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A comprehensive kinetic Monte Carlo algorithm has been developed to investigate the formation process of a polyurethane/poly(methyl methacrylate) (PU/PMMA) interpenetrating polymer network (IPN), in which a component independent strategy is proposed to perform the simulation of simultaneous polycondensation and free radical polymerization. An empiric diffusion model based on the mass fraction of polymer is used to quantify the effect of diffusional limitations on MMA polymerization. Results show that the presence of acrylic monomers has little impact on the formation rate of PU, but the presence of the PU network can accelerate the polymerization of MMA. In addition, the effects of component mass ratio, acrylic cross-linker concentration, and [NCO]/[OH] ratio on the IPN formation kinetics are investigated based on the kinetic model. It is believed that the as-developed modeling strategy can be extended to other IPN systems and provide a better understanding of the interactions between chemically independent networks. [ABSTRACT FROM AUTHOR]

In this study, the open-circuit faults diagnosis and location issue of the neutral-point-clamped (NPC) inverters are analysed. A novel fault diagnosis approach based on knowledge driven and data driven was presented for the open-circuit faults in insulated-gate bipolar transistors (IGBTs) of NPC inverter, and Concordia transform (knowledge driven) and random forests (RFs) technique (data driven) are employed to improve the robustness performance of the fault diagnosis classifier. First, the fault feature data of AC in either normal state or open-circuit faults states of NPC inverter are analysed and extracted. Second, the Concordia transform is used to process the fault samples, and it has been verified that the slopes of current trajectories are not affected by different loads in this study, which can help the proposed method to reduce overdependence on fault data. Moreover, then the transformed fault samples are adopted to train the RFs fault diagnosis classifier, and the fault diagnosis results show that the classification accuracy and robustness performance of the fault diagnosis classifier are improved. Finally, the diagnosis results of online fault diagnosis experiments show that the proposed classifier can locate the open-circuit fault of IGBTs in NPC inverter under the conditions of different loads. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive online multi-period power dispatch formulation that takes AC constraints, renewable energy, and ramping constraints into account is proposed. The AC power flow equations, voltage limits, and thermal limits are respected to ensure the obtained solution causes no static violation while guaranteeing transfer capability. A four-stage solution methodology is proposed to solve the non-linear constrained optimisation problem in which the thermal limit constraints are equivalently represented by active-set-based constraints in the third stage, and an adaptive homotopy-enhanced primal-dual interior point method (PDIPM) in solving power dispatch problem is presented in the fourth stage to reliably and efficiently obtain the solution. This solution methodology enhances both the robustness and speed of the PDIPM. The proposed four-stage solution methodology has been evaluated on several testing systems, ranging from a 30-bus system to a 3012-bus system with four time periods, with promising results. [ABSTRACT FROM AUTHOR]

Energetic materials (explosives, propellants, and pyrotechnics) are used extensively for both civilian and military applications and the development of such materials, particularly in the case of energetic salts, is subject to continuous research efforts all over the world. This Review concerns recent advances in the syntheses, properties, and potential applications of ionic salts based on tetrazole N-oxide. Most of these salts exhibit excellent characteristics and can be classified as a new family of highly energetic materials with increased density and performance, alongside decreased mechanical sensitivity. Additionally, novel tetrazole N-oxide salts are proposed based on a diverse array of functional groups and ions pairs, which may be promising candidates for new energetic materials. [ABSTRACT FROM AUTHOR]

Years of operation experience on power systems reveal that most transmission line fault events are related to seasonal alternating meteorological disasters, which have typical temporal and spatial distribution characteristics. However, power system risk assessment lacks basically accurate descriptions of failure rate time distribution for transmission lines. In this study, a method to calculate the time-varying failure rate of transmission lines in a monthly time scale is proposed to reflect the time-dependent fault regulation. However, the failure rate during any time interval cannot be derived directly from limited historical fault samples. Therefore, a simulation method of continuous time distribution function for failure rate is proposed, which adopts Fourier, Gaussian, and Weibull function assumptions. Furthermore, the parameters of these function hypotheses are fitted and compared using the fault samples of a province power grid and an urban power grid in China, respectively. Results show that the proposed simulation model is reasonable. Finally, the time-varying failure rate simulation model is adopted to quantify the risk of the verified IEEERBTS system. The risk indices also indicate that considering the time distribution characteristics of failure rate has a more significant influence on the system risk than the conventional methods. [ABSTRACT FROM AUTHOR]

Stochastic subspace identification (SSI) methods have been widely employed for oscillatory mode identification on probing and ambient data and are reported to have good performances. This work proposes a novel SSI-based approach for identifying dominant oscillatory mode from measurement data and extends the application of SSI to ringdown condition. The proposed approach first constructs an initial cluster of eigenvalues from SSI with repetitive calculations and then utilises a novel hierarchical clustering method to extract the dominant modes from the initial cluster. The repetitive calculations within the SSI are performed through varying the model order over a range defined by a novel initial order determination process. By doing so the challenge of model order determination for SSI-based methods is resolved. Moreover, benefiting from the repetitive calculations and the clustering process, the proposed approach is highly immune to prevalent noises in the measurements. Finally, the proposed approach is applied and validated on the field-measurement data from the phasor measurement units of China Southern Power Grid (CSG) through comparisons with Prony, ARMAX, and Monte Carlo methods. Test results demonstrate that the proposed approach performs with high accuracy, robustness, and efficiency in CSG. [ABSTRACT FROM AUTHOR]

As a new class of biomaterials, most supramolecular hydrogels formed by small peptides require the attachment of long alkyl chains, multiple aromatic groups, or strong electrostatic interactions. Based on the fact that the most abundant protein assemblies in nature are dimeric, we select short peptide sequences from the interface of a heterodimer of proteins with known crystal structure to conjugate with nucleobases to form nucleopeptides. Being driven mainly by hydrogen bonds, the nucleopeptides self-assemble to form nanofibers, which results in supramolecular hydrogels upon simple mixing of two distinct nucleopeptides in water. Moreover, besides being biocompatible to mammalian cells, the heterodimer of the nucleopeptides exhibit excellent proteolytic resistance against proteinase K. This work illustrates a new and rational approach to create soft biomaterials by a supramolecular hydrogelation triggered by mixing heterodimeric nucleopeptides. [ABSTRACT FROM AUTHOR]

Cyclic electron flow (CEF) plays an important role in photoprotection for angiosperms under environmental stresses. However, ferns are more sensitive to drought and their water transport systems are not as efficient as those of angiosperms, it is unclear whether CEF also contributes to photoprotection in these plants. Using Microsorum punctatum and Paraleptochillus decurrens, we studied the electron fluxes through both photosystem I (PSI) and photosystem II (PSII) under water stress and their leaf anatomies. Our goal was to determine if CEF functions in the photoprotection of these ferns and, if so, whether CEF stimulation is related to leaf anatomy. Compared with P. decurrens, M. punctatum had thicker leaves and cuticles and higher water storage capacity, but lower stomatal density and slower rate of water loss. During induced drought, the decrease in leaf water potential (Ψleaf) was more pronounced in P. decurrens than in M. punctatum. For both species, the decline in Ψleaf was associated with a lower effective PSII quantum yield, photochemical quantum yield of PSI and electron transport rate (ETR), whereas increases were found in the quantum yield of regulated energy dissipation, CEF and CEF/ ETR(II) ratio. Values for CEF and the CEF/ ETR(II) ratio peaked in M. punctatum at a light intensity of 500-600 µmol m−2 s−1 vs only 150-200 µmol m−2 s−1 in P. decurrens. Therefore, our results indicate that the stimulation of CEF in tropical ferns contributes to their photoprotection under water stress, and is related to their respective drought tolerance and leaf anatomy. [ABSTRACT FROM AUTHOR]

The scalable extension of the H.264/AVC video coding standard (SVC) demonstrates superb adaptability in video communications. Joint source and channel coding (JSCC) has been shown to be very effective for such scalable video consisting of parts of different significance. In this paper, a new JSCC scheme for SVC transmission over packet loss channels is proposed which performs two-dimensional optimization on the quality layers of each frame in a ratedistortion (R D) sense as well as on the temporal hierarchical structure of frames under dependency constraints. To compute the end-to-end R-D points of a frame, a novel reduced trellis algorithm is developed with a significant reduction of complexity from the existing Viterbi-based algorithm. The R-D points of frames are sorted under the hierarchical dependency constraints and optimal JSCC solution is obtained in terms of the best R-D performance. Experimental results show that our scheme outperforms the existing scheme of [13] with average quality gains of 0.26 dB and 0.22 dB for progressive and non-progressive modes respectively. [ABSTRACT FROM AUTHOR]

Helicobacter pylori persists deep in the human gastric mucus layer in a harsh, nutrient-poor environment. Survival under these conditions depends on the ability of this human pathogen to invoke starvation/stress responses when needed. Unlike many bacteria, H. pylori lacks starvation/stress-responding alternative sigma factors, suggesting an additional mechanism might have evolved in this bacterium. Helicobacter pylori produces polyphosphate; however, the role and target of polyphosphate during starvation/stress have not been identified. Here we show that polyphosphate accumulated during nutrient starvation directly targets transcriptional machinery by binding to the principal sigma factor in H. pylori, uncovering a novel mechanism in microbial stress response. A positively charged Lys-rich region at the N-terminal domain of the major sigma factor is identified as the binding region for polyphosphate (region P) in vivo and in vitro, revealing a new element in sigma 70 family proteins. This interaction is biologically significant because mutant strains defective in the interaction undergo premature cell death during starvation. We suggested that polyphosphate is a second messenger employed by H. pylori to mediate gene expression during starvation/stress. The putative ‘region P’ is present in sigma factors of other human pathogens, suggesting that the uncovered interaction might be a general strategy employed by other pathogens. [ABSTRACT FROM AUTHOR]

Iron homeostasis is essential to almost all organisms. In this study, we identified the putative homolog of the iron-storage protein-encoding gene, dpsL, in the intracellular pathogen Legionella pneumophila and demonstrated its expression under iron-limited conditions and its responses to multiple stresses. Quantitative real-time PCR analysis indicated that the expression of dpsL was enhanced under iron limitation regardless of the growth phase. Compared with the wild-type cells, the cells devoid of dpsL were heat and HO-sensitive. In contrast to the dps mutants of other bacteria, the growth of the dpsL mutant in an iron-deprived medium was delayed but finally reached the same cell density as wild-type cells during the stationary phase of growth. The finding that the dpsL mutant is salt resistant suggested the involvement of DpsL in virulence. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Neurodegenerative diseases are progressive and incurable and are becoming ever more prevalent. To study whether neural stem cells can reactivate or rescue functions of impaired neurons in the human aging and neurodegenerating brain, we co-cultured postmortem slices from Alzheimer patients and control participants with rat embryonic day 14 (E14) neural stem cells. Viability staining based on the exclusion of ethidium bromide by intact plasma membranes showed that there were strikingly more viable cells and fewer dead cells in slices co-cultured with neural stem cells than in untreated slices. The presence of Alzheimer pathology in the brain slices did not influence this effect, although the slices from Alzheimer patients, in general, contained fewer viable cells. Co-culturing with rat E14 fibroblasts did not improve the viability of neurons in the human brain slices. Since the human slices and neural stem cells were separated by a membrane during co-culturing our data show for the first time that neural stem cells release diffusible factors that may improve the survival of aged and degenerating neurons in human brains. [ABSTRACT FROM AUTHOR]

Melatonin not only plays a major role in the regulation of circadian rhythms, but is also involved in antioxidative defense and immunomodulation. Circulating melatonin levels are derived primarily from the pineal gland while other sources of melatonin have also been reported. Here, we show for the first time that astrocytes from the rat cortex and glioma C6 cell line synthesize melatonin in vitro. In addition, we show the presence of serotonin, the precursor of melatonin and the two key enzymes in the pathway of melatonin synthesis, i.e. N-acetyltransferase and hydroxyndole- O-methyltransferase in the cultured rat cortical astrocytes. Release of melatonin into the culture medium showed no diurnal changes. These point to astrocytes as a local source of melatonin in the rat brain. Its exact physiological function remains a topic for future studies. [ABSTRACT FROM AUTHOR]

Samples of sediments, interstitial water and overlying water were collected monthly under temperature-controlled conditions to determine the effects of sediment types on the alkaline phosphatase activity (APA) in lake systems. The relationship between the total alkaline phosphatase activity (TAPA) and soluble reactive phosphorus (SRP) concentration also was examined. The study results indicate the variations of TAPA in the overlying water, and the interstitial water in different layers from different sediments was similar over time. They were influenced not only by the phosphate concentrations, but also were correlated with submerged plant and phytoplankton biomass. The direct effects of the sediment types on the APA were not readily obvious. Although the higher APA in sediment was probably responsible for the enzymatic response to the characteristics of sediments, other factors (e.g. growth of submerged plants and phytoplankton) also should be considered. The peak of the maximum velocity of the enzyme reactions (Vmax) at deeper sediment layers suggests another stratum in which the enzymatically mediated phosphorus regeneration was active. This finding contributes to our understanding of phosphorus cycling in lake sediments. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the circadian rhythm alterations in saliva melatonin levels during aging to investigate whether free melatonin may be better suited to reveal age-related changes. Role of melatonin in the regulation of circadian rhythms; Materials and methodology of the study; Results and discussion.

This article presents a study on the effect of Alzheimer disease (AD) and the underlying mechanisms on pineal clock gene expression. Certain diurnal rhythmic expression is lost in the pineal gland of preclinical and clinical AD patients. Clock gene alterations similar as the AD pineal is shown in rat pineal deprived of suprachiasmatic nucleus control. Conclusion of the study is given.

In the title complex, [ZnCl2(C14H12N4)], ZnII is pentacoordinated by three N-atom donors from one 2-[3-(2-pyridyl)pyrazol-1-ylmethyl]pyridine ( L) ligand and by two Cl− anions in a distorted trigonal–bipyramidal geometry. Adjacent mononuclear ZnII complexes form π–π stacking interactions between pyridine and pyrazole rings of neighbouring L ligands, with centroid–centroid separations of 3.671 (1) and 3.681 (1) Å, generating one-dimensional chains. [ABSTRACT FROM AUTHOR]

In the title co-crystal, C10H11NO2·C10H13NO2, the carboxyl­ic acid moiety uses its acid H atom as the donor atom to bind strongly to the negatively charged O atom of the zwitterionic moiety [O⋯O = 2.557 (2) Å]. Meanwhile, the protonated N atom of the zwitterionic moiety forms a hydrogen bond with the double-bonded O atom of an adjacent zwitterionic moiety [N⋯O = 2.703 (2) Å] to give rise to a linear chain motif. The butenyl substituent (on the zwitterion) is disordered with respect to a butyl group and the butyl substituent (on the neutral mol­ecule) is disordered with respect to a butenyl group, the site occupancy for both being in an approximate 0.6:0.4 ratio. [ABSTRACT FROM AUTHOR]

The title compound, C12H14O4, contains two mol­ecules in the asymmetric unit, each with an intramolecular O—H⋯O hydrogen bond. [ABSTRACT FROM AUTHOR]