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Role of Cu During Sintering of Fe0.96Cu0.04 Nanoparticles
No full textNanoparticle agglomerates of passivated Fe (n-Fe) and Fe0.96Cu0.04 (n-Fe0.96Cu0.04), synthesized through the levitational gas condensation (LGC) process, were compacted and sintered using the conventional powder metallurgy method. The n-Fe0.96Cu0.04 agglomerates produced lower green density than n-Fe, and when compacted under pressure beyond 200 MPa, they underwent lateral cracking during ejection attributed to the presence of a passive oxide layer. Sintering under dynamic hydrogen atmosphere can produce a higher density of compact in n-Fe0.96Cu0.04 in comparison to n-Fe. Both the results of dilatometry and thermogravimetric (TG) measurements of the samples under flowing hydrogen revealed enhancement of the sintering process as soon as the reduction of oxide layers could be accomplished. The shrinkage rate of n-Fe0.96Cu0.04 reached a value three times higher than n-Fe at a low temperature of 723 K (450 A degrees C) during heating. This enhanced shrinkage rate was the manifestation of accumulation of Cu at the surface of the particles. The formation of a thin-surface melted layer enriched with copper during heating to isothermal holding facilitated as a medium of transport for diffusion of the elements. The compacts produced by sintering at 773 K (500 A degrees C), with relative density 82 pct, were found to be unstable and oxidized instantly when exposed to ambient atmosphere. The stable compacts of density more than 92 pct with 300- to 450-nm grain size could only be produced when sintering was carried out at 973 K (700 A degrees C) and beyond. The 0.22 wt pct residual oxygen obtained in the sintered compact is similar to what is used for conventional ferrous powder metallurgy products
Effect of Coral-Shaped Yttrium Iron Garnet Particles on the EMI Shielding Behaviour of Yttrium Iron Garnet-Polyaniline-Wax Composites
No full textWe report the physicochemical insight into the role of coral-shaped yttrium-iron-garnet (YIG) particles for high electromagnetic interference (EMI) shielding behaviour of YIG-polyaniline (PANI)-Wax composites. We studied the total shielding effectiveness (SET) of various compositions of the composites in X and K-u-band frequencies (8-18 GHz) and came upon with a critical concentration (20 wt% of YIG) for which SET is maximum (-44.8 dB). At this critical concentration, the coral shape of YIG helps in effectively increasing the YIG-PANI interfaces necessary for the multiple scattering of electromagnetic (EM) waves. The scattered microwave is then trapped within the dense coral-network of YIG until they are absorbed therein by PANI via conduction loss; thereby, dramatically enhancing the microwave attenuation. The detailed EMI shielding mechanism is explained based on electrical and magnetic properties of the composites. Our result demonstrates the importance of morphology of the dielectric/magnetic particles and their concentration in the composites for designing an efficient EMI shield
A Route to Direct Fitness: Natural and Experimentally Induced Queen Succession in the Tropical Primitively Eusocial Wasp Ropalidia marginata
No full textInsect societies are hallmarks of cooperation because one or a few queens monopolize reproduction and several non-reproductive workers cooperatively raise brood. However, the loss of the queen exposes a colony to potential reproductive conflict, which is resolved only after a new queen takes over. We studied queen succession in natural and experimental colonies of the primitively eusocial wasp Ropalidia marginata to understand the proximate behavioral strategies involved in the resolution of this conflict. Previous work has shown that in this species, experimental queen removal always results in only one worker becoming hyper-aggressive and taking over the colony as its next queen, without ever being challenged. Here we show that even during natural queen turnover, one and only one worker becomes hyper-aggressive and takes over as the next queen, without being challenged. During natural queen turn-over, aggression of the successor may sometimes begin before the loss of the old queen and may sometimes decline more rapidly, unlike in the case of experimental queen removal. The successor begins to lay eggs sooner after a natural queen turn-over as compared to experimental queen removal. This is expected because workers might detect the gradual decline of the queen preceding her disappearance. Because queen succession is expected to be more prevalent in tropical perennial species, we expect natural selection to have favored such an orderly queen succession so that a route to direct fitness is available without significant reduction in cooperation
Multidimensional Index Modulation in Wireless Communications
No full textIn index modulation schemes, information bits are conveyed through indexing of transmission entities such as antennas, subcarriers, times slots, precoders, subarrays, and radio frequency (RF) mirrors. Index modulation schemes are attractive for their advantages such as good performance, high rates, and hardware simplicity. This paper focuses on index modulation schemes in which multiple transmission entities, namely, antennas, time slots, and RF mirrors, are indexed simultaneously. Recognizing that such multidimensional index modulation schemes encourage sparsity in their transmit signal vectors, we propose efficient signal detection schemes that use compressive sensing based reconstruction algorithms. Results show that, for a given rate, improved performance is achieved when the number of indexed transmission entities is increased. We also explore indexing opportunities in load modulation, which is a modulation scheme that offers power efficiency and reduced RF hardware complexity advantages in multiantenna systems. Results show that indexing space and time in load modulated multi antenna systems can achieve improved performance
Submarine groundwater discharge derived strontium from the Bengal Basin traced in Bay of Bengal water samples
No full textEvaluating the submarine groundwater discharge (SGD) derived strontium (Sr) flux from the Bengal Basin to the Bay of Bengal (BoB) and determining its isotopic composition is crucial for understanding the marine Sr isotopic evolution over time. Measurements of spatially and temporally distributed water samples collected from the BoB show radiogenic Sr-87/Sr-86, high Sr, calcium (Ca) concentrations and high salinity in samples collected dominantly from 100-120 m depth, which can be explained only by the contribution of saline groundwater from the Bengal Basin. These results provide a direct evidence of the SGD-Sr flux to the BoB. This SGD-Sr flux is however, spatially heterogeneous and using conservative hydrological estimates of the SGD flux to the BoB, we suggest a SGD Sr flux of 13.5-40.5 x 10(5) mol/yr to the BoB. Mass balance calculations using Sr concentrations and Sr-87/Sr-86 suggest up to 7% contribution of SGD to the 100-120 m BoB water samples. The identification of SGD at 100-120 m depth also provides an explanation for the anomalous variations in barium (Ba) concentrations and the delta O-18-salinity relationship in intermediate depths of the BoB
Rainfall seasonality on the Indian subcontinent during the Cretaceous greenhouse
No full textThe Cretaceous greenhouse climate was accompanied by major changes in Earth's hydrological cycle, but seasonally resolved hydroclimatic reconstructions for this anomalously warm period are rare. We measured the delta O-18 and CO2 clumped isotope Delta(47) of the seasonal growth bands in carbonate shells of the mollusc Villorita cyprinoides (Black Clam) growing in the Cochin estuary, in southern India. These tandem records accurately reconstruct seasonal changes in sea surface temperature (SST) and seawater delta O-18, allowing us to document freshwater discharge into the estuary, and make inferences about rainfall amount. The same analytical approach was applied to well-preserved fossil remains of the Cretaceous (Early Maastrichtian) mollusc Phygraea (Phygraea) vesicularis from the nearby Kallankuruchchi Formation in the Cauvery Basin of southern India. The palaeoenvironmental record shows that, unlike present-day India, where summer rainfall predominates, most rainfall in Cretaceous India occurred in winter. During the Early Maastrichtian, the Indian plate was positioned at similar to 30 degrees S latitude, where present-day rainfall and storm activity is also concentrated in winter. The good match of the Cretaceous climate and present-day climate at similar to 30 degrees S suggests that the large-scale atmospheric circulation and seasonal hydroclimate patterns were similar to, although probably more intense than, those at present
Microwave-radiation-induced molecular structural rearrangement of hen egg-white lysozyme
No full textWe have investigated the nonthermal effect of 10 GHz/22 dBm microwave radiation on hen egg-white lysozyme (HEWL) over different irradiation times, ranging from 2 min to 1 h. To ensure a control over the radiation parameters, a pair of microwave rectangular waveguides is used to irradiate the samples. Optical spectroscopic measurements, which include UV-visible absorption spectroscopy, Raman spectroscopy, and far UV CD spectroscopy, reveal the exposure of the buried tryptophan (Trp) residues of the native molecule between 15 and 30 min of radiation. The higher duration of the perturbation leads to a compact structure of the protein and Trp residues are buried again. Interestingly, we do not find any change in the secondary structure of the protein even for 1 h duration of radiation. The relaxation dynamics of the irradiated molecules also has been discussed. We have shown that the molecules relax to their native configuration in 7-8 h after the radiation field is turned off. The structural rearrangement over the above timescale has further been probed by a model calculation, based on a modified Langevin equation. Our coarse-grained simulation approach utilizes the mean of atomic positions and net atomic charge of each amino acid of native HEWL to mimic the initial conformation of the molecule. The modified positions of the residues are then calculated for the given force fields. The simulation results reveal the nonmonotonous change in overall size of the molecule, as observed experimentally. The radiation parameters used in our experiments are very similar to those of some of the electronic devices we often come across. Thus, we believe that the results of our studies on a simple protein structure may help us in understanding the effect of radiation on complex biological systems as well
A Mechanism for the Southward Propagation of Mesoscale Convective Systems Over the Bay of Bengal
No full textEquatorward propagating precipitation episodes over the Bay of Bengal have been documented in many previous observational studies. Proposed propagation mechanisms include mean surface to midtropospheric wind shear driving the convection orthogonal to the lower tropospheric winds and the gravity currents generated by outflow from convection initiated by the diurnally varying land-ocean circulations dispersing south. In this study, we perform high-resolution simulations using the Weather Research and Forecast model capable of resolving mesoscale convective systems during the South Asian summer monsoon season. This mesoscale system is shown to have squall line-like structure with leading line/trailing stratiform. The rear inflow due to saturated downdraft and jump updraft indicates a gravity current-like structure. The rear inflow jet produces horizontal momentum tendencies in the direction of propagation. The center of convection is shown to move faster than the midtropospheric winds and at the same speed as that of the rear inflow jet near the surface. These systems are also shown to be tightly coupled to the diurnal land surface heating cycle. We perform additional model simulations with varying horizontal resolution and with the inclusion of cumulus parameterization. A model with cumulus parameterization is unable to simulate the updraft-downdraft pair and the gravity current structure of this southward propagating mesoscale system. We find that high model resolution is needed to resolve the updraft-downdraft pair and cumulus parameterization assumptions break down at such high resolutions. Using cloud microphysics exclusively becomes essential in simulating these mesoscale systems
Spectral Properties of Hypergraph Laplacian and Approximation Algorithms
No full textThe celebrated Cheeger's Inequality (Alon and Milman 1985; Alon 1986) establishes a bound on the edge expansion of a graph via its spectrum. This inequality is central to a rich spectral theory of graphs, based on studying the eigenvalues and eigenvectors of the adjacency matrix (and other related matrices) of graphs. It has remained open to define a suitable spectral model for hypergraphs whose spectra can be used to estimate various combinatorial properties of the hypergraph. In this article, we introduce a new hypergraph Laplacian operator generalizing the Laplacian matrix of graphs. In particular, the operator is induced by a diffusion process on the hypergraph, such that within each hyperedge, measure flows from vertices having maximum weighted measure to those having minimum. Since the operator is nonlinear, we have to exploit other properties of the diffusion process to recover the Cheeger's Inequality that relates hyperedge expansion with the ``second eigenvalue'' of the resulting Laplacian. However, we show that higher-order spectral properties cannot hold in general using the current framework. Since higher-order spectral properties do not hold for the Laplacian operator, we instead use the concept of procedural minimizers to consider higher-order Cheeger-like inequalities. For any k is an element of N, we give a polynomial-time algorithm to compute an O(log r)-approximation to the kth procedural minimizer, where r is the maximum cardinality of a hyperedge. We show that this approximation factor is optimal under the SSE hypothesis (introduced by Raghavendra and Steurer (2010)) for constant values of k. Moreover, using the factor-preserving reduction from vertex expansion in graphs to hypergraph expansion, we show that all our results for hypergraphs extend to vertex expansion in graphs
First Report on High Entropy Alloy Nanoparticle Decorated Graphene
No full textThis is the first report on synthesis of multimetal high entropy alloy (HEA) nanoparticle-few layer graphene composite. A two-step methodology for synthesizing multi-component HEA nanoparticle-graphene composite is provided. In the first step, high purity graphite powder was mechanically milled with metal powders (Ni, Cr, Co, Cu, Fe) to produce multimetal-graphite composite. This composite was then sonicated with sodium lauryl sulphate (SLS) for 2 hours to produce a dispersion of graphene decorated with multi-component nanoparticles with face centred cubic structure. Potentiodynamic polarization and electrochemical impedance spectroscopy methods revealed that the HEA nanoparticle graphene composite possess excellent corrosion resistance properties which was better than the corrosion resistance exhibited by milled and exfoliated graphene. The HEA nanoparticle-graphene composite can be used for corrosion resistant coating applications