Vibrational analyses of silacyclopentanes

The complete infrared and Raman spectra of 1,1-difluoro-1-silacyclopentane and 1,1-dichloro-1-silacyclopentane have been recorded and analyzed. Furthermore, a number of the vibrational frequencies of the silacyclopentane and silacyclopentane-1, 1-d₂ molecules have been reassigned.A normal coordinate calculation for each of these molecules was carried out and this demonstrated the validity of the assignments. Considerable mixing of the modes was found especially where ring vibrations and SiX₂ motions were involved.     

Observation of Brillouin scattering in mixed InxGa1−xP crystals

Brillouin scattering is observed in the In_xGa_1?xP solid solution with 0.38 ? × ? 0. The composition dependences of the longitudinal and transverse acoustic phonons propagating along the [111] direction are investigated and compared with the expressions derived by Lakshmi et al. from the random element isodisplacement theory. Pronounced broadening of the Brillouin peaks is observed with the increasing amount of In in GaP.     

Observation of a diamagnetic signal up to 132 K in a Tl−Ca−Ba−Cu−O compound

Tl–Ca–Ba–Cu–O compounds of the nominal composition of (1, 1, 1, 1) have been prepared from different starting materials and with the same heat treatment process. During the investigation of their properties a diamagnetic signal has been found up to the temperature of 132 K. This hints at the existence of a certain material content distributed into discrete superconducting domains. The parameters of it reflect a superstructure of the (2, 2, 2, 3) and (2, 1, 2, 2) compositions having a time-dependent behaviour. On the basis of the signal levels at 132 K and 4.2 K, the quantity of the high temperature superconducting material is about 0.01% of the total one at liquid He temperatures.     

Line group theory of commensurate and incommensurate modulations

It is shown that the line group formalism proposed is suitable to describe both commensurate and incommensurate modulations. Symmetry groups of modulated crystal lattices can completely be characterized by symmetry transformations existing in real space, without any application of the formalism based on reciprocal space. As typical examples of the method elaborated, the fundamental invariance and symmetry properties of spin density functions and the soliton lattice are determined. Received: 20 July 1997 / Accepted: 25 August 1997     

Probing the negative Wigner function of a pulsed single photon point by point

We investigate quantum properties of pulsed light fields point by point in phase space. We probe the negative region of the Wigner function of a single photon generated by the means of waveguided parametric down conversion. This capability is achieved by employing loss-tolerant photon-number resolving detection, allowing us to directly observe the oscillations of the photon statistics in dependence of applied displacements in phase space. Our scheme is highly mode sensitive and can reveal the single-mode character of the signal state.     

A reform in undergraduate mathematics curriculum : more emphasis on social and pedagogical skills

The paper describes the changes that are being made in the mathematics teachers' subject studies in the Department of Mathematics at the University of Joensuu, in order to provide our mathematics students both with a sufficiently deep knowledge of mathematics and science, and with present-day expertise in their profession as teachers. While the formal structure of the mathematics curriculum remains structured and taught as courses with mostly traditional names like algebra, analysis, and linear algebra, there are also totally new ‘professionally oriented’ courses. Some of the old courses—with rather traditional and rigorous contents—have been changed in a more student-driven direction. In these ‘pedagogically oriented’ courses students are encouraged, and even forced, to study co-operatively in social interaction, for example to negotiate how to solve a problem decently, or how to build a formal definition for a concept with certain wanted attributes. As an ultimate example of a pedagogical experiment we describe in more detail an abstract algebra course, where co-operative learning is combined with intensive programming in a mathematically oriented computer environment.     

The daguerreotype surface as a SERS substrate: characterization of image deterioration in plates from the 19th century studio of Southworth & Hawes

Dramatic condition changes were noted in a group of daguerreotypes during a 10 month‐long exhibition featuring masterworks of the prominent Boston‐based studio of Southworth & Hawes. The changes took the form of a hazy, extended white surface layer and of white spots that partially obscured the images after between four weeks and 10 months of exhibition. Raman spectroscopy, complemented by in situ scanning electron microscopy–energy dispersive X‐ray spectrometry (SEM–EDS), was used to nondestructively characterize this form of image deterioration in eight representative daguerreotypes from the studio. Raman proved to be a sensitive technique to noninvasively identify the compounds on the plates due to the fact that their Ag surfaces behave as surface‐enhanced Raman scattering (SERS) substrates. A band at ca 242 cm⁻¹ assigned to the Ag Cl stretching mode was observed in the areas where a white surface layer or white spots are present. In some of the areas probed, substituted aromatic compounds were also detected. The presence of Ag Cl bonds on daguerreotype surfaces has profound implications for their exhibition and preservation due to the photosensitivity of silver chloride in the ultraviolet–visible range, which can generate metallic silver that would redeposit on the surfaces. The possible sources of the compounds detected on the surfaces of the plates are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Conductivity of La1−x CaxMnO3 under magnetic resonance of Mn ions

A change in the electrical conductivity, σ, is observed in the manganese perovskite La_1?x Ca_xMnO₃, with x=0 and 0.3 under saturation of the magnetic resonance transitions of Mn ions. This effect has a maximum in the temperature range of the magnetic phase transition of the compounds. Two contributions to the change in σ are found. The first, dominating in LaMnO₃, is an increase in σ caused by heating of the sample under magnetic resonance. The second is a σ decrease due to reorientation of the Mn spins, observed in La_0.7Ca_0.3MnO₃.