Consistency Models in Distributed Systems with Physical Clocks

Most existing distributed systems use logical clocks to order events in the implementation of various consistency models. Although logical clocks are straightforward to implement and maintain, they may affect the scalability, availability, and latency of the system when being used to totally order events in strong consistency models. They can also incur considerable overhead when being used to track and check the causal relationships among events in some weak consistency models. In this thesis we explore how to efficiently implement different consistency models using loosely synchronized physical clocks. Compared with logical clocks, physical clocks move forward at approximately the same speed and can be loosely synchronized with well-known standard protocols. Hence a group of physical clocks located at different servers can be used to order events in a distributed system at very low cost. We first describe Clock-SI, a fully distributed implementation of snapshot isolation for partitioned data stores. It uses the local physical clock at each partition to assign snapshot and commit timestamps to transactions. By avoiding a centralized service for timestamp management, Clock-SI improves the throughput, latency, and availability of the system. We then introduce Clock-RSM, which is a low-latency state machine replication protocol that provides linearizability. It totally orders state machine commands by assigning them physical timestamps obtained from the local replica. By eliminating the message step for command ordering in existing solutions, Clock-RSM reduces the latency of consistent geo-replication across multiple data centers. Finally, we present Orbe, which provides an efficient and scalable implementation of causal consistency for both partitioned and replicated data stores. Orbe builds an explicit total order, consistent with causality, among all operations using physical timestamps. It reduces the number of dependencies that have to be carried in update replication messages and checked on installation of replicated updates. As a result, Orbe improves the throughput of the system

Performance Profiling in a Virtualized Environment

Virtualization is a key enabling technology for cloud computing. Many applications deployed in a cloud run in virtual machines. However, profilers based on CPU performance counters do not work well in a virtualized environment. In this paper, we explore the possibilities for achieving performance profiling in virtual machine monitors (VMMs) built on paravirtualization, hardware assistance, and binary translation. We present the design and implementation of performance profiling for a VMM based on the x86 hardware extensions, with some preliminary experimental results

Performance Profiling of Virtual Machines

Profilers based on hardware performance counters are indispensable for performance debugging of complex software systems. All modern processors feature hardware performance counters, but current virtual machine monitors (VMMs) do not properly expose them to the guest operating systems. Existing profiling tools require privileged access to the VMM to profile the guest and are only available for VMMs based on paravirtualization. Diagnosing performance problems of software running in a virtualized environment is therefore quite difficult. This paper describes how to extend VMMs to support performance profiling. We present two types of profiling in a virtualized environment: guest-wide profiling and system-wide profiling. Guest-wide profiling shows the runtime behavior of a guest. The profiler runs in the guest and does not require privileged access to the VMM. System-wide profiling exposes the runtime behavior of both the VMM and any number of guests. It requires profilers both in the VMM and in those guests. Not every VMM has the right architecture to support both types of profiling. We determine the requirements for each of them, and explore the possibilities for their implementation in virtual machines using hardware assistance, paravirtualization, and binary translation. We implement both guest-wide and system-wide profiling for a VMM based on the x86 hardware virtualization extensions and system-wide profiling for a VMM based on binary translation. We demonstrate that these profilers provide good accuracy with only limited overhead

SuperYOLO: Super Resolution Assisted Object Detection in Multimodal Remote Sensing Imagery

Accurately and timely detecting multiscale small objects that contain tens of pixels from remote sensing images (RSI) remains challenging. Most of the existing solutions primarily design complex deep neural networks to learn strong feature representations for objects separated from the background, which often results in a heavy computation burden. In this article, we propose an accurate yet fast object detection method for RSI, named SuperYOLO, which fuses multimodal data and performs high-resolution (HR) object detection on multiscale objects by utilizing the assisted super resolution (SR) learning and considering both the detection accuracy and computation cost. First, we utilize a symmetric compact multimodal fusion (MF) to extract supplementary information from various data for improving small object detection in RSI. Furthermore, we design a simple and flexible SR branch to learn HR feature representations that can discriminate small objects from vast backgrounds with low-resolution (LR) input, thus further improving the detection accuracy. Moreover, to avoid introducing additional computation, the SR branch is discarded in the inference stage, and the computation of the network model is reduced due to the LR input. Experimental results show that, on the widely used VEDAI RS dataset, SuperYOLO achieves an accuracy of 75.09% (in terms of mAP50 ), which is more than 10% higher than the SOTA large models, such as YOLOv5l, YOLOv5x, and RS designed YOLOrs. Meanwhile, the parameter size and GFLOPs of SuperYOLO are about 18 times and 3.8 times less than YOLOv5x. Our proposed model shows a favorable accuracy and speed tradeoff compared to the state-of-the-art models. The code will be open-sourced at https://github.com/icey-zhang/SuperYOLO.Comment: The article is accepted by IEEE Transactions on Geoscience and Remote Sensin

Slope Stability Analysis Considering Sliding Effect of Upper Body

Owing to the human engineering activities, the phenomenon that new landslide happen on the upper part of the old sliding body can be found everywhere. This kind of slope consisting of two sliding bodies, which are upper body and lower body, is named as double-sliding-body slope. Its stability is usually analyzed according to two slopes. However, the effect of new landslide movement on the stability of entire slope system is not taken into account. In this paper, sliding effect of upper body is analyzed, and the formula considering sliding effect of upper body is derived based on Sarma method for analysis of entire slope. Theoretical analysis and a case history indicate that the spasmodic motion of upper body has bad effect on the lower body stability; Sliding along the top face of lower body, the effect on the lower body is disadvantageous during starting instant. Nevertheless, the bad effect will disappear and transform as the advantageous effect as descending of the slope gradient and sliding acceleration. For the slope controlling, the sliding effect of upper body should be considered in the stability analysis of double-sliding-body slope, thus it will help us recognizing and mastering or forecasting the evaluative trend of double-siding-body slope. Further reliable scientific basis can be provided in order to make effective controlling measures.特集 : 「資源、新エネルギー、環境、防災研究国際セミナー

深部軟岩坑道用ハイコンベックス・ストリップボルトを用いた複合支保技術に関する研究

Based on the systematic analysis of mechanical characteristics for deep roadway excavated in soft strata, the high convex strip-bolting support technology was put forward, and a numerical analysis was carried out by FLAC3D. The process of general bolting support and high convex strip-bolting support of deep soft rock roadway were simulated. The results indicate that the convex bed of strip-band can adapt to large deformation of high pre-stressed bolting, and the high strength and high rigidity of strip can bear large axial force and moment of flexion. In addition, bolting and anchoring combined support can control the deformation of rock masses by transferring the strength of deep strata, and bolt-grouting can form stress-relief region in deep and generates high strength invert arch at shallow which can afford some support resistances. A case study is also presented and the results of field measurement show that the new support system is suitable for roadways excavated in weak rocks.特集 : 「資源、新エネルギー、環境、防災研究国際セミナー

The Protective Effect of Beraprost Sodium on Diabetic Cardiomyopathy through the Inhibition of the p38 MAPK Signaling Pathway in High-Fat-Induced SD Rats

Objective. To investigate the effect of beraprost sodium (BPS) on diabetic cardiomyopathy and the underlying mechanism. Methods. A total of 40 Sprague Dawley rats were randomly divided into the normal control group (N=10) and the model group (N=30). The model group was fed a high-fat diet followed by a one-time dose of streptozotocin (STZ) to establish the diabetes mellitus model. After that, rats were randomly divided into two groups with or without BPS intervention. After 8 weeks, we explored the role of the p38 MAPK signaling pathway in inflammation, oxidative stress, cardiac morphology, and myocardial apoptosis. Results. Compared with control, the ratio of heart-weight to body-weight and the serum levels of SOD and GSH in the BPS group significantly increased, the expression of p38 MAPK, the serum levels of MDA, TGF-β1, TNF-α, HIF-1α, MMP-9, caspase-3, BNP, ANP, and heart Bax expression significantly decreased, and heart Bcl-2 expression significantly increased. H&E staining in diabetic rats showed the cardiac muscle fibers derangement, the widening gap, the pyknotic and fragmented nuclei, and more apoptosis. Conclusions. BPS effectively showed protective effects on diabetic myocardial cells, possibly through the inhibition of p38 MAPK signaling pathway