Slip or not slip? A methodical examination of the interface formation model using two-dimensional droplet spreading on a horizontal planar substrate as a prototype system

We consider the spreading of a thin two-dimensional droplet on a planar substrate as a prototype system to compare the contemporary model for contact line motion based on interface formation of Shikhmurzaev [Int. J. Multiphas. Flow 19, 589 (1993)], to the more commonly used continuum fluid dynamical equations augmented with the Navier-slip condition. Considering quasistatic droplet evolution and using the method of matched asymptotics, we find that the evolution of the droplet radius using the interface formation model reduces to an equivalent expression for a slip model, where the prescribed microscopic dynamic contact angle has a velocity dependent correction to its static value. This result is found for both the original interface formation model formulation and for a more recent version, where mass transfer from bulk to surface layers is accounted for through the boundary conditions. Various features of the model, such as the pressure behaviour and rolling motion at the contact line, and their relevance, are also considered in the prototype system we adopt.Comment: 45 pages, 18 figure

Distance Education And Learning Styles: Some Interesting Results

The rush to offer web courses has left many questions as to what makes them effective and satisfactory. Important issues are: the perceived advantages of web-based courses; appropriate pedagogical tools (e.g., streaming media, PowerPoint presentations) to facilitate student-content interaction, media richness, and the influence of antecedent characteristics, such as gender, experience, motivation, and learning styles. Research here indicates support for media richness, web-based course advantages, some pedagogies, and minimal support for learning styles, at least Gardner’s multiple intelligences and Keirsey’s personality styles

What is central to political belief system networks?

A central challenge for identifying core components of a belief system is xamining the position of components within the structure of the entire belief system. We test whether operational (i.e. positions on issues) or symbolic (i.e. affective attachments to political groups and labels) components are most central by modeling a political belief system as a network of interconnected attitudes and beliefs. Across seven waves of representative panel data from New Zealand, we find that symbolic components are more central than perational components (d’s range 0.78 – 0.97). Symbolic components were also closer than operational components in the network to self-reported voting (d = -2.43), pro-environmental actions (d’s = -1.71 and -1.63), and religious behaviors (d = -0.74). These findings are consistent with perspectives that emphasize the importance of symbolic politics in tying belief systems together and motivating behavior, and further the link between political belief system research and network science. Keywords: Belief systems, networks, ideology, political psycholog

Cooperative phenotype predicts climate change belief and pro-environmental behaviour

Understanding the psychological causes of variation in climate change belief and pro-environmental behaviour remains an urgent challenge for the social sciences. The “cooperative phenotype” is a stable psychological preference for cooperating in social dilemmas that involve a tension between individual and collective interest. Since climate change poses a social dilemma on a global scale, this issue may evoke similar psychological processes as smaller social dilemmas. Here, we investigate the relationships between the cooperative phenotype and climate change belief and behaviour with a representative sample of New Zealanders (n = 897). By linking behaviour in a suite of economic games to self-reported climate attitudes, we show robust positive associations between the cooperative phenotype and both climate change belief and pro-environmental behaviour. Furthermore, our mediation analyses support a motivated reasoning model in which the relationship between the cooperative phenotype and pro-environmental behaviour is fully mediated by climate change belief. These findings suggest that common psychological mechanisms underlie cooperation in both micro-scale social dilemmas and larger-scale social dilemmas like climate change.Results and discussions Methods - Power analysis - Participants and sampling - Materials - Procedure - Statistical analyse

Efficient gene disruption in diverse strains of Toxoplasma gondii using CRISPR/CAS9

ABSTRACT Toxoplasma gondii has become a model for studying the phylum Apicomplexa, in part due to the availability of excel-lent genetic tools. Although reverse genetic tools are available in a few widely utilized laboratory strains, they rely on special ge-netic backgrounds that are not easily implemented in natural isolates. Recent progress in modifying CRISPR (clustered regularly interspaced short palindromic repeats), a system of DNA recognition used as a defense mechanism in bacteria and archaea, has led to extremely efficient gene disruption in a variety of organisms. Here we utilized a CRISPR/CAS9-based system with single guide RNAs to disrupt genes in T. gondii. CRISPR/CAS9 provided an extremely efficient system for targeted gene disruption and for site-specific insertion of selectable markers through homologous recombination. CRISPR/CAS9 also facilitated site-specific insertion in the absence of homology, thus increasing the utility of this approach over existing technology. We then tested whether CRISPR/CAS9 would enable efficient transformation of a natural isolate. Using CRISPR/CAS9, we were able to rapidly generate both rop18 knockouts and complemented lines in the type I GT1 strain, which has been used for forward genetic crosses but which remains refractory to reverse genetic approaches. Assessment of their phenotypes in vivo revealed that ROP18 con-tributed a greater proportion to acute pathogenesis in GT1 than in the laboratory type I RH strain. Thus, CRISPR/CAS9 extends reverse genetic techniques to diverse isolates of T. gondii, allowing exploration of a much wider spectrum of biological diversity. IMPORTANCE Genetic approaches have proven very powerful for studying the biology of organisms, including microbes. How-ever, ease of genetic manipulation varies widely among isolates, with common lab isolates often being the most amenable to suc

Functional analysis of rhomboid proteases during Toxoplasma invasion

Host cell invasion by Toxoplasma gondii and other apicomplexan parasites requires transmembrane adhesins that mediate binding to receptors on the substrate and host cell to facilitate motility and invasion. Rhomboid proteases (ROMs) are thought to cleave adhesins within their transmembrane segments, thus allowing the parasite to disengage from receptors and completely enter the host cell. To examine the specific roles of individual ROMs during invasion, we generated single, double, and triple knockouts for the three ROMs expressed in T. gondii tachyzoites. Analysis of these mutants demonstrated that ROM4 is the primary protease involved in adhesin processing and host cell invasion, whereas ROM1 or ROM5 plays negligible roles in these processes. Deletion of ROM4 blocked the shedding of adhesins such as MIC2 (microneme protein 2), causing them to accumulate on the surface of extracellular parasites. Increased surface adhesins led to nonproductive attachment, altered gliding motility, impaired moving junction formation, and reduced invasion efficiency. Despite the importance of ROM4 for efficient invasion, mutants lacking all three ROMs were viable and MIC2 was still efficiently removed from the surface of invaded mutant parasites, implying the existence of ROM-independent mechanisms for adhesin removal during invasion. Collectively, these results suggest that although ROM processing of adhesins is not absolutely essential, it is important for efficient host cell invasion by T. gondii

A bee or not a bee: an experimental test of acoustic mimicry by hoverflies

The degree of similarity between Batesian mimics and their models varies widely and occurs across a range of sensory modalities. We use three complementary experimental paradigms to investigate acoustic mimicry in hoverflies (Diptera: Syrphidae) which mimic stinging Hymenoptera. First, we analyse sounds made by 13 hoverfly species and 9 Hymenoptera species with and without simulated predation (“alarm” and “flight” sounds, respectively). We demonstrate that the bumblebees Bombus terrestris, B. hortorum, and B. lucorum, and the hoverfly Cheilosia illustrata exhibit alarm sounds that are significantly different to their respective flight sounds, and indistinguishable between species. We then demonstrate that the B. terrestris alarm sound reduces predation on artificial prey by wild birds, but that the hoverfly mimic alarm sound does not. Finally, we trained chicks to avoid distasteful food in the presence of different acoustic stimuli. Overall the chicks showed no difference in response to bee and hoverfly stimuli, demonstrating no innate aversion to the Bombus alarm sound. We therefore conclude that (i) similarity of acoustic signals exists among Hymenoptera and hoverflies, (ii) acoustic aposematic signals (but not the almost identical mimetic signals) are effective at reducing predation, and (iii) wild birds exhibit learned rather than innate aversion to certain acoustic stimuli

Fluid structure in the immediate vicinity of an equilibrium three-phase contact line and assessment of disjoining pressure models using density functional theory

We examine the nanoscale behavior of an equilibrium three-phase contact line in the presence of long-ranged intermolecular forces by employing a statistical mechanics of fluids approach, namely density functional theory (DFT) together with fundamental measure theory (FMT). This enables us to evaluate the predictive quality of effective Hamiltonian models in the vicinity of the contact line. In particular, we compare the results for mean field effective Hamiltonians with disjoining pressures defined through (I) the adsorption isotherm for a planar liquid film, and (II) the normal force balance at the contact line. We find that the height profile obtained using (I) shows good agreement with the adsorption film thickness of the DFT-FMT equilibrium density profile in terms of maximal curvature and the behavior at large film heights. In contrast, we observe that while the height profile obtained by using (II) satisfies basic sum rules, it shows little agreement with the adsorption film thickness of the DFT results. The results are verified for contact angles of 20, 40 and 60 degrees