The Weak-Coupling Limit of 3D Simplicial Quantum Gravity

We investigate the weak-coupling limit, kappa going to infinity, of 3D simplicial gravity using Monte Carlo simulations and a Strong Coupling Expansion. With a suitable modification of the measure we observe a transition from a branched polymer to a crinkled phase. However, the intrinsic geometry of the latter appears similar to that of non-generic branched polymer, probable excluding the existence of a sensible continuum limit in this phase.Comment: 3 pages 4 figs. LATTICE99(Gravity

Dose-area product measurements during Barium enema radiograph examinations -a Western Cape study

The aim of this study was to obtain a direct measurement of the typical dose delivered to an average adult patient during a barium enema examination. Measurement was done on a sample of 50 patients at three departments, using a dose-area product (DAP) meter. The comparison of the results with UK median levels indicates that the doses measured in South Africa are higher (41 Gy cm2 (dose x area) v. 48 Gy cm2 ). Patient protection can be improved by comparing local practice with national reference levels. The values obtained in this study (first quartile 35 Gy cm2, median 48 Gy cm2, third quartile 84 Gy cm2) are recommended as initial reference dose levels for barium enemas in South Africa

Continuous similarity transformation for critical phenomena: easy-axis antiferromagnetic XXZ model

We apply continuous similarity transformations (CSTs) to the easy-axis antiferromagnetic XXZ-model on the square lattice. The CST flow equations are truncated in momentum space by the scaling dimension $d$ so that all contributions with $d\le 2$ are taken into account. The resulting quartic magnon-conserving effective Hamiltonian is analyzed in the zero-, one-, and two-magnon sector. In this way, a quantitative description of the ground-state energy, the one-magnon dispersion and its gap as well as of two-magnon bound states is gained for anisotropies ranging from the gapped Ising model to the gapless Heisenberg model. We discuss the critical properties of the gap closing as well as the evolution of the one-magnon roton mininum. The excitation energies of two-magnon bound states are calculated and their decay into the two-magnon continuum is determined via the inverse participation ratio.Comment: 12 pages, 8 figure

Analytical pre-test support of boil-down test QUENCH-11

Analytische Unterstützung zur Vorbereitung des Ausdampf-Versuchs QUENCH-11 Im QUENCH-Vorhaben des Forschungszentrums Karlsruhe soll das Fluten eines teilweise zerstörten Kerns untersucht werden. Der zweite LACOMERA Versuch Q-L2 (QUENCH-11) beginnt mit einer Ausdampfphase des Bündels, bis der Wasserspiegel das untere Bündel¬ende erreicht hat. Ein derartiger Versuch wurde bislang noch nicht in der QUENCH-Anlage durchgeführt, so dass mit SCDAP/RELAP5 mod3.2.irs eine Machbarkeitsstudie erforderlich war. Die Ergebnisse zeigen, dass eine Zusatzheizung im unteren Plenum notwendig ist, um den Wasserstand und die Verdampfungsrate (Dampfmassenstrom in der Ausdampfphase) unabhängig von der angestrebten Maximaltemperatur im Bündel zu regeln. Für eine verläss¬liche Versuchsplanung sowie zur Erstellung der Energiebilanz muss die Zusatzheizung in¬nerhalb des unteren Plenums unterhalb der Wasseroberfläche installiert werden, damit die Heizleistung vollständig in das Wasser eingekoppelt wird. Um die Verdampfungsrate über längere Zeit aufrecht zu erhalten, muss zusätzlich Wasser in das untere Plenum eingespeist werden. Anhand dieser Rechnungen wird der Testablauf im Detail diskutiert. Eine entsprechende Studie zeigte die Durchführbarkeit eines solchen Ausdampftests und war die Grundlage für die oben erwähnten Änderungen in der Anlage und der Versuchs-Durchführung gegenüber früheren Tests. Eine Reihe von Vorversuche wurde durchgeführt, um die Brauchbarkeit der Änderungen an der Anlage und der geplanten Versuchsführung zu prüfen und um Daten für das thermohydraulische Verhalten der Anlage zu bekommen, an denen die Code-Modelle für die Voraus- und Nachrechnungen von QUENCH-11 getestet werden können. Im Anschluss an die Vorversuche wurden wie bei früheren QUENCH-Tests detaillierte Vorausrechnungen mit verschiedenen Codes zu Versuchsablauf und -steuerung durchgeführt. Drei Forschungs¬einrichtungen in der EU waren beteiligt. Die berechneten Ergebnisse reagieren empfindlich auf Änderungen der Versuchsparameter wie das anfängliche axiale Temperaturprofil und die eingespeiste elektrische Leistung, wie es auch für die untersuchten physikalischen Bedin¬gungen im Versuch erwartet werden kann

Signature of Electronic Correlations in the Optical Conductivity of the Doped Semiconductor Si:P

Electronic transport in highly doped but still insulating silicon at low temperatures is dominated by hopping between localized states; it serves as a model system of a disordered solid for which the electronic interaction can be investigated. We have studied the frequency-dependent conductivity of phosphorus-doped silicon in the THz frequency range (30 GHz to 3 THz) at low temperatures $T\geq 1.8$ K. The crossover in the optical conductivity from a linear to a quadratic frequency dependence as predicted by Efros and Shklovskii is observed qualitatively; however, the simple model does not lead to a quantitative agreement. Covering a large range of donor concentration, our temperature- and frequency-dependent investigations reveal that electronic correlation effects between the localized states play an important and complex role at low temperatures. In particular we find a super-linear frequency dependence of the conductivity that highlights the influence of the density of states, i.e. the Coulomb gap, on the optical conductivity. When approaching the metal-to-insulator transition by increasing doping concentration, the dielectric constant and the localization length exhibit critical behavior.Comment: 9 pages, 8 figures, 1 tabl

Drone-based photogrammetry combined with deep-learning to estimate hail size distributions and melting of hail on the ground

Hail is a major threat associated with severe thunderstorms and an estimation of the hail size is important for issuing warnings to the public. Operational radar products exist that estimate the size of the expected hail. For the verification of such products, ground based observations are necessary. Automatic hail sensors, as for example within the Swiss hail network, record the kinetic energy of hailstones and can estimate with this the hail diameters. However, due to the small size of the observational area of these sensors (0.2 m2) the estimation of the hail size distribution (HSD) can have large uncertainties. To overcome this issue, we combine drone-based aerial photogrammetry with a state-of-the-art custom trained deep-learning object detection model to identify hailstones in the images and estimate the HSD in a final step. This approach is applied to photogrammetric image data of hail on the ground from a supercell storm, that crossed central Switzerland from southwest to northeast in the afternoon of June 20, 2021. The hail swath of this intense right-moving supercell was intercepted a few minutes after the passage at a soccer field near Entlebuch (Canton Lucerne, Switzerland) and aerial images of the hail on the ground were taken by a commercial DJI drone, equipped with a 50 megapixels full frame camera system. The average ground sampling distance (GSD) that could be reached was 1.5 mm per pixel, which is set by the mounted camera objective with a focal length of 35 mm and a flight altitude of 12 m above ground. A 2D orthomosaic model of the survey area (750 m2) is created based on 116 captured images during the first drone mapping flight. Hail is then detected by using a region-based Convolutional Neural Network (Mask R-CNN). We first characterize the hail sizes based on the individual hail segmentation masks resulting from the model detections and investigate the performance by using manual hail annotations by experts to generate validation and test data sets. The final HSD, composed of 18209 hailstones, is compared with nearby automatic hail sensor observations, the operational weather radar based hail product MESHS (Maximum Expected Severe Hail Size) and some crowdsourced hail reports. Based on the retrieved drone hail data set, a statistical assessment of sampling errors of hail sensors is carried out. Furthermore, five repetitions of the drone-based photogrammetry mission within about 18 min give the unique opportunity to investigate the hail melting process on the ground for this specific supercell hailstorm and location