Economic benefits of optimal control for water-cooled chiller systems serving hotels in a subtropical climate

A water-cooled chiller system in an air-conditioned hotel can take up about one-quarter of the total electricity consumption and considerable amounts of water in the heat rejection process. This paper evaluates operating cost savings of a chiller system integrated with optimal control of cooling towers and condenser water pumps. A sophisticated chiller system model was used to ascertain how different control methods influence the annual electricity and water consumption of chillers operating for the cooling load profile of a reference hotel. It is estimated that applying load-based speed control to the cooling tower fans and condenser water pumps could reduce the annual system electricity use by 8.6% and operating cost by 9.9% relative to the equivalent system using constant speed fans and pumps with a fixed set point of 29.4 °C for cooling water temperature control. The ways to implement this advanced control for system optimization are discussed.     

刍议历史地段插建建筑形态设计

该文依据历史地段插建建筑与其所处环境之间的三种位置关系,结合具体案例对其形态设计策略进行详细探讨。     

A 60-GHz 38-pJ/bit 3.5-Gb/s 90-nm CMOS OOK Digital Radio

A 60-GHz fully integrated bits-in bits-out on–off keying (OOK) digital radio has been designed in a standard 90-nm CMOS process technology. The transmitter provides 2 dBm of output power at a 3.5-Gb/s data rate while consuming 156 mW of dc power, including the on-chip 60-GHz frequency synthesizer. A pulse-shaping filter has been integrated to support high data rates while maintaining spectral efficiency. The receiver performs direct-conversion noncoherent demodulation at data rates up to 3.5 Gb/s while consuming 108 mW of dc power, for a total average transceiver energy consumption of 38 pJ/bit in time division duplex operation. To the best of the authors' knowledge, this is the lowest energy per bit reported to date in the 60-GHz band for fully integrated single-chip CMOS OOK radios.      

Analysis of Asynchronous Band-Limited DS-CDMA with MMSE Multiuser Detector over Generalized-<Emphasis Type="Italic">k</Emphasis> Fading Channels

In this paper, we investigate bit-error-rate (BER) performance of a minimum mean-squared error (MMSE) multiuser receiver for asynchronous band-limited direct- sequence code-division multiple-access (DS-CDMA) systems. We focus on the BER performance in the presence of multitone jamming (MTJ) over frequency-selective multipath fading channels. We consider the generalized-K fading model in our analysis, as it can model a large spectrum of fading-channel characteristics. We also analyze the effects of band- limited pulse shape on the BER performance of the system. Multipath diversity based on the maximal-ratio combining (MRC) scheme is employed to combat fading effects. Our analytical expressions are valid for arbitrary diversity levels and fading parameters. Spectrum raised cosine (SRC) and Beaulieu–Tan–Damen (BTD) pulse shapes are employed for numerical analysis. Numerical results show that in the presence of MTJ and under various channel conditions, the MMSE based receiver gives better BER performance than the one without it. Moreover, the system with BTD pulses outperforms the one with SRC pulses.     

Effect of nano Al2O3 additions on the microstructure, hardness and shear strength of eutectic Sn–9Zn solder on Au/Ni metallized Cu pads

Nano-sized, nonreacting, noncoarsening Al₂O₃ particles have been incorporated into eutectic Sn–Zn solder alloys to investigate the microstructure, hardness and shear strength on Au/Ni metallized Cu pads ball grid array substrate (BGA). In the plain Sn–Zn solder joint and solder joints containing Al₂O₃ nano-particles, a scallop-shaped AuZn₃ intermetallic compound layer was found at the interfaces. In the solder joints containing Al₂O₃ nano-particles, a fine acicular-shaped Zn-rich phase and Al₂O₃ nano-particles were found to be homogeneously distributed in the β-Sn matrix. The shear strengths and hardness of solder joints containing higher percentage of Al₂O₃ nano-particles exhibited consistently higher value than those of plain solder joint and solder joints containing lower percentage of Al₂O₃ nano-particles due to control the fine microstructure as well as homogeneous distribution of Al₂O₃ nano-particles acting as a second phase dispersion strengthening mechanism. The fracture surfaces of plain Sn–Zn solder joints exhibited a brittle fracture mode with smooth surfaces while Sn–Zn solder joints containing Al₂O₃ nano-particles showed a typical ductile failure with very rough dimpled surfaces.     

Comparison of electrical stress-induced charge carrier generation/trapping and related degradation of SiO2 and HfO2/SiO2 gate dielectric stacks

We compare charge carrier generation/trapping related degradation in control oxide (SiO₂) and HfO₂/SiO₂ stack of an identical equivalent-oxide-thickness (EOT) during constant gate voltage stress of n-type metal-oxide-semiconductor (nMOS) capacitors. Irrespective of these two dielectrics, the kinetics of generation of both surface states and oxide-trapped positive charges are found to be similar. Our analysis shows that the positive oxide charge buildup during CVS is due to trapping of protons by the strained SiOSi bonds in either of the devices. We demonstrate that compared to SiO₂ devices, HfO₂ devices with an equal EOT better perform in CMOS logic applications. On the other hand, our results indicate that the control oxide is better in charge trapping memory devices. Furthermore, the lifetime of the control oxide devices is observed longer than that of HfO₂ devices at a given operating voltage.     

Iterative design of variable fractional-order IIR differintegrators

In this paper, the variable fractional-order (VFO) differintegrator is designed based on IIR-typed Farrow structure. The stability of the designed VFO IIR differintegrator is achieved by incorporating a constrained function into the objective error function. But the minimization of the original objective error function is a highly nonlinear problem, so an iterative quadratic method is proposed to overcome it. Comparing with the design based on FIR-typed Farrow structure, several designed examples, including a VFO differintegrator, a pure VFO differentiator and a pure VFO integrator, are presented to demonstrate the effectiveness of the proposed method.     

An Output-Capacitorless Low-Dropout Regulator With Direct Voltage-Spike Detection

An output-capacitorless low-dropout regulator (LDO) with a direct voltage-spike detection circuit is presented in this paper. The proposed voltage-spike detection is based on capacitive coupling. The detection circuit makes use of the rapid transient voltage at the LDO output to increase the bias current momentarily. Hence, the transient response of the LDO is significantly enhanced due to the improvement of the slew rate at the gate of the power transistor.      

灰色系统理论在垃圾填埋场稳定化研究中的应用

灰色系统理论在填埋场稳定化分析中有一定的价值。论文就稳定化因素分析运用层次分析法及灰色关联度法得到相同的结论,渗滤液回灌(产生量)对填埋场的稳定化影响最显著。进而在稳定化分析中选取沉降这一评价因子进行了研究。     

Composite beam composed of steel and precast concrete (Modularized Hybrid System,MHS). Part I: experimental investigation

An experimental investigation of composite beams composed of wide flange steel and precast concrete is presented. The bottom flange of the steel section is encased in precast concrete. Utilizing the merits of both steel and concrete material, the size of the steel beams can be reduced without sacrificing performance. The bottom flange of the steel beam is reinforced with concrete at a manufacturing plant, eliminating the use of temporary pour forms. The composite beams were tested to investigate how the size of the wide flange steel and how the top and bottom reinforcements influence the behaviour of the beams. Flexural load carrying capacity, load displacement relationships and failure modes were examined. The test specimens were T‐shaped composite beams with slabs, each measuring 10‐m long. The flexural moment strength of all of the composite beams—at both the yield limit state and the maximum load limit state—was measured and compared with the analytical flexural capacity. The stiffness degradation, ductility and dissipating energy capabilities of the composite beams were investigated based on the hysteresis curves. The composite beams tested in this study successfully reduced both the floor height of the building and the size of the steel beams needed to meet code requirements. Copyright © 2008 John Wiley & Sons, Ltd.