Back-of-the-envelope Research Articles

Back-of-the-Envelope Physics, by Clifford Swartz

<i>Back-of-the-Envelope Physics,</i> by Clifford Swartz

More Perks of Industrial Physics

Like Arthur Jensen, whose letter appeared in the December 2003 issue of Physics Today Physics Today 0031-9228 56 12 2003 19 https://doi.org/10.1063/1.1650213. (page 19) , I also had very positive experiences as a physicist working in industry. Experimental physicists should be very much at home there, addressing such projects as designing new equipment for special analytical techniques, solving an everyday commercial problem, or explaining a fundamental science question. My job was not work; it was a playground where I could make up many of the rules.My colleagues and I were designing static SIMS (secondary ion mass spectrometry) equipment before most people had heard of the term. At times I worked in the commercial field, salvaging multimillion-dollar electronic equipment installations after fires, floods, and general contamination events. Another time, a scientific explanation of why copper is such a good material for making general commercial electrical wiring and connections was published on its first submission to Physical Review B. Other projects ranged from single crystal surface analysis in ultrahigh vacuum to seeing what was under the mud on the surface of a circuit board after a flood. If you want to work on a variety of problems, go into industry.The best perk is that I did not usually have to write proposals to obtain funding. Back in the 1970s to 90s, a short walk to management’s office and a “back of the envelope” discussion were sufficient to find time and money to do what I wanted. Money may be harder to come by today, but companies are still interested in learning why things do or do not work.© 2004 American Institute of Physics.

Building Aerodynamics

Building Aerodynamics

MESAF: software for assessing the electromagnetic compatibility of complex systems

The authors describe the development of software for the computation of electromagnetic field strengths in complex systems. The code MESAF (multilevel EMC system analysis framework) offers a different way to approach the analysis of EMC problems, particularly susceptibility. It occupies the intermediate level between ‘back of the envelope’ calculations for simple geometries and the complexity of a full computational electromagnetics solution. It can also encompass the statistical variations found in real product geometries and layouts. Users are expected to be electromagnetic compatibility design engineers working in industry. The software is based on the concept of electromagnetic topology. The user defines the system electromagnetic topology, so precise geometrical details are not required, and the code then automatically generates the network of field ingress paths to a given unit in the system. A link to a transfer function database enables signal levels along these paths to be computed, so the susceptibility of the unit can be assessed. With MESAF it is possible to model the effect of design changes on the system susceptibility and to model products throughout the design cycle, with increasing accuracy as the design evolves.

Metallic structural materials in the nuclear environment: some problems illustrating new methods

The structural components of the nuclear industry are submitted to a number of aggressions, mechanical, chemical and physical (irradiation). As a consequence, the problem of durability and ageing of such structures is a key issue. The understanding of the phenomena involved implies the description and modelling of atomic scale events (irradiation point defects) resulting in fluxes of matter (diffusion under irradiation), in the dynamic evolution of structural defects (dislocation loops, cavities, …), with major consequences on mechanical properties (yield stress, fracture behaviour), with, in addition, phenomena coupled between mechanical behaviour and chemical environment. It is therefore the totality of materials science which is involved in understanding the behaviour of metallic structural materials in the nuclear environment. The aim of the present paper is to illustrate some examples currently under investigation, and some of the new approaches involved in the understanding of mechanical behaviour (a scale transition from the atomic to the macroscopic). The input from large computer simulations as well as the value of simple ‘back of the envelope’ calculations, plus the need for cautious experimental studies will be illustrated. The theme of the ageing of materials, central to this paper, finds applications in many industrial situations. To cite this article: Y. Bréchet, C. R. Physique 3 (2002) 915–922.

Using GPS to Teach More Than Accurate Positions

Undergraduate science majors need practice in critical thinking, quantitative analysis, and judging whether their calculated answers are physically reasonable. We have developed exercises using handheld GPS receivers that expose students to this recent technology and promote larger goals that transcend the simple use of a tool for precision location. Using the GPS to calculate the volume of sand in the dunes at Great Sand Dunes National Monument in Colorado requires traversing the dunes, plotting a topographic profile, calculating the volume of sand traversed, and then extrapolating to estimate the volume in the entire dune field. This exercise serves to reinforce students' abilities to think quantitatively, to make realistic “back of the envelope” assumptions, and to determine whether their final answers make physical sense. Using the GPS to measure the running track at an outdoor track and field stadium requires students to gather data, import the data into a spreadsheet such as Microsoft Excel, plot it and perform an error assessment. This exercise reinforces concepts from statistics, and allows students to estimate the precision of GPS measurements both quantitatively and qualitatively. Together these two exercises promote quantitative analysis in a geologic context.

Molecular structure calculations via path integral simulations: Estimating finite-discretization errors

Path integral simulations are now recognized as a useful tool to determine theoretically the structure of complex molecules at finite temperatures including quantum effects. In addition to statistical errors due to incomplete sampling, also systematic errors are inherent in this procedure because of the finite discretization of the path integral. Here, useful “back of the envelope” estimates to assess the systematic errors of bond-length distribution functions are introduced. These analytical estimates are tested for two small molecules, HD+ and H3+, where quasi-exact benchmark data are available. The accuracy of the formulae is shown to be sufficient in order to allow for a reliable assessment of the quality of the discretization in a given simulation. The estimates will also be applicable in condensed phase path integral simulations, and the basic idea can be generalized to other observables than those presented.

Smart Jet Engines. Case History of a Multidisciplinary Research Program.

Problems of high technological interest increasingly cut across traditional disciplinary boundaries. An integrated multidisciplinary approach not only enables greater reach in attacking such problems, but can also offer opportunities for achieving goals beyond those defined by conventional design constraints. In this lecture we illustrate such a process. The example used, which arises in the context of the development of "smart jet engines", is the dynamic control of aerodynamic instabilities in gas turbine compression systems. The lecture shows:1)the progression of technology and basic understanding of phenomena from the initial "back of the envelope calculation" stage through increasingly complex models, experiments, and physical situations, and 2)the interaction between disciplines which was necessary for program success.

Spreadsheet Aided System Engineering and Optimization

ABSTRACTThe Excel™ spreadsheet has become a valuable, powerful engineering tool that now provides strategic capabilities to: create graphical user interfaces (GUIs) command other languages like FORTRAN and C through Dynamic Link Libraries (DLLs) control an integrated object oriented programming language called Visual Basic Applications (VBA) command databasesThe GUI capability of Excel allows the system engineer to create windows like applications (icon driven) with minimum effort. This GUI capability enhances system information presentation and provides the means to manage system information flow efficiently. Excel allows a design team to redefine the “back of the envelope calculation.” This is accomplished by interfacing with other languages such as FORTRAN and C, its own programming language VBA, and an optimization tool called Solver. With the modular, platform nature of Excel, engineers can now apply the system engineering process and develop unique applications devoted to their project team needs.

Technological Innovation and the Great Depression by Rick Szostak

776 Book Reviews TECHNOLOGY AND CULTURE TechnologicalInnovation and the GreatDepression. By Rick Szostak. Boul­ der, Colo.: Westview Press, 1995. Pp. xii+366; tables, notes, bibli­ ography, index. $65.00 (cloth). This densely written book offers a technological explanation for the origins and duration ofthe Great Depression. Stated simply, eco­ nomic growth depends upon exploitation of technological innova­ tion, but “[w]ith the exception of the electric refrigerator—where sales expanded steadily through the 1930s—there was quite simply a dearth of new product technology in 1929” (p. 4). Had the innova­ tions of the late thirties—for example, television, the modern air­ plane, vitamins, and synthetic fibers—been developed a decade ear­ lier, the sickening fall in consumption and investment that characterized the Great Depression would have been moderated and recovery launched much sooner. While this explanation is not entirely new—the emphasis upon innovation draws heavily from Joseph Schumpeter and upon structural shifts, from Michael Bern­ stein—it will no doubt face hostile fire from economists and histori­ ans of technology. Experts will challenge both the author’s broad sweep and his inability to rigorously test his model. But they shouldn’t dismiss the argument out of hand. Part one sets up the argument. Advances in three areas, electric power, the internal combustion engine, and chemical knowledge, dominated 20th-century technology. The first phase of innovation based upon this triad peaked in the 1920s. By 1929, if not sooner, markets for automobiles, radios, housing, textiles, and the like were saturated. Consumers cut back on their purchases, fueling what economists label an autonomous decline in consumption. Seeing little prospect for profit, investors curtailed their spending as well. With demand drooping, firms began to lay off workers. Many of these workers could not find other employment, since there were few if any new industries to take up the slack. Indeed, the employ­ ment picture was even worse. Thanks to new processes based upon the electric motor and better machine tools, innovation in the twenties had been intensely laborsaving. Reluctant to lay off good workers, firms entered the depression with excess labor. Unem­ ployment soared as businesses shed these workers as well as those made redundant by the decline in demand. Part two provides the evidence. Here the author adopts a sectoral approach, investigating changes in manufacturing, mining, trans­ port, agriculture, and services. In each of these categories, Szostak examines the pattern of technological change—both process and product, the extent ofmarket saturation, and trends in employment. Since these thumbnail sketches are based upon the secondary litera­ ture, historians of technology will find little that is new or striking. At the end of part two, the author undertakes “back of the envelope” calculations of how much unemployment can be attributed to satu­ TECHNOLOGY AND CULTURE Book Reviews 777 rated markets and technological change. He figures that these two factors explain some three million job losses, “enough that, with a reasonable multiplier, they could account for the entire unemploy­ ment experience of the 1930s” (p. 313). TechnologicalInnovation and the GreatDepression addresses some crit­ ical issues. We do not know why consumption declined so sharply in 1929, nor can we explain why unemployment remained so high in the 1930s. Surely market saturation explains a part of the first and the patterns of technological change a portion of the second. Moreover, Szostak’s insistence upon looking closely at individual in­ dustries rather than economic aggregates promises to improve our understanding of the dynamics of the depression. However, the au­ thor has not shown how we can go about “proving” his argument. As he notes, there is “no statistical means by which the employment and output effects of technology and market saturation can be mea­ sured precisely” (p. 153). But surely there must be better methods than dozens of industry sketches and crude unemployment esti­ mates. One insight he suggests would be a good starting point for linking technological innovation and economic growth: historians of technology and business should investigate closely the process of industrial innovation, particularly as increasingly complex technolo­ gies were promoted in research laboratories. Both the rising expen­ ditures for and the changing mix of research and development may account for much of...

Economic Aspects of Endoscopic Screening for Intestinal Precancerous Conditions

The relationship of costs to effectiveness in endoscopic screening depends on the incidence rate of cancers arising from precancerous lesions, the sensitivity and specificity rates of endoscopic screening, and the effectiveness of timely diagnosis and surgery in preventing death. Because all these parameters, which enter a medical decision analysis, have a relatively large margin of error, it is not possible to resolve the issue whether a screening should be performed based on economic analyses alone. A crude "back of the envelope" comparison of different screening programs suggests that colonoscopy in ulcerative colitis would result in the highest yield and gastroscopy of the gastric stump in the lowest yield.

A Simple "Back of the Envelope" Method for Estimating the Densities and Molecular Volumes of Liquids and Solids

The method described for the estimation of densities and molecular volumes are surprisingly accurate and very simple.

The Cost of Time Off Work in Australia

It is widely accepted in Australia that absenteeism costs Australian employers billions of dollars each year. In part this stems from the view that a large majority of the Australian workforce use their full sick leave entitlement each year, and from crude ‘back of the envelope’ estimates provided by employers and sensationalized in the media. In this article an attempt is made to quantify the costs of absenteeism to Australian industry in a more rigorous manner. In particular, data collected by the Australian Bureau of Statistics is used in conjunction with survey data collected by the author from a sample of both employers and employees. Given a number of assumptions it is concluded that absence from work cost Australian employers just over $7 billion during 1990. 1993 Australian Human Resources Institute (AHRI)

Missile propulsion cost modeling

An approach for parametric propulsion system cost modeling is presented and is illustrated by Cost Estimating Relationships (CERs) for unit production costs of solid propellant booster stages. Due to their relative simplicity, the costs obtained from the CERs represent only first order approximations of booster stage costs. They were developed from cost and technical data of historical propulsion systems available in the open literature. The approach for developing the CERs is outlined and the rationale for the selection of independent parameters is presented. The analysis of the cost data revealed several generic observations and “rules of thumb”. These are given in this paper, since they might prove useful for “back of the envelope” type cost predictions.

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The Back of the Envelope.—<b>5</b> <b>5</b>(8−12), 680 (N), 778 (N), 876 (N), 972 (N), 1066 (N)

Does your hospital need a robot or a management trainer? On advising the health care executive who is interested in innovation, but uncommitted to it.

Executives of small hospitals and home health services have heard that this is the Age of Computers, Telecommunications, Robotics, and Gene Engineering, and they wonder if their organizations might benefit from the high technology and advanced management tools employed by big corporations and "leading edge" hospitals. But they are too tired and busy to greatly expand their technical/managerial expertise, especially since there are so many choices among possible innovations, ranging from robotics to management training, each choice demanding different new expertise, and each requiring an investment of time and energy. We helped several health care executives to identify their options for innovation. We offered a scoring scheme to sort out the innovation options (a simple but effective way to decide what innovation would be "right" for their organization), and a simple, "back of the envelope" tutorial on robotics in health care. The principle is to allow the administrators to make a quick evaluation of the paths they might wish to travel. Our point here is that for every "natural-born" innovator, there must be dozens of interested but uncommitted persons who need some gentle, simple help. To the extent that the diffusion of medical systems depends on a mass market, these fence-sitters must receive help and guidance.

The Back of the Envelope

The Back of the Envelope

An electronic “Back of the Envelope” A simple model for considering financial alternatives

In the course of forecasting and planning, as well as evaluating business alternatives, planners ultimately have to face the overall impact of their decisions on a company's financial profile. Most businesses focus on their balance sheets (capital structure) and several key financial ratios that point up their financial performance and well‐being. Since investment is a significant element of many business decisions, there is usually concern with the cost of capital. Given this, it seemed that a simple model for evaluating the potential importance of business decisions might offer an efficient and consistent way of determining financial outcomes. And since capital structure, financial ratios, and cost of capital don't function independently of each other, this model would need to take account of appropriate linkages.

Calculations and Measurements of the Axially Symmetric Extensional Vibrations of a Circular Disk with a Concentric Hole (A Free-Flooded Ring)

A complete mathematical model of a free-flooded ring transducer must predict the ring's surface velocity distribution when the forces acting on the ring are known. The acoustic radiation from a radially oscillating cylindrical ring is a function of its surface velocity distribution. In particular, the farfield radiation on the axis of the ring is a sensitive function of the difference between the inside and outside radial velocities and the axially directed edge velocity. Accelerometer measurements in air were made on a number of aluminum rings of varying thickness oscillating in axially symmetric extensional vibrations, and the experimental results are compared with the two-dimensional theory of Gustafsson and Kane for high-frequency extensional vibrations of elastic isotropic plates. The results indicate that the theoretical analysis is adequate to predict the surface velocity distribution of a “thick ring.” Comparisons are also made between the theoretical analysis and “back of the envelope” approximations commonly used by transducer engineers for an elastic ring's surface velocity distribution.

The Use of Models in Marketing Timing Decisions

Two cases illustrate the utility of simple models to aid pricing of obsolescent products. Both models yield surprisingly simple, easily implemented decision rules. They demonstrate that “back of the envelope” modeling can still help management decision making.