Emergence of quasi-one-dimensional physics in Mo3_3S7_7(dmit)3_3, a nearly-isotropic three-dimensional molecular crystal

We report density functional theory calculations for Mo$_3$S$_7$(dmit)$_3$. We derive an ab initio tight-binding model from overlaps of Wannier orbitals; finding a layered model with interlayer hopping terms $\sim3/4$ the size of the in-plane terms. The in-plane Hamiltonian interpolates the kagom\'e and honeycomb lattices. It supports states localized to dodecahedral rings within the plane, which populate one-dimensional (1D) bands and lead to a quasi-1D spin-one model on a layered honeycomb lattice once interactions are included. Two lines of Dirac cones also cross the Fermi energy.Comment: 5 pages, 3 figure

Activity-Aware Electrocardiogram-based Passive Ongoing Biometric Verification

Identity fraud due to lost, stolen or shared information or tokens that represent an individual\u27s identity is becoming a growing security concern. Biometric recognition - the identification or verification of claimed identity, shows great potential in bridging some of the existing security gaps. It has been shown that the human Electrocardiogram (ECG) exhibits sufficiently unique patterns for use in biometric recognition. But it also exhibits significant variability due to stress or activity, and signal artifacts due to movement. In this thesis, we develop a novel activity-aware ECG-based biometric recognition scheme that can verify/identify under different activity conditions. From a pattern recognition standpoint, we develop algorithms for preprocessing, feature extraction and probabilistic classification. We pay particular attention to the applicability of the proposed scheme in ongoing biometric verification of claimed identity. Finally we propose a wearable prototype architecture of our scheme

Modeling and performance analysis of a small scale direct driven PMSG based wind energy conversion systems

This paper proposes a small scale wind energy conversion system comprising a direct driven PMSG connected to the grid through a power electronic interface. The variable voltage variable frequency output from the wind generator is rectified, boosted and converted in to a fixed voltage fixed frequency output. The boost chopper maintains a constant DC at the inverter terminals. The modulation index of the inverter is adjusted to extract maximum power from the wind. The system components such as wind turbine, PMSG, power electronic interface are modeled in MATLAB/SIMULINK .The power flow analysis of the entire system is carried out for various wind velocities and the effect of duty ratio and modulation index is studied and optimum duty ratio for maximum power extraction at different wind speeds is found out and the simulation results are presented Keywords: wind energy conversion systems, permanent magnet synchronous generator, direct drive

Influence of spin fluctuations near the Mott transition: a DMFT study

Dynamics of magnetic moments near the Mott metal-insulator transition is investigated by a combined slave-rotor and Dynamical Mean-Field Theory solution of the Hubbard model with additional fully-frustrated random Heisenberg couplings. In the paramagnetic Mott state, the spinon decomposition allows to generate a Sachdev-Ye spin liquid in place of the collection of independent local moments that typically occurs in the absence of magnetic correlations. Cooling down into the spin-liquid phase, the onset of deviations from pure Curie behavior in the spin susceptibility is found to be correlated to the temperature scale at which the Mott transition lines experience a marked bending. We also demonstrate a weakening of the effective exchange energy upon approaching the Mott boundary from the Heisenberg limit, due to quantum fluctuations associated to zero and doubly occupied sites.Comment: 6 pages, 3 figures. V3 was largely expande

Haldane phase in the hubbard model at 2/3-filling for the organic molecular compound Mo3 S7 (dmit)3

We report the discovery of a correlated insulator with a bulk gap at 2/3 filling in a geometrically frustrated Hubbard model that describes the low-energy physics of Mo3S7(dmit)(3). This is very different from the Mott insulator expected at half-filling. We show that the insulating phase, which persists even for very weak electron-electron interactions (U), is adiabatically connected to the Haldane phase and is consistent with experiments on Mo3S7(dmit)(3)

Fast-cure ionogel electrolytes with improved ion transport kinetics at room temperature

Fast-cure 1-ethyl-3-methylimidazolium trifluoromethanesulfonate-based ionogels have been realised for the first time. The influence of curing temperature on the structure of ionogels and their performance as the electrolyte for electric double-layer capacitors (EDLCs) has been investigated. Hybrid ionogels were synthesised via a non-hydrolytic sol-gel route and were fully gelled post heat-treating at 125, 150, 175 and 200 °C for 60 min with minimal shrinkage. Charge-transfer resistance (a rate-limiting parameter in cell kinetics during charge/discharge cycles) was reduced by ∼80% by increasing the heat-treatment temperature; this was partially attributed to the interlocking effect facilitated by high curing temperature. We report a maximum areal capacitance of 95 mF cm−2. Due to ∼40% increase in the penetrability coefficient of the ionic liquid, the electrode ‘full’ wetting time dropped from 48 to 5 h when the curing temperature was increased above 150 °C. These results were supported by SEM and Raman spectroscopy to characterise the effect of high temperature heat-treatment on the electrode-ionogel interface and the degree of electrode wetting by the ionic liquid. The fast-cure fabrication process for ionogels removes one of the major hurdles in their industrial application while the improved room temperature ion transport kinetics expands the potential application of ionic liquid-based electrochemical systems

Low-energy effective theories of the two-thirds filled Hubbard model on the triangular necklace lattice

Motivated by Mo3S7(dmit)(3), we investigate the Hubbard model on the triangular necklace lattice at two-thirds filling. We show, using second-order perturbation theory, that in the molecular limit, the ground state and the low-energy excitations of this model are identical to those of the spin-one Heisenberg chain. The latter model is known to be in the symmetry-protected topological Haldane phase. Away from this limit we show, on the basis of symmetry arguments and density matrix renormalization group (DMRG) calculations, that the low-energy physics of the Hubbard model on the triangular necklace lattice at two-thirds filling is captured by the ferromagnetic Hubbard-Kondo lattice chain at half-filling. This is consistent with and strengthens previous claims that both the half-filled ferromagnetic Kondo lattice model and the two-thirds filled Hubbard model on the triangular necklace lattice are also in the Haldane phase. A connection between Hund's rules and Nagaoka's theorem is also discussed