Magnon modes and impurity spin resonance in FeBr2 doped with 1% Mn2+

We report results of far infrared magneto-absorption experiments in FeBr₂ doped with 1% MnBr₂. Using radiations from several carcinotrons covering the frequency range 77–600 GHz, we observe both the spectra corresponding to the localized Mn²⁺ impurity modes and the uniform magnon modes of the host crystal. The excitation energy gap of the A.F. magnons at zero field is E_o = 500 ± 2 GHz.     

Non-uniqueness in writing Schrödinger kernel as a functional integral

We consider a path integral in phase space involving a linear functional of the classical Hamiltonian and find the Schrödinger equation of which it is a propagator. Conversely, to any quantum Hamiltonian, we associate a whole family of functionals and hence of expressions of the same Schrödinger kernel; all this is carried out independently of any correspondence principle.     

Electromagnetic waves near perfect conductors. II. Casimir effect

The Casimir free energy of the electromagnetic field in regions bounded by thin perfect conductors with arbitrary smooth shapes is studied. This free energy is expressed as a convergent multiple scattering expansion, in which the wave is damped between scatterings taking place on conductors. The result depends neither on the large box needed to render the spectrum discrete, nor on the shape of the high frequency cut-off corresponding to slightly imperfect conductivity; this establishes the universal character of quantum electro-magnetic forces on perfectly conducting thin objects.General expansions are derived for the Casimir free energy in the low and high temperature limits. They exhibit a dependence on the topology of the conducting surfaces. At low temperature, the Casimir entropy vanishes as T³ for simply connected conductors, and as T for multiply connected ones. At high temperature, the free energy has the semiclassical behavior ?$\text{C}$$\text{T}\text{log}\text{(}\text{T}\text{h}\text{?}\text{cQ}\text{)}$. The constant $\text{C}$ = $\text{(128φ)}{}^{\mathrm{?1}}\text{?dθ(}\text{3}\text{R}{}_1{}^2\text{+}\text{3}\text{R}{}_2{}^2\text{+}\text{3}\text{R}{}_1\text{R}{}_2\text{)?n}$ may be interpreted as the number of additional modes of finite frequency created by introducing the conducting surface. It depends on the topology of the surface through its genus n, and on its local curvature radii R₁, R₂. The average wave number Q depends on the shape of the surface and its size. The symmetry between low and high temperatures is recovered for parallel plates.While a plane foil is stable against Casimir stresses at zero temperature, such stresses would tend at finite temperature to create wrinkles of dimensions larger thn 2.9 $\text{h}\text{?}\text{c}\text{T}$. The same wrinkling effect exists for an arbitrary conductor at high enough temperature. The presence of a curved conducting surface transfers the free energy of radiation from the concave to the convex side at zero temperature, and does the converse at high enough temperatures. Wedges may be considered for slightly imperfect conductors; the electro-magnetic energy is lowered at finite temperature by creation of wedges, and also at zero temperature by creation of multiple wedges as in a honeycomb structure.The formalism is also applied to evaluate Van der Waals forces and torques at arbitrary temperature between remote conductors, and to show that the Casimir energy of a cylinder at zero temperature vanishes to lowest order in the multiple scattering expansion.Finally, the sphere is used as a test for studying convergence of the multiple scattering expansions. Using radial and transverse combinations of vector spherical harmonics yields a simple expression for the electromagnetic Green functions. This expression is recovered by summation of the multiple scattering expansion; the convergence domain, in the plane kR = x + iy, of the expansion includes a neighborhood of the origin, as well as the whole region $\text{y >0.0348 |x|}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$. The numerical convergence of the Casimir free energy is rapid, the lowest order term already yields a result with less than 7% error.     

Synthesis of trans-thienyl-3-ethoxycarbonyl-2,3-dihydro[1,5]benzothiazepin-4(5H)-ones

A series of trans-thienyl-3-ethoxycarbonyl-2,3-dihydro[1,5]benzothiazepin-4(5H)-ones 6-8 was synthesized from thienylmethylidenemalonates 3a-3c and 2-aminobenzenethiol 3d in the presence of triethylamine hydrochloride at 160°. The [1,5]benzothiazepines 6-8 were alkylated using 2-dimethylaminochloroethane, 3-dimethylaminochloropropane and 3-(N-piperidino)chloropropane in order to obtain the corresponding 5-aminoalkylbenzothiazepinones 9-14 .     

A tomographic approach to Wigner's function

We propose a new derivation of Wigner's function based on the property of positivity of its integrals along straight lines in phase space. Identifying the values of these marginalizations with densities pertaining to invariant observables, we are able to reconstruct Wigner's pseudo-distribution from its slices.     

European research platform IPANEMA at the SOLEIL synchrotron for ancient and historical materials

IPANEMA, a research platform devoted to ancient and historical materials (archaeology, cultural heritage, palaeontology and past environments), is currently being set up at the synchrotron facility SOLEIL (Saint‐Aubin, France; SOLEIL opened to users in January 2008). The new platform is open to French, European and international users. The activities of the platform are centred on two main fields: increased support to synchrotron projects on ancient materials and methodological research. The IPANEMA team currently occupies temporary premises at SOLEIL, but the platform comprises construction of a new building that will comply with conservation and environmental standards and of a hard X‐ray imaging beamline today in its conceptual design phase, named PUMA. Since 2008, the team has supported synchrotron works at SOLEIL and at European synchrotron facilities on a range of topics including pigment degradation in paintings, composition of musical instrument varnishes, and provenancing of medieval archaeological ferrous artefacts. Once the platform is fully operational, user support will primarily take place within medium‐term research projects for `hosted' scientists, PhDs and post‐docs. IPANEMA methodological research is focused on advanced two‐dimensional/three‐dimensional imaging and spectroscopy and statistical image analysis, both optimized for ancient materials.     

CO disrupts the reduced H-cluster of FeFe hydrogenase. A combined DFT and protein film voltammetry study

Carbon monoxide is often described as a competitive inhibitor of FeFe hydrogenases, and it is used for probing H(2) binding to synthetic or in silico models of the active site H-cluster. Yet it does not always behave as a simple inhibitor. Using an original approach which combines accurate electrochemical measurements and theoretical calculations, we elucidate the mechanism by which, under certain conditions, CO binding can cause permanent damage to the H-cluster. Like in the case of oxygen inhibition, the reaction with CO engages the entire H-cluster, rather than only the Fe(2) subsite.