Numerical investigation of efficiency loss mechanisms in light emitting diodes and determination of radiative and non-radiative lifetimes for infrared optoelectronics

The year 2015 was defined the international year of light and light-based technologies. This title did not come unexpected, the research activity in solid-state lighting intensified during the last decade striving to improve solid-state light sources in terms of power consumption and fabrication costs. Emerging technologies are going to improve and amplify the scope of applicability of current solid-state lighting technology. This work would like to give a contribution to scientific research in solid-state lighting on two fronts. First, by contributing to the determination of the optical properties of germanium and germanium-tin alloy and second, by searching for remedies to the temperature dependent efficiency loss in GaN/InGaN based blue light emitting diodes. On these premises, this work has been splitted in two parts. In part one, the Auger recombination properties of germanium and radiative and Auger recombination properties for germanium-tin alloy have been calculated. In case of germanium, the application of a minimum biaxial tensile strain turns the material to a direct gap semiconductor, suitable for active and passive optoelectronic applications. On the other hand, the germanium-tin alloy is even more interesting due to its tunable band-gap energy and the capability to turn into a direct gap material above a certain molar fraction. On top of that, both materials may represent cheaper alternatives to materials currently used for the fabrication of high performance photodetectors and active optoelectronic devices. For both materials, the Auger and radiative recombination properties have been determined through a novel numerical approach that applies a Green’s function based model to the full band structure of the material. In part two, the temperature dependent efficiency loss, experimentally detected in a reference GaN/InGaN based single quantum well light emitting diode, has been numerically studied by measn of a commercial simulation software Crosslight APSYS © . The charge transport mechanism in the device has been modeled through an improved drift-diffusion scheme and compared to the real device current-voltage characteristics. Once an agreement between real and simulated current-voltage characteristics was achieved, the impact of Shockley-Read-Hall recombination mechanism on the device internal quantum efficiency function of temperature has been throughfully studied

Brocchi's Subapennine Fossil Conchology

The Italian geologist Giambattista Brocchi (1771–1826) is presented as a key figure in the historical period preceding young Charles Darwin's first work on transmutational theory while on the Beagle. The brief biographical account focuses on Brocchi's writings related to his analogy that species have births and deaths like individuals, and culminates in his most important work, Subapennine Fossil Conchology of 1814. Brocchi's analogy as an original and fertile way to approach the fossil record was to influence Darwin's first evolutionary thinking. Relevant passages of the book are presented for the first time in an English translation

Evolutionary Theory and the Florence Paleontological Collections

Abstract Florence has a tradition of Natural Philosophy, and since as early as the sixteenth century fossils were collected by the Granduke. The Museum of Natural History of the University of Florence houses today collections that belonged to Nicolas Steno, when fossils were for the first time used as documents to reconstruct Earth history. Natural philosophers and geologists, both Italian and foreigners, continued to study fossils collected in Tertiary strata of Tuscany until the nineteenth century, when the first speculations on the origin of species were proposed. Charles Darwin himself mentions fossil vertebrates that are today on show in our museum. In the last years, this part of the history of science has been proposed to the public. The aim was to foster an understanding of the centrality of fossils in two cultural revolutions, the discovery of deep time and the birth of evolutionary theory–connected among themselves and with the emergence of geology. Dedicated volumes, public conferences, guided visits to the collections, and field trips to paleontological sites have attracted an attentive and responsive public, showing that the history of science can help deliver modern evolutionary thinking. Other activities aimed at students of all ages have also shown that the interaction between schools, university teachers, and museum personnel is vital to form the mind of future generations on the reality of the evolution of natural systems

Brocchi, Darwin, and Transmutation: Phylogenetics and Paleontology at the Dawn of Evolutionary Biology

Giambattista Brocchi's (1814) monograph (see Dominici, Evo Edu Outreach, this issue, 2010) on the Tertiary fossils of the Subappenines in Italy—and their relation to the living molluscan fauna—contains a theoretical, transmutational perspective ("Brocchian transmutation"). Unlike Lamarck (1809), Brocchi saw species as discrete and fundamentally stable entities. Explicitly analogizing the births and deaths of species with those of individual organisms ("Brocchi's analogy"), Brocchi proposed that species have inherent longevities, eventually dying of old age unless driven to extinction by external forces. As for individuals, births and deaths of species are understood to have natural causes; sequences of births and deaths of species produce genealogical lineages of descent, and faunas become increasingly modernized through time. Brocchi calculated that over 50% of his fossil species are still alive in the modern fauna. Brocchi's work was reviewed by Horner (1816) in Edinburgh. Brocchi's influence as a transmutational thinker is clear in Jameson's (1827) "geological illustrations" in his fifth edition of his translation of Cuvier's Theory of the Earth (read by his student Charles Darwin) and in the anonymous essays of 1826 and 1827 published in the Edinburgh New Philosophical Journal—which also carried a notice of Brocchi's death in 1827. The notion that new species replace older, extinct ones—in what today would be called an explicitly phylogenetic context—permeates these essays. Herschel's (1830) discussion of temporal replacement of species and the modernization of faunas closely mirrors these prior discussions. His book, dedicated to the search for natural causes of natural phenomena, was read by Charles Darwin while a student at Cambridge. Darwin's work on HMS Beagle was in large measure an exploration of replacement patterns of "allied forms" of endemic species in time and in space. His earliest discussions of transmutation, in his essay February 1835, as well as the Red Notebook and the early pages of Notebook B (the latter two written in 1837 back in England), contain Brocchi's analogy, including the idea of inherent species longevities. Darwin's first theory of the origin of species was explicitly saltational, invoking geographic isolation as the main cause of the abrupt appearance of new species. We conclude that Darwin was testing the predicted patterns of both Brocchian and Lamarckian transmutation as early as 1832 at the outset of his work on the Beagle

NATURAL CASTS OF ENTOBIA FROM THE LATE CAENOZOIC OF SICILY

As with other ichnofossils, the study of the ichogenus Entobia Bronn, 1837, attributed to the activity of boring sponges, is useful to understand taphonomic processes and reconstruct paleoenvironments. Here we delineate a diverse Entobia assemblage from Sicily, the first described from this Mediterranean island, based on the discovery of well-preserved natural casts. The studied association is represented by seven ichnotaxa, Entobia cateniformis, E. cateniformis form A, E. geometrica, E. laquea, E. ?megastoma, E. ovula, E. ?paradoxa, which come from the late Caenozoic sites of Altavilla Milicia and Sferracavallo, in north-western Sicily. Aragonitic bivalves, mostly veneroids, served as substrate for the boring organisms responsible of producing these ichnotaxa. Entobia was also found associated with natural casts of the boring Caulostrepsis taeniola, produced by polychaetes. Ichnology and shell-bed taphonomy indicates that investigated deposits formed in conditions of low rate of sedimentation; post depositional processes involved chemical conditions favorable to the preservation of calcite shells

A man with a master plan: Steno’s observations on earth’s history

We present specific sources, including specimens of the Medicean cabinet and geological outcrops in Tuscany, probably used by Nicolaus Steno to build a theory on the origin of organic fossils, crystals and sedimentary strata, in order to construct the history of the Earth based on universal geometric principles. Phenomena he observed in Tuscany and in precedeing travels were revealing a sequence of events consistent with the biblical account. We propose that he devised his method to reconstruct a chronology of primordial events to demonstrate the historicity of the biblical creation in contrast to unorthodox thinking. This had been spreading in philosophical circles of northern Europe since the 1650s, circles frequented by Steno before his arrival in Tuscany in 1666. Steno knew in advance what places to visit to find fossils from literature such as Michele Mercati’s Metallotheca. This was a manuscript owned by the Florentine Carlo Dati, whom Steno probably heard about while in Paris in 1664-1665. In Tuscany he soon formed a tight interaction on matters regarding the interpretation of fossils with the local community of learned men. These included Giovanni Alfonso Borelli who was asked by Prince Leopoldo de’ Medici to provide Steno with fossils from Sicily and Malta. Steno’s theory and scale-independent, geometrical method of inquiry of geological objects found in Tuscany is hinted at in his Canis Carchariae Dissectum Caput, a geological essay completed in a few months in 1666. The theory was published in its most complete form in the so-called Prodromus of 1669. In both works he demonstrated that fossils in younger strata in the Tuscan hills, such as shark teeth and molluscan shells, have an origin analogous to solids which living animals form. In both essays he explicitly related the deposition of strata with marine fossils to the biblical flood, an idea foreshadowed in his oldest known manuscript of 1659, when he was a student in Copenhagen. He found no fossils in older sandstones of the Apennines and understood those strata to have formed before the creation of life. These discoveries  and other observations he made in Tuscany were, for Steno, the final proof that natural philosophy and biblical revelation disclose in synergy the mysteries of God’s creation

Review of: "The Effect of Habitat Structural Complexity on Gastropods in Anarid Mangrove Wetland"

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PALEOBIOLOGY FROM MUSEUM COLLECTIONS: COMPARING HISTORICAL AND NOVEL DATA ON UPPER MIOCENE MOLLUSCS OF THE LIVORNO HILLS

The upper Miocene mollusc collection from Monti Livornesi, Italy, collected more than a century ago, is confronted with new collections coming from the same localities of Popogna and Quarata. The study concerns the comparison of abundance data of three distinct fossil assemblages from the three vertically-stacked stratigraphic units called Luppiano, Rosignano and Raquese, of upper Tortonian-early Messinian age. Literature and museological data allowed to attribute most museum specimens to one and only one fossil assemblage. Museum collections preserve roughly the same dominant species, with similar ranks as the new quantitative field collections. Significant differences are however evident in the Luppiano assemblage from brackish-water, shallow subtidal bottoms, because new samples yield many species of small size, some of which with high dominance, that are completely lacking in museum collections, suggesting a bias due to size sorting and hinting at the overwhelming contribution of small-sized species to global mollusc diversity. On the other hand the Raquese assemblage, from an open marine shelf setting, can be similarly interpreted from the study of either the museum of new collection, yielding a similar species list and rank. The Rosignano mollusc assemblage, from a bioclastic bottom near a coral patch reef and characterised by fossils with a distinct taphonomic signature, is insufficiently represented in both historical and new collections. The systematics of the three assemblages are revised. The study contributes to the growing literature on museum “dark data” by showing that museum collections may yield abundance data significant for paleobiological analysis

Introduction: Nicolaus Steno and earth science in early modern Italy

A group of scientists interested in history of science and fascinated by the figure of Nicolaus Steno (1638-1686) gathered in Florence for the 350th anniversary of the publication of his De solido intra solidum naturaliter contento prodromus dissertationis. A public conference held at Palazzo Fenzi on 16 October 2019 and a geological fieldtrip on the following day were occasions to discuss different points of view on the last published work of the Danish natural philosopher, dedicated to "solids naturally enclosed in other solids" (De solido intra solidum naturaliter contento, or De solido in short). The title of the gathering, "Galilean foundation for a solid earth", emphasized the philosophical context that Steno found in Florence, where in 1666-1668 he established tight human and philosophical bonds with renowned Italian disciples of Galileo Galilei and members of the Accademia del Cimento. For participants to the 2019 gathering, the Museum of Natural History of the University of Florence, hosting some of Steno's geological specimens, and the region of Tuscany itself, formed the perfect location to discuss the phenomena that Steno had observed from 1666-1668, the motivations for his research, the methodology of his discovery and, generally stated, the European scientific context which informed his inquiry. Some of the talks given in that meeting are included within this volume, kindly hosted by Substantia, International Journal of the History of Chemistry published by the Florence University Press. In addition some of the invited speakers who were unable to attend, also contributed a paper to this publication. The collection is about earth science in the early modern period, when the study of minerals, rocks, and the fossilized remains of living things did not yet form a distinct path to knowledge about earth history, but was an integral part of the wider "philosophy of nature"