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On jet instability modes of a subsonic Hartmann whistle
No full textNumerical experiments to understand the resonant acoustic response of a subsonic jet impinging on the mouth of a tube, known as the Hartmann whistle configuration, were performed as large-eddy simulations. The tube length was chosen so that its fundamental duct mode, for one end closed and one end open, would match the dominant mode in the exciting jet. When the tube mouth was placed in the path of a regular stream of vortex rings, formed by the instability of the jet's bounding shear layer, a strong resonant, tonal response (whistling) was obtained. At three diameters from the jet, OASPL was 150-160 dB. A tube with a thicker lip generated a louder response. When the tube was held closer to the nozzle exit, the impinging unsteady shear layer could not provoke any significant resonance. The simulations reveal that the tonal response of a Hartmann whistle operating in subsonic mode is significant
Synthesis and Optical Properties of Highly Stabilized Peptide-Coated Silver Nanoparticles
No full textThe interaction between peptide and silver nanoparticle surfaces has been increasingly of interest for bionanotechnology applications. To fully understand how to control such interactions, we have studied the optical properties of peptide-modified silver nanoparticles. However, the impacts of peptide binding motif upon the surface characteristics and physicochemical properties of nanoparticles remain not yet fully understood. Here, we have prepared sodium citrate-stabilized silver nanoparticles and coated with peptide IVD (ID3). These nanomaterials were characterized by UV-visible, transmission electron microscopy (TEM), and z-potential measurement. The results indicate that silver nanoparticles (AgNP)-peptide interface is generated using ID3 peptide and suggested that the reactivity of peptide is governed by the conformation of the bound peptide on the nanoparticle surface. The peptide-nanoparticle interactions could potentially be used to make specific functionality into the peptide capped nanomaterials and antibacterial applications
Effect of the Crystallographic Phase of Ruthenium Nanosponges on Arene and Substituted-Arene Hydrogenation Activity
No full textIdentifying crystal structure sensitivity of a catalyst for a particular reaction is an important issue in heterogeneous catalysis. In this context, the activity of different phases of ruthenium catalysts for benzene hydrogenation has not yet been investigated. The synthesis of hcp and fcc phases of ruthenium nanosponges by chemical reduction method has been described. Reduction of ruthenium chloride using ammonia borane (AB) and tert-butylamine borane (TBAB) as reducing agents gave ruthenium nanosponge in its hcp phase. On the other hand, reduction using sodium borohydride (SB) afforded ruthenium nanosponge in its fcc phase. The as prepared hcp ruthenium nanosponge was found to be catalytically more active compared to the as prepared fcc ruthenium nanosponge for hydrogenation of benzene. The hcp ruthenium nanosponge was found to be thermally stable and recyclable over several cycles. This self-supported hcp ruthenium nanosponge shows excellent catalytic activity towards hydrogenation of various substituted benzenes. Moreover, the ruthenium nanosponge catalyst was found to bring about selective hydrogenation of aromatic cores of phenols and aryl ethers to the respective alicyclic products without hydrogenolysis of the C-O bond
A monolithic finite-element formulation for magnetohydrodynamics
No full textThis work develops a new monolithic strategy for magnetohydrodynamics based on a continuous velocity-pressure formulation. The magnetic field is interpolated in the same way as the velocity field, and the entire formulation is within a nodal finite-element framework. The velocity and pressure interpolations are chosen so that they satisfy the Babuska-Brezzi (BB) conditions. In most of the existing formulations, a stabilized formulation is used that requires a stabilization term, and some associated mesh-dependent parameters that need to be adjusted. In contrast, no such parameters need to be adjusted in the current formulation, making it more user-friendly and robust. Both transient and steady-state formulations are developed for two- and three-dimensional geometries. An exact linearization of the monolithic strategy ensures that rapid (quadratic) convergence is achieved within each time (or load) step, while the stable nature of the interpolations used ensures that no instabilities arise in the solution. An existing analytical solution is corrected. The coarse mesh accuracy is shown to be better compared with other existing strategies in several benchmark problems, showing that the developed formulation is both robust and efficient
Integrated Greywater Management Systems: A Design Proposal for Efficient and Decentralised Greywater Sewage Treatment
No full textThe aim of this paper is to explore the design possibility for improvising our approach to treating greywater sewage in the context of depleting water resources and emerging conurbations at regional levels of development. A gate-to-gate Life-cycle assessment (LCA) study focussing on use-phase was undertaken to analyse the flow characteristics and specific-energy consumption of a Membrane Bio-reactor (MBR) Sewage Treatment Plant (STP) at Indian Institute of Science, Bangalore. Moreover, a morphological analysis of existing STPs was attempted, and the possibility of proposing an alternative system for sewage treatment via technological solutions, along with a business-oriented intervention was explored at the entity and regional levels. In conclusion, a model for MBR-based compact and decentralised greywater sewage treatment, at the urban policy level seems necessary in attempting to maximize the STP's potential for self-sustaining efficiency, and therefore leading to smarter management of existing water resources. (C) 2018 The Authors. Published by Elsevier B.V
The Galling Truth: Limited Knowledge of Gall-Associated Volatiles in Multitrophic Interactions
No full textG alls are the product of enclosed internal herbivory where the gall maker induces a plant structure within which the herbivores complete their development. For successful sustained herbivory, gall makers must (1) suppress the induction of plant defenses in response to herbivory that is usually mediated through the jasmonic acid pathway and involves volatile organic compound (VOC) production, or (2) have mechanisms to cope with herbivory-induced VOCs, or (3) manipulate production of VOCs to their own advantage. Similarly, plants may have mechanisms (1) to avoid VOC suppression or (2) to attract galler enemies such as parasitoids. While research on VOCs involved in plant-herbivore-parasitoid/predator interactions is extensive, this has largely focussed on the impact of piercing, sucking, and chewing external herbivores or their eggs on VOC emissions. Despite the importance of gallers, owing to their damage to many economically valuable plants, the role of volatiles in gall-associated herbivory has been neglected; exceptions include studies on beneficial gallers and their enemies such as those that occur in brood-site pollination mutualisms. This is possibly the consequence of the difficulties inherent with studying internally occurring herbivory. This review examines the evidence for VOCs in galler attraction to host plants, potential VOC suppression by gallers, increased emission from galls and neighboring tissues, attraction of galler enemies, and the role of galler symbionts in VOC production. It suggests a research focus and ways in which studies on galler-associated VOCs can progress from a philatelic approach involving VOC listing toward a more predictive and evolutionary perspective
Dosage compensation in human pre-implantation embryos: X-chromosome inactivation or dampening?
No full textEffect of Stimulus Contrast and Visual Attention on Spike-Gamma Phase Relationship in Macaque Primary Visual Cortex
No full textBrain signals often show rhythmic activity in the so-called gamma range (30-80 Hz), whose magnitude and center frequency are modulated by properties of the visual stimulus such as size and contrast, as well as by cognitive processes such as attention. How gamma rhythm can potentially influence cortical processing remains unclear; previous studies have proposed a scheme called phase coding, in which the intensity of the incoming stimulus is coded in the position of the spike relative to the rhythm. Using chronically implanted microelectrode arrays in the primary visual cortex (area V1) of macaques engaged in an attention task while presenting stimuli of varying contrasts, we tested whether the phase of the gamma rhythm relative to spikes varied as a function of stimulus contrast and attentional state. A previous study had found no evidence of gamma phase coding for either contrast or attention in V1, but in that study spikes and local field potential (LFP) were recorded from the same electrode, due to which spike-gamma phase estimation could have been biased. Further, the filtering operation to obtain LFP could also have biased the gamma phase. By analyzing spikes and LFP from different electrodes, we found a weak but significant effect of attention, but not stimulus contrast, on gamma phase relative to spikes. The results remained consistent even after correcting the filter induced lags, although the absolute magnitude of gamma phase shifted by up to similar to 15 degrees. Although we found a significant effect of attention, we argue that a small magnitude of phase shift as well as the dependence of phase angles on gamma power and center frequency limits a potential role of gamma in phase coding in V1
Why rare-earth ferromagnets are so rare: Insights from the p-wave Kondo model
No full textMagnetic exchange in Kondo lattice systems is of the Ruderman-Kittel-Kasuya-Yosida type, whose sign depends on the Fermi wave vector k(F). In the simplest setting, for small k(F), the interaction is predominately ferromagnetic, whereas it turns more antiferromagnetic with growing k(F). It is remarkable that even though k(F) varies vastly among the rare-earth systems, an overwhelming majority of lanthanide magnets are in fact antiferromagnets. To address this puzzle, we investigate the effects of a p-wave form factor for the Kondo coupling pertinent to nearly all rare-earth intermetallics. We show that this leads to interference effects which for small k(F) are destructive, greatly reducing the size of the RKKY interaction in the cases where ferromagnetism would otherwise be strongest. By contrast, for large k(F), constructive interference can enhance antiferromagnetic exchange. Based on this, we propose a route for designing ferromagnetic rare-earth magnets
N-Heterocyclic Carbene-Catalyzed Enantioselective Synthesis of Spiro-glutarimides via alpha,beta-Unsaturated Acylazoliums
No full textNHC-catalyzed enantioselective 3 + 3] spiro-annulation of alpha,beta-unsaturated aldehydes with cyclic beta-ketoamides allowing the preparation of synthetically and biologically important spiro-glutarimide derivatives has been reported. The interception of the ketoamides with catalytically generated chiral alpha,beta-unsaturated acylazoliums proceeds in a Michael addition-intramolecular amidation pathway to deliver the spirocyclic products with good yield, diastereoselectivity, and enantioselectivity