Browsing by Author "Rorschach, Harold E., Jr."
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Item A capacitor buffer memory(1962) Schutz, Theodore Charles; Graham, Martin; Pfeiffer, Paul E.; Rorschach, Harold E., Jr.Digital information may be stored as a charge on a capacitor if suitable switches are used on the input and output lines. Characteristics of neon glow lamps (ionized from an external radio frequency source) pertinent to application in a capacitor store buffer memory were investigated. The results of this investigation and application of the results to the construction of a 64 bit buffer memory are discussed.Item A quasi-elastic neutron scattering study of hydrogen dynamics in trypsin-deuterium oxide solution (deuterium oxide)(1993) Cao, Hung Duc; Rorschach, Harold E., Jr.The quasi-elastic neutron scattering (QNS) method is a useful technique to study biomolecular dynamics. The versatility of the method makes possible motional studies of biomolecules in different forms: powder, crystalline, and solution; and at different temperatures. Thus, it allows investigation of biomolecular dynamics in different states of matter. We have used the QNS method to study the motion of the trypsin chain segments in powder and in D$\sb2$O solution at temperatures of 200K, 280K, and 300K. The scattering spectra S(Q,$\omega$) were measured in constant-Q mode. The S(Q,$\omega$) for trypsin protons in liquid solution exhibits a broadening due to diffusive motion which is absent in the powder and the frozen solution. This diffusive motion has the character of a jump diffusion. The high-frequency thermal motion obtained from the Debye-Waller factor $\langle$u$\sp2\rangle$/3 $\cong$ 0.33A$\sp2$ at T = 300K is consistent with earlier measurements. The DW factor at lower temperatures for trypsin solution shows deviation from theoretical predictions.Item Flux quantization and interference effect in superconducting niobium(1966) Carter, John Tatum; Rorschach, Harold E., Jr.The current through a circuit constructed by touching two pieces of superconducting Nb together was found to vary periodically with the applied magnetic field. This is attributed to the quantization of the flux enclosed in the circuit. The results are in agreement with those reported by Zimmerman and Silver.Item Flux quantization and off-diagonal long-range order in thin cylinders containing a "weak link"(1966) Melich, Michael Edward; Rorschach, Harold E., Jr.The equilibrium states of a thin-walled hollow cylinder containing a 'freak link", (e .g. a Josephson junction ) are examined in a Bose gas model calculation. It is found that these states may be such that the fluxoid is not an integer multiple of the flux quantum. The deviation from integer flux quantization depends upon the coupling strength of the "weak link" and the externally applied magnetic flux. The first order reduced density matrix (the 1-matrix) for the boson system is then investigated utilizing the general features of the model calculation. The fluxoid quantization and persistent currents are considered in terms of the modifications (due to the link) of the off-diagonal long- ra nge order of the 1-ma tr ix .Item I. Measurements on the nuclear magnetism in liquid HE_. II. A HE_ cryostat for nuclear magnetic resonance measurements(1960) Schwettman, Harry Alan; Rorschach, Harold E., Jr.The technique of adiabatic fast passage has been used to measure the nuclear susceptibility of liquid He3. Measurements along the vaporization curve from 1.2°K to 2.1°K indicate that anti-parallel alignment of the He3 spin system in this temperature range is more important than suggested by previous measurements. Unless existing data at temperatures below 1°K are incorrect, it appears that the susceptibility of He3 is not given precisely by the ideal Fermi-Dirac expression. A He3 cryostat has been constructed to extend the measurements to lower temperatures. Both the operating characteristics of a preliminary cryostat and the design of the final cryostat are discussed.Item Low magnetic field transitions of rhenium near the critical temperature(1972) Schreiber, Roland, 1958-; Rorschach, Harold E., Jr.A cryostat was constructed using conventional and superconducting shielding techniques. The ambient magnetic field at the sample was reduced to less than 10 to the -5 Gauss. For the single crystal rhenium sample isothermal magnetization curves were obtained with thermodynamic critical fields Hc between 4mG and 0.3G. The slope of Hc(T) vs. T was found to be not constant near the zero field transition temperature To. For Hc(T))>100mG a slope of 192 G/K was obtained, while for Hc(T)~5mg the slope decreased to 88 G/K. Whether this change in slope is due to mechanical defects in the sample or due to effects of fluctuations near T0 is at present not fully determined.Item Macromolecular dynamics studied by magnetic resonance and neutron scattering(1992) Lin, Chen; Rorschach, Harold E., Jr.Macromolecular dynamics is important for both understanding biological processes and practical applications such as MR imaging data interpretation. We have used the QNS method to study the dynamics of trypsin chain segments. Trypsin powder and trypsin in D$\sb2$O were studied for temperatures from 100K to 300K. Energy spectra of the scattered neutrons were measured for various neutron momentum transfer. Diffusive type motion of chain segments are observed for trypsin solutions at temperatures above the freezing point, while powder and frozen samples display minimum chain motion. The motion of trypsin chain segments can be fitted by a general "jump-diffusion" model which describes the conformational changes of a macromolecule as transitions between its substates. The diffusion coefficient of the trypsin chain segment is 2.4 $\times$ 10$\sp{-6}$ cm$\sp2$/sec and the average residence time of trypsin in its substates is 1.3 $\times$ 10$\sp{-11}$ second when trypsin is in D$\sb2$O at 300K. We measured the average mean square thermal vibration amplitude of trypsin (0.65 A$\sp2$) which is slightly larger than the results from computer simulations and X-ray diffraction studies. We also have tested macromolecular dynamics theory on poly-acrylic acid. We measured the frequency dependence of proton T$\sb1$ relaxation rates of poly-acrylic acid in D$\sb2$O solutions with different pDs and salt concentrations. Frequency dispersion data analyzed using both a flexible chain model and a stiff chain model give a maximum correlation time of 1.5-2.3 $\times$ 10$\sp{-7}$ second depends on the model. No significant change due pD and salt concentration difference was found.Item Magnetization measurements near the superconducting transition temperature(1967) Wells, Charles Allie; Rorschach, Harold E., Jr.The thermodynamically reversible phase transition of a metal into a superconducting state has a critical field curve, which can be represented by: The difference in the specific heat of the two phases is given by These equations predict a first order phase transition in a magnetic field and a second order transition in zero field. A singularity in the specific heat at Tc, similar to the singularity for liquid heldum at the -point due to the onset of long range order, would mean that A system of measuring the magnetization of a superconductor in an applied field has been constructed and utilized to determine the critical field curve near The system consists of a closed superconducting loop enclosing the sample, a nulling solenoid and a magnetometer probe; situated in a region of low nagnetic fields. Magnetization curves have been obtained for a sample of 99.999% pure indium over a temperature range of 3.365°K to 3.398°K. The reversibility of the curves was found to depend on the rate at which the magnetic field was applied. The critical temperature was found to be 3.409°K. The slope (dHc/dT) for measurements made was -150 oe./°K. The agreement between values found from this experiment and previous work was reasonable. There was no indication of a singularity in the temperature range investigated. [see PDF for formulas]Item Measurement of diffusion by the Spin-echo method(1967) Chang, Donald C; Rorschach, Harold E., Jr.A convenient and accurate method to measure the diffusion coefficient in a liquid is provided by nuclear magnetic resonance. It is called the "Spin-echo" method. Experimental apparatus has been built to observe spin-echos in samples of water. The results of these experiments agree with the theory of the method. An extended discussion of experimental details is given in this thesis.Item Measurements of the trapped flux in a long hollow superconducting cylinder(1963) Smith, Todd Iversen; Rorschach, Harold E., Jr.The recent discovery of quantized flux appeared to explain the extremelylong lifetime .of persistent currents in superconductors. The existence of the flux quantum indicated that the energy of a superconductor in a current carrying state is a local minimum with respect to current variations if the flux is an integer number of flux quanta. The stability is thus explained as a greatly reduced transition probability for the large current changes needed to lower the energy. Bloch and Rorschach have investigated the energetic stability of persistent currents in a long hollow superconducting cylinder, using the charged Bose gas model proposed by Schafroth. The criterion for stability was that the energy of the system could not be lowered by single particle transitions. They showed that the maximum stable magnetic field which could be trapped inside the cylinder was a function of the externally applied field and the sample dimensions, and could be less than the critical field Hc. In contrast to these results one would predict from Maxwell's equations, together with the infinite conductivity of a superconductor, that it should be possible to trap and maintain any field inside the cylinder as long as both the internal and external fields are smaller than the critical field. Measurements have been made of the maximum stable field inside a hollow tin cylinder (wall thickness d 1.5 mm, inner radius r = 7.5 mm, length L =12.5 mm) as a function of the externally applied field. The results seem to be in qualitative agreement with the Bose gas theory, in that the maximum internal field is a function of the external field. However, the theory predicts that when the external field is zero the maximum internal field should be d/r Hc = 0.2 Hc, while the experimentally determined value is 0.6 Hc. It is possible that these results are due to end effects, as the field at the cylinder walls is greater at the ends than at the center. The rate of decay of the internal field when the external field is changed indicates that these end effects may be important.Item Nuclear spin relaxation of He_ in liquid He_-He_(1965) Horvitz, Ephrem Philip; Rorschach, Harold E., Jr.The spin-lattice relaxation time, T1, and the spin-spin relaxation time, T2, of He3 nuclei in liquid mixtures of He3 and He4 at 5%, 14% and 35% He3 concentrations have been measured. T1 and T2 values were also obtained for pure He3. The technique of adiabatic fast passage was employed to measure relative magnitudes of the magnetization. The results show that T1 and T2 tend to decrease as the temperature decreases below the lambda point of the mixtures. They show also that T1 and T2 decrease as the concentration of He3 decreases. The latter implies that impurity effects become more important the lower the He3 concentration is. A model based on bulk and wall impurities was used to explain the results. This model was also used to compute the diffusion coefficient for He3 in the three mixtures. The calculations show that the diffusion coefficient increases with decreasing He3 concentration and with decreasing temperature. This implies that the superfluid component of the He4 behaves as if it were a vacuum. Khalatnikov and Zharkov1 have calculated the diffusion coefficient of He3 in Hell on the basis of the Landau theory of superfluidity. The experimentally determined diffusion coefficients are in good agreement with this theory.Item Nuclear susceptibility of helium three liquid and gas(1964) Manka, Robert Hall; Rorschach, Harold E., Jr.The technique of adiabatic fast passage has been used to measure the relative magnetic susceptibility, X , of He3 and mixtures of He3-He4 with an experimental r.m.s. deviation of ±1%. Two types of measurements were made: (1) Measurement of X versus temperature (from 1.96°X to 0.93°K) of pure He3 liquid, and He3-He4 mixtures containing 35%, 14%, and 5% He3. (2) Measurement of relative X versus density of pure He3 gas at 2.99°K, with density varying from 1.1 x 10-3 to 4.5 x 10-3 moles/cc. Preliminary measurements of X versus density, p , of He3 atoms, for 2 x 10-3Item Pressure gradients due to heat flow in liquid helium(1957) Romberg, Frederick Arnold; Rorschach, Harold E., Jr.The pressure gradient associated with the flow of heat in helium I and II has been measured using capillary tubes of diameter one-half to 1.1 millimeters. The observations in helium I can be explained as consequences of the vaporization of the liquid in the capillary. In helium II, for heat currents below a certain critical value, which depends on the dimensions of the apparatus and the temperature, the observed pressure gradients agree with the predictions of the thermo-hydrodynamic equations for liquid helium. These equations appear to break down If the critical heat current is exceeded. After this current has been exceeded, the behavior of the pressure gradient in helium II strongly resembles the behavior seen in helium I.Item Superconductivity and small magnetic fields(1964) Hendricks, John Benjamin; Rorschach, Harold E., Jr.The use of the flux-gate,magnetometer as a sensitive measuring inastrument for investigating the magnetic properties of superconductors is discussed. The construction of a magnetometer is described and an analysis of the system is included. The magnetic properties considered are the Meissner effeat, the "London field", and quantized trapped magnetic flux. The reasults of a Meissner effect experiment are given. In this case, an Indium sample is placed inside a hollow Tin cylinder in a uniform external magnetic field. The temperature is lowered until the cylinder becomes superconducting. The magnetic flux within the cylinder is then a constant, and as the sample becomes superconducting, the field inside the cylinder will rise. This transition can be detected with the magnetometer. Three critical points were obtained, and compared to recent measurements by Shaw, Mapother, and Hopkins. The three points were Tc = 3.394°K @ H=1.174 Gauss, Tc=3.367°K @H=4.859 Gauss, and Tc = 3.330°K @ H=11.92 Gauss. The comparison gave errors of -10, -8, and 0 millidegrees, respectively. To make the comparison to the data by Shaw, et. al., a least squares fit to their data was made using a standard computer program. The critical curve can be represented by, Hc = 284.39 -26.751 Tc2 + 0.096352 Tc4Item Superconductivity in molybdenum(1964) Mallon, Richard Glenn; Rorschach, Harold E., Jr.In order to determine whether molybdenum is a type I or type II superconductor, magnetic measurements are being undertaken. The molybdenum samples were prepared by electron-beam float-zone refining. Resistivity measurements on one sample indicated that it is of adequate purity. In initial experiments in a helium-4 cryostat, no superconductivity was observed at temperatures down to about 0.9° K. In order to reach lower temperatures, a helium-3 cryostat of the single condensation type has been built. Details of the design and results of preliminary operation are discussed. In this cryostat, superconductivity in molybdenum has been observed. At 0.65° K in an external field of 15 oersteds, magnetic induction in the sample was zero.Item Supercooling and trapped flux in superconducting molybdenum(1967) Pinatti, Daltro Garcia; Rorschach, Harold E., Jr.The supercooling properties of Molybdenum were studied through the use of a Dynamic Method. The KAPPA factor of Ginsburg-Landau was calculated. Using the De Gennes correction this value is 0.22 ± .02. The structure of the phase transition as a function of the rate of sweep of the magnetic field, both for increasing and decreasing field, was studied. An attempt was made to interpret the superconducting-normal transition in terms of the electrodynamic theory of Pippard and Lifshitz. This was not sufficient, and a slow process in the beginning of the transition is necessary. Experimental evidence for this process is presented, and it suggests that surface thermal resistance may be the cause for the slow process. The dynamic method proves to be a potentially useful method for measurements of electrical conductivity. At 751 °K for Molybdenum we measure [see PDF for formula]. The character of the normal-superconducting transition indicates that 2/3 of the cross section of the sample has a sudden flux expulsion. The remaining 1/3 seems to have a gradual expulsion with decreasing field.Item Temperature dependence of the nuclear spin-lattice relaxation time in CaF_:Nd(1965) Burnett, Robert Wayne; Rorschach, Harold E., Jr.Measurements of the F19 nuclear spin-lattice relaxation time T1 have been made in doped calcium fluoride over the temperature range extending from 300°K down to about 2°K. The doping element was the rare earth neodymium. Data were obtained by a pulsed nuclear resonance method for two orientations of the crystal with respect to the magnetic field. The experimental results were analyzed by means of a general expression for T1 valid for intermediate cases as well as for the diffusion limited and rapid diffusion limits. Dependence of the barrier radius on the temperature and the relaxation time of the paramagnetic impurity is taken into account in this expression. There is reasonable agreement between the experimental measurements and the theoretical expression over the entire temperature range.Item The development and applications of Fourier transformed relaxation measurements in nuclear magnetic resonance (NMR)(1988) Lin, Chen; Rorschach, Harold E., Jr.A method has been developed to measure the spin-lattice and spin-spin relaxation times of the various components of a multi-component spectrum. By Fourier transforming the free induction decay after the inversion recovery or spin echo pulse sequences, the different frequency components can be resolved and their individual relaxation times can be measured. This method has great advantages over the conventional method of analysis for multiple component decays which are very common in chemical and biological system. Based on this method, many interesting studies can now be done with NMR. The details of this method are presented with a comparison between our method and the conventional method and results and discussion of some applications.Item The effects of stochastic fluid transport phenomena in magnetic resonance imaging (MRI)(1992) Minard, Kevin R.; Rorschach, Harold E., Jr.Kubo's generalized cumulant expansion theorem is used to derive a theoretical expression for the nuclear magnetic resonance (NMR) signal received from a fluid moving in a time-dependent magnetic field gradient. Described in general terms by time-dependent correlation functions, this expression is used to investigate a new statistical model of microcirculation that incorporates both coherent and incoherent flow effects at the microscopic level. Based on a simple picture of the intravoxel environment, this model is developed by considering an arbitrary distribution of tortuous capillary flows. A statistical analysis of the Langevin equation describing slow tortuous capillary flow as a stochastic process reveals precisely how both coherent and incoherent flow effects contribute to the overall attenuation of the NMR spin-echo. Velocity compensated and non-compensated diffusion matched spin-echo imaging sequences are utilized to separate and quantify these respective effects noninvasively on phantoms of stationary and flowing fluid.Item The hydrodynamic drag force in liquid helium at high Reynold's numbers(1958) Laing, Ronald Albert; Rorschach, Harold E., Jr.The hydrodynamic drag force on a sphere falling in Helium I and Helium II at large Reynolds' Numbers was studied. It was found that for Reynolds' Numbers ~10 to the 6th the drag force can be adequately represented by the equation D=Co(1/2 pu2)A where P is the total density of the fluid, U is the velocity of the falling sphere, and A is the projected area of the sphere. In the region of Keynolds' Numbers studied in Helium II the superfluid and normal fluid appear to move together and turbulence in the superfluid seems to be present.