This paper proposes a sigma-delta fractional-N frequency synthesizer-based multi-standard I/Q carrier generation system.With reasonable frequency planning,the system can be used in multi-standard wireless communication applications(GSM,WCDMA,GPRS,TD-SCDMA,WLAN(802.11a/b/g)).The implementation is achieved by a 0.13μm RF CMOS process.The measured results demonstrate that three quadrature VCOs(QVCO) continuously cover the frequency from 3.1 to 6.1 GHz(65.2%),and through the successive divide-by-2 prescalers to achieve the frequency from 0.75 to 6.1 GHz continuously.The chip was fully integrated with the exception of an off-chip filter.The entire chip area is only 3.78 mm~2,and the system consumes a 21.7 mA@1.2 V supply without output buffers.The lock-in time of the PLL frequency synthesizer is less than 4μs over the entire frequency range with a direct frequency presetting technique and the auxiliary non-volatile memory(NVM)can store the digital configuration signal of the system,including presetting signals to avoid the calibration process case by case.
For reinforced concrete (RC) frame structures, applying more continuous longitudinal bars in the beams is the most effective way to improve the progressive collapse resistance. However, an RC frame has the possibility to experience multiple collapse mechanisms. An RC frame may not only experience progressive collapse caused by critical column removal but may also experience lateral collapse under strong earthquakes. The strong column-weak beam (SCWB) requirement in seismic design does not allow excessive longitudinal reinforcement in the beams. To solve this contradiction, a previous study proposed a novel kinked rebar (KB) configuration to enhance both the seismic and progressive collapse resistances of RC frames. This study was carried out to conduct further experimental validation and investigation of progressive collapse behaviours of RC frames with KB configurations. First, a quasi-static progressive collapse test involving 9 RC frame substructures was carried out. The test results indicated that the application of KBs could increase both the loading and deformation capacities under the catenary mechanism of RC substructures. For RC substructures, the influences on progressive collapse behaviours from various structural parameters were also investigated. Second, finite-element simulations were carried out to model the behaviours of the test specimens. This study experimentally verified that the KB configuration can improve the progressive collapse resistances of RC frame structures and clarified the progressive collapse mechanism of novel RC frame substructures with KB configurations.
No abstract is provided for this article.
Carbon fiber reinforced polymer (CFRP) laminates can effectively enhance the fatigue life of steel structures. However, few studies have investigated the influence of crack-induced debonding in the CFRP-steel interface on the CFRP strengthening efficiency and the relationship of crack propagation and debonding development. This study experimentally and numerically – with the boundary element method (BEM) – investigated crack propagation and debonding development in CFRP-strengthened cracked steel (Q345, Q460, and Q690) plates. The fatigue test specimens were subjected to a maximum stress of 50% steel yield stress and a stress ratio of 0.1, during which real-time changes in CFRP strain distribution were recorded by digital image correlation (DIC). The CFRP strain gradient calculations showed that crack-induced debonding was crack length-dependent. The numerical fatigue life results were in good agreement with the experimental data when considering debonding and overestimated the experimental data without considering debonding, demonstrating the necessity of considering crack-induced debonding in calculation and design. Furthermore, a relationship was obtained between crack propagation and debonding development.
Carbon fiber reinforced polymer (CFRP) sheets have been used to strengthen steel structures to enhance fatigue life. However there is very limited information on the influence of temperatures on the fatigue strengthening efficiency. This paper describes an investigation on the behavior of cracked steel plates strengthened with CFRP at different temperatures. Firstly, through cylinder coupon tests, mechanical properties of the resin were found to vary at different temperatures, especially when the temperature exceeds the glass transition temperature T g . Secondly, three cracked bare steel plates and five cracked steel plates strengthened with high modulus CFRP sheets were tested under fatigue loading at different temperatures. The results prove the effectiveness of CFRP strengthening technology to increase fatigue life when the temperature ranges from −40°C up to 60°C. It is concluded that the variation of temperature has an obvious influence on properties of the resin, leading to influence on fatigue life. Finally, the existing analytical method to predict fatigue lives of CFRP strengthened steel plates at ambient temperature was modified by considering the temperature effect. Experimental and theoretical results are compared and reasonable agreement is achieved. The influence of the number of CFRP layers and CFRP modulus is also found based on the proposed analytical method.
农用电泵产品是一种以潜水电机为动力，电机与水泵组装成一体潜入水下运转的提水机械，主要有小型潜水电泵、污水潜水电泵、井用潜水电泵和潜水螺杆电泵等几种类型。农用潜水泵小巧轻便，价格低廉、容易操作，在农村生产生活中起着重要作用。
Various analysis-oriented models have been developed over the past decades to predict the stress-strain relationship of fibre-reinforced polymer (FRP) confined concrete. Most of these models are built based on the path-independent assumption, and the mechanism of this kind of model has been revealed by the authors based on a 3D geometrical approach. However, it is widely recognized that FRP confined high-strength concrete (HSC) is path dependent, which means that the stress of passively confined HSC deviates from the actively confined test results. Most of the existing solutions for this problem employ an alternative stress-strain relationship instead of the original actively confined HSC model for FRP confined HSC. In this paper, the mechanism of the path-dependency of confined HSC is revealed based on the 3D geometrical method. In addition, a corresponding analysis-oriented model for confined HSC considering path dependency is proposed. This model includes an actively confined concrete model, a damage criterion and post-damaged HSC behaviours. The proposed model can identify the confining mode from the load path and can select a proper stress-strain relationship for confined HSC without artificial intervention. Finally, the proposed model is calibrated and verified by test data collected from the literature. The results show that the proposed model has better accuracy than existing path-dependent models.
The kinked rebar configuration proposed by the authors has previously demonstrated improved seismic performance and progressive collapse resistance through quasi-static tests on reinforced concrete (RC) beams and plane RC frame substructures. In this paper, shaking table tests were conducted to evaluate the seismic performance of the novel RC frame structure with kinked rebar beams and post-yield hardening columns. The beams of the proposed frame included longitudinal bars with a kinked rebar configuration, while carbon fiber reinforced polymer (CFRP) bars were adopted in the columns to achieve post-yield hardening behavior. A 1/4-scale 4-story novel RC frame was designed, constructed, and tested, with three ground motion records of varying intensity levels used in the shaking table tests. The results showed that the inter-story and residual drift ratios of the proposed novel frame were effectively reduced compared to the conventional frame, indicating better seismic performance and self-centering capability. Additionally, the damage of the novel frame was first observed at beam ends and gradually became more severe with increasing seismic intensity. However, no obvious damage was observed at column ends, even under an extremely large earthquake. Thus, a “strong column-weak beam” failure mode of the novel RC frame structure was successfully achieved, and its repairability was effectively improved.
The fiber-reinforced polymer(FRP) woven web structure(WWS) is an innovative large-span spatial structure composed of FRP strips.The FRP strips are crossed each other and woven to form a flexible web plane,and then the web is stressed integrally in an outer plane.The WWS is a tensegrity spatial structure system made of flexible members of several mechanical statues.The basic assumptions,the fundamental mechanical model,and the equations of the simple FRP WWS of ring beams and central symmetry FRP strips are studied.The equations are drawn.Based on the equations,three load cases of FRP WWS including integrally pre-stressed in an outer plane,the whole span load and half span load are analyzed in theoretical method.The numerical calculations of a simplified FRP WWS are conducted.The fundamental mechanical model of FRP WWS is established,and the theoretical approach for analyzing FRP WWS is concluded.Those provide the theoretical method for calculating of FRP WWS.Through the parameter analysis,the influence principals of parameters on stiffness of structure in service state are studied,which can be referred for the preliminary design of FRP WWS.
This study is concerned with the classification of soft-rock tunnels which could instruct the tunnel construction more efficiently and effectively. It is difficult for NATM which is based on the geological classification to adapt to soft-rock tunnel construction. Through comparative study of the numerical models with different surrounding rock and different cross-sectional dimensions, the deformation characteristics of the soft-rock tunnel is put forward. Soft-rock tunnel is divided into four classes: A, B 1 , B 2 and C. The classification is based on the proportion of the advanced displacement in the total radial displacement and the value of tunnel face extrusion. According to the different characteristics of these four classes of soft-rock tunnel, a high-speed construction with reinforcements of the surrounding rock in front of the face is put forward. The characteristics of the four classes of soft-rock tunnels are: In the general initial support conditions, the proportion of the advanced displacement in the total radial displacement of Class-A tunnels is low, which enables them to achieve self-stabilization. The corresponding proportions of Class-B 1 and Class-B 2 tunnels are beyond the limit, which can only enable them to achieve short-term stability. The extrusion of Class-B 2 tunnel’s face is larger but it does not break the limit. The extrusion of Class-C tunnels breaks the limit which cannot maintain stability if without face reinforcements.
针对252Cf源驱动噪声分析测量法中核材料浓度识别问题,采用压缩感知理论,在K最近邻(KNN)识别算法基础上,研究了一种基于压缩采样的K最近邻（CSKNN）分类识别方法,进而研究并分析了CSKNN方法的识别概率。实验结果表明,CSKNN分类识别方法只需少量的观测值(观测比M/N0.1),即可达到分类识别的目的；当信噪比提高时,识别概率将会以更快的速度收敛至100%,且对K值的敏感程度也会随之降低。这样,不仅提高了核军控核查的实时性,而且还有效降低了采样成本,为核材料浓度的在线判读提供了一种新的理论基础和实现方法。
龙仁夫的易学思想是宋代易学尤其是朱子易学在元代的进一步发展。他继承了朱子“易本义”的易学诠释方向，并吸收了前期易象学的成果，突出了“象”在筮占设教以及《易经》意、象、辞、占体系中的作用和地位。龙氏以“象辞相应之理”为关键，从取象范围和观象方法两个方面考察并推进了东汉的易象学理论；其易象学并非是东汉易学的简单复归，而主要是对朱熹易象、易占理论的继承和发展；龙氏易学的主旨为“即象诂意”与“以象解占”。他以“象”为核心，从筮占与象义两个关键点对《易经》所作的诠释是较为全面和深刻的。
Fibers applied to reinforce the cementitious matrix exhibit a wide range of scales, from distributed carbon nanomaterials, chopped short fibers to continuous fibrous reinforcements. When a cementitious matrix is jointly toughened by reinforcing fibers at multiple scales, Multi-Scale Fiber Reinforced Cementitious Composite (MSFRC) tailored built on the micromechanics-based approach and bond-slip mechanism is proposed in this study. The composite actions of MSFRC, namely, tension stiffening, ductility enhancing and synergetic effects, are explained within a universal perspective. In addition, a 1-D numerical model using spring elements is developed to simulate the tensile behavior of MSFRC based on the crack band theory, fiber-bridging model and Monte Carlo simulation. The scales, types and contents of reinforcing fibers, interface behavior and stochastic nature can be considered in the model. Finally, it is found that the predicted mechanical response and crack evolution process match well with the experimental results obtained from literatures.
