Synthesis and characterization of new radiopaque microspheres by the dispersion polymerization of an iodinated acrylate monomer for X‐ray imaging applications

Radiopaque microspheres of sizes ranging from 0.2 to 1.4 μm were formed by the dispersion polymerization of the monomer 2‐methacryloyloxyethyl(2,3,5‐triiodobenzoate) in 2‐methoxyethanol. The effects of various polymerization parameters, including the monomer concentration, initiator type and concentration, and stabilizer molecular weight and concentration, on the molecular weight, size, and size distribution of the particles were elucidated. The characterization of these iodinated microspheres was accomplished with routine methods such as Fourier transform infrared, nuclear magnetic resonance, thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, scanning electron microscopy, Brunauer–Emmett–Teller measurements, and elemental analysis. Because of the presence of iodine atoms in these microspheres, they were expected to possess a radiopaque nature. The radiopacity of these particles dispersed in water and in the dry state was demonstrated with an imaging technique based on X‐ray absorption usually used in hospitals. These novel radiopaque microspheres may be used for different X‐ray imaging needs, such as blood pooling, body organs, embolization, dental compositions, implants, prostheses, and nanocomposites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3859–3868, 2006     

Synthesis of 1,10-N,N'-phenanthroline dioxides using HOF.CH(3)CN complex

[reaction: see text] HOF.CH(3)CN, a very efficient oxygen-transfer agent, made readily from F(2), H(2)O, and CH(3)CN, was reacted with various 1,10-phenanthroline derivatives to form the corresponding N,N'-dioxides in good yields and short reaction times.     

Scale-free networks are ultrasmall

We study the diameter, or the mean distance between sites, in a scale-free network, having N sites and degree distribution p(k) proportional, variant k(-lambda), i.e., the probability of having k links outgoing from a site. In contrast to the diameter of regular random networks or small-world networks, which is known to be d approximately ln(N, we show, using analytical arguments, that scale-free networks with 23, d approximately ln(N. We also show that, for any lambda>2, one can construct a deterministic scale-free network with d approximately ln(ln(N, which is the lowest possible diameter.     

Two-dimensional pressure-driven nanorod-to-nanowire reactions in Langmuir monolayers at room temperature

Typical two-dimensional surface pressures prevalent within floating monolayer (Langmuir) films are on the order of a few dozen megapascals. One might expect, therefore, that some chemical reactions should be directly and strongly affected by this surface pressure, along with the well-known effect of pressure on the orientational order and the mere proximity of the molecules within the film. Here, we show that the two-dimensional surface pressure in Langmuir films provides a direct driving force, decreasing the activation energy of a cooperative oriented coalescence of ZnS nanorods into nanowires near room temperature. At low film surface pressure or low temperature, the nanorods do not react, while in solution, they react only above 140 degrees C, even though in all of these cases, the rods are organized in similar super-crystalline clusters. Electron microscopy and measurements of the reaction rates give a detailed picture of the order of the rods, their rearrangement, and their coalescence.     

A one-dimensional microscopic quantum mechanical theory of light enhanced desorption

A one-dimensional microscopic quantum mechanical model is used to inquire whether it is possible to enhance the desorption rate by employing a laser to induce vibrational excitation of the chemisorptive bond. For model parameters simulating CO/Cu it is found that the required laser intensity is very large, roughly 10⁴ times that of a conventional high power CO₂ laser (whose intensity we take to be $\text{5 × 10}{}^{10}\text{W}\text{cm}{}^2$). We suggest that surface roughness can be used to enhance substantially the effect of the laser and possibly to enable the observation of laser enhanced desorption.     

Simultaneous determination of ordering and amplifications of cascaded subsystems

Letn linear, time-invariant subsystems with transfer functionsT ₁(s),T ₂(s),...,T _n (s) be given. We are required to cascade these subsystems into a system with the transfer functionT(s)=kT ₁(s)T ₂(s) ...T _n (s), wherek>0, by determining the order of the subsystems and choosing for each subsystemi an amplification factork _i such thatk=k ₁ k ₂ ...k _n .We do this using the following optimality criterion: Given a setI, minimize the ratio of the maximum and the minimum of all the absolute values of all the intermediate outputs inI, for a flat input. This criterion is applicable in cases where the intermediate outputs should not be overdriven or underdriven. In particular, the method is applicable to the problem of determining an optimal ordering and intermediate amplifications of cascadedRC-active filters.The author is indebted to E. Lueder (Ref. 1) and J. Tow, who presented various criteria for optimal arrangements ofRC-active filters and motivated the formulation of this problem.     

Strong change in the mass distribution of fission-like processes around ACN = 100

The completely relaxed reaction products resulting from bombardment of ⁵⁹Co, ⁶⁵Cu, ⁷⁴Ge, ⁷⁹Br, ⁸⁵Rb and ⁸⁹Y with ³²S have been studied. At incident energies from 153 MeV to 184 MeV, compound of composite nuclei with masses, A_CN, between 91 and 121 are formed with excitation energies of 80–100 MeV. Their spins might be as high as 60–70 $\text{h}\text{?}$ which allows for fission decay. The mass distribution from the reaction ³²S on ⁸⁹Y exhibits a sharp peak corresponding to symmetric fragmentation and consistent with a fission mechanism. The mass distribution over the above range range of decaying composite nuclei continuously broadens with decreasing mass, A_CN. Maxima around the projectile and target mass gradually become more predominant and finally dominate the mass spectrum obtained in the reaction ³²S on ⁵⁹Co. These changes in the overall character of the mass distribution are discussed in terms of various mechanisms.     

Charge symmetry breaking interactions and coulomb energy differences

A detailed study of the possibility that the long standing discrepancies between theory and experiment in the values of Coulomb displacement energies have their origin in the charge asymmetry of the nuclear force is presented. A review of the present status of the theory of Coulomb displacement energies of mirror states is given. We have constructed a phenomenological charge asymmetric potential that can remove the Coulomb energy discrepancies for several mirror nuclei yet having only minimal effect on the ¹S₀ nucleon-nucleon scattering length. The form of this potential is however not compatible with the contributions due to charge asymmetric meson exchange processes that have been considered in the literature. We assume that these meson exchange effects can be reasonably described, up to strength factors, by a sum of one-pion, one-scalar-meson (σ) and one-vector-meson exchange potentials. The need for some additional type of charge asymmetric effect, e.g. three-body forces, is pointed out.     

The first general method for alpha-trifluoromethylation of carboxylic acids using BrF3

2-Carbomethoxy-1,1-bis(methylsulfide)-1-alkenes, easily made from carboxylic acids, CS(2) and MeI, were treated with BrF(3) producing eventually the desired alpha-trifluoromethyl carboxylate derivatives--RCH(CF(3))COOR'--in good yields.