Fractal reaction kinetics

Classical reaction kinetics has been found to be unsatisfactory when the reactants are spatially constrained on the microscopic level by either walls, phase boundaries, or force fields. Recently discovered theories of heterogeneous reaction kinetics have dramatic consequences, such as fractal orders for elementary reactions, self-ordering and self-unmixing of reactants, and rate coefficients with temporal "memories." The new theories were needed to explain the results of experiments and supercomputer simulations of reactions that were confined to low dimensions or fractal dimensions or both. Among the practical examples of "fractal-like kinetics" are chemical reactions in pores of membranes, excitation trapping in molecular aggregates, exciton fusion in composite materials, and charge recombination in colloids and clouds.     

Picosecond kinetics of events leading to reaction center bacteriochlorophyll oxidation

A transient absorption spectrum has been measured in Rhodopseudomonas spheroides R26 reaction centers. Its salient features indicate that both the bacteriopheophytin and bacteriochlorophyll chromophores play a role in the excited state. Decay of this state yields a rise time for oxidation of the reaction center complex of about 150 picoseconds.     

Simultaneous studies of reaction kinetics and structure development in polymer processing

The simultaneous time-resolved study of structure development and reaction kinetics during polymer processing is an experimental method that has great potential in developing a deeper understanding of the parameters that govern the formation of structure and therefore polymer properties. A combination of synchrotron radiation small-angle x-ray scattering and Fourier-transform infrared spectroscopy experiments have been performed on a series of model segmented block copolyurethanes. These studies confirm that the driving force for structure development in polyurethanes is the thermodynamics of phase separation rather than hydrogen bonding.     

过硫酸盐活化技术处理地下水中的BTEX及其动力学

利用模拟苯、甲苯、乙苯和二甲苯(BTEX)污染的地下水,研究过硫酸盐(Na2S2O8)活化氧化处理BTEX污染。结果表明,过硫酸盐对BTEX污染的地下水具有很好的处理能力。当Na2S2O8/BTEX(摩尔比)=20,Na2S2O8/Fe2+(摩尔比)=8的时候,BTEX的处理效果最好,甲苯、乙苯和二甲苯去除率均能达到80%以上;而苯的去除率稍低。整个试验过程中体系均处于强氧化环境,pH值降至3以下。过硫酸盐对苯、甲苯、乙苯和二甲苯(BTEX)的去除过程均符合二级反应动力学:1/ct=kt+1/c0。     

邻苯二甲酸酯污染对黑土转化酶与脲酶反应动力学的影响

采用室内模拟法,以东北黑土为供试土壤,以邻苯二甲酸二甲酯(DMP)和邻苯二甲酸二丁酯(DBP)为代表,采用3,5-二硝基水杨酸法和靛酚蓝比色法测定土壤转化酶和脲酶的活性,研究邻苯二甲酸酯(PAEs)污染对黑土转化酶和脲酶活性及其反应动力学的影响。结果表明,PAEs抑制了黑土中转化酶和脲酶的活性。基于土壤酶活性和PAEs浓度作线性回归,求得黑土轻微污染的临界指标(ED₁₀):DMP污染黑土中转化酶和脲酶的ED₁₀分别为24.352和5.015 mg·kg^-1;DBP污染黑土中转化酶和脲酶的ED₁₀分别为16.911和8.677 mg·kg^-1。根据ED₁₀值越小越敏感的原则,判定黑土中脲酶对PAEs污染比较敏感,可将脲酶活性作为反映PAEs污染黑土的生化指标。DMP和DBP使黑土中转化酶和脲酶酶促反应动力学参数降低,属于反竞争抑制机制。PAEs可能改变黑土的碳氮循环及其生态系统功能,进而影响黑土的可持续利用。     

化学沉淀法处理高浓度氨氮废水的动力学研究

从化学沉淀法处理高浓度氨氮废水的反应动力学角度出发,研究了温度对反应速率的影响,然后又结合动力学条件对该反应pH的影响进行了探讨。结果表明,温度对化学沉淀法处理高浓度氨氮废水的影响并不显著,而pH值的影响却很明显,一般要求反应的pH值控制在8～10之间。     

Gravitational compression of crystallized suspensions of polystyrene spheres

In a crystallized suspension of polystyrene spheres, the earth's gravitational field, acting on a vertical column of material several centimeters high, produces an elastic deformation that can be readily observed through its effect on the crystal lattice constant. This effect has been used to determine that Young's modulus for the crystalline material ranges from 1 to 3 dynes per square centimeter, depending on the concentration of spheres.     

Efflux time of soap bubbles and liquid spheres

The efflux time, T, of gas from soap bubbles of radius, R, through their blow tube of length, 1, and radius, p, is given by the equation see pdf for equation where eta is the viscosity of the gas and omicron the surface tension of the bubble solution, all in centimeter-gram-second units. Similar relations between time and diameter were established for the flow from one bubble to another or from one bubble within another. The same relations hold for the flow of liquid spheres, suspended in another liquid of equal density, following Plateau's classic method. They have been extended to the flow of spheres to cylinders and catenoids of rotation. In all these cases the driving force is the surface or interfacial tension, creating an excess pressure as defined by Laplace's equation.     

Tubular packing of spheres in biological fine structure

The symmetrical arrangements of monomers into such cylindrical structures as microfilaments of actin, flagella of bacteria, microtubules of many organisms, and the protein coats of viruses can be specified by citing the index numbers of two or three sets of contact parastichies, or helical ranks of monomers, as has been done in classical studies of phyllotaxis. This specification has the form k(m, n) or k(m, n, m+n), where m, n, and (m+n) are parastichy numbers specifying screw displacements, and k is the jugacy, or frequency of rotational symmetry. For simple structures, k = 1. This notation has the advantage of terseness and of indicating the basic isometries of these helically symmetrical structures. Theoretical models of the packing of spheres whose centers lie on the surface of a cylinder have been investigated geometrically. Their symmetry properties are discussed. Parameters of these models, such as the angular divergence, alpha, the longitudinal displacement between successive spheres, h, the radius of the cylinder, and the angles of inclination of the parastichies, have been computed for representative patterns. The ultrastructural symmetry of several biological structures of this sort has been inferred by comparison with these models. Actin, for example, has the symmetry (1, 2), Salmonella flagella, 2(2, 3, 5), the tobacco mosaic virus, (1, 16, 17) and the microtubules of many higher organisms, (6, 7, 13).     

梨茎蜂发生与环境条件关系的研究

在江西南昌观察结果表明:梨茎蜂的发生为害与气象条件及梨树抽梢长度有很大关系。在3月底~4月初,当连续晴天、日最高气温在20℃以上时,成虫开始出枝为害,为害期6~8 d。当梨树新梢长度为8~12 cm时,成虫产卵达高峰期,此时为害最严重。     

Prevention of organ allograft rejection by a specific Janus kinase 3 inhibitor

Because of its requirement for signaling by multiple cytokines, Janus kinase 3 (JAK3) is an excellent target for clinical immunosuppression. We report the development of a specific, orally active inhibitor of JAK3, CP-690,550, that significantly prolonged survival in a murine model of heart transplantation and in cynomolgus monkeys receiving kidney transplants. CP-690,550 treatment was not associated with hypertension, hyperlipidemia, or lymphoproliferative disease. On the basis of these preclinical results, we believe JAK3 blockade by CP-690,550 has potential for therapeutically desirable immunosuppression in human organ transplantation and in other clinical settings.     

梨茎蜂及其天敌生物学特性初步研究

对梨茎蜂及其天敌梨茎蜂啮小蜂的生物学特性进行研究,分析梨茎峰啮小蜂的寄生情况,发现其寄生率在逐年提高,到2006年,寄生率已达到35.00%。     

Polyolefin spheres from metallocenes supported on noninteracting polystyrene

To obviate the destructive interaction of highly reactive metallocene catalysts with classical silica-based supports while retaining the advantage of supported catalysts, a noninteracting polystyrene support was developed. Supported catalysts for the polymerization of alpha-olefins are prepared by treating lightly cross-linked, chloromethylated polystyrene beads consecutively with a secondary amine, an ammonium salt of a weakly coordinating anion, and a neutral dialkylmetallocene. Catalytic sites are distributed homogeneously throughout the support particle, and the polymerization occurs within the bead, in contrast to traditional surface-supported metallocene catalysts. The copolymerization of ethylene and 1-hexene at 40 degreesC affords discrete spherical polyolefin beads with a size (0.3 to 1.4 millimeters) that varies according to the polymerization time.     

Preparation of photonic crystals made of air spheres in titania

Three-dimensional crystals of air spheres in titania (TiO2) with radii between 120 and 1000 nanometers were made by filling the voids in artificial opals by precipitation from a liquid-phase chemical reaction and subsequently removing the original opal material by calcination. These macroporous materials are a new class of photonic band gap crystals for the optical spectrum. Scanning electron microscopy, Raman spectroscopy, and optical microscopy confirm the quality of the samples, and optical reflectivity demonstrates that the crystals are strongly photonic and near that needed to exhibit band gap behavior.     

Starvation kinetics

Reactions that take place in shock waves are slow compared to the energy present in the translational degrees of freedom. One explanation for the slow burning in a detonation is that successive surface layers of the solid or liquid must react sequentially. Another mechanism, which can also account for the slowness of reactions in shock waves in gases, is the basis for starvation kinetics: the bond that is breaking must draw its activation energy from a vibrational reservoir in disequilibrium with the translational degrees of freedom of the reacting molecule.     

Nanoengineering of inorganic and hybrid hollow spheres by colloidal templating

Hollow silica and silica-polymer spheres with diameters between 720 and 1000 nanometers were fabricated by consecutively assembling silica nanoparticles and polymer onto colloids and subsequently removing the templated colloid either by calcination or decomposition upon exposure to solvents. Scanning and transmission electron microscopy images demonstrate that the wall thickness of the hollow spheres can be readily controlled by varying the number of nanoparticle-polymer deposition cycles, and the size and shape are determined by the morphology of the templating colloid. The hollow spheres produced are envisioned to have applications in areas ranging from medicine to pharmaceutics to materials science.