Modeling of centrifugal deployment of three-section minisatellite boom

The aim of the article is to model the processes of centrifugal deployment of a three-section boom and preliminary analyze the feasibility of this deployment method for an Earth remote sensing (ERS) minisatellite (MS). During the research, methods of theoretical mechanics, multibody dynamics, control theory, and computer modeling were used. Centrifugal deployment of multi-section booms have been successfully used on spin stabilized satellites, but not on ERS satellites, which have other features of operation and require additional studies. The main part of the MS is a platform to which a transformable antenna is attached by means of a transformable boom. Before deployment, the stowed boom and antenna are attached to the MS platform. The boom sections are connected by joints with one rotational degree of freedom and deployed sequentially due to centrifugal forces when the MS rotates in the required direction. Each of the boom joints has a locking mechanism that latches when a predetermined deploy angle is reached. To model the processes of the boom deployment, the MS is presented as a system of connected bodies, where the platform and the stowed antenna are absolutely rigid bodies, and the boom consists of three flexible beams of a tubular cross-section. The differential equations of the MS dynamics during the deployment are obtained using the Lagrangian formalism, which are supplemented by algebraic equations describing the constraints from the joints. The scenarios of the boom deployment with a constant control torque and a constant angular velocity of the MS are considered. These scenarios are simulated, and estimates of the control actions needed to ensure full deployment of the boom and the stabilization of the MS after latching of the joints are calculated. Dependences of variations of the loads on the boom structure during deployment are obtained. The simulation results allow us to conclude that it is feasible to implement the method of the boom centrifugal deployment for the MS, which can perform fast rotations about the three axes of the body reference frame. Implementation of this method allows designers to reduce mass of the MS because it does not require any servo drives in the boom deployment system.

Equivalence of Euler equations and torque-angular momentum relation

Euler derived equations for rigid body rotations in the body reference frame and in the stationary reference frame by considering an infinitesimal part of the rigid body.Another derivation is possible, and it is widely used: transforming torque-angular momentum relation to the body reference frame.However, their equivalence is not shown explicitly.In this work, for a rigid body with different moments of inertia, we calculated Euler equations explicitly in the body reference frame and in the stationary reference frame and torque-angular momentum relation.We also calculated equations of motion from Lagrangian.These calculations show that all four of them are equivalent.

C-tactile touch perception in migraineurs – a case-control study

Background Migraine is characterized by sensory hypersensitivity and habituation deficits. Slow brushing over the skin activates C-tactile nerve fibers, which mediate pleasant touch and analgesic effects in healthy subjects. As this function is altered in painful conditions, we aimed to examine whether the C-tactile processing is disrupted in migraines. Methods To psychophysically assess C-tactile function, we applied optimal and suboptimal C-tactile stroking stimuli on the dorsal forearm (body reference area) and the trigeminally innervated skin of 52 interictal migraineurs and 52 matched healthy controls. For habituation testing, 60 repeated C-tactile optimal stimuli were presented in both test areas. The participants rated each stimulus on a visual analogue scale by intensity, pleasantness, and painfulness. Results Regarding C-tactile function, migraineurs showed unphysiological rating patterns but no significantly different pleasantness ratings than controls. During repeated stimulation, controls showed stable pleasantness ratings while migraineurs’ ratings decreased, especially in those experiencing tactile allodynia during headaches. Migraineurs taking triptans responded like controls. Conclusion The C-tactile function of migraineurs is subclinically altered. Repeated C-tactile stimulation leads to altered habituation but differs from previous work by the direction of the changes. Although the pathophysiology remains unknown, causative mechanisms could include central and peripheral neuronal sensitization, tactile allodynia and hedonic stimulus attributions.

Numerical investigation of the drag force reduction for homogeneous column of vehicles

This paper presents simulation studies on the aerodynamics of vehicles moving in an organized column. The object of research is a column that consist of three vehicles of the same type (homogeneous column). In this research geometry of Ford Transit was used. As a part of the studies, the air drag forces acting on individual vehicles were calculated. The results are presented in dimensionless drag coefficient. The influence of the distance between cars on the generated force was also determined. In the first stage of the work, a numerical model was developed based on the Ahmed body reference structure. The calculations were carried out for 9 different velocities. The obtained results of the drag coefficient were compared with the work of other authors. The applied turbulence model and parameters of the boundary layer were used to create a numerical model of a moving column of vehicles. Mesh independence for numerical model of van was verified. The Finite Volume Method was implemented in the ANSYS Fluent program and used for the calculations. The use of supercomputers was necessary due to the large size of the grid.

Communication Vagueness in the Literature Review Section of Journal Article Submissions

Evidence has been provided about the importance of avoiding American Psychological Association (APA) errors in the abstract, body, reference list, and table sections of empirical research articles. Specifically, authors are significantly more likely to have their manuscripts rejected for publication if they fail to avoid APA violations—and, thus, do not write with discipline—in these sections. In addition to adhering to APA, writing with discipline also includes avoiding communication vagueness. Thus, I analyzed communication vagueness in the literature review section of 71 manuscripts submitted to the journal Research in the Schools over a 3-year period. Findings revealed that the frequency of communication vagueness differed in relation to the following: (a) number of APA errors, (b) gender of lead author, (c) genre of manuscript, and (d) adjudication decisions. In particular, certain communication vagueness categories were statistically significant and practically significant predictors of whether or not a manuscript is rejected for publication by the editor. Implications of these findings are discussed.

Attitude Determination Algorithms through Accelerometers, GNSS Sensors, and Gravity Vector Estimator

Aircraft and spacecraft navigation precision is dependent on the measurement system for position and attitude determination. Rotation of an aircraft can be determined measuring two vectors in two different reference systems. Velocity vector can be determined in the inertial reference frame from a GNSS-based sensor and by integrating the acceleration measurements in the body reference frame. Estimating gravity vector in both reference frames, and combining with velocity vector, determines rotation of the body. A new approach for gravity vector estimations is presented and employed in an attitude determination algorithm. Nonlinear simulations demonstrate that using directly the positioning and velocity outputs of GNSS sensors and strap-down accelerometers, aircraft attitude determination is precise, especially in ballistic projectiles, to substitute precise attitude determination devices, usually expensive and forced to bear high solicitations as for instance G forces.

Dynamic performance of over-constrained planar mechanisms with multiple revolute clearance joints

The clearances of joints in a rigid multibody system may deteriorate the motion accuracy and even cause vibrations, noise and fatigue failure of structures. In over-constrained mechanisms, the number of degree-of-freedoms is more than that of independent coordinates which leads to numerical challenges in solving the underdetermined force equilibrium equations. A comprehensive study on the dynamic model and the performance of an over-constrained planar parallelogram mechanism with multiple clearance joints is presented in this paper. Since a common angular coordinate exists in the clearance joint associated with the redundant constraint, the degree-of-freedoms are revised by eliminating the number of redundant constraints. In planar analysis, the location of mass center and the orientation of the body reference with respect to the inertial frame are selected as the generalized coordinates of the components. Clearance joints are equivalent as the spring-damper elements and the contact forces are introduced into the dynamic equations by force constraints. The developed computational algorithm is implemented by MATLAB and may analyze the dynamic performance of this mechanism due to the elimination of kinematic constraints and the nonlinear contact-impact behavior in the clearance joints. Meanwhile, an orthogonal experimental design based on a quantitative analysis method demonstrates that the clearance size and the location of clearance joints affect the kinematic accuracy and counterbalance moment of the mechanism.

Most Common Formal Grammatical Errors Committed by Authors

Empirical evidence has been provided about the importance of avoiding American Psychological Association (APA) errors in the abstract, body, reference list, and table sections of empirical research articles. Specifically, authors are significantly more likely to have their manuscripts rejected for publication if they commit numerous APA violations—and, thus, do not write with discipline—in these sections. In addition to adhering to APA, writing with discipline also includes avoiding what I call formal grammatical errors. Thus, in this study, I analyzed formal grammatical errors committed in 117 manuscripts submitted to the journal Research in the Schools over a 6-year period. Among other results, I identified the 35 most common formal grammatical errors. The use of colloquial words/phrases (e.g., “the author did a good job”) (76.1%) represented the most common grammatical error. Further, I identified a link between the number of grammatical errors and the subsequent disposition of a manuscript (i.e., accept vs. revise and resubmit vs. reject). Finally, I identified the formal grammatical errors that best predicted whether or not a manuscript was rejected by the editor. I contend that an efficient way for authors to learn how to write with discipline is to focus initially on these most common formal grammatical errors. Further, I contend that these errors provide useful starting points for persons who teach scholarly writing. Finally, authors of the APA Publication Manual might use this information to determine which grammatical rules and guidelines to emphasize.