Superconductivity and magnetism in quaternary borocarbides

Quaternary borocarbide superconductors have attracted attention and are of current interest due to a variety of reasons. Some of them exhibit high T_c's for intermetallics, including the material which shows highest known T_c for intermetallics. Though the structure of RNi₂B₂C (R=Sc, Y, rare earth, Th, U) is effectively a layered structure like that of high T_c cuprates, rare earth ions influence the superconducting properties of these materials. Coexistence of superconductivity and magnetism has been found in these materials with magnetic ordering temperatures much higher than those of earlier known magnetic superconductors which implies stronger coupling of rare earth moment to conduction electrons. These features make quaternary borocarbides an altogether different class of materials. Being quaternary, and with the possibility of having more than one rare earth-carbon layer in the structure, this family offers the possibility of finding many new materials with wide ranging properties. Highlights of recent developments in this new subject of quaternary borocarbides are reviewed here.     

Gigabyte/s parallel fiber-optic links based on edge emitting laserdiode arrays

We present a ten-channel parallel fiber optic link consisting of a transmitter based on an edge emitting laser diode array operating nominally at 1 μm wavelength and a complementary receiver based on an InGaAs pin photodetector array. We demonstrate fiber optic link performance up to data rates of 1 Gb/s per channel with low skew at measurement time limited bit error rates lower than 10^-11 over 100 m of multimode fiber ribbon cable. The transmitter is operational, with very clear eye opening, up to baseplate temperatures of 105°C     

Effects of carrier transport on injection efficiency and wavelengthchirping in quantum-well lasers

Using the steady-state solution to the carrier transport rate equation model for the quantum-well laser that they had previously proposed, the authors derive analytic expressions for the laser internal efficiency, carrier injection efficiency, and wavelength chirping under current modulation and show that the various carrier transport times can have a significant effect on these quantities. They present experimental data and theoretical calculations that clearly demonstrate that, as in the case of device optimization for high-speed operation, one has to minimize the transport time across the optical and current confinement regions and maximize the escape time out of the quantum-well active region in order to maximize the internal and the injection efficiencies and minimize the wavelength chirping     

Traditional and novel fermented foods and beverages from tropical root and tuber crops: review

Tropical root and tuber crops [cassava, sweet potato, yams, colocasia (taro), etc] are important staples for food security for about a fifth of the world population. Bulk of cassava in Africa and Latin America are processed into fermented foods and food additives such as organic (acetic, citric and lactic) acids, mono-sodium glutamate, etc. The fermented foods from cassava are gari , fufu , lafun , chickwanghe , agbelima , attieke and kivunde in Africa, tape in Asia and ' cheese ' bread , and ' coated peanut ' in Latin America. Lactic acid bacteria and yeasts are the major group of micro-organisms associated with cassava fermentation. Similarly, sweet potatoes can be fermented into soy sauce, vinegar, lacto-juices, lacto-pickles and sochu (an alcoholic drink produced in Japan), and yams into fermented flour. Most of these fermented food products are functional foods rich in phytochemicals, dietary fibres, anti-oxidant compounds (β-carotene, anthocyanin, etc) and probiotic components (lactic acid bacteria and yeasts).     

Social class and academic guidance: A social-psychological analysis.

Canadian research has consistently shown that, compared with high social class students, a lower proportion of low social class students have high educational expectations. This difference persists even when the level of mental ability between the 2 groups is the same. To answer the question of why so many low social class students do not have high educational expectations, a sample of 1,329 Grade 8 students were administered Form A of Scale 2 of the Culture Fair Intelligence Test and a measure of academic self-confidence. Results show that academic self-concept played a critical role in the way students developed their educational expectations. Part I found that high social class students had a higher academic self-concept than low social class students, even though both groups had a similar level of mental ability. Using a subsample of low social class students with high mental ability, Part 2 found that such students' perception of guidance information was based more on their academic self-concept than on their mental ability. Their academic self-concept thus operated as a frame of reference for interpreting academic advice. Results thus extend previous research by showing that students' academic self-concept does not necessarily match the level of their mental ability, one consequence being that many low social class students develop low educational expectations even though they have high mental ability. Furthermore, even when academic guidance is offered, many of these students, on the basis of their low academic self-concept, interpret the advice as advocating low educational expectations for them. (French summary) (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrete time MRAS with reduced implementation complexity

The letter presents an identification scheme incorporating a set of relays, which lessens the online computations, for discrete-time model reference adaptive systems (MRAS).     

Modeling and Testing for Timing Faults in Synchronous Sequential Circuits

Even with proper design, integrated circuits and systems can have timing problems because of physical faults or variation of parameters. The authors introduce a fault model that takes into account timing related failures in both the combinational logic and the storage elements. Using their fault model and the system's requirements for proper operation, the authors propose ways to handle flipflop-to-flipflop delay, path selection, initialization, error propagation, race-around, and anomalous behavior. They discuss the advantages of scan designs like LSSD and the effectiveness of random delay testing.     

Study of the change of crystallinity of polyethylene on oxidation by inverse phase gas chromatography

Inverse-phase gas chromatography has been used for monitoring the oxidative degradation of low density polyethylene, which has great industrial importance. Polyethylene was oxidized in a gas chromatographic column at 145°C with an oxygen flow of 10 mL/min for different periods. After oxidation for a specified period, the crystallinity and solvent interaction parameters were monitored. For crystallinity studies, the solvent probe was n-decane, and for solvent interaction these were n-decane, o-xylene, n-butanol, and n-butyl acetate. With oxidation there was a gradual fall in crystallinity, and after 15 h the crystallinity was practically nil. Total loss of crystallinity also occurred at 175°C with 1 h passage of oxygen. This has also been confirmed by differential scanning calorimetry. The specific retention volumes of polar solvents showed a sharp increase with oxidation. The results, which are different from that reported in the literature, have been explained.     

Dielectric behaviour of dysprosium oxide films

The dielectric properties of vacuum-deposited dysprosium oxide films have been studied in the audio-frequency range (10²–10⁴ Hz) at various temperatures (78–373 K). The dielectric constant (6.7) was independent of film thickness for thicker films (d > 1000 Å). The capacitance was dependent both on temperature and frequency, but became constant for all frequencies at low temperature. Tan δ showed a frequency minimum and its variation with frequency and temperature was in agreement with the model proposed earlier by Goswami and Goswami. The breakdown field (≌10⁶ V cm^-1) followed the Forlani-Minnaja relation. The activation energy and the refractive index of these films were also measured.