bluuebunny/crossref_metadata_2025 huggingface dataset:
Asynchronous periodic contact modes for rotor vibration within an annular clearance
Authors: Cole M O T , Keogh P S
Published: October 2003

The dynamics of a multimode rotor-bearing system are analysed when the rotor contacts with a stator having annular clearance. By transforming to a rotating frame, all possible steady state rotor vibration modes that involve periodic contact with the surround may be predicted. Using a harmonic decomposition with generalized fundamental frequency, periodic solutions are obtained for rotor motions that involve asynchronous periodic contact. The analytical solutions are compared with previously published experimental results, which are predicted with considerable accuracy thus confirming the efficacy of the approach. Solutions are obtained for different test cases, which show how the amplitude and stability of the periodic contact modes are dependent on system parameters and operating conditions. In particular, for increased unbalance levels, the amplitude of the contact mode vibration is increased and the response of the rotor progresses from a bouncing forward whirl to a backward whirl-type motion. The nature of the identified rotor responses and implications for machine operation and reliability are discussed.
Calculating conjugate cam profiles by vector equations
Authors: Wu L-I
Published: October 2003

This paper presents an analytical approach for determining the profiles of conjugate disc cams. For a conjugate cam mechanism, its two normal lines through the points of contact and the line of centres must always intersect at a common point, which is an instant centre. On this basis, the contact points between the conjugate cam and the follower can be determined according to the locations of instant centres and follower position. The cam profiles, the paths of the cutter and the pressure angles can then be expressed in the form of parametric vector equations. For various types of conjugate cams, the equations for such expressions are formulated, and examples are provided to illustrate the approach. The procedure is especially simple to program.
Development of a safety/support unit for climbing service robots
Authors: Luk B L , Tso S K , Ng A , Yan S R , Xu Y S
Published: October 2003

Building maintenance tasks are labour-intensive and of a high-risk nature. Workers are often required to carry out the maintenance work, such as wall inspection and cleaning, in mid-air and at high altitudes. In order to enhance the work safety and efficiency, many research projects have been carried out worldwide to investigate the use of climbing service robots for automating these hazardous tasks. As part of each system, most of these service robots do require a safety/support unit to provide an external power source and also a safety mechanism to prevent the robot from falling in the case of accidents. In addition, the safety/support unit is also used as a control console to provide the human operator with a constant communication link with the robot for monitoring and controlling the remote maintenance operations. In order to ensure high reliability and safety of service, it is essential to have a tight integration between the robot and the safety/support system. In this paper, some of the important issues for designing the safety/support unit are discussed. Also, a fuzzy neural technique for controlling the swing and vibration of the safety wire rope is described.
A study of brake noise and the influence of the centre of pressure at the disc/pad interface, the coefficient of friction and calliper mounting geometry
Authors: Fieldhouse J D , Steel W P
Published: October 2003

It is generally accepted that the coefficient of friction between the friction pair, the pad and the rotor plays a significant role in the propensity of a brake to generate noise. Because of the ease with which changes may be made to the pad compound material it is this that is more often the subject of change when there is a problematic noisy brake with both the rotor and the calliper tending to remain ‘isolated’ from examination. This paper investigates the propensity of a brake to generate noise over a range of temperatures and pressures under conditions that allow a mechanically induced offset centre of pressure between the pad and rotor to be varied. It is shown that for a high-volume production car brake there is an increased tendency for it to generate noise when a very specific leading offset centre of pressure is engineered. With this condition it is shown that a situation is promoted whereby the brake becomes mechanically unstable, with system changes such as brake pressure and temperature variations having little influence on the brake to alter its tendency to generate noise. Furthermore, it is shown that the critical offset centre of pressure may be related to the coefficient of friction between the friction pair and the mounting geometry of the calliper. Confirmation of the findings are supported by a repeat investigation of the vehicle's alternative brake calliper. It is suggested that the source of a noisy brake may lie as much in basic mechanical design as inappropriate material choice.

Further confirmation is demonstrated through the study of a commercial sliding fist-type brake, where the brake is significantly noisier when the centre of pressure and calliper mounting arrangement provide an appropriate spragging angle related to the friction coefficient.
Roll dynamics and lateral load transfer estimation in articulated heavy freight vehicles
Authors: Kamnik R , Boettiger F , Hunt K
Published: October 2003

Roll dynamics in heavy freight vehicles is characterized in driving conditions by the lateral load transfer coefficient. The coefficient tracking requires sophisticated measurement systems for assessing the wheels’ normal loading. In this paper a new recursive non-linear lateral load transfer estimator employing sensors that are already used on a vehicle in combination with additional units that are not sophisticated for the implementation is described. The proposed algorithm integrates two subsystems—separate estimators for the tractor and the trailer. The first estimator is based on slip information of the driving wheels, while the second estimator fuses the tractor estimation and the modelled trailer dynamics by the extended Kalman filter. The novel approach was evaluated on a sophisticated computer simulator of the Freightliner Century Class tractor semitrailer. The simulation analysis shows that the proposed algorithm provides robust operation and good tracking performance. This approach enables a practical realization of a low-cost solution for the rollover prevention in real heavy freight vehicles.
A Study on enhancement of the turbulence around the spark timing by auxiliary injection during the compression process
Authors: Noh K C , Song Y S , Lee J T
Published: October 2003

It has been found in a previous study that enhancing the turbulence intensity at the beginning or middle of the compression process and generating the strong turbulence at the end by the compression effect is desirable in order to create and maintain the high level of turbulence around the spark timing. This study aims at analysing and evaluating the auxiliary injection method for inducting the pressurized air at the beginning of the compression process to enhance the level of turbulence around the spark timing. An electronic solenoid valve is fitted to the auxiliary injection device for the purpose of active control of the in-cylinder turbulence characteristics.

The level of in-cylinder turbulence with the auxiliary injection increases by about 40 per cent compared with a conventional engine. A desirable distribution of turbulence around spark timing with lower levels of turbulence around the spark plugs and cylinder wall and with a higher level near the half-radius of the cylinder is obtained by the auxiliary injection. Furthermore, the conditions suitable for injection are identified with respect to injection direction, injection pressure and injection timing.
Effects of different frequency components in turbulence on accelerating turbulent premixed combustion
Authors: Shiyong Liao , Deming Jiang , Jian Gao , Ke Zeng
Published: October 2003

A comprehensive research on correlation analysis of turbulence frequencies against turbulent premixed combustion is made in a combustion bomb. Pre-ignition turbulence is generated through the motion of a perforated plate and divided into different frequency parts by wavelet packet decomposition. High-speed Schlieren combustion photos are used to monitor flame growth and pressure traces are recorded simultaneously. The cycle-resolved mass burning rate is calculated through using a quasidimensional two-zone combustion model. Correlation coefficients between the instantaneous mass burning rate and different turbulent frequency components are then obtained. Results show that turbulence components between 4.5 and 7.5 kHz are of major importance in accelerating flame propagation in this combustion chamber and are not affected by the fuel-air ratio or different kinds of fuel/air mixtures. For all turbulence components, there is an obvious increase in correlation coefficient with the increase of flame size.
Ariane Rocket Program
Authors: Vignelles Roger
Published: October 2003

This article describes the circumstances that led Europe to go ahead with the Ariane Program in 1973 and subsequently to decide on a series of follow‐up versions, up to and including Ariane 5. The article also describes the main management principles adopted that have varied little in 20 years and includes brief details of the successive launcher configurations from Ariane 1 to Ariane 5.
Astrobiology
Authors: Morrison David
Published: October 2003

Astrobiology is a relatively new term that embraces the multidisciplinary study of the living Universe. It is the investigation of the origin, evolution, distribution, and destiny of life in the Universe. Astrobiology addresses some of the most profound questions of humankind.

Although the term had been used occasionally during previous decades as a synonym for “exobiology,” astrobiology in its present incarnation was proposed by NASA. NASA encouraged this new discipline by organizing workshops and technical meetings, establishing a NASA Astrobiology Institute, providing research funds to individual investigators, ensuring that astrobiology goals are incorporated in NASA flight missions, and initiating a program of public outreach and education. NASA's role is derived from its history of studying the origin of life and searching for evidence of life on Mars or elsewhere in our solar system. Under the umbrella of astrobiology, these efforts are expanded to include the search for life within other planetary systems, as well as investigating the response of terrestrial life to global changes on Earth and to exposure to conditions in space and in other worlds. Astrobiology addresses our origins and also our aspirations to become a space‐faring civilization.

The NASA Astrobiology road map provides an initial description of the technical content of astrobiology. This road map was formulated through a series of workshops and discussions. Astrobiology addresses three basic questions, which have been asked in some form for generations.

How does life begin and evolve? (Where did we come from?)

Does life exist elsewhere in the Universe? (Are we alone?)

What is life's future on Earth and beyond? (Where are we going in space?)

These are very general questions, and no one expects that definitive answers will be found easily. More specific is the analysis of astrobiology in terms of 10 long‐term science goals and each is addressed here.
Liquid‐Fueled Rockets
Authors: Rosen Robert , Glickstein Marvin , Joyner Russell
Published: October 2003

Since the beginning of the space age, liquid‐fueled rockets have provided the basis of everything we have accomplished in space. Whether it has been the mighty F‐1, which powered Apollo to the Moon, or the workhorse RL‐10, or the high performance SSME, all of the major missions depend on liquid‐fueled propulsion. And as we move forward to the next generation systems, the success or failure of these systems will be intimately tied to the success of its liquid‐fuel propulsion system.

The following discussion focuses on the design of liquid‐fueled rocket systems and examines the design choices that must be considered in integrating the propulsion system for a selected application. It is to be understood that liquid‐fueled systems refer to the oxidizer as well as the fuel and that both of these are carried aboard the vehicle.

Today's liquid‐fueled rocket propulsion designs originate from the theories of a Russian, Konstain E. Tsiolkovsky, and from experiments performed by an American, Robert H. Goddard and a German, Herman Oberth. Goddard and Oberth made some of the first working liquid propellant rocket engines.

A liquid‐fueled rocket propulsion system consists of a number of carefully integrated components that must be chosen and designed to function as part of the whole. The operation of an integrated system can best be viewed by identifying the required functions that must be satisfied and then considering the components that are chosen to fulfill these functions. The primary function of a rocket propulsion system is to produce thrust that accelerates the spacecraft to the final velocity required to achieve its goal. To produce a practical propulsion system, the integrated system must control the flow of propellants from the storage tanks, deliver them at the required pressures, and inject them into the combustor.

Part of this article is structured around the subsystems of an engine. But it is important to keep in mind that these engines are highly coupled systems, from both the viewpoint of mechanical systems and fluid flow. An overview of some of the design issues are given to put things in perspective.
Space Resources, Occurrence and Uses
Authors: Lewis John S.
Published: October 2003

Space resources consist of all of the useful materials, energy sources, and energy found in space. For practical purposes, this article focuses on those resources that may be accessible within the next 25 years, and for which large‐scale demand is plausible. Therefore, the principal focus of this review is the bodies of nearby space: Earth's Moon, the planets Mercury and Mars, the two small Martian moons, Phobos and Deimos, and the near‐Earth population of asteroids and comets.

This article briefly surveys the significance and promise of space resources, including scientific and technical issues and the legal and regulatory regime surrounding their economic use. Current treaty obligations are reviewed, and some suggestions made regarding legislation and treaty language that would encourage the growth of this enormous new arena of economic activity, making vast new resources available to all.
Asteroids
Authors: Morrison David
Published: October 2003

Asteroids are small members of the solar system in heliocentric orbits concentrated between Jupiter and Mars. Since most of them have orbits that are roughly similar to those of the planets (low inclination and eccentricity), they have sometimes been called minor planets, although this term is no longer in common use. More important is the distinction between asteroids and comets, where the primary difference is one of composition. Most asteroids are rocky objects, composed of the same sorts of materials as the inner planets. Comets, in contrast, contain a substantial quantity of water ice and other frozen volatiles in addition to silicates and organic compounds. However, there are ambiguities in terminology. Comets that make frequent passes around the Sun may lose their volatiles and become indistinguishable from rocky asteroids. In addition, there are many volatile‐rich objects being discovered in the outer solar system (beyond Neptune) that resist classification as either asteroids or comets. These are the Kuiper Belt Objects (KBOs).

Asteroids are too faint to be visible to the unaided eye, so their discovery belongs to the era of telescopic astronomy.

Our census of the larger asteroids is fairly complete by now, based primarily on ground‐based surveys, complemented by infrared space observations, such as those from the Infrared Astronomy Satellite (IRAS) in 1983. It is likely that we have discovered all main‐belt asteroids 25 km or more in diameter, and discovery should be more than 50% complete for diameters down to 10 km. Ceres, the largest, has a diameter just under 1000 km. This article gives information on the physical and chemical properties of asteroids and their orbits. Also discussed are techniques for study of asteroids, including space missions, and the impact hazards of asteroids.
Space Shuttle Orbiter
Authors: Cohen Aaron , Silveira Milton A.
Published: October 2003

This article gives details on the preliminary design considerations involving the Space Shuttle. Basic requirements and effects on design had to be studied. Since the Shuttle was entirely different from any other spacecrafts, engineering teams had to be organized.

The reusable main engine was a major advance in rocket engineering and development of the main engine is discussed. Orbiter specifications are given. Various orbiter systems include: Crew compartments, Guidance, Navigation control, Hydraulics, Auxillary power unit, Communications, Environmental control, Life support, Payload deployment, Payload retrieval systems.

The first Space Shuttle vehicle was the
Enterprise
, and it was not intended to fly. The orbiter was launched from a Boeing 747.
Columbia
was the first Space Shuttle to be completed and flew for the first time in 1981. Space Shuttles have flown more than 100 missions. Many studies have been conducted to consider replacements for the Shuttle. No system has shown promise yet.
Exploration of the Moon by Soviet Spacecraft
Authors: Basilevsky Alexander T.
Published: October 2003

Launches of Soviet spacecraft to the Moon started on 2 January 1959, only 15 months after the launch of the first Sputnik. The full list of missions to the Moon is given. It includes all officially declared Soviet lunar missions. According to some sources there were also several failed Soviet attempts to send spacecraft to the Moon, when for various reasons, spacecraft stayed in Earth orbit or failed even earlier. They have never been officially recognized by the Soviet Union as lunar missions, and this is why they are not mentioned here. In total, there were 29 Soviet missions to the Moon. Of them, 20 were successful, one was partly successful, and eight missions failed. Twenty‐four missions were named Luna (the Moon, in Russian); five missions were named Zond (probe, in Russian). All Soviet missions to the Moon were robotic, although there was a program of Soviet manned flights to the Moon, which was canceled in the late 1960s because of failures of the heavy booster rocket necessary for those flights.

It is necessary to mention that in the 1960s–1970s, when the Soviet Union sent spacecraft to the Moon, the space activity of both the Soviet Union and the United States was strongly politically motivated. The Soviet Union, by sending numerous lunar missions, wanted to demonstrate the superiority of its political system. The Apollo mission to the Moon, the backbone of the U.S. space program of that time, was a response to the challenge of Soviet space activity.

This article gives details on the various Soviet missions and there findings.
Military Ground Control Centers, United States
Authors: Mortensen Adam L. , Worden Simon P.
Published: October 2003

Current military space operations centers grew out of 1950s and early 1960s facilities and missions—some of those missions were quite different from those of today. The military is quite conservative when it comes to innovation and modernization. And nowhere is this more evident than in space operations. The watchword is evolutionary, not revolutionary. Thus, a facility, and even its hardware, has often been adapted from a previous mission in the same facility. Because the old mission, often critical to national security, must continue as new missions are brought on, old hardware and procedures are replaced only when new technologies and hardware are well proven. Similarly, organizations responsible for military space missions tend to be adapted from older, often quite different missions and organizations. In recent years, this is particularly evident in the U.S. Air Force's space organizations that are steadily being evolved out of and in a way that mimics air operations. Organizations such as the Air Force Space Command's 50th Space Wing, the operator of much of the Service's on‐orbit satellites, is organized exactly as a flying wing, complete with the assumption of a unit name. As this article unfolds, the reader should keep this conservatism and legacy in mind.

The U.S. military currently maintains ground control centers for three related missions: early warning, space surveillance/space control, and on‐orbit satellite operations. Early warning and space surveillance/space control evolved from the North American Air Defense mission developed jointly by the United States and Canada in the 1950s, culminating in the construction of the North American Air Defense Command (NORAD) Combat Operations Center (COC) in the early 1960s. On‐orbit satellite operations centers have a different pedigree. Shrouded in secrecy during most of the Cold War, these facilities began as control centers for the United States space‐based intelligence collection mission. As such, they were originally developed and largely operated by the still secretive National Reconnaissance Office (NRO). To understand current military operations centers, it is necessary to understand the history of these missions and organizations. This history is the focus of this article. The future of the military use of space is discussed.
Uranus and Neptune
Authors: Sromovsky Lawrence A.
Published: October 2003

Uranus and Neptune, were the first planets discovered by telescopic observation. They are of Jovian Planets similar size and much more massive than Earth (by factors of 14.5 and 17) but are still far less massive than Jupiter (by factors of 22 and 18). Both have deep atmospheres dominated by hydrogen, but unlike Jupiter and Saturn, most of their mass consists of rocky and icy components, which are in fluid form due to high interior temperatures. Both have ring systems, a diverse system of satellites, unusual tilted and offset magnetic fields, and similar atmospheric circulations. Their blue colors distinguish them from the pale tans of Jupiter and Saturn. But they also differ significantly from each other; they have very different obliquities (spin axis inclinations relative to their orbital planes), vastly different internal heat fluxes, and remarkably different weather patterns. These simularities and differences are discussed in detail in this article.
Military Use of Space
Authors: Menshikov Valeriy A.
Published: October 2003

Starting at the very beginning and continuing until now, one of a nation's objectives for the conquest of space is to obtain military strategic advantages by using such unique features of space as extraterritoriality, global access, unique physical conditions, and a number of others. Thus, in the late twentieth century, the revolutionary development of humanity's new technological capacities inexorably moved the world into a new phase of geopolitical confrontation — the race to attain strategic advantages in space, which, in turn, made military operations in space one of the most important ways to ensure national security. This implies that the significance of various arenas of confrontation will change in the twenty‐first century; space will grow considerably in importance as the arena for attaining the objectives of armed conflict. The world's leading nations thus accord space a special position in contemporary military doctrine and approaches to national security.

The U.S. and Russia both have formulated strategies for the use of space in the interest of national security. Colaboration in space is also considered.
Russian Spaceports
Authors: Kuznetsov Alexander N. , Dedus Alexander F.
Published: October 2003

Russia's spaceports (launch sites) serve as the basis for all Russian activities in space, enabling an independent policy in exploration and use of outer space. They comprise a number of facilities, equipment, and land areas designed for receiving, storing, assembling, testing, prelaunch preparation, and launching rockets with spacecraft. Depending on its location, a spaceport may have one or several launch azimuths along which tracking stations are located.

The major facilities at spaceports are the launch and technical maintenance complexes, the fueling and decontamination stations, landing complexes, storage facilities of various types, launch debris impact areas, and telemetry monitoring stations. In addition, spaceports have plants for producing rocket propellants, airports, railroads, motor vehicle roads and various supply lines, as well as living quarters and social amenities.

Now Russia has three spaceports on its territory: Plesetsk, Kapustin Yar and Svobodnyy and, in addition, uses the Baikonur spaceport, which it acquired on a 20 year lease from the Republic of Kazakhstan in 1994. A map of these spaceport locations is provided.
Russia's Launch Vehicles
Authors: Kuznetsov Alexander N.
Published: October 2003

The history of cosmonautics and rocket building in Russia may be considered to have begun at the start of the twentieth century. The founder of these disciplines was the great Russian scientist K.E. Tsiolkovsky; major theoretical contributions were made by F.A. Tsander and Yu. V. Kondratyuk. Even in the prewar years, experimental work was being conducted to develop rocket technology for a number of purposes. Early research resulted in the development of the world's best volley fire (Katyusha) and aircraft missile systems. At the same time, experimental, jet aircraft and liquid‐fueled guided missiles were being designed and developed. The production facilities and supporting fundamental and applied science for these areas developed rapidly, serving as the basis for the start of the powerful space and rocket industry in the 1950s. This article details the history of Russia's development of launch vehicles.

The current system of launch vehicles evolved during the process of addressing a whole set of tasks through design and use of previously developed military rocket and space complexes. Light class, intermediate, and heavy class vehicles are discussed. Specifications and modifications of Soyuz‐type vehicles are given. The future of Russian development is discussed. Among others, the Angara is a heavy launch vehicle under development. Reusable launch vehicles and transport systems are the focal points of future development.
Capacitive Probe Microscopy
Authors: Kopanski Joseph J.
Published: October 2003

A scanning capacitance microscope (SCM) combines a differential capacitance measurement with an atomic force microscope (AFM). The AFM controls the position and contact force of a scanning probe tip, and a sensor simultaneously measures the capacitance between that tip and the sample under test. The capacitance sensor can detect very small (≈10−21F) changes in capacitance. The sensor is electrically connected to an AFM cantilevered tip that has been coated with metal to make it electrically conductive. As the SCM/AFM tip is scanned across the sample surface, simultaneous images of topography and differential capacitance are obtained.

Currently, the most common application of SCM is imaging the carrier concentration variations (also known as dopant profiles) qualitatively within transistors that are part of silicon integrated circuits (ICs).

Another application that has encouraged the development of commercial SCMs is the need for quantitative two‐dimensional (2‐D) carrier profiling of silicon transistors.

This article reviews the history, operating principles, and applications of SCM. Special emphasis is placed on measuring quantitative 2‐D carrier profiles in silicon using SCM. This article also reviews implementation and applications of the scanning capacitance spectroscopy (SCS) technique, the intermittent contact mode of SCM (or IC‐SCM), and two other techniques that can also be classified as scanning capacitance probes: the scanning Kelvin probe microscope (SKPM), when operated at twice its drive frequency, and the scanning microwave microscope (SMWM).
Color Image Processing
Authors: Castleman Kenneth R.
Published: October 2003

The objects in a visual scene differ not only in brightness, and also in the spectral characteristics of the light that emanates from them. This is true whether they generate light themselves, as in astronomy and fluorescence microscopy, or if they merely reflect a portion of the incident illumination. The human eye responds to their overall brightness, but to the spectral content of the emanation as well. We refer to this perceptual phenomenon as “color vision.” This article addresses color image processing, which is the digital image processing counterpart of color vision.

Several systems have been developed for specifying color. They derive mainly from the large body of work that has been done on the international standardization of television transmission methodology by standards organizations. A few of the more important color systems are listed.

For image processing purposes, some techniques are naturally more successful when carried out in one system or the other. It is, thus, useful to be able to convert between rectangular (RGB) and cylindrical color coordinates.

Sometimes, a digitized color image is obtained without the proper balance between the red, green, and blue components, or the RGB values may not truly represent the characteristics of the scene. In this case it may be necessary to perform a color correction step prior to processing or display, such as color image calibration, color image enhancement, segmentation, measurement, and display.
Endoscopy
Authors: Vakil Nimish , Affi Abboud
Published: October 2003

Endoscopy is an imaging method that is used to visualize the interior of human organs. The widest application of endoscopy is in the gastrointestinal tract. Specialized instruments have been developed to image specific gastrointestinal organs. Gastroscopes, which are passed through the mouth, are used to examine the esophagus, the stomach, and the duodenum. Enteroscopes, also through the mouth, are specially designed to examine the small intestine. Colonoscopes, passed through the anal orifice, are used to examine the lower gastrointestinal tract. There are two major classes of instruments, fiber‐optic endoscopes that consisting of a bundle of coaxial fiber‐optic bundles or electronic endoscopes that rely on a charge coupled device. The electronic endoscope consists of a charge‐coupled device that transmits an electronic signal resulting in an image that is visualized on a television monitor. Modern endoscopes, whether electronic or fiber‐optic contain three systems: (1) a mechanical system used to deflect the endoscope tip, (2) a system of air/water and biopsy/suction channels with controls. Insufflation of air is important to distend the walls of the organ being studied. Suction capabilities allow the aspiration of contents from the gastrointestinal tract for examination. In other cases, fluid in the gastrointestinal tract obscures the view and suction allows the fluid to be aspirated away. (3) The imaging system which may be fiber‐optic or electronic is used to visualize tissue. The most frequent reasons for which endoscopy is performed and the organs that are visualized are listed. Examples of endoscopic images are given.
Flow Imaging
Authors: Clemens Noel T.
Published: October 2003

Imaging has a long history in fluid mechanics and has proven critical to the investigation of nearly every type of flow of interest in science and engineering. A less than exhaustive list of flows where imaging has been successfully applied would include flows that are creeping, laminar, turbulent, reacting, high‐temperature, cryogenic, rarefied, supersonic, and hypersonic. The wide range of applications for flow imaging is demonstrated by the recent development of techniques for imaging at micro‐ and macroscales.

Traditionally, flow imaging has been synonymous with “flow visualization,” which usually connotes that only qualitative information is obtained. Owing to the complex and often unpredictable nature of fluid flows, flow visualization remains one of the most important tools available in fluid mechanics research.

Most imaging in fluid mechanics research involves planar imaging, where the flow properties are measured within a two‐dimensional cross section of the flow. This is most often accomplished by illuminating the flow using a thin laser light sheet, and then recording the scattered light using a digital camera. The laser light is scattered from either molecules or particles in the flow. The primary emphasis of this article is on this type of planar laser imaging because it remains the cornerstone of quantitative imaging in fluid mechanics research. Furthermore, planar imaging is often a building block for more complex 3‐D imaging techniques. Quantitative imaging is substantially more challenging than simple visualization because a greater degree of knowledge and effort are required before the researcher can ensure that the spatial distribution of the flow property of interest is faithfully represented in the image. The first part of this article discusses some of the most important issues that need to be addressed in quantitative flow imaging. The article ends with a brief survey of primarily planar imaging techniques that have been developed. This survey will not be able to discuss all, or even most, of the techniques that have been developed, but hopefully readers will gain an appreciation for the wide range of techniques that can be applied to their flow problems.
Holography
Authors: Jeong Tung H.
Published: October 2003

In an attempt to correct the spherical aberration of the electron microscope, Dennis Gabor gave birth to the basic concepts ofholographyin 1948, for which he was awarded the Nobel Prize in physics in 1971.

However, it was not until after the invention of the laser and further contributions by E. N. Leith and J. Upatnieks and independently by Yu. N. Denisyuk that holography was developed to the present stage.

In this chapter, concentration is on optical holography, although the concepts involved are applicable to any type of coherent waves. In particular, the recording and reconstruction of the wavefronts of a three‐dimensional object is analyzed. These analyses are applicable to hybrid developments to be summarized.

Generally, the process ofholographycan be defined as the recording of the interference pattern between two mutually coherent radiation fields on a two‐ or three‐dimensional medium. The result is said to be ahologram. It is a complex diffraction grating. When one of the fields is directed at the hologram, the diffraction reconstructs the wavefronts of the other field.

Holography can be studied and appreciated at many levels. It is sufficiently simple for those without a technical background to produce beautiful works of art. Indeed, it can now be pursued at the same level as photography. A graphic model is presented which offers intuitive understanding of volume holograms.
Lidar
Authors: Argall P. S. , Sica R. J.
Published: October 2003

Light detection and ranging (lidar) is a technique in which a beam of light is used to make range‐resolved remote measurements. A lidar emits a beam of light, that interacts with the medium or object under study. Some of this light is scattered back toward the lidar. The backscattered light captured by the lidar's receiver is used to determine some property or properties of the medium in which the beam propagated or the object that caused the scattering.

The lidar technique operates on the same principle as radar; in fact, it is sometimes called laser radar. The principal difference between lidar and radar is the wavelength of the radiation used. Radar uses wavelengths in the radio band whereas lidar uses light, that is usually generated by lasers in modern lidar systems. The wavelength or wavelengths of the light used by a lidar depend on the type of measurements being made and may be anywhere from the infrared through the visible and into the ultraviolet. The different wavelengths used by radar and lidar lead to the very different forms that the actual instruments take.

The major scientific use of lidar is for measuring properties of the earth's atmosphere, and the major commercial use of lidar is in aerial surveying and bathymetry (water depth measurement). Lidar is also used extensively in ocean research and has several military applications, including chemical and biological agent detection.

Atmospheric lidar relies on the interactions, scattering, and absorption, of a beam of light with the constituents of the atmosphere. Depending on the design of the lidar, a variety of atmospheric parameters may be measured, including aerosol and cloud properties, temperature, wind velocity, and species concentration.

This article covers most aspects of lidar as it relates to atmospheric monitoring. Particular emphasis is placed on lidar system design and on the Rayleigh lidar technique.
Neutron Imaging, Radiography, andCT
Authors: Smith Graham C.
Published: October 2003

The discovery of the neutron occurred in 1932, and the first neutron diffraction experiments were performed in the late 1940s. As usage progressively increased, the neutron has become a key probe in many fields of science, and sources around the world are now oversubscribed by experimenters. The European Spallation Source (ESS), and the Spallation Neutron Source (SNS), in the United State are new, high‐intensity sources under development that attest to the importance of neutrons as a probe. Because they are uncharged, neutrons are one of the most difficult particles to detect. Only a few elements in nature have a high affinity for neutron interaction. This article is organized as follows. The fundamental reactions upon which all neutron detection relies are described. Then a series of sections describe the main techniques of neutron detection and imaging: gas‐based, scintillator based, semiconductor‐based, film and image plates, and microchannel plates. In these sections, a few applications are noted. The section next to last focuses on neutron radiography/tomography, for which scintillator detectors and image plates are the primary imaging techniques. Some important reviews from recent literature for imaging techniques and for radiography are given. Techniques for (nonimaging) neutron detection have also recently been reviewed.
Stereo and 3‐DDisplay Technologies
Authors: McAllister David F.
Published: October 2003

Recently, there have been rapid advancements in 3‐D techniques and technologies. Hardware has improved and become considerably cheaper, making real‐time and interactive 3‐D available to the hobbyist, as well as to the researcher. There have been major studies in areas such as molecular modeling, photogrammetry, flight simulation, CAD, visualization of multidimensional data, medical imaging, teleoperations such as remote vehicle piloting and remote surgery, and stereolithography. In computer graphics, the improvements in speed, resolution, and economy make interactive stereo an important capability. Old techniques have been improved, and new ones have been developed. True 3‐D is rapidly becoming an important part of computer graphics, visualization, virtual‐reality systems, and computer gaming. Numerous 3‐D systems are granted patents each year, but very few systems move beyond the prototype stage and become commercially viable. Here, the salient 3‐D systems are treated.

First, the major depth cues that one uses to determine depth relationships among objects in a scene are described.

The history of 3‐D displays and an overview of technologies follow. Details are given on the viewing devices required. Large formats, such as IMAX are discused. Autostereoscopic displays with us viewing devices are discussed.
Cathode Ray Tube Display Technology
Authors: Barbin Robert L. , Poulos Anthony S.
Published: October 2003

The invention of the cathode ray tube (CRT) is generally ascribed to Karl Ferdinand Braun in 1897. His tube was the first to combining the basic functions of today's CRTs: electron source, focusing, deflection, acceleration, phosphor screen, and a sealed mechanical structure.

The basic components of a CRT used for color displays are electron gun, deflection yoke, phosphor screen, shadow mask, and glass bulb. There are many performance measures that can be used to characterize the quality of CRT displays. Some of the more important parameters and quantify the performance levels typically obtained in color television applications are described.

The design of a CRT typically starts with the selection of several basic parameters: screen size, deflection angle, and panel contour. These parameters are usually established by engineering and sales and allow a workable and manufacturable product to be delivered to the customer market.

Essentially all of today's direct view color CRTs use tricolor electron guns, which generate three electron beams, one to illuminate each of the primary phosphor colors. These generally use common grids for the three guns in which each of the grids have three apertures, one for each of the three electron beams. The cathodes are separated so that each of the three beams can be electrically modulated.
Optical Image Formation
Authors: Mouroulis Pantazis
Published: October 2003

For the greatest part of human history, visible light has been the only image forming medium. And until recently, visual telescopes and microscopes comprised the vast majority of image forming instruments. The image formation principles examined in this article derive from such venerable ancestry but are broader in their application. Whereas visible wavelengths span a range of less than 2 : 1 in the electromagnetic (EM) spectrum, the contents of this article can find application in devices operating across a wavelength range of ∼10
6
, from nanometers to millimeters. However, the middle part of that range, from about 100 nm to about 10 µm, contains practically all of the devices that are classified as optical instruments, and those are our main concern here.

The simplest device for whole‐field imaging is the pinhole camera. It comprises a square or rectangular box that has a small opening on one side.

The projection of the pinhole on the image plane, taken as approximately the same size as the pinhole itself, provides the
resolution limit
of the pinhole camera. Image details smaller than the pinhole size cannot be resolved. Any close examination of pinhole camera images reveals considerable blur. Thus, the pinhole camera has two fundamental problems: inferior resolution and a dim image.

Both of these problems are resolved by introducing a lens in place of the pinhole.

For any nonideal lens, the focal spot size depends on the specific construction of the lens, as well as on the object and image size or the angle at which rays strike the lens. When these realistic considerations are taken into account, it is found that increasing the lens size beyond a certain point normally leads to an increase in spot size or requires a complicated lens construction.

The subject of this article is a more detailed appreciation of the contents and implications of the above. The necessary background for much of this material is that of a first‐year college physics course. Specifically, some familiarity is assumed with the elementary concepts of a thin lens and its focal length/points and the basic concepts of wave optics. In addition to that, a proper understanding of the image formation concepts in a later section assumes some familiarity with the basic mathematics of Fourier transformations. Although some basic material of Fourier theory is reviewed in the Appendix, it is primarily useful as a refresher for those who already know something about the topic. However, a reader unfamiliar with such mathematics should still be able to appreciate that material because it is largely self‐contained, although significantly compressed through omission of most mathematical proofs. A deliberate attempt has also been made to provide simple physical arguments for most equations, and many illustrations have been included. Clearly, for a detailed understanding, the reader must resort to the references given.
Electron Microscopes
Authors: Dyck Dirk Van , Amelinckx S.
Published: October 2003

In past decades, electron microscopy has matured to an indispensable tool for materials and biomedical research. Numerous are the Nobel Prizes for research work in which electron microscopy revealed crucial evidence. Despite the very small wavelength of the electrons, it has only recently been possible to visualize individual atoms. The reason for this is that magnetic lenses inevitably suffer from aberrations that, contrary to glass lenses in a light microscope, cannot easily be corrected. Recently the problem of compensating the spherical aberration has become solved on the research level.

When individual atoms, the building blocks of nature, can be revealed, electron microscopy enters into a new era. Indeed, then it becomes possible to determine the atomic structure of matter quantitatively and accurately, even for objects for which only limited prior knowledge is available. Although the goal is not yet achieved, the progress is very encouraging. In the future, as materials science evolves into materials design, and mesostructures into nanostructures, the role of electron microscopy will become even more important.

In recent years one has also seen the development of related techniques such as scanning transmission electron microscopy (STEM), electron holography, ptychography, and add‐on techniques that use complementary information such as X‐ray analysis (EDX), and energy filtering. There is now a growing tendency to incorporate all these techniques into one versatile instrument under full computer control, where they are all considered as different ways to obtain complementary information, mainly of chemical nature.

The development of scanning electron microscopy (SEM) has taken place parallel to that of TEM. The SEM is conceptually simpler than the TEM. With the aid of magnetic lenses, the electron beam is focused into a small point that is scanned over the surface of the object. The backscattered electrons, or other secondary signals, can then be detected and synchronously displayed on a cathode‐ray‐tube (CRT) screen. The SEM is relatively easy to use and does not require extensive specimen preparation and is also less expensive than the TEM. On the other hand, it can only be used to study the surface area and, because of the beam spread in the object, its resolution is rather limited and quantitative interpretation of the images is more difficult.