Interest For Many Applications Research Articles

Nanoporous-Based Sensors for Impedance Spectroscopy-Based Detection of Gaseous Pollutants

The advanced in situ detection of gaseous pollutants (e.g. NOx and SOx) is of great interest in many applications, such as the automotive and coal industries. Here, we leverage the previous successful development of impedance spectroscopy-based sensors for the detection of gaseous I2 to develop a novel sensor for the detection of these gaseous pollutants. During initial development of an I2 sensor, a metal-organic framework (MOF ZIF-8) material was utilized as an adsorbent layer deposited onto Pt interdigitated electrodes. The MOF was demonstrated to selectively adsorb I2, irreversibly, from a complex gas stream with a (>105x) change in measured impedance across the electrodes1. Further studies aimed at developing a robust sensor examined other materials, including zeolites2 and additional MOFs. It was demonstrated that utilizing MFM-300(X) (X= Al, Fe, In or Sc metal center) active materials enabled a reversible electrical response via gas adsorption/desorption3. The current work is focused on exploring these same nanoporous phases (MOFs, zeolites, etc.) for the real-time detection of NOx and SOx. The down-selection of candidate materials from bulk synthesis and gas selectivity testing will be discussed. Methods for deposition of these materials onto the Pt interdigitated electrodes and initial sensor performance during controlled gas exposures will be presented. Acknowledgements Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. References 1) Small, L.J and Nenoff, T.M., ACS Appl. Mater. Interfaces, 2017, 9 (51), 44649-44655.2) Small, L.J.; Krumhansl, J.L.; Rademacher, D.X.; Nenoff, T.M. Micro. Meso. Mater., 2019, 280, 82-87.3) Small, L.J.; Hill, R. C.; Krumhansl, J. L.; Schindelholz, M. E.; Chen, Z.; Chapman, K.W.; Zhang, X.; Yang, S.; Schroder, M.; Nenoff, T.M., ACS Applied Materials and Interfaces, 2019, 11(31), 27982-27988.

Nanomaterial Synthesis Insights from Machine Learning of Scientific Articles by Extracting, Structuring, and Visualizing Knowledge.

Nanomaterials of varying compositions and morphologies are of interest for many applications from catalysis to optics, but the synthesis of nanomaterials and their scale-up are most often time-consuming and Edisonian processes. Information gleaned from the scientific literature can help inform and accelerate nanomaterials development, but again, searching the literature and digesting the information are time-consuming manual processes for researchers. To help address these challenges, we developed scientific article-processing tools that extract and structure information from the text and figures of nanomaterials articles, thereby enabling the creation of a personalized knowledgebase for nanomaterials synthesis that can be mined to help inform further nanomaterials development. Starting with a corpus of ∼35k nanomaterials-related articles, we developed models to classify articles according to the nanomaterial composition and morphology, extract synthesis protocols from within the articles' text, and extract, normalize, and categorize chemical terms within synthesis protocols. We demonstrate the efficiency of the proposed pipeline on an expert-labeled set of nanomaterials synthesis articles, achieving 100% accuracy on composition prediction, 95% accuracy on morphology prediction, 0.99 AUC on protocol identification, and up to a 0.87 F1-score on chemical entity recognition. In addition to processing articles' text, microscopy images of nanomaterials within the articles are also automatically identified and analyzed to determine the nanomaterials' morphologies and size distributions. To enable users to easily explore the database, we developed a complementary browser-based visualization tool that provides flexibility in comparing across subsets of articles of interest. We use these tools and information to identify trends in nanomaterials synthesis, such as the correlation of certain reagents with various nanomaterial morphologies, which is useful in guiding hypotheses and reducing the potential parameter space during experimental design.

Dynamic Stability of Bi-Directional Functionally Graded Porous Cylindrical Shells Embedded in an Elastic Foundation

This paper investigates the dynamic buckling of bi-directional (BD) functionally graded (FG) porous cylindrical shells for various boundary conditions, where the FG material is modeled by means of power law functions with even and uneven porosity distributions of ceramic and metal phases. The third-order shear deformation theory (TSDT) is adopted to derive the governing equations of the problem via the Hamilton’s principle. The generalized differential quadrature (GDQ) method is applied together with the Bolotin scheme as numerical strategy to solve the problem, and to draw the dynamic instability region (DIR) of the structure. A large parametric study examines the effect of different boundary conditions at the extremities of the cylindrical shell, as well as the sensitivity of the dynamic stability to different thickness-to-radius ratios, length-to-radius ratios, transverse and longitudinal power indexes, porosity volume fractions, and elastic foundation constants. Based on results, the dynamic stability of BD-FG cylindrical shells can be controlled efficiently by selecting appropriate power indexes along the desired directions. Furthermore, the DIR is highly sensitive to the porosity distribution and to the extent of transverse and longitudinal power indexes. The numerical results could be of great interest for many practical applications, as civil, mechanical or aerospace engineering, as well as for energy devices or biomedical systems.

Robust estimator of the correlation matrix with sparse Kronecker structure for a high-dimensional matrix-variate

It is of interest in many applications to estimate the correlation matrix of a high dimensional matrix-variate X∈Rp×q. Existing works usually impose strong assumptions on the distribution of X such as sub-Gaussian or strong moment conditions. These assumptions may be violated easily in practice and a robust estimator is desired. In this paper, we consider the case where the correlation matrix has a sparse Kronecker structure and propose a robust estimator based on Kendall’s τ correlation. The proposed estimator is extended further to tensor data. The theoretical properties of the estimator are established, showing that Kronecker structure actually increases the effective sample size and leads to a fast convergence rate. Finally, we apply the proposed estimator to bigraphical model, obtaining an estimator of better convergence rate than the existing results. Simulations and real data analysis confirm the competitiveness of the proposed method.

Regression and independence based variable importance measure

Evaluating the importance of input (predictor) variables is of interest in many applications of statistical models. However, nonlinearity and correlation among variables make it difficult to measure variable importance accurately. In this work, a novel variable importance measure, called regression and independence based variable importance (RIVI), is proposed. RIVI is designed by integrating Gaussian process regression (GPR) and Hilbert-Schmidt independence criterion (HSIC) so that it is applicable to nonlinear systems. The results of two numerical examples demonstrate that RIVI is superior to several conventional measures including the Pearson correlation coefficient, PLS-β, PLS-VIP, Lasso, HSIC, and permutation importance with random forest in the variable identification accuracy.

Real monodromy action

The monodromy group is an invariant for parameterized systems of polynomial equations that encodes structure of the solutions over the parameter space. Since the structure of real solutions over real parameter spaces are of interest in many applications, real monodromy action is investigated here. A naive extension of monodromy action from the complex numbers to the real numbers is shown to be very restrictive. Therefore, we introduce a real monodromy structure which need not be a group but contains tiered characteristics about the real solutions over the parameter space. An algorithm is provided to compute the real monodromy structure. In addition, this real monodromy structure is applied to an example in kinematics which summarizes all the ways performing loops parameterized by leg lengths can cause a mechanism to change poses.

Advances in metal-organic framework coatings: versatile synthesis and broad applications.

Metal-organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure-property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

Efficiency of Target Location Scenarios in the Multi-Transmitter Multi-Receiver Passive Radar

Multi-transmitter multi-receiver passive radar, which locates target in the surveillance area by the reflected signals of the available opportunistic transmitter from the target, is of interest in many applications. In this paper, we investigate different signal processing scenarios in multi-transmitter multi-receiver passive radar. These scenarios include decentralized processing of reference and surveillance signals, decentralized processing of surveillance signals, and centralized processing of surveillance signals that have different advantages, disadvantages, and requirements. A variety of possible measurements including TDOA, GROA, AOA and their combinations are presented under different scenarios. The Cramer Rao lower band (CRLB) is presented for different signal processing scenarios for the error of the target localization. The efficiency of the target localization for different signal processing scenarios and types of measurements has been investigated by the CRLB. As shown in the simulation results, the combined use of the measurements is always better than their single use. Also centralized and decentralized processing of surveillance signals, by arranging the receiver sensors in the far distances, can have better efficiency than close distance arrangements.

In Silico Discovery and Validation of Neuropeptide-Y-Binding Peptides for Sensors.

Wearable sensors for human health, performance, and state monitoring, which have a linear response to the binding of biomarkers found in sweat, saliva, or urine, are of current interest for many applications. A critical part of any device is a biological recognition element (BRE) that is able to bind a biomarker at the surface of a sensor with a high affinity and selectivity to produce a measurable signal response. In this study, we discover and compare 12-mer peptides that bind to neuropeptide Y (NPY), a stress and human health biomarker, using independent and complimentary experimental and computational approaches. The affinities of the NPY-binding peptides discovered by both methods are equivalent and below the micromolar level, which makes them suitable for application in sensors. The in silico design protocol for peptide-based BREs is low cost, highly efficient, and simple, suggesting its utility for discovering peptide binders to a variety of biomarker targets.

Effect of the substrate temperature during gold-copper alloys thin film deposition by magnetron co-sputtering on the dealloying process

Nanoporous gold is of great interest for many applications due to its three dimensional interconnected porosity at nanoscale. Among all currently use techniques to obtain nanoporous gold, dealloying is one of the most used method to create a well-controlled nanoporous morphology. Only few studies report on the creation of nanoporous gold from alloy thin film deposited by magnetron co-sputtering. However, this deposition technique allows easy tune of the morphology at nanoscale. In this paper, we report on the creation of different morphologies of nanoporous gold obtained after dealloying in nitric acid of Au-Cu thin film deposited by magnetron co-sputtering. The influence of the substrate temperature during film deposition is studied by means of scanning electron microscopy and X-ray scattering analysis. We demonstrate the impact of the as-grown thin film morphology on the final nanoporous structure. We further explain the relationship between the different nanoporous morphologies and the residual stress on the as-grown thin film.

The static local field correction of the warm dense electron gas: An ab initio path integral Monte Carlo study and machine learning representation.

The study of matter at extreme densities and temperatures as they occur in astrophysical objects and state-of-the-art experiments with high-intensity lasers is of high current interest for many applications. While no overarching theory for this regime exists, accurate data for the density response of correlated electrons to an external perturbation are of paramount importance. In this context, the key quantity is given by the local field correction (LFC), which provides a wave-vector resolved description of exchange-correlation effects. In this work, we present extensive new path integral Monte Carlo (PIMC) results for the static LFC of the uniform electron gas, which are subsequently used to train a fully connected deep neural network. This allows us to present a representation of the LFC with respect to continuous wave-vectors, densities, and temperatures covering the entire warm dense matter regime. Both the PIMC data and neural-net results are available online. Moreover, we expect the presented combination of ab initio calculations with machine-learning methods to be a promising strategy for many applications.

A phase field model for thermo‐oxidative aging in cracked polymers

AbstractWhen dealing with polymers, the behavior of aging processes is of great interest in many applications in engineering, as the usually very complex mechanisms can result in a drastic reduction of the lifetime of machine parts. In addition, those single mechanisms are coupled, which results in even more complexity. A crack creates new surfaces deeper inside the material and thus enables oxidation processes beyond the original surface. Once being oxidized, the crack resistance might be reduced, which may result in further crack propagation, which, again, enables oxidation even deeper.In the present work, a new approach for diffusion limited oxidation is introduced. The approach is based on the phase field method, which has become an important and versatile tool to model different phase evolutions in materials. An evolution equation is underlain by a gradient energy term to capture an interface energy and by a second term, which corresponds to the phase change representing the oxidation state. A diffusion equation controls the amount of available oxygen which is able to trigger the phase change. The phase change, in turn, drains a specific amount of oxygen in the coupled system of differential equations. In this work, cracks are able to expedite the oxidation process deeper into the specimen. The model has been implemented into the FE code FEAP and investigated by means of two academic examples.

On Stress-Strength Interval-System Reliability with Applications in Heart Conditions

The random variable X represents the stress placed on the system by the operating environment and random variable Y represents the strength of the system. A system is able to perform its intended function if its strength is greater than the stress imposed upon it. Reliability of the system is defined as the probability that the system is strong enough to overcome the stress. That is, R = P(Y >X). In other words, reliability is the probability that the strengths of the unit are greater than the stresses. The stress-strength model has found interests in many applications include mechanical engineering and human heart monitoring conditions. The interval-system is defined as a system with a series of chance events that occur in a given interval of time. A k-out-of-n interval-system is a system with a series of n events in a given interval of time which successes (or functions) if and only if at least k of the events succeed (function). In short, the k-out-of-n interval-system is an interval-system which successes if and only if at least k of n events succeeds. The stress-strength reliability inference of the interval-system with a series of n independent events that occurs in a given interval of time is considered. The reliability of the interval-system is the probability that at least k out of n events in a given interval of time succeed. This paper derives uniform minimum variance unbiased and maximum likelihood reliability estimates of k-out-of-n interval-system based on stress-strength inference events where X (stress) and Y (strength) are independent two-parameter exponential random variables. An application in human heart conditions to illustrate the results is discussed.

Photochromic System among Boron Hydrides: The Hawthorne Rearrangement.

Photoswitchable molecules have attracted wide interest for many applications in chemistry, physics, and materials science. In this work, we revisit the reversible photochemical and thermal rearrangements of the two B20H182- isomers reported by Hawthorne and Pilling in 1966, whose mechanism had not been understood so far. We investigate the rearrangements by means of a joint experimental and computational study with the outcome that B20H182- represents the first boron-based photochromic system ever reported. Both photochemical and thermal isomerizations occur through the same intermediate and involve a diamond-square-diamond (DSD) mechanism. Given the absence within boron chemistry of named chemical reactions as opposed to organic chemistry, we propose to label the B20H182- photo- and thermal isomerization processes as the Hawthorne rearrangement.

Monitoring morphological and chemical properties during silver solid-state dewetting

Solid-state dewetting phenomenon in silver thin films offers a straightforward method to obtain structures having controlled shape or size -this latter in principle spanning several orders of magnitudes- with potentially strong interest in many applications involving high-tech industry and biomedicine. In this work nanostructured and polycrystalline thin films of silver are deposited by pulsed electron ablation technique and the surface modified upon thermal treatments in air at increasing temperatures. Surface chemistry and morphology are then monitored simultaneously by X-ray photoemission spectroscopy and atomic force microscopy; in particular, the power spectral density of surface heights is used to analyze the alteration of the surface texture induced by annealing. It is found that such a combined approach adds a level of information about the surface as concerns the microscopic processes at the basis of the surface reshaping and elucidates the geometrical meaning of the wavelengths brought into play by the annealing process. Our results are presented in the framework of a multidisciplinary approach, advantages and limitations of which are explored and discussed.

Effect of turbulence on drop breakup in counter air flow

Understanding the factors that lead to breakup of liquid droplets is of interest in many applications. Liquid droplet breakup processes are typically broken into regimes based on a Weber number calculated based on an average flow velocity (Solsvik et al., 2013). In turbulent flows, the instantaneous velocity may differ significantly from the average velocity. Here an experimental investigation on the role of turbulence in the breakup process is undertaken, whose continuous phase is gas. The turbulence is produced by confined counterflow into which the droplets fall. Droplet breakup mode is visualized by high speed camera, and the turbulence of counterflow is measured by Particle Image Velocimetry. The experimental results show that the breakup morphology and mode frequency varies with the turbulence intensity of the counterflow.

Ohmic Impedance: Myth or Reality?

In his seminal work on the impedance response of a blocking electrode, Newman developed the concept of frequency dispersion1 accounting for the geometric effect of the electrochemical system on the primary current distribution. More recently, this approach has been revisited for different cases, including an ideally blocking electrode,2 a blocking electrode with a local constant-phase element behavior,3and a disk electrode with faradaic reactions.4-5 It was shown that the frequency dispersion results in a high-frequency time constant that can be associated to an ohmic impedance with a non-zero imaginary component in the high frequencies.6 Interestingly, the development of local electrochemical impedance spectroscopy (LEIS) has allowed the experimental validation of this concept.7-9 However, from a practical point of view, most of the experimental work reported in the literature deals with global impedance measurements and usually neglects the contribution of current and potential distributions. This is certainly due to the fact that these contribution requires the simultaneous solution of the interfacial kinetics and Laplace’s equation in the electrochemical cell, which makes it difficult to analyze the results when comparing this approach to what can be done with equivalent electrical circuits. However, the analysis of high-frequency domains is needed for all electrochemical systems and is of special interest for many practical applications dealing with the detailed analysis of capacitive behavior of an electrode, such as supercapacitors, Mott-Schottky analysis, thin oxide films, or coatings. This analysis requires a good understanding of the processes in the high-frequency domain, including its resistive component. In this work, a particular attention has been paid to the ohmic contribution observed in the high-frequency domain both for capacitive and faradaic electrochemical responses. We introduce a detailed description of the ohmic impedance first based on synthetic data in order to devise an analytical expression as a quantity that can be easily used in any fitting procedure. An example of the ohmic impedance obtained for blocking electrodes is presented in Fig. 1. In a second step, we propose an experimental validation of our new development by studying three different electrochemical systems: the response of a blocking electrode investigated using a gold disk-electrode in a sodium sulfate solution; the CPE response due to a thin oxide film using an aluminum as electrode material in a sodium sulfate solution, and the electrochemical response of a faradaic system using the dissolution of pure iron in sulfuric acid solution. References Newman, J., Frequency dispersion in capacity measurements at a disk electrode. J. Electrochem. Soc. 1970, 117(2), 198-203. Huang, V. M.-W.; Vivier, V.; Orazem, M. E.; Pebere, N.; Tribollet, B., The apparent constant-phase-element behavior of an ideally polarized blocking electrode a global and local impedance analysis. J. Electrochem. Soc. 2007, 154(2), C81-C88. Huang, V. M.-W.; Vivier, V.; Frateur, I.; Orazem, M. E.; Tribollet, B., The global and local impedance response of a blocking disk electrode with local constant-phase-element behavior. J. Electrochem. Soc. 2007, 154(2), C89-C98. Huang, V. M.-W.; Vivier, V.; Orazem, M. E.; Pebere, N.; Tribollet, B., The apparent constant-phase-element behavior of a disk electrode with Faradaic reactions. A global and local impedance analysis. J. Electrochem. Soc. 2007, 154(2), C99-C107. Orazem, M. E.; Tribollet, B., Electrochemical Impedance Spectroscopy. 2 ed.; Wiley: Hoboken, New Jersey, 2017; p 768. Frateur, I.; Huang, V. M.; Orazem, M. E.; Tribollet, B.; Vivier, V., Experimental Issues Associated with Measurement of Local Electrochemical Impedance. J. Electrochem. Soc. 2007, 154(12), C719-C727. Zou, F.; Thierry, D.; Isaacs, H. S., A high-resolution probe for localized electrochemical impedance spectroscopy measurements. J. Electrochem. Soc. 1997, 144(6), 1957-1965. Blanc, C.; Orazem, M. E.; Pebere, N.; Tribollet, B.; Vivier, V.; Wu, S., The origin of the complex character of the Ohmic impedance. Electrochim. Acta 2010, 55(21), 6313-6321. Huang, V. M.-W.; Wu, S.-L.; Orazem, M. E.; Pebere, N.; Tribollet, B.; Vivier, V., Local electrochemical impedance spectroscopy: A review and some recent developments. Electrochim. Acta 2011, 56, 8048-8057. Figure1: Nyquist representation ohmic impedance, Ze, determined for the calculated impedance response of a blocking electrode with a pure capacitance (red circles) and a local CPE (blue triangles). The crosses correspond to the fitting of each impedance diagram with the Havriliak-Negami equation. K is the dimensionless frequency defined as K=Qωαr0/κ. Figure 1

Physical layer security over fading wiretap channels through classic coded transmissions with finite block length and discrete modulation

The chance to use existing coded transmission schemes for achieving some security at the physical layer besides reliability is of interest for many applications. In this paper, we assess the levels of physical layer security achievable by classic coding schemes over fading wiretap channels, taking into account the effects of finite block lengths and discrete modulations. In order to take these practical constraints into account, some previous works use the error rates experienced by legitimate receivers and eavesdroppers as reliability and security metrics, respectively. However, having a high error rate at the eavesdropper is a necessary but not a sufficient condition for security, thus we resort to more robust information theoretic security metrics for such a purpose. By focusing on mutual information security, we estimate the average number of attempts required by an attacker to recover the whole message in practical conditions and under outage constraints. Based on this metric, higher layer cryptographic protocols can be designed to achieve robust security built upon the physical layer. We obtain lower bounds on the wiretapper equivocation about the secret message, subject to some outage probability, and assess their tightness. We provide some examples considering classic coding and modulation techniques like extended Bose–Chaudhuri–Hocquenghem codes and convolutional codes with binary signaling.

Currents and Finite Elements as Tools for Shape Space

The nonlinear spaces of shapes (unparameterized immersed curves or submanifolds) are of interest for many applications in image analysis, such as the identification of shapes that are similar modulo the action of some group. In this paper we study a general representation of shapes that is based on linear spaces and is suitable for numerical discretization, being robust to noise. We develop the theory of currents for shape spaces by considering both the analytic and numerical aspects of the problem. In particular, we study the analytical properties of the current map and the $H^{-s}$ norm that it induces on shapes. We determine the conditions under which the current determines the shape. We then provide a finite element discretization of the currents that is a practical computational tool for shapes. Finally, we demonstrate this approach on a variety of examples.

Durable Self-Cleaning Surfaces with Superhydrophobic and Highly Oleophobic Properties.

Functional surfaces with superhydrophobic and superoleophobic properties are of great interest in many applications. However, such surfaces are generally difficult to obtain. Although a few superamphiphobic surfaces have been developed recently, a challenge still remains in preparing such a surface with good durability which is a critical issue in practical application. In this study, we demonstrate a facile method for preparing durable superhydrophobic and highly oleophobic surfaces using two kinds of nanoparticles. Epoxy resin is used as the adhesive material to improve the wear resistance of the surfaces. ZnO nanoparticles and SiO2 nanoparticles are used to create high surface roughness. The prepared surfaces exhibit excellent superhydrophobicity and high oleophobicity once the nanoparticles are treated with 1 H,1 H,2 H,2 H-perfluorodecyltriethoxydsilane (FAS-17). Water and ethylene glycol contact angles of the coatings can reach up to 172 ? 2? and 157 ? 2?, respectively. After undergoing strong adhesive tape peeling and mechanical abrasion, the coatings still maintain good amphiphobicity.