D

Abstract

DACITE.The name of a somewhat variable group of extrusive igneous rocks similar to the rhyolites but richer in plagioclase feldspar. Typical dacites are felsitic to porphyritic in texture. Dacites are the extrusive equivalents of the quartz-rich varieties of diorites and are sometimes classified as quartz-bearing andesites. The porphyritic types usually occur toward the center of the thicker dacite flows, dikes and sills, as well as the marginal zones of laccoliths. Dacites are common in the Cordilleran province of North, Central and South America. The term, dacite, was proposed by G. Stache of Austria for lavas in the old Roman province of Dacia. DACRYOCYSTITIS.Infection of the lacrimal sac of the eye. The lacrimal glands produce tears for lubrication and protection of the eye. When the naso-lacrimal duct becomes obstructed, infection of the tearproducing sac is likely. Dacryocystitis appears most often in infants and in adults over 40 years of age. Secretions which cannot drain through the obstructed duct spill back out through the eye. Medical attention is required to avoid complications, such as infection of the cornea. See also Vision and the Eye.D' ALEMBERT PRINCIPLE. The principle, first pointed out by d' Alembert in 1742, that Newton's third law (see Newton's Laws of Dynamics) holds for forces acting upon bodies entirely free to move as well as upon fixed bodies in stationary equilibrium. In the former case the "reactions" concerned are due solely to inertia. Thus, in the act of throwing a ball, one pushes upon the ball with a certain force, and the inertia of the ball causes it to push back on the hand with an equal force. The condition of the system during such a process is said to be one of kinetic equilibrium. From this point of view, obviously, any system of bodies must always be in equilibrium, either kinetic or static. DALTONIDE COMPOUNDS. See Chemical Composition.DALTON LAW. The law of partial pressures in mixed gases and vapors. If several gases not reacting chemically with each other are introduced into the same container, the pressure of the resulting mixture is equal to the sum of the pressures which would be observed if each gas were separately enclosed in that container. We may, for example, regard the atmospheric pressure as the sum of a nitrogen pressure, an oxygen pressure, an argon pressure, a carbon dioxide pressure, a water-vapor pressure, etc. The same principle holds for mixtures of the saturated vapors of two or more liquids evaporating in the same closed space, provided one liquid does not dissolve the vapor from the other (as water dissolves ammonia). Like other gas laws, this law is approximately valid only within limits. See also Combustion. Dam Classification and ConstructionDams may be classified as follows: 1) Timber dams.2) Rock-fill dams.3) Earth dams. Plain. Core wall. Hydraulic fill. 4) Masonry dams.Gravity, solid and hollow. Arch, single and multiple.Timber Dams. The timber dam is rarely used because of its short life and the limitation in height to which it may be carri...

Biochar from the Straw-Stalk of Rapeseed Plant

“…Energy from biomass is recovered by means of biochemical and thermochemical conversion processes. Among the thermochemical conversion processes pyrolysis has received considerable attention since the process conditions can be optimized to produce the desired end product. − Slow heating rates coupled with a low final maximum temperature maximize the char yield in pyrolysis. − The solid char has a wide variety of applications. ,, Charcoal produced from different types of biomass which include eucalyptus, acacia, oak, spruce, meranti, chestnut, birch, bagasse, corn cob, sweet sorghum, tropical trees, etc., has been investigated extensively. − Rapeseed is an oil plant introduced to the Turkish agriculture during the Second World War and it has been cultivated primarily for its oil since then. Utilizing rapeseed as an energy crop alongside its conventional cultivation as an oil plant seems to be gaining some momentum in recent years…”

Catalytic Desulfurization of Carbon Black on a Platinum Oxide Electrode

“…When carbon is used as a power source (i.e., a fuel) or as a catalyst support in power sources, its sulfur content must be considered. When coal is burned, the inherent organosulfur becomes SO x , which is a respiratory irritant and a precursor to acid rain . Sulfur is also introduced to carbon, usually via vulcanization, to alter the bulk and surface properties of the carbon. , The surface organosulfur of carbon can affect the properties of supported fuel-cell electrocatalysts, − and evidence is mounting that heteroatoms act as the anchor to support electrocatalyst nanoclusters on the carbon surface. − Under certain conditions, the organosulfur in Vulcan carbon can poison the activity of Pt electrocatalysts. , …”

Structure and Bonding of C2H2 on Diamond C(111)−1×1:H: Infrared Spectroscopy and Exciton Calculations

“…Assuming an average error of 2°, we obtain a separation of 27 atoms between steps in one dimension, which means that at least 4% of the surface is occupied by carbon atoms located on defect sites. In addition to the orientational flaw, as-polished C(111) surfaces have been revealed by atomic force microscopy to contain ridges and scratches with heights of 5−10 nm and a total height variation of less than 100 nm. , The ridges and scratches are large compared to the size (van der Waals length of 0.58 nm and width of 0.37 nm) of C 2 H 2 and thus can properly accommodate the molecules. With clustering effects taken into account, the content of the defect sites can readily explain the 25% coverage given by the first-stage adsorption in Figure .…”

“…As pointed out in the Introduction, both the acetylene dimer and trimer are planar and thus they both are likely to be the basic unit for the formation of the two-dimensional lattice of the monolayer (see Figure a and b). In Figure b, we draw C 2 H 2 in van der Waals radii of 1.85 Å for C and 1.2 Å for H . Compared to that of the cyclic trimer, overlap of the van der Waals radii is more severe for the commensurate dimer array because of closer packing.…”