Air Force Cambridge Research Center Research Articles

United States sea ice physics project, 1954–59

In 1954 the Geophysics Research Directorate of the Air Force Cambridge Research Center (AFCRC), at the request of Northeast Air Command, United States Air Force, organized a study of the physical properties, growth, and bearing capacity of sea ice. The object of the study was to gain information about the conditions under which various aircraft and vehicles could operate on sea ice, for supply and rescue purposes. The Navy Hydrographic Office (NHO) and the Snow, Ice and Permafrost Research Establishment (SIPRE) of the Army Corps of Engineers also took part in the project. The spheres of interest of each organization were as follows: AFCRC, the application of geophysical and crystallographic methods to the study of sea ice; NHO, the details of the relations between meteorological conditions and the growth rate and general physical properties of sea ice; and SIPRE, the variation of the strength of sea ice as determined by small-scale field tests, and the application of this information toward an analysis of the bearing capacity of sea ice.

Vertex excited surface waves on both faces of a right‐angled wedge

Communications on Pure and Applied MathematicsVolume 12, Issue 3 p. 435-455 Article Vertex excited surface waves on both faces of a right-angled wedge† Samuel N. Karp, Samuel N. KarpSearch for more papers by this authorFrank C. Karal Jr., Frank C. Karal Jr.Search for more papers by this author Samuel N. Karp, Samuel N. KarpSearch for more papers by this authorFrank C. Karal Jr., Frank C. Karal Jr.Search for more papers by this author First published: August 1959 https://doi.org/10.1002/cpa.3160120304Citations: 17 † The research reported in this paper has been sponsored by the Electronics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, under Contract No. AF 19(604)1717. A summary of this paper appears in IRE Wescon Convention Record, Part. I, 1958, pp. 101–103. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume12, Issue3August 1959Pages 435-455 RelatedInformation

Extremely High Temperatures

Conference on Extremely High Temperatures Boston, Massachusetts, March 18–19, 1958. Edited by Dr. Heinz Fischer and Lawrence C. Mansur. (Sponsored by Electronics Research Directorate, Air Force Cambridge Research Center.) Pp. xi + 258. (New York: John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1958.) 78s. net.

Explorer Rocket Research Program

Nine Jupiter-C missiles have been launched at Cape Canaveral since September 1956, the first three testing the propulsion system, airframe, guidance components and re-entry conditions of the nose cone, the remaining six were used as carriers of the Explorer satellites I through VI. This was a joint program of Jet Propulsion Laboratory and Army Ballistic Missile Agency with considerable assistance from the University of Iowa, Air Force Cambridge Research Center, the Vanguard tracking teams and many others. The Jupiter-C is a four-stage vehicle burning solid propellant. The first stage is a modified Redstone missile, developing a thrust of 83,000 lb. The second stage is powered by an annular ring of 11 solid propellant motors, patterned after the Sergeant missile. The third stage consists of three motors, identical to the second, fitted inside the ring of second-stage motors. The fourth stage is a single motor, identical to the motors of the other high speed stages. The satellite payloads of the Explorer series were contained in a shell 80-in. long by 6 in. in diameter, which, together with its package of instruments for Explorer I, weighed 30.8 lb. The experiments were designed especially to study and measure cosmic radiation in great detail. Explorer IV, the latest one to attain a successful orbit, achieved a perigee altitude of 160 miles and an apogee altitude of 1390 miles.

Operating Characteristics Determined by Binary Decisions and by Ratings

With the theory of signal detectability as a framework, two psychophysical experiments were conducted in which each observation interval was well defined for the listener. Each interval contained noise, and it either did or did not (p=0.5) contain a signal (1000 cps, 0.5 sec in duration). In separate sessions of the first experiment, either the listener gave a yes-no decision or he responded with a rating (1–4) after each observation interval. Operating characteristics were obtained with E/N0 equal to 15.8. It is clear from the data that the trained listener can perform as well when he adopts the multiple criteria necessary for the rating method as when he adopts the single criterion required by the binary-decision procedure. In the second experiment, only the rating method was used to determine the relation between d′ and E/N0. The resulting function, for d′ ⩽ 3.0, approximates a straight line which passes through the origin and which has nearly the same slope as that obtained in other laboratories. [This research was supported by the Operational Applications Laboratory, Air Force Cambridge Research Center, under Contract AF 19(604)-1962.]

Automatic Resolution of Speech Spectra into Elemental Spectra

The acoustic output for a given configuration and excitation of the vocal tract during speech production can be described in a relatively compact manner by a transfer function characterized by a reasonably small number of poles and zeros. Thus the spectrum of a speech sound (log amplitude vs frequency) may be considered to be the sum of several elemental spectra, each associated with one pole or zero. The spectrum envelope of any vowel, for example, could be approximated reasonably accurately by combinations of spectra drawn from a catalog of 30 to 40 curves that represent simple resonances at a number of different frequencies. A digital computer has been programed to perform such an approximation on spectra of vowel and some consonant sounds sampled periodically in time. Successive comparisons are made between a particular speech spectrum and spectra constructed from a catalog of elementary curves that are stored in the memory. The computer is programed to converge rapidly from a first approximation of the spectrum based on previous examinations of adjacent samples towards the synthesized spectrum that yields the best fit with the input spectrum, and reads out numbers that identify the particular elemental spectra that are finally selected. [Supported by U. S. Army (S.C.), U. S. Air Force (O.S.R., A.R.D.C.), and U. S. Navy (Office of Naval Research), and by Air Force Cambridge Research Center Contract AF 19(604)-2061.]

Aural Detection of a Gated Sinusoid as a Function of its Duration

Using the two-interval forced-choice procedure, we conducted detection tests with gated sinusoids of 1000 cps in Gaussian-process noise. The signals varied in duration from 63 msec to 10 sec. We employed four different schedules or patterns of the time intervals within each trial. Duration was a highly significant variable. The temporal pattern was not. The results confirm and extend the findings of Hamilton and of Green, Birdsall, and Tanner [J. Acoust. Soc. Am. 29, 506–511 and 523–531 (1957)]. The ratio of signal energy to noise power density required for 75% correct detection falls from about 12.5 db at 5.0 msec to about 9.5 db at 20 msec (Green), is then constant at 9.5 db out to 160 reset, and then rises to about 13.5 db at 1.0 sec and 24 db at 10 sec. The question, whether or not these results indicate that the auditory parameters are variable and adjust themselves to the task at hand, will be discussed. [This research was supported in part under Air Force Contracts AF 18(600)-1219 and AF 19(604)-2051, monitored by the Operational Applications Laboratory, Air Force Cambridge Research Center, ARDC.]

Detection of Complex Wave Forms: Effects of Signal Band Width and Duration

Detection of signals from resonant systems is of interest both for the field of speech perception and for testing the applicability of Signal Detectability Theory to signals of complex wave form. Stimuli were the output of a recurrently-excited, simple resonant circuit. The impulse frequency was fixed at 100 cps, and the resonant frequency was 500 cps. The signal was, then, a train of decaying 500 cycle sinusoids. This signal was gated for various durations and presented binaurally in a background of white noise to three observers. A two-alternative forced-choice technique was used. Five different rates of decay, giving signal band widths of 10, 30, 100, 200, and 375 cps were used. Each signal was presented at five different durations; 0.01, 0.02, 0.05, 0.1, and 0.20 sec, keeping the energy constant by varying the signal power inversely with the duration. The efficiency (η) of each of three observers was estimated for all 25 combinations of band width and duration. Results show that for narrow-band-width signals efficiency remains fairly constant over the durations studied. On the other hand, wider band-width signals produce lower performance at longer durations. The results are considered in relation to various current descriptive models, and the usefulness of “auditory band width” concepts is weighed in the light of the data. (Supported by the Office of Naval Research and Air Force Cambridge Research Center.)

Measurement of Digital Channel Capacity for a Speech Compression System

It has long been speculated that an information handling rate of 1000 binits/sec or lower might be adequate for transmission of speech, if first the redundancy of its original form could be reduced. The Formoder, a speech-band-compression system, accomplishes the reduction by extracting the main information-bearing elements from speech, presenting them in a seven channel output which requires a total band width of about 175 cps. Latest articulation tests using Harvard P.B. word lists processed by the Formoder and given to a trained crew have yielded scores of 75% and higher for some male speakers. In order to measure the digital channel capacity necessary to intelligibly transmit the Formoder output, the seven channels were digitized using a technique known as “delta modulation.” This scheme achieves time and amplitude quantization by means of a clipper, sampler, and a linear feedback network. Compared with standard pcm techniques, “delta modulation” represents considerable economy in instrumentation. Articulation tests were made for several rates in the range 500–2500 binits/sec. Results of these tests will be reported and the important features of the digitizing technique will be given. [This research is sponsored by the Air Force Cambridge Research Center under Contract No. AF 19(604)-3465.]

Proportion of Correct Responses as a Function of the Number of Stimulus-Response Alternatives

The effect of the number of stimulus-response alternatives on the human observer's probability of making a correct response was predicted by three models: a simple threshold model; the constant-ratio rule with simplifying assumptions; and the theory of signal detectability with simplifying assumptions. Four types of signal ensembles were used in these experiments: (a) speech signals; (b) a sinusoidal signal occurring in one of n intervals in time; (c) sinusoidal signals of varying amplitude; and (d) sinusoidal signals of varying frequency. In all of these experiments the listeners had complete knowledge of the set of stimuli under test and limited their responses accordingly. The simple threshold model failed to account for any of the data. The simplified version of the constant-ratio rule and the simplified version of the theory of signal detectability were both compatible with the data obtained in the speech experiments. Also, over the small range tested, both handled data obtained when a sinusoidal signal occurred in one of n intervals. No model tested was sufficiently complex to account for data when the sinusoidal signals varied only in amplitude or only in frequency. (Work under sponsorship of Operational Applications Laboratory, Air Force Cambridge Research Center, and U. S. Army, Signal Corps Engineering Laboratories, Fort Monmouth.)

IGY Bulletin: No. 22, No. 23, No. 24

This report is based on a paper given by Kenneth Hunkins, now of the Geophysics Department, Stanford University, at the IGY Symposium during the 125th Meeting of the American Association for the Advancement of Science, Washington, D. C., December 29‐30, 1958.Among the many IGY scientific programs carried out on Drifting Station Alpha, in the Arctic Ocean, were marine geophysics studies directed by the Lamont Geological Observatory of Columbia University and supported by the Terrestrial Sciences Branch of the Air Force Cambridge Research Center. The studies included seismology, gravimetry, earth magnetism, physical oceanography, and measurement of ice drift and currents.

A class of binary systematic codes correcting errors at random and in bursts

Presentation of results concerning the performance of a family of binary systematic codes of arbitrary size, correcting bursts of considerable length and/or "random" errors. The basic idea of these codes is due to C. Hobbs of the Air Force Cambridge Research Center. For the codes of two sub-families, practical decoding schemes are given. Also formulated are results concerning the use of these codes with erasure channels.

Observations of the Russian satellites and the structure of the outer terrestrial atmosphere

The launching of the artificial earth satellites gave the opportunity to gain some direct information about the outer region of the earth's atmosphere. Our radio observations were mostly made on 20 MHz with a new direction-finder developed by the firm Telefunken in Ulm. This instrument uses three pairs of adcock-antennas. The direction of the wave front and the amplitude of the received signals can be measured at the front of a television tube. A movie-camera registers the pictures with a time resolution of 0.1 sec. The accuracy of the measured azimuths is about 0.5°. For 1957 α 1, 1957 β and 1958 δ 1 optical observations of the German Moonwatch-groups were used. Further orbit data were obtained from the Moonwatch Headquarters, Cambridge, Mass., the Air Force Cambridge Research Center, Bedford, Mass., and the Vanguard Computing Center, Washington.

Supplementing the Formoder with Fixed Vocoder-Like Bands

The Formoder is a speech compression system using parametric signals. The most important parameters are those used to control the average pitch frequency; the central frequencies and intensities of (1) two damped oscillations for nonturbulent sounds tunable in the first (F1) and second (F2) formant region, and (2) two noise spectra for turbulent sounds, one tunable in the second formant region (C2), and the other in the higher frequency region (C3) from 2500 to 6000 cps. Assuming time sharing of channels for parameters of (1) and (2) there are five parametric channels. To improve the performance of the Formoder a scheme is proposed in which the original Formoder parameters describing the average pitch, F1, F2, and C2 are retained while vocoderlike fixed bands (one parameter per band} are used in the upper frequency range 2500–6000 cps. Four such bands are used for turbulent sounds to replace C3 and two bands are added for nonturbulent sounds with central frequencies set at 2500 and 3500 cps. The total number of parametric channels is thus increased from five to seven. Preliminary experiments show some promise and the detailed results will be reported. [This research is sponsored by the Air Force Cambridge Research Center under Contract No. AF19 (604)-3465.]

Mechanisms of Frequency Response Extension

There is considerable evidence that subjects in a traditional psychophysical experiment act as narrow-band receivers tuned to the frequency of a known sine-wave stimulus. Obviously wave forms in real life are complex rather than simple, and the wave forms we hear can seldom be predicted exactly. A series of experiments was conducted attempting to arrive at a model for hearing when the sine-wave signal to be presented is not absolutely predictable, but might be one of two alternative frequencies. For each experimental run of 100 trials, one of two possible tones was randomly selected for presentation on each trial in a two-alternative forced-choice detection situation: one of the tones was always 1000 cy and the other had a frequency difference of 20, 100, 200, or 500 cy above or below, giving eight pairs of tones investigated. The intensities of the tones were equated for detectability in a standard single tone preliminary detection experiment. All eight pairs were run at two different levels of background noise using different signal intensities. Under these conditions differential predictions of observers' behavior with an uncertain signal can be made within the framework of the theory of signal detectability for a number of alternative models calculated to account for the extension of frequency sensitivity. The data are compared to predictions from a scanning model, a multiplex model, a threshold model, and a variable band model. (This research was carried out under sponsorship of the Operational Applications Laboratory, Air Force Cambridge Research Center and Evans Signal Laboratory, Signal Corps Engineering Laboratories, Fort Monmouth, New Jersey.)

A geophysical determination of the thermal electron attachment coefficient of oxygen molecules.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A geophysical determination of the thermal electron attachment coefficient of oxygen molecules. Sen, Hari K. ; Dubs, Charles W. Abstract The coefficient of attachment, p, of thermal electrons to oxygen molecules in the upper part of the troposphere has been calculated using the data from a nuclear burst at an altitude between 10,000 and 50,000 ft. Total initial gamma radiation doses were measured at a number of points (i) in the vicinity of the burst and the attenuation of a telemetering signal from each of these points to a ground point was measured (Haskel et a1.). The doses and a fraction of dose rate at a certain short time after burst lead to an inverse- square and exponential-attenuation formula for the electron production rate. The electron density at this time is essentially the production rate divided by the product of p and the oxygen number density; assuming a value of p, it is calculated at points along the telemetering ray path. The electron density, the electron collision frequency, and the ray frequency of nearly 225 Mc give the index of attenuation at the points. The index is numerically integrated over the ray path to give the attenuation. The value of p is chosen to make the calculated attenuations (inversely proportional to p) agree as nearly as possible with the measured attenuations. Preliminary corrections taking into account the pressure dependence of p (2 per cent change in ~), photodetachment (5 to 15 per cent increase in 6), and absorption due to negative ions (in- crease in 6 by a factor of 1.2 to 10) lead to the calculated values of 6 in the following table: Caic. 3 Exp. a i Caic. 3 Exp. a 4 2.25 5.3 10 .552 .579 5 1.83 1.85 II .424 .367 6 1.35 3.74 13 .181 .126 7 1.23 1.51 14 .114 .0434 8 .964 3.19 15 .0752 .0438 9 .713 .821 and to a value of K, the ratio of p divided by the oxygen number density, of K = 7.2 X I0-~~ cm6 sec~'. This value of K is about three times that recently measured at room temperature by Chanin and Biondi (1958). It is interesting to note that the observed decrease in the echo rate of long-enduring echoes from Perseid and Arietid meteors, height approximately 8o km, leads to a value of K agreeing with ours within a factor of 2 (Kaiser 1953). REFERENCES Chanin and Biondi, 1958, Air Force Cambridge Research Conference, Nov. 20-23. Haskel et at., AFSWP, WT-IIoI, Appendix C (Confidential report). Kaiser, T. R. 1953, Advances in Physics II, 536. Geophysics Research Directorate, Air Force Cambridge Research Center, Cambridge, Mass. Publication: The Astronomical Journal Pub Date: 1959 DOI: 10.1086/107983 Bibcode: 1959AJ.....64Q.131S full text sources ADS |

Some Experiments on Frequency Recognition

Four frequencies in two configurations were presented separately to four observers in a random order. In one configuration the signals were separated by steps of 5 cy. In the other there were two pairs of frequencies; the members of each pair were separated by five cycles, but the pairs were separated by 500 cy. In each case the observers' task was to state which one of the four possible tones had been presented on any one trial. Frequency recognition error rates for the two configurations were nearly the same, although the patterns of errors were quite different. In the first configuration, there were frequent confusions between the two middle frequencies. In the second, there were few confusions between pairs but more confusions within the pairs. The experiment was repeated with ten cycle separations. Again there were two groups, four closely grouped frequencies, and two pairs of frequencies 10 cy apart with 500 cy separation between pairs. Again the percentages of errors were nearly the same, while the patterns were different. The results are considered in terms of a scanning model, a multiplex model, a threshold model, and variable band model. (This work was carried out under sponsorship of the Operational Applications Laboratory, Air Force Cambridge Research Center, and Evans Signal Laboratory, Signal Corps Engineering Laboratories, Fort Monmouth, New Jersey.

Far ultraviolet spectrum of the Sun.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far ultraviolet spectrum of the Sun. Violett, T. ; Rense, W. A. Abstract Solar ultraviolet spectrograms were obtained from Aerobee-Hi rocket flights on 4 June, 1958 and 30 March, 1959. In each case the instrument was a grazing-incidence grating spectrograph whose speed was increased by a suitably designed toroidal mirror placed in front of the slit at grazing incidence. The instruments were pointed at the sun by a biaxial pointing control. Z4nith heights attained by the rockets were 220 km and 204 km, respectively. About 150 emission lines in the range 84-I216A were found to appear on spectrograms from both flights. About 200 other possible lines were present. The wave lengths of the lines have been measured in most cases to within an accuracy of o.~A. Rough visual estimates of the relative intensities of the lines were made, along with a quantitative estimate of the intensity of the 3o4A Heii resonance line for several altitudes of the rockets. The Heii line was by far the most intense line other than H La, and possibly could be more intense than the latter outside the earth's atmosphere. Identification of about 6o lines was made. The neutral and ionized atoms, H, He, 0, C, N, and Si, dominate. The Ovi line at I5oA was present. A rather intense line at 84A possibly could be due to Neviii. The high intensity of the scattered light background prevented the detection of any continuum in this region. A program for the systematic identification of the remaining lines has been launched. The research reported in this paper has been sponsored by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command. Physics Department University of Colorado Boulder, Colo. Publication: The Astronomical Journal Pub Date: 1959 DOI: 10.1086/108041 Bibcode: 1959AJ.....64R.348V full text sources ADS |

Neutral hydrogen in 0B associations.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Neutral hydrogen in 0B associations. Dieter, Nannielou H. Abstract Analysis of the line profiles of the neutral hydrogen survey of the galactic plane published by Muller and Westerhout has shown many cases in which neutral hydrogen appears within OB associations. Intensity contour diagrams of regions including such associations have been constructed from the line profiles for different velocities. In Morgan's unpublished catalogue of OB associations 31 are listed which occur within the limits of the Leiden survey, and for 25 of these some measure of the radial velocity is available from optical observations. For 20 of these associations a well-defined maximum in the equal-intensity contour diagrams occurs at the velocity of the association and does not occur at other similar velocities. For the remaining six associations a maximum occurs at a particular velocity, but no identification of the gas with the association can be made without stellar radial velocity measurements. The distance of a hydrogen cloud may be estimated from the distance of the association and from its velocity and a model of galactic rotation. Comparison of the distances from the two methods shows many large discrepancies. The contour diagrams show that the maximum in the equal-intensity contours changes its longitude continuously in one direction as the velocity changes. In each of the twelve cases in which it is possible to follow the maximum through such a progression this direction is consistent with the effect of the shearing action of galactic rotation. Geophysics Research Directorate Air Force Cambridge Research Center Bedford, Mass. Publication: The Astronomical Journal Pub Date: 1959 DOI: 10.1086/107993 Bibcode: 1959AJ.....64Q.329D full text sources ADS |

Class of Binary Systematic Codes Correcting Errors Occurring at Random and in Bursts

Presentation of results concerning the performance of a family of binary systematic codes of arbitrary size, correcting bursts of considerable length and/or random errors. The basic idea of these codes is due to C. Hobbs of the Air Force Cambridge Research Center. For the codes of two sub-families, practical decoding schemes are given. Also formulated are results concerning the use of these codes with erasure channels.