Various silica grades differing in particle size (micro- versus nanosilica) and surface modification (untreated versus modified surface) have affected interfacial and mechanical properties of ...compression-molded polypropylene composites with 2, 4, 6, 8 vol% of added silica. Mechanical properties have been influenced primarily by combination of stiff fillers and tough polypropylene matrix and additionally by restructured matrix. Namely, silica particles with different surface properties have influenced nucleation and spherulite growth differently affecting thus tensile properties of the composites. All composites exhibited best tensile strength in silica content range 2–6 vol%.
We report the discovery of a 50,000-y-old birch tar-hafted flint tool found off the present-day coastline of The Netherlands. The production of adhesives and multicomponent tools is considered ...complex technology and has a prominent place in discussions about the evolution of human behavior. This find provides evidence on the technological capabilities of Neandertals and illuminates the currently debated conditions under which these technologies could be maintained. 14C-accelerator mass spectrometry dating and the geological provenance of the artifact firmly associates it with a host of Middle Paleolithic stone tools and a Neandertal fossil. The find was analyzed using pyrolysis-gas chromatography-mass spectrometry, X-ray micro-computed tomography, and optical light microscopy. The object is a piece of birch tar, encompassing one-third of a flint flake. This find is from northwestern Europe and complements a small set of well-dated and chemically identified adhesives from Middle Paleolithic/Middle Stone Age contexts. Together with data from experiments and other Middle Paleolithic adhesives, it demonstrates that Neandertals mastered complex adhesive production strategies and composite tool use at the northern edge of their range. Thus, a large population size is not a necessary condition for complex behavior and technology. The mitigation of ecological risk, as demonstrated by the challenging conditions during Marine Isotope Stage 4 and 3, provides a better explanation for the transmission and maintenance of technological complexity.
Supermolecular structure and phase morphology of the ternary isotactic polypropylene/atactic polystyrene/poly(styrene-
b-ethylene-
co-propylene) (iPP/aPS/SEP) compression molded blends with 100/0, ...90/10, 70/30, and 50/50 iPP/aPS weight ratios and with different amounts of added SEP compatibilizer were studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). SEP significantly reduced the size of dispersed aPS particles that enabled better spherulitization in the iPP matrix. Furthermore, iPP spherulites in ternary blends with 90/10 iPP/aPS weight ratio became larger in comparison with the pure iPP. TEM revealed that the SEP formed continuous interface layer around the dispersed aPS particles even when only 2.5 wt.% of SEP was added. Particle size distribution was distinctly bimodal. When the SEP content was increased to 10 wt.%, joining together smaller and bigger aPS and SEP particles formed dispersed aggregates. Additionally, both amorphous components (aPS and SEP) influenced crystallization process of iPP matrix and so modified, to some extent, its final supermolecular structure. SEP compatibilizer did not significantly affect crystallite orientation. The increase of crystallite sizes, which was more affected by the addition of aPS than by the addition of SEP, seemed to be influenced by the solidification effect rather than by the phase morphology of the blends.
A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three, or four chains connected by an ethylene spacer at the headgroup level, abbreviated as dimer, ...trimer, and tetramer) were synthesized and characterized. The influence of the degree of oligomerization on their polymorphic and mesomorphic properties was investigated by means of X-ray diffraction, polarizing optical microscopy, thermogravimetry, and differential scanning calorimetry. All compounds display layered arrangements with interdigitated dodecyl chains. The increase in the degree of oligomerization increases the interlayer distance and decreases the ordering in the solid phase; whereas the dimer sample is fully crystalline with well-developed 3D ordering and the trimer and tetramer crystallize as highly ordered crystal smectic phases. The number of thermal phase transitions and sequence of phases are markedly affected by the number of dodecyl chains. Anhydrous samples exhibit polymorphism and thermotropic mesomorphism of the smectic type, with the exception of the tetramer that displays only transitions at higher temperature associated with decomposition and melting. All hydrated compounds form lyotropic mesophases showing reversible phase transitions upon heating and cooling. The sequence of liquid-crystalline phases for the dimer, typical of concentrated ionic surfactant systems, comprises a hexagonal phase at lower temperatures and a smectic phase at higher temperatures. In contrast, the trimer and tetramer reveal textures of the hexagonal phase.
The use of surface electromyography in the field of animal locomotion has increased considerably over the past decade. However, no consensus exists on the methodology for data collection in horses. ...This study aimed to start the development of recommendations for bipolar electrode locations to collect surface electromyographic data from horses during dynamic tasks.
Data were collected from 21 superficial muscles of three horses during trot on a treadmill using linear electrode arrays. The data were assessed both quantitatively (signal-to-noise ratio (SNR) and coefficient of variation (CoV)) and qualitatively (presence of crosstalk and activation patterns) to compare and select electrode locations for each muscle.
For most muscles and horses, the highest SNR values were detected near or cranial/proximal to the central region of the muscle. Concerning the CoV, there were larger differences between muscles and horses than within muscles. Qualitatively, crosstalk was suspected to be present in the signals of twelve muscles but not in all locations in the arrays.
With this study, a first attempt is made to develop recommendations for bipolar electrode locations for muscle activity measurements during dynamic contractions in horses. The results may help to improve the reliability and reproducibility of study results in equine biomechanics.
Understanding the dynamics of woody tree species distribution in savanna systems remains a challenge despite considerable attention the topic has received in recent years. Disturbances such as fire ...and elephant effects on woody vegetation are well documented, yet the influence of these factors on emerging landscape-scale patterns such as height and species distributions continue to be poorly understood. The aim of this study was to identify how a suite of environmental variables (rainfall, temperature, aspect, slope, geology, fire frequency and elephant density) and their relative contributions, may affect woody species distribution in relation to structural height classes. Using the Maximum Entropy model for three structural height classes of the fifteen most frequently occurring woody species in the Kruger National Park (South Africa), the environmental variables best explaining each species distribution were identified. The three structural classes were defined to capture canopy height categories of specific management interest, namely Shrub (0.75-2.5 m), Brush (2.5-5.5 m) and Tree (over 5.5 m). The weighted contributions of environmental variables for each species and its associated size class were further analyzed for similarities using a resemblance matrix based on the Bray-Curtis similarity index coupled with a hierarchical clustering test. Our main findings suggest that the patterns and processes driving woody composition and structure are largely decoupled and that the distribution of different structural classes of a particular species may not be driven by the same environmental variables. Future studies should take cognizance of this as ignoring one or the other may lead to confounding results.
Background Disability, and everything it encompasses, presents major challenges to individuals, families and communities worldwide. Children with disabilities (CWD) are marginalised and excluded in ...most societies. Discrimination and prejudice towards CWD are compounded by poverty, lack of essential services and support and sometimes a hostile and inaccessible environment.Objectives The study sought to examine the psychosocial challenges experienced by CWD in the Sekhukhune district of Limpopo province, South Africa. Based on the identified, articulated and expressed challenges, the study sought to recommend improvement of the existing Integrated National Disability Strategy (INDS) for greater responsiveness to the needs of CWD at both provincial and local levels.Method The interpretivist qualitative mode of enquiry was the chosen methodology for this study. Phenomenology and descriptive research designs guided the study. Purposive sampling was employed, and data were collected from 36 participants using three triangulated methods: individual in-depth interviews, focus group discussions and key informant interviews. Thematic data analysis was used to analyse data.Results The findings revealed that CWD in Sekhukhune experienced numerous challenges which affected their social functioning, development and general well-being. Aggravating factors included stigma, labelling and discrimination; disability-specific discrimination and bullying; exclusive education; sexual exploitation; lack of governmental support and poor implementation of disability-specific policies, amongst others.Conclusion The provisions of the INDS to promote inclusion, integration, mainstreaming and equitable access to resources and services remained an ideal rather than a reality for CWD in Sekhukhune.
Machine ethics isn't merely science fiction; it's a topic that requires serious consideration, given the rapid emergence of increasingly complex autonomous software agents and robots. Machine ethics ...is an emerging field that seeks to implement moral decision-making faculties in computers and robots. We already have semiautonomous robots and software agents that violate ethical standards as a matter of course. In the case of AI and robotics, fearful scenarios range from the future takeover of humanity by a superior form of AI to the havoc created by endlessly reproducing nanobots
Wood and charcoal supply the majority of sub-Saharan Africa's rural energy needs. The long-term supply of fuelwood is in jeopardy given high consumption rates. Using airborne light detection and ...ranging (LiDAR), we mapped and investigated savanna aboveground biomass across contrasting land uses, ranging from densely populated communal areas to highly protected areas in the Lowveld savannas of South Africa. We combined the LiDAR observations with socio-economic data, biomass production rates and fuelwood consumption rates in a supply-demand model to predict future fuelwood availability. LiDAR-based biomass maps revealed disturbance gradients around settlements up to 1.5 km, corresponding to the maximum distance walked to collect fuelwood. At current levels of fuelwood consumption (67% of households use fuelwood exclusively, with a 2% annual reduction), we calculate that biomass in the study area will be exhausted within thirteen years. We also show that it will require a 15% annual reduction in consumption for eight years to a level of 20% of households using fuelwood before the reduction in biomass appears to stabilize to sustainable levels. The severity of dwindling fuelwood reserves in African savannas underscores the importance of providing affordable energy for rural economic development.
This study investigates the effect of a participative management practice, ‘mini-business activities’ (MBAs), on three outcome variables: team effectiveness, team innovation, and job satisfaction. An ...empirical approach is employed, with survey data gathered from 340 individuals working in 50 teams in South African manufacturing organisations. The results indicate that MBAs have a significant and positive effect on team effectiveness and team innovation in a similar way to that of quality circles. However, MBAs are found to have no direct or indirect effect, through employee engagement, on job satisfaction. The findings contribute to a more nuanced understanding of the impact of participative management practices in different contexts, and indicate that future research considering the impact of high unemployment levels on the relationship between participative management practices and job satisfaction would be valuable.
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