The contribution of inner electron excitation to the electronic stopping power of palladium for protons.

The electronic stopping power of palladium (Pd) for protons is investigated based on time-dependent density functional theory combined with Ehrenfest molecular dynamics simulations. The electronic stopping power of Pd with explicitly considering inner electrons for protons is calculated and the excitation mechanism for the inner electrons of Pd is revealed. The velocity proportionality of the low-energy stopping power of Pd is reproduced. Our study verified that the inner electron excitation contributes significantly to the electronic stopping power of Pd in the high energy range, which is strongly dependent on the impact parameter. The electronic stopping power obtained from the off-channeling geometry is in quantitative agreement with the experimental data in a wide velocity range, and the discrepancy around the stopping maximum is further reduced by considering the relativistic correction on the binding energy of inner electrons. The velocity dependence of the mean steady-state charge of protons is quantified, and the results showed that the participation of 4p-electrons reduces the mean steady-state charge of protons, and consequently decreases the electronic stopping power of Pd in the low energy range.

Theoretical study on collision dynamics of H(+) + CH4 at low energies.

In this work we make an investigation on collision dynamics of H(+) + CH4 at 30 eV by using time-dependent density functional theory coupled with molecular dynamics approach. All possible reactions are presented based on 9 incident orientations. The calculated fragment intensity is in nice agreement with experimental results. The mechanism of reaction transition for dissociation and proton exchange processes is explained by the intra-molecule energy transfer. However, the energy loss of the proton is in poor agreement with experimental results. The discrepancy is attributed to the mean-field treatment of potential surface. We also studied the dependence on initial velocity of both proton and methane. In addition, we find that for dynamical evolution a different self-interaction correction (SIC) may lead to different results, but with respect to the position of rainbow angle, average-density SIC seems to have reasonable correction.

Collision dynamics of proton with formaldehyde: fragmentation and ionization.

Using time-dependent density functional theory, applied to the valence electrons and coupled non-adiabatically to molecular dynamics of the ions, we study the ionization and fragmentation of formaldehyde in collision with a proton. Four different impact energies: 35 eV, 85 eV, 135 eV, and 300 eV are chosen in order to study the energy effect in the low energy region, and ten different incident orientations at 85 eV are considered for investigating the steric effect. Fragmentation ratios, single, double, and total electron ionization cross sections are calculated. For large impact parameters, these results are close to zero irrespective of the incident orientations due to a weak projectile-target interaction. For small impact parameters, the results strongly depend on the collision energy and orientation. We also give the kinetic energy releases and scattering angles of protons, as well as the cross section of different ion fragments and the corresponding reaction channels.

[Analysis of typical mangrove spectral reflectance characteristics].

Acquisition of mangrove spectrum properties and detecting the sensitive bands provide technology basis for inverse modeling and estimation by remote sensing for various indexes of mangrove. The typical mangroves of Guangxi Shankou Mangrove Reserve were taken for study objects, the standard spectrum curves of Bruguiera gymnorrhiza (Linn.) Savigny, Rhizophora stylosa, Kandelia candel, Avicennia marina, Aegiceras corniculatum, Spartina anglica and mudflat were gained by denoising analysis of field-measured spectrum curves acquired by ASD FieldSpec 2. Analyzing the spectral characteristics and their differences, the authors found that the spectrum curves for various kinds of mangrove are coincident, the bands that appeared with reflection peaks and reflection valleys are basically identical, the within-class differentiated characteristics are comparatively small, the spectrum characteristics of mangroves are obviously different with Spartina anglica and mudflat. In order to gain the quantitative description for within-class differentiated characteristics of mangrove, space distance method, correlation coefficient method and spectral angle mapping method were used to calculate the within-class differentiated characteristics. The division accuracy of correlation coefficient method is higher than spectral angle mapping method which is higher than space distance method, and the result indicates that the spectrum differences of within-class mangrove and Spartina anglica are relatively small with correlation coefficients more than 0.995, and spectrum curve angle cosine values more than 0.95.

Synergistic Effect of Hyperactive Antifreeze Protein on Inhibition of Gas-Hydrate Growth by Hydrophobic and Hydrophilic Groups.

Antifreeze proteins (AFPs) are biodegradable inhibitors that effectively prevent the formation of natural gas hydrates that block pipelines. In this study, molecular dynamics simulations were employed to establish a kinetic model of the hyperactive insect antifreeze protein (Tenebrio molitor, TmAFP) and its mutants to inhibit the growth of sI natural methane hydrate. Simulations revealed that the hydrophobic and hydrophilic groups of threonine (Thr) residues at hydrate-binding sites played a synergistic role in binding hydrates. The hydrophobic groups anchored TmAFP to the hydrate surface through residues Thr39-Thr65 by migrating pendant hydrophobic methyl groups to the hydrate semicages. The hydrophilic groups stabilized TmAFP by hydrogen bonding with water molecules and integrating them into a quasi-hydrate structure, which more effectively inhibited hydrate growth. The results suggest that the hydrate growth inhibition is attributed to both the shape complementarity and the flexibility of binding residues. The synergy between hydrophobic and hydrophilic groups provides guidance for the design of more effective hydrate inhibitors.

Electronic stopping power for slow ions in the low-hardness semimetal HgTe using first-principles calculations.

The electronic stopping power for low-velocity ions (including protons, [Formula: see text]-particles, and [Formula: see text]) is investigated in a novel semimetal HgTe system, where the data are obtained with the aid of Ehrenfest dynamics combined with time-dependent density functional theory. For the light projectile ions (protons and [Formula: see text]-particles), the linear and nonlinear behaviors of electronic stopping power in three different channel directions are analyzed in detail. In the case where the projectile ion is a proton, the linear results for the threshold velocity are correlated with an indirect band gap; the direction of the electronic stopping power depends on the radial drag force, the channeling electronic density and the trapped charge. More notably, we report an interesting channel-geometry fact, i.e. that the electronic stopping power of HgTe is powerfully modulated by the impact parameters. The parallel off-center tracks increase the electronic stopping power, making it more consistent with the SRIM data. In the case of an [Formula: see text]-particle as the projectile ion, nonlinear behavior that varies with velocity can be ascribed to the charge transfer, which is another mode of energy dissipation. In addition, when the slightly heavier projectile [Formula: see text] travels through the medium HgTe, the projectile [Formula: see text] can capture more free charges than the protons and [Formula: see text]-particles under the same circumstances. Especially, for the projectile in the off-channel, the electronic stopping power is close to the SRIM data with the decrease of the impact parameter. These results extend the study of radiation damage to a new field of materials.

Mixed-salt effects on the conformation of a short salt-bridge-forming α helix: a simulation study.

The structure of a single alanine-based ACE-AEAAAKEAAAKA-NH2 peptide in explicit aqueous solutions with mixed inorganic salts (NaCl and KCl) is investigated by using molecular simulations. The concentration of Na(+), c(Na(+)), varies from 0.0M to 1.0M, whereas the concentration of K(+) is 1-c(Na(+)). The simulated peptide is very sensitive to the change of concentration ratio between Na(+) and K(+). When the concentration ratio between Na^{+} and K^{+} is changed from 0.5/0.5, the structure of the peptide becomes loose or disordered. This specific phenomenon is confirmed via checking the changes of helix parameters and mapping the free energy along different coordinates. The higher normalized probability of forming direct and indirect salt bridges between residues Glu7(+) and Lys11(+) and the smallest probability of forming ringlike structures should be responsible for the stabilized helix structure in the 0.5 Na(+)/0.5 K(+) solution. Furthermore, a noticeable conformational transition from an extended helix to an α helix is found in the 0.5 Na(+)/0.5 K(+) solution, where a local ion cloud shows that some Na(+) ions in the inner shells are still directly binding with the peptide, while K(+) in the outer shells are moving into the inner shells, keeping the peptide in the collapsed state.

The effects of electron transfer on the energy loss of slow He²âº, C²âº, and C4⁺ ions penetrating a graphene fragment.

Electronic energy loss in the collision processes of slow ions with a graphene fragment is investigated by combining ab initio time-dependent density functional theory calculations for electrons with molecular dynamics simulations for ions in real time and real space. We study the electronic energy loss of slow He²âº, C²âº, and C4⁺ ions penetrating the graphene fragment as a function of the ion velocity, and establish the velocity-proportional energy loss for low-charged ions down to 0.1 a.u. One mechanism clarified in the simulations for electron transfer is polarization capture, which is effective for bare ions at low velocities. The other one is resonance capture, by which the incident ion can capture electrons from the graphene fragment to its electron affinity levels, which have the same, or nearly the same, energy as those of the electron donor levels. The results demonstrate that the nonlinear behavior of energy loss of C4⁺ is attributed to the large number of electrons captured by this multi-charged ion during the collision.

Electron-ion coupling effects on radiation damage in cubic silicon carbide.

A two-temperature model has been used to investigate the effects of electron-ion coupling on defect formation and evolution in irradiated cubic silicon carbide. By simulating 10 keV displacement cascades under identical primary knock-on atom conditions, we find that the final displacement and the kinetic energy of the primary knock-on atom decrease rapidly with increasing electron-ion coupling strength. Moreover, by analyzing the number of peak defects, atomic and electronic temperatures, it is found that a higher number of peak defects is created for intermediate coupling strength due to the electronic temperature making a contribution to the disorder. Strong electron-ion coupling rapidly removes energy from the cascade, thus the number of peak defects is lower. Meanwhile, there is a non-monotonic trend in the relationship between the coupling strength and the time at which the temperature of atoms reaches the minimum. Furthermore, we discuss the mechanisms involved.

[Spatiotemporal dynamic fuzzy evaluation of wetland environmental pollution risk in Dayang estuary of Liaoning Province, Northeast China based on remote sensing].

Based on the aerial image data of Dayang estuary in 2008, and by virtue of Analytic Hierarchy Process (AHP) , remote sensing technology, and GIS spatial analysis, a spatiotemporal evaluation was made on the comprehensive level of wetland environmental pollution risk in Dayang estuary, with the impacts of typical human activities on the dynamic variation of this comprehensive level discussed. From 1958 to 2008, the comprehensive level of the environmental pollution risk in study area presented an increasing trend. Spatially, this comprehensive level declined from land to ocean, and showed a zonal distribution. Tourism development activities unlikely led to the increase of the comprehensive level, while human inhabitation, transportation, and aquaculture would exacerbate the risk of environmental pollution. This study could provide reference for the sea area use planning, ecological function planning, and pollutants control of estuary region.

[Changes of wetland landscape pattern in Dayang River Estuary based on high-resolution remote sensing image].

Based on the comprehensive consideration of the high resolution characteristics of remote sensing data and the current situation of land cover and land use in Dayang River Estuary wetland, a classification system with different resolutions of wetland landscape in the Estuary was established. The landscape pattern indices and landscape transition matrix were calculated by using the high resolution remote sensing data, and the dynamic changes of the landscape pattern from 1984 to 2008 were analyzed. In the study period, the wetland landscape components changed drastically. Wetland landscape transferred from natural wetland into artificial wetland, and wetland core regional area decreased. Natural wetland's largest patch area index descended, and the fragmentation degree ascended; while artificial wetland area expanded, its patch number decreased, polymerization degree increased, and the maximum patch area index had an obvious increasing trend. Increasing human activities, embankment construction, and reclamation for aquaculture were the main causes for the decrease of wetland area and the degradation of the ecological functions of Dayang River Estuary. To constitute long-term scientific and reasonable development plan, establish wetland nature reserves, protect riverway, draft strict inspective regimes for aquaculture reclamation, and energetically develop resource-based tourism industry would be the main strategies for the protection of the estuarine wetland.