Giant negative magnetoresistance in a nonmagnetic semiconductor

Studies of a classical III–V semiconductor (InSb) doped with 3d magnetic ions (Mn²⁺, having a localized spin S=55/2) reveal some unexpected transport properties. It is found that the transition from the metallic to the low-temperature insulator phase occurs at an impurity concentration N _Mn∼N _cr=2× 10¹⁷ cm⁻³ and a temperature T<T _cr∼1 K. Under these conditions a giant negative magnetoresistance arises. The experimental results can be explained in terms of the onset of a hard Mott-Hubbard gap Δ in the impurity band formed by the shallow manganese acceptor in InSb at N _Mn∼N _cr. A model describing the gap formation is proposed. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 5, 358–362 (10 March 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Size Characterization of Fibres and Fines in Hardwood Kraft Pulps

The aim of this work was the characterisation of the primary components of papermaking pulp, i.e. fibres and fines. Although it included the measurement of fibre dimensions, this work was mainly devoted to sizing fines, applying methods other than those frequently used for pulp quality control. Therefore, in addition to the Kajaani method, image analysis, laser diffraction and the electrical sensing zone method were also utilised. A chemical pulp was tested before and after laboratory refining. Finally, an evaluation was made of the handsheet strength and optical properties prepared with these pulps, with and without fines, in order to study the effect of the beating process and of the fines.     

Calculating Shape Factors from Particle Sizing Data

It is well established that particle size and shape substantially influence the bulk properties of powdered materials. Although these characteristics are closely interrelated, the tendency has been to analyse the particle size independently from particle shape. The aim of this work was the assessment of particle shape through particle sizing data. For this purpose, three different particle shape materials – glass beads (spherical), crushed glass (moderately irregular) and mica (lamellar) – were tested, employing four particle sizers. The shape factor selected was the Wadell's sphericity, which was evaluated utilizing distinct equations. The comparison of the results reveals problems arising from the use of approximations rather than more fundamental equations.     

Synthesis and structure of 2-substituted pyrene-derived scaffolds

Pyrenes bear a propensity to form fluorescent excimers, and thus this chromophore is often found in sensors and fluorescent probes. 2-Functionalized pyrenes are of particular interest, however the preparation of these scaffolds is not trivial, involving synthetic routes that require 4,5,9,10-tetrahydropyrene as a key intermediate. Herein, the development and optimization of routes for the synthesis of 2-functionalized pyrene-derived building blocks, with potential to be used as tags in the preparation of fluorescent probes, is described. Additionally, the crystal structures of ethyl 4,5,9,10-tetrahydro-2-pyrene-5-oxopentanoate and 2-acetyl-4,5,9,10-tetrahydropyrene revealed distinct conformations of the saturated tetrahydropyrene rings.     

Synthesis of 5-substituted 2,3-dihydrobenzofurans in a one-pot oxidation/cyclization reaction

Variously substituted 2,3-dihydrobenzofurans have been synthesized according to a sequential one-pot oxidation/cyclization procedure between para-aminophenol derivatives and an azadiene.     

Characteristics of fixed-shape pulses emerging from pulsating,erupting, and creeping solitons

It is known that one of the impacts of combined higher-order effects, namely the intrapulse Raman scattering, third-order dispersion, and self-steepening, on the plain-pulsating, erupting, and creeping soliton solutions of the complex Ginzburg–Landau equation is the change of its periodic behavior and its transformation into fixed-shape solutions. In this work, we numerically find the regions in the parameters space in which these solutions exist. We also characterize their velocities, shapes, and chirp.     

Electrospray ionization mass spectrometric analysis of newly synthesized α,β‐unsaturated γ‐lactones fused to sugars

Knowledge of the fragmentation mechanisms of lactones and their behaviour under electrospray ionization (ESI) conditions can be extended to larger and more complex natural products that contain an α,β‐unsaturated γ‐lactone moiety in their structure. Moreover, little is known about the gas‐phase behaviour of α,β‐unsaturated γ‐lactones linked or fused to sugars. Therefore, five α,β‐unsaturated γ‐lactones (butenolides) fused to a pyranose ring, recently synthesized compounds with potential relevance regarding their biological properties, were investigated using ESI‐MS and ESI‐MS/MS in both positive and negative ion modes. Their fragmentation mechanisms and product ion structures were compared. It was observed that two isomers could be unambiguously distinguished in the negative ion mode by the fragmentation pathways of their deprotonated molecules as well as in the positive ion mode by the fragmentation pathways of either the protonated or the sodiated molecule. Fragmentation mechanisms are proposed taking into account the MS/MS data and semi‐empirical calculations using the PM6 Hamiltonean. The semi‐empirical calculations were also very useful in determining the most probable protonation and cationization sites. Copyright © 2010 John Wiley & Sons, Ltd.     

Growth of (Perylene)2 [Pd(mnt)2] crystals

The conditions for the growth of (Perylene)₂ [Pd(mnt)₂] crystals either by chemical oxidation and electrochemical routes are described. The electrocrystallisation is limited by close proximity of the oxidation potentials of the perylene donor and [Pd(mnt)₂]^? anion, and depending on the experimental conditions different morphologies can be obtained. (Per)₂ [Pd(mnt)₂] crystals obtained by elecrocrystallisation were found to be mainly of the β-polymorph with properties comparable to the Cu, Ni and Pt analogues previously described at variance with those obtained by chemical oxidation which are mainly of the α-polymorph .