Contains reports on five research projects

Coleman, P. D.

Goldman, Stanford

Guillemin, Ernst A.

Lally, P. M.

Maartmann-Moe, R.

Macnee, A. B.

Pearsall, C. S.

Rosebury, F.

Santelmann, W. F., Jr.

Scott, R. E.

Smullin, Louis D.

Steinberg, B. D.

Vivian, W. E.

Zingeser, P. K.

Contains reports on six research projects

Wallman, Henry

DSpace@MIT

IX. MISCELLANEOUS PROBLEMSA. ELECTRONIC DIFFERENTIAL ANALYZERThe present objectives of this project are (1) to improve existing anddevelop new computing elements for use in the electronic differentialanalyzer, and (2) to use the analyzer to solve differential equations ofinterest.1. Computing ElementsDuring the past three months, two integrators and one adder have beenadded to the operating differential analyzer. This permits the solution ofdifferential equations of orders through the sixth. The new units do notdiffer materially from those previously built and no particular difficultieshave been encountered in the solution of the higher-order equations.A considerable amount of time is being spent investigating the limita-tions of the crossed-fields multiplier (Quarterly Progress Report,January 15, 1948). The emphasis here is upon those factors which limit thedynamic range of the multiplier.A dual-purpose unit to be used for either multiplication or functiongeneration is being developed. A first model of this unit has been built,and it was used as a function generator in the solution of Equations (5) and(6) described below.A detailed study has been made of the 60-cps gate generator used withthe differential analyzer. The results of this study will permit the designof an improved gate generator.2. Differential EquationsThe equationd2 + al + a = K sin wt (1)dt ldt 0and the simultaneous equationsd2 y + a - + a y - k K sin wt (2)dt2 o dtandd 2 x+ b + boX- k = 0 (3)dt2 dt-75-(IX. MISCELLANEOUS PROBLEMS)have been solved to illustrate the use of the electronic differential ana-lyzer as a teaching tool. Solutions of Equation (1) and Equations (2) and(3) give the response of single-and double-(or stagger-) tuned circuits toa sinusoidal pulse. It is particularly easy with the analyzer to investi-gate the response of these circuits for pulse frequencies other than thebandcenter frequency.Three other equations which have been solved during the past quarterare2dt+ 008(m y y = 0, (4)2 dt 0dt+ k (L)3 + W Y = 0, (5)dtanddG -at -K e sin 0 = C. (6)Equation (6) was derived by Mr. E.E.David in connection with the studyof the starting phenomena of a microwave magnetron. Its sol.kfion on the ana-lyzer required the simultaneous use of a multiplier and a function generator.Figure IX-1 is a triple-exposure photograph of three typical solutions ofthis equation observed on the differential analyzer.A report on the electronic differential analyzer is being written.Prof. H.Wallman, Dr. A.B.Macnee, R.Maartmann-Moe,#~1/2O"vFig. IX-1. Triple-exposure photo-graph of three solutions of equationde/dt - Ke tsin = Cfor 80 = 0, C = .4306 and K/a = 2.5,6.3 and 12.5.-76-I I I0 3/a 6/at(IX. MISCELLANEOUS PROBLEMS)B. AN AUTOMATIC IMPEDANCE-FUNCTION ANALYZERDuring the past three months, work has continued on the construction ofa device for solving experimentally the approximation problem in filterdesign. As described in previous progress reports, the device consists ofa conducting plane of Teledeltos paper into which currents are introducedto represent poles and zeros of an impedance function. The voltage alongthe imaginary axis in the plane is proportional to the logarithm of themagnitude of the impedance function. It iS sampled by a set of probes alongthe axis and disyayed on the face of a cathode-ray tube. The device maybe used to find a set of poles and zeros which will give a desired form tothe impedance function.Progress has been made recently in the following three directions:(a) An analysis of the errors in the method;(b) The construction of a "double" commutator;(c) Partial construction of the Mk. 4 machine.1. Analysis of the Errors in the MethodA theoretical analysis has been carried out to determine the extent~ ofthe errors caused by a finite size of plane. It has been found that theplane must extend about four decades beyond the region in which the polesand zeros are lc ed if the errors are to be less than one per cent in theworst possible case. This size is not feasible in the ordinary Z plane,but it can be achieved fairly easily in the logarithmic strip which isobtained from the original plane by the transformationW = loge Z.The general nature and some of the inherent advantages of this trans-formation have been discussed in a previous progress report.2. Commutator ConstructionThe original mechanical commutator was capable of switching 100 linesat a repetition rate of 20 cycles per second. This device has been modifiedin two ways. The speed has been doubled in order to facilitate the displayon the cathode-ray tube. In addition, a second set of contacts has beenadded. These modifications will make it possible to obtain the phase aswell as the logarithm of the magnitude of the impedance function (see below).-77-(IX. MISCELLANEOUS PROBLEMS)3. Construction of the Mk. 4 MachineConstruction of the Mk. 4 machine is proceeding at the present time.The logarithmic strip of Teledeltos paper will be 16.7 inches wide and about50 inches long. This is the equivalent of 8 decades in the impedance plane.Two rows of 300 probes, spaced 0.1 inch apart, are being constructed to pickup the voltage along the imaginary axis. The sum of voltages from succes-sive pairs of probes in the two rows is proportional to the logarithm ofthe magnitude of the impedance function, and the difference of the voltageson successive pairs of probes is proportional to the rate of change ofphase. The actual phase will be obtained by integration.Since the actual commutator has only two sets of 100 contacts, it willbe necessary to use switches to view the whole range of the probes along theaxis. Prof. E.A.Guillemin, R.E.ScottC. PROTON-VELOCITY METERThe signal generator and phase-measuring equipment are completed. Workhas been discontinued until the Van de Graaff generator is installed.L.D.Smullin, P.LallyD. ELECTRONIC-POTENTIAL MAPPINGSince the last Progress Report, a considerable number of moving pic-tures have been taken of the heart patterns of subjects. A program willshortly be set up to get a catalogue of patterns of typical normal and ab-normal patterns as a first step in using the area display as an aid in thediagnosis of heart disease.Skull patterns of many different subjects have been observed and motionpictures of six of them have been recorded. This has been done without theaid of the tuning units mentioned in the previous progress report, sinceonly four of these units have so far been completed. The observed displayswere thus the instantaneous patterns. Direct observation showed interestingand characteristic individual patterns and movements, including a good dealof activity which was probably due to muscular movements in the presumablyrelaxed head. Probably the most interesting part of the activity, however,was the apparent presence of scanning or, at least, traveling waves. Motionpictures of the skull activity when projected in slow motion by a factor of4 to 1 (64 frames per second projected at a rate of 16 frames per second)-78-- -- ~ ICLI^1C-~. -I -----LI^LLIP- -- ~~LL-P l- ~ IIIIIYIYIYI~ YI/ LPI-)CI Y -~*-IIE I~*(IX. MISCELLANEOUS PROBLEMS)accentuated and clarified this traveling-wave activity. The principal fre-quency was around ten per second and it thus appears that these travelingwaves may be identified with the alpha rhythm observed in electro-encepha-lograms. This view is strengthened by the fact that the envelope of inten-sity of the traveling waves rises and falls at about the rate observed forthe alpha rhythm. Although detailed observations of these waves are madedifficult by artifacts, it appears that they arise in the occipital area.These waves will, of course, be studied in more detail as soon as possible.A much slower type of phenomenon was also of interest in the directobservation of one subject. This phenomenon was almost certainly of muscu-lar origin. It showed a very slowly traveling electrical activity acrossthe skull, which was originated by the subject speaking a few words. Theactivity, however, did not commence until several seconds after the speechwas finished. About twenty minutes later, when the subject was more relaxed,the subject was asked to speak the same words, but the slow travelingactivity could no longer be observed, although it had been observed everytime in many previous trials at the beginning of the test when the subjectwas more tense. It was tentatively concluded that the originally observedpattern was due to the unnecessary involvement of distant head muscles bythe subject's speaking when he was not thoroughly relaxed. This subject wasperfectly normal.The foregoing observations suggest that the area display may be usefulin studies of fatigues and in studies of spastic diseases.Dr. S.Goldman, W.F.Santelmann,Jr., W.E.VivianE. TUBE LABORATORY1. Resistance Thermometer for Temperature ControlA simple device is described for controlling high-temperature ovens andfurnaces. Use is made of a resistance-thermometer element consistingessentially of a platinum wire wound on a ceramic form. This is connectedinto a conventional a-c bridge circuit. (Fig.IX-2) which comprises a singlesmall thyratron tube, a relay and a means to set the temperature desired.The resistance-thermometer element is constructed as shown in Fig.IX-3.Small-size platinum wire (.004-inch) is wound on a fluted steatite form,one end of which is cemented into a nickel or stainless steel tube of appro-priate length. This element has been operated satisfactorily at tempera-tures slightly higher than 10000C. Connection is made by means of an-79-(IX. MISCELLANEOUS PROBLEMS)CERAMIC "INSALUTE"INSULATORS CEMENTA-C PLUG CEMENT STAINLESS STEELTUBEFig. IX-2. Resistance thermometer.FORM (SEE ABOVE)STANCEMETERITu115 V 0-A-C RELAY 0-0UUIAI I I)0 I ULOAD CIRCUITFig. IX-3. Circuit for resistance thermometer.-80-LI _ila -~IW-LIIII.-. --^ _.__ I~-I_-~P-YI~ -~-LI I~-L----~-- ---------(IX. MISCELLANEOUS PROBLEMS)ordinary a-c plug which is cemented to the other end of the metal tube. Theleads are nickel wires spot-welded to the platinum wire and brought throughtwo-hole ceramic sleeves. A cable with a female a-c plug connects the ther-mometer to the circuit. F.RoseburyF. TUBE LABORATORY - (Chemical Section)1. Aluminum Bonds to Glass, Quartz and SteatiteThe preparation of sprayed aluminum-to-glass bonds, although not a newtechnique, has not been widely used. William Hope of Philco (Philadelphia)has done some work in the sprayed aluminum-glass bond.The procedure consists of heating the glass to several hundred degreesand spraying on aluminum with a commercial metal spray gun while the glassis hot. The heating of the glass is essential to securing a good bond.Metal sprayed on a cold surface may be easily scraped off, but a sprayedcoating prepared in the manner outlined produces a tenacious bond. We haveused the same technique in preparing aluminum coatings on both quartz andsteatite.The aluminum surface may be sprayed with copper for soft soldering orit may be plated for purposes of soldering. We have also successfullysoldered the aluminum surfaces directly by means of commercial aluminumsolders. This technique produces excellent seals for vacuum work.C.S.Pearsall-81-

Miscellaneous Problems

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Miscellaneous Problems

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