A note on the generalized Friedmann equations for a thick brane

Within our thick brane approach previously used to obtain the cosmological evolution equations on a thick brane embedded in a five-dimensional Schwarzschild Anti-de Sitter spacetime it is explicitly shown that the consistency of these equations with the energy conservation equation requires that, in general, the thickness of the brane evolves in time. This varying brane thickness entails the possibility that both Newton’s gravitational constant G and the effective cosmological constant Λ₄ are time dependent.     

Organocatalytic synthesis of α-hydroxy and α-aminophosphonates

A new and highly flexible procedure is described for the synthesis of α-amino- and α-hydroxy phosphonates. In the presence of a catalytic amount of oxalic acid (10 mol %), trimethyl phosphite reacts with aldehydes or imines (generated in situ from an aldehyde and an amine) to yield the corresponding coupled products in good yield.     

Pentafluorophenylammonium triflate as an efficient, environmentally friendly and novel organocatalyst for synthesis of bis-indolyl methane derivatives

A simple, inexpensive, environmentally friendly and efficient route for the synthesis of bis-indolyl methane derivatives by the reaction of indole or N-methyl indole with aldehydes using pentafluorophenylammonium triflate (PFPAT) as a catalyst is described. PFPAT organocatalyst is air-stable, cost-effective, easy to handle, and easily removed from the reaction mixtures.     

Evaluation of laser induced breakdown spectroscopy for the determination of macronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has become an analytical tool for the direct analysis of a large variety of materials in order to provide qualitative and/or quantitative information. However, there is a lack of information for LIBS analysis of agricultural and environmental samples. In this work a LIBS system has been evaluated for the determination of macronutrients (P, K, Ca, Mg) in pellets of vegetal reference materials. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm and an Echelle spectrometer with ICCD detector. The plasma temperature was estimated by Boltzmann plots and instrumental parameters such as delay time, lens-to-sample distance and pulse energy were evaluated. Certified reference materials as well as reference materials were used for analytical calibrations of P, K, Ca, and Mg. Most results of the direct analysis of plant samples by LIBS were in reasonable agreement with those obtained by ICP OES after wet acid decomposition.     

Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has been evaluated for the determination of micronutrients (B, Cu, Fe, Mn and Zn) in pellets of plant materials, using NIST, BCR and GBW biological certified reference materials for analytical calibration. Pellets of approximately 2 mm thick and 15 mm diameter were prepared by transferring 0.5 g of powdered material to a 15 mm die set and applying 8.0 tons cm^− 2. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm (200 mJ per pulse, 10 Hz) and an Echelle spectrometer with ICCD detector. Repeatability precision varied from 4 to 30% from measurements obtained in 10 different positions (8 laser shots per test portion) in the same sample pellet. Limits of detection were appropriate for routine analysis of plant materials and were 2.2 mg kg^− 1 B, 3.0 mg kg^− 1 Cu, 3.6 mg kg^− 1 Fe, 1.8 mg kg^− 1 Mn and 1.2 mg kg^− 1 Zn. Analysis of different plant samples were carried out by LIBS and results were compared with those obtained by ICP OES after wet acid decomposition.     

新型五氟苯铵三氟有机催化剂高效合成14-芳基(烷基)-14H-二苯并[a,j]呫吨类化合物和1,8-二氧代氧杂蒽衍生物(英文)

A simple and facile synthesis of 14-aryl and alkyl-14H-dibenzo[a,j]xanthenes and 1,8-dioxooctahydroxanthene derivatives has been successfully developed by treatment of β-naphthol or dimedone with aldehydes under mild conditions in the presence of a pentafluorophenyl ammonium triflate(PFPAT) organocatalyst.These catalytic condensation reactions represent green chemical processes and the PFPAT organocatalyst is air-stable,cost-effective,easy to handle,and easily removed from the reaction mixtures.     

Magnetic moments ofb-quark baryons in broken SU(5) symmetry

The magnetic moments ofb-quark baryons within the framework of five quark models are derived. Also the transition magnetic moments of variousb-quark baryons are calculated.     

Pentafluorophenylammonium triflate: A highly efficient catalyst for the synthesis of quinoxaline derivatives in water

A simple, inexpensive, environmentally friendly and efficient route for the rapid and efficient synthesis of quinoxaline derivatives using pentafluorophenylammonium triflate (PFPAT) as a catalyst is described. Various quinoxaline derivatives were synthesized in good to excellent yields. The preparation of PFPAT catalyst from simple and readily available starting materials makes this method more affordable.     

DBU: An Efficient Base Catalyst for Synthesis of the New Oxazolo[5,4-d]pyrimidine Derivatives

New types of oxazolo[5,4-d]pyrimidines were synthesized via 1,8-diazabicyclo[5,4,0]undec-7-ene-catalyzed heteroannulation of 2-substituted 5-amino-4-cyano-1,3-oxazoles with various isothiocyanates.