Tests for the asymptotic behaviour of the gamma^* --> gamma pi^0 form factor

The gamma^* --> gamma pi^0 transition measured at different photon virtualities already provides us with a clean test for the behaviour of the pi^0 gamma^* gamma off-shell axial anomaly at large time-like squared momenta. It also allows reliable predictions for the branching ratio of heavy quarkonium decays into omega pi^0.Comment: Latex, 7 pages + 1 .ps figure, comments on the Brodsky-Lepage limit and 5 new references adde

Frequency correlation requirements on the biphoton wavefunction in an induced coherence experiment between separate sources

There is renewed interest in using the coherence between beams generated in separate down-converter sources for new applications in imaging, spectroscopy, microscopy and optical coherence tomography (OCT). These schemes make use of continuous wave (CW) pumping in the low parametric gain regime, which produces frequency correlations, and frequency entanglement, between signal-idler pairs generated in each single source. But can induced coherence still be observed if there is no frequency correlation, so the biphoton wavefunction is factorable? We will show that this is the case, and this might be an advantage for OCT applications. High axial resolution requires a large bandwidth. For CW pumping this requires the use of short nonlinear crystals. This is detrimental since short crystals generate small photon fluxes. We show that the use of ultrashort pump pulses allows improving axial resolution even for long crystal that produce higher photon fluxes

Influence of Di erent Sieving Methods on Estimation of Sand Size Parameters

Sieving is one of the most used operational methods to determine sand size parameters which are essential to analyze coastal dynamics. However, the influence of hand versus mechanical shaking methods has not yet been studied. Herein, samples were taken from inside the hopper of a trailing suction dredger and sieved by hand with sieves of 10 and 20 cm diameters on board the dredger. Afterwards, these same samples were sieved with a mechanical shaker in the laboratory on land. The results showed di erences for the main size parameters D50, standard deviation, skewness, and kurtosis. Amongst the main results, it should be noted that the highest values for D50 and kurtosis were given by the small sieves method. On the other hand, the lowest values were given by the mechanical shaker method in the laboratory. Furthermore, standard deviation and skewness did not seem to be a ected by the sieving method which means that all the grainsize distribution was shifted but the shape remained unchanged. The few samples that do not follow these patterns have a higher percentage of shells. Finally and definitely, the small sieves should be rejected as a sieving method aboard

Biochar amendment for improved and more sustainable peat stabilisation

publishedVersio

Cyanobacterial calcification in modern microbialites at the submicrometer scale

International audienceThe search for microfossils in the geological record has been a long-term challenge. Part of the problem comes from the difficulty of identifying such microfossils unambiguously, since they can be morphologically confused with abiotic biomorphs. One route to improve our ability to correctly identify microfossils involves studying fossilization processes affecting bacteria in modern settings. We studied the initial stages of fossilization of cyanobacterial cells in modern microbialites from Lake Alchichica (Mexico), a Mg-rich hyperalkaline crater lake (pH 8.9) hosting currently growing stromatolites composed of aragonite [CaCO3] and hydromagnesite [Mg5(CO3)4(OH)2 * 4(H2O)]. Most of the biomass associated with the microbialites is composed of cyanobacteria. Scanning electron microscopy analyses coupled with confocal laser scanning microscopy observations were conducted to co-localize cyanobacterial cells and associated minerals. These observations showed that cyanobacterial cells affiliated with the order Pleurocapsales become specifically encrusted within aragonite with an apparent preservation of cell morphology. Encrustation gradients from non-encrusted to totally encrusted cells spanning distances of a few hundred micrometers were observed. Cells exhibiting increased levels of encrustation along this gradient were studied down to the nm scale using a combination of focused ion beam (FIB) milling, transmission electron microscopy (TEM) and scanning transmission x-ray microscopy (STXM) at the C, O and N K-edges. Two different types of aragonite crystals were observed: one type was composed of needle-shaped nano-crystals growing outward from the cell body with a crystallographic orientation perpendicular to the cell wall, and another type was composed of larger crystals that progressively filled the cell interior. Exopolymeric substances (EPS), initially co-localized with the cells, decreased in concentration and dispersed away from the cells while crystal growth occurred. As encrustation developed, EPS progressively disappeared, but remaining EPS showed the same spectroscopic signature. In the most advanced stages of fossilization, only the textural organization of the two types of aragonite recorded the initial cell morphology and spatial distribution

Living in a Space Balloon: From Cartoon to Reality

No abstract availabl

National, regional, and global causes of mortality in 5-19-year-olds from 2000 to 2019 : a systematic analysis

Background: Investments in the survival of older children and adolescents (aged 5-19 years) bring triple dividends for now, their future, and the next generation. However, 1·5 million deaths occurred in this age group globally in 2019, nearly all from preventable causes. To better focus the attention of the global community on improving survival of children and adolescents and to guide effective policy and programmes, sound and timely cause of death data are crucial, but often scarce. Methods: In this systematic analysis, we provide updated time-series for 2000-19 of national, regional, and global cause of death estimates for 5-19-year-olds with age-sex disaggregation. We estimated separately for countries with high versus low mortality, by data availability, and for four age-sex groups (5-9-year-olds [both sexes], 10-14-year-olds [both sexes], 15-19-year-old females, and 15-19-year-old males). Only studies reporting at least two causes of death were included in our analysis. We obtained empirical cause of death data through systematic review, known investigator tracing, and acquisition of known national and subnational cause of death studies. We adapted the Bayesian Least Absolute Shrinkage and Selection Operator approach to address data scarcity, enhance covariate selection, produce more robust estimates, offer increased flexibility, allow country random effects, propagate coherent uncertainty, and improve model stability. We harmonised all-cause mortality estimates with the UN Inter-agency Group for Child Mortality Estimation and systematically integrated single cause estimates as needed from WHO and UNAIDS. Findings: In 2019, the global leading specific causes of death were road traffic injuries (115 843 [95% uncertainty interval 110 672-125 054] deaths; 7·8% [7·5-8·1]); neoplasms (95 401 [90 744-104 812]; 6·4% [6·1-6·8]); malaria (81 516 [72 150-94 477]; 5·5% [4·9-6·2]); drowning (77 460 [72 474-85 952]; 5·2% [4·9-5·5]); and diarrhoea (72 679 [66 599-82 002], 4·9% [4·5-5·3]). The leading causes varied substantially across regions. The contribution of communicable, maternal, perinatal, and nutritional conditions declined with age, whereas the number of deaths associated with injuries increased. The leading causes of death were diarrhoea (51 630 [47 206-56 235] deaths; 10·0% [9·5-10·5]) in 5-9-year-olds; malaria (31 587 [23 940-43 116]; 8·6% [6·6-10·4]) in 10-14-year-olds; self-harm (32 646 [29 530-36 416]; 13·4% [12·6-14·3]) in 15-19-year-old females; and road traffic injuries (48 757 [45 692-52 625]; 13·9% [13·3-14·3]) in 15-19-year-old males. Widespread declines in cause-specific mortality were estimated across age-sex groups and geographies in 2000-19, with few exceptions like collective violence. Interpretation: Child and adolescent survival needs focused attention. To translate the vision into actions, more investments in the health information infrastructure for cause of death and in the related life-saving interventions are needed

Zeolite-encapsulated single-atom catalysts for efficient CO2 conversion

Zeolite-supported single-atom catalysts (SACs) have emerged as a novel class of cheap and tuneable catalysts that can exhibit high activity, selectivity and stability. In this work, we conduct an extensive screening by means of density functional theory calculations to determine the usefulness of 3d, 4d and 5d transition metal (TM) SACs-supported in MFItype Silicalite-1 zeolite for CO2 conversion. Two reaction mechanisms are considered, namely the redox −direct CO2 dissociation− and associative −hydrogen-assisted CO2 dissociation− mechanisms. Early TM SACs exhibit the lowest energy barriers, which follow the redox mechanism. These energy barriers raise when going right in the periodic table up to group 10, where they become prohibitive and the associative mechanism should dominate. By also considering their resistance to aggregation, we support the use of Sc, Y, La, Ru, Rh, Ni, Pd and Pt as potentially active and stable catalysts for CO2 conversion, given their low energy barriers and strong interaction with the zeolite framework