ALBERT

Description: To enhance the feasibility of seismic full waveform inversion (FWI) for various types of geological structures, the model parameters should be updated along directions such that both long- and short-wavelength structures can be properly resolved. These long- and short-wavelength structures are primarily influenced by the low- and high-frequency components of the gradients, respectively. In some cases, however, the gradients are not flexible to reconstruct both the long- and the short-wavelength structures. This problem can be related to the scaling method using the Hessian matrix and the effect of the source spectrum. In this study, we analyse the problems of conventional scaling methods in frequency-domain FWI and propose a weighting method to compensate for these problems. The weighting method is applied to the conventional elastic FWI, where the gradient is scaled by the diagonal of the pseudo-Hessian matrix inside the frequency loop so that the effect of the source spectrum can be removed through cancellation. The weighting factors are designed using the backpropagated wavefields incited by the deconvolved residuals, which play a role in making the descent directions appropriately reflect the spectral differences between the observed data and the initial (or the inverted) modelling responses. We analyse the characteristics of the Jacobians and residuals and compare the descent directions of the two conventional waveform inversion methods with descent directions of the weighting method for thick rectangular-shaped and thin-layers models. The results indicate that the descent directions computed using the conventional inversion methods do not reflect the characteristics of deconvolved residuals and that particular frequency components are always emphasized regardless of geological models, while the spatial resolution of the descent direction calculated using the weighting method is flexibly determined depending on the differences between the true and the assumed models. Inversion results for the Marmousi-2 model show that the weighting method is not sensitive to the initial guess even though we do not apply the frequency marching strategy. Numerical examples for the SEG/EAGE salt model show that the weighting method can properly recover the high velocities of the salt body and the low velocities below the salt body. Our numerical examples are based on the assumption that low frequencies are available. Further study is needed to apply the weighting method to real field data that are noisy and do not have low-frequency components.

Description: To enhance the robustness of the l 2 -norm elastic full-waveform inversion (FWI), we propose a denoise function that is incorporated into single-frequency gradients. Because field data are noisy and modelled data are noise-free, the denoise function is designed based on the ratio of modelled data to field data summed over shots and receivers. We first take the sums of the modelled data and field data over shots, then take the sums of the absolute values of the resultant modelled data and field data over the receivers. Due to the monochromatic property of wavefields at each frequency, signals in both modelled and field data tend to be cancelled out or maintained, whereas certain types of noise, particularly random noise, can be amplified in field data. As a result, the spectral distribution of the denoise function is inversely proportional to the ratio of noise to signal at each frequency, which helps prevent the noise-dominant gradients from contributing to model parameter updates. Numerical examples show that the spectral distribution of the denoise function resembles a frequency filter that is determined by the spectrum of the signal-to-noise (S/N) ratio during the inversion process, with little human intervention. The denoise function is applied to the elastic FWI of synthetic data, with three types of random noise generated by the modified version of the Marmousi-2 model: white, low-frequency and high-frequency random noises. Based on the spectrum of S/N ratios at each frequency, the denoise function mainly suppresses noise-dominant single-frequency gradients, which improves the inversion results at the cost of spatial resolution.

Description: We fit the size distribution of liquid-ordered (Lo) domains measured from fluorescence images of model cytoplasmic myelin monolayers with an equilibrium thermodynamic expression that includes the competing effects of line tension, λ, dipole density difference, Δm, and the mixing entropy. From these fits, we extract the line tension, λ, and dipole density difference, Δm, between the Lo and liquid-disordered (Ld) phases. Both λ and Δm decrease with increasing surface pressure, , although λ/Δm2 remains roughly constant as the monolayer approaches the miscibility surface pressure. As a result, the mean domain size changed little with surface pressure, although the polydispersity increased significantly. The most probable domain radius was significantly smaller than that predicted by the energy alone, showing that the mixing entropy promotes a greater number of smaller domains. Our results also explain why domain shapes are stable; at equilibrium, only a small fraction of the domains are large enough to undergo theoretically predicted shape fluctuations. Monolayers based on the composition of myelin from animals with experimental allergic encephalomyelitis had slightly lower values of λ and Δm, and a higher area fraction of domains, than control monolayers at all . While it is premature to generalize these results to myelin bilayers, our results show that the domain distribution in myelin may be an equilibrium effect and that subtle changes in surface pressure and composition can alter the distribution of material in the monolayer, which will likely also alter the interactions between monolayers important to the adhesion of the myelin sheath.

Description: We present the results of simultaneous high resolution observations of far ultraviolet (FUV) spectra/images and precipitating electrons made for the polar region during a period of slightly disturbed geomagnetic conditions. The polar region was divided into five subregions: the dayside subauroral region, dayside auroral zone, polar cap, nightside auroral zone, and nightside subauroral region. Precipitation in the dayside subauroral region was dominated by soft electrons, and the intensity of the OI 135.6 nm line relative to the NI 149.3 nm line was significantly enhanced, while electrons of a few keV energies also existed. On the other hand, the nightside subauroral region showed the hardest electron spectrum among the five subregions, and the FUV intensity was the brightest there, with substantial increase in the long Lyman-Birge-Hopfield (LBH) band. The auroral zones showed series of inverted-V events with more energetic electrons in the nightside than in the dayside, and the corresponding FUV auroral features were also brighter and broader in the nightside. In the polar cap region, discrete polar arcs were seen, with corresponding electron beams of ∼keV, embedded in the diffuse low-intensity FUV background caused by polar rain. The relative intensity of OI 135.6 nm to the NI 149.3 nm line was evaluated for the five subregions and it was found to decrease with increasing electron characteristic energy when energy was smaller than ∼2 keV, and remained more or less the same above ∼2 keV, which was confirmed by simulations. On the other hand, the relative intensity of the long LBH band to the short LBH band increased with increasing characteristic energy over the entire energy range up to ∼4 keV. The OI 135.6 nm line and long LBH band intensities were compared with the energy flux of precipitating electrons, and they were found to have good correlations. When the energy flux was fitted as a function of the long LBH intensity by a power law, the power index was found to be 1.37 for the entire polar region with ∼75 km spatial bins, similar to the value obtained previously for inverted-V events with similar spatial averages.

Description: Protein methyltransferase (PMT)-mediated posttranslational modification of histone and nonhistone substrates modulates stability, localization, and interacting partners of target proteins in diverse cellular contexts. These events play critical roles in normal biological processes and are frequently deregulated in human diseases. In the course of identifying substrates of individual PMTs, bioorthogonal profiling...

Description: Diverse life forms have evolved internal clocks enabling them to monitor time and thereby anticipate the daily environmental changes caused by Earth's rotation. The plant circadian clock regulates expression of about one-third of the Arabidopsis genome, yet the physiological relevance of this regulation is not fully understood. Here we show that the circadian clock, acting with hormone signals, provides selective advantage to plants through anticipation of and enhanced defense against herbivory. We found that cabbage loopers (Trichoplusia ni) display rhythmic feeding behavior that is sustained under constant conditions, and plants entrained in light/dark cycles coincident with the entrainment of the T. ni suffer only moderate tissue loss due to herbivory. In contrast, plants entrained out-of-phase relative to the insects are significantly more susceptible to attack. The in-phase entrainment advantage is lost in plants with arrhythmic clocks or deficient in jasmonate hormone; thus, both the circadian clock and jasmonates are required. Circadian jasmonate accumulation occurs in a phase pattern consistent with preparation for the onset of peak circadian insect feeding behavior, providing evidence for the underlying mechanism of clock-enhanced herbivory resistance. Furthermore, we find that salicylate, a hormone involved in biotrophic defense that often acts antagonistically to jasmonates, accumulates in opposite phase to jasmonates. Our results demonstrate that the plant circadian clock provides a strong physiological advantage by performing a critical role in Arabidopsis defense.

Description: Previously, the pitch angle distribution of mono-energetic and broad-band electron precipitation has been investigated mainly by case studies. The main focus of this study is quantitative comparison of pitch angle distributions between mono-energetic and broad-band electron precipitation using long-term observations onboard one platform. From December 2003 to October 2004, Science and Technology Satellite-I (altitude ~ 680 km) regularly observed auroral electron flux and cold ambient plasma parameters during quiet and moderately disturbed conditions. Mono-energetic electron precipitation has notable perpendicular anisotropy while broad-band electron precipitation is much more field-aligned. As for other features of mono-energetic and broad-band electron precipitation, the characteristic energy of precipitating electrons is slightly higher for mono-energetic (around 1 keV) than for broad-band electron precipitation (from several hundred eV to 1 keV). For both mono-energetic and broad-band types, the characteristic energy and energy flux do not show clear correlation with cold ambient plasma density/temperature.

Description: Using multiple satellites and a ground-based radar network, the physical characteristics of a polar arc and its evolution are investigated under quiet solar wind conditions. The average electron energy is higher at the near-midnight segment than at the sunward extension of the polar arc. Both polar arc segments are positioned primarily on closed magnetic field lines. The convection reversal boundary in the fitted convection pattern was located close to the transition region in the average electron energy seen by the satellites. The topside plasma density at an altitude of 680 km is clearly enhanced around the polar arc, although the enhancement boundary does not coincide precisely with that of the precipitation. The temporal sequence of auroral images suggests that the polar arcs emerged from a double oval structure. This suggestion is supported by the observed physical characteristics of the polar arc, which are quite similar to those of double oval structures that have been reported previously.

Description: Simultaneous-source techniques have been proposed to reduce the acquisition cost and alleviate the computational overburden of data processing, and they have been applied to full waveform inversion (FWI) in recent years. These techniques are mainly based on the l 2 -norm objective function (least-squares criterion). However, if we consider that real field data contain noise such as outliers, it would be preferable to use the robust objective function in simultaneous-source FWI. In this study, we propose combining the simultaneous-source FWI with the l 1 -norm objective function (least-absolute criterion), which is known to be robust to data containing noise, specifically outliers. For the l 1 -norm-based simultaneous-source (SS-1) FWI, we first verify the crosstalk reduction and the robustness to data containing outliers. The expectations of the gradient direction directly give an evidence for the crosstalk reduction, and a signal-to-noise ratio analysis supports the convergence of our algorithm. The analysis shows that the crosstalk noise of the SS-1 FWI can be suppressed by random phase encoding. In addition, the spectrum of the weighted residuals indicates that the main property of the l 1 -norm objective function is preserved in the SS-1 FWI. Numerical examples show that the SS-1 FWI produces reliable results as the l 2 -norm simultaneous-source FWI does, similar to the case of the individual-source FWI. These results support the idea that combining the simultaneous-source FWI with the l 1 -norm objective function improves the computational efficiency and preserves the intrinsic characteristics of the l 1 -norm objective function.