrix to support this noble metal. Therefore, this review focuses on the effects of silver nanoparticles on the functional properties of ceramic-Ag nanocomposites. The chemistry, structure, morphology and topography of the coatings are analyzed with respect to the changes produced by the silver nanoparticles’ distribution, amount and sizes and by altering production process variables. To offer a clear understanding of the functionalities of these materials, the optical, electrical, mechanical, tribological, electrochemical and biological properties reported in the last decade are reviewed, focusing on the ability to tune such properties by modifying the silver distribution, morphology and composition. In particular, the surface plasmon resonance, self-lubricating ability and antibacterial effect of silver are covered in detail, establishing their correlation with factors such as silver diffusion, segregation and ionization.This research is partially sponsored by FEDER funds through the program COMPETE-Programa Operacional Factores de Competitividade and by Portuguese national funds through FCT-Fundação para a Ciência e a Tecnologia, under the projects ANTIMICROBCOAT - PTDC/CTM/102853/2008 and in the framework of the Strategic Projects PEST-C/FIS/UI607/2011, PEST-C/EME/UI0285/2011 and SFRH/BD/80947/2011. The authors would like to thank the ‘‘Surface Modification and Functionalization - Research Group (SMF)” for advice during the development of this review

First-Round Impacts of the 2008 Chilean Pension System Reform

Chile’s innovative privatized pension system has been lauded as possible model for Social Security system overhauls in other countries, yet it has also been critiqued for not including a strong safety net for the uncovered sector. In response, the Bachelet government in 2008 implemented reforms to rectify this shortcoming. Here we offer the first systematic effort to directly evaluate the reform’s impacts, focusing on the new Basic Solidarity Pension for poor households with at least one person age 65+. Using the Social Protection Survey, we show that targeted poor households received about 2.4 percent more household annual income, with little evidence of crowding-out of private transfers. We also suggest that recipient household welfare probably increased due to slightly higher expenditures on basic consumption including healthcare, more leisure hours, and improved self-reported health. While measured short-run effects are small, follow-ups will be essential to gauge longer-run outcomes.