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Application of Cp2TiCl-Promoted Radical Cyclization: A Unified Strategy for the Syntheses of Iridoid Monoterpenes
No full textAn expedient approach toward the unified total syntheses of (+)-iridomyrmecin, (-)-isoiridomyrmecin, (+)-7-epiboschnialactone, (+)-teucriumlactone, and (-)-dolichodial in chirally pure forms starting from readily available (+)-beta-citronellene is delineated combining step economy and simplicity. Highlights include a Ti(III)-mediated reductive epoxide opening-cydization for the construction of the core cyclopentac]pyran skeleton of the iridoid lactones with complete diastereoselectivity for the newly created bridgehead stereogenic centers. Subsequent transformations facilitate a short access to (+)-teucriumlactone and (-)-dolichodial and formal access to potentially other iridoids
A comprehensive analysis and rational designing of efficient Fe-based oxygen electrocatalysts for metal-air batteries
No full textPrecious metal based electrocatalysts are considered as the most efficient ones to drive kinetically sluggish oxygen evolution/reduction reactions (OER/ORR) for metal-air batteries and fuel-cells. However, their monofunctionality in addition to their exorbitant cost has stimulated the quest for economically viable bifunctional electrocatalysts for use in next generation electrochemical energy devices. Here, we report Fe-Fe3C encapsulated in Fe-Nx enriched spheres of N-doped carbon nanotubes (FCMR,M = 3, 10, 25, 40 represents the ramping rate of temperature during synthesis) as a potentially enduring, cost effective, highly efficient bifunctional electrocatalyst for total oxygen electrochemistry (ORR and OER) and a comprehensive study to elucidate the role of various Fe moieties. In addition to the improved OER/ORR activities as evident from the better onset potential, lower Tafel slopes and high current densities over commercially available RuO2/Pt-C electrocatalysts and several recently reported state-of-the-art bi-functional electrocatalysts, FC10R shows a current retention value of similar to 93 and similar to 98% after the accelerated cyclic stability test for the OER and ORR, respectively. The preferable 4e (-) pathways and suppressed peroxide generation in the ORR by FC10R further ensure maximum electrochemical energy harvesting. Remarkably, the complete oxygen electrochemistry of FC10R in alkaline medium as evaluated from Delta E (= E-j(OER) = 10 - E-1/2(ORR) = 0.758 V) is significantly lower than that of commercially available/ recently reported electrocatalysts and advocates the minimum cyclic loss. The overall study elucidates the synergistic effect of Fe-Nx coordination and Fe3C moieties on oxygen electrochemistry, and FC10R has shown its potential to serve as a non-precious metal based bifunctional electrocatalyst for next generation electrochemical energy conversion and storage devices. Finally, a prototype Al-air battery arrangement using FC10R as an air- cathode for powering a green light emitting diode has been demonstrated
Real-time compensation of errors in refractive index shift measurements of microring sensors using thermo-optic coefficients
No full textWe report a method for compensation of errors caused by temperature fluctuations in refractive index measurements using Silicon photonic microring sensors. The method involves determination of resonance wavelength shifts caused by thermal fluctuations using real-time measurement of on-chip temperature variations and thermo-optic coefficient (TOC) of analyte liquids. Resistive metal lines patterned around Silicon microrings are used to track temperature variations and TOC of analyte is calculated by measuring wavelength shifts caused by controlled increments in device temperature. The TOC of de-ionized water is determined to be -1.12 x 10(-4) / degrees C, with an accuracy of +/- 8.26 x 10 (-6) / degrees C. In our system, chip-surface temperature variations were measured with an instrument limited precision of 0.004 degrees C yielding a factor of 16 enhancement in tracking accuracy compared to conventional, bottom-of-chip temperature measurement. We show that refractive index detection limit of the microring sensor is also improved by the same factor. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
On the Observability of a Linear System With a Sparse Initial State
No full textIn this letter, we address the problem of observability of a linear dynamical system from compressive measurements and the knowledge of its external inputs. Observability of a high dimensional system state may require a large number of measurements in general, but we show that if the initial state vector admits a sparse representation, the number of measurements can be significantly reduced by using random projections for obtaining the measurements. We derive guarantees for the observability of the system using tools from probability theory and compressed sensing. Our analysis uses properties of the transfer matrix and random measurementmatrices to derive concentration ofmeasure bounds, which lead to sufficient conditions for the restricted isometry property of the observability matrix to hold. Hence, under the derived conditions, the initial state can be recovered by solving a computationally tractable convex optimization problem
Trimorphs of 4-bromophenyl 4-bromobenzoate. Elastic, brittle, plastic
No full textIntermolecular interactions and crystal packing of three polymorphs of the title compound are described in the context of their different mechanical properties. Molecular features of compounds that may be prone to such property differentiated polymorphism are discussed
Traction cytometry: regularization in the Fourier approach and comparisons with finite element method
No full textTraction forces exerted by adherent cells are quantified using displacements of embedded markers on polyacrylamide substrates due to cell contractility. Fourier Transform Traction Cytometry (FTTC) is widely used to calculate tractions but has inherent limitations due to errors in the displacement fields; these are mitigated through a regularization parameter (g) in the Reg-FTTC method. An alternate finite element (FE) approach computes tractions on a domain using known boundary conditions. Robust verification and recovery studies are lacking but essential in assessing the accuracy and noise sensitivity of the traction solutions from the different methods. We implemented the L2 regularization method and defined a maximum curvature point in the traction with g plot as the optimal regularization parameter (g*) in the Reg-FTTC approach. Traction reconstructions using g* yield accurate values of low and maximum tractions (Tmax) in the presence of up to 5% noise. Reg-FTTC is hence a clear improvement over the FTTC method but is inadequate to reconstruct low stresses such as those at nascent focal adhesions. FE, implemented using a node-by-node comparison, showed an intermediate reconstruction compared to Reg-FTTC. We performed experiments using mouse embryonic fibroblast (MEF) and compared results between these approaches. Tractions from FTTC and FE showed differences of B92% and 22% as compared to Reg-FTTC. Selection of an optimum value of g for each cell reduced variability in the computed tractions as compared to using a single value of g for all the MEF cells in this study
Generalization of unfolding operator for highly oscillating smooth boundary domains and homogenization
No full textUnfolding operators have been introduced and used to study homogenization problems. Initially, they were introduced for problems with rapidly oscillating coefficients and porous domains. Later, this has been developed for domains with oscillating boundaries, typically with rectangular or pillar type boundaries which are classified as non-smooth. In this article, we develop new unfolding operators, where the oscillations can be smooth and hence they have wider applications. We have demonstrated by developing unfolding operators for circular domains with rapid oscillations with high amplitude of O(1) to study the homogenization of an elliptic problem
Elastic and Plastic Behavior of an Ultrafine-Grained Mg Reinforced with BN Nanoparticles
No full textPure microcrystalline magnesium (A mu Mg) was reinforced with hexagonal boron nitride (hBN) nanoparticles and was fabricated by powder metallurgy process followed by hot extrusion. For comparison pure magnesium powder was consolidated by hot extrusion too. Both materials exhibited a significant fiber texture. Mg-hBN nanocomposites (nc) and pure Mg specimens were deformed between room temperature and 300 A degrees C under tension and compression mode. The yield strength and ultimate tensile and compression strength as well as characteristic stresses were evaluated and reported. The tensile and compressive strengths of Mg-hBN nc are quiet superior in values compared to monolithic counterpart as well as Mg alloys. The compressive yield strength of A mu Mg was recorded as 90 MPa, whereas the Mg-hBN nancomposite shows 125 MPa at 200 A degrees C. The tensile yield strength of A mu Mg was computed as 67 MPa which is quite lower as compared to Mg-hBN nanocomposite's value which was recorded as 157 MPa at 200 A degrees C. Under tensile stress the true stress-strain curves are flat in nature, whereas the stress-strain curves observed in compression at temperatures up to 100 A degrees C exhibited small local maxima at the onset of deformation followed by a significant work hardening
A NOVEL HIGH THROUGHPUT MICROFLUIDIC CELL TRANSIT ANALYZER USING AIR LIQUID INTERFACE AS LOCALIZED PRESSURE SENSOR
No full textWe report a novel microfluidic platform that measures pressure drop during the passage of a single cell through a mechanical constriction for mechano-phenotyping of cell populations. It uses a precisely positioned Air-Liquid Interface as a Sensor (ALIaS) near the outlet of the constriction. When cells pass through the constriction they momentarily plug the inlet resulting in a drop in the hydrodynamic pressure at the outlet of the constriction. This change in pressure leads to motion of the air-liquid interface which can be correlated to entry and transit time of the cell passage. ALIaS facilitates accurate measurements of cell entry and transit time at high throughout (>200 cells/s). The platform can reliably quantify the variation in deformability in cell populations upon treatment with Glutaraldehyde. The system presents a potential for mechanobiological studies and can be made portable through electrical measurements of interface oscillations
A double-auction mechanism for mobile data-offloading markets with strategic agents
No full textWe consider a recently proposed double-auction mechanism for mobile data-offloading. Network operators (users) derive benefit from offloading their traffic to third party WiFi or femtocell network (link-supplier). A link-supplier experiences costs for the additional capacity that he provides. Users and link supplier (collectively referred to as agents) have their utilities and cost function as private knowledge. A system-designer decomposes the problem into a network problem (with surrogate utilities and surrogate cost functions) and agent problems (one per agent). The surrogate utilities and cost functions are modulated by the agents' bids. Agents' payoffs and costs are then determined by the allocations and prices set by the system designer. So long as the agents do not anticipate the effect of their actions, a competitive equilibrium exists as a solution to the network and agent problems, and this equilibrium optimizes the system utility. This work shows that when the agents are strategic (price-anticipating), the presence of strategic supplying agents drives the system to an undesirable equilibrium with zero participation. This is in stark contrast to the setting when link suppliers are not strategic where the efficiency loss is at most 34%. The paper then proposes a Stackelberg game modification to alleviate the efficiency loss problem. The system designer first announces the allocation and payment functions. He then invites the supplying agents to announce their bids. He then invites the users to respond to the suppliers' bids. The resulting efficiency loss is characterized in terms of the suppliers' cost functions