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| 1 | Stability of a linear oscillator with damping force of the fractional-order derivative显示文摘It begins with the study of damping representation of a linear vibration system of single degree of freedom (SDOF),from the view point of fractional calculus. By using the idea of stability switch,it shows that the linear term involving the fractional-order derivative of an order between 0 and 2 always acts as a damping force,so that the unique equilibrium is asymp-totically stable. Further,based on the idea of stability switch again,the paper proposes a scheme for determining the stable gain region of a linear vibration system under a fractional-order control. It shows that unlike the classical velocity feedback which can adjust the damping force only,a fractional-order feedback can adjust not only the damping force,but also the elastic re-storing force,and in addition,a fractional-order PDα control can either enlarge the stable gain region or narrow the stable gain region. For the dynamic systems described by integer-order derivatives,the asymptotical stability of an equilibrium is guaranteed if all characteristic roots stay in the open left half-plane,while for the systems with fractional-order derivatives,the asymptotical stability of an equilibrium is guaranteed if all characteristic roots stay within a sector in the complex plane. Analysis shows that the proposed method,based on the idea of stability switch,works effectively in the stability analysis of dynamical systems with fractional-order derivatives. | WANG ZaiHua1,2 & HU HaiYan1 1 Institute of Vibration Engineering Research,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China 2 Institute of Science,PLA University of Science and Technology,Nanjing 211101,China | 2010 | Science China(Physics,Mechanics & Astronomy)2010，53，2： | 7 |
| 2 | Enhancement of cardiomyocyte differentiation from human embryonic stem cells显示文摘Several approaches have been used to encourage the differentiation of cardiomyocytes from human embryonic stem cells.However,the differentiation efficiency is low,and appropriate culture protocols are needed to produce adequate numbers of cardiomyocytes for therapeutic cell transplantation.This study investigated the effects of serum on cardiomyocyte differentiation in suspension culture medium during embryoid body(EB) formation by human embryonic stem cells.The addition of ascorbic acid,dimethylsulfoxide and 5-aza-2'-deoxycytidine during days 5-7 at the EB-forming stage resulted in an increase in the numbers of rhythmically contracting clusters of derived cardiomyocytes.Treatment with 0.1 mmol L-1 ascorbic acid alone,or more notably in combination with 10 μmol L-1 5-aza-2'-deoxycytidine,induced the formation of beating cells within EBs.Most of the beating clusters had spontaneous contraction rates similar to those found in human adults,and their contractile ac-tivity lasted for up to 194 days. | WANG YanXia1,2,CHEN GuiAn1,2,SONG TianRan1,2,MAO GenHong1,2 & BAI HaiYan1,2 1Reproductive Medicine Center,Peking University Third Hospital,Beijing 100083,China 2Stem Cell Research Center,Peking University Third Hospital,Beijing 100083,China | 2010 | Science China(Life Sciences)2010，53，5： | 5 |
| 3 | ω-Gorenstein injective modules and dimensions显示文摘Gorenstein injective modules and dimensions have been studied extensively by many authors. In this paper, we investigate Gorenstein injective modules and dimensions relative to a Wakamatsu tilting module. | ZHU HaiYan1,2 & DING NanQing3 1Department of Mathematics, Zhejiang University, Zhejiang 310027, China 2Department of Mathematics, Zhejiang University of Technology, Zhejiang 310023, China 3Department of Mathematics, Nanjing University, Nanjing 210093, China | 2011 | Science China Mathematics2011，54，3： | 2 |
| 4 | Global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback显示文摘This paper presents both analytical and numerical studies on the global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback.Based on a detailed analysis of the stability switches of the trivial equilibrium of the system,the stability charts are given in a parameter space consisting of the time delay and the feedback gains.The center manifold reduc-tion and the normal form method are used to study Hopf bifurcations with respect to the time delay.To gain an insight into the persistence of a Hopf bifurcation as the time delay varies farther away from its critical value,the method of multiple scales is used to obtain the global view of Hopf bifurcations with respect to the time delay.Both the analytical results of Hopf bifurca-tions and global view of those bifurcations are validated via a collocation scheme implemented on DDE-Biftool.The most important discovery in this paper is the well-structured global view of Hopf bifurcations for the system of concern,showing the generality of the persistence of Hopf bifurcations. | ZHANG Li1,WANG HuaiLei1 & HU HaiYan1,2 1 MOE Key Lab of Mechanics and Control of Aerospace Structures,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China 2 School of Aerospace Engineering,Beijing Institute of Technology,Beijing 100081,China | 2010 | Science China(Technological Sciences)2010，53，3： | 6 |
| 5 | Morphologies of Fe-66.7 at.%Si alloy solidified in a drop tube显示文摘Solidification of 0.1―1.0 mm diameter droplets of Fe-66.7 at.%Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and SEM measurements reveal that all the droplets are composed of the primary phase α and the α+ε eutectic. With decreasing droplet diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like to anomalous eutectic. In addition, the width of the primary phase α decreases with decreasing droplet size. The different cooling rates and undercooling levels corresponding to the samples with different sizes are responsible for the morphology changes. The cooling rates of the samples with different diameters during free fall were calculated and their effects on the microstructure formation were discussed. This kind of transition is also found inside the same sample, which is due to the larger cooling rate on the surface than at the center. | WANG Haiyan1,2, LIU Riping1, MA Mingzhen1, JING Qin1, LI Gong1, SUN Liling2 & WANG Wenkui1,2 1. Key Laboratory of Metastable Materials Science & Technology, Yanshan University, Qinhuangdao 066004, China 2. Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China | 2005 | Science China(Physics,Mechanics & Astronomy)2005，48，6： | 5 |
| 6 | DNA barcoding provides distinction between Radix Astragali and its adulterants显示文摘Based on variable nuclear and/or organellar DNA sequences among vastly divergent species as well as morphologically indistinguishable species, DNA barcoding is widely applicable in species identification, biodiversity studies, forensic analyses, and authentication of medicinal plants. The roots of Astragalus membranaceus and A. membranaceus var. mongholica are commonly used as Radix Astragali in several Asian countries, including China, Japan, and Korea. However, in addition to the two species recorded in the Chinese Pharmacopoeia, there are twenty-three species from different genera including Astragalus, Oxytropis, Hedysarum, and Glycyrrhiza, which have been used as adulterants not only in trading markets but also by the herbal medicine industry. Therefore, a simple, reliable, and accurate classification method is important for distinguishing authentic Radix Astragali from its adulterants. In this study, we acquired data for 37 samples from four related genera within the family Fabaceae. Then we compared four candidate DNA barcoding markers using ITS, matK, rbcL, and coxI sequences from nuclear, chloroplast, and mitochondrial genomes, all commonly used for plants to identify genetic variations among genera, intraspecies, and interspecies. We observed higher divergences among genera and interspecies for ITS, which have the average Kimura 2-parameter distances of 4.5% and 14.1%, respectively, whereas matK was found to have sufficient divergence at the intraspecific level. Moreover, two indels detected in the matK sequence are useful for PCR studies in distinguishing Radix Astragali from its adulterants. This study suggests that the combined barcoding regions of ITS and matK are superior barcodes for Radix Astragali and further studies should focus on evaluating the applicability and accuracy of such combined markers for a wide range of traditional Chinese herbs. | GUO HaiYan1,2, WANG WeiWei2, YANG Ning2, GUO BaoLin3, ZHANG Sun2, YANG RuiJing2, YUAN Ye2, YU JunLin4, HU SongNian2, SUN QiShi1 & YU Jun2 1School of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University, Shenyang 110016, China 2Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 101300, China 3Chinese Academy of Medical Sciences, Peking Union Medical College Institute of Medicinal Plant Development, Beijing 100094, China 4Department of Chemistry, Tonghua Normal College, Tonghua 134002, China | 2010 | Science China(Life Sciences)2010，53，8： | 7 |
| 7 | Transcriptional upregulation of restin by p53显示文摘Restin, belonging to the melanoma-associated antigen superfamily, was firstly cloned from the differentiated HL-60 cells when induced by all-trans retinoic acid ( ATRA ) in our lab. Our previous results showed that restin might be correlated to cell cycle arrest. Due to the importance of p53 in the regulation of cell growth and the relationship between p53 and ATRA, we tried to test the relationship between p53 and restin. Firstly, transfection results showed that p53 was able to upregulate the expression of restin at the transcriptional level when p53 was transfected into eukaryotic cells. Secondly, the bioinformatics analysis revealed that the upstream sequence (about 2 kb) from the first ATG of the ORF of restin gene contained a p53 binding site. In order to confirm that p53 was involved in the transcriptional regulation of restin, we cloned the upstream sequence of restin and constructed the promoter luciferase reporter system. From the luciferase activity, we demonstrated that the promoter of restin gene could be induced by ATRA. Then, another two luciferase reporter plasmids driven by the reporter of restin with no (RP?p53-luc) or mutant (mRP-luc) p53 binding site were constructed to see the regulation of restin by p53. Results showed that the transcriptional upregulation of restin gene was not due to the putative p53 binding site on the upstream of restin gene. We proposed that p53 upregulated restin transcription through an indirect way rather than direct interaction with the cis-activating element of the restin promoter. | WANG RuiHua1**, LU Fan1,2**, FU HaiYan1, WU YouSheng1, YANG GuoDong1, ZHAO WenMing2 & Zhao ZhongLiang1 1 State Key Laboratory of Cancer Biology, Department of Biochemistry and Molecular Biology, Fourth Military Medical University, Xi’an 710032, China 2 School of Life Science & Technology, Xi’an Jiaotong University, Xi’an 710049, China | 2007 | Science China(Life Sciences)2007，50，1： | 2 |
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