Search results for "SILICA"

Relaxation processes of point defects in vitreous silica from femtosecond to nanoseconds

2008

We studied ultrafast relaxation of localized excited states at Ge-related oxygen deficient centers in silica using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits a biexponential decay, which we ascribe to the departure from the Frank-Condon region of the first excited singlet state in 240 fs, followed by cooling in ∼10 ps. At later times, a nonexponential relaxation spanning up to 40 ns occurs, which is fitted with an inhomogeneous distribution of nonradiative relaxation rates, following a chi-square distribution with one degree of freedom. This reveals several analogies with phenomena such as neutron reactions, quantum dot blinking, or intramolecular vibrat…

Multiscale Computer Simulations in Physics, Chemistry, and Biology: The Example Of Silica

2002

We show to what extent molecular dynamics simulations (MD) can explore struc-tural and dynamic properties of atomic systems whereby the system under consideration is amorphous silica (SiO2). Two studies are presented: (i) a large scale simulation of the dynam-ics of a SiO2 melt and (ii) the investigation of free silica surfaces where a mixture of a classical MD and a Car-Parrinello molecular dynamics is used.

Amorphous silica modeled with truncated and screened Coulomb interactions: A molecular dynamics simulation study

2007

We show that finite-range alternatives to the standard long-range BKS pair potential for silica might be used in molecular dynamics simulations. We study two such models that can be efficiently simulated since no Ewald summation is required. We first consider the Wolf method, where the Coulomb interactions are truncated at a cutoff distance r_c such that the requirement of charge neutrality holds. Various static and dynamic quantities are computed and compared to results from simulations using Ewald summations. We find very good agreement for r_c ~ 10 Angstroms. For lower values of r_c, the long--range structure is affected which is accompanied by a slight acceleration of dynamic properties…

Optical Frequency Combs Generated in Silica Microspheres in the Telecommunication C-, U-, and E-Bands

2021

Optical frequency combs (OFCs) generated in microresonators with whispering gallery modes are demanded for different applications including telecommunications. Extending operating spectral ranges is an important problem for wavelength-division multiplexing systems based on microresonators. We demonstrate experimentally three spectrally separated OFCs in the C-, U-, and E-bands in silica microspheres which, in principle, can be used for telecommunication applications. For qualitative explanation of the OFC generation in the sidebands, we calculated gain coefficients and gain bandwidths for degenerate four-wave mixing (FWM) processes. We also attained a regime when the pump frequency was in t…

Integrated optic surface plasmon resonance measurements in a borosilicate glass substrate

2008

The surface plasmon resonance (SPR) technique is a well-known optical method that can be used to measure the refractive index of organic nano-layers adsorbed on a thin metal film. Although there are many configurations for measuring biomolecular interactions, SPR-based techniques play a central role in many current biosensing experiments, since they are the most suited for sensitive and quantitative kinetic measurements. Here we give some results from the analysis and numerical elaboration of SPR data from integrated optics experiments in a particular borosilicate glass, chosen for its composition offering the rather low refractive index of 1.4701 at 633 nm wavelength. These data regard the…

Phytoseiid mites from the Basilicata region (Southern Italy): species diversity and redescription of Typhloseiulus arzakanicus (Arutunjan) with a key…

2017

A survey of phytoseiid mites was carried out in the Basilicata region (Southern Italy) between 1976 and 2014 on wild and cultivated plants. A total of 38 species belonging to eleven genera and two subgenera were found on 59 plant species. The most common species was Euseius finlandicus (Oudemans) (39%) followed by Typhlodromus (Typhlodromus) exhilaratus Ragusa (32.2%), Kampimodromus aberrans (Oudemans) (27.1%), Typhlodromus (Anthoseius) cryptus (Athias-Henriot) (23.7%). Typhloseiulus arzakanicus (Arutunjan), found for first time in Italy, is redescribed here, while the male of this species is described for the first time. A dichotomic key of the species belonging to the genus Typhloseiulus …

Finiture storiche. Dalle sperimentazioni del XIX secolo ai brevetti per le decorazioni interne

2012

Gli esiti di questa ricerca sulle finiture architettoniche, impiegate prevalentemente nella definizione degli ambienti interni delle architetture, vogliono integrare e rendere più completo il quadro conoscitivo in materia di “pietra artificiale” tra la fine dell’Ottocento e l’inizio del Novecento. Gli esperimenti ottocenteschi di silicatizzazione artificiale ebbero ricadute evidenti sui metodi di marmorizzazione delle superfici e i procedimenti della tradizione furono ritenuti superati. Un settore particolarmente stimolante fu quello della produzione dei materiali per la pavimentazione degli ambienti interni. Lo studio di numerosi documenti conservati presso l’Archivio Centrale dello Stato …

La chiesa di Nostra Signora di Lourdes a Zagabria di Jože Plečnik. Analisi grafica

2019

Jože Plečnik (Ljubljana, 23rd January 1872 - Ljubljana, 7th January 1957) was, without any doubt, Otto Wagner's most brilliant pupil. During his tireless activity as an architect, he manages to touch a variety of absolutely heterogeneous themes, masterfully reworking the consolidated syntax of traditional architecture. In this survey we consider a relevant – although little investigated – aspect of the architect's work, that is the one linked to the typological innovations brought about by his work. In the case under examination – the work never done by the church of Our Lady of Lourdes in Zagreb – this innovation consists of the unusual arrangement of the four rows of columns that separate…

Conformational heterogeneity of the point defects in Silica Glasses: Study of the lifetime of 2.7 eV phosphorescence band

2006

Nitroarene hydrogenation catalysts based on Pd nanoparticles glued with PDA on inorganic supports: Multivariate Curve Resolution as an useful tool to…

2021

[EN] Two green catalysts based on Pd(0) nanoparticles (Pd NPs) anchored through PDA on porous silica and magnetite have been synthesized using a generalized simple and reproducible "two-step" methodology. Both catalysts were tested for a model reaction, the hydrogenation of 4-nitrophenol using NaBH4 as the hydrogenating agent, and especially good activity has been achieved in the case of the catalysts containing magnetite as inorganic core (Pd NPs-PDA@Fe3O4). We analyzed the effect associated with the catalyst separation method (centrifugation or magnetically) that affect to the distribution and aggregation degree of the Pd NPs. In addition, we also correlate the final catalyst morphology w…