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Cation exchange assisted dimensional down-conversion of perovskite thin films using vapor annealing: An interplay of tolerance factor
No full textThis work demonstrates a method to form 1-D ethylammonium lead iodide (EAPbI(3)) thin-films by dimensional down-conversion of 3-D methylammonium lead iodide (MAPbI(3)) perovskite. The process leverages cation-exchange that occurs during exposure to ethylamine vapor and subsequent annealing. Based on the extensive materials characterization, a detailed mechanism of the transformation is proposed. The transformation also improves the morphology of the films, yielding compact EAPbI(3) films with roughness of 50-100 nm, low-pin-hole density, and grain-size of 1-3 mu m. The process can be used to fabricate various EAPbI(3) optoelectronic devices. Since lower dimensional perovskites are more stable against moisture than MAPbI(3), the process can also be used to fabricate 3D-1D graded perovskite interfaces for materials study and to stabilize MAPbI(3) solar cells with a protective outer layer of EAPbI(3.
Ruthenium(II) Metalla2]catenanes and Macrocycles via Donor-Dependent Self-Assembly
No full textDonor-selective coordination-driven self-assembly of a bis(dipyrrin)-bridged new diruthenium acceptor (RuA) with dipyridyl and diimidazolyl donors has been reported. The self-assembly of the ruthenium(II) acceptor with imidazolyl donors resulted in the formation of either 2 + 2] self-assembled monomeric macrocycles (MMs) or a mixture of metalla2]catenanes (MCs) and MMs depending on the solvents used. On the contrary, similar self-assembly with the pyridyl donors resulted in simple 2 + 2] macrocycles (MMs) exclusively, irrespective of the solvents used. The new ruthenium acceptor and self-assembled macrocycles were systematically characterized by multinuclear NMR and electrospray ionization mass spectrometry study. The structure of one of the metalla2]catenanes (MC1) was further confirmed by single-crystal X-ray diffraction studies. Density functional theory calculations inferred that the interlocked structures with imidazolyl donors are stabilized by pi-pi interactions between the benzene rings, while such interactions cease to exist with the pyridyl linkers, leading to the formation of noninterlocked macrocycles
Enhancing the Dynamics of Water Confined between Graphene Oxide Surfaces with Janus Interfaces: A Molecular Dynamics Study
No full textGraphene oxide membranes have been widely studied for their potential applications in water desalination applications. To understand the influence of surface oxidation and the inherent heterogeneity imposed by opposing surfaces formed in macroscopic membranes, molecular dynamics simulations of water confined in nanopores (8-15 angstrom) made up of different surface types are carried out. The greatest differences are observed at 8 angstrom, which is the optimal separation distance for molecular sieving of ions. The dipole-dipole relaxation and HH rotational relaxation of confined water are the slowest between fully oxidized (OO) surfaces with a 2 order decrease in the dipole-dipole relaxation time observed adjacent to a graphene surface. The translational and rotational density of states show distinct blue shifts and red shifts, respectively, at the smaller separations, with the extent of the shifts dependent on the surface type. Self-intermediate scattering functions show a pronounced plateau region for the OO surfaces at 8 angstrom, suggestive of glasslike dynamics, and extended alpha-relaxations were observed for the other surfaces. Although water diffusivity is an order of magnitude smaller than bulk diffusivities at the smaller surface separations, water between the Janus surfaces always had the highest diffusivities. The free energy to transfer a water molecule from bulk water was found to be the smallest (similar to 4 kJ/mol) for the Janus surfaces, which have the lowest number of hydrophilic groups among the different systems studied. Thus, the Janus interface appears to provide the optimal environment for water transport, providing a design strategy while assembling graphene oxide-based membrane stacks for water purification
Constraining the minimal type-III seesaw model with naturalness, lepton flavor violation, and electroweak vacuum stability
No full textWe study the minimal type-III seesaw model in which we extend the standard model by adding two SU(2)(L) triplet fermions with zero hypercharge to explain the origin of the nonzero neutrino masses. We show that the naturalness conditions and the limits from lepton flavor violating decays provide very stringent bounds on the model parameters along with the constraints from the stability/metastability of the electroweak vacuum. We perform a detailed analysis of the model parameter space including all the constraints for both normal as well as inverted hierarchies of the light neutrino masses. We find that most of the regions that are allowed by lepton flavor violating decays and naturalness fall in the stable/metastable region depending on the values of the standard model parameters
Optical gradient force for tuning, actuation, and manipulation of nonlinearity in graphene nanomechanical resonator
No full textGraphene nano-mechanical resonators integrated over waveguides provide a powerful sensing platform based on the interaction of graphene with the evanescent wave. An integrated actuation scheme that does not compromise this interaction is required for optimal usage of the ultra-sensitive platform. Conventional electrical and optical actuation techniques are not favorable towards efficient utilization of the near-field interaction. We propose tuning and actuation of these resonators using on-chip optical gradient force due to the guided wave as an alternative to these conventional techniques. We have used the fundamental quasi-TM optical mode in a silicon waveguide in a finite-element model. We obtain a force-distribution that is spatially correlated with the fundamental mechanical mode of the graphene nano-mechanical resonator. We demonstrate that for an evanescent continuous-wave (CW) optical power of 8 mu W, the resonant frequency of the device can be tuned by about 24.5%. With an intensity-modulated optical power <= 0.1 mu W, the mechanical mode can be driven to nonlinearity. We also demonstrate cancellation of the Duffing nonlinearity at a CW power of 5.4 mu W, which can be used to improve the linear dynamic range of vibration. The distributed optical gradient force can produce linear resonant amplitudes that are 50% higher than those obtained using conventional actuation schemes. This actuation scheme is robust against fluctuations in the evanescent optical power and in the refractive index of the side-cladding of the waveguide. This ensures minimal cross-talk from the optical mode to the mechanical mode in nano-mechanical sensing applications
An algorithmic approach to South Indian classical music
No full textWe develop a theoretical framework for representation and automated generation of South Indian classical music. The foundational part of the latter is based on symbolic dynamics and is implemented by translating the lexicographic rules for a raga to constraints on a Markov chain whose state space is a layered graph. We analyze the statistical properties of this Markov chain from the point of view of information theory. We also develop several tools in music signal processing, such as, (a) a procedure for automated generation of gamakas or ornamental notes, unique to South Indian classical music, (b) rhythm synchronization, and (c) an algorithm for perceptual scale shifts. The Online Supplement has computer synthesized music from sankarabharadna raga, rhythm synchronized music for a Mohana raga composition, original and synthesized gamakas over madhyama for Begadda and Nilambari ragas, and perceptually scale shifted ragas Hindodla, Madhyamavati, suddha saveri, and Udaya ravi chandrika ragas from the base Mohana raga
Measurement of exclusive Upsilon photoproduction from protons in pPb collisions at root sNN=5.02 Tev
No full textThe exclusive photoproduction of (nS) meson states from protons, (nS) p (with n = 1, 2, 3), is studied in ultraperipheral pPb collisions at a centre-of-mass energy per nucleon pair of The measurement is performed using the decay mode, with data collected by the CMS experiment corresponding to an integrated luminosity of 32.6 nb(-1). Differential cross sections as functions of the nS) transverse momentum squared and rapidity y, are presented. The 1S) photoproduction cross section is extracted in the rapidity range < 2.2, which corresponds to photon-proton centre-of-mass energies in the range 91 W < 826 GeV. The data are compared to theoretical predictions based on perturbative quantum chromodynamics and to previous measurement
Global thermoacoustic oscillations in a thermally driven pulse tube
No full textWe obtain linearized, BiGlobal thermoacoustic solutions in a pulse tube driven via an imposed mean temperature gradient. Here, the pulse tube is treated as a key unit of a thermoacoustic heat engine, in which the conversion of thermal energy to useful acoustic fluctuations occurs. A primary goal of this work is to understand the hydrodynamic efficiency of the energy conversion process and how it depends upon some of the important operating parameters, including the geometry of the device which in the limit of long length-to-diameter ratio approaches the so-called narrow tube approximation. As this limit is frequently imposed in the wave propagation analyses of thermoacoustic devices, it is critical to investigate the physical connections of such a model to more realistic finite-length pulse tube configurations, which we do here. The mean flow is quiescent with an analytic mean temperature profile that still models the necessary physical details of the hot heat exchanger and regenerator. The computed thermoacoustic oscillations are found to be globally stable, approaching neutral stability conditions at the narrow tube limit. In finite-length tubes, three distinct types of modes are identified and analyzed. Here, within a linear framework, radial modes do appear to act as key enablers for longitudinal modes to be the primary carriers of acoustic energy from the pulse tube section, while the identified boundary modes, essentially numerical constructs, are ignored in the analysis. Further, a disturbance energy-based efficiency metric is constructed that provides mechanistic understanding of some of the key parameters in pulse tube operation. For finite-length tubes, it shows oscillations of the first asymmetric mode to be the most efficient, while the axisymmetric perturbations dominate for longer tubes that eventually lead to the idealized plane wave propagation
A Novel Fractional Harmonic d-q Domain Based Power Line Signaling Technique for Power Converters in a Microgrid
No full textTraditionally, the communication between power converters connected in a microgrid is established using a wired method or a wireless droop method. The shortcomings of these methods have opened up the possibility of power-line-based communication between converters. However, the conventional power line communication systems have the disadvantages of using high-frequency data carrying signals that are prone to attenuation. These systems also make use of explicit couplers, transmitters, and amplifiers that adds to the overall cost and infrastructure. In this paper, a novel fractional harmonic d-q domain based power line communication technique is proposed. A switched fractional harmonic current space vector is used to carry data. The primary control loop and the modulation algorithm of the converters are used for encoding and decoding of data. The proposed technique thus overcomes the disadvantages of the conventional power line communication systems and at the same time carries forward the advantages of it. The proposed technique is validated with sufficient experimental test results
A place for everything and everything in its place: spatial organization of individuals on nests of the primitively eusocial wasp Ropalidia marginata
No full textNon-random space use is common among animals across taxa and habitats. Social insects often use space non-randomly, outside as well as inside their nests. While such non-random space use outside the nest may improve foraging efficiency, inside the nest, it is often associated with the efficient division of labour. Non-random space use by adults on their nests has been hypothesized to result from dyadic dominance interactions, non-random distribution of tasks, differential activity levels, workers avoiding their queens or prophylactic avoidance of disease spread. These hypotheses are generally derived from species in which the tasks of the workers are themselves non-randomly distributed on the nest. Here, we study the primitively eusocial wasp Ropalidia marginata, in which tasks are not distributed non-randomly, and show that 62.4% +/- 16.2% of the adults nevertheless use space on their nest non-randomly. In this species, we find that nonrandom space use may help optimizing nutritional exchange between individuals while prophylactically minimizing disease spread among nest-mates. We did not find evidence for the roles of dominance interactions, activity levels or location of larvae in non-random space use. Spatial organization appears to be a mechanism of minimizing the costs and maximizing the benefits of social life