ON THE GEOMETRY OF RADIO REFLECTIONS FROM AURORA

1960 ◽  
Vol 38 (5) ◽  
pp. 593-603 ◽  
Author(s):  
P. A. Forsyth
Keyword(s):  
Pulse Duration ◽  
Spatial Configuration ◽  
Beam Width ◽  
Volume Scattering ◽  
Antenna Beam ◽  
The Individual ◽  
Optical Evidence ◽  
Aspect Sensitivity

By assuming that auroral radio reflections are produced by volume scattering in clouds of ionization having the same spatial configuration as the visible auroral structures, and by taking into account the radar pulse duration and antenna beam width, it is possible to predict the probability of echo occurrence as a function of range and azimuth. This echo distribution is quite similar to that observed experimentally even when "aspect sensitivity" of the individual scatterer is neglected. Unfortunately, the optical evidence is not sufficiently extensive to permit precise calculations to be made, nor the radio evidence to permit detailed comparisons, but previous estimates of the shape of the scattering structures that have been based on the azimuthal echo distribution without regard to the factors discussed here are likely to be seriously in error.

P6547The energy cost of His bundle pacing can be curtailed

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
F Zanon ◽  
L Marcantoni ◽  
G Pastore ◽  
E Baracca ◽  
C Picariello ◽  
...  
Keyword(s):  
Pulse Duration ◽  
Safety Margin ◽  
Significant Saving ◽  
His Bundle ◽  
His Bundle Pacing ◽  
On Demand ◽  
Mild Reduction ◽  
Ventricular Activation ◽  
The Individual ◽  
Current Drain

Abstract Introduction His bundle pacing (HBP) allows physiological ventricular activation and prevents the electrical and mechanical desynchronization generally induced by myocardial stimulation, which can increase the risk of atrial fibrillation and heart failure. On the other hand, reliable HBP capture often requires higher energy than conventional myocardial pacing. This reduces the expected life of the stimulator and might limit the diffusion of HBP in the clinical practice. Purpose Decreasing HBP current drain by careful management of stimulation safety margin and pulse duration. Methods In 28 patients undergoing DDD pacing with HBP, a third lead was implanted in RV apex to provide back-up pacing on demand. HBP and apical leads were connected, respectively, to the V1 and V2 channels of a 3-chamber stimulator. When HBP was effective, apical sensing occurred within the VV delay and prevented V2 stimulation. In contrast, in case of HBP failure, V2 sensing was missing and apical back-up pacing was promptly delivered at the end of the VV delay. The availability of a back-up pulse on demand allowed reducing the HBP safety margin with no risk. Furthermore, the individual HBP strength-duration curve was derived in the aim of optimizing the Hisian pulse parameters, which are the major determinants of the device current drain. Results Correct back-up inhibition by successful HBP and stimulation in the event of capture loss was achieved in all the patients. The latency from Hisian pacing to apical sensing averaged 96±14 ms. According to the pacemaker counters, no back-up pulse was delivered in daily life in 59% of patients. In the remaining, the prevalence of back-up stimulation never exceeded 15% of paced ventricular cycles. The high HBP threshold was essentially due to an increased rheobase (1.2±0.6 V), while the chronaxie ranged from 0.30 to 0.53 ms in 71% of patients (median 0.44 ms), exceeding 0.6 ms only in 29% of the cases. An average current saving of 5.4±3.0 μA was obtained at the expense of a mild reduction in HBP safety margin (from 1.6±0.2 to 1.4±0.1 times). HBP and apical back-up Conclusions Back-up stimulation on demand is a reliable option to decrease HBP current drain and prolong the stimulator service life with full safety. In most of the cases, significant saving can be achieved by pulse shortening, as the chronaxie time is in the same range as with myocardial stimulation and longer pulses are not required. A pulse duration exceeding 0.6 ms is indicated in less than 1/3 of the implants.

scholarly journals Biases caused by the instrument bandwidth and beam width on simulated brightness temperature measurements from scanning microwave radiometers

2012 ◽  
Vol 5 (6) ◽  
pp. 8085-8130
Author(s):  
V. Meunier ◽  
U. Löhnert ◽  
P. Kollias ◽  
S. Crewell
Keyword(s):  
Water Vapor ◽  
Liquid Water ◽  
Beam Width ◽  
Liquid Water Path ◽  
Water Path ◽  
Antenna Beam ◽  
Atmospheric Propagation ◽  
W Band ◽  
The Impact ◽  
Receiver Bandwidth

Abstract. More so than the traditional fixed radiometers, the scanning radiometer requires a careful design to ensure high quality measurements. Here the impact of the radiometer characteristics (e.g. antenna beam width, receiver bandwidth) and atmospheric propagation (e.g. curvature of the earth and refractivity) on the scanning radiometer measurements are presented. A forward radiative transfer model that includes all these effects to represent the instrument measurements is used to estimate the biases as differences between the measurement with and without these characteristics for three commonly used frequency bands: K, V and W-band. The receiver channel bandwidth errors are not so important in K-band and W-band. Thus, the use of a wider bandwidth to improve detection at low signal-to-noise conditions is acceptable. The impact of the antenna beam width is higher than the receiver bandwidth, but, for V-band where they are of similar importance. Using simple regression algorithms, the effects of the bandwidth and beam width biases in liquid water path, integrated water vapor, and temperature are also examined. The largest errors in liquid water path and integrated water vapor are associated with the beam width errors.

Research on the High-Power Directional Acoustic Transducer

2014 ◽  
Vol 912-914 ◽  
pp. 753-756
Author(s):  
Guo Zhu Zhao ◽  
Li Xuan Ma
Keyword(s):  
Rare Earth ◽  
Sound Source ◽  
Beam Width ◽  
Directivity Pattern ◽  
Acute Angle ◽  
The Other ◽  
Acoustic Transducer ◽  
Element Number ◽  
The Individual ◽  
Selection Of

Through studying how to affect acoustic directivity with MATLAB software, it show that selection of a relatively larger surface of the transducer and a relatively closer transducer interval will be more preferable for directivity. While an array which possess more array element number and whose frequency of the drive signal can be as large as possible in a range, directivity will be more preferable. On the other hand, when the structure of the sound radiating surface of the transducer or array layout is symmetrical, the corresponding directivity pattern will be symmetrical. At a frequency of 10kHz, the individual rare earth magnetostrictive transducers its first point of the simulation carried out before the test. Sounding board with aluminum by the method used to improve the sound source diameter. With the sound plate diameter incrementing, the smaller the angle of the directivity. The beam width of the 3×3 array is about at 23kHz, and the directivity acute angle is about 10°, with a sounding board by the method used to improve their the diameter of the sound source, so as to realize the sound has directivity is feasible.

scholarly journals Biases caused by the instrument bandwidth and beam width on simulated brightness temperature measurements from scanning microwave radiometers

2013 ◽  
Vol 6 (5) ◽  
pp. 1171-1187 ◽  
Author(s):  
V. Meunier ◽  
U. Löhnert ◽  
P. Kollias ◽  
S. Crewell
Keyword(s):  
Water Vapour ◽  
Liquid Water ◽  
Beam Width ◽  
Liquid Water Path ◽  
Water Path ◽  
Antenna Beam ◽  
W Band ◽  
Integrated Water Vapour ◽  
The Impact ◽  
Receiver Bandwidth

Abstract. More so than the traditional fixed radiometers, the scanning radiometer requires a careful design to ensure high quality measurements. Here the impact of the radiometer characteristics (e.g., antenna beam width and receiver bandwidth) and atmospheric propagation (e.g. curvature of the Earth and vertical gradient of refractive index) on scanning radiometer measurements are presented. A forward radiative transfer model that includes all these effects to represent the instrument measurements is used to estimate the biases. These biases are estimated using differences between the measurement with and without these characteristics for three commonly used frequency bands: K, V and W-band. The receiver channel bandwidth errors are less important in K-band and W-band. Thus, the use of a wider bandwidth to improve detection at low signal-to-noise conditions is acceptable at these frequencies. The biases caused by omitting the antenna beam width in measurement simulations are larger than those caused by omitting the receiver bandwidth, except for V-band where the bandwidth may be more important in the vicinity of absorption peaks. Using simple regression algorithms, the effects of the bandwidth and beam width biases in liquid water path, integrated water vapour, and temperature are also examined. The largest errors in liquid water path and integrated water vapour are associated with the beam width errors.

No-take marine reserves can enhance population persistence and support the fishery of abalone

2015 ◽  
Vol 72 (10) ◽  
pp. 1503-1517 ◽  
Author(s):  
Marisa Rossetto ◽  
Fiorenza Micheli ◽  
Andrea Saenz-Arroyo ◽  
Jose Antonio Espinoza Montes ◽  
Giulio Alessandro De Leo
Keyword(s):  
Spatial Configuration ◽  
Marine Reserve ◽  
Maximum Sustainable Yield ◽  
Dispersal Ability ◽  
Optimal Harvesting ◽  
Demographic Model ◽  
Reference Case ◽  
Negative Effect ◽  
Limited Dispersal ◽  
The Individual

A critical aspect in the design of a marine reserve (MR) network is its spatial configuration (i.e., the number, size, and spacing of the individual reserves), particularly how these features influence the effect on fisheries. Here, we derived a size-based, spatially explicit, stochastic demographic model to explore how different spatial configurations of MR networks can affect abundance and commercial yield of the green abalone (Haliotis fulgens), taking as a reference case the abalone fishery of Isla Natividad in Baja California Sur (Mexico). Our analysis suggests that a network of MRs can have a positive effect on abalone population abundance and a slightly negative effect on fishery output with respect to traditional maximum sustainable yield (MSY; i.e., with no reserves). Simulations show that maximum catches achievable with MRs are, under the best configuration, ∼2%–14% lower than traditional MSY depending on the total fraction of the fishing grounds protected. In the case of overexploitation, long-term yields can increase following the implementation of MRs. In addition, in the presence of MRs, abundances and yields are much less sensitive to systematic errors in the enforcement of the optimal harvesting rate compared with situations in which MRs are not present. Given the limited dispersal ability of the species, the best outcomes in terms of fishery output would be achieved with very small reserves — around 100 m wide — so to maximize larval export in the fishable areas. Our results indicate appropriately designed MR networks are an effective strategy for meeting both conservation and economic goals under uncertainty. While the size of the existing reserves in Isla Natividad seems adequate to protect the abalone stock, smaller reserves could maximize fishery benefits, although this poses challenges for enforcement.

Calibrating Ultrasonic Images for the NDE of Structural Materials

1994 ◽  
Vol 116 (3) ◽  
pp. 640-646 ◽  
Author(s):  
R. S. Gilmore ◽  
A. M. Glaeser ◽  
J. C. Wade
Keyword(s):  
Imaging System ◽  
Ultrasonic Transducer ◽  
Ultrasonic Imaging ◽  
Beam Width ◽  
Practical Method ◽  
Image Resolution ◽  
Detection Sensitivity ◽  
Manufacturing Companies ◽  
Turbine Engine ◽  
The Individual

Ultrasonic imaging is taking a larger and larger role in the NDE of turbine engine materials and in support of fracture mechanics calculations. It is also playing an increasing role in quality and process control. For most fracture toughness calculations, it is necessary to establish the accuracy with which a flaw’s size and shape are imaged, whether single or multiple flaws are involved, and the spacing of multiple flaws. Because of these requirements, resolution, as well as detection sensitivity, has become an issue. There are a number of resolution targets that can provide this type of calibration information for an ultrasonic imaging system. A fused quartz USAF 1951 target, similar to the patterns used in this work, was first used by Gilmore (1986), but Gilmore’s pattern was superficial and subsurface evaluations were limited to focusing on the pattern from the opposite side of the blank and monitoring the reflection from what is now the target backwall. Work by Paton (1977) did produce buried targets in titanium samples, but there was no practical method to produce buried targets in high-temperature ceramics until the techniques developed by Rodel and Glaeser (1987) were used to produce the targets described in this paper. Optically transparent resolution targets make it feasible to verify visually that the resolution target has been correctly fabricated. An image of the target with a candidate ultrasonic transducer then permits quantitative image resolution estimates to be made even when the interrogating acoustic beam contains significant refractive aberration. This is important because useful subsurface images can be acquired with the use of acoustic beams that are aberrant to the point that diffraction-limited beam-width calculations are meaningless. This work also demonstrates how the interdisciplinary skills of manufacturing companies can be combined with those of universities to produce results that any one of the individual members of the team could not have produced alone, without significant increases in labor, time, and cost.

THE EFFECTIVE ANTENNA BEAM WIDTH FOR A SATELLITE-BORNE RADIO TELESCOPE

1964 ◽  
Vol 42 (11) ◽  
pp. 2146-2152 ◽  
Author(s):  
T. R. Hartz ◽  
R. S. Roger
Keyword(s):  
Radio Telescope ◽  
Radio Signal ◽  
Beam Width ◽  
The Sun ◽  
Sweep Frequency ◽  
Antenna Beam ◽  
The Earth

For an antenna in the ionosphere above the F layer, there is a cone of directions within which a radio signal coming in to the earth can reach the antenna. Computations have been carried out of the aperture of this conical pattern for an antenna height of 1000 km, and for different ionospheric conditions. The computations are compared to experimental determinations of the aperture made using the sweep-frequency receiver in the Alouette satellite to observe the radiations from the sun.

Tunable microstrip-line coupler for adjusting the antenna beam width

2017 ◽  
Vol 59 (8) ◽  
pp. 1955-1959
Author(s):  
Chi-Hyung Ahn ◽  
Jae Hee Kim ◽  
Soon-Soo Oh
Keyword(s):  
Microstrip Line ◽  
Beam Width ◽  
Antenna Beam

Flow in Heterogeneous Porous Media

1961 ◽  
Vol 1 (03) ◽  
pp. 153-169 ◽  
Author(s):  
J.E. Warren ◽  
H.S. Price
Keyword(s):  
Effective Permeability ◽  
Transient Flow ◽  
Spatial Configuration ◽  
Geometric Mean ◽  
Laboratory Data ◽  
Heterogeneous Porous Media ◽  
Physical Models ◽  
Core Analysis ◽  
Specific Distribution ◽  
The Individual

Abstract Techniques for studying the performance characteristics of heterogeneous reservoirs have been developed. The effect of permeability variation on both the steady-state and the transient flow of a single fluid has been investigated. Limited comparisons with field and laboratory data have been made. The physical models studied consist of random three-dimensional arrays of homogeneous porous blocks. The permeabilities of the individual elements are assigned according to a specific distribution function; uniform anisotropy is introduced by varying the relative dimensions of the blocks. A particular model is perturbed simply by re-arranging its elements at random. The behavior of a physical model is determined by digitally solving its numerical analogue. Based on computational experiments, subject to the restrictions implied by the assumptions that were made, the following general conclusions have been drawn.The most probable behavior of a heterogeneous system approaches that of a homogeneous system with a permeability equal to the geometric mean of the individual permeabilities.The effects of flow geometry and anisotropy on the most probable value of the effective permeability of a heterogeneous medium are finite but not significant.The permeability determined from a pressure build-up curve for a heterogeneous reservoir gives a reasonable value for the effective permeability of the drainage area.A qualitative measure of the degree of heterogeneity and its spatial configuration are obtained from a comparative study of core analysis and pressure build-up data. It has been indicated that these conclusions are predicated on the assumption that the core analysis and the pressure build-up data represent true reservoir characteristics. Common sources of error in these data have been discussed. Introduction One of the most significant problems of reservoir engineering is that of determining the nature and the disposition of the heterogeneities that inevitably occur in petroliferous formations. It is with this problem that this paper is concerned.

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