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  • 1
    Electronic Resource
    Electronic Resource
    Matrix isolation nuclear magnetic resonance studies of methyl group spin–rotation coupling (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4504-4514 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In dilute rare gas matrices containing acetonitrile or methyl acetylene, the methyl group rotates almost freely about a fixed symmetry axis in a large fraction of the matrix trapping sites. The secular spin–rotation interaction of the methyl protons does not vanish in this case, and we show this leads to resolved, temperature dependent splitting of the proton NMR lines. In addition, ordering of the methyl spins with respect to both spin–rotation and dipolar local magnetic fields occurs after a sudden change in the matrix temperature. This is shown to be consistent with the mechanism of the Haupt effect, a spin conversion process which restores rotational equilibrium after the temperature jump. Since the spin–rotation splitting provides a direct measure of the methyl group angular momentum, dynamical information pertaining to the matrix isolated molecule is obtained from the proton spectrum, providing a considerable simplification over spin relaxation measurements. Using a 0.5% CH3CN/Kr matrix as a prototypal system, the experimental observations are found to be consistent with the proposed form of the spin–rotation interaction. Several conclusions are reached regarding the hindering of methyl rotation by the solid rare gas lattice, dynamics in the trapping site, and the distribution of these sites in the matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456789
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  • 2
    Electronic Resource
    Electronic Resource
    Piezoresistivity modeling of grain-boundary junctions in positive temperature coefficient of resistivity BaTiO3 (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5322-5334 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A phenomenological method of modeling positive temperature coefficient of resistivity junctions under different thermal and elastic boundary conditions as well as different interfacial trap distributions is detailed. Devonshire's thermodynamic approach and a modified Heywang–Jonker model are employed. Model calculations are applied to isothermal empirical results obtained in samples under uniaxial compressive loads as well as four-point bending loads of trilaminate sensors. Some explanation of discrepancies found in the literature in sign and in magnitude of piezoresistive coefficients under uniaxial loads is offered. Trilaminate sensor behavior under four-point bending loads followed satisfactorily the general trends predicted by the model. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359288
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of Alcaligenes faecalis Nitrite Reductase and a Copper Site Mutant, M150E, That Contains Zinc (1995)
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 12107-12117 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00038a003
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  • 4
    Electronic Resource
    Electronic Resource
    X-ray Structure and Site-Directed Mutagenesis of a Nitrite Reductase from Alcaligenes Faecalis S-6: Roles of Two Copper Atoms in Nitrite Reduction (1994)
    s.l. : American Chemical Society
    Biochemistry 33 (1994), S. 5246-5252 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00183a030
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  • 5
    Electronic Resource
    Electronic Resource
    Dietary folate and the prevalence of neural tube defects in the British Isles: the past two decades (2000)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 107 (2000), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Objectives To measure the changes in folate consumption and the prevalence of neural tube defects in the British and Irish populations during the past two decades.Design Ecological study.Main outcome measures Average daily dietary folate consumption for Britain for the period 1980–1996 was estimated from the National Food Survey. Annual neural tube defect prevalences for the same period were obtained from the Oxford Record Linkage Study Neural Tube Defect register, the Glasgow EUROCAT register, and the three Irish EUROCAT registers (Belfast, Dublin and Galway).Results Dietary folate consumption increased on average by 1.6% per annum in Scotland and 1.4% in England during the study period. The annual rate of decline of neural tube defect prevalence averaged 10.4% in the Irish population, 8.2% in Glasgow, and 5.2% in Oxfordshire and West Berkshire.Conclusions The decline in neural tube defect prevalence observed in all British and Irish populations since the early 1970s continued with the introduction of folate fortification of cereals, which produced measurable increases in average daily folate consumption. Further declines in neural tube defect prevalence may be achieved by targeted folate supplementation during the periconceptual period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.2000.tb11087.x
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  • 6
    Electronic Resource
    Electronic Resource
    Peltier-effect module for highly localized temperature manipulations (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4398-4403 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A Peltier-effect module suitable for applications that require manipulation of the temperature (cooling or heating) of microsized subjects or at a highly localized spot was developed. The module was constructed from a commercial electronic refrigeration device based on the Peltier effect with an array of microprobes attached to its top surface. The microprobes were fabricated using the LIGA (German acronym for lithographie, galvanoformung, abformung) process—one of the microelectromechanical systems technologies. The 1000-μm-tall microprobes were fabricated on a titanium plate and then bonded onto the top surface of a commercial Peltier device. When an electrical current was supplied to the Peltier device, the top surface (with microprobes) of the device was cooled and the other side was heated. Heat was conducted from a microsample on the tip of microprobe to the top surface of the Peltier device. A dynamic model of the module was developed and numerical simulation studies were conducted. The prototype module was tested and the experimental results matched well with those predicted by the numerical simulations. The maximum difference between the temperature of a microsample and that at the surface of the Peltier device was approximately 1 °C. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150074
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  • 7
    Electronic Resource
    Electronic Resource
    A bond graph model for the sample extraction/injection system of a microsized gas chromatographic instrument (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3252-3259 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A bond graph model of the sample extraction/injection system of a prototype portable gas chromatographic instrument has been developed. In addition to performing the same functions as current portable gas chromatographs (GCs), the new generation of GC instruments is designed to perform extraction of analytes from liquid and solid samples. The prototype instrument achieves these improvements by taking of advantage of microfabrication technologies and microprocessor control in the design. A novel sample extraction/injection module is essential to the improved performance of the portable instrument, which will include microfabricated components such as inlets, interface chips, fluid channels, control valves, optimal heater/sensor combinations, and multiport connectors. In order to achieve the desired analytical performance, all of the major components are heated to 250 °C during different stages of a sample analysis. Predicting the performance of the system in this operating regime requires the modeling and analysis of system behavior in two interacting energy domains, fluid and thermal. This article represents the first effort to understand the dynamic behavior of the thermofluid aspect of micro-GC instruments and one of the first attempts to apply the widely-used bond graph technique to modeling and analysis of microsized thermofluid systems. Simulation results using the bond graph model closely match available experimental data, with differences typically less than 10%. This demonstrates that fluid dynamic theory for macroscale systems, and the bond graph method based on it, can be readily applied to microscale systems with these dimensions. The bond graph method can be a useful computer-aided design tool for the development of a new generation of truly integrated micro-GC instruments and sensors fabricated with micromachining technology. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147405
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  • 8
    Electronic Resource
    Electronic Resource
    Is oral contraceptive use still associated with an increased risk of fatal myocardial infarction? Report of a case-control study (1991)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 98 (1991), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Objective— To investigate the association between fatal myocardial infarction and use of modern low-dose oral contraceptives.Design— A case-control study.Setting— General practices throughout England and Wales.Subjects— 161 women aged under 40 dying from myocardial infarction during 1986–1988. Living controls (2 per case), matched for age and marital status, were chosen from general practice lists. Information was collected during structured interviews with general practitioners, and from postal questionnaires sent to surviving partners of the cases and to control women.Main outcome measures— Mortality from myocardial infarction in relation to many risk factors, notably oral contraception, as measured by relative risk.Results— After allowing for the confounding effects of medical risk factors and for surgical sterilization, the overall relative risk associated with both current and past use of oral contraceptives was estimated to be 1–9 (95% CI 0–7 to 4–9, and 1–0 to 3–5 respectively). The relative risk associated with current use of preparations containing 50 μg of oestrogen, however, was estimated to be 4–2 (0–5 to 39.2). At least some of the relative risk associated with oral contraceptive use is likely to be attributable to the confounding effect of cigarette smoking, but it is impossible to estimate how much from the available data.Conclusions— If there was an increased risk of fatal myocardial infarction associated with oral contraceptive use in 1986–1988 it is likely to have been less than two-fold; in this study risks were slightly, but not significantly, elevated with both current and previous use. It may be that any increase in risk is associated solely with the older combined preparations containing 50 μg of oestrogen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1991.tb15397.x
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  • 9
    Electronic Resource
    Electronic Resource
    Alpha-Tocopherol in Microsomal Lipid Peroxidation (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 570 (1989), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1989.tb14963.x
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  • 10
    Electronic Resource
    Electronic Resource
    Stark effect on the 580 nm S1←S0 transition of isobacteriochlorin using photochemical hole-burning spectroscopy (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4335-4340 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High resolution excitation spectra of free base isobacteriochlorin in an n-octane crystal at 4.2 K have been obtained. In the 580 nm region (the 0–0 band of the lowest-lying singlet transition of the trans tautomer) five lines were observed. Using a tunable dye laser two pairs of these lines could be photochemically interconverted, while one line did not burn. With still narrower laser excitation, holes were burned in the four convertible lines which were limited in width by the laser output (0.07 cm−1). Electric fields were applied along each of the crystal axes and Stark splittings of the spectral lines and holes were observed. The splittings are linear over the range 1.21 to 50.0 kV/cm. The magnitude of the total dipole moment change (Δμ) for all lines was found to be 1.64 D; this is much larger (∼7×) than the value measured in free base chlorin. Also, the direction of this vector is a function of the position of the tautomers inner protons; it rotates 90° in going from one trans tautomer to the other. The direction cosines of the Δμ¯'s indicate that free base isobacteriochlorin's orientation in the n-octane crystal is similar to that of free base chlorin, but with the second exterior reduced double bond rotated about 25° out of the alkane chain plane. Furthermore, the burning pattern of the 580 nm 0–0 bands verifies the earlier hypothesis that these are due to the trans tautomer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451894
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