85 research outputs found
F-term inflation in Superstring Theories
A supersymmetric inflationary stage dominated by an -term has the problem
that the flatness of the potential is spoiled by supergravity corrections, that
is the slow-roll parameter gets contributions of order unity. We show
that in -term inflationary models based on strings there is natural way of
obtaining small values of . This happens in models of hybrid inflation
based on orbifold constructions, in which a modulus field is responsible
for the large value of the potential during inflation, and a second field
with appropriate modular weight is responsible for the roll-over. We
illustrate the mechanism with a model in which the inflaton potential is
provided by gaugino condensation, leading to succesful inflation.Comment: 9 pages, LaTe
Minimal Standard Heterotic String Models
Three generation heterotic-string vacua in the free fermionic formulation
gave rise to models with solely the MSSM states in the observable Standard
Model charged sector. The relation of these models to Z_2 x Z_2 orbifold
compactifications dictates that they produce three pairs of untwisted Higgs
multiplets. The reduction to one pair relies on the analysis of supersymmetric
flat directions, that give superheavy mass to the dispensable Higgs states. We
explore the removal of the extra Higgs representations by using the free
fermion boundary conditions and hence directly at the string level, rather than
in the effective low energy field theory. We present a general mechanism that
achieves this reduction by using asymmetric boundary conditions between the
left- and right-moving internal fermions. We incorporate this mechanism in
explicit string models containing three twisted generations and a single
untwisted Higgs doublet pair. We further demonstrate that an additional effect
of the asymmetric boundary conditions is to substantially reduce the
supersymmetric moduli space.Comment: 20 pages, LaTeX; added reference
Global age-sex-specific fertility, mortality, healthy life expectancy (HALE), and population estimates in 204 countries and territories, 1950â2019: a comprehensive demographic analysis for the Global Burden of Disease Study 2019
Background: Accurate and up-to-date assessment of demographic metrics is crucial for understanding a wide range of social, economic, and public health issues that affect populations worldwide. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 produced updated and comprehensive demographic assessments of the key indicators of fertility, mortality, migration, and population for 204 countries and territories and selected subnational locations from 1950 to 2019. Methods: 8078 country-years of vital registration and sample registration data, 938 surveys, 349 censuses, and 238 other sources were identified and used to estimate age-specific fertility. Spatiotemporal Gaussian process regression (ST-GPR) was used to generate age-specific fertility rates for 5-year age groups between ages 15 and 49 years. With extensions to age groups 10â14 and 50â54 years, the total fertility rate (TFR) was then aggregated using the estimated age-specific fertility between ages 10 and 54 years. 7417 sources were used for under-5 mortality estimation and 7355 for adult mortality. ST-GPR was used to synthesise data sources after correction for known biases. Adult mortality was measured as the probability of death between ages 15 and 60 years based on vital registration, sample registration, and sibling histories, and was also estimated using ST-GPR. HIV-free life tables were then estimated using estimates of under-5 and adult mortality rates using a relational model life table system created for GBD, which closely tracks observed age-specific mortality rates from complete vital registration when available. Independent estimates of HIV-specific mortality generated by an epidemiological analysis of HIV prevalence surveys and antenatal clinic serosurveillance and other sources were incorporated into the estimates in countries with large epidemics. Annual and single-year age estimates of net migration and population for each country and territory were generated using a Bayesian hierarchical cohort component model that analysed estimated age-specific fertility and mortality rates along with 1250 censuses and 747 population registry years. We classified location-years into seven categories on the basis of the natural rate of increase in population (calculated by subtracting the crude death rate from the crude birth rate) and the net migration rate. We computed healthy life expectancy (HALE) using years lived with disability (YLDs) per capita, life tables, and standard demographic methods. Uncertainty was propagated throughout the demographic estimation process, including fertility, mortality, and population, with 1000 draw-level estimates produced for each metric. Findings: The global TFR decreased from 2âą72 (95% uncertainty interval [UI] 2âą66â2âą79) in 2000 to 2âą31 (2âą17â2âą46) in 2019. Global annual livebirths increased from 134âą5 million (131âą5â137âą8) in 2000 to a peak of 139âą6 million (133âą0â146âą9) in 2016. Global livebirths then declined to 135âą3 million (127âą2â144âą1) in 2019. Of the 204 countries and territories included in this study, in 2019, 102 had a TFR lower than 2âą1, which is considered a good approximation of replacement-level fertility. All countries in sub-Saharan Africa had TFRs above replacement level in 2019 and accounted for 27âą1% (95% UI 26âą4â27âą8) of global livebirths. Global life expectancy at birth increased from 67âą2 years (95% UI 66âą8â67âą6) in 2000 to 73âą5 years (72âą8â74âą3) in 2019. The total number of deaths increased from 50âą7 million (49âą5â51âą9) in 2000 to 56âą5 million (53âą7â59âą2) in 2019. Under-5 deaths declined from 9âą6 million (9âą1â10âą3) in 2000 to 5âą0 million (4âą3â6âą0) in 2019. Global population increased by 25âą7%, from 6âą2 billion (6âą0â6âą3) in 2000 to 7âą7 billion (7âą5â8âą0) in 2019. In 2019, 34 countries had negative natural rates of increase; in 17 of these, the population declined because immigration was not sufficient to counteract the negative rate of decline. Globally, HALE increased from 58âą6 years (56âą1â60âą8) in 2000 to 63âą5 years (60âą8â66âą1) in 2019. HALE increased in 202 of 204 countries and territories between 2000 and 2019. Interpretation: Over the past 20 years, fertility rates have been dropping steadily and life expectancy has been increasing, with few exceptions. Much of this change follows historical patterns linking social and economic determinants, such as those captured by the GBD Socio-demographic Index, with demographic outcomes. More recently, several countries have experienced a combination of low fertility and stagnating improvement in mortality rates, pushing more populations into the late stages of the demographic transition. Tracking demographic change and the emergence of new patterns will be essential for global health monitoring. Funding: Bill & Melinda Gates Foundation. © 2020 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licens
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and lowâmiddle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of âsingle-useâ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for lowâmiddle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both highâ and lowâmiddleâincome countries
Effetti dello stress idrico e della reidratazione su variet\ue0 di vite innestate su due differenti ibridi portinnesti.
Lo stress idrico \ue8 un fattore critico per alcuni fondamentali processi fisiologici delle piante che si manifesta attraverso la riduzione della fotosintesi e della conduttanza stomatica. L'obiettivo del lavoro \ue8 stato quello di analizzare, utilizzando un sistema aperto LCi e una termocamera a infrarossi, gli effetti di stress idrici e della successiva reidratazione sulla fotosintesi e la conduttanza stomatica nelle variet\ue0 di vite (Vitis vinifera L.) Corvina, Corvinone e Rondinella innestate sui portinnesti Kober 5BB e 140 Ru. e coltivate su due tipi di terreno: franco-argilloso e franco. I risultati hanno mostrato che la variet\ue0 Corvinone innestata su 140 Ru. e allevata su terreno franco-argilloso manteneva valori di fotosintesi e di conduttanza stomatica ancora elevati nonostante le condizioni di stress.
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Mitochondrial DNA polymorphism analyzed by restriction endonucleases in two sardinian populations
Polymorphism of mitochondrial DNA by means of restriction endonucleases analysis has been studied in two sardinian isolates, formerly subjected to different selective pressure due to malaria. The mitochondrial DNA haplotype frequencies differ significantly between the two villages. An evaluation of variability through Wahlund variance analysis rules out selective factors and suggests drift
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