Electromagnetically induced polarization conversion

Electromagnetically induced transparency and polarization conversion due to interference between two polarization-selective plasmonic resonances coexisting in the same planar metamaterial are studied. The metasurface represents a periodic array of two topologically distinct metamolecules combined on the same substrate: i) monopole antennas connected to wires and supporting a high-Q resonance radiatively coupled to x-polarization, and ii) dipolar antennas supporting a low-Q resonance coupled to y-polarization. We demonstrate that due to the interaction between these modes through a capacitive coupling between the metamolecules, one can observe a circularly-polarized Electromagnetically Induced Transparency (EIT) and thereby achieve an efficient ultra-thin quarter-wave plate.     

Influence of MgO/CeO2 ratio on CO2-oxidative transformation of C2H6 to C2H4 over highly active and stable Cr/MgO(x)–CeO2(100−x) nanocatalysts

Cr/MgO(x)–CeO₂(100?x) nanocatalysts were synthesized by a coprecipitation method and characterized by X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray (EDX) spectroscopy, diffuse reflectance spectroscopy (DRS), and Brunauer–Emmett–Teller (BET) analysis. The effect of ceria addition on their physicochemical characteristics was investigated, and the results were correlated with their catalytic performance in oxidative dehydrogenation of ethane. A decrease in the size of the metal particles was found when adding a suitable content of ceria to the support. Crystalline Cr₂O₃ was not found in the calcined samples, indicating good dispersion of Cr species on the support. All samples showed nanosized particles with uniform morphology, with the best surface morphology for the Cr/MgO(50)–CeO₂(50) sample, on which the particle distribution mainly lay in the range of 40–60 nm. Variation of the amount of Ce in the support led to an enhancement of the Cr⁶⁺/Cr³⁺ ratio, with the highest value for the Cr/MgO(50)–CeO₂(50) sample. This catalyst effectively dehydrogenated ethane to ethylene with CO₂ at 700 °C even after 5 h on-stream, giving 42.76 % ethylene yield.

     

Phoneme representation and classification in primary auditory cortex

A controversial issue in neurolinguistics is whether basic neural auditory representations found in many animals can account for human perception of speech. This question was addressed by examining how a population of neurons in the primary auditory cortex (A1) of the naive awake ferret encodes phonemes and whether this representation could account for the human ability to discriminate them. When neural responses were characterized and ordered by spectral tuning and dynamics, perceptually significant features including formant patterns in vowels and place and manner of articulation in consonants, were readily visualized by activity in distinct neural subpopulations. Furthermore, these responses faithfully encoded the similarity between the acoustic features of these phonemes. A simple classifier trained on the neural representation was able to simulate human phoneme confusion when tested with novel exemplars. These results suggest that A1 responses are sufficiently rich to encode and discriminate phoneme classes and that humans and animals may build upon the same general acoustic representations to learn boundaries for categorical and robust sound classification.     

Multi-mode resource-constrained project scheduling problem with material ordering under bonus–penalty policies

This study emphasizes that project scheduling and material ordering (time and quantity of an order) must be considered simultaneously to minimize the total cost, as setting the material ordering decisions after the project scheduling phase leads to non-optimal solutions. Hence, this paper mathematically formulates the model for the multi-mode resource-constrained project scheduling with material ordering (MRCPSMO) problem. In order to be more realistic, bonus and penalty policies are included for the project. The objective function of the model consists of four elements: the material holding cost, the material ordering cost, the bonus paid by the client and the cost of delay in the project completion. Since MRCPSMO is NP-hard, the paper proposes three hybrid meta-heuristic algorithms called PSO-GA, GA-GA and SA-GA to obtain near-optimal solutions. In addition, the design of experiments and Taguchi method is used to tune the algorithms’ parameters. The proposed algorithms consist of two components: an outside search, in which the algorithm searches for the best schedule and mode assignment, and the inside search, which determines the time and quantity of orders of the nonrenewable resources. First, a comparison is made for each individual component with the exact or best solutions available in the literature. Then, a set of standard PROGEN test problems is solved by the proposed hybrid algorithms under fixed CPU time. The results reveal that the PSO-GA algorithm outperforms both GA-GA and SA-GA algorithms and provides good solutions in a reasonable time.     

Wave propagation and breaking in multidimensional magnetogasdynamic flows

Summary The theory of shocks evolving from weak discontinuities is applied to magnetogasdynamics and worked out in detail for two situations: a spherical disturbance propagating into a uniform magnetic field, and a planar disturbance propagating in the field of a current-carrying wire. For both cases, shock formation is delayed as the magnetoacoustic speed of propagation approaches the Alfvén speed. This agrees with the fact that Alfvén waves do not steepen to form shocks.

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Résumé On applique à la magnétogasdynamique la théorie des ondes de choc produites par l'évolution des discontinuités faibles. On présente des résultats sur la formation de chocs par des ondes magnétoacoustiques. Lorsque la vitesse de propagation de ces ondes se rapproche de la vitesse d'Alfvén, l'apparition des chocs est retardée, en accord avec le résultat bien connu que les ondes d'Alfvén ne se transforment pas pour former des chocs.

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Research supported in part by Grant No. AFOSR-73-2561.     

A Comparison of DESI-MS and LC-MS for the Lipidomic Profiling of Human Cancer Tissue

In this study, we make a direct comparison between desorption electrospray ionization-mass spectrometry (DESI-MS) and ultraperformance liquid chromatography-electrospray ionization-mass spectrometry (UPLC-ESI-MS) platforms for the profiling of glycerophospholipid (GPL) species in esophageal cancer tissue. In particular, we studied the similarities and differences in the range of GPLs detected and the congruency of their relative abundances as detected by each analytical platform. The main differences between mass spectra of the two modalities were found to be associated with the variance in adduct formation of common GPLs, rather than the presence of different GPL species. Phosphatidylcholines as formate adducts in UPLC-ESI-MS accounted for the majority of differences in negative ion mode and alkali metal adducts of phosphatidylcholines in DESI-MS for positive ion mode. Comparison of the relative abundance of GPLs, normalized to a common peak, revealed a correlation coefficient of 0.70 (P < 0.001). The GPL profile detected by DESI-MS is congruent to UPLC-ESI-MS, which reaffirms the role of DESI-MS for lipidomic profiling and a potential premise for quantification.

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Graphical Abstract ?

     

Essential oil composition of three accessions of Dracocephalum heterophyllum Benth. cultivated at Palampur, India

Seeds of three accessions of Dracocephalum heterophyllum growing wild in high altitude locations in the cold desert regions of trans-Himalaya were collected and propagated under polyhouse conditions at IHBT Palampur to evaluate, compare their growth performance and essential oil composition. Three different chemotypes viz., citronellol-rose oxides type, citronellol type and citronellal-trans rose oxide type were identified. Samples of essential oils were distilled separately from leaves and inflorescence of all the three cultivated accessions and characterised by capillary GC and GC-MS techniques, which showed variation in the volatile constituents. In all the three accessions, citronellol was higher in the inflorescence oils as compared to leaf oils. Rose oxides, which are important high odour value cyclic monoterpene ethers were found in the essential oil samples of leaves as well as in the inflorescence of accession II, whereas these constituents were absent in the leaves of other two accessions. The essential oil from the inflorescence part of accession I was devoid of both cis and trans isomers of rose oxide, while accession III contained only one isomer of trans rose oxide. Under polyhouse conditions, seed germination was higher in accession III, whereas aerial biomass was higher in accession I. In comparison to other accessions, yield of volatile oil was higher in both leaf and inflorescence of accessions I, whereas accession II had higher oil yield from inflorescence. This is the first report of volatile oil composition of three accessions of D. heterophyllum cultivated at Palampur having potential as a new source of high valued essential oil for introduction in the perfumery industry.     

Investigation of Post-Darcy Flow in Thin Porous Media

Transport in Porous Media - We present numerical simulations of post-Darcy flow in thin porous medium: one consisting of staggered arrangements of circular cylinders and one random distribution of...     

Multiaxial cyclic deformation and non-proportional hardening employing discriminating load paths

Some novel discriminating multiaxial cyclic strain paths with incremental and random sequences were used to investigate cyclic deformation behavior of materials with low and high sensitivity to non-proportional loadings. Tubular specimens made of 1050 QT steel with no non-proportional hardening and 304L stainless steel with significant non-proportional hardening were used. 1050 QT steel was found to exhibit very similar behavior under various multiaxial loading paths, whereas significant effects of loading sequence were observed for 304L stainless steel. In-phase cycles with a random sequence of axial-torsion cycles on an equivalent strain circle were found to cause cyclic hardening levels similar to 90° out-of-phase loading of 304L stainless steel. In contrast, straining with a small increment of axial-torsion on an equivalent strain circle results in higher stress than for in-phase loading of 304L stainless steel, but the level of hardening is lower than for 90° out-of-phase loading. Tanaka’s non-proportionality parameter coupled with a Armstrong–Fredrick incremental plasticity model, and Kanazawa et al.’s empirical formulation as a representative of such empirical models were used to predict the stabilized stress response of the two materials under variable amplitude axial-torsion strain paths. Consistent results between experimental observations and predictions were obtained by employing the Tanaka’s non-proportionality parameter. In contrast, the empirical model resulted in significant over-prediction of stresses for 304L stainless steel.