Orders Of Magnitude Change Research Articles

MgAl 2O 4-based humidity-sensing material for potential application in PEM fuel cells

MgAl 2O 4 ceramic pellets have been investigated as the in situ humidity sensing elements for proton exchange membrane (PEM) fuel cells. The MgAl 2O 4 powder was synthesized through EDTA-citrates method. When the temperature increased from 50 °C to 80 °C, the ohmic resistance ( R) at the whole relative humidity (RH) range decreased by about one order of magnitude while the linearity of Log( R) vs. RH remained constant. The MgAl 2O 4 specimens sintered at 1200 °C with ball-milled powder show the highest humidity sensitivity with 3.3 orders of magnitude change from RH 40% to RH 100%. Homogenous meso-pore (around 50 nm) might be the root cause for high sensitivity and the macro-pore (>50 nm) is the cause for decreasing the sensitivity of the sensing material. A precise optimization criterion for pore size has been proposed for this RH range. The MgAl 2O 4-based ceramic pellets show promising performance for the in situ RH sensing for PEM fuel cells.

Basin-Scale Consequences of Agricultural Land Use on Benthic Light Availability and Primary Production Along a Sixth-Order Temperate River

The emerging spatial scale of interest for fluvial ecosystem studies and applications is the river basin. Although much focus has been directed toward habitat availability and nutrient cycling across the fluvial landscape, light availability has received considerably less attention and has not been assessed quantitatively at the basin-scale despite it being the primary energy source for aquatic ecosystems. We developed a basin-scale light availability model that couples readily available broad spatial data with easily measured synoptic data using a GIS framework and the principles of hydraulic geometry. We used this model to (i) quantify benthic light availability (E bed) along a 160-km river in central Wisconsin, USA, (ii) predict gross primary production (GPP) along the same river, and (iii) assess the effects of agricultural land use on E bed and GPP. Overall, E bed decreased in the downstream direction due primarily to increased turbidity, and there was considerable local variation caused by changes in topography, riparian vegetation, and channel orientation. These local variations in E bed caused GPP to fluctuate greatly over short distances, as much as 2.1 g C m−2 d−1 over 260 m. When summed over the entire channel length, present-day, post-agricultural GPP (635 kg C d−1) was about eight times lower than estimated pre-agricultural GPP (4992 kg C d−1). Model simulations revealed that agricultural land use can cause an order of magnitude change in GPP, reduce or increase inter-sectional variability in GPP, and significantly alter broad spatial trends in GPP. Our basin-scale benthic light availability model is a tool that researchers can use to investigate relationships between light availability and ecosystem processes at broad spatial scales and also one that practitioners can use for more holistic fluvial ecosystem assessments.

Distance-Independent Charge-Transfer Resistance at Gold Electrodes Modified by Thiol Monolayers and Metal Nanoparticles

The electrochemical properties of Au electrodes sequentially modified by self-assembled monolayers (SAM) of carboxyl-terminated alkane thiols, ultrathin poly-l-lysine (PLL) film, and diluted monolayers of Au nanoparticles are investigated by electrochemical impedance spectroscopy (EIS). The phenomenological charge-transfer resistance (Rct) for the hexacyanoferrate redox couple at the equilibrium potential exhibited an exponential increase with increasing methylene units (x) in the SAM. The increase of Rct between x = 1 and 10 was described by a well-defined decay parameter β = 1.16 ± 0.04 per methylene unit. This behavior suggests that the kinetics of electron transfer is controlled by coherent electron tunneling across the carboxyl-terminated SAM. Adsorption of the PLL brings about an average 2.5 times decrease in Rct independent of x. The ultrathin PLL film (thickness less than 1 nm) induces an increase of the surface concentration of the redox couple without affecting the β value observed for the SAM-terminated electrodes. Diluted monolayers of Au nanoparticles with an average 19.2 ± 2.1 nm diameter generate significant changes in the dynamics of electron transfer. In contrast to the behavior in the absence of nanoparticles, a distance-independent Rct was observed for x > 5. Detailed analysis of the electrochemical responses as a function of the particle number density revealed that the rate-determining step is the charging of the nanoparticles by the redox species. It is concluded that the electronic communication between the nanoparticles and the electrode surface over distances as large as 13 Å originates from electron transport through the trapped redox probe. The several orders of magnitude changes of the apparent Rct upon nanoparticle adsorption further suggest that electron transport through the film does not occur via a classical hopping mechanism. A mechanism based on nonthermalized electron transport via the density of the redox probe at the Fermi energy (hot electron transport) is proposed to account for the experimental observations.

Probing effects of pH change on dynamic response of Claudin-2 mediated adhesion using single molecule force spectroscopy

Claudins belong to a large family of transmembrane proteins that localize at tight junctions (TJs) where they play a central role in regulating paracellular transport of solutes and nutrients across epithelial monolayers. Their ability to regulate the paracellular pathway is highly influenced by changes in extracellular pH. However, the effect of changes in pH on the strength and kinetics of claudin mediated adhesion is poorly understood. Using atomic force microscopy, we characterized the kinetic properties of homophilic trans-interactions between full length recombinant GST tagged Claudin-2 (Cldn2) under different pH conditions. In measurements covering three orders of magnitude change in force loading rate of 10 2–10 4 pN/s, the Cldn2/Cldn2 force spectrum (i.e., unbinding force versus loading rate) revealed a fast and a slow loading regime that characterized a steep inner activation barrier and a wide outer activation barrier throughout pH range of 4.5–8. Comparing to the neutral condition (pH 6.9), differences in the inner energy barriers for the dissociation of Cldn2/Cldn2 mediated interactions at acidic and alkaline environments were found to be < 0.65 k B T, which is much lower than the outer dissociation energy barrier (> 1.37 k B T). The relatively stable interaction of Cldn2/Cldn2 in neutral environment suggests that electrostatic interactions may contribute to the overall adhesion strength of Cldn2 interactions. Our results provide an insight into the changes in the inter-molecular forces and adhesion kinetics of Cldn2 mediated interactions in acidic, neutral and alkaline environments.

Plant form and function

Plant form and function

Investigation of Cathode Behavior of Model Thin Film SrTi1-xFexO3-&amp;#948; Mixed Ionic-Electronic Conducting Electrodes

AbstractThe defect structure, transport properties and band structure of the perovskite solid solution SrTi1-xFexO3-&amp;#948; (STF) can be systematically controlled, over wide limits, by variation in the Fe fraction. In this paper, the authors review recent results which show that STF exhibits model mixed ionic-electronic conducting cathode behavior and extend the composition range investigated to include compositions from SrTiO3 rich values (x = 0.05) to SrFeO3-&amp;#948; (x= 1). While the majority of the cathodes were prepared as dense films by pulsed layer deposition (PLD), selected compositions were also prepared by thermal inkjet printing. The cathodes were investigated by electrochemical impedance spectroscopy (EIS) as a function of electrode geometry, temperature and oxygen partial pressure. The electrode behavior was found to be controlled by surface exchange kinetics in almost all cases. Values for the surface exchange coefficient, k, were derived and found to be comparable in magnitude to those exhibited by other popular mixed ionic-electronic conductors such as (La,Sr)(Co,Fe)O3, thereby, confirming STF's suitability of as a model mixed conducting cathode material. Surprisingly, the magnitude of k was found to be only weakly dependent on the bulk electronic and ionic conductivities of STF which varied by many orders of magnitude (over nearly five orders of magnitude change in σel) over the x values examined in this study. The observed trends are discussed in relation to the known defect and transport properties of STF.

Study of the Log-Layer Structure in Wall Turbulence Over a Very Large Range of Reynolds Number

Studies of the logarithmic layer structure in turbulent boundary layers are presented that span three orders of magnitude change in Reynolds number. The experiments considered used two separate laboratory scale facilities, as well as the atmospheric surface layer at the SLTEST facility in Utah. Several experimental techniques were used in order to probe the three-dimensional nature of the flow structures. The main focus is on two-point correlation statistics at a given z/δ, which are found to agree well over all Reynolds numbers when scaled with an outer length-scale. Large-scale coherence recently noted in the logarithmic region of laboratory-scale boundary layers is also found to be present in the atmospheric surface layer flow. Recent findings regarding the influence of these large scale motions on the near-wall region are also presented.

Intra-irradiation changes in the signal of polymer-based dosimeter (GAFCHROMIC EBT) due to dose rate variations

The effect of dose rate on the real-time change in optical density (ΔOD) of a GAFCHROMIC® EBT film is quantified using a previously reported optical readout approach. A range of doses (5–1000 cGy) and dose rates (16–520 cGy min−1) are used, and a statistically significant difference between ΔOD of films exposed at different dose rates occurs within approximately one order of magnitude change in the dose rate. A small increase in per cent standard deviation of measured ΔOD values is also observed when the entire dose rate range was used, but in all cases combining all ΔOD values produces per cent standard deviation of <4.5%. Thus, whether the dose rate effect is clinically significant depends on the specific application of EBT and the desired accuracy.

Reynolds Number Invariance of the Structure Inclination Angle in Wall Turbulence

Cross correlations of the fluctuating wall-shear stress and the streamwise velocity in the logarithmic region of turbulent boundary layers are reported over 3 orders of magnitude change in Reynolds number. These results are obtained using hot-film and hot-wire anemometry in a wind tunnel facility, and sonic anemometers and a purpose-built wall-shear stress sensor in the near-neutral atmospheric surface layer on the salt flats of Utah's western desert. The direct measurement of fluctuating wall-shear stress in the atmospheric surface layer has not been available before. Structure inclination angles are inferred from the cross correlation results and are found to be invariant over the large range of Reynolds number. The findings justify the prior use of low Reynolds number experiments for obtaining structure angles for near-wall models in the large-eddy simulation of atmospheric surface layer flows.

Kinetics of pH Response for Copolymer Films with Dilute Carboxylate Functionality

We have investigated the effects of film composition and thickness on the rate of pH-induced response of a copolymer film containing predominately polymethylene with randomly distributed carboxylic acid side groups (denoted as PM-CO2H). These responsive films are prepared directly onto a gold electrode surface by surface-catalyzed polymerization and subsequent hydrolysis. We measured electrochemical impedance at fixed frequency (100 Hz) to monitor the barrier properties of the polymer film during a step change in pH. At a 1-3% molar acid content, the copolymer films exhibit a 2 order of magnitude change in impedance at 100 Hz when the contacting solution pH changes from 11 to 4 (or 4 to 11). For all films, the rate of protonation is slower than that of ionization, consistent with a more gradual transfer of protons through an increasingly hydrophobic film at the outermost nanometers during the protonation step. Increased acid content within the film accelerates both the rate of protonation and ionization. Thinner films (50 nm) with the same acid content show faster response rate in both directions, since water and ions have a shorter transfer path. A large and reversible pH response was obtained for all films studied, but selection of appropriate film composition and thickness can greatly influence the rate of response.

Ionic Liquid Salt Bridge in Dilute Aqueous Solutions

A new type of salt bridge composed of a hydrophobic room-temperature ionic liquid, recently proposed (T. Kakiuchi and T. Yoshimatsu, Bull. Chem. Soc. Jpn., 2006, 79, 1017), has been shown to be satisfactorily usable in dilute aqueous solutions of submillimolar range. A stable phase-boundary potential has been demonstrated between an ionic liquid, 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(8)mim+][C(1)C(1)N-), and an aqueous KCl solution of submillimolar level, which is lower than the solubility of [C(8)mim+][C(1)C(1)N-] in water, 1.6 mmol dm(-3) at 25 degrees C. The phase-boundary potential between [C(8)mim+][C(1)C(1)N-] and water is maintained constant over more than four orders of magnitude change in the concentration of an aqueous electrolyte solution. The ionic-liquid salt bridge is a superior alternative to salt bridges based on equitransferent electrolytes in practical applications, particularly, the potentiometry of samples of low ionic strengths, such as potentiometric pH measurements of rainwater.

Solidification Condition Effects on Microstructures and Creep Resistance of Sn-3.8Ag-0.7Cu Lead-Free Solder

Metallurgical, mechanical, and environmental factors all affect service reliability of lead-free solder joints and are under extensive study for preparation of the transition from Sn-Pb eutectic soldering to lead-free soldering in the electronic industry. However, there is a general lack of understanding about the effects of solidification conditions on the microstructures and mechanical behavior of lead-free solder alloys, particularly on the long-term reliability. This study attempts to examine the creep resistance of the Sn-Ag-Cu eutectic alloy (Sn-3.8Ag-0.7Cu, SAC387) with a variety of solidification conditions with cooling rates ranging from 0.3 °C/s to 17 °C/s. Results indicate that solidification conditions have a major influence on the creep resistance of SAC387 alloy; up to two orders of magnitude change in the steady-state creep rates were observed at low stress levels. An understanding of the mechanical property change with microstructures, which are determined by the solidification conditions, should shed some light on the fundamental deformation and fracture mechanisms of lead-free solder alloys and can provide valuable information for long-term reliability assessment of lead-free solder interconnections.

Laboratory measurements of the oxidation kinetics of organic aerosol mixtures using a relative rate constants approach

Organic aerosols in the atmosphere are exposed to oxidants, but the oxidation kinetics are largely unknown. We investigate the decay of organic species in laboratory‐generated organic aerosols exposed to atmospherically relevant ozone concentrations in a smog chamber. The experiments were conducted using five different organic aerosols, varying in complexity from three to twelve components. These mixtures include alkenoic acids, alkanoic acids, alkanedioic acids, n‐alkanes, and sterols and are designed to simulate meat cooking emissions. A relative rate constants approach was used to compare reaction rates of individual organic species and to compare the reaction rates of the aerosol species to gas phase tracers. Significant decay was observed for all species (except for the n‐alkanes) in at least one of the experimental systems. By relating the decomposition of condensed phase alkenoic acids to gas phase alkenes, we show that the reaction rate constants of oleic acid and palmitoleic acid evolve as the aerosol is processed, decreasing by a factor of ∼10 over the course of a 4‐hour experiment. The decay rate constants of cholesterol, oleic acid, and palmitic acid all depend strongly on aerosol composition, with more than an order of magnitude change in the effective rate constants depending on mixture composition. Effects of aerosol composition are likely to be even more significant in atmospheric aerosol, where particle compositions are highly variable. The data presented here indicate these mixture effects are complicated, making it difficult to extrapolate from simple laboratory systems to atmospherically relevant conditions.

Contributions of natural sources to high [formula omitted] and [formula omitted] events in the eastern Mediterranean

In total 562 daily PM 10 and PM 2.5 samples were collected from April 2001 to April 2002 at a rural site (Erdemli) located on the coast of the Eastern Mediterranean. The annual mean PM 10 and PM 2.5 levels were 36.4 ± 27.8 and 9.7 ± 5.9 μ g m - 3 , respectively. PM 10 and PM 2.5 concentrations indicated orders of magnitude change from day to day ( PM 10 = 2 – 326 μ g m - 3 ; PM 2.5 = 0.5 – 28 μ g m - 3 ). The highest levels of PM 10 were observed during the transition period (March, April and May) due to mineral dust transported from North Africa and during winter due to sea spray generation. However, PM 2.5 levels exhibited higher concentrations during summer resulting from an enhanced production of secondary aerosols. The PM 2.5 / PM 10 ratio (0.25) and categorization of air mass back trajectories indicated that PM 10 at the study area is dominated by primary aerosol emissions (mineral dust particles from the Saharan Desert and sea salt particles from the Mediterranean Sea itself). During the whole sampling period 28 and 51 events exceeded the recommended maximum values of 50 and 15 μ g m - 3 for PM 10 and PM 2.5 , respectively. Source apportionment analysis indicated that PM 10 exceedances originated as a consequence of natural events (mineral dust ∼ 40 % ; sea salt ∼ 50 % ) whereas PM 2.5 exceedances were accounted primarily by pollution events (in 90% of the cases).

Relationship between the geometrical and structural properties of layered fractured rocks and their effective permeability tensor. A simulation study

The influence of geometrical and structural properties of layered fractured rocks on their permeability tensor is investigated for an elementary volume at the meter scale. Various synthetic networks were generated with a three-dimensional model that incorporates a pseudo-random process controlled by mechanical rules of fracturing. The permeability is supposed to be a function of the discontinuities aperture in an impermeable matrix. Steady state, saturated laminar flow is assumed within discontinuities of constant aperture (parallel joint walls). For 81 networks associated to different sets of numerical parameters, the geometrical and structural properties are computed from 200 statistically equivalent simulations and averaged to asses the mean geometrical and structural properties. In a similar way, the mean permeability tensor associated to each network is calculated. Then, the effect of the geometrical and structural properties of the network on the permeability tensor values is studied. We show that some geometrical and structural properties may have non-negligible effects: The bedding perpendicular joint spacing and the bedding plane stopping capacity can induce more than one order of magnitude change in the permeability values, while other investigated properties (mean and standard deviation of the bedding perpendicular joints length distribution) have a very small influence. These results were compared with the permeability tensor inferred from one analytical model which provided permeability values of the same order of magnitude as those inferred from the numerical model. This model can thus be considered within the hierarchical procedure proposed to characterize rock mass permeability tensors in the field.

Shape selectivity versus functional group pre-organization in molecularly imprinted polymers

A systematic survey of related molecular probes differing in shape or functional group orientation was used to compare the effects of shape selectivity versus pre-organization of functional monomers on imprinting and rebinding performance of molecularly imprinted polymers (MIPs). These studies revealed that templates with two functional group interactions with the MIPs are influenced to a larger degree by shape selective interactions than templates with three functional group interactions. For example, with two functional group interactions, increasing side chain size of compounds 1– 5 increased selectivity 5-fold; while the same size change for compounds with three functional group interactions leads to a maximum 2-fold increase. Thus, the effects of shape selectivity and pre-organization of functional groups do not appear to work in concert with each other during the imprinting process or in the rebinding behavior. Furthermore, greater selectivity is generally found for templates with two functional groups, where the dominant mode of molecular recognition is shape selectivity. For example, the α value for the MIP elicited toward template compound 5 with two hydrogen bonding groups was 5–12-fold higher than equivalently shaped compounds 6– 8 that have three non-covalent binding interactions (Table 3). On the other hand, pre-organization of functional groups dominated the performance of MIPs elicited toward templates with three template–functional group interactions. This is observed in Tables 6–8, where compounds with identical positioning of three functional groups all show less than an order of magnitude change in α values despite changes in shape.

Layer-by-layer self-assembly aluminum Keggin ions/Prussian blue nanoparticles ultrathin films towards multifunctional sensing applications

In this study we described the nanocomposites films of specially synthesized inorganic Prussian blue (PB) nanoparticles and polyoxocation Al13 Keggin ions that possess the excellent sensing activities. Film fabrication using layer-by-layer (LBL) self-assembly technique was followed by electrochemical characterization. The assembled multilayer Al13/PB films as sensor devices for both the catalytic reduction of H2O2 and detecting the change of relative humidity were also investigated. The sensitivity of the biosensor was 0.886mAcm−2mM−1, and about two orders of magnitude change in resistance was observed as the relative humidity increasing from 5 to 95%. Both sensors exhibited good reproducibility, wide linear range. The performance and multifunctional abilities of these nanocomposites promise potential applications in biosensors, environmental controlling system and biomedical devices.

Orders of Magnitude Change in Phenotype Rate Caused by Mutation

Orders of Magnitude Change in Phenotype Rate Caused by Mutation

Time Resolved In-Situ Diffuse X-ray Scattering Measurements of the Surface Morphology of Homoepitaxial SrTiO3 Films During Pulsed Laser Deposition

AbstractHomoepitaxial SrTiO3 thin films were grown on SrTiO3 (001) using Pulsed Laser Deposition (PLD). The deposition process was monitored in-situ, via both x-ray reflectivity and surface diffuse x-ray scattering measurements in the G3 experimental station at the Cornell High Energy Synchrotron Source (CHESS). Using a CCD detector in 1D, or streak-camera, mode with approximately 0.3-second time resolution, data were collected during growths performed at two substrate temperatures: 695°C and 1000°C. While the specular reflectivity oscillations for the two growths are very similar, the diffuse scattering clearly shows a distinct change in the peak position. Using Atomic Force Microscopy (AFM), we illustrate how the peak position for the diffuse lobes of scattered intensity is directly related to the distribution of single unit cell high islands on the growing surface. Thus, the peak shift of the diffuse scattering indicates an order of magnitude change in the island density.

Efficient lookup on unstructured topologies

We present LMS, a protocol for efficient lookup on unstructured networks. Our protocol uses a virtual namespace without imposing specific topologies. It is more efficient than existing lookup protocols for unstructured networks, and thus is an attractive alternative for applications in which the topology cannot be structured as a Distributed Hash Table (DHT). We present analytic bounds for the worst-case performance of LMS. Through detailed simulations (with up to 100,000 nodes), we show that the actual performance on realistic topologies is significantly better. We also show in both simulations and a complete implementation (which includes over five hundred nodes) that our protocol is inherently robust against multiple node failures and can adapt its replication strategy to optimize searches according to a specific heuristic. Moreover, the simulation demonstrates the resilience of LMS to high node turnover rates, and that it can easily adapt to orders of magnitude changes in network size. The overhead incurred by LMS is small, and its performance approaches that of DHTs on networks of similar size