Large Exchange Research Articles

Sustainability of The Tanjung Lesung Tourist Destination

Tourism contributes large foreign exchange to tourism organizing countries. Tourism also creates jobs, provides income and quality to society. The Tanjung Lesung natural tourist area is part of Banten Province which has excellent natural beauty on par with Bali and Raja Ampat Papua. The potential natural beauty of the Tanjung Lesung area can be relied upon as a source of regional income. The Tanjung Lesung tourist area has many beach tourism objects, sand tourism, water tourism, underwater tourism, beautiful panoramas, unspoiled forests, tempting culinary delights, fruit native to Banten Province. The Tanjung Lesung tourist area also experienced problems after the tsunami disaster. So this is a challenge for Tanjung Lesung Tourism to provide tourist satisfaction and sustainability. The results of this research show a positive influence between variables, thus showing that tourists are satisfied with the improvement of the Tanjung Lesung tourist area after the tsunami disaster and give hope for tourism sustainability.

Numerical simulation and optimization of compact latent heat exchanger with micro-channel plate in shape-stabilized composite phase change material

To enable the rapid provision of domestic hot water, this study presents the independent design of a plate heat exchanger featuring a large heat exchange area and a compact structure. Utilizing a sandwich structure, the thermal storage unit integrates two shaped composite phase change materials (CPCM), namely sodium acetate trihydrate (SAT)/expanded graphite (EG) blocks of identical thickness — in conjunction with a micro-channel heat exchange plate. Multiple thermal storage units are stacked to create the heat exchanger. Experimental validation of the heat transfer performance of this thermal energy storage heat exchanger is conducted, accompanied by the establishment of a heat transfer model elucidating the interaction between the phase change material (PCM) and the fluid. The investigation explores the impact of varying thicknesses of shape-stabilized CPCM, thermo-physical parameters of CPCM, and flow rates on enhancing the thermal efficiency of the thermal energy storage heat exchanger. Results indicate a competitive relationship between the phase change enthalpy and thermal conductivity of CPCM under constant density. Increasing the mass fraction of SAT effectively boosts its heat storage density. However, this improvement is counterbalanced by a reduction in CPCM's thermal conductivity, resulting in diminished heat transfer rates within the material and reduced efficiency in transferring heat between the material and the fluid. Optimal performance is achieved when the mass fraction of sodium acetate trihydrate is 80 wt% and the CPCM thickness is 20 mm. At these parameters, the thermal energy storage heat exchanger exhibits the highest heat transfer efficiency. Furthermore, the heat exchanger is capable of producing 197.86 kg of hot water in 1365 s at an inlet flow rate of 300 L/h, achieving an impressive discharging efficiency of 82.73 %. These findings underscore the feasibility of employing the mini-channel plate thermal energy storage heat exchanger for the rapid preparation of domestic hot water.

Influence of magnetism on vertical hopping transport in CrSBr

We investigate the c-direction conduction in CrSBr in the linear regime, which is not accessible in other van der Waals (vdW) magnetic semiconductors, because of the unmeasurably low current. The resistivity, which is 108−1011 times larger than in the a and b directions, exhibits magnetic state dependent thermally activated and variable range hopping transport. In the spin-flip phase at 2 T, the activation energy is 20 meV lower than in the antiferromagnetic state due to a downshift of the conduction band edge, in agreement with calculations. In the variable range hopping regime, the average hopping length decreases from twice the interlayer distance to the interlayer distance at 2 T because in the antiferromagnetic state the large exchange energy impedes electrons hopping between adjacent layers. Our work demonstrates that the linear transport regime provides new information about electronic processes in vdW magnetic semiconductors and shows how magnetism influences these processes both in real and reciprocal space. Published by the American Physical Society 2024

Exchange Bias Modulated by Antiferromagnetic Spin-Flop Transition in 2D Van der Waals Heterostructures.

Exchange bias is extensively studied and widely utilized in spintronic devices, such as spin valves and magnetic tunnel junctions. 2D van der Waals (vdW) magnets, with high-quality interfaces in heterostructures, provide an excellent platform for investigating the exchange bias effect. To date, intrinsic modulation of exchange bias, for instance, via precise manipulation of the magnetic phases of the antiferromagnetic layer, is yet to be fully reached, owing partly to the large exchange fields of traditional bulk antiferromagnets. Herein, motivated by the low-field spin-flop transition of a 2D antiferromagnet, CrPS4, exchange bias is explored by modulatingthe antiferromagnetic spin-flop phase transition in all-vdW magnetic heterostructures. The results demonstrate that undergoing the spin-flop transition during the field cooling process, the A-type antiferromagnetic ground state of CrPS4 turns into a canted antiferromagnetic one, therefore, it reduces the interfacial magnetic coupling and suppresses the exchange bias. Via conducting different cooling fields, one can select the exchange bias effect switching among the "ON", "depressed", and "OFF" states determined by the spin flop of CrPS4. This work provides an approach to intrinsically modulate the exchange bias in all-vdW heterostructures and paves new avenues to design and manipulate 2D spintronic devices.

Investigating ecosystem connections in the shelf sea environment using complex networks

Abstract. We use complex network theory to better represent and understand the ecosystem connectivity in a shelf sea environment. The baseline data used for the analysis are obtained from a state-of-the-art coupled marine physics–biogeochemistry model simulating the North West European Shelf (NWES). The complex network built on model outputs is used to identify the functional groups of variables behind the biogeochemistry dynamics, suggesting how to simplify our understanding of the complex web of interactions within the shelf sea ecosystem. We demonstrate that complex networks can also be used to understand spatial ecosystem connectivity, identifying both the (geographically varying) connectivity length-scales and the clusters of spatial locations that are connected. We show that the biogeochemical length-scales vary significantly between variables and are not directly transferable. We also find that the spatial pattern of length-scales is similar across each variable, as long as a specific scaling factor for each variable is taken into account. The clusters indicate geographical regions within which there is a large exchange of information within the ecosystem, while information exchange across the boundaries between these regions is limited. The results of this study describe how information is expected to propagate through the shelf sea ecosystem, and how it can be used in multiple future applications such as stochastic noise modelling, data assimilation, or machine learning.

Compartmental exchange regulates steady states and stochastic switching of a phosphorylation network

The phosphoregulation of proteins with multiple phosphorylation sites is governed by biochemical reaction networks that can exhibit multistable behavior. However, the behavior of such networks is typically studied in a single reaction volume, while cells are spatially organized into compartments that can exchange proteins. In this work, we use stochastic simulations to study the impact of compartmentalization on a two-site phosphorylation network. We characterize steady states and fluctuation-driven transitions between them as a function of the rate of protein exchange between two compartments. Surprisingly, the average time spent in a state before stochastically switching to another depends nonmonotonically on the protein exchange rate, with the most frequent switching occurring at intermediate exchange rates. At sufficiently small exchange rates, the state of the system and mean switching time are controlled largely by fluctuations in the balance of enzymes in each compartment. This leads to negatively correlated states in the compartments. For large exchange rates, the two compartments behave as a single effective compartment. However, when the compartmental volumes are unequal, the behavior differs from a single compartment with the same total volume. These results demonstrate that exchange of proteins between distinct compartments can regulate the emergent behavior of a common signaling motif.

Low field-cooled induced large exchange bias effect and DFT calculations in ferromagnetic Sm2CoMnO6

In the present report, we study the large exchange bias effect in Sm2CoMnO6 (SCMO) polycrystalline samples synthesized with the presence of two crystallographic phases: ordered-phase (monoclinic; P21/n) and disordered-phase (orthorhombic; Pnma). X-ray photoelectron spectroscopy study revealed the presence of mixed valence states for Co (2+ & 3+) and Mn (4+ & 3+). M(T) data exhibits an inhomogeneous magnetic state with the presence of ferromagnetic ordering at TC ∼128 K due to the super-exchange interactions of Co2+-O2--Mn4+ and antiferromagnetic-like spin correlations for T < 50 K, attributed to Co3+-O2--Co3+, and Mn3+-O2--Mn3+ interactions. M(H) loop shift with a conventional exchange bias (EB) effect of 10 kOe for a field-cooled (HFC) of 10 kOe at 2 K was observed. Such a large value of the EB effect for low HFC in SCMO is comparable to that of large EB compounds, such as La1·5Sr0·5CoMnO6 and NiFe2O4/CoO nanocomposites. The zero-field cooled asymmetry in M(H) loop termed as spontaneous exchange bias effect (SEB) observed for T < 20 K. The systematic study of EB effects like HEB and MEB with T(K) and HFC was explained qualitatively by the presence of unidirectional anisotropy formed at the interface of inhomogeneous magnetic phases. Further, density functional theory (DFT) calculations validate the ferromagnetic ground state of SCMO with Co and Mn networks. Moreover, the semiconductor characteristics of SCMO are established with a band gap of 1.3 eV.

Magnetic Properties and THz Emission from Co/CoO/Pt and Ni/NiO/Pt Trilayers.

THz radiation emitted by ferromagnetic/non-magnetic bilayers is a new emergent field in ultra-fast spin physics phenomena with a lot of potential for technological applications in the terahertz (THz) region of the electromagnetic spectrum. The role of antiferromagnetic layers in the THz emission process is being heavily investigated at the moment. In this work, we fabricate trilayers in the form of Co/CoO/Pt and Ni/NiO/Pt with the aim of studying the magnetic properties and probing the role of very thin antiferromagnetic interlayers like NiO and CoO in transporting ultrafast spin current. First, we reveal the static magnetic properties of the samples by using temperature-dependent Squid magnetometry and then we quantify the dynamic properties with the help of ferromagnetic resonance spectroscopy. We show magnetization reversal that has large exchange bias values and we extract enhanced damping values for the trilayers. THz time-domain spectroscopy examines the influence of the antiferromagnetic interlayer in the THz emission, showing that the NiO interlayer in particular is able to transport spin current.

Inducing abundant magnetic phases and enhancing magnetic stability by edge modifications and physical regulations for NiI2 nanoribbons.

Recently, a magnetic semiconducting NiI2 monolayer was successfully fabricated. To obtain richer magneto-electronic properties and find new physics for NiI2, we studied the zigzag-type NiI2 nanoribbon (ZNiI2NR) with edges modified by different concentrations of H and/or O atoms. Results show that these ribbons hold a higher energy stability, thermal stability, and magnetic stability, and the Curie temperature can be increased to 143 from 15 K for the bare-edged ribbons. They feature a half-semiconductor, bipolar magnetic semiconductor, or half-metal, depending on the edge-terminated atomic species and concentrations, and are closely related to the ribbon edge states, impurity bands or hybridized bands. By applying strain or an electric field, ribbons can achieve a reversible multi-magnetic phase transition among a bipolar magnetic semiconductor, half-semiconductor, half-metal, and magnetic metal. This is because strain changes the Ni-I bond length, resulting in a variation of bond configurations (weight of ionic and covalent bonds) and the number of unpaired electrons. The compressive strain can increase the Curie temperature because it makes the edged Ni-I-Ni bond angle closer to 90°, leading to the FM d-p-d superexchange interaction being increased. The electric field varies the magnetic phase because it alters the electrostatic potential of the ribbon edges, and the Curie temperature is enhanced under the electric field because the ribbon is changed to a metallic state (half-metal or magnetic metal), in which the magnetic Ni atoms satisfy the Stoner criterion and hold a large magnetic exchange coefficient and electron state density at the Fermi surface.

Unlocking the potential of V/Ti-AAC: a promising eco-friendly catalyst for cyclohexene epoxidation

Abstract Bentonite is an abundant natural resource in the Maghnia region of Algeria that may have potential value in catalysis, but heretofore has been considered of low value for this purpose due to its low acidity and low catalytic activity. Low cost is one of the main criteria for choosing a suitable material for catalysis. Because bentonite is abundant and low-cost, its use as a starting material for the preparation of catalysts deserves reconsideration. The present study was undertaken, therefore, to optimize the performance of bentonite as a catalyst in one of the most promising reactions in organic synthesis, namely, cyclohexene epoxidation. The bentonite was subjected to adjustment of its structure by means of a number of laboratory treatments based on its large cation exchange capacity. These modifications aimed to achieve an environmentally friendly catalytic process by incorporating transition metals, specifically titanium and vanadium, into the modified bentonite structure through acid activation. Redox properties were enhanced and Lewis and Brønsted acidities were introduced. The vanadium oxide, supported on titania-pillared, acid-activated bentonite (5V/Ti-AAC), was characterized comprehensively using various techniques, including diffuse-reflectance UV-visible spectroscopy (DR UV-Vis), Fourier-transform infrared spectroscopy (FTIR) for surface acidity analysis, X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray elemental analysis (EDX). The catalytic activity was investigated in response to certain variables, such as catalyst mass, nature of the solvent, amount of oxidant, and reaction temperature. A kinetic study was conducted to understand the reaction behavior. The experimental results demonstrated intriguing catalytic activity, achieving a 42% conversion rate with ~68% selectivity toward the epoxide product when employing tert-butyl hydroperoxide (TBHP) as the oxidant and heptane as the solvent. This study highlights the potential of 5V/Ti-AAC as an environmentally friendly catalyst applied in the epoxidation of cyclohexene.

Energy­efficient routing protocol in wireless sensor networks

Recently, self-organizing networks have gained popularity, which are distinguished by the possibility of connecting terminals anywhere and at any time without the need for a centralized network infrastructure. Mobile self-organizing networks are a promising direction for the development of information and communication systems. However, one should take into account the problems arising from the very nature of such networks: mobile nodes lead to an increase in the dynamism of the network topology due to the possibility of disconnection and the probability of movement; the limited supply of power sources of nodes requires careful management of power consumption in the design of hardware and protocols. Energy-saving design in self-organizing networks is more complex and important than in other wireless networks. The lack of infrastructure requires mobile nodes to act as routers, which increases traffic and therefore power consumption. Also, the energy-saving mode must take into account different network performance criteria, which can be caused by different protocols and power limitations. Thanks to the latest advances in technology and the rapid development of the production of small and affordable sensors, it has become possible to use them technically and economically effectively. These electronic sensors, which have high sensitivity, measure environmental parameters and convert the received data into an electronic signal that is transmitted over a wireless channel. After processing this signal, you can get information about the properties of objects or events that occur near the sensor. The application of a large number of such sensors, which can monitor a large area and exchange data wirelessly, forms a single wireless sensor network. Route allocation is a key challenge for resource-constrained networks. With the growth of computing power in wireless sensor technology, these sensor nodes are required to be equipped with more and more capabilities to perform more complex tasks. Each sensor is limited by its energy level, processing power, and ability to perceive information. Thus, the network of these sensors forms a more reliable and accurate structure. The article discusses the issue of using the HABRP protocol for its application in wireless sensor networks. The use of the HABRP protocol allows for improvement in the efficiency of wireless sensor networks, namely their energy efficiency. Therefore, the energy efficiency and simplicity of the HABRP protocol make it an excellent candidate for use in wireless sensor networks.

Upgrading the Separators Integrated with Desolvation and Selective Deposition toward the Stable Lithium Metal Batteries.

A practical and effective approach to improve the cycle stability of high-energy density lithium metal batteries (LMBs) is to selectively regulate the growth of the lithium anode. The design of desolvation and lithiophilic structure have proved to be significant means to regulate the lithium deposition process. Here, a fluorinated polymer lithiophilic separator (LS) loaded with a metal-organic framework (MOF801) is designed, which facilitates the rapid transfer of Li+ within the separator owing to the MOF801-anchored PF6 - from the electrolyte, Li deposition is confined in the plane resulting from the polymer fiber layer rich in lithiophilic groups (C─F). The numerical simulation results confirm that LS induces a uniform electric field and Li+ concentration distribution. Visualization technology records the behavior of regular Li deposition in Li||Li and Li||Cu cells equipping LS. Therefore, LS exhibits an ultrahigh Li+ transference number (tLi + = 0.80) and a large exchange current density (j0 = 1.963mA cm-2). LS guarantees the stable operation of Li||Li cells for over 1000h. In addition, the LiNi0.8Co0.1Mn0.1O2||Li cell equipped with LS exhibits superior rate and cycle performances owing to the formation of LiF-rich robust SEI layers. This study provides a way forward for dendrite-free Li anodes from the perspective of separator engineering.

Large exchange bias enhancement and control of ferromagnetic energy landscape by solid-state hydrogen gating

Voltage control of exchange bias is desirable for spintronic device applications, however dynamic modulation of the unidirectional coupling energy in ferromagnet/antiferromagnet bilayers has not yet been achieved. Here we show that by solid-state hydrogen gating, perpendicular exchange bias can be enhanced by > 100% in a reversible and analog manner, in a simple Co/Co0.8Ni0.2O heterostructure at room temperature. We show that this phenomenon is an isothermal analog to conventional field-cooling and that sizable changes in average coupling energy can result from small changes in AFM grain rotatability. Using this method, we show that a bi-directionally stable ferromagnet can be made unidirectionally stable, with gate voltage alone. This work provides a means to dynamically reprogram exchange bias, with broad applicability in spintronics and neuromorphic computing, while simultaneously illuminating fundamental aspects of exchange bias in polycrystalline films.

Large room-temperature spontaneous exchange bias effect in LaFeO3 micro-polyhedrons

Single-phase materials with exchange bias (EB) effect at room temperature (RT) are very important for future applications in spintronic devices, magnetic storage, and sensors. To explore materials showing the EB effect at RT is an interesting and important issue. In this paper, LaFeO3 micro-polyhedrons composed of an average particle size of 66 nm nanoparticles have been synthesized by annealing LaFe(CN)6 precursors in air at 630 °C for 8 h. Magnetic hysteresis loops show that LaFeO3 micro-polyhedrons present a large spontaneous EB (SEB) effect (∼ 1.5 kOe) at RT after zero-field cooling (ZFC) and a gigant conventional EB (CEB) effect (∼ 5.6 kOe) after field cooling (FC) of 70 kOe. To the best of our knowledge, the current compound shows the largest negative EB field after ZFC at RT among SEB materials discovered so far. The successful fitting of training effect (TE) data with Binek’s model shows that the origin of SEB lies in the interface exchange coupling between different magnetic phases. The interface with the “pinning” effect of antiferromagnetic (AFM) matrix relative to ferromagnetic (FM) clusters exhibits unidirectional anisotropy, which is formed during the initial magnetization process. This interesting finding of the SEB effect at RT in single-phase perovskite LaFeO3 system may open a new direction for possible technological applications.

Does the left-digit bias affect prices in financial markets?

According to the left-digit bias, people pay more attention to the leftmost digits of a number and tend to disregard the last digits of that number. We investigate whether this bias affects traders' perception and pricing in a large financial market trading foreign exchange options. Our theoretical model predicts that the left-digit bias affects prices, causing a discontinuous jump in expected returns when comparing markets at threshold prices 10,20,…,90 with markets at prices just below these thresholds, such as 9.9,19.99, etc. The model predicts no discontinuity in returns among unbiased traders. Using a regression discontinuity approach over the returns of more than 1 million options, we find significant discontinuities in the expected returns, consistent with mispricing induced by the left-digit bias.

Enhanced Exchange Bias in Epitaxial High-Entropy Oxide Heterostructures.

High-entropy oxides (HEOs) have gained significant interest in recent years due to their unique structural characteristics and potential to tailor functional properties. However, the electronic structure of the HEOs currently remains vastly unknown. In this work, combining magnetometry measurements, scanning transmission electron microscopy, and element-specific X-ray absorption spectroscopy, the electronic structure and magnetic properties of the perovskite-HEO La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 epitaxial thin films are systemically studied. It is found that enhanced magnetic frustration emerges from competing exchange interactions of the five transition-metal cations with energetically favorable half-filled/full-filled electron configurations, resulting in an unprecedented large vertical exchange bias effect in the single-crystalline films. Furthermore, our findings demonstrate that the La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 layer with a thickness down to 1 nm can be used as a pinning layer and strongly coupled with a ferromagnetic La0.7Sr0.3MnO3 layer, leading to a notable exchange bias and coercivity enhancement in a cooling field as small as 5 Oe. Our studies not only provide invaluable insight into the electronic structure of HEOs but also pave the way for a new era of large bias materials for spintronics devices.

Spin transfer exchange torque in ferromagnet/ferromagnet structures made of half-metals with large exchange gaps

Spin transfer exchange torque in ferromagnet/ferromagnet structures made of half-metals with large exchange gaps

Research and analysis of the thermal and control characteristics of the plate-type fuel assembly for the supercritical CO2 reactor

Small nuclear reactors can be applied to micro grid power generation, island and space nuclear power systems. The plate-type fuel assembly has a compact design structure, low fuel core temperature, large heat exchange area, and high heat exchange efficiency, which is widely used in small nuclear reactors. To supplement the lack of research in S-CO2 small nuclear reactor, The Brayton cycle reactor system analysis program of S-CO2 plate-type fuel assemblies (BRESA-PFA) is developed, and the reactor control system program is developed to simulate the transient condition in this paper. This article establishes a fuel assembly flow and heat transfer model and a control rod control model using Modelica language, achieving physical and thermal coupling and power control of the reactor. The steady-state operating parameters of the developed program BRESA-PFA were studied, and the flow distribution, coolant and fuel temperature distribution of BRESA-PFA were obtained. The flow distribution conforms to the experimental parameters of CARR, and the fuel assembly radial temperature distribution is high at the center and low at the edge. After verification, the maximum fuel temperature did not exceed the limit value and met the design requirements. Transient characteristic analysis was conducted to study the rod lifting strategy during the startup process, the start-up and rod lifting process of BRESA-PFA is N2-N1-G2-G1, using the logic of step control. Research on reactor control system response under loss of coolant accident, after the accident, the coolant flow suddenly decreased to 65 % of the rated value, and the reactor power also decreased to 65 % FP, G2 and G1 control rods were inserted downwards, the coolant temperature fluctuates by 1 %∼2%. The reactor control system was able to respond quickly, ensuring the stability of coolant temperature, proving the safety and reliability of BRESA-PFA, and providing theoretical reference and scheme support for the research of S-CO2 small nuclear reactors.

Study on the effects of manifold structure on the gas flow distribution uniformity of anode of PEMFC stack with 140-cell

The gas maldistribution of the large proton exchange membrane fuel cell (PEMFC) stack leads to the deterioration of power performance. This numerical investigation studies the gas flow rate distribution in anode of two U-type stacks (a 15-cell stack and a 140-cell stack) which are composed of the same type of unit fuel cells. The anode gas channels of the two stacks are regarded as porous medium whose characteristic parameters are determined from pressure drop test data. To consider the nitrogen permeation from cathode to anode gas channel during the purging process, an expression of an additional momentum source term is proposed which helps to better fit the simulation results with pressure drop test data. Results show that the anode of the 140-cell stack has a quite good flow distribution uniformity. However, its asymmetric feed header of the manifold structure still has some negative effect. The same 140-cell stack installed with a rotational symmetric feed header is investigated and the simulation result shows that it can reduce the original maximum non-uniformity by about 50%.

Crossover from gapped-to-gapless Dirac surface states in magnetic topological insulator MnBi2Te4

Intrinsic magnetic topological insulators (MTIs) host exotic topological phases such as quantized anomalous Hall insulating phase, arising due to the large magnetic exchange gap. However, the interplay of magnetism and topology in these systems in different temperature regimes remains elusive. In this work, we present the logarithmic temperature-dependence of conductivity for sub-100 nm thick exfoliated flakes of MTI MnBi2Te4 in the presence of out-of-plane magnetic fields and extracted the linear slope, κ. We observed a characteristic change, in the low-temperature regime, indicating the gapped Dirac surface state according to Lu–Shen theory. We also report the recovery of topological properties in the system via the weak-antilocalization effect in the vicinity of antiferromagnetic to paramagnetic transition and in the paramagnetic regime. Hikami–Larkin–Nagaoka analysis suggested the presence of topological surface states. Therefore, our study helps in understanding how intrinsic magnetism masks topological properties in an MTI as long as magnetic ordering persists.