Homopolymerization of ω‐Styryl‐Polystyrene Macromonomers in the Presence of CpTiF3/MAO

Summary: ω‐Styryl‐polystyrene macromonomers were synthesized by anionic induced deactivation reactions. Their homopolymerization in the presence of a fluorinated half‐sandwich metallocene catalyst (CpTiF₃/MAO) was investigated. In spite of the intrinsic lower reactivity of these macromonomers with respect to the micromolecular monomer, coordination homopolymerization was possible. The influence of several experimental parameters on the polymerization yield and degree could be demonstrated. In most cases, under identical experimental conditions, higher polymerization yields and degrees were observed with respect to the CpTiCl₃/MAO catalyst.

The synthesis of p‐polystyryl‐substituted styrene derivatives by the homopolymerization of ω‐styryl‐polystyrene macromonomers in the presence of CpTiF₃.     

Effect of radiative cooling on collapsing charged grains

The effect of the radiative cooling of electrons on the gravitational collapse of cold dust grains with fluctuating electric charge is investigated. We find that the radiative cooling as well as the charge fluctuations, both, enhance the growth rate of the Jeans instability. However, the Jeans length, which is zero for cold grains and nonradiative plasma, becomes finite in the presence of radiative cooling of electrons and is further enhanced due to charge fluctuations of grains resulting in an increased threshold of the spatial scale for the Jeans instability.     

Automatic Structure Determination of Organic Molecules： Principle and Implementation of the LSD Program

The LSD (Logic for Structure Determination) program gener-ates organic molecular structures from 1D and 2D NMR data without resorting to chemical shift databases. Its use in the res-olution of natural product structure determination problems has been already reported in the literature. This paper describes how data and structures are internally represented and pro-cessed by LSD to build solution structures.     

Chiral close-packing of achiral star-shaped molecules on solid surfaces

From the interplay of scanning tunneling microscopy and theoretical calculations, we study the chiral self-assembly of achiral HtB-HBC molecules upon adsorption on the Cu(110) surface. We find that chirality is expressed at two different levels: a +/-5 degrees rotation of the molecular axis with respect to the close-packed direction of the Cu(110) substrate and a chiral close-packed arrangement expected for star-shaped molecules in 2D. Out of the four possible chiral expressions, only two are found to exist due the effect of van der Waals (vdW) interactions forcing the molecules to simultaneously adjust to the atomic template of the substrate geometry and self-assemble in a close-packed geometry.     

Evolution and impingement of an automotive fuel spray investigated with simultaneous Mie/LIF techniques

The spatial and temporal evolution of an automotive hollow-cone-type spray was investigated with laser-based imaging diagnostics. Optical conditions of an IC engine were emulated with a test cell that was built from an engine cylinder head to hold a high-pressure gasoline-fuel injector. The use of iso-octane fuel that was doped with 3-pentanone allowed measurements of laser-induced fluorescence (LIF) after excitation with a KrF excimer-laser beam. A versatile optical filter system was designed and built that permits simultaneous measurements of Mie-scattering and laser-induced-fluorescence images using a single laser-light sheet and a single intensified CCD camera. The influence of background signals, caused by reflection of signal light from surfaces, laser-sheet intensity attenuation and signal decrease by scattering, was characterized. Mass distributions showed a distinct pre-spray phase, more so than the Sauter mean diameter (SMD) that was determined from the ratio of LIF to Mie signals using single pulse as well as averaged image pairs. Significant changes in SMD distributions were found after the spray had impinged on a flat surface. The impingement also led to the buildup of a liquid film whose thickness was quantitatively determined from LIF images. Received: 5 December 2000 / Revised version: 28 February 2001 / Published online: 23 May 2001     

Analytic solution for a static black hole in the RSII model

We present here a static solution for a large black hole (whose horizon radius is larger than the AdS radius) located on the brane in RSII model. According to some arguments based on the AdS/CFT conjecture, a solution for the black hole located on the brane in RSII model must encode quantum gravitational effects and therefore cannot be static. We demonstrated that a static solution can be found if the bulk is not empty. The stress energy tensor of the matter distribution in the bulk for the solution we found is physical (i.e. it is non-singular with the energy density and pressure not violating any energy conditions). The scale of the solution is given by a parameter “a”. For large values of the parameter “a” we have a limit of an almost empty AdS bulk. It is interesting that the solution cannot be transformed into the Schwarzschild-like form and does not reduce to the Schwarzschild solution on the brane. We also present two other related static solutions. At the end, we discuss why the numerical methods failed so far in finding static solutions in this context, including the solutions we found analytically here.     

Time-dependent fluctuations and particle production in cosmological de Sitter and anti-de Sitter spaces

We study the evolution of time-dependent fluctuations and particle production in an expanding dS and contracting AdS universe. Using the functional Schrödinger formalism we are able to probe the time-dependent regime which is out of the reach of the standard approximations like the Bogolyubov method. In both cases, the evolution of fluctuations is governed by the harmonic oscillator equation with time-dependent frequency. In the case of an expanding dS universe we explicitly show that the frequency of fluctuations produced at a certain moment diminish in time, while the distribution of the created particles quickly approaches the thermal radiation of the dS space. In the case of a contracting AdS universe we show that the frequency of fluctuations produced at a certain moment grow in time. Nominally, the temperature of radiation diverges as the Big Crunch is approaching, however, increasing oscillations of the spectrum make the temperature poorly defined, which is in agreement with the fact that AdS space does not have an event horizon which would cause thermal radiation. Unlimited growth of fluctuations indicates that an eventual tunneling into AdS vacuum would have catastrophic consequences for our universe.     

Can primordial magnetic fields seeded by electroweak strings cause an alignment of quasar axes on cosmological scales?

The decay of nontopological electroweak strings may leave an observable imprint in the Universe today in the form of primordial magnetic fields. Protogalaxies preferentially tend to form with their axis of rotation parallel to an external magnetic field, and, moreover, an external magnetic field produces torque which tends to align the galaxy axis with the magnetic field. We demonstrate that the shape of a magnetic field left over from two looped electroweak strings can explain the observed nontrivial alignment of quasar polarization vectors and make predictions for future observations.     

Referenced Capacitively Coupled Conductivity Detector for Capillary Electrophoresis

A dual capacitively coupled contactless conductivity detector for capillary electrophoresis was developed. The two channels are arranged in a bridge configuration so that one of them acts as a reference whose signal is subtracted. This effectively compensates for the baseline conductivity of the separation buffer so that the electronic zero setting is not necessary. Changes in the buffer composition are automatically accounted for, as are temperature drifts. The system is demonstrated for the detection of inorganic model cations in capillary electrophoresis. Besides the use with two separate capillaries, one of which solely serves as reference, it was also found possible to use a single capillary which is looped back through the reference cell.