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  • 1990-1994  (1,418)
  • 1870-1879
  • 1990  (1,418)
  • Chemistry  (1,311)
  • Engineering General  (79)
  • Magnetic resonance imaging
  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyridoxylated adult human hemoglobin (HbAo) was prepared using a one molar equivalent of pyridoxal 5-phosphate (PLP) per heme and reduced with either NaCNBH3 or NaBH4. A separate sample was pyridoxylated and passed through a mixed-bed ion exchange column without reduction. All three preparations had a P50 of 29 ± 2 torr and a cooperativity of n = 2.4 ± 0.1. These preparations, in both the oxy and deoxy forms, were then treated with 7 equivalents of glutaraldehyde per tetramer at pH 6.8 at 4°C and at room temperature. The polymerization invariably reduced the P50 to 18 ± 2 torr with Hill coefficients of less than 2. These solutions, with or without further reduction using NaCNBH3, all retained the PLP in differing amounts (2-3 moles/tetramer). Methemoglobin concentrations were increased during the polymerization reaction. The normal pyridoxylation procedure, using sodium borohydride reduction, resulted in a number of different molecular species. Polymerization with glutaraldehyde caused a further proliferation of molecular species that could not be separated by anion exchange chromatography or by isoelectric focusing. The extent of polymerization, estimated by gel exclusion chromatography and SDS polyacrylamide gel electrophoresis, was from 40 to 50%. Analysis of the reverse phase chromatograms, which separate the heme and the α- and β-chains, showed extensive polymerization and distribution of the radioactively labeled PLP on the protein for all preparations. All of the polymerized and pyridoxylated samples were unstable, and showed different chromatographic patterns after storage at 4°C for 1 month. Attempts to stabilize these preparations by further reduction with NaCNBH3 gave products with a lower P50 and lower cooperativity. When the reactions were conducted with a purified HbAo, heterogeneity was somewhat decreased compared to the normally used stroma-free hemoglobin, but a large number of molecular species were still formed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 170-172 
    ISSN: 0935-6304
    Keywords: Liquid chromatography ; Gas chromatography ; LC/GC ; On-line coupling ; Metal complexes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The on-line coupled LC-GC technique was applied to the analysis of several metal chelates of N,N-diethyldithiocarbamic acid. A 10-port valve interface was used to couple the LC and GC instruments. Conditions during sample transfer into the GC gave fully concurrent solvent evaporation. The chelates investigated were separated with a short apolar fused silica column. LC preseparation was made with cyano or amino phases using a hexane/dichloromethane mixture as eluent. On-line LC-GC combination seems to be very suitable for the separation of the metal chelates studied.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 39 (1990), S. 1903-1913 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A heat-resistant rubber blend of natural rubber NR and styrene butadiene rubber (SBR-1502) was prepared according to the standard techniques. The rubber blend was loaded with different concentrations of LAMP black and general purpose furnace (GPF) black for obtaining conductive rubber composites. The obtained vulcanizates were subjected to electrical conductivity measurements over a wide range of temperature and electric field. It was found that all samples showed negative values of temperature coefficient of conductivity (TCC). The temperature developed inside the samples by the Joule heating effect was recorded as a function of time (T-t) at different values of the initial applied DC-electric power. The T-t dependence was found to obey an exponentially growing function with a time constant (τ), which was found to be dependent on the concentrations as well as the type of carbon black and the value of the initial applied power. The current-voltage characteristics of the samples showed a negative resistance behavior after a characteristic voltage (V*). It was noticed that V* decreases as the carbon black concentration increases.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 22 (1990), S. 665-671 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative rate technique has been used to measure rate constants for the reaction of chlorine atoms with nitro methane, nitro ethane, nitro propane, nitro butane, nitro pentane, ethyl nitrate, isopropyl nitrate, n-propyl nitrate, 2-pentyl nitrate, and 2-heptyl nitrate. Decay rates of these organic species were measured relative to one or more of the following reference compounds; n-butane, ethane, chloroethane, and methane. Using rate constants of 2.25 × 10-10 5.7 × 10-11, 8.04 × 10-12, and 1.0 × 10-13 cm3 molecule-1 s-1 for the reaction of Cl atoms with n-butane, ethane, chloroethane, and methane, respectively, the following rate constants were derived, in units of cm3 molecule-1 s-1: nitro methane, 〈7 × 10-15; nitro ethane, (2.05 ± 0.14) × 10-13; nitro propane, (1.13 ± 0.05) × 10-11; nitro butane, (5.13 ± 0.68) × 10-11; nitro pentane, (1.40 ± 0.14) × 10-10; ethyl nitrate, (3.70 ± 0.24) × 10-12; n-propyl nitrate, (2.15 ± 0.13) × 10-11; i-propyl nitrate, (3.94 ± 0.48) × 10-12; 2-pentyl nitrate, (1.00 ± 0.06) × 10-10; and 2-heptyl nitrate, (2.84 ± 0.50) × 10-10. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure (≃740 torr) of synthetic air. The results are discussed with respect to the previous literature data and to the modeling of these compounds in the atmosphere.
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Propellants, Explosives, Pyrotechnics 15 (1990), S. 11-13 
    ISSN: 0721-3115
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new sensitive method has been proposed for the determination of lead in some single- and double-base propellants. The method is based on the color reaction of lead(II) with hematoxylin in presence of the cationic surfactant cetyltrimethylammonium bromide. At pH 8.0, the formed ternary system possesses an absorption maximum at 605 nm with a molar absorptivity of 5.5 × 104 l · mol-1 · cm-1. The system adheres to Beer's law up to 1.78 ppm of lead, and the sensitivity index is 0.0039 μg · cm 2. The susceptibility of interference of common ions is studied and some masking agent solutions are recommended to improve the selectivity of the method. The proposed method shows good agreement with the results obtained by atomic absorption spectrometry. An average recovery of 99.3% with a standard deviation not exceeding 1.7% is observed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1920
    Keywords: Nerves, trigeminal ; Parapharyngeal space ; Masticator space ; Magnetic resonance imaging ; Cavernous sinus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 10 patients with symptoms of mandibular neuralgia formed the basis of this study. They were studied by both enhanced CT and MRI. MRI, better than CT, easily permits distinction between intrinsic and extrinsic lesions and detects involvement of the cavernous sinus and meninges. Morever, because of its multiplanar imaging capability, and ability to portray exquisite anatomic details and characteristic tissue signal intensity, MRI is helpful in the evaluation of tumor involvement for biopsy and preoperative planning for these deep tumours.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of neurology 237 (1990), S. 471-474 
    ISSN: 1432-1459
    Keywords: Amyotrophic lateral sclerosis ; Progressive muscular atrophy ; Bulbar palsy ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Magnetic resonance imaging (MRI) of the brain was evaluated in 20 patients with motor neuron disease (MND) and in a control group of 11 healthy people. Bilateral increased signal areas of various sizes in the centrum semiovale, corona radiata, internal capsule, pedunculi of midbrain, pons, medulla and even in the frontal lobe, topographically related with the corticospinal tract, were found in 8 out of 20 patients. Three out of 4 patients with progressive bulbar paralisis and 5 out of 11 cases of amyotrophic lateral sclerosis had abnormal MRI. Such MRI abnormalities have neither been found in patients with progressive muscular atrophy nor in controls, suggesting that they may be the hallmark of pyramidal tract degeneration in motor neuron disease.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1619-7089
    Keywords: Magnetic resonance imaging ; Immunoscintigraphy ; Ovarian carcinoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Eighteen patients with suspected primary or recurrent ovarian carcinoma have been investigated in each case by the assay of serum levels of the antigen CA125, immunoscintigraphy using131I-OC125 antibody and magnetic resonance imaging using a 0.15 Tesla-system. The final diagnosis was confirmed by laparotomy or laparoscopy. Serum levels of CA125 ranged between 5 and 780 units/ml (normal range 〈 35). Antibody images and MRI were truly positive in 11 patients, 2 of whom were subsequently found to have bowel tumours. MRI showed greater detail of smaller lesions whilst immunoscintigraphy was more suited to the detection of distant metastases. In 7 patients the antibody images were positive whilst the serum marker levels were normal. This pilot study provides a preliminary comparison of the more recent techniques currently being evaluated for the detection of ovarian carcinoma.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymer-water interaction parameters, sequence length distributions and contents of total, freezing and non-freezing water have been discussed for a family of hydrogels. The xerogel precursors contained N-vinyl-2-pyrrolidone (VP) with several co-monomers of different levels of hydrophobicity present in the xerogel over a wide range of composition. Common trends in the behaviour of these systems have been noted and rationalised. In particular the findings indicate that (i) in the poly-VP hydrogel ther are ca. 8-10 molecules of non-freezing water per VP unit and (ii) in the copolymeric hydrogels the maximum occurring in the variation of mole fraction of VP versus mole fraction of water is due substantially to the sharp increase in uptake of freezing (or bulk) water by copolymers rich in VP.
    Additional Material: 5 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1165-1170 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Thermal lithography on poly(ethylene terephthalate) (PET) is carried out by inducing crystallization through selective exposure of amorphous films to Infrared radiation. The obtained images can be smaller than the wavelength of the CO2 laser light. This circumvention of the diffraction limit is accomplished by taking advantage of the non-linear temperature dependence of the crystallization rate. The optical marking process is reversible through simple melting of the crystalline images. The complementary process, selective melting of an initially crystalline film, can also be accomplished. The use as a heat sink of a mask which forms the image pattern is demonstrated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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