Ultrafast photocurrent measurement of the escape time of electrons and holes from carbon nanotube p-i-n photodiodes

Ultrafast photocurrent measurements are performed on individual carbon nanotube p-i-n photodiodes. The photocurrent response to subpicosecond pulses separated by a variable time delay Δt shows strong photocurrent suppression when two pulses overlap (Δt=0). The picosecond-scale decay time of photocurrent suppression scales inversely with the applied bias V(SD), and is twice as long for photon energy above the second subband E22 as compared to lower energy. The observed photocurrent behavior is well described by an escape time model that accounts for carrier effective mass.     

Electrical transport measurements on single-walled carbon nanotubes

We review transport measurements on single-walled carbon nanotubes contacted by metal electrodes. At room temperature some devices show transistor action similar to that of p-channel field effect transistors, while others behave as gate-voltage independent wires. At low temperatures transport is usually dominated by Coulomb blockade. In this regime the quantum eigenstates of the finite-length tubes can be studied. At higher temperatures power law behaviour is observed for the temperature and bias dependence of the conductance. This is consistent with tunneling into a one-dimensional Luttinger liquid in a nanotube. We also discuss recent developments in contacting nanotubes which should soon allow study of their intrinsic transport properties. Received: 17 May 1999 / Accepted 18 May 1999 / Published online: 4 August 1999     

The FT-IR study of the brain tissue of Labeo rohita due to arsenic intoxication

The brain is believed to be particularly vulnerable to arsenic due to its high oxygen consumption rate and high level of polyunsaturated fatty acids and relatively high rate of oxygen free radical generate without commensurable level of arsenic. Hence, in the present work an attempt is made to study the changes in the biochemical contents in the brain tissues of edible fish Labeo rohita due to arsenic intoxication using Fourier Transform Infrared (FT-IR) spectroscopy. FT-IR spectra reveal significant differences in absorbance intensities between the control and arsenic intoxicated brain tissues, reflecting an alteration on the major biochemical constituents, such as lipids, proteins and nucleic acids of the brain tissues of L. rohita due to arsenic intoxication. Further, the administration of antidote DMSA improves the protein and lipid contents significantly in the brain tissues when compared to arsenic intoxicated tissues. The decrease in α-helix structure due to arsenic intoxication might be responsible for the increase in β-sheet secondary structures, which is consistent with the mechanism of β-sheet formation.     

Metro Dense Wave Division Multiplexing (DWDM)

Metro Dense Wave Division Multiplexing (DWDM) has been touted by its proponents as the future of optical telecommunications in the metro market. But is it? Its proponents have presented it as a natural extension of long haul DWDM into the metro network. But can Metro DWDM be cost justified and, if so, under what conditions? Whether and to what extent the economics of metro DWDM will change over time are other major questions certain to affect materially the acceptance of metro DWDM and thus the market opportunity for manufacturers of metro DWDM equipment. Finally, questions concerning regional variations in the market opportunity for Metro DWDM equipment must be answered.     

COMPOSITION OPERATOR ON BERS-TYPE SPACES

Necessary and sufficient conditions are established for a composition operator C f = fo to be bounded or compact on the Bers-type space Ha and the little Bers-type space Ha The boundedness and compactness of the composition operator C on A() are characterized, which generalize the case of C on Ha.