1,827 research outputs found
Exact resultants for corner-cut unmixed multivariate polynomial systems using the dixon formulation
Structural conditions on the support of a multivariate polynomial system are developed for which the Dixon-based resultant methods compute exact resultants. For cases when this cannot be done, an upper bound on the degree of the extraneous factor in the projection operator can be determined a priori, thus resulting in quick identification of the extraneous factor in the projection operator. (For the bivariate case, the degree of the extraneous factor in a projection operator can be determined a priori.) The concepts of a corner-cut support and almost corner-cut support of an unmixed polynomial system are introduced. For generic unmixed polynomial systems with corner-cut and almost corner-cut supports, the Dixon based methods can be used to compute their resultants exactly. These structural conditions on supports are based on analyzing how such supports differ from box supports of n-degree systems for which the Dixon formulation is known to compute the resultants exactly. Such an analysis also gives a sharper bound on the complexity of resultant computation using the Dixon formulation in terms of the support and the mixed volume of the Newton polytope of the support. These results are a direct generalization of the authors ’ results on bivariate systems including the results of Zhang and Goldman as well as of Chionh for generic unmixed bivariate polynomial systems with corner-cut supports
Early detection of first-time slope failures using acoustic emission measurements : large-scale physical modelling
Early warning systems for slope instability need to alert users of accelerating slope deformation behaviour to enable safety-critical decisions to be made. This study shows that acoustic emission (AE) monitoring of active waveguides (i.e. a steel tube with a granular backfill surround installed through a slope) can both detect shear surface development and quantify increasing rates of movement during slope failure, thereby providing an early detection of slope instability. A large-scale physical model was designed and built to simulate slope failures on elements of soil, through which full-scale active waveguides were installed. A shear surface develops in each test and the sliding mass accelerates during failure, reaching velocities greater than 300 mm/h and shear deformations of 50 mm. Continuous measurementswere obtained to examine the behaviour of activewaveguides subjected to first-time slope failure dynamics (i.e. development of new shear surfaces and accelerating deformation behaviour). Comparisons with continuous subsurface deformation measurements show that AE detection began during shear surface formation, and AE rates increased proportionally with displacement rates as failure occurred. Empirical AE rate–slope velocity relationships are presented for three granular backfill types, which demonstrate that generic AE rate–slope velocity relationships can be obtained for groups of backfill types; these relationships allow displacement rates to be quantified from measured AE rates to provide early detection of slope instability. © 2017, ICE Publishing. All rights reserved
Computer Science for Continuous Data:Survey, Vision, Theory, and Practice of a Computer Analysis System
Building on George Boole's work, Logic provides a rigorous foundation for the powerful tools in Computer Science that underlie nowadays ubiquitous processing of discrete data, such as strings or graphs. Concerning continuous data, already Alan Turing had applied "his" machines to formalize and study the processing of real numbers: an aspect of his oeuvre that we transform from theory to practice.The present essay surveys the state of the art and envisions the future of Computer Science for continuous data: natively, beyond brute-force discretization, based on and guided by and extending classical discrete Computer Science, as bridge between Pure and Applied Mathematics
Distance-based formulations for the position analysis of kinematic chains
This thesis addresses the kinematic analysis of mechanisms, in particular, the position
analysis of kinematic chains, or linkages, that is, mechanisms with rigid bodies (links)
interconnected by kinematic pairs (joints). This problem, of completely geometrical
nature, consists in finding the feasible assembly modes that a kinematic chain can adopt.
An assembly mode is a possible relative transformation between the links of a kinematic
chain. When an assignment of positions and orientations is made for all links with
respect to a given reference frame, an assembly mode is called a configuration. The
methods reported in the literature for solving the position analysis of kinematic chains
can be classified as graphical, analytical, or numerical.
The graphical approaches are mostly geometrical and designed to solve particular
problems. The analytical and numerical methods deal, in general, with kinematic chains
of any topology and translate the original geometric problem into a system of kinematic analysis of all the Assur kinematic chains resulting from replacing some of its revolute
joints by slider joints. Thus, it is concluded that the polynomials of all fully-parallel
planar robots can be derived directly from that of the widely known 3-RPR robot. In
addition to these results, this thesis also presents an efficient procedure, based on distance
and oriented area constraints, and geometrical arguments, to trace coupler curves
of pin-jointed Gr¨ubler kinematic chains. All these techniques and results together are
contributions to theoretical kinematics of mechanisms, robot kinematics, and distance
plane geometry.
equations that defines the location of each link based, mainly, on independent loop
equations. In the analytical approaches, the system of kinematic equations is reduced
to a polynomial, known as the characteristic polynomial of the linkage, using different
elimination methods —e.g., Gr¨obner bases or resultant techniques. In the numerical
approaches, the system of kinematic equations is solved using, for instance, polynomial
continuation or interval-based procedures.
In any case, the use of independent loop equations to solve the position analysis
of kinematic chains, almost a standard in kinematics of mechanisms, has seldom been
questioned despite the resulting system of kinematic equations becomes quite involved
even for simple linkages. Moreover, stating the position analysis of kinematic chains
directly in terms of poses, with or without using independent loop equations, introduces
two major disadvantages: arbitrary reference frames has to be included, and all formulas
involve translations and rotations simultaneously. This thesis departs from this standard
approach by, instead of directly computing Cartesian locations, expressing the original
position problem as a system of distance-based constraints that are then solved using
analytical and numerical procedures adapted to their particularities.
In favor of developing the basics and theory of the proposed approach, this thesis
focuses on the study of the most fundamental planar kinematic chains, namely, Baranov
trusses, Assur kinematic chains, and pin-jointed Gr¨ubler kinematic chains. The results
obtained have shown that the novel developed techniques are promising tools for the
position analysis of kinematic chains and related problems. For example, using these
techniques, the characteristic polynomials of most of the cataloged Baranov trusses can
be obtained without relying on variable eliminations or trigonometric substitutions and
using no other tools than elementary algebra. An outcome in clear contrast with the
complex variable eliminations require when independent loop equations are used to tackle
the problem.
The impact of the above result is actually greater because it is shown that the
characteristic polynomial of a Baranov truss, derived using the proposed distance-based
techniques, contains all the necessary and sufficient information for solving the positionEsta tesis aborda el problema de análisis de posición de cadenas cinemáticas, mecanismos con cuerpos rÃgidos (enlaces)
interconectados por pares cinemáticos (articulaciones). Este problema, de naturaleza geométrica, consiste en encontrar los
modos de ensamblaje factibles que una cadena cinemática puede adoptar. Un modo de ensamblaje es una transformación
relativa posible entre los enlaces de una cadena cinemática. Los métodos reportados en la literatura para la solución del análisis
de posición de cadenas cinemáticas se pueden clasificar como gráficos, analÃticos o numéricos.
Los enfoques gráficos son geométricos y se diseñan para resolver problemas particulares. Los métodos analÃticos y numéricos
tratan con cadenas cinemáticas de cualquier topologÃa y traducen el problema geométrico original en un sistema de ecuaciones
cinemáticas que define la ubicación de cada enlace, basado generalmente en ecuaciones de bucle independientes. En los
enfoques analÃticos, el sistema de ecuaciones cinemáticas se reduce a un polinomio, conocido como el polinomio caracterÃstico
de la cadena cinemática, utilizando diferentes métodos de eliminación. En los métodos numéricos, el sistema se resuelve
utilizando, por ejemplo, la continuación polinomial o procedimientos basados en intervalos.
En cualquier caso, el uso de ecuaciones de bucle independientes, un estándar en cinemática de mecanismos, rara vez ha sido
cuestionado a pesar de que el sistema resultante de ecuaciones es bastante complicado, incluso para cadenas simples. Por otra
parte, establecer el análisis de la posición de cadenas cinemáticas directamente en términos de poses, con o sin el uso de
ecuaciones de bucle independientes, presenta dos inconvenientes: sistemas de referencia arbitrarios deben ser introducidos, y
todas las fórmulas implican traslaciones y rotaciones de forma simultánea. Esta tesis se aparta de este enfoque estándar
expresando el problema de posición original como un sistema de restricciones basadas en distancias, en lugar de directamente
calcular posiciones cartesianas. Estas restricciones son posteriormente resueltas con procedimientos analÃticos y numéricos
adaptados a sus particularidades.
Con el propósito de desarrollar los conceptos básicos y la teorÃa del enfoque propuesto, esta tesis se centra en el estudio de las
cadenas cinemáticas planas más fundamentales, a saber, estructuras de Baranov, cadenas cinemáticas de Assur, y cadenas
cinemáticas de Grübler. Los resultados obtenidos han demostrado que las técnicas desarrolladas son herramientas
prometedoras para el análisis de posición de cadenas cinemáticas y problemas relacionados. Por ejemplo, usando dichas
técnicas, los polinomios caracterÃsticos de la mayorÃa de las estructuras de Baranov catalogadas se puede obtener sin realizar
eliminaciones de variables o sustituciones trigonométricas, y utilizando solo álgebra elemental. Un resultado en claro contraste
con las complejas eliminaciones de variables que se requieren cuando se utilizan ecuaciones de bucle independientes.
El impacto del resultado anterior es mayor porque se demuestra que el polinomio caracterÃstico de una estructura de Baranov,
derivado con las técnicas propuestas, contiene toda la información necesaria y suficiente para resolver el análisis de posición de
las cadenas cinemáticas de Assur que resultan de la sustitución de algunas de sus articulaciones de revolución por
articulaciones prismáticas. De esta forma, se concluye que los polinomios de todos los robots planares totalmente paralelos se
pueden derivar directamente del polinomio caracterÃstico del conocido robot 3-RPR. Adicionalmente, se presenta un
procedimiento eficaz, basado en restricciones de distancias y áreas orientadas, y argumentos geométricos, para trazar curvas
de acoplador de cadenas cinemáticas de Grübler. En conjunto, todas estas técnicas y resultados constituyen contribuciones a la
cinemática teórica de mecanismos, la cinemática de robots, y la geometrÃa plana de distancias.
Barcelona 13
The effect of temperature upon the growth and metabolism of aeromonas hydrophila and lactobacillus plantarum in pure and mixed culture
The effects of temperature upon the growth and metabolism of pure and mixed
populations of Aeromonas hydrophila and Lactobacillus p/an/Qrum were studied.
Initially a medium was developed to provide unbiased support for both organisms.
The effect of temperature upon lag phase, growth rate, and final population level
between pure and mixed culture was investigated. Temperature effects were only
found to be significant when comparing the final population levels of Lb. p/anlDrum
between pure and mixed culture. The lactobacilli exhibited a bomofermentative to
heterofermentative switch between pure and mixed culture. This was probably due to
substrate competition from the aeromonad population in mixed culture
The metabolism of Aer. hydrophi!a has not been well described in the literature,
compared to that of the lactobacilli. Due to the simplicity of the growth medium it was
possible to determine the substrates relatively easily, although quantification required
amino acid analysis. It was found that the organism utilized amino acids as primary
substrates, switching to available carbohydrate as the population moved from growth
to stationary phase. The principal product was found to be urea. During the stationary
phase of population development it was interesting to note that the pH of the medium
increased to well above the starting point of around S.S. This was principally due to
de-amination of the urea product. Growth temperature above recognized optimum
(28°C) was found to affect the metabolic profile of this organism, leading to low final
pH levels.
4
The pattern of temperature effect upon the metabolism of Lb. plantarum as expressed
by growth yields showed a similar pattern to the final population levels. The ratio of
lactate formed : dextrose utilized was reversed at the 100e point. Growth of Lb.
plantarum was not detected at the soe point.
A new third order polynomial model was developed to describe the tag phase of
bacterial cultures across a temperature range. The new model was compared with two
others from the literature. The new model was chosen based upon statistical results.
The pattern exhibited by final population levels at the different temperatures showed •
similar point of inflection to that expressed by the polynomiallag phase model. The
growth rate was modeled with the Schoolfield model which was proven to be the
closest estimate of the three models tested.
The theory ofhomeoviscous adaptation was used to explain the behavior patterns
observed
The Bernstein basis in set-theoretic geometric modelling
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN037062 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Polynomial continuation in the design of deployable structures
Polynomial continuation, a branch of numerical continuation, has been applied
to several primary problems in kinematic geometry. The objective of
the research presented in this document was to explore the possible extensions
of the application of polynomial continuation, especially in the field
of deployable structure design. The power of polynomial continuation as a
design tool lies in its ability to find all solutions of a system of polynomial
equations (even positive dimensional solution sets). A linkage design problem
posed in polynomial form can be made to yield every possible feasible
outcome, many of which may never otherwise have been found.
Methods of polynomial continuation based design are illustrated here by way
of various examples. In particular, the types of deployable structures which
form planar rings, or frames, in their deployed configurations are used as
design cases. Polynomial continuation is shown to be a powerful component
of an equation-based design process.
A polyhedral homotopy method, particularly suited to solving problems in
kinematics, was synthesised from several researchers’ published continuation
techniques, and augmented with modern, freely available mathematical
computing algorithms. Special adaptations were made in the areas of level-k
subface identification, lifting value balancing, and path-following. Techniques
of forming closure/compatibility equations by direct use of symmetry,
or by use of transfer matrices to enforce loop closure, were developed as appropriate
for each example.
The geometry of a plane symmetric (rectangular) 6R foldable frame was examined
and classified in terms of Denavit-Hartenberg Parameters. Its design
parameters were then grouped into feasible and non-feasible regions, before
continuation was used as a design tool; generating the design parameters
required to build a foldable frame which meets certain configurational specifications.
iv
Two further deployable ring/frame classes were then used as design cases:
(a) rings which form (planar) regular polygons when deployed, and (b) rings
which are doubly plane symmetric and planar when deployed. The governing
equations used in the continuation design process are based on symmetry
compatibility and transfer matrices respectively.
Finally, the 6, 7 and 8-link versions of N-loops were subjected to a witness
set analysis, illustrating the way in which continuation can reveal the nature
of the mobility of an unknown linkage.
Key features of the results are that polynomial continuation was able to provide
complete sets of feasible options to a number of practical design problems,
and also to reveal the nature of the mobility of a real overconstrained
linkage
Elasto-multi-body dynamics of internal combustion engines with thin-shell elastohydrodynamic journal bearings
This thesis describes problems associated with noise and vibration concern in internal
combustion engines as the result of a growing trend in the development of modern
vehicular engines with high power to light weight ratios. There are a plethora of
vibration concerns. These are owed to the increasing combustion forces in lean burn
engines and the progressive use of materials of durable, but light-weight construction.
The latter has come about as a result of a need to reduce the inertial imbalances.
These features have resulted in achieving fuel efficiency. Although the primary aims
in high output power and structural integrity have been largely achieved, these have
culminated in an assortment of sources of noise and vibration, chiefly among them
those associated with signature output of the combustion process. For the common
four stroke engines, the contributory sources are at half-engine order multiples,
referred to as engine "roughness". A holistic approach is to incorporate reduced
engine roughness contributions as an integral part of engine design and development.
The aim of this thesis is to create a methodology for fundamental design evaluation
and analysis of engine dynamics, which comprises rigid body inertial dynamics of
engine assembly, the elasto-dynamics of flexible and compliant components and
applied and reactive forces in such a complex assembly. [Continues.
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