是整数尺制还是斗口模数制?——时思寺大殿实测数据解读

该文以浙江时思寺大殿为对象,通过对其相关数据的解读,得出了该殿以整数尺寸进行空间设计的结论。考虑到它的实际建成年代,这一设计方法带有较大的滞后性,与同时期北方官式建筑中常见的斗口模数制设计方法相左。与此同时,这一遗构选用的斗口长恰为推定营造尺长的1/4,因此两者间应当存在内在逻辑关系。以此作为切入点讨论了我国传统木构设计体系由整数尺制向斗口模数制转型期间的一些过渡做法,以及明清常见斗口取值与木工营造尺长间的相互关系,并推测其成因。

分类表标记制度刍议

《图书馆杂志》去年发表了数篇关于分类表标记制度讨论的文章。引起同志们的关注。笔者也想提出一点不成熟的看法,就教于图书情报界的同志们。

关于分类标记制度的商榷

《图书馆杂志》今年第一期发表李性忠同志的文章,对“层累制等于小数制”这一流行的观点进行质疑。该文论据充实,分析入理,读后很受启发。由此而想到顺序制是否等于整数制,标记制度到底有哪些种类等问题,一并提出与有关同志商榷。层累制+数序制≠分类标记制度李性忠同志在该文的结束语中指出:“

图书分类表标记制度之我见

任何现代图书分类表均须配以标记符号,用以表示类目在表中的位置及其排列顺序。对分类表的标记制度,目前许多图书分类学专著普遍认为体系分类法的基本标记制度可分为两种:层累制和顺序制。

Stabilization of discrete nonholonomic chained system

Aimed at the stabilization of the nonholonomic chained system under fixed sample control, two control laws were proposed. The discrete model of the nonholonomic chained system under zero-hold was obtained through the integrate method to the continuous model. And the discrete model was transformed to the form with two linear subsystems through coordinate transformation. Two feedback control laws, time-invariant control law and time-varying control law, were proposed; and the local stabilization and global stabilization were realized respectively. The simulation results show the effectiveness of the proposed control laws. The discrete nonholonomic chained system can converge to zero from any initial state exponentially, and the convergence rate can be changed through changing the parameters of the control laws.

Harmony search algorithm with differential evolution based control parameter co-evolution and its application in chemical process dynamic optimization

A modified harmony search algorithm with co-evolutional control parameters(DEHS), applied through differential evolution optimization, is proposed. In DEHS, two control parameters, i.e., harmony memory considering rate and pitch adjusting rate, are encoded as a symbiotic individual of an original individual(i.e., harmony vector). Harmony search operators are applied to evolving the original population. DE is applied to co-evolving the symbiotic population based on feedback information from the original population. Thus, with the evolution of the original population in DEHS, the symbiotic population is dynamically and self-adaptively adjusted, and real-time optimum control parameters are obtained. The proposed DEHS algorithm has been applied to various benchmark functions and two typical dynamic optimization problems. The experimental results show that the performance of the proposed algorithm is better than that of other HS variants. Satisfactory results are obtained in the application.

IMC-PID tuning method based on sensitivity specification for process with time-delay

To overcome the deficiencies addressed in the conventional PID control and improve the dynamic performance and robustness of the system, a simple design and parameters tuning approach of internal model control-PID （IMC-PID） controller was proposed for the first order plus time-delay （FOPTD） process and the second order plus time-delay （SOPTD） process. By approximating the time-delay term of the process model with the first-order Taylor series, the expressions for IMC-PID controller parameters were derived, and they had only one adjustable parameter 2 which was directly related to the dynamic performance and robustness of the system. Moreover, an analytical approach of selecting 2 was given based on the maximum sensitivity Ms. Then, the robust tuning of the system could be achieved according to the value of Ms. In addition, the proposed method could be extended to the integrator plus time-delay （IPTD） process and the first order delay integrating （FODI） process. Simulation studies were carried out on various processes with time-delay, and the results show that the proposed method could provide a better dynamic performance of both the set-point tracking and disturbance rejection and robustness against parameters perturbation.

Thermodynamic design of a cascade refrigeration system of liquefied natural gas by applying mixed integer non-linear programming

Liquefied natural gas(LNG) is the most economical way of transporting natural gas(NG) over long distances. Liquefaction of NG using vapor compression refrigeration system requires high operating and capital cost. Due to lack of systematic design methods for multistage refrigeration cycles, conventional approaches to determine optimal cycle are largely trial-and-error. In this paper a novel mixed integer non-linear programming(MINLP)model is introduced to select optimal synthesis of refrigeration systems to reduce both operating and capital costs of an LNG plant. Better conceptual understanding of design improvement is illustrated on composite curve(CC) and exergetic grand composite curve(EGCC) of pinch analysis diagrams. In this method a superstructure representation of complex refrigeration system is developed to select and optimize key decision variables in refrigeration cycles(i.e. partition temperature, compression configuration, refrigeration features, refrigerant flow rate and economic trade-off). Based on this method a program(LNG-Pro) is developed which integrates VBA,Refprop and Excel MINLP Solver to automate the methodology. Design procedure is applied on a sample LNG plant to illustrate advantages of using this method which shows a 3.3% reduction in total shaft work consumption.

COMPARISON OF SIGMA-DELTA MODULATOR FOR FRACTIONAL-N PLL FREQUENCY SYNTHESIZER

This paper investigates the design of digital Sigma-Delta Modulator (SDM) for fractional-N frequency synthesizer. Characteristics of SDMs are compared through theory analysis and simulation. The curve of maximum-loop-bandwidth vs. maximum-phase-noise is suggested to be a new criterion to the performance of SDM,which greatly helps designers to select an appropriate SDM structure to meet their real application requirements and to reduce the cost as low as possible. A low-spur 3-order Mul-tistage Noise Shaping (MASH)-1-1-1 SDM using three 2-bit first-order cascaded modulators is proposed,which balances the requirements of tone-free and maximum operation frequency.

IMC based robust PID controller tuning for disturbance rejection

It is well-known that the IMC-PID controller tuning gives fast and improved set point response but slow disturbance rejection. A modification has been proposed in IMC-PID tuning rule for the improved disturbance rejection. For the modified IMC-PID tuning rule, a method has been developed to obtain the IMC-PID setting in closed-loop mode without acquiring detailed information of the process. The proposed method is based on the closed-loop step set point experiment using a proportional only controller with gain K_(c0). It is the direct approach to find the PID controller setting similar to classical Ziegler-Nichols closed-loop method. Based on simulations of a wide range of first-order with delay processes, a simple correlation has been derived to obtain the modified IMC-PID controller settings from closed-loop experiment. In this method, controller gain is a function of the overshoot obtained in the closed loop set point experiment. The integral and derivative time is mainly a function of the time to reach the first peak(overshoot). Simulation has been conducted for the broad class of processes and the controllers were tuned to have the same degree of robustness by measuring the maximum sensitivity, Ms, in order to obtain a reasonable comparison. The PID controller settings obtained in the proposed tuning method show better performance and robustness with other two-step tuning methods for the broad class of processes. It has also been applied to temperature control loop in distillation column model. The result has been compared to the open loop tuning method where it gives robust and fast response.

New parameter tuning method of washout filter-aided controller for dynamic behavior adjustment

Stabilizing unstable operating points is an effective way to enhance process benefits and safety, which motivates the development for a variety of advanced control strategies. The washout filter-aided controller(WFC), originally used for electric power system and aircraft, has been introduced to adjust the dynamic behavior of chemical process. However, the parameter tuning method faces two major limitations: the dimension of operating variables must be equal to or greater than that of state variables and only one positive real eigenvalue exists in the open loop system. To overcome the two limitations, this paper proposes a new parameter tuning method, so that the WFC is applicable in most chemical processes. By solving a constrained optimization problem, the controller parameters are determined under the constraint that the reassignment of the eigenvalues of the unstable desired operating point can satisfy the stability condition. Thus parts of the equilibrium manifold including the desired operating point are stabilized without affecting the shape of the equilibrium manifold. Finally, the effectiveness of the WFC improved by the proposed parameter tuning method is illustrated through a case study for propanediol anaerobic fermentation.

A random adaptive method to adjust MAC parameters in IEEE802.11e WLAN

The IEEE 802.11e standard is proposed to provide QoS support in WLAN by providing prioritized differentiation of traffic. Since all the stations in the same priority access category (AC) have the same set of parameters, when the number of stations increases, the probability of different stations in the same AC choosing the same values will increase, which will result in collisions. Random adaptive MAC (medium access control) parameters scheme (RAMPS) is proposed, which uses random adaptive MAC differentiation parameters instead of the static ones used in the 802.11e standard. The performance of RAMPS is compared with that of enhanced distributed coordination access (EDCA) using NS2. The results show that RAMPS can reduce collision rate of the AC and improve the throughput by using adaptive random contention window size and inter-frame spacing values. RAMPS ensures that at any given time, several flows of the same priority have different MAC parameter values. By using the random offset for the inter-frame spacing value and the backoff time, RAMPS can provide intra-AC differentiation. The simulation results show that RAMPS outperforms EDCA in terms of both throughput and end-to-end delay irrespective of the traffic load.

Digital AGC Based on Coherent Adjustment Cycle for DSSS Receiver

In order to meet the requirements for zero value stability of direct sequence spread spectrum(DSSS) signal processing in high dynamic scenario,digital automatic gain control(AGC) is employed to regulate power.However,conventional AGC causes degradation in the synchronization performance of DSSS receiver.Based on the theoretical analysis of the influence of digital AGC on DSSS signal synchronization,this paper proposes a new AGC algorithm,which is applicable to multi-channel digital DSSS signal receiver.By making power adjustment cycle and synchronization cycle coherent with each other adaptively,the influence of digital AGC on subsequent synchronization processing has been eliminated.Theoretical analysis,simulation results and experimental data verify the validity of the proposed algorithm.By virtue of the proposed algorithm,the influence of digital AGC on DSSS signal synchronization is eliminated.This algorithm applies to an aerospace engineering project successfully.

A Piecewise Curvature-Corrected CMOS Bandgap Reference with Negative Feedback

A piecewise curvature-corrected bandgap reference （BGR） with negative feedback is proposed. It features employing a temperature-dependent resistor ratio technique to get a piecewise corrected current, which corrects the nonlinear temperature dependence of the first-order BGR. The piecewise corrected current generator also forms negative feedback to improve the line regulation and power supply rejection （PSR）. Measurement results show the proposed BGR achieves a maximum temperature coefficient （TC） of 21.2ppm/℃ without trimming in the temperature range of - 50-125℃ and a PSR of - 60dB at 2.6V supply voltage. The line regulation is 0.8mV/V in the supply range of 2.6-5.6V. It is successfully implemented in an SMIC 0.35μm 5V n-well digital CMOS process with the effective chip area of 0.04mm^2 and power con- sumption of 0.18mW. The reference is applied in a 3,5V optical receiver trans-impedance amplifier.

Numerical analysis and experimental study of hydrogen production from dimethyl ether steam reforming

An experimental and theoretical study of steam reforming of dimethyl ether was carried out in a processor for fuel cell vehicles to explore the effect of temperature gradient and hydrogen content of the processor.A steady-state,laminar,two-dimensional axi-symmetric model was proposed to investigate the fluid flow,heat transfer and chemical reactions in the dimethyl ether steam reforming processor using porous medium approach.The numerical model was established with Star-CD program using SIMPLE algorithm and finite volume method.Experimental verification of the two-dimensional mathematical model was conducted.The numerical results coincided well with the experimental data.The effects of the parameters on the temperature gradient and hydrogen content of the processor were studied using the numerical model.

Non-integer power estimate in modulation spaces and its applications

We give a method to estimate non-integer power function|u|~ku in modulation space which is an open question in the study of modulation space.As an application,we can study Cauchy problem for the nonlinear Klein-Gordon equation with nonlinear term|u|~ku in modulation space,where k is not an integer.Moreover,we also study the global solution with small initial value for the Klein-Gordon-Hartree equation.The results show some advantages of modulation space both in high and low regularity cases.

An approximation algorithm for the k-median warehouse-retailer network design problem

We study the generalizedk-median version of the warehouse-retailer network design problem(kWRND).We formulate the k-WRND as a binary integer program and propose a 6-approximation randomized algorithm based on Lagrangian relaxation.

Adjusting principle of gas jet controlling inlet and numerical verification

To improve the inlet performance of a ramjet working under variable conditions,a design is proposed by controlling the inlet with jet controlling,which combines the method of reducing the sealing Mach number of the external waves and the technique of controlling inlet by jet controlling.Three inlets were designed to analyze the feasibility and a numerical simulation method was used to simulate the three inlet flow fields.The adjustment mechanism of the design was studied through analysis of the simulation results.The design was verified by comparing the performances of the three inlets.The study showed that the method of reducing the sealing Mach number of the external wave system can improve the flow coefficient when the inlet works at low Mach numbers.The technique of controlling inlet by jet controlling can homogenize inlet flow fields at high Mach numbers,reduce effective throat area and increase the total pressure recovery(TPR).Adjustable inlets controlled by jet controlling demonstrate good performance at certain working ranges.

Controllability of Non-densely Defined Neutral Functional Differential Systems in Abstract Space

In this paper, by means of Sadovskii fixed point theorem, the authors establish a result concerning the controllability for a class of abstract neutral functional differential systems where the linear part is non-densely defined and satisfies the Hille-Yosida condition. As an application, an example is provided to illustrate the obtained result.