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2.
Asymptotic Behavior of a Stochastic Predator-prey Model with Beddington-DeAngelis Functional Response and L\'{e}vy Jumps 下载免费PDF全文
A stochastic two-prey-one-predator model with Beddington-DeAngelis functional response and L\''{e}vy jumps is proposed and investigated in this paper. First of all, we prove the existence and uniqueness of the global positive solution, and stochastic ultimate boundedness of the solution. Next, under a simple assumption, by using It\^{o} formula and other important inequalities, some sufficient conditions are established to ensure the extinction and persistence in the mean of the system. The results show that neither strong white noise nor L\''{e}vy noise is conducive to the persistence of the population. Finally, the theoretical results are verified by numerical simulations. 相似文献
3.
Yaru Gong Yuteng Zhang Chao Qin Chunyi Sun Xinlong Wang Zhongmin Su 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(3):790-794
A rational synthetic strategy to construct two supramolecular isomers based on polyoxovanadate organic polyhedra with tetrahedral symmetries is presented. VMOP‐α , a low‐temperature product, has an extremely large cell volume (470 842 Å3), which is one of the top three for well‐defined MOPs. The corner‐to‐corner packing of tetrahedra leads to a quite low density of 0.174 g cm?3 with 1D channels (ca. 5.4 nm). The effective pore volume is up to 93.6 % of cell volume, nearly the largest found in MOPs. For the high‐temperature outcome, VMOP‐β , the cell volume is only 15 513 Å3. The packing mode of tetrahedra is corner‐to‐face, giving rise to a high‐density architecture (1.324 g cm?3; channel 0.8 nm). Supramolecular structural transformation between VMOP‐α and VMOP‐β can be reversibly achieved by temperature‐induced solvent‐mediated transformation. These findings give a good opportunity for understanding 3D supramolecular aggregation and crystal growth based on large molecular tectonics. 相似文献
4.
The crystal structure of ScB3 is seeked by combining the developed particle swarm optimisation algorithm for crystal structure prediction with first-principles calculations. A new monoclinic phase with the C2/m symmetry is predicted successfully, which is energetically more superior to the early reported R-3m-, P21/m-, P63/mmc-, P-6m2-, Pnma-, and Pm-3m-type structures in the pressure range from 0 to 100?GPa. The obtained elastic constants and phonon dispersion curve reveal that the C2/m-ScB3 is mechanically and dynamically stable. The predicted large bulk module, high shear modulus, small Poisson’s ratio as well as the considerable hardness indicate that the C2/m-ScB3 has outstanding mechanical property. Meanwhile, the dependences of the bulk modulus and Young’s modulus of ScB3 on the crystal orientation are investigated theoretically. Through applying the strain–stress method, the ideal tensile and shear strengths along different crystal directions are also estimated, and the obtained results confirm that the shear mode dominates the failure mode in the C2/m-ScB3 structure and it is intrinsically a hard material. The electronic structure calculation and chemical bonding analysis illustrate that the strong covalent B-B and Sc-B bonds are responsible for its structural stability and high hardness. 相似文献
5.
巯基乙酸锑(Ⅲ)配合物合成与晶体结构 总被引:6,自引:1,他引:6
以三氧化二锑和巯基乙酸在水溶液中反应合成了配合物HSb(SCH2COO)2,并通过元素分析、红外光谱、X射线粉末衍射进行了表征,利用单晶X射线四圆衍射法测定了晶体结构,结果表明该配合物晶体属于单斜晶系,C2/c空间群,晶胞参数为:a=1.40005(8)nm,b=1.19121(8)nm,c=1.23588(8)nm,β=126.822(1)°,V=1.6499(2)nm^3,Dc=2.439g·cm^-3,Z=8,R1=0.0250。并对X射线粉末衍射数据进行了指标化,其结果与单晶数据吻合。 相似文献
6.
在Rb2 CO3-Li2 CO3-Gd2 O3-H3 BO3体系中,用自发结晶的方法获得了一种钆硼酸盐Rb2 LiGdB2 O6(RLGBO)单晶,同时,用固相合成法获得了RLGBO粉末多晶.单晶结构解析表明,RLGBO属于正交晶系,Pbcm空间群,晶胞参数a=7.0259(3)?,b=9.6103(4)?,c=10.0562(4)?和z=4.热学性质表明,RLGBO在840℃下保持良好的热稳定性.在RLGBO中分别掺杂2;的Ce3+,80;的Eu3+和50;的Tb3+之后,其结构不会发生改变.在紫外光及近紫外光激发下,RLGBO:Ce3+,RLGBO:Eu3+和RLGBO:Tb3+可分别发射蓝光,红光和绿光.结果表明,RLGBO化合物可作为发光物质的基质材料. 相似文献
7.
A nano-liquid chromatographic /tandem mass spectrometric (nanoHPLC/MS/MS) method has been developed for the sensitive determination of histamine, a vital neurotransmitter. The method involved pre-column derivatization of histamine with 7-fluoro-4-nitrobenzoxadiazole (NBD-F), thus increasing the hydrophobicity of the analyte and allowing it to be retained and stacked on a nanoelectrospay emitter packed with C18 reversed-phase particles. Sodium 1-heptanesulfonate, added as an ion-pairing reagent in the mobile phase for sample loading, was found to facilitate greatly the analyte retention. The packed nanoelectrospray emitter was easily prepared using fused-silica capillary of 75 microm i.d., and included creating an electrospray emitter tip and then slurry-packing a 5 cm long column with 5 microm silica-based particles. After sample loading, the mobile phase was changed for separation and a characteristic precursor-to-product ion transition, m/z 275 --> 258, was used for the quantification. A linear calibration curve in the range from 1.0-100 ng/mL histamine with an r2 value of 0.9995 was obtained. The detection limit was estimated to be 0.1 ng/mL histamine in water. In a preliminary validation, the method was applied to determine histamine in alcoholic beverages and rat brain tissues. 相似文献
8.
Pengjun Shi Ning Li Peilong Yang Yaru Wang Huiying Luo Yingguo Bai Bin Yao 《Applied biochemistry and biotechnology》2010,162(3):707-718
An α-l-arabinofuranosidase gene, abf51S9, was cloned from Streptomyces sp. S9 and successfully expressed in Escherichia coli BL21 (DE3). The full-length gene consisted of 1,506 bp and encoded 501 amino acids with a calculated mass of 55.2 kDa. The
deduced amino acid sequence was highly homologous with the α-l-arabinofuranosidases belonging to family 51 of the glycoside hydrolases. The recombinant protein was purified to electrophoretic
homogeneity by Ni-NTA affinity chromatography and subsequently characterized. The optimal pH and temperature for the recombinant
enzyme were 6.0 and 60∼65 °C, respectively. The enzyme showed a broad pH range of stability, retaining over 75% of the maximum
activity at pH 5.0 to 11.0. The specific activity, K
m, and V
max with p-nitrophenyl-α-l-arabinofuranoside as substrate were 60.0 U mg−1, 1.45 mM, and 221 μmol min−1 mg−1, respectively. Abf51S9 showed a mild but significant synergistic effect in combination with xylanase on the degradation of
oat-spelt xylan and soluble wheat arabinoxylan substrates with a 1.19- and 1.21-fold increase in the amount of reducing sugar
released, respectively. These favorable properties make Abf51S9 a good candidate in various industrial applications. 相似文献
9.
10.
Juan Peng Lily Zu Weihai Fang Lingyun Huang Yaru Wang Dacheng He 《Journal of mass spectrometry : JMS》2010,45(6):627-634
An understanding of the dissociation of penetratin is important for improving its metabolic stability and cargo‐delivery efficiency. In this study, we describe the selective cleavage of the K15–K16 amide bond of penetratin under the low‐energy collision‐induced dissociation condition in mass spectrometry. A variety of penetratin substitutes have been studied in which key basic amino acids have been substituted within the sequence. The calculated structure indicates that an α‐helix structure prevents the fragmentation of the central peptide domain and the side chain of lysine is involved in the proton translocation process. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献