Kesavan J.,U.S. Army |
Schepers D.R.,EXCET Inc. |
Bottiger J.R.,U.S. Army |
Bottiger J.R.,EXCET Inc. |
And 2 more authors.
Aerosol Science and Technology | Year: 2013
Bioaerosol detection and identification systems need to be periodically checked for assurance that they are responsive to aerosol challenges. Herein, pressurized metered dose inhalers (pMDIs) containing ethanol suspensions of two simulants for B. anthracis spores are considered for providing suitable aerosols. Doses and shot weights from pMDIs with canisters having volumes equal to that of 200 metering-valve actuations were constant for ≤165 actuations, but drop beyond that range. There were statistically significant dose variations between replicate pMDIs and between two types of actuators used on the pMDIs. The storage halflives of pMDIs filled with Bacillus atrophaeus (BG) and Bacillus thuringiensis subsp. israelensis (Bti) spore formulations are predicted to be 32 and 136 months, respectively, if the canisters are stored under refrigeration (4°C). The prediction is based on use of a logarithmic regression model relating CFU per actuation to storage time, with data taken at times of 1-12 months. Demonstration of the utility of the concept was provided by producing responses from a polymerase chain reaction (PCR) identifier with pMDI-generated BG and Bti aerosols that were collected with a 100 L/min wetted wall bioaerosol sampling cyclone. Copyright © American Association for Aerosol Research.
Kesavan J.S.,U.S. Army |
Bottiger J.R.,U.S. Army |
Bottiger J.R.,Excet Inc. |
Schepers D.R.,Excet Inc. |
Mcfarland A.R.,PE Inc.
Aerosol Science and Technology | Year: 2014
Aerodynamic particle sizer (APS) users typically calibrate the particle sizing capabilities, but not the counting efficiency upon which aerosol concentration results are based. Herein, comparisons were made between the counts provided by an ink jet aerosol generator (IJAG) with those measured by an APS. Near-monodisperse (geometric standard deviation of about 1.06) liquid or solid aerosols in the size range of 0.95 to 13.3 μm aerodynamic diameter (AD) generated with an IJAG were released into the inner inlet-tube of the APS in a manner that rendered APS wall and aspiration losses negligible. For most experiments, the IJAG generated 75 particles/s, which rate was maintained by the IJAG system through control of electrical pulses applied to its ink jet cartridge. For particles in the size range of 2-13.3 μm AD, the ratio of relative detection efficiency (ratio of the number of particles counted by the APS to the number reported as generated by the IJAG) was 99.3 ± 1.4%; however, for test particles between 0.95 and 2 μm AD, the relative detection efficiency was somewhat lower, but the drop off was less than about 2%. This slight drop off is likely associated with the light scattering detection approach and corresponding counting algorithm of the APS. Tests were conducted where the IJAG produced 7.0 μm AD particles at rates of 1 to 500 s -1 and the results showed essentially a 1:1 correspondence between IJAG and APS counts. The presence of smaller-sized background particles did not affect the measured APS counts of larger-sized challenge particles. Copyright © American Association for Aerosol Research.
Kesavan J.,U.S. Army |
Schepers D.,Noblis |
McFarland A.R.,PE Inc.
Aerosol Science and Technology | Year: 2010
Four commercially available batch-type bioaerosol samplers, which collect time-integrated samples in liquids, were evaluated. Sampling efficiency was characterized as a function of particle size using near-monodisperse polystyrene spheres (sizes of 1-5 μm) and oleic acid droplets (3-10 μm). Results show the sampling efficiency of AGI-30 impingers range from 4-67% for particle sizes of 1 to 5.1 μm with significant variations between units; those of SKC BioSampler impingers range from 34-105% for particle sizes from 1 to 9 μm; those of a batch-type wetted wall cyclone with compensation for evaporation (BWWC-EC) range from 5 to 65% for particle sizes 1 to 10 μm; and, those of a batch-type wetted wall cyclone with no evaporation compensation (BWWC-NC) range of 55 to 88% for particle sizes of 1-8 μm. Retention efficiency was measured for 1 and 10 μm polystyrene spheres. For the AGI-30 and BWWC-EC, the retention efficiency of 1 μm particles after 1 h was less than 30%, while that of the SKC BioSampler was 59%. Due to liquid evaporation, the BWWC-NC could not be operated for 1 h. Retention efficiencies for Bacillus atrophaeus spores and Pantoea agglomerans vegetative cells were measured for the AGI-30 and the SKC BioSampler. Results for the spores were about the same as those for 1 μm non-viable polystyrene particles; however, the vegetative bacteria lose culturability and consequently show lower retention efficiencies. For the impingers, significant performance differences were observed in units delivered by vendors at different times. © American Association for Aerosol Research.
Hubbard J.A.,University of Texas at Austin |
Haglund J.S.,University of Texas at Austin |
Ezekoye O.A.,University of Texas at Austin |
McFarland A.R.,Texas A&M University |
McFarland A.R.,PE Inc.
Aerosol Science and Technology | Year: 2011
Advances in microfluidic, lab on chip, and other near-real-time biological identification technologies have driven the desire to concentrate bioaerosols into hydrosol sample volumes on the order of tens of microliters (μL). However, typical wet biological aerosol collector outputs are an order or two of magnitude above this goal. The ultimate success of bioaerosol collectors and biological identifiers requires an effective coupling at the macro-to-micro interface. Liquid collection performance was studied experimentally for a family of dynamically scaled wetted wall bioaerosol sampling cyclones (WWCs). Steady-state liquid collection rates and system response times were measured for a range of environmental conditions (temperatures from 10°C to 50°C and relative humidities from 10% to 90%), liquid input rates, and WWC airflow configurations. A critical liquid input rate parameter was discovered that collapsed all experimental data to self-similar empirical performance correlations. A system algorithm was then developed from empirical correlations to provide control over the liquid output rate and resulting concentration factor for a cyclone with an airflow rate of 100 L/min. Desired liquid output rates of 25 to 50 μL/min were maintained while sampling outdoor air over diurnal ranges of environmental conditions. These flow rates are associated with concentration factors on the order of 1,000,000 to 2,000,000 and liquid outputs that are a steady stream of 10 to 30 drops/min of 7 to 10 μL droplets. These developments should allow wetted wall cyclones to be effectively coupled to advanced biological identification systems. © American Association for Aerosol Research.
Zamani N.,P.E. Inc. |
Zamani N.,Southern Methodist University |
El Shamy U.,Southern Methodist University
International Journal of Geomechanics | Year: 2013
In this study, a three-dimensional microscale framework utilizing the discrete-element method (DEM) is presented to analyze the seismic response of soil-foundation-structure systems subjected to three-directional base motion. The proposed approach is employed to investigate the response of a single lumped mass on a square spread footing founded on a dry granular deposit. The soil is idealized as a collection of spherical particles using DEM. The spread footing is modeled as a rigid block composed of clumped particles, and its motion is described by the resultant forces and moments acting upon it. The structure is modeled as a column made of clumped particles with a concentrated mass specified for the particle at the top. Analysis is done in a fully coupled scheme in time domain while taking into account the effects of soil nonlinear behavior, possible separation between the foundation base and soil because of rocking, possible sliding of the footing, and dynamic soilfoundation interactions.Atechnique to idealize several base boundary conditions to mimic rigid and elastic rock as well as an infinite medium is also presented. Microscale energy dissipation in the soil deposit in the free field and in the presence of the structure is quantified. Simulations were conducted to investigate the response of the deposit with and without the structure to various scenarios of multidirectional shaking patterns. Vertical motion amplification in the free field was similar to that of shear wave propagation. However, there was less nonlinearity for vertical motion than there was for horizontal motion. Lateral motion had a small impact on the amplification of the vertical input motion. The inclusion of vertical motion did not influence the amplification of horizontal motion at frequencies far from the resonance frequency of vertical motion. © 2013 American Society of Civil Engineers.
Huffmaster M.,PE LLC |
Maldonado F.,Criterion Catalysts
Sulphur 2014 30th International Conference and Exhibition | Year: 2014
The Tail Gas Unit (TGU) process has been developed to remove sulfur compounds from Claus tail gas in order to comply with stringent emission regulations. From the early 1970s to today TGUs have been improved to meet higher levels of performance for ever tighter environmental requirements and to reduce capital or operating cost. Reactor performance is a critical parameter in achieving TGU environmental performance. Conversion of sulfur species to H2S is a function of catalyst activity, reactor space velocity and temperature. Reactor modeling, process chemistry and chemical equilibrium influence tail gas unit performance and provide a framework to examine the effects of space velocity and temperature. Assessment of the impact of these principal variables on both catalyst bed design and performance is the subject of this paper. Copyright © 2012 CRI/Criterion Inc. All rights reserved.
Yildirim Y.,Atatürk University |
Parish R.L.,PE LLC
Applied Engineering in Agriculture | Year: 2013
Single-disc rotary fertilizer spreaders are principally used to obtain a full fertilizer distribution pattern. These spreaders also can be used for banding application if the spreader disc is simultaneously fed by two orifices with the same shape and size. Using two orifices at the opposite angular position of 180° and the proper angular position with respect to travel direction resulted in two bands on opposite sides of the spreader. The single-disc spreader used for this study was evaluated for spreader disc height and PTO speed to control the spacing between the two bands and bandwidths. Spreader disc heights of 38, 56, and 75 cm and PTO speeds of 270, 405, and 540 rpm were used to demonstrate the effects of these variables on band spacing and width. Using triple superphosphate, band spacings from 4 to 11 m and bandwidths from 4 m left/4 m right to 9.5 m left/9.5 m right were obtained. The effect of PTO speed was more pronounced than the effect of spreader disc height for both band spacing and bandwidth. The effect of spreader disc height on both left and right bandwidth was not proportional. © 2013 American Society of Agricultural and Biological Engineers ISSN 0883-8542.
King M.D.,Texas A&M University |
McFarland A.R.,Texas A&M University |
McFarland A.R.,PE Inc.
Aerosol Science and Technology | Year: 2012
Contemporary near-real-time bioaerosol identifiers that read labeled DNA require a minimum DNA length of about 500,000 base pairs; and for critical applications, instrumental identification results must be verified through the use of classical microbiological culturing techniques. A 300 L/min Wetted Wall Cyclone (WWC) and an 800 L/min inertial impactor were used in a comparative study to collect aerosolized single cells of Escherichia coli (E. coli) at temperatures of 24°C and 46°C. Classical microbiological plating techniques showed that the culturability of E. coli collected with a WWC is a factor of about 100 higher than that of the impactor when the sampled aerosol is at room temperature (RT) and a factor of about 4000 higher when the sampled aerosol is at 46°C. DNA integrity was qualitatively evaluated with pulsed field gel electrophoresis (PFGE) and photographic evidence shows a significant difference in the amount of high molecular weight DNA (molecules larger than 500,000 base pairs) collected with the WWC compared with the impactor. Extracted DNA was also digested by the NotI enzyme, and the qualitative results of the restriction analysis showed there to be high integrity of the WWC-collected DNA, whereas the impactor-collected DNA showed considerable fragmentation. Real-Time polymerase chain reaction (RT-PCR) showed samples required for E. coli identification need to be about 100 times more concentrated if they are collected with the impactor rather than that of the WWC. Also, it appears that only the intact genomic DNA of the culturable cells provides adequate templates for traditional and RT-PCR amplification. 2011 08 16.