Linearized power flow models are of great interest in power system studies such as contingency analyses and reliability assessments, especially for large-scale systems. One of the most popular ...models-the classical DC power flow model-is widely used and praised for its state independence, robustness, and computational efficiency. Despite its advantages, however, the DC power flow model fails to consider reactive power or bus voltage magnitude. This paper closes this gap by proposing a decoupled linearized power flow (DLPF) model with respect to voltage magnitude and phase angle. The model is state independent but is distinguished by its high accuracy in voltage magnitude. Moreover, this paper presents an in-depth analysis of the DLPF model with the purpose of accelerating its computation speed, leading to the fast DLPF (FDLPF) model. The approximation that is applied to obtain the FDLPF model from the DLPF model is justified by a theoretical derivation and numerical tests. The proposed methods are provably accurate and robust for several cases, including radial distribution systems, meshed large-scale transmission systems and ill-conditioned systems. Finally, expressions for sensitivity with regard to MW flow and bus voltage are provided as a potential application.
A new challenge has arisen in power generation scheduling recently, as the rapid increase in the number of gas-fired units has made power systems more vulnerable to failures in natural gas networks. ...The large-scale integration of wind power further exacerbates the problem because gas-fired units are usually scheduled to catch up wind power uncertainty and thus lead to great variations in the state of gas network. To meet this challenge, it is necessary to commit and dispatch the gas-fired units considering both wind uncertainty and natural gas network security. However, the dynamic characteristics of gas flow are remarkably slower than those of power flow, which should be appropriately modeled to explore its benefits for power system operation. Because directly applying partial differential equations overly complicates the already complicated generation scheduling problem, we address this problem by proposing an approximated transient matrix-form gas flow model. A two-stage robust generation scheduling model is then proposed considering the dynamic security constraints of gas networks and the wind power uncertainty. Moreover, we successfully avoid the nonlinearity of gas flow constraints by developing a new solution methodology. Finally, an illustrative case is presented to demonstrate the effect of gas network dynamics in generation scheduling.
Display omitted
•New concept of resistance heat assisted ultrasonic welding (RUSW).•6061 Al and pure Cu were successfully welded by RUSW.•The output power of transducer and the temperature of the ...interface are increased significantly in RUSW.•The microstructure and the mechanical properties of the RUSW joints were improved.
This paper proposes a new welding method for joining non-ferrous metals: resistance heat assisted ultrasonic welding. Resistance heat generated by the electric Joule effect is used as an additional electrical energy source to assist ultrasonic welding process. A comparison is conducted between two dissimilar Al–Cu joints, one produced by ultrasonic welding and the other by resistance heat assisted ultrasonic welding. In the resistance heat assisted ultrasonic process, the peak power of ultrasonic vibration increases significantly. The interfacial reaction between aluminum and copper is studied as a function of the current. The thickness of the intermetallic compound layer, which is predominantly composed of CuAl2, increases with the current. At a relatively high current (1500A), resistance heat assisted ultrasonic welding produced a dendritic solidification microstructure at the interface, due to the occurrence of a eutectic reaction, α-Al+θ→L, during the welding process. The influence of current on the mechanical properties of the joints is also discussed.
Multienergy systems (MESs) are able to unlock the energy system flexibility using the coupling across multiple energy sectors. Such coupling contributes to improving the overall energy efficiency and ...promoting the accommodation of renewable energy. Among a wide range of literature, this article provides a perspective of network analytics on how to model, optimize, and conduct low-carbon analysis on MESs. The energy sector coupling involves different levels, for example, from a single building to nationwide. In this article, we categorize multienergy networks into two levels, that is, the district level that covers a relatively small area such as a campus or a community, where the energy conversion and utilization is the major focus, and the multiregion level that covers a relatively large area such as a big city, a province, or the whole country, where the energy transmission is the major concern. We first review the state-of-the-art multienergy networks standardized modeling approaches including: 1) energy hub (EH) model for district level energy networks; 2) network models, including power, heat, and gas steady-state and dynamic network models, for multiregion level energy networks; and 3) load models, including electricity, heat, and gas load forecasting models. Second, we explore the planning and operation methods for both district level and multiregion level energy networks. Third, we introduce a special technique named the carbon emission flow (CEF) model that is able to calculate the equivalent CO 2 emission associated with the energy flows in multienergy networks. We also demonstrate how the technique can help multienergy networks planning and operation toward a low carbon society. Finally, we envision several further key research topics in the field of multienergy networks.
Ultrasonic welding (UW) is an important joining technique in the electrical industry. Molecular dynamic simulation has been shown to possess several advantages for revealing the evolution of the ...atomic-scale structure and the interpretation of diffusion mechanisms at the microscopic level. However, voids associated with the understanding of microstructure evolution in the weld zone and dynamic processes that occur during ultrasonically welded materials still exist, and no UW studies at the atomic scale have so far been reported. In this study, molecular dynamic simulations of UW between Al and Cu were performed to investigate the diffusion behaviors of Al and Cu atoms. The results confirmed the occurrence of asymmetrical diffusion at the Al/Cu interface during UW. Meanwhile, recovery was noticed in the disordered Al blocks at low temperature. The thickness of the diffusion layer increased with the welding time. For relatively long welding times (1 ns), the concentrations of Al and Cu revealed the appearance of phase transitions. In addition, the diffusion during UW was identified as a dynamic and unsteady process. The diffusion coefficient was much larger than that underwent during the steady diffusion process despite the low interfacial temperature (below 375 K), which was mainly attributed to shear plastic deformation at the interface.
Accumulating data indicate that strigolactones (SLs) are implicated in the response to environmental stress, implying a potential effect of SLs on stomatal response and thus stress acclimatization. ...In this study, we investigated the molecular mechanism underlying the effect of SLs on stomatal response and their interrelation with abscisic acid (ABA) signaling.
The impact of SLs on the stomatal response was investigated by conducting SL-feeding experiments and by analyzing SL-related mutants. The involvement of endogenous ABA and ABA-signaling components in SL-mediated stomatal closure was physiologically evaluated using genetic mutants. Pharmacological and genetic approaches were employed to examine hydrogen peroxide (H2O2) and nitric oxide (NO) production.
SL-related mutants exhibited larger stomatal apertures, while exogenous SLs were able to induce stomatal closure and rescue the more widely opening stomata of SL-deficient mutants. The SL-biosynthetic genes were induced by abiotic stress in shoot tissues. Disruption of ABA-biosynthetic genes, as well as genes that function in guard cell ABA signaling, resulted in no impairment in SL-mediated stomatal response. However, disruption of MORE AXILLARY GROWTH2 (MAX2), DWARF14 (D14), and the anion channel gene SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1) impaired SL-triggered stomatal closure. SLs stimulated a marked increase in H2O2 and NO contents, which is required for stomatal closure.
Our results suggest that SLs play a prominent role, together with H2O2/NO production and SLAC1 activation, in inducing stomatal closure in an ABA-independent mechanism.
A consensus has been reached on the preferred primary outcome of all infertility treatment trials, which is the cumulative live birth rate (CLBR). Some recent randomized controlled trials (RCTs) and ...retrospective studies have compared the effectiveness of GnRH-antagonist and GnRH-agonist protocols but showed inconsistent results. Studies commonly used conservative estimates and optimal estimates to described the CLBR of one incomplete assisted reproductive technology (ART) cycle and there are not many previous studies with data of the complete cycle to compare CLBRs in GnRH-antagonist versus GnRH-agonist protocols.
A total of 18,853 patients have completed their first IVF cycle including fresh and subsequent frozen-thawed cycles during 2016-2019, 16,827 patients were treated with GnRH-a long and 2026 patients with GnRH-ant protocol. Multivariable logistic analysis was used to evaluate the difference of GnRH-a and GnRH-ant protocol in relation to CLBR. Utilized Propensity Score Matching(PSM) for sampling by up to 1:1 nearest neighbor matching to adjust the numerical difference and balance the confounders between groups.
Before PSM, significant differences were observed in baseline characteristics and the CLBR was 50.91% in the GnRH-a and 33.42% in the GnRH-ant (OR = 2.07; 95%CI: 1.88-2.28; P < 0.001). Stratified analysis showed the CLBR of GnRH-ant was lower than GnRH-a in suboptimal responders(46.89 vs 27.42%, OR = 2.34, 95%CI = 1.99-2.74; P < 0.001) and no differences of CLBR were observed in other patients between protocols. After adjusting for potential confounders, multivariable logistic analysis found the CLBR of GnRH-ant group was lower than that of GnRH-a group (OR = 2.11, 95%CI:1.69-2.63, P < 0.001). After PSM balenced the confounders between groups, the CLBR of GnRH-a group was higher than that of GnRH-ant group in suboptimal responders((38.61 vs 28.22%, OR = 1.60, 95%CI = 1.28-1.99; P < 0.001) and the normal fertilization rate and number of available embryo in GnRH-a were higher than these of GnRH-ant groups in suboptimal responders (77.39 vs 75.22%; 2.86 ± 1.26 vs 2.61 ± 1.22; P < 0.05). No significant difference was observed in other patients between different protocols.
It is crucial to optimize the utilization of protocols in different ovarian response patients and reconsider the field of application of GnRH-ant protocols in China.
This paper presents a perturbation observer based single-loop robust decoupling control scheme (RDC-PO) for DC-based DFIG with dual voltage source converters to enhance maximum power point tracking ...(MPPT) and improve fault-ride-through (FRT) capability. The unknown nonlinear effects caused by aerodynamic and modeling uncertainties are aggregated into a perturbation term, which is estimated by a sliding-mode perturbation observer. Then, a single-loop linear feedback controller with no intermediate link is designed to quickly compensate disturbance estimation in real time. Furthermore, the control algorithm does not necessitate a precise DFIG model. Additionally, the incorporation of nonlinear robust control compensates for the inherent limitations of linear control, thereby endowing the proposed control algorithm with the advantages of facile implementation akin to traditional linear control and global consistency characteristic of nonlinear robust control. Simulation results show that RDC-PO has superior transient and steady-state performance compared with double-loop feedback controller (DFC) and single-loop feedback control (SFC) in MPPT and FRT. Finally, Experiment verifies the practical operability of the proposed strategy.
The effects of welding energy on the mechanical and microstructural characteristics of ultrasonic-welded pure copper plates were investigated. Complex dynamic recrystallization and grain growth ...occurred inside the weld zone during ultrasonic welding. At a low welding energy, a thin band of straight weld interfaces was observed and had an ultra-fine grain structure. With an increase in welding energy, the weld interface progressively changed from flat to sinusoidal, and eventually turned into a convoluted wavy pattern, bearing similarities to shear instabilities, as observed in fluid dynamics. The lap shear load of the joints initially increased and then remained stable as the welding energy increased. The tensile characteristics of the joints significantly depended on the development of plastic deformation at the interface. The influence of the microstructure on the hardness was also discussed.
This study investigated ordinary Portland cement substituted with ground bottom ash (BAOPC) under various conditions of BA contents and CO2 curing. In samples without CO2 curing, the strength ...development along with degree of hydration were limited as expected. A higher BA content led to decreased compressive strength, indicating an inferior pozzolanic reaction of BA. Meanwhile, in the CO2-cured samples, a positive correlation between calcium carbonate (CC) content and compressive strength was confirmed, suggesting that CC is a key factor influencing strength development as a result of external CO2 supply. In particular, a higher amount of CC was present in the BAOPC composite with 20% BA substitution compared to the sample with 100% OPC, and substantial mechanical bonding between CC crystals was also confirmed. This study revealed that the combination of BA with limited Ca content and CO2 curing holds promise for developing eco-friendly formulations with enhanced mechanical properties and CO2 utilization.
•CO2 curing was applied to enhance reactivity of bottom ash in ordinary Portland cement (BAOPC).•CO2 curing significantly enhanced the carbonation degree of BAOPC.•The carbonation degree of BAOPC with 20% bottom ash substitution was 6% higher,•The utilization of bottom ash altered the pH of the BAOPC matrix, enhancing mechanical bonding among precipitated calcite crystals.
PDF
