2,789 research outputs found
Confinement Effects on the Crystalline Features of Poly(9,9-dioctylfluorene)
Typical device architectures in polymer-based optoelectronic devices, such as
field effect transistors organic light emitting diodes and photovoltaic cells
include sub-100 nm semiconducting polymer thin-film active layers, whose
microstructure is likely to be subject to finite-size effects. The aim of this
study was to investigate effect of the two-dimensional spatial confinement on
the internal structure of the semiconducting polymer poly(9,9-dioctylfluorene)
(PFO). PFO melts were confined inside the cylindrical nanopores of anodic
aluminium oxide (AAO) templates and crystallized via two crystallization
strategies, namely, in the presence or in the absence of a surface bulk
reservoir located at the template surface. We show that highly textured
semiconducting nanowires with tuneable crystal orientation can be thus
produced. Moreover, our results indicate that employing the appropriate
crystallization conditions extended-chain crystals can be formed in
confinement. The results presented here demonstrate the simple fabrication and
crystal engineering of ordered arrays of PFO nanowires; a system with potential
applications in devices where anisotropic optical properties are required, such
as polarized electroluminescence, waveguiding, optical switching, lasing, etc
Reevaluation of the cox1 group I intron in Araceae and angiosperms indicates a history dominated by loss rather than horizontal transfer
The origin and modes of transmission of introns remain matters of much debate. Previous studies of the group I intron in the angiosperm cox1 gene inferred frequent angiosperm-to-angiosperm horizontal transmission of the intron from apparent incongruence between intron phylogenies and angiosperm phylogenies, patchy distribution of the intron among angiosperms, and differences between cox1 exonic coconversion tracts (the first 22 nt downstream of where the intron inserted). We analyzed the cox1 gene in 179 angiosperms, 110 of them containing the intron (intron+) and 69 lacking it (intron-). Our taxon sampling in Araceae is especially dense to test hypotheses about vertical and horizontal intron transmission put forward by Cho and Palmer (1999. Multiple acquisitions via horizontal transfer of a group I intron in the mitochondrial coxl gene during evolution of the Araceae family. Mol Biol Evol. 16:1155–1165). Maximum likelihood trees of Araceae cox1 introns, and also of all angiosperm cox1 introns, are largely congruent with known phylogenetic relationships in these taxa. The exceptions can be explained by low signal in the intron and long-branch attraction among a few taxa with high mitochondrial substitution rates. Analysis of the 179 coconversion tracts reveals 20 types of tracts (11 of them only found in single species, all involving silent substitutions). The distribution of these tracts on the angiosperm phylogeny shows a common ancestral type, characterizing most intron+ and some intron- angiosperms, and several derivative tract types arising from gradual back mutation of the coconverted nucleotides. Molecular clock dating of small intron+ and intron- sister clades suggests that coconversion tracts have persisted for 70 Myr in Araceae, whose cox1 sequences evolve comparatively slowly. Sequence similarity among the 110 introns ranges from 91% to identical, whereas putative homologs from fungi are highly different, but sampling in fungi is still sparse. Together, these results suggest that the cox1 intron entered angiosperms once, has largely or entirely been transmitted vertically, and has been lost numerous times, with coconversion tract footprints providing unreliable signal of former intron presence
Weaving Equity into Infrastructure Resilience Research and Practice: A Decadal Review and Future Directions
After about a decade of research in this domain, what is missing is a
systematic overview of the research agenda across different infrastructures and
hazards. It is now imperative to evaluate the current progress and gaps. This
paper presents a systematic review of equity literature on disrupted
infrastructure during a natural hazard event. Following a systematic review
protocol, we collected, screened, and evaluated almost 3,000 studies. Our
analysis focuses on the intersection within the dimensions of the
eight-dimensional assessment framework that distinguishes focus of the study,
methodological approaches, and equity dimensions (distributional-demographic,
distributional-spatial, procedural, and capacity equity). To conceptualize the
intersection of the different dimensions of equity, we refer to pathways, which
identify how equity is constructed, analyzed, and used. Significant findings
show that (1) the interest in equity in infrastructure resilience has
exponentially increased, (2) the majority of studies are in the US and by
extension in the global north, (3) most data collection use descriptive and
open-data and none of the international studies use location-intelligence data.
The most prominent equity conceptualization is distributional equity, such as
the disproportionate impacts to vulnerable populations and spaces. The most
common pathways to study equity connect distributional equity to the
infrastructure's power, water, and transportation in response to flooding and
hurricane storms. Other equity concepts or pathways, such as connections of
equity to decision-making and building household capacity, remain understudied.
Future research directions include quantifying the social costs of
infrastructure disruptions and better integration of equity into resilience
decision-making.Comment: 37 pages, 11 figures, 2 table
Detecting Early-warning signals in Time Series of Visits to Points of Interests to Examine Population Response to COVID -19 Pandemic
The objective of this paper is to examine population response to COVID-19 and
associated policy interventions through detecting early-warning signals in time
series of visits to points of interest (POIs). Complex systems, such as cities,
demonstrate early-warning signals when they approach phase transitions
responding to external perturbation, including crises, policy changes, and
human behavior changes. In urban systems, population visits to POIs represent a
state in the complex systems that are cities. These states may undergo phase
transitions due to population response to pandemic risks and intervention
policies. In this study, we conducted early-warning signal detection on
population visits to POIs to examine population response to pandemic risks. We
examined two early-warning signals, the increase of autocorrelation at-lag-1
and standard deviation, in time series of population visits to POIs in 17
metropolitan cities in the United States of America. The results show that: (1)
early-warning signals for population response to COVID-19 were detected between
February 14 and March 11, 2020 in 17 cities; (2) detected population response
had started prior to shelter-in-place orders in 17 cities; (3) early-warning
signals detected from the essential POIs visits appeared earlier than those
from non-essential POIs; and 4) longer time lags between detected population
response and shelter-in-place orders led to a less decrease in POI visits. The
results show the importance of detecting early-warning signals during crises in
cities as complex systems. Early-warning signals could provide important
insights regarding the timing and extent of population response to crises to
inform policy makers
Towards a First-Person Perspective Mixed Reality Guidance System for Needle Interventions
While ultrasound (US) guidance has been used during central venous catheterization to reduce complications, including the puncturing of arteries, the rate of such problems remains non-negligible. To further reduce complication rates, mixed-reality systems have been proposed as part of the user interface for such procedures. We demonstrate the use of a surgical navigation system that renders a calibrated US image, and the needle and its trajectory, in a common frame of reference. We compare the effectiveness of this system, whereby images are rendered on a planar monitor and within a head-mounted display (HMD), to the standard-of-care US-only approach, via a phantom-based user study that recruited 31 expert clinicians and 20 medical students. These users performed needle-insertions into a phantom under the three modes of visualization. The success rates were significantly improved under HMD-guidance as compared to US-guidance, for both expert clinicians (94% vs. 70%) and medical students (70% vs. 25%). Users more consistently positioned their needle closer to the center of the vessel’s lumen under HMD-guidance compared to US-guidance. The performance of the clinicians when interacting with this monitor system was comparable to using US-only guidance, with no significant difference being observed across any metrics. The results suggest that the use of an HMD to align the clinician’s visual and motor fields promotes successful needle guidance, highlighting the importance of continued HMD-guidance research
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