High-field vortices in Josephson junctions with alternating critical current density

We study long Josephson junctions with the critical current density alternating along the junction. New equilibrium states, which we call the field synchronized or FS states, are shown to exist if the applied field is from narrow intervals centered around equidistant series of resonant fields, $H_m$. The values of $H_m$ are much higher than the flux penetration field, $H_s$. The flux per period of the alternating critical current density, $\phi_i$, is fixed for each of the FS states. In the $m$-th FS state the value of $\phi_i$ is equal to an integer amount of flux quanta, $\phi_i =m\phi_0$. Two types of single Josephson vortices carrying fluxes $\phi_0$ or/and $\phi_0/2$ can exist in the FS states. Specific stepwise resonances in the current-voltage characteristics are caused by periodic motion of these vortices between the edges of the junction.Comment: 4 pages, 5 figure

Clar Sextet Analysis of Triangular, Rectangular and Honeycomb Graphene Antidot Lattices

Pristine graphene is a semimetal and thus does not have a band gap. By making a nanometer scale periodic array of holes in the graphene sheet a band gap may form; the size of the gap is controllable by adjusting the parameters of the lattice. The hole diameter, hole geometry, lattice geometry and the separation of the holes are parameters that all play an important role in determining the size of the band gap, which, for technological applications, should be at least of the order of tenths of an eV. We investigate four different hole configurations: the rectangular, the triangular, the rotated triangular and the honeycomb lattice. It is found that the lattice geometry plays a crucial role for size of the band gap: the triangular arrangement displays always a sizable gap, while for the other types only particular hole separations lead to a large gap. This observation is explained using Clar sextet theory, and we find that a sufficient condition for a large gap is that the number of sextets exceeds one third of the total number of hexagons in the unit cell. Furthermore, we investigate non-isosceles triangular structures to probe the sensitivity of the gap in triangular lattices to small changes in geometry

HST Observations of the Host Galaxy of GRB970508

We report on observations of the field of GRB~970508 made in early August 1998, 454 days after outburst, with the STIS CCD camera onboard the Hubble Space Telescope. The images, taken in open filter (50CCD) mode, clearly reveal the presence of a galaxy which was obscured in earlier (June 1997) HST images by emission from the optical transient (OT). The galaxy is regular in shape: after correcting for the HST/STIS PSF, it is well-fitted by an exponential disk with a scale length of 0."046 +/- 0."006 and an ellipticity of 0.70 +/- 0.07. All observations are marginally consistent with a continuous decline in OT emission as t^{-1.3} beginning two days after outburst; however, we find no direct evidence in the image for emission from the OT, and the surface brightness profile of the galaxy is most regular if we assume that the OT emission is negligible, suggesting that the OT may have faded more rapidly at late times than is predicted by the power-law decay. Due to the wide bandwidth of the STIS clear mode, the estimated magnitude of the galaxy is dependent on the galaxy spectrum that is assumed. Using colors obtained from late-time ground-based observations to constrain the spectrum, we find V = 25.4 +/- 0.15, a few tenths of a magnitude brighter than earlier ground-based estimates that were obtained by observing the total light of the galaxy and the OT and then subtracting the estimated OT brightness assuming it fades as a single power-law. This again suggests that the OT may have faded faster at late time than the power-law predicts. The position of the OT agrees with that of the isophotal center of the galaxy to 0."01. This remarkable agreement raises the possibility that the GRB may have been associated with either an active galactic nucleus or a nuclear starburst.Comment: Submitted to the Astrophysical Journal (Letters). Thirteen pages, three encapsulated figures. Abstract slightly abridge

Reporting radiographers in Europe survey: Support, role satisfaction, and advanced clinical practice within the European federation of radiographer society (EFRS) member countries.

Increasing number of radiographers are undertaking image reporting throughout Europe. However, there are variations in practice and experience in European countries. The study aim was to investigate reporting radiographer's perceptions in relation to support for their role and workload satisfaction and elements of advanced practice that may also be undertaken. Following institutional ethical approval an online 34 item questionnaire survey was circulated via social media; Twitter, Facebook, and LinkedIn in a 12-week period in 2022 across Europe. The survey data were managed by the online secure database REDCap (Research Electronic Data Capture). Data was collected across a range of questions, of which those relating to support for, and barriers to radiographer reporting, role and job satisfaction, and other role elements are reported here. A response level of 345 individual reporting radiographers replied to the survey from 15 European countries; some questions were optional and therefore had a lower response rate. There was consensus about the need for support from radiologists and management, protected time, and funding to support the reporting role. The majority of respondents received additional pay for taking on this role and expressed satisfaction with their role and workload. In relation to elements of advanced practice, the majority of respondents were involved in educational and managerial activities, and there was interest, but limited involvement, in research. There was a consensus about the support needed, and perceived barriers to, radiographer reporting, between reporting radiographers from different countries. Whilst there is some commonality in relation to activities such as supervision and education, there was clearer variety in relation to opportunities for research between the respondents, perhaps reflecting the differences between reporting as a standalone role development and reporting as part of an advanced clinical practice role. As there is increasingly an emphasis on advanced clinical practice, reporting radiographers are likely to require support to develop their skills so that they can actively participate in the broader activities associated with this role, including education, leadership, and research. [Abstract copyright: Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.

Landmænds opfattelser af natur og aktuel naturkvalitet på bedriften. Cross cutting rapport for CC3

Landmanden er en væsentlig aktør i forhold til at udvikle og forbedre natur og landskabskvaliteter på de økologiske bedrifter. Spørgsmålet er imidlertid, om der er en sammenhæng mellem den måde landmanden opfatter værdier i natur og landskab på, den måde han handler og forvalter i forhold til disse værdier, og så den naturkvalitet han set udfra en biologisk synsvinkel har på sin bedrift. Det spørgsmål blev der arbejdet med i en cross cutting øvelse i projektet Naturkvalitet i økologisk jordbrug

Conjugation-Length Dependence of Spin-Dependent Exciton Formation Rates in Pi-Conjugated Oligomers and Polymers

We have measured the ratio, r = $\sigma_S/\sigma_T$ of the formation cross section, $\sigma$ of singlet ($\sigma_S$) and triplet ($\sigma_T$) excitons from oppositely charged polarons in a large variety of $\pi$-conjugated oligomer and polymer films, using the photoinduced absorption and optically detected magnetic resonance spectroscopies. The ratio r is directly related to the singlet exciton yield, which in turn determines the maximum electroluminescence quantum efficiency in organic light emitting diodes (OLED). We discovered that r increases with the conjugation length, CL; in fact a universal dependence exists in which $r^{-1}$ depends linearly on $CL^{-1}$, irrespective of the chain backbone structure. These results indicate that $\pi$-conjugated polymers have a clear advantage over small molecules in OLED applications.Comment: 5 pages, 4 figure

Trees with Given Stability Number and Minimum Number of Stable Sets

We study the structure of trees minimizing their number of stable sets for given order $n$ and stability number $\alpha$. Our main result is that the edges of a non-trivial extremal tree can be partitioned into $n-\alpha$ stars, each of size $\lceil \frac{n-1}{n-\alpha} \rceil$ or $\lfloor \frac{n-1}{n-\alpha}\rfloor$, so that every vertex is included in at most two distinct stars, and the centers of these stars form a stable set of the tree.Comment: v2: Referees' comments incorporate

On the algebra of quantum observables for a certain gauge model

We prove that the algebra of observables of a certain gauge model is generated by unbounded elements in the sense of Woronowicz. The generators are constructed from the classical generators of invariant polynomials by means of geometric quantization.Comment: 29 pages, 2 figure

Weak localisation, hole-hole interactions and the "metal"-insulator transition in two dimensions

A detailed investigation of the metallic behaviour in high quality GaAs-AlGaAs two dimensional hole systems reveals the presence of quantum corrections to the resistivity at low temperatures. Despite the low density ($r_{s}>10$) and high quality of these systems, both weak localisation (observed via negative magnetoresistance) and weak hole-hole interactions (giving a correction to the Hall constant) are present in the so-called metallic phase where the resistivity decreases with decreasing temperature. The results suggest that even at high $r_{s}$ there is no metallic phase at T=0 in two dimensions.Comment: 5 pages, 4 figure