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Tunneling measurements on TlBa2(Ca0.8Y0.2)Cu2O7 taken at low temperatures with a scanning tunneling microscope reveal clear evidence of single electron tunneling behavior. Topographical studies of the film with both scanning tunneling microscopy and atomic force microscopy provide a simple explanation of the source of the ultra small capacitors necessary to explain the single electron tunneling spectra as a natural result of the planar crystal structure of TlBa2(Ca0.8Y0.2)Cu2O7.

With improved signal-averaging techniques, the tunneling conductance from pulsed-laser-deposited films of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ reveals a rich fine structure in both the subgap and near-gap regions. A comparison of this structure with calculations by Tachiki et al. yields excellent agreement and indicates the origin of the fine structure is the density of electronic states on the different layered planes of this high-${\mathit{T}}_{\mathit{c}}$ material.

The surface topography of YBa2Cu3O7 thin films prepared by pulsed laser deposition is studied by atomic force microscopy and scanning tunneling microscopy. The possible contributions from observed structural features to the critical current density Jc are discussed. It is shown that the contribution of the screw dislocations associated with some structures can be either repulsive or attractive, depending on the dominant pinning mechanism. At low magnetic fields (to about 0.25 kOe) these dislocations can account for the observed critical current density values (Jc≳1011 A/m2) while for larger fields the higher‐density steplike growth structures can account for significant values of Jc. It is shown that the pinning strength associated with pinning at steps varies inversely with thickness.

A neutron transmission spectrometer has been used to determine the presence of contraband substances in sealed containers. A pulsed 'white' neutron source was created by allowing a pulsed beam of 5 MeV deuterons to impinge on a thick beryllium target. The neutron intensity was measured from about 0.8 MeV to about 4 MeV, first with the sample out of the beam and then with the sample in the beam to determine the neutron attenuation as a function of neutron energy. The neutron attenuation can be considered as the signature of the sample and can be used by a trained neutral network to identify contraband directly. The neutron attenuation can also be used along with the total cross sections to determine the number density of H, C, N and O in the neutron beam. These number densities can be used in a trained neutral network to determine the presence of contraband. Previous work used collimated neutron beams to determine the signatures of many substances individually and when imbedded in suitcases. This work is now being extended to include the complete suitcase using a a cone beam of neutrons and an array detector which covers the complete suitcase.

A high speed data acquisition system has been assembled for the identification of contraband in sealed containers. Number densities through a sample can be determined by measuring the neutron attenuation as a function of energy using pulsed beam time of flight techniques. The neutron attenuation is determined by measuring and comparing the neutron transmission with and without the container in the neutron beam. The neutron transmission is determined by measuring the time of flight of neutrons with an array of detectors. Time constraints dictate that a high speed data acquisition system be developed for time of flight measurements. This detection system includes an array of individual photomultiplier tubes (PMT) interfaced to a high speed, high density digital electronics system. The state of the art digital system operates under a LabView graphical user interface. The number of electronic components has been optimized to keep size and cost to a minimum.

Open-geometry neutron attenuation experiments, by definition, subtend large solid angles. This poses a significant background threat to time-of-flight (TOF) attenuation spectra. Tailoring a laboratory to be suitable for open-geometry experiments, while leaving the background signature virtually intact for other ongoing work in the same laboratory, presents conflicting requirements for shielding structures. Careful selection of the type and design of the materials used in these experiments is important to obtain high quality data. Background sources in one such laboratory have been experimentally evaluated. This evaluation and the techniques and materials used to reduce their effect are reported.

A computer simulation program has been written for contraband detection using neutron transmission. The program has several options including: (1) determines the number density of H, C, N and O across the face of the suitcase using regression theory, (2) uses H, C, N and O to train a neural network for contraband detection using many suitcases with and without contraband, (3) determines the presence (or absence) of contraband in unknown suitcase by determining H, C, N and O and using trained neural network, (4) determines the presence of contraband using only the shape of the neutron attenuation curves. The program has a built in option that allows one to train and then test the trained neural network program by calculating a missed explosive fraction versus a false alarm fraction using thousands of simulated suitcases. The computer program uses experimental neutron attenuation curves that are stored in the memory of the computer. The program is user friendly and allows the operator to load and test suitc...

A neutron transmission spectrometer has been used to obtain the neutron attenuation signature of a number of substances, including contraband such as drugs and explosives. The neutron attenuations of these substances were determined for the substances alone and when imbedded in suitcases. A pulsed white neutron source was created by bombarding a thick beryllium target with a 5 MeV pulsed deuteron beam. The neutron intensity was measured from about 0.75 MeV to about 4 MeV with the samples in and out of the neutron beam to determine the neutron attenuation. The experimentally determined neutron attenuation curves were used to determine the number of densities of H, C, N, and O throught the samples using measured neutron cross sections. Explosives, drugs, and plastics each fall into different portions of the 3D space formed by certain ratios of H, C, N, and O. The results are presented in 3D representations.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Measurements of the tunnel current as a function of applied voltage on the layered high-${\mathit{T}}_{\mathit{c}}$ material ${\mathrm{TlBa}}_{2}$(${\mathrm{Ca}}_{0.8}$${\mathrm{Y}}_{0.2}$)${\mathrm{Cu}}_{2}$${\mathrm{O}}_{7}$ have been shown to exhibit single-electron tunneling behavior. It has been proposed that the ultrasmall capacitance required to explain the single-electron tunneling spectra obtained with a low-temperature scanning tunneling microscope arises naturally from the planar crystal structure of this high-${\mathit{T}}_{\mathit{c}}$ material. This hypothesis is further examined using a single-electron tunneling model that incorporates three tunnel capacitors, a condition that is required by atomic-force-microscope studies of the topography of the film's surface. An improved fit to the tunneling conductance is obtained, providing further evidence that a key to understanding Coulomb blockade in layered materials like ${\mathrm{TlBa}}_{2}$(${\mathrm{Ca}}_{0.8}$${\mathrm{Y}}_{0.2}$)${\mathrm{Cu}}_{2}$${\mathrm{O}}_{7}$ is the tunnel capacitors that form between multilayer CuO planes. This conclusion has important implications for the fabrication of nanoelectronc devices based on single-electron effects.

High-intensity fast white neutron pulses are needed for pulsed fast neutron transmission spectroscopy (PFNTS). A compact tritium–tritium fusion reaction neutron generator with an integrated ion beam chopping system has been designed, simulated, and tested for PFNTS. The design consists of a toroidal plasma chamber with 20 extraction slits, concentric cylindrical electrodes, chopper plates, and a central titanium-coated beam target. The total ion beam current is 1A. The beam chopping is done at 30keV energy with a parallel-plate deflector integrated with an Einzel lens. Beam pulses with 5ns width can be achieved with a 15ns rise/fall time ±1500V sweep on the chopper plates. The neutrons are produced at 120keV energy. A three-dimensional simulation code based on Vlasov iteration was developed for simulating the ion optics of this system. The results with this code were found to be consistent with other simulation codes. So far we have measured 50ns ion beam pulses from the system.

Fast deuterium (D+) and tritium (T+) ion beam pulses are needed in some neutron-based imaging systems. A compact, integrated fast ion beam extraction and chopping system has been developed and tested at the Lawrence Berkeley National Laboratory for these applications, and beam pulses with 15ns full width at half maximum have been achieved. Computer simulations together with experimental tests indicate that even faster pulses are achievable by shortening the chopper voltage rise time. This chopper arrangement will be implemented in a coaxial neutron generator, in which a small point-like neutron source is created by multiple 120keV D+ ion beams hitting a titanium target at the center of the source.

A single-photon counting system has been developed for measuring gas laser parameters. A linear accelerator provides nanosecond-wide pulses of heavy charged particles which are injected into a specially designed cell. The charged particles excite gas mixtures, and the temporal response of the emitted radiation is observed as a function of wavelength. The resulting data is analyzed to obtain pertinent parameters such as excited-state lifetimes, reaction rate constants, and quenching rate constants. At the present time nuclear pumper laser candidate gases are being examined.

Relative excitation efficiencies are reported for the fluorescence at 173 nm in liquid xenon excited by 0.5 MeV electrons (β particle), 6 MeV alpha particles (α particle), and 90 MeV fission fragments (ff). Efficiencies at 173 nm are also reported for alpha particle and fission fragment excitation of high pressure xenon. Results are presented in the form of ratios which compare the fluorescent output per unit energy for excitation by the different particles. The β/α and α/ff ratios for liquid xenon are 1.25±0.5 and 3.5±1.2, respectively. For xenon at 2000, 3000, and 4000 Torr, the α/ff ratios are 0.60±0.25, 0.61±0.23, and 0.63±0.24, respectively.

The purpose of the present study was to determine the effect of lethal concentrations of copper and hydrogen ion on mucus secretin by rainbow trout and to examine the effect of pH change on the ability of mucus to bind Cu/sup + +/.

Although G. A. J. Cole in 1893 described Hemitrypa hibernica M9Coy as a valid species and showed that the genus was distinct from Fenestella, his description is not entirely clear in modern terms. The type material is redescribed and the relation between the main fenestelloid structure and the hexagon-mesh super-structure is discussed. The type material is from a Carboniferous limestone locality in Cork, Ireland.

The Rosroe Peninsula, on the south side of Killary Harbour, Co. Galway, is formed of the Rosroe Grits, mapped by the Geological Survey of Ireland (1875) as “Lower Silurian”. Kilroe (1907) in a rapid revisionary survey of Galway and Mayo, described the succession on Rosroe as inverted (op. cit. p. 154, n. 3):—“ Mr. McHenry informs me that the fossils (graptolites) on the south side are indicative of Upper Llandeilo, while those on the north side are Lower. This being the case, the order of the beds is inverted, as they dip northerly.”

A new genus, Levifenestella, is erected, with L. maeve n.sp. from the Tournaisian of Co. Sligo, Ireland, as type species. A new species of Fenestella, F. polynodosa, from the same horizon and locality, is described. A Russian species, F. rossica Shulga-Nesterenko, is recorded from the Tournaisian of Hook Head, Co. Wexford.

A new method has been developed for the determination of the carboxymethyl substitution in cellulose ethers. The carboxymethyl groups are cleaved using hydriodic acid with the formation of acetic acid. The acetic acid is quantitated using A Zorbax C/sub 8/ column with UV detection at 205 nm. Before quantitation, most of the iodide and iodine from the hydriodic acid must be removed due to their interference in the chromatography and detection. With the combination of oxidation and extraction, most of the iodide and iodine is removed. This method is applicable to the determination of carboxymethyl groups in the presence of other cellulose ether substituents. A model compound has shown reaction yields of +97%. The relative precision for 10 determinations at the 95% confidence level for a carboxymethyl cellulose (CMC) and a carboxymethyl hydroxyethyl cellulose (CMHEC) was found to be +/-2.4% and +/-3.0%, respectively. 12 references, 1 figure, 2 tables.

The disappearing-phase method was used to determine the extent of the solid-solution region of the PLZT system for conventionally sintered ceramics prepared at 1100° and 1300°C in a PbO atmosphere provided by pbZrO3. A decrease in the firing temperature from 1300° to 1100°C lowers the solubility limit by 5 to 8 at.% La. Beyond the limits of solubility, additional La forms La2Zr2O7 and/or La2Ti2O7. The limit determined by the disappearing-phase method (1300°C firing) is compared to values determined by the parametric method. The Curie temperature is stabilized at 5 at.% La for modified PbZrO3 (1300°C firing).

The extent of transatlantic telephone service and its growth since its inception in 1927 are outlined in this paper. It is pointed out that at the present time 85 per cent of the world's telephones are included in the area served and about 50 calls are made per business day. Analysis is given of the calls with respect to distribution by countries, by time of day, and by kind of message. The volume of calls, the rates, and a general indication of the quality of transmission are given. Plans for future extensions of the service are outlined.