2,477 research outputs found
Koopman Operator and its Approximations for Systems with Symmetries
Nonlinear dynamical systems with symmetries exhibit a rich variety of
behaviors, including complex attractor-basin portraits and enhanced and
suppressed bifurcations. Symmetry arguments provide a way to study these
collective behaviors and to simplify their analysis. The Koopman operator is an
infinite dimensional linear operator that fully captures a system's nonlinear
dynamics through the linear evolution of functions of the state space.
Importantly, in contrast with local linearization, it preserves a system's
global nonlinear features. We demonstrate how the presence of symmetries
affects the Koopman operator structure and its spectral properties. In fact, we
show that symmetry considerations can also simplify finding the Koopman
operator approximations using the extended and kernel dynamic mode
decomposition methods (EDMD and kernel DMD). Specifically, representation
theory allows us to demonstrate that an isotypic component basis induces block
diagonal structure in operator approximations, revealing hidden organization.
Practically, if the data is symmetric, the EDMD and kernel DMD methods can be
modified to give more efficient computation of the Koopman operator
approximation and its eigenvalues, eigenfunctions, and eigenmodes. Rounding out
the development, we discuss the effect of measurement noise
PI-FLAME: A parallel immune system simulator using the FLAME graphic processing unit environment
Agent-based models (ABMs) are increasingly being used to study population dynamics in complex systems, such as the human immune system. Previously, Folcik et al. (The basic immune simulator: an agent-based model to study the interactions between innate and adaptive immunity. Theor Biol Med Model 2007; 4: 39) developed a Basic Immune Simulator (BIS) and implemented it using the Recursive Porous Agent Simulation Toolkit (RePast) ABM simulation framework. However, frameworks such as RePast are designed to execute serially on central processing units and therefore cannot efficiently handle large model sizes. In this paper, we report on our implementation of the BIS using FLAME GPU, a parallel computing ABM simulator designed to execute on graphics processing units. To benchmark our implementation, we simulate the response of the immune system to a viral infection of generic tissue cells. We compared our results with those obtained from the original RePast implementation for statistical accuracy. We observe that our implementation has a 13Ă— performance advantage over the original RePast implementation
Integration of Evidence-Based Practice in Nursing Education
Evidence based practice (EBP) has gained momentum globally, to provide effective and efficient health care.
Although EBP has evolved to a great extent over the last two decades and is accepted as an important concept by all
health care professionals, its integration in practice is still challenging. Integration of EBP in nursing profession both
in nursing practice and nursing education is an important issue. This article describes the experience of the authors
in integrating evidence based practice in nursing education in Manipal University. It focuses on the training of nurse
educators in EBP, alignment of EBP in curriculum and EBP practicum in curriculum so as to enable a nurse to identify
evidences, make appropriate clinical decisions and utilize EBP in rendering scientific and quality patient care
Rubrics in Nursing Education
Evaluating assignments or course work is a challenging job for faculty of
nursing. In order to avoid the dilemmas of evaluation, nurse educators use
rubrics as an evaluation tool. In educational technology, rubric refers to
„performance standard‟ for a student population. A rubric is defined as an
assessment tool that lays out the set standards and criteria to assess a
performance, assignment or behavior. The four essential components of a
rubric are task description, scale of achievement, dimensions & description
of dimensions. Various types of scoring rubrics are available. The type of
rubric chosen for assessment depends on the task being evaluated and the
needs of the assessor. Holistic rubrics, analytic rubrics, generic rubrics,
specific rubrics are the different types of rubrics. In nursing education,
rubrics has got wide range of applications such as to; assess clinical skills,
grade assignments, evaluate clinical competency and analyze presentations.
Rubrics helps to define "quality performance” and promote awareness on
critical components in a performance. Rubrics not only act as an evaluation
tool for instructors, but also act as a feedback proforma for students. Rubrics
are vital tools that can be utilized to solve the problem of subjectivity in
evaluation. Rubrics provide consistency in evaluation, reduces subjectivity
and enhances objectivity
Galactic accretion and the outer structure of galaxies in the CDM model
We have combined the semi-analytic galaxy formation model of Guo et al.
(2011) with the particle-tagging technique of Cooper et al. (2010) to predict
galaxy surface brightness profiles in a representative sample of ~1900 massive
dark matter haloes (10^12--10^14 M_sol) from the Millennium II Lambda-CDM
N-body simulation. Here we present our method and basic results focusing on the
outer regions of galaxies, consisting of stars accreted in mergers. These
simulations cover scales from the stellar haloes of Milky Way-like galaxies to
the 'cD envelopes' of groups and clusters, and resolve low surface brightness
substructure such as tidal streams. We find that the surface density of
accreted stellar mass around the central galaxies of dark matter haloes is well
described by a Sersic profile, the radial scale and amplitude of which vary
systematically with halo mass (M_200). The total stellar mass surface density
profile breaks at the radius where accreted stars start to dominate over stars
formed in the galaxy itself. This break disappears with increasing M_200
because accreted stars contribute more of the total mass of galaxies, and is
less distinct when the same galaxies are averaged in bins of stellar mass,
because of scatter in the relation between M_star and M_200. To test our model
we have derived average stellar mass surface density profiles for massive
galaxies at z~0.08 by stacking SDSS images. Our model agrees well with these
stacked profiles and with other data from the literature, and makes predictions
that can be more rigorously tested by future surveys that extend the analysis
of the outer structure of galaxies to fainter isophotes. We conclude that it is
likely that the outer structure of the spheroidal components of galaxies is
largely determined by collisionless merging during their hierarchical assemblyComment: Accepted by MNRAS. Shortened following referee's report, conclusions
unchanged. 21 pages, 15 figure
Robust Bain distortion in the premartensite phase of platinum substituted Ni2MnGa magnetic shape memory alloy
The premartensite phase of shape memory and magnetic shape memory alloys
(MSMAs) is believed to be a precursor state of the martensite phase with
preserved austenite phase symmetry. The thermodynamic stability of the
premartensite phase and its relation to the martensitic phase is still an
unresolved issue, even though it is critical to the understanding of the
functional properties of MSMAs. We present here unambiguous evidence for
macroscopic symmetry breaking leading to robust Bain distortion in the
premartensite phase of 10% Pt substituted Ni2MnGa. We show that the robust Bain
distorted premartensite (T2) phase results from another premartensite (T1)
phase with preserved cubic-like symmetry through an isostructural phase
transition. The T2 phase finally transforms to the martensite phase with
additional Bain distortion on further cooling. Our results demonstrate that the
premartensite phase should not be considered as a precursor state with the
preserved symmetry of the cubic austenite phase
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