2,009 research outputs found
Numerical Experiments in Linear Control Theory Using Generalized X-Y Equations
Numerical investigations of the relative efficiency of Riccati versus non-Riccati based approaches to the determination of optimal feedback gains for linear dynamics-quadratic cost control processes over a finite interval are presented. The non-Riccati algorithms used are the so-called generalized X — Y functions [1] or Chandrasekhar-type [2] algorithms. The results of the experiments show that the generalized X — Y approach has significant computational advantages over the usual Riccati equation and, in many cases, the computational gain exceeds rough estimates based solely upon a count of the number of equations to be integrated. © 1976, IEEE
Angular-dependence of magnetization switching for a multi-domain dot: experiment and simulation
We have measured the in-plane angular variation of nucleation and
annihilation fields of a multi-domain magnetic single dot with a microsquid.
The dots are Fe/Mo(110) self-assembled in UHV, with sub-micron size and a
hexagonal shape. The angular variations were quantitatively reproduced by
micromagnetic simulations. Discontinuities in the variations are observed, and
shown to result from bifurcations related to the interplay of the non-uniform
magnetization state with the shape of the dot.Comment: 4 pages, 4 figures, for submission as a regular articl
Dynamic approach for micromagnetics close to the Curie temperature
In conventional micromagnetism magnetic domain configurations are calculated
based on a continuum theory for the magnetization which is assumed to be of
constant length in time and space. Dynamics is usually described with the
Landau-Lifshitz-Gilbert (LLG) equation the stochastic variant of which includes
finite temperatures. Using simulation techniques with atomistic resolution we
show that this conventional micromagnetic approach fails for higher
temperatures since we find two effects which cannot be described in terms of
the LLG equation: i) an enhanced damping when approaching the Curie temperature
and, ii) a magnetization magnitude that is not constant in time. We show,
however, that both of these effects are naturally described by the
Landau-Lifshitz-Bloch equation which links the LLG equation with the theory of
critical phenomena and turns out to be a more realistic equation for
magnetization dynamics at elevated temperatures
A Method to Assess the Organizing Behaviors Used in Physicians\u27 Counseling of Standardized Parents after Newborn Genetic Screening
Well-organized conversation can improve people’s ability to comprehend and retain information. As part of a long-term effort to adapt Quality Improvement techniques for communication, we developed an explicit criteria method to assess usage of three organizing behaviors (OBs): ‘opening behaviors’ to establish goals; ‘structuring behaviors’ to guide patients through conversation; and ‘emphasizing behaviors’ that signal a need for attention. Pairs of abstractors independently reviewed transcripts in a demonstration sample of conversations between physicians and standardized parents after newborn screening identifies carrier status for sickle cell disease. Criteria for at least one OB were identified in 50/84 transcripts (60%), including 27 with at least one opening behavior (32%), 5 with at least one structuring behavior (6%), and 38 with at least one emphasizing behavior (45%). The limited number of OBs raises concern about communication after newborn screening. Assessment and improvement of OB usage may improve understanding and allow parents to more actively participate in health care
Behavior of tumors under nonstationary theraphy
We present a model for the interaction dynamics of lymphocytes-tumor cells
population. This model reproduces all known states for the tumor. Futherly,we
develop it taking into account periodical immunotheraphy treatment with
cytokines alone. A detailed analysis for the evolution of tumor cells as a
function of frecuency and theraphy burden applied for the periodical treatment
is carried out. Certain threshold values for the frecuency and applied doses
are derived from this analysis. So it seems possible to control and reduce the
growth of the tumor. Also, constant values for cytokines doses seems to be a
succesful treatment.Comment: 6 pages, 7 figure
Implementing Jet Aircraft Training in a University Setting: Instructor Perceptions and Lessons Learned
This paper presents the findings of a phenomenological study of instructor pilot first-hand experiences when conducting training for collegiate flight students in a jet aircraft. While jet training has been conducted in simulators in the past, this was one of the first instances of training in an actual aircraft. A total of 22 students completed training in a very light jet aircraft during the spring semester of their junior year at the subject university. A group of four instructors conducted both simulator and flight training with the students. Surveys were used to collect data from instructors longitudinally throughout the length of the 16-week semester. At the conclusion of the training period, participants completed a structured interview. The results of those interviews suggested that students excelled in areas such as avionics programming, use of standardized operating procedures, and checklist usage. Students were challenged by the increased operating speeds of the jet aircraft, descent planning, and lesson preparedness. The instructors offered suggestions to enhance the course and provided a summary of the lessons learned
Three-dimensional magnetic flux-closure patterns in mesoscopic Fe islands
We have investigated three-dimensional magnetization structures in numerous
mesoscopic Fe/Mo(110) islands by means of x-ray magnetic circular dichroism
combined with photoemission electron microscopy (XMCD-PEEM). The particles are
epitaxial islands with an elongated hexagonal shape with length of up to 2.5
micrometer and thickness of up to 250 nm. The XMCD-PEEM studies reveal
asymmetric magnetization distributions at the surface of these particles.
Micromagnetic simulations are in excellent agreement with the observed magnetic
structures and provide information on the internal structure of the
magnetization which is not accessible in the experiment. It is shown that the
magnetization is influenced mostly by the particle size and thickness rather
than by the details of its shape. Hence, these hexagonal samples can be
regarded as model systems for the study of the magnetization in thick,
mesoscopic ferromagnets.Comment: 12 pages, 11 figure
Energy-resolved electron-spin dynamics at surfaces of p-doped GaAs
Electron-spin relaxation at different surfaces of p-doped GaAs is
investigated by means of spin, time and energy resolved 2-photon photoemission.
These results are contrasted with bulk results obtained by time-resolved
Faraday rotation measurements as well as calculations of the Bir-Aronov-Pikus
spin-flip mechanism. Due to the reduced hole density in the band bending region
at the (100) surface the spin-relaxation time increases over two orders of
magnitude towards lower energies. At the flat-band (011) surface a constant
spin relaxation time in agreement with our measurements and calculations for
bulk GaAs is obtained.Comment: 6 pages, 4 figure
The BFKL Pomeron in 2+1 Dimensional QCD
We investigate the high-energy scattering in the spontaneously broken Yang -
Mills gauge theory in 2+1 space--time dimensions and present the exact solution
of the leading BFKL equation. The solution is constructed in terms of
special functions using the earlier results of two of us (L.N.L. and L.S.). The
analytic properties of the -channel partial wave as functions of the angular
momentum and momentum transfer have been studied. We find in the angular
momentum plane: (i) a Regge pole whose trajectory has an intercept larger than
1 and (ii) a fixed cut with the rightmost singularity located at . The
massive Yang - Mills theory can be considered as a theoretical model for the
(non-perturbative) Pomeron. We study the main structure and property of the
solution including the Pomeron trajectory at momentum transfer different from
zero. The relation to the results of M. Li and C-I. Tan for the massless case
is discussed.Comment: 28 pages LATEX, 3 EPS figures include
Heavy quark production as sensitive test for an improved description of high energy hadron collisions
QCD dynamics at small quark and gluon momentum fractions or large total
energy, which plays a major role for HERA, the Tevatron, RHIC and LHC physics,
is still poorly understood. For one of the simplest processes, namely
bottom-antibottom production, next-to-leading-order perturbation theory fails.
We show that the combination of two recently developed theoretical concepts,
the k_perp-factorization and the next-to-leading-logarithmic-approximation BFKL
vertex, gives perfect agreement with data. One can therefore hope that these
concepts provide a valuable foundation for the description of other high energy
processes.Comment: RevTeX, 4 pages, 7 figures titel and abstract changed, several
formulations modified in the text, 1 figure droppe
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