综采放顶煤工作面回顺延接技术在大隆矿的应用

对铁法煤业集团大隆矿S1703综采放顶煤工作面两次回风顺槽对面延面工艺过程进行了分析与介绍,为不规则厚煤层综采放顶煤工作面的设计与开采总结了经验。

综采工作面旋转开采技术研究

在分析综采工作面旋转开采现状的基础上,对旋转开采技术进行了研究。结合大明煤矿开采实践,分析了综采面旋转开采工艺,解决了旋转开采实践中的关键技术,取得了显著的技术经济效果。

Effect of Ti-Al content on microstructure and mechanical properties of C_f/Al and TiAl joint by laser ignited self-propagating high-temperature synthesis

Cf/Al composites and TiAl alloys were joined by laser ignited self-propagating high-temperature synthesis（SHS） with Ni-Al-Ti interlayer. The effect of Ti-Al content on interfacial microstructure and mechanical properties of the joints was investigated. Localized melt of the substrates occurred in the joints. γ-Ni0.35Al0.30Ti0.35, NiA l3 and Ni2Al3 reaction layers formed adjacent to the substrates. Joint flaws, such as pores and cracks, made the joint density decrease and worked as the fracture source, which led to the sharp decline of joint strength. Additive Ti-Al increased joint density and strengthened the interlayer adhesion to Cf/Al. The joint flaws could be controlled by changing the Ti-Al content. When the Ti-Al content was 0.1, the joint was free of cracks with high density and reached the maximum shear strength of 24.12 MPa.

Spotsize Converter Integrated DFB Laser Diode Using Selective Area Growth of MOCVD

The characteristics of thickness enhancement fact or and bandgap wavelength of selectively grown InGaAsP are investigated.A high thi ckness enhancement factor of 2.9 is obtained.Spotsize converter integrated DFB lasers are fabricated by using the technique of SAG.The threshold current is as low as 10.8mA.The output power is 10mW at 60mA without coating and the SMSR is 35.8dB.The vertical far field angle (FWHM) is decreased from 34° to 9°.The to lerance of 1dBm misalignment is 3.4μm vertically.

Analysis of cumulative handoff delay for graded secondary users in cognitive radio networks

According to the fact that the secondary users＇ delay requirements for data transmission are not unitary in cognitive radio networks, the secondary users are divided into two classes, denoted by SU1 and SU2, respectively. It is assumed that SU1 has a higher priority to occupy the primary users＇ unutilized channels than SU2. A preemptive resume priority M/G/1 queuing network is used to model the multiple spectrum handoffs processing. By using a state transition probability matrix and a cost matrix, the average cumulative delays of SU1 and SU2 are calculated, respectively. Numerical results show that the more the primary user＇s traffic load, the more rapidly the SU2＇s cumulative handoff delay grows. Compared with the networks where secondary users are unitary, the lower the SUI＇s arrival rate, the more obviously both SUI＇s and SU2＇s handoff delays decrease. The admission access regions limited by the maximum tolerable delay can also facilitate the design of admission control rules for graded secondary users.

First-principles and experimental investigations on ductility/brittleness of intermetallic compounds and joint properties in steel/aluminum laser welding

Morphology,distribution,composition,forming ability,structural stability and intrinsic mechanical properties of the intermetallic compounds(IMCs)formed in steel/aluminum laser welding were determined through scanning electron microscope,energy dispersive spectrometer,X-ray diffractometer and first-principles calculation.It was found that the mechanical properties of the joint are limited by the Fe−Al IMCs,whose brittleness is attributed to the orbital hybridization between Al(s),Al(p)and Fe(d).However,the joint properties are improved by adding interlayer,which is ascribed to some changes of electronic structure of the generated IMCs.The transition mechanism of IMCs changing from brittle to ductile is mainly due to the weak ability of interlayer elements to attract electrons.The mechanical properties of the joint are closely related to the ductility or brittleness of the IMCs.Moreover,the addition of Ti foil interlayer effectively improves the mechanical properties of the joints,which means that the experimental verification is in good agreement with the theoretical calculation predictions.

Adaptive clustering hierarchy routing for delay tolerant network

Adaptive clustering hierarchy routing(ACHR) establishes a clusters-based hierarchical hybrid routing algorithm with two-hop local visibility for delay tolerant network(DTN).The major contribution of ACHR is the combination of single copy scheme and multi-copy scheme and the combination of hop-by-hop and multi-hop mechanism ACHR,which has the advantages in simplicity,availability and well-expansibility.The result shows that it can take advantage of the random communication opportunities and local network connectivity,and achieves 1.6 times delivery ratio and 60% overhead compared with its counterpart.

QoS Guarantees of Multiuser Video Streaming over Wireless Links: Delay Constraint and Packet Priority Drop

To provide a certain level of Quality of Service (QoS) guarantees for multiuser wireless downlink video streaming transmissions, we propose a multiuser scheduling scheme for QoS guarantees. It is based on the classic Queue-Length-Based (QLB)-rate maximum scheduling algorithm and integrated with the delay constraint and the packet priority drop. We use the large deviation principle and the effective capacity theory to construct a new analysis model to find each user's queue length threshold (delay constraint) violation probability. This probability corresponds to the upper bound of the packet drop probability, which indicates a certain level of statistical QoS guarantees. Then, we utilize the priority information of video packets and introduce the packet priority drop to further improve the quality perceived by each user. The simulation results show that the average Peak Signal to Noise Ratio (PSNR) value of the priority drop is 0.8 higher than that of the non-priority drop and the PSNR value of the most badly damaged video frame in the priority drop is on an average 4 higher than that of the non-priority drop.

A unified approach of PID controller design for unstable processes with time delay

This paper addresses a unified approach of the PID controller design for low as well as high order unstable processes with time delay.The design method is based on the direct synthesis(DS)approach to achieve the enhanced load disturbance rejection.To improve the servo response,a two-degree of freedom control scheme has been considered.A suitable guideline has been provided to select the desired reference model in the DS scheme.The direct synthesis controller has been approximated to the PID controller using the frequency response matching method.A consistently better performance has been obtained in comparison with the recently reported methods.

Dry Stone Masonry Ductility During an Earthquake

Stone structures with dry joints, that is, without mortar, have shown a surprising behavior when earthquakes occur. An example of this behavior is the perennially of the so-called Inca wall in Peru, which despite having suffered several earthquakes over time has remained stable without collapsing. This article presents the research carried out on stone masonry wails with dry joint, without mortar, subject to a seismic action. In order to understand the behavior of the masonry without mortar, it designs a Grid mode/ of Finite Elements. From the results, it is concluded that these walls with a certain thickness have ductility that allows them to withstand high displacement and rotation values, thus accommodating the movement of the earth subject to an earthquake. The individual stone blocks move relative to each other through rotations and displacements, which are processed in the free joints of any mortar. The joints work as energy sinks. The free movements in the joints dissipate the energy transmitted by the earthquake, not causing in this way the rupture of the stone blocks. The goal of this article is to understand the p importance of lack of mortar in the seismic behavior of the mansonry.

A new approach for teleoperation rendezvous and docking with time delay

Teleoperation rendezvous and docking can be used as a backup for autonomous rendezvous and docking (RVD) for an unmanned spacecraft or for guiding the chaser docking with an uncooperative target.The inherent teleoperation time delay is a rigorous problem,especially when the chaser is teleoperated on the ground.To eliminate the effect of time delay,a new approach for teleoperation RVD is studied.The characteristics of teleoperation RVD are analyzed by comparisons with the teleoperation robot and with manually controlled RVD;the relative motion of the chaser is predicted based on the C-W equation;and the processed measure information with time delay through the Kalman filter is utilized to correct the current prediction.Experimental results verify that the approach produces an 18% enhanced success rate of teleoperation RVD compared with direct visual feedback,and consumes less time and fuel.The developed approach also solves the time delay problem effectively.Teleoperation RVD using this method can be applied as a useful backup for autonomous RVD.

STABILITY ANALYSIS OF A DELAYED SIRS EPIDEMIC MODEL WITH VACCINATION AND NONLINEAR INCIDENCE

In this paper, an SIRS epidemic model with time delay and vaccination is investigated. By analyzing the corresponding characteristic equation, the local stability of diseasefree equilibrium of the model is established. By constructing Lyapunov functional, sufficient conditions are established for the local stability of an endemic equilibrium of the model. Further, a threshold value is obtained. By using comparison arguments, it is proved when the threshold value is less than unity, the diseasefree equilibrium is globally asymptoti cally stable. When the threshold value is greater than unity, by using an iteration scheme and by constructing appropriate Lyapunov functional, respectively, sufficient conditions are derived for the global stability of the endemic equilibrium of the model. Numerical simulations are carried out to illustrate the theoretical results.

A delayed SEIRS epidemic model with impulsive vaccination and nonlinear incidence rate

In this paper, a delayed SEIRS epidemic model with nonlinear incidence rate and impul- sive vaccination is investigated. In vaccination strategy, we perform impulsive vaccina- tion of newborn infants. Using the discrete dynamic system determined by stroboscopic map, we obtain an infection-free periodic solution and establish conditions, on which the solution is globally attractive. We also conclude that the disease is permanent if the parameters of the model satisfy appropriate conditions. Finally, we illustrate the effec- tiveness of our theorems with numerical simulation. The results obtained in this paper are a good extension of the results obtained in [J. Hou and Z. Teng, Continuous and impulsive vaccination of SEIR epidemic models with saturation incidence rate, Math. Comput, Simulat. 79 （2009） 3038 3054] to the corresponding delayed SEIRS epidemic model with nonlinear incidence rate and impulsive vaccination.

Global stability for multi-species Lotka-Volterra cooperative systems： One hyper-connected mutualistic-species

We propose two models of one hyper-connected mutualistic-species described by delay differential equations of Lotka-Volterra type. An hyper-connected model comprises a central species interacting with a number of peripheral species around it, that is to say, one animal species （pollinators or dispersers） that interacts with several plant species （flowering plants or fruit trees）, or several animal species that interact with one plant species. We derive a necessary and sufficient condition for the global asymptotic stability of the unique coexisting steady state of hyper-connected systems by means of novel Lyapunov functionals.