225 research outputs found

    Tomographie ultrasonore pour les arbres sur pied

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    Ultrasonic tomography on standing trees. Ultrasonic tomography was used for the detection of degradation of transversal section of a beech, attacked by white decay. The image reconstruction of the transversal section of the tree in 2D was obtained with a software, which used the values of ultrasonic velocities measured at different heights from the ground. The attacked wood is characterised by low velocities. The measurements were performed with special transducers of 1 MHz, without damaging the bark of the tree. To improve the readings of the signals, a frequency analysis was performed. The ultrasonic tomographies were compared with the corresponding photographic images and with data obtained with a “Resistograph”. A good agreement between ultrasonic tomographies and photographs was observed. The image resolution is between 4 and 5 cm. Presently, this is the best resolution ever obtained with an acoustic nondestructive method on a standing tree

    On the connection between the number of nodal domains on quantum graphs and the stability of graph partitions

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    Courant theorem provides an upper bound for the number of nodal domains of eigenfunctions of a wide class of Laplacian-type operators. In particular, it holds for generic eigenfunctions of quantum graph. The theorem stipulates that, after ordering the eigenvalues as a non decreasing sequence, the number of nodal domains Îœn\nu_n of the nn-th eigenfunction satisfies n≄Μnn\ge \nu_n. Here, we provide a new interpretation for the Courant nodal deficiency dn=n−Μnd_n = n-\nu_n in the case of quantum graphs. It equals the Morse index --- at a critical point --- of an energy functional on a suitably defined space of graph partitions. Thus, the nodal deficiency assumes a previously unknown and profound meaning --- it is the number of unstable directions in the vicinity of the critical point corresponding to the nn-th eigenfunction. To demonstrate this connection, the space of graph partitions and the energy functional are defined and the corresponding critical partitions are studied in detail.Comment: 22 pages, 6 figure

    Deontological issues - possible misdiagnosis of cerebral metastases

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    Authors analyses a number of 4588 (52, 24% over 50 years old) patients operated for cerebral tumors in the Clinic Emergency Hospital “Bagdasar-Arseni” from Bucharest, between 2000-2010, with peculiar attention to the concordance between the preoperative and postoperative diagnosis, related to the actual policy to evaluate a neurosurgical patient before surgery. 903 cases were cerebral metastases and 69,5% aged over 50 years old. In 9,7% of cases we recorded a preoperative misdiagnosis of a metastasis due to few main reasons: unavailable information about a present primitive cancer, treacherous MRI image with a single confusing appearance of a cerebral lesion, age less than 50 years old, clinical presentation and biological evaluation inconsistent with malignancy. Authors point that these situations can have serious consequences related to professional competence, deterioration of the patient-doctor relationship, increasing costs for completion of diagnosis and treatment, and inadequate information about patient’s prognosis

    Computational horizons in cancer (CHIC) : developing meta- and hyper-multiscale models and repositories for in Silico Oncology - a brief technical outline of the project

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    This paper briefly outlines the aim, the objectives, the architecture and the main building blocks of the ongoing large scale integrating transatlantic research project CHIC (http://chic-vph.eu/)

    Compact Polyelectrolyte Complexes: “Saloplastic” Candidates for Biomaterials

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    Precipitates of polyelectrolyte complexes were transformed into rugged shapes suitable for bioimplants by ultracentrifugation in the presence of high salt concentration. Salt ions dope the complex, creating a softer material with viscous fluid-like properties. Complexes that were compacted under the centrifugal field (CoPECs) were made from poly(diallyldimethyl ammonium), PDADMA, as polycation, and poly(styrene sulfonate), PSS, or poly(methacrylic acid), PMAA, as polyanion. Dynamic mechanical testing revealed a rubbery plateau at lower frequencies for PSS/PDADMA with moduli that decreased with increasing salt concentration, as internal ion pair cross-links were broken. CoPECs had significantly lower modulii compared to similar polyelectrolyte complexes prepared by the “multilayering ” method. The difference in mechanical properties was ascribed to higher water content (located in micropores) for the former and, more importantly, to their nonstoichiometric polymer composition. The modulus of PMAA/PDADMA CoPECs, under physiological conditions, demonstrated dynamic mechanical properties that were close to those of the nucleus pulposus in an intervertebral disk

    Mineral Preservatives in the Wood of Stradivari and Guarneri

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    Following the futile efforts of generations to reach the high standard of excellence achieved by the luthiers in Cremona, Italy, by variations of design and plate tuning, current interest is being focused on differences in material properties. The long-standing question whether the wood of Stradivari and Guarneri were treated with wood preservative materials could be answered only by the examination of wood specimens from the precious antique instruments. In a recent communication (Nature, 2006), we reported about the degradation of the wood polymers in instruments of Stradivari and Guarneri, which could be explained only by chemical manipulations, possibly by preservatives. The aim of the current work was to identify the minerals from the small samples of the maple wood which were available to us from the antique instruments. The ashes of wood from one violin and one cello by Stradivari, two violins by Guarneri, one viola by H. Jay, one violin by Gand-Bernardel were analyzed and compared with a variety of commercial tone woods. The methods of analysis were the following: back-scattered electron imaging, X-ray fluorescence maps for individual elements, wave-length dispersive spectroscopy, energy dispersive X-ray spectroscopy and quantitative microprobe analysis. All four Cremonese instruments showed the unmistakable signs of chemical treatments in the form of chemicals which are not present in natural woods, such as BaSO4, CaF2, borate, and ZrSiO4. In addition to these, there were also changes in the common wood minerals. Statistical evaluation of 12 minerals by discriminant analysis revealed: a. a difference among all four Cremona instruments, b. the difference of the Cremonese instruments from the French and English antiques, and c. only the Cremonese instruments differed from all commercial woods. These findings may provide the answer why all attempts to recreate the Stradivarius from natural wood have failed. There are many obvious implications with regard to how the green tone wood should be treated, which chould lead to changes in the practice of violin-making. This research should inspire others to analyze more antique violins for their chemical contents

    Characterisation and categorisation of the diversity in viscoelastic vibrational properties between 98 wood types

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    International audienceContext Increased knowledge on diversity in wood properties would have implications both for fundamental research and for promoting a diversification of uses as material. *Aims The objective is to contribute to overcoming the critical lack of data on the diversity of wood dynamic mechanical/viscoelastic vibrational properties, by testing lesser-known species and categorizing sources of variability. *Methods Air-dry axial specific dynamic modulus of elasticity (E'/γ) and damping coefficient (tanή) were measured on a wide sampling (1792 specimens) of 98 wood types from 79 species. An experimental device and protocol was designed for conducting systematic (i.e. rapid and reproducible) characterizations. *Results Diversity at the specimens' level corroborates the "standard" relationship between tanή and E'/γ, which is discussed in terms of orientation of wood elements and of chemical composition. Diversity at the species level is expressed on the basis of results for normal heartwood, with specific gravity (γ) ranging from 0.2 to 1.3. Axial E'/γ ranges from 9 to 32 GPa and tanή from 4×10-3 to 19×10-3. Properties distribution follows a continuum, but with group characteristics. The lowest values of tanή are only found in certain tropical hardwoods. Results can also suggest alternative species for musical instruments making
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