161 research outputs found
Hierarchical and High-Girth QC LDPC Codes
We present a general approach to designing capacity-approaching high-girth
low-density parity-check (LDPC) codes that are friendly to hardware
implementation. Our methodology starts by defining a new class of
"hierarchical" quasi-cyclic (HQC) LDPC codes that generalizes the structure of
quasi-cyclic (QC) LDPC codes. Whereas the parity check matrices of QC LDPC
codes are composed of circulant sub-matrices, those of HQC LDPC codes are
composed of a hierarchy of circulant sub-matrices that are in turn constructed
from circulant sub-matrices, and so on, through some number of levels. We show
how to map any class of codes defined using a protograph into a family of HQC
LDPC codes. Next, we present a girth-maximizing algorithm that optimizes the
degrees of freedom within the family of codes to yield a high-girth HQC LDPC
code. Finally, we discuss how certain characteristics of a code protograph will
lead to inevitable short cycles, and show that these short cycles can be
eliminated using a "squashing" procedure that results in a high-girth QC LDPC
code, although not a hierarchical one. We illustrate our approach with designed
examples of girth-10 QC LDPC codes obtained from protographs of one-sided
spatially-coupled codes.Comment: Submitted to IEEE Transactions on Information THeor
Restless Bandits with Average Reward: Breaking the Uniform Global Attractor Assumption
We study the infinite-horizon restless bandit problem with the average reward
criterion, under both discrete-time and continuous-time settings. A fundamental
question is how to design computationally efficient policies that achieve a
diminishing optimality gap as the number of arms, , grows large. Existing
results on asymptotical optimality all rely on the uniform global attractor
property (UGAP), a complex and challenging-to-verify assumption. In this paper,
we propose a general, simulation-based framework that converts any single-armed
policy into a policy for the original -armed problem. This is accomplished
by simulating the single-armed policy on each arm and carefully steering the
real state towards the simulated state. Our framework can be instantiated to
produce a policy with an optimality gap. In the discrete-time
setting, our result holds under a simpler synchronization assumption, which
covers some problem instances that do not satisfy UGAP. More notably, in the
continuous-time setting, our result does not require any additional assumptions
beyond the standard unichain condition. In both settings, we establish the
first asymptotic optimality result that does not require UGAP.Comment: 29 pages, 4 figure
Self-supervised Heterogeneous Graph Variational Autoencoders
Heterogeneous Information Networks (HINs), which consist of various types of
nodes and edges, have recently demonstrated excellent performance in graph
mining. However, most existing heterogeneous graph neural networks (HGNNs)
ignore the problems of missing attributes, inaccurate attributes and scarce
labels for nodes, which limits their expressiveness. In this paper, we propose
a generative self-supervised model SHAVA to address these issues
simultaneously. Specifically, SHAVA first initializes all the nodes in the
graph with a low-dimensional representation matrix. After that, based on the
variational graph autoencoder framework, SHAVA learns both node-level and
attribute-level embeddings in the encoder, which can provide fine-grained
semantic information to construct node attributes. In the decoder, SHAVA
reconstructs both links and attributes. Instead of directly reconstructing raw
features for attributed nodes, SHAVA generates the initial low-dimensional
representation matrix for all the nodes, based on which raw features of
attributed nodes are further reconstructed to leverage accurate attributes. In
this way, SHAVA can not only complete informative features for non-attributed
nodes, but rectify inaccurate ones for attributed nodes. Finally, we conduct
extensive experiments to show the superiority of SHAVA in tackling HINs with
missing and inaccurate attributes
Absolute frequency measurements with a robust, transportable ^{40}Ca^{+} optical clock
We constructed a transportable 40Ca+ optical clock (with an estimated minimum
systematic shift uncertainty of 1.3*10^(-17) and a stability of
5*10^(-15)/sqrt{tau} ) that can operate outside the laboratory. We transported
it from the Innovation Academy for Precision Measurement Science and
Technology, Chinese Academy of Sciences, Wuhan to the National Institute of
Metrology, Beijing. The absolute frequency of the 729 nm clock transition was
measured for up to 35 days by tracing its frequency to the second of
International System of Units. Some improvements were implemented in the
measurement process, such as the increased effective up-time of 91.3 % of the
40Ca+ optical clock over a 35-day-period, the reduced statistical uncertainty
of the comparison between the optical clock and hydrogen maser, and the use of
longer measurement times to reduce the uncertainty of the frequency
traceability link. The absolute frequency measurement of the 40Ca+ optical
clock yielded a value of 411042129776400.26 (13) Hz with an uncertainty of
3.2*10^(-16), which is reduced by a factor of 1.7 compared with our previous
results. As a result of the increase in the operating rate of the optical
clock, the accuracy of 35 days of absolute frequency measurement can be
comparable to the best results of different institutions in the world based on
different optical frequency measurements.Comment: 15 pages, 5 figure
Inhibitory mechanism of vortioxetine on CYP450 enzymes in human and rat liver microsomes
Vortioxetine is a novel anti-major depression disorder drug with a high safety profile compared with other similar drugs. However, little research has been done on drug-drug interactions (DDI) about vortioxetine. In this paper, the inhibitory effect of vortioxetine on cytochrome P450 (CYP450) and the type of inhibitory mechanism were investigated in human and rat liver microsomes. We set up an in vitro incubation system of 200 μL to measure the metabolism of probe substrates at the present of vortioxetine at 37°C. The concentrations of the metabolites of probe substrates were all measured by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method. It was found no time-dependent inhibition (TDI) of vortioxetine through determination of half-maximal inhibitory concentration (IC50) shift values. The enzymes and metabolites involved in this experiment in human and rats were as follows: CYP3A4/CYP3A (midazolam); CYP2B6/CYP2B (bupropion); CYP2D6/CYP2D (dextromethorphan); CYP2C8/CYP2C-1 (amodiaquine); CYP2C9/CYP2C-2 (losartan); and CYP2C19/CYP2C-3 (mephenytoin). We found that vortioxetine competitively inhibited CYP2C19 and CYP2D6 in human liver microsomes (HLMs) with inhibition constant (Ki) values of 2.17 μM and 9.37 μM, respectively. It was noncompetitive inhibition for CYP3A4 and CYP2C8, and its Ki values were 7.26 μM and 6.96 μM, respectively. For CYP2B6 and CYP2C9, vortioxetine exhibited the mixed inhibition with Ki values were 8.55 μM and 4.17 μM, respectively. In RLMs, the type of vortioxetine inhibition was uncompetitive for CYP3A and CYP2D (Ki = 4.41 and 100.9 μM). The inhibition type was competitive inhibition, including CYP2B and CYP2C-2 (Ki = 2.87 and 0.12 μM). The inhibition types of CYP2C-1 and CYP2C-3 (Ki = 39.91 and 4.23 μM) were mixed inhibition and noncompetitive inhibition, respectively. The study of the above mechanism will provide guidance for the safe clinical use of vortioxetine so that the occurrence of DDI can be avoided
Transcriptome and digital gene expression analysis reveal immune responses of mantle and visceral mass pearl culturing in Hyriopsis cumingii
Biomineralization is a widespread phenomenon in marine mollusks and is responsible for the production of shells and pearls. However, the regulatory mechanisms governing the adaptive immune responses in the mollusk mantle and visceral mass during mineralization remain unclear. In this work, we examined the mantle and visceral mass immune responses of Hyriopsis cumingii during pearl culture using high-throughput sequencing techniques. A mantle transcriptome database was established using transcriptome sequencing technology and reference to the major databases. Digital gene expression profiling was used to identify the differentially expressed genes of mantle and visceral mass at different insertion periods. Moreover, quantitative real-time PCR was used to verify the expression of five immune-related genes. Transcriptome sequencing results showed 257,457 unigenes were identified. Digital gene expression profiles showed 1389, 3572, 1888, and 2613 differentially expressed genes (DEGs) in the mantle and visceral mass at 5, 20, 50, and 90 d after insertion, respectively, with the highest number at 20 d and the lowest at 5 d after insertion (q < 0.05). A cluster analysis of the DEGs showed similar clustering and expression features in the mantle to the control group, and at 5, 50 and 90Â d, after mantle insertion. The DEGs in the visceral mass showed similar clustering and expression features to the control group and at 5, 20 and 50Â d after insertion. We also screened 22 immune-related DEGs in the mantle and visceral mass during the same pearl culture period, including serine/threonine-protein kinase NLK, C-type lectin, and galectin. The greatest number of DEGs was found 90Â d after insertion. Compared with the mantle, more immune-related DEGs were down-regulated than up-regulated in the visceral mass during pearl culture, indicating that the immune regulatory mechanisms in the visceral mass and the mantle differ during pearl culture, and that the visceral mass is liable to higher infection and mortality rates. Quantitative real-time PCR results showed that the expression of five immune-related genes was consistent with DGE results. Our findings will further knowledge of the immune systems that are present in the mantle and visceral mass during pearl culture
Elemental topological Dirac semimetal: {\alpha}-Sn on InSb(111)
Three-dimensional (3D) topological Dirac semimetals (TDSs) are rare but
important as a versatile platform for exploring exotic electronic properties
and topological phase transitions. A quintessential feature of TDSs is 3D Dirac
fermions associated with bulk electronic states near the Fermi level. Using
angle-resolved photoemission spectroscopy (ARPES), we have observed such bulk
Dirac cones in epitaxially-grown {\alpha}-Sn films on InSb(111), the first such
TDS system realized in an elemental form. First-principles calculations confirm
that epitaxial strain is key to the formation of the TDS phase. A phase diagram
is established that connects the 3D TDS phase through a singular point of a
zero-gap semimetal phase to a topological insulator (TI) phase. The nature of
the Dirac cone crosses over from 3D to 2D as the film thickness is reduced
Identification of Glycine Receptor α3 as a Colchicine-Binding Protein
Colchicine (Col) is considered a kind of highly effective alkaloid for preventing and treating acute gout attacks (flares). However, little is known about the underlying mechanism of Col in pain treatment. We have previously developed a customized virtual target identification method, termed IFPTarget, for small-molecule target identification. In this study, by using IFPTarget and ligand similarity ensemble approach (SEA), we show that the glycine receptor alpha 3 (GlyRα3), which play a key role in the processing of inflammatory pain, is a potential target of Col. Moreover, Col binds directly to the GlyRα3 as determined by the immunoprecipitation and bio-layer interferometry assays using the synthesized Col-biotin conjugate (linked Col and biotin with polyethylene glycol). These results suggest that GlyRα3 may mediate Col-induced suppression of inflammatory pain. However, whether GlyRα3 is the functional target of Col and serves as potential therapeutic target in gouty arthritis requires further investigations
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