86 research outputs found
The Method of Lines in the time domain
The Method of Lines (MoL) is a semi-analytical numerical algorithm that has been
used in the past to solve Maxwell's equations for waveguide problems. It is
mainly used in the frequency domain. In this paper it is shown how the MoL can
be used to solve initial value problems in the time domain. The required
expressions are derived for one-dimensional structures, where the materials
may be dispersive. The algorithm is verified with numerical results
for homogeneous structures, and for the concatenation of standard dielectric
and left handed materials
Self-imaging effect in multimode waveguides with longitudinal periodicity
This paper deals with the self--imaging effect in multimode waveguides. Analogies and differences to the free--space case are shown. The fields in multimode waveguides are studied. Particularly, the behavior of the fields is examined, when aperiodic perturbation is introduced
Hollow waveguides as polarization converting elements: a theoretical study
Subwavelength apertures in a metallic film act as hollow waveguides. By using a non-quadratic cross-section, an anisotropic transmission behaviour results for the two polarization states. Thus, an array of metallic subwavelength apertures may be used as polarization converter, e.g., as a half-wave plate. By varying orientation and shape of the cross-sections locally, one can design polarization shifting elements for complex wave fields. Here, we present a theoretical consideration on the physical properties and compare with dielectric form birefringence
Transcriptome profiling of ontogeny in the acridid grasshopper Chorthippus biguttulus
Acridid grasshoppers (Orthoptera:Acrididae) are widely used model organisms
for developmental, evolutionary, and neurobiological research. Although there
has been recent influx of orthopteran transcriptomic resources, many use
pooled ontogenetic stages obscuring information about changes in gene
expression during development. Here we developed a de novo transcriptome
spanning 7 stages in the life cycle of the acridid grasshopper Chorthippus
biguttulus. Samples from different stages encompassing embryonic development
through adults were used for transcriptomic profiling, revealing patterns of
differential gene expression that highlight processes in the different life
stages. These patterns were validated with semi-quantitative RT-PCR. Embryonic
development showed a strongly differentiated expression pattern compared to
all of the other stages and genes upregulated in this stage were involved in
signaling, cellular differentiation, and organ development. Our study is one
of the first to examine gene expression during post-embryonic development in a
hemimetabolous insect and we found that only the fourth and fifth instars had
clusters of genes upregulated during these stages. These genes are involved in
various processes ranging from synthesis of biogenic amines to chitin binding.
These observations indicate that post-embryonic ontogeny is not a continuous
process and that some instars are differentiated. Finally, genes upregulated
in the imago were generally involved in aging and immunity. Our study
highlights the importance of looking at ontogeny as a whole and indicates
promising directions for future research in orthopteran development
Fusões e aquisições de empresas brasileiras: criação de valor e sinergias operacionais
Efficient determination of the left-eigenvectors for the Method of Lines
The efficient determination of left eigenvectors
in the method of lines (MoL) is described in this paper.
The electromagnetic fields are expanded into eigenmodes
and the eigenmodes are determined from an explicit matrix
eigenvector problem. To study complicated structures with a moderate
numerical effort, the analysis is done with a reduced set of these eigenmodes.
The enforcements of the continuity of the transverse electric and magnetic
fields at interfaces leads to expressions with rectangular matrices.
Now left eigenvectors can be considered as inverse of these rectangular
matrices. Until now, the left eigenvectors
were determined from a second explicit eigenvalue problem. Here, it is shown how
they can be determined with simple matrix products from previously determined
right eigenvectors. This is done by utilizing
the relation between the transverse electric and magnetic fields.
The derived formulas hold for structures with Dirichlet, Neumann
or periodic boundary conditions and the materials may be lossy.
Open structures are modeled with perfectly matched layers (PML).
To verify the expressions, various devices that contain such PMLs and
lossy metals were studied. In all cases, error measures show that
the algorithm derived in this paper works very well
Mastery Profiling through Entity Linking: to Support Project Team Formation in Higher Education
Computer-supported group formation enables educators to assign students to project teams. The focus in this paper is placed on gathering data about student attributes that are relevant in the context of specific course projects. We developed a method that automatically produces learner models from existing documents, by linking students to topics and estimating the levels of skill, knowledge, and interest that students have in these topics. The method is evaluated in an experiment with student participants, wherein its performance is measured on two levels. Our results demonstrate that it is possible to link students to topics with high precision, but suggest that estimating mastery levels is a more challenging task
Designing physics game to support inquiry learning and to promote retrieval practice
Instruction in physics aims at achieving two goals: the acquisition of body of knowledge and problem solving skills in physics. This requires students to connect physical phenomena, physics principles, and physics sym-bols. Computer simulation provides students with graphical model that unites phenomenon and principles in physics. However, such minimally guided approach may harm learning since it overburdens the working mem-ory. Also, simulation is inadequate in promoting problem solving skills since students need to exercise with a variety of physics problems. Intelligent tutoring systems (ITS), in contrast, train students in solving physics problems. In this paper, we designed an online puzzle game in physics that combines simulation and pseudo-tutor (namely QTut). We addressed three challenges: extensibility, scalability, and reusability in designing our game. We conducted usability tests with 10 participants on the game prototype to study the user performances and perceptions for improvement. The results indicate the game as educative and moderately entertaining. The use of scaffolding in the game positively contributed to the game learning experience. Moreover, the game GUI expressed information well that made the game understandable, even with little instructions
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