1,194 research outputs found
Natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water: the example of West Bengal and its worldwide implications
In order to investigate the mechanism of As release to anoxic ground water in alluvial aquifers, the authors sampled ground waters from 3 piezometer nests, 79 shallow (80 m) wells, in an area 750 m by 450 m, just north of Barasat, near Kolkata (Calcutta), in southern West Bengal. High concentrations of As (200-1180 mug L-1) are accompanied by high concentrations of Fe (3-13.7 mgL(-1)) and PO4 (1-6.5 mg L-1). Ground water that is rich in Mn (1-5.3 mg L-1) contains <50 mug L-1 of As. The composition of shallow ground water varies at the 100-m scale laterally and the metre-scale vertically, with vertical gradients in As concentration reaching 200 mug L-1 m(-1). The As is supplied by reductive dissolution of FeOOH and release of the sorbed As to solution. The process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit. In well waters, thermotolerant coliforms, a proxy for faecal contamination, are not present in high numbers (<10 cfu/100 ml in 85% of wells) showing that faecally-derived organic matter does not enter the aquifer, does not drive reduction of FeOOH, and so does not release As to ground water.Arsenic concentrations are high (much greater than50 mug L-1) where reduction of FeOOH is complete and its entire load of sorbed As is released to solution, at which point the aquifer sediments become grey in colour as FeOOH vanishes. Where reduction is incomplete, the sediments are brown in colour and resorption of As to residual FeOOH keeps As concentrations below 10 mug L-1 in the presence of dissolved Fe. Sorbed As released by reduction of Mn oxides does not increase As in ground water because the As resorbs to FeOOH. High concentrations of As are common in alluvial aquifers of the Bengal Basin arise because Himalayan erosion supplies immature sediments, with low surface-loadings of FeOOH on mineral grains, to a depositional environment that is rich in organic mater so that complete reduction of FeOOH is common. (C) 2004 Published by Elsevier Ltd
Constructing Dirac linear fermions in terms of non-linear Heisenberg spinors
We show that the massive (or massless) neutrinos can be described as special
states of Heisenberg nonlinear spinors. As a by-product of this decomposition a
particularly attractive consequence appears: the possibility of relating the
existence of only three species of mass-less neutrinos to such internal
non-linear structure. At the same time it allows the possibility that neutrino
oscillation can occurs even for massless neutrinos
The developmental dynamics of terrorist organizations
We identify robust statistical patterns in the frequency and severity of
violent attacks by terrorist organizations as they grow and age. Using
group-level static and dynamic analyses of terrorist events worldwide from
1968-2008 and a simulation model of organizational dynamics, we show that the
production of violent events tends to accelerate with increasing size and
experience. This coupling of frequency, experience and size arises from a
fundamental positive feedback loop in which attacks lead to growth which leads
to increased production of new attacks. In contrast, event severity is
independent of both size and experience. Thus larger, more experienced
organizations are more deadly because they attack more frequently, not because
their attacks are more deadly, and large events are equally likely to come from
large and small organizations. These results hold across political ideologies
and time, suggesting that the frequency and severity of terrorism may be
constrained by fundamental processes.Comment: 28 pages, 8 figures, 4 tables, supplementary materia
Sigma-1 receptors control neuropathic pain and macrophage infiltration into the dorsal root ganglion after peripheral nerve injury
Neuron-immune interaction in the dorsal root ganglia (DRG) plays a pivotal role in the neuropathic pain development after nerve injury. Sigma-1 receptor (Sig-1R) is expressed by DRG neurons but its role in neuropathic pain is not fully understood. We investigated the effect of peripheral Sig-1R on neuroinflammation in the DRG after spared (sciatic) nerve injury (SNI) in mice. Nerve injury induced a decrease in NeuN staining along with the nuclear eccentricity and ATF3 expression in the injured DRG. Sig-1R was present in all DRG neurons examined, and after SNI this receptor translocated to the periphery of the soma and the vicinity of the nucleus, especially in injured ATF3 + neurons. In WT mice, injured DRG produced the chemokine CCL2, and this was followed by massive infiltration of macrophages/monocytes, which clustered mainly around sensory neurons with translocated Sig-1R, accompanied by robust IL-6 increase and mechanical allodynia. In contrast, Sig-1R knockout (Sig-1R-KO) mice showed reduced levels of CCL2, decreased macrophage/monocyte infiltration into DRG, and less IL-6 and neuropathic mechanical allodynia after SNI. Our findings point to an important role of peripheral Sig-1R in sensory neuron-macrophage/monocyte communication in the DRG after peripheral nerve injury; thus, these receptors may contribute to the neuropathic pain phenotypeNeurofarmacología del dolor de la Universidad de Granada (CTS-109)FPU grants from the Spanish Ministry of Education, Culture and Sports.Spanish Ministry of Economy and Competitiveness (MINECO, grant SAF2016-80540-R)the Junta de Andalucía (grant CTS 109)Esteve PharmaceuticalsEuropean Regional Development Fund (ERDF
The Cosmic Microwave Background and Particle Physics
In forthcoming years, connections between cosmology and particle physics will
be made increasingly important with the advent of a new generation of cosmic
microwave background (CMB) experiments. Here, we review a number of these
links. Our primary focus is on new CMB tests of inflation. We explain how the
inflationary predictions for the geometry of the Universe and primordial
density perturbations will be tested by CMB temperature fluctuations, and how
the gravitational waves predicted by inflation can be pursued with the CMB
polarization. The CMB signatures of topological defects and primordial magnetic
fields from cosmological phase transitions are also discussed. Furthermore, we
review current and future CMB constraints on various types of dark matter (e.g.
massive neutrinos, weakly interacting massive particles, axions, vacuum
energy), decaying particles, the baryon asymmetry of the Universe,
ultra-high-energy cosmic rays, exotic cosmological topologies, and other new
physics.Comment: 43 pages. To appear in Annual Reviews of Nuclear and Particle Scienc
Recommendation of an integrated index for the quality of educational services using multivariate statistics
In this work, the analysis of the surveys was carried out through a factorial analysis, which facilitates the evaluation of the validity of the selected construct for the case under study, as well as evaluating the quality of the service for each factor, with a view to determining the level of quality of the educational service, for which it integrates elements of descriptive and multivariate statistics with the management of the quality of the educational service. They are used as fundamental statistical techniques, descriptive analysis, factor analysis and analysis of variance. As a final result, it was concluded that the students of five UNITEC careers evaluated the educational service they receive as very satisfactory (4 points), highlighting the tangible elements as the most weighted factor. A significant aspect is that there are no significant differences in the perceptions of students from different careers and different sections
Precision Measurement of the Newtonian Gravitational Constant Using Cold Atoms
About 300 experiments have tried to determine the value of the Newtonian
gravitational constant, G, so far, but large discrepancies in the results have
made it impossible to know its value precisely. The weakness of the
gravitational interaction and the impossibility of shielding the effects of
gravity make it very difficult to measure G while keeping systematic effects
under control. Most previous experiments performed were based on the torsion
pendulum or torsion balance scheme as in the experiment by Cavendish in 1798,
and in all cases macroscopic masses were used. Here we report the precise
determination of G using laser-cooled atoms and quantum interferometry. We
obtain the value G=6.67191(99) x 10^(-11) m^3 kg^(-1) s^(-2) with a relative
uncertainty of 150 parts per million (the combined standard uncertainty is
given in parentheses). Our value differs by 1.5 combined standard deviations
from the current recommended value of the Committee on Data for Science and
Technology. A conceptually different experiment such as ours helps to identify
the systematic errors that have proved elusive in previous experiments, thus
improving the confidence in the value of G. There is no definitive relationship
between G and the other fundamental constants, and there is no theoretical
prediction for its value, against which to test experimental results. Improving
the precision with which we know G has not only a pure metrological interest,
but is also important because of the key role that G has in theories of
gravitation, cosmology, particle physics and astrophysics and in geophysical
models.Comment: 3 figures, 1 tabl
Hybrid management of a spontaneous ilio-iliac arteriovenous fistula: a case report
<p>Abstract</p> <p>Introduction</p> <p>Spontaneous iliac arteriovenous fistulae are a rare clinical entity. Such localized fistulation is usually a result of penetrating traumatic or iatrogenic injury. Clinical presentation can vary greatly but commonly includes back pain, high-output congestive cardiac failure and the presence of an abdominal bruit. Diagnosis, therefore, is often incidental or delayed.</p> <p>Case presentation</p> <p>We report a case of a spontaneous ilio-iliac arteriovenous fistula in a 68-year-old Caucasian man detected following presentation with unilateral claudication and congestive cardiac failure. Following computed tomography evaluation, the fistula was successfully treated with a combined endovascular (aorto-uni-iliac device) and open (femoro-femoral crossover) approach.</p> <p>Conclusion</p> <p>Endovascular surgery has revolutionized the management of such fistulae and we report an interesting case of a high-output iliac arteriovenous fistulae successfully treated with a hybrid vascular approach.</p
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