979 research outputs found
The Path-Integral Approach to Spontaneous Symmetry Breaking
We will investigate two models which exhibit SSB in the canonical approach:
the N=1 and N=2 linear sigma model. In both models the Green's functions and
the effective potential will be computed in the path-integral approach. We will
demonstrate how we get different results than in the canonical approach.Comment: PhD-thesi
Path Integrals in Polar Field Variables in QFT
We show how to transform a -dimensional Euclidean path integral in terms
of two (Cartesian) fields to a path integral in terms of polar field variables.
First we present a conjecture that states how this transformation should be
done. Then we show that this conjecture is correct in the case of two toy
models. Finally the conjecture will be proven for a general QFT model with two
fields
Profiling the vendors of COVID‐19 related product on the Darknet: An observational study
Background
In a time of unprecedented global change, the COVID-19 pandemic has led to a surge in demand of COVID-19 vaccines and related certifications. Mainly due to supply shortages, counterfeit vaccines, fake documentation, and alleged cures to illegal portfolios, have been offered on darkweb marketplaces (DWMs) with important public health consequences. We aimed to profile key DWMs and vendors by presenting some in-depth case studies.
Methods
A non-systematic search for COVID-19 products was performed across 118 DWMs. Levels of activity, credibility, content, COVID-19 product listings, privacy protocols were among the features retrieved. Open web fora and other open web sources were also considered for further analysis of both functional and non functional DWMs. Collected data refers to the period between January 2020 and October 2021.
Results
A total of 42 relevant listings sold by 24 vendors across eight DWMs were identified. Four of these markets were active and well-established at the time of the study with good levels of credibility. COVID-19 products were listed alongside other marketplace content. Vendors had a trusted profile, communicated in English language and accepted payments in cryptocurrencies (Monero or Bitcoin). Their geographical location included the USA, Asia and Europe. While COVID-19 related goods were mostly available for regional supply, other listings were also shipped worldwide.
Interpretation
Findings emerging from this study rise important questions about the health safety of certain DWMs activities and encourage the development of targeted interventions to overcome such new and rapidly expanding public health threats.
Funding
CovSaf, National Research centre on Privacy, Harm Reduction and Adversarial Influence Online (REPHRAIN), Commonwealth Fund
Effects of mud supply on large-scale estuary morphology and development over centuries to millennia
Alluvial river estuaries consist largely of sand but are typically
flanked by mudflats and salt marshes. The analogy with meandering rivers
that are kept narrower than braided rivers by cohesive floodplain formation
raises the question of how large-scale estuarine morphology and the late Holocene
development of estuaries are affected by cohesive sediment. In this study we
combine sand and mud transport processes and study their interaction effects
on morphologically modelled estuaries on centennial to millennial
timescales. The numerical modelling package Delft3D was applied in 2-DH
starting from an idealised convergent estuary. The mixed sediment was
modelled with an active layer and storage module with fluxes predicted by the
Partheniades–Krone relations for mud and Engelund–Hansen for sand. The model
was subjected to a range of idealised boundary conditions of tidal range,
river discharge, waves and mud input. The model results show that mud is
predominantly stored in mudflats on the side of the estuary. Marine mud
supply only influences the mouth of the estuary, whereas fluvial mud is
distributed along the whole estuary. Coastal waves stir up mud and remove the
tendency to form muddy coastlines and the formation of mudflats in the
downstream part of the estuary. Widening continues in estuaries with only
sand, while mud supply leads to a narrower constant width and reduced channel
and bar dynamics. This self-confinement eventually leads to a dynamic
equilibrium in which lateral channel migration and mudflat expansion are balanced on
average. However, for higher mud concentrations, higher discharge
and low tidal amplitude, the estuary narrows and fills to become a tidal
delta
Prolonged Disease Course of COVID-19 in a Patient with CTLA-4 Haploinsufficiency
Patients with primary immunodeficiencies are especially vulnerable to developing severe coronavirus disease 2019 (COVID-19) after infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Cytotoxic T lymphocyte antigen-4 (CTLA-4) is an important regulator of immune responses, and patients who suffer from CTLA4 haploinsufficiency have hyperactivation of effector T cells and infiltration of various organs. Overexpression of CTLA4 has been associated with a more severe disease course in patients with COVID-19, but there have only been a few reports on the disease course of COVID-19 in patients with CTLA4 haploinsufficiency. We report on a 33-year-old female with a history of immune thrombocytopenia, autoimmune haemolytic anaemia, granulomatous-lymphocytic interstitial lung disease, and common variable immunodeficiency who developed COVID-19. She was admitted and discharged from the hospital several times in the months thereafter and remained symptomatic and had a positive SARS-CoV-2 PCR for up to 137 days after the first symptoms. No SARS-CoV-2 antibodies were identified in the patients' serum. The disease was finally controlled after repeated infusions of convalescent plasma and treatment of concurrent bacterial and fungal infections. Genetic analysis revealed a likely pathogenic variant in CTLA4, and CTLA4 expression on regulatory T-cells was low. This case illustrates that patients with primary immunodeficiencies who have a protracted disease course of COVID-19 could benefit from convalescent plasma therapy
Improving the description of the suspended particulate matter concentrations in the southern North Sea through assimilating remotely sensed data
The integration of remote sensing data of suspended particulate matter (SPM) into numerical models is useful to improve the understanding of the temporal and spatial behaviour of SPM in dynamic shelf seas. In this paper a generic method based on the Ensemble Kalman Filtering (EnKF) for assimilating remote sensing SPM data into a transport model is presented. The EnKF technique is used to assimilate SPM data of the North Sea retrieved from the MERIS sensor, into the computational water quality and sediment transport model, Delft3D-WAQ. The satellite data were processed with the HYDROPT algorithm that provides SPM concentrations and error information per pixel, which enables their use in data assimilation. The uncertainty of the transport model, expressed in the system noise covariance matrix, was quantified by means of a Monte Carlo approach. From a case study covering the first half of 2003, it is demonstrated that the MERIS observations and transport model application are sufficiently robust for a successful generic assimilation. The assimilation results provide a consistent description of the spatial-temporal variability of SPM in the southern North Sea and show a clear decrease of the model bias with respect to independent in-situ observations. This study also identifies some shortcomings in the assimilated results, such as over prediction of surface SPM concentrations in regions experiencing periods of rapid stratification/de-stratification. Overall this feasibility study leads to a range of suggestions for improving and enhancing the model, the observations and the assimilation scheme. © 2011 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Netherlands
Quantum Extremism: Effective Potential and Extremal Paths
The reality and convexity of the effective potential in quantum field
theories has been studied extensively in the context of Euclidean space-time.
It has been shown that canonical and path-integral approaches may yield
different results, thus resolving the `convexity problem'. We discuss the
transferral of these treatments to Minkowskian space-time, which also
necessitates a careful discussion of precisely which field configurations give
the dominant contributions to the path integral. In particular, we study the
effective potential for the N=1 linear sigma model.Comment: 11 pages, 4 figure
Complete Genome Sequence of the Aerobic Facultative Methanotroph Methylocella tundrae Strain T4
Methylocella tundrae T4T is a facultative aerobic methanotroph which was isolated from an acidic tundra wetland and possesses only a soluble methane monooxygenase. The complete genome, which includes two megaplasmids, was sequenced using a combination of Illumina and Nanopore technologies. One of the megaplasmids carries a propane monooxygenase gene cluster
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