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171.
Acidity is an outstanding parameter that affect the correct preservation of most part of materials engaged in artworks and heritage objects. In spite of the new generation of advanced analytical devices, the conservation/heritage management sector claims for some kind of simple, robust and low-cost device to monitor environmental acidity wherever necessary. The purpose of this paper is to offer a suitable alternative for the estimation of environmental acidity by means of detectors to be used without electrodes, solutions, pH meters, wires or batteries.Doped sol-gel thin coatings have been used as transductors for producing pH detectors. The coatings consist of a partially densified polysiloxane network and an organic dye sensitive to pH changes. The siloxane network behaves as a host for immobilisation of the dye molecules, in such a way that chemical-optical properties of the dye are preserved as far as possible. The transductors were applied on common glass substrates by dipping. Further heat-treatment allows the coating partial densification.The optical response of the detectors was analysed by VIS absorption spectroscopy, since a change of colour took place when the detectors were submitted to different pH buffered solutions. With the aim to investigate their optical behaviour as a function of pH, several experimental measurements were undertaken: absorption intensity; maximum spectral wavelength; colour coordinates; colour purity percentages. Time response and memory effect were also studied. The detector operation conditions for monitoring environmental acidity both indoor and outdoor are discussed. 相似文献
172.
Dr. Guillem Portella Dr. Montserrat Terrazas Dr. Núria Villegas Prof. Dr. Carlos González Prof. Dr. Modesto Orozco 《Angewandte Chemie (International ed. in English)》2015,54(36):10488-10491
The stability of DNA is highly dependent on the properties of the surrounding solvent, such as ionic strength, pH, and the presence of denaturants and osmolytes. Addition of pyridine is known to unfold DNA by replacing π–π stacking interactions between bases, stabilizing conformations in which the nucleotides are solvent exposed. We show here experimental and theoretical evidences that pyridine can change its role and in fact stabilize the DNA under acidic conditions. NMR spectroscopy and MD simulations demonstrate that the reversal in the denaturing role of pyridine is specific, and is related to its character as pseudo groove binder. The present study sheds light on the nature of DNA stability and on the relationship between DNA and solvent, with clear biotechnological implications. 相似文献
173.
We propose a novel shape reconstruction technique for controlled source 3D low frequency electromagnetic induction tomography which uses a level set representation of the shapes. The main application which we have in mind in this paper is geophysical prospecting, in particular the monitoring of reservoir flooding processes in secondary oil recovery and the investigation of conductive geophysical structures at a depth of up to a few hundred metres. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
174.
C. Villegas 《Journal of multivariate analysis》1976,6(1):31-45
A multiple time series is defined as the sum of an autoregressive process on a line and independent Gaussian white noise on a hyperplane that goes through the origin and intersects the line at a single point. This process is a multiple autoregressive time series in which the regression matrices satisfy suitable conditions. It is shown that the maximum likelihood estimates of the line and the autoregression coefficients can be obtained as the values that minimize a given function, and that the remaining maximum likelihood estimates can be computed as simple functions of the first ones. It is also shown that the maximum likelihood estimates are equivariant with respect to the group of bijective linear transformations. 相似文献
175.
Fernando Rodriguez Villegas 《Mathematische Nachrichten》1993,162(1):187-191
We extend sharp forms of the classical uncertainty principle to the context of commutative hypergroups. This hypergroup setting includes Gelfand pairs, Riemannian symmetric spaces, and locally compact abelain groups. For some Gelfand pairs our inequalities will be sharper than those in a recent paper by J. A. WOLF. 相似文献
176.
Villegas ML Bertolotti SG Previtali CM Encinas MV 《Photochemistry and photobiology》2005,81(4):884-890
The interaction with amino acids of the excited states of the N-oxide resazurin and its deoxygenation product resorufin, has been studied in aqueous solution at pH 7.5. Steady-state and time-resolved studies show that the fluorescence is quenched by amino acids. Complexation of the dyes in the ground state with aromatic amino acids was also observed. The singlet quenching is attributed to electron transfer from the amino acids to the excited dye based on the dependence of the bimolecular rate constants with the ionization potential of quenchers. Flash photolysis experiments allowed determination of the quenching rate constants for the triplet deactivation of dyes by several amino acids, as well as the characterization of the transients formed in the process. These data show that the triplet is also deactivated by an electron transfer process. However, the deactivation of the N-oxide dye by tryptophan can be described by a hydrogen atom transfer. The protolytic dissociation constants of the dye radical ions are reported. The irradiation of rezasurin in the presence of amino acids leads to deoxygenation of the dye to give resorufin. This process involves the triplet excited state of resazurin and is efficient only in the presence of amino acids containing the -SH group. 相似文献
177.
178.
Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Dagenhart WD Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Karchin PE Kennedy C Kwan S Lueking LH de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review letters》1996,77(12):2392-2395
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