Rigid Binary Relations on a 4-Element Domain

An n-ary relation ρ on a set U is strongly rigid if it is preserved only by trivial operations. It is projective if the only idempotent operations in P o l ρ are projections. Rosenberg, (Rocky Mt. J. Math. 3, 631–639, 1973) characterized all strongly rigid relations on a set with two elements and found a strongly rigid binary relation on every domain U of at least 3 elements. Larose and Tardif (Mult.-Valued Log. 7(5-6), 339–362, 2001) studied the projective and strongly rigid graphs and constructed large families of strongly rigid graphs. ?uczak and Ne?et?il (J. Graph Theory. 47, 81–86, 2004) settled in the affirmative a conjecture of Larose and Tardif that most graphs on a large set are projective, and characterized all homogenous graphs that are projective. ?uczak and Ne?et?il (SIAM J. Comput. 36(3), 835–843, 2006) confirmed a conjecture of Rosenberg that most relations on a big set are strongly rigid. In this paper, we characterize all strongly rigid relations on a set with at least three elements to answer an open question by Rosenberg, (Rocky Mt. J. Math. 3, 631–639, 1973) and we classify the binary relations on the 4-element domain by rigidity and demonstrate that there are merely 40 pairwise nonisomorphic rigid binary relations on the same domain (among them 25 are pairwise nonisomorphic strongly rigid).     

The effect of suspension on mean velocity profile

The vertical gradient of suspended sediment concentration often exists in estuarine and coastal regions. The existence of such concentration gradient, particular that of cohesive suspended sediment concentration gradient, affects the flow velocity profile. Based on the wave-current full depth combined model, k-? turbulent model is employed in this paper to simulate the effect of sediment concentration on the wave-current flow. A quantitative analysis of change mechanism of mean velocity profile is presented. The results show that the change mechanism of Eulerian mean current velocity under clear water is different from that under sediment-water mixed flow.     

核心素养下运用原始物理问题培养高中生的模型构建思维

原始物理问题的解决必须经历对物理现象的分析、抽象和建立物理模型的过程,物理模型构建思维是个体基于经验事实忽略物理现象或物理问题的次要因素、抓住主要因素构建物理模型的抽象概括过程,因此解决原始物理问题能够培养高中学生的科学思维之物理模型构建思维.     

Controlling Transport and Synchronization in Non-identical Inertial Ratchets

In this paper, transport control and synchronization are investigated between two periodically driven non-identical, inertial ratchets that are able to exhibit directed transport. One of the two ratchets is acting as a drive system, while the other one represents the response system. Based on the Lyapunov stability theorem, the essential conditions, under which the error nonlinear system is transformed into an equivalent passive system and globally asymptotically stabilized at equilibrium points, are established. With these results, synchronization, not only between two non-identical ratchets with known parameters but also between two different uncertain ratchets, are realized via adaptive passive controllers and parameter update algorithm. The direction of transporting particles can be dominated along expected one and it is useful to control the motion of tiny particles, ratchetlike devices in nanoscience.     

A Multifluorination Strategy Toward Wide Bandgap Polymers for Highly Efficient Organic Solar Cells

Creating new electron-deficient unit is highly demanded to develop high-performance polymer donors for non-fullerene organic solar cells (OSCs). Herein, we reported a multifluorinated unit 4,5,6,7-tetrafluoronaphtho[2,1-b : 3,4-b′]dithio-phene (FNT) and its polymers PFNT-F and PFNT-Cl. The advantages of multifluorination: (1) it enables the polymers to exhibit low-lying HOMO (≈−5.5 eV) and wide band gap (≈2.0 eV); (2) the short interactions (F⋅⋅⋅H, F⋅⋅⋅F) endow the polymers with properties of high film crystallinity and efficient hole transport; (3) well miscibility with NFAs that leads to a more well-defined nanofibrous morphology and face-on orientation in the blend films. Therefore, the PFNT-F/Cl : N3 based OSCs exhibit impressive FF values of 0.80, and remarkable PCEs of 17.53 % and 18.10 %, which make them ranked the best donor materials in OSCs. This work offers new insights into the rational design of high-performance polymers by multifluorination strategy.     

气相色谱法同时测定糙米中6种取代苯类及酰胺类农药残留

建立了气相色谱法同时测定糙米中二甲戊灵、丙草胺等6种农药残留量的方法。采用BP225大口径毛细管柱和氮磷检测器,外标法定量。样品加标回收率为80.4%～103.0%,相对标准偏差为2.9%～10.2%。各种农药的最低检出限分别为:戊草丹、二甲戊灵0.01 mg/kg ;丙草胺、氟酰胺、灭锈胺与苯噻酰草胺0.02 mg/kg 。该方法操作简便、快速、灵敏、准确,适于批量样品的测定。     

The Flow Analysis of Viscoelastic Fluid with Fractional Order Derivative in Horizontal Well

The fractional calculus approach is introduced into the seepage mechanics. A three-dimensional relaxation model of viscoelastic fluid is built. The models based on four boundary conditions of exact solution in Laplace space for some unsteady flows in an infinite reservoir is obtained by using the Laplace transform and Fourier sine and cosine integral transform. The pressure transient behavior of non-Newtonian viscoelastic fluid is studied by using Stehfest method of the numerical Laplace transform inversion and Gauss–Laguerre numerical integral formulae. The viscoelastic fluid is very sensitive to the order of the fractional derivative. The change rules of pressure are discussed when the parameters of the models change. The plots of type pressure curves are given, and the results can be provided to theoretical basis and well-test method for oil field.     

溶质在动态改性氧化锆液相色谱柱上的保留行为

分别采用硬脂酸、环糊精和十二烷基磺酸钠动态改性自制的ZrO2微球,研究了流动相中甲醇和改性剂浓度对苯酚及苯甲酸的衍生物、苯胺衍生物及芳香烃类化合物的色谱保留行为的影响。中性及碱性化合物的保留时间较短,色谱峰对称;酸性化合物保留时间较长,色谱峰拖尾较严重。改性氧化锆表现出反相色谱性能。     

基于大体积循环进样的低丰度蛋白质富集

发展了一种大体积循环进样方法,用于富集低丰度蛋白质。在优化的色谱分离条件下,通过增加蛋白质样品的上样体积提高低丰度蛋白质的绝对含量;进一步采用增加样品进样循环次数的方法提高蛋白质的富集效率。以猪肝提取蛋白质为样品,每次上样量500 μL的大体积11次循环进样。根据色谱峰的信号强弱,选择了在原始谱图中看不到色谱峰、有较少小峰和有较多小峰出现的时间段等有代表性的馏分进行研究。在中等极性的组分中,保留时间为11.38 min和12.58 min组分的富集效率分别提高了52倍和61倍,实验结果与理论富集效率相近。所发展的方法为生物蛋白质样品研究提供了一种新的富集制备及检测方法。