Semipolar (11\bar 2\bar 2) ZnO thin films grown on LaAlO3‐buffered LSAT (112) single crystals by pulsed laser deposition

Semipolar (11\bar 2 \bar 2) ZnO was successfully grown on (112) LaAlO₃/(LaAlO₃)_0.29(Sr₂AlTaO₆)_0.35 substrate by pulsed laser deposition. The epitaxial relationship is [11\bar 23]_{\rm ZnO} // [11\bar 1]_{\rm LAO/LSAT} with the polar axis of [000\bar 1]_{\rm ZnO} pointing to the surface. For ZnO films with thickness of 1.6 μm, the threading dislocation density is ～1 × 10⁹ cm^–2, and the density of basal stacking faults is below 1 × 10⁴ cm^–1. The (11\bar 2 \bar 2) ZnO exhibits strong D⁰X emissions with a FWHM of 9 meV and very few green–yellow emissions in the low‐temperature (10 K) and room‐temperature photoluminescence spectra, respectively.

     

High oxygen pressures and the stabilization of six-coordinated Ir(VI) in an oxygen lattice

Abstract

During these last twenty five years a great efforts have been made in the Laboratoire de Chimie du Solide du CNRS in order to develop high oxygen pressure for the stabilization of unusual oxidation state of transition elements.

The aims of such research works was to correlate the increase of the Mⁿ⁺-O bond covalency versus the increase of the oxidation state n+ to the physicochemical properties of resulting oxides [1].

Iridium was an interesting element due to its position (5d) in the Periodic Table. In 1980 Ir(V) (d⁴) was stabilized in La₂LiIrO₆ in the perovskite structure [2]. Such a study had underlined the strong value of the spin-orbit coupling associated to Ir(V) [3].

The stabilization of Ir(VI) is interesting from two points of view : (i) its isotropic electronic configuration (d³), (ii) such a high oxidation state could lead to the strongest M-O bond in an oxygen lattice.

Selecting, through a specific methodology, the most appropriate local structural and chemical factors and with the help of high oxygen pressure, Ir(V1) was stabilized in the perovskite Ba₂CaIrO₆. Structural, magnetic and Mössbauer studies have been carried out in order to characterize the physicochemical properties induced by this unusual oxidation state.     

15N/14N Analysis of Amino Acids with GC-C-IRMS - Methodical Investigations and Ecotoxicological Applications

Abstract

In order to perform the ¹⁵N/¹⁴N analysis of amino acids using a gas chromatograph and isotope ratio mass spectrometer linked up via a combustion interface (GC-C-IRMS), the amino acids must be derivatized. Tert-butyldimethylsilylation is examined using various techniques (direct conversion to nitrogen gas, ConFlo-IRMS [1], GC-C-IRMS [2]) and subsequently applied to isotopic characterization of amino acids from wheat protein hydrolyzate obtained from plants exposed to ozone. The method provides a reliable tool for studying ecotoxicological effects on plants at a molecular level in addition to the investigation of the natural variations of different N fractions.     

Dynamics of surface dipole and tripole solitons in nonlocal nonlinear media with optical lattice field

We find the existence conditions for stationary dipole and tripole surface solitons formed at the interface of a nonlocal nonlinear medium and a lattice with linearly modulated frequency. We investigate how the degree of nonlocality, the depth, and the modulation frequency of the optical lattice field affect on the existence of the surface solitons and their dynamics. The relationship between the power and the model parameters is identified. The stability of the surface dipole and tripole solitons is numerically investigated.     

Size-dependent chemical transformation,structural phase change,and optical properties of nanowires

Nanowires offer a unique approach for the bottom-up assembly of electronic and photonic devices with the potential of integrating photonics with existing technologies. The anisotropic geometry and mesoscopic length scales of nanowires also make them very interesting systems to study a variety of size-dependent phenomenon where finite-size effects become important. We will discuss the intriguing size-dependent properties of nanowire systems with diameters in the 5–300?nm range, where finite-size and interfacial phenomena become more important than quantum mechanical effects. The ability to synthesize and manipulate nanostructures by chemical methods allows tremendous versatility in creating new systems with well-controlled geometries, dimensions, and functionality, which can then be used for understanding novel processes in finite-sized systems and devices.     

Acoustic behaviour and equation of state of amorphous ethylene–vinyl acetate copolymer studied by means of high-pressure Brillouin scattering spectroscopy

The determination of the equation of state (EOS) of amorphous materials is very important for fundamental understanding of the glass transition and applications as well. Simultaneous observation of both longitudinal and transverse acoustic modes by Brillouin scattering spectroscopy has been one of the major methods to obtain EOS of amorphous materials. However, the transverse acoustic mode is hardly seen from some of the amorphous polymers, which makes it difficult to derive EOS. The temperature and pressure dependences of the acoustic properties of amorphous ethylene–vinyl acetate (EVA) copolymer were measured by using high-pressure Brillouin scattering spectroscopy. The temperature variation induced large changes in the frequency shift and linewidth of the longitudinal acoustic mode due to strong coupling between the structural relaxation process and the propagating density fluctuations. The residual linewidth in the glassy state was attributed to the remnant intramolecular motions of EVA, the activation energy of which was estimated to be ～3.30 ± 0.27 kcal/mol. The pressure–density relationship of EVA could be obtained for the first time by measuring the refractive index and using the Lorentz–Lorenz equation. The density and the refractive index exhibited monotonic increase up to approximately 12 GPa. The strong reduction of the acoustic damping at low pressures below ～3 GPa was attributed to the collapsing free volume in EVA. The present study clearly shows that measuring the refractive index by high-pressure Brillouin spectroscopy may be an alternative method to get the EOS of polymeric materials whose transverse acoustic mode is too weak to be observed.     

Surfaces with simple geodesics through a point

We study compact connected surfaces inm-dimensional Euclidean spaceE ^m (3 m 5) with a point through which every geodesic is aW-curve regarded as a curve in E^m.     

Dynamic Point Location in General Subdivisions

The dynamic planar point location problem is the task of maintaining a dynamic set S of n nonintersecting (except possibly at endpoints) line segments in the plane under the following operations:

• Locate (: point): Report the segment immediately above , i.e., the first segment intersected by an upward vertical ray starting at ;

• Insert (: segment): Add segment to the collection of segments;

• Delete (: segment): Remove segment from the collection of segments.

We present a solution which requires space O(n) and has query and insertion time O(log n log log n) and deletion time O(log²n). The bounds for insertions and deletions are amortized. A query time below O(log²n) was previously only known for monotone subdivisions and subdivisions consisting of horizontal segments and required nonlinear space.     

Minimizing Maximum Weighted Error for Imprecise Computation Tasks

We consider the problem of preemptively scheduling a set of imprecise computation tasks on m ≥ 1 identical processors, with each task T_i having two weights, w_i and w′_i. Two performance metrics are considered: (1) the maximum w′-weighted error; (2) the total w-weighted error subject to the constraint that the maximum w′-weighted error is minimized. For the problem of minimizing the maximum w′-weighted error, we give an algorithm which runs in O(n³ log²n) time for multiprocessors and O(n²) time for a single processor. For the problem of minimizing the total w-weighted error subject to the constraint that the maximum w′-weighted error is minimized, we give an algorithm which also has the same time complexity.     

A remark on nilpotent Lie Algebras

Letf(n) denoted the number of essential parameters which are needed to classifyn-dimensional nilpotent Lie Algebras over the complex number field. Then $f(2n) \geqslant \tfrac{{n(n2 - 7)}}{6} - 2$ .