Stretching of polymers in isotropic turbulence: a statistical closure

We present a new closure for the mean rate of stretching of a dissolved polymer by homogeneous isotropic turbulence. The polymer is modeled by a bead-spring-type model (e.g., Oldroyd B, FENE-P, Giesekus) and the analytical closure is obtained assuming the Lagrangian velocity gradient can be modeled as a Gaussian, white-noise stochastic process. The resulting closure for the mean stretching depends upon the ratio of the correlation time for strain and rotation. Additionally, we derived a second-order expression for circumstances when strain and rotation have a finite correlation time. Finally, the base level closure is shown to reproduce results from direct numerical simulations by simply modifying the coefficients.     

The application of a transformational zone method to the calculation of radiation heat transfer inside a piston-cylinder system

A radiation heat transfer analysis has been formulated for the space inside an internal combustion engine cylinder using the principles of the Hottel zone and transformational zone methods. The space analyzed has a variable length resulting from the piston movement. The analysis presented here is for radiation in piston-cylinder systems of known temperatures of radiation gas, and internal surfaces of cylinder, head, and piston. Radiative emissions of the radiation gas in the shape of rings were determined on the basis of Stasiek's principle of surface transformation. The results obtained demonstrate the present approach satisfactorily, both qualitatively and quantitatively. Moreover, the division of the analyzed volume into infinitely small elements along the axial direction has significantly simplified the calculations in comparison with the conventionally employed classical Hottel zone method.     

Maneuver analysis methodology to predict vehicle impacts on training lands

Tactical mobility analysis techniques were merged with land management strategies to assess potential impacts of vehicle operations on training areas for rangeland planning and management. A vehicle mobility analysis was performed for a suite of vehicle types using the NATO Reference Mobility Model (NRMM II). Input parameters include terrain information (soil type, slope, vegetation, surface roughness, soil strength), terrain surface condition based on climate (terrain strength, freeze–thaw, moisture content, snow cover), and vehicle specifications (tire, power train, weight on each axle, ground clearance, dimensions, ride). The vehicle performance was spatially mapped over the terrain for different seasons of the year and used to calculate the maneuverable acreage, which was compared to acreage needed for training requirements. This can be related to land capability based on expected training impact (Maneuver Impact Miles, MIM) and Land Condition Curves which link training density to land condition. This methodology can be used to determine the suitability of training lands and the degree of land management or rehabilitation expected. The methodology was applied to the transformation of the Alaska training lands to support a new brigade unit called the Stryker Brigade Combat Team (SBCT3), but is equally useful for other training areas and military units. For summer use, Alaska training lands are capable of supporting four times the projected training requirements. For winter, when the ground is frozen, more than 10 times the area needed was available.     

Surface-strain measurements on a hemispherical shell using holographic interferometry

A method is presented for using real-time fringe counting and double-exposure single-hologram interferometry to measure surface strain on pressurized hemispherical shells. An aluminum shell is employed for experimental verification of these techniques. Surface-strain variations caused by a defect in the aluminum wall are detected and measured. Strain-gage arrays are used for comparison of experimental results. Bendix Kansas City Division is a prime contractor to the Atomic Energy Commission.     

On the development of the strip yield model for the assessment of multiple site damage

The strip yield model is used to assess the link-up of multiple fatigue cracks in a simple open hole configuration. This analysis is based upon the complex stress function formulation of the problem of multiple straight collinear cuts in an infinite sheet. The predictions of link-up and fracture are compared to results from a fatigue crack propagation test on an open hole specimen, and are shown to be in very close agreement.     

A Comparison of Textbooks' Presentation of Fractions

In the United States, fractions are an important part of the middle school curriculum, yet many middle school students struggle with fraction concepts. Teachers also have difficulty with the conceptual understanding needed to teach fractions and rely on textbooks when making instructional decisions. This reliance on textbooks, the idea that teaching and learning of fractions is a complex process, and that fraction understanding is the foundation for later topics such as proportionality, algebra, and probability, makes it important to examine the variation in presentation of fraction concepts in U.S. textbooks, especially the difference between traditional and standards‐based curricula. The purpose of this study is to determine if differences exist in the presentation of fractions in conventional and standards‐based textbooks and how these differences align with the recommendations of National Council of Teachers of Mathematics, Common Core State Standards, and the research on the teaching and learning of fractions.     

Speciation of metal(loid)s in environmental samples by X-ray absorption spectroscopy: A critical review

Element specificity is one of the key factors underlying the widespread use and acceptance of X-ray absorption spectroscopy (XAS) as a research tool in the environmental and geo-sciences. Independent of physical state (solid, liquid, gas), XAS analyses of metal(loid)s in complex environmental matrices over the past two decades have provided important information about speciation at environmentally relevant interfaces (e.g. solid–liquid) as well as in different media: plant tissues, rhizosphere, soils, sediments, ores, mineral process tailings, etc. Limited sample preparation requirements, the concomitant ability to preserve original physical and chemical states, and independence from crystallinity add to the advantages of using XAS in environmental investigations. Interpretations of XAS data are founded on sound physical and statistical models that can be applied to spectra of reference materials and mixed phases, respectively. For spectra collected directly from environmental matrices, abstract factor analysis and linear combination fitting provide the means to ascertain chemical, bonding, and crystalline states, and to extract quantitative information about their distribution within the data set. Through advances in optics, detectors, and data processing, X-ray fluorescence microprobes capable of focusing X-rays to micro- and nano-meter size have become competitive research venues for resolving the complexity of environmental samples at their inherent scale. The application of μ-XANES imaging, a new combinatorial approach of X-ray fluorescence spectrometry and XANES spectroscopy at the micron scale, is one of the latest technological advances allowing for lateral resolution of chemical states over wide areas due to vastly improved data processing and detector technology.     

Evaluations of the BET, I-point, and α-plot procedures for the routine determination of external specific surface areas of highly dispersed and porous silicas

Nitrogen adsorption isotherms of silicas and other oxidic materials are distorted by the presence of micropore adsorption and capillary condensation. This distortion affects the determination of the specific area of the material, depending on the chosen calculation procedure. Correction of the initial (total) isotherm for micropore capacity decreases or eliminates this source of error to give a useful estimate of the external surface area. In the present work, 26 silica-based adsorbent materials were studied to obtain total and external specific surface areas by the Brunauer-Emmett-Teller (BET), I-point, and α-plot procedures, using the micropore capacities from the α-plots to obtain the corrected (external) isotherms. Errors in the specific surface areas due to the presence of micropores are given by the equation ΔsA = 3.267 (m(2)/cm(3) STP) sV(mic), where sA is the specific surface area in m(2)/g and sV(mic) is the micropore capacity in cm(3) STP/g. A consistent set of conversion factors was obtained by which the external specific surface area obtained using one of these procedures can be converted, with part-per-thousand precision, to either of the others. Although the I-point procedure presents the advantage of not requiring a defined p/p(0) range, the α-plot procedure is recommended for routine determinations of external specific areas of silicas and other oxidic materials, except for cases in which the shapes of the adsorption isotherms of the sample and the reference differ significantly from one another in the p/p(0) range used for the determination.     

Biosynthesis of iron and silver nanoparticles at room temperature using aqueous sorghum bran extracts

Iron and silver nanoparticles were synthesized using a rapid, single step, and completely green biosynthetic method employing aqueous sorghum extracts as both the reducing and capping agent. Silver ions were rapidly reduced by the aqueous sorghum bran extracts, leading to the formation of highly crystalline silver nanoparticles with an average diameter of 10 nm. The diffraction peaks were indexed to the face-centered cubic (fcc) phase of silver. The absorption spectra of colloidal silver nanoparticles showed a surface plasmon resonance (SPR) peak centered at a wavelength of 390 nm. Amorphous iron nanoparticles with an average diameter of 50 nm were formed instantaneously under ambient conditions. The reactivity of iron nanoparticles was tested by the H(2)O(2)-catalyzed degradation of bromothymol blue as a model organic contaminant.     

Ab initio potential energy surface and quantum dynamics for the H + CH4 → H2 + CH3 reaction

A new full-dimensional potential energy surface for the title reaction has been constructed using the modified Shepard interpolation scheme. Energies and derivatives were calculated using the UCCSD(T) method with aug-cc-pVTZ and 6-311++G(3df,2pd) basis sets, respectively. A total number of 30,000 data points were selected from a huge number of molecular configurations sampled by trajectory method. Quantum dynamical calculations showed that the potential energy surface is well converged for the number of data points for collision energy up to 2.5 eV. Total reaction probabilities and integral cross sections were calculated on the present surface, as well as on the ZBB3 and EG-2008 surfaces for the title reaction. Satisfactory agreements were achieved between the present and the ZBB3 potential energy surfaces, indicating we are approaching the final stage to obtain a global potential energy surface of quantitative accuracy for this benchmark polyatomic system. Our calculations also showed that the EG-2008 surface is less accurate than the present and ZBB3 surfaces, particularly in high energy region.