Editorial

Machine Vision and Applications -     

A Scalable Asynchronous Cache Consistency Scheme (SACCS) for mobile environments

In the literature, there exit two types of cache consistency maintenance algorithms for mobile computing environments: stateless and stateful. In a stateless approach, the server is unaware of the cache contents at a mobile user (MU). Even though stateless approaches employ simple database management schemes, they lack scalability and ability to support user disconnectedness and mobility. On the other hand, a stateful approach is scalable for large database systems at the cost of nontrivial overhead due to server database management. We propose a novel algorithm, called Scalable Asynchronous Cache Consistency Scheme (SACCS), which inherits the positive features of both stateless and stateful approaches. SACCS provides a weak cache consistency for unreliable communication (e.g., wireless mobile) environments with small stale cache hit probability. It is also a highly scalable algorithm with minimum database management overhead. The properties are accomplished through the use of flag bits at the server cache (SC) and MU cache (MUC), an identifier (ID) in MUC for each entry after its invalidation, and estimated time-to-live (TTL) for each cached entry, as well as rendering of all valid entries of MUC to uncertain state when an MU wakes up. The stale cache hit probability is analyzed and also simulated under the Rayleigh fading model of error-prone wireless channels. Comprehensive simulation results show that the performance of SACCS is superior to those of other existing stateful and stateless algorithms in both single and multicell mobile environments.     

Surface behaviour of as-Cast Al–Fe intermetallic composites

In order to produce energy-efficient material for tribological applications, Al–Fe inter-metallic composites have been produced by liquid metallurgy route. Iron content of the composites varies from 1.67 to 11.2 wt.%. These composites have been tested for their wear properties at different parameters. Debris and wear tracks have been studied in detail to see the surface effects during dry sliding and have been correlated to wear properties. Observations show that low loads and sliding velocities are dominated by oxidative debris and largely covered wear track surface with smooth oxide layer is observed. Whereas metallic debris dominates at higher loads and sliding velocities and highly deformed wear track surface with deep grooves and gross delamination were observed. Further, wear rate is seen to increase continuously with load whereas with sliding velocity it attains a minima after initial decrease and then increases continuously. Low solubility of iron supports the formation of FeAl₃ and an increase in hardness from 95 to 179 VHN continuously improves the wear resistance with increase in percentage iron.     

深度神经网络后门防御综述

深度学习在各领域全面应用的同时, 在其训练阶段和推理阶段也面临着诸多安全威胁。神经网络后门攻击是一类典型的面向深度学习的攻击方式, 攻击者通过在训练阶段采用数据投毒、模型编辑或迁移学习等手段, 向深度神经网络模型中植入非法后门, 使得后门触发器在推理阶段出现时, 模型输出会按照攻击者的意图偏斜。这类攻击赋予攻击者在一定条件下操控模型输出的能力, 具有极强的隐蔽性和破坏性。 因此, 有效防御神经网络后门攻击是保证智能化服务安全的重要任务之一, 也是智能化算法对抗研究的重要问题之一。本文从计算机视觉领域出发, 综述了面向深度神经网络后门攻击的防御技术。首先, 对神经网络后门攻击和防御的基础概念进行阐述, 分析了神经网络后门攻击的三种策略以及建立后门防御机制的阶段和位置。然后,根据防御机制建立的不同阶段或位置, 将目前典型的后门防御方法分为数据集级、模型级、输入级和可认证鲁棒性防御四类。每一类方法进行了详细的分析和总结, 分析了各类方法的适用场景、建立阶段和研究现状。同时, 从防御的原理、手段和场景等角度对每一类涉及到的具体防御方法进行了综合比较。最后, 在上述分析的基础上, 从针对新型后门攻击的防御方法、其他领域后门防御方法、更通用的后门防御方法、和防御评价基准等角度对后门防御的未来研究方向进行了展望。     

Mechanical,morphological, and thermogravimetric analysis of alkali-treated Cordia-Dichotoma natural fiber composites

ABSTRACT

Usage of composites with natural fiber reinforcement is drastically increasing in recent times because of their low density, biodegradable nature, and low cost. However, natural fibers have certain core problems such as poor adhesion between the fiber and matrix and a relatively high degree of moisture absorption. Alkaline treatment of natural fibers is aimed at improving the adhesive strength so that effective stress transferability takes place in the composite. In the present work, Cordia-Dichotoma fibers were treated with sodium hydroxide (NaOH) and composites were prepared with different weight ratios of these fibers reinforced with epoxy. The prepared composites were tested for their tensile and flexural strengths (mechanical properties). Besides, for a comprehensive material characterization, IR spectroscopy (FT-IR), scanning electron microscope, and thermogravimetric analysis were carried out. This work investigates the influence of aforementioned NaOH treatment on thermal, mechanical, and morphological properties of the composite material.     

A compact printed multistubs loaded resonator rectangular monopole antenna design for multiband wireless systems

In the present article, a compact triple‐band multistubs loaded resonator printed monopole antenna is proposed. The antenna consists of a quarter wavelength two asymmetrical inverted L‐shaped stubs to excite two resonant modes for 3.5/5.5 GHz bands and one integrated horizontally T‐shaped stub with inverted long L‐shaped stub to excite resonant mode for 2.5 GHz band. By loading these stub resonators along y‐axis with distinct gaps, the antenna resonates at three frequencies 2.57/3.52/5.51 GHz covering the desired bands while keeping compact size of 24 × 30 mm² (0.2 × 0.25 ). The proposed antenna is fabricated on Rogers RT/duroid 5880 substrate with thickness 0.79 mm and its performance experimentally verified. The measured results reveal that the antenna has the impedance bandwidths of about 210 MHz (2.50‐2.71 GHz), 260 MHz (3.37‐3.63 GHz), and 650 MHz (5.20‐5.85 GHz), for 2.5/3.5/5.5 GHz WiMAX and 5.2/5.8 GHz WLAN band systems. The antenna provides omnidirectional radiation patterns and flat antenna gains over the three operating bands. In addition, the design approach and effects of multistubs resonator lengths on the operating bands are also examined and discussed in detail.     

Experiments in active vision with real and virtual robot heads

In the emerging paradigm of animate vision, the visual processes are not thought of as being independent of cognitive or motor processing, but as an integrated system within the context of visual behavior. Intimate coupling of sensory and motor systems have found to improve significantly the performance of behavior based vision systems. In order to study active vision systems one requires sensory-motor systems. Designing, building, and operating such a test bed is a challenging task. In this paper we describe the status of on-going work in developing a sensory-motor robotic system, R2H, with ten degrees of freedoms (DOF) for research in active vision. To complement the R2H system a Graphical Simulation and Animation (GSA) environment is also developed. The objective of building the GSA system is to create a comprehensive design tool to design and study the behavior of active systems and their interactions with the environment. GSA system aids the researchers to develop high performance and reliable software and hardware in a most effective manner. The GSA environment integrates sensing and motor actions and features complete kinematic simulation of the R2H system, it's sensors and it's workspace. With the aid of the GSA environment a Depth from Focus (DFF), Depth from Vergence, and Depth from Stereo modules are implemented and tested. The power and usefulness of the GSA system as a research tool is demonstrated by acquiring and analyzing images in the real and virtual worlds using the same software implemented and tested in the virtual world.This research was supported by the U.S. Department of Energy under the DOE's University Program in Robotics for Advanced Reactors (Universities of Florida, Michigan, Tennessee, Texas, and the Oak Ridge National Laboratory) under Contract No. DOE DE-FG02-86NE37968.     

Mutual information based registration of multimodal stereo videos for person tracking

Research presented in this paper deals with the systematic examination, development, and evaluation of a novel multimodal registration approach that can perform accurately and robustly for relatively close range surveillance applications. An analysis of multimodal image registration gives insight into the limitations of assumptions made in current approaches and motivates the methodology of the developed algorithm. Using calibrated stereo imagery, we employ maximization of mutual information in sliding correspondence windows that inform a disparity voting algorithm to demonstrate successful registration of objects in color and thermal imagery. Extensive evaluation of scenes with multiple objects at different depths and levels of occlusion shows high rates of successful registration. Ground truth experiments demonstrate the utility of the disparity voting techniques for multimodal registration by yielding qualitative and quantitative results that outperform approaches that do not consider occlusions. A basic framework for multimodal stereo tracking is investigated and promising experimental studies show the viability of using registration disparity estimates as a tracking feature.     

Multimodal fusion for multimedia analysis: a survey

This survey aims at providing multimedia researchers with a state-of-the-art overview of fusion strategies, which are used for combining multiple modalities in order to accomplish various multimedia analysis tasks. The existing literature on multimodal fusion research is presented through several classifications based on the fusion methodology and the level of fusion (feature, decision, and hybrid). The fusion methods are described from the perspective of the basic concept, advantages, weaknesses, and their usage in various analysis tasks as reported in the literature. Moreover, several distinctive issues that influence a multimodal fusion process such as, the use of correlation and independence, confidence level, contextual information, synchronization between different modalities, and the optimal modality selection are also highlighted. Finally, we present the open issues for further research in the area of multimodal fusion.     

Distributed evolutionary multi-objective mesh-partitioning algorithm for parallel finite element computations

Majority of the mesh-partitioning algorithms attempt to optimise the interprocessor communications, while balancing the computational load among the processors. However, it is desirable to simultaneously optimise the submesh aspect ratios in order to significantly improve the convergence characteristics of the domain decomposition based Preconditioned-conjugate-gradient algorithms, being used extensively in the state-of-the-art parallel finite element codes. Keeping this in view, a new distributed multi-objective mesh-partitioning algorithm using evolutionary computing techniques is proposed in this paper. Effectiveness of the proposed distributed mesh-partitioning algorithm is demonstrated by solving several unstructured meshes of practical-engineering problems and also benchmark problems.