7,832 research outputs found
Application of quasi-homogeneous anisotropic laminates in grid-stiffened panel design
Composite laminates are derived for standard configurations with quasi-homogeneous anisotropic properties, whereby in-plane and out-of-plane stiffness properties are concomitant. Dimensionless parameters, and their relationship to the well-known ply- orientation-dependent lamination parameters, are also developed from which the elements of the extensional and bending stiffness matrices are readily calculated for any fiber/resin properties. The definitive list of laminate configurations for up to 21 plies is presented, together with graphical representations of the lamination parameter design space for standard ply orientations +45, -45, 0 and 90 degrees. Finally, the potential of quasi-homogeneous anisotropic laminates as an optimum design solution for anisogid structures is explored for cases where buckling and strength constraints are both active
Properties of the Optokinetic Motor Fibres in the Rock Lobster: Build-Up, Flipback, Afterdischarge and Memory, Shown by Their Firing Patterns
The properties of sets of motor fibres responding to both clockwise and anticlockwise rotation have been studied in the oculomotor nerve of the rock lobster. There are probably three, but perhaps four, units in each set.
None of these fibres has statocyst input, but there is weak input onto the tonic fibres from the antennal joints such that the eye turns in the direction toward which the antenna points.
Many preparations show bilateral visual input onto all fibres but the degree of coupling between the eyes is very variable, and at times can be nearly totally absent.
Depending on the speed of rotation the fibres show a gradual build-up in frequency, during rotation in the preferred direction, interrupted by flipbacks. During the fast stage of the resulting nystagmic movements all agonistic fibres can be completely inhibited and all antagonistic ones can be activated, usually for a period of about 0.5 sec.
Fibre activity is demonstrated which appears to underlie an âoptokinetic memoryâ of contrasting target position in the visual field. It consists of (a) very prolonged after-discharges for a stationary striped pattern (b) resumption of discharges at an appropriate frequency after dark periods up to 2 min, and (c) adjustment of such frequencies to changes in stripe position during the dark period.
The fibres show habituation to repeated stripe movement but the response can be dishabituated by passive rotation of the animal.
The largest visual responses were obtained to intermediate speeds of stripe rotation (about 2°/sec)
Input Sources and Properties of Position-Sensitive Oculomotor Fibres in the Rock Lobster, Panulirus Interruptus (Randall)
Sets of head-up, head-down, eye-up and eye-down motor fibres were studied in the oculomotor nerve of the rock lobster. An eye-withdrawal fibre was also investigated.
Apart from the statocyst input, light distribution on the eyes has the strongest influence on the position-sensitive fibres. Weaker optokinetic input from moving targets is also present.
Strongly habituating input is obtained from the antennal joints. This input causes orientation of the eye toward the direction in which the antenna points.
The same antennule movement in the vertical plane can result in either excitation or inhibition of the head-down fibre, suggesting the presence of two opposing inputs, presumably from the statocysts and basal joint receptors of the antennule.
The inputs on to the position-sensitive fibres which indicate body position are such as to stabilize the eye position in space during body movement. The optokinetic and antennal joint inputs are probably involved in tracking and antennal pointing reactions.
The eye-withdrawal fibre is stimulated by touch of the head and around the eye, but is inhibited by the excited state
Gauge-invariant variables in general-relativistic perturbations: globalization and zero-mode problem
An outline of a proof of the local decomposition of linear metric
perturbations into gauge-invariant and gauge-variant parts on an arbitrary
background spacetime is briefly explained. We explicitly construct the
gauge-invariant and gauge-variant parts of the linear metric perturbations
based on some assumptions. We also point out the zero-mode problem is an
essential problem to globalize of this decomposition of linear metric
perturbations. The resolution of this zero-mode problem implies the possibility
of the development of the higher-order gauge-invariant perturbation theory on
an arbitrary background spacetime in a global sense.Comment: (v1) 16 pages, no figure; (v2) 9 pages, no figure. Compactified for
"2012 Awards for Essays on Gravitation" promoted by Gravity Research
Foundation. References are deleted. no ingredients is changed. This version
received Honorable Mention for 201
Parental influences on high school student achievement and goals
The present study examined parental influences on educational and career goals of high school students. Data on educational and career goals from the Perceived Life Chances Interview were derived from 124 rural adolescents. One hundred of their mothers and 36 of their fathers completed the Inventory of Parental Influence which consists of five subscales of Parental Involvement/Help, Psychological Support, Parental Pressure, Pressure for Intellectual Development, and Time Management/Monitoring. Responses from the Perceived Life Chances Interview were qualitatively analyzed in order to derive categories that reflected the varying responses from participants. These categories served as dependent variables in a series of discriminant function and regression analyses that included the five subscales of the Inventory of Parental Influence, race, and gender as the predictor variables. It was evident from present and prior research that parental influences were found to be associated with adolescent achievement and career goals
Freire re-viewed
The work of Paulo Freire is associated with themes of oppression and liberation, and his critical pedagogy is visionary in its attempts to bring about social transformation. Freire has created a theory of education that embeds these issues within social relations that center around both ideological and material domination. In this review essay, Sue Jackson explores three books: Freireâs final work Pedagogy of Indignation; Cesar Augusto Rossattoâs Engaging Paulo Freireâs Pedagogy of Possibility, which attempts to engage Freireâs pedagogy of possibility; and C.A. Bowers and Frederique Apffel-Marglinâs edited collection Re-thinking Freire, which asks readers to reconsider Freireâs work in light of globalization and environmental crises. Jackson questions the extent to which Freireâs pedagogical approaches are useful to educators as well as to âthe oppressed,â and whether challenges to re-think Freire can lead to new kinds of critical pedagogies
Waveless Approximation Theories of Gravity
The analysis of a general multibody physical system governed by Einstein's
equations in quite difficult, even if numerical methods (on a computer) are
used. Some of the difficulties -- many coupled degrees of freedom, dynamic
instability -- are associated with the presence of gravitational waves. We have
developed a number of ``waveless approximation theories'' (WAT) which repress
the gravitational radiation and thereby simplify the analysis. The matter,
according to these theories, evolves dynamically. The gravitational field,
however, is determined at each time step by a set of elliptic equations with
matter sources. There is reason to believe that for many physical systems, the
WAT-generated system evolution is a very accurate approximation to that
generated by the full Einstein theory
Robustness of Binary Black Hole Mergers in the Presence of Spurious Radiation
We present an investigation into how sensitive the last orbits and merger of
binary black hole systems are to the presence of spurious radiation in the
initial data. Our numerical experiments consist of a binary black hole system
starting the last couple of orbits before merger with additional spurious
radiation centered at the origin and fixed initial angular momentum. As the
energy in the added spurious radiation increases, the binary is invariably
hardened for the cases we tested, i.e. the merger of the two black holes is
hastened. The change in merger time becomes significant when the additional
energy provided by the spurious radiation increases the Arnowitt-Deser-Misner
(ADM) mass of the spacetime by about 1%. While the final masses of the black
holes increase due to partial absorption of the radiation, the final spins
remain constant to within our numerical accuracy. We conjecture that the
spurious radiation is primarily increasing the eccentricity of the orbit and
secondarily increasing the mass of the black holes while propagating out to
infinity.Comment: 12 pages, 12 figure
Quantization of generally covariant systems with extrinsic time
A generally covariant system can be deparametrized by means of an
``extrinsic'' time, provided that the metric has a conformal ``temporal''
Killing vector and the potential exhibits a suitable behavior with respect to
it. The quantization of the system is performed by giving the well ordered
constraint operators which satisfy the algebra. The searching of these
operators is enlightned by the methods of the BRST formalism.Comment: 10 pages. Definite published versio
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