A mild transformation of γ-FeOOH to γ-Fe2O3 using organic reagents

The layered compound, FeOCl is known to form stable intercalates with a large number of organic molecules. When the isostructural γ-FeOOH is treated with organic bases at temperatures of 120–140°C, it is quantitatively converted to the topotactically related γ-Fe₂O₃. The first step in this base assisted dehydration is presumed to be an intercalation. The second and possibly faster step could be a sequential elimination of water from the interlayer, the role of the base being catalytic. Slightly impure samples of γ-FeOOH that contain a small (5%) amount of α-FeOOH are transformed quantitatively into α-Fe₂O₃ under the above conditions but pure α-FeOOH is unaffected. A possible rationale for this observation is given.     

Co@Co3O4@PPD Core@bishell Nanoparticle‐Based Composite as an Efficient Electrocatalyst for Oxygen Reduction Reaction

Durable electrocatalysts with high catalytic activity toward oxygen reduction reaction (ORR) are crucial to high‐performance primary zinc‐air batteries (ZnABs) and direct methanol fuel cells (DMFCs). An efficient composite electrocatalyst, Co@Co₃O₄ core@shell nanoparticles (NPs) embedded in pyrolyzed polydopamine (PPD) is reported, i.e., in Co@Co₃O₄@PPD core@bishell structure, obtained via a three‐step sequential process involving hydrothermal synthesis, high temperature calcination under nitrogen atmosphere, and gentle heating in air. With Co@Co₃O₄ NPs encapsulated by ultrathin highly graphitized N‐doped carbon, the catalyst exhibits excellent stability in aqueous alkaline solution over extended period and good tolerance to methanol crossover effect. The integration of N‐doped graphitic carbon outer shell and ultrathin nanocrystalline Co₃O₄ inner shell enable high ORR activity of the core@bishell NPs, as evidenced by ZnABs using catalyst of Co@Co₃O₄@PPD in air‐cathode which delivers a stable voltage profile over 40 h at a discharge current density of as high as 20 mA cm^?2.     

A sequential hypothesis testing procedure for the process capability index Cpk

In this study, we propose a sequential method for hypothesis testing on the C_pk process capability index. We compare the properties of the sequential test with the performances of nonsequential tests by performing an extensive simulation study. The results show that the proposed sequential test makes it possible to save a large amount of sample size as compared with the fixed sample size tests while maintaining the desired α‐level and power.     

Maximum Likelihood Estimate In Intraclass Correlation Model

The use of Wald's SPRT to test hypotheses concerning the correlation coefficient is complicated by the nuisance parameters (μ _x , μ _y , σ _X , σ _y ) in the bivariate normal density function. While more general theories have been proposed to produce sequential tests in such situations, the properties of these tests are difficult to ascertain since Wald's method of approximating the OC and ASN functions (usually) breaks down. We derive several sequential tests for the correlation coefficient for which these functions are calculable.     

Precise Control of Perovskite Crystallization Kinetics via Sequential A-Site Doping

Two-step-fabricated FAPbI₃-based perovskites have attracted increasing attention because of their excellent film quality and reproducibility. However, the underlying film formation mechanism remains mysterious. Here, the crystallization kinetics of a benchmark FAPbI₃-based perovskite film with sequential A-site doping of Cs⁺ and GA⁺ is revealed by in situ X-ray scattering and first-principles calculations. Incorporating Cs⁺ in the first step induces an alternative pathway from δ-CsPbI₃ to perovskite α-phase, which is energetically more favorable than the conventional pathways from PbI₂. However, pinholes are formed due to the nonuniform nucleation with sparse δ-CsPbI₃ crystals. Fortunately, incorporating GA⁺ in the second step can not only promote the phase transition from δ-CsPbI₃ to the perovskite α-phase, but also eliminate pinholes via Ostwald ripening and enhanced grain boundary migration, thus boosting efficiencies of perovskite solar cells over 23%. This work demonstrates the unprecedented advantage of the two-step process over the one-step process, allowing a precise control of the perovskite crystallization kinetics by decoupling the crystal nucleation and growth process.     

Structural studies on Li1−xTa3O8−xFx solid solutions by full-profile refinements of guinier-hägg X-ray film data

Three compositions of solid solutions Li_1?xTa₃O_8?xF_x (x = 0) 0.25 and 0.5) have been studied by full-profile analysis of microdensitometer-measured Guinier-Hägg powder diffraction data. From sequential changes in disorder and interatomic distances within this series, the preferred lithium position is proposed to be approximately (0.11, $\text{1}\text{2}$, 0.03). The results obtained for the high temperature modification of LiTa₃O₈ by A.G. Nord and J.O. Thomas from X-ray single crystal and neutron powder diffraction data [Nord, A.G. and Thomas, J.O., Acta Chem. Scand., in press] are discussed in view of the present investigation.     

The Impact of a Dynamic Two‐Step Solution Process on Film Formation of Cs0.15(MA0.7FA0.3)0.85PbI3 Perovskite and Solar Cell Performance

This paper provides deep understanding of the formation mechanism of perovskite film fabricated by sequential solution‐based methods. It compares two sequential spin‐coating methods for Cs_0.15(MA_0.7FA_0.3)_0.85PbI₃ perovskite. First is the “static process,” with a stoppage between the two spin‐coating steps (1st PbI₂‐CsI‐dimethyl sulfoxide (DMSO)‐dimethylformamide (DMF) and 2nd methylammonium iodide (MAI)‐formamidinium iodide (FAI)‐isopropyl alcohol). Second is the “dynamic process,” where the 2nd precursor is dispensed while the substrate is still spinning from the 1st step. For the first time, such a dynamic process is used for Cs_0.15(MA_0.7FA_0.3)_0.85PbI₃ perovskite. Characterizations reveal improved film formation with the dynamic process due to the “retainment” of DMSO‐complex necessary for the intermediate phase which i) promotes intercalation between precursors and ii) slows down perovskite crystallization for full conversion. The comparison on as‐deposited perovskite before annealing indicates a more ordered film using this dynamic process. This results in a thicker, more uniform film with higher degree of preferred crystal orientation and higher carrier lifetime after annealing. Therefore, dynamic‐processed devices present better performance repeatability, achieving a higher average efficiency of 17.0% compared to static ones (15.0%). The new insights provided by this work are important for perovskite solar cells processed sequentially as the process has greater flexibility in resolving solvent incompatibility, allowing separate optimizations and allowing different deposition methods.     

Secruential Rank Tests I. Monie Carlo Studies of the Two-Sample Procedure

Monte Carlo studies of a sequential, two-sample, rank-sum test developed earlier by Wilcoxon, Rhodes and Bradley are reported. Ranking is accomplished within groups of observations in the sequential procedures and the theory is based on a model suggested by Lehmann. Design parameters are α and β, probabilities of Type I or Type II errors, m and n, the numbers of X- and Y-observations in a group of observations, and k ₁, the power in the Lehmann model wherein the alternative hypothesis states that the cdf of the Y-population is G(u) = F ^{k ₁} (U), F(u) being the cdf of the X-population. Studies are made for designs with (α = β = .05, m = n = 2(1)5, k _k = 1.5, 2.33, 4 and 9. Data appropriate to the Lehmann model are generated and studies are also made when G(u – μ _y ) = F(u).

Average sample numbers and powers of tests are estimated. The effects of truncation are examined. It is concluded that the Monte Carlo results substantiate the use of the usual Wald theory of sequential analysis and that the use of the sequential methods for data from normal populations differing only in locations is satisfactory for most practical applications.     

Efficient Perovskite Solar Cells Fabricated Through CsCl‐Enhanced PbI2 Precursor via Sequential Deposition

The fabrication of high‐quality perovskite film highly relies on chemical composition and the synthesis method of perovskite. So far, sequentially deposited MA_0.03FA_0.97Pb(I_0.97Br_0.03)₃ polycrystalline film is adopted to produce high‐performance perovskite solar cells with record power conversion efficiency (PCE). Fewer grain boundaries and incorporation of inorganic cation (e.g., cesium) would further increase device performance via sequential deposition. Here, cesium chloride (CsCl) is introduced into lead iodide (PbI₂) precursor solution that beneficially modulates the property of PbI₂ film, leading to larger grains with cesium incorporation in the resulting perovskite film. The enlarged crystal grains originate from a slower nucleation process for CsCl‐containing PbI₂ film when reacting with formamidine iodide, confirmed by in situ confocal photoluminescence imaging. Photovoltaic devices based on CsCl‐containing PbI₂ film demonstrate a higher averaging efficiency of 21.3% than 20.3% of the devices without CsCl additives for reverse scan. More importantly, the device stability is improved by CsCl additives that retain over 90% of their initial PCE value after 4000 min tracking at maximum power point under 1‐sun illumination. This work paves a way to further improve the photovoltaic performance of mixed‐cation‐halide perovskite solar cells via a sequential deposition method.     

Tests for One or Two Outliers in Normal Samples with Unknown Variance: A Correction

In a paper in this Journal, McMillan (1971) compared three procedures for the detection of outliers in samples from a Normal population. One of these was a sequential application of a maximum residual test. One step in McMillan's derivation of the probability of detecting two outliers using this test is incorrect. A correct derivation is presented in this note and some numerical results in McMillan's paper are appropriately amended. McMillan's qualitative statements on the performance of the test are essentially unaffected.     

Compressive Fatigue Behavior of Bovine Cancellous Bone and Bone Analogous Materials under Multi‐Step Loading Conditions

In this study the compressive cyclic behavior of bovine cancellous bone and three open‐cell metallic foams including AlSi7Mg foams (30 and 45 ppi) and CuSn12Ni2 foam (30 ppi) has been investigated. Multi‐step fatigue tests are carried out to study the deformation behavior under increasing compressive cyclic stresses. Short multi‐step tests, with steps of 300–500 cycles, are used to identify the cyclic yield stress (σ_cy) and the stress at failure (σ_fail). The residual strain accumulation, or cyclic creep, is observed during these tests. Long multi‐step tests, with 5000 cycles at selected stress ranges (0.4σ_cy, 0.6σ_cy, 0.8σ_cy, and σ_cy), are also carried out to study further the compressive fatigue behavior of the materials. Scanning electron microscopy (SEM) has been used to characterize the microstructure of the foams and the bone prior to and post mechanical testing. Particular attention is paid to the role of cyclic creep and buckling in the failure processes. The results show that residual strain accumulation seems to be the predominant driving force leading to failure of foams and bones. Although foams and bone fail by the same mechanism of cyclic creep, the deformation behavior at the transient region of each step is different for both materials. The maximum strain ε_max of foams decrease suddenly during the change of each step. This behavior may be explained by the rapidly developing microdamage in the cell struts that occur at the transient region of each step. Bones show more gradual decrease of ε_max, where microdamage may be accumulated progressively during the fatigue test.     

Facile preparation of carbon coated magnetic Fe3O4 particles by a combined reduction/CVD process

In this work, we report a simple method for the preparation of magnetic carbon coated Fe₃O₄ particles by a single step combined reduction of Fe₂O₃ together with a Chemical Vapor Deposition process using methane. The temperature programmed reaction monitored by Mössbauer, X-ray Diffraction and Raman analyses showed that Fe₂O₃ is directly reduced by methane at temperatures between 600 and 900 °C to produce mainly Fe₃O₄ particles coated with up to 4 wt% of amorphous carbon. These magnetic materials can be separated into two fractions by simple dispersion in water, i.e., a settled material composed of large magnetic particles and a suspended material composed of nanoparticles with an average size of 100-200 nm as revealed by Scanning Electron Microscopy and High-resolution Transmission Electron Microscopy. Different uses for these materials, e.g., adsorbents, catalyst supports, rapid coagulation systems, are proposed.     

3D Mesoporous van der Waals Heterostructures for Trifunctional Energy Electrocatalysis

The emergence of van der Waals (vdW) heterostructures of 2D materials has opened new avenues for fundamental scientific research and technological applications. However, the current concepts and strategies of material engineering lack feasibilities to comprehensively regulate the as‐obtained extrinsic physicochemical characters together with intrinsic properties and activities for optimal performances. A 3D mesoporous vdW heterostructure of graphene and nitrogen‐doped MoS₂ via a two‐step sequential chemical vapor deposition method is constructed. Such strategy is demonstrated to offer an all‐round engineering of 2D materials including the morphology, edge, defect, interface, and electronic structure, thereby leading to robustly modified properties and greatly enhanced electrochemical activities. The hydrogen evolution is substantially accelerated on MoS₂, while the oxygen reduction and evolution are significantly improved on graphene. This work provides a powerful overall engineering strategy of 2D materials for electrocatalysis, which is also enlightening for other nanomaterials and energy‐related applications.     

Algorithms for direct-access gaussian solution of structural stiffness matrix equation

Based on direct-access programming, algorithms have been developed for the generation, and solution by Gaussian elimination of the structural stiffness matrix equation resulted from application of the finite element method in engineering analyses. A large disk storage is used to store the rows of the stiffness matrix as directly accessible records. The developed algorithm BAND2R requires only 2N_b in-core words in implementing the Gaussian elimination where N_b is the semi-band width of the stiffness matrix. Algorithms BANDSQ and BDSQMX are presented which require N²_b in-core words but minimize the number of retrieving and restoring the direct-access records during the Gaussian elimination. BANDSQ has the direct-access feature in both the elimination and backward-substitution steps whereas BDSQMX has the direct-access feature only in the backward-substitution step of the Gaussian elimination. Illustrative applications of the developed algorithms are given and the computer core and time requirements for BAND2R, BANDSQ and BDSQMX are compared to those for the conventional Gaussian elimination of using sequential, in-core storages. Methods for reducing the semi-band width N_b of the structural stiffness matrix are also discussed.     

Cell-Like Capsules with “Smart” Compartments

Eukaryotic cells have inner compartments (organelles), each with distinct properties and functions. One mimic of this architecture, based on biopolymers, is the multicompartment capsule (MCC). Here, MCCs in which the inner compartments are chemically unique and “smart,” i.e., responsive to distinct stimuli in an orthogonal manner are created. Specifically, one compartment alone is induced to degrade when the MCC is contacted with an enzyme while other compartments remain unaffected. Similarly, just one compartment gets degraded upon contact with reactive oxygen species generated from hydrogen peroxide (H₂O₂). And thirdly, one compartment alone is degraded by an external, physical stimulus, namely, by irradiating the MCC with ultraviolet (UV) light. All these specific responses are achieved without resorting to complicated chemistry to create the compartments: the multivalent cation used to crosslink the biopolymer alginate (Alg) is simply altered. Compartments of Alg crosslinked by Ca²⁺ are shown to be sensitive to enzymes (alginate lyases) but not to H₂O₂ or UV, whereas the reverse is the case with Alg/Fe³⁺ compartments. These results imply the ability to selectively burst open a compartment in an MCC “on-demand” (i.e., as and when needed) and using biologically relevant stimuli. The results are then extended to a sequential degradation, where compartments in an MCC are degraded one after another, leaving behind an empty MCC lumen. Collectively, this work advances the MCC as a platform that not only emulates key features of cellular architecture, but can also begin to capture rudimentary cell-like behaviors.     

Flexible Photodetector Arrays Based on Patterned CH3NH3PbI3−xClx Perovskite Film for Real‐Time Photosensing and Imaging

The quest for novel deformable image sensors with outstanding optoelectronic properties and large‐scale integration becomes a great impetus to exploit more advanced flexible photodetector (PD) arrays. Here, 10 × 10 flexible PD arrays with a resolution of 63.5 dpi are demonstrated based on as‐prepared perovskite arrays for photosensing and imaging. Large‐scale growth controllable CH₃NH₃PbI_3?xCl_x arrays are synthesized on a poly(ethylene terephthalate) substrate by using a two‐step sequential deposition method with the developed Al₂O₃‐assisted hydrophilic–hydrophobic surface treatment process. The flexible PD arrays with high detectivity (9.4 × 10¹¹ Jones), large on/off current ratio (up to 1.2 × 10³), and broad spectral response exhibit excellent electrical stability under large bending angle (θ = 150°) and superior folding endurance after hundreds of bending cycles. In addition, the device can execute the functions of capturing a real‐time light trajectory and detecting a multipoint light distribution, indicating that it has widespread potential in photosensing and imaging for optical communication, digital display, and artificial electronic skin applications.     

An Elementary Introduction to the Theory of Probability

This paper describes modifications of the sequential, two-sample, grouped, rank tests developed earlier. A modified, sequential, configural rank test is discussed in some detail and is a procedure based on rerankings of observations as new groups of observations are obtained sequentially. A numerical application is given.

Monte Carlo results are presented on the modified, sequential, configural rank test and compared with earlier studies. Proofs of termination of the test are reported and outstanding unsolved problems noted.     

Multivariate statistical process control charts based on the approximate sequential χ2 test

Similar to the univariate CUSUM chart, a multivariate CUSUM (MCUSUM) chart can be designed to detect a particular size of the mean shift optimally based on the scheme of a sequential likelihood ratio test for the noncentrality parameter. However, in multivariate case, the probability ratio of a sequential test is intractable mathematically and the test statistic based on the ratio does not have a closed form expression which makes it impractical for real application. We drive an approximate log-likelihood ratio and propose a multivariate statistical process control chart based on a sequential χ² test to detect a change in the noncentrality parameter. The statistical properties of the proposed test statistic are explored. The average runs length (ARL) performance of the proposed charts is compared with other MCUSUM charts for process mean monitoring. The experimental results reveal that the proposed charts achieve superior, both zero-state and steady-state, ARL performance over a wide range of mean shifts, especially when the dimension of measurements is large.     

A Bayesian Predictive Analysis of Step‐Stress Accelerated Tests in Gamma Degradation‐Based Processes

Degradation modeling might be an alternative to the conventional life test in reliability assessment for high quality products. This paper develops a Bayesian approach to the step‐stress accelerated degradation test. Reliability inference of the population is made based on the posterior distribution of the underlying parameters with the aid of Markov chain Monte Carlo method. Further sequential reliability inference on individual product under normal condition is also proposed. Simulation study and an illustrative example are presented to show the appropriateness of the proposed method. Copyright © 2017 John Wiley & Sons, Ltd.     

Synthesis of bactericidal polymer coatings by sequential plasma-induced polymerization of 4-vinyl pyridine and gas-phase quaternization of poly-4-vinyl pyridine

Plasma-based technology is an alternative to produce universal polymer coatings with the appropriate requirements of robustness and stability for antibacterial applications. Here, we proposed a sequential two-step alternative to synthesize antibacterial polymer coatings. A non-isothermal plasma reactor, operated at atmospheric pressure (P_atm) and room temperature (T_room), was used to induce free radical polymerization of 4-vinyl pyridine (4VP) on high-density polyethylene (PE). In a subsequent step, the poly-4VP (P4VP) films were treated with a bromoethane/He gas stream to produce quaternized P4VP (P4VPQ) films. Chemical structure of polymer films was validated by infrared and UV–visible spectroscopy, and morphology was evaluated by optical and atomic force microscopy; scanning electron microscopy was used to determine films thickness, which was then used to estimate the surface charge density. The bactericidal capacity was determined with a standard test by using Escherichia coli. Both types of films had an estimated charge density in the order of 10¹⁶ positive charges per cm²; P4VP films removed about 95–99% of bacteria, whereas 4PVPQ films eliminated 100%. The methodology proposed for the synthesis of antibacterial polymer coatings is simpler, faster, and more environmentally friendly than other plasma-based methods; operation at T_room and P_atm may also have a significant effect on the economics and the ease of implementation of the process at commercial scale. The suggested approach may facilitate the development of new universal coatings, and operating plasma conditions could be extrapolated for engineering antibacterial coatings in industrial areas where bacterial attachment is of concern.