There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

Machine Learning is the study of methods for programming computers to learn. Computers are applied to a wide range of tasks, and for most of these it is relatively easy for programmers to design and implement the necessary software. However, there are many tasks for which this is difficult or impossible. These can be divided into four general categories. First, there are problems for which there exist no human experts. For example, in modern automated manufacturing facilities, there is a need to predict machine failures before they occur by analyzing sensor readings. Because the machines are new, there are no human experts who can be interviewed by a programmer to provide the knowledge necessary to build a computer system. A machine learning system can study recorded data and subsequent machine failures and learn prediction rules. Second, there are problems where human experts exist, but where they are unable to explain their expertise. This is the case in many perceptual tasks, such as speech recognition, hand-writing recognition, and natural language understanding. Virtually all humans exhibit expert-level abilities on these tasks, but none of them can describe the detailed steps that they follow as they perform them. Fortunately, humans can provide machines with examples of the inputs and correct outputs for these tasks, so machine learning algorithms can learn to map the inputs to the outputs. Third, there are problems where phenomena are changing rapidly. In finance, for example, people would like to predict the future behavior of the stock market, of consumer purchases, or of exchange rates. These behaviors change frequently, so that even if a programmer could construct a good predictive computer program, it would need to be rewritten frequently. A learning program can relieve the programmer of this burden by constantly modifying and tuning a set of learned prediction rules. Fourth, there are applications that need to be customized for each computer user separately. Consider, for example, a program to filter unwanted electronic mail messages. Different users will need different filters. It is unreasonable to expect each user to program his or her own rules, and it is infeasible to provide every user with a software engineer to keep the rules up-to-date. A machine learning system can learn which mail messages the user rejects and maintain the filtering rules automatically. Machine learning addresses many of the same research questions as the fields of statistics, data mining, and psychology, but with differences of emphasis. Statistics focuses on understanding the phenomena that have generated the data, often with the goal of testing different hypotheses about those phenomena. Data mining seeks to find patterns in the data that are understandable by people. Psychological studies of human learning aspire to understand the mechanisms underlying the various learning behaviors exhibited by people (concept learning, skill acquisition, strategy change, etc.).

Machine learning

Additive manufacturing of metallic components – Process, structure and properties

The objective of this program was to seek improved process control and weldment reliability during laser welding of automotive aluminum alloys while retaining the high speed and accuracy of the laser beam welding process. The effects of various welding variables on the loss of alloying elements and the formation of porosity and other geometric weld defects such as underfill and overfill were studied both experimentally and theoretically.

/pdf/laser-welding-of-automotive-aluminum-alloys-to-achieve-1f39ht90no.pdf

Laser welding of automotive aluminum alloys to achieve defect-free, structurally sound and reliable welds

The ultimate goal of welding technology is to improve the joint integrity and increase productivity. Over the years, welding has been more of an art than a science, but in the last few decades major advances have taken place in welding science and technology. With the development of new methodologies at the crossroads of basic and applied sciences, enormous opportunities and potential exist to develop a science-based tailoring of composition, structure, and properties of welds with intelligent control and automation of the welding processes.

Advances in welding science - a perspective

It was during a pleasant evening stroll through the estates of Schloss Segau in Graz, Austria, that we decided to create a journal with the intention of providing a rigorous and efficient mechanism for the dissemination of knowledge on all aspects of joining. The occasion was the 1995 meeting on the mathematical modelling of weld phenomena. It did not take us long to act on this following our journeys home. The birth of the new journal was straightforward. The first issue was published in 1996 under the auspices of the then Institute of Materials in London. There were the usual growing pains which are best forgotten, but persistence, not to mention the unquestioning faith of the Institute, paid off. The community now has what is certainly the leading journal in the subject, but also one which can hold its own against the long established tomes in the general field of materials science. This recognition is a credit to all the authors who have contributed over the years; to the Institute and to Maney Publishing for maintaining the highest standards of production and language; and to the Editorial Board and referees for their supervision of this venture. We recently reached a tally of one thousand publications and took the opportunity to celebrate – by inviting articles which are less constrained, and which may include informed speculation and some notions of the future directions of the subject. Those who were able to meet the deadlines form this special issue and we express our unreserved gratitude to them. Those who escaped are still in our minds for future projects! We will sing some further praises of the journal later, but first a taste of the contents of this issue. The monumental success of the friction stir welding process makes it fitting, once again, to refer to the original work which also stimulated academic research with some 3000 papers published on this topic over the last decade. We are pleased to report that according to the databases, STWJ is the journal of choice for the publication of these papers. The stirring process involves severe deformation and we know in other fields that such trauma leads to rotations of crystals and the development of texture. Fonda reviews this subject in the context of stir welding, for all of the prominent crystal structures of metals, with the surprising finding that there are common features irrespective of the lattice type. One wonders whether the consequences of the shared features are different for the lower symmetry crystal structures. It is now becoming increasingly clear that in some cases, friction stir welding is associated with the formation of liquid films. The problem is acute in alloys containing low melting point phases or when readily melting phases form by mixing of the alloys being welded. Gerlich, in his paper studies the relationship between this phenomenon and defect formation, to reach the conclusion that it will be necessary in some cases to limit the welding speed in order to avoid damage. It is often said that the whole is greater than the sum of its parts. The benefits of combining an arc and a laser process are extolled in the paper from Missouri University, and it is implied that the creation of a united mathematical model may lead to a better optimisation of the process. The problem is in essence similar to that stated by Babu, that existing models are far from ‘full solutions’. The general area of hybrid welding is active, including innovative permutations, for example, electrical resistance heating combined with friction stir welding; simultaneous welding and brazing; exotic methods such as HyDRA (involving double arcs) and LUPuS (laser submerged arc welding). The paper by Phanikumar et al. focuses on the modelling of dissimilar material joining and describes, for example, the challenges associated with the modelling of a hybrid laser welding–brazing method. Mathematical models are sometimes incorrectly seen to be the panacea for the future of weld design. They often are not, but nevertheless can dramatically reduce the volume of work, and hence the resources needed for development, and can yield insight into new phenomena. Babu emphasises another aspect, that the complexity of the phenomena that welders routinely have to face, means that generic solutions (models) are difficult. Indeed, as he points out, there are domains of solutions rather than unique solutions for particular requirements, making it necessary to choose. A classic multiobjective optimisation problem where any solution along the Pareto front is optimal and one has to use another convenient criterion to pick a particular one. In a fascinating paper, Hattel looks at optimisation from a different point of view. Not only should we seek to use sophisticated models with autonomous optimisation in the context of multiple objectives, but should also seek robust solutions. By this he means solutions which remain feasible in spite of some variations in the design parameter; after all, most manufacturing processes have tolerances specified. Of course, Hattel’s paper contains much more than this, a vivid discussion of friction stir weld modelling and future challenges. A critical component of friction stir welding is the tool material Oak Ridge National Laboratory, Oak Ridge, TN 37831-6095, USA Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, UK

https://www.tandfonline.com/doi/pdf/10.1179/136217111X13026027995995

1000 gems: celebration of STWJ

Additive manufacturing is a process of manufacturing that creates a three-dimensional object by progressively depositing thin layers of material guided by a digital drawing. The creation of metallic objects using this technology is one of the fastest growing implementations, although other materials such as concrete, ceramics and polymers are also amenable to this manufacturing process, enabling applications that might not otherwise have been possible. Stainless steels, aluminium, titanium and nickel alloys in the form of powders or wires are melted by heating with a high-energy source such as a laser beam, electron beam or an electric arc. Metal printing is now used in aerospace, consumer products, health care, energy, automotive, marine and other industries because in cases where it has advantages over conventional methods. Here we examine the key processes and principles for printing metallic parts, their unique features, and review how their microstructure and properties develop. There are major challenges that need to be addressed for its continued expansion, requiring imagination and ingenuity to drive the future of metal printing.

Tarasankar Debroy

Papers

Laser welding of automotive aluminum alloys to achieve defect-free, structurally sound and reliable welds

Advances in welding science - a perspective

1000 gems: celebration of STWJ

Picture to Parts, One Thin Metal Layer at a Time