1,720,989 research outputs found
Shot-noise limited detection sensitivity in multiplex CARS microscopy
No full textIn multiplex CARS microscopy the generated anti-Stokes signal is generated and detected simultaneously over a significant part of the vibrational spectrum. The signal-to-noise ratio of the thus detected spectra is limited only by shot-noise. This principle is demonstrated using a dilution series of 2-propanol in water. It is derived theoretically and shown experimentally that for low solute concentrations - in contrast to methods that suppress the non-resonant background - the CARS signal strength from a particular vibrational mode depends linearly on its concentration. Furthermore, excellent agreement is shown between the experimental data and fits to the theory. It is shown that this approach permits rapid (20 ms acquisition) detection of a single lipid mono-layer, with sufficient signal-to-noise to determine the order parameter for the acyl chain packing. Also it is demonstrated that this detection scheme provides an absolute measure of the solute concentration.Radiation Chemistry DepartmentApplied Science
Third Harmonic Generation: anomalous behavior in the THG z-response and microscopy applications
No full textThird Harmonic Generation (THG) from the vicinity of interfaces, using focused laser beams can be obtained virtually from any inhomogeneous medium. Its sensitivity to the presence and extent of inhomogeneity in the focal volume has already found a variety of applications ranging from material characterization to label free three-dimensional microscopy of biological samples. In this presentation, we demonstrate a number of new applications of THG in the microscopy of food samples and living cells. Also, we report on an anomalous behavior in the THG z-response. So far the observations and theoretical predictions supported a single peak of THG signal, with the peak position corresponding to the interface. We have observed an anomalous behavior where a single interface can give rise to two peaks located across the interface. The simulations, which we carried out using a paraxial theory of THG and measurements done on typical normally dispersive materials, suggest that this anomalous behavior is due to a particular combination of χ(3) and the magnitude of dispersion
Quantitative multiplex CARS spectroscopy in congested spectral regions
No full textA novel procedure is developed to describe and reproduce experimental coherent anti-Stokes Raman scattering (CARS) data, with particular emphasis on highly congested spectral regions. The approach - exemplified here with high-quality multiplex CARS data - makes use the maximum entropy method for phase retrieval. The retrieved imaginary part of the nonlinear susceptibility is shown to be equal to the spontaneous Raman spectrum. The phase retrieval procedure does not influence the noise contained in the spectra. The conversion of CARS to Raman data permits a quantitative interpretation of CARS spectra. This novel approach is demonstrated for highly congested multiplex CARS spectra of sucrose, fructose and glucose. This novel procedures enables extraction of vibrational information from multiplex CARS data without the use of a priori information of the sample
Adaptive optics plug-and-play setup for high-resolution microscopes with multi-actuator adaptive lens
No full textAdaptive Optics (AO) has revealed as a very promising technique for high-resolution microscopy, where the presence of optical aberrations can easily compromise the image quality. Typical AO systems however, are almost impossible to implement on commercial microscopes. We propose a simple approach by using a Multi-actuator Adaptive Lens (MAL) that can be inserted right after the objective and works in conjunction with an image optimization software allowing for a wavefront sensorless correction. We presented the results obtained on several commercial microscopes among which a confocal microscope, a fluorescence microscope, a light sheet microscope and a multiphoton microscope.Team Raf Van de Pla
Adaptive optics applied to coherent anti-Stokes Raman scattering microscopy
No full textWe report on the use of adaptive optics in coherent anti-Stokes Raman scattering microscopy (CARS) to improve the image brightness and quality at increased optical penetration depths in biological material. The principle of the technique is to shape the incoming wavefront in such a way that it counteracts the aberrations introduced by imperfect optics and the varying refractive index of the sample. In recent years adaptive optics have been implemented in multiphoton and confocal microscopy. CARS microscopy is proving to be a powerful tool for non-invasive and label-free biomedical imaging with vibrational contrast. As the contrast mechanism is based on a 3rd order non-linear optical process, it is highly susceptible to aberrations, thus CARS signals are commonly lost beyond the depth of∼100 μm in tissue. We demonstrate the combination of adaptive optics and CARS microscopy for deep-tissue imaging using a deformable membrane mirror. A random search optimization algorithm using the CARS intensity as the figure of merit determined the correct mirror-shape in order to correct for the aberrations. We highlight two different methods of implementation, using a look up table technique and by performing the optimizing in situ. We demonstrate a significant increase in brightness and image quality in an agarose/polystyrene-bead sample and white chicken muscle, pushing the penetration depth beyond 200 μm
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Time-resolved fluorescence microscopy to study biologically related applications using sol-gel derived and cellular media
Get PDFFluorescence microscopy provides a non-invasive means for visualising dynamic protein interactions. As well as allowing the calculation of kinetic processes via the use of time-resolved fluorescence, localisation of the protein within cells or model systems can be monitored. These fluorescence lifetime images (FLIM) have become the preferred technique for elucidating protein dynamics due to the fact that the fluorescence lifetime is an absolute measure, in the main independent of fluorophore concentration and intensity fluctuations caused by factors such as photobleaching. In this work we demonstrate the use of a time-resolved fluorescence microscopy, employing a high repetition rate laser excitation source applied to study the influence of a metal surface on fluorescence tagged protein and to elucidate viscosity using the fluorescence lifetime probe DASPMI
Variations on the Author
Get PDF“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
Get PDFWe 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
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