E.A. Pavlatou

The interpretation of vibrational spectra of ionic melts

Computer simulations of the short-time, vibrational dynamics of the network-forming ionic melts, LaCl3 and ZnCl2, and of their mixtures with network-breaking alkali halides are described. In the mixtures, high frequency peaks in the vibrational density of states are shown to be describable in terms of the normal coordinates of vibration of transient molecular ion species, like LaCl63− and ZnCl42−. Novel simulation methods are presented which allow this association to be established. In the pure melts, the vibrational motions retain a strong aspect of this local polyhedral unit vibrational character, but the effects of network-induced coupling between the vibrations of different units become pronounced, particularly in ZnCl2. The calculated vibrational spectra are compared with extensive Raman data on these systems, and with infrared and neutron spectra in pure ZnCl2. For the mixtures, remarkably good agreement with experiment is found, confirming the high quality of the representation of the interionic in...

Electrodeposition of Ni/SiC composites by pulse electrolysis : Electrodeposition in Electronics

SUMMARY Nickel matrix composite coatings containing micron- and nano-sized SiC particles were prepared in order to study the interdependence of the SiC particles embedding and the deposits ‘mechanical behaviour. SiC particles of two different sizes, namely 1 μm and 20 nm, were codeposited with nickel from Watts solutions under pulse current conditions. It has been observed that the embedding of SiC particles in the nickel matrix and the pulse current application result in deposits with more uniform particle distribution and better surface morphology than those obtained under direct current conditions. The study of the composite deposits revealed that the microhardness is not only increased by the presence and the reduced size of the particles, but also influenced by the current conditions, i.e. duty cycle and pulse frequency. Moreover, microhardness of the deposits can be further ameliorated by specific thermal treatment.

Nickel matrix composite coatings : Application in textile machinery and evaluation of cotton products quality

SUMMARY Coatings applied to several mechanical parts involved in the cotton textile industry are expected to improve production efficiency and to decrease the relevant costs. The quality of cotton products is one of the most crucial parameters in the development of textile industry and is significantly associated with the mechanical and tribological properties of the coated machinery parts. For this purpose, nickel matrix coatings containing silicon carbide (SiC) micro-particles, prepared under pulse plating conditions were applied on several parts. Surface morphology, preferred orientation of the crystals, incorporated SiC percentage and mechanical properties of these coatings were investigated. Moreover, the influence of the surface coating on the cotton products quality was studied by the means of a prototypal method, which determines the extent of wear on a typical cotton fabric, under strictly controlled conditions. It has been proved that Ni/SiC coatings, prepared under very well defined conditions (pulse current density, frequency, duty cycle, etc), present relatively low roughness, high microhardness, low sliding friction coefficient between the coating and typical cotton products and reduced wear against cotton fabrics or yarns.

Effect of nanostructured TiO2 crystal phase on photoinduced apoptosis of breast cancer epithelial cells

Purpose The use of nanoparticles has seen exponential growth in the area of health care, due to the unique physicochemical properties of nanomaterials that make them desirable for medical applications. The aim of this study was to examine the effects of crystal phase-nanostructured titanium dioxide particles on bioactivity/cytotoxicity in breast cancer epithelial cells. Materials and methods Cultured Michigan Cancer Foundation (MCF)-7 and human breast adenocarcinoma (MDA-MB-468) breast cancer epithelial cells were exposed to ultraviolet A light (wavelength 350 nm) for 20 minutes in the presence of aqueous dispersions of two different nanostructured titanium dioxide (TiO2) crystal phases: anatase and an anatase–rutile mixture. Detailed characterization of each titanium dispersion was performed by dynamic light scattering. A 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) colorimetric assay was employed to estimate the percentage of viable cells after each treatment. Western blot analysis of protein expression and characterization, as well as a deoxyribonucleic acid (DNA)-laddering assay, were used to detect cell apoptosis. Results Our results documented that 100% anatase TiO2 nanoparticles (110–130 nm) exhibited significantly higher cytotoxicity in the highly malignant MDA-MB-468 cancer cells than anatase– rutile mixtures (75%/25%) with the same size. On the contrary, MCF-7 cells (characterized by low invasive properties) were not considerably affected. Exposure of MDA-MB-468 cells to pure anatase nanoparticles or anatase–rutile mixtures for 48 hours resulted in increased proapoptotic Bax expression, caspase-mediated poly(adenosine diphosphate ribose) polymerase (PARP) cleavage, DNA fragmentation, and programmed cell death/apoptosis. Conclusion The obtained results indicated that pure anatase TiO2 nanoparticles exhibit superior cytotoxic effects compared to anatase–rutile mixtures of the same size. The molecular mechanism of TiO2 nanoparticle cytotoxicity involved increased Bax expression and caspase-mediated PARP inactivation, thus resulting in DNA fragmentation and cell apoptosis.

Instantaneous collision complexes in molten alkali halides: Picosecond dynamics from low-frequency Raman data

The picosecond dynamics of molten alkali halides is discussed, and the low-frequency Raman spectra of molten LiCl, CsCl, and the LiCl–CsCl eutectic are fitted to the model enabling to obtain the times of vibrational dephasing, τV and vibrational frequency modulation τω. In terms of the Wilmshurst criterion [J. Chem. Phys. 39, 1779 (1963)] and using the data of NMR studies and molecular dynamics simulations, a conclusion is drawn that molten alkali halides cannot contain long-lived stable complexes with lifetimes greater than 10−8 s. The low-frequency Raman spectra of molten alkali halides and their mixtures probe the presence of instantaneous spatial configurations of MXn−n+1 type, where M+ is the alkali metal cation and X− is the halide anion existing in melts during the time intervals equal to the time of duration of collision of oppositely charged ions τd, which is less than 0.5 ps. This time is sufficient to a collision complex to execute several (at least one) vibrations. Vibrational dephasing and mo...

Dynamic light scattering study of ionic KNO3–Ca(NO3)2 mixtures

We report spontaneous Brillouin and photon correlation spectroscopic results on the dynamics of the local density fluctuations in the ionic mixed salt xKNO3⋅yCa(NO3)2 with molar ratios 2:1, 3:2, and 1:1. For these mixtures, the density relaxation function g(t) changes from a stretched exponential (β=0.47) near the glass transition temperature Tg, to an exponential (β=1) form at high temperatures, whereas the composition dependence of the relaxation time τ reflects mainly differences between the Tg values. The 3:2 fragile glass (Tg=60 °C) is one of the few examples where g(t) is now known from the glass‐like (60–90 °C) to the liquid‐like (T>100 °C) region through the application of various dynamic scattering techniques. The τ(T) and the evolution of the width β of the distribution are discussed in terms of the physical pictures implied by current models of the liquid and glass transition phase.

Ionic interactions in molten complex chlorides from vibrational dephasing

In this article we present the first quantitative estimates of the spectroscopically active part of the interaction potential in molten complex chlorides based on dephasing studies. We have selected the molten salt systems containing quasispherical complex MCl4−2 anions (M=Mn+2 and Zn+2) and performed the study of their ν1(A1) isotropic Raman line profiles as a function of the temperature and concentration. We have analyzed the form of the time correlation function of vibrational dephasing and determined the type of modulation events, which cause the line broadening processes in these systems; these are found to be purely discrete Markovian. Within the formalism of the purely discrete Markovian modulation, we have made a judgement about spectroscopically active interactions in these systems. Interionic potential in complex chlorides is dominated by the attraction forces, which depend on the interparticle distance r as r−4, and by repulsion of the r−7-type.

Temperature and Pressure Dependence of Raman Scattering in Amorphous GeS2

The evolution of the Raman spectrum of amorphous GeS2 is reported over wide temperature (300 to 1075 K) and pressure (0 to 10.8 GPa) ranges. The temperature dependence shows that a-GeS2 turns gradually crystalline above Tg, first to the 3D-phase and then to the layered (2D)-phase, with the latter one being retained up to the melting point and upon normal cooling to 300 K. The evolution of the Ac1 companion band of a-GeS2 into the crystalline phases indicates that this band is due to the symmetric stretch of S atoms in bridges of edge-sharing Ge(S1/2)4 tetrahedra. The Raman bands of a-GeS2 harden with increasing pressure, indicating a continuous decrease of the Ge–S bond length, while the material remains amorphous throughout the pressure range. Above 10 GPa, the material becomes almost opaque, thus making difficult the observation of Raman scattering. All these pressure induced effects are reversible after bringing the sample to ambient pressure.

Effects of cis-2-butene-1,4-diol additive and pulse current imposition on production of Ni nanocrystalline coatings

Abstract Nickel nanocrystalline electrodeposits were produced from a Watts type bath with the addition of cis-2-butene-1,4-diol and simultaneous application of either direct or pulse current conditions. The surface morphology, the preferred orientation, grain size and microhardness of Ni deposits were determined as functions of the concentration of the additive in bath, the type of imposed current and the frequency of imposed current pulses. The combined imposition of predefined pulse current conditions (pulse frequency) and specific additive concentration in the bath leads to specific textural modifications ([211] and [100] preferred crystal orientations) accompanied by considerable nanosized grain refinement of the coatings. The overall experimental data indicate that the production of hard and bright nanostructured deposits could be obtained under pulse current regime and reduced amounts of cis-2-butene-1,4-diol compared to direct plating.

Multimedia Applications by Using Video-Recorded Experiments for Teaching Biology in Secondary Education

In this paper, we present five video-recorded experiments that are embedded in multimedia applications uploaded in the “Digital School-Digital educational material” platform, which is the official platform for educational material of the Greek Ministry of Education. The presented videos provide students with the basic information on how to use a microscope, observe nucleus, isolate nucleic acids and study mitosis and protein denaturation. In this way, they potentially enhance both the practical and theoretical aspects of science. It is expected that these digital applications will promote deeper knowledge of biology.