Nanostructured carbon arrays from block copolymers of polyacrylonitrile

Arrays of graphitic carbon nanoclusters were obtained by pyrolysis of nanoscale phase-separated block copolymers of polyacrylonitrile and poly(n-butyl acrylate). Upon heating in an inert atmosphere to temperatures ranging from approximately 400 to 1200 degrees C, polyacrylonitrile domains were converted into carbon nanoclusters, maintaining the overall shape and spacing, whereas the poly(n-butyl acrylate) phase was sacrificed. Preservation of the original nanoscale morphology of a block copolymer was possible only if pyrolysis was preceded by oxidation at temperatures of approximately 230 degrees C, in analogy with thermal stabilization of polyacrylonitrile precursor in the process used in the manufacturing of carbon fibers. Preorganization of the carbon precursor through self-assembly in block copolymers of polyacrylonitrile appears to be an attractive and robust strategy for templated synthesis of well-defined nanostructured carbon materials.     

Pharmaceutical approaches involving carvedilol characterization,compatibility with different excipients and kinetic studies

This study was performed to investigate the physical–chemical characteristics of carvedilol (CRV), complemented by compatibility studies with a great variety of pharmaceutical excipients. Thermogravimetry and differential scanning calorimetry, supported by diffuse reflectance infrared fourier transform spectroscopy (DRIFT), X-ray powder diffraction, and scanning electron microscopy (SEM) were selected as the solid-state techniques for the intended analyses. In addition, non-isothermal methods were employed to investigate kinetic data of CRV decomposition process under nitrogen and air atmospheres. CRV is characterized by an endothermic sharp event (T _peak = 389.81 K and ΔH _fusion of ?176.28 J g^?1) and a thermal decomposition behavior in two stages, totalizing 98 % of mass loss. The CRV pattern diffraction presents prominent peaks at 2θ: 5.92°, 14.90°, 18.62°, 24.47°, and 26.30°, and the DRIFT spectrum showed the main characteristics bands for CRV chemical functional groups. The SEM photomicrographs demonstrate that CRV is characterized by irregular blocky shaped crystals. Zero order kinetics was determined by Ozawa method in both nitrogen and air atmospheres. The compatibility results showed no evidence of any incompatibility among CRV and all the excipients analyzed.     

Binding,Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes

The bridging MeCN ligand in the dicopper(I) complexes [(DPFN)Cu₂(μ,η¹ : η¹-MeCN)][X]₂ (X=weakly coordinating anion, NTf₂ ( 1 a ), FAl[OC₆F₁₀(C₆F₅)]₃ ( 1 b ), Al[OC(CF₃)₃]₄ ( 1 c )) was replaced by white phosphorus (P₄) or yellow arsenic (As₄) to yield [(DPFN)Cu₂(μ,η² : η²-E₄)][X]₂ (E=P ( 2 a – c ), As ( 3 a – c )). The molecular structures in the solid state reveal novel coordination modes for E₄ tetrahedra bonded to coinage metal ions. Experimental data and quantum chemical computations provide information concerning perturbations to the bonding in coordinated E₄ tetrahedra. Reactions with N-heterocyclic carbenes (NHCs) led to replacement of the E₄ tetrahedra with release of P₄ or As₄ and formation of [(DPFN)Cu₂(μ,η¹ : η¹-^MeNHC)][X]₂ ( 4 a,b ) or to an opening of one E−E bond leading to an unusual E₄ butterfly structural motif in [(DPFN)Cu₂(μ,η¹ : η¹-E₄^DippNHC)][X]₂ (E=P ( 5 a,b ), E=As ( 6 )). With a cyclic alkyl amino carbene (^EtCAAC), cleavage of two As−As bonds was observed to give two isomers of [(DPFN)Cu₂(μ,η² : η²-As₄^EtCAAC)][X]₂ ( 7 a,b ) with an unusual As₄-triangle+1 unit.     

Multi-year cycles observed in air temperature data and proxy series

First, palaeoclimatic time series are analyzed under the lens of the continuous wavelet transform. Two cycles, of period 30 and 43 months respectively, are detected in millennial temperature reconstructions. These rhythms correspond to the ones detected in weather station temperature records in a previous study of the authors. It is then showed that most parts of the globe are affected by at least one of the two cycles. Their relationship with the main climatic indices is also investigated, as well as the statistical significance of the observations.     

A wavelet-based mode decomposition

We propose a wavelet-based method for analyzing non-stationary data. The idea, inspired by the empirical mode decomposition, is to decompose a data set into a finite number of components, well separated in the time-frequency plane, plus a residue, such that each component has a zero mean and is associated to one frequency only. When applied to climatic data, this method gives interesting results.     

Synthesis of hyperbranched degradable polymers by atom transfer radical (Co)polymerization of inimers with ester or disulfide groups

Degradable hyperbranched polymers with multiple alkyl halide chain ends were synthesized by the atom transfer radical polymerization of inimers containing ester (2‐(2′‐bromopropionyloxy)ethyl acrylate) or disulfide (2‐(2′‐bromoisobutyryloxy)ethyl 2′′‐methacryloyloxyethyl disulfide) groups. Both the homo‐ and copolymerizations (with styrene in the former case and methyl methacrylate in the latter) were studied. The hyperbranched polymers derived from the ester‐type inimer were hydrolytically degradable under basic conditions, whereas those derived from the disulfide‐containing inimer could be efficiently degraded in the presence of reducing agents such as tributylphosphine. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Some equivalent definitions of Besov spaces of generalized smoothness

In this paper, we present some alternative definitions of Besov spaces of generalized smoothness, defined via Littlewood–Paley‐type decomposition, involving weak derivatives, polynomials, convolutions and generalized interpolation spaces.     

In-band M1 and E2 transition rates and collective structures in Ba

Subpicosecond mean lifetimes of eight excited states in ¹²⁸Ba populated via the ⁹⁶Zr(³⁶S,4n) reaction were measured by the Doppler-shift attenuation (DSA) technique using a line-shape analysis. The differential decay-curve method (DDCM) was applied for the lifetime determination. The B(E2) values in the yrast band indicate that the first band-crossing is with a proton S-band. The configuration πh_11/2d_5/2 of the negative-parity semi-decoupled bands is confirmed by the measured B(E2, I → I − 2) and B(M1, I → I − 1) transition strengths. The higher-lying “dipole” band in ¹²⁸Ba can be described as a high-K four-quasiparticle band built on the prolate configuration (πh_11/2d_5/2) (νh_11/2g_7/2).     

Paramagnetische Relaxation im Terbiumäthylsulfat

The paramagnetic relaxation of Tb_0,01 Y_0,99(C₂H₅SO₄)₃·9H₂O at temperatures between 1,14°K and 4,21°K has been investigated with the absorption-dispersion method at frequencies between 5 sec^?1 and 10240 sec^?1 and different magnetic fields. AtH=700 Oe. The relaxation time follows the equationτ ^?1=[A H ³ coth (g _z μ _B H/2k T)+B T ⁷] sec^?1 as a function of temperature. ForH<800 Oe the paramagnetic relaxation is influenced by cross relaxation processes between the hyperfine structure levels.