Since 2020, the receptor-binding domain (RBD) of the spike protein of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been constantly mutating, producing most of the notable missense mutations in the context of “variants of concern”, probably in response to the vaccine-driven alteration of immune profiles of the human population. The Delta variant, in particular, has become the most prevalent variant of the epidemic, and it is spreading in countries with the highest vaccination rates, causing the world to face the risk of a new wave of the contagion. Understanding the physical mechanism responsible for the mutation-induced changes in the RBD’s binding affinity, its transmissibility, and its capacity to escape vaccine-induced immunity is the “urgent challenge” in the development of preventive measures, vaccines, and therapeutic antibodies against the coronavirus disease 2019 (COVID-19) pandemic. In this study, entropy–enthalpy compensation and the Gibbs free energy change were used to analyze the impact of the RBD mutations on the binding affinity of SARS-CoV-2 variants with the receptor angiotensin converting enzyme 2 (ACE2) and existing antibodies. Through the analysis, we found that the existing mutations have already covered almost all possible detrimental mutations that could result in an increase of transmissibility, and that a possible mutation in amino-acid position 498 of the RBD can potentially enhance its binding affinity. A new calculation method for the binding energies of protein–protein complexes is proposed based on the entropy–enthalpy compensation rule. All known structures of RBD–antibody complexes and the RBD–ACE2 complex comply with the entropy–enthalpy compensation rule in providing the driving force behind the spontaneous protein–protein docking. The variant-induced risk of breakthrough infections in vaccinated people is attributed to the L452R mutation’s reduction of the binding affinity of many antibodies. Mutations reversing the hydrophobic or hydrophilic performance of residues in the spike RBD potentially cause breakthrough infections of coronaviruses due to the changes in geometric complementarity in the entropy–enthalpy compensations between antibodies and the virus at the binding sites.

Smart electromagnetic interference (EMI) shielding materials capable of reversible EMI response hold great promise for application in flexible electromagnetic devices. Here, PPM hydrogels composed of poly (N‐isopropylacrylamide) (PNIPAM) and MXene/PEDOT: PSS hybrid fillers are fabricated via ice‐templated freeze‐in‐situ polymerization. The anisotropic structural design of the hydrogel enhances its mechanical properties, conductivity, and EMI shielding properties in a specific direction. Furthermore, it can rapidly adjust its internal water content under thermal and light stimulation. The EMI shielding performance of PPM hydrogels can transition from an EMI shielding status (EMI shielding on, >50 dB) to an EM‐wave‐transparent status (EMI shielding off, ≈2 dB) in the X‐band with the dynamic change in water content. Notably, the EMI SE value of PPM hydrogel in the X‐band can be quantitatively adjusted from ≈59.3 to 15.5 dB, demonstrating excellent repeatability and adjustability. A real‐time electrical switching capability in the broad GHz frequency range (8.2–40 GHz) is achieved through dual stimuli‐responsive (temperature‐responsive and light‐responsive) modulation. This study presents a new model for dynamically switchable EMI shielding and reveals the great application potential of smart on/off switchable hydrogel‐based EMI shielding materials as next‐generation multifunctional electronics.

Exploring the protein-folding problem has been a longstanding challenge in molecular biology and biophysics. Intramolecular hydrogen (H)-bonds play an extremely important role in stabilizing protein structures. To form these intramolecular H-bonds, nascent unfolded polypeptide chains need to escape from hydrogen bonding with surrounding polar water molecules under the solution conditions that require entropy-enthalpy compensations, according to the Gibbs free energy equation and the change in enthalpy. Here, by analyzing the spatial layout of the side-chains of amino acid residues in experimentally determined protein structures, we reveal a protein-folding mechanism based on the entropy-enthalpy compensations that initially driven by laterally hydrophobic collapse among the side-chains of adjacent residues in the sequences of unfolded protein chains. This hydrophobic collapse promotes the formation of the H-bonds within the polypeptide backbone structures through the entropy-enthalpy compensation mechanism, enabling secondary structures and tertiary structures to fold reproducibly following explicit physical folding codes and forces. The temperature dependence of protein folding is thus attributed to the environment dependence of the conformational Gibbs free energy equation. The folding codes and forces in the amino acid sequence that dictate the formation of β-strands and α-helices can be deciphered with great accuracy through evaluation of the hydrophobic interactions among neighboring side-chains of an unfolded polypeptide from a β-strand-like thermodynamic metastable state. The folding of protein quaternary structures is found to be guided by the entropy-enthalpy compensations in between the docking sites of protein subunits according to the Gibbs free energy equation that is verified by bioinformatics analyses of a dozen structures of dimers. Protein folding is therefore guided by multistage entropy-enthalpy compensations of the system of polypeptide chains and water molecules under the solution conditions.

Silicon carbide (SiC) is a promising material for thermoelectric power generation. The characterization of thermal transport properties is essential to understanding their applications in thermoelectric devices. The existence of stacking faults, which originate from the “wrong” stacking sequences of Si–C bilayers, is a general feature of SiC. However, the effects of stacking faults on the thermal properties of SiC are not well understood. In this study, we evaluated the accuracy of Tersoff, MEAM, and GW potentials in describing the thermal transport of SiC. Additionally, the thermal conductivity of 3C/4H-SiC nanowires was investigated using non-equilibrium molecular dynamics simulations (NEMD). Our results show that thermal conductivity exhibits an increase and then saturation as the total lengths of the 3C/4H-SiC nanowires vary from 23.9 nm to 95.6 nm, showing the size effect of molecular dynamics simulations of the thermal conductivity. There is a minimum thermal conductivity, as a function of uniform period length, of the 3C/4H-SiC nanowires. However, the thermal conductivities of nanowires weakly depend on the gradient period lengths and the ratio of 3C/4H. Additionally, the thermal conductivity of 3C/4H-SiC nanowires decreases continuously from compressive strain to tensile strain. The reduction in thermal conductivity suggests that 3C/4H-SiC nanowires have potential applications in advanced thermoelectric devices. Our study provides insights into the thermal transport properties of SiC nanowires and can guide the development of SiC-based thermoelectric materials.

The isothermal oxidation behaviours of Al₂TiO₅/TiO₂/ZrO₂ composite coating on titanium alloy (TC4) deposited by micro-arc oxidation technique were studied at different temperature points of 1073, 1173 and 1273 K in dry air. The surface morphology and phase composition of all coated samples were investigated before and after oxidation by SEM and XRD, respectively. The weight gaining curves of the coated samples were plotted and the high temperature oxidation rates were evaluated, showing that the oxidation kinetics followed the parabolic rate law. And with increasing oxidation temperature, their oxidation rates also increased. The original phases of Al₂TiO₅/TiO₂/ZrO₂ coating on TC4 alloy consisted mostly of Al₂TiO₅ and R-TiO₂ intermixed with small amounts of ZrO₂ and the phased changed into mainly of R-TiO₂, Al₂O₃ and little Al₂TiO₅ when after 1273 K oxidation for 1 h, whose average parabolic rate constant was 6.43 × 10⁻¹³ g² cm⁻⁴ s⁻¹, greatly lower than that of blank samples, 6.01 × 10⁻¹² g² cm⁻⁴ s⁻¹, indicative of a good oxidation resistance for the Al₂TiO₅/TiO₂/ZrO₂ composite coating on TC4 surface.

A thermal protection system is critical for ensuring the safe take-off and return of various aircraft. A key heat-resistant material within this system is the ceramic fiber insulation tile (CFIT), which is a porous three-dimensional network material with density ranges from 0.3 to 0.4 g/cm³ that exhibits complex mechanical behaviors. Due to the complexity of the service environment, experimental methods cannot accurately capture the mechanical behavior of a CFIT. Although simulation-based methods can provide insights, an accurate constitutive model for CFITs has yet to be established. To predict its complex mechanical behavior, an elastic–plastic damage constitutive model was established for CFITs. Based on the Hashin criteria and four fundamental assumptions, a yield rule was modified by introducing a damage factor in the TTT direction. The model was encoded into a user–material subroutine (UAMT) integrated within ABAQUS to capture the mechanical responses under four typical working conditions. The change trend of the simulation curve closely aligned with that of the experiment curve, better characterizing the stress–strain relationship of the CFIT under different working conditions such as compression, tension, and shear and the error was less than 18%. The proposed approach was validated by designing a millimeter-level indentation experiment. The results in this paper demonstrate that the maximum loading depths of the simulation and experiment were consistent, and the relative errors were within 12%, respectively. The research provides a reliable elastic–plastic damage constitutive model to predict the mechanical behavior of CFITs under complex working conditions.