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A method of quickly determining ascorbic acid and sorbic acid by capillary zone electrophoresis with ultraviolet detection was developed. The choice of background electrolyte, wavelength, injection time and applied voltage were discussed. Ascorbic acid and sorbic acid were well separated in 80 mmol L−1 boric acid-5 mmol L−1borax (pH = 8.0) in 5 min at the detecting wavelength of 270 nm. Under the optimum condition, the method has linear ranges of 2.54-352.00 mg L−1 for ascorbic acid and 1.08-336.39 mg L−1 for sorbic acid with the detection limit of 1.70 mg L−1 for ascorbic acid and 0.54 mg L−1 for sorbic acid, respectively. Other organic acids in fruit juices have no effect on the detection. This method is very feasible and simple and can be used to detect ascorbic acid and sorbic acid in fruit juices. 相似文献
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Moon-Shong Tang Tzu-chien V. Wang‡ Michael H. Patrick 《Photochemistry and photobiology》1979,29(3):511-520
Abstract— Continuous DNA degradation and resynthesis, without a net change in cellular DNA content, were observed in buffer-held, non-irradiated E. coli B/r. This constant DNA turnover probably involves most of the genome and reflects random sites of DNA repair due to the polA-dependent excision-resynthesis repair pathway. Under these non-growth conditions, it appears that at any given time there is a minimum of one repair site per 6.5 × 106 daltons DNA, each of which is at least 160 nucleotides long.
While the amount of DNA degradation is not influenced by prior exposure to UV radiation, the synthetic activity decreases with increasing UV fluence. We suggest that when sites of DNA turnover occur opposite to cyclobutyl dipyrimidines in UV-irradiated cells, repair of the latter damage can be prevented. This implies that both beneficial and deleterious processes take place in irradiated buffer-held cells, and that cell survival depends on the delicate balance between DNA turnover and repair of UV-damage. Based on these findings, we propose a model to explain the limited repair observed during post-irradiation liquid-holding and to account for the large difference in cell survival between irradiation at low fluence rates (fluence-rate dependent recovery) and at high fluence rates followed by liquid-holding (liquid-holding recovery). 相似文献
While the amount of DNA degradation is not influenced by prior exposure to UV radiation, the synthetic activity decreases with increasing UV fluence. We suggest that when sites of DNA turnover occur opposite to cyclobutyl dipyrimidines in UV-irradiated cells, repair of the latter damage can be prevented. This implies that both beneficial and deleterious processes take place in irradiated buffer-held cells, and that cell survival depends on the delicate balance between DNA turnover and repair of UV-damage. Based on these findings, we propose a model to explain the limited repair observed during post-irradiation liquid-holding and to account for the large difference in cell survival between irradiation at low fluence rates (fluence-rate dependent recovery) and at high fluence rates followed by liquid-holding (liquid-holding recovery). 相似文献
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Li Tang 《Broadcasting, IEEE Transactions on》2006,52(3):356-361
Video transmission over unreliable channels may suffer from the data loss or corruption. To facilitate the transmission, video content is compressed to save the bandwidth. The compression algorithms remove the redundancies in the video signal, meanwhile increasing the dependencies among symbols in the compressed bit-stream. Thus, when errors occur, they may propagate in both space and time. Among various error control techniques, error concealment (EC) is an effective method that is performed at the decoder to mitigate the influence of errors on the quality of reconstructed images. In this paper, a joint spatial and temporal EC algorithm (JSTEC) is presented. First, several existing temporal EC algorithms are combined in an appropriate order. Then, the spatial correlation in the video is exploited in an iterative form to improve the performance of the temporal EC. Experimental results show that JSTEC performs better both in peak signal-to-noise ratio and subjective quality of images than the existing algorithms. 相似文献
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A novel frequency offset estimation method for OFDM systems with large estimation range 总被引:4,自引:0,他引:4
Chunlin Yan Shaoqian Li Youxi Tang Xiao Luo Jiayi Fang 《Broadcasting, IEEE Transactions on》2006,52(1):58-61
In this paper, we proposed a novel frequency synchronization method which has larger estimation range than conventional method proposed by Tufvesson. A two steps frequency offset estimation method is performed in the new method. In the first step the received signal is correlated with local training sequence to eliminate the influence of training sequence which makes the estimation range of frequency offset is independent of period of the repeated data in the training sequence. The received signal is correlated with its delay in the second step to obtain the fine estimation of frequency offset. Precise estimation can be achieved in the proposed method than Tufvesson's method. The period of the repeated data in the training sequence determines the estimation range of the frequency offset in the conventional method, while in the new method they are irrelevant. Tens of subcarriers spacing can be estimated by the new method. The new method can be used in other cases as long as a known sequence is transmitted, which will introduce valuable flexibility in training sequence design. The validity of the algorithm is verified in AWGN channel and multipath fading channel. 相似文献
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