Opposite Polarity Research Articles

NHC-Catalyzed Aldimine Umpolung/6π-Electrocyclization Cascade to Access Tetracyclic Dihydrochromeno Indoles.

The umpolung of aldimines using N-heterocyclic carbenes (NHCs) is less explored compared to the established polarity reversal of aldehydes. Described herein is an NHC-catalyzed imine umpolung /6π-electrocyclization cascade, which leads to the atom- and pot-economic synthesis of biologically important dihydrochromeno indoles. For the first time, the nucleophilic aza-Breslow intermediates have been intercepted with unactivated alkynes. Preliminary mechanistic and DFT studies shed light on the role of the phenolic -OH moiety in promoting the addition of the aza-Breslow intermediate to the unactivated alkyne via an intramolecular proton transfer in a stepwise manner. DFT studies also support the regioselectivity preference for the 5-exo-dig cyclization pathway, leading to the exclusive formation of the indole products. Moreover, a comparison of Gibbs free energies provides insight into a thermodynamically preferred 6π-electrocyclization over a competing oxa-Michael pathway. Further, this strategy is applied to the formal synthesis of a Hepatitis C Virus (HCV) NS5A inhibitor in a step-economical method.

NHC‐Catalyzed Aldimine Umpolung/6π‐Electrocyclization Cascade to Access Tetracyclic Dihydrochromeno Indoles

AbstractThe umpolung of aldimines using N‐heterocyclic carbenes (NHCs) is less explored compared to the established polarity reversal of aldehydes. Described herein is an NHC‐catalyzed imine umpolung /6π‐electrocyclization cascade, which leads to the atom‐ and pot‐economic synthesis of biologically important dihydrochromeno indoles. For the first time, the nucleophilic aza‐Breslow intermediates have been intercepted with unactivated alkynes. Preliminary mechanistic and DFT studies shed light on the role of the phenolic −OH moiety in promoting the addition of the aza‐Breslow intermediate to the unactivated alkyne via an intramolecular proton transfer in a stepwise manner. DFT studies also support the regioselectivity preference for the 5‐exo‐dig cyclization pathway, leading to the exclusive formation of the indole products. Moreover, a comparison of Gibbs free energies provides insight into a thermodynamically preferred 6π‐electrocyclization over a competing oxa‐Michael pathway. Further, this strategy is applied to the formal synthesis of a Hepatitis C Virus (HCV) NS5A inhibitor in a step‐economical method.

Novel Topology for Modified Boost Series and Parallel Switching Capacitor DC-DC Converter

Theoretical and experimental work for a novel topology of DC-DC boost switching capacitor converter is introduced in this paper. This new design is an adjustment for boost series and parallel topology developed by Makowski. Thus, a comparison between the two designs presented in this paper aims to highlight the improvement in the conversion rate of the boost converter’s output voltage while using the same number and size of capacitors. Converter analyses for both with and without load are presented. Also, a boost converter with a nonlinear ferroelectric capacitor is presented to further increase the boost converter conversion rate using advantages of the ferroelectric capacitors, such as their big dielectric constant and polarization reversal.

Abstract 4138529: Acute Coronary Syndrome in a Patient with Situs Inversus Totalis

INTRODUCTION: Situs inversus totalis (SIT) occurs in 1 in 8000 births. 0.04% of cases involve ACS, posing a clinical challenge. We present a case of NSTE-ACS in a patient with SIT, where a universal diagnostic catheter was used to engage the coronary arteries. CASE PRESENTATION: 51-year-old Caucasian male with situs inversus totalis presented with worsening right-sided chest&right arm pain after shoveling snow. Initial examination was benign, but the EKG showed features of dextrocardia with T wave inversions in V2-V6. Laboratory results showed elevated CKMB (119.2)&up-trending troponin T 1.260 ng/ml. He was started on a Heparin drip and 81 mg of Aspirin with a plan for urgent cardiac catheterization. A coronary angiogram from the right radial with a 6 French Tiger Radial Catheter in the right anterior projection (RAO) 30 degrees showed minor luminal irregularities in the RCA, and 90% stenosis in the LAD. RCA was enganged anticlockwise and LCA clockwise. A 6 French XB 3.5 guide catheter was used to engage the LCA system, and the mid-LAD was stented. DAPT including Aspirin and Ticagrelor, was initiated. A TTE showed an EF of 25-30% with severe anterior, apical, and septal wall hypokinesis. The patient was discharged home with GDMT for coronary artery disease. DISCUSSION: CAD in dextrocardia can be challenging, requiring reversed limb and precordial leads and a right-sided ECG to show the extent of MI. Failure to recognize dextrocardia can lead to underestimating or missing MI. Typical findings include global negativity in lead I, positively deflected QRS in aVR, negative P-wave in lead II, reverse R-wave progression in precordial leads, and right-axis deviation. Our patient's EKG revealed polarity reversal in leads I and aVL, QS and rS patterns in precordial leads, and positive polarity in aVR, suggesting dextrocardia with T wave inversions, prompting further workup. Engaging the coronary arteries is challenging. We used a Tiger radial catheter with a reverse torque technique: anticlockwise for the RCA and clockwise for the LCA. Both arteries were engaged in the right anterior oblique view at 30 degrees. The cranial and caudal angulation remained the same, but the standard left anterior oblique view was switched with the right anterior oblique view and vice versa. The double inversion technique is useful during interventions when dealing with unfamiliar anatomy. It is not well-established whether dextrocardia is a risk factor for myocardial infarction.

Weak paleointensities from 1.6 Ga Greenland dykes: Further evidence for a billion-year period of paleomagnetic dipole low during the Paleoproterozoic

The Paleoproterozoic era is the longest in Earth's history, with significant changes hypothesised to have occurred in the deep Earth's physical and chemical conditions at this time. It has been suggested that the paleomagnetic field became weaker at this time (∼2.4 Ga) and remained weak for the next billion years. Paleomagnetism is intrinsically linked to, and is able to inform on, ancient deep Earth processes; a weak dipole strength sustained over this time period may have implications for both core and mantle evolution.We test this hypothesis here in a two-fold approach: (1) A paleointensity study on the widespread ca. 1.6 Ga diabase/dolerite Melville Bugt dyke swarm. The swarm extends along the west coast of Greenland for more than 1000 km and intruded over ∼13 million years, capturing polarity reversals of Earth's magnetic field. (2) A detailed statistical analysis on the long-term trend in average dipole moment from an improved paleointensity dataset (PINT.org) that has recently undergone a major update.Five of the Greenland dykes produce paleointensity results ranging from 1.4 μT to 5.1 μT (virtual dipole moment range 0.3–1.2 × 1022 Am2) during the mid-point of this extended period of ‘dipole low’. Our statistical study robustly confirms that this one-billion-year period was indeed associated with an anomalously weak dipole moment (2.7 × 1022 Am2) relative to 500-million-year intervals before and after, which were almost twice as strong. Sampling of more geographically diverse rocks from this time is needed to yield a clear picture of the long-term time evolution of the dipole moment.

Combined response of polar magnetotaxis to oxygen and pH: Insights from hanging drop assays and microcosm experiments

Magnetotactic bacteria (MTB) combine passive alignment with the Earth magnetic field with a chemotactic response (magneto-chemotaxis) to reach their optimal living depth in chemically stratified environments. Current magneto-aerotaxis models fail to explain the occurrence of MTB far below the oxic-anoxic interface and the coexistence of MTB cells with opposite magnetotactic polarity at depths that are unrelated with the redox gradient. Here we propose a modified model of polar magnetotaxis which explains these observations, as well as the distinct concentration profiles and magnetotactic advantages of two types of MTB inhabiting a freshwater sediment: a group of unidentified cocci (MC), and a giant rod-shaped bacterium (MB) apparently identical to M. bavaricum (MB). This model assumed that magnetotactic polarity is set by a threshold mechanism in counter gradients of oxygen and a second group of repellents, with, in case of MB, includes H+ ions. MTB possessing this type of polar magnetotaxis can shuttle between two limit depths across the redox gradient (redox taxis), as previously postulated for M. bavaricum and other members of the Nitrospirota group. The magnetotaxis of MB and MC is predominantly dipolar whenever the presence of a magnetic field ensures a magnetotactic advantage. In addition, MB can overcome unfavorable magnetic field configurations through a temporal sensing mechanism. The availability of threshold and temporal sensing mechanisms of different substances can generate a rich variety of responses by different types of MTB, enabling them to exploit multiple ecological niches.

Chromatic aberration in homogeneous diameter expansion growth of AlN crystals by the PVT method

AbstractHomogeneous diameter expansion growth is the preferred method for preparing large-sized AlN single crystals using the PVT method. However, chromatic aberration between the expansion and seed regions, as well as localized chromatic aberrations within the expansion region, are commonly observed, but not deeply investigated yet. This paper investigates the homoepitaxial lateral growth of AlN crystals using Al-polar face seeds and analyzes the crystal structure, composition, and optical properties of both the expansion and seed regions. XRD and Raman spectroscopy indicate no significant differences in crystallization quality between the expansion and seed regions. XPS and photoluminescence characterizations reveal that the light yellow color of the seed region is mainly due to $$V_{Al}$$ V Al defects. In contrast, the deeper yellow color in the expansion region is caused by $$V_{Al}$$ V Al –$$O_N$$ O N complex defects. Additionally, etching results exhibit a polarity reversal from the Al-polar to N-polar growth face in localized chromatic aberration region. The bonding angle of approximately $${90}^\circ$$ 90 ∘ at the $$B_{1}$$ B 1 bond (formation by the half-filled orbitals of the Al and N atoms) site, which occurs during the bonding of Al and N atoms, results in the polarity reversal during m-plane lateral growth. This work provides implications for the preparation of large-sized AlN single crystals.

Strain Fluctuations Unlock Ferroelectricity in Wurtzites

AbstractFerroelectrics are of practical interest for non‐volatile data storage due to their reorientable, crystallographically defined polarization. Yet efforts to integrate conventional ferroelectrics into ultrathin memories have been frustrated by film‐thickness limitations, which impede polarization reversal under low applied voltage. Wurtzite materials, including magnesium‐substituted zinc oxide (Zn,Mg)O, have been shown to exhibit scalable ferroelectricity as thin films. In this work, the origins of ferroelectricity in (Zn,Mg)O are explained, showing that large strain fluctuations emerge locally in (Zn,Mg)O and can reduce local barriers to ferroelectric switching by more than 40%. Concurrent experimental and computational evidence of these effects are provided by demonstrating polarization switching in ZnO/(Zn,Mg)O/ZnO heterostructures featuring built‐in interfacial strain gradients. These results open up an avenue to develop scalable ferroelectrics by controlling strain fluctuations atomistically.

Measurement of Pt consumption from Pt electrodes during water electrolysis using the quartz crystal microbalance (QCM) method: Effect of the water electrolysis method and the concentration of chloride ions in the aqueous solution

The consumption of the Pt electrocatalyst, which occurs when aqueous solution with neutral pH is electrolyzed with a Pt electrode to produce hydrogen or oxygen, was measured from the change in resonance frequency using the QCM method. First, it was found that the Pt consumption from the electrode during water electrolysis while applying a steady positive potential was very small, but it was almost proportional to the time the current was applied. Second, when electrolysis was performed by polarity reversal electrolysis of the anode and cathode periodically during electrolysis, the amount of Pt consumed increased in proportion to the number of polarity reversal was exchanged. The Pt consumption obtained by the QCM method was in close agreement with the value obtained by EDX method, proving the validity of the measurement method. The QCM measurement method was also proven to be a reliable method of measurement.

Distinct functions of three Wnt proteins control mirror-symmetric organogenesis in the C. elegans gonad.

Organogenesis requires the proper production of diverse cell types and their positioning/migration. However, the coordination of these processes during development remains poorly understood. The gonad in C. elegans exhibits a mirror-symmetric structure guided by the migration of distal tip cells (DTCs), which result from asymmetric divisions of somatic gonadal precursors (SGPs; Z1 and Z4). We found that the polarity of Z1 and Z4, which possess mirror-symmetric orientation, is controlled by the redundant functions of the LIN-17/Frizzled receptor and three Wnt proteins (CWN-1, CWN-2, and EGL-20) with distinct functions. In lin-17 mutants, CWN-2 promotes normal polarity in both Z1 and Z4, while CWN-1 promotes reverse and normal polarity in Z1 and Z4, respectively. In contrast, EGL-20 inhibits the polarization of both Z1 and Z4. In lin-17 egl-20 cwn-2 triple mutants with a polarity reversal of Z1, DTCs from Z1 frequently miss-migrate to the posterior side. Our further analysis demonstrates that the mis-positioning of DTCs in the gonad due to the polarity reversal of Z1 leads to mis-migration. Similar mis-migration was also observed in cki-1(RNAi) animals producing ectopic DTCs. These results highlight the role of Wnt signaling in coordinating the production and migration of DTCs to establish a mirror-symmetric organ.

Photocurrent-polarity-switching photoelectrochemical and electrochemical dual-mode sensing platform for the highly selective detection of trenbolone

As an emerging contaminant in the environment, trenbolone (TBE) has aroused a global health crisis and caused the huge impact on ecosystem. Its sensitive detection is critical to safeguard human health and ecosystem. Herein, a photocurrent polarity switching photoelectrochemical (PEC)-electrochemical (EC) dual-mode sensing platform was presented for highly selective and sensitive detection of TBE by ingeniously tailor signal probe. The tailored Cu2O@CuO-hemin acting as both photocurrent polarity reversal and electroactivity factor were cross-linked with TBE-BSA to obtain competitive conjugates for TBE. When the competitive response was initiated, numerous of Cu2O@CuO-hemin nanocomposites are introduced on the CdS-modified indium tin oxide electrode, serving as the reporting agent of EC/PEC dual-mode assay. The photocurrent polarity of the CdS-modified ITO can be effectively switched, enabling PEC analysis of TBE with distinguishing photocurrent changes. The linear response range is 1 pg/mL to 500 ng/mL, and the detection limit is 15.0 fg/mL. Meanwhile, the Cu2O@CuO could triggered the amplified current variations via effectually catalyzing the H2O2 decomposition compared to the CdS NPs, leading to the sensitive electrochemical detection of TBE with a detection limit 200 fg/mL and a linear response range from1 pg/mL to 500 ng/mL. Additionally, the developed sensing platform enabled mutual authentication of PEC/EC detection results, being conducive to increasing the assay reliability and accuracy. Such the dual-mode sensor has great potential for detecting environmental pollutants due to its improved selectivity and mutual authentication of results.

Polarization pinning at antiphase boundaries in multiferroic YbFeO3

Abstract The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO3. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO3 thin films using a combination of aberration-corrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO6 octahedra at the APB that bridges the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO6 octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains.

Microbial community acclimation via polarity reversal supports extensive dechlorination and anaerobic mineralization of 2,4,6-trichlorophenol in biocathode

In the anaerobic biocathode, reductive dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) mainly proceeded to produce 4-monochlorophenol (4-MCP) and phenol, while anaerobic mineralization was challenging. In this study, biocathodes microbial communities were first acclimated via potentials repeatedly adjusted between −0.278 V and +0.200 V (T-200), −0.278 V and +0.400 V (T-400), and −0.278 V and +0.600 V (T-600). Subsequently, all biocathode potentials were stabilized at −0.278 V for the degradation of 2,4,6-TCP. The results revealed that the T-600 achieved the highest degradation rate of 2,4,6-TCP (0.43 d−1), outperforming T-200 (0.051 d−1), T-400 (0.020 d−1), and open-circuit bioreactor (OC, 0.038 d−1) groups. In T-600, pare-dechlorination was facilitated, allowing for the conversion of 2,4,6-TCP to 2-monochlorophenol (2-MCP). Additionally, the detection of 4-hydroxybenzoic acid, an anaerobic mineralization intermediate of 2,4,6-TCP, indicated that anaerobic mineralization was also occurring. Polarity reversal occurred only in T-600 during the acclimation period, resulting in alterations to the electrical properties of the biocathode and microbial community. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) results indicated that there were more electroactive sites in biocathode of T-600, and the bidirectional extracellular electron transfer (EET) might be related to cytochrome. Mycobacterium (24.33% in slurry and 19.92% in biofilm), Thiobacillus (2.47% in slurry and 17.85% in biofilm), and Arenimonas (4.23% in slurry and 4.32% in cathode biofilm) were identified as the dominant electroactive bacteria in T-600, with Mycobacterium also playing an important role in the degradation of chlorophenols. These findings suggested that polarity reversal may represent a viable strategy for constructing microbial communities capable of achieving simultaneous dechlorination and mineralization of 2,4,6-TCP.

Diagnostics of porcelain insulators by partial discharges characteristics

RELEVANCE of the research is in the development of a non-destructive method for diagnosing porcelain insulators of high-voltage electrical equipment based on analysis of the characteristics of partial discharges (PDs). The problem of the final stage of breakdown of both the discharge gap and porcelain insulators recognizing is currently has not solved. THE PURPOSE. Recognition of PDs in solid insulation, study of PDs characteristics in a pre- breakdown situation, recognition of defective insulators based on PDs characteristics analysing. METHODS. The study of PDs characteristics for a defective and functional porcelain insulator were carried out. To study the characteristics of various types of PDs, including in the pre-breakdown situation, a system of surface-needle electrode system was used. RESULTS. The article describes compares the PDs characteristics obtained using standard R-400 device and a digital storage oscilloscope (DSO) using a telescopic antenna. A technique for recognizing the development of the pre-breakdown situation of the surface-needle discharge gap and the porcelain insulator was developed. The technique for recognizing a defective porcelain insulator from the amplitude-phase diagrams (APD) of PDs was developed. The method for assessing the breakdown voltage of porcelain insulators based on the characteristics of partial discharges was developed. CONCLUSION. At the moment of transition to the pre-breakdown stage were observed a sharp increase in the counter-movement of charges of opposite polarity. In the stage immediately before the breakdown, near zero values of the applied voltage of negative polarity, ordered PDs of the same polarity as the applied voltage were recorded in large numbers. These discharges led to an increase in leakage current and were interpreted as initial corona discharges. These discharges were recorded both by a telescopic antenna in a surface-needle system and in porcelain insulators.

A new role for excitation in the retinal direction-selective circuit.

A key feature of the receptive field of neurons in the visual system is their centre-surround antagonism, whereby the centre and the surround exhibit responses of opposite polarity. This organization is thought to enhance visual acuity, but whether and how such antagonism plays a role in more complex processing remains poorly understood. Here, we investigate the role of centre and surround receptive fields in retinal direction selectivity by exposing posterior-preferring On-Off direction-selective ganglion cells (pDSGCs) to adaptive light and recording their response to globally moving objects. We reveal that light adaptation leads to surround expansion in pDSGCs. The pDSGCs maintain their original directional tuning in the centre receptive field, but present the oppositely tuned response in their surround. Notably, although inhibition is the main substrate for retinal direction selectivity, we found that following light adaptation, both the centre- and surround-mediated responses originate from directionally tuned excitatory inputs. Multi-electrode array recordings show similar oppositely tuned responses in other DSGC subtypes. Together, these data attribute a new role for excitation in the direction-selective circuit. This excitation carries an antagonistic centre-surround property, possibly designed to sharpen the detection of motion direction in the retina. KEY POINTS: Receptive fields of direction-selective retinal ganglion cells expand asymmetrically following light adaptation. The increase in the surround receptive field generates a delayed spiking phase that is tuned to the null direction and is mediated by excitation. Following light adaptation, excitation rules the computation in the centre receptive field and is tuned to the preferred direction. GABAergic and glycinergic inputs modulate the null-tuned delayed response differentially. Null-tuned delayed spiking phases can be detected in all types of direction-selective retinal ganglion cells. Light adaptation exposes a hidden directional excitation in the circuit, which is tuned to opposite directions in the centre and surround receptive fields.

Diode and Selective Routing Functionalities Controlled by Geometry in Current-Induced Spin-Orbit Torque Driven Magnetic Domain Wall Devices.

Research on current-induced domain wall (DW) motion in heavy metal/ferromagnet structures is crucial for advancing memory, logic, and computing devices. Here, we demonstrate that adjusting the angle between the DW conduit and the current direction provides an additional degree of control over the current-induced DW motion. A DW conduit with a 45° section relative to the current direction enables asymmetrical DW behavior: for one DW polarity, motion proceeds freely, while for the opposite polarity, motion is impeded or even blocked in the 45° zone, depending on the interfacial Dzyaloshinskii-Moriya interaction strength. This enables the device to function as a DW diode. Leveraging this velocity asymmetry, we designed a Y-shaped DW conduit with one input and two output branches at +45° and -45°, functioning as a DW selector. A DW injected into the junction exits through one branch, while a reverse polarity DW exits through the other, demonstrating selective DW routing.

Spring Expanding-like Polarity Reversal in Photoelectrochemical Biosensing.

Although polarity-reversal photoelectrochemical (PEC) analysis can effectively eliminate false-positive and negative signals caused by interferents, achieving high sensitivity and accuracy is still a challenge. Hence, a spring expanding-like polarity reversal strategy with bipolar signal synergistic amplification is first proposed to help build a high-performance PEC analysis system. In this study, l-cysteine (l-cys) is discovered to not only act as a polarity regulator to elaborately reverse photocurrent via its covalent bond to Cu and Bi but also provide a relatively stable electron donor to effectively consume the photogenerated holes compared with commonly used H2O2 and ascorbic acid. More importantly, the amino and electron-rich functional acridine groups in the dye acriflavine endow an electrochemical activity to accelerate electron transfer between the electrode and solution, thus enabling bipolar synergistic signal amplification for acquiring an extremely enlarged photocurrent variation that is of great significance to overcome the rigorous signal prereversal depression and reversal amplification in traditional polarity-reversal systems. Accordingly, the PEC biosensor with the proposed spring expanding-like polarity reversal strategy exhibits excellent sensitivity and accuracy, reflecting ultralow detection limits of 0.04 fM toward lead ions (Pb2+) and good anti-interference ability in the detection of natural water samples. This work provides an avenue for exploring a new polarity reversal strategy for accomplishing high-performance PEC bioanalysis, expected to be widely applied in environmental monitoring, clinical diagnosis, and food supervision.

How Does the Critical Torus Instability Height Vary with the Solar Cycle?

The ideal magnetohydrodynamic torus instability can drive the eruption of coronal mass ejections. The critical threshold of magnetic field strength decay for the onset of the torus instability occurs at different heights in different solar active regions, and understanding this variation could therefore improve space weather prediction. In this work, we aim to find out how the critical torus instability height evolves throughout the solar activity cycle. We study a significant subset of Helioseismic and Magnetic Imager (HMI) and Michelson Doppler Imager Space-Weather HMI Active Region Patches (SHARPs and SMARPs) from 1996 to 2023, totaling 21,584 magnetograms from 4436 unique active-region patches. For each magnetogram, we compute the critical height averaged across the main polarity inversion line, the total unsigned magnetic flux, and the separation between the positive and negative magnetic polarities. We find the critical height in active regions varies with the solar cycle, with higher (lower) average critical heights observed around solar maximum (minimum). We conclude that this is because the critical height is proportional to the separation between opposite magnetic polarities, which in turn is proportional to the total magnetic flux in a region, and more magnetic regions with larger fluxes and larger sizes are observed at solar maximum. This result is noteworthy because, despite the higher critical heights, more coronal mass ejections are observed around solar maximum than at solar minimum.

Simulating overtaking interactions of dust-acoustic N-shock waves in oppositely charged dusty plasmas with Q-distributed electrons

Simulating overtaking interactions (OIs) of dust-acoustic N-shock waves (DANSWs) in dust plasmas with opposite polarities and q-distributed electrons and Boltzmann distributed ions are examined in this work. Reductive perturbation theory is used to obtain a Burgers’ equation (BE), and dust-acoustic N-shock wave solutions are derived using the Cole-Hopf transformation and exponential function. Numerical simulations show that the evolution and OIs of DANSWs and their electric fields are modified by the effects of negative/positive dust fluid kinematic viscosity, the ratio of negative dust to positive dust mass, and the nonextensive q-distribution of electrons. This work may help explain the properties of dust-acoustic shock waves in cometary tails and Jupiter's magnetosphere that support the propagation of nonlinear waves.

A Computationally Efficient Neuronal Model for Collision Detection with Contrast Polarity-Specific Feed-Forward Inhibition

Animals utilize their well-evolved dynamic vision systems to perceive and evade collision threats. Driven by biological research, bio-inspired models based on lobula giant movement detectors (LGMDs) address certain gaps in constructing artificial collision-detecting vision systems with robust selectivity, offering reliable, low-cost, and miniaturized collision sensors across various scenes. Recent progress in neuroscience has revealed the energetic advantages of dendritic arrangements presynaptic to the LGMDs, which receive contrast polarity-specific signals on separate dendritic fields. Specifically, feed-forward inhibitory inputs arise from parallel ON/OFF pathways interacting with excitation. However, none of the previous research has investigated the evolution of a computational LGMD model with feed-forward inhibition (FFI) separated by opposite polarity. This study fills this vacancy by presenting an optimized neuronal model where FFI is divided into ON/OFF channels, each with distinct synaptic connections. To align with the energy efficiency of biological systems, we introduce an activation function associated with neural computation of FFI and interactions between local excitation and lateral inhibition within ON/OFF channels, ignoring non-active signal processing. This approach significantly improves the time efficiency of the LGMD model, focusing only on substantial luminance changes in image streams. The proposed neuronal model not only accelerates visual processing in relatively stationary scenes but also maintains robust selectivity to ON/OFF-contrast looming stimuli. Additionally, it can suppress translational motion to a moderate extent. Comparative testing with state-of-the-art based on ON/OFF channels was conducted systematically using a range of visual stimuli, including indoor structured and complex outdoor scenes. The results demonstrated significant time savings in silico while retaining original collision selectivity. Furthermore, the optimized model was implemented in the embedded vision system of a micro-mobile robot, achieving the highest success ratio of collision avoidance at 97.51% while nearly halving the processing time compared with previous models. This highlights a robust and parsimonious collision-sensing mode that effectively addresses real-world challenges.