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Skyrmions can form regular arrangements, so-called skyrmion crystals (SkXs). A mode with multiple wavevectors qthen describes the arrangement. While magnetic SkXs, which can emerge in the presence of Dzyaloshinskii–Moriya interaction, are well established, polar skyrmion lattices are still elusive. Here we report the observation of polar SkXs with a well-defined double-qstate in ultrathin BiFeO3films on LaAlO3. The compressive strain induced by the LaAlO3substrate yields a dipolar topological texture with a periodic arrangement of skyrmions. The square-like superstructure with a lattice constant of 2.68 nm features a periodic modulation of polarization fields and topological charge density. The film furthermore exhibits an enhanced electromechanical response with an increased converse piezoelectric coefficient (d33) compared with SkX-free films. Transmission electron microscopy experiments in combination with phase-field simulations indicate that the dipole skyrmion texture results from the interference of two orthogonal single-qdipole patterns. We anticipate that the interference of multiple wavevectors may lead to a diversity of topological crystals with a variety of symmetries and lattice constants.

We reveal by first-principles calculations that the interlayer binding in a twisted MoS2/MoTe2heterobilayer decreases with the increasing twist angle, due to the increase of the interlayer overlapping degree, a geometric quantity describing well the interlayer steric effect. The binding energy is found to be a Gaussian-type function of the twist angle. The resistance to rotation, an analogue to the interlayer sliding barrier, can also be defined accordingly. In sharp contrast to the case of the MoS2homobilayer, here the energy band gap reduces with the increasing twist angle. We find a remarkable interlayer charge transfer from MoTe2to MoS2, which enlarges the band gap, but this charge transfer weakens with greater twisting and interlayer overlapping degree. Our discovery provides a solid basis in twistronics and a practical instruction in band structure engineering of van der Waals heterostructures.

A topological meron features a non-coplanar structure, whose order parameters in the core region are perpendicular to those near the perimeter. A meron is half of a skyrmion, and both have potential applications for information carrying and storage. Although merons and skyrmions in ferromagnetic materials can be readily obtained via inter-spin interactions, their behaviour and even existence in ferroelectric materials are still elusive. Here we observe using electron microscopy not only the atomic morphology of merons with a topological charge of 1/2, but also a periodic meron lattice in ultrathin PbTiO3films under tensile epitaxial strain on a SmScO3substrate. Phase-field simulations rationalize the formation of merons for which an epitaxial strain, as a single alterable parameter, plays a critical role in the coupling of lattice and charge. This study suggests that by engineering strain at the nanoscale it should be possible to fabricate topological polar textures, which in turn could facilitate the development of nanoscale ferroelectric devices.

Using first-principles calculations combined with a semiempirical van der Waals dispersion correction, we have investigated structural parameters, mixing enthalpies, and band gaps of buckled and planar few-layer InxGa1–xN alloys. We predict that the band gaps of buckled InxGa1–xN alloys with hydrogen passivation can be tuned from 5.6 to 0.7 eV with preservation of direct band gap and well-defined Bloch character, making them promising candidate materials for future light-emitting applications. Unlike that in their bulk counterparts, the phase separation could be suppressed in these two-dimensional systems because of reduced geometrical constraints. The disordered planar thin films undergo severe lattice distortion, nearly losing the Bloch character for valence bands, whereas the ordered planar ones maintain the Bloch character yet with the highest mixing enthalpies.

Using density functional theory combined with a semiempirical van der Waals dispersion correction, we have investigated the stability of lattice defects including boron vacancy, substitutional and interstitial X (X = H, C, B, N, O), and Σ5 tilt grain boundaries in borophene and their influence on the anisotropic mechanical properties of this two-dimensional system. The pristine borophene has significant in-plane Young’s moduli and Poisson’s ratio anisotropy due to its strong and highly coordinated B–B bonds. The concentration of B vacancy and Σ5 grain boundaries could be rather high given that their formation energies are as low as 0.10 and 0.06 eV/Å, respectively. In addition, our results also suggest that borophene can react easily with H2, O2, and N2when exposed to these molecules. We find that the mechanical strength of borophene is remarkably reduced by these defects. The anisotropy in Poisson’s ratio, however, can be tuned by some of them. Furthermore, the adsorbed H or substitutional C may induce negative Poisson’s ratio in borophene, and the substitutional C or N can significantly increase the Poisson’s ratio by constrast.

We report a first-principles study on the initial deposition of Li2O2on three rutile oxide surfaces, RuO2(110)-(1×1)-O, TiO2(110), and SnO2(110). The intermediate discharge product in a Li–air battery, LiO2, is found to be less stable on all rutile surfaces and will be further reduced to Li2O2through disproportionation reaction. For the first and second layers of deposited Li2O2, the adsorption energy is comparable to the cohesive energy of bulk Li2O2, suggesting Li2O2will likely wet the oxide surfaces and grow into thin films rather than particles. Electronic structure analyses of interfaces demonstrate Li2O2/TiO2(110) is metallic and Li2O2/SnO2(110) is semiconducting with a bandgap of 0.2 eV, substantially smaller than in bulk Li2O2. The large lattice mismatch at these interfaces could create amorphousness of Li2O2and grain boundaries might form abundantly thereafter, both of which can provide charge and ion transport channels needed for oxygen reduction and evolution reactions in Li–air batteries. Therefore, coating nanostructured carbon cathode with thin films of TiO2or employing mesoporous TiO2nanostructures as cathode could possibly lead to the formation of low-resistance Li2O2thin films and thereby enhance the rate capacity of Li–air batteries.

The dominant discharge product in Li–air batteries, lithium peroxide (Li2O2), is intrinsically a wide band gap insulator as a perfect crystal. Recent density functional theory studies have suggested both vacancy- and polaron-mediated electron transportation mechanisms. We here show computational evidence from both semilocal and hybrid density functional calculations that the Σ3(11̅00)[112̅0] tilt grain boundaries (GBs) in Li2O2can produce spin-polarized gap states. For each type of Σ3 GBs, GB1, GB2, and GB2* which has different atomic layer as the mirror plane, we have examined stoichiometric and a number of O-rich chemistry and find that stable geometry can take both forms. We find stoichiometric GBs disturb negligibly the electronic structure of Li2O2, yet the O-rich GBs produce spin-polarized gap states in a similar manner to free surface cases. Lithium deficiency leads to compression of interfacial O–O bonds, enlarges the πp–πp* split, and pushes up the antibonding πp* to (GB2) or beyond (GB2*) the Fermi energy. As a result, GB2 becomes half-metallic and GB2* becomes semiconducting with a small band gap of 1.0 eV. In both cases, spin polarization of O ions help to stabilize the GB by leaving the up spin of its gap states shifted down below the Fermi level and the down spin states open. Since Li2O2is always polycrystalline as a discharge product, the presence of GBs may enhance conductivity.

Carbon coating substantially promotes electron transport through LiFePO4nanoparticles at the positive electrode in Li-ion batteries and approaches to forming thin, tightly attached, and uniform carbon layers are extremely desirable. On the basis of our recent first principles computational discovery that the graphite crystallites are more likely standing on the LiFePO4(010) surface via C–O bonding rather than lying on van der Waals forces, we have in this work searched promising co-coating substances which can reinforce the perpendicular orientation of graphite crystallites by strengthening the C/LiFePO4binding. Among the three supervalent elements we have studied, Sc (3+), Ti (4+), and V (5+), Sc and Ti are found to show good performance. The binding energy of perpendicular graphite on the LiFePO4(010) surface increases noticeably from 0.52 to 0.58 (Sc) and 0.61 (Ti) eV/Å, whereas the binding of a parallel graphene sheet with the same surface is nearly unchanged. A strengthened perpendicular graphite orientation is very welcome for leaving diffusion channels of Li unblocked.

Coating carbon layers on LiFePO4nanoparticles used in Li-ion batteries greatly increase the electron transport in this cathode material. Using first-principles density functional theory calculations, we have theoretically investigated the interaction energies of graphene lying parallel and perpendicular to a LiFePO4 (010) surface and have found that the perpendicular orientation is energetically favorable. Our computations suggest that graphene nanosheets prefer standing vertically on LiFePO4(010) using C–O and C–Fe bonding rather than spreading on it, as has been widely assumed. The interfacial chemical bonding both fastens the coated carbon layer and facilitates electron conductivity across the interface. By contrast, encapsulating LiFePO4with parallel graphene sheets does not increase electron conductivity across the interface.

The Drosophila imaginal cells that produce epidermal hairs, the shafts of sensory bristles and the lateral extensions of the arista are attractive model systems for studying the morphogenesis of polarized cell extensions. We now report the identification and characterization of furry, an essential Drosophila gene that is involved in maintaining the integrity of these cellular extensions during morphogenesis. Mutations in furry result in the formation of branched arista laterals, branched bristles and a strong multiple hair cell phenotype that consists of clusters of epidermal hairs and branched hairs. By following the morphogenesis of arista laterals in pupae, we have determined that the branched laterals are due to the splitting of individual laterals during elongation. In genetic mosaics furry was found to act cell autonomously in the wing. The phenotypes of double mutant cells argue that furry functions independently of the frizzled planar polarity pathway and that it probably functions in the same pathway as the tricornered gene. We used a P-element insertion allele as a tag to clone the furry gene and found it to be a large and complicated gene that encodes a pair of large conserved proteins of unknown biochemical function.

It has been proposed that the reorganization of components of the actin cytomatrix could contribute to force development and the low energy cost of sustained contraction in contractile cells which lack a structured sarcomere (A.S. Battistella-Patterson, S. Wang and G.L. Wright (1997) Can J Physiol Pharmacol75:1287–1299). However, there has been no direct evidence of an apropos actin reorganization specifically linked to the contractile response in cells of this type. Remodeling of the α- and β-actin domains was studied in A7r5 smooth muscle cells during phorbol 12,13 dibutyrate (PDB)-induced contraction using immunohistologic staining and β-actin-green fluorescent protein (β-actin-GFP) fusion protein expression. Cell stained with phalloidin as well as cells expressing β-actin-GFP showed densely packed actin stress cables, arranged in parallel and extending across the cell body. PDB caused approximately 85% of cells to contract with evidence of forcible detachment from peripheral adhesion sites seen in many cells. The contraction of the cell body was not uniform but occurred along a principal axis parallel to the system of densely packed β-actin cables. During the interval of contraction, the β-actin cables shortened without evidence of disassembly or new cable formation. The use of cytochalasin to inhibit actin polymerization resulted in the dissolution of the actin cables at the central region of the cell and caused the elongation of precontracted cells. In unstimulated cells, α-actin formed cables similar in arrangement to the cell spanning β-actin cables. Within a short interval after PDB addition; however, the majority of α-actin cables disassembled and reformed into intensely fluorescing column-like structures extending vertically from the cell base at the center of clusters of α-actin filaments. The α-actin columns of contracting cells showed strong colocalization of α-actinin suggesting they could be structurally analogous to the dense bodies of highly differentiated smooth muscle cells. The results indicate that the α- and β-actin domains of A7r5 cells undergo a highly structured reorganization during PDB-induced contraction. The extent and nature of this restructuring suggest that remodeling could play a role in contractile function.

The uptake of estrone sulfate (E1S; 1 to 400 microM), harmol sulfate (HS; 5 to 900 microM), and 4-methylumbelliferyl sulfate (4MUS; 5 to 1000 microM) was investigated in isolated rat hepatocytes in the presence or absence of inhibitors. Uptake of all of the sulfate conjugates was rapid and exhibited saturation kinetics, best characterized by saturable and nonsaturable (linear transmembrane clearance) transport systems. The KM's were: 16 +/- 6, 123 +/- 28, and 64 +/- 6 microM for E1S, HS, and 4MUS, respectively, with corresponding Vmax's of 0.85 +/- 0.56, 0.48 +/- 14, and 0.42 +/- 0.07 nmol/min/10(6) cells. The nonsaturable uptake clearances, which displayed concentration-independent uptake, were 3 +/- 2, 1 +/- 0.1, 0.5 +/- 0.1 microliter/min/10(6) cells, respectively. Uptake of E1S was inhibited by ouabain (1 mM) and replacement of sodium by choline, whereas HS was insensitive to the addition or substitution. Uptake of both E1S and HS was significantly reduced by metabolic inhibitors (antimycin A, 2.7 microM, rotenone, 30 microM, and KCN, 2 mM) and temperature reduction (from 37 to 27 degrees C). 4,4'-Diisothiocyanostilbene-2-2-'disulfonic acid (2 mM), an inhibitor of anion transport, reduced E1S and HS uptake; E1S uptake was also reduced by HS. HS uptake by both saturable and nonsaturable transport components was depressed by 4MUS (300 microM); the apparent KM was increased by 83% while the Vmax remained unaltered, and the nonsaturable component was decreased by 48%. The data strongly suggest that multiple pathways exist for the uptake of E1S, HS, and 4MUS. E1S uptake is sodium-dependent, requires energy, and is inhibited by anions such as 4,4'diisothiocyanostilbene-2-2'-disulfonic acid and other sulfate conjugates. HS uptake, while being energy dependent, is not sodium dependent, and is inhibited by 4MUS in a competitive fashion. At least one of these pathways is shared.

A tweed-like structure with striated contrast has been observed in an Al62Cu17.5Co17.5Si3 decagonal quasicrystal, for the first time, by using conventional electron diffraction contrast imaging and high-resolution electron microscopy images. The contrast of these striations, as observed under two-beam conditions, is different from that resulting from dislocations, stacking faults and small-angle grain boundaries in quasicrystals, and it can be interpreted as being due to quasilattice distortions introduced by the lattice misfit between the decagonal quasicrystal matrix and the local ordering.

Misfit dislocations at the interface between Al65Cu20Co15 and Al63Cu20CO15Si3 decagonal quasicrystals and their epitaxial crystalline layers have been observed by transmission electron microscopy. Conventional contrast experiments and high-resolution electron microscopy show that the interface dislocations are in the epitaxial crystalline layer with the B2 structure.

Abstract:  Rat aortic rings maintained in organ culture for as little as 24 h show significant loss of contractile responsiveness to different agonists. Smooth muscle cells (SMC) in culture quickly de differentiate into a non-contractile phenotype with a marked capacity for proliferation. Rat aortic ring segments cultured in retinol supplemented (10–6 M) medium showed significantly increased active tension development in response to 80 mM K+ depolarization compared with 7-day cultured control rings. The improvement of contractile performance of the cultured aorta segments in retinol-supplemented media was lost when rings were denuded of endothelium prior to culture, suggesting the endothelial cell layer as the mediator of this effect. Retinol at concentrations up to 10–5 M was found to have no direct effect on proliferation of cells of the A7r5 SMC. However, retinol was found to augment significantly the growth inhibition of A7r5 cells grown in co-culture with bovine aortic endothelial cells (BAEC). It was further observed that media conditioned with BAEC treated with 10–6 M retinol expressed SMC growth inhibitory properties compared with media conditioned by untreated BAEC cells or unconditioned media. Examination of cultured rat aortic ring segments by electron microscopy and BAEC cells with phase contrast microscopy revealed that retinol had obvious effects on endothelial cell morphology and ultrastructure. These results indicate that retinol exerts its effects primarily on the endothelium, which in turn secretes stable factors that directly affect SMC proliferation and contractility.

Prilocaine is assumed to undergo significant elimination by extrahepatic organs and to differ in this respect from other commonly used local anaesthetics. In order to clarify whether the lung may play an important role as a site of elimination of prilocaine, the kinetic parameters were studied in isolated perfused rat lungs and were compared to those of isolated livers. Furthermore, the structurally related compounds bupivacaine and mepivacaine were also investigated in this system. Prilocaine was dispersed into a relatively large apparent distribution volume in perfused rat lung (139?ml versus 97?ml in controls). In single-pass perfused lungs the observed maximum of concentration was decreased by about 60% compared to controls. The mean residence time was prolonged by about 40%. These observations suggest that prilocaine is substantially retained by rat lung and that this effect occurs particularly during first-pass. However, the ability of rat lung to degrade prilocaine was relatively low. The clearance values were about 0.3?ml/min equal to about 20% of the hepatic capacity calculated per g of tissue. Thus it must be assumed that prilocaine is only transiently retained by the lung and will gain systemic availability later on. In rat lungs the kinetics of prilocaine elimination were not substantially different from those of bupivacaine and mepivacaine (16 and 12%). These observations do not support the assumption that especially prilocaine undergoes extrahepatic elimination. For low (2?µg/ml) and intermediate (10?µg/ml) drug concentrations isolated rat liver exhibited clearance values close to the perfusion flow rate. Accordingly, prilocaine was removed from the perfusion medium of isolated livers already during first-pass. At very high concentrations of 100?µg/ml, the clearance dropped to about half of the control values. Thus under these conditions approximately half of the dose escaped first-pass extraction which is probably caused by saturated metabolic clearance. Such an effect was not observed for bupivacaine and mepivacaine.

The ability of rat lung to remove the local anaesthetic drug bupivacaine from the blood was studied in isolated organs which were perfused either in an open (single-pass mode) or in a closed system (recirculating medium). Isolated perfused rat lungs exhibited a very low capacity to metabolize bupivacaine within 3?h during which the drug circulated continuously through the organ. The clearance values differed only by 0.2?ml/min from the control parameters in sham perfusions. The calculated extraction ratio was 0.2% and the elimination half-life was about 210?min. The volume of distribution of bupivacaine was 133?ml which remarkably surmounted the reference values obtained for sham perfusions. The distribution of bupivacaine into the pulmonary tissue was investigated applying the multiple indicator dilution technique to isolated lungs perfused in the single-pass mode. The mean elimination time of model compounds for distribution into the intravascular space, 14C-inulin, and the total water space, 3H-water, were 68 and 75?s at a flow rate of 6?ml/min. The volume of distribution was 5.9?ml for inulin and 6.5?ml for water. The mean transit time for concomitantly injected bupivacaine was 221?s and the volume of distribution was 14.4?ml. The respective parameters of sham perfusions performed without an isolated organ were substantially lower, i.e. mean elimination time 50, 50 and 61?s and distribution volume 4.9, 5.0 and 6.1?ml for inulin, water and bupivacaine. The volume of distribution during single-pass contact of bupivacaine to lung was not substantially influenced by an increase of the flow rate from 6 to 9 and 12?ml/min whereas the mean transit time dropped from 221 to 121 and 108?s, respectively. These results support the assumption that bupivacaine is extensively retained by the pulmonary tissue and that elimination of bupivacaine by metabolism can be neglegted for lung. The hemodynamic parameters of bronchiolar perfusion in the artificially perfused lung were determined using two fluorochrome-labeled macromolecular proteins, i.e. fluorescein-isothiocyanate (FITC)- and lissamine-rhodamine-B 200 (RB 200)-labeled globulin. After 10?min of perfusion at a flow rate of 12?ml/min in the closed system an area of 10.8% of the peribronchiolar tissue area contained the dye-label FITC. A very similar index (10.1%) of dye-coloured capillaries was obtained when the lungs of anaesthetized rats were examined 10?min after intravenous injection of the fluorochrome into the pulmonary artery in vivo. In isolated perfused rat lungs receiving both FITC and RB 200 59.5% of FITC-labeled capillaries were reached by the second fluorochrome within 2?s. This fraction accounted for 93.3% after 10?s of circulation time. This proves that isolated rat lungs were well perfused in vitro.

Two-dimensional silver nanodisks were self-assembled in ⟨111⟩ crystallography orientations forming a three-dimensional architecture. The kinetics studies of interface growth reveal that the Cu 2+ion diffusion interface diminished the concentration convection and electric convection at the growing interface. With the fluctuation greatly reduced, the effect of lattice anisotropy of the growing interface starts to dominate, which induces highly faceted regular patterns with a stable growing interface. First-principles density functional theory calculations clarified that the silver patterns grow consistently with their thermodynamic character of the face-centered-cubic phase, and show the crystallographical orientation.

Fatigue is a common cause of failure in components subjected to cyclic stresses. Repeated loads much smaller than the yield stress of the material can cause a fatigue failure. One such component subject to cyclic stresses is a titanium heart valve housing. The valve is subjected to a low level of stress with each heart beat as a disc pivots and closes against the housing. Interest in the initiation of fatigue in such components was an impetus to examine surface plasticity and accumulated damage which could lead to fatigue initiation. Grade 4 titanium used in heart valves and pure titanium have been studied.The three phases of fatigue are initiation of a crack, propagation, and catastrophic failure. Minimum defect size for crack propagation and failure are fairly well understood by scientists and engineers. However, the initiation portion of fatigue as a function of accumulated surface microplasticty is less well defined. SEM and AFM have been be used to evaluate microplasticity on the surface of titanium and correlate damage accumulation to the initiation of a crack.Fully reverse loaded four point bend testing was conducted on a an electropolished pure titanium sample 15 mm by 5 mm by 1 mm thick. The sample was oxidized at 300°C for one hour prior to fatigue testing. The sample was fatigued for 25,000 cycles using a ±45N load.

A combination of fear and declining compensation may induce cardiovascular accidents in the elderly with heart disease. An accurate cardiac diagnosis and relief of stress and pain during tooth extraction are important. The range of cardiac abnormalities and the regime followed in two clinics in the People's Republic of China are reviewed, together with the precautions which are taken to avoid emergencies or manage them should they arise