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Shewanella baltica is one of the most important bacterial species contributing to spoilage of seafood. Principally, RpoS has been recognized as the central regulator of stress resistance in many bacterial species. However, little is known about the role of RpoS in S. baltica. In this study, an rpoS mutant of S. baltica was constructed and analysed for its functions. The results showed that the survival rate of rpoS mutant decreased when treated with heat, ethanol and H2 O2, while increased the resistance to NaCl. Moreover RpoS promoted the biofilm formation of S. baltica at 30°C, while declined at 4°C. Interestingly, the rpoS-deficient mutant showed increased swimming motility. Furthermore, the results revealed that the production of quorum-sensing (QS) signals such as cyclo-(l-Pro-l-Leu) and cyclo-(l-Pro-l-Phe) reduced in rpoS mutant. Mainly, rpoS positively regulated QS response regulators, as the expression of all luxR genes in rpoS mutant significantly decreased relative to wild type. This study reveals that RpoS is a major regulator involved in stress responses, biofilm formation and quorum sensing system in S. baltica. The present work provides significant information for the control of microbiological spoilage of seafood.

Aeromonas and Pseudomonas are important bacterial species involved in spoilage of refrigerated freshwater fish. In this study, 10 Aeromonas and seven Pseudomonas bacterial strains were isolated from spoiled grass carp and identified. Twelve of seventeen bacterial strains showed high potential of biofilm formation and 14 of 17 can produce extracellular protease. In order to explore the spoilage capacity of dual-species, the sterile grass carp fillets were inoculated with mono- and dual-species of Aeromonas salmonicida and Pseudomonas azotoformans strains. The results revealed significantly higher levels of the total viable count and total volatile basic nitrogen in dual-species as compared to mono-species from day 6. The higher contents of histamine, cadaverine and serious degradation in muscles tissue were also observed in dual-species after 10 days of storage. Results of in vitro experiments showed that the co-culture of A. salmonicida and P. azotoformans significantly increased the bacterial maximum growth rate, promoted the biofilm formation and improved the spoilage capacity of bacterial strains. This study has revealed that the co-culture of Aeromonas and Pseudomonas bacterial strains accelerated spoilage process of grass carp and increased biofilm formation. It indicates that the mixed-cultures of spoilage micro-organisms pose a huge threat to food industry.

The relationships of H, O, P, S, and N impurities with the type of plasticity deformation displayed in Ni were studied using density functional theory. We found that different impurities have different segregation tendencies with regards to Ni. S, P, O, and H are most likely to occupy sites on the Ni surface, especially S and P impurity. S, P, H and O have little effect on the deformation mechanism of Ni when located in the grains of the Ni metal. Conversely, N prefers to occupy these grains, and lowers the generalized-stacking-fault energy for Ni, readily promoting the dissociation of dislocation into segments, and making cleavage fracture less likely to occur, which enhances dislocation nucleation. S, P and N cause a decrease in the plasticity of Ni, but H and O increase the probability of twinning for Ni. However, these impurities do not switch the deformation mechanism of Ni from dislocation-mediated slipping to twinning.

The tensile fracture processes of O-terminated Ni(1 1 1)/Cr2O3(0 0 0 1) interface were investigated using first-principles method. The simulation presents the strain–stress relationship, the Ni deformation and the propagation of crack tip. Atomic configuration and charge density indicate the softer Ni layers deform larger than the harder Cr2O3 layers and that fracture occurs along the metal–oxide interface. The process of bond breaking was also elucidated.

Density functional theory was employed to investigate the structure and properties of Ni/Cr2O3 and Ni/Al2O3/Cr2O3. The O-terminated Ni(1 1 1)/Cr2O3(0 0 0 1) interface was firstly found to be the most stable configuration. Based on this construction, the effects of the Al diffusion at the Ni/Cr2O3 interface were further studied. The results of total energies indicate that Al atoms originating from Ni slab prefer to diffuse into Cr2O3 slab through the interface, resulting in the formation of alumina at the Ni/Cr2O3 interface. Due to the presence of Al atoms, there was an amazing increase in the work of adhesion, whereas the Ni/Al2O3/Cr2O3 interface showed the strongest stability. Moreover, this calculated work well agrees with the reported experimental results.

Using the first-principle pseudopotential plane wave (PPW) method based on the density functional theory, structural optimization was conducted on various intermetallic compounds of the binary Mg-Nd alloy. With their ground-state energies obtained, the structural stabilities of these intermetallic compounds were studied in terms of formation heat and binding energy of the alloy. The results show that the absolute values of the binding energies of various intermetallic compounds increase with the increase of Nd content, among which the absolute value of the binding energy of MgNd is the greatest while that of Mg 12 Nd is the smallest. It is indicated that among all the intermetallic compounds formed in Mg-Nd, the structure of MgNd is the most stable while that of Mg 12 Nd is the most unstable. This result is consistent with the experiment data. The Mg 12 Nd phase does not exist in the phase diagram of Mg-Nd alloy. In addition, the densities of electronic state of these structures were calculated and an explanation was given in terms of the electronic structure.

The structural stability and electronic properties of MgF2(010), MgF2(001), MgF2(011), and MgF2(110) surfaces were investigated using density functional theory (DFT). We found that the atoms located in the top layers near the surface are obviously relaxed and that the fluorine-terminated surface structure is much more stable than the other two structures. According to the surface energy values of the four different fluorine-terminated surfaces we conclude that the structural stability of the MgF2 surfaces decreases in the following order: MgF2(110), MgF2(011), MgF2(010), and MgF2(001). The density of states of the MgF2(110) surface shows that more bonding electrons are in low level areas and, furthermore, because of the influence of the surface the fluorine atom charges gather at the surface, which makes the surface electronegative and results in an increase in its activity.

By using first-principles method based on the density functional theory(DFT), the stacking fault energy(SFE)and deformation twin energy(DTE)for the(111)[112]slip system of pure Al metal and Al-Mg alloys were investigated.The dependence of these SFE and DTE on solid-solution Mg content and its accupation were specifically analyzed.Two major approximations were made in the process of calculation,which were local density approximation(LDA)and generalized gradient approximation(GGA-PW91),respectively.The calculated SFE values by using GGA-PW91 exhibit an excellent agreement with corresponding experimental measurements.For pure Al metal,the calculated SFE values are greater than those of DTE.Moreover,it is found that under the same deformation conditions,the DTE in pure Al and Al-Mg alloys increase monotonically with the increase of deformation twin thickness.In addition,the calculated results shows that 6-layer twin possesses the lowest DTE,which is probably due to its mirror symmetry structure.Also noteworthy, our calculations reveal a noticeable decreased tendency of SFE and DTE with Mg content increasing,while Mg occupying on stacking fault and twin boundary most likely increases SFE and DTE.There are no considerably detected effects of Mg atomic occupancy variation in Al-Mg alloy on its cohesive energy and formation energy.

Employing density functional theory, we study the tensile and fracture processes of the phase interfaces in Mg—Li binary alloy. The simulation presents the strain—stress relationships, the ideal tensile strengths, and the fracture processes of three phase interfaces. The results show that the α/α and α/β interfaces have larger tensile strength than that of β/β interface. The fractures of both α/α and β/β interfaces are ductile fractures, while the α/β fractures abruptly._Further analyses show that the fracture of the α/β occurs at the interface.

The dependence of the local field enhancement in gold nanoshells was investigated as a function of the core and embedding medium dielectric constant. Numerical calculations based on quasistatic theory indicated two local field factor peaks. If the core dielectric constant is a fixed value and the dielectric constant of surrounding medium is increased from 1.0 to 6.0, the shorter wavelength peak redshifts and decreases nonlinearly, whereas the longer wavelength peak redshifts, increases first and then decreases. On the contrary, if the surrounding dielectric constant is a fixed value and the core dielectric constant is increased from 1.0 to 6.0, the shorter wavelength peak redshifts and increases nonlinearly, whereas the longer wavelength peak redshifts and decreases nonlinearly.