Number Of Small Segments Research Articles

On telescope performance evaluation

We analyse the imaging performance of synthetic-aperture optical systems (diluted aperture and segmented aperture) using the modulation transfer function. We select a single figure-of-merit, the functional cut-off frequency, over the traditional cut-off frequency, as the most useful one for assessing the optical performance of an instrument for its imaging capacity. A simplified aperture layout is proposed with the performance equivalent to that of the Keck telescope, incorporating a smaller number of segments. The detailed analysis in the spatial frequency plane leads us to observe that the central ring of the hexagons in the Keck telescope does not contribute to its resolution.

Nematic Homopolymers: From Segmented to Wormlike Chains

We present a density functional approach to orientational ordering in homopolymeric systems. The polymers are modeled as chains of identical rodlike segments connected via a simple generic bending potential. The segments are impenetrable to each other, and it is their mutual excluded volume that drives the transition from the orientationally disordered isotropic phase to the orientationally ordered nematic fluid. These excluded volume effects are accounted for within the so‐called Onsager approximation at the chain–chain level and in an independent pairwise overlap approximation at the segment–segment level. The Khokhlov and Semenov formalism for nematic wormlike polymers is shown to be an exact limiting case of our treatment. The ordering transition is studied analytically by using a linear stability analysis of the isotropic phase yielding the properties of the system at the isotropic‐nematic (I–N) bifurcation point. Using a numerical scheme, the equilibrium distribution functions in the nematic phase are calculated, and the location of the thermodynamic I–N transition is determined. For stiff bending potentials, chains with a relatively small number of segments are found to behave like wormlike chains, and we determine the regime of model parameters for which this identification holds.

Thermal modulator array for analyte modulation and comprehensive two‐dimensional gas chromatography

AbstractSegmented thermal modulators were fabricated for the modulation of column effluent in one‐dimensional gas chromatography, comprehensive two‐dimensional gas chromatography, and as sample introduction devices in other analytical techniques. Thermal desorption of analytes from the modulator was achieved by computer‐controlled application of large DC currents at low voltages sequentially to consecutive segments or stages of the modulator heaters for periods between 100 and 400 ms per segment. This procedure produced sharply focussed analyte peaks. Unsegmented heaters and heaters having 2, 4, 6, 8, and 10 segments or stages were compared with respect to their focusing efficiency. The 10‐stage heater was found to give sharper focusing than heaters with a smaller number of segments. Analyte pulses with peak widths at half‐height of ca. 150 ms were generated by the 10‐stage heater. The application of a 10‐stage modulator in a comprehensive two‐dimensional analysis of a light petroleum condensate gave results of acceptable quality.

Estimation of Antenna Factor of Wire Antenna as Emi Sensor

The ratio of incident electric field at the surface of receiving antenna to the received voltage at the antenna terminal when terminated in 50 ohms load is known as the antenna factor. It is an important parameter of a sensor used for EMI measurements. To determine electromagnetic radiation from an electronic component it is required to evaluate the field strength at a certain distance from it using the sensor. If the antenna factor of the receiver and the received voltage are known then the field can be found out applying simple relations. In this paper a simple and useful Method of Moment-based theoretical technique is described to evaluate the antenna factor of wire antenna. The wire is considered as perfectly conducting with radius much less compared to the wavelength of operation. The wire is divided in large number of small segments. A point matching technique is applied to evaluate the surface current distribution due to the incident electric field. The output impedance is found out from the short circuit current and the open circuit voltage of the wire. The received voltage and hence the antenna factor is evaluated from the equivalent circuit diagram of the antenna. The data for current distribution on the antenna in receiving and transmitting mode and input impedance for transmitting mode are well comparable to the results available in literature. Studies have been extended for off-centered antenna and for oblique incidence of electric field.

Quantitative electromyographic analysis of levator ani and external anal sphincter muscles of nulliparous women

Objectives: Our aims were to introduce a method of digital quantitative electromyography of the levator ani and external anal sphincter muscles and to establish reference values. Study Design: Fifteen nulliparous, symptom-free women underwent concentric needle electromyographic examination of the levator ani and external anal sphincter. We sampled the levator ani transvaginally at 4 sites and the external anal sphincter at 2 sites. The signal was filtered and amplified, and digital recordings were made at 3 levels of voluntary activation at each site. Analyses of motor unit action potentials and interference patterns were performed with the use of these taped signals. Normal ranges were generated and compared with those established for other striated muscles. Results: The mean age of the subjects was 28.7 ± 7.5 years. A median of 24 motor unit action potentials was recorded in each levator ani, and a median of 6 was recorded in each external anal sphincter. Parameters of the levator ani action potentials were significantly greater than those of the external anal sphincter in amplitude (0.48 vs 0.37 mV; P =.001), duration (10.40 vs 8.27 ms; P =.002), number of turns per second (2.80 vs 2.28; P <.001), and area (0.65 vs 0.36; P <.001). Parameters of the interference patterns were significantly greater in the levator ani than in the external anal sphincter in number of turns per second (241.6 vs 183.9; P =.015), amplitude (302.7 vs 225.3 μV; P <.0001), activity (95.6 vs 61.2; P =.004), envelope size (861.1 vs 567.6 μV; P <.0001), and number of small segments (105.8 vs 81.4; P =.047). There were no significant differences between levator ani, external anal sphincter, and published parameters from the biceps muscle with regard to amplitude and duration of motor unit action potentials. Conclusions: Electromyography of the levator ani and external anal sphincter is feasible and well tolerated. Our findings confirm that the levator ani muscle has larger, more readily recruited motor units than does the external anal sphincter. Ranges for important quantitative electromyographic parameters for these muscles are similar to those published for the biceps. (Am J Obstet Gynecol 2000;183:1249-56.)

Leaf area index estimates obtained for clumped canopies using hemispherical photography

A method has been developed to improve estimates of leaf area index determined from hemispherical images of plant canopies. The approach used has been to modify existing techniques for analysis of gap fraction at a range of zenith angles. Conventional analytical techniques determine the gap fraction for a number of concentric annuli and then calculate the logarithm of this quantity. This approach requires the assumption that all foliage elements are randomly arranged within each annulus. The new approach divides each annulus into a number of small segments. The gap fraction of each segment is calculated and the average of their logarithms is calculated for each annulus (log-average or segmented method). These values are then used for the analysis of leaf area index and mean leaf angle using conventional techniques. Leaf area index estimates from hemispherical images were compared with data from a destructive harvest of a sparse canopy of Gliricidia sepium in Mexico. The log-average method was shown to significantly reduce the underestimation of leaf area index obtained from analysis of hemispherical images of clumped canopies. Conventional analysis of hemispherical images resulted in an underestimate of 50% compared to the destructive harvest. The segmented analysis reduced this to 15%. A comparison of the conventional and segmented analysis of hemispherical canopy images led to the development of a simple clumping factor calculated as the ratio of segmented and conventional estimates of leaf area index. This variation was found to vary between samples and location. For a canopy of Quercus pubescens in Scotland, the clumping factor was found to vary between 1.20 and 1.75, being highest under sparse canopies. This was attributed to the effects of tree spacing and the presence of a number of canopy gaps in the forest. Thus alternative methods that apply a uniform correct factor to conventional analysis may produce erroneous results where the scale of clumping is not uniform throughout the canopy.

GPSIM: A Personal Computer-Based GPS Simulator System

Global Positioning Systems (GPS) are now in use in many applications, ranging from GIS to route guidance, automatic vehicle location (AVL), air, land, and marine navigation, and many other transportation and geographical based applications. In many applications, the GPS receiver is connected to some form of intelligent electronic system which receives the positional data from the GPS unit and then performs the required operation. When developing and testing GPS-based systems, one of the problems is that it is usually necessary to create GPS-compatible geographical data to simulate a GPS operation in real time. This paper provides the details of a Personal Computer (PC)-based GPS simulator system called GPSIM. The system receives user way-points and routes from Windows-based screen forms and then simulates a GPS operation in real time by generating most of the commonly used GPS sentences. The user-specified waypoints are divided into a number of small segments, each segment specifying a small distance in the direction of the original waypoint. The GPS sentence corresponding to the geographical coordinates of each segment is then sent out of the PC serial port. The system described is an invaluable testing tool for GPS-based system developers and also for people training to learn to use GPS-based products.

Temporal segmentation in a neural dynamic system.

Oscillatory attractor neural networks can perform temporal segmentation, i.e., separate the joint inputs they receive, through the formation of staggered oscillations. This property, which may be basic to many perceptual functions, is investigated here in the context of a symmetric dynamic system. The fully segmented mode is one type of limit cycle that this system can develop. It can be sustained for only a limited number n of oscillators. This limitation to a small number of segments is a basic phenomenon in such systems. Within our model we can explain it in terms of the limited range of narrow subharmonic solutions of the single nonlinear oscillator. Moreover, this point of view allows us to understand the dominance of three leading amplitudes in solutions of partial segmentation, which are obtained for high n. The latter are also abundant when we replace the common input with a graded one, allowing for different inputs to different oscillators. Switching to an input with fluctuating components, we obtain segmentation dominance for small systems and quite irregular waveforms for large systems.

Dynamical symmetries and temporal segmentation

Segmentation of a mixed input into recognizable patterns is a task that is common to many perceptual functions. It can be realized in neural models through temporal segmentation: formation of staggered oscillations such that within each period every nonlinear oscillator peaks once and is dominant for a short while. We investigate such behavior in a symmetric dynamical system. The fully segmented mode is one type of limit cycle that this system can exhibit. We discuss its symmetry classification and its dynamical characterization. We observe that it can be sustained for only a small number of segments and relate this fact to a limitation on the appearance of narrow subharmonic oscillations in our system.

A numerical analysis of the large deflection of an elastoplastic cantilever

A simple numerical method is applied to calculate the large deflection of a cantilever beam under an elastic-plastic deformation by dividing the deformed axis into a number of small segments. Assuming that each segment can be approximated as a circular arc, the method allows large deflections and plastic deformation to be analyzed. The main interests are the load-deflection relationship, curvature distribution along the beam and the length of the plastic region. The method is proved to be easy and particularly versatile. Comparisons with other studies are given.

Three-dimensional quasistationary approach to Cherenkov-type optical harmonic generation using a unidirectional-radiation model

A three-dimensional calculation of Cherenkov-type frequency doubling in an optical channel waveguide is implemented by slicing the lateral profile of the interacting fields into a number of small segments. In each segment, lateral field variations of the harmonic signal are neglected. This method is more simple and requires less computational effort in comparison with a direct three-dimensional beam simulation. With the unidirectional-radiation model one can predict an optimum configuration and the conversion efficiency of miniaturized frequency doublers that utilize guided–to–radiation-mode interactions in nonlinear channel waveguides. Typical results are shown for blue-light generation through frequency doubling in a proton-exchanged MgO-doped lithium niobate channel waveguide. Analyses of green-light generation in organic channel waveguides are reported as well.

Performance limitations of a GTO with near-perfect technology

The performance of multiple-cell devices is limited by a redistribution of current during turn-off, caused by minor differences between the individual cells, which becomes important at high current density. A simple model, based on Gaussian statistics, is proposed where the degree of homogeneity between cells is expressed in terms of a technological quality factor k. It turns out that the increase of turn-off current for a gate turn-off thyristor (GTO) with a large number of cells is highly nonlinear. A major issue is the influence of the external load on the maximum turn-off current of a GTO. In the case of a typical inductive load, the turn-off capability of a device with a small number of segments n (n<100) hardly shows a difference between operation without and operation with a snubber. In contrast, for large GTOs (n>1000) snubberless operation imposes severe limitations on turn-off while a snubber with a realistic leakage inductance allows for a substantially larger turn-off current.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Large Deformation Analysis of Orthodontic Appliances

The deformations of orthodontic appliances used for space closure are large so that any mathematical analysis will require a nonlinear approach. Existing incremental finite element and finite difference numerical methods suffer from excessive computational effort when analyzing these problems. An accurate segmental technique is proposed to handle these difficulties in an extremely efficient fashion. The segmental technique starts by assuming that an orthodontic appliance is composed of a number of smaller segments, the ends of which undergo small relative rotation. With an appropriate choice of local coordinate system the equilibrium equations for each segment are linearized and solved in a straightforward manner. The segments are then assembled using geometric and force compatibility relations similar to the transfer matrix method. Consequently, the original nonlinear boundary value problem is solved as a sequence of linear initial value problems which converge to the required boundary conditions. As only one segment need be considered at a time, the computations can be performed accurately and efficiently on a PC type computer. Although an iterative solution is used to match the boundary conditions, the time required to solve a given problem ranges from a few seconds to a couple of minutes depending on the initial geometric complexity. The accuracy of the segmental technique is verified by comparison with an exact solution for an initially curved cantilever beam with an end load. In addition, comparisons are made with existing experimental and numerical results as well as with a new set of experimental data. In all cases the segmental technique is in excellent agreement with the results of these other studies.

Vibrations and buckling of a beam on a variable winkler elastic foundation

Two methods for solving the eigenvalue problems of vibrations and stability of a beam on a variable Winkler elastic foundation are presented and compared. The first is based on using the exact stiffness, consistent mass, and geometric stiffness matrices for a beam on a variable Winkler elastic foundation. The second method is based on adding an element foundation stiffness matrix to the regular beam stiffness matrix, for vibrations and stability analysis. With these matrices, it is possible to find the natural frequencies and mode shapes of vibrations, and buckling load and mode shape, by using a small number of segments. It is concluded that the use of the element foundation stiffness approach yields better convergence at lower computation costs.

Measurement of interaction forces between crossed quartz glass rods in presence of adsorbed macromolecules

The interaction energy-distance curves of fractionated and unfractionated homo- and copolymers were measured. The results were compared quantitatively with the HVO theory. It was found that only a small number of segments per tail are necessary to obtain stability. The experimental energy-distance curves for low molecular weights are described sufficiently well by the HVO theory, with exponentional distribution of tail sizes. For high molecular weights the exponential distribution cannot be considered as a reasonable assumption because the number of segments in the tails is very low. Polydisperse samples of PVA with different contents of acetate groups, and similar molecular weight, indicate an increasing extension of the adsorbed polymer layer with decreasing acetate content.

Automatic analysis of the electromyographic interference pattern. Part II: Findings in control subjects and in some neuromuscular diseases.

The electromyographic (EMG) interference pattern (IP) was measured in the biceps muscle of 16 normal male and 17 normal female subjects. The activity, upper centile amplitude (UCA), and the number of small segments (NSS) (defined in a companion paper) were measured from 500-msec epochs of the IP. The normal values of these features were defined separately for men and women by plotting the UCA and NSS values against activity for each epoch and defining an area on these plots, called a "cloud," that contained more than 90% of the datum points from each study. The mean deviation of the individual datum points from the overall mean values was also calculated for each study. A study in one muscle is considered to be normal if more than 90% of the datum points from that muscle are within the normal clouds and the deviation values are within their normal range. In patients with neuropathy, the characteristic pattern was increased UCA with normal or decreased NSS. In patients with myopathy, NSS was increased and the UCA was normal or decreased. In all studies, the interpretations of the IP from the plots agreed with qualitative assessments of the IP made independently by an electromyographer. The use of these features to understand and quantitate the changes in the motor units produced by disease is demonstrated by serial studies performed in a patient with motor neuron disease.

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part II: Activity, upper centile amplitude, and number of small segments.

We have defined three new features of the electromyographic (EMG) interference pattern (IP): activity, upper centile amplitude (UCA), and number of small segments (NSS). These parameters were measured in simulated IPs constructed by adding together motor unit action potentials (MUAPs) recorded with a concentric needle EMG electrode. The activity increases linearly with the number of MUAP discharges to approximately 80% of its theoretical maximum value. The UCA correlates strongly with the peak-to-peak amplitude of the largest MUAP in the IP and the mean segment amplitude and does not depend on the discharge rate of the largest MUAPs. We infer that the UCA defines the upper limit of the peak-to-peak amplitude of the MUAPs contained in the IP. The NSS increases with the number of MUAP discharges, but reaches a constant value at higher MUAP discharge rates, probably because small amplitude MUAPs are masked by the large amplitude MUAPs. The potential value of these parameters in automated IP analysis is discussed.

Automatic analysis of the electromyographic interference pattern. Part I: Development of quantitative features.

We have developed three new features of the electromyographic interference pattern (IP), based on the turns and amplitude of the signal, to quantitate some of the features of the IP that are usually assessed subjectively by an electromyographer. The activity measures the fullness of the IP. The upper centile amplitude (UCA) defines the upper limit of the maximum peak-to-peak amplitude of the motor unit action potentials (MUAPs) contained in the IP. The number of small segments (NSS) measures the complexity of the IP, which is a reflection of the polyphasicity of the component MUAPs. The activity and the logarithm of the UCA correlate strongly with the force of muscle contraction at which the IP is measured. The NSS initially increases with the force of contraction and becomes relatively constant at higher force levels. The normal values of these features and the interpretation of their relationships are described in companion papers.

Genetic analysis of pattern-formation in the embryo ofDrosophila melanogaster : Characterization of the maternal-effect mutantBicaudal.

The mutationbicaudal (Bull, 1966) causes embryos to develop a longitudinal mirror image duplication of the posteriormost abdominal segments, while head and thorax are missing. These embryos occur with varying frequencies among eggs laid by mutant females, irrespective of the paternal genotype. Recombination and deletion mapping indicate thatbicaudal (bic) is a recessive, hypomorphic, maternal-effect mutation mapping at a single locus on the second chromosome ofDrosophila melanogaster close tovg (67.0±0.1). The frequency of bicaudal embryos depends on the age of the mother, her genetic constitution and the temperature at which she is raised. Best producers are very young females hemizygous forbic (bic/Df(2)vg B ) at 28° C. Under these conditions 80% to 90% of the eggs which differentiate can show the bicaudal embryo phenotype. Upon ageing of the mother the frequency of bicaudal embryos declines rapidly, and most of the eggs develop the normal body pattern. Temperature shift experiments suggest a temperature-sensitive period at the onset of vitellogenesis.The mutation causes several types of abnormalities in the segment pattern of theDrosophila embryo, which are interpreted as various degrees of expression of the mutant character. The most frequent abnormal phenotype is the symmetrical bicaudal embryo with one to five abdominal segments duplicated. Less frequent are asymmetrical types, in which the smaller number of segments is always in the anterior reversed part. Other phenotypes are embryos with missing or rudimentary heads, and embryos with irregular gaps in the segment pattern. In bicaudal embryos, the pole cells, formed at the posterior pole of the egg prior to blastoderm formation, are not duplicated at the anterior. The significance of thebicaudal phenotypes for embryonic pattern-formation inDrosophila is discussed.

On numerical convergence of moment solutions of moderately thick wire antennas using sinusoidal basis functions

Wire antennas are solved using a moments solution where the method of subsectional basis is applied with both the expansion and testing functions being sinusoidal distributions. This allows not only a simplification of near-field terms but also the far-field expression of the radiated field from each segment, regardless of the length <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> . Using sinusoidal basis functions, the terms of the impedance matrix obtained become equivalent to the mutual impedances between the subsectional dipoles. These impedances are the familiar impedances found using the induced EMF method. In the induced EMF method an equivalent radius is usually used in the evaluation of the self-impedance term to reduce computation time. However, it is shown that only for very thin segments that the correct equivalent radius is independent of length. When the radius to length ratio ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a/L</tex> ) is not small, an expansion for the equivalent radius in terms of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a/L</tex> is given for the self-impedance term. The use of incorrect self-term, obtained by using a constant equivalent radius term, is shown to be responsible for divergence of numerical solutions as the number of sections is increased. This occurrence is related to the ratio of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a/L</tex> of the subsections and hence becomes a problem for moderately thick wire antennas even for a reasonably small number of segments per wavelength. Examples are given showing the convergence with the correct self-terms and the divergence when only a length independent equivalent radius is used. The converged solutions are also compared to King's second- and third-order solutions for moderately thick dipoles.