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Synthesis of Furanone-Fused 1,2-Benzothiazine by Rh(III)-Catalyzed C-H Activation: Regioselective Oxidative Annulation Leading to in Situ Lactonization in One Pot
No full textA sulfoximine-directed C-H activation strategy catalyzed by a Rh(III)-catalyst leads to an efficient synthesis of furanone-fused 1,2-benzothiazine. In this reaction, cascade C-H activation, regioselective annulation, and lactonization occur in one pot. 4-Hydroxy-2-alkynoates, as coupling partners, form unsymmetrical alkynes, which undergo lactonization after C-H activation and regioselective annulation. The method shows a good scope with a wide-range of sulfoximine and alkynoates and displays regioselectivity in forming single regioisomers in good yields
Influence of interphase on the multi-physics coupled frequency of three-phase smart magneto-electro-elastic composite plates
No full textThe present article researches the influence of piezoelectric interphase thickness on the coupled frequency response of three-phase smart magneto-electro-elastic (TPS-MEE) plates with the aid of Reddy's third-order shear deformation theory (RTSDT). A three-phase smart composite constituted of CoFe2O4 piezomagnetic matrix embedded with carbon fibers in the piezoelectric shell is considered for evaluation. The coupling characteristics of the smart carbon/PZT-5A (PZT-7A)/CoFe2O4 composites significantly changes with the interphase thickness of piezoelectric interphase. Thereby the stiffness and the natural frequency of the structure composed of these three-phase MEE materials drastically changes. A finite element (FE) formulation has been derived incorporating Hamilton's principle. The equations of motion are obtained through condensation technique. The results reveal a significant effect of interphase thickness on the natural frequency of the three-phase smart magneto-electroelastic plate. Further, a special attention has been paid on evaluating the influence of carbon fiber/piezoelectric volume fraction on the free vibration behaviour of TPS-MEE plate. Also, a parametric study has been performed to investigate the effect of boundary conditions, aspect ratio and length-to-width ratio
Chandrasekharan Ramakrishnan (1939-2019): The student behind the Ramachandran map IN MEMORIAM
No full textScalar activity induced phase separation and liquid-solid transition in a Lennard-Jones system
No full textWe report scalar activity induced phase separation and crystallization in a system of 3-d Lennard-Jones particles taken at state points spanning from the gas to the liquid regime using molecular dynamics simulation (MD). Scalar activity was introduced by increasing the temperature of half of the particles (labeled `hot') while keeping the temperature of the other half constant at a lower value (labeled `cold'). The relative temperature difference between the two subsystems is considered as a measure of the activity. From our simulations we observe that the two species tend to phase separate at sufficiently high activity ratio. The extent of separation is quantified by the defined order parameter and the entropy production during this process is determined by employing the two-phase thermodynamic (2PT) model and the standard modified Benedict-Webb-Rubin (MBWR) equation of state for a LJ fluid. We observe that the extent of the phase separation and entropy production increases with the density of the system. From a cluster analysis, we obtain the mean number of clusters n(cl), and the mean size of the largest cluster n(0) in the system, complementing each other. Bond orientation order parameters reveal that the so formed largest cluster also develops solid-like order consisting of both FCC and HCP packing. The presence of such crystalline order is also supported by a common neighbor analysis
Numerical and Experimental Studies of Parasitic Heat Losses in Coldfinger of a Pulse Tube Cryocooler in Off-State Condition
No full textA pulse tube cryocooler (PTC) for future metrological satellites has been developed at one of the lead centers of the Indian Space Research Organisation in Bangalore, India for cooling on-board Infrared (IR) detectors to 80 K.A study has been conducted on the coldfinger of PTC to understand the off-state heat loads on the cooler by varying the value of gravity numerically in ANSYS FLUENT and experimentally by orienting the setup with respect to gravity. The off-state parasitic losses represent a major heat load in on-board applications that include redundant, viz. nonoperating coolers. To find out the amount of off-state parasitic heat losses in a nonoperating coldfinger of the PTC experimentally, transient warm-up technique was used. Various heat loads were applied experimentally on the cryo-tip at temperatures ranging from 80 to 100 K for determining the parasitic losses. The effect of orientation of PTC on the off-state parasitic heat load with respect to gravity is studied and presented in this paper. Enhancement due to free convection heat flow normalized by gas molecular conduction in pulse tube is analyzed using computational fluid dynamics to verify and compare with experimental results. The best orientation angle where the parasitic is low is when the cold end of the coldfinger of pulse tube cryocooler faces down (0A degrees) and high when the cold end of the coldfinger is oriented to 135A degrees
Influence of homogenisation time on evolution of eutectic phases, dispersoid behaviour and crystallographic texture for Al-Zn-Mg-Cu-Ag alloy
No full textMicrostructural changes for Al-Zn-Mg-Cu-Ag alloy at the time of homogenisation (0-48 h) at 465 degrees C were examined by optical microscope (OM), field emission scanning electron microscope (FESEM), energy dispersive X-ray Spectroscopy (EDS), transmission electron microscope (TEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) in detail. alpha (Al), eta Mg (Zn, Cu, Al)(2)], Al2Cu, and coarse Al3Fe emerged as predominant phases in the as-cast condition. The grain boundary areas were enriched with the main alloying elements i.e. Cu, Zn, Mg, and Ag. After 6 h of homogenisation, a phase change from it to S (Al2CuMg) was found to be initiated. By prolonging the homogenisation time, the dendritic network and the secondary eutectic phases were gradually dissolved in the matrix and eventually vanished after 48 h of homogenisation, which corroborated well with the proposed kinetic model. TEM micrographs demonstrated a high density of fine dispersoids after a homogenisation period for 6 h. In addition, higher homogenisation time accelerated the coarsening of dispersoids, following Ostwald ripening mechanism and lowering of Zener pinning pressure (ZPP). Crystallographic texture analysis demonstrated the presence of two completely different sets of texture components during casting and subsequent homogenisation treatments. Dominant Goss{011}< 100 >, Brass{011}< 211 >, P{011}< 111 >, CuT {552}< 115 > and S{123}< 634 > texture components appeared after casting, while Cube{100}< 001 >, rotated cube{110}< 011 >, E{111 }< 110 > and F{111}< 112 > components became dominant after homogenisation
Unraveling structural dynamics in isoenergetic excited S-1 and multi-excitonic (1)(TT) states of 9,10-bis(phenylethynyl)anthracene (BPEA) in solution via ultrafast Raman loss spectroscopy Electronic supplementary information (ESI) available: Summary of the concentration-dependent kinetics of TA of BPEA, and the molecular structure of BPEA along with its numbering on each atom. See DOI: 10.1039/c8cp06658b
No full textPolyacenes, such as anthracene, tetracene, pentacene etc., have been identified as potential candidates for singlet fission (SF) and triplet-triplet annihilation (TTA) processes in their crystalline and thin film forms as they possess significant singlet and triplet exciton couplings. Interestingly, phenyl-ethynyl substitution to anthracene at the 9,10 positions (9,10-bis(phenylethynyl)anthracene/BPEA) enhances the transverse pi-electron conjugation and retains the planar structure even in the excited state. The excited singlet state S-1 and the multi-excitonic state (1)(TT) in BPEA are separated by similar to 30 meV (similar to 250 cm(-1)) making it an ideal system for both SF and TTA applications. BPEA is very effective in photon up-conversion even for low input intensities. Transient absorption measurements of BPEA in n-hexane solution are inadequate for distinguishing the S-1 state and the multi-excitonic state (1)(TT), since the spectroscopic features are complex (mixed) due to the isoenergetic nature and the existence of an equilibrium between these states. However, ultra fast Raman loss spectroscopy reveals a systematic red shift and a blue shift in the central frequencies of the Raman modes corresponding to C C and C C vibrational frequencies with time constants of similar to 2.0 and similar to 20 ps, respectively. Such a shift in the Raman frequencies is direct evidence of the structural changes that take place while changing from excited singlet state S-1 to the multi-excitonic state on the potential surface
Latency Analysis for Distributed Coded Storage Systems
No full textModern communication and computation systems often consist of large networks of unreliable nodes. Still, it is well known that such systems can provide aggregate reliability via redundancy. While duplication may increase the load on a system, it can lead to significant performance improvement when combined with the judicious management of extra system resources. Prime examples of this abstract paradigm include multi-path routing across communication networks, content access from multiple caches in delivery networks, and master/slave computations on compute clusters. Several recent contributions in the area establish bounds on the performance of redundant systems, characterizing the latency-redundancy tradeoff under specific load profiles. Following a similar line of research, this paper introduces new analytical bounds and approximation techniques for the latency-redundancy tradeoff for a range of system loads and a class of symmetric redundancy schemes, under the assumption of Poisson arrivals, exponential service-rates, and fork-join scheduling policy. The proposed approach can be employed to efficiently approximate the latency distribution of a queueing system at equilibrium. Various metrics can subsequently be derived for this system, including the mean and variance of the sojourn time, and the tail decay rate of the stationary distribution. This paper also establishes the stability region in terms of arrival rates for redundant systems with certain symmetries. Finally, it offers selection guidelines for design parameters to provide latency guarantees based on the proposed approximations. Findings are substantiated by numerical results
Cooperative Beam-Rider Guidance for Unmanned Aerial Vehicle Rendezvous
No full textThe problem of aerial rendezvous of Unmanned Aerial Vehicles (UAVs) is considered. Beam rider approach, wherein the follower moves along a beam directed from a ground-based tracker onto the leader is proposed as a guidance strategy. Analytic guarantee for a resulting rendezvous between two same speed vehicles is derived from the line-of-sight guidance principles. Considering an approximate variation of the follower look-ahead angle, closed-form expressions are derived for time-to-rendezvous and follower lateral acceleration. Cooperative maneuvers are proposed for the leader minimizing the rendezvous engagement time. Guidance models are extended to 3D engagements and efficacy of the proposed method is demonstrated by extensive 2D and 3D simulations. Simulation results are presented complying with the analytic findings. Robustness of the proposed approach is verified against uncompensated autopilot delays, non-identical initial speeds, and wind
Inorganic polyphosphate accumulation suppresses the dormancy response and virulence in Mycobacterium tuberculosis
No full textStringent response pathways involving inorganic polyphosphate (PolyP) play an essential role in bacterial stress adaptation and virulence. The intracellular levels of PolyP are modulated by the activities of polyphosphate kinase-1 (PPK1), polyphosphate kinase-2 (PPK2), and exopolyphosphatases (PPXs). The genome of Mycobacterium tuberculosis encodes two functional PPXs, and simultaneous deletion of ppx1 and ppx2 results in a defect in biofilm formation. We demonstrate here that these PPXs cumulatively contribute to the ability of M. tuberculosis to survive in nutrient-limiting, low-oxygen growth conditions and also in macrophages. Characterization of single (Delta ppx2) and double knockout (dkppx) strains of M. tuberculosis indicated that PPX-mediated PolyP degradation is essential for establishing bacterial infection in guinea pigs. RNA-Seq-based transcriptional profiling revealed that relative to the parental strain, the expression levels of DosR regulon-regulated dormancy genes were significantly reduced in the dkppx mutant strain. In concordance, we also provide evidence that PolyP inhibits the autophosphorylation activities associated with DosT and DosS sensor kinases. The results in this study uncover that enzymes involved in PolyP homeostasis play a critical role in M. tuberculosis physiology and virulence and are attractive targets for developing more effective therapeutic interventions