Abstract
Full pump depletion corresponds to the upper limit of the generated signal photons relative to the pump pulse; this allows the highest peak power to be produced in a unit area of ...ultraintense laser amplifiers. In practical systems based on optical parametric chirped-pulse amplification, however, the typical pump depletion is only ~35%. Here, we report quasi-parametric chirped-pulse amplification (QPCPA) with a specially designed 8-cm-thick Sm:YCOB crystal that highly dissipates the idler and hence improves pump depletion. We demonstrate 56% QPCPA energy efficiency for an 810-nm signal converted from a 532-nm pump, or equivalently 85% pump depletion. As another advantage, such a record high depletion greatly suppresses the parametric superfluorescence noise in QPCPA to only ~1.5 × 10
−6
relative to the amplified signal energy. These results pave the way to beyond the ten-petawatt peak power of the currently most intense lasers.
•Without any design change, drop-in sustainable aviation fuel (SAF100) can be tailored to promote energy savings of at most 0.33 %. Such fuel would have an energy density of 34.3 GJ/m3 which is just ...inside the ± 2σ experience interval of conventional jet fuel; 34.0–35.6 GL/m3.•By eliminating the minimum aromatics content imposed on SAF100, optimized fuel could afford at most 0.40% energy savings for a fuel with an energy density of 34.2 GJ/m3, or 0.33% energy savings for a fuel with an energy density of 35.7 GJ/m3.•By raising the minimum energy density requirement (or design point reference fuel) by 4% and increasing the lower heating value of the design point reference fuel by 1%, both of which are attainable for optimized, 100% SAF without aromatics (Jet-X), supersonic aircraft can be made at most 2.3% more energy efficient.•The composition and property characteristics of optimized SAF100 and Jet-X are discussed at length in this article.
Whether the feedstock for sustainable aviation fuel (SAF) originates from agriculture or from waste streams, life cycle CO2 emissions per unit enthalpy are lower for SAF than they are for petroleum distillates primarily because of differences on the front end such as fostered growth of crops or decreased demand for resources or acreage to manage wastes. This work, however, is concerned with what happens on the consumption side. Sustainable aviation fuel is required by ASTM D4054 / D7566 to meet a higher thermal stability standard than petroleum distillate fuels and this characteristic can be leveraged to improve energy efficiency in new engine or aircraft designs where a commitment has been made to burning fuel that meets a specification beyond that of conventional JetA. Beyond thermal stability, non-drop-in SAF (Jet-X) developers have the opportunity to further increase the value of their product by infusing higher-than-conventional-JetA energy density (enthalpy per unit volume, ED) into their SAF. Finally, fuel specific energy (enthalpy per unit mass, LHV) has a direct impact on aircraft efficiency which we have determined to be 0.43% per MJ/kg increase in LHV depending on the mission and aircraft model, and this is applicable to both drop-in and non-drop-in applications. While higher energy density fuels may be leveraged in a new aircraft design to decrease drag and weight, aircraft development potential with reduced tank volumes is typically constrained by other factors such as wing packaging, passenger volume requirements and overall center of gravity and flight control law restrictions.
Market-based instruments such as white certificates offer the potential to increase efficiency gains, reduce primary energy consumption and make energy systems more resilient. The purpose of this ...paper is to provide insights into the white certificate scheme through a case study analysis. In light of increasing decarbonization and energy efficiency targets, it is important to rethink the role that policy instruments play in the energy transition, including the energy efficiency obligation schemes within which white certificate schemes fall. We focus on Italy’s white certificate scheme because it is among the longest-lived and has achieved notable results. The scheme is characterized by annually increasing energy savings targets, flexibility, the opportunity to include many interventions, and the role of energy services companies. We provide evidence based on an empirical survey and fill the research gap left by the latest updates to the scheme along with an appraisal of those updates, which covers prominent scheme innovations such as its stability mechanism. Our research can serve as a baseline for policymakers in designing white certificate schemes in countries with little related previous experience and provide useful information from countries where similar schemes have been implemented to fine-tune similar market-based mechanisms to improve energy efficiency
Non-orthogonal multiple access (NOMA) is considered as a promising technology for improving the spectral efficiency in fifth-generation systems. In this correspondence, we study the benefit of NOMA ...in enhancing energy efficiency (EE) for a multiuser downlink transmission, wherein the EE is defined as the ratio of the achievable sum rate of the users to the total power consumption. Our goal is to maximize EE subject to a minimum required data rate for each user, which leads to a nonconvex fractional programming problem. To solve it, we first establish the feasible range of the transmitting power that is able to support each user's data rate requirement. Then, we propose an EE-optimal power allocation strategy that maximizes EE. Our numerical results show that NOMA has superior EE performance in comparison with conventional orthogonal multiple access.
To overcome the "multiplicative fading effect" introduced by passive reconfigurable intelligent surface (RIS), the concept of active RIS has been recently proposed to amplify the radiated signals. ...However, the existing fully-connected architecture of active RIS consumes high power due to the additionally integrated active components. To address this issue, we propose the sub-connected architecture of active RIS. Different from fully-connected architecture, where each element integrates a dedicated power amplifier, in the sub-connected architecture, multiple elements control their phase shifts independently but share a same power amplifier, which significantly reduces the number of power amplifiers for power saving at the cost of fewer degrees of freedom (DoFs) for beamforming design. Fortunately, our analysis reveals that performance loss introduced by the sub-connected architecture is slight, indicating that it can achieve much higher energy efficiency (EE). Furthermore, we formulate the EE maximization problem in the active RIS-aided system for both architectures and develop a corresponding joint beamforming design. Simulation results verify the proposed sub-connected architecture as an energy-efficient realization of active RIS.
In a Non-Orthogonal Unicast and Multicast (NOUM) transmission system, a multicast stream intended to all the receivers is superimposed in the power domain on the unicast streams. One layer of ...Successive Interference Cancellation (SIC) is required at each receiver to remove the multicast stream before decoding its intended unicast stream. In this paper, we first show that a linearly-precoded 1-layer Rate-Splitting (RS) strategy at the transmitter can efficiently exploit this existing SIC receiver architecture. By splitting the unicast messages into common and private parts and encoding the common parts along with the multicast message into a super-common stream decoded by all users, the SIC is better reused for the dual purpose of separating the unicast and multicast streams as well as better managing the multi-user interference among the unicast streams. We further propose multi-layer transmission strategies based on the generalized RS and power-domain Non-Orthogonal Multiple Access (NOMA). Two different objectives are studied for the design of the precoders, namely, maximizing the Weighted Sum Rate (WSR) of the unicast messages and maximizing the system Energy Efficiency (EE), both subject to Quality of Service (QoS) rate requirements of all messages and a sum power constraint. A Weighted Minimum Mean Square Error (WMMSE)-based algorithm and a Successive Convex Approximation (SCA)-based algorithm are proposed to solve the WSR and EE problems, respectively. Numerical results show that the proposed RS-assisted NOUM transmission strategies are more spectrally and energy efficient than the conventional Multi-User Linear-Precoding (MU-LP), Orthogonal Multiple Access (OMA) and power-domain NOMA in a wide range of user deployments (with a diversity of channel directions, channel strengths and qualities of channel state information at the transmitter) and network loads (underloaded and overloaded regimes). It is superior for the downlink multi-antenna NOUM transmission.
A more efficient use of China’s coal resources is key to rapidly promoting the growth of the country’s industrializing economy. As such, it is essential that an effective approach for measuring and ...evaluating the current efficiency of coal resources is developed. This paper measures the efficiency of coal resources in 30 provinces in China from 2000 to 2015 using an improved DEA model of Bootstrap, and it uses Tobit regression to analyze the influencing factors on the efficiency of coal resources. The results illustrate that: 1) The proposed approach could significantly improve upon the accuracy of the measurement of the traditional DEA model. 2) The efficiency of coal resources shows an uptrend of fluctuation for the research period. With respect to the influential factors, total coal consumption has the least influence on the efficiency of coal resources. In contrast, local financial science and technology expenditures have greatest influence on the efficiency of coal resources. Among all the influential factors, local financial science and technology expenditures have the greatest negative impact on energy efficiency of coal resources and it is very critical that the government increases investment in scientific and technological investment in the mining industry.
•This paper uses Bootstrap-DEA to calculate the ECR of 30 provinces in China.•The finding that FST has negative impact on ECR is the most serious, particularly for 14 provinces in China.•GDP, IPC and SEC have negative impacts on ECR in 8 provinces.•COC has negative impact on ECR in 6 provinces.•TER and RPY have negative impacts on ECR including in 11 provinces and 9 provinces respectively.
The application of a two-phase ejector allows for the mixing of liquid and gas and provides effective heat transfer between phases. The aim of the study is a numerical investigation of the ...performance of a water-driven, condensing two-phase ejector. The research was performed using CFD methods, which can provide an opportunity to analyze this complex phenomenon in 2D or 3D. The 2D axisymmetric model was developed using CFD software Siemens StarCCM+ 2022.1.1. The Reynolds-Averaged Navier–Stokes (RANS) approach with the Realisable k-ε turbulence model was applied. The multiphase flow was calculated using the mixture model. The boiling/condensation model, where the condensation rate is limited by thermal diffusion, was applied to take into account direct contact condensation. Based on the mass balance calculations and developed pressure and steam volume fraction distributions, the ejector performance was analyzed for various boundary conditions. The influence of the suction pressure (range between 0.812 and 0.90) and the steam mass flow rate (range between 10 g/s and 25 g/s) is presented to investigate the steam condensation phenomenon inside the ejector condenser. The provided mixture of inert gas (COsub.2) with steam (Hsub.2O) in the ejector condenser was investigated also. The weakening of the steam condensation process by adding COsub.2 gas was observed, but it is still possible to achieve effective condensation despite the presence of inert gas.
Green development is critical for China's economic transformation. Enhancing green total factor energy efficiency (hereafter GTFEE) is vital to emission reduction and to win-win industrial ...development. This study uses the panel data of 30 Chinese provinces for the period 2005–2016 to investigate the relationship between environmental regulation and China's GTFEE. The spatial Durbin model is employed to control for the possible spatial spillover effect. A dynamic threshold panel model that can effectively address the endogeneity problem and regional heterogeneity is utilized to examine the potential non-linear relationship between environmental regulation and GTFEE under different conditions of environmental decentralization. The estimation results indicate that there is a significant U-shaped relationship between environmental regulation and China's GTFEE. With the further expansion of environmental decentralization, the local government's autonomous choice of pollution control is improved. The improvement of environmental decentralization can lead to negative moderating effect of environmental regulation on GTFEE. Additionally, the regression results of dynamic threshold model show that environmental decentralization can increase the negative influences of environmental regulation on GTFEE. Interestingly, the non-linear impact of environmental regulation on GTFEE is dependent on the specific type of environmental decentralization. Higher degree of environmental decentralization can lead to an increase in the restraining effect of environmental regulation on GTFEE. However, an improvement in the decentralization of environmental supervision and environmental monitoring can increase the negative influences of environmental regulation on GTFEE.
•The impact of environmental regulation on green total factor energy efficiency (GTFEE) is examined.•Environmental decentralization is introduced as moderating variables.•Spatial econometric methods and dynamic threshold models are used for empirical estimations.•There exists a significant U-shaped relationship between environmental regulation and China's GTFEE.•Environmental decentralization increases the restraining effect of environmental regulation on GTFEE.
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