摘要 :
By mixing iso-octane with octane number 100 and normal heptane with octane number 0, it was possible to obtain a primary reference fuel (PRF) with octane rating between 0 and 100. The influences of PRF fuel's octane number on the ...
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By mixing iso-octane with octane number 100 and normal heptane with octane number 0, it was possible to obtain a primary reference fuel (PRF) with octane rating between 0 and 100. The influences of PRF fuel's octane number on the combustion characteristics, operation range, performance, and emissions characteristics of homogeneous charge compression ignition (HCCI) engine were investigated. The experiments were carried out on a modified single cylinder direct injection diesel engine. The test results show that, with the increase of the octane number, the ignition timing delays, the combustion rate decreases, the combustion duration prolongs, and the cylinder pressure decreases. The HCCI combustion can be controlled, then the HCCI operating range can be extended by burning different octane number fuel at different engine modes, in which engine burns low octane number fuel at small load mode and large octane number fuel at high load mode. There exists an optimum octane number that achieves the highest indicated thermal efficiency at different engine load, With the increase of the PRF fuel octane number, NO_x HC and CO emissions increase, especially for HC emissions.
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In this paper, a new approach to burning methanol in engine is proposed, in which the engine burns dimethyl ether (DME) and methanol dual fuel in homogeneous charge compression ignition (HCCI) mode, and DME is converted from metha...
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In this paper, a new approach to burning methanol in engine is proposed, in which the engine burns dimethyl ether (DME) and methanol dual fuel in homogeneous charge compression ignition (HCCI) mode, and DME is converted from methanol. Combustion, engine performance, and pollutant emissions of the new HCCI combustion system were investigated. The results show that the stable HCCI operation of DME/methanol can be obtained over a quite broad speed and load region. Both DME and methanol affect HCCI combustion strongly, and by regulating DME/methanol proportions the HCCI combustion process could be controlled effectively. NO_x emissions are, very low overall, while HC and CO emissions are much higher than that in conventional compression ignition engines. An appropriate optimal HCCI operation can be obtained by controlling the DME and methanol supply according to operating conditions.
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This paper for the first time systematically analyzed the operation mechanism of SiC NPN transistors. Theoretical device figure-of-merits for switching power devices based on the conduction loss and switching loss were developed. ...
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This paper for the first time systematically analyzed the operation mechanism of SiC NPN transistors. Theoretical device figure-of-merits for switching power devices based on the conduction loss and switching loss were developed. The on-state loss and the switching loss of 4.5-kV SiC switching power devices (MOSFET, NPN transistor and GTO thyristor) were then compared by using theoretical and numerical calculations. Special emphasis is placed on comparing the total power loss of the devices at a given current density. Theoretical analyses and simulation results show that GTO thyristors have a large switching loss due to the long current tail at turn-off hence restricting its maximum operation frequency. High voltage SiC MOSFETs have a large on-state power dissipation at high current levels due to the resistive nature of the drift region. restricting their applications at high current densities. SiC NPN transistors have a comparable switching loss as that of SiC MOSFETs, but at the same time, SiC NPN transistors have the lowest on-state loss. This study indicates that SiC NPN transistor is the most attractive switching power device at 4.5 kV.
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The rapid advance of communication and satellite technology pushes broadband satellite networks to carry on multimedia traffic. However, the function of onboard routing cannot be provided in existing satellite networks with inter-...
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The rapid advance of communication and satellite technology pushes broadband satellite networks to carry on multimedia traffic. However, the function of onboard routing cannot be provided in existing satellite networks with inter-satellite links, and quality of service (QoS) of satellite networks cannot be reliably guaranteed because of great difficulties in processing of long distance-dependent traffic. In this paper, a two-layered low-Earth orbit and medium-Earth orbit satellite network (LMSN) is presented. A novel hierarchical and distributed QoS routing protocol (HDRP) is investigated, and an adaptive bandwidth-constrained minimum-delay path algorithm is developed to calculate routing tables efficiently using the QoS metric information composed of delays and bandwidth. The performance of LMSN and HDRP is also evaluated through simulations and theoretical analysis.
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A comprehensive analytical ON-state drain current model for poly-Si thin film transistors (TFTs) is developed to accurately fit both transfer and output characteristics of either low or high temperature processed poly-Si TFTs in b...
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A comprehensive analytical ON-state drain current model for poly-Si thin film transistors (TFTs) is developed to accurately fit both transfer and output characteristics of either low or high temperature processed poly-Si TFTs in both n- and p-types, with the same unified analytical form. The model is physical explicitly based and mathematically accurate, with no artificial factors introduced. To accomplish this, (1) the most appropriate model precisely describing the gate voltage dependent mobility degradation effect in poly-Si TFTs is determined from three previously employed models; (2) grain boundary barrier controlled carrier conduction model is adequately incorporated; and (3) a mathematically accurate analytical form for drain current is derived based on gradual channel approximation by introducing a new fitting parameter to describe the effective average channel mobility. Channel length modulation effect is introduced in modeling output characteristic. Applicability and accuracy of the model are demonstrated by fitting both n- and p-types poly-Si TFTs fabricated from very different processes.
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A polysulfone microporous membrane module was investigated for control of 1-butanol-contaminated gas streams. A diurnal loading condition, using two different butanol concentrations, was used to simulate startup and stop condition...
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A polysulfone microporous membrane module was investigated for control of 1-butanol-contaminated gas streams. A diurnal loading condition, using two different butanol concentrations, was used to simulate startup and stop conditions associated with shift work. The membrane module was also used to remove 1-butanol from air under continuous loading conditions in a bioreactor. The reactors were seeded with a mixed bacterial consortium capable of butanol biodegradation. Biokinetic parameters for butanol utilization were determined for the culture to be a maximum specific utilization rate (k) equal to 4.3 d~(-1) and a half saturation constant (K_s) equal to 8.9 mg L~(-1). A biofilter running only with diurnal loading conditions giving a "40-hr workweek" had an average 1-butanol removal rate of 29% (111 ppm, 74 gm~(-3) hr~(-1)) from a 350-ppm influent at the end of an 8-hr operational day. End-of-day removal varied between 4 and 67% during the operational period. With continuous steady-state operation followed by placement on a diurnal loading schedule and influent butanol concentrations increased to 700 ppm, butanol removal averaged 38% (269 ppm, 145 gm~(-3) hr~(-1)). Under continuous loading, steady-state conditions, 1-butanol removal from the airstream was greater than 99% (200 ppm, 73 gm~(-3) hr~(-1)). These results suggest that the bioreactor can be operated on a diurnal schedule or 40-hr week operational schedule without any decline in performance.
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The presence of a steel core in the commonly used aluminum conductor, steel reinforced (ACSR) on overhead transmission lines causes an increase in the AC resistance of the conductor, as a result of the magnetic induction in the co...
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The presence of a steel core in the commonly used aluminum conductor, steel reinforced (ACSR) on overhead transmission lines causes an increase in the AC resistance of the conductor, as a result of the magnetic induction in the core. This induction, which is higher with an odd number of aluminum layers, causes hysteresis and eddy current power losses in the steel, and a redistribution of current in the layers of aluminum wires. The effects of the total current in the conductor and the temperature of the steel core on the current distribution, the AC/DC resistance ratio and the power loss are determined for a Grackle conductor with three layers of aluminum wires. It is shown that the resistance ratio and the power loss can be significantly reduced at higher currents by careful design of the lay length (pitch) of each layer of aluminum wires.
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Activation of O—H bonds by inorganic metal-oxo complexes has been documented, but no cognate enzymatic process is known. Our mechanistic analysis of 2-hydroxyethylphosphonate dioxygenase (HEPD), which cleaves the C1—C2 bond of i...
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Activation of O—H bonds by inorganic metal-oxo complexes has been documented, but no cognate enzymatic process is known. Our mechanistic analysis of 2-hydroxyethylphosphonate dioxygenase (HEPD), which cleaves the C1—C2 bond of its substrate to afford hydroxymethyl-phosphonate on the biosynthetic pathway to the commercial herbicide phosphinothricin, uncovered an example of such an O—H-bond-cleavage event Stopped-flow UV—visible absorption and freeze-quench Mössbauer experiments identified a transient iron(IV)-oxo (ferryl) complex. Maximal accumulation of the intermediate required both the presence of deuterium in the substrate and, importantly, the use of ~2H_2O as solvent. The ferryl complex forms and decays rapidly enough to be on the catalytic pathway. To account for these unanticipated results, a new mechanism that involves activation of an O—H bond by the ferryl complex is proposed. This mechanism accommodates all available data on the HEPD reaction.
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A novel analytical model of the vertical breakdown voltage (V_(B, v)) on impurity concentration (N_d) in top silicon layer for silicon on insulator high voltage devices is first presented in this article. Based on an effective ion...
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A novel analytical model of the vertical breakdown voltage (V_(B, v)) on impurity concentration (N_d) in top silicon layer for silicon on insulator high voltage devices is first presented in this article. Based on an effective ionisation rate considering the multiplication of threshold energy ε_T in the electron, a new formula of silicon critical electric field E_(s,c) on N_d is derived by solving a 2D Poisson equation, which increases with the increase in N_d especially at higher impurity concentration, and reaches up to 68.8 V/um with N_d = 1 x 10~(17)cm~(-3) and 157.2V/μ.m with N_d = 1 x 10~(18)cm~(-3) from the conventional about 30V/μm, respectively. A new physical concept of critical energy ε_B is introduced to explain the mechanism of variable high E_(s,c) with heavy impurity concentration. From the E_(s,c), the expression of V_(B,V) is obtained, which is improved with the increasing N_d due to the enhanced E_(s,c)- V_(B,V) with a dielectric buried layer thickness (t_I) of 2 μm increases from 428 V of 1 x 10~(17) cm~(-3) to 951 V of 1 x 10~(18) cm~(-3). The dependence of N_d and top silicon layer thickness (t_S) for an optimised device is discussed. 2D simulations and some experimental results are in good agreement with the analytical results.
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A novel silicon-on-insulator (SOI) high-voltage device structure and its eliminating back-gate bias effects are presented. The structure is characterized by a compound buried layer (CBL) made of two oxide layers and a polysilicon ...
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A novel silicon-on-insulator (SOI) high-voltage device structure and its eliminating back-gate bias effects are presented. The structure is characterized by a compound buried layer (CBL) made of two oxide layers and a polysilicon layer between them. At the high-voltage blocking state, holes collected on the polysilicon bottom interface shield the SOI layer and the upper buried oxide (UBO) layer from the back-gate bias V bg, resulting in a constant breakdown voltage (BV) and the same electric field and potential distributions in the SOI layer, UBO, and polysilicon under different the back-gate biases for a CBL SOI REduced SURface Field (RESURF) Lateral Double-diffused MOS (LDMOS). V bg only impacts the field strength and voltage drop in the lower buried oxide (LBO) layer. Moreover, based on the continuity of electric displacement, the holes enhance the field in the LBO from 80 V/mum of the conventional SOI to 457 V/mum at V bg = 0 V, leading to a high BV. A 747-V CBL SOI LDMOS is fabricated, and its eliminating back-gate bias effect is verified by measurement. In addition, the CBL SOI structure can alleviate the self-heating effects due to a window in the UBO.
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