Herbert A. Fry

Improved matched-filter detection techniques

Numerous statistical approaches have been developed for small target detection in cluttered environments. Examples include orthogonal background suppression (OBS) where the initial principal components are suppressed, and the clutter matched filter (CMF) where the principal components are weighted by the inverse of the eigenvalues and the latter principal components are discarded. Our research has shown that improved target detection performance can be obtained by combining certain aspects of both OBS and CMF approaches. This is especially true in the presence of limited scene data (finite number of pixels) or an imperfect reference target spectrum. The basis of this idea is to use weighting by the inverse of the eigenvalues (from CMF) for the initial PCs and the uniform weighting for the later PCs (from OBS). Examples of this new technique and comparisons with OBS and CMF will be shown with model data with realistic clutter containing a chemical plume.

High-resolution spectra of the 1(1,1) ← 0(0,0) rotational transition of water in argon and krypton matrices

Abstract The high-resolution spectra of H 2 16 O, H 2 18 O, HD 16 O, HD 18 O, D 2 16 O, and D 2 18 O isolated in argon and krypton matrices are reported in the 10–60 cm −1 region. The high resolution is obtained by observing very dilute mixtures of water in the rare gases. No discrete absorbances attributable to pure argon or krypton are found in this region. In all cases the relative gas—matrix shifts of the isotopimers are consistent with the rotation—translation coupling model. The linewidths are found to correlate with rotation—translation coupling. The integrated intensity of the 1(1,1) — 0(0,0) transition of HDO exhibits a temperature dependence which does not deviate significantly from that expected from a Boltzmann distribution in rigid rotor energy levels.

The use of single crystal rare gas lattices to study homogeneous lineshapes of impurities: SF6 in xenon

Abstract The IR absorption spectrum of SF6 in single crystal xenon has been studied as a function of temperature. Only one trapping site is stable in single crystal xenon and the v3 linewidth for this site is dominated by homogeneous broadening throughout the entire temperature range studied (14–160 K). The v3 linewidth shows an approximate eαT dependence which is inconsistent with either elastic phonon scattering or local phonon modes independently as the dominant dephasing mechanism. The results suggest that dephasing involves both site local and bulk phonon modes with the former dominating at low temperatures and the latter at higher temperatures.

Preferred orientation of guest molecules in low-temperature matrices: SF6 in xenon

Abstract Infrared spectral observations of highly oriented SF 6 molecules on low-symmetry sites in xenon matrices formed at 10 K are reported. This study offers proof of our earlier interpretation of site-symmetry spliting and dynamic averaging of SF 6 in xenon matrices.

Cyro-vibrational spectroscopy of blue copper proteins

Abstract Resonance Raman (RR) and Fourier transform infrared (FTIR) spectra at 12K have been obtained for Pseudomonas aeruginosa azurin, spinach plastocyanin, stellacyanin, and tree laccase. The temperature dependence of the azurin, plastocyanin, and stellacyanin spectra have been recorded as have the RR excitation profiles at 12 K. Room temperature RR spectra have been obtained for azurins from Alcaligenes fecalis, Alcaligenes sp., Bortadella pretussis and Bortadella bronchiseptica; bean plastocyanin; fungal laccase, human ceruloplasmin; and zucchini squash ascorbate squash ascorbate oxidase. Isotope studies employing 63 Cu/ 65 Cu and H/D substitution have been performed on the azurins from Ps. aeruginosa, Alc. fecalis , and Alc. sp . Principal conclusion include the following; The intense RR modes near 400 cm −1 include internal ligand deformations and the Cu-S(cys) stretch, rather than the Cu-S(cys) stretch and Cu-N(his-Im) stretches as previously supposed. The Cu-N(his-Im) stretches are assignable to the ubiquitous feature near 265 cm −1 ,consistent with the frequencies of similar motions in other proteins and in model complexes. Spinach plastocyanin exhibits a frequency shift of 14 cm −1 in its cysteine CS stretching frequency ( ca. 750 cm −1 ) upon freezing of the protein solution, suggesting that extra-protein forces (e.g.,solvent structure, crystallization, or substrate binding.) can influence the conformation of the active site. Above the freezing point of the solvent the plastocyanin RR modes are unusually broad, suggesting either extremely facile due to thermally accessible conformations in the high-temperature form of the active site. No selective enhancement of either the strong or weak RR modes is observed in the S(cys)→ Cu charge transfer excitation profiles of azurin, plastocyanin, or stellacyanin at 12 K. The azurin species other than Ps. aeruginosa exhibit an ‘extra» strong RR peak near 400 cm −1 which is, however, seen to be related to an unresolved shoulder in the 12 K Ps. aeruginosa spectrum. It is therefore unnecessary to invoke higher coordination numbers than four for copper to explain the RR spectra of the azurins other than Ps. aeruginosa . RR peaks appear in the azurin spectrum below 200 K which may be due to methionine C-S stretching modes and Cu-S(met) stretch or methionine C-S-C angle bend. If these low-temperature features are indeed due to such motions,methionine must be closely coordinated to copper in azurin at low temperature. The RR spectra are consistent with a monotonic relationship between the force constant of the Cu-S(cys)bond and the energy of the ligand-field transitions of the various proteins. The isotope studies lead to tentative identification of the RR modes which contain significant contributions from M-L stretches and internal histidine motions. The results provide an initial basis for reliable structural interpretation of the RR spectra of the blue copper proteins.

DIRECT OBSERVATION OF TRANSIENT FLUORINE ATOMS WITH 25-MU M WAVELENGTH-STABILIZED DIODE LASER ABSORPTION

Through the use of continuous diode laser absorption, detection of transient fluorine atoms with an initial number density in the range of 10(14) cm(-3) has been demonstrated. A crucial part of the continuous-detection technique was laser frequency stabilization with a reference cell of atomic fluorine with Zeeman modulation of the absorption lines to generate a feedback signal. Long-term wavelength stability was demonstrated with second-harmonic phase-sensitive detection of the second-derivative signal for periods up to several hours. For determination of the short-term wavelength stability in the range of microseconds to seconds, a transient signal was generated by photolysis of F(2) with an excimer laser at 308 nm. The initial diode laser absorption was compared to a calculated value obtained from the measured excimer laser fluence, the known dissociation cross section of F(2), and the atomic fluorine absorption cross section, which included a statistical population distribution, the finite bandwidth of the laser dode, and the effects of pressure broadening. The observed absorption was approximately 33% less than the calculated value, possibly because of the diode lasers wavelength instability on the time scale of a few seconds, which is consistent with an observed amplitude instability from pulse to pulse when pulsed at 1-10 Hz.

Assessment of infrared remote chemical sensing systems with numerical simulations

A general approach to the evaluation of remote chemical sensors is described that can be used to provide evaluation of the chemical detection in a particular chemical scenario. It will be used to make comparisons of a CO2 laser differential absorption lidar sensor and a passive thermal FTIR sensor. The focus of the study will be to evaluate the advantage of the FTIR sensors spectral coverage and number of frequency channels.

Detection of transient fluorine atoms

A KrF laser with a fluence of 50 mJ/cm2 was used to photolyze either uranium hexafluoride or molecular fluorine, yielding a transient number density of fluorine atoms. The rise and decay of the atomic fluorine density was observed by transient absorption of a 25‐μm Pb‐salt diode laser. To prevent the diode laser wavelength from drifting out of resonance with the atomic fluorine line, part of the beam was split off and sent through a microwave discharge fluorine atom cell. This allowed a wavelength modulation‐feedback technique to be used to lock the diode laser wavelength onto the atomic line. The remaining diode laser beam was made collinear with the excimer laser beam using a LiF window with a 45° angle of incidence to reflect the infrared beam while transmitting most of the uv beam. Using this setup along with a transient digitizer to average between 100 and 200 transient absorption profiles, fluorine atom number densities on the order of 1014 cm−3 in a 1.7 m pathlength were detected. The signal observ...

Continuous emissions monitoring of mixed waste incinerators

A system for the real-time monitoring of emissions from incinerators must be developed which can address the needs of the DOE community and others involved in mixed waste incineration. These needs are an outgrowth of the ever-increasing waste storage problems and the growing concern of the public, as witnessed by the stricter compliance requirements of federal and state agencies, that the products of incineration are hazardous to their health and injurious to the environment. This paper focuses on the technologies being developed here at Los Alamos and other laboratories which address the detection of a broad spectrum of toxic and hazardous chemicals.