Solid state studies in ceramic alloys Quarterly progress report, 1 Jun. - 31 Aug. 1969

Solid state characteristics of ceramic alloy

Use of Hydration Inhibitors to Improve Bond Durability of Aluminum Adhesive Joints

An investigation is conducted of the mechanisms by which nitrilotris methylene phosphonic acid (NTMP) and related compounds are adsorbed onto oxidized aluminum surfaces to inhibit hydration and increase the durability of adhesive bonds formed with inhibitor-treated panels. P - O - Al bonds are identified as the basis of adsorption, and it is found that water initially adsorbed onto the etched aluminum surfaces is displaced by the NTMP. The hydration of the NTMP-treated surfaces occurs in three stages, namely the reverisble physisorption of water, the slow dissolution of NTMP followed by rapid hydration of the freshly exposed Al2O3 to AlOOH and further hydration of the surface to Al(OH)3. Five properties of an ideal inhibitor are identified

Bonding, structure and mechanical behavior of vanadium carbide single crystals

Bonding, structure, and mechanical behavior of vanadium carbide single crystal

Solid state studies in ceramic alloys Quarterly progress report no. 2, 1 Dec. 1965 - 28 Feb. 1966

Electron microscope study of boron-doped titanium carbide sample

Solid State Studies in Ceramic Alloys Quarterly Progress Report No. 1, 31 Aug. - 30 Nov. 1965

Effect of trace amounts of boron on defect structure of titanium carbide crystal

Crossover in the scaling of island size and capture zone distributions

Simulations of irreversible growth of extended (fractal and square) islands with critical island sizes i=1 and 2 are performed in broad ranges of coverage \theta and diffusion-to-deposition ratios R in order to investigate scaling of island size and capture zone area distributions (ISD, CZD). Large \theta and small R lead to a crossover from the CZD predicted by the theory of Pimpinelli and Einstein (PE), with Gaussian right tail, to CZD with simple exponential decays. The corresponding ISD also cross over from Gaussian or faster decays to simple exponential ones. For fractal islands, these features are explained by changes in the island growth kinetics, from a competition for capture of diffusing adatoms (PE scaling) to aggregation of adatoms with effectively irrelevant diffusion, which is characteristic of random sequential adsorption (RSA) without surface diffusion. This interpretation is confirmed by studying the crossover with similar CZ areas (of order 100 sites) in a model with freezing of diffusing adatoms that corresponds to i=0. For square islands, deviations from PE predictions appear for coverages near \theta=0.2 and are mainly related to island coalescence. Our results show that the range of applicability of the PE theory is narrow, thus observing the predicted Gaussian tail of CZD may be difficult in real systems.Comment: 9 pages, 7 figure

Μελέτη και σχεδίαση Ε/Γ ‐ Ο/Γ πλοίου κλειστού τύπου

128 σ.Νικόλαος Ηρ. Παναγιωτακόπουλο

Capture-zone scaling in island nucleation: phenomenological theory of an example of universal fluctuation behavior

In studies of island nucleation and growth, the distribution of capture zones, essentially proximity cells, can give more insight than island-size distributions. In contrast to the complicated expressions, ad hoc or derived from rate equations, usually used, we find the capture-zone distribution can be described by a simple expression generalizing the Wigner surmise from random matrix theory that accounts for the distribution of spacings in a host of fluctuation phenomena. Furthermore, its single adjustable parameter can be simply related to the critical nucleus of growth models and the substrate dimensionality. We compare with extensive published kinetic Monte Carlo data and limited experimental data. A phenomenological theory sheds light on the result.Comment: 5 pages, 4 figures, originally submitted to Phys. Rev. Lett. on Dec. 15, 2006; revised version v2 tightens and focuses the presentation, emphasizes the importance of universal features of fluctuations, corrects an error for d=1, replaces 2 of the figure

Algal culture studies related to a Closed Ecological Life Support System (CELSS)

In many respects, algae would be the ideal plant component for a biologically based controlled life support system, since they are eminently suited to the closely coupled functions of atmosphere regeneration and food production. Scenedesmus obliquus and Spirulina platensis were grown in three continuous culture apparatuses. Culture vessels their operation and relative merits are described. Both light and nitrogen utilization efficiency are examined. Long term culture issues are detailed and a discussion of a plasmid search in Spirulina is included

Cavity-enhanced absorption using an atomic line source: application to deep-UV measurements

Optical cavities are commonly used to increase the sensitivity of absorption measurements, but have not been extensively used below 300 nm, mainly owing to the limited light sources at these wavelengths. While some progress has been made using cavity ring-down spectroscopy, these systems rely on complex and expensive lasers. Here we investigate an approach combining Cavity-Enhanced Absorption Spectroscopy (CEAS) with an inexpensive low vapour pressure mercury lamp for sensitive absorption measurements at 253.7 nm. We demonstrate that the CEAS absorption in our system is 50 times greater than the absorption found in a single-pass configuration; using this approach, we obtained limits of detection of 8.1 pptv (66 ng m(-3)) for gaseous elemental mercury and 8.4 ppbv for ozone. We evaluate the performance of the system and discuss potential improvements and applications of this approach