Consecutive Elements Research Articles

Sector array transducers for vibro-acoustography

Vibro-acoustography is an imaging technique that maps the acoustic response of an object to a localized harmonic radiation force. This force is generated by two interfering continuous-wave ultrasound beams at slightly different frequencies f1 and f2. The system point-spread function (PSF) is related to the radiation force on a point-target. Imaging artifacts depend on the PSF sidelobes, which can be reduced by mismatching the sidelobes of each ultrasound beam. Here, we propose a beamforming approach based on an 8-element sector transducer with consecutive elements alternately driven at f1 and f2. The transducer generates two ultrasound beams skewed by 22.5° with respect to each other. The system PSF is analytically derived. The theory is validated by experiments using a small steel sphere (radius =0.2 mm) as a point-target. A laser vibrometer is used to measure the vibration of the sphere and evaluate the PSF of the system. Theoretically, the PSF sidelobes are under −15.8 dB in eight spots circularly distributed and separated by 22.5°, which agrees with the experimental results. Simulation shows that with 16 elements sidelobes are under −35.2 dB. In conclusion, sector transducers for vibro-acoustography may have lower sidelobes as the number of array elements is increased. [Work supported by Grant Nos. EB00535-01, EB2640, and IMG0100744.]

Water-cooled target modules for steady-state operation of the W7-X divertor

The stellarator WENDELSTEIN 7-X (W7-X) includes water-cooled plasma facing components (PFCs) to allow steady-state operation and to provide an efficient particle and power exhaust up to 10 MW for a maximum pulse duration of 30 min. Ten divertor units are arranged along the helical edge of the fivefold periodic plasma column. The three-dimensional shape and positioning of the target surfaces are optimized to address physics issues for a wide range of experimental parameters, which influence the topology of the boundary. The three-dimensional target surfaces are reproduced by a series of consecutive plane target elements as a set of parallel water-cooled elements positioned onto the frameworks of target modules. The design and arrangement of target modules and elements are described.

Common supply failures in linear multi-state sliding window systems

Abstract This paper considers a linear multi-state sliding window system (SWS) that consists of n linearly ordered multi-state elements. Each element can have different states: from complete failure to perfect functioning. A performance rate is associated with each state. The system fails if the sum of the performance rates of any r consecutive elements is lower than demand w . Different groups of elements (common supply groups (CSGs)) share some common resources. Failures in the resource supply system (common supply failures (CSF)) result in the simultaneous outage of several elements belonging to corresponding groups. Different groups of elements are affected by different CSF. This paper presents an algorithm for evaluating the reliability of SWS that is the subject of CSF. It also introduces the CSG reliability importance measure and suggests an algorithm for its estimation. Further, it formulates a problem of optimal element distribution among CSGs and presents a method for solving it. An illustrative example shows the application of the suggested algorithms.

Linear multi-state sliding-window systems

This paper proposes a new model that generalizes the consecutive k-out-of-r-from-n:F system to the multi-state case. In this model (linear multi-state sliding window system), the system consists of n linearly ordered multi-state elements. Each element can have various states: from complete-failure up to perfect-functioning. A performance rate is associated with each state. The sliding window system fails if the sum of the performance rates of any r consecutive multi-state elements is lower than a minimum allowable level. An algorithm for system reliability evaluation is based on an extended universal moment-generating function. Examples of system reliability evaluation are presented.

AI and machine learning techniques for managing complexity, changes and uncertainties in manufacturing

The application of pattern recognition techniques, expert systems, artificial neural networks, fuzzy systems and nowadays hybrid artificial intelligence (AI) techniques in manufacturing can be regarded as consecutive elements of a process started two decades ago. The paper outlines the most important steps of this process and introduces some new results with special emphasis on hybrid AI and multistrategy machine learning approaches. Agent-based (holonic) systems are highlighted as promising tools for managing complexity, changes and disturbances in production systems. Further integration of approaches is predicted.

Reverberation of rapid and slow trills: implications for signal adaptations to long-range communication.

Many acoustic signals in animals include trills, i.e., rapid repetitions of similar elements. Elements within these trills usually are frequency modulated and are degraded by reverberation during long-range transmission. Reverberation primarily affects consecutive elements with the same frequency characteristics and thus imposes a major constraint in the evolution of design and perception of long-range signals containing trills. Here transmission of frequency-unmodulated trills with different element repetition rates was studied. Trills were generated at different frequencies to assess frequency dependence of reverberation and then broadcast under three acoustic conditions--an open field and to assess seasonal changes in transmission properties, a deciduous forest before and after foliage had emerged. Reverberation was quantified at different positions within trills. The results show strong effects of vegetation density (season), transmission distance, frequency, element repetition rate, and element position within the trill on effects of reverberation. The experiments indicate that fast trills transmit less well than slow trills and thus are less effective in long-range communication. They show in particular that selection on trills should not act only on element repetition rate within trills but also on the trill duration as effects of reverberation increased with trill duration.

DISTRIBUTION OF GAPS BETWEEN THE INVERSES $\mathrm{mod} q$

AbstractLet $q$ be a positive integer, let $\mathcal{I}=\mathcal{I}(q)$ and $\mathcal{J}=\mathcal{J}(q)$ be subintervals of integers in $[1,q]$ and let $\mathcal{M}$ be the set of elements of $\mathcal{I}$ that are invertible modulo $q$ and whose inverses lie in $\mathcal{J}$. We show that when $q$ approaches infinity through a sequence of values such that $\varphi(q)/q\rightarrow0$, the $r$-spacing distribution between consecutive elements of $\mathcal{M}$ becomes exponential.AMS 2000 Mathematics subject classification: Primary 11K06; 11B05; 11N69

The Methods and Effects of Transducer Degradation on Image Quality and the Clinical Efficacy of Diagnostic Sonography

In diagnostic ultrasound examinations, transducer “health” is key to diagnostic efficacy. It is known that individual transducer element integrity within an array is central to overall probe performance and over time, with normal use, elements can cease working or lose sensitivity, leading to a potentially negative impact on the clinical efficacy of the ultrasound examination. Investigating this issue, the authors evaluated transducers with selected elements disabled compared to fully functioning arrays, examined how dead elements affected ultrasound beams, acoustic parameters, flow phantom/tissue phantom results as well as human imaging. Results: As few as 2 consecutive dead elements can materially impact the beam profile; four or more can significantly reduce resolution and penetration, increase the noise floor, and cause Doppler peak velocity errors, flow ambiguity and spectral broadening. Tissue phantoms proved to be equivocal in spotting defective elements. Conclusion: array heath is critical to high-quality, efficacious ultrasound studies and the potential for misdiagnosis increases as array elements degrade.

Incomplete Character Sums and Polynomial Interpolation of the Discrete Logarithm

In the first part of the paper, certain incomplete character sums over a finite field Fpr are considered which in the case of finite prime fields Fp are of the form ∑A+N−1n=Aχ(g(n))ψ(f(n)), where A and N are integers with 1≤N<p, g and f are polynomials over Fp, and χ denotes a multiplicative and ψ an additive character of Fp. Excluding trivial cases, it is shown that the above sums are at most of the order of magnitude N1/2pr/4. Recently, Shparlinski showed that a polynomial f over the integers which coincides with the discrete logarithm of the finite prime field Fp for N consecutive elements of Fp must have a degree at least of the order of magnitude Np−1/2. In this paper this result is extended to arbitrary Fpr. The proof is based on the above new bound for incomplete hybrid character sums.

Optimal allocation of elements in a linear multi-state sliding window system

This paper proposes a new model that generalizes the consecutive k-out-of-r-from-n:F system to multi-state case. In this model (named linear multi-state sliding window system) the system consists of n linearly ordered multi-state elements. Each element can have different states: from complete failure up to perfect functioning. A performance rate is associated with each state. The system fails if the sum of the performance rates of any r consecutive elements is lower than a demand W.

The distribution of inverses modulo a prime in short intervals

Abstract. Let p be an odd prime and let ν denote the multiplicative inverse of ν (mod p). Also let N = {ν (mod p) : M < ν ≤ M + N} , where M ≥ 0 and N ≥ 1 are integers such that (M,M + N ] ⊆ (0, p). To study the distribution of the elements of N in intervals, we let f(m,H) be the number of n ∈ (m,m + H] with n(mod p) ∈ N . Our main result is an estimate for the k moment of f(m,H) about its mean. From this we deduce an estimate for certain moments of lengths of gaps between consecutive elements of N .

AI AND MACHINE LEARNING TECHNIQUES FOR MANAGING COMPLEXITY, CHANGES AND UNCERTAINTIES IN MANUFACTURING

The application of pattern recognition (PR) techniques, expert systems (ESs), artificial neural networks (ANNs), fuzzy systems (FSs) and nowadays hybrid artificial intelligence (AI) techniques in manufacturing can be regarded as consecutive elements of a process started two decades ago. On the one hand, the paper outlines the most important steps of this process and introduces some new results with special emphasis on hybrid AI and multistrategy machine learning (ML) approaches. On the other hand, agent-based (holonic) systems are highlighted as promising tools for managing complexity, changes and disturbances in production systems. Further integration of approaches is predicted.

Intelligent Techniques for Managing Complexity, Changes and Uncertainties in Manufacturing

The application of pattern recognition (PR) techniques, expert systems (ESs), artificial neural networks (ANNs), fuzzy systems (FSs) and nowadays hybrid artificial intelligence (AI) techniques in manufacturing can be regarded as consecutive elements of a process started two decades ago. On the one hand, the paper outlines the most important steps of this process and introduces some new results with special emphasis on hybrid AI and multistrategy machine learning (ML) approaches. On the other hand, agent-based (holonic) systems are highlighted as promising tools for managing complexity, changes and disturbances in production systems. Further integration of approaches is predicted.

E2A and HEB activate the pre-TCR alpha promoter during immature T cell development.

The pre-TCRalpha (pTalpha) is exclusively expressed in immature thymocytes and constitutes the pre-TCR complex with TCRbeta, which regulates early T cell differentiation. Despite the recent identification of the pTalpha enhancer, the contribution of the promoter region, the direct DNA-protein interaction, and the regulation of such interaction along with T cell development have not been investigated. We analyzed the pTalpha promoter region and identified the critical elements for transcription of the pTalpha gene. The pTalpha promoter was found to contain two consecutive E-box elements that are critical for pTalpha transcription. The E-box elements in the promoter region formed the specific DNA-protein complex that was exclusively observed in immature thymocytes, not in mature thymocytes and T cells. The E proteins in this complex were identified as E2A and HeLa E-box binding protein (HEB), and overexpression of E2A and HEB resulted in activation of the pTalpha promoter. The binding complex in the consecutive E-boxes in the pTalpha promoter changed along with T cell development, as a distinct DNA-binding complex was observed in mature T cells. Comparing the E-box regions in the enhancer and the promoter, those in the promoter appear to make a greater contribution to pTalpha gene transcription.

Friction and heat transfer characteristics of laminar swirl flow through a circular tube fitted with regularly spaced twisted-tape elements

Heat transfer and pressure drop characteristics in a circular tube fitted with regularly spaced twisted-tape elements have been investigated experimentally. Laminar swirl flow of a viscous fluid having intermediate Prandtl number range was considered. The swirl was generated by regularly spaced twisted-tape elements with single twist in the tape module and connected by thin circular rods. The tape-width and the rod diameter were both varied. The effect of higher-than-zero phase angle between consecutive tape elements have been studied. Heated as well as isothermal friction factor data has been generated. The heat transfer test section was heated electrically imposing axially and circumferentially constant wall heat flux (UHF) boundary condition. Reynolds number, Prandtl number, twist ratio, space ratio, tape-width, rod-diameter and phase angle govern the characteristics. `Pinching' of the tapes in place rather than connecting the tape elements by rods is a better proposition from the thermohydraulic performance point of view. Reducing tape-widths yield poor results. Higher-than-zero phase angle is of no use; rather it increases only manufacturing complexity. The difference of heated friction factor and isothermal friction factor for the periodic swirl flow is substantially less than that in case of straight flow through plain tube.

Local characteristics of atmospheric dispersion within building arrays

Dispersion of pollutants within building arrays was examined in the field, using model obstacles that represented real structures at a nominal scale between 1 10 and 1 20 . The main purpose of the experiments was to examine the local characteristics of flow and dispersion in the vicinity of individual obstacles embedded in an array of cuboid buildings. Two building array configurations were used, namely in-line and staggered. The spacing of the buildings in the array was S/ H=1.5 (where S is the space between two consecutive array elements). This spacing was chosen after a wind tunnel flow visualisation study of the effect of obstacle spacing on dispersion. Dispersion around isolated model buildings of similar shape and orientation to the mean wind direction has already been investigated in the field (Mavroidis et al., 2000, Atmospheric Environment, submitted for publication). A comparison is presented between dispersion around an isolated building and around the same building embedded in an array of cubes, which represented an urban area. The results suggest that enhanced mixing and dispersion occur within the array. Furthermore, differences in concentrations measured in the wake of obstacles of different shape and orientation with respect to the mean wind direction are reduced within the array, compared with the isolated obstacle case.

Identification and ab initio simulations of early folding units in proteins.

The location of protein subunits that form early during folding, constituted of consecutive secondary structure elements with some intrinsic stability and favorable tertiary interactions, is predicted using a combination of threading algorithms and local structure prediction methods. Two folding units are selected among the candidates identified in a database of known protein structures: the fragment 15-55 of 434 cro, an all-alpha protein, and the fragment 1-35 of ubiquitin, an alpha/beta protein. These units are further analyzed by means of Monte Carlo simulated annealing using several database-derived potentials describing different types of interactions. Our results suggest that the local interactions along the chain dominate in the first folding steps of both fragments, and that the formation of some of the secondary structures necessarily occurs before structure compaction. These findings led us to define a prediction protocol, which is efficient to improve the accuracy of the predicted structures. It involves a first simulation with a local interaction potential only, whose final conformation is used as a starting structure of a second simulation that uses a combination of local interaction and distance potentials. The root mean square deviations between the coordinates of predicted and native structures are as low as 2-4 A in most trials. The possibility of extending this protocol to the prediction of full proteins is discussed. Proteins 2001;42:164-176.

Yields of products from fast neutron-induced fission of 233U measured by means of an isotope separator on-line (ISOL) system

A comprehensive study has been carried out of the yield pattern of fission products formed in fast neutron-induced fission of 233U. The isotope separator on-line facility at Studsvik to the R2-0 nuclear reactor was used for rapid separation of the fission products. At a target temperature of 2250°C fission products of the elements from zinc (Z = 30) to barium (Z = 56) are released, with the exception of yttrium, zirconium, niobium, molybdenum, technetium, ruthenium and rhodium. The individual isotopes are then available for study, implying that an almost complete mapping of the yield distribution can be made. In the analysis, the delay between production and measurement and the overall separator efficiency for three consecutive elements (the one under study and its parent and grand parent) are taken into account. Independent and/or cumulative yields have been obtained for 203 nuclear species, among them 59 isomeric states.

Identification and ab initio simulations of early folding units in proteins

The location of protein subunits that form early during folding, constituted of consecutive secondary structure elements with some intrinsic stability and favorable tertiary interactions, is predicted using a combination of threading algorithms and local structure prediction methods. Two folding units are selected among the candidates identified in a database of known protein structures: the fragment 15-55 of 434 cro, an all-alpha protein, and the fragment 1-35 of ubiquitin, an alpha/beta protein. These units are further analyzed by means of Monte Carlo simulated annealing using several database-derived potentials describing different types of interactions. Our results suggest that the local interactions along the chain dominate in the first folding steps of both fragments, and that the formation of some of the secondary structures necessarily occurs before structure compaction. These findings led us to define a prediction protocol, which is efficient to improve the accuracy of the predicted structures. It involves a first simulation with a local interaction potential only, whose final conformation is used as a starting structure of a second simulation that uses a combination of local interaction and distance potentials. The root mean square deviations between the coordinates of predicted and native structures are as low as 2-4 A in most trials. The possibility of extending this protocol to the prediction of full proteins is discussed. Proteins 2001;42:164-176.

Double spin-state-selective coherence transfer. Application for two-dimensional selection of multiplet components with long transverse relaxation times

The spin-state-selective coherence transfer (S3CT) pulse sequence element has earlier been introduced as a means of editing the two resonances of a doublet (Sørensen, M. D., et al. 1997, J. Biomol. NMR, 10, 181). This paper demonstrates how two consecutive S3CT elements in a mixing sequence can be used to edit the four multiplet components of a two-dimensional correlation cross peak of a two-spin system. A particular phase setting in the mixing sequence yields one component in the echo and one in the anti-echo part. However, since one of them passes through an intermediate state of zero-quantum coherence while the other passes through double-quantum coherence, a phase cycle or pulsed field gradients can separate the two. The resulting (S3CT)2 HSQC pulse sequence corresponds to transverse relaxation optimized spectroscopy (TROSY) (Pervushin, K., et al., 1997, Proc. Nat. Acad. Sci. USA, 94, 12366). Experimental confirmation is provided using a 15N-labelled protein, neural cell adhesion molecule (NCAM) modules 1 and 2, with a molecular weight of about 20kDa.