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Laser Pouch Motors: Selective and Wireless Activation of Soft Actuators by Laser-powered Liquid-to-gas Phase Change
摘要： A joint optimization problem of link-layer energy efficiency (EE) and effective capacity (EC) in a Nakagami-m fading channel under a delay-outage probability constraint and an average transmit power constraint is considered and investigated in this paper. First, a normalized multi-objective optimization problem (MOP) is formulated and transformed into a single-objective optimization problem (SOP), by applying the weighted sum method. The formulated SOP is then proved to be continuously differentiable and strictly quasiconvex in the optimum average input power, which turns out to be a cup shape curve. Furthermore, the weighted quasiconvex tradeoff problem is solved by first using Charnes–Cooper transformation and then applying Karush–Kuhn–Tucker (KKT) conditions. The proposed optimal power allocation, which includes the optimal strategy for the link-layer EE-maximization problem and the EC-maximization problem as extreme cases, is proved to be sufficient for the Pareto optimal set of the original EE–EC MOP. Moreover, we prove that the optimum average power level monotonically decreases with the importance weight, but strictly increases with the normalization factor, the circuit power and the power amplifier efficiency. Simulation results confirm the analytical derivations and further show the effects of fading severeness and transmission power limit on the tradeoff performance.
关键词： energy efficiency,weighted sum method,delay-outage probability constraint,Quality-of-service,effective capacity,multi-objective optimization problem
更新于2025-09-23 15:21:01
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A Single-Stage Low-Power AC-DC RGB-LED Driver with Switching Capacitor Control Scheme
摘要： The High Efficiency Video Coding (HEVC) standard (ITU-T H.265 and ISO/IEC 23008-2) has been developed with the main goal of providing significantly improved video compression compared with its predecessors. In order to evaluate this goal, verification tests were conducted by the Joint Collaborative Team on Video Coding of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29. This paper presents the subjective and objective results of a verification test in which the performance of the new standard is compared with its highly successful predecessor, the Advanced Video Coding (AVC) video compression standard (ITU-T H.264 and ISO/IEC 14496-10). The test used video sequences with resolutions ranging from 480p up to ultra-high definition, encoded at various quality levels using the HEVC Main profile and the AVC High profile. In order to provide a clear evaluation, this paper also discusses various aspects for the analysis of the test results. The tests showed that bit rate savings of 59% on average can be achieved by HEVC for the same perceived video quality, which is higher than a bit rate saving of 44% demonstrated with the PSNR objective quality metric. However, it has been shown that the bit rates required to achieve good quality of compressed content, as well as the bit rate savings relative to AVC, are highly dependent on the characteristics of the tested content.
关键词： Moving Picture Experts Group (MPEG),H.265,MPEG-H Part 2,Video Coding Experts Group (VCEG),High Efficiency Video Coding (HEVC),video compression,Advanced Video Coding (AVC),Joint Collaborative Team on Video Coding (JCT-VC),standards
更新于2025-09-23 15:21:01
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Understanding the effect of solvent additive in polymeric thin film: turning a bilayer in a bulk heterojunction like photovoltaic device
摘要： Here we report the effect of an additive solvent, the 1,8-diiodooctane (DIO) on the performance of a bilayer organic photovoltaic (OPV) device which active layer comprises the poly[2,7-(9,9-bis(2 ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) as the electron donor material and C60 as the electron acceptor material. We observed that when the donor layer was treated with 1% of DIO the power conversion efficiency (PCE) of the device increase 138.4% in relation to the device with a non-treated donor layer and 21.3% in relation to the device containing a donor layer submitted to a thermal annealed. The main effects that lead to this increase in PCE are the large interfacial area between donor and acceptor materials and the improved conductivity at low voltages. The increase in polymer surface roughness leads to a more effective PSiF-DBT/C60 interface for exciton dissociation. This effect, as well as the increase in the conductivity, raised the short circuit current density (JSC) to 13.89 mA/cm2 and PCE to 4.84%. Our conclusions are supported by morphological analysis, chemical cross-sectional evaluations with advanced microscopy techniques, charge mobility measurements as well as by theoretical simulations of the devices in which the changes on the donor/acceptor interfacial area were considered. The outcomes suggest that, solvent additives could be an alternative treatment to replace the thermal annealing which imposes further difficulties to perform the lab-to-manufacturing upscaling.
关键词： solvent additive,PSiF-DBT,exciton dissociation,1,8-diiodooctane,C60,organic photovoltaic,power conversion efficiency
更新于2025-09-23 15:21:01
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Single-Junction Organic Photovoltaic Cells with Approaching 18% Efficiency
摘要： Optimizing the molecular structures of organic photovoltaic (OPV) materials is one of the most effective methods to boost power conversion efficiencies (PCEs). For an excellent molecular system with a certain conjugated skeleton, fine tuning the alky chains is of considerable significance to fully explore its photovoltaic potential. In this work, the optimization of alkyl chains is performed on a chlorinated nonfullerene acceptor (NFA) named BTP-4Cl-BO (a Y6 derivative) and very impressive photovoltaic parameters in OPV cells are obtained. To get more ordered intermolecular packing, the n-undecyl is shortened at the edge of BTP-eC11 to n-nonyl and n-heptyl. As a result, the NFAs of BTP-eC9 and BTP-eC7 are synthesized. The BTP-eC7 shows relatively poor solubility and thus limits its application in device fabrication. Fortunately, the BTP-eC9 possesses good solubility and, at the same time, enhanced electron transport property than BTP-eC11. Significantly, due to the simultaneously enhanced short-circuit current density and fill factor, the BTP-eC9-based single-junction OPV cells record a maximum PCE of 17.8% and get a certified value of 17.3%. These results demonstrate that minimizing the alkyl chains to get suitable solubility and enhanced intermolecular packing has a great potential in further improving its photovoltaic performance.
关键词： nonfullerene acceptors,organic photovoltaic cells,molecular modification,power conversion efficiency
更新于2025-09-23 15:21:01
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Effect of the Interface Improved by Self-Assembled Aromatic Organic Semiconductor Molecules on Performance of OLED
摘要： This work focuses on characterization the performance of enhanced interface of organic light emitting diode (OLED) device by Self-assembled Monolayer (SAM) technique. SAM technique is popular in order to overcome the weak bonding at the organic/inorganic interface in OLED. New generation of SAM molecules, phenyl-benzoic-acid (PBA, 4-(9H-carbazol-9-il) benzoic acid (MZ39), 4-(2,5-di-2thienyl-1H-pyrrol-1-il) benzoic acid (MZ25) were coated on between Indium Tin Oxide (ITO). The two con?guration of ITO/SAM/TPD/Al and ITO/TPD/Al diode were fabricated as hole-only device to show the contribution of SAM layer on the hole mobility calculated by Space Charge Limited Current (SCLC) technique. The optical characterization of OLED devices with con?guration ITO/TPD/Alq3/Al and ITO/SAM/TPD/Alq3/Al was performed to see the effect of aromatic SAM molecules on the luminance and quantum ef?ciency. Especially, the SAM modi?ed OLED has a maximum luminance of 397 cd m?2. All devices containing SAM layer showed better performance than reference one.
关键词： Indium Tin Oxide (ITO),quantum efficiency,OLED,luminance,Space Charge Limited Current (SCLC),Self-assembled Monolayer (SAM)
更新于2025-09-23 15:21:01
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Reduction of Radius of Curvature in Thin-Sheet-Metal Bending by Ultrashort-Pulsed Laser Peen Forming
摘要： Ultrashort-pulsed laser peen forming is a method of thin-sheet-metal forming using laser-induced shock waves. The authors have applied the process to microsheet parts bending, which is accomplished by repeating line scanning. However, when a severe curvature is requested, nonnegligible reduction of sheet thickness is induced by laser ablation. In order to restrict the thickness reduction, the authors attempted to improve the bending efficiency, which would allow a reduction in the number of necessary pulses. Scanning velocity and scanning pitch were changed, while the total irradiated pulse number was constant. The obtained results showed that a scanning velocity higher than the conventional one is favorable for improving the bending efficiency. In addition, smaller scanning pitches were adopted to reduce the radius of curvature. The influence of the scanning pitch on the bending efficiency was much weaker than that of scanning velocity. From the results of the evaluation of efficiency and scanned surface asperity, a scanning velocity of 20 mm·s-1 was judged to be the best. The best scanning condition achieved a 40% smaller radius of curvature than the conventional one.
关键词： bending,bending efficiency,laser-induced shock wave,ultrashort-pulsed laser,incremental forming,scanning velocity,forming property,laser peen forming
更新于2025-09-23 15:21:01
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Self-focused amplitude modulated super Gaussian laser beam in plasma and THz radiation with high efficiency
摘要： Based on self- focusing of an amplitude modulated super Gaussian laser beam in preformed ripple density plasma, one scheme can be proposed for generating terahertz (THz) radiation at the modulation frequency when pondermotive nonlinearity is operative. The eikonal in paraxial ray approximation (PRA) along with higher order terms in the expansion of the dielectric function have been taken into account. Intensity variation in the direction transverse to the propagated laser causes a pondermotive force which generates transient transverse nonlinear current. At the modulation frequency, the mentioned current drives radiation in THz domain. Therefore, comparing to simple PRA, inclusion of terms with higher order enhances beam self-focusing, THz radiation field and, efficiency. In addition, the degree of the self-focusing is reduced in higher laser beam orders and has changed by the modulation index and the time. Here, by considering higher order paraxial ray approximation and optimizing laser beam and ripple density, plasma parameters are investigated and the efficiency of THz radiation reaches up to 6.5%. This method can be applied for the efficient types of THz radiation.
关键词： Efficiency,Self-focusing,Terahertz radiation,Super Gaussian beam,Amplitude modulated
更新于2025-09-23 15:21:01
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Improvement in efficiency and luminous power of AlGaN-based D-UV LEDs by using partially graded quantum barriers
摘要： In this article, we have demonstrated a new AlGaN-based D-UV LED (Deep-Ultraviolet Light Emitting Diode) structure and investigated improved electrical output characteristics theoretically. In the new structure, we have used partially graded quantum barriers (PQBs) rather than stepped quantum barrier (SQBs) as setup in conventional LEDs. The simulation results confirm that the usage of PQBs in new D-UV LED structure notably enhances the internal quantum efficiency (IQE), light output power (LOP) or luminous power and enhances power spectral density in the D-UV region. The reason behind this improvement is higher potential barrier for carriers in the active region which helps in improving the carrier’s confinement in the quantum wells and favors significant increment in radiative recombination.
关键词： AlGaN,Efficiency,Luminous power,GaN,LED
更新于2025-09-23 15:21:01
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Bright CsPbI <sub/>3</sub> Perovskite Quantum Dot Light-Emitting Diodes with Top-Emitting Structure and a Low Efficiency Roll-Off Realized by Applying Zirconium Acetylacetonate Surface Modification
摘要： Zirconium acetylacetonate used as a co-precursor in the synthesis of CsPbI3 quantum dots (QDs) increased their photoluminescence quantum efficiency to values over 90%. The top-emitting device structure on a Si substrate with high thermal conductivity (to better dissipate Joule heat generated at high current density) was designed to improve the light extraction efficiency making use of a strong microcavity resonance between the bottom and top electrodes. As a result of these improvements, light-emitting diodes (LEDs) utilizing Zr-modified CsPbI3 QDs with an electroluminescence at 686 nm showed external quantum efficiency (EQE) of 13.7% at a current density of 108 mA cm?2, which was combined with low efficiency roll-off (maintaining an EQE of 12.5% at a high current density of 500 mA cm?2) and a high luminance of 14 725 cd m?2, and the stability of the devices being repeatedly lit (cycled on and off at high drive current density) has been greatly enhanced.
关键词： CsPbI3 perovskite quantum dots,top-emitting light-emitting diodes,surface modification,zirconium acetylacetonate,efficiency roll-off
更新于2025-09-23 15:21:01
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Tweaking the physics of interfaces between monolayers of buckled cadmium sulfide for a superhigh piezoelectricity, excitonic solar cell efficiency and thermoelectricity
摘要： Interfaces of heterostructures are routinely studied for different applications. Interestingly, monolayers of the same material when interfaced in an unconventional manner can bring about novel properties. For instance, CdS monolayers, stacked in a particular order, are found to show unprecedented potential in the conversion of nanomechanical energy, solar energy and waste heat into electricity, which has been systematically investigated in this work, using DFT based approaches. Moreover, stable ultrathin structures showing strong capabilities for all kinds of energy conversion are scarce. The emergence of a very high out-of-plane piezoelectricity, |d33| ~ 56 pm/V, induced by the inversion symmetry broken in the buckled structure helps to supersede the previously reported bulk wurzite GaN, AlN and Janus multilayer structures of Mo and W based dichalcogenides. The piezoelectric coefficients have been found to be largely dependent on the relative stacking between the two layers. CdS bilayer is a direct band gap semiconductor with its band edges straddling the water redox potential, thereby making it thermodynamically favorable for photocatalytic applications. Strain engineering facilitates its transition from type-I to type-II semiconductor in CdS bilayer stacked over monolayer boron phosphide, and the theoretically calculated power conversion efficiency (PCE) in the 2D excitonic solar cell exceeds 27% for a fill factor of 0.8, which is much higher than that in ZnO/CdS/CuInGaSe solar cell (20% efficiency). Thermoelectric properties have been investigated using semi classical Boltzmann transport equations for electrons and phonons within the constant relaxation time approximation coupled to deformation potential theory, which reveal ultralow thermal conductivity (~ 0.78 Wm-1K-1) at room temperature due to the presence of heavy element Cd, strong anharmonicity (high mode Gruneisen parameter at long wavelength, phonon lifetime < 5 ps), low phonon group velocity (4 km/s) and low Debye temperature (260 K). Such a low thermal conductivity is lower than that of dumbbell silicene (2.86 Wm-1K-1), SnS2 (6.41 Wm-1K-1) and SnSe2 (3.82 Wm-1K-1), SnP3 (4.97 Wm-1K-1). CdS bilayer shows a thermoelectric figure of merit (ZT) ~ 0.8 for p-type and ~ 0.7 for n-type doping at room temperature. Its ultrahigh carrier mobility (μe ~2270 cm2V-1s-1) is higher than that of single layer MoS2 and comparable to that in InSe. The versatile properties of CdS bilayer together with its all-round stability supported by ab initio molecular dynamics simulation, phonon dispersion and satisfaction of Born-Huang stability criteria highlight its outstanding potential for applications in device fabrication and applications in next generation nanoelectronics and energy harvesting.
关键词： Power conversion efficiency,Excitonic solar cell,Piezoelectricity,Photocatalysis,Solar energy,Semiconductor,Thermoelectricity,Carrier mobility
更新于2025-09-23 15:21:01