Bifunctional Lewis Base Catalyzed Asymmetric N-Allylic Alkylation of 2-Hydroxypyridines.

A chiral Lewis base catalyzed enantioselective N-allylic alkylation of 2-hydroxypyridines and MBH carbonates is documented, affording a convenient access to N-alkylated 2-pyridones with up to 99% ee and 99% yield. Experimental and computational studies have revealed that the strong hydrogen bond interaction between the chiral Lewis base catalyst and 2-hydroxypyridines plays a crucial role in this reaction for the reactivity, chemoselectivity, and enantioselectivity.

[A field study on the work load and muscle fatigue at neck-shoulder in female sewing machine operators by using surface electromyography].

OBJECTIVE: To study neck and shoulder work-related muscle fatigue of female sewing machine operators. METHODS: 18 health female sewing machine operators without musculoskeletal disorders work in Beijing garment industry factory as volunteers in participate of this study. The maximal voluntary contraction (MVC) and 20% MVC of bilateral upper trapezium and cervical erectors spinae was tested before sewing operations, then the whole 20 time windows (1 time window = 10 min) sewing machine operations was monitored and the surface electromyography (sEMG) signals simultaneously was recorded after monitoring the 20%MVC was tested. Use amplitude analysis method to reduction recorded EMG signals. RESULTS: During work, the median load for the left cervical erector spinae (LCES), right cervical erector spinae (RCES), left upper trapezium (LUT) and right upper trapezium (RUT) respectively was 6.78 ± 1.05, 6.94 ± 1.12, 5.68 ± 2.56 and 6.47 ± 3.22, work load of right is higher than the left; static load analysis indicated the value of RMS(20%MVC) before work was higher than that value after work, the increase of right CES and UT RMS(20%MVC) was more; the largest 20%MVE of bilateral CES occurred at 20th time window, and that of bilateral UT happened at 16th. CONCLUSIONS: The work load of female sewing machine operators is sustained "static" load, and work load of right neck-shoulder is higher than left, right neck-shoulder muscle is more fatigable and much serious once fatigued.

Quantify work load and muscle functional activation patterns in neck-shoulder muscles of female sewing machine operators using surface electromyogram.

BACKGROUND: Work-related musculoskeletal disorders (WMSDs) have high prevalence in sewing machine operators employed in the garment industry. Long work duration, sustained low level work and precise hand work are the main risk factors of neck-shoulder disorders for sewing machine operators. Surface electromyogram (sEMG) offers a valuable tool to determine muscle activity (internal exposure) and quantify muscular load (external exposure). During sustained and/or repetitive muscle contractions, typical changes of muscle fatigue in sEMG, as an increase in amplitude or a decrease as a shift in spectrum towards lower frequencies, can be observed. In this paper, we measured and quantified the muscle load and muscular activity patterns of neck-shoulder muscles in female sewing machine operators during sustained sewing machine operating tasks using sEMG. METHODS: A total of 18 healthy women sewing machine operators volunteered to participate in this study. Before their daily sewing machine operating task, we measured the maximal voluntary contractions (MVC) and 20%MVC of bilateral cervical erector spinae (CES) and upper trapezius (UT) respectively, then the sEMG signals of bilateral UT and CES were monitored and recorded continuously during 200 minutes of sustained sewing machine operating simultaneously which equals to 20 time windows with 10 minutes as one time window. After 200 minutes' work, we retest 20%MVC of four neck-shoulder muscles and recorded the sEMG signals. Linear analysis, including amplitude probability distribution frequency (APDF), amplitude analysis parameters such as roof mean square (RMS) and spectrum analysis parameter as median frequency (MF), were used to calculate and indicate muscle load and muscular activity of bilateral CES and UT. RESULTS: During 200 minutes of sewing machine operating, the median load for the left cervical erector spinae (LCES), right cervical erector spinae (RCES), left upper trapezius (LUT) and right upper trapezius (RUT) were 6.78%MVE, 6.94%MVE, 6.47%MVE and 5.68%MVE, respectively. Work load of right muscles are significantly higher than that of the left muscles (P < 0.05); sEMG signal analysis of isometric contractions indicated that the amplitude value before operating was significantly higher than that of after work (P < 0.01), and the spectrum value of bilateral CES and UT were significantly lower than those of after work (P < 0.01); according to the sEMG signal data of 20 time windows, with operating time pass by, the muscle activity patterns of bilateral CES and UT showed dynamic changes, the maximal amplitude of LCES, RCES, LUT occurred at the 20th time window, RUT at 16th time window, spectrum analysis showed that the lower value happened at 7th, 16th, 20th time windows. CONCLUSIONS: Female sewing machine operators were exposed to high sustained static load on bilateral neck-shoulder muscles; left neck and shoulder muscles were held in more static positions; the 7th, 16th, and 20th time windows were muscle fatigue period that ergonomics intervention can protocol at these periods.

[Effects of chronic exposure of power frequency magnetic field on neurobehavior in rats].

OBJECTIVE: To observe the effect of chronic exposure to extremely low frequency magnetic field on neurobehavioral of adult rats. METHODS: Fifty Hz sinusoidal extremely low frequency magnetic field (ELF-MF) was used in this experimental procedure and the strength of magnetic field was fixed at 2 mT. Thirty male adult rats were divided randomly into 3 groups: (1) no ELF MF exposure (control group, n=10); (2) exposure to ELF MF 1 h/day (MF1h group, n=10); (3) exposure to ELF MF 4 h/day (MF4h group, n=10). The neurobehavioral changes of rats were detected by the open field test, elevated plus maze test and light/dark box test. RESULTS: Compared with controls, no significant difference was found in rats of MF1h group in any test. Rats in MF4h group showed increased thigmotaxis, more grooming in the open field test; less time spent in open arms, central part and more time spent in closed arms. However, no significant difference was observed in the light/dark test in MF1h or MF4h group. CONCLUSION: Chronic ELF MF exposure has an anxiogenic effect on rats, which is dependent on the daily exposure duration.

[Characteristics of surface electromyography and work load of the forearm extensors in repetitive wrist extending].

OBJECTIVE: To evaluate the influence of the frequency, the weight and the motion angle on the stress and the fatigue of the forearm extensors in repetitive wrist extending at low force loading level with surface electromyography (SEMG). METHODS: Sixteen male college student volunteers were recruited for the experiment. Eight tasks of wrist extending were performed for 20 minutes respectively in given weight (1.96, 4.90 N), frequency (8.0, 33.3 moves/minute) and motion angle (45 degrees, 90 degrees). The static wrist extending at the level of 20% maximum voluntary contraction (MVC) were performed before and after each task for 2 up to 3 seconds, and the SEMG signals of extensor carpi ulnaris muscle (ECU) and extensor digitorum (ED) were recorded and analyzed. RESULTS: The weight loading level was approximately equal to 1.40% or 3.50% of the MVC force. The mean power frequency (MPF) and the median frequency (MF) were decreased with the increase of 3 kinds of loading levels. The decrease of MPF of the muscle ED was significant (P < 0.05 or P < 0.01). The MF was decreased with the increase of angle and weight loading levels (P < 0.05 or P < 0.01). The root mean square (RMS) value of SEMG could be divided into 3 or 4 groups with significant difference. All three kinds of loads had positive correlation with amplitude of SEMG according to the stepwise regression analysis. CONCLUSION: The fatigue level of ED is the highest. The primary load factor for the forearm extensors is the frequency followed by the weight and the angle. MF, MPF and RMS can be used as sensitive indexes for evaluating the stress and the fatigue of the forearm extensors during repetitive performance at lower force loading level.