Fault-free Regions Research Articles

Energy Harvest of Multiple Smart Sensors With Real-Time Fault-Detection

For multiple smart sensors with limited energy supply, the relationship between the energy supply and sensor fault-free region is often unknown, and neither of the interior structure nor exterior circumstance modeling the smart sensors is easy to accurately achieve, so how to guarantee the fault-free smart sensors to harvest the most energy in the fault-free way is a very challenging topic. To address this issue, this paper first formulates the individual smart sensor as a single-input single-output (SISO) model-free system (MFS), with its energy supply and sensing error as the input and output, respectively, then makes use of Lyapunov function to deduce an upper bound of the fault-free region to realize the fault-detection of any smart sensor and disclose the relationship between the energy supply and fault-free region, and finally achieves the optimal energy supply guiding the overall energy harvest of all fault-free smart sensors to converge to the maximum with the convergence rate no larger than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa$</tex-math> </inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa\in[0,1]$</tex-math> </inline-formula> , while enjoying the real-time fault-detection. An algorithm based on the sound theoretical foundations is further proposed to implement the optimal energy supply. Theoretical analysis, simulations and field experiments jointly verify the performance of our method. To our best knowledge, it is the initial work towards this issue. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper addresses the interesting issue of how to guarantee multiple smart sensors to harvest the most energy in the free-fault way. Through the insightful disclosure of relationship between the energy supply and sensor fault-free region, and the optimal control of energy supply, this paper facilitates the overall energy harvest of all fault-free smart sensors that work under the environments, where the available energy is limited, to converge to the maximum while enjoying the real-time fault-detection, which we believe could push the development of Internet of Things (IoT) or Cyber-Physical System (CPS) that employs multiple smart sensors to sense the physical world. Simulations and field experimental investigations jointly show that the proposed solution outperforms the existing solutions.

BIST-Based Fault Diagnosis for PCM With Enhanced Test Scheme and Fault-Free Region Finding Algorithm

As one of the most promising candidates for nonvolatile memory, phase change memory (PCM) technology has shown great performance advantages in market applications. However, the conventional test methods have not kept pace with the development. In this article, focusing on specific PCM faults and others, an enhanced march test algorithm is proposed to achieve 100% fault coverage and diagnostic accuracy in bit-oriented PCM. The proposed algorithm is then converted for word-oriented PCM and equipped with capability to detect potential intraword impact. In addition, to reduce the dependence of memory test on the external devices, a novel storage scheme of fault information is devised. Through the modeling and simulation in C-language, this method is proven to improve the probability of finding the predefined fault-free regions in the tested memory. Finally, combining the enhanced test algorithm and the novel storage scheme, a built-in self-test (BIST) march test scheme is proposed, realizing the independent test of PCM without any external equipment. By comparison, the result of experiments, which are performed with C-language, proves that the proposed test scheme not only increases the fault coverage and diagnostic accuracy, but also reduces the additional area overhead.

Function-mapping on defective nano-crossbars with enhanced reliability

Several nanoscale devices now represent viable options to replace conventional complementary metal–oxide–semiconductor (CMOS)-based designs. The problem of logic synthesis using a nanoscale two-dimensional (2D) crossbar-switch architecture is studied herein. Despite offering several advantages, these tiny devices suffer from a high defect density because of process variations, which affects their usable area. Typically, many defective junctions appear spatially clustered in nano-crossbar structures following manufacture. Furthermore, junctions that lie in close proximity to defective ones are also prone to become faulty soon thereafter. Thus, albeit defect free, these junctions may not be reliable from the viewpoint of logic synthesis. The maximal rectangular regions in the crossbar that are devoid of any defects are identified herein. Such fault-free regions can be reliably used for mapping Boolean functions. To locate such regions, an efficient search technique based on the defect geometry is used; experimental results obtained with different crossbar sizes and defect densities are also reported. It is observed that the proposed technique outperforms earlier approaches for crossbars with clustered defects.

BIRA With Optimal Repair Rate Using Fault-Free Memory Region for Area Reduction

As manufacturing process technology scales down, memory capacity and density continue to grow. As the number of memory cells per area increases, so does the possibility of having defects in the memory cells. Therefore, built-in redundancy analysis (BIRA) is widely used for memory test and repair. BIRA repairs faulty cells by replacing them with healthy spare cells. To perform BIRA, the faulty memory cell information is required and is collected via a memory test. By using the faulty cell information, BIRA can analyze and perform the repair by assigning spares to defective cells. However, it requires extra hardware to store the faulty cell information. Most conventional BIRA approaches utilize content-addressable memories (CAMs) to store faulty cell information. Owing to the CAMs’ fast access speed, the repair time can be reduced. However, CAMs are the critical source of an area overhead for BIRA, and a CAM could be shared across multiple memory banks. The shared structure limits simultaneous repair operations for the banks, and when the CAM is faulty, the conventional CAM-based BIRA cannot be performed. This paper proposes a new BIRA method, which does not require extra memory and instead utilizes a fault-free memory region to store the faulty cell information. Because extra memory is not required in the proposed BIRA method, the area overhead is decreased. The proposed hierarchical repair algorithm thus helps to reduce the analysis time, while achieving optimal normalized repair rate.

Geomechanical Risk Assessments for CO2 Sequestration in Depleted Hydrocarbon Sandstone Reservoirs

Summary Depleted hydrocarbon reservoirs are attractive targets for gas storage and carbon dioxide (CO2) disposal because of proven storage capacity and seal integrity, existing infrastructure, and other reasons. Optimum well completion and injection design in depleted reservoirs would require understanding of important rock-mechanics issues considering rock/fluid-interaction effects (e.g., drillability and completion of new wells, maximum-sustainable-storage pressures avoiding fracturing, and fault reactivations). Building a field-specific geomechanical model calibrated with well and production data is a prerequisite for addressing these issues. Through a case study, this paper demonstrates a systematic approach for geomechanical risk assessments for CO2 storage in depleted reservoirs. A depleted gas reservoir at a 4,050-ft depth with the current pressure of 45 psi is considered in this study for CO2 sequestration. The study used offset-well drilling and wireline-log data to derive field stresses, formation pressure, rock strength, and elastic properties. A practical workflow was developed to characterize the interaction between pressure depletion and fracture-gradient changes. In this particular case, the results showed that the fracture gradient (FG) was as low as approximately 9.3 lbm/gal, and the wellbore-collapse pressure in the overburden shale was highly dependent on the well trajectory. If an operating mud-weight window of 0.5 lbm/ gal is required, the well inclination should be below 65° if it is planned to be oriented toward the minimum-horizontal-stress (Shmin) direction, or less than 45° if toward the maximum-horizontal-stress (Shmax) direction, to mitigate drilling risks. Field data and analytical-sanding evaluations indicate no sand-control installation would be needed for injectors. Fracturing and faulting assessments confirm that the critical pressures for fault reactivation and fracturing of caprock are significantly higher than the planned CO2-injection and -storage pressures. However, the initial CO2 injection could lead to a temperature in the near-wellbore region as low as 0.7°C. There is a high risk that a fault with cohesion of less than 780 psi could be activated because of the significant effect of reduced temperature on field stresses, and it is therefore recommended that the CO2 injectors be placed in fault-free regions. The methodology and overall workflow presented in this paper are expected to assist well engineers and geoscientists with geomechanical assessments for optimum well-completion and injection design for both natural-gas and CO2 storage in depleted reservoirs.

Fault Automatic Detection Method for Steel Cord Conveyor Belt Based on the Regularity Analysis

The X-ray images of steel cord conveyor belt are built on a repetitive unit of a pattern. Based on the statistical features and regularity analysis, a fault automatic detection method named MRB(Modified Regular Bands)was proposed to monitor the status of steel cord conveyor belt. Firstly, the input image of steel cord conveyor belt is normalized. Secondly, the normalized image is standardized. And then the MRB parameters of each pixel are calculated by the progressive scanning. Finally, after subtracting the MRB parameter mean of the whole image, the detected result whether it is a fault image or not is obtained and the fault region is extracted from the fault image, by the way of comparing with the thresholds obtained from training stage. The results of the detection of four kinds of typical steel cord conveyor belt faults show that the MRB method has a higher precision, is simple and fast enough for real-time online fault detection. Comparing with the statistical method such as the mean and variance, MRB method is sensitive to the faults and can detect the small faults. The image of MRB parameter has the higher contrast, so it can stand out the fault region from the fault-free region. And the shape of fault region is acquired well by MRB method.

Fault-Tolerant Wormhole Routing with 2 Virtual Channels in Meshes

In wormhole meshes, a reliable routing is supposed to be deadlock-free and fault-tolerant. Many routing algorithms are able to tolerate a large number of faults enclosed by rectangular blocks or special convex, none of them, however, is capable of handling two convex fault regions with distance two by using only two virtual networks. In this paper, a fault-tolerant wormhole routing algorithm is presented to tolerate the disjointed convex faulty regions with distance two or no less, which do not contain any nonfaulty nodes and do not prohibit any routing as long as nodes outside faulty regions are connected in the mesh network. The processors' overlapping along the boundaries of different fault regions is allowed. The proposed algorithm, which routes the messages by X-Y routing algorithm in fault-free region, can tolerate convex fault-connected regions with only two virtual channels per physical channel, and is deadlock-and livelock-free. The proposed algorithm can be easily extended to adaptive routing.

Fault-Tolerant Broadcasting in 2-D Wormhole-Routed Meshes

In this paper, a fault-tolerant broadcast scheme in 2-D meshes with randomly generated faults is provided. This approach is based on an early work on time-step optimal broadcasting in square-shape fault-free 2-D meshes with optimal total communication distance (TCD). An extension to any rectangular-shape fault-free 2-D meshes is first given. The fault block model is used in which all faulty nodes in the system are contained in a set of disjoint blocks. The boundary lines of blocks divide the whole mesh into a set of fault-free polygons and a sequence of rectangular fault-free regions is derived from these polygons. The broadcast process is carried out at two levels: inter-region and intra-region. In the inter-region-level broadcast, the broadcast message is sent from a given source to a special node (called eye [1]) in each rectangular fault-free region. In the intra-region-level broadcast, the extended optimal fault-free broadcast is applied. Some analytical results are given including an upper bound of TCD.

Structural relationship between pyrite and marcasite

We studied pyrite spherules built of radiating crystals to establish the relationships among microstructure, composition, and macroscopic appearance. Results of high-resolution transmission electron microscopy (HRTEM) imaging and selected-area electron diffraction (SAED) show that many pyrite crystals contain planar faults perpendicular to one of the [001] axes. A comparison between HRTEM micrographs and images simulated for defect model structures indicates that the faults can be interpreted as single (101) layers of marcasite that disrupt the regular sequence of (002) layers in pyrite. Such a marcasite layer can be described as a boundary between two pyrite crystals that are related by a 21 screw axis parallel to [100]. Energy-dispersive X-ray spectrometry (EDS) indicates that such disordered pyrite crystals contain about 3 at% As. However, the distribution of As is uniform over heavily faulted and fault-free regions, indicating the As content is not related to the occurrence of marcasite lamellae in pyrite.

Effect of Double-Layered SiO2–Si3N4 Films on Formation of Stacking Fault-Free Region in Silicon

We have studied the effect of surface conditions on the formation of a stacking fault-free region. The specimens with and without double-layered SiO2–Si3N4 films were heat-treated at 750°C for 64 h and then annealed in vacuum at 1050–1150°C for 0.5–128 h. In the specimens with double-layered films, a stacking fault-free region was formed beneath the Si–SiO2 interface, while it was formed beneath the surface in the bare specimens. Its thickness increased depending on the annealing time, t0.6±0.1. The thickness of the stacking fault-free region in the bare specimens was two to three times wider than that in the specimens with double-layered films. This difference can be explained using a model in which the Si–SiO2 interface acts as a sink of self-interstitials and the bare surface acts as not only a sink of self-interstitials, but also as a source of vacancies.

Formation of a Stacking Fault-Free Region in Thermally Oxidized Silicon

A stacking fault-free region was found to be formed beneath a Si–SiO2 interface when a silicon crystal was oxidized to generate stacking faults and subsequently annealed in nitrogen atmosphere. This region extends further with prolonged annealing, irrespective of the size and density of the stacking faults already introduced in the crystal. Experimentally it is found that the growth of a stacking fault-free region during annealing follows the equation, d=const. tnexp (-Q/kT) where n and Q are 0.63±0.06 and 4.5±0.6 eV, respectively. The stacking fault nuclei were confirmed to be dissolved after annealing of oxidized crystals.