Pseudo-non-contact AFM imaging?

Recent non-contact atomic force microscopy studies have demonstrated that imaging of single atom defects is possible. However, the imaging mechanism was unclear. Long-range forces of attraction, which are normally associated with non-contact mode, are not known to produce sufficient lateral resolution to image atoms. In this study, we suggest a mechanism that could be responsible for the resolution achieved. We use realistic interatomic interaction parameters to do numerical simulations. These simulations are in good agreement with experimental data. As a result, we are able to ‘separate' the attractive and repulsive forces acting between the AFM tip and the sample surface. Calculations indicate that the force responsible for image contrast in the experimental studies mentioned above, is in most cases the repulsive contact force, and not the long-range attractive force. We check our conclusions against a variety of interatomic interaction parameters and our results remain valid for any reasonable set of such parameters, including the power law of the attractive potential N<9.     

Optical and photoemission evidence for a Tomonaga-Luttinger liquid in the Bechgaard salts

Combined optical and photoemission experiments on the quasi-one dimensional Bechgaard salts reveal the non-Fermi liquid character of these prototype quasi-one dimensional interacting electron systems. We show that various aspects of the exotic normal state properties along the chains are consistent with the predictions of the Tomonaga-Luttinger liquid theory. We also discuss the effect of interchain coupling on the insulator-metal transition, associated with the electron confinement-deconfinement crossover. Received 17 May 1999 and Received in final form 13 July 1999     

Activation of dinitrogen at binuclear sites

TMC Literature Highlights-22,Transition Met. Chem.,15, 251 (1990).     

An excimer-pumped β-BaB2O4 opticalparametric oscillator tunable from 354 nm to 2.370 μm

A pulsed singly resonant optical parametric oscillator (OPO) has been constructed which can provide tunable coherent radiation over the entire wavelength range extending from 354 nm in the near ultraviolet, throughout the visible, to 2.370 μm in the near infrared using a single β-BaB₂O₄ crystal. The oscillator is pumped at 308 nm by a pulsed narrow band injection-seeded XeCl excimer laser in a near-field pumping configuration, and energy conversion efficiencies (optical-to-optical) in excess of 10% have been obtained in a 12-nm-long crystal across the OPO tuning range. The requirements placed upon the spectral and spatial coherence of the pump laser for optimum OPO operation are discussed. Experimental results on several oscillator parameters, including tuning range, oscillation threshold, energy conversion efficiency, and spatial and temporal characteristics, are presented     

Quadrature Vestigial Sideband (QVSB) Data Transmission

The combined use of quadrature modulation and vestigial sideband filtering is investigated as a means of obtaining a spectrally efficient modulation scheme. The name quadrature vestigial sideband (QVSB) aptly describes the new system, whereby two independent data streams are each VSB modulated into the same passband, but on quadrature related carriers. The inherent interference between the quadrature related channels is shown to be of a controlled form, similar to the intersymbol interference (ISI) in partial response (PR) systems. Techniques suitable for "unwinding" the ISI in PR systems are shown to be also applicable to QVSB. Precoding with bit-by-bit, decoding, nonoptimum and optimum probablistic decoding are investigated. The latter method results in only a 1.2 dBE_{b}/N_{0}degradation, atP_{b} = 10^{-5}, compared to coherent binary phase shift keying (BPSK), although up to a fourfold increase in spectral efficiency can be obtained.     

Fibrillation induced at powerline current levels

Electrical fibrillation of the human heart results in many unfortunate deaths. Because little information is available on short duration high current fibrillation, current levels below 1 and 50 A were used to induce ventricular fibrillation in hogs. Application times ranged between 16 ms and 3 s. Fibrillation was only produced when currents were applied during the T-wave period of the cardiac cycle. However, only 50 percent of the current application during the T-wave caused fibrillation. The total body resistance of the hogs was also measured at the high voltages and currents. The average resistance for 90 current applications was 284 omega. Trends in the data show that the total resistance decreases for increasing voltage, for increasing electrode size, and for current applications following the first current application.     

Classification of behavior using vocalizations of Pacific white-sided dolphins (Lagenorhynchus obliquidens)

Surface behavior and concurrent underwater vocalizations were recorded for Pacific white-sided dolphins in the Southern California Bight (SCB) over multiple field seasons spanning 3 years. Clicks, click trains, and pulsed calls were counted and classified based on acoustic measurements, leading to the identification of 19 key call features used for analysis. Kruskal-Wallis tests indicated that call features differ significantly across behavioral categories. Previous work had discovered two distinctive click Types (A and B), which may correspond to known subpopulations of Pacific white-side dolphins in the Southern California Bight; this study revealed that animals producing these different click types also differ in both their behavior and vocalization patterns. Click Type A groups were predominantly observed slow traveling and milling, with little daytime foraging, while click Type B groups were observed traveling and foraging. These behavioral differences may be characteristic of niche partitioning by overlapping populations; coupled with differences in vocalization patterns, they may signify that these subpopulations are cryptic species. Finally, random forest decision trees were used to classify behavior based on vocalization data, with rates of correct classification up to 86%, demonstrating the potential for the use of vocalization patterns to predict behavior.