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Recent intra-metropolitan patterns of spatial mismatch: Implications for black suburbanization and the changing geography of mismatch
No full textKain's spatial mismatch hypothesis (SMH) (1968) highlights the segregation of Black population in the inner city as well as the decentralization of jobs, both of which played a role in the poor labor market outcomes for Black residents in the inner city. Demographic and economic changes in U.S. metropolitan areas since the late 20th century have transformed the urban spatial structure. This paper aims to revisit the SMH and investigate whether the spatial pattern of mismatch has changed as a result of geographic shifts in the Black population. This paper specifically examines how the suburbanization of the Black population has affected the geographic patterns of mismatch and whether the mismatch is disappearing in the major U.S. metropolitan areas. Using spatial measures of mismatch, this paper presents intra-metropolitan spatial mismatch patterns that capture the clustering of jobs and the Black population based on their relative distributions, showing that the overall level of spatial mismatch declined in major U.S. metropolitan areas between 2000 and 2015. However, geographical evidence reveals that the spatial mismatch has shifted to the outer suburbs, replicating city-suburb spatial inequality, implying that although mismatch may have declined in the inner city due to Black suburbanization, spatial mismatch continue to persist in U.S. metropolitan areas in Black suburbs. The findings also demonstrate that although spatial mismatch generally declined in the inner city, it increased in cities with high inner city polarization, particularly New York, Chicago, San Francisco, and Seattle
Honeycomb oxide heterostructure as a candidate host for a Kitaev quantum spin liquid
No full textThe Kitaev quantum spin liquidand massively quantum entangled states, are so scarce in nature that searching for new candidate systems remains a great challenge. A honeycomb heterostructure could be a promising route to realize and utilize such an exotic quantum phase by providing additional controllability of Hamiltonian and device compatibility, respectively. Here, we provide epitaxial honeycomb oxide thin film Na3Co2SbO6, a candidate of Kitaev quantum spin liquid proposed recently. We found a spin glass and antiferromagnetic ground states depending on Na stoichiometry, signifying not only the importance of Na vacancy control but also strong frustration in Na3Co2SbO6. Despite its classical ground state, the field-dependent magnetic susceptibility shows remarkable scaling collapse with a single critical exponent, which can be interpreted as evidence of quantum criticality. Its electronic ground state and derived spin Hamiltonian from optical spectroscopy are consistent with the predicted Kitaev model. Our work provides a unique route to the realization and utilization of Kitaev quantum spin liquid
Prevention of Carbon Corrosion by TiC Formation on Ti Current Collector in Seawater Batteries
No full textSeawater batteries (SWBs) are a type of sodium-air batteries that use abundant seawater as the source of the catholyte. A cathode current collector in traditional SWBs is composed of titanium (Ti) and carbon-based current collectors. The high contact resistance between Ti and carbon-based current collectors as well as the slow kinetics of oxygen evolution and reduction reactions increase the overpotential, resulting in side reactions such as carbon corrosion. To enhance the performance of SWBs, previous studies have focused on carbon current collectors, catalysts, and polymer binders, while ignoring the importance of Ti. In this study, a facile carbon diffusion technique is employed to successfully form titanium carbide (TiC) on the surface of Ti. SWBs with engineered Ti demonstrate considerably improved performance (four times higher cycling stability, 30% increased power performance, 40% reduced voltage gap) in relation to those with pristine Ti. This significantly improved electrochemical performance is found to be attributable to the prevention of carbon corrosion due to i) the reduction of contact resistance (owing to rough TiC surface) and ii) the electrocatalytic effect of TiC. Finally, engineered Ti is applied to large-area SWBs and its potential applicability in energy storage systems is confirmed
Mechanically Stable Flexible Organic Photovoltaics with Silver Nanomesh for Indoor Applications
No full textEnhanced device performance of flexible organic solar cells (FOSCs) was achieved according to the development of organic solar cells (OSCs). OSCs are promising candidates as energy sources for low-power supply systems such as the Internet of Things (IoT) under indoor lighting environments. To apply FOSCs to flexible or wearable applications, they must be mechanically stable. In this study, we fabricated FOSCs with silver nanomesh (AgNM) as the bottom transparent conductive electrode (TCE). Instead of indium tin oxide (ITO), AgNMs were prepared using three pitches of 25, 50, and 100 mu m with a square pattern, using a poly(ethylene terephthalate) (PET) substrate. Notably, the device using AgNMs with a pitch of 25 mu m exhibited a power conversion efficiency (PCE) of 14.93% under 1 sun illumination and 17.91% under 1000 lux of light-emitting diode (LED) light conditions. Flexible devices using AgNMs maintained over 92% of their initial PCE under 1 sun illumination (PCE decreased to 12.98 from 14.04%) and over 92% when tested under 1000 lux of LED light illumination (PCE decreased to 16.57 from 17.91%) after 1000 instances of bending. These results demonstrate the advantages of using AgNMs as an alternative TCE under both 1 sun and indoor lightning environments and are promising candidates for flexible applications
Tape-Free, Digital Wearable Band for Exercise Sweat Rate Monitoring
No full textMonitoring sweat secretion rate is essential for uncovering underlying physical conditions like hyperhidrosis, mental stress, and neural disorders. Often, flexible microfluidic sweat rate monitoring devices use tape as a means of attachment to the skin to tightly seal the collection area. While these single-use, adhesive-backed devices have lightweight and thin interfaces for mounting on the skin, their form factor complicates their potential integration with available commercial wearables, such as smartwatches. Here, a tape-free device, consisting of a 3D-printed sweat collector with a concave surface that is strapped onto the skin to form an effective seal, is presented. The materials, structure, and dimensions of the sweat collector are optimized for conformal device-to-skin contact and efficient capture of sweat. The collector is interfaced with a fluidic microchannel with embedded electrodes for continuous digital monitoring of sweat rate. Long-term exercise-induced local sweat rate from multiple body locations in both multi-subject and longitudinal studies is measured, depicting the correlation between the measured sweat profile and total body fluid loss. The simple installation procedure and reusability of this tape-free device make it a good candidate for integration with the band of a watch
Nanomaterial-Based Synaptic Optoelectronic Devices for In-Sensor Preprocessing of Image Data
No full textWith the advance in information technologies involving machine vision applications, the demand for energyand time-efficient acquisition, transfer, and processing of a large amount of image data has rapidly increased. However, current architectures of the machine vision system have inherent limitations in terms of power consumption and data latency owing to the physical isolation of image sensors and processors. Meanwhile, synaptic optoelectronic devices that exhibit photoresponse similar to the behaviors of the human synapse enable insensor preprocessing, which makes the front-end part of the image recognition process more efficient. Herein, we review recent progress in the development of synaptic optoelectronic devices using functional nanomaterials and their unique interfacial characteristics. First, we provide an overview of representative functional nanomaterials and device configurations for the synaptic optoelectronic devices. Then, we discuss the underlying physics of each nanomaterial in the synaptic optoelectronic device and explain related device characteristics that allow for the in-sensor preprocessing. We also discuss advantages achieved by the application of the synaptic optoelectronic devices to image preprocessing, such as contrast enhancement and image filtering. Finally, we conclude this review and present a short prospect
An Integrated Motion Planning Scheme for Safe Autonomous Vehicles in Highly Dynamic Environments
No full textThis study proposes a new integrated approach to the motion control of autonomous vehicles, which differs from the conventional method of treating planning and tracking tasks as separate or hierarchical components. By means of the proposed approach we can reduce the side effects on the performance of autonomous vehicles under challenging driving circumstances. To this end, our approach processes both of the aforementioned tasks asynchronously and simultaneously utilizes a multi-threaded architecture to enhance control performance. Meanwhile, the behavior planning feature is integrated into the path-tracking module. Then, a linear parameter-varying model predictive control is deployed for trajectory tracking of autonomous vehicles and compared with the linear model predictive control method. Finally, the control performance of the proposed approach was evaluated through simulation trials on urban roads with placed obstacles. The outcomes revealed that the suggested framework satisfies the processing rate and high-precision criteria, while safely avoiding obstacles, indicating that it is a promising control strategy for real-world applications
Future changes in extreme heatwaves in terms of intensity and duration over the CORDEX-East Asia Phase Two domain using multi-GCM and multi-RCM chains
No full textAn extreme heatwave, in terms of intensity and duration, is projected to occur at the end of the 21st century (2071-2100) over the whole of East Asia. The projection is calculated using daily maximum temperature data of 25 km horizontal resolution produced by 12 general circulation model-regional climate model chains participating in the CORDEX-East Asia Phase 2 project. An 'extreme' heatwave is defined as one in which the heatwave magnitude (HWM), which is the accumulated daily intensity of a heatwave during the heatwave period, is higher than the 95th percentile of the HWM for the reference period (1981-2005). In historical simulations, heatwaves have occurred mainly from April to June in India, in April and May in Indochina, from June to August in China and Mongolia, and in July and August in the Korean Peninsula and Japan; most heatwaves last three to four days. In India and Indochina, long-lasting and intense heatwaves occur more often than in other regions. In future, heatwave intensity will increase, the average duration of heatwaves will be approximately two to three weeks, and the heatwave season will be lengthened. Therefore, extreme heatwaves will occur more frequently and strongly. Under two representative concentration pathway scenarios (RCP2.6 and RCP8.5) and two shared socioeconomic pathway scenarios (SSP1-2.6 and SSP5-8.5), the proportion of extreme heatwaves to all heatwave events will increase from 5.0% (historical) to 8.0%, 20.8%, 19.3%, and 36.3%, and the HWM of the extreme heatwave will be 1.4, 3.5, 3.0, and 9.0 times stronger, respectively. The main reason for the increase in the HWM of extreme heatwaves is the increased duration rather than the daily intensity of the heatwaves. In East Asia, the temporal and regional disparities of heatwave damage will be much more prominent as extreme heatwaves become stronger and more frequent in these regions and during the periods that are more affected by heatwaves in the present day
Machine-learning-assisted analysis of transition metal dichalcogenide thin-film growth
No full textIn situ reflective high-energy electron diffraction (RHEED) is widely used to monitor the surface crystalline state during thin-film growth by molecular beam epitaxy (MBE) and pulsed laser deposition. With the recent development of machine learning (ML), ML-assisted analysis of RHEED videos aids in interpreting the complete RHEED data of oxide thin films. The quantitative analysis of RHEED data allows us to characterize and categorize the growth modes step by step, and extract hidden knowledge of the epitaxial film growth process. In this study, we employed the ML-assisted RHEED analysis method to investigate the growth of 2D thin films of transition metal dichalcogenides (ReSe2) on graphene substrates by MBE. Principal component analysis (PCA) and K-means clustering were used to separate statistically important patterns and visualize the trend of pattern evolution without any notable loss of information. Using the modified PCA, we could monitor the diffraction intensity of solely the ReSe2 layers by filtering out the substrate contribution. These findings demonstrate that ML analysis can be successfully employed to examine and understand the film-growth dynamics of 2D materials. Further, the ML-based method can pave the way for the development of advanced real-time monitoring and autonomous material synthesis techniques
Heterogeneous Integration of Freestanding Bilayer Oxide Membrane for Multiferroicity
No full textTransition metal oxides exhibit a plethora of electrical and magnetic properties described by their order parameters. In particular, ferroic orderings offer access to a rich spectrum of fundamental physics phenomena, in addition to a range of technological applications. The heterogeneous integration of ferroelectric and ferromagnetic materials is a fruitful way to design multiferroic oxides. The realization of freestanding heterogeneous membranes of multiferroic oxides is highly desirable. In this study, epitaxial BaTiO3/La0.7Sr0.3MnO3 freestanding bilayer membranes are fabricated using pulsed laser epitaxy. The membrane displays ferroelectricity and ferromagnetism above room temperature accompanying the finite magnetoelectric coupling constant. This study reveals that a freestanding heterostructure can be used to manipulate the structural and emergent properties of the membrane. In the absence of the strain caused by the substrate, the change in orbital occupancy of the magnetic layer leads to the reorientation of the magnetic easy-axis, that is, perpendicular magnetic anisotropy. These results of designing multiferroic oxide membranes open new avenues to integrate such flexible membranes for electronic applications