The electronic configuration and the conductance of silicon nanograins: An application of the scattering approach

The purpose of this study is the assessment of the properties of the electronic structure and of the transport characteristics of silicon nanostructures of a size comparable with the experimental ones. Accordingly, crystalline columnar grains, sandwiched between two adsorbing aluminum contacts, with a size of several hundreds atoms and linear dimensions up to a few nanometers, have been considered. The calculation method elaborates on the scattering approach, as reported in the recent chemical literature, using the extended Hückel theory for the evaluation of either the electronic charge or the transmission function. The calculations show that the binding energy has bulk-like features, i.e. its size dependence has a nearly flat asymptote with a value close to the cohesive energy of the solid. However the effect of the loosely coordinated boundary atoms is perceptible even at the sizes few hundreds atoms and produces an oscillatory behaviour of the binding energy. The comparison between this energy and the conductance indicates that both quantities increase at the same sizes and therefore the orbitals of the loosely bounded atoms are the important conductive channels.     

A ?P-Controlled Sliding Integrating-Type Differentiator for Biomedical Signal Processing: Application to dc Ocular Rheography

This paper describes a measurement technique for precise evaluation of hematic ocular flow. The main characteristics and advantages of the proposed technique over conventional approaches are first pointed out. Next, the design criteria and the performance achievable with the prototype instrument developed to carry out the measurement completely automatically, are examined in detail. The instrument, thanks to its microprocessor-based implementation, allows a certain degree of tailoring of the measurement in accordance with the patient's peculiarities. Moreover, it provides the possibility of monitoring the ocular arterial inflow during the test, thus guaranteeing that safety limits will not be exceeded.     

Taxonomies and correlates of physique.

"Subjective" and "objective" taxonomies of human physique are more or less correlated among themselves and in different degrees with an array of nonanthropometric variables of interest to psychologists. There is probably closer corespondence between anthropometric data and function than is reported in the literature. The most advanced taxonomies can be improved, principally by: greater differentiation of predictive anatomical variables; increasing the scope of the systems to include such elements as internal body organs, the differential influences of nutrition, and age; and through use of refined multivariate statistical techniques for representing and analyzing complex data. (3-p. ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Field-enhanced carrier generation in MOS capacitors

When sufficiently high voltage steps are used for driving a metal-oxide-semiconductor capacitor (MOSC) towards deep inversion, the temporal evolution of the current and of the high-frequency capacitance during the return to equilibrium cannot be interpreted on the basis of a theory assuming a constant bulk generation lifetime. A more general theory, which takes into account field-dependent carrier emission rates, is developed and it is shown how current and h.f. capacitance measurements can be used to determine the field dependence of the bulk generation lifetime. The results of experiments performed on differently processed MOSC's are presented; they support the hypothesis that field-enhancement of carrier emission rates takes place according to a mechanism of the Poole-Frenkel-type.     

Molecular typing of Staphylococcus aureus isolated from Italian dairy products on the basis of coagulase gene polymorphism, multiple-locus variable-number tandem-repeat and toxin genes

Coagulase gene restriction fragment length polymorphism (RFLP), six-locus variable-number tandem-repeat analysis patterns (MLVA) and detection of enterotoxin genes (se) (sea, sec, sed, seg, seh, sei, sej and sel) were used to determine the phylogenetic relationship among isolates of Staphylococcus aureus isolated from dairy products from different regions of Italy. A total of 25 Staph. aureus were subtyped into 16 coagulase genotypes by RFLP, and MLVA revealed marked genomic variability. Furthermore, 17 of the isolates harboured at least one toxin gene, with the predominance of sea, sed and sej among cow isolates and sec-sel among the goat and sheep strains. Combined RFLP, MLVA polymorphism and se genes were found to be useful techniques for discriminating several genetic variants in Staph. aureus isolates.     

Backscattered electron imaging and scanning transmission electron microscopy imaging of multi-layers

Experimental and theoretical results on image contrast of semiconductor multi-layers in scanning electron microscopy investigation are reported. Two imaging modes have been considered: backscattered electron imaging of bulk specimen and scanning transmission imaging of thinned specimens. The following main results have been reached. The image resolution of the multi-layers is, in both cases, defined by the probe size. The contrast, governed by density and atomic number differences, is affected by the size of the interaction volume in backscattered electron imaging and by the beam broadening in scanning transmission. Operating in the scanning transmission mode, the contrast of bright field images can be easily related to local variation in atomic number and density of the specimen while the dark field image contrast is strongly affected by electron beam energy, detector collection angles and specimen thickness. All these factors are able to produce contrast reversals that are difficult to explain without the support of a suitable simulation code.     

Formulation of muds for pelotherapy: effects of “maturation” by different mineral waters

Spa centres in northern Italy use clayey admixtures for the formulation of muds to be used in pelotherapy. The basic ingredient (“virgin” clay) is a dressed bentonitic geomaterial with mineralogical composition: smectite 60–70%, illite 5–10%, kaolinite 10–15%, quartz 5–10%, calcite 5–10% and feldspars 2–3%.The peloid muds are obtained by “maturation” of the virgin clay with mineral waters gushing out in situ which have different geochemistry: sulphureous, Ca-sulphate, Ca–Mg-sulphate and Br–I-salty (after the Italian regulation DPR 105/92). The maturation treatment is varying with respect to the mixing procedure and lasting time.Peculiar parameters have been tested to verify the effects of various maturation treatments, i.e., changes with respect to virgin clay.Formation of organic matter is due to the presence of microorganisms and algae in the maturation habitat. The <2 μm fraction is generally decreased due to clay particles agglomeration. Mineralogical changes are mainly concerning the degradation of clay minerals, as smectite and illite, and subordinately to the dissolution of calcite. Cation exchange capacity (CEC), soluble salts, water retention, swelling index, activity, consistency parameters (WL, WP and PI), thermal behaviour and cooling kinetics are influenced by the geochemistry of mineral waters used for the maturation treatments but with some opposite trends for Br–I-salty water, and for sulphureous and Ca-sulphate waters, respectively.Noteworthy was the influence of high-pH value of the virgin clay on the pH of peloid muds (in fact, the pH of the used mineral waters is ranging around the natural value). Furthermore, the temperature reached by the peloid muds after 20 min of application (calculated after an innovative mathematical model) is influenced by water retention. An increase in plasticity index and a slower cooling are considered to improve the quality of the obtained peloid muds for pelotherapy.The observed different cation exchange behaviour and soluble salt content could be discriminant for either dermatological masks or thermal body cataplasms.A need of regulation (standard procedures) is suggested to certificate the clay geomaterials suitable for pelotherapy and also for drugs formulation.     

Selective hydrogenation of cinnamaldehyde using Pd catalysts supported on Mg/Al mixed oxides: Influence of the Pd incorporation method

A series of hydrotalcite‐like compounds was synthesized by varying Mg/Al molar ratio with values of 2, 3, and 4. After thermal treatment at 823 K, the corresponding mixed oxides were obtained and used as catalytic supports. The incorporation of a Pd metallic phase (0.5 g/g loading), was carried out by two methods: 1) in situ vapour phase thermal decomposition, and 2) impregnation by organic method. Fresh and calcined samples were characterized by XRD and N₂ sorption experiments. The basic and metal functions were analyzed by CO₂‐TPD and H₂‐TPR. The Pd‐support interaction was studied by FTIR spectroscopy using CO as a probe molecule while the morphology of Pd nanoparticles on the catalysts was studied by SEM, HRTEM, and theoretical simulation using the Fast Fourier Transform (FFT) method. Finally, the catalytic activity results showed a higher conversion towards hydrocinnamaldehyde in the cinnamaldehyde hydrogenation reaction for the catalysts prepared by vapour phase thermal decomposition, compared with those prepared by organic method, showing the significant dependence on the catalytic activity and the Pd incorporation method.     

Dynamics and Selectivity of N<Subscript>2</Subscript>O Formation/Reduction During Regeneration Phase of Pt-Based Catalysts

The formation of N₂O has been studied by means of isothermal lean-rich experiments at 150, 180 and 250 °C over Pt–Ba/Al₂O₃ and Pt/Al₂O₃ catalysts with H₂ and/or C₃H₆ as reductants. This allows to provide further insights on the mechanistic aspects of N₂O formation and on the influence of the storage component. Both gas phase analysis and surface species studies by operando FT-IR spectroscopy were performed. N₂O evolution is observed at both lean-to-rich (primary N₂O) and rich-to-lean (secondary N₂O) transitions. The production of both primary and secondary N₂O decreases by increasing the temperature. The presence of Ba markedly decreases secondary N₂O formation. FT-IR analysis shows the presence of adsorbed ammonia at the end of the rich phase only for Pt/Al₂O₃ catalyst. These results suggest that: (i) primary N₂O is formed when undissociated NO in the gas phase and partially reduced metal sites are present; (ii) secondary N₂O originates from reaction between adsorbed NH₃ and residual NO_x at the beginning of the lean phase. Moreover, N₂O reduction was studied performing temperature programming temperature experiments with H₂, NH₃ and C₃H₆ as reducing agents. The reduction is completely selective to nitrogen and occurs at temperature higher than 250 °C in the case of Pt–Ba/Al₂O₃ catalyst, while lower temperatures are detected for Pt/Al₂O₃ catalyst. The reactivity order of the reductants is the same for the two catalysts, being hydrogen the more efficient and propylene the less one. Having H₂ a high reactivity in the reduction of N₂O, it could react with N₂O when the regeneration front is developing. Moreover, also ammonia present downstream to the H₂ front could react with N₂O, even if the reaction with stored NO_x seems more efficient.