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Notes: Results from large eddy simulations (LES) and direct numerical simulations (DNS) of a two-dimensional, spatially developing, compressible planar free jet undergoing an idealized, exothermic, chemical reaction of the type F+rOx→(1+r)P are presented in order to assess several subgrid-scale (SGS) combustion models. Both a priori and a posteriori assessments are conducted. The SGS turbulence model used is the dynamic Smagorinsky model (DSM). Two classes of SGS combustion models are employed in this study. These include the conserved scalar approach and the direct closure approach. Specifically, the SGS combustion models involve several forms of direct filtered reaction rate closures, including a scale similarity filtered reaction rate model (SSFRRM), and a mixing controlled strained laminar flamelet model (SLFM) in the form of thermochemical state relationships, obtained from the DNS, and two assumed forms for the subgrid mixture fraction filtered density function (FDF). In general, LES results are in reasonable agreement with DNS results and highlight the performance of the various SGS combustion models. In particular, in the context of the present study, it is found that: (1) the SLFM cases overpredict product formation due to their inability to capture finite-rate chemistry effects; (2) due to the relatively low values of the SGS mixture fraction variance in the flow under study, the SLFM results are not sensitive to the form of the assumed FDF; and (3) in comparison to the other models investigated, the SSFRRM combustion model provides the best agreement with the DNS for product formation. © 1998 American Institute of Physics.

Notes: Recently proposed novel concept of a spherical stellarator (P. E. Moroz, "Spherical stellarator configuration,'' to appear in Phys. Rev. Lett) is enhanced by adding the plasma current to the otherwise pure stellarator system. The coil configuration of this ultra low aspect ratio system differs from that of a spherical tokamak by inclination of external parts of the toroidal field coils. It is shown that the configuration considered possesses many attractive properties, including: wide flexibility of operating regimes, compact design and coil simplicity, good access to the plasma, closed vacuum flux surfaces with large enclosed volume, significant external rotational transform, strong magnetic well, and a high plasma β [β(0) in excess of 30%] equilibrium. It is shown that the bootstrap effect in a spherical stellarator, in principle, can supply the full plasma current required for the high-β equilibrium. © 1996 American Institute of Physics.

Notes: The detailed analysis of the vacuum magnetic field structure produced by the inclined toroidal field (TF) coils is presented. This configuration has a potential for adding stellarator properties to the tokamak configuration while maintaining the simplicity of planar coils. Parameters of the system are identified that result in significant stellarator-like effects: large vacuum flux surfaces and appreciable rotational transform. Two sets of closed flux surfaces with opposite helicity are studied: the internal one and the external one. It is found that the external set of flux surfaces possesses a magnetic well and, hence, is favorable for the magnetohydrodynamic (MHD) stability. Also, it has larger enclosed volume and rotational transform. It is, hence, preferential in our studies, in comparison with the internal set that usually features a magnetic hill. Analysis of the flux surface structure and the helical harmonic spectrum yields optimization rules required for the configuration to be of practical interest for possible fusion applications. In a few examples it is demonstrated what occurs if the parameters are set differently than optimal. It is found that toroidal inhomogeneity is a key factor and vacuum flux surfaces disappear in the limit of a very high number of TF coils. The important role of the poloidal field (PF) coil system is stressed, and the possibility of the compensated PF system (with zero total current) is found. © 1995 American Institute of Physics.

Notes: We describe the design and operation of a tunable, picosecond laser system for use in time-resolved spectroscopic measurements in the visible and ultraviolet (UV) spectral region. The laser is designed for fine tuning and high wavelength stability. A Nd:YAG-pumped distributed-feedback dye laser (DFDL) generates pulses that are ∼100 ps in duration with a nearly transform-limited linewidth (∼5 GHz) at a 20 Hz repetition rate. The DFDL pulses are amplified in two bow-tie amplifiers, providing pulse energies of up to 3.0 mJ; the amplified pulses may be frequency doubled to the UV spectral region, providing up to 1.0 mJ. The DFDL wavelength is computer stabilized to within ±0.8 pm (±0.7 GHz, two standard deviations), allowing the wavelength to be stationed on a narrow atomic or molecular transition or permitting nearly continuous spectral scans. Application of the laser system to studies of OH energy transfer has been demonstrated; both laser-induced-fluorescence and degenerate-four-wave-mixing spectra have been recorded. © 2000 American Institute of Physics.

Notes: In 1980 the State of Connecticut began a tidal marsh restoration program targeting systems degraded by tidal restrictions and impoundments. Such marshes become dominated by common reed grass (Phragmites australis) and cattail (Typha angustifolia and T. latifolia), with little ecological connection to Long Island Sound. The management and scientific hypothesis was that returning tidal action, reconnecting marshes to Long Island Sound, would set these systems on a recovery trajectory. Specific restoration targets (i.e., pre-disturbance conditions or particular reference marshes) were considered unrealistic. However, it was expected that with time restored tides would return ecological functions and attributes characteristic of fully functioning tidal salt marshes. Here we report results of this program at nine separate sites within six marsh systems along 110 km of Long Island Sound shoreline, with restoration times of 5 to 21 years. Biotic parameters assessed include vegetation, macroinvertebrates, and use by fish and birds. Abiotic factors studied were soil salinity, elevation and tidal flooding, and soil water table depth. Sites fell into two categories of vegetation recovery: slow, ca. 0.5%, or fast, more than 5% of total area per year. Although total cover and frequency of salt marsh angiosperms was positively related to soil salinity, and reed grass stand parameters negatively so, fast versus slow recovery rates could not be attributed to salinity. Instead, rates appear to reflect differences in tidal flooding. Rapid recovery was characterized by lower elevations, greater hydroperiods, and higher soil water tables. Recovery of other biotic attributes and functions does not necessarily parallel those for vegetation. At the longest studied system (rapid vegetation recovery) the high marsh snail Melampus bidentatus took two decades to reach densities comparable with a nearby reference marsh, whereas the amphipod Orchestia grillus was well established on a slow-recovery marsh, reed grass dominated after 9 years. Typical fish species assemblages were found in restoration site creeks and ditches within 5 years. Gut contents of fish in ditches and on the high marsh suggest that use of restored marsh as foraging areas may require up to 15 years to reach equivalence with reference sites. Bird species that specialize in salt marshes require appropriate vegetation; on the oldest restoration site, breeding populations comparable with reference marshland had become established after 15 years. Use of restoration sites by birds considered marsh generalists was initially high and was still nearly twice that of reference areas even after 20 years. Herons, egrets, and migratory shorebirds used restoration areas extensively. These results support our prediction that returning tides will set degraded marshes on trajectories that can bring essentially full restoration of ecological functions. This can occur within two decades, although reduced tidal action can delay restoration of some functions. With this success, Connecticut's Department of Environmental Protection established a dedicated Wetland Restoration Unit. As of 1999 tides have been restored at 57 separate sites along the Connecticut coast.

Notes: Systemic growth hormone and locally administered insulin-like growth factor-I have been shown in a number of studies to improve the breaking strength of incisional wounds, especially in compromised animals. The objective of the present study was to compare these two agents when administered subcutaneously distant from an incisional wound site in pigs, as well as to examine effects of a combination growth hormone/insulin-like growth factor treatment. Growth hormone was shown to increase wound breaking strength in two experiments, whereas insulin-like growth factor-I or a more potent analog had no effect. Moreover, breaking strength was only minimally improved above the vehicle groups by the combination of growth hormone and insulin-like growth factor-I. These effects could not be explained by changes in plasma insulin-like growth factor-I concentrations which were highest in the combination groups, nor by plasma insulin-like growth factor binding protein-3 which was raised equally whenever growth hormone was administered. We conclude that systemic growth hormone but not insulin-like growth factor-I improves wound strength in normal pigs, whereas insulin-like growth factor-I reduces the magnitude of the growth hormone effect by an unknown mechanism.

Notes: Nicastrin, a type-I transmembrane glycoprotein, is a necessary component of the high molecular weight presenilin (PS) complexes that mediate intramembranous cleavage of β-amyloid precursor protein (βAPP) and Notch. Nicastrin undergoes trafficking-dependent glycosylation maturation, and PS1 interacts preferentially with these maturely glycosylated forms of nicastrin. We investigated the effects of differing levels of the immature and mature endoglycosidase-H-resistant forms of nicastrin on Aβ40- and Aβ42-peptide secretion in several cell lines stably expressing a mutant nicastrin (D336A/Y337A) that increases Aβ secretion. There was no correlation between Aβ secretion and the level of over-expression of the immature forms of nicastrin. The total level of mature nicastrin remained constant, but mutant nicastrin replaced endogenous mature nicastrin in varying degrees. Differences in the levels of mature mutant nicastrin positively correlated with Aβ secretion, but did not influence either βAPP trafficking or processing by α- and β-secretases. Proper trafficking and terminal maturation of nicastrin is therefore a necessary event for the regulated intramembranous proteolysis of βAPP.

Notes: Abstract: Under a tightly regulated expression mechanism, matrix metalloproteinases degrade extracellular matrix proteins and are though to play a role in injury repair and tumor metastasis in peripheral tissues. Little is known about the function of matrix metalloproteinases or agents that regulate their production in adult brain; however, it has been shown that the activity of a calcium-dependent metalloproteinase is elevated in Alzheimer's hippocampus. The goals of this study were to determine whether cultured rat astrocytes produce matrix metalloproteinases and to identify agents that regulate protease activity. Enriched astrocyte cultures were prepared from brains of 1-day-old rat pups, and experiments were performed 13 days later. Gelatinase activity in astrocyte conditioned medium was determined using zymography with gelatin copolymerized with acrylamide in the gel. Under basal conditions after a 24-h incubation, rat astrocytes produce gelatinases of 58 and 66 kDa. On stimulation of astrocytes with lipopolysaccharide, interleukin-1α or -β, or tumor necrosis factor-α for 24 h, a dose-dependent increase in the activity of the 58- and 66-kDa gelatinases and the induction of a 94-kDa gelatinase occurred. All three astrocyte-derived proteases showed maximal activity in the presence of millimolar levels of Ca2+, their activity was inhibited in the presence of 1,10-phenanthroline, and their proenzymes were cleaved and activated after incubation with p-aminophenylmercuric acetate. Using immunoblotting, immunopositive bands at the respective molecular sizes indicated that the 58-kDa gelatinase was gelatinase A (matrix metalloproteinase 2) and the 94-kDa activity was gelatinase B (matrix metalloproteinase 9). Induction of the 94-kDa gelatinase by lipopolysaccharide was not influenced when interleukin-1 receptor antagonist was included during the 24-h incubation period; however, the antagonist completely blocked interleukin-1β-induced 94-kDa activity and diminished the activity of the 58- and 66-kDa gelatinases. Dexamethasone inhibited both lipopolysaccharide and interleukin-1β stimulation of the 94-kDa gelatinase. These results indicate that cytokines regulate matrix metalloproteinase expression in cultured rat astrocytes. Because astrocytes become “activated” (are hypertrophic and express increased levels of glial fibrillary acidic protein) in the presence of several inflammatory cytokines, it is possible that these astrocyte-derived enzymes contribute to the activation process and may participate in tissue remodeling after brain injury.