Local Density Research Articles

Investigation of current density and temperature distribution characteristics under transient conditions based on a 108 cm2 segmented proton exchange membrane fuel cell

Visualizing the electrochemical and temperature distribution characteristics inside proton exchange membrane fuel cell (PEMFC) should greatly contribute to the product development and performance optimization. In the study, a customized 27-segment 108 cm2 fuel cell was fabricated based on the printed circuit board methodology to achieve the local current density and local voltage measurement. In addition, 27 thermocouples were embedded in the segmented cathode graphite gas flow plate for local temperature measurement. Detailed information of fuel cell core components, multi-channel data acquisition system, external temperature control system, and uncertainty analysis was presented. According to the test results of 4000 s current rising conditions and 2400 s current decreasing conditions, the measurement deviation of total current between data acquisition system and TOYO test station is 2.4%–3.2%. Meanwhile, the deviation of output voltage ranges from 0.1% to 2.6%. To quantify the degree of distribution non-uniformity, the range and standard deviation of local parameter values as well as contour map are demonstrated. The non-uniformity of local current density and local temperature becomes more significant under higher operating current conditions. Furthermore, the degree of parameter non-uniformity is more noticeable under current rising conditions compared with current decreasing conditions. The transient increase of operating current leads to the sudden overshoot phenomena of local current range, and the change of local current density among all segments is instantaneously finished. However, the range of current demonstrates relatively smooth transition trends when reactant flow rate rises. Higher temperature area appears in the middle of membrane electrode assembly, especially in the position with higher local current density. The parameter distribution and transition characteristics could provide helpful guidance for fuel cell optimization and diagnosis.

Tailoring local electron density and molecular oxygen activation behavior via potassium/halogen co-tuned graphitic carbon nitride for enhanced photocatalytic activity

Graphite carbon nitride (g-C3N4) is a promising photocatalyst,but its inadequate reactive sites, weak visible light responsiveness, and sluggish separation of photogenerated carriers hamperthe improvement of photodegradation efficiency. In this work, potassium (K) and halogen atoms co-modified g-C3N4 photocatalysts (CN-KX, X = F, Cl, Br, I) were constructed to adjust the electrical and band structure for enhanced generation of reactive oxygen species. Through an integration of theoretical calculation and experimental exploration, the doping sites of halogen atoms as well as the evolution of crystal, band, and electronic structures were investigated. The results show that a covalent bond is formed between the F atom and the C atom, substitution of the N atom occurs with a Cl atom, and doping of Br, I, or K atoms takes place at the interstitial site. CN-KX photocatalysts exhibits lower band gap, faster photogenerated electron migration, and enhanced photocatalytic activity. Specifically, the CN-KI photocatalyst exhibits the highest photodegradation efficiency because of its smaller interplanar spacing, formation of the midgap state, and adjustable local electron density. Equally, the doping of I atom not only provides a stable adsorption site for oxygen (O2) but also facilitates electron transfer, promoting the production of superoxide radicals (O2−) and contributing to the process of photodegradation.

Electronic structure, bonding, and mechanical strength at the [formula omitted]-Al2O3 (0001)/L12-Al3Zr (111) interface by first-principles calculations

The interface adhesion energy, interfacial energy, charge density difference, local density of states, and first-principles computational tensile test of α-Al2O3 (0001)/L12-Al3Zr (111) interface were investigated by first-principles calculations. The dominant factors affecting the interfacial bond strength are the type of chemical bonds and the number of electronic orbital hybrids at the interface. The first-principles computational tensile test demonstrates that Al-fcc and Al2-hcp configurations fracture at the interface, while the O-fcc configuration fractures at the Al3Zr slab rather than at the interface and has the best tensile strength. The proposed interface bonding criteria were based on the analysis of the Al2O3/Al3Zr interface bonding data. These criteria will guide the establishment of the interface model. These results will provide theoretical guidance for understanding the failure mechanism of the Al2O3/Al3Zr interface and designing new interfaces.

Home range overlaps of the brushtail possum (Trichosurus vulpecula): implications for disease transmission

Understanding how bovine tuberculosis (TB) is maintained in wildlife reservoirs is critical for the management of this disease impacting cattle in many countries. For the primary wildlife reservoir of the disease in New Zealand, the brushtail possum (Trichosurus vulpecula), transmission of this contagious bacterial disease among possums is often assumed to be linked to home range overlap. Identifying drivers of possum home range, and home range overlap between individuals, is thus important for informing wildlife reservoir TB management in New Zealand. We monitored four sub-populations of free-living possums in New Zealand native forests during 10 consecutive months using live trapping, to give the first direct insight into how the frequency and area of overlaps alters with density, sex and age. A total of 832 individuals were captured (average 9.3, range from 1 to 40 captures per animal with a median value of 7) and 35,820 home range overlaps were recorded. Both the number and area of overlaps were significantly associated with age class, with 66.6% of overlaps occurring between adults, 30% between adults and juveniles, and only 3.4% between juveniles. Overall, adult males showed significantly higher numbers of overlaps than expected, while adult and juvenile females showed significantly lower numbers of overlaps than expected and no differences were observed in juvenile males. In addition, males exhibited more and larger overlaps than females. The number and size of overlaps per individual decreased with increasing local population density. Understanding shared areas of activity among individuals can provide insights into the interactions occurring and potential pathways for diseases transmitted by contact such as TB. These results can inform to develop effective strategies for the control of diseases carried and dispersed by possums.

Potassium Phthalimide Doped with Delta‐Site Structures to Construct Ultra‐Long Cycle Life Aqueous Zn‐Polymer Batteries

AbstractAqueous Zn‐polymer batteries hold great promise for environmentally friendly energy storage systems. However, the poor cycling performance caused by irreversible structural deformation and polymer chain entanglement during the embedding and de‐embedding processes of Zn2+ and H+ ions is one of the key challenges facing their development. Here a new polyaniline cathode doped is developed with potassium phthalimide using a secondary doping approach. This polymeric electrode integrates the conjugated backbone for charge transport with an anionic phthalimide dopant for constructing a triangular‐site structure, as illustrated by the density functional theory calculations. This unique molecular structure is favorable for improving conductivity and structural stability by effectively modulating the localized electron cloud density. The Zn‐polymer battery holds an outstanding capacity retention of 76.1% after 25,000 cycles at a current density of 1 A g−1 with the coulombic efficiency maintained above 99.4%. This secondary doped polymer strategy offers a new host alternative for the ultra‐long cycle life of Zn‐polymer batteries. The molecular design strategy and the insight into the relationship between the structure and performance may provide some guidelines for developing polymer cathodes with high stability.

Constructing Sn-Cu2O Lithiophilicity Nanowires as Stable and High-Performance Lithium Metal Anodes.

Lithium (Li) metal batteries (LMBs) have garnered significant research attention due to their high energy density. However, uncontrolled Li dendrite growth and the continuous accumulation of "dead Li" directly lead to poor electrochemical performance in LMBs, along with serious safety hazards. These issues have severely hindered their commercialization. In this study, a lithiophilic layer of Sn-Cu2O is constructed on the surface of copper foam (CF) grown with Cu nanowire arrays (SCCF) through a combination of electrodeposition and plasma reduction. Sn-Cu2O, with excellent lithiophilicity, reduces the Li nucleation barrier and promotes uniform Li deposition. Simultaneously, the high surface area of the nanowires reduces the local current density, further suppressing the Li dendrite growth. Therefore, at 1 mA cm-2, the half cells and symmetric cells achieve high Coulombic efficiency (CE) and stable operation for over 410 cycles and run smoothly for more than 1350 h. The full cells using an LFP cathode demonstrate a capacity retention rate of 90.6% after 1000 cycles at 5 C, with a CE as high as 99.79%, suggesting excellent prospects for rapid charging and discharging and long-term cyclability. This study provides a strategy for modifying three-dimensional current collectors for Li metal anodes, offering insights into the construction of stable, safe, and fast-charging LMBs.

Manipulating chiral Majorana mode with additional potential in superconductor-Chern insulator heterostructures

We employed the self-consistent Bogoliubov–de Gennes equations to explore the states of chiral Majorana mode in quantum anomalous Hall insulators in proximity to a superconductor, leading to the development of an extensive topological phase diagram. Our investigation focused on how an additional potential affects the separation of chiral Majorana modes across different phase conditions. We substantiated our findings by examining the zero-energy Local Density of States spectrum and the probability distribution of the chiral Majorana modes. We established the universality of chiral Majorana mode separation by applying an additional potential. This finding serves as a vital resource for future endeavors aimed at controlling and detecting these particles, thereby contributing to the advancement of quantum computing and condensed matter physics.

Interfacial engineering of Ag/C catalysts for practical electrochemical CO2 reduction to CO.

Electrochemical CO2 reduction to value-added chemicals by renewable energy sources is a promising way to implement the artificial carbon cycle. During the reaction, especially at high current densities for practical applications, the complex interaction between the key intermediates and the active sites would affect the selectivity, while the reconfiguration of electrocatalysts could restrict the stability. This paper describes the fabrication of Ag/C catalysts with a well-engineered interfacial structure, in which Ag nanoparticles are partially encapsulated by C supports. The obtained electrocatalyst exhibits CO Faradaic efficiencies (FEs) of over 90% at current densities even as high as 1.1 A/cm2. The strong interfacial interaction between Ag and C leads to highly localized electron density that promotes the rate-determining electron transfer step by enhancing the adsorption and the stabilization of the key *COO‒ intermediate. In addition, the partially encapsulated structure prevents the reconfiguration of Ag during the reaction. Stable performance for over 600 h at 500 mA/cm2 is achieved with CO FE maintaining over 95%, which is among the best stability with such a high selectivity and current density. This work provides a novel catalyst design showing the potential for the practical application of electrochemical reduction of CO2.

Approximate Functionals for Multistate Density Functional Theory.

Recently Lu and Gao [J. Phys. Chem. Lett. 2022, 13 (33), 7762-7769] published a new, rigorous density functional theory for excited states and proved that the projection of the kinetic and electron-repulsion operators into the subspace of the lowest electronic states are a universal functional of the matrix density D(r). This is the first attempt to find an approximation to the multistate universal functional . It is shown that (i) does not explicitly depend on the number of electronic states and (ii) is an analytic matrix functional. The Thomas-Fermi-Dirac-von Weizsäcker model and the correlation energy of the homogeneous electron gas are turned into matrix functionals guided by two principles: that each matrix functional should transform properly under basis set transformations and that the ground state functional should be recovered for a single electronic state. Lieb-Oxford-like bounds on the average kinetic and electron-repulsion energies in the subspace are given. When evaluated on the numerically exact matrix density of LiF, this simple approximation reproduces the matrix elements of the electron-repulsion operator in the basis of the exact eigenstates accurately for all bond lengths. In particular the off-diagonal elements of the effective Hamiltonian that come from the interactions of different electronic states can be calculated with the same or better accuracy than the diagonal elements. Unsurprisingly, the largest error comes from the kinetic energy functional. More exact conditions that constrain the functional form of are needed to go beyond the local density approximation.

Study of structural and electronic properties of AgCl and AgBr binaries

This modest work was devoted to studying the structural and electronic properties of the AgCl and AgBr binaries in the cubic NaCl phase. In this study, we used the FP-LAPW method based on functional density theory (DFT). For the treatment of exchange potential and correlation, we used the local density approximation (LDA). The objective of this work is to predict and compare the structural and electronic properties of our materials with other theoretical and experimental results. Most of the results obtained were approximate.

Benchmarking Functionals for Strong-Field Light-Matter Interactions in Adiabatic Time-Dependent Density Functional Theory.

In recent years, time-dependent density functional theory (TDDFT) has been extensively employed for highly nonlinear optics in molecules and solids, including high harmonic generation (HHG), photoemission, and more. TDDFT exhibits a relatively low numerical cost while still describing both light-matter and electron-electron interactions ab initio, making it highly appealing. However, the majority of implementations of the theory utilize the simplest possible approximations for the exchange-correlation (XC) functional-either the local density or generalized gradient approximations, which are traditionally considered to have rather poor chemical accuracy. We present the first systematic study of the XC functional effect on molecular HHG, testing various levels of theory. Our numerical results suggest justification for using simpler approximations for the XC functional, showing that hybrid and meta functionals (as well as Hartree-Fock) can, at times, lead to poor and unphysical results. The specific source of the failure in more elaborate functionals should be topic of future work, but we hypothesize that its origin might be connected to the adiabatic approximation of TDDFT.

Bioconvective reversible (an esterification process) Casson nanofluid flow over a radiative spinning disc with microorganism

This study describes the Casson (a non-Newtonian fluid) nanofluid bioconvection flow across a spinning disc in the presence of gyrotactic microorganisms, many slips and thermal radiation. Also, the flow is considered as a reversible flow. The esterification process is taken into account. Using the proper variables, a system of extremely nonlinear PDEs is converted into a system of ODEs. To arrive to the solution of such equations, a numerical approach is used. Using the bvp4c approach, nonlinear flow equations can be numerically solved. Investigated are the effects of different numbers on the thermal field, volumetric concentration of nanoparticles and microbiological field. The key characteristics of the parameters in relation to the profiles of the velocity, temperature, concentration and microorganisms are graphically assessed with appropriate physical effects. A graphical explanation is provided for the wall shear stress, local Nusselt number, local Sherwood number and local motile density number. Rate of motile density number shows a prominent difference between reversible and irreversible flows for Brownian motion and Peclet number. The results of the theoretical simulations have dynamic applications in the fields of biotechnology and thermal engineering.

Morphological, structural, and electronic properties of green synthesized ZnO nanoparticles by experimental and DFT+U method – A review

In these decades, researchers have paid much attention to green synthesis methods because of their low cost and eco-friendliness. Among all other semiconductors, ZnO nanoparticles have huge applications in optoelectronics devices, solar cells, photocatalysis, transistors, etc. This review article explains the green synthesis methods and factors affecting the morphology of ZnO nanoparticles. The morphology shows different structures such as nanowires, cubic, hexagonal, flower-like structures, etc. The XPS peaks Zn-2p1/2, Zn-2p3/2, and O-1S suggest that the synthesized nanoparticles are ZnO. The theoretical review part explains the electronic and structural properties of wurtzite ZnO nanoparticles. The implementation of the Hubbard-U scheme in the d and p shells using Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) shows the drastic change in the electronic and structural properties of ZnO nanoparticles. The optimized lattice parameters and band gap using Hubbard parameters by different DFT codes are tabulated. Also, we compared computational and experimental results.

Economical routes to size-specific assembly of self-closing structures.

Programmable self-assembly has seen an explosion in the diversity of synthetic crystalline materials, but developing strategies that target "self-limiting" assemblies has remained a challenge. Among these, self-closing structures, in which the local curvature defines the finite global size, are prone to polymorphism due to thermal bending fluctuations, a problem that worsens with increasing target size. Here, we show that assembly complexity can be used to eliminate this source of polymorphism in the assembly of tubules. Using many distinct components, we prune the local density of off-target geometries, increasing the selectivity of the tubule width and helicity to nearly 100%. We further show that by reducing the design constraints to target either the pitch or the width alone, fewer components are needed to reach complete selectivity. Combining experiments with theory, we reveal an economical limit, which determines the minimum number of components required to create arbitrary assembly sizes with full selectivity.

Semi-supervised clustering guided by pairwise constraints and local density structures

Clustering based on local density peaks and graph cut (LDP-SC) is one of the state-of-the-art algorithms in unsupervised clustering, which first divides the data set to be multiple local trees, and then aggregates these local trees to obtain the final clustering result. However, for complex data sets, there might exist data points from different classes in the same local tree. In this article, we use pairwise constraint information to resolve this issue and propose a semi-supervised local density peaks and graph cut based clustering algorithm (SLDPC). In particular, SLDPC proposes intra-cluster conflict resolution and inter-cluster conflict resolution steps to split the local trees which are inconsistent with the provided pairwise constraint information. Theoretically, we show that the two steps will finish in a finite number of operations and the split local trees will be consistent with the pairwise constraint information. Subsequently, root node redirection and noise filtering steps are designed to avoid the local trees becoming too fragmented. Finally, we exploit the E2CP algorithm to further improve the similarity matrix between local trees using the pairwise constraint information, and the spectral clustering algorithm is adopted to obtain the clustering result. Experiments on multiple widely used synthetic and real-world data sets show that SLDPC is superior to LDP-SC and several other semi-supervised prominent clustering algorithms for most of the cases.

Validating and speeding up x-ray tomographic inversions in tokamak plasmas

X-ray tomography is a precious tool in tokamaks that provides rich information about the core plasma, such as local impurity concentration, electron temperature and density as well as magnetic equilibrium (ME) and magnetohydrodynamic activity. Nevertheless, inferring the local plasma emissivity from a sparse set of line-integrated measurements is an ill-posed problem that requires dedicated regularization and validation methods. Besides, speeding up the inversion algorithm in order to be compatible with real-time control systems is a challenging task with traditional approaches. In this contribution, in a first part we introduce tools aiming at validating and speeding up the x-ray tomographic inversions based on Tikhonov regularization, including ME constraint and parameter optimization, taking the WEST geometry as an example. In a second part, an alternative approach compatible with real-time, based on a set of neural networks is proposed and compared with the Tikhonov approach for an experimental case.

Dark matter in the Milky Way: Measurements up to 3 kpc from the Galactic plane above the Sun

We probe the gravitational force perpendicular to the Galactic plane at the position of the Sun based on a sample of red giants, with measurements taken from the DR3 Gaia catalogue. Measurements far out of the Galactic plane up to 3.5 kpc allow us to determine directly the total mass density, where dark matter is dominant and the stellar and gas densities are very low. In a complementary way, we have also used a new determination of the local baryonic mass density to help determine the density of dark matter in the Galactic plane at the solar position. For the local mass density of dark matter, we obtained $ dm $0.0008\,M$_ $ = 0.486 pm 0.030 Gev\ $. For the flattening of the gravitational potential of the dark halo, it is $q_ phi,h For its density, $q_ rho,h $=0.781pm 0.055.

Constructing Adsorption Site-Enhanced Vo-BiOCl/rGO Heterostructures for Efficient Response to NO2/NH3 Gases at Room Temperature.

Real-time detection of harmful gases at room temperature has become a serious problem in public health and environmental monitoring. Two-dimensional materials with semiconductor properties BiOCl is a promising gas-sensitive material due to its large specific surface area and adjustable band gap as well as outstanding safety characteristics. However, limited by the weak gas adsorption sites and sluggish charge-transfer ability, the performance of BiOCl could not be fully exploited. Oxygen vacancy (Vo) engineering can introduce lattice defects, thereby significantly increasing the local charge density and enhancing the adsorption of gases, which is an effective strategy to enhance the gas-sensing performance. In this work, we composite BiOCl with a vacancy (Vo-BiOCl) and reduced graphene oxide (rGO) to construct a Vo-BiOCl/rGO heterostructure with enhanced gas adsorption sites. Experimental and theoretical calculations show that Vo can enhance the adsorption of gases and the introduction of rGO forms a high-quality heterostructure with BiOCl, which can effectively reduce the band gap of BiOCl and promote electron transfer, thereby improving the sensitivity of the sensor. Benefiting from above, Vo-BiOCl/rGO achieves the ability to detect low concentrations of NO2/NH3 at room temperature, with high sensitivity (55% at 1 ppm of NO2 and -28% at 1 ppm of NH3), fast response time (40 s at 1 ppm of NO2 and 2 s at 1 ppm of NH3), good stability (over 150 days), and fully recoverable gas sensitivity.

Poster 218: Localized Acetabular Bone Density Distributions Are Altered in Unilateral Femoral Acetabular Impingement

Objectives: Femoral acetabular impingement (FAI) can lead to bony and cartilage changes at the joint, and it has been suggested that changes in bone mineral density in the acetabulum may correlate with osteoarthritic degeneration of the hip. In this study, we aimed to use opportunistic quantitative computed tomography (QCT) to map density distributions across the acetabular region in patients with unilateral FAI and determine if there were differences between the affected and unaffected side. Furthermore, we assessed if these differences in density distributions were associated with radiographic measures of FAI. Methods: Twenty patients (age 31.9 (SD 9.2), 13 female) who underwent surgery for unilateral FAI and had an associated CT scan of both hips were included in this retrospective study. Both sides of the pelvis were segmented, and 3D models were created. Estimated bone density values were mapped across the bone models via QCT. A thin-spline semi-landmarking approach was used to allow density values at equivalent anatomical points to be compared within patients and across the group. With the contralateral side used as the control, differences in bone density between sides were calculated. A mixed effect linear regression model was used to determine if there were associations between the localized bone density and radiographic measures of Tonnis grade, alpha angle, lateral center edge angle (LCEA), and cross over sign, while controlling for age and sex. To visualize the data, density changes and statistical results were color-mapped to the bone models. Results: Overall, several regions of the acetabulum were found to have increased bone density in the affected side compared to the contralateral (Figure 1). Specifically, the anterior-superior parts of the acetabular rim appeared to be most affected, along with the posterosuperior region (Figure 2). Limited associations were found between localized density and the clinical variables, with the most notable finding being a region of the superior rim that was found to be associated with the alpha angle (Figure 3). Conclusions: FAI leads to distinct patterns of bone density changes around the acetabulum, although there is still variability at the level of the individual patient. It is unclear whether these changes in bone density may be related to the underlying condition, alterations in the patient’s mechanics due to pain, or a combination of these factors. Providing detailed density maps of the bony anatomy may also assist surgical providers in planning interventions. Further research may elucidate the relationship between bone density changes and long-term degeneration of the joint.

Local clustering of relic neutrinos: comparison of kinetic field theory and the Vlasov equation

Gravitational clustering in our cosmic vicinity is expected to lead to an enhancement of the local density of relic neutrinos. We derive expressions for the neutrino density, using a perturbative approach to kinetic field theory and perturbative solutions of the Vlasov equation up to second order. Our work reveals that both formalisms give exactly the same results and can thus be considered equivalent. Numerical evaluation of the local relic neutrino density at first and second order provides some fundamental insights into the frequently applied approach of linear response to neutrino clustering (also known as the Gilbert equation). Against the naive expectation, including the second-order contribution does not lead to an improvement of the prediction for the local relic neutrino density but to a dramatic overestimation. This is because perturbation theory breaks down in a momentum-dependent fashion and in particular for densities well below unity.