241 research outputs found
Images in Christmas Balls
We describe light-reflection properties of spherically curved mirrors, like
balls in the Christmas tree. In particular, we study the position of the image
which is formed somewhere beyond the surface of a spherical mirror, when an eye
observes the image of a pointlike light source. The considered problem,
originally posed by Abu Ali Hasan Ibn al-Haitham -- alias Alhazen -- more than
a millennium ago, turned out to have the now well known analytic solution of a
biquadratic equation, being still of great relevance, e.g. for the
aberration-free construction of telescopes. We do not attempt to perform an
exhaustive survey of the rich historical and engineering literature on the
subject, but develop a simple pedagogical approach to the issue, which we
believe to be of continuing interest in view of its maltreating in many
high-school textbooks.Comment: 13 pages, 7 figures plain LaTeX; Also see
http://cft.fis.uc.pt/eef/mirrors.htm, revised version has simplified
formulas, more transparent for a wider audience, one reference adde
Working with simple machines
A set of examples is provided that illustrate the use of work as applied to
simple machines. The ramp, pulley, lever and hydraulic press are common
experiences in the life of a student and their theoretical analysis therefore
makes the abstract concept of work more real. The mechanical advantage of each
of these systems is also discussed so that students can evaluate their
usefulness as machines.Comment: 9 pages, 4 figure
Simultaneous free-volume modeling of the self-diffusion coefficient and dynamic viscosity at high pressure
International audienceA free-volume model of the dynamic viscosity and the self-diffusion coefficients was discussed. The temperature-pressure variations of the dynamic viscosity and the self-diffusion coefficients of small molecules were predicted. The compounds, carbon tetrachloride, cyclohexane, benzene, chlorotrifluoromethane, tetramethylsilane and methylcyclohexane were used for the investigation. The relation between microstructure, free volume and different complex thermophysical properties were emphasized by the model
An inverse for the Jaumann derivative and some applications to the rheology of viscoelastic fluids
By using a generalization of the matrizant of matrix calculus, it is shown how one can construct formally an inverse, or integral, for the well-known Jaumann derivative of continuum mechanics. Some applications to fluid rheology are then considered. First, it is shown that this integral provides, via the Boltzmann super-position principle, a generalization of Oldroyd's quasi-linear fluid model, which is related to the molecular model of Bueche . Explicit expressions for the stresses arising in a general laminar shear flow are then derived for this model. Secondly, it is indicated how the operation can be used with rheological equations which are nonlinear in the deformation-rate, but quasi-linear in stress, to solve explicitly for the stress in terms of kinematic quantities. As an example, a rheological equation for suspensions of viscoelastic spheres in a Newton ian fluid is treated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47218/1/397_2005_Article_BF01982423.pd
Children reading to dogs: a systematic review of the literature
Background
Despite growing interest in the value of human-animal interactions (HAI) to human mental and physical health the quality of the evidence on which postulated benefits from animals to human psychological health are based is often unclear. To date there exist no systematic reviews on the effects of HAI in educational settings specifically focussing on the perceived benefits to children of reading to dogs. With rising popularity and implementation of these programmes in schools, it is essential that the evidence base exploring the pedagogic value of these initiatives is well documented.
Methods
Using PRISMA guidelines we systematically investigated the literature reporting the pedagogic effects of reading to dogs. Because research in this area is in the early stages of scientific enquiry we adopted broad inclusion criteria, accepting all reports which discussed measurable effects related to the topic that were written in English. Multiple online databases were searched during January-March 2015; grey literature searches were also conducted. The search results which met the inclusion criteria were evaluated, and discussed, in relation to the Oxford Centre for Evidence Based Medicine levels of evidence; 27 papers were classified as Level 5, 13 as Level 4, 7 as Level 2c and 1 as Level 2b.
Conclusion
The evidence suggests that reading to a dog may have a beneficial effect on a number of behavioural processes which contribute to a positive effect on the environment in which reading is practiced, leading to improved reading performance. However, the evidence base on which these inferences are made is of low quality. There is a clear need for the use of higher quality research methodologies and the inclusion of appropriate controls in order to draw causal inferences on whether or how reading to dogs may benefit children’s reading practices. The mechanisms for any effect remain a matter of conjectur
Sucrose in the concentrated solution or the supercooled “state” : a review of caramelisation reactions and physical behaviour
Sucrose is probably one of the most studied molecules by food scientists, since it plays an important role as an ingredient or preserving agent in many formulations and technological processes. When sucrose is present in a product with a concentration near or greater than the saturation point—i.e. in the supercooled state—it possesses high potentialities for the food industry in areas as different as pastry industry, dairy and frozen desserts or films and coatings production. This paper presents a review on critical issues and research on highly concentrated sucrose solutions—mainly, on sucrose thermal degradation and relaxation behaviour in such solutions. The reviewed works allow identifying several issues with great potential for contributing to significant advances in Food Science and Technology.Authors are grateful for the valuable discussions with Teresa S. Brandao and Rosiane Lopes da Cunha during this research. Author M. A. C. Quintas acknowledges the financial support of her research by FCT grant SFRH/BPD/41715/2007
An Analytical Method To Predict Fatigue Life of Thermoplastics in Uniaxial Loading: Sensitivity to Wave Type, Frequency, and Stress Amplitude
Study on the temperature dependence of the bulk modulus of polyisoprene by molecular dynamics simulations
The temperature dependence of the bulk modulus of polyisoprene has been studied using molecular dynamics simulations. Virtual polyisoprenes have been submitted to volume contractions above and below the glass transition. Bulk modulus has been observed to be linearly dependent on temperature both above and below the glass transition respectively, and it dropped by a factor of about 2 while temperatures was risen above the glass transition. By monitoring the energy changes during volume contractions, it was observed that the bulk modulus arises mainly from the Van de Waals interactions. Nevertheless, the entropy contribution to the bulk modulus becomes significant above the glass transition. At a first order, the entropy part of the bulk modulus can be considered as independent on the temperature.Projet ANR jeunes chercheurs MELAC JC05_43403
MODIFICATION OF FOOD CHARACTERISTICS WITH CELLULOSE HYDROCOLLOIDS II: The Modified Bingham Body - A Useful Rheological Model
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