Dense State Research Articles

The Corrosion Resistance of Al Film on AZ31 Magnesium Alloys by Magnetron Sputtering

Nano Al films were prepared on AZ31 magnesium alloy samples by DC magnetron sputtering. The effects of sputtering power on the microstructure and corrosion resistance of the Al film were investigated. The results show that the surface of aluminum film is dense and polycrystalline state, and it is oriented along the Al (111) crystal plane. The grain size of Al film first increases and then decreases with the increase of sputtering power. When the sputtering power exceeds 100 W, there is no insignificant effect on the orientation of the Al crystals and the corrosion current density of the samples with Al film are reduced by two orders of magnitude. The corrosion resistance of the magnesium alloy samples with the Al film magnetron sputtered varies with the sputtering power. Compared with low sputtering power, the Al film sputtered by high power has the most excellent corrosion resistance, but too high sputtering power will lead to micro cracks on the Al film, which will adversely affect the corrosion resistance.

Does standard cosmology really predict the cosmic microwave background?

In standard Big Bang cosmology, the universe expanded from a very dense, hot and opaque initial state. The light that was last scattered about 380,000 years later, when the universe had become transparent, has been redshifted and is now seen as thermal radiation with a temperature of 2.7 K, the cosmic microwave background (CMB). However, since light escapes faster than matter can move, it is prudent to ask how we, made of matter from this very source, can still see the light. In order for this to be possible, the light must take a return path of the right length. A curved return path is possible in spatially closed, balloon-like models, but in standard cosmology, the universe is "flat" rather than balloon-like, and it lacks a boundary surface that might function as a reflector. Under these premises, radiation that once filled the universe homogeneously cannot do so permanently after expansion, and we cannot see the last scattering event. It is shown that the traditional calculation of the CMB temperature is inappropriate and that light emitted by any source inside the Big Bang universe earlier than half its "conformal age" can only become visible to us via a return path. Although often advanced as the best evidence for a hot Big Bang, the CMB actually tells against a formerly smaller universe and so do also distant galaxies.

Shear behaviour of sandy soil from Chlef river reinforced with different types of fibres

Direct shear box tests were carried out in order to evaluate the effect of different types of randomly distributed fibres; two synthetic fibres (Polypropylene and Glass fibre) and one natural fibre (Sisal fibre) on the improvement of Chlef sandy soil shear strength. All of the inclusions were randomly distributed in the soil mass with a length of 12 mm and fibre contents of (0, 0.25, 0.5, 0.75 and 1% by dry soil mass). Samples were prepared at a relative density of 50% representing medium dense state and performed at normal stresses of 50, 100 and 200 kPa. The present work is conducted in order to study the effect of material properties and fibre content on the shear strength of sand. The experimental results show that all types of fibre greatly improved the shear strength, cohesive intercept and friction angle of Chlef sand. However, samples reinforced with sisal fibres have shown a more pronounced increase in strength parameters than those reinforced with glass or polypropylene fibres. The effect of the soil initial state was also discussed.

The effect of tamping conditions on undrained shear strengths of a non-plastic sandy silt tailings

A series of direct simple shear (DSS) tests were carried out on a non-plastic sandy silt lead−zinc−silver tailings to develop a relationship between undrained shearing behaviour and density for contractive states. The critical state line was also obtained through triaxial compression tests to enable the DSS tests to be viewed in a critical state framework and allow comparison with in situ testing. It was found that the gravimetric water content (GWC) used to tamp the specimens had a significant effect on the resulting undrained strengths when attempting to achieve dense states — with higher GWC giving lower strength at a given density than a lower GWC. Intact and slurry deposited (SD) samples were also tested to access denser states without inducing tamping-related stresses. These showed a more consistent trend with the loose-tamped specimens, and with other data from the literature. Plausible explanations as to the causes of the increased strength of dense-tamped samples were obtained through estimating potential preconsolidation stresses and “locked in” horizontal stresses that may occur from dense tamping. The importance of these observations on the development of density−strength profiles in engineering practice was outlined.

Observation of a highly conductive warm dense state of water with ultrafast pump–probe free-electron-laser measurements

The electrical conductivity of water under extreme temperatures and densities plays a central role in modeling planetary magnetic fields. Experimental data are vital to test theories of high-energy-density water and assess the possible development and presence of extraterrestrial life. These states are also important in biology and chemistry studies when specimens in water are confined and excited using ultrafast optical or free-electron lasers (FELs). Here we utilize femtosecond optical lasers to measure the transient reflection and transmission of ultrathin water sheet samples uniformly heated by a 13.6 nm FEL approaching a highly conducting state at electron temperatures exceeding 20 000 K. The experiment probes the trajectory of water through the high-energy-density phase space and provides insights into changes in the index of refraction, charge carrier densities, and AC electrical conductivity at optical frequencies. At excitation energy densities exceeding 10 MJ/kg, the index of refraction falls to n = 0.7, and the thermally excited free-carrier density reaches ne = 5 × 1027 m−3, which is over an order of magnitude higher than that of the electron carriers produced by direct photoionization. Significant specular reflection is observed owing to critical electron density shielding of electromagnetic waves. The measured optical conductivity reaches 2 × 104 S/m, a value that is one to two orders of magnitude lower than those of simple metals in a liquid state. At electron temperatures below 15 000 K, the experimental results agree well with the theoretical calculations using density-functional theory/molecular-dynamics simulations. With increasing temperature, the electron density increases and the system approaches a Fermi distribution. In this regime, the conductivities agree better with predictions from the Ziman theory of liquid metals.

Demonstration of an x-ray Raman spectroscopy setup to study warm dense carbon at the high energy density instrument of European XFEL

We present a proof-of-principle study demonstrating x-ray Raman Spectroscopy (XRS) from carbon samples at ambient conditions in conjunction with other common diagnostics to study warm dense matter, performed at the high energy density scientific instrument of the European x-ray Free Electron Laser (European XFEL). We obtain sufficient spectral resolution to identify the local structure and chemical bonding of diamond and graphite samples, using highly annealed pyrolytic graphite spectrometers. Due to the high crystal reflectivity and XFEL brightness, we obtain signal strengths that will enable accurate XRS measurements in upcoming pump–probe experiments with a high repetition-rate, where the samples will be pumped with high-power lasers. Molecular dynamics simulations based on density functional theory together with XRS simulations demonstrate the potential of this technique and show predictions for high-energy-density conditions. Our setup allows simultaneous implementation of several different diagnostic methods to reduce ambiguities in the analysis of the experimental results, which, for warm dense matter, often relies on simplifying model assumptions. The promising capabilities demonstrated here provide unprecedented insights into chemical and structural dynamics in warm dense matter states of light elements, including conditions similar to the interiors of planets, low-mass stars, and other celestial bodies.

La3+ and F- dual-doped multifunctional hydroxyapatite nanoparticles: Synthesis and characterization.

Hydroxyapatite (HA) co-doped with La3+ and F- ions were synthesized by the precipitation method and sintered at 1,100°C for 1 hr. Samples were characterized by the standard experimental methods including the density, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) to investigate their microstructure, phase formation, and bonding characteristics in detail. Moreover, the materials produced were identified using the microhardness tests. It was observed that in the most of materials, the hydroxyapatite was found to be the main phase with a minor amount of β-tricalcium phosphate (β-TCP). Furthermore, the presence of fluoride and small amount of β-TCP was verified with all the characteristic FTIR bands of hydroxyapatite for the majority of samples studied. The result in SEM evaluation is that the produced HA powders have less deformed, uniformly distributed, and regularly shaped particles. Here, the material density has changed towards a less dense state with the increasing rate of La doping, but statistically significant difference was not obtained (p, .1942 > .05) with increase of the F doping. A significant difference was obtained the microhardness values between La3+ and F- ions co-doped HA materials and pure HA (p [.0053] < .05). Accordingly, this study confirmed that since the La3+ and F- ions can potentially increase the efficacy of HA. According to the spectral, mechanical, and microstructure analysis result, this material can be as a good candidate product for use as an occluding material for dental application.

Experimental Study of the Aggregate Shapes in Self-Compaction

Compaction operations have a vital role in embankments or rock fills to avoid settlement, but in some projects, such as marine ones, it is hardly possible to accomplish compaction operations due to the problems and executive limitations. In situations with no possibility of compaction, it is recommended to use single-size or self-compacted materials. From a theoretical point of view, self-compacted materials consist of coarse aggregates with no vast domain of gradation. In this case, the porosity of the materials in the dense state is not significantly different from the loose one, and a relatively dense condition occurs after it is poured; thus, the mass of materials will undergo lower volumetric changes in the future. In this study, the self-compacted characteristic of materials has been investigated using real aggregates with different gradations (the ratio of the largest to the smallest aggregate size of 1, 2, 4, and 8). The gradation and shape of aggregates are the main variables examined in the research. Real aggregates have been used in order to compare the study of self-compacted idea with ideal aggregates and the effects of sphericity and angularity of them. According to the experiments carried out on samples in the present work, it was observed that, without compaction operations, even ideal materials would not be in fully self-compacted state. However, relatively denser conditions can be achieved by observing the necessary points. Moreover, aggregates with high sphericity have better self-compacted property. Furthermore, the more uniform gradation and bigger size of materials lead to more self-compacted pile of materials.

Structural plasticity of mumps virus nucleocapsids with cryo-EM structures

Mumps virus (MuV) is a highly contagious human pathogen and frequently causes worldwide outbreaks despite available vaccines. Similar to other mononegaviruses such as Ebola and rabies, MuV uses a single-stranded negative-sense RNA as its genome, which is enwrapped by viral nucleoproteins into the helical nucleocapsid. The nucleocapsid acts as a scaffold for genome condensation and as a template for RNA replication and transcription. Conformational changes in the MuV nucleocapsid are required to switch between different activities, but the underlying mechanism remains elusive due to the absence of high-resolution structures. Here, we report two MuV nucleoprotein-RNA rings with 13 and 14 protomers, one stacked-ring filament and two nucleocapsids with distinct helical pitches, in dense and hyperdense states, at near-atomic resolutions using cryo-electron microscopy. Structural analysis of these in vitro assemblies indicates that the C-terminal tail of MuV nucleoprotein likely regulates the assembly of helical nucleocapsids, and the C-terminal arm may be relevant for the transition between the dense and hyperdense states of helical nucleocapsids. Our results provide the molecular mechanism for structural plasticity among different MuV nucleocapsids and create a possible link between structural plasticity and genome condensation.

An experimental and numerical investigation of coarse aggregate settlement in fresh concrete under vibration

Fresh concrete needs vibration to compact, fill the mould and reach a dense state. During the compaction process, coarse aggregates (CAs) tend to settle, affecting the homogeneity and eventually the long-term durability of hardened concrete. In this study, a 3-D, multi-phase numerical model for fresh concrete is developed for better understanding the CA settlement under vibration. The settlement rate of the CA in vibrated concrete is considered based on the Stokes law, and the calibrated rheological parameter of mixtures is determined by the segmented sieving method. The model prediction shows that the vibration time has the greatest effect on CA settlement, followed by the particle size of CAs, whereas the density of CAs and the plastic viscosity of mixtures contribute a little compared with the aforementioned factors. Through experimental tests, the validity of prediction results is well verified. The proposed model provides a new method to understand and estimate the settlement behaviour of CAs.

Research on continuous granular material flow detection method and sensor

The flow rate measurement of seeding and fertilization is the premise for precise control; it's difficult to measure accurately due to the particles flow in a continuous dense state. A flow rate measuring method based on the correlation between the sensor voltage and particles flow rate was introduced. Two algorithms for models building were proposed. To demonstrate the feasibility of this method and evaluate the accuracy of the algorithms, a particles flow rate sensor and test bench were designed. Wheat, rice, compound fertilizer, and urea were chosen as the experimental subject. The result showed that it has a strong correlation between the voltage and flow rate. The R2 fitted by accumulation method (AM) for the four materials were 0.9998, 0.9984, 0.9999, and 0.9998, and the R2 of sorting method (SM) were 0.9934, 0.9843, 0.9903, and 0.9928. The statistics showed the measurement accuracy of AM was higher than that of SM.

Experimental Study on the Monotonic and Cyclic Behavior of Carbonate Sand in the South China Sea

Carbonate soils have specific properties that differ from those of siliceous sand. The monotonic and cyclic behavior of carbonate sand from Jinqing Island in the South China Sea was examined by undrained monotonic and cyclic simple shear tests in this paper. The monotonic test results show that the phase transformation state friction angle is 25.7°, and the critical state friction angle decreases from 38.7° to 37.3° due to particle crushing. By comparing the experimental data from the monotonic and cyclic tests, we found that the trend of the peak shear stress ratio with shear strain in each cycle of cyclic tests was close to that of monotonic tests. If the cyclic stress ratio of symmetrical cyclic tests is normalized with the phase transformation strengths obtained by the corresponding monotonic tests, it has a good relationship with the number of cycles at failure and is not affected by the relative density and vertical consolidation stress. The effects of the relative density, vertical consolidation stress and initial static shear stress on the undrained cyclic strength are discussed. Finally, a comparison of the undrained cyclic strength of carbonate sand from different regions shows that different carbonate sands have almost identical undrained cyclic strength under the medium dense state, but significant quantitative differences are observed between these carbonate sands under the dense state.

Load-settlement response of piled raft foundations in sand

ABSTRACT The load-settlement behaviour of piled raft foundations (PRFs) resting on sand subjected to vertical uniformly distributed load is studied using three-dimensional elasto-plastic finite element (FE) analyses. The unified Clay and Sand Model (CASM), based on the critical state soil mechanics, is used as the soil constitutive model. In the present study, 38 rectangular, strip, and circular raft connected to different pile configurations resting on four different types of sands in their loose, medium, and dense states are considered. The accuracy of the finite element analysis is confirmed through verification and validation with other numerical and experimental studies. A detailed parametric study is conducted, which includes soil elastic and critical state parameters as well as different dimensions of PRFs. A guideline chart is provided, which will be helpful for a design practitioner to choose the suitable PRF configurations considering serviceability limit states of safety and economical design aspect. This flow chart is based on (i) combined effects of various parameters on PRF load settlement behaviour, (ii) load sharing between the raft and the pile groups, and (iii) a preliminary cost analysis.

Microstructural influence on damage-induced zirconia surface asperities produced by conventional and ultrasonic vibration-assisted diamond machining

Zirconia surface asperities associated with machining-induced damage and deformation jeopardize the quality of zirconia products. Conventional and emerging ultrasonic vibration-assisted machining processes are used to shape zirconia materials. However, a deep understanding of how zirconia microstructures and ultrasonic vibration amplitudes affect material removal mechanisms and surface quality in these processes is missing, rendering the proper mechanical process selection challenging. This paper reports on the 3D characterization of damage-induced surface asperities and the investigation of material removal mechanisms of pre-sintered porous and sintered dense zirconia materials in conventional and ultrasonic vibration-assisted diamond machining processes. 3D white light profilometry was used to measure surface asperities in terms of texture parameters, together with scanning electron microscopy (SEM) for imaging damage and deformation morphologies. The results show that removal mechanisms and damage-induced zirconia surface asperities depended on material microstructures and ultrasonic vibration amplitudes. Both porous and dense zirconia materials had a brittle-ductile mixed removal mode in conventional and ultrasonic vibration-assisted diamond machining processes. However, brittle fracture was dominant for the porous state and ductile deformation was presiding for the dense state. Thus, there were significantly higher fracture damage area ratios with much higher average and maximum roughness values, and maximum peak and valley heights on machined porous surfaces than dense ones. Ultrasonic assistance at an optimal vibration amplitude promoted brittle-ductile transitions on both porous and dense zirconia surfaces, resulting in reduced brittle fracture damage areas with reduced surface asperities. This microstructure-process-surface quality relation provides insights into manufacturing processes for zirconia products.

Synthesis of control Lyapunov functions and stabilizing feedback strategies using exit‐time optimal control Part I: Theory

AbstractThis work studies the problem of constructing control Lyapunov functions (CLFs) and feedback stabilization strategies for deterministic nonlinear control systems described by ordinary differential equations. Many numerical methods for solving the Hamilton–Jacobi–Bellman partial differential equations specifying CLFs typically require dense state space discretizations and consequently suffer from the curse of dimensionality. A relevant direction of attenuating the curse of dimensionality concerns reducing the computation of the values of CLFs and associated feedbacks at any selected states to finite‐dimensional nonlinear programming problems. We propose to use exit‐time optimal control for that purpose. This article is the first part of a two‐part work. First, we state an exit‐time optimal control problem with respect to a sublevel set of an appropriate local CLF and establish that, under a number of reasonable conditions, the concatenation of the corresponding value function and the local CLF is a global CLF in the whole domain of asymptotic null‐controllability. We also investigate the formulated optimal control problem. A modification of these constructions for the case when one does not find a suitable local CLF is provided as well. Our developments serve as a theoretical basis for a curse‐of‐dimensionality‐free approach to feedback stabilization, that is presented in the second part Yegorov et al. (2021) of this work together with supporting numerical simulation results.

Sustainable reuse of coarse aggregates in clay-based impervious core: Compactability and permeability

The reuse of coarse aggregate (CA) on clay-based materials is a sustainable and cost effective solution to minimize the extraction of natural farmland resources and reinforce the mechanical behaviour of impervious materials. However, limited knowledge is available regarding the compactability and permeability of CA-clay mixtures and their intrinsic connections. This study reports the results of a series of modified dynamic compaction tests and triaxial permeability tests performed on impervious clay materials reinforced with various contents of CA. Results demonstrate that compaction behaviour of CA-clay mixtures changes significantly with coarse aggregate content (Cg). A peak value of global maximum dry density is achieved at Cg = 70%, while the fine clay matrix is compacted to its densest state when Cg<30%. The permeability, as a good indication of meso-structure in CA-clay mixtures, is significantly dominated by coarse aggregate content as well as the clay matrix void ratio. From the perspective of preferential flow path concept, permeability reaches a lowest value at Cg = 30%. Due to the clay bridge effect induced by the heterogeneous density field, the larger the coarse particle size is, the smaller the permeability coefficient will become.

Effects of pyrolysis temperature, feedstock type and compaction on water retention of biochar amended soil

Recent studies on water retention behaviour of biochar amended soil rarely considers the effect of pyrolysis temperature and also feedstock type into account. It is well known that pyrolysis temperature and feedstock type influences the physical and chemical properties of biochar due to stagewise decomposition of structure and chemical bonds. Further, soil density, which is in a loose state (in agricultural applications) and dense (in geo-environmental engineering applications) can also influence water retention behaviour of biochar amended soils. The major objective of this study is to investigate the water retention properties of soil amended with three different biochars in both loose and dense state. The biochars, i.e. water hyacinth biochar (WHB), chicken manure biochar (CMB) and wood biochar (WB) were produced in-house at different pyrolysis temperature. After then, biochars at 5% and 10% (w/w%) were amended to the soil. Water retention behaviour (soil suction and gravimetric water content) was studied under drying and wetting cycle simulated by varying relative humidity (RH, 50–90%). Results show that 10% WHB produced at 300 °C were found to possess highest water retention. CMB is found to possess higher water retention than WB for 10% amendment ratio. In general, the addition of three biochars (at both 300 °C and 600 °C) at 10% (w/w) significantly improved the water retention at all suction ranges in both loose and dense compaction state as compared to that of the bare soil. The adsorption (wetting) and desorption (drying) capacity of biochar amended soils is constant at corresponding RH.

Microstructural responses of Zirconia materials to in-situ SEM nanoindentation

Development of optimal shaping processes for pre-sintered and sintered zirconia materials requires a fundamental understanding of damage and deformation mechanisms at small-scale contacts with diamond tools. This paper reports on responses of zirconia materials with distinct microstructures to nanoindentation associated with diamond machining using a Berkovich diamond indenter. In-situ nanoindentation was performed in a scanning electron microscope (SEM) and in-process filmed to record small contact events. Indentation morphology was SEM-mapped at high-magnifications. Although both pre-sintered porous and sintered dense zirconia materials mechanically revealed the quasi-plastic behavior in indentation, there were distinct responses of the two materials to quasi-plasticity at the microstructural level. For pre-sintered porous zirconia, the quasi-plasticity was attributed to shear faults resulting from breaking pore networks as microstructurally discrete interfaces, to lead to compression, fragmentation, pulverization and microcracking of zirconia crystals in indentation imprints. In contrast, sintered dense zirconia had shear band-induced quasi-plastic deformation, accompanied with localized tensile microfracture. A material index associated with the mechanical properties ranked the lower quasi-plasticity for pre-sintered porous zirconia than its sintered dense state, predicting more machining-induced damage in the former than the latter. Significantly higher indentation imprint volumes induced in indented pre-sintered porous zirconia than sintered dense state previses higher machining efficiency for the former than the latter. The microstructure-dependent indentation mechanisms provide the fundamental knowledge into micromechanics of abrasive machining of zirconia materials and may lead to a new microstructural design for zirconia materials to achieve a balanced machining efficiency and damage control.

Sodium tracer measurements of an expanded dense aluminum plasma from e-beam isochoric heating

Spatially and temporally resolved visible absorption spectroscopy is performed on sodium D-lines present as surface contaminants on an expanded dense aluminum plasma plume. An 80-ns FWHM, intense, relativistic electron beam deposits 5.4 J into a 100-μm-thick Al foil, which isochorically heats and subsequently hydrodynamically expands the material through the warm dense matter state and into a classical-like plasma state, with a coupling parameter of approximately 0.2 and a degeneracy parameter of approximately 270. The Na contamination, carried along with the expanding plume, shows saturated absorption features in the dense Al continuum for λ&amp;gt; 450 nm. X-ray photoelectron spectroscopy and laser-induced breakdown spectroscopy confirm Na is a surface contaminant with an atomic concentration of ∼0.1% when interrogating identical foil samples. A spectroscopic-quality radiation transport model is used to post-process 2D hydrodynamic simulations to interpret the plasma conditions based on the measured Na 3p-3s doublet line profiles. A sodium number density of 3×1015 cm−3 best matches the experimental spectra, which originate from a dense surface plasma with ne=3.0±0.8×1018 cm−3.

The microscopic origin of K0 on granular soils: the role of particle shape

The at-rest coefficient of lateral pressure, $$K_0$$ , is a critical macroscopic parameter for evaluating stress transmission in granular media for engineering practice. This paper revisits the microscopic origin of $$K_0$$ and its corresponding underlying physics based on micromechanics-based theories and numerical simulations, with a focus placed on the effect of particle shape. Two typical kinds of distortion (elongation and blockiness) in particle shape are considered, modeled by ellipsoids and superballs in the discrete element method. One-dimensional compression tests are performed on numerical specimens with dense and loose initial states for different particle shapes. An analytical relationship between $$K_0$$ and anisotropy of fabric measures (i.e., contact normal, contact force, and shape-related anisotropy) is established within the stress-force-fabric framework. It is found that the analytical $$K_0$$ is consistent with the measured one directly from the simulation regardless of particle shape, verifying a well-established relationship between $$K_0$$ and fabric. It is further found that contact force partition of $$K_0$$ plays the most prominent role in $$K_0$$ compared to contact normal and shape-related partitions. Results also reveal the different influence of shape distortion on $$K_0$$ and the corresponding mechanical properties related to $$K_0$$ , such as void ratio, mobilized friction angle, and coordination number. More specifically, $$K_0$$ has a ‘W’-shape relationship with elongation for dense ellipsoids and an ‘M’-shape relationship with blockiness for superballs.