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1.
A common of two-fluid flow heat exchanger, in which the heat transfer between high- and low-temperature sides obeys Newton's law [q∝△(T)], is studied in this paper. By taking entransy dissipation minimization as optimization objective, the optimum parameter distributions in the heat exchanger are derived by using optimal control theory under the condition of fixed heat load. The condition corresponding to the minimum entransy dissipation is that corresponding to a constant heat flux density. Three kinds of heat exchangers, including parallel flow, condensing flow and counter-flow, are considered, and the results show that only the counter-flow heat exchanger can realize the entransy dissipation minimization in the heat transfer process. The obtained results for entransy dissipation minimization are also compared with those obtained for entropy generation minimization by numerical examples.  相似文献   

2.
The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential synergic movement of the ganged roller group is used to complete the metal sheet forming according to the shape of the complicated and variable forming part data. The control system should meet the demands of quick response to the test requirements of the product part. A new kind of real time data driving multi-axis linkage and synergic movement control strategy of 3D roll forming is put forward in the paper. In the new control strategy, the forming data are automatically generated according to the shape of the parts, and the multi-axis linkage movement together with cooperative motion among the six stands of the 3D roll forming machine is driven by the real-time information, and the control nodes are also driven by the forming data. The new control strategy is applied to a 48 axis 3D roll forming machine developed by our research center, and the control servo period is less than 10ms. A forming experiment of variable cross section part is carried out, and the forming preci- sion is better than + 0.5mm by the control strategy. The result of the experiment proves that the control strategy has significant potentiality for the development of 3D roll forming production line with large scale, multi-axis ganged and svner~ic movement  相似文献   

3.
3 GPP LTE has approved uplink intra-cell power control and defined overload indicator (OI) for uplink inter-cell power contrQ1 to mitigate the inter-cell interference (ICI), respectively. In this pa- per, we propose a hierarchical power control ( HPC ) scheme where intra-eell and inter-cell power controls interact with each other. The inter-cell power control eommand is generated by radio re- source management (RRM) entity according to the ICI-load model together with the current ICI and served load information. This ICI-load model is proposed as a guideline for coordination among cells to enable the system to approach its system specific interference over thermal noise (IoT) work area. Simulation results show that for HPC scheme, the system' s IoT is well controlled to fit its pre-de- fined work area and the power efficiency is improved significantly. Our proposed scheme is also ro- bust to different settings of its inter-cell power control period.  相似文献   

4.
As the foundation of an industrialized country nowadays, machine tools industry is regarded as the engine of industrial development of a country. The developed countries, such as USA, Germany and Japan, have widely deployed the technology of using the patent in order to keep their strength in various fields. This research examins the CNC machine tools industry in the world by using the pa- tent analysis method. It first gives an overview about the world patent application in CNC machine tools industry from 1963 to 2010 and divides the development of the industry into five stages. It also lists the patent application of the world top 20 countries, where the top 5 countries are compared. The patents of the world top 10 companies of machine tools manufacturers are mapped according to the international patent classification (IPC), and the future trends of world machine tools industry are discussed. Finally conclusions and suggestions are presented.  相似文献   

5.
给出求函数y=(ax^2 bx c)/(a1x^2 b1x c1)值域的简洁的、程式化的方法。  相似文献   

6.
A new cross-channel interference suppression method is proposed to decrease the cross-channel interference in beat signals based on the short time Fourier transform (STY3") and the inverse short time Fourier transform (ISTFT) when the dual-orthogonal polarimetric frequency-modulated continu- ous wave (FMCW) radar adopts the opposite-slope linear frequency modulation signal pair in the simultaneous measurement mode. The STFT is applied only on the signals in the cross-interference intervals in the four polarimetric channels to decrease the computation complexity. A mask matrix for suppressing the interference is constructed using the constant false alarm ratio (CFAR) detection on the spectrograms by the STFY. The simulative results show that the cross-channel interference is effi- ciently suppressed by the proposed method. The comparison between the proposed method and the rejection method verifies the improved performance of the proposed method.  相似文献   

7.
To increase the limit of ethernet over coax (EoC) technology in the bidirectional reform of the hybrid fiber coaxial (HFC) network, an ethernet passive electronic network (EPEN) system based on Coax is proposed and experimentally demonstrated in this paper. The proposed EPEN exploits the existing capabilities of the MAC layer in the ethernet passive optical network (EPON) for reduction of cost of the HFC network. As the MPCP (multi-point control protocol) is introduced in the EPEN, bandwidth control and higher efficiency can be achieved. The experimental results exhibit the throughput of system up to 100Mbps, which meet the requirements of HFC network. To improve the performance of EPEN, frequency division multiplexing (FDM) can be used for further increase of the throughput and more hardware processing modules in the future. can be implemented to enhance the capacity  相似文献   

8.
F是一个3k元域,x3+ax2+bx+c=0是F上的三次方程。该文证明方程x3+ax2+bx+c=0在F中有一根,或一根与二重根,或三个互异的根,或没有根。  相似文献   

9.
本文对退化草场浅耕翻撩荒处理后群落演替动态进行了研究,9年的结果如下;群落植物的多样性指数在9年中呈开口向上的抛物线状发布,植物种的均匀性指数呈开口向上的抛物线状分析,群落的稳定性呈波动状态,演替过程可分为羊草11-12年生杂草,羊草群落和羊草10多年生杂类草原群三个阶段,从第7年开始,演替向原生植被方向进行,羊草重要值在九年中分布符合方程y=202.9-78.4/x-0.22/x^2,表明在演替开始的前几年,羊草重要值增加较快,随着时间推移,增加变缓并保持在一定水平。  相似文献   

10.
Packet loss protection method based on picture level adaptive frame /field coding (PAFF)was presented. Firstly,the end-to-end rate-distortion analysis for PAFF on the current frame was performed. Secondly,in order to evaluate the severity of error propagation in the following frames,the error propagation intensity and human visual quality sensitivity of different areas were taken into consideration. It was followed by the quantification of relative importance. Finally,the proper coding mode was chosen utilizing an unequal comparison procedure. The simulation results show that the proposed method can improve peak signal-to-noise ratio (PSNR) up to 0. 9 dB and 1. 6 dB comparing with the field only and the dispersed flexible macro-block ordering (FMO)only methods respectively.  相似文献   

11.
Dehydration melting of subducted continental crust is significant during exhumation, and its study from both experimental and petrological observations is of great importance to our understanding of continental geodynamics. Dehydration melting experi- ments were carried out on ultrahigh-pressure (UHP) eclogite from Bixiling in the Dabie orogen using a piston cylinder at 1.5-3.0 GPa and 800-950℃ to investigate partial melting of eclogite induced by phengite breakdown. The phengite-bearing eclogite started to melt at T≤800-850℃ and P=1.5-2.0 GPa and produced about 3% granitic melt. The products of dehydration melting vary with temperature and pressure. Such results provide valuable constraints on the micro-texture related to partial melting of UHP rocks in the Dabie-Sulu orogenic belt. Three types of polyphase inclusions were identified in garnet from the Shuanghe UHP eclogite. K-feldspar and quartz inclusions are interpreted to represent the products of segregation and crystallization of minor amounts of melt that formed during dehydration melting of phengite by the inferred reaction Phengite+Omphacite+Quartz Amphibole_+Garnet+Melt (K-feldspar+Quartz+Plagioclase). Polyphase inclusions of phengite and K-feldspar+Quartz inclusions were also found in zoisite/clinozoisite and garnet from the Shuanghe garnet-bearing paragneiss. These polyphase inclusions pro- vide evidence for a continuous process from sub-solidus dehydration to partial melting within the UHP gneissic rocks. The com- positional variation of garnets demonstrates that breakdown of epidote-group minerals may have played a crucial role during de- hydration melting reaction of phengite. The Ti-in-zircon thermometry and Si content of phengite in zircon suggest that partial melting would occur at 783-839℃ and 2.0-2.5 GPa. Therefore, both experimental results and petrological observations indicate that dehydration melting and fluid activity within the Dabie UHP rocks at micro-scale are controlled by the breakdown of phengite.  相似文献   

12.
Phytic acid (PA) is the primary storage compound of phosphorus in seeds accounting for up to 80% of the total seed phosphorus and contributing as much as 1.5% to the seed dry weight. The negatively charged phosphate in PA strongly binds to metallic cations of Ca, Fe, K, Mg, Mn and Zn making them insoluble and thus unavailable as nutritional factors. Phytate mainly accumulates in protein storage vacuoles as globoids, predominantly located in the aleurone layer (wheat, barley and rice) or in the embryo (maize). During germination, phytate is hydrolysed by endogenous phytase(s) and other phosphatases to release phosphate, inositol and micronutrients to support the emerging seedling. PA and its derivatives are also implicated in RNA export, DNA repair, signalling, endocytosis and cell vesicular trafficking. Our recent studies on purification of phytate globoids, their mineral composition and dephytinization by wheat phytase will be discussed. Biochemical data for purified and characterized phytases isolated from more than 23 plant species are presented, the dephosphorylation pathways of phytic acid by different classes of phytases are compared, and the application of phytase in food and feed is discussed.  相似文献   

13.
Objective: This study aimed to explore the effects of different types of palatal lateral excisions on the growth and development of the maxilla and dental arch, and to investigate the underlying mechanisms. Methods: A total of 112 3-week-old Sprague-Dawley (SD) male rats were randomly divided into a control and 3 experimental groups: the mucoperiosteal denudation group, the mucosal flap excision group, and the periosteum excision group. In the experimental groups, bilateral mucoperiosteal, mucosal flap and periosteum were excised respectively in the lateral one half of the palate. Four rats in each group were randomly chosen for sacrifice every two weeks. The maxilla was dissected following the excision. The widths of the maxilla and dental arch were measured and the histological phenomena were investigated at different phases. At the same time, 12 animals in each group were sequentially injected with calcein every two weeks. Three animals in each group, whose fluorescent labeling was used, were sacrificed for investigating bone formation at Week 8 following injection. Results: (1) Each experimental group presented the constriction of the maxilla and dental arch. The upper first molars in the experimental groups inclined medially. The mucoperiosteal denudation group showed the largest degree of effect followed by the periosteum excision group. The indices of the mucosal flap excision group, which retained the structures of the periosteum layer, had the most approximate values to the control group; (2) Different histological changes among the experimental groups were detected. The fibers penetrated into the palatal bone as Sharpey's fibers in the mucoperiosteal denudation group. The pattern of bone deposition was the bundle type. Sharpey's fibers were not found in the mucosal flap and periosteum excision groups and the depositions of palatal bone were the lamellar type as those in the control group; (3) The rates of bone deposition in the experimental groups decreased compared with the  相似文献   

14.
B3lyp/6-311++g** and mp2/6-311++g** calculations were used to analyze the interaction between CH3SO and HOCl. Nine (complex A: S1A-S9A) and five (complex B: S4B-S7B and S10B) minima were localized on the potential energy surface of CH3SO…HOCl complexes at b3lyp/6-311++g** and mp2/ 6-311++g** computational levels, respectively. The AIM and NBO theories were also applied to explain the nature of the complexes. Bonding energy of complexes A and B corrected with BSSE falls in the ranges of -0.4―-41.4 kJ·mol-1 and -6.9―-35.8 kJ·mol-1 at mp2/6-311++g** level, respectively. The re- sults show that a novel oxygen bond complex (S6) exists in the system, besides hydrogen bond and chlorine bond. Especially, S6B-F, S6B-Br and S7B are blue shifted complexes compared with red shifted S6A, because the electron transfer occurs between LP1(S8) and σ*(O5-Cl7), resulting in the increase of O5-Cl7 and the decrease of vibrational frequency. The complex of S10B has characteristics of both red shift and blue shift.  相似文献   

15.
Optimization of a process for extracting astaxanthin from Phaffia rhodozyma by acidic method was investigated, regarding several extraction factors such as acids, organic solvents, temperature and time. Fractional factorial design, central composite design and response surface methodology were used to derive a statistically optimal model, which corresponded to the following optimal condition: concentration of lactic acid at 5.55 mol/L, ratio of ethanol to yeast dry weight at 20.25 ml/g, temperature for cell-disruption at 30 ℃, and extraction time for 3 min. Under this condition, astaxanthin and the total carotenoids could be extracted in amounts of 1294.7 μg/g and 1516.0 μg/g, respectively. This acidic method has advantages such as high extraction efficiency, low chemical toxicity and no special requirement of instruments. Therefore, it might be a more feasible and practical method for industrial practice.  相似文献   

16.
The present drinking water purification system in Egypt uses surface water as a raw water supply without a preliminary filtration process. On the other hand, chlorine gas is added as a disinfectant agent in two steps, pre- and post-chlorination. Due to these reasons most of water treatment plants suffer low filtering effectiveness and produce the trihalomethane (THM) species as a chlorination by-product. The Ismailia Canal represents the most distal downstream of the main Nile River. Thus its water contains all the proceeded pollutants discharged into the Nile. In addition, the downstream reaches of the canal act as an agricultural drain during the closing period of the High Dam gates in January and February every year. Moreover, the wide in- dustrial zone along the upstream course of the canal enriches the canal water with high concentrations of heavy metals. The obtained results indicate that the canal gains up to 24.06 × 10^6 m^3 of water from the surrounding shallow aquifer during the closing period of the High Dam gates, while during the rest of the year, the canal acts as an influent stream losing about 99.6× 10^6 m^3 of its water budget. The reduction of total organic carbon (TOC) and suspended particulate matters (SPMs) should be one of the central goals of any treatment plan to avoid the disinfectants by-products. The combination of sedimentation basins, gravel pre-filtration and slow sand filtration, and underground passage with microbiological oxidation-reduction and adsorption criteria showed good removal of parasites and bacteria and complete elimination of TOC, SPM and heavy metals. Moreover, it reduces the use of disinfectants chemicals and lowers the treatment costs. However, this purification system under the arid climate prevailing in Egypt should be tested and modified prior to application.  相似文献   

17.
In this paper,a portable 2.42 GHz transmitter for wireless communication systems,with 8dBm output power and small size is proposed.Several novel features exist in this transmitter.First,power consumption and output are balanced by introducing a differential oscillator with input signal controlled biasing,which acts as both a carrier generator and an OOK modulator.Then,power consumption of the transmitter is reduced by the OOK modulated signal via switching the oscillator and the power amplifier at the same time.Furthermore,the area size is also reduced by a class-AB power amplifier,which uses the PCB antenna as the resonance inductance.With these features,the total chip area is reduced to 670μm×740μm(In a 0.18μm CMOS process).  相似文献   

18.
Regression analysis is often formulated as an optimization problem with squared loss functions.Facing the challenge of the selection of the proper function class with polynomial smooth techniques applied to support vector regression models,this study takes cubic spline interpolation to generate a new polynomial smooth function |x|_ε~2 in ε-insensitive support vector regression.Theoretical analysis shows that S_ε~2-function is better than p_ε~2-function in properties,and the approximation accuracy of the proposed smoothing function is two order higher than that of classical p_ε~2-function.The experimental data shows the efficiency of the new approach.  相似文献   

19.
20.
The modelling and simulation of deformable objects is a challenging topic in the field of haptic rendering between human and virtual environment. In this paper, a novel and efficient layered rhombus-chain-connected haptic deformation model based on physics is proposed for an excellent haptic rendering. During the modelling, the accumulation of relative displacements in every chain structure unit in each layer is equal to the deformation on the virtual object surface, and the resultant force of corresponding springs is equivalent to the external force. The layered rhombus-chain-con- nected model is convenient and fast to calculate, and can satisfy real-time requirement due to its simple nature. Simulation experiments in virtual human liver based on the proposed model are con- ducted, and the results demonstrate that our model provides stable and realistic haptic feeling in real time. Meanwhile, the display result is vivid.  相似文献   

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