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Polymorphism and Temperature-Induced Phase Transitions of Na2CoP2O7
No full textPolymorphism and temperature-induced phase transitions of Na2CoP2O7 were studied by in situ neutron powder diffraction and complemented by ab initio calculations to reconcile previous reports of its three polymorphs. We show that the ``blue'' form prepared at 873 K exists at room temperature in the orthorhombic Pna2(1) (= P2(1)cn) phase, which transforms via a first-order transition to the tetragonal form at the temperature close to room temperature (similar to 335 K). Just above the transition, the tetragonal form is likely incommensurately modulated with the modulation vanishing at similar to 423 K. Above that temperature the phase remains in the unmodulated tetragonal state (P4(2)/mnm) until melting at similar to 900 K. Upon cooling after melting, Na2CoP2O7 crystallizes into the ``rose'' triclinic P1 form which persists while it cools to room temperature, apparently stabilized by the barrier of the reconstructive ``rose-blue'' transition. We also discuss the relationship between the tetragonal and orthorhombic structures, the driving forces of the orthorhombic distortion, and similarity to Na2ZnP2O7 and the melilite-type structural family
Ground-state ferrimagnetism and magneto-caloric effects in Nd2NiMnO6
No full textExtending our earlier investigation of magnetic properties of Nd2NiMnO6, we show that it exhibits a magnetic transition below similar to 6 K to a ferrimagnetic state. This behavior is interpreted as arising from a long-range ordering of Nd moments antiferromagnetically coupled to the ferromagnetic Ni-Mn ordered moments. Due to the richness of its multiple magnetic transitions and the easily influenced magnetic state by the application of an external magnetic field, established in our earlier study, it has a remarkable inverse magneto-caloric effect (IMCE) at low temperatures (T < 50 K) together with a significant conventional magneto-caloric effect (CMCE) at the ferromagnetic ordering temperature (T-c similar to 200 K). IMCE and CMCE correspond to the antiferromagnetic arrangement of Nd and Ni-Mn sublattices and ferromagnetic ordering of Ni-Mn sublattices, respectively. Nd2NiMnO6 with its second order phase transition follows the universal behavior of Delta S-M(T); it also shows a power law dependency on the magnetic field as Delta S-M proportional to H-eta
Centrality and pseudorapidity dependence of the transverse energy density in pPb collisions ats root s(NN)=5.02 TeV
No full textThe almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, E-T, over 13.2 units of pseudorapidity, eta, for pPb collisions at a center-of-mass energy per nucleon pair of root s(NN) = 5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at -6.6 < eta < -5.2 is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and makes the measurement a particularly powerful test of event generators. For minimum bias pPb collisions the maximum value of dE(T)/d eta is 22 GeV, which implies an E-T per participant nucleon pair comparable to that of peripheral PbPb collisions at root s(NN) 7 = 2.76 TeV. The increase of dE(T)/d eta with centrality is much stronger for the lead-going side than for the proton-going side. The i dependence of dE(T)/d eta is sensitive to the eta range in which the centrality variable is defined. Several modern generators are compared to these results but none is able to capture all aspects of the eta and centrality dependence of the data and the correlations observed between different eta regions
A search for pair production of new light bosons decaying into muons in proton-proton collisions at 13 TeV
No full textA search for new light bosons decaying into muon pairs is presented using a data sample corresponding to an integrated luminosity of 35.9 fb(-1) of proton-proton collisions at a center-of-mass energy root s = 13 TeV, collected with the CMS detector at the CERN LHC. The search is model independent, only requiring the pair production of a new light boson and its subsequent decay to a pair of muons. No significant deviation from the predicted background is observed. A model independent limit is set on the product of the production cross section times branching fraction to dimuons squared times acceptance as a function of new light boson mass. This limit varies between 0.15 and 0.39 fb over a range of new light boson masses from 0.25 to 8.5 GeV. It is then interpreted in the context of the next-to-minimal supersymmetric standard model and a dark supersymmetry model that allows for nonnegligible light boson lifetimes. In both cases, there is significant improvement over previously published limits
Shaping Resonant Light Confinement and Optoelectronic Spectra Using Strain in Hierarchical Multiscale Structures
No full textHierarchically structured optical materials have been a topic of intriguing research interest due to the possibility of tailoring material properties beyond the limits of bulk continuum material design. Here, an optical confinement phenomenon in a hierarchically structured waveguide platform consisting of alternating clusters of nanostructured and planar microscale domains is demonstrated. An unconventional self-assembly-based strain-assisted nanomolding process is developed to fabricate these hierarchically structured multiperiodic waveguides. Further, these hierarchically patterned waveguides are used as substrates for solution-processed photodetectors. The optical confinement occurring due to the nanoscale scattering and the wavelength-dependent interaction between the planar and structured microdomains leads to an improved uniformity in the optoelectronic spectral response of these photodetectors. Furthermore, by tuning the multiperiodicity within the nanostructured domain structure, using a mechanical strain of 20%, an improvement of around 10% in the uniformity of the optoelectronic spectral response of the photodetectors is demonstrated. Simulations further show that these processes arise only in the presence of a hierarchical structure, due to multiscale interaction, through wavelength-selective coupling of scattered light from nanostructured domains to the planar microdomains. In summary, hierarchical structures can address optoelectronic problems that cannot be addressed by simpler structures
Robust variability index CFAR for non-homogeneous background
No full textRadar signal detection using constant false alarm rate (CFAR) detectors encounters many non-ideal situations making it difficult to characterise the background. These include the presence of multiple targets, clutter edges and their combination in the reference window. Designing an efficient CFAR for these situations is a non-trivial problem. Algorithms based on ordered statistics (OS), outlier rejection using sorting and sample by sample hypothesis testing, variability index (VI), ordered data VI are proposed in the literature. These approaches require expensive sorting or prior information on the depth of censoring. In this study, the authors propose robust VI CFAR (RVI-CFAR) that obviates sorting. RVI-CFAR computes the threshold in multiple stages. The first stage uses VI-CFAR to determine an adaptive threshold. Outlier rejection in the computation of background, mean ratio (MR) and VI is carried out in subsequent stages. The updated MR and VI statistics are used to refine switching decisions at every stage of processing. RVI-CFAR exhibits low CFAR loss in homogeneous and multiple target scenarios, meanwhile achieving superior performance compared to other censored CFAR techniques. The proposed RVI-CFAR is evaluated and shown to be robust for all the cases of non-homogeneity compared to OS CFAR
Discovery of Novel Approach for Regioselective Synthesis of Thioxotriaza-Spiro Derivatives via Oxalic Acid
No full textA vital approach for the synthesis of a range of novel thioxotriaza-spiro derivatives is described. These new heterocyclic systems are obtained via oxalic acid catalyzed reaction of alpha,beta-unsaturated ketones in the presence of 5,6-diamino-2-mercaptopyrimidine-4-ols; thus, spiro rings are constructed in one step. Notably, this transformation involves condensation of an amino group followed by enamine reaction with alkenes and subsequent reaction promoted by oxalic acid to afford spiro compounds with excellent regioselectivity
Petrogenesis of an alkaline lamprophyre (camptonite) with ocean island basalt (OIB)-affinity at the NW margin of the Cuddapah basin, eastern Dharwar craton, southern India
No full textWe report petrology and geochemistry (including Sr and Nd isotopes) of a fresh lamprophyre at Ankiraopalli area at the north-western margin of Paleo-Mesoproterozoic Cuddapah basin, eastern Dharwar craton, southern India. Ankiraopalli samples possess a typical lamprophyre porphyritic-panidiomorphic texture with phenocrysts of kaersutite and diopside set in a plagioclase dominant groundmass. Combined mineralogy and geochemistry classify it as alkaline lamprophyre in general and camptonite in particular. Contrary to the calc-alkaline and/or shoshonitic orogenic nature portrayed by lamprophyres occurring towards the western margin of the Cuddapah basin, the Ankiraopalli samples display trace element composition revealing striking similarity with those of ocean island basalts, Italian alkaline lamprophyres and highlights an anorogenic character. However, the Sr-87/Sr-86(initial) (0.710316 to 0.720016) and epsilon Nd-initial (-9.54 to -9.61) of the Ankiraopalli lamprophyre show derivation from an `enriched' mantle source showing long term enrichment of incompatible trace elements and contrast from those of (i) OIB, and (ii) nearby Mahbuhnagar alkaline mafic dykes of OIB affinity. Combining results of this study and recent advances made, multiple mantle domains are identified in the Eastern Dharwar craton which generated distinct Mesoproterozoic lamprophyre varieties. These include (i) Domain I, involving sub-continental lithospheric mantle source essentially metasomatized by subduction-derived melts/fluids (represented by orogenic calcalkaline and/or shoshonitic lamprophyres at the Mudigubba, the Udiripikonda and the Kadiri); (ii) Domain II, comprising a mixed sub-continental lithospheric and asthenospheric source (represented by orogenic-anorogenic, alkaline to calc-alkaline transitional lamprophyres at the Korakkodu), and (iii) Domain III, representing a sub-continental lithospheric source with a dominant overprint of an asthenospheric (plume) component (represented by essentially alkaline lamprophyres at the Ankiraopalli). Our study highlights the varied mantle source heterogeneities and complexity of geodynamic processes involved in the Neoarchean-Paleo/Mesoproterozoic evolution of the Eastern Dharwar craton
Clustering and correlations: Inferring resilience from spatial patterns in ecosystems
No full textIn diverse ecosystems, organisms cluster together in such a manner that the frequency distribution of cluster sizes is a power law function. Spatially explicit computational models of ecosystems suggest that a loss of such power law clustering may indicate a loss of ecosystem resilience; the empirical evidence in support for this hypothesis has been mixed. On the other hand, a well-known dynamical feature of systems with reduced resilience is the slower recovery from perturbations, a phenomenon known as critical slowing down (CSD). Here, we examine the relationship between spatial clustering and CSD to better understand the use of cluster size distributions as indicators of ecosystem resilience. Local positive feedback is an important driver of spatial clustering, while also affecting the dynamics of the ecosystem: Studies have demonstrated that positive feedback promotes abrupt regime shifts. Here, we analyse a spatial model of ecosystem transitions that enables us to disentangle the roles of local positive feedback and environmental stress on spatial patterns and ecosystem resilience. We demonstrate that, depending on the strength of positive feedback, power law clustering can occur at any distance from the critical threshold of ecosystem collapse. In fact, we find that for systems with strong positive feedback, which are more likely to exhibit abrupt transitions, there may be no loss of power law clustering prior to critical thresholds. Our analyses show that cluster size distributions are unrelated to the phenomenon of CSD and that loss of power law clustering is not a generic indicator of ecosystem resilience. Further, due to CSD, a power law feature does occur near critical thresholds but in a different quantity; specifically, a power law decay of spatial covariance of ecosystem state. Our work highlights the importance of links between local positive feedback, emergent spatial properties and how they may be used to interpret ecosystem resilience
Asymptotic Modeling of Nonlinear Bending and Buckling Behavior of Carbon Nanotubes
No full textThe present work investigates the nonlinear bending and buckling behavior of carbon nanotubes (CNTs) using variational asymptotic method. Considering a CNT as a slender beam structure, an asymptotically-correct nonlinear continuum beam model is presented. Through the resulting nonlinear moment-curvature relationship, the model captures the phenomenon of ovalization of the cross sections and local buckling of the CNT, which arises due to their geometrical nature. Further studies are performed in order to explore the effect of CNT wall thickness on the nonlinear bending behavior of the CNT structure. It is shown that the continuum modeling approach can capture the ovalization and further localization of the CNT deformation under bending. The study aims to provide a reduced-order modeling framework analyzing the inherent nonlinearities associated with the geometrical nature of CNTs