Sampling-theory approach to eigenwavefronts of imaging systems

We present a direct method based on the sampling theorem for computing eigenwavefronts associated with linear space-invariant imaging systems (including aberrated imaging systems). A potential application of the eigenwavefronts to inverse problems in imaging is discussed. A noise-dependent measure for the information-carrying capacity of an imaging system is also proposed.     

Synthetic-focusing strategies for real-time annular-array imaging

Annular arrays provide a means to achieve enhanced image quality with a limited number of elements. Synthetic-focusing (SF) strategies that rely on beamforming data from individual transmit-to-receive (TR) element pairs provide a means to improve image quality without specialized TR delay electronics. Here, SF strategies are examined in the context of high-frequency ultrasound (>15 MHz) annular arrays composed of five elements, operating at 18 and 38 MHz. Acoustic field simulations are compared with experimental data acquired from wire and anechoic-sphere phantoms, and the values of lateral beamwidth, SNR, contrast-to-noise ratio (CNR), and depth of field (DOF) are compared as a function of depth. In each case, data were acquired for all TR combinations (25 in total) and processed with SF using all 25 TR pairs and SF with the outer receive channels removed one by one. The results show that removing the outer receive channels led to an overall degradation of lateral resolution, an overall decrease in SNR, and did not reduce the DOF, although the DOF profile decreased in amplitude. The CNR was >1 and remained fairly constant as a function of depth, with a slight decrease in CNR for the case with just the central element receiving. The relative changes between the calculated and measured quantities were nearly identical for the 18- and 38-MHz arrays. B-mode images of the anechoic phantom and an in vivo mouse embryo using full SF with 25 TR pairs or reduced TR-pair approaches showed minimal qualitative difference.     

Microwave tomography: From theory to practical imaging systems

This paper deals with numerical processing techniques and practical applications of active microwave imaging. Different wavefront processing are presented, from an immediate use of measured projections to more complex procedures. Both spectral approaches to diffraction tomography and spatial iterative methods for generalized imaging are considered using multi-incidence of multifrequency techniques for 3D and/or 2D objects. The technology of the so-called microwave camera is presented for the fast recording of the scattered field with arrays of probes involving one- or two-dimensional sensors at a single frequency or in a broad-frequency band. Three different systems are depicted: a single-frequency linear sensor devoted to industrial applications (on-line transverse control of conveyed products), a single-frequency planar microwave camera for biomedical applications and research, and a broad-frequency linear microwave camera for civil engineering applications (detection of the rebars in reinforced concrete strctures). Microwave images obtained experimentally with the three systems are presented on configurations of practical interest for each field of application.     

Application of magnetic resonance imaging techniques to particulate systems

Magnetic resonance imaging (MRI) is a well-established technique in the medical field, typically for imaging liquid water in the human body, but it is increasingly being used in the field of engineering and materials science. A particular section of this is in the area of particulate systems and granular material flows. MRI is being used to provide a unique insight into particle distribution and motion with in situ measurements. In this paper we discuss how judicious choice and development of imaging technique applied to various different granular systems can provide us with valuable new data on the processes occurring in granular flows. Experimental results focus on rotating bed segregation, velocity imaging in vertical fluidized beds and phase-resolved velocity distributions within vertical vibro-fluidized beds. A discussion of the various imaging techniques used to acquire these data is also given.     

Design approaches to power-over-optical local-area-network systems

This paper discusses fiber optic power and signal transmission systems considering the application of dc powering to information tools such as personal computers. We discuss system requirements and technical issues for the system components, including high-power laser diodes and photovoltaic cells. It is clarified that the conversion efficiencies of photovoltaic cells are kept constant with heat radiation and improve with extremely small series resistance. The transmittable optical powers through the optical fiber limited by a nonlinear optical effect are estimated. We also discuss the system designs for the use of single- and multi-mode optical fibers.     

Status review and research strategies on product-service systems

As present trends in economic and population growth continue, the natural environment is increasingly being stressed. More and more researchers, institutes and programmes have paid attention to product-service systems (PSSes) in the last decade because PSS integrates tangible artefact and intangible service to achieve sustainability, improve enterprise competitiveness, and meet customer needs better. In order to respond to the industrial trend towards PSS and frame the related research, the state-of-the-art of PSS research and development are reported. Furthermore, in order to integrate fragmental PSS solutions, this paper proposes a framework for product-service lifecycle management (PSLM) and technologies of PSS development. So, four categories are focused on: review of PSS, research about PSS development, a framework for PSLM, and technologies for PSLM (modular product-service development and ontology-based product-service knowledge expression and reuse). The preliminary solution of the implementation roadmap and technologies for PSLM which need to be perfected is proposed to lay a basis for further development and application of PSS for the benefit of industries.     

The use of flowlines to simplify routing complexity in two-stage flowshops

Flexible manufacturing systems are often designed as flowshops supported by automated material handling devices that facilitate routing among any two processors of adjacent stages. This routing structure is complex, and results in excessive capital investment and costs of management. In this paper we propose a decomposition of two-stage flowshops into smaller independent flowlines that allow for unidirectional routing only. We solve optimally the problem of minimizing makespan on two parallel flowlines, by means of a Dynamic Programming algorithm (DP). Based on DP we develop lower bounds on the throughput performance of environments that consist of more than two flowlines. We present several heuristic algorithms and report their optimality gaps. Using these algorithms, we show that the decomposition of two stage flowshops with complicated routing into flowline-like designs with unidirectional routing is associated with minor losses in throughput performance, and hence significant savings in material handling costs.     

New paradigm for imaging systems

We describe a new paradigm for designing hybrid imaging systems. These imaging systems use optics with a special aspheric surface to code the image so that the point-spread function or the modulation transfer function has specified characteristics. Signal processing then decodes the detected image. The coding can be done so that the depth of focus can be extended. This allows the manufacturing tolerance to be reduced, focus-related aberrations to be controlled, and imaging systems to be constructed with only one optical element plus some signal processing.     

Environmetric strategies to classify, interpret and model risk assessment and quality of environmental systems

The present paper deals with the application of some environmetric approaches such as cluster analysis, projection pursuit, Kohonen maps, neuron gas, principal components analysis, chemical mass balance modelling, multiple regression on principal components, and time-series analysis in environmental data mining. Several ecologically important objects including marine sediments, wet and dry atmospheric precipitation are treated in order to obtain relevant information about monitoring data set structure and relationships. Multivariate statistical models are offered, which could help in decision making and problem solution of the local environment. In this way the case studies are a contribution to the idea of the increasing role of the environmetrics in the concept of sustainable development.     

Tomographic imaging of particulate systems

The review illustrates selected applications of tomographic analysis applied to dry and wet particulate systems. The examples show the use of the method to gain information at different levels of inspection, such as the detailed structure of individual particles, structured particulate assemblies, and on the concentration and velocity of solids in a moving mixture. The utilization of the unique spatial information derived from tomography for the purpose of model validation, and, in some cases, for the monitoring and control of processes is discussed. Emerging applications show that utilization of tomographic methods can facilitate the creation of new and sophisticated models for particulate systems.     

Push and pull strategies for controlling multistage production systems

This study considers push and pull strategies to control multistage production systems with random processing times. Such systems are important as they mirror the level of complexity often encountered in practice. We start with definitions of push and pull systems, and develop a framework to compare multistage production systems based upon work-in-process (WIP) and throughput (TP) tradeoff. Surprisingly, we find that often push out performs pull, i.e. push systems accumulate less WIP than pull systems, while maintaining higher PT Concerning pull systems we find that WIP linearly increases in the number of stages and that WIP is not affected by variation in processing time. Concerning push systems we find that the release of material into the system in deterministic time intervals greatly improves performance.     

Data acquisition and postprocessing strategies for fast quantitative sodium imaging

An efficient scheme for quantitatively mapping the three-dimensional distribution of the sodium ion in vivo using magnetic resonance imaging is described. To make the methodology totally quantitative, the data acquisition scheme is performed with very short echo times and negligible T₁ saturation. Removal of signal variation due to imperfect radiofrequency (RF) response is accomplished using RF inhomogeneity maps acquired during each study. The high efficiency of the k-space trajectories allows the entire data collection process to be performed in under 10 min. The theory underlying the data collection and processing scheme is described along with representative examples acquired at 1.5 and 3.0 T. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 544–550, 1997     

On systems with shared resources and optimal switching strategies

Simple series systems of identical components with spare parts are considered. It is shown that the cumulative distribution function of a system failure time tends to be a step function as the number of components increases and resources can be shared. An example of ‘continuous resources’ is also described. The time-sharing strategy for standby systems is investigated. It is proved that an optimal rule for a system of standby components with increasing failure rates is the single switching performed at a=t/2, where t is the mission time.     

Nomarski imaging interferometry to measure the displacement field of micro-electro-mechanical systems

We propose to use a Nomarski imaging interferometer to measure the out- of-plane displacement field of micro-electro-mechanical systems. It is shown that the measured optical phase arises from both height and slope gradients. By using four integrating buckets, a more efficient approach to unwrap the measured phase is presented, thus making the method well suited for highly curved objects. Slope and height effects are then decoupled by expanding the displacement field on a functions basis, and the inverse transformation is applied to get a displacement field from a measured optical phase map change with a mechanical loading. A measurement reproducibility of approximately 10 pm is achieved, and typical results are shown on a microcantilever under thermal actuation, thereby proving the ability of such a setup to provide a reliable full-field kinematic measurement without surface modification.     

A historical view of imaging systems and technology

When approached from a historical viewpoint the development of many important imaging systems throughout history often share common ground. Extremely important was the development of the idea of mathematical projection which provides methods for making an image that conformally represents the object. The prime example is the discovery of the stereographic projection by Hipparchus of Nicaea in the second century BC. The stereographic projection provided the basis for the astrolabe, an astronomical device that acted both as an instrument of observation and as an analog computer. The stereographic projection and similar ones also provided the basis for the world maps of the ancients which utilized a grid of longitude and latitude. When the ancient Greek books were rediscovered in the Renaissance, the maps provided the impetus for the age of exploration. The Mercator projection of the sixteenth century was obtained as a logarithmic transformation of the stereographic projection. The Mercator projection provided sea captains with maps that had a rectangular grid of latitude and longitude and also had the property that straight lines represented courses of constant compass directions. The development of the telescope and microscope in the early seventeenth century provided means to obtain images that could not be seen by the unaided eye. Galileo's discovery of the moons of Jupiter led to Roemer's determination in 1676 that light travels at a finite velocity. Unknowingly, Roemer also discovered the relativistic Doppler effect, which in the present century helped to establish our concept of the expanding universe. The relativistic Doppler factor mathematically is none other than the expression for the stereographic projection of Hipparchus. The development of high energy physics in this century has led to images of the microworld of subatomic particles. In this environment Einstein's equation E = mc² finds verification. This equation is a result of the theory of special relativity. The basic mathematics of special relativity is contained in the Lorentz transform. Again we can return to Hipparchus, because the Lorentz transform follows from a sequential application of the stereographic projection.     

Refrigerant charge in refrigerating systems and strategies of charge reduction

For some years, European regulation concerning refrigerating systems has become more and more severe. Because of their design and technology, refrigeration units cannot avoid refrigerant leaks, and can thus have a harmful impact on the environment. Many studies aimed at minimizing the charge in a refrigerating machine were thus developed. On a global level, reduction of refrigerant charges must not affect energy aspects while respecting environmental constraints [Montreal 1987, Kyoto 1997]. The architecture and refrigerant charge distribution in the systems are of particular importance; their analyses permit the determination of the target elements and thus define those in which the refrigerant charge could be reduced (heat exchangers, liquid pipes, receivers, …). This paper presents a review of the refrigerant charge studies in a refrigerating plant (methodologies of charge measurement, void fraction correlations and characteristic values for various technologies). It also evaluates the influence of the refrigerant charge on the coefficient of performance (COP) and on the cooling capacity. Finally, it inventories the different means that allow the charge in a refrigerating system to be minimized.