Gauge/gravity duality and the interplay of various fractional branes

We consider different types of fractional branes on a Z_2 orbifold of the conifold and analyze in detail the corresponding gauge/gravity duality. The gauge theory possesses a rich and varied dynamics, both in the UV and in the IR. We find the dual supergravity solution which contains both untwisted and twisted 3-form fluxes, related to what are known as deformation and N=2 fractional branes respectively. We analyze the resulting RG flow from the supergravity perspective, by developing an algorithm to easily extract it. We find hints of a generalization of the familiar cascade of Seiberg dualities due to a non-trivial interplay between the different types of fractional branes. We finally consider the IR behavior in several limits, where the dominant effective dynamics is either confining, in a Coulomb phase or runaway, and discuss the resolution of singularities in the dual geometric background.Comment: 38 pages + appendices, 15 figures; v2: refs added and typos correcte

Towards Improved QUBO Formulations of IR Tasks for Quantum Annealers

In recent years the interest in applying Quantum Computing to Information Retrieval and Recommendation Systems task has increased and several papers have proposed formulations of relevant tasks that can be solved with quantum devices (community detection, feature selection etc.), usually focusing on Quantum Annealers (QA), a special purpose device able to solve combinatorial optimization problems. However, most research only focuses on the mathematical aspect of the formulation, without accounting for the underlying physical processes of the quantum device. Indeed, theoretical studies indicate that certain characteristics make a problem difficult to solve on QA, but it is not clear how to use this knowledge to inform the development of better problem formulations that are equivalent but easier to solve on QA. This work presents a preliminary study which approaches this issue with an empirical perspective. We consider several problems both general and related to IR and Recommendation tasks to assess whether we can identify characteristics of the problem formulation or the solution space that affect the effectiveness of QA. The results indicate interesting correlations and suggest that this is a promising area to investigate further

Does the structure of the QUBO problem affect the effectiveness of quantum annealing? An empirical perspective

In recent years there has been a significant interest in exploring the potential of Quantum Annealers (QA) as heuristic solvers of Quadratic Unconstrained Binary Optimization (QUBO) problems. Some problems are more difficult to solve on QA and understanding why is not straightforward, because an analytical study of the underlying physical system is intractable for large QUBO problems. This work consists in an empirical analysis of the features making a QUBO problem difficult to solve on QA, based on clusters of QUBO instances identified with Hierarchical Clustering. The analysis reveals correlations between specific values of the features and the ability of QA to solve effectively the instances. These initial results open new research opportunities to inform the development of new AI methods supporting quantum computation (e.g., for minor embedding or error mitigation) that are better tailored to the characteristics of the problem, as well as to develop better QUBO formulations for known problems in order to improve the quality of the solutions found by QA

Application of optimally-shaped phononic crystals to reduce anchor losses of MEMS resonators

This work is focused on the application of Phononic Crystals to reduce anchor losses of MEMS contour mode resonators. Anchor losses dominates the losses in these type of released resonators at low frequency and at low temperature. The use of phononic crystals, intended as finite-periodic distribution of holes in the anchor, is fully compatible with fabrication processes and moreover it is easy to implement. The numerical results obtained in this work show how the use of these crystals can significantly reduce the anchor losses: without the use of the crystal the Q-factor related to only anchor losses is 344, with the use of the crystal it can reach up to 105900

Top-N recommendations on Unpopular Items with Contextual Knowledge

Traditional recommender systems provide recommendations of items to users; recently, some of them also consider the context related to predictions. In this paper we propose a technique that relies on classical recommendation algorithms and post-filters recommendations on the basis of contextual information available for them. Association rules are exploited to identify the most significant correlations among context and item characteristics. The mined rules are used to filter the predictions performed by traditional recommender systems to provide contextualized recommendations. Our experimental results show that the proposed approach allows improving the output of classical algorithms proposed in the literature, especially in the case of unpopular items

Towards Recommender Systems with Community Detection and Quantum Computing

After decades of being mainly confined to theoretical research, Quantum Computing is now becoming a useful tool for solving realistic problems. This work aims to experimentally explore the feasibility of using currently available quantum computers, based on the Quantum Annealing paradigm, to build a recommender system exploiting community detection. Community detection, by partitioning users and items into densely connected clusters, can boost the accuracy of non-personalized recommendation by assuming that users within each community share similar tastes. However, community detection is a computationally expensive process. The recent availability of Quantum Annealers as cloud-based devices, constitutes a new and promising direction to explore community detection, although effectively leveraging this new technology is a long-term path that still requires advancements in both hardware and algorithms. This work aims to begin this path by assessing the quality of community detection formulated as a Quadratic Unconstrained Binary Optimization problem on a real recommendation scenario. Results on several datasets show that the quantum solver is able to detect communities of comparable quality with respect to classical solvers, but with better speedup, and the non-personalized recommendation models built on top of these communities exhibit improved recommendation quality. The takeaway is that quantum computing, although in its early stages of maturity and applicability, shows promise in its ability to support new recommendation models and to bring improved scalability as technology evolves

Wide band observations of the new X-ray burster SAX J1747.0-2853 during the March 1998 outburst

We report on our discovery and follow-up observations of the X-ray source SAX J1747.0-2853 detected in outburst on 1998, March 10 with the BeppoSAX Wide Field Cameras in the energy range 2-28 keV. The source is located about half degree off the Galactic Nucleus. A total of 14 type-I X-ray bursts were detected in Spring 1998, thus identifying the object as a likely low-mass X-ray binary harboring a weakly magnetized neutron star. Evidence for photospheric radius expansion is present in at least one of the observed bursts, leading to an estimate of the source distance of about 9 kpc. We performed a follow-up target of opportunity observation with the BeppoSAX Narrow Field Instruments on March 23 for a total elapsed time of 72 ks. The source persistent luminosity was 2.6x10^36 erg/s in the 2-10 keV energy range. The wide band spectral data (1-200 keV) are consistent with a remarkable hard X-ray spectrum detected up to 150 keV, highly absorbed at low energies (Nh of the order of 10^23 cm^-2) and with clear evidence for an absorption edge near 7 keV. A soft thermal component is also observed, which can be described by single temperature blackbody emission at about 0.6 keV.Comment: 11 pages, 3 figures, accepted for publication in ApJ Letter

Health related quality of life in COVID-19 survivors discharged from acute hospitals: results of a short-form 36-item survey [version 1; peer review: awaiting peer review]

Background: Health-related quality of life (HRQL) is important for evaluating the impact of a disease in the longer term across the physical and psychological domains of human functioning. The aim of this study is to evaluate HRQL in COVID-19 survivors in Italy using the short form 36-items questionnaire (SF-36). Methods: This is an observational study involving adults discharged home following a coronavirus disease 2019 (COVID-19)-related hospital admission. Baseline demographic and clinical data including the Cumulative Illness Rating Scale (CIRS) and the Hospital Anxiety and Depression Scale (HADS) were collected. The validated Italian version of SF-36 was administered cross-sectionally. The SF-36 contains eight scales measuring limitations in physical and social functioning, the impact on roles and activities, fatigue, emotional wellbeing, pain and general health perception. Results: A total of 35 patients, with a mean age of 60 years, completed the SF-36. The results showed difficulties across the physical and psychological domains, particularly affecting the return to previous roles and activities. A higher burden of co-morbidities as well as a more severe muscle weakness was associated to a lower physical functioning. Younger age, rather than older, correlated to a perceived greater limitation in physical functioning and vitality. Conclusions: COVID-19 survivors particularly the ones of working age may need support for resuming their premorbid level of functioning and returning to work

Performance of different photocathode materials in a liquid argon purity monitor

Purity monitor devices are increasingly used in liquid noble gas time projection chambers to measure the lifetime of drifting electrons. Purity monitors work by emitting electrons from a photocathode material via the photoelectric effect. The electrons are then drifted towards an anode by means of an applied electric drift field. By measuring the difference in charge between the cathode and the anode, one can extract the lifetime of the drifting electrons in the medium. For the first time, we test the performance of different photocathode materials—silver, titanium, and aluminium—and compare them to gold, which is the standard photocathode material used for purity monitors. Titanium and aluminium were found to have a worse performance than gold in vacuum, whereas silver showed a signal of the same order of magnitude as gold. Further tests in liquid argon were carried out on silver and gold with the conclusion that the signal produced by silver is about three times stronger than that of gold