5,421 research outputs found
Application of a Numerical Model to Evaluate the Impact of Future Sea-level Change in Coastal Inundation around Chester and Delaware Counties
Coastal inundation caused by severe weather events such as hurricanes was investigated by applying a numerical simulation for the area of eastern Pennsylvania. The study area includes long extension of coastal low-lying lands by the Delaware River, including Philadelphia city as well as Chester and Delaware counties, which is under the risk of coastal inundation when hurricanes hit the mid-Atlantic regions. The SLOSH (Sea, Lake and Overland Surges from Hurricanes) model, initially developed by the National Weather Service (NWS), was implemented to the study area to evaluate the probability of inundation due to combined effect of Hurricane storm surge and the climate change and subsequent sea-level rise. Dr. Yong Hoon Kim and Ms. Dominica DeFelice, an undergraduate student in the Department of Earth and Space Science, collected coastline and topography data of the eastern Pennsylvania, digitized them into proper GIS format, and ran SLOSH simulation with these newly-collected data. The simulation results show that the low land areas around Chester, Philadelphia airport and Philadelphia Naval business area could be inundated even under category 3 hurricanes if we have a sea-level rise of 2.23 ft above the present level at year 2050 (based on IPCC 5th Assessment Report). With category 5 hurricanes, some residential areas in southwestern Philadelphia and oil storage tanks fields along Schuylkill river could also be under influence. This study shows high risk of inundation in lowland coastal areas in eastern Pennsylvania during severe Hurricanes when we have sea-level rise near future. The findings from this project will be used to teach Impact of Climate Change topic in Dr. Kim’s ESS 130 Our Coastal Ocean (Gen Ed) and other courses. This study was supported by Sustainability Research and Creative Activities Grant from Office of Sustainability, West Chester University of Pennsylvania
Object-oriented construction of a multigrid electronic-structure code with Fortran 90
We describe the object-oriented implementation of a higher-order
finite-difference density-functional code in Fortran 90. Object-oriented models
of grid and related objects are constructed and employed for the implementation
of an efficient one-way multigrid method we have recently proposed for the
density-functional electronic-structure calculations. Detailed analysis of
performance and strategy of the one-way multigrid scheme will be presented.Comment: 24 pages, 6 figures, to appear in Comput. Phys. Com
A study on the turbulent transport of an advective nature in the fluid plasma
Advective nature of the electrostatic turbulent flux of plasma energy is
studied numerically in a nearly adiabatic state. Such a state is represented by
the Hasegawa-Mima equation that is driven by a noise that may model the
destabilization due to the phase mismatch of the plasma density and the
electric potential. The noise is assumed to be Gaussian and not to be invariant
under reflection along a direction . It is found that the flux density
induced by such noise is anisotropic: While it is random along , it is
not along the perpendicular direction and the flux is not
diffusive. The renormalized response may be approximated as advective with the
velocity being proportional to in the Fourier space
Stretching-induced conductance variations as fingerprints of contact configurations in single-molecule junctions
Molecule-electrode contact atomic structures are a critical factor that
characterizes molecular devices, but their precise understanding and control
still remain elusive. Based on combined first-principles calculations and
single-molecule break junction experiments, we herein establish that the
conductance of alkanedithiolate junctions can both increase and decrease with
mechanical stretching and the specific trend is determined by the S-Au linkage
coordination number (CN) or the molecule-electrode contact atomic structure.
Specifically, we find that the mechanical pulling results in the conductance
increase for the junctions based on S-Au CN two and CN three contacts, while
the conductance is minimally affected by stretching for junctions with the CN
one contact and decreases upon the formation of Au monoatomic chains. Detailed
analysis unravels the mechanisms involving the competition between the
stretching-induced upshift of the highest occupied molecular orbital-related
states toward the Fermi level of electrodes and the deterioration of
molecule-electrode electronic couplings in different contact CN cases.
Moreover, we experimentally find a higher chance to observe the conductance
enhancement mode under a faster elongation speed, which is explained by ab
initio molecular dynamics simulations that reveal an important role of thermal
fluctuations in aiding deformations of contacts into low-coordination
configurations that include monoatomic Au chains. Pointing out the
insufficiency in previous notions of associating peak values in conductance
histograms with specific contact atomic structures, this work resolves the
controversy on the origins of ubiquitous multiple conductance peaks in
S-Au-based single-molecule junctions.Comment: 11 pages, 4 figures; to be published in J. Am. Chem. So
Nitrogen doping of carbon nanoelectrodes for enhanced control of DNA translocation dynamics
Controlling the dynamics of DNA translocation is a central issue in the
emerging nanopore-based DNA sequencing. To address the potential of heteroatom
doping of carbon nanostructures to achieve this goal, herein we carry out
atomistic molecular dynamics simulations for single-stranded DNAs translocating
between two pristine or doped carbon nanotube (CNT) electrodes. Specifically,
we consider the substitutional nitrogen doping of capped CNT (capCNT)
electrodes and perform two types of molecular dynamics simulations for the
entrapped and translocating single-stranded DNAs. We find that the
substitutional nitrogen doping of capCNTs stabilizes the edge-on nucleobase
configurations rather than the original face-on ones and slows down the DNA
translocation speed by establishing hydrogen bonds between the N dopant atoms
and nucleobases. Due to the enhanced interactions between DNAs and N-doped
capCNTs, the duration time of nucleobases within the nanogap was extended by up
to ~ 290 % and the fluctuation of the nucleobases was reduced by up to ~ 70 %.
Given the possibility to be combined with extrinsic light or gate voltage
modulation methods, the current work demonstrates that the substitutional
nitrogen doping is a promising direction for the control of DNA translocation
dynamics through a nanopore or nanogap based of carbon nanomaterials.Comment: 11 pages, 4 figure
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