Facile Synthesis of Bimetallic Ag/Ni Core/Sheath Nanowires and Their Magnetic and Electrical Properties

This paper describes a facile method for coating Ag nanowires with uniform, ferromagnetic sheaths made of polycrystalline Ni. A typical sample of these core/sheath nanowires had a saturation magnetization around 33 emu g^?1. We also demonstrated the use of this magnetic property to align the nanowires by simply placing a suspension of the nanowires on a substrate in a magnetic field and allowing the solvent to evaporate. The electrical conductivity of these core/sheath nanowires (2 × 10³ S cm^?1) was two orders of magnitude lower than that of bulk Ag (6.3 × 10⁵ S cm^?1) and Ni (1.4 × 10⁵ S cm^?1). This is likely caused by the transfer of electrons from the Ag core to the Ni sheath due to the difference in work function between the two metals. The electrons are expected to experience an increased resistance due to spin‐dependent scattering caused by the randomized magnetic domains in the polycrystalline, ferromagnetic Ni sheath. Studies on the structural changes to the Ni coating over time under different storage conditions show that storage of the nanowires on a substrate under ambient conditions leads to very little Ni oxidation after 6 months. These Ag/Ni core/sheath nanowires show promise in areas such as electronics, spintronics, and displays.     

Student Perceptions of Internet-Based Learning Tools in Environmental Engineering Education

The Internet provides an excellent framework for learning, communication, information exchange, and collaboration in engineering education. This existing electronic infrastructure was integrated into an undergraduate environmental engineering course in atmospheric physics and chemistry to foster discussion of course topics, peer evaluation, and collaborative learning. Four major Internet-based learning tools were utilized to accomplish these objectives: 1) electronic copies of partial notes allowed students to remain engaged during class, 2) an electronic bulletin board enabled interactive discussion and peer evaluation of work, 3) multimedia assignments required students to retrieve information and direct their learning, 4) publicly accessible and peer-reviewed Internet-based term project reports provided motivation for quality and creative work. Student response to these new approaches was overwhelmingly positive, although preferences vary with learning style. While students assess many Internet-based learning approaches as useful, conventional educational approaches are still viewed as important components to successful learning.     

Non-Gaussian simulation of local material properties based on a moving-window technique

In this paper, a moving-window micromechanics technique, Monte Carlo simulation, and finite element analysis are used to assess the effects of microstructural randomness on the local stress response of composite materials. The randomly varying elastic properties are characterized in terms of a field of local effective elastic constitutive matrices using a moving-window technique based on a finite element model of a given digitized composite material microstructure. Once the fields are generated, estimates of the random properties are obtained for use as input to a simulation algorithm that was developed to retain spectral, correlation, and non-Gaussian probabilistic characteristics. Rapidly generated Monte Carlo simulations of the constitutive matrix fields are used in a finite element analysis to create a series of local stress fields associated with the random material sample under uniaxial tension. This series allows estimation of the statistical variability in the local stress response for the random composite. The identification of localized extreme stress deviations from those of the aggregate or effective properties approach highlight the importance of modeling the stochastic variability of the microstructure.     

The yeast SEN1 gene is required for the processing of diverse RNA classes

A single base change in the helicase superfamily 1 domain of the yeast Saccharomyces cerevisiae SEN1 gene results in a heat-sensitive mutation that alters the cellular abundance of many RNA species. We compared the relative amounts of RNAs between cells that are wild-type and mutant after temperature-shift. In the mutant several RNAs were found to either decrease or increase in abundance. The affected RNAs include tRNAs, rRNAs and small nuclear and nucleolar RNAs. Many of the affected RNAs have been positively identified and include end-matured precursor tRNAs and the small nuclear and nucleolar RNAs U5 and snR40 and snR45. Several small nucleolar RNAs co-immunoprecipitate with Sen1 but differentially associate with the wild-type and mutant protein. Its inactivation also impairs precursor rRNA maturation, resulting in increased accumulation of 35S and 6S precursor rRNAs and reduced levels of 20S, 23S and 27S rRNA processing intermediates. Thus, Sen1 is required for the biosynthesis of various functionally distinct classes of nuclear RNAs. We propose that Sen1 is an RNA helicase acting on a wide range of RNA classes. Its effects on the targeted RNAs in turn enable ribonuclease activity.     

Impact of neighborhood biomass cooking patterns on episodic high indoor particulate matter concentrations in clean fuel homes in Dhaka,Bangladesh

Exposure to particulate matter (PM_2.5) from the burning of biomass is associated with increased risk of respiratory disease. In Dhaka, Bangladesh, households that do not burn biomass often still experience high concentrations of PM_2.5, but the sources remain unexplained. We characterized the diurnal variation in the concentrations of PM_2.5 in 257 households and compared the risk of experiencing high PM_2.5 concentrations in biomass and non‐biomass users. Indoor PM_2.5 concentrations were estimated every minute over 24 h once a month from April 2009 through April 2010. We found that households that used gas or electricity experienced PM_2.5 concentrations exceeding 1000 μg/m³ for a mean of 35 min within a 24‐h period compared with 66 min in biomass‐burning households. In both households that used biomass and those that had no obvious source of particulate matter, the probability of PM_2.5 exceeding 1000 μg/m³ were highest during distinct morning, afternoon, and evening periods. In such densely populated settings, indoor pollution in clean fuel households may be determined by biomass used by neighbors, with the highest risk of exposure occurring during cooking periods. Community interventions to reduce biomass use may reduce exposure to high concentrations of PM_2.5 in both biomass and non‐biomass using households.     

Dynamics of a mode-locked low-pressure photolytic I* laser

A longitudinally pumped photolytic iodine laser has been reliably mode-locked over a broad range of iodide pressures (1-30 Torr). Average mode-locked pulse widths ranging from 1.4-2.5 ns were observed as a function of CF₃I iodide pressure and added buffer gas (Ar). Low-pressure data indicate an increased gain bandwidth as a result of an initial nonthermal I* atom distribution following rapid (<20 ns) photolysis of the parent molecule, CF₃I. Nearly 1.75 eV of excess pump energy is available and is deposited into the internal vibrational and rotational degrees of freedom of the large radical and into the translation of the nascent iodine atom, allowing for high iodine atom velocities in the frame of observation. A diode laser system tuned to the 3-4 transition of spin-orbit excited iodine atoms was used to observe the time-dependent behavior of line center gain along the optical axis. Preliminary data indicate an I* atom velocity relaxation on the order of 1 μs for an iodide pressure of 1 Torr, and approximately 300 ns for a pressure of 10 Torr. At 5 Torr of CF₃ I, the laser mode build up time is 200 ns, allowing access to the increased gain bandwidth and resulting in mode-locked pulse widths less than the predicted transform-limited pulse width for an inhomogeneous gas laser     

Pretraining enhances recovery from visuospatial deficit following cerebellar dentate nucleus lesion.

Following bilateral lesions targeting lateral deep cerebellar nuclei, rats were subjected to a bridge test as a measure of visuomotor coordination and were trained on the Morris water maze (MWM) as a measure of visuospatial processing. Lesioned rats were significantly impaired in visuospatial processing, but not visuomotor coordination, relative to sham rats. In a 2nd experiment, rats were pretrained on a delayed spatial alternation task (T maze) before MWM training. Pretraining reversed the visuospatial deficit caused by the lesions as compared with nonpretrained rats. Results suggest that lateral deep cerebellar nuclei contribute to visuospatial processing with a negligible contribution to visuomotor skills and that visuospatial deficits resulting from lateral nuclei damage can be reversed with pretraining on a spatial working memory task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

First- and Higher-Order Correlation Detection Using Wavelet Transforms

In order to detect intermittent first- and higher-order correlation between a pair of signals in both time and frequency, a wavelet-based coherence and bicoherence technique was developed. Due to the limited averaging in a time-frequency coherence estimate, spurious correlated pockets were detected due to statistical variance. The introduction of multiresolution, localized integration windows was shown to minimize this effect. A coarse ridge extraction scheme utilizing hard thresholding was then applied to extract meaningful coherence. This thresholding scheme was further enhanced through the use of “smart” thresholding maps, which represent the likely statistical noise between uncorrelated simulated signals bearing the same power spectral density and probability-density function as the measured signals. It was demonstrated that the resulting filtered wavelet coherence and bicoherence maps were capable of capturing low levels of first- and higher-order correlation over short time spans despite the presence of ubiquitous leakage and variance errors. Immediate applications of these correlation detection analysis schemes can be found in the areas of bluff body aerodynamics, wave-structure interactions, and seismic response of structures where intermittent correlation between linear and nonlinear processes is of interest.     

Detection of charged particles with charge injection devices

A method for using charge injection devices (CIDs) for detection of high-energy charged particles from inertial-confinement fusion reactions is described. Because of the relatively small depletion region of the CID camera (depletion depth of approximately 7 mum), aluminum foils are placed in front of the device to reduce the energy of the charged particles and maximize the energy deposited in the CID. Simultaneous measurements of (2)H(d,p)(3)H protons with a CID and a surface barrier detector indicate that the CID is an efficient detector of charged fusion products. Tests using high energy alpha particles emitted from a radium-226 source are also reported.