The Chaotic Nature of Faster Gradient Descent Methods

The steepest descent method for large linear systems is well-known to often converge very slowly, with the number of iterations required being about the same as that obtained by utilizing a gradient descent method with the best constant step size and growing proportionally to the condition number. Faster gradient descent methods must occasionally resort to significantly larger step sizes, which in turn yields a rather non-monotone decrease pattern in the residual vector norm.     

Effect of Surface Coating on the Photocatalytic Function of Hybrid CdS–Au Nanorods

Hybrid semiconductor–metal nanoparticles are interesting materials for use as photocatalysts due to their tunable properties and chemical processibility. Their function in the evolution of hydrogen in photocatalytic water splitting is the subject of intense current investigation. Here, the effects of the surface coatings on the photocatalytic function are studied, with Au‐tipped CdS nanorods as a model hybrid nanoparticle system. Kinetic measurements of the hydrogen evolution rate following photocatalytic water reduction are performed on similar nanoparticles but with different surface coatings, including various types of thiolated alkyl ligands and different polymer coatings. The apparent hydrogen evolution quantum yields are found to strongly depend on the surface coating. The lowest yields are observed for thiolated alkyl ligands. Intermediate values are obtained with L‐glutathione and poly(styrene‐co‐maleic anhydride) polymer coatings. The highest efficiency is obtained for polyethylenimine (PEI) polymer coating. These pronounced differences in the photocatalytic efficiencies are correlated with ultrafast transient absorption spectroscopy measurements, which show a faster bleach recovery for the PEI‐coated hybrid nanoparticles, consistent with faster and more efficient charge separation. These differences are primarily attributed to the effects of surface passivation by the different coatings affecting the surface trapping of charge carriers that compete with effective charge separation required for the photocatalysis. Further support of this assignment is provided from steady‐state emission and time‐resolved spectral measurements, performed on related strongly fluorescing CdSe/CdS nanorods. The control and understanding of the effect of the surface coating of the hybrid nanosystems on the photocatalytic processes is of importance for the potential application of hybrid nanoparticles as photocatalysts.     

InAs Nanocrystals with Robust p-Type Doping

Robust control over the carrier type is fundamental for the fabrication of nanocrystal-based optoelectronic devices, such as the p–n homojunction, but effective incorporation of impurities in semiconductor nanocrystals and its characterization is highly challenging due to their small size. Herein, InAs nanocrystals (NCs), post-synthetically doped with Cd, serve as a model system for successful p-type doping of originally n-type InAs nanocrystals, as demonstrated in field effect transistors (FETs). Advanced structural analysis, using atomic resolution electron microscopy and synchrotron X-ray absorption fine structure spectroscopy reveal that Cd impurities reside near and on the nanocrystal surface acting as substitutional p-dopants replacing Indium. Commensurately, Cd-doped InAs FETs exhibit remarkable stability of their hole conduction, mobility, and hysteretic behavior over time when exposed to air, while intrinsic InAs NCs FETs are easily oxidized and their performance quickly declines. Therefore, Cd plays a dual role acting as a p-type dopant, and also protects the nanocrystals from oxidation, as evidenced directly by X-ray photoelectron spectroscopy measurements of air exposed samples of intrinsic and Cd-doped InAs NCs films. This study demonstrates robust p-type doping of InAs nanocrystals, setting the stage for implementation of such doped nanocrystal systems in printed electronic devices.     

High‐Throughput Scaffold System for Studying the Effect of Local Geometry and Topology on the Development and Orientation of Sprouting Blood Vessels

Live tissues require vascular networks for cell nourishing. Mimicking the complex structure of native vascular networks in vitro requires understanding the governing factors of early tubulogenesis. Current vascularization protocols allow for spontaneous formation of vascular networks; however, there is still a need to provide control over the defined network structure. Moreover, there is little understanding on sprouting decision and migration, especially within 3D environments. Here, tessellated polymer scaffolds with various compartment geometries and a novel two‐step seeding protocol are used to study vessel sprouting decisions. Endothelial cells first organize into hollow vessels tracing the shape contour with high fidelity. Subsequent sprouts emerge in specific directions, responding to compartment geometry. Time‐lapse imaging is used to track vessel migration, evidencing that sprouts frequently emerge from the side centers, mainly migrating toward opposing corners, where the density of support cells (SCs) is the highest, providing the highest levels of angiogenic factors. SCs distribution is quantified by smooth muscle actin expression, confirming the cells preference for curved compartment surfaces and corners. Displacements within the hydrogel correlate with SCs distribution during the initial tubulogenesis phase. This work provides new insight regarding vessel sprouting decisions that should be considered when designing scaffolds for vascularized engineered tissues.     

Particle formation from droplet containing nanoparticles: Internal bubble growth

ABSTRACT

Modeling spray drying is based on the behavior of individual droplets involved in the process. The drying history of single droplets is generalized to the entire spray by incorporating drying kinetics equations into Euler–Lagrange models of spray drying process. The morphological evolution of single droplet is determined by parameters of the drying agent and properties of solid material in the droplet. In this study, the possible causes for bubble inception are discussed and different morphological evolutions and deformations are examined. A novel mathematical model of single droplet containing insoluble nanoscale particles and internal bubble has been developed and parametrically studied.     

The Psychoanalytic Institute of Northern California: A graduation.

This article presents Peskin's speech at the second graduation of the Psychoanalytic Institute of Northern California. In it, he discusses psychoanalytic politics and the continuing development of psychoanalysis. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effects of harvest stage and re‐growth on yield,composition, ensilage and in vitro digestibility of new forage sorghum varieties

The effect of growth stage and re‐growth on the nutritional and ensilage characteristics of two new sorghum hybrids, BMR‐101 and Silobuster, and one commercial variety, FS‐5, was examined in this study. Varieties were sampled during the summer at the early heading (EH) stage and were harvested at the soft dough (SD) stage. Additional irrigation enabled autumn re‐growth and a second harvest. Plants of FS‐5 and BMR‐101 were resistant to lodging at EH. However, BMR‐101 and Silobuster suffered from high lodging at the SD stage of the summer harvest. Dry matter (DM) content of FS‐5 and BMR‐101 at EH was below 250 g kg^?1. DM yields of the varieties were similar at the summer harvest and higher than their respective re‐growth cuts. Ensilage DM losses were moderate and similar across varieties. Hemicellulose of SD plants was partly solubilised and most of the water‐soluble carbohydrate fermented, yielding lactic acid, ethanol and volatile fatty acids (VFA), and a pH < 4. In vitro DM digestibility of varieties was similar in summer silages, but lower in the respective re‐growth silages of FS‐5 and BMR‐101, reflecting the higher content of neutral detergent fibre and lignin in the re‐growth silages. The summer plus re‐growth cumulative yields of digestible DM of the respective FS‐5, Silobuster and BMR‐101 silages were 14.7, 16.6 and 14.5 t ha^?1. The commercial variety, FS‐5, may have some advantage over BMR‐101 and Silobuster owing to its relative resistance to lodging in addition to its high yield and good ensilage properties. Copyright © 2005 Society of Chemical Industry     

Accelerating Scientific Discovery Through Computation and Visualization II

This is the second in a series of articles describing a wide variety of projects at NIST that synergistically combine physical science and information science. It describes, through examples, how the Scientific Applications and Visualization Group (SAVG) at NIST has utilized high performance parallel computing, visualization, and machine learning to accelerate research. The examples include scientific collaborations in the following areas: (1) High Precision Energies for few electron atomic systems, (2) Flows of suspensions, (3) X-ray absorption, (4) Molecular dynamics of fluids, (5) Nanostructures, (6) Dendritic growth in alloys, (7) Screen saver science, (8) genetic programming.     

Thermal resonant tunneling rates by a generalized flux averaging method

The calculation of the thermal rate constant as a time integral over flux-flux correlation functions is a challenging task when the potential energy along the reaction coordinate cannot be associated with a distinctive single barrier. In the case of resonant tunneling through a double barrier potential, the calculations may become formidable due to the population of long-lived resonance states and the corresponding long time-decay of the flux-flux correlation functions. The flux averaging method was introduced recently in order to circumvent this problem in cases where the long time dynamics is due to a single resonance state with the longest lifetime in the system. In this work we generalize the method for calculations of thermal resonant-tunneling rates in systems of many resonances, where the long time-decay is accompanied by an internal dynamics within the quasi-bound system. This extra complication is handled by additional averaging of flux-flux correlation funcation over the time period of the internal dynamics. The result is an exact expression for the rate constant in terms of a linear combination of time integrals over flux-flux correlation functions, which reaches its asymptotic time limit in a short (direct scattering) time, regardless of the long time-decay of the flux-flux correlation functions. This is derived for an analytic model system, and demonstrated in a numerical simulation of resonant tunneling through a double barrier potential.