Subsampling Unit Root Tests for Heavy-Tailed Observations

It is shown that the subsampling methodology can be used to develop unit root tests when the noise sequence is heavy-tailed with infinite variance. Using least-squares residuals, we construct processes which approximately satisfy the null hypothesis and then, using subsampling, we approximate the null distribution of test statistics. We establish the asymptotic validity of this method and demonstrate its applicability in finite samples by means of a simulation study and a data example.     

Preparation of new heterotopic ligands

A six-step synthesis of two new heterotopic ligands, each possessing two unusual N,N,N,O tetradentate binding subunits, has been developed. This work presents a particularly facile and rapid synthetic protocol for the preparation of these ligands, which one expected to act as useful components in inorganic self-assembly for the preparation of various types of complexes.     

Mobile-Phase Velocity — a Tool for Separation of Alkaloids by OPLC

JPC – Journal of Planar Chromatography – Modern TLC - Extracts of tertiary and quaternary alkaloids from Chelidonium majus L. have been separated by OPLC. Samples of different volumes...     

Iodine-promoted silylation of alcohols with silyl chlorides. Synthetic and mechanistic studies

An efficient silylating system for 1°, 2°, and 3° alcohols, consisting of a silyl chloride/N-methylimidazole/iodine, was developed. Synthetic and mechanistic aspects of this new reagent system, and particularly the role of iodine were investigated in detail using ¹H NMR spectroscopy.     

Kinetics of H→P cross-polarization in human trabecular bone

Bloch-decay and cross-polarization (CP) ³¹P nuclear magnetic resonance (NMR) spectra of healthy human trabecular bone were acquired under magic-angle spinning (MAS) at 3 kHz. A single peak at 3.1 ppm was detected. Variable-contact time ¹H → ³¹P CP experiments revealed three signal components growing at various rates. The fast, moderate and slow components were assigned and assessed in P atom % to proton-rich (24%), hydroxyapatite (58%) and proton-deficient (18%) phosphate domains, respectively. Examination of CP kinetics is useful for the chemical characterization of bone tissue.     

The influence of different factors on the stability and ultrafiltration of emulsified oil in water

The effects of different operating conditions on ultrafiltration (regenerated cellulose with a cut-off of 100 kg/mol) of cutting oil were studied for two different cases. The factors, examined at three levels, included: pH, oil concentration, feed flow velocity, and temperature. The salt (NaCl and CaCl₂) concentration was examined at three levels as well. A lower concentration range was used initially and was increased in the second case.     

Potassium trans-[bis(oxalato)diaquacobaltate(II)] tetrahydrate: synthesis, structure, potentiometric and thermal studies

The title compound, trans-K₂[Co(C₂O₄)₂(H₂O)₂]·4H₂O, was synthesised, and characterised by elemental analysis. Acid dissociation constants for the complex were determined by potentiometric titration and calculated by STOICHIO program. The crystal structure of trans-K₂[Co(C₂O₄)₂(H₂O)₂]·4H₂O was determined by X-ray diffraction studies. The asymmetric part of the unit cell contains one symmetric anion of oxalate and water molecule bound with Co(II) ion in crystallographic special position, one potassium cation and two molecules of water. Thermal properties of the complex were examined by thermogravimetric analysis (TGA). A decomposition mechanism is proposed on the basis of the results.     

Porosity of closed carbon nanotubes compressed using hydraulic pressure

Experimental data of nitrogen adsorption (T = 77.3 K) from gaseous phase measured on commercial closed carbon nanotubes are presented. Additionally, we show the results of N₂ adsorption on compressed (using hydraulic press) CNTs. In order to explain the experimental observations the results of GCMC simulations of N₂ adsorption on isolated or bundled multi-walled closed nanotubes (four models of bundles) are discussed. We show that the changes of the experimental adsorption isotherms are related to the compression of the investigated adsorbents. They are qualitatively similar to the theoretical observations. Taking into account all results it is concluded that in the “architecture” of nanotubes very important role has been played by isolated nanotubes.     

Enantioselective Synthesis of Alcohols and Amines by Iridium‐Catalyzed Hydrogenation,Transfer Hydrogenation,and Related Processes

The preparation of chiral alcohols and amines by using iridium catalysis is reviewed. The methods presented include the reduction of ketones or imines by using hydrogen (hydrogenations), isopropanol, formic acid, or formate (transfer hydrogenations). Also dynamic and oxidative kinetic resolutions leading to chiral alcohols and amines are included. Selected literature reports from early contributions to December 2012 are discussed.     

Synthesis of Polycyclic Aminocyclobutane Systems by the Rearrangement of N‐(ortho‐Vinylphenyl) 2‐Azabicyclo[3.1.0]hexane Derivatives

The acid‐catalysed thermal rearrangements of a family of N‐aryl 2‐azabicyclo[3.1.0]hexanes is described. These substrates, designed in such a way that the aromatic system is conjugated with an alkene group located at the ortho position relative to the nitrogen atom, have been prepared by using an intramolecular Kulinkovich–de Meijere reaction. The rearrangements can then be conducted either under standard thermal conditions or with microwave activation. Depending on the conditions applied and the substitution pattern, dihydroquinoline or polycyclic aminocyclobutane derivatives can be obtained. A mechanistic discussion is provided, with the proposition of the initial protonation of the aminocyclopropane moiety to give an iminium intermediate. By analogy with related intermolecular reactions, the involvement of electrocyclic reactions among the series of elementary steps that follow is put forward.