Phase transition and the packing structure of the side mesogenic groups of liquid crystalline side-chain copolymers

Summary Copolymers consisting of cholesteryl 11-methacryloyloxy-undecanoate (ChMO-10) and t-buthyl methacrylate (t-BMA) were studied by DSC method and by small angle X-ray scattering method (SAXS). Although homopolymer (pChMO-10) has two different packing structures which are a single-layer packing structure and a two-layer packing one, copolymers (co-pChMO-10-t-BMA) have only the single layer packing one in their mesophase. Furthermore, transition entropy at a clearing point of co-pChMO-10-t-BMA (80/20) is larger than that of pChMO-10. Adequate distance of the mesogenic groups in the direction of a short axis of the mesogenic groups, produced by introduction of non-mesogenic units, seems to stabilize the single-layer packing structure.     

Image-based magnification calibration for electron microscope

Magnification calibration is a crucial task for the electron microscope to achieve accurate measurement of the target object. In general, magnification calibration is performed to obtain the correspondence between the scale of the electron microscope image and the actual size of the target object using the standard calibration samples. However, the current magnification calibration method mentioned above may include a maximum of 5 % scale error, since an alternative method has not yet been proposed. Addressing this problem, this paper proposes an image-based magnification calibration method for the electron microscope. The proposed method employs a multi-stage scale estimation approach using phase-based correspondence matching. Consider a sequence of microscope images of the same target object, where the image magnification is gradually increased so that the final image has a very large scale factor $S$ (e.g., $S=1\!,\!\!000$ ) with respect to the initial image. The problem considered in this paper is to estimate the overall scale factor $S$ of the given image sequence. The proposed scale estimation method provides a new methodology for high-accuracy magnification calibration of the electron microscope. This paper also proposes a quantitative performance evaluation method of scale estimation algorithms using Mandelbrot images which are precisely scale-controlled images. Experimental evaluation using Mandelbrot images shows that the proposed scale estimation algorithm can estimate the overall scale factor $S=1\!,\!\!000$ with approximately 0.1 % scale error. Also, a set of experiments using image sequences taken by an actual scanning transmission electron microscope (STEM) demonstrates that the proposed method is more effective for magnification calibration of a STEM compared with a conventional method.     

Characterization of a Large-Scale Nondoped YBa2Cu3O7−x Superconductor Prepared by Plastic Forming Without High-Pressure Molding

A slurry containing YBa₂Cu₃O_{7− x} particles and a fine YBa₂Cu₃(OH) _x colloid solution was prepared, and a large-scale bulk YBa₂Cu₃O_{7− x} superconductor (about 50 mm × 35 mm × 2 mm) was produced by plastic forming without high-pressure molding. The samples molded from the slurry were dried and then fired at 1223 K in air. X-ray diffraction data indicated that the samples had the characteristic orthorhombic YBa₂Cu₃O_{7− x} structure. Measurements of electrical resistance were carried out between 300 and 50 K by the standard four-probe DC electrical measurement. The samples began superconducting at an onset temperature around 92 K, and the full-transition temperature (critical temperature) ( T _c) was 88.7±1.4 K. The critical current density ( J _c) measured at 77 K was about 440 A/cm², the value of J _c was improved by the heat treatment under an oxygen atmosphere, and J _c=1.6 × 10³ A/cm² was observed. Under the magnetic field (B=1 T), the sample held its superconductivity, and demonstrated that this method can be used to produce the magnetic shielding used in magnetic resonance imaging diagnosis.     

Phase separation temperatures in the polystyrene—poly(α-methyl styrene)—methylcyclohexane system

The phase separation temperatures (PST) in the ternary system polystyrene (PS) (M_w = 1.75 × 10⁴ g mol⁻¹ — poly(α-methyl styrene) (PαMS) (M_w = 6.0 × 10⁴) — methylcyclohexane (MCH) and the binary systems PS-MCH and PαMS-MCH have been determined by using a He---Ne laser light-scattering apparatus over the total polymer weight fraction (W_{PS + PαMS}) range of 0.018 to 0.80 and various polymer blend ratios. The PST determined at a scattering angle of 0° agreed with those at 90° for the binary systems over polymer concentrations of 0.1 to 0.7 and for the ternary over W_{PS + PαMS} of higher than 0.3. Deviations of the PST determined at an angle of 90° from those at 0° were observed in the ternary system when W_{PS + PαMS} was lower than 0.3. Two phase separation temperatures, at which the intensity scattered from zero angle changed discontinuously, are observed at concentrations lower than W_{PS + PαMS} = 0.042 in the ternary system. The PST in the ternary system decreases monotonically with increasing W_{PS + PαMS} over 0.3 to 0.7. The phase diagram for the PS-PαMS-MCH system at W_{PS + PαMS} = 0.8 is characterized by a maximum PST around − 14°C.     

PERFORMANCE OF A PRESSURIZED TWO-STAGE FLUIDIZED GASIFICATION PROCESS FOR PRODUCTION OF LOW-BTU GAS FROM COAL CHAR

A two-stage pressurized fluidized-bed gasification process has been developed to produce low-heating value gases from coal char. The reactor was 0.075 m id. and 1.4 m long, and gasification experiments were conducted under pressures up to 790 kPa and at temperatures up to 1323 K. A partition disc was used to divide the fluidized bed into two stages, using the first stage as a partial combuster and gasifier and the second stage as a gasifier. The disc was designed to control compositions of coal char particles in both stages so that the heat required for the endothermic gasification reaction in the second stage can be provided by the heat of combustion in the first

For conditions examined here, the disc with an opening ratio of 40° was found to give optimum distribution of the char particles in both stages without ash agglomeration. It was also shown that all oxygen gas was completely consumed within the first stage

The heating value of the product gas increased with the char feed rale. However, there may be an oplimum Teed ratio of char and sand-particles since the higher char feed rate causes more frequent ash agglomeration as well as less carbon conversion     

Direct hydroxylation of aromatic compounds by a palladium membrane reactor

Direct hydroxylation of aromatic compounds was effectively achieved by using a newly developed Pd membrane reactor in which the Pd membrane is thin enough (ca. 1 μm) to allow permeation of hydrogen below 500 K. In this reactor, the active oxygen species is formed on the surface of Pd via the reaction between oxygen and permeated hydrogen from opposite sides of the membrane. Hydroxylation occurs on the surface of Pd via reaction of the aromatic compound and active oxygen. In the reaction of benzene at a reaction temperature of 423 K, the reactor achieved a benzene conversion of 15% and a phenol selectivity of 95%. An increase in reaction temperature, however, caused simultaneous hydrogenation. In the reaction of methyl benzoate, the reaction products were not only methyl salicylate, which is a hydroxylation product, but also numerous hydrogenation and oxidation compounds via side reactions. These side reactions were related to the gas balance between oxygen and hydrogen; oxygen-rich conditions caused complete oxidation, whereas oxygen-poor conditions (i.e., high amount of permeated hydrogen) induced high hydrogenation activity.     

Instrumented charpy impact test of epoxy resin filled with irregular-shaped silica particles

The effect of particle size on the impact properties of an epoxy resin has been studied. This resin was filled with irregular-shaped silica particles prepared by crushing fused natural raw quartz. These particles were sorted into six groups of different mean sizes ranging from 2 to 47 μm. The impact properties were measured by an instrumented Charpy type impact tested, which can record a load-displacement curve during impact fracture. The impact absorbed energy (U) was measured using specimens having a U-shaped blunt notch, and the impact fracture toughness (K_CI) was measured using specimens having a sharp crack introduced by a fresh razor blade. As the particle size decreased. U increased and K_CI decreased. The fractured surfaces and crack tip regions were observed using a scanning electron microscope to clarify the above phenomena.     

Dynamic mechanical properties of crosslinked polyisoprene under deformation

Summary Molecular motions of elastomers under deformations were observed through dynamic mechanical measurements. Composite master curves of dynamic moduli E and E and loss tangent tan over a wide range of frequency and in a state of elongation were obtained by the time-temperature superposition procedure. It is found that both moduli increase with strain, . The slope of the dispersion curve of E become more gradual with the increase in , while that of E is almost unchanged. The increment of E is generally larger than that of E, which does not agree with the N. W. Tschoegl prediction, E ^* ()=f() E _o ^* (), where E ^* () and E _o ^* () are complex moduli at the strain of and O, respectively, and f() is the function of only . The difference in the strain dependence of E from E was found to correspond to the strain dependence of the equilibrium modulus.     

Catalytic conversion of organosilanes. 1. Disproportionation of alkylsilanes over solid acid and base catalysts

Catalytic conversions of diethylsilane (E2), triethylsilane (E3) and diethyldimethylsilane (E2M2) were examined at 373–573 K in a closed recirculation reactor by using various solid acid and base catalysts. Basically two types of reaction were found: decomposition and disproportionation. Strongly acidic catalysts such as silica-alumina (SA), alumina and sulfated ZrO₂ (SO₃/ZrO₂) exhibited high disproportionation activity, while weakly acidic and basic catalysts showed low catalytic activity and gave mainly cracking products. The order of disproportionation reactivity of three silanes tested were E2M2 > E3 > E2 over SA and SO₃/ZrO₂, while it was E2E3 > E2M2 over an alumina catalyst.     

A study of brittle-ductile transition in polyethylene

The brittle-ductile transition temperatures (BDTT) of polyethylenes with different degrees of crystallinity, such as LDPE, LLDPE, MDPE, and HDPE, were evaluated using Charpy impact test. The effect of the specimen cooling condition on the BDTT was a main concern in the study. A rise in the cooling plate temperature (Tp) for high density resins brought about a fall in BDTT and an increase in the Charpy impact value Et. However, embrittlement was observed during a tensile test for HDPE samples with a rise in Tp. A crack shielding effect by microvoid formation is proposed as the toughening mechanism for HDPE.