Are web self-assessment tools useful for training?

This paper presents the negative experience carried out by using a Web self-assessment tool (WSAT) called AulaWeb, developed by the Universidad Politecnica de Madrid (UPM), Madrid, Spain, to train engineers. The main goal in using this tool was to motivate students to improve their learning and results in a computing subject. Over 800 students take this subject every year, and the failure rate is high. Nevertheless, the results achieved were the opposite of what was expected. This paper uncovers the mistakes made and provides important tips for teachers facing a similar problem with a subject or for teachers who would like to use WSATs to improve students' learning. This advice is based on the analysis and comparison of the results achieved over five consecutive academic years, in two of which AulaWeb was used.     

Polyphenolic compositions of Basque natural ciders: A chemometric study

Polyphenolic compositions of Basque natural ciders were determined by high-performance liquid chromatography, with diode array detection following thiolysis, in order to differentiate ciders according to the geographical origin of the main raw material used for their elaboration. Fifty percent of the apples used for cidermaking in the Basque Country are imported from France or Galicia (N.W. Spain); this gives beverages of different chemical compositions and sensory qualities. A data set, consisting of 64 cider samples and 33 measured variables, was evaluated using multivariate chemometric techniques. A preliminary study of data structure was performed by cluster analysis and principal component analysis. Different classification systems for the two categories were obtained on the basis of the chemical data by applying several supervised pattern recognition procedures, such as linear discriminant analysis (LDA), K-nearest neighbours (KNN), soft independent modelling of class analogy (SIMCA), and multilayer feed-forward artificial neural networks (MLF-ANN). KNN, SIMCA and the MLF neural network provided complementary results: KNN allowed the correct classification of almost all the ciders of the Galician category, SIMCA provided a model for the ciders of the French category that excluded all ciders made with Galician apples (50% of raw material), and the neural network achieved a level of hits for the classification of the ciders obtained from French apples (50% of raw material) above 95%. Polyphenolic profiles of the ciders provide enough information to develop classification rules for identifying ciders according to the geographical origin of the raw material used for cidermaking.     

Phlebotomines (Diptera: Psychodidae) collected at a Costa Rican dairy farm in a vesicular stomatitis endemic area

This study determined the species composition of sand flies in a vesicular stomatitis endemic area, at Carrizal, Alajuela, Costa Rica. Eight species were collected as follows: Lutzomyia volcanensis (Fairchild & Hertig), L. shannoni (Dyar), Lu. pia (Fairchild & Hertig), L. sanguinaria (Fairchild & Hertig), L. youngi Feliciangeli & Murillo, L. longipalpis (Lutz & Neiva), L. serrana (Damasceno & Arouck), and L. gomezi (Nitzulescu).     

Yeast alpha mating factor structure-activity relationship derived from genetically selected peptide agonists and antagonists of Ste2p

alpha-Factor, a 13-amino-acid pheromone secreted by haploid alpha cells of Saccharomyces cerevisiae, binds to Ste2p, a seven-transmembrane, G-protein-coupled receptor present on haploid alpha cells, to activate a signal transduction pathway required for conjugation and mating. To determine the structural requirements for alpha-factor activity, we developed a genetic screen to identify from random and semirandom libraries novel peptides that function as agonists or antagonists of Ste2p. The selection scheme was based on autocrine strains constructed to secrete random peptides and respond by growth to those that were either agonists or antagonists of Ste2p. Analysis of a number of peptides obtained by this selection procedure indicates that Trp1, Trp3, Pro8, and Gly9 are important for agonist activity specifically. His2, Leu4, Leu6, Pro10, a hydrophobic residue 12, and an aromatic residue 13 are important for both agonist and antagonist activity. Our results also show that activation of Ste2p can be achieved with novel, unanticipated combinations of amino acids. Finally, the results suggest the utility of this selection scheme for identifying novel ligands for mammalian G-protein-coupled receptors heterologously expressed in S. cerevisiae.     

Liver transplantation in hepatitis C. A Spanish multi-centre experience

OBJECTIVE: The purpose of this retrospective survey was to determine the prevalence and outcome of hepatitis C virus (HCV) infection in cirrhotic patients undergoing liver transplantation (OLT) in Spain in 1992. METHODS: Post-OLT HCV infection was defined by anti-HCV (second-generation ELISA) and/or PCR. Patients were divided into groups A (HCV-positive pre-OLT: n = 124, 46%) and B (HCV-negative pre-OLT: n = 145, 54%). RESULTS: HCV infection was more prevalent in patients originally diagnosed as having non-A non-B cirrhosis (97%) and cryptogenic cirrhosis (79%) than in patients with cholestatic or metabolic diseases. Group A patients were older (53.3+/-7.9 versus 47.6+/-9.7; P< 0.05) and had a higher prevalence of hepatocellular carcinoma (22% versus 4%, P< 0.05). Post-OLT HCV infection was 99% in group A versus 4% in group B (P< 0.05). Histological hepatitis developed in 39% (66% in group A versus 14% in group B, P< 0.05) with similar follow-up. Chronic rejection occurred in 6% (3% in group A versus 8.5% in group B, P= 0.07). Retransplantation rate (overall 8%) and two-year patient survival did not differ between groups (79% versus 72%). Graft survival was higher in group A (74% versus 65% at 2 years, P= 0.04). CONCLUSIONS: HCV-cirrhosis represented the most frequent indication for OLT in Spain in 1992. While HCV recurrence was universal, de novo acquisition was rare. HCV accounted for most post-OLT hepatitis (87%), but was not associated with chronic rejection, nor with a higher retransplantation rate. Patient survival was not different in HCV patients compared to a control group after a follow-up of 2-3 years. Therefore, at present, HCV-cirrhosis is an acceptable indication for OLT.     

IR uncooled bolometers based on amorphous Ge/sub x/Si/sub 1-x/O/sub y/ on silicon micromachined structures

In this work, we present the fabrication of bulk micromachined microbolometers made of amorphous germanium-silicon-oxygen compounds (Ge/sub x/Si/sub 1-x/O/sub y/) grown by reactive sputtering of a Ge/sub 0.85/Si/sub 0.15/ target. We describe the complete procedure for fabricating thermally isolated microbolometers consisting of Ge/sub x/Si/sub 1-x/O/sub y/ sensing films deposited on sputtered silicon dioxide membranes suspended over a silicon substrate. The electrical properties of the sensitive material are set by controlling the deposition parameters of the sputtering technique. Under optimum deposition conditions, Ge/sub x/Si/sub 1-x/O/sub y/ layers with moderate electrical resistivity and thermal coefficient at room temperature as high as -4.2% /spl middot/ K/sup -1/ can be obtained. Isolated structures measured at atmospheric pressure in air have a thermal conductance of 3 /spl times/ 10/sup -6/ W /spl middot/ K/sup -1/ and a thermal capacitance of 6/spl middot/10/sup -9/ W /spl middot/ s /spl middot/ K/sup -1/, yielding a response time of 1.8 ms. Bolometers with an IR responsivity of 380 V /spl middot/ W/sup -1/ and a NEDT of 3.85 K at 100 nA bias current are obtained. The use of sputtered films allows designing a fully low-temperature fabrication process, wholly compatible with silicon integrated circuit technologies.     

Nanocrystalline copper sulfide and copper selenide thin films with p-type metallic behavior

Copper chalcogenide materials are interesting for multiple applications due to the feasibility of suiting their optical absorption and electrical conduction by the creation of copper vacancies. Here, Cu _x S and Cu _x Se nanocrystalline films with p-type conductivity have been obtained by heating evaporated copper layers of various thicknesses with elemental sulfur or selenium, at temperatures ranging from 250 to 400 °C. These preparation parameters determine the composition and the crystalline structure of the samples, which in turn control their morphology, optical and electrical properties. Thus, the surface roughness increases with the mean crystallite size, whereas the hole concentration increases as the copper atomic proportion (or x value) decreases. Owing to the high carrier densities achieved, around 10²² cm^?3, the samples show a metallic behavior with plasmonic absorption in the near infrared and electrical transport dominated by phonon scattering. Apart from such common behavior, some differences have been established between the sulfide and selenide films. One is the superior thermal stability of hexagonal CuS, present in all the temperature range, with respect to hexagonal CuSe, which evolves to cubic Cu_1.8Se above 300 °C. Other is about the bandgap, wider for the sulfide than selenide samples.     

Reliable transmission of stream transported media in wireless real time communications

Wireless Networks - The Real Time Protocol (RTP) provides a well established mechanism for media transmission that typically relies on the packetization on top of the User Datagram Protocol. One...