1,721,094 research outputs found
Functional Neural Activity Mapping Using Spiking Neural Networks and EEG Signals: a Proof of Concept Study
No full textThe characterization of the intrinsic neural activity underlying neurophysiological recordings, which can be gathered through noninvasive techniques, is a major goal of computational neuroscience research. While different methods have been proposed to solve the inverse problem from a pure electromagnetic standpoint, literature regarding functional neural reconstruction modeling is limited. This study introduces a novel framework to define and quantify brain activity from a functional perspective, combining spiking neural networks with Electroencephalography (EEG) signal analysis. Single neuron dynamics is described via the Izhikevich model, and each channel activity is modeled as the outcome of a distinct population of cortical inhibitory and excitatory neurons. Functional interactions among distinct populations are also modeled. We validate this framework by testing it with a dataset of real recordings from 30 healthy subjects undergoing a cold pressure test. Our findings reveal a global enhancement of neural spiking activity during the elicitation session, especially in the β and γ bands. Results suggest that the proposed model is capable of describing the underlying functional neural activity of brain dynamics and showing significant variability between a resting state session and the cold pressure session. The proposed method paves the way for a functional alternative of brain source localization problems
Modeling ATP protonation and activity coefficients in NaClaq and KClaq by SIT and Pitzer equations
No full textThe acid-base properties of Adenosine 5′-triphosphate (ATP) in NaCl and KCl aqueous solutions at different ionic strengths (0 < I / mol L- 1 ≤ 5 for NaClaq, 0 < I / mol L- 1 ≤ 3 for KClaq) and at t = 25 °C were investigated. A selection of literature data on ATP protonation constants and on activity isopiestic coefficients was performed, together with new potentiometric measurements (by ISE-H+, glass electrode). Both literature and new experimental data were used to model the dependence on ionic strength and ionic medium of ATP protonation by SIT (Specific ion Interaction Theory) and Pitzer equations. In addition to values of first and second ATP protonation constants in NaClaq and KClaq at different ionic strengths, stability constants of NaATP3- and KATP3- complexes, SIT interaction coefficients and Pitzer parameters were calculated, together with protonation constants at infinite dilution: log TK1H = pTKa2 = 7.656 ± 0.010 and log TK2H = pTKa1 = 4.561 ± 0.006 (in the molar concentration scale, ± 95% confidence interval). Both SIT and Pitzer approaches give satisfactory results
Palladium(II) sequestration by natural and synthetic chelating agents
No full textPalladium belongs to the so called “Platinum group elements” (PGE), and it is normally present at very low concentration in the environment. In the last twenty years, there has been an increasing PGE demand in different fields such as medicine, electronics, jewellery and car industry. Moreover, palladium (and other PGE) is broadly used as catalyst in a wide number of reactions. The high catalytic properties of PGE favoured their use in the production of catalytic converters. Unfortunately, this caused a noticeable increasing of PGE concentration in the environment, mainly constituted by platinum, with a particular accumulation in urban areas. However, since 1993 platinum has been increasingly replaced by palladium as the predominant substance in catalysts. Now the release of palladium in automotive catalysts is becoming just a critical problem as that of platinum. Furthermore, whilst the emission, the environmental distribution and the possible health effects of platinum have been widely investigated, there is a clear lack of information concerning palladium. Palladium also represents an environmental risk higher than platinum, because it easily and quickly undergoes oxidation processes when put in contact with soils. If the oxidation of palladium may represent a serious environmental problem, at the same time it could represent an advantage for soil and water remediation, if an appropriate chelating agent for the metal ion removal is found. Since the sequestering ability of a chelating agent is strictly related to the stability of the complex species formed with the metal ion to be removed, the speciation studies are of great importance, and represent a fundamental step for the understanding and the optimization of the whole sequestration process. To this end, we focused our attention on the sequestering ability of a natural polyphosphate chelating agent, the so called phytic acid [myo-Inositol hexakis(dihydrogen phosphate)] and of three synthetic chelating agents: the ethylenediamine-N,N,N’,N’-tetraacetate (EDTA), the diethylenetriamine-N,N,N’,N’’,N’’-pentaacetate (DTPA) and the triethylenetetraamine-N,N,N’,N’’,N’’’,N’’’-hexaacetate (TTHA). In this contribution, a series of ISE-H+ potentiometric titrations were carried out in aqueous solutions containing different amounts of the ligands used and of palladium(II) ion, in NaNO3aq at I = 0.1 mol L-1 and t = 25°C. In some cases, some measurements were also performed in NaClaq. The use of two different supporting electrolytes was useful for the evaluation of the effect of the ionic medium on the speciation of Pd2+, with particular reference to the influence of chloride ion. In fact, palladium(II) ion forms stable complex species with this anion, whilst nitrate is weakly interacting with Pd2+. Due to the great tendency of palladium(II) to hydrolyze even at low pH, some ISE-H+ titrations were also carried out to study the acid-base behaviour of Pd2+ ion in the same experimental conditions of Pd2+-ligand systems investigated. Though the literature on the hydrolysis of palladium(II) ion in different ionic media and ionic strengths is abundant, this check was necessary owing to the evident discrepancies noticed in terms of both the number of hydrolytic species and the hydrolysis constant values reported by the different authors. The sequestering ability of the investigated ligands toward Pd2+ was then evaluated by the calculation of various pL50 values in different conditions. Finally, the dependence of pL50 on pH was modelled by simple empirical relationships
Capacità sequestrante di leganti poliammino policarbossilici nei confronti dello ione uranile
No full textPalladium(II) sequestration by phytate in aqueous solution - speciation analysis and ionic medium effects
No full textPalladium(II) speciation in the presence of phytate (Phy12-) was studied by ISE-H+ potentiometry at t = 25°C in NaNO3aq and in NaClaq at I = 0.1 mol L-1, in order to evaluate the effect of the ionic medium on the sequestering ability of phytate toward palladium(II). Owing to the discrepancies found in literature on both the nature and the stability of hydrolytic species formed by this cation, Pd2+ hydrolysis was studied under the same experimental conditions. Since palladium(II) forms stable complex species with chloride ion, the stability constants of various Pd2+ - Cl- species were also calculated, as well as those of weak species formed by nitrate. The stability constants of six palladium(II) - phytate species were determined, namely PdPhyOH11-, PdPhy10-, PdPhyH9-, PdPhyH28-, PdPhyH37-, and PdPhyH46-. The sequestering ability of this ligand toward Pd2+ was evaluated by the calculation of various pL50 values in different conditions. Phytate sequestering ability toward palladium(II) was then compared with that toward other divalent cations, in various conditions. Finally, the dependence of pL50 on pH was modeled by a simple empirical relationship
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
Pb(II) adsorption by a novel activated carbon – alginate composite material. A kinetic and equilibrium study
No full textThe adsorption capacity of an activated carbon – calcium alginate composite material (ACAA-Ca) has been tested with the aim of developing a new and more efficient adsorbent material to remove Pb(II) ion from aqueous solution. The study was carried out at pH = 5, in NaCl medium and in the ionic strength range 0.1–0.75 mol L−1. Differential Pulse Anodic Stripping Voltammetry (DP-ASV) technique was used to check the amount of Pb(II) ion removed during kinetic and equilibrium experiments. Different kinetic (pseudo first order, pseudo second order and Vermuelen) and equilibrium (Langmuir and Freundlich) models were used to fit experimental data, and were statistically compared. Calcium alginate (AA-Ca) improves the adsorption capacity (qm) of active carbon (AC) in the ACAA-Ca adsorbent material (e.g., qm = 15.7 and 10.5 mg g−1 at I = 0.25 mol L−1, for ACAA-Ca and AC, respectively). SEM-EDX and thermogravimetric (TGA) measurements were carried out in order to characterize the composite material. The results of the speciation study on the Pb(II) solution and of the characterization of the ACAA-Ca and of the pristine AA-Ca and AC were evaluated in order to explain the specific contribution of AC and AA-Ca to the adsorption of the metal ion
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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