243 research outputs found
Performance Analysis and Optimization for Movable Antenna Aided Wideband Communications
Movable antenna (MA) has emerged as a promising technology to enhance
wireless communication performance by enabling the local movement of antennas
at the transmitter (Tx) and/or receiver (Rx) for achieving more favorable
channel conditions. As the existing studies on MA-aided wireless communications
have mainly considered narrow-band transmission in flat fading channels, we
investigate in this paper the MA-aided wideband communications employing
orthogonal frequency division multiplexing (OFDM) in frequency-selective fading
channels. Under the general multi-tap field-response channel model, the
wireless channel variations in both space and frequency are characterized with
different positions of the MAs. Unlike the narrow-band transmission where the
optimal MA position at the Tx/Rx simply maximizes the single-tap channel
amplitude, the MA position in the wideband case needs to balance the amplitudes
and phases over multiple channel taps in order to maximize the OFDM
transmission rate over multiple frequency subcarriers. First, we derive an
upper bound on the OFDM achievable rate in closed form when the size of the
Tx/Rx region for antenna movement is arbitrarily large. Next, we develop a
parallel greedy ascent (PGA) algorithm to obtain locally optimal solutions to
the MAs' positions for OFDM rate maximization subject to finite-size Tx/Rx
regions. To reduce computational complexity, a simplified PGA algorithm is also
provided to optimize the MAs' positions more efficiently. Simulation results
demonstrate that the proposed PGA algorithms can approach the OFDM rate upper
bound closely with the increase of Tx/Rx region sizes and outperform
conventional systems with fixed-position antennas (FPAs) under the wideband
channel setup
Design of Ultra-compact Graphene-based Superscatterers
The energy-momentum dispersion relation is a fundamental property of
plasmonic systems. In this paper, we show that the method of dispersion
engineering can be used for the design of ultra-compact graphene-based
superscatterers. Based on the Bohr model, the dispersion relation of the
equivalent planar waveguide is engineered to enhance the scattering cross
section of a dielectric cylinder. Bohr conditions with different orders are
fulfilled in multiple dispersion curves at the same resonant frequency. Thus
the resonance peaks from the first and second order scattering terms are
overlapped in the deepsubwavelength scale by delicately tuning the gap
thickness between two graphene layers. Using this ultra-compact graphene-based
superscatterer, the scattering cross section of the dielectric cylinder can be
enhanced by five orders of magnitude.Comment: This paper has been accepted by IEEE Journal of Selected topics in
Quantum Electronic
Magnetosome Gene Duplication as an Important Driver in the Evolution of Magnetotaxis in the Alphaproteobacteria
The evolution of microbial magnetoreception (or magnetotaxis) is of great interest in the fields of microbiology, evolutionary biology, biophysics, geomicrobiology, and geochemistry. Current genomic data from magnetotactic bacteria (MTB), the only prokaryotes known to be capable of sensing the Earthβs geomagnetic field, suggests an ancient origin of magnetotaxis in the domain Bacteria. Vertical inheritance, followed by multiple independent magnetosome gene cluster loss, is considered to be one of the major forces that drove the evolution of magnetotaxis at or above the class or phylum level, although the evolutionary trajectories at lower taxonomic ranks (e.g., within the class level) remain largely unstudied. Here we report the isolation, cultivation, and sequencing of a novel magnetotactic spirillum belonging to the genus Terasakiella (Terasakiella sp. strain SH-1) within the class Alphaproteobacteria. The complete genome sequence of Terasakiella sp. strain SH-1 revealed an unexpected duplication event of magnetosome genes within the mamAB operon, a group of genes essential for magnetosome biomineralization and magnetotaxis. Intriguingly, further comparative genomic analysis suggests that the duplication of mamAB genes is a common feature in the genomes of alphaproteobacterial MTB. Taken together, with the additional finding that gene duplication appears to have also occurred in some magnetotactic members of the Deltaproteobacteria, our results indicate that gene duplication plays an important role in the evolution of magnetotaxis in the Alphaproteobacteria and perhaps the domain Bacteria
Distinct Determinants in HIV-1 Vif and Human APOBEC3 Proteins Are Required for the Suppression of Diverse Host Anti-Viral Proteins
APOBEC3G (A3G) and related cytidine deaminases of the APOBEC3 family of proteins are potent inhibitors of many retroviruses, including HIV-1. Formation of infectious HIV-1 requires the suppression of multiple cytidine deaminases by Vif. HIV-1 Vif suppresses various APOBEC3 proteins through the common mechanism of recruiting the Cullin5-ElonginB-ElonginC E3 ubiquitin ligase to induce target protein polyubiquitination and proteasome-mediated degradation. The domains in Vif and various APOBEC3 proteins required for APOBEC3 recognition and degradation have not been fully characterized.In the present study, we have demonstrated that the regions of APOBEC3F (A3F) that are required for its HIV-1-mediated binding and degradation are distinct from those reported for A3G. We found that the C-terminal cytidine deaminase domain (C-CDD) of A3F alone is sufficient for its interaction with HIV-1 Vif and its Vif-mediated degradation. We also observed that the domains of HIV-1 Vif that are uniquely required for its functional interaction with full-length A3F are also required for the degradation of the C-CDD of A3F; in contrast, those Vif domains that are uniquely required for functional interaction with A3G are not required for the degradation of the C-CDD of A3F. Interestingly, the HIV-1 Vif domains required for the degradation of A3F are also required for the degradation of A3C and A3DE. On the other hand, the Vif domains uniquely required for the degradation of A3G are dispensable for the degradation of cytidine deaminases A3C and A3DE.Our data suggest that distinct regions of A3F and A3G are targeted by HIV-1 Vif molecules. However, HIV-1 Vif suppresses A3F, A3C, and A3DE through similar recognition determinants, which are conserved among Vif molecules from diverse HIV-1 strains. Mapping these determinants may be useful for the design of novel anti-HIV inhibitors
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The catalytic core of DEMETER guides active DNA demethylation in Arabidopsis.
The Arabidopsis DEMETER (DME) DNA glycosylase demethylates the maternal genome in the central cell prior to fertilization and is essential for seed viability. DME preferentially targets small transposons that flank coding genes, influencing their expression and initiating plant gene imprinting. DME also targets intergenic and heterochromatic regions, but how it is recruited to these differing chromatin landscapes is unknown. The C-terminal half of DME consists of 3 conserved regions required for catalysis in vitro. We show that this catalytic core guides active demethylation at endogenous targets, rescuing dme developmental and genomic hypermethylation phenotypes. However, without the N terminus, heterochromatin demethylation is significantly impeded, and abundant CG-methylated genic sequences are ectopically demethylated. Comparative analysis revealed that the conserved DME N-terminal domains are present only in flowering plants, whereas the domain architecture of DME-like proteins in nonvascular plants mainly resembles the catalytic core, suggesting that it might represent the ancestral form of the 5mC DNA glycosylase found in plant lineages. We propose a bipartite model for DME protein action and suggest that the DME N terminus was acquired late during land plant evolution to improve specificity and facilitate demethylation at heterochromatin targets
Optimized Synthesis of FeS Nanoparticles with a High Cr(VI) Removal Capability
FeS nanoparticles were synthesized using chemical precipitation method involving sulfide and ferrous solutions. Effects of important synthesis parameters including stabilizer, time taken for titration, horizontal oscillation speed, and initial salt concentration on the size of synthesized FeS nanoparticles were investigated by Orthogonal Array design. Increasing the CMC dosage significantly made the hydrodynamic diameter decrease between 0.05βwt.% and 0.15βwt.% while Na2S titration, oscillation rate, and Na2S concentration did not show significant influence on the hydrodynamic diameter of FeS nanoparticles. The synthesized FeS nanoparticles were characterized by using XRD (X-ray diffraction), TEM (transmission electron microscopy), and XPS (X-ray photoelectron spectroscopy). The as-synthesized FeS nanoparticles had an average size of 25 Β± 10βnm and had a better long-term stability after storage for 150 days compared to bare FeS particles. Because of the optimized process parameters, the synthesized FeS nanoparticles had a higher Cr(VI) removal capacity of 683βmg per gram of FeS in comparison to the previously reported cases, and up to 92.48% Cr(VI) was removed from aqueous solutions. The small size, special surface property, and high reactivity make the synthesized FeS nanoparticles a promising tool for the remediation of Cr(VI) contaminated soil and groundwater
The association between dietary intake of flavonoids and its subclasses and the risk of metabolic syndrome
BackgroundThe healthiest way to prevent metabolic syndrome (MetS) is through behavioral and nutritional adjustments. We examined the relationship between total flavonoids intake, flavonoid subclasses, and clinically manifest MetS.MethodsA cross-sectional analysis was conducted among 28,719 individuals from the National Health and Nutrition Examination Survey (NHANES) and Food and Nutrient Database for Dietary Studies (FNDDS) 2007β2011 and 2017β2018. Two 24-h reviews were conducted to determine flavonoids intake and subclasses. The link between flavonoids intake and MetS was investigated using a multivariate logistic regression model.ResultsQ2 and Q3 of total flavonoids intake were associated with 20 and 19% lower risk of incident MetS after adjusting age and sex. Anthocyanidins and flavanones intake in Q2 and Q3 substantially reduced the MetS risk compared to Q1. MetS risk decreased steadily as the total intake of flavonoids increased to 237.67 mg/d. Flavanones and anthocyanidins also displayed V-shaped relationship curves (34.37 and 23.13 mg/d).ConclusionMetS was adversely linked with total flavonoids intake, flavanones, and anthocyanidins. Moreover, the most effective doses of total flavonoids, flavanones, and anthocyanidins were 237.67, 34.37, and 23.13 mg/d, respectively, potentially preventing MetS
Egocentric Image Captioning for Privacy-Preserved Passive Dietary Intake Monitoring
Camera-based passive dietary intake monitoring is able to continuously
capture the eating episodes of a subject, recording rich visual information,
such as the type and volume of food being consumed, as well as the eating
behaviours of the subject. However, there currently is no method that is able
to incorporate these visual clues and provide a comprehensive context of
dietary intake from passive recording (e.g., is the subject sharing food with
others, what food the subject is eating, and how much food is left in the
bowl). On the other hand, privacy is a major concern while egocentric wearable
cameras are used for capturing. In this paper, we propose a privacy-preserved
secure solution (i.e., egocentric image captioning) for dietary assessment with
passive monitoring, which unifies food recognition, volume estimation, and
scene understanding. By converting images into rich text descriptions,
nutritionists can assess individual dietary intake based on the captions
instead of the original images, reducing the risk of privacy leakage from
images. To this end, an egocentric dietary image captioning dataset has been
built, which consists of in-the-wild images captured by head-worn and
chest-worn cameras in field studies in Ghana. A novel transformer-based
architecture is designed to caption egocentric dietary images. Comprehensive
experiments have been conducted to evaluate the effectiveness and to justify
the design of the proposed architecture for egocentric dietary image
captioning. To the best of our knowledge, this is the first work that applies
image captioning to dietary intake assessment in real life settings
Egocentric image captioning for privacy-preserved passive dietary intake monitoring
Camera-based passive dietary intake monitoring is able to continuously capture the eating episodes of a subject, recording rich visual information, such as the type and volume of food being consumed, as well as the eating behaviors of the subject. However, there currently is no method that is able to incorporate these visual clues and provide a comprehensive context of dietary intake from passive recording (e.g., is the subject sharing food with others, what food the subject is eating, and how much food is left in the bowl). On the other hand, privacy is a major concern while egocentric wearable cameras are used for capturing. In this article, we propose a privacy-preserved secure solution (i.e., egocentric image captioning) for dietary assessment with passive monitoring, which unifies food recognition, volume estimation, and scene understanding. By converting images into rich text descriptions, nutritionists can assess individual dietary intake based on the captions instead of the original images, reducing the risk of privacy leakage from images. To this end, an egocentric dietary image captioning dataset has been built, which consists of in-the-wild images captured by head-worn and chest-worn cameras in field studies in Ghana. A novel transformer-based architecture is designed to caption egocentric dietary images. Comprehensive experiments have been conducted to evaluate the effectiveness and to justify the design of the proposed architecture for egocentric dietary image captioning. To the best of our knowledge, this is the first work that applies image captioning for dietary intake assessment in real-life settings
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