Breast-feeding and weaning practices in Venda, 1990

A stratified randOlll cluster survey, using a structured interview schedule, was performed to determine the prevalence, frequency and duration of breast-feeding alllong Venda mothers as well as the foods that Venda children commonly ate in their first 2 years of life. Nearly all children under 2 years old were being breast-fed and virtually all of these were fed on demand. Approximately 60% of infants under 3 months of age and virtually all others under 2 years old received supplementary foods daily. A further 30% ofinfants under the age of 3 months were given supplementary water daily. Forty per cent of infants under 3 months old and virtually all in the other age groups were given carbohydrates daily. Protein foods, vitamin mineral and high-energy sources were given less frequently. Only 12% in the 6 - 11-month age group and 21% in the 12 - 23-111onth age group received a balanced diet daily. A significant proportion of children in all age groups received only carbohydrates over and above breast-milk. Traditional xnixes were infrequently given. More research is needed to assess actual breast-milk production by mothers whose children are being fed supplelllentary foods. The effect of socio-economic status on weaning practices and that of weaning practices on nutritional status need to be investigated. Food supplelllentation and nutrition education progralllllles need to be intensified

Foray search: An effective systematic dispersal strategy in fragmented landscapes

In the absence of evidence to the contrary, population models generally assume that the dispersal trajectories of animals are random, but systematic dispersal could be more efficient at detecting new habitat and may therefore constitute a more realistic assumption. Here, we investigate, by means of simulations, the properties of a potentially widespread systematic dispersal strategy termed "foray search." Foray search was more efficient in detecting suitable habitat than was random dispersal in most landscapes and was less subject to energetic constraints. However, it also resulted in considerably shorter net dispersed distances and higher mortality per net dispersed distance than did random dispersal, and it would therefore be likely to lead to lower dispersal rates toward the margins of population networks. Consequently, the use of foray search by dispersers could crucially affect the extinction-colonization balance of metapopulations and the evolution of dispersal rates. We conclude that population models need to take the dispersal trajectories of individuals into account in order to make reliable predictions

Kinetics of TNF-alpha and IFN-gamma mRNA expression in islets and spleen of NOD mice

Insulin-dependent diabetes mellitus is caused by autoimmune destruction of pancreatic ß cells. Non-obese diabetic (NOD) mice spontaneously develop diabetes similar to the human disease. Cytokines produced by islet-infiltrating mononuclear cells may be directly cytotoxic and can be involved in islet destruction coordinated by CD4+ and CD8+ cells. We utilized a semiquantitative RT-PCR assay to analyze in vitro the mRNA expression of TNF-alpha and IFN-gamma cytokine genes in isolated islets (N = 100) and spleen cells (5 x 10(5) cells) from female NOD mice during the development of diabetes and from female CBA-j mice as a related control strain that does not develop diabetes. Cytokine mRNAs were measured at 2, 4, 8, 14 and 28 weeks of age from the onset of insulitis to the development of overt diabetes. An increase in IFN-gamma expression in islets was observed for females aged 28 weeks (149 ± 29 arbitrary units (AU), P<0.05, Student t-test) with advanced destructive insulitis when compared with CBA-j mice, while TNF-alpha was expressed in both NOD and CBA-j female islets at the same level at all ages studied. In contrast, TNF-alpha in spleen was expressed at higher levels in NOD females at 14 weeks (99 ± 8 AU, P<0.05) and 28 weeks (144 ± 17 AU, P<0.05) of age when compared to CBA-j mice. The data suggest that IFN-gamma and TNF-alpha expression in pancreatic islets of female NOD mice is associated with ß cell destruction and overt diabetes.1347135

First-principles theory of proximity spin-orbit torque on a two-dimensional magnet: Current-driven antiferromagnet-to-ferromagnet reversible transition in bilayer CrI₃

The recently discovered two-dimensional (2D) magnetic insulator CrI₃ is an intriguing case for basic research and spintronic applications since it is a ferromagnet in the bulk, but an antiferromagnet in bilayer form, with its magnetic ordering amenable to external manipulations. Using first-principles quantum transport approach, we predict that injecting unpolarized charge current parallel to the interface of bilayer-CrI₃/monolayer-TaSe₂ van der Waals heterostructure will induce spin-orbit torque (SOT) and thereby driven dynamics of magnetization on the first monolayer of CrI₃ in direct contact with TaSe₂. By combining calculated complex angular dependence of SOT with the Landau-Lifshitz-Gilbert equation for classical dynamics of magnetization, we demonstrate that current pulses can switch the direction of magnetization on the first monolayer to become parallel to that of the second monolayer, thereby converting CrI₃ from antiferromagnet to ferromagnet while not requiring any external magnetic field. We explain the mechanism of this reversible current-driven nonequilibrium phase transition by showing that first monolayer of CrI₃ carries current due to evanescent wavefunctions injected by metallic transition metal dichalcogenide TaSe₂, while concurrently acquiring strong spin-orbit coupling (SOC) via such proximity effect, whereas the second monolayer of CrI₃ remains insulating. The transition can be detected by passing vertical read current through the vdW heterostructure, encapsulated by bilayer of hexagonal boron nitride and sandwiched between graphite electrodes, where we find tunneling magnetoresistance of \backslashsimeq 240%

Scattering-induced and highly tunable by gate damping-like spin-orbit torque in graphene doubly proximitized by two-dimensional magnet Cr2Ge2Te6 and monolayer WS2

Using first-principles combined with quantum transport calculations, we predict that graphene sandwiched between insulating monolayers of Cr₂Ge₂Te₆ ferromagnet and WS₂ transition-metal dichalcogenide will exhibit spin-orbit torque (SOT) when unpolarized charge current is injected parallel to interfaces of Cr₂Ge₂Te₆/graphene/WS₂ van der Waals (vdW) heterostructure. Although graphene by itself is nonmagnetic and it has negligible spin-orbit coupling (SOC), both of which are required for the SOT phenomenon, Cr₂Ge₂Te₆ induces proximity magnetism into graphene while WS₂ concurrently imprints valley-Zeeman and Rashba SOCs in it. Unlike SOT on conventional metallic ferromagnets brought into contact with normal materials supplying strong SOC, the predicted SOT on such doubly proximitized graphene can be tuned by up to two orders of magnitude via combined top and back electrostatic gates. The vdW heterostructure also reveals how damping-like component of the SOT vector can arise purely from interfaces and, therefore, even in the absence of any spin Hall current from the bulk of a material with strong SOC. The SOT-driven dynamics of proximity magnetization moves it from out-of-plane to in-plane direction which opens a gap in graphene and leads to zero off current and diverging on/off ratio in such SOT field-effect transistor

Assessing the influence of socials calls on bat mist-netting success in North America

Since the introduction of the fungal disease White-Nose Syndrome in 2006, millions of North American bats have perished. For many species, the disease has caused over a 90 percent decline in abundance. With populations fluctuating as the pathogen spreads, biologists require improved methods of estimating bat demographics and abundance. Previous research indicates that mist netting success may be improved with the use of acoustic lures at mist-netting locations. Our research investigates which type of social calls improve the capture rates of North American bats, including the big brown bat (Eptesicus fuscus). Social call types used include antagonistic buzzes, distress calls, advertising calls, mother-to-offspring calls, and cohesion calls. We deployed acoustic lures at each netting site from 15 May 2017 to 15 August 2017. We created 5-hour long playlists using 10-minute blocks of each of the 5 call types, including a block of silence as control. We recorded the time of each bat capture to indicate the call block each individual entered the net. We utilized maximum likelihood analysis in program R to identify if call type had an influence on bat captures. Analysis indicated that European distress calls negatively impacted big brown bat captures. Overall, this suggests that researchers should utilize North American bat calls to improve capture rates of big brown bats

Exceptionally Slow Rise in Differential Reflectivity Spectra of Excitons in GaN: Effect of Excitation-induced Dephasing

Femtosecond pump-probe (PP) differential reflectivity spectroscopy (DRS) and four-wave mixing (FWM) experiments were performed simultaneously to study the initial temporal dynamics of the exciton line-shapes in GaN epilayers. Beats between the A-B excitons were found \textit{only for positive time delay} in both PP and FWM experiments. The rise time at negative time delay for the differential reflection spectra was much slower than the FWM signal or PP differential transmission spectroscopy (DTS) at the exciton resonance. A numerical solution of a six band semiconductor Bloch equation model including nonlinearities at the Hartree-Fock level shows that this slow rise in the DRS results from excitation induced dephasing (EID), that is, the strong density dependence of the dephasing time which changes with the laser excitation energy.Comment: 8 figure

Femtosecond Time-Resolved Reflectivity of Ge

We have measured the transient reflectivity changes of bulk Ge after excitation with 140 fs laser pulses at 1.5 eV. The electron and hole carrier dynamics arc calculated using an ensemble Monte Carlo method. The observed reflectivity changes are due to three mechanisms: Diffusion, band gap renormalization, and carrier dynamics, particularly scattering of light holes to the heavy hole band via optical phonons