1,720,969 research outputs found
Analytical SPLITT cell fractionation: Linearity and resolution study.
No full textIn this paper the analytical SPLITT (split flow thin cell) procedure is used to characterize the percentage composition of micronic polydisperse particulate samples at a given cut-off size. The linearity and resolution of the separation method have been
tested using specifically prepared starch samples, in order to compare the analytical process with two continuous (preparative) SPLITT procedures. Linearity has been checked by injecting a series of suspensions (at different concentrations) under five
different flow rate conditions. Retrieval factors F were evaluated to verify the relative amount of sample exiting the cell outlets. The effective resolution has been assessed by inspecting the SPLITT fractions with an optical microscope, counting the granules, and evaluating the percentage of granules of expected size. It has been found that the resolution is very good (around 90%) and independent of sample distribution. It is seen from the comparison that in the analytical SPLITT mode sample resolution is usually around 85–90% and it is significantly better than that of the continuous SPLITT modes, thus making the analytical mode valuable in characterizing polydisperse samples. The method was tested for the characterization of a commercial
starch sample
Analysis of kaolin by Sedimentation Field-Flow Fractionation and Electrothermal Atomic Absorption Spectrometry Detection
No full textElectrothermal (graphite furnace) atomic absorption spectrometry (ETAAS), as off-line detector for Sedimen¬tation Field-Flow Fractionation (SedFFF) is exploi¬ted in clay analysis. Quantification limits of the coupled SedFFF-ETAAS technique for the determination of a submicronic kaolin sample, considered a representative model of natural water suspended particulate, are theoretically esta¬blished and experimentally validated with reference to ETAAS Al and Si determination. A complete sample recovery for a 4 μg injected kaolin quantity was obtained by keeping adsorption in the SedFFF apparatus under control. The best experimen¬tal conditions, ensuring sample integrity, were low ionic strength (Na2CO3, 10-5 M), pH = 8 and teflon covered accumulation wall. Several different runs, revealing the various experimental parameters affecting quantitative recovery, are reported and the different physico-chemical processes affecting such recovery are discussed. The advantages and drawbacks of SedFFF-ETAAS coupling are also discussed in comparison with inducti¬vely coupled plasma-mass spectrometry (ICP-MS) techni¬que
Programmed field decay thermal field flow fractionation of polymers: A calibration method
No full textThe universal calibration procedure typical of thermal field
flow fractionation (ThFFF) under constant thermal field
operation was extended to thermal field programming
(TFP) operation. The method requires knowledge of the
following: (a) the programming function, which only
depends on the thermal field decay function, (b) the
physicochemical properties of the solvent, and (c) the
calibration plot under varying channel cold wall temperatures
(Tc). Two field flow fractionation field programming
conditions, with either a constant or a variable in time
carrier flow velocity, are exploited. The method is based
on determination, for each retention time position, of the
average ì retention value typical of TFP ThFFF. This
parameter is then used to obtain the calibration plot (i.e.,
the molecular weight of the species as a function of the
retention time position) by using the programming function
and the calibration plot under varying Tc values. The
procedure approximation errors are also derived as a
function of the programming type and solute-solvent
system. To properly test the procedure, the calibration
plot for the system constituted by polystyrene (PS) in cistrans
Decalin was determined, under varying conditions
Tc and thermal gradients, by using a set of monodisperse
PS standards of different molecular weights (M). The
procedure was first validated by simulation under two
typical cases of TFP ThFFF operation. The approximation
errors were found acceptable (in the worse cases, the
accuracy in M prediction was 3%) and are in agreement
with the theory. The procedure was then experimentally
validated under varying programming decay function
conditions. The reproducibility and accuracy of the M
determination are both better than 2%
Characterization methods for studying protein adsorption on nano-polystyrene beads
No full textThis work is dealing with the use of polystyrene (PS) nanoparticles as substrates for bioanalytical specific interactions. Different techniques were used for the accurate characterization of the PS nanoparticles of 100 nm and 196 nm before coating them with a layer of antibodies against immunoglobulins of type E (aIgE), giving to the particle a specific functionality. The formation of the aIgE adsorbed layer was monitored using centrifugal particle separation (CPS) and centrifugal field flow fractionation (CF3) experiments, which allowed to determine the size changes and the adsorbed mass. Particle sizes were also measured with DLS, used both as stand-alone instrument and coupled to CF3 (CF3-DLS). The complementary information obtained from the CPS and CF3-DLS measurements allowed the estimation of the density of the aIgE shell. The proteins immobilized at the surface fully retained their activity, as proven by the reactions between the functionalized PS-aIgE particles and immunoglobulins of type E (IgE) dispersed in suspensions prepared on purpose
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
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
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