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

A chiral Lewis base catalyzed enantioselective -allylic alkylation of 2-hydroxypyridines and MBH carbonates is documented, affording a convenient access to -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.

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).

[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.

[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).

[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.