Nanoscale Science and Technology at Los Alamos National Laboratory

Research in the emerging field of nanoscale science and technology has grown steadily at Los Alamos National Laboratory since 1990. This article summarizes some of this work, examining research highlights within the seven key categories of nanoscience in which Los Alamos has ongoing projects, capabilities, and facilities: (1) Materials and chemistry, (2) Theory and modeling, (3) Bioscience, (4) Investigative tools and facilities, (5) Sensors and devices, (6) Synthesis and fabrication, and (7) Education and outreach. Future research horizons are indicated throughout while institutional strategies for advancing nanoscale science are summarized at the end.     

The relation between the human frequency-following response and the low pitch of complex tones

The relation between the auditory brain stem potential called the frequency-following response (FFR) and the low pitch of complex tones was investigated. Eleven complex stimuli were synthesized such that frequency content varied but waveform envelope periodicity was constant. This was accomplished by repeatedly shifting the components of a harmonic complex tone upward in frequency by delta f of 20 Hz, producing a series of six-component inharmonic complex tones with constant intercomponent spacing of 200 Hz. Pitch-shift functions were derived from pitch matches for these stimuli to a comparison pure tone for each of four normal hearing adults with extensive musical training. The FFRs were recorded for the complex stimuli that were judged most divergent in pitch by each subject and for pure-tone signals that were judged equal in pitch to these complex stimuli. Spectral analyses suggested that the spectral content of the FFRs elicited by the complex stimuli did not vary consistently with component frequency or the first effect of pitch shift. Furthermore, complex and pure-tone signals judged equal in pitch did not elicit FFRs of similar spectral content.     

The extraction, determination and speciation of tributyltin in seawater

Summary Methods have been developed for the determination, by carbon-furnace atomisation atomic absorption spectrophotometry, of inorganic and of total butyltin in seawater. Concentration/separations are based on the solvent extraction of organotin species directly into toluene and of inorganic tin as its tin(IV) 8-hydroxyquinoline chelate into chloroform. Detection limits are 0.7–0.8 ng.

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Extraktion, Bestimmung und Speziation von Tributylzinn in Seewasser

     

Compatibility studies of blends of polycarbonate and poly(ethylene terephthalate)

Blends of bisphenol-A polyarbonate (PC) and poly(ethylene terephthalate) (PET) has been investigated by differential scanning calorimetry and scanning electron microscopy. Blends were prepared by screw extrusion and solution casting with weight fractions of PC in the blends varying from 0.90 to 0.10. From the measured glass transition temperature (T_g) and apparent weight fractions of PC and PET dissolved in each phase, it appears that PET dissolves more in the PC-rich phase than does the PC in the PET-rich phase. The composition-dependent values of the Flory–Huggins polymer–polymer–interaction parameter were determined and found to be from 0.054 to 0.037 for extruded blends at 275°C and from 0.058 to 0.040 for solution casting at 25°C. The interaction parameter decreases with increasing PET concentration. This result is consistent with the values of the T_gs, the microscopy study, and the measured extrudate swell ratios which show that compatibility increases more in the PET-rich compositions than in the PC-rich compositions. The PC–PET blends are not microscopically miscible for all the blend compositions.     

The existence of disjoint smallest ideals in the two natural products on β S

No abstract. September 13, 1999     

The complexity of a basic impact mapping for rigid bodies with impacts and friction

We consider two impact mappings, the Brach impact mapping and an energetic impact mapping, for rigid-body mechanisms with impacts and friction. The two impact mappings represent the opposite end of the spectrum from basic to advanced impact mappings. Both impact mappings are briefly derived and described. For the Brach impact mapping we will introduce the concept of impulse ratio and discuss how the kinetic energy changes during an impact as the impulse ratio is varied. This analysis is used to further extend the Brach impact mapping to cover situations that were previously omitted. Finally, we make comparisons between the two impact mappings and show how the Painlevé paradox appears in the two impact mappings. The conclusion of the comparisons is that while the basic impact mapping seems easy to implement in a computer simulator it may in the end be more complex and also introduce unnecessary complications that are completely artificial.     

Kr-PLIF for scalar imaging in supersonic flows

Experiments were performed to explore the use of two-photon planar laser-induced fluorescence (PLIF) of krypton gas for applications of scalar imaging in supersonic flows. Experiments were performed in an underexpanded jet of krypton, which exhibited a wide range of conditions, from subsonic to hypersonic. Excellent signal-to-noise ratios were obtained, showing the technique is suitable for single-shot imaging. The data were used to infer the distribution of gas density and temperature by correcting the fluorescence signal for quenching effects and using isentropic relations. The centerline variation of the density and temperature from the experiments agree very well with those predicted with an empirical correlation and a CFD simulation (FLUENT). Overall, the high signal levels and quantifiable measurements indicate that Kr-PLIF could be an effective scalar marker for use in supersonic and hypersonic flow applications.     

The spectrophotometric determination of cobalt after extraction of tetramethylene-bis(triphenyl-phosphonium) tetrathiocyanatocobaltate(II) with microcrystalline benzophenone

Cobalt (0–130 μg) is determined spectrophotometrically at 625 nm after its adsorptive extraction as tetramethylene-bis(triphenylphosphonium) tetrathiocyanatocobalt(II) on microcrystalline benzophenone at pH 6.5 after dissolution of the solid phase in acetylacetone. The system is applied to the determination of cobalt (0.2–10%) in high-speed tool steels without prior separation of iron.     

From extended solids to nano-scale actinide clusters

Selected highlights of more than a decade of research efforts concerning the structural chemistry of actinyl materials at the University of Notre Dame is reviewed, with an emphasis on complex topological arrangements of polyhedra to form extended structures and frameworks. Earlier work focused on structures of uranyl minerals and synthetic compounds, with increasing emphasis on neptunyl materials and the importance of cation–cation interactions in their structural details and properties. Much of the research over the past 5 years has examined a growing family of nano-scale clusters of uranyl peroxide polyhedra containing from 16 to 60 polyhedra. These clusters contain topological squares, pentagons and hexagons, and six have adopted fullerene topologies with 12 pentagons and an even number of hexagons.