245 research outputs found
Influence of Electromechanical Effects and Wetting Layers on Band Structures of AIN/GaN Quantum Dots and Spin Control
In a series of recent papers we demonstrated that coupled electromechanical effects can lead to pronounced contributions in band structure calculations of low dimensional semiconductor nanostructures LDSNs such as quantum dots QDs , wires, and even wells. Some such effects are essentially nonlinear. Both strain and piezoelectric effects have been used as tuning parameters for the optical response of LDSNs in photonics, band gap engineering, and other applications. However, the influence of spin orbit effects in presence of external magnetic field on single and vertically coupled QD has been largely neglected in the literature. The electron spin splitting terms which are coupled to the magnetic field through the Pauli spin matrix in these QDs become important in the design of optoelectronic devices as well as in tailoring properties of QDs in other applications areas. At the same time, single and vertically stacked QDs are coupled with electromagnetic and mechanical fields which become increasingly important in many applications of LDSN-based systems, in particular, where spin splitting energy is important. These externally applied electric and magnetic fields as well as the separation between the vertically coupled QDs can be used as tuning parameters. Indeed, as electromagnetic and elastic effects are often significant in LDSNs, it is reasonable to expect that the externally applied magnetic fields oriented along a direction perpendicular to the plane of two-dimensional electron gas in the QDs may also be used as a tuning parameter in the application of light emitting diodes, logic devices, for example, OR gates, AND gates and others. In this paper, by using the fully coupled model of electroelasticity, we analyze the influence of these effects on optoelectronic properties of QDs. Results are reported for III–V type semiconductors with a major focus given to AlN/GaN based QD systems
Index to NASA Tech Briefs, 1974
The following information was given for 1974: (1) abstracts of reports dealing with new technology derived from the research and development activities of NASA or the U.S. Atomic Energy Commission, arranged by subjects: electronics/electrical, electronics/electrical systems, physical sciences, materials/chemistry, life sciences, mechanics, machines, equipment and tools, fabrication technology, and computer programs, (2) indexes for the above documents: subject, personal author, originating center
Digital Model of a Generic Infrared Tracker
Personal computer based simulations are popular because of the wide availability of personal computers. In this thesis, a simple simulation model of a generic infrared tracker is developed for the personal computer. This thesis first centers on the definition of a generic infrared tracker and the development of a tracker model. The remainder of this thesis is a description of the personal computer based computer simulation model, and a discussion of results of simulation runs to characterize the tracker model response. The conclusion of this thesis is that the simple simulation model serves both as a prototype for developing a simulation model of a real tracker, and as a simple introduction to infrared trackers
Influence of electromechanical effects and wetting layers on band structures of AlN/GaN quantum dots and spin control
In a series of recent papers we demonstrated that coupled electromechanical effects can lead to pronounced contributions in band structure calculations of low dimensional semiconductor nanostructures (LDSNs) such as quantum dots (QDs), wires, and even wells. Some such effects are essentially nonlinear. Both strain and piezoelectric effects have been used as tuning parameters for the optical response of LDSNs in photonics, band gap engineering, and other applications. However, the influence of spin orbit effects in presence of external magnetic field on single and vertically coupled QD has been largely neglected in the literature. The electron spin splitting terms which are coupled to the magnetic field through the Pauli spin matrix in these QDs become important in the design of optoelectronic devices as well as in tailoring properties of QDs in other applications areas. At the same time, single and vertically stacked QDs are coupled with electromagnetic and mechanical fields which become increasingly important in many applications of LDSN-based systems, in particular, where spin splitting energy is important. These externally applied electric and magnetic fields as well as the separation between the vertically coupled QDs can be used as tuning parameters. Indeed, as electromagnetic and elastic effects are often significant in LDSNs, it is reasonable to expect that the externally applied magnetic fields oriented along a direction perpendicular to the plane of two-dimensional electron gas in the QDs may also be used as a tuning parameter in the application of light emitting diodes, logic devices, for example, OR gates, AND gates and others. In this paper, by using the fully coupled model of electroelasticity, we analyze the influence of these effects on optoelectronic properties of QDs. Results are reported for III-V type semiconductors with a major focus given to AlN/GaN based QD systems
Efficiently Solving High-Order and Nonlinear ODEs with Rational Fraction Polynomial: the Ratio Net
Recent advances in solving ordinary differential equations (ODEs) with neural
networks have been remarkable. Neural networks excel at serving as trial
functions and approximating solutions within functional spaces, aided by
gradient backpropagation algorithms. However, challenges remain in solving
complex ODEs, including high-order and nonlinear cases, emphasizing the need
for improved efficiency and effectiveness. Traditional methods have typically
relied on established knowledge integration to improve problem-solving
efficiency. In contrast, this study takes a different approach by introducing a
new neural network architecture for constructing trial functions, known as
ratio net. This architecture draws inspiration from rational fraction
polynomial approximation functions, specifically the Pade approximant. Through
empirical trials, it demonstrated that the proposed method exhibits higher
efficiency compared to existing approaches, including polynomial-based and
multilayer perceptron (MLP) neural network-based methods. The ratio net holds
promise for advancing the efficiency and effectiveness of solving differential
equations
Evolution of truncated moments of singlet parton distributions
We define truncated Mellin moments of parton distributions by restricting the
integration range over the Bjorken variable to the experimentally accessible
subset x_0 < x < 1 of the allowed kinematic range 0 < x < 1. We derive the
evolution equations satisfied by truncated moments in the general (singlet)
case in terms of an infinite triangular matrix of anomalous dimensions which
couple each truncated moment to all higher moments with orders differing by
integers. We show that the evolution of any moment can be determined to
arbitrarily good accuracy by truncating the system of coupled moments to a
sufficiently large but finite size, and show how the equations can be solved in
a way suitable for numerical applications. We discuss in detail the accuracy of
the method in view of applications to precision phenomenology.Comment: 23 pages, 6 figures, LaTeX; factors of 2nf in Appendix C correcte
Index to NASA Tech Briefs, 1975
This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs
SOM-based algorithms for qualitative variables
It is well known that the SOM algorithm achieves a clustering of data which
can be interpreted as an extension of Principal Component Analysis, because of
its topology-preserving property. But the SOM algorithm can only process
real-valued data. In previous papers, we have proposed several methods based on
the SOM algorithm to analyze categorical data, which is the case in survey
data. In this paper, we present these methods in a unified manner. The first
one (Kohonen Multiple Correspondence Analysis, KMCA) deals only with the
modalities, while the two others (Kohonen Multiple Correspondence Analysis with
individuals, KMCA\_ind, Kohonen algorithm on DISJonctive table, KDISJ) can take
into account the individuals, and the modalities simultaneously.Comment: Special Issue apr\`{e}s WSOM 03 \`{a} Kitakiush
NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 08)
This bibliography is issued in two sections: Section 1 - Abstracts, and Section 2 - Indexes. This issue of the Abstract Section cites 180 patents and applications for patents introduced into the NASA scientific and technical information system during the period July 1975 through December 1975. Each entry in the Abstract Section consists of a citation, an abstract, and, in most cases, a key illustration selected from the patent or application for patent. This issue of the Index Section contains entries for 2,905 patents and applications for patent citations covering the period May 1969 through December 1975. The Index Section contains five indexes -- subject, inventor, source, number, and accession number
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