486 research outputs found
Microplastics in Namibian river sediments – a first evaluation
The African continent is rarely the focus of microplastics research, although the ubiquity of microplastics in the environment is undisputed and still increasing. Due to the high production and use of plastic products and the partial lack of recycling systems in many parts of the African continent, it can be assumed that microplastic particles are already present in limnic and terrestrial ecosystems. Few studies, mainly from South Africa and the Northern African region, show a contamination with microplastics, especially in marine environments. This study aims to explore the presence and composition of microplastics in fluvial sediments of the major catchments in Namibia with a regional focus on the Iishana system in Northern Namibia, as one of the most densely populated areas in the country. In March 2019 and March 2021, at the end of the rainy seasons, sediments from the Iishana system and of the largest river catchments were sampled. Extraction was performed by density separation using the Microplastic Sediment Separator (MPSS) with the separation solution sodium chloride (density of 1.20 g/cm3). The particle size was determined by filtration and fractionation, and the polymer type by measurement with ATR-FTIR spectroscopy (minimum particle size 0.3 mm). Microplastics were found in the sediments of each river system, most of the particles in the Iishana system (average of 13.2 particles/kg dry weight). The perennial, the ephemeral rivers, and the Iishana system are similar concerning polymer type and particle size. Polyethylene and polypropylene were the dominant polymer types. Most of the particles were found in the size fractions 0.3 – 0.5 mm and 0.5 – 1.0 mm. The particles were found mainly as fragments and films, the majority transparent and brown
The -diagnostic -- an a posteriori error assessment for single-reference coupled-cluster methods
We propose a novel a posteriori error assessment for the single-reference
coupled-cluster (SRCC) method called the -diagnostic. We provide a
derivation of the -diagnostic that is rooted in the mathematical analysis of
different SRCC variants. We numerically scrutinized the -diagnostic, testing
its performance for (1) geometry optimizations, (2) electronic correlation
simulations of systems with varying numerical difficulty, and (3) the
square-planar copper complexes [CuCl], [Cu(NH)], and
[Cu(HO)]. Throughout the numerical investigations, the
-diagnostic is compared to other SRCC diagnostic procedures, that is, the
, , and diagnostics as well as different indices of
multi-determinantal and multi-reference character in coupled-cluster theory.
Our numerical investigations show that the -diagnostic outperforms the
, , and diagnostics and is comparable to the indices of
multi-determinantal and multi-reference character in coupled-cluster theory in
their individual fields of applicability. The experiments investigating the
performance of the -diagnostic for geometry optimizations using SRCC reveal
that the -diagnostic correlates well with different error measures at a high
level of statistical relevance. The experiments investigating the performance
of the -diagnostic for electronic correlation simulations show that the
-diagnostic correctly predicts strong multi-reference regimes. The
-diagnostic moreover correctly detects the successful SRCC computations for
[CuCl], [Cu(NH)], and [Cu(HO)], which
have been known to be misdiagnosed by and diagnostics in the past.
This shows that the -diagnostic is a promising candidate for an a posteriori
diagnostic for SRCC calculations
Does gender matter? A cross-national investigation of primary class-room discipline.
© 2018 Informa UK Limited, trading as Taylor & Francis GroupFewer than 15% of primary school teachers in both Germany and the UK are male. With the on-going international debate about educational performance highlighting the widening gender achievement gap between girl and boy pupils, the demand for more male teachers has become prevalent in educational discourse. Concerns have frequently been raised about the underachievement of boys, with claims that the lack of male ‘role models’ in schools has an adverse effect on boys’ academic motivation and engagement. Although previous research has examined ‘teaching’ as institutional talk, men’s linguistic behaviour in the classroom remains largely ignored, especially in regard to enacting discipline. Using empirical spoken data collected from four primary school classrooms in both the UK and in Germany, this paper examines the linguistic discipline strategies of eight male and eight female teachers using Interactional Sociolinguistics to address the question, does teacher gender matter?Peer reviewedFinal Accepted Versio
Dynamic generation of maximally entangled photon multiplets by adiabatic passage
The adiabatic passage scheme for quantum state synthesis, in which atomic
Zeeman coherences are mapped to photon states in an optical cavity, is extended
to the general case of two degenerate cavity modes with orthogonal
polarization. Analytical calculations of the dressed-state structure and Monte
Carlo wave-function simulations of the system dynamics show that, for a
suitably chosen cavity detuning, it is possible to generate states of photon
multiplets that are maximally entangled in polarization. These states display
nonclassical correlations of the type described by Greenberger, Horne, and
Zeilinger (GHZ). An experimental scheme to realize a GHZ measurement using
coincidence detection of the photons escaping from the cavity is proposed. The
correlations are found to originate in the dynamics of the adiabatic passage
and persist even if cavity decay and GHZ state synthesis compete on the same
time scale. Beyond entangled field states, it is also possible to generate
entanglement between photons and the atom by using a different atomic
transition and initial Zeeman state.Comment: 22 pages (RevTeX), including 23 postscript figures. To be published
in Physical Review
Distortion Product Otoacoustic Emissions Evoked by Tone Complexes
Distortion product otoacoustic emissions (DPOAEs) are traditionally evoked by two-tone stimuli. In this study, emission data from Mongolian gerbils are reported that were obtained with stimuli consisting of six to 10 tones. The stimuli were constructed by replacing one of the tones of a tone pair by a narrowband multitone complex. This produced rich spectra of the ear canal sound pressure in which many of the third-order DPOAEs originated from the interaction of triplets of stimulus components. A careful choice of the stimulus frequencies ensured that none of these DPOAE components coincided. Three groups of DPOAEs are reported, two of which are closely related to DPOAEs evoked by tone pairs. The third group has no two-tone equivalent and only arises when using a multitone stimulus. We analyzed the relation between multitone-evoked DPOAEs and DPOAEs evoked by tone pairs, and explored the new degrees of freedom offered by the multitone paradigm
Impact of Rheumatic Musculoskeletal Disease on Psychological Development in Adolescents and Young Adults
Adolescents and young adults (AYAs) undergo significant physiological and psychological transformations. When developmental milestones are combined with additional challenges of growing up with a chronic rheumatic musculoskeletal disease (RMD), it can increase AYA's susceptibility to psychological problems. Emotional issues in adolescence can often persist into adulthood and negatively impact future health, social, and work outcomes. This chapter summarises psychological challenges for AYAs and recommends ways for healthcare professionals (HCPs) to promote mental wellbeing in AYAs with RMD
Hypoxia Alters Cell Cycle Regulatory Protein Expression and Induces Premature Maturation of Oligodendrocyte Precursor Cells
Periventricular white matter injury (PWMI) is a common form of brain injury sustained by preterm infants. A major factor that predisposes to PWMI is hypoxia. Because oligodendrocytes (OLs) are responsible for myelination of axons, abnormal OL development or function may affect brain myelination. At present our understanding of the influences of hypoxia on OL development is limited. To examine isolated effects of hypoxia on OLs, we examined the influences of hypoxia on OL development in vitro.Cultures of oligodendrocyte precursor cells (OPCs) were prepared from mixed glial cultures and were 99% pure. OPCs were maintained at 21% O(2) or hypoxia (1% or 4% O(2)) for up to 7 days. We observed that 1% O(2) lead to an increase in the proportion of myelin basic protein (MBP)-positive OLs after 1 week in culture, and a decrease in the proportion of platelet-derived growth factor receptor alpha (PDGFRalpha)-positive cells suggesting premature OL maturation. Increased expression of the cell cycle regulatory proteins p27(Kip1) and phospho-cdc2, which play a role in OL differentiation, was seen as well.These results show that hypoxia interferes with the normal process of OL differentiation by inducing premature OPC maturation
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