Null Position Research Articles

Design of Robust Broadband Frequency-Invariant Broadside Beampatterns for the Differential Loudspeaker Array

The directional loudspeaker array has various applications due to its capability to direct sound generation towards the target listener and reduce noise pollution. Differential beamforming has recently been applied to the loudspeaker line array to produce a broadside frequency-invariant radiation pattern. However, the existing methods cannot achieve a compromise between robustness and broadband frequency-invariant beampattern preservation. This paper proposed a robust broadband differential beamforming design to allow the loudspeaker line array to radiate broadside frequency-invariant radiation patterns with robustness. Specifically, we propose a method to determine the ideal broadside differential beampattern by combining multiple criteria, namely null positions, maximizing the directivity factor, and achieving a desired beampattern with equal sidelobes. We derive the above ideal broadside differential beampattern into the target beampattern in the modal domain. We propose a robust modal matching method with Tikhonov regularization to optimize the loudspeaker weights in the modal domain. Simulations and experiments show improved frequency-invariant broadside beamforming over the 250–4k Hz frequency range compared with the existing modal matching and null-constrained methods.

Effect of topical brinzolamide on visual function and waveform in patients of infantile nystagmus syndrome: A randomized control trial.

To evaluate the effect of topical carbonic anhydrase inhibitor (brinzolamide) versus placebo on visual function and waveforms in infantile nystagmus syndrome (INS). Prospective, placebo-controlled, double-blind, cross-over study. Setting- A tertiary eye care center. Patients- Cases of idiopathic INS with and without abnormal head posture aged ≥10 years who had not received previous treatment for nystagmus. Intervention- Patients were randomized into two groups. Group 1 was given placebo for 3 months, and after a washout period of 7 days started on topical brinzolamide for the next 3 months. In group 2, the order was reversed. The drops were administered topically three times (every 8 hours) in both eyes. Outcome measure- Binocular best corrected visual acuity (BCVA) using the ETDRS chart, eXpanded nystagmus acuity function (NAFX) score and INS waveforms obtained from eye movement recordings, intraocular pressure (IOP) by Goldmann applanation tonometer, near stereopsis by TNO stereo test, and change in abnormal head posture before and after intervention in the null position. A total of 29 cases completed the study (23 with abnormal head posture; 6 without abnormal head posture). While brinzolamide shows improvement in visual acuity and NAFX score in idiopathic INS, its clinical significance needs further evidence.

Analysis of Underlapped Symmetrically Ported Valve-Controlled Asymmetric Cylinder Drive

The valve-controlled cylinder drive system is the most common type among hydraulic applications. Nonlinear behaviour in such systems is inevitable when the valve spool is around its null position. We utilised the component linking method to investigate the nonlinearities in a Moog valve-controlled asymmetric cylinder drive system by simulation in Fortran, in which a generalised concept is introduced and validated by comparing to the experimental results. An X factor is proposed in the generalised concept to describe the asymmetric cylinder state, which is a constant when the cylinder is extending or retracting, but numerically calculated when the valve spool is in the underlap region. This analytical solution is approximately 200 times more computationally efficient than the numerical solution method. This paper utilises the component linking method to simulate the Moog valve-controlled asymmetric cylinder drive system in Matlab Simulink, and proposes an analytical solution for the X factor when the valve spool is in the underlap region. This analytical solution is approximately 200 times more computationally efficient than the numerical solution method.

Accurate vertical nanoelectromechanical measurements

Piezoresponse Force Microscopy (PFM) is capable of detecting strains in piezoelectric materials down to the picometer range. Driven by diverse application areas, numerous weaker electromechanical materials have emerged. The smaller signals associated with them have uncovered ubiquitous crosstalk challenges that limit the accuracy of measurements and that can even mask them entirely. Previously, using an interferometric displacement sensor (IDS), we demonstrated the existence of a special spot position immediately above the tip of the cantilever, where the signal due to body-electrostatic (BES) forces is nullified. Placing the IDS detection spot at this location allows sensitive and BES artifact-free electromechanical measurements. We denote this position as xIDS/L=1, where xIDS is the spot position along the cantilever and L is the distance between the base and tip. Recently, a similar approach has been proposed for BES nullification for the more commonly used optical beam deflection (OBD) technique, with a different null position at xOBD/L≈0.6. In the present study, a large number of automated, sub-resonance spot position dependent measurements were conducted on periodically poled lithium niobate. In this work, both IDS and OBD responses were measured simultaneously, allowing direct comparisons of the two approaches. In these extensive measurements, for the IDS, we routinely observed xIDS/L≈1. In contrast, the OBD null position ranged over a significant fraction of the cantilever length. Worryingly, the magnitudes of the amplitudes measured at the respective null positions were typically different, often by as much as 100%. Theoretically, we explain these results by invoking the presence of both BES and in-plane forces electromechanical forces acting on the tip using an Euler–Bernoulli cantilever beam model. Notably, the IDS measurements support the electromechanical response of lithium niobate predicted with a rigorous electro-elastic model of a sharp PFM tip in the strong indentation contact limit [deff≈12pm/V, Kalinin et al., Phys. Rev. B 70, 184101 (2004)].

Analysis of the Frequency-Dependent Vibration Rectification Error in Area-Variation-Based Capacitive MEMS Accelerometers.

The presence of strong ambient vibrations could have a negative impact on applications such as high precision inertial navigation and tilt measurement due to the vibration rectification error (VRE) of the accelerometer. In this paper, we investigate the origins of the VRE using a self-developed MEMS accelerometer equipped with an area-variation-based capacitive displacement transducer. Our findings indicate that the second-order nonlinearity coefficient is dependent on the frequency but the VRE remains constant when the displacement amplitude of the excitation is maintained at a constant level. This frequency dependence of nonlinearity is a result of several factors coupling with each other during signal conversion from acceleration to electrical output signal. These factors include the amplification of the proof mass's amplitude as the excitation frequency approaches resonance, the nonlinearity in capacitance-displacement conversion at larger displacements caused by the fringing effect, and the offset of the mechanical suspension's equilibrium point from the null position of the differential capacitance electrodes. Through displacement transducer and damping optimization, the second-order nonlinearity coefficient is greatly reduced from mg/g2 to μg/g2.

Hybrid Electromagnetic Simulation Using 2D-FDTD and Ray-Tracing Methods for Airport Surfaces

In this paper, a hybrid electromagnetic simulation method of two-dimensional FDTD and ray-tracing methods suitable for an airport surface was proposed. The power variation due to ground reflection, refraction and creeping is calculated by two-dimensional FDTD method and ray-tracing method is used to calculate the reflecting and diffracted powers from buildings. The proposed approach was validated by measurement using a 1/50 scale-model of an airport model with a building model in various positions at 5 GHz. The proposed method allowed measured power distributions to correlate with simulated figures to within 4.8 dB and their null positions were also estimated to an error tolerance of within 0.01 m.

A new method for analyzing the thermomechanical behavior and the null point movement of energy piles

During heating or cooling, an energy pile elongates or shortens around the null point, where the thermally induced displacement is zero. Previously proposed computing methods typically require an initial null point assumption and iterations before calculating the thermomechanical response. We proposed a new method to directly calculate the thermomechanical response of energy piles based on the boundary shape function and load transfer approach, and we verified its feasibility by comparing the results with a field test. Then, this work investigated the effects of the pile head and tip restraint conditions, soil restraint, and thermal and initial mechanical load magnitudes on the thermomechanical response of energy piles through a series of case studies, particularly focusing on the interaction between the aforementioned influencing factors and the null point location. The analysis demonstrates that the position of the null point is primarily determined by the end restraint boundary conditions of the pile; however, changing the soil restraint and thermal load will cause the null point to move, and the direction and distance of the movement are related to the symmetry between the two extremity restraint conditions. Finally, changing the initial mechanical load also shifts the null point position.

Visual search in infantile nystagmus syndrome

ABSTRACT Clinical relevance Research on infantile nystagmus syndrome (INS) and visual search is limited. Conducting this research could assist practitioners in understanding how INS affects the real-life visual activities of patients and aid in developing new clinical visual function assessments for INS. Background The aim of this work is to investigate how subjects with INS perform visual search tasks, and, particularly, to assess how INS subjects perform when targets are located at their null position or away from it, and when under additional cognitive demands. Methods INS subjects (N = 15) and controls (N = 20) performed conjunction and feature search tasks, both with and without mental arithmetic. Search performance was assessed using log-transformed total search time, gaze-dependent search time, and accuracy. Cognitive demand was quantified by pupil size and the NASA task-load index score. Results INS subjects showed longer search times compared to controls in conjunction search (P < 0.01), but not in feature search. Within INS and control subjects, the total search times were significantly increased by the addition of mental arithmetic (P < 0.0001). There was no difference in gaze-dependent search times between null target position and 15° away from null target position of subjects in conjunction search (P > 0.05). Accuracies were 100% for both control and INS subjects in both conjunction and feature search. Conclusion Conjunction visual search was impaired in adult INS subjects, and further worsened under increased cognitive demand. The null position did not affect the visual search performance in INS

The long-term outcomes of the Anderson-Kestenbaum procedure.

Nystagmus is an involuntary, conjugated, rhythmic movement of the eye that can be idiopathic or secondary to ocular or neurologic pathologies. Patients with nystagmus often have a position of gaze in which their symptoms are dampened or absent, referred to as the "null zone." The Anderson-Kestenbaum procedure is a bilateral recess-resect procedure of the four horizontal rectus muscles which aims to bring the null position into the primary gaze. This study aims to further elucidate long-term outcomes and factors associated with optimal postoperative outcomes. Patients with a diagnosis of nystagmus and a surgical code for strabismus between June 1990 and August 2017 were considered for inclusion in the study. Patients were included if they had undergone the Anderson-Kestenbaum procedure and had follow-up lasting at least 24 months post-operatively. Data collected included demographic information, characteristics of the nystagmus, underlying etiology of nystagmus, and pre-and post-operative measurements. 25 patients were included. At their last recorded follow-up, 44% of patients achieved an optimal surgical outcome -an abnormal head position of 10 degrees or less. 88% of patients showed an overall improvement in their head posture at the last follow-up. The absence of an abnormal head position at the visit closest to 24 months post-operatively was found to be significantly associated with the lack of a significant head position at the last follow-up visit. Optimal surgical outcomes were not significantly associated with the underlying diagnosis, the direction of the abnormal head position, or the type of nystagmus. The relatively long follow-up of this cohort allows this study to further elucidate the long-term outcomes of the Anderson-Kestenbaum procedure. Overall, our results suggest that although improvement in head position post-operatively is likely, it is still expected that many patients will have a residual abnormal head position after the procedure. The results of this study are helpful in counseling patients, especially knowing that if they do not have a significant head position at 24 months follow-up, they are unlikely to develop one. However, due to the small sample size, larger cohorts and more standardized follow-up may provide further insight into the procedure's outcomes.

Development and tests of a thrust stand with an in-situ null position adjustment and calibration method for low power plasma thrusters

A growing number of space missions use electric propulsion systems due to their higher specific impulse and greater efficiency compared to chemical propulsion systems. Because they are able to generate relatively low thrust values, conventional thrust measurement mechanisms used for chemical propulsion systems can not be used for electric propulsion systems. Thus, millinewton level thrust measurement systems are needed to be developed for measuring the low-level thrust of these types of thrusters. At the Bogazici University Space Technologies Laboratory (BUSTLab), a double inverted pendulum type thrust stand with a changeable thrust measurement range between 6 mN – 300 mN was designed, built and tested. The measurement resolution of this thrust stand can be as low as 100 μN level and it can be adjusted by changing the flexure stiffness and the mass of a counterweight. This study investigates the BUSTLab thrust measurement system and its key design points, with a particular focus on its in-situ null position adjustment and calibration process, and methods for mitigating external perturbations during thrust measurements.

GACP: graph neural networks with ARMA filters and a parallel CNN for hyperspectral image classification

ABSTRACT In recent years, the use of convolutional neural networks (CNNs) and graph neural networks (GNNs) to identify hyperspectral images (HSIs) has achieved excellent results, and such methods are widely used in agricultural remote sensing, geological exploration, and marine remote sensing. Although many generalization classification algorithms are designed for the purpose of learning a small number of samples, there is often a problem of a low utilization rate of position information in the empty spectral domain. Based on this, a GNN with an autoregressive moving average (ARMA)-based smoothing filter samples the node information in the null spectral domain and then captures the spatial information at the pixel level via spatial feature convolution; then, the null spectral domain position information lost by the CNN is located by a coordinate attention (CA) mechanism. Finally, autoregressive, spatial convolution, and CA mechanisms are combined into multiscale features to enhance the learning capacity of the network for tiny samples. Experiments conducted on the widely used Indian Pines (IP) dataset, the Botswana (BS) dataset, Houton 2013 (H2013), and the WHU-Hi-HongHu (WHU) benchmark HSI dataset demonstrate that the proposed GACP technique can perform classification work with good accuracy even with a small number of training examples.

Axiomatic characterizations of the family of Weighted priority values

AbstractWe introduce a new family of values for TU‐games with a priority structure, which both contains the Priority value recently introduced by Béal et al. and the Weighted Shapley values (Kalai &amp; Samet). Each value of this family is called a Weighted priority value and is constructed as follows. A strictly positive weight is associated with each agent and the agents are partially ordered according to a binary relation. An agent is a priority agent with respect to a coalition if it is maximal in this coalition with respect to the partial order. A Weighted priority value distributes the dividend of each coalition among the priority agents of this coalition in proportion to their weights. We provide an axiomatic characterization of the family of the Weighted Shapley values without the additivity axiom. To this end, we borrow the Priority agent out axiom from Béal et al., which is used to axiomatize the Priority value. We also reuse, in our domain, the principle of Superweak differential marginality introduced by Casajus to axiomatize the Positively weighted Shapley values. We add a new axiom of Independence of null agent position which indicates that the position of a null agent in the partial order does not affect the payoff of the other agents. Together with Efficiency, the above axioms characterize the Weighted Shapley values. We show that this axiomatic characterization holds on the subdomain where the partial order is structured by levels. This entails an alternative characterization of the Weighted Shapley values. Two alternative characterizations are obtained by replacing our principle of Superweak differential marginality by Additivity and invoking other axioms.

Characteristic-Mode-Analysis-Aided Design of Filtering Patch Antennas

A characteristic-mode-analysis (CMA)-aided design method for filtering patch antennas is proposed in this article. The method mainly includes three parts: first, use the theory of characteristic mode (TCM) to analyze the filtering antenna without feed structure (i.e., the radiator) to find the resonant modes in the passband and predict the positions of the inherent radiation nulls, which are then utilized to obtain the suitable size of the radiator and filtering elements; second, use modal analysis to find the best feed position to excite the resonant modes and simultaneously generate the inherent radiation nulls; and third, optimize the filtering antenna to obtain the optimal overall performance. For demonstration, two different types of filtering patch antennas are investigated using the proposed method. It has been shown that the method can truly realize the independent analysis and design of the radiator structure and the feed with the help of characteristic modal analysis, making the design process of both filtering antennas clearer and more efficient. In addition, the proposed method can find out and fully utilize the inherent radiation nulls, including the modal nulls and the nonmodal nulls of the radiator itself.

Conflicting Parameter Pair Optimization for Linear Aperiodic Antenna Array using Chebyshev Taper based Genetic Algorithm

In this study, the peak side lobe level (PSLL) in the radiation pattern of a linear antenna array (LAA) is lowered without affecting its first null beam width (FNBW). Antenna array synthesis is commonly applied to achieve high directivity, low side lobes, high gain and desired null positions in the output radiation pattern. But output parameters like PSLL, null positions and beam width conflict with each other, i.e. as one parameter improves, the other deteriorates. To avoid this problem, a multi-objective optimization algorithm can be implemented, in which both the conflicting parameters can be simultaneously optimized. This work proposes a multi-objective algorithm, which takes advantages of the well-known Chebyshev tapering and genetic algorithm (GA), to lower the PSLL without broadening the beam further. Array elements are fed using Chebyshev tapered excitations while GA is incorporated to optimize the elemental spacing. The results of 28-element LAA are compared with those of multi-objective Cauchy mutated cat swarm optimization (MO-CMCSO) existing in literature, which has also been proven to be superior to multi-objective cat swarm optimization (MO-CSO) and multi-objective particle swarm optimization (MO-PSO). Results indicate that the proposed algorithm performs better by further reducing the PSLL from -21.57 dB (MO-CMCSO) to -28.18 dB, while maintaining the same FNBW of 7.4 degrees.

Bandwidth-Enhanced 5G Mobile Phone Antenna Pair With Tunable Electric Field Null

In this communication, a bandwidth-enhanced antenna pair with a tunable electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field) null for the fifth-generation (5G) mobile phone application is presented. The proposed antenna pair is composed of a stub-loaded inverted-F antenna (IFA) and a simple feeding network. The stub-loaded IFA can obtain a wider impedance bandwidth and a feeding network is designed to excite the orthogonal dipole mode and adjust the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field null position. By adjusting the phase shifter in the feeding network, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field null can be moved to the feeding position of the IFA, achieving excellent isolation performance. A sub-6 GHz antenna pair is simulated and shows an isolation of better 16.5 dB within the N78 (3.3–3.8 GHz) band. By arranging the proposed antenna pair along two long edges of the ground plane, an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> multiple-input multiple-output (MIMO) system is designed, fabricated, and measured. The measured results show that the MIMO system could achieve isolation of better than 19.5 dB and envelope correlation coefficients (ECCs) of lower than 0.03. The measured total efficiencies are greater than 43% for each port. The proposed antenna reveals a novel decoupling strategy for wider bandwidth while retaining the isolation performance and compact size based on a pair of orthogonal mode.

Structural Restoration of Cretaceous Inversion Events in the Bjørnøyrenna Fault Complex, Western Barents Shelf

Inversion structures including folds, reverse faults are observed along the Bjørnøyrenna Fault Complex in the western Barents Sea, although the fault complex is extensional in origin and developed in mid-Jurassic to Early Cretaceous. Subsidence along the fault complex was interrupted in Early Cretaceous (Valanginian to early Barremian) because of syn-rift localized tectonic inversion, itself related to the uplift of the Loppa High. The Early Cretaceous inversion caused dextral transpression along the boundary faults adjacent to the Loppa High. The second phase of inversion is interpreted to be Late Cretaceous (mid-Cenomanian) in age, coeval to the deposition of the Kolmule Formation in the Bjørnøyrenna Fault Complex. The later phase of compression is of regional significance and related to NW‒SE directed far field stresses in Late Cretaceous which caused head-on inversion in the study area. The aim of present study is to identify and decipher eventual Cretaceous inversion structures in the Bjørnøyrenna Fault Complex by means of structural restoration. To these aims, 2D MOVETM, structural modeling and analysis software by Midland Valley Exploration Ltd (Glasgow, Scotland), is used and three key seismic lines crossing the central and northern segments of the Bjørnøyrenna Fault Complex are restored. Key profiles 1 and 2 reveal null point positions at the base of the Cretaceous (Hekkingen Formation). Null point positions show progressive compressional inversion of syn-rift Early Cretaceous deposits (Knurr Formation). Below and above null points the geometries of the restored faults show normal and reverse faulting respectively. The results of the restored key profiles 1 and 2 confirm reverse faulting at the Lower Cretaceous triggered by inversion of the study area. The restored sections also show positive inversion features associated with folding of the hanging wall of the base of the Upper Cretaceous (Kolmule Formation). The reconstruction of the amount of eroded material on the footwall block also suggests reverse faulting of the base of the Upper Cretaceous. In key profile 3 the footwall block is eroded up to the base of the Upper Cretaceous (Kolmule Formation) due to the uplift of the Loppa High. The corresponding restored section shows a compressional anticline associated with both Early and Late Cretaceous inversion events.

Quasi-absolute interferometric testing of cylinders.

A three-step quasi-absolute testing method for optical cylinders is proposed in this Letter. Three measurements are taken at the so-called cat's eye position and confocal null testing positions with a computer-generated hologram (CGH) rotated around the axis parallel to that of the cylinder. The quasi-absolute surface error of the cylinder is obtained by simple operations including addition/subtraction and flip of the datasets. The uncertainty is traceable to an optical flat. Two different CGHs are used for a convex cylinder and give consistent quasi-absolute testing results of the surface error, which experimentally validates the method.

Perception of Coherent Motion in Infantile Nystagmus Syndrome.

PurposeResearch on infantile nystagmus syndrome (INS) and motion perception is limited. We investigated how individuals with INS perform coherent motion tasks. Particularly, we assessed how the null position affects their performance.MethodsSubjects with INS and controls identified the direction of coherent motion stimuli (22 subjects with INS and 13 controls) in a two-alternative forced-choice design. For subjects with INS, testing was done at the null position and 15 degrees away from it. If there was no null, testing was done at primary gaze position and 15 degrees away from primary. For controls, testing was done at primary gaze position and 20 degrees away from primary. Horizontal and vertical motion coherence thresholds were determined.ResultsSubjects with INS showed significantly higher horizontal and vertical motion coherence thresholds compared with controls at both gaze positions (P < 0.001). Within the INS group, for 12 subjects with INS who had an identified null position, no differences in coherence thresholds were found between their null and 15 degrees away from it (P > 0.05).ConclusionsCoherent motion perception was impaired in subjects with INS. The null position did not significantly influence motion coherence thresholds for either horizontal or vertical motion.

Numerical and experimental investigation of leakage behavior at null position of high-pressure electro-pneumatic servo valve

Numerical and experimental investigation of leakage behavior at null position of high-pressure electro-pneumatic servo valve

Velocity Discrimination in Infantile Nystagmus Syndrome.

PurposeResearch on infantile nystagmus syndrome (INS) and velocity discrimination is limited, and no research has examined velocity discrimination in subjects with INS at their null position and away from it. This study aims to investigate how individuals with INS perform, compared with controls, when carrying out velocity discrimination tasks. Particularly, the study aims to assess how the null position affects their performance.MethodsINS subjects (N = 21, mean age 24 years; age range, 15–34 years) and controls (N = 16, mean age 26 years; age range, 22–39 years) performed horizontal and vertical velocity discrimination tasks at two gaze positions. Eighteen INS subjects were classified as idiopathic INS and three had associated visual disorders (two had oculocutaneous albinism, and one had congenital cataract). For INS subjects, testing was done at the null position and 15° away from it. If there was no null, testing was done at primary gaze position and 15° away from primary. For controls, testing was done at primary gaze position and 20° away from primary. Horizontal and vertical velocity discrimination thresholds were determined and analyzed.ResultsINS subjects showed significantly higher horizontal and vertical velocity discrimination thresholds compared with controls at both gaze positions (P < 0.001). Horizontal thresholds for INS subjects were elevated more than vertical thresholds (P < 0.0001) for INS subjects but not for controls. Within the INS group, 12 INS subjects who had an identified null position showed significantly lower horizontal and vertical thresholds at the null than at 15° away from it (P < 0.05).ConclusionsVelocity discrimination was impaired in INS subjects, with better performance at the null. These findings could assist in understanding how INS affects the daily activities of patients in tasks involving moving objects, and aid in developing new clinical visual function assessments for INS.