Modeling, simulation, and stability of a hydraulic load-sensing pump system with investigation of a hard nonlinearity in the pump displacement control system

Certain types of Load-Sensing (LS) pumps utilize a hydro-mechanical control system designed to regulate the pressure difference, or margin pressure, between the inlet and outlet of a flow control valve. With a constant margin pressure, predictable flow control and improved efficiency can be achieved by controlling the orifice area of the flow control valve. Instability due to limit cycles (sustained oscillations) that stem from nonlinearities within the system is a common issue related to hydraulic LS systems. In this work, the stability of the pressure control system was investigated using describing function analysis. Describing function analysis is a method used to approximate a nonlinearity within a nonlinear system and was conducted to predict the existence and stability of limit cycles that occur due to saturation nonlinearities within the mechanical components of the LS system. A combination of linear and nonlinear analysis and modeling was employed to assess the stability of a particular LS pump system. Among many nonlinearities present in the hydro-mechanical LS system, of particular interest was the saturation inherent in the actuator that is used to displace the pump swash plate and the saturation within the 3-way spool valve that permits flow to reach the actuator. This saturation nonlinearity was believed to be a problematic source for limit cycles that tend to appear in LS systems. A comprehensive nonlinear model was developed as the foundation for this research as it was used for validation in direct comparison to experimentally acquired data. The nonlinear model proved to be precise and accurate in matching to the experimental test bed response based on the data that was gathered. The acquired data was compared to the NL model simulation through a root mean squared error evaluation and frequency response analysis. The nonlinear model was then used to generate a linearized model necessary for stability analysis. The saturation nonlinearities for two separate mechanical systems were isolated from

Effectiveness of an Adaptive Magnitude Comparison eBook at Home

Finding effective technology is important for children’s learning during the pandemic, as families may not have quick access to sufficient high-quality, classroom-like resources. This project is part of a larger evaluation of the effectiveness of adaptive magnitude comparison eBooks for improving preschoolers’ math skills.https://ecommons.udayton.edu/roesch_symposium_content/1046/thumbnail.jp

EMG Analysis of Latissimus Dorsi, Middle Trapezius, and Erector Spinae Muscle Activity During Spinal Rotation: A Pilot Study

Purpose/Hypothesis: Rotation of the spine is a common movement used to complete daily activities and participate in sports. As a contributing factor to back injuries, the performance of spinal rotation is an important consideration for the rehabilitation of current and prevention of future back injuries. Muscles involved in spinal rotation have been researched, though limited findings exist for one of the largest back muscles, the Latissimus Dorsi (LD). The LD muscle contributes to many movements of the trunk and limbs given its multiple attachment sites including the pelvis, ribs, scapula, and humerus. Influence of the LD on spinal rotation has not been thoroughly researched yet, but results will play a role in the patient\u27s plan of care when treating back pain. The purpose of this study was to increase understanding of muscle activity during spinal rotation and compare muscle activity in fixed and non-fixed positions. Materials/Methods: Muscle activity was recorded using EMG surface electrodes while subjects performed left and right rotation in both standing and quadruped positions. Ten spinal rotation test positions (standing non~ fixed rotation right/left, quadruped rotation right/left, and standing rotation right and left with arms fixed on the wall at 45°, 90° and 120° of shoulder flexion) were initiated by movement of the pelvis. Using Maximal Voluntary Contraction (MVC) to normalize muscle activity, findings were analyzed for significance at a=.05. Results: When significant differences were found, the perspective muscle showed increased muscle firing compared to other muscles listed. Significance was found in the right LD between non-fixed right and left rotation and fixed right rotation. During non-fixed right and left rotation as well as fixed right rotation, the right MT showed significance. Left MT showed significant differences were shown when comparing non-fixed right rotation to fixed tight and left rotation. The MT was also significant with non-fixed left rotation compared with fixed right and left rotation. Significance was found in the right ES when comparing right rotation at 45° to left rotation at 45° and 90°, as well as right and left rotation at 120°. Significance was shown with right ES when comparing 1ight rotation at 90° to 1ight and left rotation at 120°. As for the left ES, results were significant when comparing left rotation at 45° to left rotation at 90° and 120°. Discussion/Conclusion: The findings suggest the LD contiibutes significantly to fixed position contralateral spinal rotation when compared to MT and ES. In fixed positioning, the LD may be mechanically advantaged with a positive length tension relationship to contribute to spinal rotation as established with the trends correlating with increased LD muscle activity during 90 and 120 degree fixed spinal rotation. Whereas in non-fixed positioning, the LD may be at a disadvantaged due to length tension relationship and or the lack of stability from the upper exu·emities. to contribute to spinal rotation compared to ES. Clinical Relevance: This pilot study looks at the effects of the LD, MT, and ES during spinal rotation. This study is a part of ongoing research to assess the rotational movement strategies in individuals without low back pain. During daily activities, many movements require spinal rotation movements such as putting dishes away in cupboards, taking out laundty, reaching for groceries at the store, and looking behind us when driving to check for upcoming traffic. Our findings suggest clinicians should consider the LD as a possible contributor to spinal rotation. Treatment of patients with back pain should involve thorough examination and specific interventions addressing LD strength and mobility

Demystifying the Adversarial Robustness of Random Transformation Defenses

Neural networks' lack of robustness against attacks raises concerns in security-sensitive settings such as autonomous vehicles. While many countermeasures may look promising, only a few withstand rigorous evaluation. Defenses using random transformations (RT) have shown impressive results, particularly BaRT (Raff et al., 2019) on ImageNet. However, this type of defense has not been rigorously evaluated, leaving its robustness properties poorly understood. Their stochastic properties make evaluation more challenging and render many proposed attacks on deterministic models inapplicable. First, we show that the BPDA attack (Athalye et al., 2018a) used in BaRT's evaluation is ineffective and likely overestimates its robustness. We then attempt to construct the strongest possible RT defense through the informed selection of transformations and Bayesian optimization for tuning their parameters. Furthermore, we create the strongest possible attack to evaluate our RT defense. Our new attack vastly outperforms the baseline, reducing the accuracy by 83% compared to the 19% reduction by the commonly used EoT attack ($4.3\times$ improvement). Our result indicates that the RT defense on the Imagenette dataset (a ten-class subset of ImageNet) is not robust against adversarial examples. Extending the study further, we use our new attack to adversarially train RT defense (called AdvRT), resulting in a large robustness gain. Code is available at https://github.com/wagner-group/demystify-random-transform.Comment: ICML 2022 (short presentation), AAAI 2022 AdvML Workshop (best paper, oral presentation

High Harmonic Generation in SF6_{6}: Raman-excited Vibrational Quantum Beats

In a recent experiment (N. Wagner et al., PNAS v103, p13279) on SF$_{6}$, a high-harmonic generating laser pulse is preceded by a pump pulse which stimulates Raman-active modes in the molecule. Varying the time delay between the two pulses modulates high harmonic intensity, with frequencies equal to the vibration frequencies of the Raman-active modes. We propose an explanation of this modulation as a quantum interference between competing pathways that occur via adjacent vibrational states of the molecule. The Raman and high harmonic processes act as beamsplitters, producing vibrational quantum beats among the Raman-active vibrational modes that are excited by the first pulse. We introduce a rigorous treatment of the electron-ion recombination process and the effect of the ionic Coulomb field in the electron propagation outside the molecule, improving over the widely-used three-step model.Comment: submitted to PR

Rational Ground on the Rio Grande: George W. Bush and Comprehensive Immigration Reform

During his second term, George W. Bush pushed comprehensive immigration reform (CIR), a policy that addressed illegal immigration through several provisions at once. Some of those provisions were favored by conservative border security hawks, including augmenting Border Patrol efforts with technology and increased manpower, while others were favored by pro-immigration liberals, including a temporary worker program and a clear path to citizenship. To pass both at the same time was clearly a challenge, but President Bush was the perfect man for the job, due to his security credentials and his left-leaning immigration stance. Bush seized what he thought was the perfect moment to capitalize on broad public support for the general outline of CIR. For nearly two years, his push for CIR ran into problems, including two counter-movements, a sweeping change of the makeup of Congress, and xenophobic hysteria stirred up by the right wing. Bush’s prolonged failure to garner public support for CIR became the defining domestic failure of his second term. To date, no explanation of his failure on CIR accounts for his rhetoric, an oversight that deprives the historical record of understanding presidential leadership. This dissertation combines social movement theory and a generally inductive method based in the rhetorical situation to explain how Bush failed to pass CIR

Deformability of Human Mesenchymal Stem Cells Is Dependent on Vimentin Intermediate Filaments

Mesenchymal stem cells (MSCs) are being studied extensively due to their potential as a therapeutic cell source for many load-bearing tissues. Compression of tissues and the subsequent deformation of cells are just one type physical strain MSCs will need to withstand in vivo. Mechanotransduction by MSCs and their mechanical properties are partially controlled by the cytoskeleton, including vimentin intermediate filaments (IFs). Vimentin IF deficiency has been tied to changes in mechanosensing and mechanical properties of cells in some cell types. However, how vimentin IFs contribute to MSC deformability has not been comprehensively studied. Investigating the role of vimentin IFs in MSC mechanosensing and mechanical properties will assist in functional understanding and development of MSC therapies. In this study, we examined vimentin IFs’ contribution to MSCs’ ability to deform under external deformation using RNA interference. Our results indicate that a deficient vimentin IF network decreases the deformability of MSCs, and that this may be caused by the remaining cytoskeletal network compensating for the vimentin IF network alteration. Our observations introduce another piece of information regarding how vimentin IFs are involved in the complex role the cytoskeleton plays in the mechanical properties of cells

The mechanical response of fire ant rafts

Fire ants (Solenopsis invicta) cohesively aggregate via the formation of voluntary ant-to-ant attachments when under confinement or exposed to water. Once formed, these aggregations act as viscoelastic solids due to dynamic bond exchange between neighboring ants as demonstrated by rate-dependent mechanical response of 3D aggregations, confined in rheometers. We here investigate the mechanical response of 2D, planar ant rafts roughly as they form in nature. Specifically, we load rafts under uniaxial tension to failure, as well as to 50% strain for two cycles with various recovery times between. We do so while measuring raft reaction force (to estimate network-scale stress), as well as the networks' instantaneous velocity fields and topological damage responses to elucidate the ant-scale origins of global mechanics. The rafts display brittle-like behavior even at slow strain rates (relative to the unloaded bond detachment rate) for which Transient Network Theory predicts steady-state creep. This provides evidence that loaded ant-to-ant bonds undergo mechanosensitive bond stabilization or act as \say{catch bonds}. This is further supported by the coalescence of voids that nucleate due to biaxial stress conditions and merge due to bond dissociation. The characteristic timescales of void coalescence due to chain dissociation provide evidence that the local detachment of stretched bonds is predominantly strain- (as opposed to bond lifetime-) dependent, even at slow strain rates, implying that bond detachment rates diminish significantly under stretch. Significantly, when the voids are closed by restoring the rafts to unstressed conditions, mechanical recovery occurs, confirming the presence of concentration-dependent bond association that - combined with force-diminished dissociation - could further bolster network cohesion under certain stress states

Compensation effects in GaN:Mg probed by Raman spectroscopy and photoluminescence measurements

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Appl. Phys. 113, 103504 (2013) and may be found at https://doi.org/10.1063/1.4794094.Compensation effects in metal organic chemical vapour deposition grown GaN doped with magnesium are investigated with Raman spectroscopy and photoluminescence measurements. Examining the strain sensitive E2(high) mode, an increasing compressive strain is revealed for samples with Mg-concentrations lower than 7 × 1018 cm−3. For higher Mg-concentrations, this strain is monotonically reduced. This relaxation is accompanied by a sudden decrease in crystal quality. Luminescence measurements reveal a well defined near band edge luminescence with free, donor bound, and acceptor bound excitons as well as a characteristic donor acceptor pair (DAP) luminescence. Following recent results, three acceptor bound excitons and donor acceptor pairs are identified. Along with the change of the strain, a strong modification in the luminescence of the dominating acceptor bound exciton and DAP luminescence is observed. The results from Raman spectroscopy and luminescence measurements are interpreted as fingerprints of compensation effects in GaN:Mg leading to the conclusion that compensation due to defect incorporation triggered by Mg-doping already affects the crystal properties at doping levels of around 7 × 1018 cm−3. Thereby, the generation of nitrogen vacancies is introduced as the driving force for the change of the strain state and the near band edge luminescence.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement