Zigzag Type Research Articles

Ferromagnetism and Persistent Currents in Finely Dispersed Highly Oriented Pyrolytic Graphite Samples

Synthesis of finely dispersed graphite powders is described and results of their investigations by the methods of electron microscopy and magnetometry are presented. The samples have been prepared from crystal highly oriented pyrolytic graphite by grinding in an inert atmosphere for a long time with subsequent annealing at 400°C for 24 h in air or in vacuum. It is demonstrated that annealing of the powder in vacuum leads to a considerable increase in the ferromagnetic component associated with the formation of edge defects of zigzag type. The phenomenon of magnetic flux trapping is manifested in the samples annealed both in air and in vacuum upon cooling down to 10 K in a magnetic field that is indicative of the formation of superconducting regions in the samples.

Optimization and thermodynamic analysis of supercritical CO2 Brayton recompression cycle for various small modular reactors

This paper presents optimization of a supercritical carbon dioxide Brayton cycle for three types of 300-MWth small modular reactors (SMRs); a pressurized water reactor (PWR), a sodium-cooled fast reactor (SFR) and a high-temperature gas-cooled reactor (HTGR). The parameters of the pressure ratio and the flow split fraction were examined for sensitivity analysis and optimization of cycle. The optimized cycle efficiencies of PWR, SFR, and HTGR were 30.6%, 46.38%, and 50.04%, respectively. Key components, i.e. turbomachinery and heat exchangers for the SMRs were designed to develop the optimized cycles. The cycle thermal efficiency was improved by using investigating the effects of the channel shape (zigzag, s-shape, airfoil fin) of the printed circuit heat exchangers (PCHEs) on the pressure drop. The study indicated that using airfoil fin type PCHE may increase the cycle thermal efficiency by about 1.0% in comparison with zigzag type PCHE. The effect of turbomachinery efficiencies on the cycle thermal efficiency were investigated.

Copper and metals concentration from printed circuit boards using a zig-zag classifier

The consumption of electronic products has grown considerably in the last decades. These products become obsolete in a short period of time, generating electronic waste, which presents loads of materials harmful to health and metals of great value to industries. In this work, an innovative metal concentration technique for PCBs was applied aiming at the valuable metals recovery from ground printed circuit boards (PCBs) of computers that would be discarded. The PCBs were comminuted, classified by sieving and the metallic materials were processed in a zig-zag classifier type. The Schytil's phase diagram was developed to estimate the air flow rate to be used in the classifier. The product of each step was characterized. The copper content rose from 13.8% (w/w) to 48.8% (w/w) after the passage of the PCBs powder through the classifier. Its recovery and Newton's efficiency were above 89.4% and 0.91, respectively. The total content of metals was increased from 39.5% (w/w) to 89% (w/w) with a recovery of more than 82% and Newton's efficiency of 0.67 for the particle size in the range from 0.2 to 0.1mm. The gold content has increased from 200ppm to more than 8000ppm after segregation by a simple manual concentration. Results shown that the use of zig-zag classifier to separate and concentrate metals was fairly effective, do not generate liquid and gaseous effluents and eliminates a number of pyrometallurgical or hydrometallurgical steps for metals obtaining.

Edge states in gated bilayer-monolayer graphene ribbons and bilayer domain walls

Using the effective continuum model, the electron energy spectrum of gated bilayer graphene with a step-like region of decoupled graphene layers at the edge of the sample is studied. Different types of coupled-decoupled interfaces are considered, i.e., zigzag (ZZ) and armchair junctions, which result in significant different propagating states. Two non-valley-polarized conducting edge states are observed for ZZ type, which are mainly located around the ZZ-ended graphene layers. Additionally, we investigated both BA-BA and BA-AB domain walls in the gated bilayer graphene within the continuum approximation. Unlike the BA-BA domain wall, which exhibits gapped insulating behaviour, the domain walls surrounded by different stackings of bilayer regions feature valley-polarized edge states. Our findings are consistent with other theoretical calculations, such as from the tight-binding model and first-principles calculations, and agree with experimental observations.

Mechanical and electronic properties of lateral graphene and hexagonal boron nitride heterostructures

Owing to the promising applications in two dimensional devices, lateral graphene/h-BN (G/BN) heterostructures have attracted significant attentions. Here, we investigate the mechanical and electronic properties of lateral G/BN with different types of interfaces using density functional theory. For G/BN heterostructure with armchair (AC) or zigzag (ZZ) type interfaces, the intrinsic tensile strength is close to that of pristine graphene. For the heterostructure with the misorientated interface, the intrinsic tensile strength highly relies on the misorientation angle. G/BN heterostructure with Clar’s interface is found to be mechanically more stable than those with non-Clar’s interface. Moreover, with the uniaxial tensile strain increasing from 0% to 10%, the band gap of the G/BN with ZZ interfaces are nearly unchanged while the G/BN with AC interfaces shows a non-monotonic variation of band gaps. These theoretical results provide a useful picture for the interface effects on the mechanical and electronic behaviors of lateral G/BN heterostructures.

Topology in single-wall carbon nanotube of zigzag and armchair type

Single-wall carbon nanotubes can be one-dimensional (1D) topological insulators except for armchair nanotubes. The electronic states are characterized by a non-zero topological invariant, winding number, which is related to the number of 0D edge states via the bulk-edge correspondence. In the present study, we theoretically examine zigzag and armchair nanotubes to elucidate the emergence and absence of edge states. The effective 1D lattice model is employed in order to describe the fine structures due to the finite curvature of tube surface and spin-orbit interaction. We show that the lattice model for a zigzag nanotube is equivalent to the Su-Schrieffer-Heeger model, by which the formation of edge states is explained. An armchair nanotube is described by a ladder model, on the other hand, which does not host any edge states owing to the σh symmetry.

Dinuclear platinum(ii) complex dominated by a zig-zag-type cyclometalated ligand: a new approach to realize high-efficiency near infrared emission

Two new zig-zag type di- and mono-nuclear platinum(ii) complexes of (BuPh-BDIQ)Pt2(dpm)2 and (BuPh-BDIQ)Ptdpm were synthesized and characterized by using a zig-zag type cyclometalating ligand BuPh-BDIQ.

Modeling the Sensing Activity of Carbon Nanotubes Functionalized with the Carboxyl, Amino, or Nitro Group Toward Alkali Metals

The sensing activity of carbon nanotubes (CNTs) functionalized with the carboxyl, amino, or nitro group toward the atoms and ions of different metals are modeled using the semiempirical modified neglect of the diatomic overlap (MNDO) and density functional theory (DFT) methods. We discuss the mechanism by which the functional groups attach to the open end of a zig-zag type CNT to form a probe for chemical sensing. The interaction of the CNT-based probe with the potassium, sodium, and lithium atoms and ions is considered in detail. By comparing the results of the modeled sensing activity of the nanoprobes toward the elements of interest, we determine the optimal functional group for the CNT modification to produce a sensor suitable for identifying the potassium, lithium, and sodium atoms and ions, including those that occur in salts and alkali salts.

Es The Design and Mechanical Analysis of Double Zigzag Type of Adhesive Joints

es The Design and Mechanical Analysis of Double Zigzag Type of Adhesive Joints

Variation of SMSI with the Au:Pd Ratio of Bimetallic Nanoparticles on TiO2(110)

Au/Pd nanoparticles are important in a number of catalytic processes. Here we investigate the formation of Au–Pd bimetallic nanoparticles on TiO2(110) and their susceptibility to encapsulation using scanning tunneling microscopy, as well as Auger spectroscopy and low energy electron diffraction. Sequentially depositing 5 MLE Pd and 1 MLE Au at 298 K followed by annealing to 573 K results in a bimetallic core and Pd shell, with TiOx encapsulation on annealing to ~ 800 K. Further deposition of Au on the pinwheel type TiOx layer results in a template-assisted nucleation of Au nanoclusters, while on the zigzag type TiOx layer no preferential adsorption site of Au was observed. Increasing the Au:Pd ratio to 3 MLE Pd and 2 MLE Au results in nanoparticles that are enriched in Au at their surface, which exhibit a strong resistance towards encapsulation. Hence the degree of encapsulation of the nanoparticles during sintering can be controlled by tuning the Au:Pd ratio.

Control Topologies for 3-Phase SEIG used in Small Hydro Power Plant Feeding Isolated Domestic Load in Remote Mountainous Region

Objectives: This paper is to highlight the various control topologies used in 3-phase Self-Excited Induction Generator (SEIG) used in pico-hydro power generation system feeding isolated load. Methods/Statistical Analysis: The various topologies of these controllers which are also known as Electronic Load Controllers (ELC) include conventional as well as STATCOM based controllers using various power electronics devices for power system parameters regulations and power quality control. The Self-excited induction generators are most suitable for pico and micro hydro power generation systems feeding isolated load due to their advantages over conventional synchronous generators. Findings: In isolated mode of operation of self-excited induction generators, a suitable control is necessary to maintain the voltage & frequency of the generated output within permissible limits under varying loading conditions. This is achieved by using an Electronic Load Controller (ELC) and dump load in the system. The main aim of the control strategy is to control the voltage output of SEIG and to maintain the desired frequency of the generated output. These electronic load controllers regulate the dump load in the system so that total load seen by SEIG remains constant under varying consumer load conditions and thus maintaining the frequency of the system. From the analysis of various types of these controllers, it is found that simplest of the electronic load controller is conventional diode rectifier based ELC. However, it suffers with the problems of harmonics in the circuit. Modern ELCs use voltage source converters along with different transformer configurations for better power quality control and better voltage and frequency regulations under different operating conditions. Improvements: Fast computational capabilities of DSP are also used to control the STATCOM switches and chopper circuit in ELC for better and fast control. The use of different transformer configurations such as star-delta and zigzag type provide neutral path for 3-phase, 4-wire system apart from eliminating the 3rd harmonics in the system.

Three-band Hubbard model for Na2IrO3 : Topological insulator, zigzag antiferromagnet, and Kitaev-Heisenberg material

Na$_2$IrO$_3$ was one of the first materials proposed to feature the Kane-Mele type topological insulator phase. Contemporaneously it was claimed that the very same material is in a Mott insulating phase which is described by the Kitaev-Heisenberg (KH) model. First experiments indeed revealed Mott insulating behavior in conjunction with antiferromagnetic long-range order. Further refined experiments established antiferromagnetic order of zigzag type which is not captured by the KH model. Since then several extensions and modifications of the KH model were proposed in order to describe the experimental findings. Here we suggest that adding charge fluctuations to the KH model represents an alternative explanation of zigzag antiferromagnetism. Moreover, a phenomenological three-band Hubbard model unifies all the pieces of the puzzle: topological insulator physics for weak and KH model for strong electron-electron interactions as well as a zigzag antiferromagnet at intermediate interaction strength.

Results on significant anomalies of state values after key scheduling algorithm in RC4

It is already known that the internal permutation of the stream cipher RC4 generally deviates from a random permutation. These deviations are termed as biases, theoretical justification of which is being reported since early 2000. However, there are several biases (anomalies), which are not proven till date. In this study, the authors provide the theoretical proofs of all significant anomalies of RC4 in the 16-byte key setting. In the process, they also provide the theoretical justification of the zig-zag type distribution of the 31st output byte of RC4 (first discovered and presented by AlFardan et al. in USENIX 2013).

Position Sensitivity Study in Molecular Dynamics Simulations of Self-Organized Development of 3D Nanostructures

The sensitivity of defect free fusion of straight carbon nanotubes from graphene nanoribbons to the position of the nanoribbon edge positions has been investigated. A basic difference between the behavior of armchair and zigzag type nanoribbons was observed. When placing armchair type graphene nanoribbons above each other identical, fitting positions are obtained automatically. Zigzag type graphene nanoribbons, however, must not be placed above each other in identical positions. From the viewpoint of defect-free fusion, according to the MD simulations symmetric on nearly symmetric positions of the ribbon edges are favorable.

Based on the molecular dynamics characteristic research of heat conduction of graphyne nanoribbons with vacancy defects

As a kind of nano-material, graphyne nanoribbon has some physical properties and its properties should be studied for its better usage. In the process of preparing graphyne nanoribbons, it is possible that vacancy defects exist in the lattice structure, which will affect the physical properties of the graphyne nanoribbons. The flotation of graphyne is closer to the actual situation in engineering than the complete graphyne nanoribbons, and the diversity of vacancy defects can lead to various thermal conductivities, so it is very important to simulate the effects of various vacancy defects on thermal conductivity. In order to better predicte and control heat transfer characteristics of graphyne nanoribbons, this paper focuses on the effects of vacancy defects on the heat transfer characteristics of graphyne nanoribbons. According to the different cutting directions of graphyne nanoribbons, two different types of graphyne nanoribbons are obtained, i.e., armchair type and zigzag type. We compare the effects of vacancy defects on the thermal conductivity of two different chiral graphynes nanoribbons to improve the persuasiveness of the conclusion. In this paper, non-equilibrium molecular dynamics method is adopted, by applying periodic boundary conditions in the length direction of the nanoribbons, the interaction between the carbon-carbon atoms is described based on a potential function of adaptive intermolecular reactive empirical bond order (AIREBO). At 300 K, the effects of single vacancy defect in the acetylene chain, single vacancy defect in the benzene ring or double vacancy defects in the acetylene chain on the thermal conductivities of single-layer graphyne nanoribbons are simulated. Fourier's law is used to calculate the thermal conductivities of graphyne nanoribbons. The simulation results show that for the thermal conductivity of graphyne nanoribbons in a-few-dozen nanometer range:1) as a result of the phonon scattering and enhanced phonon Umklapp process, the graphyne nanoribbons with vacancy defects will cause the thermal conductivity to decrease and becomes lower than that of the complete graphyne nanoribbons; 2) due to the difference in phonon density-of-states matching degree, the vacancy defect in the benzene ring of graphyne nanoribbons has a greater effect on the thermal conductivity than that of vacancy defect in the acetylene chain of graphyne nanoribbons, the vacancy defects have a strong influence on the thermal conductivity of in the acetylene chain of graphyne nanoribbons; 3) because of the influence of size effect, the thermal conductivity of graphyne nanoribbon increases with length increasing. In this paper, the research of the thermal conductivity of graphyne nanoribbon provides the reference for controlling their thermal conductivity on a certain scale.

The prediction of a family group of two-dimensional node-line semimetals.

Using first-principles calculations, we predict a family group of two-dimensional semimetals MX (M = Pd, Pt; X = S, Se, Te), which has a zig-zag type mono-layer structure in the Pmma (no. 41) layer group. Band structure analysis reveals that node-line features are caused by band inversion and the inversion exists even in the absence of spin-orbital-coupling. First-principles calculations show the robust lattice stability of these predicted materials. This work provides the possibility of making a group of novel two-dimensional materials with semimetal features.

Experimental and first principle studies on hydrogen desorption behavior of graphene nanofibre catalyzed MgH2

With the combination of experiment and first-principles theory, we have evaluated and explored the catalytic effects of graphitic nanofibres for hydrogen desorption behaviour in magnesium hydride. Helical form of graphene nanofibres (HGNF) have larger surface area, curved configuration and high density of graphene layers resulting in large quantity of exposed carbon sheet edges. Therefore they are found to considerably improve hydrogen desorption from MgH2 at lower temperatures compared to graphene (onset desorption temperature of MgH2 catalyzed by HGNF is 45 °C lower as compared to MgH2 catalyzed by graphene). Using density functional theory, we find that graphene sheet edges, both the zigzag and armchair type, can weaken MgH bonds in magnesium hydride. When the MgH2 is catalyzed with higher electronegative and reactive graphene edge of graphene, the electron transfer occurs from Mg to carbon, due to which MgH2 is dissociated into hydrogen and MgH component. The Mg gets bonded with the graphene edge carbon atoms in the form of CMgH and CH bonds. In the as formed CMgH, the graphene edges “grab” more electronic charge as compared to the normal charge donation of Mg to H. This leads to the weakening of the MgH bond, causing hydrogen to desorbs at lower temperatures.

The Flow Behavior of Organic Liquids Inside Carbon Nanotubes

Within the methods of electron density functional and ab initio pseudopotential, it were obtained the spatial distributions of density of valence and the total energy for migration of water (or methanol) inside carbon nanotubes with clean walls and lined inside with gold atoms. It was found that the mass transfer of methanol through the carbon nanotubes of the zigzag type (15,0) is two orders of magnitude more energy than water.. It was revealed that the mass transfer of water and methanol through carbon nanotubes covered with gold atoms on the inner sides requires an order of magnitude more energy than pure nanotubes.

Zigzag type magnetic structure of the spin Jeff = ½ compound α-RuCl3 as determined by neutron powder diffraction

Using high intensity powder neutron diffraction the magnetic structure of a-RuCl3 has been determined. Following the magnetic propagation vector κ = (½, 0, ½) the Jeff = ½ spins of Ru3+ adopt a Zigzag type arrangement on the honeycomb lattice of the layered P3112 structure. The magnetic moments are oriented perpendicular to the trigonal axis. Similarities and differences to previously published single crystal data are discussed. The low value of the magnetic moments, μRu = 0.5(1) μB indicates a possible closeness of α-RuCl3 to the Kitaev spin liquid state.

Adsorption of Hydrogen Molecules on Carbon Nanotubes Using Quantum Chemistry and Molecular Dynamics.

Physisorption and storage of molecular hydrogen on single-walled carbon nanotube (SWCNT) of various diameters and chiralities are studied by means of classical molecular dynamics (MD) simulations and a force field validated using DFT-D2 and CCSD(T) calculations. A nonrigid carbon nanotube model is implemented with stretching (C-C) and valence angle potentials (C-C-C) formulated as Morse and Harmonic cosine potentials, respectively. Our results evidence that the standard Lennard-Jones potential fails to describe the H2-H2 binding energies. Therefore, our simulations make use of a potential that contains two-body term with parameters obtained from fitting CCSD(T)/CBS binding energies. From our MD simulations, we have analyzed the interaction energies, radial distribution functions, gravimetric densities (% wt), and the distances of the adsorbed H2 layers to the three zigzag type of nanotubes (5,0), (10,0), and (15,0) at 100 and 300 K.