The aims of this study are to go beyond the scope of the existing studies (e.g. (Ferrara and Pandolfi, 2010; Gasser and Holzapfel, 2007; Gasser and Holzapfel, 2006; Leng et al., 2015b)) to gain a mechanical understanding of the plaque rupture phenomenon at the microscopic scale. Firstly, a uniaxial tensile test on a single tow of collagen fibers from porcine arterial wall was performed in order to acquire the elastic modulus, tensile strength and strain at failure. Secondly, the interfacial strength of interface across fibers was obtained through best fitting of the load-displacement curve from the simulation predictions with the experimental measurements. Finally, these parameter values were used as input data for a micromechanical model of a plaque-arterial wall system, which was developed based on experimental observations and the cohesive zone model approach. The failure mechanism at the microscopic scale (such as possible collagen fiber breakage) was incorporated to develop a three-dimensional unitcellmodel, which will enable the characterization of the cohesive traction-separation relation and the factors at the micromechanical scale affecting this relation that plays an important role for the understanding of micromechanical mechanism in plaque rupture.
The Wigner-Seitz unitcell (rhombus) for a honeycomb lattice fails to establish a k -vector in the 2D space, which is required for the Bloch electron dynam- ics. Phonon motion cannot be discussed in the triangular coordinates, either. In this paper, we propose a rectangular 4-atom unitcellmodel, which allows us to discuss the electron and phonon (wave packets) motion in the k -space. The present paper discusses the band structure of graphene based on the rec- tangular 4-atom unitcellmodel to establish an appropriate k -vector k for the Bloch electron dynamics. To obtain the band energy of a Bloch electron in graphene, we extend the tight-binding calculations for the Wigner-Seitz (2- atom unitcell) model of Reich et al. ( Physical Review B , 66, Article ID: 035412 (2002)) to the rectangular 4-atom unitcellmodel. It is shown that the gra- phene band structure based on the rectangular 4-atom unitcellmodel reveals the same band structure of the graphene based on the Wigner-Seitz 2-atom unitcellmodel; the π -band energy holds a linear dispersion ( ε − k ) relations near the Fermi energy (crossing points of the valence and the conduction bands) in the first Brillouin zone of the rectangular reciprocal lattice. We then confirm the suitability of the proposed rectangular (orthogonal) unitcellmodel for graphene in order to establish a 2D k -vector responsible for the Bloch electron (wave packet) dynamics in graphene.
In this study, the results are presented of a computational and experimental investigation on the tensile behavior of Lyocell/epoxy composites. The limitations of assumptions of using linear elastic properties in modeling of regenerated cellulose composites are illustrated. The mechanical properties of Lyocell tows are investigated under dry and wet conditions showing bilinear and nonlinear elastic– plastic responses. A multi-scale unitcellmodel incorpo- rating a bilinear elastic–plastic stress–strain behavior can be approximated for the dry fibers. As the fibers absorb moisture, the knee of the stress–strain response shifts to the early stages of loading. Nonlinear behavior and a drastic loss in modulus are observed for the wet fibers. In com- posite form, the behavior under wet conditions was less pronounced due to the barrier properties of the epoxy resin. Manufacturing composites from Lyocell fibers possesses unique challenges due to the hydrophilic and pilling nature of these fibers. The use of resin infusion produced higher FVF but some unwetted areas were seen even at high vacuum pressures. The use of wet layup followed by degassing overcomes that problem, but may be an issue when thicker parts or more complex geometries are desired. The speed of preparation is also an issue since the resin takes around 35 min to harden and mold filling of large structures would need to account for this. The FE approach using p-FEA incorporating the bilinear constitu- tive response of Lyocell was proposed for possible mod- eling of these composites and predicting the composite behavioral response. The results show that the model was successfully used to predict the loading behavior of these composites under different fiber contents in dry conditions. The model can also be easily extended to determine the elastic–plastic orthotropic material constants by varying the boundary conditions. Future structural mechanics tools can use the proposed approach to incorporate the effects of moisture absorption on thermoset/regenerated cellulose composites.
Nonlinear electro-mechanical behaviors of piezoelectric materials and viscoelastic nature of po- lymers result in the overall nonlinear and hysteretic responses of active polymeric composites. This study presents a hybrid-unit-cellmodel for obtaining the effective nonlinear and rate-de- pendent hysteretic electro-mechanical responses of hybrid piezocomposites. The studied hybrid piezocomposites consist of unidirectional piezoelectric fibers embedded in a polymeric matrix, which is reinforced with piezoelectric particles. The hybrid-unit-cellmodel is derived based on a unit-cellmodel of fiber-reinforced composites consisting of fiber and matrix subcells, in which the matrix subcells are comprised of a unit-cellmodel of particle-reinforced composites. Nonlinear electro-mechanical responses are considered for the piezoelectric constituents while a viscoelas- tic solid constitutive model is used for the polymer constituent. The hybrid-unitcellmodel is used to examine the effects of different responses of the constituents, microstructural arrangements, and loading histories on the overall nonlinear and hysteretic electro-mechanical responses of the hybrid piezocomposites, which are useful in designing active polymeric composites.
Figure 3.2.13 shows the powder diffraction pattern for RbVSH. Two sets of scans were recorded. High angle data recorded between 20 values of 126° and 156° were recorded first, followed by a long scan from 14° to 156°. This was done in order to check that the high angle data was consistent Figure 3.2.13 (b) shows the two sets of high angle data recorded. The top scan was recorded first; the bottom scan was recorded ca. 16 hours later. In this alum, there is negligible change in both the positions and intensities of the high angle data for the two data sets. Figure 3.2.14 shows a plot of unitcell parameters for several high angle reflections versus the function l/2[cos^0/0 + cos%/sin0]. A straight line can be drawn through the points. The unitcell parameter is the value at the intercept which is 12.347(1) Â. No value of the unitcell obtained from any reflection is greater than 0.001 Â from the straight line joining the points indicating that this is a precise measurement Figure 3.2.15 shows the powder diffraction pattern for "Pmix45" whose Raman spectra are shown in figures 3.2.5 - 3.2.7. It is noted that there is a slight change in the relative intensities of the peaks from the two scans. This can only mean that there is some change in atomic positions, likely to be a result of either aerial oxidation or acquisition of water fi*om the atmosphere. Similar behaviour was observed for other alums whose diffraction patterns were recorded in this study. The peaks do, however, occur at the same positions for the two scans indicating that within experimental error, there is no change in the unitcell parameter.
The unitcell geometries used for the SRR, BC-SRR and DSRR structures are described in Figures 1(a), 1(b) and 1(c), respectively, where the overall cell sizes as well as the split ring dimensions are kept the same for all three structures for fair comparison of the simulation results. The unit cells shown in Figure 1 have the common geometrical parameters of L = 5 mm (side length of the square shaped substrate surface), l = 4 mm and h = 3 mm (side lengths of the rectangular shaped outer ring), g = 0.5 mm (gap distance or slit length) and w = 0.3 mm (width of the metal ring). The rings of the resonators are made of copper lines with the metal thickness of 0.03 mm and conductivity of 5.8 × 10 7 S/m. The parameter s refers to the planar
The design parameters of a doubly layered exponentially Tapered Slot Antenna (DTSA) are defined in Figures 1 and 2. Figure 1(a) illustrates the commercially available electromagnetic simulator HFSS model of the proposed geometry of DTSA. It consists of a section of slotline that is narrow at one end and has opening in an exponential flare at the other end. The antenna geometry can be classified into two categories: substrate parameters (relative dielectric constant, ε r , and thickness,
consists of two identical but oppositely oriented split tube resonators (Figure 6d). The gap between two adjacent unit cells allows air to flow through the structure. The high absorption of the sound wave has resulted from the weak coupling of two split tube resonators. A 3D printed sample is fabricated from polylactide (PLA) plastic for the experimental measurements (Figure 6d). The experimental result shows the maximum sound absorption of 82.1% at 342 Hz and no significant change in absorption under the oblique incidence (up to 60 ◦ ). Shen et al.  presented the two-dimensional ventilated acoustic metacages with a subwavelength thickness (Figure 6e). A ring-shaped structure is created by the radial arrangement of the metacages, and each metacage is composed of several shunted Helmholtz resonators with increasing heights along the radial direction. The structure is capable of shielding the noise coming from all directions while allowing substantial airflow through a gap between two adjacent metacage. An omnidirectional acoustic shielding is realized by the fabricated structure. Li et al.  demonstrated a broadband compact acoustic absorber for the low-to-mid frequency noise absorption while ensuring high ventilation for air passage. The structure is constructed by attaching the eight unit cells to the outer periphery of the square-shaped hollow tube. Each unitcell consists of a double-layered metastructure with micro-perforated holes on opposite sides. Figure 6f shows the schematics of the proposed absorbers. The perforated unit cells serve for the sound attenuation while the hollow tube provides the passage for air ventilation (70% cross-section open). They experimentally showed the high absorption (>0.5) in the frequency range of 850–1000 Hz.
The effective material values which are obtained by such techniques are an important result for the synthesis of the composites. However, their main purpose is to be used in the design process of large-scale components, where the novel properties of metamaterials shall be profitably used. Thus, the extraction results should of course be as accurate as pos- sible, in the sense that the equivalent model can describe the behavior of the metamaterial within the interesting frequency band. However, the model should also be physical, i.e. it should be passive (as long as no active materials are present on the microscopic scale) and last but not least it should be causal. As a critical review of published results (such as, e.g., in Simovski and Tretyakov, 2007) shows, these properties are sometimes not fulfilled, and it seems as if this is not a result of shortcomings in the respective implementations.
The properties of molecular monolayers can depend strongly on whether the system is above or below a phase transition. For the side-aligning domino system below the critical temperature, the system enters a crystalline phase shown in Figure 1.13, where the domino-domino correlations extend indefinitely. This phenomena can be thought of in the context of the large scale behaviour of the height function of the domino tiling, which is affected by the interactions between dominoes. In the large scale limit, the height function approximates a continuous function, with a corresponding action to determine the behaviour at a given temperature . At low temperature, a potential term promotes domino ordering. Conversely, at high temperature, an entropic term dominates, causing the height function to become rough. Indeed, in the high-temperature regime, the height fluctuations have the same Gaussian free field property as those of the non-interacting model . This property in the interacting model has been suggested for some time, but was proved recently .
The Phoenix cell reﬂectarray using proposed radiating elements has been designed and fabricated. A photograph of the reﬂectarray prototype is given in Figure 6. The reﬂectarray consists of 15 × 15 elements printed on a grounded substrate with thickness h = 1 . 6 mm and relative permittivity ε r = 4 . 4 and tan δ = 0 . 02. The element spacing is h 1 = 8 mm so that the size of the reﬂectarray is 180 × 180 mm 2 .
tion of the individual magnetic moments, it follows from Eq. (1) that the toroidal moment contains information about where the magnetic moments are located as well as on how they are oriented. Furthermore, the toroidal moment is a macroscopic multipole moment that is re- lated to the (magnetic) point group symmetry, whereas a proper symmetry analysis of antiferromagnetic order requires a treatment based on the full space group sym- metry. In particular, antiferromagnetic order is not con- nected to any particular macroscopic symmetry break- ing, i.e. all 90 magnetic point groups are compatible with the existence of antiferromagnetic order. On a mi- croscopic space group level, antiferromagnetic order of course always breaks time reversal symmetry. However, for systems where the magnetic unitcell is a multiple of the crystallographic unitcell, a primitive translation of the original nonmagnetic lattice can be combined with time reversal, and as a result the corresponding magnetic point group still contains time reversal as a symmetry element. 34 In contrast, a toroidal moment always breaks
systems like Y-123 and Bi-2212. Most of the recent theoretical studies related to ARPES electronic spectra are based on the two dimensional tight binding Hubbard model and its extension within numerical and analytical approaches and the role of third dimensional coupling on the spectra in the presence of electrons correlation effect has not been clearly understood so far. Therefore, it would be interesting to study the effect of intra cell cou- pling, inter unitcell resonant tunneling, and electronic correlations simultaneously on the spectral function in doped multilayer cuprates in normal state.
A novel improved version of unit-cell for the design of composite right left handed transmission line (CRLH TL) is reported in this paper. Comparative results of both conventional design of unit-cell and proposed design of unit-cell for CRLH TLs are presented in this article. The conventional unit-cell is designed based on inter digital capacitor (IDC) in series and vias to the ground plane at the stub ends in shunt, whereas proposed unit- cell is designed based on wire bonded interdigital capacitor (WBIDC) in series and vias to the ground plane at the stub ends in shunt . Use of WBIDC in the proposed unit-cell improves high frequency performance by reducing undesired self resonances generated in IDC at lower frequency end. A simple technique is also used in both designs to miniaturize the unit-cell profiles. Dispersion diagrams of the unit-cells show the presence of self resonances in the conventional IDC based unit-cell and absence of such self resonances in the proposed WBIDC based unit-cell, which causes the wider operational frequency band of WBIDC based unit-cell. The performances of both unit-cells are compared from dispersion curve and S-parameters characteristics. The frequency parameter and performance of the both unit-cells are evaluated by full-wave electromagnetic simulator using Ansoft Designer, based on method of moment.
In this paper, we unambiguously show that “sub-atomic like” features can arise from the back bonding configuration of a surface atom being imaged during DFM. This is done by utilising the change in bonding configuration of the surface adatoms of the Si(111) unitcell between the faulted and unfaulted half. Due to this change in symmetry across the unitcell, the features we observe cannot be assigned to any tip, or feedback artefacts. At the same time, they suggest caution should be used when interpreting “sub-atomic like” features, as our data cannot be interpreted as arising from within a single atom.