Magnetism of a free-standing W monoatomic sheet

The magnetism of a free-standing tungsten monoatomic sheet under different magnetization states has been studied by using the first-principles method based on the density functional theory. The results show that W atomic sheet at the equilibrium state is not magnetized. However, ferromagnetic or antiferromagnetic state can appear in the sheet when the lattice is elongated, moreover, the magnetism appears earlier and increases more stably and smoothly in the antiferromagnetic states than the ferromagnetic one. The antiferromagnetic states are always more stable than the ferromagnetic ones under the same lattice parameter. The most stable W atomic sheet among all the structures studied is a near-hexagonal plane structure, due to the Jahn–Teller effect. All the magnetic states studied are shown to be metallic. The electronic structure properties of various magnetic plane structures are presented, with the effect of spin–orbit coupling included.     

制冷装置增加夜间运行时间的性能分析

介绍了福建省目前的分时电价政策.基于冷库实例,模拟计算了制冷装置增加夜间运行时间,采用不同蓄冷运行方案的运行费用.结果显示,理想条件下冷库的运行电费可节省47.3%以上,现场调研的某冷库运行电费可减少约31%.根据气象台的逐时气象数据统计,厦门市夜间湿球温度下降1.2～1.8℃.计算表明,制冷装置夜间运行的COP因此比...     

Dawson结构的多金属氧酸盐对酪氨酸酶的抑制作用

按文献方法合成了两种Dawson结构的多金属氧酸盐,并对其结构进行紫外光谱和红外光谱分析。以H_6[P_2Mo_(18)O_(62)]和H_8[P_2Mo_(17)Cr(OH_2)O_(61)](简写为P_2Mo_(18)和P_2Mo_(17)Cr)为效应物,采用紫外分光光度法和酶动力学方法研究两种Dawson结构的多金属氧酸盐效应物对蘑菇酪氨酸酶二酚酶活性的抑制作用。结果表明,P_2Mo_(18)和P_2Mo_(17)Cr对酪氨酸酶二酚酶均具有显著的抑制效果,测定抑制酪氨酸酶活力下降50%的抑制浓度(IC_(50))分别为(0.482±0.009)mmol/L和(0.503±0.011)mmol/L。动力学分析表明,P_2Mo_(18)和P_2Mo_(17)Cr对酪氨酸酶的抑制作用均表现为可逆的竞争型,抑制常数K_I分别为0.212和0.249 mmol/L。其中,综合考虑IC_(50)值和抑制常数,P_2Mo_(18)对酪氨酸酶二酚酶活性的抑制效果略优于P_2Mo_(17)Cr。     

6种多金属氧酸盐的抑菌作用

合成了5种过渡金属取代的Keggin型多金属氧酸盐(Na_7PMo_(11)M(Ⅱ)O_(40)(M=Mn,Fe,Zn,Co,Ni)(简写为PMo_(11)M(Ⅱ)),并通过紫外可见分光光度计和傅里叶变换红外光谱仪对其结构进行了表征。进而运用牛津杯法研究了这5种过渡金属取代的Keggin型多金属氧酸盐和母体H_3PMo_(12)O_(40)(简写为PMo_(12))对藤黄八叠球菌、金黄色葡萄球菌、枯草芽孢杆菌和大肠杆菌的抑菌活性,并用微量肉汤二倍稀释法测得了这些(共6种)化合物对上述4种菌的最小抑菌浓度(MIC值)和最小杀菌浓度(MBC值)。结果表明,这6种化合物对4种菌均有不同程度的抑制作用,并且对2种球菌的抑制效果优于对2种杆菌的抑制效果。其中(Na_7PMo_(11)M(Ⅱ)O_(40)(M=Ni,Mn,Zn)对4种菌的抑制效果优于其它3种化合物。综合考虑,本研究能够为多金属氧酸盐用于果蔬的防腐保鲜提供更多的理论和实验支持。     

染发剂中4种p-苯二胺N位取代衍生物的高效液相色谱测定法

建立了高效液相色谱(HPLC)同时测定染发剂中N,N-双(2-羟乙基)-p-苯二胺硫酸盐(DHPD)、N,N-二甲基-p-苯二胺硫酸盐(DMPD)、N,N-二乙基-p-苯二胺硫酸盐(DEPD)、N-苯基-p-苯二胺盐酸盐(PPD)4种p-苯二胺N位衍生物的方法。采用Agilent Eclipse XDB-C18柱(150 mm×4.6 mm,5μm)为固定相,25 mmol/L磷酸缓冲液(pH 6.0,含0.1%的辛烷磺酸钠)和乙腈为流动相,梯度洗脱,流速1.0 mL/min,柱温25℃,进样量20μL,检测波长250 nm和280 nm。各组分的线性范围为0.1～400 mg/L,相关系数r为0.999 2～0.999 9,检出限为18～108 mg.kg-1,定量下限为42～320 mg.kg-1,RSD<10%,加标回收率为83%～115%。该方法具有简便、快速、准确等特点,基本满足实际样品的分析要求。     

Effect of thermal treatment on the magnetization processes of nanocrystalline Fe80Ge3Nb10B7 alloys

The dynamic magnetization processes of nanocrystalline Fe₈₀Ge₃Nb₁₀B₇ alloys after annealing at different temperatures are studied through the permeability spectroscopy. Three steps of crystallization are found when amorphous Fe₈₀Ge₃Nb₁₀B₇ alloys are heated from 300to 1200 K. The dominant magnetization process varies with different annealing temperatures. Domain wall bulging is the main magnetization mechanism under weak applied field. When the applied field exceeds pinning field H_p, the depinning-involved domain wall displacement occurs. Different annealing temperature results in different H_p. The lower value of μ′ and high relaxation frequency after heating at 923 and 973 K are due to the strengthened domain wall pinning and the increase of magnetocrystalline anisotropy.     

Coexistence of domains of attraction of nonautonomous neural networks with time-varying delays

This paper presents new dynamical behavior, i.e., the coexistence of 2^N domains of attraction of N-dimensional nonautonomous neural networks with time-varying delays. By imposing some new assumptions on activation functions and system parameters, we construct 2^N invariant basins for neural system and derive some criteria on the boundedness and exponential attractivity for each invariant basin. Particularly, when neural system degenerates into periodic case, we not only attain the coexistence of 2^N periodic orbits in bounded invariant basins but also give their domains of attraction. Moreover, our results are suitable for autonomous neural systems. Our new results improve and generalize former ones. Finally, computer simulation is performed to illustrate the feasibility of our results.     

Dynamic analysis of mathematical model of ethanol fermentation with gas stripping

In this paper, a mathematical model for ethanol fermentation with gas stripping is investigated. Firstly, the model with continuous substrate input is taken. We study the existence and local stability of two equilibrium points. According to Poincare–Bendixson Theorem, the sufficient condition for the globally asymptotical stability of positive equilibrium point is obtained, which implies that we can get stable ethanol product. Secondly, we study the model with impulsive substrate input and obtain the sufficient condition for the local stability of cell-free periodic solution by using the Floquet’s theory of impulsive differential equation and small-amplitude perturbation skills. In a certain limiting case, it is shown that a nontrivial periodic solution emerges via a supercritical (subcritical) bifurcation. Finally, our results are confirmed by means of numerical simulation.     

ABOUT HYBRID BIDIRECTIONAL ASSOCIATIVE MEMORY NEURAL NETWORKS WITH DISCRETE DELAYS

In this paper, hybrid bidirectional associative memory neural networks with discrete delays is considered. By ingeniously importing real parameters di > 0(i = 1,2,···,n) which can be adjusted, we establish some new sufficient conditions for the dynamical characteristics of hybrid bidirectional associative memory neural networks with discrete delays by the method of variation of parameters and some analysis techniques. Our results generalize and improve the related results in [10,11]. Our work is significant...     

Kolmogorov-Spieqel-Siveshinky方程大时间问题的Fourier拟谱逼近

该文讨论了Kolmogorov-Spieqel-Siveshinky方程的周期初值问题, 研究了半离散Fourier拟谱解的长时间行为, 证明了半离散系统的收敛性和整体吸引子的存在性. 构造了全离散的三层显式Fourier拟谱格式, 并证明了该格式的收敛性, 最后通过数值计算验证了格式的可信性. 数值结果表明: 该格式是长时间稳定并可取时间大步长. 作者模拟了方程的解在相空间的轨线, 得到了一些有意义的结论.