Rational proper holomorphic maps from B n into B 2 n

In this paper, we will investigate rational proper holomorphic maps from Bⁿ into B²ⁿ, when n4.Mathematics Subject Classification (2000): 32H35Partially supported by Grant-in-Aid for Scientific Research (C) no. 14540195 from Japan Society for the Promotion of Science, 2004.Acknowledgement The author thanks the referee for helpful comments and suggestions.     

A Pair in a Crowd of Unit Balls

Let F be a family of mutually nonoverlapping unit balls in the n -dimensional Euclidean space Rⁿ. The distance between the centres of A,B   F is denoted by d(A, B). We prove, among others, that if d(A, B)  <  4 and n ≥  5, then A andB are always visible from each other, that is, a light ray emanating from the surface of A reaches B without being blocked by other unit balls. Furthermore, if d(A, B)  < 2n / 2, then any small “shake’ of F can make A, B visible from each other.     

Revisiting molecular adsorption: unconventional uptake of polymer chains from solution into sub-nanoporous media

Adsorption of polymers from the solution phase has been extensively studied to cope with many demands not only for separation technologies, but also for the development of coatings, adhesives, and biocompatible materials. Most studies hitherto focus on adsorption on flat surfaces and mesoporous adsorbents with open frameworks, plausibly because of the preconceived notion that it is unlikely for polymers to enter a pore with a diameter that is smaller than the gyration diameter of the polymer in solution; therefore, sub-nanoporous materials are rarely considered as a polymer adsorption medium. Here we report that polyethylene glycols (PEGs) are adsorbed into sub-nanometer one-dimensional (1D) pores of metal–organic frameworks (MOFs) from various solvents. Isothermal adsorption experiments reveal a unique solvent dependence, which is explained by the balance between polymer solvation propensity for each solvent and enthalpic contributions that compensate for potential entropic losses from uncoiling upon pore admission. In addition, adsorption kinetics identify a peculiar molecular weight (MW) dependence. While short PEGs are adsorbed faster than long ones in single-component adsorption experiments, the opposite trend was observed in double-component competitive experiments. A two-step insertion process consisting of (1) an enthalpy-driven recognition step followed by (2) diffusion regulated infiltration in the restricted 1D channels explains the intriguing selectivity of polymer uptake. Furthermore, liquid chromatography using the MOFs as the stationary phase resulted in significant PEG retention that depends on the MW and temperature. This study provides further insights into the mechanism and thermodynamics behind the present polymer adsorption system, rendering it as a promising method for polymer analysis and separation.

Self-entangled large polymeric coils in solution can go into sub-nanometer pores by spontaneous uncoiling, which has been considered unfavorable in conventional molecular adsorption models.     

Photomechanical bending of salicylideneaniline crystals

Platelike microcrystals of N-3,5-di-tert-butylsalicylidene-3-nitroaniline repeatedly bend and straighten upon alternate irradiation with UV and visible light. The mechanism of bending was elucidated by X-ray crystallographic analyses before and after photoirradiation.     

Selective recovery of gold(III) using cotton cellulose treated with concentrated sulfuric acid

Novel utilization of cotton cellulose was developed by chemically modifying with concentrated sulfuric acid to prepare a novel kind of adsorption gel for gold. The adsorption behaviors of the gel were investigated for various metals from acidic chloride media. The gel was found to be highly selective for Au(III) over other precious and base metals tested over the whole concentration range of hydrochloric acid. The maximum adsorption capacity for Au(III) was evaluated as 6.21 mmol/g at 303 K. The amount of adsorbed Au(III) was increased with increasing temperature. A kinetic study for the adsorption of Au(III) at various temperatures confirmed the endothermic adsorption process following pseudo-first order kinetics. The activation energy was evaluated as 78.8 kJ/mol. Interestingly, it was found that the adsorbed Au(III) was reduced to elemental form which was evidenced by the clearly visible elemental gold particles which was further confirmed by means of the X-ray diffraction spectrum and optical microscope image of the gel after the adsorption of Au(III). The mechanism of Au(III) adsorption on the cotton gel and its reduction to elemental gold was proved from the results of IR-spectra. The main mechanism could be explained in terms of the coordination of Au(III) to oxygen atom of C–O–C linkage of cross linked cotton gel and to the oxygen atoms of the hydroxyl groups at C₂ and C₃ atoms of pyranose ring of cotton cellulose followed by the reduction to metallic gold. The adsorbed gold in the cotton gel can easily be recovered by incineration.     

Ag(I) ion mediated formation of a C-A mispair by DNA polymerases

Silver turns up the A-C: In the presence of Ag(I) ions, a DNA polymerase incorporated deoxyadenosine (from dATP) at the site opposite cytosine in the template strand to afford the full-length product (see scheme), meaning that DNA polymerases prefer a C-Ag(I)-A base pair to the more thermodynamically stable C-Ag(I)-C base pair.     

Reverse enantioselectivity in the lipase-catalyzed desymmetrization of prochiral 2-carbamoylmethyl-1,3-propanediol derivatives

Enantioselective acetylation of 2-carbamoylmethyl-1,3-propanediol derivatives was catalyzed effectively by lipase PS to give monoacetates with high enantioselectivity: The enantioselectivity depended on the 2-carbamoylmethyl groups. The reaction of N-monoalkylcarbamoylmethyl-1,3-propanediol afforded the monoacetate with the (S)-configuration, whereas N,N-dialkylcarbamoylmethyl-1,3-propanediol gave the monoacetate with the (R)-configuration.     

Synthesis of magnetite nanoparticles for AC magnetic heating

Magnetite particles with different average diameter (D_m) suitable for magnetic fluid hyperthermia (MFH) were synthesized by controlled coprecipitation technique. In this method, the reaction pH was stabilized using the pH buffer and the average particle diameter decreased with increasing reaction pH. The size-dependent magnetic behavior of the magnetite nanoparticles was studied and the optimum size range required for magnetic fluid hyperthermia (MFH) has been arrived at. Among the samples studied, the maximum specific absorption rate of 15.7 W/g was recorded for the magnetite sample with D_m of 13 nm, when exposed to an AC magnetic field strength of 3.2 kA/m and a frequency of 600 kHz. The AC magnetic properties suggested that the size distribution of the sample was bimodal with average particle size less than ∼13 nm.     

Heteroepitaxial film growth of layered compounds with the ZrCuSiAs-type and ThCr2Si2-type structures: From Cu-based semiconductors to Fe-based superconductors

FeAs-based layered superconductors such as F-doped LaFeAsO have recently been investigated intensively because of their high superconducting transition temperatures. Epitaxial films of these compounds are important to examine their intrinsic materials properties as well as to transfer them to device applications. In this review, we first present our research route from transparent p-type oxides semiconductors to the Fe-based superconductors. Then we review growth of epitaxial thin films for the layered oxychalcogenides and oxypnictides. Reactive solid-phase epitaxy technique was inevitable to prepare epitaxial thin films of the oxychalcogenides and Zn-based oxypnictides. On the other hand, epitaxial thin films of Mn-based oxypnictides were grown by standard pulsed laser deposition. These techniques, however, did not grow epitaxial thin films for LaFeAsO. Thus, we developed a modified pulsed laser deposition process and succeeded in obtaining epitaxial thin films of FeAs-based superconductors, LaFeAsO and cobalt-doped SrFe₂As₂.