Nano-sized polystyrene prepared using bifunctional vinyl urethane macromonomer in emulsion polymerization

The linear-type bifunctional vinyl urethane macromonomer (L-VUM: Mw; 40,453) was synthesized and applied to emulsion polymerization of styrene in DDI water. The structure of L-VUM was confirmed using ¹H NMR and FT-IR. The macromonomer served as a good nonionic surfactant resulted in stable polystyrene nanospheres. Polystyrene particles were prepared with various concentrations of macromonomoer (1–30 wt% refer to monomer), initiator (0.5–2 wt%) and different temperatures (60–80 °C). Monodisperse PS nanospheres with 30 wt% L-VUM have a number-average diameter (D_n) of 200 nm with good uniformity (1.011) and molecular weight (M_w) 231,180 g/mol. The particle morphology, molecular weight and distribution, uniformity and the stability of the nanospheres upon the reaction temperature and concentration of L-VUM will be thoroughly discussed.     

Spectral types of skewed Bernoulli shift

For the transformation for , it is proved that a real-valued function of modulus is not a multiplicative coboundary if the discontinuities of are -adic points and . It is also proved that the weakly mixing skew product transformations arising from Bernoulli shifts have Lebesgue spectrum.

     

Making and breaking covalent bonds across the magnetic transition in the giant magnetocaloric material Gd5(Si2Ge2)

A temperature-dependent, single crystal x-ray diffraction study of the giant magnetocaloric material, Gd5(Si2Ge2), across its Curie temperature (276 K) reveals that the simultaneous orthorhombic to monoclinic transition occurs by a shear mechanism in which the (Si, Ge)-(Si,Ge) dimers that are richer in Ge increase their distances by 0.859(3) A and lead to twinning. The structural transition changes the electronic structure, and provides an atomic-level model for the change in magnetic behavior with temperature in the Gd5(SixGe1-x)(4).     

Isolation of a Se-nitrososelenol: a new class of reactive nitrogen species relevant to protein Se-nitrosation

Nitric oxide (NO) is a messenger molecule implicated in a number of physiological processes. Nitrosation of selenoproteins has been suggested as playing an important role in NO-mediated cellular functions such as the inactivation of glutathione peroxidase (GPx), but no chemical information about Se-nitrosated species has been available to date. Here a stable Se-nitrososelenol (RSeNO), a new class of NO derivative, was synthesized and fully characterized by X-ray crystallography and spectroscopic methods. This Se-nitrososelenol can be formed by direct transnitrosation from an S-nitrosothiol to a selenol, as is the case in the proposed mechanism for the NO-mediated inactivation of GPx.     

Dimensions of very ample pluricanonical subsystems for compact quotients of bounded symmetric domains

A compact complex manifold X obtained by taking quotient of a bounded symmetric domain has an ample canonical line bundle. We prove that the dimension of very ample pluricanonical subsystem is strictly bigger than 2n, where n is the dimension of X. Received: 23 June 2000 / Revised version: 30 March 2001     

Decay rate for the incompressible flows in half spaces

We show that the time decay rate of norm of weak solution for the Stokes equations and for the Navier–Stokes equations on the half spaces are if the initial data and for . We also show that the decay rate is determined by the linear part of the weak solution. We use the heat kernel and Ukai's solution formula for the Stokes equations. It has been known up to now that the decay rate on the half space was , which was obtained by Borchers and Miyakawa [1] and Ukai [9]. Received: 3 November 1999; in final form: 10 May 2000 / Published online: 17 May 2001     

Reduced dose uncertainty in MRI-based polymer gel dosimetry using parallel RF transmission with multiple RF sources

In this work, we present the feasibility of using a parallel RF transmit with multiple RF sources imaging method (MultiTransmit imaging) in polymer gel dosimetry. Image quality and B₁ field homogeneity was statistically better in the MultiTransmit imaging method than in conventional single source RF transmission imaging method. In particular, the standard uncertainty of R ₂ was lower on the MultiTransmit images than on the conventional images. Furthermore, the MultiTransmit measurement showed improved dose resolution. Improved image quality and B₁ homogeneity results in reduced dose uncertainty, thereby suggesting the feasibility of MultiTransmit MR imaging in gel dosimetry.     

Efficient synthesis of unsymmetric diarylalkynes from decarboxylative coupling in a continuous flow reaction system

Unsymmetric diaryl alkynes were synthesized from the palladium-catalyzed decarboxylative coupling of aryl halides and propiolic acid using a continuous flow reaction system. This flow chemistry system continuously gave the desired products in moderate to good yields, and produced less byproduct than was formed in the batch reaction.