126 research outputs found
USING HISTORIC SITES IN DETERMINING PLANT-SOIL INTERACTIONS UNDER LONG TERM CONTAMINATED SOILS
The relationships between heavy metals in soils and crop tissues are critical in understanding the potential risk to crop yields from Zn, Cu and Ni (the principal phytotoxic elements of concern in sludge), and the possible effects on dietary Cd (the critical zootoxic element that is labile in sludge-treated soil and readily absorbed by plants. These relationships cannot be derived from the agronomic trials because the quantities of heavy metals applied to the soil in sludge are small. These are field sites have been treated with sludge for many years in operational practice and where the oncentrations of heavy metals have been significantly raised above background values, representing potentially a worse-case of soil contamination. The purpose of the study was to provide a surrogate for long-term sludge-treated agricultural soil by examining the effects on crops of heavy metals in soil irrigated with raw sewage effluent for periods of more than 80 years and containing significantly elevated concentrations of heavy metals. Methodology: Two surveys of the Gabal El Asfar Old Farm were undertaken to assess the long-term effects of heavy metals in sludge-treated soil on crop quality. In the first survey, the relationships between total and DTPA extractable heavy metals in soil and concentrations in citrus fruit were examined. Concentrations of heavy metals in leaves of citrus were measured in the second survey and related to total and DTPA extractable metals in soil.
The heavy metal contents of citrus leaves and fruit (orange - eleven sampling sites; mandarin - four sampling sites), and total and DTPA extractable concentrations in soils were measured in samples collected from different areas of the Farm during two site surveys. Total and DTPA concentrations of heavy metals in the surveyed soils showed significant enrichment by long-term irrigation with sewage effluent. For example, the maximum total concentrations of Zn and Cu were 530 and 366 mg kg-1, respectively, representing a potential risk to crop yields The maximum Cd concentration detected was 9 mg kg-1 and may be a potential risk to the human food chain from uptake into staple crops grown at the farm. DTPA extractable metals were significantly (P<0.001) correlated with the total contents of Zn (r=0.91***), Cu (r=0.83***), Ni (r=0.63***) and Pb (r=0.85***) in soil when data from both surveys were pooled for statistical evaluation. There was also evidence of a weak relationship between DTPA extractable Cd and the total soil Cadmium is the only element of concern in terms of the risk to human health from uptake into food crops grown on sludge-treated soil. The total Cd concentration in soil was raised to a value 3 times the maximum EU limit for this element in sludge-treated agricultural soil. Despite the marked increase in soil Cd content, there was no detectable transfer into citrus leaves or fruit (Figure 1). The absence of Cd uptake into citrus fruit is to be expected because fruits are amongst the least sensitive plant parts to Cd accumulation. These data emphasise the minimal risk to the human diet from Cd in fruit crops grown on sludge-treated soil. . In all cases, leaf tissue concentrations were low and in some cases Cu status was below the deficiency threshold. The Cd content in leaves was small and generally <0.02 mg kg-1 DM.
Effective dynamics for particles coupled to a quantized scalar field
We consider a system of N non-relativistic spinless quantum particles
(``electrons'') interacting with a quantized scalar Bose field (whose
excitations we call ``photons''). We examine the case when the velocity v of
the electrons is small with respect to the one of the photons, denoted by c
(v/c= epsilon << 1). We show that dressed particle states exist (particles
surrounded by ``virtual photons''), which, up to terms of order (v/c)^3, follow
Hamiltonian dynamics. The effective N-particle Hamiltonian contains the kinetic
energies of the particles and Coulomb-like pair potentials at order (v/c)^0 and
the velocity dependent Darwin interaction and a mass renormalization at order
(v/c)^{2}. Beyond that order the effective dynamics are expected to be
dissipative.
The main mathematical tool we use is adiabatic perturbation theory. However,
in the present case there is no eigenvalue which is separated by a gap from the
rest of the spectrum, but its role is taken by the bottom of the absolutely
continuous spectrum, which is not an eigenvalue.
Nevertheless we construct approximate dressed electrons subspaces, which are
adiabatically invariant for the dynamics up to order (v/c)\sqrt{\ln
(v/c)^{-1}}. We also give an explicit expression for the non adiabatic
transitions corresponding to emission of free photons. For the radiated energy
we obtain the quantum analogue of the Larmor formula of classical
electrodynamics.Comment: 67 pages, 2 figures, version accepted for publication in
Communications in Mathematical Physic
General Adiabatic Evolution with a Gap Condition
We consider the adiabatic regime of two parameters evolution semigroups
generated by linear operators that are analytic in time and satisfy the
following gap condition for all times: the spectrum of the generator consists
in finitely many isolated eigenvalues of finite algebraic multiplicity, away
from the rest of the spectrum. The restriction of the generator to the spectral
subspace corresponding to the distinguished eigenvalues is not assumed to be
diagonalizable. The presence of eigenilpotents in the spectral decomposition of
the generator forbids the evolution to follow the instantaneous eigenprojectors
of the generator in the adiabatic limit. Making use of superadiabatic
renormalization, we construct a different set of time-dependent projectors,
close to the instantaneous eigeprojectors of the generator in the adiabatic
limit, and an approximation of the evolution semigroup which intertwines
exactly between the values of these projectors at the initial and final times.
Hence, the evolution semigroup follows the constructed set of projectors in the
adiabatic regime, modulo error terms we control
Adiabatic theorems for generators of contracting evolutions
We develop an adiabatic theory for generators of contracting evolution on
Banach spaces. This provides a uniform framework for a host of adiabatic
theorems ranging from unitary quantum evolutions through quantum evolutions of
open systems generated by Lindbladians all the way to classically driven
stochastic systems. In all these cases the adiabatic evolution approximates, to
lowest order, the natural notion of parallel transport in the manifold of
instantaneous stationary states. The dynamics in the manifold of instantaneous
stationary states and transversal to it have distinct characteristics: The
former is irreversible and the latter is transient in a sense that we explain.
Both the gapped and gapless cases are considered. Some applications are
discussed.Comment: 31 pages, 4 figures, replaced by the version accepted for publication
in CM
The low-lying excitations of polydiacetylene
The Pariser-Parr-Pople Hamiltonian is used to calculate and identify the
nature of the low-lying vertical transition energies of polydiacetylene. The
model is solved using the density matrix renormalisation group method for a
fixed acetylenic geometry for chains of up to 102 atoms. The non-linear optical
properties of polydiacetylene are considered, which are determined by the
third-order susceptibility. The experimental 1Bu data of Giesa and Schultz are
used as the geometric model for the calculation. For short chains, the
calculated E(1Bu) agrees with the experimental value, within solvation effects
(ca. 0.3 eV). The charge gap is used to characterise bound and unbound states.
The nBu is above the charge gap and hence a continuum state; the 1Bu, 2Ag and
mAg are not and hence are bound excitons. For large chain lengths, the nBu
tends towards the charge gap as expected, strongly suggesting that the nBu is
the conduction band edge. The conduction band edge for PDA is agreed in the
literature to be ca. 3.0 eV. Accounting for the strong polarisation effects of
the medium and polaron formation gives our calculated E(nBu) ca. 3.6 eV, with
an exciton binding energy of ca. 1.0 eV. The 2Ag state is found to be above the
1Bu, which does not agree with relaxed transition experimental data. However,
this could be resolved by including explicit lattice relaxation in the Pariser-
Parr-Pople-Peierls model. Particle-hole separation data further suggest that
the 1Bu, 2Ag and mAg are bound excitons, and that the nBu is an unbound
exciton.Comment: LaTeX, 23 pages, 4 postscript tables and 8 postscript figure
Two Types of Planning in Neighborhoods
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68338/2/10.1177_0739456X8400300209.pd
Variação estacional dos hormônios tireoideanos e do cortisol em ovinos em ambiente tropical
Mapping geographical inequalities in childhood diarrhoeal morbidity and mortality in low-income and middle-income countries, 2000–17 : analysis for the Global Burden of Disease Study 2017
Background
Across low-income and middle-income countries (LMICs), one in ten deaths in children younger than 5 years is attributable to diarrhoea. The substantial between-country variation in both diarrhoea incidence and mortality is attributable to interventions that protect children, prevent infection, and treat disease. Identifying subnational regions with the highest burden and mapping associated risk factors can aid in reducing preventable childhood diarrhoea.
Methods
We used Bayesian model-based geostatistics and a geolocated dataset comprising 15 072 746 children younger than 5 years from 466 surveys in 94 LMICs, in combination with findings of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017, to estimate posterior distributions of diarrhoea prevalence, incidence, and mortality from 2000 to 2017. From these data, we estimated the burden of diarrhoea at varying subnational levels (termed units) by spatially aggregating draws, and we investigated the drivers of subnational patterns by creating aggregated risk factor estimates.
Findings
The greatest declines in diarrhoeal mortality were seen in south and southeast Asia and South America, where 54·0% (95% uncertainty interval [UI] 38·1–65·8), 17·4% (7·7–28·4), and 59·5% (34·2–86·9) of units, respectively, recorded decreases in deaths from diarrhoea greater than 10%. Although children in much of Africa remain at high risk of death due to diarrhoea, regions with the most deaths were outside Africa, with the highest mortality units located in Pakistan. Indonesia showed the greatest within-country geographical inequality; some regions had mortality rates nearly four times the average country rate. Reductions in mortality were correlated to improvements in water, sanitation, and hygiene (WASH) or reductions in child growth failure (CGF). Similarly, most high-risk areas had poor WASH, high CGF, or low oral rehydration therapy coverage.
Interpretation
By co-analysing geospatial trends in diarrhoeal burden and its key risk factors, we could assess candidate drivers of subnational death reduction. Further, by doing a counterfactual analysis of the remaining disease burden using key risk factors, we identified potential intervention strategies for vulnerable populations. In view of the demands for limited resources in LMICs, accurately quantifying the burden of diarrhoea and its drivers is important for precision public health
A search for the decay
We search for the rare flavor-changing neutral-current decay in a data sample of 82 fb collected with the {\sl BABAR}
detector at the PEP-II B-factory. Signal events are selected by examining the
properties of the system recoiling against either a reconstructed hadronic or
semileptonic charged-B decay. Using these two independent samples we obtain a
combined limit of
at the 90% confidence level. In addition, by selecting for pions rather than
kaons, we obtain a limit of using only the hadronic B reconstruction method.Comment: 7 pages, 8 postscript figures, submitted to Phys. Rev. Let
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