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This paper proposes predefined-time convergent guidance schemes that can drive the pursuer on a collision course corresponding to the target interception from a pre-specified impact direction, irrespective of initial engagement geometries. The target interception at the desired impact angle is first transformed into a problem of controlling the line-of-sight angle and its rate. Then, guidance commands are derived using sliding mode control (SMC) to ensure the convergence of corresponding errors to zero within a predefined time. A nonlinear disturbance observer is used to estimate the target's maneuver, and the estimation error is treated as an uncertainty while rejecting its effect by virtue of SMC. Guidance commands are also derived for the case where the target maneuver is completely unknown except for its upper bound. It was shown that the gain could be selected based on the maximum bound on target maneuver to enforce sliding mode on the chosen surface, and thus guarantees target interception at a pre-specified impact angle, provided the closing speed of the engagement is positive. Owing to the use of a nonlinear framework while deriving pursuer guidance commands, the proposed guidance strategies remain valid even for engagements with large initial deviations where schemes based on linearized dynamics may fail or have degraded performance. The efficacy of the proposed guidance methods is validated through simulations for the pursuers having constant speed and time-varying speed, for various engagement geometries. The results of proposed strategies are compared with those of existing guidance and shown to be superior. [ABSTRACT FROM AUTHOR]

In this article, a sliding mode control–based nonlinear guidance scheme for controlling both impact angle and impact time simultaneously is proposed. The problem of impact angle control is first transformed to that of controlling line-of-sight angle and its rate, while the requirement of impact time is achieved by tracking the desired time-to-go. The chosen time-to-go estimate accounts for the curvature required to meet the impact angle requirements toward the target interception. In order to satisfy both of these terminal constraints, the sliding surface is defined as a combination of impact time error and the variable pertaining to the errors in line-of-sight angle and its rate, with appropriate gains assigned to them. The interceptor first performs necessary maneuvers to meet the impact time requirements and then steers its course to achieve the target interception at a desired impact angle. The guidance law is initially derived using nonlinear engagement kinematics against stationary targets and then extended to cater to constant velocity targets using the concept of predicted interception point. Numerical simulations are performed to validate the efficacy of the proposed guidance scheme for various initial engagement geometries. The performance of the proposed guidance scheme is also compared with those of the existing guidance laws and shown to be superior. [ABSTRACT FROM AUTHOR]

Background: Peer review is at the heart of academic publishing and has long been instrumental in bringing good science to the forefront. Peer reviewer comments provide authors with valuable suggestions to improve their manuscript; thus, even a rejected manuscript with constructive reviewer comments is highly valuable. However, peer reviewer comments can sometimes be negative, rather than constructive, damaging authors' motivation and confidence levels. Objective: This study aims to make editors and peer reviewers aware of how negative reviewer comments can affect authors, and suggests ways to ensure that peer review is constructive. Methods: Through a discussion on DXY, an online community for biomedical researchers in China, authors were asked to share their experiences with negative reviewer comments; 99 participants responded. Separately, similar questions were posted on two other online communities, Academia Stack Exchange and Quora, yielding 11 responses. These responses were analyzed on the basis of their underlying emotion or message. Results: The authors' responses indicate that they appreciate receiving constructive reviewer comments and benefit from such comments. However, authors are often demoralized when they receive comments that are superficial, harsh, or overcritical, and do not provide constructive suggestions for improvement. Conclusion: While it is true that peer review work claims a lot of time and energy from busy scientists, the purpose is lost when reviewer comments are purely negative. If peer reviewers could keep in mind the feelings of authors while drawing up their reports, peer review would become more effective and a more positive experience for authors. [ABSTRACT FROM AUTHOR]