Influence of Cu on the mechanical and tribological properties of Ti3SiC2

Ti₃SiC₂/Cu composites with different contents of Cu were fabricated by mechanical alloying and spark plasma sintering method. The phase composition and structure of the composites were analyzed by X-ray diffractometry and scanning electron microscopy equipped with energy dispersive spectroscopy. The mechanical and tribological properties of Ti₃SiC₂/Cu composites were tested and analyzed compared with monolithic Ti₃SiC₂ in details. The results show that the Cu leads to the decomposition of Ti₃SiC₂ to produce TiC_x, Ti₅Si₃C_y, Cu₃Si, and TiSi₂C_z. The friction coefficient and wear rate of the composites are lower than that of monolithic Ti₃SiC₂, which is ascribed to the fixing effect of hard TiC_x, Ti₅Si₃C_y, and Cu₃Si to inhibit the abrasive friction and wear. However, at elevated temperatures (ranging from room temperature to 600 °C) the friction and wear of the composites are higher than those at room temperature. Plastic flowing and tribo-oxidation wear accompanied by material transference contribute to the increased friction and wear at elevated temperatures.     

ISFET performance enhancement by using the improved circuit techniques

An approach to enhance accuracy of the output signal obtained from ISFET interface electronics due to the body effect is proposed. Based on an MOS drawing the same drain current as the ISFET, the scheme allows reduction of influence of body effect. The presented readout interface improves the accuracy of pH measurements, while maintaining operation at constant drain-source voltage and current condition. Using only one ISFET with a differential output configuration, we obtained temperature-dependency and long-term drift as well as common noise compensation. The proposed technique is simple and has a universal use for different ISFETs. In addition, a voltage-controlled dc offset error compensation circuit modulates the extracted signal to the desired dc level for the A/D converter for each sensor. Simulation and experimental results show a great effect on monolithic ISFET integration in CMOS technology.     

Poly(vinyl chloroformate) and derivatives: 1. Polymerization of vinyl chloroformate,vinyl carbamates and vinyl carbonates

The free-radical polymerization of vinyl chloroformate and of some of its derivatives, e.g., vinyl carbamates and vinyl carbonates, has been studied. Peroxydicarbonates are the most convenient initiators, especially for vinyl chloroformate polymerization carried out in bulk and in methylene chloride solution at 35°C since they lead to high molecular-weight polymers and quantitative yields. The structure of these polymers has been examined by i.r., ¹H and ¹³C n.m.r. spectroscopy.     

Surface-plasmon-enhanced photoluminescence of CdS nanoparticles with Au/SiO2 nanocomposites

To examine the effect of metal nanostructures on the photoluminescence of CdS nanoparticles, Au/SiO₂ nanocomposites were prepared with back-reflection geometry. The contribution from the prolonged optical-path lengths was excluded, and the luminescence enhancement was attributed only to surface-plasmon resonance. The optimum nanostructures for the PL enhancement were examined, and correlated with the wavelength of the surface-plasmon peak of the Au/SiO₂ nanocomposites and the PL emission peak of CdS nanoparticles.     

Liposome encapsulated nisin Z: optimization,stability and release during milk fermentation

Liposomes prepared from different proliposomes (Pro-lipo^® H, Pro-lipo^® S, Pro-lipo^® C and Pro-lipo^® DUO) were tested for their capacity to encapsulate nisin Z. Factors affecting the entrapment process (pH and concentration of nisin Z solution and cholesterol concentration in the lipid membranes) were optimized. The use of nisin Z monoclonal antibodies made it possible to quantify, using a competitive enzyme immunoassay, and visualize, using transmission electron microscopy, nisin Z. Nisin Z was entrapped in different liposomes with encapsulation efficiencies (EE) ranging from 9.5% to 47%. The pH of nisin Z aqueous solution and nisin Z concentration had a significant effect on the amount of encapsulated nisin. An increase in cholesterol content in lipid membranes up to (20%, w/w) resulted in a slight reduction in EE. Nisin-loaded vesicles did not severely disturb Cheddar cheese fermentation and showed stability to Cheddar cheese temperature cycle. Long term stability of liposome-encapsulated nisin Z was demonstrated for 27 days at 4°C in different media including milk with different fat levels (3.25%, 2.0% and 1.0%), skim milk, sweet whey and phosphate buffer saline (PBS). Liposome stability determined as the quantity of released nisin Z was highest in milk followed by PBS and whey, respectively.     

Vapor recognition with an integrated array of polymer-coated flexural plate wave sensors

Preliminary testing of a prototype instrument employing an integrated array of six polymer-coated flexural plate wave (FPW) sensors and an adsorbent preconcentrator is described. Responses to thermally desorbed samples of individual organic solvent vapors and binary and ternary vapor mixtures are linear with concentration, and mixture responses are equivalent to the sums of the responses of the component vapors, which co-elute from the preconcentrator in most cases. Limits of detection as low as 0.3 ppm are achieved from a 60-s (34 cm³) air sample and peak widths at half-maximum range from 1 to 4 s. Tests at different flow rates suggest that the kinetics of vapor sorption in the sensor coating films may limit responses at higher flow rates, however, low data acquisition rates may also be contributory. Assessments of array performance using independent test data and Monte Carlo simulations with pattern recognition indicate that individual vapors and certain binary and ternary mixtures can be recognized/discriminated with very low error. More complex mixtures, and those containing homologous vapors, are problematic. This is the first report demonstrating multi-vapor analysis with an integrated FPW sensor array.     

Up-conversion luminescence properties of Y2O2S:Yb3+,Er3+ nanophosphors

Up-converting yttrium oxysulfide nanomaterials doped with ytterbium and erbium (Y₂O₂S:Yb³⁺,Er³⁺) were prepared with the flux method. The precursor oxide materials were prepared using the combustion synthesis. The morphology of the oxysulfides was characterized with transmission electron microscopy (TEM). The particle size distribution was 10–110 nm, depending on the heating temperature. According to the X-ray powder diffraction (XPD), the crystal structure was found hexagonal and the particle sizes estimated with the Scherrer equation agreeded with the TEM images. Upon the 970 nm infrared (IR) laser excitation, the materials yield moderate green ((²H_11/2, ⁴S_3/2) → ⁴I_15/2 transition) and strong red (⁴F_9/2 → ⁴I_15/2) luminescence. The green luminescence was enhanced with respect to the red one by an increase in both the crystallite size and erbium concentration due to the cross-relaxation (CR) processes. The most intense up-conversion luminescence was achieved with x_Yb and x_Er equal to 0.10 and 0.005, respectively. Above these concentrations, concentration quenching occurred.     

Electronic nose technique potential monitoring mandarin maturity

Over the past years, electronic nose technology opened the possibility to exploit information on behavior aroma to assess fruit ripening stage. The objective in this study was to evaluate the capacity of electronic nose to monitoring the change in volatile production of mandarin during different picking-date, using a specific electronic nose device (PEN 2). Principal component analysis (PCA) and linear discriminant analysis (LDA) were used in order to investigate whether the electronic nose was able to distinguish among different picking-date (ripeness states). The loadings analysis was used to identify the sensors responsible for discrimination in the current pattern file. The results obtained prove that the electronic nose PEN 2 can discriminate successfully different picking-date on mandarin using LDA analysis. But, electronic nose was not able to detect a clear difference in volatile profile on mandarin using PCA analysis. During external validation using LDA was obtained to classified 92% of the total samples properly. Some sensors have the highest influence in the current pattern file for electronic nose PEN 2. A subset of few sensors can be chosen to explain all the variance. This result could be used in further studies to optimize the number of sensors.     

Orientational effects in adsorption III: In-plane ordering in localized monolayers of diatomic molecules on crystalline solids

Orientational effects in monolayer films of diatomic molecules adsorbed on a single (100) face of a cubic crystal are discussed. The adsorbed molecules are assumed to take up an orientation parallel to the solid surface with their centres of mass located directly above the centres of the adsorption sites.It is shown that various orientationally ordered structures can appear and that their properties depend on the elongation of the adsorbed molecules, the size of the solid lattice, the density of the adsorbed film and the temperature. The heat capacities and the one-particle orientational distribution functions calculated for various systems are used to determine orientational properties of adsorbed films and to locate rotational transitions.     

Surface layer pH in electroless nickel plating in hypophosphite solutions

pH values of the layer of solution adjacent to the Ni-P coating being deposited from solutions containing acetate, glycine, fluoride and other additions have been measured using a glass electrode located in the reaction zone. It was found that the pH value at the surface may decrease by three units. It can be seen from data on the pH value at the surface that revision of some kinetic relationships established earlier is required. It is shown that acetate at low concentration levels has only a buffer effect and that ethylenediamine has an additional accelerating effect while glycine, citrate, malonate, lactate and succinate retard the nickel deposition process.