Advective balance in pipe-formed vortex rings

Vorticity distributions in axisymmetric vortex rings produced by a piston-pipe apparatus are numerically studied over a range of Reynolds numbers, $\mathrm{Re}$, and stroke-to-diameter ratios, $L/D$. It is found that a state of advective balance, such that $\zeta \equiv \omega_\phi/r \approx F(\psi, t)$, is achieved within the region (called the vortex ring bubble) enclosed by the dividing streamline. Here $\zeta \equiv\omega_\phi/r$ is the ratio of azimuthal vorticity to cylindrical radius, and $\psi$ is the Stokes streamfunction in the frame of the ring. Some but not all of the $\mathrm{Re}$ dependence in the time evolution of $F(\psi, t)$ can be captured by introducing a scaled time $\tau = \nu t$, where $\nu$ is the kinematic viscosity. When $\nu t/D^2 \gtrsim 0.02$, the shape of $F(\psi)$ is dominated by the linear-in-$\psi$ component, the coefficient of the quadratic term being an order of magnitude smaller. An important feature is that as the dividing streamline ($\psi = 0$) is approached, $F(\psi)$ tends to a non-zero intercept which exhibits an extra $\mathrm{Re}$ dependence. This and other features are explained by a simple toy model consisting of the one-dimensional cylindrical diffusion equation. The key ingredient in the model responsible for the extra $\mathrm{Re}$ dependence is a Robin-type boundary condition, similar to Newton's law of cooling, that accounts for the edge layer at the dividing streamline

Head-on collision of viscous vortex rings

The head-on collision of two identical axisymmetric viscous vortex rings is studied through direct simulations of the incompressible Navier-Stokes equations. The initial vorticity distributions considered are those of Hill's spherical vortex and of rings with circular Gaussian cores, each at Reynolds numbers of about 350 and 1000. The Reynolds number is defined by Gamma/Nu, the ratio of circulation to viscosity. As the vortices approach each other by self-induction, the radii increase by mutual induction, and vorticy cancels through viscous cross-diffusion across the collision plane. Following contact, the vorticity distribution in the core forms a head-tail structure (for the cases considered). The characteristic time of vorticity annihilation is compared with that of a 3D collision experiment and 3D numerical simulations. It is found that the annihilation time is somewhat longer in the axisymmetric case than it is in the symmetry plane of the experiment and 3D numerical simulation. By comparing the annihilatiom time with a viscous timescale and a circulation timescale, it is deduced that both the strain rate due to local effects and to 3D vorticity realignment are important

A note on leapfrogging vortex rings

In this paper we provide examples, by numerical simulation using the Navier-Stokes equations for axisymmetric laminar flow, of the 'leapfrogging' motion of two, initially identical, vortex rings which share a common axis of symmetry. We show that the number of clear passes that each ring makes through the other increases with Reynolds number, and that as long as the configuration remains stable the two rings ultimately merge to form a single vortex ring

User perception of information credibility of news on Twitter

In this paper, we examine user perception of credibility for news-related tweets. We conduct a user study on a crowd-sourcing platform to judge the credibility of such tweets. By analysing user judgments and comments, we find that eight features, including some that can not be automatically identified from tweets, are perceived by users as important for judging information credibility. Moreover, distinct features like link in tweet, display name and user belief consistently lead users to judge tweets as credible. We also find that users can not consistently judge or even misjudge the credibility for some tweets on politics news

Correlation analysis of reader's demographics and tweet credibility perception

When searching on Twitter, readers have to determine the credibility level of tweets on their own. Previous work has mostly studied how the text content of tweets in uences credibility perception. In this paper, we study reader demographics and information credibility perception on Twitter. We nd reader's educational background and geolocation have signi cant correlation with credibility perception. Further investigation reveals that combinations of demographic attributes correlating with credibility perception are insigni cant. Despite di erences in demographics, readers nd features regarding topic keyword and the writing style of a tweet to be independently helpful in perceiving tweets' credibility. While previous studies reported the use of features independently, our result shows that readers use combination of features to help in making credibility perception of tweets

Growth and nutritional value of a Tropical Green Alga, Ankistrodesmus convolutus corda, in Agro-industrialeffluents

Use of agro-industrial effluents for microalgal culture was investigated using a tropical freshwater green alga, Ankistrodesmus convolutus cultured in various dilutions of latex concentrate effluent (LCRE), standard Malaysian rubber effluent (SMRE) and digested palm oil mill effluent (POMED). Ankistrodesmus convolutus grown in 40%and 60%LCRE, 60%SMRE and 10% POMED showed significantly higher (P < 0.05) specific growth rate in terms of cell number and chlorophyll a than that grown in other effluent media and inorganic fertiliser (N:P:K = 1:1:0.5) as control. Total biomass of this microalgae grown in 60%LCRE, 60%SMRE and 10% POMED was significantly higher (P < 0.05) than that cultured in other effluent media and the control. Ankistrodesmus convolutus cultured in 40% and 60% LCRE, 60% SMRE and 10% POMED showed significantly (P < 0.05) higher amount of crude protein and lipid than that grown in other effluent media and the control. Significantly higher (P < 0.05) amount of most of the essential amino acids (EAAs) except a few were found in A. convolutus cultured in 60% LCRE and 60% SMRE than that grown in other effluent media and control. Ankistrodesmus convolutus cultured in 10% POMED resulted in significantly higher (P < 0.05) amount of all the EAAs except threonine and tyrosine that were grown in other POMED media and control. Ankistrodesmus convolutus grown in 40% and 60% LCRE, contained significantly higher (P < 0.05) amounts of all the C18 and C20 polyunsaturated fatty acids (PDFAs) than that cultured in other SMRE media and control, except eicosadienoic acid (20: 2n-11). A similar trend of PUFAs was recorded in A. convolutus cultured in 60% SMRE except eicosatrienoic acid (20:3n-6) and arachidonic acid (20:4n-6). It was found that A. convolutus contained significantly (P < 0.05) higher amount of PUFAs such as linoleic acid (l8:2n-6), linolenic acid (18:3n-3) and arachidonic acid (20:4n-6) when grown in 10% POMED than that cultured in other POMED media and control. This study showed that A. convolutus grown in 40-60% rubber and 10% POMED has higher nutritional value that that cultured in other effluent media and inogranic fertilizer

An agricultural investment map based on geographic information system and multi-criteria method.

The study aimed to produce an investment classification map, which shows the potential areas of investment in agriculture in Sinnar, Sudan. The spatial multi-criteria analysis was used to rank and display potential locations, while the analytical hierarchy process method was used to compute the priority weights of each criterion. The study attempted to explore the utilization of Geographic Information System (GIS) to map the potential investment areas, therefore, it did not cover a comprehensive analysis of all factors that influence investment in agriculture. In addition, the analysis was limited to criteria that had spatial reference. The investment criteria for spatial analysis were defined from the guidelines provided by the Ministry of Investment, Sudan. Even with the shortcomings of the data, it was found that the results obtained were very encouraging and provided clear indicative areas for agricultural investment in Sinnar. Government agencies can use GIS to access information regarding the potential areas of investment, and minimize investment risks. On the other hand, the economic development organizations will now have the ability to benefit from the Geographic Information System (GIS) solutions by leveraging on this technology to attract and retain business from worldwide sources. Thus, the model will serve as a decision support tool for investors and decision makers at various levels

Development and preliminary validation of socio-cultural influences on body image scale for Malaysian female adolescents

The present study aimed to develop and validate comprehensive multi-dimensional sociocultural (parental, peers, media) influence on body image scale for Malaysian female adolescents. A total of 328 female adolescents from a secondary school in Kuantan district, Pahang, Malaysiacompleted a self-administered questionnaire, which encompassed a multiple measure of sociocultural influence, Body Dissatisfaction and Body Importance subscales of Body Image Questionnaire (McCabe & Ricciardelli, 2001), and Body Change Inventory (Ricciardelli & McCabe, 2002). Through factor analysis, the three major components (parental, peers, media) of the sociocultural influence scale were found to consist of multi-dimensional constructs. Particularly, five dimensions were identified for the parental influence subscale: 1) parental teasing on weight, 2) parental encouragement on increasing muscle and weight, 3) parental social support, 4) parental preoccupation with thinness and dieting behaviour, and 5) parental feedback on body change behaviour; the peer influence subscale comprised four dimensions including 1) peer social support, 2) peer preoccupation with thinness and dieting behaviour, 3) peer teasing on weight, and 4) peer encouragement on increasing muscle and weight; and three dimensions were identified in the media influence subscale, which included 1) media encouragement on reducing weight, 2) media modeling on weight reducing behaviour, and 3) media encouragement on increasing muscle and weight. As for construct validity, there were positive correlations between the composite score of the subscales and body dissatisfaction, body importance, strategies to decrease body size and strategies to increase body size and muscle size. In short, the present study has developed a sociocultural (parental, peer, media) influences on body image scale with construct validity and good internal consistency for Malaysian female adolescents. The scale can be used to assess the various dimensions of socio-cultural influences and will be useful to determine the etiology, prevention and treatment of negative body image and its related problems for Malaysian female adolescents

Reactions of Rhenium and Manganese Carbonyl Complexes with 1,8-bis(diphenylphosphino)naphthalene: Ligand Chelation, C–H and C–P bond-cleavage Reactions

Reaction of [Re2(CO)8(MeCN)2] with 1,8-bis(diphenylphosphino)naphthalene (dppn) afforded three mono-rhenium complexes fac-[Re(CO)3(κ1:η1-PPh2C10H6)(PPh2H)] (1), fac-[Re(CO)3{κ1:κ1:η1-(O)PPh2C10H6(O)PPh(C6H4)}] (2) and fac-[ReCl(CO)3(κ2-PPh2C10H6PPh2)] (3). Compounds 1–3 are formed by Re–Re bond cleavage and P–C and C–H bond activation of the dppn ligand. Each of these three complexes have three CO groups arranged in facial fashion. Compound 1 contains a chelating cyclometalated diphenylnaphthylphosphine ligand and a terminally coordinated PPh2H ligand. Compound 2 consists of an orthometalated dppn-dioxide ligand coordinated in a κ1:κ1:η1-fashion via both the oxygen atoms and ortho-carbon atom of one of the phenyl rings. Compound 3 consists of an unchanged chelating dppn ligand and a terminal Cl ligand. Treatment of [Mn2(CO)8(MeCN)2] with a slight excess of dppn in refluxing toluene at 72 °C, gave the previously reported [Mn2(CO)8(μ-PPh2)2] (4), formed by cleavage of C–P bonds, and the new compound fac-[MnCl(CO)3(κ2-PPh2C10H6PPh2)] (5), which has an unaltered chelating dppn and a terminal Cl ligand. In sharp contrast, reaction of [Mn2(CO)8(MeCN)2] with slight excess of dppn at room temperature yielded the dimanganese [Mn2(CO)9{κ1-PPh2(C10H7)}] (6) in which the diphenylnaphthylphosphine ligand, formed by facile cleavage of one of the P–C bonds, is axially coordinated to one Mn atom. Compound 6 was also obtained from the reaction of [Mn2(CO)9(MeCN)] with dppn at room temperature. The XRD structures of complexes 1–3, 5, 6 are reported