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A Technique for Estimation of Residual Stress and Young's Modulus of Compressively Stressed Thin Films Using Microfabricated Beams
No full textPredictive design of MEMS devices and their performance evaluation require post-fabrication measurement of essential material properties, such as Young's modulus and residual stress, as these are usually affected by fabrication process conditions. To our knowledge, few techniques exist for the measurement of residual stress in micromechanical structures fabricated from compressively-stressed amorphous dielectric thin films. Here, we propose a method for estimating residual stress and Young's modulus from the post-buckling dynamic response of fixed-fixed microbeams and frequency response of cantilevers, respectively. Static deflection profiles and first natural frequencies of buckled beams are used in this analysis. Further, the proposed method uses the length of the beams as an unknown to account for the variation in the actual length of a fabricated beam due to the presence of undercut. The effective length is simultaneously determined from the analysis of the measured data using multi-parameter curve fitting. Use of post-buckling analysis makes this technique useful for thin films with high compressive stresses. Since the proposed method does not involve electrostatic actuation, it is applicable for dielectric thin films in addition to crystalline and conducting films. Using the proposed method, residual stress is estimated in amorphous silicon carbide thin films deposited by PECVD and reactive-sputtering. In addition, the modulus values of three materials (PECVD SiNx, PECVD SiC, and sputtered SiC) are estimated and compared with reported results. 2019-0090
Sparse Sampling for Inverse Problems With Tensors
No full textWe consider the problem of designing sparse sampling strategies for multidomain signals, which can be represented using tensors that admit a known multilinear decomposition. We leverage the multidomain structure of tensor signals and propose to acquire samples using a Kronecker-structured sensing function, thereby circumventing the curse of dimensionality. For designing such sensing functions, we develop low-complexity greedy algorithms based on submodular optimization methods to compute near-optimal sampling sets. We present several numerical examples, ranging from multiantenna communications to graph signal processing, to validate the developed theory
Visible-Light-Mediated Direct Decarboxylative Acylation of Electron-Deficient Heteroarenes Using alpha-Ketoacids
No full textAcylation of electron-deficient heteroaromatic compounds has been developed using visible light. alpha-Ketoacids have been used as an efficient source of acyl radicals under photoredox conditions. The in situ generated acyl radicals from alpha-ketoacids have been coupled to a wide variety of electron-deficient heteroaromatic compounds in a Minisci type reaction. This method would be attractive to access biologically attractive molecules
Simulation of viscoelastic two-phase flows with insoluble surfactants
No full textA stabilized finite element scheme is developed for computations of buoyancy driven 3D-axisymmetric viscoelastic two-phase flows with insoluble surfactants. The numerical scheme solves the Navier-Stokes equations for the fluid flow, Giesekus constitutive equation for the effects of viscoelasticity and simultaneously an evolution equation for the surfactant concentration on the interface. The interface is tracked by the coupled arbitrary Lagrangian-Eulerian (ALE) and Lagrangian approach. The interface-resolved moving meshes allow accurate incorporation of the interfacial tension force, Marangoni forces and the jumps in the material properties. Further, the tangential gradient operator technique is used to handle the curvature approximation in a semi-implicit manner. An one-level Local Projection Stabilization (LPS), which is based on an enriched approximation space and a discontinuous projection space, where both spaces are defined on a same mesh is used to stabilize the model equations. The stabilized numerical scheme allows us to use isoparametric second order conforming finite elements enriched with cubic bubble functions for velocity and viscoelastic stress, second order finite elements for surfactant concentration and discontinuous first order finite element for pressure. A number of computations are performed for a Newtonian drop rising in a viscoelastic fluid column and a viscoelastic drop rising in a Newtonian fluid column with insoluble surfactants on the interface. The influence of the Marangoni number, initial surfactant concentration and Peclet number on the dynamics of the rising drop are analyzed. The numerical study shows that a viscoelastic drop rising in a Newtonian fluid column develops an indentation around the rear stagnation point with a dimpled shape without insoluble surfactants. The presence of insoluble surfactants forces the drop to rise slowly but the drop at the tail end is pulled up more. However, a Newtonian drop rising in a viscoelastic fluid column experiences an extended trailing edge with a cusp-like shape without insoluble surfactants. The presence of surfactants pulls the tail end of the drop up slightly and makes the tail flatter with/without small undulations depending on the magnitude of the surfactant concentrations
Biochemical insights into the recombinant 10-deacetylbaccatin III-10-beta-O-acetyltransferase enzyme from the Taxol-producing endophytic fungus Lasiodiplodia theobromae
No full text10-deacetylbaccatin III-10-beta-O-acetyltransferase (DBAT) is a key rate-limiting enzyme of the Taxol biosynthetic pathway, which is uncharacterized in Taxol-producing endophytic fungi. Here, an open reading frame of DBAT was cloned from the Taxol-producing endophytic fungus Lasiodiplodia theobromae (LtDBAT). The LtDBAT enzyme was heterologously expressed and purified by the affinity and gel filtration chromatography methods. The molecular weight of the purified protein was 49 kDa and its identity was confirmed by western blot. The purified LtDBAT enzyme was capable of catalyzing 10-deacetylbaccatin III into baccatin III, as shown by liquid chromatography-mass spectroscopy. The mass spectra of baccatin III were identical to the authentic baccatin III. The LtDBAT enzyme was characterized and the kinetic parameters of catalysis were determined. In addition, localization of LtDBAT was performed by using confocal microscopy and the result showed that the enzyme was localized in lipid droplets. Together, this study provides biochemical insights into the fungal recombinant DBAT enzyme that is involved in the Taxol biosynthetic pathway. In the near future, engineering of the LtDBAT enzyme and the Taxol biosynthetic pathway in endophytic fungi could be an eco-friendly and economically feasible alternative source for production of Taxol and its precursors
Magnetic hyperthermia adjunctive therapy for fungi: in vitro studies against Candida albicans
No full textThe poor penetration of anti-fungal agents into the cornea through the intact epithelium layer makes it difficult to treat acute fungal corneal infections. Herein, we developed Amphotret (amphotericin B) antifungal drug contained polycaprolactone-Fe3O4 (PCL-FO) magnetic nanofibers (MNFs) using the electrospinning technique. These MNFs generate heat in the presence of AC magnetic field (AMF) and release drug upon heating. MNFs were compatible with human mesenchymal stem cells (hMSCs) and HeLa cells, which exhibited unaltered proliferation, ruling out any toxicity from the systems. Hyperthermia induced via MNFs from 42 degrees C to 50 degrees C compromised the viability of Candida albicans cells. Further, the efficacy of the systems was increased in the presence of both heat and drug simultaneously in vitro, leading to near 100% loss in viability of C. albicans cells at 50 degrees C with simultaneous drug release from MNFs. Thus, we propose magnetic hyperthermia as adjunctive therapy for fungal keratitis
Tinkering with targeting nucleotide signaling for control of intracellular Leishmania parasites
No full textNucleotides are one of the most primitive extracellular signalling molecules across all phyla and regulate a multitude of responses. The biological effects of extracellular nucleotides/sides are mediated via the specific purinergic receptors present on the cell surface. In mammalian system, adenine nucleotides are the predominant nucleotides found in the extracellular milieu and mediate a constellation of physiological functions. In the context of host-pathogen interaction, extracellular ATP is recognized as a danger signal and potentiates the release of pro-inflammatory mediators from activated immune cells, on the other hand, its breakdown product adenosine exerts potential anti-inflammatory and immunosuppressive actions. Therefore, it is increasingly apparent that the interplay between extracellular ATP/adenosine ratios has a significant role in coordinating the regulation of the immune system in health and diseases. Several pathogens express ectonucleotidases on their surface and exploit the purinergic signalling as one of the mechanisms to modulate the host immune response. Leishmania pathogens are one of the most successful intracellular pathogens which survive within host macrophages and manipulate protective Th1 response into disease promoting Th2 response. In this review, we discuss the regulation of extracellular ATP and adenosine levels, the role of ATP/adenosine counter signalling in regulating the inflammation and immune responses during infection and how Leishmania parasites exploit the purinergic signalling to manipulate host response. We also discuss the challenges and opportunities in targeting purinergic signalling and the future prospects
Inverted perovskite solar cells with air stable diketopyrrolopyrrole-based electron transport layer
No full textOne of the possible causes of degradation of perovskite solar cells is the instability of the electron transporting layer. In this regard, design of air stable electron transport organic semiconductors, compatible with perovskite energy levels presents challenges due to inherent vulnerability to traps, presumably originating due to water and/or oxygen. In this work, we demonstrate air stability of diketopyrrolopyrrole-based molecule (TDPP-CN4) at ambient conditions and its application as electron transporting layer (ETL) in perovskite solar cells. We investigated electron mobility and air stability of TDPP-CN4 by fabricating top-gate bottom-contact (TG-BC) thin film transistors and compared with PCBM at ambient conditions. Both TDPP-CN4 and PCBM exhibit electron transport properties with mobility of 0.13 cm(2) V-1 s(-1) and 0.03 cm(2) V-1 s(-1) respectively. However, we found remarkable air stability of the TDPP-CN4 in the OFET measurements under ambient conditions. These excellent properties of TDPP-CN4 render them as potential ETL layer in inverted planar heterojunction perovskite solar cells. Our preliminary device studies show remarkable short-circuit current (J(sc)) similar to 17.4 mA/cm(2) with moderate open-circuit voltage (V-oc) of 0.50 V. These results suggest that the electron mobility and air-stability of diketopyrrolopyrrole-based molecule hold a promise as Ell in perovskite solar cells at ambient conditions
PhenoPine: A simulation model to trace the phenological changes in Pinus roxhburghii in response to ambient temperature rise
No full textThe PhenoPine is a Growing Degree Day (GDD) simulation model that can be used to trace the phenology of pine (Pinus roxburghii) under changing regimes of ambient temperature rise. The PhenoPine was developed using field-based observations for pine - a dominant tree species under the ``Chir Pine forests'' of Indian Western Himalayan region. Phenological stages of pine have been worked out on the basis of GDD. The GDD was computed assuming zero degree Celsius as base temperature and the accumulated averaged values over different phenological stages for developing phenology of the tree. The model has been built in Fortran Simulation Translator. Initially, the model has been developed to trace the impacts of temperature considering temperature as the major driving force for the phenology, while the lack of data for other forces also made this an obvious choice. Simulation through the PhenoPine can be done to trace the stages of initiation and termination of needle (leaf) formation, litter fall, cone formation; and the longevity of each phases under the changing regime of temperature rise
Kepler Orbits in Pairs of Disks Settling in a Viscous Fluid
No full textWe show experimentally that a pair of disks settling at negligible Reynolds number (similar to 10(-4)) displays two classes of bound periodic orbits, each with transitions to scattering states. We account for these dynamics, at leading far-field order, through an effective Hamiltonian in which gravitational driving endows orientation with the properties of momentum. This treatment is successfully compared against the measured properties of orbits and critical parameters of transitions between types of orbits. We demonstrate a precise correspondence with the Kepler problem of planetary motion for a wide range of initial conditions, find and account for a family of orbits with no Keplerian analog, and highlight the role of orientation as momentum in the many-disk problem