High-density Configurations Research Articles

The kinetics of droplet wetting gas hydrate surfaces regulated by anti-agglomerant monolayers: Insights from molecular dynamics study

Anti-agglomerants (AAs) have become a promising strategy for mitigating gas hydrate risks in hydrocarbon transport systems. However, a notable limitation of AAs is their diminished effectiveness in systems with high water content. The density of the AA monolayer is a critical factor influencing the coalescence and agglomeration of hydrate particles with water droplets, but the mechanisms driving these effects remain largely unknown. In this study, molecular dynamics (MD) simulations were employed to explore the anti-wetting performance and interaction properties of Cocamide Monoethanolamine (CMEA) monolayers at varying densities on hydrate surfaces. The results indicate that in systems with low-density monolayers, CMEA molecules exhibit high degrees of freedom and increased fluctuation frequencies, allowing the water molecules of droplet to penetrate the monolayer and rapidly wet the hydrate surface. In contrast, high-density monolayer configurations show properties that hinder droplet wetting on hydrate surfaces and inhibit hydrate growth. Further investigation into the adsorption behavior of CMEA molecules on hydrate surfaces highlights the substantial impact of the solution phase on adsorption free energy, with gas-phase environments enhancing the binding strength between CMEA molecules and hydrate surfaces. These molecular insights offer valuable observations regarding the structural adaptability of AA monolayers during droplet permeation and wetting processes, providing critical information for understanding the broader interactions between anti-agglomerant molecules and hydrates.

Study on the Microscopic Mechanism of Axle Steel EA4T during Uniaxial Cyclic Deformation Process

In order to reveal the dislocation evolution law of body-centered cubic axle steel EA4T during cyclic deformation and provide an experimental basis for the subsequent construction of cyclic constitutive models based on microscopic physical mechanisms, macroscopic deformation experiments were first conducted on axle steel EA4T, including monotonic tensile experiments under different deformation amounts, symmetric strain cycling experiments under a different number of cycles, and ratcheting deformation experiments under a different number of cycles. Then, systematic observations of different samples at different deformation stages were conducted using a Transmission Electron Microscope (TEM) to investigate the dislocation configuration and evolution during strain cycling and ratcheting deformation. The observed results show that the dislocation evolution law of axle steel EA4T during the uniaxial tensile experiment, symmetrical strain cycling, and ratcheting deformation is basically the same, and the dislocation density increases with the increase in plastic deformation and number of cycles. The dislocation configuration gradually develops from low-density dislocation configurations such as dislocation lines and dislocation pileups to high-density dislocation configurations such as severe dislocation tangles and dislocation walls. The microscopic mechanism of the uniaxial ratcheting evolution of axle steel EA4T can be qualitatively explained by the dislocation configuration and evolution.

A Molecular Engineering Strategy for Achieving Blue Phosphorescent Carbon Dots with Outstanding Efficiency above 50.

Highly efficient emission has been a long-lasting pursuit for carbon dots (CDs) owing to their enormous potential in optoelectronic applications. Nevertheless, their room-temperature phosphorescence (RTP) performance still largely lags behind their outstanding fluorescence emission, especially in the bluespectral region. Herein, high-efficiency blue RTP CDs have been designed and constructed via a simple molecular engineering strategy, enabling CDs with an unprecedented phosphorescence quantum efficiency of to 50.17% and a long lifetime of 2.03 s. This treating route facilitates the formation of high-density (n, π*) configurations in the CD π-π conjugate system through the introduction of abundant functional groups, which can evoke a strong spin-orbit coupling and further promote the intersystem crossing from singlet to triplet excited states and radiative recombination from triplet excited states to ground state. With blue phosphorescent CDs as triplet donors, green, red, and white afterglow composites are successfully fabricated via effective phosphorescence Förster resonance energy transfer. Importantly, the color temperature of the white afterglow emission can be widely and facilely tuned from cool white to pure white and warm white. Moreover, advanced information encryption, light illumination, and afterglow/dynamic visual display have been demonstrated when using these multicolor-emitting CD-based afterglow systems.

Proprioceptive feedback design for gait synchronization in collective undulatory robots

The collective movement of animals has long been a source of inspiration for multi-agent swarm robotics. One of the fundamental goals for swarm robotics study is to understand how effective and robust collective behaviors can emerge from simple interaction principles. When animal or robot collectives are in high-density configurations the ability for visual or auditory sensing is diminished and the opportunities for interacting through mechanical contact are enhanced. In this paper, we study how robots that move through lateral body undulation in close proximity are capable of synchronizing their oscillatory gaits through contact interactions between adjacent robots. Critically, gait phase synchronization occurs without the requirement for robot–robot communication, and instead can be engineered as an emergent property of the robot control system. We present a proprioceptive feedback control system that generates collective gait phase synchronization of undulatory robots in experiment and simulation. We first validate this control system using a simple one-dimensional toy model to demonstrate how proprioceptive feedback governs phase synchronization. Simulations and experiments with undulatory three-link robots further demonstrate how phase synchronization can be controlled. Lastly, we demonstrate that robot pairs moving in a confined tunnel can synchronize their movements which leads to faster group locomotion through confined spaces.

An Investigation of the Quantitative Correlation between Urban Morphology Parameters and Outdoor Ventilation Efficiency Indices

Urban outdoor ventilation and pollutant dispersion have important implications for urban design and planning. In this paper, two urban morphology parameters, i.e. the floor area ratio (FAR) and the building site coverage (BSC), are considered to investigate their quantitative correlation with urban ventilation indices. An idealized model, including nine basic units with FAR equal to 5, is considered and the BSC is increased from 11% to 77%, generating 101 non-repetitive asymmetric configurations, with attention to the influence of plan density, volume ratio, and building layout on ventilation performance within urban plot areas. Computational Fluid Dynamics (CFD) simulations are used to assess the ventilation efficiency at pedestrian level (2m above the ground) within each model central area. Six indices, including the air flow rate (Q), the mean age of air (τP), the net escape velocity (NEV), the purging flow rate (PFR), the visitation frequency (VF), and the resident time (TP) are used to assess the local ventilation performance. Results clearly show that, fixing the FAR, the local ventilation performance is not linearly related to BSC, but it also depends on buildings arrangement. Specifically, as the BSC increases, the ventilation in the central area does not keep reducing. On the contrary, some forms with low BSC have poor ventilation and some particular configurations with high BSC have better ventilation, which indicates that not all high-density configurations experience poor ventilation. The local ventilation performance can be effectively improved by rationally arranging the buildings. Even though the application of these results to real cities requires further research, the present findings suggest a preliminary way to build up a correlation between urban morphology parameters and ventilation efficiency tailored to develop a feasible framework for urban designers.

HD-EEG Based Classification of Motor-Imagery Related Activity in Patients With Spinal Cord Injury.

Brain computer interfaces (BCIs) are thought to revolutionize rehabilitation after SCI, e.g., by controlling neuroprostheses, exoskeletons, functional electrical stimulation, or a combination of these components. However, most BCI research was performed in healthy volunteers and it is unknown whether these results can be translated to patients with spinal cord injury because of neuroplasticity. We sought to examine whether high-density EEG (HD-EEG) could improve the performance of motor-imagery classification in patients with SCI. We recorded HD-EEG with 256 channels in 22 healthy controls and 7 patients with 14 recordings (4 patients had more than one recording) in an event related design. Participants were instructed acoustically to either imagine, execute, or observe foot and hand movements, or to rest. We calculated Fast Fourier Transform (FFT) and full frequency directed transfer function (ffDTF) for each condition and classified conditions pairwise with support vector machines when using only 2 channels over the sensorimotor area, full 10-20 montage, high-density montage of the sensorimotor cortex, and full HD-montage. Classification accuracies were comparable between patients and controls, with an advantage for controls for classifications that involved the foot movement condition. Full montages led to better results for both groups (p < 0.001), and classification accuracies were higher for FFT than for ffDTF (p < 0.001), for which the feature vector might be too long. However, full-montage 10–20 montage was comparable to high-density configurations. Motor-imagery driven control of neuroprostheses or BCI systems may perform as well in patients as in healthy volunteers with adequate technical configuration. We suggest the use of a whole-head montage and analysis of a broad frequency range.

Statistics of velocity fluctuations of Geldart A particles in a circulating fluidized bed riser

Particle velocity fluctuations in a large-scale circulating fluidized bed are observed to be anisotropic and non-Maxwellian. Interfacial drag acting on high-density configurations lead to excursions resulting in Levy flight of particles.

Evaluating Approaches to Rendering Braille Text on a High-Density Pin Display.

Refreshable displays for tactile graphics are typically composed of pins that have smaller diameters and spacing than standard braille dots. We investigated configurations of high-density pins to form braille text on such displays using non-refreshable stimuli produced with a 3D printer. Normal dot braille (diameter 1.5 mm) was compared to high-density dot braille (diameter 0.75 mm) wherein each normal dot was rendered by high-density simulated pins alone or in a cluster of pins configured in a diamond, X, or square; and to "blobs" that could result from covering normal braille and high-density multi-pin configurations with a thin membrane. Twelve blind participants read MNREAD sentences displayed in these conditions. For high-density simulated pins, single pins were as quickly and easily read as normal braille, but diamond, X, and square multi-pin configurations were slower and/or harder to read than normal braille. We therefore conclude that as long as center-to-center dot spacing and dot placement is maintained, the dot diameter may be open to variability for rendering braille on a high density tactile display.

Optimizing Storage in High Density Shelving

This article is the first in a series exploring approaches to studying the storage density and overall efficiency (as measured in terms of number of items stored) in high density book storage facilities. The article explores foundational questions associated with increasing the number of items in high density configurations when using relatively traditional shelving facility. The parameters of the high density configuration draw on two storage models: the so-called “California” model, employed at the Northern Regional Library facility, and the “Harvard model.” Through initial analysis of the item sizing and shelving approaches of these models, this article engages in rough analysis of how these models could be adjusted and adapted to fit a specific use case at the Northern Regional Library facility. The article concludes with an analysis of potential methods for applying the theoretical findings in the real-world case of the Northern Regional Library facility through shelf-use analysis and real-world item measurement.

Challenges of pricing luxury in commercial aviation – will first class disappear?

Nowadays, in the era of commoditization of commercial aviation, airlines’ efforts to restore profitability seem to translate more than ever with a focus on economy class. Many new aircraft are ordered with high-density configurations, and the existing ones are sometimes reconfigured to offer more economy seats, either by reducing the space occupied by those seats, or by shrinking the capacity of the other cabins. Is there still any first class demand and how does it differ from the business class demand? What is luxury in commercial aviation? In this paper, we address the role of the first class cabin in commercial aviation, the challenges of pricing luxury and whether first class still has a future in the years to come versus private aviation.

Long-term High-density Microelectrode Array Recordings Evidence Stability of Neuron Locations in Organotypic Hippocampus Slices

Long-term High-density Microelectrode Array Recordings Evidence Stability of Neuron Locations in Organotypic Hippocampus Slices

Detailed study of the nuclear dependence of the EMC effect and short-range correlations

Background: The density of the nucleus has been important in explaining the nuclear dependence of the quark distributions, also known as the EMC effect, as well as the presence of high-momentum nucleons arising from short-range correlations (SRCs). Recent measurements of both of these effects on light nuclei have shown a clear deviation from simple density-dependent models.Purpose: A better understanding of the nuclear quark distributions and short-range correlations requires a careful examination of the experimental data on these effects to constrain models that attempt to describe these phenomena.Methods: We present a detailed analysis of the nuclear dependence of the EMC effect and the contribution of SRCs in nuclei, comparing to predictions and simple scaling models based on different pictures of the underlying physics. We also make a direct, quantitative comparison of the two effects to further examine the connection between these two observables related to nuclear structure.Results: We find that, with the inclusion of the new data on light nuclei, neither of these observables can be well explained by common assumptions for the nuclear dependence. The anomalous behavior of both effects in light nuclei is consistent with the idea that the EMC effect is driven by either the presence of high-density configurations in nuclei or the large virtuality of the high-momentum nucleons associated with these configurations.Conclusions: The unexpected nuclear dependence in the measurements of the EMC effect and SRC contributions appear to suggest that the local environment of the struck nucleon is the most relevant quantity for explaining these results. The common behavior suggests a connection between the two seemingly disparate phenomena, but the data do not yet allow for a clear preference between models which aim to explain this connection.

Decoupled 4T dynamic CAM suitable for high density storage

A new four-transistor dynamic CAM (DCAM) is introduced. The DCAM design addresses the inherent data retention problem by proposing a modified sensing scheme. The results indicate over an order of magnitude improvement in data retention time. In addition, the DCAM structure realises a decoupled match-line structure, which enables high density configurations not possible from previous 4T CAM approaches.

Langmuir monolayers with internal dipoles: Understanding phase behavior using Monte Carlo simulations

A coarse-grained, rigid-rod model that includes steric interactions and an internal dipole is used to study monolayers of surfactant molecules tethered to a flat interface. Monte Carlo simulations are performed in the canonical ensemble for a range of high-density configurations with varying degrees of dipole strength. Both a melting transition and a tilting transition are observed, and the dependence of the transitions on the surfactant molecules' internal dipoles is examined. Simulation results indicate that at high packing densities, the monolayers exist in a frustrated state due to dipole-dipole repulsions and steric interactions. Tilting of the surfactant molecules increases the magnitude of the dipole-dipole attractions and lowers the overall system energy, but is limited by steric repulsions. In simulations with higher dipole strengths, the melting and tilting transitions are found to be coupled. The formation of nanodomains with increased collective tilt and positional order in these systems suggests a possible mechanism for the coupling.

A first-principle study on the structure, stability and hardness of cubic BC 2N

The hardness of cubic BC 2N ( c-BC 2N) has sparked considerable debate in the literature. First-principle calculations, guided by bond counting rules, were engaged to investigate the correlation between the stability of an alloy configuration and its hardness by searching through alloy configurations in all distinct unit cells of size up to 12 atoms. The existence of many low-energy and high-density alloy configurations with formation energies in the order of 100–200 meV/atom suggests that a mixture of high-density alloy configurations in the experimental samples is likely to occur due to the high temperature and non-equilibrium conditions offered by modern growth techniques. Theoretical analysis on elastic stiffness and Vickers hardness confirm that these stable high-density c-BC 2N alloy configurations are indeed harder than c-BN.

Structural studies and polymorphism in amorphous solids and liquids at high pressure

When amorphous materials are compressed their structures are expected to change in response to densification. In some cases, the changes in amorphous structure can be discontinuous and they can even have the character of first-order phase transitions. This is a phenomenon referred to as polyamorphism. Most evidence for polyamorphic transitions between low and high density liquids or analogous transformations between amorphous forms of the same substance to date has been indirect and based on the changes in thermodynamic and other structure-related properties with pressure. Recent studies using advanced X-ray and neutron scattering methods combined with molecular dynamics simulations are now revealing the details of structural changes in polyamorphic systems as a function of pressure. Various "two state" or "two species" models are used to understand the anomalous densification behaviour of liquids with melting curve maxima or regions of negative melting slope. Thermodynamic analysis of the two state model leads to the possibility of low- to high-density liquid transitions caused by differences in bulk thermodynamic properties between different amorphous forms and on the degree of cooperativity between low- and high-density structural configurations. The potential occurrence of first-order transitions between supercooled liquids is identified as a critical-like phenomenon. In this tutorial review we discuss the background to polyamorphism, incorporating the experimental observations, simulation studies and the two-state models. We also describe work carried on several systems that are considered to be polyamorphic.

Building the Connection Between Housing Needs and Metropolitan Planning in Sydney, Australia

The theme of a more compact city has been a central feature of planning policy for Sydney's development over the last two decades. Urban consolidation, in the form of attached dwellings in medium- and high-density configurations, has become the predominant form of new residential development since the early 1990s. One of the largely untested claims for this policy is that it provides more housing choice for an increasingly diverse population and that simply building larger amounts of smaller housing in high-density concentrations will be sufficient to meet that demand. As a result, planning for higher density housing has been undertaken with little explicit recognition of the housing sub-markets higher density housing caters for or their specific spatial characteristics within the city. These issues are examined by an analysis of the socio-economic characteristics of areas with high concentrations of attached housing. These data are processed by factor analysis to identify and locate the range of sub-markets within attached housing and additional small area data used to fill out the market profiling. The results reveal that a range of specific housing needs are met by this form of housing with discriminative characteristics in certain locations. In other words, higher density housing is associated with a range of locationally specific and spatially distinctive sub-markets. These findings are particularly relevant and timely as a new metropolitan strategy is in preparation for Sydney where an estimated 60–70 per cent of new dwelling provision in the next 30 years will take place within existing suburbs through higher density redevelopment. Planning for such development must take into account the local markets for such accommodation which have very different characteristics in different parts of the city.

Do Ordinary Nuclei Contain Exotic States of Matter?

The strongly repulsive core of the short-range nucleon-nucleon interaction leads to the existence of high-momentum nucleons in nuclei. Inclusive electron scattering can be used to probe these high-momentum nucleons and study the nature of the corresponding short-range correlations in nuclei. With recent data from Jefferson Lab we have begun to map out the strength of two-nucleon correlations in nuclei, while upcoming experiments should allow us to isolate the presence of multi-nucleon correlations. In addition to their importance in describing nuclear structure, these configurations of correlated nucleons represent high density 'droplets' of hadronic matter. As the density of hadronic matter increases there should be a weakening of quark confinement, similar to the onset of deconfinement expected at extremely high temperatures. While there have been hints of non-hadronic structure in nuclei, future measurements will allow us to directly probe the quark distributions of high density configurations in nuclei. A modified quark structure in these closely packed nucleons would provide a clear signature of exotic components to the structure of nuclei.

Studies of rhodium nanoparticles using the first principles density functional theory calculations

Rhodium nanoparticles in the range of 2–55 atoms were investigated using density functional theory calculations. The binding energy increases from 1.74 eV/atom for the dimer to 4.61 eV/atom for the 55-atom cluster. The stability of these nanoparticles increases in the order of linear, planar, and high-density close-packed configurations. Analysis of the atom-resolved charge density and magnetic moment reveals that the atomic charge density only depends on the coordination number while the local magnetic moment depends not only on the coordination number but also on the coordination of the neighbouring atoms.

Self-Organization in a Two-Dimensional Cellular Automaton Model of Traffic Flow

The jam phases in a two-dimensional cellular automaton model of traffic flow are investigated by computer simulations. Two different types of jam phases are discussed. The low-density jam configurations show fractality and self-organization. The high-density jam configurations show randomness.