Predicting heat capacity and experimental investigations in the Al-Fe and Al-Fe-Si systems as part of the CALPHAD-type assessment of the Al-Fe-Mg-Si system

The aim of this work was to improve the heat capacity estimation of a material for usage within a CALPHAD-type assessment. An algorithm is derived that estimates the trend of heat capacity with temperature based on zero Kelvin properties and the thermal expansion coefficient at the Debye temperature. The algorithm predicts not only the trend of heat capacity but also the temperature trend of the volume and the bulk modulus, which can be also included in new thermodynamic databases. The algorithm is used to assess thermophysical properties of the intermetallic phases eta (Fe2Al5), epsilon~(Fe5Al8) and tau4 (FeAl3Si2). The heat capacity of the intermetallic phases zeta, eta, theta and epsilon of the Al-Fe system and of tau4 of the Al-Fe-Si system was measured using DSC. For the phases zeta, eta, and theta, a non-linearly increasing heat capacity approaching the melting temperature was observed. In addition, the heat capacity of three bcc-based Al-Fe samples including the B2-->A2 transition were determined. The Al-rich section of the Al-Fe phase diagram was studied using DTA and quenching experiments. The homogeneity ranges of the intermetallic phases were determined using SEM/WDS measurements. Based on own and literature values, a thermodynamic description of the Al-Fe system was assessed including the modelling of A2/B2 ordering and the homogeneity range of all intermetallic phases. In addition, thermodynamic parameters of the Al-Fe-Si, Al-Fe-Mg, and the Fe-Mg-Si system were assessed to obtain a thermodynamic description of the Al-rich side of the Al-Fe-Si-Mg system, which can be used to study phase transitions of typical A356-aluminium alloys

4th PhD conference: Sustainability? - Your research - our world ; Abstracts

These are the abstracts of the oral and poster presentations of the 4th PhD conference held on 06. June 2019 in Freiberg

Electronic transport in metallic carbon nanotubes with mixed defects within the strong localization regime

We study the electron transport in metallic carbon nanotubes (CNTs) with realistic defects of different types. We focus on large CNTs with many defects in the mesoscopic range. In a recent paper we demonstrated that the electronic transport in those defective CNTs is in the regime of strong localization. We verify by quantum transport simulations that the localization length of CNTs with defects of mixed types can be related to the localization lengths of CNTs with identical defects by taking the weighted harmonic average. Secondly, we show how to use this result to estimate the conductance of arbitrary defective CNTs, avoiding time consuming transport calculations

6th PhD Conference - Abstracts: Give it a Benefit! - What do you Research for?

These are the abstracts of the oral presentations of the 6th PhD conference held on 10. June 2022 in Freiberg

Improved recursive Green's function formalism for quasi one-dimensional systems with realistic defects

We derive an improved version of the recursive Green's function formalism (RGF), which is a standard tool in the quantum transport theory. We consider the case of disordered quasi one-dimensional materials where the disorder is applied in form of randomly distributed realistic defects, leading to partly periodic Hamiltonian matrices. The algorithm accelerates the common RGF in the recursive decimation scheme, using the iteration steps of the renormalization decimation algorithm. This leads to a smaller effective system, which is treated using the common forward iteration scheme. The computational complexity scales linearly with the number of defects, instead of linearly with the total system length for the conventional approach. We show that the scaling of the calculation time of the Green's function depends on the defect density of a random test system. Furthermore, we discuss the calculation time and the memory requirement of the whole transport formalism applied to defective carbon nanotubes

Würm-Rückzugsstadien vom Schwarzwald bis zur Hohen Tatra

Ein Überblick über die Würm-Rückzugsstadien in den höheren Gebirgen Mitteleuropas außerhalb der Alpen ermöglicht die Aufstellung einer (einschließlich dem z. T. mehrgliedrigen Maximalstand) neunteiligen Serie prähistorischer Gletscherstände. Historische Moränen scheinen sich nirgends nachweisen zu lassen. Außerdem ergeben sich neue Werte für die unterschiedlich groß gewesene Schneegrenz-Depression in den behandelten Gebirgen. Schließlich wird eine vorläufige Parallelisierung dieser Rückzugsstadien mit denjenigen der Alpen versucht (zum Vergleich auch Mount Kenya).researc

Gleiche Würm-Rückzugsstadien in den Gebirgen Mitteleuropas und Ostafrikas?

Vergleiche der von B. H. Baker gefundenen Gletscherstände am Mt. Kenya mit der Karte 1 : 25000 des Mt. Kenya und mit den Würm-Rückzugsstadien der alpinen Gletscher ergeben interessante Anregungen für die weitere Erforschung dieses Fragenkomplexes.researc

An improved Green's function algorithm applied to quantum transport in carbon nanotubes

The renormalization-decimation algorithm (RDA) of L\'opez Sancho et al. is used in quantum transport theory to calculate bulk and surface Green's functions. We derive an improved version of the RDA for the case of very long quasi one-dimensional unit cells (in transport direction). This covers not only long unit cells but also supercell-like calculations for structures with disorder or defects. In such large systems, short-range interactions lead to sparse real-space Hamiltonian matrices. We show how this and a corresponding subdivision of the unit cell in combination with the decimation technique can be used to reduce the calculation time. Within the resulting algorithm, separate RDA calculations of much smaller effective Hamiltonian matrices must be done for each Green's function, which enables the treatment of systems too large for the common RDA. Finally, we discuss the performance properties of our improved algorithm as well as some exemplary results for chiral carbon nanotubes

Gran Paradiso — Mont Blanc: Prähistorische und historische Gletscherstände

Das Untersuchungsgebiet umfaßt die westlichen und südlichen Teile der Aosta-Region vom Hauptkamm der M. Blanc-Gruppe bis zum nach N entwässernden Teil der Paradiso-Gruppe. Die Untergrenze bildet das Moränengebiet von Aymavilles-Sarre, etwa 5, km westlich Aosta. Verfolgt werden die durch Moränen gekennzeichneten Gletscherstände vom „Aymavilles" (= „Gschnitz") bis zur Gegenwart und die Vermessungsergebnisse ab 1929—31 (Karte 1 : 25 000); die letzten genaueren Höhenwerte liegen für 1950—53 vor. Moränen aus historischer Zeit gibt es etwa von 1600, 1680, 1770, 1820, 1860 und 1920. Nur wenige Gletscher weisen deutliche noch jüngere Moränen auf. Tiefliegende Moränen aus dem 17. und 18. Jahrh. lassen sich leider nicht immer eindeutig einem der drei Stände dieses Zeitraumes zuordnen. Innerhalb der bisher als „Courmayeur" bezeichneten und dem „Daun" gleichgesetzten Moränen kann man deutlich zwei Gruppen unterscheiden. Es wird deshalb vorgeschlagen, die Bezeichnung „Courmayeur" durch zwei neue Lokalnamen aus der Umgebung von Cogne, „Epinel" (= „Daun") und „Valnontey" (= „Egesen"), zu ersetzen. Zum Schluß wird versucht, die Geschichte der Gletscher im Untersuchungsgebiet kurz darzustellen.researc