Field induced magnetic transition and metastability in Co substituted Mn2SbMn_{2}Sb

A detailed investigation of first order ferrimagnetic (FRI) to antiferromagnetic (AFM) transition in Co (15%) doped $Mn_2Sb$ is carried out. These measurements demonstrate anomalous thermomagnetic irreversibility and glass-like frozen FRI phase at low temperatures. The irreversibility arising between the supercooling and superheating spinodals is distinguised in an ingenious way from the irreversibility arising due to kinetic arrest. Field annealing measurements shows reentrant FRI-AFM-FRI transition with increasing temperature. These measurements also show that kinetic arrest band and supercooling band are anitcorrelated i.e regions which are kinetically arrested at higher temperature have lower supercooling temperature and vice versa.Comment: 10 pages, 8 figure

AuNx stabilization with interstitial nitrogen atoms: A Density Functional Theory Study

Researchers have been studying 4d and 5d Series Transition Metal Nitrides lately as a result of the experimental production of AuN, PtN, CuN. In this paper, we used the Density Functional Theory (DFT) implementing a pseudopotential plane-wave method to study the incorporation of nitrogen atoms in the face-centered cube (fcc) lattice of gold (Au). First, we took the fcc structure of gold, and gradually located the nitrogen atoms in tetrahedral (TH) and octahedral (OH) interstitial sites. AuN stabilized in: 2OH (30%), 4OH and 4TH (50%), 4OH - 2TH (close to the wurtzite structure) and 6TH (60%). This leads us to think that AuN behaves like a Transition Metal Nitride since the nitrogen atoms look for tetrahedral sites. © Published under licence by IOP Publishing Ltd

Observation of Selective Plasmon-Exciton Coupling in Nonradiative Energy Transfer: Donor-Selective versus Acceptor-Selective

Cataloged from PDF version of article.We report selectively plasmon-mediated nonradiative energy transfer between quantum dot (QD) emitters interacting with each other via Forster-type resonance energy transfer (FRET) under controlled plasmon coupling either to only the donor QDs (i.e., donor-selective) or to only the acceptor QDs (i.e., acceptor-selective). Using layer-by-layer assembled colloidal QD nanocrystal solids with metal nanoparticles integrated at carefully designed spacing, we demonstrate the ability to enable/disable the coupled plasmon-exciton (plexciton) formation distinctly at the donor (exciton departing) site or at the acceptor (exciton feeding) site of our choice, while not hindering the donor exciton-acceptor exciton interaction but refraining from simultaneous coupling to both sites of the donor and the acceptor in the FRET process.. In the case of donor-selective plexciton, we observed a substantial shortening in the donor QD lifetime from 1.33 to 0.29 ns as a result of plasmon-coupling to the donors and the FRET-assisted exciton transfer from the donors to the acceptors, both of which shorten the donor lifetime. This consequently enhanced the acceptor emission by a factor of 1.93. On the other hand, in the complimentary case of acceptor-selective plexciton, we observed a 2.70-fold emission enhancement in the acceptor QDs, larger than the acceptor emission enhancement of the donor-selective plexciton, as a result of the combined effects of the acceptor plasmon coupling and the FRET-assisted exciton feeding. Here we present the comparative results of theoretical modeling of the donor- and acceptor-selective plexcitons of nonradiative energy transfer developed here for the first time, which are in excellent agreement with the systematic experimental characterization. Such an ability to modify and control energy transfer through mastering plexcitons is of fundamental importance, opening up new applications for quantum dot embedded plexciton devices along with the development of new techniques in FRET-based fluorescence microscopy

Collaborative Agency in Youth Online and Offline Creative Production in Scratch

Few studies have focused on how youth develop agency to organize and participate in online unstructured creative collaborations. This paper describes and analyzes how youth programmers organized collaborative groups in response to a programming “Collab Challenge” in the Scratch Online Community and in an accompanying workshop with high school students. The analyses focused on modalities of online collaborations, determined the breadth of online participation, and examined local teens’ awareness of the online community. The discussion addresses youth’s collaborative agency in these new networked contexts, studied the role that online social awareness plays in completing tasks and makes recommendations for the support of online programming communities

Macroscopic quantum coherence in mesoscopic ferromagnetic systems

In this paper we study the Macroscopic Quantum Oscillation (MQO) effect in ferromagnetic single domain magnets with a magnetic field applied along the hard anistropy axis. The level splitting for the ground state, derived with the conventional instanton method, oscillates with the external field and is quenched at some field values. A formula for quantum tunneling at excited levels is also obtained. The existence of topological phase accounts for this kind of oscillation and the corresponding thermodynamical quantities exhibit similar interference effects which resembles to some extent the electron quantum phase interference induced by gauge potential in the Aharonov-Bohm effect and the $\Theta$-vacuum in Yang-Mills field theory..Comment: 12 pages, 4 figures, to appear in Phys. Rev.

Multi-spectral Material Classification in Landscape Scenes Using Commodity Hardware

We investigate the advantages of a stereo, multi-spectral acquisition system for material classication in ground-level landscape images. Our novel system allows us to acquire high-resolution, multi- spectral stereo pairs using commodity photographic equipment. Given additional spectral information we obtain better classication of vege- tation classes than the standard RGB case. We test the system in two modes: splitting the visible spectrum into six bands; and extending the recorded spectrum to near infra-red. Our six-band design is more prac- tical than standard multi-spectral techniques and foliage classication using acquired images compares favourably to simply using a standard camera

Vented Methane-air Explosion Overpressure Calculation—A simplified approach based on CFD

This paper presents new correlations developed through numerical simulations to estimate peak overpressures for vented methane-air explosions in cylindrical enclosures. A series of experimental tests are carried out first and the results are used to validate the numerical models developed with the commercial CFD software FLACS. More than 350 simulations consisting of 16 enclosure scales, 12 vent area to enclosure roof area ratios, 8 gas equivalence ratios and 9 vent activation pressures are then carried out to develop the Vented Methane-air Explosion Overpressure Calculation (VMEOC) correlations. Parameters associated with burning velocity and turbulence generation, oscillatory combustion and flame instabilities in vented gas explosion are taken into account in the development of new correlations. Comparing to CFD simulations, the VMEOC correlations provide a faster way to estimate the peak overpressure of a vented explosion. Additionally, it is proved in this study that the VMEOC correlations are easier to use and more accurate than the equations given in the up-to-date industrial standard- NFPA-68 2013 edition