Specific Chemical Nature Research Articles

Surface control of luminescence in silicon nanoparticles

The intensity of visible photoluminescence from thin films of silicon nanoparticles is shown to be dependent upon the degree of surface passivation on the nanoparticles, while the emission energy is independent of the specific chemical nature of the passivating species. Nanoparticles are deposited into films using a pulsed laser ablation supersonic expansion source. Surface chemistry is controlled with a variety of postdeposition processing steps, including acid, methanol, and iodine treatments. These steps are then correlated with the visible photoluminescence behavior of the sample and the surface chemistry as characterized by x-ray photoelectron spectroscopy. Surface passivation controls the emission intensity through the elimination of competing nonradiative carrier relaxation pathways. The chemical nature of the passivating species does not determine the emission energy and can be easily changed with no anomalous photoluminescence behavior resulting. All results are consistent with a simple quantum confinement model of emission where particle size determines emission energy and surface passivation determines emission intensity.

Basic considerations in flowing electrorheological fluids

The physical and chemical properties of electrorheological (ER) fluids are reviewed, and an outline theory of their mode of action is proposed. Rheologically, the Bingham plastic model gives an acceptable representation of ER fluids flowing in a field and it has recently been shown that the plastic viscosity may be field-dependent in some circumstances, as well as the yield stress. The variation of the former with field is strongly influenced by the specific chemical nature of the ER fluid, while the field dependence of the latter has a similar form in all the ER fluids investigated. However, interpretation of observations is complicated by concentration of solid in the working gap and interplay between local electrical conductivity and shear rate.

Stretching frequency versus bond distance correlation of OD(H)⋯Y (Y  N, O, S, Se, Cl, Br, I) hydrogen bonds in solid hydrates

From a compilation of spectroscopic and structural data of solid hydrates 61 different compounds containing more than 250 OD(H)⋯Y groups have been selected, for which uncoupled OD stretching frequencies, hydrogen bond distances and assignments of sufficient reliability and accuracy are available. ν (OD) versus R(O⋯Y) and R(H⋯Y) diagrams and calculated correlation curves are presented for Y  N, O, S, Se, Cl, Br, I. Depending on the scatter of points and the number of data included in the plots the predictive value and the statistical significance varies from very high for O, S and Cl acceptors down to rather poor for Br and I acceptors. At equal bond distances the frequencies may differ by up to about 150 cm −1 depending on the specific chemical nature of the proton acceptors included in a plot, while the influence of different cation—water contacts is less significant and distinct. Anion effects play, therefore, a dominant role in producing large scatters, while action effects and experimental inaccuracies are of minor importance. Furthermore it is shown, that the relation between ν (OD) and ν (OH) frequencies is almost perfect and the frequency—distance correlations involving ν (OD) are also representative without serious restrictions for corresponding correlations involving ν (OH).

Solvent effect on the dissociation of o-nitroanilinium ion in methanol-propylene glycol media at 25°C

The dissociation constants ( K s ) of o-nitroanilinium ion have been determined at 25° in methanol, propylene glycol and mixtures of the two components containing 10, 30, 50, 70 and 90 wt. % propylene glycol by spectrophotometric measurements. Standard free energies of transfer, Δ G° t (B) of o-nitroaniline from methanol to the other solvents have been evaluated from the measurement of solubilities at 25°C. The solvent effect on the proton transfer process of this acid: Δ G° t [BH +−B] sys = 2.303 RT[p( K s −p( K m )] has been discussed in terms of the free energies of transfer Δ G° t from methanol to other solvents, of the uncharged based B, of the hydrochloride of the base (BHCl) computed from the corresponding values for HCl and also of the individual ions assessed from the previous knowledge of Δ G° t (Cl −). The corresponding data for the protonated tris(hydroxymethyl)methyl amine [TrisH +] and p-nitroanilinium ion in the same solvent system obtained from the literature are also compared. Δ G° t [BH +−B] sys values for the dissociation of o-nitroanilinium ion have been found to increase less readily with wt.% propylene glycol compared to p-nitroanilinium ion and are in contrast with the decreasing nature of the corresponding values for the TrisH + ion of different chemical nature. Electrostatic effect being negligible in this solvent system, the overall behaviour of these acids is found to be dictated by specific chemical nature of solute-solvent interactions besides the effect of relative solvent basicities.

Remarks on the terminology used for the chemical transformations of fuels

The technical vocabulary used to describe the chemical transformations of fuels is critically revised with the objective of establishing a simple and coherent classification. The criterion used for such classification is based on the unique and specific chemical nature of each of the transformations. Thus three distinct categories are defined: thermal decomposition reactions, oxidation reactions and reduction reactions. The scope of application of these categories as well as their subdivisions are also discussed.

Mutagens and potential mutagens in the biosphere I. DDT and its metabolites, polychlorinated biphenyls, chlorodioxins, polycyclic aromatic hydrocarbons, haloethers

For a proper assessment of actual risks, it is essential that the interactions between different modes of administration of a toxicant be understood and that the probable impingement of the environmental substances upon the various portals of entry be known. To best understand this last requirement we must know how the toxicants in question are distributed in and are transported through the environment to finally impact on man. In this review, we have attempted to evaluate but a small number of mutagens and potential mutagens ( e.g., DDT and its metabolites, polychlorinated biphenyls, chlorinated dioxins, polycyclic aromatic hydrocarbons and haloethers) in terms of their occurrence, use patterns, distributions and impact in the environment. In many cases, the information is fragmentary. For example, patterns of region and local variation of the toxicants have been only superficially investigated and the detailed pathways of residues within the trophic networks are poorly understood. The physiological and ecological effects of the toxicants at sub-lethal levels are also to a large extent unknown. We must have more information as to (1) the production (nature of reactants, amounts, reactivity, disposal, etc.), import and export data for specific potential environmental toxicants, (2) the nature and routes of their global transport, and (3) the concentration, longevity, biochemical and toxicological activity of their residues (including specific chemical nature) that occur in their various biosphere compartments including air, water, soil, and biota.

An alternative explanation for polywater

A variety of polywater experiments have been carried out. Analytical experiments have repeatedly demonstrated the presence of high concentrations of contaminants and ESCA studies have elucidated the specific chemical nature of these contaminants. Specific carbon compounds, consistent with the analyses, may be responsible for many of the properties including the infrared spectrum. A preparation of poly-D 2O results in material with the same infrared spectrum as poly-H 2O. The failure to observe the predicted isotope frequency shifts indicates that the reported infrared features do not originate from H 2O units. On the basis of these experiments it appears very unlikely that a polymer of water exists.

Mechanism of environmental stress cracking in linear polyethylene

By means of a constant stress test, the environmental stress-cracking behavior of linear polyethylene has been studied on a macro and micro scale in an effort to determine the mechanism of the process. Upon the application of stress, linear polyethylene develops a network of very fine, elliptical fissures, the edges of which are connected by cold-drawn material. In the absence of an active environment, these fissures slowly grow and interconnect, resulting ultimately in the formation of a “neck.” When exposed to an active environment, however, the cold-drawn material ruptures as it is formed at the tips of the fissures. Unsupported, these fissures grow rapidly and interconnect resulting in sample failure. Fissures form both around and through the centers of spherulites with less cold drawing occurring at the interspherulite boundaries. Macroscopic studies confirmed the observation that active environments attack stressed polyethylene specifically at microzones of cold drawing. The effect of low molecular weight hydrocarbon species on the stress-crack resistance of linear polyethylene was evaluated. The role of flaws in the process is also discussed. Attempts have been made to establish a criterion of environmental activity. All of the active stress-cracking agents studied were found to reach similar levels of absorption in polyethylene; however, the specific chemical nature of the environment and not merely its level of absorption determines its ability to cause stress cracking.

Physiological Effect of Organic Phosphorus Insecticides on Several Species of Fish

Abstract Fish brain acetylcholinesterase is inhibited in vivo by organic phosphorus insecticides at concentrations of 0.1 mg/1 and lower. The degree of inhibition is a function of the concentration of the insecticide, the extent of exposure, specific chemical nature of the inhibiting substance, and fish species. Species used were largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus), golden shiner (Notemigonus crysoleucas), goldfish (Carassius auratus), and fathead minnow (Pimephales promelas). Fish removed from exposure to acetylcholinesterase-inhibiting insecticides, prior to reaching lethal limits, demonstrate the capacity for regeneration of this enzyme. The time required to regenerate the brain acetylcholinesterase to normal levels depends on the extent of the initial inhibition, the specific nature of the compound producing the inhibition, and the particular species. The curve of brain enzyme inactivation and recovery, as defined by percentage changes in normal activity, describes ...

Degration of Cotton in an Oxygen Atmosphere by Gamma Radiation.

To determine the mechanism of the radiation-induced reactions of cellulose and to evaluate these chemical alterations of the cellulose molecule with relation to the production of new cotton products, the specific chemical nature of the oxidized groups formed must be known. Even though previous work indicated that only small differences in properties were produced, the atmosphere under which the irradiation was carried out is very important in respect to the exact chemical nature of the groups produced. Investigations of the specific nature of the groups formed on cotton cellulose in an atmosphere of oxygen at a gamma radiation dose of 10/sup 8/ r are reported. The penetrating power of gamma -rays, and probably most other kinds of high energy radiation, makes the oxidative degradation of the cellulose molecule unique when compared to ordinary chemical oxidations. The ionizations induced in cellulose are not hindered by the crystalline-amorphous nature of the cellulose structure. The gamma irradiation of cellulose produces chain cleavage, reducing groups and acid groups. The chain cleavage ratio for this work was found to be 19: 0.5: 1 as compared to 20: 1: 1 found by Arthur and Blouin. The distribution of acid groups between the various fractions of themore » irradiated cellulose indicated that acid group production was principally a chain-end effect and that one acid group was produced per every two chains formed. The data suggested that activation of the C/sub 2/, C/sub 3/, C/sub 5/, and C/sub 6/ positions of the polymer caused reducing group formation with evolution of hydrogen and without chain cleavage. The carbon monoxide and carbon dioxide evolved in the irradiation are considered to be secondary degradation products from aldehydes and/or ketones for CO and decarboxylation of carboxyl groups in the case of CO/sub 2/. (B.O.G.)« less

Lipid distribution in the Sertoli cell and Leydig cell of the rat testis as related to experimental alterations of the pituitary-gonad system.

INTRODUCTION NUMEROUS histochemical reactions have been suggested to determine the specific nature of the lipid contained within the Leydig cell primarily to find support for the hypothesis that Leydig cells produce androgen (Pollock, 1942; Dempsey and Wislocki, 1946; Ashbel and Seligman, 1949; Cain, 1950). Sertoli cell lipid has been investigated less extensively although histochemical studies indicate that it consists in part of cholesterol and cholesterol esters (Permian, 1950). It shall be the purpose of this paper to present our findings of the distribution of testicular lipids as they relate to certain alterations of the pituitary-gonad system with no attempt to determine the specific chemical nature of the lipid. In a previous communication we have related changes in distribution of testicular lipids to age (Lynch and Scott, 1950).

Societies and Academies

Societies and Academies