A DSP-based mixed-signal waveform generator

As it currently stands, waveform generators are being employed in many diverse areas, such as radar applications, communication systems, simulation, and testing. There is considerable interest in exploring the beacon of opportunity posed by using digital signal processor (DSP)-based systems to replace costly and inadequate conventional waveform generators. The availability of high performance DSPs allows for the design of highly flexible equipment capable of real-time processing. The arbitrary waveform generator introduced in this paper consists of a DSP, a FIFO memory, a video palette, and a PC interface. A program running on the PC creates a digital representation of a waveform according to user parameters and sends it to the DSP's RAM. The DSP algorithmically converts the digital representation to a point-by-point representation of the desired analog signal. The data points are sent to the FIFO buffer, which latches the data to a video palette that serves a three-channel digital-to-analog converter. The system employs a high-speed serial port interface to communicate with a PC, to allow for readily programmed signals. In addition to the production of traditional signals, such as sinusoids and squarewaves, a mathematical tool known as splines is employed to aid in the development of customized arbitrary waveforms. Finally, a picture of our new device is presented in the paper.     

Time-dependent linear systems derivable from a variational principle

This paper presents a study of time-varying linear systems of second order ordinary differential equations, which can be derived from a Lagrangian after multiplication by a suitable matrix. It concerns a generalization of previous studies on systems with constant coefficients. After a simplification of the Helmholtz conditions, it is shown that the problem is reduced to a purely algebraic one, provided one can solve a matrix differential equation which produces the transformation to canonical form of the given system. This further leads to a theoretical characterization of all systems admitting a multiplier. Various algebraic relations are derived, involving constant matrices only, which can help to detect, prior to any integration procedure, whether or not: a multiplier exists. They are referred to as the generalized commutativity conditions. The first of these, which is sufficient for the existence of a Lagrangian, is shown to allow also a simple construction of a quadratic first integral, and to have some other interesting features. The paper ends with an example.     

A filter for on-line estimation of spectral content

A robust filter algorithm to extract, a posteriori, the rational signal model from a noisy measurement, with little a priori information, is proposed. The spectrum and the statistics of the signal and of the corrupting noise are assumed unknown, except that the signal is assumed to have a rational spectrum. An algorithm based on system and signal theory is derived to select a set of frequencies where the signal-to-noise ratio (SNR) is high from a given measurement spectrum. The density of selected frequencies weights the importance of the measurement as a function of frequency, An estimate of the signal model is obtained from the best weighted least-squares fit to the measurement spectrum at the selected frequencies. The proposed filter has applications to control and signal processing, and a wide variety of applications are presented. Applications include: system identification of a dc motor and a two-link manipulator, extraction of a myo-electric signal from a noisy measurement, the assignment of a rational model to a vegetation tissue's impedance, and to the number density profile of atmospheric oxygen     

On the equilibrium of a linear elastic layer

A general method for the construction of a 3D solution applicable to the equilibrium of a linear elastic layer which is subjected to a general load of bending or stretching is discussed. In the special case of a layer with faces free of stress, the general solution is derived explicitly. The general solution has a sufficient number of arbitrary functions to allow it to be used to solve a whole class of practical 3D problems, e.g. an inclusion, a partial through-the-thickness crack, a cylindrical hole etc.     

COMPUTER AIDED DESIGN OF HORN RADIATORS FOR SATELLITE COMMUNICATION BY LEAST SQUARES OPTIMIZATION

Computer aided design optimization of corrugated horns became a powerful tool to reduce development costs on the one hand and to improve performance of space antennas on the other. In this paper the physical model is outlined, based on Maxwell's equations, and it is shown how a complete numerical simulation of a circular corrugated horn can be achieved, assuming that the interior geometry of the horn is known. In order to compute the electromagnetic properties of a horn, the so-called scattering matrix is assembled. This matrix is needed to relate mode amplitudes of reflected and transmitted waves in horn sections with different diameters. Envelope functions, determined by a few geometric design parameters, are used to describe the inner geometry of a horn. These parameters are applied to formulate a least squares optimization problem. As a starting point, an amplitude spectrum in the aperture has to be determined which radiates a given far field. The differences between those amplitudes and the amplitudes predicted by the model are to become as small as possible by adapting the design variables. Moreover, the return loss is to be minimized. The resulting least squares optimization problem can be solved by a standard sequential quadratic programming (SQP) code after a suitable transformation into a nonlinear programming problem, by which typical features of Gauss-Newton methods are retained. Some numerical results are included to show the successful application of the introduced advance to design a circular corrugated horn which radiates a given far field.     

The Department of Health perspective on handling uncertainties in health sciences

Recognizing and working with uncertainty in handling risk are part of both clinical practice and the policy-making process. The Department of Health recognizes the inherent challenges that uncertainty brings and employs a wide range of research mechanisms, drawing on a diverse set of disciplines, to provide an evidence base to inform both policy creation and implementation, and clinical practice. This paper describes a variety of situations and the Government response to them, each time highlighting the use of science to reduce unknowns and to support decision-making. It highlights the need for a strong research infrastructure to support the Department's requirements, and those of the NHS, both in real time to respond to emergencies and to establish a high standard of care. However, although science provides a powerful tool to reduce uncertainty, it will not always produce definitive answers and often provides the start point for a dialogue between decision makers and researchers.     

All-optical 100-Gbit/s word packet time-division-multiplexed access node in a looped-back configuration: enabling technologies for sequential add-drop functionality

We experimentally demonstrate the adding, dropping, and passing through of 100-Gbit/s word packets in a looped-back all-optical time-division-multiplexed (TDM) access node. Packets are routed with a 17-dB contrast ratio and demultiplexed with a 20-dB contrast ratio. This node uses short 100-Gbit/s words to demonstrate its potential to process data packets from multiple sources and to perform packet switching in a multinode ring network configuration. The ability to tolerate timing jitter as well as varying input signal characteristics is essential to an all-optical access node in a multinode network. For 2-ps input pulses, the header processor has a timing window of ~5 ps, and the demultiplexer has a timing window of ~5.5 ps. This allows for tolerance to bit-to-bit timing jitters or to an increase in the pulse width of as much as 3 ps. Packet-to-packet timing jitter is detected and compensated by the technique used to synchronize the local source to each packet. The key enabling technologies of an all-optical TDM packet add-drop multiplexer are discussed, including an erbium-doped fiber laser, a nonlinear optical loop mirror logic gate, self-synchronization to incoming packets with a fast-saturation/slow-recovery gain element followed by an intensity discriminator, a two-wavelength nonlinear optical loop mirror demultiplexer, and synchronization of new packets to the network packet rate with a phase-locked loop. The local source is automatically synchronized to the incoming packet, because it uses an extracted pulse from the packet, which has a contrast ratio of >20 dB to the rest of the packet. Finally, new packets are added by use of a local laser and a synchronization method, which gives a timing jitter of ~1 ps. Using a statistical method of measuring Q value with picosecond resolution, we show that a header processor with two cascaded logic gates has a Q value of 7.1 with a 95% confidence level.     

Modeling of ultrasonic wave propagation in integrated piezoelectric structures under residual stress

The objective of this study is to understand the role of residual stress in piezoelectric layers in order to predict the performance of integrated structures. This is of particular importance in thick or thin film technology. Considering a bulk piezoelectric material, the Christoffel equation for a piezoelectric material is modified to take into account a uniform residual stress on a given cross section. A numerical study of its influence is carried out on the slowness curves and coupling coefficients of a lithium niobate material. In a second part, modified Christoffel tensor is used to calculate the dispersion curves of Lamb waves in a piezoelectric plate. The Lamb modes are found to be sensitive to the residual stress. In particular, it is shown how the behavior of the first Lamb modes is modified with residual stress. In a third part, these results are extended to a piezoelectric film laid down on a substrate in order to model the importance of these phenomena on the behavior of an integrated structure. The numerical study of guided waves in a lithium niobate plate is performed first, then the case of a lithium niobate film laid down on a silicon substrate is considered.     

Scheduling of open-pit phosphate mine extraction

Open-pit deposits are often characterised by a stack of layers of different geological nature. Some layers are worthless while the ore of the others is of a varying economic value depending on grade. To reach a layer, it is necessary to have first removed the upper layers above the extraction zone. This action results in uncovering the layer in this particular place and in facilitating access to the layers below. This extraction process involves a series of 2–7 basic operations; each one is performed by a machine, some of which are able to perform up to three different operations. Ensuring the consistency of mining extraction scheduling over a few months, in order to meet known or forecast demand, is a challenging task. A mining extraction model based on mathematical programming is proposed but it is hardly usable, due to its size. Therefore, a model based on a Discrete Event Simulation, is created to test how ore supplies are affected by the tactical and operational decisions relating to the choice of parcels to be processed and to the allocation of machines to the different basic operations.     

Final purchase and trade-in decisions in response to a component phase-out announcement: a deterministic analysis

We investigate a problem faced by a durable goods manufacturer of a product that is no longer manufactured but still under warranty. A supplier announces that a component of the product will be phased out and specifies a deadline for the final order. A common response in traditional practice is to place a final order sufficient to cover future warranty claims. We analyse and compare this policy with two policies that use trade-in programmes to supplement the final order quantity: (i) A full trade-in policy where the firm issues a one-time offer to the entire population that has the product under warranty, and (ii) a matching trade-in policy where the firm issues a trade-in offer to a fraction of the warranty population in each period. Our analysis of a deterministic model leads to two main conclusions. First, we find that the savings from the use of a trade-in programme can be significant, and we identify easy-to-estimate measures that drive the magnitude of savings. Second, we find that a full trade-in policy is likely to be preferred over a matching trade-in policy. The policy is also easier and more practical to implement. However, if uncertainty in warranty demand is introduced, then a firm may benefit by combining elements of both policies – an initial offer to a sizable fraction of the warranty population followed by periodic offers to remaining segments over time.     

Neural networks for contract bridge bidding

The objective of this study is to explore the possibility of capturing the reasoning process used in bidding a hand in a bridge game by an artificial neural network. We show that a multilayer feedforward neural network can be trained to learn to make an opening bid with a new hand. The game of bridge, like many other games used in artificial intelligence, can easily be represented in a machine. But, unlike most games used in artificial intelligence, bridge uses subtle reasoning over and above the agreed conventional system, to make a bid from the pattern of a given hand. Although it is difficult for a player to spell out the precise reasoning process he uses, we find that a neural network can indeed capture it. We demonstrate the results for the case of one-level opening bids, and discuss the need for a hierarchical architecture to deal with bids at all levels.     

The inviscid dynamics of vorticity structures and their interaction with a solid body

A simple model is proposed to study the interaction of a vorticity structure with a solid body in a two dimensional flow at large Reynolds numbers. The vorticity dynamics is efficiently described in inviscid terms by a multilevel Contour Dynamics technique and the boundary layer is modelled as a vortex sheet attached to the body wall. The collision between two Lamb dipoles, initially with parallel shifted axis, is investigated as a first application of the model in the free space. The evolution of the vorticity field leads to the formation of complicated structures, including filaments and high stretched regions, which require a careful control of the time integration accuracy to gain a better confidence in the numerical results. Several first integrals of motion (e.g. global circulation, vorticity moments, excess energy) are introduced to this purpose and extended, when possible, to the case of vorticity evolution in presence of a solid body.The motion of a finite core vortex, induced by a circular cylinder co-rotating or counter-rotating with respect to the vortex itself, is analyzed first by a Boundary Elements scheme. In this case the interaction doesn't lead to a collision and the model's main features, i.e. the inviscid Contour Dynamics and the vortex sheet attached to the body boundary, seem to be consistent and appropriate to study the vorticity patch evolution. The collision between a Lamb dipole and a circular cylinder has been also investigated. This case is more complex and it would imply a continuous generation of vorticity at the body wall and its separation due to the action of viscosity leading eventually to the vortex rebound phenomenon. Therefore, the present model is suitable only to study the effect of the vorticity structure initial configuration and its behavior in the first stage of the collision process.     

Designing a Bayesian network for preventive maintenance from expert opinions in a rapid and reliable way

In this study, a Bayesian Network (BN) is considered to represent a nuclear plant mechanical system degradation. It describes a causal representation of the phenomena involved in the degradation process. Inference from such a BN needs to specify a great number of marginal and conditional probabilities. As, in the present context, information is based essentially on expert knowledge, this task becomes very complex and rapidly impossible. We present a solution, which consists of considering the BN as a log-linear model on which simplification constraints are assumed. This approach results in a considerable decrease in the number of probabilities to be given by experts. In addition, we give some simple rules to choose the most reliable probabilities. We show that making use of those rules allows to check the consistency of the derived probabilities. Moreover, we propose a feedback procedure to eliminate inconsistent probabilities. Finally, the derived probabilities that we propose to solve the equations involved in a realistic Bayesian network are expected to be reliable. The resulting methodology to design a significant and powerful BN is applied to a reactor coolant sub-component in EDF Nuclear plants in an illustrative purpose.     

Coordination of joint pricing-production decisions in a supply chain

We consider the coordination of dynamic, joint pricing-production/ordering decisions in a decentralized supply chain where a manufacturer outsources her product distribution/retailing function to an independent distributor/retailer. The manufacturer produces and wholesales her product to the distributor who, after some further processing, sells the product to an external market. In a leader-follower setting with convex production/ordering cost functions, both parties make pricing and production/ordering decisions over a discrete, finite-time horizon (a selling season) to maximize their respective profits. For a given manufacturer's (the leader's) wholesale price schedule, we develop a simple forward algorithm to solve the distributor's problem optimally, and prove a planning horizon property of the solution. Our key result is to show the existence of a manufacturer's price schedule that induces distributor to adopt decisions in the decentralized setting to achieve the performance of a centralized supply chain. Based on this channel-optimal pricing policy we then develop an incentive scheme for the manufacturer to achieve channel coordination. A numerical example is provided to compare the performance of different policies and lo reinforce key managerial insights generated through analysis.     

Allocating work in process in a multiple-product CONWIP system with lost sales

To operate a multiple-product manufacturing system under a CONWIP control policy, one must decide how to assign kanbans to products. With a fixed total number of kanbans in a competitive environment, the goal is to determine their allocation to product types in order to minimize lost sales equitably. In particular, we consider systems in which the products may make multiple visits to the same station with a different processing time distribution on each repeat visit. With a fixed number of kanbans dedicated to each product, the system is modeled as a multiple-chain multiple-class closed queuing network. A nonlinear program simultaneously provides an approximate performance evaluation and optimizes the allocation of kanbans to product types. In numerical examples, the allocations identified are similar to those obtained by exhaustive enumeration with simulation, but frequently differ significantly from a naïve allocation according to demand rates. A variant of the model that minimizes the total work-in-process to achieve specified throughput targets yields results similar to a previous heuristic method.     

Toughness-dominated Hydraulic Fracture with Leak-off

This paper considers the problem of a hydraulic fracture in which an incompressible Newtonian fluid is injected at a constant rate to drive a fracture in a permeable, infinite, brittle elastic solid. The two cases of a plane strain and a penny-shaped fracture are considered. The fluid pressure is assumed to be uniform and thus the lag between the fracture front and the fluid is taken to be zero. The validity of these assumptions is shown to depend on a parameter, which has the physical interpretation of a dimensionless fluid viscosity. It is shown that when the dimensionless viscosity is negligibly small, the problem depends only on a single parameter, a dimensionless time. Small and large time asymptotic solutions are derived which correspond to regimes dominated by storage of fluid in the fracture and infiltration of fluid into the rock, respectively. Evolution from the small to the large time asymptotic solution is obtained using a fourth order Runge–Kutta method.     

Performance of a drag transducer under simulated PWR refill/refloodflow conditions

A strain gage-based drag transducer developed to measure two-phase flow in simulated PWR (pressurized-water reactor) test facilities is discussed. The drag sensor was designed to sample a large amount of the flow with minimum disturbance to the flow, to be sensitive over a 1000-to-1 range, to be accurate over a 200:1 turndown ratio, and to survive in a hostile steam/water environment. The drag transducer consists of a unique combination of an elongated proving ring, a temperature-compensated, full-bridge strain gage configuration, and a drag target that utilized part of the test vessel internals. The drag body measurement system produced high-quality data for a variety of test conditions, which has led to a better understanding of the phenomena occurring during the refill/reflood stages of a postulated PWR loss-of-coolant accident     

A case-based reasoning approach toward developing a belief about the cost of concept

It is generally acknowledged that product development involves a sequence of decision making under uncertainty, including setting target requirements for a new product, selecting product concept, and developing conceptual and detailed design of a chosen concept. To select a product concept, engineers need to assess the uncertainty of a future market share, market size, and a cost of concept (cost of the final product developed from a concept). This paper proposes a case-based reasoning (CBR) approach to model beliefs about the uncertainty of a cost of concept. The proposed CBR approach consists of storing information about various products in a knowledge-base, defining a new product concept, retrieving a cluster of products in the knowledge-base that are highly similar to the concept, and adapting the cost of the retrieved product to construct a distribution of the cost of concept. This paper illustrates the proposed approach using printers as an example.     

An approach to the dynamic modelling of manufacturing systems

Because of their complexity manufacturing systems are difficult to model. However, modelling is very often required in order to study the behaviour of the system. In this paper an approach is described, where an analogy is drawn between the behaviour of a manufacturing and a mechanical system. Manufacturing systems have to respond to a dynamic demand, namely, a demand that changes over time. Flexibility of a manufacturing system can be thought of as the ability and the rapidness with which the system responds to the dynamic demand. This resembles the behaviour of a mechanical system under the excitation of a force that changes over time. The paper attempts to establish a modelling method based on this analogy and uses this method in the study of a real industrial system.