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We perform a first-principles calculation to investigate the effect of a vacancy on the sliding of an iron (Fe) Σ5 (310) [001] tilt grain boundary (GB). We calculate vacancy formation energies in order to determine the site preference of the vacancy at the Fe GB. We show that vacancies can easily segregate to the GB region, which is attributed to special atomic configurations of the GB. We demonstrate that the maximal sliding energy barrier of the GB with a monovacancy is 2.78 J/m2, 15% lower than that of the vacancy-free GB, suggesting that the presence of vacancy at the GB increases the GB mobility. [ABSTRACT FROM AUTHOR]

We have investigated the effects of noble gas elements (helium, neon, argon and krypton) on the dissolution and accumulation behavior of hydrogen (H) in tungsten (W) using a first-principles method, as well as the behaviors of themselves. Noble gas atoms energetically prefer to occupy the tetrahedral interstitial site (TIS) in W, as the same of H. The TIS → TIS is their optimal diffusion path, and the diffusion energies increase with the increasing of atomic radius. All of them are energetically favorable clustering by self-trapping. It is found that the presence of the noble gas elements have significant effect on H behavior in W. Both interstitial noble gas atoms and their complex with vacancy can serve as strong trapping centers of H, which can be attributed to the redistribution of electron density and lattice distortion induced by noble gas. Most importantly, we have demonstrated that H trapping capability of noble gas clusters will increase with the increasing of the number of noble gas atoms in both interstitial and vacancy-complex cases. The H trapping energy surrounding the noble gas clusters with four atoms is comparable to that in noble gas-free vacancy. Further, the formation of noble gas clusters is much easier than that of vacancy due to the self-trapping interaction between noble gas atoms (>1 eV for interstitial case and >4 eV for vacancy-complex case), and thus the H trapping centers will rapidly increase after noble gas pre-irradiation/implantation. Consequently, the self-trapping character of noble gas induces their strong trapping effect on H. [ABSTRACT FROM AUTHOR]

When an impurity is doped in a solid, it inevitably induces a local stress, tending to expand or contract the lattice. Consequently, strain can be applied to change the solubility of impurity in a solid. Generally, the solubility responds to strain "monotonically," increasing (decreasing) with the tensile (compressive) strain if the impurity induces a compressive stress or vice versa. Using first-principles calculations, however, we discovered that the H solubility can be enhanced by anisotropic strain in some bcc metals, almost independent of the sign of strain. This anomalous behavior is found to be caused by a continuous change of H location induced by anisotropic strain. Our finding suggests a cascading effect of H bubble formation in bcc metals: the H solution leads to H bubble formation that induces anisotropic strain that in turn enhances H solubility to further facilitate bubble growth. [ABSTRACT FROM AUTHOR]

On the basis of high-spin metal-cyanide clusters of MnIII6MIII (M = Cr, Fe, Co), three one-dimensional (1D) chain complexes, [Mn(salen)]6[Cr(CN)6]2·6CH3OH·H2O (1), [Mn(5-CH3)salen)]6[Fe(CN)6]2·2CH3CN·10H2O (2), and [Mn(5-CH3)salen)]6[Co(CN)6]2·2CH3CN·10H2O (3) [salen = N,N′-ethylenebis(salicylideneiminato) dianion], have been synthesized and characterized structurally as well as magnetically. Complexes 2 and 3 are isomorphic but slightly different from complex 1. All three complexes contain a 1D chain structure which is comprised of alternating high-spin metal-cyanide clusters of [Mn6M]3+ and a bridging group [M(CN)6]3- in the trans mode. Furthermore, the three complexes all exhibit extended 3D supramolecular networks originating from short intermolecular contacts. Magnetic investigation indicates that the coupling mechanisms are intrachain antiferromagnetic interactions for 1 and ferromagnetic interactions for 2, respectively. Complex 3 is a magnetic dilute system due to the diamagnetic nature of CoIII. Further magnetic investigations show that complexes 1 and 2 are dominated by the 3D antiferromagnetic ordering with TN = 7.2 K for 1 and 9.5 K for 2. It is worth noting that the weak frequency-dependent phenomenon of AC susceptibilities was observed in the low-temperature region in both 1 and 2, suggesting the presence of slow magnetic relaxations. [ABSTRACT FROM AUTHOR]

In neural prosthetic systems, a low-impedance electrode-tissue interface is important for maintaining signal quality for recording, as well as effective charge transfer for stimulation. However, neural microelectrodes often have high impedance due to their small surface areas. In this paper, we present a simple method of increasing their effective surface areas by introducing nanostructures on the electrode sites. The method combines photolithography and electron-beam evaporation with a locally patterned anodized porous alumina template to integrate Au-nanorod arrays on the flexible thin-film microelectrode, which can significantly increase the effective surface area and decrease impedance due to its 3-D and compact nanostructures. Moreover, the geometrical and electrical properties of Au-nanorod electrodes were demonstrated and compared with conventional planar microelectrodes by using a scanning electron microscope and an impedance spectroscopy system. Experimental results showed that approximately 25 times lower interface impedance was achieved for this nanostructured microelectrode. Such Au-nanorod integrated microelectrode arrays will be a promising tool for neural engineering. [ABSTRACT FROM AUTHOR]

We investigate the behaviors of rhenium (Re) and osmium (Os) and their interactions with point defects in tungsten (W) using a first-principles method. We show that Re atoms are energetically favorable to disperse separately in bulk W due to the Re–Re repulsive interaction. Despite the attractive interaction between Os atoms, there is still a large activation energy barrier of 1.10 eV at the critical number of 10 for the formation of Os clusters in bulk W based on the results of the total nucleation free energy change. Interestingly, the presence of vacancy can significantly reduce the total nucleation free energy change of Re/Os clusters, suggesting that vacancy can facilitate the nucleation of Re/Os in W. Re/Os in turn has an effect on the stability of the vacancy clusters (Vn) in W, especially for small vacancy clusters. A single Re/Os atom can raise the total binding energies of V2 and V3 obviously, thus enhancing their formation. Further, we demonstrate that there is a strong attractive interaction between Re/Os and self-interstitial atoms (SIAs). Re/Os could increase the diffusion barrier of SIAs and decrease their rotation barrier, while the interstitial-mediated path may be the optimal diffusion path of Re/Os in W. Consequently, the synergistic effect between Re/Os and point defects plays a key role in Re/Os precipitation and the evolution of defects in irradiated W. [ABSTRACT FROM AUTHOR]

The effects of helium (He) on the sliding and mechanical properties of a vanadium (V)Σ5(310)/[001] grain boundary (GB) have been investigated using a first-principles method. It has been found that He was energetically favorable sitting at the GB region with a segregation energy of −0.27 eV, which was attributed to the special atomic configurations and charge density distributions of the GB. The maximal sliding energy barrier of the He-doped GB was calculated to be 1.73 J/m2, ∼ 35% larger than that of the clean GB. This suggested that the presence of He would hinder the V GB mobility. Based on the thermodynamic criterion, the total energy calculations indicated that the embrittlement of V GB would be enhanced by He segregation. [ABSTRACT FROM AUTHOR]

In the structure of the title compound, 1-(4-cyano­benzyl)-4-methyl­pyridinium 7,7,8,8-tetra­cyano­quinodimethanide, C14H13N2+·[C8H4(CN)4]−, the asymmetric unit contains one cation and one anion. Intra- and inter­molecular C—H⋯N hydrogen bonds and π–π stacking inter­actions seem to be effective in the stabilization of the crystal structure. [ABSTRACT FROM AUTHOR]

The slow diffusion reaction of octacyanometallate [MoV(CN)8]3-, lanthanide ions (Gd-Lu), and 1,10-phenanthroline (phen) in CH3CN/H2O has yielded eight isostructural one-dimensional chains, [LnIII(phen)2(H2O)MoV(CN)8]2[(n-C4H9)4N](NO3)·2CH3CN·4H2O (Ln = Gd(1), Tb(2), Dy(3), Ho(4), Er(5), Tm(6), Yb(7), Lu(8)), in which [LnIII(phen)2(H2O)]3+ and [MoV(CN)8]3- units are linked alternatively through cyanide groups, generating left- and right-handed helices. Interestingly, 1-8 undergo a resolvation-recrystallization process upon prolonging the diffusion-reaction time, together with the valence change from V to IV of Mo center and structural dimensionalities switching from helical chains to trinuclear clusters, (Hphen)2.5[LnIII0.5(phen)(H2O)][MoIV(CN)8]·1.5CH3CN (Ln = Gd(9), Tb(10), Dy(11), Ho(12), Er(13), Tm(14), Yb(15), Lu(16)). Magnetic studies of 1-16 revealed the typical effects induced by single-ion magnetic anisotropy and/or the population of low-lying excited states, and 11 and 13 showed extraordinary field-induced slow magnetic relaxations. [ABSTRACT FROM AUTHOR]

Fission gas retention or release has a critical impact on the function of advanced nuclear materials. Helium trapping in, and release from, radiation defects induced by neutrons and by α decay in YSZ (yttria-stabilized zirconia) is experimentally simulated using synchronized Zr+ and He+ dual ion beam irradiation. The measured damage profiles consist of two peaks which agree well with the calculated profiles of implantation induced excess point defects. This special implantation related effect has to be carefully considered in the evaluation of experimental investigations which simulate isotropic irradiation effects such as α decay. First-principles calculations show that helium is energetically favorable to be trapped by Zr vacancies in YSZ. Implanted helium alone in YSZ is accumulated in undesirable helium bubbles and results in local surface swelling and lift-off. However, under dual beam irradiation helium is released from vacancy defects and is out-diffused at room temperature. Helium is mobilized by a vacancy-assisted trapping/detrapping mechanism induced by the simultaneous Zr+ ion implantation. This behavior avoids the deleterious helium bubble formation and contributes to the suitable application characteristics of YSZ which result in its excellent radiation hardness. [ABSTRACT FROM AUTHOR]

The article presents a study on the combined effect of hybrid on-line optimal control strategy for producing α-Amylase by Bacillus subtilis. The optimal combination in the extraction for α-amylase production was identified by the interaction of wheat bran and cotton seed. The temperature-limited strategy was suggested to solve the proteolytic problem and the hybrid strategy of α-amylase increased productivity and efficiency.

Vacancy-type defects created by helium implantation in tungsten and their impact on the nano-hardness characteristics were investigated by correlating the results from the positron annihilation spectroscopy and the nano-indentation technique. Helium implantation was performed at room temperature (RT) and at an elevated temperate of 600 °C. Also, the effect of post-annealing of the RT implanted sample was studied. The S parameter characterizing the open volume in the material was found to increase after helium irradiation and is significantly enhanced for the samples thermally treated at 600 °C either by irradiation at high temperature or by post-annealing. Two types of helium-vacancy defects were detected after helium irradiation; small defects with high helium-to-vacancy ratio (low S parameter) for RT irradiation and large defects with low helium-to-vacancy ratio (high S parameter) for thermally treated tungsten. The hardness of the heat treated tungsten coincides with the S parameter, and hence is controlled by the large helium-vacancy defects. The hardness of tungsten irradiated at RT without thermal treatment is dominated by manufacturing related defects such as dislocation loops and impurity clusters and additionally by trapped He atoms from irradiation effects, which enhance hardness. He-stabilized dislocation loops mainly cause the very high hardness values in RT irradiated samples without post-annealing. [ABSTRACT FROM AUTHOR]

We have explored the retention of hydrogen (H) in tungsten (W) by investigating its dissolution and aggregation in vacancy clusters (VCs) using a first-principles method and thermodynamic models. The solution energy of a single H in the VCs is in the range of  −0.99 to  −0.64 eV, much lower than that at a mono-vacancy (~  −0.37 eV) and interstitial site (~1.01 eV) in W. Such a remarkable discrepancy is rationalized on the electronic interaction of H with its neighboring W atoms, which varies from repulsion to attraction with H moving from perfect crystal to vacancy/VCs. Specifically, the solution/trapping energies of H in VCs can be well categorized by the coordination number of its neighboring W atoms, i.e. the lower the coordination number of W, the stronger the H–W attraction and the lower the H solution/trapping energy. Furthermore, taking the cluster as an example, it is observed that the multiple H atoms form a multilayer nested cage configuration at the VC surface initially, and then the stable H2 molecules form in the center of the VCs. Interestingly, the pre-existing H atoms in the VC inner surface have a shielding effect on the H–W interaction, decreasing the electron density of the central region of the VCs and facilitating the formation of H2 molecules. Moreover, the desorption temperatures of H in the VCs are also predicted based on the Polanyi–Wigner equation, and are in good agreement with the available thermal desorption spectroscopy experiments. Our calculations provide a good reference to understand the influence of VCs on the retention and evolution of H in W. [ABSTRACT FROM AUTHOR]

The slow diffusion reaction of octacyanometalate [W(CN)8]3-, lanthanide ions, and 4,4'-bipyridyl-N,N'-dioxide (bpdo) has generated a series of isostructural three-dimensional pillared-layer networks with general formula [Ln(bpdo)1.5(H2O)W(CN)8]·0.5CH3OH·6H2O (Ln = Dy-Yb, Gd), in which Ln(III) atoms adopted an unusual seven-coordinated geometry in the cyanometalate-based lanthanide system. This building approach on the basis of the simultaneous employment of cyanide and bpdo bridges offers potential possibilities for designing and constructing 5d-4f coordination networks with high dimensionalities. Interestingly, the LnIII-bpdo-WV(CN)8 system has undergone an unique two-step phase transition upon prolonging the diffusion reaction time, together with the structural changing from initial ion pair through two-dimensional layer to final three-dimensional pillared-layer network. Magnetic studies of all compounds revealed typical and dominant single-ion magnetic behaviors over the weak coupling interactions between spin centers. [ABSTRACT FROM AUTHOR]

Two polynuclear mixed-valence manganese clusters, [Mn13] and [Mn16], containing mixed chelating ligands were synthesized and structurally characterized. The alternating current (AC) susceptibilities of both complexes reveal nonzero frequency-dependent out-of-phase (χM′′) signals. [ABSTRACT FROM AUTHOR]

The influence of degenerate four-wave mixing (FWM) on the performance of supercontinuum-based multiwave-length optical source has been investigated in detail experimentally and theoretically. Numerical simulation results show that the degenerate FWM effect has a deteriorative influence on the spectral uniformity and the optical signal-to-noise ratio (OSNR) of supercontinuum-based optical source, and by suppressing degenerate FWM effect the performance enhancement of the supercontinuum can be achieved successfully. These results are also confirmed by our experiments. Experimentally, by suppressing degenerate FWM the crosstalk of adjacent channels to the filtered channel can be reduced by as much as 15 dB, and consequently the measured receiver sensitivity at 10 Gbit/s for the filtered optical source is improved from -1.7 to -17.8 dBm. [ABSTRACT FROM AUTHOR]

Oclacyanotungstate(V) reacts with Cu(NO3)2 2HO and 1,4,7tdmethyl-1 ,4,7-tdazacyclononane in methanol, resulting in an eicosanuclear duster [Cu13W7], which shows a diamondoid shape with a Tolkowsky cuI and bears intracluster ferromagnelic coupling. [ABSTRACT FROM AUTHOR]

We have investigated the effects of Re on the behaviors of H in W as well as their interaction with point defects using a first-principles method in combination with thermodynamic models. It is clearly found that the influence of Re on H is directly related to the distribution of Re in W. For the state of Re dispersed distribution, both a single Re and its complexes with point defects have very slight effect on H dissolution and retention in W. However, the influence of Re clusters (for the state of Re aggregation) on H is extraordinary stronger than that of a single Re. The retention of H in W can be significantly decreased by Re clusters, and their influences will be enhanced with the increasing of the number of Re atoms. This can be attributed to the electronic interaction between H and Re/W, in which the repulsion of Re–H is stronger than that of W–H. We have further examined the retention of H at different temperature in W based on the Polanyi–Wigner equation. It is found that a Re4-vacancy complex can only accommodate 4 H atoms at room temperature, ~33% lower than the maximum number of H atoms in a mono-vacancy. These results give a reasonable interpretation for the experimentally observed D retention significantly decreasing in damaged W–Re alloy in comparison with that in damaged pure W. Consequently, our calculations provide a good reference for evaluating the influence of Re on the performance of W-PFM. [ABSTRACT FROM AUTHOR]