First and second order ferromagnetic transition at T=0 in a 1D itinerant system

We consider a modified version of the one-dimensional Hubbard model, the t1-t2 Hubbard chain, which includes an additional next-nearest-neighbor hopping. It has been shown that at weak coupling this model has a Luttinger liquid phase or a spin liquid phase depending upon the ratio of t2 to t1. Additionally if the on-site interaction U is large enough, the ground state is fully polarized. Using exact diagonalization and the density-matrix renormalization group, we show that the transition to the ferromagnetic phase is either of first or second order depending on whether the Luttinger liquid or spin liquid is being destabilized. Since we work at T=0, the second order transition is a quantum magnetic critical point

Cavity-induced damping and level shifts in a wide aperture spherical resonator

We calculate explicitly the space dependence of the radiative relaxation rates and associated level shifts for a dipole placed in the vicinity of the center of a spherical cavity with a large numerical aperture and a relatively low finesse. In particular, we give simple and useful analytic formulas for these quantities, that can be used with arbitrary mirrors transmissions. The vacuum field in the vicinity of the center of the cavity is actually equivalent to the one obtained in a microcavity, and this scheme allows one to predict significant cavity QED effects.Comment: 28 pages, 5 figures. In v2 some references and appendices adde

Caenorhabditis nomenclature

Genetic nomenclature allows the genetic features of an organism to be structured and described in a uniform and systematicway. Genetic features, including genes, variations (both natural and induced), and gene products, are assigned descriptorsthat inform on the nature of the feature. These nomenclature designations facilitate communication among researchers (in publications,presentations, and databases) to advance understanding of the biology of the genetic feature and the experimental utilizationof organisms that contain the genetic feature. The nomenclature system that is used for C. elegans was first employed by Sydney Brenner (1974) in his landmark description of the genetics of this model organism, and then substantially extended and modified in Horvitz et al., 1979. The gene, allele, and chromosome rearrangement nomenclature, described below, is an amalgamation of that from bacteria andyeast, with the rearrangement types from Drosophila. The nomenclature avoids standard words, subscripts, superscripts, and Greek letters and includes a hyphen (-) to separatethe gene name from gene number (distinct genes with similar phenotypes or molecular properties). As described by Jonathan Hodgkin, ‘the hyphen is about 1 mm in length in printed text and therefore symbolizes the 1 mm long worm’. These nomenclature propertiesmake C. elegans publications highly suitable for informatic text mining, as there is minimal ambiguity. From the founding of the CaenorhabditisGenetics Center (CGC) in 1979 until 1992, Don Riddle and Mark Edgley acted as the central repository for genetic nomenclature. Jonathan Hodgkin was nomenclature czar from 1992 through 2013; this was a pivotal period with the elucidation of the genome sequence of C. elegans, and later that of related nematodes, and the inception of WormBase. Thus, under the guidance of Hodgkin, the nomenclature system became a central feature of WormBase and the number and types of genetic features significantly expanded. The nomenclature system remains dynamic, with recentadditions including guidelines related to genome engineering, and continued reliance on the community for input. WormBase assigns specific identifying codes to each laboratory engaged in dedicated long-term genetic research on C. elegans. Each laboratory is assigned a laboratory/strain code for naming strains, and an allele code for naming genetic variation(e.g., mutations) and transgenes. These designations are assigned to the laboratory head/PI who is charged with supervisingtheir organization in laboratory databases and their associated biological reagents that are described on WormBase, in publications, and distributed to the scientific community on request. The laboratory/strain code is used: a) to identifythe originator of community-supplied information on WormBase, which, in addition to attribution, facilitates communicationbetween the community/curators and the originator if an issue related to the information should arise at a later date; andb) to provide a tracking code for activities at the CGC. The laboratory/strain designation consists of 2-3 uppercase letters while the allele designation has 1-3 lowercase letters.The final letter of a laboratory code should not be an “O” or an “I” so as not to be mistaken for the numbers “0” or “1” respectively.Additionally, allele designations should also not end with the letter “l” which could also be mistaken for the number “1.” These codes are listed at the CGC and in WormBase. Investigators generating strains, alleles, transgenes, and/or defining genes require these designations and should applyfor them at [email protected]. Information for several other nematode species, in addition to C. elegans, is curated at WormBase. All species are referred to by their Linnean binomial names (e.g,. Caenorhabditis elegans or C. elegans). Details of all the genomes available at WormBase and the degree of their curation can be found at www.wormbase.org/species/al

Computational Inorganic and Analytical Chemistry

Our research activity in computational chemistry at the university of Fribourg is briefly presented including topics like: Electronic structure calculation of coordination compounds, density functional theory, multiplet structure calculation, modelling the optical and magnetic properties of metal complexes and inorganic materials, molecular dynamics, redox polymers, thin layer cells

Low density ferromagnetism in the Hubbard model

A single-band Hubbard model with nearest and next-nearest neighbour hopping is studied for $d=1$, 2, 3, using both analytical and numerical techniques. In one dimension, saturated ferromagnetism is found above a critical value of $U$ for a band structure with two minima and for small and intermediate densities. This is an extension of a scenario recently proposed by M\"uller--Hartmann. For three dimensions and non-pathological band structures, it is proven that such a scenario does not work.Comment: 4 pages, 3 postscript figure

Total Ionizing Dose Effects in MOSFET Devices at 77 K

Total ionizing dose effects on thermal oxide and reoxidized nitrided oxide (RNO) MOSFET devices at 77 K were studied. The MOSFETs were immersed in liquid nitrogen and irradiated, using a 60Co source, up to 1 Mrad(Si) at a dose rate of 107 rads(Si)-sec. Drain current-gate voltage characteristics were obtained and used to determine threshold voltage and transconductance. At 77 K the subthreshold slopes indicated no observed buildup of interface states in any of the transistors. Furthermore, all transistors experienced very little change in the transconductance. Typical negative shifts in threshold voltage as dose increased were observed in all of the thermal oxide devices. The threshold voltage shifts of the RNO devices were typically less than those for thermal oxide devices

Electronic fine structure calculation of metal complexes with three-open-shell s, d, and p configurations

The ligand field density functional theory (LFDFT) algorithm is extended to treat the electronic structure and properties of systems with three-open-shell electron configurations, exemplified in this work by the calculation of the core and semi-core 1s, 2s, and 3s one-electron excitations in compounds containing transition metal ions. The work presents a model to non-empirically resolve the multiplet energy levels arising from the three-open-shell systems of non-equivalent ns, 3d, and 4p electrons and to calculate the oscillator strengths corresponding to the electric-dipole 3dm → ns13dm4p1 transitions, with n = 1, 2, 3 and m = 0, 1, 2, …, 10 involved in the s electron excitation process. Using the concept of ligand field, the Slater-Condon integrals, the spin-orbit coupling constants, and the parameters of the ligand field potential are determined from density functional theory (DFT). Therefore, a theoretical procedure using LFDFT is established illustrating the spectroscopic details at the atomic scale that can be valuable in the analysis and characterization of the electronic spectra obtained from X-ray absorption fine structure or electron energy loss spectroscopies