Unixial compression testing of M30 and JA2 gun propellants using a statistical design strategy

A statistical factorial design strategy is used to determine the uniaxial compressive mechanical response of two energetic polymers, M30 and JA2 gun propellants, as a function of strain rate,, temperature,T, specimen aspect ratio,l/d, and specimen-end lubrication,L. A model of the mechanical response,y=y(,T,l/d,L) is formed using least-squares minimization of observed behavior with a secondorder polynomial model in the independent variables. It is found that aspect ratio and end-lubrication variables can influence the overall mechanical behavior of these materials, so that their effects must be quantitatively evaluated and screened prior to the development of constitutive models. Model predictions and global root-mean-square, RMS, errors in yield stress and strain, strain-energy density at yield, compressive and failure moduli for these materials compare favorably with historical values obtained from a replicate test design strategy.     

On common values of <Emphasis Type="Italic">φ</Emphasis>(<Emphasis Type="Italic">n</Emphasis>) and <Emphasis Type="Italic">σ</Emphasis>(<Emphasis Type="Italic">m</Emphasis>). I

We show, conditional on a uniform version of the prime k-tuples conjecture, that there are x/(log x)^1+o(1) numbers not exceeding x common to the ranges of φ and σ. Here φ is Euler’s totient function and σ is the sum-of-divisors function.     

Optimizing standard sequential extraction protocol with lake and ocean sediments

The environmental mobility/availability behavior of radionuclides in soils and sediments depends on their speciation. Experiments have been carried out to develop a simple but robust radionuclide sequential extraction method for identification of radionuclide partitioning in sediments and soils. The sequential extraction protocol was optimized for temperature, concentration of reagents and reaction time. Optimum extraction conditions were chosen based on the release of ^239,240Pu, ²³⁸U and stable elements. Results from the experiments with lake sediment (SRM 4354) are compared to the previous trials where the sequential extraction protocol was optimized with the ocean sediment (SRM 4357). Based on these two trials the NIST standard sequential extraction protocol is established for defined extraction settings for temperature, reagent concentration and time.     

Sharp probability estimates for random walks with barriers

We give sharp, uniform estimates for the probability that a random walk of n steps on the reals avoids a half-line [y,∞) given that it ends at the point x. The estimates hold for general continuous or lattice distributions provided the fourth moment is finite.     

Systems-based decomposition schemes for the approximate solution of multi-term fractional differential equations

We give a comparison of the efficiency of three alternative decomposition schemes for the approximate solution of multi-term fractional differential equations using the Caputo form of the fractional derivative. The schemes we compare are based on conversion of the original problem into a system of equations. We review alternative approaches and consider how the most appropriate numerical scheme may be chosen to solve a particular equation.     

Temperature Dependence of the Emission Spectrum of Silicon Nanoparticles in Acetone and Isopropanol Solvents

This study investigated the emission spectra of select silicon nanoparticles when subjected to various temperature changes. Two sizes of silicon nanoparticles, dispersed in both isopropanol and acetone solvents, were studied. Photoluminescence responses of the samples were measured in an environmental chamber that allowed exposure to temperatures in the range of ?73 to 65 °C (?100 to 150 °F). These silicon nanoparticles exhibited emission dependence on the temperature of their environment. The emission become brighter as the temperature decreased and less intense as the temperature increased. Thus, the response of these silicon nanoparticles in a harsh environment has been qualified.