To further improve the quantitative forecasting ability of high-frequency (HF) communication frequency, we propose a maximum usable frequency (MUF) adaptive forecasting method. This method has four ...new features: 1) The Volterra filter is introduced to this method, which is easy to implement due to the simple structure. 2) This method can forecast M(3000)F2 based on past measurements without using any previous or forecast data of geomagnetic and solar activity parameters. 3) The spatial characteristics of the M(3000)F2 can be obtained by the improved reconstruction method based on geomagnetic coordinates. 4)The high prediction accuracy can be obtained by the training data set on the 27-day (one solar rotation period). Through the statistical analysis of the measurements and predictions, the results show that the forecast values are in good agreement consistent with the measurement during the geomagnetic quiet or the disturbance periods. This method is proven to have good adaptability and usability and has a further performance improvement compared with ITU and long-term forecast models. And the root-mean-square error of MUF forecasts decreased by 1.9MHz and 0.9MHz on average, and the relative root-mean-square error decreased by 12.6% and 2.9% on average.
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•Characterization of a member of the new MuF polymorphic toxin family.•The MuF polymorphic toxin from Streptococcus pneumoniae is a (p)ppApp synthetase.•Two immune proteins inhibit ...the toxin and hydrolyze (p)ppApp.•Distinct signatures for (p)ppGpp and (p)ppApp synthetases.•(p)ppApp synthetases are found associated with T6SS and temperate phages.
Polymorphic toxins (PTs) are a broad family of toxins involved in interbacterial competition and pathogenesis. PTs are modular proteins that are comprised of a conserved N-terminal domain responsible for its transport, and a variable C-terminal domain bearing toxic activity. Although the mode of transport has yet to be elucidated, a new family of putative PTs containing an N-terminal MuF domain, resembling the Mu coliphage F protein, was identified in prophage genetic elements. The C-terminal toxin domains of these MuF PTs are predicted to bear nuclease, metallopeptidase, ADP-ribosyl transferase and RelA_SpoT activities. In this study, we characterized the MuF-RelA_SpoT toxin associated with the temperate phage of Streptococcus pneumoniae SPNA45. We show that the RelA_SpoT domain has (p)ppApp synthetase activity, which is bactericidal under our experimental conditions. We further determine that the two genes located downstream encode two immunity proteins, one binding to and inactivating the toxin and the other detoxifying the cell via a pppApp hydrolase activity. Finally, based on protein sequence alignments, we propose a signature for (p)ppApp synthetases that distinguishes them from (p)ppGpp synthetases.
Methylsiloxanes are accumulated easily in aquatic organisms and may pose potential risks. However, available information on their uptake and accumulation in terrestrial species remains scarce. This ...study investigated the uptake, elimination and accumulation of eight typical methylsiloxanes in hens after a single oral exposure. At 1440 min after oral exposure, methylsiloxanes were mainly accumulated in kidney, liver and ovary, representing for 29.5 %, 20.4 % and 17.4 % of the summed methylsiloxanes in all tissues, respectively; all investigated chemicals were also detected in brains and unformed yolks. We found much higher mass uptake fractions (MUFs) of cyclic (27.5–66.5 %) than linear chemicals (9.9–17.3 %) by hens via this exposure, and the observed MUFs of individual cyclic congeners were comparable to the higher values of those reported for rats or fish previously. However, the metabolic half-life (t1/2) of these chemicals in hen tissues were in the range of 1.04–57.5 h based on kinetic analyses, indicating higher clearances in comparison with those reported for fish and rats. More research is needed on the metabolic mechanism of these chemicals in hens. Our findings provide important information for further understanding of transportation and transformation of these chemicals in terrestrial organisms and the associated potential risks.
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•First report of the pharmacokinetics of methylsiloxanes in poultry•Lower bioavailability of these chemicals via oral exposure was observed.•Methylsiloxanes can be quickly eliminated from hens.•These chemicals tend to be eliminated in kidney, intestine and liver.
•The curing characteristics of low molecular weight melamine-urea–formaldehyde (LMW-MUF) resin-impregnated wood (RIW) were studied.•With the increase in LMW-MUF resin solution concentration, the ...resin curing reaction in RIW was more difficult.•Due to the wood steric hindrance, the resin curing reaction in RIW was slower than the LMW-MUF resin solution itself.•The time–temperature-curing degree function of LMW-MUF resin solution in RIW was fitted during the curing process.
The curing characteristics of low molecular weight melamine-urea–formaldehyde (MUF) resin within impregnated wood during the drying process remain unclear, making the setting and optimization of the drying process highly challenging. As a result, drying efficiency and drying quality of resin-impregnated wood (RIW) are limited. This study explores the effects of resin solution concentration (moisture content) and wood on resin curing characteristics to facilitate the development and optimization of the drying schedule for RIW. Poplar wood (Populus tomentosa) impregnated with 20%, 30%, 40%, and 50% MUF resin solutions were analyzed by differential scanning calorimetry (DSC). The optimum curing temperature was obtained by extrapolation. Kinetic parameters of curing reaction of resin-impregnated wood were calculated using the Kissinger differential method, Ozawa integral method, and Crane equation. Subsequently, the function of curing time–temperature-curing degree of MUF RIW was obtained. The peak temperature shifts to a higher temperature with increased RIW moisture. The optimum curing temperatures of the four RIW samples were 103.50, 98.05, 91.34, and 84.28 °C, respectively, while their corresponding apparent curing reaction activation energies were 117.58, 91.92, 81.34, and 63.38 kJ/mol, respectively. The relationship between curing degree and curing time under 50, 60, 70, and 80 °C isothermal conditions was simulated based on the kinetic parameters of resin curing. Additionally, the complete curing time of RIW with different moisture contents was estimated under different isothermal conditions. Parametric analysis and calculation based on the kinetic model of curing reaction showed that the moisture and wood hinder the curing and cross-linking of the resin, and the curing time increases with moisture content. This study could provide data support for the drying of RIW.
Using engineered wood products (EWPs) in the building technologies is very crucial in terms of sustainable approaches. They provide; low weight, high structural stiffness, carbon storage capacity and ...easy erection on site. EWPs are composite materials that are influenced by a variety of factors that play a critical role in their formation. The chemical ingredients of the wood, the curing process of the adhesive, the type of wood, the relationship between the adhesive and the wood species, the curing temperature, the geometric configuration of the lamellae, etc. can all be included under the heading of these factors. In contrary with massive wood, to obtain EWPs different types of adhesives can be used. Therefore adhesive type and its application method affects the quality of wooden structural element. Choosing the appropriate adhesive is one of the steps to be taken to obtain the structurally correct product. Based on this approach, it was decided to investigate the adhesion performance of different adhesive types. This paper aims to present the best bonding method among the melamine urea formaldehyde (MUF) and epoxy adhesives by considering the fiber directions of the wood and the type of adhesive according to the load. One of the aims of this study is to investigate the effect of changing the fiber direction of wood on adhesion performance, taking into account the current gap in the literature. Pull-off tests were conducted to assess the bonding performance of different types of adhesive in wood samples with varying fiber direction. The wood samples were bonded to the wood surface with varying grain directions. During the pull-off tests, ruptures in the glue line of the test samples were commonly observed. The results have shown that in cylindrical samples bonded with epoxy, the highest bonding strength values were observed in scenarios where the wood fibers were oriented parallel to the load direction and perpendicular to the ground plane. Similarly, for wood samples used as the bonding surface, the highest bonding strength values were achieved when the wood fibers were oriented parallel to the load direction and perpendicular to the surface plane. On the other hand, the highest value in pull-off test setups was found with melamine urea formaldehyde adhesive; commonly used in laminated timber, between the wood samples with grains perpendicular to the load direction and the wood adherence surfaces with a parallel grain direction. In summary, the highest strength value was obtained from the test setup in which epoxy was used as the adhesive and both the wood specimens and the wood bonding surface had fiber directions parallel to the load direction.
•The fiber directions of wood in terms of bonding performance are evaluated.•Epoxy provides stronger adhesion than MUF in EWP’s technology.•The parallel grain direction of wood exhibits the strongest bonding performance relative to the applied load.•The perpendicular direction of the wood fibres to the applied load is the most critical point in terms of strength.
Transparent and colorless melamine-urea-formaldehyde (MUF) resins make it difficult to identify the area of wood failure percentage (WFP) in the fracture surface of bonded wood specimens. Therefore, ...in this study, we develop a method of measuring WFP after the adhesion strength measurement of MUF resins under shear s tress. The fractured wood surface of b lock shear strength (BSS) specimens bonded with cold-setting MUF resins at three melamine contents (20%, 30%, and 40%) was marked black, and then, WFP was accurately measured via image analysis. WFP values measured using this method consistently increased with BSS as the melamine content increased, showing the reliability of this new method. The results suggested that this new method is useful and reliable for measuring the WFP of the fracture surface of wood specimens bonded with colorless adhesives such as urea-formaldehyde, MUF, and melamine-formaldehyde resins.
High-frequency (HF) communication plays a vital role in military and commercial fields because of its characteristics of transhorizon propagation. Accurate prediction of the maximum usable frequency ...(MUF) is critical to improve the efficiency of HF ionospheric propagation. Deep learning has demonstrated remarkable performance in time-series prediction in recent years. However, the MUF is a nonstationary time series with complex properties of multiple time scales. Therefore, we must fully explore the features of the MUF sequence to provide reliable support for selecting deep-learning prediction models. In this article, we first decompose the real-world MUF-measured data from vertical sounding stations to obtain different components. After analyzing the phenomena of each component at different positions, we propose the capability requirements of the MUF prediction model and verify the capability requirements by comparing the existing most advanced deep-learning prediction models. Then, we calculate the complexity of the MUF sequence based on multiscale entropy. Through the entropy series at different time scales, the key to improving the model's prediction performance is the fitting ability of the nonlinear change of the long-term trend component in the short-period scale. Furthermore, we propose a quantitative prediction scheme of MUF based on multiscale entropy similarity tolerance. Based on the Fano inequality, we calculate and compare the upper and lower bounds of the predictability on the quantization sequence and the original data and verify the effectiveness of the proposed scheme. Through experimental results, as the latitude decreases, the models based on time-series decomposition have better prediction performance over the state-of-the-art schemes. Compared to nontime-series decomposition deep-learning models, the root mean square error (RMSE) of the predicted MUF values for four cities, ranging from low to high latitude, decreased by an average of 0.11, 0.20, 0.02, and 0.03 MHz, respectively.
To improve the water resistance of melamine-urea-formaldehyde (MUF) resins, different levels of blocked polymeric 4,4 diphenyl methane diisocyanate (B-pMDI) were blended with MUF resins to prepare ...B-pMDI/MUF hybrid adhesives, and their adhesion performances were evaluated for the surface lamination of fancy veneer on plywood. FT-IR spectra showed that the de-blocked –NCO groups reacted with the –OH of hydroxymethyl groups of the MUF resins to form urethane bonds at 2% B-pMDI/MUF, which was detected before and after their hydrolysis. The mass loss after the hydrolysis consistently decreased as the B-pMDI level increased, indicating an improvement in the water resistance. As the B-pMDI level increased, the activation energy of hybrid adhesives decreased, which improved the reactivity of the hybrid adhesives. Additionally, the water resistance improvement of the hybrid adhesives increased the tensile shear strength of the surface laminated plywood in semi-water proof and water-proof by 23 % and 8 %, respectively, at 2% B-pMDI level. This was likely due to the urethane linkages in the hybrid adhesives. However, the formaldehyde emission from plywood panels bonded with the hybrid adhesives increased in the dry state, indicating incomplete curing of the hybrid adhesives. KCI Citation Count: 8
As the properties of the melamine-urea-formaldehyde (MUF) resins were changing during their storage time, this study investigated the impacts of the synthesis method and melamine content of the MUF ...resins on the pH, apparent viscosity, molecular weights, and crystallinity to estimate these properties over storage times of up to 30 days. Melaminesat three addition levels (5, 10, and 20 wt% based on the resin solids) were simultaneously reacted with urea and formaldehyde (MUF-A resins), while those at the same addition levels were first reacted with formaldehyde and then with urea(MUF-B resins). The pH values of the MUF-A and MUF-B resins decreased linearly as the storage time increased; the apparent viscosity increased linearly for the low melamine contents (5% and 10%) but increased exponentially for 20%. As anticipated, the molecular weights (Mw and Mn) increased linearly with the storage time, with a steeper increase in the Mw of the MUF-B resins compared with that of the MUF-A resins. The crystallinity of the two resin types decreased with storage time at higher melamine content. The relationships between these properties and the storage time made it possible to estimate the property changes in these resins synthesized by the different synthesis methods and melamine contents; this could help predict the properties of such resins in the industry during their storage. KCI Citation Count: 6
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