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1

Electronic Resource

Stabilization of Z pinch by velocity shear (2000)

DeSouza-Machado, S. ; Hassam, A. B. ; Sina, Ramin

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 7 (2000), S. 4632-4643

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ISSN: 1089-7674

Source: AIP Digital Archive

Topics: Physics

Notes: A numerical experiment is run to assess the stabilization of ideal magnetohydrodynamic (MHD) instabilities by externally applied velocity shear. A Z pinch, unstable to both kink and interchange (sausage) instabilities, is subjected to an external force that drives sheared mass flow along the axis. The turbulence from the MHD instabilities is found to be suppressed significantly with increasing Mach number of the flow. At sonic Mach numbers of 4–5, the "discharge" is seen to have recovered to its laminar state in more than 95% of the volume, there being a small residual wobble at the center of the column. For lower Mach numbers, the wobble becomes more significant. This is consistent with analytic theories that predict supersonic sheared flows are needed to stabilize MHD instability. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1316086

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2

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Kinetic modes in a hot magnetized and weakly collisional plasma (1999)

De Souza-Machado, S.

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 6 (1999), S. 2323-2331

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ISSN: 1089-7674

Source: AIP Digital Archive

Topics: Physics

Notes: Velocity space perturbations associated with low-frequency waves launched in a weakly collisional plasma are shown to consist of a discrete spectrum of modes. Collisions are modeled using an energy and momentum conserving one-dimensional Fokker–Planck operator. The linearized Vlasov–Poisson–Fokker–Planck system of equations is solved by expanding the perturbed ion-distribution function in terms of Hermite polynomials, from which an eigenvalue problem is set up. The eigenvalues and eigenvectors yield the ion acoustic mode that is weakly damped [J. Dougherty, Physics of Fluids 7, 1788 (1964)], as well as a discrete spectrum of kinetic modes. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.873504

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3

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Direct determination of ion wave fields in a hot magnetized and weakly collisional plasma (1996)

Sarfaty, M. ; De Souza-Machado, S. ; Skiff, F.

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 4316-4324

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ISSN: 1089-7674

Source: AIP Digital Archive

Topics: Physics

Notes: Electrostatic ion cyclotron wave fields are determined in a magnetized and weakly collisional plasma. A phased-locked Laser Induced Fluorescence (LIF) diagnostic is used to directly measure the wave perturbed ion velocity distribution. Comparing these local LIF measurements with a theoretical model uniquely determines the wave parameters, such as the wave potential, the three-dimensional wave vector, and the effective wave damping. The self-consistent wave–particle interaction is modeled by Boltzmann–Poisson equations in the limit of weak collisions. The wave parameters determined from local measurements agree with those determined from spatial scans. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.871581

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4

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Regulation of alcohol-oxidizing capacity in chemostat cultures of Acetobacter pasteurianus (1995)

Salgueiro Machado, S. ; Luttik, M. A. H. ; Dijken, J. P. ; [et al.]

Springer

Applied microbiology and biotechnology 43 (1995), S. 1061-1066

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ISSN: 1432-0614

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology

Notes: Abstract Acetobacter pasteurianus LMG 1635 was studied for its potential application in the enantioselective oxidation of alcohols. Batch cultivation led to accumulation of acetic acid and loss of viability. These problems did not occur in carbon-limited chemostat cultures (dilution rate = 0.05 h−1) grown on mineral medium supplemented with ethanol, L-lactate or acetate. Nevertheless, biomass yields were extremely low in comparison to values reported for other bacteria. Cells exhibited high oxidation rates with ethanol and racemic glycidol (2,3-epoxy-1-propanol). Ethanol- and glycidol-dependent oxygen-uptake capacities of ethanol-limited cultures were higher than those of cultures grown on lactate or acetate. On all three carbon sources, A. pasteurianus expressed NAD-dependent and dye-linked ethanol dehydrogenase activity. Glycidol oxidation was strictly dye-linked. In contrast to the NAD-dependent ethanol dehydrogenase, the activity of dye-linked alcohol dehydrogenase depended on the carbon source and was highest in ethanol-grown cells. Cell suspensions from chemostat cultures could be stored at 4°C for over 30 days without significant loss of ethanol- and glycidol-oxidizing activity. It is concluded that ethanol-limited cultivation provides an attractive system for production of A. pasteurianus biomass with a high and stable alcohol-oxidizing activity.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00166926

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5

Electronic Resource

High area Ni-Zn and Ni-Co-Zn codeposits as hydrogen electrodes in alkaline solutions (1992)

Giz, M. J. ; Machado, S. A. S. ; Avaca, L. A. ; [et al.]

Springer

Journal of applied electrochemistry 22 (1992), S. 973-977

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ISSN: 1572-8838

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology

Notes: Abstract This paper describes the preparation of Ni−Zn and Ni−Co−Zn coatings by electrodeposition on a mild steel substrate. After treatment in a KOH solution to leach out part of the zinc, the materials were evaluated as cathodes for the hydrogen evolution reaction in alkaline solutions. The materials were found to have high surface areas and low Tafel slopes. Overpotentials at current densities of technological interest are significantly lower than those of the traditional materials used in water electrolysis.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01024146

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6

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A novel procedure in the galvanic deposition of Zn alloys for the preparation of large area Ni and Ni-Co surfaces (1996)

Machado, S. A. S. ; Tiengo, J. ; Lima Neto, P. ; [et al.]

Springer

Journal of applied electrochemistry 26 (1996), S. 431-437

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ISSN: 1572-8838

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology

Notes: Abstract A new methodology for the electrodeposition of Ni-Zn and Ni-Co-Zn alloys that prevents zinc being in contact with the substrate and allows total elimination of this metal during alkaline leaching is fully described. This is achieved by a careful control of the plating bath composition during the electrolysis. The resulting coatings show a multilayer structure and the desirable concentration profile for all the metallic species involved, as revealed by SEM and EDX analyses. The electrochemical active area of the deposits after leaching of the zinc was measured by cyclic voltammetry. They were of the order of 1100 and 4400 times the geometric area for Ni and Ni-Co, respectively. These highly porous structures are very active for hydrogen evolution in alkaline solutions, showing extremely low overpotentials for relatively high current densities, as well as good stability for long term operation. Other possible applications for these structures are briefly discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00251329

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7

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Spatial and Temporal Variability of Corn Grain Yield: Site-Specific Relationships of Biotic and Abiotic Factors (2000)

Machado, S. ; Bynum, E. D. ; Archer, T. L. ; [et al.]

Springer

Precision agriculture 2 (2000), S. 359-376

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ISSN: 1573-1618

Keywords: differential global positioning system (DGPS) ; geographical information system (GIS) ; soil index (SI) ; site-specific farming (SSF) ; variable rate technology (VRT)

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Inadequate information on factors affecting crop yield variability has contributed to the slow adoption of site-specific farming (SSF). This study was conducted to determine the effects of biotic and abiotic factors on the spatial and temporal variability of irrigated corn grain yields and to derive information useful for SSF. The effects of water (80% evapotranspiration (ET) and 50% ET), hybrid (drought-tolerant and -susceptible), elevation, soil index (SI)(texture), soil NO3–N, arthropods, and diseases on corn grain yield were investigated at Halfway, TX on geo-referenced locations. Grain yields were influenced by interrelationships among biotic and abiotic factors. Grain yields were consistently high under high water treatment, at higher elevations, and on soils with high SI (high clay and silt). Soil NO3–N increased grain yields when water was adequate. Management zones for variable rate fertilizer and water application should, therefore, be based on information on elevation, SI, and soil NO3–N. The effects of arthropods, diseases, and crop stress (due to drought and N) on corn grain yield were unpredictable. Spider mite (Oligonychus pratensis) and common smut (Ustilago zeae) damage occurred under hot and dry conditions in 1998. Spider mite infestations were high in areas with high soil NO3–N. Moderate air temperatures and high relative humidity in 1999 favored southwestern corn borer (Diatraea grandiosella) and common rust (Puccinia maydis) incidences. Knowledge of conditions that favor arthropods and diseases outbreak and crop stress can improve the efficiency of scouting and in-season management of SSF. Management of SSF can be improved when effects of biotic and abiotic factors on grain yield are integrated and evaluated as a system.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1012352032031

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Ground effects of the 18 October 1992, Murindo earthquake (NW Colombia), using the Environmental Seismic Intensity Scale (ESI 2007) for the assessment of intensity (2009)

Mosquera-Machado, S. ; Lalinde-Pulido, C. ; Salcedo-Hurtado, E. ; [et al.]

In: Geological Society Special Publication 316: 123-144.

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Publication Date: 2009-06-22

Description: The macroseismic intensity of the 18 October 1992 Murindo-Atrato earthquake that affected the northwestern states of Colombia (Choco and Antioquia) is reassessed using the newly developed INQUA Environmental Seismic Intensity Scale (ESI 2007) which is based on the evaluation of earthquake environmental effects. To generate the ESI 2007 isoseismal map of northwestern Colombia, a geographical information system was used. Unifying the available information on the seismological and active tectonics framework including historical seismicity, hypocentral depths, foreshocks, aftershocks, focal mechanism, macroseismic data under the same GIS and the map of Quaternary faults allowed us to reinterpret the geological and environmental effects of the 1992 earthquakes sequence. A total of 24 sites from the areas of Quibdo, Bojaya, Rio Sucio, Murindo, Vigia del Fuerte and Turbo were evaluated. A systematic comparison among evaluated intensities (Modified Mercalli and ESI scale) revealed differences from one to two degrees. According to the ESI 2007 scale, the epicentral intensity Io is XI. This represents one degree higher than the epicentral intensity obtained using MM and Medveded Sponhauer Karnik (MSK) intensity scales, probably due to the lack of suitable observations on building damage in this poorly populated and developed region. This information is also useful in order to shed some light on the persistent question of the exact location and dimension of the main rupture zone associated with the earthquake. The isoseismal map derived from the integration of the whole set of environmental effects with other macroseismic data strongly suggests that the causative tectonic structure is the Murindo fault. However, the rupture length derived from the distribution of ground effects is greater than the Murindo fault length, implying that other nearby fault segments were activated during the 1992 event. The new isoseismal map resulting from this work is relevant for the assessment of future seismic risk in the northwestern region of Colombia. Overall, the application of the ESI 2007 scale to the 18 October 1992 earthquake, and to similar strong events in the region, can be useful for disaster management and planning, estimation of damage, and post-earthquake recovery efforts.

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