Photophysics of a xanthenic derivative dye useful as an "on/off" fluorescence probe

The photophysical behavior of a new fluorescein derivative has been explored by using absorption and steady-state and time-resolved fluorescence measurements. The influence of ionic strength, as well as total buffer concentration, on both the absorbance and fluorescence has been investigated. The apparent acidity constant of the dye determined by absorbance is almost independent of the added buffer and salt concentrations. A semiempirical model is proposed to rationalize the variations in the apparent pKa values. The excited-state proton-exchange reaction around the physiological pH becomes reversible upon addition of phosphate buffer, inducing a pH-dependent change of the steady-state fluorescence and decay times. Fluorescence decay traces, collected as a function of total buffer concentration and pH, were analyzed by global compartmental analysis, yielding the following values of the rate constants describing excited-state dynamics: k01 = 1.29 x 10(10) s(-1), k02 = 4.21 x 10(8) s(-1), k21 approximately 3 x 10(6) M(-1) s(-1), k12B= 6.40 x 10(8) M(-1) s(-1), and k21B = 2.61 x 10(7) M(-1) s(-1). The decay rate constant values of k01, k21, k21B, along with the low molar absorption coefficient of the neutral form, mean that coupled decays are practically monoexponential at buffer concentrations higher than 0.02 M and any pH. Thus, the pH and buffer concentration can modulate the main lifetime of the dye.     

Multilayered artifacts in the pre-Columbian metallurgy from the North of Peru

Three types of alloys were recognized when analyzing pre-Columbian artifacts from the North of Peru: gold, silver, and copper alloys; gilded copper and silver; silvered copper; tumbaga, i.e., copper or silver enriched on gold at the surface by depletion gilding. In this paper, a method is described to differentiate gold alloys from gilded copper and from copper–gold tumbaga, and silver alloys from silvered copper and copper–silver tumbaga. This method is based on the use of energy-dispersive X-ray fluorescence, i.e., on a sophisticated analysis of XRF-spectra carrying out an accurate determination of Cu(K _α /K _β ), Ag(K _α /K _β ), Au(L _α /L _β ), and Au-L _α /Cu-K _α or Ag-K _α /Cu-K _α ratios. That implies a dedicated software for the quantitative determination of the area of X-ray peaks. This method was first checked by a relevant number of standard samples and then it was applied to pre-Columbian alloys from the North of Peru.     

(Co)Homology Theories for Oriented Algebras

We study three different (co)homology theories for a family of pullbacks of algebras that we call oriented. We obtain a Mayer Vietoris long exact sequence of Hochschild and cyclic homology and cohomology groups for these algebras. We give examples showing that our sequence for Hochschild cohomology groups is different from the known ones. In case the algebras are given by quiver and relations, and that the simplicial homology and cohomology groups are defined, we obtain a similar result in a slightly wider context. Finally, we also study the fundamental groups of the bound quivers involved in the pullbacks.     

On some mixed variational principles in electro-elastostatics

Some mixed variational principles are presented for problems involving electro-elastic interactions, whereby the electric field follows from a scalar potential. Firstly, in order to set the stage, we consider the basic case of merely free space. Secondly, to increase the complexity, we immerse an electro-active but mechanically rigid body into vacuum. As our final goal we thirdly treat a geometrically non-linear deformable electro-elastic body that is surrounded by free space. Electro-elastic bodies are of particular interest since they can develop large elastic deformations as a response to the presence of electric fields.     

Nonlinear electroelastostatics: a variational framework

Different formulations of the constitutive laws and governing equations for nonlinear electroelastic solids are reviewed and two new variational principles for electroelastostatics are introduced. One is based on use of the electrostatic scalar potential and one on the vector potential, combined with the deformation function. In each case Lagrangian forms of the electric variables are used. Their connections with several formulations of nonlinear electroelasticity in the literature are established and some differences highlighted.      

Nonlinear electroelastostatics: a variational framework

Different formulations of the constitutive laws and governing equations for nonlinear electroelastic solids are reviewed and two new variational principles for electroelastostatics are introduced. One is based on use of the electrostatic scalar potential and one on the vector potential, combined with the deformation function. In each case Lagrangian forms of the electric variables are used. Their connections with several formulations of nonlinear electroelasticity in the literature are established and some differences highlighted.     

C−H and C−F Bond Activation Reactions of Fluorinated Propenes at Rhodium: Distinctive Reactivity of the Refrigerant HFO‐1234yf

The reaction of [Rh(H)(PEt₃)₃] ( 1 ) with the refrigerant HFO‐1234yf (2,3,3,3‐tetrafluoropropene) affords an efficient route to obtain [Rh(F)(PEt₃)₃] ( 3 ) by C?F bond activation. Catalytic hydrodefluorinations were achieved in the presence of the silane HSiPh₃. In the presence of a fluorosilane, 3 provides a C?H bond activation followed by a 1,2‐fluorine shift to produce [Rh{(E)‐C(CF₃)=CHF}(PEt₃)₃] ( 4 ). Similar rearrangements of HFO‐1234yf were observed at [Rh(E)(PEt₃)₃] [E=Bpin ( 6 ), C₇D₇ ( 8 ), Me ( 9 )]. The ability to favor C?H bond activation using 3 and fluorosilane is also demonstrated with 3,3,3‐trifluoropropene. Studies are supported by DFT calculations.     

A variational formulation for a boundary value problem considering an electro-sensitive elastomer interacting with two bodies

We present a variational formulation for an electro-elastic body in contact with two semi-infinite rigid bodies, which are electric conductors and have a distribution of free charge. These three bodies are surrounded by free space, where far away we have a given electric displacement and an electric potential on disjoint surfaces.     

Numerical solution of finite geometry boundary-value problems in nonlinear magnetoelasticity

This paper provides examples of the numerical solution of boundary-value problems in nonlinear magnetoelasticity involving finite geometry based on the theoretical framework developed by Dorfmann and co-workers. Specifically, using a prototype constitutive model for isotropic magnetoelasticity, we consider two two-dimensional problems for a block with rectangular cross-section and of infinite extent in the third direction. In the first problem the deformation induced in the block by the application of a uniform magnetic field far from the block and normal to its larger faces without mechanical load is examined, while in the second problem the same magnetic field is applied in conjunction with a shearing deformation produced by in-plane shear stresses on its larger faces. For each problem the distribution of the magnetic field throughout the block and the surrounding space is illustrated graphically, along with the corresponding deformation of the block. The rapidly (in space) changing magnitude of the magnetic field in the neighbourhood of the faces of the block is highlighted.