Weak Channel Research Articles

Channel–molecule attraction mediated molecule transport in confined nanochannels of COF membranes for nanofiltration

AbstractPorous membranes, a type of material widely used in nanofiltration, are confronted with the limitation that the influence of channel–molecule interactions on transport behaviors has yet been investigated in detail. Herein, covalent organic framework membranes with adjustable pore sizes (⁓ 2.5 nm and ⁓ 1.2 nm) and chemical groups (−F, −OH, and −CO−) were prepared by interfacial polymerization. We demonstrate that strong channel–molecule attraction induces the formation of stable solvent layers along nanochannel walls, which protect central molecules from the attraction of chemical groups. Significantly, stable solvent layers permit fast transport of ethanol (245.6 L m−2 h−1 bar−1) with reactive black (RB) rejection of 96%. Likely, for membranes with weak channel–molecule attraction, no solvent layers are formed and molecules also transport smoothly. Interestingly, membranes that exhibit moderate channel–molecule attraction exert metastable solvent layers, thus displaying high transport resistance. This hindrance effect on molecule transport becomes more pronounced in smaller nanochannels.

Meta-surface extinction theorem: a light-microscopic observation on the interference from meta-atoms

The macroscopic mechanism of light traveling based on the general Snell’s laws records the interactions between the gradient phases of meta-surfaces and the involved fields, but it can hardly adequately account for the detailed contributions of meta-atoms to the behaviors of light. Here, we demonstrate the light-microscopic observation of the interference from meta-atoms to characterize the meta-surface with the inhomogeneous spatial distribution of surface susceptibility. The meta-surface will generate multi-order diffractions with a main propagating channel and several other weaker channels, and the light emitted by the meta-atoms will also coherently cancel out the original incidence. Such an extinction theorem in the meta-surface regime can sufficiently predict the negative refraction with a phase gradient beyond the critical angle, instead of vanishing when following the route of general Snell’s laws.

The role of conformation states in the heterogeneity of fluorescence decay times in FAD in water–alcohol mixtures

We present the results of experimental and theoretical studies of excited state dynamics of flavin adenine dinucleotide (FAD) in water–methanol and water–ethanol mixtures as a function of alcohol concentration. The experimental studies have been carried out by recording time-resolved polarized fluorescence in FAD after excitation with short laser pulses using the time-correlated single photon counting method. The results obtained have shown that in aqueous solution fluorescence decay in FAD could be presented as a sum of four exponents with decay times of 20 ps, 210 ps, 2.70 ns, and 3.85 ns. Addition of methanol, or ethanol only insignificantly affected the decay time values, however caused dramatic changes in the contributions of the exponents to the fluorescence decay signal. Molecular dynamics (MD) simulations and QM/MM calculations in water–methanol and water–ethanol mixtures have been carried out and revealed the existence of three distinct conformation groups of FAD: Stack I, Stack III, and Open, which differ by mutual positions of the adenine and isoalloxazine rings and interaction between them. A model has been developed for elucidation of the excited state dynamics in FAD and of the nature of the heterogeneity of the recorded fluorescence decay times. The model classifies several relaxation channels in FAD after excitation by short laser pulses and suggests that the sub-nanosecond decay times of 20 ps and 210 ps both reflect fast fluorescence quenching due to electron transfer reactions in the vicinity of a conical intersection in the Stack III and Stack I conformations of FAD. The Stack I conformation is mostly stabilized by intramolecular forces due to π-stacking interactions between the adenine and isoalloxazine rings and internal hydrogen bonds, while the Stack III conformation is stabilized to a large extent by hydrogen bonds with external water molecules. It was also suggested that the nanosecond decay times of 2.70 and 3.85 ns were governed mostly by relatively weak non-radiative decay channels from the bottom of the lowest excited electronic state either via direct relaxation to the ground state, or via tunneling to a redox-pair excited state through potential barrier. The decay time of 2.70 ns was shown to refer mainly to folded conformations and the decay time of 3.85 ns to open conformations.

Strangeness production in sNN = 3 GeV Au+Au collisions at RHIC

We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of sNN = 3 GeV with the STAR experiment at RHIC. KS0 meson and Λ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of Λ and KS0 are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4π yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.

Computation of 2D Supercritical Free-Surface Flow in Rectangular Weak Channel Bends

Computation of 2D Supercritical Free-Surface Flow in Rectangular Weak Channel Bends

Performance of a mass recovery microchannel membrane-based heat/mass exchanger in an absorption chiller

Solution heat exchanger plays a vital role to recover the heat and improve the system coefficient of performance (COP) in absorption chiller. This study introduces an innovative microchannel membrane-based heat/mass exchanger (MMHX), aiming at replacing conventional heat exchangers. The MMHX notably increases the solution concentration difference between absorber and desorber, leading to an improved COP. This research comprehensively analyzes the heat and mass transfer performance, along with the solution pressure drop characteristics of the MMHX, in both co-current and counter-current flows, comparing these with a traditional microchannel heat exchanger (MicroHX). Due to the lower thermal conductivity of the porous membrane, the MMHX demonstrates a heat transfer capacity that is 3.5 times and 2.1 times lower than the MicroHX in the respective flow directions. However, the absorption chillers equipped with the MMHX outperform those with MicroHX at solution flow rate above 0.03 kg/s, with average improvement in COP of 15.76 %. While introducing a gap between strong and weak solution channels in the MMHX aids mass transfer, it also reduces heat recovery efficiency, impacting the COP negatively. Consequently, a gap-less MMHX is identified as an optimal solution, enhancing COP and advancing the development of efficient, compact absorption chillers for future space cooling.

Supply chain finance on corporate debt financing behavior under uncertainty

At present, the world is undergoing a major change that has not been seen in a century. How to deal with the increase in environmental uncertainty has become an important problem facing the high-quality development of Chinese enterprises. Chinese enterprises generally face financing constraints, and weak debt financing channels hinder the process of high-quality development of enterprises. How to improve debt financing capabilities has become a practical problem that Chinese enterprises urgently need to solve in response to the increase in environmental uncertainty. This paper first introduces the concept, characteristics and common patterns of supply chain finance , and also explains the definition of uncertainty environment and its impact on corporate operations and financing. By systematically combing through relevant domestic and foreign literature, this paper summarizes the results of existing research on supply chain finance, uncertainty environment and corporate debt financing behavior, laying a theoretical foundation for subsequent analysis. Secondly, this paper demonstrates the specific application of supply chain finance in an uncertain environment and its impact on corporate debt financing behavior through case analysis. By analyzing the success factors of these cases, such as risk management, support from financial institutions and technological innovation, the application value of supply chain finance in an uncertain environment is revealed. It is hoped that theoretical support and practical guidance will be provided for policymakers, financial institutions and enterprises to promote the development of supply chain finance and promote sound financing of enterprises.

Joint optimization of spatial correlation for space-constrained MIMO underwater optical wireless communication system in weak turbulence

For the space-constrained underwater installations, spatial correlation is an essential factor affecting the reliability of the underwater optical wireless communication (UOWC) system with multiple-input multiple-output (MIMO) technology. In this paper, a joint optimization method for the layout and transmit power allocation of the light-emitting diode (LED)-based UOWC system is proposed and demonstrated under the weak turbulent channel. To analysis the transmission performance of the MIMO UOWC system, a composite channel model incorporating absorption, scattering and weak turbulence effects is established, and the channel spatial correlation characteristics with various system parameters is analyzed based on this model. Among these parameters, we take a 9 × 9 MIMO UOWC system as an example to simulate the communication performance of the optimization method under different turbulence intensities. The simulation results show the optimized system exhibits a channel capacity improvement of 13bps/Hz compared to the original system at the signal-to-noise ratio (SNR) of 20 dB and the same turbulence intensity. Moreover, the SNR of jointly optimized system can achieve a gain of 5 dB at the same bit error rate (BER). By extending the joint optimization algorithm to a 16 × 16 MIMO UOWC system, the optimized SNR can also obtain a gain of 7.5 dB which effectively demonstrates the universality of the proposed joint optimization algorithm.

On Superposition Lattice Codes for the K-User Gaussian Interference Channel.

In this study, we work with lattice Gaussian coding for a K-user Gaussian interference channel. Following the procedure of Etkin et al., in which the capacity is found to be within 1 bit/s/Hz of the capacity of a two-user Gaussian interference channel for each type of interference using random codes, we work with lattices to take advantage of their structure and potential for interference alignment. We mimic random codes using a Gaussian distribution over the lattice. Imposing constraints on the flatness factor of the lattices, the common and private message powers, and the channel coefficients, we find the conditions to obtain the same constant gap to the optimal rate for the two-user weak Gaussian interference channel and the generalized degrees of freedom as those obtained with random codes, as found by Etkin et al. Finally, we show how it is possible to extend these results to a K-user weak Gaussian interference channel using lattice alignment.

The Utility of Infrasound in Global Monitoring of Extraterrestrial Impacts: A Case Study of the 2008 July 23 Tajikistan Bolide

Among the various observational techniques used for the detection of large bolides on a global scale is a low-frequency sound known as infrasound. Infrasound, which is also one of the four sensing modalities used by the International Monitoring System, offers continuous global monitoring and can be leveraged for planetary defense. Infrasonic records can provide an additional dimension for event characterization and a distinct perspective that might not be available through any other observational method. This paper describes the infrasonic detection and characterization of the bolide that disintegrated over Tajikistan on 2008 July 23. This event was detected by two infrasound stations at distances of 1530 and 2130 km. Propagation paths to one of the stations were not predicted by the model, despite being clearly detected. The presence of the signal is attributed to the acoustic energy being trapped in a weak but leaky stratospheric AtmoSOFAR channel. The infrasound signal analysis indicates that the shock originated at the point of the main breakup at an altitude of 35 km. The primary mode of the shock production of the signal detected at the two stations was a spherical blast resulting from the main gross fragmentation episode. The energy estimate, based on the signal period, is 0.17–0.51 kt of TNT equivalent, suggesting a mass of 6.6–23.5 tons. The corresponding object radius, assuming the chondritic origin, was 0.78–1.18 m.

Some strange things about the mechanical properties of glass

Glasses and crystals from the same chemical system mostly share the same interatomic bond strength. Nevertheless, they differ by the arrangement of bonds in space, which gives birth to different atomic packing efficiencies. We show in this review that as far as the elastic moduli and hardness are concerned, the atomic packing density predominates over the bond strength. The shear modulus of crystalline phases is usually much larger than the one of glasses with the same stoichiometric composition, thanks to a more efficient packing of atoms in the former. In contrast, the increase in hardness is quite limited, likely because of the additional contribution of dislocation activity to the deformation processes beneath the indenter in the case of crystals (shear plasticity). We also show that the occurrence of chemical heterogeneities (weak channels) at the mesoscopic scale in glasses, which is often associated with the lack of long range atomic ordering, promotes easy fracture paths and is responsible for the low toughness and fracture surface energy.

Identifying a selection mechanism of distribution channel for the supply chain: The barriers to the application of web 3.0

The application of Web 3.0 will bring unprecedented changes to the supply chain, where many industries are seeing significant cost reductions. However, due to the requirement of stability for supply chain, sometimes the total cost of supply chain cannot decrease effectively under Web 2.0, which may hinder the application of Web 3.0. Following the application from Web 2.0 to Web 3.0, this paper discusses the selection of distribution channel whose cost is under user stickiness and the degree of digitalization. The system optimum model, which is commonly used in dynamic traffic allocation, is applied to solve the distribution channel selection problem. The results implies that when the degree of digitalization is low, the distribution channel cost first decreases and then increases as user stickiness increases. This trend of channel cost illustrates the price induction on user stickiness initially, and gradually adjust the price to be higher when user stickiness makes channel transformation costly. Customers with unclear user stickiness perceptions and weak channel control can easily be trapped in the transition from Web 2.0 to Web 3.0. Distributors will also be forced to accept high product costs due to the price induction from product distribution channels.

Much ado about nothing? Giorgia Meloni’s government and immigration

ABSTRACT Italy as an immigration country has been characterized by high rates of irregular migration due to the weak legal admission channels available and the combination of apowerful internal demand of foreign workers and intense external pressure on itsborders. Despite the growing salience of migration issues in the political arena, the country has shown a marked inertia in addressing the structural causes of the phenomenon. The gap between political grandstanding and effective governance hasbeen highlighted by numerous studies. This article analyses the first year of Giorgia Meloni’s government by assessing the coherence between the highly restrictive electoral promises and the implemented policies, and by weighing the degree of novelty of its approach in relation to migration management over the last twenty years. Results show that, beyond the multiplication of proclamations and emergency interventions with respect to recurring border crises, there has been an overall pragmatic and rather open attitude, far from the radical stances of the opposition years. In addition, the full confirmation of that model of ‘reluctant openness’ that has characterized the Italian approach to immigration, combining irregularity as the main route of access with an almost complete overlook of other important dimensions like migrants’ integration.

Transmitter design and AE–AR region characterization for NOMA-SLIPT UWOC systems with uniformly distributed message and Imp-SIC

This paper investigates simultaneous lightwave and information transfer (SLIPT) based non-orthogonal multiple access (NOMA) in underwater optical wireless communication (UWOC) systems. At the user signal separation (SS) based SLIPT scheme is employed. Imperfect successive interference cancellation (SIC) at the near user is considered. Firstly, we derive the maximum allowable electrical power for message symbols at the transmitter, ensuring input to the laser diode lies within the linear region and. A novel linearity-constrained transmitter design is proposed for the uniformly distributed message, followed by calculations of instantaneous data rate and instantaneous harvested energy for both users. Then, closed-form expressions for average data rates (AR) and average energy harvested (AE) under weak turbulence-induced fading channels using Holtzman’s approximation are derived. The tightness of the approximation is confirmed by Monte-Carlo simulations. AE–AR boundaries for both users show an initial rise and subsequent decline in data rates with increased harvested energy, owing to higher bias values restricting transmitter power. The study also examines trade-offs between AE and AR across various system parameters including beam divergence angles, imperfection of SIC, power allocation coefficients, and water types, is conducted. We observe shifting and shrinking/expansion of the AE–AR region depending upon the variation of the various system parameters. We also show that the discussed SS scheme is general and encompasses time-switching (TS), and power-splitting (PS) schemes as special cases. We also briefly discuss as to how the developed framework could be extended to more than two users. In summary, the overall effective energy consumption deduces owing to the adoption of SLIPT at the users, making the considered setup more energy-efficient.

Rethinking Underwater Crab Detection via Defogging and Channel Compensation

Crab aquaculture is an important component of the freshwater aquaculture industry in China, encompassing an expansive farming area of over 6000 km2 nationwide. Currently, crab farmers rely on manually monitored feeding platforms to count the number and assess the distribution of crabs in the pond. However, this method is inefficient and lacks automation. To address the problem of efficient and rapid detection of crabs via automated systems based on machine vision in low-brightness underwater environments, a two-step color correction and improved dark channel prior underwater image processing approach for crab detection is proposed in this paper. Firstly, the parameters of the dark channel prior are optimized with guided filtering and quadtrees to solve the problems of blurred underwater images and artificial lighting. Then, the gray world assumption, the perfect reflection assumption, and a strong channel to compensate for the weak channel are applied to improve the pixels of red and blue channels, correct the color of the defogged image, optimize the visual effect of the image, and enrich the image information. Finally, ShuffleNetV2 is applied to optimize the target detection model to improve the model detection speed and real-time performance. The experimental results show that the proposed method has a detection rate of 90.78% and an average confidence level of 0.75. Compared with the improved YOLOv5s detection results of the original image, the detection rate of the proposed method is increased by 21.41%, and the average confidence level is increased by 47.06%, which meets a good standard. This approach could effectively build an underwater crab distribution map and provide scientific guidance for crab farming.

Influence of atmospheric turbulence on coherent detection performance of space coherent optical communication

Space coherent optical communication technology is considered to be an important way to overcome the bottleneck in current high-speed space communication. However, atmospheric turbulence seriously limits its realization. Based on the Huygens-Fresnel principle and the low-frequency compensation power spectrum inversion method, this work first investigates the random distribution characteristics of the amplitude and phase of a Gaussian beam after it has been transmitted through atmospheric turbulence. Then, using the coherent mixing efficiency and communication bit error rate model, the influence of atmospheric turbulence on the performance of spatial coherent optical communication systems is obtained. Finally, a laser heterodyne detection experimental system is built to quantitatively study the influence of atmospheric turbulence on the coherent detection performance of spatial coherent optical communication. The conclusions drawn from this study are as follows. 1) The spatial phase distortion caused by the weak turbulence channel is relatively small and will hardly affect the light intensity distribution characteristics of the Gaussian beam. In the case of weak turbulence, the influence of weak turbulence on the performance of coherent optical communication system is almost negligible. The communication bit error rate will decrease rapidly with the increase of the number of single bit data photons. The communication signal-to-noise ratio can be better than 10<sup>–5</sup> when the number of single-bit photons is greater than 10. 2) Moderate turbulence will change the intensity distribution characteristics of the Gaussian beam, but will not cause a serious shift in the center of the spot. Under moderate turbulence conditions, the coherent mixing efficiency decreases rapidly as the turbulence intensity continues to increase, but the communication bit error rate still decreases rapidly with the increase of the number of single bit data photons. At this time, increasing the number of single-bit photons can suppress the negative influence of moderate intensity turbulence on the performance of coherent optical communication systems. 3) Strong turbulence will cause severe spatial phase distortion of the beam, destroy the consistency of the light intensity distribution, and cause a serious shift in the center of the spot. Under strong turbulence conditions, the coherent mixing efficiency of coherent optical communication systems approaches zero, and increasing the number of single bit data photons cannot significantly reduce the bit error rate, seriously affecting the quality of coherent optical communication. Atmospheric turbulence is an important limiting factor for developing space coherent optical communication. This study can provide useful references for evaluating the performance of space coherent optical communication systems.

Balancing of Attenuation Disparity to Restore the Weak Color Channels in Underwater Images

Balancing of Attenuation Disparity to Restore the Weak Color Channels in Underwater Images

Weak feature confocal channel regulation for underwater sonar target detection

Weak feature confocal channel regulation for underwater sonar target detection

Weak Conductive Channel Effect of Glass Fabric on Deep Charging of Polyimide in GEO

Weak Conductive Channel Effect of Glass Fabric on Deep Charging of Polyimide in GEO

Gain Assisted Raman Induced Classical and Quantum Talbot Imaging

Abstract2D Raman generated classical and quantum Talbot imaging is proposed in a three‐level gain assisted system. First, a 2D Raman induced grating (RIG) will be constructed by modulating transmission function in the weak probe channel using a strong control standing wave field. Furthermore, RIG will diffract a probe field, by shining a probing light beam on an optically generated lattice within a rubidium vapor cell. This study uses gain assisted Raman medium [Nature 406, 277 (2000)] to examine classical and quantum Talbot imaging. In the case of Raman‐induced classical imaging, the diffraction pattern repeats itself at planes with integer multiple Talbot lengths. Additionally, by taking into account entangled photon pairs, the scenario of Raman‐induced quantum imaging is investigated. This study also looks at the RIG's amplitude and phase information with adjustable image size variation. As a result of the gain feature and zero absorption, this system is anticipated to be more suitable from the perspective of application. This analysis may pave the way for further research into the Talbot effect's nonlinear and quantum dynamical properties. Also, it provide a non‐destructive, lensless method for imaging very cold atoms or molecules.