86 research outputs found
Featureless and non-fractionalized Mott insulators on the honeycomb lattice at 1/2 site filling
Within the Landau paradigm, phases of matter are distinguished by spontaneous
symmetry breaking. Implicit here is the assumption that a completely symmetric
state exists: a paramagnet. At zero temperature such quantum featureless
insulators may be forbidden, triggering either conventional order or
topological order with fractionalized excitations. Such is the case for
interacting particles when the particle number per unit cell, f, is not an
integer. But, can lattice symmetries forbid featureless insulators even at
integer f? An especially relevant case is the honeycomb (graphene) lattice ---
where free spinless fermions at f=1 (the two sites per unit cell mean f=1 is
half filling per site) are always metallic. Here we present wave functions for
bosons, and a related spin-singlet wave function for spinful electrons, on the
f=1 honeycomb, and demonstrate via quantum to classical mappings that they do
form featureless Mott insulators. The construction generalizes to symmorphic
lattices at integer f in any dimension. Our results explicitly demonstrate that
in this case, despite the absence of a non-interacting insulator at the same
filling, lack of order at zero temperature does not imply fractionalization.Comment: v2: major revision including new result on SU(2) spinful electron
state and additional author. v3: PNAS published version. 7 pages, 5 figures;
appendix 5 pages, 3 figure
The power of presence: The role of mindfulness at work for daily levels and change trajectories of psychological detachment and sleep quality.
High Performance Multicell Series Inverter-Fed Induction Motor Drive
This document is the Accepted Manuscript version of the following article: M. Khodja, D. Rahiel, M. B. Benabdallah, H. Merabet Boulouiha, A. Allali, A. Chaker, and M. Denai, ‘High-performance multicell series inverter-fed induction motor drive’, Electrical Engineering, Vol. 99 (3): 1121-1137, September 2017. The final publication is available at Springer via DOI: https://doi.org/10.1007/s00202-016-0472-4.The multilevel voltage-source inverter (VSI) topology of the series multicell converter developed in recent years has led to improved converter performance in terms of power density and efficiency. This converter reduces the voltage constraints between all cells, which results in a lower transmission losses, high switching frequencies and the improvement of the output voltage waveforms. This paper proposes an improved topology of the series multicell inverter which minimizes harmonics, reduces torque ripples and losses in a variable-speed induction motor drive. The flying capacitor multilevel inverter topology based on the classical and modified phase shift pulse width modulation (PSPWM, MPSPWM) techniques are applied in this paper to minimize harmonic distortion at the inverter output. Simulation results are presented for a 2-kW induction motor drive and the results obtained demonstrate reduced harmonics, improved transient responses and reference tracking performance of the voltage in the induction motor and consequently reduced torque ripplesPeer reviewe
Identifying Topological Order by Entanglement Entropy
Topological phases are unique states of matter incorporating long-range
quantum entanglement, hosting exotic excitations with fractional quantum
statistics. We report a practical method to identify topological phases in
arbitrary realistic models by accurately calculating the Topological
Entanglement Entropy (TEE) using the Density Matrix Renormalization Group
(DMRG). We argue that the DMRG algorithm naturally produces a minimally
entangled state, from amongst the quasi-degenerate ground states in a
topological phase. This proposal both explains the success of this method, and
the absence of ground state degeneracy found in prior DMRG sightings of
topological phases. We demonstrate the effectiveness of the calculational
procedure by obtaining the TEE for several microscopic models, with an accuracy
of order when the circumference of the cylinder is around ten times
the correlation length. As an example, we definitively show the ground state of
the quantum antiferromagnet on the kagom\'e lattice is a topological
spin liquid, and strongly constrain the full identification of this phase of
matter.Comment: 20 pages, 6 figure
Cell cycle phase perturbations and apoptosis in tumour cells induced by aplidine
Aplidine, dehydrodidemnin B, is a marine depsipeptide isolated from the Mediterranean tunicate Aplidium albicans currently in phase II clinical trial. In human Molt-4 leukaemia cells Aplidine was found to be cytotoxic at nanomolar concentrations and to induce both a G1 arrest and a G2 blockade. The drug-induced cell cycle perturbations and subsequent cell death do not appear to be related to macromolecular synthesis (protein, RNA, DNA) since the effects occur at concentrations (e.g. 10 nM) in which macromolecule synthesis was not markedly affected. Ten nM Aplidine for 1 h inhibited ornithine decarboxylase activity, with a subsequently strong decrease in putrescine levels. This finding has questionable relevance since addition of putrescine did not significantly reduce the cell cycle perturbations or the cytotoxicity of Aplidine. The cell cycle perturbations caused by Aplidine were also not due to an effect on the cyclin-dependent kinases. Although the mechanism of action of Aplidine is still unclear, the cell cycle phase perturbations and the rapid induction of apoptosis in Molt-4 cells appear to be due to a mechanism different from that of known anticancer drugs
A survey on modeling of microgrids—From fundamental physics to phasors and voltage sources
Die Verkn�pfungen von Frequenz, D�mpfung und Steuerwinkel beim Schwingkreiswechselrichter
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