Background Solution Research Articles

Geoelectrical Signatures of Reactive Mixing: A Theoretical Assessment

AbstractCharacterizing the effects of subsurface fluid mixing on biogeochemical reactions is a key step toward monitoring and understanding a range of processes and applications in which fluids of different chemical compositions mix, such as aquifer remediation, CO2 sequestration, or groundwater‐surface water interactions. Yet the development of noninvasive methods to monitor mixing processes remains an outstanding challenge. Mixing processes are controlled by concentration gradients that develop at scales below the spatial resolution of hydrogeophysical imaging techniques. To overcome this difficulty, we propose to focus on the geoelectrical response of mixing‐driven chemical reactions, for which the products are electrically more conductive than the background solution. For such reactions, we investigate the impact of reactive mixing on the resulting effective electrical conductivity. The transport equations are solved using the Lamellar Mixing Theory for a range of velocity gradients representative of the stretching rates experienced by mixing fronts in heterogeneous porous media. Focusing on simple shear flows, we demonstrate that such reactions may result in substantial changes (several orders of magnitude) in the effective conductivity over time, thus providing geoelectrical signatures of reactive mixing dynamics. The temporal evolution of the effective conductivity depends on the relative orientations of the applied electrical potential gradient, mean flow, and velocity gradient, yielding different sensitivities to dispersion processes, stretching rates, and reaction kinetics. These results suggest that the use of chemical reactions with electrically conductive products could help to overcome present limitations of time‐lapse geophysical imaging in the monitoring of the spatiotemporal dynamics of subsurface reactive mixing processes.

Causality violations in Lovelock theories

Higher-derivative gravity theories, such as Lovelock theories, generalize Einstein's general relativity (GR). Modifications to GR are expected when curvatures are near Planckian and appear in string theory or supergravity. But can such theories describe gravity on length scales much larger than the Planck cutoff length scale? Here we find causality constraints on Lovelock theories that arise from the requirement that the equations of motion (EOM) of perturbations be hyperbolic. We find a general expression for the "effective metric" in field space when Lovelock theories are perturbed around some symmetric background solution. In particular, we calculate explicitly the effective metric for a general Lovelock theory perturbed around cosmological Friedman-Robertson-Walker backgrounds and for some specific cases when perturbed around Schwarzschild-like solutions. For the EOM to be hyperbolic, the effective metric needs to be Lorentzian. We find that, unlike for GR, the effective metric is generically not Lorentzian when the Lovelock modifications are significant. So, we conclude that Lovelock theories can only be considered as perturbative extensions of GR and not as truly modified theories of gravity. We compare our results to those in the literature and find that they agree with and reproduce the results of previous studies.

Effect of composition and microstructure of humic acid on 3,3',4,4'-tetrachlorobiphenyl sorption.

The fate and transport of polychlorinated biphenyls (PCBs), a class of persistent organic compounds, in soils was markedly affected by their sorption/desorption on soil organic matters (SOM) due to high hydrophobicity of PCBs. Humic acid (HA), an important fraction of SOM, has no steady composition and microstructure from different origins, resulting in their diverse sorption capacity. Therefore, the effect of composition and microstructure of HA on sorption of 3,3',4,4'-tetrachlorobiphenyl (PCB77) was investigated in this study. The primary sorption mechanism of PCB77 on HAs was also demonstrated by using Fourier transform infrared (FTIR) and solid-state carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy analysis. Elemental content analysis of three HAs showed that the content of unsaturated C (the total of aromatic, carboxylic, and carbonyl carbon) followed an order of YHA>SHA>AHA. Furthermore, YHA and SHA had remarkably rough and complicated particle surfaces but AHA had relatively smooth surface and the well-proportioned and interspersed particle sizes. The results of the sorption experiment showed that the sorption capacity of PCB77 on HAs followed a similar order of YHA>SHA>AHA, indicating the content of unsaturated C of HAs controlled the sorption of PCB77 on HAs. Sorption of PCB77 on either AHA or SHA did not change with increasing ionic strength of background solution, implying that there was no H-bond or electrostatic interaction between PCB77 and HAs. The result of FTIR and 13C-NMR spectra showed the primarily possible mechanism was π-π conjugative interaction and hydrophobic binding between PCB77 and HAs.

A future-proof architecture for telemedicine using loose-coupled modules and HL7 FHIR

Background and objectivesMost telemedicine solutions are proprietary and disease specific which cause a heterogeneous and silo-oriented system landscape with limited interoperability. Solving the interoperability problem would require a strong focus on data integration and standardization in telemedicine infrastructures. Our objective was to suggest a future-proof architecture, that consisted of small loose-coupled modules to allow flexible integration with new and existing services, and the use of international standards to allow high re-usability of modules, and interoperability in the health IT landscape. MethodsWe identified core features of our future-proof architecture as the following (1) To provide extended functionality the system should be designed as a core with modules. Database handling and implementation of security protocols are modules, to improve flexibility compared to other frameworks. (2) To ensure loosely coupled modules the system should implement an inversion of control mechanism. (3) A focus on ease of implementation requires the system should use HL7 FHIR (Fast Interoperable Health Resources) as the primary standard because it is based on web-technologies. ResultsWe evaluated the feasibility of our architecture by developing an open source implementation of the system called ORDS. ORDS is written in TypeScript, and makes use of the Express Framework and HL7 FHIR DSTU2. The code is distributed on GitHub. All modules have been tested unit wise, but end-to-end testing awaits our first clinical example implementations. ConclusionsOur study showed that highly adaptable and yet interoperable core frameworks for telemedicine can be designed and implemented. Future work includes implementation of a clinical use case and evaluation.

Transport and retention of surfactant- and polymer-stabilized engineered silver nanoparticles in silicate-dominated aquifer material.

Packed column experiments were conducted to investigate the transport and blocking behavior of surfactant- and polymer-stabilized engineered silver nanoparticles (Ag-ENPs) in saturated natural aquifer media with varying content of material < 0.063 mm in diameter (silt and clay fraction), background solution chemistry, and flow velocity. Breakthrough curves for Ag-ENPs exhibited blocking behavior that frequently produced a delay in arrival time in comparison to a conservative tracer that was dependent on the physicochemical conditions, and then a rapid increase in the effluent concentration of Ag-ENPs. This breakthrough behavior was accurately described using one or two irreversible retention sites that accounted for Langmuirian blocking on one site. Simulated values for the total retention rate coefficient and the maximum solid phase concentration of Ag-ENPs increased with increasing solution ionic strength, cation valence, clay and silt content, decreasing flow velocity, and for polymer-instead of surfactant-stabilized Ag-ENPs. Increased Ag-ENP retention with ionic strength occurred because of compression of the double layer and lower magnitudes in the zeta potential, whereas lower velocities increased the residence time and decreased the hydrodynamics forces. Enhanced Ag-ENP interactions with cation valence and clay were attributed to the creation of cation bridging in the presence of Ca2+. The delay in breakthrough was always more pronounced for polymer-than surfactant-stabilized Ag-ENPs, because of differences in the properties of the stabilizing agents and the magnitude of their zeta-potential was lower. Our results clearly indicate that the long-term transport behavior of Ag-ENPs in natural, silicate dominated aquifer material will be strongly dependent on blocking behavior that changes with the physicochemical conditions and enhanced Ag-ENP transport may occur when retention sites are filled.

Time-dependent mass of cosmological perturbations in the hybrid and dressed metric approaches to loop quantum cosmology

Loop quantum cosmology has recently been applied in order to extend the analysis of primordial perturbations to the Planck era and discuss the possible effects of quantum geometry on the cosmic microwave background. Two approaches to loop quantum cosmology with admissible ultraviolet behavior leading to predictions that are compatible with observations are the so-called hybrid and dressed metric approaches. In spite of their similarities and relations, we show in this work that the effective equations that they provide for the evolution of the tensor and scalar perturbations are somewhat different. When backreaction is neglected, the discrepancy appears only in the time- dependent mass term of the corresponding field equations. We explain the origin of this difference, arising from the distinct quantization procedures. Besides, given the privileged role that the big bounce plays in loop quantum cosmology, e.g. as a natural instant of time to set initial conditions for the perturbations, we also analyze the positivity of the time-dependent mass when this bounce occurs. We prove that the mass of the tensor perturbations is positive in the hybrid approach when the kinetic contribution to the energy density of the inflaton dominates over its potential, as well as for a considerably large sector of backgrounds around that situation, while this mass is always nonpositive in the dressed metric approach. Similar results are demonstrated for the scalar perturbations in a sector of background solutions that includes the kinetically dominated ones; namely, the mass then is positive for the hybrid approach, whereas it typically becomes negative in the dressed metric case. More precisely, this last statement is strictly valid when the potential is quadratic for values of the inflaton mass that are phenomenologically favored.

The exact rogue wave recurrence in the NLS periodic setting via matched asymptotic expansions, for 1 and 2 unstable modes

The focusing Nonlinear Schrödinger (NLS) equation is the simplest universal model describing the modulation instability (MI) of quasi monochromatic waves in weakly nonlinear media, the main physical mechanism for the generation of rogue (anomalous) waves (RWs) in Nature. In this paper we investigate the x-periodic Cauchy problem for NLS for a generic periodic initial perturbation of the unstable constant background solution, in the case of N=1,2 unstable modes. We use matched asymptotic expansion techniques to show that the solution of this problem describes an exact deterministic alternate recurrence of linear and nonlinear stages of MI, and that the nonlinear RW stages are described by the N-breather solution of Akhmediev type, whose parameters, different at each RW appearance, are always given in terms of the initial data through elementary functions. This paper is motivated by a preceding work of the authors in which a different approach, the finite gap method, was used to investigate periodic Cauchy problems giving rise to RW recurrence.

The supersonic flow past a wedge with large curved boundary

In this paper, we construct a piecewise smooth solution for a 2-D supersonic potential flow past a curved wedge, whose boundary is assumed to have large variation. In fact, we originally provide a background solution, which is constructed by assuming the coming flow has limit speed. Its shock coincides with the curved wedge and the flow behind the shock is defined only along the wedge. Then our problem can be treated as a perturbation of this background solution and the solution is obtained by showing specific estimates.

Contravariant geometry and emergent gravity from noncommutative gauge theories

We investigate a relation of the contravariant geometry to the emergent gravity from noncommutative gauge theories. We give a refined formulation of the contravariant gravity, and provide solutions to the contravariant Einstein equation. We linearize the equation around background solutions, including curved ones. A noncommutative gauge theory on the Moyal plane can be rewritten as an ordinary gauge theory on a curved background via the Seiberg–Witten map; this is known as emergent gravity. We show that this phenomenon also occurs for a gauge theory on a noncommutative homogeneous Kähler background. We argue that the resulting geometry can be naturally described by the contravariant geometry under an identification of the fluctuation of the Poisson tensor with the field strength obtained by the Seiberg–Witten map. These results indicate that the contravariant gravity is a suitable framework for noncommutative spacetime physics.

Higher derivatives in Type II and M-theory on Calabi-Yau threefolds

The four- and five-dimensional effective actions of Calabi-Yau threefold compactifications are derived with a focus on terms involving up to four space-time derivatives. The starting points for these reductions are the ten- and eleven-dimensional supergravity actions supplemented with the known eight-derivative corrections that have been inferred from Type II string amplitudes. The corrected background solutions are determined and the fluctuations of the Kähler structure of the compact space and the form-field back-ground are discussed. It is concluded that the two-derivative effective actions for these fluctuations only takes the expected supergravity form if certain additional ten- and eleven-dimensional higher-derivative terms for the form-fields are included. The main results on the four-derivative terms include a detailed treatment of higher-derivative gravity coupled to Kähler structure deformations. This is supplemented by a derivation of the vector sector in reductions to five dimensions. While the general result is only given as an expansion in the fluctuations, a complete treatment of the one-Kähler modulus case is presented for both Type II theories and M-theory.

Linearization instability for generic gravity in AdS spacetime

In general relativity, perturbation theory about a background solution fails if the background spacetime has a Killing symmetry and a compact spacelike Cauchy surface. This failure, dubbed as {\it linearization instability}, shows itself as non-integrability of the perturbative infinitesimal deformation to a finite deformation of the background. Namely, the linearized field equations have spurious solutions which cannot be obtained from the linearization of exact solutions. In practice, one can show the failure of the linear perturbation theory by showing that a certain quadratic (integral) constraint on the linearized solutions is not satisfied. For non-compact Cauchy surfaces, the situation is different and for example, Minkowski space having a non-compact Cauchy surface, is linearization stable. Here we study, the linearization instability in generic metric theories of gravity where Einstein's theory is modified with additional curvature terms. We show that, unlike the case of general relativity, for modified theories even in the non-compact Cauchy surface cases, there are some theories which show linearization instability about their anti-de Sitter backgrounds. Recent $D$ dimensional critical and three dimensional chiral gravity theories are two such examples. This observation sheds light on the paradoxical behavior of vanishing conserved charges (mass, angular momenta) for non-vacuum solutions, such as black holes, in these theories.

Leber's Hereditary Optic Neuropathy: Novel Views and Persisting Challenges.

Leber's hereditary optic neuropathy is an inherited form of optic neuropathy, genetically and pathophysiologically based on mitochondrial insufficiency causing bilateral loss of central vision mostly amongst young adults. Despite being one of the most common mitochondrial diseases, the explanation for its pathophysiological background and effective clinical solutions remain elusive. Widening the scope in the search for pathological findings beyond the optic system has yielded several non-ophthalmologic findings, which might imply that Leber's hereditary optic neuropathy is in fact a multi-systemic disease. The aim of this review is to provide an overview of literature regarding the epidemiology, etiology, pathogenesis, clinical features, diagnostics and possible treatment options and drug targets, as well as presenting challenges related to the disease and proposing a diagnostic algorithm based on current clinical experience.

Influence of dissolved organic matter and activated carbon pore characteristics on organic micropollutant desorption

By simulating decreasing inflow concentrations, the extent of desorption of organic micropollutants (OMP) from three activated carbons (AC) was examined in laboratory batch tests. The tested AC showed strong differences in pore size distribution and could therefore be characterized as typical micro-, meso- and macroporous AC, respectively. Adsorption and desorption conditions were varied by using drinking water (containing dissolved organic matter (DOM)) and DOM-free pure water as background solutions to examine the influence of DOM on OMP desorption for the different AC. Under ideal conditions (adsorption and desorption in pure water) adsorption of the tested OMP was found to be highly up to completely reversible for all tested AC. Under real conditions (adsorption and desorption in drinking water) additional DOM adsorption affects desorption in different ways depending on the AC pore structure. For the micro- and mesoporous AC, an increased irreversibility of OMP adsorption was found, which shows that DOM adsorption prevents OMP desorption. This could be referred to pore blockage effects that occur during the parallel adsorption of DOM and OMP. For the macroporous AC, DOM adsorption led to an enhanced OMP desorption which could be attributed to displacement processes. These results show that smaller pores tend to be blocked by DOM which hinders OMP from desorption. The overall larger pores of the macroporous AC do not get blocked which could allow (i) OMP to desorb and (ii) DOM to enter and displace OMP.

Advanced-step Multistage Nonlinear Model Predictive Control

We present a real-time implementable robust Nonlinear Model Predictive Control (NMPC) framework that simultaneously addresses model uncertainty and unmeasured disturbances based on a multistage scenario tree to describe the evolution of uncertainties. The multistage scenario tree computes a control action that hedges against all possible uncertainty realizations and optimizes expected performance. However, the scenario tree structure inevitably increases the optimization problem size, as robust horizons become longer. This presents a challenge to solve large-scale problems in real-time. We propose a parallelizable advanced-step multistage NMPC (as-msNMPC) that precomputes a set of solutions in background so that the online computation effort is negligible. We apply an as-msNMPC framework to a CSTR example to show the controller’s robustness and improved online performance over competing robust NMPC methods.

Colloidal Cerium Oxide Nanoparticles: Preparation and Corrosion Inhibition Performance on AA5005 Aluminum Alloy

This study investigated the potential of ceria nanoparticles to reduce the corrosion rates of AA5005 immersed in chloride-rich media at neutral pH. The colloidal ceria nanoparticle dispersion was prepared via precipitation of cerium (III) ions in presence of citric acid. Transmission electron microscopy and dynamic light scattering confirmed the fine structure of ceria; crystallites lower than 10 nm with a hydrodynamic diameter average size of about 30 nm were obtained. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements were conducted on bare AA5005 panels exposed to 0.1 M NaCl with different quantities of ceria nanoparticles. Polarization curves revealed a significant reduction of cathodic current densities for AA5005 immersed in ceria containing electrolytes when compared to the background solution, i.e. a shift toward lower current densities of about one order of magnitude for those containing 5.0 and 7.5% of ceria. Impedance spectra with higher moduli at low frequencies were obtained for AA5005 immersed in ceria containing electrolytes. In general, while in contact to the ceria-containing electrolytes the rates of localized corrosion attacks at the surface of AA5005 were found to decrease and, the outputs from the electrochemical tests suggested an inhibition effect of the colloidal ceria nanoparticles prepared in this work.

Massive gravity and the suppression of anisotropies and gravitational waves in a matter-dominated contracting universe

We consider a modified gravity model with a massive graviton, but which nevertheless only propagates two gravitational degrees of freedom and which is free of ghosts. We show that non-singular bouncing cosmological background solutions can be generated. In addition, the mass term for the graviton prevents anisotropies from blowing up in the contracting phase and also suppresses the spectrum of gravitational waves compared to that of the scalar cosmological perturbations. This addresses two of the main problems of the matter bounce scenario.

A conductometric creatinine biosensor prepared through contact printing of polyvinyl alcohol/polyethyleneimine based enzymatic membrane

A conductometric creatinine biosensor was prepared through creatinine deaminase entrapped into a polyvinyl alcohol/polyethyleneimine/gold nanoparticles composite film, previously deposited on the surface of a PDMS stamp and then, after glutaraldehyde coupling, transferred on interdigitated microelectrodes by contact printing method. The detection of creatinine in a sucrose background solution, revealed a wide linear calibration plot (10–600μM creatinine concentration range), with a limit of detection of 2μM (S/N=3), a good repeatability. The resulting creatinine biosensor exhibits a drastic increase of detection range compared to that of the biosensor prepared by simple dropping: 10–300μM creatinine concentration range. The developed biosensor was validated by determining creatinine in spiked artificial blood serum.

Intestinal Farnesoid X Receptor Activation by Pharmacologic Inhibition of the Organic Solute Transporter α-β.

Background & AimsThe organic solute transporter α-β (OSTα-OSTβ) mainly facilitates transport of bile acids across the basolateral membrane of ileal enterocytes. Therefore, inhibition of OSTα-OSTβ might have similar beneficial metabolic effects as intestine-specific agonists of the major nuclear receptor for bile acids, the farnesoid X receptor (FXR). However, no OSTα-OSTβ inhibitors have yet been identified.MethodsHere, we developed a screen to identify specific inhibitors of OSTα-OSTβ using a genetically encoded Förster Resonance Energy Transfer (FRET)–bile acid sensor that enables rapid visualization of bile acid efflux in living cells.ResultsAs proof of concept, we screened 1280 Food and Drug Administration–approved drugs of the Prestwick chemical library. Clofazimine was the most specific hit for OSTα-OSTβ and reduced transcellular transport of taurocholate across Madin–Darby canine kidney epithelial cell monolayers expressing apical sodium bile acid transporter and OSTα-OSTβ in a dose-dependent manner. Moreover, pharmacologic inhibition of OSTα-OSTβ also moderately increased intracellular taurocholate levels and increased activation of intestinal FXR target genes. Oral administration of clofazimine in mice (transiently) increased intestinal FXR target gene expression, confirming OSTα-OSTβ inhibition in vivo.ConclusionsThis study identifies clofazimine as an inhibitor of OSTα-OSTβ in vitro and in vivo, validates OSTα-OSTβ as a drug target to enhance intestinal bile acid signaling, and confirmed the applicability of the Förster Resonance Energy Transfer–bile acid sensor to screen for inhibitors of bile acid efflux pathways.

Solubility Model for Ferrous Iron Hydroxide, Hibbingite, Siderite, and Chukanovite in High Saline Solutions of Sodium Chloride, Sodium Sulfate, and Sodium Carbonate

A solubility model is presented for ferrous iron hydroxide (Fe(OH)2(s)), hibbingite (Fe2Cl(OH)3(s)), siderite (FeCO3(s)), and chukanovite (Fe2CO3(OH)2(s)). The Pitzer activity coefficient equation was utilized in developing the model to account for the excess free energies of aqueous species in the background solutions of high ionic strength. Solubility limiting minerals were analyzed before and after experiments using X-ray diffraction. Formation of Fe(OH)2(s) was observed in the experiments that were initiated with Fe2Cl(OH)3(s) in Na2SO4 solution. Coexistence of siderite and chukanovite was observed in the experiments in Na2CO3 + NaCl solutions. Two equilibrium constants that had been reported by us for the dissolution of Fe(OH)2(s) and Fe2Cl(OH)3(s) (Nemer et al.) were rederived in this paper, using newer thermodynamic data selected from the literature to maintain internal consistency of the series of our data analyses in preparation, including this paper. Three additional equilibrium constants for th...

Existence and asymptotic behavior of smooth solutions to bipolar hydrodynamic model

ABSTRACTWe are interested in the existence and asymptotic behavior of smooth solutions to the hydrodynamic model of semiconductors with non-zero doping profile. Within the insulating boundary conditions, recently, a steady state for any doping profile with large amplitude was obtained by using the calculus of variations. In this paper, the obtained steady state is regarded as the background solution. Utilizing energy methods and entropy analysis, we prove the existence of smooth solutions to the hydrodynamic model. As a by-product, we show the smooth solution convergent to the background solution with exponential decay rate.