1,721,505 research outputs found
Zero-inertia instabilities in rheopectic fluids
No full textThe emergence of fluid instabilities in the relevant limit of vanishing fluid inertia (i.e., arbitrarily close to zero Reynolds number) has been investigated for the well-known Kolmogorov flow. The time-lagged viscosity change from lower to higher values due to shear changes is the crucial ingredient for the instabilities to emerge. This behavior characterizes the so-called rheopectic fluids. The instability does not emerge in shear-thinning or -thickening fluids where viscosity adjustment to local shear occurs instantaneously. No instability arbitrarily close to zero Reynolds number is either observed in thixotropic fluids, even though the viscosity adjustment time to shear is finite like in rheopectic fluids. Numerical tools (through suitable eigenvalue problems from the linear stability analysis) and multiple-scale homogenization techniques are utilized to lead to our conclusions. Our findings may have important consequences in all situations where purely hydrodynamic fluid instabilities or mixing are inhibited due to negligible inertia, such as in microfluidics. To trigger mixing in these situations, suitable (not necessarily viscoelastic) non-Newtonian fluid solutions appear as a valid answer. Our results open interesting questions and challenges in the field of smart (fluid) materials
Zero-inertia instabilities in rheopectic fluids
No full textThe emergence of fluid instabilities in the relevant limit of vanishing fluid inertia (i.e., arbitrarily close to zero Reynolds number) has been investigated for the well-known Kolmogorov flow. The time-lagged viscosity change from lower to higher values due to shear changes is the crucial ingredient for the instabilities to emerge. This behavior characterizes the so-called rheopectic fluids. The instability does not emerge in shear-thinning or -thickening fluids where viscosity adjustment to local shear occurs instantaneously. No instability arbitrarily close to zero Reynolds number is either observed in thixotropic fluids, even though the viscosity adjustment time to shear is finite like in rheopectic fluids. Numerical tools (through suitable eigenvalue problems from the linear stability analysis) and multiple-scale homogenization techniques are utilized to lead to our conclusions. Our findings may have important consequences in all situations where purely hydrodynamic fluid instabilities or mixing are inhibited due to negligible inertia, such as in microfluidics. To trigger mixing in these situations, suitable (not necessarily viscoelastic) non-Newtonian fluid solutions appear as a valid answer. Our results open interesting questions and challenges in the field of smart (fluid) materials
Multi applicable stereocomplex PLA particles decorated with cyclodextrins
No full textIn this work, an innovative approach to covalently anchor cyclodextrins (CDs) on the surface of submicrometric particles, prepared from an equimolar mixture of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), was developed. The idea of the applied method lays in the potential reactivity of amino CDs towards the polymer functionalities to produce an aminolysis reaction, which should lead to the direct grafting of cyclodextrin molecules on the polymer surface. A preliminary investigation demonstrated the significant capacity of the modified particles to adsorb a model pollutant (alizarin red) and a hydrophobic drug (ketoprofen)
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
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
Molecular Structure and Internal Dynamics of 2′-Hydroxyacetophenone by Free-Jet Absorption Millimeter-Wave Spectroscopy
No full textThe rotational spectrum of (Formula presented.) -hydroxyacetophenone has been recorded and assigned for the first time using a Stark-modulated free-jet absorption millimeter-wave (FJ-AMMW) spectrometer in the 59.6–74.5 GHz frequency range. The most stable conformer has been detected and assigned: A = 2277.076(11), B = 1212.113(5) and C = 795.278(5) MHz. It is characterized by a (Formula presented.) symmetry where a strong hydrogen bond between the acetyl oxygen atom and the hydroxyl atom takes place. The transition lines show a fine structure due to the internal rotation of the methyl group, which allowed the determination of a (Formula presented.) = 565.1(5) (Formula presented.) barrier. The corresponding tunneling splittings have been estimated to be 51 MHz. Calculations at the B3LYP-D3(BJ)/Def2-TZVP level underestimate the height of the barrier by about 156 (Formula presented.). This value decreases to 25 (Formula presented.) with MP2/aug-cc-pVTZ
Free-jet absorption millimeter-wave spectrum of 2’-aminoacetophenone
No full textThe rotational spectrum of 2'-aminoacetophenone has been recorded and assigned using a Stark-modulated Free-Jet Absorption Millimeter-Wave (FJ-AMMW) spectrometer in the 59.6-74.4 GHz frequency range. Some transition lines show a hyperfine structure due to the internal rotation of the methyl group. A global fitting including previous measurements performed in the microwave region allowed the determination of the DJ and DK quartic centrifugal distortion constants and methyl internal rotation barrier V 3 = 644(3) cm-1 value. The A-E tunnelling splitting is estimated to be d 0 = 23 MHz. Calculations at the MP2/aug-cc-pVTZ level underestimate the height of the V 3 barrier by about 23 cm-1. This difference increases to 150 cm-1 with B3LYP-D3(BJ)/Def2-TZVP
Multicompartment hydrogels for the local delivery of chemotherapic drugs
No full textOver 85% of human cancers are solid tumors. The effectiveness of anticancer therapy in solid tumors depends on adequate delivery of the therapeutic agent to tumor cells. Inadequate delivery would result in residual tumor cells, which in turn would lead to regrowth of tumors and possibly development of resistant cells. The most prominent option, for now, is the local delivery of chemotherapic drugs into the cavity resection of the tumor. However, the burst release of massive concentrations of the drugs usually boosts the side effects of chemotherapy. Aiming to block the burst release a new drug delivery system (DDS) for the local delivery of Doxorubicin (DOX) was designed and tested, combining different materials and techniques. Following a bottom-up approach, porous spherical calcium carbonate (CaCO3) microspheres, with high loading properties, were loaded with DOX and Layer by Layer (LbL) assembled by biocompatible and biodegradable polyelectrolytes, dextran sodium sulfate (DSS) and polyarginine (PARG). Then, a protocol for the fabrication of alginate (Alg) hydrogels associated with LbL coated drug loaded CaCO3 microspheres were developed by combining internal and external gelation. Therefore, injectable multicompartment hydrogels (MCH) for the local and sustained delivery of chemotherapeutic drugs, with the ability to block the burst release, were developed and characterized
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