9,863 research outputs found
Mott insulating phases and quantum phase transitions of interacting spin-3/2 fermionic cold atoms in optical lattices at half filling
We study various Mott insulating phases of interacting spin-3/2 fermionic
ultracold atoms in two-dimensional square optical lattices at half filling.
Using a generalized one-band Hubbard model with hidden SO(5) symmetry, we
identify two distinct symmetry breaking phases: the degenerate
antiferromagnetic spin-dipole/spin-octupole ordering and spin-quadrupole
ordering, depending on the sign of the spin-dependent interaction. These two
competing orders exhibit very different symmetry properties, low energy
excitations and topological characterizations. Near the SU(4) symmetric point,
a quantum critical state with a -flux phase may emerge due to strong
quantum fluctuations, leading to spin algebraic correlations and gapless
excitations.Comment: 11 pages, 4 figure
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Chiral Sulfinamidourea and Strong Brønsted Acid–Cocatalyzed Enantioselective Povarov Reaction to Access Tetrahydroquinolines
This protocol describes a method for the laboratory synthesis of enantiomerically enriched, chiral tetrahydroisoquinolines through the application of a chiral sulfinamido urea catalyst for the Povarov reaction. Tetrahydroisoquinolines are bicyclic organic frameworks present in a wide assortment of natural and synthetic biologically important compounds including ​martinelline, ​scoulerine and ​tubocurarine. The methodology involves the [4+2] cycloaddition of a N-arylimines with electron-rich olefins such as vinyl lactams and dihydropyrroles in the presence of a two-catalyst system consisting of an achiral strong Brønsted acid (​o-nitrobenzenesulfonic acid), together with the chiral sulfinamido urea derivative 1. The anion-binding properties of the ​urea lead to the association of the ion pair that results from protonation of the imine substrate. Cycloaddition is followed by spontaneous proton loss with re-aromatization to provide the tetrahydroisoquinoline products in highly enantio-enriched form.Chemistry and Chemical Biolog
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Fluid drag-reducing effect and mechanism of superhydrophobic
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this paper, drag-reducing property and mechanism of superhydrophobic surface are investigated.
Superhydrophobic surfaces with micro-nano textures were fabricated and tested using SEM and contact
angle measurement. Experiments on a channel and a flat plate with superhydrophobic surface were
conducted separately. For the channel flow, the drag was acquired by measuring the pressure loss. A 54%
drag reduction was found both in laminar and turbulent flow over Re range from 500 to 5000. For flow over
a plate, PIV measurement was used to obtain the velocity distribution at Reδ=12000. There was a 19%
reduction on the total stress in the whole boundary layer. Suppressions of the turbulence intensities and the
Reynolds shear stress were found, which may cause the drag reduction
Quantum spin Hall effect and spin-charge separation in a kagome lattice
A two-dimensional kagome lattice is theoretically investigated within a
simple tight-binding model, which includes the nearest neighbor hopping term
and the intrinsic spin-orbit interaction between the next nearest neighbors. By
using the topological winding properties of the spin-edge states on the
complex-energy Riemann surface, the spin Hall conductance is obtained to be
quantized as () in insulating phases. This result keeps
consistent with the numerical linear-response calculation and the
\textbf{Z} topological invariance analysis. When the sample boundaries
are connected in twist, by which two defects with flux are introduced, we
obtain the spin-charge separated solitons at 1/3 (or 2/3) filling.Comment: 13 NJP pages, 7 figure
5d SCFTs from Isolated Complete Intersection Singularities
In this paper, we explore the zoo of 5d superconformal field theories (SCFTs)
constructed from M-theory on Isolated Complete Intersection Singularities
(ICIS). We systematically investigate the crepant resolution of such
singularities, and obtain a classification of rank models with a
smooth crepant resolution and smooth exceptional divisors, as well as a number
of infinite sequences with the same smoothness properties. For these models, we
study their Coulomb branch properties and compute the flavor symmetry algebra
from the resolved CY3 and/or the magnetic quiver. We check the validity of the
conjectures relating the properties of the 5d SCFT and the 4d
SCFT from IIB superstring on the same singularity. When the 4d
SCFT has a Lagrangian quiver gauge theory description, one can obtain the
magnetic quiver of the 5d theory by gauging flavor symmetry, which encodes the
5d Higgs branch information. Regarding the smoothness of the crepant resolution
and integrality of 4d Coulomb branch spectrum, we find examples with a smooth
resolved CY3 and smooth exceptional divisors, but fractional 4d Coulomb branch
spectrum. Moreover, we compute the discrete (higher)-symmetries of the 5d/4d
SCFTs from the link topology for a few examples.Comment: v2, 87 page
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