130 research outputs found
Instability of antiferromagnetic magnons in strong fields
We predict that spin-waves in an ordered quantum antiferromagnet (AFM) in a
strong magnetic field become unstable with respect to spontaneous two-magnon
decays. At zero temperature, the instability occurs between the threshold field
and the saturation field . As an example, we investigate the
high-field dynamics of a Heisenberg antiferromagnet on a square lattice and
show that the single-magnon branch of the spectrum disappears in the most part
of the Brillouin zone.Comment: RevTeX, 4 pages, 3 figures, accepted to PR
Gauge invariant Boltzmann equation and the fluid limit
This article investigates the collisionless Boltzmann equation up to second
order in the cosmological perturbations. It describes the gauge dependence of
the distribution function and the construction of a gauge invariant
distribution function and brightness, and then derives the gauge invariant
fluid limit.Comment: 36 page
How close can an Inhomogeneous Universe mimic the Concordance Model?
Recently, spatially inhomogeneous cosmological models have been proposed as
an alternative to the LCDM model, with the aim of reproducing the late time
dynamics of the Universe without introducing a cosmological constant or dark
energy. This paper investigates the possibility of distinguishing such models
from the standard LCDM using background or large scale structure data. It also
illustrates and emphasizes the necessity of testing the Copernican principle in
order to confront the tests of general relativity with the large scale
structure.Comment: 15 pages, 7 figure
Density growth in Kantowski-Sachs cosmologies with cosmological constant
In this work the growth of density perturbations in Kantowski-Sachs
cosmologies with a positive cosmological constant is studied, using the 1+3 and
1+1+2 covariant formalisms. For each wave number we obtain a closed system for
scalars formed from quantities that are zero on the background and hence are
gauge-invariant. The solutions to this system are then analyzed both
analytically and numerically. In particular the effects of anisotropy and the
behaviour close to a bounce in the cosmic scale factor are considered. We find
that typically the density gradient in the bouncing directions experiences a
local maximum at or slightly after the bounce.Comment: 33 pages, 17 picture
Recommended from our members
Field method for preservation of total mercury in waters, including those associated with artisanal scale gold mining â
Analysis of mercury (Hg) in natural water samples has routinely been impractical in many environments, for example, artisanal and small-scale gold mines (ASGM), where difficult conditions make monitoring of harmful elements and chemicals used in the processes highly challenging. Current sampling methods require the use of hazardous or expensive materials, and so difficulties in sample collection and transport are elevated. To solve this problem, a solid-phase extraction-based method was developed for the sampling and preservation of dissolved Hg in natural water samples, particularly those found around ASGM sites. Recoveries of 85% ± 10% total Hg were obtained during 4 weeks of storage in refrigerated (4 °C, dark) and unrefrigerated (16 °C, dark) conditions, and from a representative river water spiked to 1 ÎŒg Lâ1 Hg2+, 94% ± 1% Hg recovery was obtained. Solid-phase extraction loading flow rates were tested at 2, 5, and 10 mL minâ1 with no breakthrough of Hg, and sorbent stability showed no breakthrough of Hg up to 2 weeks after functionalisation. The method was deployed across five artisanal gold mines in Kakamega gold belt, Kenya, to assess Hg concentrations in mine shaft water, ore washing ponds, and river and stream water, including drinking water sources. In all waters, Hg concentrations were below the WHO guideline limit value of 6 ÎŒg Lâ1, but drinking water sources contained trace concentrations of up to 0.35 ÎŒg Lâ1 total Hg, which may result in negative health effects from long-term exposure. The SPE method developed and deployed here is a robust sampling method that can therefore be applied in future Hg monitoring, toxicology, and environmental work to provide improved data that is representative of total dissolved Hg in water samples
Changing risk of environmental Campylobacter exposure with emerging poultry production systems in Ethiopia
Campylobacter is a leading cause of diarrhoea, and its presence in chickens is a significant risk for zoonotic infection. Poultry production is becoming increasingly intensive in Ethiopia and is incorporating more high-producing breeds into traditionally managed smallholdings, especially in peri-urban areas. This cross-sectional study sampled 219 household environments in one peri-urban and two rural areas of Ethiopia, and an additional 20 semi-intensive farms in the peri-urban district. Campylobacter was detected by polymerase chain reaction (PCR)-specific assays in 44 samples; 16 of which could be identified as C. jejuni. Flocks in the peri-urban area were at significantly greater odds of detection, including those which only kept indigenous birds under a scavenging system. It was also noted that scavenging flocks of exotic high-production birds (Rhode Island Red) were at slightly greater risk, perhaps as exotic birds are under more stress when kept under traditional management systems. We suggest that changes to the system of chicken production may alter the ecology and epidemiology of Campylobacter in the environment, chickens and people, which may drive emergence of new epidemiological patterns of disease. Further research is needed to determine the extent to which the current management intensification and the distribution programmes of exotic and/or improved indigenous birds may alter Campylobacter epidemiology, ecology and public health risk, before their widespread adoption
Antimicrobial resistance of Campylobacter isolates from small scale and backyard chicken in Kenya
Background Thermophilic Campylobacter species are a major cause of bacterial
foodborne diarrhoea in humans worldwide. Poultry and their products are the
predominant source for human campylobacteriosis. Resistance of Campylobacter
to antibiotics is increasing worldwide, but little is known about the
antibiotic resistance in Campylobacter isolated from chicken in Kenya. In this
study, 35 suspected Campylobacter strains isolated from faeces and cloacal
swabs of chicken were tested for their susceptibility to seven antibiotics
using a broth microdilution assay and molecular biological investigations.
Results Overall, DNA of thermophilic Campylobacter was identified in 53
samples by PCR (34 C. jejuni, 18 C. coli and one mix of both species) but only
35 Campylobacter isolates (31 C. jejuni and 4 C. coli) could be re-cultivated
after transportation to Germany. Isolates were tested for their susceptibility
to antibiotics using a broth microdilution assay. Additionally, molecular
biological detection of antibiotic resistance genes was carried out. C. jejuni
isolates showed a high rate of resistance to nalidixic acid, tetracycline and
ciprofloxacin of 77.4, 71.0 and 71.0 %, respectively. Low resistance (25.8 %)
was detected for gentamicin and chloramphenicol. Multidrug resistance in C.
jejuni could be detected in 19 (61.3 %) isolates. Resistance pattern of C.
coli isolates was comparable. Resistance to ciprofloxacin was confirmed by
MAMAâPCR and PCRâRFLP in all phenotypically resistant isolates. The tet(O)
gene was detected only in 54.5 % of tetracycline resistant C. jejuni isolates.
The tet(A) gene, which is also responsible for tetracycline resistance, was
found in 90.3 % of C. jejuni and in all C. coli isolates. Thirteen
phenotypically erythromycin-resistant isolates could not be characterised by
using PCRâRFLP and MAMAâPCR. Conclusions To the best of our knowledge, this
study is the first report about resistance to antibiotics in thermophilic
Campylobacter originating from chicken in Kenya. Campylobacter spp. show a
high level of resistance to ciprofloxacin, nalidixic acid and tetracycline but
also a remarkable one to chloramphenicol and gentamicin and they are multidrug
resistant. Resistance to antibiotics is a global public health concern. In
Kenya, resistance surveillance needs further attention in the future. Efforts
to establish at least a National Laboratory with facilities for performing
phenotypic and genotypic characterization of thermophilic Campylobacter is
highly recommended
Exploring alternatives for livestock production in Bama, Burkina Faso: Playing the transformation game: Report of ResLeSS Workshop 2
Editorial: The society for environmental geochemistry and health (SEGH): 50Â years and beyond
When the SEGH international board released a short editorial paper back in 2019, we described an aim to increase the membership offering, whilst improving the diversity of input regionally, by scientific discipline and to ensure greater and more regular contact across the regions from 2020 onwards. Wider aspirations described in 2019 (Watts et al. 2019) are discussed within this short communication at the end of 2021 to evaluate progress made. In particular, how the SEGH community adapted to the unprecedented circumstances that have challenged each and every one of us throughout the COVID-19 pandemic since early 2020 and are likely to influence our activities for the foreseeable future
Approaches in biotechnological applications of natural polymers
Natural polymers, such as gums and mucilage, are biocompatible, cheap, easily available and non-toxic materials of native origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties, as well as they are considered alternative sources of raw materials since they present characteristics of sustainability, biodegradability and biosafety. As definition, gums and mucilages are polysaccharides or complex carbohydrates consisting of one or more monosaccharides or their derivatives linked in bewildering variety of linkages and structures. Natural gums are considered polysaccharides naturally occurring in varieties of plant seeds and exudates, tree or shrub exudates, seaweed extracts, fungi, bacteria, and animal sources. Water-soluble gums, also known as hydrocolloids, are considered exudates and are pathological products; therefore, they do not form a part of cell wall. On the other hand, mucilages are part of cell and physiological products. It is important to highlight that gums represent the largest amounts of polymer materials derived from plants. Gums have enormously large and broad applications in both food and non-food industries, being commonly used as thickening, binding, emulsifying, suspending, stabilizing agents and matrices for drug release in pharmaceutical and cosmetic industries. In the food industry, their gelling properties and the ability to mold edible films and coatings are extensively studied. The use of gums depends on the intrinsic properties that they provide, often at costs below those of synthetic polymers. For upgrading the value of gums, they are being processed into various forms, including the most recent nanomaterials, for various biotechnological applications. Thus, the main natural polymers including galactomannans, cellulose, chitin, agar, carrageenan, alginate, cashew gum, pectin and starch, in addition to the current researches about them are reviewed in this article.. }To the Conselho Nacional de Desenvolvimento CientfĂico e TecnolĂłgico (CNPq) for fellowships (LCBBC and MGCC) and the Coordenação de Aperfeiçoamento de Pessoal de NvĂel Superior (CAPES) (PBSA). This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit, the Project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and COMPETE 2020 (POCI-01-0145-FEDER-006684) (JAT)
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