Electronic properties of EuB6 in the ferromagnetic regime: Half-metal versus semiconductor

To understand the halfmetallic ferromagnet EuB6 we use the Kondo lattice model for valence and conduction band. By means of a recently developed many-body theory we calculate the electronic properties in the ferromagnetic regime up to the Curie temperature. The decreasing magnetic order induces a transition from halfmetallic to semiconducting behavior along with a band broadening. We show the temperature dependence of the quasiparticle density of states and the quasiparticle dispersion as well as the effective mass, the number of carriers and the plasma frequency which are in good agreement with the experimental data

Natural path to the understanding and use of accounting: Barter bookkeeping and the double entry system, the case of Benjamin Barns Sayle

Barter bookkeeping was employed well into the 20th Century in some rural communities of the U.S. Those who used it often did so because it was adequate for their needs, not because they were unfamiliar with the double entry system. One such individual, Benjamin Barns Sayle, employed both systems simultaneously, to address the needs of his different enterprises. His story and records illustrate an almost natural progression in the understanding and use of accounting records from the limited, simple but effective barter bookkeeping system to the more expansive double entry system by individuals. Sayle\u27s experiences suggest that by emphasizing familiar barter transactions, students, even at the elementary school level might easily grasp some fundamentals of making journal entries. This paper suggests that simple barter bookkeeping exercises may be useful in engaging elementary school children in the AICPA 360 Degrees of Financial Literary Program and in developing a stronger appreciation for accounting. The simplicity of the system makes it easy enough for teachers with little background in accounting to grasp and employ as an enhancement to their existing curriculum

1.55-μm mode-locked quantum-dot lasers with 300 MHz frequency tuning range

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 106, 031114 (2015) and may be found at https://doi.org/10.1063/1.4906451.Passive mode-locking of two-section quantum-dot mode-locked lasers grown by metalorganic vapor phase epitaxy on InP is reported. 1250-μm long lasers exhibit a wide tuning range of 300 MHz around the fundamental mode-locking frequency of 33.48 GHz. The frequency tuning is achieved by varying the reverse bias of the saturable absorber from 0 to −2.2 V and the gain section current from 90 to 280 mA. 3 dB optical spectra width of 6–7 nm leads to ex-facet optical pulses with full-width half-maximum down to 3.7 ps. Single-section quantum-dot mode-locked lasers show 0.8 ps broad optical pulses after external fiber-based compression. Injection current tuning from 70 to 300 mA leads to 30 MHz frequency tuning.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/FP7/EU/264687/Postgraduate Research on Photonics as an Enabling Technology/PROPHE

Behaviour of the V²⁺ Ground State in Tetrahedrally Coordinated II–VI Semiconductors

The ground state of the lattice-neutral charge state of vanadium in tetrahedrally coordinated II—VI materials is a 4T1 term and is hence subject to a Jahn-Teller (JT) effect. In this paper photo-luminescence and EPR investigations on V2+ (3d3) in ZnS, ZnSe, ZnTe, and CdTe are combined with Tanabe-Sugano calculations including JT interaction. For ZnS the no-phonon structure is explained by a tunnelling splitting

Resource mattress. The potential of refuse materials

Mattresses are multi-material products whose exact composition is mostly unknown to the waste collector, so they can hardly be recycled and continue to be incinerated. Valuable resources are lost and no longer returned to the material cycle. Foam re-use and mechanical recycling account for only a negligible share of the market. The research presented here explores the potential of re-using mattresses as thermal and acoustic insulation for construction projects and attempts to find re-purpose in order to reduce waste and emissions, save resources and provide the insulation needed. This specific case study serves as a method to identify and demonstrate the flow and potential on a much larger scale. Considering comparable and possibly compatible properties of different foams this study explores the possibility of using them in a larger format. The approach is based on an unbiased exploration of the material, which only as a second step uses scientific methods to measure the intuitive exploration of the properties

Topology Optimization of Flow Problems Modeled by the Incompressible Navier-Stokes Equations

This work is concerned with topology optimization of incompressible flow problems. While size and shape optimization methods are limited to modifying existing boundaries, topology optimization allows for merging boundaries as well as creating new ones. Since topology optimization methods do not require a good initial guess, they are powerful tools for finding new and non-intuitive designs. The latter is particularly beneficial for flow problems which are typically nonlinear as well as transient. Depending on the complexity of the flow problem, predicting a solution may be challenging. Determining an improved or optimized design for complex flow problems is an even greater challenge as it not only requires a solution to the flow problem for a given design, but also a prediction on how a design change will affect the flow. Fluid topology optimization commonly uses a material interpolation approach for describing the geometry during the optimization process: solid material is modeled via an artificial porosity that penalizes the flow velocities. While this approach works well for simple steady-state problems aiming to minimize the dissipated energy, the current study shows that using the porosity approach may cause issues for more complex problems such as coupled fluid-structure-interaction (FSI) systems, unsteady flow problems or problems aiming to match a target performance. To overcome these issues a geometric boundary description based on level sets is developed. This geometric boundary description is applied to both, a steady-state hydrodynamic lattice Boltzmann formulation and a stabilized finite element formulation of the steady-state Navier-Stokes equations. The enforcement of the no-slip condition along the fluid-solid interface is handled via an immersed boundary technique in case of the lattice Boltzmann method, while the Navier-Stokes formulation uses an extended finite element method (XFEM). Through the research conducted in this work, the spectrum of flow problems that can be solved by topology optimization techniques has been broadened significantly

"Rethinking global sisterhood"

Die vorliegende Arbeit beschäftigt sich mit dem Gender Diskurs der Internationalen Entwicklung vor dem Hintergrund von postkolonialer feministischer Kritik. Anhand einer Diskursanalyse der Dokumente der zwei UN-Weltfrauenkonferenzen 1985 in Nairobi und 1995 in Peking werden diskursive Prozesse und Verschiebungen in Bezug auf zwei zentrale Kritikpunkte postkolonialer Feministinnen herausgearbeitet: Auf der strukturellen Ebene interessiert die Auseinandersetzung mit Geschlechterverhältnissen: Wie werden diese beschrieben und gedacht? Von welchen Annahmen über Machtbeziehungen und Geschlecht gehen die Dokumente aus? Auf der Ebene der Identitäten steht der Umgang mit Kategorien und Differenzierungsprozessen im Zentrum der Analyse: Wie gehen die Dokumente mit Identitäten und Kategorien um? Gibt es (systematische) Differenzierungen? Spielen strukturelle Kategorien wie Ethnizität, Klasse, Behinderung, etc. eine Rolle? Als methodisches Rahmengerüst dient Siegfried Jägers Konzept der kritischen Diskursanalyse