23 research outputs found
A gauge theoretic approach to elasticity with microrotations
We formulate elasticity theory with microrotations using the framework of
gauge theories, which has been developed and successfully applied in various
areas of gravitation and cosmology. Following this approach, we demonstrate the
existence of particle-like solutions. Mathematically this is due to the fact
that our equations of motion are of Sine-Gordon type and thus have soliton type
solutions. Similar to Skyrmions and Kinks in classical field theory, we can
show explicitly that these solutions have a topological origin.Comment: 15 pages, 1 figure; revised and extended version, one extra page;
revised and extended versio
Historical roots of gauge invariance
Gauge invariance is the basis of the modern theory of electroweak and strong
interactions (the so called Standard Model). The roots of gauge invariance go
back to the year 1820 when electromagnetism was discovered and the first
electrodynamic theory was proposed. Subsequent developments led to the
discovery that different forms of the vector potential result in the same
observable forces. The partial arbitrariness of the vector potential A brought
forth various restrictions on it. div A = 0 was proposed by J. C. Maxwell;
4-div A = 0 was proposed L. V. Lorenz in the middle of 1860's . In most of the
modern texts the latter condition is attributed to H. A. Lorentz, who half a
century later was one of the key figures in the final formulation of classical
electrodynamics. In 1926 a relativistic quantum-mechanical equation for charged
spinless particles was formulated by E. Schrodinger, O. Klein, and V. Fock. The
latter discovered that this equation is invariant with respect to
multiplication of the wave function by a phase factor exp(ieX/hc) with the
accompanying additions to the scalar potential of -dX/cdt and to the vector
potential of grad X. In 1929 H. Weyl proclaimed this invariance as a general
principle and called it Eichinvarianz in German and gauge invariance in
English. The present era of non-abelian gauge theories started in 1954 with the
paper by C. N. Yang and R. L. Mills.Comment: final-final, 34 pages, 1 figure, 106 references (one added with
footnote since v.2); to appear in July 2001 Rev. Mod. Phy
Spin of an almost-axial, almost-symmetric, torque-free gyrostat near an osculation condition
Access to Infrastructure in Brazilian Dwellings: An Analysis for 1981/2002 (Infra-Estrutura dos Domicilios Brasileiros: Uma Analise para o Periodo 1981/2002)
Analysis of distribution patterns of yellow European eels in the Loire catchment using logistic models based on presence-absence of different size-classes.
We used logistic models to analyse the longitudinal distribution patterns of yellow European eels in the Loire catchment (France). Our models for predicting the presence of yellow eels supported contrasting spatial patterns according to the size of individuals and catchments. The smallest eels (mainly <150 mm and secondly 150–300 mm) were confined to downstream areas, but rapidly colonised upstream reaches. By contrast, larger eels were distributed further inland but tended to become more sedentary. In addition, a higher density of barriers to migration in the Maine catchment (a large catchment within the Loire catchment) probably delayed the upstream colonisation compared with the rest of the Loire catchment. These results suggest that logistic models may be a useful and efficient tool: (1) for the assessment of eel status and trends in freshwater systems; and (2) for the assessment of the consequences of local perturbations or conversely improvement of colonisation
A beginning exploration of text generation abilities in university students with a history of reading difficulties
There is a fundamental lack of understanding of how university students with a history of reading difficulties perform on various demanding literacy tasks. We compared the text generation skills, measured with timed summary writing and proofreading tasks, of university students with a history of reading difficulties to those of students with no such history. We further examined whether between-group differences in text generation skills remained after controlling for transcription skills (spelling and handwriting fluency), word reading, and reading comprehension. Forty-six university students with a history of reading difficulties were matched on age, gender, and non-verbal intelligence to 46 students without this history. We found that the students with a history of reading difficulties performed poorer on both measures of text generation than students without this history. When differences in transcription skills, word reading, and reading comprehension were controlled, we found that only differences in timed summary writing remained significant. These results suggest that students with a history of reading difficulties experience challenges with specific aspects of text generation that are beyond what one would expect from their difficulties with transcription and word reading. We suggest that, if not addressed, text generation deficits are likely to create obstacles for academic success