Driven weak to strong pinning crossover in partially nanopatterned 2H-NbSe2 single crystal

Investigations into the heterogeneous pinning properties of the vortex state created by partially nano-patterning single crystals of 2H-NbSe2 reveal an atypical magnetization response which is significantly drive dependent. Analysis of the magnetization response shows non-monotonic behavior of the magnetization relaxation rate with varying magnetic field sweep rate. With all the patterned pinning centers saturated with vortices, we find that the pinning force experienced by the vortices continues to increase with increasing drive. Our studies reveal an unconventional dynamic weak to strong pinning crossover where the flow of the vortex state appears to be hindered or jammed as it is driven harder through the interstitial voids in the patterned pinning lattice.Comment: 15 pages with 5 figure

Magnetic and transport properties of iron-platinum arsenide Ca10(Pt4-{\delta}As8)(Fe2-xPtxAs2)5 single crystal

We report superconducting properties of single crystalline Ca10(Pt4-{\delta}As8)(Fe2-xPtxAs2)5 by X-ray diffraction, magnetization, resistivity, and magneto-optical imaging measurements. The magnetization measurements reveal fish-tail hysteresis loop and relatively high critical current density Jc ~ 0.8\times105 A/cm2 at low temperatures. The exponential temperature dependence of Jc, which arises from nonlinear effective flux-creep activation energy, has been observed. Upper critical field determined by resistive transition shows a relatively large anisotropy. The magneto-optical images reveal homogenous current flow within the crystal.Comment: 6 pages, 6 figures, Accepted for publication in Phys. Rev.

A micromechanics based ductile damage model for anisotropic titanium alloys

The hot-workability of Titanium (Ti) alloys is of current interest to the aerospace industry due to its widespread application in the design of strong and light-weight aircraft structural components and engine parts. Motivated by the need for accurate simulation of large scale plastic deformation in metals that exhibit macroscopic plastic anisotropy, such as Ti, a constitutive model is developed for anisotropic materials undergoing plastic deformation coupled with ductile damage in the form of internal cavitation. The model is developed from a rigorous micromechanical basis, following well-known previous works in the field. The model incorporates the porosity and void aspect ratio as internal damage variables, and seeks to provide a more accurate prediction of damage growth compared to previous existing models. A closed form expression for the macroscopic yield locus is derived using a Hill-Mandel homogenization and limit analysis of a porous representative volume element. Analytical expressions are also developed for the evolution of the internal variables, porosity and void shape. The developed yield criterion is validated by comparison to numerically determined yield loci for specific anisotropic materials, using a numerical limit analysis technique developed herein. The evolution laws for the internal variables are validated by comparison with direct finite element simulations of porous unit cells. Comparison with previously published results in the literature indicates that the new model yields better agreement with the numerically determined yield loci for a wide range of loading paths. Use of the new model in continuum finite element simulations of ductile fracture may be expected to lead to improved predictions for damage evolution and fracture modes in plastically anisotropic materials

An unusual age presentation of mature cystic teratoma: a case report

Mature cystic teratoma compromise 20-30% of all ovarian tumours. They are mostly seen in patients between 20 and 40 years of age and are mostly asymptomatic. Malignancy incidence is high in postmenopausal group. Here, we report a case of mature cystic teratoma presenting unusually in a 65 year old postmenopausal woman with pain abdomen. A 65 year old postmenopausal woman presented with lower abdominal pain of 15 days duration. Upon examination, a mass of size 7×8 cm felt on bimanual examination. CT showed the same cyst that has a focal enhancing mural nodule with fat density in it. Total abdominal hysterectomy with bilateral salpingo oopherectomy done. Histopathological examination confirmed mature cystic teratoma. Although mature cystic teratoma is rare after 40 years age, especially in postmenopausal women and are usually malignant in that age group, it can have an unusual age presentation at 65 years with benign nature as in our case

A Contribution to the Modeling of Metal Plasticity and Fracture: From Continuum to Discrete Descriptions

The objective of this dissertation is to further the understanding of inelastic behavior in metallic materials. Despite the increasing use of polymeric composites in aircraft structures, high specific strength metals continue to be used in key components such as airframe, fuselage, wings, landing gear and hot engine parts. Design of metallic structures subjected to thermomechanical extremes in aerospace, automotive and nuclear applications requires consideration of the plasticity, creep and fracture behavior of these materials. Consideration of inelasticity and damage processes is also important in the design of metallic components used in functional applications such as thin films, flexible electronics and micro electro mechanical systems. Fracture mechanics has been largely successful in modeling damage and failure phenomena in a host of engineering materials. In the context of ductile metals, the Gurson void growth model remains one of the most successful and widely used models. However, some well documented limitations of the model in quantitative prediction of the fracture strains and failure modes at low triaxialities may be traceable to the limited representation of the damage microstructure in the model. In the first part of this dissertation, we develop an extended continuum model of void growth that takes into account details of the material microstructure such as the texture of the plastically deforming matrix and the evolution of the void shape. The need for such an extension is motivated by a detailed investigation of the effects of the two types of anisotropy on the materials' effective response using finite element analysis. The model is derived using the Hill-Mandel homogenization theory and an approximate limit analysis of a porous representative volume element. Comparisons with several numerical studies are presented towards a partial validation of the analytical model. Inelastic phenomena such as plasticity and creep result from the collective behavior of a large number of nano and micro scale defects such as dislocations, vacancies and grain boundaries. Continuum models relate macroscopically observable quantities such as stress and strain by coarse graining the discrete defect microstructure. While continuum models provide a good approximation for the effective behavior of bulk materials, several deviations have been observed in experiments at small scales such as an intrinsic size dependence of the material strength. Discrete dislocation dynamics (DD) is a mesoscale method for obtaining the mechanical response of a material by direct simulation of the motion and interactions of dislocations. The model incorporates an intrinsic length scale in the dislocation Burgers vector and potentially allows for size dependent mechanical behavior to emerge naturally from the dynamics of the dislocation ensemble. In the second part of this dissertation, a simplified two dimensional DD model is employed to study several phenomena of practical interest such as strain hardening under homogeneous deformation, growth of microvoids in a crystalline matrix and creep of single crystals at elevated temperatures. These studies have been enabled by several recent enhancements to the existing two-dimensional DD framework described in Chapter V. The main contributions from this research are: (i) development of a fully anisotropic continuum model of void growth for use in ductile fracture simulations and (ii) enhancing the capabilities of an existing two-dimensional DD framework for large scale simulations in complex domains and at elevated temperatures

Non-harmonic MM-elliptic pseudo differential operators on manifolds

In this article, we introduce and study $M$-elliptic pseudo-differential operators in the framework of non-harmonic analysis of boundary value problems on a manifold $\Omega$ with boundary $\partial \Omega$, introduced by Ruzhansky and Tokmagambetov ( Int. Math. Res. Not. IMRN, (12), 3548-3615, 2016) in terms of a model operator $\mathfrak{L}$. More precisely, we consider a weighted $\mathfrak{L}$-symbol class $M_{\rho, 0, \Lambda}^{m}, m\in \mathbb{R},$ associated to a suitable weight function $\Lambda$ on a countable set $\mathcal{I}$ and study elements of the symbolic calculus for pseudo-differential operators associated with $\mathfrak{L}$-symbol class $M_{\rho, 0, \Lambda}^{m},$ by deriving formulae for the composition, adjoint, and transpose. Using the notion of $M$-ellipticity for symbols belonging to $\mathfrak{L}$-symbol class $M_{\rho, 0, \Lambda}^{m}$, we construct the parametrix of $M$-elliptic pseudo-differential operators. Further, we investigate the minimal and maximal extensions for $M$-elliptic pseudo-differential operators and show that they coincide when the symbol $\sigma\in M_{\rho, 0, \Lambda}^{m},$ is $M$-elliptic. We provide a necessary and sufficient condition to ensure that the pseudo-differential operators $T_{\sigma}$ with symbol in the $\mathfrak{L}$-symbol class $M_{\rho, 0,\Lambda}^{0}$ is a compact operator in $L^{2}(\Omega)$ or a Riesz operator in $L^{p}(\Omega).$ Finally, we prove G\"arding's inequality for pseudo-differential operators associated with symbol from $M_{\rho, 0,\Lambda}^{0}$ in the setting of non-harmonic analysis.Comment: 4