Vortex Washboard Voltage Noise in Type-II Superconductors

In order to characterize flux flow through disordered type-II superconductors, we investigate the effects of columnar and point defects on the vortex velocity / voltage power spectrum in the driven non-equilibrium steady state. We employ three-dimensional Metropolis Monte Carlo simulations to measure relevant physical observables including the force-velocity / current-voltage (I-V) characteristics, vortex spatial arrangement and structure factor, and mean flux line radius of gyration. Our simulation results compare well to earlier findings and physical intuition. We focus specifically on the voltage noise power spectra in conjunction with the vortex structure factor in the presence of weak columnar and point pinning centers. We investigate the vortex washboard noise peak and associated higher harmonics, and show that the intensity ratios of the washboard harmonics are determined by the strength of the material defects rather than the type of pins present. Through varying columnar defect lengths and pinning strengths as well as magnetic flux density we further explore the effect of the material defects on vortex transport. It is demonstrated that the radius of gyration displays quantitatively unique features that depend characteristically on the type of material defects present in the sample.Comment: Latex, 17 pages, 14 figure

Discount Rates for Nonindustrial Private Forest Landowners in Mississippi: How High a Hurdle?

Mississippi forest landowners were surveyed to determine average discount rates or “hurdle rates”—the lowest rates of return they consider acceptable—for 3 nonforestry investments, and for 5, 15, and 25 yr forestry investments. The survey included 829 individuals who owned at least 20 ac of uncultivated land and had harvested timber during a recent 5 yr period; survey results are therefore oriented toward commercially active forest landowners. On average, the private nonindustrial forest landowners included in the survey expect timberland investments to earn higher rates of compound interest than relatively low-risk bank savings accounts and certificates of deposit. Relatively short-term (5 yr) timberland investments, however, have lower minimum rates of return than stocks, bonds, and mutual funds. With forestry investments, all else equal, Mississippi nonindustrial private forest landowners prefer shorter time periods—average hurdle rates in nominal terms before taxes were 8.0% for forestry investments lasting 5 yr, 11.3% for those lasting 15 yr, and 13.1% for those lasting 25 yr. Household income significantly influenced the lowest rate of return considered acceptable for 5 yr forestry investments—the rate was 9% for landowners with annual incomes above $50,000 and 7.4$50,000. On a hurdle rate basis, higher income private landowners in Mississippi generally find forestry investments lasting 15 yr to be competitive with stocks, bonds, and mutual funds. However, Mississippi landowners’ 13.1% required rate of return for 25 yr forestry investments was higher than the rate considered acceptable for the other investments included in the survey. Reforestation tax incentives, cost-shares, and related public policies that reduce the front-end costs incurred by NIPF landowners tend to increase the projected rate of return for relatively long-term reforestation investments. South. J. Appl. For. 26(1):26–31

Virtual materials for the prediction of concrete mechanical properties

Physical properties such as compressive strength and elastic moduli are of the utmost importance for the structural stability and design of cement-based materials. These properties are strictly related to the microstructure of the binder paste, which in turn varies in time, as a function of the hydration kinetics. Therefore, the development of the elastic properties and mechanical strength can in principle be controlled by affecting the microstructure and hydration kinetics. This can be achieved through an appropriate mix-design, which encompasses a careful selection of phase proportions, grain-size distribution, amount of water and aggregates, and use of additives. Changing such variables by a trial-and-error process can be extremely time consuming and has a significant impact in terms of resources employed. Moreover, a fully quantitative approach to the study of the cement microstructure and hydration kinetics requires significant efforts in terms of experimental testing, often encompassing analytical techniques such as X-ray diffraction, scanning electron microscopy and isothermal calorimetry, among others. In this contribution, an alternative quantitative characterization of the cement paste in time is illustrated, based on the numerical modeling of cement-based systems. Virtual cement pastes and mortars are generated using the software VCCTL (http://www.nist.gov/el/building_materials/inorganic/vcctl.cfm), using as input parameters the clinker phase composition, the water/cement ratio, and the size and shape distribution of the particles. The elastic moduli and compressive strength of such virtual samples is then computed from the developed microstructure by a finite element method. Extensive calibration and testing has been performed against experimental data, and the good agreement between the calculated and measured elastic and mechanical properties shows that VCCTL can be used as a truly predictive tool. Although experimental testing remains a fundamental aspect of concrete science, the coupling of experiments with computational methods provides a viable tool towards a knowledge-based mix design, with a potential reduction of costs and environmental impact

Reforestation of harvested Timberlands in Mississippi: Behavior and Attitudes of Non-Industrial, Private Forest Landowners

Southern forests play an increasingly important role in the timber economy as per capita demand for wood continues to expand. Moreover, harvest restrictions in the Pacific Northwest in the early 1990s shifted a large portion of United States demand for softwoods to the South. In Mississippi, most of the forestland is owned by non-industrial private forest (NIPF) landowners. Approximately 314,000 NIPF landowners control 66 percent of the state’s forestland base (Hartsell and London 1995). The sizable acreage of timberland held by NIPF landowners nationally and in-state underscores the importance of their role in the timber economy and weighs heavily in the supply of raw material to the state’s $11.4 billion forest products industry (Munn 1998)

Virtual materials for the prediction of concrete mechanical properties

Physical properties such as compressive strength and elastic moduli are of the utmost importance for the structural stability and design of cement-based materials. These properties are strictly related to the microstructure of the binder paste, which in turn varies in time, as a function of the hydration kinetics. Therefore, the development of the elastic properties and mechanical strength can in principle be controlled by affecting the microstructure and hydration kinetics. This can be achieved through an appropriate mix-design, which encompasses a careful selection of phase proportions, grain-size distribution, amount of water and aggregates, and use of additives. Changing such variables by a trial-and-error process can be extremely time consuming and has a significant impact in terms of resources employed. Moreover, a fully quantitative approach to the study of the cement microstructure and hydration kinetics requires significant efforts in terms of experimental testing, often encompassing analytical techniques such as X-ray diffraction, scanning electron microscopy and isothermal calorimetry, among others. In this contribution, an alternative quantitative characterization of the cement paste in time is illustrated, based on the numerical modeling of cement-based systems. Virtual cement pastes and mortars are generated using the software VCCTL (http://www.nist.gov/el/building_materials/inorganic/vcctl.cfm), using as input parameters the clinker phase composition, the water/cement ratio, and the size and shape distribution of the particles. The elastic moduli and compressive strength of such virtual samples is then computed from the developed microstructure by a finite element method. Extensive calibration and testing has been performed against experimental data, and the good agreement between the calculated and measured elastic and mechanical properties shows that VCCTL can be used as a truly predictive tool. Although experimental testing remains a fundamental aspect of concrete science, the coupling of experiments with computational methods provides a viable tool towards a knowledge-based mix design, with a potential reduction of costs and environmental impact

Comparison Between Regenerators and Non-Regenerators in Mississippi: A Discriminant Analysis

Nonindustrial private forestland (NIPF) landowners in Mississippi who recently harvested timber were surveyed to examine their regeneration behavior. Differences between regenerators and nonregenerators were investigated by looking at the different factors affecting reforestation decisions. A discriminant analysis was used to identify factors that were useful in differentiating between regenerators and nonregenerators. Ownership size; sociodemographic characteristics such as income, education, place of residence, and age; awareness of existing government incentive/assistance programs; and participation in educational programs were significant variables in differentiating between regenerators and nonregenerators. Landowners who own larger timberlands had a higher propensity to engage in regeneration activities after harvests. This also was true for landowners who had higher income levels and educational attainment, and were younger, city resident, and white. Landowners who were aware of existing government incentive/assistance programs and those who participated in educational programs also were more likely to participate in pine regeneration. Landowners in Mississippi considered both ecological and economic reasons as highly important considerations in their decision to regenerate. The belief that the land would reforest itself to pine naturally, the high cost of reforestation, and lack of information on reforestation options were top reasons cited by landowners for their decision not to regenerate. South. J. Appl. For. 28(4):189 –19

Implementation of an innovative teaching project in a Chemical Process Design course at the University of Cantabria, Spain

This paper shows the planning, the teaching activities and the evaluation of the learning and teaching process implemented in the Chemical Process Design course at the University of Cantabria, Spain. Educational methods to address the knowledge, skills and attitudes that students who complete the course are expected to acquire are proposed and discussed. Undergraduate and graduate engineers' perceptions of the methodology used are evaluated by means of a questionnaire. Results of the teaching activities and the strengths and weaknesses of the proposed case study are discussed in relation to the course characteristics. The findings of the empirical evaluation shows that the excessive time students had to dedicate to the case study project and dealing with limited information are the most negative aspects obtained, whereas an increase in the students' self-confidence and the practical application of the methodology are the most positive aspects. Finally, improvements are discussed in order to extend the application of the methodology to other courses offered as part of the chemical engineering degree.This work was partially supported with the financial help of the University of Cantabria, 1st and 2nd Teaching Innovation Programs 2011-2012, 2013-2014, Projects Innodesign 1 and 2

Differential expression analysis for sequence count data

*Motivation:* High-throughput nucleotide sequencing provides quantitative readouts in assays for RNA expression (RNA-Seq), protein-DNA binding (ChIP-Seq) or cell counting (barcode sequencing). Statistical inference of differential signal in such data requires estimation of their variability throughout the dynamic range. When the number of replicates is small, error modelling is needed to achieve statistical power.

*Results:* We propose an error model that uses the negative binomial distribution, with variance and mean linked by local regression, to model the null distribution of the count data. The method controls type-I error and provides good detection power. 

*Availability:* A free open-source R software package, _DESeq_, is available from the Bioconductor project and from "http://www-huber.embl.de/users/anders/DESeq":http://www-huber.embl.de/users/anders/DESeq