Flowing fibers as a proxy of turbulence statistics

The flapping states of a flexible fiber fully coupled to a three-dimensional turbulent flow are investigated via state-of-the-art numerical methods. Two distinct flapping regimes are predicted by the phenomenological theory recently proposed by Rosti et al. [Phys. Rev. Lett. 121, 044501, 2018]: the under-damped regime, where the elasticity strongly affects the fiber dynamics, and the over-damped regime, where the elastic effects are strongly inhibited. In both cases we can identify a critical value of the bending rigidity of the fiber by a resonance condition, which further provides a distinction between different flapping behaviors, especially in the under-damped case. We validate the theory by means of direct numerical simulations and find that, both for the over-damped regime and for the under-damped one, fibers are effectively slaved to the turbulent fluctuations and can therefore be used as a proxy to measure various two-point statistics of turbulence. Finally, we show that this holds true also in the case of a passive fiber, without any feedback force on the fluid

Misura indiretta della deformazione delle rotaie del bacino n.1 dell\u27INSEAN: correzione in tempo reale della misura delle immersioni per le prove in assetto libero

In the present report we analyzed the deformation of the rails of the towing tank n.1 at INSEAN and its influence on the measurement of sinkage and trim for classical resistance tests. The rails of the towing Tank n.1, through the years, have undergone a deformation mainly in the terminal segment (last 100 meters). This deformation (of order of few millimeters) makes very problematic the measurement with the model in fixed conditions, but also affects the measurement of trim and, mainly, sinkage in free conditions. In particular, it influences the measurement of the submersion at bow and stern due to the changing distance between carriage and water surface during the run. The introduced error is a function of the carriage position along the basin. It is important to remark that the maximum deformation is about 3 mm and mostly regards the end of the rails, while for the initial segment of the rails (up to 200 meters) the deformation is lower than 1 mm. The compromise is to limit the tests with the model in fixed condition at 200 meters, while for the free conditions test a correction for the submersion measurements has to be applied in order to improve the quality of data and extend the run to the rails end. A function fr(x), where x is the carriage position along the rails has been obtained by fitting the acquired data by a ultrasonic probe during a carriage run.Il presente rapporto riguarda la misura delle deformazioni delle rotaie del bacino n.1 dell\u27INSEAN e la loro influenza sulla misura degli assetti nelle prove di rimorchio in assetto libero. Le rotaie del bacino n.1 dell\u27INSEAN, nel corso degli anni, hanno subito una deformazione principalmente nel tratto finale della corsa. Tale deformazione - dell\u27ordine di pochi millimetri - rende problematiche le misure di campo in assetto bloccato, ma incide anche sulla correttezza delle misure delle immersioni per le prove in assetto libero. In particolare introduce nella misura un errore dipendente dalla posizione del carro lungo la corsa dovuto alla differente distanza delle rotaie e quindi del carro dalla superficie libera. ? da rimarcare il fatto che la massima deformazione (circa 3 mm) si ha nella parte finale della corsa, mentre nella parte centrale la deformazione ? dell\u27ordine del millimetro. Come detto, nelle prove ad assetto bloccato sarebbe problematico operare una correzione e si preferisce allo stato attuale limitare la corsa alla parte centrale del bacino, dove le deformazioni sono meno influenti sulla misura finale. D\u27altra parte la limitazione della corsa per le prove in assetto libero che sono le pi? frequenti comporterebbe un aumento delle corse importante. Per questo tipo di prove, considerando che la resistenza non ? affetta da questo errore, si ? deciso di operare una correzione della misura degli assetti in tempo reale. A partire dalla misura della distanza della superficie libera dal carro durante la corsa, ? stata sviluppata una funzione continua fr(x) in grado di descrivere, per ogni posizione x del carro, l\u27entit? della deformazione, al fine di apportare le opportune correzioni alle misure delle immersioni in tempo reale in fase di acquisizione

Time-resolved nonlinear ghost imaging

Terahertz (THz) spectroscopy systems are widely employed to retrieve the chemical and material composition of a sample. This is single-handed the most important driving motivation in the field and has largely contributed to shaping THz science as an independent subject. The limited availability of high-resolution imaging devices, however, still represents a major technological challenge in this promising field of research. In this theoretical work, we tackle this challenge by developing a novel nonlinear Ghost Imaging (GI) approach that conceptually outperforms established single-pixel imaging protocols at inaccessible wavelengths. Our methodology combines nonlinear THz generation with time-resolved field measurements, as enabled by state-of-the-art Time Domain Spectroscopy (TDS) techniques. As an ideal application target, we consider hyperspectral THz imaging of semi-transparent samples with nonnegligible delay contribution and we demonstrate how time-resolved, full-wave acquisition enables accurate spatiotemporal reconstruction of complex inhomogeneous samples

Analysis of the human Y-chromosome haplogroup Q characterizes ancient population movements in Eurasia and the Americas

Background: Recent genome studies of modern and ancient samples have proposed that Native Americans derive from a subset of the Eurasian gene pool carried to America by an ancestral Beringian population, from which two well-differentiated components originated and subsequently mixed in different proportion during their spread in the Americas. To assess the timing, places of origin and extent of admixture between these components, we performed an analysis of the Y-chromosome haplogroup Q, which is the only Pan-American haplogroup and accounts for virtually all Native American Y chromosomes in Mesoamerica and South America. Results: Our analyses of 1.5 Mb of 152 Y chromosomes, 34 re-sequenced in this work, support a "coastal and inland routes scenario" for the first entrance of modern humans in North America. We show a major phase of male population growth in the Americas after 15 thousand years ago (kya), followed by a period of constant population size from 8 to 3 kya, after which a secondary sign of growth was registered. The estimated dates of the first expansion in Mesoamerica and the Isthmo-Colombian Area, mainly revealed by haplogroup Q-Z780, suggest an entrance in South America prior to 15 kya. During the global constant population size phase, local South American hints of growth were registered by different Q-M848 sub-clades. These expansion events, which started during the Holocene with the improvement of climatic conditions, can be ascribed to multiple cultural changes rather than a steady population growth and a single cohesive culture diffusion as it occurred in Europe. Conclusions: We established and dated a detailed haplogroup Q phylogeny that provides new insights into the geographic distribution of its Eurasian and American branches in modern and ancient samples

The Casimir-Polder effect for an approximate Pauli-Fierz model: the atom plus wall case

We study a system composed of a hydrogen atom interacting with an infinite conductor wall. The interaction energy decays like $L^{-3}$, where $L$ is the distance between the atom and the wall, due to the emergence of the van der Waals forces. In this paper we show how, considering the contributions from the quantum fluctuations of the electromagnetic field, the interaction is weakened to a decay of order $L^{-4}$ giving rise to the retardation effects which fall under the name of Casimir-Polder effect. The analysis is done by studying a suitable Pauli-Fierz model associated to the system, in dipole approximation and reduced to the interaction with 0 and 1 photon

Synthesis and characterization of zinc manganite thin films for zinc-ion battery applications

LAUREA MAGISTRALELe batterie sono, e saranno sempre di più, una tecnologia essenziale. La società vuole avanzare verso un futuro sempre più sostenibile, e ciò da un lato traina il mercato delle batterie, dall’altro richiede anche a queste ultime una maggiore sostenibilità, sicurezza e uno smaltimento a basso impianto ambientale. Le attuali batterie agli ioni di litio faticano a tenere il passo con queste richieste. Uno dei fronti in sviluppo sono le batterie agli ioni di zinco, che possono implementare elettroliti non organici, non infiammabili, più facilmente gestibili durante lo smaltimento. Inoltre, le batterie allo zinco possono anche evitare l’impiego di cobalto, che è raro, costoso e tossico per l’uomo e l’ambiente. Una delle sfide nel portare tali batterie a performance adeguate è la progettazione del catodo. Uno dei possibili materiali per questa componente delle batterie agli ioni di zinco è lo ZnMn2]O4 (ZMO). Lo ZMO è composto da elementi comuni e abbondanti nella crosta terrestre: lo zinco e il manganese. Sebbene il materiale compatto allo stato puro non sembri mostrare prestazioni elettrochimiche sufficienti, se propriamente preparato, andando ad agire sulla sua composizione e sulla morfologia a livello nanostrutturale, lo ZMO diventa un buon candidato come catodo per le batterie agli ioni di zinco. Nonostante siano presenti in letteratura diversi studi sul materiale, ancora non si sono compresi appieno i suoi meccanismi elettrochimici principali. Nel mio lavoro sono stati prodotti film sottili di ZMO tramite l’uso della Pulsed Laser Deposition (PLD). Sono state ottimizzate le condizioni di deposizione in vuoto e atmosfere di ossigeno a diverse pressioni (1-150 Pa). I campioni sono stati caratterizzati dopo la deposizione mediante lo Scanning Electron Microscope (SEM) per valutarne la morfologia, e con la Energy Dispersive X-ray Spectroscopy (EDXS) per le prime analisi stechiometriche. A pressioni di ossigeno elevate (100 e 150 Pa) si ottengono film porosi con nanostrutture a foresta. Si è determinato inoltre, usando la spettroscopia Raman, che i film depositati sono amorfi. Per ottenere la cristallizzazione del materiale sono stati eseguiti trattamenti termici (annealing) sui campioni. Sono stati identificati i limiti inferiori di temperatura (500°C) per la cristallizzazione del materiale in aria e in vuoto. La spettroscopia Raman è stata utilizzata per valutare la cristallizzazione del film di ZMO, comparando gli spettri acquisiti con quelli riportati in letteratura. Si è inoltre studiato come diverse temperature di annealing in aria modifichino la morfologia e lo spettro Raman del campione, concludendo che una temperatura di annealing maggiore aumenta le dimensioni della grana cristallina. Nel mio lavoro presento una trattazione estensiva di come la pressione di deposizione di ossigeno influenzi i campioni trattati termicamente. Si è verificato tramite spettroscopia Raman che i campioni, dopo la ricottura, depositati in vuoto o a 1 Pa di ossigeno hanno degli spettri Raman con differenze marcate rispetto a quelli dei film depositati a più alte pressioni di ossigeno. La morfologia dei film è stata analizzata e comparata prima e dopo l’annealing, mostrando come la porosità tenda ad aumentare e si formino nanocristalli di ZMO dopo il trattamento termico. I campioni depositati ad alte pressioni di ossigeno (100-150 Pa) mantengono la nanostruttuta a foresta cristallina, che è una condizione favorevole per l’elettrochimica dello ZMO. Infine, alcune misure ottiche sono state effettuate su film cristallizzati di ZMO depositati a diverse pressioni di ossigeno su substrati di vetro. L’ultima parte della sperimentazione sono stati i primi test elettrochimici sui film cristallizzati depositati a diverse pressioni di ossigeno (1 Pa, 50 Pa e 100 Pa) su substrato di vetro coperto da FTO. I test elettrochimici si sono dimostrati promettenti, in quanto, non solo hanno mostrato l’attività elettrochimica aspettata, ma i film si sono mantenuti intatti durante i trattamenti. In particolare, le ciclovoltammetrie (CV) sono state eseguite sui campioni con range da -0.75 V a +0.75 V vs. Pt-QRefe e velocità di scansione pari a 20 mV/s per 8 cicli. Le CV sono state condotte in una cella con elettrolita acquoso con disciolti ZnSO4 2 M + MnSO4 0.1 M (elettrolita ZMS). Le CV sono risultate diverse per ogni campione. Al fine di individuare i possibili meccanismi elettrochimici dei film, sono state eseguite alcune misure potenziostatiche (PS), con elettrolita ZMS, sul campione depositato a 100 Pa di ossigeno. Dopo ogni misura PS ho misurato lo spettro Raman del campione elettrochimicamente trattato. Il risultato principale è stata la riduzione evidente dei picchi Raman associati allo ZMO. La ragione di tale riduzione e riattivazione dei picchi attribuiti allo ZMO è stata associata a tre meccanismi simultanei: 1) la intercalazione/deintercalazione dello zinco dallo ZMO, 2) la dissoluzione ed elettrodeposizione di MnO2, 3) la intercalazione di zinco nel MnO2 elettrodeposiato. Concludendo, la PLD si è rivelata un metodo adeguato alla produzione di film di ZMO sia per la caratterizzazione del materiale in sé, sia ai fini di sviluppi e ricerca elettrochimica. La ricerca su questi film richiede ulteriori indagini su entrambi i fronti menzionati. Futuri sviluppi di questa ricerca possono vertere sulla caratterizzazione del materiale e la produzione di film usando diversi parametri di deposizione, oppure sulla parte elettrochimica dove solo i test preliminari sono stati effettuati.Batteries are, and will increasingly be, an essential technology. Society wants to progress toward an increasingly sustainable future, and this drives the battery market; on the other hand, it also requires batteries to be more sustainable, safe, and disposed of in an environmentally friendly manner. Current lithium-ion batteries are struggling to keep up with these demands. One of the developing fronts is the zinc-ion battery, which can implement non-organic, and non-flammable aqueous electrolytes that are more easily managed during disposal. In addition, zinc-ion batteries can also avoid employing cobalt, which is rare, expensive, and toxic to humans and to the environment, and can directly rely on Zn metal as the anode. One of the challenges in bringing such batteries to adequate performance is the cathode design. Common cathode materials are Mn and V oxides, metal vanadates, and Prussian blue analogues; another possible cathode candidate is spinel ZnMn2O4 (ZMO). ZMO is composed of common and abundant elements in the Earth’s crust: zinc and manganese. While the bulk material does not seem to show sufficient electrochemical performance, if properly prepared (by acting on its composition and morphology at the nanoscale), ZMO becomes a good cathode candidate for zinc-ion batteries. Although there are several studies on the material in the literature, its main electrochemical mechanisms are still not fully understood. In my work, thin films of ZMO were produced by Pulsed Laser Deposition (PLD). Deposition conditions were optimized in vacuum and oxygen atmospheres at different pressures (1-150 Pa). Samples were characterized after deposition by Scanning Electron Microscopy (SEM) to evaluate their morphology, and by Energy Dispersive X-Ray Spectroscopy (EDXS) for initial stoichiometric analyses. At high oxygen pressures (100 and 150 Pa), low-density porous films formed by forest-like nanostructures were obtained. It was also determined using Raman spectroscopy that the as-deposited films are amorphous. To achieve crystallization of the material, annealing was performed on the samples. The lower temperature limits (500°C) for crystallization of the material in air and vacuum were identified. Raman spectroscopy was employed to evaluate the crystallization of the ZMO films to the expected spinel phase by comparing the acquired spectra with those reported in the literature. I also studied how different annealing temperatures in air affect the morphology and the Raman spectrum of the sample, concluding that a higher annealing temperature increases the crystal grain size and improves the crystalline quality. In my work, I present an extensive discussion about how oxygen deposition pressure affects the annealed samples. I verified by Raman spectroscopy that crystallized samples deposited in vacuum or at 1 Pa of oxygen have Raman spectra with distinct differences from those of films deposited at higher oxygen pressures. The morphology of the films was analysed and compared before and after annealing, showing how porosity tends to increase and ZMO nanocrystals form after heat treatment. Samples deposited at high oxygen pressures (100-150 Pa) maintain the nanostructured crystalline forest, which is a favorable condition for the electrochemistry of ZMO. Finally, some optical measurements were conducted on ZMO films deposited at different oxygen pressures on glass substrates. The last part of the experimentation focused on preliminary electrochemical tests on the crystallized ZMO films deposited at different oxygen pressures (1 Pa, 50 Pa, and 100 Pa) on FTO-coated glass substrates. The electrochemical tests have proved promising as not only did they show the expected electrochemical activity but the films remained intact during the treatments. Specifically, cyclic voltammetry (CV) was performed on the samples in the range of -0.75 V to +0.75 V vs. Pt-QRef. in an aqueous electrolyte consisting of ZnSO44 2 M + MnSO4 0.1 M (ZMS electrolyte). CVs were different for each sample, thus demonstrating the effect of film morphology and surface area on electrochemical performances. In order to identify the possible electrochemical mechanisms, some potentiostatic (PS) measurements were performed, in ZMS electrolyte, on the sample deposited at 100 Pa of oxygen, followed by Raman and SEM investigation. The main result was the pronounced reduction of the Raman peaks associated with ZMO. I ascribed the reason for this reduction and reactivation of the ZMO-attributed peaks to three simultaneous mechanisms: 1) the intercalation/deintercalation of zinc/protons from ZMO; 2) the dissolution and electrodeposition of MnO2; 3) the intercalation of zinc in the electrodeposited MnO2. Concluding, PLD has proven to be a suitable method for the production of ZMO films both for the characterization of the material itself and for electrochemical developments and research. Research on these films requires further investigation on both fronts mentioned. Future developments of this research may focus on the characterization of the material with complementary techniques (XRD, XPS, XAS) and the production of films using different deposition parameters, or on the electrochemical side where only preliminary tests have been completed

The Casimir–Polder effect for an approximate Pauli–Fierz model: the atom plus wall case

We study a system composed of a hydrogen atom interacting with an infinite conductor wall. The interaction energy decays like $L^{- 3}$ , where is the distance between the atom and the wall, due to the emergence of the van der Waals forces. In this paper we show how, considering the contributions from the quantum fluctuations of the electromagnetic field, the interaction is weakened to a decay of order L ́4 giving rise to the retardation effects which fall under the name of Casimir-Polder effect. The analysis is done by studying a suitable Pauli-Fierz model associated to the system, in dipole approximation and reduced to the interaction with 0 and 1 photo

Darwin’s wind hypothesis: does it work for plant dispersal in fragmented habitats?

Using the wind-dispersed plant Mycelis muralis, we examined how landscape fragmentation affects variation in seed traits contributing to dispersal. Inverse terminal velocity (Vt−1) of field-collected achenes was used as a proxy for individual seed dispersal ability. We related this measure to different metrics of landscape connectivity, at two spatial scales: in a detailed analysis of eight landscapes in Spain and along a latitudinal gradient using 29 landscapes across three European regions. In the highly patchy Spanish landscapes, seed Vt−1 increased significantly with increasing connectivity. A common garden experiment suggested that differences in Vt−1 may be in part genetically based. The Vt−1 was also found to increase with landscape occupancy, a coarser measure of connectivity, on a much broader (European) scale. Finally, Vt−1 was found to increase along a south–north latitudinal gradient. Our results for M. muralis are consistent with ‘Darwin’s wind dispersal hypothesis’ that high cost of dispersal may select for lower dispersal ability in fragmented landscapes, as well as with the ‘leading edge hypothesis’ that most recently colonized populations harbour more dispersive phenotypes.

Ground State Properties in the Quasi-Classical Regime

We study the ground state energy and ground states of systems coupling non-relativistic quantum particles and force-carrying Bose fields, such as radiation, in the quasi-classical approximation. The latter is very useful whenever the force-carrying field has a very large number of excitations,and thus behaves in a semiclassical way, while the non-relativistic particles, on the other hand, retain their microscopic features. We prove that the ground state energy of the fully microscopic model converges to the one of a nonlinear quasi-classical functional depending on both the particles' wave function and the classical configuration of the field. Equivalently, this energy can be interpreted as the lowest energy of a Pekar-like functional with an effective nonlinear interaction for the particles only. If the particles are confined, the ground state of the microscopic system converges as well, to a probability measure concentrated on the set of minimizers of the quasi-classical energy.Comment: 52 pages, pdfLaTe