On the Parameterized Complexity of Layered Graph Drawing

We consider graph drawings in which vertices are assigned to layers and edges are drawn as straight line-segments between vertices on adjacent layers. We prove that graphs admitting crossing-free h-layer drawings (for fixed h) have bounded pathwidth. We then use a path decomposition as the basis for a linear-time algorithm to decide if a graph has a crossing-free h-layer drawing (for fixed h). This algorithm is extended to solve related problems, including allowing at most k crossings, or removing at most r edges to leave a crossing-free drawing (for fixed k or r). If the number of crossings or deleted edges is a non-fixed parameter then these problems are NP-complete. For each setting, we can also permit downward drawings of directed graphs and drawings in which edges may span multiple layers, in which case either the total span or the maximum span of edges can be minimized. In contrast to the Sugiyama method for layered graph drawing, our algorithms do not assume a preassignment of the vertices to layers. Research initiated at the International Workshop on Fixed Parameter Tractability in Graph Drawing, Bellairs Research Institute of McGill University, Holetown, Barbados, Feb. 9–16, 2001, organized by S. Whitesides. Research of Canada-based authors is supported by NSERC; research of Quebec-based authors is also supported by a grant from FCAR. Research of D.R. Wood completed while visiting McGill University. Research of G. Liotta supported by CNR and MURST.     

The Antibiotic Doxycycline Impairs Cardiac Mitochondrial and Contractile Function

Tetracycline antibiotics act by inhibiting bacterial protein translation. Given the bacterial ancestry of mitochondria, we tested the hypothesis that doxycycline—which belongs to the tetracycline class—reduces mitochondrial function, and results in cardiac contractile dysfunction in cultured H9C2 cardiomyoblasts, adult rat cardiomyocytes, in Drosophila and in mice. Ampicillin and carbenicillin were used as control antibiotics since these do not interfere with mitochondrial translation. In line with its specific inhibitory effect on mitochondrial translation, doxycycline caused a mitonuclear protein imbalance in doxycycline-treated H9C2 cells, reduced maximal mitochondrial respiration, particularly with complex I substrates, and mitochondria appeared fragmented. Flux measurements using stable isotope tracers showed a shift away from OXPHOS towards glycolysis after doxycycline exposure. Cardiac contractility measurements in adult cardiomyocytes and Drosophila melanogaster hearts showed an increased diastolic calcium concentration, and a higher arrhythmicity index. Systolic and diastolic dysfunction were observed after exposure to doxycycline. Mice treated with doxycycline showed mitochondrial complex I dysfunction, reduced OXPHOS capacity and impaired diastolic function. Doxycycline exacerbated diastolic dysfunction and reduced ejection fraction in a diabetes mouse model vulnerable for metabolic derangements. We therefore conclude that doxycycline impairs mitochondrial function and causes cardiac dysfunction.     

An Impulse System for 60-GHz Wireless Networks Based on Polymer Optical Fiber

A specific impulse optical fiber system has been achieved to enhance the connectivity of 60-GHz wireless networks. Using an impulse technology, this original configuration is an efficient alternative to the conventional 60-GHz radio-over-fiber systems. Baseband subnanosecond pulses first modulate the amplitude of a 60-GHz radio-frequency carrier and second the intensity of a distributed feedback laser operating at 1300 nm. Properties of the multimode plastic optical fiber based on a perfluorinated material are exploited to transmit such signals. The overall system performance has been tested experimentally in a multihop configuration; bit-error-rate measurements are better than for transmission data rates up to 200 Mb/s.     

Constructing the Lyee method with a method engineering approach

This paper proposes an Evolution driven ME approach aiming to support the evolution of an existing method (the As–Is method) in order to obtain a new method (the To–Be method) better adapted to a given engineering situation and/or satisfying new methodogical requirements. The proposed approach is used in order to evolve the existing Lyee method into a Lyee user driven method.¹     

Fast algorithm for 3-D vascular tree modeling

In this short paper, accelerated three-dimensional computer simulations of vascular trees development, preserving physiological and haemodynamic features, are reported. The new computation schemes deal: (i). with the geometrical optimization of each newly created bifurcation; and (ii). with the recalculation of blood pressures and radii of vessels in the whole tree. A significant decrease of the computation time is obtained by replacing the global optimization by the fast updating algorithm allowing more complex structure to be simulated. A comparison between the new algorithms and the previous one is illustrated through the hepatic arterial tree.     

Design and assessment of microlenslet-array relay optics

Recent progress in micro-optics fabrication and optical modeling software opens the opportunity to investigate how microlenslet-array-based compact relay systems can be designed and assessed. We present various optical configurations that include an appropriate baffle computation to eliminate ghost images, followed by an analysis of image quality. The investigation shows the existing trade-off between compactness of the system and a tiling effect observed in the corresponding image, an effect we refer to as lensletization. To yield meaningful optical modeling results, we provide insight into ray-tracing optimization while ensuring a sufficient signal-to-noise ratio. The results show that, given no discernable lensletization, the most compact configuration to image gray-scale images is the 5f-based system. Finally, simulations of the imaging of gray scale and color bitmaps through microlenslet arrays are demonstrated for the first time to our knowledge.     

Design of an ultralight and compact projection lens

Driven by the need for lightweight head-mounted displays, we present the design of an ultralight and compact projection lens for a head-mounted projective display (HMPD). An HMPD consists of a pair of miniature projection lenses, beam splitters, and miniature displays mounted on the helmet and retroreflective sheeting materials placed strategically in the environment. The HMPD has been proposed recently as an alternative modality for three-dimensional visualization. After demonstrating the concept, building a first-generation custom-designed prototype, and investigating perception issues and application potentials, we designed an ultralight and compact projective lens with a diffractive optical element (DOE), plastic components, and aspheric surfaces for the next-generation prototype. The key contribution here lies in the conception, optimization, and assessment of the projection optics. Thus a brief review of the HMPD technology and related research is followed by a detail discussion of the conception and optimization of the ultralight and high-performance projection optics. The design of the DOE will be particularly described in detail. Finally, the diffraction efficiency of the DOE will be evaluated, and the overall performance of the optics will be assessed in both object space for the optical designer and visual space for possible end-users of the technology.     

Task-based optimization and performance assessment in optical coherence imaging

Optimization of an optical coherence imaging (OCI) system on the basis of task performance is a challenging undertaking. We present a mathematical framework based on task performance that uses statistical decision theory for the optimization and assessment of such a system. Specifically, we apply the framework to a relatively simple OCI system combined with a specimen model for a detection task and a resolution task. We consider three theoretical Gaussian sources of coherence lengths of 2, 20, and 40 microm. For each of these coherence lengths we establish a benchmark performance that specifies the smallest change in index of refraction that can be detected by the system. We also quantify the dependence of the resolution performance on the specimen model being imaged.     

Engineering of head-mounted projective displays

Head-mounted projective displays (HMPD's) are a novel type of head-mounted display. A HMPD consists of a miniature projection lens mounted upon the user's head and retroreflective sheeting material placed strategically in the environment. First, the imaging concept of a HMPD is reviewed and its potential advantages and disadvantages are discussed. The design and a bench prototype implementation are then presented. Finally, the effects of retroreflective materials on the imaging properties and the optical properties of HMPD's are comprehensively investigated.     

Evidence of residual edge dislocations in czochralski grown Si crystals in 〈110〉 direction

The published work on the type of residual dislocations in Si crystals grown in 〈110〉 direction by Czochralski method indicate that screw dislocations are difficult to be eliminated as they are known to run parallel to the axis of growth. Our work shows on the contrary that it is edge type dislocations which are rather difficult to be eliminated. Extensive X-ray topographic studies have been made to establish the type of dislocations and their movements. Also our work on the growth of dislocation-free Si crystals in 〈110〉direction and their mechanism of dislocation movements are briefly described.