2,644 research outputs found
Driven polymer translocation through nanopores: slow versus fast dynamics
We investigate the dynamics of polymer translocation through nanopores under
external driving by 3D Langevin Dynamics simulations, focusing on the scaling
of the average translocation time versus the length of the polymer,
. For slow translocation, i.e., under low driving force
and/or high friction, we find where
denotes the Flory exponent. In contrast, is observed for
fast translocation due to the highly deformed chain conformation on the trans
side, reflecting a pronounced non-equilibrium situation. The dependence of the
translocation time on the driving force is given by and
for slow and fast translocation, respectively. These
results clarify the controversy on the magnitude of the scaling exponent
for driven translocation.Comment: 6 pages, 7 figures, to appear in EPL (Europhysics Letters
Crash Analysis of Work Zone Lane Closures with Left-Hand Merge and Downstream Lane Shift
The Arkansas State Highway and Transportation Department (AHTD) began the Interstate Rehabilitation Program (IRP) in the spring of 2000 that ultimately rebuilt approximately 380 miles, or 60% of Arkansas' 655-mile Interstate system. While these projects were underway, a new lane closure method, the "Iowa weave," or lane closure with a left-hand merge and lane shift, was introduced to AHTD to effectively save time ensuring that these IRP projects were completed on schedule. Contractors on the projects used the Iowa weave at least 50% of the time for each of the projects. The settings between the Iowa weave and the conventional right-lane closure were rotated on a periodic basis depending on the work to be completed on each side of the lane. Construction officials in AHTD agreed that the use of the Iowa weave helped them to complete the rehabilitation program on time and improved traffic safety, as no major concerns were noted due to this new technique. However, the crash analysis of this weaving pattern as opposed to the conventional right-lane closure has not been assessed to determine which lane closure strategy has an advantage on the basis of actual crash experience. This research examined the work zone crashes in both of the lane closure settings by assessing them with a set of independent variables that have been known to be the factors that influence work zone crashes. In order to properly assess the comparison between the two lane closure strategies, the following primary research objectives were pursued: Examination of crash experience results from the two traffic control methods, and Reexamination of the advantages and disadvantages of the Iowa weave method as compared to the conventional right-lane closure. This study analyzed the crash data between January 1, 2000 and December 31, 2005 on the characteristics of lane closure strategies in Arkansas. The findings of the analyses were organized by: 1) Raw number of crashes (Pearson chi-square and One-Way ANOVA tests); 2) Crash rates (paired t-test); and Crash severity (binary logistic regression modeling). The analysis results of this study may be used for DOTs to reference the impressive rehabilitation work that the AHTD has completed by incorporating the use of the Iowa weave. The results of the statistical analyses showed that there was approximately a 30 percent reduction in crash rate when the Iowa weave configuration was used. Nonetheless, the final results of the logistic regression model found that the safety advantages between the Iowa weave and conventional right-lane closure in changing crash severity were not statistically significant. Traffic volume was found to be the parameter that most significantly affected crash severity in the logistic regression model. Also, the effects of lighting conditions and intersecting streets on the severity of crashes were found to be insignificant
Sequence dependence of DNA translocation through a nanopore
We investigate the dynamics of DNA translocation through a nanopore using 2D
Langevin dynamics simulations, focusing on the dependence of the translocation
dynamics on the details of DNA sequences. The DNA molecules studied in this
work are built from two types of bases and , which has been shown
previously to have different interactions with the pore. We study DNA with
repeating blocks for various values of , and find that the
translocation time depends strongly on the {\em block length} as well as
on the {\em orientation} of which base entering the pore first. Thus, we
demonstrate that the measurement of translocation dynamics of DNA through
nanopore can yield detailed information about its structure. We have also found
that the periodicity of the block sequences are contained in the periodicity of
the residence time of the individual nucleotides inside the pore.Comment: 4 pages, 4 figures, minor change
Investigation of the transient fuel preburner manifold and combustor
A computational fluid dynamics (CFD) model with finite rate reactions, FDNS, was developed to study the start transient of the Space Shuttle Main Engine (SSME) fuel preburner (FPB). FDNS is a time accurate, pressure based CFD code. An upwind scheme was employed for spatial discretization. The upwind scheme was based on second and fourth order central differencing with adaptive artificial dissipation. A state of the art two-equation k-epsilon (T) turbulence model was employed for the turbulence calculation. A Pade' Rational Solution (PARASOL) chemistry algorithm was coupled with the point implicit procedure. FDNS was benchmarked with three well documented experiments: a confined swirling coaxial jet, a non-reactive ramjet dump combustor, and a reactive ramjet dump combustor. Excellent comparisons were obtained for the benchmark cases. The code was then used to study the start transient of an axisymmetric SSME fuel preburner. Predicted transient operation of the preburner agrees well with experiment. Furthermore, it was also found that an appreciable amount of unburned oxygen entered the turbine stages
Optimal Power Allocation for Two-Way Decode-and-Forward OFDM Relay Networks
This paper presents a novel two-way decode-and-forward (DF) relay strategy
for Orthogonal Frequency Division Multiplexing (OFDM) relay networks. This DF
relay strategy employs multi-subcarrier joint channel coding to leverage
frequency selective fading, and thus can achieve a higher data rate than the
conventional per-subcarrier DF relay strategies. We further propose a
low-complexity, optimal power allocation strategy to maximize the data rate of
the proposed relay strategy. Simulation results suggest that our strategy
obtains a substantial gain over the per-subcarrier DF relay strategies, and
also outperforms the amplify-and-forward (AF) relay strategy in a wide
signal-to-noise-ratio (SNR) region.Comment: 5 pages, 2 figures, accepted by IEEE ICC 201
Nuclear wastewater decontamination by 3D-Printed hierarchical zeolite monoliths
3D-printed monoliths of zeolites chabazite and 4A were made, characterized, and shown effective for removing strontium and caesium from water
Towards Accurate One-Stage Object Detection with AP-Loss
One-stage object detectors are trained by optimizing classification-loss and
localization-loss simultaneously, with the former suffering much from extreme
foreground-background class imbalance issue due to the large number of anchors.
This paper alleviates this issue by proposing a novel framework to replace the
classification task in one-stage detectors with a ranking task, and adopting
the Average-Precision loss (AP-loss) for the ranking problem. Due to its
non-differentiability and non-convexity, the AP-loss cannot be optimized
directly. For this purpose, we develop a novel optimization algorithm, which
seamlessly combines the error-driven update scheme in perceptron learning and
backpropagation algorithm in deep networks. We verify good convergence property
of the proposed algorithm theoretically and empirically. Experimental results
demonstrate notable performance improvement in state-of-the-art one-stage
detectors based on AP-loss over different kinds of classification-losses on
various benchmarks, without changing the network architectures. Code is
available at https://github.com/cccorn/AP-loss.Comment: 13 pages, 7 figures, 4 tables, main paper + supplementary material,
accepted to CVPR 201
Minimum energy path for the nucleation of misfit dislocations in Ge/Si(001) heteroepitaxy
A possible mechanism for the formation of a 90{\deg} misfit dislocation at
the Ge/Si(001) interface through homogeneous nucleation is identified from
atomic scale calculations where a minimum energy path connecting the coherent
epitaxial state and a final state with a 90{\deg} misfit dislocation is found
using the nudged elastic band method. The initial path is generated using a
repulsive bias activation procedure in a model system including 75000 atoms.
The energy along the path exhibits two maxima in the energy. The first maximum
occurs as a 60{\deg} dislocation nucleates. The intermediate minimum
corresponds to an extended 60{\deg} dislocation. The subsequent energy maximum
occurs as a second 60{\deg} dislocation nucleates in a complementary, mirror
glide plane, simultaneously starting from the surface and from the first
60{\deg} dislocation. The activation energy of the nucleation of the second
dislocation is 30% lower than that of the first one showing that the formation
of the second 60{\deg} dislocation is aided by the presence of the first one.
The simulations represent a step towards unraveling the formation mechanism of
90{\deg} dislocations, an important issue in the design of growth procedures
for strain released Ge overlayers on Si(100) surfaces, and more generally
illustrate an approach that can be used to gain insight into the mechanism of
complex nucleation paths of extended defects in solids
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