This paper proposes a parabolic dish/AMTEC solar thermal power system and evaluates its overall thermal–electric conversion performance. The system is a combined system in which a parabolic dish ...solar collector is cascaded with an alkali metal thermal to electric converter (AMTEC) through a coupling heat exchanger. A separate type heat-pipe receiver is selected to isothermally transfer the solar energy from the collector to the AMTEC. To assess the system’s overall thermal–electric conversion performance, a theoretical analysis has been undertaken in conjunction with a parametric investigation by varying relevant parameters, i.e., the average operating temperature and performance parameters associate with the dish collector and the AMTEC. Results show that the overall conversion efficiency of parabolic dish/AMTEC system could reach up to 20.6% with a power output of 18.54
kW corresponding to an operating temperature of 1280
K. Moreover, it is found that the optimal condenser temperature, corresponding to the maximum overall efficiency, is around 600
K. This study indicates that the parabolic dish/AMTEC solar power system exhibits a great potential and competitiveness over other solar dish/engine systems, and the proposed system is a viable solar thermal power system.
The convection heat loss from cavity receiver in parabolic dish solar thermal power system can significantly reduce the efficiency and consequently the cost effectiveness of the system. It is ...important to assess this heat loss and subsequently improve the thermal performance of the receiver. This paper aims to present a comprehensive review and systematic summarization of the state of the art in the research and progress in this area. The efforts include the convection heat loss mechanism, experimental and numerical investigations on the cavity receivers with varied shapes that have been considered up to date, and the Nusselt number correlations developed for convection heat loss prediction as well as the wind effect. One of the most important features of this paper is that it has covered numerous cavity literatures encountered in various other engineering systems, such as those in electronic cooling devices and buildings. The studies related to those applications may provide valuable information for the solar receiver design, which may otherwise be ignored by a solar system designer. Finally, future development directions and the issues that need to be further investigated are also suggested. It is believed that this comprehensive review will be beneficial to the design, simulation, performance assessment and applications of the solar parabolic dish cavity receivers.
The large, positive correlation between speaking time and leader emergence is well-established. As such, some authors have argued for a “babble hypothesis” of leadership, suggesting that only the ...quantity of speaking, not its quality, determines leader emergence. However, previous tests of this notion may have been problematic. Some studies have asserted a causal effect of speaking time on leader emergence based on experimental studies, but have limited participant communication, access to reliable information, or both. Other studies have used more ecologically valid designs, but have not always controlled for relevant participant traits or roles, suggesting potential endogeneity effects. Testing the babble hypothesis thus requires a study that is both ecologically valid and supports strong inference. The current study fills that gap and finds that speaking time retains its direct effect on leader emergence when accounting for intelligence, personality, gender, and the endogeneity of speaking time.
Adverse childhood experiences (ACEs), which include abuse and neglect and various household challenges such as exposure to intimate partner violence and substance use in the home, can have negative ...impacts on the lifelong health of affected individuals. Among various strategies for mitigating the adverse effects of ACEs is to enhance connectedness and social support for those who have experienced them. However, how the social networks of those who experienced ACEs differ from the social networks of those who did not is poorly understood.
In this study, we used Reddit and Twitter data to investigate and compare social networks between individuals with and without ACE exposure.
We first used a neural network classifier to identify the presence or absence of public ACE disclosures in social media posts. We then analyzed egocentric social networks comparing individuals with self-reported ACEs with those with no reported history.
We found that, although individuals reporting ACEs had fewer total followers in web-based social networks, they had higher reciprocity in following behavior (ie, mutual following with other users), a higher tendency to follow and be followed by other individuals with ACEs, and a higher tendency to follow back individuals with ACEs rather than individuals without ACEs.
These results imply that individuals with ACEs may try to actively connect with others who have similar previous traumatic experiences as a positive connection and coping strategy. Supportive interpersonal connections on the web for individuals with ACEs appear to be a prevalent behavior and may be a way to enhance social connectedness and resilience in those who have experienced ACEs.
Abstract
Studying extreme ideas in routine choices and discussions is of utmost importance to understand the increasing polarization in society. In this study, we focus on understanding the ...generation and influence of extreme ideas in routine conversations which we label “eccentric” ideas. The eccentricity of any idea is defined as the deviation of that idea from the norm of the social neighborhood. We collected and analyzed data from two sources of different nature: public social media and online experiments in a controlled environment. We compared the popularity of ideas against their eccentricity to understand individuals’ fascination towards eccentricity. We found that more eccentric ideas have a higher probability of getting a greater number of “likes”. Additionally, we demonstrate that the social neighborhood of an individual conceals eccentricity changes in one’s own opinions and facilitates generation of eccentric ideas at a collective level.
The reciprocating-airfoil (RA) driven vertical take-off and landing (VTOL) aircraft is a new aircraft concept that utilizes the reciprocating motion of the wings to provide lift for take-off and ...landing. The RA wings are shaped like the wings of a fixed-wing airplane and work as fixed wings while cruising. The wing undergoes substantial linear motion during take-off and may generate lift similar to a fixed-wing aircraft. The unique structural characteristics of reciprocating wings are their high inertia and lifting force loadings. This study aims to conduct an internal structural analysis of the wing under the maximum lift and inertia force to validate the wing’s performance. The reciprocating motion of the wing in a stroke was analyzed to determine its maximum speed in the stroke and its inertia force loading in conjunction with a reciprocating driver. A 3D computational fluid dynamic (CFD) analysis was conducted at the highest angle of attack (AoA) and the determined maximum speed to obtain maximum lift and drag. The results of a finite element analysis (FEA) revealed acceptable stresses, demonstrating a safe load-carrying capacity of the wing structure, which may ensure the suitability of the wing for integration with the RA UAV module.
In the design stage of an aircraft, structural analyses are commonly employed to test the integrity of the aircraft components to demonstrate the capability of the structural elements to withstand ...what they are designed for, as well as predict potential failure of the components. This research focused on the structural design and analysis of a high-lift, low Reynolds number airfoil profile, the Selig S1223, under reciprocating inertial force loading, to determine the feasibility of its use in a new reciprocating airfoil (RA) driven VTOL UAV. The material selected for the wing structures including ribs, spars, and skin, was high-strength carbon fiber. The wing was designed in SolidWorks, while finite element analysis was performed with ANSYS mechanical in conjunction with the inertia forces due to the reciprocating motion of the wing and the lift and drag forces that were derived from the aerodynamic wing analyses. The structural stress and strain determined under the loading conditions were satisfactory and the designed wing could sustain the high reciprocating inertia forces in the RA-driven VTOL UAV module. The results of this study indicate that the Selig S1223 airfoil profile, due to its superior performance at low Reynolds numbers, high-lift, and reduced noise characteristics at low angles of attack, combined with the use of the high strength carbon fiber, proves to be an excellent choice for this RA-driven aircraft application.
The thermal management of electronics is essential, since their lifetime and reliability are highly dependent on their operating temperature and temperature uniformity. Regarding that, ...Reciprocating-Mechanism Driven Heat Loop (RMDHL) technology has been invented and shows potentiality to become an effective high heat flux cooling system. In this paper, the performance of a reciprocating cooling loop, in terms of heat transfer and temperature distribution, is studied experimentally and analytically. The experimental results showed that, as the reciprocating flow amplitude increases, the loop surface temperature decreases, and the temperature uniformity along the loop improves. However, in contrast to the amplitude effect, a higher frequency may not necessarily improve the temperature uniformity, although the condenser section temperature may be lower. Further, adiabatic section temperature appears to be insensitive to the reciprocating frequency. The experimental results were then summarized in a semi-empirical correlation that demonstrates a useful design tool for the thermal engineer community. Additionally, the analytical results provide critical design requirements that should be considered during Reciprocating-Mechanism Driven Heat Loop (RMDHL) system design.
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