The generation and measurement of aerosols

Aerosols are of extreme importance to many branches of science and technology although this is seldom realized by non-specialists. The disperse phase of an aerosol may consist of virtually any known material and so includes liquids, pure and unadulterated, as well as solids of simple composition and regular shape in one extreme to complex materials which may be radioactive, electrically charged and of complex shape in the other extreme.The basic characteristics and some of the most important methods of generating aerosols are reviewed. The difficulties that arise in attempting to produce standard aerosols are indicated. In considering measurements on aerosols the difficultues in collecting representative samples are outlined. Diagnostic methods which do not perturb the aerosol such as photographic and holographic techniques as well as light interaction methods are considered in some detail.     

Stabilization of the 108 K superconducting phase in the Bi0.7Pb0.3SrCaCu1.8Oy system

Samples having the nominal composition Bi_0.7Pb_0.3SrCaCu_1.8O _y , were prepared by a solid-state reaction and characterized by energy-dispersive x-ray microanalysis, resistivity measurements, and magnetically modulated microwave absorption (MAMMA). Longer annealing times resulted in more homogeneous samples having a single superconducting transition to zero resistance at 108 and 105 K at 0.1 and 1 mA, respectively. The MAMMA measurements clearly show differences in sample homogeneity with different annealing times.     

Coverage of rough substrates by ZnS using vacuum evaporation and atomic layer epitaxy

The effects of various deposition techniques on the growth of ZnS thin films on a sintered BaTiO₃-based complex perovskite substrate, using the scanning electron microscope have been studied. The results clearly show a non-uniform and incomplete coverage of the sub strate in the case of films grown by electron-beam evaporation and resistance-heated evaporation. A shadowing effect is observed in these films. Increase in the thickness of the films tends to decrease the shadowing effect. On the contrary, films grown by the atomic layer epitaxy method, exhibit a complete and uniform coverage of the substrate, even for thin (< 100 nm) ZnS films.     

Characterization of YBa2Cu3O7/PrBa2Cu3O7 superlattices

We investigated the structural and superconducting properties ofc-axis oriented (YBa₂Cu₃O₇) _nY /(PrBa₂Cu₃O₇) _npr superlattices with thicknesses of the individual layers down to one unit cell (10nY1; 18>nPr 1). By transmission electron microscopy and X-ray diffraction we find an excellent structural quality of the samples, though the quantitative analysis shows the existence of defects. In superlattices with decoupled YBa₂Cu₃O₇ layers of two unit cell thickness we find a highT _c value of 75 K. We probed the flux line structure in the superlattices by measurements of the critical current density in magnetic fields. The experiments show that the flux-line dynamics is dominated by the movement of pancake vortices.     

Gradual deviations to BCS superconductivity and Ginzburg-Landau parameters of Zr-Cu amorphous alloys

We report on the superconducting properties of a series of sputtered, amorphous Zr_100–x Cu_x (19x48) alloys. From the thermodynamic parameters, we conclude that there is a very good agreement with the BCS theory on the high-Cu-concentration side. When Zr content increases, and then the coupling strength, a very continuous and progressive deviation from the BCS limit occurs, which is in rather good agreement with theoretical predictions for crystalline alloys. However, a departure develops at high Zr concentration. Despite the surprising behavior of the electronic density of states N(E _F) characteristic of these highly disordered alloys, a correlation is found between N(E _F) and the Ginzburg-Landau parameter .     

Single crystal ZnSr:Mn prepared by ion implantation

Single crystal ZnS was implanted with 100 keV Mn⁺ ions. Low-temperature ZnS:Mn emission spectra were obtained using 5 keV electrons for excitation. Phonon structure was observed in thermally annealed material, and Mn diffusion was measured using a depth-selective emission profile.     

Histologic Changes in Continuous, Long-Term Electrical Stimulation of a Peripheral Nerve

The chronic stimulation of peripheral nerves has, in the past, usually been of an intermittent or relatively short-term nature. Histologic changes which have taken place have been attributed to the trauma caused by mechanical factors and/or the effects of electrical charges. Investigators, speculating on the effects of electro-stimulation, have designed electrodes specifically to minimize tissue damage. The purpose of the present investigation is to determine which pathologic alterations, if any, are caused specifically by electrical?as distinct from mechanical?factors. Dogs were divided into two groups, differing only in that one group?the controls?had electrodes implanted around the phrenic nerve, but stimulation was never applied. Duration of the test was up to 308 days. The results indicated that no histologic alterations could be attributed specifically to electrical stimulation, as contrasted to mechanical trauma, to the phrenic nerve.     

Preparation and characterization of thin films of MgO,Al2O3 and MgAl2O4 by atomic layer deposition

MgO, Al₂O₃ and MgAl₂O₄ thin films were deposited on silicon substrates at various temperatures by the atomic layer deposition (ALD) method using bis(cyclopentadienyl)magnesium, triethylaluminum, and H₂O and were characterized systematically. High-quality polycrystalline MgO films were deposited for a substrate temperature above 500°C, and amorphous thin films were deposited around 400°C. The deposited Al₂O₃ and MgAl₂O₄ thin films were characterized as amorphous in structure. Applicability of ALD to complex oxides is discussed.     

Photocatalytic degradation of methylorange Using TiO2, WO3 and mixed thin films under controlled pH and H2O2

Wastewaters resulting from textile industry sector have a different chemistry compared with most of the other wastewaters. The different dyes in excess are usually very stable and even small quantities can have a major impact to the effluent. In order to treat these wastewaters, photodegradation is a largely investigated process that can be up-scaled. Photocatalysts based on wide band gap semiconductors can be used in heterogeneous photocatalysis and mostly reported are TiO2 and WO3. Under UV irradiation they form electron-hole pairs that produce active species that can oxidize the dye molecules. The electron-hole recombination represents the main cause for low efficiencies and is limited by the use of oxidant systems like H2O2. Doctor blade technique, a reproducible, up-scalable and low cost technique was used to obtain thin films. The reference dye, used in this experiment is methylorange in solution of 0.0125 mM, corresponding to average polluted water. In order to reduce the recombination in the catalysts, H2O2 is used. Another important aspect of the dye photocatalysis process, investigated in the paper is the adsorption of the dye molecule on the photocatalyst surface, strongly depending on pH which affects the dye's structure and the surface charge. Experiments are conducted at fixed pH values: 3, and respectively 7 covering values below and over the ZPC of the photocatalysts. The results show that TiO2/WO3 films have higher efficiency then the TiO2 and WO3 films, mainly due to the surface morphology of the films. By adding H2O2, higher efficiencies are obtained, confirming that the electron-hole pair recombination is reduced. From the point of view of pH, higher efficiencies are obtained in acidic solutions and the results are comparatively discussed considering the dye's ionic/neutral structure and the photocatalyst surface charge. The efficiency was calculated using UV-VIS spectrophotometer measurements of the solution and the thin films were characterized by AFM and XRD.