1,458 research outputs found
Parametrization for 2-D SH full waveform inversion
No full textWith single-parameter full waveform inversion, estimating the inverse of the Hessian matrix will accelerate the convergence, but is computationally expensive. Therefore, an approximate Hessian, which is easier to compute, is often used. Similarly, in the case of multi-parameter full waveform inversion, the computation of the Hessian terms that contain derivatives with respect to more than one type of parameter, called cross-parameter Hessian terms, is not usually feasible. If the nonlin- ear inverse problem is well-posed, then the result should be independent of the parametrization choice provided we start close to the global minimum. However, the choice of parametrization will affect the rate of convergence to the exact solution and the “best” choice of parametrization is the one with the fastest rate. If the inverse problem is ill-posed the choice of parametrization introduces a bias towards a particular solution among the non-unique ones that explain the data. This obfuscates the search for the “best” parametrization. We investigated parametrization choices for a 2-D SH experiment where only the reflected wavefield is recorded. Our numerical examples suggest that certain type of scatterers are better inverted by one parametrization choice than another due to the parametrization bias. Therefore, there is nothing like a “best” parametrization in these single-component SH examples.Geoscience & EngineeringCivil Engineering and Geoscience
Looking ahead of a tunnel boring machine with 2-D SH full waveform inversion
No full textIn the near-surface with unconsolidated soils, shear properties can be well imaged, sometimes better than P-wave properties. To facilitate ground prediction ahead of a tunnel boring machine (TBM), active ‘surveys’ with shear-wave vibrators are carried out during boring. In such surveys, only a few shear-wave vibrators can be placed in front of the machine’s cutter head. The vibrators inject a force in the direction perpendicular to the drilling path. We use a vibrator that is capable of exciting low frequencies. Therefore, a full waveform inversion (FWI) approach can be used, which would make the imaging more automatic. Imaging with conventional migration methods suffers from artifacts caused by incomplete aperture and inadequate velocity analysis. In this abstract, we examine the potential of 2-D SH FWI to reconstruct anomalies. In contrast to FWI for hydrocarbon exploration, we have access to reliable low frequencies in the data and are working in the near-field regime. The very limited maximum offset causes diving waves to be absent. This lack of aperture makes it difficult to reconstruct the shear-wave velocity away from the source-receiver array even in the presence of low frequencies. Our study shows that FWI with SH waves should offer a valuable lookahead capability.Geoscience & EngineeringCivil Engineering and Geoscience
ω-3 fatty acid eicosapentaenoic acid attenuates MPP+-induced neurodegeneration in fully differentiated human SH-SY5Y and primary mesencephalic cells
No full textEicosapentaenoic acid (EPA), a neuroactive omega-3 fatty acid, has been demonstrated to exert neuroprotective effects in experimental models of Parkinson's disease (PD), but the cellular mechanisms of protection are unknown. Here, we studied the effects of EPA in fully differentiated human SH-SY5Y cells and primary mesencephalic neurons treated with MPP(+) . In both in-vitro models of PD, EPA attenuated an MPP(+) -induced reduction in cell viability. EPA also prevented the presence of electron-dense cytoplasmic inclusions in SH-SY5Y cells. Then, possible mechanisms of the neuroprotection were studied. In primary neurons, EPA attenuated an MPP(+) -induced increase in Tyrosine-related kinase B (TrkB) receptors. In SH-SY5Y cells, EPA down-regulated reactive oxygen species and nitric oxide. This antioxidant effect of EPA may have been mediated by its inhibition of neuronal NADPH oxidase and cyclo-oxygenase-2 (COX-2), as MPP(+) increased the expression of these enzymes. Furthermore, EPA prevented an increase in cytosolic phospholipase A2 (cPLA2), an enzyme linked with COX-2 in the potentially pro-inflammatory arachidonic acid cascade. Lastly, EPA attenuated an increase in the bax:bcl-2 ratio, and cytochrome c release. However, EPA did not prevent mitochondrial enlargement or a decrease in mitochondrial membrane potential. This study demonstrated cellular mechanisms by which EPA provided neuroprotective effects in experimental PD.
(© 2012 The Authors Journal of Neurochemistry © 2012 International Society for Neurochemistry.
ω-3 fatty acid eicosapentaenoic acid attenuates MPP+-induced neurodegeneration in fully differentiated human SH-SY5Y and primary mesencephalic cells.
No full textEicosapentaenoic acid (EPA), a neuroactive omega-3 fatty acid, has been demonstrated to exert neuroprotective effects in experimental models of Parkinson's disease (PD), but the cellular mechanisms of protection are unknown. Here, we studied the effects of EPA in fully differentiated human SH-SY5Y cells and primary mesencephalic neurons treated with MPP(+) . In both in-vitro models of PD, EPA attenuated an MPP(+) -induced reduction in cell viability. EPA also prevented the presence of electron-dense cytoplasmic inclusions in SH-SY5Y cells. Then, possible mechanisms of the neuroprotection were studied. In primary neurons, EPA attenuated an MPP(+) -induced increase in Tyrosine-related kinase B (TrkB) receptors. In SH-SY5Y cells, EPA down-regulated reactive oxygen species and nitric oxide. This antioxidant effect of EPA may have been mediated by its inhibition of neuronal NADPH oxidase and cyclo-oxygenase-2 (COX-2), as MPP(+) increased the expression of these enzymes. Furthermore, EPA prevented an increase in cytosolic phospholipase A2 (cPLA2), an enzyme linked with COX-2 in the potentially pro-inflammatory arachidonic acid cascade. Lastly, EPA attenuated an increase in the bax:bcl-2 ratio, and cytochrome c release. However, EPA did not prevent mitochondrial enlargement or a decrease in mitochondrial membrane potential. This study demonstrated cellular mechanisms by which EPA provided neuroprotective effects in experimental PD
Morphologic and functional correlates of synaptic pathology in the cathepsin D knockout mouse model of congenital neuronal ceroid lipofuscinosis
No full textMutations in the cathepsin D (CTSD) gene cause an aggressive neurodegenerative disease (congenital neuronal ceroid lipofuscinosis) that leads to early death. Recent evidence suggests that presynaptic abnormalities play a major role in the pathogenesis of CTSD deficiencies. To identify the early events that lead to synaptic alterations, we investigated synaptic ultrastructure and function in presymptomatic CTSD knockout (Ctsd) mice. Electron microscopy revealed that there were significantly greater numbers of readily releasable synaptic vesicles present in Ctsd mice than in wild-type control mice as early as postnatal day 16. The size of this synaptic vesicle pool continued to increase with disease progression in the hippocampus and thalamus of the Ctsd mice. Electrophysiology revealed a markedly decreased frequency of miniature excitatory postsynaptic currents (mEPSCs) with no effect on paired-pulse modulation of the evoked excitatory post synaptic potentials in the hippocampus of Ctsd mice. The reduced mEPSCs frequency was observed before the appearance of epilepsy or any morphologic sign of synaptic degeneration. Taken together, these data indicate that CTSD is required for normal synaptic function and that a failure in synaptic trafficking or recycling may bean early and important pathologic mechanism in Ctsd mice; these presynaptic abnormalities may initiate synaptic degeneration in advance of subsequent neuronal loss
HIGH RESOLUTION, ELECTRONIC SPECTROSCOPY OF THE RARE GAS (Ne, Ar, Kr) SH/D VAN DER WAALS COMPLEXES
No full textAuthor Institution: Laser Spectroscopy Facility, Department of Chemistry, The Ohio State UniversityThe rotationally resolved, jet-cooled, electronic spectra of the SH/D rare gas complexes, Rg SH/D(Rg = Ne, Ar, Kr) have been recorded. The complexes were produced by the UV photolysis of small percentage mixtures of either or in He with the appropriate rare gas and then probed via LIF with a pulse amplified cw ring dye laser. We were able to resolve ( 300 MHz lasser linewidth) both fine and hyperfine components of these complexes. Data for both pure van der Waals stretch bands as well as bend-stretch combination bands have been recorded for each complex. The analysis of these spectra will be presented and discussed
A uniform-sensitivity omnidirectional shear-horizontal (SH) wave transducer based on a thickness poled, thickness-shear (d(15)) piezoelectric ring
No full textThe fundamental shear horizontal (SH0) wave in plates is of great importance in the field of nondestructive testing (NDT) and structural health monitoring (SHM) since it is the unique non-dispersive guided wave mode. For practical applications, a phased array system based on omnidirectional SH0 wave transducers is most useful as it can cover a wide range of a plate. However, so far very few omnidirectional SH wave transducers have been developed. In this work, we proposed an omnidirectional SH wave piezoelectric transducer (OSH-PT) based on a thickness poled piezoelectric ring. The ring is equally divided into twelve sectors and the electric field is circumferentially applied, resulting in a new thickness-shear (d(15)) mode. Finite element analysis shows that the proposed OSH-PT can excite single-mode SH0 wave and receive the SH0 wave only. Experiments were then conducted to examine the performance of the proposed OSH-PT. Results indicated that it can generate and receive single-mode SH0 wave in a wide frequency range with nearly uniform sensitivities along all directions. Considering its quite simple configuration, compact size and low cost, the proposed OSH-PT is expected to greatly promote the applications of SH waves in the field of NDT and SHM.National Natural Science Foundation of China [11422216, 11672003, 11521202]SCI(E)ARTICLE82
The stereodynamics study on the isotopic substitution C+SH(D,T) → H(D,T)+CS reactions on the new HCS(X2A′) potential energy surface
No full textThe quasi-classical trajectory calculations are carried out to investigate the isotopic substitution effect on title reactions based on the recently developed, accurate potential energy surface of the HCS(X2A') (Song, Zhang, et al. Sci. Rep. 6, 37734 (2016)). The total integral cross sections (ICSs) and vibrational state resolved ICSs are obtained for C + SH(D, T) → H(D, T) + CS reactions. In addition, differential cross sections and two angle distribution functions P(θr), P(r) at different collision energies are investigated. It is found that the peaks of P(θr) and P(r) become lower with the reagent molecule SH turning into SD and ST.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
CHARACTERIZATION OF THE GROUND STATE OF THE (R=Ne, Ar, Kr) COMPLEXES
No full textAuthor Institution: Laser Spectroscopy Facility, Department of Chemistry, The Ohio State UniversityInformation characterizing the state of the complexes has been obtained from two complimentary experimental techniques. The spin-vibronic energy levels have been determined by wavelength resolved fluorescence subsequent to laser excitation of specific vibronic levels of the state. Both moderate and high resolution laser induced fluorescence has also been used to characterize the state owing to the observation of ``hot'' bands from excited spin-vibronic levels of . The experimental data have been used to construct very simple models for the ground state potential energy surface for each complex. These models show that the most stable conformation for each complex is linear H-bonded, but the barrier to isomerization to the S-bonded complex is quite low. The overall bonding is somewhat weaker and more isotropic than the corresponding hydroxyl complexes
DISPERSED FLUORESCENCE SPECTRA AND GROUND STATE POTENTIAL OF COMPLEXES (R=Ne, Ar AND Kr)
No full textM. -L. Dubenet, D. Flower and J.M. Hutson, {J. Phys. Chem}. \textbf{94}, 7602(1991)Author Institution: Laser Spectroscopy Facility, Department of Chemistry, The Ohio State UniversityThe dispersed fluorescence spectra of R.SH have been observed following laser excitation of specific excited vibronic levels. There are three possible emission mechanisms; (1)re-emission from the pumped level, (2)relaxation to lower vibrational levels and emission therefrom, and (3) a dissociation mechanism: . This latter mechanism has little contribution because the lifetime of the excited state SH is very short ; therefore more of the SH will dissociate rather then emitting photons. Mechanisms (1)and (2) can be separated by careful comparison of spectra from adjacent vibrational levels. From the resulting analysis much can be learned about the state’s vibrational structure. The ground states of R-SH can be described as near the free rotor limit. Most of the observed emission features are terminated on the internal SH-rotor levels in the ground state but in Ne-SH and Ar-SH, transitions to levels associated with excitation of the R-SH stretch are also observed. Due to the experimental resolution one does not resolve the P structure in the ground state. Using the dispersed flurescence data, the ground state angular potential can be fit to the model developed by Dubernet {et al}. The details of the analysis will be presented
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