Transportation - The inaccuracy of traffic forecasts has long stood as a central research theme in the field of infrastructure and transportation studies. The literature presents several motives... 相似文献
Many studies have investigated the effects of transit-oriented development (TOD) on travel behavior, especially on transit ridership. However, most studies do not explicitly and effectively address the issue of residential self-selection in their analyses. The aim of this paper is to use cross-sectional data and propensity score matching (PSM) technique to quantify the contribution of residential self-selection to the analysis of mode choice in TOD areas across the metropolitan areas of Washington, D.C. and Baltimore, MD. The authors use PSM because it does not make substantive assumptions to the structure of the self-selection problem (e.g., explicit modeling of outcome and treatment). The results of PSM indicate that, even though the self-selection effect is considerable in the analysis of mode choice in TOD areas (about 7.65% in Washington, D.C. and 5.05% in Baltimore), living in TOD still has a significant impact on encouraging transit and other active modes of transportation.
Transportation - Autonomous vehicle (AV) technologies are under constant improvement with pilot programs now underway in several urban areas worldwide. Modeling and field-testing efforts are... 相似文献
Most efficient indeces and query techniques over XML (extensible markup language) data are based on a certain labeling scheme, which can quickly determine ancestor-descendant and parent-child relationship between two nodes. The current basic labeling schemes such as containment scheme and prefix scheme cannot avoid relabeling when XML documents are updated. After analyzing the essence of existing dynamic XML labels such as compact dynamic binary string (CDBS) and vector encoding, this paper gives a common unifying framework for the numeric-based generalized dynamic label, which can be implemented into a variety of dynamic labels according to the different user-defined value comparison methods. This paper also proposes a novel dynamic labeling scheme called radical sign label. Extensive experiments show that the radical sign label performs well for the initialization, insertion and query operations, and especially for skewed insertion where the storage cost of the radical sign label is better than that of former methods. 相似文献
Skin detection has been considered as the principal step in many machine vision systems, such as face detection and adult
image filtering. Among all these techniques, skin color is the most welcome cue because of its robustness. However, traditional
color-based approaches poorly perform on the classification of skin-like pixels. In this paper, we propose a new skin detection
method based on the cascaded adaptive boosting (AdaBoost) classifier, which consists of minimum-risk based Bayesian classifier
and models in different color spaces such as HSV (hue-saturation-value), YCgCb (brightness-green-blue) and YCgCr (brightness-green-red).
In addition, we have constructed our own database that is larger and more suitable for training and testing on filtering adult
images than the Compaq data set. Experimental results show that our method behaves better than the state-of-the-art pixel-based
skin detection techniques on processing images with skin-like background. 相似文献
Indoor air pollutants impact human health, comfort and productivity. The method of photocatalysis has been applied mainly
in flow reactors and little information is available on indoor air pollutant removal in airtight reactors. In the paper, experiments
were carried out to remove formaldehyde (HCHO), ammonia (NH3) and volatile organic compounds (VOCs) in the airtight and ventilated chambers. Results demonstrated that 90.4% of HCHO,
92.3% of NH3 and 57.9% of VOCs were removed in the amine adsorption process, while 67.5% (hereinbefore, these are the mass fraction) of
HCHO, 60.0% of NH3, and 61.2% of VOCs were removed in the photocatalytic process. However, ozone-assisted photocatalytic process showed great
potential to degrade indoor air pollutants in the ventilated chamber. Factors and mechanisms of the photocatalytic degradation
of HCHO, NH3 and VOCs were also discussed. 相似文献
A method of underwater simultaneous localization and mapping (SLAM) based on on-board looking forward sonar is proposed. The
real-time data flow is obtained to form the underwater acoustic images and these images are pre-processed and positions of
objects are extracted for SLAM. Extended Kalman filter (EKF) is selected as the kernel approach to enable the underwater vehicle
to construct a feature map, and the EKF can locate the underwater vehicle through the map. In order to improve the association
efficiency, a novel association method based on ant colony algorithm is introduced. Results obtained on simulation data and
real acoustic vision data in tank are displayed and discussed. The proposed method maintains better association efficiency
and reduces navigation error, and is effective and feasible. 相似文献
The asymmetric deformation and eccentricity problems of near hemispherical diaphragm under the uniform surface load are quantitatively
characterized in the paper. The analysis is based on a 3D finite element analysis (FEA) model established according to elastic-plasticity
and large displacement nonlinear finite element method. Besides, the deformation experiments are taken to validate the reliability
of FEA model which shows that the simulation results are in good agreement with the experimental results. Then, three angle
parameters, deflection angle β, circumvolving angle θ and distributing angle γ, are introduced and expressed to characterize the asymmetric deformation and eccentricity quantitatively. According to the
angle parameters, the inversion processes of uniform thickness diaphragm and varying thickness diaphragm are calculated respectively.
The inversion process of varying thickness diaphragm is much steadier than that of uniform thickness diaphragm. The present
results show that the asymmetric deformation process can be characterized by curve of three angle parameters (β, θ, γ) exactly, the degrees of eccentricity can be indicated by the final value of deflection angle and the eccentricity position
can be characterized by the final values of the three angle parameters. 相似文献
Underwater gliders are highly efficient, buoyancy-driven, and winged autonomous underwater vehicles. Their dynamics are multivariable
nonlinear systems with unstable internal dynamics and thus their motion control is a significant challenge. To improve the
inherent efficiency and enhance the behavior of the underwater glider over a wide operating regime, a nonlinear feedforward
and feedback controller was developed. The nonlinear feedforward control design is based on a new stable inversion technique
which determines a causal and bounded solution for the unstable internal dynamics. The feedback control law was designed by
a quadratic optimal control method. Simulation results show that the derived control system is able to deal with nonminimum
phase system and successfully achieves the tracking of planned output trajectories from initial to final conditions. Furthermore,
the control effort is very low, which means the glider with limited power storage has longer range and higher endurance. 相似文献
This paper presents experimental results of the post-fire behavior of tubular T-joints. The research aims at the failure modes
and the residual strengths of the T-joints after fire. Three tests of full-scale tubular T-joints are conducted. The first
one is carried out to study the mechanical behavior of T-joints under ambient temperature. The other two tests are performed
to study the influence of pre-load, heating and cooling phase on residual load-bearing capacity of the tubular T-joints. The
test results show that the sustained axial load on the brace has remarkable influence on the residual deflection of the T-joints
which is cooled down to room temperature. The results of the experiments also indicate that the axial load level and heating
and cooling history have more significant effects on the compressive stiffness of the T-joints than the residual strength.
In the numerical study, the result of finite element model agrees well with the test result. The work in this paper provides
a basis for further parametric analysis and theoretical study on the structural evaluation after fire. 相似文献