Renormalization group analysis of competing quantum phases in the J1-J2 Heisenberg model on the kagome lattice

Recent discoveries in neutron scattering experiments for Kapellasite and Herbertsmithite as well as theoretical calculations of possible spin liquid phases have revived interest in magnetic phenomena on the kagome lattice. We study the quantum phase diagram of the S=1/2 Heisenberg kagome model as a function of nearest neighbor coupling J1 and second neighbor coupling J2. Employing the pseudofermion functional renormalization group, we find four types of magnetic quantum order (q=0 order, cuboc order, ferromagnetic order, and Sqrt{3}x\Sqrt{3} order) as well as extended magnetically disordered regions by which we specify the possible parameter regime for Kapellasite. In the disordered regime J2/J1<<1, the flatness of the magnetic susceptibility at the zone boundary which is observed for Herbertsmithite can be reconciled with the presence of small J2>0 coupling. In particular, we analyze the dimer susceptibilities related to different valence bond crystal (VBC) patterns, which are strongly inhomogeneous indicating the rejection of VBC order in the RG flow.Comment: 4+e pages, 3 figures; 2 pages of supplementary materia

Evaluating general purpose automated theorem proving systems

AbstractA key concern of ATP research is the development of more powerful systems, capable of solving more difficult problems within the same resource limits. In order to build more powerful systems, it is important to understand which systems, and hence which techniques, work well for what types of problems. This paper deals with the empirical evaluation of general purpose ATP systems, to determine which systems work well for what types of problems. This requires also dealing with the issues of assigning ATP problems into classes that are reasonably homogeneous with respect to the ATP systems that (attempt to) solve the problems, and assigning ratings to problems based on their difficulty

Alternatives Verfahren für die Störfestigkeitsprüfung von elektronischen Messwandlern in Schaltanlagen

Mittelspannungsschaltanlagen ermöglichen in Energieversorgungsnetzen eine Änderung der Netztopologie, bzw. den selektiven Schutz des Netzes im Fehlerfall. Schalthandlungen in den Mittelspannungskreisen verursachen Vorund Rückzündungslichtbögen, die transiente Überspannungen mit kurzen Anstiegszeiten zur Folge haben. Diese breitbandigen Transienten koppeln auf die Niederspannungsseite über und wirken dort auf die elektronischen Schutzund Steuereinheiten (engl. intelligent electronic devices, kurz: IEDs) ein. Um das Risiko einer Fehlfunktion des Netzschutzes zu minimieren sind für die analogen Eingänge eines IEDs spezielle Typprüfungen vorgesehen. Durch die zunehmende Verbreitung von elektronischen Messwandlern nach IEC 60044-8, wie z.B. Rogowski-Sensoren, ergeben sich Unsicherheiten in Bezug auf das genormte Prüfverfahren. In diesem Beitrag werden die Unterschiede zwischen den konventionellen Stromwandlern (engl. current transformer, kurz: CT) und der neuen Technik vorgestellt. Beide Technologien werden hinsichtlich der Koppelpfade für Störgrößen verglichen. Anschließend werden das genormte Prüfverfahren und die Probleme bei dessen Anwendung auf IEDs mit elektronischen Messwandlern beschrieben. Es wird ein alternatives Prüfverfahren vorgeschlagen, dass die reale Beanspruchung für hochohmige Eingänge besser nachbildet. Die Vergleichbarkeit der Störpegel bei Prüfung und realem Schaltanlagenbetrieb wird dabei im Zeitund Frequenzbereich gezeigt

Renormalization group analysis of competing quantum phases in the J_1- J_2 Heisenberg model on the kagome lattice

Recent discoveries in neutron scattering experiments for Kapellasite and Herbertsmithite as well as theoretical calculations of possible spin liquid phases have revived interest in magnetic phenomena on the kagome lattice. We study the quantum phase diagram of the S=1/2 Heisenberg kagome model as a function of nearest neighbor coupling J_1 and second neighbor coupling J_2. Employing the pseudofermion functional renormalization group (PFFRG), we find four types of magnetic quantum order (q=0 order, cuboc order, ferromagnetic order, and √3×√3 order) as well as extended magnetically disordered regions by which we specify the possible parameter regime for Kapellasite. In the disordered regime J_2/J_1≪1, the flatness of the magnetic susceptibility at the zone boundary which is observed for Herbertsmithite can be reconciled with the presence of small J_2>0 coupling. In particular, we analyze the dimer susceptibilities related to different valence-bond crystal (VBC) patterns, which are strongly inhomogeneous, indicating the rejection of VBC order in the RG flow

Variation in postoperative outcomes of patients with intracranial tumors: insights from a prospective international cohort study during the COVID-19 pandemic

Background: This study assessed the international variation in surgical neuro-oncology practice and 30-day outcomes of patients who had surgery for an intracranial tumor during the COVID-19 pandemic. Methods: We prospectively included adults aged ≥18 years who underwent surgery for a malignant or benign intracranial tumor across 55 international hospitals from 26 countries. Each participating hospital recorded cases for 3 consecutive months from the start of the pandemic. We categorized patients’ location by World Bank income groups (high [HIC], upper-middle [UMIC], and low- and lower-middle [LLMIC]). Main outcomes were a change from routine management, SARS-CoV-2 infection, and 30-day mortality. We used a Bayesian multilevel logistic regression stratified by hospitals and adjusted for key confounders to estimate the association between income groups and mortality. Results: Among 1016 patients, the number of patients in each income group was 765 (75.3%) in HIC, 142 (14.0%) in UMIC, and 109 (10.7%) in LLMIC. The management of 200 (19.8%) patients changed from usual care, most commonly delayed surgery. Within 30 days after surgery, 14 (1.4%) patients had a COVID-19 diagnosis and 39 (3.8%) patients died. In the multivariable model, LLMIC was associated with increased mortality (odds ratio 2.83, 95% credible interval 1.37–5.74) compared to HIC. Conclusions: The first wave of the pandemic had a significant impact on surgical decision-making. While the incidence of SARS-CoV-2 infection within 30 days after surgery was low, there was a disparity in mortality between countries and this warrants further examination to identify any modifiable factors

The Design of the CADE-13 ATP System Competition

. Running a competition for Automated Theorem Proving (ATP) systems is a difficult and arguable venture. However, the potential benefits of such an event by far outweigh the controversial aspects. The motivations for running the CADE-13 ATP System Competition were to contribute to the evaluation of ATP systems, to stimulate ATP research and system development, and to expose ATP systems to researchers both within and outside the ATP community. This paper identifies and discusses the issues that determine the nature of such a competition. Choices and motivated decisions for the CADE-13 competition, with respect to the issues, are given. Key words: Automated theorem proving, competition, design 1. Introduction Running a competition for Automated Theorem Proving (ATP) systems 1 is a difficult and arguable venture. The reasons for this are that existing ATP systems require different amounts of user interaction, are designed for different types of reasoning, are based on different logics..

The Procedures of the CADE-13 . . .

This paper describes the practical procedures that were used to run the CADE13 ATP System Competition. The paper describes the hardware and software environments, the system installation, the soundness testing performed, the preparation of problems for the competition, the choice of the number of problems and the time limit, and the execution of the systems

The CADE-14 ATP System Competition

. This paper documents the design, competing systems, results, and conclusions of the CADE-14 ATP System Competition (CASC-14). 1. Introduction The CADE-14 ATP System Competition (CASC-14) was held on Wednesday 16th July 1997, as part of CADE-14 at the Sheraton Breakwater Hotel, Townsville, Australia. CASC-14 was the second CADE ATP system competition, following the successful competition at CADE-13 in 1996 at Rutgers University, New Brunswick, USA [SS97b]. CASC-14 evaluated the performance of sound, fully automatic, 1st order ATP systems. The evaluation was in terms of the number of problems solved and the average runtime for successful solutions. The evaluation was done in the context of a bounded number of eligible problems chosen from the TPTP Problem Library [SSar, SS97e] and a specified time limit for each solution attempt. Eighteen ATP systems, listed in Table I, were entered into the various competition and demonstration divisions. The competition was run on nine SUN Ultra 140s..