High-performance polarization-sensitive photodetectors on two-dimensional ß-InSe.

Two-dimensional (2D) indium selenide (InSe) has been widely studied for application in transistors and photodetectors, which benefit from its excellent optoelectronic properties. Among the three specific polytypes (γ-, ϵ- and ß-phase) of InSe, only the crystal lattice of InSe in ß-phase (ß-InSe) belongs to a non-symmetry point group of [Formula: see text], which indicates stronger anisotropic transport behavior and potential in the polarized photodetection of ß-InSe-based optoelectronic devices. Therefore, we prepare the stable p-type 2D-layered ß-InSe via temperature gradient method. The anisotropic Raman, transport and photoresponse properties of ß-InSe have been experimentally and theoretically proven, showing that the ß-InSe-based device has a ratio of 3.76 for the maximum to minimum dark current at two orthogonal orientations and a high photocurrent anisotropic ratio of 0.70 at 1 V bias voltage, respectively. The appealing anisotropic properties demonstrated in this work clearly identify ß-InSe as a competitive candidate for filter-free polarization-sensitive photodetectors.

Influence of blood group, Glucose-6-phosphate dehydrogenase and Haemoglobin genotype on Falciparum malaria in children in Vihiga highland of Western Kenya.

BACKGROUND: Genetic diversity of ABO blood, glucose-6-phosphate dehydrogenase (G6PD) deficiency and haemoglobin type and their ability to protect against malaria vary geographically, ethnically and racially. No study has been carried out in populations resident in malaria regions in western Kenya. METHOD: A total of 574 malaria cases (severe malaria anaemia, SMA = 137 and non-SMA = 437) seeking treatment at Vihiga County and Referral Hospital in western Kenya, were enrolled and screened for ABO blood group, G6PD deficiency and haemoglobin genotyped in a hospital-based cross-sectional study. RESULT: When compared to blood group O, blood groups A, AB and B were not associated with SMA (P = 0.380, P = 0.183 and P = 0.464, respectively). Further regression analysis revealed that the carriage of the intermediate status of G6PD was associated with risk to SMA (OR = 1.52, 95%CI = 1.029-2.266, P = 0.035). There was, however, no association between AS and SS with severe malaria anaemia. Co-occurrence of both haemoglobin type and G6PD i.e. the AA/intermediate was associated with risk to SMA (OR = 1.536, 95%CI = 1.007-2.343, P = 0.046) while the carriage of the AS/normal G6PD was associated with protection against SMA (OR = 0.337, 95%CI = 0.156-0.915, P = 0.031). CONCLUSION: Results demonstrate that blood group genotypes do not have influence on malaria disease outcome in this region. Children in Vihiga with blood group O have some protection against malaria. However, the intermediate status of G6PD is associated with risk of SMA. Further, co-inheritance of sickle cell and G6PD status are important predictors of malaria disease outcome. This implies combinatorial gene function in influencing disease outcome.

Layer-Dependent Properties of Ultrathin GeS Nanosheets and Application in UV-Vis Photodetectors.

Two-dimensional germanium sulfide (GeS), an analogue of phosphorene, has attracted broad attention owing to its excellent environmental stabilities, fascinating electronic and optical properties, and applications in various nanodevices. In spite of the current achievements on 2D GeS, the report of ultrathin few-layer GeS nanosheets within 5 nm is still lacking. Here in this contribution, we have achieved preparation of ultrathin few-layer GeS nanosheets with thicknesses of 1.3 ± 0.1 nm [approximately three layers (∼3L)], 3.2 ± 0.2 nm (∼6L), and 4.2 ± 0.3 nm (∼8L) via a typical liquid-phase exfoliation (LPE) method. Based on various experimental characterizations and first-principles calculations, the layer-dependent electronic, transport, and optical properties are investigated. For the few-layer GeS nanosheets, enhanced light absorption in the UV-vis region and superior photoresponse behavior with increasing layer number is observed, while for the thin films above 10 nm, the properties degenerate to the bulk feature. In addition, the as-prepared ultrathin nanosheets manifest great potential in the applications of photoelectrochemical (PEC)-type photodetectors, exhibiting excellent and stable periodic photoresponse behavior under the radiation of white light. The ∼8L GeS-based photodetector exhibits superior performance than the thinner GeS nanosheets (<4 nm), even better as compared to the bulk or film (above 10 nm) counterparts in terms of higher photoresponsivity along with remarkable photodetection performance in the UV-vis region. This work not only provides direct and solid evidence of the layer-number evolutionary band structure, mobility, and optical properties of ultrathin 2D GeS nanosheets but also promotes the foreseeable applications of 2D GeS as energy-related photoelectric devices.

Monolayer ß-tellurene: a promising p-type thermoelectric material via first-principles calculations.

Inspired by the experimental growth of two-dimensional (2D) tellurene (Yixin et al., Nat. Electron, 2018, 1, 228-236) and the recent study of unusually low thermal conductivity of atomically thin 2D tellurium (Jie Ren et al., Nanoscale, 2018, 10, 12997), we carried out systematic calculations for monolayer ß-tellurene, focusing on its electrical transport and electronic and thermoelectric properties by means of density functional theory (DFT) combined with deformation potential theory and Boltzmann transport theory. We have found that monolayer ß-tellurene exhibits a band gap of 1.5 eV. The carrier transport is highly direction-temperature-dependent, with a high room-temperature transport mobility of 1343 cm2 V-1 s-1 and a relaxation time of 283 fs in the armchair direction for hole transport at room-temperature. It is coincidently favourable in the armchair direction for both the Seebeck coefficient and the electrical conductivity, making the p-type monolayer ß-tellurene a highly promising thermoelectric candidate. With a low intrinsic lattice thermal conductivity, the maximum figure of merit (ZT) is 2.9 and 0.84 along the armchair and zigzag directions for p-type doping at 700 K, respectively. The predicted properties demonstrate that monolayer ß-tellurene can be a prospective material towards thermoelectric applications.

Liquefaction of water on the surface of anisotropic two-dimensional atomic layered black phosphorus.

The growth and wetting of water on two-dimensional(2D) materials are important to understand the development of 2D material based electronic, optoelectronic, and nanomechanical devices. Here, we visualize the liquefaction processes of water on the surface of graphene, MoS2 and black phosphorus (BP) via optical microscopy. We show that the shape of the water droplets forming on the surface of BP, which is anisotropic, is elliptical. In contrast, droplets are rounded when they form on the surface of graphene or MoS2, which do not possess orthometric anisotropy. Molecular simulations show that the anisotropic liquefaction process of water on the surface of BP is attributed to the different binding energies of H2O molecules on BP along the armchair and zigzag directions. The results not only reveal the anisotropic nature of water liquefaction on the BP surface but also provide a way for fast and nondestructive determination of the crystalline orientation of BP.

Electronic and Optical Properties of Two-Dimensional Tellurene: From First-Principles Calculations.

Tellurene is a new-emerging two-dimensional anisotropic semiconductor, with fascinating electric and optical properties that differ dramatically from the bulk counterpart. In this work, the layer dependent electronic and optical properties of few-layer Tellurene has been calculated with the density functional theory (DFT). It shows that the band gap of the Tellurene changes from direct to indirect when layer number changes from monolayer (1 L) to few-layers (2 L-6 L) due to structural reconstruction. Tellurene also has an energy gap that can be tuned from 1.0 eV (1 L) to 0.3 eV (6 L). Furthermore, due to the interplay of spin-orbit coupling (SOC) and disappearance of inversion symmetry in odd-numbered layer structures resulting in the anisotropic SOC splitting, the decrease of the band gap with an increasing layer number is not monotonic but rather shows an odd-even quantum confinement effect. The optical results in Tellurene are layer dependent and different in E ⊥ C and E || C directions. The correlations between the structure, the electronic and optical properties of the Tellurene have been identified. Despite the weak nature of interlayer forces in their structure, their electronic and optical properties are highly dependent on the number of layers and highly anisotropic. These results are essential in the realization of its full potential and recommended for experimental exploration.

Influence of blood meal and age of mosquitoes on susceptibility to pyrethroids in Anopheles gambiae from Western Kenya.

BACKGROUND: Physiological characteristics (age and blood feeding status) of malaria vectors can influence their susceptibility to the current vector control tools that target their feeding and resting behaviour. To ensure the sustainability of the current and future vector control tools an understanding of how physiological characteristics may contribute to insecticide tolerance in the field is fundamental for shaping resistance management strategies and vector control tools. The aim of this study was to determine whether blood meal and mosquito age affect pyrethroid tolerance in field-collected Anopheles gambiae from western Kenya. METHODS: Wild mosquito larvae were reared to adulthood alongside the pyrethroid-susceptible Kisumu strain. Adult females from the two populations were monitored for deltamethrin resistance when they were young at 2-5 days old and older 14-16 days old and whether fed or unfed for each age group. Metabolic assays were also performed to determine the level of detoxification enzymes. Mosquito specimens were further identified to species level using the polymerase chain reaction (PCR) method. RESULTS: Anopheles gambiae sensu stricto was the predominant species comprising 96% of specimens and 2.75% Anopheles arabiensis. Bioassay results showed reduced pyrethroid induced mortality with younger mosquitoes compared to older ones (mortality rates 83% vs. 98%), independently of their feeding status. Reduced mortality was recorded with younger females of which were fed compared to their unfed counterparts of the same age with a mortality rate of 35.5% vs. 83%. Older blood-fed females showed reduced susceptibility after exposure when compared to unfed females of the same age (mortality rates 86% vs. 98%). For the Kisumu susceptible population, mortality was straight 100% regardless of age and blood feeding status. Blood feeding status and mosquito age had an effect on enzyme levels in both populations, with blood fed individuals showing higher enzyme elevations compared to their unfed counterparts (P < 0.0001). The interaction between mosquito age and blood fed status had significant effect on mosquito mortality. CONCLUSION: The results showed that mosquito age and blood feeding status confers increased tolerance to insecticides as blood feeding may be playing an important role in the toxicity of deltamethrin, allowing mosquitoes to rest on insecticide-treated materials despite treatment. These may have implications for the sustained efficacy of indoor residual spraying and insecticide-treated nets based control programmes that target indoor resting female mosquitoes of various gonotrophic status.

Two Dimensional ß-InSe with Layer-Dependent Properties: Band Alignment, Work Function and Optical Properties.

Density functional theory calculations of the layer (L)-dependent electronic band structure, work function and optical properties of ß-InSe have been reported. Owing to the quantum size effects (QSEs) in ß-InSe, the band structures exhibit direct-to-indirect transitions from bulk ß-InSe to few-layer ß-InSe. The work functions decrease monotonically from 5.22 eV (1 L) to 5.0 eV (6 L) and then remain constant at 4.99 eV for 7 L and 8 L and drop down to 4.77 eV (bulk ß-InSe). For optical properties, the imaginary part of the dielectric function has a strong dependence on the thickness variation. Layer control in two-dimensional layered materials provides an effective strategy to modulate the layer-dependent properties which have potential applications in the next-generation high performance electronic and optoelectronic devices.

Distribution of Biomphalaria Snails in Associated Vegetations and Schistosome Infection Prevalence Along the Shores of Lake Victoria in Mbita, Kenya: A Cross-Sectional Study.

BACKGROUND: Schistosomiasis due to Schistosoma mansoni remains a major public health problem and cause of morbidity and mortality in sub-Saharan Africa despite the implementation of control programmes. More than 6 million Kenyans are at risk of infection. Regarding control measures, Biomphalaria snail species, which are the obligatory intermediate hosts for transmission of S. mansoni, have been neglected. Mbita subcounty in Homa Bay County, western Kenya, along Lake Victoria basin, has a high prevalence of S. mansoni infection despite mass drug administration. This study aimed to determine the abundance of Biomphalaria, with their associated vegetation and schistosome infection rates, along Mbita shoreline. METHODS: Sixteen purposively selected sites along the Mbita shoreline were sampled for Biomphalaria snails using a 30-minute scooping technique. Global positioning system technology was used to map selected sites. The associated vegetation at sampling sites were collected and identified. Schistosome infection status among the snails was determined via the detection of cercaria shedding. RESULTS: A total of 3,135 Biomphalaria sudanica snails were collected. The number of snails collected differed significantly between the 16 sites (F=11.735; degrees of freedom [df]=15.836; P<.001). Significant mean differences (MD) were also observed in terms of the number of snails collected per vegetation type (F=7.899; df=5.846; P<.001). The mean number of snails collected from Cyprus gracilis was significantly higher than that from Enydra fluactuants (MD= 2.03; P<.001), Eichhornia crassipes (MD=4.15; P<.010), and E. fluactuants mixed with E. crassipes (MD=2.516; P<.010). A total of 21 (0.67%) snails shed human cercariae, while 27 (0.86%) snails shed nonhuman cercariae, despite 14 sites having human faeces contamination. CONCLUSION: Although the schistosome infection prevalence among the snails was low, these sites may still be important exposure sites. C. gracilis is the main vegetation type associated with a high abundance of Biomphalaria snails. Molecular techniques are necessary for verification of schistosome positivity among the snails.

Omnipotent phosphorene: a next-generation, two-dimensional nanoplatform for multidisciplinary biomedical applications.

Phosphorene, also known as single- or few-layer black phosphorus (FLBP), is a new member of the two-dimensional (2D) material family and has attracted significant attention in recent years for applications in optoelectronics, energy storage and biomedicine due to its unique physicochemical properties and excellent biocompatibility. FLBP is regarded as a potential biological imaging agent for cancer diagnosis due to its intrinsic fluorescence (FL) and photoacoustic (PA) properties and negligible cytotoxicity. FLBP-based photothermal and photodynamic therapies have emerged with excellent anti-tumour therapeutic efficacies due to their unique physical properties, such as near-infrared (NIR) optical absorbance, large extinction coefficients, biodegradability and reactive oxygen species (ROS) or heat generation upon light irradiation. Furthermore, FLBP is a promising drug delivery platform because of its high drug-loading capacity due to its puckered layer structure with an ultralarge surface area, and FLBP is size-controllable with facile surface chemical modification. Because of the marked advantages of FLBP nanomaterials in biomedical applications, an overview of the latest progress and paradigms of FLBP-based nanoplatforms for multidisciplinary biomedical applications is presented in this tutorial review.

Novel concept of the smart NIR-light-controlled drug release of black phosphorus nanostructure for cancer therapy.

A biodegradable drug delivery system (DDS) is one the most promising therapeutic strategies for cancer therapy. Here, we propose a unique concept of light activation of black phosphorus (BP) at hydrogel nanostructures for cancer therapy. A photosensitizer converts light into heat that softens and melts drug-loaded hydrogel-based nanostructures. Drug release rates can be accurately controlled by light intensity, exposure duration, BP concentration, and hydrogel composition. Owing to sufficiently deep penetration of near-infrared (NIR) light through tissues, our BP-based system shows high therapeutic efficacy for treatment of s.c. cancers. Importantly, our drug delivery system is completely harmless and degradable in vivo. Together, our work proposes a unique concept for precision cancer therapy by external light excitation to release cancer drugs. If these findings are successfully translated into the clinic, millions of patients with cancer will benefit from our work.

Theoretical insights into nucleation of CO2 and CH4 hydrates for CO2 capture and storage.

We present a hybrid three-dimensional (3D) theoretical approach, the density functional theory (DFT) integrated with the reference interaction site model (RISM), to investigate the nucleation of CO2 and CH4 hydrates. Within the theoretical framework, the 3D-RISM is applied to describe gas density distributions in hydrate cages, and the 3D-DFT is used to describe the interfacial structure and properties of the two hydrates, as well as their nucleation. The crystal-liquid phase equilibria of CO2 and CH4 hydrates are predicted by the hybrid 3D-DFT-RISM, and compared with the available experimental data to examine the theoretical model. In particular, the local and interfacial structure and properties, the critical nucleus radii and free-energy barriers at moderate concentration supersaturation are presented to analyze their nucleation. The formation enthalpies for the two hydrates are calculated to evaluate the possibility of CO2 storage by CH4-CO2 replacement in hydrate.

A Model for Sustainable Development of Child Mental Health Infrastructure in the LMIC World: Vietnam as a Case Example.

Children and adolescents are among the highest need populations in regards to mental health support, especially in low and middle income countries (LMIC). Yet resources in LMIC for prevention and treatment of mental health problems are limited, in particular for children and adolescents. In this paper, we discuss a model for development of child and adolescent mental health (CAMH) resources in LMIC that has guided a ten year initiative focused on development of CAMH treatment and research infrastructure in Vietnam. We first review the need for development of mental health resources for children and adolescents in general, and then in Vietnam. We next present the model that guided our program as it developed, focused on the twin Capacity Development Goals of efficacy and sustainability, and the Capacity Development Targets used to move towards these goals. Finally we discuss our CAMH development initiative in Vietnam, the center of which has been development of a graduate program in clinical psychology at Vietnam National University, linking program activities to this model.

Development of Clinical Psychology and Mental Health Resources in Vietnam.

In this paper, we discuss development of the Vietnam National University graduate Clinical Psychology Program, which has the goal of training both Vietnamese researchers who will develop and evaluate culturally appropriate mental health treatments, as well as Vietnamese clinicians who will implement and help disseminate these evidence-based treatments. We first review the background situation in Vietnam regarding mental health, and its infrastructure and training needs, and discuss the process through which the decision was made to develop a graduate program in clinical psychology as the best approach to address these needs. We then review the development process for the program and its current status, and our focus on the schools as a site for service provision and mental health task shifting. Finally, we outline future goals and plans for the program, and discuss the various challenges that the program has faced and our attempts to resolve them.

Malaria in Kakuma refugee camp, Turkana, Kenya: facilitation of Anopheles arabiensis vector populations by installed water distribution and catchment systems.

BACKGROUND: Malaria is a major health concern for displaced persons occupying refugee camps in sub-Saharan Africa, yet there is little information on the incidence of infection and nature of transmission in these settings. Kakuma Refugee Camp, located in a dry area of north-western Kenya, has hosted ca. 60,000 to 90,000 refugees since 1992, primarily from Sudan and Somalia. The purpose of this study was to investigate malaria prevalence and attack rate and sources of Anopheles vectors in Kakuma refugee camp, in 2005-2006, after a malaria epidemic was observed by staff at camp clinics. METHODS: Malaria prevalence and attack rate was estimated from cases of fever presenting to camp clinics and the hospital in August 2005, using rapid diagnostic tests and microscopy of blood smears. Larval habitats of vectors were sampled and mapped. Houses were sampled for adult vectors using the pyrethrum knockdown spray method, and mapped. Vectors were identified to species level and their infection with Plasmodium falciparum determined. RESULTS: Prevalence of febrile illness with P. falciparum was highest among the 5 to 17 year olds (62.4%) while malaria attack rate was highest among the two to 4 year olds (5.2/1,000/day). Infected individuals were spatially concentrated in three of the 11 residential zones of the camp. The indoor densities of Anopheles arabiensis, the sole malaria vector, were similar during the wet and dry seasons, but were distributed in an aggregated fashion and predominantly in the same zones where malaria attack rates were high. Larval habitats and larval populations were also concentrated in these zones. Larval habitats were man-made pits of water associated with tap-stands installed as the water delivery system to residents with year round availability in the camp. Three percent of A. arabiensis adult females were infected with P. falciparum sporozoites in the rainy season. CONCLUSIONS: Malaria in Kakuma refugee camp was due mainly to infection with P. falciparum and showed a hyperendemic age-prevalence profile, in an area with otherwise low risk of malaria given prevailing climate. Transmission was sustained by A. arabiensis, whose populations were facilitated by installation of man-made water distribution and catchment systems.

The prevalence of psychiatric disorders among Vietnamese children and adolescents.

OBJECTIVE: To determine the prevalence of psychiatric disorders among Vietnamese children and adolescents living in Perth, Western Australia. DESIGN, PARTICIPANTS AND SETTING: A list of Vietnamese households was drawn from Perth telephone directories. A computer program generated a systematic probability sample of households. All children and adolescents aged 9-17 in these households were invited to participate in the study. Children and their parents were interviewed in their home using the Diagnostic Interview Schedule for Children, version 2.3 (DISC-2.3). The child version (DISC-C) was used for children and the parent version (DISC-P) for adults. The study was conducted between July and December 1997. MAIN OUTCOME MEASURES: The prevalence of psychiatric disorders in children and adolescents, based on DISC-C and DISC-P data. RESULTS: Results were based on the 519 children (89.2%) for whom complete data were available. Twenty-three parents (4.4%) reported that their child had one or more disorders on the DISC-P, 82 children (15.8%) reported one or more disorders on the DISC-C, and 18.3% of children were reported to have a disorder on either the DISC-C or the DISC-P. Parent-child concordance on specific diagnoses was very low (0.6%). The great majority of disorders reported were anxiety disorders, especially simple and social phobias. CONCLUSIONS: The combined prevalence of psychiatric disorders among Vietnamese children aged 9-17 was similar to that found among children in Western Australia's general population. Vietnamese children in our study were much more likely to report symptoms of a psychiatric disorder than were their parents.