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We have studied the effects of first and second generation sulphonylureas on the release of insulin and neuropeptide tyrosine (NPY) from hamster insulinoma tumour (HIT T15) cells and isolated rat islets. In the presence of 5.5 mmol/l glucose all sulphonylureas stimulated insulin release from the HIT cells (P<0.01 ANOVA, n> or =4) but only glibenclamide (GLIB, 10 micromol/l) stimulated the release of NPY (mean+/-s.e.m. control 11.1+/-1.3 vs GLIB 28.4+/-4.1 fmol/h per 10(6) cells, P<0001, n=16). In isolated perifused rat islets both glibenclamide (10 micromol/l) (control 3.5+/-0.3 vs GLIB 6. 3+/-0.2 fmol/min per islet, P<0.01, n=6) and tolbutamide (50 micromol/l) (control 4.7+/-0.1 vs TOLB 6.7+/-0.3 fmol/min per islet, P<0.01, n=6) enhanced glucose (8 mmol/l)-stimulated insulin release. However, only glibenclamide stimulated the release of NPY from the islets (control 3.4+/-0.8 vs GLIB 24.5+/-5 attomol/min per islet, P<0.01, n=6). Similar results were obtained in islets isolated from dexamethasonetreated rats. Glibenclamide treatment of HIT cells showed a prompt insulin release (10 min) while NPY secretion was slower (60 min), suggesting that internalization of the sulphonylurea is required to stimulate NPY release. Glibenclamide, the most common oral therapeutic agent in type 2 diabetes mellitus, is associated with release of the autocrine insulin secretion inhibitor, NPY.

The core part of the popular tracking-by-detection trackers is the discriminative classifier, which distinguishes the tracked target from the surrounding environment. Correlation filter-based visual tracking methods have the advantage of computing efficiency over the traditional methods by exploiting the properties of circulant matrix in learning process, and the significant progress in efficiency has been achieved by making use of the fast Fourier transform at detection and learning stages. But most existing correlation filter-based approaches are mainly restricted to translation estimation, which are susceptible to drifting in long-term tracking. In this article, a compressed multiple feature and adaptive scale estimation method is presented, which uses multiple features, including histogram of orientation gradients, color-naming, and raw pixel value to further improve the stability and accuracy of translation estimation. And for the scale estimation, another correlation filter is trained, which uses the compressed histogram of orientation gradients and raw pixel value to construct a multiscale pyramid of the target, and the optimal scale is obtained by exhaustively searching. The translation and scale estimation are unified with an iterative searching strategy. Extensively experimental results on the benchmark data set of scale variation show that the performance of the proposed compressed multiple feature and adaptive scale estimation algorithm is competitive against state-of-the-art methods with scale estimation capabilities in terms of robustness and accuracy.

Characterizing the physical properties of individual nanostructures is rather challenging because of the difficulty in manipulating the objects of sizes from nanometer to micrometer. Most of the nanomeasurements have been carried using STM and AFM. In this presentation, we demonstrate that transmission electron microscopy can be a powerful tool for quantitative measurements the mechanical, electrical and thermodynamic properties of a single nanostructure, such as a carbon nanotube or a nanoparticle.Using a customer-built specimen holder, in-situ measurements on the mechanical properties of carbon nanotubes has been carried out using the resonance phenomenon induced by an externally applied alternating voltage [1]. If an oscillating voltage is applied on the nanotube with tunable frequency, resonance can be induced (Fig. 1). The bending modulus is calculated from the resonance frequency. The bending modulus is as high as 1.2 TPa (as strong as diamond) for nanotubes with diameters smaller than 8 nm, and it drops to as low as 0.2 TPa for those with diameters larger than 30 nm.

Carbon tubes or spheres synthesized by arc-discharge are usually mixed with other byproducts, prohibiting direct measurements of their physical properties by the well established optical techniques because a large quantity of pure specimen is required. Electron energy-loss spectroscopy (EELS)is a unique technique that can be applied to probe the electronic structure of a single carbon tube or sphere. In this paper, the classical dielectric response theory is applied to calculate the EELSspectra acquired from a graphitic carbon sphere at various impact parameters. Graphite is an anisotropic dielectric medium whose dielectric function is described by a tensor. A graphitic carbon sphere is composed of concentric graphitic shells whose dielectric tensor in the spherical geometry, under the local response approximation, is given by (Figure 1)where are the dielectric function of graphite for an electric field perpendicular and parallel, respectively, to the c axis. In the non-relativistic approximation, the surface excitation is calculated by [1]

The catalytic activity and selectivity of nanosize colloidal platinum (Pt) nanocrystals may depend strongly on their sizes and shapes. To determine the shape dependent catalytic behavior of Pt nanocrystals, two key steps are involved. First, shape controlled Pt nanocrystals must be synthesized at a high yield. Secondly, the passivation layer on the nanocrystal must be removed in order to measure the catalytic selectivity and activity while the particle shape is preserved. The former had been successfully demonstrated by us that platinum nanoparticles with a high percentage of cubic-, tetrahedral- and octahedral-like shapes, respectively, can be synthesized by a colloidal chemistry method [1,2]. The growth of the shape controlled Pt nanocrystal has been found to be the result of kinetic process [3]. To measure the shape dependent catalytic activity and selectivity of the Pt nanocrystals, the capping polymer must be removed. One method could be annealing the nanocrystals supported on a substrate for evaporating the capping polymer. Several questions, however, must be considered: (1) how high does the annealing temperature need to be to remove the capping polymer while the particle shape is still preserved? (2) to what temperature is the particle shape still stable? (3) is there a temperature induced shape transformation due to surface diffusion? (4) how high is the melting point of the Pt particles? and (5) what is the effect of substrate on nanoparticle melting? These questions have not only fundamental importance, but also practical impact on the catalysis applications of the particles because the chemical reaction may take place at a higher temperature.

Ordered self-assembly of nanocrystals is scientifically interesting due to not only the unique properties of the nanocrystals, but also the collective properties of the assembly. Compared to lithography method, self-assembly is limited by a lack of control over the sizes of the ordered arrays, resulting in difficulties in characterizing their physical and chemical properties. New techniques are needed to manipulate the self-assembling process and the nanostructures formed.In this work, polystyrene (PS) spheres were used as the template to form large bulk ordered anatase nanostructure with cobalt doping. The ordered PS template was infiltrated with absolute alcohol solution of titanium butoxide. After the precursor was dried, it was treated at 160°C for 5 hours and then at 450°C for another 5 hours. To dope cobalt into the structure, the porous titania host was immersed in a heptane solution with cobalt carbonyl. After drying in vacuum at room temperature, it was treated at 160°C.

Some properties of transition metal oxides are related to the presence of elements with mixed valences. In electron energy-loss spectroscopy (EELS), the L or M ionization edges of transition-metal, rare-earth and actinide elements usually display sharp threshold peaks known as white-lines. EELS experiments have shown that a change in cation valence state introduces a significant change in the White-line intensity ratio [1]. With the use of valence state information provided by the white lines, an experimental approach is demonstrated here to map the valence state distributions of Mn and Co using an energy-filtered transmission electron microscope (TEM). A spatial resolution of ˜ 2 nm has been achieved. This technique should be particularly useful in studying valence states of cations in magnetic oxides.To map the distribution of ionization states, an energy window of ˜ 10 eV in width is required to isolate the L3from L2white lines (Figure 1).

Ordered assembly of hollow structures of silica and carbon have drawn much attention recently because of their applications in low-loss dielectrics, catalysis, filtering and photonics. The structure is ordered on the length-scale of the template spheres and the pore sizes are in submicron to micron range. Alternatively, ordered porous silica with much smaller pore sizes in nanosize range (< 30 nm), produced deliberately by introducing surfactant, has also been processed, in which the porosity is created by co-polymers. In this research, a new silica nanostructure with double length-scale ordered porosities was processed, one being at the submicron scale of hollow spheres created by a template of polystyrene (PS), and the other at nano-scale created by self-assembled co-polymers.Typical processing route includes three steps. Firstly, the ordered template of PS was created. The as-received PS with mean particle size of 203 nm was used as the raw material.

Silicon carbide is a versatile material possessing properties such as a wide energy bandgap, high thermal conductivity, high elastic modulus and high-temperature creep resistance, which enable it to be used in a variety of electronic, optical and structural applications. Chemical vapor infiltration/deposition (CVI/CVD)coupled with the application of a temperature gradient and forced flow of reagents is particularly suited to the production of SiCstructural composites due to the benefits of reduced infiltration time and uniform composite density. In this work, the growth and orientation of polycrystalline SiC on graphite during CVIis investigated using TEMand HRTEM.The composites studied possess a laminated matrix of alternating layers of carbon and SiCwhich were deposited by alternating the reagent streams from one layer to the next. Specimens for TEMexamination were obtained by cutting ∽1 mm thickness slices from the bulk sample with a low speed diamond saw.

Although crystal lattices can be determined reasonably well using high-resolution electron microscopy, determination of local chemistry at high spatial-resolution remains a challenge. An energy-filtering system has made it possible to perform chemically sensitive imaging in a transmission electron microscope (TEM). This type of imaging usually relies on the signal of the inner shell ionization edge, the intensity of which is affected by the threshold energy-loss and the ionization cross-section of the edge. Therefore, the spatial resolution of a core loss image image is strongly affected by the signal-to-noise ratio. In this respect, lower loss electrons from the plasmon or valence region of the energy loss spectrum (10-100 eV) are favorable for chemically sensitive imaging due to the much higher signal intensity, provided any delocalization effects are small in comparison to the required spatial resolution. Compositionally sensitive imaging using the aluminum plasmon energy-loss electrons has been shown to produce ∼2nm resolution for an atomically sharp Al/Ti interface.

Colossal magnetoresistive (CMR) has been observed in a class of oxides, La1-xAxMnO3(A = Ca, Sr, or Ba). Transition and rare earth metal elements with mixed valences are usually present in these materials for stimulating structural and chemical evolutions, leading to specific functionality. The partial substitution of trivalent La3+by divalent element A2+is balanced by the conversion of Mn valence states between Mn3+and Mn4+and the creation of oxygen vacancies as well, since the ionic structure of La1-xAxMnO3-yis proposed to bein which the valence conversion is the key for determining the material's properties. In practice, quantifying of oxygen vacancies is a challenge to existing microscopy techniques particularly for thin film specimens because of the strong effect from the defects at the substrate-film interface and the surface disordering.

Electroluminescence (EL)-based displays are an emerging technology for next generation flat panel displays. ZnS is an important component material for light emitting devices and EL-displays. To make this material useful for high efficiency and low voltage EL applications, the density of dislocations is required to be low. High quality single crystalline ZnS thin films have recently been grown by chemical beam epitaxy [1]. This paper focuses on studying the formation mechanism of stacking faults in the film and its relation with the interface structure between the substrate and the film [2].Stacking faults are the main defects present in the film (Fig. 1). All four stacking faults (sf) are intrinsic and sf1, growing towards the left-hand side from the interface, is only of short range since after crossing sf2the defect is terminated by a Shockley partial dislocation and the normal stacking sequence is restored. This is the mechanism that annihilates most of the stacking faults generated from the interface within the first 70 nm thickness range.

Transition and rare earth metal elements have played a vital role in synthesis of functional and smart materials because of their unique electronic structures and mixed valences. Experimental measurement of the valence states is thus important for understanding the mechanism which drives the functional properties. Lai1.xSrxCoO3-y(LSCO), for example, is an ionic conductor with potential applications in fuel cells and many other fields. In this type of materials, the anion deficiency is directly associated with the ratio of Co2+/Co3+(or Co3+/Co4+) present in the specimen. It is known that the anion deficiency of the material depends on the operation temperature, but a direct measurement of anion deficiency is a challenge to existing microscopy techniques. In this paper, we present the in-situanalysis of Co valence in LSCO using electron energy-loss spectroscopy (EELS) in a transmission electron microscope.LSCO thin films (with x = 0.5) were grown on polished MgO(00l) substrate by liquid source metal-organic chemical vapor deposition (MOCVD) method [1].

Nanocrystal materials are an emerging research field of chemistry, physics and materials science. The size and shape specificity of nanocrystals suggests them as building blocks for constructing selfassembly passivated nanocrystals superlattices (NCS's) or nanocrystals arrays (NCA) [1-6]. In this paper, NCAs of CoO with controlled tetrahedral shape are reported and their structural stability is examined by in-situ TEM.Cobalt oxide nanocrystals were synthesized by chemical decomposition of Co2(CO)8in toluene under oxygen atmosphere, as given in detail elsewhere [1].Sodium bis(2-ethylhexyl) sulfosuccinate (Na(AOT)) was added as a surface active agent, forming an ordered monolayer passivation (called the thiolate) over the nanocrystal surface. The particle size was controlled by adjusting the wt.% ratio between the precursor and Na(AOT). The as-prepared solution contained Co, CoO and possibly C03O4 nanoparticles, and pure CoO nanoparticles were separated by applying a small magnetic field, which is generated by a horseshoe permanent magnet in vertical direction.

Of recent interest in the science of nano-scale materials is the production and characterization of substances composed of ordered lattices of up to millions of identical nanometer scale particles. Silver nanocrystals of ∼ 4.5 nm diameter passivated with dodecanthiol surfactant were produced in the aerosol phase. Characterization of the individual particles and the subsequent supercrystals (SXs) resulting from their periodic packing was brought about using Mass Spectrometry, Transmission Electron Microscopy (TEM)/Electron Diffraction (ED), Scanning Electron Microscopy and Atomic Force Microscopy (AFM). It was determined that the micrometer and greater sized faceted SXs exhibited an hexagonal-close-packed (HCP) superstructure (fig.l) resulting in triangular shapes bounded by ﹛1100﹜ facets (fig. la); their platlet-like nature (∼20 nanocrystal layers thick) owing to their particular growth pattern. Knowledge of the growth mechanism is important to production of these materials on a macroscopic scale. Here we report a proposed growth model for these supercrystals.

Nanoparticles and the physical and chemical functional specificity and selectivity they possess, suggest them as ideal building blocks for two- and three-dimensional cluster self-assembled superlattice structures, in which the particles behave as well-defined molecular matter and they are arranged with long-range translation and even orientation order [1]. Self-assembled arrays involve self-organization into monolayers, thin films, and superlattices of size-selected nanoclusters encapsulated in protective compact organic coating. The macroscopic properties of the nanocrystal superlattice (NCS) are determined not only by the properties of each individual particle but by the coupling/interaction between nanocrystals interconnected and isolated by a monolayer of thin organic molecules.Periodic packing of nanocrystals is different from the 3-D packing of atoms. First, to an excellent approximation atoms are spherical, while nanoparticles can be faceted polyhedra, thus, the 3-D packing of particles can be critically affected by their shapes and sizes.

NiAl is an important high temperature structural material, with a high melting point (1640°C), low density and excellent high temperature oxidation resistance. The room temperature ductility of NiAl may potentially be improved with the use of nanocrystalline grain size. However, a key question concerning the application of nanostructured NiAl is about its structural stability at high temperature. The current study is thus focused on the investigation of the structural stability of nanocrystalline NiAl using in-situ transmission electron microscopy (TEM) and differential thermal analysis (DTA).Nanocrystalline B2-NiAl was prepared by ball milling (24 hrs) from elemental Ni and Al powders. Subsequent consolidation into bulk form was performed using dynamic consolidation employing a 3-capsule plate-impact fixture at approximately 400 m/s [1-3]. Powder nanocrystalline NiAl was dispersed on a holey carbon film for TEM observation. TEM specimens of shock compacted bulk NiAl nanocrystals were prepared by cutting, polishing, dimpling and ion milling.

ZnS particles consisting of nanocrystallites have potential applications as light emitters for displays. The possibility of encapsulating chemicals into porous particles and the temperature-controlled release of them could also be of interest in chemical engineering. The objective of this study is to determine the size distribution, shape and morphology of ZnS particles synthesized under different conditions, since they strongly influence the optical and electric properties.The ZnS powders were prepared by precipitation from homogeneous aqueous solutions, following a procedure described elsewhere1-3The initial solution consists of a zincsalt precursor dissolved in ultrapure water under acidic pH conditions. Adding Thioacetamide (TAA: CH3C(S)NH2) to this acidic solution at elevated temperature leads to the precipitation of ZnS nanocrystals. Four different types of zincsalt precursors were used to study their influence on the precipitation process and the final powder morphology: acetate (CH3COO), chloride (Cl-), trifluoromethanesulfonate (tFMS: CF3SO3-) and dimethyldithiocarbamate (dMdTC: S4N2C6H12-). The dried powder were subjected to 350°C and 700°C heat treatments, respectively.

A recent development in the study of nanocrystalline materials has been the self-assembly of passivated nanometer scale building blocks into larger, well ordered structures reaching the micron scale. Nanocrystal supercrystals (NCS) have been observed in metallic, semiconductor, and magnetic materials. In most cases the nanocrystals (NXs) are encapsulated in some inert medium that effectively protects the nanocrystal core and its unique electronic and optical properties. Here we describe the self-assembly of gold nanocrystals (∼4.5 nm core diameter), passivated with hexanethiol self-assembled-monolayers into ordered regions exhibiting a body-centered-cubic (bcc) superstructure. Transmission Electron Microscopy (TEM) imaging and Electron Diffraction (ED) experiments were used to characterize the NCSs and their resulting superstructures.A large agglomeration of NCSs can be seen in figure 1. One can clearly see regions of periodicity within the nanocrystal aggregation.

Magnetoresistance describes a phenomenon in which the electrical resistance of the material depends strongly on an externally applied magnetic field. Colossal magnetoresistance (CMR) was observed in a new class of oxides, (La,A)MnO3(A = Ca, Sr, or Ba), and the Magnetoresistance ratio of ΔR/R(H)> -100,000% has been reported in epitaxially grown La0.67Ca0.33MnO3films. The new types of intrinsic magnetoresistive oxides offer exciting possibilities for improved magnetic sensors, magnetoresistive read heads, and magnetoresistive random access memory (MRAM).The CMR magnetic oxides have a perovskite-type crystal structure with ferromagnetic ordering in the a-b planes and antiferromagnetic ordering along the c-axis (Figure 1). The ferromagnetically ordered Mn-O layers of the a-b planes are isolated by a non-magnetic La(A)-O monolayer. This spin-coupling structure is intrinsic. La1-xAxMn03 compounds having the extreme values x = 0, 1 are neither ferromagnetic nor good electrical conductors; they are semiconductors. Only compounds with intermediate values of x are ferromagnetic,

Quantitative analysis of structural information provided by transmission electron diffraction and imaging strongly relies on computer simulations. An important quantity in dynamic calculation is the “absorption” potential. The absorption here actually means that the electron is not absorbed by the specimen rather it is scattered out of the elastic state (or Bragg peaks) due to energy-loss and momentum transfer, resulting in a decrease in the intensity of the elastic wave. This is the effect of inelastic scattering (or diffuse scattering) on the Bragg reflected waves [1]. Almost all of the model calculations for the absorption potential have been based on the approximation o riginally introduced by Y o sh ioka, in which the Green's function is approximated by its form in free-space. Thus, the absorption potential is simplified into a non-local function that depends only on the nature of the inelastic scattering.

The ordering of size selected nanocrystaline particles into large, well ordered supercrystals has been under recent study. Here we describe the ordering of silver nanocrystals, of core diameter ca. 4.5nm, passivated with alkythiolate self-assembled monolayers. The faceted nanocrystals are found to size selectively condense into ordered supercrystals with edge lengths on the order of 0.1 to 0.5 microns. Further, evidence has been found in High Resolution TEM micrographs of packed monolayers of these same nanocrystals implying an orientational ordering of the silver nanocrystals’ atomic lattices within and co-aligning with the supercrystal’s “superlattice”. A three dimensional model using a truncated octahedron for the nanocrystal core morphology is constructed from this evidence into an FCC superlattice which fits the remaining experimental observations.Micrographs of the same region of a nanocrystal Ag supercrystal (NCASX) are shown in figure 1 under differing defocus conditions.

The selectivity and activities of platinum (Pt) particles strongly depend on their sizes and shapes. A technique has been recently reported for controlling the shapes and sizes of Pt particles [1]. Pt particles were prepared by bubbling Ar gas through the solution of K2PtCl4, and the Pt ions were reduced by flowing H2gas through the solution. The shape control was performed by changing the ratio of the concentration of the capping polymer material to that of the platinum cations used in the reductive synthesis of colloidal particles in solution at room temperature [2]. High percentage of cubic, tetrahedral and octahedral particles have been prepared at room temperature, making it possible for studying the chemical activities of particles with different shapes and facets. This paper aims to study the surface structures of Pt particles prepared by the shape-controlling synthesis technique using high-resolution transmission electron microscopy (HRTEM).