15 research outputs found
Monopoles and clusters
We define and study certain hyperkaehler manifolds which capture the
asymptotic behaviour of the SU(2)-monopole metric in regions where monopoles
break down into monopoles of lower charges. The rate at which these new metrics
approximate the monopole metric is exponential, as for the Gibbons-Manton
metric.Comment: v2.: relation to calorons mentioned; added explanation
Renormalization group analysis of the 2D Hubbard model
Salmhofer [Commun. Math. Phys. 194, 249 (1998)] has recently developed a new
renormalization group method for interacting Fermi systems, where the complete
flow from the bare action of a microscopic model to the effective low-energy
action, as a function of a continuously decreasing infrared cutoff, is given by
a differential flow equation which is local in the flow parameter. We apply
this approach to the repulsive two-dimensional Hubbard model with nearest and
next-nearest neighbor hopping amplitudes. The flow equation for the effective
interaction is evaluated numerically on 1-loop level. The effective
interactions diverge at a finite energy scale which is exponentially small for
small bare interactions. To analyze the nature of the instabilities signalled
by the diverging interactions we extend Salmhofers renormalization group for
the calculation of susceptibilities. We compute the singlet superconducting
susceptibilities for various pairing symmetries and also charge and spin
density susceptibilities. Depending on the choice of the model parameters
(hopping amplitudes, interaction strength and band-filling) we find
commensurate and incommensurate antiferromagnetic instabilities or d-wave
superconductivity as leading instability. We present the resulting phase
diagram in the vicinity of half-filling and also results for the density
dependence of the critical energy scale.Comment: 16 pages, RevTeX, 16 eps figure
Properties of hyperkahler manifolds and their twistor spaces
We describe the relation between supersymmetric sigma-models on hyperkahler
manifolds, projective superspace, and twistor space. We review the essential
aspects and present a coherent picture with a number of new results.Comment: 26 pages. v2: Sign mistakes corrected; Kahler potential explicitly
calculated in example; references added. v3: Published version--several small
clarifications per referee's reques
Global Carbon Budget 2018
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere â the âglobal carbon budgetâ â is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFF) are based on energy statistics and cement production data, while emissions from land use and land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) and terrestrial CO2 sink (SLAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1Ï. For the last decade available (2008â2017), EFF was 9.4±0.5âGtCâyrâ1, ELUC 1.5±0.7âGtCâyrâ1, GATM 4.7±0.02âGtCâyrâ1, SOCEAN 2.4±0.5âGtCâyrâ1, and SLAND 3.2±0.8âGtCâyrâ1, with a budget imbalance BIM of 0.5âGtCâyrâ1 indicating overestimated emissions and/or underestimated sinks. For the year 2017 alone, the growth in EFF was about 1.6â% and emissions increased to 9.9±0.5âGtCâyrâ1. Also for 2017, ELUC was 1.4±0.7âGtCâyrâ1, GATM was 4.6±0.2âGtCâyrâ1, SOCEAN was 2.5±0.5âGtCâyrâ1, and SLAND was 3.8±0.8âGtCâyrâ1, with a BIM of 0.3âGtC. The global atmospheric CO2 concentration reached 405.0±0.1âppm averaged over 2017. For 2018, preliminary data for the first 6â9 months indicate a renewed growth in EFF of +2.7â% (range of 1.8â% to 3.7â%) based on national emission projections for China, the US, the EU, and India and projections of gross domestic product corrected for recent changes in the carbon intensity of the economy for the rest of the world. The analysis presented here shows that the mean and trend in the five components of the global carbon budget are consistently estimated over the period of 1959â2017, but discrepancies of up to 1âGtCâyrâ1 persist for the representation of semi-decadal variability in CO2 fluxes. A detailed comparison among individual estimates and the introduction of a broad range of observations show (1) no consensus in the mean and trend in land-use change emissions, (2) a persistent low agreement among the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) an apparent underestimation of the CO2 variability by ocean models, originating outside the tropics. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding the global carbon cycle compared with previous publications of this data set (Le QuĂ©rĂ© et al., 2018, 2016, 2015a, b, 2014, 2013). All results presented here can be downloaded from https://doi.org/10.18160/GCP-2018
Surface ecophysiological behavior across vegetation and moisture gradients in tropical South America
The âDevelopmental Originsâ hypothesis: relevance to the obstetrician and gynecologist
The recognition of âfetal origins of adult diseaseâ has placed new responsibilities on the obstetrician, as antenatal care is no longer simply about ensuring good perinatal outcomes, but also needs to plan for optimal long-term health for mother and baby. Recently, it has become clear that the intrauterine environment has a broad and long-lasting impact, influencing fetal and childhood growth and development as well as future cardiovascular health, non-communicable disease risk and fertility. This article looks specifically at the importance of the developmental origins of ovarian reserve and ageing, the role of the placenta and maternal nutrition before and during pregnancy. It also reviews recent insights in developmental medicine of relevance to the obstetrician, and outlines emerging evidence supporting a proactive clinical approach to optimizing periconceptional as well as antenatal care aimed to protect newborns against long-term disease susceptibility
Information Technology Skills and Training Needs of Health Information Management Professionals in Nigeria: A Nationwide Study
The consolidated European synthesis of CO2 emissions and removals for EU27 and UK: 1990-2018
Reliable quantification of the sources and sinks of atmospheric carbon dioxide (CO2), including that of their trends and uncertainties, is essential to monitoring the progress in mitigating anthropogenic emissions under the Kyoto Protocol and the Paris Agreement. This study provides a consolidated synthesis of estimates for all anthropogenic and natural sources and sinks of CO2 for the European Union and UK (EU27 + UK), derived from a combination of state-of-the-art bottom-up (BU) and top-down (TD) data sources and models. Given the wide scope of the work and the variety of datasets involved, this study focuses on identifying essential questions which need to be answered to properly understand the differences between various datasets, in particular with regards to the less-well characterized fluxes from managed ecosystems. The work integrates recent emission inventory data, process-based ecosystem model results, data-driven sector model results, and inverse modelling estimates, over the period 1990â2018. BU and TD products are compared with European national GHG inventories (NGHGI) reported under the UNFCCC in 2019, aiming to assess and understand the differences between approaches. For the uncertainties in NGHGI, we used the standard deviation obtained by varying parameters of inventory calculations, reported by the Member States following the IPCC guidelines. Variation in estimates produced with other methods, like atmospheric inversion models (TD) or spatially disaggregated inventory datasets (BU), arise from diverse sources including within-model uncertainty related to parameterization as well as structural differences between models. In comparing NGHGI with other approaches, a key source of uncertainty is that related to different system boundaries and emission categories (CO2 fossil) and the use of different land use definitions for reporting emissions from Land Use, Land Use Change and Forestry (LULUCF) activities (CO2 land). At the EU27 + UK level, the NGHGI (2019) fossil CO2 emissions (including cement production) account for 2624 Tg CO2 in 2014 while all the other seven bottom-up sources are consistent with the NGHGI and report a mean of 2588 (± 463 Tg CO2). The inversion reports 2700 Tg CO2 (± 480 Tg CO2), well in line with the national inventories. Over 2011â2015, the CO2 land sources/sinks from NGHGI estimates report â90 Tg C yrâ1 ± 30 Tg C while all other BU approaches report a mean sink of â98 Tg yrâ1 (± 362 Tg C from DGVMs only). For the TD model ensemble results, we observe a much larger spread for regional inversions (i.e., mean of 253 Tg C yrâ1 ± 400 T g C yrâ1). This concludes that a) current independent approaches are consistent with NGHGI b) their uncertainty is too large to allow a "verification" because of model differences and probably also because of the definition of "CO2 flux" obtained from different approache