Experimental study of vertically upward flame spread over polymethyl methacrylate slabs at different altitudes

Experiments of vertically upward flame spread over polymethyl methacrylate slabs were conducted in Hefei (with an altitude of 29.8 m) and Lhasa (with an altitude of 3658.0 m). Measurements were taken for the flame heights, the flame heat flux to the fuel surface and the flame spread rate. Two regions were identified for the dependence of the flame height on the heat release rate per unit width . When is less than 22 kW/m, the flame height scales as while it scales as , when is greater than 22 kW/m. The flame heights in Lhasa are approximately 1.34 and 1.25 times, respectively, of those in Hefei for these two regions. The flame heat flux to the fuel surface decreases significantly from the pyrolysis front to the flame tip, whereas it decreases slowly above the flame tip. In both regions, it can be correlated reasonably well with (x ? x_p)/(x_f ? x_p) using the form of . The flame heat flux to the fuel surface in Lhasa is approximately 0.75 times of that in Hefei. The flame spread process can be divided into three stages, which correspond to a flow region of laminar, transitional, and turbulent, respectively. The transition to a turbulent flow is delayed in Lhasa compared with Hefei. The flame spread rate in Lhasa is about half of that in Hefei because of the lower flame heat flux caused by the lower ambient pressure. Copyright © 2015 John Wiley & Sons, Ltd.     

Mechanical characterization of boron carbide single crystals

Out-of-plane anisotropy in the mechanical response of boron carbide was studied by performing nanoindentation experiments on four specific crystallographic orientations of single crystals, that is, , , , and . For each orientation of the single crystals, in-plane variations of indentation modulus and hardness were also studied by monitoring the relative rotation between the crystal surface and a Berkovich indenter tip. A significant out-of-plane anisotropy in indentation modulus was observed with ~80 GPa difference between the highest and lowest values. A smaller but measurable out-of-plane anisotropy in indentation hardness was also observed. In-plane anisotropy, on the other hand, was found to be significantly influenced by the scatter in the data and geometrical imperfections of the indenter tip. Investigations of indentation pop-in events suggested that deformation is entirely elastic prior to the first pop-in. Furthermore, quasi-plastic flow along the orientation of the single crystals was found to be more homogeneous than the other tested orientations. For select indents, cross-sectional transmission electron microscopy (TEM) of the indented regions showed formation of a quasi-plastic zone in the form of lattice rotation and various microstructural defects. The quasi-plastic zone grew in size with increasing the indentation depth. The TEM observations also suggested the crystal slip to be a potential mechanism of quasi-plasticity and a precursor for formation of amorphous bands that could eventually lead to cracking and fragmentation. The proposed failure mechanism provides valuable insights for calibrating constitutive computational models of failure in boron carbide.     

Fabrication and characterization of tetragonal yttria-stabilized zirconia single-crystalline thin film

Tetragonal yttria-stabilized zirconia thin film was successfully fabricated by a pulsed laser deposition method. The thin film grew heteroepitaxially with the orientation relationship of ZrO₂‖Al₂O₃. Energy dispersive X-ray spectroscopy mapping revealed that Y³⁺ ions were distributed homogeneously without local segregations. X-ray and electron-diffraction analysis confirmed a single crystalline structural feature of the film. On the other hand, high-resolution scanning transmission electron microscopy observations show that this film contains small-angle tilt grain boundaries, which is composed of the periodic array of dislocations with the Burgers vector .     

Cycling- and heating-induced evolution of piezoelectric and ferroelectric properties of CuO-doped K0.5Na0.5NbO3 ceramic

For accepter-doped perovskite piezoelectric ceramics, macroscopic properties of the materials (eg, hardening, fatigue, and aging) are closely related to microscopic characteristics (eg, oxygen vacancies and defect dipoles). In this work, the relationship of macroscopic and microscopic characteristics in CuO-doped K_0.5Na_0.5NbO₃ (KNN) ceramic has been studied by subjecting the material to electric field cycling, quenching, heating, and consequently aging. The introduction of CuO in KNN generates and . The defect dipoles exhibit obviously the pinning effect on ferroelectric domains and thus induce a completely pinched/double P-E loop and excellent hardening piezoelectricity of high Q_m of 2235. With the destruction of short-range symmetry uniformity between defect dipoles and ferroelectric dipoles induced by electric field cycling, quenching and heating, the ceramic can be depinned and softened. As a result, the depinned ceramic possesses an opened single ferroelectric hysteresis loop and the significantly decreasing Q_m. A distinctive aging is observed in the depinned ceramic. This study provides deep insights into the evolution of electrical properties of accepter-modified alkali niobate perovskite ceramics under electric field cycling, quenching, and heating.     

Effect of Various Electrolytes on the Phase Separation and Thermodynamic Properties of p-Tert-Alkylphenoxy Poly (Oxyethylene) Ether in the Absence/Presence of Drugs

Cloud point (CP) measurements of 4-(1,1,3,3-tetramethylbutyl) phenyl-polyethyleneglycol (Triton X-100 (TX-100)) were performed in aqueous solution in the presence of drug Amikacin sulfate (AS)/Neomycin sulfate (NS)/(AS/NS+ different inorganic salts). In aqueous solution, the CP values of TX-100 first decrease with increasing concentration and then increase with increasing surfactant concentration. The CP values of TX-100 solutions were found to increase with the increasing concentration of the AS/NS drug. The CP values of TX-100-AS/NS mixtures were also observed to decrease with the increase of the concentration of salt. Different thermodynamic parameters such as standard free energy (), standard enthalpy () as well as the standard entropy () change of phase separation were calculated and discussed in relation to molecular interactions.     

Effect of pressurization on the fracture toughness of borosilicate glasses

In this study, hot-compression is applied to two multicomponent borosilicate glasses, Borofloat33 (Boro33) and N-BK7, using molecular dynamics simulations. The effects of pressure on elastic properties, surface energy, and fracture toughness ( are investigated. It is found that the impact on is mainly dominated by the change of Young's modulus under pressure, which is proportional to the relative change in density. Between the two glasses under investigation, can be improved more effectively by the hot-compression process for Boro33, due to its higher concentration of 3-coordinated boron (B³), which facilitates densification via B³ to B⁴ conversion under compression.     

Fouling mitigation in crossflow filtration using chaotic advection: A numerical study

Fouling mitigation in a crossflow filtration system using chaotic advection is numerically studied. A barrier-embedded partitioned pipe mixer (BPPM) is selected as a static mixer, creating chaotic advection in a laminar flow regime. Mixing characteristics are controlled via two design parameters, the mixing protocol and the dimensionless barrier height (β). The average dimensionless concentration boundary layer thickness () and the surface-averaged dimensionless wall concentration () dramatically decrease with the introduction of the BPPM, incorporating a chaotic flow system. and decrease as β increases, and the largest reduction of is observed in the counter-rotational protocol. A semi-ring configuration is revealed to be the most appropriate configuration to characterize mixing near the membrane surface. It is found that a filtration system with a globally chaotic flow shows the best mixing performance and the largest reduction of fouling.     

On the Use of Side-Chain NMR Relaxation Data to Derive Structural and Dynamical Information on Proteins: A Case Study Using Hen Lysozyme

Values of and order parameters derived from NMR relaxation measurements on proteins cannot be used straightforwardly to determine protein structure because they cannot be related to a single protein structure, but are defined in terms of an average over a conformational ensemble. Molecular dynamics simulation can generate a conformational ensemble and thus can be used to restrain and order parameters towards experimentally derived target values (exp) and (exp). Application of and order-parameter restraining MD simulation to bond vectors in 63 side chains of the protein hen egg white lysozyme using 51 (exp) target values and 28 (exp) target values shows that a conformational ensemble compatible with the experimentally derived data can be obtained by using this technique. It is observed that order-parameter restraining of C−H bonds in methyl groups is less reliable than order-parameter restraining because of the possibly less valid assumptions and approximations used to derive experimental (exp) values from NMR relaxation measurements and the necessity to adopt the assumption of uniform rotational motion of methyl C−H bonds around their symmetry axis and of the independence of these motions from each other. The restrained simulations demonstrate that side chains on the protein surface are highly dynamic. Any hydrogen bonds they form and that appear in any of four different crystal structures, are fluctuating with short lifetimes in solution.     

Frequency dispersion model of the complex permeability of soft ferrites in the microwave frequency range

The complex permeability of Cu-doped nickel-zinc polycrystalline ferrites is strongly dependent on microstructure, particularly, on relative density () and average grain size (). In this study, a mathematical model, able to fit the measured magnetic permeability spectra from 10⁶ to 10⁹ Hz, is proposed and validated for a width range of average grain sizes (3.40–23.15 μm) and relative densities (0.83–0.96). To the authors’ knowledge, domain-wall motion and spin rotation contributions to magnetic permeability have been integrated jointly with the microstructure for the first time in the proposed model, highlighting the relative influence of each magnetizing mechanism and microstructure on the magnetic permeability at different angular frequencies.     

Large-scale synthesis of hafnium carbide nanowires via a Ni-assisted polymer infiltration and pyrolysis

Hafnium carbide (HfC) nanowires were successfully synthesized on C/C composites via a Ni-assisted polymer infiltration and pyrolysis. Before synthesizing HfC nanowires, the composition and microstructure of the organic HfC precursor and its pyrolyzed products were characterized by Fourier transform infrared spectra, X-ray photoelectron spectroscopy, and X-ray diffraction. The effect of heat-treatment temperature on the morphology and microstructure of HfC nanowires were investigated by scanning electron microscopy and transmission electron microscopy. Results show that HfC nanowires exhibits three-layer core-shell structure, including HfC core, HfO₂ inner shell (~2 nm) and carbon nanosheet outer shell (~1 nm). The obtained HfC nanowire is typically grown along <01> with the diameters of ~100 nm and the length of several micrometers. The growth of HfC nanowire follows the combination of top-type vapor-liquid-solid and solid-liquid-solid mechanism.     

The Influence of an Organic Salt on Micellization Behavior of Tetradecyltrimethylammonium Bromide in Aqueous Solutions of Trisubstituted Ionic Liquid [Odmim][Cl]

The influence of sodium benzoate (Na-Bz) on micellization behavior of the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) in aqueous media of trisubstituted imidazolium-based ionic liquid (IL), 1,2-dimethyl-3-octylimidazolium chloride [odmim][Cl], was investigated using conductometry, tensiometry, fluorescence,¹H NMR, Dynamic Light Scattering (DLS), and Rheology techniques. It was observed that with an increase in salt concentration, the critical micelle concentration (CMC) values of the system decrease. The CMC and various thermodynamic parameters like standard Gibbs free energy of micellization (), standard enthalpy change (), and standard entropy change () were calculated using conductometry and surface parameters such as surface pressure at the interface (П_cac), maximum surface excess concentration (Г_max), minimum surface area per molecule (A_min), and pC₂₀ (adsorption efficiency) were calculated using the tensiometry technique. The aggregation number (N_agg) was calculated using fluorescence measurements. ¹H NMR spectra shed light on interactions between the salt and the cationic surfactant in 0.1 wt% IL. DLS gives information about the size distribution of micelles in solution at different concentrations of salt.     

Stepwise Self‐Assembly and Dynamic Exchange of Supramolecular Snowflakes

Snowflake, a highly symmetrical hexagram figure, is challenging to be expressed by chemistry/supramolecular chemistry due to the complex structure. Herein, we have constructed super snowflake supramolecules using terpyridine (tpy)‐based metal‐organic building blocks with tpy‐Ru(II)‐tpy and tpy‐Zn(II)‐tpy connectivities through stepwise strategies in high yield. The structures were characterized by multi‐dimensional mass spectrometry and multi‐dimensional NMR spectrometry. In order to address the stability/tolerance of our designed super snowflake structures, ligand exchange behaviors between different supramolecules with various arm length were fully investigated by mass spectrometry. The study revealed that three modes could exist in such binary systems, including full exchange, partial exchange and self‐sorting (no exchange) depending on the length difference of ligands.     

Heat release rate determination of pool fire at different pressure conditions

This research deals with the experimental determination of the heat release rate (HRR) of n‐heptane pool fire at different pressure conditions based on oxygen consumption method. The method, initially developed for open atmosphere fires, is modified for pool fires in ventilated chamber under different pressure conditions. The calculation equation of the HRR with consideration of ambient pressure is presented. The experiments are performed in the large‐scale ventilated altitude chamber of size 2 × 3 × 4.65 m under series of pressure, 24, 38, 64, and 75 to 90 kPa. Based on the experimental data, the effects of pressure on the mass burning rate and HRR are discussed; meanwhile, the calculation method of HRR is verified. The results show that the mean mass burning rate at the steady burning stage increases exponentially with pressure as , with α = 0.68. The maximum HRR increases from 27 to 63 kW as the pressure rises from 24 to 90 kPa. It is concluded that the ambient pressure has a significant effect on the fire HRR and will further influence on other fire parameters.     

Shear rheology and scaling of semiflexible polymers: Effect of polymer-solvent interactions in the semidilute regime

Semiflexible polymers and their assemblies are important in biology as cross-linked networks of semiflexible polymers form a major structural component of tissue and living cells. This research used shear rheology to demonstrate the tuning from worm-like to rod-like conformation in semiflexible polymers by polymer-solvent interactions. The conformation was assessed by the persistence length l_p, and its influence, in the semidilute regime, was assessed by the scaling of zero-shear viscosity η_o with concentration c and molecular weight . The polymers were poly n-butyl and poly n-octyl isocyanate (PBIC and POIC, respectively). PBIC exhibited the largest l_p in chlorinated solvents, and the solutions obeyed the scaling law . However, when PBIC was dissolved in benzene the l_p was greatly reduced and the scaling law now was , consistent with a worm-like conformation. On the other hand, POIC dissolved in chlorinated and benzenic solvents exhibited a worm-like conformation and the scaling was . These results were contrasted with those of hydroxypropyl cellulose (HPC) aqueous solutions, which exhibit worm-like conformation, the solutions obeyed the scaling η_o ∝ c^2.5 . Finally, the shear viscosity of the polyisocyanates and HPC obeyed the Saito scaling, valid for anisotropic particles in solution.     

Design of a defect-induced orange persistent luminescence phosphor BaZnGeO4:Bi3+

We report a novel bright orange persistent luminescence (PersL) phosphor BaZnGeO₄:Bi³⁺ with broad emission and PersL spectra. Its crystal structure, photoluminescence (PL) spectra, thermoluminescence (TL) spectra and PersL spectra were investigated in detail. The two emission bands at 440 nm and 595 nm originate from Bi³⁺ ions in normal Ba²⁺ sites (Bi1) and Ba²⁺ sites close to vacancy defects (Bi2), respectively. The introduction of and defects improves the emission intensity of Bi2 more than that of Bi1, demonstrating that Bi2 is related to the vacancy defects. The orange emission and PersL properties of BZGO:Bi³⁺ can be improved when a little and defects are introduced, because the introduction of and defects makes it easier for Bi³⁺ to enter in Ba²⁺ sites; and for PersL, and defects can perform as the effective trap centers to capture more charges, which is beneficial for PersL. BZGO:Bi³⁺ has quite good thermal stability, and the bright orange PersL can be observed by the naked eye for 1 h. Finally, a feasible PersL mechanism of BZGO:Bi³⁺ was proposed to clarify the PersL-generation process.     

Quantitative analyses of electric field–induced phase transition in (Na,K)0.5Bi0.5TiO3:Eu ceramics by photoluminescence

Most reported results about phase transition probed by the photoluminescence (PL) spectra of Eu³⁺ ions are qualitative, but the quantitative analyses of phase transition were presented in this work. We fabricated (Na_0.8, K_0.2)_0.5Bi_0.497Eu_0.003TiO₃ (NKBT20:Eu) ferroelectric ceramics and investigated the phase structures and the PL spectra of NKBT20:Eu ceramics before and after poling at different electric fields. The PL spectra indicate a phase transition from tetragonal phase (T phase) to rhombohedral phase (R phase) within NKBT20:Eu ceramics after poling, consistent with the analyses by X-ray diffraction (XRD). Moreover, the emission intensity ratios of the “hypersensitive” transition to the magnetic dipole transition could be used to calculate the fractions of the phase transition quantitatively, which were further confirmed by XRD Rietveld refinements. This study provides a different perspective to investigate the phase transition induced by electric field for NKBT20:Eu ceramics, qualitatively and quantitatively, and the method is expected to be useful in more cases of phase analyses.     

Synchrotron x-ray spectroscopy investigation of the Ca1−xLnxZrTi2−x(Al,Fe)xO7 zirconolite ceramics (Ln = La,Nd, Gd,Ho, Yb)

When incorporating actinides into zirconolite for high-level radioactive waste immobilization, Al³⁺ and Fe³⁺ ions generally act as charge compensators. In this study, we rationally designed a series of (Ln = La, Nd, Gd, Ho, Yb) to unravel the dopant solubility and evolutions of the crystalline phase and local environment of cations through synchrotron X-ray methods. It was found that single zirconolite phase is difficult to obtain and the fraction of perovskite have an increase with x from 0.1 to 0.9 in . Formation of both zirconolite-2M and zirconolite-3O phases was observed in and . Phase transformation from zirconolite-2M to 3O occurs at x = 0.7 for while x = 0.9 for . The solubility of and to form single zirconolite-2M can reach to 0.9 f.u. and 0.7 f.u., respectively. The evolution of lattice parameters of zirconolite in is greatly related to the ionic radii of cations and substitution mechanism among the cations. X-ray absorption near edge spectroscopy revealed that Fe³⁺ ions replace both five- and six-coordinated Ti sites and the ratio of TiO₅ to TiO₆ decreases when increasing dopant concentration in the . For the local environment of Zr⁴⁺, the major form is ZrO₇ with a trace of ZrO₈.     

Experimental methods in chemical engineering: X‐ray photoelectron spectroscopy‐XPS

X‐ray photoelectron spectroscopy (XPS) is a quantitative surface analysis technique used to identify the elemental composition, empirical formula, chemical state, and electronic state of an element. The kinetic energy of the electrons escaping from the material surface irradiated by an x‐ray beam produces a spectrum. XPS identifies chemical species and quantifies their content and the interactions between surface species. It is minimally destructive and is sensitive to a depth between 1–10nm. The elemental sensitivity is in the order of 0.1 atomic %. It requires ultra high vacuum ( Pa) in the analysis chamber and measurement time varies from minutes to hours per sample depending on the analyte. XPS dates back 50 years ago. New spectrometers, detectors, and variable size photon beams, reduce analysis time and increase spatial resolution. An XPS bibliometric map of the 10 000 articles indexed by Web of Science^[1] identifies five research clusters: (i) nanoparticles, thin films, and surfaces; (ii) catalysis, oxidation, reduction, stability, and oxides; (iii) nanocomposites, graphene, graphite, and electro‐chemistry; (iv) photocatalysis, water, visible light, and ; and (v) adsorption, aqueous solutions, and waste water.     

A Methodology for Identifying Phenomenological-Based Models using a Parameter Hierarchy

In this study, a methodology for parametric identification of phenomenological based semiphysical models (PBSMs) is presented. The proposed methodology relies on a hierarchy of the relevance of parameters with respect to the model outputs. This hierarchy is accomplished by means of the Hankel matrix of the process model and its singular value decomposition (SVD). In this way, parameters having a major impact on the process output are prioritized. Two concepts, parameter interpretability and sacrifice parameter, are coined to be used in such a methodology. The proposed scheme is tested in simulation by using two realistic examples, both selected as batch processes due to their inherent difficulty: -endotoxins production by means of Bacillus thuringiensis and the production of polyhydroxyalkanoates (PHA). Our results show a reduction of 92 % and 39 % in the integral of time-weighted absolute error (ITAE), in the first and second examples, respectively, with respect to a conventional identification procedure.     

A green resin acid ester surfactant from colophony and xylitol: Synthesis,self-assembly in nonaqueous solvents,and thermodynamics

An environmental friendly oil-soluble surfactant colophony xylitol ester (CXE) is first synthesized from natural colophony and xylitol with the use of hot-compressed water and subcritical CO₂ in a steel autoclave. In this solvent-free system, the conversion of the reaction was up to 90.30% in 4 h. Thermal gravimetric analysis determine that its thermal stability was as high as 310°C. CXE is effective in reducing the surface tension of six different organic solvents. The greatest effect of surface tension reduction by CXE is in the case of dimethyl sulfoxide, the surface tension of the surfactant solution was as low as 36.26 mN/m at its critical micelle concentration value of 7.49 mM; The greatest effect of interfacial tension reduction by CXE is in the case of turpentine and water, the interfacial tension low to 1.51 mN/m. Furthermore, transmission electron microscope and particle size measurement showed that CXE is successfully self-assembled into micelles, vesicles, and heteromorphic vesicles in six kinds of organic solvents. Finally, the critical micelle concentration curves at different temperatures provided the thermodynamic parameters of the aggregate formation, found that , , and are negative and increased as the temperature increased.