1,721,134 research outputs found
Pullulan as a permanent hydrophilic coating in capillary electrophoresis: applications to penicillin G acylase as chiral selector
No full textStudy on the photostability of guaiazulene by high-performance liquid chromatography/mass spectrometry and gas chromatography/mass spectrometry
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Simultaneous HS-SPME GC-MS determination of short chain fatty acids, trimethylamine and trimethylamine N-oxide for gut microbiota metabolic profile
No full textTrimethylamine (TMA), trimethylamine-N-oxide (TMAO) and short chain fatty acids (SCFAs), as acetic, propionic, butyric and valeric acids are among the most important products of the gut microbiota (GM) metabolism. The present study is aimed at the determination of TMA, TMAO and SCFAs by a double step headspace-solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) analysis, allowing the simultaneous quantitation of both the acidic and basic metabolites in faecal samples. TMAO amount was evaluated after its reduction to TMA by using Fe(II)-EDTA complex as a reagent. Under the fully validated experimental conditions, adequate sensitivity (LOQ 0.011–0.23 μmol g−1), good accuracy (79 – 110%) and precision (CV% < 11%) were achieved for all the target analytes. The presented method is successfully applied to the quantitation of the considered gut metabolites in faecal samples from Italian healthy volunteers
Archeometallurgical Investigation of a Fragment from a Medieval Sword Blade
No full textA fragment from a medieval sword blade was investigated by metallography, Vickers microhardness tests and slag inclusions analysis are to extract technological information about its manufacturing process. Optical microscopy observations and microhardness measurements indicated that the sword blade was forged via hammer welding, combining different steel bars for an optimal balance of hardness and toughness. A steeling technique involved wrapping a steel bar around a composite billet, crafted by enclosing a hypoeutectoid steel bar around a near-eutectoid steel core. Moreover, it was found that the hardness of the cutting edges was increased with a quenching heat treatment. After quenching, the blade exhibited martensitic microstructure with Vickers microhardness ranging from 500 to 640 HV0.3. The compositional data of a large set of nonmetallic inclusions were collected by scanning electron microscopy coupled with X-ray dispersive spectroscopy. Slag inclusion analysis and multivariate statistics confirmed the blade's composite nature and revealed distinct smelting and forging-related SI groups. Liquidus temperatures indicated smelting temperatures of at least 1156 degrees C for the external section and 1031 degrees C for the internal. The forging temperature was estimated at a minimum of 1143 degrees C. These findings provide insight into the blade's metallurgical history
A novel hydrophilic interaction liquid chromatography method for the determination of underivatized amino acids in alimentary supplements
No full textAmino acids playing important roles in metabolic processes are often included in dietary supplements whose use has largely expanded over the last 20 years not only in patients with particular deficiencies, but also in athletes and even common people that want to enrich their regular daily diet. In the present study, a bare silica Kinetex core-shell 2.6 um HILIC column was used for separation of some important hydrophilic amino acids and amino acids-like molecules i.e., aspartic acid, creatine, carnitine, arginine and the tripeptide glutathione (GSH), by optimizing the chromatographic conditions for their determination in complex alimentary supplements. The contribution of partition, adsorption and ion exchange on the retention mechanism was studied by varying parameters such as water content and the counter-ion concentration in the mobile phase. Optimum conditions employed a Phenomenex Kinetex core-shell 2.6 um HILIC (100 x 4.6 mm i.d.) column and a mobile phase of acetonitrile/potassium phosphate buffer (12.5 mM; pH = 2.8) 85:15, v/v, at the flow rate of 1.4 mL/min, using UV detection at 200 nm. A reference HPLC method for the selective determination of GSH by using 1,4-naphthoquinone as derivatization reagent was also introduced for comparative purposes. The developed HILIC method was validated and applied to the analysis of the considered compounds in dietary supplements. Interestingly, in some of the real samples, oxidized glutathione which is an inactive impurity of GSH, was found at the level of about 20%. The proposed study confirms the importance of simple analytical methods for a rigorous quality control of dietary supplements containing unstable active ingredients
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
Archeometallurgical study of a renaissance spearhead from northern Italy
No full textA metallurgical study of a Renaissance spearhead from northern Italy was performed to provide new deep insights into both smelting and smithing technologies which are involved in the manufacturing process. Optical microscopy observations, Vickers microhardness measurements, and optical emission spectroscopy analyses demonstrated that the spearhead was skillfully assembled and shaped from different steel bars, and a slack-quenching heat treatment was performed on the blade to improve its functionality. The chemistry of a large sample of nonmetallic inclusions was characterized by scanning electron microscopy coupled with X-ray dispersive spectroscopy. A multivariate statistical data treatment based on logistic regression was applied to assess the technological origin of the steel bars. The results allowed to conclude that the spearhead steel was obtained following the indirect steel-making route. The temperatures reached during both smelting and smithing stages were estimated in the FeO–SiO2–CaO system at 1470 °C and 1200 °C, respectively
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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