1,289 research outputs found
Fracton topological order via coupled layers
In this work, we develop a coupled layer construction of fracton topological
orders in spatial dimensions. These topological phases have sub-extensive
topological ground-state degeneracy and possess excitations whose movement is
restricted in interesting ways. Our coupled layer approach is used to construct
several different fracton topological phases, both from stacked layers of
simple topological phases and from stacks of fracton topological
phases. This perspective allows us to shed light on the physics of the X-cube
model recently introduced by Vijay, Haah, and Fu, which we demonstrate can be
obtained as the strong-coupling limit of a coupled three-dimensional stack of
toric codes. We also construct two new models of fracton topological order: a
semionic generalization of the X-cube model, and a model obtained by coupling
together four interpenetrating X-cube models, which we dub the "Four Color Cube
model." The couplings considered lead to fracton topological orders via
mechanisms we dub "p-string condensation" and "p-membrane condensation," in
which strings or membranes built from particle excitations are driven to
condense. This allows the fusion properties, braiding statistics, and
ground-state degeneracy of the phases we construct to be easily studied in
terms of more familiar degrees of freedom. Our work raises the possibility of
studying fracton topological phases from within the framework of topological
quantum field theory, which may be useful for obtaining a more complete
understanding of such phases.Comment: 20 pages, 18 figures, published versio
"Why me, why now?" Using clinical immunology and epidemiology to explain who gets nontuberculous mycobacterial infection
BACKGROUND: The prevalence of nontuberculous mycobacterial (NTM) disease is rising. An understanding of known risk factors for disease sheds light on the immunological and physical barriers to infection, and how and why they may be overcome. This review focuses on human NTM infection, supported by experimental and in vitro data of relevance to the practising clinician who seeks to understand why their patient has NTM infection and how to further investigate. DISCUSSION: First, the underlying immune response to NTM disease is examined. Important insights regarding NTM disease susceptibility come from nature's own knockouts, the primary immune deficiency disorders. We summarise the current knowledge surrounding interferon-gamma (IFNγ)-interleukin-12 (IL-12) axis abnormalities, followed by a review of phagocytic defects, T cell lymphopenia and rarer genetic conditions known to predispose to NTM disease. We discuss how these define key immune pathways involved in the host response to NTM. Iatrogenic immunosuppression is also important, and we evaluate the impact of novel biological therapies, as well as bone marrow transplant and chemotherapy for solid organ malignancy, on the epidemiology and presentation of NTM disease, and discuss the host defence dynamics thus revealed. NTM infection and disease in the context of other chronic illnesses including HIV and malnutrition is reviewed. The role of physical barriers to infection is explored. We describe how their compromise through different mechanisms including cystic fibrosis, bronchiectasis and smoking-related lung disease can result in pulmonary NTM colonisation or infection. We also summarise further associations with host factors including body habitus and age. We use the presented data to develop an over-arching model that describes human host defences against NTM infection, where they may fail, and how this framework can be applied to investigation in routine clinical practice
Reconstructing the History of Energy Condition Violation from Observational Data
We study the likelihood of energy condition violations in the history of the
Universe. Our method is based on a set of functions that characterize energy
condition violation. FLRW cosmological models are built around these
"indication functions". By computing the Fisher matrix of model parameters
using type Ia supernova and Hubble parameter data, we extract the principal
modes of these functions' redshift evolution. These modes allow us to obtain
general reconstructions of energy condition violation history independent of
the dark energy model. We find that the data suggest a history of strong energy
condition violation, but the null and dominant energy conditions are likely to
be fulfilled. Implications for dark energy models are discussed.Comment: v1: 6 pages, 7 figures, 1 table. Comments welcome; v2: 7 pages,
expanded & corrected, accepted by Ap
The effects of weather and climate change on dengue
There is much uncertainty about the future impact of climate change on vector-borne diseases. Such uncertainty reflects the difficulties in modelling the complex interactions between disease, climatic and socioeconomic determinants. We used a comprehensive panel dataset from Mexico covering 23 years of province-specific dengue reports across nine climatic regions to estimate the impact of weather on dengue, accounting for the effects of non-climatic factors
The effectiveness of public health interventions to reduce the health impact of climate change:a systematic review of systematic reviews
Climate change is likely to be one of the most important threats to public health in the coming years. Yet despite the large number of papers considering the health impact of climate change, few have considered what public health interventions may be of most value in reducing the disease burden. We aimed to evaluate the effectiveness of public health interventions to reduce the disease burden of high priority climate sensitive diseases
Mechanical power production assessment during weightlifting exercises. A systematic review
The assessment of the mechanical power production is of great importance for researchers and practitioners. The purpose of this review was to compare the differences in ground reaction force (GRF), kinematic, and combined (bar velocity x GRF) methods to assess mechanical power production during weightlifting exercises. A search of electronic databases was conducted to identify all publications up to 31 May 2019. The peak power output (PPO) was selected as the key variable. The exercises included in this review were clean variations, which includes the hang power clean (HPC), power clean (PC) and clean. A total of 26 articles met the inclusion criteria with 53.9% using the GRF, 38.5% combined, and 30.8% the kinematic method. Articles were evaluated and descriptively analysed to enable comparison between methods. The three methods have inherent methodological differences in the data analysis and measurement systems, which suggests that these methods should not be used interchangeably to assess PPO in Watts during weightlifting exercises. In addition, this review provides evidence and rationale for the use of the GRF to assess power production applied to the system mass while the kinematic method may be more appropriate when looking to assess only the power applied to the barbell
Theory and simulation of photogeneration and transport in Si-SiOx superlattice absorbers
Si-SiOx superlattices are among the candidates that have been proposed as high band gap absorber material in all-Si tandem solar cell devices. Owing to the large potential barriers for photoexited charge carriers, transport in these devices is restricted to quantum-confined superlattice states. As a consequence of the finite number of wells and large built-in fields, the electronic spectrum can deviate considerably from the minibands of a regular superlattice. In this article, a quantum-kinetic theory based on the non-equilibrium Green's function formalism for an effective mass Hamiltonian is used for investigating photogeneration and transport in such devices for arbitrary geometry and operating conditions. By including the coupling of electrons to both photons and phonons, the theory is able to provide a microscopic picture of indirect generation, carrier relaxation, and inter-well transport mechanisms beyond the ballistic regime
Factors Affecting Temporal and Spatial Variations of Microcystins in Gonghu Bay of Lake Taihu, with Potential Risk of Microcystin Contamination to Human Health
A field survey of the seasonal variation of microcystin (MC) concentration was performed in Gonghu Bay (a total of 15 sampling sites) of Lake Taihu from January to December 2008. Microcystis spp. biomass and intra-/extracellular MCs were significantly correlated with water temperature, suggesting the importance of temperature in cyanobacterial blooming in the lake. Higher MC concentration was found in summer and autumn, and peaks of Microcystis biomass and intra-/extracellular MC concentrations were all present in October. Spatially, risk of MCs was higher in littoral zones than in the pelagic area. There were significant correlations between N or P concentrations, and Microcystis biomass or MC content, suggesting that N and P levels affected MC production through influencing Microcystis biomass. Intra-/extracellular MCs and Microcystis biomass had negative exponential relationships with TN:TP, and the maximum values all occurred when TN:TP was <25. Multivariate analyses by PCCA indicated that intra- and extracellular MC concentrations had better correlations with biological factors (such as Microcystis biomass and chl-a) than with physicochemical factors. The maximum MC concentration reached up to 17 mu g/L MC-LReq, considerably higher than the drinking water safety standard (1 mu g/L) recommended by the WHO. So it is necessary to take measures to reduce the exposure risk of cyanobacterial toxins to human beings
The Influence of Free Quintessence on Gravitational Frequency Shift and Deflection of Light with 4D momentum
Based on the 4D momentum, the influence of quintessence on the gravitational
frequency shift and the deflection of light are examined in modified
Schwarzschild space. We find that the frequency of photon depends on the state
parameter of quintessence : the frequency increases for and
decreases for . Meanwhile, we adopt an integral power number
() to solve the orbital equation of photon. The photon's
potentials become higher with the decrease of . The behavior of
bending light depends on the state parameter sensitively. In
particular, for the case of , there is no influence on the
deflection of light by quintessence. Else, according to the H-masers of GP-A
redshift experiment and the long-baseline interferometry, the constraints on
the quintessence field in Solar system are presented here.Comment: 12 pages, 2 figures, 4 tables. European Physical Journal C in pres
- …