Materials Of Different Sizes Research Articles

Processing, properties and some novel applications of magnetic nanoparticles

Magnetic nanoparticles have been prepared by various soft chemical methods including self-assembly. The bare or surface-modified particles find applications in areas such as hyperthermia treatment of cancer and magnetic field-assisted radioactive chemical separation. We present here some of the salient features of processing of nanostructured magnetic materials of different sizes and shapes, their properties and some possible applications. The materials studied included metals, metal-ceramic composites, and ferrites.

Study of the Combined Temperature, Rate, and Size Effects on the Tungsten Crystalline Block Strength

Understanding the responses of materials of different sizes at various temperatures and strain rates is essential to evaluating the integrity and safety of microelectromechanical and nanoelectromechanical system devices under extreme loading conditions. Although material properties are size, rate, and temperature dependent in nature, little has been achieved in investigating the combined specimen size, loading rate, and temperature effects on the material properties. Based on the experimental and computational capabilities available, therefore, an attempt is made in this paper to formulate a hypersurface in spatial, temporal, and thermal domains to predict the combined size, rate, and temperature effects on the material properties of a tungsten crystalline block. It appears from the preliminary results that the proposed procedure might provide an effective means of bridging different spatial and temporal scales in a unified multi-scale modelling framework at different temperatures.

Monolithic polymer/carrier materials: Versatile composites for fine chemical synthesis

At our institutes composite materials were developed, which ideally allow to combine polymer functionalization utilized for organic synthesis with good mass transfer properties of monolithic carriers. Starting with a megaporous glass carrier material, a polymer is introduced into the pore volume of this support. During the precipitation co-polymerization small polymer spheres are formed, which are connected by polymer bridges, resulting in a rigid polymer monolith intruding the glass. This unique combination leads to versatile materials for organic synthesis, which can be used in a flow-through mode. Based on these monolithic materials with different polymer functionalities a wide variety of different chemical reactions was conducted such as selective reductions, Suzuki cross coupling reactions, nucleophilic substitutions and catalytic transfer hydrogenations. These reactions were performed with reactors constructed from monolithic materials of different sizes allowing to achieve production capacities ranging from the millimole range to several gramms.

Effects during plasma nitriding of shaped materials of different sizes

Plasma nitriding of shaped materials and materials of different sizes may yield non-uniform nitrided layers and/or reproducibility problems limiting its industrial-scale use to specific cases. The energy balance at the substrate surface and several non-uniformity effects related to geometry, size and sample position in the chamber during plasma nitriding are discussed. To investigate several of these effects, rods of SAE 1020 steel, of 8 mm in diameter, with different heights (1, 3, 5, 8 and 10 mm) were plasma nitrided in a mixture of N 2–H 2 (20%) at different temperatures (673, 773 and 843 K) and pressures (200 and 500 Pa). The samples were characterized by optical and electron microscopy, X-ray diffraction and microhardness testing. Hardness increases from the center to the edge of the samples. In the case of samples nitrided at 500 Pa, a macroscopically visible ring is obtained with low hardness inside the ring. The diameter of the ring increases for taller samples. The various formed phases, the thickness of nitrided layer and the microhardness of the samples are directly related to the height of the rod. This is associated with surface energy balance. The results show that the top surface temperature increases with height.

Miniaturized electrochemical flow cells.

Several novel types of miniaturized electrochemical flow cells are described. The flow cells are fabricated in fluorinated ethylene propylene using a novel technique where channels with inner diameters down to 13 microm are integrated with electrodes. The channel is formed by shrinking and simultaneous melting of a heat shrink/melt tubing around a channel template (a tungsten wire) and electrodes followed by removal of the channel template. The technique allows incorporation of different electrode materials of different sizes. The electrode configuration consists of one or two working electrodes inside the channel and a counter electrode located in the channel outlet reservoir. Electrode configurations with different channel and working electrode sizes, different electrode materials including carbon fibers, glassy carbon rods, poly(tetrafluoroethylene)/carbon composite material, and platinum wires, and different arrangements have been assembled. Hydrodynamic voltammograms in dual-electrode (generator-collector) experiments indicate good potential control for cells with 25-microm channels, while there is some iR drop in cells with 13-microm channels. Cells prepared with a cylindrical working electrode tangent and perpendicular to a flow channel show a flow rate dependence consistent with thin-layer cell behavior. Electrode areas can be made in the range of 10(-10)-10(-8) m2.

Polymer characterization by combining liquid chromatography with MALDI and ESI mass spectrometry.

High-performance polymers are complex mixtures of materials of different size and chemical composition and with different end groups and architecture. To determine the molecular heterogeneity of such systems, hyphenation of several techniques is required. The value of coupling mass spectrometry (MS) with separation techniques has already been recognized - such methods have proved to be among the most powerful for molecular characterization of complex polymer systems. The review focuses on matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) MS coupled with liquid chromatography (LC). Such hyphenation has been used for most polymer analysis by mass spectrometry coupled with separation techniques. The advantages and/or limitations of these techniques for polymer characterization are discussed. Future prospects are briefly outlined.

Effects of light intensity and quality on the obligate shade plantAglaonema commutatum.I. Leaf size and leaf shape

The effect of different light intensities and light qualities were studied on Aglaonema commutatum plants grown in controlled environments. Three light intensities—2.7, 5.4 and 20.0 junolm-2s-1 provided by two light sources (fluorescent and blended-light lamps) were tested on two plant materials of different size. When plants completed their adaptation to low light intensities (2.7 and 5.4 umol m“2s_1) readaptation to high irradiances (20.0 (xmol m-2s_1) was studied. Ten to twelve months were required for a leaf initiated in each light treatment to become fully expanded. The adaptation of this species to low light was far slower than other sun- or shade-plants. Plants grown at 2.7 |xmol m-2s~‘ expanded smaller and thinner leaves, with lower length: width ratio. These responses were affected by the size of the primordia at the beginning of the light treatments. Light quality affected these too but the responses were weak and lacked a defined pattern. The readaptation to high light intensity of plants adapt...

An erosion technique for the measurement of the shear stress field on a flat plate

A simple technique for the measurement of the shear stress field on a flat surface is presented. The technique is based on a correlation established between the erosion patterns of fine grains spread on a horizontal smooth plate and the known shear stress values obtained by conventional, well established, means for the flow produced by a round jet perpendicular to a flat plate. The critical shear stress values are found to be practically independent of the overall flow configuration and properties, and depend on the particle distribution and characteristics. Various granular materials of different sizes, shapes and densities were used at varying surface concentration and flow conditions. The experimental scatter of the results is small enough to make the erosion technique useful for quantitative assessment of wall shear stresses with an accuracy compatible with most practical applications. Furthermore it combines simplicity with promptness, given that in each run a curve of constant shear stress is obtained instead of a single local value.

セラミックインプラントを応用した咀嚼機能回復に関する実験的研究

At one month after two implants of single crystal alminum oxide were implanted in the mandible of adult monkeys, a superstructure was cemented connecting the two implants without connection with the natural teeth. Adaptation of the surrounding tissue of the implants under occlusal function were observed for 12 months from one month after cementing, and clinical, roentogenographic, light microscopic investigations were made. The results were as follows : 1. Clinically, the gingiva surrounding the implants healed favorably and showed findings similar to those of the adjacent natural teeth one month after cementing of the superprosthesis and thereafter. The implants were immobile by finger. The depth of pockets of the surrounding gingiva was within the range of 0.5-1.0mm for both S and T types 12 months after cementing. No deep pockets were formed and no marked difference in depth was seen from that of the gingival sulcus of the adjacent natural teeth. 2. Roentogenographically, no marked changes were seen between one month after and immediately after insertion of the superprosthesis. At three months and thereafter, however, lamina dura indicative of newly generated bone formation was observed around the implants for both S and T types. Lamina dura widened with time at 6 and 12 months. In one of the three monkeys of 3-month cases, a thin radiolucent area was seen between the implant and the bone. 3. In the gingival epithelium, down-growth of epithelium bordering the implant reached as far as infrabone in one of T type of 1-month cases, two each of S and T types of 3-month, one each of S and T types of 6-month, and one of S type of 12-month. In the others, the extent was slight. 4. At the lamina propria of the gingiva, inflammation was slight and the connective fibers were arranged densely surrounding the implants. In the surface facing the implant, however, they were running parallel to the axis. 5. In the cases of one month after insertion, the implant was surrounded by young new bone for both S and T types and bone trabeculae grew dense with time at 3, 6, and 12 months. Haversian canals were formed after 3 months. 6. In one of the three monkeys of 3-month cases, a layer of fibrous connective tissue interposed between the implant and the bone for both S and T types. Its width was within the range of 150-250μm for S type and 50-100μm for T type. In one of the three monkeys of 6-month cases, the screw of S type was in direct contact with the bone in some parts, and in other parts fibrous connective tissue interposed between the screw and the bone. The tissue width was within the range of 100-200μm. Except for these cases and 1-month cases, all the implants were in direct contact with the bone for both S and T types. 7. Scanning electron microscopically, in both 6-month and 12-month cases, epithelial cells and fibroblasts were attached at the post on the surface of the implant for S and T types. Where the implant was in direct contact with the bone, only many amorphous materials of different sizes were observed and cell-like structures were not seen. On the basis of the foregoing, it was confirmed that : (1) the surrounding tissue healed favorably even under functional conditions after insertion of implants of single crystal alminum oxide, (2) abnormal findings such as foreign-body reaction were not seen, (3) histo-compatibility was excellent, and (4) connecting two implants without connecting them with natural teeth enabled them to withstand biting pressure sufficiently, provided that load was not excessive physiologically. For use for longer duration, however, it was thought that oral hygiene and harmonious occlusion were important. For clinical application, it was thought the use of implants with discrestion would bring favorable results.

Ultrastructure of pycnidiospore walls and hyphae of Septoria nodorum

Fine-structural features of pycnidiospore walls and hyphae of Septoria nodorum were studied using thin sections stained with tannic acid, freeze-fracturing and freeze-etching techniques. The wall was composed of two layers, an outer electron-dense layer and an inner electron-transparent layer. Fine-structural features of the walls of hyphae and pycnidiospores appeared to be similar. The fracture faces of the cytoplasmic membrane of pycnidiospores were seen in the freeze-fractured cells. Thin fibrillar and globular material of different sizes partly covered the etched surface of the cell. The fibrillar material was best visualized with the freeze-etching technique. The globular material was clearly revealed using the rotatory shadowing technique.

Impact of particles of a granular material on a hard surface

The recovery coefficient for the particle velocities of a number of granular materials of different sizes and shapes are determined experimentally.

Preliminary Scanning Electron Microscope Observations on Orbitolina from Lower Cretaceous Glen Rose Formation, Texas: ABSTRACT

The foram Orbitolina occurs profusely on the outcrop. The fossils vary in size and shape, probably depending on whether they are either microspheric or megalospheric in their initial stage. Their internal structure as well as external features are being studied. Heretofore, only the specimens with a megalospheric initial stage have been studied in detail. For this purpose, many specimens have been etched with dilute hydrochloric and acetic acids, and the results have been quite satisfactory except for the extreme outer marginal zone of the test. Orbitolina, besides the embryonic apparatus, has a very complex and delicate internal structure. This structure is divided into 3 zones: the central complex, the radial, and the marginal. Preliminary observations were concentrated on the radial zone in general, and on the marginal zone in particular, as these are present in all specimens and play an important role in the test. The radial and marginal zones consist of chambers, and the chamber passages with connecting tubes, called stolons, cover and encircle the entire test in successive offsetting layers. This pattern is striking and beautifully delicate. The chamber walls, as well as the chamber passages and their stolons, apparently have been strengthened by the cementation of calcite crystals, as evidenced by the holes left after etching. Between the chambers, chamber passages and stolons, the living Orbitolina may have filled the space with crystals and foreign material of different sizes. The finest crystals were observed in the outermost part of the marginal zone and the coarser seem to have been confined to the chambers and chamber passages. Many specimens were etched to obtain the chamber, chamberlets, and cellules of the marginal zone. Only 1 specimen was successfully etched, yielding several chambers with chamberlets and cellules. After the crystals between the chamberlets and cellules were dissolved by acid, voids or empty spaces remained. These, when observed with transmitted light, appeared to be the features previously described as partitions and/or plates in axial and horizontal thin sections of Orbitolina. Without the aid of the scanning microscope, some minute details within Orbitolina either would not have been known, at least to the writer, or would have been difficult to interpret using only the stereoscopic microscope. These observations, and others to be made in the near future, will contribute toward making the morphology of Orbitolina more readily understood. End_of_Article - Last_Page 1692------------

514. RI製造における中性子自己遮蔽効果の評価

The thermal neutron flux distributions inside and outside cylindrical target materials of different sizes and different neutron absorption cross sections have been determined to provide information necessary for deciding the shape and arrangement of target materials for radioisotope production.A geometrical function independent of the size and cross section of the target material is presented, which approximates the neutron flux distribution experimentally obtained. Calculations have been made for hollow cylinders of infinitely thin wall and for thin disks. For such geometry the neutron flux decrease is proportional to the solid angle projected between source and target.The experimental values have been found practically in agreement with the values calculated by the formulas. The self-shielding effect of most kinds of targets for radioisotope production can well be estimated approximately by using the formulas presented.