Flat Lattice Research Articles

ULTRA-WIDEBAND SCANNING ANTENNA ARRAY WIRE EMITTERS

The aim of the work is to determine the properties of the ultra-wideband scanning antenna array of wire emitters. A single element of the grid is a three-dimensional antenna Vivaldi. Numerical simulation of antenna arrays and single Vivaldi emitters was carried out by the method of integral equations in the thin-wire approximation using the original program and the MMANA program. The dimensions of all elements of a single emitter are determined by the criterion of matching and the shape of the radiation pattern for operation in the frequency range 2–18 GHz. The described variant of the antenna according to the matching criterion (SWR < 2) has a frequency overlap coefficient of 12. The narrowing of the frequency band of a single emitter in the composition of non-scanning and scanning gratings within the angle of 30 degrees is determined. The article deals with the range properties of antenna arrays depending on the parameters of the emitters and the possibility of phase scanning. It is shown that the greatest frequency band in agreement has a lattice with a minimum step of placement of emitters. In a flat antenna array, when scanning in the H-plane, the frequency band according to the matching criterion decreases by 2–3 times. It is shown that the linear lattice without scanning has a frequency overlap coefficient equal to 6 according to the criterion of matching emitters. This ratio decreases as the phase scan sector increases. In a flat lattice, the frequency overlap coefficient and the phase scan sector are smaller than in a linear lattice and decrease with the number of rows. The reduced antenna array has a number of design advantages and can be used in systems with ultra-wideband signals.

Symmetry breaking and lattice kirigami: Finite temperature effects

Recent work has analysed how deformations due to the insertion of a defect in a flat hexagonal lattice affect the ground state structure of an interacting fermion field theory. Such modifications result in an increase of the order parameter in the vicinity of the defect and can be explained by a kirigami effect, that is the combined effect of the curvature, locally introduced by the deformation in the lattice tessellation, and of a synthetic gauge field induced by the boundary conditions along the cut, performed to introduce the defect. In this work, we extend the formalism and previous results to include finite temperature effects.

Динамика импульсного перемагничивания магнитоодноосных наночастиц

The magnetic moment response of a magneto-uniaxial nanoparticle and a flat lattice of similar nanoparticles are being studied under the action of a short Gaussian pulse of a magnetic field in the presence and in the absence of its modulation. The periodic dependence of the final orientation and duration of a response of the magnetic moments on the pulse duration and its peak value have been revealed and analyzed. The effect on processes magnetization reversal of a weak magnetizing field and the deviation of the pulse of field from the transverse orientation has been studied. Have been shown that the influence of the dipole-dipole interaction leads to modulation of the response to the pulse action.

Symmetry Breaking and Lattice Kirigami.

We consider an interacting quantum field theory on a curved two-dimensional manifold that we construct by geometrically deforming a flat hexagonal lattice by the insertion of a defect. Depending on how the deformation is done, the resulting geometry acquires a locally nonvanishing curvature that can be either positive or negative. Fields propagating on this background are forced to satisfy boundary conditions modulated by the geometry and that can be assimilated by a nondynamical gauge field. We present an explicit example where curvature and boundary conditions compete in altering the way symmetry breaking takes place, resulting in a surprising behavior of the order parameter in the vicinity of the defect. The effect described here is expected to be generic and of relevance in a variety of situations.

Gephyrin: a key regulatory protein of inhibitory synapses and beyond.

Scaffolding proteins underlying postsynaptic membrane specializations are important structural and functional components of both excitatory and inhibitory synapses. At inhibitory synapses, gephyrin was identified as anchoring protein. Gephyrin self-assembles into a complex flat submembranous lattice that slows the lateral mobility of glycine and GABAA receptors, thus allowing for their clustering at postsynaptic sites. The structure and stability of the gephyrin lattice is dynamically regulated by posttranslational modifications and interactions with binding partners. As gephyrin is the core scaffolding protein for virtually all inhibitory synapses, any changes in the structure or stability of its lattice can profoundly change the packing density of inhibitory receptors and, therefore, alter inhibitory drive. Intriguingly, gephyrin plays a completely independent role in non-neuronal cells, where it facilitates two steps in the biosynthesis of the molybdenum cofactor. In this review, we provide an overview of the role of gephyrin at inhibitory synapses and beyond. We discuss its dynamic regulation, the nanoscale architecture of its synaptic lattice, and the implications of gephyrin dysfunction for neuropathologic conditions, such as Alzheimer's disease and epilepsy.

Matrix Synthesis of Graphene on a Diamond Surface and Its Simulation

A quantum-chemical simulation is performed for the transformation of the upper sublayer of carbon atoms in the lattice of single-crystal diamond into a flat graphene lattice under the influence of the atoms of a molten copper film on the diamond surface. It is established that the stable system configuration corresponds to the thermally activated motion of carbon atoms in the lower sublayer of the interface diamond layer to the position of graphene, i.e., at the same level as the atoms of the upper sublayer. The energy gain in comparison to the noninteracting subsystems of the copper and diamond atoms is approximately 0.7 eV per atom of the lower sublayer. The maximum size of the resulting graphene film is estimated and a possible mechanism for its rupture is considered.

Interference Processes During Reradiation of Attosecond Pulses of Electromagnetic Field by Graphene

Interference spectra during reradiation of attosecond pulses of electromagnetic field by graphene sheets are considered. Analytical expressions for calculations of spectral distributions are derived. As an example, the interference spectra of a graphene sheet and a flat rectangular lattice are compared.

Mass Constituents of a Flat Lattice Multiverse: Conclusion from Similarity between Two Universal Numbers, the Rocksalt-Type 2<i>D</i> Madelung Constant and the Golden Mean

In fairly good agreement with the consensus range of dark energy to matter this ratio of the critical density is suggested to be connected with the golden mean φ=0.6180339887, yielding for dark energy to matter mass fractions . Assuming the baryonic matter to be only 4.432%, the ratio of matter to baryonic matter would be , and further the ratio of dark matter to baryonic one . If one subtracts from the dark matter a contribution of antimatter with the same mass of baryonic matter, according to the antigravity theories of Villata respectively Hajdukovic, the remaining mass ratio would yield . Replacing the “Madelung” constant α of Villata’s “lattice universe” by φ, one reaches again 1 + φ as the ratio of the repulsive mass contribution to the attractive one. Assuming instead of a 3D lattice a flat 2D one of rocksalt type, the numerical similarity between the Madelung constant and φ−1 could not be just coincidence. The proposed scaling of the cosmological mass fractions with the square of the most irrational universal number φ may indicate that the chaotic cosmological processes have reached a quite stable equilibrium. This may be confirmed by another, but similar representation of the mass constituents by the Archimedes’ constant π, giving for respectively for the dark components . However, the intimate connection of φ with its reciprocal may ignite the discussion whether our universe is intertwined with another universe or even part of a multiverse with the dark constituents contributed from there.

Permeation through graphene ripples

Real graphene sheets show limited anti-permeation performance deviating from the ideally flat honeycomb carbon lattice that is impermeable to gases. Ripples in graphene are prevalent and they could significantly influence carrier transport. However, little attention has been paid to the role of ripples in the permeation properties of graphene. Here, we report that gases can permeate through graphene ripples at room temperature. The feasibility of gas permeation through graphene ripples is determined by detecting the initial oxidation sites of Cu surface covered with isolated graphene domain. Nudged elastic band (NEB) calculations demonstrate that the oxygen atom permeation occurs via the formation of C–O–C bond, in which process the energy barrier through the rippled graphene lattice is much smaller than that through a flat graphene lattice, rendering permeation through ripples more favorable. Combining with the recent advances in atoms intercalation between graphene and metal substrate for transfer-free and electrically insulated graphene, this discovery provides new perspectives regarding graphene’s limited anti-permeation performance and evokes for rational design of graphene-based encapsulation for barrier and selective gas separation applications through ripple engineering.

Structural Dynamics of Endocytosis by High-Speed Atomic Force Microscopy

Clathrin-mediated endocytosis is one of the major endocytosis pathways. Formation of clathrin coated vesicles (CCV) begins from relatively flat plasma membrane regions. Clathrin molecules bind to the CCV budding sites and assemble into a lattice covering growing vesicle. Initial flat clathrin lattice displays a hexagonal honeycomb architecture whereas the final CCV displays a mixture of hexagons and pentagons. The relation between clathrin lattice conversion and curvature generation in that process remains unknown. No dynamic structural analysis of the detailed mechanisms during CCV budding was achieved so far. High-speed atomic force microscopy (HS-AFM) permits observation of structural dynamics in biological processes because it allows performing imaging with nanometer spatial and subsecond temporal resolution. To study the CCV transformation by HS-AFM, we use a cell-free endocytosis assay based on plasma membrane patches. Combination of HS-AFM together with cell-free assay should permit direct, real-time observation of clathrin lattice rearrangement during CCV budding.

Additive lattice kirigami.

Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes.

Supersonic flow past a flat lattice of cylindrical rods

Two-dimensional supersonic laminar ideal gas flows past a regular flat lattice of identical circular cylinders lying in a plane perpendicular to the free-stream velocity are numerically simulated. The flows are computed by applying a multiblock numerical technique with local boundary-fitted curvilinear grids that have finite regions overlapping the global rectangular grid covering the entire computational domain. Viscous boundary layers are resolved on the local grids by applying the Navier–Stokes equations, while the aerodynamic interference of shock wave structures occurring between the lattice elements is described by the Euler equations. In the overlapping grid regions, the functions are interpolated to the grid interfaces. The regimes of supersonic lattice flow are classified. The parameter ranges in which the steady flow around the lattice is not unique are detected, and the mechanisms of hysteresis phenomena are examined.

Distinct Morphology of Human T-Cell Leukemia Virus Type 1-Like Particles.

The Gag polyprotein is the main retroviral structural protein and is essential for the assembly and release of virus particles. In this study, we have analyzed the morphology and Gag stoichiometry of human T-cell leukemia virus type 1 (HTLV-1)-like particles and authentic, mature HTLV-1 particles by using cryogenic transmission electron microscopy (cryo-TEM) and scanning transmission electron microscopy (STEM). HTLV-1-like particles mimicked the morphology of immature authentic HTLV-1 virions. Importantly, we have observed for the first time that the morphology of these virus-like particles (VLPs) has the unique local feature of a flat Gag lattice that does not follow the curvature of the viral membrane, resulting in an enlarged distance between the Gag lattice and the viral membrane. Other morphological features that have been previously observed with other retroviruses include: (1) a Gag lattice with multiple discontinuities; (2) membrane regions associated with the Gag lattice that exhibited a string of bead-like densities at the inner leaflet; and (3) an arrangement of the Gag lattice resembling a railroad track. Measurement of the average size and mass of VLPs and authentic HTLV-1 particles suggested a consistent range of size and Gag copy numbers in these two groups of particles. The unique local flat Gag lattice morphological feature observed suggests that HTLV-1 Gag could be arranged in a lattice structure that is distinct from that of other retroviruses characterized to date.

Spontaneous ripple formation in phosphorene: electronic properties and possible applications

According to the Mermin-Wagner theorem and theory of elasticity, long-range order in two-dimensional (2D) crystals will be inevitably destroyed due to a thermal fluctuation. Thus, a 2D lattice prefers a corrugation meaning that a 2D crystal is easy to present a ripple. In this work, we, via employing ab initio molecular dynamics (AIMD) simulations, for the first time evidenced that the inherent dynamics of phosphorene would lead to a spontaneous formation of ripples at room temperature. The height of a ripple closely associates with the temperature and the width. Via density functional theory (DFT) calculations, we further demonstrated that the emergence of ripples would remarkably reduce the bandgap of phosphorene. Via the construction of the unique phosphorene structure, we finally found that such a rippled structure is expected to be used in the light-emitting field. These results give us further knowledge of phosphorene, which goes beyond the current scope of phosphorene limited to the flat lattice.

Fuel lattice design in a boiling water reactor using a knowledge-based automation system

A knowledge-based fuel lattice design automation system for BWRs is developed and applied to the design of 10×10 fuel lattices. The knowledge implemented in this fuel lattice design automation system includes the determination of gadolinium fuel pin location, the determination of fuel pin enrichment and enrichment distribution. The optimization process starts by determining the gadolinium distribution based on the pin power distribution of a flat enrichment lattice and some heuristic rules. Next, a pin power distribution flattening and an enrichment grouping process are introduced to determine the enrichment of each fuel pin enrichment type and the initial enrichment distribution of a fuel lattice design. Finally, enrichment group peaking equalizing processes are performed to achieve lower lattice peaking. Several fuel lattice design constraints are also incorporated in the automation system such that the system can accomplish a design which meets the requirements of practical use. Depending on the axial position of the lattice, a different method is applied in the design of the fuel lattice. Two typical fuel lattices with U235 enrichment of 4.471% and 4.386% were taken as references. Application of the method demonstrates that improved lattice designs can be achieved through the enrichment grouping and the enrichment group peaking equalizing method. It takes about 11min and 1h 11min of CPU time for the automation system to accomplish two design cases on an HP-8000 workstation, including the execution of CASMO-4 lattice code. The results obtained with the application of the implemented system show the potential of the proposed methodology in the fuel lattice design automation for BWRs.

ENDOCYTOSIS. Endocytic sites mature by continuous bending and remodeling of the clathrin coat.

During clathrin-mediated endocytosis (CME), plasma membrane regions are internalized to retrieve extracellular molecules and cell surface components. Whether endocytosis occurs by direct clathrin assembly into curved lattices on the budding vesicle or by initial recruitment to flat membranes and subsequent reshaping has been controversial. To distinguish between these models, we combined fluorescence microscopy and electron tomography to locate endocytic sites and to determine their coat and membrane shapes during invagination. The curvature of the clathrin coat increased, whereas the coated surface area remained nearly constant. Furthermore, clathrin rapidly exchanged at all stages of CME. Thus, coated vesicle budding appears to involve bending of a dynamic preassembled clathrin coat.

Bend me, shape me: Clathrin in action

Endocytosis Endocytic clathrin-coated pits were among the first cellular structures described by electron microscopy over five decades ago. Despite this, the question remains: Does clathrin bind to the membrane as a flat lattice and then bend during coated pit invagination, or does clathrin assemble with a defined curvature as membranes invaginate? Avinoam et al. applied two state-of-the-art imaging approaches to resolve this conflict. They suggest that clathrin assembles into a defined flat lattice early in endocytosis, which predetermines the size of the vesicle. The assembled clathrin coat then rearranges through dynamic exchange of clathrin with the cytosolic pool to wrap around the forming vesicle. Science , this issue p. [1369][1] [1]: /lookup/doi/10.1126/science.aaa9555

Graphene with wedge disclination in the presence of intrinsic and Rashba spin orbit couplings

In this article, the modified Kane-Mele Hamiltonian is derived for graphene with wedge disclination and spin orbit couplings (intrinsic and Rashba). The wedge disclination changes the flat lattice into the conical lattice and hence modifies the spin orbit couplings. The Hamiltonian is exactly solved for the intrinsic spin orbit interaction and perturbatively for the Rashba spin orbit interaction. It is shown that there exists Kramer's degenerate midgap localized spin separated fluxon states around the defect. These zero energy spin separated states occur at the external magnetic flux value Φ±ΔΦ. The external magnetic flux Φ is introduced to make the wave function periodic when the electron circulates around the defect. It is found that this separation occurs due to the effect of the conical curvature on the spin orbit coupling. Further, we find these results are robust to the addition of the Rashba spin orbit interaction which is important for the application to spintronics and nanoelectronics.

Electron cryotomography studies of maturing HIV-1 particles reveal the assembly pathway of the viral core.

To better characterize the assembly of the HIV-1 core, we have used electron cryotomography (ECT) to image infected cells and the viral particles cryopreserved next to them. We observed progressive stages of virus assembly and egress, including flower-like flat Gag lattice assemblies, hemispherical budding profiles, and virus buds linked to the plasma membrane via a thin membrane neck. The population of budded viral particles contains immature, maturation-intermediate, and mature core morphologies. Structural characteristics of the maturation intermediates suggest that the core assembly pathway involves the formation of a CA sheet that associates with the condensed ribonucleoprotein (RNP) complex. Our analysis also reveals a correlation between RNP localization within the viral particle and the formation of conical cores, suggesting that the RNP helps drive conical core assembly. Our findings support an assembly pathway for the HIV-1 core that begins with a small CA sheet that associates with the RNP to form the core base, followed by polymerization of the CA sheet along one side of the conical core toward the tip, and then closure around the body of the cone. During HIV-1 assembly and release, the Gag polyprotein is organized into a signature hexagonal lattice, termed the immature lattice. To become infectious, the newly budded virus must disassemble the immature lattice by proteolyzing Gag and then reassemble the key proteolytic product, the structural protein p24 (CA), into a distinct, mature hexagonal lattice during a process termed maturation. The mature HIV-1 virus contains a conical capsid that encloses the condensed viral genome at its wide base. Mutations or small molecules that interfere with viral maturation also disrupt viral infectivity. Little is known about the assembly pathway that results in the conical core and genome encapsidation. Here, we have used electron cryotomography to structurally characterize HIV-1 particles that are actively maturing. Based on the morphologies of core assembly intermediates, we propose that CA forms a sheet-like structure that associates with the condensed viral genome to produce the mature infectious conical core.

Monoatomically thin polarizable sheets

We consider a flat lattice of dipoles modeled by harmonic oscillators interacting with the electromagnetic field in the dipole approximation. Eliminating the variables from the coupled equations of motion, we come to effective Maxwell equations. These allow for taking the lattice spacing $a$ to zero. As a result, we obtain reflection coefficients for the scattering of electromagnetic waves off the sheet. These are a generalization of that known from the hydrodynamic model. For instance, we get a nontrivial scattering for polarizability perpendicular to the sheet. Also, we show that the case of polarizability parallel to the sheet can be obtained in a natural way from a plasma layer of finite thickness. As an alternative approach, we discuss the elimination of the electromagnetic fields resulting in effective equations for the oscillators. These are shown, for $a\ensuremath{\rightarrow}0$, divergent behavior, resulting from the electrostatic interaction of the dipoles.