Kaonic atoms measurements at the DAΦNE accelerator

Radioactive ⁵⁷Mn⁺(T _1/2?= 1.5 min) ions have been implanted at the ISOLDE facility at CERN with 60 keV energy to fluences <10¹²/cm² into p-type Si_1???x Ge _x (x < 0.1) single crystals held at 300–600 K. The implantation and annealing processes result in the majority of the implanted Mn ions occupying substitutional lattice sites. In the subsequent ⁵⁷Mn nuclear β ^???-decay to the 14.4 keV Mössbauer state of ⁵⁷Fe (T _1/2?= 100 ns), an average recoil energy of 40 eV is imparted to the ⁵⁷Fe daughter atoms which results in a large fraction being expelled into tetrahedral interstitial sites and the creation of a vacancy. The remainder occupies substitutional sites. This technique of recoil production of ^57m Fe_I thus allows for the study of the diffusion characteristics of interstitial Fe. From the temperature dependent line broadening, the activation energies have been determined and decrease with increasing Ge concentration which contributes significantly to the increase of the jump frequency. A similar result has been obtained in n-type SiGe but there the values for the activation energies were much higher.     

Synthesis and properties of europium-based phosphors on the nanometer scale: Eu2O3, Gd2O3:Eu, and Y2O3:Eu

Nanocrystals of oxides containing europium as the main constituent or as a doping element in RE2O3 ( RE=Y, Gd) have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by high-resolution TEM, absorption spectroscopy, and luminescence spectroscopy. The samples obtained consisted of concentrated and colloidally stable suspensions of luminescent oxide nanoparticles with an average grain diameter in the range 2-5 nm. The nanoparticles were found to be highly crystalline despite their ultrasmall size and the low temperature of 180 degrees C applied during the synthesis. Upon UV excitation, the red luminescence relative to the 5D0-->7Fn transition within the cubic form of RE2O3 exhibits some important differences from that usually found in bulk materials.     

The lachrymatory factor of the onion: an NMR study

The lachrymatory factor of the onion is shown by NMR analysis to be a 19 to 1 mixture of (Z)- and (E)-propanethial S-oxide.     

Synthesis, spectroscopic and thermal studies of the reactions of the donors piperazine and N,N′-dimethylpiperazine with σ- and π-acceptors

The interactions of the electron donors piperazine (PIP) and N,N′-dimethylpiperazine (DMPIP) with the σ-acceptor iodine and the π-acceptors tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) were studied spectrophotometrically in chloroform at 25 °C. The electronic and infrared spectra of the resulting charge-transfer complexes were recorded, in addition to thermal analysis. The results obtained showed that the stoichiometries of the reactions are not fixed and depend on the nature of both the donor and the acceptor. The formed CT-complexes have the formulas of , [(PIP)(TCNE)₂], [(PIP)(DDQ)₂], , [(DMPIP)(TCNE)₂] and [(DMPIP)(DDQ)₂]. A general mechanism explaining the formation of triiodide complexes was suggested.     

Phase‐Transfer Activation of Transition Metal Catalysts

With metal‐based catalysts, it is quite common that a ligand (L) must first dissociate from a catalyst precursor (L′_nM?L) to activate the catalyst. The resulting coordinatively unsaturated active species (L′_nM) can either back react with the ligand in a k_?1 step, or combine with the substrate in a k₂ step. When dissociation is not rate determining and k_?1[L] is greater than or comparable to k₂[substrate], this slows the rate of reaction. By introducing a phase label onto the ligand L and providing a suitable orthogonal liquid or solid phase, dramatic rate accelerations can be achieved. This phenomenon is termed “phase‐transfer activation”. In this Concept, some historical antecedents are reviewed, followed by successful applications involving fluorous/organic and aqueous/organic liquid/liquid biphasic catalysis, and liquid/solid biphasic catalysis. Variants that include a chemical trap for the phase‐labeled ligands are also described.     

Electrochemical degradation of buprofezin insecticide in aqueous solutions by anodic oxidation at boron-doped diamond electrode

Buprofezin (2-tert-butylimino-3-isopropyl-5-phenyl-1,3,5-thiadiazinan-4-one) is identified as a commonly used chemical with satisfactory biological activities against sucking insect pests, but its disposal causes serious environmental problems. This pesticide was treated by an electrolysis system using a boron-doped diamond (BDD) as anode and platinum as cathode. A number of experiments were run on a laboratory scale and the results are presented. The chemical oxygen demand (COD) measurement during the processing permitted the evaluation of the kinetic of organic matter decay and the instantaneous current efficiency. Different operating conditions and factors affecting the treatment process including current density, conductive electrolyte, pH, concentration of buprofezin, and time of electrolysis were studied and optimized. The best obtained conditions for COD removal on the BDD anode to degrade buprofezin solutions (COD₀ = 1,200 mg L^?1) include operating at 60 mA cm^?2 and 25 ± 3 °C. The high efficiency of this technology can be explained in terms of the direct electrooxidation at the BDD surface and the oxidation carried out by hydroxyl radicals (OH^?) and other electro-generated oxidants (Cl^?, ClO^?).     

Chitosan as an eco-friendly inhibitor for copper corrosion in acidic medium: protocol and characterization

Natural biopolymer chitosan organic compound (COC) has been used as a copper corrosion inhibitor in molar hydrochloric medium. This study was conducted by weight loss, polarization curves and electrochemical impedance spectroscopy measurements. Scanning electron microscopy, energy dispersive X-ray spectrometry and atomic force microscopy studies were used to characterize the surface of uninhibited and inhibited copper specimens. The study of the temperature effect was carried out to reveal the chemical nature of adsorption. The inhibition efficiency tends to increase by increasing inhibitor concentration to reach a maximum of 87% at 10^?1 mg L^?1. The values of inhibitor efficiency estimated by different electrochemical and gravimetric methods indicate the performance of copper in HCl medium containing COC. Adsorption of COC was found to follow the Langmuir adsorption isotherm. In order to get a better understanding of the relationship between the inhibition efficiency and molecular structure of COC, quantum chemical and molecular dynamics simulation approaches were performed to get a better understanding of the relationship between the inhibition efficiency and molecular structure of chitosan.     

A novel method for modeling skidding for systems with nonholonomic constraints

In this paper, the effect of wheel skidding on the steering motion of a simple vertical rolling disk is investigated. By modifying the nonholonomic constraints, two novel dynamic models are proposed. The first model rotates the constraints and enforces them along a plane correlated to the skid angle. It then relates the skidding in a wheel to the Lagrange multipliers associated with the kinematic constraints of that wheel. The second model relaxes the no-skidding constraint, allowing its transgression and relates the skidding to the generalized velocities of the actuated degrees of freedom of the system. To validate our model, we compare it to one in the literature and we analyze the motion of the disk on icy and snowy road conditions, where skidding can be significant.