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Experimental work was carried out to study the effect of surface enhancement on the crystallization fouling in a double pipe heat exchanger under forced convective heat transfer. The experiments were performed using a hot fluid (salt solution) that had a temperature of 40 °C and Reynolds number range between Re h = 5300 and 20,000. The normal solubility salt (sodium sulfate, Na 2 SO 4 ) was used at its saturation concentration. The temperature of the cold fluid (distilled water) was 10 °C and Reynolds number (Re c ) range was between 13,000 and 22,000. The cold fluid was pumped through the inner tube and the hot fluid was pumped counter currently through the outer tube. This caused the sodium sulfate to precipitate on the outside surface of the tube. The impact of scale fouling on the heat transfer coefficient and fouling resistance was investigated for both a smooth and an enhanced surface. The effect of surface enhancement on the fouling process was studied by installing a coiled wire insert on the inside or outside surface of the inner tube. The results revealed that the surface enhancement increased the heat transfer rate by 150%–80% depending on Re h and Re c . In addition, it significantly decreased the fouling resistance (R f ). It was found that installing the coiled wire insert onto the outer surface of the inner tube is more effective in reducing fouling resistance than installing it on the inside surface of the inner tube. At low Re c and Re h , the surface enhancement is more effective in reducing fouling than at higher Re c and Re h . The reduction in fouling resistance due to the surface enhancement was up to 86% at low Re c and Re h and 46% at high Re c and Re h .

This paper describes an adaptive quarter wave tube used to attenuate a tone from the exhaust noise of a large diesel engine. A sliding-Goertzel algorithm was used to calculate the phase angle of the transfer function between a microphone in the adaptive quarter wave tube and in the main exhaust duct. The control system adjusted the length of the adaptive quarter wave tube until the phase angle was 90 and caused the sound pressure level at the cylinder ring frequency in the exhaust duct to be minimized. The system was able to adapt to changes in engine speed, exhaust gas temperature, and load applied to the engine. The results demonstrate that the sliding-Goertzel algorithm can be used eectively to estimate the phase angle in an adaptive

It is well known that the acoustic performance of silencing elements decreases with an increase in exhaust gas flow. Tests were conducted on three orifice geometries of side-branches on an adaptive quarter-wave tube to determine which was the least compromised by the high-speed exhaust gas passing over the side-branch. The side-branch geometries that were tested were a sharp edge, a backward inclined branch, and a bell mouth. The experimental results show that the side-branch with a bell-mouth geometry resulted in the greatest noise reduction by an adaptive quarter-wave tube.

Crystallization fouling experiments were performed in a channel for a cross flow of hot saturated sodium sulphate (Na 2 SO 4 ) solution over a pipe containing cold water. The heat transfer coefficient and fouling thermal resistance were determined from measurements of local surface temperature and the thickness of the crystalline fouling layer. A systematic assessment of the asymptotic variation of these parameters with time was obtained for a range of hot salt solution Reynolds number based on pipe diameter ( Re hD ) of 165–485, salt solution bulk temperature of 30 °C–50 °C, and cold water (at 5 °C) Reynolds number in the pipe ( Re c ) of 7500–25000. It was found that the temperature of the salt solution has a large effect on the fouling rate. Increasing the pipe surface temperature decreases the crystallization fouling rate. Increasing the hot solution Reynolds number, via the velocity, decreases the fouling thermal resistance, while increasing the cold water Reynolds number, via the velocity, decreases the fouling thermal resistance, but at the same time it increases the fouling layer thickness. The crystallization process that applies here was found to be under activation control (i.e. chemical kinetic control) so that the mass transport of salt plays only a minor role.

Epithermal/thermal boron neutron-capture therapy (BNCT) is a promising treatment method for malignant tumors. Because the doses and dose rates for medical therapeutic radiation are very close to the normal tissue tolerance, small errors in radiation delivery can result in harmful overdoses. A substantial need exists for a device that will monitor, in real time, the radiation dose being delivered to a patient. Pacific Northwest Laboratory (PNL) has developed a scintillating glass optical fiber that is sensitive to thermal neutrons. The small size of the fibers offers the possibility of in vivo dose monitoring at several points within the radiation field. The count rate of such detectors may approach 10 MHz because the lifetime of the cerium activator is fast. Fluxes typical of those in BNCT (i.e., 10/sup 9/ n/cm/sup 2//sec) may be measured with a single fiber because of this potentially high count rate and the small diameter of the fiber. >

We demonstrate the conversion of a time-varying (50-400-MHz) electrical current into an optical power with fidelity 0.8 dB (1.35 dB after correction for detection efficiency) beyond the standard quantum limit by drive-current modulation of an injection-locked quantum-well laser.

High power InGaAs multi-mode broad area semiconductor lasers emitting between 190 nm and 980 nm are required as optical pumps for Er+ and Yb+ doped double clad fiber lasers and amplifiers. In this paper, we present performance and reliability of two generations of 100 micrometer aperture broad area devices emitting at 920 nm and 970 nm. The first generation devices have been deployed in the field with up to 2.5 W ex-facet optical power. More than 500,000 device-hrs of actual multi-cell lifetest data, and nearly 100 million accelerated device-hrs have been accumulated with 91FIT at 1.2W and 25 degrees Celsius or 1.9 million hrs MTBF at 2W and 25 degrees Celsius. A next-generation design further reduces thermal resistance, optical loss, and far-field divergence resulting in up to 4W ex-facet CW output power with superb reliability. Multi-mode fiber coupled modules demonstrate high coupling efficiency due to the reduced divergence angles of the new design. Lifetest of the new generation devices demonstrate the reliability of 167 FIT at 2W and 25 degrees Celsius or 499,000 hrs MTBF at 4W and 25 degrees Celsius.

The ability to collect broadband spectroscopic information about chemical analytes is highly desirable. We report on a technique that combines chemically selective coatings and optical spectroscopy. A 1-meter fiber 150 micrometers in diameter has approximately 5 cm2 surface area. This entire surface is used by incorporating selective moieties into the fiber cladding. The Large-Area Chemical Sensor concept for chemical sensing and measurement is based on a combination of three techniques. Specifically, it uses: (1) optical waveguides as the sensor substrate, (2) selectively adsorbing or absorbing materials to concentrate the target materials, and (3) spectroscopic interrogation for verification and quantification. The concept has been demonstrated for an iodine sensor by co-polymerizing methyl, phenyl siloxane into di-methyl siloxane. The phenyl group forms a charge-transfer complex with iodine which has an absorption at ca. 500 nm. Fused silica is the waveguide core. This system provides sensitivities in the 10-ppm range. The concept has been implemented into a prototype field iodine sensor unit. Work on the sensor concept continues with the goal of improving the sensitivity by allowing each photon multiple opportunities to interact with a target molecule.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In a conventional FTIR, the spectral content of the light is analyzed by a Michelson interferometer or other interferometer with a moving arm. The transmitted light intensity is measured by a wavelength-insensitive detector. The interferogram derived from a Michelson interferometer lies in the temporal domain. An alternative method for obtaining the interferogram involving no moving parts is demonstrated. For this, the interferogram lies in the spatial domain. This concept has many applications to sensor systems, for instance, forming a low-cost demodulator for Bragg-grating systems or field-portable spectrometers.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pacific Northwest National Laboratory is developing a fiber optic grating sensor demodulator using a low cost static Fourier-transform interferometer. The spectrometer uses a fiber optic source and a plane mirror to form an interferogram in the spatial domain that is recorded by a linear photodiode array detector. Using this instrument with an interferogram fringe spacing of 20 microns provides fiber grating strain resolution of about 700-microstrain.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High power single-mode AlGaAs semiconductor lasers operating between 820 nm and 860 nm (SDL-5400 series diodes) have been successfully qualified for deployment in many free-space inter-satellite communication link programs. Traditionally these high power devices did not have sufficient bandwidth for direct high speed modulation because of large device and package parasitics. We have improved the device parasitics of the SDL-5430 laser diode, i.e. reduced the RC product, from 240 ps to about 40 ps. The initial measurements indicate that this device (SDL-5480) is suitable for high power optical inter-satellite link (OISL) applications at data rates greater than 1 Gbit/s. The preliminary life test indicates that the new device has better a reliability than the previous design.

Pacific Northwest National Laboratory is developing a large- area, fiber-optic chemical sensor that combines chemically selective coatings and optical spectroscopy. This is a potentially hyphenated sensing technique because of the ability to collect broadband spectroscopic information in addition to sensing the quantity of the target species. Selective compound coating of optical waveguides enables the production of chemical sensors in large lot sizes. This paper describes the progress to date to produce iodine vapor selective fiber sensors that use through the fiber absorption spectroscopy. Spectra have been collected on uncalibrated I2/N2 gas mixtures using visible light.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We review data on the high temperature operation of a high speed data link operating at 1 micrometer wavelength. The single mode fiber packaged transmitter consists of an 'uncooled' high speed laser diode packaged with a commercial laser driver chip and operates at data rates up to 1.2 Gbit/s. The single mode fiber packaged receiver consists of a high speed photodiode packaged with a combination of a commercial transimpedance amplifier and a limiting amplifier. The link operates with high stability and very low error rates without an optical isolator. The maximum data rate and the minimum link sensitivity are currently limited by the electronic component design.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We describe advances in the development of high-power diffraction-limited lasers for single- mode fiber-coupled sources. The development of the tapered amplifier has led to the realization of a monolithic MOPA diode laser, which provides up to 3 W cw of single-spatial- mode output power. We further describe the implementation of the MOPA in fiber-coupled architectures that provide up to 1.2 W cw coupled into a single-mode optical fiber and some of the optical considerations unique to devices based on tapered amplifiers.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present data on the wide temperature operation of a high speed data link operating at nominally 1 micrometer wavelength. The single mode fiber packaged transmitter running at 1.2 GBit/s consists of a high speed laser diode packaged with a commercial laser driver chip. The laser is not cooled in any manner over the temperature range of operation and the link operates with low error rates without an optical isolator. The single mode fiber packaged receiver consists of a high speed photodiode packaged with a combination of a commercial transimpedance amplifier and a limiting amplifier.

Pacific Northwest Laboratory (PNL) has fabricated cerium-activated lithium silicate scintillating fibers via a hot-downdraw process. These fibers typically have a operational transmission length (e-1 length) of greater than 2 meters. This permits the fabrication of devices which were not possible to consider. Scintillating fibers permit conformable devices, large-area devices, and extremely small devices; in addition, as the thermal-neutron sensitive elements in a fast neutron detection system, scintillating fibers can be dispersed within moderator, improving neutron economy, over that possible with commercially available 3He or BF3 proportional counters. These fibers can be used for national-security applications, in medical applications, in the nuclear-power industry, and for personnel protection at experimental facilities. Data are presented for devices based on single fibers and devices made up of ribbons containing many fibers under high-and low-flux conditions.

Pacific Northwest Laboratory is developing a large-area chemical sensor that combines chemically selective coatings and optical spectroscopy to detect target compounds. The chemically selective material is incorporated into the cladding of an optical fiber waveguide. The material is interrogated using optical spectroscopic techniques to determine the concentration of target compounds. The optical interrogation method includes two spectroscopies: visible-near infrared absorption spectroscopy and Raman spectroscopy. This work develops the physical and mathematical models of such a sensor and provides a set of tools with which to make design predictions for the large-area chemical sensors. The theoretical relationships derived herein allow the use of bulk absorption parameters and bulk Raman coefficients to predict sensor performance.

Pacific Northwest Laboratory (PNL) has fabricated cerium-activated, lithium-silicate glass scintillating fiber neutron sensors via a hot-downdraw process. These fibers typically have a transmission length (e{sup {minus}1} length) of greater than 2 meters. The underlying physics of, the properties of, and selected devices incorporating these fibers are described. These fibers constitute an enabling technology for a wide variety of neutron sensors.

The reliability of high power continuous-wave (CW) 1 cm monolithic AlGaAs (808 nm) laser diodes is extensively investigated. Lasers with two total aperture sizes, 1800 micrometers and 3000 micrometers , are life tested at power levels of 10 W and 20 W, respectively for 1500 hours to 4000 hours at 30 degree(s)C heatsink temperature. These lasers exhibit no failures during the lifetests (total device hours of 45,000 hours for the 10 W lasers and 42,000 hours for the 20 W lasers). We demonstrate a mean time between failures (MTBF) exceeding 50,000 hours and a median life (ML) of 40,000 hours for the 10 W laser diode and a MTBF over 48,000 hours and a ML of 13,000 hours for the 20 W laser diode.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The SDL-5400 series commercial AlGaAs laser diode was characterized and screened for potential use as communication laser in the SILEX program. The lasers were initially tested through environmental extremes and for vacuum reliability to obtain preliminary indications that the laser was suitable to the requirement. Potential flight lasers were then built and screened for use. Endurance testing of samples from the potential flight lot has been completed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Long duration life tests of approximately 6,000 hours on AlGaAs single-mode lasers operating at 200 mW and 50 degree(s)C indicate that high reliability can be obtained under these conditions. The projected median life is 140,000 hr and MTBF is 100,000 hr. These results compare favorably with data from other material systems.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Prior work has shown that there is a correlation between trap densities and scintillation efficiency of cerium-activated, lithium-aluminosilicate glasses. Raman spectroscopy has strongly suggested that phase separation may be playing an important role in governing the scintillation efficiency. In this study, we relate the thermoluminescence glow-curve data and microstructural analysis for a compositional series. The thermoluminescence data provide information about the traps in the neighborhood of the activator (Ce3+). The microscopy and crystallization of the glasses provide direct evidence of activator partitioning.

Pacific Northwest Laboratory (PNL) has fabricated cerium-activated lithium silicate scintillating fibers via a hot-downdraw process. These fibers, which, as produced, typically have a transmission length (e−1 length) of greater than 2 meters, are found to undergo aging when subjected to room air. The aging, which is complete in a few weeks, reduces the transmission length to the order of 0.5 meter. Because of the high alkali content of the glass (on the order of 20-30 mole % lithia), we have attributed this aging to aqueous corrosion at the polymer cladding/glass interface. Changes in transmission with chemical treatment of the surface support the corrosion model. Fiber transmission performance has been preserved by modifying the hot-downdraw to a double crucible to produce glass-on-glass waveguides.

Results are presented on catastrophic damage limits and life-test measurements for four types of high-power laser diodes operating at wavelengths between 980 nm and 690 nm. The laser diodes under consideration are CW multimode lasers, CW laser bars, quasi-CW bars/2D stacked arrays, and single transverse mode lasers.

Spectral properties of commercially available Fabry-Perot and distributed Bragg reflector (DBR) GaAlAs and InGaAs laser diodes operating under deep current modulation are presented. At kHz modulation frequencies spectral widths of commercial diodes are 2.5 nm 15 dB down from the maximum intensity. Structural modifications can narrow this value to 0.4 nm. Prototype DBR devices with maximum output power of 110 mW exhibit extremely narrow CW linewidths of 4 MHz, and are suitable for coherent communication as well as direct detection communication formats.

Most neutron detection sensors presently employ 3He gas-filled detectors. Despite their excellent performance and widespread use, there are significant limitations to this technology. A significant alternative neutron sensor utilizing neutron-active material incorporated into a glass scintillator is presented that offers novel commercial sensors not possible or practical with gas tube technology. The scintillating optical fiber permits sensors with a multitude of sizes ranging from devices of a single fiber of 150µm to sensors with tens of thousands of fibers with areas as large as 5 m2 depending on the neutron flux to be measured. A second significant advantage is the use of high-speed electronics that allow a greater dynamic range, not possible with gas detectors. These sensors are flexible, conformable and less sensitive to vibration that optimizes the source-to-detector geometry and provides robust performance in field applications. The glass-fibers are sensitive to both gamma-rays and neutrons. However, the coincidence electronics are optimized for neutron to gamma-ray discrimination allowing very sensitive measurements with a low false-alarm rate. Applications include SNM surveillance, material control and accountability (MC&A), safeguard inspections, Pu health physics/bioassay and environmental characterization.

We demonstrate both common electrode and addressable arrays of single mode semiconductor lasers suitable for optical computing and optical data storage. In the common electrode geometry, eight lasers have been fabricated on a single chip which show excellent spectral and power uniformity. Total optical power obtained from this array has been in excess of 1.2 Watts CW. We have also fabricated two and nine element monolithic, individually addressable arrays with emitter spacings between 10 jim and 150 p m. Separately addressed, each element emits in a single spatial mode to greater than 0.1 Watts. For the nine element array, uniformity of better than 1.0 nanometer in wavelength and 1 milliamp in operating current across the array has been obtained. Results on crosstalk and reliability of the arrays are presented.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Existing and planned hydrologic and climatic models have important implications for water resource management in the twenty-first century and, yet, the science of validation of such models is inadequately developed to warrant full reliance on these models. Tools for such validation must be carefully crafted and broadly tested in a critical environment. Here we develop a set of validation tools and a recommended protocal for validation using graphical workstations and the programming language “S” as the key support elements. The protocol is illustrated by an example, and the recommended validation protocol is summarized in Table 1.

We investigated the effects of increasing excitation on the performance of semiconductor laser amplifiers. Amplified spontaneous emission (ASE) is a limitation to the power scaling of these devices. A Rigrod analysis is used to study the effects of ASE on the gain, signal-to-noise ratio and efficiency for different values of injection current, facet reflectivity and input laser intensity. Comparisons are made between bulk and quantum well gain media.

Optical fibers developed for sensor applications often exhibit high optical losses. While these losses may be entirely acceptable for the design application, efforts to improve fiber performance still require loss quantification and the identification of optical loss mechanisms. Existing fiber loss characterization techniques (e.g., optical time domain reflectometry) are generally only appropriate for low loss (communication grade) fibers and may give little or no information on loss mechanisms. At the Pacific Northwest Laboratory, techniques have been developed for the characterization of high-loss (tens of dB per meter) optical fibers which allow discrimination between scattering and absorptive losses. Two techniques are presented. In the "differential scattering" method, differential fiber scattering losses are acquired over the length of the fiber to obtain a scattering loss coefficient. This information combined with a conventional total fiber loss measurement (e.g., using the "cut-back" method) allows inference of the absorptive part of the fiber loss. In the second method, "scanning aperture" characteriza-tion, the fiber is scanned by a moving aperture to yield curves of differential and integral scatter intensity versus length. This curve not only provides corroboration of the previously acquired differential scattering data, but also points out high-loss regions in the optical fiber. Both methods will be fully described. Experimental data on representative fibers will be presented.

We have observed amplitude noise levels as much as 1.8 dB below the Standard quantum limit in the light generated by an external-cavity-stabilized index-guided quantum-well laser operating at room temperature. The measured amplitude noise remains more than 1.5 dB below the Standard quantum limit as the lasing wavelength of this system is tuned from 831 to 841 nm.

High-impedance pump noise suppression was used to generate amplitude squeezing in an index-guided quantum-well laser. Light exhibiting photon-number noise 1.4 dB below the shot-noise limit was observed, and the corresponding polarization properties were examined. Close-coupled laser-detector measurements made with an unsaturated detector revealed 2.9 dB of squeezing.

Operation Intercept was launched along the United States-Mexico border in September of 1969, ostensibly to halt the flow of marijuana, heroin, and dangerous drugs. In reality, however, it was designed not to interdict narcotics but to publicize the new administration's war on crime and force Mexican compliance with Washington's antidrug campaign. With the exception of border residents, the much-heralded operation has been forgotten by most Americans a decade later. But as President Jimmy Carter discovered during his visit in early 1979, Mexicans, and particularly their presidents, have keen memories. Hastily conceived, unilateral programs such as Operation Intercept go far in explaining why.

(1985). Illicit Drug Traffic and U.S.-Latin American Relations. The Washington Quarterly: Vol. 8, No. 4, pp. 105-124.

A high‐power low‐threshold graded‐index separate confinement heterostructure AlGaAs single quantum well laser on Si substrates has been demonstrated for the first time by a hybrid growth of migration‐enhanced molecular beam epitaxy followed by metalorganic vapor phase epitaxy. The quantum well laser showed an output power of more than 400 mW per facet under pulsed conditions. A room‐temperature threshold current of 300 mA was obtained with a differential quantum efficiency of 40% without facet coating. The threshold current density was 550 A/cm2 for a cavity length of 500 μm. These results show the highest peak power reported to date for low‐threshold lasers on Si substrates. The full width at half maximum of the far‐field pattern parallel to the junction was 6°. Threshold current densities as low as 250 A/cm2 were obtained for lasers on GaAs substrates.

Raman-band intensities for sputter-deposited TiO2/SiO2 multilayer coatings are found to exhibit a strong dependence on excitation wavelength of the probe laser. A model based on standing waves within the stack correctly predicts the magnitude and wavelength dependence of the observed enhancements.