Zero field muon spin lattice relaxation rate in a Heisenberg ferromagnet at low temperature

We provide a theoretical framework to compute the zero field muon spin relaxation rate of a Heisenberg ferromagnet at low temperature. We use the linear spin wave approximation. The rate, which is a measure of the spin lattice relaxation induced by the magnetic fluctuations along the easy axis, allows one to estimate the magnon stiffness constant.Comment: REVTeX 3.0 manuscript, 5 pages, no figure. Published in Phys. Rev. B 52, 9155 (1995

High-resolution radio imaging of two luminous quasars beyond redshift 4.5

Context. Radio-loud active galactic nuclei in the early Universe are rare. The quasars J0906+6930 at redshift z=5.47 and J2102+6015 at z=4.57 stand out from the known sample with their compact emission on milliarcsecond (mas) angular scale with high (0.1-Jy level) flux densities measured at GHz radio frequencies. This makes them ideal targets for very long baseline interferometry (VLBI) observations. Aims. By means of VLBI imaging we can reveal the inner radio structure of quasars and model their brightness distribution to better understand the geometry of the jet and the physics of the sources. Methods. We present sensitive high-resolution VLBI images of J0906+6930 and J2102+6015 at two observing frequencies, 2.3 and 8.6 GHz. The data were taken in an astrometric observing programme involving a global five-element radio telescope array. We combined the data from five different epochs from 2017 February to August. Results. For one of the highest redshift blazars known, J0906+6930, we present the first-ever VLBI image obtained at a frequency below 8 GHz. Based on our images at 2.3 and 8.6 GHz, we confirm that this source has a sharply bent helical inner jet structure within ~3 mas from the core. The quasar J2102+6015 shows an elongated radio structure in the east-west direction within the innermost ~2 mas that can be described with a symmetric three-component brightness distribution model at 8.6 GHz. Because of their non-pointlike mas-scale structure, these sources are not ideal as astrometric reference objects. Our results demonstrate that VLBI observing programmes conducted primarily with astrometric or geodetic goals can be utilized for astrophysical purposes as well.Comment: 8 pages, 3 figures, accepted for publication in Astronomy & Astrophysic

Genes, Economics, and Happiness

We explore the influence of genetic variation on subjective well-being by employing a twin design and genetic association study. In a nationally-representative twin sample, we first show that about 33% of the variation in life satisfaction is explained by genetic variation. Although previous studies have shown that baseline happiness is significantly heritable, little research has considered molecular genetic associations with subjective well-being. We study the relationship between a functional polymorphism on the serotonin transporter gene (5-HTTLPR) and life satisfaction. We initially find that individuals with the longer, transcriptionally more efficient variant of this genotype report greater life satisfaction (n=2,545, p=0.012). However, our replication attempts on independent samples produce mixed results indicating that more work needs to be done to better understand the relationship between this genotype and subjective well-being. This work has implications for how economists think about the determinants of utility, and the extent to which exogenous shocks might affect individual well-being.life satisfaction, twin study, genetic association, serotonin transporter gene, 5-HTTLPR, rs2020933

Genes, Economics and Happiness

A major finding from research into the sources of subjective well-being is that individuals exhibit a "baseline" level of happiness. We explore the influence of genetic variation by employing a twin design and genetic association study. We first show that about 33% of the variation in happiness is explained by genes. Next, using two independent data sources, we present evidence that individuals with a transcriptionally more efficient version of the serotonin transporter gene (SLC6A4) report significantly higher levels of life satisfaction. These results are the first to identify a specific gene that is associated with happiness and suggest that behavioral models benefit from integrating genetic variation.wellbeing, socio-demographics, happiness, genetics, life satisfaction

Conformations of confined biopolymers

Nanoscale and microscale confinement of biopolymers naturally occurs in cells and has been recently achieved in artificial structures designed for nanotechnological applications. Here, we present an extensive theoretical investigation of the conformations and shape of a biopolymer with varying stiffness confined to a narrow channel. Combining scaling arguments, analytical calculations, and Monte Carlo simulations, we identify various scaling regimes where master curves quantify the functional dependence of the polymer conformations on the chain stiffness and strength of confinement.Comment: 5 pages, 4 figures, minor correction

Fluctuation-Dissipation Theorem for the Microcanonical Ensemble

A derivation of the Fluctuation-Dissipation Theorem for the microcanonical ensemble is presented using linear response theory. The theorem is stated as a relation between the frequency spectra of the symmetric correlation and response functions. When the system is not in the thermodinamic limit, this result can be viewed as an extension of the fluctuation-dissipation relations to a situation where dynamical fluctuations determine the response. Therefore, the relation presented here between equilibrium fluctuations and response can have a very different physical nature from the usual one in the canonical ensemble. These considerations imply that the Fluctuation-Dissipation Theorem is not restricted to the context of thermal equilibrium, where it is usually derived. Dispersion relations and sum rules are also obtained and discussed in the present case. Although analogous to the Kramers-Kronig relations, they are not related to the frequency spectrum but to the energy dependence of the response function.Comment: 15 pages, v3: final version, new text added, new reference

Critical dynamics of ballistic and Brownian particles in a heterogeneous environment

The dynamic properties of a classical tracer particle in a random, disordered medium are investigated close to the localization transition. For Lorentz models obeying Newtonian and diffusive motion at the microscale, we have performed large-scale computer simulations, demonstrating that universality holds at long times in the immediate vicinity of the transition. The scaling function describing the crossover from anomalous transport to diffusive motion is found to vary extremely slowly and spans at least 5 decades in time. To extract the scaling function, one has to allow for the leading universal corrections to scaling. Our findings suggest that apparent power laws with varying exponents generically occur and dominate experimentally accessible time windows as soon as the heterogeneities cover a decade in length scale. We extract the divergent length scales, quantify the spatial heterogeneities in terms of the non-Gaussian parameter, and corroborate our results by a thorough finite-size analysis.Comment: 14 page

Extended polarized semiclassical model for quantum-dot cavity QED and its application to single-photon sources

We present a simple extension of the semi-classical model for a two-level system in a cavity, in order to incorporate multiple polarized transitions, such as those appearing in neutral and charged quantum dots (QDs), and two nondegenerate linearly polarized cavity modes. We verify the model by exact quantum master equation calculations, and experimentally using a neutral QD in a polarization non-degenerate micro-cavity, in both cases we observe excellent agreement. Finally, the usefulness of this approach is demonstrated by optimizing a single-photon source based on polarization postselection, where we find an increase in the brightness for optimal polarization conditions as predicted by the model.Comment: 8 pages, for simple code see https://doi.org/10.5281/zenodo.347666

The impact of resource dependence of the mechanisms of life on the spatial population dynamics of an in silico microbial community

Biodiversity has a critical impact on ecosystem functionality and stability, and thus the current biodiversity crisis has motivated many studies of the mechanisms that sustain biodiversity, a notable example being non-transitive or cyclic competition. We therefore extend existing microscopic models of communities with cyclic competition by incorporating resource dependence in demographic processes, characteristics of natural systems often oversimplified or overlooked by modellers. The spatially explicit nature of our individual-based model of three interacting species results in the formation of stable spatial structures, which have significant effects on community functioning, in agreement with experimental observations of pattern formation in microbial communities. Published by AIP Publishing