Hypervariable digital DNA codes for human paternal lineages: MVR-PCR at the Y-specific minisatellite, MSY1 (DYF155S1)

We describe the first haploid minisatellite, the human Y chromosome-specific locus, MSY1. It consists of an array of 48-114 AT-rich 25 bp repeats of at least five different variant types. A minisatellite variant repeat PCR (MVR-PCR) system gives Y-specific DNA codes, with a virtual heterozygosity of 99.9%, making MSY1 by far the single most variable locus on the Y. African populations contain the most diverged MSY1 structures. MSY1 is the only Y-chromosomal system where the characteristics of large numbers of mutations can be studied in detail: it provides a uniquely powerful tool both for the investigation of mutation in a haploid system, and for the dating of paternal lineages.     

Information technology enhanced learning in distance andconventional education

The rapid growth of the Internet and the media-rich extensions of the World Wide Web allow new developments in the way instructors transfer knowledge to their students. There is no doubt that nothing will replace synchronous learning through face to face interaction but it is sometimes not feasible for students to attend conventional classes due to distance or time constraints. This paper presents a model for using information technology to enhance the learning experience for conventional on-campus students, as well as for those students whose circumstances require that they be asynchronous in time or space. The approach described emphasizes a solution which allows students to attend the class in real time via the Internet, or to access asynchronously digitally stored video material with hyperlinks to online training resources at any time. The proposed solution permits interaction in real-time and asynchronously among students and between students and instructor, which is a key for effective learning. In addition, the instructor maintains a significant level of spontaneity in using multimedia material prepared in advance or using conventional chalkboard or hand written materials via traditional overhead projection. The paper describes the technical issues involved and the chosen solutions to provide enhanced live and archived classes. This paper provides some comments on the evaluation of the learning experience using this method of delivery for on-campus and distance education students. Finally the authors share their vision on future trends to improve the proposed learning environment and the need for an optimal balance between expositive teaching and active learning for both synchronous and asynchronous activities     

Intelligent Open Switch Fault Detection for Power Converter in Wind Energy System

This paper proposes a simple and fast fuzzy logic-based open switch fault detection method for rotor side converter (RSC) in doubly fed induction generator (DFIG) wind turbine system. In the proposed scheme, only the mean values of the three-phase rotor currents are used to identify the power switch in which the open-circuit fault has occurred.

The wind energy conversion system model developed for the design and evaluation of the proposed fault detection technique including three principal controls. the first control ensure the regulation of the electromagnetic torque and the reactive stator power (named Rotor Side Converter (RSC) control), the second regulates the DC-link voltage at the desired level (named Grid Side Converter (GSC) control) and in order to achieve maximum power at any wind speed condition a maximum power point tracking (MPPT) control strategy has been used. The simulation model was developed in MATLAB/Simulink environment. The results show that the proposed fault detection scheme is able to rapidly and effectively identify open switch faults among other fault types in a time less than one period.     

Experimental and modeling investigation of the failure resistance of Advanced High Strength Steels spot welds

Damage of Advanced High Strength Steel resistance spot welds is investigated in Cross Tension by means of coupled microtomography, metallography and fractography. Three main failure mechanisms and failure zones are identified: (i) strain localization in the base metal/sub-critical Heat Affected Zone (HAZ), (ii) ductile shear around the weld and (iii) semi-brittle fracture in the weld nugget. A finite element model is developed in order to illustrate how the mechanisms compete and lead to a given failure type. The local constitutive behavior is obtained from tensile tests on simulated HAZ microstructures. The model enables capturing the main trends in the transition between failure types as a function of weld geometry as well as a reliable estimation of the load bearing capacity.     

Distance spectra and performance bounds of space-time trellis codes over quasistatic fading channels

This correspondence presents a general approach to upper bounding coded system performance over quasistatic fading channels (QSFC). This approach has the advantage of yielding a closed-form upper bound that converge for all signal-to-noise ratios (SNRs). The proposed approach is used to upper-bound the performance of space-time trellis codes (STTC) over QSFCs. The resulting upper bounds for STTCs are better adapted to the QSFC and present an improvement over worst case pairwise error probability (PEP) analysis used so far. In its second part, this correspondence investigates several ways to reduce the complexity of computing the distance spectrum of STTCs. The combined result obtained from using the new upper bounds and the computed distance spectra are shown to be close to simulated performance for all SNRs.     

An upper bound on turbo codes performance over quasi-static fading channels

This letter proposes an upper bound on the performance of turbo-codes over quasi-static fading channels. First an upper bound is derived for the case of a single-input single-output channel. The result is then extended to the case of a serial concatenation of a turbo-code and a space-time block code. Unlike a simple extension of the union bound, the derived upper bounds are shown to converge for all signal-to-noise ratios. Additionally the closed form upper bounds obtained confirm analytically that, unlike over additive white Gaussian noise channels, turbo-code performance does not improve by increasing frame length over quasi-static fading channels.     

Liquid zinc embrittlement of twinning-induced plasticity steel

The susceptibility of a Fe22Mn0.6C twinning-induced plasticity steel to liquid zinc embrittlement has been investigated by performing hot tensile tests on bare and electrogalvanized specimens using a Gleeble thermomechanical simulator. Tensile tests were carried out at different temperatures and strain rates. The studied steel can be severely embrittled by liquid zinc (drastic reductions in elongation at rupture and fracture strength) given particular conditions of temperature and strain rate.     

Experimental determination of the carbon solubility limit in ferritic steels

Despite the existence of a number of published results, the data on the solubility of carbon in alpha iron are still inaccurate. An analysis of published experimental results shows that available values vary greatly (between 50 and 100 ppm by wt, for example, at 600 °C). These discrepancies make it difficult to optimize the metallurgical processes of low-carbon or ultralow-carbon alloys. An experimental methodology, using the measurement of the thermo-electric power (TEP) of the alloy, was set up. This enabled us to deduce the quantity of free interstitials in the matrix by measuring the amount of interstitials which segregate on dislocations after a deformation of the sample. This technique was used in the case of an Al-killed steel containing 0.2 pct Mn. The limit of solubility of carbon was determined with a precision of ±2 ppm between 550 °C and 730 °C. This limit of solubility can be analytically described by the relation C_{(wt pct)}=6.63 exp (−11.8_kcal·mol ⁻¹/RT), which is shown to be valid only for temperatures above 400 °C. We show experimentally that the residual concentration of carbon at low temperature is much greater than the value predicted by the extrapolation of this relation. Complementary studies on steels with various C and Mn contents allow us to verify the validity of the proposed methodology.