The role of interparticle and external forces in nanoparticle assembly

The past 20 years have witnessed simultaneous multidisciplinary explosions in experimental techniques for synthesizing new materials, measuring and manipulating nanoscale structures, understanding biological processes at the nanoscale, and carrying out large-scale computations of many-atom and complex macromolecular systems. These advances have led to the new disciplines of nanoscience and nanoengineering. For reasons that are discussed here, most nanoparticles do not 'self-assemble' into their thermodynamically lowest energy state, and require an input of energy or external forces to 'direct' them into particular structures or assemblies. We discuss why and how a combination of self- and directed-assembly processes, involving interparticle and externally applied forces, can be applied to produce desired nanostructured materials.     

Complex investigation of electronic structure transformations in Lead Sulphide nanoparticles using a set of electron spectroscopy techniques

It has been reported recently that kinetic energy of photoelectrons emitted from core levels decreases with decreasing of the nanocrystal size. This phenomenon is called the size shift. The size shift value is the same for donor and acceptor in the compound. The present work is aimed on the explanation of this phenomenon. Crystals of lead sulfide PbS with different size from 50 to 350 nm were grown by chemical bath deposition (CBD) technique from alkaline solution onto Si and GaAs substrates. The morphology and size of crystals were analyzed by high resolution scanning electron microscopy (HRSEM). Complex electron spectroscopy investigations of electronic structure were carried out. In recent experiments X-ray photoelectron spectroscopy (XPS) was used for determination of Pb 4f, and S 2p electronic level positions and their size shifts. To explain the observed dependences in this work, we applied the following methods: analysis of PbS valence band (VB) and Pb 5d electronic level structure in the range ∼0-30 eV by XPS, high resolution electron energy losses spectroscopy (HREELS) for analysis of band gap transformations and work function measurements by Kelvin probe microscopy for the contact potential difference (CPD). The influence of work function increasing, widening of the band gap, transformations in VB and inter-level energy distances with decreasing of nanocrystal size on the size shift function ΔE(R) is discussed.     

Jewish Nationalism,European Colonialism and Modernity: The Origins of the Israeli Public Housing System

Since the middle of the 19th century, housing the growing number of Jews immigrating to Palestine demanded resources that were not available to all immigrants. Housing projects were initiated either by Jewish philanthropists or building associations established by leaders of local communities. Numbers of immigrants rose sharply with the increasing involvement of the Zionist national movement in Palestine and the establishment of the British Mandatory regime. Most houses were built then by the private sector, widening the gap among different socio-economic groups. Only after the 1948 war and the termination of the colonial regime, was the newly established State of Israel able to initiate large-scale housing projects, due to its control of former Arabowned lands. The distribution of those lands raised conflicts between different sectors of the Israeli society, such as in the following two cases of public housing projects initiated in the Tel Aviv metropolitan area.     

Microstructure and corrosion resistance of alloys of the Mg-Zn-Ag system

New alloys of the Mg-Zn-Ag system are studied. The capacity for precipitation hardening and mechanical properties of extruded Mg-Zn alloys are determined depending on the degree of their alloying with silver. The microstructure of the alloys is studied with the help of light and electron microscopes; the grain sizes are measured before and after the extrusion. The hardness and the mechanical properties of extruded alloys are determined after single and double aging.     

Pelvic splenosis mimicking endometriosis, causing low abdominal mass and pain

Splenosis is the heterotopic autotransplantation of splenic tissue that usually follows traumatic splenectomy. The clinical significance of these splenic implants and the need for surgical removal is debatable. A case of a 35 year old woman, with post-traumatic splenectomy presenting with low abdominal pain and pelvic mass is reported. Laparoscopic removal of the pelvic splenic implants dispelled all complaints.     

Hierarchical assembly of ultranarrow alkylamine-coated ZnS nanorods: a synchrotron surface X-ray diffraction study

The packing of anisotropic ultranarrow nanoparticles ( r 相似文献   

In situ X-ray Diffraction Studies of a Multilayered Membrane Fluid under Confinement and Shear

The structure of a fluid membrane system composed of surfactant-co-surfactant-oil-water mixtures has been investigated under confinement and shear conditions. Small angle x-ray scattering (SAXS) was employed with a second generation x-ray surface forces apparatus (XSFA-II) to study the time evolution of the orientational structure of the lamellar fluid under oscillatory shear. In a regime of relatively big confinement gap (800 m) and small shear amplitude (40 m), direct evidence of an orientational phase separation behavior, where a surface boundary layer adopts different orientation and separates from the bulk region, was observed for the first time. Under continuous shearing, the surface boundary layer grows in thickness and aligns towards a shear-favored (low friction) state while the bulk orientation remains unchanged. To further investigate the effects of surface confinement, we spatially mapped, in 1 m sections, the orientation structure of the lamellar fluid sample confined between two glass surfaces using a micro-focused x-ray beam produced by a linear Bragg–Fresnel lens at the Advanced Photon Source. The data confirmed the expected trend that the smectic domains align progressively better with respect to the surface as they approach the surface.     

A New Nonparametric Pairwise Clustering Algorithm Based on Iterative Estimation of Distance Profiles

We present a novel pairwise clustering method. Given a proximity matrix of pairwise relations (i.e. pairwise similarity or dissimilarity estimates) between data points, our algorithm extracts the two most prominent clusters in the data set. The algorithm, which is completely nonparametric, iteratively employs a two-step transformation on the proximity matrix. The first step of the transformation represents each point by its relation to all other data points, and the second step re-estimates the pairwise distances using a statistically motivated proximity measure on these representations. Using this transformation, the algorithm iteratively partitions the data points, until it finally converges to two clusters. Although the algorithm is simple and intuitive, it generates a complex dynamics of the proximity matrices. Based on this bipartition procedure we devise a hierarchical clustering algorithm, which employs the basic bipartition algorithm in a straightforward divisive manner. The hierarchical clustering algorithm copes with the model validation problem using a general cross-validation approach, which may be combined with various hierarchical clustering methods.We further present an experimental study of this algorithm. We examine some of the algorithm's properties and performance on some synthetic and standard data sets. The experiments demonstrate the robustness of the algorithm and indicate that it generates a good clustering partition even when the data is noisy or corrupted.