Engineering topics
Yang, Xiaojing
Publications and source records attributed to Yang, Xiaojing.
Light-induced protein structural dynamics in bacteriophytochrome revealed by time-resolved x-ray solution scattering
Bacteriophytochromes (BphPs) are photoreceptors that regulate a wide range of biological mechanisms via red light–absorbing (Pr)–to–far-red light–absorbing (Pfr) reversible photoconversion. The structural dynamics underlying Pfr-to-Pr photoconversion in a liquid solution phase are not well understood. We used time-resolved x-ray solution scattering (TRXSS) to capture light-induced structural transitions in the bathy BphP photosensory module of Pseudomonas aeruginosa. Kinetic analysis of the TRXSS data identifies three distinct structural species, which are attributed to lumi-F, meta-F, and Pr, connected by time constants of 95 μs and 21 ms. Structural analysis based on molecular dynamics simulations shows that the light activation of PaBphP accompanies quaternary structural rearrangements from an “II”-framed close form of the Pfr state to an “O”-framed open form of the Pr state in terms of the helical backbones. This study provides mechanistic insights into how modular signaling proteins such as BphPs transmit structural signals over long distances and regulate their downstream biological responses.
Crystal structure and molecular mechanism of an E/F type bilin lyase-isomerase
Explore the source record for details and available documents.
On-chip Crystallization and Large-Scale Serial Diffraction at Room Temperature
Explore the source record for details and available documents.
The effect of caustic soda treatment to recover rare earth elements from secondary feedstocks with low concentrations
Caustic soda (NaOH) treatment has enhanced rare earth element (REE) extraction from monazite. Here, this study examined the effectiveness of caustic soda for RE-phosphates with lower concentrations for extraction from coal overburden, an alternative feedstock derived from mining waste. Pourbaix (Eh-pH) diagrams were constructed for La, Ce, Nd, Eu, and Y-PO 4 -H 2 O systems to understand the thermodynamics of NaOH-facilitated acid leaching for low-concentration RE-phosphates and oxides and to elucidate the difference in recoveries among individual REEs. The Eh-pH diagrams indicated that low crystallinity is beneficial for extraction. Nd was thermodynamically most favorable for the extraction process among the five elements examined, and Y was the least promising. Experiments were conducted using three Pennsylvania coal overburden samples to validate the effect of caustic soda on rare earth leaching. The experimental results showed that for NaOH (6 M), a leaching time of 2 h at 125 °C was sufficient to obtain twice the recovery values compared to those without the NaOH treatment. After implementing the caustic soda treatment, a high total REE recovery (>60%), especially for Nd and Pr, could be achieved with diluted HCl and more environmentally friendlier citric acid. The results were similar for both coarse and fine particles. This novel approach is likely to improve the feasibility of REE extraction from coal-associated feedstock in a more environmentally benign manner.
A Singular Perturbation Approach for Time-Domain Assessment of Phase Margin
This paper considers the problem of time-domain assessment of the Phase Margin (PM) of a Single Input Single Output (SISO) Linear Time-Invariant (LTI) system using a singular perturbation approach, where a SISO LTI fast loop system, whose phase lag increases monotonically with frequency, is introduced into the loop as a singular perturbation with a singular perturbation (time-scale separation) parameter Epsilon. First, a bijective relationship between the Singular Perturbation Margin (SPM) max and the PM of the nominal (slow) system is established with an approximation error on the order of Epsilon(exp 2). In proving this result, relationships between the singular perturbation parameter Epsilon, PM of the perturbed system, PM and SPM of the nominal system, and the (monotonically increasing) phase of the fast system are also revealed. These results make it possible to assess the PM of the nominal system in the time-domain for SISO LTI systems using the SPM with a standardized testing system called "PM-gauge," as demonstrated by examples. PM is a widely used stability margin for LTI control system design and certification. Unfortunately, it is not applicable to Linear Time-Varying (LTV) and Nonlinear Time-Varying (NLTV) systems. The approach developed here can be used to establish a theoretical as well as practical metric of stability margin for LTV and NLTV systems using a standardized SPM that is backward compatible with PM.