Stable localized modes in asymmetric waveguides with gain and loss

It is shown that asymmetric waveguides with gain and loss can support a stable propagation of optical beams. This means that the propagation constants of modes of the corresponding complex optical potential are real. A class of such waveguides is found from a relation between two spectral problems. A particular example of an asymmetric waveguide, described by the hyperbolic functions, is analyzed. The existence and stability of linear modes and of continuous families of nonlinear modes are demonstrated.Comment: 10 pages, 4 figures. Accepted in Optics Letters, 201

Relative Contributions of Internal and External Features to Face Recognition

The central challenge in face recognition lies in understanding the role different facial features play in our judgments of identity. Notable in this regard are the relative contributions of the internal (eyes, nose and mouth) and external (hair and jaw-line) features. Past studies that have investigated this issue have typically used high-resolution images or good-quality line drawings as facial stimuli. The results obtained are therefore most relevant for understanding the identification of faces at close range. However, given that real-world viewing conditions are rarely optimal, it is also important to know how image degradations, such as loss of resolution caused by large viewing distances, influence our ability to use internal and external features. Here, we report experiments designed to address this issue. Our data characterize how the relative contributions of internal and external features change as a function of image resolution. While we replicated results of previous studies that have shown internal features of familiar faces to be more useful for recognition than external features at high resolution, we found that the two feature sets reverse in importance as resolution decreases. These results suggest that the visual system uses a highly non-linear cue-fusion strategy in combining internal and external features along the dimension of image resolution and that the configural cues that relate the two feature sets play an important role in judgments of facial identity

Evaluation of Spam Impact on Arabic Websites Popularity

The expansion of the Web and its information in all aspects of life raises the concern of how to trust information published on the Web especially in cases where publisher may not be known. Websites strive to be more popular and make themselves visible to search engines and eventually to users. Website popularity can be measured using several metrics such as the Web traffic (e.g. Website: visitors\u27 number and visited page number). A link or page popularity refers to the total number of hyperlinks referring to a certain Web page. In this study, several top ranked Arabic Websites are selected for evaluating possible Web spam behavior. Websites use spam techniques to boost their ranks within Search Engine Results Page (SERP). Results of this study showed that some of these popular Websites are using techniques that are considered spam techniques according to Search Engine Optimization guidelines

Software Testing Techniques and Tools: A Review

The software development process is closely related to the creation and evaluation processes. The problem with this software development is that it often lacks testing which leads to software failures. In order To maintain a high quality product in excellent performance condition, testing becomes critical. The software can be tested by using White Box, Black-Box, or Gray testing techniques. In this investigation, the types of tests were reviewed. Performing Testing with White Box Testing uses a number of testing methodologies based on path testing, including the production of flowcharts, cyclomatic complexity assessment, and independent path testing. As a result, it is possible to implement a foundation path testing technique and white box approach to testing. This review included several axes, namely the definition of white box testing tools, then the testing techniques in general, the benefits and gains of each of these technologies, the levels of testing, and finally the steps of conducting the test. This review then came to several conclusions that are mentioned at the end of this paper

Enhancement of permeability estimation by high order polynomial regression for capillary pressure curve correlation with water saturation

Suggesting a cost-effective and straightforward approach is indispensable for obtaining permeability estimates in carbonate reservoirs utilizing available well logs. In this study, several procedures were conducted to reach an optimum approach, primarily by constructing a correlation between capillary pressure and water saturation using core data plotted and utilized a good polynomial regression to obtain a better relationship, which leads to calculating the permeability. The second step is to use different theoretical models which Tixier introduces, Timur, Coats, and Dumanior, which resulted not good matching with the permeability from core analysis and modified Brown and Husseini correlation which used and gave better matching than others correlations by comparing the results with the calculated permeability depending on core data. The proposed approach in this study based on modified Husseini equation using the well logs data by applying Statistical regression techniques within capillary pressure prediction to enhance reservoir characterization can potentially advantage reservoir simulation efforts. Obtained results of permeability prediction based on capillary pressure correlation was examined for a certain well and compared with the measured permeability value of cores. There was a good matching between the predicted and measured permeability

A Novel Root Based Arabic Stemmer

Stemming algorithms are used in information retrieval systems, indexers, text mining, text classifiers etc., to extract stems or roots of different words, so that words derived from the same stem or root are grouped together. Many stemming algorithms were built in different natural languages. Khoja stemmer is one of the known and widely used Arabic stemmers. In this paper, we introduced a new light and heavy Arabic stemmer. This new stemmer is presented in this study and compared with two well-known Arabic stemmers. Results showed that accuracy of our stemmer is slightly better than the accuracy yielded by each one of those two well-known Arabic stemmers used for evaluation and comparison. Evaluation tests on our novel stemmer yield 75.03% accuracy, while the other two Arabic stemmers yield slightly lower accuracy

MECHANICAL DEGRADATION OF HIGH MOLECULAR WEIGHT POLYMER WITH SURFACTANT ADDITION IN A ROTATING DISK APPARATUS

Mechanical degradation hampers the practical usage of polymers for turbulent drag reduction application. Mechanical degradation refers to the chemical process in which the activation energy of polymer chain scission is exceeded by mechanical action on the polymer chain, and bond rupture occurs. When a water-soluble polymer and surfactant are mixed in water solution, the specific structures (aggregates) are formed, in which polymer film is formed around micelle. In this work, Xanthan gum (XG) – Sodium lauryl ether sulfate (SELS) complex formation and its effect on percentage viscosity reduction (%VR) was studied. It was found that SELS surfactant reduced the mechanical degradation of XG much more efficiently than this polymer alone. Xanthan Gum (XG) has been tested for its shear stability and degradability. 0.5% and 1.0 % by weight concentration solutions were exposed to shear stirring at different speeds and time; also 0.5% through 1.5% by weight concentration solutions of SELS were added to XG solutions to determine the ability of SELS to reduce the mechanical degradation of XG. It has been noticed by measuring the percentage viscosity reduction (%VR) of the mixture of XG-SELS that the % VR decreases when added this surfactant to XG polyme

Blackbox Modelling Of a 6 Rotor Helicopter

Aerial robotics have received a considerable interest in both private builders and research laboratories for several years. In this respect, modeling is needed in the first step of developing aerial robotics or multi-rotor UAV and there are various methods that can be used for modeling. In this paper, the authors discussed and compared two types of blackbox modeling method that is the Continuous State Space using PEM method and the commonly used Second Order Underdamped System with Delay process model. Based on a comparison analysis of the two methods drawn from experimental data, it was found that the Second Order Underdamped System with Delay Modeling gives better similarity for a hexarotor pitch angle model. In contrast, the Continuous State Space model using PEM method in Polynomial gives better similarity to the hexarotor roll angle model. Finally, both tested methods deliver similar similarity for hexarotor yaw angle model