Search results for "Gel"

Carta pastoral del Ilustrísimo Señor D. Fr. Veremundo Arias y Teyxeiro, al clero y pueblo de su diócesis siendo Obispo de Pamplona el 13 de diciembre…

Acoustic characterization of Silica aerogel clamped plates for perfect absorption purpose

2017

International audience; Silica aerogel has been widely studied as bulk material for its extremely low density and thermal conductivity. Plates or membranes made of this extremely soft materials exhibits interesting properties for sound absorption. A novel signal processing method for the characterization of an acoustic metamaterial made of silica aerogel clamped plates is presented. The acoustic impedance of a silica aerogel clamped plate is derived from the elastic theory for the flexural waves, while the transfer matrix method is used to model reflection and transmission coefficients of a single plate. Experimental results are obtained by using an acoustic impedance tube. The difference b…

Spectroscopic and physicochemical properties of rare-earth phthalocyanines entrapped in sol-gel glasses

1997

Abstract The electronic absorption spectra of samarium and neodymium phthalocyanines in DMSO and entrapped in glasses obtained via the sol-gel technique have been obtained. Decrease in concentration of metallophtalocyanines in DMSO leads to observed changes in the relative intensifies of the two bands in the Q-band region. This behavior could be explained by the shifts in equilibrium between the LnPc 2 and LnPc + forms, caused by the dilution. In view of this interpretation, the entrapment of the metallophthalocyanines in the sol-gel glass matrices shifts the diphthalocyanine ⇆ monophthalocyanine equilibrium towards the monophthalocyanine (LnPc + ) form.

Temperature effects on the IR absorption bands of hydroxyl and deuteroxyl groups in silica glass

2009

Abstract In this report we will show the changes of the band shape of the hydroxyl group (SiOH) infrared (IR) absorption band (∼3670 cm −1 ) in silica glass induced by lowering temperature in the range from 290 to 20 K. This band is considered as the overlap of several spectral components associated to the vibrational activity of hydroxyl groups in different bond configurations. By a suitable analysis of the experimental band profile in terms of different sub-bands, we studied the thermal evolution of each component and we reconsidered their assignations. For comparison we examined the SiOD absorption band (∼2710 cm −1 ) as a function of temperature as well. Our data can be interpreted as a…

Spectroscopic and electrochromical properties of metallophthalocyanines in silicate bulks and thin films prepared by the sol–gel method

2000

Abstract Magnesium phthalocyanine (MgPc) and praseodymium bisphthalocyanine (Pr(Pc) 2 ) have been entrapped in bulks and thin films of porous silicate xerogels prepared via the sol–gel method. The electronic absorption data obtained for the complexes immobilized in bulk sol–gel matrices indicate the formation of complex equilibria between their monomeric forms and respective agglomerates. Thin xerogel films doped with metallophthalocyanines and connecting two slides of transparent ITO electrodes display changes in the absorption spectra caused by varying of the applied voltage. These changes appear to be reversible in certain ranges of the applied voltages.

Ag11(SG)7 : A New Cluster Identified by Mass Spectrometry and Optical Spectroscopy

2014

We report a one-step and high yield synthesis of a red-luminescent silver cluster with the molecular formula, Ag11(SG)7 (SG: glutathionate) via reduction of silver ions by sodium borohydride in the presence of the tripeptide, glutathione (GSH). The as-prepared cluster shows prominent absorption features at 485 and 625 nm in its UV-vis absorption spectrum. Aging of the as-prepared cluster solution led to the disappearance of the 625 nm peak, followed by broadening of the 485 nm peak to give three maxima at ?487, 437, and 393 nm in its absorption spectrum. These peaks remain unchanged even after polyacrylamide gel electrophoresis (PAGE), where a single band was observed confirming high purity…

Problematic Social Media Use and Health among Adolescents

2021

1) Background: The use of social media has become an integral part of adolescents’ daily lives. However, the intensive use of social media can develop into a health-threatening addiction, but unfavourable health consequences can occur even with less use. Social media user groups categorized as no-risk, moderate risk (of developing problematic behaviour), and problematic use were examined with reference to their prevalence, their associations with individual determinants and health, and the increased health risk between groups. (2) Methods: The Finnish nationally representative HBSC data (persons aged 11, 13, and 15, n = 3408) and descriptive and binary logistic regression analysis were appl…

Experimental and robust modeling approach for lead(II) uptake by alginate gel beads: influence of the ionic strength and medium composition.

2014

Abstract Systematic kinetic and equilibrium studies on the lead ions removal ability by Ca-alginate gel beads have been performed by varying several internal parameters, namely, number of gel beads, nature and composition of the ionic medium and pH, which allowed us to model a wastewater in order to closely reproduce the composition of a real sample. Moreover, the effects brought about the different ionic species present in the reacting medium have been evaluated. Differential Pulse Anodic Stripping Voltammetry (DP-ASV), has been systematically used to perform kinetic and equilibrium measurements over continuous time in a wide range of concentration. Kinetic and equilibrium data have been q…

Chromo-Fluorogenic Detection of Nerve-Agent Mimics Using Triggered Cyclization Reactions in Push-Pull Dyes

2010

A family of azo and stilbene derivatives (1-9) are synthesized, and their chromo-fluorogenic behavior in the presence of nerve-agent simulants, diethylchlorophosphate (DCP), diisopropylfluorophosphate (DFP), and diethylcyanophosphate (DCNP) in acetonitrile and mixed solution of water/acetonitrile (3:1 v/v) buffered at pH 5.6 with MES, is investigated. The prepared compounds contain 2-(2-N,N-dimethylaminophenyl)ethanol or 2-[(2-N,N-dimethylamino)phenoxy]ethanol reactive groups, which are part of the conjugated pi-system of the dyes and are able to give acylation reactions with phosphonate substrates followed by a rapid intramolecular N-alkylation. The nerve-agent mimic-triggered cyclization …

Sample Preparation Improvement in Polycyclic Aromatic Hydrocarbons Determination in Olive Oils by Gel Permeation Chromatography and Liquid Chromatogr…

2005

Abstract The determination of 15 polycyclic aromatic hydrocarbons (PAHs) in olive oil samples has been improved in order to obtain a fast methodology with a low limit of detection through the combination of liquid–liquid extraction with acetonitrile and preparative gel permeation chromatography (GPC) prior to the injection of purified extracts into a C18 column. Acetonitrile–water was used as the mobile phase with a gradient from 50 to 95%, w/w, acetonitrile in 30 min. The oven temperature was maintained at 15°C, and fluorometric detection was made at a fixed excitation wavelength of 264 nm and variable, optimal emission wavelength for each analyte ranging from 352 nm for 11-H-benzo(b)fluor…