Solution of Linear Programming Problems using a Neural Network with Non-Linear Feedback

This paper presents a recurrent neural circuit for solving linear programming problems. The objective is to minimize a linear cost function subject to linear constraints. The proposed circuit employs non-linear feedback, in the form of unipolar comparators, to introduce transcendental terms in the energy function ensuring fast convergence to the solution. The proof of validity of the energy function is also provided. The hardware complexity of the proposed circuit compares favorably with other proposed circuits for the same task. PSPICE simulation results are presented for a chosen optimization problem and are found to agree with the algebraic solution. Hardware test results for a 2–variable problem further serve to strengthen the proposed theory

A study of the Haor areas of Sylhet-Mymensing districts with ERTS imageries (winter crop estimation)

There are no author-identified significant results in this report

Monthly and Diurnal Variability of Rain Rate and Rain Attenuation during the Monsoon Period in Malaysia

Rain is the major source of attenuation for microwave propagation above 10 GHz. In tropical and equatorial regions where the rain intensity is higher, designing a terrestrial and earth-to-satellite microwave links is very critical and challenging at these frequencies. This paper presents the preliminary results of rain effects in a 23 GHz terrestrial point-to-point communication link 1.3km long. The experimental test bed had been set up at Skudai, Johor Bahru, Malaysia. In this area, a monsoon equatorial climate prevails and the rainfall rate can reach values well above 100mm/h with significant monthly and diurnal variability. Hence, it is necessary to implement a mitigation technique for maintaining an adequate radio link performance for the action of very heavy rain. Since we now know that the ULPC (Up Link Power Control) cannot guarantee the desired performance, a solution based on frequency band diversity is proposed in this paper. Here, a secondary radio link operating in a frequency not affected by rain (C band for instance) is placed parallel with the main link. Under no rain or light rain conditions, the secondary link carries without priority radio signals. When there is an outage of the main link due to rain, the secondary link assumes the priority traffic. The outcome of the research shows a solution for higher operating frequencies during rainy events

The Swap Matching Problem Revisited

In this paper, we revisit the much studied problem of Pattern Matching with Swaps (Swap Matching problem, for short). We first present a graph-theoretic model, which opens a new and so far unexplored avenue to solve the problem. Then, using the model, we devise two efficient algorithms to solve the swap matching problem. The resulting algorithms are adaptations of the classic shift-and algorithm. For patterns having length similar to the word-size of the target machine, both the algorithms run in linear time considering a fixed alphabet.Comment: 23 pages, 3 Figures and 17 Table

Pulse-induced acoustoelectric vibrations in surface-gated GaAs-based quantum devices

We present the results of a numerical investigation which show the excitation of acoustoelectric modes of vibration in GaAs-based heterostructures due to sharp nano-second electric-field pulses applied across surface gates. In particular, we show that the pulses applied in quantum information processing applications are capable of exciting acoustoelectric modes of vibration including surface acoustic modes which propagate for distances greater than conventional device dimensions. We show that the pulse-induced acoustoelectric vibrations are capable of inducing significant undesired perturbations to the evolution of quantum systems.Comment: To be published in Phys. Rev.

Antimicrobial Diterpenes: Recent Development From Natural Sources

Antimicrobial resistance has been posing an alarming threat to the treatment of infectious diseases over the years. Ineffectiveness of the currently available synthetic and semisynthetic antibiotics has led the researchers to discover new molecules with potent antimicrobial activities. To overcome the emerging antimicrobial resistance, new antimicrobial compounds from natural sources might be appropriate. Secondary metabolites from natural sources could be prospective candidates in the development of new antimicrobial agents with high efficacy and less side effects. Among the natural secondary metabolites, diterpenoids are of crucial importance because of their broad spectrum of antimicrobial activity, which has put it in the center of research interest in recent years. The present work is aimed at reviewing recent literature regarding different classes of natural diterpenes and diterpenoids with significant antibacterial, antifungal, antiviral, and antiprotozoal activities along with their reported structure–activity relationships. This review has been carried out with a focus on relevant literature published in the last 5 years following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 229 diterpenoids from various sources like plants, marine species, and fungi are summarized in this systematic review, including their chemical structures, classification, and significant antimicrobial activities together with their reported mechanism of action and structure–activity relationships. The outcomes herein would provide researchers with new insights to find new credible leads and to work on their synthetic and semisynthetic derivatives to develop new antimicrobial agents

Implications of a Quantum Mechanical Treatment of the Universe

We attempt to treat the very early Universe according to quantum mechanics. Identifying the scale factor of the Universe with the width of the wave packet associated with it, we show that there cannot be an initial singularity and that the Universe expands. Invoking the correspondence principle, we obtain the scale factor of the Universe and demonstrate that the causality problem of the standard model is solved.Comment: LaTex, 5 pages, 1 figure, to be published in Mod. Phys. Lett.

Tailoring light-sound interactions in a single mode fiber for the high-power transmission or sensing applications

A full-vectorial numerically efficient Finite Element Method (FEM) based computer code is developed to study complex light-sound interactions in a single mode fiber (SMF). The SBS gain or SBS threshold in a fiber is highly related to the overlap between the optical and acoustic modes. For a typical SMF the acoustic-optic overlap strongly depends on the optical and acoustic mode profiles and it is observed that the acoustic mode is more confined in the core than the optical mode and reported overlap is around 94 % between these fundamental optical and acoustic modes. However, it is shown here that selective co-doping of Aluminum and Germanium in core reduces the acoustic index while keeping the optical index of the same value and thus results in increased acoustic- optic overlap of 99.7%. On the other hand, a design of acoustic anti-guide fiber for high-power transmission systems is also proposed, where the overlap between acoustic and optical modes is reduced. Here, we show that by keeping the optical properties same as a standard SMF and introducing a Boron doped 2ndlayer in the cladding, a very low value of 2.7% overlap is achieved. Boron doping in cladding 2ndlayer results in a high acoustic index and acoustic modes shifts in the cladding from the core, allowing much high power delivery through this SMF

Characterization and Modeling of Asphalt Concrete for Dynamic Properties and Performances

The recently developed mechanistic-empirical pavement design guide (MEPDG, also known as Pavement M-E design method) uses the nationally calibrated, binder viscosity-based dynamic modulus predictive model for the design and analysis of asphalt pavements. In this study, this model is assessed for its appropriateness for asphalt-aggregate mixtures typically used in New Mexico. In essence, this study investigates the predictability issue of complex modulus of New Mexico mixes. A total of 54 Superpave mixes with different aggregate gradations, air voids, and binder grades were collected from the mixing plants and from the pavement construction sites. The loose asphalt mixtures were then compacted, cored, and sawed to cylindrical specimens and tested for dynamic modulus and phase angle in the laboratory. Independence assurance testing was performed to assess the precision and accuracy of the test results. The time-temperature superposition principle was applied to develop mastercurves of complex modulus and phase angle functions of the asphalt concrete samples. The evaluated complex modulus mastercurve parameters were then used to calibrate the viscosity-based Witczak model for predicting dynamic or complex modulus of local asphalt concrete materials. The assessment of this model indicated significant underprediction and bias of the model in its current form for predicting complex modulus of the Superpave asphalt-aggregate mixes of New Mexico. To this end, a new set of regression-based models for predicting dynamic modulus and phase angle functions of local asphalt mixtures were developed and validated in this study. Material properties such as mix volumetrics, aggregate gradations, and asphalt binder characteristics are the main factors that affect the viscoelastic material functions, such as the complex modulus of asphalt concrete. A goal is to examine the effects of these mixture variables on the complex modulus of asphalt concrete and thus modify existing predictive models or develop a new model to predict the complex modulus of asphalt concrete more accurately. With the aim at hand, the effects of aggregate gradation parameters on the complex modulus function of asphalt concrete were determined. To characterize various aggregate gradations, the two well-known gradation parameters of the aggregate blend, namely, the fineness modulus and the uniformity coefficient, were considered. Next, the effects of these two parameters on the complex modulus and phase angle functions were determined, and used in developing new predictive models. Statistical evaluation showed that fairly accurate estimations of dynamic modulus and phase angle of the local mixes can be possible by using these new predictive models. While the above models use binder’s viscosity, a new set of models were developed using binder’s shear modulus. Indeed, M-E design has a binder shear modulus based dynamic modulus model. Various researcher claimed that the binder shear modulus based model is more biased and inaccurate when compared to the tested data or the predicted data from viscosity based model. The new binder shear modulus based model also uses gradation parameters and mixture volumetrics. To develop this model, asphalt binders were tested for complex shear modulus and phase angle using dynamic shear rheometer. Dynamic shear modulus and phase angle functions were generated by applying time-temperature superposition principle. Non-linear optimization technique was used to correlate the model parameters to the material properties to develop the final form of the model. Statistical evaluation showed good accuracy of the predictions made by these models. Apart from the regression-based modeling and to improve the accuracy of the characterization problem, an advanced dynamic modulus and phase angle predictive model is developed in this study based on the artificial neural network methodology. A database containing 1,620 dynamic moduli with phase angle were used to develop this artificial neural network. A neural architecture with two hidden layers, each with 12 nodes was found to be suitable for predicting the dynamic modulus and phase angle of asphalt concrete. Statistical evaluation showed an excellent prediction ability of this model. It is known that viscoelastic time-domain material functions, such as, relaxation modulus and creep compliance, or frequency domain function, such as, complex modulus can be used to characterize the linear viscoelastic behavior of asphalt concrete in modeling of pavement structure. Among these, the complex modulus has been adopted in the recent pavement M-E design method. However, for advanced analysis of pavement, such as, use of finite element method requires that the complex modulus function to be converted into relaxation modulus or creep compliance functions. There are a number of exact or approximate methods available in the literature to convert one linear viscoelastic material function to another. All these methods (i.e. exact or approximate methods) are applicable for any linear viscoelastic material up to a certain level of accuracy. However, the applicability and accuracy of these interconversion methods for asphalt concrete material were not studied very much in the past. Thus, a question arises if these methods are even applicable in case of asphalt concrete, and if so, what is the precision level of the interconversion method being used. To investigate these facts, this study has undertaken an effort to validate a numerical interconversion technique by conducting representative laboratory tests. The method was previously used in asphalt industry with adopting a simplification of considering time constants to be identical in generalized Maxwell and generalized Voigt model. However, in the present context, the assumption is regarded as over-simplification and therefore, an exact approach to estimate the time constants in these two mechanical models is developed. For validation, cylindrical asphalt concrete specimens were tested for complex modulus, relaxation modulus, and creep compliance at different test temperatures and loading rates. The time-temperature superposition principle was applied to develop linear viscoelastic material functions. The numerical interconversion technique was used to convert one material function to another, and hence, were compared to the laboratory tested material functions. The conversion showed good agreement with the laboratory test data. A statistical evaluation was conducted to determine if the interconverted material functions are similar to the laboratory tested material functions. Besides finite element modeling technique was also used to validate the interconversion method