Output Power Ratio Research Articles

Effect Of Variable Practice On The Motor Learning Process In Manual Wheelchair Propulsion

Handrim wheelchair propulsion is a cyclic skill that needs to be learned during rehabilitation. It has been suggested that a higher intra-individual variability benefits the motor learning process of wheelchair propulsion. PURPOSE: The goal of the current study was to determine the effect of variable practice, in the form of wheelchair basketball and skills training, on the motor learning process of wheelchair propulsion in novice able-bodied participants. Motor learning was operationalized as improvements in mechanical efficiency (ratio of power output and energy expenditure) and propulsion technique. METHODS: 11 Participants performed a pre-test, 7 practice sessions and a post-test. During the practice sessions, participants performed one-hour of variable practice, consisting of five wheelchair-skill tests and a 30 min wheelchair basketball game. Pre- and post-test were performed in a wheelchair on a motor-driven treadmill (1.11 m/s) at a relative power output of 0.23 W/kg. Energy consumption and the propulsion technique variables were calculated. RESULTS: Comparison of the pre- and the post-test showed that variable practice resulted in a 27% relative increase in mechanical efficiency (4.5 ± 0.6 vs. 5.7 ± 0.7%, p<0.001). With regard to propulsion technique, the push frequency reduced (65.4 ± 12.3 vs. 57.8 ± 8.6 pushes/min, p=0.011), the contact angle of the hand with the handrim increased (67.0 ± 8.6 vs. 77.6 ± 9.1°, <0.001) and the braking torque at (de)coupling reduced (-1.1 ± 0.8 vs. -0.5 ± 0.4 Nm, <0.001). No significant changes were found for the positive work (9.0 ± 1.8 vs. 9.7 ± 1.8 J, p=0.369) and peak torque per push (12.5 ± 2.2 vs. 11.6 ± 1.9 Nm, p=0.084) CONCLUSION: The present study showed that variable practice results in an increase in mechanical efficiency and an improvement in propulsion technique. Interestingly the large relative improvement in mechanical efficiency was concomitant with only moderate improvements in the propulsion technique, suggesting that other factors besides propulsion technique contributed to the higher efficiency. It may be that variable practice facilitated the exploitation of the dynamics of the task and improved coordination, which may have contributed to a less straining propulsion

Lithographic wavelength control of an external cavity laser with a silicon photonic crystal cavity-based resonant reflector.

We report the experimental demonstration of a new design for external cavity hybrid lasers consisting of a III-V semiconductor optical amplifier (SOA) with fiber reflector and a photonic crystal (PhC)-based resonant reflector on SOI. The silicon reflector is composed of an SU8 polymer bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and side-mode suppression ratios of more than 25 dB.

多段ランキンサイクルにおける熱源間温度差と最大出力に関する研究

Low-grade Thermal Energy Conversion (LTEC) utilizes the unutilized heat source. The important to improvement performance of LTEC system is the thermal efficiency enhancement because of a small temperature difference between high- and low-temperature heat sources. This paper investigates on the influence of the temperature difference between high- and low-temperature heat sources on the system performance of the multi-stage Rankine cycle. As a result, maximum power and heat sources temperature change increase with an increase of the temperature difference. On the other hand, the temperature difference has little influence on the effectiveness ratio of maximum power output.

Optimum design method of Organic Rankine Cycle system based on semi-empirical model and experimental validation

In this paper, a practical method for designing Organic Rankine Cycle (ORC) power generation system was proposed. The design method was aimed to optimize the cost performance of ORC system and based on experiments and theoretically modeling. In this study, two experimental systems have been built. The first experimental system was used to offer data which were essential to establish the relationships needed to build the semi-empirical model. The second experimental system was employed to validate the model. In the semi-empirical model, objective function was established to quantify the ratio of power output to heat exchangers’ area (preheater, evaporator and condenser’s area), which was used to characterize the cost performance of ORC systems. By combining the experimental data from the first experimental system and theoretical formulas, the objective function was derived with a single variable: evaporation temperature. In the objective function, the optimized evaporation temperature could be obtained by using extremum method. Then other parameters of the ORC system could be also acquired through the model which would allow the ORC system to have good or the best cost performance.

미세입자의 정밀제어를 위한 표면탄성파 장치의 특성연구 및 설계

Surface acoustic wave(SAW) device is used for transporting and patterning micro-scale particles such as cells. In this research, velocity of particles was investigated moved by SAW device with two types of interdigital electrode transducers(IDTs) under various conditions. SAW devices which have single IDTs and double IDTs were designed and fabricated. On the previous studies, resultant velocities of particles were predicted considering output power and power ratio between IDTs-shape. For more accurate prediction, power loss in SAW device and a power difference between two types of IDTs-shape were considered. Maximum error between the test results and predicted values was 5 % so the power loss must be considered in the velocity prediction of the particles.

Analytical Design Methodology for Generic Doherty Amplifier Architectures Using Three-Port Input/Output Networks

In this paper, a new Doherty amplifier architecture along with an analytical based design methodology is proposed. The proposed architecture uses novel three-port network as the output matching/combining network (OMCN). The three-port OMCN performs the power combining for any arbitrary output power ratios from the two transistors of the Doherty amplifier. It also performs the impedance matching from any arbitrary complex load impedance to the optimum impedances for both transistors at peak output power. Commonly in Doherty amplifiers, an optimum performance at peak power and a sub-optimum performance at power back-off are often obtained. Using the proposed output network, optimum performance can be reached at power back-off, as well as at peak power. Another three-port network is proposed for input matching/dividing network (IMDN) at the input of the proposed Doherty amplifier. The three-port IMDN is designed to perform the power division with any arbitrary division ratio, adjust the arbitrary phase difference between the input signals to the two transistors, and provide the impedance matching from any arbitrary complex source impedance to the optimal source impedances for the two transistors. To verify the provided theory, two prototype amplifiers are designed and tested. A 12-W amplifier is designed for a 50- $\Omega$ source and load impedances at 1 GHz. Another 12-W amplifier is designed at 1 GHz for complex source and load impedances. Both amplifiers have efficiency of higher than 50% at 7-dB output power range.

Economic performances optimization of an organic Rankine cycle system with lower global warming potential working fluids in geothermal application

The aim of this study is to investigate the economic optimization for an ORC system utilizing the geothermal energy. An economic parameter of net power output index, which is the ratio of net power output to the total cost, is proposed to optimize the ORC system using zero ODP and lower GWP working fluids. The maximum net power output index is obtained and the corresponding optimal pinch point temperature differences of heat exchangers are also evaluated for the ORC system. Furthermore, the analyses of the corresponding operating temperatures and pressures on the optimal economic performances of the ORC system are carried out. The effects of turbine inlet temperatures and their corresponding optimization are also discussed. The results show that R600 performs the most satisfactorily followed by R600a, R1233zd, R1234yf, R1234ze, and R290 under economic performance optimization. Moreover, the pinch point temperature differences in the evaporator vary more significantly than those in the condenser in optimal economic evaluations. The ORC system operated with R600, R600a, and R1233zd would have reductions in the proportion of equipment purchased cost from large to small attributed to lower operating pressures.

Investigation and simulation of photonic crystal directional coupler switch

The photonic crystal optical switch is one of the most important applications of photonic crystals in telecommunication networks. Switching is a main process in digital computers and signal processing systems. The growth of optical signal processing systems draws particular attention to the design of ultra-fast optical switches. In this reported work, first a directional coupler switch based on photonic crystals is designed and the linear state has been analysed and simulated. Then, the principles of nonlinear optics are used to perform optical switching at a wavelength of 1550 nm by COMSOL Multiphysics in micron dimension. The dielectric rods of this photonic crystal lattice are made of AlGaAs. The central row is an important factor for attaining the required power in nonlinear switching performance. Finally, the radius of rods in the central nonlinear row is changed several times and the results are compared with each other. In this switch, the output power ratio, called the extinction ratio, and the required refractive index change for the nonlinear status are taken into account. The former is for the evaluation of directional coupler efficiency and the latter is generally an important factor in optical nonlinear switches.

Two-stage evaporation strategy to improve system performance for organic Rankine cycle

Abstract The organic Rankine cycle (ORC) is a promising technology for heat recovery. However, evaporator leads to the highest irreversible loss and results in reducing cycle efficiency. In this paper, the heat source was segmented into two temperature ranges, which provides the possibility of two-stage evaporation. Based on cycle configuration, parallel two-stage organic Rankine cycle (PTORC) and series two-stage organic Rankine cycle (STORC) were put forward. The objective is to evaluate system performances, thereby elucidating their respective availability. Geothermal water inlet temperature (GWIT) ranges from 90 to 120 °C, with R245fa as the working fluid. The ratio of net power output to the total thermal conductance was chosen as the objective function. The results show that PTORC and STORC are significantly influenced by intermediate geothermal water temperature (IGWT) and evaporating temperatures. PTORC and STORC could evidently reduce the irreversible loss, and STORC is more significant. PTORC and STORC can output more net power, depending on cycle configuration and GWIT. STORC enhances the net power output with GWIT, whereas PTORC is just the opposite. The total thermal conductance of PTORC and STORC are almost equal with that of ORC. STORC presents more excellent system performance and deserves to be popularized in engineering applications.

Experimental study on the performance of single-screw expander with different inlet vapor dryness

A single-screw expander with 155 mm diameter screw has been developed. In order to investigate the performance of this prototype with different inlet vapor dryness, an organic Rankine cycle experimental system was built, and experiments were conducted at different inlet vapor dryness by adjusting the mass flow rate of working fluid into evaporator. The results indicated that with the increase of inlet vapor dryness, the power output and expansion ratio were increased，however， the volume efficiency and overall efficiency were decreased. The maximums of power output, expansion ratio, volumetric efficiency and total efficiency of single-screw expander were 5.12 kW, 4.55, 80.5% and 49.5%, respectively.

Exergy-based thermodynamic analysis of solar driven Organic Rankine Cycle

In this paper thermodynamic modeling of organic Rankine cycle (ORC) driven by parabolic trough solar collectors is presented. Eight working fluids for the ORC were examined. The effect of turbine inlet temperature on main energetic and exergetic performance parameters were studied. The influences of turbine inlet temperature on turbine size parameter, turbine outlet volume flow rate and expansion ratio were also investigated. Important exergetic parameters including irreversibility ratio and total exergy destruction rate were also included in the analysis and evaluated. The study reveals that increasing the turbine inlet temperature results in increasing the net electric efficiency, net power output, exergy efficiency and expansion ratio while the total exergy destruction rate and turbine size parameter are reduced. From the considered working fluids, o-xylene gives the best energetic and exergetic performance. The results of the study also show that the main source of exergy destruction occurs in the solar collector where 74.9% of the total exergy loss is destructed. Next to collectors, 18.2% of the total destructed exergy occurs in the condenser

Efficiency of piezoelectric mechanical vibration energy harvesting

Harvesting efficiency of a piezoelectric vibration energy harvesting system is investigated to provide design guidelines for harvesting devices with optimal performance. Harvesting power efficiency (η), defined as the ratio of device output power (Pout) to mechanical input power (Pin), is an essential but unexplored metric for comparison of harvesters operating in different power-input environments. Power extracted from piezoelectric harvesters has been of primary interest and proper accounting of mechanical input power and efficiency metrics has not been considered. Here, we present a closed form solution for harvesting efficiency that allows device comparison and furthermore, efficiency-optimized versus power-optimized electrical loading conditions are compared along with a case study. A key finding is that optimal design parameters for efficiency are quite different than optima for output power (e.g., a single optimum versus dual optima at different frequencies), requiring multi-objective design. These new findings provide guidelines on system parameters that can be manipulated for optimized performance in different ambient source conditions.

Fast optical frequency sweeping using voltage controlled oscillator driven single sideband modulation combined with injection locking.

An ultrafast optical frequency sweeping technique for narrow linewidth lasers is reported. This technique exploits the large frequency modulation bandwidth of a wideband voltage controlled oscillator (VCO) and a high speed electro-optic dual parallel Mach-Zehnder modulator (DPMZM) which works on the state of carrier suppressed single sideband modulation(CS-SSB). Optical frequency sweeping of a narrow linewidth fiber laser with 3.85 GHz sweeping range and 80 GHz/μs tuning speed is demonstrated, which is an extremely high tuning speed for frequency sweeping of narrow linewidth lasers. In addition, injection locking technique is adopted to improve the sweeper's low optical power output and small side-mode suppression ratio (SMSR).

A Physics-Based Modeling Approach for Performance Monitoring in Gas Turbine Engines

Performance deterioration monitoring is an essential part of the prognostics and health management (PHM) of gas turbine engines (GTEs). This paper proposes a physics-based modeling approach for performance deterioration monitoring with two model-based performance indicators, heat loss index and power deficit index, for GTE PHM applications. A comprehensive nonlinear thermodynamic model for a single shaft GTE is developed to establish the relation between the operating conditions and the cycle parameters. The model, once properly calibrated, is able to predict the GTE cycle parameters in a healthy condition as the baseline, while in reality, the measured parameters gradually deviate from the baseline, which reflects the performance deterioration of the GTE. To represent the degradation level, the heat loss index is defined as the normalized measure of the thermal power that is being wasted in the GTE compared to the healthy condition. Similarly, the power deficit index is defined as the deficiency ratio of the GTE output power due to the performance deterioration. The effectiveness of the performance indicators in monitoring performance deterioration and their robustness to the variations of the operating conditions are examined by using three years of typical operating data of an industrial GTE. The results clearly reveal the trends of both the short term recoverable deterioration due to fouling effects in the compressor, and the long term non-recoverable deterioration caused by structural degradation. The technique is especially advantageous for prognostic applications where there is no access to internal cycle parameters of a GTE, and only the operating data are available, hence no additional sensors are required.

Economic performances optimization of the transcritical Rankine cycle systems in geothermal application

The aim of this study is to investigate the economic optimization of a TRC system for the application of geothermal energy. An economic parameter of net power output index, which is the ratio of net power output to the total cost, is applied to optimize the TRC system using CO2, R41 and R125 as working fluids. The maximum net power output index and the corresponding optimal operating pressures are obtained and evaluated for the TRC system. Furthermore, the analyses of the corresponding averaged temperature differences in the heat exchangers on the optimal economic performances of the TRC system are carried out. The effects of geothermal temperatures on the thermodynamic and economic optimizations are also revealed. In both optimal economic and thermodynamic evaluations, R125 performs the most satisfactorily, followed by R41 and CO2 in the TRC system. In addition, the TRC system operated with CO2 has the largest averaged temperature difference in the heat exchangers and thus has potential in future application for lower-temperature heat resources. The highest working pressures obtained from economic optimization are always lower than those from thermodynamic optimization for CO2, R41, and R125 in the TRC system.

Reactive Power and Soft-Switching Capability Analysis of Dual-Active-Bridge DC-DC Converters with Dual-Phase-Shift Control

This paper focuses on a systematical and in-depth analysis of the reactive power and soft-switching regions of Dual Active Bridge (DAB) converters with dual-phase-shift (DPS) control to achieve high efficiency in a wide operating range. The key features of the DPS operating modes are characterized and verified by analytical calculation and experimental tests. The mathematical expressions of the reactive power are derived and the reductions of the reactive power are illustrated with respect to a wide range of output power and voltage conversion ratios. The ZVS soft-switching boundary of the DPS is presented and one more leg with ZVS capability is achieved compared with the CPS control. With the selection of the optimal operating mode, the optimal phase-shift pair is determined by performance indices, which include the minimum peak or rms inductor current. All of the theoretical analysis and optimizations are verified by experimental tests. The experimental results with the DPS demonstrate the efficiency improvement for different load conditions and voltage conversion ratios.

Efficient Dual-Wavelength Synchronously Mode- Locked Picosecond Laser Operating on the 4F 3/2 → 4I11/2 Transition With Compactly Combined Dual Gain Media

A novel concept based on the dual gain media is originally proposed for achieving a compact efficient dual-wavelength synchronously mode-locked diode-end-pumped Nd laser on the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3/2</sub> → <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11/2</sub> transition. We theoretically and experimentally realize that the output power ratio between two spectral outputs could be flexibly controlled simply by varying the waist position of the pump beam inside the composite gain medium. With the developed tactic, the total output power at 1.06 μm for balancing two-color intensities reaches 2.9 W. Moreover, suppressing the excitation of a few high-order transverse modes enables a fairly stable picosecond pulse train to be achieved with the self mode locking, where the mode-locked pulse width and repetition rate are measured to be 47 ps and 2.86 GHz, respectively. A series of 0.32 THz ultrashort pulses with the effective duration of 1.6 ps is further generated through the optical beating between two carrier frequencies of dual-wavelength synchronous pulses.

Modelling and optimization of organic Rankine cycle based on a small-scale radial inflow turbine

In most of the organic Rankine cycle (ORC) studies, constant expander efficiency is considered for a wide range of cycle operating conditions and for various working fluids. This study presents an optimized modelling approach for the ORC based on radial inflow turbine, where the constant expander efficiency is replaced by dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. Considering the size and performance of the ORC, the model was used to identify the key input variables that have significant effects on the turbine overall size and the cycle net electric power output. These parameters were then included in the optimization process using the DIRECT algorithm to maximize the ratio of cycle net electric power output to the turbine overall size (objective function) for six organic fluids. Results showed that, dynamic efficiency approach predicted considerable differences in the turbine efficiencies of various working fluids. The maximum difference of 6.13% between the turbine efficiencies of R245fa and isobutane was predicted. Also the optimization results showed that, the maximum objective function of 0.5748kW/mm was achieved by isobutane with the cycle net electric power output and the turbine overall size of 90.3kW and 157.2mm respectively. Such results are better than the other studies and highlight the potential of the optimization technique to further improve the performance and reduce the size of the ORC based on small-scale radial turbines.

High Output Power and Burst Extinction Ratio λ-Tunable ONU Transmitter Using Burst-Mode Booster SOA for WDM/TDM-PON

This paper proposes a high output power and high burst extinction ratio wavelength (λ)-tunable optical network unit (ONU) transmitter for long-reach and high-splitting ratio wavelength-division multiplexing and time-division multiplexing passive optical network (WDM/TDM-PON) systems. Our λ-tunable ONU burst-mode transmitter (B-Tx) utilizes a simply configured burst-mode controlled booster semiconductor optical amplifier (SOA) that employs the pattern effect mitigation technique of gain peak detuning. A high output power and burst extinction ratio are successfully achieved at all upstream wavelength channels, over +10.0 dBm and 66.0 dB, respectively. This burst extinction ratio performance satisfies the ONU requirement for a 64-split WDM/TDM-PON with crosstalk penalty of better than under 0.1 dB. Moreover, the pattern effect is greatly mitigated and 40 km transmission penalty of under 0.8 dB is achieved. We successfully demonstrate over a 41 dB loss budget and 40 km reach λ-tunable WDM/TDM-PON without an optical-amplifier-based PON repeater.

An Equivalent-Asymmetric Coupling Coefficient DFB Laser With High Output Efficiency and Stable Single Longitudinal Mode Operation

An equivalent-asymmetric coupling coefficient (EACC) distributed feedback laser (DFB) semiconductor laser with equivalent-half apodization grating (EHAG) structure is proposed and experimentally demonstrated for the first time; the EHAG profile is equivalently realized by linearly changing the duty cycle of a sampled Bragg grating along the one half cavity, while that of the other half cavity is kept uniform. Compared with the equivalent-symmetric coupling coefficient DFB laser, the simulated intensity distribution of the EACC DFB laser shows that the light power is concentrated not only on near the phase-shift region and that the power at the front end is enlarged. Therefore, the longitudinal spatial hole burning may be reduced; the output efficiency and the single-mode stability may be improved. The experimental results show that the output power ratio between the front and rear facets is about 2.17 and the side-mode suppression ratios are over 50 dB when the injection current is in the range from 60 to 200 mA.