T-shaped Intersection Research Articles

RETRACTED ARTICLE: Numerical simulation on pollutant dispersion from vehicle exhaust in street configurations

The impact of the street configurations on pollutants dispersion from vehicles exhausts within urban canyons was numerically investigated using a computational fluid dynamics (CFD) model. Three-dimensional flow and dispersion of gaseous pollutants were modeled using standard kappa - epsilon turbulence model, which was numerically solved based on Reynolds-averaged Navier-Stokes equations by the commercial CFD code FLUENT. The concentration fields in the urban canyons were examined in three cases of street configurations: (1) a regular-shaped intersection, (2) a T-shaped intersection and (3) a Skew-shaped crossing intersection. Vehicle emissions were simulated as double line sources along the street. The numerical model was validated against wind tunnel results in order to optimize the turbulence model. Numerical predictions agreed reasonably well with wind tunnel results. The results obtained indicate that the mean horizontal velocity was very small in the center near the lower region of street canyon. The lowest turbulent kinetic energy was found at the separation and reattachment points associated with the corner of the down part of the upwind and downwind buildings in the street canyon. The pollutant concentration at the upwind side in the regular-shaped street intersection was higher than that in the T-shaped and Skew-shaped street intersections. Moreover, the results reveal that the street intersections are important factors to predict the flow patterns and pollutant dispersion in street canyon.

Impact of street intersections on air quality in an urban environment

The impact of the street intersections on flow and gaseous pollutants from vehicles exhausts within urban canyons was numerically investigated using a computational fluid dynamics (CFD) model. Three-dimensional flow and dispersion of gaseous pollutants were modeled using standard κ− ε turbulence model, which was numerically solved based on Reynolds-averaged Navier–Stokes equations by the commercial CFD code FLUENT. The concentration fields in the urban canyons were examined in three street configurations cases: (i) a regular-shaped intersection, (ii) T-shaped intersection and (iii) skew-shaped crossing intersection. Vehicle emissions were simulated as double line sources along the street. The numerical model was validated against wind tunnel results in order to optimize the turbulence model. Numerical predictions agreed reasonably with wind tunnel results. The results obtained indicate that the mean horizontal velocity was observed very small in the center near the lower region of street canyon. The lowest turbulent kinetic energy was found at the separation and reattachment points associated with the corner of the down part of the upwind and downwind buildings in the street canyon. The pollutant concentration at the upwind side in the regular-shaped street intersection was higher than that in the T-shaped and skew-shaped street intersections. Moreover, the results approve that the street intersections are important factor to predict the flow patterns and pollutant dispersion in street canyon.

Study of traffic flow at an unsignalized T-shaped intersection by cellular automata model

In this paper, the traffic flow at an unsignalized T-shaped intersection in which there are three input directions of vehicles and two right-turnings and one left-turning has been investigated by using the cellular automata traffic model. The interactions between vehicles on different lanes and effects of traffic flow states of different roads on capacity of T-shaped intersection system are analyzed. The phase transition characteristics of traffic states on different lanes are studied. The research indicates that the model can be applied to the real traffic analysis and traffic forecast.

CELLULAR AUTOMATON MODEL SIMULATING TRAFFIC FLOW AT AN UNCONTROLLED T-SHAPED INTERSECTION

Traffic flow at an uncontrolled T-shaped intersection is modelled by a cellular automaton model. A priority probability of the through car is introduced. The phase diagram of the system and the effect of the turning car on the whole traffic situation are investigated. Our simulation results suggest that priority should be given to either through cars or to turning cars according to the ratio of the turning cars in order to obtain the optimization of the system.

Breaking Up Isn’t Hard To Do

Forcing water drops through a T-shaped intersection of tubes breaks them into droplets of reproducible size.

Lasing from a single-quantum wire

A laser with an active volume consisting of only a single-quantum wire in the one-dimensional (1D) ground state is demonstrated. The single wire is formed quantum mechanically at the T-shaped intersection of a 14 nm Al0.07Ga0.93As quantum well and a 6 nm GaAs quantum well, and is embedded in a 1D single-mode optical waveguide. We observe single-mode lasing from the quantum-wire ground state by optical pumping. The laser operates from 5 to 60 K, and has a low threshold pumping power of 5 mW at 5 K.

Enhanced confinement energy in strained asymmetric T-shaped quantum wires

A new type of T-shaped quantum wire, based on a strained asymmetric structure, has been grown and characterised. A narrow GaAs well is overgrown on an multi quantum well structure consisting of wide InAlGaAs wells with Al 0.3Ga 0.7As barriers. Since the lattice constants of the InAlGaAs wells and bulk GaAs are different, the overgrown well is strained at the T-shaped intersection. The influence of the strain on the confinement energy is investigated by comparison with similar unstrained asymmetric structures and calculated values. A strain-induced enhancement of the confinement energy of 5–10 meV is found for In molefractions of 10% and 15% in the multi quantum wells. For an In mole fraction of 20% no quantum wire states are observed, probably due to dislocation formation in the overgrown layers.

Meshless analysis of steady-state electro-osmotic transport

An emerging technology in the area of microsystems is micro-total analysis systems (/spl mu/TAS) for biological sample analysis. We have simulated electro-osmosis-a common transport mechanism within these devices-by developing meshless techniques. Numerical simulation of electro-osmotic transport requires the solution of the Laplace equation, the Poisson-Boltzmann equation and the incompressible Stokes or Navier-Stokes equations. We describe the development and implementation of meshless techniques for all the governing equations. In particular we introduce a stabilized Stokes solver for very-low Reynolds number flows and a multistep Navier-Stokes solver for a wide range of Reynolds number flows. We have analyzed electro-osmotic transport in three geometries typically encountered in biological devices: a straight channel, a cross-shaped intersection, and a T-shaped intersection.

Optimization of the confinement energy of quantum-wire states in T-shaped GaAs/AlxGa1-xAs structures.

We report on an optimization of the wire confinement energies of the confined electronic states at the T-shaped intersection of GaAs and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wells. These structures can be produced by the cleaved edge overgrowth technique. We present an analytical model for the confinement to give insight into the basic mechanism. The optimization of the confinement energy is done by calculations in a six-band k\ensuremath{\cdot}p approximation for the valence band and in an isotropic effective-mass approximation for the conduction band. The confined valence-band states are only weakly bound at the T-shaped intersection due to the large and anisotropic hole effective masses. Employing optimized sample parameters, confinement energies for the free-electron-hole pairs are nearly doubled compared to symmetric structures, and 34 meV are predicted for a 3-nm overgrown GaAs well. This is expected to be further enhanced by the Coulomb interaction, that is neglected in the numerical model. The experimental structures grown using the optimized geometry show wire confinement energies of up to 54 meV, which is significantly larger than KT at room temperature and larger than previously reported. \textcopyright{} 1996 The American Physical Society.

Danger estimation of the Robotic Travel Aid (RoTA) at intersection

We have been developing Robotic Travel Aid (RoTA) system since 1991 which guides the blind on a road or a sidewalk. One of the most difficult problems for RoTA is how to cross the intersection without a traffic accident. So, danger estimation for vehicles at the intersection is proposed in this paper. This method is implemented on an image processing system. The location, velocity, and the moving direction of a vehicle are measured by computer vision and its danger coefficient is evaluated. About 90% of vehicles in a T-shaped intersection have been correctly interpreted in danger judgments in real world scenes.

Towards optimization of T-shaped quantum structures

An accurate analysis of the wire-like states at the T-shaped intersections of cleaved-edge overgrown (CEO) semiconductor quantum structures is presented with the accent on their optimization for high-temperature laser device applications. This is done by making the proper choice of the structure geometry, which gives the largest energy separation between quasi-2D and quasi-1D exciton states. As a possible modification of the simple T-shaped structure, consistent with the CEO technique, we propose a double T-shaped intersection, with an even stronger binding of the quasi-1D state.

Stimulated Emission from Excitons in a Quantum Wire Laser Fabricated by Cleaved Edge Overgrowth

Quantum wires which form at the T-shaped intersection of two 7 nm wide quantum wells have been embedded in the active region of AlGaAs/GaAs lasers. The quantum wires whose dimensions can be precisely controlled on a monolayer length scale have been prepared by cleaved edge overgrowth, a molecular beam growth technique which involves regrowth on the cleavage plane of a previously grown multilayer structure. The quantum wire emission wavelength is found to be nearly independent of the optical excitation level. This absence of band-gap renormalization effects at all pump intensities implies that the gain mechanism in our laser is excitonic, and further indicates a marked increase in the stability of the excitonic gas phase in one dimension. This is consistent with the observed increase in the exciton binding energy by more than 50% compared to the two–dimensional case.

Correspondence

Correspondence To the Editor: When I was In Prof. Lewis Simpson's NEH Seminar last summer, I told some of your colleagues about the following experience. Before visiting Newport, R. I., I asked my son who lives there to find out exactly where Henry James's house was. He asked the tour guides, the newspaper, and several longtime residents, but no one knew. When I arrived I went to the library, where I found that several librarians did not know that Will and Henry were related. We spent some time in the Newport Room and there found a mention of onetime resident Will James. I left my telephone number, and that afternoon a research librarian called me to say that the family had lived at the corner of Spring and Lee Streets. We drove to that corner, a T-shaped Intersection, where we found a parking lot on one corner, a funeral home on the other, and one of the large typical Newport mansions and grounds facing them. We decided that the parking lot must have been the site of the James house and went home. Later I decided to make one more try. I called the funeral home, and a man named O'Neill was pleased to tell me that the building had been owned and inhabited by the James family. He was quite excited to receive my query and invited me to come over for a tour. By that time I was ready to fly back to Alabama, but I promised to visit him on my next trip to Rhode Island. I asked him why he did not place a small plaque somewhere to help curiosity seekers like myself, and he replied that he had thought It would not be In good taste. The aftermath of the story Is that his son and mine have become golfing friends. I enclose a picture because I thought you might like to see how the home now looks. Sincerely yours, Dr. Sue L. Klmbal I 274 House in Newport occupied by James family. Photo by Nancy Lemme. 275 ...