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  • 1
    Electronic Resource
    Electronic Resource
    Crystallization and preliminary X-ray diffraction analysis of the heterotetrameric dihydroorotate dehydrogenase B of Lactococcus lactis, a flavoprotein enzyme system consisting of two PyrDB subunits and two iron–sulfur cluster containing PyrK subunits (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 802-804 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Dihydroorotate dehydrogenases are flavin-containing enzymes which catalyze the conversion of (S)-dihydroorotate to orotate. Dihydroorotate dehydrogenase B (DHODB) from Lactococcus lactis is a heterotetramer containing two subunits of the protein encoded by the pyrDb gene (PyrDB) and two subunits of the protein encoded by the pyrK gene (PyrK). In addition, DHODB contains two molecules of flavin mononucleotide, two molecules of flavin adenine dinucleotide and two [2Fe–2S] iron–sulfur clusters as tightly bound cofactors. Yellow crystals of this enzyme have been grown using the hanging-drop vapour-diffusion technique from solutions of 2.5 M ammonium sulfate and 0.1 M sodium acetate, pH 4.6. The crystals have been shown to contain both the PyrDB and the PyrK subunits and fluorescence measurements indicate that the two different subunits interact very closely with each other in the active-site region. Native data sets have been collected to 2.6 Å with a conventional X-ray source and to 2.2 Å using synchrotron radiation. The crystals are rhombohedral, space group R32, with correspondin8 hexagonal unit-cell dimensions a = b = 202.3 and c = 81.0 Å. The asymmetric unit in the crystal contains one PyrDB subunit and one PyrK subunit, which suggests that the two halves of the heterotetramer are related by a crystallographic twofold axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444997006203
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  • 2
    Electronic Resource
    Electronic Resource
    Flow Phenomena in Chemical Vapor Deposition of Thin Films (1991)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 23 (1991), S. 197-232 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fl.23.010191.001213
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  • 3
    Electronic Resource
    Electronic Resource
    Modeling of pyrolytic laser-assisted chemical vapor deposition: Mass transfer and kinetic effects influencing the shape of the deposit (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 198-206 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The laser-assisted chemical vapor deposition of metals is modeled. The case of pyrolytic deposition induced by a continuous laser source is considered. The heat transfer in the solid substrate is considered to be transient, while the gas-phase heat and mass transfer are assumed to be in the quasi-steady state. The model accommodates the use of temperature-dependent physical properties and the occurrence of irregularly shaped deposits. The modeling equations are solved by a finite element approach which is briefly described. Volcanolike deposits are predicted under certain conditions of gas pressure and laser intensity. Model predictions show that depletion effects and adsorption-desorption phenomena are major factors in influencing the occurrence of volcanolike deposits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340490
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  • 4
    Electronic Resource
    Electronic Resource
    Electromigration of aluminum cathodes in polymer-based electroluminescent devices (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3941-3943 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dark, nonemissive defects form on the metal cathode in most molecular organic and polymer-based light emitting devices and eventually lead to the failure of the device. These defects have been characterized in situ using optical microscopy and ex situ using atomic force microscopy and Auger electron spectroscopy. On the basis of these observations, an electromigration mechanism for the formation of dark spot defects is proposed. The high current density required to operate polymer-based light emitting devices leads to electron-induced diffusion of the Al cathode when a short circuit forms in the emissive polymer layer. This process results in a "pileup'' of metal at the short circuit (anode) and a surrounding circular region where the Al is depleted, appearing as a dark spot on the cathode. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117577
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  • 5
    Electronic Resource
    Electronic Resource
    n-AlGaSb and GaSb/AlGaSb double-heterostructure lasers grown by organometallic vapor phase epitaxy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 400-402 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: n-type doping of AlxGa1−xSb epilayers (0≤x≤1) grown by organometallic vapor phase epitaxy has been achieved by using tritertiarybutylaluminum, triethylgallium, and trimethylantimony as the organometallic precursors and diethyltellurium as the doping source. Electron concentrations exceed 1017 cm−3 for layers with x〈0.3, and decrease to ∼1016 cm−3 for x=1 as a result of higher residual acceptor concentration. Lattice-mismatched double-heterostructure diode lasers with AlGaSb cladding layers and GaSb active layer are demonstrated, and indicate the potential of OMVPE for growth of GaSb-based materials for electronic and optoelectronic devices. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116698
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  • 6
    Electronic Resource
    Electronic Resource
    Tritertiarybutylaluminum as an organometallic source for epitaxial growth of AlGaSb (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1384-1386 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new organometallic source, tritertiarybutylaluminum (TTBAl), has been used in growth of AlxGa1−xSb epilayers by low pressure organometallic vapor phase epitaxy. Ternary alloys were grown over the whole composition range 0〈x≤1 on GaSb and GaAs substrates from TTBAl, triethylgallium, and triethylantimony (TESb) or trimethylantimony (TMSb). All layers exhibited mirror surface morphologies. Photoluminescence was observed for layers with x〈0.2, the composition that corresponds to the indirect transition. The background of C and O in AlSb grown with TESb was ∼2×1018 and ∼6×1019 cm−3, respectively, and ∼1.5×1019 and ∼1.5×1019 cm−3, respectively, for AlSb grown with TMSb. All layers exhibited p-type conductivity with hole concentration increasing with x, and saturating ∼5×1018 cm−3 for x=1, which is about 10 times lower compared to layers grown with conventional Al sources. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115541
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  • 7
    Electronic Resource
    Electronic Resource
    Electrospray organometallic chemical vapor deposition—A novel technique for preparation of II–VI quantum dot composites (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2795-2797 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel technique combining electrospray and organometallic chemical vapor deposition (OMCVD) has been developed for the synthesis of new II–VI quantum dot composites. CdSe nanocrystals (quantum dots) of selected size are dispersed in a pyridine/acetonitrile mixture. The nanocrystals are transferred by electrospray into the growth zone of an OMCVD reactor and codeposited on a ZnSe matrix grown from hydrogen selenide and diethyl zinc. Composites consisting of CdSe nanocrystals and an amorphous or polycrystalline ZnSe matrix have been deposited on glass substrates at temperatures of 150–250 °C. Room-temperature absorption and photoluminescence spectra show optical transitions characteristic of the initial nanocrystal dispersions. The emission wavelength may be tuned in a broad spectral region by incorporating nanocrystals of varying sizes. The composites have been characterized by Auger electron spectroscopy, high resolution transmission electron microscopy, and scanning transmission electron microscopy. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112568
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  • 8
    Electronic Resource
    Electronic Resource
    Role of transcription pausing in the control of the pyrE attenuator in Escherichia coli (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Expression of the Escherichia coli pyrE gene is regulated by transcription attenuation in the intercistronic orfE–pyrE region and modulated by the distance between the transcribing RNA polymerase and the leading ribosome as a function of the supply of UTP and GTP. In this communication we show that pyrE expression is hyper-repressed in vivo following addition of uracil in strains carrying the nusAcs10 mutation. This phenotype, previously seen in rpsL 1204 strains whose ribosomes are pseudodependent on streptomycin and work at suboptimal elongation rate, indicates that RNA polymerase escapes from the ribosomes in the pyrE attenuator region in the nusA mutant. In vitro transcription studies revealed that the build-up of the full-length attenuated orfE transcript occurred more slowly in the presence of the NusA protein than in its absence. Moreover, the NusA protein enhanced several transcription pauses through the orfE gene. These effects were more pronounced when low concentrations of either UTP or GTP were used than at low concentrations of either CTP or ATP. The results indicate that the NusA protein is required for proper regulation of pyrE gene expression and is involved, together with the NTP pools, in maintaining the coupling between transcription and translation in the pyrE attenuator region by inhibiting RNA chain elongation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1991.tb02113.x
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  • 9
    Electronic Resource
    Electronic Resource
    Molecular and mutational analysis of three genes preceding pyrE on the Escherichia coli chromosome (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nucleotide sequence of two kilobase pairs (kb) 5′ to the orfE-pyrE operon has been determined. The sequence revealed two open reading frames, orfX and orfY, consisting of 286 and 274 codons, respectively, and having a transcriptional orientation opposite that of the orfE-pyrE operon. Analysis of transcription initiations showed that the promoters of orfE and orfX constitute a pair of divergent promoters with overlapping -35 regions and that orfY is transcribed from an independent promoter. Translational analysis indicated that the orfs are expressed in Escherichia coli.The orfE, orfX, and orfY genes were inactivated on the bacterial chromosome by deletion-insertion mutagenesis using a kanamycin resistance cassette. The mutants were all viable. However, the orfE deletion caused a dramatic reduction in the level of pyrE expression and a partial pyrimidine requirement, because this mutation prevented transcription of pyrE. The orfE protein seemed without significance for pyr-gene expression in E. coli, and the mutations in orfX and orfY were without detectable phenotypes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00184.x
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  • 10
    Electronic Resource
    Electronic Resource
    Evaluation of changeover control policies by singular value analysis - Effects of scaling (1985)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 135-146 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A method for assessing control performance at different operating conditions in a chemical process is developed using singular value analysis. The control potential of the system is established by analyzing the singular values of the steady-state system matrix. Dynamic considerations and interaction analysis can be included in the framework of the method described. The approach enables the process engineer to consider controllability of the process as well as economics in synthesizing a changeover control policy. Singular values depend on the scaling of the system, i.e., the definition of the physical dimensions of the system. The effects of scaling on the analysis are first investigated by scaling the steady-state system matrix with empirical methods, equilibration, and geometric scaling. Using the insights gained from these studies a scaling method, variable normalization and equation equilibration, which is intuitively appealing and suited for the purpose, is devised. Two typical systems, continuous stirred tank reactor and a polymerization reaction system, demonstrate the usefulness of this method.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690310116
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