• Proceedings of the International Microelectronics And Packaging Society Conference
• /
• 2002.05a
• /
• pp.138-141
• /
• 2002

There are continuous efforts in the electronics industry to a reduced electronic package size. Reducing the size of electronic packages can be achieved by a variety of means, and for ball grid array(BGA) packages an effective method is to decrease the pitch between the individual balls. Chip scale package(CSP) and BGA are now one of the major package types. However, a reduced package size has the negative effect of reducing board-level reliability. The reliability concern is for the different thermal expansion rates of the two-substrate materials and how that coefficient CTE mismatch creates added stress to the BGA solder joint when thermal cycled. The point of thermal fatigue in a solder joint is an important factor of BGA packages and knowing at how many thermal cycles can be ran before failure in the solder BGA joint is a must for designing a reliable BGA package. Reliability of the package was one of main issues and underfill was required to improve board-level reliability. By filling between die and substrate, the underfill could enhance the reliability of the device. The effect of underfill on various thermomechanical reliability issues in $\mu$BGA packages is studied in this paper.

• Journal of Fashion Business
• /
• v.9 no.5
• /
• pp.152-167
• /
• 2005

This study aims to aid hair fashion design for using hair style change by knowing the hair fashion images' characteristics. To accomplish this purpose, posed a questions to capital area university women students from June 3. 2005. to June 23. 2005. The hair fashion images' characteristics are; (1) avant-garde - unique style of every categories, (2) ethnic - korean style of center part, no volume, down chignon, inactivated texture, (3) romantic pretty - girl like cute style of long, wide wave, wide braid, center part or bang, activated texture, using pin or ribon, (4) elegance - graceful style of down point up style having wave, volume and activated texture, (5) sexy - sexual attractive style of long & wide wave or straight with high volume, activated texture(wet feeling hair styles also possible), (6) sophisticate - refined urban style of inactivated textured graduation and layered straight hair, (7) natural - inartificial style of no volume, inactivated long straight and binding hair, (8) sporty - activated style of activated and inactivated textured short hair.

• Nuclear Engineering and Technology
• /
• v.53 no.2
• /
• pp.647-656
• /
• 2021

Knowing a material's true stress-strain curve is essential for performing a nonlinear finite element analysis to solve an elastoplastic problem. This study presents a simple methodology to determine the true stress-strain curve of type 304 and 316 austenitic stainless steels in the full range of strain from a typical tensile test. Before necking, the true stress and strain values are directly converted from engineering stress and strain data, respectively. After necking, a true stress-strain equation is determined by iteratively conducting finite element analysis using three pieces of information at the necking and the fracture points. The Hockett-Sherby equation is proposed as an optimal stress-strain model in a non-uniform deformation region. The application to the stainless steel under different temperatures and loading conditions verifies that the strain hardening behavior of the material is adequately described by the determined equation, and the estimated engineering stress-strain curves are in good agreement with those of experiments. The presented method is intrinsically simple to use and reduces iterations because it does not require much experimental effort and adopts the approach of determining the stress-strain equation instead of correcting the individual stress at each strain point.

• 제어로봇시스템학회:학술대회논문집
• /
• 1990.10a
• /
• pp.663-668
• /
• 1990

This paper deals with the application of a Generalized Predictive Control (CPC) to a Pressurized Water Reactor (P.W.R) Nuclear Power Plant. Generalized Predictive Control is a sort of Explicit Self-Tuning Control. Current self-tuning algorithms lack robustness to prior choices of either dead-time (input time delay of a plant) or model order. GPC is shown by simulation studies to be superior to accepted self-tuning techniques such as minimum variance and pole-placement from the viewpoint that it is robust to prior choices of dead-time or model order. In this paper a GPC controller is designed to control the P.W.R. nuclear power rlant with varying dead-time and through the designing procedure the designer is free from the constraint of knowing the exact dead-time. The controller is constructed based on the 2nd order linear model approximated in the vicinity of operating point. To ensure that this low-order model describes the complex real dynamics well enough for control purposes, model parameters are updated on-line with a Recursive Least Squares algorithm. Simulation results are successful and show the possibilities of the GPC control application to actual plants with varying or unknown dead-time.

• Journal of the Korea Institute of Building Construction
• /
• v.10 no.5
• /
• pp.69-74
• /
• 2010

It is the law that injured workers must be paid compensation through occupational health and safety insurance. But sometimes, construction companies cover the compensation for an accident by themselves in order to conceal the fact of an accident. The reason for this concealment is that they wish to get a high mark in PQ. From the point of view of a subcontractor, another reason is to avoid any negative consequences in bids. According to interviewees, some workers, knowing the vulnerability of their employers in this area, demand unreasonable levels of compensation. This study examined the circumstances, influences and participants' perception of accidents on construction sites.

• International conference on construction engineering and project management
• /
• 2022.06a
• /
• pp.686-693
• /
• 2022

Construction is a collaborative endeavor. The complexity in delivering construction projects successfully is impacted by the effective collaboration needs of a multitude of stakeholders throughout the project life-cycle. Technologies such as Building Information Modelling and relational project delivery approaches such as Alliancing and Integrated Project Delivery have developed to address this conundrum. However, with the onset of the pandemic, the digital economy has surged world-wide and advances in technology such as in the areas of machine learning (ML) and Artificial Intelligence (AI) have grown deep roots across specializations and domains to the point of matching its capabilities to the human mind. Several recent studies have both explored the role of AI in the construction process and highlighted its benefits. In contrast, literature in the organization studies field has highlighted the fear that tasks currently done by humans will be done by AI in future. Motivated by these insights and with the understanding that construction is a labour intensive sector where knowledge is both fragmented and predominantly tacit in nature, this paper explores the integration of AI in construction processes across project phases from planning, scheduling, execution and maintenance operations using literary evidence and experiential insights. The findings show that AI can complement human skills rather than provide a substitute for them. This preliminary study is expected to be a stepping stone for further research and implementation in practice.

• Journal of Communications and Networks
• /
• v.6 no.4
• /
• pp.352-361
• /
• 2004

In this paper, we study how to achieve the maximum capacity under delay constraints for large mobile wireless networks. We develop a systematic methodology for studying this problem in the asymptotic region when the number of nodes n in the network is large. We first identify a number of key parameters for a large class of scheduling schemes, and investigate the inherent tradeoffs among the capacity, the delay, and these scheduling parameters. Based on these inherent tradeoffs, we are able to compute the upper bound on the maximum per-node capacity of a large mobile wireless network under given delay constraints. Further, in the process of proving the upper bound, we are able to identify the optimal values of the key scheduling parameters. Knowing these optimal values, we can then develop scheduling schemes that achieve the upper bound up to some logarithmic factor, which suggests that our upper bound is fairly tight. We have applied this methodology to both the i.i.d. mobility model and the random way-point mobility model. In both cases, our methodology allows us to develop new scheduling schemes that can achieve larger capacity than previous proposals under the same delay constraints. In particular, for the i.i.d. mobility model, our scheme can achieve (n-1/3/log3/2 n) per-node capacity with constant delay. This demonstrates that, under the i.i.d. mobility model, mobility increases the capacity even with constant delays. Our methodology can also be extended to incorporate additional scheduling constraints.

• English Language & Literature Teaching
• /
• v.11 no.1
• /
• pp.225-243
• /
• 2005

Korean students in English novel class read presentable papers about a novel, but if asked about some parts of the novel, they are helpless. How do they know the whole novel without knowing its parts? Because most Korean students cannot read through an English novel in a short time, they are awfully pressed with preparation for papers to be presented in the class. That makes their papers composed entirely of appropriated ideas from references. Being conscious of students' inability to read through a novel, some teachers select and read only some important parts or chapters of the novel. That makes students take a novel not as literary art, but as a prose work for abstract ideas. In order to solve the problem, I propose chapter analysis. Attentive reading new critics applied to poetry and short story is applicable to the chapter of a novel. Because no critic or scholar analyzes a novel chapter by chapter in his/her articles or books, students cannot wholly mosaic their papers with ideas from references. Chapter analysis will enable Korean students to interpret a novel with their own view point. This paper includes such sections as the theoretical background of fictional chapters, some items to be considered for chapter analysis in the class, and examples of analysis of a short story and two chapters from a novel.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.16 no.1
• /
• pp.177-182
• /
• 2016

Geofence is a generic concept for describing geographic aspects of PoI(Point of Interest) enabling users to proactively induce context-based actions. However there is no need to maintain continuity when you reflect geofence in case of temporary events, accidents and isolation. Therefore we propose a geofence platform so-called TemG by adding time-limited information to support PoI. The proposed geofence platform TemG ensures the persistency and continuity of geofence. Furthermore, the proposed TemG can not only provide to automatically activate or deactivate the specified geofence during a period of timestamp but also support to the basic context-aware service knowing in/out in the zone. In the near future, the proposed TemG will be need to extend HPS(Hybrid Positioning System) for IoT(Internet of Things).

• Advances in aircraft and spacecraft science
• /
• v.9 no.5
• /
• pp.449-462
• /
• 2022

Space-telescopes placed in the Sun-Earth second Lagrange point (L2) observe the sky following a scan strategy that is usually based on a spin-precession motion. Knowing which regions of the sky will be more observed by the instrument is important for the science operations and the instrument calibration. Computing sky observation parameters numerically (discretizing time and the sky) can consume large amounts of time and computational resources, especially when high resolution isrequired.This problem becomesmore critical if quantities are evaluated at detector level instead of considering the instrument entire Field of View (FoV). In previous studies, the authors have derived analytic solutions for quantities that characterize the observation of each point in the sky in terms of observation time according to the scan strategy parameters and the instrument FoV. Analytic solutions allow to obtain results faster than using numerical methods as well as capture detailed characteristics which can be overseen due to discretization limitations. The original approach is based on the analytic expression of the instrument trace over the sky. Such equations are implicit and thusrequiresthe use of numeric solversto compute the quantities.In this work, a new and simpler approach for computing one ofsuch quantities(mean observation time) is presented.The quantity is first computed for pure spin motion and then the effect of the spin axis precession is incorporated under the assumption that the precession motion is slow compared to the spin motion.In this sense, this new approach further simplifies the analytic approach, sparing the use of numeric solvers, which reduces the complexity of the implementation and the computing time.