Quantum walks: a comprehensive review

Quantum walks, the quantum mechanical counterpart of classical random walks, is an advanced tool for building quantum algorithms that has been recently shown to constitute a universal model of quantum computation. Quantum walks is now a solid field of research of quantum computation full of exciting open problems for physicists, computer scientists, mathematicians and engineers. In this paper we review theoretical advances on the foundations of both discrete- and continuous-time quantum walks, together with the role that randomness plays in quantum walks, the connections between the mathematical models of coined discrete quantum walks and continuous quantum walks, the quantumness of quantum walks, a summary of papers published on discrete quantum walks and entanglement as well as a succinct review of experimental proposals and realizations of discrete-time quantum walks. Furthermore, we have reviewed several algorithms based on both discrete- and continuous-time quantum walks as well as a most important result: the computational universality of both continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing Journa

New Bisimulation Semantics for Distributed Systems

Bisimulation semantics are a very pleasant way to define the semantics of systems, mainly because the simplicity of their definitions and their nice coalgebraic properties. However, they also have some disadvantages: they are based on a sequential operational semantics defined by means of an ordinary transition system, and in order to be bisimilar two systems have to be “too similar”. In this work we will present several natural proposals to define weaker bisimulation semantics that we think properly capture the desired behaviour of distributed systems. The main virtue of all these semantics is that they are real bisimulation semantics, thus inheriting most of the good properties of bisimulation semantics. This is so because they can be defined as particular instances of Jacobs and Hughes’ categorical definition of simulation, which they have already proved to satisfy all those properties

Cross section of the reaction 18O(p,γ)19F at astrophysical energies: The 90 keV resonance and the direct capture component

The observation of oxygen isotopes in giant stars sheds light on mixing processes operating in their interiors. Due to the very strong correlation between nuclear burning and mixing processes it is very important to reduce the uncertainty on the cross sections of the nuclear reactions that are involved. In this paper we focus our attention on the reaction 18O(p, γ)19F. While the 18O(p, α)15Nchannel is thought to be dominant, the (p,γ) channel can still be an important component in stellar burning in giants, depending on the low energy cross section. So far only extrapolations from higher-energ

SARS-CoV-2-specific nasal IgA wanes 9 months after hospitalisation with COVID-19 and is not induced by subsequent vaccination

BACKGROUND: Most studies of immunity to SARS-CoV-2 focus on circulating antibody, giving limited insights into mucosal defences that prevent viral replication and onward transmission. We studied nasal and plasma antibody responses one year after hospitalisation for COVID-19, including a period when SARS-CoV-2 vaccination was introduced. METHODS: In this follow up study, plasma and nasosorption samples were prospectively collected from 446 adults hospitalised for COVID-19 between February 2020 and March 2021 via the ISARIC4C and PHOSP-COVID consortia. IgA and IgG responses to NP and S of ancestral SARS-CoV-2, Delta and Omicron (BA.1) variants were measured by electrochemiluminescence and compared with plasma neutralisation data. FINDINGS: Strong and consistent nasal anti-NP and anti-S IgA responses were demonstrated, which remained elevated for nine months (p < 0.0001). Nasal and plasma anti-S IgG remained elevated for at least 12 months (p < 0.0001) with plasma neutralising titres that were raised against all variants compared to controls (p < 0.0001). Of 323 with complete data, 307 were vaccinated between 6 and 12 months; coinciding with rises in nasal and plasma IgA and IgG anti-S titres for all SARS-CoV-2 variants, although the change in nasal IgA was minimal (1.46-fold change after 10 months, p = 0.011) and the median remained below the positive threshold determined by pre-pandemic controls. Samples 12 months after admission showed no association between nasal IgA and plasma IgG anti-S responses (R = 0.05, p = 0.18), indicating that nasal IgA responses are distinct from those in plasma and minimally boosted by vaccination. INTERPRETATION: The decline in nasal IgA responses 9 months after infection and minimal impact of subsequent vaccination may explain the lack of long-lasting nasal defence against reinfection and the limited effects of vaccination on transmission. These findings highlight the need to develop vaccines that enhance nasal immunity. FUNDING: This study has been supported by ISARIC4C and PHOSP-COVID consortia. ISARIC4C is supported by grants from the National Institute for Health and Care Research and the Medical Research Council. Liverpool Experimental Cancer Medicine Centre provided infrastructure support for this research. The PHOSP-COVD study is jointly funded by UK Research and Innovation and National Institute of Health and Care Research. The funders were not involved in the study design, interpretation of data or the writing of this manuscript

Target characterizations for direct measurement of the 13C(α, n)16O reaction at LUNA 400

The 13C(α, n)16O reaction is the main neutron source for the s-process in low mass AGB stars. Although several direct measurements have been performed, no dataset reaches the Gamow window due to the low cross section. Moreover a dominant component of systematic uncertainty comes from target behaviour under beam irradiation. This work presents a detailed characterization of enriched 13C targets in order to test reproducibility and uniformity of the evaporation method, stability and purity of targets under a high intensity proton beam (100-200 uA) for the study of this reaction at the Laboratory for Underground Nuclear Astrophysics (LUNA) facility installed at Laboratori Nazionali del Gran Sasso (LNGS, INFN). A procedure to evaluate the target thickness and to monitor its degradation is discussed and preliminary results are presented

Target characterizations for direct measurement of the

The 13C(α, n)16O reaction is the main neutron source for the s-process in low mass AGB stars. Although several direct measurements have been performed, no dataset reaches the Gamow window due to the low cross section. Moreover a dominant component of systematic uncertainty comes from target behaviour under beam irradiation. This work presents a detailed characterization of enriched 13C targets in order to test reproducibility and uniformity of the evaporation method, stability and purity of targets under a high intensity proton beam (100-200 uA) for the study of this reaction at the Laboratory for Underground Nuclear Astrophysics (LUNA) facility installed at Laboratori Nazionali del Gran Sasso (LNGS, INFN). A procedure to evaluate the target thickness and to monitor its degradation is discussed and preliminary results are presented

Vascular function of the peripheral circulation in patients with nephrosis

Background. Nephrotic syndrome is associated with abnormal lipoprotein metabolism and increased risk of coronary heart disease. Endothelial dysfunction, an early phase of atherogenesis that manifests as impaired flow-mediated dilation (FMD) of the peripheral circulation, may link these associations. Methods. We examined endothelial function of the brachial artery and forearm resistance arteries in 15 patients with nephrosis (NP), 15 patients with primary hyperlipidemia (HL) alone, and 15 normolipidemic, nonproteinuric subjects (NC) matched for age, sex, and weight. The NP and HL groups had similar serum cholesterol and triglyceride concentrations. Postischemic FMD (endothelium-dependent) and glyceryl trinitrate-mediated dilation (GTNMD; endothelium-independent) of the brachial artery were studied using ultrasonography and computerized edge detection software. Postischemic forearm blood flow was also measured using plethysmography. Results. Postischemic FMD of the brachial artery was significantly lower in the NP and HL groups compared with NC group (mean ± SE): NP 4.91 ± 0.8%, HL 4.53 ± 0.6%, NC 8.45 ± 0.5% (P < 0.001). There were no significant differences among the groups in baseline diameter and GTNMD of the brachial artery, nor in maximal forearm blood flow and flow debt repayment of the forearm microcirculation. Significant differences in FMD among the groups were principally related to differences in serum low-density lipoprotein cholesterol. Conclusions. Patients with NP have abnormal endothelium-dependent but preserved endothelium-independent dilation of the brachial artery following an ischemic stimulus. Postischemic forearm microcirculatory function is unimpaired. Dyslipoproteinemia is probably the principal cause of endothelial dysfunction of conduit arteries in patients with NP and the basis for their increased risk of cardiovascular disease