James J. O'Brien

Absorption spectra and absorption coefficients for methane in the 750–940 nm region obtained by intracavity laser spectroscopy

Abstract The intracavity laser spectroscopy technique has been employed to record the absorption spectrum of methane in the visible to near-infrared region. Results for room temperature methane in the 10,635– 13,300 cm −1 region and for liquid nitrogen temperature (77 K ) methane in the 10,860– 11,780 cm −1 region are presented. Methane spectra are acquired at a resolution of 400,000–500,000 and wavelength positions are calibrated using spectra of iodine (in a heated extra-cavity cell) or water vapor (via intracavity absorption) as reference. From the methane spectra, absorption coefficients are determined and these are presented as averages over 1 A and 1 cm −1 intervals. In order to obtain the results, spectra are deconvolved for the instrument function using a Fourier transform technique. The results are compared with low-resolution, room temperature measurements on methane and with absorption coefficients derived from methane features observed in spectra of the outer planets and Titan.

Laboratory measurements of absorption coefficients for the 727 nm band of methane at 77 K and comparison with results derived from spectra of the Giant planets

Abstract A high resolution absorption spectrum of the 727 nm band of methane at 77 K is obtained using the intracavity laser spectroscopy technique. Absorption coefficients are determined and are reported as averages over 1 cm−1 intervals throughout the region 13,470–14,025 cm−1. An intensity of 753 cm−1 km−1 am−1 is obtained for the entire band. Positions of the vibration-rotation lines in this band are determined to an accuracy of ±0.02 cm−1 and, for the stronger lines, absorption coefficients at the center of the absorption line are reported. The results are compared with previous room temperature measurements on methane, with the gas phase band intensity calculated from measurements on liquid methane, and with absorption coefficients derived from methane features observed in the albedo spectra of the Giant planets and Titan.

Measurement of pressure-broadening and lineshift coefficients at 77 and 296 K of methane lines in the 727 nm band using intracavity laser spectroscopy

Abstract Pressure-broadening coefficients and pressure-induced lineshifts of several rotational- vibrational lines have been measured in the 727 nm absorption band of methane at temperatures of 77 and 296 K, using nitrogen, hydrogen, and helium as the foreign-gas collision partners. A technique involving intracavity laser spectroscopy is used to record the methane spectra. Average values of the broadening coefficients (cm -1 atm -1 ) at 77 K are: 0.199, 0.139, 0.055, and 0.29 for collision partners N 2 , H 2 , He, and CH 4 , respectively. Typical average values of the pressure-induced lineshifts (cm -1 atm -1 ) at 77 K and for the range of foreign gas pressures between 10 and 200 torr are -0.052 for N 2 , -0.063 for H 2 , and +0.031 for He. All the values obtained at 296 K are considerably different from the corresponding values at 77 K. This represents the first report of pressure-broadening and shifting coefficients for the methane transitions in a region where the Δ v C-H = 5 band occurs.

Cyber Security Issues for Protective Relays; C1 Working Group Members of Power System Relaying Committee

This report covers issues concerning the security of electronic communication paths to protection relays. It is the goal of this paper to present the reader with some background material and discussions by which they can become more aware of the concerns associated with electronic communications in the power industry.

Intensity measurements of methane lines in the 727 nm band studied by intracavity laser spectroscopy at temperatures down to 77 K

Abstract A time-resolved, quasi-cw form of intracavity laser absorption spectroscopy has been used to measure intensities of vibration-rotation lines of methane in the 727 nm region. Temperatures of 77, 195 and 296 K are employed. A 0.68 meter long, low temperature absorption cell, enclosed inside the resonator cavity of a dye laser, has been used to obtain effective absorption pathlengths of 0.6–4.0 km. Intensities of several vibration-rotation methane lines obtained by directly fitting Voigt profiles to the absorption lines are reported for the first time for absorption in the 727 nm band.

Justifying pilot protection on transmission lines

This paper concerns the justification of the use of pilot protection on transmission lines.

Redundancy considerations for protective relaying systems

The basic concept of redundancy is simple. Instead of relying on a single piece of equipment, there are duplicate or triplicate sets that perform the same function. Consequently, if one piece of equipment fails, the function will still be performed by a redundant device. Redundancy of components plays a major role in elevating the reliability of protection systems. The impact on the power system when a protection device is not functioning when required is much less severe when there is a redundant device that takes over the job. If the redundant devices are of equal performance, there should be no detrimental effect at all on power system operations, and a non-functioning device would just need to be repaired or replaced. While local redundancy is generally applied, it is not the only mitigation that can be used to improve reliability. Remote protection systems may provide adequate protection system reliability in some situations, provided that remote protection can detect faults and provide clearing times that meet performance requirements. Different users have different terminology for referring to the redundant protection systems. They may be called “System 1” and “System 2” or “System A” and “System B” or sometimes “Primary” and “Backup.” This latter terminology, “Primary” and “Backup”, implies, although unintentionally, that one of the two systems serves the main function of protection and the other serves to assist in the case of failure of the first system, analogous to carrying an undersized spare tire in the trunk of a car in case of a flat. In actual practice, the redundant systems are each fully capable, each system is able to detect and clear faults on its own, and each system serves as a backup to the other. Note that this paper is a summary of the full report. The report will be available on www.pes-psrc.org – Published Reports – in May-June of 2010.

Hα (balmer) spectral profiles obtained from H2 rf plasma discharges studied by intracavity laser spectroscopy

Hα (Balmer) spectral absorption profiles are obtained for 13.56 MHz rf discharges of hydrogen at pressures from 25 m Torr to 3.0 Torr. The Hα transitions are monitored by intracavity laser spectroscopy using high spectral resolution. Spatially resolved concentrations of atomic hydrogen in the n=2 state (H*) are measured across the region between the power and ground electrode. The H* density distribution follows the glow space. The electron densities are (1–3) × 1010 cm−3. The profiles indicate that the 2S12 and 2P12 states are populated first in the discharges. The system is not in thermodynamic equilibrium but comes closer to it at pressures greater than 500 m Torr.

Absorption coefficients for the 727 nm band of methane at 77 K determined by intracavity laser spectroscopy

Methane spectral features in the visible to near-IR region are prominent in the spectra of the outer planets but laboratory data for the appropriate methane conditions are required to interpret the observational data. By use of the intracavity laser spectroscopy technique, a moderately high resolution (≥500,000) absorption spectrum of the 727 nm band of methane at 77 K is obtained. The methane absorption bands in the visible to near-IR region are very weak, but intracavity laser spectroscopy provides sufficient sensitivity to perform the measurements and to extract quantitative data for methane at low temperatures. Absorption coefficients are determined and are reported as averages at one Å intervals throughout the region 7127–7420 Å. By integrating over the band, an intensity of 753 cm−1 km−1 am−1 is obtained. The results compare well with previous low resolution measurements on methane at room temperature, with gas phase results calculated using the absorption spectrum of liquid methane, and with absorption coefficients derived from methane features observed in the spectra of the outer planets and Titan.

Temperature and population measurements of n = 2 hydrogen atoms in H2RF discharges from Hα (Balmer) spectral profiles obtained by intracavity laser spectroscopy

Abstract Spatially resolved H α (Balmer) absorption profiles are obtained using intracavity laser spectroscopy for 13.56 MHz RF discharges of hydrogen gas at pressures from 25 mTorr to 1.0 Torr. At the high spectral resolution employed, fine structure is observed in the profiles which originate from the three closely spaced levels of n = 2 atomic hydrogen (H ∗ ). The profiles indicate that the H ∗ temperature changes significantly over the pressure range. In the model developed to explain the profiles, two groups of H ∗ are indicated. The sub-states for one H ∗ group are at thermodynamic equilibrium with the walls of the container (≈ 320 K), whereas the sub-states for the other H ∗ group are at higher temperatures (500 to 2500 K) and are not statistically distributed. For the latter H ∗ atoms, the computed temperatures decrease with increasing H 2 pressure. For the pressures and electron densities (≈10 9 –1o 10 cm −3 ) employed, only Doppler broadening needs to be considered in explaining the observed profiles.