171 research outputs found
Synthesis, Properties, and Their Potential Application of Covalent Organic Frameworks (COFs)
Covalent organic frameworks (COFs) represent an emerging class of crystalline porous polymers, which are ingeniously assembled with organic building blocks through reversible covalent bonds. The well-defined crystalline porous structures, easy functional modification, high surface area, together with structural designability and diversity have offered the COFs superior potential in various applications, such as catalysis, gas adsorption and separation, and optoelectricity. Since the pioneer work of Omar Yaghi in 2005, this field has developed rapidly and attracted much attention from researchers with diverse expertise. In this chapter, we describe the basic design concepts, the recent synthetic advancements, and the frontiers of functional exploration in gas adsorption and storage. Special emphasis is placed on their potential application in heterogeneous catalysis field. Finally, the prospects of COFs and remaining issues in these fields are indicated
Safeguarding Massive MIMO Aided HetNets Using Physical Layer Security
This paper exploits the potential of physical layer security in massive
multiple-input multiple-output (MIMO) aided two-tier heterogeneous networks
(HetNets). We focus on the downlink secure transmission in the presence of
multiple eavesdroppers. We first address the impact of massive MIMO on the
maximum receive power based user association. We then derive the tractable
upper bound expressions for the secrecy outage probability of a HetNets user.We
show that the implementation of massive MIMO significantly improves the secrecy
performance, which indicates that physical layer security could be a promising
solution for safeguarding massive MIMO HetNets. Furthermore, we show that the
secrecy outage probability of HetNets user first degrades and then improves
with increasing the density of PBSs
Electrochemistry of myoglobin on grapheneâSnO2 nanocomposite modified electrode and its electrocatalysis
AbstractIn this paper direct electrochemistry and electrocatalysis of myoglobin (Mb) immobilized on a graphene (GR)âSnO2 nanocomposite modified carbon ionic liquid electrode was reported. GRâSnO2 nanocomposite was synthesized by a simple solution method and further characterized by TEM and SEM, which exhibited large surface area beneficial for Mb immobilization. Spectroscopic results indicated Mb retained its native structure without denaturation after mixed with nanocomposite. Electrochemical investigation showed that a pair of well-defined redox peaks appeared on cyclic voltammogram, indicating that direct electron transfer of Mb with the underlying electrode was realized. The results could be attributed to the presence of GRâSnO2 nanocomposite that could enhance the electron transfer between the protein and the electrode. The Mb modified electrode exhibited good stability and catalytic activity to the electroreduction of NaNO2 in the concentration range from 0.2 to 350.0ÎŒmolLâ1 with wider dynamic range and lower detection limit. Therefore the fabricated electrode has the potential application in the third-generation electrochemical biosensor
Acetylation-defective mutant of PparÎł is associated with decreased lipid synthesis in breast cancer cells.
In our prior publications we characterized a conserved acetylation motif (K(R)xxKK) of evolutionarily related nuclear receptors. Recent reports showed that peroxisome proliferator activated receptor gamma (PPARÎł) deacetylation by SIRT1 is involved in delaying cellular senescence and maintaining the brown remodeling of white adipose tissue. However, it still remains unknown whether lysyl residues 154 and 155 (K154/155) of the conserved acetylation motif (RIHKK) in PparÎł1 are acetylated. Herein, we demonstrate that PparÎł1 is acetylated and regulated by both endogenous TSA-sensitive and NAD-dependent deacetylases. Acetylation of lysine 154 was identified by mass spectrometry (MS) while deacetylation of lysine 155 by SIRT1 was confirmed by in vitro deacetylation assay. An in vivo labeling assay revealed K154/K155 as bona fide acetylation sites. The conserved acetylation sites of PparÎł1 and the catalytic domain of SIRT1 are both required for the interaction between PparÎł1 and SIRT1. Sirt1 and PparÎł1 converge to govern lipid metabolism in vivo. Acetylation-defective mutants of PparÎł1 were associated with reduced lipid synthesis in ErbB2 overexpressing breast cancer cells. Together, these results suggest that the conserved lysyl residues K154/K155 of PparÎł1 are acetylated and play an important role in lipid synthesis in ErbB2-positive breast cancer cells
Resolving the genetic paradox of invasions: Preadapted genomes and postintroduction hybridization of bigheaded carps in the Mississippi River Basin
The genetic paradox of biological invasions is complex and multifaceted. In particular, the relative role of disparate propagule sources and genetic adaptation through postintroduction hybridization has remained largely unexplored. To add resolution to this paradox, we investigate the genetic architecture responsible for the invasion of two invasive Asian carp species, bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) (bigheaded carps) that experience extensive hybridization in the Mississippi River Basin (MRB). We sequenced the genomes of bighead and silver carps (~1.08G bp and ~1.15G bp, respectively) and their hybrids collected from the MRB. We found moderateâtoâhigh heterozygosity in bighead (0.0021) and silver (0.0036) carps, detected significantly higher dN/dS ratios of singleâcopy orthologous genes in bigheaded carps versus 10 other species of fish, and identified genes in both species potentially associated with environmental adaptation and other invasionârelated traits. Additionally, we observed a high genomic similarity (96.3% in all syntenic blocks) between bighead and silver carps and over 90% embryonic viability in their experimentally induced hybrids. Our results suggest intrinsic genomic features of bigheaded carps, likely associated with life history traits that presumably evolved within their native ranges, might have facilitated their initial establishment of invasion, whereas ex-situ interspecific hybridization between the carps might have promoted their range expansion. This study reveals an alternative mechanism that could resolve one of the genetic paradoxes in biological invasions and provides invaluable genomic resources for applied research involving bigheaded carps
Single âSwiss-rollâ microelectrode elucidates the critical role of iron substitution in conversion-type oxides
Advancing the lithium-ion battery technology requires the understanding of electrochemical processes in electrode materials with high resolution, accuracy, and sensitivity. However, most techniques today are limited by their inability to separate the complex signals from slurry-coated composite electrodes. Here, we use a three-dimensional âSwiss-rollâ microtubular electrode that is incorporated into a micrometer-sized lithium battery. This on-chip platform combines various in situ characterization techniques and precisely probes the intrinsic electrochemical properties of each active material due to the removal of unnecessary binders and additives. As an example, it helps elucidate the critical role of Fe substitution in a conversion-type NiO electrode by monitoring the evolution of Fe2O3 and solid electrolyte interphase layer. The markedly enhanced electrode performances are therefore explained. Our approach exposes a hitherto unexplored route to tracking the phase, morphology, and electrochemical evolution of electrodes in real time, allowing us to reveal information that is not accessible with bulk-level characterization techniques
Electronically phase separated nano-network in antiferromagnetic insulating LaMnO3/PrMnO3/CaMnO3 tricolor superlattice
Strongly correlated materials often exhibit an electronic phase separation
(EPS) phenomena whose domain pattern is random in nature. The ability to
control the spatial arrangement of the electronic phases at microscopic scales
is highly desirable for tailoring their macroscopic properties and/or designing
novel electronic devices. Here we report the formation of EPS nanoscale network
in a mono-atomically stacked LaMnO3/CaMnO3/PrMnO3 superlattice grown on SrTiO3
(STO) (001) substrate, which is known to have an antiferromagnetic (AFM)
insulating ground state. The EPS nano-network is a consequence of an internal
strain relaxation triggered by the structural domain formation of the
underlying STO substrate at low temperatures. The same nanoscale network
pattern can be reproduced upon temperature cycling allowing us to employ
different local imaging techniques to directly compare the magnetic and
transport state of a single EPS domain. Our results confirm the one-to-one
correspondence between ferromagnetic (AFM) to metallic (insulating) state in
manganite. It also represents a significant step in a paradigm shift from
passively characterizing EPS in strongly correlated systems to actively
engaging in its manipulation
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