Singularly perturbed dynamics of the tippedisk

The tippedisk is a mathematical-mechanical archetype for a peculiar friction-induced instability phenomenon leading to the inversion of an unbalanced spinning disc, being reminiscent of (but different from) the well-known inversion of the tippetop. A reduced model of the tippedisk, in the form of a three-dimensional ordinary differential equation, has been derived recently, followed by a preliminary local stability analysis of stationary spinning solutions. In the current paper, a global analysis of the reduced system is pursued using the framework of singular perturbation theory. It is shown how the presence of friction leads to slow–fast dynamics and the creation of a two-dimensional slow manifold. Furthermore, it is revealed that a bifurcation scenario involving a homoclinic bifurcation and a Hopf bifurcation leads to an explanation of the inversion phenomenon. In particular, a closed-form condition for the critical spinning speed for the inversion phenomenon is derived. Hence, the tippedisk forms an excellent mathematical-mechanical problem for the analysis of global bifurcations in singularly perturbed dynamics.

Boring worms (Sipuncula and Annelida: Polychaeta): their early impact on Eastern Tropical Pacific coral reefs

The form, condition, and survival of coral reefs depends on the balance between construction and destruction. Natural processes such as bioerosion can cause this balance to lean towards destruction, threatening these ecosystems. Polychaetes and sipunculids are members of the boring community; however, knowledge of their identity and role in the bioerosive process and their capacity to remove calcium carbonate (CaCO3) in the coral reefs of the Eastern Tropical Pacific (ETP) is scarce. To tackle this problem, 5 experimental units of Pocillopora spp. branches were deployed in 4 reef zones (back-reef, reef-flat, reef-front, reef-slope) at 2 reefs (La Azufrada, Playa Blanca) for 2 time periods (P1: 6 mo, P2: 9 mo; n = 80) in Gorgona National Natural Park, Colombia. All worms (polychaetes and sipunculids) were identified and net removal and bioerosion rate were determined. In total, 137 worms were found: 64.2% in La Azufrada and 35.8% in Playa Blanca. There were no significant effects of reef, reef-zone, or duration of exposure (6 vs. 9 mo) for either net removal of CaCO3 or bioerosion rate. Irrespective of reef or exposure duration, average net removal was 0.022 and 0.027 g during P1 and P2, and 0.032 and 0.018 g at La Azufrada and Playa Blanca, respectively. Average bioerosion rate, also irrespective of reef or exposure duration, was 2.553 and 2.011 g kg-1 yr-1 for P1 and P2, and 2.839 and 1.807 g kg-1 yr-1 at La Azufrada and Playa Blanca, respectively. The trend between periods was opposite for net removal and bioerosion rate, which indicates a decelerating impact of worms on the coral substrate as time passes. We suggest that, regardless of the small size of the boring worms, their role in CaCO3 removal is very important. The information provided here—species involved and amounts removed—is key in understanding the bioerosion process in ETP coral reefs.

ANALISIS PRODUKSI DAN EFISIENSI BERAS

The purpose of this study to find out if the factors of production could give contribution tu the production or income and the cost of rice production, theeconomy efficiensy of rice production. It is hoped thet the result of this study could give information to farmers and local government in Deli Serdang about the contributions of the factors of production to the production or income and the cost of rice farm opration production. From the study, it is shown that the characteristic of model of production, the using of the factors of production and teh cost of production opportunity is increasing returns to scale or decreasing cost industries. The economy scale of rice production describes that the estimate cost of corn farm production. The analysis of economy efficiensy from the rice production was taken form condition that the produtions marginal cost is lowerthan the corn scale. From the contributions of field, seed, fertilizer and labortoward the rice production, it can be explained that rice production can be raisedby increasing the field, seed, fertilizer, and labor usings.

THE PROCESSING OF ENGLISH PREFIXED WORDS BY CHINESE-ENGLISH BILINGUALS

The present study examined whether Chinese-English bilinguals showed morphological sensitivity toward prefixed words. In the experiment, English monolinguals showed masked priming effects in a Transparent condition (disagree-AGREE) and an Opaque condition (mischief-CHIEF), but not in a Form condition (stranger-ANGER). In contrast, bilinguals showed equivalent priming effects across the three conditions. Indeed, the difference between the magnitude of priming in the Form condition relative to that in the other two conditions was statistically smaller for the bilinguals than for the monolinguals. These findings suggest Chinese-English bilinguals are less sensitive to the morphological status of prefixes, compared with monolinguals.

Educational (Geo)Politics as an Interaction Place in Space or Towards Geo(Philo)Sophy of Education

The article discusses educational policy. However, the policy in general and educational policy specifically are viewed through the lens of geographical space and time as well as the philosophy of becoming. The aim is to answer the question which value-based and norm-based substances, structures of power and strain, processes of becoming and transition form (condition) the educational space in Lithuania? In this context, the instruments of educational management acquire the dimension of educational geopolitics. In terms of space, each policy is geopolitics, whereas geopolitics – policy (policy of ideas, strategies and practices) realised in a specific geographical space and location. Regardless of the way of approach to education – as a composite part of culture, economics, politics or as a separate field of public activity – it is always influenced, structured, constructed by the same geographical factors, i.e. place, space and environment. By implementing the educational policy (various strategies and practices), public authorities (entities) construct spatial educational geopolitical identity. The subjects of space, place, geographical scales (from global to local) in relation to and interaction with geopolitical, sociocultural phenomena form the geopolitical and geophilosophical space of education in Lithuania. Geosophy and geophilosophy express mental, spiritual, value-based and cognitive approach of a person and relation to geographical environment, space, its objects, reflect our individual associations with geography and philosophy. As it is claimed in the summary of the research, educational (geo)politics that is based on diverse authentic relations, explication of meanings, excitation of imagination in relation to / interaction with geographical environment creates an essential, sustainable, self-identical space of educational geo(philo)sophy.

Two-Phase Flow CFD Simulations of Bubble Crystallization Tube

At present, the studies of bubble crystallization focus on the gas velocity, crystallization efficiency and crystallization yield, the effects of other factors were not considered. So it is very important to study factors comprehensively that effect on the gas-liquid two-phase flow of bubble crystallization. In this paper, Fluent was used as a computing platform and RNG k-ε turbulence model and VOF multi-phase model was selected to simulate gas-liquid two-phase flow of bubble crystallization. The results show that as the gas inlet velocity increases, slug bubbles are more and more bigger, more and more dispersed bubbles are below the slug bubbles, crystallization efficiency first increases and then decreases; Under the gas pulse-inlet form condition, the better operating parameters are: gas velocity 1.0m/s, pulse duration 0.4s, interval time 0.8s, crystallization tube diameter 40mm. Simulations agree well with experimental data.

On unknotting numbers and knot trivadjacency

We prove for rational knots a conjecture of Adams et al. that an alternating unknotting number one knot has an alternating unknotting number one diagram. We use this then to show a refined signed version of the Kanenobu-Murakami theorem on unknotting number one rational knots. Together with a similar refinement of the linking form condition of Montesinos-Lickorish and the HOMFLY polynomial, we prove a condition for a knot to be $2$-trivadjacent, improving the previously known condition on the degree-2-Vassiliev invariant. We finally show several partial cases of the conjecture that the knots with everywhere $1$-trivial knot diagrams are exactly the trivial, trefoil and figure eight knots. (A knot diagram is called everywhere $n$-trivial, if it turns into an unknot diagram by switching any set of $n$ of its crossings.)

Miedo e incertidumbre

Fear and Uncertainty discusses Robert Gordon’s thesis according to which fear is an epistemic —as opposed to factive— emotion inasmuch as S’s fearing p requires S’s being uncertain whether p or ∼p, and also requires that the uncertainty implicit in fearing be of a non-deliberative or ‘external’ kind. Hansberg argues against both parts of this thesis, which purports to offer part of the structure of the emotion of fear. First, she says, Gordon cannot account for those cases of weakness of the will in which an agent fears that when the moment comes he himself will not act upon his own previous purpose. So an external uncertainty proves to be not so essential a requisite. Now, what about the uncertainty, whatever its form, condition? Hansberg finds several examples in which someone fears p even though he actually is certain that p (when one fears, forexample, a medical treatment known to be painful, or when one fears one’s own inminent death, say, by suicide). She also argues against Gordon’s distinction between propositional fearsand mere ‘states of fear’ with no semantic content, and disapproves of his inclusion of certain fears —like fear of a violent death, fear of injury to oneself, and many phobias— in the lattercategory. Those supposedly non-propositional states can, and often do, give rise to propositional states and intentional actions; so Gordon would have to explain how this is possible: some of those supposedly mere states of fear need a place in an explanationby- reasons scheme. Finally, Hansberg claims that all fears do have a propositional structure, even though some fears have it in a concealed way. So, for example, if someone is afraid of death, he is afraid that he will die young, or that he will go to hell, and so on. Thus it is always possible to find propositional contents for fears which apparently have none, although in some cases this might be a difficult task. [Laura Lecuona]