119 research outputs found
Level Set Dynamics and the Non-blowup of the 2D Quasi-geostrophic Equation
In this article we apply the technique proposed in Deng-Hou-Yu (Comm. PDE,
2005) to study the level set dynamics of the 2D quasi-geostrophic equation.
Under certain assumptions on the local geometric regularity of the level sets
of , we obtain global regularity results with improved growth estimate
on . We further perform numerical simulations to
study the local geometric properties of the level sets near the region of
maximum . The numerical results indicate that the
assumptions on the local geometric regularity of the level sets of in
our theorems are satisfied. Therefore these theorems provide a good explanation
of the double exponential growth of observed in this
and past numerical simulations.Comment: 25 pages, 10 figures. Corrected a few typo
On Singularity Formation of a Nonlinear Nonlocal System
We investigate the singularity formation of a nonlinear nonlocal system. This
nonlocal system is a simplified one-dimensional system of the 3D model that was
recently proposed by Hou and Lei in [13] for axisymmetric 3D incompressible
Navier-Stokes equations with swirl. The main difference between the 3D model of
Hou and Lei and the reformulated 3D Navier-Stokes equations is that the
convection term is neglected in the 3D model. In the nonlocal system we
consider in this paper, we replace the Riesz operator in the 3D model by the
Hilbert transform. One of the main results of this paper is that we prove
rigorously the finite time singularity formation of the nonlocal system for a
large class of smooth initial data with finite energy. We also prove the global
regularity for a class of smooth initial data. Numerical results will be
presented to demonstrate the asymptotically self-similar blow-up of the
solution. The blowup rate of the self-similar singularity of the nonlocal
system is similar to that of the 3D model.Comment: 28 pages, 9 figure
Exploiting Active RIS in NOMA Networks with Hardware Impairments
Active reconfigurable intelligent surface (ARIS) is a promising way to
compensate for multiplicative fading attenuation by amplifying and reflecting
event signals to selected users. This paper investigates the performance of
ARIS assisted non-orthogonal multiple access (NOMA) networks over cascaded
Nakagami-m fading channels. The effects of hardware impairments (HIS) and
reflection coefficients on ARIS-NOMA networks with imperfect successive
interference cancellation (ipSIC) and perfect successive interference
cancellation (pSIC) are considered. More specifically, we develop new precise
and asymptotic expressions of outage probability and ergodic data rate with
ipSIC/pSIC for ARIS-NOMA-HIS networks. According to the approximated analyses,
the diversity orders and multiplexing gains for couple of non-orthogonal users
are attained in detail. Additionally, the energy efficiency of ARIS-NOMA-HIS
networks is surveyed in delay-limited and delay-tolerant transmission schemes.
The simulation findings are presented to demonstrate that: i) The outage
behaviors and ergodic data rates of ARIS-NOMA-HIS networks precede that of ARIS
aided orthogonal multiple access (OMA) and passive reconfigurable intelligent
surface (PRIS) aided OMA; ii) As the reflection coefficient of ARIS increases,
ARIS-NOMA-HIS networks have the ability to provide the strengthened outage
performance; and iii) ARIS-NOMA-HIS networks are more energy efficient than
ARIS/PRIS-OMA networks and conventional cooperative schemes
A Mild Dyssynchronous Contraction Pattern Detected by SPECT Myocardial Perfusion Imaging Predicts Super-Response to Cardiac Resynchronization Therapy
Background: Using single photon emission computed tomography myocardial perfusion imaging (SPECT MPI) with phase analysis (PA), we aimed to identify the predictive value of a new contraction pattern in cardiac resynchronization therapy (CRT) response. Methods: Left ventricular mechanical dyssynchrony (LVMD) was evaluated using SPECT MPI with PA in non-ischemic dilated cardiomyopathy (DCM) patients with left bundle branch block (LBBB) indicated for CRT. CRT super-response was defined as LV ejection fraction (EF) ≥50% or an absolute increase of LVEF \u3e15%. The LV contraction was categorized as the mild dyssynchronous pattern when the phase standard deviation (PSD) ≤ 40.3° and phase histogram bandwidth (PBW) ≤ 111.9°, otherwise it was defined as severe dyssynchronous pattern which was further characterized as U-shaped, heterogeneous or homogenous pattern. Results: The final cohort comprised 74 patients, including 32 (43.2%) in mild dyssynchronous group, 17 (23%) in U-shaped group, 19 (25.7%) in heterogeneous group, and 6 (8.1%) in homogenous group. The mild dyssynchronous group had lower PSD and PBW than U-shaped, heterogeneous, and homogenous groups ( \u3c 0.0001). Compared to patients with the heterogeneous pattern, the odds ratios (ORs) with 95% confidence intervals (CIs) for CRT super-response were 10.182(2.43-42.663), 12.8(2.545-64.372), and 2.667(0.327-21.773) for patients with mild dyssynchronous, U-shaped, and homogenous pattern, respectively. After multivariable adjustment, mild dyssynchronous group remained associated with increased CRT super-response (adjusted OR 5.709, 95% CI 1.152-28.293). Kaplan-Meier curves showed that mild dyssynchronous group demonstrated a better long-term prognosis. Conclusions: The mild dyssynchronous pattern in patients with DCM is associated with an increased CRT super-response and better long-term prognosis
The molecular biological characteristics of Vibrio vulnificus isolated in Guangzhou
ObjectiveTo investigate the molecular and biological characteristics of Vibrio vulnificus (V. vulnificus)isolated from Guangzhou.MethodsThirty-eight strains of V. vulnificus were collected from Guangzhou, and whole-genome sequences were obtained. The population structure of V. vulnificus was inferred by utilizing 50 publicly available genome sequences obtained from NCBI. FineSTRUCTURE software was employed for this analysis. Antibiotic resistance and virulence factors were identified using CARD, ResFinder, and VFDB databases.ResultsFour well-supported phylogenetic groups or lineages (L1-L4) were identified, and all genomes of the strains in Guangzhou were classified into L1 (47%) and L2 (53%). The predominant ST were ST357, ST157, ST136, ST139, ST345, ST303, and so on, which showed regional aggregation. Multiple genome identification of V. vulnificus revealed 11 drug resistance genes: acrF, CRP, catB9, rpoC, ugd, and others. MCR genes related to polymyxin resistance were identified in V. vulnificus for the first time. The species also carries 23 virulence genes in five classes encoding flagellin, type Ⅱ secretory system protein, capsular polysaccharide, RtxA toxin, iron overload, and other virulence-related genes.ConclusionVibrio vulnificus in Guangzhou undergoes highly homologous recombination and carries a variety of antimicrobial resistance genes and virulence-related genes. Therefore, monitoring and management of Vibrio vulnificus should be strengthened
Chemical Genetic Analysis and Functional Characterization of Staphylococcal Wall Teichoic Acid 2-Epimerases Reveals Unconventional Antibiotic Drug Targets
Here we describe a chemical biology strategy performed in Staphylococcus aureus and Staphylococcus epidermidis to identify MnaA, a 2-epimerase that we demonstrate interconverts UDP-GlcNAc and UDP-ManNAc to modulate substrate levels of TarO and TarA wall teichoic acid (WTA) biosynthesis enzymes. Genetic inactivation of mnaA results in complete loss of WTA and dramatic in vitro β-lactam hypersensitivity in methicillin-resistant S. aureus (MRSA) and S. epidermidis (MRSE). Likewise, the β-lactam antibiotic imipenem exhibits restored bactericidal activity against mnaA mutants in vitro and concomitant efficacy against 2-epimerase defective strains in a mouse thigh model of MRSA and MRSE infection. Interestingly, whereas MnaA serves as the sole 2-epimerase required for WTA biosynthesis in S. epidermidis, MnaA and Cap5P provide compensatory WTA functional roles in S. aureus. We also demonstrate that MnaA and other enzymes of WTA biosynthesis are required for biofilm formation in MRSA and MRSE. We further determine the 1.9Å crystal structure of S. aureus MnaA and identify critical residues for enzymatic dimerization, stability, and substrate binding. Finally, the natural product antibiotic tunicamycin is shown to physically bind MnaA and Cap5P and inhibit 2-epimerase activity, demonstrating that it inhibits a previously unanticipated step in WTA biosynthesis. In summary, MnaA serves as a new Staphylococcal antibiotic target with cognate inhibitors predicted to possess dual therapeutic benefit: as combination agents to restore β-lactam efficacy against MRSA and MRSE and as non-bioactive prophylactic agents to prevent Staphylococcal biofilm formation.publishe
Associations of Amylin with Inflammatory Markers and Metabolic Syndrome in Apparently Healthy Chinese
BACKGROUND: Cellular and animal studies implicate multiple roles of amylin in regulating insulin action, glucose and lipid metabolisms. However, the role of amylin in obesity related metabolic disorders has not been thoroughly investigated in humans. Therefore, we aimed to evaluate the distribution of circulating amylin and its association with metabolic syndrome (MetS) and explore if this association is influenced by obesity, inflammatory markers or insulin resistance in apparently healthy Chinese. METHODS: A population-based sample of 1,011 Chinese men and women aged 35-54 years was employed to measure plasma amylin, inflammatory markers (C-reactive protein [CRP] and interleukin-6 [IL-6]), insulin, glucose and lipid profiles. MetS was defined according to the updated National Cholesterol Education Program Adult Treatment Panel III criteria for Asian-Americans. RESULTS: Plasma amylin concentrations were higher in overweight/obese participants than normal-weight counterparts (P<0.001) without sex difference. Circulating amylin was positively associated with CRP, IL-6, BMI, waist circumference, blood pressure, fasting glucose, insulin, amylin/insulin ratio, HOMA-IR, LDL cholesterol and triglycerides, while negatively associated with HDL cholesterol (all P<0.001). After multiple adjustments, the risk of MetS was significantly higher (odds ratio 3.71; 95% confidence interval: 2.53 to 5.46) comparing the highest with the lowest amylin quartile. The association remained significant even further controlling for BMI, inflammatory markers, insulin or HOMA-IR. CONCLUSIONS: Our study suggests that amylin is strongly associated with inflammatory markers and MetS. The amylin-MetS association is independent of established risk factors of MetS, including obesity, inflammatory markers and insulin resistance. The causal role of hyperamylinemia in the development of MetS needs to be confirmed prospectively
MCP-1 Upregulates Amylin Expression in Murine Pancreatic β Cells through ERK/JNK-AP1 and NF-κB Related Signaling Pathways Independent of CCR2
BACKGROUND: Amylin is the most abundant component of islet amyloid implicated in the development of type 2 diabetes. Plasma amylin levels are elevated in individuals with obesity and insulin resistance. Monocyte chemoattractant protein-1 (MCP-1, CCL2) is involved in insulin resistance of obesity and type 2 diabetes. We investigated the effect of MCP-1 on amylin expression and the underlying mechanisms with murine pancreatic β-cell line MIN6 and pancreatic islets. METHODOLOGY/PRINCIPAL FINDINGS: We found that MCP-1 induced amylin expression at transcriptional level and increased proamylin and intermediate forms of amylin at protein level in MIN6 cells and islets. However, MCP-1 had no effect on the expressions of proinsulin 1 and 2, as well as prohormone convertase (PC) 1/3 and PC2, suggesting that MCP-1 specifically induces amylin expression in β-cells. Mechanistic studies showed that although there is no detectable CCR2 mRNA in MIN6 cells and islets, pretreatment of MIN6 cells with pertussis toxin inhibited MCP-1 induced amylin expression, suggesting that alternative Gi-coupled receptor(s) mediates the inductive effect of MCP-1. MCP-1 rapidly induced ERK1/2 and JNK phosphorylation. Inhibitors for MEK1/2 (PD98059), JNK (SP600125) or AP1 (curcumin) significantly inhibited MCP-1-induced amylin mRNA expression. MCP-1 failed to induce amylin expression in pancreatic islets isolated from Fos knockout mice. EMSA showed that JNK and ERK1/2 were involved in MCP-1-induced AP1 activation. These results suggest that MCP-1 induces murine amylin expression through AP1 activation mediated by ERK1/2 or JNK. Further studies showed that treatment of MIN6 cells with NF-κB inhibitor or overexpression of IκBα dominant-negative construct in MIN6 cells significantly inhibited MCP-1-induced amylin expression, suggesting that NF-κB related signaling also participates in MCP-1-induced murine amylin expression. CONCLUSIONS/SIGNIFICANCE: MCP-1 induces amylin expression through ERK1/2/JNK-AP1 and NF-κB related signaling pathways independent of CCR2. Amylin upregulation by MCP-1 may contribute to elevation of plasma amylin in obesity and insulin resistance
Aridity-driven shift in biodiversity–soil multifunctionality relationships
From Springer Nature via Jisc Publications RouterHistory: received 2021-01-07, accepted 2021-08-12, registration 2021-08-25, pub-electronic 2021-09-09, online 2021-09-09, collection 2021-12Publication status: PublishedFunder: National Natural Science Foundation of China (National Science Foundation of China); doi: https://doi.org/10.13039/501100001809; Grant(s): 31770430Abstract: Relationships between biodiversity and multiple ecosystem functions (that is, ecosystem multifunctionality) are context-dependent. Both plant and soil microbial diversity have been reported to regulate ecosystem multifunctionality, but how their relative importance varies along environmental gradients remains poorly understood. Here, we relate plant and microbial diversity to soil multifunctionality across 130 dryland sites along a 4,000 km aridity gradient in northern China. Our results show a strong positive association between plant species richness and soil multifunctionality in less arid regions, whereas microbial diversity, in particular of fungi, is positively associated with multifunctionality in more arid regions. This shift in the relationships between plant or microbial diversity and soil multifunctionality occur at an aridity level of ∼0.8, the boundary between semiarid and arid climates, which is predicted to advance geographically ∼28% by the end of the current century. Our study highlights that biodiversity loss of plants and soil microorganisms may have especially strong consequences under low and high aridity conditions, respectively, which calls for climate-specific biodiversity conservation strategies to mitigate the effects of aridification
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