Biomedical subjects

R B Hallock

Publications and source records attributed to R B Hallock.

7 recordsLinked to original sources

PubMed2005

Observation of two-dimensional classical wave localization: third sound on superfluid 4He films on a disordered substrate.

We present the results of measurements of the propagation of third sound waves on superfluid 4He adsorbed to two-dimensional ordered and disordered substrates. In the disordered case we compare the experimental results to theoretical predictions of classical wave localization in such systems and conclude that classical wave localization is present in our system.

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PubMed2004

Statistical characterization of thermally evaporated rough CaF2 films.

Thermal deposition of CaF2 onto a glass substrate creates a nanoscale rough surface. A series of samples with differing nominal CaF2 film thicknesses have been fabricated, and the topography has been investigated using atomic force microscopy. Measured values for the statistical characterization of the samples are presented including the exponents describing the scaling behavior of the surfaces. We find that the roughness exponent alpha=0.88+/-0.03 , the growth exponent beta=0.75+/-0.03 , and the dynamical exponent z=alpha/beta=1.17+/-0.06 . We also measure the multifractal spectra and nearest neighbor height difference probability distribution. The results are consistent with noise dominated by a power-law distribution with exponent mu+1 approximately equal to 4.6. Profilometer measurements were used to determine the porosity phi of the deposited films, which we find to be constant for all film thicknesses with phi approximately 0.46 .

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PubMed2004

Kosterlitz-Thouless transition for 4He films adsorbed to rough surfaces.

We report the study of adsorption isotherms of 4He on several well characterized rough CaF2 surfaces using a quartz crystal microbalance technique at 1.672 K. The signature of decoupled mass observed on crossing the Kosterlitz-Thouless transition as a function of 4He film thickness decreases and becomes increasingly difficult to identify as the surface roughness is increased. A peak in the dissipation, indicative of the onset of superfluidity, changes little with roughness.

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PubMed2004

Evidence for power-law dominated noise in vacuum deposited CaF2.

We have studied the surface roughness of CaF2 vacuum deposited on glass using atomic force microscopy for film coverages spanning an order of magnitude. We find the roughness exponent alpha=0.88+/-0.03, the growth exponent beta=0.75+/-0.03, and the dynamic exponent z=alpha/beta=1.17+/-0.06. Multifractality is also present, along with power-law behavior in the nearest neighbor height difference probability distribution. The results indicate noise dominated by a power-law distribution with exponent micro+1 approximately 4.6.

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PubMed2003

Superfluid Avalanches in Nuclepore: Constrained versus Free-Boundary Experiments and Simulations.

Superfluid 4He exhibits hysteretic behavior in the percolated nanoporous material Nuclepore during the filling and draining of pores due to capillary condensation, and one observes avalanches during the pore draining. We observe that the size and frequency of the avalanches depend upon whether the fluid flow off the substrate during draining is impeded or unimpeded. We simulate the draining of superfluid 4He from Nuclepore with and without a perturbation of the pore menisci and find results similar to the results seen in the experiments in the presence or the absence of flow inhibition.

Journal Article↗

PubMed2001

Heat-capacity studies of (3)He in (3)He-(4)He mixture films and the coverage dependence of the two-dimensional (3)He Landau Fermi-liquid parameters.

The heat capacity of (3)He in (3)He-(4)He mixture films on a nuclepore substrate is reported over the temperature range 90<T<124 mK, for (3)He coverages between 0.05 and 1.4 bulk-density atomic layers, and a (4)He film thickness of 4.33 bulk-density atomic layers. A step structure appears in the specific heat as a function of (3)He coverage. Combining NMR and specific heat data for (3)He atoms on the same substrate and for the same (4)He coverage allows the two-dimensional Landau Fermi-liquid parameters F(A)(0) and F(S)(1) to be extracted as a function of (3)He coverage. We conclude that in the submonalayer (3)He coverage regime p-state pairing is favored.

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PubMed1989

Immunoassay based on surface plasmon oscillations.

An in situ immunoassay technique is described which is sensitive to specific binding to surface immobile antigen or antibody. The phenomena of surface plasmon oscillations are shown to be sensitive to antigen-antibody binding on a substrate. An advantage of the technique is that no molecular labeling is required. The technique allows the detection of the presence of approximately 6 X 10(8) molecules on the approximately 1 mm2 area of detection (approximately 1.5 X 10(-8) g/cm2). An elementary apparatus is described which allows the kinetics of the antigen-antibody binding to be accurately recorded in real time. A detailed example is presented. A second version of the apparatus of similar accuracy with improved temporal resolution is described.

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