Range-Dependent Channel Calibration for High-Resolution Wide-Swath Synthetic Aperture Radar Imagery.

High-resolution and wide-swath (HRWS) synthetic aperture radar (SAR) imaging with azimuth multi-channel always suffers from channel phase and amplitude errors. Compared with spatial-invariant error, the range-dependent channel phase error is intractable due to its spatial dependency characteristic. This paper proposes a novel parameterized channel equalization approach to reconstruct the unambiguous SAR imagery. First, a linear model is established for the range-dependent channel phase error, and the sharpness of the reconstructed Doppler spectrum is used to measure the unambiguity quality. Furthermore, the intrinsic relationship between the channel phase errors and the sharpness is revealed, which allows us to estimate the optimal parameters by maximizing the sharpness of the reconstructed Doppler spectrum. Finally, the results from real-measured data show that the suggested method performs exceptionally for ambiguity suppression in HRWS SAR imaging.

Antifatigue effect of naringin on improving antioxidant capacity and mitochondrial function and preventing muscle damage.

The aim of this study was to explore effects of naringin (Nar) on antifatigue ability; the weight-loaded and non-loading swimming tests were performed. Compared with the control group, dietary supplementation of Nar significantly prolonged the weight-loaded swimming time to exhaustion of mice (P < 0.01). Nar significantly reduced the serum lactic acid (LD) level (P < 0.05) and lactate dehydrogenase (LDH) activity (P < 0.001), while increased the serum non-esterified free fatty acids (NEFA) level (P < 0.001). In addition, Nar significantly increased the liver glycogen and muscle glycogen contents (P < 0.05) and the phosphoenolpyruvate carboxykinase (PEPCK) (P < 0.01) and glucokinase (GCK) mRNA levels (P < 0.001) in liver and gastrocnemius (GAS) muscle. Furthermore, Nar significantly improved the antioxidant capacity, mitochondrial function, and muscle mitochondrial fatty acid ß-oxidation (P < 0.05), and decreased inflammation and muscle damage-related gene expression (P < 0.05). These findings suggested that Nar can improve antifatigue effect by enhancing antioxidant capacity and mitochondrial function and preventing muscle damage.

Effect of dietary L-theanine supplementation on skeletal muscle fiber type transformation in vivo.

The aim of this study was to investigate the effect of dietary L-theanine supplementation on skeletal muscle fiber type transition in mice. Our data indicated that dietary 0.15% L-theanine supplementation significantly increased the mRNA expression levels of muscle fiber type related genes (MyHC I, MyHC IIa, PGC-1α, Sirt1, Tnnt1, Tnnc1, Tnni1, MEF2C) and the protein expression levels of MyHC IIa, myoglobin, PGC-1α, Sirt1 and Troponin I-SS, but significantly decreased the mRNA and protein expression levels of MyHC IIb. Dietary 0.15% L-theanine supplementation significantly increased the activities of SDH and MDH and decreased the activity of LDH. Furthermore, immunofluorescence demonstrated that dietary 0.15% L-theanine supplementation significantly increased the percentage of type I fibers, and significantly decreased the percentage of type II fibers. In addition, we found that dietary 0.15% L-theanine supplementation increased the fatigue-resistant, antioxidant capacity, mitochondrial biogenesis, and function in skeletal muscle of mice. Furthermore, dietary 0.15% L-theanine supplementation significantly increased the mRNA levels of prox1, CaN and NFATc1, the protein levels of prox1, CNA and NFATc1 and the activity of CaN in GAS muscle when compared with the control group. These results indicated that dietary L-theanine supplementation promoted skeletal muscle fiber transition from type II-type I, which might be via activation of CaN and/or NFATc1 signaling pathway.

Naringin induces skeletal muscle fiber type transformation via AMPK/PGC-1α signaling pathway in mice and C2C12 myotubes.

A large number of studies have shown that polyphenols can regulate skeletal muscle fiber type transformation through AMPK signal. However, the effects and mechanism of naringin (a natural polyphenol) on muscle fiber type transformation still remains unclear. Thus, we hypothesized that naringin would induce the transformation of skeletal muscle fibers from type II to type I by AMPK signaling. C2C12 myotubes and BALB/c mice models were used to test this hypothesis. We found that naringin significantly increased the protein expression of slow myosin heavy chain (MyHC), myoglobin and troponin I type I slow skeletal (Troponin I-SS) and the activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH), and significantly decreased fast MyHC protein expression and lactate dehydrogenase (LDH) activity, accompanied by the activation of AMPK and the activity of peroxisome proliferator activated receptor-γ coactivator-1α (PGC-1α) in mice and C2C12 myotubes. Further inhibition of AMPK activity by compound C showed that the above effects were significantly inhibited in C2C12 myotubes. In conclusion, naringin promotes the transformation of skeletal muscle fibers from type II to type I through AMPK/PGC-1α signaling pathway, which not only enriches the nutritional and physiological functions of naringin, but also provides a theoretical basis for the regulation of muscle fiber type transformation by nutritional approaches.