A. James Clark School of Engineering
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- ItemCreep Rupture Properties of Tin Tested at Constant Stress(1954) Breen, John E.; Huff, Wilbert J.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)This investigation was initiated to study the creep characteristics of a simple, relatively pure, material at constant stress as compared to that tested at constant load. Tin was selected for the investigation. A series of creep tests were run to rupture at constant stress and constant load. The test variables were adjusted in these tests so that time to rupture varied from approximately 300 minutes to 33500 minutes (5 hours to 558 hours) at room temperature, and from 40 minutes to 2500 (0.67 hours to 41.7 hours) at 200 degrees F.
- ItemThe Application of the Gyrator Concept to Transistors(1956) Breeskin, Sol Daniel; Corcoran, George F.; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
- ItemSunspots, and the Solar Influence Upon High Frequency Radio Communications(1960) Jacobs, George; Reed, Henry R.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
- ItemStudy of a UHF Command Destruct Missile Antenna System(1960) Mullins, Elwood Hatcher; Schuchard, E.A.; Electrical and Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
- ItemBoiling Heat Transfer to Liquid Nitrogen and to Liquid Helium(1960) Mann, Horace Tharp; Shreeve, C.A. Jr; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Experimental data on free convection and nucleate boiling was taken in liquid nitrogen and liquid helium using platinum wires as heating elements. The results in liquid helium and particularly in liquid nitrogen were found not to agree with the generally accepted results in other liquids. In particular it was found that the transition from free convection to nucleate boiling would not take place until the temperature of the wire was much greater than that found for nucleate boiling. An "extended region" thus must be added to the free convection curve. This extended region did not reoccur in the reverse transition from nucleate boiling to free convection. It is usual to represent nucleate boiling heat transfer data to liquids as an equation of the form g/a = CΔT^n where g/ a is the rate of heat transferred per unit area, ΔT is the excess temperature of the heating surface and C and n are independent constants. There is universal agreement that 2.5 ≤ n ≤ 4 for all liquids. However, it is found for liquid nitrogen that n is not in this region but is about 11. It is then shown that C is a function of n and the equation in liquid nitrogen reduces to one with a single arbitrary constant of the form. g/a = exp^(10.25 - 2.45n) ΔT^n 5 ≤ n ≤ ∞ This equation represents a family of curves which intersect at the maximum observed value of g/a for . 0,008 inch wires. The existing mechanisms used to explain the high heat, transfer rates in nucleate boiling are reviewed and shown to be quantitatively invalid in liquid nitrogen. A "hot" molecule hypothesis is proposed, wherein a single hot molecule is assumed to supply all of the energy requirements for the growth of a bubble. It is shown that this hypothesis is invalid in itself but the calculations lead to an alternative hypothesis. This alternative hypothesis proposes that the excess energy stored in the bubble boundary acts as an energy sorting mechanism which must be present to keep a growing bubble from violating the laws of' thermodynamics. Experimental data is presented tor nucleate boiling from platinum wires in liquid helium. This data is also unusual but is more or less consistent with the results obtained in liquid nitrogen. An extended region is not, however, observed in liquid helium.
- ItemGamma Ray Spectra and Shielding Survey of the University of Maryland Reactor(1963) Nhiep, Nguyen; Duffey, Dick; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The gamma ray spectra of the University of Maryland reactor were measured at the beam tube which extends from the side of the reactor to the core, the thermal column and the top of the reactor. There were three gamma ray spectra measurements at the beam tube : gamma ray spectra recorded by a single-channel spectrometer when the reactor was shut down and when the reactor was operated at different power levels and the gamma ray spectra recorded by a 256-channel spectrometer when the reactor was at different levels of power. However, only the single channel spectrometer was used to measure gamma ray spectra at the thermal column and the top of the reactor; some gamma ray spectra were recorded at the thermal column when the reactor was operated at various power levels and a gamma ray spectrum was recorded at the top of the reactor when the reactor was operated at full licensed power of 10 kw. The gamma ray shielding survey of the reactor was done by a Geiger-Muller survey meter when the reactor was running at full power of 10 kw. The highest level found was about 0.8 millirem per hour which was at the side of the reactor at core level. A calculated gamma ray level was near this value.
- ItemCerenkov Light Production in a Water Moderated Nuclear Reactor(1963) Madey, Robert William; Duffey, Dick; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)An experimental investigation of the production of Cerenkov radiation in a water moderated nuclear reactor is conducted using a photomultiplier as a light sensor. The variations in light intensity are studied during various phases of reactor operation, namely: startup, steady state and shutdown. The relevant theory is presented as an aid in interpreting and extrapolating the experimental results. It is found that for transients such as startup, the light signal is directly related to reactor power for periods (e - folding time) faster than about 20 seconds. Additional transient data acquired from measurements performed on a TRIGA pulsed-type reactor illustrate the excellent agreement between the Cerenkov detector and a conventional ionization chamber for measuring pulse characteristics such as peak power, pulse half-width, and prompt period. The proportionality between reactor power and Cerenkov signal is no longer valid for whole core measurements made at steady state power level because of the gradual increase of the Cerenkov signal as a result mainly of fission product contributions. Selective scanning of the Cerenkov spectrum through the use of interference filters over the wavelength range 3500 Å to 5530 Å results in a lower buildup fraction. Indications are that measurements further into the short wavelength region may yield a light sensor, and hence a good power detector, independent of any fission product buildup. The decrease in the Cerenkov light intensity after shutdown is measured for reactor operating times from 20 minutes to 4 hours. Comparison of the empirical data with theoretical considerations results in good agreement for shutdown times ranging from 500 seconds to 10,000 seconds. Spectral measurements made through 17 feet of water with a Hilger quartz spectrograph show a spectral distribution ranging from 2500 Å to 6000 Å. A calculated spectral distribution is compared with the measured spectrum after correcting for water attenuation.
- ItemA Study of Combustion in Supersonic Streams(1964) Billig, Frederick Stucky; Shreeve, Charles A. Jr.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Supersonic combustion of reactive aluminum alkyl fuels has been experimentally demonstrated in two-dimensional ducted combustors and adjacent to a flat plate. Fuel was injected from the combustor walls through multiple orifices and ignited spontaneously. Stable supersonic heat release was maintained as evidenced by schlieren and direct motion pictures of the flow field and deduced from static and pitot pressure measurements in the combustion zone. The results of the ducted combustor tests were correlated with elementary one-dimensional and pseudo-one-dimensional theoretical models of the flow field. This agreement permitted a reason.able determination of combustion efficiency to be made. In the ducted combustor tests a favorable effect of preheating the fuel to approximately 250°F was noted and a simple empirical factor was found which satisfactorily correlated all of the data for the range of conditions tested. A theoretical model of constant pressure heat release on a flat plate in supersonic flow is postulated. Normal force coefficients and specific impulse values are tabulated for a variety of flight Mach numbers and altitudes. Additional refinements in this theoretical model were required to adequately describe the experimental results. In a test simulating Mach 5 flight at 66,000 feet altitude a side force specific impulse of 1350 seconds was measured at equivalence ratio of one. Combustion was only partially completed 12 inches downstream of fuel injection. Based on the theoretical mode l an additional 12 inches of combustor length and 36 inches of expansion length would be required to obtain the estimated theoretical impulse of 5760 sec. The interaction of a vaporizing liquid droplet with a supersonic stream is considered. Additional refinements were made in the existing theories on droplet trajectory to include the influences of a separated zone and the normal component of velocity of the external stream. Calculations of the trajectory and evaporation of the estimated mean droplet size based on the modified technique were in general agreement with the observed flame zone and deduced combustion efficiency.
- ItemPRESENTATION OF A NEW HIGH-FREQUENCY COMMUNICATION SYSTEM PERFORMANCE PREDICTION TECHNIQUE(1965) Gatts, Thomas Fiscus Jr.; Reed, Henry R.; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The prediction technique developed by the National Bureau of Standards has been used extensively by high-frequency communicators. An adaption of this technique is used to demonstrate the type of results obtained when applied to the Buffalo, N.Y. to Boston, Mass. (B/B) link for January and July 1965. A new prediction technique is presented which will allow the HF communicator to predict system performance between the maximum useable frequency (MUF) and the lowest useable frequency (LUF) and which is flexible enough to allow system parameter changes to be made and the effect on the overall system determined. The new technique is demonstrated by applying it to the B/B link for January and July 1965 and displaying the results in the form of relative gain contours, which show the effect on communication capability of reducing the LUF by increasing system gain and the increase in process gain that may be achieved for the purpose of raising the data rate or decreasing transmission error rate. Some of the many applications of the results of this new technique are presented. The results are used: (1) to facilitate the selection of necessary operating frequencies to provide communication throughout a 24-hour period, (2) to estimate the severity and length of occurrence of multipath, (3) to investigate possible frequency adaption, and (4) to investigate possible power adaption.
- ItemFast Neutron Flux in the University of Maryland Reactor(1965) Berman, Philip Gilbert; Duffey, Dick; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The fast neutron flux distribution in the experimental facilities of the University of Maryland Reactor (UMR) was studied by means of neutron activation threshold foils with the reactor at a power level of 10 kw. The foils used were sulfur, magnesium, and aluminum which detected neutrons of energies greater than 3.0 Mev, 6.3 Mev, and 8.1 Mev, respectively. The activities of the foils were measured by calibrated beta and gamma scintillation detection systems. A central row of fuel elements, the west beam port, and the through tube were studied using all three types of foils. The fast neutron flux above 3.0 Mev was measured in each element of the core. The maximum fast neutron flux above 3.0 Mev available in the central ''glory hole " was about 2x10^10 n/cm^2 -sec. The flux above 6.3 Mev and above 8.1 Mev was about 5.5x10^8 n/cm^2 -sec and about 4.5x10^8n/cm^2 -sec, respectively. Available in the west beam port was a maximum fast neutron flux above 3.0 Mev of about 2.6x10^9 n/cm^2 -sec adjacent to the core and of about 1.2x10^7 n/cm^2 -sec at the inner face of the beam port shield plug. The fast neutron flux above 3.0 Mev available in the center of the through tube was 1.7x10^9 n/cm^2 -sec. The minimum at both east and west ends, at the inner faces of the shield plugs, was about 7x10^5 n/cm^2 -sec.
- ItemThe Effect of Nuclear Reactor Radiation on the Electrical and Mechanical Properties of Epoxide Polymers(1965) Kincaid, Charles Vernon; Duffey, Dick; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The effect of nuclear reactor radiation on the volume resistivity, bulk compressibility, specific volume, and hardness of three epoxide polymers was studied. The polymers were thermally polymerized and then subjected to varying radiation doses in the enriched uranium, water moderated, heterogeneous nuclear reactor located at the University of Maryland. Changes in the volume resistivity as a function of temperature for the various radiation doses was then determined by the use of an electrometer to measure the potential drop across the specimen. The effect of radiation on the bulk compressibility was determined by means of a special compressibility tester over the pressure range one to 8,000 atmospheres and temperatures 25°C to 250°C. The specific volume and hardness were measured for each sample before and after irradiation using standard techniques. The temperature dependence of the electrical volume resistivity was initially increased by exposure to 2.5 Mrads. Further irradiation up to 25 Mrads caused severe degradation of the temperature dependence of the electrical resistivity for all epoxide polymers studied . The magnitude of the compressibility for the polymers was found to be relatively unaffected by irradiation up to 25 Mrads; however, determination of the pressure-induced glass transition yielded anomalous results. No significant change in the hardness of the polymers was noted after varying amounts of radiation. The specific volume of an aromatic cured epoxide was not affected to any extent , but the aliphatic cured polymer showed a decreased specific volume.
- ItemCorrelation Studies of Pressure Fluctuations on the Ground Beneath a Turbulent Boundary Layer(1965) Priestley, Joseph Tant; Faller, Alan J.; Department of Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Narrow-band pressure correlation measurements in the frequency range ,008 to 1 Hz(cps) were obtained from a cross spectral analysis between pairs of microphones placed on level ground beneath the wind stream. The measurements were made over a range of wind speeds from 2.1 to 7.2 meters per second and a range of hemispheric solar radiation conditions varying from 0 to 44 Langleys per hour. Plausibility arguments are presented which predict for the narrow-band longitudinal and lateral correlation coefficients: -0'~ Rw(£,0) = e cos(kg) and Rw(O~~) = e-S~ where~ and~ are the longitudinal and lateral separations, respectively, and 0', S, and k are determined by the experiment. Contrary to similarity considerations ct and k were found not to be strictly proportional, but rather 0' = 0.4lk 1 ' 28 , 0' and k being expressed in (meters)-1 , over a range 2 < (1/ot) < 500 meters. The relation between 2 .74 Q -1 ct and S was found to be: ~ = 1. 0' , 0' and ~ expressed in (meters) , over a range 3 < (1/~) < 500 meters. For an arbitrary angle with respect to wind direction evidence is presented which indicates that Rw(~,~) is very slightly larger than the product Rw(g,O)Rw(O,~). A small amount of data taken relating the convection velocity versus wavelength to anemometer readings indicates the possibility of predicting the wind profile from pressure fluctuations on the ground.
- ItemA Computer Study of Nuclear Characteristics of the University of Maryland Reactor(1967) Altomare, Philip M.; Duffey, Dick; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)An analytical study of the University of Maryland Reactor was performed using an IBM 7094 computer. The nuclear analysis codes employed in the study were GAM-I, for fast group cross-section evaluation, Tempest-II, for thermal cross-sections, WANDA, for one-dimensional neutron transport calculations and PDQ, for two-dimensional transport calculations. A computer program, XS-1, for the calculation of effective control rod cross-sections was written as part of this study. The method employed in the determination of fast energy broad group cross-sections for non-fuel regions from that normally used. The neutron leakage from the fuel was used as a source of neutrons in lieu of the fission spectrum. This method was felt to give a better estimate of the neutron flux distribution in energy. The analytical results compared favorably with experimental data. The predicted K- effective was 0.993 versus 1.006 actual. The thermal neutron flux calculated and measured at the center of fuel elements generally agreed within 10%. The calculated neutron flux above 3 Mev, which is more difficult to match, was found to be low by approximately 30%. Control rod worth was predicted to be 5.6% Δρ for the center shim rod and 2.7% Δρ for the outside shim rod. Measured values are reported as 3.6% Δρ and 2.0% Δρ respectively.
- ItemA Set of Karnaugh Map Manipulation Computer Routines for Use in Logic Design(1968) Shub, Charles Martin; Marcovitz, Alan B.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The Karnaugh map provides a convenient visual aid for the manipulation of switching functions for both the design engineer and the student of logic design. Algorithms for the minimization of switching functions by the manipulation of information displayed on a Karnaugh map are presented, along with a method of obtaining more information than was previously possible from the Karnaugh map. A dynamic, flexible, and easy to use collection of computer subroutines written in the MAD language to accomplish such manipulations as a subset of an entire logic design system of computer programs is described. A user's manual for the entire system is included, as well as descriptions of the programs used in conjunction with the map manipulation process. Several examples are included.
- ItemA Comparison of Some Analytical Models with Experiment for the University of Maryland Reactor(1968) Ross, Malcolm Fred Jr; Duffey, Dick; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)It is often desirable in the operation of a research reactor to make adjustments in the nuclear core configuration. These adjustments may occur for a variety of reasons, such as the rearrangement of fuel to perform a particular experiment. It is beneficial to the reactor operator and experimenter to have an adequate analytical model with which to predict the changes in nuclear characteristics which occur with core rearrangement. Several analytical models have been investigated and compared with experimental results for the semipermanent, or normal, core configuration for the University of Maryland Reactor. These models were selected because, while somewhat time consuming with respect to the use of computers, the computer time utilized is much less than needed by more complex methods. At the same time, the methods used tend to minimize the large inherent error associated with simple hand calculations . The methods used consist of a two-dimensional few group diffusion theory coupled with several cross section models from which macroscopic cross sections were obtained. The cross section models used for the above thermal energy groups were the volume integrated P-1 method and the Fourier transform B-1 method. Thermal energy group cross sections we reobtained using the Wigner-Wilkins model and the Maxwell-Boltzmann model. The volume integrated P-1 model and the Wigner-Wilkins model coupled with the two-dimensional group diffusion method were found to give the best agreement with experiment for the semi-permanent core configuration. This model was then tested over a range of experiments. The conclusion of this analysis was that the model was capable of predicting, with reasonable accuracy, the changes in core reactivity with core rearrangement.
- ItemReactivity Measurements on the University of Maryland Reactor by Conventional Methods and Statistical Processes and Comparison with Calculational Methods(1970) Zubieta, Agustin Diaz; Duffey, Dick; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The accurate experimental determination of nuclear reactor core physics parameters is of great importance for its safe operation. In particular, the accurate determination and prediction of criticality during the initial fuel loading of a nuclear reactor are essential for a safe nuclear reactor startup. Also, the degree of subcriticality or shutdown margin of a nuclear core with its control rods inserted is an important parameter for the operation of a nuclear reactor throughout the core operating lifetime. There are several methods utilized to determine both the criticality and the shutdown margins. All of these methods depend on measuring the response of neutron detectors and the calibration of the control rods. However, neutron detectors respond only to the neutron flux in the cor e in the vicinity of the nuclear detectors. During initial reactor core fuel loading, the reactivity of the core is determined from the multiplication of the neutrons of the startup source by the addition of nuclear fuel. Reactivity is determined from the multiplication factor by a constant which is related to the source-detector geometry in the core. In this research a method was studied which allowed the determination of reactivity independent of the source-detector geometry. Reactivity measurements of the 10 kw University of Maryland pool training reactor (UMR) were made by conventional methods and by a statistical process, the variance-to-mean ration method, and the results were compared with calculational methods. The theoretical method selected to determine the UMR core reactivity was based on the multigroup, multiregion, diffusion theory. The accuracy of the theoretical model was determined for the just critical UMR core. Agreement to within 0.2% ΔK/K was obtained between the control rod measured and the calculated reactivity for the UMR full core, and smaller UMR supercritical cores. The statistical technique of the variance-to-mean ratio of the number of counts for various counting gate openings, as a means to determine the degree of subcriticality, or shutdown margin, has been proven to be an effective method. A BF3, thermal neutron proportional detector, with a sensitivity of 12.1 counts/sec per n/cm2/sec, was placed inside of an eleven feet long aluminum tubing. The end of the tubing containing the detector was inserted in the center Glory Hole of the UMR core. The current pulses from the proportional detector was amplified and fed to a TMC 1024-channel pulse analyzer. The pulses were counted for different Δt gate openings from 10-4 seconds to 10 seconds. For each Δt gate opening, 1023 samples were taken. The printed output from the TMC-1024 was collected, giving the number of counts received per Δt, as well as the integral of all the counts received during a period of time, equal to 1023 x Δt seconds. From the integrated value for the number of counts the average count c for the gate opening Δt was obtained. The printed output was transferred to IBM cards acceptable to a "Reactor Noise" code written for the IBM-7090. This code calculated the average value, c, for each Δt (which gave a check on the validity of the data transferred to the IBM cards by comparing it with the value obtained during the measurement), the standard deviation o, and the variance-to-mean ratio for all the data taken for each Δt seconds gate opening. Plots of the values of the variance-to-mean ratio versus gate openings were obtained for several UMR full core with the rods banked at various degrees of insertion (shutdown margins), and also for various UMR subcritical cores. Measurements of the shutdown margins by the variance-to-mean technique were in agreement with the values obtained from the rod calibration for negative reactivities of less than -1. 00% ΔK/K, and within ten percent for negative reactivities of approximately -2. 0% ΔK/K. Measurements of the reactivity of small UMR cores indicated that for UMR core conditions of 0. 5% ΔK/K subcritical, experiment and theory for 1-Keff were found to be only 6 parts in 100 apart, and for 2. 0% ΔK/K subcritical, experiment and theory were found to be only 8 parts in 100 apart. The variance-to-mean technique was compared to the inverse multiplication method for determination of criticality during the UMR fuel loading, and was found to be a more accurate method, primarily, because of its independence of the source-detector geometry effects. The system utilized for the statistical data processing is exact, however cumbersome, due to the amount of data to process and the amount of peripheral hardware utilized in the reduction of the data. It appears from this study that greater overall counting efficiency for the same amount of statistical data would permit more accurate measurements at larger degrees of subcriticality, perhaps, in the region of -4. 0% ΔK / K to -5. 0% ΔK / K . A system is proposed in this study to measure negative reactivity continuously, and directly, by means of a small computer capable of accepting the output of a multichannel scaler. The computer would have a fixed internal logic capable of calculating reactivity from the variance-to-mean analysis of the neutron detector counts.
- ItemThermal Displacement in Copper-Gold Alloys(1971) Gilmore, Charles M.; Bolsaitis, P.; Skolnick, L.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The thermal displacements and Debye temperatures are determined for single crystals of copper and Cu-Au solid solutions including Cu3Au of four degrees of long range order (0.0, 0.53; 0.8, .98). Other solid solution compositions studied were .91Cu-.09Au and .2Cu-.8Au. At the .91Cu-.09Au composition a one week anneal produced a nonequilibrium structure. After a one month anneal the thermal displacements decreased to a value nearly equal to the value for pure Cu. The thermal displacements in the quenched .75Cu-.25Au crystal were also nearly equal to the value for pure Cu, but the thermal displacements increased as the Cu3Au crystal approached the equilibrium condition of full order. In the Cu3Au crystals, which were partially or fully ordered, the thermal displacements of the individual Cu and Au atoms were determined. It was observed that the vibration amplitudes of the Cu atoms are not isotropic in this diatomic cubic crystal. The vibrations of the Au atoms are equal in the  and  directions within experimental uncertainty. Also, the thermal displacements decrease as the crystal is changed from fully ordered to fully disordered. This is consistent with calculations of the vibrational spectrum for ordered and disordered Cu3Au. The static displacements for the partially ordered S = .80 crystal were also determined from the same experiments as the thermal displacements. An Einstein model was developed to calculate thermal displacements and Einstein frequencies from interatomic potentials. The calculated thermal displacements are 10 to 20 percent less than the experimental values. This is due to the simplifying assumptions in the model. The model calculation and the experimental results do agree on the changes in the thermal displacements with alloying. The Einstein model is also used to calculate the vibrational entropy in alloys.
- ItemSome Characteristics of Broadband Delta-Sigma Modulation(1971) Biegalski, Robert J.; Tretter, Steven; Electrical and Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)This paper presents an analysis using correlation techniques of an idealized Delta-Sigma Modulation system. An analytical assumption of errors with a marginally Gaussian distribution is shown to yield accurate results for broadband modulation with a maximum input-output cross correlation. It is also shown that this maximum is greatest for the degenerate case of only "hard limiting" with no feedback and no integration. A case of highly correla~ed inputs for Delta- Sigma Modulation is also discussed to compare it with broad- band performance and "hard limiting."
- ItemLocal Atomic Arrangments and Solution Strengthening of Ta-Mo and Ta-Nb Alloys(1975) Predmore, Roamer Edward; Arsenault, Richard J.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Ta-Nb alloys are shown to form random solid solutions by x-ray diffuse scattering measurements. These alloys have equal size atoms in their pure state with lattice parameters that are invariant in composition, obey Vegard's law, and exhibit an absence of solid solution hardening and an absence of fracture embrittlement at high solute concentrations. Ta-Mo atoms of about 5% difference in atomic size form short range ordered solid solutions with large atomic displacement effects. The Ta-Mo, and Ta-W, Nb-Mo and Nb-W alloys have in common a lattice parameter that varies in composition with a negative deviation from Vegard's Law. There is also a negative heat of mixing which is well correlated with short range order. In addition, all these alloys show linear solid solution hardening to high solute concentrations at room temperature and fracture embrittlement at high solute concentrations. Diffuse ex-ray scattering measurements on Ta-Mo alloys give the short range order parameters and atomic size displacements. The hardening is attributed to a combination of size effect induced substitutional solid solution hardening and short range order induced hardening.
- ItemAmbiguous Behavior of Logic Bistable Systems(1975-10-04) Hurtado, Marco; Elliott, David L.The standard specification of logic bistable devices do not specify the behavior under conditions in which the input is logically undefined or in which certain kinds of multiple input changes occur. These conditions are unavoidable in logic synchronizers and arbiters. A general deterministic model of bistable devices is proposed, consisting of a non-liner differential system with some adequate properties. Analysis of this model shows that bistable devices can be driven into a logically undefined region by certain admissible inputs and can remain in this region for an unbounded length of time.