1,721,215 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
Chromatography as Lévy Stochastic Process
No full textThe Stochastic Theory of Chromatography has been revised in light of some of the most relevant Lévy's findings in Theory of Probability, including the so-called Lévy's distance, the characteristic function and the theory of infinitesimally divisible distributions. These concepts represent the key to exploit and understand, at a molecular basis, phenomena typical of chromatographic separations under linear conditions, such as peak tailing and splitting. In particular, Lévy's distance has been used to quantify the degree of convergence of real peaks towards an ideal Gaussian shape; the characteristic function properties, introduced by Lévy to deal with the problem of the addition of independent random variables, have been employed to solve a wide variety of chromatographic models (including adsorption on heterogeneous surfaces) and to interpret mobile phase dispersion from a probabilistic point of view. Finally, Lévy's studies concerning infinitesimally divisible distributions have allowed to introduce in the stochastic description of chromatography, effects associated to dispersion in mobile phase. It has been demonstrated that, according to Lévy's canonical representation of stochastic processes, the basis of chromatography is a mobile phase Poisson Process. Represented as a Lévy's process, the microscopic-probabilistic model of chromatography permits the establishment of a connection between single-molecule properties and their statistical fluctuations and shapes of real chromatographic peaks allowing, at the same time, for the constitution of a link between different branches of physical sciences
Decoding complex multicomponent chromatograms by Fourier Analysis
No full textThe present work discusses the many attributes - classified as observable, intrinsic or hidden - which can be conceived for any complex multicomponent chromatogram. Discussion ensues on how to decode such chromatograms, i.e. determining the intrinsic and/or hidden attributes from those which can be observed. There are two main steps. The first is based on Fourier Analysis (FA) and determines the intrinsic attributes: i.e., the number of single components which can be detected; their distribution over the available Chromatographie space and peak capacity. The second evaluates the hidden attributes: i.e., the effects of incomplete separation, the number of peaks created by one or more single components as well as their degree of purity. The hidden attributes can be obtained by applying the theory of Statistical Degree of peak Overlapping (SDO) and the paper goes into the extent to which the SDO step depends on the FA results. In addition, the role Exponential distribution plays as a point of reference for the distribution of both single component peak position interdistances and peak heights is discussed. Finally, a simplified graphical FA procedure is presented and the main achievements in this field are reviewed. © 1997 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH
Thermal Field-Flow Fractionation of Charged Submicrometer Particles in Aqueous Media
No full textThermal field-flow fractionation (ThFFF) of various types of submicrometer silica particles in aqueous media is experimentally investigated under an extended range of medium ionic strengths with and without the presence of surfactant. The experiments were designed to examine the applicability to submicrometer particles of the theory of charged nanoparticles thermodiffusion recently proposed by Parola and Piazza (Parola, A.; Piazza, R. Eur. Phys. J. E. 2004, 15, 255-263). In particular, the expression for the calibration function in terms of particle radius and channel temperature is derived and experimentally verified. Moreover, retention is expected to be dependent on particle surface potential and charge, and on ionic strength. These dependences are experimentally investigated and the pertinent relationships and correlations derived. The effect of heavy metal adsorption on the silica surface was investigated, and significant ThFFF retention changes were measured. Independent measurements of the zeta potential (-potential) indicated that a decrease in the surface charge of a silica particle is a consequence of heavy metal adsorption, which is, in turn, correlated to the observed decrease in ThFFF retention
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
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%
Molecular detection of Anaplasma phagocytophilum in hair and spleen of cats revealed a possible underestimation of feline vector-borne pathogens
Full text linkFeline Vector-Borne Diseases show increased global prevalence and some Anaplasma and Ehrlichia species may
pose a risk to human health. The diagnosis of Anaplasma and Ehrlichia species infection in cats is achieved by the
combined use of different methods as cytologic examination evidencing intracytoplasmic morulae, serologic tests
and molecular assays. The peripheral whole blood is considered the sample of choice for Anaplasma and Ehrlichia
species DNA detection in cats, but false negative results are reported leading to underestimation of infection
prevalence. In order to have a more accurate assessment of the spread of feline vector-borne pathogens, the
presence of Anaplasma spp. and Ehrlichia spp. DNA in 37 owner and shelter cats subjected to necropsy were
prospectively investigated by testing in end-point PCR spleen, bone marrow, blood clot and hair samples. The
bacteria identified were genetically characterised. Three shelter cats tested positive for A. phagocytophilum DNA
in spleen (one cat) or in hair samples (two cats). None of the cats tested positive in bone marrow and blood
samples. From the results obtained, it can be assumed that the use of spleen or hair samples could allow a more
reliable detection of A. phagocytophilum DNA in cats with blood tested negative. In the phylogeny constructed
with a fragment of the heat shock (groEL) gene nucleotide sequences, all the identified A. phagocytophilum
clustered with bacteria infecting a wide range of hosts, including humans, showing a potential zoonotic role
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