Models of electron transport in single layer graphene

The main features of the conductivity of doped single layer graphene are analyzed, and models for different scattering mechanisms are presented.Comment: 15 pages. Submitted to the Proceedings of the ULTI symposium on Quantum Phenomena and Devices at Low Temperatures, Espoo, Finland, to be published in the Journ. of Low. Temp. Phy

Water toxicity and cyto-genotoxicity biomarkers in the fish Oreochromis niloticus (Cichlidae)

Micronucleus (MN) and nuclear abnormalities (NA) tests were used as biomarkers in the fish Oreochromis niloticus from a polluted pond in winter, spring and summer. Samples of water column were taken aiming to evaluate physical-chemical parameters and acute toxicity to the microcrustacean Daphnia similis. The pond waters were toxic to D. similis in spring and winter, but this toxicity was not detected in summer. The pond waters presented low levels of dissolved oxygen in spring and summer; higher ammonia concentrations in winter, and high hardness and conductivity. Fish collected at the polluted pond exhibited higher rates of DNA damage, as indicated by increased rates of MN and NA in erythrocytes when compared to the negative control, which were associated to water toxicity and physical-chemical variable. Thus, this study shows that results of water toxicity tests and genotoxic biomarkers in fish may be associated and theses approaches may be used together for the water quality assessment.Keywords: fish, cyto-genotoxicity, pollution, ecotoxicology, water quality

Os sistemas agroflorestais como alternativa de sustentabilidade em ecossistemas de várzea no Amazonas.

Os sistemas agroflorestais (SAFs) representam uma alternativa agroecológica de produção, sob regime sustentável, para os agricultores familiares na várzea dos Rios Solimões/Amazonas, principalmente no que se refere ao manejo florestal, à diversidade de produtos e à geração de renda. Diante disso, o objetivo deste trabalho foi compreender as diferentes formas de apropriação e de manejo dos recursos naturais através dos SAFs, nos subsistemas roça, sítio e lagos, como componente para a sustentabilidade dos agricultores familiares da localidade Costa da Terra Nova, município do Careiro da Várzea, Amazonas. O método empregado foi o Estudo de Caso com aplicação de questionários, entrevistas e observação participante. A produção familiar na Costa da Terra Nova é representada pelos SAFs, constituído pelos os subsistemas: roça quintal e lago, que proporcionam produtos tanto para subsistência quanto para comercialização local, e estabelecendo a agricultura como fundamental atividade na localidade. O principal produto para comercialização é obtido das hortaliças cultivadas na época da vazante no subsistema roça nas comunidades São Francisco e Nossa Senhora da Conceição; e do extrativismo pesqueiro no subsistema lago, na época da cheia, principalmente na comunidade São José. A criação de animal se dá no subsistema sítio e é apenas para subsistência, sendo as aves e os suínos os principais animais domésticos criados nas três comunidades. Portanto os SAFs tradicionais, constituídos pelos subsistemas, roça, sitio e lago, são responsáveis pela sustentabilidade socioeconômica da localidade pesquisada, servindo, como alternativa agrícola melhor adaptada às condições locais das áreas de várzea na Amazônia

Tensor Correlations Measured in 3He(e,e'pp)n

We have measured the 3He(e,e'pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum, $p_{tot}$. For pair relative momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low $p_{tot}$ and rises to approximately 0.5 at large $p_{tot}$. This shows the dominance of tensor over central correlations at this relative momentum.Comment: 4 pages, 4 figures, submitted to PR

Measurement of the nuclear multiplicity ratio for Ks0K^0_s hadronization at CLAS

The influence of cold nuclear matter on lepto-production of hadrons in semi-inclusive deep inelastic scattering is measured using the CLAS detector in Hall B at Jefferson Lab and a 5.014 GeV electron beam. We report the $K_s^0$ multiplicity ratios for targets of C, Fe, and Pb relative to deuterium as a function of the fractional virtual photon energy $z$ transferred to the $K_s^0$ and the transverse momentum squared $p_{T}^2$ of the $K_s^0$. We find that the multiplicity ratios for $K^0_s$ are reduced in the nuclear medium at high $z$ and low $p_{T}^2$, with a trend for the $K^0_s$ transverse momentum to be broadened in the nucleus for large $p_{T}^2$.Comment: Submitted to Phys. Lett.

Second generation anticoagulant rodenticide residues in red kites 2020

Second generation anticoagulant rodenticides (SGARs) can be toxic to all mammals and birds if consumed. Various studies have shown that, in Britain, there is widespread exposure to SGARs in a diverse range of predatory mammals and birds, including red kites (Milvus milvus) which scavenge dead rats, a target species for rodent control. The Wildlife Incident Investigation Scheme1 (WIIS) and the Predatory Bird Monitoring Scheme (PBMS) have shown that some mortalities result from this secondary exposure. In the present study, we analysed liver SGAR residues in 25 red kites that had been found dead in Britain in 2020. The carcasses were submitted to and necropsied by the Disease Risk Analysis and Health Surveillance (DRAHS) programme, the PBMS, the WIIS for England & Wales, the WIIS for Scotland and the Raptor Health Scotland study. All the organisations are partners in the WILDCOMS (Wildlife Disease & Contaminant Monitoring & Surveillance Network) network that promotes collaboration among surveillance schemes that monitor disease and contaminants in vertebrate wildlife in the UK. The UK Rodenticide Stewardship Regime began to come into force in mid-2016 as reregistration of products for use in the UK was approved by the HSE; full implementation of the scheme was in early 2018. The key aim of this stewardship initiative is to support competence among all SGAR users, a potential benefit of this may be the reduced exposure of non-target wildlife to anticoagulant rodenticides. However, the number and density of SGAR-contaminated rats may remain unchanged although diligent searching, removal and safe disposal of poisoned rats, as promoted by the stewardship regime, might be expected to reduce the availability of poisoned dead rats to red kites (and other scavengers) and thereby reduce the proportion of birds that are exposed and/or the magnitude of exposure. Concomitant with the stewardship scheme was a relaxation of the indoor-use-only-restriction previously applied to brodifacoum, flocoumafen and difethialone, the three most acutely toxic SGARs. Any consequent increase in outdoor use of these three SGARs could increase the risk of secondary exposure in red kites. We therefore compared the data in the current report with that collected in 2015 and 2016 to determine if there was any evidence of a change in pattern or magnitude of exposure in red kites that might be connected to stewardship and/or change in usage restriction. All but one of the 21 red kites from England & Wales and two of the four red kites from Scotland had detectable liver residues of at least one type of SGAR. When considering the sample of red kites as a whole, brodifacoum, difenacoum and bromadiolone were each detected in 21, 19 and 17 red kites, respectively. Difethialone was found in four individuals while flocoumafen was detected in one bird. The proportion of analysed red kites exposed to SGARs in 2015 (91%), 2016 (90%) 2017 (96%), 2018 (100%) 2019 (91%) and 2020 (88%) was similar at circa 88% or more; the higher percentages in 2017 and 2018 were principally due to a greater proportion of birds from Scotland containing residues than observe in other years. Difenacoum, brodifacoum, and bromodialone were the most prevalent compounds (detected in 86%, 85%, and 76% of red kites across the six years for each compound, respectively). On average, there were detectable residues of three different SGARs in each red kite liver likely demonstrating multiple exposures. Sum liver SGAR concentrations in birds from 2020 ranged between non-detectable and 1086 ng/g wet weight (arithmetic mean: 371 ng/g wet weight, median 307 ng/g wet weight). Necropsy examinations indicated that three (13%) of red kites examined had internal haemorrhaging that was not associated with detectable trauma and also had detectable liver SGAR concentrations. These birds had sum SGAR liver concentrations of 663, 905 and 1086 ng/g wet weight. SGARs were considered a contributory cause of death resulting from unspecified use in these cases. SGARs were a contributory cause of death in 17% of the red kite cases examined across all six years. Over the period 2015 to 2020, a reduction has been observed in the percentage of red kites examined that were diagnosed as birds in which SGARs were implicated as a contributory cause of death. However, given that the WIIS scheme specifically examines suspected poisoning incidents, it is likely that poisoned birds are over represented in this sample compared to the population as a whole in all six years. Due to these reasons, caution should be used when interpreting evident changes in mortality rates due to the sampling protocols used in this study that may lead to over reporting of mortality rates, and those rates being subject to variations in relative contribution of the WIIS and PBMS to each year’s sample. There was no statistically significant difference between years, irrespective of cause of death, in median summed SGAR residues, and no evidence that the magnitude of accumulated summed SGAR residues has changed consistently over time. Sum bromadiolone and difenacoum concentrations were lower in 2016 than 2015, however, there was no difference for sum brodifacoum, flocoumafen, and difethialone concentrations. Data on presence/absence of detectable brodifacoum, flocoumafen or difethialone residues were compared for 2015/16 and 2017/18/19/20. The proportion of red kites with detectable residues of these three SGARs was 82% in 2015/16 and similar proportions were observed in 2017/18/19/20 (86%). Similarly, there was no significant difference in the proportion of red kites with detectable liver difenacoum or bromadiolone residues (90% in 2015/16 vs. 93% in 2017/18/19/20). Since the implementation of the stewardship regime no difference in exposure pattern relating to active ingredient has been detected. Our findings do not indicate that there has been a broad scale change in exposure in red kites to SGARs following implementation of stewardship in terms of either the proportion of the sample exposed or the magnitude of sum SGARs residues detected. There is some evidence (depending upon the statistical approach used) that the proportion of red kites in which SGARs were implicated as a contributory mortality factor has decreased in more recent years. Alternative approaches to monitoring SGARs in red kites could be considered that analyses a random but representative sample, and as part of such a programme there may also be value in monitoring SGARs in the blood of tracked individuals. There was no clear evidence that relaxation of usage restrictions on brodifacoum, difethialone and flocoumafen has altered the pattern of residues for these compounds in red kites to date. However, data following full implementation of the rodenticide stewardship scheme is currently limited to four years

Demonstration of a novel technique to measure two-photon exchange effects in elastic e±pe^\pm p scattering

The discrepancy between proton electromagnetic form factors extracted using unpolarized and polarized scattering data is believed to be a consequence of two-photon exchange (TPE) effects. However, the calculations of TPE corrections have significant model dependence, and there is limited direct experimental evidence for such corrections. We present the results of a new experimental technique for making direct $e^\pm p$ comparisons, which has the potential to make precise measurements over a broad range in $Q^2$ and scattering angles. We use the Jefferson Lab electron beam and the Hall B photon tagger to generate a clean but untagged photon beam. The photon beam impinges on a converter foil to generate a mixed beam of electrons, positrons, and photons. A chicane is used to separate and recombine the electron and positron beams while the photon beam is stopped by a photon blocker. This provides a combined electron and positron beam, with energies from 0.5 to 3.2 GeV, which impinges on a liquid hydrogen target. The large acceptance CLAS detector is used to identify and reconstruct elastic scattering events, determining both the initial lepton energy and the sign of the scattered lepton. The data were collected in two days with a primary electron beam energy of only 3.3 GeV, limiting the data from this run to smaller values of $Q^2$ and scattering angle. Nonetheless, this measurement yields a data sample for $e^\pm p$ with statistics comparable to those of the best previous measurements. We have shown that we can cleanly identify elastic scattering events and correct for the difference in acceptance for electron and positron scattering. The final ratio of positron to electron scattering: $R=1.027\pm0.005\pm0.05$ for $=0.206$ GeV$^2$ and $0.830\leq \epsilon\leq 0.943$