Measurements of air temperature distribution and optimum cooling condition inside the computer system

Measurements of the temperature distributions of the cooling air flow inside a computer system have been made. An investigation of the optimum cooling condition for the computer system has also been made. Seventy-one K-type (Chromega-Alumega) thermocouples were used to measure distributions of the air flow temperature inside the computer system. They were calibrated against the standard platinum resistance thermometer (PRT) in a constant water circulating bath within an accuracy of ± 0.15 °C. It was found that the number and position of cooling fans as well as their operating condition, whether air intake or air discharge, can greatly influence the cooling effectiveness in the computer system. The results show that the flow rate of intake air should not be higher than that of the discharge air for the most effective cooling. It follows that the optimum cooling has been achieved inside the computer when the three fans are positioned in the inlet front, outlet back, and outlet top in the computer, respectively. Under these conditions, not only is the average temperature inside the computer system maintained at an appropriate level, but the most effective cooling around the central processor (CPU) and graphic card which are responsible for the largest amount of heat dissipation can be accomplished. This paper was recommended for publication in revised form by Associate Editor Man-Yeong Ha Dae Hee Lee received a B.S. degree in Mechanical Engineering from Hanyang University in 1984. He then went on to receive his M.S. and Ph.D. degrees from University of California at Davis in 1984 and 1987, respectively. Dr. Lee is currently a Professor at the School of Mechanical Engineering and a Dean of Academic Affairs at Inje University in Korea. Dr. Lee’s research interests are in the area of Convection Heat Transfer, Liquid Crystal Thermography, Co-generation, and Renewable Energy.     

Robust Cognitive‐Radio‐Based OFDM Architecture with Adaptive Traffic Allocation in Time and Frequency

Cognitive radio (CR) has been proposed as an effective technology for flexible use of the radio spectrum. The interference between primary users and CR users, however, becomes a critical problem when they are using adjacent frequency channels with different transmission power levels. In this paper, a robust CR orthogonal frequency division multiplexing (OFDM) architecture, which can effectively suppress interference to nearby primary users and overcome adjacent channel interference (ACI) to the CR user, is proposed. This new approach is characterized by adaptive data repetition for subcarriers under heavy ACI, and adaptive time spreading for subcarriers near the borders of the CR user's spectrum. The data repetition scheme provides extra power gain against the ACI coming from primary users. Time spreading guarantees an acceptable interference level to nearby primary users. By computer simulation, we demonstrate that, under a CR environment, the proposed CR OFDM architecture outperforms conventional OFDM systems in terms of throughput and BER performance.     

Low-k film damage-resistant CO chemistry-based ash process for low-k/Cu interconnection in flash memory devices

In this paper, CO chemistry-based ash processes have been suggested to reduce carbon depletion and moisture absorption from plasma discharges for low-k/Cu interconnection in 40 nm-node Flash memory. We analyzed ash processes utilizing Fourier transform infrared spectroscopy (FTIR), k-value measurements, and sidewall-shrinking profile measurements based on a cross-sectional scanning electron microscope (SEM) image obtained before and after filling trench with Cu. In an effort to better understand the role of ash processes in ultra-narrow capacitors, we also evaluated the distribution of breakdown voltages as a function of voltage for trench-patterned wafers. In this paper, we successfully found that low-damage ash processes for low-k/Cu interconnection by adopting CO chemistry-based ash process.     

Numerical analysis of turbulent flow over a backward-facing step using reynolds stress closure model

Reynolds stress turbulence models are adopted and applied for calculating turbulent flow over a backward-facing step. For the diffusion term in the transport equations for the Reynolds stresses, two gradient-type models are employed and compared. In addition, investigations on the modified ∈ equations are carried out. The results of the computations are compared with the extant experimental data. As a consequence, it is concluded that the Reynolds stress models predict the flow field better than the standardk-∈ model in the recirculating region. However, after the reattachment the return to the ordinary turbulent boundary layer is shown to be too slow to predict the flow field irrespective of turbulence models.     

Efficient cell design and fabrication of concentration‐gradient composite electrodes for high‐power and high‐energy‐density all‐solid‐state batteries

All‐solid‐state batteries are promising energy storage devices in which high‐energy‐density and superior safety can be obtained by efficient cell design and the use of nonflammable solid electrolytes, respectively. This paper presents a systematic study of experimental factors that affect the electrochemical performance of all‐solid‐state batteries. The morphological changes in composite electrodes fabricated using different mixing speeds are carefully observed, and the corresponding electrochemical performances are evaluated in symmetric cell and half‐cell configurations. We also investigate the effect of the composite electrode thickness at different charge/discharge rates for the realization of all‐solid‐state batteries with high‐energy‐density. The results of this investigation confirm a consistent relationship between the cell capacity and the ionic resistance within the composite electrodes. Finally, a concentration‐gradient composite electrode design is presented for enhanced power density in thick composite electrodes; it provides a promising route to improving the cell performance simply by composite electrode design.     

Bone morphogenetic protein‐2 immobilization on porous PCL‐BCP‐Col composite scaffolds for bone tissue engineering

The objective of this study was to develop novel porous composite scaffolds for bone tissue engineering through surface modification of polycaprolactone–biphasic calcium phosphate‐based composites (PCL–BCP). PCL–BCP composites were first fabricated with salt‐leaching method followed by aminolysis. Layer by layer (LBL) technique was then used to immobilize collagen (Col) and bone morphogenetic protein (BMP‐2) on PCL–BCP scaffolds to develop PCL–BCP–Col–BMP‐2 composite scaffold. The morphology of the composite was examined by scanning electron microscopy (SEM). The efficiency of grafting of Col and BMP‐2 on composite scaffold was measured by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Both XPS and FTIR confirmed that Col and BMP‐2 were successfully immobilized into PCL–BCP composites. MC3TC3‐E1 preosteoblasts cells were cultivated on composites to determine the effect of Col and BMP‐2 immobilization on cell viability and proliferation. PCL–BCP–Col–BMP‐2 showed more cell attachment, cell viability, and proliferation bone factors compared to PCL–BCP‐Col composites. In addition, in vivo bone formation study using rat models showed that PCL–BCP–Col–BMP‐2 composites had better bone formation than PCL–BCP‐Col scaffold in critical size defect with 4 weeks of duration. These results suggest that PCL–BCP–Col–BMP‐2 composites can enhance bone regeneration in critical size defect in a rat model with 4 weeks of duration. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45186.     

Effect of nonsolvent coagulant on the morphology and radionuclide detection efficiency of CAYS‐impregnated polysulfone films

Single‐ or double‐layered porous films consisting of polysulfone (PSF) and cerium‐activated yttrium silicate (CAYS) were prepared through the phase inversion of polymeric solutions. For a single‐layered structure, a casting solution including n‐methylpyrrolidone (NMP) as a solvent was cast on a glass substrate and solidified by immersing into a nonsolvent bath. In a double‐layered structure, the bottom layer is a dense PSF film, prepared by vacuum coagulation of a methylene chloride/PSF solution. The top layer was formulated by coagulating the NMP solution, cast over the dense film, in a nonsolvent bath. The morphology and the radionuclide detection efficiency of the prepared films were significantly affected by the nonsolvent coagulants used. The water‐coagulated, double‐layered film showed a relatively clear‐cut interface between the two layers, indicating the rapid coagulation of the second layer. On the contrary, the film coagulated by isopropanol retained well‐developed sponge structures highly intertwined in the interface, associated with the delayed precipitation of the second layer. When spotted on the prepared films, radionuclides stayed mainly on the top surface of the isopropanol‐coagulated film, but went deep into the substructure of the film coagulated with water. In comparison with the mono‐layered films, the double‐layered ones improved the detection capacity of the spotted radionuclides, owing to the dense support layer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99:1903–1909, 2006     

Control of a hybrid active-passive vibration isolation system

Precision vibration control is a major issue in nanotechnology. In particular, nano-precision measurement systems such as Atomic force microscopes (AFM) and Scanning probe microscopes (SPM) are sensitive to ground vibrations. The amplitude of a ground vibration is typically sub-micrometer and ground vibrations adversely affect both the precision and accuracy of these measuring equipment. Consequently, hybrid active-passive vibration isolation systems are typically used as they reduce ground vibrations. This paper presents a hybrid vibration isolation system composed of four spiral metal springs for passive isolation and eight voice coil motors for active isolation. H-infinite and Proportional–integral–derivative (PID) controllers are applied to its 6-DOF vibration control system using six velocity sensors to measure system vibrations. The transmissibility of the presented hybrid isolation system is in the range -10 to -48 dB at its passive resonance frequency and is at least -4 dB better than hybrid isolation systems employing acceleration sensors. The results of various tests conducted to verify the control performance of the developed system with a separately developed shaker indicate that it can serve as a bench-top device for precision measurement machines.