Browsing by Author "Zhang, Wei"

Now showing 1 - 4 of 4
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    Climate warming promotes pesticide resistance through expanding overwintering range of a global pest
    (Springer Nature, 2021) Ma, Chun-Sen; Zhang, Wei; Peng, Yu; Zhao, Fei; Chang, Xiang-Qian; Xing, Kun; Zhu, Liang; Ma, Gang; Yang, He-Ping; Rudolf, Volker H. W.
    Climate change has the potential to change the distribution of pests globally and their resistance to pesticides, thereby threatening global food security in the 21st century. However, predicting where these changes occur and how they will influence current pest control efforts is a challenge. Using experimentally parameterised and field-tested models, we show that climate change over the past 50 years increased the overwintering range of a global agricultural insect pest, the diamondback moth (Plutella xylostella), by ~2.4 million km2 worldwide. Our analysis of global data sets revealed that pesticide resistance levels are linked to the species’ overwintering range: mean pesticide resistance was 158 times higher in overwintering sites compared to sites with only seasonal occurrence. By facilitating local persistence all year round, climate change can promote and expand pesticide resistance of this destructive species globally. These ecological and evolutionary changes would severely impede effectiveness of current pest control efforts and potentially cause large economic losses.
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    Nematic Quantum Critical Fluctuations in BaFe2−xNixAs2
    (American Physical Society, 2016) Liu, Zhaoyu; Gu, Yanhong; Zhang, Wei; Gong, Dongliang; Zhang, Wenliang; Xie, Tao; Lu, Xingye; Ma, Xiaoyan; Zhang, Xiaotian; Zhang, Rui; Zhu, Jun; Ren, Cong; Shan, Lei; Qiu, Xianggang; Dai, Pengcheng; Yang, Yi-feng; Luo, Huiqian; Li, Shiliang
    We have systematically studied the nematic fluctuations in the electron-doped iron-based superconductor BaFe2−xNixAs2 by measuring the in-plane resistance change under uniaxial pressure. While the nematic quantum critical point can be identified through the measurements along the (110) direction, as studied previously, quantum and thermal critical fluctuations cannot be distinguished due to similar Curie-Weiss-like behaviors. Here we find that a sizable pressure-dependent resistivity along the (100) direction is present in all doping levels, which is against the simple picture of an Ising-type nematic model. The signal along the (100) direction becomes maximum at optimal doping, suggesting that it is associated with nematic quantum critical fluctuations. Our results indicate that thermal fluctuations from striped antiferromagnetic order dominate the underdoped regime along the (110) direction. We argue that either there is a strong coupling between the quantum critical fluctuations and the fermions, or more exotically, a higher symmetry may be present around optimal doping.
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    Response evaluation of nonlinear dynamic systems endowed with fractional-order derivatives under evolutionary stochastic excitation
    (2023-12-01) Zhang, Wei; Spanos, Pol D
    Natural hazards and excitations often exhibit stochastic characteristics, such as winds, earthquakes, and ocean waves. These load scenarios deserve extensive attention and investigation that account for the uncertain characteristics; otherwise, it may lead to unpredictable damage. In addition, the viscoelasticity phenomenon is prevalent in a variety of engineering materials. When resisted by dynamic loads, the viscoelastic materials exhibit viscous, smoothly varying, and time-dependent deformation, associated with energy dissipation. It can be essential to understand the viscoelastic behavior and its potential influence on structural response, particularly when structural design and response analysis are considered. In this regard, during recent decades it has been shown that the implementation of fractional derivatives allows a more descent description of the viscoelasticity phenomenon. Therefore, in this thesis, the challenge of viscoelastic oscillators subjected to evolutionary stochastic loads is addressed. More specifically, the fractional-order derivative element is introduced to effectively represent the viscoelastic nature of the materials. Further, several analytical and numerical methods are examined. To start, the statistical linearization method is extended for oscillators with fractional derivative elements, where a quite versatile discretization approach is introduced that makes the proposed method applicable to any kind of nonlinearity. Next, the stochastic averaging method is applied on fractional oscillators reducing the dimensionality of the system, and thus accelerates the following computation. Thirdly, the wavelets-galerkin method is adopted to address the evolutionary response statistics of either linear or nonlinear systems. Note that, by accounting unnoticeable overlapping of the basis wavelets functions, the method predicts accurately responses of relatively flexible and/or lightly damped systems. Results in juxtaposition with the pertinent Monte Carlo simulation data demonstrate the reliability and accuracy of the proposed methods of analysis.
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    X-ray structural determination and biophysical characterization of HemAT, a chemotaxis receptor from Bacillus subtilis
    (2004) Zhang, Wei; Phillips, George N., Jr.
    The heme-based aerotaxis transducer (HemAT) from B. subtilis is a heme-containing protein and functions as an oxygen sensor. It can detect oxygen and transmit the signal generated from oxygen binding to regulatory proteins through its putative methyl-accepting chemotactic domain. Through other components, the signaling information is transferred to motor proteins, which control the direction of rotation of flagella and in turn lead to changes in the swimming behavior of bacteria. There is a great deal of information known about chemotaxis signaling transduction for Escherichia coli and Salmonella typhimurium. However, the detailed molecular mechanism of chemotaxis of Bacillus subtilis is in a sense reversed, because attractant binding to chemotactic receptors strengthens the activity of the downstream histidine kinase, instead of inhibiting reaction in Escherichia coli and Salmonella typhimurium. Multiple-wavelength anomalous dispersion (MAD) data were collected from crystals of HemAT using the intrinsic anomalous scatterer, iron, with synchrotron radiation. Three wavelength iron MAD data were collected to 2.8A resolution. The native data set was collected to 2.15A resolution. The crystallographic analysis reveals that the crystal belongs to P21212 1 space group with the cell dimension a = 50.00A, b = 80.12A, c = 85.95A. There are two molecules in one asymmetric unit with 40% solvent content. I have determined the crystal structures of the HemAT sensor domain in liganded and unliganded forms at resolutions of 2.15A and 2.7A. The structures show that the HemAT sensor domain is a dimeric protein with one heme group in each subunit. The structure of liganded form of HemAT sensor domain reveals a more symmetrical organization than that of the unliganded form. Tyrosine70 in one subunit shows distinct conformations in the liganded and unliganded structures. Our study suggests that disruption of HemAT symmetry plays an important role in initiating the chemotaxis signaling transduction pathway. Our kinetic and thermodynamic studies of ligand binding suggest that HemAT may employ negative cooperativity for detecting external ligand in the signal transduction. The sensor domain provides the structural evidence for such a molecular mechanism.