Low-energy local density of states of the 1D Hubbard model

We examine the local density of states (DOS) at low energies numerically and analytically for the Hubbard model in one dimension. The eigenstates represent separate spin and charge excitations with a remarkably rich structure of the local DOS in space and energy. The results predict signatures of strongly correlated excitations in the tunneling probability along finite quantum wires, such as carbon nanotubes, atomic chains or semiconductor wires in scanning tunneling spectroscopy (STS) experiments. However, the detailed signatures can only be partly explained by standard Luttinger liquid theory. In particular, we find that the effective boundary exponent can be negative in finite wires, which leads to an increase of the local DOS near the edges in contrast to the established behavior in the thermodynamic limit.Comment: 6 pages, 4 figures, more information can be found at http://www.physik.uni-kl.de/eggert/papers/index.htm

Opinion Monitor for Development Policy 2021: Media content, information, appeals and their impact on public opinion

The DEval Opinion Monitor 2021 examines five key questions: (1) How often and in what way does the media report on the topic of development policy? (2) What impact do arguments for and against development cooperation used in the media have on the general public’s attitude towards the topic? (3) What impact does information on the effectiveness of development cooperation projects have on attitudes towards the topic? (4) What role do moral arguments and various foundations of morality play in attitudes towards the topic? (5) What expectations do citizens have of development cooperation? The report also explores how public opinion on development policy and on specific development policy measures has developed during the coronavirus pandemic. Therefor, the DEval Opinion Monitor 2021 gives development policy decision-makers feedback on the general public’s attitudes to development policy. The publication follows the Opinion Monitor for Development Policy 2018 and the Opinion Monitor for Development Policy 2019, which examined attitudes towards development cooperation and sustainable development in Germany (2018) and media use with a focus on international reporting and global poverty (2019)

Feminist Development Policy: What does the Population think?

The continued lack of gender equality is an urgent global challenge. Against this backdrop, the German Federal Government announced in 2021 that it would include a feminist foreign policy in its coalition agreement. The aim of this policy is to strengthen the rights, representation and resources of women and marginalised groups and to promote the recognition of diversity. However, a feminist orientation in foreign and development policy meets with diverging views in political debate and provides cause for discussion in the (social) media. But what is the attitude of the general public? Aiming to answer this question, DEval examined public opinion on feminist development policy as part of its Opinion Monitor for Development Policy 2022. This Policy Brief summarises the results of the representative survey

Bending Strength and Stiffness of Caribbean Pine from Trinidad and Tobago

Small samples of Caribbean pine wood grown in Trinidad were measured for specific gravity, modulus of elasticity, and modulus of rupture in bending. Core and outer wood and samples from along the length of the tree were studied. Mechanical properties and specific gravity varied along and across the trees. Linear relationships between specific gravity and mechanical properties were better for the outer wood than for the core wood. Core wood was weaker than outer wood. The bolts varied in properties along the tree, with a maximum in the second 2-m bolt

Attitudes towards Development Policy in the Context of the War against Ukraine

Russia launched its war of aggression against Ukraine in February 2022. Global prices for energy and foodstuffs rose in part dramatically. Against this backdrop, the German Institute for Development Evaluation (DEval) has explored three questions based on a representative survey conducted by the Development Engagement Lab (DEL) in October 2022: 1. How does public perception of the state of the German economy correlate with approval for DC? 2. What attitudes do people have towards various development policy measures in response to the war against Ukraine? 3. How does agreement to such measures differ according to individuals' political orientation and assessment of the general state of the economy, and their own, personal economic situation and income

Sustainable Consumption in the face of Global Challenges: Opportunities and Obstacles; Findings of the DEval Opinion Monitor for Development Policy 2022

Sustainable consumption contributes to sustainable global development. Due to the interdependencies between consumption behaviour in industrialised countries and people's living conditions in countries of the Global South, the issue is also highly relevant to development policy. Up to now, however, there is hardly any evidence with regard to the extent that citizens perceive their own consumption as having a global impact. The DEval Opinion Monitor for Development Policy 2022 looked into this question. This Policy Brief summarises the findings of the study

Wigner crystal vs. Friedel oscillations in the 1D Hubbard model

We analyze the fermion density of the one-dimensional Hubbard model using bosonization and numerical DMRG calculations. For finite systems we find a relatively sharp crossover even for moderate short range interactions into a region with $4k_F$ density waves as a function of density. The results show that the unstable fixed point of a spin-incoherent state can dominate the physical behavior in a large region of parameter space in finite systems. The crossover may be observable in ultra cold fermionic gases in optical lattices and in finite quantum wires.Comment: 6 pages, 6 figures. Published version. The most recent file can be found at http://www.physik.uni-kl.de/eggert/papers/index.htm

Signatures of a Bardeen-Cooper-Schrieffer Polariton Laser

Microcavity exciton polariton systems can have a wide range of macroscopic quantum effects that may be turned into better photonic technologies. Polariton Bose-Einstein condensation (BEC) and photon lasing have been widely accepted in the limits of low and high carrier densities, but identification of the expected Bardeen-Cooper-Schrieffer (BCS) state at intermediate densities remains elusive. While all three phases feature coherent photon emission, essential differences exist in their matter media. Most studies to date characterize only the photon field. Here, using a microcavity with strong- and weak-couplings co-existing in orthogonal linear polarizations, we directly measure the electronic gain in the matter media of a polariton laser, demonstrating a BCS-like polariton laser above the Mott transition density. Theoretical analysis reproduces the absorption spectra and lasing frequency shifts, revealing an electron distribution function characteristic of a polariton BCS state but modified by incoherent pumping and dissipation

Meinungsmonitor Entwicklungspolitik 2018: Einstellungen zu Entwicklungszusammenarbeit und nachhaltiger Entwicklung

Die Studie befasst sich mit den Einstellungen, dem Wissen und dem Engagement der Bevölkerung Deutschlands zu Entwicklungspolitik, Entwicklungszusammenarbeit und globaler nachhaltiger Entwicklung. Sie stellt staatlichen und zivilgesellschaftlichen Akteuren in diesem Themenbereich aktuelle Informationen und Analysen bereit, die diese für die strategische Ausrichtung ihrer Arbeit sowie für die Kommunikations- und Bildungsarbeit nutzen können. Als Datenbasis dient im Wesentlichen der Aid Attitudes Tracker, eine ländervergleichende Panelbefragung, die seit 2013 Daten in Deutschland, Frankreich, Großbritannien und den USA erhebt