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  • 1
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    Impacts of Hurricanes Katrina and Rita on the microbial landscape of the New Orleans area (2007)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © The Author(s), 2007. This is the author's version of the work. It is posted here by permission of National Academy of Sciences of the USA for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 104 (2007): 9029-9034, doi:10.1073/pnas.0610552104.
    Description: Floodwaters in New Orleans from Hurricanes Katrina and Rita were observed to contain high levels of fecal indicator bacteria and microbial pathogens, generating concern about long-term impacts of these floodwaters on the sediment and water quality of the New Orleans area and Lake Pontchartrain. We show here that fecal indicator microbe concentrations in offshore waters from Lake Pontchartrain returned to prehurricane concentrations within 2 months of the flooding induced by these hurricanes. Vibrio and Legionella species within the lake were more abundant in samples collected shortly after the floodwaters had receded compared with samples taken within the subsequent 3 months; no evidence of a long-term hurricane-induced algal bloom was observed. Giardia and Cryptosporidium were detected in canal waters. Elevated levels of fecal indicator bacteria observed in sediment could not be solely attributed to impacts from floodwaters, as both flooded and nonflooded areas exhibited elevated levels of fecal indicator bacteria. Evidence from measurements of Bifidobacterium and bacterial diversity analysis suggest that the fecal indicator bacteria observed in the sediment were from human fecal sources. Epidemiologic studies are highly recommended to evaluate the human health effects of the sediments deposited by the floodwaters.
    Description: This work was funded by NSF-NIEHS Oceans and Human Health Program (NSF OCE0432368, OCE0432479, OCE0430724 and NIEHS P50 ES12736, ES012740, ES012742), the NSF-SGER Program (OCE 0554402, OCE 0554674, OCE 0554850, OCE0600130), the NSF-REU Program, and by the Georgia Sea Grant College Program (NA04OAR170033).
    Keywords: Lake Pontchartrain ; Water quality
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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    PAPER (OA)
  • 2
    Electronic Resource
    Electronic Resource
    Biaxial and uniaxial stress in gallium arsenide on silicon: A linear polarized photoluminescence study (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 369-371 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed anisotropic behavior of the polarization of low-temperature photoluminescence from thick gallium arsenide grown on silicon substrates. The identification of the observed transitions was obtained from analysis of the selection rules, the temperature dependence of the feature intensities, and the transition energies. We find that the low-temperature doublet peaks are due to the emissions from two regions of material experiencing two different kinds of stress, one being biaxial and the other uniaxial. The anisotropy is due to the preferential direction created by parallel microcracks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347147
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  • 3
    Electronic Resource
    Electronic Resource
    Profile control in BF3 plasma doping (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3198-3201 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma doping (PD) is an alternative technique to form shallow junctions in deep-submicrometer microelectronic devices. Previous studies have demonstrated that PD produces shallow junctions with better efficiency than those by conventional low energy beam-line doping (BD). In addition, even though cross-sectional transmission electron microscopy reveals that the surface layer is amorphized after high dose BF3 PD or BD implantation, PD samples show less residual defects after rapid thermal annealing. For ultrashallow junctions, doping profiles with a high dopant concentration near the surface are required for the formation of low resistant contacts. In this article, we demonstrate the use of nonideal voltage pulse shape in achieving advantageous doping profiles that are difficult to obtain via BD. By performing particle-in-cell (PIC) simulation, we derive the ion energy distributions for different sample voltage pulse shapes for BF3 PD. Comparison of the PD boron depth profiles simulated by PIC and an assumed Gaussian implant profile to the BD boron depth profiles simulated by TRIM shows a low energy component that does not exist in BD samples. The rise and fall time of the sample voltage pulse contributes to the overall energy distribution since a long rise or fall time increases the low energy component. We postulate that these low energy ions may also change the nature of the amorphized layer and are one of the reasons for the reduction of residual defects after rapid thermal annealing. The preferred sample voltage pulse for plasma doping is suggested to be a short one with a relatively long rise and fall time. This is something that is very difficult to achieve by beam-line ion implantation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288012
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  • 4
    Electronic Resource
    Electronic Resource
    Universality in the quasiperiodic route to chaos (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 6 (1996), S. 32-42 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerous physical systems with two competing frequencies exhibit frequency locking and chaos associated with quasiperiodicity. In this paper we review certain universal aspects of the quasiperiodic route to chaos by making use of the standard circle map. Particular attention is paid to the golden mean and silver mean with a view to comparison with experimental work. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166155
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  • 5
    Electronic Resource
    Electronic Resource
    Metallic contamination in hydrogen plasma immersion ion implantation of silicon (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3743-3749 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In plasma immersion ion implantation (PIII), ions bombard all surfaces inside the PIII vacuum chamber, especially the negatively pulsed biased sample stage and to a lesser extent the interior of the vacuum chamber. As a result, contaminants sputtered from these exposed surfaces can be reimplanted into or adsorb on the silicon wafer. Using particle-in-cell theoretical simulation, we determine the relative ion doses incident on the top, side, and bottom surfaces of three typical sample chuck configurations: (i) a bare conducting stage with the entire sample platen and high-voltage feedthrough/supporting rod exposed and under a high voltage, (ii) a stage with only the sample platen exposed to the plasma but the high-voltage feedthrough protected by an insulating quartz shroud, and (iii) a bare stage with a silicon extension or guard ring to reduce the number of ions bombarding the side and bottom of the sample platen. Our simulation results reveal that the ratio of the incident dose impacting the top of the sample platen to that impacting the side and bottom of the sample stage can be improved to 49% using a guard ring. To corroborate our theoretical results, we experimentally determine the amounts of metallic contaminants on 100 mm silicon wafers implanted using a bare chuck and with a 150 mm silicon wafer inserted between the 100 mm wafer and sample stage to imitate the guard ring. We also discuss the effectiveness of a replaceable all-silicon liner inside the vacuum chamber to address the second source of contamination, that from the interior wall of the vacuum chamber. Our results indicate a significant improvement when an all-silicon liner and silicon guard ring are used simultaneously. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1404422
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  • 6
    Electronic Resource
    Electronic Resource
    Photoreflectance study of gallium arsenide grown on Si (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1775-1777 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature linear polarized photoreflectance is used to study the stress and its release in thick GaAs grown on Si. We find that the GaAs layer is mainly composed of two regions with two kinds of stress, biaxial and uniaxial. Four features, two from each region due to the split valence band, are observed. Their polarization selection rules enable us to distinguish the nature of the strain as well as the nature of the transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104121
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  • 7
    Electronic Resource
    Electronic Resource
    Ultralong minority-carrier lifetime epitaxial GaAs by photon recycling (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1088-1090 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The minority-carrier lifetime has been measured by time-resolved photoluminescence in epitaxial films of GaAs grown by metalorganic chemical vapor deposition. The measured lifetimes in thicker devices are 4 to 6 times the theoretical or radiative lifetime. These long lifetimes are the result of photon recycling or self-generation of the self-absorbed radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101713
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  • 8
    Electronic Resource
    Electronic Resource
    Direct current plasma implantation using a grounded conducting grid (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4094-4097 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel plasma implantation technique performed in a low pressure steady state dc mode utilizing a grounded conducting grid on top of the wafer stage is presented. By numerically simulating the ion paths by the particle-in-cell method, it is observed that the ion paths are optimized for certain implant geometry. In the optimal configuration, the directional angle of the acceleration vector does not depend on the mass and charge state of the ions, and the ratio of the partial differential of the scalar potential φ along the radial and longitudinal directions remains constant for varying applied voltages. The retained dose and impact energy uniformity are totally determined by the ratio of the radius of the wafer stage r, radius of the vacuum chamber R, distance between the wafer stage and the grid H, and thickness of the wafer stage D. The optimal ratio is r:R:H:D=1:4:2.5:2, that is, suggesting a disk shape vacuum chamber, which is quite different from that of a conventional plasma immersion ion implanter. In addition to retaining the large area and parallel processing advantages of plasma immersion ion implantation (PIII), the implantation energy can be extended far beyond the limit of PIII as the technique obviates the use of the power modulator, which not only limits the implantation energy but also is the most expensive and technologically complex hardware component in a PIII system. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373035
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  • 9
    Electronic Resource
    Electronic Resource
    Quasi-direct current plasma immersion ion implantation (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3044-3046 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quasi-dc (direct current) plasma immersion ion implantation (PIII) is demonstrated in the long-pulse mode. To prevent plasma extinction as a result of the sheath reaching the vacuum chamber wall in long-pulse experiments, a grounded grid is used to partition the chamber into two halves. The pulse width can be readily increased to 500 μs that is more than 10 times longer than that in typical low-pressure PIII experiments for monoenergetic implantation (ion mean free path(very-much-greater-than)sheath thickness). The electron saturation current measured by the Langmuir probe indicates that the grounded grid indeed stops the propagation of the plasma sheath. After the plasma sheath reaches the grounded grid, the pulse current drops to a smaller value indicative of the quasi-dc PIII mode. The plasma recovery time is found to be 800 μs thereby limiting the maximum pulsing frequency to below 1 kHz, and the preferred pulse duration window is between 100 and 500 μs. The secondary ion mass spectrometry profiles show that low energy ions are reduced using long pulses. This operation mode thus offers the unique advantage of a smaller low-energy ion component, that is, more monoenergetic ion distribution, and less surface damage compared to conventional short-pulse PIII. When compared to dc-PIII, this mode retains the discharge characteristics and works well for insulators. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415404
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  • 10
    Electronic Resource
    Electronic Resource
    Development and isotype diversity of antibodies to inhalant and dietary antigens in childhood atopic eczema (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Clinical and experimental dermatology 18 (1993), S. 0 
    Details
    ISSN: 1365-2230
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: This study demonstrated that a major feature of childhood atopic eczema (AE) is the presence of serum IgG and IgE anti-house dust mite (anti-HDM) antibodies in almost all AE individuals. IgG anti-HDM antibodies, usually of the IgG1 isotype, became prevalent in AE children over the age of 4 years with the highest antibody levels in children in their early teens. In contrast, immunological sensitization to dietary antigens, notably milk and eggs, occurred in both AE children and age-matched non-atopic control children, and was often associated with IgG4 antibodies during early childhood. These became less prevalent with increasing age in control children but persisted in AE children, sometimes together with IgE antibodies. The later occurrence of anti-HDM antibodies in AE children could reflect immunological sensitization following inhalation of antigen, whereas sensitization to dietary antigens appears to be a natural event in early childhood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2230.1993.tb02173.x
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