Fixed-point Measurements Research Articles

Bootstrapping point processes with some applications

We study the weak limit behavior of certain types of point processes obtained by replacing the original observations by the bootstrap sample. The usual bootstrap fails asymptotically in cases for which there exists a Poisson point process or a fixed point measure in the limit. In some cases, by subsampling at the rate m= m( n)=o( n)→∞ in the bootstrap (where n is the sample size), this problem will be resolved and convergence holds in probability. If m log log n/n→0 then asymptotic results are valid almost surely. The method is applied to some statistical problems.

An Experimental Study of Rain Effects on Fine Structures of Wind Waves

Abstract Previous experiments suggested that rain had dual effects on wind waves: damping in the gravity range and enhancement in the capillary–gravity/capillary range. These results in the frequency domain obtained from fixed-point measurements, however, might be contaminated by the Doppler effect. In the present study, wave slopes were spatially mapped with a scanning laser slope gauge under wind velocities of 3, 5, and 7 m s−1 and rain intensities of 42, 68, and 115 mm h−1. Synthesized spectral densities, which are not affected by the Doppler effect, were obtained by processing the data in both “fixed point” and “spatial scan” modes. The existence of dual effects is clarified with the present results.

Observations and parametrization of momentum transfer in heterogeneous terrain consisting of regularly spaced obstacles

Tethered balloon data collected over a heterogeneous, semi-rural area of southern England are presented. The terrain within which the observations were taken is dominated by regularly spaced bluff obstacles that form the boundaries to grass fields. The data are compared with previous surface data to assess how representative these fixed-point measurements are of area-averaged values. It is found that there is a vertical height above which the flow approximates to being homogeneous and observations made above it are representative of the area average. The effective roughness length for momentum is then compared with that derived from a model describing the drag partition around isolated obstacles that are either non-porous or porous to the incident flow. It is shown that the method chosen to partition the drag is of the right order to produce reasonable predictions of the effective roughness length for different roughness densities.

Cloud concentration statistics and dosage

A new measure of the dilution of contaminant cloud concentration values is introduced. The expected-mass-fraction function is shown to have both experimental and theoretical advantages. There are virtually no measurements of dilution for a contaminant cloud. A cloud in homogeneous turbulence is used as an illustrative example. These calculations can be validated with conventional, fixed-point concentration measurements in a wind tunnel.

Detection of a volcanic fracture opening in Japan using Global Positioning System measurements

THE Global Positioning System (GPS) is a powerful tool for detecting crustal deformation1; for example, the technique has been used to detect plate boundary movements in California2. Here we report observations of crustal deformation associated with seismic swarm and sea-floor volcanic activity off the east coast of the Izu Peninsula, Japan, in July 1989, using a fixed-point GPS network. These measurements have enabled us to capture some rarely observed features of seismic and volcanic activity. We have, for the first time, used GPS fixed-point measurements to follow the evolution with time of the crustal movements; such measurements provide a continuous uninterrupted record of deformation. Our observations were supported by independent data from other sources, thus providing further evidence for the utility of the GPS.

Observations of boundary‐layer structure over complex terrain

AbstractTurbulence data collected in an area of complex terrain using a number of instrument packages attached to the tether cable of a captive balloon are presented. Eddy correlation measurements of the turbulent momentum flux are used to determine the magnitude of the roughness length from the drag coefficient and also to show that the roughness length is a useful concept in parametrizing the surface stress in such areas. the relationship between the terrain characteristics and the roughness length is examined using a simple formula, results from a numerical model and previous experimental estimates of the roughness length for complex terrain. It is found that a formula based on numerical model results for separated flows gives reasonable predictions and that the measured roughness length is representative of an area of order 100 km2.Non‐dimensionalized turbulence data are compared with similar data obtained over flat homogeneous surfaces. This comparison suggests that the structure of the turbulent boundary layer over complex terrain is remarkably similar to that over flat homogeneous surfaces. Because of the limitations of fixed point measurements in complex terrain, results from a numerical study of turbulent flow over two‐dimensional sinusoidal orography are shown to indicate the magnitudes of the perturbations introduced into the boundary‐layer flow by large undulations in the underlying surface. the model results demonstrate the validity of the analysis carried out with the data.

Observations of boundary-layer structure over complex terrain

Turbulence data collected in an area of complex terrain using a number of instrument packages attached to the tether cable of a captive balloon are presented. Eddy correlation measurements of the turbulent momentum flux are used to determine the magnitude of the roughness length from the drag coefficient and also to show that the roughness length is a useful concept in parametrizing the surface stress in such areas. the relationship between the terrain characteristics and the roughness length is examined using a simple formula, results from a numerical model and previous experimental estimates of the roughness length for complex terrain. It is found that a formula based on numerical model results for separated flows gives reasonable predictions and that the measured roughness length is representative of an area of order 100 km2. Non-dimensionalized turbulence data are compared with similar data obtained over flat homogeneous surfaces. This comparison suggests that the structure of the turbulent boundary layer over complex terrain is remarkably similar to that over flat homogeneous surfaces. Because of the limitations of fixed point measurements in complex terrain, results from a numerical study of turbulent flow over two-dimensional sinusoidal orography are shown to indicate the magnitudes of the perturbations introduced into the boundary-layer flow by large undulations in the underlying surface. the model results demonstrate the validity of the analysis carried out with the data.

Atmospheric carbon dioxide and sulphur dioxide on an urban/rural transect—I. Continuous measurements at the transect ends

Carbon dioxide and sulphur dioxide concentrations have been measured on a transect between urban Nottingham and a rural area 15 km to the south-west. In Part I, the results of fixed point measurements at the ends of the transect are described. Seasonal averages showed no significant difference for CO 2 or SO 2 concentrations in the summer; in winter the mean CO 2 concentration in the city centre was 5 μl ℓ −1 larger than the rural mean. These figures conceal large differences in the diurnal variation between the two sites.

Review of ISO and ANSI standards for the determination of sound power levels of noise sources using sound intensity measurements

Sound intensity measurements can now be used to determine accurately the in situ sound power of machinery noise sources in the presence of high levels of background noise. Meetings of working group ISO/TC43/SC1/WG25 began in 1982 and a first draft standard was produced in late 1985. Meetings of working group ANSI S12-21 began in 1983 and produced first draft of a standard in 1984. The ANSI draft standard was circulated for balloting as a standard in 1987, and the ISO third draft was circulated in 1988. Although the ISO and ANSI drafts are similar, there are some differences. The ISO draft allows precision, engineering, and survey grade determinations and requires four indicators to be measured to decide the grade achieved. The ANSI draft only allows engineering determinations of sound power. The ISO draft only allows fixed point measurements, while the ANSI draft allows either fixed point or scanning measurements of intensity on a surface enclosing the source. Last year, 17 laboratories in North America took part in a round robin using the ANSI draft.

ANSI round robin test on determination of sound power from sound intensity

The use of the sound intensity technique to determine the sound power output of a source has become very popular over the years. An American National Standards Institute committee, ANSI S12-21, is currently engaged in developing a suitable standard for making sound power measurements using the sound intensity technique. The draft version of the proposed standard permits the use of both fixed point measurements and also continous hand scanning on the enclosed surface. To check the validity of the sound power measurements and to help make suitable changes to the measurement procedure, many optional data quality indicators are also included in the draft. Recently, the working group ANSI S12-21 organized a round robin test on a standard reference sound power source. Various organizations across the United States participated in the round robin test. This paper summarizes and discusses the sound power measurement results obtained on the reference sound source.

Skew Fluxes in Polarized Wave Fields

Abstract The scalar flux due to small amplitude waves that exhibit a preferred sense of rotation or polarization is shown to consist of a component. FS, that is skewed, being everywhere orthogonal to the mean scalar gradient, ∇Q. The skew flux is parameterized by FS = −D ∇Q where D, a vector diffusivity, is a measure of particle mean angular momentum. The skew flux may affect the evolution of mean scalar since its divergence, ∇·FS = US·∇Q, may be nonzero if the velocity US≈−∇ × D is up or down the mean gradient. For statistically steady waves, US corresponds to the Stokes velocity of particle drift. Integral theorems for new skew transport and the interpretation of fixed-point measurements are discussed, and the skew flux illustrated through several examples.

Progress with the ISO and ANSI Standards for the determination of sound power levels of noise sources using sound intensity measurements

Intensity measurements offer the possibility of accurate determination of the in situ sound power of machinery noise sources in the presence of high levels of extraneous noise. Meetings of working group ISO/TC43/SCI/WG25 began in 1982. Early meetings were devoted to discussing various measurement difficulties with a draft Standard produced in late 1985. Meetings of working group ANSI S12‐21 began in 1983 and produced the first draft of a standard in 1984. It is planned to submit a draft standard to ANSI for trial and study. Although there are many similarities between the ISO and ANSI drafts, there are presently some differences. The ISO draft allows both precision and engineering grade measurements and uses a number of indicators to determine the grade achieved. The ANSI draft presently only allows engineering measurements. The ISO draft concentrates on fixed point measurements on a surface, while the ANSI draft also includes the possibility of scanning.

Fixed point measurement of seam stress (in German and English)

Fixed point measurement of seam stress (in German and English)

Absorption, emission and lifetime data on Cu + in some alkali halides

The lifetime of the 3d 94s→3d 10 transition of Cu + in several alkali halides has been measured as a function of temperature from L.He.T. (⋍8 K) to R.T. Original instrumentation was developed allowing the automatic continuous recording, as a function of temperature, of single decay time constants even if varying at a rather high rate. Accurate fixed-point measurements by the single photon technique were also performed at R.T., L.N.T. and L.He.T. Two regions of variation of τ versus T have been observed. The interpretation which seems more plausible is that the Cu + ion in its relaxed excited state is essentially in-center in the lower temperature region while for T >40 K it goes off-center even if not so strongly as in the ground state. In NaCl the behaviour of Cu + is quite similar with the difference that in the ground state it is in-center over the whole temperature range from L.He.T. to R.T.

Absorption, emission and lifetime data on Cu + in some alkali halides

The lifetime of the 3d 9 4s → 3d 10 transition of Cu + in several alkali halides has been measured as a function of temperature from L.He.T. (⋍8 K) to R.T. Original instrumentation was developed allowing the automatic continuous recording, as a function of temperature, of single decay time constants even if varying at a rather high rate. Accurate fixed-point measurements by the single photon technique were also performed at R.T., L.N.T. and L.He.T. Two regions of variation of τ versus T have been observed. The interpretation which seems more plausible is that the Cu + ion in its relaxed excited state is essentially in-center in the lower temperature region while for T > 40 K it goes off-center even if not so strongly as in the ground state. In NaCI the behaviour of Cu + is quite similar with the difference that in the ground state it is in-center over the whole temperature range from L.He.T. to R.T..

Urban Influence on a Strong Daytime Air Flow as Determined from Tetroon Flights

Tetroon flights across Oklahoma City indicate the influence of an isolated urban area on the horizontal and vertical air velocity at heights near 400 m in relatively strong (13 m sec−1) daytime flow. The Lagrangian measurements so obtained are collated with fixed-point measurements of horizontal and vertical velocity on a 460 m television tower. Above the city in the morning there is a mean trajectory turning toward lower pressure of 10°. This turning, presumably fractionally induced, is noted only weakly in the afternoon and not all in the evening, but there is slight evidence for a bending of the trajectories around the city at these later times. During the day the city appears as the source of a plume of ascending air motion extending at least 30 km downwind of the city, with both tetroon and tower measurements indicating a mean upward velocity of almost 0.4 m sec−1 ten kilometers downwind of city-center at heights near 400 m. On the average the magnitude of the stress determined from the covariance of the eddy velocity components along the tetroon flights is about 70% of the magnitude measured on the tower, and there is a correlation of nearly 0.5 between individual measurements of stress by the two techniques. The magnitude of the tetroon stress is intimately related to building height and density, with a stress maximum of at least 3 dyn cm−2 located 10 km downwind of city-center in comparison with stress values near 1 dyn cm−2 beyond the city outskirts. The fraction of the stress associated with Lagrangian oscillations of 1–10 min period (in comparison with 1–30 min period) increases from 20% upwind of the city to 80% downwind of the city in the daytime average.

C.R.T. Displays of Wind Eddies and Some Lagrangian Deductions from a Vortex Model of Turbulence

Abstract The concept of atmospheric turbulence in a two-dimensional field as a mixture of circular eddies of different diameters and circulation velocities is considered, and from this an argument is presented to show how the frequency of air fluctuations relative to the mean flow (the Lagrangian) is related to that measured at a fixed point. A technique described in earlier papers by the author, for presenting wind fluctuations at various positions in the field as vectors correspondingly arranged on a cathode-ray tube, is used for examining the plausibility of the theory, and some supporting evidence is given in the form of multi-vector oscillograms. It is argued that, in narrow bands, the ratio of fixed point (Eulerian) to Lagrangian frequencies is inversely proportional to the intensity of turbulence and may be calculated from fixed point measurements. A practical method of measuring the ratio has been tried and statistical results covering a range of wind speeds, frequencies and atmospheric stabilitie...

Bridge for Tracing the Tunnel Diode I–V and Conductance Curves

A bridge circuit is described in this paper which permits tracing of both the I–V and conductance curves of tunnel diodes. To insure accuracy, a constant voltage ac source employing feedback is used for the derivative measurement. Equipment used is relatively simple and the majority of it is commercially available. The circuit also allows fixed point measurements to be made at the user's option. Reproducibility and accuracy are mainly dependent on output indicator and the parameter being measured. Equations for small errors introduced by the bridge are presented (Appendix); they can be used to determine when a measurement is subject to excessive error. Measurements at other than room temperatures may be made with the bridge by physically isolating the high frequency circuitry containing the diode from the remainder of the bridge. Representative data from the bridge are presented.

Propagation at 412 Megacycles from a High-Power Transmitter

Extended measurements are reported which indicate the existence of pronounced nocturnal superrefraction during an appreciable percentage of the summer and of very persistent scattering by atmospheric turbulence near the surface in all seasons. The measurements were taken over rolling midwestern terrain at a distance of about 100 miles. Mobile road tests were made to supplement the fixed-point measurements and to provide an approximate indication of the relation between field strength and distance. Aerial tests were made to show the effects of antenna height at large distance. Graphs are provided which show the effects of distance, terrain, antenna height, and time upon the field strength. The practical significance of the results in the broadcast and commmunication fields is indicated.