Echo Height Research Articles

The Temperature Dependence of the N-14 NQR Spectrum, Relaxation Times, and Line Shapes of Cyanuric Fluoride

Measurements of the N -14 NQR spectrum, relaxation times, and line shapes as functions of temperature of cyanuric fluoride are reported. This material exhibits very wide lines and thus lends itself to determining the profile of the lines from measurements of the echo heights. The material also exhibits a phase transition similar to that found in s-triazine. The phase transition occurs at 115 ± 5 K. A comparison of the results is made with those obtained previously for cyanuric chloride and s-triazine.

超音波による電子ビーム溶接欠陥のインプロセスモニタリング 電子ビーム溶接の欠陥発生及び防止に関する研究 ８

This paper reports the possibility of detecting bead deflection defects during electron beam welding (EBW) using in-process monitoring by ultrasonics. Experiments were conducted using a 6 kW (150 kV) high vacuum type welding machine and a 5 MHz ultrasonic transducer. All welding was performed at a 30 mm penetration depth in the flat position on SM41 steel plates. A coupling method of the ultrasonic transducer to the plate at a high temperature in the vacuum chamber was investigated. A 1 mm gap was maintained by using 0-rings between the transducer and the steel plate surface and silicon oil was pumped into the gap for coupling and cooling.The following points were concluded from the study.(1) It is possible to monitor the bead deflection during EBW by detecting the time difference between the ultrasonic echo from the weld metal and that from the groove face.(2) The detected voltage of the bead deflection is proportional to the measured bead deflection and the accuracy of detection is within ±10%.(3) A bead deflection defect as small as 0.6 mm can be detected.(4) The maximum echo height from the weld metal is obtained using the following conditions:(a) the measurement depth equals the maximum depth of penetration, (b) the measurement distance is 15 mm behind the weld cavity.(5) The echoes from the weld metal are those arising from the root defects which occur at the bottom of the weld zone.

Ultrasonic Techniques for the Measurement of the Interfacial Stress between a Metallic Punch and Non-metallic Plates

This paper is concerned with the appilicability of the ultrasonic technique to the measurement of the interfacial stress between metallic punch and some non-metallic plates. The characteristics of the ultrasonic wave due to the variation of the interfacial stress between metal and polymers are graphically presented. The changes in ultrasonic beam density due to spreading near the edge of the punch are then investigated, and the scattering characteristics of the wave are estimated on the basis of variation of the echo height as the probe is moved. The stress field of non-metallic plates indented by the punch is depicted in plots of the interfacial stress distribution, and quantitative ultrasonic techniques for the determination of an interfacial stress in polymers are discussed.

Radar auroral echo heights as seen by a 398‐MHz phased array radar operated at Homer, Alaska

The first results of an investigation of the altitude characteristics of auroral echoes at 398 MHz are presented. The data were collected over two nights in the spring of 1973 with a phased array radar operated at Homer, Alaska. Heights of maximum backscattered power can be determined with an accuracy approaching 2 km, a temporal resolution as short as 20 s, and a horizontal spatial resolution of 40 km. The spatial distributions of the height of echoing in two premidnight periods are shown to be consistent with a model of scattering from a continuous range of heights between 97 and 117 km; within this interval, the height tends to change in such a way that the echoes come from directions nearly perpendicular to the earth's magnetic field. In a postmidnight period, the echo activity was confined to a region of considerably more restricted (5–10 km) vertical extent. In all cases, the echo region was sharply bounded from below at 96–98 km. The heights may have short‐term (minutes) and small‐scale (< 100 km) structure. Adjacent structures are sometimes observed to differ in height by as much as 10 km.

Ultrasonic techniques for the measurement of the interfacial stress between a metallic punch and non-metallic plates.

This paper is concerned with the applicability of the ultrasonic technique to the measurement of the interfacial stress between a metallic punch and some non-metallic plates. The characteristics of the ultrasonic wave due to the variation of the interfacial stress between a metal and polymers are presented graphically. The changes in the ultrasonic beam density due to spreading near the edge of the punch are then investigated, and the scattering characteristics of the wave are estimated on the basis of the variation of the echo height as the probe is moved. The behavior of the stress field of nonmetallic plates indented by the punch is depicted in plots of the interfacial stress distribution, and quantitative ultrasonic techniques for the determination of an interfacial stress in polymers are discussed.

集束探触子による表層欠陥の探傷試験

The present study proposes a method of ultrasonic nondestructive evaluations of flaws in surface layer which can hardly be detected by the conventional methods, of ultrasonic testing due to lapping of both surface and flaw echoes. The echo patterns for various types of flaws in the surface layer of steel test specimens are measured with a single focusing probe and theoretically analysed by theory of sound, from which the effects of the water distance and the flaw depth on the echo pattern are clarified. Moreover, the applicability of this method with scanning device for inspection of flaws in welds is confirmed by microscopic examination. A summary of the results is as follows.When the focus of the ultrasonic beam is beneath the position of flaw, there appear two peaks in the echo pattern which are corresponding to the surface echo and the flaw echo, respectively. As the focus approaches to the flaw position, the peak of flaw echo disappears. This peak of echo consists of multiple echoes and is most conspicuous when the ultrsaonic beam is mostly focused by its multiple reflection and thus its sound pressure is highest. The echo height of flaw depends upon the flaw depth and water distance, and the peak position in the echo pattern is independent from the flaw depth under the constant water ditsance. According to the peak profile of scanning detection for weld interfaces of clad, there are two types of echo patterns, that is, wave-shaped and flat-shaped patterns reflected at interspersed flaws and flat-shaped flaws, respectively.

Two-dimensional electron spin echo spectroscopy and slow motions

A technique is described for the study of slow molecular motions that employs two-dimensional electron spin echo (2D-ESE) spectroscopy. An ‘‘echo-induced ESR spectrum’’ is obtained with a two pulse 90° (τ)/() 180° sequence by recording the echo height as the dc field is swept. A series of sweeps with different τ are Fourier transformed to yield a two-dimensional spectrum comprised of an echo-induced spectrum along the x axis and the homogeneous widths along the y axis. A convenient theoretical analysis appropriate for slow motions is given and it is shown that the 2D spectrum may be regarded as a graph of the widths vs the resonance positions of the individual ‘‘dynamics spin packets’’ that constitute the spectrum. An experimental study of the spin probe Tempone in 85% glycerol/H2O solvent for slow motions (i.e., rotational correlational times of order 10−5–10−6 s) shows variations in homogeneous widths (i.e., T−12) over the spectrum. This is analyzed in terms of canonical models of rotational reorientation—Brownian, free, and jump diffusion, and it is found that the variations of T−12 across the spectrum show features similar to a Brownian model. A special normalized contour plot of the 2D spectra is introduced which clearly emphasizes the variation of T−12 across the spectrum. The enhanced information content of these 2D spectra is discussed, and it is shown how 2D-ESE spectroscopy is both an improvement on and a complement to cw techniques for studying motional dynamics. Experimental extensions and limitations are also discussed.

表層はく離割れについて

In T or corner joints, a type of crack which is caused by subsurface oxide inclusions and shrinkage stresses due to welding is likely to occur. Therefore, this cracking is similar to lamellar tearing. In this paper, the phenomenon has been named 'subsurface tearing'.Subsurface tearing has the following features;1. The oxide inclusions exist too near to the surface to detect with ordinary U.T. However, after welding the joint the subsurface tearing is easily detected by U.T. as a result of vanishing back echo.2. The oxide inclusions are sparsely distributed in the plate. Therefore, destructive tests, for example short transverse tensile tests, can not be used to reveal its susceptibility because most specimen will probably not contain oxide inclusions.3. The size of the subsurface tearing is small because the inclusions are small and isolated and cracking can occur near them.In this paper, a newly developed method for assessing the subsurface oxide inclusions was introduced. And a prevention method for the subsurface tearing was proposed.The main results are as follows;1. The special U.T. system, which consists of a very short pulse, high frequency transmitter/receiver and a small diameter probe with delay line, can detect subsurface oxide inclusions even when they are about 1 mm to the surface.2. The echo height of the subsurface tearing is about twice that of the oxide inclusions. The size of the subsurface tearing is a little larger than the total length of the inclusions.3. In tensile tests and fatigue tests on cruciform joints containing the subsurface tears, the reduction in strength was not observed. However, large size cracks were propagated by fatigue tests.4. Precautions against these cracks should be taken in both steel making and fabricating. In steel making, the subsurface oxide inclusions of the steel plate should be reduced by various means, i.e. Catreatment, non-oxidation pouring etc. In fabrication, it is thought that area to be welded should be checked using the special U.T. and any areas which are found to be defective should be buttered.

Improvement of ultrasonic testing by phased arrays

Methods for defect reconstruction and classification using the flexible and fast electronic beam forming with phased arrays have been described. Using the electronic sector scan, a reflecting point is represented as a short circular curve, the length of which is dependent upon beam width and system sensitivity. By superimposing all sector displays on a storage tube, a defect is reconstructed by the inner envelope of the circular curves. If, instead of the circular curves, only their centers (intensity maxima) are recorded, a defect is reconstructed by individual image points. This representation has the important advantage that is to a large extent independent of beam width and system sensitivity. The reconstruction by compound scanning which includes, as a special case, the conventional focused probe technique with B-scan presentation, has a high redundancy; and in the case of testing coarse grained materials, the coherent noise is essentially reduced (intensity averaging). By recording the maximum echo height during sector scanning with open beam, a compound scan amplitude-locus curve (VAOK) is generated which represents the directivity of the defect.

VHF Echoes from the High-Latitude Mesosphere and Lower Thermosphere: Observations and Interpretations

Recently published data (Ecklund and Balsley) describing VHF radar echo characteristics from the Arctic mesosphere and lower thermosphere show a remarkable seasonal dependence of both the echo height and echo intensity: during the three-month period around the summer solstice, intense and nearly continuous echoes are returned from a narrow (±2 km half-power) region centered at 86 km; during the remainder of the year, however, the echoes are much weaker, more sporadic and occur at a much lower altitude (70 km ± 9 km). In this paper, we present additional data that suggest that the summer echoes are primarily the result of shear instability of low-frequency (tidal) motions in the region of high stratification above the Arctic summer mesopause, while the winter echoes arise from the nonlinear breakup of upward-propagating gravity waves.

NMR observations of fluorine ion-implanted into polyacetylene and graphite

19FNMR spectroscopy has been used to characterize fluorine implanted into polyacetylene and highly orientated pyrolytic graphite. The intensities of the 19F NMR spectra at 4.5 K show that essentially all the fluorine is retained in these materials after the implantation process is over. The Une width of the spectrum of the graphite sample indicates that the fluorine remains where it was deposited. For the polyacetylene sample the ratio of the NMR solid echo height to the spin echo height, as calibrated herein, shows that the predominant nuclear diploar interaction of the implanted fluorine is heteronuclear.

Application of the Ramfjordmoen partial reflection experiment to the study of auroral precipitation events

The application of the partial reflection technique to the study of auroral radio absorption events is investigated. It is demonstrated that the technique measures the radio absorption due to the most energetic of the precipitated electrons, accounting for no more than a few percent of the total radio absorption as measured with a riometer, but usefully indicating the effective upper limit of the energy spectrum and the lowest altitudes affected by events at different times of day. The characteristic signature of the short-lived spike event is described. It is shown that the echoing regions are persisting structures of the neutral atmosphere, which produce partial radio reflections when they are “illuminated” from time to time by a sufficient flux of ionizing particles. Thus, the echo height tends to step between discrete levels as the event develops or decays, though at times there are more gradual vertical movements suggesting wavelike notions.

An amplified and saturated readout echo in piezoelectric powder

Even during the reading process, the repetitive application of an incident pulse gives rise to an increase and a saturation in the echo height in piezoelectric powder. This phenomenon was experimentally measured in detail as a function of the repetition period, the applied field strength, and the driving frequency. An attempt was made to explain the amplified and saturated readout echo theoretically by introducing an elementary model based on the particle rotational mechanism. In addition to the efficient enhancement of the deviation of the particle orientation, a fluctuation component was macroscopically investigated assuming that the increase and decrease is in unequilibrium during the repetitive application of the readout pulse sequence. The fluctuation was considered especially in the reading process to be caused by the deviation of the dipolar field associated with the statice deviation of the particle orientation caused by the two-pulse sequence. Calculated results derived from the fluctuation mechanism showed satisfactory agreement with experimental results.

Sensitivity of a Cloud Microphysical Model to an Urban Environment

Abstract Observations showed increased concentrations of cloud condensation nuclei (CCN) in air samples collected over and downwind of St. Louis when compared to upwind samples. Aircraft observations of urban clouds showed corresponding increased concentrations of cloud base droplets. In addition, observations indicated higher cloud bases and decreased elevations of average first echo base heights in the St. Louis/East St. Louis area as compared with similar clouds over rural areas. The purpose of this paper is to examine the possible role of CCN chemical composition and number concentration in producing the observed phenomena. A closed parcel model of condensation and collection was employed for this purpose. The results suggest that the observed differences of depth from cloud base to first echo height between urban and rural clouds do not result from concentration differences in any CCN size range. Results of model calculations also suggest that variations in chemical composition of the largest CCN (≥1...

Repetitive readout effect of a polarization echo

The repetitive readout effect of a polarization echo has been experimentally studied, using LiNbO3 powder. The repetitive reading-pulse application causes the readout echo height to increase and to be saturated at certain repetitive reading times. The effect is affected by the writing-pulse-application repetition times.

The Probability of Hail in Relation to Radar Echo Heights on the South African Highveld

Thunderstorms in the vicinity of Johannesburg and Pretoria have been tracked by an S-band radar since 1971. A total of 181 individual cells which occurred during 1974/75 was selected for this study. Of these, the numbers that did and did not produce hail on the ground were 77 and 104, respectively. The mean of the maximum heights of hail-producing cells was found to be 6.3 km AGL for the 40 dBZ contour and 9.1 km for echo tops (23 dBZ). These parameters in rain-producing cells reached only 4.5 and 6.4 km, respectively. The mean temperature in the free atmosphere at echo top height was −37°C for hail-producing cells and −20°C for rain-producing cells. No strict correlation was found for the temperature distribution and for the position of the freezing level versus the occurrence of hail on the ground There is at least a 50% chance for thunderstorm cells exceeding 7 km to produce hail on the ground. Probability graphs relating the occurrence of hail on the ground to heights of the 23 and 40 dBZ reflectivity contours as well as to temperatures at maximum echo-top heights were plotted. Such graphs could be used for the evaluation of hail suppression experiments. The bi-modal distribution of the probability graph of hail can be explained in terms of differences in the height distributions of the 40 dBZ contour of cells producing hailstones ≤1 cm and >1 cm in diameter.

Effects of St. Louis on Convective Cloud Heights

Abstract Heights and locations of the tallest 3 cm radar echoes at each half-hour through the convective parts of 140 summer days were measured during Project METROMEX. Comparison of the area-weighted frequencies of echoes occurring over and downwind of St. Louis, Mo., with those over a large nearby rural area, shows a substantial enhancement in the frequency of tall echoes over the city and near-down-wind areas. This enhancement comes mainly during the late morning and early afternoon and possibly again during the evening hours. The data also show a substantially different echo height distribution over urban and rural areas. Whereas the rural height distribution is distinctly bimodal, the urban height distribution shows no such bimodal character. This means that urban clouds are frequently able to penetrate mid-level arresting levels which limit the growth of rural clouds. These observations suggest an important role for urban-enhanced cloud dynamics in causing the St. Louis rainfall anomaly.

Radar Characteristics of Tropical Convection Observed During GATE: Mean Properties and Trends Over the Summer Season

Radar echo patterns observed daily during GATE have been analyzed to determine their mean characteristics and variations over the summer season. The characteristics analyzed were average echo areas, maximum heights, durations, number of high-intensity cores, motions, formation and dissipation modes, and orientations of echo lines. As in tropical convective echo patterns in other parts of the world, small echoes (< 102 km2 area) dominated the total number of echoes while large echoes (> 103 km2 area) accounted for most of the area covered by precipitation. Echo height, duration and number of embedded cores were all positively correlated with echo area, and the most intense echo cores were found in the largest echoes, indicating that echo regions > 104 km2 in area were the areas of most enhanced convection. Echo areas, heights and durations tended to be log-normally distributed. During late summer, the convection in large echoes (> 104 km2 area) was enhanced, showing greater vertical development as well as more numerous and more intense embedded cores than earlier in the summer. Lower tropospheric winds appeared to control echo motions and played a role in the horizontal alignment of echo lines.

溶込み不足が曲げ疲れ強さに及ぼす影響

This study is carried out to clarify the relation between stress concentration and fatigue strength, and between initiation and propagation of crack and fatigue strength.For this purpose, double-Vee butt joints with incomplete penetration are used. As non-destructive inspection, ultrasonic inspection and X-ray inspection are used and compared with the characteristics.The results obtained are summarized as follows.(1) By the bend fatigue test of specimen with incomplete penetration, it is found that the fatigue strength decreases rapidly as the size of incomplete penetration is increased.(2) The failure do not occur lower than a certain value of initial range in stress intensity factor ΔKi dependent upon size of incomplete penetration in this experiment.(3) By the ultrasonic inspection, the range in fatigue strength is estimated by the maximum echo height.(4) By the ultrasonic inspection, fatigue crack initiation is identified up to about 30% in total fatigue life. On the other hand, by the X-ray inspection, the total fatigue life is divided into three regions. In 1st region, incomplete penetration is undetectable, in 2nd region, incomplete penetration is detectable and in 3rd region, initiation and propagation of crack is identified.(5) The relation between the crack propagation rate da/dN and the range in stress intensity factor ΔK is given by the following expression da/dN=5.48×10-14(ΔK)5.7.(6) By the bend fatigue test of specimen with incomplete penetration, stress concentration factor a and fatigue notch factor β is rapidly increased as the size of incomplete penetration is increased.

Precipitation characteristics during the Venezuela rainy season

AbstractAn extensive program of observations designed to determine the structure of tropical mesoscale rain areas over land and their relation to synoptic envelopes was carried out during the rainy season of 1969 (June to September) in eastern Venezuela.The frequency distribution of precipitation in the area seen by radar (radius 100 km), as given by the average of 30 stations, was highly skewed: 14 per cent of the days in the experiment delivered half of the precipitation; 80 per cent could be attributed to rain episodes related to mobile synoptic systems. On the hourly basis, 0·45 per cent of all hours (or 10 hours) produced half of the precipitation.Daily precipitation in the radar circle was not correlated with radar echo height but markedly with echo area. Heavy rainfall occurs when a few very large clouds appear.A cloud distribution in terms of area and rain productiveness was determined for rainy and for dry days. Rain productivity increases with cloud area; however, since the number of clouds also decreases as their size increases, water yield to the ground is almost independent of cloud scale. No clear difference in the 200 mb flow could be found between cloud ensemble.On rainy days the temperature is lower and the specific humidity higher than on dry days confirming that cold‐core precipitation takes place also over Venezuela. A mean ascending velocity appears to exist in and out of clouds in the convection cores, but could not be found prior to onset of afternoon convection.