ALBERT

Description: This paper presents the performance of a wind power system under failures in the lubricant system, and a procedure is proposed to detect the failure. According to the fact that the friction torque caused by the lubricant system, failure makes the maximum power point (MPP) of the wind system to be smaller than that of normal operation; for MPP tracking operations, the difference between actual and simulated (estimated) output power of the wind system is an indicator for the lubricant system failure. However, for non-MPP tracking operations, in which the demanded power is small enough to be satisfied by the failed wind system, the above indicator cannot be used to detect the lubricant system failure. In this case, the predetermined angular shaft speed ratio is used to detect the lubricant system failure. Moreover, the converter failure is considered in this paper, and a model-based fault detection filter is designed to detect the DC/DC converter failure in a wind system. The proposed detection filter consists of an observer combined with a residual signal generator, where the driving torque is assumed as an unknown bounded input in the proposed failure detection scheme. Numerical simulation results support the proposed detection procedures.

Description: We studied the optical absorption and luminescence of agate (SiO 2 ), topaz (Al 2 [SiO 4 ](F,OH) 2 ), beryl (Be 3 Al 2 Si 6 O 18 ), and prehnite (Ca 2 Al(AlSi 3 O 10 )(OH) 2 ) doped with different concentrations of transition metal ions and exposed to fast neutron irradiation. The exchange interaction between the impurity ions and the defects arising under neutron irradiation causes additional absorption as well as bands' broadening in the crystals. These experimental results allow us to suggest the method for obtaining new radiation-defect induced jewellery colors of minerals due to neutron irradiation.

Description: We analyzed carefully the experimental kinetics of the low-temperature diffusion-controlled F, H center recombination in a series of irradiated alkali halides and extracted the migration energies and pre-exponential parameters for the hole H centers. The migration energy for the complementary electronic F centers in NaCl was obtained from the colloid formation kinetics observed above room temperature. The obtained parameters were compared with data available from the literature.

Description: The effect of low-temperature uniaxial deformation on the self-trapping-limited mean free path of excitons in a KI–Tl crystal was revealed from x-ray luminescence spectra. The analysis of the dependence of the intensity ratio of the Tl-center emission (2.85 eV) and the luminescence of self-trapped excitons (π-component; 3.3 eV) on the extent of low-temperature deformation showed that in the KI–Tl crystal (3 × 10 −3 mol. %) the self-trapping-limited mean free path of excitons is comparable with the distance between Tl atoms (20–27) a under a deformation ε = 2%. As the compression increases to ε ≥ 2%–5%, the mean free path drops to (27-5.35) a . The results of modeling based on the continuum approximation showed that with increasing temperature and the degree of low-temperature deformation the height of the potential barrier for the exciton self-trapping drops, which is consistent with the reduction of the mean free path of excitons in the KI–Tl crystal.

Description: Free volume and pore size distribution size in functional micro and macro-micro-modified Cu 0.4 Co 0.4 Ni 0.4 Mn 1.8 O 4 ceramics are characterized by positron annihilation lifetime spectroscopy in comparison with Hg-porosimetry and scanning electron microscopy technique. Positron annihilation results are interpreted in terms of model implication positron trapping and ortho-positronium decaying. It is shown that free volume of positron traps are the same type for macro and micro modified Cu 0.4 Co 0.4 Ni 0.4 Mn 1.8 O 4 ceramics. Classic Tao-Eldrup model in spherical approximation is used to calculation of the size of nanopores smaller than 2 nm using the ortho-positronium lifetime.

Description: In order to predict optical properties of insulating materials under intensive laser excitation, we generalized methods of quantum electrodynamics, allowing us to simulate excitation of electrons and holes, interacting with each other and acoustic phonons. The prototypical model considers a two-band dielectric material characterized by the dispersion relations for electron and hole states. We developed a universal description of excited electrons, holes and acoustic phonons within joint quantum kinetics formalism. Illustrative solutions for the quasiparticle birth-annihilation operators, applicable at short laser pulses at 0 K, are obtained by the transition from the macroscopic description to the quantum field formalism.

Description: Monoclinic antiferromagnetic NiWO 4 was studied by far-infrared (30–600 cm −1 ) absorption spectroscopy in the temperature range of 5–300 K using the synchrotron radiation from SOLEIL source. Two isomorphous CoWO 4 and ZnWO 4 tungstates were investigated for comparison. The phonon contributions in the far-infrared range of tungstates were interpreted using the first-principles spin-polarized linear combination of atomic orbital calculations. No contributions from magnetic excitations were found in NiWO 4 and CoWO 4 below their Neel temperatures down to 5 K.

Description: The creation spectrum of stable F centres (being part of F-H pairs of Frenkel defects) by synchrotron radiation of 7–40 eV has been measured for highly pure NaCl single crystals at 12 K using a highly sensitive luminescent method. It is shown that the efficiency of F centre creation in a closely packed NaCl is low at the decay of anion or cation excitons (7.8–8.4 and 33.4 eV, respectively) or at the recombination of relaxed conduction electrons and valence holes. Only the recombination of nonrelaxed (hot) electrons with holes provides the energy exceeding threshold value E FD , which is sufficient for the creation of Frenkel defects at low temperature.

Description: An unambiguous attribution of the absorption spectra to definite paramagnetic centres identified by the EPR techniques in the most cases is problematic. This problem may be solved by applying of a direct measurement techniques—the EPR detected via the magnetic circular dichroism, or briefly MCD–EPR. The present survey reports on the advantages and disadvantages applying the MCD–EPR techniques to simple and complex paramagnetic centres in crystals as well as glasses and glass-ceramics.

Description: Luminescence properties of SiO 2 in different structural states are compared. Similar comparison is made for GeO 2 . Rutile and α-quartz structures as well as glassy state of these materials are considered. Main results are that for α-quartz crystals the luminescence of self-trapped exciton is the general phenomenon that is absent in the crystal with rutile structure. In rutile structured SiO 2 (stishovite) and GeO 2 (argutite) the main luminescence is due to a host material defect existing in as-received (as-grown) samples. The defect luminescence possesses specific two bands, one of which has a slow decay (for SiO 2 in the blue and for GeO 2 , in green range) and another, a fast ultraviolet (UV) band (4.75 eV in SiO 2 and at 3 eV in GeO 2 ). In silica and germania glasses, the luminescence of self-trapped exciton coexists with defect luminescence. The latter also contains two bands: one in the visible range and another in the UV range. The defect luminescence of glasses was studied in details during last 60–70 years and is ascribed to oxygen deficient defects. Analogous defect luminescence in the corresponding pure nonirradiated crystals with α-quartz structure is absent. Only irradiation of a α-quartz crystal by energetic electron beam, γ-rays and neutrons provides defect luminescence analogous to glasses and crystals with rutile structure. Therefore, in glassy state the structure containing tetrahedron motifs is responsible for existence of self-trapped excitons and defects in octahedral motifs are responsible for oxygen deficient defects.

Description: The ground state properties of cubic scandium trifluoride (ScF 3 ) perovskite were studied using first-principles calculations. The electronic structure of ScF 3 was determined by linear combination of atomic orbital (LCAO) and plane wave projector augmented-wave (PAW) methods using modified hybrid exchange-correlation functionals within the density functional theory (DFT). The comprehensive comparison of the results obtained by two methods is presented. Both methods allowed us to reproduce the lattice constant found experimentally in ScF 3 at low temperatures and to predict its electronic structure in good agreement with known experimental valence-band photoelectron and F 1 s x-ray absorption spectra.

Description: Photoluminescence and excitation spectra of microcrystalline and nanocrystalline nickel tungstate (NiWO 4 ) were measured using UV-VUV synchrotron radiation source. The origin of the bands is interpreted using comparative analysis with isostructural ZnWO 4 tungstate and based on the results of recent first-principles band structure calculations. The influence of the local atomic structure relaxation and of Ni 2+ intra-ion d–d transitions on the photoluminescence band intensity are discussed.

Description: In this paper a novel method for synthesis of LaInO 3 :Er 3+ is reported and upconversion luminescence properties of the synthesized material at different temperatures (9–300 K) are studied. The samples were prepared by co-precipitation and subsequent heat treatment of lanthanum, indium and erbium hydroxides. It is shown that the excitation at 980 nm leads to a strong green upconversion luminescence in the material. At the concentrations above 0.1 mol. % of Er 3+ the energy transfer upconversion mechanism of the luminescence becomes evident. Further increase of Er 3+ content in the material leads to higher red-to-green upconversion luminescence intensity ratio. The mechanisms responsible for the observed variation are discussed.

Description: Possible proximity effects in gases of cold, multiply charged atoms are discussed. Here we deal with rarefied gases with densities n d of multiply charged ( Z ≫ 1) atoms at low temperatures in the well-known Thomas-Fermi (TF) approximation, which can be used to evaluate the statistical properties of single atoms. In order to retain the advantages of the TF formalism, which is successful for symmetric problems, the external boundary conditions accounting for the finiteness of the density of atoms (donors), n d ≠ 0, are also symmetrized (using a spherical Wigner-Seitz cell) and formulated in a standard way that conserves the total charge within the cell. The model shows that at zero temperature in a rarefied gas of multiply charged atoms there is an effective long-range interaction E proxi ( n d ), the sign of which depends on the properties of the outer shells of individual atoms. The long-range character of the interaction E proxi is evaluated by comparing it with the properties of the well-known London dispersive attraction E Lond ( n d ) 〈 0, which is regarded as a long-range interaction in gases. For the noble gases argon, krypton, and xenon E proxi 〉0 and for the alkali and alkaline-earth elements E proxi 〈 0. At finite temperatures, TF statistics manifests a new, anomalously large proximity effect, which reflects the tendency of electrons localized at Coulomb centers to escape into the continuum spectrum. The properties of thermal decay are interesting in themselves as they determine the important phenomenon of dissociation of neutral complexes into charged fragments. This phenomenon appears consistently in the TF theory through the temperature dependence of the different versions of E proxi . The anomaly in the thermal proximity effect shows up in the following way: for T ≠ 0 there is no equilibrium solution of TS statistics for single multiply charged atoms in a vacuum when the effect is present. Instability is suppressed in a Wigner-Seitz model under the assumption that there are no electron fluxes through the outer boundary R 3 ∝ n −1 d of a Wigner-Seitz cell. E proxi corresponds to the definition of the correlation energy in a gas of interacting particles. This review is written so as to enable comparison of the results of the TF formalism with the standard assumptions of the correlation theory for classical plasmas. The classic example from work on weak solutions (including charged solutions)—the use of semi-impermeable membranes for studies of osmotic pressure—is highly appropriate for problems involving E proxi . Here we are speaking of one or more sharp boundaries formed by the ionic component of a many-particle problem. These may be a metal-vacuum boundary in a standard Casimir cell in a study of the vacuum properties in the 2 l gap between conducting media of different kinds or different layered systems (quantum wells) in semiconductors, etc. As the mobile part of the equilibrium near a sharp boundary, electrons can (should) escape beyond the confines of the ion core into a gap 2 l with a probability that depends, among other factors, on the properties of E proxi for the electron cloud inside the conducting walls of the Casimir cell (quantum well). The analog of the Casimir sandwich in semiconductors is the widely used multilayer heterostructures referred to as quantum wells of width 2 l with sides made of suitable doped materials, which ensure statistical equilibrium exchange of electrons between the layers of the multilayer structure. The thermal component of the proximity effects in semiconducting quantum wells provides an idea of many features of the dissociation process in doped semiconductors. In particular, a positive E proxi 〉 0 (relative to the bottom of the conduction band) indicates that TF donors with a finite density n d ≠ 0 form a degenerate, semiconducting state in the semiconductor. At zero temperature, there is a finite density of free carriers which increases with a power-law dependence on T .

Description: Research on hybrid systems has emerged in recent years due to the current and growing global interest in the search for energy resources that lead to a decrease in fossil fuel use for power generation. Such systems are coupled to both conventional and non-conventional sources. Therefore, in this paper we present a review of hybrid energy systems, with emphasis on those which are engaged in photovoltaic solar energy. The purpose is to identify the different integration frameworks and types of storage capacities according to energy demand, geographic area, and other parameters. Finally, an overview of Mexico in relation to hybrid systems is presented as an attempt to motivate researchers, industry, and government to implement and develop these systems.

Description: This paper proposes a fuzzy control method for tracking maximum power point in photovoltaic (PV) power systems to solve a fast irradiation change problem. Perturb and Observe (P&O) is known as a very simple maximum power point tracking and is extensively disseminated. Fuzzy logic is also simple to investigate and provides fast dynamics. The suggested technique combines both fuzzy logic and P&O advantages. A fuzzy logic-based P&O algorithm is illustrated to identify the fault direction tracking of conventional P&O algorithm under trapezoidal irradiation change. The proposed algorithm is verified using Matlab/Simulink™ software. The robust tracking capability under rapidly increasing and decreasing irradiance is verified experimentally with a PV array emulator. Simulation and experimental results confirm that the proposed algorithm provides effective, fast, and accurate tracking compared to the conventional P&O algorithm.

Description: The increasing penetration of distributed generators (DGs) makes further interconnection of multiple energy carriers possible. In this paper, an integration model comprising IEEE-33 bus distribution network and a correspondingly designed water system is proposed with DG coupling of thermal and electrical energy. The integrated energy system incorporates the constraints of the distribution network, water system, and DGs and ensures that the electrical and thermal demands of the integrated energy system are satisfied simultaneously by energy flow. An optimal procedure including optimal sizing, positioning, and operation of DGs and gas boilers in a given system was implemented while minimizing the total costs of investment and operation. The model constitutes a mixed integer nonlinear problem, as it takes the power flow calculation and the nonlinear characteristics of DG efficiency into consideration. Therefore, the particle swarm optimization algorithm is employed to simulate the proposed model. The simulation results in conjunction with numerical studies reveal the impact of the water system on the optimal configuration of DGs and the advantages of the integrated energy system on economic considerations, voltage level, and net loss.

Description: The radiation properties and the electronic structure of hybrid composites based on suspension polystyrene (PS) and nanocrystals of BaZrO 3 (BZO) ( d 〈 50 nm) have been studied using luminescent spectroscopy and x-ray analysis. A strong cathodoluminescence (CL) in BZO-nanocrystals is observed in temperature range 80–293 K. It is modified in BZO-PS composites: both the low- and a high-energy bands (near 4 eV) appear, together with a significant reduction in the CL intensity. A decrease of the lattice parameter a for BZO phase in the composite and the modification of CL spectra indicate for changes in the nanocrystalline structure induced by the polymer.

Description: Fresh and aged melt-grown or gas-phase grown CdI 2 crystals are studied by means of low-temperature photoluminescence spectroscopy. Noticeable transformations of emission spectra are observed after long-term aging. The formation of nanostructures containing cadmium oxide and cadmium hydroxide as well as the changes in local surrounding of iodine atoms and the possible growth of polytypic modifications of CdI 2 are taken into account when considering the diversity of optical spectra.

Description: Developing countries like Pakistan need a continuous supply of clean and cheap energy. It is a very common fear in today's world that the fossil fuels will be depleted soon and the cost of energy is increasing day-by-day. Renewable energy sources and technologies have the potential to provide solutions to long-standing energy problems faced by developing countries. Currently, Pakistan is experiencing a critical energy crisis and renewable energy resources can be the best alternatives for quickly terminating the need for fossil fuels. The renewable energy sources such as solar energy, wind energy, and biomass energy combined with fuel cell technology can be used to overcome the energy shortage in Pakistan. Biomass is a promising renewable energy source and is gaining more interest because it produces a similar type of fuel like crude oil and natural gas. Energy from biomass only depends upon the availability of raw materials; therefore, biomass can play an important role to fulfill the energy requirements of the modern age. The use of energy has increased greatly since the last century and almost all human activities have become more dependent on energy. Biomass, being a potential and indigenous candidate, could be a good solution to meet the energy needs of Pakistan. In this review paper, the detailed current energy requirements and solutions from available energy resources and the scope, potential, and implementation of biomass conversion to energy in Pakistan are explored with a special focus on the major province of Punjab and the advantages of biomass for energy purposes.

Description: Reducing wake losses in wind farms by deflecting the wakes through turbine yawing has been shown to be a feasible wind farm controls approach. Nonetheless, the effectiveness of yawing depends not only on the degree of wake deflection but also on the resulting shape of the wake. In this work, the deflection and morphology of wakes behind a porous disk model of a wind turbine operating in yawed conditions are studied using wind tunnel experiments and uniform inflow. First, by measuring velocity distributions at various downstream positions and comparing with prior studies, we confirm that the non-rotating porous disk wind turbine model in yaw generates realistic wake deflections. Second, we characterize the wake shape and make observations of what is termed as curled wake, displaying significant spanwise asymmetry. The wake curling observed in the experiments is also reproduced qualitatively in Large Eddy Simulations using both actuator disk and actuator line models. Results suggest that when a wind turbine is yawed for the benefit of downstream turbines, the curled shape of the wake and its asymmetry must be taken into account since it affects how much of it intersects the downstream turbines.

Description: Analytical calculations of the potential barrier hindering rotation of the hydrogen molecules in the molecular field of neighboring molecules are performed for molecular solid hydrogen. The calculations are made for the four-sublattice Pca 2 1 lattice which minimizes the electrostatic energy of classical quadrupoles on an hcp lattice.

Description: The model describing the effect of anharmonicity on the spin-crossover properties of Fe(II) complex is proposed. It is shown that anharmonicity can be one of the important factors controlling the magnetic transitions of the low-spin high-spin type.

Description: We report Raman light scattering in the phase separated superconducting single crystal Rb 0.77 Fe 1.61 Se 2 with T c = 32 K over a wide temperature region 3–500 K. The observed phonon lines from the majority vacancy ordered Rb 2 Fe 4 Se 5 (245) antiferromagnetic phase with T N = 525 K demonstrate modest anomalies in the frequency, intensity and halfwidth at the superconductive phase transition. We identify phonon lines from the minority compressed Rb δ Fe 2 Se 2 (122) conductive phase. The superconducting gap with d x 2 − y 2 symmetry has been detected in our spectra. In the range 0–600 cm −1 we observe a weak but highly polarized B 1 g -type background which becomes well-structured upon cooling. A possible magnetic or multiorbital origin of this background is discussed. We argue that the phase separation in M 0.8+ x Fe 1 . 6+y Se 2 is of pure magnetic origin. It occurs below the Néel temperature when the magnetic moment of iron reaches a critical value. We state that there is a spacer between the majority 245 and minority 122 phases. Using ab initio spin-polarized band structure calculations we demonstrate that the compressed vacancy ordered Rb 2 Fe 4 Se 5 phase can be conductive and therefore may serve as a protective interface spacer between the purely metallic Rb δ Fe 2 Se 2 phase and the insulating Rb 2 Fe 4 Se 5 phase providing percolative Josephson-junction like superconductivity all throughout of Rb 0.8+ x Fe 1.6+ y Se 2 . Our lattice dynamics calculations show significant differences in the phonon spectra of the conductive and insulating Rb 2 Fe 4 Se 5 phases.

Description: The relative elongation ε of samples of high purity (99.9999 mol. % with respect to nonhydrogenic impurities) parahydrogen ( p -H 2 , ∼0.2% o -H 2 ) with different amounts of the stable hydrogen isotope deuterium is measured as a function of applied stress σ at temperatures of 1.8–4.2 K. The samples were subjected to uniaxial tension by stepwise loading. The ratio [D]/[H] of the number [D] of deuterium atoms to the number [H] of p -H 2 hydrogen atoms ranged from 0.0055 ± 0.0005 at. % up to 0.07 at. %. For deuterium enriched p- H 2 , the easy slip dislocation stage vanished from the σ(ε) curves and there was a significant reduction in the total relative elongation of the samples, as well as a substantial increase in the hardening coefficient d σ/ d ε. Deformation of samples of p- H 2 with deuterium contents higher than the natural amount produces an unusual change in their shape owing to the appearance of a rotational component of the low-temperature plastic mass transfer.

Description: Raman spectrum of single-crystal SmFe 3 (BO 3 ) 4 was studied in the frequency range from 3 to 1500 cm −1 at temperatures 10–300 K. All the A 1 and E phonon modes predicted by the group theory for a given symmetry of the crystal were observed. The magnitudes of splitting between the LO and TO components of polar E phonons were determined. It was found that under the transition to a magnetically ordered phase, the behavior of the intensity of the line corresponding to the A 1 vibrational mode is anomalous. It was shown that at low temperatures the spectrum of two-magnon excitations has a complex shape and is observed with both nondiagonal and diagonal components of the scattering tensor. This complex shape reflects the features in the density of states of the magnetic branches. An estimate of the magnon energy E m at the Brillouin zone boundary gave ∼47 cm −1 . The structure of the ground multiplet 6 H 5/2 of a Sm +3 ion in paramagnetic and antiferromagnetic states as well as the effect of the magnetic phase transition on it were studied. Electron-phonon interaction for the electronic excitation at 225 cm −1 was revealed.

Description: Two series of nanosized cobalt spinel ferrites CoFe 2 O 4 are synthesized from metal salts using high-energy ball milling with the addition of NaCl as a growth agent (series CFO-NaCl), and without (CFO Series). The particle properties are characterized using atomic force microscopy, as well as magnetic and calorimetric measurements. It is shown that the average sizes of the nanoparticles were ∼5.6 and ∼10.3 nm for CFO and CFO-NaCl series, respectively. We performed magnetostatic measurements and determined the parameters that are required to analyze the magnetic state and remagnetization processes of the nanoparticles. It is shown that the blocking temperature is ≈160 K for CFO samples and ≈300 K for the CFO-NaCl series. It was concluded that at 293 K the CFO series particles exhibit a superparamagnetic state, whereas the CFO-NaCl series are in the blocked state. The specific loss power that is scattered by the synthesized nanoparticle ensembles placed in an alternating magnetic field, is measured experimentally and theoretically assessed. The nature of the processes that determine the thermal characteristics of the nanoparticles is analyzed.

Description: Amplification of acoustic in-plane phonons due to an external temperature gradient (∇ T ) in single-layer graphene (SLG) was studied theoretically. The threshold temperature gradient ( ∇ T ) 0 g and the threshold voltage ( V T ) 0 g in SLG were evaluated. For T = 77   K , the calculated value for ( ∇ T ) 0 g = 746.8     K / cm and ( V T ) 0 g = 6.6   mV . The calculation was done in the hypersound regime. Further, the dependence of the normalized amplification ( Γ / Γ 0 ) on the frequency ω q and ∇ T / T were evaluated numerically and presented graphically. The calculated threshold temperature gradient ( V T ) 0 g for SLG was higher than that obtained for homogeneous semiconductors ( n -InSb) ( ∇ T ) 0 hom ≈ 10 3   K / cm , superlattices ( ∇ T ) 0 S L ≈ 384   K / cm , and cylindrical quantum wire ( ∇ T ) 0 c q w ≈ 10 2   K / cm . This makes SLG a much better material for thermoelectric phonon amplification.

Description: We found that the coupled system of Josephson junctions under external electromagnetic radiation demonstrates a cascade of parametric instabilities. These instabilities appear along the IV characteristics within bias current intervals corresponding to Shapiro step subharmonics and lead to charging in the superconducting layers. The amplitudes of the charge oscillations increase with increasing external radiation power. We demonstrate the existence of longitudinal plasma waves at the corresponding bias current values. An essential advantage of the parametric instabilities in the case of subharmonics is the lower amplitude of radiation that is needed for the creation of the longitudinal plasma wave. This fact gives a unique possibility to create and control longitudinal plasma waves in layered superconductors. We propose a novel experiment for studying parametric instabilities and the charging of superconducting layers based on the simultaneous variation of the bias current and radiation amplitude.

Description: The Coulombic effect on the stability range of the photo-excited electron gas on liquid helium is shown to favor formation of domains of different densities. Domains appear to eliminate or greatly reduce regions with negative conductivity. An analysis of the density domain structure allows explaining remarkable observations reported recently for the photo-excited electron gas.

Description: We present thoroughly analyzed experimental results that demonstrate the anomalous manifestation of the exciton self-trapping effect, which is already well-known in bulk crystals, in ordered molecular nanoclusters called J -aggregates. Weakly-coupled one-dimensional (1D) molecular chains are the main structural feature of J -aggregates, wherein the electron excitations are manifested as 1D Frenkel excitons. According to the continuum theory of Rashba-Toyozawa, J -aggregates can have only self-trapped excitons, because 1D excitons must adhere to barrier-free self-trapping at any exciton-phonon coupling constant g = ε LR /2β, wherein ε LR is the lattice relaxation energy, and 2β is the half-width of the exciton band. In contrast, very often only the luminescence of free, mobile excitons would manifest in experiments involving J -aggregates. Using the Urbach rule in order to analyze the low-frequency region of the low-temperature exciton absorption spectra has shown that J -aggregates can have both a weak ( g 〈 1) and a strong ( g 〉 1) exciton-phonon coupling. Moreover, it is experimentally demonstrated that under certain conditions, the J -aggregate excited state can have both free and self-trapped excitons, i.e., we establish the existence of a self-trapping barrier for 1D Frenkel excitons. We demonstrate and analyze the reasons behind the anomalous existence of both free and self-trapped excitons in J -aggregates, and demonstrate how exciton-self trapping efficiency can be managed in J -aggregates by varying the values of g , which is fundamentally impossible in bulk crystals. We discuss how the exciton-self trapping phenomenon can be used as an alternate interpretation of the wide band emission of some J -aggregates, which has thus far been explained by the strongly localized exciton model.

Description: We present results of theoretical and experimental studies of the electronic structure and magnetic properties of RFe 4 Al 8 , RMn 4 Al 8 , and RCr 4 Al 8 compounds with nonmagnetic elements R = Sc, Y, La, and Lu. The electron spectrum and field induced magnetic moment, as well as their dependences on the unit cell volume, are calculated for the paramagnetic phase of the RT 4 Al 8 systems. The calculations are supplemented by measurements of the magnetic susceptibility of representative RT 4 Al 8 compounds as a function of temperature and hydrostatic pressure.

Description: Negative magnetoresistance of InSb whiskers with different impurity concentrations 4.4 × 10 16 –7.16 × 10 17 cm −3 was studied in longitudinal magnetic field 0–14 T in the temperature range 4.2–77 K. The negative magnetoresistance reaches about 50% for InSb whiskers with impurity concentration in the vicinity to the metal–insulator transition. The negative magnetoresistance decreases to 35 and 25% for crystals with Sn concentration from the metal and dielectric side of the transition. The longitudinal magnetoresistance twice crosses the axis of the magnetic field induction for the lightly doped crystals. The behavior of the negative magnetoresistance could be explained by the existence of classical size effect, in particular boundary scattering in the subsurface whisker layer.

Description: Changes in the topology of distribution networks which is due to connecting or disconnecting of distributed generations (DGs) is a critical challenge in maintaining protection coordination in these networks. Protection coordination is generally retrieved after deciding optimal capacity and location of installing DGs. Nevertheless, in this paper, a new method is presented which merges the protection coordination of distribution networks in the process of sizing and siting DGs. The presented approach of this paper, in addition to identifying the optimal location and capacity of DGs with the purpose of increasing the benefits and reducing cost of installing these resources, is to also create a robust protection coordination. In order to provide a robust protection coordination, the capacity and location of fault current limiters are identified parallel with sizing and siting DGs. The protection coordination considered in this paper results in grouping different topologies of the network according to allowable memory of protective relays. On this basis, the protection coordination of all operational topologies of the network is guaranteed. In order to coordinate each group interval linear programming is suggested. This method reduces the number of protection coordination constraints of each group and simplifies appropriate protection coordination for the group. The proposed method is tested on Zanjan Regional Electric Board, Iran. Simulation results are reported and discussed.

Description: Vegetable insulating oils (VIOs) have attracted wide attention for their high flash point, high insulation performance and degradability. However, the unsaturated fatty acids contained in VIOs reduce their oxidation stability, which requires the addition of some antioxidants to ensure their usage. Here, we establish a high-performance liquid chromatography (HPLC) method for determination of antioxidants in VIOs. The standard calibration curves of 3 analytes (PG, BHA, BHT) all show high linearity, and the correlation coefficients are all above 0.9994. Limits of detection of all three analytes range from 0.003 to 0.010 mg/ml; limits of quantitation range from 0.010 to 0.033 mg/ml. The new HPLC method is proved ideally suitable for the analysis of commercialized transformer oil Cooper-FR3 with precision (%RSD = 0.3%–0.7%) and accuracy (%recovery = 100.0%–102.1%), suggesting that this method is an efficient tool for routine screening of antioxidant contents in VIOs. We used this method to monitor the changes of antioxidant contents in the oxidation of two VIOs–soybean oil and rapeseed oil.

Description: This paper introduces a stochastic reliability evaluation methodology for quantifying the impact of unmanaged plug-in hybrid electric vehicles (PHEVs') charging on the transformers' hottest spot temperature (HST)-dependent aging failures. Further, a novel PHEVs' charging management method has been proposed from the distribution transformers' dynamic thermal modeling perspective. The proposed reliability evaluation method provided the precise stochastic model corresponding to the PHEV owners' behavior. The introduced reliability evaluation methodology has been applied to an actual distribution system of the Hormozgan Regional Electrical Company in Iran under various PHEVs' charging scenarios. The numerical results imply that the distribution transformers' failures are adversely affected due to unmanaged PHEVs charging. The system under study has been simulated during a 10-year-period. The test results show that the transformers' HST-dependent failures due to the PHEVs' charging demand load exponentially increased as a function of system age. As revealed by the results, the proposed PHEVs' charging management methodology mitigates the aggregated peak load and transformers' HST by deferring the peak charging load to midnight.

Description: Under partial shading conditions, the power–voltage (P-U) curve may exhibit multiple local maxima. This makes it challenging to track the global maximum power point (GMPP). Additionally, in such conditions, conventional maximum power point tracking (MPPT) methods cannot be used to extract the GMPP. This paper describes a modified firefly algorithm (MFA) that can rapidly and accurately extract the GMPP under partial shading conditions. The algorithm introduces the concepts of the global and local firefly densities during each iteration, and devises two elimination mechanisms to adaptively adjust the firefly population. The proposed method is compared with the traditional MPPT algorithms under four different partial shading conditions. Simulation results demonstrate that the MFA can immediately and accurately track the global maximum under the partially shaded conditions, and that the proposed method outperforms conventional techniques in terms of tracking efficiency and speed.

Description: The parameters influencing gas alternative water (WAG) for CO 2 flooding in the low permeability block of the Jilin oil fields in China were investigated using the numerical simulation software, Eclipse. The minimum miscibility pressure was first determined based on slim tube tests. Comparisons were made between continuous water flooding, continuous CO 2 flooding, and WAG flooding methods. The oil recovery ratio of “gas injection first method” was higher than that of “water injection first method” and the mechanism of CO 2 displacement was analyzed. The optimum parameters for WAG flooding were 7 for the number of slugs, 0.3845 PV for the total injection volume, approximately 0.5742 for the gas/water slug ratio, and 120 days for the stewing time. The optimum injection timing of the switching depletion development to the WAG injection was 0.25 years and the earlier switching to the WAG injection after water flooding was more suitable for enhanced oil recovery. The maximal cumulative water injection by water flooding or by WAG flooding yielded the highest oil recovery ratio for homogeneous reservoir. The results do not only play a very important role in optimizing different development schemes but also provide theoretical basis for CO 2 flooding in low permeability hydrocarbon reservoirs.

Description: Experimental results on the performances of ten solar stills with different glass inclination angles are presented. The inclination angles selected are 10–55 in steps of 5°. Results demonstrate that the angles between 30° and 35° may be associated with the least still performance while those between 20° and 25° provide the optimum performance as far as the clean water productivity and cost effectiveness are concerned. Empirical modeling of the still operation produced good agreement with the experimental data.

Description: Water intake structure is an important element technology for small hydroelectric generation. Currently, intake structures with bar screens have been broadly introduced; however, these require constant maintenance to avoid the clogging of bars by dust or gravel. This study considers the optimal structure of bottom intakes by focusing on two criteria: efficient water intake and prevention of clogs by trapping trash. Grating was selected as the intake structure because it is convenient to construct, widely available, and cheaper than other materials. A flume experiment was conducted to examine the relation between the grating structure and the intake efficiency and trash-trapping rate. Results indicate a clear linear relation between the installation angle and water intake capacity. Furthermore, the trash-trapping rate is low for gratings that have high opening area ratios because their surface areas are small and friction resistance is low.

Description: Earth-abundant kesterite Cu 2 ZnSnSe 4 material is a promising candidate for the mass production of low-cost thin film solar cells. However, the synthesis of single-phase kesterite films is especially challenging, since the kesterite single-phase region in the equilibrium phase diagram is very narrow. In this study, the metal composition was varied within the Cu-poor composition range in order to study the presence of Sn-Se secondary phases. Both SnSe and SnSe 2 are found in copper-poor CZTSe absorbers where Zn/Sn   1 because the studied composition range is actually copper-poor zinc-rich and tin-rich. The Sn-Se secondary phases can be detected using X-ray diffraction, a bulk detection method. They are also detected at the absorber's surface by SEM and Raman spectroscopy. Therefore, when the Sn-Se phases are present, at least a part of them is located at the absorber's surface, which is highly detrimental to device performance. Acting as shunting paths, they reduce the device power conversion efficiency and demonstrate an apparent quantum efficiency effect under reverse bias. Removal of these phases from the surface by chemical etching greatly reduces their detrimental influence.

Description: Solar irradiation is the main potential energy source used in various processes. An accurate estimation of solar irradiation becomes a challenge due to the unavailability of weather data in Algeria. Therefore, an operated model can offer an important alternative for calculating the solar irradiation including the minimum of the input data. The present study derives a simple model from a review of our previously published work. It aims to develop a new approach for the estimation of the global irradiation on the horizontal plane only based on the measured sunshine duration. Maps of solar energy are required by many system designs; for this reason, it is mandatory to draw the global solar irradiation maps for Algeria for all types of sky. Algebraic relative errors were used as indicators of the agreement between the experimental and the calculated global irradiation. It has been proved that the highest intensity of the solar irradiation is located around the area of Djanet and Tamanrasset, whereas the less intense area extends from Skikda zone to Annaba, and more exactly in around 7° longitude.

Description: A Luminescent Solar Concentrator (LSC) greenhouse and an identical control greenhouse were constructed with photovoltaic (PV) cells attached to the roof panels of both structures. The placement and types of PV cells used in the LSC panels were varied for performance comparisons. Solar power generation was monitored continuously for one year, with leading LSC panels exhibiting a 37% increase in power production compared to the reference. The 22.3 m 2 greenhouse was projected to generate a total of 1342 kWh per year, or 57.4 kWh/m 2 if it were composed solely of the leading panel of Criss Cross panel design. The LSC panels showed no signs of degradation throughout the trial demonstrating the material's robustness in field conditions.

Description: This paper presents the performance analysis of a new maximum power point tracking (MPPT) algorithm for solar photovoltaic (SPV) system using LUO converter. For effective utilization of the SPV panel, MPPT is essential. Hence, it is significant to simplify the tracking control algorithm with faster response, reduced ripple, higher efficiency, and cost-effective system. The proposed technique performs MPPT using a simple control technique by fine-tuning the duty cycle of the converter so as to make the input resistance of converter equal to the load resistance of the solar panel. Hence, the need for proportional–integral control loop is eliminated. The performance analysis of the proposed MPPT algorithm is compared with an existing perturb-and-observe algorithm in MATLAB simulation and experiment results of the proposed MPPT is implemented with the field programmable gate array controller using LUO converter with 40 W solar panel. From the results, it is proved that the response of the proposed method is faster than the existing perturb-and-observe method under varying solar irradiation conditions for the same step size. The input and output side ripples are considerably low and also the proposed algorithm has higher efficiency and low cost.

Description: The environmental concerns are gaining importance nowadays for power producing companies in the context of clean energy act. The efforts of reducing the harmful emissions beyond a certain level are being made by most of the power utilities in the developing countries. Consequently, the minimization of harmful emissions has also become an important objective function while solving the hydrothermal scheduling problem. The heuristic approaches are considered as potential solution methodologies for non-convex hydrothermal scheduling. This paper presents an Evaporation Rate based Water Cycle Algorithm (ERWCA) for the solution of non-convex Environmental Economic Scheduling of Hydrothermal Energy Systems (EESHES). This algorithm has been evolved from the water cycle nature of raining, formation of streams, and their movement towards the rivers and finally into the sea. ERWCA has been investigated on the standard test system of EESHES with three case studies: (i) Economic Cost Scheduling, (ii) Environmental Economic Scheduling, (iii) Economic Environmental and Cost Scheduling. The comparison of obtained results with the recent results in the literature shows the superiority of ERWCA in terms of both lower fuel cost and fuel emissions. Hence, ERWCA is a worthwhile addition to the algorithms which have successfully solved this complex and combinatorial bi-objective optimization problem.

Description: With the deterioration of the global greenhouse effect, the study of carbon dioxide emissions has received more and more international attention and accurate prediction of carbon dioxide emissions is also important for the formulation of reasonable energy-saving emission reduction measures. In this paper, the genetic algorithm is used to optimize the initial connection weights and thresholds of the traditional back propagation neural network (BPNN) which can give full play to the advantages of the genetic algorithm's global search capacity and BPNN's local search. The data of Hebei province in China during the period 1978–2012 are selected to carry out the carbon dioxide emissions prediction with the established model. In the view of the choice of input variables, the coal consumption, gross domestic product, total population, and urbanization level are examined by Pearson coefficient test. Auto correlation and partial correlation are applied to analyze the inner relationships between the historic carbon dioxide emissions, thus to select the input variables of BPNN. Besides, in order to verify the validity of the built model, the residual auto correlation and partial correlation are done upon the training set. The prediction results suggest the proposed model outperforms the compared models.

Description: A recent trend of the power system is the ever increasing number of distributed generators (DGs) utilizing renewable energy sources, which have output powers that fluctuate due to unpredictable weather and ambient conditions. This causes fluctuations in system frequency and bus voltages, resulting in poor quality power, higher prices for electricity, and increased chances of reverse power flow and voltage collapse. In order to allow higher levels of DG penetration, methods of reducing the effects of fluctuations must be implemented. This paper proposes a method to mitigate these fluctuations using controllable loads such as heat pump water heaters (HPs) and battery storage systems. The HPs are controlled using a decentralized bang-bang (on/off) control based on the cumulative distribution of water temperature of HPs in the local area and the local frequency. Battery systems are controlled using a smart frequency and voltage droop characteristics based control. The decentralized bang-bang control mitigates local frequency fluctuations by increasing active power consumption to lower frequency as well as decreasing active power consumption to increase the frequency. The smart droop characteristics based control applies a commonly used droop characteristics control to voltage and frequency; however, the control system monitors the state of charge (SOC) of the battery system and takes appropriate actions to prevent the SOC from reaching a critical level. The results of simulations show that fluctuations in frequency and bus voltage are mitigated by the application of the proposed control methodologies without adversely affecting the comfort level of consumers.

Description: This paper presents a model-based algorithm for fast tracking of maximum power point of a photovoltaic panel. Parameters of an equivalent circuit have been estimated based on experimental data and characteristic data provided by manufacturer. Since photoelectric current is highly temperature-dependent, the effect of temperature is considered in the model. The proposed method is based on the maximum power point locus of the solar panel. So the tracking speed is much faster than a model-free method. In the suggested technique, the voltage of maximum power point can be determined using output voltage and current of solar panel and the voltage of a point on the maximum power point locus with the same current, in three steps. The main novelty of the proposed model-based method is that there is no need to measure solar radiation. Experiment results are presented and prove the feasibility of the proposed maximum power point tracking method.

Description: A new simulation tool aimed at characterizing the thermal behavior of parabolic trough collectors over a wide range of pressures and gas mixtures in the vacuum chamber is presented in this study. The model is able to accurately predict overall efficiency and heat losses obtained in a number of experimental sources based on both on-sun and off-sun testing, with vacuum in the annulus and no hydrogen. Excellent agreement of the simulations with experiments including different gas compositions, especially with high hydrogen concentrations, is achieved through the use of molecular dynamics results for the determination of the accommodation coefficient of the mixture. Additional experiments were carried out to validate the accuracy of the model over a range of pressures between 10 −4 and 130 mbar. The accurate modelling of rarefied gas dynamics presented here also leads to an excellent agreement between simulations and experiments over the whole pressure range. An accurate determination of the performance in such extreme conditions is critical for an adequate Operation & Maintenance strategy, as well as the development of effective predictive and preventives plans.

Description: Study on how renewable energy use and economic growth interact with each other has been an active area of research. This study examines the impacts of renewable energy production (and consumption) on local economic development and income, for a panel data of the 31 provinces of China over the period 2000–2010 within a multivariable framework. Using regression with panels corrected standard errors, this study investigates the effects of renewable energy use on provincial real gross domestic production and local rural income. It is found that deployment of renewable energy use in rural areas has shown significant positive effects on income increase of rural households. But in general, most renewable energy use has negative impacts on economic growth except hydro power generation, improving the economic efficiency of renewable energy production and adjusting renewable energy related subsidy policies are of prime importance.

Description: There is an imperative need of developing new strategies and models for meeting the swelling demand of electricity in developing nations like India. One of the promising models for this would be Decentralized Distributed Generation (DDG). DDG locates the power generating source closer to the consumer utilizing locally available Renewable Energy (RE) resources, thereby decreasing the Transmission and Distribution (T&D) losses. Despite the numerous advantages with DDG, there have been some minor issues preventing its large scale deployment and utilization in India. This paper discusses the various technology options which can be used for DDG in India and the problems which the Indian power sector has been facing for a long time. This paper aims to provide a complete analysis of the best possible RE based technology options for DDG in India along with their cost of generation, benefits, barriers, applications, and the possible pathways for its deployment.

Description: Energy, especially oil, plays a special and irreplaceable role in the economic development, modern civilization, and social progress. With the rapid growth over the past few decades, China has gradually become a big power in oil consumption. In order to solve the contradiction between supply and demand as well as minimize social costs, it is necessary and useful to forecast the trend of China's oil consumption. In addition, reasonable and effective oil production and scheduling through forecasting progress also makes an important impact on the health economic development, social stability, and sustainable development. However, it is a challenging task to carry out such a forecasting because oil consumption is influenced by a number of factors, such as technology development, economic level, government policy, natural disaster, unexpected politic events, and so on. Therefore, it is difficult to forecast such a complex system with a single traditional model. This paper proposes an improved hybrid method known as GGNN, which combined the grey models, the back propagation (BP) neural network, and the genetic algorithm (GA) to take the advantages of linear model, nonlinear model, and swarm intelligence optimization, respectively. GM (1, 1) and improved grey models including an unbiased GM (1, 1), initial correction GM (1, 1), p value GM (1, 1), and background value GM (1, 1)are applied to capture the linear information. BP is widely used due to its nonlinear mapping capability; in this paper, it is used to capture the nonlinear information. Moreover, the GA is also applied to obtain the optimum weights and thresholds of the GGNN which is made up of all grey models and BP neural model. The superiority of this proposed method is examined by using the historical data of China's oil consumption. Assessment results demonstrate that the proposed method GGNN can improve the forecasting accuracy compared with some other existing methods.

Description: Anomalously strong change of ferromagnetic ordering parameters upon a small variation of aluminum content was revealed in low-temperature experimental studies of electrical resistivity and galvanomagnetic properties of iron-vanadium-aluminum magnetic alloys with the compositions near the stoichiometric Fe 2 VAl. By comparing the temperature and magnetic field dependences of the electrical resistivity and Hall effect in Fe 2.1 V 0.91 Al 0.99 and Fe 2.05 V 0.91 Al 1.04 alloys, it was shown that a small increase of aluminum content leads to doubling of the Curie temperature and a sharp change in the temperature dependences of the magnetoresistance and saturation of the spontaneous magnetization.

Description: Specific heat C M ( T ) of polycrystalline Dy 0.6 Y 0.4 Rh 4 B 4 and Dy 0.6 Y 0.4 Rh 3.85 Ru 0.15 B 4 was studied in the temperature range of 0.5–9 K and magnetic fields 0–10 kOe for the first time. It was found that the λ-anomaly in the specific heat exists at T c ≈ 6 K for Dy 0.6 Y 0.4 Rh 4 B 4 and at T c ≈ 6.6 K for Dy 0.6 Y 0.4 Rh 3.85 Ru 0.15 B 4. It is suppressed in a magnetic field and shifted to lower temperatures. Partial substitution of Rh by Ru enhances superconductivity, presumably, due to stronger inner magnetism of the dysprosium sublattice in Dy 0.6 Y 0.4 Rh 4 B 4 as compared with Dy 0.6 Y 0.4 Rh 3.85 Ru 0.15 B 4 . Furthermore, it was observed that the molar heat capacity C M ( T ) of Dy 0.6 Y 0.4 Rh 3.85 Ru 0.15 B 4 increases with decreasing temperature for T 〈 4 K. In Dy 0.6 Y 0.4 Rh 4 B 4 , an increase in C M ( T ) with decreasing temperature is accompanied by the appearance of a maximum at T max = 1.5 K, which might be a manifestation of the magnetic phase transition in the dysprosium subsystem at this temperature.

Description: The thermoluminescence spectra of impurity-helium condensates (IHC) submerged in superfluid helium have been observed for the first time. Thermoluminescence of impurity-helium condensates submerged in superfluid helium is explained by neutralization reactions occurring in impurity nanoclusters. Optical spectra of excited products of neutralization reactions between nitrogen cations and thermoactivated electrons were rather different from the spectra observed at higher temperatures, when the luminescence due to nitrogen atom recombination dominates. New results on current detection during the IHC destruction are presented. Two different mechanisms of nanocluster charging are proposed to describe the phenomena observed during preparation and warm-up of IHC samples in bulk superfluid helium, and destruction of IHC samples out of liquid helium.

Description: X-ray diffractometry is used to study samples of type PM-A group B polyimide (Kapton H) subjected to uniaxial tension at room temperature and cooling to liquid nitrogen and helium temperatures. An asymmetry in the halo of the diffraction pattern from the amorphous sample is observed as a result of deformation and cooling of the samples. Deformation and cooling are found to have different effects on the intensity distribution. Thus, deformation produces “stretched” regions, while cooling produces “compressed” regions. An analysis of the diffraction patterns shows that uniaxial tension leads to partial ordering of the polyimide molecules in a sample along the direction of the applied load. The observed changes in the structure during cooling of films may indicate that mutual ordering of some of the molecules relative to one another is taking place.

Description: Integrated phosphorescence spectra of meta-bromobenzophenone crystals were measured in the temperature range from 1.6 to 297 K. The spectra were found to contain two series of monomeric bands associated with the stretching mode of the C=O carbonyl at all temperatures. Above 70 K in the red spectral region, a broad structureless band of unknown nature was observed, the center of gravity of which was shifted to red with increasing temperature. The above phenomena and others anomalies can be due to the structural properties of both the molecule and the crystal.

Description: The energy spectrum of a quasi-two-dimensional electron gas in an in-plane magnetic field is studied using the perturbation theory and quasiclassical approach in the presence of the Rashba and Dresselhaus spin-orbit coupling. The existence of the intersection of energy sublevels in electron spectrum is demonstrated. The reciprocal mass tensor of electrons is analyzed. The heat capacity of the degenerate electron gas is examined, and its relations with the key features of the spectrum are shown.

Description: We discuss and analyze the dependence spectra of the transmission coefficient T on the quasiparticle energy E of one variety of graphene-based Fibonacci superlattices (SL). The SL is built from armchair graphene nanoribbons (GNR), and the quasi-periodicity is produced by metal-like (MGNR) and semiconductor (SCGNR) ribbons, placed along the lattice growth axis in accordance with the Fibonacci sequence, which are used as individual SL elements. It is shown that the difference in the values of quantized transverse quasi-momentum of electrons in MGNR and SCGNR is enough to form an effective quasi-periodic modulation in the examined structure (no additional factors required), and the optimal nanoribbon width range for this purpose is determined. We also analyzed the dependence of the spectral properties of the test structure on the geometric parameters of the superlattice, and the external electrostatic potential. We paid particular attention to the fact that each Fibonacci generation had a Dirac superlattice band gap. The results of the study can be useful in the determination of optimal parameters for graphene-based nanoelectronic devices.

Description: Quasistable laminar flow of He II at a temperature of 140 mK is studied experimentally. The liquid flow was excited by a vibrating quartz tuning fork with a resonance frequency of about 24 kHz. It was found that for velocities of the tuning fork oscillations from 0.046 to 0.16 m/s, the He II flow can be both quasistable laminar and turbulent. Transitions between these flow regimes were observed. When the velocity of the tuning fork oscillations increases more rapidly, the velocity at which the quasistable flow becomes unstable and undergoes a transition to a turbulent flow is higher. Mechanisms for the dissipation of the energy of the oscillating tines of the tuning fork in the quasistable laminar flow regime are analyzed. It is found that there is an additional mechanism for dissipation of the energy of the oscillating tuning fork beyond internal friction in the quartz. This mechanism is associated with mutual friction owing to scattering of thermal excitations of He II on quantized vortices and leads to a cubic dependence of the exciting force on the fluid velocity.

Description: We study the dynamics of a qubit-resonator system, when the resonator is driven by two signals. The interaction of the qubit with the high-amplitude driving we consider in terms of the qubit dressed states. Interaction of the dressed qubit with the second probing signal can essentially change the amplitude of this signal. We calculate the transmission amplitude of the probe signal through the resonator as a function of the qubit's energy and the driving frequency detuning. The regions of increase and attenuation of the transmitted signal are calculated and demonstrated graphically. We present the influence of the signal parameters on the value of the amplification, and discuss the values of the qubit-resonator system parameters for an optimal amplification and attenuation of the weak probe signal.

Description: The previously derived equations for the components of the order parameter (OP) of dense superfluid neutron matter (SNM) with anisotropic spin-triplet p-wave pairing and with taking into account the effects of magnetic field and finite temperatures are reduced to the single equation for the one-component OP in the limit of zero magnetic field. Here this equation is solved analytically for arbitrary parametrization of the effective Skyrme interaction in neutron matter and as the main results the energy gap (in the energy spectrum of neutrons in SNM) is obtained as nonlinear function of temperature T and density n in two limiting cases: for low temperatures near T = 0 and in the vicinity of phase transition temperature T c 0 ( n ) for dense neutron matter from normal to superfluid state. These solutions for the energy gap are specified for generalized BSk21 and BSk24 parametrizations of the Skyrme forces (with additional terms dependent on density n ) and figures are plotted on the interval 0.1 n 0 〈 n 〈 2.0 n 0 , where n 0 = 0.17 fm −3 is nuclear density.

Description: An analysis of known experimental literature data on the temperature dependence of magnetic susceptibility of beryllium. It is shown that this dependence can be explained if we take into account that beryllium has an electron topological transition of 3½ kind near the Fermi level.

Description: The electronic structure and optical properties of the SmNi 5– x Cu x ( x = 0, 1, 2) compounds are studied. The band spectra of the studied intermetallics were calculated with LDA + U + SO method supplementing the local density approximation with a correction for strong electron interaction on the shell of the rare-earth element. Optical properties were studied by ellipsometry method in the wide wavelength range. It was found that the substitution of copper for nickel leads to local changes in the optical conductivity spectra. Both the spectroscopic measurements and theoretical calculations demonstrate the presence of a broad absorption band around 4 eV associated with the Cu 3 d → Ni 3 d electron transitions and increasing with the grown of copper content. The experimental dispersion curves of optical conductivity in the interband absorption region were interpreted using the results of the calculations.

Description: Magnetoresistance Δρ( H , T ) of several heavy-fermion compounds, CeAl 2 , CeAl 3 and CeCu 6 , substitutional solid solutions with quantum critical behavior CeCu 6– x Au x ( x = 0.1, 0.2) and alloys with magnetic ground state Ce(Al 1– x M x ) 2 (M = Co, Ni, x ≤ 0.8) was studied in a wide range of temperatures (1.8–40 K) in magnetic fields up to 80 kOe. It was shown that a consistent interpretation of the field dependences of the resistance for both non-magnetic and magnetically ordered cerium-based intermetallic compounds with strong electron correlations can be achieved within the framework of an approach that accounts for scattering of charge carriers by localized magnetic moments in a metal matrix. Within this approach, three different components of the magnetoresistance of cerium intermetallic compounds were identified: the negative Brillouin contribution proportional to the local magnetization ( − Δ ρ / ρ ∼ M loc 2 ), the alternating linear contribution ( Δ ρ / ρ ∼ H ) and the magnetic component, saturating in magnetic fields below 15 kOe. In the framework of the Yosida model for the cerium alloys under study, estimates of the local magnetic susceptibility χ loc ( H , T 0 ) were obtained from the magnetoresistance data. Numerical differentiation of the magnetoresistance with respect to the magnetic field and analysis of the obtained d ( Δ ρ / ρ ) / d H = f ( H , T ) dependences allowed us to reconstruct the H–T magnetic phase diagrams of the strongly correlated electron systems under study as well as to examine the effects of spin polarization and renormalization of the electronic states on charge transport both in the regime of quantum critical behavior and in the magnetically ordered state.

Description: We consider the field dependence of magnetization in the paramagnetic phase of manganese monosilicde, MnSi, which is characterized by an anomalously large effective magnetic moment μ* = 5.3μ B , and a small saturation magnetization M 0 = 0.3μ B /Mn. It follows from the conducted analysis, that neither the theory of band magnetism, nor the cluster approach can explain the experimental data, but an adequate description is possible within the framework of the spin-polaron model, in which the spin-polaron is a quasi-bonded state of the band electron and localized magnetic moment of Mn. It is found that the inclusion of specific interaction for a simple ferrimagnet-like configuration that characterizes the spin-polaron, allows us to explain the experimental data, wherein the observed values of μ* are not associated with large localized magnetic moments in the sample volume. The possible methods of experimental verification of the spin-polaron model are analyzed, including experimentum crucis . The obtained results show that the paramagnetic phase of MnSi should be regarded as a phase in which its physical properties are determined by the magnetic inhomogeneities on a nanometer spatial scale.

Description: The extraction of maximum power from solar photovoltaic (PV) using Maximum Power Point Tracking (MPPT) methods is a promising research area in the recent past. Many methods including conventional methods, such as Hill Climbing and Incremental Conductance, and methods based on neural network, Fuzzy logic and bio-inspired algorithms, were proposed for MPPT application. However, all these methods suffer from drawbacks such as slower convergence, reduced power output, predominant steady state oscillations, larger memory requirement, and complex structure. Hence, in this paper an attempt is made to enhance existing Particle Swarm Optimization technique by emphasizing proper initial value selection. The key features of this method include the ability to track the global peak power accurately under partial shading conditions with almost zero steady state oscillations, faster dynamic response, and easy implementation. Simulations are carried out for different shading patterns and the results obtained are compared with existing methods. Further, simulation results are validated via experimental values.

Description: This study presents full transient numerical simulations of a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type) with particular emphasis on the analysis of hydrodynamic characteristics. Turbine design and performance are studied using a time-accurate Reynolds-averaged Navier–Stokes commercial solver. A physical transient rotor-stator model with a sliding mesh technique is used to capture changes in flow field at a particular time step. A shear stress transport k-ω turbulence model was initially employed to model turbulent features of the flow. Two dimensional simulations are used to parametrically study the influence of selected geometrical parameters of the airfoil (camber, thickness, and symmetry-asymmetry) on the performance prediction (torque and force coefficients) of the turbine. As a result, torque increases with blade thickness-to-chord ratio up to 15% and camber reduces the average load in the turbine shaft. Additionally, the influence of blockage ratio, profile trailing edge geometry, and selected turbulence models on the turbine performance prediction is investigated.

Description: This paper reports the effects of engine design and operating parameters such as stroke length, ratio of bore to stroke length, compression ratio, equivalence ratio, engine load, biodiesel percentage, friction coefficient, engine speed and mean piston speed on engine performance and energy losses by experiments and a theoretical model based on the finite-time thermodynamics. In this study, the performance of a single cylinder, four-stroke, direct injection diesel engine fueled with diesel-biodiesel mixtures has been experimentally and theoretically investigated. The simulation results agree with the experimental data. After model verification, parametrical studies have been conducted for various conditions. The results showed that the biodiesel percentage and the cycle pressure ratio affect positively the engine performance. The friction coefficient has negative influence on the engine performance. The effective efficiency decreases with the increasing of the engine load, stroke length, and engine speed but effective power increases with increasing them. The effective power always increases with the increasing mean piston speed. However, the effective efficiency decreases at the constant stroke length condition, as it increases at the constant engine speed condition. The effective power and the effective efficiency increase with increasing equivalence ratio to a specified value and then begin to decrease for constant bore/stroke length conditions. The effective efficiency increases with decreasing equivalence ratio as effective power has an optimum value for constant compression ratio condition. The effects of bore/stroke length change at different conditions. At the constant compression ratio condition, the engine performance increases with increasing ratio of bore to stroke length. They are the optimum values which provide the maximum effective efficiency and maximum effective power at the other conditions. This study also reports the energy losses as the ratio of fuel energy and they are classified as friction losses, incomplete combustion losses, heat transfer losses, and exhaust losses. They are defined with respect to compression ratio. With the increasing compression ratio, the friction losses are constant for constant cycle temperature ratio and equivalence ratio, whereas the incomplete combustion losses increase at a constant cycle temperature ratio condition and are constant at constant equivalence ratio condition. The heat transfer losses increase and the exhaust losses decrease for both the conditions. The presented model could be used to optimize the performance of diesel engines fueled with biodiesel and it can be developed for all kinds of engines running at different conditions with various fuels.

Description: Exchange bias phenomenon, evident of antiferromagnetic–ferromagnetic phase segregation state, has been observed in (Nd 1− x Y x ) 2/3 Ca 1/3 MnO 3 ( x = 0, 0.1) compounds at low temperatures. A contribution to the total magnetization of the compounds due to the ferromagnetic phase has been evaluated. It has been found that yttrium doping leads to the growth of the ferromagnetic phase fraction. The ferromagnetic phase in the doped compound has a lower coercivity H c and more rectangular form of the hysteresis loop. The values of the exchange bias field H EB and coercivity are found to be strongly dependent on the cooling magnetic field H cool . In sufficiently high magnetic fields, H cool 〉 5 kOe, H EB in the doped compound is about twice as low as in the parent compound. This difference is attributed to a lower exchange interaction and higher saturation magnetization of the ferromagnetic phase in (Nd 0.9 Y 0.1 ) 2/3 Ca 1/3 MnO 3 .

Description: The construction and operating principle of a pendulum magnetometer for measuring the magnetic susceptibility of solids under high gas pressures are described. This device is distinctive in having the pendulum mounted directly in the high pressure chamber. Experimental plots of the susceptibility of the compound V 4 S 9 Br 4 as a function of pressure up to 2 kbar at temperatures of 60–300 K are presented as an example of the use of the magnetometer.

Description: A study of the magnetocaloric effect for Tm 2 Fe 16 , Tm 2 Fe 17 , Tm 2 Fe 18 , Tm 2 Fe 19 , Tm 2 Fe 17− x Mn x ( x ≤ 1.5), Ce 2 Fe 17− x Mn x H y ( x 〈 2, y ≤ 3), Lu 2 Fe 17− x Mn x ( x ≤ 2) systems at magnetic ordering temperatures T C , T N and a ferro-antiferromagnet phase transition Θ T , from magnetization measurements. In alloys with ground ferromagnetic and high-temperature antiferromagnetic states, the change in the magnetic entropy peak −Δ S M increases as the magnetic phase transition temperatures Θ T and T N converge with varying compound composition. Extrapolating the difference T N − Θ T to zero for the initial and doped alloys allows us to determine the maximum possible value of −Δ S M in such systems and the composition of the corresponding alloy. A superposition of the −Δ S M (T) maxima at Θ T and T N for compounds with two magnetic phase transitions creates much higher values of relative cooling power in comparison to compounds with only one magnetic phase transition at T C .

Description: The electronic structure of (Ti,Mn)O 2 diluted magnetic semiconductors was investigated theoretically from first principles using the fully relativistic Dirac linear muffin-tin orbital band structure method. The electronic structure was obtained with the local spin-density approximation taking into account strong Coulomb correlations in the frame of the LSDA + U approximation. The x-ray absorption spectra and x-ray magnetic circular dichroism spectra at the Mn and Ti L 2,3 and O K edges were investigated theoretically from first principles. The origin of the XMCD spectra in these compounds was examined. The calculated results are compared with available experimental data.

Description: In this paper, the energy efficiency of airlines is measured. Number of employees and tons of aviation kerosene are chosen as the inputs. Revenue tonne kilometers, revenue passenger kilometers, and total business income are the outputs. Capital stock is selected as the dynamic factor. A new model, Virtual Frontier Dynamic range adjusted measure (RAM), is proposed to calculate the energy efficiencies of 22 airlines from 2008 to 2012. In Virtual Frontier Dynamic RAM, the reference DMU (decision-making unit) set and the evaluated DMU set are two different sets to distinguish between efficient DMUs. The results demonstrate the following: (1) Air Greenland exhibits the highest energy efficiency, while the efficiency score of Air France-KLM is at the bottom of the 22 airlines. (2) Aggregate airline energy efficiency consistently increased from 2008 to 2012.

Description: A new type of n-p-n transistor photovoltaic device based on CdS/multi-wall carbon nanotube (MWNT)/n-Si configuration was fabricated in a facile process. CdS quantum dots were deposited on fluorine-doped tin-oxide glass using a chemical bath deposition method, and MWNT film was coated on n-type Si substrate by airbrushing. The materials used for the n-p-n transistor solar cells were characterized by multiple techniques including X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman, Ultraviolet visible (UV-vis) spectrophotometer, and I-V characteristic measurements. The CdS layer acts as a good n-type material for the transistor solar cells. The thickness of the CdS layer can be controlled by the chemical bath deposition time to achieve different photovoltaic responses. I-V characteristic measurements show that the efficiency increases with increasing the thickness of the CdS thin layer. Compared with the tandem solar cells based on (p/n)–(p/n) semiconductor junctions, our n-p-n transistor solar cell has a simple structure without using tunnel junctions or wafer bonding schemes for interconnecting the cells.

Description: This study proposes a new method for direct generation of synthetic wind power time series for a wind farm. The method combines the random nature of wind with the operational information of the wind turbines (i.e., failure and repair rates). It uses chronological or sequential Monte Carlo Simulation instead of non-sequential one due to its usefulness and flexibility in preserving statistical characteristics of the chronological processes. The validity of the synthetic values generated by the proposed method and the conventional Markov Chain Monte Carlo methods is compared with the measured data in terms of average and variance values, Probability Distribution Function, and Auto-Correlation Function. Due to increasing interest in the use of the storage system in paralleling with wind power generation, a practical application of the proposed method is also included. Optimal sizing of various energy storage technologies is obtained through a cost-benefit analysis in a typical Micro-Grid.

Description: Food waste along with its two individual components, noodle waste and rice waste, were tested for bio-hydrogen production by using sludge as a source of mix consortia of Clostridium under different physical conditions (pH 5, 6, and 7; temperature 37 °C and 55 °C). The increase in pH increased the bio-hydrogen yield for all tested wastes, whereas an increase in temperature increased the bio-hydrogen yield just for food waste. The highest experimental yield of 115.76 ml/VS removed was produced in the mesophilic noodle waste reactor at pH 7. The drop in pH from 7 to 4.8 ± 0.2 was found optimum for bio-hydrogen production for all tested wastes under mesophilic as well as thermophilic conditions. Most of the hydrogen production was observed within 72 h of incubation, which can be used as the optimum bio-hydrogen production period for food waste. The bio-hydrogen yield, final volatile fatty acids (VFA), and glucose consumption at 72 h were analyzed with the help of the response surface methodology. The resultant plots represented an increase in glucose consumption with the increase in pH from 5 till pH 6 ± 0.5, after which glucose consumption started to decrease up to pH 7. The final VFA represented a similar trend as that observed for glucose except that the change in VFA production was observed due to the temperature and transition was observed at 47.5 ± 1.5 °C for food waste as well as for noodle waste.

Description: A new approach based on the use of external frequency converters for Nd:YAG solar pumped lasers providing effective conversion of solar-to-laser power is proposed. The possibility of a more than four-fold increase in Nd:YAG solar pumped laser efficiency is shown by the simulation calculation method.

Description: This paper uses monthly data for the time span 2006:M01 to 2014:M06, to study the relationship between electricity generation regimes, both ordinary and special, and economic activity in Portugal. An autoregressive distributed lag bounds test approach is pursued to analyse the short- and long-run dynamics between renewable/non-renewable electricity sources and industrial production. Results show that both ordinary thermal sources and hydro sources are driving forces behind electricity from the special regime. Economic activity is stimulating the special regime, but, conversely, the special regime hampers the growth of industrial production. It is demonstrated that a crucial role is being played by large-scale hydropower in accommodating the special regime in the electricity mix. This source is causing economic activity, while at the same time, backing up new renewable sources.

Description: CuZnS is a new promising material in thin film photovoltaics which is earth abundant and eco-friendly. Its electrical and optical properties can be controlled by varying atomic ratios of Copper and Zinc, so as to use it as absorber or window layers. Type of conductivity of this material can also be changed from n to p by adjusting Cu/Zn value. In the present work, we report improvement of cell parameters of CuZnS/In 2 S 3 hetero junction considerably from our own earlier reported values just by increasing Cu to Zn ratio in CuZnS. Current density increased from 5.4 mA/cm 2 to 10.7 mA/cm 2 , thereby enhancing conversion efficiency from 1% to 1.95%. Results are explained on the basis of improvement of multiple band structure.

Description: Lithium iron phosphate (LiFePO 4 ) batteries are widely used as power batteries for electric vehicle applications. For safety issues, it is important to estimate the State of Charge (SOC) of a battery accurately. The improved Thevenin equivalent circuit model is established according to the characteristics of the LiFePO 4 battery, and the model parameters are identified by experimental testing. Furthermore, a novel algorithm of SOC online estimation is proposed, which combines the open-circuit voltage method, ampere-hour integration, and Kalman filtering. The simulations and experimental results show that the improved Thevenin equivalent circuit model can enhance the accuracy of SOC estimation. This proposed algorithm could estimate the SOC precisely even with inaccurate initial values and current measurement errors and distinguish the performances between the batteries. The performance of the proposed SOC estimation method when the voltage sensor is unavailable has been investigated and presented as well. From the characteristics mentioned above, this novel approach is able to guarantee the reliability and safety of the batteries.

Description: The availability of reasonably accurate global solar radiation data is vital for the success of any solar project. However, only a few meteorological stations around the world capture these data as a result of the high cost of measuring equipment and the lack of technical capability in calibrating them. In an attempt to resolve this challenge, engineers and researchers have developed various alternatives to generate the data. In this paper, we surveyed the methods used in generating synthetic global solar radiation with a view to classifying them and bringing out the advantages and the challenges of each. This could motivate the development of a new set of robust prediction techniques that combines the strengths of different existing models for prediction purposes. The various prediction techniques can be generally classified into four categories: the regression techniques, the artificial intelligence methods, the statistical approaches, and the satellite imagery techniques. It is shown from the review that the regression techniques are widely used for the prediction of global solar radiation because of their simplicity. However, their accuracy depends on the completeness of the meteorological data employed in predicting global solar radiation. The statistical methods are based on the assumption that data have an internal linear structure that can be identified and used for prediction purposes. However, it is observed in the literature that the techniques, especially the time series techniques, are generally not good for short time prediction as the error in the prediction of the next value in a series is usually large. Satellite imagery is desirable if surface data for location does not exist. Generally, the use of surface measurements together with a cloud index based on satellite imagery is encouraged to increase the accuracy of prediction. Artificial intelligence methods have been generally favoured for their capability to handle complex relationships between the global solar radiation and the other meteorological data, and as well provide better accuracy and efficiency. This paper is important to engineers and researchers who are interested in the global solar radiation prediction methods.

Description: When the photovoltaic (PV) system is fully illuminated, the voltage-power characteristic of the array has one maximum power point (MPP). This point can be tracked by conventional maximum power point tracker algorithms. On the other hand, in partially shaded PV, the voltage--power characteristic has only one global MPP (GMPP) and multiple local MPPs. It is important to operate the PV system at GMPP for achieving optimal operation. This paper presents the application of two novel meta-heuristic optimization algorithms to extract GMPP from the PV system under partial shading conditions: The mine blast algorithm (MBA) and the teaching learning based optimization algorithm (TLBO). A proposed constrained objective function representing the PV array output power is also presented. Different patterns of shadows that strike the PV array surface are studied. The studied patterns are uniform ones, changing from 0% to 375% with steps of 25%, and non-uniform patterns with different locations of GMPP. The obtained results from each algorithm are compared, and the results show that the MBA based tracker is more reliable, more efficient, and superior to TLBO. A comparison with fuzzy logic control and adaptive neuro-fuzzy and particle swarm optimization based trackers has been done. The results ensure that the reliability of the MBA in solving the problem is addressed.

Description: Aiming at the multiple peaks phenomenon on the power-voltage characteristic curve of photovoltaic (PV) array under partially shaded conditions, this paper proposes a fast global maximum power point tracking method based on sliding mode control (SMC). First, according to the operating characteristics of PV arrays, a reduced scanning range is adopted to avoid large power fluctuations and the optimal scanning direction of global maximum power point (GMPP) is determined to avoid the repeating scanning of the PV curve, both of which reduce the scanning time greatly. Second, during the scanning and tracking process, SMC is introduced to move the operating point quickly to the reference value, which improves the scanning speed further. Finally, when the operating point is close to the GMPP, the control mode is switched from the SMC based tracking control to the SMC based maximum power point tracking control, which quickly stabilizes the operating point of the PV array at the GMPP, reducing the power ripple during steady-state operation. Furthermore, the proposed method is independent of PV parameters, due to the new open circuit voltage detection method proposed in this paper, which does not occupy extra time. Simulation and experimental results validate that the proposed method can guarantee accurate convergence to the GMPP with fast tracking process and low energy loss under partially shaded conditions.

Description: Geothermal heat pumps have several advantages over conventional heating and cooling systems. They can operate in both winter and summer, have high efficiencies, and do not directly emit any greenhouse gases during operation. Investors (in developing countries) can use Clean Development Mechanism as a source of financing for new or existing renewable energy facilities by selling Certified Emission Reductions credits (CERs), which represent the amount of CO 2 emission (1 CER = 1 tCO 2 eq) that is avoided using renewable energy. The aim of this paper is to analyze the possibility of CO 2 reduction by using geothermal heat pumps for fossil fuel displacement with applying Clean Development Mechanism. Results have shown that by using geothermal heat pumps during a 7-year crediting period, the estimated emission reduction would be 79.45 tCO 2 (equal to 80 CERs), enabling the investor to achieve profit from selling 80 CERs and thus helping to fund the proposed project activity. Three main factors which influence the amount of CO 2 reduction have been identified: carbon-dioxide emission factor for electricity source, efficiency of technology used for baseline scenario, and coefficient of performance (COP) of heat pumps.

Description: The utilization of lignocelluloses for biogas production is limited for several aspects, and an efficient pre-treatment is essential to increase the enzyme accessibility of cellulose. This research focused on the mechanism of biogas production and biodegradation properties under the treatments with different acid agents, including sulfuric acid (H 2 SO 4 ), acetic acid (CH 3 COOH), and phosphoric acid (H 3 PO 4 ). The H 3 PO 4 pretreated corn stover was then co-digested with cow dung in a pilot test to investigate the performance of acid pretreatment in practice. The results showed that the main compositions of corn stover were cellulose, hemicellulose, and lignin, and their proportions in the corn stovers were increased after the acid pretreatments. This hence increased the final biogas yields (up to 40.75%), methane content, and promoted the biodegradation process. More significantly, the acid pretreatments delayed the appearance of the peak value of the biogas yield for 3 to 8 days depending on the acid concentrations. This study proposed that the dilute weak acid pretreatment, especially H 3 PO 4 pretreatment, efficiently enhanced the biogas production by increasing the degradation of hemicellulose. Further on, the H 3 PO 4 pretreatment also improved the stability of fermentation, which would benefit the biogas generation in practice. This research contributes to a better understanding of the mechanism of acid influence on enhancing the biogas generation and substrate biodegradation, and provides pratically sound guidance for reclamation of lignocellulosic materials.

Description: A 1 kW e integrated auxiliary power unit (APU) system consisting of an autothermal reformer and a solid oxide fuel cell (SOFC) unit, as well as balance-of-plant components, was designed and analyzed. A relatively easy-to-approach SOFC model was developed in order to conveniently calculate V-I and P-I curves and the system's net efficiency at different operating conditions. The effects of steam to carbon and oxygen to carbon ratios in the reactants, channel dimensions of the SOFC unit, and hydrocarbon fuel types on the integrated APU system's performance were discussed. Five hydrocarbon fuels including diesel, Jet-A, gasoline, ethanol, and methanol were studied as fuel sources for the APU system. The system's net efficiency around 35% is possible for all the tested fuels in the current density range of 100–400 mA/cm 2 . The APU system was also verified to be thermally self-sustainable in the steady state operation by a thermal management analysis.

Description: This study describes a method to quantify the visual impact of an offshore wind farm, as seen from the coast. In brief, the method involves distinguishing between the visual impact due to the intrusion in the observer's vision field and the un-aesthetic effect of the arrangement unevenness. Both parameters, visual intrusion and unevenness, can be quantifiable; therefore, a final indicator for the visual impact of the wind farm can be calculated for a specific wind farm layout. Two approaches are presented to calculate the visual intrusion, which give rise to similar results. The method has been programmed and included in an application that has been tested with two known wind farm layouts, showing a complete coherence of the results given by the method. This method provides the designer with a tool that allows him to take into account the estimated visual impact of a wind farm under study. If an algorithm is used to look for the optimum location/layout for an offshore wind farm, its programmer can include this method in order to obtain a trade-off between maximum profitability and minimum visual impact.

Description: F-I-S tunnel junctions of Co 2 CrAl-I-Pb and Co 2 Cr 0.6 Fe 0.4 Al-I-Pb based on films of semimetal ferromagnetic Heusler alloys Co 2 CrAl (Curie temperature T C ≈ 334 K) have been fabricated and the features of spin-polarized current in them studied. A theoretical model of spin blocking of the tunnel current shows that the degree of spin polarization of the conduction electrons in quasi-single crystal films of Co 2 Cr 0.6 Fe 0.4 Al and Co 2 CrAl with B 2- and L 2 1 -type order is 0.91–0.97.

Description: We report an experimental investigation of the electric response of superfluid helium. Our results confirm the presence of electric potential that appears at the relative oscillatory motion of normal fluid and superfluid components in helium generated by the heater. The resonance of the electric potential was observed in the first four harmonics. A suggested method for the detection of the electric response allows the required resonance peak to be distinguished from spurious signals. Our results are in qualitative agreement with the data published by previous researchers. The reasons for the discrepancy in the measured values of the potential difference are discussed.

Description: A continuation of the theoretical study of the intrinsic properties of dislocation and crowdion structural defects in 2D crystals [V. D. Natsik and S. N. Smirnov, Fiz. Nizk. Temp. 40 , 1366 (2014) and V. D. Natsik and S. N. Smirnov, Fiz. Nizk. Temp. 41 , 271 (2015)]. The atomic lattice model of conservative (glide) and non-conservative (climb) defect movement is discussed in detail. It is shown that given a continuum description of the 2D crystal, an individual defect can be examined as a point carrier of plastic deformation, its value being determined by the topological charge, which is compliant with the crystal geometry defect parameters. It is found that the strain rate depends on the rate at which the defect center moves, as well as its topological charge. The elastic forces acting on the dislocation and crowdion centers in the field of applied mechanical stresses, and the forces of elastic interaction between defects, are calculated in terms of the linear theory of elasticity of a 2D crystal. The non-linear effect pertaining to the interaction between defects and bending deformation of the crystalline membrane, which is specific to 2D crystals, is also discussed.

Description: The main aim of this paper is to review different optimization techniques and to describe the importance of the Honey Bee Mating Optimization (HBMO) Algorithm for the modeling of fuel cells. HBMO algorithm is a nature inspired one that simulates the process of real Honey Bee Mating and the natural foraging behavior of honey bee has been discussed. The objective function has been framed for the static modeling of proton exchange membrane fuel cell by considering certain constraints. HBMO is implemented to optimize the appropriate parameter and it is mainly dependent upon the parameter decisions; therefore, it results in improved computation. The proposed HBMO is compared with the conventional algorithms like simulated annealing, pattern search, particle swarm, and genetic algorithm reported in the literature. By using the HBMO technique, the electrical, fuel processor, hydrogen, oxygen, and water response times are analyzed and compared with the other algorithms. The results are validated. The proposed HBMO algorithm surpasses the above mentioned optimizers in terms of accuracy.

Description: This study aims to analyze the relationship between carbon dioxide (CO 2 ) emissions, economic growth, and coal and oil consumption in Brazil, Russia, India, China, Turkey, and South Africa by using the bounds test approach autoregressive distributed lag (ARDL) over the period from 1969 to 2011. According to ARDL analysis results, it is determined short-run and long-run relationships among selected variables. Three long-run estimators: ARDL cointegration, dynamic ordinary least squares, and fully modified ordinary least squares are utilized to test the robustness of the estimation results. The Granger causality and the forecast error variance decomposition approaches indicate the evidence of a causal relation between variables. According to empirical results, there are the evidence of a uni-directional Granger causality from real gross domestic product (GDP) to carbon dioxide (CO 2 ) emissions in analyzed countries, uni-directional causality from coal consumption to carbon dioxide (CO 2 ) emissions, uni-directional causality from oil consumption to carbon dioxide (CO 2 ) emissions in China, India, Turkey, and South Africa and bi-directional causality in Brazil and Russia. Meanwhile, there is bidirectional causality from GDP to coal consumption, from coal consumption to oil consumption for Brazil, Russia, China, Turkey, and South Africa. India's causality results reveal a bidirectional causality from GDP to coal consumption, oil consumption, and carbon dioxide (CO 2 ) emissions, and the results of forecast error variance supported the results of the causality test.

Description: A thin cupric oxide film (CuO), straddled with graphene nanoparticles, is proposed as a promising absorber layer for solar cell application. The influence of the graphene nano-particles on the optical, electrical, and photovoltaic properties of the CuO thin film is investigated in detail. Graphene nano-particles incorporated CuO (G-CuO) film, grown via sol-gel deposition, shows a reduction in the optical transmittance and reflectance, and an enhancement in its electrical conductivity. Photovoltaic properties, investigated through a p -(G-CuO)/ n -Si heterojunction cell, shows a significant increase in short circuit current from 0.12 mA/cm 2 to 0.82 mA/cm 2 . The fill factor was also found to increase to 40% from 20%. The significant improvement in efficiency of the G-CuO solar cell is attributed to the synergetic effect provided by graphene in enhancing the absorption of visible light and increasing its electrical conductivity, while concurrently suppressing charge recombination in the bulk semiconductor.

Description: The paper estimates solar radiation in the Southern areas of Pakistan using the climate data of thirty years (1981–2010) for 25 meteorological stations located in the three provinces of Pakistan, i.e., Baluchistan, Punjab, and Sindh. For this purpose, five different radiation models are designed: Sunshine hour-based model, Temperature-based model, Cloud-based model, Meteorological parameters-based model, and Meteorological and Geographical Parameters-based Model. The forecasting efficiency of these models is evaluated using mean predicted errors and Theil inequality coefficient. The results reveal that the Meteorological and Geographical parameters-based models are the most accurate methods for estimating solar radiation in Pakistan. Forecasting efficiency results show that the estimates of solar radiation of all the models is much better for Baluchistan as compared to Punjab and Sindh.

Description: Photovoltaic companies have been developing very rapidly in China and facing huge financial crisis as well. By adopting the Z-score and multi-regression models, this paper evaluated the financial risks of China's 57 solar photovoltaic companies, in an attempt to reveal the relationships between managerial power, ownership concentration, and their financial risks. Empirical results show that the expansion of photovoltaic companies' managerial power significantly increases the financial risks of these companies. More specifically, (1) combining board chairman and the Chief Executive Officer (CEO) increases their financial risks; (2) the size of the board of directors and the tenure of the CEO have positive correlations with their financial risks; and (3) the percentage of management shareholdings and the degree of ownership concentration have negative correlations with their financial risks. Management implications are proposed accordingly based on the findings of this study.

Description: Conventional methods for solving distribution systems planning (DSP) problem are related to the expansion of distribution systems such as substation reinforcement and feeder replacement. Nowadays, distributed generations (DGs) in various types are a new option for DSP. This paper presents a new approach to solve the DSP problem including DGs with respect to the reliability of the system. The impact of different types of DGs in order to improve the system reliability are modeled and studied by the adequacy transition rate using the Markov model. The objective functions of this optimization problem are power losses, DGs installation and operation cost, reliability indices such as energy not supplied, average interruption frequency, and average interruption duration. Since this optimization problem has a nonlinear complex nature, classical mathematical methods cannot guarantee to achieve the global optimum solution. To solve this problem, a fuzzy interactive multi-objective particle swarm optimization is developed based on Pareto solutions. The model resolves decision variables as follows: location, size, and type of the DG units. The results on IEEE 34-bus distribution system show the effectiveness of the proposed method rather than previous works for reliability assessment.

Description: This paper presents a model based method to estimate the internal core temperature of a service power cable subject to intermittent loading. The estimation is then used to control the loading so that the cable can be safely utilized to the limit of its capability. The method considers the temperature dependence of the cable resistance and is insensitive to the variations in the environment. The model is backed by laboratory experiment and the effectiveness of the dynamic rating approach is evaluated by simulation.

Description: The effect of chemically synthesized activated carbon (AC) on the performance of microbial fuel cell (MFC) was investigated in this study. Coconut fiber was used as a source material for synthesizing the AC. The AC with different ranges (5, 10, and 15 mg/cm 2 ) was coated on the anode electrode surface to investigate and compare the performance of MFC with the control electrode (plain surface). The experimental results showed that the AC-5 (5 mg/cm 2 ) coated electrode produced a peak power density (5.8 W/m 3 ) which was higher than the control (plain) electrode (3.8 W/m 3 ). The MFC performance in terms of power density and chemical oxygen demand (COD) removal efficiency was increased with increasing loading quantity of AC. When an AC-15 (15 mg/cm 2 ) coated was electrode used in the MFC, the highest power density of 9.5 W/m 3 with a COD removal efficiency of 74.8% was observed. Cyclic voltammetry analysis visualized the clear enhancement in electrochemical activity with an AC coated electrode. The effect of wastewater COD concentration on the performance was also investigated. The AC derived from coconut fibers can be considered as a biocompatible material to enhance MFC performance.