Frequency dependence of the dielectric and electro-optic response in suspensions of charged rod-like colloidal particles

We have performed an experimental investigation on the electrokinetic properties of charged rod-like fluorinated latex colloids. Systematic measurements of electrophoretic mobility, dielectric constant and electric birefringence have been performed as a function of the concentration of added nonionic surfactant and salt. In the investigated range of parameters, the zeta potential is a strongly decreasing function of the concentration of nonionic surfactant, while it is basically independent from ionic strength. We have obtained the frequency dependence of dielectric constant and Kerr constant as a function of zeta-potential and ionic strength. We observe the transition from a low frequency behavior, where both the dielectric constant and the Kerr constant are enhanced by the presence of the double layer, to a high frequency behavior, where both quantities take the value expected for unchanged particles in an insulating medium. The shape of the frequency dispersion of the Kerr constant coincides with that of the dielectric constant, but the cut-off frequencies are the same only when the zeta-potential of the particles is low.     

Nuclear fusion in excited hydrogen molecules

We evaluate the nuclear fusion rates in the excited vibrational states of molecules of hydrogen isotopes. The ground state fusion rate is increased by about eight orders of magnitude but even in the most favorable situation it is out of any possible experimental test. We discuss the effects due to the nuclear potential in different hyperfine states, and the improvements attainable using coherent states and a solid phase.     

Importance of complex band structure and resonant states for tunneling

The paper aims at understanding the tunneling process in epitaxial magnetic tunnel junctions. Firstly, we stress the importance of the complex band structure of the insulator for the tunneling of the metal electrons. For large insulator thicknesses the tunneling current is carried by very few states, i.e., those states in the gap of the semiconductor having the smallest imaginary component of the k-vector. In the case of GaAs, ZnSe and MgO these are Δ₁-states at the -point. Secondly, we discuss the role of resonant interface states for tunneling. Based on simple model calculations and ab initio results we demonstrate that for symmetrical barriers the minority conductance can be dominated in an intermediate thickness range by few ‘hot spots’ in the surface Brillouin zone, arising from resonant interface states. In these hot spots full transmission can still be obtained, when all other states are already strongly attenuated, so that the usual exponential decay can be considerably delayed.     

Tailored Cyclic and Linear Polycarbosilazanes by Barium‐Catalyzed N−H/H−Si Dehydrocoupling Reactions

Ba[CH(SiMe₃)₂]₂(THF)₃ catalyzes the fast and controlled dehydrogenative polymerization of Ph₂SiH₂ and p‐xylylenediamine to afford polycarbosilazanes. The structure (cyclic versus linear; end‐groups) and molecular weight of the macromolecules can be tuned by adjusting the Ph₂SiH₂/diamine feed ratio. A detailed analysis of the resulting materials (mol. wt up to ca. 10 000 g mol^?1) is provided.     

Study of Blood Porphyrin Spectral Profile for Diagnosis of Tumor Progression

Renal cell carcinoma (RCC) accounts for approximately 3% of new cancer incidence and mortality in the United States. Unfortunately many RCC masses remain asymptomatic and nonpalpable until they are advanced. Diagnosis and localization of early carcinoma play an important role in the prevention and curative treatment of RCC. The autofluorescence of blood porphyrin of healthy and tumor induced in male SCID mice was analyzed using fluorescence and excitation spectroscopy. A significant contrast between normal and tumor blood could be established. Blood porphyrin fluorophore showed enhanced fluorescence band (around 630 nm) in function of the tumor growth. This indicates that either the autofluorescence intensity of the blood fluorescence may provide a good parameter for the “first approximation” characterization of the tumor stage.     

Ab Initio Calculation of Hyperfine Interaction Parameters: Recent Evolutions, Recent Examples

For some years already, ab initio calculations based on Density Functional Theory (DFT) belong to the toolbox of the field of hyperfine interaction studies. In this paper, the standard ab initio approach is schematically sketched. New features, methods and possibilities that broke through during the past few years are listed, and their relation to the standard approach is explained. All this is illustrated by some highlights of recent ab initio work done by the Nuclear Condensed Matter Group at the K.U.Leuven.     

Synthesis and thermal transformations of zinc-substituted magnetites

In the present study, zinc-substituted magnetites of the Fe_3???X Zn _X O₄ type were prepared by co-precipitation in the range 0 ≤?X?≤ 1 and, further, annealed in free atmosphere, at 800° for 3 h. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy. The results showed that the annealed samples were oxidized and converted into Fe₂O₃ and ZnFe₂O₄, in relative amounts that varied with X.     

The bang of a white hole in the early universe from a 6D vacuum state: origin of astrophysical spectrum

Using a previously introduced model in which the expansion of the universe is driven by a single scalar field subject to gravitational attraction induced by a white hole during the expansion (from a 6D vacuum state), we study the origin of squared inflaton fluctuations spectrum on astrophysical scales.     

Warm Inflation and Scalar Perturbations of the Metric

A second-order expansion for the quantum fluctuations of the matter field was considered in the framework of the warm inflation scenario. The friction and Hubble parameters were expanded by means of a semiclassical approach. The fluctuations of the Hubble parameter generates fluctuations of the metric. These metric fluctuations produce an effective term of curvature. The power spectrum for the metric fluctuations can be calculated on the infrared sector.