Two-particle dynamics on an electrode in ac electric fields

The relative motion between pairs of negatively charged latex particles 9.7 microm in diameter and deposited on an electrode was measured by optical microscopy and image analysis. At an rms field of approximately 30 V cm(-1), the two particles moved toward each other at frequencies below 500 Hz, but they separated at 1000 Hz. In the cases of aggregation, there are several interesting characteristics. First, when the center-to-center separation of a pair was initially 6 particle radii or more apart, a transient 'incubation' period of tens of seconds was observed before the particles began to move toward each other. Second, the two particles never came into contact, rather at long times the pair maintained a stationary gap between them equal to approximately one-half the particle radius. This stationary gap between particles was also observed for the aggregation of clusters of three or more particles. Finally, the rate of approach for a pair of particles decreased as the frequency increased. Larger fields are required to move particles together in ac compared to dc fields; at 30 Hz the ac field must be 130 times greater than the dc field to achieve the same rate of approach. Taking advantage of the qualitative and quantitative differences of the cooperative motion of particles in dc vs. ac fields, one should be able to re-position particles by alternating between these two modes. We demonstrated that the same pair of particles can be brought together at low frequency (100 or 200 Hz) and then separated at high frequency (1000 Hz).     

Grain boundaries and stacking faults in a Pm3n cubic mesophase

A monodendron that over a broad temperature range self-assembles in quasi-spherical supramolecular aggregates organized on a thermotropic cubic Pm3n lattice was examined by TEM. Grain boundaries were found parallel to the (1 0 0) and (3 2 0) planes. In well annealed specimens, in which grain boundaries are rare, two types of stacking fault were numerous, suggesting their relatively low energy. In the original Pm 3n lattice and in the two stacking fault arrangements, the supramolecular aggregates are distorted to an oblate shape, which is likely to be favoured by a crowded microscopic interface between core and tail moieties. Symmetry and phase selection for the ordered arrangement of amphiphilic molecules is discussed.     

EFFECT OF FORESTLAND AVAILABILITY BY OWNERSHIP TYPE ON LICENSE SALES FOR HUNTING: A SPATIAL APPROACH

Abstract The effect of forestland availability under different ownership types on license sales for hunting in nine Southeastern states is empirically evaluated. An equation that represents license sales for hunting is estimated assuming the sale of hunting licenses in a particular county is related to the characteristics of that county as well as the characteristics and license sales for hunting in its neighboring counties. The positive effects of the amounts of both national and private forestland on license sales reaffirm the potential benefits of maintaining forestland to stimulate hunting. The positive spillover effect of national forests on license sales for hunting suggests that availability and close access to hunting in national forests within neighboring counties are important in supporting hunting license sales in a county. This study contributes to the general understanding of the drivers affecting individuals’ decisions to use natural resources for hunting. Advances in natural resource modeling, specifically the spatial process model and geospatial data used in this research, make it possible to examine the interactions between the spatial dynamics and ownership attributes of the natural system, allowing policy makers to design natural resource management practices that respond to a system characterized by these interactions.     

尿素法合成高结晶度类水滑石

尿素的高温分解特性被用于控制层状化合物合成过程中的pH值。室温下尿素可与硝酸盐形成均一溶液，当其高温分解时可以保证溶液内部各点的pH值始终一致，因而可获得高结晶度的水滑石样品。利用该法可合成出Mg-Al、Zn-Al及Ni-Al类水滑石，但难以合成出Co-Al，Mn-Al及Co-Cr类水滑石，相信这与不同金属离子发生沉淀时所需的pH值有关。     

Embedded Surfaces for Symplectic Circle Actions

The purpose of this article is to characterize symplectic and Hamiltonian circle actions on symplectic manifolds in terms of symplectic embeddings of Riemann surfaces.More precisely, it is shown that(1) if(M, ω) admits a Hamiltonian S~1-action, then there exists a two-sphere S in M with positive symplectic area satisfying c1(M, ω), [S] 0,and(2) if the action is non-Hamiltonian, then there exists an S~1-invariant symplectic2-torus T in(M, ω) such that c1(M, ω), [T] = 0. As applications, the authors give a very simple proof of the following well-known theorem which was proved by Atiyah-Bott,Lupton-Oprea, and Ono: Suppose that(M, ω) is a smooth closed symplectic manifold satisfying c1(M, ω) = λ· [ω] for some λ∈ R and G is a compact connected Lie group acting effectively on M preserving ω. Then(1) if λ 0, then G must be trivial,(2) if λ = 0, then the G-action is non-Hamiltonian, and(3) if λ 0, then the G-action is Hamiltonian.     

Low field CIDNP of amino acids and proteins: characterization of transient radicals and NMR sensitivity enhancement

A new method for measuring and exploiting the magnetic field dependence of chemically induced dynamic nuclear polarization (CIDNP) is described. A solution of an amino acid or protein together with a flavin photosensitizer is irradiated with laser light at a position in the bore of a superconducting NMR magnet where the field is between 0.1 T and 7.0 T. The polarized sample is then transferred by rapid injection into an NMR tube at the centre of the magnet (at 9.4 T), where the spectrum is recorded. The observed ¹H CIDNP field dependence of tyrosine agrees well with the diffusion model of the radical pair mechanism. The field dependence of histidine, tryptophan and methionine CIDNP allows the g values of the transient radicals responsible for the polarization to be determined. Experiments in which amino acids compete for the photoexcited flavin indicate that methionine residues could be used as probes of surface accessibility, especially if the polarization is generated in low fields (～ 0.7 T) and detected in high fields (≥ 9.4 T). Possible extensions of the technique to study protein folding and the structures of partially denatured states of proteins are discussed.     

一类无穷矩阵代数的乘法序列连续性

设λ，μ是两个序列空间并有符号弱滑脊性，（λ，μ）是变换λ进入μ的无穷矩阵算子所成的无穷矩阵代数，本文研究了这类代数的强，Mackey、弱乘法序列连续性问题。     

Facile preparative route to alkanethiolate-coated Au38 nanoparticles: postsynthesis core size evolution

A facile preparative route to alkanethiolate (Cn) Au38 nanoparticles, where n = 4, 6, 8, 10, and 12, is described. Subnanometer-sized nanoparticles are initially produced by a modified Brust synthesis, which undergo core-size evolution upon removal of reaction impurities that have served as additional protecting layers. C4-C12 Au38 nanoparticles are prepared in approximately 300 mg quantities by the selective removal of reaction impurities with dimethyl sulfoxide. The prepared nanoparticles are 1.1-1.2 nm in core size, and all exhibit optical and electrochemical characteristics of Au38 nanoparticles. Voltammetry of these Au38 nanoparticles reveals that the energy gap between the first one-electron oxidation and the first reduction is rather insensitive to the ligand employed. By contrast, the energy gaps between the first and second oxidations and between the second and third oxidations are ligand-dependent; both substantially increase with ligand thickness. The charging energetics of alkanethiolate-coated Au38 nanoparticles can thus be described as a sum of electron addition energies and the discrete electronic energy levels of the Au38 core.     

Entropy of Partitions on Sequential Effect Algebras

By using the sequential effect algebra theory, we establish the partitions and refinements of quantum logics and study their entropies.