124,646 research outputs found
L'articolo Taming Axial Dispersion in Hydrodynamic Chromatographic Columns through Wall Patterning, Physics of Fluids 30, 042002 (2018); doi: 10.1063/1.5022257 di A. Adrover, S. Cerbelli, M Giona e' stato selezionato come Top papers in Physics of Fluids 2018
No full textA well-known limitation of hydrodynamic chromatography arises from the synergistic interaction
between transverse diffusion and streamwise convection, which enhances axial dispersion through
the Taylor-Aris mechanism. We show that a periodic sequence of slip/no-slip conditions at the channel
walls (e.g., representing wall indentations hosting stable air pockets) can significantly reduce axial
dispersion, thus enhancing separation performance. The theoretical/numerical analysis is based on a
generalization of Brenner’s macrotransport approach to solute transport, here modified to account for
the finite-size of the suspended particles. The most effective dispersion-taming outcome is observed
when the alternating sequence of slip/no-slip conditions yields non-vanishing cross-sectional flow
components. The combination of these components with the hindering interaction between the chan-
nel boundaries and the finite-sized particles gives rise to a non-trivial solution of Brenner’s problem
on the unit periodic cell, where the cross-sectional particle number density departs from the spa-
tially homogeneous condition. In turn, this effect impacts upon the solution of the so-called b-field
defining the large-scale dispersion tensor, with an overall decremental effect on the axial disper-
sion coefficient and on the Height Equivalent of a Theoretical Plate. Published by AIP Publishing
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
An unusual ulcer
No full textThis clinical case describes a 78-year-old female patient who underwent total thyroidectomy and parathyroidectomy due to thyroid cancer; surgery was followed by radioiodine therapy. The patient was treated with 20 μg of teriparatide once a day for 7 years and consistently showed above normal blood calcium levels. In addition, following the operation, the patient began taking 50 000 units of vitamin D orally every month and 1 g of calcium per os a day. A painful eschar had appeared on the front of her left leg 3 months before; it had developed into a deep, painful ulcer. The patient did not present arterial or venous diseases. Arterial hypertension was effectively managed with 5 mg of ramipril per day, renal function was normal, and the patient was not suffering from diabetes. A computed tomography scan gave evidence of extensive dermo-hypodermitis calcification in the ulcer area. A biopsy was performed and the histological examination revealed calciphylaxis. The patient was treated by suspending teriparatide, which actually had been suspended months before, and replacing it with bisphosphonate; suspension of calcium and vitamin D and the oral administration of 250 units of sulodexide every 12 hours. Local therapy was adapted according to the advancement of the ulcer’s stages. This case represents one of non-uremic calciphylaxis determined by an overly lengthy administration of a parathyroid hormone that caused drug-induced hyperthyroidism over a long period of time. A revision of the worldwide literature on the topic was carried out and an etiopathogenetic hypothesis concerning the clinical case is put forward
Solitary nonfamilial desmoplastic trichoepithelioma of the external auditory canal
No full textSolitary desmoplastic trichoepithelioma is a benign adnexal neoplasm first described by Brownstein and Shapiro in 1976. It can be solitary or multiple, familial or not familial.
We present the case of a young man affected by solitary non familial desmoplastic trichoepithelioma of the external auditor canal (EAC). Clinical and histological findings are described. To our knowledge this is the first reported case of solitary desmoplastic trichoepithelioma of the EAC
Taming axial dispersion in hydrodynamic chromatography columns through wall patterning
No full textA well-known limitation of hydrodynamic chromatography arises from the synergistic interaction
between transverse diffusion and streamwise convection, which enhances axial dispersion through
the Taylor-Aris mechanism. We show that a periodic sequence of slip/no-slip conditions at the channel
walls (e.g., representing wall indentations hosting stable air pockets) can significantly reduce axial
dispersion, thus enhancing separation performance. The theoretical/numerical analysis is based on a
generalization of Brenner’s macrotransport approach to solute transport, here modified to account for
the finite-size of the suspended particles. The most effective dispersion-taming outcome is observed
when the alternating sequence of slip/no-slip conditions yields non-vanishing cross-sectional flow
components. The combination of these components with the hindering interaction between the chan-
nel boundaries and the finite-sized particles gives rise to a non-trivial solution of Brenner’s problem
on the unit periodic cell, where the cross-sectional particle number density departs from the spa-
tially homogeneous condition. In turn, this effect impacts upon the solution of the so-called b-field
defining the large-scale dispersion tensor, with an overall decremental effect on the axial disper-
sion coefficient and on the Height Equivalent of a Theoretical Plate. Published by AIP Publishing.
https://doi.org/10.1063/1.502225
Quantitative analysis of mixing structures in chaotic flows generated by infinitely fast reactions in the presence of diffusion
No full textThe interplay between diffusive and convective mixing processes may have a strong, impact upon apparent reaction rates. This paper analyzes the interaction of convection and diffusion mechanisms by considering an infinitely fast irreversible reaction A + B --> products, occurring in a two-dimensional chaotic flow. Attention is focused on the aeometric properties of mixing patterns and on the overall reactant consumption. We show that the length of the reaction interface undergoes a transition from a kinematics-dominated exponential growth to a persistent oscillatory regime. This regime results from two competing mechanisms, namely, recursive stretching and folding of the interface caused by chaotic advection and merging of contiguous striations patterns owed to diffusive transport. In the case of globally chaotic flows, a singular transition is observed in the scaling of the dominant eigenvalue with the Peclet number. The geometric information arising from the analysis of the reaction interface is also exploited for deriving a simple one-dimensional model that predicts the apparent rates over a wide range of Peclet numbers
Eigenvalue–eigenfunction analysis of infinitely fast reactions and micromixing regimes in regular and chaotic bounded flows
No full textWe analyze the dynamics of a single irreversible reaction A+B? Products, occurring in a bounded incompressible flow. Within the limits of infinitely fast kinetics, the system is reduced to an advection–diffusion equation for the scalar ?, representing the difference between the reactant concentrations. By the linearity of the governing PDE, the system evolution is determined by the properties of the eigenvalue–eigenfunction spectrum associated with the advection–diffusion operator. In particular, the dependence of the dominant eigenvalue ?—yielding the time-scale controlling the asymptotic reactant decay—as a function of the molecular diffusivity, View the MathML source, for different stirring protocols is analyzed. We find View the MathML source, where the exponent ??[0,1] depends upon the kinematic features of the stirring flow. When the kinematics is regular within most of the flow domain (e.g. two-dimensional autonomous flows or time-periodic protocols possessing large quasiperiodic islands) a purely diffusive scaling, ?=1 settles as View the MathML source. The singular scaling ?=0 is found in the case of globally chaotic kinematics, whereas mixed regimes, 0<?<1, occur in flows that are characterized by the coexistence of quasiperiodic and chaotic behavior. The analysis of spectral properties of the advection–diffusion operator provides a new classification of micromixing regimes, and new mixing indices for quantifying homogenization performances in the presence of diffusion
Articolo selezionato come articolo d copertina di Physics of Fluids, April 2018
No full textA well-known limitation of hydrodynamic chromatography arises from the synergistic interaction
between transverse diffusion and streamwise convection, which enhances axial dispersion through
the Taylor-Aris mechanism. We show that a periodic sequence of slip/no-slip conditions at the channel
walls (e.g., representing wall indentations hosting stable air pockets) can significantly reduce axial
dispersion, thus enhancing separation performance. The theoretical/numerical analysis is based on a
generalization of Brenner’s macrotransport approach to solute transport, here modified to account for
the finite-size of the suspended particles. The most effective dispersion-taming outcome is observed
when the alternating sequence of slip/no-slip conditions yields non-vanishing cross-sectional flow
components. The combination of these components with the hindering interaction between the chan-
nel boundaries and the finite-sized particles gives rise to a non-trivial solution of Brenner’s problem
on the unit periodic cell, where the cross-sectional particle number density departs from the spa-
tially homogeneous condition. In turn, this effect impacts upon the solution of the so-called b-field
defining the large-scale dispersion tensor, with an overall decremental effect on the axial disper-
sion coefficient and on the Height Equivalent of a Theoretical Plate. Published by AIP Publishing.
https://doi.org/10.1063/1.502225
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