A comparative study of threshold effects in the energy loss moments of protons,electrons and positrons using dielectric models for band-gap materials

A comparative study of the energy loss, mean free path and straggling of protons, positrons and electrons in an electron gas is performed using three dielectric models which represent the case of metals (Lindhard model for a free electron gas) and the cases of semiconductors and insulators (Levine and Louie model and Brandt and Reinheimer model for systems with a band gap). The properties of individual and collective contributions according to each model and for each of the particles are analyzed. In particular, the effects produced by the band gap of the material and by the properties of the incident particle are analyzed in detail. Significant differences related to the mass and to the indistinguishability (in the case of electrons) are described. Analytical expressions for the high-energy limit are derived in a simple way using the plasmon-pole approximation.     

Second harmonic generation by micropowders: a revision of the Kurtz–Perry method and its practical application

We theoretically study the second harmonic generation by powder crystal monolayers and by thick samples of crystalline powder with particle size in the range of microns. Contrary to usual treatments, the light scattering by the particles is explicitly introduced in the model. The cases of powder in air and in an index-matching liquid under the most common experimental geometries are considered. Special attention is paid to the possibility of determining the value of some nonlinear optical coefficients from the experiments. The limitations and shortcomings of the classical Kurtz and Perry method (Kurtz and Perry in J Appl Phys 39:3798, 1968) and the most common practical misuses of it are discussed. It is argued that many of the experimental works based on that method oversimplify the technique and contain important errors. In order to obtain reliable values of the nonlinear coefficients, an appropriate experimental configuration and analysis of the data are pointed out. The analysis is especially simple in the case of uniaxial phase-matchable materials for which simple analytical expressions are derived.     

On the pre-dose sensitization of the various components of the LM-OSL signal of annealed quartz; comparison with the case of 110 °C TL peak

Pre-dose sensitization of various components of LM-OSL signal of a Nigerian annealed quartz sample has been investigated along side with that of 110 °C TL peak in this work. Successive cycles of irradiations and TL/OSL readings using different heating rates were employed to attain pre-dose sensitization. The results showed that the pre-dose sensitization factor of 110 °C TL peak depends strongly on the heating rate of thermal activation. The pre-dose sensitization of 110 °C TL and all components of RT LM-OSL yield HR dependence on the sensitization after TA. This dependence was ascribed to the different heating time associated with each HR. Sensitization of LM-OSL measured at 125 °C generally does not show dependence on HR of TA. This was with the exception of components C₁ and C₃. Increasing sensitization pattern with increasing HR suggests a correlation between the TL glow-peak at 110 °C, the component C₄ of RT LM-OSL and the component C₃ of the LM-OSL signal at 125 °C. Extension of the present investigation to diverse quartz kinds from different origins was suggested in order to study the prevalence of the pre-dose sensitization on component C₄ of RT LM-OSL. Finally fast heating is suggested for lower sensitization of fast component while applying OSL dating protocols.     

Essential oils in combination and their antimicrobial properties

Essential oils (EOs) have been long recognized for their antibacterial, antifungal, antiviral, insecticidal and antioxidant properties. They are widely used in medicine and the food industry for these purposes. The increased interest in alternative natural substances is driving the research community to find new uses and applications of these substances. EOs and their components show promising activities against many food-borne pathogens and spoilage microorganisms when tested in vitro. In food systems, higher concentrations of EOs are needed to exert similar antibacterial effects as those obtained in in vitro assays. The use of combinations of EOs and their isolated components are thus new approaches to increase the efficacy of EOs in foods, taking advantage of their synergistic and additive effects. The purpose of this review is to provide an overview on the antimicrobial efficacy of these combinations. A survey of the methods used for the determination of the interactions and mechanisms involved in the antimicrobial activities of these combinations are also reported.     

Electroclinic effect near a smectic A-chiral smectic I transition

The electroclinic effect in the S_A phase of (S) (4'-decyloxy-2'-hydroxybenzylidene)-4-amino(1-ethoxycarbonylethyl) cinnamate has been studied. The induced tilt angles have been measured as a function of temperature near the S_A-S*_I transition at 87°C. The response of the material to different voltages and frequencies has been analysed by using two complementary optical techniques. At low A.C. probe fields the amplitude of the induced tilt shows a relaxational behaviour which can be described by a single relaxation time. The relaxation frequencies have been found to be linear in temperature near the transition, in a similar way to the S_A-S*_C transition.     

A Structural Investigation of Some Terminally Cyano-Substituted Side Chain Liquid-Crystalline Polysiloxanes

A series of terminally cyano substituted side chain polysiloxanes have been characterized using optical microscopy, D.S.C., and X-ray diffraction. Values for the lamellar spacings, d, of the interdigitated smectic A phases were obtained, and the variations in d with temperature and length of the flexible aliphatic spacer are discussed. The spacing for m = 4, 5, and 6 increased regularly with m whereas the short m = 3 spacer gave an anomalously high value.     

Flow injection analysis of high chloride levels in electroplating baths using on-line dialysis and potentiometric detection

A method for the flow injection analysis (FIA) of high concentrations of chloride in electroplating baths using potentiometric detection is proposed. The system includes a unit of dialysis to promote dilution of samples and a tubular electrode with an homogeneous crystalline membrane as detector. The system was optimized in order to analyse samples within a broad range of concentrations and at high levels of chloride, thereby making pretreatment of the samples unnecessary. It results in a simple manifold applicable over the 4.0×10^–2 and 3.0 mol L^–1 range with a throughput of about 30 samples/h. Seven different plating bath samples were analysed by the proposed method and the quality of the results compared with those obtained by the conventional procedure. Satisfactory agreement was observed.     

Reaction of singlet oxygen with Ir(I) and Rh(I) thiolato complexes: oxidative addition vs. S-oxidation

Singlet oxygen reacts with Ir(I) and Rh(I) thiolato complexes to form the corresponding Ir(III) and Rh(III) peroxo thiolato complexes which do not undergo intramolecular oxidation of the thiolate moiety.