Microstructural and mechanical characterizations of heat treatable Al-Mg-Si-Cu based wrought aluminum alloys have been studied. The aim of this work was to produce fine grained, high strength alloy by adjusting processing conditions: deformation, solutionizing and aging. First, primary characterization was carried out via SEM-EDS analyses and tensile tests. Then an extensive experimental study has been carried out on two sets of samples. The first set has been studied to determine the ideal conditions for solutionizing and aging processes by analyzing the variation of hardness with different solutionizing and aging time and temperature. The second set, have first been mechanically deformed by swaging at four different deformations and four different temperatures, then heat treated. The hardness measurements have been carried out before and after solutionizing and also after aging. Finally, recrystallization behavior has been investigated by measuring grain size before and after solutionizing treatment using image analyzer software. The initial characterizations showed that Mg2Si and complex iron, manganese bearing intermetallics were the primary particles observed in the &amp / #945 / -Al matrix. Nearly 140HB hardness could be obtained with solutionizing at 530&deg / C and aging at 175&deg / C for 8 hours which was determined as the optimum treatment for obtaining peak hardness. When shaping (deformation) was concerned / strength loss was the overall outcome of any hot or cold deformation before solutionizing / which was most probably due to the destruction of the initial microstructure. Improvement in the percent elongation was the promising aspect of this application. Strength loss was increased for samples deformed at higher temperatures and higher reductions.

Barium strontium titanate thin film varactors have been widely investigated for the purpose of creating tunable front-ends for RF and microwave systems. There is an abundance of literature observing the capacitance-voltage behavior and methods on improving tunability. However, there is a lack of thorough investigations on the nonlinear behavior, specifically the third order intermodulation distortion, and the parameters that impact it. There is also a research void that needs to be filled for nanoscale barium strontium titanate varactors as nanotechnology becomes increasingly prevalent in the design of RF and microwave components. This work aims to advance the understanding of nonlinear properties of barium strontium titanate varactors. Temperature and voltage impacts on the third order intermodulation distortion products of BST varactors are observed by two-tone measurements. The material properties of the films are correlated with the nonlinear behavior of the varactors. Additionally, size reduction capabilities are shown by fabricating planar barium strontium titanate interdigital varactors with nanoscale size gaps between the electrodes. Modeling techniques are also investigated.

No description available.

<p><font face="TimesNewRomanPSMT"> <p align="left">Natural radioactivity studies have been carried out to study the textural characteristics, heavy mineral composition, provenance, sediment transport, and depositional environment of beach placer deposits. The naturally occurring radionuclides such as properties of beach sands, which reflect the geological characteristics such as transport and sorting processes and the depositional environment. The present work focuses on the radiometric characteristics of beach sand deposits along the west coastof South Africa. Beach sands samples were collected at the Melkbosstrand (MBS) and Ouskip (OSK) beach. The activity concentrations of these radionuclides were determined by high-resolution gamma-ray spectrometry using a high-purity germanium (HPGe) detector in a low-background configuration.</p> </font></p>

Meandering rivers and associated vegetation communities are highly dynamic systems that interact through various geomorphic and successional processes. However, much is still unknown about these interactions. Studies that focus on system integration rather than examining fluvial-related and vegetation dynamics individually will benefit science and the management of river systems. Tree communities in riparian areas, although consisting mainly of bottomland hardwood species, can be very diverse. Diversity has been linked to environmental influences such as meander migration, and changes in elevation and soil texture. This study focused on a single meander bend of the lower Trinity River in southeast Texas. The purpose of this research was to examine interactions between soil texture variation and the establishment and succession of riparian tree communities, as such interactions contribute to the formation of complex riparian landscapes. A bend-scale approach was utilized to provide a detailed study of vegetation pattern and of soil texture resulting from sedimentation processes, to examine for any relationships between them. Aerial imagery was used to assist in interpreting patterns of vegetation succession. The field portion of the study collected species and size class data on trees and soil samples for textural analysis. These data were analyzed separately to understand variations in tree communities and soils, but also together, to determine any relationships between soil texture and what tree communities are able to establish. Mean annual flow data from gauges upstream and downstream of the site were analyzed for changes in flow following dam construction upstream, as river regulation could potentially alter the vegetation establishment regime. Results showed five distinct communities or zones of vegetation. Soils on the site were strongly skewed toward finer sands and high silt and clay content. Zone locations and community structure were not directly related to soil texture; however, given species had clear relationships of relative density or dominance with specific soil textures. No changes in flow were noted between pre- and post- dam construction periods, indicating that the riparian system at this site may operate under near-natural conditions. Further studies in species-soil texture interactions, and for rare and invasive species in particular, may prove beneficial in improving understanding of the complex functioning of riparian systems and in providing valuable information for their management and restoration.

High strain rate plastic deformation of metals results in the formation of localized zones of severe shear strain known as adiabatic shear bands (ASBs), which are a precursor to shear failure. The formation of ASBs in a high-strength low alloy steel, namely AISI 4340, was examined based on prior heat treatments (using different austenization and tempering temperatures), testing temperatures, and impact strain rates in order to map out grain size and grain deformation behaviour during the formation of ASBs. In the current experimental investigation, ASB formation was shown to be a microstructural phenomenon which depends on microstructural properties such as grain size, shape, orientation, and distribution of phases and hard particles—all controlled by the heat treatment process. Each grain is unique and its material properties are heterogeneous (based on its size, shape, and the complexity of the microstructure within the grain). Using measurements of grain size at various heat treatments as well as dynamic stress-strain data, a finite element model was developed using Matlab and explicit dynamic software LSDYNA to simulate the microstructural deformation of grains during the formation of ASBs. The model simulates the geometrical grain microstructure of steel in 2D using the Voronoi Tessellation algorithm and takes into account grain size, shape, orientation, and microstructural material property inhomogeneity between the grains and grain boundaries. The model takes advantage of the Smooth Particle Hydrodynamics (SPH) meshless method to simulate highly localized deformation as well as the Johnson-Cook Plasticity material model for defining the behavior of the steel at various heat treatments under high strain rate deformation.The Grain Model provides a superior representation of the kinematics of ASB formation on the microstructural level, based on grain size, shape and orientation. It is able to simulate the microstructural mechanism of ASB formation and grain refinement in AISI 4340 steel, more accurately and realistically than traditional macroscopic models, for a wide range of heat treatment and testing conditions.

Στόχος της παρούσας διατριβής είναι η μελέτη των ιζηματολογικών και γεωχημικών χαρακτηριστικών του νεογενούς σχηματισμού Μετόχια στην νήσο Γαύδο με κατεύθυνση την αναζήτηση πιθανών μητρικών πετρωμάτων υδρογονανθράκων. Στο πρώτο κεφάλαιο γίνεται βιβλιογραφική ανασκόπηση της γεωλογίας της περιοχής μελέτης καθώς και γενικότερα της λεκάνης Μεσσαρά-Γαύδου, περιγραφή της τομής δειγματοληψίας και τέλος της γεωδυναμικής και παλαιογεωγραφικής εξέλιξης της ευρύτερης περιοχής. Στο δεύτερο κεφάλαιο καταρχήν πραγματοποιείται μια επιγραμματική αναφορά των συνθηκών που απαιτούνται για την γένεση πεδίων υδρογονανθράκων και κατόπιν δίνεται έμφαση στα χαρακτηριστικά του οργανικού υλικού που εγκλωβίζεται στα ιζήματα και στον τρόπο δημιουργίας των μητρικών πετρωμάτων. Στο τρίτο κεφάλαιο περιγράφονται οι γεωχημικές αναλύσεις που πραγματοποιήθηκαν. Το κεφάλαιο αυτό χωρίζεται σε δυο μέρη. Στο πρώτο περιγράφεται η ανάλυση ανθρακικού ασβεστίου και τα αποτελέσματα της. Στο δεύτερο μέρος παρουσιάζονται βιβλιογραφικά δεδομένα του ολικού οργανικού άνθρακα από την περιοχής της Μεσσαρά και τα αποτελέσματα της ανάλυσης του ολικού οργανικού άνθρακα καθώς και τα χαρακτηριστικά του οργανικού υλικού που προέκυψαν από την παρούσα διατριβή. Στο τέταρτο κεφάλαιο γίνεται μια περιγραφή των μεθόδων κοκκομετρικής ανάλυσης που χρησιμοποιήθηκαν, η σύγκριση των μεθόδων, τα αποτελέσματα και η σύγκριση των αποτελεσμάτων που προέκυψαν. Τέλος στο πέμπτο κεφάλαιο παρουσιάζονται τα αποτελέσματα της παρούσας διατριβής. / The aim of this thesis is to study the sedimentological and geochemical characteristics of the Neogene Metochia formation on the island of Gavdos towards the exploration for potential hydrocarbon source rocks. The first chapter is a review of the geology of the study area and generally the geology of the Messara-Gavdos basin, a description of the sampling section and the geodynamic and paleogeographic evolution of the area. In the second chapter a brief review of the conditions required for the genesis of hydrocarbons fields is provided, and then the characteristics of the organic material trapped in sediments and how source rock being creating, is emphasised. In the third chapter the geochemical analysis don are described. This chapter is divided into two parts. First part describes the analysis of the total calcium carbonate and the results obtained. Second part presents bibliographical data for total organic carbon from Messara area samples and the results of the total organic carbon analysis derived from this thesis, as well as the characteristics of organic material of the studied samples. The fourth chapter describes the grain-size analysis methods used in this thesis, a comparison of these methods, the results obtained and a comparison of them. Finally in the fifth chapter the outcomes of this thesis are presented.

Η εργασία αυτή έχει ως σκοπό τη συλλογή και την εργαστηριακή επεξεργασία ενός α-ριθμού δειγμάτων από τη νοτιοδυτική Κρήτη και συγκεκριμένα από τον Πλάτανο. Τα δείγματα μελετήθηκαν εργαστηριακά με τη μέθοδο του ανθρακικού ασβεστίου, του ορ-γανικού υλικού με τιτλοδότηση και της κοκκομετρίας με κόσκινα (για τα πιο ανδρομε-ρή κλάσματα)και με πιπέττες (για τα λεπτόκοκκα κλάσματα). Τα αποτελέσματα που προκύπτουν φανερώνουν το περιβάλλον και τις συνθήκες απόθεσης των δειγμάτων της περιοχής, τις διαδικασίες μεταφοράς και απόθεσης, την περιεκτικότητα τους σε CaCO3 και TOC. Στην συνέχεια, εφόσον είναι γνωστοί αυτοί οι παράγοντες σε συνδι-ασμό με τη γενικότερη γεωλογία της περιοχής μπορούμε να εξετάστηκαν οι πιθανότη-τες που υπάρχουν να σχηματιστούν οι υδρογονάνθρακες, να αποθηκευτούν αλλά και να μεταναστέψουν. / Sedimetological analysis of 42 samples, sieve and pipette grain size analysis in rela-tion with statistical analysis, from a cross-section from Platanos basin in NW Crete island, shows that sedimentation took place in a shelf environment with low energy, where sediments transported through suspension. Depositional conditions changed during sedimentation, with changes in depositional depth from shallower to deeper. The main lithology is sandy clay and from the samples is seen that the fraction of clay has small values. TOC analysis showed that organic matter ranges from 0% to 2.38%. The presence of TOC values, more than 0.5%>, suggest that the studied de-posits could be source rocks under special conditions. CaCO3 analysis, with values from 34,87to 87,47, with an average 53.3%, indicate rapid sedimentary conditions. Comparison between TOC-CaCO3 seems to show that majority of samples are negative with low TOC and CaCO3 showing increased oxidative environment condi-tions sedimentation. At least 3 cases where we have increased TOC could character-ize the relationship as positive. Where high rates of both indicators show the oxidiz-ing conditions of the environment to maintain the high rate of organic carbon may be due to the high rate of sedimentation in a quickly plunge basin. Finally, in the heterolithic phase where most changes occur in the rates of both indicators also confirm the alternation of lithology showing strong variation of depth due to sedi-mentation apparently of tectonic activity. In this case it could and the correlation mentioned above to be connected with the change of tectonic regime in the passage from the phase of clay in heterolithic phase

Λαμβάνοντας υπόψη ιζηματογενείς δομές και υφές, και την βιοστρωματογραφία κατα-λήγουμε στο συμπέρασμα ότι η ιζηματογενής ακολουθία κατά μήκος της νότιας ακτής της Ζακύνθου από το χωριό Κερί μέχρι και τη χερσόνησο του Άγιου Σώστη έχει επη-ρεαστεί από ισχυρή τεκτονική δραστηριότητα, παράγοντας τουλάχιστον τέσσερις κύ-κλους με αυξανόμενο κοκκομετρικό μέγεθος προς τα πάνω. Η παρουσία της ακολου-θίας Bouma και των οριζόντων ολίσθησης συστήνουν ένα βαθύ θαλάσσιο περιβάλλον απόθεσης. Η κοκκομετρική ανάλυση έδειξε μια σταδιακή πλήρωση του κάθε κύκλου ιζηματογένεσης, αλλά και ολόκληρης της περιοχής. Επιπροσθέτως, η ανάλυση του TOC και του CaCO3 έδειξε ότι υπάρχει μια σχέση του ποσοστού τους με το περιβάλ-λον απόθεσης, καθώς και ότι υπάρχουν αρκετά καλές πιθανότητες για ανάπτυξη μη-τρικών πετρωμάτων με μέτρια έως καλή δυνατότητα γένεσης υδρογονανθράκων. / Taking into account sedimentary structures and textures, and biostratigraphy we conclude that the sedimentary sequence along the southern coast of Zakynthos is-land from Keri village as far as Ag. Sostis peninsula was influenced by strong tec-tonic activity, producing at least four coarsening upward cycles. The presence of Bouma sequence and slump horizons within the studied sediments introduce gener-ally deep sea depositional conditions. Grain size analysis showed a gradual upward swallowing of depositional conditions both to each cycle and general to the whole area. In addition, TOC and CaCΟ3 analysis showed that there is a relation of their content with the depositional conditions and moreover there are quite enough condi-tions for the development of source rocks with fair to good hydrocarbon generation.

To explore whether the dispersion of sediments in the North Atlantic can be related to modern and past Atlantic Meridional Overturning Circulation (AMOC) flow speed, particle size distributions (weight%, Sortable Silt mean grain size) and grain-size separated (0–4, 4–10, 10–20, 20–30, 30–40 and 40–63 μm) Sm-Nd isotopes and trace element concentrations are measured on 12 cores along the flow-path of Western Boundary Undercurrent and in the central North Atlantic since the Last glacial Maximum (LGM). North Atlantic is a useful place to explore how size-specific sediment provenance is related to sedimentary inputs and deep-current advection because mantle-derived materials in Iceland is a unique sedimentary source compared to crustal-derived terranes in Europe, Greenland and North America. The four main processes transporting sediments from continents to the North Atlantic (bottom currents, turbidity currents, ice-rafting events, airborne inputs) can be well distinguished through the size-specific physical and geochemical records. When primarily advected by the bottom currents, Holocene sediments show that the finer-sized fractions (0–4, 4–10, 10–20 μm) were transported further, and the coarser size fraction (40–63 μm) matched local inputs. In the deep coretops (> 2700 m) proximal to southern Greenland, fine-slit size fraction (10–20 μm) instead of clay size fraction (0–4 μm) observed more Icelandic-material contribution. In the past, the 20–30, 30–40 and 40–63 μm particles in the shallower Iceland-proximal core (1249 m) reflect Icelandic composition variation due to the abrupt volcanic eruption around 13–9 ka; while in the deeper Iceland-proximal core (2303 m) they were sensitive to the changing bottom flow speed. Downstream in cores proximal to southern Greenland (> 2272 m) and eastern North America (3555 m), composition of the 20–63 μm sediments could be used as an indicator for the retreating of the Greenland and Laurentide Ice Sheets which affect the sediment accessibility of the covered geological terranes; while the 0–4, 4–10 and 10–20 μm particles were more sensitive towards the changing direction (northern-sourced or southern-sourced) and velocity of the bottom current. In the open North Atlantic, the composition of the 0–10 μm particles were less variable between the cold and warm climate intervals compared to the 10–63 μm particles, and the 30–40 and 40–63 μm size fractions were sensitive towards both ice-rafting events and bottom flow direction. During LGM, shallower and vigorous northern-sourced water (NSW) was observed overlaying the deeper southern-sourced water (SSW), with the boundary between 2133 to 2303 m in southern Iceland, and ~ 2272 m in southern Greenland. Reduced NSW occurred during Heinrich Stadial 1, until AMOC above ~ 3500 m recovered to vigorous modern-like version no later than ~ 13.5 ka. Sluggish overflow was observed in North Atlantic between 12.2–11.7 ka above ~ 3500 m. Reduction of Iceland-Scotland Overflow Water occurred around 9.7 ka, and started recovering to its modern vigorous no later than ~ 8.6 ka. These relative past AMOC strength variations (vigorous/sluggish) are firstly converted to actual bottom-current speed (in cm/s) using laminar advection model in this work: vertical settling velocity of particle having the most Icelandic contribution is calculated by Stokes’ Law, and the lateral deep-sea current speed is calculated when the vertical settling depth and the lateral advection distance of the particle traveled before settling are constrained. Primary modelling errors originating from temperature/salinity variations in past deep seawater, winnowing process in fine particles, basaltic-signature dilution by crustal input, and lateral advection pathways of Icelandic-material are further discussed, indicating relatively low modelling error (< ~ 10–20 %). The modelling results agree well with modern deep-sea current speed measurements and backtrack-trajectory eddy resolving model (Ocean model for the Earth Simulator, OFES18), indicating reasonable quantifications of past AMOC flow speeds.