A study of spin fluctuations in antiferromagnetic metals described by a nesting-type model

The effect of spin fluctuations in antiferromagnetic metals described by a nesting-type model is studied for paramagnetic states and for commensurate spin-density-wave states by the application of the renormalized spin fluctuation theory to the Rice model as well as to the Shibatani-Motizuki-Nagamiya model. Comparison is made between the spin fluctuation property in the nesting-type model and that in a band-type model; in the latter all the portions of the band are considered to be responsible for the antiferromagnetism. Although the effect of spin fluctuations in the nesting-type model is far less significant than that in the band-type model, this effect does become notable as the nesting between the two bands is made worse.     

Selective dimerization of diisobutylene by oxo acids: Synthesis of isobutylene tetramer

Isobutylene tetramers (IB₄) were obtained in high yield by the cationic dimerization of commercial diisobutylene (DIB) (2,4,4-trimethyl-1-pentene with isomeric impurities) with CF₃SO₃O₃H or CH₃COClO₄ as catalyst. The best IB₄ yields (80–90%) were achieved at 0–30°C in nonpolar solvents (n-hexane and CCl₄). The major components in the IB₄ produced under these conditions were 2,2,6,6,8,8-hexamethyl-4-methylenenonane (8) and 2,2,4,6,6,8,8-heptamethyl-4-nonene (9) that arose via simple linear dimerization of DIB. The yield of IB₄ was almost independent of the monomer concentration ranging from 10 to 50 vol % at 0°C, but decreased at higher temperatures (>50°C) or in a polar solvent [(CH₂Cl)₂] because of the formation of higher oligomers and side reactions such as cracking. A Lewis acid catalyst (AlEtCl₂) resulted in a very complex mixture of C₁₂–C₂₀ hydrocarbons at 0°C in CCl₄; the yield of IB₄ was less than 40%. The catalytic difference between oxo acids and metal halides is discussed.     

Transit-time-induced microwave negative resistance in Ga1?xAlxas?GaAs heterostructure diodes

Following recent experimental observations by Immorlica and Pearson that the saturated drift velocity of electrons in Ga0.62Al0.38As is considerably lower than in GaAs, a heterostructure transit-time diode is proposed. The resulting device is shown to have a relatively large negative resistance, a small Q factor and low noise measure. Large-signal calculations predict a maximum efficiency of 18%.     

Effect of mixing on melt flow properties of high-density polyethylene

An investigation has been made into the effect of mixing by a screw extruder upon the molecular characteristics and the melt flow properties of high-density polyethylene. The crosslinking between molecules predominates over the scission of a molecule at an early stage of mixing, but with further increase in the degree of mixing, this situation reverses itself to bring about the formation of branched polymers. Static flow and dynamic viscoelastic properties of molten high-density polyethylene change considerably with increase in the degree of mixing. The apparent viscosity drops rather sharply after mixing. The dynamic properties for the original resin show smaller frequency dependence of the viscosity and larger dependence of the rigidity than those for extrudates. The relaxation spectra become broader with increase in mixing. These may mainly be due to the change of the molecular characteristics of high-density polyethylene with mixing by an extruder.     

Dataflow computing and eager and lazy evaluations

Eager and lazy evaluations in a dataflow model are proposed, Such evaluation enables nonstrict evaluation, structure data manipulation and nondeterminate computation. Several dataflow computation models are discussed from the viewpoint of their by-value and by-reference mechanisms, i. e., their token to data correspondence. It is shown that effective implementation is achieved by unifying both mechanisms. This implies the effective implementation of the lenient cons and lazy cons concept in list manipulation. Nonstrict list manipulation is shown to be useful for stream-oriented processing, and for nondeterminate computation combined with the nonstrict primitive operator, Arbiter. Several sample programs are included to show that concurrent processes and object-oriented programs can be intuitively described in functional language.     

Regulation of protein binding toward a ligand on chromatographic matrixes by masking and forced-releasing effects using thermoresponsive polymer

A novel concept of affinity regulation based on masking and forced-releasing effects using a thermoresponsive polymer was elucidated. Affinity chromatographic matrixes were prepared using either poly(glycidyl methacrylate-co-ethyleneglycol dimethacrylate) or poly(glycidyl methacrylate-co-triethyleneglycol dimethacrylate) beads immobilized with ligand molecule, Cibacron Blue F3G-A (CB), together with poly(N-isopropylacrylamide) (PIPAAm), a polymer with a cloud point of 32 degrees C. Two different lengths of spacer molecules were used for the immobilization of CB while maintaining the PIPAAm size constant. Chromatographic analyses using bovine serum albumin as a model protein showed a clear correlation between spacer length and binding capacity at temperatures lower than the lower critical solution temperature (LCST) of PIPAAm. The binding capacity under the LCST was significantly reduced only when the calculated spacer length was shorter than the mean size of the extended PIPAAm. Furthermore, the adsorbed protein could be desorbed (released) from the matrix surface by lowering the temperature to below the LCST while maintaining other factors such as pH and ion strength. Selective recovery of human albumin from human sera was demonstrated using this newly developed thermoresponsive affinity column.     

Development of optical coatings for 157-nm lithography. II. Reflectance,absorption, and scatter measurement

The total loss that can be suffered by an antireflection (AR) coating consists of reflectance loss, absorption loss, and scatter loss. To separate these losses we developed a calorimetric absorption measurement apparatus and an ellipsoidal Coblentz hemisphere based scatterometer for 157-nm optics. Reflectance, absorption, and scatter of AR coatings were measured with these apparatuses. The AR coating samples were supplied by Japanese vendors. Each AR coating as supplied was coated with the vendor's coating design by that vendor's coating process. Our measurement apparatuses, methods, and results for these AR coatings are presented here.     

Dextran-magnetite complex: conformation of dextran chains and stability of solution

Three kinds of dextran-magnetite (DM) complexes were prepared using alkali-treated dextrans with molecular weights of 1900, 4200 and 9600, respectively. The number of dextrans binding to a magnetite core was determined. The number was proportional to the area of core surface and the area occupied by a dextran was 2.5 nm² for molecular weight of 1900, 2.8 for 4200 and 3.8 for 9600. The binding of dextrans to core may be conditioned by the conformation of dextran chains in water (possibly by the steric hindrance between dextrans covering core). Stability of the DM solution was examined at 80 °C. Aggregation and/or precipitation of DM particles were observed within two weeks. The stability of DM solution was found to increase with increasing molecular weight of dextran. The dissociation of dextran from the core may cause the aggregation and subsequent precipitation of DM particles (the dissociation constant at 20 °C, 3.7 x 10 ^-6 for a molecular weight of 1900 and 5.4 x 10⁷ for 9600).