599 research outputs found
Robust, gapped, flat bands at half-filling in the minimal model of the superconducting metal-organic framework, Cu-BHT
The superconducting metal-organic framework Cu-BHT forms a kagome lattice
with metals at the vertices and ligands along the bonds. We show that a
tight-binding model with metal and ligand sites on this lattice yields five
flat topological bands (FTBs), three of which are partially occupied at
half-filling, with large gaps between them and all other bands. Long-range
hopping induces curvature in the FTBs but leaves them flatter and more isolated
than those in twisted bilayer graphene. Thus, framework materials are ideal
materials for exploring flat band physics at high electronic densities.Comment: 5 pages, 3 figure
Photonic quantum signatures of chaos and boson sampling
Boson sampling is a paradigmatic example of a task that can be performed by a
quantum photonic computer yet is hard for digital classical computers. In a
typical boson sampling experiment, the scattering amplitude is determined by
the permanent of a submatrix of a unitary drawn from an ensemble of random
matrices. Random matrix theory plays a very important role in quite diverse
fields while at the same time being intimately related to quantum signatures of
chaos. Within this framework, a chaotic quantum system exhibits level
statistics characteristic of ensembles of random matrices. Such quantum
signatures are encoded in the unitary evolution and so in this work we combine
the dynamics of chaotic systems with boson sampling. One of the key results of
our work is that we demonstrate the intimate relation between out-of-time-order
correlators and boson sampling. We show that the unitary dynamics of a Floquet
system may be exploited to perform sampling tasks with identical particles
using single-mode phase shifters and multiport beamsplitters. At the end of our
paper propose a photonic implementation of the multiparticle kicked rotor,
which provides a concrete example of our general approach.Comment: 17 pages, 7 figures. Comments are welcom
Electron microscopy structure of human APC/C-CDH1-EMI1 reveals multimodal mechanism of E3 ligase shutdown.
The anaphase-promoting complex/cyclosome (APC/C) is a similar to 1.5-MDa multiprotein E3 ligase enzyme that regulates cell division by promoting timely ubiquitin-mediated proteolysis of key cell-cycle regulatory proteins. Inhibition of human APC/C-CDH1 during interphase by early mitotic inhibitor 1 (EMI1) is essential for accurate coordination of DNA synthesis and mitosis. Here, we report a hybrid structural approach involving NMR, electron microscopy and enzymology, which reveal that EMI1's 143-residue C-terminal domain inhibits multiple APC/C-CDH1 functions. The intrinsically disordered D-box, linker and tail elements, together with a structured zinc-binding domain, bind distinct regions of APC/C-CDH1 to synergistically both block the substrate-binding site and inhibit ubiquitin-chain elongation. The functional importance of intrinsic structural disorder is explained by enabling a small inhibitory domain to bind multiple sites to shut down various functions of a 'molecular machine' nearly 100 times its size
Gate control of Mott metal-insulator transition in a 2D metal-organic framework
Strong electron-electron Coulomb interactions in materials can lead to a vast
range of exotic many-body quantum phenomena, including Mott metal-insulator
transitions, magnetic order, quantum spin liquids, and unconventional
superconductivity. These many-body phases are strongly dependent on band
occupation and can hence be controlled via the chemical potential. Flat
electronic bands in two-dimensional (2D) and layered materials such as the
kagome lattice, enhance strong electronic correlations. Although theoretically
predicted, correlated-electron phases in monolayer 2D metal-organic frameworks
(MOFs) - which benefit from efficient synthesis protocols and tunable
properties - with a kagome structure have not yet been realised experimentally.
Here, we synthesise a 2D kagome MOF comprised of 9,10-dicyanoanthracene
molecules and copper atoms on an atomically thin insulator, monolayer hexagonal
boron nitride (hBN) on Cu(111). Scanning tunnelling microscopy (STM) and
spectroscopy reveal an electronic energy gap of ~200 meV in this MOF,
consistent with dynamical mean-field theory predictions of a Mott insulating
phase. By tuning the electron population of kagome bands, via either
template-induced (via local work function variations of the hBN/Cu(111)
substrate) or tip-induced (via the STM probe) gating, we are able to induce
Mott metal-insulator transitions in the MOF. These findings pave the way for
devices and technologies based on 2D MOFs and on electrostatic control of
many-body quantum phases therein.Comment: 19 pages, 4 figure
Important HIV-associated conditions in HIV-infected infants and children
This article is the last in a series of 6 articles that discussed the management of HIV-infected children in a clinically orientated, practical and concise fashion. The topics covered previously include; 1) Preventing and diagnosing HIV-infection in infants and children, 2) Initiating anti-retroviral therapy in HIV-infected infants and children, 3) Maintaining HIV-infected infants and children on anti-retroviral therapy, 4) Common opportunistic infection in HIV-infected children: Part 1-respiratory infections and 5) Part 2 non-respiratory infections.
South African Family Practice Vol. 49 (4) 2007: pp.19-2
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