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A derivative-free upscaled theory for analysis of defects
No full textNotwithstanding its recent focus on microstructure-driven nonclassical aspects, a breakthrough model in continuum mechanics that can evolve the macroscopic deformation of a solid body undergoing fracture whilst systematically incorporating the microstructural information remains elusive. In addressing this issue, we presently obtain, based on the molecular level information, a derivativefree balance law pertaining to a higher scale of interest and useful in a continuum or discrete setting. Derived using a probabilistic projection technique, the law exploits certain microstructural information in a weakly unique manner. The projection generalizes the notion of directional derivative and, depending on the application, may be interpreted as a discrete CauchyBorn map with the structure of the classical deformation gradient emerging in the infinitesimal limit. As an illustration, we use the Tersoff-Brenner potential and obtain a discrete macroscopic model for studying the deformation of a singlewalled carbon nanotube (SWCNT). The macroscopic (or continuum) model shows the effect of chirality - a molecular phenomenon - in its deformation profile. We also demonstrate the deformation of a fractured SWCNT, which is a firstofitskind simulation, and predict crack branching phenomena in agreement with molecular dynamics simulations. As another example, we have included simulation results for fractured SWCNT bundle with a view to establishing our claim regarding the efficacy of the proposed method. (C) 2018 Elsevier Ltd. All rights reserved
An algorithm for triangulating smooth three-dimensional domains immersed in universal meshes
No full textWe describe an algorithm to recover a boundary-fitting triangulation for a bounded C-2-regular domain omega subset of R3 immersed in a nonconforming background mesh of tetrahedra. The algorithm consists in identifying a polyhedral domain omega(h) bounded by facets in the background mesh and morphing omega(h) into a boundary-fitting polyhedral approximation omega(h) of omega. We discuss assumptions on the regularity of the domain, on element sizes and on specific angles in the background mesh that appear to render the algorithm robust. With the distinctive feature of involving just small perturbations of a few elements of the background mesh that are in the vicinity of the immersed boundary, the algorithm is designed to benefit numerical schemes for simulating free and moving boundary problems. In such problems, it is now possible to immerse an evolving geometry in the same background mesh, called a universal mesh, and recover conforming discretizations for it. In particular, the algorithm entirely avoids remeshing-type operations and its complexity scales approximately linearly with the number of elements in the vicinity of the immersed boundary. We include detailed examples examining its performance
An AFM tip replacement system compatible with all ambient media and operation modalities
No full textReplacement of an atomic force microscope (AFM) probe is an unavoidable aspect of the instrument's use, since its tip gets blunted or contaminated with use. Here, we propose a technique to replace only the tip of the AFM probe. Significantly, the technique is compatible with all the conventional modalities and media in which AFM is operated. The proposed technique employs a paraffin wax micro-particle as an integrated adhesive microgripper. By suitably controlling the phase of this material, it is employed to pick up and detach tips, and to grip them firmly while interacting with samples. The strategy has been experimentally demonstrated to work under conditions that are most likely to affect the microgripper integrity, namely, during contact mode imaging and in water. Despite this, the obtained images are shown to be identical to that obtained in air and with conventional probes. Further, reliability studies on the microgripper revealed that its lifetime is significantly higher than that of the probe-tip. Finally, the gripper has also been demonstrated to enable detachment of the AFM tip
Retreating rate of Chaturangi glacier, Garhwal Himalaya, India derived from kinematic GPS survey and satellite data
No full textThe regular monitoring of glaciers is important to determine their retreating rate and mass balance for overall glacier health. Chaturangi glacier, a major inactive tributary of the Gangotri glacier system was selected for the present study due to its dynamic nature and also because there are no previous records of its retreating rates. In order to reconstruct past retreating rates, total area loss, volume change and shift in snout position were measured through multi-temporal satellite data from 1989 to 2016 and kinematic GPS survey from 2015 to 2016. The results obtained from satellite data indicate that in the last 27 years Chaturangi glacier snout has retreated 1172.57 +/- 38.3 m (average = 45.07 +/- 4.31 m/year) with a total area and volume loss of 0.626 +/- 0.001 sq. km and 0.139 km(3) respectively. The field measurements through differential global positioning system survey revealed that the annual retreating rate was 22.84 +/- 0.05 m/year. The large variations in results derived from both the methods are probably because of higher difference in their accuracy. Nevertheless, the results derived from both the methods are in agreement that Chaturangi glacier is retreating at a considerable rate
Structural basis for species-selective targeting of Hsp90 in a pathogenic fungus
No full textNew strategies are needed to counter the escalating threat posed by drug-resistant fungi. The molecular chaperone Hsp90 affords a promising target because it supports survival, virulence and drug-resistance across diverse pathogens. Inhibitors of human Hsp90 under development as anticancer therapeutics, however, exert host toxicities that preclude their use as antifungals. Seeking a route to species-selectivity, we investigate the nucleotide-binding domain (NBD) of Hsp90 from the most common human fungal pathogen, Candida albicans. Here we report structures for this NBD alone, in complex with ADP or in complex with known Hsp90 inhibitors. Encouraged by the conformational flexibility revealed by these structures, we synthesize an inhibitor with >25-fold binding-selectivity for fungal Hsp90 NBD. Comparing co-crystals occupied by this probe vs. anticancer Hsp90 inhibitors revealed major, previously unreported conformational rearrangements. These insights and our probe's species-selectivity in culture support the feasibility of targeting Hsp90 as a promising antifungal strategy
Computational Modeling of the Crosstalk Between Macrophage Polarization and Tumor Cell Plasticity in the Tumor Microenvironment
No full textTumor microenvironments contain multiple cell types interacting among one another via different signaling pathways. Furthermore, both cancer cells and different immune cells can display phenotypic plasticity in response to these communicating signals, thereby leading to complex spatiotemporal patterns that can impact therapeutic response. Here, we investigate the crosstalk between cancer cells and macrophages in a tumor microenvironment through in silico (computational) co-culture models. In particular, we investigate how macrophages of different polarization (M1 vs. M2) can interact with epithelial-mesenchymal plasticity of cancer cells, and conversely, how cancer cells exhibiting different phenotypes (epithelial vs. mesenchymal) can influence the polarization of macrophages. Based on interactions documented in the literature, an interaction network of cancer cells and macrophages is constructed. The steady states of the network are then analyzed. Various interactions were removed or added into the constructed-network to test the functions of those interactions. Also, parameters in the mathematical models were varied to explore their effects on the steady states of the network. In general, the interactions between cancer cells and macrophages can give rise to multiple stable steady-states for a given set of parameters and each steady state is stable against perturbations. Importantly, we show that the system can often reach one type of stable steady states where cancer cells go extinct. Our results may help inform efficient therapeutic strategies
Unveiling regions in multi-scale Feynman integrals using singularities and power geometry
No full textWe introduce a novel approach for solving the problem of identifying regions in the framework of Method of Regions by considering singularities and the associated Landau equations given a multi-scale Feynman diagram. These equations are then analyzed by an expansion in a small threshold parameter via the Power Geometry technique. This effectively leads to the analysis of Newton Polytopes which are evaluated using a Mathematica based convex hull program. Furthermore, the elements of the Grobner Basis of the Landau Equations give a family of transformations, which when applied, reveal regions like potential and Glauber. Several one-loop and two-loop examples are studied and benchmarked using our algorithm which we call ASPIRE
In Situ Neutron Diffraction Studies of LiCe(WO4)(2) Polymorphs: Phase Transition and Structure-Property Correlation
No full textPolymorphs of LiCe(WO4)(2) alpha-LiCe(WO4)(2) and beta-LiCe(WO4)(2)] were successfully synthesized by a citric acid-assisted sol-gel method for the first time. Phase purity and crystallinity were confirmed by powder X-ray diffraction and further characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, Raman, and thermogravimetric-differential thermal analysis measurements. Investigation of the effect of calcination temperature and time indicated the existence of an irreversible structural phase transition from low-temperature (LT) beta-phase to high-temperature (HT) alpha-phase, which is systematically followed by in situ HT powder neutron diffraction (NPD) studies. Rietveld refinements using NPD data revealed that alpha-LiCe(WO4)(2) crystallizes in tetragonal Scheelite-type structure (I4(1)/a), while beta-LiCe(WO4)(2) crystallizes in triclinic alpha-LiPr-(WO4)(2)-type structure (P (1) over bar). Furthermore, beta-LiCe(WO4)(2) undergoes a reconstructive phase transition where WO6 of the beta-phase rearranges to WO4 at HT in alpha-phase and is supported by Raman measurements. Anodic redox activities of these polymorphs were determined by cyclic voltammetry and galvanostatic charge-discharge measurements. Interestingly, beta-phase has shown promising results compared with that of alpha-phase, which is attributed to the easy Li-ion diffusion in between the parallel layers of WO6 and also to the greater structural stability of the beta-phase. Thus, our initial understanding on the structure-property of these LiCe(WO4)(2) polymorphs provides insights into the design of new insertion anode electrodes for Li-ion batteries
Sound radiation from a finite perforated panel set in a rigid baffle: A fully coupled analysis
No full textA fully coupled formulation is presented for sound radiation from a finite flexible perforated panel set in an infinite rigid unperforated baffle. The panel is excited by a point harmonic force and radiates sound into the acoustic medium on both sides of the baffle. Prior to coupling with the fluid, the change in the inertial and stiffness properties of the panel due to perforations and their effect on the in vacuo natural frequencies and mode shapes are accounted for using the receptance method. The coupled acoustic and structural equations are formulated using the 2-D wavenumber transforms. Since the formulation is in terms of the panel velocity, a certain square root singularity that typically appears in the denominator is avoided. The self- and inter-modal coupling coefficients are evaluated either analytically or numerically. The radiated power, panel mean quadratic velocity and radiation efficiency plots are obtained for different perforation ratios for both center and off-center excitations. At first, our formulation is validated against an unperforated case using a study available in the literature. Next, for our perforated panel case, we assume that both the half-spaces are filled with the acoustic fluid. It is observed that the radiation efficiency decreases with the increase in the perforation ratio, irrespective of the surrounding acoustic medium. However, for the water-loaded panel, the radiation efficiency is found to be lower than when the panel is immersed in air. It is found that for a light fluid like air, a one-way coupled formulation is adequate. The natural frequencies of a water-loaded perforated panel are also presented. It is found that for a given mode, the natural frequency increases with increase in the perforation ratio, (C) 2018 Elsevier B.V. All rights reserved
Antecedents of behavioural and reproductive dominance in pairs of the primitively eusocial wasp Ropalidia marginata
No full textWhat factors predispose some individuals to become reproductively dominant in a group where every member can reproduce? Antecedents of reproductive dominance have often been investigated in primitively eusocial species where reproductive skew exists despite adult reproductive potential displayed by every group-member, but such studies have rarely focused on small, incipient colonies. Here, I investigated antecedents of behavioural and reproductive dominance in pairs of the Indian paper wasp Ropalidia marginata. Common antecedents of behavioural dominance such as body size and age were inoperative in pairs of R. marginata. Moreover, age and behavioural dominance, but not body size, influenced reproductive dominance in pairs. These findings are not only different from other primitively eusocial insects, but also different from the colonies of R. marginata. It is likely that antecedents of reproductive dominance are different not only in different species, but also change with group size within a species, such that the role of behavioural dominance to achieve reproductive monopoly remains more effective in small groups such as pairs, and becomes less effective as the group size increases. These results require further investigations into the effect of group size on individual behaviour in group-living animals