Flat-topped Structures Research Articles

Tunable flat-top filter with cascaded compound gratings based on lithium niobate assisted by quasi-bound states in the continuum

We propose a tunable filter with cascaded compound gratings based on lithium niobate (LN). Herein, the reflectivity spectrum with a narrow-band and flat-top line shape can be obtained by using the quasi-bound states in the continuum (quasi-BICs) and selecting the appropriate grating offset. Simultaneously, we apply a voltage on LN to modulate the refractive index to achieve wavelength tunability. The demonstrated structure is sensitive to the incident angle, which can be used for angle sensing. Interestingly, an accidental BIC occurs by varying the length of the Fabry–Perot cavity to achieve phase shift conditions between the two grating layers. The presented tunable flat-top filter structure has promising applications in integrated sensing and communication.

Study on the construction of twisted cosine partially coherent beams and their propagation characteristics

We propose a novel Schell model source for generating twisted partially coherent beams with an initial radius of curvature, which is called a twisted flat-topped cosine Gaussian Schell-model (TFCGSM) source. The TFCGSM beam comprises a wavefront phase and a flat-top structure, with the source degree of coherence determined by two cosine functions. Based on the Huygens–Fresnel principle, the general analytical expression of the cross-spectral density function of the TFCGSM beam propagating through the paraxial ABCD optical system is derived, and then its propagation properties are studied. The results show that the conversion of the array of the beam and the non-uniform structure can be realized by adjusting the parameters in the source plane. As the propagation distance of the TFCGSM beam increases, it rotates around the axis and increases the intensity of the array distribution. Surprisingly, the initial radius of curvature can cause the beam to rotate. The unique shape and properties of the TFCGSM beam create new possibilities for optical communication and enhanced optical functions.

A Fatigue Method in the Tension-Compression Axial Stress Control Test of Automotive Sheet Steel

Abstract Focused on the common problem of easy buckling of specimens in the tension-compression axial stress control fatigue test of automobile sheet steel, a stress fatigue test method for thickness less than 2.5 mm was proposed. For two kinds of automobile sheet materials with different strength levels and thicknesses, fatigue specimens with different widths of test section, parallel lengths, and fillet radii are designed. Without the anti-buckling device, high-cycle fatigue tests with a stress ratio Rs = −1 at different stress levels were carried out, and the shape and size of the fatigue specimens of automobile sheet materials were determined by the number of fatigue life cycles of specimens with different sizes under the same stress cycle form. The results show that for automobile sheet steel with a thickness of 1.0–2.5 mm, the recommended sizes of the uniform-gauge fatigue specimens are width of test section w = (1–3) t, parallel length Lp = (1–3) w, and fillet radius r = (3–10) t. For automobile sheet steel with a thickness less than 1 mm, because the time-displacement curve jitters during the test, it is recommended to install an anti-buckling device, specifically the anti-buckling device with mortise and tenon structure by self-design and with a flattop structure recommended by ISO 1099-2017, Metallic Materials—Fatigue Testing—Axial Force-Controlled Method.

Confocal nonlinear optical imaging on hexagonal boron nitride nanosheets

Optical microscopy with optimal axial resolution is critical for precise visualization of two-dimensional flat-top structures. Here, we present sub-diffraction-limited ultrafast imaging of hexagonal boron nitride (hBN) nanosheets using a confocal focus-engineered coherent anti-Stokes Raman scattering (cFE-CARS) microscopic system. By incorporating a pinhole with a diameter of approximately 30 μm, we effectively minimized the intensity of side lobes induced by circular partial pi-phase shift in the wavefront (diameter, d0) of the probe beam, as well as nonresonant background CARS intensities. Using axial-resolution-improved cFE-CARS (acFE-CARS), the achieved axial resolution is 350 nm, exhibiting a 4.3-folded increase in the signal-to-noise ratio compared to the previous case with 0.58 d0 phase mask. This improvement can be accomplished by using a phase mask of 0.24 d0. Additionally, we employed nondegenerate phase matching with three temporally separable incident beams, which facilitated cross-sectional visualization of highly-sample-specific and vibration-sensitive signals in a pump-probe fashion with subpicosecond time resolution. Our observations reveal time-dependent CARS dephasing in hBN nanosheets, induced by Raman-free induction decay (0.66 ps) in the 1373 cm−1 mode.

Correlated dynamics of collective droplet excitations in a one-dimensional harmonic trap

We address the existence and dynamics of one-dimensional harmonically confined quantum droplets, appearing in two-component mixtures by deploying a nonperturbative approach. We find that, in symmetric homonuclear settings, beyond Lee-Huang-Yang correlations result in flat-top droplet configurations for either decreasing intercomponent attraction or larger atom number. Asymmetric mixtures feature spatial mixing among the involved components with the more strongly interacting or heavier one exhibiting flat-top structures. Applying quenches on the harmonic trap we trigger the lowest-lying collective droplet excitations. The interaction-dependent breathing frequency, being slightly reduced in the presence of correlations, shows a decreasing trend for stronger attractions. Semi-analytical predictions are also obtained within the Lee-Huang-Yang framework. For relatively large quench amplitudes the droplet progressively delocalizes and higher-lying motional excitations develop in its core. Simultaneously, enhanced intercomponent entanglement and long-range two-body intracomponent correlations arise. In sharp contrast, the dipole motion remains robust irrespectively of the system parameters. Species selective quenches lead to a correlation-induced dephasing of the droplet or to irregular dipole patterns due to intercomponent collisions.

Разнообразие рельефа подводных вулканических гор Северо-Восточной Атлантики

The structure of the volcanic seamounts of the Atlantis-Great Meteor group, as well as areas of the archipelagos of the Cape Verde Islands, the Canary Islands and the Azores was analyzed. Their simplest type is a cone-like structure with one peak (Mt. Maio). A more complex type is represented by two closely spaced volcanic edifices (Mt. Nola). Seamounts were also formed as a result of the activity of a central-type volcano and a fissure system (Mt. Te-Paps). A more complex morphology is represented by mountains that were formed as a result of the activity of an underwater volcano of the central type, which was combined with the activity of 3–4 radial fissure volcanic systems (Mt.Tropic). Seamounts were also formed only during fissure eruptions (Mts. Kondor, Kadamosto). They are ridges, tens of kilometers long without a clearly defined peak. All of the above types of mountains, with their rise above sea level, subsequent abrasion and subsidence, lead to the creation of flat-topped structures (guyots) (Mt. Sengor).

Formation and quench of homonuclear and heteronuclear quantum droplets in one dimension

We exemplify the impact of beyond Lee-Huang-Yang (LHY) physics, especially due to intercomponent correlations, in the ground state and the quench dynamics of one-dimensional so-called quantum droplets using an ab-initio nonperturbative approach. It is found that the droplet Gaussian-shaped configuration arising for intercomponent attractive couplings becomes narrower for stronger intracomponent repulsion and transits towards a flat-top structure either for larger particle numbers or weaker intercomponent attraction. Additionally, a harmonic trap prevents the flat-top formation. At the balance point where mean-field interactions cancel out, we show that a correlation hole is present in the few particle limit of these fluids as well as for flat-top droplets. Introducing mass-imbalance, droplets experience intercomponent mixing and excitation signatures are identified for larger masses. Monitoring the droplet expansion (breathing motion) upon considering interaction quenches to stronger (weaker) attractions we explicate that beyond LHY correlations result in a reduced velocity (breathing frequency). Strikingly, the droplets feature two-body anti-correlations (correlations) at the same position (longer distances). Our findings pave the way for probing correlation-induced phenomena of droplet dynamics in current ultracold atom experiments.

Experimental Investigation of Combustion Characteristics on Opposed Piston Two-Stroke Gasoline Direct Injection Engine

The combustion characteristics of an opposed-piston two-stroke gasoline engine are investigated with experiment. The energy conversion and exergy destruction are analyzed and the organization method of the combustion process is summarized. The effects of phase difference, scavenging pressure, injection timing, ignition timing, and dual spark plug ignition scheme on the combustion process and engine performance are discussed, respectively. The heat release rate of the opposed-piston two-stroke gasoline engine is consistent with the conventional gasoline engine. With the increase of opposed-piston motion phase difference, the scavenging efficiency decreases and overmuch residual exhaust gas is not beneficial to the combustion process. Meanwhile, the faster relative velocity of the opposed-piston near the inner dead center enhances the cylinder working volume change rate, which leads to the rapid decline of in-cylinder pressure and temperature. The 15 °CA of opposed-piston motion phase difference improves the scavenging and combustion process effectively. When scavenging pressure is 0.12 MPa, the scavenging efficiency and heat release rate are improved at medium-high speed conditions. With the delay of injection timing, the flame developing period decreases gradually, and the rapid burning period decreases and then increases. The rapid burning period may reach the minimum value when the injection advance angle is 100 °CA. With the delay of ignition timing, the flame developing period increases gradually, and the rapid combustion period decreases and then increases. The rapid combustion period may reach the minimum value when the ignition advance angle is 20 °CA. Notably, the flat-top piston structure should be matched with the dual spark plug, which the ignition advance angle is 20 °CA at medium-high load conditions.

Study of initial stage of entry of a solid sphere into shallow liquid with Synthetic Schlieren technique

Vertical entry of a 213 mm diameter solid sphere moving with a low speed of 16–40 mm/s onto a shallow liquid layer is investigated experimentally. The focus of the study is on deformation of the free surface before the actual contact between solid and liquid in presence of air cushioning. Owing to local character of air cushioning, the sphere is modeled by a spherical segment. The measurements were conducted with Synthetic-Schlieren technique, adapted to the present experimental configuration. In the studied range of parameters, the value of the Weber number is order O(1), giving rise to capillary oscillations of the free surface below the sphere. The primary solid-liquid contact at higher impact speeds (higher Weber number) occurs due to growth of a circular rim; the radius of contact is predicted satisfactory by existing theories assuming the lubrication/inviscid balance as a key mechanism. At lower speeds (lower Weber number), the contact is significantly delayed, being related with the effects due to surface tension and final horizontal extent of the spherical segment. In case of delayed contact, the evolution of free surface can be studied over a significant time span: the radial profile of the rim evolves into a flat-top structure, reminiscent of axisymmetric bore wave. The front of this wave propagates with constant speed, defined (with a good accuracy) by the condition that group velocity is equal to phase velocity of the waves. This condition is satisfied in i) the long-wave limit and ii) for the capillary waves of lowest admissible phase velocity. The second case is observed in the present experiments. The capillary waves generated by the impact “ride” on the top of the bore wave. The bore wave itself generates capillary waves in front of it, thereby producing a structure reminiscent of dispersive shock waves. Phase velocity and wavenumber of capillary waves are described well by linear theory of gravity-capillary waves in a liquid of finite depth.

Analysis of the Possibility of Using Wavelet Transform to Assess the Condition of the Surface Layer of Elements with Flat-Top Structures

The paper focused on a topic related to the possibilities of using wavelet analysis to evaluate the changes in the geometrical structures of the surfaces arising during the honing process with whetstones with variable granularity. The cylinder liners of the combustion engine are machined elements. The basics of the wavelet analysis and the differences between filtering with standardized filters (e.g., Gauss filter), Fourier analysis, and the analysis of the results obtained when measuring the surface roughness with other wavelets were described. Trials of honing four cylinder liners were carried out. Roughness measurements of 3D spatial structures of the prepared liners were made. The principle of selecting wavelets for roughness assessment of structures with cross-hatch pattern was described. Roughness structures generated on the honed surfaces of cylinder liners were assessed using Gaussian filtration and Morlet, Daubechies Db6, and Mexican hat wavelets. In order to demonstrate the differences generated when the Gaussian filtration and selected wavelets were used on surface structures, the surfaces obtained with the use of these filtering tools were subtracted from each other, which allowed obtaining information about the changes occurring on the assessed surfaces, which were generated after the use of various filtering tools. For the assessed surfaces, during the subtraction operation, the mean square error was calculated, informing about the degree of similarity of both compared surfaces. The result of the work carried out is the creation of basic recommendations for the selection of wavelets when assessing honed surfaces with different degrees of regularity of the traces generated on them.

Nondegenerate solitons and their collisions in Manakov systems.

Recently, we have shown that the Manakov equation can admit a more general class of nondegenerate vector solitons, which can undergo collision without any intensity redistribution in general among the modes, associated with distinct wave numbers, besides the already-known energy exchanging solitons corresponding to identical wave numbers. In the present comprehensive paper, we discuss in detail the various special features of the reported nondegenerate vector solitons. To bring out these details, we derive the exact forms of such vector one-, two-, and three-soliton solutions through Hirota bilinear method and they are rewritten in more compact forms using Gram determinants. The presence of distinct wave numbers allows the nondegenerate fundamental soliton to admit various profiles such as double-hump, flat-top, and single-hump structures. We explain the formation of double-hump structure in the fundamental soliton when the relative velocity of the two modes tends to zero. More critical analysis shows that the nondegenerate fundamental solitons can undergo shape-preserving as well as shape-altering collisions under appropriate conditions. The shape-changing collision occurs between the modes of nondegenerate solitons when the parameters are fixed suitably. Then we observe the coexistence of degenerate and nondegenerate solitons when the wave numbers are restricted appropriately in the obtained two-soliton solution. In such a situation we find the degenerate soliton induces shape-changing behavior of nondegenerate soliton during the collision process. By performing suitable asymptotic analysis we analyze the consequences that occur in each of the collision scenario. Finally, we point out that the previously known class of energy-exchanging vector bright solitons, with identical wave numbers, turns out to be a special case of nondegenerate solitons.

Kajian Struktur dan Komunikasi Organisasi Universitas Padjadjaran (Unpad)

In 2016, Rector of Universitas Padjadjaran (Unpad) issued a regulation on the organization and working procedures of Unpad managers. In the framework of university management in a formal context, the academic community of Unpad involves organizational communication. Organizational communication is used primarily within the structural scope of university or faculty managers. The messages dissemination from leaders to subordinates, inputs and suggestions from subordinates to leaders, and exchange of messages between officials is done through organizational communication. The research method used in this study is a descriptive-qualitative method. Using documentation method, the author seeks to explain and focus on how the structure and communication of management organization in Unpad. The results of the study indicate that Unpad's organizational structure is included in the organizational structure carrying out organizational levels between two and three levels, called flat top organization structure. Based on the organizational structure chart, Unpad adheres to a form of centralization in its organizational structure. While organizational communication that can be applied to Unpad's communication structure includes internal communication within the organization and external communication to/from outside the organization which are based on Unpad's organizational culture, RESPECT.

Weak scattering of multi-Gaussian Schell-model vortex beams on a deterministic medium

The scattering of a multi-Gaussian Schell-model (MGSM) vortex beam upon a deterministic medium is investigated within the accuracy of the first-order Born approximation. The explicit expression for the cross-spectral density function of the far-zone scattered field is derived, and some numerical examples are given to show the dependences of the spectral density and spectral degree of coherence on the source parameters and the scatterer parameter. It is found that by adjusting these parameters (especially the transverse coherence width of the source) we can shape the scattered beam profile into a quasi-Gaussian, flat-topped, or subsidence structure. Besides, for the distributions of the modulus of the spectral degree of coherence, secondary maxima occur when the incident beam is a vortex beam.

Phase portrait analysis of super solitary waves and flat top solutions

The phase portrait analysis of super solitary waves has revealed a new kind of intermediate solution which defines the boundary between the two types of super solitary waves, viz., Type I and Type II. A Type I super solitary wave is known to be associated with an intermediate double layer while a Type II solution has no such association. The intermediate solution at the boundary has a flat top structure and is called a flat top solitary wave. Its characteristics resemble an amalgamation of a solitary wave and a double layer. It was found that, mathematically, such kinds of structures may emerge due to the presence of an extra nonlinearity. Although they are relatively unfamiliar in the realm of plasma physics, they have much wider applications in other physical systems.

Highly Efficient Chip-Scale Package LED Based on Surface Patterning

Chip-scale package (CSP) light-emitting diodes (LEDs) are considered as the next generation of highly efficient package LED. However, they suffer from total internal reflection that limits their light extraction efficiency (LEE). In this letter, surface patterning, in terms of microstructures, as a well-controlled surface roughness method is designed and applied on CSP-LED to improve the LEE. Based on simulation results, pyramid and flat top pyramid structures have been designed and optimized. Four types of layouts, including tightly, interlaced, distant and chessboard layout, are also compared. A LEE enhancement of more than 20% is achieved. Furthermore, the four layouts with pyramid structures are fabricated using nano-imprint technology. The experimental results match the simulated results well with only a mismatch of 2.9%. The fabricated layout shows an enhancement of 20.31% when pyramid structures are fully filling the surface. Surface patterned CSP-LED, therefore, exhibits a great potential for high efficient LED.

Delicate scale multipeak and flat-top structures of solitary waves in multi-component plasmas

Numerically the delicate scale multipeak structures of the electrostatic solitary waves are found for the three-component (electron-positron-ion, i.e., EPI) plasmas. The complicated homoclinic phase portraits for this two-degree-of-freedom system are presented, which indicate that the system exhibits more abundant nonlinear phenomena. This finding is very useful to unveil the coherent dynamical behavior in laser-plasma interaction. It has an implication of electron acceleration by a laser with soliton wave mechanism.

Performance Assessment of Flexible Plasma Actuator with Flat-topped Structure

Performance Assessment of Flexible Plasma Actuator with Flat-topped Structure

405 nm laser processing of thin SU-8 polymer film

This paper presents a comprehensive study on the effect of laser fluence on a negative tone thin film resist, SU-8, using an all-fibre 405nm laser direct writing technique. 405nm Gaussian beam is delivered on the spin-coated SU-8 thin film using single mode fibre, followed by subsequent chemical developing process. Disc structure is formed where its dimension is affected by the laser fluence. We found that polymer processing using this technique can be categorized into three stages. In the first stage (fluence>90J/cm2), lens shaped structure is formed with linear increase in diameter with logarithmic increase in laser fluence. In second stage (fluence>600J/cm2), flat-top disc structure is formed and the increase in disc diameter slows down with increasing laser fluence. In the third stage (fluence>49kJ/cm2), crater is formed at the centre of the disc due to laser ablation. Moreover, relatively large exposure fluence above the value required for complete polymerization has allowed collateral thermal-polymerization of the surrounding of the disc structure and reduced aspect ratio of the structure. Hence, by controlling laser writing fluence, different structures mentioned above can be produced. This understanding serves as a basis for polymer patterning using the proposed all-fibre laser direct writing technique, which finds potential application in micro-lens array, polymer optical waveguide, photomask and Lab-On-Chip fabrication.

Vortex-induced morphology on a two-fluid interface and the transitions.

We investigate experimentally the steady flows in a cylinder containing two immiscible liquids, with the primary fluid being driven by the upper boundary rotating at constant speeds. The system exhibits interesting interplays between the flow fields and the morphology of the interface, with evidence showing that the remarkable flattop structure is a consequence of the vortex breakdown discovered decades ago, and that the deformability of the interface also feedbacks positively to the development of the vortices. Monitoring the topological structure of the flow fields defines the base states and transitions behind the morphology, whereas our survey over different aspect ratios also reveals rich phenomena of surface instabilities accompanying these steady states.

Optical properties of antireflective flat or rough patterned topped silicon cones gratings

Achieving a broadband antireflection property from material surfaces is one of the highest priorities in photosensing applications. To demonstrate a low reflectance, we are concerned with the study of the optical response of flat-, patterned- and rough-top silicon cone gratings. Based on previous work exploring pyramid gratings, we first designed several flat top structures that theoretically demonstrate an antireflective character within the middle infrared region. In order to extend the antireflective properties up to the visible wavelengths, patterned- and rough-topped cones have been fabricated as well. Optical characterizations of several samples were carried out in the visible and mid infrared range, in order to determine the effect of structuration on the performances of the different cones gratings.