High Velocity Coefficient Research Articles

Indium-Doped SnO2 Based Surface Acoustic Wave Gas Sensor with Ba0.6Sr0.4TiO3 Film

SnO2-based gas sensors have been widely synthesized and used for the detection of various hazardous gases. However, the use of doped SnO2 in sensing applications has recently attracted increased interest due to the formation of a synergistic effect between the dopant and the host. Moreover, in the case of a surface acoustic wave (SAW) sensor, the piezoelectric material used in the fabrication of the sensor plays a crucial role in defining the response of the SAW sensor. As a ferroelectric material, barium strontium titanate (Ba0.6Sr0.4TiO3) has recently been studied due to its intriguing dielectric and electromechanical properties. Its high acoustic velocity and coupling coefficient make it a promising candidate for the development of acoustic devices; however, its use as a piezoelectric material in SAW sensors is still in its infancy. In this paper, we present the design, fabrication and validation of an indium doped SnO2-based SAW gas sensor on Ba0.6Sr0.4TiO3 thin film for room temperature (RT) applications. Pulsed laser deposition was used to deposit thin films of Ba0.6Sr0.4TiO3 and indium-doped SnO2. Different characterization techniques were employed to analyze the morphology and crystallization of the films. The performance of the fabricated sensor was validated by exposing it to different concentrations of ethanol and then analyzing the recorded frequency shift. The sensor exhibited fast response (39 s) and recovery (50 s) times with a sensitivity of 9.9 MHz/Δ. Moreover, the sensor had good linear response and reproducibility. The fabricated indium-doped SnO2-based SAW gas sensor could be suitable for practical room temperature applications.

Investigations of Coal-Rock Parting-Coal Structure (CRCS) Slip and Instability by Excavation

Slip and instability of coal-rock parting-coal structure (CRCS) subjected to excavation disturbance can easily induce coal-rock dynamic phenomena in deep coal mines. In this paper, the failure characteristics and influencing factors of CRCS slip and instability were investigated by theoretical analysis, numerical simulations, and field observations. The following main results are addressed: (1) the slip and instability of CRCS induced by excavation are due to stress release, and the damage of the rock parting is partitioned into three parts: shear failure zone, slipping zone, and splitting failure zone from inside to outside with slip; (2) the slip and instability process of CRCS is accompanied by initiation, expansion, and intersection of shear and tensile cracks. The development of the cracks is dominated by shear behaviour, while the tensile crack is the main factor affecting fracture and instability of CRCS; and (3) slip and instability of CRCS are characterized by stick-slip first and then stable slip, accompanied with high P-wave velocity and rockburst danger coefficient based on microseismic tomography.

Analysis of the Effect of Sio2 Film on the Characteristics of Rayleigh Wave in Zno/Sic Structure

The influence of SiO2 film on the phase velocity and the electromechanical coupling coefficient of ZnO/SiC structure was analyzed by finite element method. The results show that the middle SiO2 film layer reduces the phase velocity of Rayleigh wave and significantly increases the electromechanical coupling coefficient. When the top SiO2 film layer thickness is larger than the ZnO film thickness, the Rayleigh wave phase velocity increases. Otherwise, the Rayleigh wave phase velocity decreases. The electromechanical coupling coefficient increases first and then decreases. These conclusions can guide the development of surface acoustic wave devices with high phase velocity and high electromechanical coupling coefficient.

Stability control of in-wheel motor electric vehicles under extreme conditions

To investigate the stability of in-wheel motor electric vehicles (IWMEVs) under extreme conditions, a novel control strategy including active rear steering (ARS) mode and direct yaw moment control (DYC) mode is proposed in this paper, utilizing the adaptive dynamic neural network (ADNN) algorithm to make the most of the two control modes. Firstly, a three-degree of freedom nonlinear vehicle model as well as some subsystems is established. Then, a two-layer stability control strategy is put forward, where the upper-layer calculates the desired rear steering angle as well as the differential torque of the rear wheels and the lower-layer executes commands and returns relevant signals. Besides, a stability controller based on ADNN algorithm is designed in the upper-layer so as to take advantage of the two modes under extreme conditions. Next, the impacts of initial values of the connection weights on the ability of ADNN algorithm to train and learn are revealed. Consequently, the optimal initial values can be ascertained before the following simulations. Finally, the closed loop simulations of ARS and DYC are carried out under some extreme conditions such as high velocity and low adhesion coefficient roads, and the results indicate that compared with DYC’s difficulty in playing its role, ARS mode can significantly improve the stability of IWMEVs even under extreme conditions.

Thermal conductance of graphene/hexagonal boron nitride heterostructures

The lattice-based scattering boundary method is applied to compute the phonon mode-resolved transmission coefficients and thermal conductances of in-plane heterostructures built from graphene and hexagonal boron nitride (hBN). The thermal conductance of all structures is dominated by acoustic phonon modes near the Brillouin zone center that have high group velocity, population, and transmission coefficient. Out-of-plane modes make their most significant contributions at low frequencies, whereas in-plane modes contribute across the frequency spectrum. Finite-length superlattice junctions between graphene and hBN leads have a lower thermal conductance than comparable junctions between two graphene leads due to lack of transmission in the hBN phonon bandgap. The thermal conductances of bilayer systems differ by less than 10% from their single-layer counterparts on a per area basis, in contrast to the strong thermal conductivity reduction when moving from single- to multi-layer graphene.

On numerical modeling of the contaminant transport equations of the wetland hydrology and water quality model WETSAND

The reliability of the MacCormack finite difference method for solving the contaminant transport equations of wetland model WETSAND is investigated. WETSAND solves the coupled advection-dispersion-reaction equations for the nitrogen cycle, total nitrogen and total phosphorus concentrations by using the implicit finite difference method. In addition to the implicit scheme, the MacCormack algorithm is implemented within WETSAND. Then, the results obtained by using the MacCormack algorithm are compared with the results obtained by using the implicit finite difference method for both synthetic examples and real data which is collected at the restored wetland site of Duke University at Sandy Creek watershed. Results show that the numerical methods are in good agreement. While the MacCormack scheme may be computationally more efficient for small velocities and dispersion coefficients (as is commonly the case for wetlands and lakes), much longer computational times are needed for the cases with high velocity and dispersion coefficient values (e.g., streams) since the magnitude of the time step has to be selected according to the CFL stability condition.

MBE growth of entire-indium-composition-tunable In<italic><sub>x</sub></italic>Ga<sub>1-<italic>x</italic></sub>N alloy

As a direct band-gap semiconductor, ternary nitride alloy In x Ga1- x N has a tunable energy band-gap from 3.43 eV (for GaN) to 0.64 eV (for InN) with increasing In content, which covers the spectrum from 0.36 to 1.9 μm. In x Ga1- x N alloy has high electron drift velocity and absorption coefficient, which shows great potential application in devices such as full spectrum solar cells and light-emitting devices. Due to lack of proper substrate, In x Ga1- x N is usually grown on sapphire or GaN template. In this article, we review the growth and properties of InN and InGaN with tuable In composition grown on sapphire substrate and GaN/sapphire template by MBE. A boundary-temperature-controlled method is proposed, which successfully lead to a high-electron-mobility InN layers on sapphire substrate by MBE. The temperature-controlled epitaxy method used to grow In x Ga1- x N layers with tunable In composition on GaN/sapphire template.

Simulation of Characteristics of ZnO/Diamond/Si Surface Acoustic Wave

Based on the recursive stiffness matrix method, the effective surface permittitivity model of multilayered Surface Acoustic Wave structure was established. By this model the phase velocity dispersive of ZnO/Si layered structure was calculated. The calculation results is in agreement with the experimental results ,which verifies effectiveness and accuracy of the model. Furthermore, the model was also carried out for the determination of the phase velocity and electromechanical coupling coefficients of ZnO/Diamond/Si structure. The best combination of high velocity and high coupling coefficient of the structure was obtained, which provided a good reference for the design of the high performance and high capability Surface Acoustic Wave device.

Simulation of characteristics of ZnO/diamond/Si structure surface acoustic wave

Based on the recursive stiffness matrix method, the effective surface permittitivity model of multilayered surface acoustic wave structure is established. By this model, the frequency dispersive characteristic of phase velocity for the ZnO/Si layered structure is calculated. The calculation results are in agreement with the experimental results, which verifies the effectiveness and accuracy of the model. Furthermore, the model is also established for the determination of the phase velocity and electromechanical coupling coefficients of ZnO/Diamond/Si structure. The best combination of high velocity and high coupling coefficient of the structure is obtained, which provides a good reference for the design of a high-performance and high-capability surface acoustic wave device.

Simultaneous Increase in Gas and Liquid Relative Permeabilities and Reduction of High-Velocity Coefficient From Wettability Alteration

Summary The alteration of the wettability from liquid-wetting to intermediate gas-wetting results in improved liquid mobility, which has been demonstrated by a number of authors in recent years. In this work, we show that the gas-phase mobility may either increase or decrease in the state of intermediate gas-wetting. The increase or decrease in the gas-phase mobility is a function of the minimum liquid saturation. We also confirm that, as a result of the wettability alteration, there may be a substantial decrease in the two-phase high-velocity coefficient compared to the unaltered wettability state. The increase in the gas- and liquid-phase relative permeabilities and a decrease in the high-velocity coefficient of the two-phase flow from the wettability alteration contribute to improved gas well productivity.

High Velocity Oblique Impact and Coefficient of Restitution for Head Disk Interface Operational Shock

With the increased use of hard disk drives (HDDs) in mobile and consumer applications combined with the requirement of higher areal density, there is enhanced focus on reducing head disk spacing, and consequently there is higher susceptibility of slider/disk impact damage during HDD operation. To investigate this impact process, a dynamic elastic-plastic finite element model of a sphere (representing a slider corner) obliquely impacting a thin-film disk was created to study the effect of the slider corner radius and the impact velocity on critical contact parameters. To characterize the energy losses due to the operational shock impact damage, the coefficient of restitution for oblique elastic-plastic impact was studied using the finite element model. A modification to an existing physics-based elastic-plastic oblique impact coefficient of restitution model was proposed to accurately predict the energy losses for a rigid sphere impacting a half-space. The analytical model results compared favorably to the finite element results for the range from low impact angles (primarily normal impacts) to high impact angles (primarily tangential impacts).

Effect of Wettability on High-Velocity Coefficient in Two-Phase Gas/Liquid Flow

Summary Gas-well productivity is affected by two distinct mechanisms: liquid blocking and high-velocity flow in two-phase flow. The former has been studied extensively recently, but the understanding of the latter is limited. High-velocity gas flow in single phase has been studied thoroughly by a large number of authors. Despite the fact that high-velocity coefficient in the presence of an immobile and a mobile liquid phase is much higher than that in single phase, only a handful of studies have been made on the subject. In this work, we have measured the high-velocity coefficient, A in steady-state two-phase gas/liquid flow. The results are presented as a function of liquid relative permeability and liquid saturation. In our measurements, the wetting state is varied by the treatment with a fluorochemical compound. Then, the effect of wettability on the high-velocity coefficient in two-phase flow is investigated. Results show that when the liquid is strongly wetting, the high-velocity coefficient increases approximately 270-fold in water/gas two-phase flow. However, our data show a systematic reduction of high-velocity coefficients for the altered wetting state in two-phase flow. We present measurements of the velocity coefficients in single-phase flow and two-phase flow, for both oil/gas and water/gas flow and strong liquid-wetting and altered-wetting states. On the basis of our measurements, we conclude that the treatment of the wellbore region can result in significant improvement in well deliverability from the large reduction of high-velocity coefficients.

Effect of Nozzle Geometry on the Flow Dynamics of Hydroentangling Jet

Hydroentangling technique uses extremely fine nozzles to direct high-energy water jets against a loose fiber web. This study investigates the effect of nozzle geometry on the flow dynamics of hydroentangling jet by simulating water-jet formation from cone-up, streamline, and cone-down geometries. The simulation results reveal that water contacts with the nozzle wall all the way when it goes through the cone-up and streamline nozzles. In contrast, the cone-down geometry can form a constricted water-jet because of a sharp turning angle at the nozzle entrance. Consequently, the cone-down nozzle has higher velocity coefficient and the water-jet discharged from the nozzle has a longer intact length than the two others because of the absence of cavitation and wall friction. Part of the results is in excellent agreement with earlier experimental studies.

Overview: Natural Gas Technology/Monetization (April 2007)

Our industry prides itself on the development of innovative and cost-effective technologies to address the world's ever-growing demand for energy. Technology is being developed and applied at an unprecedented pace to all parts of the natural gas supply chain, from production to distribution, as we continue to develop this resource into a leading global energy supply. Over the past year, industry news has highlighted technology developments in many of the downstream areas, including liquefied natural gas, international gas-pipeline projects, gas-to-wire applications, and clean fuels derived from natural gas. In reviewing papers for this feature, I found that development of upstream technology to address production of the world's gas reserves is moving ahead at a pace that rivals downstream-technology developments. New gas resources are becoming more challenging to develop because of geological and reservoir complexities. Sustaining well productivity continues to challenge our production methods as more reservoirs tap unconventional gas, deep-horizon gas, and condensate reservoirs. The upstream sector is responding with an increased focus in developing new technologies to address these challenges. And it is being done in all sectors of the industry, from the national and major energy companies to service and equipment companies to research institutions. The selected papers highlight just a few of the technologies that are being investigated, are under development, or are being applied to recovery and production issues. The papers describe newly developed methods to monitor and optimize production, address near-wellbore problems through optimization of methods in practice today, and discuss potential future applications in near-wellbore conditioning. Our choice in making natural gas a leading source of energy for the world will be driven by technology and by an industry investing in that technology today and tomorrow. I encourage readers to review the additional-reading list to gain a full appreciation for the wide spectrum of technology development under way throughout the natural gas supply chain. Natural Gas Technology/Monetization additional reading available at the SPE eLibrary: www.spe.org SPE 102100 "Phase Behavior Study of Hydrocarbon/Water/Methanol Mixtures at Reservoir Conditions" by V. Bang, SPE, U. of Texas at Austin, et al. SPE 102773 "Effect of Wettability on High-Velocity Coefficient in Two-Phase Gas/Liquid Flow" by M. Noh, SPE, Reservoir Engineering Research Inst., et al. SPE 102160 "Onshore LNG Production Process Selection" by S. Mokhatab, SPE, U. of Wyoming, et al.

ZnO/AlN/diamond layered structure for SAW devices combining high velocity and high electromechanical coupling coefficient

A new layered structure ZnO/AlN/diamond, is studied for high-frequency and high electromechanical coupling ( K 2) SAW devices. Theoretical study was performed to calculate the phase velocity and K 2 dispersion curves of the Rayleigh mode and its higher modes as well as the leaky waves. Both high values of K 2 (>4%) and acoustic velocities higher than 15 km/s are expected with this new structure according to the theoretical results. To confirm the simulation results, SAW filters were processed on ZnO/AlN/diamond structure. First experimental results are in agreement with the theory and confirm the high potential of this new structure high-performance and high-frequency SAW filters.

Piezoelectric Aluminum Nitride Films Deposited by Triode Sputtering for Surface Acoustic Wave Devices

Aluminum nitride (A1N) thin films have been widely used in various applications due to their excellent properties such as chemical stability, electrical isolation, high acoustic wave velocity and large electromechanical coupling coefficient. For surface acoustic wave(SAW) applications, structures having A1N films on high acoustic velocity substrates such as diamond or sapphire offer much interest in forming high frequency SAW devices with phase velocities greater than 10000m/s. In this study, A1N films have been deposited on (001) sapphire and (100) silicon substrates by triode sputtering at low temperature in argon-nitrogen gas mixture. The crystal orientation, stoechiometry, optical acoustic and electrical properties were investigated. Dense AIN layers with very high electrical resistivity were obtained at high deposition rates. SAW filters were formed by development of interdigital transducers on the A1N/Silicon and A1N/Sapphire structures. The phase velocity was measured by a network analyzer as a function of A1N film thickness and substrate type.