Abstract: Theoretical models of the detective quantum efficiency (DQE) provide insight into fundamental performance limitations and standards to which particular systems can be compared. Over the past several years, cascaded models have been developed to describe the DQE of several flat panel detectors. This article summarizes the governing principles of cascaded models, and conditions that must be satisfied to prevent misuse. It is shown how to incorporate: a) poly-energetic x rays; b) Swank noise; c) the Lubberts effect; d) reabsorption of K x rays from photo-electric interactions; e)secondary quantum noise; and, f)noise aliasing. Cascaded models involve cascading theoretical expressions of the noise-power spectrum (NPS) through multiple stages. Most expressions involve two or three terms, requiring the manipulation of algebraic expressions consisting of hundreds of terms. This practical limitation is alleviated using MATLAB's Simulink programming environment and symbolic math manipulations. It is shown that even for an 'indirect' detector, noise aliasing reduces the DQE by up to 50 percent at the cut-off frequency. Secondary quantum noise is generally a small effect, but reabsorption can reduce the DQE by 20-25 percent over a wide range of spatial frequencies.

Abstract: This paper addresses the problem of space compaction of test responses of combinational and scan-based sequential circuits. In a general circuit, compaction of output space to a single output with zero-aliasing cannot always be achieved by earlier known approaches. In this work, it is shown that given a precomputed test set T, the test responses at the functional outputs of any arbitrary circuit-under-test (CUT) can be compacted to a single periodic output, with guaranteed zero aliasing. All the errors that are produced by T at the outputs of the CUT will also appear at the output of the compactor. The method is independent of the fault model and the structure of the CUT and uses only the knowledge of the test set T and the corresponding fault-free responses. A new concept of distinguishing outputs and a characteristic function is used to design the compactor. The test vectors in T are appropriately ordered to optimize the compactor logic, which to achieve zero-aliasing uses a test pattern counter to designate the sequence of test application and a special code checker. A design procedure is described to synthesize the compactor using logic synthesis tools, and relevant experimental results on hardware overhead for several benchmark circuits are presented. It is further shown that the overhead can be significantly reduced if the constraint of exact zero aliasing is slightly relaxed.

Abstract: A system for temporary aliasing is provided. A representative system includes a database system operable to store a plurality of network profiles, each network profile being associated with a user. The database system being further operable to provide a first user with a temporary alias to allow addition of the temporary alias to a network profile associated with a second user. The system further includes a service manager coupled to the database system and operable to remove the temporary alias from the network profile of the second user. Methods and other systems for temporary aliasing are also provided.

Abstract: The possibility of aliasing between objects constitutes one of the primary challenges in understanding and reasoning about correctness of object-oriented programs. Ownership types provide a principled way of specifying statically enforcable restrictions on object aliasing. Ownership types have been used to aid program understanding and evolution, verify absence of data races and deadlocks in multithreaded programs, and verify absence of memory errors in programs with explicit deallocation. This paper describes an efficient technique for supporting safe runtime downcasts with ownership types. This technique uses the type passing approach, but avoids the associated significant space overhead by storing runtime ownership information only for objects that are potentially involved in downcasts. Moreover, this technique does not use any interprocedural analysis, so it preserves the separate compilation model of Java. We implemented our technique in the context of Safe Concurrent Java, which is an extension to Java that uses ownership types to guarantee the absence of data races and deadlocks in well-typed programs. Our approach is JVM-compatible: our implementation translates programs to bytecodes that can be run on regular JVMs.

Abstract: An insufficient sampling rate can cause the introduction of unwanted effects in the samples of the image: the aliasing phenomenon. The aim of this paper is to investigate the possibility to mitigate the aliasing effects, trying to respect as much as possible the Shannon criteria for the image sampling. A model for the system modulation transfer function (MTF) of a hyperspectral push-broom sensor is developed. Quantitative quality indexes are adopted in order to assess the aliasing effects on the images. By using the MTF and the quality indexes, the relationship between aliasing and parameters of the optical system or of the electronic apparatus will be investigated. An alternative and more effective solution could be to try to respect as much as possible the Shannon criteria. Recent improvements in CCD technology make hexagonal sampling feasible for practical applications and bring a new interest on this topic. In our work, the advantages of hexagonal sampling with respect to conventional rectangular sampling are analysed under general assumptions. Nevertheless, using a hexagonal detector has an impact on the detection and imaging chain. In particular, processing steps must take into account the improved sampling geometry. This leads to adaptation of existing algorithms and even new processing architectures.

Abstract: Aliasing and routing of plural MPEG data streams are disclosed. Disclosed apparatus embodiments include, e.g., a router or a cross-point switch that can route data packets from any source location(s) to any destination location(s). Such locations may be on multiple targets on a single processing board or may be on multiple boards in a chassis with a backplane linking the boards together. The disclosed aliasing and routing is achieved by processing MPEG data streams with associated PIDs so they can be transported between communicatively linked locations. This is achieved by generating a PID alias table with plural PID aliases for each input data stream; by removing at least one PID from each input data stream to thereby produce filtered data streams; by determining target destination(s) for each of the filtered data streams; and by buffering the filtered data streams so the filtered data streams can then be read and transported to respective target destination(s).

Abstract: Simulation is the most widely used technique to prove data refinement. We define forward simulation for a language with recursive classes, inheritance, type casts and tests, dynamic binding, class based visibility, mutable state (without aliasing), and specification constructs from refinement calculi. It is a language based on sequential Java, but it also includes specification and deseign mechanisms appropriate for the construction of programs based on refinement. We show simulation to be sound for data refinement of classes in this language.

Abstract: In Obliq, a lexically scoped, distributed, object-oriented programming language, object migration was suggested as the creation of a copy of the state of an object at the target site, followed by turning the object itself into an alias, also called surrogate, for the remote copy. We consider the creation of object surrogates as an abstraction of the above-mentioned style of migration. We introduce Ojeblik, a typed distribution-free subset of Obliq, and provide four different configuration-style semantics, which only differ in the respective aliasing model. We show that two of the semantics, one of which matches Obliq's implementation, render migration unsafe, while our new proposal allows for safe migration at least for a large class of program contexts. In addition, we propose a type system that allows a programmer to statically guarantee that programs belong to that class. Our work suggests a straightforward repair of Obliq's aliasing model.

Abstract: We integrate existential types into a strongly typed C-like language. In particular, we show how a bad combination of existential types, mutation, and aliasing can cause a subtle violation of type safety. We explore two independent ways to strengthen the type system to restore safety. One restricts the mutation of existential packages. The other restricts the types of aliases of existential packages. We use our framework to explain why other languages with existential types are safe.

Abstract: Line-pair phantoms are commonly used for evaluating screen-film systems. When imaged digitally, aliasing effects give rise to additional periodic patterns. This paper examines one such effect that medical physicists are likely to encounter, and which can be used as an indicator of super-resolution.

Abstract: One of the primary challenges in building and evolving large object-oriented systems is understanding aliasing between objects. Unexpected aliasing can lead to broken invariants, mistaken assumptio...

Abstract: We present a learning algorithm for two player stochastic games. The algorithm generates optimal deterministic finite automata (DFA) strategies against opponents who can be modeled by probabilistic action automata. The algorithm generates dynamic history trees based on statistical tests to eliminate state aliasing. Experiments are conducted in an iterated prisoner's dilemma environment.

Abstract: This paper describes a technique for utilizing predication to support software pipelining on EPIC architectures in the presence of dynamic memory aliasing. The essential idea is that the compiler generates an optimistic software-pipelined schedule that assumes there is no memory aliasing. The operations in the pipeline kernel are predicated, however so that if memory aliasing is detected by a run-time check, the predicate registers are set to disable the iterations that are so tightly overlapped as to violate the memory dependences. We refer to these disabled kernel operations as software bubbles.

Abstract: The Woods Problem is a difficult problem for purely reactive systems to handle. The difficulties are related to the perceptual aliasing problem, and the use of internal memory has been suggested to solve the problem. In this paper a novel approach in evolutionary computation is introduced to quantify the amount of memory required for a given task. The approach has been applied to Woods Problems such as wood101, woods102, Sutton's gridworld and woodsl4. Finite state machine controllers are used, as these permit easy measurement of the amount of memory in the controller. A concurrent evolutionary search for the minimal but optimal control structure in memory-based systems, using an evolutionary Pareto-optimal search mechanism, determines the best behavior fitness for each level of controller memory. This memory analysis demonstrates the effect of internal memory in evolved controllers for Woods Problems and is also used to investigate the relationship between the number of sensors available to an agent and the amount of memory necessary for effective behavior.

Abstract: The Woods Problem is a difficult problem for purely reactive systems to handle. The difficulties are related to the perceptual aliasing problem, and the use of internal memory has been suggested to solve the problem. In this paper a novel approach in evolutionary computation is introduced to quantify the amount of memory required for a given task. The approach has been applied to Woods Problems such as wood101, woods102, Sutton's gridworld and woods14.Finite state machine controllers are used, as these permit easy measurement of the amount of memory in the controller. A concurrent evolutionary search for-the minimal but optimal control structure in memory-based systems, using an evolutionary Pareto-optimal search mechanism, determines the best behavior fitness for each level of controller memory. This memory analysis demonstrates the effect of internal memory in evolved controllers for Woods Problems and is also used to investigate the relationship between the number of sensors available to an agent and the amount of memory necessary for effective behavior.

Abstract: In this paper we present ATNoSFERES, a new framework based on an indirect encoding Genetic Algorithm which builds finite-state automata controllers able to deal with perceptual aliasing We compare it with XCSM, a memory-based extension of the most studied Learning Classifier System, XCS, through a benchmark experiment We then discuss the assets and drawbacks of ATNoSFERES in the context of that comparison

Abstract: Spatially variant longitudinal aliasing plagues most volumes reconstructed from single-slice helical computed tomography data, and its presence can degrade resolution and distort image structures. We have recently developed a Fourier-based approach to longitudinal interpolation in helical computed tomography that can, for scans performed at pitch 1 or lower, essentially eliminate this longitudinal aliasing by exploiting a generalization of the Whittaker-Shannon sampling theorem whose conditions are satisfied by the interlaced pairs of direct and complementary longitudinal samples. However, the algorithm is computationally intensive and cannot be pipelined. In this paper, we address this shortcoming by deriving two spatial-domain, projection-data weighting functions that approximate the application of the Fourier-based approach, and preserve its aliasing suppression properties to some degree, while allowing for a pipelined implementation. The first approach, which we call simply 180AA, for anti-aliasing, is a direct spatial-domain approximation of the 180FT approach. The second approach, which we call 180BSP, is based on an approximate generalized interpolation approach making use of B-splines. Studies of aliasing and resolution properties in reconstructions from simulated data indicate that while the 180AA and 180BSP approaches do not perfectly replicate the favorable aliasing suppression and resolution properties of the 180FT approach, they do represent an improvement over the clinically standard 180LI approach on these fronts.

Abstract: A-36 RAY-BASED ANTI-ALIASING FOR DEPTH MIGRATION S.NGUYEN 1 R. BAINA 2 M. NOBLE 1 and P. THIERRY 1 Abstract 1 Operator/Imaging aliasing introduced in Kirchhoff migration is often tackled by trace tapering aperture truncation or a time and offset-variant filtering. The latter being the most suitable. However most implementations and published results using this technique are derived for Kirchhoff time migration and assume a constant velocity media. In this paper we introduce an anti-aliasing filter for ray-based pre-stack depth migration and valid for heterogeneous velocity models. We illustrate the benefits of such a scheme on a numerical and a real

Abstract: In this work, we investigate longitudinal sampling and aliasing effects in multi-slice helical CT. We demonstrate that longitudinal aliasing can be a significant, complicated, and potentially detrimental effect in multi-slice helical CT reconstructions. Multi-slice helical CT scans are generally undersampled longitudinally for all pitches of clinical interest, and the resulting aliasing effects are spatially variant. As in the single-slice case, aliasing is shown to be negligible at the isocentre for circularly symmetric objects due to a fortuitous aliasing cancellation phenomenon. However, away from the isocentre, aliasing effects can be significant, spatially variant, and highly pitch dependent. This implies that measures more sophisticated than isocentre slice sensitivity profiles are needed to characterize longitudinal properties of multi-slice helical CT systems. Such measures are particularly important in assessing the question of whether there are preferred pitches in helical CT. Previous analyses have generally focused only on isocentre sampling patterns, and our more global analysis leads to somewhat different conclusions than have been reached before, suggesting that pitches 3, 4, 5, and 6 are favourable, and that half-integer pitches are somewhat suboptimal.

Abstract: The effects of aliasing and polar data gap have been investigated analytically and numerically for the upcoming dedicated gravity satellite missions. It is verified that they could cause more significant systematic error in the solution via least-squares estimation than the effect from the instrument’s noise. Both effects produce similar error trends in the geoid height estimation, while they corrupt coefficients corresponding to different spectral domains.

Abstract: SOUND AND VIBRATION/DECEMBER 2002 A key step in any digital processing of real world analog signals is converting the analog signals into digital form. We sample continuous data and create a discrete signal. Unfortunately, sampling can introduce aliasing, a nonlinear process which shifts frequencies. Aliasing is an inevitable result of both sampling and sample rate conversion. It can be addressed with a properly designed antialiasing filter (AAF). An analog AAF must be applied before the initial sampling process. If any sample rate conversion, such as decimation, is performed, a digital AAF must also be applied. An AAF is one of the limiting factors in system performance. An improperly designed AAF, or improper application of one, can introduce distortion artifacts that may interfere with certain types of analysis. Modern AAF architectures eliminate these artifacts. The Nyquist sampling theorem defines the minimum sampling frequency to completely represent a continuous signal with a discrete one. If the sampling frequency is at least twice the highest frequency in the continuous baseband signal, the samples can be used to exactly reconstruct the continuous signal. A sine wave can be described by at least two samples per cycle (consider drawing two dots on a picture of a single cycle, then try and draw a single cycle of a different frequency that passes through the same two dots). Sampling at slightly less than two samples per cycle, however, is indistinguishable from sampling a sine wave close to but below the original frequency. This is aliasing – the transformation of high frequency information into false low frequencies that were not present in the original signal. The Nyquist frequency, also called the folding frequency, is equal to half the sampling frequency fs and is the demarcation between frequencies that are correctly sampled and those that will cause aliases. Aliases will be ‘folded’ from the Nyquist frequency back into the useful frequency range. Thus a tone 1 kHz above the Nyquist frequency will fold back to 1 kHz below, while a tone 1 kHz below the sampling frequency will appear at 1 kHz as shown in Figure 1. Frequencies above the sampling frequency are also folded back. Aliasing is irreversible. There is no way to examine the samples and determine which content to ignore because it came from aliased high frequencies. Aliasing can only be prevented by attenuating high frequency content before the sampling process as shown in Figure 2. To prevent aliasing completely, we must apply a perfect filter that passes all energy from DC to the highest frequency of interest and rejects all energy at the Nyquist frequency and above. Unfortunately, perfect filters are not physically realizable in analog or digital form. Physically realizable filters must have variation in the passband, a smooth transition from the passband to the stopband, and finite attenuation in the stopband. Therefore, we must design a filter with unity gain and low variation in the passband and with the lowest tolerable attenuation in the stopband. Note that finite attenuation means that you cannot eliminate aliasing, only reduce it. Suppose you sample a signal that contains a 1 V tone at 1 kHz and a 1 V tone at 39.9 kHz. You wish to analyze the data to 20 kHz, so the sampling frequency fs is 40 kHz. If the AAF gain is –80 dB in the stopband (above 20 kHz) then the sampled signal will appear as a 1 V, 1 kHz tone and a 0.1 mV, 100 Hz tone (the 39.9 kHz tone aliases to 100 Hz and is attenuated 80 dB). The amplitude of the alias is dependant on the original amplitude of the out-of-band components and the amount of attenuation in the AAF. The effect is harder to analyze in the more realistic case of broadband energy that must be rejected. All of the broadband energy will fold back into the analysis band. In general, the AAF attenuation must be chosen considering the desired noise floor and the frequency content of the energy that needs to be rejected. The next consideration is the width of the transition band. Consider designing a system with a useful frequency bandwidth of 20 kHz and 80 dB of alias protection. If the sampling frequency is 40 kHz, the AAF gain must change from 0 dB at 20 kHz to –80 dB at just over 20 kHz. We must increase the sampling frequency to make the filter realizable. Consider a sampling frequency fs = 51.2 kHz. The Nyquist frequency is 25.6 kHz, which means that frequencies above 31.2 kHz will fold back into the band of interest. Therefore, the AAF gain must go from 0 dB at 20 kHz down to –80 dB at 31.2 kHz (see Figure 3). The region between the highest useful frequency and the Nyquist frequency is known as the guard band. Frequencies in this range will be attenuated and may suffer from aliasing, and are usually discarded in the presentation of spectral results. So far we have considered the rejection band attenuation and guardband width as performance limits in AAF design. Three more error sources are passband variation, dispersion, and channel to channel match. These error sources are in the passband, and are thus very important in determining the overall performance of the system. Passband variation creates absolute accuracy errors, while dispersion, or nonconstant group delay, spreads out signals over time. Channel to channel match is important when making cross channel measurements. Low variation and low dispersion are both desirable, but are hard to achieve with high order analog filters. Channel to channel match is compromised by analog component variations. In the above example, sampling at 51.2 kHz and keeping 20 kHz of information required an 8th order elliptic filter. This filter has high variation and dispersion across the passband and is difficult to fabricate. If we could increase the sampling rate, we could make the filter less aggressive, thus reducing the variation and dispersion and making it easier to manufacture. We could even sample at a very high rate, then perform digital filtering (Figure 2). It is much easier to make low variation filters digitally, and dispersion can be essentially eliminated. Digital filters are trivially duplicated across channels. This technique is used in a class of analog to digital converters called delta-sigma ADCs. For a 51.2 kHz sample rate, these converters often sample at 3.2768 MHz, making the Nyquist frequency 1.6384 MHz. A 3rd order Butterworth filter provides sufficient anti-alias protection in this situation. A Butterworth filter is maximally flat in the passband, has maximally low dispersion, and is easier to fabricate than an elliptic filter. Additionally, the lower order means there are fewer parts, improving the channel to channel match. The rest of the filtering and sample rate conversion is performed digitally inside the ADC with digital filters that can be designed with essentially zero dispersion. The advantage of the Butterworth antialias filter in dispersion performance is significant. Dispersion corresponds to filter delay that varies with respect to frequency. For instance, a pure delay corresponds to a linear phase shift. If the phase is not a straight line, the delay will be different for different frequencies. Thus, broadband signals, like transients, will be spread in time, or dispersed. The derivative of the phase with respect to frequency provides a measure of the delay. If we examine this function for the two proposed AAFs shown in Figure 4, we see that the 8th order elliptic filter has over Effects of Sampling and Aliasing on the Conversion of Analog Signals to Digital Format

Abstract: AbstnactIn this paper, we present a new reinforcement learning approach compensating for the perceptual aliasing problem by varying policies depending on the behavior context. For this approach, motiuatwd vdue(M-value) is introduced as a parameter emphasizing specific future action selection probabilities temporarily according to the context. In the learning phase, a Q-value renewal error linked with the current state-action pair is memorized as M-value linked with past visited experiences. In the control phase, t o motivate a next action, an agent awakes M-values linked with the current state and memorized in past experiences. By combining Mvalue with Q-value, even if an agent observes the same sensory inputs under the different states ,the agent can generate different action selection policies with the context. The advantage of the proposed approach is that the learning/control system reflecting the difference of context can be realized easily, in spite of the saving of computational memories, by the simple extension of general reinforcement learning: Q-learning. In order to investigate the validity of the proposed method, we apply the method to the maze problem containing perceptual aliasing problem, and compare it with the case of general Q-learning. The result on maze environment experiment shows that the proposed approach can work effectively in the non-Markov decision process environment involving perceptual aliasing problems. Keywordsreinforcement learning, Q-learning, POMDPs, perceptual aliasing.

Abstract: We investigate limitations of the minimum mean square error (MMSE) solution for subband adaptive equalisers due to aliasing and error in power complementarity. By deriving the Wiener solution for the subband equaliser and comparing it against simulations, we verify that aliasing caused in the subband decimation can be considered equivalent to channel noise. We discuss how these limitations can be mitigated by careful system design.

Abstract: Ojeblik is a lexically-scoped, object-based calculus that represents a distribution-free subset of the LAN-based programming language Obliq. The surrogate operation on Ojeblik-objects, which is the abstraction of migration on Obliq-objects, is a combined operation derived from the more primitive operations cloning and aliasing. In short, surrogation on an object turns the object into an alias for a clone of itself; it amounts to migration when the original and the clone reside on different distribution sites.In previous work, we studied the conditions under which surrogation is safe, i.e., transparent to object clients. To this aim, we developed two complementary formal descriptions of Ojeblik's semantics, one as an operational semantics on Ojeblik-configurations, and another one by translation into a process calculus. We used the former to explain typical (mis-)behaviors of Ojeblik programs, but only the latter to perform rigorous correctness proofs w.r.t. may-equivalence.In this paper, we offer new formal proofs, now based on the operational semantics of Ojeblik, making the results as well as the proofs accessible also to readers not familiar with process calculi. Furthermore, we strengthen our former results by using, in addition to may-equivalence, the much more distinguishing notion of must-equivalence.

Abstract: Systems and methods are provided for improved two pass resampling in a computing system. The systems and methods address both bottleneck problem(s) and aliasing problem(s) to improve upon prior art two pass resampling techniques. In view of both bottleneck problem(s) and aliasing problem(s), for each of four possibilities associated with two pass resampling, the four possibilities being (1) pre-rotating the 2-D data and performing row-first processing (2) pre-rotating the 2-D data and performing column-first processing, (3) not pre-rotating the 2-D data and performing row-first processing and (4) not pre-rotating the 2-D data and performing column-first processing, the bottleneck error and the aliasing error associated with the possibility are calculated. Also, for each possibility, a value is computed based upon the bottleneck error and the aliasing error. The choice of the four possibilities is then selected in accordance with a comparison of the values.

Abstract: Aliasing during migration (“operator aliasing”) is widely recognized as a problem for Kirchhoff migration. It occurs when high-frequency reflection data are swept out at steep angles, with the problem being worst for very coarse input-trace spacing. The problem can be solved either by data interpolation to a finer-spaced grid of input traces or, more commonly, by anti-aliasing the migration operator (Gray, 1992; Lumley et al., 1994; Abma et al., 1999; Biondi, 2001, Zhang et al., 2001a). Although there is no general agreement on the best way to perform Kirchhoff migration anti-aliasing for all problems, especially those involving irregular spatial sampling, there is agreement on the underlying principle. That is, the diffraction surface used by the migration to accumulate data into the image at a single point should sample the input traces adequately (Figure 1). For two-dimensional (2D) poststack migration, “adequately” means that the diffraction curve must sample adjacent traces with a time delay no greater than one-half period at any frequency present in the data.

Abstract: Aliasing due to undersampling is commonly present in all digital imagery. The imaging characteristics of the sensor, including optical blur, detector integration blur and electronic filter blur, determine the potential for aliasing in the digital images produced by that sensor. The actual extent of aliasing in any particular image depends on the scene spatial content. In this paper, we analyze the potential for aliasing in imagery from some current remote sensing systems, including the Landsat-7 Enhanced Thematic Mapper + (ETM+), Terra MODIS and EO-1 Advanced Land Imager (ALI). A metric is proposed and calculated for the aliasing potential of each sensor. The results show that the EO-1 ALI is the most susceptible to aliasing because of its relatively high MTF compared to that of ETM+ and MODIS. Real image examples are used to illustrate aliasing, including the use of aliasing to measure the sensor spatial response from certain types of targets.