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Talks Alex Steffen: Inspired Ideas for a Sustainable Future

REA Catalogado

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4

Promedio: 4 (1 reseña)

Es un excelente video, dónde en forma clara y sencilla, el conferencista explica lo que es la huella ecológica y la problematica de no realizar los cambios necesarios para proteger y corregir los problemas del medio ambiente. Además deja un claro mensaje de como el apoyo social y la transferencia de educación a los que no tienen recursos puede cambiar el mundo en el que todos vivimos. Y muestra increibles inventos para resolver problemas de medio ambiente, como resultado del respeto y registro de la creatividad de personas pobres que viven los problemas y que creativamente los resuelven.

Tema: general: 

• Negocios y Economía›Economía›Historia de la Economía›General

Scaling, Sensitivity and Stability in the Numerical Solution of Quadratic Eigenvalue Problems

REA Auditado

The most common way of solving the quadratic eigenvalue problem (QEP)
$(\l^2 M + \l D + K)x=0$ is to convert it into a linear problem
$(\l X + Y)z=0$ of twice the dimension and solve the linear problem
by the QZ algorithm or a Krylov method.
In doing so, it is important to understand the influence of the linearization
process on the accuracy and stability of the computed solution.
We discuss these issues for three particular linearizations:
the standard companion linearization
and two linearizations that preserve symmetry in the problem.
For illustration we employ
a model QEP describ

Tema: general: 

• Ciencias›Matemáticas

Scaling, Sensitivity and Stability in the Numerical Solution of Quadratic Eigenvalue Problems

REA Auditado

The most common way of solving the quadratic eigenvalue problem (QEP)
$(\l^2 M + \l D + K)x=0$ is to convert it into a linear problem
$(\l X + Y)z=0$ of twice the dimension and solve the linear problem
by the QZ algorithm or a Krylov method.
In doing so, it is important to understand the influence of the linearization
process on the accuracy and stability of the computed solution.
We discuss these issues for three particular linearizations:
the standard companion linearization
and two linearizations that preserve symmetry in the problem.
For illustration we employ
a model QEP describ

Tema: general: 

• Ciencias›Matemáticas

Scaling, Sensitivity and Stability in the Numerical Solution of Quadratic Eigenvalue Problems

REA Auditado

The most common way of solving the quadratic eigenvalue problem (QEP)
$(\l^2 M + \l D + K)x=0$ is to convert it into a linear problem
$(\l X + Y)z=0$ of twice the dimension and solve the linear problem
by the QZ algorithm or a Krylov method.
In doing so, it is important to understand the influence of the linearization
process on the accuracy and stability of the computed solution.
We discuss these issues for three particular linearizations:
the standard companion linearization
and two linearizations that preserve symmetry in the problem.
For illustration we employ
a model QEP describ

Tema: general: 

• Ciencias›Matemáticas

Detecting a definite Hermitian pair and a hyperbolic or elliptic quadratic eigenvalue problem, and associated nearness problems

REA Auditado

An important class of generalized eigenvalue problems Ax=λBx is those in which A and B are Hermitian and some real linear combination of them is definite. For the quadratic eigenvalue problem (QEP) with Hermitian A, B and C and positive definite A, particular interest focuses on problems in which (x*Bx)2−4(x*Ax)(x*Cx) is one-signed for all non-zero x—for the positive sign these problems are called hyperbolic and for the negative sign elliptic. The important class of overdamped problems arising in mechanics is a sub-class of the hyperbolic problems.

Tema: general: 

• Ciencias›Matemáticas

Detecting and Solving Hyperbolic Quadratic Eigenvalue Problems

REA Auditado

Hyperbolic quadratic matrix polynomials $Q(\lambda) = \lambda^2 A +
\lambda B + C$ are an important class of
Hermitian matrix polynomials
with real eigenvalues, among which the overdamped quadratics are those
with nonpositive eigenvalues.
Neither the definition of overdamped nor any of the standard
characterizations provides an efficient way to test if a given $Q$
has this property.
We show that a quadratically convergent matrix iteration based on
cyclic reduction, previously studied by Guo and Lancaster,
provides necessary and sufficient conditions for $Q$ to be overdamped.
For wea

Tema: general: 

• Ciencias›Matemáticas

Detecting and Solving Hyperbolic Quadratic Eigenvalue Problems

REA Auditado

Hyperbolic quadratic matrix polynomials $Q(\lambda) = \lambda^2 A +
\lambda B + C$ are an important class of
Hermitian matrix polynomials
with real eigenvalues, among which the overdamped quadratics are those
with nonpositive eigenvalues.
Neither the definition of overdamped nor any of the standard
characterizations provides an efficient way to test if a given $Q$
has this property.
We show that a quadratically convergent matrix iteration based on
cyclic reduction, previously studied by Guo and Lancaster,
provides necessary and sufficient conditions for $Q$ to be overdamped.
For wea

Tema: general: 

• Ciencias›Matemáticas

Detecting and Solving Hyperbolic Quadratic Eigenvalue Problems

REA Auditado

Hyperbolic quadratic matrix polynomials $Q(\lambda) = \lambda^2 A +
\lambda B + C$ are an important class of
Hermitian matrix polynomials
with real eigenvalues, among which the overdamped quadratics are those
with nonpositive eigenvalues.
Neither the definition of overdamped nor any of the standard
characterizations provides an efficient way to test if a given $Q$
has this property.
We show that a quadratically convergent matrix iteration based on
cyclic reduction, previously studied by Guo and Lancaster,
provides necessary and sufficient conditions for $Q$ to be overdamped.
For wea

Tema: general: 

• Ciencias›Matemáticas

An inside analysis of a genetic-programming based optimizer

REA Auditado

The use of evolutionary algorithms has been proposed as a powerful random search strategy to solve the join order problem. Specifically, genetic programming used in query optimization has been proposed as an alternative to the limitations of dynamic programming with large join queries. However, very little is known about the impact and behavior of the genetic operations used in this type of algorithms. In this paper, we present an analysis that helps us to understand the effect of these operations during the optimization execution.

Tema: general: 

• Ingeniería y Ciencias Aplicadas›Ciencias Computacionales

Quinolone resistance in Escherichia colifrom Accra, Ghana

REA Auditado

Abstract Background Antimicrobial resistance is under-documented and commensal Escherichia coli can be used as indicator organisms to study the resistance in the community. We sought to determine the prevalence of resistance to broad-spectrum antimicrobials with particular focus on the quinolones, which have recently been introduced in parts of Africa, including Ghana. Results Forty (13.7%) of 293 E. coli isolates evaluated were nalidixic acid-resistant. Thirteen (52%) of 2006 and 2007 isolates and 10 (66.7%) of 2008 isolates were also resistant to ciprofloxacin.

Tema: general: 

• Ciencias›Biología