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Blagojevic B.,Science and Engineering Services, Inc.
IEEE Sensors Journal | Year: 2010

In this paper, an analytical model of a receiver operating characteristic (ROC) curve for digital fluorescence lidar sensing of an aerosol biowarfare agent (BWA) simulant in the presence of a single aerosol interferent is presented. The BWA simulant and interferent are characterized by their concentrations, particle size distributions, fluorescence cross sections, and complex refractive indexes. The ROC curve calculation is performed for simulant and interferent lidar signals that are plotted in a biodiscrimination plane defined by normalized particle size ratio $X$ and particle fluorescence ratio $Y$. Probability density functions (PDFs) of BWA simulant and interferent in the biodiscrimination plane are due to finite signal-to-noise lidar measurements. These functions are modeled with a joint distribution density function of $X$ and $Y$ as correlated variables. The $X$ and $Y$ variables are calculated from the corresponding lidar equations that compute signal and noise from elastic backscatter and fluorescence cross sections, the concentration of aerosol particles, and lidar optical system parameters. Elastic backscatter is calculated from Mie scattering theory using a particle size distribution approximated by a log-normal distribution. Fluorescence cross sections of BWA simulant or interferent aerosols given in the literature are approximated as being independent/dependent from particle size distribution in the model. Each point of the ROC curve of BWA simulant in the presence of an interferent is defined as the integral of the interferent PDF over the elliptical contour projection of BWA simulant PDF in the biodiscrimination plane for a fixed threshold of aerosol cloud detection, and thus, a fixed probability of aerosol cloud detection. Presented ROC curve method can be generalized to the case of the simultaneous presence of several interferents to the discrimination of one BWA simulant. Calculated elliptical contour projections of the bioaerosol PDF in the biodiscrimination plane, and corresponding ROC curves are computed and presented for the parameters of an experimental lidar that was tested during BWA simulant and interferent aerosol cloud releases, where aerosol cloud particle concentrations and size distributions were also measured. When the number and identity of interferents and their corresponding concentrations are unknown, the ROC curve can be estimated by assuming a constant bioaerosol PDF in the biodiscrimination plane. © 2006 IEEE.


Li G.,Masstech, Inc. | Lei J.,Science and Engineering Services, Inc. | Prasad C.,Science and Engineering Services, Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Formaldehyde is a trace species that plays a key role in atmospheric chemistry. It is an important indicator of nonmethane volatile organic compound emissions. Also, it is a key reactive intermediate formed during the photochemical oxidation in the troposphere. Because the lifetime of formaldehyde in the atmosphere is fairly short (several hours), its presence signals hydrocarbon emission areas. The importance of measuring formaldehyde concentrations has been recognized by the National Academy's Decadal Survey and two of NASA's forthcoming missions the GEO-CAPE and GACM target its measurement. There are several techniques some of which are highly sensitive (detection limit ∼ 50 parts-per-trillion) for in-situ measurement of formaldehyde and many reported atmospheric measurements. However there appear to be no reported standoff lidar techniques for range resolved measurements of atmospheric formaldehyde profiles. In this paper, we describe a formaldehyde lidar profiler based on differential laser induced fluorescence technique. The UV absorption band in the 352 - 357nm is well suited for laser excitation with frequency tripled Neodymium lasers and measuring the strong fluorescence in the 390 - 500nm region. Preliminary nighttime measurements of formaldehyde were demonstrated with a lidar using a commercial Nd:YAG laser (354.7 nm) with a rather large linewidth (∼.02 nm). The measured sensitivity was ∼1 ppb at 1 km with 100 meters range resolution even with this non-optimized system. In this paper we describe our approach for increasing the sensitivity by many orders and for daytime operation by improving the laser parameters (power and linewidth) and optimizing the receiver. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).


Shi W.,Masstech, Inc. | Li G.,Masstech, Inc. | Prasad C.,Science and Engineering Services, Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Water vapor is the most important atmospheric greenhouse gas, but its variability and distribution, particularly the vertical profile, are not well known due to a lack of reliable long-term observations in the upper troposphere and stratosphere. Additional design and testing is necessary to extend Water Vapor Sensor System (WVSS) sensitivity to water vapor from a threshold of 100 ppmv to 2.8 ppmv to support operational and climate applications. Laser photoacoustic spectroscopy (LPAS) technique can extend the sensitivity to this level without extending absorption chamber path or using expensive laser emitting at stronger absorption line. A laser photoacoustic spectroscopy sensor based on inexpensive telecommunication style packaged, fiber-coupled near IR distributed feedback (DFB) laser diodes was developed to quantify concentrations of water vapor (H2O), CO2, and methane in ambient air. The LPAS sensor assembled in a compact package was designed for airborne, real-time measurements of atmospheric components. A resonant photoacoustic cell is used to increase the photoacoustic signal, electrical modulation is applied to replace mechanical chopper, and wavelength modulation spectroscopy is used to minimize the interfering background signal from window absorption in the sample cell. The minimum detection sensitivities (1σ) of 5 ppm at 1.39 μm (5 mW) for water vapor, 6 ppm at 1.6 μm (15 mW) for CO2, and 3 ppm at 1.6 μm (15 mW) for methane, are reported. © 2012 SPIE.


Patent
Science and Engineering Services, Inc. | Date: 2011-06-24

A mass spectrometry (MS) method which includes generating in a vicinity of the quadrupole ion trap hydrogen molecules, directing at least part of the hydrogen molecules into the quadrupole ion trap cell, applying AC and DC voltages to quadrupole ion trap cell electrodes to create a combined AC/DC trapping field, placing sample ions inside the quadrupole ion trap cell, cooling at least part of said ions using said hydrogen molecules as a buffer gas, changing the combined AC/DC trapping field to eject the ions from the quadrupole ion trap cell, and detecting the ejected ions


Patent
Science and Engineering Services, Inc. | Date: 2010-05-21

A method for fragmentation of analyte ions for mass spectroscopy and a system for mass spectroscopy. The method produces gas-phase analyte ions, produces gas-phase odd-electron containing species separately from the analyte ions, and mixes the gas-phase analyte ions and the odd-electron containing species at substantially atmospheric pressure conditions to produce fragment ions prior to introduction into a mass spectrometer. The system includes a gas-phase analyte ion source, a gas-phase odd-electron containing species source separate from the gas-phase analyte ion source, a mixing region where the gas-phase analyte ions and the odd-electron containing species are mixed at substantially atmospheric pressure to produce fragment ions of the analyte ions, a mass spectrometer having an entrance where at least a portion of the fragment ions are introduced into a vacuum of the mass spectrometer, and a detector in the mass spectrometer which determines a mass to charge ratio analysis of the fragment ions.


Patent
Science and Engineering Services, Inc. | Date: 2011-08-19

A device and method for transporting ions along a longitudinal direction in an elevated gas pressure region. The device includes a multipole ion guide having a set of rods positioned along the longitudinal direction on an inscribed diameter equal to or less than 3.5 mm, a voltage source which provides alternating voltages to at least a subset of the rods to create a trapping field in a transverse direction, and a conductance limit having an opening d and placed at the exit of the multipole ion guide. At the end of this configuration near the opening of the conductance limit, a converging continuum gas flow through the conductance limit is provided that transfers the ions collimating near a center of the ion guide into a low gas pressure region. The method injects ions into the elevated gas pressure region of the ion guide, and transports the ions in the converging continuum gas flow into the low gas pressure region.


Patent
Science and Engineering Services, Inc. | Date: 2010-04-07

A measuring cell of an ICR mass spectrometer and a method of operating a measuring cell of the ICR mass spectrometer. The method and system trap ions in a first compartment of the ICR measuring cell by generating an electric potential well in the direction of the magnetic field with a minimum of the electric potential well located inside the first compartment. The method and system excite cyclotron motion of the ions trapped in the first compartment. The method and system transfer at least a part of the excited ions from the first compartment to a second compartment of the ICR measuring cell by displacement of a position of the minimum of the electric potential well from the first compartment to the second compartment. The ions are transferred by displacing the position of the minimum of the electric potential well from the first compartment to the second compartment preferably over a period of time equal to or longer than a characteristic period of ion oscillations along the direction of the magnetic field in the electric potential well. The method and system detect ion cyclotron motion of at least a part of the ions in the second compartment.


Patent
Science and Engineering Services, Inc. | Date: 2010-04-07

A method and system for deconvolution of a frequency spectrum obtained in an ICR mass spectrometer based on a detection of ion oscillation overtones of the M-th order (where the integer M>1). A plurality of frequency peaks is collected within the frequency spectrum corresponding respectively to oscillations of different groups of ions, and associates at least one of the frequency peaks having a frequency f and a measured amplitude A with a particular group of the ions. The method and system identify whether the frequency peak is related to one of an overtone frequency, a subharmonic frequency, a higher harmonic frequency, or a side-shifted frequency of the oscillations of the different group of ions. The method and system derive calculated amplitudes of the overtone frequency peaks associated with the groups of ions by incorporating measured amplitudes of the frequency peaks related to the subharmonic frequency, the higher harmonic frequency, or the side-shifted frequency associated with the groups of ions into the calculated amplitudes of the overtone frequency peaks. The method and system generate a deconvoluted frequency spectrum including the overtone frequency peaks associated with the different groups of ions.


Patent
Science and Engineering Services, Inc. | Date: 2011-09-16

A liquid chromatography interface is provided having an integrated column/ESI tip assembly including a liquid chromatography separation column, an ESI tip for generating ions having at least one emitting channel, and a temperature-controlled enclosure surrounding the liquid chromatography separation column. The enclosure has at least one opening and the ESI tip is exposed outside the enclosure through the opening. The enclosure has a heating or cooling device providing a substantially homogeneous distribution of temperature throughout an internal space of the enclosure where the liquid chromatography separation column is disposed. The enclosure includes at least one gas flow mixing element to permit heat exchange by directing a flow of gas toward the ESI tip. The integrated column/ESI tip assembly resides within a thermo-stabilized volume of substantially the same temperature from an entrance of the liquid chromatography separation column to the outlet of the ESI tip.


Grant
Agency: Department of Defense | Branch: Army | Program: SBIR | Phase: Phase II | Award Amount: 712.98K | Year: 2010

A novel method of using fluctuations in laser backscatter from atmospheric aerosol concentrations to remotely measure wind speed and direction is proposed. Using pulsed laser beams projected from two small spotting telescopes and range gated detectors, we are able to remotely measure 2-D wind vectors at contiguous range intervals along a 3-km targeting range with the accuracy and resolution needed to significantly improve ballistic trajectory prediction and decrease dispersion. The technology is simple, robust, and builds on decades of development by several groups and the principal investigator, using scanning aerosol backscatter lidar. The turbulent flow of air in the lowest layers of the atmosphere insures an abundant supply of airborne aerosols to serve as tracers of atmospheric motion. Innovative SESI lidar technology turns what were previously one-of-a-kind scientific research instruments into a compact, rugged, and affordable operational wind profiling instrument suitable for military and civilian applications. SESI''s Phase II instrument will be a production prototype suitable for use on the Aberdeen Test Center''s various gun test ranges. Versions small enough to be man portable are contemplated for sniper teams, or weapon mounted for howitzers. Civilian applications include airfield wind mapping on a continuous basis and wind surveys needed for developing wind energy farms.

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