1,721,090 research outputs found
Detecting asbestos fibres and cleavage fragments produced after mechanical tests on ophiolite rocks: clues for the asbestos hazard evaluation
No full textThe generation of particulate matter emitted by management (e.g., mining, crushing, grinding, and
milling) of ophiolite rock masses induces environmental impact due to production and dispersion of fibrous particles,
which can be potentially classifiable as asbestos. Accordingly, characteristics of particles generated after mechanical stress
on rocks are preparatory features to evaluate the environmental impact due to the asbestos hazard. This study deals
with the characteristics (in terms of size, morphology and mineral classification) of particles generated after application
of three different mechanical stress procedures (i.e. crushing, micronizing, and abrasion) on five ophiolite lithotypes
and a man-made material obtained from rock mixing. A petrographic investigation has been addressed to classify the
rock samples in terms of their internal fabric (foliated vs massive) and to individuate textural locus of fibrous minerals
within the rock mass. The application of mechanical tests reveal that all the investigated lithotypes resulted able to spread
out fibres as a consequence of rock disaggregation, with a prevalent amount of liberated fibres coming from samples
characterised by pervasive foliation. The combined use of transmission electron microscopy and particle size analyser
has been addressed to analyse morphological properties of the particulate matter. Different counting criteria have been
used to distinguish asbestos fibres and non-asbestos particles (cleavage fragments). The results show that the counting
criteria adopted for the fibre classification led to divergent interpretations in differentiating asbestos fibres and cleavage
fragments and to determine the amount of asbestos. It derives the importance to define univocal criteria to define particle
as asbestiform for supporting procedures and normatives addressed to evaluate the asbestos hazard in environmental
sites
Multilayer optical routing by means of vertical directional coupler with long range surface plasmons
No full textWe show that efficient multilayer optical routing is achievable with long range surface plasmon polaritons (LR-SPP) through an accurate design of vertical directional couplers (VDC). Our theoretical results suggest that by suitably tuning some geometrical parameters, in particular the path length and bend radius, it is possible to obtain a good control on the overall interaction, even in presence of fabrication non-idealities. We present a top-down fabrication process flow for LR-SPP multilayer optical circuits, obtained by stacking multiple ultrathin nanometric metal films within a polymeric dielectric background; the overall structure has a good degree of mechanical stability. By profiting from the topological advantage given by VDCs, as one of the useful applications of our work, we propose a new optical integrated circuit architecture scheme, capable of connecting two separate circuit paths without influencing the geometry or significantly promoting crosstalk with any other path in the middle. The possibility to develop vertically stacked optical integrated circuits upon electronic integrated circuits makes LR-SPPs a good technology for the production of inexpensive and high-density network systems
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
Scanning Probe Microscopies for the Study at Nanoscale of Nanomaterials and Nanosystems:
No full textMagnetic nanomaterials due to their various features different from the ordinary bulk matter in their mechanical, thermal, magnetic, optical properties, are attracting more and more attention in both theoretical research and practical applications in various fields.
Magnetic nanoparticles (MNPs) are a very important branch of magnetic nanomaterials due to their nanoscale sizes, being relatively long in vivo half-life and limited agglomeration. These make them ideal for biomedical applications such as magnetic labeling, hyperthermia cancer treatment, targeted drug delivery, and contrast enhancement agents in magnetic resonance imaging (MRI). In drug delivery applications, MNPs can be determined with high accuracy [1]. It would be of interest to localize and characterize MNPs at the nanoscale for biological applications. However, very limited studies exist on detecting and characterizing the magnetic signals of nanoparticles in biological science.
Many methods in surface structure analysis are used as nano-characterization techniques, such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), field electron microscopy (FEM), field ion microscope (FIM), low energy electron diffraction (LEED), Auger electron spectroscopy (AES), photoelectron spectroscopy (ESCA) and electron probe. These techniques detect the surface or interface to show the physical and chemical properties at the nanoscale. But any kind of these techniques has the limitations of one kind or another. For example, LEED and X-ray diffraction method require that the sample has a periodic structure; the resolution of optical microscopy and SEM are insufficient to distinguish surface atoms; high-resolution TEM is mainly used for thin bulk samples and interfacial studies to detect the magnetic properties, but the sample preparation process to get cell sections for TEM analysis is time consuming, and only a small part of cell section can be analyzed; FEM and FIM can only detect the tip radius of less than 100 nm of the atomic structure in two-dimensional geometry. Most commonly, studies which analyze the magnetic nature of MNPs use a superconducting quantum interference device (SQUID) and vibrating sample magnetometer (VSM). But due to low sensitivity and ultimately poor accuracy neither is an appropriate technique to measure the magnetic moment of individual MNPs, whatever in air or in liquid environment.
Proper characterization and monitoring the properties of MNPs system are important for their potential applications. Currently, one of the most common methods for intracellular imaging of magnetic nanoparticles is fluorescence microscopy [2]. A disadvantage of this technique is that nanoparticles must first be labeled with fluorescent probes in order to be visualized. Due to the inherent limitations, the resolution of optical instruments is restricted by the wavelength of the light [3]. In 2010, Sun et al. conjugated fluorescent probes to the surface of magnetic nanoparticles to map cellular uptake pathways [4]. Relative to fluorescence microscopy, two-photon microscopy (TPM) offers improved resolution to study cellular interactions with magnetic nanoparticles, requiring the particles to be labeled with a two-photon fluorescent dye [5]. However it has been known that the imaging depth in TPM cannot be increased indefinitely, meanwhile optimization of the two-photon excitation efficiency is limited by the degree of damage the specimen can tolerate [6]. Due to the relatively poor resolution and reliability of these techniques, scanning probe microscopes (SPM) emerged out. SPM is a generation of scanning tunneling microscope based on a variety of new probe microscopes, such as atomic force microscopy (AFM), lateral force microscopy (LFM) and electrostatic force microscope (EFM). Among these techniques magnetic force microscope (MFM), a label-free in vitro detection method for magnetic materials, has the capability to detect nanoscale magnetic domains and simultaneously obtain atomic force microscopy topography images. Due to its ability to localize, characterize and distinguish magnetic materials from other materials at the nanoscale, as well as the advantage of three-dimensional information, MFM offers the great potential for the in vivo research.
The scope for MFM lies in detecting the presence of magnetic nanomaterials and spatially localizing magnetic domains. It is likely that magnetic nanomaterials (occur in clusters or aggregates) are embedded in a biological matrix to different depth, and surrounded by bio-molecules. The development and application of MFM for detecting MNPs hold great promise in biology. Spatially localizing magnetic plaques, at nanometer resolution in ambient atmospheric environment, will provide a better understanding of the deposition mechanism of magnetic material derivatives in the biological tissues.
The background on magnetic materials and nanoparticles is presented in chapter 1 and AFM/MFM experimental apparatus and technique is illustrated in chapter 2. In the last three chapters of the thesis the results of three different typologies of experiments are reported. The studies I have conducted are developed in the framework of the research activities of the laboratory of Scanning Probe Microscopy of EMiNaLab (coordinator prof. Marco Rossi), at the Department of Basic and Applied Sciences for Engineering of Sapienza University of Rome.
In particular, in Chapter 3, we investigate bacterial biofilms at the first time, which are colonies of microbes embedded in a self-produced exopolysaccharides extracellular matrix presenting a major concern in health care. We will demonstrate an approach based on magnetic force microscopy to perform accurate measurement of the thickness of soft thin films - although it may easily extended even to stiff films - deposited on periodically patterned magnetic substrates. By detecting the biofilm thickness MFM will provide a novel method to study the thin film.
In the second part of the thesis, MFM is applied to visualize and quantitatively measure magnetically labeled vesicular system. Vesicles containing magnetic nanoparticles as magnetic target carrier can be used for a wide range of biological application. The encapsulation of drugs in vesicles can minimize drug degradation and inactivation by increasing drug bioavailability and targeting to the pathological area. Many different non-contact techniques have been proposed. Nevertheless, MFM has never been used to study vesicular systems embedding MNPs, either qualitatively or quantitatively. MFM will be illustrated to evaluate the amount of MNPs incorporated in single vesicle, together with discussion on its merits and possible sources of uncertainty.
In the last part of the thesis, we developed the capability of AFM/MFM to detect magnetically labeled materials of biological interest, which are magnetoferritin, APTES functionalized Fe3O4 nanoparticles and cells labeled Fe@Au nanoparticle. AFM/MFM will allow us to detect magnetic nanoparticles within submembranes and without severe deformation of samples. In our study, We expect to demonstrate the potential of MFM for the study of magnetic properties of different nano-biosystems, illustrating our approaches which aim at deducing quantitative information from MFM characterizations. Such a research is useful for future applications of MFM, indicating the potential to image magnetic nanoparticles unlabelled and unmodified in living cellular systems.
The overall target of the thesis is to develop and standardize reliable innovative protocols, using scanning probe microscopy-based techniques that could be implemented in rapid and early theranostic methods.Marco Rossi, Daniele Passeri, Erusmus schorlarshi
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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