5,940 research outputs found
Analysis of a diffusive effective mass model for nanowires
We propose in this paper to derive and analyze a self-consistent model
describing the diffusive transport in a nanowire. From a physical point of
view, it describes the electron transport in an ultra-scaled confined
structure, taking in account the interactions of charged particles with
phonons. The transport direction is assumed to be large compared to the wire
section and is described by a drift-diffusion equation including effective
quantities computed from a Bloch problem in the crystal lattice. The
electrostatic potential solves a Poisson equation where the particle density
couples on each energy band a two dimensional confinement density with the
monodimensional transport density given by the Boltzmann statistics. On the one
hand, we study the derivation of this Nanowire Drift-Diffusion Poisson model
from a kinetic level description. On the other hand, we present an existence
result for this model in a bounded domain
Widely Linear vs. Conventional Subspace-Based Estimation of SIMO Flat-Fading Channels: Mean-Squared Error Analysis
We analyze the mean-squared error (MSE) performance of widely linear (WL) and
conventional subspace-based channel estimation for single-input multiple-output
(SIMO) flat-fading channels employing binary phase-shift-keying (BPSK)
modulation when the covariance matrix is estimated using a finite number of
samples. The conventional estimator suffers from a phase ambiguity that reduces
to a sign ambiguity for the WL estimator. We derive closed-form expressions for
the MSE of the two estimators under four different ambiguity resolution
scenarios. The first scenario is optimal resolution, which minimizes the
Euclidean distance between the channel estimate and the actual channel. The
second scenario assumes that a randomly chosen coefficient of the actual
channel is known and the third assumes that the one with the largest magnitude
is known. The fourth scenario is the more realistic case where pilot symbols
are used to resolve the ambiguities. Our work demonstrates that there is a
strong relationship between the accuracy of ambiguity resolution and the
relative performance of WL and conventional subspace-based estimators, and
shows that the less information available about the actual channel for
ambiguity resolution, or the lower the accuracy of this information, the higher
the performance gap in favor of the WL estimator.Comment: 20 pages, 7 figure
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Measuring regional progress: regional index of sustainable economic well-being (R-ISEW) for all the English regions
This report describes the development and application of a Regional Index of Sustainable Economic Well-Being (R-ISEW), and calculates it for all English regions
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The 2008 R-ISEW (regional index of sustainable economic well-being) for all the English regions
This report presents new data calculated in 2008 for the years 1994–2006. The latest data, which also includes the updating of several sets of figures which previously had to be estimated for 2005, show that a 10-year increase in R-ISEW since 1994 has come to a halt, and that R-ISEW per capita actually began declining between 2004 and 2006 despite increasing GVA
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The 2009 R-ISEW (regional index of sustainable economic well-being) for all the English regions
This latest report presents new data calculated in 2009 for the years 1994–2007. The data, which also includes the updating of several sets of figures that previously had to be estimated for 2006, show that a nine-year increase in the English R-ISEW since 1994, began to peter out in 2003, such that total per capita growth between 2003 and 2007 was only 2.4%. Indeed, between 2005 and 2006, per capita R-ISEW fell slightly
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The 2010 R-ISEW (regional index of sustainable economic well-being) for all the English regions
This is the fourth consecutive report presenting R-ISEW (regional index of sustainable economic well-being) calculations for the nine Government Office Regions (GORs) of England.1 New data available in the summer of 2010 allows a continuous time series from 1994 to 2008 – 15 years. Because of the nature of the data required for the R-ISEW, there is always a two-year lag before results for any given year can be completed
Exploring the Use of Drones for Conducting Traffic Mobility and Safety Studies
ABSTRACT
Advanced traffic data collection methods, including the application of aerial sensors (drones) as traffic data collectors, can provide real-time traffic information more efficiently, effectively, and safely than traditional methods. Traffic trajectory data like vehicles’ coordinates and point timestamps are challenging to obtain at intersections using traditional field survey methods. The coordinates and timestamps crucial in calculating trajectories can be obtained using drones and their particular integrated software. Thus, this study explores the use of unmanned aerial systems (UAS), particularly tethered drones, to obtain traffic parameters for traffic mobility and safety studies at an unsignalized intersection in Tallahassee, Florida. Tethered drones provided more flexibility in heights and angles and collected data over a relatively larger space needed for the proposed approach.
Turning movement counts, gap study, speed study, and Level of Service (LOS) analysis for the stated intersection were the traffic studies conducted in this research. The turning movements were counted through ArcGIS Pro. From the drone footages, the gap study followed by the LOS analysis was carried out. A speed algorithm was developed to calculate speed during a speed study. Based on the results, the intersection operates under capacity with LOS B during the time. Also, the results indicated that the through movement traffic tends to slow down as they approach the intersection while south-bound right and east-bound left-turning traffic increase their speeds as they make a turn. Accuracy assessment was done by comparing the drone footages with the results displayed in ArcGIS software. The drone’s data collection was 100% accurate in traffic movement counting and 96% accurate in traffic movement classification. The level of accuracy is sufficient compared to other advanced traffic data collection methods.
In this study, safety was assessed by the surrogate safety measures (SSMs). SSMs can be the viable alternatives for locations with insufficient historical data and indicate potential future conflicts between roadway users. The surrogate measures used in this study include the Time to Collision (TTC), Deceleration-based Surrogate Safety Measure (DSSM), and Post-encroachment Time (PET). TTC and DSSM were used for rear-end conflicts, while PET was used to evaluate cross conflicts and other conflicts such as sideswipes.
The number of potential conflicts obtained in a one-hour study period was around 20 per 1000 vehicles traversing the intersection. The number of potential conflicts in one non-peak hour may indicate a safety problem associated with the intersection. This study’s findings can help develop appropriate guidelines and recommendations to transportation agencies in evaluating and justifying the feasibility of using tethered drones as safer and cheaper data collection alternatives while significantly improving intersection safety and operations
An effective mass theorem for the bidimensional electron gas in a strong magnetic field
We study the limiting behavior of a singularly perturbed
Schr\"odinger-Poisson system describing a 3-dimensional electron gas strongly
confined in the vicinity of a plane and subject to a strong uniform
magnetic field in the plane of the gas. The coupled effects of the confinement
and of the magnetic field induce fast oscillations in time that need to be
averaged out. We obtain at the limit a system of 2-dimensional Schr\"odinger
equations in the plane , coupled through an effective selfconsistent
electrical potential. In the direction perpendicular to the magnetic field, the
electron mass is modified by the field, as the result of an averaging of the
cyclotron motion. The main tools of the analysis are the adaptation of the
second order long-time averaging theory of ODEs to our PDEs context, and the
use of a Sobolev scale adapted to the confinement operator
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