When Amdahl Meets Young/Daly

International audienceThis paper investigates the optimal number of processors to execute a parallel job, whose speedup profile obeys Amdahl's law, on a large-scale platform subject to fail-stop and silent errors. We combine the traditional checkpointing and rollback recovery strategies with verification mechanisms to cope with both error sources. We provide an exact formula to express the execution overhead incurred by a periodic checkpointing pattern of length T and with P processors, and we give first-order approximations for the optimal values T * and P * as a function of the individual processor failure rate λind. A striking result is that P * is of the order λ −1/4 ind if the checkpointing cost grows linearly with the number of processors, and of the order λ −1/3 ind if the checkpointing cost stays bounded for any P. We conduct an extensive set of simulations to support the theoretical study. The results confirm the accuracy of first-order approximation under a wide range of parameter settings

Emergency Localization for Mobile Ground Users: An Adaptive UAV Trajectory Planning Method

In emergency search and rescue scenarios, the quick location of trapped people is essential. However, disasters can render the Global Positioning System (GPS) unusable. Unmanned aerial vehicles (UAVs) with localization devices can serve as mobile anchors due to their agility and high line-of-sight (LoS) probability. Nonetheless, the number of available UAVs during the initial stages of disaster relief is limited, and innovative methods are needed to quickly plan UAV trajectories to locate non-uniformly distributed dynamic targets while ensuring localization accuracy. To address this challenge, we design a single UAV localization method without hovering, use the maximum likelihood estimation (MLE) method to estimate the location of mobile users and define the upper bound of the localization error by considering users' movement.Combining this localization method and localization error-index, we utilize the enhanced particle swarm optimization (EPSO) algorithm and edge access strategy to develop a low complexity localization-oriented adaptive trajectory planning algorithm. Simulation results demonstrate that our method outperforms other baseline algorithms, enabling faster localization without compromising localization accuracy

Revisiting Stereo Triangulation in UAV Distance Estimation

Distance estimation plays an important role for path planning and collision avoidance of swarm UAVs. However, the lack of annotated data seriously hinders the related studies. In this work, we build and present a UAVDE dataset for UAV distance estimation, in which distance between two UAVs is obtained by UWB sensors. During experiments, we surprisingly observe that the stereo triangulation cannot stand for UAV scenes. The core reason is the position deviation issue due to long shooting distance and camera vibration, which is common in UAV scenes. To tackle this issue, we propose a novel position correction module, which can directly predict the offset between the observed positions and the actual ones and then perform compensation in stereo triangulation calculation. Besides, to further boost performance on hard samples, we propose a dynamic iterative correction mechanism, which is composed of multiple stacked PCMs and a gating mechanism to adaptively determine whether further correction is required according to the difficulty of data samples. We conduct extensive experiments on UAVDE, and our method can achieve a significant performance improvement over a strong baseline (by reducing the relative difference from 49.4% to 9.8%), which demonstrates its effectiveness and superiority. The code and dataset are available at https://github.com/duanyuan13/PCM.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Quand Amdahl rencontre Young/Daly

This paper investigates the optimal number of processors to execute a parallel job, whose speedup profile obeys Amdahl's law, on a large-scale platform subject to fail-stop and silent errors. We combine the traditional checkpointing and rollback recovery strategies with verification mechanisms to cope with both error sources. We provide an exact formula to express the execution overhead incurred by a periodic checkpointing pattern of length $T$ and with $P$ processors,and we give first-order approximations for the optimal values $T^{*}$ and $P^{*}$as a function of the individual processor failure rate $\lambda_{\mathrm{ind}}$. A striking result is that$P^{*}$ is of the order $\lambda_{\mathrm{ind}}^{-1/4}$ when the checkpointing cost grows linearly with thenumber of processors, andof the order $\lambda_{\mathrm{ind}}^{-1/3}$ when the checkpointing cost stays bounded for any $P$.We conduct an extensive set of simulations to support the theoretical study. The results confirm the accuracy of the first-order approximation under a wide range of parameter settings.Cet article étudie le nombre optimal de processeurs pour exécuter un travail parallèle dont le profil d'accélération obéit à la loi d'Amdahl, sur une plateforme à grande échelle exposée aux pannes et aux erreurs silencieuses. Nous combinons l'approche traditionnelle de checkpointing/recovery avec des mécanismes de vérification pour faire face aux deux types d'erreurs. Nous fournissons une formule exacte pour mesurer le surcoût du temps d'exécution induit par un motif de checkpoint périodique de longueur $T$ et avec $P$ processeurs, et nous donnons une approximation au premier ordre des valeurs optimales de $T^{*}$ et $P^{*}$ en fonction du taux d'erreur individuel d'un processeur $\lambda_{\mathrm{ind}}$Un résultat frappant est que $P^{*}$ est de l'ordre de $\lambda_{\mathrm{ind}}^{-1/4}$ quand le coût de checkpoint croît linéairement avec le nombre de processeurs, et de l'ordre de $\lambda_{\mathrm{ind}}^{-1/3}$ quand le coût de checkpoint reste borné par $P$.Nous menons une large campagne de simulations pour appuyer l'étude théorique. Les résultats confirmes la précision de l'approximation au premier ordre pour une large gamme de paramètres

Study on the Thermal Distribution Characteristics of High-Speed and Light-Load Rolling Bearing Considering Skidding

Skidding, which frequently occurs in high-speed rolling bearings, has a significant effect on the thermal distribution and service reliability of the bearings. An improved theoretical model of friction power loss distribution in high-speed and light-load rolling bearings (HSLLRBs) considering skidding is established, and the effects of various operating parameters on the friction power loss are investigated. The results show that the friction power loss of the inner ring and outer ring as well as the total friction power loss of the bearing increase as the slip ratio increases, but that the friction power loss of the cage guide surface and roller oil churning show a reverse trend. In addition, the increase in inner ring speed and kinematic viscosity leads to an increase in bearing friction power loss. The steady and transient temperature field distribution of HSLLRBs is obtained by the finite element method (FEM), and the results show that the inner ring raceway has the highest temperature, whereas the cage has the lowest. The temperature distribution test rig of a full-size roller bearing is constructed, and the influence mechanism of the slip ratio, rotation speed, load, lubrication, and surface topography on the bearing temperature distribution are obtained. The experimental results are consistent with the theoretical results, which also validates the theoretical method

Hot Topics and Trends in Zero-Energy Building Research—A Bibliometrical Analysis Based on CiteSpace

With the development of a low-carbon economy, zero-energy structures will become prevalent and take center stage in the construction industry. This paper uses the CiteSpace software to create knowledge maps of authors, institutions and keywords, and then examined and commented on research publications regarding zero-energy buildings in order to understand the research state and development trends of zero-energy buildings. The findings demonstrate that: (1) Since its inception in 2000, research on zero-energy buildings has advanced significantly; (2) A subject analysis approach is used to identify development trends and research emphasis, and the four research areas with the most papers published are energy fuels, construction building technology, civil engineering and green sustainable science technology; (3) China, the United States and Italy are the countries with the most activity in zero-energy building research; (4) Out of the eight most prominent keywords for the study subjects, the design of zero-energy buildings, the estimation of the carbon emissions of zero-energy buildings, the technical challenges of zero-energy buildings and the follow-up energy-saving measures of zero-energy buildings are the four fundamental topics covered in the most cited papers; (5) There are three obstacles to the development of zero-carbon buildings: unclear standards, immature technology and insufficient development momentum. The following three problems should receive more attention in the future: how to develop a widely accepted zero-carbon building standard; how to coordinate national support to achieve technological breakthroughs; and the establishment of an effective incentive mechanism at the international and national levels to promote the development of zero-carbon buildings

Exploring accountability in an entrepreneurial firm

We present qualitative empirical evidence on the use of accountability within a small entrepreneurial firm. Using the ethnographic approach of participant observation to fully immerse ourselves in the business, we explore how accountability issues that have been commonly acknowledged in Western literature can be addressed and overcome in a developing economy. In doing so, we highlight the tensions and issues that are confronted by a strong owner-manager, with a global perspective and international education. Our analysis considers issues of control, risk, information, communication and monitoring. Overall we present, for the first time, evidence that accountability, as conceived by Western academics, exists in China, but that cultural tensions can lead to difficulties in its implementation. Educating SMEs in developing economies about the advantages of transparent communication is a lesson to be learned from our findings