Hyungsuk Kim

INDUCTWISE: inductance-wise interconnect simulator and extractor

We develop a robust, efficient, and accurate tool, which integrates inductance extraction and simulation, called INDUCTWISE. This paper advances the state-of-the-art inductance extraction and simulation techniques and contains two major parts. In the first part, INDUCTWISE extractor, we discover the recently proposed inductance matrix sparsification algorithm, the K-method[1], albeit its great benefits of efficiency, has a major flaw on the stability. We provide both a counter example and a remedy for it. A window section algorithm is also presented to preserve the accuracy of the sparsification method. The second part, INDUCTWISE simulator, demonstrates great efficiency of integrating the nodal analysis formulation with the improved K-method. Experimental results show that INDUCTWISE has over 250x speedup compared to SPICE3. The proposed sparsification algorithm accelerates the simulator another 175x and speeds up the extractor 23.4x within 0.1% of error. INDUCTWISE can extract and simulate an 118K-conductor RKC circuit within 18 minutes. It has been well tested and released on the web for public usage. (http://vlsi.ece.wisc.edu/Inductwise.htm)

Harpoon: a flow-level traffic generator for router and network tests

We describe Harpoon, a new application-independent tool for generating representative packet traffic at the IP flow level. Harpoon is a configurable tool for creating TCP and UDP packet flows that have the same byte, packet, temporal, and spatial characteristics as measured at routers in live environments. We validate Harpoon using traces collected from a live router and then demonstrate its capabilities in a series of router performance benchmark tests.

Attenuation estimation using spectral cross-correlation

Estimation of the local attenuation coefficient in soft tissue is important both for clinical diagnosis and for further analysis of ultrasound B-mode images. However, it is difficult to extract spectral properties in a small region of interest from noisy backscattered ultrasound radio frequency (RF) signals. Diffraction effects due to transducer beam focal properties also have to be corrected for accurate estimation of the attenuation coefficient. In this paper, we propose a new attenuation estimation method using spectral cross-correlation between consecutive power spectra obtained from the backscattered RF signals at different depths. Since the spectral cross-correlation method estimates the spectral shift by comparing the entire power spectra, it is more robust and stable to the spectral noise artifacts in the backscattered RF signals. A diffraction compensation technique using a reference phantom with a known attenuation coefficient value is also presented. Local attenuation coefficient estimates obtained using spectral cross-correlation are within 2.3% of the actual value with small estimation variances, as demonstrated in the simulation results

HYBRID SPECTRAL DOMAIN METHOD FOR ATTENUATION SLOPE ESTIMATION

Attenuation estimation methods for medical ultrasound are important because attenuation properties of soft tissue can be used to distinguish between benign and malignant tumors and to detect diffuse disease. The classical spectral shift method and the spectral difference method are the most commonly used methods for the estimation of the attenuation; however, they both have specific limitations. Classical spectral shift approaches for estimating ultrasonic attenuation are more sensitive to local spectral noise artifacts and have difficulty in compensating for diffraction effects because of beam focusing. Spectral difference approaches, on the other hand, fail to accurately estimate attenuation coefficient values at tissue boundaries that also possess variations in the backscatter. In this paper, we propose a hybrid attenuation estimation method that combines the advantages of the spectral difference and spectral shift methods to overcome their specific limitations. The proposed hybrid method initially uses the spectral difference approach to reduce the impact of system-dependent parameters including diffraction effects. The normalized power spectrum that includes variations because of backscatter changes is then filtered using a Gaussian filter centered at the transmit center frequency of the system. A spectral shift method, namely the spectral cross-correlation algorithm is then used to compute spectral shifts from these filtered power spectra to estimate the attenuation coefficient. Ultrasound simulation results demonstrate that the estimation accuracy of the hybrid method is better than the centroid downshift method (spectral shift method), in uniformly attenuating regions. In addition, this method is also stable at boundaries with variations in the backscatter when compared with the reference phantom method (spectral difference method). Experimental results using tissue-mimicking phantom also illustrate that the hybrid method is more robust and provides accurate attenuation estimates in both uniformly attenuating regions and across boundaries with backscatter variations. The proposed hybrid method preserves the advantages of both the spectral shift and spectral difference approaches while eliminating the disadvantages associated with each of these methods, thereby improving the accuracy and robustness of the attenuation estimation.

Estimation of ultrasound attenuation from broadband echo-signals using bandpass filtering

A problem with video signal analysis for estimating frequency-dependent ultrasonic attenuation is that relative echogenicity versus depth curves are distorted when broadband pulses are used. In this correspondence, we present results that demonstrate improved accuracy of attenuation estimates computed from B-mode or envelope data derived after narrowband (1 MHz BW) filtering at different frequencies around the center frequency of the broadband echo signal. Based on the premise that transducer center frequencies are selected in part on penetration or imaging depth requirements, simulation and experimental results for a typical ultrasound imaging system show that narrowband video signal analysis for frequencies lower than or at the center frequency of the broadband pulse provide unbiased attenuation estimation over this depth. Filtered signals above the center frequency of the pulse yield accurate results only at shallow depths.

Variable-region sequences of five human λ-chain proteins reacting with an idiotypic antibody to the MCG bence-jones protein☆

An antibody to the V-region of BJ protein MCG has been used to detect other human lambda-chains with similar idiotypic specificities. Five such proteins have been found and sequenced. They show relatively strong sequence homologies to some segments of the MCG V-region. The results of this study indicate that L-chains which contain short segments of their V-regions that are identical can be readily detected by the use of appropriate antisera.

P2F-8 Performance Comparison of Attenuation Estimation Techniques

Ultrasound attenuation measurements in soft tissue is important both for the clinical diagnosis of various pathological conditions as well as for further analysis of ultrasound B-mode images artifacts such as shadowing and enhancement. In this paper, we present a new method for estimating local attenuation coefficients using spectral cross-correlation between consecutive power spectra obtained from the backscattered radiofrequency echo signals at different depths. Since the spectral cross-correlation method estimates the spectral shift by comparing the entire power spectra, it is more robust and stable to the noise artifacts in the backscattered radiofrequency signals. We compare the attenuation estimation performance of spectral cross-correlation to the centroid downshift, and reference phantom methods reported in the literature. Ultrasound simulations that incorporate variations in the transducer dependent parameters and backscatter properties of tissue are utilized to compare the accuracy and precision of each method. Simulation results demonstrate that the estimation accuracy of the reference phantom and spectral cross-correlation methods are better than the centroid downshift method in uniform backscatter regions. However, as backscatter properties change along the beam propagation path, the reference phantom method fails to estimate attenuation coefficients at the boundaries where the backscatter changes occur while the spectral cross-correlation and centroid downshift are fairly independent of backscatter variations. Experimental results using tissue mimicking phantoms also illustrate that the spectral cross-correlation method is more robust towards changes in tissue backscatter properties

P3E-5 Attenuation Estimations from B-Mode Image Data Derived using Bandpass Filtering

Frequency-dependent ultrasound attenuation in soft tissue is an important parameter for discriminating normal from diseased tissues. A previously described video signal analysis method computes the ratio of mean echo intensities from a sample to that from a reference phantom scanned using identical transducer settings. The relative echogenicity versus depth yields information on the attenuation of the sample. A problem with VSA, however, is that the relative echogenicity versus depth curves derived in this manner are distorted when broadband pulses common in pulse-echo ultrasound systems are utilized. In this paper, we present results that show the accuracy of attenuation estimates computed from image data derived after narrowband bandpass filtering of the backscattered radiofrequency echo signals at different center frequencies around the center frequency of the broadband echo signal. Envelope or B-mode signals derived from the narrow bandpass filtered radiofrequency data are processed to estimate attenuation using the video signal analysis method. Since higher frequency components are more severely attenuated than lower frequencies, even with a 1 MHz bandwidth filter, narrow band video signal analysis data for center frequencies above the center frequency of the pulse yielded significant underestimation of the attenuation, particularly at large depths. On the other band, filtered signals with center frequencies lower than or at the center frequency of the broadband pulse produced unbiased attenuation estimates. Local attenuation coefficient estimates using the video signal analysis method with narrow bandpass filtering demonstrate comparable results to other existing estimation methods, while maintaining computational efficiency for real-time implementation

Linear time hierarchical capacitance extraction without multipole expansion

Hierarchical capacitance extraction algorithms have been shown an efficient and accurate capacitance extraction algorithm. An improved algorithm is also proposed to remove its runtime dependency on the number of conductors by a combination of hierarchical and multipole expansion algorithm. In this paper, we show that with the introduction of hierarchical merging operation and super-node representation, we can achieve linear runtime and accuracy without involving multipole expansion. Experimental results show over 10/spl times/ runtime improvement and 20/spl times/ memory saving over the multipole approaches with comparable accuracy and better numerical stability.