Contains reports on four research projects

Goldman, Stanford

Guillemin, Ernst A.

Maartmann-Moe, R.

Macnee, A. B.

Santelmann, W. F., Jr.

Scott, R. E.

Vivian, W. E.

Wallman, Henry

Wyckoff, H. W.

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X. MISCELLANEOUS PROBLEMSA. ELECTRONIC DIFFERENTIAL ANALYZERProf. Henry WallmanDr. A. B. MacneeR. Maartmann-MoeEngineering of the computing elements of the electronic differentialanalyzer is continuing. The differential analyzer and the more recentlydeveloped Fourier Transformer have been used in the solution of variousproblems. The analyzer has also been used to evaluate solutions ofSchl6milch's Integral Equation.1. Computing ElementsThe entire differential analyzer exclusive of the output oscilloscopehas been mounted in two standard relay racks. The units are so interconnectedthat the analyzer can be turned on or off by throwing two switches.2. Differential EquationsMr. L. Biedenharn has used the analyzer to investigate solutions of thesimultaneous equations+ fu = - , (1)dtd-- + (f - -) w =- AT (2)dt twhere f and N are constants.3. Integral EquationsThe Fourier Transformer has been used by Mr. E. Callahan and Mr. N. H.Knudtzon during the past quarter. Mr. Callahan used the analyzer to obtainFourier series expansions of a number of periodic functions. Bot. Mr.Knudtzon and Mr. Callahan used the analyzer to obtain cosine transforms ofexperimentally measured auto-correlation functions.During the past quarter Mr. A. Soltes of the Cambridge Field Stationand Mr. J. Turtora of the Camp Evans Signal Corps Laboratory visited thisgroup for a two-week period. During his visit Mr. Soltes used the analyzercomputing elements to solve Schlomilch's Integral Equationr/2f(x) = F(x sin ) dO . (3)0This equation relates the dynamic and static characteristics of a detector_ _~1111^~_ ~_ _I _ _11_ III^ ~l _1_I___I___I____YIlll L llllllsll~(X. MISCELLANEOUS PROBLEMS)for sinusoidal inputs. It has the solution (1)F(x) = f(0) + x f'(x sin P) d (4)which has been evaluated with the electronic differential analyzer computingelements. A typical dynamic characteristic f(x) and the static characteris-tic solution F(x) are given in Figure X-1.f(x)0F(x)I0-L-I I I - I I0 ab x 0 a xFig. X-1 Observed solution of Schlbmilch's Integral Equation.B. AN AUTOMATIC IMPEDANCE-FUNCTION ANALYZERProf. E. A. GuilleminR. E. ScottThe fundamental laws of linear passive networks are well known. Themechanical difficulties of applying them to a given problem, however, maybe enormous. The primary purpose of the automatic impedance-function ana-lyzer is to reduce this labour. In many cases, however, the machine goesbeyond this and provides the possibility of a new philosophy of networkdesign, with the approximation problem as its core.The central importance of the approximation problem in network theoryhas only lately been recognized. Dr. Guillemin has shown, for example, thatany impedance characteristic may be represented by an RC network, providingthat the approximation problem is solved in a certain fashion. The machinewhich is described here provides a logical extension of this philosophy toother types of networks. For example, the machine makes it possible todesign a given impedance using coils of a specified "Q".-75-f(x)0(X. MISCELLANEOUS PROBLEMS)1. Construction of the Mark 4 MachineThe Mark 4 machine has been completed with the exception of a possibleintegrator for the phase function. The machine consists of four basic com-ponents:a. A conducting sheet of Teledeltos paper.b. Probes which introduce currents into the paper.c. Probes which measure voltages in the paper.d. A commutator which displays these voltages onthe face of a cathode ray tube.The sheet of Teledeltos conducting paper is 53 inches by 15.8 inches.It rests upon a layer of cork and is held at each end by clamps. This sheetis an analogue for the logarithmic frequency plane which is formed by ap-plying the transformation W = Loge Z to the usual complex frequency plane.The advantages of this transformation are that it removes any difficultieswith the finite size of the analogue, and that it allows a direct utilizationof a great deal of the standard gain-phase network theory (also called log-dbtheory). For convenience in using the device a graph of the original fre-quency variable has been printed upon the logarithmic plane.There are 72 probes to introduce currents into the plane. They areconstructed of steel needles embedded in a polystyrene holder and held inplace by nickel sleeves which are spot welded to the steel. They representthe poles and zeros of the impedance function. Four distinct types arenecessary: positive and negative currents for poles and zeros, and half-value positive and negative currents for the poles and zeros on the realaxis. This distinction is made necessary because only the upper half-planeis used in the analogy.The voltage probes are permanently fixed along the center of the plane,along the imaginary axis. They are in two rows of 300 probes covering threedecades of the frequency domain. Physically they consist of phonographneedles pressed through a bakelite mount, and soft-soldered at the butt endto bare copper lead-off wires. They are spaced 1/10 inch apart each way.The logarithm of the magnitude of the impedance function is obtained by takingthe sum of the voltages on the two separate rows of probes. The phase isobtained by integrating the difference of the voltages on the two separaterows. As an alternative the paper may be shifted and either row may be usedseparately for the magnitude function.The commutator is a mechanical one consisting of two separate sets of100 brass contacts. They are flush-mounted in bakelite and the rotatingmembers which contact them are silvered springs. To prevent the rotating-76--I "YP-^" ~"-~"^1LI-L"I L~1-L -- ~.11II .~LIIL~IC~--) .~--^--^-.1   II~_I*~ Ylldl~_Y---^.LI~ I^~ Plll/r --~C lili~---111/1)I~------U1--Y- ~ - L~C- i-ii~L l-_C~i~.*~lI_ P~IL -.-~-- I~L Y(X. MISCELLANEOUS PROBLEMS)contacts from wearing the bakelite and becoming dirty it has been foundnecessary to lubricate them with vaseline. The commutator will operatesatisfactorily for periods of 4 to 8 hours at a speed of 1200 rpm. Then itmust be cleaned and regreased with vaseline.2. Method of UseThe machine has just been completed and exhaustive tests have not yetbeen made. However, some idea of its usefulness may be obtained from thefollowing. It was desired to explore the possibility of approximating aseries resonant circuit by means of low "Q" elements. The circuit is shownin Figure X-2.L= 1.25 C=.8Z = s1 +.8 s +1El Z1 D R= E2 SYII .8 s +2(.4)s+I= Y, HEREFig X-2 Diagram of circuit for producing resonantbehavior with low "Q" elements.LUI I giIOdb7ACTUAL CURVE10 100LOG(FREQ)+6db/OCT I -6db/OCTFig. X-3 The logarithm of the magnitude of theimpedance, Y1 1 , sketched against the frequency.Using the machine this characteristic was matched with poles and zeroson the real axis. The function obtained was (neglecting the constant multi-plier)Y(s) = s(s + 5)(s + .2(s + 1)This is not positive real and cannot be realized as a driving pointadmittance. However, it can be realized as a transfer admittance by standardmethods.The scope of the machine will be investigated more fully in the nearfuture. In particular, attention will be given to the following three prob-lems:-77-(X. MISCELLANEOUS PROBLEMS)a. The design of networks to use elements ofa particular type.b. The design of networks to have a particularform, e.g., ladder networks, double-tunedcircuits, etc.c. The related transient response for variousnetworks giving the same magnitude for theirtransfer impedances.The transient response could be obtained in several ways. If a some-what faster commutator were available it could be integrated directly fromthe steady state phase and amplitude responses on Dr. Macnee's Fourier Trans-form Machine. Alternatively it can be inferred from the position of thepoles and the residues at the poles. The residues can be obtained experi-mentally by removing the pole and measuring the voltage at the same point.C. ELECTRONIC-POTENTIAL MAPPINGDr. S. GoldmanW. F. Santelmann, Jr.W. E. VivianThis is the final report on the project. R.L.E. Technical ReportNo. 121, "Electronic Mapping of the Electrical Activity of the Heart andBrain", will give a detailed story of the history of the project, the tech-niques developed and the results obtained. A summary of the results isgiven here.In this project an attempt has been made to supplement and extend thetechniques of electrocardiography and electroencephalography by introducingarea displays. In these area displays, the two dimensional distribution ofelectrical potential across the surface of the chest or the skull is shownon the screen of a cathode-ray tube. The change in light intensity on the sur-face of the screen is proportional to the instantaneous potential at the corre-sponding point on the body. Then by watching the screen of the cathode-raytube, or motion pictures of it shown in slow motion, one can follow the elec-trical activity on the surface of the chest or the skull, which in turn givesimportant information about the electrical activity of the heart and brain.In this project it has been standard practice to use 16 pickup elec-trodes (2). In the case of the chest for example, these are distributed asshown in Figure X-4. In order to display these potentials on the screen ofa cathode-ray tube it is necessary to send them through a commutating, syn-chronizing, and scanning system. A block diagram of the system finallydeveloped is shown in Figure X-5.-78-i _ __IIIII___IIPLI___I__ I~-C ~UI~- L- ll~--- -_I._~.- illllLI*L~-IIY-~- IllIr -~  1. IIIIXIII(L.----tll~~lll-LI ~-_- -~^ ~_IIL-~~ .l^l -..l IIY^ --- --- ~ I1^--.I^ (1^I1I-^l- C- 1(X. MISCELLANEOUS PROBLEMS)Fig. X-4 Location of pick-up elec-trodes on the chest.As a result of pictures of the electrical activity of normal and abnor-mal hearts taken with this equipment it appears that this apparatus is apowerful tool for the study of the physiology of the normal heart and forFig. X-5 Block diagram of theelectronic circuit commutator system.PICK-UP ELECTRODES-79-(X. MISCELLANEOUS PROBLEMS)diagnosis of disease in the abnormal heart. A report of the findings in aseries of patients with abnormal hearts will be published in the AmericanHeart Journal.In the case of the brain, pictures taken with this equipment have shownfor the first time that the alpha rhythm of electroencephalography consistsof traveling waves in the individual lobes of the brain (3). It is expectedthat this apparatus will be useful both in studies of the physiology of thenormal brain and in the differential diagnosis and localization of pathologi-cal conditions of the brain.Starting July 1i, 1949, Dr. S.Goldman will continue the development andapplication of this apparatus at Syracuse University.D. HYDROGEN ARC ULTRA-VIOLET SOURCEH. W. WyckoffFor such purposes as monochromator illumination and ultra-violet micros-copy, a high-intensity, long-life, small-volume, wide-angle source of theultra-violet continuum, 2000-3500 A, with no spectral lines is much needed.In 1941, A. J. Allen (4) reported a low-voltage arc in hydrogen, at 6 mm Hgwith a ten-ampere capacity running at about 60 volts d-c, which far surpassesany tube which is yet commercially available. We have tried to duplicatehis reported performance and improve on it.In his tube, the arc passes from an oxide-coated nickel screen cathodethrough a 1/8-inch diameter hole in the wall of a copper cylinder surroundingit and strikes the anode. We use these same principles. Our modificationomits the inner cylinder, and includes a central baffle, an insulated cathode,a wider angle of view, a larger cathode placed at least 1/2-inch from theconstriction, higher-melting-point metals, and a side port for observation.This design is shown in Figure X-6.No lifetime was mentioned in Allen's paper, but in a recent personalcommunication he indicated that 100 to 200 hours was not unreasonable. Anerror, or rather an unexplained diagrammatic representation in the paper,led us to build our first tubes in such a way that they had lifetimes ofonly about 25 hours. The cathode should be rotated 90* on its long axisfrom the way it is drawn in Allen's paper. One tube closely approximatinghis design ran 500 hours at 10 amperes before an accident terminated therun. At this time, the light output was down and the voltage at 10 ampereswas up to 110, due to separate causes.The diameter of the constriction has generally been kept at 1/8 inch.In arbitrary units, the output of the 500-hour tube was initially 0.8, on-80-(X. MISCELLANEOUS PROBLEMS)ACCESSORY PORTFig. X-6 Hydrogen arc ultra-violet source.-81-ARC IS \ALONG ]AXIS~C~ ~--L ~CeL~B~a=r(X. MISCELLANEOUS PROBLEMS)axis. The highest on-axis intensity at the same ten-ampere current was 1.63,obtained in a tube with a 1/2 inch long x 1/8 inch diameter constriction.At 20 amperes, the output of the latter was increased to 2.3. Output isapproximately proportional to the square root of the current. A quarter-inch-long constriction gave intensities only 20 per cent less than the half-inchone, but the output dropped off sharply when the length was further decreased.A tube with a constriction of rectangular cross-section 1/8 inch x 1/4 inchand 7/8 inch along the are axis had an on-axis output about the same as the1/2 inch tubular constriction. Pressure was not found to be very importantso far as output was concerned.Roughly comparable measurements on the Hanovia small-angle, high-voltagehydrogen are gave on-axis intensities of 0.9 at its maximum current and whennew. From the geometry of the Hanovia tube, it is obvious that at 1 1/20off-axis, less than half of the source is visible. Measurements on tubes,such as that diagrammed, indicated a constant intensity up to 70 off theaxis. Thus the total light flux is at least 2300 per cent greater than thatof the Hanovia lamp.The are behaves and appears like a normal arc with a hot cathode butwith insufficient thermal emission to carry the whole current. The constric-tion, with respect to current-voltage characteristics, behaves qualitativelylike a Langmuir cold probe.Many types of cathode have been tried, including coiled-coil oxide-filled tungsten, pure tungsten, indirectly heated oxide-coated-nickel cylin-ders, and sintered thoria-tungsten directly heated.Starting techniques employed include "floating" the constriction, addingan insulated tickler ring, and the use of chokes or booster transformers inthe d-c line. The life of the long-constriction-tubes (as determined byability to strike an are at about 100 volts) was always short, despite anyof the above-mentioned starting tricks.Further work will proceed in the direction of establishing an optimumpractical source, and will be carried on in the Biology Department at M.I.T.References(1) E. T. Whittaker and G. N. Watson, "A Course of Modern Analysis", Cambridge UniversityPress (England, 1945) pp. 229-230.(2) S. Goldman, W. E. Vivian, C. K. Chien and H. N. Bowes, Science, 108, 2817(Dec. 24, 1948) p. 720-723.(3) S. Goldman, W. F. Santelmann, Jr., W. E. Vivian and D. Goldman, Science, 109, 2838(May 20, 1949) p. 524.(4) A. J. Allen, J. Opt. Soc. Am. 31, (March, 1941) pp. 268-370.-82-( _~_ 1_~1_~ ~_^~I_ I ~LII - I- ~-~Ca -* I-L-~C---- .. i... -._-.--~I *..ll_--^( -X -II--. IX~illlll IXILII -C~__

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