1,720,972 research outputs found
First principles studies on boron sites in Zeolites
No full textA systematic computational investigation on protonated and nonprotonated boron-containing zeolites (boralites) performed by using different periodic density functional theory approximations, is presented. Both minimum energy structures and finite temperature behavior of model boron sodalites were analyzed. All of the adopted computational schemes agree in predicting an acid site composed of a silanol Si-OH group loosely linked to a planar BO3 structure in the protonated system and a BO4 tetrahedral site in the sodium-containing zeolite. Calculated structural and vibrational properties are in line with experimental data. Comparisons of the protonated boralite site with Al and Ga zeolitic acid sites are discussed as well. Results indicate that this class of mild acid catalysts is characterized by significant framework flexibility and pronounced thermal effects due to the loosely bound acid site
H2O-induced trigonal-to-tetrahedral transition in boron zeolites
No full textThe behaviour of a protonated
boron-containing zeolite at intermediate hydration
degree has been investigated by means of
periodic DFT approaches. Results of a combined
room-temperature Car-Parrinello molecular dynamics
bluemoon path sampling simulation indicate that,
in line with experimental findings,
the BO3/Si-OH acid site
typical of dry samples is converted to
a hydrated H3O+ hydrogen bonded to
tetrahedral BO4- at moderate water content (four H2O per B site)
with an activation free barrier of the order
of few kT
Water in acid boralites: Hydration effects on framework B sites
No full textProperties and behavior of protonated boron-containing zeolites at different hydration degree have been investigated by means of periodic DFT approaches. Geometry optimization and room-temperature Car-Parrinello molecular dynamics results, in line with experimental findings, indicate that the BO3-bound silanolic acid site typical of dry boralites should convert to a solvated H3O+ hydrogen bonded to tetrahedral BO4 at moderate water content. By increasing the water loading, the tetrahedral structure of the B site is stabilized and the physicochemical properties of the water molecules solvating the acid proton gradually approach the liquid-phase ones. A relevant role of structural and vibrational properties of the zeolite framework in the water-induced trigonal-to-tetrahedral transition at the B site is highlighted by simulation results
Roughening of close-packed singular surfaces
Full text linkAn upper bound to the roughening temperature of a close-packed singular surface, fee Al (111), is obtained via free-energy calculations based on thermodynamic integration using the embedded-atom interaction model. Roughening of Al (111) is predicted to occur at around 890 K, well below bulk melting (933 K), and it should therefore be observable, save fur possible kinetic hindering
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
Coordination compounds in cancer: past, present and perspectives
Full text linkMetal-based coordination compounds have been used throughout the history of human
medicine to treat various diseases, including cancer. Since the discovery of cisplatin in 1965, a great
number of metal coordination complexes, such as platinum, ruthenium, gold or copper have been
designed, synthesised and tested in order to develop clinically effective and safe drugs. Currently,
many reviews cover applications of cytostatic metal complexes pointing out the most promising
examples of platinum- and non-platinum-based compounds in preclinical and clinical trials. However,
recent comprehensive reviews covering chemical and biological aspects of metal-based coordination
compounds in cancer therapy are still rare. In this review we wish to provide an overview of the
coordination chemistry of current and novel cytostatic compounds, including an outline of their design
and rationale of synthesis, and summarize bio-chemical reactivity and physicochemical properties of
candidate metal complexes
Repeated maternal separation in C57BL/6J mice: Changes in hippocampal GABAergic and glutamatergic synaptic function and increased voluntary ethanol consumption
No full textVariations 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
ETHANOL MODULATES IN A BIPHASIC MANNER HYPERPOLARIZATION-ACTIVATED CURRENTS (I-H) IN RAT HIPPOCAMPAL CA3 PYRAMIDAL NEURONS
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