Mössbauer studies of stoichiometry of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>: characterization of nanoparticles for biomedical applications

The iron oxide Fe₃O₄, the mineral magnetite sometimes called ferrosoferric oxide, is notoriousy non-stoichiometric even in bulk form so its formula may be written Fe_3?δO₄. In nanoparticle form, where it has applications in medicine and information technology, it is even more susceptible to oxidation. In this paper we report synthesis and studies of superparamagnetic Fe₃O₄ nanoparticles with controlled diameters of 5.3, 10.6 and 11.9 nm. In room temperature spectra, departures from stoichiometry δ of up to 0.02 were estimated from the relative amounts of Fe ³⁺/ Fe ²⁺ and from their isomer shifts. This cannot be used for very small particles of diameter 10.6 nm and less as they are superparamagnetic at room temperature and do not show hyperfine splitting owing to fast relaxation. Such particles have promise for use in enhancing MRI signals. The magnetic spectrum is restored by the application of a relatively small magnetic field (10 kG). As the temperature is lowered the relaxation slows down and 6-line magnetic hyperfine patterns appear below a blocking temperature T_B. The values of T_B obtained are lower than those of many other researchers reported in the literature, suggesting that our particles are less affected by magnetic interactions between them. At low temperatures all the spectra are similar and closely resemble that of bulk Fe₃O₄ confirming that departures from stoichiometry are small.     

Human salivary gland stem cells ameliorate hyposalivation of radiation-damaged rat salivary glands

Salivary function in mammals may be defective for various reasons, such as aging, Sjogren''s syndrome or radiation therapy in head and neck cancer patients. Recently, tissue-specific stem cell therapy has attracted public attention as a next-generation therapeutic reagent. In the present study, we isolated tissue-specific stem cells from the human submandibular salivary gland (hSGSCs). To efficiently isolate and amplify hSGSCs in large amounts, we developed a culture system (lasting 4–5 weeks) without any selection. After five passages, we obtained adherent cells that expressed mesenchymal stem cell surface antigen markers, such as CD44, CD49f, CD90 and CD105, but not the hematopoietic stem cell markers, CD34 and CD45, and that were able to undergo adipogenic, osteogenic and chondrogenic differentiation. In addition, hSGSCs were differentiated into amylase-expressing cells by using a two-step differentiation method. Transplantation of hSGSCs to radiation-damaged rat salivary glands rescued hyposalivation and body weight loss, restored acinar and duct cell structure, and decreased the amount of apoptotic cells. These data suggest that the isolated hSGSCs, which may have characteristics of mesenchymal-like stem cells, could be used as a cell therapy agent for the damaged salivary gland.     

小度数循环图的计数

循环图已被用于平行计算，网络等方面．循环图研究的一个基本问题是对互不同构的循环图进行计数．对于给定的一个正整数ｎ，用Ｃ（ｎ，ｋ）表示互不同构的具有几个顶点，度数为ｋ的连通循环图的个数．文中给出了度数为 ４和５的循环图的一般结构，并对ｎ＝ｐａｑｂ（ｐ，ｑ皆为素数，ａ，ｂ＞０），给出了Ｃ（ｎ，４）的计算公式．     

Two-dimensional offsets and medial axis transform

We present a mathematical theory of the two-dimensional offset curves from the viewpoint of medial axis transform. We explore the local geometry of the offset curve in relation with the medial axis transform, culminating in the classification of points on the offset curve. We then study the domain decomposition from the viewpoint of offsets, and in particular introduce the concept of monotonic fundamental domain as a device for detecting the correct topology of offsets as well as for stable numerical computation. The monotonic fundamental domains are joined by peaks or valleys of the medial axis transform, or by what we call the critical horizonal section whose algebro-geometric properties are rigorously treated as well. First author holds joint appointment in the Research Institute of Mathematics, Seoul National University.     

Rough isometry and energy finite solutions of elliptic equations on Riemannian manifolds

We prove that if the s-harmonic boundary of a complete Riemannian manifold consists of finitely many points, then the set of bounded energy finite solutions for certain nonlinear elliptic operators on the manifold is one to one corresponding to , where l is the cardinality of thes-harmonic boundary. We also prove that the finiteness of cardinality of s-harmonic boundary is a rough isometric invariant, moreover, in this case, the cardinality is preserved under rough isometries between complete Riemannian manifolds. This result generalizes those of Yau, of Donnelly, of Grigor'yan, of Li and Tam, of Kim and the present author, of Holopainen, and of the present author, but with different techniques which are demanded by the peculiarity of nonlinearity. Received October 13, 1999 / Revised November 23, 1999 / Published online July 20, 2000     

The efficient one-step chlorination of methylsulfanyl group on pyrimidine ring system with sulfuryl chloride

A facile one-step transformation of methylsulfanyl and arylsulfanyl groups on pyrimidine ring system into the corresponding chloride group was achieved using sulfuryl chloride in acetonitrile/dichloromethane.     

Synthesis of poly(ethynylplatinumporphyrin) and its application as an oxygen pressure-sensitive paint

5-(4-Trimethylsilyethynylphenyl)-10,15,20-triphenylplatinumporphyrin was synthesized and copolymerized with trimethylsilylpropyne to give a new high-molecular-weight porphyrin polymer. The polymer formed a smooth and tough coating on many types of surfaces. The coating showed a strong blue luminescence from the platinumporphyrin residue which was quenched in the presence of oxygen. The relationship of the luminescence intensity vs oxygen pressure displayed a remarkably high pressure sensitivity in the low oxygen pressure area, which was ascribed to the high oxygen permeability of the polymer.