Modeling Impacts of Speed Reduction on Traffic Efficiency on Expressway Uphill Sections

Road geometric design is a key factor impacting driving safety and efficiency. In highway profile design, speed reduction is used to determine critical length of grade. Previous research generally concentrated on the relationship between speed reduction and crash involvement rate to establish the recommended value. Limited research results have been reported at this point concerning speed reduction and traffic efficiency. This study aims to fill the gap by investigating tolerable speed reduction with different vertical slopes considering traffic efficiency. Firstly, appropriate experimental sections were determined after field survey. Traffic data including vehicle count, timely speed, vehicle type, and headway time were then collected on an expressway in Shaanxi Province. The associated traffic efficiency was derived from traffic volume and average speed. After this, the modeling between speed reduction and traffic efficiency was processed with different slopes. The correlation between speed reduction and traffic efficiency was therefore verified. Finally, the prediction model of optimum speed reduction concerning traffic efficiency under different vertical slopes was introduced. It was found that the critical length of grade can be longer with traffic efficiency as the major design control incorporated with slopes of 3–3.5%. The existing regulation in critical length of grade at 3.5–5% can benefit both safety and efficiency. The findings can provide a reference for vertical alignment design, leading to high-efficiency road systems.

Download Full-text

Record High External Quantum Efficiency of 19.2% Achieved in Light-Emitting Diodes of Colloidal Quantum Wells Enabled by Hot-Injection Shell Growth

10.26434/chemrxiv.9777632 ◽

2019 ◽

Author(s):

Baiquan Liu ◽

Yemliha Altintas ◽

Lin Wang ◽

Sushant Shendre ◽

Manoj Sharma ◽

...

Keyword(s):

Quantum Wells ◽

Quantum Efficiency ◽

External Quantum Efficiency ◽

High Performance ◽

High Efficiency ◽

Light Emitting Diodes ◽

Shell Growth ◽

Light Emitting ◽

Hot Injection ◽

Key Factor

Colloidal quantum wells (CQWs) are regarded as a new, highly promising class of optoelectronic materials thanks to their unique excitonic characteristics of high extinction coefficient and ultranarrow emission bandwidth. Although the exploration of CQWs in light-emitting diodes (LEDs) is impressive, the performance of CQW-LEDs lags far behind compared with other types of LEDs (e.g., organic LEDs, colloidal quantum-dot LEDs, and perovskite LEDs). Herein, for the first time, the authors show high-efficiency CQW-LEDs reaching close to the theoretical limit. A key factor for this high performance is the exploitation of hot-injection shell (HIS) growth of CQWs, which enables a near-unity photoluminescence quantum yield (PLQY), reduces nonradiative channels, ensures smooth films and enhances the stability. Remarkably, the PLQY remains 95% in solution and 87% in film despite rigorous cleaning. Through systematically understanding their shape-, composition- and device- engineering, the CQW-LEDs using CdSe/Cd0.25Zn0.75S core/HIS CQWs exhibit a maximum external quantum efficiency of 19.2%. Additionally, a high luminance of 23,490 cd m-2, extremely saturated red color with the Commission Internationale de L’Eclairage coordinates of (0.715, 0.283) and stable emission are obtained. The findings indicate that HIS grown CQWs enable high-performance solution-processed LEDs, which may pave the path for CQW-based display and lighting technologies.

Download Full-text

Determination of Curve Speed Zones for Mountainous Freeways

Mathematical Problems in Engineering ◽

10.1155/2020/8844004 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Yongtao Liu ◽

Jie Qiao ◽

Yanting Hu ◽

Tengyuan Fang ◽

Ting Xu ◽

...

Keyword(s):

Traffic Safety ◽

Warning Signs ◽

Driving Safety ◽

Warning Sign ◽

Speed Limit ◽

Vehicle Speed ◽

Estimation Model ◽

Traffic Efficiency ◽

Safety Warning ◽

The Difference

Different vehicular speed limits may have an impact on the balance between safety and efficiency of travel on mountainous road corners associated with complex road conditions. Placing suitable speed limit warning signs does not merely effectively improve traffic safety but can also improve traffic efficiency. In this study, a global positioning system (GPS) terminal and Metrocount were used to collect vehicle speed data from more than 40 provincial-level curves in 8 provinces over the course of 1 year. Each road data collection time-period lasted approximately 8 hours. A descriptive statistics method was adopted by means of data screening and pretreatment. Additionally, both a velocity difference estimation model was established and a linear model of velocity differential estimation was constructed. Quantitative analysis was carried out on the safe speed, the driver’s expected speed, and the location of the speed limit warning signs. This demonstrated a positive correlation with the initial speed. When the difference in speed was greater than 15 km/h, a safety warning sign was required to limit the design speed to 80 km/h. A safety warning sign was also required when the corner radius was less than 300 m. The location of safety warning signs could be calculated based on the operating speed and taking driving safety and the visual range of drivers into consideration. The results can provide a theoretical reference for setting up appropriate safe speed limiting signs on road corners in mountainous areas.

Download Full-text

Using Heuristic Value Prediction and Dynamic Task Granularity Resizing to Improve Software Speculation

The Scientific World JOURNAL ◽

10.1155/2014/478013 ◽

2014 ◽

Vol 2014 ◽

pp. 1-18

Author(s):

Fan Xu ◽

Li Shen ◽

Zhiying Wang ◽

Bo Su ◽

Hui Guo ◽

...

Keyword(s):

High Efficiency ◽

Low Cost ◽

Parallel Execution ◽

Analytic Model ◽

Parallel Model ◽

Conventional Model ◽

Value Prediction ◽

Dynamic Task ◽

Control Overhead ◽

Key Factor

Exploiting potential thread-level parallelism (TLP) is becoming the key factor to improving performance of programs on multicore or many-core systems. Among various kinds of parallel execution models, the software-based speculative parallel model has become a research focus due to its low cost, high efficiency, flexibility, and scalability. The performance of the guest program under the software-based speculative parallel execution model is closely related to the speculation accuracy, the control overhead, and the rollback overhead of the model. In this paper, we first analyzed the conventional speculative parallel model and presented an analytic model of its expectation of the overall overhead, then optimized the conventional model based on the analytic model, and finally proposed a novel speculative parallel model named HEUSPEC. The HEUSPEC model includes three key techniques, namely, the heuristic value prediction, the value based correctness checking, and the dynamic task granularity resizing. We have implemented the runtime system of the model in ANSI C language. The experiment results show that when the speedup of the HEUSPEC model can reach 2.20 on the average (15% higher than conventional model) when depth is equal to 3 and 4.51 on the average (12% higher than conventional model) when speculative depth is equal to 7. Besides, it shows good scalability and lower memory cost.

Download Full-text

Stern Flap–Waterjet–Hull Interactions and Mechanism: A Case of Waterjet-Propelled Trimaran With Stern Flap

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4045498 ◽

2020 ◽

Vol 142 (2) ◽

Author(s):

Lei Zhang ◽

Jianing Zhang ◽

Yuchen Shang

Keyword(s):

High Efficiency ◽

Navier Stokes ◽

Local Effects ◽

Resistance Components ◽

Leading Role ◽

Resistance Reduction ◽

Sinkage And Trim ◽

Improved Performance ◽

Design Speed ◽

Pressure Resistance

Abstract To research the stern flap (SF) and waterjet–hull interaction, unsteady Reynolds-averaged Navier–Stokes (URANS) simulations for a waterjet-propelled trimaran considering sinkage and trim are performed. Uncertainty analysis of the numerical results for the bare hull (BH) model is presented. At the design speed Froude number (Fr) of 0.6 and under displacement state, the model-scaled trimaran, installed with stern flaps of varied angle and length, tests the BH and self-propulsion (SP) performance based on URANS simulations. For the resistance, the global effects due to motions and the local effects of SF, waterjets (WJ), and the coupled term between SF and WJ on the hull are separately analyzed. Taking the waterjet propulsion system into account, an SP model with reasonable stern flap effectively reduces the trim, the resistance acting on the hull and the waterjet thrust deduction which contributes to energy-saving and high-efficiency propulsion. The mechanism of the improved performance of the waterjet-propelled trimaran with stern flaps is discussed. For the resistance increment, the global effects, the local effects of SF and WJ are the major reason for resistance increase, and the nonlinear coupled term of local effects contributes to the resistance reduction most. In addition, the different resistance components of frictional, hydrostatic, and hydrodynamic are separately researched, which shows that the pressure resistance components plays a leading role in the total resistance reduction in the SP model with the suitable SF.

Download Full-text

Highly selective self-condensation of cyclohexanone: the distinct catalytic behaviour of HRF5015

Royal Society Open Science ◽

10.1098/rsos.200123 ◽

2020 ◽

Vol 7 (10) ◽

pp. 200123

Author(s):

Xiujing Peng ◽

Shah Zeb ◽

Jianguo Zhao ◽

Miaomiao Zhang ◽

Yu Cui ◽

...

Keyword(s):

High Efficiency ◽

Cluster Structure ◽

Nitrogen Atmosphere ◽

Future Application ◽

Resin Catalyst ◽

Transmission Electron ◽

Key Factor ◽

Good Potential ◽

Diffuse Reflectance Infrared

HRF5015, a perfluorosulfonic acid resin catalyst with unique pore structures, was investigated in the catalytic self-condensation of cyclohexanone under mild conditions. The morphology of HRF5015 was characterized by transmission electron microscopy (TEM) and atomic force microscope (AFM), and the reaction mechanism was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The effects of reaction time and temperature on the yield of dimer were investigated under the nitrogen atmosphere. The results show that the reaction temperature is low, and especially, the selectivity of the dimer is close to 100%. The apparent activation energy for the dimer formation reaction is 54 kJ mol −1 . Synergistic action of cluster structure formed by sulfonic groups and nanopores in HRF5015 may be the key factor of high-efficiency catalytic activity and high selectivity. In situ infrared spectra indicate that the intermediate is stable in the reaction process. HRF5015 is environmentally friendly and re-usable, which shows good potential in a future application.

Download Full-text

A Novel High Efficiency Solution of High Power LED Lighting

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.301-303.121 ◽

2011 ◽

Vol 301-303 ◽

pp. 121-126

Author(s):

Qiang Fan ◽

Xian Song Fu ◽

Yi Li Liu ◽

Ping Juan Niu ◽

Tie Cheng Gao

Keyword(s):

High Power ◽

High Efficiency ◽

Supply Voltage ◽

High Reliability ◽

Current Mode ◽

Constant Current ◽

Output Current ◽

High Power Led ◽

Key Factor ◽

Continuous Current

High power LED is a kind of ideal green lighting source, which owns longer life, higher efficiency and lower electricity power consumption than incandescent lamps and fluorescent bulbs. Constant current driver is the most key factor for high power LED’s premium properties. Based on the specific chip LM3478, a novel Boost DC/DC converting circuit to drive LED was proposed. The whole circuit structure was simple, and owned high reliability with over current protection. The circuit operates continuous current mode (CCM), with normal supply voltage 12V. The constant output current is 700mA, which can drive two-row LED series, 5 LEDs at least each series. The test results show that the electricity efficiency is up to 93.20% and that the output current deviation is 7.71%. The operating temperature range is -40~+125°C.

Download Full-text

A Detailed Study of the Interaction Between Two Rows of Cooling Holes

Journal of Turbomachinery ◽

10.1115/1.4038833 ◽

2018 ◽

Vol 140 (4) ◽

Cited By ~ 2

Author(s):

Y. Jiang ◽

L. Capone ◽

P. Ireland ◽

E. Romero

Keyword(s):

Flat Plate ◽

Film Cooling ◽

High Efficiency ◽

Nonlinear Effects ◽

Suction Side ◽

Complex Problem ◽

Correct Prediction ◽

Blowing Ratio ◽

Key Factor ◽

Plate Geometry

An optimal design of film cooling is a key factor in the effort of producing high-efficiency gas turbine. Understanding of the fluid dynamics interaction between cooling holes can help engineers to improve overall thermal effectiveness. Correct prediction through modeling is a very complex problem since multiple phenomena are involved such as mixing, turbulence, and heat transfer. The present work performs an investigation of different cooling configurations ranging from single hole up to two rows. The main objective is to evaluate the double-rows interaction and the effect on film cooling. Strong nonlinear effects are underlined by different simulations, while varying blowing ratio (BR) and geometrical configuration of cooling holes. Meanwhile an initial analysis is performed using flat plate geometry, verification and validation is then extended to realistic stage of high pressure (HP) turbine. Multiple cooling holes configurations are embedded on the pressure side (PS) and suction side (SS) of the single stage. The main outcome is the verification of the thermal effectiveness improvement obtained by cooling jets interaction of multiple rows design. The effects of curvature surface and frame of reference rotation are also evaluated, underlying the differences with standard flat plate test cases.

Download Full-text

MEMS Based Metal Plated Silicon Package for High Power LED

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.326-328.309 ◽

2006 ◽

Vol 326-328 ◽

pp. 309-312 ◽

Cited By ~ 1

Author(s):

Sung Jun Lee ◽

Ji Hyun Park ◽

Chang Hyun Lim ◽

Won Kyu Jeong ◽

Seog Moon Choi ◽

...

Keyword(s):

Thermal Resistance ◽

High Power ◽

Power Dissipation ◽

Heat Dissipation ◽

High Efficiency ◽

Low Cost ◽

Wafer Level ◽

High Power Led ◽

Key Factor ◽

Mems Technology

By the development of high power LED for solid states lighting, the requirement for driving current has increased critically, thereby increasing power dissipation. Heat flux corresponds to power dissipation is mainly generated in p-n junction of LED, so the effective removal of heat is the key factor for long lifetime of LED chip. In this study, we newly proposed the silicon package for high power LED using MEMS technology and estimated its heat dissipation characteristic. Our silicon package structure is composed of base and reflector cup. The role of base is that settle LED chip at desired position and supply electrical interconnection for LED operation, and finally transfer the heat from junction region to outside. For improved heat transfer, we introduced the heat conductive metal plated trench structure at the opposite side of LED attached side. The depth and the diameter of trench were 150 and 100um, respectively. Copper with high thermal conductivity than silicon was filled in trench by electroplating and the thickness of copper was about 100um. Reflector cup was formed by anisotropic wet etching and then, silicon package platform could be fabricated by eutectic bonding between base and reflector cup. The thermal resistance of silicon package was about 6 to 7K/W from junction to case, and also, thermal resistance reduction of 0.64K/W was done by metal plated trench. This result could be comparable to that of other high power LED package. Our silicon package platform is easy to be expanded into array and wafer level package. So, it is suitable for future high efficiency and low cost package.

Download Full-text

Record High External Quantum Efficiency of 19.2% Achieved in Light-Emitting Diodes of Colloidal Quantum Wells Enabled by Hot-Injection Shell Growth

10.26434/chemrxiv.9777632.v1 ◽

2019 ◽

Cited By ~ 1

Author(s):

Baiquan Liu ◽

Yemliha Altintas ◽

Lin Wang ◽

Sushant Shendre ◽

Manoj Sharma ◽

...

Keyword(s):

Quantum Wells ◽

Quantum Efficiency ◽

External Quantum Efficiency ◽

High Performance ◽

High Efficiency ◽

Light Emitting Diodes ◽

Shell Growth ◽

Light Emitting ◽

Hot Injection ◽

Key Factor

Download Full-text

The Dependence of Airport Profit on Passenger Satisfaction and Operational Efficiency

MAD - Magazine of Aviation Development ◽

10.14311/mad.2017.02.02 ◽

2017 ◽

Vol 5 (2) ◽

pp. 11

Author(s):

Roman Vokáč ◽

Milan Lánský ◽

Stanislav Szabo

Keyword(s):

Cost Reduction ◽

High Efficiency ◽

Arrival Rate ◽

Air Transport ◽

Process Efficiency ◽

Service Rate ◽

Basic Process ◽

Passenger Satisfaction ◽

Key Factor

Since the airports are in fact commercial companies, their main objective is to make profit. Therefore, it is important for the airports to identify the business activities that may increase the income as well as those that may reduce the costs. The terminal process, handling the passengers’ baggage both on their departure and arrival, is a basic process at all airports that are intended for the commercial air transport. The quality of the terminal process provided by the airports has a significant impact on the passengers especially in terms of their satisfaction. In this text, the passenger satisfaction is regarded as a key factor of the terminal process affecting a whole range of other areas. Its high efficiency leads to cost reduction from the perspective of the airport. As it is proposed here, there is a connection between the passenger satisfaction and the process efficiency. For example, the queues that form due to the check-in process may be a result of the imbalance between the passenger arrival rate and the service rate. Therefore, there is a necessity of improving not only the passenger satisfaction but also the process efficiency.

Download Full-text