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The moon is recognized as an important destination for space science and exploration. To find a satisfactory answer for the mystery of the universe and to make use of the lunar resources for the welfare of human beings, several space agencies are planning manned and unmanned missions on the moon. As a result, the concept of lunar vehicles has begun with an advanced descent scheme to execute a precise and safe landing on the surface of the moon. On the contrary, the energy budget is an important issue for any space mission. To reduce the cost of a space mission, it is necessary to design the vehicle trajectory based on optimized energy resources. Fuel is the main energy in a space mission. Therefore, a fuel-optimized energy generation technique is focused on this research. The design of an algorithm that generates a real-time trajectory for the descent and landing of a lunar probe is critical to ensuring a successful lunar landing mission. A scheme of dual-step trajectory generation for lunar descent is also investigated in this paper. In the algorithm developing process, the thrust-to-mass ratio is considered as a principle variable. Algorithm design along with mathematical modeling and simulation results are described in detail. In addition, the proposed method for generating reference trajectory profiles is also analyzed for fuel consumption and robustness.

An organic solar cell (OSC), competitive with traditional one (Si-based), draws attention to future renewable energy sources due to its low-cost and continually rising efficiency. The tandem or multijunction structure undoubtedly offers an efficient way to boost the performance of OSCs. This work has explored the optical modeling of different organic photoactive materials to identify the potential materials for efficient tandem structure. The performance of double, triple, and quadruple junction tandem OSCs with suitable bandgaps has been analyzed with photoactive materials. The absorption efficiency enhances considerably using the thickness optimization of each subcell in tandem structures. Current matching in all subcells, an essential factor for efficient device operation, is taken into account while optimizing tandem structures. The quadruple design can achieve better photovoltaic performance than double or triple junction devices. The efficiency predicted from our proposed quadruple structure is ~15.45%, with a short-circuit current density, $\text{J}_{\mathrm {SC}}$ of $\sim 9$ mA/cm2 and an open-circuit voltage, $\text{V}_{\mathrm {OC}}$ of ~2.64 V. These results are one of the high-performance in terms of organic photovoltaic (OPV). Therefore, the above findings indicate that OSCs are very potential for future photovoltaic applications.

In this paper, we study a multiple scales perturbation and numerical solution for vibrations analysis and control of a system which simulates the vibrations of a nonlinear composite beam model. System of second order differential equations with nonlinearity due to quadratic and cubic terms, excited by parametric and external excitations, are presented. The controller is implemented to control one frequency at primary and parametric resonance where damage in the mechanical system is probable. Active control is applied to the system. The multiple scales perturbation (MSP) method is implemented to obtain an approximate analytical solution. The stability analysis of the system is obtained by frequency response (FR). Bifurcation analysis is conducted using various control parameters such as natural frequency (ω1), detuning parameter (σ1), feedback signal gain (β), control signal gain (γ), and other parameters. The dynamic behavior of the system is predicted within various ranges of bifurcation parameters. All of the stable steady state (point attractor), stable periodic attractors, unstable steady state, and unstable periodic attractors are determined efficiently using bifurcation analysis. The controller’s influence on system behavior is examined numerically. To validate our results, the approximate analytical solution using the MSP method is compared with the numerical solution using the Runge-Kutta (RK) method of order four.

Grid extension from the distribution network is being used to meet the demand for rural electricity all over the world. Due to the extra cost of extending electric lines to rural villages, it is not feasible as the installing and commissioning costs are directly related to several constraints such as distance from the main grid, the land location, utilities to be used, and the size of the approximate load. Consequently, it becomes a challenge to apply technoeconomic strategies for rural electrification. Therefore, considering the above issues of rural electrification through grid power, the renewable energy system can be an attractive solution. This research analyzes different types of loads considering domestic, industrial, and agricultural requirements for a remote village in a developing country like Bangladesh. In this paper, four types of demand scenarios are developed considering the income level of inhabitants of the village. The investigation identifies the optimal scope for renewable energy-based electrification and provides a suitable technoeconomic analysis with the help of HOMER software. The obtained results show that a combined architecture containing solar panel, diesel generator, and battery power is a viable solution and economically beneficial. The optimal configuration suggested for the primary scenario consists of 25 kW diesel generators to fulfill the basic demand. The hybrid PV-diesel-battery system becomes the optimal solution while the demand restriction is removed for secondary, tertiary, and full-option scenarios. Commercial and productive loads are considered in the load profile for these three scenarios of supply. For the primary scenario of supply, the electricity cost remains high as $0.449/kWh. On the other hand, the lowest electricity cost ($0.30/kWh) is obtained for the secondary scenario. Although the suggested optimal PV-diesel-battery might not reduce the cost of electricity (COE) and NPC significantly, it is capable to reduce dependency on diesel utilization. Hence, the emission of carbon is reduced due to less utilization of diesel that helps to minimize the greenhouse effect on the environment.

In this paper, we focus on applying active control to nonlinear dynamical beam system to eliminate its vibration. We analyzed stability using frequency-response equations and bifurcation. The analytical solution of the nonlinear differential equations describing the above system is investigated using multiple time scale method (MTSM). All resonance cases were extracted from second order approximations. Numerical solutions of the system are included. The effects of most system parameters were investigated. The results demonstrated that proposed controller is efficient to suppress the vibrations. Increasing the quadratic stiffness coefficient term vanished the multi-valued solution. Bifurcation diagrams refiled the effects of various system parameters on its stability showing different bifurcation cases. Finally, we conclude that for low values of natural frequencies dynamical system, the controller is more effective. The results show that the analytical solutions of the system are in good agreement with the numerical solutions.

The article applies the robust generalized dynamic inversion control methodology to the problem of stabilizing upright equilibrium configuration of the under-actuated rotary inverted pendulum system while tracking rotary motion of the actuated arm. The proposed robust generalized dynamic inversion control law comprised equivalent and switching control parts. The equivalent control part works to enforce a virtual constraint dynamics of the controlled state variables by means of Moore–Penrose generalized inversion. The switching control part is of the sliding mode type, and it improves robustness against unmodeled system dynamics, parametric uncertainties, and external disturbances. The robust generalized dynamic inversion control design on the linearized model of the under-actuated rotary inverted pendulum is shown to guarantee semi-global asymptotically stable tracking performance. Numerous computer simulations and experiments are conducted on the Quanser rotary inverted pendulum system, revealing that the proposed algorithm has better convergence and tracking performance than conventional sliding mode and generalized dynamic inversion control strategies when both are applied separately.

Novel GaN-based van der Walls (vdW) hetero-bilayer (HBL) is systemically studied through the first-principles density functional theory (DFT) framework to explore its optoelectronic property facilitated photocatalytic activity for hydrogen (H2) fuel production. The vdW concept of planar GaN with GeC monolayer, together making stacked hetero-bilayer, shows unique and tunable optoelectronic properties that fulfill all the photocatalysis attributes. The confirmation of chemical and dynamical stabilities is made with negative interlayer binding energy and non-negative frequency in phonon spectra, respectively. Among the dynamically stable hetero-bilayers, binding energy in HBL 2 (AB1) is the lowest and interlayer distance ~2.954A is the smallest. The HBLs are sensitive to the stacking arrangements, where HBL 2 demonstrates type-I direct bandgap and HBL 6 (AB6) is Type-II direct bandgap. The intrinsic HBLs show superior carrier mobility as their effective masses are lower from their constituent monolayers. Also, the intrinsic absorption coefficient of the HBLs increase as high as ~106 cm−1, 10 times greater than conventional perovskite materials, which show outperforming optoelectronic conversion efficiency. Additionally, the HBLs are highly tunable in both bandgap and type due to biaxial strains and cross-plane electric fields. With biaxial strains, from compressive to tensile, both HBLs show monotonous bandgap lowering with a dominant direct-indirect bandgap splitting in HBL 2. Interestingly, for all the biaxial strains within the −6% to +6% range, both HBLs have sufficient kinetic overpotential for photocatalytic water splitting and an increase in visible peak by 3.5 (2) times in the HBL 6 (HBL 2). Electric fields also increase the photocatalytic water splitting performance with a net bandgap lowering and increasing the visible absorption peak by ~1.5 times compared with intrinsic HBLs. These promising properties that we have found in the planar GaN/GeC vdW hetero-bilayer are highly suggestive for the impending use of this material in photocatalytic water splitting technology to produce H2 fuel.

Dioctyl phthalate (DOP) is industrially commonly used as a polyvinyl chloride (PVC) plasticiser. As DOP does not form a chemical link with PVC, it migrates from flexible PVC segments into the media in contact, a matter that arose concerns due to its noxious effect. Despite the introduction of several non-DOP-based plasticisers recently, most of these new plasticisers are petroleum derived, which is a non-renewable resource. Accordingly, this research aims to produce a natural-based plasticiser using clean production method. Epoxidised 2-ethylhexyl oleate (E-2-EHO) was produced through an esterification and epoxidation reaction between oleic acid and 2-ethyl hexanol; both reactions occur simultaneously, in the presence of hydrogen peroxide as oxygen donor in a solvent-free environment. Candida antarctica lipase (Novozym 435) was used as a cleaner biocatalyst. Several reaction parameters that affect the synthesis of (E-2-EHO) were analysed using response surface methodology based on full factorial central composite design for four variables. The maximum experimental conversion was 94.2% while the value of the predicted conversion was 95.3%. The operation conditions were a temperature of 65 °C, enzyme load of 4 wt%, alcohol-to-oleic acid molar ratio of 4:1, hydrogen peroxide-to-C=C molar ratio of 0.5:1, molecular sieve/g acid of 0.425 g and reaction time of 2 h. In addition, the plasticising effectiveness of (E-2-EHO) to substitute toxic DOP was studied. Comparison with conventional DOP highlighted that (E-2-EHO) had superior and significantly reduced glass transition temperature (tg) and improved mechanical properties. In the proposed study, (E-2-EHO) was proved to be an efficient substitute to DOP by replacing up to 80% of the total plasticiser. Moreover, the product yield obtained in a short time reaction along with the proven stability of Novozym 435 during operation both showed that this ecofriendly and maintainable alternative is favourable when used in large-scale applications.

Carbon nanotube (CNT) structures reported in the literature often have a black color with low reflectance and matt surface appearance. Only a few papers reported the high reflectance and glossy appearance of the CNT surface on a substrate. To our knowledge, no one has reported the glossy appearance of freestanding CNT. Herein, we have successfully fabricated a freestanding multi-walled CNT sheet with a glossy or mirror-like surface appearance. Raman spectroscopy confirmed that both matt and glossy freestanding CNT sheets have the same chemical composition. We found that the glossy freestanding CNT sheet has a relatively flat surface morphology compared to matt freestanding CNT sheet, as seen in the atomic force microscopy results. We attributed the glossy appearance due to a relatively flat surface morphology of the freestanding CNT sheet.

Herein, we utilize freestanding sheets of multi-walled carbon nanotube (MWCNT), fabricated through a surface-engineered and controlled approach, to provide direct measurements of activities of MWCNT toward the hydrogen evolution reaction (HER). Since conventional fabrication methods of MWCNT materials can result in different carbonaceous residue contents (as reported in literature), the effect of carbonaceous impurities on the activity of MWCNT toward the HER becomes interesting (not previously recognized). Our results show that increasing amounts of carbonaceous impurities (in the form of carbon black additives) can initially increase the catalytic activity of MWCNT toward the HER, but will result in a lower electrochemical stability and lower activity at higher rates of charge transfer or longer times of charging, for which we propose an electrolytic transport mechanism, related to a debris-formation phenomenon occurring over carbonaceous impurities. The work suggests that carbonaceous impurities’ content should be accounted for during electrochemical studies of MWCNT toward the HER.

Control engineers and researchers face challenges to design an efficient controller for Ball and beam system due to its nonlinear and unstable properties. This paper investigates two Degrees of Freedom fractional order control of the ball and beam system. It involves the model based method to design controllers’ parameters for the corresponding linear model. The fractional order controllers are specially tuned to have a constant phase margin of the open-loop. This characteristic ensures the robustness of the controllers to the variations of system gain. This paper presents a proper evaluation and comparison between integer and fractional order controllers. Performance of each controller is evaluated in terms of set-point tracking, disturbance rejection, and robustness. The comparison between two controllers is validated through both simulation and experimental results. Strengths and weaknesses in the real-time control are also indicated.

Recently, InGaN grown on semipolar and non-polar orientation has caused special attraction due to reduction in the built-in polarization field and increased confinement of high energy states compared to traditional polar c-plane orientation. However, any widespread-accepted report on output power and frequency response of the InGaN blue laser in non-c-plane orientation is readily unavailable. This work strives to address an exhaustive numerical investigation into the optoelectronic performance and frequency response of In0.17Ga0.83N/GaN quantum well laser in polar (0001), non-polar (101&macr, 0) and semipolar (101&macr, 2), (112&macr, 2) and (101&macr, 1) orientations by working out a 6 &times, 6 k.p Hamiltonian at the &Gamma, point using the tensor rotation technique. It is noticed that there is a considerable dependency of the piezoelectric field, energy band gap, peak optical gain, differential gain and output power on the modification in crystal orientation. Topmost optical gain of 4367 cm&minus, 1 is evaluated in the semipolar (112&macr, 2)-oriented laser system at an emission wavelength of 448 nm when the injection carrier density is 3.7 &times, 1018 cm&minus, 3. Highest lasing power and lowest threshold current are reported to be 4.08 mW and 1.45 mA in semipolar (112&macr, 2) crystal orientation. A state-space model is formed in order to achieve the frequency response which indicates the highest magnitude (dB) response in semipolar (112&macr, 2) crystal orientation.

In this article, a Quasi D-Shape dual core Photonic Crystal Fiber Surface Plasmon Resonance sensor is offered and numerically analyzed. The offered model is established comprising of circular air holes having an external sensing polishing layer coated with gold (Au) in order to ensure simple and straightforward design. The performance parameters are examined by means of modal analysis incorporated finite element method utilizing COMSOL multiphysics software. The sensor performance is analyzed with modifying the geometrical parameters like metal (Au) layer and pitch. It is observed; this model shows maximum amplitude sensitivity of 230 RIU−1 and wavelength sensitivity of 15,000 nm-RIU−1 incorporating amplitude interrogation method and wavelength interrogation method, respectively. The Figure of Merit is similarly considered and measured to 45 per RIU inbetween the refractive index ranging 1.42 RIU to 1.46 RIU. As a final point, a comparison has been given among the work explained in this paper with existing works.

In the current study, a novel Zeonex based porous core photonic crystal fiber (PC-PCF) is presented for polarization-maintaining and dispersion flattened in the terahertz (THz) region. For minimizing the Effective Material Loss (EML), an array of three rectangular and six triangular air holes are surrounded by hexagonal-shaped cladding. Finite Element Method (FEM) is employed through Comsol V5.3a software to design and examine the essential features of the proposed porous core fiber which revealed that it has an extremely small EML of 0.04 cm−1 at 1.2 THz and has almost zero flattened dispersion of 0.8 ± 0.08 ps/THz/cm in 1.0–1.4 THz frequency spectrum. Moreover, the optimum designing parameters offer an extremely high value of birefringence (0.043 at 1.2 THz). Besides, other major features notably bending loss, effective area, and confinement loss are also found to be precise and relatively low. For effective, adaptable and fitting transmission characteristics, this type of design would lay the foundations for broadband THz radiation wide variety of usage in the THz regime.

Consumption of formalin with food is a worldwide concern and has become a serious social problem in recent years, especially in the developing societies, which are at a higher risk of danger because of the lack of satisfactory monitoring and policies. The Frequent consumption of formalin causes severe health issues that lead to critical and fatal diseases like chronic cancer. Formalin detection in food is an urgent concern, which is becoming a national issue in developing countries. In this article, a graphene-MoS2 composite 2D sheets with a TiO2-SiO2 nano-layered surface plasmon resonance (SPR) based sensor is presented for formalin detection. Analytical analysis is carried out on the performance parameters of the sensor using MATLAB commercial software. The effect of amalgamation of Graphene-MoS2 with TiO2-SiO2 layers has been studied. The sensitivity and quality factor of the sensor are found to be 98 deg. RIU−1 and 88.89 RIU−1, respectively. This sensor detects the existence of formalin by using attenuated total reflection (ATR) and evaluating the reflectance vs SPR angle and transmittance vs surface plasmon resonance frequency (SPRF) attributes. It is found that, the sensitivity of the traditional SPR based sensor is 70°/RIU, on the other hand, the graphene-MoS2 based sensor improves this sensitivity to 76°/RIU. Finally, a comparative performance study of the traditional SPR sensors and the proposed sensor is also presented.

Wearable electronics require flexible supercapacitors with specially fabricated electrode materials, i.e., foldable and freestanding. Although activated carbon is the most used electrode’s active material for aqueous supercapacitors, it is a challenge to pack the particulates into flexible electrodes. Typically, polytetrafluoroethylene binder and polymeric flexible substrate are used, rendering a large amount of inactive-material. Here, we successfully fabricated multiwalled carbon nanotube/activated-carbon (MWCNT-AC) freestanding sheet via a scalable surface-engineered tape-casting technique to be used as a flexible electrode for aqueous supercapacitors. Instead of focusing on improving MWCNTs as active materials, the sheets act as a conducting matrix that binds together the activated-carbon particulates. MWCNT-AC has a specific capacitance of 135.17 Fg−1 (123.9 Fg−1 after 1000 cycles) at 1 Ag−1 from − 0.8 to 0.2 V vs. Hg/HgO (in three-electrode cell).

The presence of impurities within multiwalled carbon nanotubes (MWCNTs) have major, but as-yet-unrecognized, effects on the electrochemical behavior of MWCNTs in vanadium redox flow batteries. We show that MWCNTs constitute a high-surface-area, electrically conductive, inactive carbon matrix that acts as a bridge between and a support for carbonaceous impurities that are highly active toward the VO2+/VO2+ redox couple. We use freestanding sheets of MWCNTs, either purified and subsequently not modified with impurities (pure) or purified and subsequently contaminated with carbonaceous impurities (impure), as electrodes to eliminate the need for a substrate and thus undesired mixed kinetics. Electrodes fabricated with pure MWCNTs show low activities; attributed to relatively inactive basal sites. In contrast, impure electrodes show high activities due to the increased number of defects and edge sites resulting from the presence of the impurities. Functionalization of pure MWCNTs surface with oxygen-containing groups substantially improve the activity of the electrodes. However, functionalization is not as effective when carbonaceous impurities are present. The carbonaceous impurities form a continuous debris layer over the nanotube fibers, which reduces the effect of the oxidation treatment. Our results indicate that the impurity content of MWCNTs should be considered in studies of their activity and functionalization.

Double-gate (DG) metal---oxide---semiconductor field-effect transistors (MOSFETs) with GaN channel material are very promising for use in future high-performance low-power nanoscale device applications. In this work, GaN-based sub-10-nm DG-MOSFETs with different gate work function, $$\varPhi $$ź, were designed and their performance evaluated. Short-channel effects (SCEs) were significantly reduced by introduction of gates made of dual metals. Use of gold at the source side, having higher $$\varPhi $$ź ($$\varPhi _{\mathrm{Au}}=5.11\,\hbox {eV}$$źAu=5.11eV) compared with aluminum ($$\varPhi _{\mathrm{Al}}=4.53\,\hbox {eV}$$źAl=4.53eV), at the drain side enhanced the gate control over the channel and screened the effect of the drain on the channel. Dual-metal (DM) DG-MOSFETs showed better results in the nanoscale regime and were more robust to SCEs. Therefore, GaN-based sub-10-nm DM DG-MOSFETs are suitable candidates for use in future complementary metal---oxide---semiconductor (CMOS) technology.

This paper elucidates the details of exciton localization dynamics in InGaN/GaN and GaN/AlInN quantum wells (QWs) using Monte Carlo simulation for a wide range of temperatures (10---300 K). We find that the phonon-induced variation of exciton lifetimes has remarkable effects on the photoluminescence (PL) peak position and the line-width. The red-shift of PL peak position at high temperature is clarified. The combined effects of phonon-induced radiative lifetime of excitons and the band-gap shrinkage at high temperature show the most reasonable agreement with the experimentally observed red-shift of the PL peak position. We have also quantitatively explained the temperature dependence of the W-shaped line-width in both InGaN/GaN and GaN/AlInN QWs. These results are highly significant to understand the emission properties of III-nitride QWs optoelectronic devices.

Conventionally, production of 3D graphene (3DG) results in non-uniform particle size and random structures. Although important, the effect of the 3DG particle size on the kinetics of CNT electrodes toward the Vanadium Redox Flow Battery (VRFB) electrolyte has not been investigated. Herein, we manipulate in-lab fabricated CNT sheets with variable particle sizes of electroactive porous 3D graphene (3DG) additives, resulting in variable porous characteristics due to the spacing effect of the 3DG within the as-fabricated CNT fibers. We show that the particle size of 3DG affects both the kinetics and the mass transport capabilities of buckypaper electrodes. The results show that the 3DG additives did not only act as spacers between the CNT fibers opening up channels for increased mass flow to occur, but also improved the heterogeneous rate constants of the reactions. The improvement in kinetics, however, became more significant as the 3DG particle size decreased. Nevertheless, the results also suggest that the use of electroactive materials with controlled particle sizes is a promising strategy for the preparation of porous CNT materials for VRFBs. Graphical abstract Download : Download high-res image (194KB) Download : Download full-size image

A hybrid system combining the energy and attitude control task uses flywheels to store energy and control the attitude of small satellites. Various journal papers containing previous works have recognized this combined architecture. However, due to the uncertainties of on-board performances, it is a challenge in terms of attitude pointing accuracy. Therefore, this paper focuses a full state-feedback control solution to increase the satellite attitude performances. Mathematical model and numerical treatments for full state-feedback control of combined energy and attitude regulating scheme for a small satellite are presented. Simulation results show that an enhanced pitch pointing accuracy can be achieved up to 0.0010 for the proposed control approach. The paper contains an over view of a flywheel architecture along with state space representation of the scheme. A brief description of conventional control scheme is also presented with sample simulated results for comparison. Design of a full state-feedback controller and analysis of simulated results are also presented to show the achieved attitude performances specifically.

Typically, multiwalled carbon nanotubes (MWCNTs) are drop-casted on the surface of the underlying carbon substrates; the outcome is a randomly distributed MWCNT layers leading to uncontrollable structure and unreproducible results. Additionally, we suspect that the electrochemical response is influenced by the primary carbon-based substrate. Herein, we propose the use of freestanding sheets of MWCNTs (buckypapers, BP electrodes) as electrode materials for vanadium redox flow batteries to directly probe the electrochemical activity of MWCNTs toward VO 2+ /VO 2 + and V 2+ /V 3+ redox couples; henceforth, eliminating the need for an underlying carbon substrate. The amount of surfactant and the sonication time used during the fabrication of BP electrodes affect their morphological characteristics and electrochemical performances. Although the electrical conductivity of BP electrodes decreases with increasing surfactant amount and increasing sonication time, the heterogeneous rate constants for both redox couples increase as these fabrication variables are increased, indicating that the performance-limiting process is not electrical conductivity but the number of active sites available for the electrochemical reaction. The standard heterogeneous rate constant of the BP electrode with the highest amount of surfactant is comparable to those of state-of-the-art electrodes. Our promising results call for more research on the potential use of BP electrodes in redox flow batteries.

Highly aligned titania (TiO 2 ) nanotube (NT) arrays have been grown on titanium sheet by using a self organized anodic oxidation method at different potentials (34–74 V) in a NH 4 F and ethylene glycol based electrolyte. Two sets of TiO 2 NT arrays have been fabricated with and without using cooling systems. Without cooling system, the solution temperature is increased from 25 °C (room temperature) to 63 °C with increase of anodization potential from 34 to 74 V. The temperature has been maintained to 25 °C by using water based cooling system. In both sets of samples, the pore diameter of TiO 2 NT arrays increases with increase of anodization potential. The maximum pore diameter has been (outer: 224 nm, inner: 172 nm) achieved with TiO 2 NT arrays (at 74 V) without using cooling system. The photocatalytic activity of the TiO 2 NT arrays is evaluated by the decomposition of methanol by the use of Fourier transform infrared spectrophotometer. The TiO 2 NT (at 44 V) sample has been fabricated without using cooling system, which shows the higher photocatalytic activity than the sample at other potentials. Using cooling system, the TiO 2 NT (at 54 V) sample shows the higher photo-decomposing property than the sample at other potentials. The TiO 2 NT (at 54 V) sample with cooling system shows the higher rate (photocatalytic activity) constant ( k = 0.0216) than the TiO 2 NT (at 44 V) sample without using cooling system ( k = 0.0186). The photocatalytic activity has been correlated with the nanostructural variation of TiO 2 NT arrays at different potentials without (self-grown solution temperature) and with water based cooling systems.

Various applications of freestanding multi-walled carbon nanotube (MWCNT) sheets (also known as buckypapers), although very promising in the laboratory, failed to meet the technology readiness level for commercialisation due to the use of non-scalable fabrication methods. Herein, we developed a surface-engineered tape-casting (SETC) technique which is a facile and scalable preparation method to fabricate freestanding, flexible and foldable buckypapers using tape-casting on a surface-engineered conveyor-belt without a mould. The SETC technique has several advantages: it can be implemented in both batch and roll-to-roll processing; has a high throughput; produces a large area with tuneable length, thickness, density and composition; and produces sheets from any commercially available carbon nanotubes with superior properties. The SETC technique solves the main challenge of tape-casting which is the separation of the dried MWCNT sheet from the supporting-substrate. This challenge originates from the fact that MWCNTs always tend to stick to the substrate which makes it almost impossible to peel as a perfect sheet. We found out that easy peeling of the buckypaper from a substrate can be achieved if the following conditions are satisfied: (a) enough difference between MWCNTs and substrate surface energies and (b) the micro-pyramid pore structure of the substrate morphology. Moreover, the SETC technique was able to preserve the MWCNT alignment within the sheet. We demonstrated the application of a SETC-made MWCNT–LiFePO4 buckypaper composite in lithium-ion batteries with an excellent specific capacity of 86.79 mA h gLiFePO4−1 (61.20 mA h gMWCNT+LiFePO4−1) at a high discharge rate of 1905 mA gLiFePO4−1 (1270 mA gMWCNT+LiFePO4−1) for 1000 cycles.

Although free-standing sheets of multiwalled carbon nanotubes (MWCNT) can provide interesting electrochemical and physical properties as electrodes for redox flow batteries, the full potential of this class of materials has not been accessible as of yet. The conventional fabrication methods produce sheets with micro-porous and meso-porous structures, which significantly resist mass transport of the electrolyte during high-current flow-cell operation. Herein, we developed a method to fabricate high performance macro-porous carbon nano-foam free standing sheets (Puffy Fibers, PF), by implementing a freeze-drying step into our low cost and scalable surface-engineered tape-casting (SETC) fabrication method, and we show the improvement in the performance attained as compared with a MWCNT sheet lacking any macro pores (Tape-cast, TC). We attribute the higher performance attained by our in-lab fabricated PF papers to the presence of macro pores which provided channels that acted as pathways for electrolytic transport within the bulk of the electrode. Moreover, we propose an electrolytic transport mechanism to relate ion diffusivity to different pore sizes to explain the different modes of charge transfer in the negative and the positive electrolytes. Overall, the PF papers had a high wettability, high porosity, and a large surface area, resulting in improved electrochemical and flow-cell performances.

The formation of ohmic contact to p-InGaN has been analyzed here using the Metal induced Gap States (MIGS) model with an ultrathin interfacial layer of insulator. The position of Fermi level and barrier height modulation has been investigated for two different combinations of Metal-Insulator with p-InGaN. In case of p-InGaN with 2nm layer of NiO, Au formed a barrier height of 0.49 eV. The contact resistivity for $\mathbf{Au}/\mathbf{NiO}(\pmb{2}\ \mathbf{nm})/\mathbf{p-}\mathbf{In}_{\pmb{0.48}}\mathbf{Ga}_{\pmb{0.52}}\mathbf{N}$ is found to be $\pmb{2.35\times 10^{-4} \Omega-}\mathbf{cm}^{\pmb{2}}$ at 300K and $\pmb{1.15\times 10^{-4} \Omega-}\mathbf{cm}^{\pmb{2}}$ at 600K. It is also observed that the metal with higher work function gives lower barrier height and contact resistivity in case of p-InGaN. For Pt/AI 2 O 3 (2 nm)/p-In 0.48 Ga 0.52 N, the barrier height becomes 0.312 eV and the contact resistivity is estimated as $\pmb{1.9\times 10^{-4}\Omega-} \mathbf{cm}^{\pmb{2}}$ at 300K and $\pmb{0.75\times 10^{-4}\Omega-}\mathbf{cm}^{\pmb{2}}$ at 600K. Thus, Pt contact shows better performance than Au contact to p-InGaN. This information of MIS contact could be a good insight for conventional CMOS in case of source/drain applications.

Clinically approved iron chelators are effective in decreasing significant transfusional iron accumulation. Starch-Deferoxamine (S-DFO), a novel high molecular weight iron chelator, was produced to increase binding capacity to iron and reduce toxicity. Although its efficacy was established in one small cohort clinical trial, its potential adverse effect was not adequately addressed. We utilized zebrafish model to assess S-DFO toxicity using following assays: mortality, teratogenicity, hatching rate, tail flicking, Acridine Orange staining for apoptosis detection, o-dianisidine staining for hemoglobin synthesis, and the level of Hsp70 as a general stress indicator. Embryos were exposed to different concentrations of S-DFO, Zinc Oxide nanoparticle (ZnO) (positive control), along with untreated control (UC). S-DFO showed no significant mortality nor deformities at all tested concentrations (0.0-1000 μM). Thus, the LC50 is expected to >1000 μM. 100 μM S-DFO treatment did not affect embryo development (as judged by hatching rate); neuromuscular activity (as judged by tail flicking); and hemoglobin synthesis. Neither apoptosis, nor increase in Hsp70 level was noticed upon S-DFO treatment. Our assays demonstrate that S-DFO does not induce cellular or biochemical stress and has no adverse effect on organ development of zebrafish embryos, suggesting its safe use as an iron chelator. Funding information: Qatar University, Grant/Award Number: University Internal Grant/QUUG-CAS-DHS-15\16-21.

This paper has studied the metal–insulator-semiconductor (MIS) contact for both p- and n-InGaN. We found that the insulator layer thickness has a remarkable effect on the Fermi level pinning and barrier height reduction in MIS contacts. Schottky's formation with doped InGaN is explained by extending the MIS contacts' using the metal-induced gap states (MIGS) model. The J-V characteristics clarify the current transport mechanism through the MIS contact with InGaN semiconductor for different temperatures. We observed less control on the barrier height reduction in the case of n-InGaN through changing the thickness of the interfacial layer. The calculated contact resistivities of MIS contact with p- and n-InGaN show better results than the metal–semiconductor contact counterparts. These findings are highly significant to design and fabricate the InGaN based switching devices for converter applications.

The aim of this paper is to discuss the stability of a symmetric cross-ply composite laminated piezoelectric plate subject to combined excitations. Multiple timescale perturbation method is implemented to solve the nonlinear governing equations including the second-order approximation. The case of 1:1:3 internal resonance and primary resonance case is investigated. The stability of the system is discussed using frequency, force response curves. A bifurcation analysis was performed using the amplitude of parametric excitation force as the bifurcation parameter. It is found that there are two Hopf bifurcation points: the first one is at $$f_{11}=5.592$$ , and the other one is at $$f_{11}=13.96$$ . It is observed that the system is dominated by the periodic attractor in the ranges of $$(5.592< f_{11 }< 7.21)$$ and $$(13.31< f_{11 }< 13.96)$$ . The system is enriched with period doublings which are the main way leading to chaotic behavior. Some recommendations regarding the parameters limit of the dynamic system are reported.

This work was carried out to investigate the comparative effects of phosphorus and boron doing in vapor–liquid–solid (VLS) growth. Doped Si microneedles were grown by VLS mechanism at the temperature of 700 °C or less using Au as the catalyst. VLS growth using in-situ doping with the mixed gas of Si2H6 and PH3 produced phosphorus doped n-Si microneedles at Au dot sites, whereas, the mixed gas of Si2H6 and B2H6 produced boron doped p-Si microneedles. The variation of growth rate, diameter, resistivity, impurity concentration and carrier (electron, hole) mobility of these n-Si and p-Si microneeedles were investigated and compared with the variation of dopant gas (PH3 or B2H6) flow, with a fixed flow of Si gas (Si2H6). This comparative study shall be helpful while fabricating devices by growing n-Si and p-Si microneedles one above another by multistep (2-step or 3-step) VLS growth.

In Faranah Province (Guinea), the ratio of supply and demand of corn is approximately 1:2. The production is low and the deficit is covered by maize importation. This study was initiated in order to improve corn production by evaluating the effects of increasing doses of mineral fertilizers on the yield and economic profitability of corn. The experiment was conducted on a farm in Kamedankoude in a split plot with three replicates. Treatments included two varieties of maize (Perta and Kilissi113) and five doses of chemical fertilizers (D0=unfertilized control, D1=300 kg NPKS+200 kg urea • hm−2; D2=400 kg NPKS+800 kg urea • hm−2; D3= 200 kg NPKS+400 kg urea • hm−2 and D4=500 kg NPKS+600 kg urea • hm−2). The results showed that all the agronomic parameters increased with increasing dose of fertilizers, except for the number of ears per plant. The two varieties of corn tested produced similar yields. However, the profitability of mineral fertilizers decreased with increased doses and with value/cost ratio of 3. We recommended a mineral fertilizer dose of 300 kg NPKS + 200 kg urea. The high prices of mineral fertilizers were often barriers to intensive maize cultivation, especially for low-income farmers. This study was a contribution to rational fertilization and adapted the socio-economic conditions of the region, with the background knowledge that most farmers in the regions earned low incomes.

A highly sensitive Photonic Crystal Fiber (PCF) based Surface Plasmon Resonance (SPR) sensor is demonstrated in this paper in the optimized form of circular slotted lattice (CSL) structure. This proposed model performance is numerically scrutinized by using Finite Element Method (FEM) in presence of Perfectly Matched Layer (PML) and Scattering Boundary Condition. Plasmonic material ‘Gold’ which is chemically inert is used in this structure at the outer surface of the slotted area to mitigate fabrication challenge. This model indicates the highest wavelength sensitivity of 16000 nm/RIU using wavelength interrogation, the amplitude sensitivity of 780 RIU−1 by using amplitude interrogation method and the average spectral sensitivity of 6666 nm/RIU, respectively. Besides, this sensor has the potentiality of detecting analytes within Refractive Index (RI) range 1.4 to 1.46 with maximum wavelength resolution of 6.25 × 10−6 RIU and amplitude resolution of 1.28 × 10−6 RIU, respectively and the maximum figure of merits of 400 RIU−1. Moreover, the variation of structural parameters (such as pitch, plasmon layer thickness etc.) and the impact of these changes are also discussed in details. According to the high sensitivity performance, polynomial fit and high Figure of Merit (FOM), this amend structure can be a strong competitor in the field of biosensing.

In this paper, an enhanced performance of dual core D-shape photonic crystal fiber utilizing surface plasmon resonance (DD-PCF-SPR) based sensor is numerically proposed and analyzed. The thickness of gold and pitch parameter are optimized to 30 nm and 1.9 um, respectively, which ensures superior sensor performance. It is revealed; at optimized geometrical parameter, the offered sensor displays a supreme wavelength sensitivity of 8000 nm/RIU, wavelength resolution of 1.25 × 10−5 RIU, a supreme amplitude sensitivity of 700 RIU−1, amplitude resolution 1.7857 × 10−5 RIU and a figure of merit (FoM) of 138 RIU−1 due to the analyte refractive index changing from 1.47 RIU to 1.48 RIU. The identifying features are investigated using modal analysis based finite element method (FEM) incorporating COMSOL commercial software. Finally, a relative review is executed comparing amplitude sensitivity, resolution and wavelength sensitivity of the offered sensor with previously reported sensors. As high sensitivity, simple structure, and tremendous linear polynomial characteristics, the offered sensor will be a talented candidate for the detection of various biochemical and biological samples (DNA, mRNA, proteins, sugar). Keywords: Amplitude sensitivity, Dual core-PCF, FoM, Wavelength sensitivity, SPR, Resolution

An analytical model of the photocurrent-voltage characteristics has been utilized to analyze important properties of organic bulk-heterojunction solar cells, e.g., generation rate, electron current density, hole current density and the total photocurrent density. The generation rate of P3HT:PCBM based solar cell critically depends on the absorption coefficient. For measuring the electron and hole current density solution of carrier continuity equation is used in MATLAB. Then the effects of electron and hole current density on the performance of P3HT solar cells have been studied. The result of this paper demonstrate that current density due to electron plays a major role in photocurrent production while hole current density has a very little impact. Effect of electron and hole mobility variation are investigated separately which indicate that increasing electron mobility are extremely important than hole mobility to increase the power conversion efficiency of P3HT:PCBM blend. The dependence of electron and hole current densities as a function of the blend thickness is also analyzed.

Tandem solar cell provides an effective way to improve power conversion efficiency of organic solar cell by combining two or more organic solar cells. Each cell has different absorption maximum and width so it provides the amenities of using the photon energy more effectively. Due to the limited absorption band of organic materials, single junction organic solar cells suffer from low efficiency. Here, we demonstrate the performance of single layer devices based on the solution of carrier continuity equation in MATLAB. Polymers P3HT:PCBM, pBBTDPP2:PCBM and PCDTBT:PCBM provide power conversion efficiency of 3%, 3.15% and 6.2% respectively. Hence series connected tandem cell P3HT:PCBM as front cell and pBBTDPP2:PCBM as rear cell is designed to achieve higher efficiency where the proposed model gives the power conversion efficiency of 6%. A major back through came when the front cell is replaced by PCDTBT:PCBM solar cell in the device configuration which provides the power conversion efficiency of 8.8%, till now the maximum efficiency for organic solar cell.

Although important, very little has been demonstrated in the literature to experimentally demonstrate the effects of porosities and pore size on the evaporation flux in polymeric membranes. Additionally, we suspect that a batch-mode setup, i.e., stagnant water, could cause a build-up of heat in the system, influencing the evaporation mass-flux mechanism, and jeopardizing the ability to attain a real correlation between evaporation and effects of pore characteristics. Herein, we fabricate polyvinylidene fluoride membranes containing variable amounts of a Fumed Silica additive to achieve membranes with variable properties, and we investigate the change in the performance of the solar-assisted thin-film evaporation utilizing an in-house built continuous flow evaporation setup (to avoid heat build-up effects in the bulk of the water and demonstrate a continuous flow system). Our membrane design approach had two important advantages: (1) the achievement of similar heat transfer and solar absorbance properties and (2) the achievement of variable pore sizes and volume porosities. We show that the mass flux increased as the mean pore size decreased, indicating that the mode of mass transfer occurred due to the thin-film region of the meniscus from the small fluid velocities near the interface, and we attribute the results to the increase in the capillary pumping effects through the mesoporous channels as they get thinner.

A theoretical analysis shows that polymers interacting with particles in a shear flow experience enhanced streamwise stretch that grows in amplitude and spatial extent with increasing Deborah number. This results in shear thickening of the viscosity and first normal stress coefficient of a particle suspension in a Boger fluid.

The models for investigating the phase diagram of InGaN thin films have been anticipated by considering the effects of strain energy, the self-energy of misfit dislocations and surface energy to Gibbs free energy. Total Gibb's free energy varies with Indium composition and thickness of the epitaxial thin film. The calculated results indicate that over critical thickness, energy of the films increases with increasing thickness. The phase diagrams of InGaN films grown on GaN substrate have been calculated. There is a small effect of surface energies of solid phases on the phase diagrams of epitaxial film. With increasing the thickness of InGaN films the wurtzite phase is found to be decreased. This is due to the increase of thickness, misfit dislocations and the commencing of phase separation. Accurate information of InGaN nano film is applicable for the innovation of III-nitride based nano-electronics system.