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Overexpressing key enzymes of biosynthetic pathways for overproduction of value-added products usually imposes metabolic burdens on cells, which can be circumvented by improving the key enzyme activities. p -Coumarate: CoA ligase (4CL) is a critical enzyme in the phenylpropanoid pathway that synthesizes various natural products. To screen for 4CL with improved activity, a biosensor of resveratrol whose biosynthetic pathway involves 4CL was designed by engineering the TtgR regulatory protein. The biosensor exhibited good specificity and robustness, allowing rapid and sensitive selection of resveratrol hyper-producers. A 4CL variant with improved activity was selected from a 4CL mutagenesis library constructed in the resveratrol biosynthetic pathway in Escherichia coli . This mutant led to increased production of not only resveratrol but also the flavonoid naringenin, when introduced in their corresponding biosynthetic pathways. These findings demonstrate the feasibility of improving key enzyme activities in important biosynthetic pathways with the aid of designed biosensors of pathway products. [ABSTRACT FROM AUTHOR]

The modern science of networks has brought significant advances to our understanding of complex systems. We employ the probabilistic graphical model to build complex networks to model the global ionospheric variations. The global ionospheric maps (GIMs) of vertical total electron content (VTEC) for the 12 months in 2012 have been selected analyze the ionospheric variations from the perspective of complex network. The information flow in the networks represents the causal interactions between the ionospheric variations at different locations. The distributions of the edges' geospatial distances in the ionospheric networks show that the information flow in the ionosphere is mainly transmitted locally, almost obeying the geospatial proximity principle. The asymmetric distribution of the edges' distances probably elucidates the more efficient transmission of ionospheric variations in the westward and southward directions. The community topologies within the ionospheric networks indicate the effect of the geomagnetic field and geographical distance on the information flow in the ionosphere. The geomagnetic field has shown an enhanced effect on the meridional interaction in the ionosphere, causing the vertical community topologies within the ionospheric networks at middle and low latitudes. For the ionospheric cells located at high latitudes in GIM, the geographical distances result in the horizontal community topologies. The fractal analysis reveals the existence of self-similar structure in the ionospheric networks on the global scale. The fractality in the ionospheric information flow may indicate the reasonability of the VTEC's prediction at a certain location by spatial prediction based on the data obtained in known regions. [ABSTRACT FROM AUTHOR]

Combining analyses of spatial and temporal characteristics of the ionosphere is of great significance for scientific research and engineering applications. Tensor decomposition is performed to explore the temporal-longitudinal-latitudinal characteristics in the ionosphere. Three-dimensional tensors are established based on the time series of ionospheric vertical total electron content maps obtained from the Centre for Orbit Determination in Europe. To obtain large-scale characteristics of the ionosphere, rank-1 decomposition is used to obtain U(1), U(2), and U(3), which are the resulting vectors for the time, longitude, and latitude modes, respectively. Our initial finding is that the correspondence between the frequency spectrum of U(1) and solar variation indicates that rank-1 decomposition primarily describes large-scale temporal variations in the global ionosphere caused by the Sun. Furthermore, the time lags between the maxima of the ionospheric U(2) and solar irradiation range from 1 to 3.7 h without seasonal dependence. The differences in time lags may indicate different interactions between processes in the magnetosphere-ionosphere-thermosphere system. Based on the dataset displayed in the geomagnetic coordinates, the position of the barycenter of U(3) provides evidence for north-south asymmetry (NSA) in the large-scale ionospheric variations. The daily variation in such asymmetry indicates the influences of solar ionization. The diurnal geomagnetic coordinate variations in U(3) show that the large-scale EIA (equatorial ionization anomaly) variations during the day and night have similar characteristics. Considering the influences of geomagnetic disturbance on ionospheric behavior, we select the geomagnetic quiet GIMs to construct the ionospheric tensor. The results indicate that the geomagnetic disturbances have little effect on large-scale ionospheric characteristics. [ABSTRACT FROM AUTHOR]

To solve the problem of the mismatch of the wideband underdetermined direction of arrival (DOA) estimation under the condition of the On‐grid model, this paper extends the narrowband Off‐Grid model to wideband and proposes a new DOA estimation algorithm for Off‐Grid sources based on group sparsity. The proposed algorithm first obtains the preliminary estimation result under the current predefined discrete grid through the group sparsity wideband DOA estimation algorithm. Then, the Off‐Grid optimisation problem is adopted to calculate the Off‐Grid deviation vector. It is also assumed that the off‐grid deviation vectors of each frequency subband are exactly the same, thereby reducing the number of parameters to be estimated. Therefore, the proposed algorithm can not only maintain similar or even better estimation accuracy but also greatly reduce the computational complexity. Finally, simulation is conducted and the results verify the effectiveness and performance of the proposed method. [ABSTRACT FROM AUTHOR]

Given the problem of the direction of arrival (DOA) estimation of quasi‐stationary signals, a sparse reconstruction algorithm based on the sparse array is proposed in this study to improve the DOA estimation performance. Specifically, the quasi‐stationary signal is modelled based on the interleaved array (IA), where the algorithm makes full use of the high degree of freedom (DOF) and large array aperture of the interleaved array in the virtual domain. Then, the angle parameters are estimated depending on sparse reconstruction and the Khatri‐Rao transform, which can achieve a higher number of DOF. Compared with the angle measurement algorithm based on uniform linear array and nested linear array, the algorithm proposed in this study not only increases the DOF of angle measurement significantly, but also improves the accuracy of angle measurement. Finally, numerical simulations demonstrate the validity of the proposed method. [ABSTRACT FROM AUTHOR]

The virtual material model is now widely applied for modeling the dynamical performance of assembled structures since it can effectively represent the complicated contact behavior of joint interfaces despite being relatively simple to create. In this study, a virtual material model is adopted for modeling the dominant physics of a bolted joint subject to a set of pretightening conditions. The unknown virtual material parameters are acquired by an inverse identification procedure that uses the surface response methodology. The greatest advantage of this approach is the ease with which it acquires the joint parameters without taking apart a built-up structure to do special measurements on each separated component. Intricate theoretical calculations can also be avoided when this method is used. This study addresses the responses of virtual material parameters under different pretightening considerations. Predictions based on the identified virtual material parameters are compared with the corresponding results obtained using the analytical method. The correlation between the two sets of results at all preload levels is promising, which indicates the successful identification of the virtual material parameters. [ABSTRACT FROM AUTHOR]