Orthogonal Ones Research Articles

CFD analysis of novel two-pass, sinusoidal corrugated, trapezoidal channel for solar air heater

Solar is regarded as a clean and reliable source of energy. Solar air heaters (SAHs) are one of the most prevalent applications of solar energy. SAHs have normally low thermal efficiency. In order to increase thermal efficiency, a sinusoidal wave corrugation is employed on the base wall of the twin-pass channel of an absorbent plate with a sharp bend. A parametric study was conducted to study the effect of flow and geometric parameters i.e. wave height, pitch, and propagation angle of the wave with respect to flow inlet on performance parameters. Computational Fluid Dynamics (CFD) tool was implemented to examine the performance parameters i.e. heat transfer enhancement, pressure drop, and thermal performance factor. In comparison to the orthogonal ones, inclined corrugation is more efficient in terms of heat transfer. With the increase in roughness height, pitch, and corrugation angle, an increasing trend was observed in Thermal Performance Factor, followed by a diminishing trend. The corrugated channel having a roughness height ratio of 19, two waves in a single block with a 45° wave propagation angle seemed to be an optimal configuration with 35% enhancement in thermal performance factor as compared to the smooth channel, hence representing promising augmentation.

Assessment of airport security culture in Nigeria

The increase in technology and other parameters for security does not guarantee the expected secured airports without the appropriate behaviour, attitude, and customs of stakeholders. This study examines the airport security culture practices in Nigeria. The study adopted the Airports Council International (ACI 2021) survey instrument developed to assess security culture at airports. The instrument was designed as a questionnaire that presents eight dimensions of security culture with twenty-six (26) indicators using a 5-point Likert scale in order of agreement. The questionnaire was administered randomly to airport stakeholders, and a total response of 472 was recorded for data analysis. The data was subjected to exploratory factor analysis (EFA) to summarise and reduce the items to a few orthogonal ones representing Nigeria's common airport security culture practices. The study found that three (3) indicators relating to leadership roles do not significantly contribute to the factors serving as common security practices at airports in Nigeria. However, eight (8) common security practices were identified to be significant at airports in Nigeria. Strikingly, the study found that corporate security practices were not significant at Nigeria’s airports. The study highlights the need for airport managers to enhance security culture by adopting security as their corporate culture.

Implantation accuracy and operative variables in robot-assisted stereoelectroencephalography.

The stereoelectroencephalography (SEEG) procedure provides a unique 3D overview of the seizure-onset zone. Although the success of SEEG relies on the accuracy of depth electrode implantation, few studies have investigated how different implantation techniques and operative variables affect accuracy. This study examined the effect of two different electrode implantation techniques (external vs internal stylet) on implantation accuracy while controlling for other operative variables. The implantation accuracy of 508 depth electrodes from 39 SEEG cases was measured after coregistration of postimplantation CT or MR images with planned trajectories. Two different implantation techniques were compared: preset length with internal stylet use and measured length with external stylet use. Correlations between implantation accuracy and technique type, entry angle, intended implantation depth, and other operative variables were determined statistically using multiple regression analysis. Multiple regression analysis showed that the internal stylet technique exhibited a larger target radial error (p = 0.046) and angular deviation (p = 0.039) with a smaller depth error (p < 0.001) than the external stylet technique. Entry angle and implantation depth were positively correlated with target radial error (p = 0.007 and < 0.001, respectively) only for the internal stylet technique. Better target radial accuracy was achieved when an external stylet was used to open the intraparenchymal pathway for the depth electrode. In addition, more oblique trajectories were equally accurate to orthogonal ones with the usage of an external stylet, while more oblique trajectories were associated with larger target radial errors with the usage of an internal stylet (without an external stylet).

STAR-RIS-Enabled Short-Packet NOMA Systems

This paper analyzes the performance of simultaneous transmitting and reflecting (STAR) reconfigurable intelligent surface (RIS)-enabled short-packet non-orthogonal multiple access (NOMA) systems. A mode-switching protocol combined with partition strategies (MSPS) for the STAR-RIS design is proposed to simultaneously serve multiple actuators along with the discrete phase-shift alignment in order to reduce the STAR-RIS implementation costs. Approximate and asymptotic closed-form expressions for the average block error rate (BLER) and achievable rate have been derived to reveal some useful insights, such as the actuators' diversity order, coding gain, the power allocation factor, packet length, and the number of information bits. Numerical results confirm that: i) the considered system achieves better BLER balance among the actuators than classical RIS-based short-packet NOMA systems and higher achievable sum rate than RIS-based short-packet orthogonal multiple access ones; ii) the STAR-RIS with discrete phase shift design using 3-bit quantization achieves near-optimal performance with the continuous phase shift; iii) there is a trade-off between using bit quantizer and the total number of STAR-RIS elements; and iv) the power allocation strategy provides better average sum rate improvement than block-length increasing strategy.

Crowding expands and is less sensitive to target-flanker differences during a shift of visual attention

Target-flanker similarity and critical spacing control visual crowding when attention is pre-allocated, but these have not been studied when attention shifts. Flanked target Gabors appeared 8° left and right of central fixation throughout each 1.5 s trial. Subjects reported target Gabor tilt. In Expt. 1, target blinks increased accuracy, and flanker blinks decreased it, but only when attention shifted left or right from a central RSVP cue, hardly before it, indicating an exogenous/endogenous synergy. Whether parallel or orthogonal, flankers of the same wavelength as the target crowded substantially. Parallel half-wavelength flankers also crowded, but orthogonal half-wavelength ones did not. In Expt. 2, crowding when attention shifts was the same for targets and flankers within Bouma’s bound (2.5° apart) as outside it (5.0° apart.) In Expt. 3, Bouma’s bound was restored when attention was focused continuously on the target. We conclude that crowding temporarily expands and becomes less discriminative when attention shifts.

Broadband RCS Reduction Using Circular Sector Structure

In this paper, a new metasurface structure is designed to reduce radar cross section (RCS). In order to reduce the radar cross section (RCS), a new metasurface structure is designed. The unit adopts the polarization conversion metasurface structure, which is composed of asymmetric double arrow-shaped metal structure and etched on the dielectric substrate on the back of the metal plate. This polarization conversion metasurface (PCM) unit consists of asymmetric double arrow-shaped metal structure, and it is etched on a dielectric substrate backed with metallic plate. It can realize converting linear polarized waves to orthogonal ones in a broadband from 18.1 GHz to 32.7 GHz efficiently. According to the further development of the triangle chessboard layout, we also designed several new circular fan-shaped configurations, which realize RCS reduction in a wider -10 dB bandwidth compared with the triangle chessboard configuration. Finally, an optimized 8-lobed circular sector configuration composed of the designed PCM unit is selected for processing and testing. It can realize the RCS reduction greater than 10 dB in a wide bandwidth ranging from 13.7 GHz to 27.5 GHz, compared with the equal-sized metallic-backed dielectric substrate plate. The experimental results basically agree with the simulation ones. The proposed broadband circular sector structure has broad application prospects such as phased array antenna technology, electromagnetic stealth technology, and electromagnetic absorption technology.

Rationally-extended Dunkl oscillator on the line

It is shown that the extensions of exactly-solvable quantum mechanical problems connected with the replacement of ordinary derivatives by Dunkl ones and with that of classical orthogonal polynomials by exceptional orthogonal ones can be easily combined. For such a purpose, the example of the Dunkl oscillator on the line is considered and three different types of rationally-extended Dunkl oscillators are constructed. The corresponding wavefunctions are expressed in terms of exceptional orthogonal generalized Hermite polynomials, defined in terms of the three different types of X m -Laguerre exceptional orthogonal polynomials. Furthermore, the extended Dunkl oscillator Hamiltonians are shown to be expressible in terms of some extended Dunkl derivatives and some anharmonic oscillator potentials.

Chiral Metasurface Enabled Circularly Polarized OAM-Generating Folded Transmitarray Antenna With High-Gain Low-Profile and Broadband Characteristics

A broadband low-profile high-gain folded transmitarray antenna (FTA) is proposed to generate orbital angular momentum (OAM) with circular polarization. A chiral metasurface is employed as the top layer with the function of reflecting anticipant circularly polarized (CP) incident waves while transmitting the orthogonal ones. The geometric phase is then introduced to achieve 360° coverage of the transmission phase without affecting the reflection one. To obtain a high-gain and compact planar source, a 2 × 2 patch antenna array, integrated with the bottom metallic ground, is selected as the feed. Two proof-of-concept prototypes for vortex beam generation are constructed and experimentally measured. Both simulated and measured results demonstrate that <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> =–1 and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> =+1 OAM mode beams can be generated from 8.7 GHz to 9.5 GHz, and the measured maximum gains for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> =–1 and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> =+1 reach 18.1 dBi and 18.3 dBi with the corresponding peak aperture efficiencies of 6.1% and 6.4%, respectively. Meanwhile, the axial ratios (ARs) of the peak of far-field patterns are less than 3 dB over the entire operating frequency range, providing broadband CP vortex beams. The proposed high-gain low-profile broadband FTA antenna shows a promising perspective in OAM-based wireless communication.

Rapid live-cell sequential multiplexed imaging with fluorogenic RNAs.

Multiplexed detection of different cellular targets is an important goal in cell biology. However, multiplexed imaging in living cells is still extremely challenging. In terms of fluorescence imaging, significant spectral overlaps limit the number of distinguishable fluorophores that can be detected simultaneously. To solve this problem, in this project, we introduce a sequential imaging strategy termed “sequential Fluorogenic RNA Imaging-Enabled Sensor” (seqFRIES), to separately detect these spectrally overlapped fluorophores over time. Fluorogenic RNA aptamers are RNA strands that recognize and activate the fluorescence of otherwise non-fluorescent dye molecules. Here, we explored a list of reported fluorogenic RNA/dye pairs and identified five orthogonal ones. After genetically encoding all these fluorogenic RNAs together in cells, the corresponding dye molecules are added, imaged, and removed in a sequential manner. A very fast fluorescence activation and deactivation (in several minutes) was observed with these RNA/dye pairs. Taking advantages of such “image-and-wash” cycles, the multiplexing capacity of this imaging system is no longer limited by the excitation/emission spectral overlap of the fluorescent molecules. As a proof of concept, we show that the seqFRIES can perform robustly in both bacterial and mammalian cells, enabling multiplexed imaging of different RNAs, metabolites, and signaling molecules. We envision that this versatile multiplexed reporter system can be potentially adapted for imaging the cellular colocalization and dynamics of various target analytes, again inside living cells.

Improving the steady-state coherence and entanglement of two coupled qubits via composite system-reservoir interactions

In this work, we study the improvement of steady-state coherence (SSC) and steady-state entanglement (SSE) of two coupled qubits by means of composite system-reservoir interaction constructed by a linear combination of orthogonal and parallel ones. We show that in the non-equilibrium case, the SSC and SSE can be significantly enhanced by increasing the parallel components of the interaction Hamiltonian between the system of interest and the heat reservoirs. In addition, we find that in the non-equilibrium case, increasing the parallel components can enlarge the temperature (temperature difference) region where the SSC can maintain nonzero values. In the equilibrium situation, however, the SSC and SSE are not affected by the parallel components of the composite system-reservoir interactions.

A dual-broadband h-shaped metasurface for cross-polarization and asymmetric transmission with high stable incidence angle

This letter presents a bi-layered chiral metasurface to achieve angularly stable dual-broadband cross-polarization conversion and asymmetric transmission properties of electromagnetic waves with linear polarization. In this regard, any unit cell of the recommended chiral metasurface consists of two new h-shaped resonators configured on two opposite sides of a dielectric slab. Investigations of the simulated and experimental electromagnetic responses validate that the impinging x − (y−) and y − (x−) polarized waves can convert into transmitted y − (x−) and x − (−y) polarized waves at 7.5–8.6 GHz and 15–16.6 GHz, if the incident waves pass through the structure along −z (+z) direction, respectively. The obtained polarization conversion ratio (PCR) and asymmetric transmission parameters are more than 0.9 and 0.55 at both operated frequency bands, sequentially. Therefore, the proposed CMS has a significant potential to transform x- and y- polarized waves to orthogonal ones over the related frequency bands. The mechanism of the polarization conversions for any incident polarized wave has been verified by studying surface current distributions.

About grid generation in constructions bounded by the surfaces of revolution

For constructions bounded by the surfaces of revolution, structured grid generation technique is presented. Its technology has been elaborated within the variational approach for constructing optimal grids satisfying optimality criteria: closeness of grids to uniform ones, closeness of grids to orthogonal ones and adaptation to a given function. Grid generation has been designed for numerical solution of the differential equations modeling the vortex processes of multi-component hydrodynamics. In the technology, the three-dimensional construction in which it is required to construct a grid is represented in the form of the curvilinear hexahedron defining its configuration. The specific feature of the required configurations is that some faces of a curvilinear hexahedron lie in one plane and along edges of adjoining faces grid cells degenerate into prisms. Grid generation in the considered constructions has started to be developed by the elaboration of algorithms for the volume of revolution which has become the basic construction. The basic construction is obtained by the rotation through 180? around the axis of a generatrix consisting of straight line segments, arcs of circles and ellipses. Then the deformed volumes of revolutions are considered along with the generalizations of the volume of revolution which represent constructions obtained by the surfaces of revolution with parallel axis of rotation. The aim of the further development of the technology is to consider more and more complicated constructions and elaborate the technology for them. In the presentation, the current state of the development of the technology is given. Examples of generated grids are supplied.

TDAF: Top-Down Attention Framework for Vision Tasks

Human attention mechanisms often work in a top-down manner, yet it is not well explored in vision research. Here, we propose the Top-Down Attention Framework (TDAF) to capture top-down attentions, which can be easily adopted in most existing models. The designed Recursive Dual-Directional Nested Structure in it forms two sets of orthogonal paths, recursive and structural ones, where bottom-up spatial features and top-down attention features are extracted respectively. Such spatial and attention features are nested deeply, therefore, the proposed framework works in a mixed top-down and bottom-up manner. Empirical evidence shows that our TDAF can capture effective stratified attention information and boost performance. ResNet with TDAF achieves 2.0% improvements on ImageNet. For object detection, the performance is improved by 2.7% AP over FCOS. For pose estimation, TDAF improves the baseline by 1.6%. And for action recognition, the 3D-ResNet adopting TDAF achieves improvements of 1.7% accuracy.

Intrinsic in-plane nodal chain and generalized quaternion charge protected nodal link in photonics

Nodal lines are degeneracies formed by crossing bands in three-dimensional momentum space. Interestingly, these degenerate lines can chain together via touching points and manifest as nodal chains. These nodal chains are usually embedded in two orthogonal planes and protected by the corresponding mirror symmetries. Here, we propose and demonstrate an in-plane nodal chain in photonics, where all chained nodal lines coexist in a single mirror plane instead of two orthogonal ones. The chain point is stabilized by the intrinsic symmetry that is specific to electromagnetic waves at the Г point of zero frequency. By adding another mirror plane, we find a nodal ring that is constructed by two higher bands and links with the in-plane nodal chain. The nodal link in momentum space exhibits non-Abelian characteristics on a C2T - invariant plane, where admissible transitions of the nodal link structure are determined by generalized quaternion charges. Through near-field scanning measurements of bi-anisotropic metamaterials, we experimentally mapped out the in-plane nodal chain and nodal link in such systems.

Cayley Map for Symplectic Groups

Despite of their importance, the symplectic groups are not so popular like orthogonal ones as they deserve. The only explanation of this fact seems to be that their algebras can not be described so simply. While in the case of the orthogonal groups they are just the anti-symmetric matrices, those of the symplectic ones should be split in four blocks that have to be specified separately. It turns out however that in some sense they can be presented by the even dimensional symmetric matrices. Here, we present such a scheme and illustrate it in the lowest possible dimension via the Cayley map. Besides, it is proved that by means of the exponential map all such matrices generate genuine symplectic matrices.

2D Geometric Moment Invariants from the Point of View of the Classical Invariant Theory

The aim of this paper is to clear up the question of the connection between the geometric moment invariants and the invariant theory, considering a problem of describing the 2D geometric moment invariants as a problem of the classical invariant theory. We give a precise statement of the problem of computation of the 2D geometric invariant moments, introducing the notions of the algebras of simultaneous 2D geometric moment invariants, and prove that they are isomorphic to the algebras of joint $$\hbox {SO}(2)$$ -invariants of several binary forms. Also, to simplify the calculating of the invariants, we proceed from an action of Lie group $$\hbox {SO}(2)$$ to an action of its Lie algebra $${{\mathfrak {so}}}_2$$ . Though the 2D geometric moments are not as effective as the orthogonal ones are, the author hopes that the results will be useful to the researchers in the fields of image analysis and pattern recognition.

Efficient Orthogonal Bicomplex Bilinear DSP Algorithm Design

Abstract The present paper describes the development of a new technique for designing orthogonal bicomplex Digital Signal Processing (DSP) algorithms. In contrast to those previously reported on, this novel method is of universal application while being unaffected by either the type or the order of the real digital processing algorithm employed as a prototype. The proposed technique builds on Watanabe and Nishihara’s complex orthogonal transformation, and converts real or complex orthogonal transfer functions into bicomplex orthogonal ones. In this study, the new technique is applied to the design and testing of orthogonal bilinear bicomplex filters with a canonical number of elements, the main advantage of which is that they are several times lower in order. In this way, bilinear bicomplex orthogonal transfer functions are made up of real coefficient ones of the fourth-order, thereby reducing the order of the filter by a factor of four. The experiments demonstrate that the properties of the prototype filter are acquired by the bicomplex orthogonal filters, irrespective of the prototype being complex or real in nature.

Ext-groups in the Category of Strict Polynomial Functors

Abstract The aim of this paper is to study, by using the mathematical tools developed by Chałupnik, Touzé, and Van der Kallen, the effect of the Frobenius twist on $\operatorname{Ext}$-group in the category of strict polynomial functors. As an application, we obtain explicit formulas of cohomology of the orthogonal groups and symplectic ones.

An Ultra-Wide Band Polarization-Independent Random Coding Metasurface for RCS Reduction

In this paper, a novel ultra-wide band (UWB) random 3-bit coding metasurface with polarization independence has been designed to realize radar cross-section (RCS) reduction. The proposed structure consists of polarization conversion metasurfaces (PCMs), which possess the capability of rotating linear polarization waves to their orthogonal ones in an UWB. The polarization-independent property can be attributed to the random rotation angle of each constituting unit. Due to the randomness of 3-bit coding and rotation angle of each element, the divergence of the reflected beam is greatly improved. In addition, the effect of RCS reduction with respect to the unit period length and the unit position are also discussed. Finally, a prototype is fabricated and measured to validate the simulation. The experimental results demonstrate that an ultra-wide band RCS reduction over 10 dB, ranging from 18.3–42.2 GHz, can be attained by the proposed coding metasurface and the maximum reduction is 28.7 dB.

The connection between quadratic bent–negabent functions and the Kerdock code

In this paper we prove that all bent functions in the Kerdock code, except for the coset of the symmetric quadratic bent function, are bent–negabent. In this direction, we characterize the set of quadratic bent–negabent functions and show some results connecting quadratic bent–negabent functions and the Kerdock code. Further, we note that there are bent–negabent preserving nonsingular transformations outside the well known class of orthogonal ones that might provide additional functions in the bent–negabent set. This is the first time we could identify non-orthogonal (nonsingular) linear transformations that preserve bent–negabent property for a special subset.