Static Displacements and Short-Range Order in Ni-14 at. % Ir Alloy

In this paper, we are proposing a novel method to estimate static displacements of atoms caused by size effects in fcc substitutional binary polycrystalline solid solutions. Fourier transforms of static displacements of the atoms on every considered shell were calculated using the equations that include dynamical matrix and Fourier transform of interatomic forces. Short-range order parameters on the first seven shells of Ni-14 at. % Ir alloy have been identified from X-ray diffuse scattering intensity by accounting microscopic static displacements of atoms on a particular shell. Pairwise interatomic potentials on the considered shells and critical temperature of disorder-order phase transition were calculated using values of short-range order parameters.

Magnetic Normal Mode Calculations in Big Systems: A Highly Scalable Dynamical Matrix Approach Applied to a Fibonacci-Distorted Artificial Spin Ice

We present a new formulation of the dynamical matrix method for computing the magnetic normal modes of a large system, resulting in a highly scalable approach. The motion equation, which takes into account external field, dipolar and ferromagnetic exchange interactions, is rewritten in the form of a generalized eigenvalue problem without any additional approximation. For its numerical implementation several solvers have been explored, along with preconditioning methods. This reformulation was conceived to extend the study of magnetization dynamics to a broader class of finer-mesh systems, such as three-dimensional, irregular or defective structures, which in recent times raised the interest among researchers. To test its effectiveness, we applied the method to investigate the magnetization dynamics of a hexagonal artificial spin-ice as a function of a geometric distortion parameter following the Fibonacci sequence. We found several important features characterizing the low frequency spin modes as the geometric distortion is gradually increased.

A dynamical extracellular matrix coat regulates moruloid-blastuloid transitions of ovarian cancer spheroids

SummaryOvarian cancer metastasizes into the peritoneum through dissemination of transformed epithelia as multicellular spheroids 1, 2. Harvested from the malignant ascites of patients, spheroids exhibit startling features of organization typical to homeostatic glandular tissues3: lumen surrounded by smoothly contoured, adhered, and immotile epithelia. Herein, we demonstrate that cells of specific ovarian cancer lines in suspension, aggregate into dysmorphic solid ‘moruloid’ clusters that permit intercellular movement and penetration by new cells. Moruloid clusters can coalesce to form bigger clusters. Upon further culture, moruloid clusters mature into ‘blastuloid’ spheroids with smooth contours, lumen and immotile cells. Blastuloid spheroids neither coalesce nor allow penetration by new cells. Ultrastructural examination reveals a basement membrane-like matrix coat on the surface of blastuloid, but not moruloid, spheroids: immunocytochemistry confirms the presence of extracellular matrix proteins: Collagen IV and Laminin-322. Enzymatic debridement of the coat results in a reversible loss of lumen and contour. Debridement also allows spheroidal coalescence and cell intrusion in blastuloid spheroids and enhances adhesion to peritoneal substrata. Therefore, the dynamical matrix coat regulates both the morphogenesis of cancer spheroids and their adhesive interaction with their substrata, affecting ultimately the progression of the disease.ResultsSurvival of women afflicted with epithelial ovarian cancer (EOC) trails behind other gynecological malignancies, despite improvements in surgical-pharmacological approaches4,5. The morbidity associated with the disease is a consequence of its transcoelomic route of metastasis: transformed epithelia of the fallopian tubes and ovaries in the form of spheroids, eventually home and adhere to the mesothelial lining of the peritoneum, occasionally invade through the underlying collagenous extracellular matrix and form secondary metastatic foci around abdominal organs1, 6, 7. EOC spheroids impede the drainage of the fluid from the peritoneal cavity and alter its composition; in turn the fluid, now known as malignant ascites serves as a pro-tumorigenic milieu for the spheroids8, 9The formation and presence of spheroids within ascites of an ovarian cancer patient is strongly associated with recurrence of cancer and greater resistance to chemotherapy10. Therefore, in order to develop novel strategies to target spheroidal metastatic niche, it is essential to investigate mechanisms that underlie their morphogenesis. Several proteins have been proposed to mediate the adhesion between ovarian cancer epithelia that give rise to spheroids. These include transmembrane receptors such as CD4411, cell adhesion molecules, such as E-cadherin and N-cadherin12, matrix adhesion-inducing proteins such as integrins13, 14. Remarkably, a phase-contrast microscopic examination of spheroids from patients, or from aggregated epithelia of immortalized cancer lines cultured on low attachment substrata, shows features of morphogenetic organization: presence of a central lumen, radially arranged apposed epithelia and compacted surfaces. Such traits are cognate to organized morphogenesis within the glandular epithelial organs,15 which are built through principles that include, but are not limited to, cell-cell adhesion16, 17. In fact, loss of tissue architecture seen in tumorigenesis involves the disappearance of such morphogenetic traits (such as matrix adhesion and polarity)18, 19.In this manuscript, we investigate how these traits are recapitulated in a fluid metastatic context. Using spheroids from patients with high grade serous adenocarcinoma and ovarian cancer cell lines, we show that the development of a basement membrane (BM)-like coat of extracellular matrix is responsible for the compaction and stability of cancer spheroids, for decreasing the motility of cells within it and for generation of lumen. The coat, which is rapidly replenished by cells upon enzymatic debridement, also prevents the attachment of spheroids to matrix substrata. This may have significant implications for the build-up of the massive cellular fraction within the malignant ascites of patients afflicted with ovarian cancer.

Phonon heat transport properties of graphene based on molecular dynamics simulations and lattice dynamics

To choose an ideal method to study the phonon properties of graphene, the results of thermal conductivity (TC) of graphene computed using the equilibrium molecular dynamics (EMD), reverse nonequilibrium molecular dynamics (RNEMD) and direct nonequilibrium molecular dynamics (DNEMD) with Tersoff potential are compared, and we find that all of them are very close to each other. While two of them have been compared in the past, there is a lack of comparison of the three methods. Eventually, we choose the Green–Kubo method to study the temperature dependence of TC in graphene and find that the [Formula: see text] diverges with the system temperature T as [Formula: see text]T[Formula: see text] with [Formula: see text] and [Formula: see text] for the direction of armchair and zigzag, respectively, which is in reasonable agreement with the one in recent theoretical and experimental researches. To gain further insight into the TC, the phonon dispersion and the phonon density of states (PDOS), which depend on evaluating the eigenvalues and the eigenvectors of dynamical matrix, are calculated for graphene with dimensions of 30 × 30 unit cell by a combination of EMD simulations and lattice dynamics calculations.

Short-Range Order and Static Displacements in Polycrystalline Ni-13.1at. %W Alloy

A methodology accounting for the contributions of static displacements of atoms to X-ray diffuse scattering by binary solid solutions with a face-centered cubic lattice was proposed. By microscopic accounting of static displacements of the atoms on the particular shell, we identified short- range order parameters on the first eight shells of Ni-13.1at. %W alloy from the intensity of X-ray diffuse scattering. The Fourier transform of static displacement of the atoms on every considered shell was calculated with the De Launay model using expressions of elements of dynamical matrix and Fourier transforms of quasi elastic forces, which are calculated by the pseudopotential method.

Enhancement of thermoelectric figure of merit in zigzag graphene nanoribbons with periodic edge vacancies

The influence of periodic edge vacancies and antidot arrays on the thermoelectric properties of zigzag graphene nanoribbons (ZGNRs) are investigated. Using Green’s function method, the tight-binding approximation for the electron Hamiltonian and the 4th nearest neighbor approximation for the phonon dynamical matrix, we calculate the Seebeck coefficient and the thermoelectric figure of merit. It is found that, at a certain periodic arrangement of vacancies on both edges of zigzag nanoribbon, a finite band gap opens and almost twofold degenerate energy levels appear. As a result, a marked increase in the Seebeck coefficient takes place. It is shown that an additional enhancement of the thermoelectric figure of merit can be achieved by a combination of periodic edge defects with an antidot array.