Twin boundary spacing-dependent deformation behaviours of twinned silver nanowires

Twin boundary spacing (TBS) plays a significant role in the yield behaviour of twinned nanowires (NWs). However, few studies have shown an overall view of the effects on the mechanical response of twinned silver NWs under tensile loading. In this article, the mechanical properties of 〈111〉-oriented NWs with different TBSs are studied using molecular dynamics simulations. In elastic region, it is found that the addition of twin boundaries (TBs) to crystalline NWs can not only cause strengthening but also softening effect, which depending on the S_T/S_F (the ratio of the total area of TBs to the area of lateral free surfaces). Furthermore, our simulation results show that the evolution of reduced number of different types of atoms in twinned Ag NWs has a strong dependence on TBS. For twinned NWs with larger TBSs, the dislocation–TB interaction dominates the plastic deformation process. While for twinned NWs with smaller TBSs, shear banding is activated as the incipient plastic deformation, leading to the atoms clustering into disorder near the surfaces. The study will be helpful to the further understanding of TB-related mechanical properties of nanomaterials.     

The deformation behaviour of silver nanowires with kinked twin boundaries under tensile loading

ABSTRACT

Atomistic simulations are used to investigate the mechanical properties of silver nanowires (NWs) with kinked twin boundaries (TBs) under tensile loading. For comparison, a different ledge width of twinned NWs with both square and circular kink-steps are considered in this study. The embedded-atom-method potential is employed to describe the atomic interactions. To identify the defect evolution and incipient plastic deformation mechanism, the centrosymmetry parameter is implemented in our self-developed programme. Twinned NWs with both square and circular ledges are shown to have a reduced impact on yield stress as compared to their perfect TBs counterpart models in elastic deformation. In twinned NWs with rectangular ledges, a strain-hardening effect was observed in defective NWs. The incipient plastic deformation is influenced by the ledge width. While in twinned NWs with circular ledges, the ledges rather than the surface effect are the only dislocation source in their incipient plastic deformation. Our findings offer a view of imperfection in twinned NWs, and it is believed that the attention being paid to defective TBs will be helpful to further understanding of the mechanical properties of TB-strengthened NWs.     

Effects of crystal orientation and aspect ratio on plastic response of aluminium nanowires under torsion

The plastic response of perfect face-centred cubic single-crystal aluminium (Al) nanowires (NWs) under torsion is studied using molecular dynamics simulations. The Al–Al interaction is described by the many-body tight-binding potential. The effects of the crystal orientation and aspect ratio of the NWs on their deformation are evaluated in terms of atomic trajectories, potential energy, a centrosymmetry parameter and the torque required for deformation. Simulation results clearly show that for NWs, regardless of crystal orientation, dislocations nucleate and propagate on the (1 1 1) close-packed plane. In a NW under torsion, dislocations begin at the surface, extend to the interior along the (1 1 1) close-packed plane and finally diffuse to the middle part. A 〈1 1 0〉-oriented NW has the lowest required torque for deformation due to the occurrence of homogeneous deformation. The mechanism of the plastic response of an Al NW depends on its crystal orientation. For a long NW, geometry instability occurs before material instability (buckling).     

Effect of temperature on welding of metallic nanowires investigated using molecular dynamics simulations

The mechanism of welding of Au–Au, Ag–Ag and Au–Ag nanowires (NWs) with head-to-head contact is studied using molecular dynamics simulations based on the second-moment approximation of the many-body tight-binding potential. The effect of temperature in the range of 300–900 K is investigated. Simulation results show that at the initial welding, an incomplete jointing area forms through the interactions of the van der Waals attractive force, and that the jointing area increases with increasing the extent of contact between the two NWs during the welding process and temperature. Few defects form along the (1 1 1) close-packed plane during the welding process because the acting stress is quite low. Among the three NW pairs, the Au–Au NWs have the best cold-welding quality, whereas the Au–Ag NWs have the worst cold-welding quality due to the welding of different materials. With an increase in temperature, the weld stress and the mechanical strength of the NWs significantly decrease, and the number of disordered structures increases. The welding fails when the temperature exceeds the molten temperature of the NWs.     

Investigation on the mechanical behaviour of faceted Ag nanowires

Using molecular-dynamic (MD) simulation, we investigated the mechanical response of faceted silver nanowires (NWs) to tensile deformations. The investigation considers different frustum heights, temperatures and 3D void effects to study the yield elasticity, incipient plasticity and ductility of the faceted NWs. The embedded-atom-method (EAM) potential is employed to describe the atomic interactions. To identify the defect evolution and deformation mechanism, the centrosymmetry parameter is implemented in our self-developed programme. A detailed discussion of surface-dominated deformation behaviour has been presented. It is found that the faceted NWs show brittle breaking behaviour in low temperature, which has never been reported in other NWs. This temperature-dependent breaking mode, as reported in this paper, might be useful in avoiding certain deformation mechanisms of metallic NWs in future.     

Modifying and Fine Controlling of Silver Nanoparticle Nucleation Sites and SERS Performance by Double Silicon Etching Process

Different forms of modified and well-controlled plasmonic silver nanoparticles (AgNPs) were synthesized by silver ion reduction process of porous silicon (PS). Fine control of PS surface morphology was accomplished by employing two etching processes: light-induced etching (LIE) and photo electrochemical etching (PECE). The idea was to prepare excellent and reproducible surface-enhanced Raman scattering (SERS) substrates with high enhancement performance. PS surface modification was employed to create efficient and nearly uniformly distributed AgNP hotspot regions with very high specific surface areas. Reproducibility deviation of no more than 5% and enhancement factor of 1.2 × 10¹⁴ were obtained by SERS measurements at very low, rhodamine 6G (R6G) dye, concentration 10^?15 M. The PS morphology SERS substrate was well discussed and analyzed using field emission scanning electron microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), and Raman measurements.     

Preparation,characterization of silver phyto nanoparticles and their impact on growth potential of Lupinus termis L. seedlings

The current study reports rapid and easy method for synthesis of eco-friendly silver nanoparticles (AgNPs) using Coriandrum sativum leaves extract as a reducing and covering agent. The bio-reductive synthesis of AgNPs was monitored using a scanning double beam UV-vis spectrophotometer. Transmission electron microscopy (TEM) was used to characterize the morphology of AgNPs obtained from plant extracts. X-ray diffraction (XRD) patterns of AgNPs indicate that the structure of AgNPs is the face centered cubic structure of metallic silver. The surface morphology and topography of the AgNPs were examined by scanning electron microscopy and the energy dispersive spectrum revealed the presence of elemental silver in the sample. The silver phyto nanoparticles were collected from plant extract and tested growth potential and metabolic pattern in (Lupinus termis L.) seedlings upon exposure to different concentrations of AgNPs. The seedlings were exposed to various concentrations of (0, 0.1, 0.3 and 0.5 mg L^?1) AgNPs for ten days. Significant reduction in shoot and root elongation, shoot and root fresh weights, total chlorophyll and total protein contents were observed under the higher concentrations of AgNPs. Exposure to 0.5 mg L^?1 of AgNPs decreased sugar contents and caused significant foliar proline accumulation which considered as an indicator of the stressful effect of AgNPs on seedlings. AgNPs exposure resulted in a dose dependent decrease in different growth parameters and also caused metabolic disorders as evidenced by decreased carbohydrates and protein contents. Further studies needed to find out the efficacy, longevity and toxicity of AgNPs toward photosynthetic system and antioxidant parameters to improve the current investigation.     

A role for Notch signaling in trophoblast endovascular invasion and in the pathogenesis of pre-eclampsia

Placental trophoblasts (TBs) invade and remodel uterine vessels with an arterial bias. This process, which involves vascular mimicry, re-routes maternal blood to the placenta, but fails in pre-eclampsia. We investigated Notch family members in both contexts, as they play important roles in arterial differentiation/function. Immunoanalyses of tissue sections showed step-wise modulation of Notch receptors/ligands during human TB invasion. Inhibition of Notch signaling reduced invasion of cultured human TBs and expression of the arterial marker EFNB2. In mouse placentas, Notch activity was highest in endovascular TBs. Conditional deletion of Notch2, the only receptor upregulated during mouse TB invasion, reduced arterial invasion, the size of maternal blood canals by 30-40% and placental perfusion by 23%. By E11.5, there was litter-wide lethality in proportion to the number of mutant offspring. In pre-eclampsia, expression of the Notch ligand JAG1 was absent in perivascular and endovascular TBs. We conclude that Notch signaling is crucial for TB vascular invasion.     

Monte Carlo simulations of structure and entanglements in polymer melts

Atomistic models of short chain branched (SCB) polyethylene melts have been equilibrated at 450 K using a connectivity altering Monte Carlo method. Quantities related to the chain dimensions and entanglements have been determined. The simulated tube diameters, 〈a_pp〉, of SCB melts are found to scale with the backbone weight fraction, ?, as 〈a_pp〉～?^? 0.46, close to the scaling predicted by the binary contact model, 〈a_pp〉～?^? 0.5. Similar relationships are observed experimentally for polymer solutions, and reproduced by the present methods.     

Absorption Enhancements in Plasmonic Solar Cells Coated with Metallic Nanoparticles

We find that three mechanisms lead to the absorption enhancements of light in a thin-film amorphous silicon solar cell coated with a periodic array of silver nanoparticles on the rear surface according to our simulation. They are localized surface plasmon modes of the silver nanoparticles, Fabry–Pérot resonant cavity modes and waveguide effects. Each enhancing mechanism can yield a maximum absorption enhancement of over two times at the corresponding resonant wavelengths when the nanoparticles cover 20 % of the solar cell surface, and an average absorption enhancement of up to 57 % can be achieved in the AM 1.5 G solar spectrum. The absorption enhancements can also be tuned in spectrum to optimize the total absorption in a plasmonic solar cell.     

Ultrasurface structure of oromandibular area in a hill stream teleost Glyptothorax trilineatus Blyth, 1860

Ultrasurface structure of the oromandibular area of a hillstream catfish Glyptothorax trilineatus Blyth 1860, an inhabitant of the sub‐Himalayan streams of India is described. Scanning electron microscopic (SEM) study of these areas revealed a series of punctuation elevation from the general surface epithelium. Two types (types I and II) of taste buds (TB) could be identified where one type is with microvillar projections and others without any projection. Another type of cell, the basal cells, without any apical microvilli was also recorded. TBs were more concentrated on the ventral surface of the barbels. In most of the TBs, the pore is located at the centre of the elevation and surrounded by a circular area. Jaw sheath bears a single type of teeth, the papilliform teeth.     

In Situ Optical Extinction Measurement for Locally Control of Surface Plasmon Resonance During Nanosecond Laser Irradiation of Silver Ion Exchanged Silicate Glass

Online UV/visible extinction measurement have been achieved during nanosecond Nd:YAG laser irradiation at 532 nm of a silver-exchanged silicate glass after each shot. We have explained the evolution of the integrated spectral evolution with the help of a few observed spots after the laser/glass interaction and completed them by optical and surface measurements. This optical method allows to in situ follow silver ions precipitation in nanoparticles (NPs) and the consequently surface plasmon resonance evolution (SPR). In this study, we focus on the interest of this method for one silver-exchanged soda-lime glass by direct observation of the sample surface. Scanning electron microscopy measurement and optical microscopy were used to identify the various ablation mechanisms. Profilometry was used to evaluate the material distribution and the surface roughness evolution (Rms parameter). Thus, we explain the silver NPs effect on glass matrix at various micrometric scales according to the deposited fluence and silver concentration.     

Introducing tree belt designer - A QGIS plugin for designing agroforestry systems in terms of potential insolation

Agroforestry systems support all categories of ecosystem services (ESs). In providing the regulating category of ESs, these systems have become an important strategy used to attenuate drought impacts and biodiversity losses on agricultural landscapes. Within the agroforestry design process aimed at ES provision, one of the agroforestry types used is tree belts (TBs). Unfortunately, due to the inappropriate spatial arrangement of TBs, agricultural landscapes often become too shaded or too sunny. In existing agricultural models of the TB impact on light conditions, only the average values of all TB parameters are considered. Moreover, these models can only be used for whole study plots, or a given plot can be divided into several zones parallel to the TB. Therefore, we developed the QGIS plugin to design TB simulations on a spatially continuous scale for more effective estimation of their impact on potential insolation. The design process is based on the user library containing the tree and shrub species, soil data, parcel-based layout, and digital surface model. In this study, we tested our plugin and its outcomes in terms of predicting changes in potential insolation.     

The novel human MRC1 gene polymorphisms are associated with susceptibility to pulmonary tuberculosis in Chinese Uygur and Kazak populations

The MRC1 gene, encoding the human mannose receptor (MR), is a member of the C-type lectin receptors family. MR can recognize and bind to Mycobacterium tuberculosis by the extracellular structure, and play a role in antigen-presenting and maintaining a stable internal environment. This study aimed to investigate potential associations of SNPs in exon 7 of the MRC1 gene with pulmonary tuberculosis (TB). G1186A, G1195A, T1212C, C1221G, C1303T and C1323T were genotyped using PCR and DNA sequencing in 595 Chinese Uygur and 513 Kazak subjects. In the Uygur, the frequency of allele G (P = 0.031, OR = 1.29, 95 % CI = 1.02–1.62) and AA genotype (P = 0.033, OR = 1.64, 95 % CI = 1.04–2.60) for G1186A was lower in the pulmonary TB than healthy control and were significantly correlated with pulmonary TB. After adjustment for age and gender, G1186A was found to be additive models in association with pulmonary TB (P = 0.04, OR = 1.27, 95 % CI = 1.01–1.60). By calculating linkage disequilibrium, the frequency of haplotype GGTCCT (P = 0.032, OR = 0.75, 95 % CI = 0.57–0.97) and GGTCCC (P = 0.044, OR = 0.57, 95 % CI = 0.33–0.99) was significantly associated with pulmonary TB. No association was found between other SNPs and pulmonary TB. In the Kazak, all SNPs were not associated with pulmonary TB. Our results suggest that genetic factors play an important role in susceptibility to pulmonary TB at the individual level, and provide an experimental basis to clarify the pathogenesis of pulmonary TB.     

Identification of genetic associations of SP110/MYBBP1A/RELA with pulmonary tuberculosis in the Chinese Han population

Genetic factors play important roles in the development of tuberculosis (TB). SP110 is a promising candidate target for controlling TB infections. However, several studies associating SP110 single nucleotide polymorphisms (SNPs) with TB have yielded conflicting results. This may be partly resolved by studying other genes associated with SP110, such as MYBBP1A and RELA. Here, we genotyped 6 SP110 SNPs, 8 MYBBP1A SNPs and 5 RELA SNPs in 702 Chinese pulmonary TB patients and 425 healthy subjects using MassARRAY and SNaPshot methods. Using SNP-based analysis with Bonferroni correction, rs3809849 in MYBBP1A [Pcorrected (cor) = 0.0038] and rs9061 in SP110 (Pcor = 0.019) were found to be significantly associated with TB. Furthermore, meta-analysis of rs9061 in East Asian populations showed that the rs9061 T allele conferred significant risk for TB [P = 0.002, pooled odds ratio (OR), 1.24, 95 % confidence interval (CI) = 1.08–1.43]. The MYBBP1A GTCTTGGG haplotype and haplotypes CGACCG/TGATTG within SP110 were found to be markedly and significantly associated with TB (P = 2.00E?06, 5.00E?6 and 2.59E?4, respectively). Gene-based analysis also demonstrated that SP110 and MYBBP1A were each associated with TB (Pcor = 0.011 and 0.035, respectively). The logistic regression analysis results supported interactions between SP110 and MYBBP1A, indicating that subjects carrying a GC/CC genotype in MYBBP1A and CC genotype in SP110 possessed the high risk of developing TB (P = 1.74E?12). Our study suggests that a combination of SP110 and MYBBP1A gene polymorphisms may serve as a novel marker for identifying the risk of developing TB in the Chinese Han population.     

Lectin histochemistry on mucous substances of the taste buds and adjacent epithelia of different vertebrates

In the present study carbohydrate residues in taste buds (TBs) and adjacent epithelial formations of a teleostean fish, a frog and the rabbit were detected by means of lectin histochemistry. Biotinylated lectins from Pisum sativum (PSA), Arachis hypogaea (PNA), Dolichos biflorus (DBA), Triticum vulgaris (WGA and succinylated WGA), Glycine max (SBA) and Ulex europaeus (UEA I) have been applied. The lectins were bound to an avidin-biotin-peroxidase-complex (ABC) and visualized by diaminobenzidine/H2O2. Most intensive reactivity was observed at the taste disc cells of the frog with DBA, S-WGA and SBA. PNA did not bind to the TBs of any of the animals tested. As shown in SBA preparations, sialic acid is present in a nonacylated and an acylated form in the mucosa of the frog's tongue. The TBs of the fish possess all the sugars we looked for except for the disaccharide D-galactose-(1-3)-beta-D-N-acetyl-galactosamine (Gal/GalNAc) and sialic acid. The TBs of the rabbit contain GalNAc, as detected with DBA, but not with SBA; and fucose (Fuc), mannose (Man) and N-acetyl-glucosamine (GlcNAc). As revealed by preincubation of the tissue sections with neuraminidase in TB cells of the rabbit, sialic acid masks Gal/GalNAc and GalNAc. These lectin-binding characteristics show that in the TBs of some selected representatives which belong to different vertebrate classes exist different mucous substances. These substances possess different binding characteristics to specific sugars, and this is possibly of particular interest to chemoreception phenomena.     

Effects of the nitrogen doping configuration and site on the thermal conductivity of defective armchair graphene nanoribbons

The influence of the nitrogen (N) doping configuration on the thermal conductivity (TC) of armchair graphene nanoribbons (AGNRs) of size 15.7 nm × 7.26 nm was investigated using classical molecular dynamics (MD) simulations with the optimized Tersoff potential at room temperature. The effect of changing the N-doping site in defects on the TC of AGNRs was also investigated in detail. The variations with N concentration of the TCs of AGNRs presenting graphitic N (quarternary N), pyridinic N, and pyrrolic N doping configurations were studied. Results of MD simulations showed that, among these three doping configurations, pyridinic N was associated with the highest TC, and pyrrolic N with the lowest TC. The highest TC values were obtained when the N dopant atoms were located at the edges and at defects in the AGNR. The presence of both pyrrolic N and Stone–Wales type 1 (SW-1) defects led to a higher TC than the presence of both pyrrolic N and SW-2 defects. Phonon–defect scattering was found to be influenced by changes in C–C bond orientation. SW-1 defects were found to exert a greater influence on the TC than graphitic N doping. Furthermore, the influence on the TC of the N-doping site location in SW-1 defects was examined. Doping the central sites of SW-1 defects was found to yield higher TC values than doping the edge sites of defects. Graphitic-N doping of the more central sites in a SW-1 defect led to a higher TC than the random graphitic-N doping of sites in a SW-1 defect.     

Theoretical calculation on the reaction of alkene molecules on H-terminated Si(100)-3×1 surface

A study on mechanisms of radical initiated surface chain reaction of ethylene molecule on H-terminated Si(100)-3 × 1 has been carried out in a supercell approach by using density functional theory and ab initio molecular dynamic method. On the H-terminated Si(100)-3 × 1 surface, one of the crucial steps of the surface chain reaction, namely, the abstraction of a H atom from a nearby surface hydride unit, is found to have a somewhat smaller activation energy from the nearest silicon site than from the next-nearest silicon site. From the intermediate state to the final state, the transition state has bigger activation energy. Ab initio molecular dynamics (MD) shows that the H-abstraction on Si(100)-3 × 1 surface bound organic group with a carbon-centered radical is very easy to be obtained from the transition state, and it also shows that the C…H bond at methyl group is formed in a very short MD time, and the Si…C bond between the Si surface and the alkyl chain oscillates with time evolution on Si(100)-3 × 1 surface.     

Influence of Femtosecond Laser Ablated Silver Nanoparticles on the Nonlinear Optical Properties of Basic Fuchsin dye

We investigate the linear and nonlinear optical properties of Basic Fuchsin influenced by femtosecond laser ablated silver nanoparticles in deionised water. Single beam z-scan technique using a Q-switched Nd:YAG laser (Spectra PhysicsLAB-1760, 532 nm, 7 ns, 10 Hz) is used for the present study. Quenching of fluorescence is observed in the presence of silver nanoparticles. Transmission electron microscopic observation reveals that the nanoparticles are spherical in shape, with an average size of 7 nm. The samples show self-defocusing nonlinearity and better nonlinear absorption behavior in the presence of silver sol. The nonlinear absorption varies with varying input fluence and concentration. The results show that the variations in the nonlinear parameters are also due to the surface plasmon resonance of silver nanoparticles. The nonlinearity of the dye is increased in the presence of silver nanoparticles, which makes the material suitable for various photonic and optoelectronic applications.