A Remedial Control for Short-Circuit Fault in NPC/H-Bridge Inverters without Redundant Component

In this paper, a five-level neutral-point-clamped (NPC) inverter with short-circuit fault-tolerant capability is presented. Based on the proposed approach, in order to ensure service continuity subsequent to a short-circuit fault event in a switch, two steps are carried out. First of all, destructive consequences arising from short-circuit fault in a power switch is prevented. Afterwards, according to the defected component, remedial actions are taken. The proposed strategy does not require any redundant component. The service continuity is acquired by applying a remedial control and modifying switching commands applied to the power switches. Using the proposed approach helps to restore the rated voltage and rated current at the terminal, and there is no limit for modulation index during fault-tolerant operation under remedial control. Furthermore, compared to healthy operation, harmonic content of the terminal voltage and current is not deteriorated during fault-tolerant operation. Moreover, additional components, such as bidirectional switches and contactors, are not employed in this strategy. Only some fast fuses are placed in the converter circuit for protection purposes which do not impose a noticeable cost compared to the bidirectional switches and contactors.

Bone marrow stromal cell transplantation ameliorates cytopenia caused by depletion FAP-α expressing cells

The marrow microenvironment is a complex and heterogeneous mixture of hematopoietic and stromal progenitors necessary for haematopoiesis. Whilst the hematopoietic progenitors are well described, the stromal cellular composition is not fully elucidated due to the low cells numbers, localisation-distribution-accessibility, and the lack of specific biomarkers. Cellular taxonomy studies have recently identified new populations of stromal subsets with distinct gene signature and regulatory properties of hematopoietic regeneration. Fibroblast activation protein-α (FAP), a stromal cell type first identified in cancer is also rarely found in normal tissues but might play an essential role in tissue homeostasis. Using FAPDM2 transgenic mouse in which FAP-expressing cells can be ablated with Diphtheria Toxin (DTX) FAP+ cells were depleted in healthy mice. Whilst FAP+ cells constituted 5% of all marrow cells; its ablation caused a rapid loss of PDGFR-α, Leptin-R, gp38 and SDC2 stromal cells populations, endothelial cells and vascular disruption. These resulted in anaemia, thrombocytopenia and neutropenia in peripheral blood (PB) and extreme hypo-cellularity in marrow with abnormalities within the hematopoietic progenitors. In an effort to reverse the phenotypes caused by FAP+ cell loss, a single intravenous injection of syngeneic bone marrow-derived stromal cells was administered. In a short-term evaluation, anaemia, thrombocytopenia and neutropenia ameliorated in PB and the numbers of marrow hematopoietic progenitors increased. Our data suggest FAP-expressing cells are a non-redundant component of the marrow microenvironment, necessary for marrow homeostasis and haematopoiesis. These data also provided evidence that stromal cell ablation can be rescued by stromal cell therapy.Significance StatementFAP-expressing cells depletion led to collateral damage in PB and marrow, including haematological defects that can be ameliorated by adoptive transfer of low-dose, ex-vivo expanded FAP-expressing marrow stromal cells. We suggest that stromal cell loss is a feature of severe immune-mediated inflammatory diseases – such as Graft versus Host Disease and sepsis - and that FAPDM2 model represents a novel tool to explore the native function of the recently identified stromal cell sub-populations.

Developing an Efficient Approach for Unmanned Aerial Vehicle Reliability Analysis

Unmanned Aerial Vehicles (UAV) are increasingly get popularity in many applications. Their operation requires high level of safety and reliability to accomplish successful missions. In this study, the reliability was comparatively analyzed by different available approaches to select the efficient method. First, failure model of the system is developed. Then, three different scenarios are considered to study the effect of redundancies on the system reliability results. In the first scenario, there is no redundancy where in the second scenario there is only one redundant component and in the third scenario, there are three redundant components. Static reliability analysis such as Fault Tree Analysis (FTA), Reliability Block Diagram (RBD), Markov Chain (MC), and Bayesian Networks (BN) are applied on proposed scenarios and results are obtained. Regarding to time dependencies between redundant components, a dynamic-based methodology is also developed in this study through applying Dynamic Fault Tree (DFT) analysis. Proposed static and dynamic approaches are applied on an UAV as a case study and results are discussed. Finally, characteristics of each methodology and related conditions are clarified for selecting the efficient reliability analysis approach.

Cascade stress-strength system Reliability Estimation of Inverse Rayleigh Distribution

The electronic devices, equipment and complex machines used in many fields such as telecommunications, medicine, astronautics and others are all subject to malfunctions, which cause material and moral losses, waste of time and other damages. Hence the importance of reliability issue in our working life by evaluating the performance and efficiency of these systems and Measuring the reliability of any device will be the basis for the development of most of these devices . Then In this paper will discussed the Estimation of Reliability Rn for cascade system when the stress and strength are Inverse Rayleigh distributed random variables. under-voltage rating. The cascade system is a redundant component system, which is a redundant component with under-voltage rating and independently distributed power, in which the redundant component replaces the faulty component.. Cascade system is a special case of Stress- Strength models system. Also we discussed the Estimation of Marginal Reliabilities R1, R2 and R3 for Cascade system by three estimation methods (Max. likelihood, Weighted Least Square, Least Square) and Compare between the estimators of R4. © 2018 JASET, International Scholars and Researchers Association

The ROMY project: A 4-component ring laser for geophysics and geodesy

<p>The ROMY ring laser was constructed with 4 non-orthogonal triangular-shaped cavities of 12 m side length in the Geophysical Observatory outside Munich, Germany, in 2016. The large dimensions of the individual rings have the benefit of allowing high sensitivity surpassing in principle the sensitivity of the G-ring at the Fundamentalstation Wettzell. However, the concrete construction of ROMY is geometrically less stable than the G-ring that is built on a rigid Xerodur plate. Each of the four rings has its own Sagnac frequency. The horizontal triangular ring laser at the top of the inverted tetrahedral ROMY structure allows direct comparison of teleseismic signals and noise with the G-ring at a distance of 200km. It also serves as redundant component. In principle, three orthogonal components of rotational ground motion can be obtained by linear combination from any combination of three rings, that - due to the variable Sagnac frequency - have different noise characteristics. We report on the behavior and observations of ROMY from a seismological point of view. It is fair to say that ROMY provides the most accurate direct 3-component rotational ground motion seismic observations to date. In combination with a collocated broadband seismometer as well as a surrounding small-scale seismic array, we analyse regional, teleseismic events, and ocean-generated noise and compare with array-derived rotation.</p>

K-mixed strategy: A new redundancy strategy for reliability problems

This article presents a new redundancy strategy for system reliability optimization. The proposed strategy is a general form of a recently introduced strategy called “Mixed Strategy.” Adding parallel redundant component is a common approach in order to improve the reliability of a specific system. This approach is known as redundancy allocation problem. The redundancy allocation problem is a challenging issue for many researchers which has been subjected to investigation in this study. Generally, in the redundancy allocation problem, there are three redundancy strategies for using the redundant components: active, standby and mixed. The new emerging mixed strategy is a general form which involves both active and standby strategies. In this article, a general form of the mixed strategy called “K-mixed,” will be introduced and mathematical formulation for calculating the reliability of this new strategy will be presented. In order to evaluate the efficiency of the K-mixed strategy, a single specific subsystem with four components will be used and reliability of the subsystem will be computed by considering all three previous strategies and the new one. To have a better understanding about the performance of these four strategies, the effect of switch reliability and component reliability will be further examined.

Reliability Analysis of Two Dissimilar-Cold Standby Redundant Systems Subject to Inspection with Preventive Maintenance Using Copula

The objective of this chapter is to study the system reliability through redundant component and additional preventive maintenance of operative and standby units. The considered system consists of two units in cold-standby, one is main unit and other is standby. The configuration of main unit is of 1-out-of-2: G whereas standby unit is of (n-1)-out-of-n: F and (n-2)-out-of-n: D nature. Main unit of the system has two modes viz. operable and failed and standby unit of the system has three modes viz. operable, degraded and failed. Both units after failure go for inspection where the type of the failure is detected and accordingly repairing action is decided. The failure and repair times follow exponential and general time distributions respectively. The system is studied by using the supplementary variable technique, Laplace transformation and Gumbel-Hougaard family of copula to obtain reliability, availability, downtime, busy period, M.T.T.F. and cost effectiveness of the system. At last some special cases of the system have been discussed.

Prioritising Redundant Network Component for HOWBAN Survivability Using FMEA

Deploying redundant component is the ubiquitous approach to improve the reliability and survivability of a hybrid optical wireless broadband access network (HOWBAN). Much work has been done to study the cost and impact of deploying redundant component in the network but no formal tools have been used to enable the evaluation and decision to prioritise the deployment of redundant facilities in the network. In this paper we show how FMEA (Failure Mode Effect and Analysis) technique can be adapted to identify the critical segment in the network and prioritise the redundant component to be deployed to ensure network survivability. Our result showed that priority must be given to redundancy to mitigate grid power outage particularly in less developed countries which is poised for rapid expansion in broadband services.

Exploration of joint redundancy but not task space variability facilitates supervised motor learning

The number of joints and muscles in a human arm is more than what is required for reaching to a desired point in 3D space. Although previous studies have emphasized how such redundancy and the associated flexibility may play an important role in path planning, control of noise, and optimization of motion, whether and how redundancy might promote motor learning has not been investigated. In this work, we quantify redundancy space and investigate its significance and effect on motor learning. We propose that a larger redundancy space leads to faster learning across subjects. We observed this pattern in subjects learning novel kinematics (visuomotor adaptation) and dynamics (force-field adaptation). Interestingly, we also observed differences in the redundancy space between the dominant hand and nondominant hand that explained differences in the learning of dynamics. Taken together, these results provide support for the hypothesis that redundancy aids in motor learning and that the redundant component of motor variability is not noise.

ON STOCHASTIC COMPARISONS FOR LOAD-SHARING SERIES AND PARALLEL SYSTEMS

We study the allocation strategies for redundant components in the load-sharing series/parallel systems. We show that under the specified assumptions, the allocation of a redundant component to the stochastically weakest (strongest) component of a series (parallel) system is the best strategy to achieve its maximal reliability. The results have been studied under cumulative exposure model and for a general scenario as well. They have a clear intuitive meaning; however, the corresponding additional assumptions are not obvious, which can be seen from the proofs of our theorems.