1,721,035 research outputs found
Raman acoustic levitation spectroscopy of red blood cells and Plasmodium falciparum trophozoites
No full textMethods to probe the molecular structure of living cells are of paramount importance in understanding drug interactions and environmental influences in these complex dynamical systems. The coupling of an acoustic levitation device with a micro-Raman spectrometer provides a direct molecular probe of cellular chemistry in a containerless environment minimizing signal attenuation and eliminating the affects of adhesion to walls and interfaces. We show that the Raman acoustic levitation spectroscopic (RALS) approach can be used to monitor the heme dynamics of a levitated 5 µL suspension of red blood cells and to detect hemozoin in malaria infected cells. The spectra obtained have an excellent signal-to-noise ratio and demonstrate for the first time the utility of the technique as a diagnostic and monitoring tool for minute sample volumes of living animal cells
Online investigation of respiratory quotients in Pinus sylvestris and Picea abies during drought and shading by means of cavity-enhanced Raman multi-gas spectrometry
Full text linkPhotosynthesis and respiration are major components of the plant carbon balance. During stress, like drought, carbohydrate supply from photosynthesis is reduced and the Krebs cycle respiration must be fueled with other stored carbon compounds. However, the dynamics of storage use are still unknown. The respiratory quotient (RQ, CO2 released per O2 consumed during respiration) is an excellent indicator of the nature of the respiration substrate. In plant science, however, online RQ measurements have been challenging or even impossible so far due to very small gas exchange fluxes during respiration. Here we apply cavity-enhanced multi-gas Raman spectrometry (CERS) for online in situ RQ measurements in drought-tolerant pine (Pinus sylvestris [L.]) and drought-intolerant spruce (Picea abies [L. H. Karst]). Two different treatments, drought and shading, were applied to reduce photosynthesis and force dependency on stored substrates. Changes in respiration rates and RQ values were continuously monitored over periods of several days with low levels of variance. The results show that both species switched from COH-dominated respiration (RQ = 1.0) to a mixture of substrates during shading (RQ = 0.77–0.81), while during drought only pine did so (RQ = 0.75). The gas phase measurements were complemented by concentration measurements of non-structural carbohydrates and lipids. These first results suggest a physiological explanation for greater drought tolerance in pine. CERS was proven as powerful technique for non-consumptive and precise real-time monitoring of respiration rates and respirational quotients for the investigation of plant metabolism under drought stress conditions that are predicted to increase with future climate change
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
Raman spectroscopy of antibiotics in body fluids
Full text linkThis study explores methods for the detection of antibiotics in body fluids, closely tied to therapeutic drug monitoring (TDM), which measures drug concentrations and adjusts dosages accordingly. In patients, physiological changes can alter antibiotic pharmacokinetics, complicating correct dosing. Over- or underdosing may promote resistance, worsening treatment outcomes. Therefore, antibiotic therapy must be tailored, monitored, and adjusted as required. While current techniques like chromatography, bioassays, and electrochemical methods are highly sensitive and specific, they are often time-consuming and resource-intensive. Raman spectroscopy offers rapid, non-destructive, multi-component detection, though signal enhancement is required due to the weak scattering process. Deep-UV laser excitation was employed to match molecule-specific electronic transitions, enhancing vibrations while reducing fluorescence interference. In TDM, body fluids act as complex matrices, contributing their own signals to the Raman spectrum, which can overlap with antibiotic marker bands and hinder quantification. This work aims to overcome these challenges by identifying antibiotics at clinically relevant concentrations. Reference-based spectral comparison reveals characteristic marker bands, while chemometric models utilizing significant spectral ranges estimate concentrations. These methods enable both sensitive detection of antibiotics and the monitoring of drug degradation, while pharmacokinetic simulations further demonstrate the versatility and potential of resonance Raman spectroscopy for TDM applications
Raman spectroscopy of antimalarials and drug-target complexes
Full text linkDespite extensive research, malaria remains a major infectious disease, aggravated by the rapid development of drug resistance. The precise mechanisms of many antimalarial agents remain unclear, impeding therapeutic progress. Deep ultraviolet resonance Raman (DUV-RR) spectroscopy has emerged as a powerful tool for investigating molecular interactions due to its high specificity and sensitivity, enabling detailed spectral analysis of subtle changes. This thesis integrates spectroscopic and analytical techniques to examine antimalarial compounds and their interactions. Here, the selectivity of DUV-RR spectroscopy was assessed using arylisoquinolines (AIQs), a promising novel drug class. The excitation wavelength determined the resonant enhancement of specific structural regions, allowing differentiation within the compound class, supported by density functional theory (DFT) calculations. Additionally, ferroquine (FQ), a high-potential antimalarial, was detected at physiologically relevant micromolar concentrations. The method’s sensitivity enabled detection below intraerythrocytic levels. FQ’s distinct transport mechanism was analyzed in biomimetic solutions, revealing spectral variations confirmed by DFT studies. Furthermore, the interaction of artesunate (AS) with synthetic malaria pigment β-hematin was investigated in the visible resonance range using two-dimensional correlation analysis (2D-Corr). Subtle spectral changes were systematically interpreted to elucidate molecular binding mechanisms at their target structure. The integration of (DUV-)RR spectroscopy, advanced data analysis, and supporting DFT calculations proved highly effective in identifying and characterizing intracellular transport mechanisms as well as molecular interactions of antimalarial agents with their target structures
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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