Benchmarking the Competitiveness of the United States in Mechanical Engineering Basic Research (2007)

To determine the overall position of U.S. basic research in mechanical engineering relative to research performed in other regions or countries, the panel analyzed journals (paper authorship, most-cited journals, and journal articles) and panel-generated virtual congresses, which are described in more detail later in this chapter. The panel used the collective results of all of these data to draw conclusions of the relative research competitiveness of U.S. mechanical engineering. The panel tried to interpret the gathered information objectively, but it also recognized its responsibility to make collective subjective judgments when needed. In addition, certain boundaries were needed to keep the exercise timely and relevant to the broader mechanical engineering community.

The assessment of U.S. mechanical engineering research begins with a look at U.S. contributions to journal articles and most-cited journal articles. This is then followed by the virtual congresses, which were tabulated by the committee based on input from experts in mechanical engineering around the world. Finally, the panel provides leadership assessments for the different areas of mechanical engineering based on the journal and virtual congress data presented earlier in the chapter.

Publishing research results is essential for scientific and technological progress. Thus, looking at the quantity and quality of journal articles being published in the world is an important and largely objective measure of scientific and engineering research leadership. For this analysis, the panel conducted broad literature searches as well as more targeted searches of specific mechanical engineering journals using the Scopus¹ database. Given the broad range of journals in which mechanical engineers publish, and in an effort to assess current trends in the directions of mechanical engineering research, the panel selected the journals as follows:

• Journals with broad coverage of mechanical engineering (e.g., ASME Journal of Applied Mechanics)

• Leading journals for each subarea of mechanical engineering:

  • Area-specific journals in which researchers from various sciences and/or engineering disciplines publish, along with researchers from mechanical engineering., (e.g., Journal of Power Sources)

  • Area-specific journals where mechanical engineering researchers are the primary contributors, e.g. Journal of Fluid Mechanics

The full list of 68 mechanical engineering-related journals considered by the panel, including impact factors² and country of publication, is given in appendix Table C-1. The journals in that list include high profile journals with high impact factors, as well as journals important to subareas of mechanical engineering but that may have low impact factors.

The panel largely focused its analysis of journal publications data on the change in publication rates and citations over roughly the 10 years 1995-2005, with particular attention paid to the change in the percentage of contributions from U.S. researchers.

Examination of the number of articles published annually in the broader scientific literature on a regional basis shows that the profile of scientific activity worldwide has changed dramatically over the 15 years from 1988 to 2003 (Figure 2-1).³ The long-standing scientific dominance of the United States persists, but other areas of the world are closing the gap.⁴ In 1988, the United States was the largest contributor to S&E publications, even when compared to other regions. While the absolute number of U.S. S&E articles grew by 19 percent between 1988 and 2003, the output of articles from Western European nations combined increased by 67 percent and surged past the U.S. total. Dramatic growth was seen for articles from Korea (1,683 percent), China (630 percent), and Taiwan (556 percent). The percentage of articles coming from Asia and the subcontinent as a whole, which include China and India, have almost tripled in going from 4 to 10 percent. The percentage of all S&E articles from U.S. authors dropped from 38 percent to 30 percent between 1988 and 2003.

The panel conducted a literature search of the full catalog of journals in the Scopus database⁵ using the search term “mechanical” in the author affiliation or source title to get a count of numbers of journal articles published for the period1988-2006. Based on these data, the panel found that the trend for the U.S. share of mechanical engineering journal articles is similar to the overall trend for S&E. Table 2-1 shows that the U.S. percentage contribution dropped from 40 percent for 1988 to 20 percent in 2006. In comparison, China’s contribution increased dramatically from 2 percent in 1988 to 23 percent in 2006 (Figure 2-2). In 2006, China published more mechanical engineering articles than the United States, with 9,043 articles, while the United States authored 7,823 articles.

FIGURE 2-2 Comparison of U.S. and China’s percentage share of contributions to overall mechanical engineering journal articles, 1988-2006. SOURCE: Scopus database (http://www.scopus.com/scopus/home.url) search, “mechanical” in source title or author affiliation, and country in author affiliation.

Although the number of articles published by China and the United States are comparable, the journal titles where these two countries publish most of their research are quite different from each other (Table 2-2). Most of the journals in China’s list are Chinese-language journals such at Jixie Gongcheng Xuebao (Chinese Journal of Mechanical Engineering), not indexed in the 2006 Journal Citation Reports^® (JCR). On the other hand, the U.S. journals are U.S. or European based English-language journals with international editorial boards. All but one of the journals in the U.S. list are listed in JCR, and with impact factors of more than 1. China does have a growing number (currently 75) journal titles across various disciplines listed in JCR.

At the same time, U.S. contributions to top international mechanical engineering journals have remained quite steady over the last five years (1999-2005). From a list of 68 journals analyzed (see appendix Table C-2), the average U.S. contribution to mechanical engineering journal articles remained at around 40 percent between 1999 and 2005, with some mechanical engineering areas having significantly higher contributions from U.S. authors. Figure 2-3 (ranked from highest to lowest percentage U.S. contribution) shows the breakdown for journals according to year and area of mechanical engineering.

Journal article citations provide a better gauge of research leadership than numbers of articles. At the same time, counting citations is somewhat limited, since high citation counts often result from important past research results rather than current results. Nevertheless, this information on U.S. contributions to most-cited articles was obtained in two different ways in order to identify contributions to mechanical engineering. First, the Scopus database was used to determine the 50 most-cited articles for the 12 area-representative mechanical engineering journals (appendix table C-2), by year and country authorship. The average of the individual journal results (appendix Table C-3) show that U.S. authors contributed to 40-50 percent of the most-cited articles in these journals for all six years (Figure 2-4).

FIGURE 2-4 Average percentage contribution of most-cited mechanical engineering articles by U.S. authors out of the 50 most-cited mechanical engineering articles.

In a slightly different approach, the Scopus database was used to search for “mechanical” in the author affiliation or source title in all journals indexed for the periods 1987-1991, 1992-1996, 1997-2001, and 2002-2006. The top 100 most-cited articles from these periods were then searched for country of authorship to determine the U.S. contribution. Table 2-3 provides a summary of the results, showing the clear leadership position of the United States with 65 or more out of 100 articles over these times.

The journal titles of the top 100 most-cited articles for each period were also sorted in order to evaluate mechanical engineering area contributions. Journals appearing in the top 100 three or more times are listed in Table 2-4.

Overall, bioengineering, thermal systems and heat transfer, computational, and materials-related journals figure prominently among the lists. As expected, the most recent list for 2002-2006, largely includes nanotechnology, materials, and biologically focused articles in journals such as Acta Materialia (5), Nano Letters (5), and Science (5). However, the journal at the top of the list for this time period, with 6 articles out of the top 100, is the International Journal of Heat and Mass Transfer (all U.S. authored).

In another effort to evaluate the status of U.S. leadership in mechanical engineering, the panel called on an international group of leaders in the field for their qualitative assessment of the areas and subareas of mechanical engineering. This exercise is referred to as the virtual world congress (VWC), and it is based on the experience of past benchmarking panels.⁶ To carry out the exercise, the field of mechanical engineering was divided into 11 major areas—and each area was subdivided into 2-5 subareas. The panel members individually identified 8-10 respected leaders throughout the world in each subarea. The selected organizers (listed in Appendix D) were asked to imagine that they were about to organize a VWC on the subarea topic; then, regardless of travel costs, visa restrictions, or the opinions of their peers, they were asked who would be the 10-20 speakers that must be a part of the imaginary session. A summary of the area results of the VWC (percentage of U.S. speakers chosen by area) presented in Figure 2-5. A detailed tabulation of the VWC results is given in appendix Table D-1. U.S. representation ranges from a high of 80 percent in the area of design and computer-aided design (CAD) to a low of 48 percent in the area of tribology. This is likely influenced by the origin of the VWC organizers (see Figure D-1). Overall about 70 percent of the VWC organizers were from the United States, and as expected, U.S. organizers were biased toward choosing U.S. speakers. U.S. organizers selected an average of 67 percent U.S. speakers, whereas non-U.S. organizers selected an average of 43 percent U.S. speakers. Also, because the VWC representation is largely populated by researchers with well-established reputations resulting from a long career, U.S. domination probably reflects past rather than present leadership.

FIGURE 2-5 Summary of the percentage of U.S. speakers for the 11 areas of mechanical engineering, as determined by virtual world congress organizers.

The panel also qualitatively evaluated the different areas and subareas of mechanical engineering, and made assessments of leadership based on the combined analysis of journal citations and VWC results. U.S. leadership was determined based on the criteria shown in Box 2-1.

Acoustics and dynamics both deal with time-dependent phenomena that are ubiquitous in nature as well as in the designed objects of our technologically based world. Acoustics is the engineering and science of fluid oscillations that lead to perceived sound or noise (if the sound is

unwanted). Dynamics is the study of motion of mechanical objects as they may occur in nature (e.g., birds, trees) or as constructed (e.g., aircraft, automobiles, spacecraft).

To assess the current status of U.S. contributions in acoustics and dynamics, the following representative subareas were examined:

• Nonlinear Phenomena. Current research and (to an increasing extent) practice deal with large or nonlinear motions of very complex systems with many (perhaps millions of) degrees of freedom. Motions at small scales such as nanodevices and phenomena, so-called micro air vehicles, and MEMS devices are now more often the applications of interest.

• Complex Systems. Complex systems that involve a large number of degrees of freedom as may arise in computational models of fluid, structural, and molecular systems. Complex systems also arise due to the interaction of multimedia such as fluids interacting with structures or multiscale systems ranging from quantum to molecular to continuum models.

• Computational Models. Modeling the large variety of nonlinearities that arise in fluids and solids, constructing computationally efficient models of systems with many degrees of freedom, and multiscale modeling of events at the nanoscale are current major research challenges.

• Experimental Methods. Experimentally measuring the acoustic fields and dynamic response of complex nonlinear systems at very large to very small scales is also a major goal of current research.

An average of 50 percent of the 303 VWC speakers selected in the area of acoustics and dynamics were from the United States. In the subareas, there was a 60 percent U.S. contribution in dynamics and a 41 percent U.S. contribution in acoustics.

The U.S. contribution to journal articles and article citations is more mixed. In 2005, the U.S. contribution to most-cited articles in the Journal of Sound and Vibration was 44 percent. The U.S. contribution is greater than 50 percent in U.S.-based ASME and Acoustical Society of America (ASA) journals, but 30 percent or lower in the internationally based Journal of Sound and Vibration and Journal of Fluids and Structures. Between 1999 and 2005, the average percentage U.S. contribution to articles published in acoustics and dynamics journals increased from 34 to 41 percent. Based on the combined analysis of journal citations (30-50 percent U.S.) and VWC data (50 percent U.S.), the United States is among the leaders in acoustics and dynamics basic research.

The field of biomechanics is concerned with motion, deformation, and forces in biological systems. Initially the field of biomechanics developed from contributions by experts trained in fields as diverse as auditory mechanics, cardiovascular mechanics, hemodynamics,

musculoskeletal bioengineering, neuromuscular control and respiratory mechanics, and mechanism of propulsion for animal locomotion (walking, running, flying, and swimming). The first journal specializing in bioengineering appeared in the mid-1960s with the publication of the Journal of Biomechanics in 1965, which was followed by the ASME Journal of Biomechanical Engineering in 1976. Since then, biomechanical engineers have been at the forefront of medical device developments with tremendous clinical implications ranging from heart valves (e.g., the DeBakey-Noon heart pump), to artificial joints and more recent work on functional tissue engineering constructs, as well as pioneering multiscale and hierarchical strategies to connect physiologic function to cellular and molecular mechanisms. The diverse field of biomechanics may be subdivided into the following areas:

• Biomechanics of auditory, cardiovascular, musculoskeletal, and respiratory systems. Involves in vivo, in vitro, and computational studies of the electrical and mechanical function of physiological systems.

• Constitutive modeling of hard and soft tissues. Has to do with the development of physical models that represent tissue-microstructure and related biophysical processes, largely for clinical applications.

• Molecular and cellular biomechanics. Deals with understanding mechanical processes in organisms at the microsopic level, such as mechanosensitivity of bone cells to fluid shear stress.

• Functional tissue engineering. Involves repairing or replacing tissues that provide mechanical physiological properties.

• Biomaterials. Deals with the development of physiologically compatible materials, which are largely used in medical devices and implants.

An average of 75 percent of the 194 VWC speakers in the area of bioengineering and biomechanics came from the United States. These overall results are also consistent with those obtained from the chemical engineering panel,⁷ which had significant overlap of both VWC organizers and speakers with the mechanical engineering panel.

The share of U.S. contributions to journal articles is somewhat different. U.S. contributions to the most-cited articles in Biomaterials ranged from 20 to 40 percent between 1995 and 2005. As shown in Table 2-4, the most-cited mechanical engineering journal articles for the periods shown included a significant number of bioengineering journals—which are largely U.S. authored. Five bioengineering journals that currently have the top five greatest impact factors—Biomaterials, Journal of Orthopaedic Research, Journal of Biomedical Materials Research, Journal of Biomechanics, and Annals of Biomedical Engineering—were examined. In addition, from 1999 to 2005, U.S. authors consistently provided roughly 40 to 45 percent of the content of these journals.

When taken in combination, the overwhelming virtual congress results (75 percent U.S.) and the relatively stable publications rate in the top bioengineering journals (40 percent U.S.),

the United States can be considered the leader in the area of bioengineering and biomechanics basic research.

Computational mechanics is concerned with the use of numerical methods and computer devices to study and predict the behavior of mechanical systems. Computational mechanics is a vital area of mechanical engineering, making possible the analysis, design, and optimization of systems at a level of sophistication not attainable by other means. At present, a large list of vital new technologies is on the horizon that will rely on advances in computational mechanics. These include new computational paradigms for nanomanufacturing design of new materials, patient-specific predictive surgery, drug design and delivery, weather and climate prediction, pollution remediation and detection and control of toxic agents, optimal design of mechanical systems, and many more. The successful development of a new generation of computer simulation tools that will make possible these technological advances will require substantial research efforts.

While it can be argued that the field of computational mechanics began in the United States in the 1950s and 1960s, substantial early work was also conducted in the United Kingdom and Germany. Important developments came later in France and Japan, and new work and engineering applications occur worldwide. The major components of computational mechanics are (1) computational and applied mathematics, (2) modeling (including the development of algorithms software, and (3) computing, including the development of computational devices that enable large-scale computations; data storage, retrieval, and distribution; and the use of computational grids

The major subareas of computational mechanics are computational fluid dynamics (CFD) and computational solid mechanics (CSM). Significant work in other subareas also exists, including computational electromagnetics, optimization, and biomedicine. These subareas of computational mechanics are described below:

• Computational fluid dynamics. Includes the study of turbulent flow, combustion modeling, compressible flow and aerodynamics, multiphase flow, flow in porous media, rarified gas dynamics, and kinetic theory.

• Computational solid mechanics. Includes the fields of computational materials, computational structural mechanics, impact dynamics, penetration mechanics, geosciences, and geotechnical engineering.

• Computational electromagnetics and electromechanical systems. Has to do the with modeling of electromagnetic phenomenon in mechanical systems, such as guided waves, radiation, and scattering.

• Computational methods in design and optimization. Include operations research, mechanical design, inverse analyses, control, and optimization.

• Computational bio-engineering: Involves computational methods applied to biomechanical systems.

An average of 49 percent of the 489 VWC speakers for this area was from the United States. The percentage of most-cited articles in the International Journal for Numerical Methods in Engineering averaged 50 percent between 1995 and 2005. At the same time, only one-third of the articles written in 2005 were by U.S. authors, down from an estimated 50 to 60 percent in the 1980s. The percentage of articles by U.S. authors in two leading computational mechanics journals International Journal of Numerical Methods in Engineering and Computer Methods in Applied Mechanics and Engineering has been around 33 percent for several years. Overall, the United States is among the leaders in computational mechanics research, and decreases in the share of U.S. contributions to journal articles indicate that the margin of leadership is diminishing.

Design in mechanical engineering involves a number of diverse topics, all related to the process of developing and producing products, systems, processes, and infrastructures. This includes fundamental theories underlying product realization processes and the types of decisions that are made in a design process, issues in the modeling and simulation of systems, challenges in the synthesis and optimization of systems, and emerging topics in design informatics and environments.

A holistic view of design is where a total system, life-cycle context recognizes the need for advanced understanding of the process of innovation, the identification and definition of preferences, the evaluation of alternatives, the effective accommodation of uncertainty in decisionmaking, and the relationship between information and knowledge in a digitallysupported design process. Mechanical engineering design in the United States is especially strong. However, this strong leadership across all areas of design is beginning to diminish, as Germany, France, England, Japan, Korea, China, and Australia each gain ground, while other European nations are also establishing themselves as leading authorities in specific areas of design.

The subfields within design have been identified by examining both the historical foundations of the field of design and the modern research areas that are both defining and shaping this dynamic field.

• Design Theory. Includes some of the basic pillars and frameworks of design and the types of models and decisions that are necessary in a design process. It includes research in the realm of “design for” capabilities, including studying system architecting and platforming. In addition, underlying research in the divergent and convergent processes underlying any design process is critical. Lastly, validation of these models and developments lies at the core of the research in design theory to effectively support fundamental decisions in design.

• Design Modeling and Simulation. Includes the vast scientific challenges underlying the approaches to the geometric and analytical modeling of design artifacts and processes. In addition, a number of more recent theoretical, experimental, and computational topics in multiscale and distributed modeling of systems are germane to this subfield. As system complexity increases, there is a need to move beyond deterministic models and

incorporate uncertainty and risk in design models, including adeptly developing appropriate surrogate modeling approaches.

• Design Informatics and Environments. Includes the growing research challenges involved in capturing, representing, and manipulating the information and knowledge that is inherently woven throughout design processes. It includes information technology areas such as cyberinfrastructure development and design, digital libraries, and ontologies and human-computer interaction areas such as visualization, haptics, and web environments.

• Design Synthesis. Includes the research challenges in design optimization such as inverse methods, numerical algorithms, global search, multimodal solutions, discrete problems, constrained models, and distributed processing among others. It also includes a number of difficult issues in synthesizing complex design processes and products such as multidisciplinary optimization, coordination processes, hierarchical methods, and agent networks.

Mechanical engineering design in the United States is especially strong and has been in a global leadership role since the emergence of the field in the middle to late twentieth century. There is a strong U.S. representation in the VWC for this area, where an average of 79 percent of the 532 speakers are from universities, government agencies, and industries in the United States, with universities being the largest contingent.

Primary venues to publish design research contributions are the Journal of Mechanical Design, Research in Engineering Design, Journal of Engineering Design, Design Studies, Computer-Aided Design, and Journal of Computing and Information Science in Engineering. Many design-related articles are also published in operations research, numerical methods, and aerospace journals, along with publications closely related to specific engineering application fields such as manufacturing, product development, and process management. In 2005, U.S. authors contributed 29 percent of the articles and 34 percent of the 50 most-cited articles in the journal Computer-Aided Design. At the same time, there is an average U.S. contribution of about 30-40 percent of the journals listed above. The Journal of Mechanical Design has about 50 percent U.S. based authors, whereas the U.K.-based Design Studies has about 20 percent. Taken together, the VWC (>70 percent U.S.) and journal data (30-50 percent) indicate that the United States is the leader in computer-aided design research.

The discipline of dynamic systems and control deals with the analysis and synthesis of control systems that typically include feedback loops. Feedback control systems involve system components such as a plant, a feedback controller, actuators, and sensors.

The control community is multidisciplinary, and active researchers come from aerospace engineering, electrical engineering, chemical engineering, mechanical engineering, and applied mathematics. For example, the American Control Conference, one of the most important conferences in the field, is sponsored by the American Automatic Control Council and

membership societies including American Institute of Aeronautics and Astronautics, American Institute of Chemical Engineers, Association for Iron and Steel Technology, American Society for Civil Engineers, American Society of Mechanical Engineers, Institute of Electrical and Electronics Engineers, ISA-The Instrumentation, Systems, and Automation Society), and Society for Computer Simulation.

In the 1960s, major advances in the state of space control system design methodologies, including optimal control theory, were made in the United States and the Soviet Union. These advances resulted from the pursuit of space exploration, and the United States still remains the world leader in the subfield of control system design methodologies, particularly in optimal and robust control theories (see discussion in the assessment below).

For the purpose of the present study, the discipline is divided into the following subfields:

• Modeling and Identification. In the design of control systems, it is important to understand the dynamics of the controlled plant; therefore, the controlled plant is modeled and identified.

• Control System Design Methodologies or Control Theories. The feedback controller and other types of controllers must be designed to achieve various objectives such as stability, performance, robustness, and autoadaptive capability, and this is done with control system design methodologies and control theories.

• Enabling Technologies (ET). ET such as sensors or actuators and hardware components are important because the actual synthesis of control systems must be supported by them.

• Mechatronics and Applications. Motivations for research in the subfield of dynamic systems and control are often found in application domains, and application-oriented research has mechatronics aspects. Mechatronics refers to the synergistic integration of physical systems, decision-making, and electronic components such as digital signal processing (DSP) and intelligent sensors.

• Robotics and Automation (R&A). In the mechanical engineering community, there are a number of application domains such as vehicles, transportation, manufacturing, biomedical systems, modeling, and control at micro- or nanoscales and so on. R&A may be regarded as an application area, but its coverage and scope are broad.

An average of 49 percent of the 714 speakers identified in the VWC were from the United States (appendix Table D-1), but the results for the subareas varied considerably. For example, about 60 percent of invited speakers in the subarea of control methodologies and control theories were from the United States, whereas there were 40 percent in mechatronics and applications.

The two leading journals in the field with strong methodology orientation are Automatica and IEEE Transactions on Automatic Control. In these journals, U.S. authors made up 23 and 36 percent of the authors represented in 2005, respectively. The difference in representation of U.S. experts as authors of publications in journals versus U.S. speakers at virtual congresses can be attributed to the broad scope of this discipline in terms of the number of researchers and the number of topics.

In other subareas, the dominance of the United States is not as evident, but the United States is certainly among the leaders. This is illustrated by the U.S. contribution to the most-cited articles in IEEE Robotics and Automation,⁸ of 54, 46, 38, 34, and 48 percent respectively for the years 1995, 1997, 1999, 2001, and 2003. In the subarea of mechatronics and applications, 40 percent of virtual congress speakers are from the United States. This is consistent with the percentages of U.S. authors in application-oriented periodicals published in the United States: IEEE Transactions on Control Systems Technology (49 percent), and IEEE-ASME Transactions on Mechatronics (37 percent). U.S. authors, however, represent only 10 to 20 percent in Control Engineering Practice (CEP), another application-oriented periodical. This may be attributed to the preference of U.S. researchers to publish papers in ASME and IEEE journals, which are regarded as premier control journals in the international community; CEP is published by Elsevier in the Netherlands. In the ASME Journal of Dynamic Systems, Measurement, and Control, which covers the broad discipline of dynamic systems and control, 34 out of 81 articles (42 percent) were contributed by U.S. researchers.

Taken together, the VWC (49 percent U.S.) and journal results (30-50 percent U.S) indicate that the United States is among the world leader in dynamic systems and controls.

Energy systems allow the conversion of an energy source (fossil fuel, nuclear plants, solar conversion) into a form that can be used immediately or stored and then recovered to fulfill a useful purpose (transportation, local power, etc.) The key issues and challenges in the subarea of energy systems presently center on reducing reliance on fossil fuels because of concerns regarding unstable supplies of petroleum, global climate change due to combustion product gases released into the atmosphere, and pollution resulting from fossil fuel production and conversion. With a few exceptions, federal research funding in this area has been very poor for some decades. The subareas that can be identified are (1) renewable energy systems and sources, (2) energy conversion and storage, and (3) nuclear energy.

• Renewable energy systems and sources. Include solar, wind, biomass, ocean thermal energy conversion (OTEC), and geothermal energy, and the systems used for converting energy from these sources into useful forms.

• Energy conversion (power plants, engines, fuel cells, photovoltaic, thermionic, etc.). Includes devices and systems for converting a primary energy source into a useful energy form.

• Energy storage (batteries, flywheels, phase change, etc.). Methods and systems for storing energy so that intermittent or steady energy production can be matched with intermittent or steady energy loads.

• Nuclear energy (modeling of reactor fuel and computational fluid dynamics for reactor design). Includes design, analysis, and testing of advanced nuclear power systems such as high-temperature gas cooled reactors, as well as modification and safety analysis of existing nuclear systems.

The VWC for the area of energy systems resulted in 68 percent of the 274 speakers being from the United States, which indicates a strong leadership position in this area. However, an examination of article authorship in seven journals (see appendix Table C-1) in this area showed the average U.S. contributions to be about 30 percent. U.S. contributions to the Journal of Power Sources are around 20 percent, while U.S. contributions to the most-cited articles in this journal average around 22 percent over the 1995-2005. The combined VWC representation (68 percent U.S.) and the journal article results (20-30 percent) indicates that the United States is among the leaders in energy systems with well-recognized researchers, and the lack of recent publications in this area shows a significant weakening of leadership.

Manufacturing is the production of goods and services using raw materials and labor, Many of the specific issues associated with manufacturing are being done by mechanical engineers and include development of processes for creation of materials and material surfaces (textures) and interfaces, by machining and molding, for such varied uses as reducing drag of automobiles, creating the next generation of data storage devices, and developing concepts and tools (electrooptomechanical) for automated assembly.

For the purposes of this study, manufacturing was divided into five subareas: processes, tooling and equipment, systems, metrology, and quality.

• Manufacturing Processes. Involve materials removal processes (e.g., turning, milling, drilling, grinding), nonconventional materials processes (e.g., electrical discharge machining, electrochemical machining, energy beams such as laser, ion focus beam, or water jet), materials deformation processes (e.g., sheet forming, bulk forming, rolling, extrusion), casting processes, sinter and powder metallurgy (e.g., ceramic, powder metals), joining processes, and assembly processes

• Manufacturing Toolings and Equipment. Covers cutting tools, dies and molds, and fixtures, as well as computer numerical control and high-speed machines).

• Manufacturing Systems. Have to do with flexible manufacturing systems, reconfigurable manufacturing systems, group technologies, and process planning.

• Manufacturing Metrology. Involves coordinate measuring machines, optical gauges, and in-process inspection.

• Manufacturing Quality. Covers statistical process control (e.g., “6-Sigma”), variation reduction, and root cause identification)

According to the VWC results, about 50 percent of the 389 speakers named were from the United States. This was consistent across all the manufacturing subareas. This leadership position is further supported by an analysis of journals in this area. In the ASME Journal of

Manufacturing Science and Engineering, U.S. contributions to the top 50 most-cited articles amounted to about 70 percent. In addition, four out of the five manufacturing journals analyzed showed greater than 50 percent U.S. contributions on average (Appendix Table C-2). Together, these results indicate that the United States is the leader in manufacturing basic research.

This field has a long history both inside and outside the United States. Research in the United States has maintained a strong leadership due to the ability of researchers to rapidly apply the concepts of mechanics to new and evolving problems. Current and future fields of intense interest include mechanics of materials at very small length scales, application to complex hierarchical biological materials, and multiscale modeling and experimentation. Such foci permeate traditional fields such as damage mechanics and experimental mechanics by providing important new applications for mechanics and new tools by which to further our understanding of materials and enable the creation of devices and materials for the well-being of society.

• Nanomechanics and nanomaterials. Involves understanding at the nanometer level the mechanisms and limits of mechanical changes, the stability of materials, and the transfer of energy to and from materials.

• Durability mechanics. Has to do with the material science of large physical structures, largely involving fracture mechanics and the deterioration of materials.

• Computational materials. Involves numerical methods for the analysis of the nonlinear continuum response of materials, which includes: elasticity, inelasticity, molecular statics and dynamics modeling across atomistic, molecular, and continuum scales.

• Experimental mechanics. Has to do with understanding the mechanical behavior of materials, structures, and systems, especially at small scales and bridging between scales and bridging to theory.

• Multiscale mechanics: involves the use of theory, experiment, and numerical simulation in combination, to understand heterogeneous materials, biomaterials, composites, and micromechanics at all levels of function.

The VWC results for mechanics of engineering materials show that U.S. organizers picked more than 70 percent U.S. speakers, while international researchers named 50 percent U.S. speaker’s to participate.

U.S. researchers in the mechanics of engineering materials publish in a widerange of journals, some focused on the area of mechanics, such as the premier mechanics journal, Journal of Mechanics and Physics of Solids (JMPS), and with significant presence in journals specific to fields of application, such as Journal of Biomedical Materials Research. In JMPS, U.S. authors publish an average of about 65 percent of the most-cited articles. In addition, researchers have begun to broaden the visibility of the field and its contributions with publications in top general science journals such as Science, Nature, and Nature Materials. Overall, U.S. authorship is at

about 50 percent for all articles combined in relevant journals. Together, these results indicate that the United States is the leader in the mechanics of engineering materials research.

Microelectromechanical systems (MEMS) is the technology of very small devices and systems having important dimensions at the micrometer level (i.e., between a micrometer and a millimeter), too small to machine with traditional physical methods but too large to build with chemical syntheses. Born from the semiconductor integrated circuit (IC) fabrication processes, MEMS technologies typically use deposition and etching of materials along with photolithographically defined mask patterns. Today, the fabrication arsenal has been enriched by several IC processes commercialized specifically for MEMS (e.g., deep reactive ion etching) and many non-IC processes modified for microfabrication (e.g., microelectrodischarge machining, electroplating into micromolds). MEMS is considered coming of age with a few commercial successes of high visibility (e.g., automobile airbag sensor, micromirror array for high-definition display, inkjet printhead). Although the success is most often viewed through applications, the fabrication technologies constitute the indispensable basis for the next wave of success across fields beyond electronics (e.g., biomedical). With the focus of funding shifted to application research years ago however, MEMS appears to have lost support in fundamental and core research rather prematurely. Despite dramatic miniaturization, MEMS is still within the realm of continuum mechanics.

Nanotechnology (Nano) is poorly defined today, but it generally deals with engineering at the nanometer scale. Originally inspired by molecular engineering in its core intent (i.e., building three-dimensional structures molecule-by-molecule in bottom-up approaches), nanotechnology is currently dominated by material syntheses, thinfilms, and nanoscale ICs.

To assess the current status of the U.S. contribution to MEMS/Nano, the following representative subareas were examined:

• Fundamental Issues in MEMS and Nano. The physics unique to the scale are the main points of focus for the field. As an example for both MEMS and Nano, the surface-to-volume ratio is extremely large compared to conventional mechanical engineering devices and systems. The scale effects are prohibitive in some cases but enabling in others. Understanding the fundamentals allows one to avoid the problems and take advantages of the unique opportunities of being in the given scale.

• Design and Modeling. Design and Modeling are based on the fundamental issues and allow one to design products and predict their performance, minimizing the trial-and-error development cycles. Modeling in MEMS typically requires simultaneous solution of multiphysics issues. Modeling for Nano often requires simulation at the molecular level, and the boundaries may be blurred between mechanical engineering and chemistry even for machines in nanometer scale.

• Micro/Nano Process Technologies. The ability to fabricate objects in micro- or nanometer scale is a major obstacle. MEMS processes typically use top-down methods, forming the shape by removing unnecessary portions. Nano processes are said to be based on bottom-up methods, building by placing the minimum unit of materials one at a time. However, most

nanofabrication methods today are extensions of known methods (e.g., embossing into molds having submicrometer features).

• Micro/Nano Devices and Systems. The components or final products whose key functions originate from micro- or nanoscale features are Micro/Nano devices and systems. For example, an airbag deployment sensor is a complete microdevice or system, which in turn is a component of an automobile. The same can be said for a digital light processor (DLP) for high-definition television (HDTV) or the printhead of an inkjet printer. On the contrary, examples of devices are rare as yet in the Nano field.

For the VWC, 57 percent of the 83 speakers were from the United States (non-U.S. speakers were largely from Japan and the Netherlands), indicating U.S. leadership in this area.

MEMS researchers publish in the Journal of Microelectromechanical Systems (IEEE-ASME, U.S.), Journal Micromechanics and Microengineering (Institute of Physics, U.K.), Sensors and Actuators (Elsevier, the Netherlands), and Lab on a Chip (Royal Society of Chemistry, U.K.), among others. Nano researchers publish in a much wider range of journals, most notably in Nano Letters (American Chemical Society, U.S.). However, more Nano-related articles are published in many other established journals in chemistry and material science journals.

Based on journal analysis of the 50 most cited articles, U.S. authors represent 70 percent and 20 percent of the authors respectively in the Journal Microelectromechanical Systems and the Journal of Micromechanics and Microengineering. At the same time, in 2005, the U.S. contribution was about 70 percent of the 146 articles published in the Journal Microelectromechanical Systems and about 30 percent of the 353 articles in the Journal Of Micromechanics and Microengineering.

Based on the combined results of the VWC (>50 percent U.S.) and journal analysis (30-50 percent U.S.), the United States is among the leaders in the world in both MEMS/Nano research.

Research and development in thermal systems and heat transfer span a variety of fields including fluid mechanics (e.g., multiphase flows, plasmas, turbulence, biofluids), heat transfer (e.g., convection, conduction, radiation, phase change), and micro- and nanothermofluid systems and applications. Applications and technology development have been led by U.S. researchers include aerospace, nuclear, propulsion, electronics and photonics thermal management, advanced manufacturing, laser-material interactions, HVAC (heating, ventilation, and air conditioning), and flow control.

• Combustion. Involves experimental and analytical studies in combustion, applications in power generation, propulsion, and fire safety.

• Heat transfer. Has to do with studies of fundamental heat transfer phenomena in radiation, conduction, convection, mixed modes, and phase change.

• Fluid mechanics. Includes plasmas, multiphase flow, turbulence, biofluids, supersonic and hypersonic flows, and shocks.

• Nano/Micro systems. Involve thermal properties and heat transfer in fluids, nanofluidics, and nanocomposites; and near-field effects in radiation, phonon and photon transfer, and property modifications at a small scale.

• Applications. Are very wide ranging, including electronic cooling, aerospace, nuclear, propulsion, advanced manufacturing, laser-material interactions, HVAC, flow control, power generation, and electronics cooling.

The VWC results for the area of thermal systems and heat transfer show that an average of 65 percent of the 562 speakers were from the United States. This is similar to the U.S. contribution to the ASME Journal of Heat Transfer. An average of 50 percent of the 50 most-cited articles for the ASME Journal of Fluids Engineering were U.S. authored. In 2005, an average of 40 percent of 10 selected journal articles in this area were U.S. authored (see appendix Table C-2). Based on the combined results of the VWC (65 percent U.S.) and journal analysis (30-50 percent U.S.), the United States is the world leader in thermal systems research.

Tribology is the study of surfaces in relative motion. It encompasses the areas of friction, lubrication, and wear. Tribology is an enabling technology in that all mechanical systems involve surfaces in relative motion that require control of friction, motion, and wear. Mechanical systems could not operate without triboelements. New mechanical systems, or upgrades of existing mechanical systems, often require new developments in tribology to accommodate increases in speed, load, or operating temperature. Research in tribology tends to be done in the mechanical engineering community, although considerable contributions also come from the physics, chemistry, material science, and applied mathematics communities.

The term tribology originated in Great Britain in 1966, and the British, along with Americans, tend to dominate the field. Other countries making significant contributions tribology include France, Japan, Germany, and to a lesser extent Israel, Norway, Finland, Sweden, The Netherlands, Switzerland, and China. Prior to the collapse of the Soviet Union there were considerable contributions from that country. The continuous driver in tribology research is to push mechanical systems to higher loads, higher temperatures, higher speeds, and longer more reliable life.

Tribology can be divided into five subareas.

• Hydrodynamic phenomena. Are concerned with those situations in which the surfaces are separated by a fluid, either a liquid or a gas, and a pressure in the fluid is generated by the relative motion of the surfaces, or an external source, sufficient to support the load on the surfaces and keep the surfaces from contacting one another.

• Friction and wear. Is concerned with solid surfaces in relative motion and in contact with one another resulting in friction forces resisting motion and resulting in the wear of surfaces.

• Tribomaterials. Involves all types of material development and selection for tribological elements such as bearings, brakes, cams, and tires, and the lubricants used in triboelements.

• Contact mechanics and surface engineering. Has to do with surface and near surface material deformation and fatigue resulting from highly concentrated loads occurring in some triboelements, such as rolling element bearings and rail-wheel contact.

• Diagnostics. Involves developing techniques for early detection of mechanical failure in machinery.

An average of about 50 percent of the 471 VWC speakers in the area of tribology were from the United States. The other countries with large contributions of speakers include the United Kingdom, France, and Germany in that order. There are also significant numbers from Japan, the Netherlands, Finland, Italy, and Sweden. The United Kingdom is strong in all subsubfields, while France is strong in hydrodynamic phenomena and Germany is strong in the area of tribomaterials.

Primary venues to publish tribology research contributions are the ASME Journal of Tribology, the Society of Tribologists and Lubrication Engineers’ STLE Tribology Transactions, Wear, Tribology International, and Tribology Letters. Many tribology-related articles are also published in physics, chemistry, and material science journals, as well as publications closely related to specific engineering applications fields such as transportation, environmental control, and manufacturing. Of the 50 most-cited articles in the journal Wear, an average of about 20 percent were by U.S. authors. U.S. authors appear more frequently among the most-cited authors than among authors in general in that publication. The reason U.S. authors appear less frequently in Wear than among the VWC authors may be that U.S. authors are more likely to publish in the two major U.S. publications in tribology—ASME Journal of Tribology and STLE Tribology Transactions. Wear is published in Europe.

At the same time, about 30-50 percent of authors in the U.S.-based tribology journals mentioned above are from the United States, while in the British based journals, about 20 percent of the authors are from the United States. Tribology Letters has about 40 percent U.S. based authors.

Based on the combined results of the VWC (50 percent U.S.) and journal analysis (20-50 percent U.S.), the United States is among the world leaders in tribology.

Mechanical engineering is the foundation for the creation of the industrialized world, and it is a central element of all engineering disciplines. It is at the heart of design, creation, and manufacturing of wealth-generating devices in the twenty-first century. Research in mechanical engineering is no doubt essential to future technological innovation. Evidence for current basic

research leadership in mechanical engineering comes from an analysis of journal articles, most-cited articles, and virtual congresses conducted by the panel. Overall, the United States is certainly among the leaders in mechanical engineering basic research. However, excellent mechanical engineers throughout the world provide stiff competition for the United States.

• In 2002-2006, the United States published 24 percent of the mechanical engineering articles in the world. For 1987-1991, the U.S. contribution was 48 percent.

• U.S. mechanical engineers contribute strongly as authors to the leading research journals in this field, accounting for about 40 percent of the articles and 40 percent of the most-cited articles in the 68 selected journals.

• U.S. mechanical engineers contributed 65 or more out of the 100 most-cited articles in the Scopus database for the timeframe 1987 to 2006.

• The combined virtual congress and journal analysis supports that the United States is the leader or among the leaders in all areas of mechanical engineering basic research (Table 2-5).

Overall, the United States is among the leaders in mechanical engineering research, with the following average contributions:

• 50 percent of VWC speakers,

• 40 percent of journal articles, and

• 40 percent of most-cited articles.