Mutations in ClC channel proteins may cause serious functional changes and even diseases. The function of ClC proteins mainly manifests as Cl− transport, which is related to the binding free energies of chloride ions. Therefore, the influence of a mutation on ClC function can be studied by investigating the mutational effect on the binding free energies of chloride ions. The present study provides quantitative and systematic investigations on the influences of residue mutations on the electrostatic binding free energies in Escherichia coli ClC (EcClC) proteins, using all-atom molecular dynamics simulations. It was found that the change of the electrostatic binding free energy decreases linearly with the increase of the residue-chloride ion distance for a mutation. This work reveals how changes in the charge of a mutated residue and in the distance between the mutated residue and the binding site govern the variations in the electrostatic binding free energies, and therefore influence the transport of chloride ions and conduction in EcClC. This work would facilitate our understanding of the mutational effects on transport of chloride ions and functions of ClC proteins, and provide a guideline to estimate which residue mutations will have great influences on ClC functions.

In this article, a gas sensing technique utilizing a compact multi‐pass absorption cell in a triangular configuration was proposed for open‐path trace gases detection. To demonstrate this technique, an open‐path gas sensor system was developed by combing the innovated triangular multi‐pass cell with a near infrared distributed feedback diode laser (at 1.65 μm) for simultaneous detection of atmospheric CH4 and H2O. A Gaussian‐noise‐limited limit of detection of approximate 52 ppb and 445 ppm were achieved for CH4 and H2O, respectively, with 1 Hz sampling rate and at normal atmospheric pressure. Allan variance analysis indicates that a sensitivity of 5.5 ppb (for CH4) and 75 ppm (for H2O) could be obtained at the optimal averaging time of 300 s, which is comparative with the mid‐infrared laser based gas sensors. This technique will be a critical tool for developing low‐cost open‐path trace gas monitoring networks for environmental, industrial, and public security applications.

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Material Point Method (MPM) mesoscale simulation was used to study the constitutive relation of a polymer bonded explosive (PBX) consisting of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and a fluorine polymer binder F2314. The stress-strain variations of the PBX were calculated for different temperatures and different porosities, and the results were found to be consistent with experimental observations. The stress-strain relations at different temperatures were used to develop the constitutive equation of the PBX by using numerical data fitting. Stress-strain data for different porosities were used to establish the constitutive equation by fitting the simulation data to an improved Hashion-Shtrikman model. The equation can be used to predict the shear modulus and bulk modulus of the PBX at different densities of the sample. The constitutive equations developed for TATB/F2314 PBX by MPM mesoscale simulation are important equations for the numerical simulations of the PBX at macroscale. The method presented in this study provides an alternative approach for studying the constitutive relations of PBX.

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