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The role of time versus climate in the formation of deep soils of the Apennine fringe of the Po valley, Italy
No full textTwo very deep, red soils on a loess-mantled fluvial terrace of the Trebbia River in northern Italy were sampled and analyzed to determine their history and pedologic significance. Magnetostratigraphy confirms that the upper part of the terrace gravel and all of the 4-m-thick loess cover is normally magnetized and therefore less than about 780,000 yr. Artifacts collected from the oldest loess suggest an age of about 400,000 yr for the inception of loess deposition in this area. The soil horizons in loess dominantly have argillic or albic character, with redoximorphic features that include mottles, glossic tongues, and zones of ferromanganese concretions. Soil colors become progressively redder with depth in the loess cover and are most red, a 2.5 YR color hue, in the top of the terrace gravel. The upper horizons in gravel have abundant ghosts of completely weathered marl and sandstone. Rubification and weathering of stones diminishes with depth to fresh, slightly carbonate enriched parent material at 12 m. The heavy mineral composition of the sand fraction suggests minor discontinuities in loess-derived horizons. Abundance of opaque heavy minerals and picotite, which are resistant to weathering, increases from the soil surface to the base of the loess, is highest in the upper part of the terrace gravel, and decreases from there to the C horizon in gravel. Depth functions of major elements to Si in the medium silt fraction (10-30 μm) indicate a downward increase in degree of decalcification and of dissolution of primary minerals. Micromorphology adds detail to the interpretation of these complex soils: yellow complex ferriargillans are present in almost all horizons; they are rare at the top of the sequence in loess and become progressively more abundant with depth, reaching a maximum in the upper 3 m of the gravel and then decreasing with further depth to 12 m. We interpret this peak in abundance of yellow cutans to result from long continued clay illuviation to this depth from a succession of eluvial zones in the aggrading loessial sequence above. Distinctive red, hematite-rich argillans are abundant only in the upper horizons in the gravel. The red argillans relate to initial development of the soil in gravel, because they are included as pedorelicts in the deepest loess layer, where they are embedded in the yellow argillans. Stratigraphic and pedologic evidence indicates that these soils began forming in terrace gravel for perhaps 300,000 yr during the early middle Pleistocene. From this relict core these soils continued developing, both downward by continuing deep decalcification and argilluviation and upward as a sequence of wet Alfisols developed in a succession of loess layers that began aggrading about 400,000 yr ago. A paleoclimatic record can be perceived weakly in these soils, mainly by thick horizons of Fe-Mn nodules that mark boundaries between episodes of loess deposition that took place during glacial cold phases. Paleofeatures from one unit to another are similar in kind and intensity, indicating a degree of continuity of a basic set of pedogenic processes, principally decalcification, argilluviation, and redoximorphism. These soils can be regarded as Vetusols because a single dominant set of pedogenic features are represented in all parts of these soils and deeper parts of these aggrading super profiles have never been isolated from continuing pedogenic change to the present
Deep soils on stable or slowly aggrading surfaces: time versus climate as soil-forming factors
No full textContinental rejuvenated mountains are represented by three types of mountain belts: the Mongolia-Siberian, Ural-Appalachian and margin-continental or East-Asian types. Orogenic belts of the Mongolia-Siberian type are when tectonic relief has clear paragenesis with deep structure. Mountain belts of the Ural-Appalachian type form in the zones of rapprochment of continental platform. Mountain belts of the East-Asian type are formed along the margins of intensive subsidences in the basins of the Pacific ocean marginal seas. The reasons and conditions for the formation of rejuvenated orogenic belts are diverse. Of great importance in their formation are the protrusions of asthenoliths (anomalous mantle) and inclined bedding of the asthenospheric roof, above which there is the development of zones of linear warping or narrow structural block uplift. -from Autho
Innovative optoelectronic and photonic devices and systems for Space applications
Get PDFLe missioni spaziali per osservazione della Terra o per scopi scientifici richiedono giroscopi per la misurazione della velocità angolare con performance elevate (risoluzione nell’intervallo 0.1 – 1 °/h e stabilità della polarizzazione nell’intervallo 0.001 – 0.1 °/h) per un accurato controllo dell’ assetto e dell’orbita del satellite.
Affidabilità, resistenza alle radiazioni, robustezza, tolleranza agli urti, volume ridotto e basso consumo energetico sono i requisiti tipici dei sensori di velocità angolare di nuova generazione per applicazioni spaziali.
In tale contesto, i risonatori ad anello fotonici stanno emergendo come elementi chiave di sistemi con elevate performance e dimensioni compatte. In particolare, per testarne l’affidabilità in ambiente spaziale, è stata dimostrata sperimentalmente un’ elevata resistenza alle radiazioni di un risonatore ad anello in InP investito da radiazioni γ.
Nella tesi sono state discusse le potenzialità di un risonatore ad anello con elevato fattore di qualità Q, che funge da elemento sensibile di un giroscopio ottico risonante (RMOG) miniaturizzato con performance elevate. L'elemento chiave del giroscopio proposto è un semplice risonatore ad anello basato su Si3N4 con un cristallo fotonico monodimensionale presente lungo l’intera circonferenza del risonatore ad anello, denominato 1D-PhCRR. Il funzionamento si basa sullo sfruttamento dell'effetto di luce lenta, tipico dei cristalli fotonici, che garantisce un miglioramento del fattore di qualità di oltre 3 ordini di grandezza rispetto ad un semplice risonatore ad anello con medesimo raggio. Un PhCRR con fattore di qualità > 109, è stato teoricamente dimostrato mediante l’utilizzo di un modello matematico basato sulla teoria dei modi accoppiati (CMT). Tali performance garantiscono una risoluzione teorica del giroscopio < 0.05 °/h con un volume ridotto (< 1 cm3), conforme ai requisiti degli operatori spaziali. Lo sviluppo del 1D-PhCRR è stato condotto nell'ambito del contratto NPI dell'Agenzia Spaziale Europea (ESA), che sponsorizza le attività di dottorato.
Oltre a risultare idoneo come elemento sensibile nei sottosistemi di controllo di assetto e orbita, il PhCRR potrebbe essere utilizzato per implementare diverse funzionalità nei payload di futura generazione per telecomunicazioni o per l’ osservazione della Terra.
Negli ultimi anni, un notevole interesse è stato rivolto verso payload per telecomunicazioni in grado di essere adattati ed ottimizzati dopo il lancio, secondo le diverse esigenze degli utenti in termini di larghezza di banda, area di interesse ed allocazione delle frequenze. La fotonica nel regime delle microonde risulta essere l’approccio più adatto per soddisfare i requisiti dei payload di futura generazione per telecomunicazioni. In tale contesto, è stato proposto un filtro notch basato su PhCRR in silicio con larghezza di banda B = 10.43 GHz ed extinction ratio ER > 40 dB, con risposta in frequenza con profilo gaussiano, ottenuta mediante inserimento ed ingegnerizzazione di difetti all’interno del cristallo fotonico. Implementando giunzioni p-i-n in corrispondenza dei difetti, è stato dimostrato un ampio intervallo di variazione della frequenza centrale di filtraggio (15 GHz), in un rapido tempo di commutazione (≈ 1 ns) ed un consumo di energia pari a 47 mW.
Inoltre, è stata proposta l’architettura innovativa di un’ oscillatore optoelettronico miniaturizzato in banda Ka, basata sul PhCRR progettato. È stato calcolato teoricamente un rumore di fase a 10 kHz di offset dalla portante (40 GHz) pari a circa -155 dBc/Hz con potenza elettrica in uscita> 10 dBm. Tali performance rappresentano un notevole miglioramento rispetto agli oscillatori optoelettronici riportati allo stato dell'arte.
L'elevata purezza del segnale oscillante è stata sfruttata per la progettazione di un generatore di segnale chirpato, utile per i sistemi SAR (radar ad apertura sintetica) ad alta risoluzione per l'osservazione della Terra, con un prodotto tempo-larghezza di banda di 3200 e un rumore di fase di circa -116 dBc/Hz. Per sistemi SAR, è stata progettata una linea di ritardo fotonica tunabile in banda X, basata su un cristallo fotonico realizzato mediante pattern di uno strato di grafene, in grado di garantire un elevato angolo di puntamento in fase di trasmissione del segnale e la più alta figura di merito riportata allo stato dell’ arte.Science and Earth observation missions require high-class gyroscopes, having a resolution in the range 0.1 – 1 °/hr and a bias stability in the range 0.001 – 0.1 °/hr, for an accurate control of the satellite attitude and orbit.
High reliability, high radiation resistance, high robustness, high shock tolerance, small volume, low power consumption and reduced mass are typical requirements of new generation angular rate sensors for Space applications.
In this context, the photonic ring resonators are emerging as key building blocks. The radiation hardness of a ring resonator useful for Space applications has been investigated, demonstrating a negligible worsening of the performance under γ radiations.
In this thesis, the potentiality of an ultra-high-Q ring resonator, acting as sensitive element of a resonant micro-optic gyroscope architecture (RMOG), has been discussed, aiming to design a chip-scale, high performing gyroscope.
The key element of the proposed RMOG configuration is a Si3N4-based simple ring resonator with a one-dimensional photonic crystal included along the whole optical path, called as 1D-PhCRR. Its operation is based on the exploitment of the slow light effect, typical of the PhC, providing an improvement of the Q-factor respect a simple ring resonator more than 3 order of magnitude. The Si3N4 PhCRR with Q > 109, has been theoretically demonstrated by using a self-made mathematical model, based on the Coupled Mode Theory (CMT). This performance ensures a gyro resolution < 0.05 °/hr with a small volume (< 1 cm3), compliant to the Space operators’ requirements. The development of the 1D-PhCRR has been carried out in the framework of the European Space Agency NPI contract, that sponsor the PhD activities.
Besides its suitability for attitude and orbit control sub-systems, the PhCRR could be used to implement several functionalities in the next photonic-based generation telecom payloads and for Earth observation purpose.
Telecom satellites are the most mature Space applications. In the last decades, Space operators require flexible telecom payload that can be adapted and optimized after the launch, according to the varying user demands in terms of bandwidth, coverage, and frequency allocation. The microwave photonic represents the most suitable approach to fulfil the next-generations telecom payloads requirements.
In this context, photonic-based microwave filters have been investigated, and the design of a silicon – based PhCRR with a bandwidth B = 10.43 GHz and ER > 40 dB, acts as notch filter, has been reported. By inserting and engineering defects into the PhC section, superimposed the PhC on a ring resonator section, a Gaussian-shaped frequency response, with very steep sidewalls, has been simulated. A continuous tuning of the filtering central frequency (15 GHz), with a fast switching time (≈ 1 ns) and power consumption of 47 mW is ensured, by exploiting the free carrier plasma dispersion effect in correspondence of PhC defects.
Furthermore, the theoretical feasibility of a miniaturized Ka-band optoelectronic oscillator, based on the designed PhCRR, with a phase noise at 10 kHz offset from the carrier of about -155 dBc/Hz and an output electric power > 10 dBm has been demonstrated, that represent a remarkable improvement respect to the state-of-the-art.
The high purity of the oscillating signal has been exploited for the design of a linearly chirped microwave generator, useful for high-resolution Synthetic Aperture Radar (SAR) systems for Earth Observation, with a time-bandwidth product of 3200 and a phase noise of about -116 dBc/Hz.
The design of an ultra-compact graphene-based optical delay line useful for the beamsteering/beamforming in X-band, is reported to ensure a wide swath size of SAR systems, with high range resolution, simulating the highest figure of merit reported at the state-of-the-art
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
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
Cross coupling of vinyl triflates and alkyl Grignard reagents catalysed by nyckel(0)-complexes
No full textDispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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