1,721,036 research outputs found
Study of edge turbulence in magnetically confined fusion plasmas
No full textUnderstanding turbulent transport in magnetised plasmas is a subject of great importance for comprehending and optimising experiments and for designing a future fusion rector. In fact turbulence has since long been found to be the dominant reason for the observed limited confinement especially in the edge of fusion devices.
The edge of all fusion experiments, reversed field pinches, tokamaks and stellerators, is characterised by the flow of plasma toward material surfaces and by the outflow of heat and particles from the plasma core through transport. In particular this transport cannot be explained in the framework of classical theory, and understanding its underlying physics remains the outstanding critical issue of thermonuclear fusion physics. Nowadays it is commonly recognised that the main cause of this anomalous transport in the plasma edge is due to turbulence, both electrostatic and magnetic, and many progresses in its understanding have been done experimentally using electrostatic Langmuir probes and optical diagnostics like the gas puff imaging, and theoretically by the development of simulation codes.
Experimental measurements have pointed out that most of the outward transport in the edge is due to coherent structures such as blobs ejected from the edge.
In this thesis the characterisation of the edge turbulence in fusion experiments is carried out mainly by means of the optical diagnostic called gas puff imaging (GPI). Also Langmuir probes and fast magnetic pick-up coils are used. I studied the spectral and statistical properties of the turbulent signals, showing their universal behaviour independently from the magnetic configuration, indicating that the responsible mechanism should be common. The edge fluctuations are not self similar, i.e. their statistical properties depend on the time scale of the fluctuations themselves.
By comparing the data from the gas puff imaging optical diagnostic and the ones from Langmuir probes, the structure of density-potential blobs is characterised. Then, using the new gas puff imaging diagnostic, through the tomographic algorithm I have developed, I have directly shown the presence in the edge of RFX-mod device of coherent structures propagating along the toroidal direction and responsible for the greatest part of the anomalous transport. The link between these blobs and high frequency magnetic fluctuations can be explained if the edge structures are related to current filaments extending along the magnetic field lines.
Beyond the interaction with the magnetic field, also the link between the edge turbulence and the kinetic pressure is studied, as its gradient is normally considered one of the sources of free energy for the development of the turbulence. I made this studies in particular on the NSTX tokamak, and the results are compatible with the picture of blobs born near the separatrix (in the region of maximum radial gradient of electron pressure) and moving outward while becoming larger and larger.
In NSTX tokamak, also the relation between the edge turbulence and the transition from L-mode to the better confinement mode (H-mode) has been studied. This transition is always observed to be accompained by the development of a transport barrier in the edge, which is commonly correlated with edge turbulence suppression. With the gas puff imaging diagnostic I observed a drastic reduction in the linear density of edge structures during the transition to the H-mode. Differences between the two plasma regimes are also observed in the perpendicular k-spectrum, which can be interpreted in the L-mode with the presence of an inverse energy cascade toward the small k that is not observed in the H-mode. All these studies highlight the importance of the reduction of the edge turbulence in the development of the edge transport barrier and in the consequent formation of the H-mode
Surface-acoustic-wave based biosensors and microfluidic devices for Life-science applications
No full textIn 2015 over half of the total deaths worldwide were due to the top ten causes
of mortality, as stated by the World Health Organization. Heart disease, cancer,
and diabetes are particularly prominent, especially in developing countries.
In the last decades a significant amount of effort has been made by the scientific community in order to address these pathologies, from both the screening and the treatment points of view. To date, early-detection seems to be one of the most effective strategies in reducing the mortality. By diagnosing one of these pathologies at very early stages, the survival rate can be significantly enhanced. For example, the 5-year survival rate of women with breast cancer is ⇡72% for stage III (before metastasis), ⇡93% for stage II and close to 100% for stage I and 0 (American Cancer Society data).
Automated, cheap, and portable devices that can help in diagnosing these illnesses would be a breakthrough for life-science applications, particularly for point-of-care (PoC) purposes. These devices are the so-called lab-on-chips (LoCs). LoCs are chips with a small surface (mm2–cm2) that embed many operations that are usually performed by trained personnel in a centralized laboratory facility. These operations include centrifugation, reagent mixing, heating, particle separation, cell counting, analyte detection, amongst many others. By making use of innovative plastic materials, piezoelectric substrates and cleanroom facilities for fabrication, it is possible to realize these novel devices that can potentially fulfill all the requirements for early-detection and PoC.
In this PhD thesis, I present my research on this topic. During my studies,
I exploited two promising technologies for LoCs, namely surface acoustic
wave (SAW) and surface plasmon resonance (SPR), through which I explored
novel configurations for microfluidics and biosensing on nanostructured devices.
I started studying the effects of SAWs on liquid droplets, with particular
attention to the heating and mixing and how these phenomena could be
exploited for treating biological samples. I investigated how SAWs affect cell cultures and how they can improve cell-proliferation by generating fluid motion
inside standard Petri dishes. Then, I demonstrated a microfluidic SPR
biosensor enhanced by the presence of SAW-induced fluid mixing. By means
of the SAW-generated fluid recirculation, this device can detect analytes in
a significantly reduced time. Next, I demonstrated two different SAW-based
biosensors, a cantilever with a SAW-based readout and a SAW-resonator. The
performance of both of them were suitable for biomedical assays. In particular,
the SAW-resonator is promising in the light of cancer biomarker detection,
as it is almost ten times more sensitive than similar commercially available
sensing units. Finally, I moved towards the development of a full-SAW microfluidic
platform for biosensing, combining SAW-microfluidics and SAWbiosensing.
I further improved the SAW-resonator chip design by integrating
multiplexing and microfluidic channels for liquid sample handling. I also
developed custom-made software for fast and reliable data acquisition and
post-processing. The experiments presented here are performed with artificial
fluids: biotin-avidin was chosen for the biorecognition model, as it is
well known to mimic the biomolecular processes of biomarkers detection. In
final chapters I show and discuss experiments in the presence of biological
noise (i.e., non-specific binding molecules) and evaluate the biosensor performance
with samples more similar to body fluids. The studies I carried out
are promising in the light of development of versatile, portable, and sensitive
SAW-based LoC for early-detection of pathologies, and show enhanced
performance in both detection of biomolecules and reduced detection times
with respect to traditional methods
Full-SAW Microfluidics-Based Lab-on-a- Chip for Biosensing
Get PDFMany approaches to diagnostic testing remain decades old. Well-established biosensing
technologies (e.g., enzyme-linked immunosorbent assays and radio-immunoassays) typically cannot fulfill
the requirements of portability and ease of use necessary for point-of-care purposes. Several alternatives
have been proposed (e.g., quartz-crystal-microbalances, electrochemical sensors, cantilevers, and surfaceplasmon-
resonance sensors) but often lack high performance or still necessitate bulk ancillary instruments to
operate. Here we present a highly sensitive, versatile, and easily integrable micro uidic lab-on-a-chip (LoC)
for biosensing, fully based on surface acoustic waves (SAWs). By using ultra-high-frequency resonatorbiosensors,
we showthat it is possible to perform highly sensitive assays in complex media. This all-electrical
readout platform is benchmarked with the biotin-streptavidin binding in presence of non-specific binding
proteins (serum albumin) at physiological concentration. The benchmark experiments were performed
with the idea of mimicking a biological fluid, in which other molecular species at high concentration are
present together with the analytes. We demonstrate that this LoC can detect sub-nanomolar concentrations
of analytes in complex media. As a comparison with similar acoustic-wave-based systems, this full-SAW
platform outperforms the standard commercial gravimetric sensors (i.e., quartz-crystal-microbalances) and
the more common Love-SAW biosensors. This full-SAW LoC could be further developed for the detection
of biomarkers in biological fluids
Filippo Nuvoloni (1441-1478)
No full textFilippo Nuvoloni scrisse un canzoniere di 122 componimenti, intitolato "Sonetti e canzone morale e de amore ... a nome de lo illustre ... misere Alberto da Este". Il titolo già lascia intendere che nella raccolta, come in diverse di questi anni, oggetto del corteggiamento sarà non solo l'amata, ma anche un illustre destinatario. Questo dualismo motiva l’esistenza di due pezzi incipitari, e di altre specificità qui illustrate.Filippo Nuvoloni wrote a songwriter of 122 compositions, titled "Sons and moral song and love ... on behalf of the illustrious ... messer Alberto da Este". The title already suggests that in the collection, as in several of these years, the subject of courtship is not only the beloved, but also a distinguished recipient. This dualism motivates the existence of two initiating pieces, and other specificities illustrated here
Polydimethylsiloxane (PDMS) irreversible bonding to untreated plastics and metals for microfluidics applications
Get PDFIn order to properly manipulate liquids into microfluidic networks, an accurate sealing of the device is of paramount importance. Polydimethylsiloxane
(PDMS) is ubiquitously used for fabricating microfluidic components, owing to its low cost, easy and fast fabrication, and
optical transparency. However, PDMS is characterized by low surface energy, making its bonding to many substrates not trivial. Here is
presented a versatile technique for PDMS microchannel bonding on untreated plastic and metal surfaces. First, the PDMS surface is functionalized
with (3-aminopropyl) triethoxysilane (APTES) for further cross-linking with epoxy groups. Then, the PDMS-APTES surface is coated
with Norland Optical Adhesive 74 (NOA74). Finally, the PDMS-APTES-NOA74 is put in contact with the target material and the glue is
cured under a UV light. In order to characterize the bonding strength, a complete PDMS-on-gold microfluidic device is fabricated and tested
with increasing injection pressures. Different liquids and a gas (nitrogen) are applied without leakage up to 2 bars, a value comparable to the
one reported for the standard glass-PDMS bonding through plasma oxygen activation. The same technique is then successfully replicated
with other nonmetallic substrates of interest for microfluidics, i.e., glass, poly(methyl methacrylate), polystyrene, polyethylene terephthalate,
cyclic olefin copolymer, demonstrating its great versatility and potential for, but not limited to, microfluidic applications and LOC
engineering
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
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
Probing the mechanism of neutrinoless double-beta decay in multiple isotopes
No full textA large experimental program is being mounted to search for neutrinoless double-beta decay over the next decade. Multiple experiments using different target isotopes are being prepared to explore the whole parameter space allowed for inverted-ordered light neutrinos, and have the potential to make discoveries in several other scenarios, including normal-ordered light neutrinos and other exotic mechanisms. We investigate to what extent long-range and exotic short-range contributions may be distinguished by combining measurements of the decay half-life across isotopes in the framework of a global Bayesian analysis. We demonstrate how measurements in two isotopes will constrain the parameter space up to a two-fold degeneracy, and how a further measurement in a third isotope removes such a degeneracy. We also discuss the impact of uncertainties and correlations in nuclear matrix element calculations. Our work motivates an experimental program measuring neutrinoless double-beta decay in more than one isotope, as this would break parameter degeneracies and advance our understanding of particle physics beyond the Standard Model
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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