Antisymmetric Distribution Research Articles

A Model of Temporal Encoding of Stimulus Orientation by Neuronal Responses in the Primary Visual Cortex

It has been shown experimentally that the stimulus orientation that elicits the optimal response in an orientation column in the primary visual cortex (area V1) undergoes rapid systemic changes that last 10–100 ms. These changes allow different orientation columns to encode information from multiple items in the visual space (the so-called temporal encoding). However, the mechanism of these changes is still unknown. In addition, most of the modern biophysical models are unable to reproduce these changes; the peak orientation of their responses is constant over time. In this paper, we suggest a method to improve the firing-rate ring model of the orientation hypercolumn by replacing the spatial symmetric distribution of local connections with a spatial anti-symmetric distribution. As a result, we obtained a more perfect model that is capable of reproducing such changes. Moreover, their amplitude is proportional to the extent of asymmetry in the spatial distribution of local connections.

Relation between nonlocal surface and bulk dark solitons

Abstract We investigate the existence and stability of nonlocal surface dark solitons at the interface formed by a nonlocal nonlinear self-defocusing medium and a linear medium. We find that nonlocal fundamental surface dark solitons are always stable in their entire existence domain, while high-order surface dark solitons are oscillatory stable. Comparing with nonlocal bulk dark solitons in amplitude and boundary conditions, nonlocal surface dark solitons can be regarded as the half of the corresponding bulk dark solitons with antisymmetrical amplitude distribution.

Giant amplification of terahertz plasmons in a double-layer graphene

The amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. The plasmon wave in a symmetric double-layer graphene structure splits into two branches with a symmetric and an antisymmetric distribution of tangential to graphene component of the electric field across the plane of symmetry of the structure. It is shown that, normalized to the wavelength, the terahertz plasmon amplification factor of the symmetric mode in the double-layer graphene structure could be greater than that in a single graphene layer by four orders of magnitude.

SURFACE ELECTROMAGNETIC WAVES IN A GAP BETWEEN TWO LEFT-HANDED MATERIALS

The slow surface electromagnetic waves that propagate along the planar waveguide structure that contains two identical isotropic left-handed material with the vacuum (or air) gap has been considered. The possibility of propagation of slow surface electromagnetic waves of TM and TE polarizations in the frequency range at which the dielectric permittivity and magnetic permeability are negative are shown. By selecting a frequency, one, two or three modes can be excited simultaneously. The group and phase velocities of the TE polarization waves are directed in opposite directions. The frequency range of the existence of the TE mode with an antisymmetric field distribution lies above the frequency range of the existence of the TE mode with a symmetric field distribution. The TM wave, depending on the wavelength, can be either forward or backward, or have zero group velocity. The wave of TM-polarization has a slightly varying group velocity in a sufficiently wide frequency range. A rich set of different properties of these waves make them promising in applications.

Horizontal Directional Coupler Formed With Waveguides of Different Heights for Mode-Division Multiplexing

We propose a horizontal directional coupler formed with two parallel waveguides of different heights. By breaking the symmetry in both the horizontal and the vertical direction, this directional coupler can be designed to allow us coupling between any two spatial modes of a few-mode waveguide, regardless of their symmetry properties, whereas a conventional directional coupler formed with planar waveguides of equal heights only allows us coupling between two spatial modes of the same symmetry in the vertical direction. As an example, we design and fabricate such a directional coupler with polymer material for the (de)multiplexing of the LP01 and the LP11b mode, which have a symmetric and an antisymmetric field distribution in the vertical direction, respectively. Our typical fabricated device shows a coupling ratio higher than 95% in the wavelength range from 1530 to 1560 nm. The insertion losses for the LP01 and LP11b modes are 9.6 and 12.8 dB, respectively. The performance of the device is weakly sensitive to temperature variations. The proposed directional coupler is easy to fabricate and can be used as a basic structure for the implementation of mode-controlling devices for mode-division-multiplexing applications.

Self-referenced refractive index sensing with hybrid-Tamm-plasmon-polariton modes in sub-wavelength analyte layers

A coupled Tamm-plasmon-polariton (TPP) hybrid-mode based self-referenced refractive-index sensor is proposed. The geometry is comprised of a sub-wavelength analyte (sensing) layer sandwiched between two metal-clad distributed-Bragg-reflectors (DBRs). Reflection spectrum of the geometry exhibits two discernible reflectivity minima within the photonic-bandgap of DBR. The reflectivity minima are essentially due to excitation of two hybrid modes which have symmetric and anti-symmetric field distribution about the center resulting in an anti-crossing behaviour exhibited by hybrid-TPP mode dispersion curves. The low frequency symmetric mode exhibits strong dispersive properties by virtue of significant presence of mode-field in sensing medium. On the other hand, the high-frequency anti-symmetric mode remains unchanged with alterations in sensing layer. Thus, we propose a self-referenced sensing scheme using hybrid-TPP modes with sensitivity varying from to in the visible band. In addition, the TPP resonance are appreciably sharp as compared to surface-plasmon based geometries which results in improved detection accuracy and figure of merit. We also present an analysis for optimizing the sensor design for enhancing the sensitivity as well as detection accuracy.

Self-inscribed antisymmetric long-period grating in a dual-core As2Se3-PMMA fiber.

We report for the first time that transmission of optical pulses centered at a wavelength of 1550 nm through a tapered dual-core As2Se3-PMMA fiber inscribes an antisymmetric long-period grating. The pulse power is equally divided between even and odd modes that superpose along the dual-core fiber to form an antisymmetric intensity distribution. A permanent refractive-index change that matches the antisymmetric intensity distribution is inscribed due to photosensitivity at the pulse central wavelength. The evolution of the transmission spectrum of the dual-core fiber is experimentally measured as the accumulated time that the fiber is exposed to the pulse is increased. A theoretical model of an antisymmetric long-period grating in a dual-core fiber computationally reproduces the experimentally observed evolution of the transmission spectrum. Experimental results indicate that antisymmetric long-period gratings induce effective group-velocity matching between the even and odd modes of the dual-core fiber, and reveal for the first time that long-period gratings can lead to slow light propagation velocities.

初期不整が軸方向圧縮力と単調逆対称曲げモーメントを受ける角形鋼管柱の弾塑性挙動に与える影響

It is well know that initial imperfections (e.g. bow-shaped imperfection of member, bow-shaped imperfection of plate and residual stress) have an influence on the performance of the columns. Most studies regarding this issue are investigated under single axial load or single shear force. In reality, the columns of steel structures are subjected to axial load and bending moment. Therefore, it is necessary to clarify the influence of the initial imperfections under combined loading. The influences of initial imperfections on the performance of square steel tubular columns under compressive axial force with one end monotonic bending moment were investigated by means of FEM in our previous study. As mentioned before, the columns of steel structures are subjected to axial load and bending moment, and the moment diagram is antisymmetric bending moment distribution or bending moment distribution close to antisymmetric. Therefore, it is not enough to clarify one end bending moment distribution. Also, in the previous study, the influence of the residual stress in the circumferential direction was not considered despite it exists in the member. In this study, the influences of initial imperfection on the performance of the square steel tubular column which is subjected to a compressive axial force with monotonic antisymmetric bending moment are investigated. The bow-shaped imperfection of the member (global imperfection) and continuous bow-shaped of the plate (local imperfection) are selected as geometrical initial imperfections and these imperfections are described by trigonometric function to reproduce easily. The residual stress in the longitudinal direction and the residual stress in the circumferential direction are selected as material initial imperfections. Firstly, the influence of initial imperfection on the performance and on the elastic-plastic behavor is investigated individually. Secondly, the influence of combined initial imperfections on the performance of the columns and on the elasto-plastic behavor is investigated; comparison between the experimental results are shown. Firstly, followings were found from the analysis results where initial imperfection is introduced in the member individually. 1) When the ultimate state was determined by local buckling, the global initial imperfection had a small impact on the performance. When the ultimate state was determined by bending deformation in in-plane, the direction of global imperfection had an impact on the performance as well its amplitude. 2) The amplitude of the local imperfection had a great impact on the performance of the columns. The maximum bending moment and the deformation capacity significantly decreased when its maximum amplitude exceeded 10% of permissible deviation. 3) When the ultimate state was determined by bending deformation, the plastic deformation capacity decreased with the increase of the amplitude of the residual stress in the longitudinal direction; initial stiffiness gradually decreased with the increace of its magnitude. 4) Regardless of the ultimate states, with the increase of the amplitude of the residual stress in the circumferential direction, the maximum bending moment and plastic deformation capacity decreased. Secondly, followings were found from the analysis results, where combined initial imperfections are introduced in the member. 5) In comparison with analysis results which were introduced the initial imperfection individually, the influence of the combination of initial imperfections on the variation trend of the performance was not confirmed. The local imperfection had the most significant influence on the perfomance in the imperfections that are considered in this study. 6) Validation of the numerical simulation was also performed; initial imperfections that could simulate test results in reasonable accuracy was shown.

A possible long-term activity cycle for ι Horologii: First results from SPI-HKα project

To detect stellar activity cycles and study the possible star-planet interactions (SPI's), we have developed both HK$\alpha$ and SPI-HK$\alpha$ projects since 1999 and 2012 respectively. In this work, we present preliminary results of possible SPI's studying the chromospheric activity and look for possible correlations between stellar activity and stellar/planetary parameters. We find that for stars with similar T$_{eff}$, stellar activity increases with the mass of the planet, similar to previous works. However, stellar ages can also play a role and a larger stellar sample is needed to verify these trends. We also note that some of these stars present a remarkably high level of chromospheric activity, even comparable with RSCvn or BY Dra active stars. In addition, we do not observe any correlation between stellar activity and semi-major axis. We present the first long-term activity study of the star $\iota$ Horologii, a young solar-type star which hosts a non-transiting Jovian planet and presents a high activity level. We analyze our own spectra, obtained between 2002 and 2015, combined with public HARPS observations. We calculate the Ca II indexes derived from the 987 CASLEO and HARPS spectra and convert them to the Mount-Wilson scale. We found a long-term activity cycle of $\sim$ 5 years which fits the active sequence of Bohm-Vitense. The amplitude of this longer cycle is irregular, as was also observed for the shorter one. This fact could be attributed to an antisymmetric distribution of active regions on the stellar surface.

Optical Activity Governed by Local Chiral Structures in Two-Dimensional Curved Metallic Nanostructures.

Chiral nanostructures show macroscopic optical activity. Local optical activity and its handedness are not uniform in the nanostructure, and are spatially distributed depending on the shape of the nanostructure. In this study we fabricated curved chain nanostructures made of gold by connecting linearly two or more arc structures in a two-dimensional plane. Spatial features of local optical activity in the chain structures were evaluated with near-field circular dichroism (CD) imaging, and analyzed with the aid of classical electromagnetic simulation. The electromagnetic simulation predicted that local optical activity appears at inflection points where arc structures are connected. The handedness of the local optical activity was dependent on the handedness of the local chirality at the inflection point. Chiral chain structures have odd inflection points and the local optical activity distributed symmetrically with respect to structural centers. In contrast, achiral chain structures have even inflection points and showed antisymmetric distribution. In the near-field CD images of fabricated chain nanostructures, the symmetric and antisymmetric distributions of local CD were observed for chiral and achiral chain structures, respectively, consistent with the simulated results. The handedness of the local optical activity was found to be determined by the handedness of the inflection point, for the fabricated chain structures having two or more inflection points. The local optical activity was thus governed primarily by the local chirality of the inflection points for the gold chain structures. The total effect of all the inflection points in the chain structure is considered to be a predominant factor that determines the macroscopic optical activity. Chirality 28:540-544, 2016. © 2016 Wiley Periodicals, Inc.

Hybrid micro/nano-structure formation by angular laser texturing of Si surface for surface enhanced Raman scattering.

Surface enhanced Raman spectroscopy (SERS) has drawn much research interest in the past decades as an efficient technique to detect low-concentration molecules. Among many technologies, which can be used to fabricate SERS substrates, laser ablation is a simple and high-speed method to produce large-area SERS substrates. This work investigates the angular texturing effect by dynamic laser ablation and its influence on SERS signals. By tuning the angle between the Si surface and laser irradiation, the distributions and sizes of laser induced hybrid micro/nano-structures are studied. By decorating with a silver film, plenty of hot spots can be created among these structures for SERS. It is found that when the incident laser angle is 15° at the laser fluence of 16.0 J/cm2, the SERS performance is well optimized. This work realizes antisymmetric distribution of nanoparticles deposited on Si surface, which provides a flexible tuning of the hybrid micro/nano-structures' fabrication with high controllability for practical applications.

Influence of a Deformable Contour Ring on the Nonlinear Dynamic Response of Cable Nets

The interaction between a cable net and its contour ring is investigated, regarding the nonlinear dynamic response of the system subjected to harmonic loads or wind action. Similarities and differences are highlighted between a network with fixed cable ends, accounting for rigid supports, and one with the cables anchored to a deformable ring, representing flexible supports. The sensitivity of the dynamic response of cable nets to their boundary conditions is demonstrated. Modelling the contour ring is proved to be indispensable, as it is responsible for new vibration modes, which may transform the entire behaviour of the net and modify the results with respect to the ones referring to the net with rigid supports. It is verified that the existence of the in-plane mode of the ring influences significantly the amplitude of the net oscillation for uniform spatial distribution of the load, while for antisymmetric spatial load distribution the presence of the ring does not alter significantly the net's dynamic response.

Snake states and their symmetries in graphene

Snake states are open trajectories for charged particles propagating in two dimensions under the influence of a spatially varying perpendicular magnetic field. In the quantum limit they are protected edge modes that separate topologically inequivalent ground states and can also occur when the particle density rather than the field is made nonuniform. We examine the correspondence of snake trajectories in single-layer graphene in the quantum limit for two families of domain walls: (a) a uniform doped carrier density in an antisymmetric field profile and (b) antisymmetric carrier distribution in a uniform field. These families support different internal symmetries but the same pattern of boundary and interface currents. We demonstrate that these physically different situations are gauge equivalent when rewritten in a Nambu doubled formulation of the two limiting problems. Using gauge transformations in particle-hole space to connect these problems, we map the protected interfacial modes to the Bogoliubov quasiparticles of an interfacial one-dimensional p-wave paired state. A variational model is introduced to interpret the interfacial solutions of both domain wall problems.

Stressed states and persistent defects in confined nematic elastica

We analyse the variety of solutions, both defect-free and containing defects in a confined nematic elastomer, arising as a result of competition between nematic ordering and elastic stresses. Phase field analysis predicts bifurcation of solutions with symmetric and antisymmetric distribution of nematic alignment from a perfectly aligned stressed state. The antisymmetric branch always has a lower energy, as confirmed by numerical computations away from the bifurcation point. At still higher deviations, states containing persistent defect pairs become preferable but defect-free states and states with defects coexist in a wide parametric range.

Strong Coupling between ZnO Excitons and Localized Surface Plasmons of Silver Nanoparticles Studied by STEM-EELS.

We investigated the strong coupling between the excitons of ZnO nanowires (NWs) and the localized surface plasmons (LSPs) of individual Ag nanoparticles (NPs) by monochromated electron energy loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscopy (STEM) instrument. The EELS results confirmed that the hybridization of the ZnO exciton with the LSPs of the Ag NP created two plexcitons: the lower branch plexcitons (LPs) with a symmetrical dipole distribution and the upper branch plexcitons (UPs) with an antisymmetrical dipole distribution. The spatial maps of the LP and UP excitations reveal the nature of the LSP-exciton interactions. With decreasing size of the Ag NP the peak energies of the LPs and UPs showed a blue-shift and an anticrossing behavior at the ZnO exciton energy was observed. The coupled oscillator model explains the dispersion curve of the plexcitons and a Rabi splitting energy of ∼170 meV was deduced. The high spatial and energy resolution STEM-EELS approach demonstrated in this work is general and can be extended to study the various coupling interactions of a plethora of metal-semiconductor nanocomposite systems.

On the mixing induced by tightly confined spheres in bounded shear flows

The mixing of solute tracers produced by a dilute suspension of spheres undergoing shear flow is examined in the limit that the gap between the sphere and the bounding walls becomes vanishingly small. Such tight confinement produces an envelope of flipping trajectories in the vicinity of the sphere giving rise to swift mixing of an anti-symmetric concentration distribution across the central plane of the gap. The size of this flipping envelope is demonstrated to be only weakly dependent on the angular velocity of the sphere and is accurately approximated by a two parameter model. This model can be used to calculate the additional mass transfer arising due to flipping. The degree of mixing in the system is directly related to the intensity of flipping which is shown to be a function of a single parameter χ given by γ̇a2ϕsD where γ̇ is the shear rate, a is the radius of the sphere, ϕs is the volume fraction of the spheres, and D is the diffusivity. As χ varies from 0 to ∞, the concentration distribution across the gap goes from being linear everywhere to being uniform across the flipping envelope, with the overall flux increasing by a factor of ∼3.

Lamb wave band structure in phononic crystal composed of multiple square stubs symmetric or anti-symmetric deposited on a homogeneous plate

This paper theoretically investigates the propagation of Lamb waves in a two-dimensional (2D) phononic crystal (PC) structure composed of multiple square stubs symmetric or anti-symmetric deposited on a thin homogeneous plate. The dispersion relations, the power transmission spectra and the displacement fields of the eigenmodes are studied by using the finite-element method (FEM). We investigate the effect of the distance between adjacent square stubs on the band gaps (BGs). The results show that the distance between adjacent square stubs can remarkably change the location and the width of the BGs. Meanwhile, we conducted a numerically study on the different results between the anti-symmetric and symmetric distribution of the scatterers. The band structure of the anti-symmetric structure PC is significantly different from the symmetric structure. In general, the distribution of the square stubs has an influence on the band structures. We further identify the physical mechanism of the distinction in the formation of the BG between the anti-symmetric and the symmetric model through the displacement fields of the eigenmodes. In addition, we find that the variation of the PC BGs in anti-symmetric and symmetric structure are sensitive to the distance between adjacent square stubs, which could be indispensable to practical applications such as BG tuning.

Study of High-Power Ka-Band Rectangular Double-Grating Sheet Beam BWO

It is attractive to use sheet beam vacuum devices to generate high frequency, high-power microwave radiation. In this paper, we present the numerical and experimental studies of a high-power Ka-band sheet electron beam backward wave oscillator (BWO), in which the double-grating rectangular waveguide is used as the slow wave structure (SWS) for its thermal and mechanical robustness. The fundamental mode of this kind of SWS is an antisymmetric mode which has an antisymmetric longitudinal field distribution and will nonsynchronously interact with the electron beam on two sides of the electron channel along the vertical direction. We put forward a method to overcome this trouble in this paper. To drive this BWO, a high-power sheet beam is used with a cross section of 30 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\times\,$ </tex-math></inline-formula> 1 mm. A thin graphite cathode is used for its superiority in producing a high current, high-quality electron beam. For an experimental electron beam of 141 kV and 1668 A, the output power of over 46.8 MW at 31.68 GHz is obtained, which corresponds to a beam–wave interaction efficiency of 19.9%. Compared with the conventional hollow beam BWO and the single-grating rectangular waveguide sheet beam BWO, the double-grating sheet beam BWOs efficiency is higher, which indicates that the double-grating sheet beam device is promising for producing millimeter wave radiation with high power and high efficiency.

Evaluation Method of Shear Capacity of Steel Reinforced Concrete Beam Considering Shear-span Ratio and Support Condition

A number of calculation equations for the design shear capacity of steel reinforced concrete (SRC) members with simple support are given in the Design Standards for Railway Structures and Commentary (Steel-Concrete Hybrid Structures). However, there are some equations that are applicable to a certain member because the scope of application for these equations is unclear. In addition, support conditions for transverse beams on railway viaducts are different from simple supports because both transverse beam ends are fixed. In this study, the scope of application for existing equations was clarified, and an equation to calculate the shear capacity of SRC beams under antisymmetric moment distribution was proposed.

Cavity length measurement: bias from misalignment and mismatching

SR-POEM, the sounding rocket principle of equivalence measurement, uses a set of six tracking-frequency laser gauges operating in Fabry-Perot cavities to determine the relative acceleration of two test masses (TMs) that are chemically different. One end of each cavity is a flat mirror on a TM; the other end is a concave coupling mirror mounted to a common reference plate. The tracking-frequency laser gauges work by locking a variable frequency laser to the cavity by the method of Pound, Drever, and Hall. Because the TMs are unconstrained, they are expected to rotate slightly during measurement. Although the distance measurements are intended to be based on the TEM₀₀ cavity mode, any misalignment will couple into higher-order transverse modes, particularly the TEM₁₀ and TEM₀₁. Light thus coupled will contribute a spurious signal to the cavity locking servo that causes a bias (i.e., a systematic error) in the length determination. The spurious signal proportional to the misalignment has an antisymmetric distribution at the detector and thus has a zero average, but causes a distance bias because of the inhomogeneity of the detector responsivity. To prevent such bias, SR-POEM includes a servo to keep the incoming laser beam aligned with the cavity. The required performance of that alignment servo is less stringent than has already been achieved by other projects. There is also a spurious signal proportional to the square of the misalignment that produces a symmetric distribution at the detector. This signal is also made unimportant by the operation of an alignment servo, even when operating well above the shot noise limit. We also look at the locking of a laser to a high finesse cavity and conclude that the alignment quality sets a bound on the ratio of measurement accuracy to cavity linewidth.