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1
Tunçer, Erdal, Tarkan Sandalci, Saban Pusat, Özgün Balcı et Yasin Karagöz. « Cycle-skipping strategy with intake air cut off for natural gas fueled Si engine ». Science Progress 104, no 3 (juillet 2021) : 003685042110310. http://dx.doi.org/10.1177/00368504211031074.
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In this study, cycle-skipping was investigated for a natural gas engine which has single cylinder, unsupercharged with 1.16 L volume and spark ignition. Additionally, inlet manifold air was switched off during cycle-skipping to minimize pumping losses. Thus, cycle-skipping strategy was carried out, and its effects on emission and engine performance were investigated. Indicated mean effective pressure, indicated efficiency, specific emissions (CO, HC, and NOX) and combustion characteristics (in-cylinder pressure and rate of heat release) were investigated in the study. As a result of performed study, it is predicted that a significant improvement can be achieved in indicated thermal efficiency as 22.8% and 13.4% by different cycle-skipping strategies. However, there is not a continuous change in emissions for different cycle-skipping strategies. While CO and NOX emissions increased in 3N1S (three normal, one cycle-skip) condition, HC emissions decreased in accordance with normal condition. For both cycle-skipping strategies, all the emissions have an increase in accordance with normal condition. In 3N1S and 2N1S (two normal, one cycle-skip) cycle skip engine operating conditions, compared to engine operating under normal condition, CO emissions increased by 14.7 and 51.7 times, respectively. In terms of HC emissions, while emission values decreased by 27.8% under 3N1S operating conditions, they increased by 67.2% under 2N1S operating conditions. Finally, in 3N1S and 2N1S cycle skip engine operating conditions, NOx emissions increased by 3.7 and 6.9 times, respectively, compared to normal operating condition. Another significant result of this study is that peak in-cylinder pressure increased as the cycle-skipping rate increased.
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Huang, Guanghui, Rami Nammour et William W. Symes. « Source-independent extended waveform inversion based on space-time source extension : Frequency-domain implementation ». GEOPHYSICS 83, no 5 (1 septembre 2018) : R449—R461. http://dx.doi.org/10.1190/geo2017-0333.1.
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Source signature estimation from seismic data is a crucial ingredient for successful application of seismic migration and full-waveform inversion (FWI). If the starting velocity deviates from the target velocity, FWI method with on-the-fly source estimation may fail due to the cycle-skipping problem. We have developed a source-based extended waveform inversion method, by introducing additional parameters in the source function, to solve the FWI problem without the source signature as a priori. Specifically, we allow the point source function to be dependent on spatial and time variables. In this way, we can easily construct an extended source function to fit the recorded data by solving a source matching subproblem; hence, it is less prone to cycle skipping. A novel source focusing annihilator, defined as the distance function from the real source position, is used for penalizing the defocused energy in the extended source function. A close data fit avoiding the cycle-skipping problem effectively makes the new method less likely to suffer from local minima, which does not require extreme low-frequency signals in the data. Numerical experiments confirm that our method can mitigate cycle skipping in FWI and is robust against random noise.
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Asano, Fumihiko, et Masashi Suguro. « Limit cycle walking, running, and skipping of telescopic-legged rimless wheel ». Robotica 30, no 6 (29 novembre 2011) : 989–1003. http://dx.doi.org/10.1017/s0263574711001226.
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SUMMARYThis paper investigates the efficiency and properties of limit cycle walking, running, and skipping of a planar, active, telescopic-legged rimless wheel. First, we develop the robot equations of motion and design an output following control for the telescopic-legs' action. We then numerically show that a stable walking gait can be generated by asymmetrizing the impact posture. Second, we numerically show that a stable running gait can be generated by employing a simple feedback control of the control period, and compare the properties of the generated running gait with those of the walking gait. Furthermore, we find out another underlying gait called skipping that emerges as an extension of the walking gait. Through numerical analysis, we show that the generated skipping gaits are inherently stable and are less efficient than the other two gaits.
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Yao, Gang, Nuno V. da Silva, Michael Warner, Di Wu et Chenhao Yang. « Tackling cycle skipping in full-waveform inversion with intermediate data ». GEOPHYSICS 84, no 3 (1 mai 2019) : R411—R427. http://dx.doi.org/10.1190/geo2018-0096.1.
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Full-waveform inversion (FWI) is a promising technique for recovering the earth models for exploration geophysics and global seismology. FWI is generally formulated as the minimization of an objective function, defined as the L2-norm of the data residuals. The nonconvex nature of this objective function is one of the main obstacles for the successful application of FWI. A key manifestation of this nonconvexity is cycle skipping, which happens if the predicted data are more than half a cycle away from the recorded data. We have developed the concept of intermediate data for tackling cycle skipping. This intermediate data set is created to sit between predicted and recorded data, and it is less than half a cycle away from the predicted data. Inverting the intermediate data rather than the cycle-skipped recorded data can then circumvent cycle skipping. We applied this concept to invert cycle-skipped first arrivals. First, we picked up the first breaks of the predicted data and the recorded data. Second, we linearly scaled down the time difference between the two first breaks of each shot into a series of time shifts, the maximum of which was less than half a cycle, for each trace in this shot. Third, we moved the predicted data with the corresponding time shifts to create the intermediate data. Finally, we inverted the intermediate data rather than the recorded data. Because the intermediate data are not cycle-skipped and contain the traveltime information of the recorded data, FWI with intermediate data updates the background velocity model in the correct direction. Thus, it produces a background velocity model accurate enough for carrying out conventional FWI to rebuild the intermediate- and short-wavelength components of the velocity model. Our numerical examples using synthetic data validate the intermediate-data concept for tackling cycle skipping and demonstrate its effectiveness for the application to first arrivals.
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Thakur, Joyeeta, Monali Goswami et Subho Roy. « Understanding menstrual characteristics from the perspective of reproductive energetics : a study on the adolescent Oraon tribal populations ». Anthropological Review 83, no 2 (1 juin 2020) : 109–28. http://dx.doi.org/10.2478/anre-2020-0009.
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AbstractThe energetic costs of ovarian functions rely on the oxidizable fuels synthesized from carbohydrate, protein and fat that contribute to body’s fat storage. Energy deficient diet in association with low body fat may disrupt normal ovulatory function and lead to several menstrual irregularities. We examined the association of nutritional status with menstrual characteristics among a group of adolescent Oraon tribal population of West Bengal, India. We selected 301 adolescent girls, aged 10-19 years. Information on socio-demographic status, menstrual characteristics and assessment of the dietary intake and nutritional status were collected following standard protocol. ‘Healthy weight’ participants more likely reported irregularity in periods and skipping of menstrual cycle and shorter cycle length. Multivariate analysis revealed PBF has inverse association with PMS, duration of discharge and skipping of cycle (p<0.05); carbohydrate intake has direct association with duration of menstrual discharge (p<0.05); increased dietary fat intake has direct association with skipping of cycle, but not with BMI (p<0.05); increase in MUAC has direct association with dysmenorrhoea (p<0.05). Conclusion: Our study indicates energy deficiency does alter the menstrual characteristics of the Oraon adolescent girls.
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Hu, Yong, Li-Yun Fu, Qingqing Li, Wubing Deng et Liguo Han. « Frequency-Wavenumber Domain Elastic Full Waveform Inversion with a Multistage Phase Correction ». Remote Sensing 14, no 23 (22 novembre 2022) : 5916. http://dx.doi.org/10.3390/rs14235916.
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Elastic full waveform inversion (EFWI) is essential for obtaining high-resolution multi-parameter models. However, the conventional EFWI may suffer from severe cycle skipping without the low-frequency components in elastic seismic data. To solve this problem, we propose a multistage phase correction-based elastic full waveform inversion method in the frequency-wavenumber domain, which we call PC-EFWI for short. Specifically, the seismic data are first split using 2-D sliding windows; for each window, the seismic data are then transformed into the frequency-wavenumber domain for PC-EFWI misfit. In addition, we introduced a phase correction factor in the PC-EFWI misfit. In this way, it is possible to reduce phase differences between measured and synthetic data to mitigate cycle skipping by adjusting the phase correction factor in different scales. Numerical examples with the 2-D Marmousi model demonstrate that the frequency-wavenumber domain PC-EFWI with multistage strategy is an excellent way to reduce the risk of EFWI cycle skipping and build satisfactory start models for the conventional EFWI.
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Tunçer, Erdal, Tarkan Sandalcı et Yasin Karagöz. « Investigation of cycle skipping methods in an engine converted to positive ignition natural gas engine ». Advances in Mechanical Engineering 13, no 9 (septembre 2021) : 168781402110454. http://dx.doi.org/10.1177/16878140211045454.
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In this study, a single cylinder of 1.16 L, naturally aspirated engine was converted to a spark ignition engine, which was a diesel engine operating with natural gas as fuel. By placing electronic throttle, electronic ignition module, gas fuel injectors and proximity sensors on the test engine, the engine has been turned into a positive ignition engine that can work with natural gas as fuel, thanks to the electronic control unit developed by our project team. Then, in the study performed, different cycle skipping strategies were experimentally investigated at a constant engine speed of 1565 rpm, in accordance with the generator operating conditions. Engine performance, emissions (CO, HC, and NOx), and combustion characteristics (cylinder pressure, rate of heat release, etc.) of cycle skipping strategies were experimentally investigated with natural gas as fuel in Normal, 3N1S, 2N1S, and 1N1S engine operating modes. According to the results obtained, specific fuel consumption, CO and HC values improved in all cycle skipping operating conditions, except for NOx, but the best results were obtained in 2N1S operating conditions; it was concluded that the specific fuel consumption, CO and HC values improved by 11.19%, 61.89%, and 65.60%, respectively.
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Nadamoto, Tomonori, Fumiko Fujisawa, Yosuke Ito et Ryuzo Ikeuchi. « Skipping Breakfast Alters Diurnal Cycle of Salivary Corticosteroids in Humans ». Nippon Eiyo Shokuryo Gakkaishi 56, no 2 (2003) : 103–7. http://dx.doi.org/10.4327/jsnfs.56.103.
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Ramos-Martínez, Jaime, Lingyun Qiu, Alejandro A. Valenciano, Xiaoyan Jiang et Nizar Chemingui. « Long-wavelength FWI updates in the presence of cycle skipping ». Leading Edge 38, no 3 (mars 2019) : 193–96. http://dx.doi.org/10.1190/tle38030193.1.
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Full-waveform inversion (FWI) has become the tool of choice for building high-resolution velocity models. Its success depends on producing seamless updates of the short- and long-wavelength model features while avoiding cycle skipping. Classic FWI implementations use the L2 norm to measure the data misfit in combination with a gradient computed by a crosscorrelation imaging condition of the source and residual wavefields. The algorithm risks converging to an inaccurate result if the data lack low frequencies and/or the initial model is far from the true one. Additionally, the model updates may display a reflectivity imprint before the long-wavelength features of the model are fully recovered. We propose a new solution to this fundamental challenge by combining the quadratic form of the Wasserstein distance (W2 norm) for measuring the data misfit with a robust implementation of a velocity gradient. The W2 norm reduces the risk of cycle skipping, whereas the velocity gradient effectively eliminates the reflectivity imprint and emphasizes the long-wavelength model updates. We illustrate the performance of the new solution on a field survey acquired offshore Brazil. We demonstrate how FWI successfully updates the earth model and resolves a high-velocity carbonate section missing from the initial velocity model.
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Ma, Yong, et Dave Hale. « Wave-equation reflection traveltime inversion with dynamic warping and full-waveform inversion ». GEOPHYSICS 78, no 6 (1 novembre 2013) : R223—R233. http://dx.doi.org/10.1190/geo2013-0004.1.
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In reflection seismology, full-waveform inversion (FWI) can generate high-wavenumber subsurface velocity models but often suffers from an objective function with local minima caused mainly by the absence of low frequencies in seismograms. These local minima cause cycle skipping when the low-wavenumber component in the initial velocity model for FWI is far from the true model. To avoid cycle skipping, we discovered a new wave-equation reflection traveltime inversion (WERTI) to update the low-wavenumber component of the velocity model, while using FWI to only update high-wavenumber details of the model. We implemented the low- and high-wavenumber inversions in an alternating way. In WERTI, we used dynamic image warping (DIW) to estimate the time shifts between recorded data and synthetic data. When compared with correlation-based techniques often used in traveltime estimation, DIW can avoid cycle skipping and estimate the time shifts accurately, even when shifts vary rapidly. Hence, by minimizing traveltime shifts estimated by dynamic warping, WERTI reduces errors in reflection traveltime inversion. Then, conventional FWI uses the low-wavenumber component estimated by WERTI as a new initial model and thereby refines the model with high-wavenumber details. The alternating combination of WERTI and FWI mitigates the velocity-depth ambiguity and can recover subsurface velocities using only high-frequency reflection data.
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da Silva, Sérgio Luiz E. F., João M. de Araújo, Erick de la Barra et Gilberto Corso. « A Graph-Space Optimal Transport Approach Based on Kaniadakis κ-Gaussian Distribution for Inverse Problems Related to Wave Propagation ». Entropy 25, no 7 (28 juin 2023) : 990. http://dx.doi.org/10.3390/e25070990.
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Data-centric inverse problems are a process of inferring physical attributes from indirect measurements. Full-waveform inversion (FWI) is a non-linear inverse problem that attempts to obtain a quantitative physical model by comparing the wave equation solution with observed data, optimizing an objective function. However, the FWI is strenuously dependent on a robust objective function, especially for dealing with cycle-skipping issues and non-Gaussian noises in the dataset. In this work, we present an objective function based on the Kaniadakis κ-Gaussian distribution and the optimal transport (OT) theory to mitigate non-Gaussian noise effects and phase ambiguity concerns that cause cycle skipping. We construct the κ-objective function using the probabilistic maximum likelihood procedure and include it within a well-posed version of the original OT formulation, known as the Kantorovich–Rubinstein metric. We represent the data in the graph space to satisfy the probability axioms required by the Kantorovich–Rubinstein framework. We call our proposal the κ-Graph-Space Optimal Transport FWI (κ-GSOT-FWI). The results suggest that the κ-GSOT-FWI is an effective procedure to circumvent the effects of non-Gaussian noise and cycle-skipping problems. They also show that the Kaniadakis κ-statistics significantly improve the FWI objective function convergence, resulting in higher-resolution models than classical techniques, especially when κ=0.6.
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Yang, Yunan, Björn Engquist, Junzhe Sun et Brittany F. Hamfeldt. « Application of optimal transport and the quadratic Wasserstein metric to full-waveform inversion ». GEOPHYSICS 83, no 1 (1 janvier 2018) : R43—R62. http://dx.doi.org/10.1190/geo2016-0663.1.
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Conventional full-waveform inversion (FWI) using the least-squares norm as a misfit function is known to suffer from cycle-skipping issues that increase the risk of computing a local rather than the global minimum of the misfit. The quadratic Wasserstein metric has proven to have many ideal properties with regard to convexity and insensitivity to noise. When the observed and predicted seismic data are considered to be two density functions, the quadratic Wasserstein metric corresponds to the optimal cost of rearranging one density into the other, in which the transportation cost is quadratic in distance. Unlike the least-squares norm, the quadratic Wasserstein metric measures not only amplitude differences but also global phase shifts, which helps to avoid cycle-skipping issues. We have developed a new way of using the quadratic Wasserstein metric trace by trace in FWI and compare it with the global quadratic Wasserstein metric via the solution of the Monge-Ampère equation. We incorporate the quadratic Wasserstein metric technique into the framework of the adjoint-state method and apply it to several 2D examples. With the corresponding adjoint source, the velocity model can be updated using a quasi-Newton method. Numerical results indicate the effectiveness of the quadratic Wasserstein metric in alleviating cycle-skipping issues and sensitivity to noise. The mathematical theory and numerical examples demonstrate that the quadratic Wasserstein metric is a good candidate for a misfit function in seismic inversion.
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Li, Yuanyuan, Yunseok Choi, Tariq Alkhalifah, Zhenchun Li et Kai Zhang. « Full-waveform inversion using a nonlinearly smoothed wavefield ». GEOPHYSICS 83, no 2 (1 mars 2018) : R117—R127. http://dx.doi.org/10.1190/geo2017-0312.1.
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Conventional full-waveform inversion (FWI) based on the least-squares misfit function faces problems in converging to the global minimum when using gradient methods because of the cycle-skipping phenomena. An initial model producing data that are at most a half-cycle away from the observed data is needed for convergence to the global minimum. Low frequencies are helpful in updating low-wavenumber components of the velocity model to avoid cycle skipping. However, low enough frequencies are usually unavailable in field cases. The multiplication of wavefields of slightly different frequencies adds artificial low-frequency components in the data, which can be used for FWI to generate a convergent result and avoid cycle skipping. We generalize this process by multiplying the wavefield with itself and then applying a smoothing operator to the multiplied wavefield or its square to derive the nonlinearly smoothed wavefield, which is rich in low frequencies. The global correlation-norm-based objective function can mitigate the dependence on the amplitude information of the nonlinearly smoothed wavefield. Therefore, we have evaluated the use of this objective function when using the nonlinearly smoothed wavefield. The proposed objective function has much larger convexity than the conventional objective functions. We calculate the gradient of the objective function using the adjoint-state technique, which is similar to that of the conventional FWI except for the adjoint source. We progressively reduce the smoothing width applied to the nonlinear wavefield to naturally adopt the multiscale strategy. Using examples on the Marmousi 2 model, we determine that the proposed FWI helps to generate convergent results without the need for low-frequency information.
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Williams, Claire G., et J. Edward de Steiguer. « Value of Production Orchards Based on Two Cycles of Breeding and Testing ». Forest Science 36, no 1 (1 mars 1990) : 156–68. http://dx.doi.org/10.1093/forestscience/36.1.156.
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Abstract As breeding cycles become increasingly shorter, it may not be profitable to install a production seed orchard at the completion of each cycle. Using a case study approach, we compare two mutually exclusive orchard strategies: skipping a third-generation seed orchard (while upgrading an existing second-generation orchard) versus establishing a third-generation orchard. Using net present value as a decision-making criterion, skipping a third-generation loblolly pine orchard is the better strategy when (a) genetic gain in height from third-generation parents is less than or equal to 7% over first generation parents, (b) annual demand for seedlings is less than 4000 ac annually, and (c) harvest in a third-generation orchard begins at least 11 years before it becomes obsolete. Foregoing a third-generation orchard saves establishment capital but carries a stringent commitment to accelerated breeding and testing. Acceptance of the risk associated with genetic gain projection is critical to the third-generation orchard decision. For. Sci. 36(1):156-168.
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Ogata, Hitomi, Masaki Horie, Momoko Kayaba, Yoshiaki Tanaka, Akira Ando, Insung Park, Simeng Zhang et al. « Skipping Breakfast for 6 Days Delayed the Circadian Rhythm of the Body Temperature without Altering Clock Gene Expression in Human Leukocytes ». Nutrients 12, no 9 (12 septembre 2020) : 2797. http://dx.doi.org/10.3390/nu12092797.
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Breakfast is often described as “the most important meal of the day” and human studies have revealed that post-prandial responses are dependent on meal timing, but little is known of the effects of meal timing per se on human circadian rhythms. We evaluated the effects of skipping breakfast for 6 days on core body temperature, dim light melatonin onset, heart rate variability, and clock gene expression in 10 healthy young men, with a repeated-measures design. Subjects were provided an isocaloric diet three times daily (3M) or two times daily (2M, i.e., breakfast skipping condition) over 6 days. Compared with the 3M condition, the diurnal rhythm of the core body temperature in the 2M condition was delayed by 42.0 ± 16.2 min (p = 0.038). On the other hand, dim light melatonin onset, heart rate variability, and clock gene expression were not affected in the 2M condition. Skipping breakfast for 6 days caused a phase delay in the core body temperature in healthy young men, even though the sleep–wake cycle remained unchanged. Chronic effects of skipping breakfast on circadian rhythms remain to be studied.
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Chen, Yuqing, Zongcai Feng, Lei Fu, Abdullah AlTheyab, Shihang Feng et Gerard Schuster. « Multiscale reflection phase inversion with migration deconvolution ». GEOPHYSICS 85, no 1 (1 janvier 2020) : R55—R73. http://dx.doi.org/10.1190/geo2018-0751.1.
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Reflection full-waveform inversion (RFWI) can recover the low-wavenumber components of the velocity model along with the reflection wavepaths. However, this requires an expensive least-squares reverse time migration (LSRTM) to construct the perturbation image that can still suffer from cycle-skipping problems. As an inexpensive alternative to LSRTM, we use migration deconvolution (MD) with RFWI. To mitigate cycle-skipping problems, we develop a multiscale reflection phase inversion (MRPI) strategy that boosts the low-frequency data and should only explain the phase information in the recorded data, not its magnitude spectrum. We also use the rolling-offset strategy that gradually extends the offset range of data with an increasing number of iterations. Numerical results indicate that the MRPI + MD method can efficiently recover the low-wavenumber components of the velocity model and is less prone to getting stuck in local minima compared to conventional RFWI.
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Zhang, Yang, et Biondo Biondi. « Moveout-based wave-equation migration velocity analysis ». GEOPHYSICS 78, no 2 (1 mars 2013) : U31—U39. http://dx.doi.org/10.1190/geo2012-0082.1.
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Current wave-equation migration velocity analysis schemes suffer from problems such as severe nonlinearity (which causes the issue of cycle skipping) and imprecise objective functions (which can accrue velocity errors by honoring residuals caused by model complexity and incomplete acquisition). To provide an improvement, we developed an alternative method to perform wave-equation migration velocity analysis by maximizing the flatness of the angle-domain common image gathers. We replaced the ray-based tomographic operator with the wave-equation-based one, although keeping the conventional moveout-based tomography work flow. Instead of maximizing the image-stack-power objective function directly with respect to the slowness, we linked the objective function to the slowness indirectly through an intermediate moveout parameter. By focusing on the common image gather kinematics, this approach greatly reduced the risk of cycle skipping in the absence of low-frequency data, and it produced high-quality gradients. In addition, the proposed method did not require explicit picking of the moveout parameters. Our numerical examples demonstrated the great potential of this method: in the first example, in which there is a Gaussian-shaped slowness anomaly, our method produced a well-behaved gradient; in the second example, in which there is a horizontally gradual increase of slowness, the result verified that our method is robust against cycle skipping; in the third example, the result showed that our method works well with reflectors of variable dips. Finally, our test on the Marmousi models concluded that the proposed method converges to a high-quality model that uniformly flattens the angle-domain common-image gathers.
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Sulzer, Valentin, Peyman Mohtat, Sravan Pannala, Jason B. Siegel et Anna G. Stefanopoulou. « Accelerated Battery Lifetime Simulations Using Adaptive Inter-Cycle Extrapolation Algorithm ». Journal of The Electrochemical Society 168, no 12 (1 décembre 2021) : 120531. http://dx.doi.org/10.1149/1945-7111/ac3e48.
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We propose algorithms to speed up physics-based battery lifetime simulations by one to two orders of magnitude compared to the state-of-the-art. First, we propose a reformulation of the Single Particle Model with side reactions to remove algebraic equations and hence reduce stiffness, with 3x speed-up in simulation time (intra-cycle reformulation). Second, we introduce an algorithm that makes use of the difference between the “fast” timescale of battery cycling and the “slow” timescale of battery degradation by adaptively selecting and simulating representative cycles, skipping other cycles, and hence requires fewer cycle simulations to simulate the entire lifetime (adaptive inter-cycle extrapolation). This algorithm is demonstrated with a specific degradation mechanism but can be applied to various models of aging phenomena. In the particular case study considered, simulations of the entire lifetime are performed in under 5 s. This opens the possibility for much faster and more accurate model development, testing, and comparison with experimental data.
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Wang, Guanchao, Sanyi Yuan et Shangxu Wang. « Retrieving Low-Wavenumber Information in FWI : An Efficient Solution for Cycle Skipping ». IEEE Geoscience and Remote Sensing Letters 16, no 7 (juillet 2019) : 1125–29. http://dx.doi.org/10.1109/lgrs.2019.2892998.
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Yang, Jizhong, Yunyue Elita Li, Yuzhu Liu, Yanwen Wei et Haohuan Fu. « Mitigating the cycle-skipping of full-waveform inversion by random gradient sampling ». GEOPHYSICS 85, no 6 (22 octobre 2020) : R493—R507. http://dx.doi.org/10.1190/geo2020-0099.1.
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Full-waveform inversion (FWI) is a highly nonlinear and nonconvex problem. To mitigate the dependence of FWI on the quality of starting model and on the low frequencies in the data, we apply the gradient sampling algorithm (GSA) introduced for nonsmooth, nonconvex optimization problems to FWI. The search space is hugely expanded to have more freedom to accommodate large velocity errors in the starting model. The original implementation of GSA requires explicit calculation of the gradient at each sampled vector, which is prohibitively expensive. Based on the observation that a slight perturbation in the velocity model causes a small spatial shift of the wavefield, we have approximated the sampled gradients by crosscorrelating the space-shifted source- and receiver-side wavefields. Theoretical derivation suggests that the two wavefields should be shifted in the same direction to obtain reasonable low-wavenumber updates. The final descent search direction is obtained by summing all the shifted gradients. For practical implementation, we only take one random space shift at each time step during the gradient calculation. This simplification provides an efficient realization in which the computational costs and memory requirements are the same as conventional FWI. Multiple numerical examples demonstrate that the proposed method alleviates the cycle-skipping problem of conventional FWI when starting from very crude initial velocity models without low-frequency data.
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Godari Akhila, Asra Shaik et R. Dinesh Kumar. « Current factors affecting the menstrual cycle ». International Journal of Research in Hospital and Clinical Pharmacy 2, no 1 (3 avril 2020) : 18–21. http://dx.doi.org/10.33974/ijrhcp.v2i1.165.
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A regular menstrual cycle is an important indicator of a healthy reproductive system. Menstrual problems affect not only women but also families, social & national economy as well. The menstrual cycle is divided into two 14-day phases. In normal healthy women, menarche occurs between the ages 10 and 16 years, with an average rhythm of 28 days, inclusive of 4–6 days of bleeding, with some common minor variations like Amenorrhoea, Oligomenorrhoea, Polymenorrhoea, Menorrhagia, Hypomenorrhoea, etc., these menstrual disorders frequently affect the quality of life of young adults women, some of the lifestyle factors like obesity, intake of junk food, stress, lack of physical activity, skipping breakfast are associated with irregular menstruation. The purpose of this study is to identify menstrual irregularities and assess the impact of lifestyle factors and on the menstrual patterns in reproductive-age females.
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Song, Chao, et Tariq Alkhalifah. « A reflection-based efficient wavefield inversion ». GEOPHYSICS 86, no 4 (1 juillet 2021) : R497—R508. http://dx.doi.org/10.1190/geo2019-0664.1.
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Full-waveform inversion (FWI) is popularly used to obtain a high-resolution subsurface velocity model. However, it requires either a good initial velocity model or low-frequency data to mitigate the cycle-skipping issue. Reflection-waveform inversion (RWI) uses a migration/demigration process to retrieve a background model that can be used as a good initial velocity in FWI. The drawback of conventional RWI is that it requires the use of least-squares migration, which is often computationally expensive, and it is still prone to cycle skipping at far offsets. To improve the computational efficiency and overcome cycle skipping in the original RWI, we have incorporated it into a recently introduced method called efficient wavefield inversion (EWI) by inverting for the Born-scattered wavefield instead of the wavefield itself. In this case, we use perturbation-related secondary sources in the modified source function. Unlike conventional RWI, the perturbations are calculated naturally as part of the calculation of the scattered wavefield in an efficient way. Because the sources in the reflection-based EWI (REWI) are located in the subsurface, we are able to update the background model along the reflection wavepath. In the background velocity inversion, we calculate the background perturbation by a deconvolution process at each frequency. After obtaining the REWI inverted velocity model, a sequential FWI or EWI is needed to obtain a high-resolution model. We determine the validity of our approach using synthetic data generated from a section of the Sigsbee2A model. To further demonstrate the effectiveness of our approach, we test it on an ocean-bottom cable data set from the North Sea. We find that our methodology leads to improved velocity models as evidenced by flatter angle gathers.
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Liu, Yike, Bin He, Huiyi Lu, Zhendong Zhang, Xiao-Bi Xie et Yingcai Zheng. « Full-intensity waveform inversion ». GEOPHYSICS 83, no 6 (1 novembre 2018) : R649—R658. http://dx.doi.org/10.1190/geo2017-0682.1.
Texte intégralRésumé :
Many full-waveform inversion schemes are based on the iterative perturbation theory to fit the observed waveforms. When the observed waveforms lack low frequencies, those schemes may encounter convergence problems due to cycle skipping when the initial velocity model is far from the true model. To mitigate this difficulty, we have developed a new objective function that fits the seismic-waveform intensity, so the dependence of the starting model can be reduced. The waveform intensity is proportional to the square of its amplitude. Forming the intensity using the waveform is a nonlinear operation, which separates the original waveform spectrum into an ultra-low-frequency part and a higher frequency part, even for data that originally do not have low-frequency contents. Therefore, conducting multiscale inversions starting from ultra-low-frequency intensity data can largely avoid the cycle-skipping problem. We formulate the intensity objective function, the minimization process, and the gradient. Using numerical examples, we determine that the proposed method was very promising and could invert for the model using data lacking low-frequency information.
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Fujiwara, Tomoko. « Comprehensive analysis of female reproductive dysfunction induced by clock genes due to asynchronous feeding rhythm ». Impact 2022, no 5 (13 octobre 2022) : 28–30. http://dx.doi.org/10.21820/23987073.2022.5.28.
Texte intégralRésumé :
Dieting can be harmful, particularly for adolescents who are still developing. For example, diet and reproductive health are closely linked and dieting in adolescence can have long-term effects on reproductive health. Indeed, the incidence of gynaecological disease is rising, in parallel with food skipping and dieting in young women. Dr Tomoko Fujiwara, Department of Human Life Environments, Kyoto Notre Dame University, Japan is exploring the little known links between menstrual pain and eating habits, with a focus on female students. She and her team are interested in the concept of hunger stress and the implications of negative hunger stress and are using animal models to explore this concept and interrelated ideas in more detail. In a world first, the researchers reported that breakfast skipping is associated with menstrual pain and menstrual pain worsens after dieting and, building on this result, they conducted research to establish further links between dietary habits and menstrual disorders and explore whether breakfast skipping can be an effective predictor for the management and prevention of menstrual disorders. In another project, Fujiwara and the team unearthed findings that support the existence of a new hypothesis called Adolescent Dietary Habit-induced Obstetric and Gynecologic Disease (ADHOGD) and plan to elucidate further detailed mechanisms that will lead to preventative methods. In another study, the researchers explored the effects of meal timing during the circadian cycle on ovarian function and confirmed that the timing of food intake during the circadian cycle is a key factor influencing reproductive function.
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He, Bin, Yike Liu et Yanbao Zhang. « Improving the least-squares image by using angle information to avoid cycle skipping ». GEOPHYSICS 84, no 6 (1 novembre 2019) : S581—S598. http://dx.doi.org/10.1190/geo2018-0816.1.
Texte intégralRésumé :
In the past few decades, the least-squares reverse time migration (LSRTM) algorithm has been widely used to enhance images of complex subsurface structures by minimizing the data misfit function between the predicted and observed seismic data. However, this algorithm is sensitive to the accuracy of the migration velocity model, which, in the case of real data applications (generally obtained via tomography), always deviates from the true velocity model. Therefore, conventional LSRTM faces a cycle-skipping problem caused by a smeared image when using an inaccurate migration velocity model. To address the cycle-skipping problem, we have introduced an angle-domain LSRTM algorithm. Unlike the conventional LSRTM algorithm, our method updates the common source-propagation angle image gathers rather than the stacked image. An extended Born modeling operator in the common source-propagation angle domain is was derived, which reproduced kinematically accurate data in the presence of velocity errors. Our method can provide more focused images with high resolution as well as angle-domain common-image gathers (ADCIGs) with enhanced resolution and balanced amplitudes. However, because the velocity model is not updated, the provided image can have errors in depth. Synthetic and field examples are used to verify that our method can robustly improve the quality of the ADCIGs and the finally stacked images with affordable computational costs in the presence of velocity errors.
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Kim, Doyeun, Seulki Song, Dae-Yoon Kim, Dongchan Kim, Nam Hoon Kwon, Byung-Su Kim, Hyun Jung Lee et al. « Exon Skipping of AIMP2 and Lymphomagenesis ». Blood 132, Supplement 1 (29 novembre 2018) : 2630. http://dx.doi.org/10.1182/blood-2018-99-117596.
Texte intégralRésumé :
Abstract ARS-interacting multifunctional protein 2 (AIMP2), the component of aminoacyl-tRNA synthase complex, acts as a potent tumor suppressor in conjunction with p53. The second exon deficient AIMP2 generated by alternative splicing mechanism (AIMP2-DX2) induces loses its important role as a signaling modulator. Previously, it predisposes mouse to increase lung cancer, but it did not induce tumorigenesis by itself. To further validate the oncogenic role of AIMP2-DX2 in mouse model, we generated inducible transgenic mouse which express DX2 in doxycycline dependent manner. Unexpectedly, we report the late onset spontaneous lymphoma development instead of lung cancer in this model. Polyclonal expansion of pre-B cells and infiltration to multi-organ, especially kidney, was major events. More importantly, switching off the transgene by doxycycline removal reduced pre-B cell hyperplasia by inducing apoptotic cell death. Destabilization of p53 and dysregulation of cell cycle gene by DX2 overexpression underlined the increased lymphoid cell proliferation. Coincident with the results, in International Cancer Genome Consortium (ICGC) data analysis, AIMP2-DX2 expression was the highest in Burkitt lymphoma (BL) and diffuse large B cell lymphoma (DLBCL) among various cancer subtypes. When analysis was performed using RNA sequencing data of various B-cell lymphoid malignancies, germinal B-cell origin (GCB) DLBCL, B-acute lymphoid leukemia and BL showed completely different gene expression pattern according to the AIMP2-DX2 expression status suggesting a distinct disease entity. AIMP2-DX2 expression in DLBCL cell line and tissue samples was validated and regulation of DX2 in lymphoma cell line affected cell viability as well as p53 stability. Lastly, we confirmed expression of AIMP2-DX2 in FFPE tissue of 35 lymphoma patients using RNA in situ hybridization (ISH) with specifically designed probes that capture the exon 1-3 junction of AIMP2 transcript. In summary, our data demonstrate the causality of AIMP2-DX2 in lymphoma oncogenesis and provide evidence that AIMP2-DX2 is a potential therapeutic target especially in DLBCL and BL. Figure. Figure. Disclosures No relevant conflicts of interest to declare.
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Sohail, Muhammad, et Jiuyong Xie. « Evolutionary Emergence of a Novel Splice Variant with an Opposite Effect on the Cell Cycle ». Molecular and Cellular Biology 35, no 12 (13 avril 2015) : 2203–14. http://dx.doi.org/10.1128/mcb.00190-15.
Texte intégralRésumé :
Alternative splicing contributes greatly to the diversification of mammalian proteomes, but the molecular basis for the evolutionary emergence of splice variants remains poorly understood. We have recently found a novel class of splicing regulatory elements between the polypyrimidine tract (Py) and 3′ AG (REPA) at intron ends in many human genes, including the multifunctionalPRMT5(for protein arginine methyltransferase 5) gene. The PRMT5 element is comprised of two G tracts that arise in most mammals and accompany significant exon skipping in human transcripts. The G tracts inhibit splicing by recruiting heterogeneous nuclear ribonucleoprotein (hnRNP) H and F (H/F) to reduce U2AF65 binding to the Py, causing exon skipping. The resulting novel shorter variant PRMT5S exhibits a histone H4R3 methylation effect similar to that seen with the original longer PRMT5L isoform but exhibits a distinct localization and preferential control of critical genes for cell cycle arrest at interphase in comparison to PRMT5L. This report thus provides a molecular mechanism for the evolutionary emergence of a novel splice variant with an opposite function in a fundamental cell process. The presence of REPA elements in a large group of genes implies their wider impact on different cellular processes for increased protein diversity in humans.
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Wu, Zedong, et Tariq Alkhalifah. « Selective data extension for full-waveform inversion : An efficient solution for cycle skipping ». GEOPHYSICS 83, no 3 (1 mai 2018) : R201—R211. http://dx.doi.org/10.1190/geo2016-0649.1.
Texte intégralRésumé :
Standard full-waveform inversion (FWI) attempts to minimize the difference between observed and modeled data. However, this difference is obviously sensitive to the amplitude of observed data, which leads to difficulties because we often do not process data in absolute units and because we usually do not consider density variations, elastic effects, or more complicated physical phenomena. Global correlation methods can remove the amplitude influence for each trace and thus can mitigate such difficulties in some sense. However, this approach still suffers from the well-known cycle-skipping problem, leading to a flat objective function when observed and modeled data are not correlated well enough. We optimize based on maximizing not only the zero-lag global correlation but also time or space lags of the modeled data to circumvent the half-cycle limit. We use a weighting function that is maximum value at zero lag and decays away from zero lag to balance the role of the lags. The resulting objective function is less sensitive to the choice of the maximum lag allowed and has a wider region of convergence compared with standard FWI. Furthermore, we develop a selective function, which passes to the gradient calculation only positive correlations, to mitigate cycle skipping. Finally, the resulting algorithm has better convergence behavior than conventional methods. Application to the Marmousi model indicates that this method converges starting with a linearly increasing velocity model, even with data free of frequencies less than 3.5 Hz. Application to the SEG2014 data set demonstrates the potential of our method.
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Amgain, Kapil, et Sujana Neupane. « Effects of Food Habits on Menstrual Cycle among Adolescent Girls ». Europasian Journal of Medical Sciences 1, no 1 (30 décembre 2019) : 53–61. http://dx.doi.org/10.46405/ejms.v1i1.35.
Texte intégralRésumé :
Background: Menstruation, a normal physiological process in a woman’s body is affected by dietary habit and it can arise different menstrual disorders. The aim of this study is to find out the menstrual health status of young females and their association with their food habits. Methods: A cross-sectional study was conducted among the nursing students of Maharajgunj Nursing Campus from March 2019 to September 2019.. Pretested and the semistructured questionnaire were used to collect the data regarding menstrual history, dietary habits, fast food intake, and food skipping behavior. HEAT (Healthy Eating Assessment Tool) Score was used to assess the food habit and the Visual Analogue Scale (VAS) was used to assess the intensity of dysmenorrhea. Result: Data was collected among 140 students. The mean age was 24.56±2.65 years. The study showed that 87.9% had problems, and 80.7% have dysmenorrhea. The occurrence of the menstrual problems was more in the participants who were having a non-vegetarian diet than in a vegetarian diet which was statistically significant (p<0.001). Similarly, 68.6% of the participants eat fast food and 91.6 % of them have menstrual problems. Meal skipping habit was found to significantly associated with the menstrual problems (P=0.03). Similarly, 105 (75%) of the participants had good food eating habits, and 32 (22.9%) of the participants had poor eating habits. The poor eating habit was significantly associated with menstrual problems. The intensity of dysmenorrhea was more in the participant having a nonvegetarian diet. Further, the pain was more severe among the participants who consume tea and coffee more frequently. Conclusion: The menstrual problems were the alarming problems in the adolescent college going girls of Kathmandu Valley. Excessive intake of junk/fast food, alcohol, and tea/coffee had a significant association with menstrual problems.
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Hess, D., S. Boehm, A. Delmonte, E. Gallerani, P. Barbieri, S. Pace, P. Carminati, S. Marsoni, N. Coceani et C. Sessa. « Clinical development of namitecan (ST1968), a novel camptothecin derivative with high antitumor activity : Phase I clinical data ». Journal of Clinical Oncology 27, no 15_suppl (20 mai 2009) : 2570. http://dx.doi.org/10.1200/jco.2009.27.15_suppl.2570.
Texte intégralRésumé :
2570 Background: Namitecan is a new water-soluble camptothecin analogue which showed high antitumor activity in preclinical models. Aim of this trial was to determine safety, PK profile and activity in adult patients with advanced solid tumors. Methods: The dose escalation started at 2.5 mg i.v. on days 1 and 8 of a 21 day cycle (D1, D8 Q21D) and increased according to 3+3 cohort design depending on the observed toxicity. Dose limiting toxicity (DLT) definitions were: ANC <0.5x109/L for >5 days; PLT ≥ Grade 3 (CTC V3); grade ≥2 liver/renal toxicity not recovered by D22; any non-hematologic toxicity ≥ Grade 3; D8 dose skipping due to toxicity. Maximum tolerated dose (MTD) and recommended dose (RD) were the primary end-points. Blood and urine samples were collected at cycle 1 for PK evaluation. Results: 31 pts (11 endometrial ca., 5 CRC, 5 ovarian ca., 2 NSCLC, 8 other) have been included, with 6 dose levels evaluated (2.5; 5; 10; 15; 17.5 and 20 mg). 17.5 mg was introduced later when 2/7 DLTs at 20 mg were observed (ANC G4>5days, one with D8 skipping). At 17.5mg 2/4 pts experienced DLTs (ANC G4; D8 skipped). Uncomplicated neutropenia and thrombocytopenia were the most relevant G3/4 hematological toxicities. Other toxicities were mild or moderate asthenia, fatigue and alopecia. The MTD was defined at 17.5 mg and the RD was 15 mg. Stable disease ≥ 6 cycles was recorded in 6 pts (2 stable diseases ≥ 10 cycles). PK was linear and data suggest an entero-hepatic recirculation. No metabolites were found in plasma and the product resulted poorly excreted into urine. Conclusions: The MTD and RD of D1, D8 Q21D schedule have been identified. The study will continue with the evaluation of MTD and RD of a single administration per cycle (D1 Q21D), to optimize the schedule of treatment. [Table: see text]
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Choi, Yunseok, et Tariq Alkhalifah. « Time-domain full-waveform inversion of exponentially damped wavefield using the deconvolution-based objective function ». GEOPHYSICS 83, no 2 (1 mars 2018) : R77—R88. http://dx.doi.org/10.1190/geo2017-0057.1.
Texte intégralRésumé :
Full-waveform inversion (FWI) suffers from the cycle-skipping problem when the available frequency-band of data is not low enough. We have applied an exponential damping to the data to generate artificial low frequencies, which helps FWI to avoid cycle skipping. In this case, the least-squares misfit function does not properly deal with the exponentially damped wavefield in FWI because the amplitude of traces decays almost exponentially with increasing offset in a damped wavefield. Thus, we use a deconvolution-based objective function for FWI of the exponentially damped wavefield. The deconvolution filter includes inherently a normalization between the modeled and observed data; thus, it can address the unbalanced amplitude of a damped wavefield. We specifically normalize the modeled data with the observed data in the frequency-domain to estimate the deconvolution filter and selectively choose a frequency-band for normalization that mainly includes the artificial low frequencies. We calculate the gradient of the objective function using the adjoint-state method. The synthetic and benchmark data examples indicate that our FWI algorithm generates a convergent long-wavelength structure without low-frequency information in the recorded data.
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Hu, Wenyi, Yuchen Jin, Xuqing Wu et Jiefu Chen. « Progressive transfer learning for low-frequency data prediction in full-waveform inversion ». GEOPHYSICS 86, no 4 (1 juin 2021) : R369—R382. http://dx.doi.org/10.1190/geo2020-0598.1.
Texte intégralRésumé :
To effectively overcome the cycle-skipping issue in full-waveform inversion (FWI), we have developed a deep neural network (DNN) approach to predict the absent low-frequency (LF) components by exploiting the hidden physical relation connecting the LF and high-frequency (HF) data. To efficiently solve this challenging nonlinear regression problem, two novel strategies are proposed to design the DNN architecture and to optimize the learning process: (1) the dual data feed structure and (2) progressive transfer learning. With the dual data feed structure, not only the HF data, but also the corresponding beat tone data, are fed into the DNN to relieve the burden of feature extraction. The second strategy, progressive transfer learning, enables us to train the DNN using a single evolving training data set. Within the framework of progressive transfer learning, the training data set continuously evolves in an iterative manner by gradually retrieving the subsurface information through the physics-based inversion module, progressively enhancing the prediction accuracy of the DNN and propelling the inversion process out of the local minima. The synthetic numerical experiments suggest that, without any a priori geologic information, the LF data predicted by the progressive transfer learning are sufficiently accurate for an FWI engine to produce reliable subsurface velocity models free of cycle-skipping artifacts.
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Zhang, Chao, Cheng Li et Jian Cai. « Geometrical-Feature-Preserving Adjoint Tomography of Near-Surface Structure with Seismic Early Arrival ». Shock and Vibration 2022 (22 juin 2022) : 1–13. http://dx.doi.org/10.1155/2022/3404496.
Texte intégralRésumé :
Early arrival waveform inversion (EWI) is an essential approach to obtaining velocity structures in near-surface. Due to suffering from a cycle‐skipping issue, it is difficult to reach the global minima for conventional EWI with the misfit function of least-squares norm (L2‐norm). Following the optimal transportation theory, we developed an EWI solution with a new objective function based on quadratic‐Wasserstein‐metric (W2-norm) to maintain the geometric characteristics of the distribution and improve the stability and convexity of the inverse problem. First, we gave the continuous form of the adjoint source and the Frechet gradient of the Wasserstein metric for seismic early arrival, which leads to an easy and efficient way to implement in the adjoint-state method. Then, we conducted two synthetic experiments on the target model containing some velocity anomalies and hidden layers to test its effectiveness in mapping accurate and high-resolution near-surface velocity structure. The results show that the W2-normed EWI can mitigate cycle-skipping issues compared with the L2-normed EWI. In addition, it can deal with hidden layers and is robust in terms of noise. The application to a real dataset indicates that this new solution can recover more details in the shallow structure, especially in the aspect of dealing with hidden layers.
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Pladys, Arnaud, Romain Brossier, Nishant Kamath et Ludovic Métivier. « Robust full-waveform inversion with graph-space optimal transport : Application to 3D ocean-bottom cable Valhall data ». GEOPHYSICS 87, no 3 (11 mars 2022) : R261—R280. http://dx.doi.org/10.1190/geo2021-0268.1.
Texte intégralRésumé :
Improving full-waveform inversion robustness to cycle-skipping has been the subject of a large number of studies. From the several families of approaches developed, one of the most documented consists in modifying the least-squares distance misfit function. From all the propositions made to improve and replace the least-squares distance, only a few of them have been applied to field data. One of the methods proposed recently, the graph space optimal transport distance, presents appealing properties for field data applications. We compare it with the least-squares distance in an analysis performed on the three-dimensional ocean bottom cable data from the Valhall field. We first perform this comparison starting the inversion from the reflection traveltime tomography model used in previous studies. We then perform a second comparison from a crude, linearly varying in-depth one-dimensional velocity model. Starting from this model, least-squares-based full-waveform inversion fails to provide a meaningful estimate of the pressure-wave velocity model due to cycle skipping. We illustrate how the graph-space optimal transport-based full-waveform inversion mitigates this issue. A meaningful estimate of the pressure-wave velocity model is obtained in the zone sampled by both diving and reflected waves, down to almost two kilometers depth.
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Liu, Yike, Bin He, Zhendong Zhang, Yingcai Zheng et Peng Li. « Reflection intensity waveform inversion ». GEOPHYSICS 85, no 3 (8 avril 2020) : R263—R273. http://dx.doi.org/10.1190/geo2019-0590.1.
Texte intégralRésumé :
Traditional iteration-based full-waveform inversion (FWI) methods encounter serious challenges if the initial velocity model is far from the true model or if the observed data are lacking low-frequency content. As such, the optimization algorithm may be trapped in local minima and fail to go to a global optimal model. In addition, the traditional FWI method requires long-offset data to update the deep structure of a velocity model with diving waves. To overcome the disadvantages of traditional FWI under these circumstances, we have developed a reflection intensity waveform inversion method. This method aims to minimize the seismic intensity differences between the modeled reflection data and field data. Our method is less dependent on the starting model, and long-offset data are no longer required. The wave intensity, proportional to the square of the original data amplitude, can have a low-frequency band and a higher frequency band, even for waveforms without initial low-frequency content. Our multiscale intensity inversion starts from the low-frequency information in the intensity data, and it can largely avoid the cycle-skipping problem. Synthetic and field data examples demonstrate that our method is able to overcome cycle skipping in handling data with no low-frequency information.
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Liu, Zhiyang, et Jie Zhang. « Joint traveltime, waveform, and waveform envelope inversion for near-surface imaging ». GEOPHYSICS 82, no 4 (1 juillet 2017) : R235—R244. http://dx.doi.org/10.1190/geo2016-0356.1.
Texte intégralRésumé :
The first-arrival traveltimes without large offsets constrain very shallow velocities, the waveform envelope presents low-frequency data, and the high-frequency waveform itself includes information regarding structural details. We have developed a joint traveltime, waveform, and waveform envelope (JTWE) inversion method for inverting near-surface velocity structures. By inverting three types of data, we are able to recover the low- and high-wavenumber structures and mitigate the cycle-skipping problem in waveform inversion. The calculation of traveltimes and raypaths is fast. Most of the computation effort is focused on dealing with the waveform and waveform envelope. JTWE backward propagates the waveform residual and envelope residual simultaneously to calculate the model updating gradients. This simultaneous backward-propagation strategy ensures that the computational cost of JTWE is similar to the cost of inverting waveform alone. In a synthetic experiment, we determine that JTWE mitigates the cycle-skipping problem and recovers the near-surface structures without the need for additional low-frequency data. The final results of JTWE indicate that it delivers improved results with low-velocity inclusions compared with full-waveform inversion. For field data from the Middle East, JTWE helps resolve a complex near-surface model with rugged topography and fit all three types of data.
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Yüksek, Levent, Orkun Özener et Tarkan Sandalcı. « Cycle-skipping strategies for pumping loss reduction in spark ignition engines : An experimental approach ». Energy Conversion and Management 64 (décembre 2012) : 320–27. http://dx.doi.org/10.1016/j.enconman.2012.05.025.
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Huang, Guanghui, Rami Nammour et William W. Symes. « Volume source-based extended waveform inversion ». GEOPHYSICS 83, no 5 (1 septembre 2018) : R369—R387. http://dx.doi.org/10.1190/geo2017-0330.1.
Texte intégralRésumé :
Full-waveform inversion (FWI) faces the persistent challenge of cycle skipping, which can result in stagnation of the iterative methods at uninformative models with poor data fit. Extended reformulations of FWI avoid cycle skipping through adding auxiliary parameters to the model so that a good data fit can be maintained throughout the inversion process. The volume-based matched source waveform inversion algorithm introduces source parameters by relaxing the location constraint of source energy: It is permitted to spread in space, while being strictly localized at time [Formula: see text]. The extent of source energy spread is penalized by weighting the source energy with distance from the survey source location. For transmission data geometry (crosswell, diving wave, etc.) and transparent (nonreflecting) acoustic models, this penalty function is stable with respect to the data-frequency content, unlike the standard FWI objective. We conjecture that the penalty function is actually convex over much larger region in model space than is the FWI objective. Several synthetic examples support this conjecture and suggest that the theoretical limitation to pure transmission is not necessary: The inversion method can converge to a solution of the inverse problem in the absence of low-frequency data from an inaccurate initial velocity model even when reflections and refractions are present in the data along with transmitted energy.
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Hu, Wenyi, Jiefu Chen, Jianguo Liu et Aria Abubakar. « Retrieving Low Wavenumber Information in FWI : An Overview of the Cycle-Skipping Phenomenon and Solutions ». IEEE Signal Processing Magazine 35, no 2 (mars 2018) : 132–41. http://dx.doi.org/10.1109/msp.2017.2779165.
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Métivier, Ludovic, Aude Allain, Romain Brossier, Quentin Mérigot, Edouard Oudet et Jean Virieux. « Optimal transport for mitigating cycle skipping in full-waveform inversion : A graph-space transform approach ». GEOPHYSICS 83, no 5 (1 septembre 2018) : R515—R540. http://dx.doi.org/10.1190/geo2017-0807.1.
Texte intégralRésumé :
Optimal transport distance has been recently promoted as a tool to measure the discrepancy between observed and seismic data within the full-waveform-inversion strategy. This high-resolution seismic imaging method, based on a data-fitting procedure, suffers from the nonconvexity of the standard least-squares discrepancy measure, an issue commonly referred to as cycle skipping. The convexity of the optimal transport distance with respect to time shifts makes it a good candidate to provide a more convex misfit function. However, the optimal transport distance is defined only for the comparison of positive functions, while seismic data are oscillatory. A review of the different attempts proposed in the literature to overcome this difficulty is proposed. Their limitations are illustrated: Basically, the proposed strategies are either not applicable to real data, or they lose the convexity property of optimal transport. On this basis, we introduce a novel strategy based on the interpretation of the seismic data in the graph space. Each individual trace is considered, after discretization, as a set of Dirac points in a 2D space, where the amplitude becomes a geometric attribute of the data. This ensures the positivity of the data, while preserving the geometry of the signal. The differentiability of the misfit function is obtained by approximating the Dirac distributions through 2D Gaussian functions. The interest of this approach is illustrated numerically by computing misfit-function maps in schematic examples before moving to more realistic synthetic full-waveform exercises, including the Marmousi model. The better convexity of the graph-based optimal transport distance is shown. On the Marmousi model, starting from a 1D linearly increasing initial model, with data without low frequencies (no energy less than 3 Hz), a meaningful estimation of the P-wave velocity model is recovered, outperforming previously proposed optimal-transport-based misfit functions.
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Lee, Donguk, et Sukjoon Pyun. « Seismic full-waveform inversion using minimization of virtual scattering sources ». GEOPHYSICS 85, no 3 (1 mai 2020) : R299—R311. http://dx.doi.org/10.1190/geo2019-0533.1.
Texte intégralRésumé :
Full-waveform inversion (FWI) is a powerful tool for imaging underground structures with high resolution; however, this approach commonly suffers from the cycle-skipping issue. Recently, various FWI methods have been suggested to address this problem. Such methods are mainly classified into either data-space manipulation or model-space extension. We developed an alternative FWI method that belongs to the latter class. First, we define the virtual scattering source based on perturbation theory. The virtual scattering source is estimated by minimizing the differences between observed and simulated data with a regularization term penalizing the weighted virtual scattering source. The inverse problem for obtaining the virtual scattering source can be solved by the linear conjugate gradient method. The inverted virtual scattering source is used to update the wavefields; thus, it helps FWI to better approximate the nonlinearity of the inverse scattering problem. As the second step, the virtual scattering source is minimized to invert the velocity model. By assuming that the variation of the reconstructed wavefield is negligible, we can apply an approximated full Newton method to the velocity inversion with reasonable cost comparable to the Gauss-Newton method. From the numerical examples using synthetic data, we confirm that the proposed method performs better and more robust than the simple gradient-based FWI method. In addition, we show that our objective function has fewer local minima, which helps to mitigate the cycle-skipping problem.
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Sun, Mengyao, Jie Zhang et Wei Zhang. « Alternating first-arrival traveltime tomography and waveform inversion for near-surface imaging ». GEOPHYSICS 82, no 4 (1 juillet 2017) : R245—R257. http://dx.doi.org/10.1190/geo2016-0576.1.
Texte intégralRésumé :
Near-surface seismic imaging often plays a significant role in producing quality data processing results for the deep subsurface in land and shallow marine environments. First-arrival traveltime tomography is a common approach for near-surface imaging due to its high efficiency and simplicity. However, the method faces issues of missing hidden layers and resolving the structures with low resolution. On the other hand, waveform inversion should offer better solutions for dealing with these issues, but it may suffer from the cycle-skipping problem. We intend to use the advantages and reduce the disadvantages of the two methods by developing a new strategy of alternately applying traveltime tomography and waveform inversion through iterations. First-arrival traveltime tomography applies a wavefront raytracer and a nonlinear inversion approach. Waveform inversion is a multiscale approach in which a wavelet transform is applied in the data domain to better handle the cycle-skipping problem. By alternating the two inversions rather than performing a joint inversion, we reduce the memory requirements and avoid nonphysical scaling problems between the two approaches. Using one synthetic and two real data examples, we determine that alternating inversions minimize two separate objective functions at the same time and constrain the near-surface structures fairly well compared with the waveform inversion method alone. For the field examples, the new method avoids generating the obvious artifacts and provides results consistent with the geology analysis of those areas.
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Hasselmo, Michael E. « Neuronal rebound spiking, resonance frequency and theta cycle skipping may contribute to grid cell firing in medial entorhinal cortex ». Philosophical Transactions of the Royal Society B : Biological Sciences 369, no 1635 (5 février 2014) : 20120523. http://dx.doi.org/10.1098/rstb.2012.0523.
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Data show a relationship of cellular resonance and network oscillations in the entorhinal cortex to the spatial periodicity of grid cells. This paper presents a model that simulates the resonance and rebound spiking properties of entorhinal neurons to generate spatial periodicity dependent upon phasic input from medial septum. The model shows that a difference in spatial periodicity can result from a difference in neuronal resonance frequency that replicates data from several experiments. The model also demonstrates a functional role for the phenomenon of theta cycle skipping in the medial entorhinal cortex.
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Pandey, Manishi, Gary D. Stormo et Susan K. Dutcher. « Alternative Splicing During the Chlamydomonasreinhardtii Cell Cycle ». G3: ; Genes|Genomes|Genetics 10, no 10 (18 août 2020) : 3797–810. http://dx.doi.org/10.1534/g3.120.401622.
Texte intégralRésumé :
Genome-wide analysis of transcriptome data in Chlamydomonas reinhardtii shows periodic patterns in gene expression levels when cultures are grown under alternating light and dark cycles so that G1 of the cell cycle occurs in the light phase and S/M/G0 occurs during the dark phase. However, alternative splicing, a process that enables a greater protein diversity from a limited set of genes, remains largely unexplored by previous transcriptome based studies in C. reinhardtii. In this study, we used existing longitudinal RNA-seq data obtained during the light-dark cycle to investigate the changes in the alternative splicing pattern and found that 3277 genes (19.75% of 17,746 genes) undergo alternative splicing. These splicing events include Alternative 5′ (Alt 5′), Alternative 3′ (Alt 3′) and Exon skipping (ES) events that are referred as alternative site selection (ASS) events and Intron retention (IR) events. By clustering analysis, we identified a subset of events (26 ASS events and 10 IR events) that show periodic changes in the splicing pattern during the cell cycle. About two-thirds of these 36 genes either introduce a pre-termination codon (PTC) or introduce insertions or deletions into functional domains of the proteins, which implicate splicing in altering gene function. These findings suggest that alternative splicing is also regulated during the Chlamydomonas cell cycle, although not as extensively as changes in gene expression. The longitudinal changes in the alternative splicing pattern during the cell cycle captured by this study provides an important resource to investigate alternative splicing in genes of interest during the cell cycle in Chlamydomonas reinhardtii and other eukaryotes.
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LAGRUE, C., et R. POULIN. « Lack of seasonal variation in the life-history strategies of the trematode Coitocaecum parvum : no apparent environmental effect ». Parasitology 135, no 10 (29 juillet 2008) : 1243–51. http://dx.doi.org/10.1017/s0031182008004782.
Texte intégralRésumé :
SUMMARYParasites with complex life cycles have developed numerous and very diverse adaptations to increase the likelihood of completing this cycle. For example, some parasites can abbreviate their life cycles by skipping the definitive host and reproducing inside their intermediate host. The resulting shorter life cycle is clearly advantageous when definitive hosts are absent or rare. In species where life-cycle abbreviation is facultative, this strategy should be adopted in response to seasonally variable environmental conditions. The hermaphroditic trematode Coitocaecum parvum is able to mature precociously (progenesis), and produce eggs by selfing while still inside its amphipod second intermediate host. Several environmental factors such as fish definitive host density and water temperature are known to influence the life-history strategy adopted by laboratory raised C. parvum. Here we document the seasonal variation of environmental parameters and its association with the proportion of progenetic individuals in a parasite population in its natural environment. We found obvious seasonal patterns in both water temperature and C. parvum host densities. However, despite being temporally variable, the proportion of progenetic C. parvum individuals was not correlated with any single parameter. The results show that C. parvum life-history strategy is not as flexible as previously thought. It is possible that the parasite's natural environment contains so many layers of heterogeneity that C. parvum does not possess the ability to adjust its life-history strategy to accurately match the current conditions.
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Pladys, Arnaud, Romain Brossier, Yubing Li et Ludovic Métivier. « On cycle-skipping and misfit function modification for full-wave inversion : Comparison of five recent approaches ». GEOPHYSICS 86, no 4 (1 juillet 2021) : R563—R587. http://dx.doi.org/10.1190/geo2020-0851.1.
Texte intégralRésumé :
Full-waveform inversion, a high-resolution seismic imaging method, is known to require sufficiently accurate initial models to converge toward meaningful estimations of the subsurface mechanical properties. This limitation is due to the nonconvexity of the least-squares distance with respect to the kinematic mismatch. We propose a comparison of five misfit functions promoted recently to mitigate this issue: adaptive waveform inversion, instantaneous envelope, normalized integration, and two methods based on optimal transport. We explain which principles these methods are based on and illustrate how they are designed to better handle kinematic mismatch than a least-squares misfit function. By doing so, we can exhibit specific limitations of these methods in canonical cases. We further assess the interest of these five approaches for application to field data based on a synthetic Marmousi case study. We illustrate how adaptive waveform inversion and the two methods based on optimal transport possess interesting properties, making them appealing strategies applicable to field data. Another outcome is the definition of generic tools to compare misfit functions for full-waveform inversion.
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Nandi, Papia, et Uwe K. Albertin. « Wave-equation migration velocity analysis in the common-offset domain to avoid cycle-skipping for FWI ». Journal of Applied Geophysics 180 (septembre 2020) : 104115. http://dx.doi.org/10.1016/j.jappgeo.2020.104115.
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Li, Chao, Guochang Liu et Yong Deng. « Nonstationary phase-corrected full-waveform inversion with attenuation compensation in viscoacoustic medium ». Journal of Geophysics and Engineering 19, no 4 (29 juillet 2022) : 724–38. http://dx.doi.org/10.1093/jge/gxac046.
Texte intégralRésumé :
Abstract Full-waveform inversion (FWI) acts as an effective technique to estimate subsurface parameter by iteratively reducing the difference between the predictions and the observations. The classic FWI suffers from the problem of converging to the local minimum when the starting model is poor, which is known as the notorious cycle skipping phenomenon. Moreover, due to the anelasticity of the earth, seismic waves always suffer from energy dissipation and phase distortion while their propagation, which leads to an attenuated gradient for FWI, decelerates the convergence rate of the inversion processing. We have proposed a new method referred to as Q-compensated nonstationary phase-corrected FWI (QNPCFWI) to compensate for the attenuation-induced gradient energy loss and the phase mismatch caused by the less-accurate initial velocity model and phase dispersion simultaneously in viscoacoustic medium. We incorporated attenuation compensation mechanism and nonstationary phase correction method for improved inversion efficiency in the case that a poor initial model is used. The main points of this paper can be concluded as follows: (i) we compensate the lost energy for gradient calculation during wave propagation for improved inversion efficiency. (ii) As we know, Q model estimation for real data is challenging and an accurate Q model is hard to get. The proposed QNPCFWI can also work using an approximate Q model. (iii) The proposed method has the ability to mitigate cycle skipping even if the low-frequency components of seismic data are absent. Numerical examples validate the effectiveness and efficiency of our proposed method.
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Sengupta, Shouvonik, Kelsi O. West, Laura Agosto-Rosa, Kristen W. Lynch, Robert Watson, Kristin Patrick et Mireia Guerau-De-Arellano. « Role of PRMT5 on splicing events in T cell biology ». Journal of Immunology 206, no 1_Supplement (1 mai 2021) : 25.04. http://dx.doi.org/10.4049/jimmunol.206.supp.25.04.
Texte intégralRésumé :
Abstract Protein Arginine Methyltransferase (PRMT) 5 catalyzes symmetric dimethylation of arginine, a post-translational modification involved in cancer and embryonic development. The mechanisms by which PRMT5 modulates T helper (Th) cell activity are still not completely understood. Here we find that PRMT5 in T cells promotes spliceosome component methylation and influences splicing in resting and activated cells. RNAseq of resting and activated wildtype (WT) and PRMT5-knockout (KO) CD4 T cells show the breadth of pathways affected by knockout of PRMT5. Importantly, metabolic processing, signaling, cell cycle and protein localization were affected. We also used a novel software, Modeling Alternative Junction Inclusion Quantification (MAJIQ), to extract information on the classes of alternative splicing (AS) events – Exon skipping, Intron retention, Alternative 5′ splice site and Alternative 3′ splice site. In our samples, we noticed a bias towards exon skipping. We took a closer look at the number of alternative junctions (AJ) arising from these events and the location of the local splice variants (LSV). Analysis of WT and KO T cells showed 9071 AJs upon T cell activation and 2136 AJs dependent on PRMT5. This work demonstrates that PRMT5 modulates the gene expression splicing profile of T cells.
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Lu, Kai, Jing Li, Bowen Guo, Lei Fu et Gerard Schuster. « Tutorial for wave-equation inversion of skeletonized data ». Interpretation 5, no 3 (31 août 2017) : SO1—SO10. http://dx.doi.org/10.1190/int-2016-0241.1.
Texte intégralRésumé :
Full-waveform inversion of seismic data is often plagued by cycle-skipping problems such that an iterative optimization method often gets stuck in a local minimum. To avoid this problem, we simplify the objective function so that the iterative solution can quickly converge to a solution in the vicinity of the global minimum. The objective function is simplified by only using parsimonious and important portions of the data, which are defined as skeletonized data. We have developed a mostly nonmathematical tutorial that explains the theory of wave-equation inversion of skeletonized data. We also demonstrate its effectiveness with examples.