DFT study of undoped and As-doped Si nanowires approaching the bulk limit

The electronic properties of pure and As-doped Si nanowires (NWs) with radii up to 9.53 nm are studied using large scale density functional theory (DFT) calculations. We show that, for the undoped NWs, the DFT bandgap reduces with increasing diameter and converges to its bulk value, a trend in agreement with experimental data. Moreover, we show that the atoms closest to the surface of the nanowire (NW) contribute less to the states near the band edges, when compared with atoms close to the centre; this is shown to be due to differences in Si-Si atomic distances, as well as surface passivation effects. When considering As-doped Si NWs we show that dopant placement within the NW plays an important role in deciding electronic properties. We show that a low velocity band is introduced by As doping, in the gap, but close to the conduction band edge. The curvature of this low velocity band depends on the dopant location, with the curvature reducing when the dopant is placed closer to the center. We also show that asymmetry of dopant location with the NW leads to splitting of the valence band edge

Employability of Management Graduates of State Universities in Sri Lanka: Problems and Prospects

Employability must have to be attained in the journey to success in one’s career life. Graduates must be equipped with employability skills, knowledge, and personal attributes as the government of Sri Lanka allocates substantial resources for higher education. However, after graduation, a considerable number of graduates in the field of social sciences including management fail to find suitable employment, hence, are forced to accept lower-paying jobs that are not commensurate with their qualifications and some graduates are unemployed or underemployed. In this context, this study examines the level of employment and employability of management graduates of state universities in Sri Lanka, identifies problems and difficulties faced by management graduates in finding suitable jobs in the industry, and proposes policy measures for improving the employability of management undergraduates of state universities in Sri Lanka. Quantitative research methods were used to achieve the objectives of the study. Among 10,033 Management Graduates from 09 state universities, a sample of 1333 students was selected based on a stratified random sample method. A postal survey with a structured questionnaire was used to collect the data. Descriptive statics were used to analyze the data. The employability level of Management Graduates is higher than the average level. Nearly, 90% of them are employed or self-employed, but most of them are seeking a new job. The degree,personality, work experience, English proficiency and professional qualifications are the most important reasons for getting their current job. Age and lack of experience are the major constraints faced by graduates in finding a suitable job. The study proposes policy measures to enhance the level of employment and the employability of Management Graduates. Keywords: Employability, Employment Level, Management Graduates, State Universities, Sri Lank

A Preliminary survey of domiciliary cockroaches and their oothecal parasites in Sri Lanka

A survey of domiciliary cockroaches and their oothecal parasites was carriedout in 17 districts. The study was based on empty and live cockroach oothecaecollected from dwelling houses. Five species of cockroaches; Periplanetaamericana (L.) Neostylopyga rhombifolia (Stoll) Periplaneta australasiae (F.)Supella longfpalpa (F.) and Blatella germanica (L.) were found frequentinghouses. Of them, P. american a was the most abundant and widely distributedspecies, while B. germanlca was the least abundant species. P. americana andN. rhombifolia were present in all but one district, while P. australaslae and S.longipalpa were confined to 12 and 08 districts respectively. Mannar districtwas peculiar in that only one domiciliary species, N. rhombifolia was recordedfrom there. Only two species of oothecal parasites, Tetrastlchus hagenowli(Ratz.) and Evania appendlgaster (L.) were encountered during the study. Eachof these parasite species was characterized by the size of the emergence hole theymade in cockroach oothecae. Thus on the basis of the emergence hole alone itwas possible to categorize the empty oothecae as being parasitized. Of theoothecae, those of P. americana and P. australiasae were parasitized by bothspecies of parasites, while oothecae of N. rhombifolla was parasitized by T.hagenowii only. Oothecae of S. longipalpa and B. germanica were not parasitiizedat all. There appears to be a great paucity in the oothecal parasite fauna ofSri Lanka, compared to India where eight species of hymenopterans are known toparasitize oothecae of domiciliary cockroaches. The possibility of controllinghousehold cockroaches using local and introduced parasites remains to be explored.The shortcomings in this preliminary survey are also reported

Structural properties of Silicon-Germanium and Germanium-Silicon Core-Shell Nanowires

Core-shell nanowires made of Si and Ge can be grown experimentally with excellent control for different sizes of both core and shell. We have studied the structural properties of Si/Ge and Ge/Si core-shell nanowires aligned along the [110] direction, with diameters up to 10.2 nm and varying core to shell ratios, using linear scaling Density Functional Theory (DFT). We show that Vegard's law, which is often used to predict the axial lattice constant, can lead to an error of up to 1%, underlining the need for a detailed ab initio atomistic treatment of the nanowire structure. We analyse the character of the intrinsic strain distribution and show that, regardless of the composition or bond direction, the Si core or shell always expands. In contrast, the strain patterns in the Ge shell or core are highly sensitive to the location, composition and bond direction. The highest strains are found at heterojunction interfaces and the surfaces of the nanowires. This detailed understanding of the atomistic structure and strain paves the way for studies of the electronic properties of core-shell nanowires and investigations of doping and structure defects

Design of MRI Structured Spiking Neural Networks and Learning Algorithms for Personalized Modelling, Analysis, and Prediction of EEG Signals

Abstract This paper proposes a novel method and algorithms for the design of MRI structured personalized 3D spiking neural network models (MRI-SNN) for a better analysis, modeling, and prediction of EEG signals. It proposes a novel gradient-descent learning algorithm integrated with a spike-time-dependent-plasticity algorithm. The models capture informative personal patterns of interaction between EEG channels, contrary to single EEG signal modeling methods or to spike-based approaches which do not use personal MRI data to pre-structure a model. The proposed models can not only learn and model accurately measured EEG data, but they can also predict signals at 3D model locations that correspond to non-monitored brain areas, e.g. other EEG channels, from where data has not been collected. This is the first study in this respect. As an illustration of the method, personalized MRI-SNN models are created and tested on EEG data from two subjects. The models result in better prediction accuracy and a better understanding of the personalized EEG signals than traditional methods due to the MRI and EEG information integration. The models are interpretable and facilitate a better understanding of related brain processes. This approach can be applied for personalized modeling, analysis, and prediction of EEG signals across brain studies such as the study and prediction of epilepsy, peri-perceptual brain activities, brain-computer interfaces, and others

Gapless spinons and a field-induced soliton gap in the hyper-honeycomb Cu oxalate framework compound [(C2_{2}H5_{5})3_{3}NH]2_{2}Cu2_{2}(C2_{2}O4_{4})3_{3}

We report a detailed study of the specific heat and magnetic susceptibility of single crystals of a spin liquid candidate: the hyper-honeycomb Cu oxalate framework compound [(C$_2$H$_5$)$_3$NH]$_2$Cu$_2$(C$_2$O$_4$)$_3$. The specific heat shows no anomaly associated with a magnetic transition at low temperatures down to $T\sim$ 180 mK in zero magnetic field. We observe a large linear-in-$T$ contribution to the specific heat $\gamma T$, $\gamma = 98(1)$ mK/mol K$^{2}$, at low temperatures, indicative of the presence of fermionic excitations despite the Mott insulating state. The low-$T$ specific heat is strongly suppressed by applied magnetic fields $H$, which induce an energy gap, $\Delta (H)$, in the spin-excitation spectrum. We use the four-component relativistic density-functional theory (DFT) to calculate the magnetic interactions, including the Dzyaloshinskii-Moriya antisymmetric exchange, which causes an effective staggered field acting on one copper sublattice. The magnitude and field dependence of the field-induced gap, $\Delta (H) \propto H^{2/3}$, are accurately predicted by the soliton mass calculated from the sine-Gordon model of weakly coupled antiferromagnetic Heisenberg chains with all parameters determined by our DFT calculations. Thus our experiment and calculations are entirely consistent with a model of [(C$_2$H$_5$)$_3$NH]$_2$Cu$_2$(C$_2$O$_4$)$_3$ in which anisotropic magnetic exchange interactions due to Jahn-Teller distortion cause one copper sublattice to dimerize, leaving a second sublattice of weakly coupled antiferromagnetic chains. We also show that this model quantitatively accounts for the measured temperature-dependent magnetic susceptibility. Thus [(C$_2$H$_5$)$_3$NH]$_2$Cu$_2$(C$_2$O$_4$)$_3$ is a canonical example of a one-dimensional spin-1/2 Heisenberg antiferromagnet and not a resonating-valence-bond quantum spin liquid, as previously proposed.Comment: 8 pages, 6 figure

Bioactive plasma coatings on orthodontic brackets: In Vitro metal ion release and cytotoxicity

The metal ion release characteristics and biocompatibility of meta-based materials are key factors that influence their use in orthodontics. Although stainless steel-based alloys have gained much interest and use due to their mechanical properties and cost, they are prone to localised attack after prolonged exposure to the hostile oral environment. Metal ions may induce cellular toxicity at high dosages. To circumvent these issues, orthodontic brackets were coated with a functional nanothin layer of plasma polymer and further immobilised with enantiomers of tryptophan. Analysis of the physicochemical properties confirmed the presence of functional coatings on the surface of the brackets. The quantification of metal ion release using mass spectrometry proved that plasma functionalisation could minimise metal ion release from orthodontic brackets. Furthermore, the biocompatibility of the brackets has been improved after functionalisation. These findings demonstrate that plasma polymer facilitated surface functionalisation of orthodontic brackets is a promising approach to reducing metal toxicity without impacting their bulk properties.Lasni Samalka Kumarasinghe, Neethu Ninan, Panthihage Ruvini Lakshika Dabare, Alex Cavallaro, Esma J. Dogramacı, Giampiero Rossi-Fedele ... et al

Thermoelectric power factor under strain-induced band-alignment in the half-Heuslers NbCoSn and TiCoSb

Band convergence is an effective strategy to improve the thermoelectric performance of complex bandstructure thermoelectric materials. Half-Heuslers are good candidates for band convergence studies because they have multiple bands near the valence bad edge that can be converged through various band engineering approaches providing power factor improvement opportunities. Theoretical calculations to identify the outcome of band convergence employ various approximations for the carrier scattering relaxation times (the most common being the constant relaxation time approximation) due to the high computational complexity involved in extracting them accurately. Here, we compare the outcome of strain-induced band convergence under two such scattering scenarios: i) the most commonly used constant relaxation time approximation and ii) energy dependent inter- and intra-valley scattering considerations for the half-Heuslers NbCoSn and TiCoSb. We show that the outcome of band convergence on the power factor depends on the carrier scattering assumptions, as well as the temperature. For both materials examined, band convergence improves the power factor. For NbCoSn, however, band convergence becomes more beneficial as temperature increases, under both scattering relaxation time assumptions. In the case of TiCoSb, on the other hand, constant relaxation time considerations also indicate that the relative power factor improvement increases with temperature, but under the energy dependent scattering time considerations, the relative improvement weakens with temperature. This indicates that the scattering details need to be accurately considered in band convergence studies to predict more accurate trends.Comment: 21 pages, 8 figures. arXiv admin note: text overlap with arXiv:1905.0795

The Koolungar Moorditj Healthy Skin Project: Elder and Community Led Resources Strengthen Aboriginal Voice for Skin Health

In partnership with local Aboriginal Community Controlled Health Organisations, the Elder-led co-designed Koolungar Moorditj Healthy Skin project is guided by principles of reciprocity, capacity building, respect, and community involvement. Through this work, the team of Elders, community members, clinicians and research staff have gained insight into the skin health needs of urban-living Aboriginal koolungar (children); and having identified a lack of targeted and culturally appropriate health literacy and health promotion resources on moorditj (strong) skin, prioritised development of community-created healthy skin resources. Community members self-appointed to Aboriginal Community Advisory Groups (CAG) on Whadjuk (Perth) and Wardandi (Bunbury) boodjar (land/place) provided local leadership and led the development of moorditj skin resources. Over several online and face-to-face meetings facilitated by an Aboriginal project officer, CAG members shared local perspectives and cultural knowledge to develop and inform the messaging, medium, and dissemination of health literacy and health promotion resources for healthy skin. All CAG-created research approaches, resources and materials were presented to the Elder Researchers for discussion, final review, and implementation by the project team. Culturally appropriate moorditj skin resources, designed by community for community, build on knowledge of healthy skin to achieve moorditj skin and moorditj health for urban-living Aboriginal koolungar