130 research outputs found
Real-space recipes for general topological crystalline states
Topological crystalline states are short-range entangled states jointly
protected by onsite and crystalline symmetries. While the non-interacting limit
of these states, e.g., the topological crystalline insulators, have been
intensively studied in band theory and have been experimentally discovered, the
classification and diagnosis of their strongly interacting counterparts are
relatively less well understood. Here we present a unified scheme for
constructing all topological crystalline states, bosonic and fermionic, free
and interacting, from real-space "building blocks" and "connectors". Building
blocks are finite-size pieces of lower dimensional topological states protected
by onsite symmetries alone, and connectors are "glue" that complete the open
edges shared by two or multiple pieces of building blocks. The resulted
assemblies are selected against two physical criteria we call the "no-open-edge
condition" and the "bubble equivalence", which, respectively, ensure that each
selected assembly is gapped in the bulk and cannot be deformed to a product
state. The scheme is then applied to obtaining the full classification of
bosonic topological crystalline states protected by several onsite symmetry
groups and each of the 17 wallpaper groups in two dimensions and 230 space
groups in three dimensions. We claim that our real-space recipes give the
complete set of topological crystalline states for bosons and fermions, and
prove the boson case analytically using a spectral sequence expansion of group
cohomology.Comment: 17+44 pages, 7+1 figures, 0+2 tables. The content is the same as the
published version, but arranged differentl
Diagnosis for topological semimetals in the absence of spin-orbital coupling
Topological semimetals are under intensive theoretical and experimental
studies. The first step of these studies is always the theoretical (numerical)
predication of one of several candidate materials, starting from first
principles. In these calculations, it is crucial that all topological band
crossings, including their types and positions in the Brillouin zone, are
found. While band crossings along high-symmetry lines, which are routinely
scanned in numerics, are simple to locate, the ones at generic momenta are
notoriously time-consuming to find, and may be easily missed. In this paper, we
establish a theoretical scheme of diagnosis for topological semimetals where
all band crossings are at generic momenta in systems with time-reversal
symmetry and negligible spin-orbital coupling. The scheme only uses the
symmetry (inversion and rotation) eigenvalues of the valence bands at
high-symmetry points in the BZ as input, and provides the types, numbers and
configurations of all topological band crossings, if any, at generic momenta.
The nature of new diagnosis scheme allows for full automation and
parallelizations, and paves way to high throughput numerical predictions of
topological materials.Comment: 21 pages, 5 figures, 1 table; v4: accepted in PRX, a "PRELIMINARIES"
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Location- and keyword-based querying of geo-textual data: a survey
With the broad adoption of mobile devices, notably smartphones, keyword-based search for content has seen increasing use by mobile users, who are often interested in content related to their geographical location. We have also witnessed a proliferation of geo-textual content that encompasses both textual and geographical information. Examples include geo-tagged microblog posts, yellow pages, and web pages related to entities with physical locations. Over the past decade, substantial research has been conducted on integrating location into keyword-based querying of geo-textual content in settings where the underlying data is assumed to be either relatively static or is assumed to stream into a system that maintains a set of continuous queries. This paper offers a survey of both the research problems studied and the solutions proposed in these two settings. As such, it aims to offer the reader a first understanding of key concepts and techniques, and it serves as an āindexā for researchers who are interested in exploring the concepts and techniques underlying proposed solutions to the querying of geo-textual data.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversityThis research was supported in part by MOE Tier-2 Grant MOE2019-T2-2-181, MOE Tier-1 Grant RG114/19, an NTU ACE Grant, and the Singtel Cognitive and Artificial Intelligence Lab for Enterprises (SCALE@NTU), which is a collaboration between Singapore Telecommunications Limited (Singtel) and Nanyang Technological University (NTU) that is funded by the Singapore Government through the Industry Alignment Fund Industry Collaboration Projects Grant, and by the Innovation Fund Denmark centre, DIREC
Analysis of Peptides and Proteins in Their Binding to GroEL
The GroEL-GroES is an essential molecular chaperon system that assists protein folding in cell. Binding of various substrate proteins to GroEL is one of the key aspects in GroEL-assisted protein folding. Small peptides may mimic segments of the substrate proteins in contact with GroEL, and allow detailed structural analysis of the interactions. A model peptide SBP has been shown to bind to a region in GroEL that is important for binding of substrate proteins. Here, we investigated whether the observed GroEL-SBP interaction represented those of GroEL-substrate proteins, and whether SBP was able to mimic various aspects of substrate proteins in GroE- assisted protein folding cycle. We found that SBP competed with substrate proteins, including Ī±-lactalbumin, rhodanese, and malate dehydrogenase, in binding to GroEL. SBP stimulated GroEL ATP hydrolysis rate in a manner similar to that of Ī±-lactalbumin. SBP did not prevent GroES from binding to GroEL, and GroES association reduced the ATPase rates of GroEL/SBP and GroEL/Ī±-lactalbumin to a comparable extent. Binding of both SBP and Ī±-lactalbumin to apo GroEL was dominated by hydrophobic interaction. Interestingly, association of Ī±- lactalbumin to GroEL/GroES was thermodynamically distinct from that to GroEL with reduced affinity and decreased contribution from hydrophobic interaction. However, SBP did not display such differential binding behaviors to apo GroEL and GroEL/GroES, likely due to the lack of a contiguous polypeptide chain that links all of the bound peptide fragments. Nevertheless, studies using peptides provide valuable information on the nature of GroEL-substrate protein interaction, which is central to understand the mechanism of GroEL-assisted protein folding
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Oligomeric Procyanidin Nanoliposomes Prevent Melanogenesis and UV Radiation-Induced Skin Epithelial Cell (HFF-1) Damage
The potential protective effect of nanoliposomes loaded with lotus seedpod oligomeric procyanidin (LSOPC) against melanogenesis and skin damaging was investigated. Fluorescence spectroscopy showed that, after encapsulation, the LSOPC-nanoliposomes still possessed strong inhibitory effects against melanogenesis, reducing the activity of both monophenolase and diphenolase. Molecular docking indicated that LSOPC could generate intense interactive configuration with tyrosinase through areneāH, areneāarene, and hydrophobic interaction. An ultraviolet radiated cell-culture model (human foreskin fibroblast cell (HFF-1)) was used to determine the protective effects of the LSOPC-nanoliposomes against skin aging and damage. Results showed that LSOPC-nanoliposomes exerted the highest protective effects against both ultraviolet B (UVB) and ultraviolet A (UVA) irradiation groups compared with non-encapsulated LSOPC and a control (vitamin C). Superoxide dismutase (SOD) and malonaldehyde (MDA) assays demonstrated the protection mechanism may be related to the anti-photooxidation activity of the procyanidin. Furthermore, a hydroxyproline assay suggested that the LSOPC-nanoliposomes had a strong protective effect against collagen degradation and/or synthesis after UVA irradiation
All "Magic Angles" Are "Stable" Topological
We show that the electronic structure of the low-energy bands in the small
angle-twisted bilayer graphene consists of a series of semi-metallic and
topological phases. In particular we are able to prove, using an approximate
low-energy particle-hole symmetry, that the gapped set of bands that exist
around all magic angles has what we conjecture to be a stable topological index
stabilized by a magnetic symmetry and reflected in the odd winding of the
Wilson loop in the Moir\'e BZ. The approximate, emergent particle-hole symmetry
is essential to the topology of graphene: when strongly broken, non-topological
phases can appear. Our paper underpins topology as the crucial ingredient to
the description of low-energy graphene. We provide a -band short range
tight-binding model whose lower bands have the same topology, symmetry, and
flatness as those of the twisted graphene, and which can be used as an
effective low-energy model. We then perform large-scale ( atoms per unit
cell, 40 days per -point computing time) ab-initio calculations of a
series of small angles, from to , which show a more complex
and somewhat qualitatively different evolution of the symmetry of the
low-energy bands than that of the theoretical Moir\'e model, but which confirms
the topological nature of the system. At certain angles, we find no insulating
filling in graphene at electrons per Moir\'e unit cell. The ab-initio
evolution of gaps tends to differ from that of the continuum Moir\'e model.Comment: 7+23 pages, 3+12 figures, 2+3 tables; v2: references added, note
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