You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Linear Machines for Long Stroke Applications—A Review 
Chapter Title:  D. FAULT-TOLERANT CAPABILITY 
1. Abstract of Cited Paper (BIB001):  A new linear permanent-magnet (PM) motor, termed as modular linear flux-reversal PM (M-LFRPM) motor, is proposed. This is particularly attractive for high reliability urban rail transit. Its PM materials and armature windings are set in the mover (train), while the long stator (rail) is composed of irons, hence improving efficiency and reducing cost. The key of the proposed motor incorporates the concept of fault-tolerant teeth to provide the desired decoupling among phases. The structure and features of the proposed motor are presented, and an optimal design is performed. By using finite element method, the advantages and validity of the proposed motor are verified. The analysis results show that the proposed M-LFRPM motor not only retains the advantages of the conventional LFRPM motor, but also improves its fault-tolerant capability. 
2. Abstract of Cited Paper (BIB002):  In the recent years, linear propulsion technology has been increasingly adopted in transportation, electromagnetic launch and aerospace applications. Compared with the conventional rotary-to-lin-early propulsion, the linear propulsion can offers many advantages, such as high efficiency, reduced maintenance cost, vibration and noise [1]-[4]. Among various kinds of linear motors for linear propulsion system, the linear permanent magnet (PM) motors has gained more and more attention due to the merits of high power density and efficiency. However, since the PMs or windings are set on the long stator, the conventional PM motors suffers from high cost for the long stroke applications such as rail transit. The linear flux reversal permanent magnet (FRPM) motor combining PMs and windings on the mover has been regarded as a potential solution, but its fault tolerance is poor [4]-[6]. In [4], the fault tolerance of linear FRPM motor was improved by utilizing a modular mover structure. However, it suffers from the low PM magnetic field utilization and force density due to its homopolar flux linkage. Furthermore, its force ripple and cogging force is very large, which deteriorate the force performance. In order to improve these problems, a new linear FRPM motor with modular mover will be proposed in this paper, which not only retains the advantages of the existing modular linear FRPM motor such as fault tolerance and reduced PM consuming, but also significantly enhances its force density and reduces its force ripple. 
3. Abstract of Cited Paper (BIB003):  This paper proposes a new modular-stator tubular permanent-magnet (PM) Vernier motor. The proposed motor offers a good fault-tolerant capability and an improved force performance, suitable for the electromagnetic active vehicle suspension. The proposed motor artfully integrates PM Vernier motors and tubular motors together, offering a zero-net radial force between the armature and mover, and the robust mover structure and high thrust force. Meanwhile, the modular complementary stator structure is designed to decouple the adjacent phase windings, hence offering the desired fault-tolerant capability. Moreover, the PMs with two magnetized directions are adopted, namely radially and axially. One is used to produce the main flux, while another can reduce fringing leakage flux, hence increasing the thrust force. The electromagnetic performances are analyzed by using the finite-element method, verifying the effectiveness of the theoretical analysis.

Literature Review:
Fault tolerance is achieved by reducing the ratio between the mutual inductance and the self inductance. This can be achieved with the adoption of fault tolerant teeth BIB002 , BIB003 . The idea behind fault-tolerant teeth is that it serves as a return path for the flux generated by a phase. In this way, the different phases can share less flux, enhancing their electromagnetic isolation. Modular configurations are an even better solution for improving the fault-tolerance of LMs BIB003 , BIB004 , BIB001 . What is interesting with this topology is that if the distance between the modules is increased, the decoupling between phases is increased. If there is a big enough margin from the machine size point of view, the designer has the flexibility of deciding which the adequate displacement is.