Effective transition rates for epitaxial growth using fast modulation

Thin-film deposition is an industrially important process that is highly dependent on the processing conditions. Most films are grown under constant conditions, but a few studies show that modified properties may be obtained with periodic inputs. However, assessing the effects of modulation experimentally becomes impractical with increasing material complexity. Here we consider periodic conditions in which the period is short relative to the time scales of growth. We analyze a stochastic model of thin-film growth, computing effective transition rates associated with rapid periodic process parameters. Combinations of effective rates may exist that are not attainable under steady conditions, potentially enabling new film properties. An algorithm is presented to construct the periodic input for a desired set of effective transition rates. These ideas are demonstrated in three simple examples using kinetic Monte Carlo simulations of epitaxial growth

Restrictiveness and guidance in support systems

Restrictiveness and guidance have been proposed as methods for improving the performance of users of support systems. In many companies computerized support systems are used in demand forecasting enabling interventions based on management judgment to be applied to statistical forecasts. However, the resulting forecasts are often ‘sub-optimal’ because many judgmental adjustments are made when they are not required. An experiment was used to investigate whether restrictiveness or guidance in a support system leads to more effective use of judgment. Users received statistical forecasts of the demand for products that were subject to promotions. In the restrictiveness mode small judgmental adjustments to these forecasts were prohibited (research indicates that these waste effort and may damage accuracy). In the guidance mode users were advised to make adjustments in promotion periods, but not to adjust in non-promotion periods. A control group of users were not subject to restrictions and received no guidance. The results showed that neither restrictiveness nor guidance led to improvements in accuracy. While restrictiveness reduced unnecessary adjustments, it deterred desirable adjustments and also encouraged over-large adjustments so that accuracy was damaged. Guidance encouraged more desirable system use, but was often ignored. Surprisingly, users indicated it was less acceptable than restrictiveness

The generic character table of a Sylow pp-subgroup of a finite Chevalley group of type D4D_4

Let $U$ be a Sylow $p$-subgroup of the finite Chevalley group of type $D_4$ over the field of $q$ elements, where $q$ is a power of a prime $p$. We describe a construction of the generic character table of $U$

Dynamics from diffraction

A model-independent approach for the extraction of detailed lattice dynamical information from neutron powder diffraction data is described. The technique is based on a statistical analysis of atomistic configurations generated using reverse Monte Carlo structural refinement. Phonon dispersion curves extracted in this way are shown to reproduce many of the important features found in those determined independently using neutron triple-axis spectroscopy. The extent to which diffraction data are sensitive to lattice dynamics is explored in a range of materials. The prospect that such detailed dynamical information might be accessible using comparatively facile experiments such as neutron powder diffraction is incredibly valuable when studying systems for which established spectroscopic methods are prohibitive or inappropriate

Tracking and data systems support for the Helios project. Volume 2: DSN support of Project Helios April 1975 - May 1976

Deep Space Network activities in the development of the Helios B mission from planning through entry of Helios 2 into first superior conjunction (end of Mission Phase II) are summarized. Network operational support activities for Helios 1 from first superior conjunction through entry into third superior conjunction are included

Globular Clusters and Dwarf Spheroidal Galaxies

Traditionally globular clusters and dwarf spheroidal galaxies have been distinguished by using one or more of the following criteria: (1) mass, (2) luminosity, (3) size, (4) mass-to-light ratio and (5) spread in metallicity. However, a few recently discovered objects show some overlap between the domains in parameter space that are occupied by galaxies and clusters. In the present note it is shown that ellipticity can, in some cases, be used to help distinguish between globular clusters and dwarf spheroidal galaxies.Comment: MNRAS (Letters), in pres

Modeling Elementary Heterogeneous Chemistry and Electrochemistry in Solid-Oxide Fuel Cells

This paper presents a new computational framework for modeling chemically reacting flow in anode-supported solid-oxide fuel cells (SOFC). Depending on materials and operating conditions, SOFC anodes afford a possibility for internal reforming or catalytic partial oxidation of hydrocarbon fuels. An important new element of the model is the capability to represent elementary heterogeneous chemical kinetics in the form of multistep reaction mechanisms. Porous-media transport in the electrodes is represented with a dusty-gas model. Charge-transfer chemistry is represented in a modified Butler-Volmer setting that is derived from elementary reactions, but assuming a single rate-limiting step. The model is discussed in terms of systems with defined flow channels and planar membrane-electrode assemblies. However, the underlying theory is independent of the particular geometry. Examples are given to illustrate the model

Plio-Pleistocene Glacial Deposits in Northeastern Nebraska: New Exposures and Interpretations

A field trip sponsored by the Nebraska Geological Society. Trip Leaders: Dr. M.R. Voorhies, University of Nebraska State Museum. & Dr. R.G. Goodwin, HWS Technologies Inc. Spring 1989 Recent interpretation of oxygen isotopic data for benthic and planktonic foraminifera recovered during ocean drilling programs suggest that world ice volume was greater than the ice volume of 18 thousand years ago (Late Wisconsinan) approximately 2.5 million years ago (Prentice and Matthews, Geology, November, 1988). This agrees well With biostratigraphic and paleoecologic interepretations drawn from sediment cores obtained from the Arctic Ocean Basin. The latter data suggest complete ice cover of the basin during the period 2.2-2.4 million years ago (Scott et at., G.S.A. Bulletin, February, 1989). John Boollstorff inferred that one or more glacial tills of the North American mid-continent were deposited at this time. BoeUstorff drew his conclusions primarily from subsurface samples and from volcanic ash horizons dated by the fisssion-track method. The purpose of this trip is to examine fossil-bearing outcrops of sand and gravel or silt that are associated With volcanic ash or glacial till and that provide information about the timing of glacier advance into northeastern Nebraska. The trip Will begin at the Knox County Court House, Center, Nebraska at noon on saturday May 6, 1989. Participants are responsible for providing their own transportation

Plio-Pleistocene Glacial Deposits in Northeastern Nebraska: New Exposures and Interpretations

A field trip sponsored by the Nebraska Geological Society. Trip Leaders: Dr. M.R. Voorhies, University of Nebraska State Museum. & Dr. R.G. Goodwin, HWS Technologies Inc. Spring 1989 Recent interpretation of oxygen isotopic data for benthic and planktonic foraminifera recovered during ocean drilling programs suggest that world ice volume was greater than the ice volume of 18 thousand years ago (Late Wisconsinan) approximately 2.5 million years ago (Prentice and Matthews, Geology, November, 1988). This agrees well With biostratigraphic and paleoecologic interepretations drawn from sediment cores obtained from the Arctic Ocean Basin. The latter data suggest complete ice cover of the basin during the period 2.2-2.4 million years ago (Scott et at., G.S.A. Bulletin, February, 1989). John Boollstorff inferred that one or more glacial tills of the North American mid-continent were deposited at this time. BoeUstorff drew his conclusions primarily from subsurface samples and from volcanic ash horizons dated by the fisssion-track method. The purpose of this trip is to examine fossil-bearing outcrops of sand and gravel or silt that are associated With volcanic ash or glacial till and that provide information about the timing of glacier advance into northeastern Nebraska. The trip Will begin at the Knox County Court House, Center, Nebraska at noon on saturday May 6, 1989. Participants are responsible for providing their own transportation