An alternative functional renormalization group approach to the single impurity Anderson model

We present an alternative functional renormalization group (fRG) approach to the single-impurity Anderson model at finite temperatures. Starting with the exact self-energy and interaction vertex of a small system ('core') containing a correlated site, we switch on the hybridization with a non-interacting bath in the fRG-flow and calculate spectra of the correlated site. Different truncations of the RG-flow-equations and choices of the core are compared and discussed. Furthermore we calculate the linear conductance and the magnetic susceptibility as functions of temperature and interaction strength. The signatures of Kondo physics arising in the flow are compared with numerical renormalization group results.Comment: 16 page

Internetbasierte Ermittlung von Preisbereitschaften

Durch die Möglichkeiten des Internet wird der Ruf in Wissenschaft und Praxis immer lauter, Kunden individuelle Produkte anzubieten, um somit deren Bedürfnisse vollständig zu befriedigen. Im Sinne dieses One-to-One-Marketing bietet das Internet auch die Chance, individuelle Preisbereitschaften von Kunden zu ermitteln. Das bekanntest Beispiel stellt wohl Ebay.com dar, welches Auktionen als Preisfindungsmechanismus einsetzt. Eine zweite Möglichkeit stellt das sog. Bietpreismodell dar. Dem Kunden wird hierbei die Gelegenheit geboten, den Preis für ein Produkt aus einer vorgegebenen Produktpalette vollständig selbst und unabhängig von Geboten anderer Teilnehmer zu bestimmen. Nur wenn das Kaufangebot des Kunden die Kosten des Anbieters nicht mehr deckt, wird dieses Angebot abgelehnt. Mit dieser Idee profitieren Anbieter wie Priceline.com einerseits davon, durch Abschöpfen der individuellen Zahlungsbereitschaften seiner Kunden die Deckungsbeiträge zu steigern. Ein besonderes Potential ist jedoch auch darin zu sehen, die individuellen Preisangaben der Kunden als Informationsgrundlage zu benutzen, um das Preismanagement in traditionellen oder anderen digitalen Absatzkanälen stärker an der Nachfrage auszurichten und die Preise so gewinnoptimal zu gestalten. So können in der vorliegenden Arbeit unterschiedliche Verläufe von Preis-Absatz-Funkionen auf Basis dieses Bietpreismodells für die Produktgattungen Telefon (lineares Modell), Designerstuhl (multiplikatives Modell), Scanner (Attraktionsmodell) und Computerspiel (Gutenbergmodell) ermittelt werden

ANNUAL DAYLIGHT SIMLUATIONS WITH EvalDRC: ASSESSING THE PERFORMANCE OF DAYLIGHT REDIRECTING COMPONENTS

EvalDRC is a newly developed daylight analysis tool for the evaluation of Daylight Redirecting Components (DRC) in architectural spaces. It focuses on the accurate simulation of light redirection with help of the lighting software environment RADIANCE. It employs various key technologies, among them are: a) the daylight coefficient method, b) characterisation of the light redirection behaviour of materials and specially designed systems with appropriate data models, and c) daylight metrics. We present several enhancements to these key technologies and the currently existing tools. In the context of daylight coefficients, we improve the solar contribution calculation by using realistic 0.5° solid angle sun primitives, thus generating True Sun coefficients. For simulating light redirection behaviour, we introduce Contribution Photon Mapping, a recent add-on to the RADIANCE environment. In addition, we introduce monthly breakdowns of the established daylight metrics Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE), to provide a more detailed assessment of DRC performance throughout the course of a year. The paper gives an overview of the mentioned annual daylight simulation key technologies, and explains how our enhancements and developments surpass the current approaches and lead to a versatile tool, capable of producing meaningful and detailed simulation results.  A description of the implementation and an application example is given, rounded off by a discussion of the current state of the ongoing work and a tentative outlook

MDAT- Aligning multiple domain arrangements

Background: Proteins are composed of domains, protein segments that fold independently from the rest of the protein and have a specific function. During evolution the arrangement of domains can change: domains are gained, lost or their order is rearranged. To facilitate the analysis of these changes we propose the use of multiple domain alignments. Results: We developed an alignment program, called MDAT, which aligns multiple domain arrangements. MDAT extends earlier programs which perform pairwise alignments of domain arrangements. MDAT uses a domain similarity matrix to score domain pairs and aligns the domain arrangements using a consistency supported progressive alignment method. Conclusion: MDAT will be useful for analysing changes in domain arrangements within and between protein families and will thus provide valuable insights into the evolution of proteins and their domains. MDAT is coded in C++, and the source code is freely available for download at http://www.bornberglab.org/pages/mda

Probing transport in quantum many-fermion simulations via quantum loop topography

Quantum many-fermion systems give rise to diverse states of matter that often reveal themselves in distinctive transport properties. While some of these states can be captured by microscopic models accessible to numerical exact quantum Monte Carlo simulations, it nevertheless remains challenging to numerically access their transport properties. Here we demonstrate that quantum loop topography (QLT) can be used to directly probe transport by machine learning current-current correlations in imaginary time. We showcase this approach by studying the emergence of superconducting fluctuations in the negative-U Hubbard model and a spin-fermion model for a metallic quantum critical point. For both sign-free models, we find that the QLT approach detects a change in transport in very good agreement with their established phase diagrams. These proof-of-principle calculations combined with the numerical efficiency of the QLT approach point a way to identify hitherto elusive transport phenomena such as non-Fermi liquids using machine learning algorithms.Comment: 7 pages, 5 figure

High-Precision Measurement of Sine and Pulse Reference Signals using Software-Defined Radio

This paper addresses simultaneous, high-precision measurement and analysis of generic reference signals by using inexpensive commercial off-the-shelf Software Defined Radio hardware. Sine reference signals are digitally down-converted to baseband for the analysis of phase deviations. Hereby, we compare the precision of the fixed-point hardware Digital Signal Processing chain with a custom Single Instruction Multiple Data (SIMD) x86 floating-point implementation. Pulse reference signals are analyzed by a software trigger that precisely locates the time where the slope passes a certain threshold. The measurement system is implemented and verified using the Universal Software Radio Peripheral (USRP) N210 by Ettus Research LLC. Applying standard 10 MHz and 1 PPS reference signals for testing, a measurement precision (standard deviation) of 0.36 ps and 16.6 ps is obtained, respectively. In connection with standard PC hardware, the system allows long-term acquisition and storage of measurement data over several weeks. A comparison is given to the Dual Mixer Time Difference (DMTD) and Time Interval Counter (TIC), which are state-of-the-art measurement methods for sine and pulse signal analysis, respectively. Furthermore, we show that our proposed USRP-based approach outperforms measurements with a high-grade Digital Sampling Oscilloscope.Comment: 10 pages, 15 figures, and 4 table