932 research outputs found
Co-Evolution of Transportation and Land Use: Modeling HIstorical Dependencies in Land Use and Decision-Making
The interaction between land use and transportation has long been the central issue in urban and regional planning. Models of such interactions provide vital information to support many public policy decisions, such as land supply, infrastructure provision, and growth management. Both the transportation and land use systems exhibit historical dependencies in policy decisions. For instance, the expansion of a roadway today will change travel demand patterns, and make certain other roads more or less likely to be expanded in the future. A specific land supply decision made at one point in time, by changing the relative attractiveness of other areas in the region, can have a profound impact on future land supply decisions. Today’s land use decisions clearly influence future transportation policies and vice versa. This project examines the land use-transportation interaction from an evolutionary perspective — once a certain set of goals are determined and pursued by politicians and planners, their land supply and transportation investment decisions are, to a large extent, driven by their previous decisions and supply-demand dynamics in the urban system. Built upon this recognition of historical dependency and a transportation network growth model previously developed by the P.I., a model of the co-evolution of land use and transportation is proposed in this project. Different from existing integrated land use and transportation models that assume exogenous network investment decisions, the co-evolution model considers both land use growth and transportation network growth as endogenous and market-driven. The central research question is how market and policies translate into transportation facilities and land use developments on the ground. The co-evolution model achieves an Urban Growth Equilibrium, which is a useful concept for planning and policy analysis. An agent-based simulation approach is employed to integrate an existing land use model and the transportation network growth model
Mirror QCD phase transition as the origin of the nanohertz Stochastic Gravitational-Wave Background detected by the Pulsar Timing Arrays
Recent independent announcements by several collaborations have shown strong
evidence of a Stochastic Gravitational-Wave Background (SGWB) detected through
Pulsar Timing Arrays (PTAs). In this study, we investigate the implications of
a first-order phase transition occurring within the early universe's dark
quantum chromodynamics (dQCD) epoch, specifically within the framework of the
mirror twin Higgs dark sector model. Our analysis indicates a distinguishable
SGWB signal originating from this phase transition, which can explain the
measurements obtained by PTAs. Remarkably, a significant portion of the
parameter space within the mirror twin Higgs model that accounts for the SGWB
signal also effectively resolves the existing tensions in both the and
measurements in Cosmology. This intriguing correlation suggests a
possible common origin for these three phenomena. Furthermore, the parameter
region, , where the mirror dark matter
component constitutes less than of the total dark matter abundance, can
accommodate all current cosmological observations and PTA measurements.Comment: 6 pages, 3 figure
Recommended from our members
In Situ TEM Study of the Degradation of PbSe Nanocrystals in Air
PbSe
nanocrystals have attracted widespread attention due to a
variety of potential applications. However, the practical utility
of these nanocrystals has been hindered by their poor air stability,
which induces undesired changes in the optical and electronic properties.
An understanding of the degradation of PbSe nanocrystals when they
are exposed to air is critical for improving the stability and enhancing
their applications. Here, we use in situ transmission electron microscopy
(TEM) with an environmental cell connected to air to study PbSe nanocrystal
degradation triggered by air exposure. We have also conducted a series
of complementary studies, including in situ environmental TEM study
of PbSe nanocrystals exposed to pure oxygen and PbSe nanocrystals
in H2O using a liquid cell, and ex situ experiments, such
as O2 plasma treatment and thermal heating of PbSe nanocrystals
under different air exposure. Our in situ observations reveal that
when PbSe nanocrystals are exposed to air (or oxygen) under electron
beam irradiation, they experience a series of changes, including shape
evolution of individual nanocrystals with the cuboid intermediates,
coalescence between nanocrystals, and formation of PbSe thin films
through drastic solid-state fusion. Further studies show that the
PbSe thin films transform into an amorphous Pb rich phase or eventually
pure Pb, which suggest that Se reacts with oxygen and can be evaporated
under electron beam illumination. These various in situ and ex situ
experimental results indicate that PbSe nanocrystal degradation in
air is initiated by the dissociation and removal of ligands from the
PbSe nanocrystal surface
Physical properties and chemical composition of the cores in the California molecular cloud
We aim to reveal the physical properties and chemical composition of the
cores in the California molecular cloud (CMC), so as to better understand the
initial conditions of star formation. We made a high-resolution column density
map (18.2") with Herschel data, and extracted a complete sample of the cores in
the CMC with the \textsl{fellwalker} algorithm. We performed new
single-pointing observations of molecular lines near 90 GHz with the IRAM 30m
telescope along the main filament of the CMC. In addition, we also performed a
numerical modeling of chemical evolution for the cores under the physical
conditions. We extracted 300 cores, of which 33 are protostellar and 267 are
starless cores. About 51\% (137 of 267) of the starless cores are prestellar
cores. Three cores have the potential to evolve into high-mass stars. The
prestellar core mass function (CMF) can be well fit by a log-normal form. The
high-mass end of the prestellar CMF shows a power-law form with an index
that is shallower than that of the Galactic field stellar
mass function. Combining the mass transformation efficiency ()
from the prestellar core to the star of and the core formation
efficiency (CFE) of 5.5\%, we suggest an overall star formation efficiency of
about 1\% in the CMC. In the single-pointing observations with the IRAM 30m
telescope, we find that 6 cores show blue-skewed profile, while 4 cores show
red-skewed profile. []/[HNC] and []/ in protostellar cores are higher than those in prestellar cores;
this can be used as chemical clocks. The best-fit chemical age of the cores
with line observations is ~years.Comment: Accepted by Astronomy & Astrophysics (A&A
Exploring Mirror Twin Higgs Cosmology with Present and Future Weak Lensing Surveys
We explore the potential of precision cosmological data to study non-minimal
dark sectors by updating the cosmological constraint on the mirror twin Higgs
model (MTH). The MTH model addresses the Higgs little hierarchy problem by
introducing dark sector particles. In this work, we perform a Bayesian global
analysis that includes the latest cosmic shear measurement from the DES
three-year survey and the Planck CMB and BAO data. In the early Universe, the
mirror baryon and mirror radiation behave as dark matter and dark radiation,
and their presence modifies the Universe's expansion history. Additionally, the
scattering between mirror baryon and photon generates the dark acoustic
oscillation process, suppressing the matter power spectrum from the cosmic
shear measurement. We demonstrate how current data constrain these corrections
to the CDM cosmology and find that for a viable solution to the little
hierarchy problem, the proportion of MTH dark matter cannot exceed about
of the total dark matter density, unless the temperature of twin photon is less
than of that of the standard model photon. While the MTH model is
presently not a superior solution to the observed tension compared to the
CDM+ model, we demonstrate that it has the
potential to alleviate both the and tensions, especially if the
tension persists in the future and approaches the result reported by the
Planck SZ (2013) analysis. In this case, the MTH model can relax the tensions
while satisfying the DES power spectrum constraint up to . If the MTH model is indeed accountable for the and
tensions, we show that the future China Space Station Telescope (CSST) can
determine the twin baryon abundance with a level precision.Comment: 32 pages, 12 figures, 4 table
Black Holes as the source of the dark energy: a stringent test with the high-redshift JWST AGNs
It has been suggested that there is evidence for cosmological coupling of
black holes (BHs) with an index of and hence the BHs serve as the
astrophysical source of the dark energy. The data sample however is limited for
the redshifts . Recently, the James Webb Space Telescope (JWST) has
detected more than 180 high-redshift Active Galactic Nuclei (AGNs) and quasars.
Among the JWST NIRSpec/NIRCam resolved AGNs, three are identified in early-type
host galaxies with a redshift . Their and , however, are in tension with the prediction of the cosmological coupling
of black holes with at a confidence level of , which is not
in support of the hypothesis that BHs serve as the origin of dark energy. The
future observations of high-redshift AGNs by JWST will further test such a
hypothesis by identifying more early-type host galaxies in the higher mass
range.Comment: 9 pages, 3 figures, 1 table; Submitted to ApJL. Comments are welcome
Three-dimensional Electrochemical Micromachining on Metal and Semiconductor by Confined Etchant Layer Technique (CELT)
Contacting Author: Zhao W. Tian is with the State key laboratory for
Physical Chemistry of Solid Surfaces, Xiamen, China
(phone: 86-592-2185797; fax: 86-592-2085349; email: [email protected]
Application of Ionic Liquids in the Microwave-Assisted Extraction of Proanthocyanidins from Larix gmelini Bark
Ionic liquid based, microwave-assisted extraction (ILMAE) was successfully applied to the extraction of proanthocyanidins from Larix gmelini bark. In this work, in order to evaluate the performance of ionic liquids in the microwave-assisted extraction process, a series of 1-alkyl-3-methylimidazolium ionic liquids with different cations and anions were evaluated for extraction yield, and 1-butyl-3-methylimidazolium bromide was selected as the optimal solvent. In addition, the ILMAE procedure for the proanthocyanidins was optimized and compared with other conventional extraction techniques. Under the optimized conditions, satisfactory extraction yield of the proanthocyanidins was obtained. Relative to other methods, the proposed approach provided higher extraction yield and lower energy consumption. The Larix gmelini bark samples before and after extraction were analyzed by Thermal gravimetric analysis, Fourier-transform infrared spectroscopy and characterized by scanning electron microscopy. The results showed that the ILMAE method is a simple and efficient technique for sample preparation
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