Orders Of Magnitude Variation Research Articles

Numerical simulations of texture development and associated rheological anisotropy in regions of complex mantle flow

The development of Lattice Preferred Orientations (LPO) within olivine aggregates under flow in the upper mantle leads to seismic and rheological (or viscoplastic) anisotropies. We compare predictions from different micromechanical models, applying several commonly used theoretical descriptions to an upwelling flow scenario representing a typical oceanic spreading center. Significant differences are obtained between models in terms of LPO and associated rheology, in particular in regions where the flow direction changes rapidly, with superior predictions for the recently proposed Second‐Order approach. This highlights the limitations of ad hoc formulations. LPO‐induced rheological anisotropy may have a large effect on actual flow patterns with 1–2 orders of magnitude variation in directional viscosities compared to the isotropic case.

The Buncefield explosion: a benchmark for infrasound analysis across Central Europe

SUMMARY A large explosion occurred at the Buncefield Oil Depot, United Kingdom, on the 2005 December 11, as the result of a spillage of 300 tonnes of petrol. The explosion generated large amplitude infrasonic signals that were recorded at ranges of up to 1400 km. We present an analysis of data from across Central Europe using seven infrasound arrays, four of which recorded a total of 20 infrasonic arrivals, and 49 seismometers, which recorded 89 air-toground coupled arrivals. Exceptionally high amplitude stratospheric winds occurred at the time of the explosion, propagating east–southeast with speeds of up to 130 m s −1 , generating a highly efficient duct for infrasound propagation. The Buncefield explosion can therefore be considered as a benchmark for studying the influence of different propagation algorithms and atmospheric models on phase identification, source location and yield estimation. Significant improvements are made in phase identification using accurate atmospheric parametrizations and 3-D modelling, where we identify 18 of the 20 observed phases, compared to seasonal atmospheric models and 1-D ray tracing which only identify seven of the phases. Additionally, various location scenarios are considered, including cross-bearings and least-squares traveltime and backazimuth inversion, all of which estimate locations within 35 km of ground truth. A novel single array location method using multiple phases works comparably well. Yield estimates made using the stratospheric arrival amplitudes exhibit one order of magnitude variability across the network, with a mean estimate of 51 tonnes high explosive equivalent. Detailed studies, such as this, are important for developing a successful monitoring regime for atmospheric or surface events, and for assessing the capability of the infrasound monitoring component of the Comprehensive Nuclear-Test-Ban Treaty verification system.

Hepatitis B virus clearance rate estimates

We read the study by Dandri et al.1 with much interest. The authors sought to estimate hepatitis B virus (HBV) half-life based on several baseline serum and intrahepatic parameters measured from 80 untreated patients with chronic HBV, including intrahepatic HBV-DNA–containing capsids and serum HBV DNA levels. A mathematical model2 that couples baseline viremia and intracellular virion productivity was applied by Dandri et al. and showed a strong inverse correlation between baseline viremia and HBV half-life. In addition, they estimated that virion clearance is very fast (median half-life [t1/2] 46 minutes [interquartile range, 4 minutes to 3.7 hours] in patients positive for hepatitis B e antigen (HBeAg) and 2.5 minutes [interquartile range, 24 seconds to 13 minutes] in HBeAg-negative patients). More striking is their finding (shown in their figure 2) that the HBV t1/2 varies more than 6 orders of magnitude among patients, with t1/2 being about 0.01 minutes when HBV DNA levels are 103 copies/mL or lower. For simian immunodeficiency virus, the rate of clearance in the presence and absence of high titer neutralizing antibodies differs by a factor of about four,3 leaving unexplained how a 6 order of magnitude increase in HBV clearance could occur in infected patients with low baseline viral loads. Further, when infection is initiated, HBV DNA levels should be low and clearance with a t1/2 of the order of seconds might preclude infection from taking hold. Estimated HBV half-life versus baseline HBV DNA. Free HBV half-life was estimated via mathematical modeling from the first phase HBV DNA decline during therapy in HBeAg-positive patients (circles or triangles) and HBeAg-negative patients (squares). Values were copied from Lewin et al.,7 Colombatto et al.,8 Mihm et al.,9 and Wolters et al.10 Patient 13 from Lewin et al.,7 with HBV DNA = 5.7 × 10 5 copies/mL and HBV half-life = 91 hours, is not shown but was included in the statistical analysis that shows no significant correlation (P = 0.5) between baseline HBV DNA and virion half-life (SPSS version 15; SPSS Inc., Chicago, IL). A number of previous studies have analyzed the rate of HBV virion clearance by using antiviral drugs to inhibit viral production and have come to decidedly different conclusions. Drug perturbation analysis showed no correlation between virion half-life and baseline viremia (Fig. 1), and estimated significantly slower virion clearance (median t1/2 ≈21 hours and ≈9 hours in treated HBeAg-positive and HBeAg-negative patients, respectively (Fig. 1) with less than one order of magnitude variation among patients; see also table 3 by Sypsa et al.4). The discrepancy between the findings of Dandri et al.1 and drug perturbation analysis (Fig. 1) is striking. To resolve the discrepancy, we suggest other approaches such as (1) infusion of viral particles5 and (2) plasma apheresis.6 For simian immunodeficiency virus the clearance rate was estimated from the disappearance of viral particles from plasma after intravenous bolus injection (or constant rate infusion) into rhesus macaques.5 This approach seems feasible to apply in chimpanzees. For both human immunodeficiency virus (type 1) and hepatitis C virus clearance rates were measured using plasma apheresis in which viral clearance was temporarily increased while viral production was unaffected.6 Interestingly, estimates of the hepatitis C virus half-life of 2-3 hours from plasma apheresis6 is similar to drug pertubation analysis estimates.11 This approach seems feasible to apply in patients with chronic HBV as well. This research was performed under the auspices of the U.S. Department of Energy under contract DE-AC52-06NA25396 and supported by National Institutes of Health (NIH) grants RR06555, AI28433, and AI065256 (to A.S.P.). H.D. is supported by the University of Illinois Gastrointestinal and Liver Disease (GILD) Association. Harel Dahari*, Scott J. Cotler*, Thomas J. Layden*, Alan S. Perelson , * Department of Medicine, University of Illinois at Chicago, Chicago, IL, Theoretical Biology and Biophysics, Los Alamos National Laboratory, Los Alamos, NM.

Parallel scalable adjoint-based adaptive solution of variable-viscosity Stokes flow problems

We present a framework for parallel adaptive solution of variable-viscosity Stokes flow problems. We focus on data structures, algorithms, and solvers that can scale to thousands of processor cores. The problem is discretized by octree-based finite elements with explicit enforcement of continuity constraints at hanging nodes. The parallel octree structure allows for fast neighbor-finding and facilitates local coarsening and refinement of the mesh. Mesh adaptivity is driven by a posteriori error indicators, including adjoint-based goal-oriented techniques. Dynamic load-balancing is achieved by dynamically partitioning a Morton-ordered space-filling curve. The Stokes system is solved iteratively using the minimum residual method (MINRES), preconditioned by a Schur-complement-based approximate inverse that employs algebraic multigrid V-cycle approximations of the inverses of the Poisson-like operators. We demonstrate the effectiveness of this framework on several testbed problems with up to 6 orders of magnitude variation in viscosity and up to 1.7 billion unknowns, on up to 4096 cores. The results indicate that the overhead due to all AMR components is less than 3% of the overall solve time, the solver exhibits very good algorithmic and parallel implementation scalability, the solver is insensitive to the magnitude of viscosity variation, and adjoint-based adaptivity results in over two orders of magnitude reduction in number of unknowns and up to an order of magnitude improvement in runtime relative to a uniform mesh, for the same level of error.

Analysis of worldwide regulatory guidance for surface soil contamination

Regulations are emerging worldwide to address surface soil contamination. Many of these use regulatory guidance values (RGVs) to specify concentrations above which action is required. However, because so many independent jurisdictions develop these values, the results are highly variable. Recent studies have demonstrated that the RGVs used by US states vary by several orders of magnitude. This manuscript presents results from an effort that identified 62 surface soil RGV datasets containing 3574 values from 31 other nations and compiled them into a database titled International Surface Soil Regulatory Guidance Values (IS2RGV). Analysis indicates that there are also orders of magnitude variability in the RGVs used worldwide, and that this variability has much in common with US state RGV variability. Results are presented for the 30 most frequently regulated organic, 20 most frequently regulated inorganic, and all regulated element contaminants. Trichloroethylene, cyanide, and mercury are used to illustrate how worldwide RGV variability compares with that of US states, and how data may be commingled to help identify emerging consensuses.

Some nonlinear challenges in biology

Driven by a deluge of data, biology is undergoing a transition to a more quantitative science. Making sense of the data, building new models, asking the right questions and designing smart experiments to answer them are becoming ever more relevant. In this endeavour, nonlinear approaches can play a fundamental role. The biochemical reactions that underlie life are very often nonlinear. The functional features exhibited by biological systems at all levels (from the activity of an enzyme to the organization of a colony of ants, via the development of an organism or a functional module like the one responsible for chemotaxis in bacteria) are dynamically robust. They are often unaffected by order of magnitude variations in the dynamical parameters, in the number or concentrations of actors (molecules, cells, organisms) or external inputs (food, temperature, pH, etc). This type of structural robustness is also a common feature of nonlinear systems, exemplified by the fundamental role played by dynamical fixed points and attractors and by the use of generic equations (logistic map, Fisher–Kolmogorov equation, the Stefan problem, etc.) in the study of a plethora of nonlinear phenomena. However, biological systems differ from these examples in two important ways: the intrinsic stochasticity arising from the often very small number of actors and the role played by evolution. On an evolutionary time scale, nothing in biology is frozen. The systems observed today have evolved from solutions adopted in the past and they will have to adapt in response to future conditions. The evolvability of biological system uniquely characterizes them and is central to biology. As the great biologist T Dobzhansky once wrote: ‘nothing in biology makes sense except in the light of evolution’.

Modeling the inactivation kinetics of bacillus spores by glutaraldehyde

Our goal was to develop a mathematical kinetic model to predict the sporicidal activity of glutaraldehyde, which is an active ingredient frequently used in commercial products employed for liquid disinfection and decontamination. We used our previously published data on spore inactivation by glutaraldehyde to develop a predictive model obtained by calculating multiple independent modifying functions. The model was then validated by comparing model predicted values to new experimental data. For model validation, quality-controlled spores of Bacillus athrophaeus (previously and generally known as Bacillus subtilis globigii) were exposed under conditions where several physicochemical variables were modified simultaneously, and the spore surviving fractions were measured by titration. The model predicted within one order of magnitude variations in sporicidal effectiveness due to changes in main parameters (glutaraldehyde concentration, temperature or time-duration of the treatment). Other parameters such pH, salinity and the effect of serum concentration were also addressed, albeit with less accuracy. The model should be useful to quantitatively estimate the effectiveness of glutaraldehyde-based disinfectants, decontaminants, and germicides under the described conditions, particularly when limited data are available or when spore virulence (like that of Bacillus anthracis) precludes extensive experimentation. A similar approach could predict the effectiveness of a variety of decontaminant and disinfecting agents.

Significance of transient luminous events to neutral chemistry: Experimental measurements

For many years it has been suggested that transient luminous events (TLE) occurring over thunderstorms may produce significant modifications to neutral atmospheric chemistry. Some have speculated that large ionisation increases from red sprites, one type of TLE, could result in enhancements of odd nitrogen. In this study we make use of nighttime NO2 observations by the GOMOS instrument to test whether TLE are producing significant NOx enhancements in the middle atmosphere on a regional scale. Comparing regional variations of NO2 with 2–3 order of magnitude variations in lightning activity, we show that there is no significant impact of red sprites, giant jets or blue jets upon NOx levels in the stratosphere and mesosphere (20–70 km), within the detection levels of the instrument. While individual TLE may cause a local variation in NOx, these do not appear to be significant on regional scales (or beyond).

Control of spin coherence in semiconductor double quantum dots

We propose a scheme to manipulate the spin coherence in vertically coupled GaAs double quantum dots. Up to 10 orders of magnitude variation of the spin relaxation and 2 orders of magnitude variation of the spin dephasing can be achieved by a small gate voltage vertically applied on the double dot. Specially, large variation of spin relaxation still exists at $0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In the calculation, the equation-of-motion approach is applied to obtain the electron decoherence time and all the relevant spin decoherence mechanisms, such as the spin-orbit coupling together with the electron-bulk-phonon scattering, the direct spin-phonon coupling due to the phonon-induced strain, the hyperfine interaction, and the second-order process of electron-phonon scattering combined with the hyperfine interaction, are included. The condition to obtain the large variations of spin coherence is also addressed.

CrossRef Listing of Deleted DOIs

Carefully sized and characterized chalcopyrite concentrates were produced from eleven different geographical localities, and were subsequently leached in both ferric chloride-hydrochloric acid and ferric sulfate-sulfuric acid media. When the leaching rates were corrected for the amount of CuFeS2 in the particular sample, similar leaching rates (±50 pet) were observed for all eleven chalcopyrites under all experimental conditions. Furthermore, all the relatively pure chalcopyrites leached according to the same reaction and yielded >95 pet elemental sulfur as a sulfidic reaction product. In light of the current experimental observations, various reasons are offered for the order of magnitude variations in the chalcopyrite leaching rates often reported in the literature.

Ideal vitrification, barrier hopping, and jamming in fluids of modestly anisotropic hard objects

Our recent theory for the glassy dynamics of fluids and suspensions of hard nonspherical objects is applied to several modestly anisotropic shapes. The role of bond length and aspect ratio is studied for diatomics, triatomics, and spherocylinders. As spherical symmetry is broken the ideal kinetic glass transition volume fraction of all objects increases linearly with aspect ratio with the same slope, in surprising agreement with the jamming phase diagram of hard granular ellipsoids. The ideal glass boundary of all shapes is a nonmonotonic function of aspect ratio which is also in qualitative accord with the jamming behavior of spherocylinders and ellipsoids. The maximum glass volume fraction shifts to higher values, and larger aspect ratios, as the object becomes smoother. Suggestions for why the nonequilibrium jamming and kinetic ideal glass formation (dynamical crossover) boundaries are similar are advanced. Beyond the ideal glass volume fraction the nonequilibrium free energy acquires a localization well and entropic barrier. Although its form is highly nonuniversal, if different shapes are compared at constant barrier height then a good collapse is found. Collapse of the volume fraction dependence of the barrier height for different shapes is also predicted for modest shape anisotropy, but increasingly fails as the aspect ratio exceeds 2. For a given volume fraction the mean barrier hopping times are nonmonotonic functions of aspect ratio. The functional form of this dependence, and order of magnitude variation with aspect ratio, is distinct for each object.

Predicting PAH Bioaccumulation and Toxicity in Earthworms Exposed to Manufactured Gas Plant Soils with Solid-Phase Microextraction

Soils from former manufactured gas plant (MGP) sites are often heavily contaminated with polycyclic aromatic hydrocarbons (PAHs). Current risk assessment methods that rely on total PAH concentrations likely overstate adverse effects of such soils since bioavailability is ignored. In this study, solid-phase microextraction (SPME) was applied to estimate bioavailable PAH concentrations and toxicity in earthworms exposed to 15 MGP soils. In addition, PAH sorption to all soils (K0o values) was determined. The results showed a several orders of magnitude variation in Koc values, demonstrating that generic organic carbon-normalized sorption coefficients will typically be overconservative at MGP sites. SPME-predicted bioaccumulation generally was within a factor of 10 of measured bioaccumulation (in earthworm bioassays), in contrast to current risk assessment model estimates that overpredicted bioaccumulation 10-10 000 times. Furthermore, on the basis of estimated total body residues of narcotic PAHs, SPME correctly predicted worm mortality observed during bioassays in the majority of cases. For MGP sites where current risk assessment procedures indicate concerns, SPME thus provides a useful tool for performing a refined, site-specific assessment.

Relationship between dispersion metric and properties of PMMA/SWNT nanocomposites

Particle spatial dispersion is a crucial characteristic of polymer composite materials and this property is recognized as especially important in nanocomposite materials due to the general tendency of nanoparticles to aggregate under processing conditions. We introduce dispersion metrics along with a specified dispersion scale over which material homogeneity is measured and consider how the dispersion metrics correlate quantitatively with the variation of basic nanocomposite properties. We then address the general problem of quantifying nanoparticle spatial dispersion in model nanocomposites of single-walled carbon nanotubes (SWNTs) dispersed in poly(methyl methacrylate) (PMMA) at a fixed SWNT concentration of 0.5% using a ‘coagulation’ fabrication method. Two methods are utilized to measure dispersion, UV–vis spectroscopy and optical confocal microscopy. Quantitative spatial dispersion levels were obtained through image analysis to obtain a ‘relative dispersion index’ (RDI) representing the uniformity of the dispersion of SWNTs in the samples and through absorbance. We find that the storage modulus, electrical conductivity, and flammability property of the nanocomposites correlate well with the RDI. For the nanocomposites containing the same amount of SWNTs, the relationships between the quantified dispersion levels and physical properties show about four orders of magnitude variation in storage modulus, almost eight orders of magnitude variation in electric conductivity, and about 70% reduction in peak mass loss rate at the highest dispersion level used in this study. The observation of such a profound effect of SWNT dispersion indicates the need for objective dispersion metrics for correlating and understanding how the properties of nanocomposites are determined by the concentration, shape and size of the nanotubes.

Variability in invasion risk for ballast water exchange on the Scotian Shelf of eastern Canada

A semi-quantitative risk assessment model for dispersion of ballast water organisms in shelf seas is applied to the Scotian Shelf region of eastern Canada. The ballast water exchange process is simulated as the dispersion of tracer released into the surface layer of an ocean circulation model of the region. Circulation model variability is driven by wind stress from a cyclical year of forcing representing climatological storminess. Dispersion metrics related to invasion risk are developed and incorporated into a risk equation that computes the relative overall risk of invasion for ballast water exchange segments along vessel tracks crossing the shelf. Three hundred and sixty dispersion simulations are done for each segment of each of six tracks. Because the flow fields represent climatological variability in shelf circulation, the application of the risk assessment model captures the expected variability in invasion risk. Model results indicate that more than an order of magnitude variation in risk can exist along a given vessel track, and that tracks with offshelf segments provide a lower risk option compared to onshelf tracks. The model provides quantitative guidance to regulators regarding what is an acceptable trip diversion and can aid in numerous other management decisions.

Phylogenetic diversity in cadmium : phosphorus ratio regulation by marine phytoplankton

We examined the effect of irradiance and growth rate on cadmium : phosphorus ratio in five species of phytoplankton representing four different phylogenetic groups to determine the relative importance of growth rate, irradiance, and taxonomic differences on Cd : P ratios. Irradiance and growth rate are responsible for >2 orders of magnitude variation in the Cd : P of phytoplankton. Diatoms exhibit an increase; cyanobacteria, a decrease; and prasinophyte and dinoflagellate species, no functional response in Cd : P with increasing growth rate because of changes in irradiance. These results are consistent with a metabolic demand for Cd in diatoms and a metabolic sensitivity to Cd by cyanobacteria.

Permeability upscaling of fault zones in the Aztec Sandstone, Valley of Fire State Park, Nevada, with a focus on slip surfaces and slip bands

The effect of open and filled slip surfaces on the upscaled permeability of two fault zones with 6 and 14 m strike-slip in an eolian Aztec Sandstone, Nevada, USA is evaluated. Each fault zone is composed of several fault components: a fault core, bounded by filled through-going slip surfaces referred to as slip bands, and a surrounding damage zone that contains joints and deformation bands. Slip band geometry, composition, and petrophysical properties are characterized. Measurements and modeling show that slip band permeabilities can vary over 12 orders of magnitude depending on the degree of fill within the slip bands. The slip bands along with other fault zone components are represented in finite volume numerical calculations and the impact of various slip-band representations on upscaled fault zone permeability is tested. The results show 2 orders of magnitude variation in upscaled fault zone permeability in the fault-normal direction and a factor of 2 variation in the fault-parallel direction. The numerical results presented here are compared to the earlier numerical results in which structured Cartesian grids were used for the numerical simulations, and are in qualitative agreement with earlier calculations but use about a factor of 250–400 fewer numerical cells.

129I Variability in precipitation over Europe

We present results and an overview of studies on 129I in precipitation over Europe during the last decade, covering latitudes 37–70°N. The data show about three orders of magnitude variability in concentrations but without specific correlation to latitude when all Europe is considered. The total amount of 129I provided annually by precipitation over Europe composes only a tiny portion of the annual marine discharge but a significant portion of the gaseous discharges from the nuclear reprocessing facilities. Contribution of gaseous releases seems to be significant, although difficult to estimate. As shown by this study, a unified sampling procedure and systematic measurements of 129I in precipitation throughout Europe are needed to achieve a coherent picture about the loading and sources of 129I in precipitation and the atmosphere.

Nev] Imaging of N49 in the Large Magellanic Cloud

We present sub-arcsecond imaging in [Ne V] of N49, the brightest optical SNR in the LMC. Between the cool optical and hot X-ray regimes, [Ne V] emission indicates intermediate temperatures for collisionally excited plasmas (2--6 x 10E5 K), for which imaging has been extremely limited. We compare the flux in these images to the O VI measured spectroscopically by FUSE in individual apertures and find dereddened line ratios that are reasonably consistent with our predictions for intermediate velocity shocks. The overall luminosity in [Ne V] for the entire remnant is 1.2E36 erg/s, which, given the measured line ratios, implies an overall O VI luminosity of 1.5E38 erg/s. These large radiative losses indicate that this material must have been shocked recently relative to the total lifetime of the remnant. We also explore the complex spatial structure. We find [Ne V] tracing the [O III] emission more closely than it does H-alpha, measure significant shifts (~0.1 pc) between the peaks of different emission lines, and find two orders of magnitude variations in the flux ratios for different filaments across the remnant. These properties as well as the general filamentary character of the optical emission suggest thermally unstable intermediate velocity shocks.

Magnetohydrodynamic Turbulent Mixing Layers: Equilibrium Cooling Models

We present models of turbulent mixing at the boundaries between hot (T ∼ 10 6 7 K) and warm material (T ∼ 10 4 K) in the interstellar medium, using a three-dimensional magnetohydrodynamical code, with radiative cooling. The source of turbulence in our simulations is a Kelvin-Helmholtz instability, produced by shear between the two media. We found, that because the growth rate of the large scale modes in the instability is rather slow, it takes a significant amount of time (∼ 1 Myr) for turbulence to produce effective mixing. We find that the total column densities of the highly ionized species (C IV, N V, and O VI) per interface (assuming ionization equilibrium) are similar to previous steady-state non-equilibrium ionization models, but grow slowly from logN ∼ 10 11 to a few ×10 12 cm 2 as the interface evolves. However, the column density ratios can differ significantly from previous estimates, with an order of magnitude variation in N(C IV)/N(O VI) as the mixing develops. Subject headings: ISM: general — ISM: structure — magnetohydrodynamics: MHD — turbulence

Can Basin‐Scale Recharge Be Estimated Reasonably with Water‐Balance Models?

We examine in‐place recharge as an example of the complex, basin‐scale hydrologic processes that are being represented with simplified numerical models. The rate and distribution of recharge depend on local meteorological conditions and hydrogeologic properties. The pattern of recharge is defined predominantly by the distribution of net precipitation (precipitation less evapotranspiration), but different pedotransfer functions (PTFs) predict different fractions of precipitation that become in‐place recharge at a given location. At any single location, these differences can often be explained on the basis of the PTF characteristics, but because of the complex averaging that occurs across a basin, the combined effects of meteorological variation and soil textural variation on the basin‐wide recharge rates cannot be predicted on the basis of the characteristics of different PTFs. In fact, we show that the same basin‐scale numerical model, using identical inputs and modeling options, can produce almost an order of magnitude variation in predicted basin total recharge depending on the choice of PTF. This suggests that sensitivity analyses should be performed on the choice of constitutive relationship (e.g., PTF) when assessing the predictive capability of basin‐scale hydrologic models.