Arrival Fluctuations Research Articles

Statistical analysis of angle-of-arrival on 4.1km line-of-sightlaser link at 0.83 µm across central London

Statistics from 18 months of measurements of clear air angle of arrival fluctuations on an 0.83 /spl mu/m line-of-sight laser link propagating on a 4.1 km path across central London are presented. Analysis of the probability density function estimates of angle of arrival for a range of values of the structure parameter C/sub n//sup 2/ shows virtually no departure from a Gaussian distribution. The standard deviation of the angle of arrival increases as the strength of turbulence increases with values up to 100 /spl mu/rad. A range of angle of arrival of up to /spl plusmn/300 /spl mu/rad was measured.

Interference noise spectrum above a rough sea surface at small glancing angles

The interference noise spectrum due to sea clutter has been investigated using statistical scattering theory. The scattered field was calculated in the tangent-plane approximation. The bearings of a motionless source are taken in the bistatic case. Taking the function of shadows on a spatially inhomogeneous random surface into account, we were able to explain the nonmonotonic dependence of the width of the spectrum of arrival angle fluctuations on the distance as well as the presence of maxima in the spectrum at frequencies substantially higher than that of the maximum of a rough sea surface. The theoretical results are compared with data from a full-scale experiment.

Solar scintillation and the monitoring of solar seeing

A non-telescopic method of determining the quality of atmospheric seeing is discussed for large angular diameter objects, such as the Sun. In this method the concept of thermodynamic fluctuations is used to relate the observed intensity fluctuations to the r.m.s. angular diameter of the atmospheric seeing cells and telescopic angle of arrival fluctuations. Comparison between the measured r.m.s. cell size and telescopic angle of arrival fluctuations are presented for various degrees of seeing. Cross-correlation coefficients of 0.95 have been measured during such comparisons.

東北地方北部で観測される遠地P波の振幅及び走時の空間的変動

東北地方北部で観測される遠地P波の振幅及び走時の空間的変動

A matched filter network for estimating pulse arrival times

Pulse arrival times are often close to the arrival times of pulses at nearby positions. A method that estimates arrival times from a series of closely related receptions has been developed. It combines the matched filter with the minimum path algorithm of network programming. In an environment where noise is present, the arrival time estimates using traditional matched filter processing degrade, owing to arrival time jumps equal to a period of the carrier. Results obtained from experimental and simulated pulses demonstrate that the method removes the jumps while retaining smaller-scale arrival time fluctuations that are of interest. >

Probability of arrival of rays of light for propagation through random media: Connection with rotational brownian motion

An expression is derived for the probability of arrival of rays of light for propagation through a random medium with isotropic and homogeneous correlation function for the refractive index fluctuations. This expression is shown to be similar to the density matrix for rotational brownian motion. The diffusion constant for angle of arrival fluctuations is seen to be determined from the correlation functions of ▿ n's, in a manner similar to the Kubo formula for rotational brownian motion.

Queueing in high-performance packet switching

The authors study the performance of four different approaches for providing the queuing necessary to smooth fluctuations in packet arrivals to a high-performance packet switch. They are (1) input queuing, where a separate buffer is provided at each input to the switch; (2) input smoothing, where a frame of b packets is stored at each of the input line to the switch and simultaneously launched into a switch fabric of size Nb*Nb; (3) output queuing, where packets are queued in a separate first-in first-out (FIFO) buffer located at each output of the switch; and (4) completely shared buffering, where all queuing is done at the outputs and all buffers are completely shared among all the output lines. Input queues saturate at an offered load that depends on the service policy and the number of inputs N, but is approximately 0.586 with FIFO buffers when N is large. Output queuing and completely shared buffering both achieve the optimal throughput-delay performance for any packet switch. However, compared to output queuing, completely shared buffering requires less buffer memory at the expense of an increase in switch fabric size.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer simulation of atmospherically corrupted signals at the focal plane of a parabolic antenna

AbstractA simulation procedure for generating the signals appearing at the focal plane of a parabolic reflector is presented. The procedure consists of generating the time series of the angle‐of ‐arrival fluctuation and intensity scintillation directly from their temporal power spectra and combining the two processes. An example of the procedure is also given.

Monte Carlo Simulation of Precipitate Nucleation and Growth: Time Dependent Results

AbstractA three-dimensional Monte Carlo computer program has been developed to study the heterogeneous nucleation and growth of oxide precipitates during the thermal treatment of crystalline silicon. In the simulations, oxygen atoms move on a lattice with randomly selected lattice points serving as nucleation sites. The change in free energy that the oxygen cluster would experience in gaining or losing one oxygen atom is used to govern growth or dissolution of the cluster. All the oxygen atoms undergo a jump or a growth decision during each time step of the anneal. The growth and decay kinetics of each nucleation site display interesting fluctuation phenomena. The time dependence of the cluster size generally differs from the expected 3/2 power law due to the fluctuations in oxygen arrival at and incorporation in a precipitate. Competition between growing sites and coarsening are observed.

Effects of fluctuations in the quantity of work arriving on waiting time, idle time and rate of losing customers

SUMMARY In a job shop, the intervals between job arrivals and the job processing times fluctuate and cannot be forecast. When many jobs (customers) arrive at a job shop at the same time, some customers may not place an order because they do not want to wait. To prevent such a situation, the job shop may temporarily increase the process capacity, thereby reducing the waiting time. If its timing is not correct, however, such an increase can also unexpectedly increase the idle time in the process. In this paper, the effects of fluctuations in the quantity of work arriving on waiting time, idle time and the rate of losing customers is studied using numerical calculations which assume extreme fluctuations. These characteristics show different delays in their response to fluctuations in job arrivals. The paper deals with the index and timing for temporarily increasing and decreasing the process capacity to absorb the fluctuations in the quantity of work arriving, that is under what circumstances to do so and when.

A theoretical and experimental study of angular scintillations in earth space paths

The theoretical framework and experimental results of an antenna offsetting technique which has been used to investigate angle of arrival fluctuations in the microwave region for medium ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30\deg</tex> ) and low elevation ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9\deg</tex> ) angles is presented. The receiver antenna is depointed by a small angle and the antenna gain slope in dB/deg transforms angle fluctuations into amplitude fluctuations. The sensitivity and resolution of the apparatus together with the limitations due to amplitude scintillations, their time variability, and the noise floor of the system are discussed in detail. Experimental results are presented and compared with the theory developed in the paper. The study reveals that the important parameter is the product <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C^{2}_{n}L</tex> and values are presented and discussed. The experimental values for the root mean square (rms) angular deviation <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma(\theta)</tex> and of the spectral density <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W_{\theta}(f)</tex> show a great variability between day and night and between winter and summer with values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma(\theta)</tex> ranging from below 1 mdeg up to 20 mdeg. Low elevation studies at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9\deg</tex> indicate angular scintillations less intense than expected, and never exceeding 4 mdeg.

Routine Analysis of Periodic Queues

Abstract Many queues are characterized by predictable periodic fluctuations as well as by random fluctuations. Queues that arise at copiers or duplicators usually involve such predictable fluctuations in work-load arrival. This note describes a series of approximations that have been combined into a simple inexpensive computer program. This program is being routinely used by the Xerox Corporation to approximate the average turnaround time at nonstationary single-server queues with nonexponential service time distributions.

Preliminary results of underwater acoustic measurements at a mid-ocean site, 1977

The Mid-ocean Acoustics Transmission Experiment 1977 (MATE), was conducted to measure the acoustic variability at four frequencies from 2 to 13 kHz over an 18 km path at Cobb Seamount. Preliminary results indicate time of arrival fluctuations for a single refracted path are well predicted by internal wave theories. The variation in acoustic intensity of the single path, however, is not well predicted. Simultaneous environmental measurements make possible a careful comparison between the observed acoustics and the physical fields. The environmental data sets suggest alternative mechanisms which must be considered in predicting the observed acoustic variability. [Work supported by ONR.]

Some new results on propagation of electromagnetic waves in strongly turbulent media

New results for the covariance of the intensity fluctuations of a plane wave propagating in a strongly turbulent medium are presented, and the consequences of these new results on aperture averaging, angle of arrival fluctuations, and the temporal frequency spectrum of the intensity scintillations are evaluated. The differences between the strong turbulence and weak turbulence cases are generally quite significant.

Fluctuations in Surface-Reflected Pulsed cw Arrivals

A pulse of 168-cps sound was scattered from the ocean surface and analyzed for fluctuation as a function of the angle of incidence. A (cosφ)2.5 relation is found between the relative standard deviation of the energy and the incident angle, as measured from the normal.