C 1s NEXAFS study of rare-earth’s (La,Eu)-graphite intercalation compounds

Electronic structure of unoccupied states of Eu- and thin surface layer of La-intercalation compounds was studied by light polarization dependent NEXAFS at the C 1s threshold in a bulk sensitive (E_kin=1–2 eV) and a more surface sensitive (E_kin=265 eV) partial electron yield mode. It was shown that the C 1s spectra in both cases are mainly characterized by the π*- and σ*-symmetry graphite-derived features. For both systems the π*-derived peak was found at similar energies of exciting photons as for pristine graphite. A decrease of relative intensity of the π*-originated structure in intercalation compounds can be understood by partial occupation of the π*-derived states upon intercalation due to a charge transfer from rare-earth (RE) atoms. NEXAFS features found on both sides of the π* response may be related to pd hybrids forming as a result of chemical interaction between RE atoms and graphite layers.     

Unconventional trapping of ultracold neutrons

In unconventional storage experiments we filled ultracold neutrons (UCN) into a Fomblin-grease coated trap and then immediately removed the UCN from the storage volume by an absorber, until their residual density in the trap was measured to be negligible. When subsequently the absorber was withdrawn a significant number of UCN of higher energies emerged from the trap. Their appearance cannot be attributed to heating or cooling of residual UCN. Further experiments were performed to investigate the origin of these UCN which we call `late UCN'. We noticed that application of a magnetic field gradient at the trap wall as well as a replacement of Fomblin grease on the surface by Fomblin oil gave rise to small but measurable alterations of storage behavior. These phenomena are consistent with the hypothesis of temporary adhesion of a few UCN to a rough wall.     

Crystallization of ultraphosphates via the gas phase. The crystal structures of FeP4O11, ZnP4O11 and CdP4O11

The new ultraphosphates FeP₄O₁₁, ZnP₄O₁₁ and CdP₄O₁₁ of the CuP₄O₁₁ structure type were synthesized from the corresponding meta- or polyphosphates and P₄O₁₁. Crystallization via the gas phase has been achieved at elevated temperatures using a mixture of P (3 mg) and I₂ (50 mg) as mineralizer. The crystal structure consists of a two-dimensional phosphate network, built from four crystallographically independent 10-membered polyphosphate rings. Each ring contains four secondary and six tertiary PO₄-groups. Two crystallographically independent metal sites showing sixfold coordination by terminal oxygen atoms are located inbetween the phosphate layers. FeO₆-octahedra (2.028(3) Å < d̄ FeO₆ < 2.268(3) Å) and ZnO₆ octahedra (2.002(2) Å < d̄ ZnO₆ < 2.256(2) Å) exhibit slightly larger radial distortion than the CdO₆-octahedra (2.215(7) Å < d̄ CdO₆ < 2.383(3) Å).     

Problèmes elliptiques avec non-linéarité discontinue et second membre L1

We define the notion of (very) weak solution for a class of semilinear elliptic problems with discontinuous nonlinearity and L¹ data. We prove the existence of such a solution by an approximation technique with L² datas.     

Extracellular release of a recombinant gene product by osmotic shock from immobilized microalga in electroconductive membrane

The unicellular blue green alga Synechococcus was immobilized in an electroconductive membrane of polypyrrole-agarose. The Synechococcus was recombinant with a plasmid vector encoding the ampicillin resistance gene. The gene product β-lactamase, a periplasm enzyme of Escherichia coli, was released to medium repeatedly by osmotic shocks. The immobilized cells were stable for over a month and kept their viability under electrical potentials from −0.5 V to 0.6 V vs. Ag/AgCl.     

The effect of random matter density perturbations on the MSW solution to the solar neutrino problem

We consider the implications of solar matter density random noise upon resonant neutrino conversion. The evolution equation describing MSW-like conversion is derived in the framework of the Schrödinger approach. We study quantitatively the effect of such matter perturbations upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active v_e → v_μ,τ as well as active-sterile v_e → v_s conversion channels. We find that the small mixing MSW solution is much more stable (especially in Δm² than the large mixing solution. The possible existence of solar matter density noise at the few percent level could be tested at future solar neutrino experiments, especially Borexino.     

On the stable sampling rate for binary measurements and wavelet reconstruction

This paper is concerned with the problem of reconstructing an infinite-dimensional signal from a limited number of linear measurements. In particular, we show that for binary measurements (modelled with Walsh functions and Hadamard matrices) and wavelet reconstruction the stable sampling rate is linear. This implies that binary measurements are as efficient as Fourier samples when using wavelets as the reconstruction space. Powerful techniques for reconstructions include generalized sampling and its compressed versions, as well as recent methods based on data assimilation. Common to these methods is that the reconstruction quality depends highly on the subspace angle between the sampling and the reconstruction space, which is dictated by the stable sampling rate. As a result of the theory provided in this paper, these methods can now easily use binary measurements and wavelet reconstruction bases.     

The crooked property

Crooked permutations were introduced twenty years ago to construct interesting objects in graph theory. These functions, over ${\mathbb{F}}_{2^n}$ with odd n, are such that their derivatives have as image set a complement of a hyperplane. The field of applications was extended later, in particular to cryptography. However binary crooked functions are rare. It is still unknown if non quadratic crooked functions do exist. We extend the concept and propose to study the crooked property for any characteristic. A function F, from ${\mathbb{F}}_{p^n}$ to itself, satisfies this property if all its derivatives have as image set an affine subspace. We show that the partially-bent vectorial functions and the functions satisfying the crooked property are strongly related. We later focus on the components of these functions, establishing that the existence of linear structures is here decisive. We then propose a symbolic approach to identify the linear structures. We claim that this problem consists in solving a system of linear equations, and can often be seen as a combinatorial problem.