Mode locked pulse generation has been reported using both active and passive mode locking schemes. Active mode locking technique has been proven to be an effective way to generate high-repetition-rate pulses by incorporating a modulator inside the laser cavity. Compared to actively mode locked lasers, passively mode locked lasers can generate pulse train at ultrashort pulse width but with relatively lower repetition rate. Thus, it is a brilliant idea to build a hybrid mode locked system combining both active and passive mode lockers. In this review, several hybrid mode locked fiber ring laser systems are discussed and summarized. Hybrid mode locking is a promising method to generate high-speed ultrashort optical pulses for fiber-optic telecommunication system.
Recent progress of high-speed all-optical logic gates based on dual semiconductor optical amplifiers (SOAs) has been reviewed in this article. These schemes include using quantum-dot semiconductor optical amplifier (QD-SOA) and two-photon absorption (TPA). Numerical simulation method was presented by solving the rate equations of gain dynamics in the SOA. Performance of all-optical logic operation is discussed by calculating the quality factor and plotting the eye diagram. Results show that the dual SOA scheme is a promising method for the realization of high-speed all-optical logic systems in the future.
Titanium oxide is as ancient in age as our planet but its use for photoanode is more recent. It exists naturally as rutile (the second most abundant), anatase and brookite ores. The anatase several metastable states trigger diverse spectral responses with Magnifera Indica Linn. (M.indica L) dye as it is synthesized with an N719 dye grown on its matrix. Facile doctor blade method and high temperature sintering at 723K were used in fabrication. Doping of titanium oxide in effect lowers the band gap of TiO2 for photo-excitation caused by a bathochromic shift and simultaneously decreases the rate of recombination in photogenerated electron-hole pairs. This study explored the visible light induced photocatalytic action of doped M.indica L DSSC towards reduction of titanium oxide bandgap. The SEM micrographs reveal the molecular interactions and the interplay as electrolytes percolate the intricate N719 dye/Titania framework. Detailed analysis stem from comparison of M.indica L crude faction and the batch separated faction using FTIR spectroscopy. The absorbance peak, rates of reaction and % transmittance identify the particular chromophores responsible for the reaction. Result shows the batch-separated hexane faction approximately 1000 times more efficient than its crude faction although the ff of the crude was only about twice that of the hexane faction. The optical study showed that doping ions lead to an increase in the absorption edge wavelength, and a decrease in the band gap energy of TiO2 nanoparticles. The doped TiO2 nanoparticles in general showed higher photocatalytic activities than the pure ones.
Thermodynamics for ideal plastic deformation causing no disorganization of the structure in the deformed body, which was discussed by P. W. Bridgman studied (1950), revealed that the concept of entropy was still applicable to its irreversible process. Noting that the structural invariability in an ideal plastic body is physically equivalent to the prerequisite of thermodynamics, namely, thermodynamic quantities must be independent of the macroscopic body shape, the generalized concept of entropy can be extended to the other thermodynamic potentials such as internal energy, free energies and so on. Here the extended generalization for ideal plastic deformation is theoretically justified on the basis of the irreversible thermodynamics constructed by Prigogine and his discipline. Thermodynamic state of the ideally deformed body is found to be specified both by the generalized thermodynamic potential (S, U, F, H or G) and by the irreversible potential energy J which drives the plastic deformation.
In this article, authors report experimental results obtained, with different diagnostics setups, for radon activity concentration measurement in underground water for human use. An overview is given about the performance of different measurement techniques, based on experimental data. The following parameters are compared and discussed: counting efficiency, minimum detectable activity, measurement uncertainty, background, sample volume and treatment. The estimated average value for radon-specific activity in underground water was compared with that one derived from different legislations and directives/guidelines and it was used, with the dose conversion factor for Rn-222, to estimate the annual effective dose, for adult members of public of the investigated region, due to the groundwater radon ingestion.
Santhiagu A, India Emmanuel Mawuli Abalo, Ghana Fidelis Abam, Nigeria Akbar Abbasi, Cyprus Haider Abd, Iraq Saleh Abd El-Aleem, Egypt Juman Abdeen, Sri Lanka Shehata Abdel Raheem, Saudi Arabia Abdelhakim Abdelhadi, Saudi Arabia Sbihi Abdelkader, France Oday Abdullah, Germany Dr Rozi Abdullah, Malaysia Basma Abbas Abdulmajeed, Iraq Alessandro Abena, United Kingdom Mohamed Abosaf, United Kingdom Omar Abu Arqub, Jordan Ahmed Abul’Wafa, Egypt Leonardo Acho, Spain Olusola Adesina, Nigeria Olanrewaju Adesusi, Nigeria Philip Adewuyi, Nigeria Michael Kanisuru Adeyeri, Nigeria Behnam Adhami, Islamic Republic Of Iran Hojjatollah Adibi, Islamic Republic Of Iran Daniel Adu, China George Affenzeler, United States Richard Afolabi, Nigeria Neelofar Afzal, India Pradeep Agarwal, India Aaron Agbo, Ghana Olayinka Agboola, Nigeria Stephen Agyeman, Ghana Abdalqader Ahmad, United Kingdom Muhammad Abbas Ahmad Zaini, Malaysia Syed Hassan Ahmed, China Farooq Ahmed, Pakistan Morteza Aieneravaie, Islamic Republic Of Iran Abel Airoboman, Nigeria Abiola Ajayeoba, Nigeria Priya Ak, India Ali Akbari Motlagh, Islamic Republic Of Iran Andac Akdemir, Turkey Basil Akinnuli, Nigeria Isabelle Akkerman, Germany Mudathir Akorede, Nigeria Alireza Akrami, Islamic Republic Of Iran Isam Al Zubaidi, Canada Guido Ala, Italy Ahmed Abdulamier Hussain Al-Amiery, Malaysia Alma Y. Alanis, Mexico Mohamed Al-Ashhab, Egypt Rawaa Al-Dabbagh, Iraq Alessio Alexiadis, United Kingdom Lokman Ali, Bangladesh Javed Ali, Germany M. D. S. Aliyu, Saudi Arabia Farideh Alizadeh, Malaysia Hassan Aljaberi, Malaysia Dhiya Al-Jumeily, United Kingdom Ghazaleh Allameh, Islamic Republic Of Iran Sana Almi, Algeria Karam Al-Obaidi, Malaysia Francisco Alonso, Spain Ehab Alshamaileh, Jordan Wisam Al-Shohani, United Kingdom Luis Alvarez-Icaza, Mexico Baurzhan Alzhanov, Kazakhstan Hussein Alzoubi, Jordan Amirmostafa Amirjani, Islamic Republic Of Iran Mutiu Amosa, South Africa Sanjeev Anand, India Yatheshth Anand, India Vivek Anandaan, India Parinya Anantachaisilp, Thailand Pradeep Anjana, India Sadiya Anjum, India Iyswarya Annapoorani, India Eugene Ansah, Ghana Kashif Ansari, India Mohammad Khalid Ansari, India Emmanuel Anye Ngang, United Kingdom Zoubir Aoulmi, Algeria Amir Arablouei, United States Dominique Armellini, Canada Yogendra Arya, India Tatsunori Asaoka, Japan Nestor Asiamah, Ghana Alireza Aslani, Finland Nikos Aspragathos, Greece Samuel Asumadu-Sarkodie, Ghana Abdullah Ates, Turkey Youssef Attai, Egypt Farnaz Avarzamani, Islamic Republic Of Iran Wael Awad, Jordan Hediye Aydın, Turkey Sohail Ayub, India Faieza Aziz, Malaysia Nagarajan B, India B.Chitti Babu, India Sudhakar Babu, India Senior Editors, Cogent Engineering (2018), 5: 1433607 https://doi.org/10.1080/23311916.2018.1433607
The space-time fractional-coupled Burgers equations and the space-time fractional foam drainage equation are important as an electro-hydro-dynamical model to progress the local electric field and ion acoustic waves in plasma, the shallow water wave problems, and also fluid flow of liquid through foam arisen by gravity and capillarity. In this article, we determine new and further general exact wave solutions to the above-mentioned space-time fractional equations using the generalized (G/G)-expansion method with the assistance of the fractional complex transformation. It is shown that the method is further effective, convenient, and can be used to establish new solutions for other kind non-linear fractional differential equations arising in mathematical physics. Finally, we depict the 3D and 2D figures of the obtained wave solutions in order to interpret them in geometrical sense.
We put forth a dynamic closure modeling framework for the large eddy simulations of the Burgers equation based upon the use of the approximate deconvolution (AD) procedure to compute the Smagorinsky constant self-adaptively from the resolved flow quantities. In our proposed framework, the test filtering process of the standard dynamic model is replaced by the AD procedure. The robustness of the model has been tested considering the Burgers equation in its conservative and skew-symmetric forms. Our numerical assessments for solving the single-mode sine wave and the decaying Burgers turbulence problems show that the present framework effectively damps grid-to-grid oscillations and yields an improved shock capturing property for central numerical schemes as underlying discretizations.
The atomic volume of rare earth metal dysprosium (Dy) has been measured up to high pressures of 35 GPa and low temperatures between 200 and 7 K in a diamond anvil cell using angle dispersive X-ray diffraction at a synchrotron source. The hexagonal close-packed (hcp), alpha-Samarium (alpha-Sm), and double hexagonal close-packed (dhcp) phases are observed to be stable in Dy under high-pressure and low-temperature conditions achieved in our experiments. Dy is known to undergo magnetic ordering below 176 K at ambient pressure with magnetic ordering Neel temperature (T-N]) that changes rapidly with increasing pressure. Our experimental measurement shows that Dy has near-zero thermal expansion in the magnetically ordered state and normal thermal expansion in the paramagnetic state for all the three known high pressure phases (hcp, alpha-Sm, and dhcp) to 35 GPa. This near-zero thermal expansion behavior in Dy is observed below the magnetic ordering temperature T-N at all pressures up to 35 GPa.
The exploration of closed form wave solutions of nonlinear evolution equations (NLEEs) is an important research area in the field of physical sciences and engineering. In this article, we investigate closed form wave solution of two nonlinear equations, namely, the time regularized long wave equation and the (2 + 1)-dimensional nonlinear Schrodinger equation by the modified simple equation method. These equations play significant role in nonlinear sciences. The solutions are obtained in explicit form of the variables in the considered equations. The derived solutions are revealed in the form of exponential and trigonometric functions including solitary and periodic solutions. It is shown that the method is effective and an essential mathematical tool for constructing the closed form wave solutions of NLEEs in mathematical physics.
Cd-doped ZnO nanosheet (ZnO NS) were investigated using a full-potential linearized augmented plane wave method within the generalized gradient approximation (GGA) to calculate the electronic structure and its optical response. The calculated band structures have shown that the Cd-doped ZnO NS is a direct band gap semiconductor at Gamma with 1.50 eV band gap. The contribution of each atom/orbital were commented in light of total and partial densities of states. We also derived the optical constants (mainly the dielectric constants epsilon(1) (0) and epsilon(2) (0)), the absorption coefficient I(omega), refractive index n(omega), extinction coefficient k(omega), and energy-loss function L(omega). The spectrum of absorption coefficient has revealed to increase rapidly for photon energies higher than 2.5 eV. The absorption spectrum was found to be limited in energy region due to different contributions electronic transitions that occurred within ZnO NS and effect of Cd doping. Reducing the band gap of ZnO NS to low values is suitable process for light-emitting devices and solar cells applications.
The most incompressible transition metal osmium (Os) has been studied under high pressure. There is significant interest in Os because of the structural anomalies attributed to topological transitions in the Fermi surface for valence electrons in the hexagonal close-packed phase. We report on measurements of structural parameters and equation of state on Os metal to a pressure of 207 GPa at ambient temperature using platinum as a pressure standard. We obtained angle-dispersive X-ray diffraction data at a synchrotron source with closely spaced pressure intervals to observe any discontinuities or anomalies in the axial c/a ratio at high pressures. Rietveld refinements of X-ray diffraction data show a slowly varying axial ratio (c/a) with a broad minimum at 75 GPa. Our data do not provide any evidence of anomalous behavior in the c/a ratio in Os at 25 or 150 GPa as have been reported in previous studies. Our experimental results are in agreement with theoretical calculations that do not predict any anomalous behavior in c/a ratio in Os under extreme conditions. We present an equation of state for Os to 207 GPa (V/V-0 = 0.761) at ambient temperature and compare our results with the previously published data.
Structural, elastic, electronic, optical, thermodynamic, and superconducting properties of the Laves phase superconductor LaRu2 with T-c similar to 1.63K were investigated using the first-principles calculations for the first time. The corresponding evaluated structural parameters are in good agreement with the available theoretical values. The different elastic properties like as, elastic constants, bulk modulus B, shear modulus G, Young's modulus E, and Poisson ratio were calculated using the Voigt-Reuss-Hill approximation. The ductility nature appears in both values of Cauchy pressure and Pugh's ratio. The band structure and Cauchy pressure shows that the material behaves metallic nature. The calculated total density of state is 6.80 (electrons/eV) of LaRu2. The optical properties such as reflectivity, absorption spectrum, refractive index, dielectric function, conductivity, and energy loss spectrum are also calculated. The photoconductivity reveals the metallic nature of LaRu2 and absorption coefficient is good in the infrared region. The evaluated density and Debye temperature are 9.55 gm/cm(3) and 110.51K, respectively. In addition, the study of thermodynamic properties like as minimum thermal conductivity, melting temperature, and Dulong-Petit limit are 0.26 (Wm(-1)K(-1)), 1,471.65K, and 74.80 (J/mole K), respectively. Finally, the investigated electron-phonon coupling constant is 0.66 of LaRu2 superconductor.
The scheme to realize high speed (~250Gb/s) all-optical Boolean logic gates using semiconductor optica amplifiers with quantum-dot (QD-SOA) is introduced and analyzed in this review. Numerical simulation method was presented by solving the rate equation and taking into account nonlinear dynamics including carrier heating and spectral hole-burning. Binary phase shift keyed (BPSK) signal and on-off keyed signal are used to generate high speed all-optical logic gates. The applications based on all-optical logic gates such as, all-optical latches, pseudo random bit sequence (PRBS) generation and all-optical encryption, are also discussed in this review. Results show that the scheme based on QD-SOA is a promising method for the realization of high speed all-optical communication system in the future.
We employ Real-Time Time-Dependent Density Functional Theory to study hole oscillations within a B-DNA monomer (one base pair) or dimer (two base pairs). Placing the hole initially at any of the bases which make up a base pair, results in THz oscillations, albeit of negligible amplitude. Placing the hole initially at any of the base pairs which make up a dimer is more interesting: For dimers made of identical monomers, we predict oscillations with frequencies in the range f approximate to 20-40 THz, with a maximum transfer percentage close to 1. For dimers made of different monomers, f approximate to 80-400 THz, but with very small or small maximum transfer percentage. We compare our results with those obtained recently via our Tight-Binding approaches and find that they are in good agreement.
The Kundu-Eckhaus equation and the derivative nonlinear Schrodinger equation describe various physical processes in nonlinear optics, plasma physics, fluid mechanics, magneto-hydrodynamic equation in the presence of the Hall Effect. Thus, closed form solutions of these equations are very important to realize the obscurity of the phenomena. The modified simple equation (MSE) method is highly effective and competent mathematical tool to examine closed form wave solutions of nonlinear evolution equations (NLEEs) arising in mathematical physics, applied mathematics and engineering. In this article, the MSE method is suggested and executed to construct closed form wave solutions of the above-mentioned equations involving parameters. When the parameters receive special values, impressive solitary wave solutions are derived from the exact solutions.
Effect of LaCl3 concentration on the electrical conduction mechanism of LaF3 /porous silicon (PS) structure has been investigated in this work. LaF3 layers have been deposited by a novel chemical bath deposition (CBD) technique. With this simple technique, LaF3 produced as LaCl3 are made to react with hydrofluoric (HF) acid on the porous silicon substrate. This enables direct deposition of LaF3 on the pore walls of the porous silicon leading to a successful passivation of PS. The compositions of the deposited LaF3 were confirmed by Energy Dispersive of X-ray (EDX) analysis. The electrical conduction study has been done by impedance analyzer (HP4294A). From this study it can be concluded that the conductance increases with LaCl3 concentration but decreases for higher concentration.
After analyzing the characteristics and pricing models on the Russian wholesale electricity market, some important features for econometric modeling are introduced. This paper suggests econometric forecasting models developed to predict daily and hourly electricity prices on the day-ahead market for two price zones in Russia: European and Siberian ones. A set of 24 models, which are similar in nature but different in included regressors, are introduced. On the basis of the actual database for 2014, different modifications of price formation are offered and analyzed with the help of the Eviews econometric package. Dynamic forecasts on various distances (day, week, and month) are conducted and the most suitable models from the point of minimizing the norms of the vectors residuals are chosen. Constructed ARMA models have high predictive power and are able to reflect the price trend on the base of exogenous factors and the previous price values.
Abstract Wild-growing mushrooms are a complementary foodstuff, widely consumed as a delicacy, in Italy. They are considered excellent bioindicators of environmental pollution and the accumulation of radionuclides can pose a radiological hazard. 137Cs and 40K activity concentrations were measured through HPGe gamma-spectrometry in different mushroom species (Agaricus arvensis, Leccinum quercinum, Boletus aereus, Lactarius deliciosus, Boletus edulis, Macrolepiota konradii, Cantharellus lutescens) collected from four different sampling sites in the Calabria region, south of Italy. Experimental values were found to be in the range from (0.3 ± 0.1) Bq/kg f.m. (fresh mass) to (73.1 ± 4.6) Bq/kg f.m. for 137Cs and from (46.9 ± 10.7) Bq/kg f.m. to (161.3 ± 12.9) Bq/kg f.m. for 40K, respectively. All values were much lower than the specific activity limit set by the international legislation at 600 Bq/kg f.m. for 137Cs and at 1,258 Bq/kg f.m. for 40K, respectively. Experimental activity concentrations allowed us to determine the effective dose due to the ingestion of mushrooms by adult members of the population. It was found in the range from 0.25 to 1.35 μSv/y, much lower than the recommended level for the public (1 mSv/y). Data obtained in this article provide useful information on the environmental risk and can be further used for a radiological mapping of the studied area.
Birkhoff's theorem states that the external gravitational field of any spherically-symmetric system is static and is described by Schwarzschild metric. In this paper, we demonstrate that it is inconsistent with the direct post-Newtonian solution to Einstein field equations in the weak field limit. Moreover, we identify the flaw in the derivation of Birkhoff's theoremthe consequences of making the coordinate transformations for solving Einstein field equations are ignored, which is due to the misuse of the covariance in general relativity.
