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  • 11
    ISSN: 1432-1246
    Keywords: CNS symptoms ; Human exposure ; Irritative effects ; Methyl isobutyl ketone ; Toxicokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The toxicokinetics as well as irritative effects and CNS symptoms of methyl isobutyl ketone (MIBK) were studied in human volunteers during inhalation exposure. The volunteers were exposed (2 h, 50 W) in an exposure chamber on four different occasions to about 10,100 and 200 mg/m3 MIBK and to a combination of about 100 mg/m3 MIBK and 150 mg/m3 toluene. The relative pulmonary uptake of MIBK was about 60% and the total uptake increased linearly with increasing exposure concentration. The concentration of MIBK in blood rose rapidly after the onset of exposure and no plateau level was reached during exposure. No tendency for saturation kinetics could be observed within the dose interval and the apparent blood clearance was 1.6 l/h/kg at all exposure levels. The concentration of unchanged MIBK in the urine after exposure was proportional with the total uptake. Only 0.04% of the total MIBK dose was eliminated unchanged via the kidneys within 3 h post exposure. The concentrations of the metabolites 4-hydroxy-4-methyl-2-pentanone and 4-methyl-2-pentanol were below the detection limit (5 nmol/l). Irritative and CNS symptoms occurred during exposure. The degree of both irritative and CNS symptoms increased during exposure to 100 and 200 mg/m3 compared with 10 mg/m3, but combination exposure with toluene exhibited the most pronounced effect. There were no significant effects from exposure on the performance of a simple reaction time task or a test of mental arithmetic.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 1439-6327
    Keywords: Electromyography ; Muscle contraction ; Exercise ; Isometric fatigue ; Frequency analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The influence of the strength of contraction on surface recorded myoelectric power spectra was studied for three elbow flexors. Four subjects performed brief (3–5 s) isometric contraction levels (5–80% MVC). The experiment was repeated 23–26 times on different days. The surface myoelectric signal was recorded from the biceps brachii, the brachialis and the brachioradialis. By fast Fourier transform the myoelectric power spectrum was computed. The mean power frequency (MPF) was calculated and used as a single estimate of the myoelectric power spectrum. The MPF was found to increase with contraction strength with low level contractions. At levels in excess of 25–30% of MVC, the MPF became independent of contraction level. This dependence of the MPF on low level contractions is explained by tissue filtering effects and the recruitment order and distribution of motor units.
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 1439-6327
    Keywords: Electromyography ; Frequency analysis ; Isometric contraction ; Trapezius muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Surface electromyographic (EMG) amplitude and mean power frequency (MPF) were used to study the isometric muscular activity of the right versus the left upper trapezius muscles in 14 healthy right-handed women. The EMG activity was recorded simultaneously with force signals during a 10–15 s gradually increasing exertion of force, up to maximal force. Only one side at a time was tested. On both sides there was a significant increase in EMG amplitude (μV) during the gradually increasing force from 0% to 100% maximal voluntary contraction (MVC). The right trapezius muscle showed significantly less steep slopes for regression of EMG amplitude versus force at low force levels (0%–40% MVC) compared intra-individually with high force levels (60%–100% MVC). This was not found for the left trapezius muscle. At 40% MVC a significantly lower MPF value was found for the right trapezius muscle intra-individually compared with the left. An increase in MPF between 5% and 40% MVC was statistically significant when both sides were included in the test. The differences in EMG activity between the two sides at low force levels could be due to more slow-twitch (type I fibres) motor unit activity in the right trapezius muscles. It is suggested that this is related to right-handed activity.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2990-2992 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Grating-coupled surface-emitting InGaAs/AlGaAs lasers with a single large area output coupler were fabricated by integrating a second order surface grating with corner reflectors. The grating as well as the corner reflectors were fabricated using electron beam lithography and chemically assisted ion beam etching, producing a uniform rectangular grating and high quality corner facets. A thin etch-stop layer incorporated in the epitaxial structure made it possible to combine precise control of the grating position with a strained layer SQW-GRINSCH structure. Well behaved lateral modes were observed in 70-μm-wide lasers, emitting narrow beams in both the lateral and the longitudinal direction. Threshold current densities as low as 99 A/cm2 were measured for 1200-μm-long lasers.
    Type of Medium: Electronic Resource
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