DC motor proportional control system for orthotic devices

Multi-channel proportional control system for operation of dc motors for use with externally-powered orthotic arm braces is described. Components of circuitry and principles of operation are described. Schematic diagram of control circuit is provided

Changes in Property Tax Progressivity for Florida Homeowners after the “Save Our Homes Amendment?

The “Save Our Homes Amendment?to Florida’s constitution limits annual increases in the taxable value of a homestead property to 3 percent or the rate of inflation (whichever is less) as long as the property is owned by the same owner. The amount of property value protected from taxation throughout the state by this amendment has grown to over $246 billion (13.9 percent of total property value) since the amendment’s implementation in 1995. This study tests whether the protection has accrued disproportionately over time among homestead property owners, the very group of people the amendment was intended to protect. The results suggest that the amendment has reduced the degree of progressivity in the state’s property tax system such that the owners of lower value home properties are shouldering an increasing proportion of the property tax burden relative to the owners of higher value homestead properties. The differential impacts of the SOHA across value ranges of homestead properties are likely attributable to differential appreciation and ownership transfers for higher and lower value homestead properties throughout the state.

Identifying Determinants of Horizontal Property Tax Inequity: Evidence from Florida

In the property tax literature, an ad valorem property tax is considered equitable if all properties in the taxing jurisdiction are subject to the same effective tax rate. That is, all properties, regardless of value or type, should be taxed at the same percentage of their market value. Because market value is a theoretical construct and not directly observable, errors in estimating market value may result in systematic inequity, with some properties taxed at higher effective rates than others. This study extends previous research on property tax inequity by examining potential determinants of errors in the property valuation process for a sample of single-family homes in Palm Beach County, Florida. The results indicate that assessment difficulty (as measured by the variation around the mean assessment to transaction price ratio) is positively related to lot size, living area, age of the home and the percentage of minority residents in the neighborhood and is negatively related to market activity levels, resident income levels, whether the property is the permanent residence of its owner, and whether the property has a swimming pool. The generality of these results is limited by the use of transaction price as a proxy for unobservable market value.

Progressive failure methodologies for predicting residual strength and life of laminated composites

Two progressive failure methodologies currently under development by the Mechanics of Materials Branch at NASA Langley Research Center are discussed. The damage tolerance/fail safety methodology developed by O'Brien is an engineering approach to ensuring adequate durability and damage tolerance by treating only delamination onset and the subsequent delamination accumulation through the laminate thickness. The continuum damage model developed by Allen and Harris employs continuum damage laws to predict laminate strength and life. The philosophy, mechanics framework, and current implementation status of each methodology are presented

Development of optical data processing techniques applicable to detection and study of meteor trails

Development of coherent optical data processing techniques applicable to detection of meteor trails and examination of propertie

Fluoride solid lubricants for extreme temperatures and corrosive environments

Fluoride solid lubricants for extreme temperature and corrosive environment

The Transition between Nonorthogonal Polarization Modes in PSR B2016+28 at 1404 MHz

Polarization observations of the radio emission from PSR B2016+28 at 1404 MHz reveal properties that are consistent with two, very different, interpretations of the pulsar's viewing geometry. The pulsar's average polarization properties show a rapid change in position angle (PA) near the pulse center, suggesting that the observer's sightline nearly intersects the star's magnetic pole. But single pulse, polarization observations of the pulsar show nearly orthogonal modes of polarization following relatively flat and parallel PA trajectories across the pulse, suggesting that the sightline is far from the pole. Additionally, PA histograms reveal a "modal connecting bridge", of unknown origin, joining the modal PA trajectories over much of the pulse and following the rapid PA change shown in the average data. The nonorthogonality of polarization modes is incorporated in a statistical model of radio polarization to account for the deviations from mode orthogonality that are observed in the pulsar. The model is used to interpret the rapid PA change and modal connecting bridge as a longitudinally-resolved transition between modes of nonorthogonal polarization. Thus, the modal PA trajectories are argued to reflect the pulsar's true viewing geometry. This interpretation is consistent with the pulsar's morphological classification, preserves the Radhakrishnan & Cooke model of pulsar radio emission, and avoids the complication that the modal connecting bridge might be produced by some other emission mechanism. The statistical model's ability to simulate the rich variety of polarization properties observed in the emission lends additional support to the model's applicability and its underlying assumption that the polarization modes occur simultaneously.Comment: Accepted for publication in Ap

Thermal decomposition of a honeycomb-network sheet - A Molecular Dynamics simulation study

The thermal degradation of a graphene-like two-dimensional triangular membrane with bonds undergoing temperature-induced scission is studied by means of Molecular Dynamics simulation using Langevin thermostat. We demonstrate that the probability distribution of breaking bonds is highly peaked at the rim of the membrane sheet at lower temperature whereas at higher temperature bonds break at random anywhere in the hexagonal flake. The mean breakage time $\tau$ is found to decrease with the total number of network nodes $N$ by a power law $\tau \propto N^{-0.5}$ and reveals an Arrhenian dependence on temperature $T$. Scission times are themselves exponentially distributed. The fragmentation kinetics of the average number of clusters can be described by first-order chemical reactions between network nodes $n_i$ of different coordination. The distribution of fragments sizes evolves with time elapsed from a $\delta$-function through a bimodal one into a single-peaked again at late times. Our simulation results are complemented by a set of $1^{st}$-order kinetic differential equations for $n_i$ which can be solved exactly and compared to data derived from the computer experiment, providing deeper insight into the thermolysis mechanism.Comment: 21pages, 9 figures, LaTeX, revised versio

Evaluation and study of advanced optical contamination, deposition, measurement, and removal techniques

A program is described to design, fabricate and install an experimental work chamber assembly (WCA) to provide a wide range of experimental capability. The WCA incorporates several techniques for studying the kinetics of contaminant films and their effect on optical surfaces. It incorporates the capability for depositing both optical and contaminant films on temperature-controlled samples, and for in-situ measurements of the vacuum ultraviolet reflectance. Ellipsometer optics are mounted on the chamber for film thickness determinations, and other features include access ports for radiation sources and instrumentation. Several supporting studies were conducted to define specific chamber requirements, to determine the sensitivity of the measurement techniques to be incorporated in the chamber, and to establish procedures for handling samples prior to their installation in the chamber. A bibliography and literature survey of contamination-related articles is included

The Bacterial Photosynthetic Reaction Center as a Model for Membrane Proteins

Membrane proteins participate in many fundamental cellular processes. Until recently, an understanding of the function and properties of membrane proteins was hampered by an absence of structural information at the atomic level. A landmark achievement toward understanding the structure of membrane proteins was the crystallization (1) and structure determination (2-5) the photosynthetic reaction center (RC) from the purple bacteria Rhodopseudomonas viridis, followed by that of the RC from Rhodobacter sphaeroides (6-17). The RC is an integral membrane protein-pigment complex, which carries out the initial steps of photosynthesis (reviewed in 18). RCs from the purple bacteria Rps. viridis and Rb. sphaeroides are composed of three membrane-associated protein subunits (designated L, M, and H), and the following cofactors: four bacteriochlorophylls (Bchl or B), two bacteriopheophytins (Bphe or [phi]), two quinones, and a nonheme iron. The cofactors are organized into two symmetrical branches that are approximately related by a twofold rotation axis (2, 8). A central feature of the structural organization of the RC is the presence of 11 hydrophobic [alpha]-helixes, approximately 20-30 residues long, which are believed to represent the membrane-spanning portion of the RC (3, 9). Five membrane-spanning helixes are present in both the L and M subunits, while a single helix is in the H subunit. The folding of the L and M subunits is similar, consistent with significant sequence similarity between the two chains (19-25). The L and M subunits are approximately related by the same twofold rotation axis that relates the two cofactor branches. RCs are the first membrane proteins to be described at atomic resolution; consequently they provide an important model for discussing the folding of membrane proteins. The structure demonstrates that [alpha]-helical structures may be adopted by integral membrane proteins, and provides confirmation of the utility of hydropathy plots in identifying nonpolar membrane-spanning regions from sequence data. An important distinction between the folding environments of water-soluble proteins and membrane proteins is the large difference in water concentration surrounding the proteins. As a result, hydrophobic interactions (26) play very different roles in stabilizing the tertiary structures of these two classes of proteins; this has important structural consequences. There is a striking difference in surface polarity of membrane and water-soluble proteins. However, the characteristic atomic packing and surface area appear quite similar. A computational method is described for defining the position of the RC in the membrane (10). After localization of the RC structure in the membrane, surface residues in contact with the lipid bilayer were identified. As has been found for soluble globular proteins, surface residues are less well conserved in homologous membrane proteins than the buried, interior residues. Methods based on the variability of residues between homologous proteins are described (13); they are useful (a) in defining surface helical regions of membrane and water-soluble proteins and (b) in assigning the side of these helixes that are exposed to the solvent. A unifying view of protein structure suggests that water-soluble proteins may be considered as modified membrane proteins with covalently attached polar groups that solubilize the proteins in aqueous solution