Hybrid Uncertain Analysis for Exterior Acoustic Field Prediction with Interval Random Parameters

For exterior acoustic field problems that lack sufficient information to construct precise probability distributions, an interval random model is introduced to deal with the uncertain parameters. In the interval random model, the probability variables are employed to treat the uncertain parameters, whereas some distribution parameters of random variables are modeled as interval variables instead of precise values. Based on the interval random model, the interval random finite element equation for exterior acoustic fields is established and a hybrid uncertain analysis method is presented to solve the exterior acoustic field problem with interval random variables. In the presented method, by temporarily neglecting the uncertainties of interval variables, a first-order stochastic perturbation method is adopted to calculate the expectation and the variance of the response vector. According to the monotonicity of the expectation and variance of the response vector with respect to the interval variables, the lower and upper bounds of the expectation and variance of the response vector can be calculated by the vertex method. In addition, in order to ensure accuracy of the proposed method, the subinterval technique is introduced and investigated. The numerical example of a square flexible shell model is presented to demonstrate the effectiveness of the proposed method.</jats:p

Squeal reduction of a disc brake system with fuzzy uncertainties

Automotive brake squeal has become one of the major concerns in the automotive industry. The researches on suppressing brake squeal are of great practical significances. However, most of the existing researches have not taken into account the parameters uncertainties, although it is well known that uncertain factors widely exist in the brake systems. To reduce disc brake squeal more effectively, a practical approach for the stability analysis and improvement of an automotive disc brake system with fuzzy uncertainties is proposed. In the proposed approach, the uncertainties associated with friction coefficient, material properties and loading properties are taken into consideration, and the uncertain parameters of the brake system are represented by fuzzy numbers. The brake system stability is investigated by performing complex eigenvalue analysis (CEA), and response surface methodology (RSM) is employed to approximate the implicit relationship between the dominant unstable mode and system parameters. Then, the stability analysis model of the brake is constructed based on RSM, CEA and fuzzy analysis. As a numerical example, the stability analysis of a commercial disc brake system with fuzzy uncertainties is carried out, and the influences of different uncertain parameters on system stability are investigated. The analysis results show that the stability of the fuzzy brake can be improved effectively by increasing the specific modulus of back plate. The proposed approach can be considered as a potential method for squeal reduction of automotive disc brake systems under fuzzy case

Mechanisms Of Cannabinoid Cb 2 Receptor-Mediated Reduction Of Dopamine Neuronal Excitability In Mouse Ventral Tegmental Area

Background: We have recently reported that activation of cannabinoid type 2 receptors (CB 2 Rs)reduces dopamine (DA)neuron excitability in mouse ventral tegmental area (VTA). Here, we elucidate the underlying mechanisms. Methods: Patch-clamp recordings were performed in mouse VTA slices and dissociated single VTA DA neurons. Findings: Using cell-attached recording in VTA slices, bath-application of CB 2 R agonists (JWH133 or five other CB 2 R agonists)significantly reduced VTA DA neuron action potential (AP)firing rate. Under the patch-clamp whole-cell recording model, JWH133 (10 μM)mildly reduced the frequency of miniature excitatory postsynaptic currents (mEPSCs)but not miniature inhibitory postsynaptic currents (mIPSCs). JWH133 also did not alter evoked EPSCs or IPSCs. In freshly dissociated VTA DA neurons, JWH133 reduced AP firing rate, delayed AP initiation and enhanced AP after-hyperpolarization. In voltage-clamp recordings, JWH133 (1 μM)enhanced M-type K + currents and this effect was absent in CB 2−/− mice and abolished by co-administration of a selective CB 2 R antagonist (10 μM, AM630). CB 2 R-mediated inhibition in VTA DA neuron firing can be mimicked by M-current opener (10 μM retigabine)and blocked by M-current blocker (30 μM XE991). In addition, enhancement of neuronal cAMP by forskolin (10 μM)reduced M-current and increased DA neuron firing rate. Finally, pharmacological block of synaptic transmission by NBQX (10 μM), D-APV (50 μM)and picrotoxin (100 μM)in VTA slices failed to prevent CB 2 R-mediated inhibition, while intracellular infusion of guanosine 5\u27-O-2-thiodiphosphate (600 μM, GDP-β-S)through recording electrode to block postsynaptic G-protein function prevented JWH133-induced reduction in AP firing. Interpretation: Our results suggest that CB 2 Rs modulate VTA DA neuron excitability mainly through an intrinsic mechanism, including a CB 2 R-mediated reduction of intracellular cAMP, and in turn enhancement of M-type K + currents. Fund: This research was supported by the Barrow Neuroscience Foundation, the BNI-BMS Seed Fund, and CNSF (81771437)