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Gyung-jin Park - One of the best experts on this subject based on the ideXlab platform.
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optimization of the loading path for the tube hydroforming process
Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 2016Co-Authors: Hwanhak Jang, Youngmyung Lee, Gyung-jin ParkAbstract:In general, hydroforming optimization aims to make a desired shape of a plastically deformed structure under dynamic forces. The automotive industry has shown great interest in tube hydroforming, which is a metal-forming process. The forces from the hydraulic fluid are utilized to deform a tube. The internal pressures and the axial feedings (of the axial forces) determine the quality of the deformed product. In this research, an optimization process is employed to evaluate the appropriate external forces but defects are prevented. The equivalent static loads method for non-linear static Response structural optimization is used for the optimization process because the tube-hydroforming process is analysed by non-linear dynamic Response analysis. The equivalent static loads are the static loads that generate the same Response Field as that of non-linear dynamic analysis and are utilized as the loading conditions in linear static Response optimization. A novel process is added to the original equivalent stat...
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nonlinear dynamic Response topology optimization using the equivalent static loads method
Computer Methods in Applied Mechanics and Engineering, 2015Co-Authors: Hyunah Lee, Gyung-jin ParkAbstract:Abstract A novel method for nonlinear dynamic Response topology optimization is proposed using the equivalent static loads (ESLs) method. The ESLs are the loads that generate the same Response Field of linear static analysis as that of nonlinear dynamic analysis at each time step. In the proposed procedure, nonlinear dynamic analysis is performed, ESLs are made and linear static topology optimization is carried out with the ESLs. The process cyclically proceeds until the convergence criterion, which is specifically defined for this problem, is satisfied. Since the density method for topology optimization is utilized, the low-density finite elements can cause mesh distortion in nonlinear dynamic analysis. Transformation variables are introduced for a new update method for the incorporating process of the topology results into nonlinear dynamic analysis. Also, a new objective function is proposed to minimize the peaks of the time dependent transient Responses. A couple of standard problems and a practical problem are solved to validate the proposed method.
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shape optimization of the workpiece in the forging process using equivalent static loads
Finite Elements in Analysis and Design, 2013Co-Authors: Jaejun Lee, Uijin Jung, Gyung-jin ParkAbstract:The forging process, which is the shaping of a workpiece using compressive loads, is a representative plastic manufacturing process and typically consists of a multi-step process with a preforming process. The workpiece shape is an important factor because it influences the quality of the final product. After the forging process, defects such as an unfilled area, flash and crack can occur, and the effective strains may not be evenly distributed. Shape optimization of the workpiece is nonlinear dynamic Response optimization because nonlinearities are involved in the analysis of the forging process. Many researches are performed to predetermine the workpiece shape using conventional methods. It is well known that the conventional methods are quite costly due to repeated nonlinear analysis for the calculation of function and sensitivity information. In this paper, the equivalent static loads method for non linear static Response structural optimization (ESLSO) is employed to determine the workpiece shape which leads to the desired final shape and even distribution of the effective strain. Equivalent static loads (ESLs) are defined as the static loads for linear analysis, which generate the same Response Field as that of nonlinear analysis. In ESLSO, the dynamic loads for nonlinear analysis are transformed to ESLs. The ESLs, which have the characteristics of nonlinearities and dynamic loads, are utilized as the loading conditions in linear static Response optimization. The design is updated from the results of linear static Response optimization using ESLs. Nonlinear analysis is carried out with the updated design, and the process proceeds in a cyclic manner until the convergence criteria of the design variables are satisfied. Two kinds of ESLs are proposed and they are the ESLs for the displacements and the ESLs for the effective strains. Examples of the forging process are formulated and solved.
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a preliminary study on the optimal preform design in the forging process using equivalent static loads
13th AIAA ISSMO Multidisciplinary Analysis Optimization Conference, 2010Co-Authors: Jaejun Lee, Uijin Jung, Gyung-jin ParkAbstract:The forging process is the shaping of a workpiece using dynamic loads and typically consists of the multi-step process with the preforming process. Defects such as flash and unfilling occur and the distribution of effective strains is not even in the workpiece after the forging process. An optimized preform is necessary for reduction of the defects in the desired final forging. Optimization of the forging process is nonlinear dynamic Response optimization because nonlinearities are involved in the analysis. When the conventional method is utilized in optimization of the forging process, the cost is extremely high due to repeated nonlinear analyses for function and sensitivity calculation. In this paper, the equivalent static loads method for non linear static Response structural optimization (ESLSO) is employed to determine the preform shape which leads to reduction of the unfilled area and even distribution of the effective strain in the final forging shape. ESLSO is a structural optimization method where nonlinear dynamic loads are transformed to equivalent static loads (ESLs). ESLs are defined as the loads for linear analysis, which generate the same Response Field as that of nonlinear analysis. Two kinds of ESLs are proposed and they are the ESLs for the displacements and the ESLs for the effective strains. Examples of the forging process are solved using these ESLs and the results are discussed.
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nonlinear dynamic Response structural optimization using equivalent static loads
Computer Methods in Applied Mechanics and Engineering, 2010Co-Authors: Yongil Kim, Gyung-jin ParkAbstract:It is well known that nonlinear dynamic Response optimization using a conventional optimization algorithm is fairly difficult and expensive for the gradient or non-gradient based optimization methods because many nonlinear dynamic analyses are required. Therefore, it is quite difficult to find practical large scale examples with many design variables and constraints for nonlinear dynamic Response structural optimization. The equivalent static loads (ESLs) method is newly proposed and applied to nonlinear dynamic Response optimization. The equivalent static loads are defined as the linear static load sets which generate the same Response Field in linear static analysis as that from nonlinear dynamic analysis. The ESLs are made from the results of nonlinear dynamic analysis and used as external forces in linear static Response optimization. Then the same Response from nonlinear dynamic analysis can be considered throughout linear static Response optimization. The updated design from linear Response optimization is used again in nonlinear dynamic analysis and the process proceeds in a cyclic manner until the convergence criteria are satisfied. Several examples are solved to validate the method. The results are compared to those of the conventional method with sensitivity analysis using the finite difference method.
Shihab A Shamma - One of the best experts on this subject based on the ideXlab platform.
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rapid task related plasticity of spectrotemporal receptive Fields in primary auditory cortex
Nature Neuroscience, 2003Co-Authors: Jonathan B Fritz, Shihab A Shamma, Mounya Elhilali, David KleinAbstract:We investigated the hypothesis that task performance can rapidly and adaptively reshape cortical receptive Field properties in accord with specific task demands and salient sensory cues. We recorded neuronal Responses in the primary auditory cortex of behaving ferrets that were trained to detect a target tone of any frequency. Cortical plasticity was quantified by measuring focal changes in each cell's spectrotemporal Response Field (STRF) in a series of passive and active behavioral conditions. STRF measurements were made simultaneously with task performance, providing multiple snapshots of the dynamic STRF during ongoing behavior. Attending to a specific target frequency during the detection task consistently induced localized facilitative changes in STRF shape, which were swift in onset. Such modulatory changes may enhance overall cortical responsiveness to the target tone and increase the likelihood of 'capturing' the attended target during the detection task. Some receptive Field changes persisted for hours after the task was over and hence may contribute to long-term sensory memory.
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spectro temporal Response Field characterization with dynamic ripples in ferret primary auditory cortex
Journal of Neurophysiology, 2001Co-Authors: Didier A. Depireux, Jonathan Z. Simon, David Klein, Shihab A ShammaAbstract:To understand the neural representation of broadband, dynamic sounds in primary auditory cortex (AI), we characterize Responses using the spectro-temporal Response Field (STRF). The STRF describes,...
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analysis of dynamic spectra in ferret primary auditory cortex i characteristics of single unit Responses to moving ripple spectra
Journal of Neurophysiology, 1996Co-Authors: Nina Kowalski, Didier A. Depireux, Shihab A ShammaAbstract:1. Auditory stimuli referred to as moving ripples are used to characterize the Responses of both single and multiple units in the ferret primary auditory cortex. Moving ripples are broadband complex sounds with a sinusoidal spectral profile that drift along the logarithmic frequency axis at a constant velocity. 2. Neuronal Responses to moving ripples are locked to the phase of the ripple, i.e., they exhibit the same periodicity as that of the moving ripple profile. Neural Responses are characterized as a function of ripple velocity (temporal property) and ripple frequency (spectral property). Transfer functions describing the Response to these temporal and spectral modulations are constructed. Temporal transfer functions are inverse Fourier transformed to obtain impulse Response functions that reflect the cell's temporal characteristics. Ripple transfer functions are inverse Fourier transformed to obtain the Response Field, a measure analogous to the cell's Response area. These operations assume linearity in the cell's Response to moving ripples. 3. Transfer functions and other Response functions are shown to be fairly independent on the overall level or depth of modulation of the ripple stimuli. Only downward moving ripples were used in this study. 4. The temporal and ripple transfer functions are found to be separable, in that their shapes remain unchanged for different test parameters. Thus ripple transfer functions and Response Fields remain statistically similar in shape (to within an overall scale factor) regardless of the ripple velocity or whether stationary or moving ripples are used in the measurement. The same stability in shape holds for the temporal transfer functions and the impulse Response functions measured with different ripple frequencies. Separability implies that the combined spectrotemporal transfer function of a cell can be written as the product of a purely ripple and a purely temporal transfer functions, and thus that the neuron can be computationally modeled as processing spectral and temporal information in two separate and successive stages. 5. The ripple parameters that characterize cortical cells are distributed somewhat evenly, with the characteristic ripple frequencies ranging from 0.2 to > 2 cycles/octave and the characteristic angular frequency typically ranging from 2 to 20 Hz. 6. Many Responses exhibit periodicities in the spectral envelope of the stimulus. These periodicities are of two types. Slow rebounds, not found in the spectral envelope, and with a period of approximately 150 ms, appear with various strengths in approximately 30% of the cells. Fast regular firings with interspike intervals of approximately 10 ms are much less common and appear to correspond to interactions between the component tones that make up a ripple.
Matthew S Foster - One of the best experts on this subject based on the ideXlab platform.
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Response theory of the ergodic many body delocalized phase keldysh finkel stein sigma models and the 10 fold way
Annals of Physics, 2017Co-Authors: Yunxiang Liao, Alex Levchenko, Matthew S FosterAbstract:Abstract We derive the finite temperature Keldysh Response theory for interacting fermions in the presence of quenched short-ranged disorder, as applicable to any of the 10 Altland–Zirnbauer classes in an Anderson delocalized phase with at least a U(1) continuous symmetry. In this formulation of the interacting Finkel’stein nonlinear sigma model, the statistics of one-body wave functions are encoded by the constrained matrix Field, while physical correlations follow from the hydrodynamic density or spin Response Field, which decouples the interactions. Integrating out the matrix Field first, we obtain weak (anti) localization and Altshuler–Aronov quantum conductance corrections from the hydrodynamic Response function. This procedure automatically incorporates the correct infrared cutoff physics, and in particular gives the Altshuler–Aronov–Khmelnitsky (AAK) equations for dephasing of weak (anti)localization due to electron–electron collisions. We explicate the method by deriving known quantumcorrections in two dimensions for the symplectic metal class AII, as well as the spin-SU(2) invariant superconductor classes C and CI. We show that quantum conductance corrections due to the special modes at zero energy in nonstandard classes are automatically cut off by temperature, as previously expected, while the Wigner–Dyson class Cooperon modes that persist to all energies are cut by dephasing. We also show that for short-ranged interactions, the standard self-consistent solution for the dephasing rate is equivalent to a particular summation of diagrams via the self-consistent Born approximation. This should be compared to the corresponding AAK solution for long-ranged Coulomb interactions, which exploits the Markovian noise correlations induced by thermal fluctuations of the electromagnetic Field. We discuss prospects for exploring the many-body localization transition as a dephasing catastrophe in short-range interacting models, as encountered by approaching from the ergodic side.
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Response theory of the ergodic many body delocalized phase keldysh finkel stein sigma models and the 10 fold way
arXiv: Disordered Systems and Neural Networks, 2017Co-Authors: Yunxiang Liao, Alex Levchenko, Matthew S FosterAbstract:We derive the finite temperature Keldysh Response theory for interacting fermions in the presence of quenched disorder, as applicable to any of the 10 Altland-Zirnbauer classes in an Anderson delocalized phase with at least a U(1) continuous symmetry. In this formulation of the interacting Finkel'stein nonlinear sigma model, the statistics of one-body wave functions are encoded by the constrained matrix Field, while physical correlations follow from the hydrodynamic density or spin Response Field, which decouples the interactions. Integrating out the matrix Field first, we obtain weak (anti)localization and Altshuler-Aronov quantum conductance corrections from the hydrodynamic Response function. This procedure automatically incorporates the correct infrared physics, and in particular gives the Altshuler-Aronov-Khmelnitsky (AAK) equations for dephasing of weak (anti)localization due to electron-electron collisions. We explicate the method by deriving known quantum corrections in two dimensions for the symplectic metal class AII, as well as the spin-SU(2) invariant superconductor classes C and CI. We show that conductance corrections due to the special modes at zero energy in nonstandard classes are automatically cut off by temperature, as previously expected, while the Wigner-Dyson class Cooperon modes that persist to all energies are cut by dephasing. We also show that for short-ranged interactions, the standard self-consistent solution for the dephasing rate is equivalent to a diagrammatic summation via the self-consistent Born approximation. This should be compared to the AAK solution for long-ranged Coulomb interactions, which exploits the Markovian noise correlations induced by thermal fluctuations of the electromagnetic Field. We discuss prospects for exploring the many-body localization transition from the ergodic side as a dephasing catastrophe in short-range interacting models.
Douglas P. Munoz - One of the best experts on this subject based on the ideXlab platform.
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contribution of the primate superior colliculus to inhibition of return
Journal of Cognitive Neuroscience, 2002Co-Authors: Michael C Dorris, Stefan Everling, Raymond M Klein, Douglas P. MunozAbstract:The phenomenon of inhibition of return (IOR) has generated considerable interest in cognitive neuroscience because of its putative functional role in visual search, that of placing inhibitory tags on objects that have been recently inspected so as to direct further search to novel items. Many behavioral parameters of this phenomenon have been clearly delineated, and based on indirect but converging evidence, the widely held consensus is that the midbrain superior colliculus (SC) is involved in the generation of IOR. We had previously trained monkeys on a saccadic IOR task and showed that they displayed IOR in a manner similar to that observed in humans. Here we recorded the activity of single neurons in the superficial and intermediate layers of the SC while the monkeys performed this IOR task. We found that when the target was presented at a previously cued location, the stimulus-related Response was attenuated and the magnitude of this Response was correlated with subsequent saccadic reaction times. Surprisingly, this observed attenuation of activity during IOR was not caused by active inhibition of these neurons because (a) they were, in fact, more active following the presentation of the cue in their Response Field, and (b) when we repeated the same experiment while using the saccadic Response time induced by electrical micro-stimulation of the SC to judge the level of excitability of the SC circuitry during the IOR task, we found faster saccades were elicited from the cued location. Our findings demonstrate that the primate SC participates in the expression of IOR; however, the SC is not the site of the inhibition. Instead, the reduced activity in the SC reflects a signal reduction that has taken place upstream.
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neuronal activity in monkey superior colliculus during an antisaccade task
1999Co-Authors: Stefan Everling, Michael C Dorris, Douglas P. MunozAbstract:It well known that the primate superior colliculus (SC) is involved in the generation of visually guided saccadic eye movements (for review see Sparks and Hartwich-Young 1989). Its intermediate layers contain neurons which display motor bursts for saccades within the Response Field of the neuron. These neurons project directly to preoculomo-toneurons in paramedian pontine reticular formation and the rostral interstitial nucleus of the medial longitudinal fasciculus, which provide the input to the extraocular muscle motoneurons (for review see Moschovakis et al. 1996).
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saccadic probability influences motor preparation signals and time to saccadic initiation
The Journal of Neuroscience, 1998Co-Authors: Michael C Dorris, Douglas P. MunozAbstract:One must be prudent when selecting potential saccadic targets because the eyes can only move to one location at a time, yet movements must occur quickly enough to permit interaction with a rapidly changing world. This process of efficiently acquiring relevant targets may be aided by advanced planning of a movement toward an upcoming target whose location is gathered via environmental cues or situational experience. We studied how saccadic reaction times (SRTs) and early pretarget neuronal activity covaried as a function of saccadic probability. Monkeys performed a saccadic task in which the probability of the required saccade being directed into the Response Field of a neuron varied systematically between blocks of trials. We recorded simultaneously the early pretarget activity of saccade-related neurons in the intermediate layers of the superior colliculus. We found that, as the likelihood of the saccade being generated into the Response Field of the neuron increased, the level of neuronal activity preceding target presentation also increased. Our data suggest that this early activity codes motor preparation because its activity was related to not only the metrics but also the timing of the saccade, with 94% (29/31) of the neurons tested having significant negative correlations between discharge rate and SRT. This view is supported by cases in which exceptionally high levels of pretarget activity were associated with anticipatory saccades into the Response Field of a neuron that occurred in advance of the target being presented. This study demonstrates how situational experience can expedite motor behavior via the advanced preparation of motor programs.
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neuronal activity in monkey superior colliculus related to the initiation of saccadic eye movements
The Journal of Neuroscience, 1997Co-Authors: Michael C Dorris, Martin Pare, Douglas P. MunozAbstract:The introduction of a temporal gap between the disappearance of an initially fixated target and the appearance of an eccentric saccadic target results in a general reduction of saccadic reaction times (SRTs)—the gap effect—and often in the production of express saccades, the latencies of which approach the conduction time of the shortest neural pathways from the retina to the eye muscles. We investigated saccade initiation by recording neuronal activity in the superior colliculus in monkeys performing the gap paradigm. Fixation-related neurons reduced their discharge rate during the gap period, regardless of the SRT. This reduction in activity is consistent with the hypothesized release of ocular fixation that facilitates premotor processes and may contribute to the gap effect. In addition to saccade-related discharges, many saccade-related neurons displayed phasic target-related Responses and/or low-frequency preparatory activity during the gap period. The level of this preparatory activity correlated with both SRT and express saccade occurrence when the saccade was made into the Response Field of the neuron. Evidence indicates that advanced motor preparation is required for express saccade generation, which may be subserved by specific increases in the preparatory activity of saccade-related neurons. Increased preparatory activity may allow the target-related Responses to trigger short-latency express saccades directly. This study provides insights into the functional mechanism of saccade initiation and may be relevant to the generation of all voluntary motor Responses.
David Klein - One of the best experts on this subject based on the ideXlab platform.
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rapid task related plasticity of spectrotemporal receptive Fields in primary auditory cortex
Nature Neuroscience, 2003Co-Authors: Jonathan B Fritz, Shihab A Shamma, Mounya Elhilali, David KleinAbstract:We investigated the hypothesis that task performance can rapidly and adaptively reshape cortical receptive Field properties in accord with specific task demands and salient sensory cues. We recorded neuronal Responses in the primary auditory cortex of behaving ferrets that were trained to detect a target tone of any frequency. Cortical plasticity was quantified by measuring focal changes in each cell's spectrotemporal Response Field (STRF) in a series of passive and active behavioral conditions. STRF measurements were made simultaneously with task performance, providing multiple snapshots of the dynamic STRF during ongoing behavior. Attending to a specific target frequency during the detection task consistently induced localized facilitative changes in STRF shape, which were swift in onset. Such modulatory changes may enhance overall cortical responsiveness to the target tone and increase the likelihood of 'capturing' the attended target during the detection task. Some receptive Field changes persisted for hours after the task was over and hence may contribute to long-term sensory memory.
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spectro temporal Response Field characterization with dynamic ripples in ferret primary auditory cortex
Journal of Neurophysiology, 2001Co-Authors: Didier A. Depireux, Jonathan Z. Simon, David Klein, Shihab A ShammaAbstract:To understand the neural representation of broadband, dynamic sounds in primary auditory cortex (AI), we characterize Responses using the spectro-temporal Response Field (STRF). The STRF describes,...
