A Multidimensional Paper Recommender: Experiments and Evaluations

Paper recommender systems in the e-learning domain must consider pedagogical factors, such as a paper's overall popularity and learner background knowledge — factors that are less important in commercial book or movie recommender systems. This article reports evaluations of a 6D paper recommender. Experimental results from a human subject study of learner preferences suggest that pedagogical factors help to overcome a serious cold-start problem (not having enough papers or learners to start the recommender system) and help the system more appropriately support users as they learn.     

Densification and phase transformation of Si3N4 in the presence of mechanically activated BaCO3–Al2O3–SiO2 mixture

Densification as well as the →β phase transformation of Si₃N₄ were monitored as a function of activation time of the BaCO₃–Al₂O₃–SiO₂ additive mixture. The composition of the ternary mixture corresponded to celsian (BaAl₂Si₂O₈—BAS). Previously, mechanically activated powder mixtures for various lengths of time were added to Si₃N₄ in the amount of 10–30%. Sintering was performed at 1650–1700°C in nitrogen atmosphere up to 8 h. The changes in densification degree, as well as phase composition, were followed as a function of heating time and the time of mechanical activation of the additive mixture. The results obtained showed that mechanical activation retarded densification in samples heated up to 1700°C. On the other hand, for the constant sintering time, →β transformation of Si₃N₄ was enhanced with increasing activation time, and the amount of additives.     

An inverse gas chromatographic study of the adsorption of alkanes on hydroxyapatite

Saturated alkanes adsorption on synthetic well-crystallized hydroxyapatite was studied by the inverse gas chromatography method, at zero coverage. Hydroxyapatite was prepared from Ca(OH)₂ and H₃PO₄ aqueous solutions by a slow titration technique. The powder was characterized by XR diffraction, surface area measurement, and chemical analysis. Adsorption of saturated alkanes was investigated in the temperature range 338–353 K, using a flame ionization detector, and nitrogen as a carrier gas. The gas/solid partition coefficients were calculated from the retention data as well as the standard thermodynamic functions of adsorption, H⁰ _d, S⁰ _a and G⁰ _a. Linear relationships between lnK and 1/T and between G⁰ _a and the number of carbon atoms in saturated alkanes were observed. The dispersive component of the surface free energy was calculated for the investigated temperature region. A possible analytical application of hydroxyapatite to n-alkanes separation is given.     

Hydrogenation properties of Hf-Ni intermetallics - Experimental and theoretical investigation

The hydrogenation properties of HfNi and Hf₂Ni₇ intermetallics were investigated at the constant pressure of 1 bar and in the temperature ranges 373-573 K for HfNi and 323-473 K for Hf₂Ni₇. The kinetic parameters, rate constants and activation energies of the absorption processes were determined. Maximal hydrogen absorption, i.e., number of hydrogen atoms absorbed per metal atom, H/M, are 1.05 and 0.04 achieved at 373 K for HfNi and Hf₂Ni₇, respectively. Multiple hydriding/dehydriding was found to influence the improvement of the kinetic parameters. XRD and SEM methods were used to investigate the structural and morphological changes of the samples due to hydrogen absorption. The thermodynamic parameters of hydriding together with the structural properties of the intermetallics and their hydrides, calculated using the full-potential linearized augmented plane waves (FP-LAPW) code based on the density functional theory (DFT), were utilized for the sake of explaining the experimental investigations.     

Development of the dendritic fields of layer 3 pyramidal cells in the kitten's visual cortex

The cat's visual cortex is immature at birth and undergoes extensive postnatal development. For example, cells of layers 2 and 3 do not complete migration until about 3 weeks after birth. Despite the importance of dendritic growth for synaptic and functional development, there have been few studies of dendritic development in the cat's visual cortex to correlate with numerous studies of functional and synaptic development. Accordingly, we used the Golgi method to study the development of the dendrites of layer 3 pyramidal cells in the visual cortex of a series of cats ranging in age from 2 days to 3 years. Blocks of visual cortex were impregnated by the Golgi-Kopsch method and sectioned in the tangential plane. Layer 3 pyramidal cells were drawn with a camera lucida and analyzed by Sholl diagrams and vector addition. In kittens < 1 week old, these cells were very immature, with only an apical dendrite and no basal dendrites. Basal dendrites appeared during the second week. By 2 weeks, all of the basal dendrites had emerged from the soma, but they had few branches and were tipped with growth cones. By 4 weeks, they had finished branching but continued to grow in length until, by 5 weeks, they reached their adult size. Examination of the basal dendritic fields in the tangential plane revealed that their dendritic fields were more elongated at 2 weeks than at later ages, perhaps because of their smaller size. The distribution of dendritic field orientations was uniform at all ages except 3 and 4 weeks, when there was a preponderance of fields oriented in the rostrocaudal direction. Because dendritic growth and branching occurred very rapidly over a period that precedes and overlaps with the peak periods of synaptogenesis and of sensitivity to the effects of early visual experience, they may depend on afferent visual activity. The early emergence of primary dendrites, however, suggests that this process is independent of afferent activity. The coincident timing of dendritic branching with the presence of dendritic growth cones suggests that branching may occur at growth cones.     

A serial sample loading system: interfacing multiwell plates with microfluidic devices

There is an increasing demand for novel high-throughput screening (HTS) technologies in the pharmaceutical and biotechnological industries. The robotic sample-handling techniques currently used in these industries, although fast, are still limited to operating in multiwell plates with the sample volumes per reaction in the microliter regime. Digital microfluidics offers an alternative for reduction in sample volume consumption for HTS but lacks a reliable technique for transporting a large number of samples to the microfluidic device. In this report, we develop a technique for serial delivery of sample arrays to a microfluidic device from multiwell plates, through a single sample inlet. Under this approach, a serial array of sample plugs, separated by an immiscible carrier fluid, is loaded into a capillary and delivered to a microfluidic device. Similar approaches have been attempted in the past, however, either with a slower sample loading device such as a syringe pump or vacuum-based sample loading with limited driving pressure. We demonstrated the application of our positive-pressure-based serial sample loading (SSL) system to load a series of sample plugs into a capillary. The adaptability of the SSL system to generate sample plugs with a variety of volumes in a predictable manner was also demonstrated.     

Computationally Efficient Formulation of Sparse Color Image Recovery in the JPEG Compressed Domain

Sparse representations provide a powerful framework for various image processing tasks, among which image recovery seems to be an already classical application. While most developments of image recovery applications are focused on finding the best dictionary, the possibility of using already existing sparse image representations tends to be ignored. This is the case of the JPEG compressed image representation, which is a sparse image representation in terms of the discrete cosine transform (DCT) dictionary. The development of sparse frameworks directly on the JPEG encoded image representation can lead to computationally efficient approaches. Here we introduce a DCT-based JPEG compressed domain formulation of the color image recovery process within a sparse representation framework and we prove mathematically and experimentally not only its numerical efficiency as compared to the pixel level formulation (the processing time is reduced up to 40 %), but also the good quality of the restoration results.     

Epidemiology of end‐stage renal disease and hemodialysis treatment in Serbia at the turn of the millennium

The study presents the epidemiological features of patients treated with renal replacement therapy (RRT) in Serbia from 1997 to 2009 and compares the results of hemodialysis treatment in 1999 and 2009. Epidemiological data were obtained from the National Registry of RRT patients and data on hemodialysis treatment from special surveys conducted in 1999 and 2009. Within the period 1997–2009 the incidence of patients on RRT increased from 108 to 179 per million population (pmp), prevalence rose from 435 to 699 pmp, while mortality rate fell from 20.7% to 16.7%. The frequency of patients with glomerulonephritis decreased, while that of patients with diabetes and hypertensive nephropathy increased. In late 2009 there were 5208 patients receiving RRT in Serbia. Within the examined period new hemodialysis and reverse osmosis equipment were purchased, high‐flux dialyzers with synthetic membranes were increasingly used and the number of patients receiving hemodiafiltration increased to 17.6%. Kt/V greater than 1.2 was recorded in 16% of the patients in 1999 but 52% in 2009. Options for correction of anemia and mineral disorders have also improved. The percentage of patients with HbsAg (13.8% vs. 4.8%) as well as anti‐hepatitis C virus antibodies positive patients (23.2% vs. 12.7%) was significantly lower in 2009 than in 1999. Both the incidence and prevalence of RRT patients in Serbia are rising continuously, while the mortality rate is falling. More favorable conditions for dialysis treatment have brought about significant improvement in the results over the last 10 years.     

The use of new intelligent techniques in designing retaining walls

Engineering with Computers - The stability of retaining walls against overturning is analyzed in this study using artificial intelligence methods. Five input parameters including wall height, wall...