1,721,088 research outputs found
Ionic substitutions in calcium phosphates synthesized at low temperature.
No full textIonic substitutions have been proposed as a tool to improve the biological performance of calcium phosphate
based materials. This review provides an overview of the recent results achieved on ion-substituted
calcium phosphates prepared at low temperature, i.e. by direct synthesis in aqueous medium or through
hydrolysis of more soluble calcium phosphates. Particular attention is focused on several ions, including
Si, Sr, Mg, Zn and Mn, which are attracting increasing interest for their possible biological role, and on the
recent trends and developments in the applications of ion-substituted calcium phosphates in the biomedical
field
Time Course of Zoledronate Interaction with Hydroxyapatite Nanocrystals
No full textZoledronate-modified hydroxyapatite nanocrystals (HAZOL) can be successfully obtained through direct synthesis in aqueous solution in spite of the great affinity of this bisphosphonate for calcium ions, which should promote the precipitation of calcium zoledronate. This study investigates the time course of the reaction in order to clarify the peculiar interaction of zoledronate (ZOL) with hydroxyapatite (HA). The results demonstrate that the first precipitate during the direct synthesis of HAZOL is indeed constituted of a relevant amount of amorphous calcium zoledronate together with small
nanocrystals; however, the relative amount of crystalline material
increases at the expenses of the amorphous phase during the time
course of the reaction. The final HAZOL nanocrystals are smaller and display reduced lengths of the coherently scattering domains with respect to the control hydroxyapatite nanocrystals. Zoledronate incorporation, which can be detected also through Raman spectroscopy, amounts to 7.4 wt %, and it provokes a reduction of zeta potential. The suitable coordination geometry of
Ca atoms in HA justifies the high affinity of the bisphosphonate for hydroxyapatite structure, which leads to ZOL inclusion between the coherently scattering domains during HA crystal growth. At variance, zoledronate chemisorption on preformed HA nanocrystals increases up to 3.3 wt % without causing appreciable morphological and structural modifications
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
Sintesi e proprietà termiche di poli(butilene isoftalato) contenente lunghe ramificazioni e gruppi ionici
No full textPoly(thiodiethylene adipate): melting behavior, crystallization kinetics, morphology, and crystal structure.
No full textThe melting behavior and crystallization kinetics of poly(thiodiethylene adipate) (PSDEA) were investigated with differential scanning calorimetry and hotstage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature (Tc) and ascribed to melting and recrystallization processes. Linear and nonlinear treatments were applied to estimate the equilibrium melting temperature for PSDEA with the corrected values of the melting temperature. The nonlinear estimation yielded a higher value by about 9 °C. Isothermal crystallization kinetics were analyzed according to Avrami’s treatment. Values of Avrami’s exponent close to 3 were obtained, independently of Tc, in agreement with a crystallization process originating from predetermined nuclei and
characterized by three-dimensional spherulitic growth. As a matter of fact, space-filling spherulites were observed by optical microscopy at all Tc’s. The rate of crystallization became lower as Tc increased, as usual at a low undercooling, the crystallization process being controlled by nucleation. Moreover, the crystal structure of PSDEA was determined from powder X-ray diffraction data by full profile fitting. A triclinic unit cell containing two polymer chains arranged parallel to the c axis was found
Glycolipid biomaterials: synthesis and solid-state properties of a poly(sophorolipid)
No full textStructural complexity inherited from a microbial synthesis of glycolipids was translated into unique poly(sophorolipid) biomaterials. ROMP polymn. of natural diacetylated lactonic sophorolipids gave a high mol. wt. polymer with asym. bola-amphiphilic repeating units. The poly(sophorolipid) chain alternates C18 oleic-like aliph. segments (90% cis-configured double bonds) with bulky diacetylated disaccharide moieties. The poly(sophorolipid) is a solid at room temp. that undergoes the glass transition at 61 °C and melts at 123 °C. The crystal phase is assocd. with ordered packing of the aliph. chain segments. The semicryst. poly(sophorolipid) also displays a long-range order (d = 2.44 nm) involving sophorose groups that persist after crystal phase melting (in high-T diffractograms) with a slightly shortened distance (2.27 nm)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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