A preliminary study on chemical micro-machining of complex three-dimensional patterns on silicon substrates

Chemical micro-machining of complex 3-dimensional (3-D) patterns of silicon substrates was preliminarily explored by the confined etchant layer technique (CELT). Through systematic investigation, we demonstrated that cysteine as a scavenger and Br₂ as an etchant can be used to etch silicon substrates. The CELT has the potential to develop into a new means of micro-machining complex 3-D patterns on silicon substrates. However, due to the highly corrosive property of the chemicals used for the silicon etched system, great effort must be made to overcome these problems including the mold electrode with high chemical stability.Dedicated to Professor Gygy Horyi on the occasion of his 70th birthday     

Coupled mass transfer and reaction in water of an oil soluble chemical: A CT scan study

Chemical compounds of the family of alkoxysilanes, such as tetramethyl orthosilicate (TMOS), are soluble in oil but can be dissolved in water where they undergo a hydrolysis and a condensation reaction to form a stable silica gel. We have investigated in detail the coupled mass transfer–reaction process that takes place when oil with dissolved TMOS is brought in contact with water in a well-defined geometry. The main physical parameters (initial TMOS concentration in the oil phase, initial water to oil volume ratio, and water pH and salinity) were varied during the experiment. X-ray CT was used to visualize and quantify concentration changes in the oil and the water phases. We found that varying the initial concentration does not affect mass transfer rates out of the oil phase, but increasing initial concentrations do speed up gelation. The water to oil volume ratio has a larger impact on mass transfer, with a transfer rate that increases with increasing water to oil volume ratio. Low pH of the water phase promotes mass transfer, whereas high pH and addition of salt has no significant effect. Gelation is however more profoundly affected by both increasing pH and addition of salts.     

A study of lithium uptake and location in the brain using the nuclear track technique

The nuclear track technique was used to study the lithium uptake and location in the brains of rats. This study indicated that a maximum lithium concentration was reached in the brain eight hours after an intraperitoneal injection.     

A chemical study ofPlectranthus glaucocalyx Maxim.

Summary A previously unknown crystalline substance C₂₀H₂₈O₄, calledplectrin, has been isolated from the leaves ofPlectranthus glaucocalyx Maxim., family Labiatae.Khimiya Prirodnykh Soedinenii, Vol. 1, No. 6, pp. 427–428, 1965     

A study of PP/PET composites: Factorial design,mechanical and thermal properties

Due to the economic importance of polypropylene (PP) and polyethylene terephthalate (PET), and the large amount of composites made with PP matrix and recycled PET as reinforcing material; an investigation was performed regarding the mechanical and thermal behavior of PP composites containing recycled polyethylene terephthalate fibers (rPET). Interfacial adhesion between the two materials was achieved by adding a compatibilizer, maleic anhydride grafted polypropylene, PP-g-MA. Mechanical behavior was assessed by tensile, flexural, impact and fatigue tests, and thermal behavior by HDT (Heat Deflection Temperature). Fractured surfaces and fiber were investigated by scanning electron microscopy. Multiple regression statistical analysis was performed to interpret interaction effects of the variables. Tensile strength, tensile modulus, flexural strength, flexural modulus and HDT increased after rPET fiber incorporation while strain at break, impact strength and fatigue life decreased. Addition of compatibilizer increased tensile strength, flexural strength and flexural modulus, fatigue life and HDT while tensile modulus, strain at break and impact strength decreased. However, at low fiber content, the impact strength increased, probably due to nucleation effects on PP.     

Synthetic pH sensitive polyampholyte hydrogels: A preliminary study

A combined capillary drop viscometer-pH cell has been constructed and used to study the solution properties of some polymeric weak acids, bases, and ampholytes containing methacrylic acid (MAA), dimethylaminoethyl methacrylate (DMAEMA), and 2-hydroxyethyl methacrylate (HEMA). The behavior of polyelectrolytes based on MAA or DMAEMA is consistent with established thinking, and is dominated by the chain expansions which accompany ionization of acidic (MAA) or protonation of basic (DMAEMA) functionality. The solution behavior of the polyampholytes is complex and was studied as a preliminary to investigations of crosslinked hydrogel analogues. Briefly, it was found that changes in polymer coil dimensions were dictated by the formation or breakage of intramolecular salt bridges by, for example, lowering the solution pH to protonate weakly acidic, or raising the pH to deprotonate weakly basic functionality. Similar effects were observed on adding counterions which preferentially complex with one of the bound ions. The pH sensitivity of polymer coil dimensions increased with the concentration of charged functionality in the polymer. Chemically crosslinked polyampholytes were prepared and equilibrium water contents were measured as a function of pH. In contrast, due to network constraints, the pH sensitivity of the hydrogels, as measured by changes in equilibrium water uptake, increased with a decrease in the level of charged functionality in the polymer.     

Nonadiabatic transitions in chemical reactions: A quantum mechanical study

This work presents an exact quantum mechanical treatment of a reactive three-atom collinear model system incorporating nonadiabatic couplings. It was assumed that nonadiabatic transitions are induced by the vibrational motion only. The main findings are: (i) The reaction process can create conditions in which weak nonadiabatic couplings terms ( for which the Massey parameter was round 10) may cause large probabilities (～0.5) for transitions from one electronic surface to the other. In other words, the reaction process is able in certain cases to create a near resonance situation which makes the non-adiabatic transition almost independent of the magnitude of the coupling term. For this to happen the two surfaces need not be proximate, nor need they “almost” cross along a certain line (ii) In cases where the main nonadiabatic transitions take place outside the interaction region one may, at least qualitatively, decouple the reaction process from the nonadiabatic one. Thus, under the conditions specified one may first treat the reactive system on the ground state surface without including the excited interacting surface and then treat the nonadiabatic process independently.     

Ion chromatography: A powerful and versatile analytical technique for environmental chemical characterization

The advanced IC instrumentation systems currently offered on the market are attractive due to their particular ability to solve a great number of analytical problems in different fields of utilization, including the environment. The most significant features of the IC system are:

• the versatility in assuming a proper configuration tailored for the actual features of the analysis;

• the possibility of preconcentrating the analytes on line and eliminating most of the interference components of the sample matrix, by using ancillary columns and devices in the same IC environment;

• the ability to separate and determine solutes which have similar chemical behavior and are present in the sample in an extreme mass ratio (f.i. 1:10⁸);

• the low detector limits (namely ppb or sub-ppb) which can be reached by changing the loop volume, or by using columns (and the associated flow paths) with a low internal diameter;

• the large dynamic range (typically four or five decades);

• the large number of analytes that can be analyzed per run (up to 10 well-separated peaks in a 20-min run), coupled to a short reequilibration time between runs;

• the large number of classes of compounds (ionic, nonionic, organic, inorganic, etc.) which can be separated and detected;

• the low coefficient of variation (typically 0.2–1% for the concentration range 0.1–50 ppm; 10% for lower concentrations).

For all the above features IC is becoming the most competitive instrumental technique in the environment for the analysis of major, minor, and trace components in natural water, snow, ice, rain, and air. Some significant results obtained with modern advanced IC instrumentation are illustrated. Instrumental precision and accuracy are also discussed.     

Applications of PET–CT in clinical practice: Present and future

Radionuclide imaging and specially positron emission tomography (PET) has already demonstrated its benefits in three major medical subjects, i.e. neurology, cardiology and particularly clinical oncology. More recently the combination of PET and X-ray computed tomography (CT) as PET–CT led to a significant increment of the already large number of clinical applications of this imaging modality. This “anatomy-metabolic fusion” also known as Metabolic Imaging has its future assured if we can: (1) improve resolution reducing partial volume effect, (2) achieve very fast whole body imaging, (3) obtain accurate quantification of specific functions with higher contrast resolution and, if possible, (4) reduce exposure rates due to the unavoidable use of ionizing radiation.     

A combined quantum chemical/molecular mechanical study of hydrogen-bonded systems

A computational approach, which involves the combination of the OPLS force field and molecular orbital MNDO , AM 1, and PM 3 methods, has been developed to describe the effects of a large, molecular mechanically simulated environment on the Hamiltonian of a quantum chemical system. To test the validity of the combined quantum mechanical/molecular mechanical (QM /MM ) potential, a systematic study of the structures and energies of neutral and charged hydrogen-bonded complexes has been carried out, including comparisons with pure semiempirical calculations and available experimental and ab initio data. It is shown that, in many cases, the hybrid QM /MM potential behaves better than do related MNDO /M , AM 1, and PM 3 methods. As a case in point, the draw-back of AM 1 favoring bifurcated H-bonded structures over single ones is not presented in the combined AM 1/OPLS scheme. Possible ways of improvement of the combined QM /MM potential are discussed. © 1992 John Wiley & Sons, Inc.     

A preliminary study of gross alpha/beta activity concentrations in drinking waters from Albania

A pilot study involving screening measurements of gross alpha/beta activity concentration in drinking water was performed in 12 cities with the highest population density in Albania. The aim of this study was to develop a first insight regarding the radiological quality of drinking and bottled water supplies. The tap and bottled water samples investigated are acceptable for consumption, complying with the WHO recommendations for drinking water. The average gross alpha and beta activity concentrations were \( 36_{ - 18}^{ + 37} \) and \( 269_{ - 150}^{ + 337} \)  mBq/L, respectively in tap waters. While for bottled water the gross alpha and beta activities were respectively \( 39_{ - 23}^{ + 55} \) and \( 220_{ - 132}^{ + 336} \)  mBq/L. The data obtained can provide information for authorities regarding the quality of drinking water and a baseline for future contaminations.     

Heterogeneous uptake of ozone on reactive components of mineral dust aerosol: an environmental aerosol reaction chamber study

We have undertaken a kinetic study of heterogeneous ozone decomposition on alpha-Fe2O3 (hematite) and alpha-Al2O3 (corundum) aerosols under ambient conditions of temperature, pressure, and relative humidity in order to better understand the role of mineral dust aerosol in ozone loss mechanisms in the atmosphere. The kinetic measurements are made in an environmental aerosol reaction chamber by use of infrared and ultraviolet spectroscopic probes. The apparent heterogeneous uptake coefficient, gamma, for ozone reaction with alpha-Fe2O3 and alpha-Al2O3 surfaces is determined as a function of relative humidity (RH). The uptake of ozone by the iron oxide surface is approximately an order of magnitude larger than that by the aluminum oxide sample, under dry conditions. At the pressures used, alpha-Fe2O3 shows clear evidence for catalytic decomposition of ozone while alpha-Al2O3 appears to saturate at a finite ozone coverage. The measured uptake for both minerals decreases markedly as the RH is increased. Comparison with other literature reports and the atmospheric implications of these results are discussed.     

Ellipsometry of DNA adsorbed at mercury electrodes: A preliminary study

The adsorption of DNA at a mercury electrode can be detected ellipsometrically. Native DNA is probably more weakly absorbed at positive charges than at negative charges. Denatured DNA is more strongly adsorbed in the reduced form than in the protonated form and is desorbed at large negative charges. Adsorption of both forms is characterized by small negative values of δΔ/δ. It is suggested that these results should be interpreted in terms of an anisotropic film.     

The chemical state of arsenic in minerals of environmental interest--an XPS and an XAES study

A systematic analytical study using X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) has been carried out to characterize the chemical state of arsenic in complex environmental samples. The conventional approach, which relies on the chemical shift of the core levels As3d, provides ambiguous results in determining the chemical environment of arsenic. A more accurate approach, based on the Auger parameter and on the Wagner (Chemical State) plot, which combines AsLMM kinetic energy and As3d binding energy, was adopted. This novel method for determining the chemical state of arsenic was employed to completely characterize arsenic in complex environmental samples.     

Sandwich compounds of second-row elements: A quantum chemical study

The structures and stabilities of a number of neutral and charged sandwich-type boron, carbon, and nitrogen compounds designed based on the cyclophane cage and obeying the “electron octet” rule were studied by the B3LYP/6−311+G** density functional method. The possibility of targeted modification of the electronic structures of such compounds by varying the basal or bridging atomic groups was investigated. Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1825–1835, November, 2006.     

A study of chemical reactions in coarse-grained simulations

We introduce a reaction model for use in coarse-grained simulations to study the chemical reactions in polymer systems at mesoscopic level. In this model, we employ an idea of reaction probability in control of the whole process of chemical reactions. This model has been successfully applied to the studies of surface initiated polymerization process and the network structure formation of typical epoxy resin systems. It can be further modified to study different kinds of chemical reactions at mesoscopic scale.