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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
Pharmaceutical Salts
No full textMost drugs are formulated, when possible, as salts, for their better technological parameters, such as solubility, handling, stability, crystallinity, etc. However this modification of the chemical form, beside many advantages, originates in turn a series of problems, such as formation of hydrates, polimorphs, thermal instability, in the solid state; and/or hydrolysis, acid-base equilibrium, etc. in solution, which limit their applications.
The choice of the optimum salt forming agent for a given molecule is a problem not yet solved and is left to the sensitivity of the experimenter, as well as well the selection of a salt to improve a given parameter. From this point of view sodium salt, for acidic drugs, and hydrochloride, for basic drugs, represent the first choice, even though in the pharmaceutical market, different salts are present and many of them without being approved by FDA. An increased number of aliphatic amines are used to form salt with NSAID, opening new applications (e.g. absorption of the active principle via ion-pairs) or troubles for the taste or volatility of the bases.
The main advantage deriving from the formation of a salt is the improvement of the solubility in water: most of acidic drugs form a dimer in the solid state, where the carboxyl groups face together by hydrogen bonds, preventing thus the hydrophilic portion to interact with water. This structure is destroyed by an increase of pH or the formation of the ionic structure of a salt. Diffractometric examination of the salt crystals can highlight the intimate structure of the compound, useful to interpret its behavior.
A salt, with respect to the acidic parent drug, offers a better solubility and dissolution rate, provided that this chemical form is prevented to come into contact with the acidic gastric environment after its oral administration. However even in the case of destruction of the salt form in acidic medium, the drug precipitates in particles of very small size, guaranteeing a prompt dissolution when pH turns favorable. Not always the use of hydroxy organic bases, as salt forming agents, improving hydrophilicity of the salt, improves its solubility, since the promotion of hydrogen bonds in the solid state between anion and cation represents an unforeseen increase of the melting point and therefore decrease of solubility of the salt. In some case a depressed solubility is looked for depressed by the formation of a salt with heavy metal cation (e.g. calcium) for stability problem or for a masked taste.
Many salts form hydrates, including water molecules into the crystal lattice. Thermal and thermogravimetric analysis are necessary to evidence the stoichiometry of the salt. In these cases the question is: which is the most stable or useful form, the one hydrate or the other one de-hydrated on heating? Dehydration can be accompanied by the formation of amorphous structures or thermal instability. Storage in controlled relative humidity is necessary in each case.
All the situations reported above, which are rather general for pharmaceutical salts, were found studying the properties of the salts of the non-steroidal anti-inflammatory drug diclofenac, and represent the results of our most recent research
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
The arc-fault circuit protection
No full textIn electrical power systems bolted short-circuits are rare and the fault usually involves arcing and burning; mostly the limit value of minimum short-circuit depends really on arcing-fault. In AC low voltage systems, the paper examines the arcing-fault branch circuits as weak points. Different protection measures are available against the arc-faults. A first measure that can guarantee a probabilistic protection is allowed by the adoption of overcurrent protective devices (OCPD), optimizing the design of the structure of the system and/or the coordination of protection. A well known complete protection is allowed by adopting are-fault circuit interrupters (AFCI) for the protection of branch circuits. The authors suggest a new complete protection allowed wiring the branch circuits, including particularly extension cords, with special power cables, protected by ordinary ground fault protective devices (GFPD). The suggested design for single-core or multi-core power cables is that each insulated core has a concentric conductor shield. Converting the line-to-line fault into a line to ground fault or into a mixed type is the goal of this special cable type Faults Ground-Forced Cable (FGFC)
Examples of polymorphism among diclofenac salts
No full textThe formation of pharmaceutical salts is widely recognized as a tool to improve the solubility in water of many acidic or basic drugs and modify their technological properties. This is also the case of diclofenac, an important member of non steroidal anti-inflammatory drug class, whose low solubility in water suggested formulations in the form of sodium and potassium salt, for oral delivery, and of diethylamine and N-pyrrolidine ethanol salts for topical applications.
The interesting behavior of this last salt (DHEP), which forms polymorphs with different extent of hydration, and the easiness of dehydration of some alkaline diclofenac salts suggested the need of better examining the nature of the solid state of these salts, soon after their preparation or after equilibration with water in order to state the formation of hydrate and their stoichiometry. Diclofenac was studied with a variety of aliphatic amines with the aim to prepare salts with improved solubility, for a rapid availability. The crystal structure of many of these salts have been described and emerged that, beside the electrostatic interaction, typical of an ionic compound, a rather constant presence of hydrogen bonding between anion and cation contributes to a build a close contiguity between ions in the crystal lattice. This aspect, when present, could negatively affect the solubility in water, making useless the use of hydrophilic base to increase aqueous solubility of diclofenac salts.
Diclofenac salts with aliphatic, cyclic or linear, hydrophilic or hydrophobic bases were examined by means of thermal analysis and displayed a wide range of behavior in the solid state, with the formation of hydrate and/or polimorphs and demonstrating a notable thermal instability.
In particular, besides the case of DHEP, recently described, we observed bys HSM other polimorphism cases among these diclofenac salts and namely those prepared with the following bases: monoethanolamine, diethanolamine, N-methyl monoethanolamine and triethylamine
Thermal analysis of some diclofenac salts with alkyl and alkylhydroxy amines
No full textA range of diclofenac salts was prepared with a variety of alkyl, hydroxyalkyl and alkyl hydroxyalkyl linear amines, and characterized by
thermal analysis (DSC, TGA, and HSM). Another seven similar salts, previously described, were also prepared for a more careful analysis and
comparison. The aim of this paper is a deeper knowledge of this class of compounds, previously poorly examined and that have, on the contrary,
proved to offer complex situations in the solid state, as resulted by thermal analysis. The whole class of these salts presents a variety of behaviours,
ranging from the formation of hydrates to polymorphs and hydrate polymorphs in the solid state. The salts with diethanolamine, triethanolamine,
N-ethyl monoethanolamine and TRIS bases crystallize anhydrous. All the salts demonstrated thermal instability at temperature above the melting
point, showing a dramatic loss of weight. In each case the TGA profile indicates that it corresponds to the base content inside the salt: this event is
associated with a broad endotherm in the DSC thermogram that follows or overlaps with that of the melting endotherm. Prolonged heating in the
oven of salts with very volatile amines causes decomposition, even at low temperatures, leaving the starting acidic diclofenac as residue. Different
phases, in the case of polymorphs, were revealed, registering melting/re-crystallization by hot stage microscopy, as in the case of the salts with
triethylamine and N-methyl monoethanolamine; while in the case of the salt with monoethanolamine evidence was obtained by means of DSC.
The relationship between the structure of the starting bases and solid-state nature of these diclofenac salts studied is briefly discussed
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