9,934 Works

Binnendifferenzierung der Professur : Interdisziplinäre Analysen zu Hochschulrecht und hochschulischer Praxis

Roni Deger & Thorben Sembritzki
In den vergangenen anderthalb Jahrzehnten hat sich im deutschen Wissenschaftssystem eine Vielzahl neuer Professur-Varianten herausgebildet. Dieses Working Paper fasst diese Entwicklung als eine Binnendifferenzierung des Stellentypus der Professur, die nicht zuletzt durch den gestiegenen Wettbewerb zwischen Ländern und Hochschulen bedingt ist – einen Wettbewerb, der durch die Föderalismusreform und Bund-Länder-Programme, wie die Exzellenzinitiative und das Tenure-Track-Programm, forciert wurde. Aufbauend auf rechtshistorisch-rekonstruktiven und ländervergleichenden Analysen der hochschulrechtlichen Rahmenbedingungen wird das Ausmaß der Binnendifferenzierung der Professur in...

Studienfachwahl an der LUH : Befunde und Handlungsvorschläge

Irina Gewinner & Mara Esser
Dieser Bericht liefert Ergebnisse einer Studierendenbefragung, die an der Leibniz Universität Hannover Ende 2018 durchgeführt wurde. Das Ziel, das sich das Forschungsteam vom Institut für Soziologie gesetzt hat, war die Analyse der Studien- und Berufswahl junger Menschen, basierend auf Genderideologien und geschlechtsspezifischen Stereotypen als Erklärungsgrundlage. Insgesamt wurden folgende Themen schwerpunktmäßig näher untersucht: soziodemographische Charakteristika (Geschlecht, Alter), Nutzung digitaler Medien, Sozialisation und Familie, Schule und Lehrereinfluss sowie individuelle Idealvorstellungen und kulturelle Werte. Neben der Vorstellung der...

Modal particles and sentence type restrictions: A construction grammar perspective

Maria Alm, Janina Behr & Kerstin Fischer
The problem addressed in this study is the sentence type restrictions of modal particles. In the literature on modal particles, it is often noted that these items cannot occur freely in all kinds of sentence types, but are restricted to certain grammatical host structures. In this article, we first discuss previous work on the semantic, formal and functional factors that determine the usage of modal particles in different grammatical configurations. The results of this discussion...

Gelatin-methacryloyl (GelMA) formulated with human platelet lysate supports mesenchymal stem cell proliferation and differentiation and enhances the hydrogel’s mechanical properties

Antonina Lavrentieva, Marline Kirsch, Luise Birnstein, Iliyana Pepelanova, Wiebke Handke, Jessica Rach, Axel Seltsam & Thomas Scheper
Three-dimensional (3D) cell culture is a major focus of current research, since cultivation under physiological conditions provides more reliable information about in vivo cell behavior. 3D cell cultures are used in basic research to better understand intercellular and cell-matrix interactions. However, 3D cell culture plays an increasingly important role in the in vitro testing of bioactive substances and tissue engineering. Gelatin-methacryloyl (GelMA) hydrogels of different degrees of functionalization (DoFs) are a versatile tool for 3D...

Observation of the local structure of landau bands in a disordered conductor

T. Schmidt, Rolf J. Haug, V.I. Fal'ko, K. V. Klitzing, A. Förster & H. Lüth
The local density of states of heavily doped GaAs is explored at high magnetic fields, where only a single or few Landau bands are occupied. Our experiment is based on resonant tunneling through impurity states and images the local density of states both below and above the Fermi level. Fan-type mesoscopic fluctuations are observed in the energy-magnetic-field plane, which we attribute to the interplay of Landau quantization and quantum interference of scattered electron waves in...

Phonon excitations of composite-fermion Landau levels

F. Schulze-Wischeler, Frank Hohls, U. Zeitler, D. Reuter, A.D. Wieck & Rolf J. Haug
The phonon excitations of fractional quantum Hall (FQH) states at filling factors ν =1÷3,2÷5, 4÷7, 3÷5, 4÷3, and 5÷3 were investigated. The excitations were found to be based on Landau-level transitions of composite fermions (CF). It was observed that at filling factor ν = 2÷3, a linear field dependence of the excitation energy in the high field regime showed a spin transition, which was excited by the phonons. All the transport gaps, except the one...

Impurity effects in quantum dots: Toward quantitative modeling

E. Räsänen, J. Könemann, Rolf J. Haug, M.J. Puska & R.M. Nieminen
We have studied the single-electron transport spectrum of a quantum dot in GaAs/AlGaAs resonant tunneling device. The measured spectrum has irregularities indicating a broken circular symmetry. We model the system with an external potential consisting of a parabolic confinement and a negatively charged Coulombic impurity placed in the vicinity of the quantum dot. The model leads to good agreement between the calculated single-electron eigenenergies and the experimental spectrum. Furthermore, we use the spin-density-functional theory to...

Multiple transitions of the spin configuration in quantum dots

M.C. Rogge, C. Fühner & Rolf J. Haug
Single electron tunneling is studied in a many electron quantum dot in high magnetic fields. For such a system multiple transitions of the spin configuration are theoretically predicted. With a combination of spin blockade and Kondo effect we are able to detect five regions with different spin configurations. Transitions are induced with changing electron numbers. © 2006 The American Physical Society.

Numerical and experimental investigations of the anisotropic transformation strains during martensitic transformation in a low alloy Cr-Mo steel 42CrMo4

Bernd-Arno Behrens, Anas Bouguecha, Christian Bonk & Alexander Chugreev
Hot forming as a coupled thermo-mechanical process comprises of numerous material phenomena with a corresponding impact on the material behavior during and after the forming process. Within the subsequent heat treatment, possible rapid cooling of the hot formed parts leads to the diffusionless decomposition of austenite into martensite. In this context, in addition to the elastic, plastic and linear thermal strain components, complex isotropic as well as anisotropic transformation strains can occur. Irreversible anisotropic transformation...

Increasing productivity in turning of hard-to-cut materials by means of modified flank faces

Berend Denkena, B. Bergmann, T. Grove & O. Pape
The high thermo-mechanical tool load during cutting of hard-to-cut material leads to an increased tool wear, which affects the surface integrity and tool life adversely. An innovative approach to counter the wear is to retract the tools flank face at a certain distance from the cutting edge. The so-called flank face modification geometrically limits the tool wear and increases the available material of the tool, which can be removed by the abrasive cutting process until...

Instrument data simulations for GRACE Follow-on: Observation and noise models

Neda Darbeheshti, Henry Wegener, Vitali Müller, Majid Naeimi, Gerhard Heinzel & Martin Hewitson
The Gravity Recovery and Climate Experiment (GRACE) mission has yielded data on the Earth's gravity field to monitor temporal changes for more than 15 years. The GRACE twin satellites use microwave ranging with micrometre precision to measure the distance variations between two satellites caused by the Earth's global gravitational field. GRACE Follow-on (GRACE-FO) will be the first satellite mission to use inter-satellite laser interferometry in space. The laser ranging instrument (LRI) will provide two additional...

Effects of soil pre-treatment with Basamid® granules, Brassica juncea, Raphanus sativus, and tagetes patula on bacterial and fungal communities at two apple replant disease sites

Bunlong Yim, Heike Nitt, Andreas Wrede, Samuel Jacquiod, Søren J. Sørensen, Traud Winkelmann & Kornelia Smalla
Nurseries producing apple and rose rootstock plants, apple orchards as well as rose production often experience replanting problems after several cultivations at the same site when a chemical soil disinfectant is not applied. The etiology of apple and rose replanting problems is most likely caused by soil-borne pathogen complex, defined as “replant disease (RD)”. Symptoms typical of RD are reduced shoot and root growth, a smaller leaf area, a significant decrease in plant biomass, yield...

Physical properties and seismic structure of Izu-Bonin-Mariana fore-arc crust: Results from IODP Expedition 352 and comparison with oceanic crust

G.L. Christeson, S. Morgan, S. Kodaira, M. Yamashita, R.R. Almeev, K. Michibayashi, T. Sakuyama, E.C. Ferré & W. Kurz
Most of the well-preserved ophiolite complexes are believed to form in suprasubduction zone (SSZ) settings. We compare physical properties and seismic structure of SSZ crust at the Izu-Bonin-Mariana (IBM) fore arc with oceanic crust drilled at Holes 504B and 1256D to evaluate the similarities of SSZ and oceanic crust. Expedition 352 basement consists of fore-arc basalt (FAB) and boninite lavas and dikes. P-wave sonic log velocities are substantially lower for the IBM fore arc (mean...

Giant anisotropy of zeeman splitting of quantum confined acceptors in Si/Ge

K.-M. Haendel, R. Winkler, U. Denker, O.G. Schmidt & Rolf J. Haug
Shallow acceptor levels in Si/Ge/Si quantum well heterostructures are characterized by resonant-tunneling spectroscopy in the presence of high magnetic fields. In a perpendicular magnetic field we observe a linear Zeeman splitting of the acceptor levels. In an in-plane field, on the other hand, the Zeeman splitting is strongly suppressed. This anisotropic Zeeman splitting is shown to be a consequence of the huge light-hole-heavy-hole splitting caused by a large biaxial strain and a strong quantum confinement...

Observation of an interedge magnetoplasmon mode in a degenerate two-dimensional electron gas

G. Sukhodub, Frank Hohls & Rolf J. Haug
The propagation of edge magnetoplasmons (EMP) in a degenerated two-dimensional electron gas was analyzed. Investigations show that an interedge EMP mode attributed to the excitations of boundary between two regions with constant but different charge densities. The splitting of an incident voltage pulse into several EMP modes propagating with different velocities was also observed. The results show that the internal spatial parameters of the edge structure were derived from the analysis of the propagation velocities...

Phonons in InAs/AlAs single quantum dots observed by optical emission

D. Sarkar, H.P. Van Der Meulen, J.M. Calleja, J.M. Becker, Rolf J. Haug & Klaus Pierz
Photoluminescence emission spectra of self-assembled single InAs/AlAs quantum dots with variable size reveal typical sharp lines below 1.8 eV, corresponding to transitions between fully confined states. Above this energy the sharp peaks disappear due to the Γ-X scattering of conduction electrons. Excitation spectra of the biexciton line in single quantum dots show marked maxima at the optical-phonon frequency of the quantum dot and at its first overtone. The quantum dot phonon energy observed is 31...

Intake of Minerals from Food Supplements in a German Population - A Nationwide Survey

Janina Willers, Michaela Heinemann, Norman Bitterlich & Andreas Hahn
Introduction: Studies indicate that 17.9% - 60% of adults in Germany and Europe regularly use food supplements. Some reports suggest that their use might be responsible for excessive nutrient intake. The purpose of this survey was to examine the quantitative mineral intakes from food supplements: whether the tolerable upper intake levels (ULs) with supplements alone, or in combination with food was exceeded was checked. Methods: The survey was carried out by the Association for Consumer...

Investigation of the Transition Reaction of Tobermorite to Xonotlite under Influence of Additives

Andrea Hartmann, David Schulenberg & Josef-Christian Buhl
The objective of the present work was to investigate the transition reaction of the calcium silicate hydrate tobermorite into xonotlite under influence of additives. Tobermorite is the main binding agent in steam hardened building materials and the appearance of xonotlite indicates the progress of hardening and an overcuring of the material. Hydrothermal experiments under addition of sucrose, calcium formate and calcium chloride dihydrate to the main components quartz and lime were done using temperatures of...

Magnetoresistance induced by rare strong scatterers in a high-mobility two-dimensional electron gas

L. Bockhorn, I.V. Gornyi, D. Schuh, C. Reichl, W. Wegscheider & Rolf J. Haug
We observe a strong negative magnetoresistance at nonquantizing magnetic fields in a high-mobility two-dimensional electron gas. This strong negative magnetoresistance consists of a narrow peak around zero magnetic field and a huge magnetoresistance at larger fields. The peak shows parabolic magnetic field dependence and is attributed to the interplay of smooth disorder and rare strong scatterers. We identify the rare strong scatterers as macroscopic defects in the material and determine their density from the peak...

Interaction-induced spin polarization in quantum dots

M.C. Rogge, E. Räsänen & Rolf J. Haug
The electronic states of lateral many-electron quantum dots in high magnetic fields are analyzed in terms of energy and spin. In a regime with two Landau levels in the dot, several Coulomb-blockade peaks are measured. A zigzag pattern is found as it is known from the Fock-Darwin spectrum. However, only data from Landau level 0 show the typical spin-induced bimodality, whereas features from Landau level 1 cannot be explained with the Fock-Darwin picture. Instead, by...

Quantized current source with mesoscopic feedback

Lukas Fricke, Frank Hohls, Niels Ubbelohde, Bernd Kaestner, Vyacheslavs Kashcheyevs, Christoph Leicht, Philipp Mirovsky, Klaus Pierz, Hans W. Schumacher & Rolf J. Haug
We study a mesoscopic circuit of two quantized current sources, realized by nonadiabatic single-electron pumps connected in series with a small micron-sized island in between. We find that quantum transport through the second pump can be locked onto the quantized current of the first one by a feedback due to charging of the mesoscopic island. This is confirmed by a measurement of the charge variation on the island using a nearby charge detector. Finally, the...

Noise at a Fermi-edge singularity in self-assembled InAs quantum dots

Niels Maire, Frank Hohls, T. Lüdtke, Klaus Pierz & Rolf J. Haug
We present noise measurements of self-assembled InAs quantum dots at high magnetic field. In comparison to I-V characteristics at zero magnetic field, we notice a strong current overshoot that is due to a Fermi-edge singularity. We observe an enhanced suppression in the shot noise power simultaneous to the current overshoot that is attributed to the electron-electron interaction at the Fermi-edge singularity. © 2007 The American Physical Society.

Methods for intraoperative, sterile pose-setting of patient-specific microstereotactic frames

Benjamin Vollmann, Samuel Müller, Dennis Kundrat, Tobias Ortmaier & Lüder Alexander Kahrs
This work proposes new methods for a microstereotactic frame based on bone cement fixation. Microstereotactic frames are under investigation for minimal invasive temporal bone surgery, e.g. cochlear implantation, or for deep brain stimulation, where products are already on the market. The correct pose of the microstereotactic frame is either adjusted outside or inside the operating room and the frame is used for e.g. drill or electrode guidance. We present a patientspecific, disposable frame that allows...

Numerical modeling of a MEMS actuator considering several magnetic force calculation methods

Thomas Preisner, Christian Bolzmacher, Andreas Gerber, Karin Bauer, Eckhard Quandt & Wolfgang Mathis
Purpose: The purpose of this paper is to investigate the accuracy of different force calculation methods and their impact on mechanical deformations. For this purpose, a micrometer scaled actuator is considered, which consists of a micro-coil and of a permanent magnet (PM) embedded in a deformable elastomeric layer. Design/methodology/approach: For the magnetic field evaluation a hybrid numerical approach (finite element method/boundary element method (FEM/BEM) coupling and a FEM/BEM/Biot-Savart approach) is used, whereas FEM is implemented...

Influence of the channel design on the heat and mass exchange of induction channel furnace

E. Baake, A. Jakovics, S. Pavlovs & M. Kirpo
Purpose - The purpose of this paper is to present in-depth numerical modelling of heat and mass exchange in industrial induction channel furnace (ICF). Design/methodology/approach - The turbulent heat and mass exchange in the melt is calculated using a three-dimensional (3D) electromagnetic model and a 3D transient large eddy simulation method. The simulation model has been verified by flow velocity and temperature measurements, which were carried out using an industrial sized channel inductor operating with...

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