Spectroscopies and Electron Microscopies Unravel the Origin of the First Colour Photographs

The first colour photographs were created by a process introduced by Edmond Becquerel in 1848. The nature of these photochromatic images colours motivated a debate between scientists during the XIX^th century, which is still not settled. We present the results of chemical analysis (EDX, HAXPES and EXAFS) and morphology studies (SEM, STEM) aiming at explaining the optical properties of the photochromatic images (UV-visible spectroscopy and low loss EELS). We rule out the two hypotheses (pigment and interferences) that have prevailed since 1848, respectively based on variations in the oxidation degree of the compound forming the sensitized layer and periodically spaced photolytic silver planes. A study of the silver nanoparticles dispersions contained in the coloured layers showed specific localizations and sizes distributions of the nanoparticles for each colour. These results allow us to formulate a plasmonic hypothesis on the origin of the photochromatic images colours.     

The effect of dissipation on coherent quantum tunnelling in a double-well system: Two-level model using an adjoint equation approach

We examine the effect of dissipation on coherent quantum tunnelling between the two lowest levels of a double-well system using an adjoint equation approach developed previously in the treatment of quantum-optical problems. Dissipation is modelled by a linear coupling to a bath of harmonic oscillators. The high frequency portion of the bath is adiabatically eliminated using a cumulant expansion technique, which generates frequency renormalisation terms. Making a low temperature assumption, an approximate two-level model is developed in the form of three coupled stochastic differential equations. With a decorrelation approximation, the two-level equations can be solved to yield familiar results. However, the adjoint equation also permits the use of direct stochastic simulation as a means of solution, and simulations are carried out for a range of parameters. A comparison with the decorrelation approximation is made.     

Free states of the canonical anticommutation relations

Each gauge invariant generalized free state _A of the anticommutation relation algebra over a complex Hilbert spaceK is characterized by an operatorA onK. It is shown that the cyclic representations induced by two gauge invariant generalized free states _A and _B are quasi-equivalent if and only if the operatorsA ^1/2–B ^1/2 and (I–A)^1/2–(I–B)^1/2 are of Hilbert-Schmidt class. The combination of this result with results from the theory of isomorphisms of von Neumann algebras yield necessary and sufficient conditions for the unitary equivalence of the cyclic representations induced by gauge invariant generalized free states.Work supported in part by US Atomic Energy Commission, under Contract AT (30-1)-2171 and by the National Science Foundation.     

Search for giant Franz-Keldysh-like effects in GaSe and other layered semiconductors

Recently, an anomalously large redshift of the absorption edge with electric field was claimed for -GaSe_1–x S _x layered crystals. We have studied Bridgman grown -GaSe crystals as well as vapor transport grown -GaS, and 2H-WSe₂. While we have observed a shift in the absorption edge for -GaSe similar to that reported in previous work, our results demonstrate that the redshift arises from Joule heating, and is thus temperature induced, rather than intrinsic. For -GaS, much larger resistivities virtually eliminate Joule heating, and our measurements of the electric field induced absorption edge shift yield an estimated upper limit of approximately 0.04 meV · cm/kV for a field of 2.4×10³ kV/cm, in good agreement with the theoretical value expected for the Franz-Keldysh effect.Also at University of Konstanz     

Hadronic equation of state and the onset of kaon condensation

An equation of state is presented which takes the finite size of baryons and of mesons consistently into account and incorporates the contributions of both nonstrange and strange hadrons. All extensive quantities (energy, particle number, entropy) are modified by a factor taking into account the excluded volume due to baryon repulsion. Intensive quantities (pressure) are not modified. This is achieved by introducing a baryon chemical potential, _B, which is shifted from its point-like value, _B ⁰ , by a term proportional to the finite volume of a hadron,V ₀, as follows: _B= _B ⁰ + V₀[P⁰(T, _B ⁰ )–P⁰(T, 0)], whereP ⁰ is the pressure for pointlike particles. The last term is necessary to conserve baryon number at the phase transition point. The differences between the new equation of state and those considered previously in the literature are discussed. It is shown that kaon condensation sets in only in the mixed phase of the transition, where hadrons, quarks and gluons are present simultaneously in thermodynamical equilibrium.     

Reducing system of parameters and the Cohen-Macaulay property

Let R be a local ring and let (x ₁, …, x _r) be part of a system of parameters of a finitely generated R-module M, where r < dim_R M. We will show that if (y ₁, …, y _r) is part of a reducing system of parameters of M with (y ₁, …, y _r) M = (x ₁, …, x _r) M then (x ₁, …, x _r) is already reducing. Moreover, there is such a part of a reducing system of parameters of M iff for all primes P ε Supp M ∩ V _R(x ₁, …, x _r) with dim_R R/P = dim_R M − r the localization M _P of M at P is an r-dimensional Cohen-Macaulay module over R _P. Furthermore, we will show that M is a Cohen-Macaulay module iff y _d is a non zero divisor on M/(y ₁, …, y _d−1) M, where (y ₁, …, y _d) is a reducing system of parameters of M (d:= dim_R M).     

Phase transition to hyperon matter in neutron stars

Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated. We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of R approximately equal 8 km.     

Experimental evidence for supercontinuum generation by fission of higher-order solitons in photonic fibers

We report on an experimental study of supercontinuum generation in photonic crystal fibers with low-intensity femtosecond pulses, which provides evidence for a novel spectral broadening mechanism. The observed results agree with our theoretical calculations carried out without making the slowly varying envelope approximation. Peculiarities of the measured spectra and their theoretical explanation demonstrate that the reason for the white-light generation in photonic crystal fibers is fission of higher-order solitons into redshifted fundamental solitons and blueshifted nonsolitonic radiation.     

From Multifractal Measures to Multifractal Wavelet Series

Given a positive locally finite Borel measure μ on R, a natural way to construct multifractal wavelet series is to set , where . Indeed, under suitable conditions, it is shown that the function F_μ inherits the multifractal properties of μ. The transposition of multifractal properties works with many classes of statistically selfsimilar multifractal measures, enlarging the class of processes which have self-similarity properties and controlled multifractal behaviors. Several perturbations of the wavelet coefficients and their impact on the multifractal nature of F_μ are studied. As an application, multifractal Gaussian processes associated with F_μ are created. We obtain results for the multifractal spectrum of the so-called W-cascades introduced by Arnéodo et al.     

Beam lifetimes of low-charged ions in storage rings

The beam lifetimes and the charge-changing cross-sections for fast low-charged ions are calculated for the energy range of 1–100 MeV/u and compared with experimental data for Mg¹⁺ and U¹⁰⁺ ions recently measured at SIS GSI, Darmstadt. A moderate agreement of calculations with experiment was obtained. The results show that the heavy components of the residual gas (N₂ and Ar) play a key role for projectile charge-changing processes in the energy range considered. This revised version was published online in July 2006 with corrections to the Cover Date.