Zig Zag Research Articles

Electronic and magnetic properties of MoS2 nanoribbons with sulfur line vacancy defects

Motivated by the recent experimental result that single sulfur vacancies in monolayer MoS2 are mobile under the electron beam and easily agglomerate into the sulfur line vacancy defects [Physical Review B 88, 035301(2013)] , the structural, electronic and magnetic properties of one dimensional zigzag (ZZ) and armchair (AC) edge MoS2 nanoribbons with single or double staggered sulfur line vacancy defects (hereafter, abbreviated as SV or DV, respectively), parallel to their edges, have been investigated systematically by density functional theory calculations. It is very interesting to find that the bond strains induced by the sulfur line vacancy defect can cause a much larger out-of plane distortions in the ZZ edge MoS2 nanoribbon than in the AC edge counterpart. Besides, the defective ZZ edge MoS2 nanoribbons with SV or DV are both metals, having their two respective degenerate ground states with the same energy, among which one is ferromagnetic (FM “++”) and the other is antiferromagnetic (AFM “+−”). But the AC edge MoS2 nanoribbons with SV or DV are both nonmagnetic semiconductors, having very different gap values. Finally, the sulfur line vacancy defects would induce some defect states in the electronic structures of the defective MoS2 nanoribbons. All these important results could provide a new route of tuning the electronic properties of MoS2 nanoribbons and its derivatives for their promising applications in nanoelectronics and optoelectronics.

Assessment of a hydraulic network model for zig–zag cooled power transformer windings

The prediction of mass flow distribution is a first, though crucial, step in the thermal design of zig–zag cooled power transformer windings. Typically this prediction is based on thermo-hydraulic network models, which critically depend on the applied correlations. In this paper new correlations for flow through elbows and for dividing/merging flow in T-junctions are numerically extracted from dedicated CFD studies and applied to a case study. It is shown that the new correlations are superior for the prediction of the mass flow distribution for this test case in comparison to correlations thus far available in literature.

Two novel coordination polymers in the family of lanthanide complexes with o-phenylenedioxydiacetato as ligand

Two novel coordination polymers [Ce(PDOA)(NO3)(H2O)2]n (1) and {[Ce(PDOA)(NO3)(H2O)3]·H2O}n (2) (PDOA=o-phenylenedioxydiacetato) have been prepared using hydrothermal conditions and have been structurally characterized. In both crystal structures 1 and 2 the Ce(III) atoms are decacoordinated by oxygen atoms from PDOA ligands with chelating and bridging functions, chelating nitrato ligands and aqua ligands. While in 1 the PDOA ligand presents a hexadentate coordination mode, in 2 it is coordinated in a pentadentate manner; this difference leads to different types of one-dimensional structural motifs: in 2 there are zig–zag chains of the –Ce–O–C–O–Ce– type with syn–anti carboxylate bridges and in 1 these chains are additionally interlinked by further syn–anti carboxylate bridges leading to a strip- or ribbon-like arrangement formed of {Ce3} fused triangles. The endothermic dehydration of 1 within the temperature range 69–199°C is at least a two-step process as suggested by TG and DTA methods. A variable temperature (2–300K) magnetic study reveals Curie–Weiss behavior for 1 with θ=−35.5K observed above 50K. The origin of the observed behavior is discussed.

The transition metal surface passivated edges of hexagonal boron nitride (h-BN) and the mechanism of h-BN's chemical vapor deposition (CVD) growth.

Edge structure and stability are crucial in determining both the morphology and the growth behaviours of hexagonal boron nitride (h-BN) domains in chemical vapour deposition (CVD) growth under near thermal equilibrium conditions. In this study, various edges of h-BN on three typical transition metal surfaces used for h-BN's CVD growth, Cu(111), Ni(111) and Rh(111), are explored with density functional theory calculations. Different from that in vacuum, our study shows that the formation of non-hexagonal rings, such as pentagon, heptagon or their pairs, is energetically not preferred and both zigzag (ZZ) edges are more stable than the armchair (AC) edge on all the explored catalyst surfaces under typical conditions of h-BN's CVD growth, which explains the broad experimental observation of triangular h-BN domains. More importantly, our results indicate that, instead of the pristine ZZ edge terminated with nitrogen atoms (ZZN), the triangular BN domains observed in experiments are likely to be enclosed with ZZ Klein edges having dangling atoms, ZZB + N or ZZN + B. By applying the theory of Wulff construction, we predicted that the equilibrium shape of a BN domain could be a hexagon enclosed with nitrogen-rich AC edges, triangles enclosed with two different types of ZZ Klein edges or a hexagon enclosed with boron-rich AC edges if the growth is in a N-rich, neutral or B-rich environment, respectively. This study presents how the edges and equilibrium shapes of h-BN domains can be controlled during the CVD synthesis and provides guidelines for further exploring the growth behaviours and improving the quality of CVD-prepared h-BN films.

The reconstructed edges of the hexagonal BN

As an important two-dimensional material which shows exceptional mechanical and chemical stability, superior electronic properties, along with broad applications, the hexagonal-BN (h-BN) has drawn great attention recently. Here we report a systematic study on the structural stability, electronic and magnetic properties of various h-BN edges, including both bare and hydrogen-terminated ones. It is found that along the armchair (AC) direction, the pristine edge is the most stable one because of the formation of a triple B≡N bond, while, along the zigzag (ZZ) directions, the reconstructed ones, ZZB + N and ZZN57 are more stable. The pristine edges are more stable in bare BN in most cases if saturated with hydrogen. By applying the theory of Wulff construction, we predicted that an unpassivated BN domain prefers the hexagonal shape enclosed with bare AC edges i.e., AC-Ns, AC, AC-Bs if the feedstock varies from N-rich to B-rich. However, the evolution from ZZN edged triangular domain, to hexagonal domain enclosed with AC edges, and ZZB edged triangle may occur if the edges are terminated by hydrogen atoms. Further calculation shows that these edges present rich type-dependent properties and thus are important for various applications. This theoretical study showed that controlling the morphologies of BN domains and BN edges is crucial for various applications.

The Spanish American Crónica Modernista, Temporality and Material Culture: Modernismo’s Unstoppable Presses by Andrew Reynolds (review)

Reviewed by: The Spanish American Crónica Modernista, Temporality and Material Culture: Modernismo’s Unstoppable Presses by Andrew Reynolds Viviane Mahieux Reynolds, Andrew. The Spanish American Crónica Modernista, Temporality and Material Culture: Modernismo’s Unstoppable Presses. Lewisburg: Bucknell UP, 2012. 189pp. The genre of the crónica began to claim critical attention in academic and literary circles in the 1980s and early 1990s, when three groundbreaking works that focused on the journalistic genre’s formative phase during Spanish American Modernismo were published: Aníbal González’s La crónica modernista hispanoamericana (1983); Julio Ramos’s Desencuentros de la modernidad en América Latina (1989); and Susana Rotker’s La invención de la crónica (1992). In the more than twenty years since these three indispensable works first appeared, the chronicle has become an important source of scholarship in Latin American literary and cultural studies, although more contemporary expressions of the genre have garnered the greatest attention. New voices in the study of the chronicle during Spanish American Modernismo have long been overdue. Andrew Reynolds’s book represents a timely addition to the field, partly because it revisits some of the main questions that had guided previous studies of the chronicle during Modernismo, such as the genre’s constant negotiations between literature and journalism, as well as the temporal concerns that accompanied the long-lived ambitions of literature in tension with the perceived transience of journalism. But more importantly, this book engages with the materiality of the chronicle in novel and productive ways by drawing from archival material and detailing how the transatlantic collaborations of chroniclers went beyond writing, as did Enrique Gómez Carrillo’s work as editor for the Spanish daily El Liberal. [End Page 403] The first chapter studies the relationship between the figure of the cronista as poet and that of the reporter in the light of Bourdieu’s idea of habitus. Reynolds focuses on the self-representation of cronistas by taking into account their conceptualization of literary aesthetics and their consciousness of a growing number of readers. Unlike previous scholars of the crónica Modernista who wrote before the widespread acceptance of cultural studies, Reynolds no longer needs to make the case for the literary value of the genre. This enables him to go further in exploring the intertwined relationship between literature and the industrial press. The author argues that the literary field during Modernismo was shaped from the sphere of journalism and by the mechanics that framed and constrained journalistic production. The journalistic experience is thus posited as the enabler, rather than the counterpart, of the literary aesthetics of Modernismo. This central argument is backed up by readings of four chronicles: “Los estudiantes” by Enrique Gómez Carrillo, “La última gigantomaquia” by José Juan Tablada, “Mis lunes” by Amado Nervo, and “Zig Zag Newyorkinos” by José Martí. As in the following chapters, Reynolds here works from little-known chronicles, a valuable choice given that the dispersed nature of the genre often limits scholars and students to refer to the same select texts again and again. The second chapter focuses on temporality, both as a philosophical inquiry related to the processes of modernity and as a reflection of the time constraints of the journalistic practice. Taking cues from both Bourdieu’s concept of difference and Deleuze’s notion of repetition, the author contends that elements inherent to journalism, such as technology and travel, framed the temporal consciousness that came to define the Modernista movement. The most original facet of this argument lies in the focus on the constant stream of textual output brought forth by the crónica Modernista. This repetitive production placed the literary movement in a constant state of becoming, shaped by the high productivity of writers who used the press as a means to repeatedly assert their standing and reaffirm their status and visibility. In this chapter, Reynolds gives particular attention to two texts, Rubén Darío’s “El hipogrifo” and Julián del Casal’s “En el tranvía,” the latter offering one of the few instances in which questions of gender in relation to the chronicle are addressed. The last two chapters of the book are the...

Coexistence of size-dependent and size-independent thermal conductivities in phosphorene

Thermal conductivity of single layer black phosphorus (BP) is investigated by combining density functional calculations and Peierls-Boltzmann transport equation. Differing from isotropic and divergent thermal conductivities in two-dimensional graphene and MoS$_2$, an compelling co-existence of size-dependent and size-independent thermal conductivities are discovered for single layer BP along zigzag (ZZ) and armchair (AM) direction, respectively. Besides, thermal conductivities in single layer BP are found to be highly anisotropic because of orientation dependent group velocities, e.g., thermal conductivities at 300 K are 83.5 and 24.3 W/m-K along ZZ and AM directions for single layer BP with a size of 10 $\mu m$, respectively.

Single File Dynamics Advances with a Focus on Biophysical Relevance

In this review (appearing in the Special Issue on single file dynamics in biophysics and related extensions), three recently treated variants in file dynamics are presented: files with density that is not fixed, files with heterogeneous particles, and files with slow particles. The results in these files include:• In files with a density law that is not fixed, but decays as a power law with an exponent a the distance from the origin, the particle in the origin mean square displacement (MSD) scales like MSD ~ t[1+a]/2, with a Gaussian probability density function (PDF). This extends the scaling, MSD ~ t1/2, seen in a constant density file.• When, in addition, the particles' diffusion coefficients are distributed like a power law with an exponent γ (around the origin), the MSD follows MSD ~ t[1-γ]/[2/(1+a) - γ], with a Gaussian PDF.• In anomalous files that are renewal, namely, when all particles attempt a jump together, yet, with jump times taken from a PDF that decays as a power law with an exponent -1 - ε, ψ(t) ~ t-1-ε, the MSD scales like the MSD of the corresponding normal file, in the power ε.• In anomalous files of independent particles, the MSD is very slow and scales like MSD ~ log2(t). Even more exciting, the particles form clusters, defining a dynamical phase transition: depending on the anomaly power ε, the percentage of particles in clusters ξ follows [Formula: see text], yet when ε > 1, fluidity rather than clusters is seen.We talk about utilizing these results while focusing on biophysical processes and applications: dynamics in channels, membranes, biosensors, etc.[Formula: see text] Special Issue Comments: In this article, results about recently suggested variants in single file dynamics appear: heterogeneous files and slow files, yet also, the relevance with biophysical processes. It is related to the Special Issue articles about expansions in files,61files with force,62and the zig zag occurrences in files.63

Interacting Single-File System: Fractional Langevin Formulation Versus Diffusion-Noise Approach

We review the latest advances in the analytical modelling of single file diffusion. We focus first on the derivation of the fractional Langevin equation that describes the motion of a tagged file particle. We then propose an alternative derivation of the very same stochastic equation by starting from the diffusion-noise formalism for the time evolution of the file density. [Formula: see text] Special Issue Comments: This article presents mathematical formulations and results on the dynamics in files with applied potential, yet also general files. This article is connected to the Special Issue articles about the zig zag phenomenon,72 advanced statistical properties in single file dynamics,73 and expanding files.74

Single-valued multiple polylogarithms and a proof of the zig–zag conjecture

A long-standing conjecture in quantum field theory due to Broadhurst and Kreimer states that the periods of the zig–zag graphs are a certain explicit rational multiple of the odd values of the Riemann zeta function. In this paper we prove this conjecture by constructing a certain family of single-valued multiple polylogarithms which correspond to multiple zeta values ζ(2,…,2,3,2,…2) and using the method of graphical functions. The zig–zag graphs are the only infinite family of primitive graphs in ϕ44 theory (in fact, in any renormalisable quantum field theory in four dimensions) whose periods are now known.

An Evaluation of Plaque Removal Efficacy of Five Commercially Available Toothbrushes: A Comparative Clinical Study

Background and Objectives – The aim of the study is to compare the plaque removal efficacy of five commercially available tooth brushes. Materials & Methods –The study group consisted of 75 subjects with age ranging 17 to 27 years distributed into five groups- Group A [Colgate Supershine], Group B [Colgate Zig zag], Group C [Oral B Allrounder], Group D [Oral B Fresh Clean], Group E [Pepsodent double action]. Study was single blinded, randomized clinical trial. Turesky- Gilmore- Glickmann Modification of Quigley-Hein Plaque Index and Modified Sulcular bleeding index were assessed at baseline, 4 weeks and 8 weeks. Results – All brushes showed significant reduction in plaque score over 8 weeks. The percentage of plaque reduction from baseline to 4 weeks for Group A, B, C, D & E is 58.74, 61.95, 57.86, 50.28 & 53.59 respectively. The percentage of plaque reduction from baseline to 8 weeks for Group A, B, C, D & E is 67.83, 76.11, 62.86, 56.42 & 60.13 respectively. The percentage of plaque reduction from 4 weeks to 8 weeks for Group A, B, C, D & E is 22.03, 37.21, 11.86, 12.36 & 14.08 respectively. However, the reduction of plaque scores is greater in Group B [76%] when compared to other groups. Conclusion – Within the limitations of the study, the data derived from the study shows that all the tooth brushes has shown decrease in plaque scores. In comparison, Colgate Zig zag [Group B] has some beneficial effects in reduction of plaque scores.

Luminescent zinc aliphatic dicarboxylate coordination polymers with bis(4-pyridylmethyl)piperazine: Effect of chain length and steric bulk on topology and water molecule aggregation

Hydrothermal reaction of zinc nitrate, aliphatic dicarboxylic acids, and the long-spanning hydrogen-bonding capable tethering ligand bis(4-pyridylmethyl)piperazine (4-bpmp) has produced seven coordination polymer solids that were characterized via single-crystal X-ray crystallography. [Zn(suc)(4-bpmp)(H2O)2]n (1, suc=succinate) shows 2D+2D→3D mutually inclined interpenetrated parallel coordination polymer layers with (4,4) grid topology. {[Zn2(dms)2(4-bpmp)]·2H2O}n (2, dms=2,2-dimethylsuccinate) exhibits 1-D [Zn2(dms)2]n ribbons featuring {Zn2(OCO)2} dimeric units pillared into 2-D by 4-bpmp ligands. {[Zn(glu)(4-bpmp)]·6H2O}n (3, glu=glutarate) manifests a 3-fold interpenetrated 3-D 66 diamondoid topology with embedded C(10)A(4) water chains. [Zn(22dmg)(4-bpmp)]n (4, 22dmg=2,2-dimethylglutarate) and [Zn(33dmg)(4-bpmp)]n (5, 33dmg=3,3-dimethylglutarate) both display stacked zig–zag (4,4) grid layered topologies, and do not entrain any co-crystallized water molecules. Reduction of the steric hindrance by using 3-methylglutarate (3mg) afforded {[Zn(3mg)(4-bpmp)]·3H2O}n (6), which also displays a (4,4) grid topology, but with embedded R(4)A(2) water molecule hexamers connecting to three different layer motifs. [Zn(adp)(4-bpmp)]n (7, adp=adipate) possesses a system of 5-fold interpenetrated diamondoid nets. Thermal and luminescent properties of these materials are discussed herein.

Thermal Stability of FGM Sandwich Plates Under Various Through-the-Thickness Temperature Distributions

A thermal stability analysis of functionally graded material (FGM) isotropic and sandwich plates is carried out by virtue of a refined quasi-3D Equivalent Single Layer (ESL) and Zig-Zag (ZZ) plate models developed within the framework of the Carrera Unified Formulation (CUF) and implemented within the Hierarchical Trigonometric Ritz Formulation (HTRF). The Principle of Virtual Displacements (PVD) is used both to derive the thermal stability differential equations with natural boundary conditions and to develop the HTRF. Uniform, linear, and non-linear temperature rises through-the-thickness direction are taken into account. The non-linear temperature distribution is given in different forms: 1) functionally graded; 2) solution of the one-dimensional Fourier heat conduction equation; and 3) sinusoidal. Several FGM sandwich plate configurations are investigated. Parametric studies are carried out in order to evaluate the effects of significant parameters, such as volume fraction index, length-to-thickness ratio, boundary conditions, aspect ratio, sandwich plate type, and temperature distribution through-the-thickness direction, on the critical buckling temperatures.

Assessment of air pollutant emissions from brick kilns

India has more than 100,000 brick kilns producing around 250 billion bricks annually. Indian brick industry is often a small scale industry and third largest consumer of coal in the country. With the growing demand for building materials and characterised by lack of pollution control measures the brick industry has a potential to cause adverse effects on the environment. This paper presents assessment of five brick making technologies based on the measurements carried out at seventeen individual brick kilns. Emissions of PM, SO2, CO and CO2 were measured and these emissions were used to estimate the emission factors for comparing the emissions across different fuel or operating conditions. Estimated emission from brick kilns in South Asia are about 0.94 million tonnes of PM; 3.9 million tonnes of CO and 127 million tonnes of CO2 per year. Among various technologies that are widely used in India, Zig zag and vertical shaft brick kilns showed better performance in terms of emissions over the traditional fixed chimney Bull's trench kilns. This suggests that the replacement of traditional technologies with Zig zag, vertical shaft brick kilns or other cleaner kiln technologies will contribute towards improvements in the environmental performance of brick kiln industry in the country. Zig zag kilns appear to be the logical replacement because of low capital investment, easy integration with the existing production process, and the possibility of retrofitting fixed chimney Bull's trench kilns into Zig zag firing.

Free vibrations of free-form doubly-curved shells made of functionally graded materials using higher-order equivalent single layer theories

The theoretical framework of the present manuscript covers the dynamic analysis of doubly-curved shell structures using the generalized displacement field of the Carrera Unified Formulation (CUF), including the Zig-Zag (ZZ) effect given by the Murakami’s function. The partial differential system of equations is solved by using the Generalized Differential Quadrature (GDQ) method. This numerical approach has been proven to be accurate, reliable and stable in several engineering applications. The current paper focuses on Functionally Graded (FG) doubly-curved shells and panels using various higher-order equivalent single layer theories, introduced and applied for the first time by the authors to completely doubly-curved shell structures, and different through-the-thickness volume fraction distributions, such as four-parameter power law, Weibull and exponential distributions. Moreover, the classic theory of mixtures is compared to the Mori–Tanaka scheme for the calculation of the mechanical properties of the materials. In particular, the numerical applications presented in this work are related to particular FG configurations in which it is possible to model a soft-core structure using a continuous variation of the mechanical properties of the materials at hand. The natural frequencies and mode shapes of several structures are presented and compared to numerical solutions taken from the literature.

Investigation of Passive DEFC Mini-Stacks at Ambient Temperature

In this work we show the results of ministacks of direct ethanol fuel cells (DEFC) at 25 oC. Result obtained with a passive DEFC using 2 mgPtRu/C in anodes and 3 mg of Pt in cathodes, when the alcohol concentration was 1 M, showed a power density equal to 0.875 mWcm-2 for electrodes with area equal to 25 mm2 . Results related with Nafion content in the catalytic layers are discussed. Stacks using three similar cells showed 2.4 mWcm-2 indicating the good performance of the system.The performance of mini stacks operated with electrodes of 5 mm2 showed the dependence of the mass transport of ethanol and of the configuration of the stacks (zig zag and flip flop). The better results were obtained with a zig zag interconexion.A comparison from fuel cell performance was done using ethanol and methanol. The best result of the stack using methanol (5M) was 60% higher than when ethanol (2M) was used.

Electronic States at the Graphene–Hexagonal Boron Nitride Zigzag Interface

The electronic properties of graphene edges have been predicted to depend on their crystallographic orientation. The so-called zigzag (ZZ) edges haven been extensively explored theoretically and proposed for various electronic applications. However, their experimental study remains challenging due to the difficulty in realizing clean ZZ edges without disorder, reconstructions, or the presence of chemical functional groups. Here, we propose the ZZ-terminated, atomically sharp interfaces between graphene and hexagonal boron nitride (BN) as experimentally realizable, chemically stable model systems for graphene ZZ edges. Combining scanning tunneling microscopy and numerical methods, we explore the structure of graphene-BN interfaces and show them to host localized electronic states similar to those on the pristine graphene ZZ edge.

Thermoelectric transport properties through a single-walled zig–zag carbon nanotube side coupled to a correlated quantum dot: Atomic approach for the finite U-impurity Anderson model

We study the thermopower S, linear thermal conductance κ, linear electric conductance G and thermoelectric figure of merit Z properties of a single-walled zig–zag carbon nanotube side coupled to a correlated quantum dot (QD). We employ the recently developed U-finite atomic approach for the Single Impurity Anderson model (SIAM). The quantum dot is linked to the localized states in the model, considering a finite Coulombic repulsion U, and the conduction band in the model is associated with the single walled zig–zag metallic carbon nanotube (n=3), and is described by a tight-binding approximation in order to obtain Green׳s function of the nanotube. The thermoelectric transport coefficients were obtained using the Keldysh non-equilibrium Green׳s function technique with the Onsager relation in the linear regime automatically satisfied. Results indicate that this system can be employed in possible thermoelectric device applications at low temperatures when strong charge fluctuations are present in the QD.

Phase diagram study of a dimerized spin-S zig–zag ladder

The phase diagram of a frustrated spin-S zig–zag ladder is studied through different numerical and analytical methods. We show that for arbitrary S, there is a family of Hamiltonians for which a fully-dimerized state is an exact ground state, being the Majumdar–Ghosh point for a particular member of the family. We show that the system presents a transition between a dimerized phase to a Néel-like phase for S = 1/2, and spiral phases can appear for large S. The phase diagram is characterized by means of a generalization of the usual mean field approximation. The novelty in the present implementation is to consider the strongest coupled sites as the unit cell. The gap and the excitation spectrum is analyzed through the random phase approximation. Also, a perturbative treatment to obtain the critical points is discussed. Comparisons of the results with numerical methods like the Density Matrix Renormalization Group are also presented.

New manganese (II) structures derived from 2,6-dichlorobenzoic acid: Syntheses, crystal structures and magnetism

One novel coordination polymer [Mn2(μ-2,6-DCBA)3(μ2-CH3CO2)2(2H2O)]·2H2O (2,6-DCBA = 2,6-dichlorobenzoato) (compound 1) has been synthesized by self-assembly of bridging ligand 2,6-dichlorobenzoic acid and manganese acetate tetrahydrate. Single crystal X-ray diffraction analysis reveals that this compound crystallizes in space group P21/c with a = 10.1547(7), b = 24.5829(2), c = 12.6606(2) Å, β = 93.707(3), V = 3153.9(3) Å3 and Z = 4. The Mn(II) ions are connected by 2,6-DCBA and acetate group in μ-bridging mode to form 1D chains. Two water molecules are in the inter-layer space forming strong hydrogen bonds originating 2D layer structure. The preparation of this compound is very sensitive to the synthesis conditions, mainly to the solution pH and solvent yielding other two compounds 2 and 3. In compound 1 Mn(II) atoms in octahedral coordination are arranged in a zig–zag chain, with a trimeric structure repeated periodically along the chain, giving two exchange parameters: J1 related to a syn–syn bond; and J2 related to a bond of type anti–anti. A theoretical model was developed and then fitted to the magnetic susceptibility data, revealing an antiferromagnetic arrangement along the chain.