Doctor of Philosophy (PhD), Ohio University, 2022, Clinical Psychology (Arts and Sciences)

Social anxiety disorder (SAD) is associated with diffuse impairment and constitutes a substantial public health burden. To better understand how social anxiety develops, it is crucial to identify how risk factors contribute to social anxiety. Anxiety sensitivity social concerns (ASSC), defined as the fear of publicly observable anxiety symptoms, and fear of negative evaluation (FNE), defined as distress arising from concerns about negative judgment, are risk factors that may amplify anxiety following social stressors. However, it is unclear how ASSC and FNE influence acute anxiety following stressors in naturalistic settings. In the current study, the impact of ASSC and FNE on anxious arousal (panic symptoms) and anxious apprehension (worry symptoms) following stressors was examined in a sample of community adults (N = 83; M age = 29.66 years, SD = 12.49, 59.0% female) who completed questionnaires five times per day over a two-week period. Dynamic structural equation modeling was used to examine predictors of overall levels of anxiety as well as anxiety following social and nonsocial stressors. ASSC interacted with the presence of social stressors, such that ASSC positively predicted anxious arousal following social stressors. FNE interacted with the presence of nonsocial stressors to predict anxious arousal and anxious apprehension, such that FNE positively predicted anxiety following nonsocial stressors. These findings suggest ASSC may specifically amplify anxious arousal following social stressors, whereas FNE may broadly amplify anxiety following nonsocial stressors.

Committee: Nicholas Allan Ph.D. (Advisor) Subjects: Clinical Psychology

MS, University of Cincinnati, 2018, Engineering and Applied Science: Mechanical Engineering

Squeeze Film Dampers, or SFDs, are used in high-speed rotor dynamic systems to reduce rotor vibrations and provide system stability. They are commonly used in aircraft engines to dampen rotor vibrations and provide structural isolation to the rotating shaft system. An SFD consists of a thin pressurized fluid film between two annular cylinders, a stationary housing and a whirling journal within the housing. Sag and non-circular whirl orbits are a real-world phenomenon that occur during an SFD operation. In an ideal scenario, the center of the journal whirls about the center of the housing to produce a uniform squeeze action on the lubricant. However, due to gravity the journal orbit becomes recessed and centers about an arbitrary point between the center of the journal and housing. It is also hard to achieve pure circular whirl orbits in a real-world SFD operation. It is therefore important to understand each of their effects on the damping performance of an SFD. The non-circular whirl orbits are produced using a mathematical equation by adding higher frequency components of the order n = 2 and 3 to the base frequency. Using pure n = 2 and n = 3 harmonics produces non-circular orbits that are symmetric. Pure harmonics are used as a first step in this study to understand the effect of non-circular whirl orbits on the damper performance. The objective of this thesis is to numerically study the effect of sag and non-circular whirl orbits on the damping performance of an SFD. A transient dynamic mesh approach is used in ANSYS Fluent v15.0, a commercial Computational Fluid Dynamics (CFD) software to simulate the whirling motion of the journal inside an SFD. The numerical methodology is first verified using two theoretical SFD configurations, long and short SFD, for which analytical solutions for pressures and damping forces are derived using Reynolds equation. The derivation of analytical expressions for both configurations limit the effect of fluid inertia. Therefore, (open full item for complete abstract)

Committee: Urmila Ghia Ph.D. (Committee Chair); Jay Kim Ph.D. (Committee Member); Tod Steen MSME (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy in Engineering, University of Toledo, 2009, Mechanical Engineering

Working prototypes of a Hydraulic Hybrid Vehicle (HHV) are already under testing and investigation. One of the problems reported from testing is that the noise levels emitted by the hydraulic system are not acceptable. Therefore, there is a need to perform extensive research to improve the HHV systems in terms of noise and performance. The pump is the main source of noise in HHV systems. However, the lack of space, the high pressure and the dynamics of components within the pump have prevented either direct observation or measurement of potential noise causing mechanisms within the pump structure. As a result, there are several theories as to the source of the noise from the pump units but little concrete information to further isolate and reduce the noise generation.Currently, the industry use “cut and try” methods in order to study the noise issue. This necessities the development of a theoretical tool that will enable us to avoid the costly (time and money) cut and try procedure already employed in the current efforts. This work creates a dynamic and geometric model of a bent axis pump for this purpose. Elements of the model include finding the variation of pressure, flow rate, and dynamic forces acting on the pump components and case as a function of angular rotations of both the main shaft and the yoke. The model was constructed using MathematicaTM” software and verified against test data. In turn, this study identifies and analyzes the dominant forces in both the time and frequency domains. The solution of the theoretical model using MathematicaTM is verified by a dynamic model created using ADAMS/View software. The kinematic model was able to predict the variations of the angular velocities and accelerations and the velocities and the accelerations of the center of gravity of the entire pump's parts starting from the main shaft up to the yoke. This work presents all equations necessary to solve for the piston pressure and pump flow rate as a function of main (open full item for complete abstract)

Committee: Walter Olson PhD (Advisor); Mohammad Elahinia PhD (Committee Member); Maria Coleman PhD (Committee Member); Sorin Cioc PhD (Committee Member); Efstratios Nikolaidis PhD (Committee Member) Subjects: Engineering; Fluid Dynamics; Mathematics; Mechanical Engineering; Mechanics; Technology

Master of Science, The Ohio State University, 2012, Electrical and Computer Engineering

This thesis is concerned with a problem of balancing the humanoid robot after an external impact. Dynamic model of the humanoid robot is derived using Lagrangian dynamic formulation. Use of the maximum joint accelerations to reject disturbance is studied. In our approach, we propose the use of non-natural force like thruster on the torso of the humanoid robot for balance recovery. Mathematical simulation of derived dynamic model is performed using MATLAB. Plotted results prove the validity and usefulness of the proposed approach. We also show that, acceleration compensation and using thruster are complementary to each other. We prove that both techniques can be used together to reject large disturbances in minimum time.

Committee: Dr. Yuan Zheng (Advisor); Dr. Hooshang Hemami (Committee Member) Subjects: Electrical Engineering; Engineering; Mechanical Engineering; Robotics; Robots

Doctor of Philosophy, The Ohio State University, 2006, Electrical Engineering

The increasing use of autonomous assets in modern military operations has led to renewed interest in (multi-player) Pursuit-Evasion (PE) differential games. However, the current differential game theory in the literature is inadequate for dealing with this newly emerging situation. The purpose of this dissertation is to study general PE differential games with multiple pursuers and multiple evaders in continuous time. The current differential game theory is not applicable mainly because the terminal states of a multi-player PE game are difficult to specify. To circumvent this difficulty, we solve a deterministic problem by an indirect approach starting with a suboptimal solution based on “structured” controls of the pursuers. If the structure is set-time-consistent, the resulting suboptimal solution can be improved by the optimization based on limited look-ahead. When the performance enhancement is applied iteratively, an optimal solution can be approached in the limit. We provide a hierarchical method that can determine a valid initial point for this iterative process. The method is also extended to the stochastic game case. For a problem where uncertainties only appear in the players' dynamics and the states are perfectly measured, the iterative method is largely valid. For a more general problem where the players's measurement is not perfect, only a special case is studied and a suboptimal approach based on one-step look-ahead is discussed. In addition to the numerical justification of the iterative method, the theoretical soundness of the method is addressed for deterministic PE games under the framework of viscosity solution theory for Hamilton-Jacobi equations. Conditions are derived for the existence of solutions of a multi-player game. Some issues on capturability are also discussed for the stochastic game case. The fundamental idea behind the iterative approach is attractive for complicated problems. When a direct solution is difficult, an alternative appro (open full item for complete abstract)

Committee: Jose Cruz (Advisor) Subjects:

Doctor of Philosophy (PhD), Ohio University, 1994, Electrical Engineering & Computer Science (Engineering and Technology)

The main objective of this research is to explore the computing power of a network of workstations for the distributed execution of computationally intensive programs and to evaluate the overall network performance for such applications. The dynamic scheduling mechanism developed for this purpose requires that an application program be represented as a collection of subprograms in a task graph format showing the subprograms' dependency. An application program, described in such a format, is scheduled for parallel execution in the network in accordance with the load status information of the workstations as follows. The independent subtasks in a particular level of the task graph are distributed among the idle or lightly loaded processors (slaves) in the network by the user workstation (master) for parallel execution. The partial results are then collected by the master to ensure the synchronization among the slaves. This is repeated until all the subprograms at the different levels of the task graph are executed concurrently, and the final result is accumulated in the master station. The performance of the network for this distributed program execution is characterized by the system speedup, which is defined as the ratio of the sequential execution time in a single workstation to the parallel execution in the network. The theoretical speedup equation is derived by modeling the network and considering various performance degradation factors including scheduling time, network load and size, communication time, TCP/IP communication overhead, task execution and synchronization time. The sequential and parallel execution times and the performance degradation factors were measured during the implementation for various network and station loads. The measurement values and theoretical results have shown that the system performance is degraded mostly by the heavily loaded nodes, the TCP/IP overhead (0.2 s), and the network size.

Committee: Mehmet Celenk (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2010, Mechanical Engineering

The objective of this research is to develop a constitutive model to predict the steady-state response of a rubber compound under cyclic loading. An MTS servo-hydraulic machine was used to obtain the dynamic hysteresis curves for a rubber compound in uniaxial tension-compression. The material tests were performed with mean strains from -0.1 to 0.1, strain amplitudes ranging from 0.02 to 0.1, and strain rates between 0.01 and 10s-1. Creep, the Payne effect and rate-dependence were observed from the experimental results. The uniaxial test results motivated the development of a three-dimensional constitutive model involving an equilibrium spring with temporary material set in parallel with a Maxwell element. A cornerstone of this constitutive modeling was to devise a scheme for evaluating a material set function for creep and a viscosity function for hysteresis. Material properties for the hyperelastic springs and viscous damper were identified from the uniaxial cyclic tension-compression test results. The constitutive equations were implemented into ABAQUS Standard via a user-defined material subroutine, UMAT. Numerical predictions of the cyclic hysteresis curves were found to be good agreement with the uniaxial test results. Cyclic torsion tests were also performed on the rubber cylinders to evaluate the accuracy of the proposed constitutive model and the UMAT was used to predict the response of the rubber cylinder under torsion. Good agreement with the torsion test results was also reported from the finite element analysis.

Committee: Michelle Hoo Fatt Dr. (Advisor) Subjects: Mechanical Engineering