1,720,974 research outputs found
1,3-bridged p-Methyloctahomotetraoxacalix[4]arene-bis-crown-3
No full textThe title compound, 13,21,35,43-tetramethyl-3,6,9,17,25,28,31,39,46,49- decaoxaheptacyclo[21.21.3.311,33.02,41.010,15 .019,24.032,37]pentaconta-1,10,12,14,19,21,23,32,34,36, 41,43-dodecaene, C44H52O10, differs from previously reported 1,3-bridged calix[4]arene-bis-crown compounds in having an enlarged calixarene ring and shorter polyoxyethylene bridges. The cavity is partly filled by the bridges
HF-SCF study of the ground state geometry and harmonic vibrational frequencies of borazine derivatives
No full textThe results of ab initio HF-SCF calculations of the B-monosubstituted borazine derivatives B3N3H5X (X = NH2, NO2, F, Cl, CN, NC, OH, N2 +, CCH, CHO, CH3, NH3 + and SiH3) are reported. The equilibrium geometries of the molecules were determined from gradient optimizations carried out employing the 6-31G* and 6-31G** basis sets. HF/6-31G* level calculations of disubstituted and trisubstituted F and Cl borazine derivatives and of trimethylborazine are included. The effects of the substituents on the geometry of the borazine ring were investigated. Vibrational frequencies were calculated for some B-monosubstituted molecules and the splittings of the degenerate modes of borazine due to symmetry lowering occurring in the B-monosubstituted molecules were examined. © 1993
Study and analytical characterisation of corrosion products from minting dies and punches belonging to the Estense Collection of Modena
No full textDigital detection in radiography applied to Cultural Heritage
No full textTwo CCD based detectors were assembled and compared both each other and with a classical photographic film. Preliminary checks were performed on Cultural heritage object both in lab and in situ. Main advantages attained were the very low exposition time, the hige sensitivity and wide dynamic rang
From the X-rays to a reliable “Low cost” computational structure of caffeic acid: DFT, MP2, HF and integrated molecular dynamics X-ray diffraction approach to condensed phases
No full textThe ability of caffeic acid to act as antioxidant against hyperoxo-radicals as well as its recently found therapeutic properties in the treatment of hepatocarcinoma, still make this compound, more than 20 years later the refinement of its crystal structure, object of study. It belongs to the vast family of humic substances, which play a key role in the biodegradation processes and easily form complexes with ions widely diffused in the environment. This class of compounds is therefore interesting for potential environmental chemistry applications concerning the possible complexation of heavy metals. Our study focused on the characterization of caffeic acid as a starting necessary step, which will be followed in the future by the application of our findings on the study of the properties of caffeate anion interaction with heavy metal ions. To reach this goal, we applied a low cost approach - in terms of computational time and resources aimed at the achievement of a high resolution, robust and trustable structure using the X-ray single crystal data, recollected with a higher resolution, as touchstone for a detailed check. A comparison between the calculations carried out with density functional theory (DFT), Hartree-Fock (HF) method and post SCF second order Moller-Plesset perturbation method (MP2), at the 6-31G** level of the theory, molecular mechanics (MM) and molecular dynamics (MD) was performed. As a consequence we explained on one hand the possible reasons for the pitfalls of the DFT approach and on the other the benefits of using a good and robust force field developed for condensed phases, as AMBER, with MM and MD. The reliability of the latter, highlighted by the overall agreement extended up to the anisotropic displacement parameters calculated by means of MD and the ones gathered by X-ray measurements, makes it very promising for the above-mentioned goals. (C) 2011 Elsevier B.V. All rights reserved
X-ray Structure and AM1 Studies of the Proton-Transfer Adduct between 2,5-Dihydroxy-p-quinone and 4-(N,N-Dimethylamino)pyridine
No full textThe structure of the crystalline 1:1 adduct obtained by reacting 2,5-dihydroxy-/?-quinone (DHpQ) and 4-(N,N-dimethylamino)pyridine (DAPY) has been determined by X-ray single-crystal diffraction. The compound consists of ribbons of the two components linked by proton-transfer bonds. Each bond is due to a proton of the 4-(N,N-dimethylamino)pyridinium cation (r(N-H) =1.13 Å), bifurcated between two oxygen atoms of the monoprotonated anion. Antiparallel stacks of DHpQ-DAPY adducts are present in the solid. According to AM1 and molecular mechanics calculations, it has been shown that the interaction between stacked adducts is the prerequisite for the establishing of proton-transfer bonds (O-⋯HN+) between DHpQ and DAPY. It is suggested that electrostatic interactions such as the dipole-dipole coupling play a major role in establishing this type of hydrogen bond within each stack. © 1996 American Chemical Society
Multianalytical Non-Invasive Characterization of ‘Mater Boni Consilii’ Iconography Oil Painting
Full text linkThis paper presents the results of non-invasive diagnostic investigations performed on the canvas oil painting depicting the Marian iconography “Mater Boni Consilii”. The painting, whose author and origin are unknown, was found in an old shop in Florence following the overflowing of the Arno River in 1966. In order to define the importance of the artwork, a multianalytical analysis was performed on the painting, using multispectral imaging, X-ray fluorescence (XRF), and Fourier Transform Infrared Spectroscopy (FTIR-ATR) for the definition of materials, with a particular focus on the identification of pigments. The results allowed for the drawing up of a color palette, composed mainly of ochre and earth pigments, cinnabar, lithopone, lead white, and ultramarine pigments. After cross-referencing the acquired information with other findings, it was possible to place the painting in the period between the end of the XIXth and the beginning of the XXth centuries
Analisi a raggi X, fotogrammetria e realtà virtuale per lo studio e la valorizzazione di contesti archeologici: un caso di studio dalla necropoli di Crustumerium.
No full textIn this paper we present the application of established methodologies to innovatively study a soil block from the necropolis of Crustumerium, north-east of Rome. The find contains human remains and metal artefacts and it is dated to the VII century BC. X-ray analysis and digital acquisition were conducted for the study of the sample to better understand the composition. During the archaeological excavation, if well preserved, artefacts are directly recovered. While if they are fragile and of difficult identification, it is preferred creating a soil block to recover artefacts later by micro-excavation in a controlled environment and after appropriate analysis. This helps to preserve most of the information still present and the best way to acquire this data is through X-ray analysis, in a completely non-invasive technique. Using X-ray imaging (radiography and computed tomography) it is possible to obtain information about distribution, shape, dimensions and state of preservation of the artefacts while also allowing the study of the inner part, invisible to macroscopic analysis. XRF and XRPD give us elemental and molecular information on constituent materials (i.e. alloy, corrosion products, etc.). In this sense, photogrammetry also becomes a useful tool for acquiring data, particularly those of the surface.
The study, digitization, manipulation and restoration of human remains in a virtual environment is called Virtual Anthropology (VA). This case study aims to show how the combination of both virtual anthropology and X-ray techniques can be useful tools to study and preserve the remains, especially when it is not possible to move and handle a fragile specimen. From the digital acquisition of archaeological contexts, through the integration with photogrammetry and laser scanning methodologies, it was possible to proceed with the construction of digital environments in virtual reality (VR): within these the digital finds can be freely manipulated, allowing the implementation of innovative museum contents in 3D and different formats (audio, video, VR, AR). It is thus possible to
involve and educate the public through storytelling, enriching the museum experience, and also providing support for the accessibility of different types of public, including those with disabilities
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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