Ribbon Length Research Articles

Modeling and Simulation of Graphene-Based Transducers in NEMS Accelerometers.

The mechanical characteristics of graphene ribbons with an attached proof mass that can be used as NEMS transducers have been minimally studied, which hinders the development of graphene-based NEMS devices. Here, we simulated the mechanical characteristics of graphene ribbons with an attached proof mass using the finite element method. We studied the impact of force, residual stress, and geometrical size on displacement, strain, resonant frequency, and fracture strength of graphene ribbons with an attached proof mass. The results show that the increase of width and thickness of graphene ribbons would result in a decrease of the displacement and strain but also an increase of resonant frequency. The increase of the length of graphene ribbons has an insignificant impact on the strain, but it could increase the displacement and decrease the resonant frequency. The increase of residual stress in the graphene ribbons decreases its strain and displacement. The estimated fracture strength of graphene shows limited dependence on its thickness, with an estimated value of around 148 GPa. These findings contribute to the understanding of the mechanical characteristics of graphene ribbons with an attached proof mass and lay the solid foundation for the design and manufacture of high-performance graphene-based NEMS devices such as accelerometers.

Line Edge Roughness Effects on the Thermoelectric Properties of Armchair Black Phosphorene Nanoribbons

AbstractThis study delves into the thermoelectric properties of armchair black phosphorene nanoribbons while considering the presence of line edge roughness. Employing the tight‐binding method in conjunction with non‐equilibrium Green's function techniques and Landauer formulas, the impact of various parameters on thermoelectric performance is explored. These findings reveal that the electrical conductivity and, consequently, the power factor exhibits an increasing trend with expanding ribbon length and width. This behavior can be attributed to heightened collision rates, particularly in narrow ribbons, induced by line edge roughness as length increases. Remarkably, the Seebeck coefficient at the Fermi energy corresponding to the maximum power factor remains nearly constant across different widths, lengths, temperatures, and transport regimes. Furthermore, the thermoelectric figure of merit (ZT) demonstrates a positive correlation with both ribbon length and width. In narrow widths and lengths ≈1000 nm, the power factor and figure of merit exhibit an upward trend with ribbon width. However, with further increases in ribbon width, the influence of line edge roughness on thermal conductivity diminishes. Consequently, the figure of merit decreases due to the rise in thermal conductivity. Notably, the thermoelectric figure of merit is higher for short and narrow ribbons and long and wider ribbons.

The Effects of Aging on Rod Bipolar Cell Ribbon Synapses.

The global health concern posed by age-related visual impairment highlights the need for further research focused on the visual changes that occur during the process of aging. To date, multiple sensory alterations related to aging have been identified, including morphological and functional changes in inner hair cochlear cells, photoreceptors, and retinal ganglion cells. While some age-related morphological changes are known to occur in rod bipolar cells in the retina, their effects on these cells and on their connection to other cells via ribbon synapses remain elusive. To investigate the effects of aging on rod bipolar cells and their ribbon synapses, we compared synaptic calcium currents, calcium dynamics, and exocytosis in zebrafish (Danio rerio) that were middle-aged (MA,18 months) or old-aged (OA, 36 months). The bipolar cell terminal in OA zebrafish exhibited a two-fold reduction in number of synaptic ribbons, an increased ribbon length, and a decrease in local Ca2+ signals at the tested ribbon location, with little change in the overall magnitude of the calcium current or exocytosis in response to brief pulses. Staining of the synaptic ribbons with antibodies specific for PKCa revealed shortening of the inner nuclear and plexiform layers (INL and IPL). These findings shed light on age-related changes in the retina that are related to synaptic ribbons and calcium signals.

Effects of a Uniform Magnetic Field on Twisted Graphene Nanoribbons

AbstractIn the present work, the relativistic quantum motion of massless fermions in a helicoidal graphene nanoribbon under the influence of a uniform magnetic field is investigated. Considering a uniform magnetic field (B) aligned along the axis of helicoid, this problem is explored in the context of Dirac equation in a curved space‐time. As this system does not support exact solutions due to considered background, the bound‐state solutions and local density of states (LDOS) are obtained numerically by means of the Numerov method. The combined effects of width of the nanoribbon (D), length of ribbon (L), twist parameter (ω), and B on the equations of motion and LDOS are analyzed and discussed. It is verified that the presence of B produces a constant minimum value of local density of state on the axis of helicoid, which is possible only for values large enough of ω, in contrast to the case for already studied in the literature.

Prediction of the ribbon length to determine the viscosity of ladle-refining powder containing CaF2 using inclined plane test and advanced mathematical model

ABSTRACT In the present research, the inclined plane test (IPT) and an author-developed advanced mathematical model were used to determine the viscosity of ladle-refining + CaF2 powder containing 3–10% CaF2 (LRC powder). The ladle slag powder is composed of such compounds as CaO, Al2O3, SiO2 containing percentages of CaF2 to make special changes to the chemical and physical properties of the compound. The procedure for determination of the viscosity obtained by IPT method was supported using a high-temperature viscometer. The results showed that the ribbon lengths of LRC powder obtained by using the IPT method were related to an Arrhenius relationship of viscosity. Furthermore, from the advanced mathematical relationships, it was found that there is a very close relationship between the oxygen-to-silicon molar ratio (O/Si), basic/acidic oxide molar ratio (B/A), the number of non-bridging oxygen per tetrahedrally-coordinated atoms (NBO/T), and the chemical compositions of LRC powder. Hence, the advanced mathematical relationships from the software output, and Statistical Package for the Social Sciences (SPSS), were used to determine the prediction model of the viscosity of LRC powder based on its chemical composition. This model had a very good correlation with the actual values obtained.

Full analytical solution of finite-length armchair/zigzag nanoribbons

Finite-length armchair graphene nanoribbons can behave as one-dimensional topological materials, that may show edge states in their zigzag-terminated edges, depending on their width and termination. We show here a full solution of tight-binding graphene rectangles of any length and width that can be seen as either finite-length armchair or zigzag ribbons. We find exact analytical expressions for both bulk and edge eigenstates and eigenenergies. We write down exact expressions for the Coulomb interactions among edge states and introduce a Hubbard-dimer model to analyze the emergence and features of different magnetic states at the edges, whose existence depends on the ribbon length. We find ample room for experimental testing of our predictions in $N=5$ armchair ribbons. We compare the analytical results with ab initio simulations to benchmark the quality of the dimer model and to set its parameters. A further detailed analysis of the ab initio Hamiltonian allows us to identify those variations of the tight-binding parameters that affect the topological properties of the ribbons.

Investigation the Effect of Sample Length in Different Currents and Frequencies of Measurement on the Magneto Impedance, Sensitivity and Extinction Field of Amorphous Cobalt Based Ribbons

In this paper, the effect of sample length on different currents and frequencies of measurement on magneto impedance (MI) of amorphous cobalt based ribbons was investigated. Firstly, we cut the ribbon to 4 cm length and then measurements of MI were carried out in constant current of 8 mA and frequency ranges between 1 to 15 MHz. The maximum sensitivity (9.16 Oe-1) at a frequency of 11 MHz was obtained. Also, the maximum extinction field was obtain 41.6 Oe. In the next step, the currents of 6 to 14 mA and the frequencies from 1 to 6 MHz were examined and in the optima conditions the maximum MI reached to 195%. In the next step, the length of ribbon was reduced to 2 cm and the MI was measured at previous currents and frequencies that results showed the reduction of MI in the most of conditions. In addition, at frequency ranges between 1 to 15 MHz, the maximum sensitivity was 10.2 Oe-1 and the maximum extinction field was 52.3 Oe. As a result, by decreasing the length of the ribbon, the MI reduce, but the sensitivity and excitation field increases, which is suitable for sensing applications. This behavior can be explained due to the demagnetization field, which is strongly dependent on the sample length.

Ribbonlength of twisted torus knots

The ribbonlength Rib[Formula: see text] of a knot [Formula: see text] is the infimum of the ratio of the length of any flat knotted ribbon with core [Formula: see text] to its width. A twisted torus knot [Formula: see text] is obtained from the torus knot [Formula: see text] by twisting [Formula: see text] adjacent strands [Formula: see text] full twists. In this paper, we show that the ribbonlength of [Formula: see text] is less then or equal to [Formula: see text] where [Formula: see text] and [Formula: see text] are positive. Furthermore, if [Formula: see text], then the ribbonlength of [Formula: see text] is less then or equal to [Formula: see text].

Theoretical study of heat transfer across biphenylene/h-BN superlattice nanoribbons

Controlling thermal conductivity of nanostructures is a key element in manufacturing tailor-made nanodevices for thermoelectric applications. Moreover, superlattice nanostructures have been demonstrated to be useful in achieving minimal thermal conductivity for the employed nanomaterials. In this work, we model two-dimensional biphenylene, a recently-synthesized sp2-hybridized allotrope of carbon atoms, for the implementation of a biphenylene/hexagonal Boron-Nitride (biphenylene/h-BN) superlattice nanoribbons. The effects of the length of ribbon and its superlattice period (lp) on the thermal conductivity are explored using molecular dynamics simulations. We calculated the length-independent intrinsic thermal conductivity (Kα) of the superlattice nanostructure, which was approximately 68% and 55% lower than the thermal conductivity of pristine h-BN and biphenylene nanosheets, respectively. The superlattice period largely determines the minimum thermal conductivity, which was at 64.1 W m−1k−1 for a period value of lp = 2.51 nm. This work opens a new window to tune and/or minimize thermal conductivity in nanoribbons when designing thermoelectric and thermal insulation materials for favorable applications.

Morphosedimentological features of the sea floor in the outer sector of the Bahia Blanca estuary, Argentina

The purpose of this paper is to analyze the morphology of the Quaternary relict features and bedforms that characterize the outer zone of an extensive mesomareal system, which is part of the Bahía Blanca estuary (Argentina), and to estimate the prevailing hydro-sedimentological conditions on the continental shelf adjacent to the estuary. Surveys with a multibeam bathymetric system, side-scan sonar and a high-resolution seismic system (3.5 kHz) were carried out and bottom sediment samples were collected. In general, the seafloor presents a varied configuration, marked by changes in its physiography. The Quaternary relict features are composed of two terraces (12–14 m and 18–22 m deep), with steeply sloping escarpments, that are oriented approximately parallel to the current coastline. Associated with these terraces, wide abrasion platforms develop with irregular and plateau-like structures up to 4 m high, together with large rocky blocks up to 6 m in diameter. Here, the predominant sediment corresponds to a gravel-sized material composed of quartzite boulders, siltstone fragments of up to 7 cm, and biogenic remains with different degrees of fragmentation. These sedimentological data, together with the bathymetric and seismostratigraphic information, indicate that the terraces and abrasion platforms are ancient shorelines that originated in an environment with high wave energy, corresponding to periods of stabilization of sea level rise during the final stage of the last postglacial transgression (late Pleistocene-Early Holocene). On the other hand, asymmetric dunes of different sizes (0.5 m < height < 5 m, 5 m < wavelength < 200 m), sand ribbons (length > 300 m) and comet marks originated in equilibrium with the present-day hydro-sedimentological conditions. The availability of sandy material mobilized as bedload is the determining factor for the generation of the varied bedforms. Thus, sand ribbons and comet marks are generated especially in the northern sector of the area, with mobile sediment thicknesses ≤ 0.5 m. With larger thicknesses the formation of dunes occurs. Their size and asymmetry show an intense transport of sand as bedload towards the continental shelf, the southern sector of the area being the main route of the sediment that leaves the estuary. This sediment is the supply source of the sandy shoals that are part of the great ebb delta developed on the continental shelf in the external area of the Bahía Blanca estuary.

Computational study of the effect of different doping elements on the thermal conduction properties of graphene nanoribbons

The dopant's atoms of various elements can be incorporated into the crystal lattice of graphene for the purpose of modulating its structural, optical and electrical properties. While the dopant's presence negatively affects the thermal conductivity, the exact effect of doping is still poorly understood and the mechanisms involved remain obscure. The effect of different doping elements on the thermal conductivity of graphene ribbons was investigated by performing molecular dynamics simulations to understand how impurities affect the thermal conduction properties of the nanostructured material. Graphene ribbons were doped with silicon, boron, or nitrogen elements to modify their nanostructure and thermal properties. The importance of edge structure was evaluated in comparison with that of doping. The Callaway model and the Einstein's model were used to provide the theoretical upper and lower bounds on the thermal conductivity. The contribution of optical phonons at different temperatures was evaluated in order to further understand the microscopic mechanisms of thermal conduction in the two-dimensional doped crystal. A computational analysis of thermal behavior was carried out in terms of the maximum density of states. The results indicated that a small number of dopant atoms can greatly change the ability to conduct heat. The thermal conductivity of the doped nanomaterial decreases successively in the order of nitrogen, boron, and silicon. Acoustical phonons still dominate the thermal conduction in the doped crystal, but the contribution of optical phonons become larger, especially at higher temperatures. The contribution of phonons in the optical branches increases with the doping concentration and can be as large as 6.0 %. In the presence of doping, the edge structure does not significantly affect the thermal conductivity and the maximum density of states. When graphene is heavily doped, the effect of ribbon length is insignificant while doping becomes dominant. The results have significant implications for the understanding of the relations between doping elements and thermal conduction properties.

Computational Study of the Thermal Rectification Properties of a Graphene-Based Nanostructure.

Thermally rectifying materials would have important implications for thermal management, thermal circuits, and the field of phononics in general. Graphene-based nanostructures have very high intrinsic thermal conductance, but they normally display no thermal rectification effects. The present study relates to a thermally rectifying material and, more particularly, to a graphene-based nanomaterial for controlling heat flux and the associated method determining the rectification coefficient. Thermal rectifiers using a graphene-based nanostructure as thermal conductors were designed. Vacancy defects were introduced into one end of the nanostructure to produce an axially non-uniform mass distribution. Modified Monte Carlo methods were used to investigate the effects of defect size and shape, vacancy concentration, and ribbon length on the thermal rectification properties. Anharmonic lattice dynamics calculations were carried out to obtain the frequency-dependent phonon properties. The results indicated that the nanoscale system conducts heat asymmetrically, with a maximum available rectification coefficient of about 70%. Thermal rectification has been achieved, and the difference in temperature dependence of thermal conductivity is responsible for the phenomenon. Defects can be tailored to modulate the temperature dependence of thermal conductivity. The power-law exponent can be negative or positive, depending upon the ribbon length and vacancy concentration. A computational method has been developed, whereby the numerous variables used to determine the rectification coefficient can be summarized by two parameters: the power-law exponent and the thermal resistance ratio. Accordingly, the rectification coefficient can be obtained by solving a simple algebraic expression. There are several structure factors that cause noticeable effects on the thermal rectification properties. Defect size, vacancy concentration, and ribbon length can affect the thermal conductance of the nanostructure symmetrically and significantly. Graphene-based nanostructure thermal rectifiers can be arranged in an array so as to provide thermal rectification on a macroscopic scale.

Quantum teleportation between the narrow armchair graphene nanoribbons with zigzag ends

We study quantum teleportation between the narrow armchair graphene nanoribbons (GNRs) with zigzag ends. Several influences including Coulomb repulsion among electrons, temperature and ribbon length on the output state and teleportation fidelity are discussed in detail. Moreover, we derive the entanglement of the output state and corresponding fidelity as a function of the input and channel entanglement. For practical applications, we also propose a scheme for implementing the single-qubit gates (X, Z and H gates) and two-qubit controlled-NOT gate in GNRs, based on the Bang-Bang control strategy and synchronous step magnetic field.

Molecular investigation and description of Iberozospeum n. gen., including the description of one new species (Eupulmonata, Ellobioidea, Carychiidae)

The subterranean realm of the Cantabrian-Pyrenean region of northern Spain harbours a rich diversity of Zospeum. Due to their tiny size and the difficulty of finding them alive, scarce animal material has been available for scientific investigation. Recent investigations of Zospeum shells have provided valuable, but limited insights towards our understanding of the evolutionary processes occurring within this taxon in northern Spain. In an integrative study, we investigate 57 populations of Zospeum from northern Spanish caves using two mitochondrial (COI and 16S) and two nuclear markers (H3 and 5.8 S rRNA + ITS2). Revealed is a separate radiation of the northern Spanish species for which the new genus, Iberozospeum, is proposed. The independent radiation of Dinaric Zospeum from that of northern Spain justifies the designation of Iberozospeum n. gen. Morphological evidence is provided via histological analysis of Iberozospeum vasconicum and SEM analyses of radulae of eastern Alpine, Dinaric and Iberian species. Important differences in morphological structure and character states are presented, including the first view of the sexually mature female and the presence of the giant albumen gland in an individual of the subterranean, troglobitic Carychiidae. Significant differences are revealed in superficial crystallographic structure of the columellar lamellae, the morphology of the columellar muscle and in the radula. Radular ribbon length, ribbon broadness, straightness of the ribbon base and cusp configuration are distinctive in the Iberian species. One new species is described corroborated by genetic and morphological characters.

Investigation of the rupture of a synthetic tape within the framework of the percolation theory

Within the framework of the percolation theory (bond problem), a new model of breaking a complex synthetic tape is proposed as a continuous-type phase transition when the state jump is zero. The percolation threshold and accompanying characteristics are calculated for the model of rupture of a synthetic reinforced tape when flowing along the first and second neighbours. The knots of the tape form a strip of a square lattice, the width of which is fixed. All nodes are intact and cannot be damaged, links (tape threads) can be intact and broken (blocked). The dependences of the percolation threshold in the bond problem and the relative deviation of the threshold from the ribbon length are calculated. It is proved that for the simplest model of one-dimensional percolation with percolation along the nearest neighbours (the problem of nodes), the percolation threshold in the thermodynamic limit is equal to unity. It is shown that, with an accuracy of 10%, the percolation threshold for a sufficiently long ribbon is equal to unity. This indicates that the system is quasi-one-dimensional. Thus, using the method of computer simulation, the percolation threshold, root-mean-square and relative threshold deviations were calculated. The critical susceptibility index was also calculated. In contrast to the usual percolation problem, in the proposed model it makes sense to consider only the region above the percolation threshold. The proposed model can be generalized to the case when nodes are also damaged (blocked), then we come to a mixed percolation model, which is supposed to be considered in the future.

Peeling and sliding of graphene nanoribbons with periodic van der Waals interactions

The peeling and sliding behaviors of graphene nanoribbons (GNRs) atop a graphene substrate are studied by a continuum model and numerical simulations. A periodic potential energy function is used to simulate the van der Waals interactions between the GNRs and the substrate in both the normal and tangential directions, coupling adhesion and friction within the same model. Numerical simulations and associated analyses reveal remarkably rich dynamics in peeling and sliding of GNRs. It is found that the simple 90-degree peeling of a GNR depends primarily on the normal (adhesive) interactions, with negligible sliding or shear interactions. In contrast, peeling with the end fixed in the in-plane directions leads to stick-slip sliding, with a higher peeling force and a critical peeling angle depending on both adhesion and friction. Notably, the stick-slip sliding is facilitated by formation and gliding of strain solitons in GNRs, and different types of strain solitons may form in the zigzag, armchair and chiral GNRs, including tensile, shear and mixed types. Unconstrained sliding is typically accompanied by both lateral and normal displacements, while constraining the displacements in the normal or lateral directions would generally lead to a higher pulling force for sliding. The peak pulling force as a measure of the sliding friction depends on the ribbon width quasi-linearly but becomes nearly independent of the ribbon length for relatively long GNRs (L >20 nm). Finally, two cases with coupled peeling and sliding of GNRs are considered, and a simple analysis is proposed to simultaneously determine the adhesion and friction properties of GNRs from measurable quantities in potential experiments.

Size effect on phonon hydrodynamics in graphite microstructures and nanostructures

The understanding of hydrodynamic heat transport in finite-sized graphitic materials remains elusive due to the lack of an efficient methodology. In this paper, we develop a computational framework enabling an accurate description of heat transport in anisotropic graphite ribbons by a kinetic theory approach with full quantum mechanical first-principles input. A unified analysis of the size scaling of the thermal conductivity in the longitudinal and transverse directions of the system is made within the computational framework complemented with a macroscopic hydrodynamic approach. As a result, we demonstrate a strong end effect on the phonon Knudsen minimum, as a hallmark of the transition from ballistic to hydrodynamic heat transports, along a rectangular graphite ribbon with finite length and width. The phonon Knudsen minimum is found to take place only when the ribbon length is \ensuremath{\sim}5--10 times the upper limit of the width range in the hydrodynamic regime. This paper contributes to a unique methodology with high efficiency and a deeper understanding of the size effect on phonon hydrodynamics, which would open opportunities for its theoretical and experimental investigation in graphitic micro- and nanostructures.

Применение метода блочной дискретизации для анализа электрической проводимости графеносодержащего шунгита.

Применение метода блочной дискретизации для анализа электрической проводимости графеносодержащего шунгита.

Synaptic ribbons foster active zone stability and illumination-dependent active zone enrichment of RIM2 and Cav1.4 in photoreceptor synapses

Rod photoreceptor synapses use large, ribbon-type active zones for continuous synaptic transmission during light and dark. Since ribbons are physically connected to the active zones, we asked whether illumination-dependent changes of ribbons influence Cav1.4/RIM2 protein clusters at the active zone and whether these illumination-dependent effects at the active zone require the presence of the synaptic ribbon. We found that synaptic ribbon length and the length of presynaptic Cav1.4/RIM2 clusters are tightly correlated. Dark-adaptation did not change the number of ribbons and active zone puncta. However, mean ribbon length and length of presynaptic Cav1.4/RIM2 clusters increased significantly during dark-adaptation when tonic exocytosis is highest. In the present study, we identified by the analyses of synaptic ribbon-deficient RIBEYE knockout mice that synaptic ribbons are (1) needed to stabilize Cav1.4/RIM2 at rod photoreceptor active zones and (2) are required for the darkness-induced active zone enrichment of Cav1.4/RIM2. These data propose a role of the ribbon in active zone stabilization and suggest a homeostatic function of the ribbon in illumination-dependent active zone remodeling.

Aligned monolayer MoS2 ribbons growth on sapphire substrate via NaOH-assisted chemical vapor deposition

This study reports the growth of aligned monolayer molybdenum disulfide (MoS2) ribbons on a sapphire substrate via NaOH-assisted chemical vapor deposition. The length of MoS2 ribbon is up to 400 μm. The MoS2 ribbon has excellent single crystal properties, a carrier mobility of {150 cm2 V−1 s−1, and a optical response of 103 mA W−1 at a wavelength of 550 nm. The growth model of MoS2 ribbons was given. NaOH reacts with MoO3 to form sodium molybdate droplets, which increase the fluidity of the molybdenum source on the substrate, realizing the vapor–liquid–solid growth of MoS2 on sapphire. The monolayer MoS2 ribbons have two kinds of arrangements on the sapphire substrate, one is the oriented growth affected by the interlayer van der Waals force and the lattice, and the other is the aligned growth constrained by the sapphire step. Our results promote the basic research and device applications of MoS2, and introduce a new way of synthesizing other one dimensional (1D) and 2D nanostructures.