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Density functional theory calculations are performed to systematically investigate the electronic and magnetic properties of few-layer and bulk Fe3SiSe2 (FSS). We predict that the bulk FSS has a metallic ground state and a layered structure displaying intralayer ferromagnetic ordering and interlayer antiferromagnetic ordering. The itinerant magnetism in the FSS was determined by the Stoner criterion. Predictions of the absence of unstable phonon modes and a moderate cleavage energy of only 28.3 meV/Å2 suggest the possibility of stabilizing FSS in a monolayer form. The calculated spin–orbit coupling facilitates not only a large magnetocrystalline anisotropy energy, around 500 μeV/Fe, but also spontaneous valley polarization in odd-numbered layer systems. These systems have net magnetic moments as the magnetic moments of AFM-ordered layers are not fully compensated in the odd-numbered layer case and are predicted to show 2D metallic behaviors. The magnitude of the valley polarization in odd-numbered layered systems decreases from 18 meV with layer number but is absent in even-layered structures, thus showing an odd–even oscillation effect. Experimental realization of this bidimensional metallic magnet is, therefore, expected to widen the arena of two-dimensional materials that show exotic phenomena.

Two-dimensional (2D) multiferroic materials with coexisting ferroelasticity (FA) and ferroelectricity (FE) have potential applications in high-density data storage and sonar detectors. Here, based on first-principles calculations, we predict a series of stable 2D FA-FE multiferroic structures, namely γ-XOOH (X = Al, Ga, and In) monolayers. By analyzing the lattice symmetry and orientational distribution of hydroxyls, we find that XOOH monolayers possess both in-plane ferroelastic and ferroelectric polarization, as well as antiferroelectric ordering caused by the anti-parallel alignment of hydroxyls. Interestingly, the perpendicular reorientation of in-plane FE polarization accompanies 90° ferroelastic switching. Besides, they show an unusual negative transverse piezoelectric effect originated from the clamping-ion term. The multiferroic properties of the XOOH monolayers provide an excellent platform to study electroelastic effects.

The cycling performance of high-capacity lithium ion battery anodes can be significantly improved by adopting 3D nanoporous structures that can efficiently accommodate large volume changes during lithiation and de-lithiation. In this study, various molybdenum oxide nanoporous asymmetric membranes were fabricated on a large scale via a spontaneous non-solvent-induced phase separation process. We explored the effects of polymer precursor, membrane geometry, and annealing condition on the porosity, composition, and electrochemical properties of the membranes as lithium ion battery anodes. We demonstrate that 97% initial capacity of MoO2 planar asymmetric membrane electrode can be retained in 165 cycles at 120 mA g−1. 74% initial capacity can be maintained while the current density is increased from 60 to 480 mA g−1. This efficient and scalable process to prepare molybdenum oxide-based LIB anode provides another alternative to enhance the electrochemical performance of transition metal oxide anodes at a relatively low fabrication cost.

Density functional theory (DFT) calculations are performed to predict the structural, electronic and magnetic properties of electrically neutral or charged few-atomic-layer (AL) oxides whose parent systems are based on polar perovskite $KTaO_{3}$. Their properties vary greatly with the number of ALs ($n_{AL}$) and the stoichiometric ratio. In the few-AL limit ($n_{AL}\leqslant 14$), the even AL (EL) systems with chemical formula $(KTaO_{3})_{n}$ are semiconductors, while the odd AL (OL) systems with formula ($K_{n+1}Ta_{n}O_{3n+1}$ or $K_{n}Ta_{n+1}O_{3n+2}$) are half-metal except for the unique $KTa_{2}O_{5}$ case which is a semiconductor due to the large Peierls distortions. After reaching certain critical thickness ($n_{AL}>14$), the EL systems show ferromagnetic surface states, while ferromagnetism disappears in the OL systems. These predictions from fundamental complexity of polar perovskite when approaching the two-dimensional (2D) limit may be helpful for interpreting experimental observations later., Phys. Chem. Chem. Phys., 2021

Carbon nanosphere templates were prepared hydrothermally using glucose as a carbon source. A coated composite was formed by encapsulating the nanospheres with n-butyl titanate and calcinating the composite according to a controlled temperature programme to remove the carbon nanosphere templates; hollow-structured TiO2 nanospheres were obtained. Then, a TiO2/CQD nanocomposite was prepared with carbon quantum dots (CQDs) by covalent bonding. The structure and morphology of the carbon sphere templates, CQDs, TiO2 nanospheres and composite were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and other characterization techniques. The photocatalytic degradation of a methyl orange (MO) solution by the TiO2/CQD composite nanomaterial was studied. The results showed that the nanocomposites were hollow TiO2 spheres with a diameter of approximately 1.1 μm, a thickness of approximately 50 nm and a specific surface area of approximately 27.9 m2 g−1. The composite exhibited the highest visible light photocatalytic activity when the CQD content was 4.0%. The corresponding apparent first-order rate constant was 0.00429 min−1, which is 2.6 times greater than that of hollow TiO2.

Two-dimensional (2D) multiferroic materials, with combined large magnetic anisotropic energy (MAE) and high Curie temperature $({\mathbit{T}}_{C})$, have great potential in emerging electronic device applications, such as high-density multistate data storage and fast operation. However, various 2D spintronic materials fabricated in experiment, so far have small MAE and low ${\mathbit{T}}_{C}$. Using first-principles calculations, we proposed two $\mathrm{V}X$ $(X=\mathrm{P}, \mathrm{As})$ monolayers, which are identified to possess robust stability dynamically, thermally, and mechanically. $\mathrm{V}X$ monolayers are half-metals with coexisting ferroelastic and ferromagnetic properties. Moreover, their ground states exhibit significant in-plane MAEs of 101.48 and $262.68\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{eV}$ per V atom for VP and VAs monolayers, respectively. Additionality, the Curie temperatures of VP and VAs monolayers predicted from Heisenberg model are as high as 545 and 890 K, respectively, and the ferromagnetism could survive at room temperature. Our results are beneficial for further research on 2D multiferroics and provide the possibility for future nanodevices.

Two-dimensional ferromagnetic topological semi-metals have attracted much interest owing to their fascinating spintronic applications. Using first-principles calculations, we propose a stable transition metal nitrogen halide compound, namely, VNI monolayer, to display intrinsic ferromagnetism with high Curie temperature TC (∼510 K) and strong out-of-plane magnetism. It is found to be a topological Weyl nodal line material, which can be fully spin-polarized by controlling the on-site Coulomb interaction. Its nodal line can be destroyed by orienting the magnetization axis. Additionally, biaxial strain enables efficient tuning of the magnetic properties by switching the easy magnetic axis from an out-of-plane to in-plane direction with an enhanced TC to 540 K. These results highlight the great application potential of a VNI monolayer in low-dimensional topological magnets.

Transition-metal dichalcogenides are rich in their structural phases, e.g., $1T\ensuremath{-}\mathrm{Ta}{\mathrm{S}}_{2}$ and $1T\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$ form charge density wave (CDW) under low temperature with interesting and exotic properties. Here, we present a systematic study of different structures in two-dimensional $\mathrm{Ta}{X}_{2}$ ($X=\mathrm{S}$, Se, Te) using density-functional theory calculations with consideration of van der Waals interaction. All the normal phases present metal characteristics with various ground state and magnetic properties. The lattice reconstruction of CDW drastically affects the electronic and structural characteristics of $1T\ensuremath{-}\mathrm{Ta}{\mathrm{S}}_{2}$ and $1T\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$, leading to a transition from metal to insulator and an emergence of magnetic moment within periodic atomic clusters called the Star of David. The evaluated Heisenberg couplings indicate the weak ferromagnetic coupling between the clusters in monolayer. Furthermore, in bilayer commensurate CDW cases, we find the intriguing phenomenon of the varying magnetic properties with different stacking orders. The magnetic moment in each layer disappears when two layers are coupled, but may sustain in certain stackings of interlayer antiferromagnetic configurations.

Silicon as a promising candidate for the next-generation high-capacity lithium-ion battery anode is characterized by outstanding capacity, high abundance, low operational voltage, and environmental benignity. However, large volume changes during Si lithiation and de-lithiation can seriously impair its long-term cyclability. Although extensive research efforts have been made to improve the electrochemical performance of Si-based anodes, there is a lack of efficient fabrication methods that are low cost, scalable, and self-assembled. In this report, co-axial fibrous silicon asymmetric membrane has been synthesized using a scalable and straightforward phase inversion method combined with dip coating as inspired by the hollow fiber membrane technology that has been successfully commercialized over the last decades to provide billions of gallons of purified drinking water worldwide. We demonstrate that ~ 90% initial capacity of co-axial fibrous Si asymmetric membrane electrode can be maintained after 300 cycles applying a current density of 400 mA g−1. The diameter of fibers, size of silicon particles, type of polymers, and exterior coating have been identified as critical factors that can influence the electrode stability, initial capacity, and rate performance. Much enhanced electrochemical performance can be harvested from a sample that has thinner fiber diameter, smaller silicon particle, lower silicon content, and porous carbon coating. This efficient and scalable approach to prepare high-capacity silicon-based anode with outstanding cyclability is fully compatible with industrial roll-to-roll processing technology, thus bearing a great potential for its future commercialization.

Two-dimensional (2D) multiferroic materials with controllable magnetism have promising prospects in miniaturized quantum device applications, such as high-density data storage and spintronic devices. Here, using first-principles calculations, we propose a coexistence of antiferromagnetism and ferroelasticity in multiferroic $MnF_{4}$ monolayer. The $MnF_{4}$ monolayer is found to be an intrinsic wide-gap semiconductor with large spin polarization ~3 $\mu_{B}$/Mn, in which the antiferromagnetic order originates from the cooperation and competition of the direct exchange and super exchange. $MnF_{4}$ monolayer is also characterized by strongly uniaxial magnetic anisotropic behavior, that can be manipulated by the reversible ferroelastic strain and carrier doping. Remarkably, the carrier doping not only leads to an antiferromagnetic to ferromagnetic phase transformation, bult also could switch the easy magnetization axis between the in-plane and out-of-plane directions. In addition, the N\'eel temperature was evaluated to be about 140 K from the Monte Carlo simulations based on the Heisenberg model. The combination of antiferromagnetic and ferroelastic properties in $MnF_{4}$ monolayer provides a promising platform for studying the magnetoelastic effects, and brings about new concepts for next-generation nonvolatile memory and multi-stage storage.

Two-dimensional (2D) multiferroics have been casted great attention owing to their promising prospects for miniaturized electronic and memory devices.Here, we proposed a highly stable 2D multiferroic, VOF monolayer, which is an intrinsic ferromagnetic half semiconductor with large spin polarization ~2 $\mu_{B}/V$ atom and a significant uniaxial magnetic anisotropy along a-axis (410 $\mu eV/V$ atom). Meanwhile, it shows excellent ferroelectricity with a large spontaneous polarization 32.7 $\mu C/cm^{2}$ and a moderate energy barrier (~43 meV/atom) between two ferroelectric states, which can be ascribed to the Jahn-Teller distortion.Moreover, VOF monolayer harbors an ultra-large negative Poisson's ratio in the in-plane direction (~-0.34). The Curie temperature evaluated from the Monte Carlo simulations based on the Ising model is about 215 K, which can be enhanced room temperature under -4% compressive biaxial strain.The combination of ferromagnetism and ferroelectricity in the VOF monolayer could provide a promising platform for future study of multiferroic effects and next-generation multifunctional nanoelectronic device applications.

Two-dimensional (2D) multiferroic materials have great potential applications in multifunctional nanoelectronics devices. Here, we construct a series of stable and isolated monolayers as 2D manganese nitrohalides MnNX (X = F, Cl, Br, and I) and systematically investigate the structural, electronic and magnetic properties using first-principles and Monte Carlo simulations. We find that ground states simultaneously show in-plane ferroelasticity and room-temperature ferromagnetic properties. We also reveal that the in-plane magnetic anisotropy can be tunable by the uniaxial ferroelastic strain. Our results will provide significant implications for future experiments and the design of new functional materials at the nanoscale.

The nature of the interaction between magnetism and topology in magnetic topological semimetals remains mysterious, but may be expected to lead to a variety of novel physics. We present $ab$ $initio$ band calculations, electrical transport and angle-resolved photoemission spectroscopy (ARPES) measurements on the magnetic semimetal EuAs$_3$, demonstrating a magnetism-induced topological transition from a topological nodal-line semimetal in the paramagnetic or the spin-polarized state to a topological massive Dirac metal in the antiferromagnetic (AFM) ground state at low temperature, featuring a pair of massive Dirac points, inverted bands and topological surface states on the (010) surface. Shubnikov-de Haas (SdH) oscillations in the AFM state identify nonzero Berry phase and a negative longitudinal magnetoresistance ($n$-LMR) induced by the chiral anomaly, confirming the topological nature predicted by band calculations. When magnetic moments are fully polarized by an external magnetic field, an unsaturated and extremely large magnetoresistance (XMR) of $\sim$ 2$\times10^5$ % at 1.8 K and 28.3 T is observed, likely arising from topological protection. Consistent with band calculations for the spin-polarized state, four new bands in quantum oscillations different from those in the AFM state are discerned, of which two are topologically protected. Nodal-line structures at the $Y$ point in the Brillouin zone (BZ) are proposed in both the spin-polarized and paramagnetic states, and the latter is proven by ARPES. Moreover, a temperature-induced Lifshitz transition accompanied by the emergence of a new band below 3 K is revealed. These results indicate that magnetic EuAs$_3$ provides a rich platform to explore exotic physics arising from the interaction of magnetism with topology., 15 pages, with METHODS AND EXTENDED DATA

The nature of the interaction between magnetism and topology in magnetic topological semimetals remains mysterious, but may be expected to lead to a variety of novel physics. We systematically studied the magnetic semimetal EuAs3, demonstrating a magnetism-induced topological transition from a topological nodal-line semimetal in the paramagnetic or the spin-polarized state to a topological massive Dirac metal in the antiferromagnetic ground state at low temperature. The topological nature in the antiferromagnetic state and the spin-polarized state has been verified by electrical transport measurements. An unsaturated and extremely large magnetoresistance of ~2 × 105% at 1.8 K and 28.3 T is observed. In the paramagnetic states, the topological nodal-line structure at the Y point is proven by angle-resolved photoemission spectroscopy. Moreover, a temperature-induced Lifshitz transition accompanied by the emergence of a new band below 3 K is revealed. These results indicate that magnetic EuAs3 provides a rich platform to explore exotic physics arising from the interaction of magnetism with topology., Magnetic topological materials have a variety of interesting properties, but very few material realizations exist. Here, the authors report a topological nodal-line semimetal and a topological massive Dirac metal phase in EuAs3 and demonstrate a magnetism-driven transition between these phases.

The successful preparation of the freestanding perovskite materials down to the monolayer limit [Ji et al., Nature (London) 570, 87 (2019)] provided the opportunity to make the two-dimensional (2D) oxide and heterostructure, which could be significantly distinctive from the conventional oxide superlattices and other 2D van der Waals heterostructures. By stacking one unit-cell $\mathrm{BaTi}{\mathrm{O}}_{3}$ (BTO) and one unit-cell $\mathrm{SrTi}{\mathrm{O}}_{3}$ (STO) on top of each other, we constructed two isolated bilayers of the 2D heterostructure systems. From our density functional theory simulation, their ground states exhibit an in-plane ferroelectricity in both BTO layer and STO layer, while the antiferrodistortive mode of the STO layer is totally suppressed. These two systems show band gaps in the range of 2--2.5 eV (by using HSE06), which are smaller than their monolayer and bulk phases. The layer arrangement strongly influences their electronic properties. We reveal that they adopt the type-II electronic band alignment. The tensile biaxial strain can strongly promote the ferroelectricity and increase the band gaps of these systems. Our results will contribute to the further understanding of layered materials based on the transition metal oxide perovskites and developing relevant experimental devices.

Density functional theory calculations were performed for the electronic and the ferroelectric properties of the bulk and the monolayer benzylammonium lead-halide (BA2PbCl4). Our calculations indicate that both the bulk and monolayer systems display a band gap of ∼3.3 eV (HSE06+SOC) and a spontaneous polarization of ∼5.4 μC/cm2. The similar physical properties of bulk and monolayer systems suggest a strong decoupling among the layers in this hybrid organic-inorganic perovskite. Both the ferroelectricity, through associated structure distortion, and the spin-orbit coupling, through splitting induced in the electronic bands, significantly influence the band gaps. Most importantly, we found for the first time in a two-dimensional hybrid organic-inorganic class of material, a peculiar spin texture topology such as a unidirectional spin-orbit field, which may lead to a protection against spin decoherence.

Two-dimensional (2D) transition-metal oxide perovskites greatly expand the field of available 2D multifunctional material systems. Here, based on density functional theory calculations, we predicted the presence of ferromagnetism orders accompanying with an insulator-metal phase transition in bilayer $KNbO_{3}$ and $KTaO_{3}$ by applying strain engineering and/or external electric field. Our results will contribute to the applications of few-layer transition metal oxide perovskites in the emerging spintronics and straintronics., Comment: J. Phys. Chem. C 2021

Gadolinium hexaboride $({\mathrm{GdB}}_{6})$ is a well-known field emitter material that has been investigated for more than three decades. We perform a systematical density-functional theory study of ${\mathrm{GdB}}_{6}$ by using the generalized-gradient approximation and considering the electron interaction parameter $U$. The basic structural and electronic properties are carefully revised, as well as a strong $U$-value dependence in determining the antiferromagnetic (AFM) magnetic structures of Gd $4f$ electronic states. We found a small $U\phantom{\rule{4pt}{0ex}}(0\ensuremath{\sim}3$ eV) showing the most consistent experimental ground-state properties, which gives rise to a magnetic structure with a ground state of C-AFM and a second stable E-AFM. Moreover, we find the distortion modes of boron octahedron play an important role in the interaction between spin and lattice structures in this system. These results will deepen our understanding of the boron-based correlated rare earth compounds.

Temporary structures refer systems and assemblies without a permanent foundation, which will be removed after a certain period of time. In the past decades there have been numerous significant collapses of temporary structures in United States. To ensure structural stability and the safety, there is increasingly demand of developing an industry wide standard code, technology and procedure of temporary structure design, erecting, maintenance, monitoring and evaluation for practicing engineers and contractors. In this study, Digital Image Correlation was utilized for structure monitoring and failure detection of temporary structure during construction or loading period. The experimental results demonstrated the displacement measurement at the structural nodes could be used to determine the safety stage of the structure, predict the structural failure time and location. The aim of this research is to advance this state of the art measurement technology and facilitate a real-time automated monitoring and detection system for of structural failures of temporary structures.

Bamboo is a light weight, high strength natural composite. Although it has been wildly used in the world for thousand years, the mechanism of material enhancement and microstructure/property relationships has not been well understood yet. In this study, triple points bending tests were conducted for mechanical behavior characterization of natural composite-bamboo. Digital Image Correlation was utilized to determine the deformation and strain of a bamboo beam. It was found that (a) the material responses to the applied load had both a linear and a non-linear range, (b) the beam was stiffer when it had node at two ends, (c) the neutral axis shifted toward the tensile side of the beam during loading process, (d) when samples were reloaded, the material responses to the load were different, (e) negative Poisson’s ration was found in the high fiber density of the beam.

Continuing progress in high technology has created numerous industrial applications for new advanced composite materials. Among these materials, carbon fiber-reinforced plastic (CFRP) laminate composite is typically used for low-weight carrying structures that require high specific strength. In this study, the damage mechanism of a compact tension (CT) specimen of woven CFRP laminates is described in terms of strain and displacement changes and crack growth behavior. The digital image correlation (DIC) method (which is employed here as a computer vision technique) is analyzed. Acoustic emission (AE) characteristics are also acquired during fracture tests. The results demonstrate the usefulness of these methods in evaluating the damage mechanism for woven CFRP laminate composites. From the results, we show these methods are so useful in order to evaluate the damage mechanism for woven CFRP laminate composites.

An inverse approach for the identification of pressure loading on a structure has been proposed and developed. In this approach, surface measurements of structural response (e.g. strain, displacement and velocity field measurements, such as can be measured with 3D digital image correlation) are utilized as input data and are combined with numerical simulations to identify the pressure load on a structure. The inverse approach has been verified by numerical benchmarks involving pressure identification under quasi-static as well as dynamic impulse loading conditions, and also been validated by an experiment involving a quasi-static pressure load. The results indicate that the proposed inverse method can identify not only the magnitude of the quasi-static pressure but also the impulsive pressure loading history. The developed inverse approach offers an opportunity to apply inverse analysis techniques to identify interactive pressure loads (such as those resulting from a blast wave) on structures in explosive events.

A high-speed stereo-vision system is employed to quantify dynamic material response during buried blast loading. Deformation measurements obtained using 3D image correlation of synchronized, patterned stereo-vision images obtained with an inter-frame time in the range 16 μs ≤ t ≤ 40 μs indicate that (a) buried blast loading initially induces highly localized material response directly under the buried blast location, with severity of the blast event a strong function of depth of explosive burial, (b) for relatively shallow (deep) depth of explosive burial, plate surface velocities and accelerations exceed 220 m s−1 (100 m s−1) and 6 × 106 m s−2 (1.5 × 106 m s−1) during the first 30 μs (80 μs) after detonation, respectively. In addition, full-field plate deformation measurements demonstrate that the specimen experienced (c) measured effective strains exceeding 8% (5%) and effective strain rates exceeding 4000 s−1 (1500 s−1) during the first 50 μs (80 μs), respectively and (d) a blast-induced, circularly symmetric, transient bending wave was induced in the plate that travels with radial velocity of Mach 2 (1.25) during blast loading. By combining the Cowper–Symonds constitutive relation with full-field strain and strain rate measurements, well-defined yield boundaries are evident on the plate surface during blast loading; the presence of spatial gradients in yield stress has the potential to affect plate failure processes during transient blast loading events.

Texture patterns on transverse, longitudinal and horizontal cross-sections in friction stir welds (FSW) have been studied experimentally, and their variations with welding parameters have been analyzed. Numerical simulations of the FSW process have been carried out to understand the texture patterns. Results of this study suggest that the texture patterns are complex but a dominant theme is the appearance of bands, which occur in the advancing-side material. The banded pattern on the transverse cross-section is often in the form of onion rings. The spacing between the bands on the longitudinal and horizontal cross-sections equals the distance traveled by the welding tool in one revolution. The texture patterns are found to correlate well with equivalent plastic strain contours from simulations of the corresponding FSW process, suggesting that the texture patterns may be formed because periodically spaced material regions experience very different levels of plastic deformation during the FSW process.

The menopause-related expansion of the proximal femoral marrow cavity is thought to have implications for the long-term cohesion of hip prostheses. This theory would be further strengthened if there was evidence to show that the expansion of the proximal femur marrow cavity takes place after the occurrence of a femoral neck fracture, which, it is often recommended, should be fixed with a hip prosthesis. But till now, the temporal relationship between those two osteoporotic-related changes has not been checked carefully. The objective of the current study was to examine the temporal relationship between the marrow cavity expansion of the proximal femur and the biomechanical deterioration of the femoral neck in a rat model. To do so, a cross-sectional study with multiple time points was carried out on 6-month old Sprague-Dawley rats, which were ovariectomized or sham-operated (as controls). The biomechanical properties of the femur neck and geometrical parameters of the femur shaft were evaluated at 0, 3, 6, 9, 12, 15, 18, and 21 weeks postoperatively, with special reference to the timescale of the observed changes. We found that the maximum load of the femoral neck in ovariectomized rats could bear decreased significantly compared, to that of controls, at 9 weeks postoperatively (p=0.03), while the marrow cavity of the proximal femur in ovariectomized rats turned out to be significantly enlarged at 15 weeks postoperatively (p=0.04). Conclusion: Our result demonstrated that the osteoporosis-related marrow-enlarged posterior led to the collapse of femoral neck strength. If the change in postmenopausal women is analogous to that in ovariectomized rats, the menopause-related marrow cavity expansion would be a risk factor for the longevity of hip prostheses., Scandinavian Journal of Laboratory Animal Sciences, Vol 34, No 1 (2007)

Solid mechanics based finite element models and computational procedures have been developed by the authors to study and simulate the friction stir welding process. In this paper, two-dimensional simulation results of the material flow pattern and spatial velocity field around the rotating tool pin during welding, and the positions of material particles around the pin after welding, are presented. Material flow pattern predictions are found to compare favorably with experimental observations. Simulation results suggest that material particles in front of the tool pin tend to pass and get behind the rotating pin from the retreating side of the pin. Similarities between predicted velocity fields based on two different tool-workpiece interface models are described in detail, and implications of these findings (e.g., to fluid dynamics based models) are discussed.

The performance between the watermark scheme using contourlet tranform and that using non-subsampled contourlet transform (NSCT) is compared by a conventional watermark algorithm in this paper, which is rarely mentioned in existing literatures. The transparency analyses with subjective and objective evaluation indicators are performed on watermark scheme using contourlet tranform or NSCT. In addition, the corresponding robustness analyses to various attacks are also carried out. Through the contrast of the transparency and robustness, a conclusion can be drawn that NSCT is more suitable for watermark application than contourlet tranform.

A constrained three-dimensional atomistic model of a cracked aluminum single crystal has been employed to investigate the growth behavior of a nanoscale crack in a single crystal using molecular dynamics simulations with the EAM potential. This study is focused on the stress field around the crack tip and its evolution during fast crack growth. Simulation results of the observed nanoscale fracture behavior are presented in terms of atomistic stresses. Major findings from the simulation results are the following: (a) crack growth is in the form of void nucleation, growth and coalescence ahead of the crack tip, thus resembling that of ductile fracture at the continuum scale; (b) void nucleation occurs at a certain distance ahead of the current crack tip or the forward edge of the leading void ahead of the crack tip; (c) just before void nucleation the mean atomic stress (or equivalently its ratio to the von Mises effective stress, which is called the stress constraint or triaxiality) has a high concentration at the site of void nucleation; and (d) the stress field ahead of the current crack tip or the forward edge of the leading void is more or less self-similar (so that the forward edge of the leading void can be viewed as the effective crack tip).

A series of pressurization and tensile loading experiments on mouse carotid arteries is performed with deformation measurements acquired during each experiment using three-dimensional digital image correlation. Using a combination of finite element analysis and a microstructure-based constitutive model to describe the response of biological tissue, the measured surface strains during pressurization, and the average axial strains during tensile loading, an inverse procedure is used to identify the optimal constitutive parameters for the mouse carotid artery. The results demonstrate that surface strain measurements can be combined with computational methods to identify material properties in a vascular tissue. Additional computational studies using the optimal material parameters for the mouse carotid artery are discussed with emphasis on the significance of the qualitative trends observed.

There has been a great deal of effort focused on engineering polymer composites with hierarchical microstructures consisting of one or more ingredients that can be organized differently across multiple length scales. However, there are hierarchical microstructures that have evolved over eons in biological materials. These unique structure-property relationships may serve as templates for engineering hierarchically structured polymer composites with tailored properties. One such biological material is the Palmetto wood of South Carolina, which was successfully used as a protective structure during the Revolutionary and Civil Wars to absorb cannon shot. Through an assembly of microfibers into macrofibers embedded in a cellulose matrix, the Palmetto wood has optimized its ability to resist failure when subjected to extreme dynamic loading events, such as hurricanes. Understanding of the dynamic and static structure-property relationship in Palmetto wood can facilitate the development of new hierarchically structured polymer composites with increased resistance to failure. Therefore, the structure-property relationship in Palmetto wood has been studied using novel multiscale microstructural and mechanical characterization techniques. Models have been developed that indicate that the hierarchical structure of Palmetto wood obeys the linear Rule-of-Mixtures across multiple length scales. This understanding has led to the development of new polymer composite structures that exhibit properties similar to Palmetto wood using conventional laminated carbon fiber-epoxy composites and new polymer nanocomposites consisting of carbon nanofibers. The use of the nanofibers appears to enhance the interaction between the composite components in a manner similar to the interaction between fibers in the Palmetto wood that enables the laminated composite to behave more like the individual layers by resisting the tendency to delaminate and increasing the Weibull statistical parameters closer to those observed in Palmetto wood.