The assembly of organic radical anions between metal-borate scaffolds

Metal-organic frameworks based on the Pb[B(Im)(4)](+) unit form layered structures analogous to those observed in clays and double layered hydroxide minerals. These layers can act as scaffolds for the organization of anionic organic guests. In this report, we use this scaffold to assemble TEMPO and PROXYL carboxylates in the interlayer spacings of Pb[B(Im)(4)](4-carboxy-TEMPO) 1 and Pb[B(Im)(4)](3-carboxy-PROXYL)(H(2)O)2, respectively. The resultant materials are paramagnetic, and the organization of the radical units differs between the two compounds. This results in changes in electronic structure of the radical unit, as observed by EPR spectroscopy.     

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Notices bibliographiques

     

Cell-based biosensors

Different classes of cell-based biosensors are introduced. These include devices to measure cell-cell contact and set-ups to determine metabolic products. Main emphasis is put on sensors based on nerve-cell networks which are able to detect neuro-active compounds. The different experimental set-ups are explained and examples for typical applications are given. A main point concerns new achievements and prospects for future developments. Received: 26 August 1999 / Revised: 29 November 1999 / Accepted: 11 December 1999     

On quantitative aspects of the unit sum number problem

We investigate the function u _K,S (n; q) which counts the number of representations of algebraic integers α with |N_{K/\mathbb Q}(a)| ￡ q{|N_{K/{\mathbb Q}}(\alpha)| \leq q} for some real positive q that can be written as sums of exactly n S-units of the number field K.     

Arithmetic progressions on Pell equations

In this paper we consider arithmetic progressions on Pell equations, i.e. integral solutions (X,Y) whose X-coordinates or Y-coordinates are in arithmetic progression.     

The primes contain arbitrarily long polynomial progressions

We establish the existence of infinitely many polynomial progressions in the primes; more precisely, given any integer-valued polynomials P ₁, …, P _k  ∈ Z[m] in one unknown m with P ₁(0) = … = P _k (0) = 0, and given any ε > 0, we show that there are infinitely many integers x and m, with 1 \leqslant m \leqslant x^e1 \leqslant m \leqslant x^\varepsilon, such that x + P ₁(m), …, x + P _k (m) are simultaneously prime. The arguments are based on those in [18], which treated the linear case P _j  = (j − 1)m and ε = 1; the main new features are a localization of the shift parameters (and the attendant Gowers norm objects) to both coarse and fine scales, the use of PET induction to linearize the polynomial averaging, and some elementary estimates for the number of points over finite fields in certain algebraic varieties.     

Non-superconducting and rendered superconducting YBa2Cu3O7−x . An in-situ photoemission study

We present X-ray photoemission spectroscopy (XPS) results obtained on polycrystalline YBa₂Cu₃O_7–x in the non-metallic (x>0.6) and metallic state (x<0.6) by an in-situ oxygen deloading/loading procedure, thus avoiding uncontrolled surface contaminations. The transition to the metallic (superconducting) state is characterized by corresponding changes in the O1s and Cu2p photoelectron lineshapes being in accordance with charge transfer from CuO₂ planes to CuO chains. In particular, a peak at 531.1 eV binding energy is related to the presence of oxygen hole states (O^–).