1,721,031 research outputs found
Reference Pricing as a Deterrent to Entry: Evidence from the European Pharmaceutical Market
Full text linkExternal reference pricing (ERP), the practice of benchmarking domestic drug prices to foreign prices, generates an incentive for firms to withhold products from low-income countries. Using a novel moment inequality approach, we estimate a structural model to measure how ERP policies affect access to innovative drugs across Europe. We find that ERP increases entry delays in eight low-income European countries by up to one year per drug. The European Union could remove these delays without replacing ERP by compensating firms through lump-sum transfers at the cost of around €18 million per drug
Fluctuations of polyspectra in spherical and Euclidean random wave models
Full text linkWe consider polynomial transforms (polyspectra) of Berry's model - the Euclidean Random Wave model - and of Random Hyperspherical Harmonics. We determine the asymptotic behavior of variance for polyspectra of any order in the high-frequency limit. In particular, we are able to treat polyspectra of any odd order q >= 5, whose asymptotic behavior was left as a conjecture in the case of Random Hyperspherical Harmonics by Marinucci and Wigman (Comm. Math. Phys. 2014). To this end, we exploit a relation between the variance of polyspectra and the distribution of uniform random walks on Euclidean space with finitely many steps, which allows us to rely on technical results in the latter context
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
Mechanochemistry, an Easy Technique to Boost the Synthesis of CuI Pyrazine Coordination Polymers
No full textDepending on the experimental conditions, the solid-state reactions of CuI with pyrazine (pyz) yield three distinct coordination polymers (CPs): a double chain polymer [Cu2I2(pyz)]n (yellow powder) and a single strand [CuI(pyz)]n (red powder) and its new isomeric compound [(CuI)2(pyz)2]n (orange powder), which present dimers of CuI bridged by the pyrazine ligands. The conversions among the three CPs were studied: by heating to 110 °C, [CuI(pyz)]n or [(CuI)2(pyz)2]n convert into [Cu2I2(pyz)]n, which reverts to the starting compounds upon kneading or grinding in the presence of pyrazine. The orange isomer [(CuI)2(pyz)2]n is obtained only when the solid-state reaction is performed with neat grinding or by direct melting of the pyrazine; it is unstable in the presence of solvent or vapor, and it readily transforms into the red isomer. The structure of [(CuI)2(pyz)2]n was determined by X-ray powder diffraction. [Cu2I2(pyz)]n reacts also with 4-cyanopyrazine to yield the mixed ligand compound [(CuI)(4CN-py)2 py]n, which, when heated, decomposes into [Cu2I2(pyz)]n and [(CuI)4(4CN-py)5]n.
Polymorph and isomer conversion of complexes based on CuI and PPh 3 easily observed via luminescence
No full textReactions between copper(i) iodide and triphenylphosphine have been explored in solution and in the solid state and six luminescent coordination complexes have been obtained and characterized by X-ray diffraction and UV-vis spectroscopy and photophysics. Solid-state reactions of CuI with PPh 3 in different conditions (kneading, vapour digestion) and stoichiometries resulted in the formation of high ratio ligand:metal compounds while tetrameric structures could be obtained only by solution reactions. Crystal structures were determined by single crystal X-ray diffraction while purity of the bulk product was checked by powder diffraction (XRPD). Three different tetrameric structures with 1:1 stoichiometry have been synthesized: two closed cubane-type polymorphs [CuI(PPh 3)] 4 (form 1a) and [CuI(PPh 3)] 4 (form 1b) and an open step-like isomer [CuI(PPh 3)] 4 (form 2). The conversions between the polymorphs and isomers have been studied and characterized by XRPD. The most stable form [CuI(PPh 3)] 4 (form 1b) can convert into the open step-like isomer [CuI(PPh 3)] 4 (form 2) in a slurry experiment with EtOH or CH 2Cl 2 or AcCN and converts back into [CuI(PPh 3)] 41b when exposed to vapors of toluene. At room temperature all the tetrameric compounds exhibit luminescence in the solid state and, notably, the two polymorphs show a dissimilar dual emission at low temperature. The luminescence features in the solid state seem to be peculiarly related to the presence of the aromatic phosphine ligand and depend on the Cu-Cu distance in the cluster. © 2012 The Royal Society of Chemistry
Self-organizing maps as a data-driven approach to elucidate the packing motifs of perylene diimide derivatives
Full text linkThe efficient classification or prediction of crystal structures into a small number of families of related structures can be extremely important in the design of materials with specific packing and properties. In this respect, the traditional way to classify the crystal packing of organic semiconductors as herringbone, sandwich-herringbone, and beta- or gamma-sheets by visual inspection has its limitations. Herein, we present the use of a clustering method based on a combination of self-organizing maps and principal component analysis as a data-driven approach to classify different pi-stacking arrangements into families of similar crystal packing. We explored the pi-stacking arrangements within the crystal structures deposited in the Cambridge Structural Database of perylene diimide (PDI) derivatives with different types and positions of the substituents. The structures were characterised by a set of descriptors that were then used for classification. Six different packing families of PDIs were identified and their characteristics are discussed here. Finally, the effects of different substituent types and positions on the resulting packing arrangement are discussed
Thorough investigation on the high-temperature polymorphism of dipentyl-perylenediimide: thermal expansion vs. polymorphic transition
Full text linkN,N′-Dipentyl-3,4,9,10-perylendiimide (PDI-C5) is an organic semiconducting material which has been extensively investigated as model compound for its optoelectronic properties. It is known to be highly thermally stable, that it exhibits solid-state transitions with temperature and that thermal treatments lead to an improvement in its performance in devices. Here we report a full thermal characterization of PDI-C5 by combination of differential scanning calorimetry, variable temperature X-ray diffraction, hot stage microscopy, and variable temperature Raman spectroscopy. We identified two high temperature polymorphs, form II and form III, which form respectively at 112 °C and at 221 °C and we determined their crystal structure from powder data. Form II is completely reversible upon cooling with low hysteresis, while form III revealed a different thermal behaviour upon cooling depending on the technique and crystal size. The crystal structure features of the different polymorphs are discussed and compared, and we looked into the role of the perylene core and alkyl chains during solid-state transitions. The thermal expansion principal axis of PDI-C5 crystal forms is reported showing that all the reported forms possess negative thermal expansion (X1) and large positive thermal expansion (X3) which are correlated to thermal behaviour observed
Direct derivation of the crystalline fraction of highly potent active pharmaceutical ingredients by X-ray powder diffraction
No full textDirect derivation (DD) is a novel Powder X-ray diffraction quantification method based on intensity–composition equation, which can determine the weight fraction of individual phases in a mixture of components by chemical formulas. The DD method was applied to determine crystallinity degree of binary mixtures containing amorphous hydroxypropyl methylcellulose and crystalline monohydrate α-lactose in weight percentage ≤ 15% w/w. Three different scenarios were considered: a) the unit cell parameters of the crystalline phases are available b) the unit cell parameters are unknown but the patterns of pure crystalline and amorphous references are available and c) only the mixtures’ patterns are available. Relative errors in scenarios a and b were comparable and reasonable (<20%), while in c, the crystalline degree was clearly underestimated evidencing the importance of determining the maximum number of crystalline reflections This can be easily achieved when the unit cell parameters and/or the patterns of pure references are available. To simulate the quantification of high potent API, the method was evaluated considering the scenario b, in samples covered by Kapton® film as containment system. In this case, an accurate quantification was achieved by subtracting the film signal from the observed pattern
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