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  • 11
    Electronic Resource
    Electronic Resource
    Nonlinear geostrophic adjustment, cyclone/anticyclone asymmetry, and potential vorticity rearrangement (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 1087-1100 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Within the context of the rotating shallow water equations, it is shown how initially unbalanced states possessing certain symmetries dynamically evolve to lose those symmetries during nonlinear geostrophic adjustment. Using conservation law methods, it is demonstrated that the adjustment of equal and opposite (circular) mass imbalances results in a balanced end state where cyclones are stronger than anticyclones; the reverse holds true for momentum imbalances. In both cases, the degree of this asymmetry is shown to be directly proportional to the amount of initial imbalance (a measure of the nonlinearity occurring during time-dependent adjustment). On the other hand, the degree of asymmetry is maximal for imbalances of Rossby deformation scale. As for the potential vorticity, it is shown that its final profile can be noticeably different from its initial one; from an Eulerian perspective, this rearrangement is not confined to uniform shifts of potential vorticity fronts. Direct 2D numerical initial value problems confirm the asymmetry in the predicted final states and establish a relatively fast time scale for adjustment to complete. The robustness of these results is confirmed by studying, in addition, the adjustment of elliptical mass imbalances. The numerical integrations reveal that, during geostrophic adjustment, potential vorticity rearrangement occurs irreversibly on a fast wave time scale. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870363
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  • 12
    Electronic Resource
    Electronic Resource
    Inhomogeneous broadening in quantum dots with ternary aluminum alloys (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2701-2703 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study how the optical properties of InAs self-assembled quantum dots (QDs) grown on GaAs substrate are affected when using AlGaAs barriers to increase the carrier confinement. The inhomogeneous broadening of the QD ensemble is found to increase when ternary aluminum alloys are used next to or within the QDs. By growing thin GaAs spacers to separate the QDs from the AlGaAs barriers, we obtain QD ensembles which exhibit little photoluminescence quenching and well-defined excited states up to room temperature. Postgrowth rapid thermal annealing is then used to intermix these InAs/GaAs/AlGaAs QDs and diffuse the Al towards the QDs. In contrast with QDs having thick binary GaAs barriers, the inhomogeneous broadening of QDs with nearby AlGaAs barriers is not decreased with intermixing, leading to unresolved excited state peaks when the interdiffusion length becomes comparable to the GaAs spacer thickness. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1410333
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  • 13
    Electronic Resource
    Electronic Resource
    Laser-induced InAs/GaAs quantum dot intermixing (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3583-3585 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser annealing of InAs/GaAs quantum-dot (QD) microstructures has been investigated for selective area tuning of their electronic shell structure. Extensive blueshifts of the QD excited states were observed following 20–40 s laser irradiation. In the most extreme case, we were able to shift the position of the ground state transition by 298 meV, i.e., to the spectral region where the photoluminescence signal originates from the as-grown InAs wetting layer. A reduction from ∼50 to 8 meV of the full width at half maximum of the PL peak corresponding to this transition indicates a drastic change in the structural characteristics of the investigated QD ensemble. The attractive feature of the laser-QD-intermixing technique is that it offers the possibility of obtaining targeted blueshifts and inter-sublevel energy spacing on the lateral scale required in the fabrication of QD-based integrated optoelectronic devices and, possibly, photonic band gap crystals. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323997
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  • 14
    Electronic Resource
    Electronic Resource
    Lasing in quantum-dot ensembles with sharp adjustable electronic shells (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 986-988 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantum-dot laser diodes with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QDs) grown by molecular-beam epitaxy. Shape-engineered stacks of self-aligned QDs with improved uniformity are used to increase the gain in the active region. Lasing is observed in the upper QD shells for small-gain media, and progresses towards the QD ground states for longer cavity lengths. We obtained at 77 K thresholds of Jth=15 A/cm2 for a 2 mm cavity lasing in the first excited state (p shell), and Jth=125 A/cm2 for a 1 mm cavity lasing in n=3 (d shell). At 300 K for a 1 mm cavity, Jth is 490 A/cm2 with lasing in n=4 (f shell). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124253
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  • 15
    Electronic Resource
    Electronic Resource
    Migration and coalescence of Xe nanoprecipitates in Al induced by electron irradiation at 300 K (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2611-2613 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Effects of 1 MeV electron irradiation on Xe precipitates in Al, formed by ion implantation, have been observed in situ by high-voltage transmission electron microscopy. Individual Xe precipitates undergo melting and recrystallization, migration which leads to coalescence, and shape changes. These processes are driven by the production of defects without either cascade defect production or the introduction of additional Xe atoms. Precipitate migration is due to an irradiation-induced surface diffusion process on the Xe/Al interfaces. Coalescence of close precipitates is enhanced by directed motion as a result of the net displacement of Al atoms out of the volume between them. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123913
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  • 16
    Electronic Resource
    Electronic Resource
    Metabolic Dysfunction in Familial, but Not Sporadic, Amyotrophic Lateral Sclerosis (1998)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 71 (1998), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Autosomal dominant familial amyotrophic lateral sclerosis (FALS) is associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Previous studies have implicated the involvement of metabolic dysfunction in ALS pathogenesis. To further investigate the biochemical features of FALS and sporadic ALS (SALS), we examined SOD activity and mitochondrial oxidative phosphorylation enzyme activities in motor cortex (Brodmann area 4), parietal cortex (Brodmann area 40), and cerebellum from control subjects, FALS patients with and without known SOD mutations, SALS patients, and disease controls (Pick's disease, progressive supranuclear palsy, diffuse Lewy body disease). Cytosolic SOD activity, predominantly Cu/Zn SOD, was decreased ∼50% in all regions in FALS patients with SOD mutations but was not significantly altered in other patient groups. Marked increases in complex I and II–III activities were seen in FALS patients with SOD mutations but not in SALS patients. We also measured electron transport chain enzyme activities in a transgenic mouse model of FALS. Complex I activity was significantly increased in the forebrain of 60-day-old G93A transgenic mice overexpressing human mutant SOD1, relative to levels in transgenic wild-type animals, supporting the hypothesis that the motor neuron disorder associated with SOD1 mutations involves a defect in mitochondrial energy metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1998.71010281.x
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  • 17
    Electronic Resource
    Electronic Resource
    Evidence of Increased Oxidative Damage in Both Sporadic and Familial Amyotrophic Lateral Sclerosis (1997)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 69 (1997), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Some cases of autosomal dominant familial amyotrophic lateral sclerosis (FALS) are associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1), suggesting that oxidative damage may play a role in ALS pathogenesis. To further investigate the biochemical features of FALS and sporadic ALS (SALS), we examined markers of oxidative damage to protein, lipids, and DNA in motor cortex (Brodmann area 4), parietal cortex (Brodmann area 40), and cerebellum from control subjects, FALS patients with and without known SOD mutations, SALS patients, and disease controls (Pick's disease, progressive supranuclear palsy, diffuse Lewy body disease). Protein carbonyl and nuclear DNA 8-hydroxy-2′-deoxyguanosine (OH8dG) levels were increased in SALS motor cortex but not in FALS patients. Malondialdehyde levels showed no significant changes. Immunohistochemical studies showed increased neuronal staining for hemeoxygenase-1, malondialdehyde-modified protein, and OH8dG in both SALS and FALS spinal cord. These studies therefore provide further evidence that oxidative damage may play a role in the pathogenesis of neuronal degeneration in both SALS and FALS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1997.69052064.x
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  • 18
    Electronic Resource
    Electronic Resource
    Cation Disorder and Vacancy Distribution in Nonstoichiometric Magnesium Aluminate Spinel, MgO·xAl2O3 (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Neutron diffractometry and X-ray diffractometry were used to characterize the cation disorder and vacancy distribution in nonstoichiometric spinel, MgO·xAl2O3, where x greaterthan equal to 1.0. Both synthetic and natural samples were examined. Least-squares refinements of integrated intensities for single crystals and Rietveld profile refinements for powders yielded the average scattering “power” from tetrahedral and octahedral sites within the almost-perfect cubic close-packed oxygen sublattice. The cation disorder was calculated assuming models in which the vacancies resided on tetrahedral, octahedral, or both types of sites. No degree of cation disorder was consistent with the tetrahedral vacancy model, and vacancies most likely resided on octahedral sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02242.x
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  • 19
    Electronic Resource
    Electronic Resource
    Evidence of Racial Discrimination in Different Dimensions of Owner-Occupied Housing Search (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Real estate economics 24 (1996), S. 0 
    Details
    ISSN: 1540-6229
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper examines the incidence and extent of racial discrimination in various dimensions of owner-occupied housing search. Audit data for sales units (1980-90) from the Fair Housing Center of metropolitan Detroit is used in an ordered probit framework. Agents' own prejudices and the prejudices of their customers are shown to be significant in explaining discrimination. Results also indicate that white home seekers are steered toward more white and affluent neighborhoods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1540-6229.00685
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  • 20
    Electronic Resource
    Electronic Resource
    Dwelling Age Heteroskedasticity in Repeat Sales House Price Equations (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Real estate economics 26 (1998), S. 0 
    Details
    ISSN: 1540-6229
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: Several authors have attributed the heteroskedasticity observed in repeat sales house price equations to the length of time between sales. Recently, Goodman and Thibodeau (1995) developed a theoretical model that relates heteroskedasticity in hedonic house price equations to dwelling age. Using data for nearly 2,000 repeat sales in Dallas, Texas, this research examines whether repeat sales heteroskedasticity is related to dwelling age, to the length of time between sales, or to both. An iterative generalized least squares procedure that explicitly models the residual variance is used to obtain robust parameter estimates and to increase the efficiency of the usual repeat sales price indices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1540-6229.00742
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