Modeling the transport of organic chemicals between polyethylene passive samplers and water in finite and infinite bath conditions.

PubMed

Tcaciuc, A Patricia; Apell, Jennifer N; Gschwend, Philip M

2015-12-01

Understanding the transfer of chemicals between passive samplers and water is essential for their use as monitoring devices of organic contaminants in surface waters. By applying Fick's second law to diffusion through the polymer and an aqueous boundary layer, the authors derived a mathematical model for the uptake of chemicals into a passive sampler from water, in finite and infinite bath conditions. The finite bath model performed well when applied to laboratory observations of sorption into polyethylene (PE) sheets for various chemicals (polycyclic aromatic hydrocarbons, polychlorinated biphenyls [PCBs], and dichlorodiphenyltrichloroethane [DDT]) and at varying turbulence levels. The authors used the infinite bath model to infer fractional equilibration of PCB and DDT analytes in field-deployed PE, and the results were nearly identical to those obtained using the sampling rate model. However, further comparison of the model and the sampling rate model revealed that the exchange of chemicals was inconsistent with the sampling rate model for partially or fully membrane-controlled transfer, which would be expected in turbulent conditions or when targeting compounds with small polymer diffusivities and small partition coefficients (e.g., phenols, some pesticides, and others). The model can be applied to other polymers besides PE as well as other chemicals and in any transfer regime (membrane, mixed, or water boundary layer-controlled). Lastly, the authors illustrate practical applications of this model such as improving passive sampler design and understanding the kinetics of passive dosing experiments. © 2015 SETAC.

Vertical Diffusivities of Active and Passive Tracers

NASA Technical Reports Server (NTRS)

Canuto, V. M.; Cheng, Y.; Howard, A. M.

2010-01-01

The climate models that include a carbon-cycle need the vertical diffusivity of a passive tracer. Since an expression for the latter is not available, it has been common practice to identify it with that of salt. The identification is questionable since T, S are active, not passive tracers. We present the first derivation of the diffusivity of a passive tracer in terms of Ri (Richardson number) and Rq (density ratio, ratio of salinity over temperature z-gradients). The following results have emerged: (a) The passive tracer diffusivity is an algebraic function of Ri, Rq. (b) In doubly stable regimes (DS, partial derivative of T with respect to z > 0, partial derivative of S with respect to z < 0), the passive scalar diffusivity is nearly the same as that of salt/heat for any values of Rq < 0 and Ri > 0. (c) In DC regimes (diffusive convection, partial derivative of T with respect to z < 0, partial derivative of S with respect to z < 0, Rq > 1), the passive scalar diffusivity is larger than that of salt. At Ri = O(1), it can be more than twice as large. (d) In SF regimes (salt fingers, partial derivative of T with respect to z > 0, partial derivative of S with respect to z > 0, Rq < 1), the passive scalar diffusivity is smaller than that of salt. At Ri = O(1), it can be less than half of it. (e) The passive tracer diffusivity predicted at the location of NATRE (North Atlantic Tracer Release Experiment) is discussed. (f) Perhaps the most relevant conclusion is that the common identification of the tracer diffusivity with that of salt is valid only in DS regimes. In the Southern Ocean, where there is the largest CO2 absorption, the dominant regime is diffusive convection discussed in (c) above.

Evaluation of passive diffusion bag samplers, dialysis samplers, and nylon-screen samplers in selected wells at Andersen Air Force Base, Guam, March-April 2002

USGS Publications Warehouse

Vroblesky, Don A.; Joshi, Manish; Morrell, Jeff; Peterson, J.E.

2003-01-01

During March-April 2002, the U.S. Geological Survey, Earth Tech, and EA Engineering, Science, and Technology, Inc., in cooperation with the Air Force Center for Environmental Excellence, tested diffusion samplers at Andersen Air Force Base, Guam. Samplers were deployed in three wells at the Main Base and two wells at Marianas Bonins (MARBO) Annex as potential ground-water monitoring alternatives. Prior to sampler deployment, the wells were tested using a borehole flowmeter to characterize vertical flow within each well. Three types of diffusion samplers were tested: passive diffusion bag (PDB) samplers, dialysis samplers, and nylon-screen samplers. The primary volatile organic compounds (VOCs) tested in ground water at Andersen Air Force Base were trichloroethene and tetrachloroethene. In most comparisons, trichloroethene and tetrachloroethene concentrations in PDB samples closely matched concentrations in pumped samples. Exceptions were in wells where the pumping or ambient flow produced vertical translocation of water in a chemically stratified aquifer. In these wells, PDB samplers probably would be a viable alternative sampling method if they were placed at appropriate depths. In the remaining three test wells, the trichloroethene or tetrachloroethene concentrations obtained with the diffusion samplers closely matched the result from pumped sampling. Chloride concentrations in nylon-screen samplers were compared with chloride concentrations in dialysis and pumped samples to test inorganic-solute diffusion into the samplers across a range of concentrations. The test showed that the results from nylon-screen samplers might have underestimated chloride concentrations at depths with elevated chloride concentrations. The reason for the discrepancy in this investigation is unknown, but may be related to nylon-screen-mesh size, which was smaller than that used in previous investigations.

Calculating the diffusive flux of persistent organic pollutants between sediments and the water column on the Palos Verdes shelf superfund site using polymeric passive samplers.

PubMed

Fernandez, Loretta A; Lao, Wenjian; Maruya, Keith A; Burgess, Robert M

2014-04-01

Passive samplers were deployed to the seafloor at a marine Superfund site on the Palos Verdes Shelf, California, USA, and used to determine water concentrations of persistent organic pollutants (POPs) in the surface sediments and near-bottom water. A model of Fickian diffusion across a thin water boundary layer at the sediment-water interface was used to calculate flux of contaminants due to molecular diffusion. Concentrations at four stations were used to calculate the flux of DDE, DDD, DDMU, and selected PCB congeners from sediments to the water column. Three passive sampling materials were compared: PE strips, POM strips, and SPME fibers. Performance reference compounds (PRCs) were used with PE and POM to correct for incomplete equilibration, and the resulting POP concentrations, determined by each material, agreed within 1 order of magnitude. SPME fibers, without PRC corrections, produced values that were generally much lower (1 to 2 orders of magnitude) than those measured using PE and POM, indicating that SPME may not have been fully equilibrated with waters being sampled. In addition, diffusive fluxes measured using PE strips at stations outside of a pilot remedial sand cap area were similar to those measured at a station inside the capped area: 240 to 260 ng cm(-2) y(-1) for p,p'-DDE. The largest diffusive fluxes of POPs were calculated at station 8C, the site where the highest sediment concentrations have been measured in the past, 1100 ng cm(-2) y(-1) for p,p'-DDE.

Developing a new, passive diffusion sampling array to detect helium anomalies associated with volcanic unrest

USGS Publications Warehouse

Dame, Brittany E; Solomon, D Kip; Evans, William C.; Ingebritsen, Steven E.

2015-01-01

Helium (He) concentration and 3 He/ 4 He anomalies in soil gas and spring water are potentially powerful tools for investigating hydrothermal circulation associated with volca- nism and could perhaps serve as part of a hazards warning system. However, in operational practice, He and other gases are often sampled only after volcanic unrest is detected by other means. A new passive diffusion sampler suite, intended to be collected after the onset of unrest, has been developed and tested as a relatively low-cost method of determining He- isotope composition pre- and post-unrest. The samplers, each with a distinct equilibration time, passively record He concen- tration and isotope ratio in springs and soil gas. Once collected and analyzed, the He concentrations in the samplers are used to deconvolve the time history of the He concentration and the 3 He/ 4 He ratio at the collection site. The current suite consisting of three samplers is sufficient to deconvolve both the magnitude and the timing of a step change in in situ con- centration if the suite is collected within 100 h of the change. The effects of temperature and prolonged deployment on the suite ’ s capability of recording He anomalies have also been evaluated. The suite has captured a significant 3 He/ 4 He soil gas anomaly at Horseshoe Lake near Mammoth Lakes, California. The passive diffusion sampler suite appears to be an accurate and affordable alternative for determining He anomalies associated with volcanic unrest.

Passive sampling of DDT, DDE and DDD in sediments: accounting for degradation processes with reaction-diffusion modeling.

PubMed

Tcaciuc, A Patricia; Borrelli, Raffaella; Zaninetta, Luciano M; Gschwend, Philip M

2018-01-24

Passive sampling is becoming a widely used tool for assessing freely dissolved concentrations of hydrophobic organic contaminants in environmental media. For certain media and target analytes, the time to reach equilibrium exceeds the deployment time, and in such cases, the loss of performance reference compounds (PRCs), loaded in the sampler before deployment, is one of the common ways used to assess the fractional equilibration of target analytes. The key assumption behind the use of PRCs is that their release is solely diffusion driven. But in this work, we show that PRC transformations in the sediment can have a measurable impact on the PRC releases and even allow estimation of that compound's transformation rate in the environment of interest. We found that in both field and lab incubations, the loss of the 13 C 2,4'-DDT PRC from a polyethylene (PE) passive sampler deployed at the sediment-water interface was accelerated compared to the loss of other PRCs ( 13 C-labeled PCBs, 13 C-labeled DDE and DDD). The DDT PRC loss was also accompanied by accumulation in the PE of its degradation product, 13 C 2,4'-DDD. Using a 1D reaction-diffusion model, we deduced the in situ degradation rates of DDT from the measured PRC loss. The in situ degradation rates increased with depth into the sediment bed (0.14 d -1 at 0-10 cm and 1.4 d -1 at 30-40 cm) and although they could not be independently validated, these rates compared favorably with literature values. This work shows that passive sampling users should be cautious when choosing PRCs, as degradation processes can affect some PRC's releases from the passive sampler. More importantly, this work opens up the opportunity for novel applications of passive samplers, particularly with regard to investigating in situ degradation rates, pathways, and products for both legacy and emerging contaminants. However, further work is needed to confirm that the rates deduced from model fitting of PRC loss are a true reflection of DDT transformation rates in sediments.

Comparison between active (pumped) and passive (diffusive) sampling methods for formaldehyde in pathology and histology laboratories.

PubMed

Lee, Eun Gyung; Magrm, Rana; Kusti, Mohannad; Kashon, Michael L; Guffey, Steven; Costas, Michelle M; Boykin, Carie J; Harper, Martin

2017-01-01

This study was to determine occupational exposures to formaldehyde and to compare concentrations of formaldehyde obtained by active and passive sampling methods. In one pathology and one histology laboratories, exposure measurements were collected with sets of active air samplers (Supelco LpDNPH tubes) and passive badges (ChemDisk Aldehyde Monitor 571). Sixty-six sample pairs (49 personal and 17 area) were collected and analyzed by NIOSH NMAM 2016 for active samples and OSHA Method 1007 (using the manufacturer's updated uptake rate) for passive samples. All active and passive 8-hr time-weighted average (TWA) measurements showed compliance with the OSHA permissible exposure limit (PEL-0.75 ppm) except for one passive measurement, whereas 78% for the active and 88% for the passive samples exceeded the NIOSH recommended exposure limit (REL-0.016 ppm). Overall, 73% of the passive samples showed higher concentrations than the active samples and a statistical test indicated disagreement between two methods for all data and for data without outliers. The OSHA Method cautions that passive samplers should not be used for sampling situations involving formalin solutions because of low concentration estimates in the presence of reaction products of formaldehyde and methanol (a formalin additive). However, this situation was not observed, perhaps because the formalin solutions used in these laboratories included much less methanol (3%) than those tested in the OSHA Method (up to 15%). The passive samplers in general overestimated concentrations compared to the active method, which is prudent for demonstrating compliance with an occupational exposure limit, but occasional large differences may be a result of collecting aerosolized droplets or splashes on the face of the samplers. In the situations examined in this study the passive sampler generally produces higher results than the active sampler so that a body of results from passive samplers demonstrating compliance with the OSHA PEL would be a valid conclusion. However, individual passive samples can show lower results than a paired active sampler so that a single result should be treated with caution.

Passive sampler for formaldehyde in air using 2,4-dinitrophenylhydrazine-coated glass fiber filters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levin, J.O.; Lindahl, R.; Andersson, K.

1986-12-01

A method utilizing diffusive sampling of formaldehyde in air has been developed. A glass fiber filter, impregnated with 2,4-dinitrophenylhydrazine (DNPH) and phosphoric acid and mounted into a modified aerosol-sampling cassette, is used for sampling by controlled diffusion. The formaldehyde hydrazone formed is desorbed and determined by high-performance liquid chromatography with UV detection. The sampling rate of the sampler was determined to 61 mL/min, with a standard deviation of 5%. The sampling rate is independent of formaldehyde concentrations between 0.1 and 5 mg/m/sup 3/ and sampling times between 15 min and 8 h. The sensitivity of the diffusive method is approximatelymore » 0.005 mg/m/sup 3/ (5 ppm) in an 8-h sample, and the reproducibility is better than 3%.« less

Diffusive gradients in thin-films (DGT) for in situ sampling of selected endocrine disrupting chemicals (EDCs) in waters.

PubMed

Chen, Wei; Pan, Suhong; Cheng, Hao; Sweetman, Andrew J; Zhang, Hao; Jones, Kevin C

2018-06-15

A passive water sampler based on the diffusive gradients in thin-films (DGT) technique was developed and tested for 3 groups of endocrine disrupting chemicals (EDCs, including oestrogens, alkyl-phenols and bisphenols). Three different resins (hydrophilic-lipophilic-balanced (HLB), XAD18 and Strata-XL-A (SXLA)) were investigated for their suitability as the binding phase for DGT devices. Laboratory tests across a range of pH (3.5-9.5), ionic strength (0.001-0.5 M) and dissolved organic matter concentration (0-20 mg L -1 ) showed HLB and XAD18-DGT devices were more stable compared to SXLA-DGT. HLB-DGT and XAD18-DGT accumulated test chemicals with time consistent with theoretical predictions, while SXLA-DGT accumulated reduced amounts of chemical. DGT performance was also compared in field deployments up to 28 days, alongside conventional active sampling at a wastewater treatment plant. Uptake was linear to the samplers over 18 days, and then began to plateau/decline, indicating the maximum deployment time in those conditions. Concentrations provided by the DGT samplers compared well with those provided by auto-samplers. DGT integrated concentrations over the deployment period in a way that grab-sampling cannot. The advantages of the DGT sampler over active sampling include: low cost, ease of simultaneous multi-site deployment, in situ analyte pre-concentration and reduction of matrix interferences compared with conventional methods. Compared to other passive sampler designs, DGT uptake is independent of flow rate and therefore allows direct derivation of field concentrations from measured compound diffusion coefficients. This passive DGT sampler therefore constitutes a viable and attractive alternative to conventional grab and active water sampling for routine monitoring of selected EDCs. Copyright © 2018 Elsevier Ltd. All rights reserved.

Optical effects module and passive sample array

NASA Technical Reports Server (NTRS)

Linton, R. C.

1983-01-01

The Optical Effects Module (OEM) has the objective to monitor the effects of the deposition and adhesion of both molecular species and particles on optical surfaces in the Shuttle cargo bay environment. The OEM performs inflight measurements of the ultraviolet (253.7 nm) transmittance and diffuse reflectance of five optical samples at regular intervals throughout the orbital mission. Most of the obtained results indicates or implies the absence of a significant accumulation of contamination other than particulates on the samples. The contaminant species (or particulates) adhering to the samples of the Passive Sample Array (PSA) were identified by means of Auger and X-ray energy dispersive analyses. The elements silicon, chlorine, and phosphorus were discovered.

Geophysical logging and geologic mapping data in the vicinity of the GMH Electronics Superfund site near Roxboro, North Carolina

USGS Publications Warehouse

Chapman, Melinda J.; Clark, Timothy W.; Williams, John H.

2013-01-01

Geologic mapping, the collection of borehole geophysical logs and images, and passive diffusion bag sampling were conducted by the U.S. Geological Survey North Carolina Water Science Center in the vicinity of the GMH Electronics Superfund site near Roxboro, North Carolina, during March through October 2011. The study purpose was to assist the U.S. Environmental Protection Agency in the development of a conceptual groundwater model for the assessment of current contaminant distribution and future migration of contaminants. Data compilation efforts included geologic mapping of more than 250 features, including rock type and secondary joints, delineation of more than 1,300 subsurface features (primarily fracture orientations) in 15 open borehole wells, and the collection of passive diffusion-bag samples from 42 fracture zones at various depths in the 15 wells.

Extracting dielectric fixed charge density on highly doped crystalline-silicon surfaces using photoconductance measurements

NASA Astrophysics Data System (ADS)

To, A.; Hoex, B.

2017-11-01

A novel method for the extraction of fixed interface charge, Qf, and the surface recombination parameters, Sn0 and Sp0, from the injection-level dependent effective minority carrier lifetime measurements is presented. Unlike conventional capacitance-voltage measurements, this technique can be applied to highly doped surfaces provided the surface carrier concentration transitions into strong depletion or inversion with increased carrier injection. By simulating the injection level dependent Auger-corrected inverse lifetime curve of symmetrically passivated and diffused samples after sequential annealing and corona charging, it was revealed that Qf, Sn0, and Sp0 have unique signatures. Therefore, these important electronic parameters, in some instances, can independently be resolved. Furthermore, it was shown that this non-linear lifetime behaviour is exhibited on both p-type and n-type diffused inverted surfaces, by demonstrating the approach with phosphorous diffused n+pn+ structures and boron diffused p+np+ structures passivated with aluminium oxide (AlOx) and silicon nitride, respectively (SiNx). The results show that the approximation of a mid-gap Shockley-Read-Hall defect level with equal capture cross sections is able to, in the samples studied in this work, reproduce the observed injection level dependent lifetime behaviour.

Effect of ultrasonic cavitation on the diffusivity of a point defect in the passive film on formed Nb in 0.5 M HCl solution.

PubMed

Li, D G

2015-11-01

This work primarily focused on the influence of ultrasonic cavitation on the transport property of the point defect in the passive film on formed Nb in 0.5M HCl solution via electrochemical techniques based on the point defect model (PDM). The influence of ultrasonic cavitation on the composition and structure of the passive film was detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The transport property of a point defect in the passive film was characterized by the diffusivity of the point defect (D0). The influences of the ultrasonic cavitation power, passivated time and the distance between horn bottom and sample surface on D0 were analyzed. The results demonstrated that the passive film formed on Nb was an n-type semiconductor with a donor density (ND) ranging from 10(19) cm(-3) to 10(20) cm(-3) in the case of static state, while the order of ND increased one to two times by applying ultrasonic cavitation during film formation. The diffusivity of the point defect (D0) in the passive film formed on Nb at 0.5 V for 1 h in a 0.5 M HCl solution in the static state was calculated to be 9.704×10(-18) cm(2) s(-1), and it increased to 1.255×10(-16) cm(2) s(-1), 7.259×10(-16) cm(2) s(-1) and 7.296×10(-15) cm(2) s(-1) when applying the 180 W, 270 W and 450 W ultrasonic cavitation powers during film formation. D0 increased with the increment of the ultrasonic cavitation power, and decreased with the increased in formation time and distance between the horn bottom and sample surface. AES results showed the film structure and composition were changed by applying the ultrasonic cavitation. XPS results revealed that the passive film was mainly composed of Nb2O5 in the static state, and the low valence Nb-oxide (NbO) appeared in the passive film except Nb2O5 in the case of applying a 270 W ultrasonic cavitation power. Copyright © 2015 Elsevier B.V. All rights reserved.

Quantitative passive soil vapor sampling for VOCs--part 1: theory.

PubMed

McAlary, Todd; Wang, Xiaomin; Unger, Andre; Groenevelt, Hester; Górecki, Tadeusz

2014-03-01

Volatile organic compounds are the primary chemicals of concern at many contaminated sites and soil vapor sampling and analysis is a valuable tool for assessing the nature and extent of contamination. Soil gas samples are typically collected by applying vacuum to a probe in order to collect a whole-gas sample, or by drawing gas through a tube filled with an adsorbent (active sampling). There are challenges associated with flow and vacuum levels in low permeability materials, and leak prevention and detection during active sample collection can be cumbersome. Passive sampling has been available as an alternative to conventional gas sample collection for decades, but quantitative relationships between the mass of chemicals sorbed, the soil vapor concentrations, and the sampling time have not been established. This paper presents transient and steady-state mathematical models of radial vapor diffusion to a drilled hole and considerations for passive sampler sensitivity and practical sampling durations. The results indicate that uptake rates in the range of 0.1 to 1 mL min(-1) will minimize the starvation effect for most soil moisture conditions and provide adequate sensitivity for human health risk assessment with a practical sampling duration. This new knowledge provides a basis for improved passive soil vapour sampler design.

Passive ultrasonics using sub-Nyquist sampling of high-frequency thermal-mechanical noise.

PubMed

Sabra, Karim G; Romberg, Justin; Lani, Shane; Degertekin, F Levent

2014-06-01

Monolithic integration of capacitive micromachined ultrasonic transducer arrays with low noise complementary metal oxide semiconductor electronics minimizes interconnect parasitics thus allowing the measurement of thermal-mechanical (TM) noise. This enables passive ultrasonics based on cross-correlations of diffuse TM noise to extract coherent ultrasonic waves propagating between receivers. However, synchronous recording of high-frequency TM noise puts stringent requirements on the analog to digital converter's sampling rate. To alleviate this restriction, high-frequency TM noise cross-correlations (12-25 MHz) were estimated instead using compressed measurements of TM noise which could be digitized at a sampling frequency lower than the Nyquist frequency.

Performance evaluation of a tailor-made passive sampler for monitoring of tropospheric ozone.

PubMed

Ozden, Ozlem; Döğeroğlu, Tuncay

2012-09-01

This study presents the performance evaluation of a tailor-made passive sampler developed for the monitoring of tropospheric ozone. The performance of the passive sampler was tested in the field conditions in terms of accuracy, precision, blank values, detection limit, effects of some parameters such as sampling site characteristics and sampling period on the field blanks, self-consistency, experimental and theoretical uptake rates, shelf life and comparison with commercial passive samplers. There was an agreement (R (2) = 0.84) between the responses of passive sampler and the continuous automatic analyser. The accuracy of the sampler, expressed as percent relative error, was obtained lower than 15%. Method precision in terms of coefficient of variance for three simultaneously applied passive samplers was 12%. Sampler detection limit was 2.42 μg m(-3) for an exposure period of 1 week, and the sampler can be stored safely for a period of up to 8 weeks before exposure. Satisfactory self-consistency results showed that extended periods gave the same integrated response as a series of short-term samplers run side by side. The uptake rate of ozone was found to be 10.21 mL min(-1) in a very good agreement with the theoretical uptake rate (10.32 mL min(-1)). The results of the comparison study conducted against a commercially available diffusion tube (Gradko diffusion tube) showed a good linear relationship (R (2) = 0.93) between two passive samplers. The sampler seems suitable to be used in large-scale measurements of ozone where no data are available or the number of existing automated monitors is not sufficient.

Solid phase microextraction for active or passive sampling of methyl bromide during fumigations

USDA-ARS?s Scientific Manuscript database

The high diffusivity and volatility of methyl bromide make it an ideal compound for Solid Phase Micro Extraction (SPME)-based sampling of air prior to gas-chromatographic quantifications. SPME fibers can be used as active methyl bromide samplers, with high capacities and an equilibrium time of 1-2 m...

A field evaluation of a SO 2 passive sampler in tropical industrial and urban air

NASA Astrophysics Data System (ADS)

Cruz, Lícia P. S.; Campos, Vânia P.; Silva, Adriana M. C.; Tavares, Tania M.

Passive samplers have been widely used for over 30 years in the measurement of personal exposure to vapours and gases in the workplace. These samplers have just recently been applied in the monitoring of ambient air, which presents concentrations that are normally much smaller than those found in occupational environments. The locally constructed passive sampler was based on gas molecular diffusion through static air layer. The design used minimizes particle interference and turbulent diffusion. After exposure, the SO 2 trapped in impregnated filters with Na 2CO 3 was extracted by means of an ultrasonic bath, for 15 min, using 1.0×10 -2 mol L -1 H 2O 2. It was determined as SO 4-2 by ion chromatography. The performance of the passive sampler was evaluated at different exposure periods, being applied in industrial and urban areas. Method precision as relative standard deviation for three simultaneously applied passive samplers was within 10%. Passive sampling, when compared to active monitoring methods under real conditions, used in urban and industrial areas, showed an overall accuracy of 15%. A statistical comparison with an active method was performed to demonstrate the validity of the passive method. Sampler capacity varied between 98 and 421 μg SO 2 m -3 for exposure periods of one month and one week, respectively, which allows its use in highly polluted areas.

Comparison of Pumped and Diffusion Sampling Methods to Monitor Concentrations of Perchlorate and Explosive Compounds in Ground Water, Camp Edwards, Cape Cod, Massachusetts, 2004-05

USGS Publications Warehouse

LeBlanc, Denis R.; Vroblesky, Don A.

2008-01-01

Laboratory and field tests were conducted at Camp Edwards on the Massachusetts Military Reservation on Cape Cod to examine the utility of passive diffusion sampling for long-term monitoring of concentrations of perchlorate and explosive compounds in ground water. The diffusion samplers were constructed of 1-inch-diameter rigid, porous polyethylene tubing. The results of laboratory tests in which diffusion samplers were submerged in containers filled with ground water containing perchlorate, RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) indicate that concentrations inside the diffusion samplers equilibrated with concentrations in the containers within the 19-day-long test period. Field tests of the diffusion samplers were conducted in 15 wells constructed of 2- or 2.5-inch-diameter polyvinyl chloride pipe with 10-foot-long slotted screens. Concentrations of perchlorate, RDX, and HMX in the diffusion samplers placed in the wells for 42 to 52 days were compared to concentrations in samples collected by low-flow pumped sampling from 53 days before to 109 days after retrieval of the diffusion samples. The results of the field tests indicate generally good agreement between the pumped and diffusion samples for concentrations of perchlorate, RDX, and HMX. The concentration differences indicate no systematic bias related to contaminant type or concentration levels.

Simple rules for passive diffusion through the nuclear pore complex

PubMed Central

Mironska, Roxana; Kim, Seung Joong

2016-01-01

Passive macromolecular diffusion through nuclear pore complexes (NPCs) is thought to decrease dramatically beyond a 30–60-kD size threshold. Using thousands of independent time-resolved fluorescence microscopy measurements in vivo, we show that the NPC lacks such a firm size threshold; instead, it forms a soft barrier to passive diffusion that intensifies gradually with increasing molecular mass in both the wild-type and mutant strains with various subsets of phenylalanine-glycine (FG) domains and different levels of baseline passive permeability. Brownian dynamics simulations replicate these findings and indicate that the soft barrier results from the highly dynamic FG repeat domains and the diffusing macromolecules mutually constraining and competing for available volume in the interior of the NPC, setting up entropic repulsion forces. We found that FG domains with exceptionally high net charge and low hydropathy near the cytoplasmic end of the central channel contribute more strongly to obstruction of passive diffusion than to facilitated transport, revealing a compartmentalized functional arrangement within the NPC. PMID:27697925

User's guide for polyethylene-based passive diffusion bag samplers to obtain volatile organic compound concentrations in wells. Part I, Deployment, recovery, data interpretation, and quality control and assurance

USGS Publications Warehouse

Vroblesky, Don A.

2001-01-01

Diffusion samplers installed in observation wells were found to be capable of yielding representative water samples for chlorinated volatile organic compounds. The samplers consisted of polyethylene bags containing deionized water and relied on diffusion of chlorinated volatile organic compounds through the polyethylene membrane. The known ability of polyethylene to transmit other volatile compounds, such as benzene and toluene, indicates that the samplers can be used for a variety of volatile organic compounds. In wells at the study area, the volatile organic compound concentrations in water samples obtained using the samplers without prior purging were similar to concentrations in water samples obtained from the respective wells using traditional purging and sampling approaches. The low cost associated with this approach makes it a viable option for monitoring large observation-well networks for volatile organic compounds.

User's guide for polyethylene-based passive diffusion bag samplers to obtain volatile organic compound concentrations in wells. Part 2, Field tests

USGS Publications Warehouse

Vroblesky, Don A.

2001-01-01

Diffusion samplers installed in observation wells were found to be capable of yielding representative water samples for chlorinated volatile organic compounds. The samplers consisted of polyethylene bags containing deionized water and relied on diffusion of chlorinated volatile organic compounds through the polyethylene membrane. The known ability of polyethylene to transmit other volatile compounds, such as benzene and toluene, indicates that the samplers can be used for a variety of volatile organic compounds. In wells at the study area, the volatile organic compound concentrations in water samples obtained using the samplers without prior purging were similar to concentrations in water samples obtained from the respective wells using traditional purging and sampling approaches. The low cost associated with this approach makes it a viable option for monitoring large observation-well networks for volatile organic compounds.

Calibration of passive remote observing optical and microwave instrumentation; Proceedings of the Meeting, Orlando, FL, Apr. 3-5, 1991

NASA Technical Reports Server (NTRS)

Guenther, Bruce W. (Editor)

1991-01-01

Various papers on the calibration of passive remote observing optical and microwave instrumentation are presented. Individual topics addressed include: on-board calibration device for a wide field-of-view instrument, calibration for the medium-resolution imaging spectrometer, cryogenic radiometers and intensity-stabilized lasers for EOS radiometric calibrations, radiometric stability of the Shuttle-borne solar backscatter ultraviolet spectrometer, ratioing radiometer for use with a solar diffuser, requirements of a solar diffuser and measurements of some candidate materials, reflectance stability analysis of Spectralon diffuse calibration panels, stray light effects on calibrations using a solar diffuser, radiometric calibration of SPOT 23 HRVs, surface and aerosol models for use in radiative transfer codes. Also addressed are: calibrated intercepts for solar radiometers used in remote sensor calibration, radiometric calibration of an airborne multispectral scanner, in-flight calibration of a helicopter-mounted Daedalus multispectral scanner, technique for improving the calibration of large-area sphere sources, remote colorimetry and its applications, spatial sampling errors for a satellite-borne scanning radiometer, calibration of EOS multispectral imaging sensors and solar irradiance variability.

Passive lipoidal diffusion and carrier-mediated cell uptake are both important mechanisms of membrane permeation in drug disposition.

PubMed

Smith, Dennis; Artursson, Per; Avdeef, Alex; Di, Li; Ecker, Gerhard F; Faller, Bernard; Houston, J Brian; Kansy, Manfred; Kerns, Edward H; Krämer, Stefanie D; Lennernäs, Hans; van de Waterbeemd, Han; Sugano, Kiyohiko; Testa, Bernard

2014-06-02

Recently, it has been proposed that drug permeation is essentially carrier-mediated only and that passive lipoidal diffusion is negligible. This opposes the prevailing hypothesis of drug permeation through biological membranes, which integrates the contribution of multiple permeation mechanisms, including both carrier-mediated and passive lipoidal diffusion, depending on the compound's properties, membrane properties, and solution properties. The prevailing hypothesis of drug permeation continues to be successful for application and prediction in drug development. Proponents of the carrier-mediated only concept argue against passive lipoidal diffusion. However, the arguments are not supported by broad pharmaceutics literature. The carrier-mediated only concept lacks substantial supporting evidence and successful applications in drug development.

PERFORMANCE OF A NEW PASSIVE DIFFUSION SAMPLER FOR SOIL GAS AND GROUND WATER SAMPLING

EPA Science Inventory

Conventional practice to estimate intrusion of fuel vapors from ground water to buildings measures the concentration of BTEX in ground water beneath the building using a conventional well screened across the water table. Conventional practice assumes that the concentration of co...

DGT Passive Sampling for Quantitative in Situ Measurements of Compounds from Household and Personal Care Products in Waters.

PubMed

Chen, Wei; Li, Yanying; Chen, Chang-Er; Sweetman, Andrew J; Zhang, Hao; Jones, Kevin C

2017-11-21

Widespread use of organic chemicals in household and personal care products (HPCPs) and their discharge into aquatic systems means reliable, robust techniques to monitor environmental concentrations are needed. The passive sampling approach of diffusive gradients in thin-films (DGT) is developed here and demonstrated to provide in situ quantitative and time-weighted average (TWA) measurement of these chemicals in waters. The novel technique is developed for HPCPs, including preservatives, antioxidants and disinfectants, by evaluating the performance of different binding agents. Ultrasonic extraction of binding gels in acetonitrile gave good and consistent recoveries for all test chemicals. Uptake by DGT with HLB (hydrophilic-lipophilic-balanced) as the binding agent was relatively independent of pH (3.5-9.5), ionic strength (0.001-0.1 M) and dissolved organic matter (0-20 mg L -1 ), making it suitable for applications across a wide range of environments. Deployment time and diffusion layer thickness dependence experiments confirmed DGT accumulated chemicals masses are consistent with theoretical predictions. The technique was further tested and applied in the influent and effluent of a wastewater treatment plant. Results were compared with conventional grab-sampling and 24-h-composited samples from autosamplers. DGT provided TWA concentrations over up to 18 days deployment, with minimal effects from biofouling or the diffusive boundary layer. The field application demonstrated advantages of the DGT technique: it gives in situ analyte preconcentration in a simple matrix, with more quantitative measurement of the HPCP analytes.

Evidence-based approach to assess passive diffusion and carrier-mediated drug transport.

PubMed

Di, Li; Artursson, Per; Avdeef, Alex; Ecker, Gerhard F; Faller, Bernard; Fischer, Holger; Houston, J Brian; Kansy, Manfred; Kerns, Edward H; Krämer, Stefanie D; Lennernäs, Hans; Sugano, Kiyohiko

2012-08-01

Evidence supporting the action of passive diffusion and carrier-mediated (CM) transport in drug bioavailability and disposition is discussed to refute the recently proposed theory that drug transport is CM-only and that new transporters will be discovered that possess transport characteristics ascribed to passive diffusion. Misconceptions and faulty speculations are addressed to provide reliable guidance on choosing appropriate tools for drug design and optimization. Copyright © 2012 Elsevier Ltd. All rights reserved.

Finite-time robust passive control for a class of switched reaction-diffusion stochastic complex dynamical networks with coupling delays and impulsive control

NASA Astrophysics Data System (ADS)

Syed Ali, M.; Yogambigai, J.; Kwon, O. M.

2018-03-01

Finite-time boundedness and finite-time passivity for a class of switched stochastic complex dynamical networks (CDNs) with coupling delays, parameter uncertainties, reaction-diffusion term and impulsive control are studied. Novel finite-time synchronisation criteria are derived based on passivity theory. This paper proposes a CDN consisting of N linearly and diffusively coupled identical reaction- diffusion neural networks. By constructing of a suitable Lyapunov-Krasovskii's functional and utilisation of Jensen's inequality and Wirtinger's inequality, new finite-time passivity criteria for the networks are established in terms of linear matrix inequalities (LMIs), which can be checked numerically using the effective LMI toolbox in MATLAB. Finally, two interesting numerical examples are given to show the effectiveness of the theoretical results.

Cellular automaton formulation of passive scalar dynamics

NASA Technical Reports Server (NTRS)

Chen, Hudong; Matthaeus, William H.

1987-01-01

Cellular automata modeling of the advection of a passive scalar in a two-dimensional flow is examined in the context of discrete lattice kinetic theory. It is shown that if the passive scalar is represented by tagging or 'coloring' automation particles a passive advection-diffusion equation emerges without use of perturbation expansions. For the specific case of the hydrodynamic lattice gas model of Frisch et al. (1986), the diffusion coefficient is calculated by perturbation.

Labile, dissolved and particulate PAHs and trace metals in wastewater: passive sampling, occurrence, partitioning in treatment plants.

PubMed

Gourlay-Francé, C; Bressy, A; Uher, E; Lorgeoux, C

2011-01-01

The occurrence and the partitioning of polycyclic aromatic hydrocarbons (PAHs) and seven metals (Al, Cd, Cr, Cu, Ni, Pb and Zn) were investigated in activated sludge wastewater treatment plants by means of passive and active sampling. Concentrations total dissolved and particulate contaminants were determined in wastewater at several points across the treatment system by means of grab sampling. Truly dissolved PAHs were sampled by means of semipermeable membrane devices. Labile (inorganic and weakly complexed) dissolved metals were also sampled using the diffusive gradient in thin film technique. This study confirms the robustness and the validity of these two passive sampling techniques in wastewater. All contaminant concentrations decreased in wastewater along the treatment, although dissolved and labile concentrations sometimes increased for substances with less affinity with organic matter. Solid-liquid and dissolved organic matter/water partitioning constants were estimated. The high variability of both partitioning constants for a simple substance and the poor relation between K(D) and K(OW) shows that the binding capacities of particles and organic matter are not uniform within the treatment and that other process than equilibrium sorption affect contaminant repartition and fate in wastewater.

A modified method for diffusive monitoring of 3-ethenylpyridine as a specific marker of environmental tobacco smoke

NASA Astrophysics Data System (ADS)

Kuusimäki, Leea; Peltonen, Kimmo; Vainiotalo, Sinikka

A previously introduced method for monitoring environmental tobacco smoke (ETS) was further validated. The method is based on diffusive sampling of a vapour-phase marker, 3-ethenylpyridine (3-EP), with 3 M passive monitors (type 3500). Experiments were done in a dynamic chamber to assess diffusive sampling in comparison with active sampling in charcoal tubes or XAD-4 tubes. The sampling rate for 3-EP collected on the diffusive sampler was 23.1±0.6 mL min -1. The relative standard deviation for parallel samples ( n=6) ranged from 4% to 14% among experiments ( n=9). No marked reverse diffusion of 3-EP was detected nor any significant effect of relative humidity at 20%, 50% or 80%. The diffusive sampling of 3-EP was validated in field measurements in 15 restaurants in comparison with 3-EP and nicotine measurements using active sampling. The 3-EP concentration in restaurants ranged from 0.01 to 9.8 μg m -3, and the uptake rate for 3-EP based on 92 parallel samples was 24.0±0.4 mL min -1. A linear correlation ( r=0.98) was observed between 3-EP and nicotine concentrations, the average ratio of 3-EP to nicotine being 1:8. Active sampling of 3-EP and nicotine in charcoal tubes provided more reliable results than sampling in XAD-4 tubes. All samples were analysed using gas chromatography-mass spectrometry after elution with a 15% solution of pyridine in toluene. For nicotine, the limit of quantification of the charcoal tube method was 4 ng per sample, corresponding to 0.04 μg m -3 for an air sample of 96 L. For 3-EP, the limit of quantification of the diffusive method was 0.5-1.0 ng per sample, corresponding to 0.04-0.09 μg m -3 for 8 h sampling. The diffusive method proved suitable for ETS monitoring, even at low levels of ETS.

Visualizing Molecular Diffusion through Passive Permeability Barriers in Cells: Conventional and Novel Approaches

PubMed Central

Lin, Yu-Chun; Phua, Siew Cheng; Lin, Benjamin; Inoue, Takanari

2013-01-01

Diffusion barriers are universal solutions for cells to achieve distinct organizations, compositions, and activities within a limited space. The influence of diffusion barriers on the spatiotemporal dynamics of signaling molecules often determines cellular physiology and functions. Over the years, the passive permeability barriers in various subcellular locales have been characterized using elaborate analytical techniques. In this review, we will summarize the current state of knowledge on the various passive permeability barriers present in mammalian cells. We will conclude with a description of several conventional techniques and one new approach based on chemically-inducible diffusion trap (C-IDT) for probing permeable barriers. PMID:23731778

Surface characteristics, corrosion and bioactivity of chemically treated biomedical grade NiTi alloy.

PubMed

Chembath, Manju; Balaraju, J N; Sujata, M

2015-11-01

The surface of NiTi alloy was chemically modified using acidified ferric chloride solution and the characteristics of the alloy surface were studied from the view point of application as a bioimplant. Chemically treated NiTi was also subjected to post treatments by annealing at 400°C and passivation in nitric acid. The surface of NiTi alloy after chemical treatment developed a nanogrid structure with a combination of one dimensional channel and two dimensional network-like patterns. From SEM studies, it was found that the undulations formed after chemical treatment remained unaffected after annealing, while after passivation process the undulated surface was filled with oxides of titanium. XPS analysis revealed that the surface of passivated sample was enriched with oxides of titanium, predominantly TiO2. The influence of post treatment on the corrosion resistance of chemically treated NiTi alloy was monitored using Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS) in Phosphate Buffered Saline (PBS) solution. In the chemically treated condition, NiTi alloy exhibited poor corrosion resistance due to the instability of the surface. On the other hand, the breakdown potential (0.8V) obtained was highest for the passivated samples compared to other surface treated samples. During anodic polarization, chemically treated samples displayed dissolution phenomenon which was predominantly activation controlled. But after annealing and passivation processes, the behavior of anodic polarization was typical of a diffusion controlled process which confirmed the enhanced passivity of the post treated surfaces. The total resistance, including the porous and barrier layer, was in the range of mega ohms for passivated surfaces, which could be attributed to the decrease in surface nickel content and formation of compact titanium oxide. The passivated sample displayed good bioactivity in terms of hydroxyapatite growth, noticed after 14days immersion in Hanks' solution. Copyright © 2015 Elsevier B.V. All rights reserved.

Influence of wind-speed on short-duration NO2 measurements using Palmes and Ogawa passive diffusion samplers

NASA Astrophysics Data System (ADS)

Masey, Nicola; Gillespie, Jonathan; Heal, Mathew R.; Hamilton, Scott; Beverland, Iain J.

2017-07-01

We assessed the precision and accuracy of nitrogen dioxide (NO2) concentrations over 2-day, 3-day and 7-day exposure periods measured with the following types of passive diffusion samplers: standard (open) Palmes tubes; standard Ogawa samplers with commercially-prepared Ogawa absorbent pads (Ogawa[S]); and modified Ogawa samplers with absorbent-impregnated stainless steel meshes normally used in Palmes tubes (Ogawa[P]). We deployed these passive samplers close to the inlet of a chemiluminescence NO2 analyser at an urban background site in Glasgow, UK over 32 discrete measurement periods. Duplicate relative standard deviation was <7% for all passive samplers. The Ogawa[P], Ogawa[S] and Palmes samplers explained 93%, 87% and 58% of temporal variation in analyser concentrations respectively. Uptake rates for Palmes and Ogawa[S] samplers were positively and linearly associated with wind-speed (P < 0.01 and P < 0.05 respectively). Computation of adjusted uptake rates using average wind-speed observed during each sampling period increased the variation in analyser concentrations explained by Palmes and Ogawa[S] estimates to 90% and 92% respectively, suggesting that measurements can be corrected for shortening of diffusion path lengths due to wind-speed to improve the accuracy of estimates of short-term NO2 exposure. Monitoring situations where it is difficult to reliably estimate wind-speed variations, e.g. across multiple sites with different unknown exposures to local winds, and personal exposure monitoring, are likely to benefit from protection of these sampling devices from the effects of wind, for example by use of a mesh or membrane across the open end. The uptake rate of Ogawa[P] samplers was not associated with wind-speed resulting in a high correlation between estimated concentrations and observed analyser concentrations. The use of Palmes meshes in Ogawa[P] samplers reduced the cost of sampler preparation and removed uncertainty associated with the unknown manufacturing process for the commercially-prepared collection pads.

Development of a miniaturized diffusive sampler for true breathing-zone sampling and thermal desorption gas chromatographic analysis.

PubMed

Lindahl, Roger; Levin, Jan-Olof; Sundgren, Margit

2009-07-01

Exposure measurements should be performed as close as possible to the nose and mouth for a more correct assessment of exposure. User-friendly sampling equipment, with a minimum of handling before, during and after measurement, should not affect ordinary work. In diffusive (passive) sampling, no extra equipment as sampling pumps is needed, making the measurements more acceptable to the user. The diffusive samplers are normally attached on a shoulder, on a breast-pocket or on the lapel. There are, however, difficulties if true breathing-zone sampling is to be performed, since available diffusive samplers normally cannot be arranged close to the nose/mouth. The purpose of this work was to study the performance of a miniaturized tube type diffusive sampler attached to a headset for true breathing-zone sampling. The basis for this miniaturization was the Perkin Elmer ATD tube. Both the size of the tube and the amount of adsorbent was decreased for the miniaturized sampler. A special tube holder to be used with a headset was designed for the mini tube. The mini tube is thermally desorbed inside a standard PE tube. The new sampler was evaluated for the determination of styrene, both in laboratory experiments and in field measurements. As reference method, diffusive sampling with standard Perkin Elmer tubes, thermal desorption and gas chromatographic (GC) analysis was used. The sampling rate was determined to 0.356 mL min(-1) (CV 9.6%) and was not significantly affected by concentration, sampling time or relative humidity.

Simulating and explaining passive air sampling rates for semi-volatile compounds on polyurethane foam passive samplers

PubMed Central

Petrich, Nicholas T.; Spak, Scott N.; Carmichael, Gregory R.; Hu, Dingfei; Martinez, Andres; Hornbuckle, Keri C.

2013-01-01

Passive air samplers (PAS) including polyurethane foam (PUF) are widely deployed as an inexpensive and practical way to sample semi-volatile pollutants. However, concentration estimates from PAS rely on constant empirical mass transfer rates, which add unquantified uncertainties to concentrations. Here we present a method for modeling hourly sampling rates for semi-volatile compounds from hourly meteorology using first-principle chemistry, physics, and fluid dynamics, calibrated from depuration experiments. This approach quantifies and explains observed effects of meteorology on variability in compound-specific sampling rates and analyte concentrations; simulates nonlinear PUF uptake; and recovers synthetic hourly concentrations at a reference temperature. Sampling rates are evaluated for polychlorinated biphenyl congeners at a network of Harner model samplers in Chicago, Illinois during 2008, finding simulated average sampling rates within analytical uncertainty of those determined from loss of depuration compounds, and confirming quasi-linear uptake. Results indicate hourly, daily and interannual variability in sampling rates, sensitivity to temporal resolution in meteorology, and predictable volatility-based relationships between congeners. We quantify importance of each simulated process to sampling rates and mass transfer and assess uncertainty contributed by advection, molecular diffusion, volatilization, and flow regime within the PAS, finding PAS chamber temperature contributes the greatest variability to total process uncertainty (7.3%). PMID:23837599

Passive absolute age and temperature history sensor

DOEpatents

Robinson, Alex; Vianco, Paul T.

2015-11-10

A passive sensor for historic age and temperature sensing, including a first member formed of a first material, the first material being either a metal or a semiconductor material and a second member formed of a second material, the second material being either a metal or a semiconductor material. A surface of the second member is in contact with a surface of the first member such that, over time, the second material of the second member diffuses into the first material of the first member. The rate of diffusion for the second material to diffuse into the first material depends on a temperature of the passive sensor. One of the electrical conductance, the electrical capacitance, the electrical inductance, the optical transmission, the optical reflectance, or the crystalline structure of the passive sensor depends on the amount of the second material that has diffused into the first member.

Visualizing molecular diffusion through passive permeability barriers in cells: conventional and novel approaches.

PubMed

Lin, Yu-Chun; Phua, Siew Cheng; Lin, Benjamin; Inoue, Takanari

2013-08-01

Diffusion barriers are universal solutions for cells to achieve distinct organizations, compositions, and activities within a limited space. The influence of diffusion barriers on the spatiotemporal dynamics of signaling molecules often determines cellular physiology and functions. Over the years, the passive permeability barriers in various subcellular locales have been characterized using elaborate analytical techniques. In this review, we will summarize the current state of knowledge on the various passive permeability barriers present in mammalian cells. We will conclude with a description of several conventional techniques and one new approach based on chemically inducible diffusion trap (CIDT) for probing permeable barriers. Copyright © 2013 Elsevier Ltd. All rights reserved.

Recombination reduction at the c-Si/RCA oxide interface through Ar-H2 plasma treatment

NASA Astrophysics Data System (ADS)

Landheer, Kees; Bronsveld, Paula C. P.; Poulios, Ioannis; Tichelaar, Frans D.; Kaiser, Monja; Schropp, Ruud E. I.; Rath, Jatin K.

2017-02-01

An Ar-H2 plasma treatment was applied on an ultrathin RCA oxide to create well-passivated silicon wafers with symmetric c-Si/SiOx:H/a-Si:H passivation layer stacks. The effective lifetime of these samples increased from 10 μs to 4 ms after annealing at 200 °C through Ar-H2 plasma treatment of the oxide. The results indicate that the plasma treatment can modify the RCA oxide and this enables atomic hydrogen diffusion at low annealing temperature, leading to a well passivated c-Si/SiOx:H interface. This might provide new possibilities to use wet chemical oxides in c-Si solar cells, for example as tunnel contacts.

Examination of factors dominating the sediment-water diffusion flux of DDT-related compounds measured by passive sampling in an urbanized estuarine bay.

PubMed

Feng, Yan; Wu, Chen-Chou; Bao, Lian-Jun; Shi, Lei; Song, Lin; Zeng, Eddy Y

2016-12-01

The fate of hydrophobic organic compounds in aquatic environment are largely determined by their exchange at sediment-water interface, which is highly dynamic and subject to rapidly evolving environmental conditions. In turn, environmental conditions may be governed by both physicochemical parameters and anthropogenic events. To examine the importance of various impact factors, passive sampling devices were deployed at the seafloor of Hailing Bay, an urbanized estuarine bay in Guangdong Province of South China to measure the sediment-water diffusion fluxes of several metabolites of dichlorodiphenyltrichloroethane (DDT), p,p'-DDE, p,p'-DDD and o,p'-DDD. The physicochemical properties of water (temperature, pH, salinity and dissolved oxygen) and surface sediment (sediment organic matter, physical composition, pH, water content, colony forming unit and catalase activity) were also measured. The results showed that the diffusion fluxes of o,p'-DDD, p,p'-DDD and p,p'-DDE at sites A1 and A2 near a fishing boat maintenance facility ranged from 0.42 to 4.73 ng m -2 d -1 (from sediment to overlying water), whereas those at offshore sites varied between -0.03 and -3.02 ng m -2 d -1 (from overlying water to sediment), implicating A1 and A2 as the sources of the target compounds. The distribution patterns of the diffusion fluxes of the target compounds were different from those of water and sediment parameters (water temperature, salinity, sediment texture, pH, colony forming unit and catalase activity) at six sampling sites. This finding suggested that none of these parameters were critical in dictating the sediment-water diffusion fluxes. Besides, decreases in the contents of kerogen and black carbon by 6.7% and 11% would enhance the diffusion fluxes of the target compounds by 11-14% and 12-23%, respectively, at site A1, indicating that kerogen and black carbon were the key factors in mediating the sediment-water diffusion fluxes of DDT-related compounds in field environments. Copyright © 2016 Elsevier Ltd. All rights reserved.

A novel enhanced diffusion sampler for collecting gaseous pollutants without air agitation.

PubMed

Pan, Xuelian; Zhuo, Shaojie; Zhong, Qirui; Chen, Yuanchen; Du, Wei; Cheng, Hefa; Wang, Xilong; Zeng, Eddy Y; Xing, Baoshan; Tao, Shu

2018-03-06

A novel enhanced diffusion sampler for collecting gaseous phase polycyclic aromatic hydrocarbons (PAHs) without air agitation is proposed. The diffusion of target compounds into a sampling chamber is facilitated by continuously purging through a closed-loop flow to create a large concentration difference between the ambient air and the air in the sampling chamber. A glass-fiber filter-based prototype was developed. It was demonstrated that the device could collect gaseous PAHs at a much higher rate (1.6 ± 1.4 L/min) than regular passive samplers, while the ambient air is not agitated. The prototype was also tested in both the laboratory and field for characterizing the concentration gradients over a short distance from the soil surface. The sampler has potential to be applied in other similar situations to characterize the concentration profiles of other chemicals.

Sample integrity evaluation and EPA method 325B interlaboratory comparison for select volatile organic compounds collected diffusively on Carbopack X sorbent tubes

NASA Astrophysics Data System (ADS)

Oliver, Karen D.; Cousett, Tamira A.; Whitaker, Donald A.; Smith, Luther A.; Mukerjee, Shaibal; Stallings, Casson; Thoma, Eben D.; Alston, Lillian; Colon, Maribel; Wu, Tai; Henkle, Stacy

2017-08-01

A sample integrity evaluation and an interlaboratory comparison were conducted in application of U.S. Environmental Protection Agency (EPA) Methods 325A and 325B for diffusively monitoring benzene and other selected volatile organic compounds (VOCs) using Carbopack X sorbent tubes. To evaluate sample integrity, VOC samples were refrigerated for up to 240 days and analyzed using thermal desorption/gas chromatography-mass spectrometry at the EPA Office of Research and Development laboratory in Research Triangle Park, NC, USA. For the interlaboratory comparison, three commercial analytical laboratories were asked to follow Method 325B when analyzing samples of VOCs that were collected in field and laboratory settings for EPA studies. Overall results indicate that the selected VOCs collected diffusively on sorbent tubes generally were stable for 6 months or longer when samples were refrigerated. This suggests the specified maximum 30-day storage time of VOCs collected diffusively on Carbopack X passive samplers and analyzed using Method 325B might be able to be relaxed. Interlaboratory comparison results were in agreement for the challenge samples collected diffusively in an exposure chamber in the laboratory, with most measurements within ±25% of the theoretical concentration. Statistically significant differences among laboratories for ambient challenge samples were small, less than 1 part per billion by volume (ppbv). Results from all laboratories exhibited good precision and generally agreed well with each other.

A study of X100 pipeline steel passivation in mildly alkaline bicarbonate solutions using electrochemical impedance spectroscopy under potentiodynamic conditions and Mott-Schottky

NASA Astrophysics Data System (ADS)

Gadala, Ibrahim M.; Alfantazi, Akram

2015-12-01

The key steps involved in X100 pipeline steel passivation in bicarbonate-based simulated soil solutions from the pre-passive to transpassive potential regions have been analyzed here using a step-wise anodizing-electrochemical impedance spectroscopy (EIS) routine. Pre-passive steps involve parallel dissolution-adsorption in early stages followed by clear diffusion-adsorption control shortly before iron hydroxide formation. Aggressive NS4 chlorides/sulfate promote steel dissolution whilst inhibiting diffusion in pre-passive steps. Diffusive and adsorptive effects remain during iron hydroxide formation, but withdraw shortly thereafter during its removal and the development of the stable iron carbonate passive layer. Passive layer protectiveness is evaluated using EIS fitting, current density analysis, and correlations with semiconductive parameters, consistently revealing improved robustness in colder, bicarbonate-rich, chloride/sulfate-free conditions. Ferrous oxide formation at higher potentials results in markedly lower impedances with disordered behavior, and the involvement of the iron(III) valence state is observed in Mott-Schottky tests exclusively for 75 °C conditions.

An efficient passive planar micromixer with ellipse-like micropillars for continuous mixing of human blood.

PubMed

Tran-Minh, Nhut; Dong, Tao; Karlsen, Frank

2014-10-01

In this paper, a passive planar micromixer with ellipse-like micropillars is proposed to operate in the laminar flow regime for high mixing efficiency. With a splitting and recombination (SAR) concept, the diffusion distance of the fluids in a micromixer with ellipse-like micropillars was decreased. Thus, space usage for micromixer of an automatic sample collection system is also minimized. Numerical simulation was conducted to evaluate the performance of proposed micromixer by solving the governing Navier-Stokes equation and convection-diffusion equation. With software (COMSOL 4.3) for computational fluid dynamics (CFD) we simulated the mixing of fluids in a micromixer with ellipse-like micropillars and basic T-type mixer in a laminar flow regime. The efficiency of the proposed micromixer is shown in numerical results and is verified by measurement results. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

In planta passive sampling devices for assessing subsurface chlorinated solvents.

PubMed

Shetty, Mikhil K; Limmer, Matt A; Waltermire, Kendra; Morrison, Glenn C; Burken, Joel G

2014-06-01

Contaminant concentrations in trees have been used to delineate groundwater contaminant plumes (i.e., phytoscreening); however, variability in tree composition hinders accurate measurement of contaminant concentrations in planta, particularly for long-term monitoring. This study investigated in planta passive sampling devices (PSDs), termed solid phase samplers (SPSs) to be used as a surrogate tree core. Characteristics studied for five materials included material-air partitioning coefficients (Kma) for chlorinated solvents, sampler equilibration time and field suitability. The materials investigated were polydimethylsiloxane (PDMS), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polyoxymethylene (POM) and plasticized polyvinyl chloride (PVC). Both PDMS and LLDPE samplers demonstrated high partitioning coefficients and diffusivities and were further tested in greenhouse experiments and field trials. While most of the materials could be used for passive sampling, the PDMS SPSs performed best as an in planta sampler. Such a sampler was able to accurately measure trichloroethylene (TCE) and tetrachloroethylene (PCE) concentrations while simultaneously incorporating simple operation and minimal impact to the surrounding property and environment. Copyright © 2013 Elsevier Ltd. All rights reserved.

Partitioning of hydrophobic organic contaminants between polymer and lipids for two silicones and low density polyethylene.

PubMed

Smedes, Foppe; Rusina, Tatsiana P; Beeltje, Henry; Mayer, Philipp

2017-11-01

Polymers are increasingly used for passive sampling of neutral hydrophobic organic substances (HOC) in environmental media including water, air, soil, sediment and even biological tissue. The equilibrium concentration of HOC in the polymer can be measured and then converted into equilibrium concentrations in other (defined) media, which however requires appropriate polymer to media partition coefficients. We determined thus polymer-lipid partition coefficients (K PL ) of various PCB, PAH and organochlorine pesticides by equilibration of two silicones and low density polyethylene (LDPE) with fish oil and Triolein at 4 °C and 20 °C. We observed (i) that K PL was largely independent of lipid type and temperature, (ii) that lipid diffusion rates in the polymers were higher compared to predictions based on their molecular volume, (iii) that silicones showed higher lipid diffusion and lower lipid sorption compared to LDPE and (iv) that absorbed lipid behaved like a co-solute and did not affect the partitioning of HOC at least for the smaller molecular size HOC. The obtained K PL can convert measured equilibrium concentrations in passive sampling polymers into equilibrium concentrations in lipid, which then can be used (1) for environmental quality monitoring and assessment, (2) for thermodynamic exposure assessment and (3) for assessing the linkage between passive sampling and the traditionally measured lipid-normalized concentrations in biota. LDPE-lipid partition coefficients may also be of use for a thermodynamically sound risk assessment of HOC contained in microplastics. Copyright © 2017 Elsevier Ltd. All rights reserved.

Groundwater geochemical and selected volatile organic compound data, Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, July 2013

USGS Publications Warehouse

Huffman, Raegan L.

2014-01-01

Previous investigations indicate that concentrations of chlorinated volatile organic compounds (CVOCs) are substantial in groundwater beneath the 9-acre former landfill at Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington. The U.S. Geological Survey has continued to monitor groundwater geochemistry to ensure that conditions remain favorable for contaminant biodegradation as specified in the Record of Decision for the site. This report presents groundwater geochemical and selected CVOC data collected at Operable Unit 1 by the U.S. Geological Survey during July 9–18, 2013, in support of longterm monitoring for natural attenuation. Groundwater samples were collected from 13 wells and 9 piezometers, as well as from 10 shallow groundwater passive-diffusion sampling sites in the nearby marsh. Samples from all wells and piezometers were analyzed for oxidation-reduction (redox) sensitive constituents and dissolved gases. Samples from all piezometers and four wells also were analyzed for CVOCs, as were all samples from the passive-diffusion sampling sites. In 2013, concentrations of redox-sensitive constituents measured at all wells and piezometers were consistent with those measured in previous years, with dissolved oxygen concentrations at all except an upgradient well 0.2 milligrams per liter or less; little to no detectable nitrate; abundant dissolved manganese, iron, and methane; and commonly detected sulfide. In the upper aquifer of the northern plantation in 2013, CVOC concentrations at all piezometers were similar to those measured in previous years, and concentrations of the reductive dechlorination byproducts ethane and ethene were slightly lower or the same as concentrations measured in 2012. In the upper aquifer of the southern plantation, CVOC concentrations measured in piezometers during 2013 continued to be variable as in previous years, and often very high, and reductive dechlorination byproducts were detected in two of the three wells and in all but one piezometer. Beneath the marsh adjacent to the southern plantation, chloroethene concentrations measured in 2013 continued to vary spatially and temporaly, and also were very high. Total CVOC concentrations, at what have been historically the most contaminated passive-diffusion sampler sites (S-4, S-4B, S-5, and S-5B) remained elevated. For the intermediate aquifer in 2013, concentrations of reductive dechlorination byproducts ethane and ethene and CVOCs were consistent with those measured in previous years.

A new in-situ method to determine the apparent gas diffusion coefficient of soils

NASA Astrophysics Data System (ADS)

Laemmel, Thomas; Paulus, Sinikka; Schack-Kirchner, Helmer; Maier, Martin

2015-04-01

Soil aeration is an important factor for the biological activity in the soil and soil respiration. Generally, gas exchange between soil and atmosphere is assumed to be governed by diffusion and Fick's Law is used to describe the fluxes in the soil. The "apparent soil gas diffusion coefficient" represents the proportional factor between the flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gases through the soil. One common way to determine this coefficient is to take core samples in the field and determine it in the lab. Unfortunately this method is destructive and needs laborious field work and can only reflect a small fraction of the whole soil. As a consequence insecurity about the resulting effective diffusivity on the profile scale must remain. We developed a new in-situ method using new gas sampling device, tracer gas and inverse soil gas modelling. The gas sampling device contains several sampling depths and can be easily installed into vertical holes of an auger, which allows for fast installation of the system. At the lower end of the device inert tracer gas is injected continuously. The tracer gas diffuses into the surrounding soil. The resulting distribution of the tracer gas concentrations is used to deduce the diffusivity profile of the soil. For Finite Element Modeling of the gas sampling device/soil system the program COMSOL is used. We will present the results of a field campaign comparing the new in-situ method with lab measurements on soil cores. The new sampling pole has several interesting advantages: it can be used in-situ and over a long time; so it allows following modifications of diffusion coefficients in interaction with rain but also vegetation cycle and wind.

Diffusive sampling of methylene chloride with solid phase microextraction.

PubMed

Chen, Cheng-Yao; Hsiech, Chunming; Lin, Jia-Ming

2006-12-29

This study examined the characteristics of a solid phase microextraction (SPME) assembly as a passive sampler to determine the short-term exposure level (STEL) of methylene chloride. Two types of SPME fibers and six sampling-related factors were chosen and nested in an L(18) Taguchi's orthogonal array. Samples were thermally desorpted and analyzed by gas chromatograph equipped with an electron capture detector (GC/ECD). The use of 85-mum Carboxen/polydimethylsiloxane (Car/PDMS) fibers resulted in greater adsorbed mass, which was highly correlated with the product of concentration and sampling time (r>0.99, p<0.0001), than 85-microm polyacrylate fibers. The sampling rate (SR) of the 85-microm Carboxen/polydimethylsiloxane fibers was not significantly affected by variations in relative humidity (0-80%) and coexistent toluene (none to 100 ppm). Variance of sampling rate was predominantly attributed to the diffusive path length (86.4%) and sampling time (5.7%). With diffusive paths of 3, 10 and 15 mm, the sampling rates of 85-microm Carboxen/polydimethylsiloxane fibers for methylene chloride were 1.4 x 10(-2), 7.7 x 10(-3) and 5.1 x1 0(-3)mL min(-1), respectively. The measured sampling rates were greater than the theoretical values, and decreased with increment of sampling time until they came to constant.

Retardation mechanism of ultrathin Al2O3 interlayer on Y2O3 passivated gallium nitride surface.

PubMed

Quah, Hock Jin; Cheong, Kuan Yew

2014-05-28

A systematic investigation was carried out by incorporating an ultrathin aluminum oxide (Al2O3) as an interlayer between yttrium oxide (Y2O3) passivation layer and GaN substrate. The sandwiched samples were then subjected to postdeposition annealing in oxygen ambient from 400 to 800 °C. The Al2O3 interlayer was discovered to play a significant role in slowing down inward diffusion of oxygen through the Y2O3 passivation layer as well as in impeding outward diffusion of Ga(3+) and N(3-) from the decomposed GaN surface. These beneficial effects have suppressed subsequent formation of interfacial layer. A mechanism in association with the function of Al2O3 as an interlayer was suggested and discussed. The mechanism was explicitly described on the basis of the obtained results from X-ray diffraction, X-ray photoelectron spectroscopy, energy-filtered transmission electron microscopy (TEM), high resolution TEM, and electron energy loss spectroscopy line scan. A correlation between the proposed mechanism and metal-oxide-semiconductor characteristics of Y2O3/Al2O3/GaN structure has been proposed.

Turbulent transport of a passive-scalar field by using a renormalization-group method

NASA Technical Reports Server (NTRS)

Hossain, Murshed

1992-01-01

A passive-scalar field is considered to evolve under the influence of a turbulent fluid governed by the Navier-Stokes equation. Turbulent-transport coefficients are calculated by small-scale elimination using a renormalization-group method. Turbulent processes couple both the viscosity and the diffusivity. In the absence of any correlation between the passive-scalar fluctuations and any component of the fluid velocity, the renormalized diffusivity is essentially the same as if the fluid velocity were frozen, although the renormalized equation does contain higher-order nonlinear terms involving viscosity. This arises due to the nonlinear interaction of the velocity with itself. In the presence of a finite correlation, the turbulent diffusivity becomes coupled with both the velocity field and the viscosity. There is then a dependence of the turbulent decay of the passive scalar on the turbulent Prandtl number.

Determination of deployment specific chemical uptake rates for SDB-RPD Empore disk using a passive flow monitor (PFM).

PubMed

O'Brien, Dominique; Bartkow, Michael; Mueller, Jochen F

2011-05-01

The use of the adsorbent styrenedivinylbenzene-reverse phase sulfonated (SDB-RPD) Empore disk in a chemcatcher type passive sampler is routinely applied in Australia when monitoring herbicides in aquatic environments. One key challenge in the use of passive samplers is mitigating the potentially confounding effects of varying flow conditions on chemical uptake by the passive sampler. Performance reference compounds (PRCs) may be applied to correct sampling rates (R(s)) for site specific changed in flow and temperature however evidence suggests the use of PRCs is unreliable when applied to adsorbent passive samplers. The use of the passive flow monitor (PFM) has been introduced for the assessment of site-specific changes in water flow. In the presented study we have demonstrated that the R(s) at which both atrazine and prometryn are accumulated within the SDB-RPD-Empore disk is dependent on the flow conditions. Further, the calibration of the measured R(s) for chemical uptake by the SDB-RPD-Empore disk to the mass lost from the PFM has shown that the PFM provides an accurate measure of R(s) for flow velocities from 0 to 16cms(-1). Notably, for flow rates >16cms(-1), a non linear increase in the R(s) of both herbicides was observed which indicates that the key resistance to uptake into the SDB-RPD Empore disk is associated with the diffusion through the overlying diffusion limiting membrane. Overall the greatest uncertainty remains at very low flow conditions, which are unlikely to often occur in surface waters. Validation of the PFM use has also been undertaken in a limited field study. Copyright © 2011 Elsevier Ltd. All rights reserved.

Carrier characteristics influence the kinetics of passive drug loading into lipid nanoemulsions.

PubMed

Göke, Katrin; Bunjes, Heike

2018-05-01

Passive loading as a novel screening approach is a material-saving tool for the efficient selection of a suitable colloidal lipid carrier system for poorly water soluble drug candidates. This method comprises incubation of preformed carrier systems with drug powder and subsequent determination of the resulting drug load of the carrier particles after removal of excess drug. For reliable routine use and to obtain meaningful loading results, information on the kinetics of the process is required. Passive loading proceeds via a dissolution-diffusion-based mechanism, where drug surface area and drug water solubility are key parameters for fast passive loading. While the influence of the drug characteristics is mostly understood, the influence of the carrier characteristics remains unknown. The aim of this study was to examine how the lipid nanocarriers' characteristics, i.e. the type of lipid, the lipid content and the particle size, influence the kinetics of passive loading. Fenofibrate was used as model drug and the loading progress was analyzed by UV spectroscopy. The saturation solubility in the nanocarrier particles, i.e. the lipid type, did not influence the passive loading rate constant. Low lipid content in the nanocarrier and a small nanocarrier particle size both increased passive loading speed. Both variations increase the diffusivity of the nanocarrier particles, which is the primary cause for fast loading at these conditions: The quicker the carrier particles diffuse, the higher is the speed of passive loading. The influence of the diffusivity of the lipid nanocarriers and the effect of drug dissolution rate were included in an overall mechanistic model developed for similar processes (A. Balakrishnan, B.D. Rege, G.L. Amidon, J.E. Polli, Surfactant-mediated dissolution: contributions of solubility enhancement and relatively low micelle diffusivity, J. Pharm. Sci. 93 (2004) 2064-2075). The resulting mechanistic model gave a good estimate of the speed of passive loading in nanoemulsions. Whilst the drug's characteristics - apart from drug surface area - are basically fixed, the lipid nanocarriers can be customized to improve passive loading speed, e.g. by using small nanocarrier particles. The knowledge of the loading mechanism now allows the use of passive loading for the straightforward, material-saving selection of suitable lipid drug nanocarriers. Copyright © 2017 Elsevier B.V. All rights reserved.

Record Charge Carrier Diffusion Length in Colloidal Quantum Dot Solids via Mutual Dot-To-Dot Surface Passivation.

PubMed

Carey, Graham H; Levina, Larissa; Comin, Riccardo; Voznyy, Oleksandr; Sargent, Edward H

2015-06-03

Through a combination of chemical and mutual dot-to-dot surface passivation, high-quality colloidal quantum dot solids are fabricated. The joint passivation techniques lead to a record diffusion length for colloidal quantum dots of 230 ± 20 nm. The technique is applied to create thick photovoltaic devices that exhibit high current density without losing fill factor. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dosimeter for monitoring vapors and aerosols of organic compounds

DOEpatents

Vo-Dinh, Tuan

1987-01-01

A dosimeter is provided for collecting and detecting vapors and aerosols of organic compounds. The dosimeter comprises a lightweight, passive device that can be conveniently worn by a person as a badge or placed at a stationary location. The dosimeter includes a sample collector comprising a porous web treated with a chemical for inducing molecular displacement and enhancing phosphorescence. Compounds are collected onto the web by molecular diffusion. The web also serves as the sample medium for detecting the compounds by a room temperature phosphorescence technique.

Novel method for minority-carrier mobility measurement using photoconductance decay with chemically passivated and plasma damaged surfaces

NASA Astrophysics Data System (ADS)

Stephens, A. W.; Green, M. A.

1996-10-01

A method for measuring minority-carrier mobility using microwave-detected photoconductance decay without requiring bulk lifetime, estimates is presented. Three different measurements on a single sample yield values for surface recombination velocity, bulk lifetime, and diffusivity. For each measurement the surface conditions of the sample are changed, allowing extraction of different parameters. The usefulness of 0.08 molar ethanol/iodine solution as a means of achieving such good surface passivation is demonstrated. The following procedure was used to achieve high surface recombination. A CF4 plasma surface etch was shown to achieve the same level of surface damage as mechanical abrasion. The advantage of the new method is that it completely eliminates the chance of breaking samples during the abrasion process, which is of particular advantage for thin samples. The new experimental method for minority-carrier mobility measurement is evaluated using carrier lifetime measurements made on a commercially available Leo Giken ``Wafer-τ'' lifetime tester.

Passivity analysis for uncertain BAM neural networks with time delays and reaction-diffusions

NASA Astrophysics Data System (ADS)

Zhou, Jianping; Xu, Shengyuan; Shen, Hao; Zhang, Baoyong

2013-08-01

This article deals with the problem of passivity analysis for delayed reaction-diffusion bidirectional associative memory (BAM) neural networks with weight uncertainties. By using a new integral inequality, we first present a passivity condition for the nominal networks, and then extend the result to the case with linear fractional weight uncertainties. The proposed conditions are expressed in terms of linear matrix inequalities, and thus can be checked easily. Examples are provided to demonstrate the effectiveness of the proposed results.

Error in measuring radon in soil gas by means of passive detectors

USGS Publications Warehouse

Tanner, A.B.

1991-01-01

Passive detection of radon isotopes depends on diffusion of radon atoms from the sites of their generation to the location of the detecting or collecting device. Because some radon decays en route to a passive detector in soil, the radon concentration measured by the detector must be less than the concentration in those soil pores where it is undiminished by diffusion to the detector cavity. The true radon concentration may be significantly underestimated in moist soils. -Author

Passive scalars: Mixing, diffusion, and intermittency in helical and nonhelical rotating turbulence

NASA Astrophysics Data System (ADS)

Imazio, P. Rodriguez; Mininni, P. D.

2017-03-01

We use direct numerical simulations to compute structure functions, scaling exponents, probability density functions, and effective transport coefficients of passive scalars in turbulent rotating helical and nonhelical flows. We show that helicity affects the inertial range scaling of the velocity and of the passive scalar when rotation is present, with a spectral law consistent with ˜k⊥-1.4 for the passive scalar variance spectrum. This scaling law is consistent with a phenomenological argument [P. Rodriguez Imazio and P. D. Mininni, Phys. Rev. E 83, 066309 (2011), 10.1103/PhysRevE.83.066309] for rotating nonhelical flows, which follows directly from Kolmogorov-Obukhov scaling and states that if energy follows a E (k ) ˜k-n law, then the passive scalar variance follows a law V (k ) ˜k-nθ with nθ=(5 -n ) /2 . With the second-order scaling exponent obtained from this law, and using the Kraichnan model, we obtain anomalous scaling exponents for the passive scalar that are in good agreement with the numerical results. Multifractal intermittency models are also considered. Intermittency of the passive scalar is stronger than in the nonhelical rotating case, a result that is also confirmed by stronger non-Gaussian tails in the probability density functions of field increments. Finally, Fick's law is used to compute the effective diffusion coefficients in the directions parallel and perpendicular to rotation. Calculations indicate that horizontal diffusion decreases in the presence of helicity in rotating flows, while vertical diffusion increases. A simple mean field argument explains this behavior in terms of the amplitude of velocity fluctuations.

A novel passive water sampler for in situ sampling of antibiotics.

PubMed

Chen, Chang-Er; Zhang, Hao; Jones, Kevin C

2012-05-01

Passive water sampling has several advantages over active methods; it provides time-integrated data, can save on time and cost compared to active methods, and yield high spatial resolution data through co-deployment of simple, cheap units. However, one problem with many sampler designs in current use is that their uptake rates for trace substances of interest are flow-rate dependent, thereby requiring calibration data and other information to enable water concentrations to be derived from the mass per sampler. However, the 'family' of samplers employing the principle of diffusive gradients in thin films (DGT) provides an in situ means of quantitatively measuring labile species in aquatic systems without field calibration. So far, this technique has only been tested and applied in inorganic substances: metals, radionuclides, nutrients, etc. Design and applications of DGT to trace organic contaminants ('o-DGT') would be of widespread interest. This study describes the laboratory testing and performance characteristics of o-DGT, with the antibiotic sulfamethoxazole (SMX) as a model compound and XAD18 as the novel binding agent. o-DGT uptake of SMX increased with time and decreased with diffusion layer thickness, confirming the principle for SMX. XAD18 showed sufficiently high capacity for SMX for routine field applications. o-DGT measurement of SMX was independent of pH (6-9) and ionic strength (0.001-0.1 M) and not affected by flow rate once above static conditions. The diffusion coefficient of SMX in the sampler was measured using an independent diffusion cell and information is presented to allow temperature correction and derivation of aqueous concentrations from deployed samplers. The potential use of o-DGT for in situ measurement of pharmaceutical antibiotics is confirmed by this study and applications are briefly discussed.

Scaling laws of passive-scalar diffusion in the interstellar medium

NASA Astrophysics Data System (ADS)

Colbrook, Matthew J.; Ma, Xiangcheng; Hopkins, Philip F.; Squire, Jonathan

2017-05-01

Passive-scalar mixing (metals, molecules, etc.) in the turbulent interstellar medium (ISM) is critical for abundance patterns of stars and clusters, galaxy and star formation, and cooling from the circumgalactic medium. However, the fundamental scaling laws remain poorly understood in the highly supersonic, magnetized, shearing regime relevant for the ISM. We therefore study the full scaling laws governing passive-scalar transport in idealized simulations of supersonic turbulence. Using simple phenomenological arguments for the variation of diffusivity with scale based on Richardson diffusion, we propose a simple fractional diffusion equation to describe the turbulent advection of an initial passive scalar distribution. These predictions agree well with the measurements from simulations, and vary with turbulent Mach number in the expected manner, remaining valid even in the presence of a large-scale shear flow (e.g. rotation in a galactic disc). The evolution of the scalar distribution is not the same as obtained using simple, constant 'effective diffusivity' as in Smagorinsky models, because the scale dependence of turbulent transport means an initially Gaussian distribution quickly develops highly non-Gaussian tails. We also emphasize that these are mean scalings that apply only to ensemble behaviours (assuming many different, random scalar injection sites): individual Lagrangian 'patches' remain coherent (poorly mixed) and simply advect for a large number of turbulent flow-crossing times.

Evidence for equivalence of diffusion processes of passive scalar and magnetic fields in anisotropic Navier-Stokes turbulence.

PubMed

Jurčišinová, E; Jurčišin, M

2017-05-01

The influence of the uniaxial small-scale anisotropy on the kinematic magnetohydrodynamic turbulence is investigated by using the field theoretic renormalization group technique in the one-loop approximation of a perturbation theory. The infrared stable fixed point of the renormalization group equations, which drives the scaling properties of the model in the inertial range, is investigated as the function of the anisotropy parameters and it is shown that, at least at the one-loop level of approximation, the diffusion processes of the weak passive magnetic field in the anisotropically driven kinematic magnetohydrodynamic turbulence are completely equivalent to the corresponding diffusion processes of passively advected scalar fields in the anisotropic Navier-Stokes turbulent environments.

Multi-layer light-weight protective coating and method for application

NASA Technical Reports Server (NTRS)

Wiedemann, Karl E. (Inventor); Clark, Ronald K. (Inventor); Taylor, Patrick J. (Inventor)

1992-01-01

A thin, light-weight, multi-layer coating is provided for protecting metals and their alloys from environmental attack at high temperatures. A reaction barrier is applied to the metal substrate and a diffusion barrier is then applied to the reaction barrier. A sealant layer may also be applied to the diffusion barrier if desired. The reaction barrier is either non-reactive or passivating with respect to the metal substrate and the diffusion barrier. The diffusion barrier is either non-reactive or passivating with respect to the reaction barrier and the sealant layer. The sealant layer is immiscible with the diffusion barrier and has a softening point below the expected use temperature of the metal.

Groundwater geochemical and selected volatile organic compound data, Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, June and October 2012

USGS Publications Warehouse

Huffman, R.L.

2013-01-01

Previous investigations indicate that concentrations of chlorinated volatile organic compounds are substantial in groundwater beneath the 9-acre former landfill at Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington. The U.S. Geological Survey has continued to monitor groundwater geochemistry to ensure that conditions remain favorable for contaminant biodegradation as specified in the Record of Decision for the site. This report presents groundwater geochemical and selected chlorinated volatile organic compound data collected at Operable Unit 1 by the U.S. Geological Survey during June and October 2012, in support of long-term monitoring for natural attenuation. Groundwater samples were collected from 13 wells and 9 piezometers, as well as from 10 shallow groundwater passive-diffusion sampling sites in the nearby marsh. Samples from all wells and piezometers were analyzed for oxidation-reduction (redox) sensitive constituents and dissolved gases. Samples from all piezometers also were analyzed for chlorinated volatile organic compounds, as were all samples from the passive-diffusion sampling sites. In 2012, concentrations of redox-sensitive constituents measured at all wells and piezometers were consistent with those measured in previous years, with dissolved oxygen concentrations all at 0.4 milligram per liter or less; little to no detectable nitrate; abundant dissolved manganese, iron, and methane; and commonly detected sulfide. In the upper aquifer of the northern plantation in 2012, chlorinated volatile organic compound (CVOC) concentrations at all piezometers were similar to those measured in previous years, and concentrations of the reductive dechlorination byproducts ethane and ethene were slightly higher or the same as concentrations measured in 2011. In the upper aquifer of the southern plantation, CVOC concentrations measured in piezometers during 2012 continued to be extremely variable as in previous years, and often very high, and reductive dechlorination byproducts were detected in two of the four wells and in all piezometers. Beneath the marsh adjacent to the southern plantation, chloroethene concentrations measured in 2012 continued to vary spatially and temporarily, and also were very high. Additionally, CVOC concentrations measured in samplers deployed in access tubes were about two to four times less than those measured in the two samplers buried nearby, beneath the marsh stream. Total CVOC concentration, at what has been historically the most contaminated passive-diffusion sampler site (S-4), continued an increasing trend. For the intermediate aquifer in 2012, concentrations of reductive dechlorination byproducts ethane and ethene were consistent with those measured in previous years.

Surface passivation of nano-textured fluorescent SiC by atomic layer deposited TiO2

NASA Astrophysics Data System (ADS)

Lu, Weifang; Ou, Yiyu; Jokubavicius, Valdas; Fadil, Ahmed; Syväjärvi, Mikael; Petersen, Paul Michael; Ou, Haiyan

2016-07-01

Nano-textured surfaces have played a key role in optoelectronic materials to enhance the light extraction efficiency. In this work, morphology and optical properties of nano-textured SiC covered with atomic layer deposited (ALD) TiO2 were investigated. In order to obtain a high quality surface for TiO2 deposition, a three-step cleaning procedure was introduced after RIE etching. The morphology of anatase TiO2 indicates that the nano-textured substrate has a much higher surface nucleated grain density than a flat substrate at the beginning of the deposition process. The corresponding reflectance increases with TiO2 thickness due to increased surface diffuse reflection. The passivation effect of ALD TiO2 thin film on the nano-textured fluorescent 6H-SiC sample was also investigated and a PL intensity improvement of 8.05% was obtained due to the surface passivation.

Dosimeter for monitoring vapors and aerosols of organic compounds

DOEpatents

Vo-Dinh, T.

1987-07-14

A dosimeter is provided for collecting and detecting vapors and aerosols of organic compounds. The dosimeter comprises a lightweight, passive device that can be conveniently worn by a person as a badge or placed at a stationary location. The dosimeter includes a sample collector comprising a porous web treated with a chemical for inducing molecular displacement and enhancing phosphorescence. Compounds are collected onto the web by molecular diffusion. The web also serves as the sample medium for detecting the compounds by a room temperature phosphorescence technique. 7 figs.

A Novel MicroElectroMechanical System (MEMS) Device for Passive Sampling of Hydrophobic Compounds

DTIC Science & Technology

2011-05-01

bioavailability  Samplers are removed, extracted for CoC, analyzed ▬ For organics: solid phase micro extraction ( SPME ) fibers, semi- permeable membrane...devices (SPMD), polyoxymethylene (POM) ▬ For metals: diffuse gradients in thin films (DGT) SPME fiber ESTCP project, Reible and Lotufo Applications to...Predict Bioaccumulation You et al. 2006, EST, 40: 6348 SPME concentrations were predictive of tissue concentrations of PCBs in field-contaminated

Coupling of active motion and advection shapes intracellular cargo transport.

PubMed

Khuc Trong, Philipp; Guck, Jochen; Goldstein, Raymond E

2012-07-13

Intracellular cargo transport can arise from passive diffusion, active motor-driven transport along cytoskeletal filament networks, and passive advection by fluid flows entrained by such cargo-motor motion. Active and advective transport are thus intrinsically coupled as related, yet different representations of the same underlying network structure. A reaction-advection-diffusion system is used here to show that this coupling affects the transport and localization of a passive tracer in a confined geometry. For sufficiently low diffusion, cargo localization to a target zone is optimized either by low reaction kinetics and decoupling of bound and unbound states, or by a mostly disordered cytoskeletal network with only weak directional bias. These generic results may help to rationalize subtle features of cytoskeletal networks, for example as observed for microtubules in fly oocytes.

Buried structure for increasing fabrication performance of micromaterial by electromigration

NASA Astrophysics Data System (ADS)

Kimura, Yasuhiro; Saka, Masumi

2016-06-01

The electromigration (EM) technique is a physical synthetic growth method for micro/nanomaterials. EM causes atomic diffusion in a metal line by high-density electron flows. The intentional control of accumulation and relaxation of atoms by EM can lead to the fabrication of a micro/nanomaterial. TiN passivation has been utilized as a component of sample in the EM technique. Although TiN passivation can simplify the cumbersome processes for preparing the sample, the leakage of current naturally occurs because of the conductivity of TiN as a side effect and decreases the performance of micro/nanomaterial fabrication. In the present work, we propose a buried structure, which contributes to significantly decreasing the current for fabricating an Al micromaterial by confining the current flow in the EM technique. The fabrication performance was evaluated based on the threshold current for fabricating an Al micromaterial using the buried structure and the previous structure with the leakage of current.

Carrier-Mediated Cocaine Transport at the Blood-Brain Barrier as a Putative Mechanism in Addiction Liability

PubMed Central

Chapy, Hélène; Smirnova, Maria; André, Pascal; Schlatter, Joël; Chiadmi, Fouad; Couraud, Pierre-Olivier; Scherrmann, Jean-Michel; Declèves, Xavier

2015-01-01

Background: The rate of entry of cocaine into the brain is a critical factor that influences neuronal plasticity and the development of cocaine addiction. Until now, passive diffusion has been considered the unique mechanism known by which cocaine crosses the blood-brain barrier. Methods: We reassessed mechanisms of transport of cocaine at the blood-brain barrier using a human cerebral capillary endothelial cell line (hCMEC/D3) and in situ mouse carotid perfusion. Results: Both in vivo and in vitro cocaine transport studies demonstrated the coexistence of a carrier-mediated process with passive diffusion. At pharmacological exposure level, passive diffusion of cocaine accounted for only 22.5% of the total cocaine influx in mice and 5.9% in hCMEC/D3 cells, whereas the carrier-mediated influx rate was 3.4 times greater than its passive diffusion rate in vivo. The functional identification of this carrier-mediated transport demonstrated the involvement of a proton antiporter that shared the properties of the previously characterized clonidine and nicotine transporter. The functionnal characterization suggests that the solute carrier (SLC) transporters Oct (Slc22a1-3), Mate (Slc47a1) and Octn (Slc22a4-5) are not involved in the cocaine transport in vivo and in vitro. Diphenhydramine, heroin, tramadol, cocaethylene, and norcocaine all strongly inhibited cocaine transport, unlike benzoylecgonine. Trans-stimulation studies indicated that diphenhydramine, nicotine, 3,4-methylenedioxyamphetamine (ecstasy) and the cathinone compound 3,4-methylenedioxypyrovalerone (MDPV) were also substrates of the cocaine transporter. Conclusions: Cocaine transport at the BBB involves a proton-antiporter flux that is quantitatively much more important than its passive diffusion. The molecular identification and characterization of this transporter will provide new tools to understand its role in addictive mechanisms. PMID:25539501

Effective Drug Delivery in Diffuse Intrinsic Pontine Glioma: A Theoretical Model to Identify Potential Candidates

PubMed Central

El-Khouly, Fatma E.; van Vuurden, Dannis G.; Stroink, Thom; Hulleman, Esther; Kaspers, Gertjan J. L.; Hendrikse, N. Harry; Veldhuijzen van Zanten, Sophie E. M.

2017-01-01

Despite decades of clinical trials for diffuse intrinsic pontine glioma (DIPG), patient survival does not exceed 10% at two years post-diagnosis. Lack of benefit from systemic chemotherapy may be attributed to an intact bloodbrain barrier (BBB). We aim to develop a theoretical model including relevant physicochemical properties in order to review whether applied chemotherapeutics are suitable for passive diffusion through an intact BBB or whether local administration via convection-enhanced delivery (CED) may increase their therapeutic potential. Physicochemical properties (lipophilicity, molecular weight, and charge in physiological environment) of anticancer drugs historically and currently administered to DIPG patients, that affect passive diffusion over the BBB, were included in the model. Subsequently, the likelihood of BBB passage of these drugs was ascertained, as well as their potential for intratumoral administration via CED. As only non-molecularly charged, lipophilic, and relatively small sized drugs are likely to passively diffuse through the BBB, out of 51 drugs modeled, only 8 (15%)—carmustine, lomustine, erlotinib, vismodegib, lenalomide, thalidomide, vorinostat, and mebendazole—are theoretically qualified for systemic administration in DIPG. Local administration via CED might create more therapeutic options, excluding only positively charged drugs and drugs that are either prodrugs and/or only available as oral formulation. A wide variety of drugs have been administered systemically to DIPG patients. Our model shows that only few are likely to penetrate the BBB via passive diffusion, which may partly explain the lack of efficacy. Drug distribution via CED is less dependent on physicochemical properties and may increase the therapeutic options for DIPG. PMID:29164054

Characterization of the olfactory impact around a wastewater treatment plant: optimization and validation of a hydrogen sulfide determination procedure based on passive diffusion sampling.

PubMed

Colomer, Fernando Llavador; Espinós-Morató, Héctor; Iglesias, Enrique Mantilla; Pérez, Tatiana Gómez; Campos-Candel, Andreu; Lozano, Caterina Coll

2012-08-01

A monitoring program based on an indirect method was conducted to assess the approximation of the olfactory impact in several wastewater treatment plants (in the present work, only one is shown). The method uses H2S passive sampling using Palmes-type diffusion tubes impregnated with silver nitrate and fluorometric analysis employing fluorescein mercuric acetate. The analytical procedure was validated in the exposure chamber. Exposure periods ofat least 4 days are recommended. The quantification limit of the procedure is 0.61 ppb for a 5-day sampling, which allows the H2S immission (ground concentration) level to be measured within its low odor threshold, from 0.5 to 300 ppb. Experimental results suggest an exposure time greater than 4 days, while recovery efficiency of the procedure, 93.0+/-1.8%, seems not to depend on the amount of H2S collected by the samplers within their application range. The repeatability, expressed as relative standard deviation, is lower than 7%, which is within the limits normally accepted for this type of sampler. Statistical comparison showed that this procedure and the reference method provide analogous accuracy. The proposed procedure was applied in two experimental campaigns, one intensive and the other extensive, and concentrations within the H2S low odor threshold were quantified at each sampling point. From these results, it can be concluded that the procedure shows good potential for monitoring the olfactory impact around facilities where H2S emissions are dominant.

Characterization of the olfactory impact around a wastewater treatment plant: Optimization and validation of a hydrogen sulfide determination procedure based on passive diffusion sampling.

PubMed

Colomer, Fernando Llavador; Espinós-Morató, Héctor; Iglesias, Enrique Mantilla; Pérez, Tatiana Gómez; Campos-Candel, Andreu; Coll Lozano, Caterina

2012-08-01

A monitoring program based on an indirect method was conducted to assess the approximation of the olfactory impact in several wastewater treatment plants (in the present work, only one is shown). The method uses H 2 S passive sampling using Palmes-type diffusion tubes impregnated with silver nitrate and fluorometric analysis employing fluorescein mercuric acetate. The analytical procedure was validated in the exposure chamber. Exposure periods of at least 4 days are recommended. The quantification limit of the procedure is 0.61 ppb for a 5-day sampling, which allows the H 2 S immission (ground concentration) level to be measured within its low odor threshold, from 0.5 to 300 ppb. Experimental results suggest an exposure time greater than 4 days, while recovery efficiency of the procedure, 93.0 ± 1.8%, seems not to depend on the amount of H 2 S collected by the samplers within their application range. The repeatability, expressed as relative standard deviation, is lower than 7%, which is within the limits normally accepted for this type of sampler. Statistical comparison showed that this procedure and the reference method provide analogous accuracy. The proposed procedure was applied in two experimental campaigns, one intensive and the other extensive, and concentrations within the H 2 S low odor threshold were quantified at each sampling point. From these results, it can be concluded that the procedure shows good potential for monitoring the olfactory impact around facilities where H 2 S emissions are dominant. [Box: see text].

Evaluation of Titanium Dioxide as a Binding Phase for the Passive Sampling of Glyphosate and Aminomethyl Phosphonic Acid in an Aquatic Environment.

PubMed

Fauvelle, Vincent; Nhu-Trang, Tran-Thi; Feret, Thibaut; Madarassou, Karine; Randon, Jérôme; Mazzella, Nicolas

2015-06-16

Glyphosate is the most widely used herbicide on a world scale for the last 40 years, for both urban and agricultural uses. Here we describe the first passive sampling method for estimating the concentration of glyphosate and AMPA (aminomethyl phosphonic acid, one of its major degradation products) in surface water. The sampling method is based on a newly developed configuration of the diffusive gradient in thin-film (DGT) technique, which includes a TiO2 binding phase, already in use for a wide range of anions. Glyphosate and AMPA were retained well on a TiO2 binding phase, and elution in a 1 mL of 1 M NaOH led to recoveries greater than 65%. We found no influence of pH or flow velocity on the diffusion coefficients through 0.8 mm polyacrylamide gels, although they did increase with temperature. TiO2 binding gels were able to accumulate up to 1167 ng of P for both glyphosate and AMPA, and linear accumulation was expected over several weeks, depending on environmental conditions. DGT sampling rates were close to 10 mL day(-1) in ultrapure water, while they were less than 1 mL day(-1) in the presence of naturally occurring ions (e.g., copper, iron, calcium, magnesium). These last results highlighted (i) the ability of DGT to measure only the freely dissolved fraction of glyphosate and AMPA in water and (ii) the needs to determine which fraction (total, particulate, dissolved, freely dissolved) is indeed bioactive.

Body mass scaling of passive oxygen diffusion in endotherms and ectotherms

PubMed Central

Gillooly, James F.; Gomez, Juan Pablo; Mavrodiev, Evgeny V.; Rong, Yue; McLamore, Eric S.

2016-01-01

The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick’s law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption. PMID:27118837

Body mass scaling of passive oxygen diffusion in endotherms and ectotherms.

PubMed

Gillooly, James F; Gomez, Juan Pablo; Mavrodiev, Evgeny V; Rong, Yue; McLamore, Eric S

2016-05-10

The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick's law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption.

Comparison of temporal trends in VOCs as measured with PDB samplers and low-flow sampling methods

USGS Publications Warehouse

Harte, P.T.

2002-01-01

Analysis of temporal trends in tetrachloroethylene (PCE) concentration determined by two sample techniques showed that passive diffusion bag (pdb) samplers adequately sample the large variation in PCE concentrations at the site. The slopes of the temporal trends in concentrations were comparable between the two techniques, and the pdb sample concentration generally reflected the instantaneous concentration sampled by the low-flow technique. Thus, the pdb samplers provided an appropriate sampling technique for PCE at these wells. One or two wells did not make the case for widespread application of pdb samples at all sites. However, application of pdb samples in some circumstances was appropriate for evaluating temporal and spatial variations in VOC concentrations, thus, should be considered as a useful tool in hydrogeology.

Determination of sub-part-per-million levels of formaldehyde in air using active or passive sampling on 2,4-dinitrophenylhydrazine-coated glass fiber filters and high-performance liquid chromatography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levin, J.O.; Andersson, K.; Lindahl, R.

1985-05-01

Formaldehyde is sampled from air with the use of a standard miniature glass fiber filter impregnated with 2,4-dinitrophenylhydrazine and phosphoric acid. The formaldehyde hydrazone is desorbed from the filter with acetonitrile and determined by high-performance liquid chromatography using UV detection at 365 nm. Recovery of gas-phase-generated formaldehyde as hydrazone from a 13-mm impregnated filter is 80-100% in the range 0.3-30 ..mu..g of formaldehyde. This corresponds to 0.1-10 mg/m/sup 3/ in a 3-L air sample. When the filter sampling system is used in the active mode, air can be sampled at a rate of up to 1 L/min, affording an overallmore » sensitivity of about 1 ..mu..g/m/sup 3/ based on a 60-L air sample. Results are given from measurements of formaldehyde in indoor air. The DNP-coated filters were also evaluated for passive sampling. In this case 37-mm standard glass fibers were used and the sampling rate was 55-65 mL/min in two types of dosimeters. The diffusion samplers are especially useful for personal exposure monitoring in the work environment. 24 references, 2 figures, 4 tables.« less

Study of surface passivation as a function of InP closed-ampoule solar cell fabrication processing variables

NASA Technical Reports Server (NTRS)

Faur, Mircea; Faur, Maria; Jenkins, Phillip; Goradia, Manju; Goradia, Chandra; Bailey, Sheila; Weinberg, Irving; Jayne, Douglas

1990-01-01

The effects of various surface preparation procedures, including chemical treatment and anodic or chemical oxidation, closed-ampoule diffusion conditions, and post-diffusion surface preparation and annealing conditions, on the passivating properties of InP have been investigated in order to optimize the fabrication procedures of n(+)p InP solar cells made by closed-ampoule diffusion of sulfur into p-type InP. The InP substrates used were p-type Cd-doped to a level of 1.7 x 10 to the 16th/cu cm, Zn-doped to levels of 2.2 x 10 to the 16th and 1.2 x 10 to the 18th/cu cm, and n-type S-doped to 4.4 x 10 to the 18th/cu cm. The passivating properties have been evaluated from photoluminescence (PL) and conductance-voltage (G-V) data. Good agreement was found between the level of surface passivation and the composition of different surface layers as revealed by X-ray photoelectron spectroscopy (XPS) analysis.

Passivation of phosphorus diffused silicon surfaces with Al2O3: Influence of surface doping concentration and thermal activation treatments

NASA Astrophysics Data System (ADS)

Richter, Armin; Benick, Jan; Kimmerle, Achim; Hermle, Martin; Glunz, Stefan W.

2014-12-01

Thin layers of Al2O3 are well known for the excellent passivation of p-type c-Si surfaces including highly doped p+ emitters, due to a high density of fixed negative charges. Recent results indicate that Al2O3 can also provide a good passivation of certain phosphorus-diffused n+ c-Si surfaces. In this work, we studied the recombination at Al2O3 passivated n+ surfaces theoretically with device simulations and experimentally for Al2O3 deposited with atomic layer deposition. The simulation results indicate that there is a certain surface doping concentration, where the recombination is maximal due to depletion or weak inversion of the charge carriers at the c-Si/Al2O3 interface. This pronounced maximum was also observed experimentally for n+ surfaces passivated either with Al2O3 single layers or stacks of Al2O3 capped by SiNx, when activated with a low temperature anneal (425 °C). In contrast, for Al2O3/SiNx stacks activated with a short high-temperature firing process (800 °C) a significant lower surface recombination was observed for most n+ diffusion profiles without such a pronounced maximum. Based on experimentally determined interface properties and simulation results, we attribute this superior passivation quality after firing to a better chemical surface passivation, quantified by a lower interface defect density, in combination with a lower density of negative fixed charges. These experimental results reveal that Al2O3/SiNx stacks can provide not only excellent passivation on p+ surfaces but also on n+ surfaces for a wide range of surface doping concentrations when activated with short high-temperature treatments.

Characteristics and Corrosion Behavior of Pure Titanium Subjected to Surface Mechanical Attrition

NASA Astrophysics Data System (ADS)

Fu, Tianlin; Wang, Xiao; Liu, Jianxiong; Li, Li; Yu, Xiaohua; Zhan, Zhaolin

2017-10-01

A stable passive film exhibiting good corrosion resistance in a 3.5 wt.% NaCl solution was formed on the surface of pure titanium (Ti) subjected to a surface mechanical attrition treatment (SMAT). The corrosion potential (-0.21 V) of the film was significantly higher than that (-0.92 V) of the untreated sample. Moreover, the corrosion current density was an order of magnitude lower than that of the untreated sample. SMAT resulted in a decrease in the vacancy condensation in the TiO2 film, thereby inhibiting the invasion and diffusion of Cl- in the film.

An Isotope Study of Hydrogenation of poly-Si/SiOx Passivated Contacts for Si Solar Cells: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnabel, Manuel; Nemeth, William; van de Loo, Bas, W.H.

2017-06-26

For many years, the record Si solar cell efficiency stood at 25.0%. Only recently have several companies and institutes managed to produce more efficient cells, using passivated contacts of made doped poly-Si or a-Si:H and a passivating intrinsic interlayer in all cases. Common to these designs is the need to passivate the layer stack with hydrogen. In this contribution, we perform a systematic study of passivated contact passivation by hydrogen, using poly-Si/SiOx passivated contacts on n-Cz-Si, and ALD Al2O3 followed by a forming gas anneal (FGA) as the hydrogen source. We study p-type and n-type passivated contacts with implied Vocmore » exceeding 690 and 720 mV, respectively, and perform either the ALD step or the FGA with deuterium instead of hydrogen in order to separate the two processes via SIMS. By examining the deuterium concentration at the SiOx in both types of samples, we demonstrate that the FGA supplies negligible hydrogen species to the SiOx, regardless of whether the FGA is hydrogenated or deuterated. Instead, it supplies the thermal energy needed for hydrogen species in the Al2O3 to diffuse there. Furthermore, the concentration of hydrogen species at the SiOx can saturate while implied Voc continues to increase, showing that the energy from the FGA is also required for hydrogen species already at the SiOx to find recombination-active defects to passivate.« less

Thermal Remote Anemometer Device

NASA Technical Reports Server (NTRS)

Heyman, Joseph S.; Heath, D. Michele; Winfree, William P.; Miller, William E.; Welch, Christopher S.

1988-01-01

Thermal Remote Anemometer Device developed for remote, noncontacting, passive measurement of thermal properties of sample. Model heated locally by scanning laser beam and cooled by wind in tunnel. Thermal image of model analyzed to deduce pattern of airflow around model. For materials applications, system used for evaluation of thin films and determination of thermal diffusivity and adhesive-layer contact. For medical applications, measures perfusion through skin to characterize blood flow and used to determine viabilities of grafts and to characterize tissues.

Improved Assessment Strategies for Vapor Intrusion Passive Samplers and Building Pressure Control

DTIC Science & Technology

2013-09-01

pressure control. Matrix Analyte Method Container Holding Time (Days) Vapor Radon McHugh , Hammond, Nickels , and Hartman, 2008 Tedlar ® bag 14...2: Diffusive Sampling,” ISO 16017-2:2003. McHugh T. E., D. E. Hammond, T. Nickels , and B. Hartman. 2008. “Use of Radon Measurements for Evaluation...Control I. D. Rivera-Duarte D. B. Chadwick SSC Pacific T. McAlary H. Groenevelt T. Creamer D. Bertrand Geosyntec Consultants, Inc. T. McHugh

Development of Solid Ceramic Dosimeters for the Time-Integrative Passive Sampling of Volatile Organic Compounds in Waters.

PubMed

Bonifacio, Riza Gabriela; Nam, Go-Un; Eom, In-Yong; Hong, Yong-Seok

2017-11-07

Time-integrative passive sampling of volatile organic compounds (VOCs) in water can now be accomplished using a solid ceramic dosimeter. A nonporous ceramic, which excludes the permeation of water, allowing only gas-phase diffusion of VOCs into the resin inside the dosimeter, effectively captured the VOCs. The mass accumulation of 11 VOCs linearly increased with time over a wide range of aqueous-phase concentrations (16.9 to 1100 μg L -1 ), and the linearity was dependent upon the Henry's constant (H). The average diffusivity of the VOCs in the solid ceramic was 1.46 × 10 -10 m 2 s -1 at 25 °C, which was 4 orders of magnitude lower than that in air (8.09 × 10 -6 m 2 s -1 ). This value was 60% greater than that in the water-permeable porous ceramic (0.92 × 10 -10 m 2 s -1 ), suggesting that its mass accumulation could be more effective than that of porous ceramic dosimeters. The mass accumulation of the VOCs in the solid ceramic dosimeter increased in the presence of salt (≥0.1 M) and with increasing temperature (4 to 40 °C) but varied only slightly with dissolved organic matter concentration. The solid ceramic dosimeter was suitable for the field testing and measurement of time-weighted average concentrations of VOC-contaminated waters.

High-resolution passive sampling of dissolved methane in the water column of lakes in Greenland

NASA Astrophysics Data System (ADS)

Goldman, A. E.; Cadieux, S. B.; White, J. R.; Pratt, L. M.

2013-12-01

Arctic lakes are important participants in the global carbon cycle, releasing methane in a warming climate and contributing to a positive feedback to climate change. In order to yield detailed methane budgets and understand the implications of warming on methane dynamics, high-resolution profiles revealing methane behavior within the water column need to be obtained. Single day sampling using disruptive techniques has the potential to result in biases. In order to obtain high-resolution, undisturbed profiles of methane concentration and isotopic composition, this study evaluates a passive sampling method over a multi-day equilibration period. Selected for this study were two small lakes (<1km2) within a narrow valley stretching between Russells Glacier and Søndre Strømfjord in southwestern Greenland, which are part of an ongoing study of a series of seven lakes. Commercially available, 150 mL, polyethylene Passive Diffusion Bags (PDB's) were deployed in July 2013 for five days at 0.5-meter depth intervals. PDB samples were compared to samples collected with a submersible, electric pump taken immediately before PBD deployment. Preliminary CH4 concentrations and carbon isotopes for one lake were obtained in the field using a Los Gatos Research Methane Carbon Isotope Analyzer. PDB sampling and pump sampling resulted in statistically similar concentrations (R2=0.89), ranging from 0.85 to 135 uM from PDB and 0.74 to 143 uM from pump sampling. In anoxic waters of the lake, where concentrations were high enough to yield robust isotopic results on the LGR MCIA, δ13C were also similar between the two methods, yielding -73‰ from PDB and -74‰ from pump sampling. Further investigation will produce results for a second lake and methane carbon and hydrogen isotopic composition for both lakes. Preliminary results for this passive sampling method are promising. We envision the use of this technique in future studies of dissolved methane and expect that it will provide a more finely resolved vertical profile, allowing for a more complete understanding of lacustrine methane dynamics.

Personal child and mother carbon monoxide exposures and kitchen levels: methods and results from a randomized trial of woodfired chimney cookstoves in Guatemala (RESPIRE).

PubMed

Smith, Kirk R; McCracken, John P; Thompson, Lisa; Edwards, Rufus; Shields, Kyra N; Canuz, Eduardo; Bruce, Nigel

2010-07-01

During the first randomized intervention trial (RESPIRE: Randomized Exposure Study of Pollution Indoors and Respiratory Effects) in air pollution epidemiology, we pioneered application of passive carbon monoxide (CO) diffusion tubes to measure long-term personal exposures to woodsmoke. Here we report on the protocols and validations of the method, trends in personal exposure for mothers and their young children, and the efficacy of the introduced improved chimney stove in reducing personal exposures and kitchen concentrations. Passive diffusion tubes originally developed for industrial hygiene applications were deployed on a quarterly basis to measure 48-hour integrated personal carbon monoxide exposures among 515 children 0-18 months of age and 532 mothers aged 15-55 years and area samples in a subsample of 77 kitchens, in households randomized into control and intervention groups. Instrument comparisons among types of passive diffusion tubes and against a continuous electrochemical CO monitor indicated that tubes responded nonlinearly to CO, and regression calibration was used to reduce this bias. Before stove introduction, the baseline arithmetic (geometric) mean 48-h child (n=270), mother (n=529) and kitchen (n=65) levels were, respectively, 3.4 (2.8), 3.4 (2.8) and 10.2 (8.4) p.p.m. The between-group analysis of the 3355 post-baseline measurements found CO levels to be significantly lower among the intervention group during the trial period: kitchen levels: -90%; mothers: -61%; and children: -52% in geometric means. No significant deterioration in stove effect was observed over the 18 months of surveillance. The reliability of these findings is strengthened by the large sample size made feasible by these unobtrusive and inexpensive tubes, measurement error reduction through instrument calibration, and a randomized, longitudinal study design. These results from the first randomized trial of improved household energy technology in a developing country and demonstrate that a simple chimney stove can substantially reduce chronic exposures to harmful indoor air pollutants among women and infants.

Personal child and mother carbon monoxide exposures and kitchen levels: Methods and results from a randomized trial of woodfired chimney cookstoves in Guatemala (RESPIRE)

PubMed Central

SMITH, KIRK R.; McCRACKEN, JOHN P.; THOMPSON, LISA; EDWARDS, RUFUS; SHIELDS, KYRA N.; CANUZ, EDUARDO; BRUCE, NIGEL

2015-01-01

During the first randomized intervention trial (RESPIRE: Randomized Exposure Study of Pollution Indoors and Respiratory Effects) in air pollution epidemiology, we pioneered application of passive carbon monoxide (CO) diffusion tubes to measure long-term personal exposures to woodsmoke. Here we report on the protocols and validations of the method, trends in personal exposure for mothers and their young children, and the efficacy of the introduced improved chimney stove in reducing personal exposures and kitchen concentrations. Passive diffusion tubes originally developed for industrial hygiene applications were deployed on a quarterly basis to measure 48-hour integrated personal carbon monoxide exposures among 515 children 0–18 months of age and 532 mothers aged 15–55 years and area samples in a subsample of 77 kitchens, in households randomized into control and intervention groups. Instrument comparisons among types of passive diffusion tubes and against a continuous electrochemical CO monitor indicated that tubes responded nonlinearly to CO, and regression calibration was used to reduce this bias. Before stove introduction, the baseline arithmetic (geometric) mean 48-h child (n=270), mother (n=529) and kitchen (n=65) levels were, respectively, 3.4 (2.8), 3.4 (2.8) and 10.2 (8.4) p.p.m. The between-group analysis of the 3355 post-baseline measurements found CO levels to be significantly lower among the intervention group during the trial period: kitchen levels: −90%; mothers: −61%; and children: −52% in geometric means. No significant deterioration in stove effect was observed over the 18 months of surveillance. The reliability of these findings is strengthened by the large sample size made feasible by these unobtrusive and inexpensive tubes, measurement error reduction through instrument calibration, and a randomized, longitudinal study design. These results from the first randomized trial of improved household energy technology in a developing country and demonstrate that a simple chimney stove can substantially reduce chronic exposures to harmful indoor air pollutants among women and infants. PMID:19536077

Electrical and optical characterization of surface passivation in GaAs nanowires.

PubMed

Chang, Chia-Chi; Chi, Chun-Yung; Yao, Maoqing; Huang, Ningfeng; Chen, Chun-Chung; Theiss, Jesse; Bushmaker, Adam W; Lalumondiere, Stephen; Yeh, Ting-Wei; Povinelli, Michelle L; Zhou, Chongwu; Dapkus, P Daniel; Cronin, Stephen B

2012-09-12

We report a systematic study of carrier dynamics in Al(x)Ga(1-x)As-passivated GaAs nanowires. With passivation, the minority carrier diffusion length (L(diff)) increases from 30 to 180 nm, as measured by electron beam induced current (EBIC) mapping, and the photoluminescence (PL) lifetime increases from sub-60 ps to 1.3 ns. A 48-fold enhancement in the continuous-wave PL intensity is observed on the same individual nanowire with and without the Al(x)Ga(1-x)As passivation layer, indicating a significant reduction in surface recombination. These results indicate that, in passivated nanowires, the minority carrier lifetime is not limited by twin stacking faults. From the PL lifetime and minority carrier diffusion length, we estimate the surface recombination velocity (SRV) to range from 1.7 × 10(3) to 1.1 × 10(4) cm·s(-1), and the minority carrier mobility μ is estimated to lie in the range from 10.3 to 67.5 cm(2) V(-1) s(-1) for the passivated nanowires.

Stabilized liquid membrane device (SLMD) for the passive, integrative sampling of labile metals in water

USGS Publications Warehouse

Brumbaugh, W.G.; Petty, J.D.; Huckins, J.N.; Manahan, S.E.

2002-01-01

A stabilized liquid membrane device (SLMD) is described for potential use as an in situ, passive, integrative sampler for cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in natural waters. The SLMD (patent pending) consists of a 2.5-cm-wide by 15-cm-long strip of low-density polyethylene (LDPE) layflat tubing containing 1 mL of an equal mixture (v/v) of oleic acid (cis-9-octadecenoic acid) and EMO-8Q (7-[4-ethyl-1-methyloctyl]-8-quinolinol). The reagent mixture continuously diffuses to the exterior surface of the LDPE membrane, and provides for sequestration of several divalent metals for up to several weeks. Depending on sampler configuration, concentration factors of several thousand can be realized for these metal ions after just a few days. In addition to in situ deployment, the SLMD may be useful for laboratory determination of labile metal species in grab samples. Methods for minimizing the effects of water flow on the sampling rate are currently under investigation.

Passivation and activation of Mg acceptors in heavily doped GaN

NASA Astrophysics Data System (ADS)

Zvanut, M. E.; Uprety, Y.; Dashdorj, J.; Moseley, M.; Alan Doolittle, W.

2011-08-01

Electron paramagnetic resonance measurements are used to monitor the passivation and activation of the Mg-related acceptor in GaN doped with different concentrations of Mg, up to 2 × 1020 cm-3. Samples were annealed in either forming gas (H2:N2) or pure N2 between 200 and 900 °C. As expected, the Mg-related EPR signal is reduced by at least a factor of ten during the forming gas treatment; while the pure N2 environment revives the signal. However, the study also shows that reactions between Mg and hydrogen occur at a temperature as low as 525 °C in the 1020 cm-3 Mg doped samples; while in more lightly doped samples, temperatures greater than 700 °C are required to observe changes in the Mg signal intensity. While the observations support the model in which a hydrogen atom ionizes at the Mg impurity and the remaining proton bonds at a near neighbor, the different temperature dependence suggests that hydrogen diffusion is affected by the increased Mg concentration.

Development of a new passive sampler based on diffusive milligel beads for copper analysis in water.

PubMed

Perez, M; Reynaud, S; Lespes, G; Potin-Gautier, M; Mignard, E; Chéry, P; Schaumlöffel, D; Grassl, B

2015-08-26

A new passive sampler was designed and characterized for the determination of free copper ion (Cu(2+)) concentration in aqueous solution. Each sampling device was composed of a set of about 30 diffusive milligel (DMG) beads. Milligel beads with incorporated cation exchange resin (Chelex) particles were synthetized using an adapted droplet-based millifluidic process. Beads were assumed to be prolate spheroids, with a diameter of 1.6 mm and an anisotropic factor of 1.4. The milligel was controlled in chemical composition of hydrogel (monomer, cross-linker, initiator and Chelex concentration) and characterized in pore size. Two types of sampling devices were developed containing 7.5% and 15% of Chelex, respectively, and 6 nm pore size. The kinetic curves obtained demonstrated the accumulation of copper in the DMG according to the process described in the literature as absorption (and/or adsorption) and release following the Fick's first law of diffusion. For their use in water monitoring, the typical physico-chemical characteristics of the samplers, i.e. the mass-transfer coefficient (k0) and the sampler-water partition coefficient (Ksw), were determined based on a static exposure design. In order to determine the copper concentration in the samplers after their exposure, a method using DMG bead digestion combined to Inductively Coupled Plasma - Atomic Emission Spectrometry (ICP-AES) analysis was developed and optimized. The DMG devices proved to be capable to absorb free copper ions from an aqueous solution, which could be accurately quantified with a mean recovery of 99% and a repeatability of 7% (mean relative uncertainty). Copyright © 2015 Elsevier B.V. All rights reserved.

Passive sampler for PM10-2.5 aerosol.

PubMed

Leith, David; Sommerlatt, Darrell; Boundy, Maryanne G

2007-03-01

This study investigates the use of a small passive sampler for aerosol particles to determine particulate matter (PM)10-2.5 concentrations in outdoor air. The passive sampler collects particles by gravity, diffusion, and convective diffusion onto a glass coverslip that is then examined with an optical microscope; digital images are processed with free software and the resultant PM10-2.5 concentrations determined. Both the samplers and the analyses are relatively inexpensive. Passive samplers were collocated with Federal Reference Method (FRM) samplers in Chapel Hill, NC; Phoenix, AZ; and Birmingham, AL; for periods from 5 to 15 days. Particles consisted primarily of inorganic dusts at some sites and a mix of industrial and inorganic materials at other sites. Measured concentrations ranged from < 10 microg/m3 to approximately 40 microg/m3. Overall, PM10-2.5 concentrations measured with the passive samplers were within approximately 1 standard deviation of concentrations measured with the FRM samplers. Concentrations determined with passive samplers depend on assumptions about particle density and shape factors and may also depend somewhat on local wind speed and turbulence; accurate values for these parameters may not be known. The degree of agreement between passive and FRM concentrations measured here suggests that passive measurements may not be overly dependent on accurate knowledge of these parameters.

Effects of molecular weight on the diffusion coefficient of aquatic dissolved organic matter and humic substances.

PubMed

Balch, J; Guéguen, C

2015-01-01

In situ measurements of labile metal species using diffusive gradients in thin films (DGT) passive samplers are based on the diffusion rates of individual species. Although most studies have dealt with chemically isolated humic substances, the diffusion of dissolved organic matter (DOM) across the hydrogel is not well understood. In this study, the diffusion coefficient (D) and molecular weight (MW) of 11 aquatic DOM and 4 humic substances (HS) were determined. Natural, unaltered aquatic DOM was capable of diffusing across the diffusive gel membrane with D values ranging from 2.48×10(-6) to 5.31×10(-6) cm(2) s(-1). Humic substances had diffusion coefficient values ranging from 3.48×10(-6) to 6.05×10(-6) cm(2) s(-1), congruent with previous studies. Molecular weight of aquatic DOM and HS samples (∼500-1750 Da) measured using asymmetrical flow field-flow fractionation (AF4) strongly influenced D, with larger molecular weight DOM having lower D values. No noticeable changes in DOM size properties were observed during the diffusion process, suggesting that DOM remains intact following diffusion across the diffusive gel. The influence of molecular weight on DOM mobility will assist in further understanding and development of the DGT technique and the uptake and mobility of contaminants associated with DOM in aquatic environments. Copyright © 2014 Elsevier Ltd. All rights reserved.

Investigation and Application of a New Passive Sampling Technique for in Situ Monitoring of Illicit Drugs in Waste Waters and Rivers.

PubMed

Guo, Changsheng; Zhang, Tingting; Hou, Song; Lv, Jiapei; Zhang, Yuan; Wu, Fengchang; Hua, Zhendong; Meng, Wei; Zhang, Hao; Xu, Jian

2017-08-15

Illicit drugs constitute a class of emerging contaminants that has been drawing significant concern due to its potent pharmacological and biological activities. In this study, an in situ passive sampling approach that uses diffusive gradients in thin films (DGT) was successfully tested for measuring ketamine (KET), methamphetamine (METH), and amphetamine (AMP) in water. The diffusion coefficients of KET, METH, and AMP in diffusive gel were (8.13 ± 0.12) × 10 -6 , (8.55 ± 0.14) × 10 -6 , and (7.72 ± 0.18) × 10 -6 cm 2 s -1 at 22 °C, respectively. The capacities of an XAD binding gel for KET, METH, and AMP were 92, 57, and 45 μg per binding gel disc, which were suitable for long-term environmental monitoring. The DGT measurement of these drugs was not influenced by the pH (4 to 9) and the ionic strength (0.001 M - 0.1 M) and unaffected by the water flow, demonstrating the effectiveness of the XAD-based DGT for the in situ monitoring of illicit drugs. DGT samplers were deployed in a WWTP influent and natural rivers in Beijing, China. The ng L -1 levels of the drugs were high in the wastewater influent and low in river waters, with an insignificant fluctuation during the seven-day monitoring. The DGT-measured concentrations were comparable to the average concentrations determined by SPE method, which suggested that the average data measured by DGT could be substituted for high-frequency grab sampling. This study has demonstrated systematically for the first time that DGT is effective and accurate for monitoring illicit drugs in wastewater and surface waters, and provides a powerful tool to investigating the presence, transport, and environmental behaviors of these drugs in the aquatic ecosystem.

Microfluidic Mixing: A Review

PubMed Central

Lee, Chia-Yen; Chang, Chin-Lung; Wang, Yao-Nan; Fu, Lung-Ming

2011-01-01

The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either “active”, where an external energy force is applied to perturb the sample species, or “passive”, where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers. PMID:21686184

Diffusion barriers

NASA Technical Reports Server (NTRS)

Nicolet, M. A.

1983-01-01

The choice of the metallic film for the contact to a semiconductor device is discussed. One way to try to stabilize a contact is by interposing a thin film of a material that has low diffusivity for the atoms in question. This thin film application is known as a diffusion barrier. Three types of barriers can be distinguished. The stuffed barrier derives its low atomic diffusivity to impurities that concentrate along the extended defects of a polycrystalline layer. Sacrificial barriers exploit the fact that some (elemental) thin films react in a laterally uniform and reproducible fashion. Sacrificial barriers have the advantage that the point of their failure is predictable. Passive barriers are those most closely approximating an ideal barrier. The most-studied case is that of sputtered TiN films. Stuffed barriers may be viewed as passive barriers whose low diffusivity material extends along the defects of the polycrystalline host.

Volatile organic compounds at two oil and natural gas production well pads in Colorado and Texas using passive samplers.

PubMed

Eisele, Adam P; Mukerjee, Shaibal; Smith, Luther A; Thoma, Eben D; Whitaker, Donald A; Oliver, Karen D; Wu, Tai; Colon, Maribel; Alston, Lillian; Cousett, Tamira A; Miller, Michael C; Smith, Donald M; Stallings, Casson

2016-04-01

A pilot study was conducted in application of the U.S. Environmental Protection Agency (EPA) Methods 325A/B variant for monitoring volatile organic compounds (VOCs) near two oil and natural gas (ONG) production well pads in the Texas Barnett Shale formation and Colorado Denver-Julesburg Basin (DJB), along with a traffic-dominated site in downtown Denver, CO. As indicated in the EPA method, VOC concentrations were measured for 14-day sampling periods using passive-diffusive tube samplers with Carbopack X sorbent at fenceline perimeter and other locations. VOCs were significantly higher at the DJB well pad versus the Barnett well pad and were likely due to higher production levels at the DJB well pad during the study. Benzene and toluene were significantly higher at the DJB well pad versus downtown Denver. Except for perchloroethylene, VOCs measured at passive sampler locations (PSs) along the perimeter of the Barnett well pad were significantly higher than PSs farther away. At the DJB well pad, most VOC concentrations, except perchloroethylene, were significantly higher prior to operational changes than after these changes were made. Though limited, the results suggest passive samplers are precise (duplicate precision usually ≤10%) and that they can be useful to assess spatial gradients and operational conditions at well pad locations over time-integrated periods. Recently enacted EPA Methods 325A/B use passive-diffusive tube samplers to measure benzene at multiple fenceline locations at petrochemical refineries. This pilot study presents initial data demonstrating the utility of Methods 325A/B for monitoring at ONG facilities. Measurements revealed elevated concentrations reflective of production levels and spatial gradients of VOCs relative to source proximity at the Barnett well pad, as well as operational changes at the DJB well pad. Though limited, these findings indicate that Methods 325A/B can be useful in application to characterize VOCs at well pad boundaries.

Carrier-mediated cocaine transport at the blood-brain barrier as a putative mechanism in addiction liability.

PubMed

Chapy, Hélène; Smirnova, Maria; André, Pascal; Schlatter, Joël; Chiadmi, Fouad; Couraud, Pierre-Olivier; Scherrmann, Jean-Michel; Declèves, Xavier; Cisternino, Salvatore

2014-10-31

The rate of entry of cocaine into the brain is a critical factor that influences neuronal plasticity and the development of cocaine addiction. Until now, passive diffusion has been considered the unique mechanism known by which cocaine crosses the blood-brain barrier. We reassessed mechanisms of transport of cocaine at the blood-brain barrier using a human cerebral capillary endothelial cell line (hCMEC/D3) and in situ mouse carotid perfusion. Both in vivo and in vitro cocaine transport studies demonstrated the coexistence of a carrier-mediated process with passive diffusion. At pharmacological exposure level, passive diffusion of cocaine accounted for only 22.5% of the total cocaine influx in mice and 5.9% in hCMEC/D3 cells, whereas the carrier-mediated influx rate was 3.4 times greater than its passive diffusion rate in vivo. The functional identification of this carrier-mediated transport demonstrated the involvement of a proton antiporter that shared the properties of the previously characterized clonidine and nicotine transporter. The functionnal characterization suggests that the solute carrier (SLC) transporters Oct (Slc22a1-3), Mate (Slc47a1) and Octn (Slc22a4-5) are not involved in the cocaine transport in vivo and in vitro. Diphenhydramine, heroin, tramadol, cocaethylene, and norcocaine all strongly inhibited cocaine transport, unlike benzoylecgonine. Trans-stimulation studies indicated that diphenhydramine, nicotine, 3,4-methylenedioxyamphetamine (ecstasy) and the cathinone compound 3,4-methylenedioxypyrovalerone (MDPV) were also substrates of the cocaine transporter. Cocaine transport at the BBB involves a proton-antiporter flux that is quantitatively much more important than its passive diffusion. The molecular identification and characterization of this transporter will provide new tools to understand its role in addictive mechanisms. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Passive phloem loading and long-distance transport in a synthetic tree-on-a-chip.

PubMed

Comtet, Jean; Jensen, Kaare H; Turgeon, Robert; Stroock, Abraham D; Hosoi, A E

2017-03-20

Vascular plants rely on differences in osmotic pressure to export sugars from regions of synthesis (mature leaves) to sugar sinks (roots, fruits). In this process, known as Münch pressure flow, the loading of sugars from photosynthetic cells to the export conduit (the phloem) is crucial, as it sets the pressure head necessary to power long-distance transport. Whereas most herbaceous plants use active mechanisms to increase phloem sugar concentration above that of the photosynthetic cells, in most tree species, for which transport distances are largest, loading seems, counterintuitively, to occur by means of passive symplastic diffusion from the mesophyll to the phloem. Here, we use a synthetic microfluidic model of a passive loader to explore the non-linear dynamics that arise during export and determine the ability of passive loading to drive long-distance transport. We first demonstrate that in our device, the phloem concentration is set by the balance between the resistances to diffusive loading from the source and convective export through the phloem. Convection-limited export corresponds to classical models of Münch transport, where the phloem concentration is close to that of the source; in contrast, diffusion-limited export leads to small phloem concentrations and weak scaling of flow rates with hydraulic resistance. We then show that the effective regime of convection-limited export is predominant in plants with large transport resistances and low xylem pressures. Moreover, hydrostatic pressures developed in our synthetic passive loader can reach botanically relevant values as high as 10 bars. We conclude that passive loading is sufficient to drive long-distance transport in large plants, and that trees are well suited to take full advantage of passive phloem loading strategies.

Extraction of thermal Green's function using diffuse fields: a passive approach applied to thermography

NASA Astrophysics Data System (ADS)

Capriotti, Margherita; Sternini, Simone; Lanza di Scalea, Francesco; Mariani, Stefano

2016-04-01

In the field of non-destructive evaluation, defect detection and visualization can be performed exploiting different techniques relying either on an active or a passive approach. In the following paper the passive technique is investigated due to its numerous advantages and its application to thermography is explored. In previous works, it has been shown that it is possible to reconstruct the Green's function between any pair of points of a sensing grid by using noise originated from diffuse fields in acoustic environments. The extraction of the Green's function can be achieved by cross-correlating these random recorded waves. Averaging, filtering and length of the measured signals play an important role in this process. This concept is here applied in an NDE perspective utilizing thermal fluctuations present on structural materials. Temperature variations interacting with thermal properties of the specimen allow for the characterization of the material and its health condition. The exploitation of the thermographic image resolution as a dense grid of sensors constitutes the basic idea underlying passive thermography. Particular attention will be placed on the creation of a proper diffuse thermal field, studying the number, placement and excitation signal of heat sources. Results from numerical simulations will be presented to assess the capabilities and performances of the passive thermal technique devoted to defect detection and imaging of structural components.

Development of More Cost-Effective Methods for Long-Term Monitoring of Soil Vapor Intrusion to Indoor Air Using Quantitative Passive Diffusive-Adsorptive Sampling Techniques

DTIC Science & Technology

2015-05-01

challenging component of assessing human health risks associated with contaminated soil and groundwater since the late 1990s, during which time...and analysis. 1.3 REGULATORY DRIVERS Regulatory guidance for assessment and management of risks associated with VI has been issued by at least 27...requirements to assess potential human health risks , and this possibility exists where VOCs are present in the subsurface near occupied buildings

Demonstration of the AGI Universal Samplers (F.K.A. the GORE Modules) for Passive Sampling of Groundwater

DTIC Science & Technology

2014-03-27

Coefficient from Water into the Sorbent KOW Octanol-Water Partition Coefficient LF Low Flow LNAPL Light Non-aqueous Phase Liquid LTM Long-Term...Once in the vapor phase, the molecule can then diffuse through the mem- ERDC/CRREL TR-14-4 5 brane while liquid water is prevented from passing...remediation at this site was conducted in two phases. Phase I consisted of vertical contamina- tion profiling followed by the in situ injection of an

Demonstration of the AGI Universal Samplers (F.K.A. the GORE (registered trademark) Modules) for Passive Sampling of Groundwater

DTIC Science & Technology

2014-03-01

Coefficient from Water into the Sorbent KOW Octanol-Water Partition Coefficient LF Low Flow LNAPL Light Non-aqueous Phase Liquid LTM Long-Term...Once in the vapor phase, the molecule can then diffuse through the mem- ERDC/CRREL TR-14-4 5 brane while liquid water is prevented from passing...remediation at this site was conducted in two phases. Phase I consisted of vertical contamina- tion profiling followed by the in situ injection of an

Hydrodynamic effects on phase transition in active matter

NASA Astrophysics Data System (ADS)

Gidituri, Harinadha; Akella, V. S.; Panchagnula, Mahesh; Vedantam, Srikanth; Multiphase flow physics lab Team

2017-11-01

Organized motion of active (self-propelled) objects are ubiquitous in nature. The objective of this study to investigate the effect of hydrodynamics on the coherent structures in active and passive particle mixtures. We use a mesoscopic method Dissipative Particle Dynamics (DPD). The system shows three different states viz. meso-turbulent (disordered state), polar flock and vortical (ordered state) for different values of activity and volume fraction of active particles. From our numerical simulations we construct a phase diagram between activity co-efficient, volume fraction and viscosity of the passive fluid. Transition from vortical to polar is triggered by increasing the viscosity of passive fluid which causes strong short-range hydrodynamic interactions. However, as the viscosity of the fluid decreases, both vortical and meso-turbulent states transition to polar flock phase. We also calculated the diffusion co-efficients via mean square displacement (MSD) for passive and active particles. We observe ballistic and diffusive regimes in the present system.

Hydrodynamic collective effects of active protein machines in solution and lipid bilayers

PubMed Central

Mikhailov, Alexander S.; Kapral, Raymond

2015-01-01

The cytoplasm and biomembranes in biological cells contain large numbers of proteins that cyclically change their shapes. They are molecular machines that can function as molecular motors or carry out various other tasks in the cell. Many enzymes also undergo conformational changes within their turnover cycles. We analyze the advection effects that nonthermal fluctuating hydrodynamic flows induced by active proteins have on other passive molecules in solution or membranes. We show that the diffusion constants of passive particles are enhanced substantially. Furthermore, when gradients of active proteins are present, a chemotaxis-like drift of passive particles takes place. In lipid bilayers, the effects are strongly nonlocal, so that active inclusions in the entire membrane contribute to local diffusion enhancement and the drift. All active proteins in a biological cell or in a membrane contribute to such effects and all passive particles, and the proteins themselves, will be subject to them. PMID:26124140

Numerical investigation of metal-semiconductor-insulator-semiconductor passivated hole contacts based on atomic layer deposited AlO x

NASA Astrophysics Data System (ADS)

Ke, Cangming; Xin, Zheng; Ling, Zhi Peng; Aberle, Armin G.; Stangl, Rolf

2017-08-01

Excellent c-Si tunnel layer surface passivation has been obtained recently in our lab, using atomic layer deposited aluminium oxide (ALD AlO x ) in the tunnel layer regime of 0.9 to 1.5 nm, investigated to be applied for contact passivation. Using the correspondingly measured interface properties, this paper compares the theoretical collection efficiency of a conventional metal-semiconductor (MS) contact on diffused p+ Si to a metal-semiconductor-insulator-semiconductor (MSIS) contact on diffused p+ Si or on undoped n-type c-Si. The influences of (1) the tunnel layer passivation quality at the tunnel oxide interface (Q f and D it), (2) the tunnel layer thickness and the electron and hole tunnelling mass, (3) the tunnel oxide material, and (4) the semiconductor capping layer material properties are investigated numerically by evaluation of solar cell efficiency, open-circuit voltage, and fill factor.

A novel personal air sampling device for collecting volatile organic compounds: a comparison to charcoal tubes and diffusive badges.

PubMed

Rossner, Alan; Farant, Jean-Pierre

2004-02-01

Evacuated canisters have been used for many years to collect ambient air samples for gases and vapors. Recently, significant interest has arisen in using evacuated canisters for personal breathing zone sampling as an alternative to sorbent sampling. A novel flow control device was designed and built at McGill University. The flow control device was designed to provide a very low flow rate, <0.5 mL/min, to allow a sample to be collected over an extended period of time. Previous experiments run at McGill have shown agreement between the mathematical and empirical models to predict flow rate. The flow control device combined with an evacuated canister (capillary flow control-canister) was used in a series of experiments to evaluate its performance against charcoal tubes and diffusive badges. Air samples of six volatile organic compounds were simultaneously collected in a chamber using the capillary flow control-canister, charcoal tubes, and diffusive badges. Five different concentrations of the six volatile organic compounds were evaluated. The results from the three sampling devices were compared to each other and to concentration values obtained using an online gas chromatograph (GC). Eighty-four samples of each method were collected for each of the six chemicals. Results indicate that the capillary flow control-canister device compares quite favorably to the online GC and to the charcoal tubes, p > 0.05 for most of the tests. The capillary flow control-canister was found to be more accurate for the compounds evaluated, easier to use, and easier to analyze than charcoal tubes and passive dosimeter badges.

Random walk of passive tracers among randomly moving obstacles.

PubMed

Gori, Matteo; Donato, Irene; Floriani, Elena; Nardecchia, Ilaria; Pettini, Marco

2016-04-14

This study is mainly motivated by the need of understanding how the diffusion behavior of a biomolecule (or even of a larger object) is affected by other moving macromolecules, organelles, and so on, inside a living cell, whence the possibility of understanding whether or not a randomly walking biomolecule is also subject to a long-range force field driving it to its target. By means of the Continuous Time Random Walk (CTRW) technique the topic of random walk in random environment is here considered in the case of a passively diffusing particle among randomly moving and interacting obstacles. The relevant physical quantity which is worked out is the diffusion coefficient of the passive tracer which is computed as a function of the average inter-obstacles distance. The results reported here suggest that if a biomolecule, let us call it a test molecule, moves towards its target in the presence of other independently interacting molecules, its motion can be considerably slowed down.

Stable carbon isotope ratio in atmospheric CO2 collected by new diffusive devices.

PubMed

Proto, Antonio; Cucciniello, Raffaele; Rossi, Federico; Motta, Oriana

2014-02-01

In this paper, stable carbon isotope ratios (δ (13)C) were determined in the atmosphere by using a Ca-based sorbent, CaO/Ca12Al14O33 75:25 w/w, for passively collecting atmospheric CO2, in both field and laboratory experiments. Field measurements were conducted in three environments characterized by different carbon dioxide sources. In particular, the environments under consideration were a rather heavily trafficked road, where the source of CO2 is mostly vehicle exhaust, a rural unpolluted area, and a private kitchen where the major source of CO2 was gas combustion. Samplers were exposed to the free atmosphere for 3 days in order to allow collection of sufficient CO2 for δ(13)C analysis, then the collected CO2 was desorbed from the adsorbent with acid treatment, and directly analyzed by nondispersive infrared (NDIR) instrument. δ (13)C results confirmed that the samplers collected representative CO2 samples and no fractionation occurred during passive trapping, as also confirmed by an appositely designed experiment conducted in the laboratory. Passive sampling using CaO/Ca12Al14O33 75:25 w/w proved to be an easy and reliable method to collect atmospheric carbon dioxide for δ (13)C analysis in both indoor and outdoor places.

Intercomparison of active, passive and continuous instruments for radon and radon progeny measurements in the EML chamber and test facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

George, A.C.; Knutson, E.O.; Tu, K.W.

1995-12-01

The results from the May 1995 Intercomparison of Active, Passive and Continuous Instruments for Radon and Radon Progeny Measurement conducted in the EML radon exposure and test facility are presented. Represented were 13 participants that measure radon with open faced and diffusion barrier activated carbon collectors, 10 with nuclear alpha track detectors, 9 with short-term and long-term electret/ionization chambers, and 13 with active and passive commercial electronic continuous monitors. For radon progeny, there were four participants that came in person to take part in the grab sampling methodology for measuring individual radon progeny and the potential alpha energy concentration (PAEC).more » There were 11 participants with continuous and integrating commercial electronic instruments that are used for measuring the PAEC. The results indicate that all the tested instruments that measure radon fulfill their intended purpose. All instruments and methods used for grab sampling for radon progeny did very well. However, most of the continuous and integrating electronic instruments used for measuring the PAEC or working level appear to underestimate the potential risk from radon progeny when the concentration of particles onto which the radon progeny are attached is <5,000 cm{sup -3}.« less

Use of Inert Gases to Study the Interaction of Blood Flow and Diffusion during Passive Absorption from the Gastrointestinal Tract of the Rat

PubMed Central

Levitt, Michael D.; Levitt, David G.

1973-01-01

Measurement of the relative absorption rates of inert gases (H2, He, CH4, SF6, and 133Xe) was used to investigate the interaction between diffusion and blood flow during passive absorption from the stomach, small bowel, and colon of the rat. If uptake is blood flow limited, the gases should be absorbed in proportion to their solubilities in blood, but if diffusion limited, uptake should be proportional to the diffusion rate of the gases in mucosal tissues. The observed absorption data were fitted to a series of models of interaction between perfusion and diffusion. A simple model accurately predicted the absorption rates of the gases from all segments of bowel. In this model, gas is absorbed into two distinct blood flows: one which flows in proximity to the lumen and completely equilibrates with the lumen, and a second which is sufficiently rapid and distant from the lumen that its gas uptake is entirely diffusion limited. The fraction of the total absorption attributable to the equilibrating flow can be readily calculated and equalled 93%, 77%, and 33% for the small bowel, colon, and stomach, respectively. Thus the rate of passive absorption of gases from the small bowel is limited almost entirely by the blood flow to the mucosa, and absorption from the stomach is largely limited by the diffusion rate of the gases. The flow which equilibrates with the lumen can be quantitated, and this flow may provide a useful measure of “effective” mucosal blood flow. Images PMID:4719667

Assessment of passive muscle elongation using Diffusion Tensor MRI: Correlation between fiber length and diffusion coefficients.

PubMed

Mazzoli, Valentina; Oudeman, Jos; Nicolay, Klaas; Maas, Mario; Verdonschot, Nico; Sprengers, Andre M; Nederveen, Aart J; Froeling, Martijn; Strijkers, Gustav J

2016-12-01

In this study we investigated the changes in fiber length and diffusion parameters as a consequence of passive lengthening and stretching of the calf muscles. We hypothesized that changes in radial diffusivity (RD) are caused by changes in the muscle fiber cross sectional area (CSA) as a consequence of lengthening and shortening of the muscle. Diffusion Tensor MRI (DT-MRI) measurements were made twice in five healthy volunteers, with the foot in three different positions (30° plantarflexion, neutral position and 15° dorsiflexion). The muscles of the calf were manually segmented on co-registered high resolution anatomical scans, and maps of RD and axial diffusivity (AD) were reconstructed from the DT-MRI data. Fiber tractography was performed and mean fiber length was calculated for each muscle group. Significant negative correlations were found between the changes in RD and changes in fiber length in the dorsiflexed and plantarflexed positions, compared with the neutral foot position. Changes in AD did not correlate with changes in fiber length. Assuming a simple cylindrical model with constant volume for the muscle fiber, the changes in the muscle fiber CSA were calculated from the changes in fiber length. In line with our hypothesis, we observed a significant positive correlation of the CSA with the measured changes in RD. In conclusion, we showed that changes in diffusion coefficients induced by passive muscle stretching and lengthening can be explained by changes in muscle CSA, advancing the physiological interpretation of parameters derived from skeletal muscle DT-MRI. Copyright © 2016 John Wiley & Sons, Ltd.

Groundwater geochemical and selected volatile organic compound data, Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington, June and September 2014

USGS Publications Warehouse

Huffman, Raegan L.

2015-01-01

Previous investigations indicate that concentrations of chlorinated volatile organic compounds (CVOCs) are substantial in groundwater beneath the 9-acre former landfill at Operable Unit 1, Naval Undersea Warfare Center, Division Keyport, Washington. The U.S. Geological Survey has continued to monitor groundwater geochemistry to ensure that conditions remain favorable for contaminant biodegradation at the site. This report presents groundwater geochemical and selected CVOC data collected at Operable Unit 1 by the U.S. Geological Survey during June 23–25 and September 4, 2014, in support of long-term monitoring for natural attenuation. Groundwater samples were collected from 13 wells and 9 piezometers, as well as from 10 shallow groundwater passive-diffusion sampling sites in the nearby marsh. Samples from all wells and piezometers were analyzed for oxidation-reduction (redox) sensitive constituents and dissolved gases. Samples from all piezometers and four wells also were analyzed for CVOCs, as were all samples from the passive-diffusion sampling sites. In 2014, concentrations of redox-sensitive constituents measured at all wells and piezometers were consistent with those measured in previous years, with dissolved oxygen concentrations all less than 1 milligram per liter; little to no detectable nitrate; abundant dissolved manganese, iron, and methane; and commonly detected sulfide. In the upper aquifer of the northern plantation in 2014, CVOC concentrations at all piezometers were similar to those measured in previous years, and concentrations of the reductive dechlorination byproducts ethane and ethene were slightly lower or the same as concentrations measured in 2013. In the upper aquifer of the southern plantation, CVOC concentrations measured in piezometers during 2014 continued to be variable as in previous years, often high, and reductive dechlorination byproducts were detected in one of the three wells and in all but two piezometers. Beneath the marsh adjacent to the southern plantation, chloroethene concentrations measured in 2014 continued to vary spatially and temporally, and were high. Trends for total CVOC concentration continued to increase at the historically most contaminated passive‑diffusion sampler sites (S-4, S-4B, and S-5). For the intermediate aquifer in 2014, concentrations of reductive dechlorination byproducts ethane and ethene and CVOCs were consistent with those measured in previous years.

Passivation of phosphorus diffused silicon surfaces with Al{sub 2}O{sub 3}: Influence of surface doping concentration and thermal activation treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richter, Armin, E-mail: armin.richter@ise.fraunhofer.de; Benick, Jan; Kimmerle, Achim

2014-12-28

Thin layers of Al{sub 2}O{sub 3} are well known for the excellent passivation of p-type c-Si surfaces including highly doped p{sup +} emitters, due to a high density of fixed negative charges. Recent results indicate that Al{sub 2}O{sub 3} can also provide a good passivation of certain phosphorus-diffused n{sup +} c-Si surfaces. In this work, we studied the recombination at Al{sub 2}O{sub 3} passivated n{sup +} surfaces theoretically with device simulations and experimentally for Al{sub 2}O{sub 3} deposited with atomic layer deposition. The simulation results indicate that there is a certain surface doping concentration, where the recombination is maximal duemore » to depletion or weak inversion of the charge carriers at the c-Si/Al{sub 2}O{sub 3} interface. This pronounced maximum was also observed experimentally for n{sup +} surfaces passivated either with Al{sub 2}O{sub 3} single layers or stacks of Al{sub 2}O{sub 3} capped by SiN{sub x}, when activated with a low temperature anneal (425 °C). In contrast, for Al{sub 2}O{sub 3}/SiN{sub x} stacks activated with a short high-temperature firing process (800 °C) a significant lower surface recombination was observed for most n{sup +} diffusion profiles without such a pronounced maximum. Based on experimentally determined interface properties and simulation results, we attribute this superior passivation quality after firing to a better chemical surface passivation, quantified by a lower interface defect density, in combination with a lower density of negative fixed charges. These experimental results reveal that Al{sub 2}O{sub 3}/SiN{sub x} stacks can provide not only excellent passivation on p{sup +} surfaces but also on n{sup +} surfaces for a wide range of surface doping concentrations when activated with short high-temperature treatments.« less

The Role of Surface Passivation in Controlling Ge Nanowire Faceting.

PubMed

Gamalski, A D; Tersoff, J; Kodambaka, S; Zakharov, D N; Ross, F M; Stach, E A

2015-12-09

In situ transmission electron microscopy observations of nanowire morphologies indicate that during Au-catalyzed Ge nanowire growth, Ge facets can rapidly form along the nanowire sidewalls when the source gas (here, digermane) flux is decreased or the temperature is increased. This sidewall faceting is accompanied by continuous catalyst loss as Au diffuses from the droplet to the wire surface. We suggest that high digermane flux and low temperatures promote effective surface passivation of Ge nanowires with H or other digermane fragments inhibiting diffusion and attachment of Au and Ge on the sidewalls. These results illustrate the essential roles of the precursor gas and substrate temperature in maintaining nanowire sidewall passivation, necessary to ensure the growth of straight, untapered, ⟨111⟩-oriented nanowires.

Calibration of silicone rubber rods as passive samplers for pesticides at two different flow velocities: Modeling of sampling rates under water boundary layer and polymer control.

PubMed

Martin, Alexis; Margoum, Christelle; Jolivet, Antoine; Assoumani, Azziz; El Moujahid, Bachir; Randon, Jérôme; Coquery, Marina

2018-04-01

There is a need to determine time-weighted average concentrations of polar contaminants such as pesticides by passive sampling in environmental waters. Calibration data for silicone rubber-based passive samplers are lacking for this class of compounds. The calibration data, sampling rate (R s ), and partition coefficient between silicone rubber and water (K sw ) were precisely determined for 23 pesticides and 13 candidate performance reference compounds (PRCs) in a laboratory calibration system over 14 d for 2 water flow velocities, 5 and 20 cm s -1 . The results showed that an in situ exposure duration of 7 d left a silicone rubber rod passive sampler configuration in the linear or curvilinear uptake period for 19 of the pesticides studied. A change in the transport mechanism from polymer control to water boundary layer control was observed for pesticides with a log K sw of approximately 3.3. The PRC candidates were not fully relevant to correct the impact of water flow velocity on R s . We therefore propose an alternative method based on an overall resistance to mass transfer model to adjust R s from laboratory experiments to in situ hydrodynamic conditions. We estimated diffusion coefficients (D s ) and thickness of water boundary layer (δ w ) as adjustable model parameters. Log D s values ranged from -12.13 to -10.07 m 2  s -1 . The estimated δ w value showed a power function correlation with water flow velocity. Environ Toxicol Chem 2018;37:1208-1218. © 2017 SETAC. © 2017 SETAC.

Response to a small external force and fluctuations of a passive particle in a one-dimensional diffusive environment

NASA Astrophysics Data System (ADS)

Huveneers, François

2018-04-01

We investigate the long-time behavior of a passive particle evolving in a one-dimensional diffusive random environment, with diffusion constant D . We consider two cases: (a) The particle is pulled forward by a small external constant force and (b) there is no systematic bias. Theoretical arguments and numerical simulations provide evidence that the particle is eventually trapped by the environment. This is diagnosed in two ways: The asymptotic speed of the particle scales quadratically with the external force as it goes to zero, and the fluctuations scale diffusively in the unbiased environment, up to possible logarithmic corrections in both cases. Moreover, in the large D limit (homogenized regime), we find an important transient region giving rise to other, finite-size scalings, and we describe the crossover to the true asymptotic behavior.

Laboratory calibration and field testing of the Chemcatcher-Metal for trace levels of rare earth elements in estuarine waters.

PubMed

Petersen, Jördis; Pröfrock, Daniel; Paschke, Albrecht; Broekaert, Jose A C; Prange, Andreas

2015-10-01

Little knowledge is available about water concentrations of rare earth elements (REEs) in the marine environment. The direct measurement of REEs in coastal waters is a challenging task due to their ultra-low concentrations as well as the high salt content in the water samples. To quantify these elements at environmental concentrations (pg L(-1) to low ng L(-1)) in coastal waters, current analytical techniques are generally expensive and time consuming, and require complex chemical preconcentration procedures. Therefore, an integrative passive sampler was tested as a more economic alternative sampling approach for REE analysis. We used a Chemcatcher-Metal passive sampler consisting of a 3M Empore Chelating Disk as the receiving phase, as well as a cellulose acetate membrane as the diffusion-limiting layer. The effect of water turbulence and temperature on the uptake rates of REEs was analyzed during 14-day calibration experiments by a flow-through exposure tank system. The sampling rates were in the range of 0.42 mL h(-1) (13 °C; 0.25 m s(-1)) to 4.01 mL h(-1) (13 °C; 1 m s(-1)). Similar results were obtained for the different REEs under investigation. The water turbulence was the most important influence on uptake. The uptake rates were appropriate to ascertain time-weighted average concentrations of REEs during a field experiment in the Elbe Estuary near Cuxhaven Harbor (exposure time 4 weeks). REE concentrations were determined to be in the range 0.2 to 13.8 ng L(-1), where the highest concentrations were found for neodymium and samarium. In comparison, most of the spot samples measured along the Chemcatcher samples had REE concentrations below the limit of detection, in particular due to necessary dilution to minimize the analytical problems that arise with the high salt content in marine water samples. This study was among the first efforts to measure REE levels in the field using a passive sampling approach. Our results suggest that passive samplers could be an effective tool to monitor ultra-trace concentrations of REEs in coastal waters with high salt content.

The influence of geometry and draught shields on the performance of passive samplers.

PubMed

Hofschreuder, P; van der Meulen, W; Heeres, P; Slanina, S

1999-04-01

Passive samplers provide an excellent opportunity to perform indicative measurements or establish a dense network of measuring sites. A drawback compared with conventional active measuring methods is the larger spread of results. This variation can, to a large extent, be attributed to the influence of temperature, sampler geometry and wind on sampling results. A proper design of sampler geometry and optimum choice of draught shield can reduce the influence of wind velocity on a badge type sampler to less than 10%. Wire mesh screens prove to be inadequate in damping turbulence. Filters give good results. Attention should be paid to the size and isolation value of the walls of the sampler to prevent thermal updrafts occurring within the sampler. Tube type samplers are less influenced by wind, provided that turbulence is prevented from influencing diffusion within the sampler.

Role of Passive Diffusion, Transporters, and Membrane Trafficking-Mediated Processes in Cellular Drug Transport.

PubMed

Cocucci, E; Kim, J Y; Bai, Y; Pabla, N

2017-01-01

Intracellular drug accumulation is thought to be dictated by two major processes, passive diffusion through the lipid membrane or membrane transporters. The relative role played by these distinct processes remains actively debated. Moreover, the role of membrane-trafficking in drug transport remains underappreciated and unexplored. Here we discuss the distinct processes involved in cellular drug distribution and propose that better experimental models are required to elucidate the differential contributions of various processes in intracellular drug accumulation. © 2016 American Society for Clinical Pharmacology and Therapeutics.

Relative contributions of active mediated transport and passive diffusion of fluoroquinolones with various lipophilicities in a Calu-3 lung epithelial cell model.

PubMed

Brillault, Julien; De Castro, Whocely Victor; Couet, William

2010-01-01

The transport characteristics of six fluoroquinolones (FQs) with various lipophilicities were compared in a Calu-3 cell model. For each FQ, an active polarized transport was observed in the direction of the apical side. However, the apparent permeability of FQs resulted from active transport and passive diffusion that were highly variable between compounds and mainly governed by lipophilicity. Therefore, active transport was predominant for compounds with relatively low lipophilicity but minor for FQs with higher lipophilicity.

Outdoor air 1,3-butadiene monitoring: Comparison of performance of Radiello® passive samplers and active multi-sorbent bed tubes

NASA Astrophysics Data System (ADS)

Gallego, Eva; Teixidor, Pilar; Roca, Francisco Javier; Perales, José Francisco; Gadea, Enrique

2018-06-01

A comparison was made between the relative performance of active and passive sampling methods for the analysis of 1,3-butadiene in outdoor air. Active and passive sampling was conducted using multi-sorbent bed tubes (Carbotrap, Carbopack X, Carboxen 569) and RAD141 Radiello® diffusive samplers (filled with Carbopack X), respectively. Daily duplicate samples of multi-sorbent bed tubes were taken over a period of 14 days (9 + 5 days) at El Morell (Tarragona, Spain), near the petrochemical area. As 1,3-butadiene is a reactive pollutant and can be rapidly oxidized, half of the samplers were equipped with ozone scrubbers. Samples consisted in two tubes connected in series (front and back) to allow the determination of breakthrough. Quadruplicate samples of Radiello® tubes were taken over a period of 14 days (9 days and 5 days), too. During those days, ozone concentration was measured using RAD172 Radiello® samplers. In addition to this, daily duplicate samples of multi-sorbent bed tubes were taken in the city of Barcelona over a period of 8 days. Simultaneously, 4 samples of Radiello® tubes were exposed to outdoor air. Sampling was done throughout June and July 2017. Analysis was performed by thermal desorption coupled with gas chromatography/mass spectrometry. Analytical performance of the two sampling methods was evaluated by describing several quality assurance parameters, with results showing that performances are quite similar. They display low detection limits, good precision, linearity and desorption efficiency, low levels of blank values, and low breakthrough for multi-sorbent bed tubes. However, Radiello® samplers were not able to uptake episodic 1,3-butadiene high concentrations, leading to underestimation of real values. Hence, we can conclude that Radiello® samplers can be used for baseline 1,3-butadiene levels whereas multi-sorbent bed tubes would be advisable when relevant episodes are expected.

Diffusive mixing through velocity profile variation in microchannels

NASA Astrophysics Data System (ADS)

Yakhshi-Tafti, Ehsan; Cho, Hyoung J.; Kumar, Ranganathan

2011-03-01

Rapid mixing does not readily occur at low Reynolds number flows encountered in microdevices; however, it can be enhanced by passive diffusive mixing schemes. This study of micromixing of two miscible fluids is based on the principle that (1) increased velocity at the interface of co-flowing fluids results in increased diffusive mass flux across their interface, and (2) diffusion interfaces between two liquids progress transversely as the flow proceeds downstream. A passive micromixer is proposed that takes advantage of the peak velocity variation, inducing diffusive mixing. The effect of flow variation on the enhancement of diffusive mixing is investigated analytically and experimentally. Variation of the flow profile is confirmed using micro-Particle Image Velocimetry (μPIV) and mixing is evaluated by color variations resulting from the mixing of pH indicator and basic solutions. Velocity profile variations obtained from μPIV show a shift in peak velocities. The mixing efficiency of the Σ-micromixer is expected to be higher than that for a T-junction channel and can be as high as 80%. The mixing efficiency decreases with Reynolds number and increases with downstream length, exhibiting a power law.

The role of surface passivation in controlling Ge nanowire faceting

DOE PAGES

Gamalski, A. D.; Tersoff, J.; Kodambaka, S.; ...

2015-11-05

In situ transmission electron microscopy observations of nanowire morphologies indicate that during Au-catalyzed Ge nanowire growth, Ge facets can rapidly form along the nanowire sidewalls when the source gas (here, digermane) flux is decreased or the temperature is increased. This sidewall faceting is accompanied by continuous catalyst loss as Au diffuses from the droplet to the wire surface. We suggest that high digermane flux and low temperatures promote effective surface passivation of Ge nanowires with H or other digermane fragments inhibiting diffusion and attachment of Au and Ge on the sidewalls. Furthermore, these results illustrate the essential roles of themore » precursor gas and substrate temperature in maintaining nanowire sidewall passivation, necessary to ensure the growth of straight, untapered, <111>-oriented nanowires.« less

CVD-Based Valence-Mending Passivation for Crystalline-Si Solar Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Meng

2015-03-01

The objective of this project is to investigate a new surface passivation technique, valence-mending passivation, for its applications in crystalline-Si solar cells to achieve significant efficiency improvement and cost reduction. As the enabling technique, the project includes the development of chemical vapor deposition recipes to passivate textured Si(100) and multicrystalline-Si surfaces by sulfur and the characterization of the passivated Si surfaces, including thermal stability, Schottky barrier height, contact resistance and surface recombination. One important application is to replace the Ag finger electrode in Si cells with Al to reduce cost, by ~$0.1/Wp, and allow terawatt-scale deployment of crystalline-Si solar cells.more » These all-Al Si cells require a low-temperature metallization process for the Al electrode, to be compatible with valence-mending passivation and to prevent Al diffusion into n-type Si. Another application is to explore valence-mending passivation of grain boundaries in multicrystalline Si by diffusing sulfur into grain boundaries, to reduce the efficiency gas between monocrystalline-Si solar cells and multicrystalline-Si cells. The major accomplishments of this project include: 1) Demonstration of chemical vapor deposition processes for valence-mending passivation of both monocrystalline Si(100) and multicrystalline Si surfaces. Record Schottky barriers have been demonstrated, with the new record-low barrier of less than 0.08 eV between Al and sulfur-passivated n-type Si(100) and the new record-high barrier of 1.14 eV between Al and sulfur-passivated p-type Si(100). On the textured p-type monocrystalline Si(100) surface, the highest barrier with Al is 0.85 eV by valence-mending passivation. 2) Demonstration of a low-temperature metallization process for Al in crystalline-Si solar cells. The new metallization process is based on electroplating of Al in a room-temperature ionic liquid. The resistivity of the electroplated Al is ~7×10–6 ohm-cm, similar to that of screen-printed Ag. 3) Demonstration of two all-Al, Ag-free Si solar cells, with an electroplated Al front electrode and a screen-printed Al back electrode. One cell is an industrial p-type front-emitter cell, and the other is an n-type back-emitter cell. The efficiency of the p-type cell is close to 15%. This is an industrial cell and its efficiency is capped at ~18%. 4) Demonstration of grain boundary passivation by both hydrogen and sulfur using hydrogen sulfide (H2S). When the new grain boundary passivation is combined with Al2O3 surface passivation and post-annealing, the minority carrier lifetime in the p-type multicrystalline Si samples shows a significant improvement up to 68 fold. 5) In a side project, a simple green process is developed which is capable of recycling over 90% of the Si material in end-of-life crystalline-Si solar cells. The recycled Si meets the specifications for solar-grade Si and can be used as a new poly-Si feedstock for ingot growth.« less

Comparison of low cost measurement techniques for long-term monitoring of atmospheric ammonia.

PubMed

Sutton, M A; Miners, B; Tang, Y S; Milford, C; Wyers, G P; Duyzer, J H; Fowler, D

2001-10-01

An inter-comparison of techniques for long-term sampling of atmospheric ammonia (NH3) was conducted with a view to establishing a national network with > 50 sites. Key requirements were for: a low cost system, simplicity and durability to enable a postal exchange with local site operators, a precision of < +/- 20% for monthly sampling at expected NH3 concentrations of 1-2 micrograms m-3, a detection limit sufficient to resolve the small NH3 concentrations (< 0.2 microgram m-3) expected in remote parts of the UK, and a quantitative means to establish quality control. Five sampling methods were compared: A, a commercially available membrane diffusion tube (exposed in triplicate), with membranes removed immediately after sampling; B, the above method, with the membranes left in place until analysis; C, open-ended diffusion tubes (exposed with 4 replicates); D, a new active sampling diffusion denuder system; and E, an active sampling bubbler system. Method D consisted of two 0.1 m acid coated glass denuders in series with sampling at approximately 0.3 l min-1. These methods were deployed at 6 locations in the UK and the Netherlands and compared against reference estimates. Method D was the most precise and sensitive of the techniques compared, with a detection limit of < 0.1 microgram m-3. The bubbler provided a less precise estimate of NH3 concentration, and also suffered several practical drawbacks. The diffusion tubes were found to correlate with the reference at high concentrations (> 3 micrograms m-3), but were less precise and overestimated NH3 at smaller concentrations. Of the passive methods, A was the most precise and C the least precise. On the basis of the results, method D has been implemented in the national network, together with application of method A to explore spatial variability in regions with expected high NH3 concentrations.

Discreet passive explosive detection through 2-sided waveguided fluorescence

DOEpatents

Harper, Ross James [Stillwater, OK; la Grone, Marcus [Cushing, OK; Fisher, Mark [Stillwater, OK

2011-10-18

The current invention provides a passive sampling device suitable for collecting and detecting the presence of target analytes. In particular, the passive sampling device is suitable for detecting nitro-aromatic compounds. The current invention further provides a passive sampling device reader suitable for determining the collection of target analytes. Additionally, the current invention provides methods for detecting target analytes using the passive sampling device and the passive sampling device reader.

Low cost fuel cell diffusion layer configured for optimized anode water management

DOEpatents

Owejan, Jon P; Nicotera, Paul D; Mench, Matthew M; Evans, Robert E

2013-08-27

A fuel cell comprises a cathode gas diffusion layer, a cathode catalyst layer, an anode gas diffusion layer, an anode catalyst layer and an electrolyte. The diffusion resistance of the anode gas diffusion layer when operated with anode fuel is higher than the diffusion resistance of the cathode gas diffusion layer. The anode gas diffusion layer may comprise filler particles having in-plane platelet geometries and be made of lower cost materials and manufacturing processes than currently available commercial carbon fiber substrates. The diffusion resistance difference between the anode gas diffusion layer and the cathode gas diffusion layer may allow for passive water balance control.

Performance of a passive direct ethanol fuel cell

NASA Astrophysics Data System (ADS)

Pereira, J. P.; Falcão, D. S.; Oliveira, V. B.; Pinto, A. M. F. R.

2014-06-01

Ethanol emerges as an attractive fuel since it is less toxic and has higher energy density than methanol and can be produced from biomass. Direct ethanol fuel cells (DEFCs) appear as a good choice for producing sustainable energy for portable applications. However, they are still far from attaining acceptable levels of power output, since their performance is affected by the slow electrochemical ethanol oxidation and water and ethanol crossover. In the present work, an experimental study on the performance of a passive DEFC is described. Tailored MEAs (membrane electrode assembly) with different catalyst loadings, anode diffusion layers and membranes were tested in order to select optimal working conditions at high ethanol concentrations and low ethanol crossover. The performance increased with an increase of membrane and anode diffusion layer thicknesses and anode catalyst loading. A maximum power density of 1.33 mW cm-2, was obtained using a Nafion 117 membrane, 4 mg cm-2 of Pt-Ru and 2 mg cm-2 of Pt on the anode and cathode catalyst layers, ELAT as anode diffusion layer, carbon cloth as cathode diffusion layer and an ethanol concentration of 2 M. As far as the authors are aware this is the first work reporting an experimental optimization of passive DEFCs.

Bioaccumulation Using Surrogate Samplers (Bass): Evaluation Of A Passive Sampler As An Alternative Monitoring Tool For Environmental Contaminants At The Savannah River Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paller, M.; Knox, A.; Kuhne, W.

2015-10-15

DOE sites conduct traditional environmental monitoring programs that require collecting, processing, and analyzing water, sediment, and fish samples. However, recently developed passive sampling technologies, such as Diffusive Gradient in Thin films (DGT), may measure the chemical phases that are available and toxic to organisms (the bioavailable fraction), thereby producing more accurate and economical results than traditional methods.  Our laboratory study showed that dissolved copper concentrations measured by DGT probes were strongly correlated with the uptake of copper by Lumbriculus variegatus, an aquatic worm, and with concentrations of copper measured by conventional methods.  Dissolved copper concentrations in DGT probes increased with timemore » of exposure, paralleling the increase in copper with time that ocurred in Lumbriculus.  Additional studies with a combination of seven dissolved metals showed similar results.  These findings support the use of DGT as a biomimetic monitoring tool and provide a basis for refinement of these methods for cost-effective environmental monitoring at DOE sites.« less

Discreet passive explosive detection through 2-sided wave guided fluorescence

DOEpatents

Harper, Ross James; la Grone, Marcus; Fisher, Mark

2012-10-16

The current invention provides a passive sampling device suitable for collecting and detecting the presence of target analytes. In particular, the passive sampling device is suitable for detecting nitro-aromatic compounds. The current invention further provides a passive sampling device reader suitable for determining the collection of target analytes. Additionally, the current invention provides methods for detecting target analytes using the passive sampling device and the passive sampling device reader.

HfO2 Gate Dielectric on (NH4)2S Passivated (100) GaAs Grown by Atomic Layer Deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, P.T.; /Stanford U., Materials Sci. Dept.; Sun, Y.

2007-09-28

The interface between hafnium oxide grown by atomic layer deposition and (100) GaAs treated with HCl cleaning and (NH{sub 4}){sub 2}S passivation has been characterized. Synchrotron radiation photoemission core level spectra indicated successful removal of the native oxides and formation of passivating sulfides on the GaAs surface. Layer-by-layer removal of the hafnia film revealed a small amount of As{sub 2}O{sub 3} formed at the interface during the dielectric deposition. Traces of arsenic and sulfur out-diffusion into the hafnia film were observed after a 450 C post-deposition anneal, and may be the origins for the electrically active defects. Transmission electron microscopymore » cross section images showed thicker HfO{sub 2} films for a given precursor exposure on S-treated GaAs versus the non-treated sample. In addition, the valence-band and the conduction-band offsets at the HfO{sub 2}/GaAs interface were deduced to be 3.18 eV and a range of 0.87-0.97 eV, respectively. It appears that HCl+(NH{sub 4})2{sub S} treatments provide a superior chemical passivation for GaAs and initial surface for ALD deposition.« less

Uptake of PAHs into polyoxymethylene and application to oil-soot (lampblack)-impacted soil samples.

PubMed

Hong, Lei; Luthy, Richard G

2008-05-01

Polyoxymethylene (POM) is a polymeric material used increasingly in passive sampling of hydrophobic organic contaminants such as PAHs and PCBs in soils and sediments. In this study, we examined the sorption behavior of 12 PAH compounds to POM and observed linear isotherms spanning two orders of magnitude of aqueous concentrations. Uptake kinetic studies performed in batch systems for up to 54 d with two different volume ratios of POM-to-aqueous phase were evaluated with coupled diffusion and mass transfer models to simulate the movement of PAHs during the uptake process and to assess the physicochemical properties and experimental conditions that control uptake rates. Diffusion coefficients of PAHs in POM were estimated to be well correlated with diffusants' molecular weights as D(POM) proportional, variant(MW)(-3), descending from 2.3 x 10(-10) cm(2) s(-1) for naphthalene to 7.0 x 10(-11) cm(2) s(-1) for pyrene. The uptake rates for PAHs with log K(ow)<5.8 were controlled by the POM phase and the hydrophobicity of PAH compounds. For more hydrophobic PAH compounds, the aqueous boundary layer played an increasingly important role in determining the overall mass transfer rate. The POM partitioning technique was demonstrated to agree well with two other procedures for measuring PAH soil-water distribution coefficients in oil-soot (lampblack) containing soil samples.

Investigation of polyethylene passive diffusion samplers for sampling volatile organic compounds in ground water at Davis Global Communications, Sacramento, California, August 1998 to February 1999

USGS Publications Warehouse

Vroblesky, Don A.; Borchers, J.W.; Campbell, T.R.; Kinsey, Willey

2000-01-01

Fourteen wells were instrumented with diffusion samplers as a test to determine whether the samplers could be used to obtain representative volatile organic compound concentrations at a study site in Sacramento, California. Single diffusion samplers were placed in 10-foot-long well screens, and multiple diffusion samplers were positioned in 20-foot-long well screens. Borehole geophysical logs and electromagnetic flowmeter tests were run in selected wells with 20-foot-long well screens prior to deploying the samplers. The diffusion samplers were recovered after 25 to 30 days, and the wells were then sampled by using the purge-and-sample method. In most wells, the concentrations obtained by using the downhole diffusion samplers closely matched those obtained by using the purge-and-sample method. In seven wells, the concentrations differed between the two methods by only 2 micrograms per liter (g/L) or less. In three wells, volatile organic compounds were not detected in water obtained by using either method. In the four remaining wells, differences between the methods were less than 2g/L in the 0.2- to 8.5-g/L concentration range and from 1.2 to 8.7g/L in the 10- to 26-g/L concentration range. Greater differences (23 percent or 14.5g/L, 31 percent or 66g/L, and 46 percent or 30g/L) between the two methods were observed for tetrachloroethene concentrations, which ranged between 30 and 211g/L in three wells. The most probable explanation for the differences is that in some wells, the purging induced drawdowns and introduced water that differed in volatile organic compound concentrations from the in situ water in contact with the screened interval of the well. Alternate explanations include the possibility of unrecorded changes in nearby contaminant-extraction-well operation during the equilibration period. The data suggest that the combined use of borehole flowmeter tests and diffusion samplers may be useful in optimizing the radius of capture of contaminated ground water by the contaminant-removal wells. Overall, the data suggest that the use of diffusion samplers provided an alternative sampling method to the purge-and-sample approach. 1U.S. Geological Survey, Stephenson Center, Suite 129, 720 Gracern Road, Columbia, South Carolina 29210-7651. 2U.S. Geological Survey, 6000 J Street, Sacramento, California 95819-6129.

Influence of ground level SO2 on the diffuse to direct irradiance ratio in the middle ultraviolet

NASA Technical Reports Server (NTRS)

Klenk, K. F.; Green, A. E. S.

1977-01-01

The dependence of the ratio of the diffuse to direct irradiances at the ground were examined for a wavelength of 315.1 nm. A passive remote sensing method based on ratio measurements for obtaining the optical thickness of SO2 in the vertical column was proposed. If, in addition to the ratio measurements, the SO2 density at the ground is determining using an appropriate point-sampling technique then some inference on the vertical extent of SO2 can be drawn. An analytic representation is presented of the ratio for a wide range of SO2 and aerosol optical thicknesses and solar zenith angles which can be inverted algebraically to give the SO2 optical thickness in terms of the measured ratio, aerosol optical thickness and solar zenith angle.

Development of high-efficiency solar cells on silicon web

NASA Technical Reports Server (NTRS)

Meier, D. L.; Greggi, J.; Rai-Choudhury, P.

1986-01-01

Work is reported aimed at identifying and reducing sources of carrier recombination both in the starting web silicon material and in the processed cells. Cross-sectional transmission electron microscopy measurements of several web cells were made and analyzed. The effect of the heavily twinned region on cell efficiency was modeled, and the modeling results compared to measured values for processed cells. The effects of low energy, high dose hydrogen ion implantation on cell efficiency and diffusion length were examined. Cells were fabricated from web silicon known to have a high diffusion length, with a new double layer antireflection coating being applied to these cells. A new contact system, to be used with oxide passivated cells and which greatly reduces the area of contact between metal and silicon, was designed. The application of DLTS measurements to beveled samples was further investigated.

Passive Samplers for Investigations of Air Quality: Method Description, Implementation, and Comparison to Alternative Sampling Methods

EPA Science Inventory

This Paper covers the basics of passive sampler design, compares passive samplers to conventional methods of air sampling, and discusses considerations when implementing a passive sampling program. The Paper also discusses field sampling and sample analysis considerations to ensu...

Understanding of Relationship between Phospholipid Membrane Permeability and Self-Diffusion Coefficients of Some Drugs and Biologically Active Compounds in Model Solvents.

PubMed

Blokhina, Svetlana V; Volkova, Tatyana V; Golubev, Vasiliy A; Perlovich, German L

2017-10-02

In this work we measured self-diffusion coefficients of 5 drugs (aspirin, caffeine, ethionamide, salicylic acid, and paracetamol) and 11 biologically active compounds of similar structure in deuterated water and 1-octanol by NMR. It has been found that an increase in the van der Waals volume of the molecules of the studied substances result in reduction of their diffusion mobility in both solvents. The analysis of the experimental data showed the influence of chemical nature and structural isomerization of the molecules on the diffusion mobility. Apparent permeability coefficients of the studied compounds were determined using an artificial phospholipid membrane made of egg lecithin as a model of in vivo absorption. Distribution coefficients in 1-octanol/buffer pH 7.4 system were measured. For the first time the model of the passive diffusion through the phospholipid membrane was validated based on the experimental data. To this end, the passive diffusion was considered as an additive process of molecule passage through the aqueous boundary layer before the membrane and 1-octanol barrier simulating the lipid layer of the membrane.

Scaling behavior in corrosion and growth of a passive film.

PubMed

Aarão Reis, F D A; Stafiej, Janusz

2007-07-01

We study a simple model for metal corrosion controlled by the reaction rate of the metal with an anionic species and the diffusion of that species in the growing passive film between the solution and the metal. A crossover from the reaction-controlled to the diffusion-controlled growth regime with different roughening properties is observed. Scaling arguments provide estimates of the crossover time and film thickness as functions of the reaction and diffusion rates and the concentration of anionic species in the film-solution interface, including a nontrivial square-root dependence on that concentration. At short times, the metal-film interface exhibits Kardar-Parisi-Zhang (KPZ) scaling, which crosses over to a diffusion-limited erosion (Laplacian growth) regime at long times. The roughness of the metal-film interface at long times is obtained as a function of the rates of reaction and diffusion and of the KPZ growth exponent. The predictions have been confirmed by simulations of a lattice version of the model in two dimensions. Relations with other erosion and corrosion models and possible applications are discussed.

Passive sampling methods for contaminated sediments: Scientific rationale supporting use of freely dissolved concentrations

PubMed Central

Mayer, Philipp; Parkerton, Thomas F; Adams, Rachel G; Cargill, John G; Gan, Jay; Gouin, Todd; Gschwend, Philip M; Hawthorne, Steven B; Helm, Paul; Witt, Gesine; You, Jing; Escher, Beate I

2014-01-01

Passive sampling methods (PSMs) allow the quantification of the freely dissolved concentration (Cfree) of an organic contaminant even in complex matrices such as sediments. Cfree is directly related to a contaminant's chemical activity, which drives spontaneous processes including diffusive uptake into benthic organisms and exchange with the overlying water column. Consequently, Cfree provides a more relevant dose metric than total sediment concentration. Recent developments in PSMs have significantly improved our ability to reliably measure even very low levels of Cfree. Application of PSMs in sediments is preferably conducted in the equilibrium regime, where freely dissolved concentrations in the sediment are well-linked to the measured concentration in the sampler via analyte-specific partition ratios. The equilibrium condition can then be assured by measuring a time series or a single time point using passive samplers with different surface to volume ratios. Sampling in the kinetic regime is also possible and generally involves the application of performance reference compounds for the calibration. Based on previous research on hydrophobic organic contaminants, it is concluded that Cfree allows a direct assessment of 1) contaminant exchange and equilibrium status between sediment and overlying water, 2) benthic bioaccumulation, and 3) potential toxicity to benthic organisms. Thus, the use of PSMs to measure Cfree provides an improved basis for the mechanistic understanding of fate and transport processes in sediments and has the potential to significantly improve risk assessment and management of contaminated sediments. Integr Environ Assess Manag 2014;10:197–209. © 2014 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of SETAC. PMID:24288295

Uniformity and passivation research of Al2O3 film on silicon substrate prepared by plasma-enhanced atom layer deposition.

PubMed

Jia, Endong; Zhou, Chunlan; Wang, Wenjing

2015-01-01

Plasma-enhanced atom layer deposition (PEALD) can deposit denser films than those prepared by thermal ALD. But the improvement on thickness uniformity and the decrease of defect density of the films deposited by PEALD need further research. A PEALD process from trimethyl-aluminum (TMA) and oxygen plasma was investigated to study the influence of the conditions with different plasma powers and deposition temperatures on uniformity and growth rate. The thickness and refractive index of films were measured by ellipsometry, and the passivation effect of alumina on n-type silicon before and after annealing was measured by microwave photoconductivity decay method. Also, the effects of deposition temperature and annealing temperature on effective minority carrier lifetime were investigated. Capacitance-voltage and conductance-voltage measurements were used to investigate the interface defect density of state (D it) of Al2O3/Si. Finally, Al diffusion P(+) emitter on n-type silicon was passivated by PEALD Al2O3 films. The conclusion is that the condition of lower substrate temperature accelerates the growth of films and that the condition of lower plasma power controls the films' uniformity. The annealing temperature is higher for samples prepared at lower substrate temperature in order to get the better surface passivation effects. Heavier doping concentration of Al increased passivation quality after annealing by the effective minority carrier lifetime up to 100 μs.

Numerical study of air ingress transition to natural circulation in a high temperature helium loop

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franken, Daniel; Gould, Daniel; Jain, Prashant K.

Here, the generation-IV high temperature gas cooled reactors (HTGRs) are designed with many passive safety features, one of which is the ability to passively remove heat under a loss of coolant accident (LOCA). However, several common reactor designs do not prevent against a large break in the coolant system and may therefore experience a depressurized LOCA. This would lead to air entering into the reactor system via several potential modes of ingress: diffusion, gravity currents, and natural circulation. At the onset of a LOCA, the initial rate of air ingress is expected to be very slow because it is governedmore » by molecular diffusion. However, after several hours, natural circulation would commence, thus, bringing the air into the reactor system at a much higher rate. As a consequence, air ingress would cause the high temperature graphite matrix to oxidize, leading to its thermal degradation and decreased passive heat (decay) removal capability. Therefore, it is essential to understand the transition of air ingress from molecular diffusion to natural circulation in an HTGR system. This paper presents results from a computational fluid dynamics (CFD) model to study the air ingress transition behavior. These results are validated against an h-shaped high temperature helium loop experiment. Details are provided to quantitatively predict the transition time from molecular diffusion to natural circulation.« less

Numerical study of air ingress transition to natural circulation in a high temperature helium loop

DOE PAGES

Franken, Daniel; Gould, Daniel; Jain, Prashant K.; ...

2017-09-21

Here, the generation-IV high temperature gas cooled reactors (HTGRs) are designed with many passive safety features, one of which is the ability to passively remove heat under a loss of coolant accident (LOCA). However, several common reactor designs do not prevent against a large break in the coolant system and may therefore experience a depressurized LOCA. This would lead to air entering into the reactor system via several potential modes of ingress: diffusion, gravity currents, and natural circulation. At the onset of a LOCA, the initial rate of air ingress is expected to be very slow because it is governedmore » by molecular diffusion. However, after several hours, natural circulation would commence, thus, bringing the air into the reactor system at a much higher rate. As a consequence, air ingress would cause the high temperature graphite matrix to oxidize, leading to its thermal degradation and decreased passive heat (decay) removal capability. Therefore, it is essential to understand the transition of air ingress from molecular diffusion to natural circulation in an HTGR system. This paper presents results from a computational fluid dynamics (CFD) model to study the air ingress transition behavior. These results are validated against an h-shaped high temperature helium loop experiment. Details are provided to quantitatively predict the transition time from molecular diffusion to natural circulation.« less

A MULTI-STREAM MODEL FOR VERTICAL MIXING OF A PASSIVE TRACER IN THE CONVECTIVE BOUNDARY LAYER

EPA Science Inventory

We study a multi-stream model (MSM) for vertical mixing of a passive tracer in the convective boundary layer, in which the tracer is advected by many vertical streams with different probabilities and diffused by small scale turbulence. We test the MSM algorithm for investigatin...

Pesticide impact on aquatic invertebrates identified with Chemcatcher® passive samplers and the SPEAR(pesticides) index.

PubMed

Münze, Ronald; Orlinskiy, Polina; Gunold, Roman; Paschke, Albrecht; Kaske, Oliver; Beketov, Mikhail A; Hundt, Matthias; Bauer, Coretta; Schüürmann, Gerrit; Möder, Monika; Liess, Matthias

2015-12-15

Pesticides negatively affect biodiversity and ecosystem function in aquatic environments. In the present study, we investigated the effects of pesticides on stream macroinvertebrates at 19 sites in a rural area dominated by forest cover and arable land in Central Germany. Pesticide exposure was quantified with Chemcatcher® passive samplers equipped with a diffusion-limiting membrane. Ecological effects on macroinvertebrate communities and on the ecosystem function detritus breakdown were identified using the indicator system SPEARpesticides and the leaf litter degradation rates, respectively. A decrease in the abundance of pesticide-vulnerable taxa and a reduction in leaf litter decomposition rates were observed at sites contaminated with the banned insecticide Carbofuran (Toxic Units≥-2.8), confirming the effect thresholds from previous studies. The results show that Chemcatcher® passive samplers with a diffusion-limiting membrane reliably detect ecologically relevant pesticide pollution, and we suggest Chemcatcher® passive samplers and SPEARpesticides as a promising combination to assess pesticide exposure and effects in rivers and streams. Copyright © 2015 Elsevier B.V. All rights reserved.

Optical tracer size differences allow quantitation of active pumping rate versus Stokes-Einstein diffusion in lymphatic transport

NASA Astrophysics Data System (ADS)

DSouza, Alisha V.; Marra, Kayla; Gunn, Jason R.; Samkoe, Kimberley S.; Pogue, Brian W.

2016-10-01

Lymphatic uptake of interstitially administered agents occurs by passive convective-diffusive inflow driven by interstitial concentration and pressure, while the downstream lymphatic transport is facilitated by active propulsive contractions of lymphatic vessel walls. Near-infrared fluorescence imaging in mice was used to measure these central components of lymphatic transport for the first time, using two different-sized molecules-methylene blue (MB) and fluorescence-labeled antibody immunoglobulin G (IgG)-IRDye 680RD. This work confirms the hypothesis that lymphatic passive inflow and active propulsion rates can be separated based upon the relative differences in Stokes-Einstein diffusion coefficient. This coefficient specifically affects the passive-diffusive uptake when the interstitial volume and pressure are constant. Parameters such as mean time-to-peak signal, overall fluorescence signal intensities, and number of active peristaltic pulses, were estimated from temporal imaging data. While the mean time to attain peak signal representative of diffusion-dominated flow in the lymph vessels was 0.6±0.2 min for MB and 8±6 min for IgG, showing a size dependence, the active propulsion rates were 3.4±0.8 pulses/min and 3.3±0.5 pulses/min, respectively, appearing size independent. The propulsion rates for both dyes decreased with clearance from the interstitial injection-site, indicating intrinsic control of the smooth muscles in response to interstitial pressure. This approach to size-comparative agent flow imaging of lymphatic function can enable noninvasive characterization of diseases related to uptake and flow in lymph networks.

An in situ method for real-time monitoring of soil gas diffusivity

NASA Astrophysics Data System (ADS)

Laemmel, Thomas; Maier, Martin; Schack-Kirchner, Helmer; Lang, Friederike

2016-04-01

Soil aeration is an important factor for the biogeochemistry of soils. Generally, gas exchange between soil and atmosphere is assumed to be governed by molecular diffusion and by this way fluxes can be calculated using by Fick's Law. The soil gas diffusion coefficient DS represents the proportional factor between the gas flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gas through the soil. One common way to determine DS is taking core samples in the field and measuring DS in the lab. Unfortunately this method is destructive and laborious and it can only reflect a small fraction of the whole soil. As a consequence, uncertainty about the resulting effective diffusivity on the profile scale, i.e. the real aeration status remains. We developed a method to measure and monitor DS in situ. The set-up consists of a custom made gas sampling device, the continuous injection of an inert tracer gas and inverse gas transport modelling in the soil. The gas sampling device has seven sampling depths (from 0 to -43 cm of depth) and can be easily installed into vertical holes drilled by an auger, which allows for fast installation of the system. Helium (He) as inert tracer gas was injected continuously at the lower end of the device. The resulting steady state distribution of He was used to deduce the DS depth distribution of the soil. For Finite Element Modeling of the gas-sampling-device/soil system the program COMSOL was used. We tested our new method both in the lab and in a field study and compared the results with a reference lab method using soil cores. DS profiles obtained by our in-situ method were consistent with DS profiles determined based on soil core analyses. Soil gas profiles could be measured with a temporal resolution of 30 minutes. During the field study, there was an important rain event and we could monitor the decrease in soil gas diffusivity in the top soil due to water infiltration. The effect of soil water infiltration deeper into the soil on soil gas diffusivity could be observed during the following hours. Our new DS determination device can be quickly and easily installed and allows for monitoring continuously soil gas transport over a long time. It allows following modifications of soil gas diffusivity due to rain events. In addition it enables the analysis of non-diffusive soil gas transport processes.

Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison

PubMed Central

2018-01-01

This work presents the results of an international interlaboratory comparison on ex situ passive sampling in sediments. The main objectives were to map the state of the science in passively sampling sediments, identify sources of variability, provide recommendations and practical guidance for standardized passive sampling, and advance the use of passive sampling in regulatory decision making by increasing confidence in the use of the technique. The study was performed by a consortium of 11 laboratories and included experiments with 14 passive sampling formats on 3 sediments for 25 target chemicals (PAHs and PCBs). The resulting overall interlaboratory variability was large (a factor of ∼10), but standardization of methods halved this variability. The remaining variability was primarily due to factors not related to passive sampling itself, i.e., sediment heterogeneity and analytical chemistry. Excluding the latter source of variability, by performing all analyses in one laboratory, showed that passive sampling results can have a high precision and a very low intermethod variability (

Connecting Ellipses to Rectangles in Passive Scalar Transport

NASA Astrophysics Data System (ADS)

Aminian, Manuchehr; Bernardi, Francesca; Camassa, Roberto; Harris, Daniel; McLaughlin, Richard

2017-11-01

We study how passive scalar transport in Poiseuille flow is affected by the shape of the pipe cross section. Our previous results have established nontrivial dependence of the skewness of the tracer distribution upon the pipe shape. Previously, we have studied the families of rectangles and ellipses, with the behavior past diffusive timescales primarily depending on aspect ratio, and the type of geometry being secondary. However, at timescales well before the diffusion timescale, the family of ellipses is distinct compared to rectangles. We investigate this phenomenon by studying a collection of exotic cross sections connecting the ellipses and rectangles, using a combination of theoretical and computational tools.

pH Dependent but not P-gp Dependent Bidirectional Transport Study of S-propranolol: The Importance of Passive Diffusion.

PubMed

Zheng, Yi; Benet, Leslie Z; Okochi, Hideaki; Chen, Xijing

2015-08-01

Recent controversial publications, citing studies purporting to show that P-gp mediates the transport of propranolol, proposed that passive biological membrane transport is negligible. Based on the BDDCS, the extensively metabolized-highly permeable-highly soluble BDDCS class 1 drug, propranolol, shows a high passive permeability at concentrations unrestricted by solubility that can overwhelm any potential transporter effects. Here we reinvestigate the effects of passive diffusion and carrier-mediated transport on S-propranolol. Bidirectional permeability and inhibition of efflux transport studies were carried out in MDCK, MDCK-MDR1 and Caco-2 cell lines at different concentrations. Transcellular permeability studies were conducted at different apical pHs in the rat jejunum Ussing chamber model and PAMPA system. S-propranolol exhibited efflux ratios lower than 1 in MDCK, MDCK-MDR1 and Caco-2 cells. No significant differences of Papp, B->A in the presence and absence of the efflux inhibitor GG918 were observed. However, an efflux ratio of 3.63 was found at apical pH 6.5 with significant decrease in Papp, A->B and increase in Papp, B->A compared to apical pH 7.4 in Caco-2 cell lines. The pH dependent permeability was confirmed in the Ussing chamber model. S-propranolol flux was unchanged during inhibition by verapamil and rifampin. Furthermore, pH dependent permeability was also observed in the PAMPA system. S-propranolol does not exhibit active transport as proposed previously. The "false" positive efflux ratio can be explained by the pH partition theory. As expected, passive diffusion, but not active transport, plays the primary role in the permeability of the BDDCS class 1 drug propranolol.

pH dependent but not P-gp dependent bidirectional transport study of S-propranolol: the importance of passive diffusion

PubMed Central

Zheng, Yi; Benet, Leslie Z.; Okochi, Hideaki; Chen, Xijing

2016-01-01

Purpose Recent controversial publications, citing studies purporting to show that P-gp mediates the transport of propranolol, proposed that passive biological membrane transport is negligible. Based on the BDDCS, the extensively metabolized-highly permeable-highly soluble BDDCS class 1 drug, propranolol, shows a high passive permeability at concentrations unrestricted by solubility that can overwhelm any potential transporter effects. Here we reinvestigate the effects of passive diffusion and carrier-mediated transport on S-propranolol. Methods Bidirectional permeability and inhibition of efflux transport studies were carried out in MDCK, MDCK-MDR1 and Caco-2 cell lines at different concentrations. Transcellular permeability studies were conducted at different apical pHs in the rat jejunum Ussing chamber model and PAMPA system. Results S-propranolol exhibited efflux ratios lower than 1 in MDCK, MDCK-MDR1 and Caco-2 cells. No significant differences of Papp, B->A in the presence and absence of the efflux inhibitor GG918 were observed. However, an efflux ratio of 3.63 was found at apical pH 6.5 with significant decrease in Papp, A->B and increase in Papp, B->A compared to apical pH 7.4 in Caco-2 cell lines. The pH dependent permeability was confirmed in the Ussing chamber model. S-propranolol flux was unchanged during inhibition by verapamil and rifampin. Furthermore, pH dependent permeability was also observed in the PAMPA system. Conclusions S-propranolol does not exhibit active transport as proposed previously. The "false" positive efflux ratio can be explained by the pH partition theory. As expected, passive diffusion, but not active transport, plays the primary role in the permeability of the BDDCS class 1 drug propranolol. PMID:25690341

Configurations and calibration methods for passive sampling techniques.

PubMed

Ouyang, Gangfeng; Pawliszyn, Janusz

2007-10-19

Passive sampling technology has developed very quickly in the past 15 years, and is widely used for the monitoring of pollutants in different environments. The design and quantification of passive sampling devices require an appropriate calibration method. Current calibration methods that exist for passive sampling, including equilibrium extraction, linear uptake, and kinetic calibration, are presented in this review. A number of state-of-the-art passive sampling devices that can be used for aqueous and air monitoring are introduced according to their calibration methods.

Passivation Using Molecular Halides Increases Quantum Dot Solar Cell Performance.

PubMed

Lan, Xinzheng; Voznyy, Oleksandr; Kiani, Amirreza; García de Arquer, F Pelayo; Abbas, Abdullah Saud; Kim, Gi-Hwan; Liu, Mengxia; Yang, Zhenyu; Walters, Grant; Xu, Jixian; Yuan, Mingjian; Ning, Zhijun; Fan, Fengjia; Kanjanaboos, Pongsakorn; Kramer, Illan; Zhitomirsky, David; Lee, Philip; Perelgut, Alexander; Hoogland, Sjoerd; Sargent, Edward H

2016-01-13

A solution-based passivation scheme is developed featuring the use of molecular iodine and PbS colloidal quantum dots (CQDs). The improved passivation translates into a longer carrier diffusion length in the solid film. This allows thicker solar-cell devices to be built while preserving efficient charge collection, leading to a certified power conversion efficiency of 9.9%, which is a new record in CQD solar cells. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Li4SiO4-Based Artificial Passivation Thin Film for Improving Interfacial Stability of Li Metal Anodes.

PubMed

Kim, Ji Young; Kim, A-Young; Liu, Guicheng; Woo, Jae-Young; Kim, Hansung; Lee, Joong Kee

2018-03-14

An amorphous SiO 2 (a-SiO 2 ) thin film was developed as an artificial passivation layer to stabilize Li metal anodes during electrochemical reactions. The thin film was prepared using an electron cyclotron resonance-chemical vapor deposition apparatus. The obtained passivation layer has a hierarchical structure, which is composed of lithium silicide, lithiated silicon oxide, and a-SiO 2 . The thickness of the a-SiO 2 passivation layer could be varied by changing the processing time, whereas that of the lithium silicide and lithiated silicon oxide layers was almost constant. During cycling, the surface of the a-SiO 2 passivation layer is converted into lithium silicate (Li 4 SiO 4 ), and the portion of Li 4 SiO 4 depends on the thickness of a-SiO 2 . A minimum overpotential of 21.7 mV was observed at the Li metal electrode at a current density of 3 mA cm -2 with flat voltage profiles, when an a-SiO 2 passivation layer of 92.5 nm was used. The Li metal with this optimized thin passivation layer also showed the lowest charge-transfer resistance (3.948 Ω cm) and the highest Li ion diffusivity (7.06 × 10 -14 cm 2 s -1 ) after cycling in a Li-S battery. The existence of the Li 4 SiO 4 artificial passivation layer prevents the corrosion of Li metal by suppressing Li dendritic growth and improving the ionic conductivity, which contribute to the low charge-transfer resistance and high Li ion diffusivity of the electrode.

An assessment of polyurethane foam passive samplers for atmospheric metals compared with active samplers.

PubMed

Li, Qilu; Yang, Kong; Li, Jun; Zeng, Xiangying; Yu, Zhiqiang; Zhang, Gan

2018-05-01

In this study, we conducted an assessment of polyurethane foam (PUF) passive sampling for metals combining active sampling. Remarkably, we found that the metals collected in the passive samples differed greatly from those collected in active samples. By composition, Cu and Ni accounted for significantly higher proportions in passive samples than in active samples, leading to significantly higher uptake rates of Cu and Ni. In assessing seasonal variation, metals in passive samples had higher concentrations in summer (excluding Heshan), which differed greatly from the pattern of active samples (winter > summer), indicating that the uptake rates of most metals were higher in summer than in winter. Overall, due to the stable passive uptake rates, we considered that PUF passive samplers can be applied to collect atmospheric metals. Additionally, we created a snapshot of the metal pollution in the Pearl River Delta using principal component analysis of PUF samples and their source apportionment. Copyright © 2018 Elsevier Ltd. All rights reserved.

Calculating the Diffusive Flux of Persistent Organic Pollutants between Sediments and the Water Column on the Palos Verdes Shelf Superfund Site using Polymeric Passive Samplers

EPA Science Inventory

Passive samplers were used to determine water concentrations of persistent organic pollutants (POPs) in the surface sediments and near-bottom water of a marine Superfund site on the Palos Verdes Shelf, California, USA. Measured concentrations in the porewater and water column at...

Measurement of VOCs Using Passive Sorbent Tubes near Oil & Natural Gas Production Pads in Colorado and Texas

EPA Science Inventory

A U.S. EPA team, consisting of the Office of Research and Development and Region 6 (Dallas) and Region 8 (Denver), deployed passive-diffusive sorbent tubes as part of a method evaluation study around one oil and natural gas production pad in both the Barnett Shale Basin in Texas ...

Wavelength Coded Image Transmission and Holographic Optical Elements.

DTIC Science & Technology

1984-08-20

system has been designed and built for transmitting images of diffusely reflecting objects through optical fibers and displaying those images at a...passive components at the end of a fiber-optic designed to transmit high-resolution images of diffusely imaging system as described in this paper... designing a system for viewing diffusely reflecting The authors are with University of Minnesota. Electrical Engi- objects, one must consider that a

A novel in-situ method for real-time monitoring of gas transport in soil

NASA Astrophysics Data System (ADS)

Laemmel, Thomas; Maier, Martin; Schack-Kirchner, Helmer; Lang, Friederike

2017-04-01

Gas exchange between soil and atmosphere is important for the biogeochemistry of soils. Gas transport in soil is commonly assumed to be governed by molecular diffusion and is usually described by the soil gas diffusion coefficient DS characterizing the ability of the soil to "transport passively" gas through the soil. One way to determine DS is sampling soil cores in the field and measuring DS in the lab. Unfortunately this method is destructive and laborious. Moreover, a few previous field studies identified other gas transport processes in soil to significantly enhance the diffusive gas transport. However, until now, no method is available to measure gas transport in situ in the soil. We developed a novel method to monitor gas transport in soil in situ. The method includes a custom made gas sampling device, the continuous injection of an inert tracer gas and inverse gas transport modelling in the soil. The gas sampling device has several sampling depths and can be easily installed into a vertical hole drilled by an auger, which allows for fast installation of the system. Helium (He) as inert tracer gas was injected continuously at the lower end of the device. The resulting steady state distribution of He was used to deduce the depth profile of DS. Gas transport in the soil surrounding the gas-sampling-device/soil system was modeled using the Finite Element Modeling program COMSOL . We tested our new method both in the lab and during two short field studies and compared the results with a reference method using soil cores. DS profiles obtained by our in-situ method were consistent with DS profiles determined based on soil core analyses. During a longer monitoring field campaign, typical soil-moisture effects upon gas diffusivity such as an increase during a drying period or a decrease after rain could be observed consistently. Under windy conditions we additionally measured for the first time the direct enhancement of gas transport in soil due to wind-induced pressure-pumping which could increase the effective DS up to 30% in the topsoil. Our novel monitoring method can be quickly and easily installed and allows for monitoring continuously soil gas transport over a long time. It allows monitoring physical modifications of soil gas diffusivity due to rain events or evaporation but it also allows studying non-diffusive gas transport processes in the soil.

Diffusion-limited mixing by incompressible flows

NASA Astrophysics Data System (ADS)

Miles, Christopher J.; Doering, Charles R.

2018-05-01

Incompressible flows can be effective mixers by appropriately advecting a passive tracer to produce small filamentation length scales. In addition, diffusion is generally perceived as beneficial to mixing due to its ability to homogenize a passive tracer. However we provide numerical evidence that, in cases where advection and diffusion are both actively present, diffusion may produce negative effects by limiting the mixing effectiveness of incompressible optimal flows. This limitation appears to be due to the presence of a limiting length scale given by a generalised Batchelor length (Batchelor 1959 J. Fluid Mech. 5 113–33). This length scale limitation may in turn affect long-term mixing rates. More specifically, we consider local-in-time flow optimisation under energy and enstrophy flow constraints with the objective of maximising the mixing rate. We observe that, for enstrophy-bounded optimal flows, the strength of diffusion may not impact the long-term mixing rate. For energy-constrained optimal flows, however, an increase in the strength of diffusion can decrease the mixing rate. We provide analytical lower bounds on mixing rates and length scales achievable under related constraints (point-wise bounded speed and rate-of-strain) by extending the work of Lin et al (2011 J. Fluid Mech. 675 465–76) and Poon (1996 Commun. PDE 21 521–39).

A DNS study of turbulent mixing of two passive scalars

NASA Astrophysics Data System (ADS)

Juneja, A.; Pope, S. B.

1996-08-01

We employ direct numerical simulations to study the mixing of two passive scalars in stationary, homogeneous, isotropic turbulence. The present work is a direct extension of that of Eswaran and Pope from one scalar to two scalars and the focus is on examining the evolution states of the scalar joint probability density function (jpdf) and the conditional expectation of the scalar diffusion to motivate better models for multi-scalar mixing. The initial scalar fields are chosen to conform closely to a ``triple-delta function'' jpdf corresponding to blobs of fluid in three distinct states. The effect of the initial length scales and diffusivity of the scalars on the evolution of the jpdf and the conditional diffusion is investigated in detail as the scalars decay from their prescribed initial state. Also examined is the issue of self-similarity of the scalar jpdf at large times and the rate of decay of the scalar variance and dissipation.

Laser doping of boron-doped Si paste for high-efficiency silicon solar cells

NASA Astrophysics Data System (ADS)

Tomizawa, Yuka; Imamura, Tetsuya; Soeda, Masaya; Ikeda, Yoshinori; Shiro, Takashi

2015-08-01

Boron laser doping (LD) is a promising technology for high-efficiency solar cells such as p-type passivated locally diffused solar cells and n-type Si-wafer-based solar cells. We produced a printable phosphorus- or boron-doped Si paste (NanoGram® Si paste/ink) for use as a diffuser in the LD process. We used the boron LD process to fabricate high-efficiency passivated emitter and rear locally diffused (PERL) solar cells. PERL solar cells on Czochralski Si (Cz-Si) wafers yielded a maximum efficiency of 19.7%, whereas the efficiency of a reference cell was 18.5%. Fill factors above 79% and open circuit voltages above 655 mV were measured. We found that the boron-doped area effectively performs as a local boron back surface field (BSF). The characteristics of the solar cell formed using NanoGram® Si paste/ink were better than those of the reference cell.

Anomalous scaling of passive scalars in rotating flows.

PubMed

Rodriguez Imazio, P; Mininni, P D

2011-06-01

We present results of direct numerical simulations of passive scalar advection and diffusion in turbulent rotating flows. Scaling laws and the development of anisotropy are studied in spectral space, and in real space using an axisymmetric decomposition of velocity and passive scalar structure functions. The passive scalar is more anisotropic than the velocity field, and its power spectrum follows a spectral law consistent with ~ k[Please see text](-3/2). This scaling is explained with phenomenological arguments that consider the effect of rotation. Intermittency is characterized using scaling exponents and probability density functions of velocity and passive scalar increments. In the presence of rotation, intermittency in the velocity field decreases more noticeably than in the passive scalar. The scaling exponents show good agreement with Kraichnan's prediction for passive scalar intermittency in two dimensions, after correcting for the observed scaling of the second-order exponent.

Arctic sea-ice diffusion from observed and simulated Lagrangian trajectories

NASA Astrophysics Data System (ADS)

Rampal, Pierre; Bouillon, Sylvain; Bergh, Jon; Ólason, Einar

2016-07-01

We characterize sea-ice drift by applying a Lagrangian diffusion analysis to buoy trajectories from the International Arctic Buoy Programme (IABP) dataset and from two different models: the standalone Lagrangian sea-ice model neXtSIM and the Eulerian coupled ice-ocean model used for the TOPAZ reanalysis. By applying the diffusion analysis to the IABP buoy trajectories over the period 1979-2011, we confirm that sea-ice diffusion follows two distinct regimes (ballistic and Brownian) and we provide accurate values for the diffusivity and integral timescale that could be used in Eulerian or Lagrangian passive tracers models to simulate the transport and diffusion of particles moving with the ice. We discuss how these values are linked to the evolution of the fluctuating displacements variance and how this information could be used to define the size of the search area around the position predicted by the mean drift. By comparing observed and simulated sea-ice trajectories for three consecutive winter seasons (2007-2011), we show how the characteristics of the simulated motion may differ from or agree well with observations. This comparison illustrates the usefulness of first applying a diffusion analysis to evaluate the output of modeling systems that include a sea-ice model before using these in, e.g., oil spill trajectory models or, more generally, to simulate the transport of passive tracers in sea ice.

Determination of nitrogen dioxide in ambient air by use of a passive sampling technique and triethanolamine as absorbent

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krochmal, D.; Gorski, L.

1991-03-01

The effects of temperature, humidity, and storage on a diffusive sampler were tested by use of the Amaya-Sugiura method, modified previously. Several materials were used as carriers for triethanolamine in the sampler. The mass of NO{sub 2} absorbed in the sampler was determined spectrophotometrically as nitrite by using Saltzman solution. The collection efficiency of the sampler was lower than that calculated from Fick's law of diffusion due to significant contribution of liquid phase in the overall sampler diffusive resistance. This resulted in an increase of the mass of NO{sub 2} absorbed in the sampler by ca. 20% per 10{degree}C ofmore » temperature growth and by ca. 25% when the relative humidity rose from 0 to 100%. Dependence of concentration of TEA solution in the sampler on the relative humidity of the air was noted. The relative precision of the method characterized by RSD was 10%; the detection limit of NO{sub 2} was 10 {mu}g/m{sup 3} for a 24-h exposure.« less

Material transport in a wind and buoyancy forced mixed layer

NASA Astrophysics Data System (ADS)

Mensa, J. A.; Özgökmen, T.; Poje, A. C.; Imberger, J.

2016-02-01

Flows in the upper ocean mixed layer are responsible for the transport and dispersion of biogeochemical tracers, phytoplankton and buoyant pollutants, such as hydrocarbons from an oil spill. Material dispersion in mixed layer flows subject to diurnal buoyancy forcing and weak winds (|u10|=5ms-1) are investigated using a non-hydrostatic model. Both purely buoyancy-forced and combined wind- and buoyancy-forced flows are sampled using passive tracers, as well as 2D and 3D particles to explore characteristics of horizontal and vertical dispersion. It is found that the surface tracer patterns are determined by the convergence zones created by convection cells within a time scale of just a few hours. For pure convection, the results displayed the classic signature of Rayleigh-Benard cells. When combined with a wind stress, the convective cells become anisotropic in that the along-wind length scale gets much larger than the cross-wind scale. Horizontal relative dispersion computed by sampling the flow fields using both 2D and 3D passive particles is found to be consistent with the Richardson regime. Relative dispersion is an order of magnitude higher and 2D surface releases transition to Richardson regime faster in the wind-forced case. We also show that the buoyancy-forced case results in significantly lower amplitudes of scale-dependent horizontal relative diffusivity, kD(l), than those reported by Okubo (1970), while the wind- and buoyancy forced case shows a good agreement with Okubo's diffusivity amplitude, and scaling consistent with Richardson's 4/3rd law, kD(l) l4/3. The modelling results provide a framework for measuring material dispersion by mixed layer flow in future observational programs.

Material transport in a convective surface mixed layer under weak wind forcing

NASA Astrophysics Data System (ADS)

Mensa, Jean A.; Özgökmen, Tamay M.; Poje, Andrew C.; Imberger, Jörg

2015-12-01

Flows in the upper ocean mixed layer are responsible for the transport and dispersion of biogeochemical tracers, phytoplankton and buoyant pollutants, such as hydrocarbons from an oil spill. Material dispersion in mixed layer flows subject to diurnal buoyancy forcing and weak winds (| u10 | = 5m s-1) are investigated using a non-hydrostatic model. Both purely buoyancy-forced and combined wind- and buoyancy-forced flows are sampled using passive tracers, as well as 2D and 3D particles to explore characteristics of horizontal and vertical dispersion. It is found that the surface tracer patterns are determined by the convergence zones created by convection cells within a time scale of just a few hours. For pure convection, the results displayed the classic signature of Rayleigh-Benard cells. When combined with a wind stress, the convective cells become anisotropic in that the along-wind length scale gets much larger than the cross-wind scale. Horizontal relative dispersion computed by sampling the flow fields using both 2D and 3D passive particles is found to be consistent with the Richardson regime. Relative dispersion is an order of magnitude higher and 2D surface releases transition to Richardson regime faster in the wind-forced case. We also show that the buoyancy-forced case results in significantly lower amplitudes of scale-dependent horizontal relative diffusivity, kD(ℓ), than those reported by Okubo (1970), while the wind- and buoyancy-forced case shows a good agreement with Okubo's diffusivity amplitude, and the scaling is consistent with Richardson's 4/3rd law, kD ∼ ℓ4/3. These modeling results provide a framework for measuring material dispersion by mixed layer flows in future observational programs.

Multigrid techniques for the solution of the passive scalar advection-diffusion equation

NASA Technical Reports Server (NTRS)

Phillips, R. E.; Schmidt, F. W.

1985-01-01

The solution of elliptic passive scalar advection-diffusion equations is required in the analysis of many turbulent flow and convective heat transfer problems. The accuracy of the solution may be affected by the presence of regions containing large gradients of the dependent variables. The multigrid concept of local grid refinement is a method for improving the accuracy of the calculations in these problems. In combination with the multilevel acceleration techniques, an accurate and efficient computational procedure is developed. In addition, a robust implementation of the QUICK finite-difference scheme is described. Calculations of a test problem are presented to quantitatively demonstrate the advantages of the multilevel-multigrid method.

Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison

EPA Science Inventory

This work presents the results of an international interlaboratory comparison on ex situ passive sampling in sediments. The main objectives were to map the state of the science in passively sampling sediments, identify sources of variability, provide recommendations and practica...

Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison

EPA Science Inventory

This work presents the results of an international interlaboratory comparison on ex situ passive sampling in sediments. The main objectives were to map the state of the science in passively sampling sediments, identify sources of variability, provide recommendations and practical...

Passive Sampling in Regulatory Chemical Monitoring of Nonpolar Organic Compounds in the Aquatic Environment.

PubMed

Booij, Kees; Robinson, Craig D; Burgess, Robert M; Mayer, Philipp; Roberts, Cindy A; Ahrens, Lutz; Allan, Ian J; Brant, Jan; Jones, Lisa; Kraus, Uta R; Larsen, Martin M; Lepom, Peter; Petersen, Jördis; Pröfrock, Daniel; Roose, Patrick; Schäfer, Sabine; Smedes, Foppe; Tixier, Céline; Vorkamp, Katrin; Whitehouse, Paul

2016-01-05

We reviewed compliance monitoring requirements in the European Union, the United States, and the Oslo-Paris Convention for the protection of the marine environment of the North-East Atlantic, and evaluated if these are met by passive sampling methods for nonpolar compounds. The strengths and shortcomings of passive sampling are assessed for water, sediments, and biota. Passive water sampling is a suitable technique for measuring concentrations of freely dissolved compounds. This method yields results that are incompatible with the EU's quality standard definition in terms of total concentrations in water, but this definition has little scientific basis. Insufficient quality control is a present weakness of passive sampling in water. Laboratory performance studies and the development of standardized methods are needed to improve data quality and to encourage the use of passive sampling by commercial laboratories and monitoring agencies. Successful prediction of bioaccumulation based on passive sampling is well documented for organisms at the lower trophic levels, but requires more research for higher levels. Despite the existence of several knowledge gaps, passive sampling presently is the best available technology for chemical monitoring of nonpolar organic compounds. Key issues to be addressed by scientists and environmental managers are outlined.

How does passive lengthening change the architecture of the human medial gastrocnemius muscle?

PubMed

Bolsterlee, Bart; D'Souza, Arkiev; Gandevia, Simon C; Herbert, Robert D

2017-04-01

There are few comprehensive investigations of the changes in muscle architecture that accompany muscle contraction or change in muscle length in vivo. For this study, we measured changes in the three-dimensional architecture of the human medial gastrocnemius at the whole muscle level, the fascicle level and the fiber level using anatomical MRI and diffusion tensor imaging (DTI). Data were obtained from eight subjects under relaxed conditions at three muscle lengths. At the whole muscle level, a 5.1% increase in muscle belly length resulted in a reduction in both muscle width (mean change -2.5%) and depth (-4.8%). At the fascicle level, muscle architecture measurements obtained at 3,000 locations per muscle showed that for every millimeter increase in muscle-tendon length above the slack length, average fascicle length increased by 0.46 mm, pennation angle decreased by 0.27° (0.17° in the superficial part and 0.37° in the deep part), and fascicle curvature decreased by 0.18 m -1 There was no evidence of systematic variation in architecture along the muscle's long axis at any muscle length. At the fiber level, analysis of the diffusion signal showed that passive lengthening of the muscle increased diffusion along fibers and decreased diffusion across fibers. Using these measurements across scales, we show that the complex shape changes that muscle fibers, whole muscles, and aponeuroses of the medial gastrocnemius undergo in vivo cannot be captured by simple geometrical models. This justifies the need for more complex models that link microstructural changes in muscle fibers to macroscopic changes in architecture. NEW & NOTEWORTHY Novel MRI and DTI techniques revealed changes in three-dimensional architecture of the human medial gastrocnemius during passive lengthening. Whole muscle belly width and depth decreased when the muscle lengthened. Fascicle length, pennation, and curvature changed uniformly or near uniformly along the muscle during passive lengthening. Diffusion of water molecules in muscle changes in the same direction as fascicle strains. Copyright © 2017 the American Physiological Society.

Enhanced diffusion of pollutants by self-propulsion.

PubMed

Zhao, Guanjia; Stuart, Emma J E; Pumera, Martin

2011-07-28

Current environmental models mostly account for the passive participation of pollutants in their environmental propagation. Here we demonstrate the paradigm-changing concept that pollutants can propagate themselves with a rate that is greater than the rate for standard molecular diffusion by five orders of magnitude. This journal is © the Owner Societies 2011

Uptake of 2, 4-Dichlorophenoxyacetic acid by Pseudomonas fluorescens

USGS Publications Warehouse

Wedemeyer, G.A.

1966-01-01

Factors influencing the uptake of the sodium salt of 2,4-dichlorophenoxyacetic acid (2,4-D), under conditions in which no net metabolism occurred, were investigated in an effort to determine both the significance of “nonmetabolic” uptake as a potential agent in reducing pesticide levels and the mechanisms involved. Uptake of 2,4-D was affected by pH, temperature, and the presence of other organic and inorganic compounds. Uptake was more pronounced at pH values less than 6, which implies that there may be some interaction between charged groups on the cell and the ionized carboxyl group of 2,4-D. Active transport, carriermediated diffusion, passive diffusion, and adsorption were considered as possible mechanisms. Though uptake was inhibited by glucose, sodium azide, and fluorodinitrobenzene (but not by uranylion), 2,4-D was not accumulated against a concentration gradient, a necessary consequence of an active transport system, nor was isotope counterflow found to occur. Thus, carrier-mediated diffusion was finally precluded, implying that uptake probably occurs by a two-step process: sorption onto the cell wall followed by passive diffusion into the cytoplasm.

Uptake of 2,4-dichlorophenoxyacetic acid by Pseudomonas fluorescens

USGS Publications Warehouse

Wedemeyer, Gary

1966-01-01

Factors influencing the uptake of the sodium salt of 2,4-dichlorophenoxyacetic acid (2,4-D), under conditions in which no net metabolism occurred, were investigated in an effort to determine both the significance of “non-metabolic” uptake as a potential agent in reducing pesticide levels and the mechanisms involved. Uptake of 2,4-D was affected by pH, temperature, and the presence of other organic and inorganic compounds. Uptake was more pronounced at pH values less than 6, which implies that there may be some interaction between charged groups on the cell and the ionized carboxyl group of 2,4-D. Active transport, carrier-mediated diffusion, passive diffusion, and adsorption were considered as possible mechanisms. Though uptake was inhibited by glucose, sodium azide, and fluorodinitrobenzene (but not by uranyl ion), 2,4-D was not accumulated against a concentration gradient, a necessary consequence of an active transport system, nor was isotope counterflow found to occur. Thus, carrier-mediated diffusion was finally precluded, implying that uptake probably occurs by a two-step process: sorption onto the cell wall followed by passive diffusion into the cytoplasm.

Fenceline Measurements of Speciated VOCs Using Passive Sorbent Tubes Deployed Around Oil and Natural Gas Production Pads in Colorado and Texas

EPA Science Inventory

A U.S. EPA team, consisting of the Office of Research and Development and Region 6 (Dallas) and Region 8 (Denver), deployed passive-diffusive sorbent tubes as part of a method evaluation study around one oil and natural gas production pad in both the Barnett Shale Basin in Texas ...

Surface passivation and aging of InGaAs/InP heterojunction phototransistors

NASA Astrophysics Data System (ADS)

Park, Min-Su; Razaei, Mohsen; Barnhart, Katie; Tan, Chee Leong; Mohseni, Hooman

2017-06-01

We report the effect of different surface treatment and passivation techniques on the stability of InGaAs/InP heterojunction phototransistors (HPTs). An In0.53Ga0.47As surface passivated with aqueous ammonium sulfide ((NH4)2S), aluminum oxide (Al2O3) grown by atomic layer deposition (ALD), and their combination is evaluated by using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All samples were kept in the air ambient, and their performances were periodically measured to investigate their long-term stability. Raman spectroscopy revealed that the peak intensity of the GaAs-like longitudinal optical phonon of all passivated samples is decreased compared with that of the control sample. This is attributable to the diminution of the carriers near the passivated surfaces, which was proven by extracted surface potential (Vs). The Vs of all passivated samples was decreased to less than half of that for the control sample. XPS evaluation of As3d spectra showed that arsenic oxides (As2O3 and As2O5) on the surfaces of the samples can be removed by passivation. However, both Raman and XPS spectra show that the (NH4)2S passivated sample reverts back over time and will resemble the untreated control sample. When capped with ALD-grown Al2O3, passivated samples irrespective of the pretreatment show no degradation over the measured time of 4 weeks. Similar conclusions are made from our experimental measurement of the performance of differently passivated HPTs. The ALD-grown Al2O3 passivated devices show an improved optical gain at low optical powers and long-term stability.

Mathematical modelling of the Phloem: the importance of diffusion on sugar transport at osmotic equilibrium.

PubMed

Payvandi, S; Daly, K R; Zygalakis, K C; Roose, T

2014-11-01

Plants rely on the conducting vessels of the phloem to transport the products of photosynthesis from the leaves to the roots, or to any other organs, for growth, metabolism, and storage. Transport within the phloem is due to an osmotically-generated pressure gradient and is hence inherently nonlinear. Since convection dominates over diffusion in the main bulk flow, the effects of diffusive transport have generally been neglected by previous authors. However, diffusion is important due to boundary layers that form at the ends of the phloem, and at the leaf-stem and stem-root boundaries. We present a mathematical model of transport which includes the effects of diffusion. We solve the system analytically in the limit of high Münch number which corresponds to osmotic equilibrium and numerically for all parameter values. We find that the bulk solution is dependent on the diffusion-dominated boundary layers. Hence, even for large Péclet number, it is not always correct to neglect diffusion. We consider the cases of passive and active sugar loading and unloading. We show that for active unloading, the solutions diverge with increasing Péclet. For passive unloading, the convergence of the solutions is dependent on the magnitude of loading. Diffusion also permits the modelling of an axial efflux of sugar in the root zone which may be important for the growing root tip and for promoting symbiotic biological interactions in the soil. Therefore, diffusion is an essential mechanism for transport in the phloem and must be included to accurately predict flow.

Mechanisms of Ocean Heat Uptake

NASA Astrophysics Data System (ADS)

Garuba, Oluwayemi

An important parameter for the climate response to increased greenhouse gases or other radiative forcing is the speed at which heat anomalies propagate downward in the ocean. Ocean heat uptake occurs through passive advection/diffusion of surface heat anomalies and through the redistribution of existing temperature gradients due to circulation changes. Atlantic meridional overturning circulation (AMOC) weakens in a warming climate and this should slow the downward heat advection (compared to a case in which the circulation is unchanged). However, weakening AMOC also causes a deep warming through the redistributive effect, thus increasing the downward rate of heat propagation compared to unchanging circulation. Total heat uptake depends on the combined effect of these two mechanisms. Passive tracers in a perturbed CO2 quadrupling experiments are used to investigate the effect of passive advection and redistribution of temperature anomalies. A new passive tracer formulation is used to separate ocean heat uptake into contributions due to redistribution and passive advection-diffusion of surface heating during an ocean model experiment with abrupt increase in surface temperature. The spatial pattern and mechanisms of each component are examined. With further experiments, the effects of surface wind, salinity and temperature changes in changing circulation and the resulting effect on redistribution in the individual basins are isolated. Analysis of the passive advection and propagation path of the tracer show that the Southern ocean dominates heat uptake, largely through vertical and horizontal diffusion. Vertical diffusion transports the tracer across isopycnals down to about 1000m in 100 years in the Southern ocean. Advection is more important in the subtropical cells and in the Atlantic high latitudes, both with a short time scale of about 20 years. The shallow subtropical cells transport the tracer down to about 500m along isopycnal surfaces, below this vertical diffusion takes over transport in the tropics; in the Atlantic, the MOC transports heat as deep 2000m in about 30 years. Redistributive surface heat uptake alters the total amount surface heat uptake among the basins. Compared to the passive-only heat uptake, which is about the same among the basins, redistribution nearly doubles the surface heat input into the Atlantic but makes smaller increases in the Indian and Pacific oceans for a net global increase of about 25%, in the perturbation experiment with winds unchanged. The passive and redistributive heat uptake components are further distributed among the basins through the global conveyor belt. The Pacific gains twice the surface heat input into it through lateral transport from the other two basins, as a result, the Atlantic and Pacific gain similar amounts of heat even though surface heat input is in the Atlantic is much bigger. Of this heat transport, most of the passive component comes from the Indian and the redistributive component comes from the Atlantic. Different surface forcing perturbation gives different circulation change pattern and as a result yield different redistributive uptake. Ocean heat uptake is more sensitive to wind forcing perturbation than to thermohaline forcing perturbation. About 2% reduction in subtropical cells transport and southern ocean transport, in the wind-change perturbation experiment, resulted in about 10% reduction in the global ocean heat uptake of wind-unchanged experiment. The AMOC weakened by about 35% and resulted in a 25% increase in passive heat uptake in the wind-unchanged experiment. Surface winds weakening reduces heat uptake by warming the reservoir surface temperatures, while MOC weakening increases heat input by a cooling reservoir surface temperatures. Thermohaline forcing perturbation is combination of salinity and temperature perturbations, both weaken the AMOC, however, they have opposite redistributive effects. Ocean surface freshening gives positive redistributive effect, while surface temperature increase gives negative redistributive effect on heat uptake. The salinity effect dominates the redistributive effect for thermohaline perturbation.

Field application of passive SBSE for the monitoring of pesticides in surface waters.

PubMed

Assoumani, A; Coquery, M; Liger, L; Mazzella, N; Margoum, C

2015-03-01

Spot sampling lacks representativeness for monitoring organic contaminants in most surface waters. Passive sampling has emerged as a cost-effective complementary sampling technique. We recently developed passive stir bar sorptive extraction (passive SBSE), with Twister from Gerstel, for monitoring moderately hydrophilic to hydrophobic pesticides (2.18 < log K ow < 5.11) in surface water. The aims of the present study were to assess this new passive sampler for the determination of representative average concentrations and to evaluate the contamination levels of two French rivers. Passive SBSE was evaluated for the monitoring of 16 pesticides in two rivers located in a small vineyard watershed during two 1-month field campaigns in spring 2010 and spring 2011. Passive SBSE was applied for periods of 1 or 2 weeks during the field campaigns and compared with spot sampling and weekly average automated sampling. The results showed that passive SBSE could achieve better time-representativeness than spot sampling and lower limits of quantification than automated sampling coupled with analytical SBSE for the pesticides studied. Finally, passive SBSE proved useful for revealing spatial and temporal variations in pesticide contamination of both rivers and the impact of rainfall and runoff on the river water quality.

Modeling uptake of hydrophobic organic contaminants into polyethylene passive samplers.

PubMed

Thompson, Jay M; Hsieh, Ching-Hong; Luthy, Richard G

2015-02-17

Single-phase passive samplers are gaining acceptance as a method to measure hydrophobic organic contaminant (HOC) concentration in water. Although the relationship between the HOC concentration in water and passive sampler is linear at equilibrium, mass transfer models are needed for nonequilibrium conditions. We report measurements of organochlorine pesticide diffusion and partition coefficients with respect to polyethylene (PE), and present a Fickian approach to modeling HOC uptake by PE in aqueous systems. The model is an analytic solution to Fick's second law applied through an aqueous diffusive boundary layer and a polyethylene layer. Comparisons of the model with existing methods indicate agreement at appropriate boundary conditions. Laboratory release experiments on the organochlorine pesticides DDT, DDE, DDD, and chlordane in well-mixed slurries support the model's applicability to aqueous systems. In general, the advantage of the model is its application in the cases of well-agitated systems, low values of polyethylene-water partioning coefficients, thick polyethylene relative to the boundary layer thickness, and/or short exposure times. Another significant advantage is the ability to estimate, or at least bound, the needed exposure time to reach a desired CPE without empirical model inputs. A further finding of this work is that polyethylene diffusivity does not vary by transport direction through the sampler thickness.

Measurement of minority carrier diffusion lengths in GaAs nanowires by a nanoprobe technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Darbandi, A.; Watkins, S. P., E-mail: simonw@sfu.ca

Minority carrier diffusion lengths in both p-type and n-type GaAs nanowires were studied using electron beam induced current by means of a nanoprobe technique without lithographic processing. The diffusion lengths were determined for Au/GaAs rectifying junctions as well as axial p-n junctions. By incorporating a thin lattice-matched InGaP passivating shell, a 2-fold enhancement in the minority carrier diffusion lengths and one order of magnitude reduction in the surface recombination velocity were achieved.

A novel in-plane passive microfluidic mixer with modified Tesla structures.

PubMed

Hong, Chien-Chong; Choi, Jin-Woo; Ahn, Chong H

2004-04-01

An innovative in-plane passive micromixer using modified Tesla structures, which are used as passive valves, has been designed, simulated, fabricated and successfully characterized in this paper. Simulation and experimental results of the developed novel micromixer have shown excellent mixing performance over a wide range of flow conditions in the micro scale. The micromixer realized in this work has achieved even better mixing performance at a higher flow rate, and its pressure drop is less than 10 KPa at the flow rate of 100 microl min(-1). This micromixer shows characteristics similar to Taylor dispersion, with contributions from both diffusion and convection. The mixer has a diffusion domain region at low flow rate, but it moves to a convection domain region at high flow rate. Due to the simple in-plane structure of the novel micromixer explored in this work, the mixer can be easily realized and integrated with on-chip microfluidic devices and micro total analysis systems (micro-TAS).

Stirring Up the Biological Pump: Vertical Mixing and Carbon Export in the Southern Ocean

NASA Astrophysics Data System (ADS)

Stukel, Michael R.; Ducklow, Hugh W.

2017-09-01

The biological carbon pump (BCP) transports organic carbon from the surface to the ocean's interior via sinking particles, vertically migrating organisms, and passive transport of organic matter by advection and diffusion. While many studies have quantified sinking particles, the magnitude of passive transport remains poorly constrained. In the Southern Ocean weak thermal stratification, strong vertical gradients in particulate organic matter, and weak vertical nitrate gradients suggest that passive transport from the euphotic zone may be particularly important. We compile data from seasonal time series at a coastal site near Palmer Station, annual regional cruises in the Western Antarctic Peninsula (WAP), cruises throughout the broader Southern Ocean, and SOCCOM (Southern Ocean Carbon and Climate Observations and Modeling) autonomous profiling floats to estimate spatial and temporal patterns in vertical gradients of nitrate, particulate nitrogen (PN), and dissolved organic carbon. Under a steady state approximation, the ratio of ∂PN/∂z to ∂NO3-/∂z suggests that passive transport of PN may be responsible for removing 46% (37%-58%) of the nitrate introduced into the surface ocean of the WAP (with dissolved organic matter contributing an additional 3-6%) and for 23% (19%-28%) of the BCP in the broader Southern Ocean. A simple model parameterized with in situ nitrate, PN, and primary production data suggested that passive transport was responsible for 54% of the magnitude of the BCP in the WAP. Our results highlight the potential importance of passive transport (by advection and diffusion) of organic matter in the Southern Ocean but should only be considered indicative of high passive transport (rather than conclusive evidence) due to our steady state assumptions.

Status and Progress of High-efficiency Silicon Solar Cells

NASA Astrophysics Data System (ADS)

Xiao, Shaoqing; Xu, Shuyan

High-efficiency Si solar cells have attracted more and more attention from researchers, scientists, engineers of photovoltaic (PV) industry for the past few decades. Many high-quality researchers and engineers in both academia and industry seek solutions to improve the cell efficiency and reduce the cost. This desire has stimulated a growing number of major research and research infrastructure programmes, and a rapidly increasing number of publications in this filed. This chapter reviews materials, devices and physics of high-efficiency Si solar cells developed over the last 20 years. In this chapter there is a fair number of topics, not only from the material viewpoint, introducing various materials that are required for high-efficiency Si solar cells, such as base materials (FZ-Si, CZ-Si, MCZ-Si and multi-Si), emitter materials (diffused emitter and deposited emitter), passivation materials (Al-back surface field, high-low junction, SiO2, SiO x , SiN x , Al2O3 and a-Si:H), and other functional materials (antireflective layer, TCO and metal electrode), but also from the device and physics point of view, elaborating on physics, cell concept, development and status of all kinds of high-efficiency Si solar cells, such as passivated emitter and rear contact (PERC), passivated emitter and rear locally diffused (PERL), passivated emitter and rear totally diffused (PERT), Pluto, interdigitated back-contacted (IBC), emitter-wrap-through (EWT), metallization-wrap-through (MWT), Heterojunction with intrinsic thin-layer (HIT) and so on. Some representative examples of high-efficiency Si solar cell materials and devices with excellent performance and competitive advantages are presented.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Willemin, Marie-Emilie; Lumen, Annie, E-mail: Anni

Thyroid homeostasis can be disturbed due to thiocyanate exposure from the diet or tobacco smoke. Thiocyanate inhibits both thyroidal uptake of iodide, via the sodium-iodide symporter (NIS), and thyroid hormone (TH) synthesis in the thyroid, via thyroid peroxidase (TPO), but the mode of action of thiocyanate is poorly quantified in the literature. The characterization of the link between intra-thyroidal thiocyanate concentrations and dose of exposure is crucial for assessing the risk of thyroid perturbations due to thiocyanate exposure. We developed a PBPK model for thiocyanate that describes its kinetics in the whole-body up to daily doses of 0.15 mmol/kg, withmore » a mechanistic description of the thyroidal kinetics including NIS, passive diffusion, and TPO. The model was calibrated in a Bayesian framework using published studies in rats. Goodness-of-fit was satisfactory, especially for intra-thyroidal thiocyanate concentrations. Thiocyanate kinetic processes were quantified in vivo, including the metabolic clearance by TPO. The passive diffusion rate was found to be greater than NIS-mediated uptake rate. The model captured the dose-dependent kinetics of thiocyanate after acute and chronic exposures. Model behavior was evaluated using a Morris screening test. The distribution of thiocyanate into the thyroid was found to be determined primarily by the partition coefficient, followed by NIS and passive diffusion; the impact of the latter two mechanisms appears to increase at very low doses. Extrapolation to humans resulted in good predictions of thiocyanate kinetics during chronic exposure. The developed PBPK model can be used in risk assessment to quantify dose-response effects of thiocyanate on TH. - Highlights: • A PBPK model of thiocyanate (SCN{sup −}) was calibrated in rats in a Bayesian framework. • The intra-thyroidal kinetics of thiocyanate including NIS and TPO was modeled. • Passive diffusion rate for SCN{sup −} seemed to be greater than the NIS-mediated uptake. • The dose-dependent kinetics of SCN{sup −} was captured after an acute and chronic exposure. • The PBPK model of thiocyanate was successfully extrapolated to humans.« less

Performance of active feedforward control systems in non-ideal, synthesized diffuse sound fields.

PubMed

Misol, Malte; Bloch, Christian; Monner, Hans Peter; Sinapius, Michael

2014-04-01

The acoustic performance of passive or active panel structures is usually tested in sound transmission loss facilities. A reverberant sending room, equipped with one or a number of independent sound sources, is used to generate a diffuse sound field excitation which acts as a disturbance source on the structure under investigation. The spatial correlation and coherence of such a synthesized non-ideal diffuse-sound-field excitation, however, might deviate significantly from the ideal case. This has consequences for the operation of an active feedforward control system which heavily relies on the acquisition of coherent disturbance source information. This work, therefore, evaluates the spatial correlation and coherence of ideal and non-ideal diffuse sound fields and considers the implications on the performance of a feedforward control system. The system under consideration is an aircraft-typical double panel system, equipped with an active sidewall panel (lining), which is realized in a transmission loss facility. Experimental results for different numbers of sound sources in the reverberation room are compared to simulation results of a comparable generic double panel system excited by an ideal diffuse sound field. It is shown that the number of statistically independent noise sources acting on the primary structure of the double panel system depends not only on the type of diffuse sound field but also on the sample lengths of the processed signals. The experimental results show that the number of reference sensors required for a defined control performance exhibits an inverse relationship to control filter length.

Passive micromixer using by convection and surface tension effects with air-liquid interface.

PubMed

Ju, Jongil; Warrick, Jay

2013-12-01

This article describes a passive micromixer that utilizes an air-liquid interface and surface tension effects to enhance fluid mixing via convection and Marangoni effects. Performance of the microfluidic component is tested within a passive-pumping-based device that consists of three microchannels connected in succession using passive micro-mixers. Mixing was quantified at 5 key points along the length of the device using microscope images of patterned streams of Alexa 488 fluorescent-dyed water and pure DI water flowing through the device. The passive micro-mixer mixed fluid 15-20 times more effectively than diffusion between laminar flow streams alone and is a novel micro-mixer embodiment that provides an additional strategy for removing external components from microscale devices for simpler, autonomous operation.

Passive micromixer using by convection and surface tension effects with air-liquid interface

PubMed Central

Ju, Jongil; Warrick, Jay

2014-01-01

This article describes a passive micromixer that utilizes an air-liquid interface and surface tension effects to enhance fluid mixing via convection and Marangoni effects. Performance of the microfluidic component is tested within a passive-pumping-based device that consists of three microchannels connected in succession using passive micro-mixers. Mixing was quantified at 5 key points along the length of the device using microscope images of patterned streams of Alexa 488 fluorescent-dyed water and pure DI water flowing through the device. The passive micro-mixer mixed fluid 15–20 times more effectively than diffusion between laminar flow streams alone and is a novel micro-mixer embodiment that provides an additional strategy for removing external components from microscale devices for simpler, autonomous operation. PMID:25104979

Influence of La addition on the semi-conductive properties of passive films formed on Cu-Ni alloy

NASA Astrophysics Data System (ADS)

Leng, Xiang; Zhang, Yadong; Zhou, Qiongyu; Zhang, Yinghui; Wang, Zhigang; Wang, Hang; Yang, Bin

2018-05-01

The semi-conductive properties of passive films formed on Cu-Ni alloy and Cu-Ni-La alloy were investigated in 0.1 M NaOH solution, by employing electrochemical impedance spectroscopy (EIS), Mott–Schottky analysis and point defect model (PDM). Results indicate that both the passive films formed on Cu-Ni alloy and Cu-Ni-La alloy display p-type semi-conductive characteristics with cation vacancies in order of magnitude of 1020 cm3. Compared with Cu-Ni alloy, La addition could significantly improve the corrosion resistance, due to a superior barrier passive film formed Cu-Ni-La alloy with a bigger film resistance (R f), increased passive film thickness (L ss) in conjunction with decreased diffusion coefficient (D 0).

Passivity of Directed and Undirected Complex Dynamical Networks With Adaptive Coupling Weights.

PubMed

Wang, Jin-Liang; Wu, Huai-Ning; Huang, Tingwen; Ren, Shun-Yan; Wu, Jigang

2017-08-01

A complex dynamical network consisting of N identical neural networks with reaction-diffusion terms is considered in this paper. First, several passivity definitions for the systems with different dimensions of input and output are given. By utilizing some inequality techniques, several criteria are presented, ensuring the passivity of the complex dynamical network under the designed adaptive law. Then, we discuss the relationship between the synchronization and output strict passivity of the proposed network model. Furthermore, these results are extended to the case when the topological structure of the network is undirected. Finally, two examples with numerical simulations are provided to illustrate the correctness and effectiveness of the proposed results.

Spectral Analysis and Computation of Effective Diffusivities for Steady Random Flows

DTIC Science & Technology

2016-04-28

even in the motion of sea ice floes influenced by winds and ocean currents. The long time, large scale behavior of such systems is equivalent to an...flow plays a key role in many important processes in the global climate system [55] and Earth’s ecosys- tems [14]. Advection of geophysical fluids...HOMOGENIZATION OF THE ADVECTION-DIFFUSION EQUATION The dispersion of a cloud of passive scalars with density φ diffusing with molecular dif- fusivity ε and

Numerically exploring habitat fragmentation effects on populations using cell-based coupled map lattices

Treesearch

Michael Bevers; Curtis H. Flather

1999-01-01

We examine habitat size, shape, and arrangement effects on populations using a discrete reaction-diffusion model. Diffusion is modeled passively and applied to a cellular grid of territories forming a coupled map lattice. Dispersal mortality is proportional to the amount of nonhabitat and fully occupied habitat surrounding a given cell, with distance decay. After...

Modeling of molecular diffusion and thermal conduction with multi-particle interaction in compressible turbulence

NASA Astrophysics Data System (ADS)

Tai, Y.; Watanabe, T.; Nagata, K.

2018-03-01

A mixing volume model (MVM) originally proposed for molecular diffusion in incompressible flows is extended as a model for molecular diffusion and thermal conduction in compressible turbulence. The model, established for implementation in Lagrangian simulations, is based on the interactions among spatially distributed notional particles within a finite volume. The MVM is tested with the direct numerical simulation of compressible planar jets with the jet Mach number ranging from 0.6 to 2.6. The MVM well predicts molecular diffusion and thermal conduction for a wide range of the size of mixing volume and the number of mixing particles. In the transitional region of the jet, where the scalar field exhibits a sharp jump at the edge of the shear layer, a smaller mixing volume is required for an accurate prediction of mean effects of molecular diffusion. The mixing time scale in the model is defined as the time scale of diffusive effects at a length scale of the mixing volume. The mixing time scale is well correlated for passive scalar and temperature. Probability density functions of the mixing time scale are similar for molecular diffusion and thermal conduction when the mixing volume is larger than a dissipative scale because the mixing time scale at small scales is easily affected by different distributions of intermittent small-scale structures between passive scalar and temperature. The MVM with an assumption of equal mixing time scales for molecular diffusion and thermal conduction is useful in the modeling of the thermal conduction when the modeling of the dissipation rate of temperature fluctuations is difficult.

Evaluation of the polyurethane foam (PUF) disk passive air sampler: Computational modeling and experimental measurements

NASA Astrophysics Data System (ADS)

May, Andrew A.; Ashman, Paul; Huang, Jiaoyan; Dhaniyala, Suresh; Holsen, Thomas M.

2011-08-01

Computational fluid dynamics (CFD) simulations coupled with wind tunnel-experiments were used to determine the sampling rate (SR) of the widely used polyurethane foam (PUF) disk passive sampler. In the wind-tunnel experiments, water evaporation rates from a water saturated PUF disk installed in the sampler housing were determined by measuring weight loss over time. In addition, a modified passive sampler designed to collect elemental mercury (Hg 0) with gold-coated filters was used. Experiments were carried out at different wind speeds and various sampler angles. The SRs obtained from wind-tunnel experiments were compared to those obtained from the field by scaling the values by the ratios of air diffusivities. Three-dimensional (3D) CFD simulations were also used to generate SRs for both polychlorinated biphenyls (PCBs) and Hg 0. Overall, the modeled and measured SRs agree well and are consistent with the values obtained from field studies. As previously observed, the SRs increased linearly with increasing wind speed. In addition, it was determined that the SR was strongly dependent on the angle of the ambient wind. The SRs increased when the base was tilted up pointing into the wind and when the base was tilted down (i.e., such that the top of the sampler was facing the wind) the SR decreased initially and then increased. The results suggest that there may be significant uncertainty in concentrations obtained from passive sampler measurements without knowledge of wind speed and wind angle relative to the sampler.

Passive Imaging in Nondiffuse Acoustic Wavefields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mulargia, Francesco; Castellaro, Silvia

2008-05-30

A main property of diffuse acoustic wavefields is that, taken any two points, each of them can be seen as the source of waves and the other as the recording station. This property is shown to follow simply from array azimuthal selectivity and Huygens principle in a locally isotropic wavefield. Without time reversal, this property holds approximately also in anisotropic azimuthally uniform wavefields, implying much looser constraints for undistorted passive imaging than those required by a diffuse field. A notable example is the seismic noise field, which is generally nondiffuse, but is found to be compatible with a finite aperturemore » anisotropic uniform wavefield. The theoretical predictions were confirmed by an experiment on seismic noise in the mainland of Venice, Italy.« less

The role of halide ions on the electrochemical behaviour of iron in alkali solutions

NASA Astrophysics Data System (ADS)

Begum, S. Nathira; Muralidharan, V. S.; Basha, C. Ahmed

2008-02-01

Active dissolution and passivation of transition metals in alkali solutions is of technological importance in batteries. The performance of alkaline batteries is decided by the presence of halides as they influence passivation. Cyclic voltammetric studies were carried out on iron in different sodium hydroxide solutions in presence of halides. In alkali solutions iron formed hydroxo complexes and their polymers in the interfacial diffusion layer. With progress of time they formed a cation selective layer. The diffusion layer turned into bipolar ion selective layer consisted of halides, a selective inner sublayer to the metal side and cation selective outer layer to the solution side. At very high anodic potentials, dehydration and deprotonation led to the conversion of salt layer into an oxide.

Development of a model using the MATLAB System identification toolbox to estimate (222)Rn equilibrium factor from CR-39 based passive measurements.

PubMed

Abo-Elmagd, M; Sadek, A M

2014-12-01

Can and Bare method is a widely used passive method for measuring the equilibrium factor F through the determination of the track density ratio between bare (D) and filtered (Do) detectors. The dimensions of the used diffusion chamber are altering the deposition ratios of Po-isotopes on the chamber walls as well as the ratios of the existing alpha emitters in air. Then the measured filtered track density and therefore the resultant equilibrium factor is changed according to the diffusion chamber dimensions. For this reason, high uncertainty was expected in the measured F using different diffusion chambers. In the present work, F is derived as a function of both track density ratio (D/Do) and the dimensions of the used diffusion chambers (its volume to the total internal surface area; V/A). The accuracy of the derived formula was verified using the black-box modeling technique via the MATLAB System identification toolbox. The results show that the uncertainty of the calculated F by using the derived formula of F (D/Do, V/A) is only 5%. The obtained uncertainty ensures the quality of the derived function to calculate F using diffusion chambers with wide range of dimensions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Evaluation of passive samplers for the collection of dissolved organic matter in streams.

PubMed

Warner, Daniel L; Oviedo-Vargas, Diana; Royer, Todd V

2015-01-01

Traditional sampling methods for dissolved organic matter (DOM) in streams limit opportunities for long-term studies due to time and cost constraints. Passive DOM samplers were constructed following a design proposed previously which utilizes diethylaminoethyl (DEAE) cellulose as a sampling medium, and they were deployed throughout a temperate stream network in Indiana. Two deployments of the passive samplers were conducted, during which grab samples were frequently collected for comparison. Differences in DOM quality between sites and sampling methods were assessed using several common optical analyses. The analyses revealed significant differences in optical properties between sampling methods, with the passive samplers preferentially collecting terrestrial, humic-like DOM. We assert that the differences in DOM composition from each sampling method were caused by preferential binding of complex humic compounds to the DEAE cellulose in the passive samplers. Nonetheless, the passive samplers may provide a cost-effective, integrated sample of DOM in situations where the bulk DOM pool is composed mainly of terrestrial, humic-like compounds.

Enhancement of diffusive transport in oscillatory flows

NASA Technical Reports Server (NTRS)

Knobloch, E.; Merryfield, W. J.

1992-01-01

The theory of transport of passive scalars in oscillatory flows is reexamined. The differences between transport in standing and traveling waves are emphasized. Both Lagrangian and Eulerian diffusivities are calculated, and the conditions for their applicability are discussed. Numerical simulations are conducted to understand the expulsion of gradients from time-dependent eddies and the resulting transport. The results indicate that it is the Eulerian diffusivity that is of primary relevance for describing enhanced transport on spatial scales larger than that of the eddies.

Nitridation of SiO2 for surface passivation

NASA Technical Reports Server (NTRS)

Lai, S. K. C.

1985-01-01

An attempt is made to relate the electrical properties of silicon dioxide film to the process history. A model is proposed to explain some of the observed results. It is shown that with our present knowledge of the dielectric, silicon dioxide film shows a lot of promise for its use in surface passivation, both for its resistance to impurity diffusion and for its resistance to radiation damage effects.

Impact of Moisture Content and Grain Size on Hydrocarbon Diffusion in Porous Media

NASA Astrophysics Data System (ADS)

McLain, A. A.; Ho, C. K.

2001-12-01

Diffusion of hydrocarbon vapors in porous media can play an important role in our ability to characterize subsurface contaminants such as trichloroethylene (TCE). For example, traditional monitoring methods often rely on direct sampling of contaminated soils or vapor. These samples may be influenced by the diffusion of vapors away from the contaminant source term, such as non-aqueous-phase TCE liquid. In addition, diffusion of hydrocarbon vapors can also impact the migration and dispersion of the contaminant in the subsurface. Therefore, understanding the diffusion rates and vapor transport processes of hydrocarbons in variably-saturated, heterogeneous porous media will assist in the characterization and detection of these subsurface contaminants. The purpose of this study was to investigate the impact of soil heterogeneity and water-moisture content on the diffusion processes for TCE. A one-dimensional column experiment was used to monitor the rates of vapor diffusion through sand. Experiments were performed with different average water-moisture contents and different grain sizes. On one end of the column, a reservoir cap is used to encase the TCE, providing a constant vapor boundary condition while sealing the end. The other end of the column contains a novel microchemical sensor. The sensor employs a polymer-absorption resistor (chemiresistor) that reversibly swells and increases in resistance when exposed to hydrocarbons. Once calibrated, the chemiresistors can be used to passively monitor vapor concentrations. This unique method allows the detection of in-situ vapor concentrations without disturbing the local environment. Results are presented in the form of vapor-concentration breakthrough curves as detected by the sensor. The shape of the breakthrough curve is dependent on several key parameters, including the length of the column and parameters (e.g., water-moisture content and grain-size) that affect the effective diffusion coefficient of TCE in air. Comparisons are made between theoretical and observed breakthrough curves to evaluate the diffusion of TCE and other relevant physical processes (e.g., air-water partitioning of TCE). The relative impact of water-moisture content and grain size on the diffusion of TCE vapor in porous media is also addressed. The authors thank Bob Hughes, who developed the chemiresistor sensors, and Chad Davis, who assisted with the calibrations. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells

NASA Astrophysics Data System (ADS)

Swanson, Drew E.; Reich, Carey; Abbas, Ali; Shimpi, Tushar; Liu, Hanxiao; Ponce, Fernando A.; Walls, John M.; Zhang, Yong-Hang; Metzger, Wyatt K.; Sampath, W. S.; Holman, Zachary C.

2018-05-01

As single-junction silicon solar cells approach their theoretical limits, tandems provide the primary path to higher efficiencies. CdTe alloys can be tuned with magnesium (CdMgTe) or zinc (CdZnTe) for ideal tandem pairing with silicon. A II-VI/Si tandem holds the greatest promise for inexpensive, high-efficiency top cells that can be quickly deployed in the market using existing polycrystalline CdTe manufacturing lines combined with mature silicon production lines. Currently, all high efficiency polycrystalline CdTe cells require a chloride-based passivation process to passivate grain boundaries and bulk defects. This research examines the rich chemistry and physics that has historically limited performance when extending Cl treatments to polycrystalline 1.7-eV CdMgTe and CdZnTe absorbers. A combination of transmittance, quantum efficiency, photoluminescence, transmission electron microscopy, and energy-dispersive X-ray spectroscopy clearly reveals that during passivation, Mg segregates and out-diffuses, initially at the grain boundaries but eventually throughout the bulk. CdZnTe exhibits similar Zn segregation behavior; however, the onset and progression is localized to the back of the device. After passivation, CdMgTe and CdZnTe can render a layer that is reduced to predominantly CdTe electro-optical behavior. Contact instabilities caused by inter-diffusion between the layers create additional complications. The results outline critical issues and paths for these materials to be successfully implemented in Si-based tandems and other applications.

Comparative Measurements of Radon Concentration in Soil Using Passive and Active Methods in High Level Natural Radiation Area (HLNRA) of Ramsar

PubMed Central

Amanat, B; Kardan, M R; Faghihi, R; Hosseini Pooya, S M

2013-01-01

Background: Radon and its daughters are amongst the most important sources of natural exposure in the world. Soil is one of the significant sources of radon/thoron due to both radium and thorium so that the emanated thoron from it may cause increased uncertainties in radon measurements. Recently, a diffusion chamber has been designed and optimized for passive discriminative measurements of radon/thoron concentrations in soil. Objective: In order to evaluate the capability of the passive method, some comparative measurements (with active methods) have been performed. Method: The method is based upon measurements by a diffusion chamber, including two Lexan polycarbonate SSNTDs, which can discriminate the emanated radon/thorn from the soil by delay method. The comparative measurements have been done in ten selected points of HLNRA of Ramsar in Iran. The linear regression and correlation between the results of two methods have been studied. Results: The results show that the radon concentrations are within the range of 12.1 to 165 kBq/m3 values. The correlation between the results of active and passive methods was measured by 0.99 value. As well, the thoron concentrations have been measured between 1.9 to 29.5 kBq/m3 values at the points. Conclusion: The sensitivity as well as the strong correlation with active measurements shows that the new low-cost passive method is appropriate for accurate seasonal measurements of radon and thoron concentration in soil. PMID:25505760

Passivation of c-Si surfaces by sub-nm amorphous silicon capped with silicon nitride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Yimao, E-mail: yimao.wan@anu.edu.au; Yan, Di; Bullock, James

2015-12-07

A sub-nm hydrogenated amorphous silicon (a-Si:H) film capped with silicon nitride (SiN{sub x}) is shown to provide a high level passivation to crystalline silicon (c-Si) surfaces. When passivated by a 0.8 nm a-Si:H/75 nm SiN{sub x} stack, recombination current density J{sub 0} values of 9, 11, 47, and 87 fA/cm{sup 2} are obtained on 10 Ω·cm n-type, 0.8 Ω·cm p-type, 160 Ω/sq phosphorus-diffused, and 120 Ω/sq boron-diffused silicon surfaces, respectively. The J{sub 0} on n-type 10 Ω·cm wafers is further reduced to 2.5 ± 0.5 fA/cm{sup 2} when the a-Si:H film thickness exceeds 2.5 nm. The passivation by the sub-nm a-Si:H/SiN{sub x} stack is thermally stable at 400 °C in N{sub 2} formore » 60 min on all four c-Si surfaces. Capacitance–voltage measurements reveal a reduction in interface defect density and film charge density with an increase in a-Si:H thickness. The nearly transparent sub-nm a-Si:H/SiN{sub x} stack is thus demonstrated to be a promising surface passivation and antireflection coating suitable for all types of surfaces encountered in high efficiency c-Si solar cells.« less

Diffusive Milli-Gels (DMG) for in situ assessment of metal bioavailability: A comparison with labile metal measurement using Chelex columns and acute toxicity to Ceriodaphnia dubia for copper in freshwaters.

PubMed

Perez, Magali; Simpson, Stuart L; Lespes, Gaëtane; King, Josh J; Adams, Merrin S; Jarolimek, Chad V; Grassl, Bruno; Schaumlöffel, Dirk

2016-12-01

Fluctuations in concentrations of bioavailable metals occur in most natural waters. In situ measurements are desirable to predict risks of adverse effects to aquatic organisms. We evaluated Diffusive Milli-Gels (DMG), a new in situ passive sampler, for assessing the bioavailability and toxicity of copper in waters exhibiting a wide range of characteristics. The performance was compared to an established Chelex-column method that measures labile copper concentrations by discrete sampling, and the ability to predict acute toxicity to the cladoceran, Ceriodaphnia dubia. The labile copper concentrations measured by the DMG and Chelex-column methods decreased with increasing dissolved organic carbon (DOC) (1.9-15 mg L -1 ) and hardness (21-270 mg CaCO 3  L -1 hardness), with 20-70% of total dissolved copper being present as labile copper. Toxicity decreased with increasing DOC and hardness. Strong linear relationships existed between the EC50 for C. dubia and DOC, and when the EC50 was related to either the labile copper concentrations measured by DMG (r 2  = 0.874) or the Chelex column (0.956) methods. The study demonstrates that the DMG passive sampler is a relevant tool for the in situ assessment of environmental risks posed by metals whose toxicity is strongly influenced by speciation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Air quality assessment in Southern Kuwait using diffusive passive samplers.

PubMed

Ramadan, A A

2010-01-01

Measurements of fortnightly average concentrations of NO, NO2, SO2, H2S, NH3, and volatile organic compounds (VOCs) (aromatics=benzene, toluene, o-xylene, m+p-xylene, ethyl benzene; non-aromatics=nonane and octane) were carried out in the period from 26/10/05 to 24/11/05 at 20 points in the southern part of Kuwait as part of a baseline environmental impact assessment study requested by Kuwait National Petroleum Company. Two waves of triplicate diffusive passive samplers were used. A high volume air sampler was used to measure PM10 too. During the sampling period, the wind was observed to be mainly from the west and northwest with an average of 4.28 m/s. The consistency of the results allowed the production of spatial distribution maps of the pollutants measured and consequently the comparison between levels of air pollution at different locations. A comparison between the measured concentrations and the applicable air quality standards promulgated by Kuwait Environment Public Authority (KEPA) showed that those compounds had low concentrations compared to both industrial and residential KEPA standards. For other compounds which are not covered by KEPA standards, the results were compared with relevant limits of US Environment Protect Agency (USEPA) and US Department of Labor, Occupational Safety and Health Administration. The comparison showed that the measured compounds had low concentrations compared to the existing standards and, accordingly, no violation of air quality standards is reported.

Absorption of resveratrol by vascular endothelial cells through passive diffusion and an SGLT1-mediated pathway.

PubMed

Chen, Ming-liang; Yi, Long; Jin, Xin; Xie, Qi; Zhang, Ting; Zhou, Xi; Chang, Hui; Fu, Yu-jie; Zhu, Jun-dong; Zhang, Qian-yong; Mi, Man-tian

2013-11-01

Resveratrol is a natural polyphenol that exerts potent effects to suppress atherosclerosis. However, its low concentration in plasma has placed this role in doubt. Thus, resveratrol effects might be dependent on its transport into vascular endothelium, a question not previously addressed in spite of its obvious and fundamental importance. Via high-performance liquid chromatography and liquid chromatography/mass spectrometry, we found that resveratrol was absorbed by human umbilical vein endothelial cells in a temperature-, concentration- and time-dependent manner, suggesting the involvement of passive diffusion and active transport. As determined by confocal laser scanning microscopy, resveratrol primarily distributed throughout the cytoplasm. Furthermore, resveratrol absorption was modulated by serum proteins and sodium-dependent glucose transporter 1 (SGLT1) yet inhibited by glucose (an SGLT1 substrate) and phlorizin (an SGLT1 selective inhibitor), as well as SGLT1 siRNA transfection. Additionally, Sprague-Dawley rats were intragastrically administrated with 100mg/kg of resveratrol and the concentration of resveratrol in blood vessels declined more slowly up to 24h compared to that in the blood. Our results suggested that resveratrol uptake by vascular endothelial cells involved both passive diffusion and an SGLT1-mediated process, at least partially. Moreover, the intracellular resveratrol pool may be more important than the serum level in vivo. These provide new insights into the cardiovascular benefits of resveratrol. Copyright © 2013 Elsevier Inc. All rights reserved.

Characterization of iron in silicon by low-temperature photoluminescence and deep-level transient spectroscopy

NASA Astrophysics Data System (ADS)

Nakamura, Minoru; Murakami, Susumu; Udono, Haruhiko

2018-03-01

We investigate the relationship between the intensity of band-edge (BDE) photoluminescence (PL) from 10 to 70 K and the concentration of iron diffused in boron-doped p-type silicon. Because of the nonradiative recombination activity of the interstitial iron-boron complex (FeiB center), the BDE-PL intensity at each temperature varies distinctively and systematically with the iron concentration, which means that this method has the potential to make the accurate measurements of a wide range of interstitial iron concentrations in silicon. The iron precipitates formed in the bulk and/or at the surface are found to exert much weaker recombination activity for excess carriers than FeiB center by exploiting both PL and deep-level transient spectroscopy (DLTS) measurements. The unexpected enhancement in BDE-PL intensity from iron-diffused silicon between 20 and 50 K is attributed to the passivation of the Si-oxide/Si interface by iron. For the samples diffused with trace amounts of iron, the iron concentration within 20 μm of the surface is significantly greater than that in the bulk, as measured by DLTS. This result is tentatively attributed to the affinity of iron with the Si-oxide.

Fluorescent recovery after photobleaching (FRAP) analysis of nuclear export rates identifies intrinsic features of nucleocytoplasmic transport.

PubMed

Cardarelli, Francesco; Tosti, Luca; Serresi, Michela; Beltram, Fabio; Bizzarri, Ranieri

2012-02-17

A quantitative description of carrier-mediated nuclear export in live cells is presented. To this end, we fused a prototypical leucine-rich nuclear export signal (NES) to GFP as a cargo model and expressed the fluorescent chimera in live CHO-K1 cells. By modeling FRAP data, we calculate the NES affinity for the export machinery and the maximum rate of nuclear export achievable at saturation of endogenous carriers. The measured active-export time through the Nuclear Pore Complex (NPC) is 18 ms, remarkably similar to the previously determined active-import rate. Also, our results reveal that active export/import and active export/passive diffusion fluxes are uncoupled, thus complementing previous reports on active import/passive diffusion uncoupling. These findings suggest differential gating at the NPC level.

Managing evaporation for more robust microscale assays. Part 2. Characterization of convection and diffusion for cell biology.

PubMed

Berthier, Erwin; Warrick, Jay; Yu, Hongmeiy; Beebe, David J

2008-06-01

Cell based microassays allow the screening of a multitude of culture conditions in parallel, which can be used for various applications from drug screening to fundamental cell biology research. Tubeless microfluidic devices based on passive pumping are a step towards accessible high throughput microassays, however they are vulnerable to evaporation. In addition to volume loss, evaporation can lead to the generation of small flows. Here, we focus on issues of convection and diffusion for cell culture in microchannels and particularly the transport of soluble factors secreted by cells. We find that even for humidity levels as high as 95%, convection in a passive pumping channel can significantly alter distributions of these factors and that appropriate system design can prevent convection.

Isotopic fractionation of volatile species during bubble growth in magmas

NASA Astrophysics Data System (ADS)

Watson, E. B.

2016-12-01

Bubbles grow in decompressing magmas by simple expansion and also by diffusive supply of volatiles to the bubble/melt interface. The latter phenomenon is of significant geochemical interest because diffusion can fractionate isotopes, raising the possibility that the isotopic character of volatile components in bubbles may not reflect that of volatiles dissolved in the host melt over the lifetime of a bubble—even in the complete absence of equilibrium vapor/melt isotopic fractionation. None of the foregoing is conceptually new, but recent experimental studies have established the existence of isotope mass effects on diffusion in silicate melts for several elements (Li, Mg, Ca, Fe), and this finding has now been extended to the volatile (anionic) element chlorine (Fortin et al. 2016; this meeting). Knowledge of isotope mass effects on diffusion of volatile species opens the way for quantitative models of diffusive fractionation during bubble growth. Significantly different effects are anticipated for "passive" volatiles (e.g., noble gases and Cl) that are partitioned into existing bubbles but play little role in nucleation and growth, as opposed to "active" volatiles whose limited solubilities lead to bubble nucleation during magma decompression. Numerical solution of the appropriate diffusion/mass-conservation equations reveals that the isotope effect on passive volatiles partitioned into bubbles growing at a constant rate in a static system depends (predictably) upon R/D, Kd and D1/D2 (R = growth rate; D = diffusivity; Kd = bubble/melt partition coefficient; D1/D2 = diffusivity ratio of the isotopes of interest). Constant R is unrealistic, but other scenarios can be explored by including the solubility and EOS of an "active" volatile (e.g., CO2) in numerical simulations of bubble growth. For plausible decompression paths, R increases exponentially with time—leading, potentially, to larger isotopic fractionation of species partitioned into the growing bubble.

Corrosion Properties of Dissimilar Friction Stir Welded 6061 Aluminum and HT590 Steel

NASA Astrophysics Data System (ADS)

Seo, Bosung; Song, Kuk Hyun; Park, Kwangsuk

2018-05-01

Corrosion properties of dissimilar friction stir welded 6061 aluminum and HT590 steel were investigated to understand effects of galvanic corrosion. As cathode when coupled, HT590 was cathodically protected. However, the passivation of AA6061 made the aluminum alloy cathode temporarily, which leaded to corrosion of HT590. From the EIS analysis showing Warburg diffusion plot in Nyquist plots, it can be inferred that the stable passivation layer was formed on AA6061. However, the weld as well as HT590 did not show Warburg diffusion plot in Nyquist plots, suggesting that there was no barrier for corrosion or even if it exists, the barrier had no function for preventing and/or retarding charge transport through the passivation layer. The open circuit potential measurements showed that the potential of the weld was similar to that of HT590, which lied in the pitting region for AA6061, making the aluminum alloy part of the weld keep corrosion state. That resulted in the cracked oxide film on AA6061 of the weld, which could not play a role of corrosion barrier.

Diffusion tensor imaging reveals changes in the adult rat brain following long-term and passive moderate acoustic exposure.

PubMed

Abdoli, Sherwin; Ho, Leon C; Zhang, Jevin W; Dong, Celia M; Lau, Condon; Wu, Ed X

2016-12-01

This study investigated neuroanatomical changes following long-term acoustic exposure at moderate sound pressure level (SPL) under passive conditions, without coupled behavioral training. The authors utilized diffusion tensor imaging (DTI) to detect morphological changes in white matter. DTIs from adult rats (n = 8) exposed to continuous acoustic exposure at moderate SPL for 2 months were compared with DTIs from rats (n = 8) reared under standard acoustic conditions. Two distinct forms of DTI analysis were applied in a sequential manner. First, DTI images were analyzed using voxel-based statistics which revealed greater fractional anisotropy (FA) of the pyramidal tract and decreased FA of the tectospinal tract and trigeminothalamic tract of the exposed rats. Region of interest analysis confirmed (p < 0.05) that FA had increased in the pyramidal tract but did not show a statistically significant difference in the FA of the tectospinal or trigeminothalamic tract. The results of the authors show that long-term and passive acoustic exposure at moderate SPL increases the organization of white matter in the pyramidal tract.

Diffuse Extension of the Southern Mariana Margin: Implications for Subduction Zone Infancy and Plate Tectonics

NASA Astrophysics Data System (ADS)

Martinez, F.; Stern, R. J.; Kelley, K. A.; Ohara, Y.; Sleeper, J. D.; Ribeiro, J. M.; Brounce, M. N.

2017-12-01

Opening of the southern Mariana margin takes place in contrasting modes: Extension normal to the trench forms crust that is passively accreted to a rigid Philippine Sea plate and forms along focused and broad accretion axes. Extension also occurs parallel to the trench and has split apart an Eocene-Miocene forearc terrain accreting new crust diffusely over a 150-200 km wide zone forming a pervasive volcano-tectonic fabric oriented at high angles to the trench and the backarc spreading center. Earthquake seismicity indicates that the forearc extension is active over this broad area and basement samples date young although waning volcanic activity. Diffuse formation of new oceanic crust and lithosphere is unusual; in most oceanic settings extension rapidly focuses to narrow plate boundary zones—a defining feature of plate tectonics. Diffuse crustal accretion has been inferred to occur during subduction zone infancy, however. We hypothesize that, in a near-trench extensional setting, the continual addition of water from the subducting slab creates a weak overriding hydrous lithosphere that deforms broadly. This process counteracts mantle dehydration and strengthening proposed to occur at mid-ocean ridges that may help to focus deformation and melt delivery to narrow plate boundary zones. The observations from the southern Mariana margin suggest that where lithosphere is weakened by high water content narrow seafloor spreading centers cannot form. These conditions likely prevail during subduction zone infancy, explaining the diffuse contemporaneous volcanism inferred in this setting.

Diffusive Insights: On the Disagreement of Christian Bohr and August Krogh at the Centennial of the Seven Little Devils

ERIC Educational Resources Information Center

Gjedde, Albert

2010-01-01

The year 2010 is the centennial of the publication of the "Seven Little Devils" in the predecessor of "Acta Physiologica". In these seven papers, August and Marie Krogh sought to refute Christian Bohr's theory that oxygen diffusion from the lungs to the circulation is not entirely passive but rather facilitated by a specific cellular activity…

Process Research of Polycrystalline Silicon Material (PROPSM)

NASA Technical Reports Server (NTRS)

Culik, J. S.

1984-01-01

An investigation was begun into the usefulness of molecular hydrogen annealing on polycrystalline solar cells. No improvement was realized even after twenty hours of hydrogenation. Thus, samples were chosen on the basis of: (1) low open circuit voltage; (2) low shunt conductance; and (3) high light generated current. These cells were hydrogenated in molecular hydrogen at 300 C. The differences between the before and after hydrogenation values are so slight as to be negligible. These cells have light generated current densities that indicate long minority carrier diffusion lengths. The open circuit voltage appears to be degraded, and quasi-neutral recombination current enhanced. Therefore, molecular hydrogen is not usful for passivating electrically active defects.

A study of the feasibility and performance of an active/passive imager using silicon focal plane arrays and incoherent continuous wave laser diodes

NASA Astrophysics Data System (ADS)

Vollmerhausen, Richard H.

This dissertation describes an active/passive imager (API) that provides reliable, nighttime, target acquisition in a man-portable package with effective visual range of about 4 kilometers. The reflective imagery is easier to interpret than currently used thermal imagery. Also, in the active mode, the API provides performance equivalent to the big-aperture, thermal systems used on weapons platforms like tanks and attack helicopters. This dissertation describes the research needed to demonstrate both the feasibility and utility of the API. Part of the research describes implementation of a silicon focal plane array (SFPA) capable of both active and passive imaging. The passive imaging mode exceeds the nighttime performance of currently fielded, man-portable sensors. Further, when scene illumination is insufficient for passive imaging, the low dark current of SFPA makes it possible to use continuous wave laser diodes (CWLD) to add an active imaging mode. CWLD have advantages of size, efficiency, and improved eye safety when compared to high peak-power diodes. Because of the improved eye safety, the API provides user-demanded features like video output and extended range gates in the active as well as passive imaging modes. Like any other night vision device, the API depends on natural illumination of the scene for passive operation. Although it has been known for decades that "starlight" illumination is actually from diffuse airglow emissions, the research described in this dissertation provides the first estimates of the global and temporal variation of ground illumination due to airglow. A third related element of the current research establishes the impact of atmospheric aerosols on API performance. We know from day experience that atmospheric scattering of sunlight into the imager line-of-sight can blind the imager and drastically degrade performance. Atmospheric scattering of sunlight is extensively covered in the literature. However, previous literature did not cover the impact of atmospheric scattering when the target is diffusely illuminated by airglow.

Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Zaunbrecher, Katherine N.; Kuciauskas, Darius; Swartz, Craig H.; Dippo, Pat; Edirisooriya, Madhavie; Ogedengbe, Olanrewaju S.; Sohal, Sandeep; Hancock, Bobby L.; LeBlanc, Elizabeth G.; Jayathilaka, Pathiraja A. R. D.; Barnes, Teresa M.; Myers, Thomas H.

2016-08-01

Heterostructures with CdTe and CdTe1-xSex (x ˜ 0.01) absorbers between two wider-band-gap Cd1-xMgxTe barriers (x ˜ 0.25-0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ˜6 μm, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 μs with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 μs.

Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaunbrecher, Katherine N.; Kuciauskas, Darius; Swartz, Craig H.

Heterostructures with CdTe and CdTe 1-xSex (x ~ 0.01) absorbers between two wider-band-gap Cd1-xMgxTe barriers (x ~ 0.25-0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects havemore » a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ~6 um, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 us with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 us.« less

A quantum diffusion law

NASA Astrophysics Data System (ADS)

Satpathi, Urbashi; Sinha, Supurna; Sorkin, Rafael D.

2017-12-01

We analyse diffusion at low temperature by bringing the fluctuation-dissipation theorem (FDT) to bear on a physically natural, viscous response-function R(t) . The resulting diffusion-law exhibits several distinct regimes of time and temperature, each with its own characteristic rate of spreading. As with earlier analyses, we find logarithmic spreading in the quantum regime, indicating that this behavior is robust. A consistent R(t) must satisfy the key physical requirements of Wightman positivity and passivity, and we prove that ours does so. We also prove in general that these two conditions are equivalent when the FDT holds. Given current technology, our diffusion law can be tested in a laboratory with ultra cold atoms.

In-Situ Electrochemical Corrosion Behavior of Nickel-Base 718 Alloy Under Various CO2 Partial Pressures at 150 and 205 °C in NaCl Solution

NASA Astrophysics Data System (ADS)

Zhang, Yubi; Zhao, Yongtao; Tang, An; Yang, Wenjie; Li, Enzuo

2018-07-01

The electrochemical corrosion behavior of nickel-base alloy 718 was investigated using electrochemical impedance spectroscopy and potentiodynamic polarization techniques at various partial pressures of CO2 (P_{{{CO}2 }}s) in a 25 wt% NaCl solution at 150 and 205 °C. The passive films composed of FeCO3 exhibit good corrosion resistance with a feature of Warburg impedance, Tafel plots show a complete passivation and the anodic reactions was dominated by a diffusion process at low P_{{{CO}2 }}s (1.8-9.8 MPa) at 150 °C. While numerous dented corrosion areas appeared on the sample surface for the P_{{{CO}2 }} of 11.6 MPa at 205 °C, the Tafel plot with three anodic peaks and the Nyquist diagram with an atrophied impedance arc were present. This dented corrosion attribute to the synergistic effects of stress, temperature, P_{{{CO}2 }} and Cl-, the temperature and stress could play crucial roles on the corrosion of the alloy 718.

Levels and distribution of dissolved hydrophobic organic contaminants in the Morava river in Zlín district, Czech Republic as derived from their accumulation in silicone rubber passive samplers.

PubMed

Prokeš, Roman; Vrana, Branislav; Klánová, Jana

2012-07-01

Dissolved waterborne polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were assessed over a period of one year at five sampling sites in a model industrial region in the Czech Republic using silicone rubber passive samplers. The spatial variability of POPs in the studied region in water was small and diffusive pollution sources predominate. Concentrations of the most volatile PAHs decreased with increasing water temperature in the whole region, which reflects the seasonality in atmospheric deposition. The dissolved concentrations of more hydrophobic PAHs, PCBs and OCPs in and downstream the industrial zone are related to desorption from suspended particles. Upstream the industrial area, a positive correlation of dissolved and particle-bound contamination was observed only for DDT metabolites and hexachlorobenzene. Calculated fugacities in water and bottom sediment indicated a fair degree of equilibrium between these compartments for OCPs and PCBs, whereas sediment represented a potential source of PAHs. Copyright © 2012 Elsevier Ltd. All rights reserved.

In-Situ Electrochemical Corrosion Behavior of Nickel-Base 718 Alloy Under Various CO2 Partial Pressures at 150 and 205 °C in NaCl Solution

NASA Astrophysics Data System (ADS)

Zhang, Yubi; Zhao, Yongtao; Tang, An; Yang, Wenjie; Li, Enzuo

2018-03-01

The electrochemical corrosion behavior of nickel-base alloy 718 was investigated using electrochemical impedance spectroscopy and potentiodynamic polarization techniques at various partial pressures of CO2 (P_{{{CO}2 }} s) in a 25 wt% NaCl solution at 150 and 205 °C. The passive films composed of FeCO3 exhibit good corrosion resistance with a feature of Warburg impedance, Tafel plots show a complete passivation and the anodic reactions was dominated by a diffusion process at low P_{{{CO}2 }} s (1.8-9.8 MPa) at 150 °C. While numerous dented corrosion areas appeared on the sample surface for the P_{{{CO}2 }} of 11.6 MPa at 205 °C, the Tafel plot with three anodic peaks and the Nyquist diagram with an atrophied impedance arc were present. This dented corrosion attribute to the synergistic effects of stress, temperature, P_{{{CO}2 }} and Cl-, the temperature and stress could play crucial roles on the corrosion of the alloy 718.

Method for sampling and analysis of volatile biomarkers in process gas from aerobic digestion of poultry carcasses using time-weighted average SPME and GC-MS.

PubMed

Koziel, Jacek A; Nguyen, Lam T; Glanville, Thomas D; Ahn, Heekwon; Frana, Timothy S; Hans van Leeuwen, J

2017-10-01

A passive sampling method, using retracted solid-phase microextraction (SPME) - gas chromatography-mass spectrometry and time-weighted averaging, was developed and validated for tracking marker volatile organic compounds (VOCs) emitted during aerobic digestion of biohazardous animal tissue. The retracted SPME configuration protects the fragile fiber from buffeting by the process gas stream, and it requires less equipment and is potentially more biosecure than conventional active sampling methods. VOC concentrations predicted via a model based on Fick's first law of diffusion were within 6.6-12.3% of experimentally controlled values after accounting for VOC adsorption to the SPME fiber housing. Method detection limits for five marker VOCs ranged from 0.70 to 8.44ppbv and were statistically equivalent (p>0.05) to those for active sorbent-tube-based sampling. The sampling time of 30min and fiber retraction of 5mm were found to be optimal for the tissue digestion process. Copyright © 2017 Elsevier Ltd. All rights reserved.

A comparison of passive and active acoustic sampling for a bat community impacted by White-nose syndrome

USGS Publications Warehouse

Coleman, Laci S.; Ford, W. Mark; Dobony, Christopher A.; Britzke, Eric R.

2014-01-01

In the summers of 2011 and 2012, we compared passive and active acoustic sampling for bats at 31 sites at Fort Drum Military Installation, New York. We defined active sampling as acoustic sampling that occurred in 30-min intervals between the hours of sunset and 0200 with a user present to manipulate the directionality of the microphone. We defined passive sampling as acoustic sampling that occurred over a 12-h period (1900–0700 hours) without a user present and with the microphone set in a predetermined direction. We detected seven of the nine possible species at Fort Drum, including the federally endangered Indiana bat Myotis sodalis, the proposed-for-listing northern bat M. septentrionalis, the little brown bat M. lucifugus, and the big brown bat Eptesicus fuscus, which are impacted by white-nose syndrome (WNS); and the eastern red bat Lasiurus borealis, the hoary bat L. cinereus, and the silver-haired bat Lasionycteris noctivagans, which are not known to be impacted by WNS. We did not detect two additional WNS-impacted species known to historically occur in the area: the eastern small-footed bat Myotis leibii and the tri-colored bat Perimyotis subflavus. Single-season occupancy models revealed lower detection probabilities of all detected species using active sampling versus passive sampling. Additionally, overall detection probabilities declined in detected WNS-impacted species between years. A paired t-test of simultaneous sampling on 21 occasions revealed that overall recorded foraging activity per hour was greater using active than passive sampling for big brown bats and greater using passive than active sampling for little brown bats. There was no significant difference in recorded activity between methods for other WNS-impacted species, presumably because these species have been so reduced in number that their “apparency” on the landscape is lower. Finally, a cost analysis of standard passive and active sampling protocols revealed that passive sampling is substantially more cost-effective than active sampling per hour of data collection. We recommend passive sampling over active sampling methodologies as they are defined in our study for detection probability and/or occupancy studies focused on declining bat species in areas that have experienced severe WNS-associated impacts.

Passive Ventricular Mechanics Modelling Using MRI of Structure and Function

PubMed Central

Wang, V.Y.; Lam, H.I.; Ennis, D.B.; Young, A.A.; Nash, M.P.

2009-01-01

Patients suffering from dilated cardiomyopathy or myocardial infarction can develop left ventricular (LV) diastolic impairment. The LV remodels its structure and function to adapt to pathophysiological changes in geometry and loading conditions and this remodeling process can alter the passive ventricular mechanics. In order to better understand passive ventricular mechanics, a LV finite element model was developed to incorporate physiological and mechanical information derived from in vivo magnetic resonance imaging (MRI) tissue tagging, in vivo LV cavity pressure recording and ex vivo diffusion tensor MRI (DTMRI) of a canine heart. MRI tissue tagging enables quantitative evaluation of cardiac mechanical function with high spatial and temporal resolution, whilst the direction of maximum water diffusion (the primary eigenvector) in each voxel of a DTMRI directly correlates with the myocardial fibre orientation. This model was customized to the geometry of the canine LV during diastasis by fitting the segmented epicardial and endocardial surface data from tagged MRI using nonlinear finite element fitting techniques. Myofibre orientations, extracted from DTMRI of the same heart, were incorporated into this geometric model using a free form deformation methodology. Pressure recordings, temporally synchronized to the tissue tagging MRI data, were used to simulate the LV deformation during diastole. Simulation of the diastolic LV mechanics allowed us to estimate the stiffness of the passive LV myocardium based on kinematic data obtained from tagged MRI. This integrated physiological model will allow more insight into the regional passive diastolic mechanics of the LV on an individualized basis, thereby improving our understanding of the underlying structural basis of mechanical dysfunction in pathological conditions. PMID:18982680

CdCl2 Passivation of Polycrystalline CdMgTe and CdZnTe Absorbers for Tandem Photovoltaic Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Metzger, Wyatt K; Swanson, Drew; Reich, Carey

As single-junction silicon solar cells approach their theoretical limits, tandems provide the primary path to higher efficiencies. CdTe alloys can be tuned with magnesium (CdMgTe) or zinc (CdZnTe) for ideal tandem pairing with silicon. A II-VI/Si tandem holds the greatest promise for inexpensive, high-efficiency top cells that can be quickly deployed in the market using existing polycrystalline CdTe manufacturing lines combined with mature silicon production lines. Currently, all high efficiency polycrystalline CdTe cells require a chloride-based passivation process to passivate grain boundaries and bulk defects. This research examines the rich chemistry and physics that has historically limited performance when extendingmore » Cl treatments to polycrystalline 1.7-eV CdMgTe and CdZnTe absorbers. A combination of transmittance, quantum efficiency, photoluminescence, transmission electron microscopy, and energy-dispersive X-ray spectroscopy clearly reveals that during passivation, Mg segregates and out-diffuses, initially at the grain boundaries but eventually throughout the bulk. CdZnTe exhibits similar Zn segregation behavior; however, the onset and progression is localized to the back of the device. After passivation, CdMgTe and CdZnTe can render a layer that is reduced to predominantly CdTe electro-optical behavior. Contact instabilities caused by inter-diffusion between the layers create additional complications. The results outline critical issues and paths for these materials to be successfully implemented in Si-based tandems and other applications.« less

Passive ventricular mechanics modelling using MRI of structure and function.

PubMed

Wang, V Y; Lam, H I; Ennis, D B; Young, A A; Nash, M P

2008-01-01

Patients suffering from dilated cardiomyopathy or myocardial infarction can develop left ventricular (LV) diastolic impairment. The LV remodels its structure and function to adapt to pathophysiological changes in geometry and loading conditions and this remodeling process can alter the passive ventricular mechanics. In order to better understand passive ventricular mechanics, a LV finite element model was developed to incorporate physiological and mechanical information derived from in vivo magnetic resonance imaging (MRI) tissue tagging, in vivo LV cavity pressure recording and ex vivo diffusion tensor MRI (DTMRI) of a canine heart. MRI tissue tagging enables quantitative evaluation of cardiac mechanical function with high spatial and temporal resolution, whilst the direction of maximum water diffusion (the primary eigenvector) in each voxel of a DTMRI directly correlates with the myocardial fibre orientation. This model was customized to the geometry of the canine LV during diastasis by fitting the segmented epicardial and endocardial surface data from tagged MRI using nonlinear finite element fitting techniques. Myofibre orientations, extracted from DTMRI of the same heart, were incorporated into this geometric model using a free form deformation methodology. Pressure recordings, temporally synchronized to the tissue tagging MRI data, were used to simulate the LV deformation during diastole. Simulation of the diastolic LV mechanics allowed us to estimate the stiffness of the passive LV myocardium based on kinematic data obtained from tagged MRI. This integrated physiological model will allow more insight into the regional passive diastolic mechanics of the LV on an individualized basis, thereby improving our understanding of the underlying structural basis of mechanical dysfunction in pathological conditions.

Intra-urban and street scale variability of BTEX, NO 2 and O 3 in Birmingham, UK: Implications for exposure assessment

NASA Astrophysics Data System (ADS)

Vardoulakis, Sotiris; Solazzo, Efisio; Lumbreras, Julio

2011-09-01

Automatic monitoring networks have the ability of capturing air pollution episodes, as well as short- and long-term air quality trends in urban areas that can be used in epidemiological studies. However, due to practical constraints (e.g. cost and bulk of equipment), the use of automatic analysers is restricted to a limited number of roadside and background locations within a city. As a result, certain localised air pollution hotspots may be overlooked or overemphasised, especially near heavily trafficked street canyons and intersections. This has implications for compliance with regulatory standards and may cause exposure misclassification in epidemiological studies. Apart from automatic analysers, low cost passive diffusion tubes can be used to characterise the spatial variability of air pollution in urban areas. In this study, BTEX, NO 2 and O 3 data from a one-year passive sampling survey were used to characterise the intra-urban and street scale spatial variability of traffic-related pollutants in Birmingham (UK). In addition, continuous monitoring of NO 2, NO x, O 3, CO, SO 2, PM 10 and PM 2.5 from three permanent monitoring sites was used to identify seasonal and annual pollution patterns. The passive sampling measurements allowed us to evaluate the representativeness of a permanent roadside monitoring site that has recorded some of the highest NO 2 and PM 10 concentrations in Birmingham in recent years. Dispersion modelling was also used to gain further insight into pollutant sources and dispersion characteristics at this location. The strong spatial concentration gradients observed in busy streets, as well as the differences between roadside and urban background levels highlight the importance of appropriate positioning of air quality monitoring equipment in cities.

Porous Electrode Studies.

DTIC Science & Technology

1980-07-01

the reac- tion modes of the Ag/AgCl, AgO/Ag 2O/Ag, and Zn/ ZnO electrodes and to testing various theories that predict electrode behavior. v LOCKHEED...of sudden passivation was related to a simul- taneous precipitation of flocculent ZnO , and this passivation was removed by addi- tion of fresh...vation occurred more slowly by covering with a thin, adherent film, and that a dis- solution, diffusion, deposition mode prevailed in the formation of ZnO

Effect of dual-dielectric hydrogen-diffusion barrier layers on the performance of low-temperature processed transparent InGaZnO thin-film transistors

NASA Astrophysics Data System (ADS)

Tari, Alireza; Wong, William S.

2018-02-01

Dual-dielectric SiOx/SiNx thin-film layers were used as back-channel and gate-dielectric barrier layers for bottom-gate InGaZnO (IGZO) thin-film transistors (TFTs). The concentration profiles of hydrogen, indium, gallium, and zinc oxide were analyzed using secondary-ion mass spectroscopy characterization. By implementing an effective H-diffusion barrier, the hydrogen concentration and the creation of H-induced oxygen deficiency (H-Vo complex) defects during the processing of passivated flexible IGZO TFTs were minimized. A bilayer back-channel passivation layer, consisting of electron-beam deposited SiOx on plasma-enhanced chemical vapor-deposition (PECVD) SiNx films, effectively protected the TFT active region from plasma damage and minimized changes in the chemical composition of the semiconductor layer. A dual-dielectric PECVD SiOx/PECVD SiNx gate-dielectric, using SiOx as a barrier layer, also effectively prevented out-diffusion of hydrogen atoms from the PECVD SiNx-gate dielectric to the IGZO channel layer during the device fabrication.

Impurity gettering in semiconductors

DOEpatents

Sopori, B.L.

1995-06-20

A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device is disclosed. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500 C to about 700 C for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal. 1 fig.

Impurity gettering in semiconductors

DOEpatents

Sopori, Bhushan L.

1995-01-01

A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500.degree. C. to about 700.degree. C. for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal.

Very Hard Corrosion-Resistant Roll-Bonded Cr Coating on Mild Steel in Presence of Graphite

NASA Astrophysics Data System (ADS)

Kumar, Pankaj; Khara, S.; Shekhar, S.; Mondal, K.

2017-12-01

The present work discusses the development of very hard Cr and Cr-carbide coating by roll bonding of Cr powder on a mild steel followed by annealing at 800, 1000, 1100 and 1200 °C with and without the presence of graphite powder packing in argon environment. In addition, the effect of a roll skin pass of 5% prior to the application of coating was studied. The presence of graphite allows diffusion of both carbon and Cr in the mild steel substrate, leading to the formation of Cr-carbide on the outer surface, making the surface very hard (VHN 1800). Depending on the annealing temperature and processing condition, diffusion layer thickness of Cr is found to be in the range of 10-250 μm with Cr content of 12.5-15 wt.% across the diffusion layer. Excellent stable passivity of the coated surface is observed in 0.2 N H2SO4, which is comparable to a highly passivating 304 stainless steel, and very low corrosion rate of the coating is observed as compared to the substrate mild steel.

Multiple mechanisms quench passive spiral galaxies

NASA Astrophysics Data System (ADS)

Fraser-McKelvie, Amelia; Brown, Michael J. I.; Pimbblet, Kevin; Dolley, Tim; Bonne, Nicolas J.

2018-02-01

We examine the properties of a sample of 35 nearby passive spiral galaxies in order to determine their dominant quenching mechanism(s). All five low-mass (M⋆ < 1 × 1010 M⊙) passive spiral galaxies are located in the rich Virgo cluster. This is in contrast to low-mass spiral galaxies with star formation, which inhabit a range of environments. We postulate that cluster-scale gas stripping and heating mechanisms operating only in rich clusters are required to quench low-mass passive spirals, and ram-pressure stripping and strangulation are obvious candidates. For higher mass passive spirals, while trends are present, the story is less clear. The passive spiral bar fraction is high: 74 ± 15 per cent, compared with 36 ± 5 per cent for a mass, redshift and T-type matched comparison sample of star-forming spiral galaxies. The high mass passive spirals occur mostly, but not exclusively, in groups, and can be central or satellite galaxies. The passive spiral group fraction of 74 ± 15 per cent is similar to that of the comparison sample of star-forming galaxies at 61 ± 7 per cent. We find evidence for both quenching via internal structure and environment in our passive spiral sample, though some galaxies have evidence of neither. From this, we conclude no one mechanism is responsible for quenching star formation in passive spiral galaxies - rather, a mixture of mechanisms is required to produce the passive spiral distribution we see today.

Fluorescent Recovery after Photobleaching (FRAP) Analysis of Nuclear Export Rates Identifies Intrinsic Features of Nucleocytoplasmic Transport*

PubMed Central

Cardarelli, Francesco; Tosti, Luca; Serresi, Michela; Beltram, Fabio; Bizzarri, Ranieri

2012-01-01

A quantitative description of carrier-mediated nuclear export in live cells is presented. To this end, we fused a prototypical leucine-rich nuclear export signal (NES) to GFP as a cargo model and expressed the fluorescent chimera in live CHO-K1 cells. By modeling FRAP data, we calculate the NES affinity for the export machinery and the maximum rate of nuclear export achievable at saturation of endogenous carriers. The measured active-export time through the Nuclear Pore Complex (NPC) is 18 ms, remarkably similar to the previously determined active-import rate. Also, our results reveal that active export/import and active export/passive diffusion fluxes are uncoupled, thus complementing previous reports on active import/passive diffusion uncoupling. These findings suggest differential gating at the NPC level. PMID:22190681

Correction of Altitude-Induced Changes in Performance of the Volumetric Diffusive Respirator

DTIC Science & Technology

2017-04-05

to a plateau pressure. The positive pressure delivery of each percussive pulse is followed by a passive fall in pressure as the spring moves the ...AFRL-SA-WP-SR-2017-0007 Correction of Altitude- Induced Changes in Performance of the Volumetric Diffusive Respirator Thomas...Blakeman, MSc RRT April 2017 Air Force Research Laboratory 711th Human Performance Wing U.S. Air Force School of Aerospace

Optimization of Integrative Passive Sampling Approaches for Use in the Epibenthic Environment

DTIC Science & Technology

2016-12-23

Passive sampler, POCIS, Integrative, Sediment , Benthic 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a...Unexploded ordnance, Passive sampler, POCIS, Integrative, Sediment , Benthic v Acknowledgements Dr. Shane Morrison and Ms. Ingrid...flow and turbulence near the sampler. In complex environments at the sediment – water interface, this may limit the utility of passive sampling

Whole-body tissue stabilization and selective extractions via tissue-hydrogel hybrids for high-resolution intact circuit mapping and phenotyping.

PubMed

Treweek, Jennifer B; Chan, Ken Y; Flytzanis, Nicholas C; Yang, Bin; Deverman, Benjamin E; Greenbaum, Alon; Lignell, Antti; Xiao, Cheng; Cai, Long; Ladinsky, Mark S; Bjorkman, Pamela J; Fowlkes, Charless C; Gradinaru, Viviana

2015-11-01

To facilitate fine-scale phenotyping of whole specimens, we describe here a set of tissue fixation-embedding, detergent-clearing and staining protocols that can be used to transform excised organs and whole organisms into optically transparent samples within 1-2 weeks without compromising their cellular architecture or endogenous fluorescence. PACT (passive CLARITY technique) and PARS (perfusion-assisted agent release in situ) use tissue-hydrogel hybrids to stabilize tissue biomolecules during selective lipid extraction, resulting in enhanced clearing efficiency and sample integrity. Furthermore, the macromolecule permeability of PACT- and PARS-processed tissue hybrids supports the diffusion of immunolabels throughout intact tissue, whereas RIMS (refractive index matching solution) grants high-resolution imaging at depth by further reducing light scattering in cleared and uncleared samples alike. These methods are adaptable to difficult-to-image tissues, such as bone (PACT-deCAL), and to magnified single-cell visualization (ePACT). Together, these protocols and solutions enable phenotyping of subcellular components and tracing cellular connectivity in intact biological networks.

Hydromorphone transfer into breast milk after intranasal administration.

PubMed

Edwards, Jeffrey E; Rudy, Anita C; Wermeling, Daniel P; Desai, Nirmala; McNamara, Patrick J

2003-02-01

To determine the distribution of hydromorphone into breast milk and the potential exposure of the suckling infant, and whether the distribution of hydromorphone into milk can be predicted accurately by a passive diffusion model. Single-dose, pharmacokinetic study. University clinical research unit. Eight lactating, nonsmoking, healthy women aged 24-32 years. Hydromorphone HCl 2 mg was given intranasally to the women to characterize its pharmacokinetics and extent of its transfer into breast milk. Plasma and milk samples were analyzed using liquid chromatography with tandem mass spectrometry detection. The milk:plasma ratio (M:P) was calculated as the total area under the concentration-time curve (AUC) of the milk divided by the total AUC of the plasma. Predicted in vitro M:P ratios were calculated using a diffusion model. Protein binding in milk and plasma, partitioning into milk fat (whole milk:skim milk ratios), as well as pH partitioning between plasma and milk were incorporated in the model. Protein binding was determined by equilibrium dialysis. Protein binding was minimal in both milk and plasma, with unbound fractions of 1 and 0.84, respectively There was little partitioning into milk fat, as demonstrated by the whole milk:skim milk ratio of 0.98. The observed and predicted M:P ratios +/- SD for hydromorphone were 2.57 +/- 0.47 and 1.11 +/- 0.28, respectively. The 95% confidence interval for the observed M:P ratio overlapped the confidence interval of the predicted M:P ratio, a finding that supports a role for both passive diffusion and active transport as mechanisms of hydromorphone transfer into milk. Hydromorphone distributes rapidly from plasma into breast milk; however, the drug does not partition into fat. The suckling infant would receive approximately 0.67% of the maternal dose of hydromorphone (adjusted for body weight). As this is a limited exposure, further studies are needed to determine any potential impact to an infant who is fed breast milk from a mother treated with hydromorphone.

Healthy environment--indoor air quality of Brazilian elementary schools nearby petrochemical industry.

PubMed

Godoi, Ricardo H M; Godoi, Ana F L; Gonçalves Junior, Sérgio J; Paralovo, Sarah L; Borillo, Guilherme C; Gonçalves Gregório Barbosa, Cybelli; Arantes, Manoela G; Charello, Renata C; Rosário Filho, Nelson A; Grassi, Marco T; Yamamoto, Carlos I; Potgieter-Vermaak, Sanja; Rotondo, Giuliana G; De Wael, Karolien; van Grieken, Rene

2013-10-01

The mitigation of pollution released to the environment originating from the industrial sector has been the aim of all policy-makers and its importance is evident if the adverse health effects on the world population are considered. Although this concern is controversial, petroleum refinery has been linked to some adverse health effects for people living nearby. Apart from home, school is the most important indoor environment for children and there is increasing concern about the school environment and its impact on health, also in developing countries where the prevalence of pollution is higher. As most of the children spend more than 40% of their time in schools, it is critical to evaluate the pollution level in such environment. In the metropolitan region of Curitiba, South Brazil, five schools nearby industries and highways with high density traffic, were selected to characterize the aerosol and gaseous compounds indoor and outdoor of the classrooms, during 2009-2011. Size segregated aerosol samples were collected for analyses of bulk and single particle elemental profiles. They were analyzed by electron probe X-ray micro-analysis (EPXMA), and by energy-dispersive X-ray fluorescence (EDXRF), to investigate the elemental composition of individual particles and bulk samples. The concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX); NO2; SO2; acetic acid; and formic acid were assessed indoor and outdoor using passive diffusion tubes. BTEX were analyzed by GC-MS and other collected gasses by ion chromatography. Individual exposition of BTEX was assessed by personal passive diffusion tubes. Results are interpreted separately and as a whole with the specific aim of identifying compounds that could affect the health of the scholars. In view of the chemical composition and size distribution of the aerosol particles, local deposition efficiencies in the children's respiratory systems were calculated, revealing the deposition of particles at extrathoracic, tracheobronchial and pulmonary levels. Copyright © 2013 Elsevier B.V. All rights reserved.

Anomalous, non-Gaussian tracer diffusion in crowded two-dimensional environments

NASA Astrophysics Data System (ADS)

Ghosh, Surya K.; Cherstvy, Andrey G.; Grebenkov, Denis S.; Metzler, Ralf

2016-01-01

A topic of intense current investigation pursues the question of how the highly crowded environment of biological cells affects the dynamic properties of passively diffusing particles. Motivated by recent experiments we report results of extensive simulations of the motion of a finite sized tracer particle in a heterogeneously crowded environment made up of quenched distributions of monodisperse crowders of varying sizes in finite circular two-dimensional domains. For given spatial distributions of monodisperse crowders we demonstrate how anomalous diffusion with strongly non-Gaussian features arises in this model system. We investigate both biologically relevant situations of particles released either at the surface of an inner domain or at the outer boundary, exhibiting distinctly different features of the observed anomalous diffusion for heterogeneous distributions of crowders. Specifically we reveal an asymmetric spreading of tracers even at moderate crowding. In addition to the mean squared displacement (MSD) and local diffusion exponent we investigate the magnitude and the amplitude scatter of the time averaged MSD of individual tracer trajectories, the non-Gaussianity parameter, and the van Hove correlation function. We also quantify how the average tracer diffusivity varies with the position in the domain with a heterogeneous radial distribution of crowders and examine the behaviour of the survival probability and the dynamics of the tracer survival probability. Inter alia, the systems we investigate are related to the passive transport of lipid molecules and proteins in two-dimensional crowded membranes or the motion in colloidal solutions or emulsions in effectively two-dimensional geometries, as well as inside supercrowded, surface adhered cells.

Mesure du coewicient d'absorption optique dans le silicium multicristallin de type P pour photopiles solaires

NASA Astrophysics Data System (ADS)

Gervais, J.

1993-07-01

The minority carrier diffusion length L characterizes the electrical quality of multicrystalline silicon wafers used for photovoltaics. Its determination before and after different treatments (impurity diffusion, passivation, metallisation) is needfull and requires the accurate knowledge of the optical absorption coefficient α in the near infrared. We have determinated the spectral variation of α in the range between 0.86 and 1.06 μm and we propose an analytic expression which is very close to those proposed for solar grade single crystals. In addition we have verified that the values of α are not affected by long phosphorus diffusion needed to getter metallic impurities. La longueur de diffusion des porteurs minoritaires L caractérise la qualité du silicium multicristallin utilisé pour la conversion photovoltaïque. Sa détermination avant et après les divers traitements (diffusion d'impuretés, passivation des défauts, métallisation) est indispensable et nécessite la connaissance précise du coefficient d'absorption optique α dans le proche infrarouge. Nous avons déterminé expérimentalement la variation spectrale de α entre 0,86 et 1,06 μm et nous proposons un développement qui est très proche de ceux trouvés dans des monocristaux de silicium de qualité solaire. La variation de α n'est pas influencée par des diffusions de phosphore prolongées nécessaires à l'extraction et au piégeage d'impuretés métalliques.

Localization of Protein Aggregation in Escherichia coli Is Governed by Diffusion and Nucleoid Macromolecular Crowding Effect

PubMed Central

Coquel, Anne-Sophie; Jacob, Jean-Pascal; Primet, Mael; Demarez, Alice; Dimiccoli, Mariella; Julou, Thomas; Moisan, Lionel

2013-01-01

Aggregates of misfolded proteins are a hallmark of many age-related diseases. Recently, they have been linked to aging of Escherichia coli (E. coli) where protein aggregates accumulate at the old pole region of the aging bacterium. Because of the potential of E. coli as a model organism, elucidating aging and protein aggregation in this bacterium may pave the way to significant advances in our global understanding of aging. A first obstacle along this path is to decipher the mechanisms by which protein aggregates are targeted to specific intercellular locations. Here, using an integrated approach based on individual-based modeling, time-lapse fluorescence microscopy and automated image analysis, we show that the movement of aging-related protein aggregates in E. coli is purely diffusive (Brownian). Using single-particle tracking of protein aggregates in live E. coli cells, we estimated the average size and diffusion constant of the aggregates. Our results provide evidence that the aggregates passively diffuse within the cell, with diffusion constants that depend on their size in agreement with the Stokes-Einstein law. However, the aggregate displacements along the cell long axis are confined to a region that roughly corresponds to the nucleoid-free space in the cell pole, thus confirming the importance of increased macromolecular crowding in the nucleoids. We thus used 3D individual-based modeling to show that these three ingredients (diffusion, aggregation and diffusion hindrance in the nucleoids) are sufficient and necessary to reproduce the available experimental data on aggregate localization in the cells. Taken together, our results strongly support the hypothesis that the localization of aging-related protein aggregates in the poles of E. coli results from the coupling of passive diffusion-aggregation with spatially non-homogeneous macromolecular crowding. They further support the importance of “soft” intracellular structuring (based on macromolecular crowding) in diffusion-based protein localization in E. coli. PMID:23633942

Evaluating the Relationship between Equilibrium Passive ...

EPA Pesticide Factsheets

This review evaluates passive sampler uptake of hydrophobic organic contaminants (HOCs) as it relates to organism bioaccumulation in the water column and interstitial water. Fifty-five studies were found where both passive samplers and organism bioaccumulation were used to measured water quality. Of these investigations, 19 provided direct comparisons relating passive sampler concentrations and organism bioaccumulation. Passive sampling polymers included in the review were: low density polyethylene (LDPE); polyoxymethylene (POM); and polydimethylsiloxane (PDMS), and organisms ranged from polychaetes and oligochaetes to bivalves, aquatic insects, and gastropods. Log-linear regressions correlating bioaccumulation (CL) and passive sampler concentration (CPS) were used to assess the strength of observed relationships. In general, the passive sampler concentrations resulted in statistically-significant, logarithmic, predictive relationships, most of which were within one to two orders of magnitude of measured bioaccumulation. Overall, bioaccumulation values were greater than passive sampler concentrations. A mean ratio of CL to CPS was 10.8 ± 18.4 (n = 609) for available data. Given that all studies presented resulted in a strong CL versus CPS relationship suggests that using passive sampling as a surrogate for organism bioaccumulation is viable when biomonitoring organisms are not available. Passive sampling based measurements can provide useful information for ma

Selecting Performance Reference Compounds (PRCS)for Polyethylene Passive Samplers Deployed at Contaminated Sediment Sites

EPA Science Inventory

Use of equilibrium passive samplers for performing aquatic environmental monitoring at contaminated sediment sites, including Superfund sites, is becoming more common. However, a current challenge in passive sampling is determining when equilibrium is achieved between the sampl...

A passivity criterion for sampled-data bilateral teleoperation systems.

PubMed

Jazayeri, Ali; Tavakoli, Mahdi

2013-01-01

A teleoperation system consists of a teleoperator, a human operator, and a remote environment. Conditions involving system and controller parameters that ensure the teleoperator passivity can serve as control design guidelines to attain maximum teleoperation transparency while maintaining system stability. In this paper, sufficient conditions for teleoperator passivity are derived for when position error-based controllers are implemented in discrete-time. This new analysis is necessary because discretization causes energy leaks and does not necessarily preserve the passivity of the system. The proposed criterion for sampled-data teleoperator passivity imposes lower bounds on the teleoperator's robots dampings, an upper bound on the sampling time, and bounds on the control gains. The criterion is verified through simulations and experiments.

Coexistence of passive and carrier-mediated processes in drug transport.

PubMed

Sugano, Kiyohiko; Kansy, Manfred; Artursson, Per; Avdeef, Alex; Bendels, Stefanie; Di, Li; Ecker, Gerhard F; Faller, Bernard; Fischer, Holger; Gerebtzoff, Grégori; Lennernaes, Hans; Senner, Frank

2010-08-01

The permeability of biological membranes is one of the most important determinants of the pharmacokinetic processes of a drug. Although it is often accepted that many drug substances are transported across biological membranes by passive transcellular diffusion, a recent hypothesis speculated that carrier-mediated mechanisms might account for the majority of membrane drug transport processes in biological systems. Based on evidence of the physicochemical characteristics and of in vitro and in vivo findings for marketed drugs, as well as results from real-life discovery and development projects, we present the view that both passive transcellular processes and carrier-mediated processes coexist and contribute to drug transport activities across biological membranes.

A Fractional PDE Approach to Turbulent Mixing; Part II: Numerical Simulation

NASA Astrophysics Data System (ADS)

Samiee, Mehdi; Zayernouri, Mohsen

2016-11-01

We propose a generalizing fractional order transport model of advection-diffusion kind with fractional time- and space-derivatives, governing the evolution of passive scalar turbulence. This approach allows one to incorporate the nonlocal and memory effects in the underlying anomalous diffusion i.e., sub-to-standard diffusion to model the trapping of particles inside the eddied, and super-diffusion associated with the sudden jumps of particles from one coherent region to another. For this nonlocal model, we develop a high order numerical (spectral) method in addition to a fast solver, examined in the context of some canonical problems. PhD student, Department of Mechanical Engineering, & Department Computational Mathematics, Science, and Engineering.

Mixing of a passive scalar by the instability of a differentially rotating axial pinch

NASA Astrophysics Data System (ADS)

Paredes, A.; Gellert, M.; Rüdiger, G.

2016-04-01

The mean-field diffusion of passive scalars such as lithium, beryllium or temperature dispersals due to the magnetic Tayler instability of a rotating axial pinch is considered. Our study is carried out within a Taylor-Couette setup for two rotation laws: solid-body quasi-Kepler rotation. The minimum magnetic Prandtl number used is 0.05, and the molecular Schmidt number Sc of the fluid varies between 0.1 and 2. An effective diffusivity coefficient for the mixing is numerically measured by the decay of a prescribed concentration peak located between both cylinder walls. We find that only models with Sc exceeding 0.1 basically provide finite instability-induced diffusivity values. We also find that for quasi-Kepler rotation at a magnetic Mach number Mm ≃ 2, the flow transits from the slow-rotation regime to the fast-rotation regime that is dominated by the Taylor-Proudman theorem. For fixed Reynolds number, the relation between the normalized turbulent diffusivity and the Schmidt number of the fluid is always linear so that also a linear relation between the instability-induced diffusivity and the molecular viscosity results, just in the sense proposed by Schatzman (1977, A&A, 573, 80). The numerical value of the coefficient in this relation reaches a maximum at Mm ≃ 2 and decreases for larger Mm, implying that only toroidal magnetic fields on the order of 1 kG can exist in the solar tachocline.

Quantitative assessment of passive electrical properties of the cardiac T-tubular system by FRAP microscopy

PubMed Central

Scardigli, M.; Ferrantini, C.; Gabbrielli, T.; Silvestri, L.; Coppini, R.; Tesi, C.; Rog-Zielinska, E. A.; Kohl, P.; Cerbai, E.; Poggesi, C.; Pavone, F. S.; Sacconi, L.

2017-01-01

Well-coordinated activation of all cardiomyocytes must occur on every heartbeat. At the cell level, a complex network of sarcolemmal invaginations, called the transverse-axial tubular system (TATS), propagates membrane potential changes to the cell core, ensuring synchronous and uniform excitation–contraction coupling. Although myocardial conduction of excitation has been widely described, the electrical properties of the TATS remain mostly unknown. Here, we exploit the formal analogy between diffusion and electrical conductivity to link the latter with the diffusional properties of TATS. Fluorescence recovery after photobleaching (FRAP) microscopy is used to probe the diffusion properties of TATS in isolated rat cardiomyocytes: A fluorescent dextran inside TATS lumen is photobleached, and signal recovery by diffusion of unbleached dextran from the extracellular space is monitored. We designed a mathematical model to correlate the time constant of fluorescence recovery with the apparent diffusion coefficient of the fluorescent molecules. Then, apparent diffusion is linked to electrical conductivity and used to evaluate the efficiency of the passive spread of membrane depolarization along TATS. The method is first validated in cells where most TATS elements are acutely detached by osmotic shock and then applied to probe TATS electrical conductivity in failing heart cells. We find that acute and pathological tubular remodeling significantly affect TATS electrical conductivity. This may explain the occurrence of defects in action potential propagation at the level of single T-tubules, recently observed in diseased cardiomyocytes. PMID:28507142

Passive sampling: A cost-effective method for understanding antibiotic fate, behaviour and impact.

PubMed

Chen, Chang-Er; Zhang, Hao; Ying, Guang-Guo; Zhou, Li-Jun; Jones, Kevin C

2015-12-01

The occurrence of antibiotics in the environment has raised much concern in recent years. Understanding their release, fate and behaviour in the environment is vital to assess potential risks. In this study, a novel passive water sampler - diffusion gradients in thin-films for organics (o-DGT) - was employed to assess the occurrence and removal of antibiotics in two waste water treatment plants (WWTPs) - one in China and the other in the United Kingdom (UK). Of the targeted compounds, 11 of 19 were detected in the Chinese WWTP (ND-200ng/L) and 10 of 40 were found in the UK plant (ND-1380ng/L). Florfenicol, lincomycin, ofloxacin and roxithromycin were most abundant in the Chinese WWTP (influent), while anhydrous erythromycin, ciprofloxacin, trimethoprim, ofloxacin and sulfapyridine were the most abundant in the UK influent samples. Estimated Chinese and UK consumption data are used to interpret the results. Neither of the WWTPs was very effective at removing antibiotics: ~40-50% (overall) was removed by the two plants, with the rest being discharged into the receiving rivers. This is the first study using o-DGT to assess the occurrence and removal of antibiotics in WWTPs. o-DGT is a useful, cost-effective tool to assess WWTP performance and can highlight the effectiveness of treatment steps, which can be applied to wastewater based epidemiology studies. Copyright © 2015 Elsevier Ltd. All rights reserved.

PAH and OPAH Flux during the Deepwater Horizon Incident

PubMed Central

Tidwell, Lane G.; Allan, Sarah E.; O'Connell, Steven G.; Hobbie, Kevin A.; Smith, Brian W.; Anderson, Kim A.

2016-01-01

Passive sampling devices were used to measure air vapor and water dissolved phase concentrations of 33 polycyclic aromatic hydrocarbons (PAHs) and 22 oxygenated PAHs (OPAHs) at four Gulf of Mexico coastal sites prior to, during and after shoreline oiling from the Deepwater Horizon oil spill (DWH). Measurements were taken at each site over a 13 month period, and flux across the water-air boundary was determined. This is the first report of vapor phase and diffusive flux of both PAHs and OPAHs during the DWH. Vapor phase sum PAH and OPAH concentrations ranged between 6.6 and 210 ng/m3 and 0.02 and 34 ng/m3 respectively. PAH and OPAH concentrations in air exhibited different spatial and temporal trends than in water, and air-water flux of 13 individual PAHs was shown to be at least partially influenced by the DWH incident. The largest PAH volatilizations occurred at the sites in Alabama and Mississippi at nominal rates of 56,000 and 42,000 ng/m2/day in the summer. Naphthalene was the PAH with the highest observed volatilization rate of 52,000 ng/m2/day in June 2010. This work represents additional evidence of the DWH incident contributing to air contamination, and provides one of the first quantitative air-water chemical flux determinations with passive sampling technology. PMID:27391856

Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

NASA Astrophysics Data System (ADS)

Wan, Yimao; Bullock, James; Cuevas, Andres

2015-05-01

This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta2O5) underneath plasma enhanced chemical vapour deposited silicon nitride (SiNx). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta2O5 and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Ω.cm and n-type 1.0 Ω.cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm2 and 68 fA/cm2 are measured on 150 Ω/sq boron-diffused p+ and 120 Ω/sq phosphorus-diffused n+ c-Si, respectively. Capacitance-voltage measurements reveal a negative fixed insulator charge density of -1.8 × 1012 cm-2 for the Ta2O5 film and -1.0 × 1012 cm-2 for the Ta2O5/SiNx stack. The Ta2O5/SiNx stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.

Resolvent-based modeling of passive scalar dynamics in wall-bounded turbulence

NASA Astrophysics Data System (ADS)

Dawson, Scott; Saxton-Fox, Theresa; McKeon, Beverley

2017-11-01

The resolvent formulation of the Navier-Stokes equations expresses the system state as the output of a linear (resolvent) operator acting upon a nonlinear forcing. Previous studies have demonstrated that a low-rank approximation of this linear operator predicts many known features of incompressible wall-bounded turbulence. In this work, this resolvent model for wall-bounded turbulence is extended to include a passive scalar field. This formulation allows for a number of additional simplifications that reduce model complexity. Firstly, it is shown that the effect of changing scalar diffusivity can be approximated through a transformation of spatial wavenumbers and temporal frequencies. Secondly, passive scalar dynamics may be studied through the low-rank approximation of a passive scalar resolvent operator, which is decoupled from velocity response modes. Thirdly, this passive scalar resolvent operator is amenable to approximation by semi-analytic methods. We investigate the extent to which this resulting hierarchy of models can describe and predict passive scalar dynamics and statistics in wall-bounded turbulence. The support of AFOSR under Grant Numbers FA9550-16-1-0232 and FA9550-16-1-0361 is gratefully acknowledged.

Mesoscale Elucidation of Surface Passivation in the Li-Sulfur Battery Cathode.

PubMed

Liu, Zhixiao; Mukherjee, Partha P

2017-02-15

The cathode surface passivation caused by Li 2 S precipitation adversely affects the performance of lithium-sulfur (Li-S) batteries. Li 2 S precipitation is a complicated mesoscale process involving adsorption, desorption and diffusion kinetics, which are affected profoundly by the reactant concentration and operating temperature. In this work, a mesoscale interfacial model is presented to study the growth of Li 2 S film on carbon cathode surface. Li 2 S film growth experiences nucleation, isolated Li 2 S island growth and island coalescence. The slow adsorption rate at small S 2- concentration inhibits the formation of nucleation seeds and the lateral growth of Li 2 S islands, which deters surface passivation. An appropriate operating temperature, especially in the medium-to-high temperature range, can also defer surface passivation. Fewer Li 2 S nucleation seeds form in such an operating temperature range, thereby facilitating heterogeneous growth and potentially inhibiting the lateral growth of the Li 2 S film, which may ultimately result in reduced surface passivation. The high specific surface area of the cathode microstructure is expected to mitigate the surface passivation.

Three-compartment model for contaminant accumulation by semipermeable membrane devices

USGS Publications Warehouse

Gale, Robert W.

1998-01-01

Passive sampling of dissolved hydrophobic contaminants with lipid (triolein)-containing semipermeable membrane devices (SPMDs) has been gaining acceptance for environmental monitoring. Understanding of the accumulation process has employed a simple polymer film-control model of uptake by the polymer-enclosed lipid, while aqueous film control has been only briefly discussed. A more complete three-compartment model incorporating both aqueous film (turbulent-diffusive) and polymer film (diffusive) mass transfer is developed here and is fit to data from accumulation studies conducted in constant-concentration, flow-through dilutors. This model predicts aqueous film control of the whole device for moderate to high Kow compounds, rather than polymer film control. Uptake rates for phenanthrene and 2,2‘,5,5‘-tetrachlorobiphenyl were about 4.8 and 4.2 L/day/standard SPMD, respectively. Maximum 28 day SPMD concentration factors of 30 000 are predicted for solutes with log Kow values of >5.5. Effects of varying aqueous and polymer film thicknesses and solute diffusivities in the polymer film are modeled, and overall accumulation by the whole device is predicted to remain under aqueous film control, although accumulation in the triolein may be subject to polymer film control. The predicted half-life and integrative response of SPMDs to pulsed concentration events is proportional to log KSPMD.

Verification of diffusive and pumped samplers for volatile organic compounds using a controlled atmosphere test facility

NASA Astrophysics Data System (ADS)

Martin, Nicholas A.; Leming, Edward J.; Henderson, Malcolm H.; Lipscombe, Robert P.; Black, John K.; Jarvis, Scott D.

2010-09-01

There is a requirement to verify the performance of sorbent-based passive or active samplers and to extend their use, where possible, to monitor volatile organic compounds (VOCs) that are known to be photochemical ozone pre-cursors or are relevant to the activities of the petrochemical industry. We report measurements of the 14-day diffusive uptake rates for the VOCs: i-butane (2-methyl propane), n-butane, i-pentane (2-methyl butane), n-pentane, n-hexane, benzene, toluene, and m-xylene (at environmental level concentrations) for industry standard axial samplers (Perkin-Elmer-type samplers) containing the sorbents Carbopack-X, -Z, -B or Tenax-TA. We also present data on back-diffusion, blank levels, and storage for the above sorbents, and describe the simultaneous use of the sorbent Carbopack-X for pumped sampling of certain VOCs. The results were obtained by dosing samplers in a controlled atmosphere test facility (CATFAC) operating under well-defined conditions of concentration, nominal temperature of 20 °C, wind speed of 0.5 m s -1, and relative humidities of 0% and 80%. Field measurements were also obtained to provide supplementary data to support the laboratory study. Results are compared to existing published data, where these are available.

Evaluation of spot and passive sampling for monitoring, flux estimation and risk assessment of pesticides within the constraints of a typical regulatory monitoring scheme.

PubMed

Zhang, Zulin; Troldborg, Mads; Yates, Kyari; Osprey, Mark; Kerr, Christine; Hallett, Paul D; Baggaley, Nikki; Rhind, Stewart M; Dawson, Julian J C; Hough, Rupert L

2016-11-01

In many agricultural catchments of Europe and North America, pesticides occur at generally low concentrations with significant temporal variation. This poses several challenges for both monitoring and understanding ecological risks/impacts of these chemicals. This study aimed to compare the performance of passive and spot sampling strategies given the constraints of typical regulatory monitoring. Nine pesticides were investigated in a river currently undergoing regulatory monitoring (River Ugie, Scotland). Within this regulatory framework, spot and passive sampling were undertaken to understand spatiotemporal occurrence, mass loads and ecological risks. All the target pesticides were detected in water by both sampling strategies. Chlorotoluron was observed to be the dominant pesticide by both spot (maximum: 111.8ng/l, mean: 9.35ng/l) and passive sampling (maximum: 39.24ng/l, mean: 4.76ng/l). The annual pesticide loads were estimated to be 2735g and 1837g based on the spot and passive sampling data, respectively. The spatiotemporal trend suggested that agricultural activities were the primary source of the compounds with variability in loads explained in large by timing of pesticide applications and rainfall. The risk assessment showed chlorotoluron and chlorpyrifos posed the highest ecological risks with 23% of the chlorotoluron spot samples and 36% of the chlorpyrifos passive samples resulting in a Risk Quotient greater than 0.1. This suggests that mitigation measures might need to be taken to reduce the input of pesticides into the river. The overall comparison of the two sampling strategies supported the hypothesis that passive sampling tends to integrate the contaminants over a period of exposure and allows quantification of contamination at low concentration. The results suggested that within a regulatory monitoring context passive sampling was more suitable for flux estimation and risk assessment of trace contaminants which cannot be diagnosed by spot sampling and for determining if long-term average concentrations comply with specified standards. Copyright © 2016 Elsevier B.V. All rights reserved.

Passive antibody-mediated immunotherapy for the treatment of malignant gliomas.

PubMed

Mitra, Siddhartha; Li, Gordon; Harsh, Griffith R

2010-01-01

Despite advances in understanding the molecular mechanisms of brain cancer, the outcome of patients with malignant gliomas treated according to the current standard of care remains poor. Novel therapies are needed, and immunotherapy has emerged with great promise. The diffuse infiltration of malignant gliomas is a major challenge to effective treatment; immunotherapy has the advantage of accessing the entire brain with specificity for tumor cells. Therapeutic immune approaches include cytokine therapy, passive immunotherapy, and active immunotherapy. Cytokine therapy involves the administration of immunomodulatory cytokines to activate the immune system. Active immunotherapy is the generation or augmentation of an immune response, typically by vaccination against tumor antigens. Passive immunotherapy connotes either adoptive therapy, in which tumor-specific immune cells are expanded ex vivo and reintroduced into the patient, or passive antibody-mediated therapy. In this article, the authors discuss the preclinical and clinical studies that have used passive antibody-mediated immunotherapy, otherwise known as serotherapy, for the treatment of malignant gliomas.

Effects of soil water saturation on sampling equilibrium and kinetics of selected polycyclic aromatic hydrocarbons.

PubMed

Kim, Pil-Gon; Roh, Ji-Yeon; Hong, Yongseok; Kwon, Jung-Hwan

2017-10-01

Passive sampling can be applied for measuring the freely dissolved concentration of hydrophobic organic chemicals (HOCs) in soil pore water. When using passive samplers under field conditions, however, there are factors that might affect passive sampling equilibrium and kinetics, such as soil water saturation. To determine the effects of soil water saturation on passive sampling, the equilibrium and kinetics of passive sampling were evaluated by observing changes in the distribution coefficient between sampler and soil (K sampler/soil ) and the uptake rate constant (k u ) at various soil water saturations. Polydimethylsiloxane (PDMS) passive samplers were deployed into artificial soils spiked with seven selected polycyclic aromatic hydrocarbons (PAHs). In dry soil (0% water saturation), both K sampler/soil and k u values were much lower than those in wet soils likely due to the contribution of adsorption of PAHs onto soil mineral surfaces and the conformational changes in soil organic matter. For high molecular weight PAHs (chrysene, benzo[a]pyrene, and dibenzo[a,h]anthracene), both K sampler/soil and k u values increased with increasing soil water saturation, whereas they decreased with increasing soil water saturation for low molecular weight PAHs (phenanthrene, anthracene, fluoranthene, and pyrene). Changes in the sorption capacity of soil organic matter with soil water content would be the main cause of the changes in passive sampling equilibrium. Henry's law constant could explain the different behaviors in uptake kinetics of the selected PAHs. The results of this study would be helpful when passive samplers are deployed under various soil water saturations. Copyright © 2017 Elsevier Ltd. All rights reserved.

THE IMPACT OF PASSIVE SAMPLING METHODOLOGIES USED IN THE DEARS

EPA Science Inventory

This abstract details the use of passive sampling methodologies in the Detroit Exposure and Aerosol Research Study (DEARS). A discussion about the utility of various gas-phase passive samplers used in the study will be described along with examples of field data measurements empl...

Parameters influencing the course of passive drug loading into lipid nanoemulsions.

PubMed

Göke, Katrin; Bunjes, Heike

2018-05-01

Passive drug loading can be used to effectively identify suitable colloidal lipid carrier systems for poorly water-soluble drugs. This method comprises incubation of preformed carrier systems with drug powder and subsequent determination of the resulting drug load of the carrier particles. Until now, the passive loading mechanism is unknown, which complicates reliable routine use. In this work, the influence of drug characteristics on the course of passive loading was investigated systematically varying drug surface area and drug solubility. Fenofibrate and flufenamic acid were used as model drugs; the carrier system was a trimyristin nanodispersion. Loading progress was analyzed by UV spectroscopy or by a novel method based on differential scanning calorimetry. While increasing drug solubility by micelle incorporation did not speed up passive loading, a large drug surface area and high water solubility were key parameters for fast loading. Since both factors are crucial in drug dissolution as described by the Noyes-Whitney equation, these findings point to a dissolution-diffusion-based passive loading mechanism. Accordingly, passive loading also occurred when drug and carrier particles were separated by a dialysis membrane. Knowledge of the loading mechanism allows optimizing the conditions for future passive loading studies and assessing the limitations of the method. Copyright © 2017 Elsevier B.V. All rights reserved.

Evaluating the Relationship between Equilibrium Passive ...

EPA Pesticide Factsheets

This Critcal Review evaluates passive sampler uptake of hydrophobic organic contaminants (HOCs) in water column and interstitial water exposures as a surrogate for organism bioaccumulation. Fifty-seven studies were found where both passive sampler uptake and organism bioaccumulation were measured and 19 of these investigations provided direct comparisons relating passive sampler uptake and organism bioaccumulation. Polymers compared included low-density polyethylene (LDPE), polyoxymethylene (POM), and polydimethylsiloxane (PDMS), and organisms ranged from polychaetes and oligochaetes to bivalves, aquatic insects, and gastropods. Regression equations correlating bioaccumulation (CL) and passive sampler uptake (CPS) were used to assess the strength of observed relationships. Passive sampling based concentrations resulted in log–log predictive relationships, most of which were within one to 2 orders of magnitude of measured bioaccumulation. Mean coefficients of determination (r2) for LDPE, PDMS, and POM were 0.68, 0.76, and 0.58, respectively. For the available raw, untransformed data, the mean ratio of CL and CPS was 10.8 ± 18.4 (n = 609). Using passive sampling as a surrogate for organism bioaccumulation is viable when biomonitoring organisms are not available. Passive sampling based estimates of bioaccumulation provide useful information for making informed decisions about the bioavailability of HOCs. This review evaluates passive sampler uptake of hydrophobi

Focal Plane Array Technology for IR Detectors

DTIC Science & Technology

1996-06-01

samples are determined. Our results on p-(HgCd)Te coated with passivation layers are evident from Figs 3.1 and 3.2. In the first case (native sulphides ...samples are evident from the Table II. We studied influence of (a) atmosphere, (b) ZnS passivation, (c) native sulphides + ZnS passivation. The (HgCd)Te...native sulphides + ZnS, full symbols RH<O, open symbols RH>O. 10 5 6408A3 10- 010o E 102 000 2 days after passivation 10 : 80 days after passivation 0

Non-local transport in turbulent MHD convection

NASA Technical Reports Server (NTRS)

Miesch, Mark; Brandenburg, Axel; Zweibel, Ellen; Toomre, Juri

1995-01-01

The nonlocal non-diffusive transport of passive scalars in turbulent magnetohydrodynamic (MHD) convection is investigated using transilient matrices. These matrices describe the probability that a tracer particle beginning at one position in a flow will be advected to another position after some time. A method for the calculation of these matrices from simulation data which involves following the trajectories of passive tracer particles and calculating their transport statistics, is presented. The method is applied to study the transport in several simulations of turbulent, rotating, three dimensional compressible, penetrative MDH convection. Transport coefficients and other diagnostics are used to quantify the transport, which is found to resemble advection more closely than diffusion. Some of the results are found to have direct relevance to other physical problems, such as the light element depletion in sun-type stars. The large kurtosis found for downward moving particles at the base of the convection zone implies several extreme events.

Diffuse shear wave imaging: toward passive elastography using low-frame rate spectral-domain optical coherence tomography

NASA Astrophysics Data System (ADS)

Nguyen, Thu-Mai; Zorgani, Ali; Lescanne, Maxime; Boccara, Claude; Fink, Mathias; Catheline, Stefan

2016-12-01

Optical coherence tomography (OCT) can map the stiffness of biological tissue by imaging mechanical perturbations (shear waves) propagating in the tissue. Most shear wave elastography (SWE) techniques rely on active shear sources to generate controlled displacements that are tracked at ultrafast imaging rates. Here, we propose a noise-correlation approach to retrieve stiffness information from the imaging of diffuse displacement fields using low-frame rate spectral-domain OCT. We demonstrated the method on tissue-mimicking phantoms and validated the results by comparison with classic ultrafast SWE. Then we investigated the in vivo feasibility on the eye of an anesthetized rat by applying noise correlation to naturally occurring displacements. The results suggest a great potential for passive elastography based on the detection of natural pulsatile motions using conventional spectral-domain OCT systems. This would facilitate the transfer of OCT-elastography to clinical practice, in particular, in ophthalmology or dermatology.

Diffuse shear wave imaging: toward passive elastography using low-frame rate spectral-domain optical coherence tomography.

PubMed

Nguyen, Thu-Mai; Zorgani, Ali; Lescanne, Maxime; Boccara, Claude; Fink, Mathias; Catheline, Stefan

2016-12-01

Optical coherence tomography (OCT) can map the stiffness of biological tissue by imaging mechanical perturbations (shear waves) propagating in the tissue. Most shear wave elastography (SWE) techniques rely on active shear sources to generate controlled displacements that are tracked at ultrafast imaging rates. Here, we propose a noise-correlation approach to retrieve stiffness information from the imaging of diffuse displacement fields using low-frame rate spectral-domain OCT. We demonstrated the method on tissue-mimicking phantoms and validated the results by comparison with classic ultrafast SWE. Then we investigated the in vivo feasibility on the eye of an anesthetized rat by applying noise correlation to naturally occurring displacements. The results suggest a great potential for passive elastography based on the detection of natural pulsatile motions using conventional spectral-domain OCT systems. This would facilitate the transfer of OCT-elastography to clinical practice, in particular, in ophthalmology or dermatology.

Enhanced Organic Solar Cell Stability through the Effective Blocking of Oxygen Diffusion using a Self-Passivating Metal Electrode.

PubMed

Lee, Hansol; Jo, Sae Byeok; Lee, Hyo Chan; Kim, Min; Sin, Dong Hun; Ko, Hyomin; Cho, Kilwon

2016-03-08

A new and simple strategy for enhancing the stability of organic solar cells (OSCs) was developed by using self-passivating metal top electrodes. Systematic investigations on O2 permeability of Al top electrodes revealed that the main pathways for oxidation-induced degradation could be greatly suppressed by simply controlling the nanoscale morphology of the Al electrode. The population of nanoscale pinholes among Al grains, which critically decided the diffusion of O2 molecules toward the Al-organic interfaces that are vulnerable to oxidation, was successfully regulated by rapidly depositing Al or promoting lateral growth among the Al grains, accompanied by increasing the deposition thickness. Our observations suggested that the stability of OSCs with conventional architectures might be greatly enhanced simply by controlling the fabrication conditions of the Al top electrode, without the aid of additional secondary treatments. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Use of a parallel artificial membrane system to evaluate passive absorption and elimination in small fish.

PubMed

Kwon, Jung-Hwan; Katz, Lynn E; Liljestrand, Howard M

2006-12-01

A parallel artificial lipid membrane system was developed to mimic passive mass transfer of hydrophobic organic chemicals in fish. In this physical model system, a membrane filter-supported lipid bilayer separates two aqueous phases that represent the external and internal aqueous environments of fish. To predict bioconcentration kinetics in small fish with this system, literature absorption and elimination rates were analyzed with an allometric diffusion model to quantify the mass transfer resistances in the aqueous and lipid phases of fish. The effect of the aqueous phase mass transfer resistance was controlled by adjusting stirring intensity to mimic bioconcentration rates in small fish. Twenty-three simple aromatic hydrocarbons were chosen as model compounds for purposes of evaluation. For most of the selected chemicals, literature absorption/elimination rates fall into the range predicted from measured membrane permeabilities and elimination rates of the selected chemicals determined by the diffusion model system.

RANS modeling of scalar dispersion from localized sources within a simplified urban-area model

NASA Astrophysics Data System (ADS)

Rossi, Riccardo; Capra, Stefano; Iaccarino, Gianluca

2011-11-01

The dispersion of a passive scalar downstream a localized source within a simplified urban-like geometry is examined by means of RANS scalar flux models. The computations are conducted under conditions of neutral stability and for three different incoming wind directions (0°, 45°, 90°) at a roughness Reynolds number of Ret = 391. A Reynolds stress transport model is used to close the flow governing equations whereas both the standard eddy-diffusivity closure and algebraic flux models are employed to close the transport equation for the passive scalar. The comparison with a DNS database shows improved reliability from algebraic scalar flux models towards predicting both the mean concentration and the plume structure. Since algebraic flux models do not increase substantially the computational effort, the results indicate that the use of tensorial-diffusivity can be promising tool for dispersion simulations for the urban environment.

High-Performance Quantum Dot Thin-Film Transistors with Environmentally Benign Surface Functionalization and Robust Defect Passivation.

PubMed

Jung, Su Min; Kang, Han Lim; Won, Jong Kook; Kim, JaeHyun; Hwang, ChaHwan; Ahn, KyungHan; Chung, In; Ju, Byeong-Kwon; Kim, Myung-Gil; Park, Sung Kyu

2018-01-31

The recent development of high-performance colloidal quantum dot (QD) thin-film transistors (TFTs) has been achieved with removal of surface ligand, defect passivation, and facile electronic doping. Here, we report on high-performance solution-processed CdSe QD-TFTs with an optimized surface functionalization and robust defect passivation via hydrazine-free metal chalcogenide (MCC) ligands. The underlying mechanism of the ligand effects on CdSe QDs has been studied with hydrazine-free ex situ reaction derived MCC ligands, such as Sn 2 S 6 4- , Sn 2 Se 6 4- , and In 2 Se 4 2- , to allow benign solution-process available. Furthermore, the defect passivation and remote n-type doping effects have been investigated by incorporating indium nanoparticles over the QD layer. Strong electronic coupling and solid defect passivation of QDs could be achieved by introducing electronically active MCC capping and thermal diffusion of the indium nanoparticles, respectively. It is also noteworthy that the diffused indium nanoparticles facilitate charge injection not only inter-QDs but also between source/drain electrodes and the QD semiconductors, significantly reducing contact resistance. With benign organic solvents, the Sn 2 S 6 4- , Sn 2 Se 6 4- , and In 2 Se 4 2- ligand based QD-TFTs exhibited field-effect mobilities exceeding 4.8, 12.0, and 44.2 cm 2 /(V s), respectively. The results reported here imply that the incorporation of MCC ligands and appropriate dopants provide a general route to high-performance, extremely stable solution-processed QD-based electronic devices with marginal toxicity, offering compatibility with standard complementary metal oxide semiconductor processing and large-scale on-chip device applications.

Using bioavailability to assess contaminated sediment risk: Passive sampling and Pore Water Remedial Guidelines (PWRGs)

EPA Science Inventory

Hosted by the Contaminated Sediment Forum, this half-day course will introduce the RPM to the use of passive samplers to assess bioavailability and in ecological risk assessment. Passive sampling devices (PSD) are a technology with growing acceptance for measuring porewater conce...

Overview of the US EPA/SERDP/ESTCP: Laboratory, Field ...

EPA Pesticide Factsheets

Passive sampling can be used for applications at contaminated sediment sites including performing assessments of contaminant bioavailability (i.e., freely dissolved concentration (Cfree)), conducting remedial investigations and feasibility studies, and assessing the potential for contaminant bioaccumulation. Previous research articles and documents have discussed many aspects of passive sampling however no definitive guidance on the laboratory, field and analytical procedures for using passive sampling at contaminated sediment sites has been provided. The document discussed in this presentation provides passive sampler users with the guidance necessary to apply the technology to evaluate contaminated sediments. Contaminants discussed include polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and the metals, cadmium, copper, nickel, lead and zinc. The document is divided into sections including discussions of different types of samplers used commonly in the United States, the selection and use of performance reference compounds (PRCs), the extraction and instrumental analysis of passive samplers, data analysis and quality assurance/quality control, and a list of passive sampling related references. The document is not intended to serve as a series of standard operating procedures (SOPs) but rather seeks to provide users with the information needed to develop their own SOPs. The document also includes the names of selected passive sam

Not an 'iron pipeline', but many capillaries: regulating passive transactions in Los Angeles' secondary, illegal gun market.

PubMed

Chesnut, Kelsie Y; Barragan, Melissa; Gravel, Jason; Pifer, Natalie A; Reiter, Keramet; Sherman, Nicole; Tita, George E

2017-08-01

California has strict firearm-related laws and is exceptional in its regulation of firearms retailers. Though evidence suggests that these laws can reduce illegal access to guns, high levels of gun violence persist in Los Angeles (LA), California. This research seeks to describe the sources of guns accessed by active offenders in LA, California and reports offenders' motivations for obtaining guns. Los Angeles County Jail (LACJ) system (four facilities). Random sampling from a screened pool of eligible participants was used to conduct qualitative semistructured interviews with 140 incarcerated gun offenders in one of four (LACJ) facilities. Researchers collected data on firearm acquisition, experiences related to gun violence, and other topics, using a validated survey instrument. Grounded theory guided the collection and analysis of data. Respondents reported possession of 77 specific guns (79.2% handguns) collectively. Social networks facilitate access to illegal guns; the majority of interviewees acquired their illegal guns through a social connection (85.7%) versus an outside broker/unregulated retailer (8.5%). Most guns were obtained through illegal purchase (n=51) or gift (n=15). A quarter of gun purchasers report engaging in a passive transaction, or one initiated by another party. Passive gun buyers were motivated by concerns for personal safety and/or economic opportunity. In LA's illegal gun market, where existing social relationships facilitate access to guns across a diffuse network, individuals, influenced by both fear and economic opportunity, have frequent opportunities to illegally possess firearms through passive transactions. Gun policies should better target and minimise these transactions. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

Modelling passive diastolic mechanics with quantitative MRI of cardiac structure and function.

PubMed

Wang, Vicky Y; Lam, H I; Ennis, Daniel B; Cowan, Brett R; Young, Alistair A; Nash, Martyn P

2009-10-01

The majority of patients with clinically diagnosed heart failure have normal systolic pump function and are commonly categorized as suffering from diastolic heart failure. The left ventricle (LV) remodels its structure and function to adapt to pathophysiological changes in geometry and loading conditions, which in turn can alter the passive ventricular mechanics. In order to better understand passive ventricular mechanics, a LV finite element (FE) model was customized to geometric data segmented from in vivo tagged magnetic resonance images (MRI) data and myofibre orientation derived from ex vivo diffusion tensor MRI (DTMRI) of a canine heart using nonlinear finite element fitting techniques. MRI tissue tagging enables quantitative evaluation of cardiac mechanical function with high spatial and temporal resolution, whilst the direction of maximum water diffusion in each voxel of a DTMRI directly corresponds to the local myocardial fibre orientation. Due to differences in myocardial geometry between in vivo and ex vivo imaging, myofibre orientations were mapped into the geometric FE model using host mesh fitting (a free form deformation technique). Pressure recordings, temporally synchronized to the tagging data, were used as the loading constraints to simulate the LV deformation during diastole. Simulation of diastolic LV mechanics allowed us to estimate the stiffness of the passive LV myocardium based on kinematic data obtained from tagged MRI. Integrated physiological modelling of this kind will allow more insight into mechanics of the LV on an individualized basis, thereby improving our understanding of the underlying structural basis of mechanical dysfunction under pathological conditions.

Hydrogen passivation of titanium impurities in silicon: Effect of doping conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santos, P.; Coutinho, J., E-mail: jose.coutinho@ua.pt; Torres, V. J. B.

2014-07-21

While the contamination of solar silicon by fast diffusing transition metals can be now limited through gettering, much attention has been drawn to the slow diffusing species, especially the early 3d and 4d elements. To some extent, hydrogen passivation has been successful in healing many deep centers, including transition metals in Si. Recent deep-level transient spectroscopy (DLTS) measurements concerning hydrogen passivation of Ti revealed the existence of at least four electrical levels related to Ti{sub i}H{sub n} in the upper-half of the gap. These findings challenge the existing models regarding both the current level assignment as well as the structure/speciesmore » involved in the defects. We revisit this problem by means of density functional calculations and find that progressive hydrogenation of interstitial Ti is thermodynamically stable in intrinsic and n-doped Si. Full passivation may not be possible to attain in p-type Si as Ti{sub i}H{sub 3} and Ti{sub i}H{sub 4} are metastable against dissociation and release of bond-centered protons. All DLTS electron traps are assigned, namely, E40′ to Ti{sub i}H(-/0), E170′ to Ti{sub i}H{sub 3}(0/+), E(270) to Ti{sub i}H{sub 2}(0/+), and E170 to Ti{sub i}H(0/+) transitions. Ti{sub i}H{sub 4} is confirmed to be electrically inert.« less

Comparison of Lichen, Conifer Needles, Passive Air Sampling Devices, and Snowpack as Passive Sampling Media to Measure Semi-Volatile Organic Compounds in Remote Atmospheres

PubMed Central

SCHRLAU, JILL E.; GEISER, LINDA; HAGEMAN, KIMBERLY J.; LANDERS, DIXON H.

2011-01-01

A wide range of semi-volatile organic compounds (SOCs), including pesticides and polycyclic aromatic hydrocarbons (PAHs), were measured in lichen, conifer needles, snowpack and XAD-based passive air sampling devices (PASDs) collected from 19 different U.S. national parks in order to compare the magnitude and mechanism of SOC accumulation in the different passive sampling media. Lichen accumulated the highest SOC concentrations, in part because of its long (and unknown) exposure period, while PASDs accumulated the lowest concentrations. However, only the PASD SOC concentrations can be used to calculate an average atmospheric gas-phase SOC concentration because the sampling rates are known and the media is uniform. Only the lichen and snowpack SOC accumulation profiles were statistically significantly correlated (r = 0.552, p-value <0.0001) because they both accumulate SOCs present in the atmospheric particle-phase. This suggests that needles and PASDs represent a different composition of the atmosphere than lichen and snowpack and that the interpretation of atmospheric SOC composition is dependent on the type of passive sampling media used. All four passive sampling media preferentially accumulated SOCs with relatively low air-water partition coefficients, while snowpack accumulated SOCs with higher log KOA values compared to the other media. Lichen accumulated more SOCs with log KOA > 10 relative to needles and showed a greater accumulation of particle-phase PAHs. PMID:22087860

Market diffusion and the effect of demonstrations: A study of Denver metro passive solar home program

NASA Astrophysics Data System (ADS)

Lilien, G. L.

1981-10-01

The reactions to and effects of the Denver metro passive solar home demonstration program, conducted in the spring of 1981 are reported. The program provides impetus to builders for incorporating passive solar designs in spec built homes and demonstrates those designs to prospective buyers to increase buyer receptivity. A pre-post exposure analysis of the effect of the program is reported and four separate groups of prospective new home buyers are studied. The first group heard publicity about and voluntarily visited a demonstration home. The second group saw the home, but was recruited to come to the side. The third group, also in Denver, did not see the site, but answered the same set of questions after receiving a description of and pictures of passive solar homes. The fourth group was a control group, similar to the third, but located in Kansas City.

Gallium-Doped Poly-Si:Ga/SiO 2 Passivated Emitters to n-Cz Wafers With iV oc >730 mV

DOE PAGES

Young, David L.; Lee, Benjamin G.; Fogel, Derek; ...

2017-09-26

Here, we form gallium-doped poly-Si:Ga/SiO 2 passivated contacts on n-type Czochralski (n-Cz) wafers using ion implantation of Ga and Ga-containing spin-on dopants. After annealing and passivation with Al 2O 3, the contacts exhibit i Voc values of >730 mV with corresponding Joe values of <5 fA/cm 2. These are among the best-reported values for p-type poly-Si/SiO 2 contacts. Secondary ion mass spectroscopic depth profile data show that, in contrast to B, Ga does not pileup at the SiO 2 interface in agreement with its known high diffusivity in SiO 2. This lack of Ga pileup may imply fewer dopant-related defectsmore » in the SiO 2, compared with B dopants, and account for the excellent passivation.« less

Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaunbrecher, Katherine N.; National Renewable Energy Laboratory, Golden, Colorado 80401; Kuciauskas, Darius

Heterostructures with CdTe and CdTe{sub 1-x}Se{sub x} (x ∼ 0.01) absorbers between two wider-band-gap Cd{sub 1-x}Mg{sub x}Te barriers (x ∼ 0.25–0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have amore » zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ∼6 μm, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 μs with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 μs.« less

Coiled to diffuse: Brownian motion of a helical bacterium.

PubMed

Butenko, Alexander V; Mogilko, Emma; Amitai, Lee; Pokroy, Boaz; Sloutskin, Eli

2012-09-11

We employ real-time three-dimensional confocal microscopy to follow the Brownian motion of a fixed helically shaped Leptospira interrogans (LI) bacterium. We extract from our measurements the translational and the rotational diffusion coefficients of this bacterium. A simple theoretical model is suggested, perfectly reproducing the experimental diffusion coefficients, with no tunable parameters. An older theoretical model, where edge effects are neglected, dramatically underestimates the observed rates of translation. Interestingly, the coiling of LI increases its rotational diffusion coefficient by a factor of 5, compared to a (hypothetical) rectified bacterium of the same contour length. Moreover, the translational diffusion coefficients would have decreased by a factor of ~1.5, if LI were rectified. This suggests that the spiral shape of the spirochaete bacteria, in addition to being employed for their active twisting motion, may also increase the ability of these bacteria to explore the surrounding fluid by passive Brownian diffusion.

PASSIVE/DIFFUSIVE SAMPLERS FOR PESTICIDES IN RESIDENTIAL INDOOR AIR

EPA Science Inventory

Pesticides applied indoors vaporize from treated surfaces (e.g., carpets and baseboards) resulting in elevated air concentrations that may persist for long periods after applications. Estimating long-term respiratory exposures to pesticide vapors in residential indoor environme...

Effect of concentration boundary layers on passive solute flows in a system of two polymeric membranes positioned in vertical planes.

PubMed

Slezak, Andrzej; Jasik-Slezak, Jolanta; Dworecki, Kazimierz

2003-01-01

The results of studies of influence of concentration boundary layers on passive diffusive transport in a double-membrane osmo-diffusive cell, containing a series of two (Ml and M(r)) vertically positioned, flat, microporous and symmetric polymer membranes (Nephrophane and Cellulose IMP-1) are presented in this paper. The membranes separated three compartments (l, m, r) containing binary, heterogeneous and non-ionic solutions (aqueous solutions of glucose or ethanol) or ternary non-electrolyte solutions (glucose solutions in 0.75 mol.l-1 solution of ethanol or ethanol solutions in 0.1 mol.l-1 aqueous solution of glucose). Solution concentrations fulfilled the condition C(k)l > C(k)m > C(k)r. The intermembrane compartment (m) was an infinitesimal solution layer. The volume of the m compartment and the volumes of the external (l and r) compartments fulfilled the condition Vl = Vr approximately 170 Vm. The tests were performed for configurations A and B of a double-membrane osmo-diffusive cell. In configuration A, the solution was located behind the M(r) membrane, and water was placed behind the Ml membrane, while in configuration B this sequence was reversed. The results obtained during experiment were interpreted in the categories of convective instability, which increased the value of diffusive permeability coefficient of the system: concentration boundary layer/membrane/concentration boundary layer.

Application of passive sampling for measuring dissolved concentrations of organic contaminants in the water column at three marine superfund sites.

PubMed

Burgess, Robert M; Lohmann, Rainer; Schubauer-Berigan, Joseph P; Reitsma, Pamela; Perron, Monique M; Lefkovitz, Lisa; Cantwell, Mark G

2015-08-01

Currently, there is an effort under way to encourage remedial project managers at contaminated sites to use passive sampling to collect freely dissolved concentrations (Cfree ) of hydrophobic organic contaminants to improve site assessments. The objective of the present study was to evaluate the use of passive sampling for measuring water column Cfree for several hydrophobic organic contaminants at 3 US Environmental Protection Agency Superfund sites. Sites investigated included New Bedford Harbor (New Bedford, MA, USA), Palos Verdes Shelf (Los Angeles, CA, USA), and Naval Station Newport (Newport, RI, USA); and the passive samplers evaluated were polyethylene, polydimethylsiloxane-coated solid-phase microextraction fibers, semipermeable membrane devices, and polyoxymethylene. In general, the different passive samplers demonstrated good agreement, with Cfree values varying by a factor of 2 to 3. Further, at New Bedford Harbor, where conventional water sample concentrations were also measured (i.e., grab samples), passive sampler-based Cfree values agreed within a factor of 2. These findings suggest that all of the samplers were experiencing and measuring similar Cfree during their respective deployments. Also, at New Bedford Harbor, a strong log-linear, correlative, and predictive relationship was found between polyethylene passive sampler accumulation and lipid-normalized blue mussel bioaccumulation of polychlorinated biphenyls (r(2)  = 0.92, p < 0.05). The present study demonstrates the utility of passive sampling for generating scientifically accurate water column Cfree values, which is critical for making informed environmental management decisions at contaminated sediment sites. Published 2015 SETAC. This article is a US Government work and is in the public domain in the USA.

Ammonia excretion and urea handling by fish gills: present understanding and future research challenges.

PubMed

Wilkie, Michael Patrick

2002-08-01

In fresh water fishes, ammonia is excreted across the branchial epithelium via passive NH(3) diffusion. This NH(3) is subsequently trapped as NH(4)(+) in an acidic unstirred boundary layer lying next to the gill, which maintains the blood-to-gill water NH(3) partial pressure gradient. Whole animal, in situ, ultrastructural and molecular approaches suggest that boundary layer acidification results from the hydration of CO(2) in the expired gill water, and to a lesser extent H(+) excretion mediated by apical H(+)-ATPases. Boundary layer acidification is insignificant in highly buffered sea water, where ammonia excretion proceeds via NH(3) diffusion, as well as passive NH(4)(+) diffusion due to the greater ionic permeability of marine fish gills. Although Na(+)/H(+) exchangers (NHE) have been isolated in marine fish gills, possible Na(+)/NH(4)(+) exchange via these proteins awaits evaluation using modern electrophysiological and molecular techniques. Although urea excretion (J(Urea)) was thought to be via passive diffusion, it is now clear that branchial urea handling requires specialized urea transporters. Four urea transporters have been cloned in fishes, including the shark kidney urea transporter (shUT), which is a facilitated urea transporter similar to the mammalian renal UT-A2 transporter. Another urea transporter, characterized but not yet cloned, is the basolateral, Na(+) dependent urea antiporter of the dogfish gill, which is essential for urea retention in ureosmotic elasmobranchs. In ureotelic teleosts such as the Lake Magadi tilapia and the gulf toadfish, the cloned mtUT and tUT are facilitated urea transporters involved in J(Urea). A basolateral urea transporter recently cloned from the gill of the Japanese eel (eUT) may actually be important for urea retention during salt water acclimation. A multi-faceted approach, incorporating whole animal, histological, biochemical, pharmacological, and molecular techniques is required to learn more about the location, mechanism of action, and functional significance of urea transporters in fishes. Copyright 2002 Wiley-Liss, Inc.

Generation and precise control of dynamic biochemical gradients for cellular assays

NASA Astrophysics Data System (ADS)

Saka, Yasushi; MacPherson, Murray; Giuraniuc, Claudiu V.

2017-03-01

Spatial gradients of diffusible signalling molecules play crucial roles in controlling diverse cellular behaviour such as cell differentiation, tissue patterning and chemotaxis. In this paper, we report the design and testing of a microfluidic device for diffusion-based gradient generation for cellular assays. A unique channel design of the device eliminates cross-flow between the source and sink channels, thereby stabilizing gradients by passive diffusion. The platform also enables quick and flexible control of chemical concentration that makes highly dynamic gradients in diffusion chambers. A model with the first approximation of diffusion and surface adsorption of molecules recapitulates the experimentally observed gradients. Budding yeast cells cultured in a gradient of a chemical inducer expressed a reporter fluorescence protein in a concentration-dependent manner. This microfluidic platform serves as a versatile prototype applicable to a broad range of biomedical investigations.

Renormalization group analysis of anisotropic diffusion in turbulent shear flows

NASA Technical Reports Server (NTRS)

Rubinstein, Robert; Barton, J. Michael

1991-01-01

The renormalization group is applied to compute anisotropic corrections to the scalar eddy diffusivity representation of turbulent diffusion of a passive scalar. The corrections are linear in the mean velocity gradients. All model constants are computed theoretically. A form of the theory valid at arbitrary Reynolds number is derived. The theory applies only when convection of the velocity-scalar correlation can be neglected. A ratio of diffusivity components, found experimentally to have a nearly constant value in a variety of shear flows, is computed theoretically for flows in a certain state of equilibrium. The theoretical value is well within the fairly narrow range of experimentally observed values. Theoretical predictions of this diffusivity ratio are also compared with data from experiments and direct numerical simulations of homogeneous shear flows with constant velocity and scalar gradients.

Evaluating the Relationship between Equilibrium Passive ...

EPA Pesticide Factsheets

This review evaluates passive sampler uptake of hydrophobic organic contaminants (HOCs) in water column and interstitial water exposures as a surrogate for organism bioaccumulation. Fifty-four studies were found where both passive sampler uptake and organism bioaccumulation were measured and 19 of these investigations provided direct comparisons relating passive sampler uptake and organism bioaccumulation. Polymers compared included low density polyethylene (LDPE), polyoxymethylene (POM), and polydimethylsiloxane (PDMS), and organisms ranged from polychaetes and oligochaetes to bivalves, aquatic insects, and gastropods. Regression equations correlating bioaccumulation (CL) and passive sampler uptake (CPS) were used to assess the strength of observed relationships. Passive sampling based concentrations resulted in logarithmic predictive relationships, most of which were within one to two orders of magnitude of measured bioaccumulation. Mean coefficients of determination (r2) for LDPE, PDMS and POM were 0.68, 0.76 and 0.58, respectively. For the available raw data, the mean ratio of CL and CPS was 10.8 ± 18.4 (n = 609). This review concludes that in many applications passive sampling may serve as a reliable surrogate for biomonitoring organisms when biomonitoring organisms are not available. When applied properly, passive sampling based estimates of bioaccumulation provide useful information for making informed decisions about the bioavailability of HOCs

Investigating axial diffusion in cylindrical pores using confocal single-particle fluorescence correlation spectroscopy.

PubMed

Chen, Fang; Neupane, Bhanu; Li, Peiyuan; Su, Wei; Wang, Gufeng

2016-08-01

We explored the feasibility of using confocal fluorescence correlation spectroscopy to study small nanoparticle diffusion in hundred-nanometer-sized cylindrical pores. By modeling single particle diffusion in tube-like confined three-dimensional space aligned parallel to the confocal optical axis, we showed that two diffusion dynamics can be observed in both original intensity traces and the autocorrelation functions (ACFs): the confined two-dimensional lateral diffusion and the unconfined one-dimensional (1D) axial diffusion. The separation of the axial and confined lateral diffusion dynamics provides an opportunity to study diffusions in different dimensions separately. We further experimentally studied 45 nm carboxylated polystyrene particles diffusing in 300 nm alumina pores. The experimental data showed consistency with the simulation. To extract the accurate axial diffusion coefficient, we found that a 1D diffusion model with a Lorentzian axial collection profile needs to be used to analyze the experimental ACFs. The diffusion of the 45 nm nanoparticles in polyethyleneglycol-passivated 300 nm pores slowed down by a factor of ∼2, which can be satisfactorily explained by hydrodynamic frictions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Passive Diffusion as a Mechanism Underlying Ribbon Synapse Vesicle Release and Resupply

PubMed Central

Graydon, Cole W.; Zhang, Jun; Oesch, Nicholas W.; Sousa, Alioscka A.; Leapman, Richard D.

2014-01-01

Synaptic ribbons are presynaptic protein structures found at many synapses that convey graded, “analog” sensory signals in the visual, auditory, and vestibular pathways. Ribbons, typically anchored to the presynaptic membrane and surrounded by tethered synaptic vesicles, are thought to regulate or facilitate vesicle delivery to the presynaptic membrane. No direct evidence exists, however, to indicate how vesicles interact with the ribbon or, once attached, move along the ribbon's surface to reach the presynaptic release sites at its base. To address these questions, we have created, validated, and tested a passive vesicle diffusion model of retinal rod bipolar cell ribbon synapses. We used axial (bright-field) electron tomography in the scanning transmission electron microscopy to obtain 3D structures of rat rod bipolar cell terminals in 1-μm-thick sections of retinal tissue at an isotropic spatial resolution of ∼3 nm. The resulting structures were then incorporated with previously published estimates of vesicle diffusion dynamics into numerical simulations that accurately reproduced electrophysiologically measured vesicle release/replenishment rates and vesicle pool sizes. The simulations suggest that, under physiologically realistic conditions, diffusion of vesicles crowded on the ribbon surface gives rise to a flow field that enhances delivery of vesicles to the presynaptic membrane without requiring an active transport mechanism. Numerical simulations of ribbon–vesicle interactions predict that transient binding and unbinding of multiple tethers to each synaptic vesicle may achieve sufficiently tight association of vesicles to the ribbon while permitting the fast diffusion along the ribbon that is required to sustain high release rates. PMID:24990916

Passive diffusion as a mechanism underlying ribbon synapse vesicle release and resupply.

PubMed

Graydon, Cole W; Zhang, Jun; Oesch, Nicholas W; Sousa, Alioscka A; Leapman, Richard D; Diamond, Jeffrey S

2014-07-02

Synaptic ribbons are presynaptic protein structures found at many synapses that convey graded, "analog" sensory signals in the visual, auditory, and vestibular pathways. Ribbons, typically anchored to the presynaptic membrane and surrounded by tethered synaptic vesicles, are thought to regulate or facilitate vesicle delivery to the presynaptic membrane. No direct evidence exists, however, to indicate how vesicles interact with the ribbon or, once attached, move along the ribbon's surface to reach the presynaptic release sites at its base. To address these questions, we have created, validated, and tested a passive vesicle diffusion model of retinal rod bipolar cell ribbon synapses. We used axial (bright-field) electron tomography in the scanning transmission electron microscopy to obtain 3D structures of rat rod bipolar cell terminals in 1-μm-thick sections of retinal tissue at an isotropic spatial resolution of ∼3 nm. The resulting structures were then incorporated with previously published estimates of vesicle diffusion dynamics into numerical simulations that accurately reproduced electrophysiologically measured vesicle release/replenishment rates and vesicle pool sizes. The simulations suggest that, under physiologically realistic conditions, diffusion of vesicles crowded on the ribbon surface gives rise to a flow field that enhances delivery of vesicles to the presynaptic membrane without requiring an active transport mechanism. Numerical simulations of ribbon-vesicle interactions predict that transient binding and unbinding of multiple tethers to each synaptic vesicle may achieve sufficiently tight association of vesicles to the ribbon while permitting the fast diffusion along the ribbon that is required to sustain high release rates. Copyright © 2014 the authors 0270-6474/14/348948-15$15.00/0.

Colloidal transport through trap arrays controlled by active microswimmers

NASA Astrophysics Data System (ADS)

Yang, Wen; Misko, Vyacheslav R.; Marchesoni, Fabio; Nori, Franco

2018-07-01

We investigate the dynamics of a binary mixture consisting of active and passive colloidal particles diffusing in a 2D array of truncated harmonic wells, or traps. We explore the possibility of using a small fraction of active particles to manipulate a much larger fraction of passive particles, for instance, to confine them in or extract them from the traps. The results of our study have potential application in biology and medical sciences, for example, to remove dead cells or undesired contaminants from biological systems by means of self-propelled nano-robots.

Confocal imaging to quantify passive transport across biomimetic lipid membranes.

PubMed

Li, Su; Hu, Peichi; Malmstadt, Noah

2010-09-15

The ability of a molecule to pass through the plasma membrane without the aid of any active cellular mechanisms is central to that molecule's pharmaceutical characteristics. Passive transport has been understood in the context of Overton's rule, which states that more lipophilic molecules cross membrane lipid bilayers more readily. Existing techniques for measuring passive transport lack reproducibility and are hampered by the presence of an unstirred layer (USL) that dominates transport across the bilayer. This report describes assays based on spinning-disk confocal microscopy (SDCM) of giant unilamellar vesicles (GUVs) that allow for the detailed investigation of passive transport processes and mechanisms. This approach allows the concentration field to be directly observed, allowing membrane permeability to be determined easily from the transient concentration profile data. A series of molecules of increasing hydrophilicity was constructed, and the transport of these molecules into GUVs was observed. The observed permeability trend is consistent with Overton's rule. However, the values measured depart from the simple partition-diffusion proportionality model of passive transport. This technique is easy to implement and has great promise as an approach to measure membrane transport. It is optimally suited to precise quantitative measurements of the dependence of passive transport on membrane properties.

Mesoscale Elucidation of Surface Passivation in the Li–Sulfur Battery Cathode

DOE PAGES

Liu, Zhixiao; Mukherjee, Partha P.

2017-01-23

We report the cathode surface passivation caused by Li 2S precipitation adversely affects the performance of lithium-sulfur (Li-S) batteries. Li 2S precipitation is a complicated mesoscale process involving adsorption, desorption and diffusion kinetics, which are affected profoundly by the reactant concentration and operating temperature. In this work, a mesoscale interfacial model is presented to study the growth of Li 2S film on carbon cathode surface. Li 2S film growth experiences nucleation, isolated Li 2S island growth and island coalescence. The slow adsorption rate at small S 2- concentration inhibits the formation of nucleation seeds and the lateral growth of Limore » 2S islands, which deters surface passivation. An appropriate operating temperature, especially in the medium-to-high temperature range, can also defer surface passivation. Fewer Li 2S nucleation seeds form in such an operating temperature range, which facilitates heterogeneous growth and thereby inhibits the lateral growth of the Li 2S film, which may also result in reduced surface passivation. Finally, the high specific surface area of the cathode microstructure is expected to mitigate the surface passivation.« less

Quantitative passive soil vapor sampling for VOCs--Part 4: Flow-through cell.

PubMed

McAlary, Todd; Groenevelt, Hester; Seethapathy, Suresh; Sacco, Paolo; Crump, Derrick; Tuday, Michael; Schumacher, Brian; Hayes, Heidi; Johnson, Paul; Parker, Louise; Górecki, Tadeusz

2014-05-01

This paper presents a controlled experiment comparing several quantitative passive samplers for monitoring concentrations of volatile organic compound (VOC) vapors in soil gas using a flow-through cell. This application is simpler than conventional active sampling using adsorptive tubes because the flow rate does not need to be precisely measured and controlled, which is advantageous because the permeability of subsurface materials affects the flow rate and the permeability of geologic materials is highly variable. Using passive samplers in a flow-through cell, the flow rate may not need to be known exactly, as long as it is sufficient to purge the cell in a reasonable time and minimize any negative bias attributable to the starvation effect. An experiment was performed in a 500 mL flow-through cell using a two-factor, one-half fraction fractional factorial test design with flow rates of 80, 670 and 930 mL min(-1) and sample durations of 10, 15 and 20 minutes for each of five different passive samplers (passive Automatic Thermal Desorption Tube, Radiello®, SKC Ultra, Waterloo Membrane Sampler™ and 3M™ OVM 3500). A Summa canister was collected coincident with each passive sampler and analyzed by EPA Method TO-15 to provide a baseline for comparison of the passive sampler concentrations. The passive sampler concentrations were within a factor of 2 of the Summa canister concentrations in 32 of 35 cases. Passive samples collected at the low flow rate and short duration showed low concentrations, which is likely attributable to insufficient purging of the cell after sampler placement.

Comparison of sampling methodologies for nutrient monitoring in streams: uncertainties, costs and implications for mitigation

NASA Astrophysics Data System (ADS)

Audet, J.; Martinsen, L.; Hasler, B.; de Jonge, H.; Karydi, E.; Ovesen, N. B.; Kronvang, B.

2014-07-01

Eutrophication of aquatic ecosystems caused by excess concentrations of nitrogen and phosphorus may have harmful consequences for biodiversity and poses a health risk to humans via the water supplies. Reduction of nitrogen and phosphorus losses to aquatic ecosystems involves implementation of costly measures, and reliable monitoring methods are therefore essential to select appropriate mitigation strategies and to evaluate their effects. Here, we compare the performances and costs of three methodologies for the monitoring of nutrients in rivers: grab sampling, time-proportional sampling and passive sampling using flow proportional samplers. Assuming time-proportional sampling to be the best estimate of the "true" nutrient load, our results showed that the risk of obtaining wrong total nutrient load estimates by passive samplers is high despite similar costs as the time-proportional sampling. Our conclusion is that for passive samplers to provide a reliable monitoring alternative, further development is needed. Grab sampling was the cheapest of the three methods and was more precise and accurate than passive sampling. We conclude that although monitoring employing time-proportional sampling is costly, its reliability precludes unnecessarily high implementation expenses.

Comparison of sampling methodologies for nutrient monitoring in streams: uncertainties, costs and implications for mitigation

NASA Astrophysics Data System (ADS)

Audet, J.; Martinsen, L.; Hasler, B.; de Jonge, H.; Karydi, E.; Ovesen, N. B.; Kronvang, B.

2014-11-01

Eutrophication of aquatic ecosystems caused by excess concentrations of nitrogen and phosphorus may have harmful consequences for biodiversity and poses a health risk to humans via water supplies. Reduction of nitrogen and phosphorus losses to aquatic ecosystems involves implementation of costly measures, and reliable monitoring methods are therefore essential to select appropriate mitigation strategies and to evaluate their effects. Here, we compare the performances and costs of three methodologies for the monitoring of nutrients in rivers: grab sampling; time-proportional sampling; and passive sampling using flow-proportional samplers. Assuming hourly time-proportional sampling to be the best estimate of the "true" nutrient load, our results showed that the risk of obtaining wrong total nutrient load estimates by passive samplers is high despite similar costs as the time-proportional sampling. Our conclusion is that for passive samplers to provide a reliable monitoring alternative, further development is needed. Grab sampling was the cheapest of the three methods and was more precise and accurate than passive sampling. We conclude that although monitoring employing time-proportional sampling is costly, its reliability precludes unnecessarily high implementation expenses.

Determination of silicone rubber and low-density polyethylene diffusion and polymer/water partition coefficients for emerging contaminants.

PubMed

Pintado-Herrera, Marina G; Lara-Martín, Pablo A; González-Mazo, Eduardo; Allan, Ian J

2016-09-01

There is a growing interest in assessing the concentration and distribution of new nonregulated organic compounds (emerging contaminants) in the environment. The measurement of freely dissolved concentrations using conventional approaches is challenging because of the low concentrations that may be encountered and their temporally variable emissions. Absorption-based passive sampling enables the estimation of freely dissolved concentrations of hydrophobic contaminants of emerging concern in water. In the present study, calibration was undertaken for 2 polymers, low-density polyethylene (LDPE) and silicone rubber for 11 fragrances, 5 endocrine-disrupting compounds, 7 ultraviolet (UV) filters, and 8 organophosphate flame retardant compounds. Batch experiments were performed to estimate contaminant diffusion coefficients in the polymers (Dp ), which in general decreased with increasing molecular weight. The values for fragrances, endocrine-disrupting compounds, and UV filters were in ranges similar to those previously reported for polycyclic aromatic hydrocarbons, but were 1 order of magnitude lower for organophosphate flame retardant compounds. Silicone rubber had higher Dp values than LDPE and was therefore selected for further experiments to calculate polymer/water partition coefficients (KPW ). The authors observed a positive correlation between log KPW and log octanol/water partition coefficient values. Field testing of silicone rubber passive samplers was undertaken though exposure in the River Alna (Norway) for an exposure time of 21 d to estimate freely dissolved concentration. Some fragrances and UV filters were predominant over other emerging and regulated contaminants, at levels up to 1600 ng L(-1) for galaxolide and 448 ng L(-1) for octocrylene. Environ Toxicol Chem 2016;35:2162-2172. © 2016 SETAC. © 2016 SETAC.

Active and passive transport of cargo in a corrugated channel: A lattice model study

NASA Astrophysics Data System (ADS)

Dey, Supravat; Ching, Kevin; Das, Moumita

2018-04-01

Inside cells, cargos such as vesicles and organelles are transported by molecular motors to their correct locations via active motion on cytoskeletal tracks and passive, Brownian diffusion. During the transportation of cargos, motor-cargo complexes (MCCs) navigate the confining and crowded environment of the cytoskeletal network and other macromolecules. Motivated by this, we study a minimal two-state model of motor-driven cargo transport in confinement and predict transport properties that can be tested in experiments. We assume that the motion of the MCC is directly affected by the entropic barrier due to confinement if it is in the passive, unbound state but not in the active, bound state where it moves with a constant bound velocity. We construct a lattice model based on a Fokker Planck description of the two-state system, study it using a kinetic Monte Carlo method and compare our numerical results with analytical expressions for a mean field limit. We find that the effect of confinement strongly depends on the bound velocity and the binding kinetics of the MCC. Confinement effectively reduces the effective diffusivity and average velocity, except when it results in an enhanced average binding rate and thereby leads to a larger average velocity than when unconfined.

Slow positron studies of hydrogen activation/passivation on SiO2/Si(100) interfaces

NASA Astrophysics Data System (ADS)

Lynn, K. G.; Asoka-Kumar, P.

The hydrogen atoms are one of the most common impurity species found in semiconductor systems owing to its large diffusivity, and are easily incorporated either in a controlled process like in ion implantation or in an uncontrolled process like the one at the fabrication stage. Hydrogen can passivate dangling bonds and dislocations in these systems and hence can be used to enhance the electrical properties. In a SiO2/Si system, hydrogen can passivate electronic states at the interface and can alter the fixed or mobile charges in the oxide layer. Since hydrogen is present in almost all of the environments of SiO2/Si wafer fabrication, the activation energy of hydrogen atoms is of paramount importance to a proper understanding of SiO2/Si based devices and has not been measured on the technologically most important Si(100) face. There are no direct, nondestructive methods available to observe hydrogen injection into the oxide layer and subsequent diffusion. The positrons are used as a 'sensitive', nondestructive probe to observe hydrogen interaction in the oxide layer and the interface region. A new way is described of characterizing the changes in the density of the interface states under a low temperature annealing using positrons.

Uncertainties in monitoring of SVOCs in air caused by within-sampler degradation during active and passive air sampling

NASA Astrophysics Data System (ADS)

Melymuk, Lisa; Bohlin-Nizzetto, Pernilla; Prokeš, Roman; Kukučka, Petr; Přibylová, Petra; Vojta, Šimon; Kohoutek, Jiří; Lammel, Gerhard; Klánová, Jana

2017-10-01

Degradation of semivolatile organic compounds (SVOCs) occurs naturally in ambient air due to reactions with reactive trace gases (e.g., ozone, NOx). During air sampling there is also the possibility for degradation of SVOCs within the air sampler, leading to underestimates of ambient air concentrations. We investigated the possibility of this sampling artifact in commonly used active and passive air samplers for seven classes of SVOCs, including persistent organic pollutants (POPs) typically covered by air monitoring programs, as well as SVOCs of emerging concern. Two active air samplers were used, one equipped with an ozone denuder and one without, to compare relative differences in mass of collected compounds. Two sets of passive samplers were also deployed to determine the influence of degradation during longer deployment times in passive sampling. In active air samplers, comparison of the two sampling configurations suggested degradation of particle-bound polycyclic aromatic hydrocarbons (PAHs), with concentrations up to 2× higher in the denuder-equipped sampler, while halogenated POPs did not have clear evidence of degradation. In contrast, more polar, reactive compounds (e.g., organophosphate esters and current use pesticides) had evidence of losses in the sampler with denuder. This may be caused by the denuder itself, suggesting sampling bias for these compounds can be created when typical air sampling apparatuses are adapted to limit degradation. Passive air samplers recorded up to 4× higher concentrations when deployed for shorter consecutive sampling periods, suggesting that within-sampler degradation may also be relevant in passive air monitoring programs.

A simple linear model for estimating ozone AOT40 at forest sites from raw passive sampling data.

PubMed

Ferretti, Marco; Cristofolini, Fabiana; Cristofori, Antonella; Gerosa, Giacomo; Gottardini, Elena

2012-08-01

A rapid, empirical method is described for estimating weekly AOT40 from ozone concentrations measured with passive samplers at forest sites. The method is based on linear regression and was developed after three years of measurements in Trentino (northern Italy). It was tested against an independent set of data from passive sampler sites across Italy. It provides good weekly estimates compared with those measured by conventional monitors (0.85 ≤R(2)≤ 0.970; 97 ≤ RMSE ≤ 302). Estimates obtained using passive sampling at forest sites are comparable to those obtained by another estimation method based on modelling hourly concentrations (R(2) = 0.94; 131 ≤ RMSE ≤ 351). Regression coefficients of passive sampling are similar to those obtained with conventional monitors at forest sites. Testing against an independent dataset generated by passive sampling provided similar results (0.86 ≤R(2)≤ 0.99; 65 ≤ RMSE ≤ 478). Errors tend to accumulate when weekly AOT40 estimates are summed to obtain the total AOT40 over the May-July period, and the median deviation between the two estimation methods based on passive sampling is 11%. The method proposed does not require any assumptions, complex calculation or modelling technique, and can be useful when other estimation methods are not feasible, either in principle or in practice. However, the method is not useful when estimates of hourly concentrations are of interest.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Zhixiao; Mukherjee, Partha P.

We report the cathode surface passivation caused by Li 2S precipitation adversely affects the performance of lithium-sulfur (Li-S) batteries. Li 2S precipitation is a complicated mesoscale process involving adsorption, desorption and diffusion kinetics, which are affected profoundly by the reactant concentration and operating temperature. In this work, a mesoscale interfacial model is presented to study the growth of Li 2S film on carbon cathode surface. Li 2S film growth experiences nucleation, isolated Li 2S island growth and island coalescence. The slow adsorption rate at small S 2- concentration inhibits the formation of nucleation seeds and the lateral growth of Limore » 2S islands, which deters surface passivation. An appropriate operating temperature, especially in the medium-to-high temperature range, can also defer surface passivation. Fewer Li 2S nucleation seeds form in such an operating temperature range, which facilitates heterogeneous growth and thereby inhibits the lateral growth of the Li 2S film, which may also result in reduced surface passivation. Finally, the high specific surface area of the cathode microstructure is expected to mitigate the surface passivation.« less

Optimized ultra-thin manganin alloy passivated fine-pitch damascene compatible bump-less Cu-Cu bonding at sub 200 °C for three-dimensional Integration applications

NASA Astrophysics Data System (ADS)

Panigrahi, Asisa Kumar; Hemanth Kumar, C.; Bonam, Satish; Ghosh, Tamal; Rama Krishna Vanjari, Siva; Govind Singh, Shiv

2018-02-01

Enhanced Cu diffusion, Cu surface passivation, and smooth surface at the bonding interface are the key essentials for high quality Cu-Cu bonding. Previously, we have demonstrated optimized 3 nm thin Manganin metal-alloy passivation from oxidation and also helps to reduce the surface roughness to about 0.8 nm which substantially led to high quality Cu-Cu bonding. In this paper, we demonstrated an ultra fine-pitch (<25 µm) Cu-Cu bonding using an optimized Manganin metal-alloy passivation. This engineered surface passivation approach led to high quality bonding at sub 200 °C temperature and 0.4 MPa. Very low specific contact resistance of 1.4 × 10-7 Ω cm2 and the defect free bonded interface is clear indication of high quality bonding for future multilayer integrations. Furthermore, electrical characterization of the bonded structure was performed under various robust conditions as per International Technology Roadmap for Semiconductors (ITRS Roadmap) in order to satisfy the stability of the bonded structure.

Headspace needle-trap analysis of priority volatile organic compounds from aqueous samples: application to the analysis of natural and waste waters.

PubMed

Alonso, Monica; Cerdan, Laura; Godayol, Anna; Anticó, Enriqueta; Sanchez, Juan M

2011-11-11

Combining headspace (HS) sampling with a needle-trap device (NTD) to determine priority volatile organic compounds (VOCs) in water samples results in improved sensitivity and efficiency when compared to conventional static HS sampling. A 22 gauge stainless steel, 51-mm needle packed with Tenax TA and Carboxen 1000 particles is used as the NTD. Three different HS-NTD sampling methodologies are evaluated and all give limits of detection for the target VOCs in the ng L⁻¹ range. Active (purge-and-trap) HS-NTD sampling is found to give the best sensitivity but requires exhaustive control of the sampling conditions. The use of the NTD to collect the headspace gas sample results in a combined adsorption/desorption mechanism. The testing of different temperatures for the HS thermostating reveals a greater desorption effect when the sample is allowed to diffuse, whether passively or actively, through the sorbent particles. The limits of detection obtained in the simplest sampling methodology, static HS-NTD (5 mL aqueous sample in 20 mL HS vials, thermostating at 50 °C for 30 min with agitation), are sufficiently low as to permit its application to the analysis of 18 priority VOCs in natural and waste waters. In all cases compounds were detected below regulated levels. Copyright © 2011 Elsevier B.V. All rights reserved.

FIELD METHOD COMPARISON BETWEEN PASSIVE AIR SAMPLERS AND CONTINUOUS MONITORS FOR VOLATILE ORGANIC COMPOUNDS AND NO2 IN EL PASO, TEXAS, USA

EPA Science Inventory

Passive sampling of gas-phase air toxics and criteria pollutants has become an attractive monitoring method in human exposure studies due to the relatively low sampling cost and ease of use. This study evaluates the performance of Model 3300 Ogawa(TM) Passive NO2 Samplers and 3...

NHEXAS PHASE I ARIZONA STUDY--STANDARD OPERATING PROCEDURE FOR COLLECTION OF FIXED SITE INDOOR AND OUTDOOR FORMALDEHYDE PASSIVE SAMPLES (UA-F-13.1)

EPA Science Inventory

The purpose of this SOP is to describe the methods used to sample residential indoor and outdoor atmospheres for the presence of formaldehyde using the PF-1 passive formaldehyde sampler. The PF-1 passive sampler is used as a fixed location monitor to determine time integrated ex...

Noncontact true temperature measurement, 2

NASA Technical Reports Server (NTRS)

Lee, Mark C.; Allen, James L.

1988-01-01

A laser pyrometer was developed for acquiring the true temperature of a levitated sample. The reflectivity is measured by first expanding the laser beam to cover the entire cross-sectional surface of the diffuse target. The reflectivity calibration of this system is determined from the surface emissivity of a target with a blackbody cavity. The emissivity of the real target can then be calculated. The overall system constant is obtained by passively measuring the radiance of the blackbody cavity (emissivity = 1.0) at a known, arbitrary temperature. Since the photosensor used is highly linear over the entire operating temperature range, the true temperature of the target can then be computed. The latest results available from this on-going research indicate that true temperatures thus obtained are in very good quantitative agreement with thermocouple measured temperatures.

Whole-body tissue stabilization and selective extractions via tissue-hydrogel hybrids for high-resolution intact circuit mapping and phenotyping

PubMed Central

Treweek, Jennifer B; Deverman, Benjamin E; Greenbaum, Alon; Lignell, Antti; Xiao, Cheng; Cai, Long; Ladinsky, Mark S; Bjorkman, Pamela J; Fowlkes, Charless C; Gradinaru, Viviana

2016-01-01

To facilitate fine-scale phenotyping of whole specimens, we describe here a set of tissue fixation-embedding, detergent-clearing and staining protocols that can be used to transform excised organs and whole organisms into optically transparent samples within 1–2 weeks without compromising their cellular architecture or endogenous fluorescence. PACT (passive CLARITY technique) and PARS (perfusion-assisted agent release in situ) use tissue-hydrogel hybrids to stabilize tissue biomolecules during selective lipid extraction, resulting in enhanced clearing efficiency and sample integrity. Furthermore, the macromolecule permeability of PACT- and PARS-processed tissue hybrids supports the diffusion of immunolabels throughout intact tissue, whereas RIMS (refractive index matching solution) grants high-resolution imaging at depth by further reducing light scattering in cleared and uncleared samples alike. These methods are adaptable to difficult-to-image tissues, such as bone (PACT-deCAL), and to magnified single-cell visualization (ePACT). Together, these protocols and solutions enable phenotyping of subcellular components and tracing cellular connectivity in intact biological networks. PMID:26492141

Modified Perfluorocarbon Tracer Method for Measuring Effective Multizone Air Exchange Rates

PubMed Central

Shinohara, Naohide; Kataoka, Toshiyuki; Takamine, Koichi; Butsugan, Michio; Nishijima, Hirokazu; Gamo, Masashi

2010-01-01

A modified procedure was developed for the measurement of the effective air exchange rate, which represents the relationship between the pollutants emitted from indoor sources and the residents’ level of exposure, by placing the dosers of tracer gas at locations that resemble indoor emission sources. To measure the 24-h-average effective air exchange rates in future surveys based on this procedure, a low-cost, easy-to-use perfluorocarbon tracer (PFT) doser with a stable dosing rate was developed by using double glass vials, a needle, a polyethylene-sintered filter, and a diffusion tube. Carbon molecular sieve cartridges and carbon disulfide (CS2) were used for passive sampling and extraction of the tracer gas, respectively. Recovery efficiencies, sampling rates, and lower detection limits for 24-h sampling of hexafluorobenzene, octafluorotoluene, and perfluoroallylbenzene were 40% ± 3%, 72% ± 5%, and 84% ± 6%; 10.5 ± 1.1, 14.4 ± 1.4, and 12.2 ± 0.49 mL min−1; and 0.20, 0.17, and 0.26 μg m−3, respectively. PMID:20948928

Modified perfluorocarbon tracer method for measuring effective multizone air exchange rates.

PubMed

Shinohara, Naohide; Kataoka, Toshiyuki; Takamine, Koichi; Butsugan, Michio; Nishijima, Hirokazu; Gamo, Masashi

2010-09-01

A modified procedure was developed for the measurement of the effective air exchange rate, which represents the relationship between the pollutants emitted from indoor sources and the residents' level of exposure, by placing the dosers of tracer gas at locations that resemble indoor emission sources. To measure the 24-h-average effective air exchange rates in future surveys based on this procedure, a low-cost, easy-to-use perfluorocarbon tracer (PFT) doser with a stable dosing rate was developed by using double glass vials, a needle, a polyethylene-sintered filter, and a diffusion tube. Carbon molecular sieve cartridges and carbon disulfide (CS₂) were used for passive sampling and extraction of the tracer gas, respectively. Recovery efficiencies, sampling rates, and lower detection limits for 24-h sampling of hexafluorobenzene, octafluorotoluene, and perfluoroallylbenzene were 40% ± 3%, 72% ± 5%, and 84% ± 6%; 10.5 ± 1.1, 14.4 ± 1.4, and 12.2 ± 0.49 mL min⁻¹; and 0.20, 0.17, and 0.26 μg m⁻³, respectively.

Comparison of using polyurethane foam passive samplers and tree bark samples from Western China to determine atmospheric organochlorine pesticide.

PubMed

Li, Qiuxu; Lu, Yao; Jin, Jun; Li, Guangyao; Li, Peng; He, Chang; Wang, Ying

2016-03-01

Polyurethane foam (PUF) passive samplers were deployed and tree bark samples were collected at 15 sites across western China in 2013, and the organochlorine pesticide (OCP) concentrations in the samples were determined. Dichlorodiphenyltrichloroethane and its degradation products (collectively called DDTs), hexachlorocyclohexanes (HCHs), and hexachlorobenzene (HCB) were the dominant OCPs in the PUF samples and tree bark samples. The mean DDTs, HCHs and HCB concentrations were 33, 22 and 18ng/sample in the PUF samples, and 428, 74, and 43ng/(g lipid weight (lw)) in the tree bark, respectively. The OCP concentrations in the air, calculated using PUF-air and tree-bark-air partitioning models, were of the same order of magnitude. Both sample types showed that relatively fresh inputs of DDT and HCHs to the environment have occurred in western China. Meanwhile, PUF passive samplers were compared with the use of tree bark samples as passive samplers. The OCP compositions in the PUF and tree bark samples were different. Only the relatively stable OCPs (such as HCB, β-HCH and p,p'-dichlorodiphenyldichloro-ethylene (DDE)) were consistent in the PUF and tree bark samples. Copyright © 2015. Published by Elsevier B.V.

Grab and passive sampling applied to pesticide analysis in the São Lourenço river headwater in Campo Verde - MT, Brazil.

PubMed

Berton, André; Brugnera, Michelle F; Dores, Eliana F G C

2018-04-03

In this study, the quality of surface water in the headwaters of São Lourenço River in Mato Grosso, Brazil, was evaluated in relation to contamination by pesticides. For this purpose, samples were collected between December 2015 and June 2016 by grab sampling and by passive sampling using an integrative polar organic compound sampler installed in the field during four 14-day cycles between March and June 2016. The analyses were performed by gas chromatography (CG/MS) and by liquid chromatography (UPLC-MS/MS). The results showed the detection of two pesticides (atrazine and pyraclostrobin) of the five analyzed by passive sampling and eight active principles among the 20 analyzed (malathion, diuron, carbofuran, carbendazim, trifluralin, imidacloprid, metolachlor, and acetamiprid) by grab sampling. The detection of 10 pesticides, even almost a decade after the beginning of a recovery process of the ciliary forest, confirms the headwaters' vulnerability to these contaminants and passive sampling proved to be an important tool in capturing small concentrations of pesticides constituting an interesting complement to grab sampling.

Population pharmacokinetic modelling of non-linear brain distribution of morphine: influence of active saturable influx and P-glycoprotein mediated efflux

PubMed Central

Groenendaal, D; Freijer, J; de Mik, D; Bouw, M R; Danhof, M; de Lange, E C M

2007-01-01

Background and purpose: Biophase equilibration must be considered to gain insight into the mechanisms underlying the pharmacokinetic-pharmacodynamic (PK-PD) correlations of opioids. The objective was to characterise in a quantitative manner the non-linear distribution kinetics of morphine in brain. Experimental approach: Male rats received a 10-min infusion of 4 mg kg−1 of morphine, combined with a continuous infusion of the P-glycoprotein (Pgp) inhibitor GF120918 or vehicle, or 40 mg kg−1 morphine alone. Unbound extracellular fluid (ECF) concentrations obtained by intracerebral microdialysis and total blood concentrations were analysed using a population modelling approach. Key results: Blood pharmacokinetics of morphine was best described with a three-compartment model and was not influenced by GF120918. Non-linear distribution kinetics in brain ECF was observed with increasing dose. A one compartment distribution model was developed, with separate expressions for passive diffusion, active saturable influx and active efflux by Pgp. The passive diffusion rate constant was 0.0014 min−1. The active efflux rate constant decreased from 0.0195 min−1 to 0.0113 min−1 in the presence of GF120918. The active influx was insensitive to GF120918 and had a maximum transport (Nmax/Vecf) of 0.66 ng min−1 ml−1 and was saturated at low concentrations of morphine (C50=9.9 ng ml−1). Conclusions and implications: Brain distribution of morphine is determined by three factors: limited passive diffusion; active efflux, reduced by 42% by Pgp inhibition; low capacity active uptake. This implies blood concentration-dependency and sensitivity to drug-drug interactions. These factors should be taken into account in further investigations on PK-PD correlations of morphine. PMID:17471182

Controlled release of optimized electroporation enhances the transdermal efficiency of sinomenine hydrochloride for treating arthritis in vitro and in clinic

PubMed Central

Feng, Shun; Zhu, Lijun; Huang, Zhisheng; Wang, Haojia; Li, Hong; Zhou, Hua; Lu, Linlin; Wang, Ying; Liu, Zhongqiu; Liu, Liang

2017-01-01

Sinomenine hydrochloride (SH) is an ideal drug for the treatment of rheumatoid arthritis and osteoarthritis. However, high plasma concentration of systemically administered SH can release histamine, which can cause rash and gastrointestinal side effects. Topical delivery can increase SH concentration in the synovial fluid without high plasma level, thus minimizing systemic side effects. However, passive diffusion of SH was found to be inefficient because of the presence of the stratum corneum layer. Therefore, an effective method is required to compensate for the low efficiency of SH passive diffusion. In this study, transdermal experiments in vitro and clinical tests were utilized to explore the optimized parameters for electroporation of topical delivery for SH. Fluorescence experiment and hematoxylin and eosin staining analysis were performed to reveal the mechanism by which electroporation promoted permeation. In vitro, optimized electroporation parameters were 3 KHz, exponential waveform, and intensity 10. Using these parameters, transdermal permeation of SH was increased by 1.9–10.1 fold in mice skin and by 1.6–47.1 fold in miniature pig skin compared with passive diffusion. After the electroporation stimulation, the intercellular intervals and epidermal cracks in the skin increased. In clinical tests, SH concentration in synovial fluid was 20.84 ng/mL after treatment with electroporation. Therefore, electroporation with optimized parameters could significantly enhance transdermal permeation of SH. The mechanism by which electroporation promoted permeation was that the electronic pulses made the skin structure looser. To summarize, electroporation may be an effective complementary method for transdermal permeation of SH. The controlled release of electroporation may be a promising clinical method for transdermal drug administration. PMID:28670109

Evolution of Antibody-Drug Conjugate Tumor Disposition Model to Predict Preclinical Tumor Pharmacokinetics of Trastuzumab-Emtansine (T-DM1).

PubMed

Singh, Aman P; Maass, Katie F; Betts, Alison M; Wittrup, K Dane; Kulkarni, Chethana; King, Lindsay E; Khot, Antari; Shah, Dhaval K

2016-07-01

A mathematical model capable of accurately characterizing intracellular disposition of ADCs is essential for a priori predicting unconjugated drug concentrations inside the tumor. Towards this goal, the objectives of this manuscript were to: (1) evolve previously published cellular disposition model of ADC with more intracellular details to characterize the disposition of T-DM1 in different HER2 expressing cell lines, (2) integrate the improved cellular model with the ADC tumor disposition model to a priori predict DM1 concentrations in a preclinical tumor model, and (3) identify prominent pathways and sensitive parameters associated with intracellular activation of ADCs. The cellular disposition model was augmented by incorporating intracellular ADC degradation and passive diffusion of unconjugated drug across tumor cells. Different biomeasures and chemomeasures for T-DM1, quantified in the companion manuscript, were incorporated into the modified model of ADC to characterize in vitro pharmacokinetics of T-DM1 in three HER2+ cell lines. When the cellular model was integrated with the tumor disposition model, the model was able to a priori predict tumor DM1 concentrations in xenograft mice. Pathway analysis suggested different contribution of antigen-mediated and passive diffusion pathways for intracellular unconjugated drug exposure between in vitro and in vivo systems. Global and local sensitivity analyses revealed that non-specific deconjugation and passive diffusion of the drug across tumor cell membrane are key parameters for drug exposure inside a cell. Finally, a systems pharmacokinetic model for intracellular processing of ADCs has been proposed to highlight our current understanding about the determinants of ADC activation inside a cell.

Towards Stable Lithium-Sulfur Batteries with a Low Self-Discharge Rate: Ion Diffusion Modulation and Anode Protection.

PubMed

Xu, Wen-Tao; Peng, Hong-Jie; Huang, Jia-Qi; Zhao, Chen-Zi; Cheng, Xin-Bing; Zhang, Qiang

2015-09-07

The self-discharge of a lithium-sulfur cell decreases the shelf-life of the battery and is one of the bottlenecks that hinders its practical applications. New insights into both the internal chemical reactions in a lithium-sulfur system and effective routes to retard self-discharge for highly stable batteries are crucial for the design of lithium-sulfur cells. Herein, a lithium-sulfur cell with a carbon nanotube/sulfur cathode and lithium-metal anode in lithium bis(trifluoromethanesulfonyl)imide/1,3-dioxolane/dimethyl ether electrolyte was selected as the model system to investigate the self-discharge behavior. Both lithium anode passivation and polysulfide anion diffusion suppression strategies are applied to reduce self-discharge of the lithium-sulfur cell. When the lithium-metal anode is protected by a high density passivation layer induced by LiNO3 , a very low shuttle constant of 0.017 h(-1) is achieved. The diffusion of the polysulfides is retarded by an ion-selective separator, and the shuttle constants decreased. The cell with LiNO3 additive maintained a discharge capacity of 97 % (961 mAh g(-1) ) of the initial capacity after 120 days at open circuit, which was around three times higher than the routine cell (32 % of initial capacity, corresponding to 320 mAh g(-1) ). It is expected that lithium-sulfur batteries with ultralow self-discharge rates may be fabricated through a combination of anode passivation and polysulfide shuttle control, as well as optimization of the lithium-sulfur cell configuration. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemical passivation as a method of improving the electrochemical corrosion resistance of Co-Cr-based dental alloy.

PubMed

Rylska, Dorota; Sokołowski, Grzegorz; Sokołowski, Jerzy; Łukomska-Szymańska, Monika

2017-01-01

The purpose of the study was to evaluate corrosion resistance of Wirobond C® alloy after chemical passivation treatment. The alloy surface undergone chemical passivation treatment in four different media. Corrosion studies were carried out by means of electrochemical methods in saline solution. Corrosion effects were determined using SEM. The greatest increase in the alloy polarization resistance was observed for passive layer produced in Na2SO4 solution with graphite. The same layer caused the highest increase in corrosion current. Generally speaking, the alloy passivation in Na2SO4 solution with graphite caused a substantial improvement of the corrosion resistance. The sample after passivation in Na2SO4 solution without graphite, contrary to others, lost its protective properties along with successive anodic polarization cycles. The alloy passivation in Na3PO4 solution with graphite was the only one that caused a decrease in the alloy corrosion properties. The SEM studies of all samples after chemical passivation revealed no pit corrosion - in contrast to the sample without any modification. Every successive polarization cycle in anodic direction of pure Wirobond C® alloy enhances corrosion resistance shifting corrosion potential in the positive direction and decreasing corrosion current value. The chemical passivation in solutions with low pH values decreases susceptibility to electrochemical corrosion of Co-Cr dental alloy. The best protection against corrosion was obtained after chemical passivation of Wirobond C® in Na2SO4 solution with graphite. Passivation with Na2SO4 in solution of high pH does not cause an increase in corrosion resistance of WIROBOND C. Passivation process increases alloy resistance to pit corrosion.

Determination of trichloroanisole and trichlorophenol in wineries' ambient air by passive sampling and thermal desorption-gas chromatography coupled to tandem mass spectrometry.

PubMed

Camino-Sánchez, F J; Bermúdez-Peinado, R; Zafra-Gómez, A; Ruíz-García, J; Vílchez-Quero, J L

2015-02-06

The present paper describes the calibration of selected passive samplers used in the quantitation of trichlorophenol and trichloroanisole in wineries' ambient air, by calculating the corresponding sampling rates. The method is based on passive sampling with sorbent tubes and involves thermal desorption-gas chromatography-triple quadrupole mass spectrometry analysis. Three commercially available sorbents were tested using sampling cartridges with a radial design instead of axial ones. The best results were found for Tenax TA™. Sampling rates (R-values) for the selected sorbents were determined. Passive sampling was also used for accurately determining the amount of compounds present in the air. Adequate correlation coefficients between the mass of the target analytes and exposure time were obtained. The proposed validated method is a useful tool for the early detection of trichloroanisole and its precursor trichlorophenol in wineries' ambient air while avoiding contamination of wine or winery facilities. Copyright © 2015 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, David L.; Lee, Benjamin G.; Fogel, Derek

Here, we form gallium-doped poly-Si:Ga/SiO 2 passivated contacts on n-type Czochralski (n-Cz) wafers using ion implantation of Ga and Ga-containing spin-on dopants. After annealing and passivation with Al 2O 3, the contacts exhibit i Voc values of >730 mV with corresponding Joe values of <5 fA/cm 2. These are among the best-reported values for p-type poly-Si/SiO 2 contacts. Secondary ion mass spectroscopic depth profile data show that, in contrast to B, Ga does not pileup at the SiO 2 interface in agreement with its known high diffusivity in SiO 2. This lack of Ga pileup may imply fewer dopant-related defectsmore » in the SiO 2, compared with B dopants, and account for the excellent passivation.« less

PCDD/PCDF and dl-PCB in the ambient air of a tropical Andean city: passive and active sampling measurements near industrial and vehicular pollution sources.

PubMed

Cortés, J; González, C M; Morales, L; Abalos, M; Abad, E; Aristizábal, B H

2014-09-01

Concentration gradients were observed in gas and particulate phases of PCDD/F originating from industrial and vehicular sources in the densely populated tropical Andean city of Manizales, using passive and active air samplers. Preliminary results suggest greater concentrations of dl-PCB in the mostly gaseous fraction (using quarterly passive samplers) and greater concentrations of PCDD/F in the mostly particle fraction (using daily active samplers). Dioxin-like PCB predominance was associated with the semi-volatility property, which depends on ambient temperature. Slight variations of ambient temperature in Manizales during the sampling period (15°C-27°C) may have triggered higher concentrations in all passive samples. This was the first passive air sampling monitoring of PCDD/F conducted in an urban area of Colombia. Passive sampling revealed that PCDD/F in combination with dioxin-like PCB ranged from 16 WHO-TEQ2005/m(3) near industrial sources to 7 WHO-TEQ2005/m(3) in an intermediate zone-a reduction of 56% over 2.8 km. Active sampling of particulate phase PCDD/F and dl-PCB were analyzed in PM10 samples. PCDD/F combined with dl-PCB ranged from 46 WHO-TEQ2005/m(3) near vehicular sources to 8 WHO-TEQ2005/m(3) in the same intermediate zone, a reduction of 83% over 2.6 km. Toxic equivalent quantities in both PCDD/F and dl-PCB decreased toward an intermediate zone of the city. Variations in congener profiles were consistent with variations expected from nearby sources, such as a secondary metallurgy plant, areas of concentrated vehicular emissions and a municipal solid waste incinerator (MSWI). These variations in congener profile measurements of dioxins and dl-PCBs in passive and active samples can be partly explained by congener variations expected from the various sources. Copyright © 2014 Elsevier B.V. All rights reserved.

Relative distance between tracers as a measure of diffusivity within moving aggregates

NASA Astrophysics Data System (ADS)

Pönisch, Wolfram; Zaburdaev, Vasily

2018-02-01

Tracking of particles, be it a passive tracer or an actively moving bacterium in the growing bacterial colony, is a powerful technique to probe the physical properties of the environment of the particles. One of the most common measures of particle motion driven by fluctuations and random forces is its diffusivity, which is routinely obtained by measuring the mean squared displacement of the particles. However, often the tracer particles may be moving in a domain or an aggregate which itself experiences some regular or random motion and thus masks the diffusivity of tracers. Here we provide a method for assessing the diffusivity of tracer particles within mobile aggregates by measuring the so-called mean squared relative distance (MSRD) between two tracers. We provide analytical expressions for both the ensemble and time averaged MSRD allowing for direct identification of diffusivities from experimental data.

Spatial variations in nitrogen dioxide concentrations in an urban area

NASA Astrophysics Data System (ADS)

Nicholas Hewitt, C.

Fortnightly average NO 2 concentrations have been measured at 49 sites in the small city of Lancaster, U.K., over a continuous 1-year period using passive diffusion tubes. At sampling sites on a congested main road in the city centre considerable spatial and temporal variability in concentrations was found. An annual mean concentration of 63 μgm -3 was found witha range of 12-222 μgm -3. The mean concentration in an adjacent main road was 58 μgm -3 with a range of 5-107 μgm -3. Rather less variability was seen in a suburban main road and in a suburban residential street, which had annual mean concentrations of 38 and 30 μm -3, respectively. Concentrations in a city centre pedestrian precinct decreased with distance from the main road, having an annual mean value of 30μm -3. The data suggest that the precise location of a sampling device may be crucial in determining whether or not a given NO 2, concentration or standard is exceeded.

A combination of nonionic surfactants and iontophoresis to enhance the transdermal drug delivery of ondansetron HCl and diltiazem HCl.

PubMed

Silva, Sérgio M C; Hu, Longsheng; Sousa, João J S; Pais, Alberto A C C; Michniak-Kohn, Bozena B

2012-04-01

The present work reports the evaluation of three nonionic ether-monohydroxyl surfactants (C(12)E(1), C(12)E(5,) and C(12)E(8)) as skin permeation enhancers in the transdermal drug delivery of two drugs: ondansetron hydrochloride and diltiazem hydrochloride, formulated as hydrogels. The enhancers are used alone, or in combination with iontophoresis (0.3 mA - 8h). After 1h of pre-treatment with 0.16 M enhancer solutions in propylene glycol (PG), passive and iontophoretic 24 h in vitro studies across dermatomed porcine skin were performed using vertical Franz diffusion cells. Data obtained showed that the nonionic surfactant C(12)E(5) was the most effective permeation enhancer, both for the passive process as well as for samples subjected to iontophoresis, resulting in cumulative amounts of ondansetron HCl after 24h of approximately 93 μg/cm(2) and 336 μg/cm(2), respectively. Data obtained using diltiazem HCl showed a similar trend. The use of the nonionic surfactant C(12)E(5) resulted in higher enhancement ratios (ER) in passive studies, but C(12)E(8) yielded slightly higher values of drug permeated (2678 μg/cm(2)) than C(12)E(5) (2530 μg/cm(2)) when iontophoresis was also employed. Skin integrity studies were performed to assess potential harmful effects on the tissues resulting from the compounds applied and/or from the methodology employed. Skin samples used in permeation studies visualized by light microscopy and Scanning Electron Microscopy (SEM) at different levels of magnification did not show significant morphological and structural changes, when compared to untreated samples. Complementary studies were performed to gain information regarding the relative cytotoxicity of the penetration enhancers on skin cells. MTS assay data using human epidermal keratinocytes (HEK) and human dermal fibroblasts (HDF) indicated that HEK are more sensitive to the presence of the enhancers than HDF and that the toxicity of these compounds is enhancer molecular weight dependent. Copyright © 2011 Elsevier B.V. All rights reserved.

Influence of In-Well Convection on Well Sampling

USGS Publications Warehouse

Vroblesky, Don A.; Casey, Clifton C.; Lowery, Mark A.

2006-01-01

Convective transport of dissolved oxygen (DO) from shallow to deeper parts of wells was observed as the shallow water in wells in South Carolina became cooler than the deeper water in the wells due to seasonal changes. Wells having a relatively small depth to water were more susceptible to thermally induced convection than wells where the depth to water was greater because the shallower water levels were more influenced by air temperature. The potential for convective transport of DO to maintain oxygenated conditions in a well was diminished as ground-water exchange through the well screen increased and as oxygen demand increased. Convective flow did not transport oxygen to the screened interval when the screened interval was deeper than the range of the convective cell. The convective movement of water in wells has potential implications for passive, or no-purge, and low-flow sampling approaches. Transport of DO to the screened interval can adversely affect the ability of passive samplers to produce accurate concentrations of oxygen-sensitive solutes, such as iron. Other potential consequences include mixing the screened-interval water with casing water and potentially allowing volatilization loss at the water surface. A field test of diffusion samplers in a convecting well during the winter, however, showed good agreement of chlorinated solvent concentrations with pumped samples, indicating that there was no negative impact of the convection on the utility of the samplers to collect volatile organic compound concentrations in that well. In the cases of low-flow sampling, convective circulation can cause the pumped sample to be a mixture of casing water and aquifer water. This can substantially increase the equilibration time of oxygen as an indicator parameter and can give false indications of the redox state. Data from this investigation show that simple in-well devices can effectively mitigate convective transport of oxygen. The devices can range from inflatable packers to simple baffle systems.

Vertical Profiling of Soil Vapor Concentrations Using a New Passive Diffusion Sampler at a UST Site

EPA Science Inventory

Understanding the transport of volatile contaminants in soil gas, particularly those associated with underground storage tanks (USTs), requires a detailed knowledge about the depth-dependent distribution of chemical species in the subsurface. Traditional monitoring wells generall...

Active transport of vesicles in neurons is modulated by mechanical tension.

PubMed

Ahmed, Wylie W; Saif, Taher A

2014-03-27

Effective intracellular transport of proteins and organelles is critical in cells, and is especially important for ensuring proper neuron functionality. In neurons, most proteins are synthesized in the cell body and must be transported through thin structures over long distances where normal diffusion is insufficient. Neurons transport subcellular cargo along axons and neurites through a stochastic interplay of active and passive transport. Mechanical tension is critical in maintaining proper function in neurons, but its role in transport is not well understood. To this end, we investigate the active and passive transport of vesicles in Aplysia neurons while changing neurite tension via applied strain, and quantify the resulting dynamics. We found that tension in neurons modulates active transport of vesicles by increasing the probability of active motion, effective diffusivity, and induces a retrograde bias. We show that mechanical tension modulates active transport processes in neurons and that external forces can couple to internal (subcellular) forces and change the overall transport dynamics.

Active transport of vesicles in neurons is modulated by mechanical tension

PubMed Central

Ahmed, Wylie W.; Saif, Taher A.

2014-01-01

Effective intracellular transport of proteins and organelles is critical in cells, and is especially important for ensuring proper neuron functionality. In neurons, most proteins are synthesized in the cell body and must be transported through thin structures over long distances where normal diffusion is insufficient. Neurons transport subcellular cargo along axons and neurites through a stochastic interplay of active and passive transport. Mechanical tension is critical in maintaining proper function in neurons, but its role in transport is not well understood. To this end, we investigate the active and passive transport of vesicles in Aplysia neurons while changing neurite tension via applied strain, and quantify the resulting dynamics. We found that tension in neurons modulates active transport of vesicles by increasing the probability of active motion, effective diffusivity, and induces a retrograde bias. We show that mechanical tension modulates active transport processes in neurons and that external forces can couple to internal (subcellular) forces and change the overall transport dynamics. PMID:24670781

Radiative transfer model for aerosols in infrared wavelengths for passive remote sensing applications.

PubMed

Ben-David, Avishai; Embury, Janon F; Davidson, Charles E

2006-09-10

A comprehensive analytical radiative transfer model for isothermal aerosols and vapors for passive infrared remote sensing applications (ground-based and airborne sensors) has been developed. The theoretical model illustrates the qualitative difference between an aerosol cloud and a chemical vapor cloud. The model is based on two and two/four stream approximations and includes thermal emission-absorption by the aerosols; scattering of diffused sky radiances incident from all sides on the aerosols (downwelling, upwelling, left, and right); and scattering of aerosol thermal emission. The model uses moderate resolution transmittance ambient atmospheric radiances as boundary conditions and provides analytical expressions for the information on the aerosol cloud that is contained in remote sensing measurements by using thermal contrasts between the aerosols and diffused sky radiances. Simulated measurements of a ground-based sensor viewing Bacillus subtilis var. niger bioaerosols and kaolin aerosols are given and discussed to illustrate the differences between a vapor-only model (i.e., only emission-absorption effects) and a complete model that adds aerosol scattering effects.

Internal quantum efficiency mapping analysis for a >20%-efficiency n-type bifacial solar cell with front-side emitter formed by BBr3 thermal diffusion

NASA Astrophysics Data System (ADS)

Simayi, Shalamujiang; Mochizuki, Toshimitsu; Kida, Yasuhiro; Shirasawa, Katsuhiko; Takato, Hidetaka

2017-10-01

This paper presents a large-area (239-cm2) high-efficiency n-type bifacial solar cell that is processed using tube-furnace thermal diffusion employing liquid sources BBr3 for the front-side boron emitter and POCl3 for the rear-side phosphorus back surface field (BSF). The SiN x /Al2O3 stack was applied to the front-side boron emitter as a passivation layer. Both the front and rear-side electrodes are obtained using screen-printed contacts with H-patterns. The resulting highest-efficiency solar cell has front- and rear-side efficiencies of 20.3 and 18.7%, respectively, while the corresponding bifaciality is up to 92%. Finally, the passivation quality of the SiN x /Al2O3 stack on the front-side boron emitter and rear-side phosphorus BSF is investigated and visualized by measuring the internal quantum efficiency mapping of the bifacial solar cell.

A Biophysical Basis for Mucus Solids Concentration as a Candidate Biomarker for Airways Disease

PubMed Central

Hill, David B.; Vasquez, Paula A.; Mellnik, John; McKinley, Scott A.; Vose, Aaron; Mu, Frank; Henderson, Ashley G.; Donaldson, Scott H.; Alexis, Neil E.; Boucher, Richard C.; Forest, M. Gregory

2014-01-01

In human airways diseases, including cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), host defense is compromised and airways inflammation and infection often result. Mucus clearance and trapping of inhaled pathogens constitute key elements of host defense. Clearance rates are governed by mucus viscous and elastic moduli at physiological driving frequencies, whereas transport of trapped pathogens in mucus layers is governed by diffusivity. There is a clear need for simple and effective clinical biomarkers of airways disease that correlate with these properties. We tested the hypothesis that mucus solids concentration, indexed as weight percent solids (wt%), is such a biomarker. Passive microbead rheology was employed to determine both diffusive and viscoelastic properties of mucus harvested from human bronchial epithelial (HBE) cultures. Guided by sputum from healthy (1.5–2.5 wt%) and diseased (COPD, CF; 5 wt%) subjects, mucus samples were generated in vitro to mimic in vivo physiology, including intermediate range wt% to represent disease progression. Analyses of microbead datasets showed mucus diffusive properties and viscoelastic moduli scale robustly with wt%. Importantly, prominent changes in both biophysical properties arose at ∼4 wt%, consistent with a gel transition (from a more viscous-dominated solution to a more elastic-dominated gel). These findings have significant implications for: (1) penetration of cilia into the mucus layer and effectiveness of mucus transport; and (2) diffusion vs. immobilization of micro-scale particles relevant to mucus barrier properties. These data provide compelling evidence for mucus solids concentration as a baseline clinical biomarker of mucus barrier and clearance functions. PMID:24558372

Use of passive samplers to measure atmospheric ammonia levels in a high-density industrial hog farm area of eastern North Carolina

NASA Astrophysics Data System (ADS)

Wilson, Sacoby M.; Serre, Marc L.

Hog concentrated animal feeding operations (CAFOs) in North Carolina release ammonia (NH 3), hydrogen sulfide, VOCs, and particulate matter to the atmosphere. These operations are located mainly in the NC coastal plain and can create potential health hazards for nearby human populations. Limited work has been performed to measure NH 3 at the community level to assess potential human exposure. In an effort to address this issue, a study was designed to measure NH 3 levels near hog CAFOs and community locations (i.e. homes and schools) in Eastern NC. NH 3 was collected using passive diffusion tubes in triplicate exposed primarily in weekly intervals. Sampling occurred from October 2003 to May 2004 (20 sites) and from July 2004 to October 2004 (23 sites) at varying distances from hog CAFOs in close proximity to homes and schools. Average weekly NH3 levels were measured as mass (μg NH 3-N) and converted to concentration (ppb). Mean level of 13.8 ppb near homes and schools (<2 km) was 4-12 times greater than ambient background levels (1-3 ppb), reaching as high as 80 ppb. Exposed sites (<2 km from a hog CAFO) had a mean level of 12.8 ppb which was over 2 times higher than the mean level of 5.5 ppb at less exposed sites (>2 km from a hog CAFO). The study establishes that passive sampling can be effectively used to measure average atmospheric ammonia levels at community locations near hog CAFOs in Eastern NC. The collected data indicate the relative exposure for human populations who live near a hog CAFO. The closer a populace is to the hog CAFO, the more intense the exposure. These results require more validation in the field by comparison to a reference method.

Diffusion and cellular uptake of drugs in live cells studied with surface-enhanced Raman scattering probes

NASA Astrophysics Data System (ADS)

Bálint, Štefan; Rao, Satish; Sánchez, Mónica Marro; Huntošová, Veronika; Miškovský, Pavol; Petrov, Dmitri

2010-03-01

An understanding of the mechanisms of drug diffusion and uptake through cellular membranes is critical for elucidating drug action and in the development of effective drug delivery systems. We study these processes for emodin, a potential anticancer drug, in live cancer cells using surface-enhanced Raman scattering. Micrometer-sized silica beads covered by nanosized silver colloids are passively embedded into the cell and used as sensors of the drug. We demonstrate that the technique offers distinct advantages: the possibility to study the kinetics of drug diffusion through the cellular membrane toward specific cell organelles, the detection of lower drug concentrations compared to fluorescence techniques, and less damage imparted on the cell.

Soil gas screening for chlorinated solvents at three contaminated karst sites in Tennessee

USGS Publications Warehouse

Wolfe, W.J.; Williams, S.D.

2002-01-01

Soil gas was sampled using active sampling techniques and passive collectors at three sites in Tennessee to evaluate the effectiveness of these techniques for locating chlorinated solvent sources and flowpaths in karst aquifers. Actively collected soil gas samples were analyzed in the field with a portable gas chromatograph, and the passive soil gas collectors were analyzed in the lab with gas chromatography/mass spectrometry. Results of the sampling indicate that the effectiveness of both techniques is highly dependent on the distribution of the contaminants in the subsurface, the geomorphic and hydrogeologic characteristics of the site, and, in one case, on seasonal conditions. Both active and passive techniques identified areas of elevated subsurface chlorinated solvent concentrations at a landfill site where contamination remains concentrated in the regolith. Neither technique detected chlorinated solvents known to be moving in the bedrock at a manufacturing site characterized by thick regolith and an absence of surficial karst features. Passive soil gas sampling had varied success detecting flowpaths for chloroform in the bedrock at a train derailment site characterized by shallow regolith and abundant surficial karst features. At the train derailment site, delineation of the contaminant flowpath through passive soil gas sampling was stronger and more detailed under Winter conditions than summer.

Evaluation of Space Power Materials Flown on the Passive Optical Sample Assembly

NASA Technical Reports Server (NTRS)

Jaworske, Donald A.; deGroh, Kim K.; Skowronski, Timothy J.; McCollum, Tim; Pippin, Gary; Bungay, Corey

1999-01-01

Evaluating the performance of materials on the exterior of spacecraft is of continuing interest, particularly in anticipation of those applications that will require a long duration in low Earth orbit. The Passive Optical Sample Assembly (POSA) experiment flown on the exterior of Mir as a risk mitigation experiment for the International Space Station was designed to better understand the interaction of materials with the low Earth orbit environment and to better understand the potential contamination threats that may be present in the vicinity of spacecraft. Deterioration in the optical performance of candidate space power materials due to the low Earth orbit environment, the contamination environment, or both, must be evaluated in order to propose measures to mitigate such deterioration. The thirty two samples of space power materials studied here include solar array blanket materials such as polyimide Kapton H and SiO(x) coated polyimide Kapton H, front surface aluminized sapphire, solar dynamic concentrator materials such as silver on spin coated polyimide and aluminum on spin coated polyimide, CV 1144 silicone, and the thermal control paint Z-93-P. The physical and optical properties that were evaluated prior to and after the POSA flight include mass, total, diffuse, and specular reflectance, solar absorptance, and infrared emittance. Additional post flight evaluation included scanning electron microscopy to observe surface features caused by the low Earth orbit environment and the contamination environment, and variable angle spectroscopic ellipsometry to identify contaminant type and thickness. This paper summarizes the results of pre- and post-flight measurements, identifies the mechanisms responsible for optical properties deterioration, and suggests improvements for the durability of materials in future missions.

Low-temperature fabrication of an HfO2 passivation layer for amorphous indium-gallium-zinc oxide thin film transistors using a solution process.

PubMed

Hong, Seonghwan; Park, Sung Pyo; Kim, Yeong-Gyu; Kang, Byung Ha; Na, Jae Won; Kim, Hyun Jae

2017-11-24

We report low-temperature solution processing of hafnium oxide (HfO 2 ) passivation layers for amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). At 150 °C, the hafnium chloride (HfCl 4 ) precursor readily hydrolyzed in deionized (DI) water and transformed into an HfO 2 film. The fabricated HfO 2 passivation layer prevented any interaction between the back surface of an a-IGZO TFT and ambient gas. Moreover, diffused Hf 4+ in the back-channel layer of the a-IGZO TFT reduced the oxygen vacancy, which is the origin of the electrical instability in a-IGZO TFTs. Consequently, the a-IGZO TFT with the HfO 2 passivation layer exhibited improved stability, showing a decrease in the threshold voltage shift from 4.83 to 1.68 V under a positive bias stress test conducted over 10,000 s.

Uptake of L-nicotine and of 6-hydroxy-L-nicotine by Arthrobacter nicotinovorans and by Escherichia coli is mediated by facilitated diffusion and not by passive diffusion or active transport.

PubMed

Ganas, Petra; Brandsch, Roderich

2009-06-01

The mechanism by which l-nicotine is taken up by bacteria that are able to grow on it is unknown. Nicotine degradation by Arthrobacter nicotinovorans, a Gram-positive soil bacterium, is linked to the presence of the catabolic megaplasmid pAO1. l-[(14)C]Nicotine uptake assays with A. nicotinovorans showed transport of nicotine across the cell membrane to be energy-independent and saturable with a K(m) of 6.2+/-0.1 microM and a V(max) of 0.70+/-0.08 micromol min(-1) (mg protein)(-1). This is in accord with a mechanism of facilitated diffusion, driven by the nicotine concentration gradient. Nicotine uptake was coupled to its intracellular degradation, and an A. nicotinovorans strain unable to degrade nicotine (pAO1(-)) showed no nicotine import. However, when the nicotine dehydrogenase genes were expressed in this strain, import of l-[(14)C]nicotine took place. A. nicotinovorans pAO1(-) and Escherichia coli were also unable to import 6-hydroxy-l-nicotine, but expression of the 6-hydroxy-l-nicotine oxidase gene allowed both bacteria to take up this compound. l-Nicotine uptake was inhibited by d-nicotine, 6-hydroxy-l-nicotine and 2-amino-l-nicotine, which may indicate transport of these nicotine derivatives by a common permease. Attempts to correlate nicotine uptake with pAO1 genes possessing similarity to amino acid transporters failed. In contrast to the situation at the blood-brain barrier, nicotine transport across the cell membrane by these bacteria was not by passive diffusion or active transport but by facilitated diffusion.

Direct numerical simulation of turbulent mixing at very low Schmidt number with a uniform mean gradient

NASA Astrophysics Data System (ADS)

Yeung, P. K.; Sreenivasan, K. R.

2014-01-01

In a recent direct numerical simulation (DNS) study [P. K. Yeung and K. R. Sreenivasan, "Spectrum of passive scalars of high molecular diffusivity in turbulent mixing," J. Fluid Mech. 716, R14 (2013)] with Schmidt number as low as 1/2048, we verified the essential physical content of the theory of Batchelor, Howells, and Townsend ["Small-scale variation of convected quantities like temperature in turbulent fluid. 2. The case of large conductivity," J. Fluid Mech. 5, 134 (1959)] for turbulent passive scalar fields with very strong diffusivity, decaying in the absence of any production mechanism. In particular, we confirmed the existence of the -17/3 power of the scalar spectral density in the so-called inertial-diffusive range. In the present paper, we consider the DNS of the same problem, but in the presence of a uniform mean gradient, which leads to the production of scalar fluctuations at (primarily) the large scales. For the parameters of the simulations, the presence of the mean gradient alters the physics of mixing fundamentally at low Peclet numbers. While the spectrum still follows a -17/3 power law in the inertial-diffusive range, the pre-factor is non-universal and depends on the magnitude of the mean scalar gradient. Spectral transfer is greatly reduced in comparison with those for moderately and weakly diffusive scalars, leading to several distinctive features such as the absence of dissipative anomaly and a new balance of terms in the spectral transfer equation for the scalar variance, differing from the case of zero gradient. We use the DNS results to present an alternative explanation for the observed scaling behavior, and discuss a few spectral characteristics in detail.

Outer-membrane translocation of bulky small molecules by passive diffusion

PubMed Central

van den Berg, Bert; Prathyusha Bhamidimarri, Satya; Dahyabhai Prajapati, Jigneshkumar; Kleinekathöfer, Ulrich; Winterhalter, Mathias

2015-01-01

The outer membrane (OM) of gram-negative bacteria forms a protective layer around the cell that serves as a permeability barrier to prevent unrestricted access of noxious substances. The permeability barrier of the OM results partly from the limited pore diameters of OM diffusion channels. As a consequence, there is an “OM size-exclusion limit,” and the uptake of bulky molecules with molecular masses of more than ∼600 Da is thought to be mediated by TonB-dependent, active transporters. Intriguingly, the OM protein CymA from Klebsiella oxytoca does not depend on TonB but nevertheless mediates efficient OM passage of cyclodextrins with diameters of up to ∼15 Å. Here we show, by using X-ray crystallography, molecular dynamics simulations, and single-channel electrophysiology, that CymA forms a monomeric 14-stranded β-barrel with a large pore that is occluded on the periplasmic side by the N-terminal 15 residues of the protein. Representing a previously unidentified paradigm in OM transport, CymA mediates the passive diffusion of bulky molecules via an elegant transport mechanism in which a mobile element formed by the N terminus acts as a ligand-expelled gate to preserve the permeability barrier of the OM. PMID:26015567

Diffusion, spread, and migration of botulinum toxin.

PubMed

Ramirez-Castaneda, Juan; Jankovic, Joseph; Comella, Cynthia; Dashtipour, Khashayar; Fernandez, Hubert H; Mari, Zoltan

2013-11-01

Botulinum toxin (BoNT) is an acetylcholine release inhibitor and a neuromuscular blocking agent used for the treatment of a variety of neurologic and medical conditions. The efficacy and safety of BoNT depends on accurate selection and identification of intended targets but also may be determined by other factors, including physical spread of the molecule from the injection site, passive diffusion, and migration to distal sites via axonal or hematogenous transport. The passive kinetic dispersion of the toxin away from the injection site in a gradient-dependent manner may also play a role in toxin spread. In addition to unique properties of the various BoNT products, volume and dilution may also influence local and systemic distribution of BoNT. Most of the local and remote complications of BoNT injections are thought to be due to unwanted spread or diffusion of the toxin's biologic activity into adjacent and distal muscles. Despite widespread therapeutic and cosmetic use of BoNT over more than three decades, there is a remarkable paucity of published data on the mechanisms of distribution and its effects on clinical outcomes. The primary aim of this article is to critically review the available experimental and clinical literature and place it in the practical context. © 2013 International Parkinson and Movement Disorder Society.

Hydrogen passivation of n+p and p+n heteroepitaxial InP solar cell structures

NASA Technical Reports Server (NTRS)

Chatterjee, B.; Ringel, S. A.; Hoffman, R., Jr.

1995-01-01

High-efficiency, heteroepitaxial (HE) InP solar cells, grown on GaAs, Si or Ge substrates, are desirable for their mechanically strong, light-weight and radiation-hard properties. However, dislocations, caused by lattice mismatch, currently limit the performance of the HE cells. This occurs through shunting paths across the active photovoltaic junction and by the formation of deep levels. In previous work we have demonstrated that plasma hydrogenation is an effective and stable means to passivate the electrical activity of dislocations in specially designed HE InP test structures. In this work, we present the first report of successful hydrogen passivation in actual InP cell structures grown on GaAs substrates by metalorganic chemical vapor deposition (MOCVD). We have found that a 2 hour exposure to a 13.56 MHz hydrogen plasma at 275 C reduces the deep level concentration in HE n+n InP cell structures from as-grown values of approximately 10(exp 15)/cm(exp -3), down to 1-2 x 10(exp 13)/cm(exp -3). The deep levels in the p-type base region of the cell structure match those of our earlier p-type test structures, which were attributed to dislocations or related point defect complexes. All dopants were successfully reactivated by a 400 C, 5 minute anneal with no detectable activation of deep levels. I-V analysis indicated a subsequent approximately 10 fold decrease in reverse leakage current at -1 volt reverse bias, and no change in the forward biased series resistance of the cell structure which indicates complete reactivation of the n+ emitter. Furthermore, electrochemical C-V profiling indicates greatly enhanced passivation depth, and hence hydrogen diffusion, for heteroepitaxial structures when compared with identically processed homoepitaxial n+p InP structures. An analysis of hydrogen diffusion in dislocated InP will be discussed, along with comparisons of passivation effectiveness for n+p versus p+n heteroepitaxial cell configurations. Preliminary hydrogen-passivated HE InP cell results will also be presented.

Impact of pesticide use by smallholder farmers on water quality in the Wakiso District, Uganda

NASA Astrophysics Data System (ADS)

Oltramare, Christelle; Weiss, Frederik T.; Atuhaire, Aggrey; Staudacher, Philipp; Niwagaba, Charles; Stamm, Christian

2017-04-01

As in many tropical countries, farmers of the Wakiso District rely on heavy use of pesticides to protect crops and animals. This may impair human and environmental health due to poor application techniques, misuse of pesticide bins or diffuse pesticide losses from the treated fields during intense tropical rainstorms. The extent of pollution in different environmental compartments however, are generally only poorly documented. The same holds true for quantitative data on the relevance of different transport pathways of pesticides into the environment. Part of the limited knowledge is caused by the demanding sampling and analytical techniques that are necessary to obtain robust data on the actual pollution status. Especially in surface waters, pesticide concentration may vary rapidly in time such that grab samples may yield a very incomplete picture. This incompleteness was often enhanced because of limited analytical windows that covered only a small fraction of the pesticides actually used. In this presentation, we describe an approach to overcome these limitations to a large extent by using three different passive sampling devices and two broad analytical techniques (GC-MS/MS, LC HR-MS) that allow the quantification of about 260 different pesticides. We will present how these approaches are implemented in the catchment area of the Wakiso District in Uganda. This area is intensively used by smallholder farmers who grow a large set of different crops. Diffuse losses are expected to occur mainly during the two rainy seasons (March to May and September to November). Accordingly, the study will focus on this situation.

Friction Regimes of Water-Lubricated Diamond (111): Role of Interfacial Ether Groups and Tribo-Induced Aromatic Surface Reconstructions

NASA Astrophysics Data System (ADS)

Kuwahara, Takuya; Moras, Gianpietro; Moseler, Michael

2017-09-01

Large-scale quantum molecular dynamics of water-lubricated diamond (111) surfaces in sliding contact reveals multiple friction regimes. While water starvation causes amorphization of the tribological interface, small H2O traces are sufficient to preserve crystallinity. This can result in high friction due to cold welding via ether groups or in ultralow friction due to aromatic surface passivation triggered by tribo-induced Pandey reconstruction. At higher water coverage, Grotthuss-type diffusion and H2O dissociation yield dense H /OH surface passivation leading to another ultralow friction regime.

Trapping behavior of Shockley-Read-Hall recombination centers in silicon solar cells

NASA Astrophysics Data System (ADS)

Gogolin, R.; Harder, N. P.

2013-08-01

We investigate the correlation between increased apparent carrier lifetime in photoconductance-based lifetime measurements and actually reduced recombination lifetime as measured by photoluminescence measurements. These findings are further reconfirmed by I-V curve measurements of solar cells. In particular, we show experimental results for lifetime samples and solar cells with and without hydrogen passivation. In the samples and solar cells without hydrogen passivation, we find both a stronger trapping behavior and a lower recombination lifetime. Our model provides a consistent description of the observation of both, the increased apparent lifetime from carrier trapping and the decreasing recombination lifetime. In our model, both are caused by a single physical mechanism; i.e., by Recombination-Active-Trap (RAT) states. Upon fitting the experimental lifetime data, we find that the RAT-defect parameters for the hydrogen-passivated and non-hydrogen-passivated lifetime samples and solar cells are identical except for the defect concentration: hydrogen-passivation reduced the defect density by 50% in both, the lifetime samples and solar cells. We conclude that trapping should be considered as an indication for hidden, yet potentially strongly increased, low injection recombination activity.

Method for fabricating silicon cells

DOEpatents

Ruby, Douglas S.; Basore, Paul A.; Schubert, W. Kent

1998-08-11

A process for making high-efficiency solar cells. This is accomplished by forming a diffusion junction and a passivating oxide layer in a single high-temperature process step. The invention includes the class of solar cells made using this process, including high-efficiency solar cells made using Czochralski-grown silicon.

Anisotropic diffusion in mesh-free numerical magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.

2017-04-01

We extend recently developed mesh-free Lagrangian methods for numerical magnetohydrodynamics (MHD) to arbitrary anisotropic diffusion equations, including: passive scalar diffusion, Spitzer-Braginskii conduction and viscosity, cosmic ray diffusion/streaming, anisotropic radiation transport, non-ideal MHD (Ohmic resistivity, ambipolar diffusion, the Hall effect) and turbulent 'eddy diffusion'. We study these as implemented in the code GIZMO for both new meshless finite-volume Godunov schemes (MFM/MFV). We show that the MFM/MFV methods are accurate and stable even with noisy fields and irregular particle arrangements, and recover the correct behaviour even in arbitrarily anisotropic cases. They are competitive with state-of-the-art AMR/moving-mesh methods, and can correctly treat anisotropic diffusion-driven instabilities (e.g. the MTI and HBI, Hall MRI). We also develop a new scheme for stabilizing anisotropic tensor-valued fluxes with high-order gradient estimators and non-linear flux limiters, which is trivially generalized to AMR/moving-mesh codes. We also present applications of some of these improvements for SPH, in the form of a new integral-Godunov SPH formulation that adopts a moving-least squares gradient estimator and introduces a flux-limited Riemann problem between particles.

Study of drug diffusion rate by laser beam deflection technique

NASA Astrophysics Data System (ADS)

Swapna, Mohanachandran Nair. S.; Anitha, Madhu J.; Sankararaman, Sankaranarayana Iyer

2017-06-01

Drug administration is an unavoidable part of treatment. When a drug is administered orally or intravenously, it gets absorbed into the blood stream. The rate and efficiency of absorption depend on the route of administration. When a drug is administered through the oral route, it penetrates the epithelial cells of the intestinal mucosa. The diffusion of the drug into the blood stream depends on various parameters, such as concentration, temperature, and the nature of the mucous membrane. The passive diffusion of drugs is found to obey Fick's law. Water soluble drugs penetrate the cell membrane through aqueous channel or pores. Hence, the study of diffusion of drugs into the water and finally into the blood stream is important. An attempt has been made to study the diffusion of the drug in water as 60% to 80% of human body is water. For the study of drug diffusion in water, a commonly used cough syrup of specific gravity 1.263 is used. It is found that the diffusion rate increases with the concentration of the drug.

Intercomparison of active and passive instruments for radon and radon progeny in North America

DOE Office of Scientific and Technical Information (OSTI.GOV)

George, A.C.; Tu, Keng-Wu; Knutson, E.O.

1995-02-01

An intercomparison exercise for radon and radon progeny instruments and methods was held at the Environmental Measurements Laboratory (EML) from April 22--May 2, 1994. The exercise was conducted in the new EML radon test and calibration facility in which conditions of exposure are very well controlled. The detection systems of the intercompared instruments consisted of. (1) pulse ionization chambers, (2) electret ionization chambers, (3) scintillation detectors, (4) alpha particle spectrometers with silicon diodes, surface barrier or diffused junction detectors, (5) registration of nuclear tracks in solid-state materials, and (6) activated carbon collectors counted by gamma-ray spectrometry or by alpha- andmore » beta-liquid scintillation counting. 23 private firms, government laboratories and universities participated with a 165 passive integrating devices consisting of: Activated carbon collectors, nuclear alpha track detectors and electret ionization chambers, and 11 active and passive continuous radon monitors. Five portable integrating and continuous instruments were intercompared for radon progeny. Forty grab samples for radon progeny were taken by five groups that participated in person to test and evaluate their primary instruments and methods that measure individual radon progeny and the potential alpha energy concentration (PAEC) in indoor air. Results indicate that more than 80% of the measurements for radon performed with a variety of instruments, are within {plus_minus}10% of actual value. The majority of the instruments that measure individual radon progeny and the PAEC gave results that are in good agreement with the EML reference value. Radon progeny measurements made with continuous and integrating instruments are satisfactory with room for improvement.« less

Electromigration Critical Product to Measure Effect of Underfill Material in Suppressing Bi Segregation in Sn-58Bi Solder

NASA Astrophysics Data System (ADS)

Zhao, Xu; Takaya, Satoshi; Muraoka, Mikio

2017-08-01

Recently, we detected length-dependent electromigration (EM) behavior in Sn-58Bi (SB) solder and revealed the existence of Bi back-flow, which retards EM-induced Bi segregation and is dependent on solder length. The cause of the back-flow is attributed to an oxide layer formed on the SB solder. At present, underfill (UF) material is commonly used in flip-chip packaging as filler between chip and substrate to surround solder bumps. In this study, we quantitatively investigated the effect of UF material as a passivation layer on EM in SB solder strips. EM tests on SB solder strips with length of 50 μm, 100 μm, and 150 μm were conducted simultaneously. Some samples were coated with commercial thermosetting epoxy UF material, which acted as a passivation layer on the Cu-SB-Cu interconnections. The value of the critical product for SB solder was estimated to be 38 A/cm to 43 A/cm at 353 K to 373 K without UF coating and 59 A/cm at 373 K with UF coating. The UF material acting as a passivation layer suppressed EM-induced Bi segregation and increased the threshold current density by 37% to 55%. However, at very high current density, this effect became very slight. In addition, Bi atoms can diffuse to the anode side through the Sn phase, hence addition of microelements to the Sn phase to form obstacles, such as intermetallic compounds, may retard Bi segregation in SB solder.

Passive radon/thoron personal dosimeter using an electrostatic collector and a diffused-junction detector

NASA Astrophysics Data System (ADS)

Bigu, J.; Raz, R.

1985-01-01

A solid-state alpha dosimeter has been designed and tested suitable for personal and environmental radon/thoron monitoring. The dosimeter basically consists of an electrostatic collector and an alpha-particle counting system with spectroscopy capabilities. The sensitive volume (˜20 cm3) of the electrostatic collector consists of a cylindrically shaped metal wire screen and a diffused-junction silicon alpha-detector covered with a thin aluminized Mylar sheet. A dc voltage (˜500 V) is applied between the wire screen and the Mylar sheet, with the latter held at negative potential relative to the former. Data can be retrieved during or after sampling by means of a microcomputer (Epson HX20) via a RS-232 communication interface unit. The dosimeter has been calibrated in a large (26 m3) radon/thoron test facility. A linear relationship was found between the dosimeter's alpha-count and both radon gas concentration and radon daughter working level. The dosimeter is mounted on top of an ordinary miner's cap lamp battery and is ideally suited for personal monitoring in underground uranium mines and other working areas. The dosimeter presented here is a considerably improved version of an earlier prototype.

Homojunction silicon solar cells doping by ion implantation

NASA Astrophysics Data System (ADS)

Milési, Frédéric; Coig, Marianne; Lerat, Jean-François; Desrues, Thibaut; Le Perchec, Jérôme; Lanterne, Adeline; Lachal, Laurent; Mazen, Frédéric

2017-10-01

Production costs and energy efficiency are the main priorities for the photovoltaic (PV) industry (COP21 conclusions). To lower costs and increase efficiency, we are proposing to reduce the number of processing steps involved in the manufacture of N-type Passivated Rear Totally Diffused (PERT) silicon solar cells. Replacing the conventional thermal diffusion doping steps by ion implantation followed by thermal annealing allows reducing the number of steps from 7 to 3 while maintaining similar efficiency. This alternative approach was investigated in the present work. Beamline and plasma immersion ion implantation (BLII and PIII) methods were used to insert n-(phosphorus) and p-type (boron) dopants into the Si substrate. With higher throughput and lower costs, PIII is a better candidate for the photovoltaic industry, compared to BL. However, the optimization of the plasma conditions is demanding and more complex than the beamline approach. Subsequent annealing was performed on selected samples to activate the dopants on both sides of the solar cell. Two annealing methods were investigated: soak and spike thermal annealing. Best performing solar cells, showing a PV efficiency of about 20%, was obtained using spike annealing with adapted ion implantation conditions.

Comparison of Passive and Active Air Sampling (PAAS) Methods for PCBs – A Pilot Study in New York City Schools

EPA Science Inventory

PCBs were used extensively in school building materials (caulk and lighting fixture ballasts) during the approximate period of 1950-1978. Most of the schools built nationwide during this period have not had indoor air sampling conducted for PCBs. Passive air sampling holds promi...

Mixing of a passive scalar in isotropic and sheared homogeneous turbulence

NASA Technical Reports Server (NTRS)

Shirani, E.; Ferziger, J. H.; Reynolds, W. C.

1981-01-01

In order to calculate the velocity and scalar fields, the three dimensional, time-dependent equations of motion and the diffusion equation were solved numerically. The following cases were treated: isotropic, homogeneous turbulence with decay of a passive scalar; and homogeneous turbulent shear flow with a passive scalar whose mean varies linearly in the spanwise direction. The solutions were obtained at relatively low Reynolds numbers so that all of the turbulent scales could be resolved without modeling. Turbulent statistics such as integral length scales, Taylor microscales, Kolmogorov length scale, one- and two-point correlations of velocity-velocity and velocity-scalar, turbulent Prandtl/Schmidt number, r.m.s. values of velocities, the scalar quantity and pressure, skewness, decay rates, and decay exponents were calculated. The results are compared with the available expermental results, and good agreement is obtained.

Comparison of active and passive sampling strategies for the monitoring of pesticide contamination in streams

NASA Astrophysics Data System (ADS)

Assoumani, Azziz; Margoum, Christelle; Guillemain, Céline; Coquery, Marina

2014-05-01

The monitoring of water bodies regarding organic contaminants, and the determination of reliable estimates of concentrations are challenging issues, in particular for the implementation of the Water Framework Directive. Several strategies can be applied to collect water samples for the determination of their contamination level. Grab sampling is fast, easy, and requires little logistical and analytical needs in case of low frequency sampling campaigns. However, this technique lacks of representativeness for streams with high variations of contaminant concentrations, such as pesticides in rivers located in small agricultural watersheds. Increasing the representativeness of this sampling strategy implies greater logistical needs and higher analytical costs. Average automated sampling is therefore a solution as it allows, in a single analysis, the determination of more accurate and more relevant estimates of concentrations. Two types of automatic samplings can be performed: time-related sampling allows the assessment of average concentrations, whereas flow-dependent sampling leads to average flux concentrations. However, the purchase and the maintenance of automatic samplers are quite expensive. Passive sampling has recently been developed as an alternative to grab or average automated sampling, to obtain at lower cost, more realistic estimates of the average concentrations of contaminants in streams. These devices allow the passive accumulation of contaminants from large volumes of water, resulting in ultratrace level detection and smoothed integrative sampling over periods ranging from days to weeks. They allow the determination of time-weighted average (TWA) concentrations of the dissolved fraction of target contaminants, but they need to be calibrated in controlled conditions prior to field applications. In other words, the kinetics of the uptake of the target contaminants into the sampler must be studied in order to determine the corresponding sampling rate constants (Rs). Each constant links the mass of the a target contaminant accumulated in the sampler to its concentration in water. At the end of the field application, the Rs are used to calculate the TWA concentration of each target contaminant with the final mass of the contaminants accumulated in the sampler. Stir Bar Sorptive Extraction (SBSE) is a solvent free sample preparation technique dedicated to the analysis of moderately hydrophobic to hydrophobic compounds in liquid and gas samples. It is composed of a magnet enclosed in a glass tube coated with a thick film of polydimethysiloxane (PDMS). We recently developed the in situ application of SBSE as a passive sampling technique (herein named "Passive SBSE") for the monitoring of agricultural pesticides. The aim of this study is to perform the calibration of the passive SBSE in the laboratory, and to apply and compare this technique to active sampling strategies for the monitoring of 16 relatively hydrophobic to hydrophobic pesticides in streams, during 2 1-month sampling campaigns. Time-weighted averaged concentrations of the target pesticides obtained from passive SBSE were compared to the target pesticide concentrations of grab samples, and time-related and flow-dependent samples of the streams. Results showed passive SBSE as an efficient alternative to conventional active sampling strategies.

a Thermally Desorbable Miniature Passive Dosimeter for Organic Vapors

NASA Astrophysics Data System (ADS)

Gonzalez, Jesus Antonio

A thermally desorbable miniature passive dosimeter (MPD) for organic vapors has been developed in conformity with theoretical and practical aspects of passive dosimeter design. The device was optimized for low sample loadings resulting from short-term and/or low concentration level exposure. This was accomplished by the use of thermal desorption rather than solvent elution, which provided the GC method with significantly higher sensitivity. Laboratory evaluation of this device for factors critical to the performance of passive dosimeters using benzene as the test vapor included: desorption efficiency (97.2%), capacity (1400 ppm-min), sensitivity (7ng/sample or 0.06 ppmv for 15 minutes sampling) accuracy and precision, concentration level, environmental conditions (i.e., air face velocity, relative humidity) and sample stability during short (15 minutes) and long periods of time (15 days). This device has demonstrated that its overall accuracy meets NIOSH and OSHA requirements for a sampling and analytical method for the exposure concentration range of 0.1 to 50 ppm (v/v) and 15 minutes exposures. It was demonstrated that the MPD operates in accordance with theoretically predicted performance and should be adequate for short-term and/or low concentration exposure monitoring of organic vapors in the workplace. In addition a dynamic vapor exposure evaluation system for passive dosimeters have been validated using benzene as the test vapor. The system is capable of generating well defined short-square wave concentration profiles suitable for the evaluation of passive dosimeters for ceiling exposure monitoring.

Sorbent-based sampling methods for volatile and semi-volatile organic compounds in air. Part 2. Sorbent selection and other aspects of optimizing air monitoring methods.

PubMed

Woolfenden, Elizabeth

2010-04-16

Sorbent tubes/traps are widely used in combination with gas chromatographic (GC) analytical methods to monitor the vapour-phase fraction of organic compounds in air. Applications range from atmospheric research and ambient air monitoring (indoor and outdoor) to occupational hygiene (personal exposure assessment) and measuring chemical emission levels. Part 1 of this paper reviewed the main sorbent-based air sampling strategies including active (pumped) tube monitoring, diffusive (passive) sampling onto sorbent tubes/cartridges plus sorbent trapping/focusing of whole air samples that are either collected in containers (such as canisters or bags) or monitored online. Options for subsequent extraction and transfer to GC(MS) analysis were also summarised and the trend to thermal desorption (TD)-based methods and away from solvent extraction was explained. As a result of this trend, demand for TD-compatible sorbents (alternatives to traditional charcoal) is growing. Part 2 of this paper therefore continues with a summary of TD-compatible sorbents, their respective advantages and limitations and considerations for sorbent selection. Other analytical considerations for optimizing sorbent-based air monitoring methods are also discussed together with recent technical developments and sampling accessories which have extended the application range of sorbent trapping technology generally. Copyright 2010 Elsevier B.V. All rights reserved.

Efflux of drugs and solutes from brain: the interactive roles of diffusional transcapillary transport, bulk flow and capillary transporters.

PubMed

Groothuis, Dennis R; Vavra, Michael W; Schlageter, Kurt E; Kang, Eric W-Y; Itskovich, Andrea C; Hertzler, Shannon; Allen, Cathleen V; Lipton, Howard L

2007-01-01

We examined the roles of diffusion, convection and capillary transporters in solute removal from extracellular space (ECS) of the brain. Radiolabeled solutes (eight with passive distribution and four with capillary or cell transporters) were injected into the brains of rats (n=497) and multiple-time point experiments measured the amount remaining in brain as a function of time. For passively distributed compounds, there was a relationship between lipid:water solubility and total brain efflux:diffusional efflux, which dominated when k(p), the transcapillary efflux rate constant, was >10(0) h(-1); when 10(-1)

Improvement of Electrical Characteristics and Stability of Amorphous Indium Gallium Zinc Oxide Thin Film Transistors Using Nitrocellulose Passivation Layer.

PubMed

Shin, Kwan Yup; Tak, Young Jun; Kim, Won-Gi; Hong, Seonghwan; Kim, Hyun Jae

2017-04-19

In this research, nitrocellulose is proposed as a new material for the passivation layers of amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs). The a-IGZO TFTs with nitrocellulose passivation layers (NC-PVLs) demonstrate improved electrical characteristics and stability. The a-IGZO TFTs with NC-PVLs exhibit improvements in field-effect mobility (μ FE ) from 11.72 ± 1.14 to 20.68 ± 1.94 cm 2 /(V s), threshold voltage (V th ) from 1.85 ± 1.19 to 0.56 ± 0.35 V, and on/off current ratio (I on/off ) from (5.31 ± 2.19) × 10 7 to (4.79 ± 1.54) × 10 8 compared to a-IGZO TFTs without PVLs, respectively. The V th shifts of a-IGZO TFTs without PVLs, with poly(methyl methacrylate) (PMMA) PVLs, and with NC-PVLs under positive bias stress (PBS) test for 10,000 s represented 5.08, 3.94, and 2.35 V, respectively. These improvements were induced by nitrogen diffusion from NC-PVLs to a-IGZO TFTs. The lone-pair electrons of diffused nitrogen attract weakly bonded oxygen serving as defect sites in a-IGZO TFTs. Consequently, the electrical characteristics are improved by an increase of carrier concentration in a-IGZO TFTs, and a decrease of defects in the back channel layer. Also, NC-PVLs have an excellent property as a barrier against ambient gases. Therefore, the NC-PVL is a promising passivation layer for next-generation display devices that simultaneously can improve electrical characteristics and stability against ambient gases.

Method for fabricating silicon cells

DOEpatents

Ruby, D.S.; Basore, P.A.; Schubert, W.K.

1998-08-11

A process is described for making high-efficiency solar cells. This is accomplished by forming a diffusion junction and a passivating oxide layer in a single high-temperature process step. The invention includes the class of solar cells made using this process, including high-efficiency solar cells made using Czochralski-grown silicon. 9 figs.

Evaluation of a New Passive Diffusion Sampler for Improving the Calibration of Models to Evaluate Vapor Movement at UST Sites

EPA Science Inventory

Understanding transport of volatile contaminants in soil gas and ground water, particularly those associated with underground storage tanks (USTs), requires a detailed knowledge about the depth-dependent distribution of chemical species in the subsurface. A risk assessment of th...

A New Passive Diffusion Sampler for Improving the Calibration of Models to Evaluate Vapor Movement at UST Sites

EPA Science Inventory

Understanding transport of volatile contaminants in soil gas and ground water, particularly those associated with underground storage tanks (USTs), requires a detailed knowledge about the depthdependent distribution of chemical species in the subsurface. A risk assessment of the...

PERFORMANCE OF A NEW PASSIVE DIFFUSION SAMPLER FOR MONITORING BENZENE IN EITHER SOIL GAS OR GROUND WATER

EPA Science Inventory

Understanding transport of volatile contaminants in soil gas and ground water, particularly those associated with underground storage tanks, requires a detailed knowledge about the depth-dependent distribution of chemical species in the subsurface. A risk assessment of the moveme...

In situ bioavailability of DDT and Hg in sediments of the Toce River (Lake Maggiore basin, Northern Italy): accumulation in benthic invertebrates and passive samplers.

PubMed

Pisanello, Francesca; Marziali, Laura; Rosignoli, Federica; Poma, Giulia; Roscioli, Claudio; Pozzoni, Fiorenzo; Guzzella, Licia

2016-06-01

DDT and mercury (Hg) contamination in the Toce River (Northern Italy) was caused by a factory producing technical DDT and using a mercury-cell chlor-alkali plant. In this study, DDT and Hg contamination and bioavailability were assessed by using different approaches: (1) direct evaluation of sediment contamination, (2) assessment of bioaccumulation in native benthic invertebrates belonging to different taxonomic/functional groups, and (3) evaluation of the in situ bioavailability of DDT and Hg using passive samplers. Sampling sites were selected upstream and downstream the industrial plant along the river axis. Benthic invertebrates (Gammaridae, Heptageniidae, and Diptera) and sediments were collected in three seasons and analyzed for DDT and Hg content and the results were used to calculate the biota sediment accumulation factor (BSAF). Polyethylene passive samplers (PEs) for DDT and diffusive gradients in thin films (DGTs) for Hg were deployed in sediments to estimate the concentration of the toxicants in pore water. Analysis for (DDx) were performed using GC-MS. Accuracy was within ±30 % of the certified values and precision was >20 % relative standard deviation (RSD). Total mercury concentrations were determined using an automated Hg mercury analyzer. Precision was >5 % and accuracy was within ±10 % of certified values. The results of all the approaches (analysis of sediment, biota, and passive samplers) showed an increasing contamination from upstream to downstream sites. BSAF values revealed the bioavailability of both contaminants in the study sites, with values up to 49 for DDx and up to 3.1 for Hg. No correlation was found between values in sediments and the organisms. Concentrations calculated using passive samplers were correlated with values in benthic invertebrates, while no correlation was found with concentrations in sediments. Thus, direct analysis of toxicant in sediments does not provide a measurement of bioavailability. On the contrary, analysis of bioaccumulation in benthic organisms provides the most realistic picture of the site-specific bioavailability of DDx and Hg, but this approach is time-consuming and not always feasible. On the other hand, the in situ deployment of passive samplers proved to be a powerful tool, providing a good surrogate measure of bioaccumulation.

Multilayer Protective Coatings for High-Level Nuclear Waste Storage Containers

NASA Astrophysics Data System (ADS)

Fusco, Michael

Corrosion-based failures of high-level nuclear waste (HLW) storage containers are potentially hazardous due to a possible release of radionuclides through cracks in the canister due to corrosion, especially for above-ground storage (i.e. dry casks). Protective coatings have been proposed to combat these premature failures, which include stress-corrosion cracking and hydrogen-diffusion cracking, among others. The coatings are to be deposited in multiple thin layers as thin films on the outer surface of the stainless steel waste basket canister. Coating materials include: TiN, ZrO2, TiO2, Al 2O3, and MoS2, which together may provide increased resistances to corrosion and mechanical wear, as well as act as a barrier to hydrogen diffusion. The focus of this research is on the corrosion resistance and characterization of single layer coatings to determine the possible benefit from the use of the proposed coating materials. Experimental methods involve electrochemical polarization, both DC and AC techniques, and corrosion in circulating salt brines of varying pH. DC polarization allows for estimation of corrosion rates, passivation behavior, and a qualitative survey of localized corrosion, whereas AC electrochemistry has the benefit of revealing information about kinetics and interfacial reactions that is not obtainable using DC techniques. Circulation in salt brines for nearly 150 days revealed sustained adhesion of the coatings and minimal weight change of the steel samples. One-inch diameter steel coupons composed of stainless steel types 304 and 316 and A36 low alloy carbon steel were coated with single layers using magnetron sputtering with compound targets in an inert argon atmosphere. This resulted in very thin films for the metal-oxides based on low sputter rates. DC polarization showed that corrosion rates were very similar between bare and coated stainless steel samples, whereas a statistically significant decrease in uniform corrosion was measured on coated, as opposed to bare, mild steel. Passivation and passive breakdown was largely unaffected by the coating materials. Activation parameters were determined for corrosion rates and passive breakdown potential based on measurements performed between 20°C and 80°C to simulate elevated waste canister temperatures due to decay heat. Electrochemical impedance spectroscopy (EIS) was used to study the metal-electrolyte interface and the passive film formed on types 304 and 316 stainless steel. Capacitance values were calculated by utilizing the constant phase element and a conversion technique proposed in the literature. This method was shown to remove the frequency dependence of the capacitance that is often seen in electrochemical analysis. The dielectric constant was estimated from impedance and potentiostatic current measurements, and film defect densities were calculated to be on the order of 1020 cm-3, which is consistent with highly-doped semiconductive films. EIS was also employed to study reactively-sputtered TiO2 films on stainless steel type 304, which was substantially thicker than initial TiO2 coatings. The impedance spectra of TiO2-coated stainless steel exhibited several distinctions from its uncoated counterpart and were clearly dominated by the dielectric coating material. Film defect density was on the order of 1017 cm-3, which is several orders of magnitude lower than the bare steel and is more consistent with solid-state semiconductors. This research shows the potential of these coating materials to alter the corrosion behavior of the outer surface of a HLW storage canister. Although the initial single layered coatings had little effect on the corrosion and passivity of the stainless steel substrates, it is possible that with a thicker multi-layered coating system the substrate may be sufficiently isolated from the environment. Moreover, the thin single layer coatings were able to reduce corrosion of A36 steel, showing the promise of these coating materials in reducing uniform corrosion. Further optimization of deposition parameters and testing of multilayer coatings is necessary for serious consideration of these coatings in the future.

Computation of wake/exhaust mixing downstream of advanced transport aircraft

NASA Technical Reports Server (NTRS)

Quackenbush, Todd R.; Teske, Milton E.; Bilanin, Alan J.

1993-01-01

The mixing of engine exhaust with the vortical wake of high speed aircraft operating in the stratosphere can play an important role in the formation of chemical products that deplete atmospheric ozone. An accurate analysis of this type of interaction is therefore necessary as a part of the assessment of the impact of proposed High Speed Civil Transport (HSCT) designs on atmospheric chemistry. This paper describes modifications to the parabolic Navier-Stokes flow field analysis in the UNIWAKE unified aircraft wake model to accommodate the computation of wake/exhaust mixing and the simulation of reacting flow. The present implementation uses a passive chemistry model in which the reacting species are convected and diffused by the fluid dynamic solution but in which the evolution of the species does not affect the flow field. The resulting analysis, UNIWAKE/PCHEM (Passive CHEMistry) has been applied to the analysis of wake/exhaust flows downstream of representative HSCT configurations. The major elements of the flow field model are described, as are the results of sample calculations illustrating the behavior of the thermal exhaust plume and the production of species important to the modeling of condensation in the wake. Appropriate steps for further development of the UNIWAKE/PCHEM model are also outlined.

Active and realistic passive marijuana exposure tested by three immunoassays and GC/MS in urine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mule, S.J.; Lomax, P.; Gross, S.J.

Human urine samples obtained before and after active and passive exposure to marijuana were analyzed by immune kits (Roche, Amersham, and Syva) and gas chromatography/mass spectrometry (GC/MS). Seven of eight subjects were positive for the entire five-day test period with one immune kit. The latter correlated with GC/MS in 98% of the samples. Passive inhalation experiments under conditions likely to reflect realistic exposure resulted consistently in less than 10 ng/mL of cannabinoids. The 10-100-ng/mL cannabinoid concentration range essential for detection of occasional and moderate marijuana users is thus unaffected by realistic passive inhalation.

Comparison of the Electrochemical Behavior of Ti and Nanostructured Ti-Coated AISI 304 Stainless Steel in Strongly Acidic Solutions

NASA Astrophysics Data System (ADS)

Attarzadeh, Farid Reza; Elmkhah, Hassan; Fattah-Alhosseini, Arash

2017-02-01

In this study, the electrochemical behaviors of pure titanium (Ti) and nanostructured (NS) Ti-coated AISI 304 stainless steel (SS) in strongly acidic solutions of H2SO4 were investigated and compared. A type of physical vapor deposition method, cathodic arc evaporation, was applied to deposit NS Ti on 304 SS. Scanning electron microscope and X-ray diffraction were used to characterize surface coating morphology. Potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott-Schottky (M-S) analysis were used to evaluate the passive behavior of the samples. Electrochemical measurements revealed that the passive behavior of NS Ti coating was better than that of pure Ti in 0.1 and 0.01 M H2SO4 solutions. M-S analysis indicated that the passive films behaved as n-type semiconductors in H2SO4 solutions and the deposition method did not affect the semiconducting type of passive films formed on the coated samples. In addition, this analysis showed that the NS Ti coating had lower donor densities. Finally, all electrochemical tests showed that the passive behavior of the Ti-coated samples was superior, mainly due to the formation of thicker, yet less defective passive films.

Flow-Meter and Passive Diffusion Bag Tests and Potential Influences on the Vertical Distribution of Contaminants in Wells at Galena Airport, Galena, Alaska, August to October 2002

USGS Publications Warehouse

Vroblesky, Don A.; Peterson, J.E.

2004-01-01

Past activities at Galena Airport, a U.S. Air Force Base in Galena, Alaska, have resulted in ground-water contamination by volatile organic compounds. The primary contaminants are petroleum hydrocarbons and chlorinated aliphatic hydrocarbons. The U.S. Geological Survey and Earth Tech, in cooperation with the Air Force Center for Environmental Excellence, conducted investigations at Galena Airport from August to October 2002 using polyethylene diffusion bag samplers and borehole flow-meter testing to examine the vertical distribution of ground-water contamination in selected wells. This investigation was limited to the vicinity of building 1845 and to the area between building 1845 and the Yukon River. In addition, the U.S. Geological Survey was asked to determine whether additional wells are needed to more clearly define the nature and extent of the ground-water contamination at the Air Force Base. Little or no vertical water movement occurred under ambient conditions in the wells tested at Galena Airport, Alaska, in August 2002. All of the ambient vertical flows detected in wells were at rates less than the quantitative limit of the borehole flow meter (0.03 gallons per minute). In wells 06-MW-07 and 10-MW-01, no vertical flow was detected. In wells where ambient flow was detected, the direction of flow was downward. In general, concentrations of volatile organic compounds detected in the low-flow samples from wells at Galena Airport were approximately the same concentrations detected in the closest polyethylene diffusion bag sample for a wide variety of volatile organic compounds. The data indicate that the polyethylene diffusion bag sample results are consistent with the low-flow sample results. Vertical profiling of selected wells using polyethylene diffusion bag samplers at Galena Airport showed that from September 30 to October 1, 2002, little vertical change occurred in volatile organic compound concentrations along the screen length despite the fact that little or no vertical flow was measured in most of the tested wells in August 2002. Two of the wells (10-MW-03 and 06-MW-01) had slightly greater vertical concentration variation for some constituents. In these wells, the contaminant depth probably is lithologically influenced. The close match between concentrations measured in polyethylene diffusion bag and low-flow samples indicates that the bag samples accurately represent the distribution of volatile organic compounds in the wells. It is unclear, however, whether the distribution of volatile organic compounds in the wells, as indicated by the bag samplers, represents contaminant distributions in the aquifer or transient movement within the wells. The probable change in well hydraulics between August and late September to October indicates that the relatively uniform vertical distribution of volatile organic compounds in some of the wells may represent in-well mixing. This uncertainty could be clarified by the installation and sampling of well clusters at various times of the year. Additional insight into the vertical distribution of contamination and flow possibly could be obtained by conducting flow-meter tests and collecting polyethylene diffusion bag samples from selected wells at different times of the year. The westernmost contaminant plume at Million Gallon Hill appears to be surrounded by sufficient monitoring wells to detect changes in the plume extent; however, the installation of additional wells at Galena Airport has the potential to provide additional information on the extent of ground-water contamination in the remaining plumes. The additional information to be gained includes better definition of the vertical and lateral extents of the plumes and better definition of the ground-water flow directions.

Performance of passive samplers for monitoring estuarine water column concentrations: 2. Emerging contaminants.

PubMed

Perron, Monique M; Burgess, Robert M; Suuberg, Eric M; Cantwell, Mark G; Pennell, Kelly G

2013-10-01

Measuring dissolved concentrations of emerging contaminants, such as polybrominated diphenyl ethers (PBDEs) and triclosan, can be challenging due to their physicochemical properties resulting in low aqueous solubilities and association with particles. Passive sampling methods have been applied to assess dissolved concentrations in water and sediments primarily for legacy contaminants. Although the technology is applicable to some emerging contaminants, the use of passive samplers with emerging contaminants is limited. In the present study, the performance of 3 common passive samplers was evaluated for sampling PBDEs and triclosan. Passive sampling polymers included low-density polyethylene (PE) and polyoxymethylene (POM) sheets, and polydimethylsiloxane (PDMS)-coated solid-phase microextraction (SPME) fibers. Dissolved concentrations were calculated using measured sampler concentrations and laboratory-derived partition coefficients. Dissolved tri-, tetra-, and pentabrominated PBDE congeners were detected at several of the study sites at very low pg/L concentrations using PE and POM. Calculated dissolved water concentrations of triclosan ranged from 1.7 ng/L to 18 ng/L for POM and 8.8 ng/L to 13 ng/L for PE using performance reference compound equilibrium adjustments. Concentrations in SPME were not reported due to lack of detectable chemical in the PDMS polymer deployed. Although both PE and POM were found to effectively accumulate emerging contaminants from the water column, further research is needed to determine their utility as passive sampling devices for emerging contaminants. © 2013 SETAC.

Deriving sediment Interstitial Water Remediation Goals (IWRGs) for the protection of benthic organisms from direct toxicity

EPA Science Inventory

Background/Objectives. Passive sampling is becoming a frequently used measurement technique at Superfund sites with contaminated sediments. Passive sampling measures the concentrations of freely dissolved chemicals (Cfrees) in the sediment interstitial water. The freely dissol...

Measurement of cyclic volatile methylsiloxanes in the aquatic environment using low-density polyethylene passive sampling devices using an in-field calibration study--challenges and guidance.

PubMed

Bruemmer, Janine; Falcon, Raquel; Greenwood, Richard; Mills, Graham A; Hastie, Colin; Sparham, Chris; van Egmond, Roger

2015-03-01

Cyclic volatile methylsiloxanes (cVMS) are used in personal care products and are hydrophobic, volatile and persistent. Their environmental water concentrations are low and are difficult to detect using conventional sampling methods. This study shows the potential of passive sampling for cVMS. We used low-density polyethylene (LDPE) samplers and in-field calibration methods for octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). (13)C-D4 and (13)C-D5, methyltris(trimethylsiloxy)silane (MT), tetrakis(trimethylsiloxy)silane (TK), and five deuterated polycyclic aromatic hydrocarbons (PAHs) were used as performance reference compounds (PRCs). Samplers were calibrated (7-d) using effluent at a treatment plant, with uptake of cVMS and losses of the PRCs measured at 12 time-points. Concentrations of D4 (53ngL(-1)) and D5 (1838ngL(-1)) were stable in the effluent. Uptake of D4 and loss of (13)C-D4 were isotropic and equilibrium was approached by 7-d. Two estimates of sampler uptake rate (Rs) were 2.1Ld(-1) and 2.5Ld(-1). The estimated log LDPE/water partition coefficient was 4.4. The uptake of D5 was slower (Rs=0.32Ld(-1)) and equilibrium was not reached. Offloading of (13)C-D5, MT and TK were slow, and isotropic behaviour was not demonstrated for D5. Offloading of PAHs followed the predicted pattern for LDPE. Uptake of cVMS appeared to be under membrane control, due to low diffusion coefficients in LDPE. Samplers can monitor time-weighted average concentrations of D4 for less than a week, and D5 for longer periods. LDPE samplers allow cVMS to be determined at lower concentrations than by spot sampling methods. Copyright © 2014 Elsevier Ltd. All rights reserved.

Assessment of Envi-Carb™ as a passive sampler binding phase for acid herbicides without pH adjustment.

PubMed

Seen, Andrew; Bizeau, Oceane; Sadler, Lachlan; Jordan, Timothy; Nichols, David

2014-05-01

The graphitised carbon solid phase extraction (SPE) sorbent Envi-Carb has been used to fabricate glass fibre filter- Envi-Carb "sandwich" disks for use as a passive sampler for acid herbicides. Passive sampler uptake of a suite of herbicides, including the phenoxyacetic acid herbicides 4-chloro-o-tolyloxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (Dicamba), was achieved without pH adjustment, demonstrating for the first time a suitable binding phase for passive sampling of acid herbicides at neutral pH. Passive sampling experiments with Duck River (Tasmania, Australia) water spiked at 0.5 μg L(-1) herbicide concentration over a 7 d deployment period showed that sampling rates in Duck River water decreased for seven out of eight herbicides, and in the cases of 3,6-dichloro-2-pyridinecarboxylic acid (Clopyralid) and Dicamba no accumulation of the herbicides occurred in the Envi-Carb over the deployment period. Sampling rates for 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid (Picloram), 2,4-D and MCPA decreased to approximately 30% of the sampling rates in ultrapure water, whilst sampling rates for 2-(4,6-dimethylpyrimidin-2-ylcarbamoylsulfamoyl) benzoic acid, methyl ester (Sulfometuron-methyl) and 3,5,6-Trichloro-2-pyridinyloxyacetic acid (Triclopyr) were approximately 60% of the ultrapure water sampling rate. For methyl N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-D-alaninate (Metalaxyl-M) there was little variation in sampling rate between passive sampling experiments in ultrapure water and Duck River water. SPE experiments undertaken with Envi-Carb disks using ultrapure water and filtered and unfiltered Duck River water showed that not only is adsorption onto particulate matter in Duck River water responsible for a reduction in herbicide sampling rate, but interactions of herbicides with dissolved or colloidal matter (matter able to pass through a 0.2 μm membrane filter) also reduces the herbicide sampling rate. Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.

ALD TiO x as a top-gate dielectric and passivation layer for InGaZnO115 ISFETs

NASA Astrophysics Data System (ADS)

Pavlidis, S.; Bayraktaroglu, B.; Leedy, K.; Henderson, W.; Vogel, E.; Brand, O.

2017-11-01

The suitability of atomic layer deposited (ALD) titanium oxide (TiO x ) as a top gate dielectric and passivation layer for indium gallium zinc oxide (InGaZnO115) ion sensitive field effect transistors (ISFETs) is investigated. TiO x is an attractive barrier material, but reports of its use for InGaZnO thin film transistor (TFT) passivation have been conflicting thus far. In this work, it is found that the passivated TFT’s behavior depends on the TiO x deposition temperature, affecting critical device characteristics such as threshold voltage, field-effect mobility and sub-threshold swing. An O2 annealing step is required to recover TFT performance post passivation. It is also observed that the positive bias stress response of the passivated TFTs improves compared the original bare device. Secondary ion mass spectroscopy excludes the effects of hydrogen doping and inter-diffusion as sources of the temperature-dependent performance change, therefore indicating that oxygen gettering induced by TiO x passivation is the likely source of oxygen vacancies and, consequently, carriers in the InGaZnO film. It is also shown that potentiometric sensing using ALD TiO x exhibits a near Nernstian response to pH change, as well as minimizes V TH drift in TiO x passivated InGaZnO TFTs immersed in an acidic liquid. These results add to the understanding of InGaZnO passivation effects and underscore the potential for low-temperature fabricated InGaZnO ISFETs to be used as high-performance mobile chemical sensors.

Passive sampling to measure baseline dissolved persistent organic pollutant concentrations in the water column of the Palos Verdes Shelf Superfund site.

PubMed

Fernandez, Loretta A; Lao, Wenjian; Maruya, Keith A; White, Carmen; Burgess, Robert M

2012-11-06

Passive sampling was used to deduce water concentrations of persistent organic pollutants (POPs) in the vicinity of a marine Superfund site on the Palos Verdes Shelf, California, USA. Precalibrated solid phase microextraction (SPME) fibers and polyethylene (PE) strips that were preloaded with performance reference compounds (PRCs) were codeployed for 32 d along an 11-station gradient at bottom, surface, and midwater depths. Retrieved samplers were analyzed for DDT congeners and their breakdown products (DDE, DDD, DDMU, and DDNU) and 43 PCB congeners using GC-EI- and NCI-MS. PRCs were used to calculate compound-specific fractional equilibration achieved in situ for the PE samplers, using both an exponential approach to equilibrium (EAE) and numerical integration of Fickian diffusion (NI) models. The highest observed concentrations were for p,p'-DDE, with 2200 and 990 pg/L deduced from PE and SPME, respectively. The difference in these estimates could be largely attributed to uncertainty in equilibrium partition coefficients, unaccounted for disequilibrium between samplers and water, or different time scales over which the samplers average. The concordance between PE and SPME estimated concentrations for DDE was high (R(2) = 0.95). PCBs were only detected in PE samplers, due to their much larger size. Near-bottom waters adjacent to and down current from sediments with the highest bulk concentrations exhibited aqueous concentrations of DDTs and PCBs that exceeded Ambient Water Quality Criteria (AWQC) for human and aquatic health, indicating the need for future monitoring to determine the effectiveness of remedial activities taken to reduce adverse effects of contaminated surface sediments.

Thermally oxidized titania nanotubes enhance the corrosion resistance of Ti6Al4V.

PubMed

Grotberg, John; Hamlekhan, Azhang; Butt, Arman; Patel, Sweetu; Royhman, Dmitry; Shokuhfar, Tolou; Sukotjo, Cortino; Takoudis, Christos; Mathew, Mathew T

2016-02-01

The negative impact of in vivo corrosion of metallic biomedical implants remains a complex problem in the medical field. We aimed to determine the effects of electrochemical anodization (60V, 2h) and thermal oxidation (600°C) on the corrosive behavior of Ti-6Al-4V, with serum proteins, at physiological temperature. Anodization produced a mixture of anatase and amorphous TiO2 nanopores and nanotubes, while the annealing process yielded an anatase/rutile mixture of TiO2 nanopores and nanotubes. The surface area was analyzed by the Brunauer-Emmett-Teller method and was estimated to be 3 orders of magnitude higher than that of polished control samples. Corrosion resistance was evaluated on the parameters of open circuit potential, corrosion potential, corrosion current density, passivation current density, polarization resistance and equivalent circuit modeling. Samples both anodized and thermally oxidized exhibited shifts of open circuit potential and corrosion potential in the noble direction, indicating a more stable nanoporous/nanotube layer, as well as lower corrosion current densities and passivation current densities than the smooth control. They also showed increased polarization resistance and diffusion limited charge transfer within the bulk oxide layer. The treatment groups studied can be ordered from greatest corrosion resistance to least as Anodized+Thermally Oxidized > Anodized > Smooth > Thermally Oxidized for the conditions investigated. This study concludes that anodized surface has a potential to prevent long term implant failure due to corrosion in a complex in-vivo environment. Copyright © 2015 Elsevier B.V. All rights reserved.

Selecting Performance Reference Compounds (PRCS) for Low Density Polyethylene Passive Samplers

EPA Science Inventory

Use of equilibrium passive samplers for performing aquatic environmental monitoring at contaminated sites is becoming more common. However, a current challenge in passive sampling is determining when equilibrium is achieved between the sampler, target contaminants, and environm...

Processes for producing low cost, high efficiency silicon solar cells

DOEpatents

Rohatgi, Ajeet; Chen, Zhizhang; Doshi, Parag

1996-01-01

Processes which utilize rapid thermal processing (RTP) are provided for inexpensively producing high efficiency silicon solar cells. The RTP processes preserve minority carrier bulk lifetime .tau. and permit selective adjustment of the depth of the diffused regions, including emitter and back surface field (bsf), within the silicon substrate. Silicon solar cell efficiencies of 16.9% have been achieved. In a first RTP process, an RTP step is utilized to simultaneously diffuse phosphorus and aluminum into the front and back surfaces, respectively, of a silicon substrate. Moreover, an in situ controlled cooling procedure preserves the carrier bulk lifetime .tau. and permits selective adjustment of the depth of the diffused regions. In a second RTP process, both simultaneous diffusion of the phosphorus and aluminum as well as annealing of the front and back contacts are accomplished during the RTP step. In a third RTP process, the RTP step accomplishes simultaneous diffusion of the phosphorus and aluminum, annealing of the contacts, and annealing of a double-layer antireflection/passivation coating SiN/SiO.sub.x.

Interpreting the Weibull fitting parameters for diffusion-controlled release data

NASA Astrophysics Data System (ADS)

Ignacio, Maxime; Chubynsky, Mykyta V.; Slater, Gary W.

2017-11-01

We examine the diffusion-controlled release of molecules from passive delivery systems using both analytical solutions of the diffusion equation and numerically exact Lattice Monte Carlo data. For very short times, the release process follows a √{ t } power law, typical of diffusion processes, while the long-time asymptotic behavior is exponential. The crossover time between these two regimes is determined by the boundary conditions and initial loading of the system. We show that while the widely used Weibull function provides a reasonable fit (in terms of statistical error), it has two major drawbacks: (i) it does not capture the correct limits and (ii) there is no direct connection between the fitting parameters and the properties of the system. Using a physically motivated interpolating fitting function that correctly includes both time regimes, we are able to predict the values of the Weibull parameters which allows us to propose a physical interpretation.

Passive Sampling Methods for Contaminated Sediments: Practical Guidance for Selection, Calibration, and Implementation

EPA Science Inventory

This article provides practical guidance on the use of passive sampling methods(PSMs) that target the freely dissolved concentration (Cfree) for improved exposure assessment of hydrophobic organic chemicals in sediments. Primary considerations for selecting a PSM for a specific a...

On the passive and semiconducting behavior of severely deformed pure titanium in Ringer's physiological solution at 37°C: A trial of the point defect model.

PubMed

Ansari, Ghazaleh; Fattah-Alhosseini, Arash

2017-06-01

The effects of sever plastic deformation through multi-pass accumulative roll bonding on the passive and semiconducting behavior of pure titanium is evaluated in Ringer's physiological solution at 37°C in the present paper. Produced results by polarization plots and electrochemical impedance spectroscopy measurements revealed a significant advance in the passive response of the nano-grained sample compared to that of the annealed pure titanium. Also, Mott-Schottky test results of the nano-grained pure titanium represented a lower donor density and reduced flat-band potential in the formed passive film in comparison with the annealed sample. Moreover, based on the Mott-Schottky analysis in conjunction with the point defect model, it was suggested that with increase in formation potential, the calculated donor density of both annealed and nano-grained samples decreases exponentially and the thickness of the passive film linearly increases. These observations were consistent with the point defect model predictions, considering that the point defects within the passive film are metal interstitials, oxygen vacancies, or both. From the viewpoint of passive and semiconducting behavior, nano-grained pure titanium appeared to be more suitable for implant applications in simulate human body environment compared to annealed pure titanium. Copyright © 2017 Elsevier B.V. All rights reserved.

CONSTRUCTION AND INSTALLATION OF A NEW PASSIVE DIFFUSION SAMPLER CAPABLE OF MONITORING BENZENE IN EITHER SOIL GAS OR GROUND WATER

EPA Science Inventory

Conventional practice to estimate intrusion of fuel vapors from ground water to buildings measures the concentration of BTEX in ground water beneath the building using a conventional well screened across the water table. This practice assumes that the concentration of contaminant...

4 pitfalls to clinical integration.

PubMed

Redding, John

2012-11-01

Four common mistakes can easily thwart clinical integration: Assuming that EHR adoption is the cornerstone of successful integration; Delaying the development of ambulatory services that support clinical integration; Believing that knowledge of clinical integration initiatives will passively diffuse through the ranks; Attaching too much weight to Federal Trade Commission/Department of Justice approval of a clinical integration model.

Evaluation of a New Passive Diffusion Sampler for Monitoring for Soil Gas and Ground Water at Two UST Sites

EPA Science Inventory

Historically, conventional practice to estimate intrusion of fuel vapors from soil and ground water to buildings measures the concentration of BTEX beneath the building using vapor probes or monitoring wells screened across the water table. Standard practice assumes that the co...

Molecular assemblies as protective barriers and adhesion promotion interlayer

DOEpatents

King, David E.; Czanderna, Alvin W.; Kennedy, Cheryl E.

1996-01-01

A protective diffusion barrier having adhesive qualifies for metalized surfaces is provided by a passivating agent having the formula HS--(CH.sub.2).sub.11 --COOH Which forms a very dense, transparent organized molecular assembly or layer that is impervious to water, alkali, and other impurities and corrosive substances that typically attack metal surfaces.

Multifunctional Organic-Semiconductor Interfacial Layers for Solution-Processed Oxide-Semiconductor Thin-Film Transistor.

PubMed

Kwon, Guhyun; Kim, Keetae; Choi, Byung Doo; Roh, Jeongkyun; Lee, Changhee; Noh, Yong-Young; Seo, SungYong; Kim, Myung-Gil; Kim, Choongik

2017-06-01

The stabilization and control of the electrical properties in solution-processed amorphous-oxide semiconductors (AOSs) is crucial for the realization of cost-effective, high-performance, large-area electronics. In particular, impurity diffusion, electrical instability, and the lack of a general substitutional doping strategy for the active layer hinder the industrial implementation of copper electrodes and the fine tuning of the electrical parameters of AOS-based thin-film transistors (TFTs). In this study, the authors employ a multifunctional organic-semiconductor (OSC) interlayer as a solution-processed thin-film passivation layer and a charge-transfer dopant. As an electrically active impurity blocking layer, the OSC interlayer enhances the electrical stability of AOS TFTs by suppressing the adsorption of environmental gas species and copper-ion diffusion. Moreover, charge transfer between the organic interlayer and the AOS allows the fine tuning of the electrical properties and the passivation of the electrical defects in the AOS TFTs. The development of a multifunctional solution-processed organic interlayer enables the production of low-cost, high-performance oxide semiconductor-based circuits. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Turing mechanism for homeostatic control of synaptic density during C. elegans growth

NASA Astrophysics Data System (ADS)

Brooks, Heather A.; Bressloff, Paul C.

2017-07-01

We propose a mechanism for the homeostatic control of synapses along the ventral cord of Caenorhabditis elegans during development, based on a form of Turing pattern formation on a growing domain. C. elegans is an important animal model for understanding cellular mechanisms underlying learning and memory. Our mathematical model consists of two interacting chemical species, where one is passively diffusing and the other is actively trafficked by molecular motors, which switch between forward and backward moving states (bidirectional transport). This differs significantly from the standard mechanism for Turing pattern formation based on the interaction between fast and slow diffusing species. We derive evolution equations for the chemical concentrations on a slowly growing one-dimensional domain, and use numerical simulations to demonstrate the insertion of new concentration peaks as the length increases. Taking the passive component to be the protein kinase CaMKII and the active component to be the glutamate receptor GLR-1, we interpret the concentration peaks as sites of new synapses along the length of C. elegans, and thus show how the density of synaptic sites can be maintained.

Active Generation and Propagation of Ca2+ Signals within Tunneling Membrane Nanotubes

PubMed Central

Smith, Ian F.; Shuai, Jianwei; Parker, Ian

2011-01-01

A new mechanism of cell-cell communication was recently proposed after the discovery of tunneling nanotubes (TNTs) between cells. TNTs are membrane protrusions with lengths of tens of microns and diameters of a few hundred nanometers that permit the exchange of membrane and cytoplasmic constituents between neighboring cells. TNTs have been reported to mediate intercellular Ca2+ signaling; however, our simulations indicate that passive diffusion of Ca2+ ions alone would be inadequate for efficient transmission between cells. Instead, we observed spontaneous and inositol trisphosphate (IP3)-evoked Ca2+ signals within TNTs between cultured mammalian cells, which sometimes remained localized and in other instances propagated as saltatory waves to evoke Ca2+ signals in a connected cell. Consistent with this, immunostaining showed the presence of both endoplasmic reticulum and IP3 receptors along the TNT. We propose that IP3 receptors may actively propagate intercellular Ca2+ signals along TNTs via Ca2+-induced Ca2+ release, acting as amplification sites to overcome the limitations of passive diffusion in a chemical analog of electrical transmission of action potentials. PMID:21504718

Including carrier-mediated transport in oral uptake prediction of nutrients and pharmaceuticals in humans.

PubMed

O'Connor, Isabel A; Veltman, Karin; Huijbregts, Mark A J; Ragas, Ad M J; Russel, Frans G M; Hendriks, A Jan

2014-11-01

Most toxicokinetic models consider passive diffusion as the only mechanism when modeling the oral uptake of chemicals. However, the overall uptake of nutrients and xenobiotics, such as pharmaceuticals and environmental pollutants, can be increased by influx transport proteins. We incorporated carrier-mediated transport into a one-compartment toxicokinetic model originally developed for passive diffusion only. The predictions were compared with measured oral uptake efficiencies of nutrients and pharmaceuticals, i.e. the fraction of the chemical reaching systemic circulation. Including carrier-mediated uptake improved model predictions for hydrophilic nutrients (RMSE=10% vs. 56%, Coefficient of Efficiency CoE=0.5 vs. -9.6) and for pharmaceuticals (RMSE=21% vs. 28% and CoE=-0.4 vs. -1.1). However, the negative CoE for pharmaceuticals indicates that further improvements are needed. Most important in this respect is a more accurate estimation of vMAX and KM as well as the determination of the amount of expressed and functional transport proteins both in vivo and in vitro. Copyright © 2014 Elsevier B.V. All rights reserved.

Effect of sulfur passivation on the InP surface prior to plasma-enhanced chemical vapor deposition of SiNx

NASA Astrophysics Data System (ADS)

Tang, Hengjing; Wu, Xiaoli; Xu, Qinfei; Liu, Hongyang; Zhang, Kefeng; Wang, Yang; He, Xiangrong; Li, Xue; Gong, Hai Mei

2008-03-01

The fabrication of Au/SiNx/InP metal-insulator-semiconductor (MIS) diodes has been achieved by depositing a layer of SiNx on the (NH4)2Sx-treated n-InP. The SiNx layer was deposited at 200 °C using plasma-enhanced chemical vapor deposition (PECVD). The effect of passivation on the InP surface before and after annealing was evaluated by current-voltage (I-V) and capacitance-voltage (C-V) measurements, and Auger electron spectroscopy (AES) analysis was used to investigate the depth profiles of several atoms. The results indicate that the SiNx passivation layer exhibits good insulative characteristics. The annealing process causes distinct inter-diffusion in the SiNx/InP interface and contributes to the decrease of the fixed charge density and minimum interface state density, which are 1.96 × 1012 cm-2 and 7.41 × 1011 cm-2 eV-1, respectively. A 256 × 1 InP/InGaAs/InP heterojunction photodiode, fabricated with sulfidation and SiNx passivation layer, has good response uniformity.

Development and deployment of a passive sampling system in groundwater to characterize the critical zone through isotope tracing

NASA Astrophysics Data System (ADS)

Gal, Frédérick; Négrel, Philippe; Chagué, Bryan

2017-04-01

The Critical Zone (CZ) is the evolving boundary layer where rock, soil, water, air, and living organisms interact, zone controlling the transfer and storage of water and chemical elements. For investigating the CZ, we have developed an integrative sampling system to concentrate the chemical elements in groundwater (CRITEX project). Aims are to measure concentrations and isotopic ratios in groundwater through integrative sampling. In the frame of the groundwater analysis, particularly those located in the critical zone (0-100 m depth), this system makes it possible to create a water flow in a support of passive samplers using Diffusive Gradient in Thin type (DGT) and thus to pre-concentrate the chemical species on a chelating resin by diffusion through a membrane and over a given period in order to facilitate subsequent laboratory measurements. Because DGTs are generally used in surface waters with a high flow rate, the current objective is to create a sufficient flow of water in the sampler to optimize the trapping of elements. Different options and geometries have been modelled by simulation of the flow (agitation of water supplied by a motor and a propeller, pumping ...). The economic model of the device is based on an assembly of commercially available equipment, the novation is based on the support, fully designed in house (patent pending). The device aims to recreate sufficient water flow to avoid the creation of a too large Diffusion Boundary Layer (DBL) on the DGT surface and then to mimic the uptake conditions that prevail in surface waters. The simulations made it possible to optimize the position of the DGT and the velocity of the fluid in order to obtain the maximum flow at its surface and avoid the creation of the DBL. Conditions equivalent to those of a circulation of weakly agitated surface water are thus recreated. The first tests were carried out at lab, in a column simulating a piezometer, including pump, DGT holder and flow meter. Initial functional tests were carried out with tap water to observe the flow of water in the device, to determine the technical characteristics of the system (current, voltage, flow...) and to perform blank measurements to ensure that the device brings no contamination. We then carried out 6 days of immersion of the system on a piezometer of the BRGM site. In parallel, daily sampling was performed using conventional pumping method. Finally, we carried out tests on drillings in the Coët Dan experimental basin (Naizin, Morbihan, France). We established a screening of chemical elements on which isotopic measurements can be done by comparing the accumulated mass in the DGT with respect to the concentration of the elements in water. This suggests that the isotopic determination is possible for U, Sr, Nd and Ni with the exception of Cu and Zn at the moment. Possible contamination of DGTs themselves and/or during field investigations should be further studied in order to rule if Cu or Zn isotope analyses can be foreseen in the future.

A holistic passive integrative sampling approach for assessing the presence and potential impacts of waterborne environmental contaminants

USGS Publications Warehouse

Petty, J.D.; Huckins, J.N.; Alvarez, D.A.; Brumbaugh, W. G.; Cranor, W.L.; Gale, R.W.; Rastall, A.C.; Jones-Lepp, T. L.; Leiker, T.J.; Rostad, C. E.; Furlong, E.T.

2004-01-01

As an integral part of our continuing research in environmental quality assessment approaches, we have developed a variety of passive integrative sampling devices widely applicable for use in defining the presence and potential impacts of a broad array of contaminants. The semipermeable membrane device has gained widespread use for sampling hydrophobic chemicals from water and air, the polar organic chemical integrative sampler is applicable for sequestering waterborne hydrophilic organic chemicals, the stabilized liquid membrane device is used to integratively sample waterborne ionic metals, and the passive integrative mercury sampler is applicable for sampling vapor phase or dissolved neutral mercury species. This suite of integrative samplers forms the basis for a new passive sampling approach for assessing the presence and potential toxicological significance of a broad spectrum of environmental contaminants. In a proof-of-concept study, three of our four passive integrative samplers were used to assess the presence of a wide variety of contaminants in the waters of a constructed wetland, and to determine the effectiveness of the constructed wetland in removing contaminants. The wetland is used for final polishing of secondary-treatment municipal wastewater and the effluent is used as a source of water for a state wildlife area. Numerous contaminants, including organochlorine pesticides, polycyclic aromatic hydrocarbons, organophosphate pesticides, and pharmaceutical chemicals (e.g., ibuprofen, oxindole, etc.) were detected in the wastewater. Herein we summarize the results of the analysis of the field-deployed samplers and demonstrate the utility of this holistic approach.

NEW APPLICATION OF PASSIVE SAMPLING DEVICES FOR ASSESSMENT OF RESPIRATORY EXPOSURE TO PESTICIDES IN INDOOR AIR

EPA Science Inventory

The United States Environmental Protection Agency (EPA) has long maintained an interest in potential applications of passive sampling devices (PSDs) for estimating the concentrations of various pollutants in air. Typically PSDs were designed for the workplace monitoring of vola...

Air sampling procedures to evaluate microbial contamination: a comparison between active and passive methods in operating theatres.

PubMed

Napoli, Christian; Marcotrigiano, Vincenzo; Montagna, Maria Teresa

2012-08-02

Since air can play a central role as a reservoir for microorganisms, in controlled environments such as operating theatres regular microbial monitoring is useful to measure air quality and identify critical situations. The aim of this study is to assess microbial contamination levels in operating theatres using both an active and a passive sampling method and then to assess if there is a correlation between the results of the two different sampling methods. The study was performed in 32 turbulent air flow operating theatres of a University Hospital in Southern Italy. Active sampling was carried out using the Surface Air System and passive sampling with settle plates, in accordance with ISO 14698. The Total Viable Count (TVC) was evaluated at rest (in the morning before the beginning of surgical activity) and in operational (during surgery). The mean TVC at rest was 12.4 CFU/m3 and 722.5 CFU/m2/h for active and passive samplings respectively. The mean in operational TVC was 93.8 CFU/m3 (SD = 52.69; range = 22-256) and 10496.5 CFU/m2/h (SD = 7460.5; range = 1415.5-25479.7) for active and passive samplings respectively. Statistical analysis confirmed that the two methods correlate in a comparable way with the quality of air. It is possible to conclude that both methods can be used for general monitoring of air contamination, such as routine surveillance programs. However, the choice must be made between one or the other to obtain specific information.

Passive alcohol sensors tested in 3 states for youth alcohol enforcement

DOT National Transportation Integrated Search

1996-05-01

Passive alcohol sensors were tested in three states to determine their effectiveness in enforcing zero tolerance or low BAC laws for under 21 age drivers. The passive alcohol sensor was designed to sample the air immediately around the suspect for si...

Equilibrium Passive Sampling of POP in Lipid-Rich and Lean Fish Tissue: Quality Control Using Performance Reference Compounds.

PubMed

Rusina, Tatsiana P; Carlsson, Pernilla; Vrana, Branislav; Smedes, Foppe

2017-10-03

Passive sampling is widely used to measure levels of contaminants in various environmental matrices, including fish tissue. Equilibrium passive sampling (EPS) of persistent organic pollutants (POP) in fish tissue has been hitherto limited to application in lipid-rich tissue. We tested several exposure methods to extend EPS applicability to lean tissue. Thin-film polydimethylsiloxane (PDMS) passive samplers were exposed statically to intact fillet and fish homogenate and dynamically by rolling with cut fillet cubes. The release of performance reference compounds (PRC) dosed to passive samplers prior to exposure was used to monitor the exchange process. The sampler-tissue exchange was isotropic, and PRC were shown to be good indicators of sampler-tissue equilibration status. The dynamic exposures demonstrated equilibrium attainment in less than 2 days for all three tested fish species, including lean fish containing 1% lipid. Lipid-based concentrations derived from EPS were in good agreement with lipid-normalized concentrations obtained using conventional solvent extraction. The developed in-tissue EPS method is robust and has potential for application in chemical monitoring of biota and bioaccumulation studies.

Increased concentrations of polycyclic aromatic hydrocarbons in Alpine streams during annual snowmelt: investigating effects of sampling method, site characteristics, and meteorology.

PubMed

Shahpoury, Pourya; Hageman, Kimberly J; Matthaei, Christoph D; Alumbaugh, Robert E; Cook, Michelle E

2014-10-07

Silicone passive samplers and macroinvertebrates were used to measure time-integrated concentrations of polycyclic aromatic hydrocarbons (PAHs) in alpine streams during annual snowmelt. The three sampling sites were located near a main highway in Arthur's Pass National Park in the Southern Alps of New Zealand. A similar set of PAH congeners, composed of 2-4 rings, were found in silicone passive samplers and macroinvertebrates. The background PAH concentrations were similar at all sites, implying that proximity to the highway did not affect concentrations. In passive samplers, an increase of PAH concentrations by up to seven times was observed during snowmelt. In macroinvertebrates, the concentration changes were moderate; however, macroinvertebrate sampling did not occur during the main pulse observed in the passive samplers. The extent of vegetation in the catchment appeared to affect the concentration patterns seen at the different stream sites. A strong correlation was found between PAH concentrations in passive samplers and the amount of rainfall in the study area, indicating that the washout of contaminants from snowpack by rainfall was an important process.

Effect of surface pre-treatments on biocompatibility of magnesium.

PubMed

Lorenz, Carla; Brunner, Johannes G; Kollmannsberger, Philip; Jaafar, Leila; Fabry, Ben; Virtanen, Sannakaisa

2009-09-01

This study reports the influence of Mg surface passivation on the survival rate of human HeLa cells and mouse fibroblasts in cell culture experiments. Polished samples of commercially pure Mg show high reactivity in the cell culture medium, leading to a pH shift in the alkaline direction, and therefore cell adhesion and survival is strongly impaired. Passivation of the Mg surface in 1M NaOH can strongly enhance cell survival. The best initial cell adhesion is observed for Mg samples incubated in simulated body fluid (M-SBF), which leads to the formation of a biomimetic, amorphous Ca/Mg-phosphate layer with high surface roughness. This surface layer, however, passivates and seals the Mg surface only partially. Subsequent Mg dissolution leads to a significantly stronger pH increase compared to NaOH-passivated samples, which prevents long-term cell survival. These results demonstrate that surface passivation with NaOH and M-SBF together with the associated changes of surface reactivity, chemistry and roughness provide a viable strategy to facilitate cell survival on otherwise non-biocompatible Mg surfaces.

Thermal control materials on EOIM-3

NASA Technical Reports Server (NTRS)

Finckenor, Miria M.; Linton, Roger C.; Kamenetzky, Rachel R.; Vaughn, Jason A.

1995-01-01

Thermal control paints, anodized aluminum, and beta cloth samples were flown on STS-46 as part of the Evaluation of Oxygen Interaction with Materials Experiment (EOIM-3). The thermal control paints flown on EOIM-3 include ceramic and polyurethane-based paints. Passively exposed samples are compared to actively heated samples and controlled exposure samples. Optical property measurements of absorptivity, emissivity, and spectrofluorescence are presented for each paint. Several variations of anodized aluminum, including chromic acid anodize, sulfuric acid anodize, and boric/sulfuric acid anodize were flown on the actively heated trays and the passive exposure trays. The post-flight optical properties are within tolerances for these materials. Also flown were two samples of yellow anodized aluminum. The yellow anodized aluminum samples darkened noticeably. Samples of aluminized and unaluminized beta cloth, a fiberglass woven mat impregnated with TFE Teflon, were flown with passive exposure to the space environment. Data from this part of the experiment is correlated to observations from LDEF and erosion of the Teflon thin film samples also flown on EOIM-3 and LDEF.

Use of Inert Gases and Carbon Monoxide to Study the Possible Influence of Countercurrent Exchange on Passive Absorption from the Small Bowel

PubMed Central

Bond, John H.; Levitt, David G.; Levitt, Michael D.

1974-01-01

The purpose of the present study was to quantitate the influence of countercurrent exchange on passive absorption of highly diffusible substances from the small intestine of the rabbit. The absorption of carbon monoxide, which is tightly bound to hemoglobin and therefore cannot exchange, was compared to the absorption of four unbound gases (H2, He, CH4, and 133Xe), which should exchange freely. The degree to which the observed absorption of the unbound gases falls below that predicted from CO absorption should provide a quantitative measure of countercurrent exchange. CO uptake at high luminal Pco is flow-limited and, assuming that villus and central hemoglobin concentrations are equal, the flow that equilibrates with CO (Fco) was calculated to equal 7.24 ml/min/100 g. The observed absorption rate of the unbound gases was from two to four times greater than would have been predicted had their entire uptake been accounted for by equilibration with Fco. This is the opposite of what would occur if countercurrent exchange retarded absorption of the unbound gases. The unbound gases have both flow- and diffusion-limited components, and Fco should account for only the fraction of absorption that is flow limited. A simple model of perfusion and diffusion made it possible to calculate the fraction of the total uptake of unbound gases that was flow limited. This fraction of the total observed absorption rate was still about 1.8 times greater than predicted by CO absorption. A possible explanation for this discrepancy is that plasma skimming reduces the hemoglobin of villus blood to about 60% of that of central blood. Thus, Fco is actually about 1.7 times greater than initially calculated, and with this correction, there is close agreement between the predicted and observed rates of absorption of each of the unbound gases. We conclude that countercurrent exchange does not influence passive absorption under the conditions of this study. PMID:4436431

Passive Sampling in Regulatory Chemical Monitoring of Nonpolar Organic Compounds in the Aquatic Environment

EPA Science Inventory

We reviewed compliance monitoring requirements in the European Union (EU), the United States(USA), and the Oslo-Paris Convention for the protection of the marine environment of the North-East Atlantic (OSPAR), and evaluated if these are met by passive sampling methods for nonpola...

The effect of light soaking on crystalline silicon surface passivation by atomic layer deposited Al2O3

NASA Astrophysics Data System (ADS)

Liao, Baochen; Stangl, Rolf; Mueller, Thomas; Lin, Fen; Bhatia, Charanjit S.; Hoex, Bram

2013-01-01

The effect of light soaking of crystalline silicon wafer lifetime samples surface passivated by thermal atomic layer deposited (ALD) Al2O3 is investigated in this paper. Contrary to other passivation materials used in solar cell applications (i.e., SiO2, SiNx), using thermal ALD Al2O3, an increase in effective carrier lifetime after light soaking under standard testing conditions is observed for both p-type (˜45%) and n-type (˜60%) FZ c-Si lifetime samples. After light soaking and storing the samples in a dark and dry environment, the effective lifetime decreases again and practically returns to the value before light soaking. The rate of lifetime decrease after light soaking is significantly slower than the rate of lifetime increase by light soaking. To investigate the underlying mechanism, corona charge experiments are carried out on p-type c-Si samples before and after light soaking. The results indicate that the negative fixed charge density Qf present in the Al2O3 films increases due to the light soaking, which results in an improved field-effect passivation. Numerical calculations also confirm that the improved field-effect passivation is the main contributor for the increased effective lifetime after light soaking. To further understand the light soaking phenomenon, a kinetic model—a charge trapping/de-trapping model—is proposed to explain the time dependent behavior of the lifetime increase/decrease observed under/after light soaking. The trap model fits the experimental results very well. The observed light enhanced passivation for ALD Al2O3 passivated c-Si is of technological relevance, because solar cell devices operate under illumination, thus an increase in solar cell efficiency due to light soaking can be expected.

Active flow control of subsonic flow in an adverse pressure gradient using synthetic jets and passive micro flow control devices

NASA Astrophysics Data System (ADS)

Denn, Michael E.

Several recent studies have shown the advantages of active and/or passive flow control devices for boundary layer flow modification. Many current and future proposed air vehicles have very short or offset diffusers in order to save vehicle weight and create more optimal vehicle/engine integration. Such short coupled diffusers generally result in boundary layer separation and loss of pressure recovery which reduces engine performance and in some cases may cause engine stall. Deployment of flow control devices can alleviate this problem to a large extent; however, almost all active flow control devices have some energy penalty associated with their inclusion. One potential low penalty approach for enhancing the diffuser performance is to combine the passive flow control elements such as micro-ramps with active flow control devices such as synthetic jets to achieve higher control authority. The goal of this dissertation is twofold. The first objective is to assess the ability of CFD with URANS turbulence models to accurately capture the effects of the synthetic jets and micro-ramps on boundary layer flow. This is accomplished by performing numerical simulations replicating several experimental test cases conducted at Georgia Institute of Technology under the NASA funded Inlet Flow Control and Prediction Technologies Program, and comparing the simulation results with experimental data. The second objective is to run an expanded CFD matrix of numerical simulations by varying various geometric and other flow control parameters of micro-ramps and synthetic jets to determine how passive and active control devices interact with each other in increasing and/or decreasing the control authority and determine their influence on modification of boundary layer flow. The boundary layer shape factor is used as a figure of merit for determining the boundary layer flow quality/modification and its tendency towards separation. It is found by a large number of numerical experiments and the analysis of simulation data that a flow control device's influence on boundary layer quality is a function of three factors: (1) the strength of the longitudinal vortex emanating from the flow control device or devices, (2) the height of the vortex core above the surface and, when a synthetic jet is present, (3) the momentum added to the boundary layer flow.

Influence of peptide dendrimers and sonophoresis on the transdermal delivery of ketoprofen.

PubMed

Manikkath, Jyothsna; Hegde, Aswathi R; Kalthur, Guruprasad; Parekh, Harendra S; Mutalik, Srinivas

2017-04-15

The aim of this study was to determine the individual and combined effects of peptide dendrimers and low frequency ultrasound on the transdermal permeation of ketoprofen. Arginine terminated peptide dendrimers of varying charges (4 + , 8 + and 16 + , named as A4. A8 and A16 respectively) were synthesized and characterized. Ketoprofen was subjected to passive, peptide dendrimer-assisted and sonophoretic permeation studies (with and without dendrimer application) across Swiss albino mouse skin, both in vitro and in vivo. The studies revealed that the synthesized peptide dendrimers considerably increased the transdermal permeation of ketoprofen and displayed enhancement ratios of up to 3.25 (with A16 dendrimer), compared to passive diffusion of drug alone in vitro. Moreover, the combination of peptide dendrimer treatment and ultrasound application worked in synergy and gave enhancement ratios of up to 1369.15 (with ketoprofen-A16 dendrimer complex). In vivo studies demonstrated that dendrimer and ultrasound-assisted permeation of drug achieved much higher plasma concentration of drug, compared to passive diffusion. Comparison of transdermal and oral absorption studies revealed that transdermal administration of ketoprofen with A8 dendrimer showed comparable absorption and plasma drug levels with oral route. The excised mouse skin after in vivo permeation study with dendrimers and ultrasound did not show major toxic reactions. This study demonstrates that arginine terminated peptide dendrimers combined with sonophoresis can effectively improve the transdermal permeation of ketoprofen. Copyright © 2017 Elsevier B.V. All rights reserved.

Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Yimao, E-mail: yimao.wan@anu.edu.au; Bullock, James; Cuevas, Andres

2015-05-18

This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta{sub 2}O{sub 5}) underneath plasma enhanced chemical vapour deposited silicon nitride (SiN{sub x}). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta{sub 2}O{sub 5} and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Ω·cm and n-type 1.0 Ω·cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm{sup 2} and 68 fA/cm{sup 2} are measured on 150 Ω/sq boron-diffused p{sup +} and 120 Ω/sq phosphorus-diffused n{sup +} c-Si, respectively. Capacitance–voltage measurements reveal a negativemore » fixed insulator charge density of −1.8 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5} film and −1.0 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5}/SiN{sub x} stack. The Ta{sub 2}O{sub 5}/SiN{sub x} stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.« less

The Effects of Applied Stress and Sensitization on the Passive Film Stability of Al-Mg Alloys

DTIC Science & Technology

2013-06-01

and residual tensile and compressive stresses impact the passive layer film and the material’s electrochemistry. Sample plates of AA5083 were...electrochemistry. Sample plates of AA5083 were sensitized to different levels to promote the formation of intergranular β phase (Al3Mg2). The...41  A.  MATERIAL PROCESSING: FABRICATION AND APPLIED STRESSES OF TEST SAMPLES

Permeability, transport, and metabolism of solutes in Caco-2 cell monolayers: a theoretical study.

PubMed

Sun, Huadong; Pang, K Sandy

2008-01-01

We explored the properties of a catenary model that includes the basolateral (B), apical (A), and cellular compartments via simulations under linear and nonlinear conditions to understand the asymmetric observations arising from transporters, enzymes, and permeability in Caco-2 cells. The efflux ratio (EfR; P(app,B-->A)/P(app,A-->B)), obtained from the effective permeability from the A-->B and B-->A direction under linear conditions, was unity for passively permeable drugs whose transport does not involve transporters; the value was unaffected by cellular binding or metabolism, but increased with apical efflux. Metabolism was asymmetric, showing lesser metabolite accrual for the B-->A than A-->B direction because of inherent differences in the volumes for A and B. Moreover, the net flux (total - passive permeation) due to saturable apical efflux, absorption, or metabolism showed nonconformity to simple Michaelis-Menten kinetics against C(D,0), the loading donor concentration. EfR values differed with saturable apical efflux and metabolism (>1), as well as apical absorption (EfRs <1), but approached unity with high passive diffusive clearance (CL(d)) and increasing C(D,0) at a higher degree of saturation of the process. The J(max) (apparent V(max) estimated for the carrier system) and K(m)(') [or the K(m)('') based on a modified equation with the Hill coefficient (beta)] estimates from the Eadie-Hofstee plot revealed spurious correlations with the assigned V(max) and K(m). The sampling time, CL(d), and parameter space of K(m) and V(max) strongly influenced both the correlation and accuracy of estimates. Improved correlation was found for compounds with high CL(d). These observations showed that the catenary model is appropriate in the description of transport and metabolic data in Caco-2 cells.

Acid rock drainage passive remediation using alkaline clay: Hydro-geochemical study and impacts of vegetation and sand on remediation.

PubMed

Plaza, Fernando; Wen, Yipei; Liang, Xu

2018-10-01

Acid rock drainage (ARD) is one of the most adverse environmental problems of the mine industry, especially in regions with an abundance of coal refuse (CR) deposits (e.g. the Northern Appalachian Coalfield in the USA) where surface and ground waters are affected by this pollution due to the acidity and high content of sulfates and heavy metals. This study explores the effectiveness of the ARD passive remediation method using alkaline clay (AC) through a series of static and long-term kinetic laboratory experiments (over three years) complemented with field measurements and geochemical modeling. Two important issues associated with this passive and auto-sustainable ARD remediation method were investigated: 1) the hydrogeochemical study of the mixture in terms of the percentages of AC and CR, and, 2) impacts of vegetation cover and a saturated sand barrier on the remediation. Both the field measurements and the samples used for the experiments came from a local coal waste site. Through the analysis of the field measurements and the outcome of the laboratory experiments and the geochemical modeling, alkaline clay proved to be an effective remediation material for ARD, in terms of achieving a neutral pH in the leachate and immobilization of sulfate and metals such as Fe, Mn, Cu, Zn, Ni, Pb, Cd, Co. Moreover, it has been demonstrated that the use of vegetation and a saturated sand barrier are beneficial. Vegetation acted as a phytoaccumulation/phytoextraction agent, causing an additional immobilization of metals. The saturated sand barrier blocked downward the oxygen and water diffusion, reducing pyrite oxidation rates. The proposed remediation approach ensures that the acidity consumption will likely occur before all the alkalinity is exhausted. Copyright © 2018 Elsevier B.V. All rights reserved.

Design of a Three-Layer Antireflection Coating for High Efficiency Indium Phosphide Solar Cells Using a Chemical Oxide as First Layer

NASA Technical Reports Server (NTRS)

Moulot, Jacques; Faur, Mircea; Faur, Maria; Goradia, Chandra; Goradia, Manju; Bailey, Sheila

1995-01-01

It is well known that the behavior of III-V compound based solar cells is largely controlled by their surface, since the majority of light generated carriers (63% for GaAs and 79% for InP) are created within 0.2 microns of the illuminated surface of the cell. Consequently, the always observed high surface recombination velocity (SRV) on these cells is a serious limiting factor for their high efficiency performance, especially for those with the p-n junction made by either thermal diffusion or ion implantation. A good surface passivation layer, ideally, a grown oxide as opposed to a deposited one, will cause a significant reduction in the SRV without adding interface problems, thus improving the performance of III-V compound based solar cells. Another significant benefit to the overall performance of the solar cells can be achieved by a substantial reduction of their large surface optical reflection by the use of a well designed antireflection (AR) coating. In this paper, we demonstrate the effectiveness of using a chemically grown, thermally and chemically stable oxide, not only for surface passivation but also as an integral part of a 3- layer AR coating for thermally diffused p(+)n InP solar cells. A phosphorus-rich interfacial oxide, In(PO3)3, is grown at the surface of the p(+) emitter using an etchant based on HNO3, o-H3PO4 and H2O2. This oxide has the unique properties of passivating the surface as well as serving as a fairly efficient antireflective layer yielding a measured record high AM0, 25 C, open-circuit voltage of 890.3 mV on a thermally diffused InP(Cd,S) solar cell. Unlike conventional single layer AR coatings such as ZnS, Sb2O3, SiO or double layer AR coatings such as ZnS/MgF2 deposited by e-beam or resistive evaporation, this oxide preserves the stoichiometry of the InP surface. We show that it is possible to design a three-layer AR coating for a thermally diffused InP solar cell using the In(PO3)3 grown oxide as the first layer and Al2O3, MgF2 or ZnS, MgF2 as the second and third layers respectively, so as to yield an overall theoretical reflectance of less than 2%. Since chemical oxides are readily grown on III-V semiconductor materials, the technique of using the grown oxide layer to both passivate the surface as well as serve as the first of a multilayer AR coating, should work well for essentially all III-V compound-based solar cells.

Design of a three-layer antireflection coating for high efficiency indium phosphide solar cells using a chemical oxide as first layer

NASA Technical Reports Server (NTRS)

Moulot, Jacques; Faur, M.; Faur, M.; Goradia, C.; Goradia, M.; Bailey, S.

1995-01-01

It is well known that the behavior of III-V compound based solar cells is largely controlled by their surface, since the majority of light generated carriers (63% for GaAs and 79% for InP) are created within 0.2 mu m of the surface of the illuminated cell. Consequently, the always observed high surface recombination velocity (SRV) on these cells is a serious limiting factor for their high efficiency performance, especially for those with p-n junction made by either thermal diffusion or ion implantation. A good surface passivation layer, ideally a grown oxide as opposed to a deposited one, will cause a significant reduction in the SRV without adding interface problems, thus improving the performance of III-V compound based solar cells. Another significant benefit to the overall performance of the solar cells can be achieved by a substantial reduction of their large surface optical reflection by the use of a well designed antireflection (AR) coating. In this paper, we demonstrate the effectiveness of using a chemically grown thermally and chemically stable oxide, not only for surface passivation but also as an integral part of a 3-layer AR coating for thermally diffused p+n InP solar cells. A phosphorus-rich interfacial oxide, In(PO3)3, is grown at the surface of the p+ emitter using an etchant based on HNO3, o-H3PO4 and H2O2. This oxide has the unique properties of passivating the surface as well as serving as an efficient antireflective layer yielding a measured record high AMO open-circuit voltage of 890.3 mV on a thermally diffused InP(Cd,S) solar cell. Unlike conventional single layer AR coatings such as ZnS, Sb2O3, SiO or double layer AR coatings such as ZnS/MgF2 deposited by e-beam or resistive evaporation, this oxide preserves the stoichiometry of the InP surface. We show that it is possible to design a three-layer AR coating for a thermally diffused InP solar cell using the In(PO3)3 grown oxide as the first layer and Al2O3 and MgF2 as the second and third layers respectively, so as to yield an overall theoretical reflectance of less than 2%. Since chemical oxides are readily grown on III-V semiconductors materials, the technique of using the grown oxide layer to both passivate the surface as well as serve as the first of a multilayer AR coating should work well for all III-V compound-based solar cells.

Assembly of bipolar microtubule structures by passive cross-linkers and molecular motors

NASA Astrophysics Data System (ADS)

Johann, D.; Goswami, D.; Kruse, K.

2016-06-01

During cell division, sister chromatids are segregated by the mitotic spindle, a bipolar assembly of interdigitating antiparallel polar filaments called microtubules. The spindle contains the midzone, a stable region of overlapping antiparallel microtubules, that is essential for maintaining bipolarity. Although a lot is known about the molecular players involved, the mechanism underlying midzone formation and maintenance is still poorly understood. We study the interaction of polar filaments that are cross-linked by molecular motors moving directionally and by passive cross-linkers diffusing along microtubules. Using a particle-based stochastic model, we find that the interplay of motors and passive cross-linkers can generate a stable finite overlap between a pair of antiparallel polar filaments. We develop a mean-field theory to study this mechanism in detail and investigate the influence of steric interactions between motors and passive cross-linkers on the overlap dynamics. In the presence of interspecies steric interactions, passive cross-linkers mimic the behavior of molecular motors and stable finite overlaps are generated even for non-cross-linking motors. Finally, we develop a mean-field theory for a bundle of aligned polar filaments and show that they can self-organize into a spindlelike pattern. Our work suggests possible ways as to how cells can generate spindle midzones and control their extensions.

Toxicological Assessment of ISS Air Quality: April - May 2013. [Increment 35

NASA Technical Reports Server (NTRS)

Meyers, Valerie

2013-01-01

A summary of the analytical results from 4 mini-grab sample (mGSCs) collected on ISS and returned aboard 33S is shown in Table 1. Due to the launch delay of the ATV4 resupply mission, monthly samples were reduced in April and May by omitting sampling of the Service Module in order to ensure contingency samplers were available if needed. Complete data tables of all measured concentrations and corresponding T-values based on 180-day SMACs are enclosed. detection limit for all target compounds, except m/p-xylenes and hexachloro-1, 3-butadiene was 0.025 mg/cu m. The detection limit for m/p-xylenes and hexachloro-1, 3-butadiene and all non-target compounds was 0.05 mg/cu m. The average recoveries of the 3 surrogate standards from the mGSCs were as follows: C-13-acetone, 116 +/- 12%; D-5-fluorobenzene, 117 +/- 7%; and D-5-chlorobenzene, 111 +/- 15%. Initial measured sample pressures were between 13.9 and 14.1 psia for all samples, indicating nominal sample collection. A summary of the analytical results from 3 pairs of passive-diffusion formaldehyde badges collected on ISS and returned aboard 33S is also provided in Table 1. In an effort to conserve samples due to the delay of the ATV4 resupply mission, FMK sampling was only conducted in the US Lab in May. Positive control recoveries (1 trip and 2 lab controls) were 79%, 87%, and 116% respectively.

Passive Rocket Diffuser Testing: Reacting Flow Performance of Four Second-Throat Geometries

NASA Technical Reports Server (NTRS)

Jones, Daniel R.; Allgood, Daniel C.; Saunders, Grady P.

2016-01-01

Second-throat diffusers serve to isolate rocket engines from the effects of ambient back pressure. As one of the nation's largest rocket testing facilities, the performance and design limitations of diffusers are of great interest to NASA's Stennis Space Center. This paper describes a series of tests conducted on four diffuser configurations to better understand the effects of inlet geometry and throat area on starting behavior and boundary layer separation. The diffusers were tested for a duration of five seconds with a 1455-pound thrust, LO2/GH2 thruster to ensure they each reached aerodynamic steady state. The effects of a water spray ring at the diffuser exits and a water-cooled deflector plate were also evaluated. Static pressure and temperature measurements were taken at multiple axial locations along the diffusers, and Computational Fluid Dynamics (CFD) simulations were used as a tool to aid in the interpretation of data. The hot combustion products were confirmed to enable the diffuser start condition with tighter second throats than predicted by historical cold-flow data or the theoretical normal shock method. Both aerodynamic performance and heat transfer were found to increase with smaller diffuser throats. Spray ring and deflector cooling water had negligible impacts on diffuser boundary layer separation. CFD was found to accurately capture diffuser shock structures and full-flowing diffuser wall pressures, and the qualitative behavior of heat transfer. However, the ability to predict boundary layer separated flows was not consistent.

Field intercomparison of ammonia passive samplers: results and lessons learned.

NASA Astrophysics Data System (ADS)

Stephens, Amy; Leeson, Sarah; Jones, Matthew; van Dijk, Netty; Kentisbeer, John; Twigg, Marsailidh; Simmons, Ivan; Braban, Christine; Martin, Nick; Poskitt, Janet; Ferm, Martin; Seitler, Eva; Sacco, Paolo; Gates, Linda; Stolk, Ariën; Stoll, Jean-Marc; Tang, Sim

2017-04-01

Ammonia pollution contributes significantly to eutrophication and acidification of ecosystems with resultant losses of biodiversity and ecosystem changes. Monitoring of ambient ammonia over a wide spatial and long temporal scales is primarily done with low-cost diffusive samplers. Less frequently, surface flux measurements of ammonia can be made using passive samplers at plot scale. This paper will present a field intercomparison conducted within the MetNH3 project to assess the performance of passive samplers for ambient measurements of ammonia. Eight different designs of commercial passive samplers housed in shelters provided by the manufacturer/laboratory were exposed over an 8-week period at the Whim experimental field site in Scotland between August and October 2016. Whim Bog has a facility in place for controlled releases of ammonia (http://www.whimbog.ceh.ac.uk/). Automated conditional release from the line source occurs when the wind direction in the preceding minute is from the northeast (wind sector 180-215°) and wind speed is > 5 m s-1. The passive samplers were exposed at different distances from the release source (16, 32 and 60 m) and also at a background location. Most were exposed for 2 x 4-week long periods and some for 4 x 2-week long periods. At the 32 m position, an active denuder method, the CEH DELTA sampler and a continuous high temporal resolution wet chemistry ammonia instrument (AiRRmonia, Mechatronics, NL.) were also deployed alongside the passive samplers to provide reference measurements of ammonia. Results are presented within the context of the MetNH3 CATFAC controlled laboratory exposure assessments. The results are discussed in terms of typical deployments of passive samplers and quality control. Measurement for policy evidence for both local and regional studies using passive samplers are discussed.

The active and passive sampling of benzene, toluene, ethyl benzene and xylenes compounds using the inside needle capillary adsorption trap device.

PubMed

Shojania, S; Oleschuk, R D; McComb, M E; Gesser, H D; Chow, A

1999-08-23

A new and simple method of solventless extraction of volatile organic compounds (VOCs) from air is presented. The sampling device has an adsorbing carbon coating on the interior surface of a hollow needle, and is called the inside needle capillary adsorption trap (INCAT). This paper describes a study of the reproducibility in the preparation and sampling of the INCAT device. In addition, this paper examines the effects of sample volume in active sampling and exposure time in passive sampling on the analyte adsorption. Analysis was achieved by sampling the air from an environmental chamber doped with benzene, toluene, ethyl benzene and xylenes (BTEX) compounds. Initial rates of adsorption were found to vary among the different compounds, but ranged from 0.0099 to 0.016 nmol h(-1) for passive sampling and from 2.2 to 10 nmol h(-1) for active sampling. Analysis was done by thermal desorption of the adsorbed compounds directly into a gas chromatograph injection port. Quantification of the analysis was done by comparison to actively sampled activated carbon solid phase extraction (SPE) measurements.

Continued geophysical logging near the GMH Electronics National Priorities List Superfund site near Roxboro, North Carolina

USGS Publications Warehouse

Antolino, Dominick J.; Chapman, Melinda J.

2017-01-06

The U.S. Geological Survey South Atlantic Water Science Center collected borehole geophysical logs and images and continuous water-level data near the GMH Electronics National Priorities List Superfund site near Roxboro, North Carolina, during December 2012 through July 2015. Previous work by the U.S. Geological Survey South Atlantic Water Science Center at the site involved the collection of borehole geophysical log data in 15 wells, in addition to surface geologic mapping and passive diffusion bag sampling. In a continued effort to assist the U.S. Environmental Protection Agency in developing a conceptual groundwater model to assess current contaminant distribution and future migration of contaminants, more than 900 subsurface features (primarily fracture orientations) in 10 open borehole wells were delineated and continuous water-level data information from 14 monitoring wells within close proximity of the initially drilled boreholes was collected to observe any induced water-level fluctuations during drilling operations

Active hyperspectral imaging using a quantum cascade laser (QCL) array and digital-pixel focal plane array (DFPA) camera.

PubMed

Goyal, Anish; Myers, Travis; Wang, Christine A; Kelly, Michael; Tyrrell, Brian; Gokden, B; Sanchez, Antonio; Turner, George; Capasso, Federico

2014-06-16

We demonstrate active hyperspectral imaging using a quantum-cascade laser (QCL) array as the illumination source and a digital-pixel focal-plane-array (DFPA) camera as the receiver. The multi-wavelength QCL array used in this work comprises 15 individually addressable QCLs in which the beams from all lasers are spatially overlapped using wavelength beam combining (WBC). The DFPA camera was configured to integrate the laser light reflected from the sample and to perform on-chip subtraction of the passive thermal background. A 27-frame hyperspectral image was acquired of a liquid contaminant on a diffuse gold surface at a range of 5 meters. The measured spectral reflectance closely matches the calculated reflectance. Furthermore, the high-speed capabilities of the system were demonstrated by capturing differential reflectance images of sand and KClO₃ particles that were moving at speeds of up to 10 m/s.

Comparison of diffusion- and pumped-sampling methods to monitor volatile organic compounds in ground water, Massachusetts Military Reservation, Cape Cod, Massachusetts, July 1999-December 2002

USGS Publications Warehouse

Archfield, Stacey A.; LeBlanc, Denis R.

2005-01-01

To evaluate diffusion sampling as an alternative method to monitor volatile organic compound (VOC) concentrations in ground water, concentrations in samples collected by traditional pumped-sampling methods were compared to concentrations in samples collected by diffusion-sampling methods for 89 monitoring wells at or near the Massachusetts Military Reservation, Cape Cod. Samples were analyzed for 36 VOCs. There was no substantial difference between the utility of diffusion and pumped samples to detect the presence or absence of a VOC. In wells where VOCs were detected, diffusion-sample concentrations of tetrachloroethene (PCE) and trichloroethene (TCE) were significantly lower than pumped-sample concentrations. Because PCE and TCE concentrations detected in the wells dominated the calculation of many of the total VOC concentrations, when VOC concentrations were summed and compared by sampling method, visual inspection also showed a downward concentration bias in the diffusion-sample concentration. The degree to which pumped- and diffusion-sample concentrations agreed was not a result of variability inherent within the sampling methods or the diffusion process itself. A comparison of the degree of agreement in the results from the two methods to 13 quantifiable characteristics external to the sampling methods offered only well-screen length as being related to the degree of agreement between the methods; however, there is also evidence to indicate that the flushing rate of water through the well screen affected the agreement between the sampling methods. Despite poor agreement between the concentrations obtained by the two methods at some wells, the degree to which the concentrations agree at a given well is repeatable. A one-time, well-bywell comparison between diffusion- and pumped-sampling methods could determine which wells are good candidates for the use of diffusion samplers. For wells with good method agreement, the diffusion-sampling method is a time-saving and cost-effective alternative to pumped-sampling methods in a long-term monitoring program, such as at the Massachusetts Military Reservation.

Measuring charge carrier diffusion in coupled colloidal quantum dot solids.

PubMed

Zhitomirsky, David; Voznyy, Oleksandr; Hoogland, Sjoerd; Sargent, Edward H

2013-06-25

Colloidal quantum dots (CQDs) are attractive materials for inexpensive, room-temperature-, and solution-processed optoelectronic devices. A high carrier diffusion length is desirable for many CQD device applications. In this work we develop two new experimental methods to investigate charge carrier diffusion in coupled CQD solids under charge-neutral, i.e., undepleted, conditions. The methods take advantage of the quantum-size-effect tunability of our materials, utilizing a smaller-bandgap population of quantum dots as a reporter system. We develop analytical models of diffusion in 1D and 3D structures that allow direct extraction of diffusion length from convenient parametric plots and purely optical measurements. We measure several CQD solids fabricated using a number of distinct methods and having significantly different doping and surface ligand treatments. We find that CQD materials recently reported to achieve a certified power conversion efficiency of 7% with hybrid organic-inorganic passivation have a diffusion length of 80 ± 10 nm. The model further allows us to extract the lifetime, trap density, mobility, and diffusion coefficient independently in each material system. This work will facilitate further progress in extending the diffusion length, ultimately leading to high-quality CQD solid semiconducting materials and improved CQD optoelectronic devices, including CQD solar cells.

A novel rumor diffusion model considering the effect of truth in online social media

NASA Astrophysics Data System (ADS)

Sun, Ling; Liu, Yun; Zeng, Qing-An; Xiong, Fei

2015-12-01

In this paper, we propose a model to investigate how truth affects rumor diffusion in online social media. Our model reveals a relation between rumor and truth — namely, when a rumor is diffusing, the truth about the rumor also diffuses with it. Two patterns of the agents used to identify rumor, self-identification and passive learning are taken into account. Combining theoretical proof and simulation analysis, we find that the threshold value of rumor diffusion is negatively correlated to the connectivity between nodes in the network and the probability β of agents knowing truth. Increasing β can reduce the maximum density of the rumor spreaders and slow down the generation speed of new rumor spreaders. On the other hand, we conclude that the best rumor diffusion strategy must balance the probability of forwarding rumor and the probability of agents losing interest in the rumor. High spread rate λ of rumor would lead to a surge in truth dissemination which will greatly limit the diffusion of rumor. Furthermore, in the case of unknown λ, increasing β can effectively reduce the maximum proportion of agents who do not know the truth, but cannot narrow the rumor diffusion range in a certain interval of β.

Opposing Effects of cAMP and T259 Phosphorylation on Plasma Membrane Diffusion of the Water Channel Aquaporin-5 in Madin-Darby Canine Kidney Cells

PubMed Central

Koffman, Jennifer S.; Arnspang, Eva C.; Marlar, Saw; Nejsum, Lene N.

2015-01-01

Aquaporin-5 (AQP5) facilitates passive water transport in glandular epithelia in response to secretory stimuli via intracellular pathways involving calcium release, cAMP and protein kinase A (PKA). In epithelial plasma membranes, AQP5 may be acutely regulated to facilitate water transport in response to physiological stimuli by changes in protein modifications, interactions with proteins and lipids, nanoscale membrane domain organization, and turnover rates. Such regulatory mechanisms could potentially be associated with alteration of diffusion behavior, possibly resulting in a change in the plasma membrane diffusion coefficient of AQP5. We aimed to test the short-term regulatory effects of the above pathways, by measuring lateral diffusion of AQP5 and an AQP5 phospho-mutant, T259A, using k-space Image Correlation Spectroscopy of quantum dot- and EGFP-labeled AQP5. Elevated cAMP and PKA inhibition significantly decreased lateral diffusion of AQP5, whereas T259A mutation showed opposing effects; slowing diffusion without stimulation and increasing diffusion to basal levels after cAMP elevation. Thus, lateral diffusion of AQP5 is significantly regulated by cAMP, PKA, and T259 phosphorylation, which could be important for regulating water flow in glandular secretions. PMID:26218429

Passivation effect on optical and electrical properties of molecular beam epitaxy-grown HgCdTe/CdTe/Si layers

NASA Astrophysics Data System (ADS)

Kiran, Rajni; Mallick, Shubhrangshu; Hahn, Suk-Ryong; Lee, T. S.; Sivananthan, Sivalingam; Ghosh, Siddhartha; Wijewarnasuriya, P. S.

2006-06-01

The effects of passivation with two different passivants, ZnS and CdTe, and two different passivation techniques, physical vapor deposition (PVD) and molecular beam epitaxy (MBE), were quantified in terms of the minority carrier lifetime and extracted surface recombination velocity on both MBE-grown medium-wavelength ir (MWIR) and long-wavelength ir HgCdTe samples. A gradual increment of the minority carrier lifetime was reported as the passivation technique was changed from PVD ZnS to PVD CdTe, and finally to MBE CdTe, especially at low temperatures. A corresponding reduction in the extracted surface recombination velocity in the same order was also reported for the first time. Initial data on the 1/ f noise values of as-grown MWIR samples showed a reduction of two orders of noise power after 1200-Å ZnS deposition.

Measuring variability in trophic status in the Lake Waco/Bosque River Watershed

PubMed Central

Rodriguez, Angela D; Matlock, Marty D

2008-01-01

Background Nutrient management in rivers and streams is difficult due to the spatial and temporal variability of algal growth responses. The objectives of this project were to determine the spatial and seasonal in situ variability of trophic status in the Lake Waco/Bosque River watershed, determine the variability in the lotic ecosystem trophic status index (LETSI) at each site as indicators of the system's nutrient sensitivity, and determine if passive diffusion periphytometers could provide threshold algal responses to nutrient enrichment. Methods We used the passive diffusion periphytometer to measure in-situ nutrient limitation and trophic status at eight sites in five streams in the Lake Waco/Bosque River Watershed in north-central Texas from July 1997 through October 1998. The chlorophyll a production in the periphytometers was used as an indicator of baseline chlorophyll a productivity and of maximum primary productivity (MPP) in response to nutrient enrichment (nitrogen and phosphorus). We evaluated the lotic ecosystem trophic status index (LETSI) using the ratio of baseline primary productivity to MPP, and evaluated the trophic class of each site. Results The rivers and streams in the Lake Waco/Bosque River Watershed exhibited varying degrees of nutrient enrichment over the 18-month sampling period. The North Bosque River at the headwaters (NB-02) located below the Stephenville, Texas wastewater treatment outfall consistently exhibited the highest degree of water quality impact due to nutrient enrichment. Sites at the outlet of the watershed (NB-04 and NB-05) were the next most enriched sites. Trophic class varied for enriched sites over seasons. Conclusion Seasonality played a significant role in the trophic class and sensitivity of each site to nutrients. Managing rivers and streams for nutrients will require methods for measuring in situ responses and sensitivities to nutrient enrichment. Nutrient enrichment periphytometers show significant potential for use in nutrient gradient studies. PMID:18271947

Measuring variability in trophic status in the Lake Waco/Bosque River Watershed.

PubMed

Rodriguez, Angela D; Matlock, Marty D

2008-01-11

Nutrient management in rivers and streams is difficult due to the spatial and temporal variability of algal growth responses. The objectives of this project were to determine the spatial and seasonal in situ variability of trophic status in the Lake Waco/Bosque River watershed, determine the variability in the lotic ecosystem trophic status index (LETSI) at each site as indicators of the system's nutrient sensitivity, and determine if passive diffusion periphytometers could provide threshold algal responses to nutrient enrichment. We used the passive diffusion periphytometer to measure in-situ nutrient limitation and trophic status at eight sites in five streams in the Lake Waco/Bosque River Watershed in north-central Texas from July 1997 through October 1998. The chlorophyll a production in the periphytometers was used as an indicator of baseline chlorophyll a productivity and of maximum primary productivity (MPP) in response to nutrient enrichment (nitrogen and phosphorus). We evaluated the lotic ecosystem trophic status index (LETSI) using the ratio of baseline primary productivity to MPP, and evaluated the trophic class of each site. The rivers and streams in the Lake Waco/Bosque River Watershed exhibited varying degrees of nutrient enrichment over the 18-month sampling period. The North Bosque River at the headwaters (NB-02) located below the Stephenville, Texas wastewater treatment outfall consistently exhibited the highest degree of water quality impact due to nutrient enrichment. Sites at the outlet of the watershed (NB-04 and NB-05) were the next most enriched sites. Trophic class varied for enriched sites over seasons. Seasonality played a significant role in the trophic class and sensitivity of each site to nutrients. Managing rivers and streams for nutrients will require methods for measuring in situ responses and sensitivities to nutrient enrichment. Nutrient enrichment periphytometers show significant potential for use in nutrient gradient studies.

Influence of Sulfide Nanoparticles on Dissolved Mercury and Zinc Quantification by Diffusive Gradient in Thin-Film Passive Samplers.

PubMed

Pham, Anh Le-Tuan; Johnson, Carol; Manley, Devon; Hsu-Kim, Heileen

2015-11-03

Diffusive gradient in thin-film (DGT) passive samplers are frequently used to monitor the concentrations of metals such as mercury and zinc in sediments and other aquatic environments. The application of these samplers generally presumes that they quantify only the dissolved fraction and not particle-bound metal species that are too large to migrate into the sampler. However, metals associated with very small nanoparticles (smaller than the pore size of DGT samplers) can be abundant in certain environments, yet the implications of these nanoparticles for DGT measurements are unclear. The objective of this study was to determine how the performance of the DGT sampler is affected by the presence of nanoparticulate species of Hg and Zn. DGT samplers were exposed to solutions containing known amounts of dissolved Hg(II) and nanoparticulate HgS (or dissolved Zn(II) and nanoparticulate ZnS). The amounts of Hg and Zn accumulated onto the DGT samplers were quantified over hours to days, and the rates of diffusion of the dissolved metal (i.e., the effective diffusion coefficient D) into the sampler's diffusion layer were calculated and compared for solutions containing varying concentrations of nanoparticles. The results suggested that the nanoparticles deposited on the surface of the samplers might have acted as sorbents, slowing the migration of the dissolved species into the samplers. The consequence was that the DGT sampler data underestimated the dissolved metal concentration in the solution. In addition, X-ray absorption spectroscopy was employed to determine the speciation of the Hg accumulated on the sampler binding layer, and the results indicated that HgS nanoparticles did not appear to directly contribute to the DGT measurement. Overall, our findings suggest that the deployment of DGT samplers in settings where nanoparticles are relevant (e.g., sediments) may result in DGT data that incorrectly estimated the dissolved metal concentrations. Models for metal uptake into the sampler may need to be reconsidered.

Performance Evaluation of Automated Passive Capillary Sampler for Estimating Water Drainage in the Vadose Zone

USDA-ARS?s Scientific Manuscript database

Passive capillary samplers (PCAPs) are widely used to monitor, measure and sample drainage water under saturated and unsaturated soil conditions in the vadose zone. The objective of this study was to evaluate the performance and accuracy of automated passive capillary sampler for estimating drainage...

Measurement of gaseous PAHs with an innovative passive sampler in community exposure studies

EPA Science Inventory

A sensitive, simple, and cost-effective passive sampling methodology was developed to quantify gaseous polycyclic aromatic hydrocarbons (PAHs) in personal, indoor and outdoor air. A Fan-Lioy passive PAH sampler (FL-PPS) is constructed from four 80 sections of 1 cm long SPB-5 GC c...

An Application of Passive Samplers to Understand Atmospheric Mercury Concentration and Dry Deposition Spatial Distributions

EPA Science Inventory

Two modified passive samplers were evaluated at multiple field locations. The sampling rate (SR) of the modified polyurethane foam (PUF)-disk passive sampler for total gaseous mercury (TGM) using gold-coated quartz fiber filters (GcQFF) and gaseous oxidized mercury (GOM) using io...

Active Nuclear Import of Membrane Proteins Revisited

PubMed Central

Laba, Justyna K.; Steen, Anton; Popken, Petra; Chernova, Alina; Poolman, Bert; Veenhoff, Liesbeth M.

2015-01-01

It is poorly understood how membrane proteins destined for the inner nuclear membrane pass the crowded environment of the Nuclear Pore Complex (NPC). For the Saccharomyces cerevisiae proteins Src1/Heh1 and Heh2, a transport mechanism was proposed where the transmembrane domains diffuse through the membrane while the extralumenal domains encoding a nuclear localization signal (NLS) and intrinsically disordered linker (L) are accompanied by transport factors and travel through the NPC. Here, we validate the proposed mechanism and explore and discuss alternative interpretations of the data. First, to disprove an interpretation where the membrane proteins become membrane embedded only after nuclear import, we present biochemical and localization data to support that the previously used, as well as newly designed reporter proteins are membrane-embedded irrespective of the presence of the sorting signals, the specific transmembrane domain (multipass or tail anchored), independent of GET, and also under conditions that the proteins are trapped in the NPC. Second, using the recently established size limit for passive diffusion of membrane proteins in yeast, and using an improved assay, we confirm active import of polytopic membrane protein with extralumenal soluble domains larger than those that can pass by diffusion on similar timescales. This reinforces that NLS-L dependent active transport is distinct from passive diffusion. Thirdly, we revisit the proposed route through the center of the NPC and conclude that the previously used trapping assay is, unfortunately, poorly suited to address the route through the NPC, and the route thus remains unresolved. Apart from the uncertainty about the route through the NPC, the data confirm active, transport factor dependent, nuclear transport of membrane-embedded mono- and polytopic membrane proteins in baker’s yeast. PMID:26473931

Migration of the guinea pig sperm membrane protein PH-20 from one localized surface domain to another does not occur by a simple diffusion-trapping mechanism.

PubMed

Cowan, A E; Myles, D G; Koppel, D E

1991-03-01

The redistribution of membrane proteins on the surface of cells is a prevalent feature of differentiation in a variety of cells. In most cases the mechanism responsible for such redistribution is poorly understood. Two potential mechanisms for the redistribution of surface proteins are: (1) passive diffusion coupled with trapping, and (2) active translocation. We have studied the process of membrane protein redistribution for the PH-20 protein of guinea pig sperm, a surface protein required for sperm binding to the egg zona pellucida (P. Primakoff, H. Hyatt, and D. G. Myles (1985). J. Cell Biol. 101, 2239-2244). PH-20 protein is localized to the posterior head plasma menbrane of the mature sperm cell. Following the exocytotic acrosome reaction, PH-20 protein moves into the newly incorporated inner acrosomal membrane (IAM), placing it in a position favorable for a role in binding sperm to the egg zona pellucida (D. G. Myles, and P. Primakoff (1984), J. Cell Biol. 99, 1634-1641). To analyze the mechanistic basis for this protein migration, we have used fluorescence microscopy and digital image processing to characterize PH-20 protein migration in individual cells. PH-20 protein was observed to move against a concentration gradient in the posterior head plasma membrane. This result argues strongly against a model of passive diffusion followed by trapping in the IAM, and instead suggests that an active process serves to concentrate PH-20 protein toward the boundary separating the posterior head and IAM regions. A transient gradient of PH-20 concentration observed in the IAM suggests that once PH-20 protein reaches the IAM, it is freely diffusing. Additionally, we observed that migration of PH-20 protein was calcium dependent.

Transcellular movement of hydroxyurea is mediated by specific solute carrier transporters

PubMed Central

Walker, Aisha L.; Franke, Ryan M.; Sparreboom, Alex; Ware, Russell E.

2015-01-01

Objective Hydroxyurea has proven laboratory and clinical therapeutic benefits for sickle cell anemia (SCA) and other diseases, yet many questions remain regarding its in vivo pharmacokinetic and pharmacodynamic profiles. Previous reports suggest that hydroxyurea passively diffuses across cells, but its observed rapid absorption and distribution are more consistent with facilitated or active transport. We investigated the potential role of solute carrier (SLC) transporters in cellular uptake and accumulation of hydroxyurea. Materials and Methods Passive diffusion of hydroxyurea across cell membranes was determined using the parallel artificial membrane permeability assay. SLC transporter screens were conducted using in vitro intracellular drug accumulation and transcellular transport assays in cell lines and oocytes overexpressing SLC transporters. Gene expression of SLC transporters was measured by real-time PCR in human tissues and cell lines. Results Hydroxyurea had minimal diffusion across a lipid bilayer but was a substrate for 5 different SLC transporters belonging to the OCTN and OATP families of transporters and urea transporters A and B. Further characterization of hydroxyurea transport revealed that cellular uptake by OATP1B3 is time and temperature dependent and inhibited by known substrates of OATP1B3. Urea transporters A and B are expressed differentially in human tissues and erythroid cells, and transport hydroxyurea bidirectionally via facilitated diffusion. Conclusions These studies provide new insight into drug transport proteins that may be involved in the in vivo absorption, cellular distribution, and elimination of hydroxyurea. Elucidation of hydroxyurea transcellular movement should improve our understanding of its pharmacokinetics and pharmacodynamics, and may help explain some of the inter-patient drug variability observed in patients with SCA. PMID:21256917

Evaluating the Relationship between Equilibrium Passive ...

EPA Pesticide Factsheets

Objectives. This review evaluates passive sampler uptake of hydrophobic organic contaminants (HOCs) in water column and interstitial water exposures as a surrogate for organism bioaccumulation. Approach/Activities. Fifty-five studies were found where both passive sampler uptake and organism bioaccumulation were measured and 19 of these investigations provided direct comparisons relating passive sampler uptake and organism bioaccumulation. Polymers compared included low density polyethylene (LDPE), polyoxymethylene (POM), and polydimethylsiloxane (PDMS), and organisms ranged from polychaetes and oligochaetes to bivalves, aquatic insects, and gastropods. Regression equations correlating bioaccumulation (CL) and passive sampler uptake (CPS) were used to assess the strength of observed relationships. Results/Lessons Learned. Passive sampling based concentrations resulted in strong logarithmic regression relationships, most of which were within one to two orders of magnitude of measured bioaccumulation. Mean coefficients of determination (r2) for LDPE, PDMS and POM were 0.68, 0.76 and 0.58, respectively. For the available raw data, the mean ratio of CL and CPS was 10.8 ± 18.4 (n = 609). Passive sampler uptake and bioaccumulation were not found to be identical (i.e., CPS ≠ CL) but the logarithmic-based relationships between these values were consistently linear and predictive. This review concludes that in many applications passive sampling may serve as a

Molecular assemblies as protective barriers and adhesion promotion interlayer

DOEpatents

King, D.E.; Czanderna, A.W.; Kennedy, C.E.

1996-01-30

A protective diffusion barrier having adhesive qualities for metalized surfaces is provided by a passivating agent having the formula HS--(CH{sub 2}){sub 11}--COOH which forms a very dense, transparent organized molecular assembly or layer that is impervious to water, alkali, and other impurities and corrosive substances that typically attack metal surfaces. 8 figs.

Performance Evaluation and Quality Validation System for Optical Gas Imaging Cameras that Visualize Fugitive Hydrocarbon Gas Emissions

EPA Science Inventory

A U.S. EPA team, consisting of the Office of Research and Development and Region 6 (Dallas) and Region 8 (Denver), deployed passive-diffusive sorbent tubes as part of a method evaluation study around one oil and natural gas production pad in both the Barnett Shale Basin in Texas ...

Overview of the U.S. EPA/SERDP/ESTCP: Laboratory, Field, and Analytical Procedures for Using Passive Sampling in the Evaluation of Contaminated Sediments: User’s Manual

EPA Science Inventory

Passive sampling can be used for applications at contaminated sediment sites including performing assessments of contaminant bioavailability (i.e., freely dissolved concentration (Cfree)), conducting remedial investigations and feasibility studies, and assessing the potential for...

Overview of the U.S. EPA/SERDP/ESTCP: Laboratory, Field, and Analytical Procedures for Using Passive Sampling in the Evaluation of Contaminated Sediments: User’s Manual.

EPA Science Inventory

Passive sampling is used for applications at contaminated sediment sites including performing assessments of contaminant bioavailability (i.e., freely dissolved concentration (Cfree)), conducting remedial investigations and feasibility studies, and assessing the potential for con...

Passive Sampling to Measure Baseline Dissolved Persistent Organic Pollutant Concentrations in the Water Column of the Palos Verdes Shelf Superfund Site

EPA Science Inventory

Passive sampling was used to deduce water concentrations of persistent organic pollutants (POPs) in the vicinity of a marine Superfund site on the Palos Verdes Shelf, California, USA. Pre-calibrated solid phase microextraction (SPME) fibers and polyethylene (PE) strips that were...

Developing Sediment Remediation Goals at Superfund Sites Based on Pore Water for the Protection of Benthic Organisms from Direct Toxicity to Non-ionic Organic Contaminants

EPA Science Inventory

A methodology for developing remediation goals for sites with contaminated sediments is provided. The remediation goals are based upon the concentrations of chemicals in the sediment interstitial water measured using the passive sampling technique. The passive sampling technique ...

Air sampling procedures to evaluate microbial contamination: a comparison between active and passive methods in operating theatres

PubMed Central

2012-01-01

Background Since air can play a central role as a reservoir for microorganisms, in controlled environments such as operating theatres regular microbial monitoring is useful to measure air quality and identify critical situations. The aim of this study is to assess microbial contamination levels in operating theatres using both an active and a passive sampling method and then to assess if there is a correlation between the results of the two different sampling methods. Methods The study was performed in 32 turbulent air flow operating theatres of a University Hospital in Southern Italy. Active sampling was carried out using the Surface Air System and passive sampling with settle plates, in accordance with ISO 14698. The Total Viable Count (TVC) was evaluated at rest (in the morning before the beginning of surgical activity) and in operational (during surgery). Results The mean TVC at rest was 12.4 CFU/m3 and 722.5 CFU/m2/h for active and passive samplings respectively. The mean in operational TVC was 93.8 CFU/m3 (SD = 52.69; range = 22-256) and 10496.5 CFU/m2/h (SD = 7460.5; range = 1415.5-25479.7) for active and passive samplings respectively. Statistical analysis confirmed that the two methods correlate in a comparable way with the quality of air. Conclusion It is possible to conclude that both methods can be used for general monitoring of air contamination, such as routine surveillance programs. However, the choice must be made between one or the other to obtain specific information. PMID:22853006

Personal exposure to metal fume, NO2, and O3 among production welders and non-welders.

PubMed

Schoonover, Todd; Conroy, Lorraine; Lacey, Steven; Plavka, Julie

2011-01-01

The objective of this study was to characterize personal exposures to welding-related metals and gases for production welders and non-welders in a large manufacturing facility. Welding fume metals and irritant gases nitrogen dioxide (NO(2)) and ozone (O(3)) were sampled for thirty-eight workers. Personal exposure air samples for welding fume metals were collected on 37 mm open face cassettes and nitrogen dioxide and ozone exposure samples were collected with diffusive passive samplers. Samples were analyzed for metals using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and welding fume metal exposure concentrations were defined as the sum of welding-related metals mass per volume of air sampled. Welding fume metal exposures were highly variable among similar types of welding while NO(2) and O(3) exposure were less variable. Welding fume metal exposures were significantly higher 474 μg/m(3) for welders than non-welders 60 μg/m(3) (p=0.001). Welders were exposed to higher concentrations of NO(2) and O(3) than non-welders but the differences were not statistically significant. Welding fume metal exposure concentrations for welders performing gas metal arc welding (GMAW) and shielded metal arc welding (SMAW) were higher than welders performing gas tungsten arc welding (GTAW). Non-welders experienced exposures similar to GTAW welders despite a curtain wall barrier separating welding and non-welding work areas.

Transferring mixtures of chemicals from sediment to a bioassay using silicone-based passive sampling and dosing.

PubMed

Mustajärvi, Lukas; Eriksson-Wiklund, Ann-Kristin; Gorokhova, Elena; Jahnke, Annika; Sobek, Anna

2017-11-15

Environmental mixtures of chemicals consist of a countless number of compounds with unknown identity and quantity. Yet, chemical regulation is mainly built around the assessment of single chemicals. Existing frameworks for assessing the toxicity of mixtures require that both the chemical composition and quantity are known. Quantitative analyses of the chemical composition of environmental mixtures are however extremely challenging and resource-demanding. Bioassays may therefore serve as a useful approach for investigating the combined toxicity of environmental mixtures of chemicals in a cost-efficient and holistic manner. In this study, an unknown environmental mixture of bioavailable semi-hydrophobic to hydrophobic chemicals was sampled from a contaminated sediment in a coastal Baltic Sea area using silicone polydimethylsiloxane (PDMS) as an equilibrium passive sampler. The chemical mixture was transferred to a PDMS-based passive dosing system, and its applicability was demonstrated using green algae Tetraselmis suecica in a cell viability assay. The proportion of dead cells increased significantly with increasing exposure level and in a dose-response manner. At an ambient concentration, the proportion of dead cells in the population was nearly doubled compared to the control; however, the difference was non-significant due to high inter-replicate variability and a low number of replicates. The validation of the test system regarding equilibrium sampling, loading efficiency into the passive dosing polymer, stability of the mixture composition, and low algal mortality in control treatments demonstrates that combining equilibrium passive sampling and passive dosing is a promising tool for investigating the toxicity of bioavailable semi-hydrophobic and hydrophobic chemicals in complex environmental mixtures.

Study of Active Micromixer Driven by Electrothermal Force

NASA Astrophysics Data System (ADS)

Huang, Kuan-Rong; Chang, Jeng-Shian; Chao, Sheng D.; Wung, Tzong-Shyan; Wu, Kuang-Chong

2012-04-01

Biochemical applications of microchips often require a rapid mixing of different fluid samples. At the microscale level, fluid flow is usually a highly ordered laminar flow and diffusion is the primary mechanism for mixing owing to the lack of disturbances, yielding inefficiency for practical biochemical analysis. In this work, we design a prototype active micromixer by employing the electrothermal effect. We apply to the flow microchannel a non-uniform AC electric field, which can generate an electrothermal force on the fluid flow and induce vortex pairs for enhancing mixing efficiency. The performance of this active micromixer is studied and compared, under the same mixing quality, with that of a conventional passive micromixer of the same size with obstacles in the flow channel by three-dimensional finite element simulations. The numerical results show that the pressure drop between the inlet and the outlet for the active micromixer is much less than (only 3000th) that for the passive micro-mixer with the same mixing quality. To obtain an optimal mixing quality, we have systematically studied the mixing quality by varying the geometrical arrangements of the electrodes. An almost complete mixing can be obtained using a specific design. Moreover, the temperature increases around the electrodes are lower than 3 K, which does not adversely affect the biochemical analysis. It is suggested that the prototype active micromixer designed is promising and effective and useful for biochemical analysis.

Chemical and toxicologic assessment of organic contaminants in surface water using passive samplers

USGS Publications Warehouse

Alvarez, D.A.; Cranor, W.L.; Perkins, S.D.; Clark, R.C.; Smith, S.B.

2008-01-01

Passive sampling methodologies were used to conduct a chemical and toxicologic assessment of organic contaminants in the surface waters of three geographically distinct agricultural watersheds. A selection of current-use agrochemicals and persistent organic pollutants, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and organochlorine pesticides, were targeted using the polar organic chemical integrative sampler (POCIS) and the semipermeable membrane device passive samplers. In addition to the chemical analysis, the Microtox assay for acute toxicity and the yeast estrogen screen (YES) were conducted as potential assessment tools in combination with the passive samplers. During the spring of 2004, the passive samplers were deployed for 29 to 65 d at Leary Weber Ditch, IN; Morgan Creek, MD; and DR2 Drain, WA. Chemical analysis of the sampler extracts identified the agrochemicals predominantly used in those areas, including atrazine, simazine, acetochlor, and metolachlor. Other chemicals identified included deethylatrazine and deisopropylatrazine, trifluralin, fluoranthene, pyrene, cis- and trans-nonachlor, and pentachloroanisole. Screening using Microtox resulted in no acutely toxic samples. POCIS samples screened by the YES assay failed to elicit a positive estrogenic response. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

A Passive Earth-Entry Capsule for Mars Sample Return

NASA Technical Reports Server (NTRS)

Mitcheltree, Robert A.; Kellas, Sotiris

1999-01-01

A combination of aerodynamic analysis and testing, aerothermodynamic analysis, structural analysis and testing, impact analysis and testing, thermal analysis, ground characterization tests, configuration packaging, and trajectory simulation are employed to determine the feasibility of an entirely passive Earth entry capsule for the Mars Sample Return mission. The design circumvents the potential failure modes of a parachute terminal descent system by replacing that system with passive energy absorbing material to cushion the Mars samples during ground impact. The suggested design utilizes a spherically blunted 45-degree half-angle cone forebody with an ablative heat shield. The primary structure is a hemispherical, composite sandwich enclosing carbon foam energy absorbing material. Though no demonstration test of the entire system is included, results of the tests and analysis presented indicate that the design is a viable option for the Mars Sample Return Mission.

Dispersion-relation phase spectroscopy of neuron transport

NASA Astrophysics Data System (ADS)

Wang, Ru; Wang, Zhuo; Millet, Larry; Gillette, Martha; Leigh, Joseph Robert; Sobh, Nahil; Levine, Alex; Popescu, Gabreil

2012-02-01

Molecular motors move materials along prescribed biopolymer tracks. This sort of active transport is required to rapidly move products over large distances within the cell, where passive diffusion is too slow. We examine intracellular traffic patterns using a new application of spatial light interference microscopy (SLIM) and measure the dispersion relation, i.e. decay rate vs. spatial mode, associated with mass transport in live cells. This approach applies equally well to both discrete and continuous mass distributions without the need for particle tracking. From the quadratic experimental curve specific to diffusion, we extracted the diffusion coefficient as the only fitting parameter. The linear portion of the dispersion relation reveals the deterministic component of the intracellular transport. Our data show a universal behavior where the intracellular transport is diffusive at small scales and deterministic at large scales. We further applied this method to studying transport in neurons and are able to use SLIM to map the changes in index of refraction across the neuron and its extended processes. We found that in dendrites and axons, the transport is mostly active, i.e., diffusion is subdominant.

Low temperature surface passivation of crystalline silicon and its application to interdigitated back contact silicon heterojunction (ibc-shj) solar cell

NASA Astrophysics Data System (ADS)

Shu, Zhan

With the absence of shading loss together with improved quality of surface passivation introduced by low temperature processed amorphous silicon crystalline silicon (a-Si:H/c-Si) heterojunction, the interdigitated back contact silicon heterojunction (IBC-SHJ) solar cell exhibits a potential for higher conversion efficiency and lower cost than a traditional front contact diffused junction solar cell. In such solar cells, the front surface passivation is of great importance to achieve both high open-circuit voltage (Voc) and short-circuit current (Jsc). Therefore, the motivation of this work is to develop a low temperature processed structure for the front surface passivation of IBC-SHJ solar cells, which must have an excellent and stable passivation quality as well as a good anti-reflection property. Four different thin film materials/structures were studied and evaluated for this purpose, namely: amorphous silicon nitride (a-SiNx:H), thick amorphous silicon film (a-Si:H), amorphous silicon/silicon nitride/silicon carbide (a-Si:H/a-SiN x:H/a-SiC:H) stack structure with an ultra-thin a-Si:H layer, and zinc sulfide (ZnS). It was demonstrated that the a-Si:H/a-SiNx:H/a-SiC:H stack surpasses other candidates due to both of its excellent surface passivation quality (SRV<5 cm/s) and lower absorption losses. The low recombination rate at the stack structure passivated c-Si surface is found to be resulted from (i) field effect passivation due to the positive fixed charge (Q fix~1x1011 cm-2 with 5 nm a-Si:H layer) in a-SiNx:H as measured from capacitance-voltage technique, and (ii) reduced defect state density (mid-gap Dit~4x1010 cm-2eV-1) at a-Si:H/c-Si interface provided by a 5 nm thick a-Si:H layer, as characterized by conductance-frequency measurements. Paralleled with the experimental studies, a computer program was developed in this work based on the extended Shockley-Read-Hall (SRH) model of surface recombination. With the help of this program, the experimental injection level dependent SRV curves of the stack passivated c-Si samples were successfully reproduced and the carrier capture cross sections of interface defect states were extracted. Additionally, anti-reflection properties of the stack structure were optimized and optical losses were analyzed. The Voc over 700 mV and Jsc over 38 mA/cm2 were achieved in IBC-SHJ solar cells using the stack structure for front surface passivation. Direct comparison shows that such low temperature deposited stack structure developed in this work achieves comparable device performance to the high temperature processed front surface passivation structure used in other high efficiency IBC solar cells. However, the lower fill factor (FF) of IBC-SHJ solar cell as compared with traditional front a-Si:H/c-Si heterojunction cell (HIT cell) greatly limits the overall performance of these devices. Two-dimensional (2D) simulations were used to comparatively model the HIT and IBC-SHJ solar cells to understand the underlying device physics which controls cell performance. The effects of a wide range of device parameters were investigated in the simulation, and pathways to improve the FF of IBC-SHJ solar cell were suggested.

Wilson Corners SWMU 001 2014 Annual Long Term Monitoring Report Kennedy Space Center, Florida

NASA Technical Reports Server (NTRS)

Langenbach, James

2015-01-01

This document presents the findings of the 2014 Long Term Monitoring (LTM) that was completed at the Wilson Corners site, located at the National Aeronautics and Space Administration (NASA) John F. Kennedy Space Center (KSC), Florida. The goals of the 2014 annual LTM event were to evaluate the groundwater flow direction and gradient and to monitor the vertical and downgradient horizontal extent of the volatile organic compounds (VOCs) in groundwater at the site. The LTM activities consisted of an annual groundwater sampling event in December 2014, which included the collection of water levels from the LTM wells. During the annual groundwater sampling event, depth to groundwater was measured and VOC samples were collected using passive diffusion bags (PDBs) from 30 monitoring wells. In addition to the LTM sampling, additional assessment sampling was performed at the site using low-flow techniques based on previous LTM results and assessment activities. Assessment of monitoring well MW0052DD was performed by collecting VOC samples using low-flow techniques before and after purging 100 gallons from the well. Monitoring well MW0064 was sampled to supplement shallow VOC data north of Hot Spot 2 and east of Hot Spot 4. Monitoring well MW0089 was sampled due to its proximity to MW0090. MW0090 is screened in a deeper interval and had an unexpected detection of trichloroethene (TCE) during the 2013 LTM, which was corroborated during the March 2014 verification sampling. Monitoring well MW0130 was sampled to provide additional VOC data beneath the semi-confining clay layer in the Hot Spot 2 area.

Characterization of five passive sampling devices for monitoring of pesticides in water.

PubMed

Ahrens, Lutz; Daneshvar, Atlasi; Lau, Anna E; Kreuger, Jenny

2015-07-31

Five different passive sampler devices were characterized under laboratory conditions for measurement of 124 legacy and current used pesticides in water. In addition, passive sampler derived time-weighted average (TWA) concentrations were compared to time-integrated active sampling in the field. Sampling rates (RS) and passive sampler-water partition coefficients (KPW) were calculated for individual pesticides using silicone rubber (SR), polar organic chemical integrative sampler (POCIS)-A, POCIS-B, Chemcatcher(®) SDB-RPS and Chemcatcher(®) C18. The median RS (Lday(-1)) decreased as follows: SR (0.86)>POCIS-B (0.22)>POCIS-A (0.18)>Chemcatcher(®) SDB-RPS (0.05)>Chemcatcher(®) C18 (0.02), while the median logKPW (Lkg(-1)) decreased as follows: POCIS-B (4.78)>POCIS-A (4.56)>Chemcatcher(®) SDB-RPS (3.17)>SR (3.14)>Chemcatcher(®)C18 (2.71). The uptake of the selected compounds depended on their physicochemical properties, i.e. SR showed a better uptake for more hydrophobic compounds (log octanol-water partition coefficient (KOW)>5.3), whereas POCIS-A, POCIS-B and Chemcatcher(®) SDB-RPS were more suitable for hydrophilic compounds (logKOW<0.70). Overall, the comparison between passive sampler and time-integrated active sampler concentrations showed a good agreement and the tested passive samplers were suitable for capturing compounds with a wide range of KOW's in water. Copyright © 2015 Elsevier B.V. All rights reserved.

Calibration and field application of passive sampling for episodic exposure to polar organic pesticides in streams.

PubMed

Fernández, Diego; Vermeirssen, Etiënne L M; Bandow, Nicole; Muñoz, Katherine; Schäfer, Ralf B

2014-11-01

Rainfall-triggered runoff is a major driver of pesticide input in streams. Only few studies have examined the suitability of passive sampling to quantify such episodic exposures. In this study, we used Empore™ styrene-divinylbenzene reverse phase sulfonated disks (SDB disks) and event-driven water samples (EDS) to assess exposure to 15 fungicides and 4 insecticides in 17 streams in a German vineyard area during 4 rainfall events. We also conducted a microcosm experiment to determine the SDB-disk sampling rates and provide a free-software solution to derive sampling rates under time-variable exposure. Sampling rates ranged from 0.26 to 0.77 L d(-1) and time-weighted average (TWA) concentrations from 0.05 to 2.11 μg/L. The 2 sampling systems were in good agreement and EDS exceeded TWA concentrations on average by a factor of 3. Our study demonstrates that passive sampling is suitable to quantify episodic exposures from polar organic pesticides. Copyright © 2014 Elsevier Ltd. All rights reserved.

Passive Membrane Permeability: Beyond the Standard Solubility-Diffusion Model.

PubMed

Parisio, Giulia; Stocchero, Matteo; Ferrarini, Alberta

2013-12-10

The spontaneous diffusion of solutes through lipid bilayers is still a challenge for theoretical predictions. Since permeation processes remain beyond the capabilities of unbiased molecular dynamics simulations, an alternative strategy is currently adopted to gain insight into their mechanism and time scale. This is based on a monodimensional description of the translocation process only in terms of the position of the solute along the normal to the lipid bilayer, which is formally expressed in the solubility-diffusion model. Actually, a role of orientational and conformational motions has been pointed out, and the use of advanced simulation techniques has been proposed to take into account their effect. Here, we discuss the limitations of the standard solubility-diffusion approach and propose a more general description of membrane translocation as a diffusion process on a free energy surface, which is a function of the translational and rotational degrees of freedom of the molecule. Simple expressions for the permeability coefficient are obtained under suitable conditions. For fast solute reorientation, the classical solubility-diffusion equation is recovered. Under the assumption that well-defined minima can be identified on the free energy landscape, a mechanistic interpretation of the permeability coefficient in terms of all possible permeation paths is given.

Modeling of a Von Platen-Munters diffusion absorption refrigeration cycle

NASA Astrophysics Data System (ADS)

Agostini, Bruno; Agostini, Francesco; Habert, Mathieu

2016-09-01

This article presents a thermodynamical model of a Von-Platen diffusion absorption refrigeration cycle for power electronics applications. It is first validated by comparison with data available in the literature for the classical water-ammonia-helium cycle for commercial absorption fridges. Then new operating conditions corresponding to specific ABB applications, namely high ambient temperature and new organic fluids combinations compatible with aluminium are simulated and discussed. The target application is to cool power electronics converters in harsh environments with high ambient temperature by providing refrigeration without compressor, for passive components losses of about 500 W, with a compact and low cost solution.

Morphogen transport

PubMed Central

Müller, Patrick; Rogers, Katherine W.; Yu, Shuizi R.; Brand, Michael; Schier, Alexander F.

2013-01-01

The graded distribution of morphogens underlies many of the tissue patterns that form during development. How morphogens disperse from a localized source and how gradients in the target tissue form has been under debate for decades. Recent imaging studies and biophysical measurements have provided evidence for various morphogen transport models ranging from passive mechanisms, such as free or hindered extracellular diffusion, to cell-based dispersal by transcytosis or cytonemes. Here, we analyze these transport models using the morphogens Nodal, fibroblast growth factor and Decapentaplegic as case studies. We propose that most of the available data support the idea that morphogen gradients form by diffusion that is hindered by tortuosity and binding to extracellular molecules. PMID:23533171

3D Numerical Simulation versus Experimental Assessment of Pressure Pulsations Using a Passive Method for Swirling Flow Control in Conical Diffusers of Hydraulic Turbines

NASA Astrophysics Data System (ADS)

TANASA, C.; MUNTEAN, S.; CIOCAN, T.; SUSAN-RESIGA, R. F.

2016-11-01

The hydraulic turbines operated at partial discharge (especially hydraulic turbines with fixed blades, i.e. Francis turbine), developing a swirling flow in the conical diffuser of draft tube. As a result, the helical vortex breakdown, also known in the literature as “precessing vortex rope” is developed. A passive method to mitigate the pressure pulsations associated to the vortex rope in the draft tube cone of hydraulic turbines is presented in this paper. The method involves the development of a progressive and controlled throttling (shutter), of the flow cross section at the bottom of the conical diffuser. The adjustable cross section is made on the basis of the shutter-opening of circular diaphragms, while maintaining in all positions the circular cross-sectional shape, centred on the axis of the turbine. The stagnant region and the pressure pulsations associated to the vortex rope are mitigated when it is controlled with the turbine operating regime. Consequently, the severe flow deceleration and corresponding central stagnant are diminished with an efficient mitigation of the precessing helical vortex. Four cases (one without diaphragm and three with diaphragm), are numerically and experimentally investigated, respectively. The present paper focuses on a 3D turbulent swirling flow simulation in order to evaluate the control method. Numerical results are compared against measured pressure recovery coefficient and Fourier spectra. The results prove the vortex rope mitigation and its associated pressure pulsations when employing the diaphragm.

Status of Diffused Junction p(+)n InP Solar Cells for Space Applications

NASA Technical Reports Server (NTRS)

Faur, Mircea; Faur, Maria; Flood, D. J.; Brinker, D. J.; Goradia, C.; Fatemi, N. S.; Jenkins, P. P.; Wilt, D. M.; Bailey, S.

1994-01-01

Recently, we have succeeded in fabricating diffused junction p(+)n(Cd,S) InP solar cells with measured AMO, 25 C open circuit voltage (V(sub OC)) of 887.6 mV, which, to the best of our knowledge, is higher than previously reported V(sub OC) values for any InP homojunction solar cells. The experiment-based projected achievable efficiency of these cells using LEC grown substrates is 21.3%. The maximum AMO, 25 C efficiency recorded to date on bare cells is, however, only 13.2%. This is because of large external and internal losses due to non-optimized front grid design, antireflection (AR) coating and emitter thickness. This paper summarizes recent advances in the technology of fabrication of p(+)n InP diffused structures and solar cells, resulted from a study undertaken in an effort to increase the cell efficiency. The topics discussed in this paper include advances in: 1) the formation of thin p(+) InP:Cd emitter layers, 2) electroplated front contacts, 3) surface passivation and 4) the design of a new native oxide/AI203/MgF2 three layer AR coating using a chemically-grown P-rich passivating oxide as a first layer. Based on the high radiation resistance and the excellent post-irradiation annealing and recovery demonstrated in the early tests done to date, as well as the projected high efficiency and low-cost high-volume fabricability, these cells show a very good potential for space photovoltaic applications.

Thermal diffusivity of four Apollo 17 rock samples

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horai, K.; Winkler, J.L. Jr.

1976-01-01

The thermal diffusivities of four Apollo 17 rock samples (70017,77; 70215,18; 72395,14; and 77035,44) are measured in the temperature range between 180/sup 0/K and 460/sup 0/K at interstitial gaseous pressures of 1 atm and 10/sup -6/ torr of air. The thermal diffusivities at 1 atm are decreasing functions of temperature. Basalt samples (70017,77 and 70215,18) show higher thermal diffusivities than breccias (72395,14 and 77035,44), indicating that the thermal contact between mineral grains is better in crystalline rocks than in breccias. The magnitude of thermal diffusivities of the Apollo 17 basalt samples is intermediate between published diffusivities of Apollo 11 andmore » 12 basalts, suggesting that the intergranular cohesion of Apollo 17 basalts is weaker than that of Apollo 11 basalts but is stronger than that of Apollo 12 basalt. The thermal diffusivities measured at 10/sup -6/ torr are less temperature dependent. The basalt samples still show higher thermal diffusivities than the breccias, however. The low thermal diffusivity of the porous breccia sample (72395,14) is comparable to the lunar anorthositic gabbro (77017,24) studied by Mizutani and Osako (1974) that has the lowest thermal diffusivity of lunar rock samples ever reported. The difference between the thermal diffusivities the samples exhibit under atmospheric and vacuum conditions cannot be explained by the effect of thermal conduction through the gas medium filling the interstices of the samples that are absent under vacuum condition. A hypothesis is presented that the thermal conduction across the intergranular contact surfaces is strongly influenced by the adsorption of gas molecules on the surfaces of mineral grains. Measurements are also made in carbon dioxide atmosphere, in the temperature range between 200/sup 0/K and 460/sup 0/K.« less

Developing sediment remediation goals at superfund sites based on pore water for the protection of benthic organisms from direct toxicity to non-ionic organic contaminants (presentation)

EPA Science Inventory

Passive sampling is becoming a frequently used measurement technique at Superfund sites with contaminated sediments. Passive sampling measures the concentrations of freely dissolved chemicals (Cfrees) in the sediment pore water. Cfree has been found to be a very practical means f...

Comparison of lichen, conifer needles, passive air sampling devices, and snowpack as passive sampling media to measure semi-volatile organic compounds in remote atmospheres

EPA Science Inventory

The impact of extensively used arsenic-containing herbicides on groundwater beneath golf courses has become a topic of interest. Although currently used organoarsenicals are less toxic, their application into the environment may produce the more toxic inorganic arsenicals. The ob...

Significant mobility improvement of amorphous In-Ga-Zn-O thin-film transistors annealed in a low temperature wet ambient environment

NASA Astrophysics Data System (ADS)

Jallorina, Michael Paul A.; Bermundo, Juan Paolo S.; Fujii, Mami N.; Ishikawa, Yasuaki; Uraoka, Yukiharu

2018-05-01

Transparent amorphous oxide semiconducting materials such as amorphous InGaZnO used in thin film transistors (TFTs) are typically annealed at temperatures higher than 250 °C to remove any defects present and improve the electrical characteristics of the device. Previous research has shown that low cost and low temperature methods improve the electrical characteristics of the TFT. With the aid of surface and bulk characterization techniques in comparison to the device characteristics, this work aims to elucidate further on the improvement mechanisms of wet and dry annealing ambients that affect the electrical characteristics of the device. Secondary Ion Mass Spectrometry results show that despite outward diffusion of -H and -OH species, humid annealing ambients counteract outward diffusion of these species, leading to defect sites which can be passivated by the wet ambient. X-ray Photoelectron Spectroscopy results show that for devices annealed for only 30 min in a wet annealing environment, the concentration of metal-oxide bonds increased by as much as 21.8% and defects such as oxygen vacancies were reduced by as much as 18.2% compared to an unannealed device. Our work shows that due to the oxidizing power of water vapor, defects are reduced, and overall electrical characteristics are improved as evidenced with the 150 °C wet O2, 30 min annealed sample which exhibited the highest mobility of 5.00 cm2/V s, compared to 2.36 cm2/V s for a sample that was annealed at 150 °C in a dry ambient atmospheric environment for 2 h.

The origin of ultra diffuse galaxies: stellar feedback and quenching

NASA Astrophysics Data System (ADS)

Chan, T. K.; Kereš, D.; Wetzel, A.; Hopkins, P. F.; Faucher-Giguère, C.-A.; El-Badry, K.; Garrison-Kimmel, S.; Boylan-Kolchin, M.

2018-05-01

We test if the cosmological zoom-in simulations of isolated galaxies from the FIRE project reproduce the properties of ultra diffuse galaxies (UDGs). We show that outflows that dynamically heat galactic stars, together with a passively aging stellar population after imposed quenching, naturally reproduce the observed population of red UDGs, without the need for high spin halos, or dynamical influence from their host cluster. We reproduce the range of surface brightness, radius and absolute magnitude of the observed red UDGs by quenching simulated galaxies at a range of different times. They represent a mostly uniform population of dark matter-dominated dwarf galaxies with M* ˜ 108 M⊙, low metallicity and a broad range of ages; the more massive the UDGs, the older they are. The most massive red UDG in our sample (M* ˜ 3 × 108M⊙) requires quenching at z ˜ 3 when its halo reached Mh ˜ 1011 M⊙. Our simulated UDGs form with normal stellar-to-halo ratios and match the central enclosed masses and the velocity dispersions of the observed UDGs. Enclosed masses remain largely fixed across a broad range of quenching times because the central regions of their dark matter halos complete their growth early. If our simulated dwarfs are not quenched, they evolve into bluer low-surface brightness galaxies with M/L similar to observed field dwarfs. While our simulation sample covers a limited range of formation histories and halo masses, we predict that UDG is a common, and perhaps even dominant, galaxy type around M* ˜ 108 M⊙, both in the field and in clusters.

The origin of ultra diffuse galaxies: stellar feedback and quenching

NASA Astrophysics Data System (ADS)

Chan, T. K.; Kereš, D.; Wetzel, A.; Hopkins, P. F.; Faucher-Giguère, C.-A.; El-Badry, K.; Garrison-Kimmel, S.; Boylan-Kolchin, M.

2018-07-01

We test if the cosmological zoom-in simulations of isolated galaxies from the FIRE project reproduce the properties of ultra diffuse galaxies (UDGs). We show that outflows that dynamically heat galactic stars, together with a passively aging stellar population after imposed quenching, naturally reproduce the observed population of red UDGs, without the need for high spin haloes, or dynamical influence from their host cluster. We reproduce the range of surface brightness, radius, and absolute magnitude of the observed red UDGs by quenching simulated galaxies at a range of different times. They represent a mostly uniform population of dark matter-dominated dwarf galaxies with M* ˜ 108 M⊙, low metallicity, and a broad range of ages; the more massive the UDGs, the older they are. The most massive red UDG in our sample (M* ˜ 3 × 108 M⊙) requires quenching at z ˜ 3 when its halo reached Mh ˜ 1011 M⊙. Our simulated UDGs form with normal stellar-to-halo ratios and match the central enclosed masses and the velocity dispersions of the observed UDGs. Enclosed masses remain largely fixed across a broad range of quenching times because the central regions of their dark matter haloes complete their growth early. If our simulated dwarfs are not quenched, they evolve into bluer low surface brightness galaxies with M/L similar to observed field dwarfs. While our simulation sample covers a limited range of formation histories and halo masses, we predict that UDG is a common, and perhaps even dominant, galaxy type around M* ˜ 108 M⊙, both in the field and in clusters.

Damage detection and isolation via autocorrelation: a step toward passive sensing

NASA Astrophysics Data System (ADS)

Chang, Y. S.; Yuan, F. G.

2018-03-01

Passive sensing technique may eliminate the need of expending power from actuators and thus provide a means of developing a compact and simple structural health monitoring system. More importantly, it may provide a solution for monitoring the aircraft subjected to environmental loading from air flow during operation. In this paper, a non-contact auto-correlation based technique is exploited as a feasibility study for passive sensing application to detect damage and isolate the damage location. Its theoretical basis bears some resemblance to reconstructing Green's function from diffusive wavefield through cross-correlation. Localized high pressure air from air compressor are randomly and continuously applied on the one side surface of the aluminum panels through the air blow gun. A laser Doppler vibrometer (LDV) was used to scan a 90 mm × 90 mm area to create a 6 × 6 2D-array signals from the opposite side of the panels. The scanned signals were auto-correlated to reconstruct a "selfimpulse response" (or Green's function). The premise for stably reconstructing the accurate Green's function requires long sensing times. For a 609.6 mm × 609.6 mm flat aluminum panel, the sensing times roughly at least four seconds is sufficient to establish converged Green's function through correlation. For the integral stiffened aluminum panel, the geometrical features of the panel expedite the formation of the diffusive wavefield and thus shorten the sensing times. The damage is simulated by gluing a magnet onto the panels. Reconstructed Green's functions (RGFs) are used for damage detection and damage isolation based on an imaging condition with mean square deviation of the RGFs from the pristine and the damaged structure and the results are shown in color maps. The auto-correlation based technique is shown to consistently detect the simulated damage, image and isolate the damage in the structure subjected to high pressure air excitation. This technique may be transformed into passive sensing applied on the aircraft during operation.

Considering the reversibility of passive and reactive transport problems: Are forward-in-time and backward-in-time models ever equivalent?

NASA Astrophysics Data System (ADS)

Engdahl, N.

2017-12-01

Backward in time (BIT) simulations of passive tracers are often used for capture zone analysis, source area identification, and generation of travel time and age distributions. The BIT approach has the potential to become an immensely powerful tool for direct inverse modeling but the necessary relationships between the processes modeled in the forward and backward models have yet to be formally established. This study explores the time reversibility of passive and reactive transport models in a variety of 2D heterogeneous domains using particle-based random walk methods for the transport and nonlinear reaction steps. Distributed forward models are used to generate synthetic observations that form the initial conditions for the backward in time models and we consider both linear-flood and point injections. The results for passive travel time distributions show that forward and backward models are not exactly equivalent but that the linear-flood BIT models are reasonable approximations. Point based BIT models fall within the travel time range of the forward models, though their distributions can be distinctive in some cases. The BIT approximation is not as robust when nonlinear reactive transport is considered and we find that this reaction system is only exactly reversible under uniform flow conditions. We use a series of simplified, longitudinally symmetric, but heterogeneous, domains to illustrate the causes of these discrepancies between the two model types. Many of the discrepancies arise because diffusion is a "self-adjoint" operator, which causes mass to spread in the forward and backward models. This allows particles to enter low velocity regions in the both models, which has opposite effects in the forward and reverse models. It may be possible to circumvent some of these limitations using an anti-diffusion model to undo mixing when time is reversed, but this is beyond the capabilities of the existing Lagrangian methods.

Passive Sampling for Indoor and Outdoor Exposures to Chlorpyrifos, Azinphos-Methyl, and Oxygen Analogs in a Rural Agricultural Community.

PubMed

Gibbs, Jenna L; Yost, Michael G; Negrete, Maria; Fenske, Richard A

2017-03-01

Recent studies have highlighted the increased potency of oxygen analogs of organophosphorus pesticides. These pesticides and oxygen analogs have previously been identified in the atmosphere following spray applications in the states of California and Washington. We used two passive sampling methods to measure levels of the ollowing organophosphorus pesticides: chlorpyrifos, azinphos-methyl, and their oxygen analogs at 14 farmworker and 9 non-farmworker households in an agricultural region of central Washington State in 2011. The passive methods included polyurethane foam passive air samplers deployed outdoors and indoors and polypropylene deposition plates deployed indoors. We collected cumulative monthly samples during the pesticide application seasons and during the winter season as a control. Monthly outdoor air concentrations ranged from 9.2 to 199 ng/m 3 for chlorpyrifos, 0.03 to 20 ng/m 3 for chlorpyrifos-oxon, < LOD (limit of detection) to 7.3 ng/m 3 for azinphos-methyl, and < LOD to 0.8 ng/m 3 for azinphos-methyl-oxon. Samples from proximal households (≤ 250 m) had significantly higher outdoor air concentrations of chlorpyrifos, chlorpyrifos-oxon, and azinphos-methyl than did samples from nonproximal households ( p ≤ 0.02). Overall, indoor air concentrations were lower than outdoors. For example, all outdoor air samples for chlorpyrifos and 97% of samples for azinphos-methyl were > LOD. Indoors, only 78% of air samples for chlorpyrifos and 35% of samples for azinphos-methyl were > LOD. Samples from farmworker households had higher indoor air concentrations of both pesticides than did samples from non-farmworker households. Mean indoor and outdoor air concentration ratios for chlorpyrifos and azinphos-methyl were 0.17 and 0.44, respectively. We identified higher levels in air and on surfaces at both proximal and farmworker households. Our findings further confirm the presence of pesticides and their oxygen analogs in air and highlight their potential for infiltration of indoor living environments. Citation: Gibbs JL, Yost MG, Negrete M, Fenske RA. 2017. Passive sampling for indoor and outdoor exposures to chlorpyrifos, azinphos-methyl, and oxygen analogs in a rural agricultural community. Environ Health Perspect 125:333-341; http://dx.doi.org/10.1289/EHP425.

A Physical Mechanism for the Asymmetry in Top-Down and Bottom-Up Diffusion.

NASA Astrophysics Data System (ADS)

Wyngaard, J. C.

1987-04-01

Recent large-eddy simulations of the vertical diffusion of a passive, conservative scalar through the convective boundary layer (CBL) show strikingly different eddy diffusivity profiles in the `top-down' and `bottom-up' cases. These results indicate that for a given turbulent velocity field and associated scalar flux, the mean change in scalar mixing ratio across the CBL is several times larger if the flux originates at the top of the boundary layer (i.e., in top-down diffusion) rather than at the bottom. The large-eddy simulation (LES) data show that this asymmetry is due to a breakdown of the eddy-diffusion concept.A simple updraft-downdraft model of the CBL reveals a physical mechanism that could cause this unexpected behavior. The large, positive skewness of the convectively driven vertical velocity gives an appreciably higher probability of downdrafts than updrafts; this excess probability of downdrafts, interacting with the time changes of the mean mixing ratio caused by the nonstationarity of the bottom-up and top-down diffusion processes, decreases the equilibrium value of mean mixing-ratio jump across the mixed layer in the bottom-up case and increases it in the top-down case. The resulting diffusion asymmetry agrees qualitatively with that found through LES.

Highly Stable Near-Unity Photoluminescence Yield in Monolayer MoS2 by Fluoropolymer Encapsulation and Superacid Treatment.

PubMed

Kim, Hyungjin; Lien, Der-Hsien; Amani, Matin; Ager, Joel W; Javey, Ali

2017-05-23

Recently, there has been considerable research interest in two-dimensional (2D) transition-metal dichalcogenides (TMDCs) for future optoelectronic applications. It has been shown that surface passivation with the organic nonoxidizing superacid bis(trifluoromethane)sulfonamide (TFSI) produces MoS 2 and WS 2 monolayers whose recombination is at the radiative limit, with a photoluminescence (PL) quantum yield (QY) of ∼100%. While the surface passivation persists under ambient conditions, exposure to conditions such as water, solvents, and low pressure found in typical semiconductor processing degrades the PL QY. Here, an encapsulation/passivation approach is demonstrated that yields near-unity PL QY in MoS 2 and WS 2 monolayers which are highly stable against postprocessing. The approach consists of two simple steps: encapsulation of the monolayers with an amorphous fluoropolymer and a subsequent TFSI treatment. The TFSI molecules are able to diffuse through the encapsulation layer and passivate the defect states of the monolayers. Additionally, we demonstrate that the encapsulation layer can be patterned by lithography and is compatible with subsequent fabrication processes. Therefore, our work presents a feasible route for future fabrication of highly efficient optoelectronic devices based on TMDCs.

Effects of epitaxial structure and processing on electrical characteristics of InAs-based nBn infrared detectors

NASA Astrophysics Data System (ADS)

Du, X.; Savich, G. R.; Marozas, B. T.; Wicks, G. W.

2017-02-01

The conventional processing of the III-V nBn photodetectors defines mesa devices by etching the contact n-layer and stopping immediately above the barrier, i.e., a shallow etch. This processing enables great suppression of surface leakage currents without having to explore surface passivation techniques. However, devices that are made with this processing scheme are subject to lateral diffusion currents. To address the lateral diffusion current, we compare the effects of different processing approaches and epitaxial structures of nBn detectors. The conventional solution for eliminating lateral diffusion current, a deep etch through the barrier and the absorber, creates increased dark currents and an increased device failure rate. To avoid deep etch processing, a new device structure is proposed, the inverted-nBn structure. By comparing with the conventional nBn structure, the results show that the lateral diffusion current is effectively eliminated in the inverted-nBn structure without elevating the dark currents.

Effect of cyclic and static tensile loading on water content and solute diffusion in canine flexor tendons: an in vitro study.

PubMed

Hannafin, J A; Arnoczky, S P

1994-05-01

This study was designed to determine the effects of various loading conditions (no load and static and cyclic tensile load) on the water content and pattern of nutrient diffusion of canine flexor tendons in vitro. Region D (designated by Okuda et al.) of the flexor digitorum profundus was subjected to a cyclic or static tensile load of 100 g for times ranging from 5 minutes to 24 hours. The results demonstrated a statistically significant loss of water in tendons subjected to both types of load as compared with the controls (no load). This loss appeared to progress with time. However, neither static nor cyclic loading appeared to alter the diffusion of 3H-glucose into the tendon over a 24-hour period compared with the controls. These results suggest that any benefit in tendon repair derived from intermittent passive motion is probably not a result of an increase in the diffusion of small nutrients in response to intermittent tensile load.

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers.

PubMed

Colombara, Diego; Werner, Florian; Schwarz, Torsten; Cañero Infante, Ingrid; Fleming, Yves; Valle, Nathalie; Spindler, Conrad; Vacchieri, Erica; Rey, Germain; Guennou, Mael; Bouttemy, Muriel; Manjón, Alba Garzón; Peral Alonso, Inmaculada; Melchiorre, Michele; El Adib, Brahime; Gault, Baptiste; Raabe, Dierk; Dale, Phillip J; Siebentritt, Susanne

2018-02-26

Copper indium gallium diselenide-based technology provides the most efficient solar energy conversion among all thin-film photovoltaic devices. This is possible due to engineered gallium depth gradients and alkali extrinsic doping. Sodium is well known to impede interdiffusion of indium and gallium in polycrystalline Cu(In,Ga)Se 2 films, thus influencing the gallium depth distribution. Here, however, sodium is shown to have the opposite effect in monocrystalline gallium-free CuInSe 2 grown on GaAs substrates. Gallium in-diffusion from the substrates is enhanced when sodium is incorporated into the film, leading to Cu(In,Ga)Se 2 and Cu(In,Ga) 3 Se 5 phase formation. These results show that sodium does not decrease per se indium and gallium interdiffusion. Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries. The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to more effective chemical and electrical passivation strategies, and more efficient solar cells.

The role of hydrodynamics, matrix and sampling duration in passive sampling of polar compounds with Empore SDB-RPS disks.

PubMed

Vermeirssen, Etiënne L M; Asmin, Josef; Escher, Beate I; Kwon, Jung-Hwan; Steimen, Irene; Hollender, Juliane

2008-01-01

There is an increasing need to monitor concentrations of polar organic contaminants in the aquatic environment. Integrative passive samplers can be used to assess time weighted average aqueous concentrations, provided calibration data are available and sampling rates are known. The sampling rate depends on environmental factors, such as temperature and water flow rate. Here we introduce an apparatus to investigate the sampling properties of passive samplers using river-like flow conditions and ambient environmental matrices: river water and treated sewage effluent. As a model sampler we selected Empore SDB-RPS disks in a Chemcatcher housing. The disks were exposed for 1 to 8 days at flow rates between 0.03 and 0.4 m s(-1). Samples were analysed using a bioassay for estrogenic activity and by LC-MS-MS target analysis of the pharmaceuticals sulfamethoxazole, carbamazepine and clarithromycin. In order to assess sampling rates of SDB disks, we also measured aqueous concentrations of the pharmaceuticals. Sampling rates increased with increasing flow rate and this relationship was not affected by the environmental matrix. However, SDB disks were only sampling in the integrative mode at low flow rates <0.1 m s(-1) and/or for short sampling times. The duration of linear uptake was particularly short for sulfamethoxazole (1 day) and longer for clarithromycin (5 days). At 0.03 m s(-1) and 12-14 degrees C, the sampling rate of SDB disks was 0.09 L day(-1) for clarithromycin, 0.14 L day(-1) for sulfamethoxazole and 0.25 L day(-1) for carbamazepine. The results show that under controlled conditions, SDB disks can be effectively used as passive sampling devices.

Guidelines for the use of the semipermeable membrane device (SPMD) and the polar organic chemical integrative sampler (POCIS) in environmental monitoring studies

USGS Publications Warehouse

Alvarez, David A.

2010-01-01

The success of an environmental monitoring study using passive samplers, or any sampling method, begins in the office or laboratory. Regardless of the specific methods used, the general steps include the formulation of a sampling plan, training of personnel, performing the field (sampling) work, processing the collected samples to recover chemicals of interest, analysis of the enriched extracts, and interpretation of the data. Each of these areas will be discussed in the following sections with emphasis on specific considerations with the use of passive samplers. Water is an extremely heterogeneous matrix both spatially and temporally (Keith, 1991). The mixing and distribution of dissolved organic chemicals in a water body are controlled by the hydrodynamics of the water, the sorption partition coefficients of the chemicals, and the amount of organic matter (suspended sediments, colloids, and dissolved organic carbon) present. In lakes and oceans, stratification because of changes in temperature, water movement, and water composition can occur resulting in dramatic changes in chemical concentrations with depth (Keith, 1991). Additional complications related to episodic events, such as surface runoff, spills, and other point source contamination, can result in isolated or short-lived pulses of contaminants in the water. The application of passive sampling technologies for the monitoring of legacy and emerging organic chemicals in the environment is becoming widely accepted worldwide. The primary use of passive sampling methods for environmental studies is in the area of surface-water monitoring; however, these techniques have been applied to air and groundwater monitoring studies. Although these samplers have no mechanical or moving parts, electrical or fuel needs which require regular monitoring, there are still considerations that need to be understood in order to have a successful study. Two of the most commonly used passive samplers for organic contaminants are the semipermeable membrane device (SPMD) and the polar organic chemical integrative sampler (POCIS). The tips given in this document focus on these two samplers but are applicable to most types of passive sampling devices. The information in this guide is heavily weighted towards the sampling of water; however, information specific to the use of SPMDs for air sampling will also be covered.

Passive sampling approaches used for time-integrated environmental monitoring and Risk Assessment in the tropical Río Tapezco catchment in Costa Rica

NASA Astrophysics Data System (ADS)

Weiss, Frederik; Wey, Hannah; Stamm, Christian; Ruepert, Clemens; Zurbrügg, Christian; Eggen, Rik

2017-04-01

Highest pesticide application rates and high surface runoff potentials are found in tropical countries. Global data indicate that among these countries, Costa Rica's agriculture is one of the most pesticide intensive worldwide. After use, pesticides can be transported from the fields into surface water through heavy raining events via wash-off, leaching, surface runoff and erosion processes, or direct as point source due to poor pesticide application practices and deteriorate the water quality and impair aquatic organisms. Even if the risk of pesticide pollution is well documented in Costa Rica, comprehensive information about the diffuse and direct pesticide entry routes, their environmental behavior, and the degree of water pollution is often lacking. Generally, only grab samples are taken and time integrated methods for environmental monitoring are seldom used so far. There is a need for more time integrated data at catchment scale. Current passive sampling techniques are low-costs options that, when combined with advanced analytical screening methods, allow for a broad assessment of pesticide pollution in streams. This will lead to a better systematic understanding of the environmental fate of pesticides and to describe their impacts to non-target organisms in tropical aquatic environments in the short- and long-term. We implemented such an approach in the tropical Río Tapezco catchment in the Zarcero canton, Costa Rica. The area covers 5112 ha, ranges between an altitude of 1100 and 2200 m above sea level and receives an average annual precipitation of 2000 - 2500 mm/yr. The catchment is intensively used for the horticultural production of vegetables, potatoes and herbs and it is specially characterized by its agricultural fields with steep slopes. The area is a hot spot of pesticide use with an average application rate of about 22 kg/ha of arable land and cropping cycle. For time-integrated monitoring, the rivers of the study area were sampled at five points in biweekly intervals between end of July and beginning of October 2015 by using three passive sampling systems (Camcather® with styrene-divinylbenzene reverse phase sulfonated discs, polydimethylsiloxane sheets, and a water level proportional water sampler). Additionally, pressure loggers were installed at all sites for recording water temperature and level continuously and daily precipitation data from one meteorological station (Zarcero Palmira) were available. For the quantification of about 260 substances GC-MS/MS and LC HR-MS was used. In 2015, more than 60 pesticides were detected in the Río Tapezco catchment with biweekly time weighted average concentrations ranging from few ng/L to several µg/L. Furthermore the available European environmental quality standards for several compounds were exceeded and present a potential risk for water organisms.

Office of Naval Research Overview of Corrosion S&T Program

DTIC Science & Technology

2010-12-02

a carbon induced passivity for LTCSS treated austenitic stainless steels - Low temp. allows interstitial C diffusion, but not substitutional...paraequilibrium carburization mechanism(s) that lead to the enhanced corrosion resistance seaw ater crevice corrosion on 316 Stainless Steel LTC...Treated 316 untreated LTC process TTT diagram LTCSS Surface Modification: • Carbon concentrations > 12 at. % in 316 stainless steel while maintaining

Using Passive Samplers to Calculate the Diffusive Flux of DDTs and PCBs from Sediments to Water Column at the Palos Verdes Shelf Superfund Site

EPA Science Inventory

Background/Objectives. The Palos Verdes Shelf (PVS) Superfund site is in over 50 meters of water on the continental shelf and slope off the coast of southern California (USA). The site includes over 25 km2 of sediments contaminated over several decades by municipal treatment pla...

Passive asymmetric transport of hesperetin across isolated rabbit cornea.

PubMed

Srirangam, Ramesh; Majumdar, Soumyajit

2010-07-15

Hesperetin, an aglycone of the flavanone hesperidin, is a potential candidate for the treatment of diabetic retinopathy and macular edema. The purpose of this investigation was to determine solubility, stability and in vitro permeability characteristics of hesperetin across excised rabbit corneas. Aqueous and pH dependent solubility was determined using standard shake flask method. Solution stability was evaluated as a function of pH (1.2-9) and temperature (25 and 40 degrees C). Permeability of hesperetin was determined across the isolated rabbit cornea utilizing a side-bi-side diffusion apparatus, in the apical to basolateral (A-B) and basolateral to apical (B-A) directions. Hesperetin displayed asymmetrical transcorneal transport with a 2.3-fold higher apparent permeability in the B-A direction compared to the A-B direction. The transport process was observed to be pH dependent. Surprisingly, however, the involvement of efflux transporters or proton-coupled carrier-systems was not evident in this asymmetric transcorneal diffusion process. The passive and pH dependent corneal transport of hesperetin could probably be attributable to corneal ultrastructure, physicochemical characteristics of hesperetin and the role of transport buffer components. Copyright (c) 2010 Elsevier B.V. All rights reserved.

Comparison study and thoron interference test of different radon monitors.

PubMed

Sumesh, C G; Kumar, A Vinod; Tripathi, R M; Puranik, V D

2013-03-01

A comparison study and thoron interference test for different continuous radon monitors were carried out. The comparison study includes three passive diffusion monitors [one pulse ionisation chamber based-Alpha Guard and two silicon semi-conductor based-Radon Scout Plus (RSP)] and one silicon semi-conductor-based active radon thoron discriminating monitor--RAD 7. Radon emanation standard, supplied by National Institute of Science and Technology, has been utilised for the comparison study to qualify the calibration of the continuous radon monitors. All the instruments showed good agreement with the estimated radon concentration using (226)Ra/(222)Rn emanation standard. It was found that the active radon monitoring system is having a higher initial response towards the transient radon concentration than the passive radon monitors studied. The instruments measuring radon concentration without energy discrimination are likely to have some sensitivity towards the thoron concentration. Thus, thoron interference study was carried out in the above monitors. Nine percent interference in measured radon concentration in the Alpha Guard monitor and 4 % interference in the semi-conductor-based RSP monitors was observed. Study indicates that the interference of thoron in radon monitors depends on the area of diffusion of gas, volume of detection and sensitivity factor.

Active generation and propagation of Ca2+ signals within tunneling membrane nanotubes.

PubMed

Smith, Ian F; Shuai, Jianwei; Parker, Ian

2011-04-20

A new mechanism of cell-cell communication was recently proposed after the discovery of tunneling nanotubes (TNTs) between cells. TNTs are membrane protrusions with lengths of tens of microns and diameters of a few hundred nanometers that permit the exchange of membrane and cytoplasmic constituents between neighboring cells. TNTs have been reported to mediate intercellular Ca(2+) signaling; however, our simulations indicate that passive diffusion of Ca(2+) ions alone would be inadequate for efficient transmission between cells. Instead, we observed spontaneous and inositol trisphosphate (IP(3))-evoked Ca(2+) signals within TNTs between cultured mammalian cells, which sometimes remained localized and in other instances propagated as saltatory waves to evoke Ca(2+) signals in a connected cell. Consistent with this, immunostaining showed the presence of both endoplasmic reticulum and IP(3) receptors along the TNT. We propose that IP(3) receptors may actively propagate intercellular Ca(2+) signals along TNTs via Ca(2+)-induced Ca(2+) release, acting as amplification sites to overcome the limitations of passive diffusion in a chemical analog of electrical transmission of action potentials. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Electrochemical properties of 316L stainless steel with culturing L929 fibroblasts

PubMed Central

Hiromoto, Sachiko; Hanawa, Takao

2005-01-01

Potentiodynamic polarization and impedance tests were carried out on 316L stainless steel with culturing murine fibroblast L929 cells to elucidate the corrosion behaviour of 316L steel with L929 cells and to understand the electrochemical interface between 316L steel and cells, respectively. Potential step test was carried out on 316L steel with type I collagen coating and culturing L929 cells to compare the effects of collagen and L929 cells. The open-circuit potential of 316L steel slightly shifted in a negative manner and passive current density increased with cells, indicating a decrease in the protective ability of passive oxide film. The pitting potential decreased with cells, indicating a decrease in the pitting corrosion resistance. In addition, a decrease in diffusivity at the interface was indicated from the decrease in the cathodic current density and the increase in the diffusion resistance parameter in the impedance test. The anodic peak current in the potential step test decreased with cells and collagen. Consequently, the corrosion resistance of 316L steel decreases with L929 cells. In addition, collagen coating would provide an environment for anodic reaction similar to that with culturing cells. PMID:16849246

Recombination activity of grain boundaries in high-performance multicrystalline Si during solar cell processing

NASA Astrophysics Data System (ADS)

Adamczyk, Krzysztof; Søndenâ, Rune; Stokkan, Gaute; Looney, Erin; Jensen, Mallory; Lai, Barry; Rinio, Markus; Di Sabatino, Marisa

2018-02-01

In this work, we applied internal quantum efficiency mapping to study the recombination activity of grain boundaries in High Performance Multicrystalline Silicon under different processing conditions. Wafers were divided into groups and underwent different thermal processing, consisting of phosphorus diffusion gettering and surface passivation with hydrogen rich layers. After these thermal treatments, wafers were processed into heterojunction with intrinsic thin layer solar cells. Light Beam Induced Current and Electron Backscatter Diffraction were applied to analyse the influence of thermal treatment during standard solar cell processing on different types of grain boundaries. The results show that after cell processing, most random-angle grain boundaries in the material are well passivated, but small-angle grain boundaries are not well passivated. Special cases of coincidence site lattice grain boundaries with high recombination activity are also found. Based on micro-X-ray fluorescence measurements, a change in the contamination level is suggested as the reason behind their increased activity.