1,721,024 research outputs found
Simulation and optimization of power-programmed sdfff: Applications for fractionating and characterizing submicrometer particulate matter in river water
No full textThe submicrometer fraction of the particulate matter suspended in river water is characterized by decay- programmed sedimentation field-flow fractionation (SdFFF). The power program was chosen because of its ability to yield a homogeneous fractionating power with respect to the analysis of broadly dispersed particulate samples. An appropriate search for the optimum power program setup is performed by numerical simulation. Comparison between simulated and experimental fractograms proves to be feasible in establishing the physical features of the sample (i.e., number of components, their relative dimensions, polydispersity, and absolute amount). A method is presented coupling SdFFF with electron microscopy (EM) techniques. Both the separation achieved and the sample model on which SdFFF simulation has been based are then verified using this coupled approach. Examples of EM morphological characterization on SdFFF-fractionated samples of river-borne particulate matter are reported. Under optimized power programming conditions, some effects of particulate sample treatments on SdFFF fractograms are presented. Chemical oxidation and sample aging are shown to influence the SdFFF- based, dimensional distribution of the particles. © Oxford University Press 1992
SIMULATION OF FRACTOGRAMS OF FAT EMULSIONS IN POWER-PROGRAMMED SEDIMENTATION FIELD-FLOW FRACTIONATION (SDFFF)
No full textA quasi-empirical approach to the simulation of fractograms was examined to verify that the elution behavior of emulsions in power-based field programmed sedimentation field-flow fractionation (SdFFF) is consistent and predictable. The approach was applied to Intralipid, a commercial soybean emulsion and to an investigational medium chain triglyceride emulsion. The simulations predicted the fractograms that were obtained under various conditions of field strength, field decay and velocity of the suspending fluid, using distribution parameters obtained from one preliminary measurement of size distribution profile. Predicted fractograms were compared to experimental ones, under various fractionating powers. Good agreement was observed in most cases, in which interference of the secondary relaxation effects was not effective. The agreement confirmed the applicability of the approach to emulsions and that the simulations can be used instead of actual experiments for the optimization of their characterization by power-programmed SdFFF. © 1995
High temperature thermal field‐flow fractionation of polyethylene and polystyrene
No full textIn this paper the high‐temperature thermal field flow fractionation method is exploited for the analysis of polyethylene (PE). The experimental apparatus set‐up, obtained by simply modifying a commercial instrument, is presented. The numerical procedure for deriving retention calibration plot versus molecular weight is discussed with reference to the specific polymer‐solvent pair, PE‐o‐dichlorobenzene (ODCB), here employed. Different methods for computing the physicochemical data set of the solvent, necessary for calibration, are compared. The selectivity of the checked PE‐ODCB system proves comparable with respect to the values currently found in thermal field‐flow fractionation (ThFFF) analysis. Differences are found between PE and polystyrene (PS) analysis in the same solvent. The conditions for high temperature ThFFF operation in PE analysis and their advantages are discussed with respect to the standard SEC technique for PE, PS, and PE‐PS copolymer analysis. Molecular weight distributions obtained by ThFFF of two PE commercial samples agree with those obtained by SEC. © 1995 John Wiley & Sons, Inc. Copyright © 1995 John Wiley & Sons, Inc
Liposomes characterization for market approval as pharmaceutical products: Analytical methods, guidelines and standardized protocols
Full text linkLiposomes are nano-sized lipid-based vesicles widely studied for their drug delivery capabilities. Compared to standard carries they exhibit better properties such as improved site-targeting and drug release, protection of drugs from degradation and clearance, and lower toxic side effects. At present, scientific literature is rich of studies regarding liposomes-based systems, while 14 types of liposomal products have been authorized to the market by EMA and FDA and many others have been approved by national agencies. Although the interest in nanodevices and nanomedicine has steadily increased in the last two decades the development of documentation regulating and standardizing all the phases of their development and quality control still suffers from major inadequacy due to the intrinsic complexity of nano-systems characterization. Many generic documents (Type 1) discussing guidelines for the study of nano-systems (lipidic and not) have been proposed while there is a lack of robust and standardized methods (Type 2 documents). As a result, a widespread of different techniques, approaches and methodologies are being used, generating results of variable quality and hard to compare with each other. Additionally, such documents are often subject to updates and rewriting further complicating the topic. Within this context the aim of this work is focused on bridging the gap in liposome characterization: the most recent standardized methodologies suitable for liposomes characterization are here reported (with the corresponding Type 2 documents) and revised in a short and pragmatical way focused on providing the reader with a practical background of the state of the art. In particular, this paper will put the accent on the methodologies developed to evaluate the main critical quality attributes (CQAs) necessary for liposomes market approval
Optimization of signal denoising in discrete wavelet transform
No full textA method to optimize the parameters used in signal denoising in the wavelet domain is presented. The method, which is based on cross-validation CV.procedure, permits to select the best decomposition level and the best wavelet filter function to denoise a signal in the discrete wavelet domain. The procedure was validated by using computer generated signals to which white noise was added. Signals having different features and a range of signal to noise ratios were explored. The method was shown to give reliable results for all cases studied. The proposed method was applied to experimental gravitation field flow fractionation records, and the results were compared with classical low pass filtering in the Fourier domain
Fourier analysis of multicomponent chromatograms. Numerical evaluation of statistical parameters
No full textA procedure based on the power spectrum (PS) model of a multicomponent chromatogram is introduced by which the number m of detectable components (or single-component peaks) and the parameters of the single-component peak such as standard deviation and asymmetry factor can be evaluated. In essence, when fitted to theoretical models, the experimental PS-expressing the chromatographic response variance dependence on the time distance-provides the Information necessary to accept or reject the model and to give the necessary parameter estimations. The procedure is tested by using computer-generated multicomponent chromatograms with Poissonian retention time distribution and random and uncorrelated peak heights, in which density, asymmetry and height distribution are widely varied. How to obtain unbiased PS numerical determination by windowing is also discussed. It Is shown that unbiased parameter estimations are obtained, the only procedure limitation being the approximation made In the evaluation of the single-component peak height dispersion. An example Is given of how a retention time distribution other than the Poissonian can be detected. © 1990, American Chemical Society. All rights reserved
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
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