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Showing papers by "Southwest University published in 2012"


Journal ArticleDOI
TL;DR: The prevalence of chronic kidney disease in China was high in north and southwest and southwest regions compared with other regions, and economic development was independently associated with the presence of albuminuria.

1,588 citations


Journal ArticleDOI
TL;DR: In this paper, a facile, low cost and high yield method has been developed to prepare single and multi-layer graphene quantum dots (GQDs) from XC-72 carbon black by chemical oxidation.
Abstract: A facile, low cost and high yield method has been developed to prepare single- and multi-layer graphene quantum dots (GQDs) from XC-72 carbon black by chemical oxidation. The single-layer GQDs are demonstrated to be excellent probes for cellular imaging, while the multi-layer GQDs may offer great potential applications in optoelectronic devices.

537 citations


Journal ArticleDOI
Zhou Ch1, Wang Y
TL;DR: This work systematically reviewed the recent researches and developments of the whole range of triazole compounds as medicinal drugs, including antifungal, anticancer, antibacterial, antitubercular, antiviral, anti-inflammatory and analgesic, anticonvulsant, antiparasitic, antidiabetic and anti-obesitic.
Abstract: Triazole compounds containing three nitrogen atoms in the five-membered aromatic azole ring are readily able to bind with a variety of enzymes and receptors in biological system via diverse non-covalent interactions, and thus display versatile biological activities. The related researches in triazole-based derivatives as medicinal drugs have been an extremely active topic, and numerous excellent achievements have been acquired. Noticeably, a large number of triazole compounds as clinical drugs or candidates have been frequently employed for the treatment of various types of diseases, which have shown their large development value and wide potential as medicinal agents. This work systematically reviewed the recent researches and developments of the whole range of triazole compounds as medicinal drugs, including antifungal, anticancer, antibacterial, antitubercular, antiviral, anti-inflammatory and analgesic, anticonvulsant, antiparasitic, antidiabetic, anti-obesitic, antihistaminic, anti-neuropathic, antihypertensive as well as other biological activities. The perspectives of the foreseeable future in the research and development of triazole-based compounds as medicinal drugs are also presented. It is hoped that this review will serve as a stimulant for new thoughts in the quest for rational designs of more active and less toxic triazole medicinal drugs.

455 citations


Journal ArticleDOI
TL;DR: This tutorial review attempts to summarize the recent important progress towards the development of nanoporous metals, with special emphasis on fabrication methods and advanced electrochemical applications, such as electrocatalysts, chemical sensors and energy systems.
Abstract: Nanoporous metals, a representative type of nanostructured material, possess intriguing properties to generate enormously promising potentials for various important applications. In particular, with the advances of fabrication strategies, nanoporous metals with a variety of superior properties including unique pore structure, large specific surface area and high electrical conductivity have fuelled up great interests to explore their electrocatalytic properties and greatly extend their emerging applications in electrochemical sensing and energy systems. This tutorial review attempts to summarize the recent important progress towards the development of nanoporous metals, with special emphasis on fabrication methods and advanced electrochemical applications, such as electrocatalysts, chemical sensors and energy systems. Key scientific issues and prospective directions of research are also discussed.

420 citations


Journal ArticleDOI
TL;DR: In this article, a composite TFA anode is proposed for Li-ion batteries, which not only provides large interfacial area for lithium insertion/extraction but also reduces the diffusion pathways for electronic and ionic transport, leading to improved capacity retention on cycling even at high discharge-charge rates.
Abstract: Highly ordered TiO2@α-Fe2O3 core/shell arrays on carbon textiles (TFAs) have been fabricated by a stepwise, seed-assisted, hydrothermal approach and further investigated as the anode materials for Li-ion batteries (LIBs). This composite TFA anode exhibits superior high-rate capability and outstanding cycling performance. The specific capacity of the TFAs is much higher than that of pristine carbon textiles (CTs) and TiO2 nanorod arrays on carbon textiles (TRAs), indicating a positive synergistic effect of the material and structural hybridization on the enhancement of the electrochemical properties. This composite nanostructure not only provides large interfacial area for lithium insertion/extraction but should also be beneficial in reducing the diffusion pathways for electronic and ionic transport, leading to the improved capacity retention on cycling even at high discharge–charge rates. It is worth emphasizing that the CT substrates also present many potential virtues for LIBs as flexible electronic devices owing to the stretchable, lightweight and biodegradable properties. The fabrication strategy presented here is facile, cost-effective, and scalable, which opens new avenues for the design of optimal composite electrode materials for high performance LIBs.

417 citations


Journal ArticleDOI
TL;DR: The basic reproduction number and its computation formulae are established for reaction-diffusion epidemic models with compartmental structure and are applied to a spatial model of rabies to study the influence of spatial heterogeneity and population mobility on disease transmission.
Abstract: The theory of the principal eigenvalue is developed for an elliptic eigenvalue problem associated with a linear parabolic cooperative system with some zero diffusion coefficients. Then the basic reproduction number and its computation formulae are established for reaction-diffusion epidemic models with compartmental structure. These theoretical results are applied to a spatial model of rabies to study the influence of spatial heterogeneity and population mobility on disease transmission.

357 citations


Journal ArticleDOI
TL;DR: Using the Ito formula, Lyapunov function, and Halanay inequality, several mean-square stability criteria are established from which the feasible bounds of impulses are estimated, provided that parameter uncertainty and stochastic perturbations are well-constrained.
Abstract: This paper focuses on the hybrid effects of parameter uncertainty, stochastic perturbation, and impulses on global stability of delayed neural networks By using the Ito formula, Lyapunov function, and Halanay inequality, we established several mean-square stability criteria from which we can estimate the feasible bounds of impulses, provided that parameter uncertainty and stochastic perturbations are well-constrained Moreover, the present method can also be applied to general differential systems with stochastic perturbation and impulses

319 citations


Journal ArticleDOI
26 Jun 2012-ACS Nano
TL;DR: This multimodal AuNR-ASP-Ce6 conjugate offers a remarkably improved and synergistic therapeutic effect compared to PTT or PDT alone, providing high specificity and therapeutic efficiency, which can be generalized to other types of cancer therapies.
Abstract: An aptamer switch probe (ASP) linking chlorin e6 (Ce6), a photosensitizer molecule, to the surface of gold nanorods (AuNRs) was used to target cancer cells for photodynamic therapy (PDT) and photothermal therapy (PTT). In the presence of target cancer cells, the ASP changes conformation to drive Ce6 away from the gold surface, thereby producing singlet oxygen for PDT upon light irradiation. Since each AuNR is modified with many ASP-Ce6 molecules, the AuNR-ASP-Ce6 conjugate yields enhanced binding and therapeutic effect by the added ability to carry many photosensitizers. In addition, absorption of radiation by the gold nanorods enables further cell destruction by the photothermal effect. Consequently, this multimodal AuNR-ASP-Ce6 conjugate offers a remarkably improved and synergistic therapeutic effect compared to PTT or PDT alone, providing high specificity and therapeutic efficiency, which can be generalized to other types of cancer therapies.

318 citations


Journal ArticleDOI
01 Mar 2012
TL;DR: In this paper, a generalized Dijkstra algorithm is proposed to handle SPP in an uncertain environment and the graded mean integration representation of fuzzy numbers is adopted to improve the classical Dijksta algorithm.
Abstract: A common algorithm to solve the shortest path problem (SPP) is the Dijkstra algorithm. In this paper, a generalized Dijkstra algorithm is proposed to handle SPP in an uncertain environment. Two key issues need to be addressed in SPP with fuzzy parameters. One is how to determine the addition of two edges. The other is how to compare the distance between two different paths with their edge lengths represented by fuzzy numbers. To solve these problems, the graded mean integration representation of fuzzy numbers is adopted to improve the classical Dijkstra algorithm. A numerical example of a transportation network is used to illustrate the efficiency of the proposed method.

315 citations


Journal ArticleDOI
TL;DR: Graphene was electrochemically deposited on carbon cloth to fabricate an anode for a Pseudomonas aeruginosa mediatorless microbial fuel cell and the graphene modification improved power density and energy conversion efficiency.

304 citations


Journal ArticleDOI
TL;DR: It is shown that macrophages and neutrophils play distinct functions in tissue regeneration, efficiently resolving inflammation and facilitating tissue remodeling and regrowth.

Journal ArticleDOI
TL;DR: HS demonstrated its potential as a treatment for burn wound dressing and showed powerful antibacterial efficacy up to 100% to Staphylococcus aureus and Escherichia coli, significantly superior to chitosan and honey used separately.

Journal ArticleDOI
TL;DR: In this paper, the secondary electron multiplier (SEM) protocol for multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been developed for high-precision and high-resolution 230Th dating of coral and speleothem carbonates.

Journal ArticleDOI
TL;DR: It is demonstrated that GBOs recorded over SI always predict the subjective pain intensity, even when saliency is reduced by repetition, which provides evidence for a close relationship between G BOs and the cortical activity subserving pain perception.
Abstract: Electroencephalographic gamma band oscillations (GBOs) induced over the human primary somatosensory cortex (SI) by nociceptive stimuli have been hypothesized to reflect cortical processing involved directly in pain perception, because their magnitude correlates with pain intensity. However, as stimuli perceived as more painful are also more salient, an alternative interpretation of this correlation is that GBOs reflect unspecific stimulus-triggered attentional processing. In fact, this is suggested by recent observations that other features of the electroencephalographic (EEG) response correlate with pain perception when stimuli are presented in isolation, but not when their saliency is reduced by repetition. Here, by delivering trains of three nociceptive stimuli at a constant 1 s interval, and using different energies to elicit graded pain intensities, we demonstrate that GBOs recorded over SI always predict the subjective pain intensity, even when saliency is reduced by repetition. These results provide evidence for a close relationship between GBOs and the cortical activity subserving pain perception.

Journal ArticleDOI
TL;DR: In general, the MoCA-BJ is an acceptable tool for MCI screening in both urban and rural regions of Beijing, however, presumably due to the linguistic and cultural differences between the original English version and the Chinese version of the scale, and the lower education level of Chinese older adults, it is not much better than the MMSE in detecting MCI.
Abstract: A cross-sectional validation study was conducted in several urban and rural communities in Beijing, China, to evaluate the effectiveness of the Beijing version of the Montreal Cognitive Assessment (MoCA-BJ) as a screening tool to detect mild cognitive impairment (MCI) among Chinese older adults. The MoCA-BJ and the Mini-Mental State Examination (MMSE) were administered to 1001 Chinese elderly community dwellers recruited from three different regions (i.e., newly developed, old down-town, and rural areas) in Beijing. Twenty-one of these participants were diagnosed by experienced psychiatrists as having dementia, 115 participants were diagnosed as MCI, and 865 participants were considered to be cognitively normal. To analyze the effectiveness of the MoCA-BJ, we examined its psychometric properties, conducted item analyses, evaluated the sensitivity and specificity of the scale, and compared the scale with the MMSE. Demographic and regional differences among our subjects were also taken into consideration. Under the recommended cut-off score of 26, the MoCA-BJ demonstrated an excellent sensitivity of 90.4%, and a fair specificity (31.3%). The MoCA-BJ showed optimal sensitivity (68.7%) and specificity (63.9%) when the cut-off score was lowered to 22. Among all the seven cognitive sub-domains, delayed recall was shown to be the best index to differentiate MCI from the normal controls. Regional differences disappeared when the confounding demographic variables (i.e., age and education) were controlled. Item analysis showed that the internal consistency was relatively low in both naming and sentence repetition tasks, and the diagnostic accuracy was similar between the MoCA-BJ and the MMSE. In general, the MoCA-BJ is an acceptable tool for MCI screening in both urban and rural regions of Beijing. However, presumably due to the linguistic and cultural differences between the original English version and the Chinese version of the scale, and the lower education level of Chinese older adults, the MoCA-BJ is not much better than the MMSE in detecting MCI, at least for this study sample. Further modifications to several test items of the MoCA-BJ are recommended in order to improve the applicability and effectiveness of the MoCA-BJ in MCI screening among the Chinese population.

Journal ArticleDOI
TL;DR: Regression analyses revealed that personality factors play an important role in how SNS are used, and extraverts are more likely to use the communicative function of SNS including status update, comment, and adding more friends.

Journal ArticleDOI
Ying Chen1, Jin Xu1, Jiao Su1, Yun Xiang1, Ruo Yuan1, Yaqin Chai1 
TL;DR: The proposed strategy combines the amplification power of the DNA HCR and the inherent high sensitivity of the ECL technique and enables low femtomolar detection of sequence specific DNA.
Abstract: In this work, we describe a new universal and highly sensitive strategy for electrochemiluminescent (ECL) detection of sequence specific DNA at the femtomolar level via in situ hybridization chain reaction (HCR) signal amplification. The DNA capture probes are self-assembled on a gold electrode. The presence of the target DNA and two hairpin helper DNAs leads to the formation of extended dsDNA polymers through HCR on the electrode surface. The in situ, HCR-generated dsDNA polymers cause the intercalation of numerous ECL indicators (Ru(phen)32+) into the dsDNA grooves, resulting in significantly amplified ECL signal output. The proposed strategy combines the amplification power of the DNA HCR and the inherent high sensitivity of the ECL technique and enables low femtomolar detection of sequence specific DNA. The developed strategy also shows high selectivity against single-base mismatch sequences, which makes our new universal and highly sensitive HCR-based method a useful addition to the amplified DNA det...

Journal ArticleDOI
TL;DR: In this paper, a self-assembled whisker-like manganese dioxide arrays on carbon fiber paper (MOWAs) were synthesized via a simple in situ redox replacement reaction between potassium permanganate (KMnO4) and carbon fibre paper (CFP) without any other oxidant or reductant addition.
Abstract: Self-assembled well-ordered whisker-like manganese dioxide (MnO2) arrays on carbon fiber paper (MOWAs) were synthesized via a simple in situ redox replacement reaction between potassium permanganate (KMnO4) and carbon fiber paper (CFP) without any other oxidant or reductant addition. The CFP serves as not only a sacrificial reductant and converts aqueous permanganate (MnO4−) to insoluble MnO2 in this reaction, but also a substrate material and guarantees MnO2 deposition on the surface. The electrochemical properties were examined by cyclic voltammograms (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) in a three-electrode cell. According to the CV results, the ordered MOWAs yield high-capacitance performance with specific capacitance up to 274.1 F g−1 and excellent long cycle-life property with 95% of its specific capacitance kept after 5000 cycles at the current density of 0.1 A g−1. The high-performance hybrid composites result from a synergistic effect of large surface area and high degree of ordering of the ultrathin layer of MnO2 nanowhisker arrays, combined with the flexible CFP substrate and can offer great promise in large-scale energy storage device applications.

Journal ArticleDOI
29 Oct 2012-Analyst
TL;DR: Results of electron paramagnetic resonance (ESR) suggest that the catalyse-mimic activity of the Ch-Ag nanostructures effectively catalyzed the decomposition of H( 2)O(2) into ˙OH radicals, and a simple, sensitive and selective visual and colorimetric method with TMB as substrate has been designed for glucose detection when combined with glucose oxidase (GOx).
Abstract: Chitosan stabilized silver nanoparticles (Ch-Ag NPs) were successfully synthesized by a one-step method and were found to possess intrinsic peroxidase-like activity, could catalytically oxidize substrates, such as TMB, and OPD, by H2O2 to produce a typical colour reaction such as from colorless to blue for TMB and from colorless to red for OPD. Our results demonstrate that the Ch-Ag NPs exhibit higher thermal and pH durance than HRP, thus could be suitable in a wider range of harsh conditions. Results of electron paramagnetic resonance (ESR) suggest that the catalyse-mimic activity of the Ch-Ag nanostructures effectively catalyzed the decomposition of H2O2 into ˙OH radicals. Based on this finding, a simple, sensitive and selective visual and colorimetric method with TMB as substrate has been designed for glucose detection when combined with glucose oxidase (GOx). This colorimetric method can be used for detection of glucose in biological samples with a detection limit as low as 100 nM and a dynamic range from 5.0 × 10−6 to 2.0 × 10−4 M.

01 Jan 2012
TL;DR: A method of transforming Z-number to classical fuzzy number is proposed according to the Fuzzy Expectation of fuzzy set, and a simple example is used to illustrated the procedure.
Abstract: The notion Z-number introduced by Zadeh in 2011 has more capability to describe the uncertain information. Now that the theories about Z-number is not mature, how to convert Z-number to classical fuzzy number is rather signicant for application. In this paper, a method of transforming Z-number to classical fuzzy number is proposed according to the Fuzzy Expectation of fuzzy set. At last, a simple example is used to illustrated the procedure of the proposed approach.

Journal ArticleDOI
Jianxin Xie1, Xiaodan Zhang1, Hui Wang1, Huzhi Zheng1, Yuming Huang1 
TL;DR: Recently, the intrinsic enzyme-like activity of nanoparticles (NPs) has become a growing area of interest as mentioned in this paper, and these enzymes are stable against denaturing, low in cost, and highly resistant to high concentrations of substrate.
Abstract: Recently, the intrinsic enzyme-like activity of nanoparticles (NPs) has become a growing area of interest. Compared with natural enzymes, these enzyme-like NPs are stable against denaturing, low in cost, and highly resistant to high concentrations of substrate. These advantages make them promising in various applications. In this review, we focus on recent advances in NPs as enzyme mimetics and their analytical and environmental applications. We pay special attention to the enzyme-like activity of magnetic NPs, cerium-oxide NPs, noble-metal NPs, carbon and other nanomaterials.

Journal ArticleDOI
Fangxin Hu1, Shihong Chen1, Chengyan Wang1, Ruo Yuan1, Dehua Yuan1, Cun Wang1 
TL;DR: The outstanding film forming ability of RGO-MWNTs hybrid materials endowed the modified electrode enhanced stability and the fabricated sensor was applied for the simultaneous determination of HQ, CC, PC and NO(2)(-) in the river water sample.

Journal ArticleDOI
TL;DR: With the hierarchical pores and unique VSG, an optimized bioanode delivered a remarkable maximum power density of 1530 mW m(-2) in a mediator-less MFC, 78 times higher than a carbon cloth anode.
Abstract: The bioanode is the defining feature of microbial fuel cell (MFC) technology and often limits its performance. In the current work, we report the engineering of a novel hierarchically porous architecture as an efficient bioanode, consisting of biocompatible chitosan and vacuum-stripped graphene (CHI/VSG). With the hierarchical pores and unique VSG, an optimized bioanode delivered a remarkable maximum power density of 1530 mW m(-2) in a mediator-less MFC, 78 times higher than a carbon cloth anode.

Journal ArticleDOI
TL;DR: It is concluded that the mouse embryonic head is a previously unappreciated site for HSC emergence within the developing embryo, and the physiological contribution of cerebrovascular endothelium to postnatal HSCs and multilineage hematopoiesis is revealed.

Journal ArticleDOI
TL;DR: In this article, a facile method for the preparation of Pd-rich PdxCo alloy nanoparticles supported on carbon, using an adsorbate-induced surface segregation effect, was described.
Abstract: The rational synthesis of active, durable, and low-cost catalysts is of particular interest to fuel cell applications. Here, we describe a facile method for the preparation of Pd-rich PdxCo alloy nanoparticles supported on carbon, using an adsorbate-induced surface segregation effect. The electronic properties of Pd were modulated by alloying with different amounts of Co, which affects the oxygen reduction reaction (ORR) activity. The electrocatalytic activity of the Pd3Co@Pd/C nanoparticles for the ORR was enhanced by spontaneously depositing a nominal monolayer of Pt. The activities of the different catalysts for the ORR could be correlated with the oxygen adsorption energy and the d-band center of the catalyst surface, as calculated using density functional theory, which is in agreement with previous theoretical studies. The materials synthesized herein are promising cathode catalysts for fuel cell applications and the facile synthesis method could be readily adapted to other catalyst systems, facilita...

Journal ArticleDOI
19 Jul 2012-ACS Nano
TL;DR: This study demonstrates a facial approach to fabricate a smart nanostructured graphene-based functional biofilm that provides a powerful and reliable platform to the real-time study of biointeresting molecules released from living cells, thus rendering potential broad applications in neuroscience, screening drug therapy effect, and live-cell assays.
Abstract: It is always challenging to construct a smart functional nanostructure with specific physicochemical properties to real time detect biointeresting molecules released from live-cells. We report here a new approach to build a free-standing biomimetic sensor by covalently bonding RGD-peptide on the surface of pyrenebutyric acid functionalized graphene film. The resulted graphene biofilm sensor comprises a well-packed layered nanostructure, in which the RGD-peptide component provides desired biomimetic properties for superior human cell attachment and growth on the film surface to allow real-time detection of nitric oxide, an important signal yet short-life molecule released from the attached human endothelial cells under drug stimulations. The film sensor exhibits good flexibility and stability by retaining its original response after 45 bending/relaxing cycles and high reproducibility from its almost unchanged current responses after 15 repeated measurements, while possessing high sensitivity, good selectiv...

Journal ArticleDOI
TL;DR: This comprehensive map provides a solid basis for exploring the epigenetic mechanisms of adipose deposition and muscle growth in pig as a model and identifies the differentially methylated regions in promoters.
Abstract: It is evident that epigenetic factors, especially DNA methylation, have essential roles in obesity development. Here, using pig as a model, we investigate the systematic association between DNA methylation and obesity. We sample eight variant adipose and two distinct skeletal muscle tissues from three pig breeds living within comparable environments but displaying distinct fat level. We generate 1,381 Gb of sequence data from 180 methylated DNA immunoprecipitation libraries, and provide a genome-wide DNA methylation map as well as a gene expression map for adipose and muscle studies. The analysis shows global similarity and difference among breeds, sexes and anatomic locations, and identifies the differentially methylated regions. The differentially methylated regions in promoters are highly associated with obesity development via expression repression of both known obesity-related genes and novel genes. This comprehensive map provides a solid basis for exploring epigenetic mechanisms of adipose deposition and muscle growth.

Journal ArticleDOI
Zhongwei Wang1, Qing Li1, Zuxin She1, Funan Chen1, Longqin Li1 
TL;DR: In this article, a low-cost and large-scale fabrication method to an environmentally-friendly superhydrophobic coating on magnesium alloy is reported in which rough surface structure could be facilely obtained by electrodeposition of copper.
Abstract: A low-cost and large-scale fabrication method to an environmentally-friendly superhydrophobic coating on magnesium alloy is reported in this paper. The rough surface structure could be facilely obtained by electrodeposition of copper. Then the rough surface could be changed from hydrophilic to superhydrophobic via modification with lauric acid. The as-prepared coatings were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), X-ray diffractometry (XRD), electrochemical corrosion test and electrochemical impedance spectroscopy (EIS). The as-prepared superhydrophobic coatings have ultra-low slide angles (2°) and contact angles of 154°. Our method is of great value for the industrial fabrication of superhydrophobic coatings. It has an excellent anti-corrosion effect and self-cleaning effect.

Journal ArticleDOI
18 Sep 2012-PLOS ONE
TL;DR: It is demonstrated that (i) TALENs can be used in silkworm and (ii) heritable large chromosomal deletions can be induced by two pairs of TALens in whole organisms.
Abstract: Establishment of efficient genome editing tools is essential for fundamental research, genetic engineering, and gene therapy. Successful construction and application of transcription activator-like effector nucleases (TALENs) in several organisms herald an exciting new era for genome editing. We describe the production of two active TALENs and their successful application in the targeted mutagenesis of silkworm, Bombyx mori, whose genetic manipulation methods are parallel to those of Drosophila and other insects. We will also show that the simultaneous expression of two pairs of TALENs generates heritable large chromosomal deletion. Our results demonstrate that (i) TALENs can be used in silkworm and (ii) heritable large chromosomal deletions can be induced by two pairs of TALENs in whole organisms. The generation and the high frequency of TALENs-induced targeted mutagenesis in silkworm will promote the genetic modification of silkworm and other insect species.

Journal ArticleDOI
TL;DR: In this paper, the Parkes Pulsar Timing Array (PPTA) project has developed the first pulsar-based time-scale that has a precision comparable to the uncertainties in International Atomic Time-scales (TAI).
Abstract: Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based time-scale that has a precision comparable to the uncertainties in International Atomic Time-scales (TAI). Our ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the free atomic time-scale Echelle Atomique Libre. The EPS can be used to detect fluctuations in atomic time-scales and therefore can lead to a new realization of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the TAI, and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar time-scale.