Rayleigh backscatter effects on 1550-nm CATV distribution systemsemploying optical amplifiers

We analyzed the applicability of externally modulated 1550-nm laser transmitters for trunking and distribution of AM CATV channels using power and in-line EDFA's. The distribution of multiple AM CATV channels over long fiber spans is degraded by the presence of Rayleigh backscatter-induced low-frequency interferometric noise. When the laser source is modulated externally, the low-frequency interferometric noise is mixed and translated around the AM carriers. Furthermore, when isolators are not used with the optical amplifiers, the low end of the broadcast channels could be severely degraded due to doubly amplified Rayleigh backscatter. Employing narrow-linewidth semiconductor or Nd:YAG laser sources at the transmitter will lower the tail of the low-frequency interferometric noise level but will increase the translated noise peak level at each AM carrier. Therefore, the standard CNR measurement techniques, which assumes the noise spectrum is flat, may not reveal the correct video picture quality seen at the customer premises. In this analysis, we compared NCTA RF CNR and baseband video SNR results using CCIR recommended unified weighting filter. We determined that for laser linewidth less than 1 MHz and with long fiber spans, baseband video SNR as opposed to RF CNR measurements should be used to characterize the performance of AM-VSB CATV broadcast distribution systems. Finally, an experimental 78-channel AM-VSB CATV distribution system is constructed employing two EDFA's simulating head-end and hub sites and we compared RF CNR and baseband video SNR measurements using a 700-kHz linewidth externally modulated 1550-nm DFB transmitter     

Catalysis in Polymerization

Hardly a single polymerization process exists in which certain accelerating, regulating, and modifying ingredients are not used with great advantage even though they might be present only in very small quantities. In the early years of the art, when there did not yet exist a well-founded understanding of the mechanism of polymerization processes, the action of these ingredients and additives so much resembled the phenomenon of normal catalysis that the name catalysts was used for them. Today, in the clarifying hindsight of a rather well-developed theory of polymerization reactions, it is evident that in most cases the role of these substances during the formation of macromolecules does not fall in the domain of the classical definitions of the words catalysis and catalyst.     

An investigation and comparison of machine learning approaches for intrusion detection in IoMT network

The Journal of Supercomputing - Internet of Medical Things (IoMT) is network of interconnected medical devices (smart watches, pace makers, prosthetics, glucometer, etc.), software applications,...     

Real‐time density‐based crowd simulation

Virtual characters in games and simulations often need to plan visually convincing paths through a crowded environment. This paper describes how crowd density information can be used to guide a large number of characters through a crowded environment. Crowd density information helps characters avoid congested routes that could lead to traffic jams. It also encourages characters to use a wide variety of routes to reach their destination. Our technique measures the desirability of a route by combining distance information with crowd density information. We start by building a navigation mesh for the walkable regions in a polygonal two‐dimensional (2‐D) or multilayered three‐dimensional (3‐D) environment. The skeleton of this navigation mesh is the medial axis. Each walkable region in the navigation mesh maintains an up‐to‐date density value. This density value is equal to the area occupied by all the characters inside a given region divided by the total area of this region. These density values are mapped onto the medial axis to form a weighted graph. An A^* search on this graph yields a backbone path for each character, and forces are used to guide the characters through the weighted environment. The characters periodically replan their routes as the density values are updated. Our experiments show that we can compute congestion‐avoiding paths for tens of thousands of characters in real‐time. Copyright © 2012 John Wiley & Sons, Ltd.     

Variability in reading ability gains as a function of computer-assisted instruction method of presentation

This study examines the effects on early reading skills of three different methods of presenting material with computer-assisted instruction (CAI): (1) learner-controlled picture menu, which allows the student to choose activities, (2) linear sequencer, which progresses the students through lessons at a pre-specified pace, and (3) mastery-based adaptive sequencer, which progresses students through lessons based on whether or not the student has mastered the given skill. Preschool- and kindergarten-aged children (n = 183) were randomly assigned to one of the three CAI groups and spent 40 min a week, for 13 weeks, using the software program in a computer lab. An additional control group of students attending typical preschool or kindergarten received no CAI. ANCOVA results examining post-test reading ability sum score, covarying pre-test score, indicated that the mastery-based sequencer group significantly outperformed the learner-control and control groups, but was not statistically different from the linear sequence group. Analysis by task, rather than overall reading score, revealed significantly better performance for the linear sequence group over controls and picture menu group on the Initial Sound Fluency task, while the mastery-based sequencer group outperformed all three other groups on Non Word Fluency. In sum, these results suggest that the use of a sequencer is a very important element in presenting computerized reading content for young children.