Fatigue Behavior of Electrodeposited Nanocrystalline Nickel Films

AbstractMaterial characterization of thin film for MEMS/nano structures is a building block for the reliability assessment. One of the most significant barriers for reliable MEMS/nano structure is the long term reliability which is different from those of bulk materials. Nano-indenter has been used widely to get the elastic modulus of materials in a very simple way but other testing machines are required for tensile and endurance properties. For the long term reliability assessment of micro/nano structures, a new micro fatigue testing machine was developed to obtain the high cycles fatigue behavior of thin films. Nanocrystalline nickel thin films exhibited significant rate dependency on tensile and fatigue behavior even in room temperature due to grain size related behavior in contrast to coarse grained wrought nickels

Understanding the Visitation Aspect of Black-headed Gull (Larus ridibundus) in the Long Period at Nakdong Estuary, Busan, Republic of Korea

AbstractThis study analyzes data in the first half of 1990 (May, 1989 - April, 1993) and mid-2000 (May, 2002 - April, 2006) to understand long-term status of black-headed gulls (Larus ridibundus) in the estuary of the Nakdong River under rapid changes. During the period (May, 1989 - April, 1993 and May, 2002 - April, 2003 for a total of 8 years), a total of 201,519 individuals of Laridae were discovered at the estuary and the number of the black-headed gulls (Larus ridibundus) was 32,538 (16.15%). Monthly average of the black-headed gulls showed that there were just a small number of individuals arrived in July and August, but the number increased from September, reached the highest in April for the first term (1989 - 1993). The second term showed that some individuals were discovered in summer (June - August), then the number increased from October and reached the peak in April. Monthly average in the latter period marked 5.7 times higher than that of the former. In the aspect of individuals, there is a significant difference between the two period (P<0.05) and it is discovered that the number of individuals in 2000s (Mean= 6923.50) was higher than that of 1990s (Mean=1211.00). Comparing individuals of gulls, herring gulls (Larus argentatus) and black-headed gulls for 8 years, it was found out that the herring gulls (Larus argentatus) showed the largest number (average=5313.13), followed by the black-headed gulls (average=4067.25) and gulls (average= 1207.63). The fluctuation on individuals of black-headed gulls in the mid-2000s (May, 2005 - April, 2006) recorded the average number of 472.75, then 113.50 in DMD, 244.00 in JJ and SJD, 635.25 in SJ and DY, 727.50 in LUD and 643.50 in USD, showing significant differences among regions (P<0.05)

Use of Multiple Antennas for DS/CDMA Code Acquisition

Manuscript received August 13, 2001; revised February 19, 2002; accepted March 6, 2002. The editor coordinating the review of this paper and approving it for publication is R. A. Valenzuela.A generalized acquisition scheme is proposed for direct sequence code-division multiple-access systems with multiple antennas. The proposed scheme employs grouping of multiple antennas as a means of a tradeoff between two important factors determining the mean acquisition time, combining gain and search time. The performance of the proposed acquisition scheme is analyzed in frequency-selective Rayleigh-fading channels with consideration of spatial correlations. Numerical results show that the use of the largest number of antenna groups is preferable to reducing the mean acquisition time at low signal-to-interference ratio (SIR) values. At high SIR values, on the contrary, the mean acquisition time is found to increase in proportion to the number of antenna groups. In a typical environment, the presence of spatial correlation is shown to increase or decrease the mean acquisition time within 50% compared with the uncorrelated fading case.This work was supported in part by the Brain Korea 21 Project

Utilization of Multipaths for Spread-Spectrum Code Acquisition in Frequency-Selective Rayleigh Fading Channels

Paper approved by Z. Kostic, the Editor for Wireless Communication of the IEEE Communications Society. Manuscript received February 22, 2000; revised July 2, 2000. This paper was presented in part at the 11th IEEE Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC 2000), London, U.K., September 2000.A novel acquisition scheme that utilizes multipaths to improve acquisition performance is proposed for frequency-selective fading channels. The proposed acquisition scheme employs nonconsecutive search and joint triple-cell detection. The performance is analyzed in frequency-selective Rayleigh fading channels. Equations for the probabilities of detection and false alarm are derived, and an expression for the mean acquisition time is developed. The mean acquisition time performance of the proposed and conventional acquisition schemes is evaluated and compared. It is found that the proposed acquisition scheme significantly outperforms the conventional one. The effects of various channel parameters such as the number of resolvable paths, the shape of the multipath intensity profile (MIP) and the signal-to-interference ratio (SIR) on acquisition performance are also investigated.This work was supported by the Brain Korea 21 Project

Performance Comparison of FFH and MCFH Spread-Spectrum Systems with Optimum Diversity Combining in Frequency-Selective Rayleigh Fading Channels

Paper approved by Z. Kostic, the Editor for Wireless Communication of the IEEE Communications Society. Manuscript received June 5, 1999; revised May 12, 2000. This paper was presented in part at the 10th IEEE Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC99), Osaka, Japan, September 1999.In this letter, the performance of frequency-hopping spread-spectrum systems employing noncoherent reception and transmission diversity is analyzed for frequency-selective Rayleigh fading channels. Two different types of transmission diversity systems, a fast frequency-hopping (FFH) system and a multicarrier frequency-hopping (MCFH) system, are investigated. In order to combine received signals from transmit diversity channels, the optimum diversity combining rule based on the maximum-likelihood criterion is developed. Probability of error equations are derived, and utilized to evaluate the performance of the two systems. MCFH systems are found to outperform FFH systems when the channel delay spread is severe, while FFH systems are superior to MCFH systems when a channel varies rapidly. Furthermore, it is found that performance enhancement due to an increase of diversity order is more significant for MCFH systems than for FFH systems in frequency-selective fading channels. The effect of frequency-selective fading is also investigated in determining optimum frequency deviations of binary frequency-shift keying signals.This work was supported by the Brain Korea 21 Project

Differentially Coherent Combining for Double-Dwell Code Acquisition in DS-CDMA Systems

Paper approved by L. Wei, the Editor for Wireless CDMA Systems of the IEEE Communications Society. Manuscript received January 9, 2002; revised June 15, 2002 and December 3, 2002. This paper was presented in part at the 12th IEEE Symposium on Personal, Indoor, and Mobile Radio Communications, San Diego, CA, September-October, 2001.The use of differentially coherent combining is proposed to improve the performance of a double-dwell acquisition system by increasing the reliability of a decision in the verification stage. The detection and mean acquisition time performance of the acquisition scheme with the proposed combining scheme is analyzed in frequency-selective Rayleigh fading channels, and compared with that of two previously published double-dwell acquisition schemes based on long correlation intervals and noncoherent combining. It is shown that the proposed acquisition scheme outperforms the previous ones, and that the performance improvement increases as the frequency offset increases.This work was supported by the Brain Korea 21 Project

Transmit Power Allocation for BER Performance Improvement in Multicarrier Systems

This paper was presented in part at the IEEE International Symposium on Personal, Indoor, and Mobile Radio Communications, Lisbon, Portugal, September 2002.In a multicarrier system, transmit power allocation over different subchannels is an effective means of improving the performance. We develop the optimal transmit power allocation scheme to improve bit-error rate (BER) performance in a multicarrier system with diversity reception. A simple suboptimal scheme is also derived from the optimal one, and an asymptotic case referred to as the equal-signal-to-noise ratio scheme is discussed. Numerical results show that the optimal and suboptimal power allocation schemes significantly outperform the equal power allocation scheme. The effects of the modulation level, the number of receiving antennas, and the number of subchannels on the BER performance are also investigated

Transmit Power Allocation for Successive Interference Cancellation in Multicode MIMO Systems

Paper approved by X. Wang, the Editor for Multiuser Detection and Equalization of the IEEE Communications Society. Manuscript received June 10, 2005; revised November 2, 2006 and July 23, 2007. This paper was presented in part at the IEEE International Conference on Communications, Seoul, Korea, May 2005.Multiple-input multiple-output (MIMO) system with multicode transmission can provide high speed data services by transmitting independent parallel substreams from multiple antennas and through multicode channelization. In this paper, we first introduce an iterative two-stage successive interference cancellation (SIC) detection scheme for a multicode MIMO system. The proposed technique cancels the interference signals successively in the space domain followed by the code domain. Next, we develop various transmit power allocation schemes over different data substreams for the proposed detection process to improve error rate performance. The joint transmit power allocation is derived to make the post-detection signal-to-interferenceplus- noise ratio (SINR) become the same for all substreams in both the space and code domains. As a computationally efficient scheme, we propose a two-stage power allocation scheme, which allocates the total transmit power to the substreams in the code domain at the first stage, and allocates this code domain power to the substreams in the space domain at the second stage. Furthermore, variable and constant power ratio (PR) schemes are derived to reduce the feedback overhead. In particular, the constant PR scheme utilizes the transmit power ratio determined by the long-term statistical properties of the fading channel amplitudes, and achieves significantly reduced feedback rate. Numerical results show that the proposed transmit power allocation schemes for the two-stage SIC significantly outperform the equal power allocation scheme

Statistical Multimode Transmit Antenna Selection for Limited Feedback MIMO Systems

This paper was presented in part at the Asia-Pacific Conference on Communications, Busan, Korea, August 2006.In a wireless multiple-input multiple-output (MIMO) system, transmit antenna selection is an effective means of achieving good performance with low complexity. We consider spatial multiplexing with linear receivers, and equal power and equal rate allocation over different selected transmit antennas in order to reduce feedback overhead. Under these constraints, we address the problem of statistical multimode transmit antenna subset selection to improve the capacity of spatially correlated MIMO fading channels. In particular, we first derive an analytical closed-form expression for the expectation of the lower bound on the capacity using the smallest eigenvalue distribution of a Wishart matrix. Then, we propose a transmit antenna subset selection criterion of maximizing this average lower-bound capacity