Showing papers by "Hanyang University published in 1995"

Scheduling algorithm of data sampling times in the integrated communication and control systems

Abstract: Integrated communication and control systems (ICCS) consist of several distributed control processes which share a network medium. Performance of several feedback control loops in the ICCS is subject to the network-induced delays from sensor to controller and from controller to actuator. The network-induced delays are directly dependent upon the data sampling times of the control components which share a network medium. In this study, a scheduling algorithm of determining data sampling times is developed using the window concept, where the sampled data from the control components in the ICCS share a limited number of windows, so that the performance requirement of each control loop is satisfied as well as the utilization of network resources is considerably increased. The scheduling algorithm is verified by discrete-event/continuous-time simulation model of an example of ICCS. >

Dietary factors and stomach cancer: a case-control study in Korea.

Abstract: Background. Stomach cancer is the most common cancer among Koreans. There is wide agreement that dietary factors are important in gastric carcinogenesis, but the role of many Korean food items remains unknown. Methods. A case-control investigation involving 213 incident cases of histologically confirmed stomach cancer and an equal number of controls, matched by age (within 2 years) and sex, was conducted from June 1990 to October 1991. Results. An increased risk of stomach cancer was noted among those with high consumption of stewed foods such as soybean paste stew and hot pepper-soybean stew, broiled fish, and those who liked salty food. However, mung bean pancake, tofu (soybean curd), cabbage, spinach, and sesame oil decreased the risk of stomach cancer. Stratified analysis by sall in combined foods, such as stewed foods and pickled vegetables, disclosed salt as being an important risk factor. Analysis of cooking methods showed that broiling and salting increased the risk of stomach cancer, but that frying tended to decrease the risk. These results suggest that the cooking method might modify the gastric carcinogenicity of foods. As non-dietary factors, smoking and a family history of stomach cancer increased the risk, but use of a refrigerator decreased the risk of cancer. Conclusions. Heavy salt consumption and cooking methods like broiling and salting seem to play a major role in gastric carcinogenesis among Koreans

Numerical Simulations of the 1960 Chilean Tsunami Propagation and Inundation at Hilo, Hawaii

Abstract: An explicit staggered leap-frog finite difference model is used to simulate the transoceanic propagation of the 1960 Chilean tsunami and the associated inundation at Hilo, Hawaii. In computing the transoceanic tsunami propagation, linear shallow water equations with Coriolis force are solved. However, spatial grid sizes and time step sizes are chosen in such a way that the numerical dispersion introduced by the leap-frog finite difference scheme is almost the same as the frequency dispersion in the linear Boussinesq equations. Because the grid size and the time step depend on the local depth, a nested multiple-grid system is developed for the numerical model.

Bursting, spiking, chaos, fractals, and universality in biological rhythms

Abstract: Biological systems offer many interesting examples of oscillations, chaos, and bifurcations. Oscillations in biology arise because most cellular processes contain feedbacks that are appropriate for generating rhythms. These rhythms are essential for regulating cellular function. In this tutorial review, we treat two interesting nonlinear dynamic processes in biology that give rise to bursting, spiking, chaos, and fractals: endogenous electrical activity of excitable cells and Ca2+ releases from the Ca2+ stores in nonexcitable cells induced by hormones and neurotransmitters. We will first show that each of these complex processes can be described by a simple, yet elegant, mathematical model. We then show how to utilize bifurcation analyses to gain a deeper insight into the mechanisms involved in the neuronal and cellular oscillations. With the bifurcating diagrams, we explain how spiking can be transformed to bursting via a complex type of dynamic structure when the key parameter in the model varies. Understanding how this parameter would affect the bifurcation structure is important in predicting and controlling abnormal biological rhythms. Although we describe two very different dynamic processes in biological rhythms, we will show that there is universality in their bifurcation structures.

Notched Strength and Fracture Criterion in Fabric Composite Plates Containing a Circular Hole

Abstract: The effects of the hole size and the specimen width on the fracture behavior of several woven fabric composite plates are experimentally investigated in tension. It is shown in this paper that the characteristic length (do) in the Point Stress Criterion (PSC) depends on the hole size and the specimen width. A modified PSC for predicting the notched strength is proposed. An excellent agreement is found between the experimental results and the analytical predictions using the modified PSC. When the unstable fracture occurred, the equivalent critical crack length (ac) corresponding to the damage zone size is about twice the characteristic length. The characteristic length decreases with an increase in the notched strength. The critical energy release rate (Gc) corresponding to the unstable fracture criterion is independent of the hole size for the same specimen width. Gc increases with an increase in the specimen width. These results can be explained by the correlation between the Gc and the notch sensitivit...

Factorization and polarization in linearized gravity.

Abstract: We investigate all the four-body graviton interaction processes: gX\ensuremath{\rightarrow}\ensuremath{\gamma}X, gX\ensuremath{\rightarrow}gX, and gg\ensuremath{\rightarrow}gg with X as an elementary particle of spin less than 2 in the context of linearized gravity except the spin-3/2 case. We show explicitly that gravitational gauge invariance and Lorentz invariance cause every four-body graviton scattering amplitude to be factorized. We explore the implications of this factorization property by investigating polarization effects through the covariant density matrix formalism in each four-body graviton scattering process.

Implantation: Leukaemia inhibitory factor in human endometrium during the menstrual cycle: cellular origin and action on production of glandular epithelial cell prostaglandin in vitro

Abstract: Leukaemia inhibitory factor (LIF) is a pleiotrophic cytokine which plays an obligatory role in mouse implantation. To investigate its potential role in the regulation of uterine function in the human, LIF secretion by isolated human endometrial glandular epithelial and stromal cells in primary culture was determined. Endometrial cells secreted a detectable amount of LIF protein during the first 48 h of culture. In the follicular and late-luteal phases, LIF secretion by both cell types was low. At every stage of the menstrual cycle, the epithelial cells secreted significantly more LIF than did stromal cells. Glandular epithelial cells of the mid-luteal phase, at the expected time of implantation in the human, secreted significantly more LIF than at other stages of the cycle. Stromal cells showed a similar, but nonsignificant, LIF secretion pattern. It could be concluded that endometrial LIF expression was dependent on cell type and stage of the menstrual cycle, and might thus play a role in human implantation. Oestradiol-17 beta stimulated both prostaglandin (PG) F and E release by the epithelial cells in both follicular and luteal phases. PGE release during the luteal phase was greater than in the follicular phase. However, addition of recombinant human LIF did not change either PGF or PGE release in either follicular or luteal phases, in the presence or absence of oestradiol.

Adaptive Huffman coding of 2-D DCT coefficients for image sequence compression

Abstract: This paper presents a new approach to adaptive Huffman coding of 2-D DCT coefficients for image sequence compression. Based on the popular motion-compensated interframe coding, the proposed method employs self-switching multiple Huffman codebooks for entropy coding of quantized transform coefficients. Unlike the existing multiple codebook approaches where the type of block (intra/inter or luminance/chrominance) selects a codebook, the proposed method jointly utilizes the type of block, the quantizer step size, and the zigzag scan position for the purpose of codebook selection. In addition, as another utilization of the quantizer step size and the scan position, the proposed method uses a variable-length “Escape” sequence for encoding rare symbols. Experimental results show that the proposed method with two codebooks provides 0.1–0.4 dB improvement over the single-codebook scheme and this margin turns out to be substantially larger than that the MPEG-2, two-codebook approach has over the single-codebook approach.

Representing the Voronoi diagram of a simple polygon using rational quadratic Bézier curves

Abstract: The Voronoi diagram of a set of geometric entities on a plane, such as points, line segments, or arcs, is a collection of Voronoi polygons associated with each entity, where the Voronoi polygon of an entity is a set of points which are closer to the associated entity than any other entity. A Voronoi diagram is one of the most fundamental geometrical constructs, and it is well known for its theoretical elegance and the wealth of applications. Various geometric problems can be solved with the aid of Voronoi diagrams. The paper discusses an algorithm to construct the Voronoi diagram of the interior of a simple polygon which consists of simple curves such as line segments as well as arcs in a plane with O(N log N) time complexity by the use of a divide-and-conquer scheme. Particular emphasis is placed on the parameterization of bisectors using a rational quadratic Bezier curve representation which unifies four different bisector cases.

Inertia identification for the speed observer of the low speed control of induction machines

Abstract: This paper presents a control method for induction machines in a low speed range with an instantaneous speed observer and inertia identification. When a low resolution incremental-type encoder is used for the speed detection, only the average speed in the interval of the encoder pulses is observed, and it usually makes the speed controller unstable at the very low speed range. This paper, therefore, proposes a low speed control method with a speed observer which is implemented by the disturbance observer using a low precision shaft encoder. Furthermore, to improve the performance of the speed controller, the authors perform the identification of the inertia which is estimated by the periodic test signal. They show that this proposed method is superior to the conventional method by comparing simulation and experimental results.

Lower Bounding Procedures for Multiperiod Telecommunications Network Expansion Problems

Abstract: This paper suggests an improved formulation for the multiperiod network topology and capacity expansion problem and proposes new lower bounding schemes based on it. It differs from earlier formulations and solution methods in that entirely new and different subproblems are solved and a number of lower bound tightening schemes are added within the framework of a Lagrangian relaxation. Dual ascent and multiplier adjustment procedures are suggested for the Lagrange multiplier updating procedure. Computational results are reported to demonstrate the tightness of the bounds generated by the suggested procedures. Heuristics based on converting the dual information obtained from the Lagrangian procedure into primal feasible solutions are tested. The tests show that the Lagrangian-based heuristics generate solutions superior to solutions generated by other heuristics proposed in the literature.

Effect of grain size and mechanical processing on the dielectric properties of BaTiO3

Abstract: Dielectric properties of polycrystalline BaTiO3 ceramics having grain sizes of 1 to 40 μm have been studied. Fine-grained ceramic BaTiO3 of 1 μm average grain size has 90°domains and has shown higher dielectric constant, lower ferroelectric transition temperature (Tc), and lower transition energy than coarser-grained material. 90°domain switching was preferentially produced in the fine-grained BaTiO3 as a result of abrasion. For the fine-grained BaTiO3, the dielectric constant decreased with one-dimensional pressure, whereas, for the coarse-grained material, the dielectric constant increased before decreasing with the pressure. The one-dimensional pressure resulted in increased Tc of both the fine- and coarse-grained BaTiO3, with the effect being the greatest for the coarse-grained material. The relationship between these results and internal stress, and the effect of external pressure imposed on internally stressed lattice, were discussed.

Observer-Based Identification of Nonlinear System Parameters

Abstract: This paper deals with an observer-based nonlinear system parameter identification method utilizing repetitive excitation. Although methods for physical parameter identification of both linear and nonlinear systems are already available, they are not attractive from a practical point of view since the methods assume that all the system, x, and the system input are available. The proposed method is based on a sliding observer and a least-square method. A sufficient condition for the convergence of the parameter estimates is provided in the case of Lipschitz nonlinear second-order systems. The observer is used to estimate signals which are difficult or expensive to measure. Using the estimated states of the system with repetitive excitation, the parameter estimates are obtained. The observer based identification method has been tested on a half car simulation and used to identify the parameters ofa halfcar suspension test rig. The estimates of nonlinear damping coefficients of a vehicle suspension, suspension stiffness, pitch moment inertia, equivalent sprung mass, and unsprung mass are obtained by the proposed method. Simulation and experimental results show that the identifier estimates the vehicle parameters accurately. The proposed identifier will be useful for parameter identification of actual vehicles since vehicle parameters can be identified only using vehicle excitation tests rather than component testing.

Refractive index and loss changes produced by current injection in InGaAs(P)-InGaAsP multiple quantum-well (MQW) waveguides

Abstract: We have theoretically estimated the carrier-induced changes in the refractive index /spl delta/n and the optical loss /spl delta//spl alpha/ produced by the injection of free carriers in InGaAs(P)-InP multiple quantum-well (MQW) optical waveguides. MQW structures are specially designed for the tuning layer in carrier injection type tunable laser diodes, such as tunable twin-guide laser diode (TTG-LD), at the lasing wavelength /spl lambda/ of 1.55 /spl mu/m. Anomalous dispersion and plasma effect for /spl delta/n and IVBA (intervalance band absorption) for /spl delta//spl alpha/ were included. A valance-band mixing, an overlap integral of electron-hole, and confinement factors of carriers in the well were considered to include quantum-size effect of carriers in /spl delta/n and /spl delta//spl alpha/. Predictions of /spl delta/n are in reasonably good agreement with the experimental results. Systematic analysis shows that the following InGaAs(P)(well)-InGaAsP (barrier) MQW structures ace promising in order to obtain a large /spl delta/nat a given injection current density J: 1) well materials: InGaAsP alloy with its bulk bandgap wavelength of around 1.55 /spl mu/m, 2) barrier materials: InGaAsP alloy with its bulk bandgap wavelength of around 1.4 /spl mu/m, 3) as many as possible number of wells, typically about 15./spl delta//spl alpha/ is also estimated by calculating the carrier distributions in MQW structures and by fitting experimental data of bulk and MQW waveguides. The maximum well number is limited by the increase of optical loss. According to these results, we have found that 1.55-/spl mu/m InGaAsP (well 1.8-nm thick)/1.40 /spl mu/m InGaAsP (barrier 14-nm thick) MQW, with the well number of around 15, will be the optimum tuning layer structure for 1.55-/spl mu/m band tunable LD's. Over 10 nm continuous tuning range, with moderate output power, is expected for TTG-LD's. >

A broadband ring network: multichannel optical slotted ring

Abstract: This paper presents a multichannel optical ring network for broadband integrated services. The network uses a multichannel architecture with wavelength division multiplexing (WDM) and photonic packet switching devices for its access mechanism. The electronic speed bottleneck is removed out of the ring, which allows utilization of the full bandwidth for the optical fiber transmission medium. For compatibility with B-ISDN, the network uses a similar cell structure to that of an ATM based cell with a slotted ring concept. Fiber optic delay line matched filters are used as a means of address detection at the destination nodes. The network architecture is described and a design of the optical switching node is presented. A novel technique is devised in order to measure the average transfer delay of a cell in the multichannel slotted ring network. The analytical results show an excellent agreement with simulation results over a broad range of parameters. The results show that the major part of the cell transfer delay is coming from the propagation delay from a source to a destination. It is also observed that the throughput characteristic of the network depends upon the aggregated transmission capacity of the network.

Minima of the orientation phenomena for direct s-p electron-ion excitations in dense plasmas.

Abstract: Close-encounter effects on electron-ion s\ensuremath{\rightarrow}p oriented excitations in dense plasmas are investigated using a first-order semiclassical straight-line trajectory method. Plasma-screened interaction potential is given by the classical nonspherical Debye-H\"uckel model. Without using the dipole approximation, the transition probabilities and orientation parameters are obtained, for various Debye lengths and projectile energies. Including the plasma-screening effects, the transition probabilities are increased for 1s\ensuremath{\rightarrow}2${\mathit{p}}_{+1}$ transitions and decreased for 1s\ensuremath{\rightarrow}2${\mathit{p}}_{\mathrm{\ensuremath{-}}1}$ transitions. The close-encounter effects appreciably change the transition probabilities and orientation parameters for small impact parameters. It is found that the 1s\ensuremath{\rightarrow}2${\mathit{p}}_{+1}$ transition probabilities and orientation parameters have minima that correspond to the complete 1s\ensuremath{\rightarrow}2${\mathit{p}}_{\mathrm{\ensuremath{-}}1}$ transitions.

Bilateral renal cortical necrosis with the changes in clinical features over the past 15 years (1980-1995).

Abstract: A rare case of bilateral renal cortical necrosis (BRCN) diagnosed only by the characteristic and specific findings of a contrast-enhanced CT scan during the acute initial phase of the disease is presented in this paper. Furthermore, twenty-eight patients of BRCN in the world literatures in English after 1980 were analyzed to investigate the changes in its clinical features over the past 15 years in comparison with the reported data before 1980 from two large centers in France (F) and India (I). Obstetric causes decreased from 68% (F) and 71% (I) before 1980 to 28% after 1980, whereas nonobstetric causes increased from 32% (F) and 29% (I) to 72% after 1980. Among the nonobstetric causes of BRCN, the leading causes were sepsis in 4 out of 12 patients (F) and snake bite in 6 out of 14 patients (I) before 1980, but, in contrast, drugs in 4 out of 21 patients after 1980. As a definite diagnostic procedure for BRCN, 95 to 100% before 1980 but 86% after 1980 performed renal biopsy, of which renal biopsy while living was done in only 42% (F) and 16% (I) before 1980 and 67% after 1980. None showed renal calcification in abdominal X-ray, and only 25% (3/12) had nonspecific echo findings in renal ultrasonography, whereas the high sensitivity for BRCN was noted in renal arteriography in 100% (6/6) and contrast-enhanced CT scan in 88% (7/8). The mortality of BRCN decreased from 55% (F) and 86% (I) before 1980 to 36% after 1980. This review of BRCN, in conclusion, revealed the distinctive changes over the past 15 years in the etiology with a higher incidence of non-obstetric causes than obstetric ones, diagnostic procedures with less dependence on renal biopsy but new trials of non-invasive radioimagings including CT scan and even MRI, and a further declining mortality rate.