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  • 1
    Electronic Resource
    Electronic Resource
    BACTERIAL CELL DIVISION (1999)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Genetics 33 (1999), S. 423-448 
    Details
    ISSN: 0066-4197
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Formation of the bacterial division septum is catalyzed by a number of essential proteins that assemble into a ring structure at the future division site. Assembly of proteins into the cytokinetic ring appears to occur in a hierarchial order that is initiated by the FtsZ protein, a structural and functional analog of eukaryotic tubulins. Placement of the division site at its correct location in Escherichia coli requires a division inhibitor (MinC), that is responsible for preventing septation at unwanted sites near the cell poles, and a topological specificity protein (MinE), that forms a ring at midcell and protects the midcell site from the division inhibitor. However, the mechanism responsible for identifying the position of the midcell site or the polar sites used for spore septum formation is still unclear. Regulation of the division process and its coordination with other cell cycle events, such as chromosome replication, are poorly understood. However, a protein has been identified in Caulobacter (CtrA) that regulates both the initiation of chromosome regulation and the transcription of ftsZ, and that may play an important role in the coordination process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.genet.33.1.423
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  • 2
    Electronic Resource
    Electronic Resource
    Macromolecular neutron crystallography facilities at Brookhaven National Laboratory's high flux beam reactor (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3843-3846 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Neutron crystal diffraction experiments are complementary to x-ray diffraction studies of macromolecules because neutrons are strongly scattered by hydrogen and/or deuterium and can therefore be used to locate these atoms directly in a macromolecule. Since hydrogen atoms constitute about half of the total number of atoms in a macromolecule, and are functionally and structurally important in determining the biological properties of the system, a detailed knowledge of their location can often provide unique information about the system under study. However, because of the relatively low flux (on the order of 106 neutrons/s/cm2) of neutrons available at the highest flux steady-state reactors, high resolution diffraction experiments require large crystals and long data collection times. Typical crystal volumes exceed a cubic millimeter and data collection times approach three to four months to collect complete data to atomic resolution. Because of these limitations, relatively few high resolution neutron structures have been completed to date. To improve data collection efficiency and throughput, we have redesigned the macromolecular neutron crystallography beam line (H3A) at Brookhaven National Laboratory's high flux beam reactor. In this report, the new facility is described. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147285
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  • 3
    Electronic Resource
    Electronic Resource
    (5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,4,8,11-tetraene-N,N',N'',N''')nickel(II) diperchlorate (1999)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 160-162 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270198012116
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  • 4
    Electronic Resource
    Electronic Resource
    Spectroscopic Study of SiO2-TiO2 Sols Prepared Using Stabilizing Agents (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 235-241 
    Details
    ISSN: 1573-4846
    Keywords: polymer ; spectroscopy ; modifying agent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two chemical routes were employed to prepare Si-Ti polymers, using acetylacetone (acacH) and acetic acid (HOAc) as modifying agents. The homogeneous and transparent sols were studied at different aging times. The characterization techniques were 29Si NMR, FTIR, UV-Vis and TGA. When HOAc was used, the oligomeric species in the first stages of polymerization were assigned by 29Si NMR. The Ti–O–Si bond vibration was detected by FTIR in the 950–960 cm–1 region. UV-Vis spectroscopy showed bands of acac bonded to Ti at 300 nm and 365 nm, and OAc– bonded to Ti was found at 320 nm. The TGA study allowed the establishment of the xerogel formulas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026441709416
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  • 5
    Electronic Resource
    Electronic Resource
    Spectroscopic study of SiO2−TiO2 sols prepared using stabilizing agents (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 235-241 
    Details
    ISSN: 1573-4846
    Keywords: polymer ; spectroscopy ; modifying agent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two chemical routes were employed to prepare Si−Ti polymers, using acetylacetone (acacH) and acetic acid (HOAc) as modifying agents. The homogeneous and transparent sols were studied at different aging times. The characterization techniques were29Si NMR, FTIR, UV-Vis and TGA. When HOAc was used, the oligomeric species in the first stages of polymerization were assigned by29 Si NMR. The Ti−O−Si bond vibration was detected by FTIR in the 950–960 cm−1 region. UV-Vis spectroscopy showed bands of acac bonded to Ti at 300 nm and 365 nm, and OAc− bonded to Ti was found at 320 nm. The TGA study allowed the establishment of the xerogel formulas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436846
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  • 6
    Electronic Resource
    Electronic Resource
    Diaqua tetrabenzo (b,f,j,n,) {1,5,9,13} tetraazacyclohexadecine copper(II) and nickel(II) bisanthraflavates: crystal and molecular structure (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 825-830 
    Details
    ISSN: 1572-8854
    Keywords: Anthraflavates ; tetraaza ; TAAB
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Charge transfer molecular solids [diaqua tetrabenzo (b,f,j,n,) {1,5,9,13) tetraazacyclohexadecine] Ni(II) and Cu(II) bisanthraflavates were synthesized and characterized by IR, Mass Spectrometry, TGA, and X-ray diffraction on single crystals. Unit cell dimensions (Å) a = 12.291(1), c = 14.574(1) Å and a = 12.434(1), c = 14.066(1) Å for Cu(II) and Ni(II) derivatives, respectively, space group P42/n in both cases. The obtained compounds show expected chemical and structural similarities. Tetraazamacrocycles are surrounded individually by a zig-zag, ribbon-like motif extending in the crystal by head-to-tail hydrogen bonding of monosubstituted anthraflavates. Electric conductivities were measured by the four points method as pellets from the variation of electric current through the sample as a function of temperature, for fixed voltages in the ohmic regime. Preliminary results indicate low conductivity values at room temperature but semiconductivity behaviour in the temperature range −150 to 170°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021879804444
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  • 7
    Electronic Resource
    Electronic Resource
    The surface chemistry of chloroform as an extreme-pressure lubricant additive at high concentrations (1995)
    Springer
    Tribology letters 1 (1995), S. 39-46 
    Details
    ISSN: 1573-2711
    Keywords: chloroform ; extreme-pressure lubrication ; additives ; surface chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Carbon tetrachloride is an extremely good extreme-pressure (EP) lubricant additive at low concentrations (〈3 wt% chlorine) since it can react to form a high-melting-point Fe3C antiseizure layer. In contrast, small hydrogen-containing additive molecules (CH2Cl2, CHCl3) decompose to form FeCl2 which melts at ~940 K and limits the maximum seizure load to ~3500 N as measured hi a pin and v-block apparatus. However, both thermodynamic calculations and results of a Mössbauer analysis of an iron foil heated in CHCl3 at 830 K indicate that iron carbide can be formed from chloroform. In addition, it is also found in that case that a plot of seizure load versus concentration, after initially forming a plateau, once again increases with higher additive concentrations (〉4 wt% chlorine) in accord with the idea that a higher melting point carbide film can be formed. It has been shown previously that asymptotes in the plot of removal rate versus applied load correspond to melting of the interfacial anti-seizure film. When using 9.0 wt% chlorine from chloroform as the additive, a drastic increase in removal rate is found at an interfacial temperature of ~940 K corresponding to the melting of FeCl2 and an additional asymptote is evident at ~1500 K due to the melting of Fe3C in accord with the thermodynamic and Mössbauer results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00157974
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  • 8
    Electronic Resource
    Electronic Resource
    The surface chemistry of chlorinated hydrocarbonextreme-pressure lubricant additives (1997)
    Springer
    Tribology letters 3 (1997), S. 303-309 
    Details
    ISSN: 1573-2711
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Chlorinated or sulfurized hydrocarbons are commonly added to abase fluid to synthesize lubricants used under extreme-pressure(EP) conditions. It has been demonstrated that the interfacialtemperature in the EP regime varies linearly with the appliedload and that temperatures in excess of 1000 K can be attained.At these temperatures, both microbalance experiments carried outat high pressure as well as molecular beam experiments performedin ultrahigh vacuum reveal that chlorinated hydrocarbonsthermally decompose forming a film that consists of a layer ofiron chloride and which can also incorporate small (~50 Ådiameter) carbon particles. These particles may affect the coefficient of friction of the film. The lubricant fails andseizure takes place when the film is removed sufficientlyrapidly for metal-metal contact to occur so that EP lubricationis described as a dynamic phenomenon. Under appropriatecircumstances, sufficient carbon can be incorporated into theiron substrate that it becomes a carbide. In this case, seizureis prevented even when the halide layer is removed because ofthe hardness and high melting temperature of this carbide.Ultrahigh vacuum experiments also suggest that carbon diffusioninto the iron and presumably also ultimately carbide formation,is facilitated by co-adsorbed chlorine which may then explain the excellent extreme-pressure properties of carbon tetrachloride.Finally, a similar tribological model is successfully appliedto dimethyl disulfide where, in this case, FeS forms the anti-seizure layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019162028761
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  • 9
    Electronic Resource
    Electronic Resource
    The surface and tribological chemistry of carbon tetrachloride on iron (1999)
    Springer
    Tribology letters 6 (1999), S. 195-198 
    Details
    ISSN: 1573-2711
    Keywords: carbon tetrachloride ; molecular beams ; ultrahigh vacuum ; Auger spectroscopy ; reactivity ; carbide formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The thermal decomposition of carbon tetrachloride on clean iron was studied in ultrahigh vacuum using molecular beam strategies, where it is found that carbon tetrachloride thermally decomposes on the surface to deposit iron and carbon with exactly identical kinetics as found at high pressures. No gas‐phase products are detected and the activation energy for the reaction (14.2 ± 0.5 kcal/mol) is in good agreement with the value measured at high pressures. Little carbon is detected on the surface using Auger spectroscopy following reaction and it is found that this diffuses into the surface much faster when formed from CCl4 than from CH2Cl2. This effect is ascribed to the effect of co‐adsorbed chlorine on the adsorbed carbon, which is proposed to decrease the activation energy for diffusion into the bulk of the sample. This effect explains the increased tendency for carbon tetrachloride to form carbides under extreme‐pressure tribological conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019128227311
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  • 10
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    Tracer Diffusion in a Brownian Fluid Permeating a Porous Medium (1995)
    American Physical Society
    Details
    Publication Date: 1995-07-24
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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