Interplay between lattice dynamics and the low-pressure phase of simple cubic polonium

Low-pressure structural properties of simple cubic polonium are explored through first-principles density-functional theory based relativistic total energy calculations using pseudopotentials and plane-wave basis set, as well as linear-response theory. We have found that Po undergoes structural phase transition at low pressure near 2 GPa, where the element transforms from simple cubic to a mixture of two trigonal phases namely, hR1 (α=86°) and hR2 (α=97.9°) structures. The lattice dynamics calculations provide strong support for the observed phase transition, and show the dynamical stability (instability) of the hR2 (hR1) phase.     

Microwave‐Assisted Synthesis of Quinoline Derivatives from Isatin

Microwave irradiation has been used for a rapid and efficient synthesis of quinoline‐4‐carboxylic acids 5a–g and 1,2,3,4‐tetrahydroacridine‐9‐carboxylic acid (6) from the reaction of isatins 1–3 with acyclic and cyclic ketones in basic medium. 2‐Hydroxyquinoline‐4‐carboxylic acid (11) was also obtained by irradiating a mixture of isatin 1 and malonic acid in AcOH. The esters of 5f and 11 and their respective hydrazides 8 and 13 were also prepared under MWI.     

A new technique to characterize mono-molecular micelles in random ethylene–propylene copolymers

A new technique to investigate the nano-structure of ethylene–propylene (EP) random copolymers has been developed. It consists in the measurement of the turbidity which develops at a lower critical solution temperature (LCST) in pentane solutions. The information on the solution comes from different types of turbidity obtained during a step-by-step temperature increase. The transient turbidity (h_i) is associated with random coils (I) and structured coils (II) while the stable turbidity comes from aggregates (III). The proportion of (I), (II) and (III) depends on the solution history and on the solvent. The M_w distribution can be obtained from the set h_i (T_i) of (I). Turbidity (II) has an unexpected gap in the h_i (T_i) trace. The gap (10–20 K) is explained by the presence of two entities in solution. Their temperatures of phase separation permit their identification as monomolecular micelles, whose outer core is either E-rich or P-rich. This nano-structure is thought to exist in the solid and also in solution as a metastable state. The technique can differentiate between mobile chains in solutions (I, II) and attached chains in a network (III) through the sedimentation behaviour of the concentrated phase. Three samples with a similar (EP) content (0.75) made with different catalysts have been analysed by LCST and slow calorimetry.     

Independent component analysis as a pretreatment method for parallel factor analysis to eliminate artefacts from multiway data

Parallel factor analysis (PARAFAC) has successfully been used in many applications for the analysis of excitation-emission fluorescence data. However, some measurement “artefacts”, such as Rayleigh or Raman scattering, can pose a problem for the extraction of the PARAFAC components and their interpretation. Replacing the spectral zones corresponding to these signals by missing values in the data is not necessarily a method of choice in the cases where informative signals lie in the same wavelength regions. In this article, independent component analysis (ICA) is used on the unfolded cubic array, and the independent components related to the Rayleigh and Raman scattering are identified and removed prior to the reconstruction of the excitation-emission fluorescence data cube. PARAFAC is then applied on these data reconstructed after selective artefact removal, and satisfactory models can be obtained. This procedure, although particularly useful for 3D fluorescence data, may be applied to other types of data as well.     

Effect of organic modifier and temperature on the resolution of betamethasone and dexamethasone using a porous graphitic carbon column: application to their identification and confirmation in human urine by LC-ESI-MS/MS

The effects of temperature, organic modifier and the type of acid on the retention factor, the resolution and peak shape of betamethasone and dexamethasone are described. The study is performed using narrow bore porous graphitic carbon (PGC) columns online with diode-array detector (DAD) and ESI MS/MS. The results show that temperature affects the retention behaviour of the two compounds and ACN yields the best separation while no effect is obtained by changing the type of organic acid. The developed method is applied for the confirmation of dexamethasone and betamethasone in human urine.     

Preparation and characterization of In<Subscript>2</Subscript>S<Subscript>3</Subscript> semiconductor thin films using the sol–gel method

This study describes the In₂S₃ semiconductor thin film coating on glass substrate by sol–gel method. The In₂S₃ thin film samples were prepared and examined by the X-ray diffraction (XRD), the UV–visible optical absorption and transmission study, and the Scanning Electron Microscope (SEM) image analyses. The XRD analysis results show that the In₂S₃ semiconductor thin films prepared by sol–gel method is formed at T~360–520 °C temperature interval. Band gap energy and optical absorption spectrum analysis of the In₂S₃ thin films reveal that Eg~2.51 eV for the In₂S₃ thin films. According to the EDX result the film was In-rich with the In/S = 1.42 ratio. The thickness of prepared In₂S₃ layer is about 400 nm.     

Imposing changes of band and spin–orbit gaps in GaNBi

We present first-principles pseudopotential plane-wave calculations to explore the effects of alloying of non conventional III–V compound GaN with bismuth. We found a highly nonlinear reduction of the energy gap of GaN for small Bi composition. Consequently the optical band gap bowing is found extremely important and composition dependent. The stronger contribution is due principally to structural and, to less extent, to charge transfer effects. Moreover, because of strong relativistic effects caused by bismuth, we found a giant bowing for the spin–orbit splitting energy of valence band, by far the largest of any III–V ternary alloys.     

Nonlinear forced vibrations of rotating anisotropic beams

This work deals with forced vibration of nonlinear rotating anisotropic beams with uniform cross sections. Coupling the Galerkin method with the balance harmonic method, the nonlinear intrinsic and geometrically exact equations of motion for anisotropic beams subjected to large displacements, are converted into a static formulation. This latter is treated with two continuation methods. The first one is the asymptotic-numerical method, where power series expansions and Padé approximants are used to represent the generalized vector of displacement and the frequency. The second one is the pseudo-arclength continuation method. Numerical tests dealing with isotropic and anisotropic beams are considered. The natural frequencies obtained for prismatic beams are compared with the literature. Response curves are obtained and the nonlinearity is investigated for various geometrical conditions, excitation amplitudes and kinematical conditions. The nonlinearity related to the angular speed for prismatic isotropic beam is thus identified. The stability of the solution branch is examined, in the frequency domain using the Floquet theory.     

Unifying description of the optical properties of InN from first principles

The optical properties of hexagonal InN have been studied using the all-electron approach based on density functional theory (DFT). The full-potential augmented plane wave method is employed with two different exchange-correlation potentials, the Perdew–Wang (PW) and the Engel–Vosko (EV) approximations. In addition, both non-relativistic and relativistic approximations are considered. We found that the PW and relativistic approximations give a metallic ground state; whereas using the EV and non-relativistic approximations a semiconductor phase is obtained, opening the gap up to 0.83 eV. Besides, the calculated interband transitions of the complex dielectric function up to 13 eV show favourable agreement with the recent spectroscopic ellipsometry results.     

Relativistic effects on the structural and transport properties of III–V compounds: A first-principles study

We have performed ab initio self-consistent calculations based on the full potential linear augmented plane-wave method (FP-LAPW) with the local density approximation (LDA) and the Generalised Gradient Approximation (GGA) to investigate the relativistic effects, on the structural, and transport properties of III–V compounds. We found that the stabilisation (destabilisation) of s, p^∗(p,d) orbital energies (i) reduces the lattice parameters of III–V compounds, considerably reduces the band gaps of the III–V compounds, (ii) reduces the effective masse, and (iii) induces strong spin orbit splitting of heavier III–V compounds. Furthermore we circumvent the negative gap problem by combining non relativistic and Engel–Vosko approximations. These approaches open the gap of the most III–V compounds, and leads to a realistic band structure.