Secondary Layer Research Articles

Research on high‐temperature creep properties of Al2O3‐MgAl2O4 refractory

AbstractIn this study, the Al2O3‐MgAl2O4 refractory samples were prepared with tabular alumina and fused magnesia‐alumina spinel as the raw materials. A creep resistance test was performed at 1400°C and studied. The tested samples after the creep resistance test were characterized and analyzed by X‐ray diffraction, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy to investigate the effect of adding the amount and particle size of MgAl2O4 on high‐temperature creep resistance of Al2O3‐MgAl2O4 refractory, as well as its mechanism. As indicated by the results, under the same amount of spinel added, the sample with 3‐1 mm spinel had higher creep resistance than the sample with 1‐0 mm spinel. In the creep test, spinel aggregates would react with the alumina matrix to form a secondary spinel layer around the spinel particles, thereby connecting the matrix and the aggregates and improving the creep resistance of the specimens. As clearly indicated by the observed result of the microstructure, in the formation of the secondary spinel layer, Mg2+ had a higher migration rate and showed the secondary spinel layer's higher thickness ratio on both sides of the reaction interface, which would induce the Kirkendall effect. Accordingly, considerable pores generated and accumulating at the interface tended to reduce the creep resistance of the material, and this effect was highly dependent on the size of the spinel and the activation solid solution reaction intensity.

Cloud-convection Feedback in Brown Dwarf Atmospheres

Numerous observational evidence has suggested the presence of active meteorology in the atmospheres of brown dwarfs. A near-infrared brightness variability has been observed. Clouds have a major role in shaping the thermal structure and spectral properties of these atmospheres. The mechanism of such variability is still unclear, and neither 1D nor global circulation models can fully study this topic due to resolution. In this study, a convective-resolving model is coupled to gray-band radiative transfer in order to study the coupling between the convective atmosphere and the variability of clouds over a large temperature range with a domain of several hundred kilometers. Six types of clouds are considered, with microphysics including settling. The clouds are radiatively active through the Rosseland mean coefficient. Radiative cloud feedback can drive spontaneous atmospheric variability in both temperature and cloud structure, as modeled for the first time in three dimensions. Silicate clouds have the most effect on the thermal structure with the generation of a secondary convective layer in some cases, depending on the assumed particle size. Iron and aluminum clouds also have a substantial impact on the atmosphere. Thermal spectra were computed, and we find the strongest effect of the clouds is the smoothing of spectral features at optical wavelengths. Compared to observed L and T dwarfs on the color–magnitude diagram, the simulated atmospheres are redder for most of the cases. Simulations with the presence of cloud holes are closer to observations.

Natural gas development prospect in Changqing gas province of the Ordos Basin

At present, natural gas accounts for a low proportion in China's primary energy consumption structure and is highly dependent on foreign sources. Changqing gas province of the Ordos Basin where PetroChina Changqing Oilfield Company (referred to as Changqing Oilfield) is located is one of China's four major natural gas production bases. It bears the important responsibility for ensuring people's livelihood and promoting the healthy development of society economy. In recent years, Changqing Oilfield actively implements national instructive spirit on vigorously promoting domestic oil and gas exploration and development strength and formulates the secondary acceleration development strategies. Its annual natural gas production in 2020 reaches 448.5 × 108 m3 and oil and gas equivalent exceeds 6000 × 104 t, tamping its important position of “Western Daqing” in this industry. In order to further promote the continuous stable production and realize the goal of quality and efficiency improvement in Changqing gas province, this paper analyzes the situations and challenges of natural gas development in this gas province, prepares the development technological countermeasures and forecast the natural gas development prospect. And the following research results are obtained. First, the natural gas exploration and development in Changqing gas province is divided into four stages and the main technologies for the development of low-permeability carbonate gas reservoir, low-permeability sandstone gas reservoir and tight sandstone gas reservoir are formed. Second, the natural gas development in Changqing gas province faces six challenges, such as low reserve production degree, sharp decline of production rates and complex distribution of remaining undeveloped reserves of developed gas fields. And twenty-six development technological countermeasures are put forward correspondingly, such as well pattern thickening, extension and reserve increase, secondary production layer potential tapping and fine gas well management. Third, the development direction and goal of natural gas development in Changqing gas province is to pay equal attention to the stable production of old gas fields and the production increase of new areas and carry out conventional gas and unconventional gas research simultaneously. In conclusion, the annual natural gas production of Changqing gas province will maintain a sound momentum of steady growth and will exceed 500 × 108 m3 at the end of the 14th Five-Year Plan and maintain at a stable level for a long term, which is conducive to the optimization of domestic energy consumption structure and realization of “carbon peak and carbon neutrality”.

Simulation of the impact of using a novel neutron conversion screen on detector time characteristics and efficiency

To directly measure the DT neutrons from inertial confinement fusion with a high time resolution, a new type of neutron conversion composed of a CH2 conversion layer, a metal moderation layer, and a CsI secondary electron emission layer is proposed. The conversion screen is based on the principle that recoil protons produced by elastic scattering of the neutrons in CH2 interact with CsI to generate secondary electrons. The moderation layer can filter the energy spectrum of protons to prevent low-energy protons from reaching CsI, which shortens the duration of the secondary electron pulse and improves the temporal resolution of the conversion screen. Based on the Monte Carlo method, both the neutron impulse and background γ-rays response of this conversion screen were calculated. The simulation indicates that the temporal resolution of the conversion screen can reach up to 4.9 ps when the thickness of the gold layer is 100 µm. The detection efficiency of secondary electrons/neutrons can reach 7.4 × 10−3. The detection efficiency of the neutron conversion screen for secondary electrons/γ-rays is an order of magnitude lower than the neutron impulse response, and the response time of γ-rays is 20 ps earlier than the neutron pulses. This means that using this conversion screen is beneficial to distinguish between neutrons and γ-rays and has a good signal-to-noise ratio.

Hierarchical energy management system with multiple operation modes for hybrid DC microgrid

This paper presents a developed energy management system (EMS) with a hierarchical three-level distributed control approach proposed for a photovoltaic/wind turbine/diesel generator with energy storage in an islanded hybrid DC microgrid (MG). In the hierarchical three-level control structure, the power to be transferred by the distributed energy sources (DER) is provided by controlling the converters in the primary control layer. The secondary control layer is used to achieve DC bus voltage restoration and increase current-sharing accuracy simultaneously. In the tertiary control layer, it is aimed to minimize the production cost by performing optimum load-sharing. For the operation of this control structure, a strategy is proposed to optimally manage the energy demand of the hybrid system autonomously under variable load conditions. The EMS with three different operating modes (Mode-I, Mode-II, Mode-III) is proposed to share power between DC MG sources optimally. In Mode-I, renewable energy sources (RES) are enabled to operate with MPPT operation. Energy consumption minimization strategy (ECMS)-based linear programming (LP), genetic algorithm (GA) and pattern search (PS) algorithms are used to minimize the fuel consumption and carbon emissions of the diesel generator (DG) in Mode-II operating Mode. In Mode-III operating mode, DG is not needed, and the power flow between DERs is optimized by using the fuzzy logic controller (FLC) and state machine control strategy (SMCS). The amount of fuel consumed, the cost of fuel consumption and ESS's SOC level are used as the EMS's performance criteria for the MG. The minimum fuel consumption of the DG is calculated as 2.328 L for the operation of LP-based ECMS, and the fuel cost, in this case, is found to be $3.26. Considering the charging of the ESS, the highest SOC level is achieved with 64.87% for the PS-based ECMS-SMCS combination. By considering fuel minimization and SOC level together, it can be seen that the best result is achieved with the LP-based ECMS-SMCS combination.

Numerical and Experimental Study on the Duration of Nozzle Starting of the Reflected High-Enthalpy Shock Tunnel

The starting process of the flow in the nozzle of the JF-14 shock tunnel (1.6 m in length, 500 mm in outlet diameter) in the State Key Laboratory of High Temperature Gas Dynamics is analyzed by calculation and experiment. Two key factors which directly affect the duration of the nozzle starting are the velocity of the expansion wave and the low-velocity zone generated by the interaction between the secondary shock wave and boundary layer on the wall surface. In the process of the nozzle starting, the flow field stabilizes at the center of the nozzle outlet first, and then gradually stabilizes along the radius direction, thus defining the central startup and complete startup of the nozzle. It is found that there is a critical initial pressure. When the initial pressure is lower than the critical pressure, the airflow can reach stability in the nozzle outlet center with the shortest time, otherwise, the time required is much longer. The time required for the airflow to stabilize in the whole outlet section is mainly affected by the size of the low-velocity zone. It is also found that only at a very low initial pressure can the airflow simultaneously reach stability at the entire outlet of the nozzle.

Distributed Cooperative Neural Inverse Optimal Control of Microgrids for Island and Grid-Connected Operations

In this paper, a novel distributed secondary cooperative control based on neural inverse optimal control scheme is synthesized for microgrids considering island and grid-connected modes. This approach is developed for each distributed generator to track frequency and voltage predefined values for island mode, and to track active and reactive power references for grid-connected mode, and for smooth switching between these two modes. To achieve these goals, a secondary control layer is proposed to define the required currents trajectories, which then are controlled using the primary controller. Both control layers are synthesized using recurrent high order neural network on-line trained using an extended Kalman filter, which builds up neural models and is to be used to implement the respective inverse optimal controllers. In addition, a pinning technique is also used for achieving synchronization of all distributed generators only requiring neighborhood information. Thus, a large reduction in the communication network complexity is obtained and the control system reliability is improved. Simulations are performed to evaluate the effectiveness of the proposed scheme with a microgrid benchmark. The obtained results illustrate adequate performances of the proposed scheme to operate the microgrids in island mode, grid-connected mode, and to achieve seamless switching between these two modes.

The Secondary Layer of Meaning in Epic The Case of “Rostam and Sohrab”

The Secondary Layer of Meaning in Epic The Case of “Rostam and Sohrab”

An adaptive multiagent control system for autonomous economic operation and resilience assurance in a hybrid-energy islanded microgrid

Multi-agent control is widely recognized as an effective management system for modern microgrids. This paper proposes a hierarchical distributed multi-agent control system for an islanded microgrid with hybrid-energy resources and a battery-storage bank. The dispatchable dispersed generators are to be online-controlled to stabilize the islanded microgrid and minimize operation cost. A non-dispatchable agent is assigned to each bus with a non-dispatchable generator or a load. A dispatchable agent is assigned to each bus with a dispatchable generator. The control scheme is organized into three layers. The primary control layer comprises only the agent which runs the very fast local voltage/frequency droop-control of the battery-storage bank. It achieves a quasi-instantaneous power balance under any disturbance to maintain the frequency and voltage stability of the microgrid. The secondary control layer is formed by fast control algorithms on the dispatchable agents working at 2 ms time step. It is responsible for regulating the islanded microgrid frequency and voltage at minimum participation time of the battery-storage bank. The tertiary control layer is made by relatively slow control algorithms on the dispatchable agents working at a time step of 200 ms. It copes with the economic operation of the microgrid. Each agent behaves autonomously and shares data with others via communication links. The architecture and control algorithms of each layer are presented. Besides, the coordination protocol between different layers is described. The scheme is implemented by a parallel Matlab-Jade computing setup. Results of a case study islanded microgrid are analysed and compared to literature.

Bimetallic Multi-Level Layered Co-NiOOH/Ni3 S2 @NF Nanosheet for Hydrogen Evolution Reaction in Alkaline Medium.

Development of efficient non-noble metal catalysts for water splitting is of great significance but challenging due to the sluggish kinetics of the hydrogen evolution reaction (HER) in alkaline medium. Herein, a bimetallic multi-level layered catalytic electrode composed of Ni3 S2 nanosheets with secondary Co-NiOOH layer of 3D porous and free-standing cathode in alkaline medium is reported. This integrated synergistic catalytic electrode exhibits excellent HER electrocatalytic performance. The resultant Ni0.67 Co0.33 /Ni3 S2 @NF electrode displays the highest HER activity with only overpotentials of 87 and 203mV to afford current densities of 10 and 100 mA·cm-2 , respectively, and its Tafel slope is 80 mV·dec-1 . The chronopotentiometry operated at high current density of 50 mA·cm-2 shows negligible deterioration, indicating better stability of Ni0.67 Co0.33 /Ni3 S2 @NF electrode than Pt/C (20wt.%). Such a desirable catalytic performance is attributed to the modification of physical and electronic structure that exposes abundant active sites and improves the intrinsic catalytic activity toward HER, which is also confirmed by electrochemically active surface area and X-ray photoelectron spectroscopy analysis. This work provides a strong support for the rational design of high-performance bimetallic electrodes for industrial water splitting.

Distributed event-triggered average consensus control strategy with fractional-order local controllers for DC microgrids

Recently, direct current (DC) microgrids have become prominent due to their less complicated architecture and better integration of renewable energy sources (RES). Energy storage systems (ESSs) and RES, such as photovoltaic (PV) panels and fuel cells (FCs), are internally DC. Hence, it is easier for them to be integrated into DC microgrids compared to AC systems. However, DC microgrids have low inertia, and voltage stability is harder to achieve due to the inexistence of reactive power compensators. Therefore, this paper suggests a novel distributed control system for DC microgrids to achieve voltage stabilization and accurate energy balancing of ESSs based on event-triggered average consensus protocol and fractional-order proportional-integral (FOPI) local controllers. The fractional-order controller has many advantages over the integer-order classical controller, such as achieving better performance, flexibility, and a higher degree of freedom in the controller design. In this regard, the FOPI local controllers provide accurate load sharing for the droop mechanism. The distributed secondary layer controller compensates for the voltage offset, meanwhile balancing the energy level of ESSs. In the conventional distributed control strategies, the communication between the agents is periodically at discrete sampling time, resulting in network traffic increase and excessive energy consumption in the devices. Therefore, in this paper, the average consensus protocol is event-based, saving considerable network capacity for other microgrid communication needs. The effectiveness of the proposed control strategy is confirmed by the simulation of a 380V DC microgrid in MATLAB/Simulink that shows the achievement of the control objectives. Simulation results show the proper voltage stabilization and accurate energy balancing of ESSs in both islanded and grid-connected modes and a significant reduction in the transmitted information between agents.

Adsorption of paper strength additives to hardwood fibres with different surface charges and their effect on paper strength

Light-weight paper products that contain less fibres, but with a maintained bulk and improved strength properties, are highly desirable due to the low cost of raw materials and improved logistics of packaged goods. In this respect, the adsorption capacity of dry strength additives onto fibres, which is affected by the surface charge of said fibres, is very important for the development of these mechanically robust paper products. The influence of the surface charge on the adsorption of strength additives was investigated for, dissolving grade fibres, kraft fibres and kraft fibres modified with carboxymethyl cellulose (CMC) with different surface charge densities, but the same fibre dimensions. The strength additives investigated were cationic starch (CS), anionic polyacrylamide (APAM) and polyelectrolyte complexes (PECs), containing CS and APAM. A linear relationship was found between the surface charge of the fibres and the saturated adsorbed amount of CS. However, when either APAM or PECs adsorbed as secondary layers onto the CS, no correlation between cellulose charge and the saturation adsorption could be observed. The adsorption of APAM was dramatically affected by the pre-adsorbed amount of CS, whereas PECs were less influenced. Moreover, the additives improved the tensile strength (60%) and strain at break (> 100%) of handsheets formed with the kraft fibres and adsorbed APAM. It was also found that CS/APAM increased the sheet density while CS/PECs lowered it. In conclusion, the gained fundamental understanding of these adsorption of additives is of significant importance to facilitate the industrial development of sustainable low-cost high-end packaging products.Graphical abstract

Hierarchical Control for DC Microgrids Using an Exact Feedback Controller with Integral Action

This paper addresses the problem of the optimal stabilization of DC microgrids using a hierarchical control design. A recursive optimal power flow formulation is proposed in the tertiary stage that ensures the global optimum finding due to the convexity of the proposed quadratic optimization model in determining the equilibrium operative point of the DC microgrid as a function of the demand and generation inputs. An exact feedback controller with integral action is applied in the primary and secondary controller layers, which ensures asymptotic stability in the sense of Lyapunov for the voltage variables. The dynamical model of the network is obtained in a set of reduced nodes that only includes constant power terminals interfaced through power electronic converters. This reduced model is obtained by applying Kron’s reduction to the linear loads and step nodes in the DC grid. Numerical simulations in a DC microgrid with radial structure demonstrate the effectiveness and robustness of the proposed hierarchical controller in maintaining the stability of all the voltage profiles in the DC microgrid, independent of the load and generation variations.

Mapping intrashell variation in Mg/Ca of brachiopods to external growth lines: Mg enrichment corresponds to seasonal growth slowdown

Determining secular changes in seawater temperature and Mg/Ca ratio is of high importance in paleooceanographic, paleoenvironmental and paleoecological studies. On the one hand, intra-shell variation in Mg/Ca in brachiopod shells is used to reconstruct historical changes in temperature and in seasonality. On the other hand, intra-shell analyses show a weak relationship between Mg/Ca and δ18O, but a positive correlation between Mg/Ca and Sr/Ca, and an increase of Mg/Ca at growth lines, indicating that Mg/Ca does not simply track seawater temperature alone. Internal growth lines are rarely visible in brachiopod shells, and the relation between growth lines that mark growth slowdown or cessation and Mg/Ca fluctuation is thus not properly understood. Here, using four species of extant brachiopods from the NE Pacific and the SW Pacific, from environments with low seasonality in seawater temperature (<5 °C), and two species of Late Triassic brachiopods (Western Carpathians), we measure intra-shell ontogenetic variation in Mg/Ca, S/Ca and Sr/Ca with laser ablation ICP-MS and electron microprobe. In contrast to previous studies, we map variation in Mg, S, and Sr to external growth lines. We find that, first, zones of Mg/Ca enrichment in the secondary layer form 10–50 μm-thick discrete bands or clusters of micrometric bands that consistently terminate at major external, predominantly annual growth lines that are associated with distinct notches that correspond to mantle retractions in most species. These bands generate distinct peaks in Mg/Ca that stand above low, more uniformly distributed background Mg/Ca values along laser-ablation and microprobe transects. The magnitude of Mg/Ca in these bands is comparable to Mg/Ca in the primary layer, exceeding background values of Mg/Ca in the secondary layer by 5–20 mmol/mol (by a factor of two to five). Second, Mg enrichment in discrete bands is closely associated with an increase in S concentrations in the secondary layer. Therefore, even when Mg and S uptake is expected to be highest under fast precipitation rate, these empirical observations show that Mg and S enrichment occur in the zones that were precipitated at times of a significant growth reduction (e.g., in cold-temperate brachiopods studied here during winters when primary productivity is low). The mechanisms for this paradox are unclear but can be related to uptake of Mg by amorphous calcium carbonate (ACC) to delay the transformation of ACC to calcite during the formation of growth lines. Therefore, intra-shell variation in Mg/Ca in brachiopods with major growth lines is primarily determined by seasonal decline or cessation in shell growth and not by seasonal changes in seawater temperature.

Effect of thermal nonequilibrium on the shock interaction mechanism for carbon dioxide mixtures on double-wedge geometries

The effect of thermal nonequilibrium on shock interactions of carbon dioxide (CO2) hypersonic flows is investigated. Given the relatively low characteristic vibrational temperature of the CO2 molecule, it is expected that excited vibrational modes play a significant role in the physics of shock/shock and shock/boundary layer interactions. The shock interference mechanism resulting from a CO2-dominated flow over different double-wedge geometries is investigated by numerically solving the Navier–Stokes equations within the framework of a two-temperature model that considers translational energy–vibrational energy transfer. To assess the impact of vibrational relaxation, a comparative assessment of the patterns obtained with three thermo-physical models is presented, with the two-temperature model flow pattern being compared to thermally perfect and perfect ideal gas ones. Results obtained with the two-temperature model show that increasing the aft angle significantly enlarges the separated region in the compression corner and generates numerous secondary shock waves and shear layers. Peaks of heat flux and pressure occur along the surface due to boundary layer reattachment downstream of the compression corner, except for the case of the higher angle, which results in the largest peaks due to shock impingement. Different assumptions on the excitation of vibrational modes are shown to largely influence the size of the recirculation bubble in the compression corner, shock interaction mechanism, and surface loads. The more energy transferred to the vibrational mode, the lower post-shock temperatures are obtained, which tends to reduce the post-shock density, leading to weaker shock interactions characterized by delayed onsets of separation, reduced separation regions, and smaller standoff distances.

Accessing greater thickness and new morphology features in polyamide active layers of thin-film composite membranes by reducing restrictions in amine monomer supply.

Polyamide formation, via interfacial polymerization (IP) during thin-film composite (TFC) membrane fabrication, is regarded as self-limiting-in the sense that the polyamide film limits its own growth as it forms. During IP, trimesoyl chloride (TMC) and m-phenylenediamine (MPD) react rapidly to form an incipient polyamide film that densifies and slows the diffusion of the more permeable monomer (MPD), thereby limiting polyamide growth and yielding films that typically exhibit thicknesses <350 nm. The morphology of these polyamide films is characterized by a basal layer of void nodular and leaf-like features that is sometimes overlaid by a secondary layer of overlapping flat features. Here, we present evidence showing that polyamide active layers are substantially permeable to MPD, and that minimizing certain restrictions in the MPD supply conditions during IP can result in polyamide active layers of thicknesses several times greater (>1 μm) than those typically reported in the literature. In addition to the basal layer of void nodular features and secondary layer of overlapping flat features that characterize typical polyamide active layers, the thicker films also exhibited three additional morphological features: blanket-like layers atop the basal layer or other void features, multi-layer void structures, and/or void mega-nodules (up to over a micron in diameter). Overall, the results indicate that reducing restrictions in the MPD supply conditions during IP: (1) overcomes the limited polyamide growth observed in conventional TFC membrane fabrication and (2) leads to film morphologies with a more prominent void structure. This latter observation is consistent with recent literature describing the role of CO2 degassing and nanobubble confinement in the development of polyamide active layer morphology. Future studies could vary MPD supply conditions as a new tool to expand the range of achievable thicknesses in active layer casting, regulate active layer morphology and optimize nanobubble confinement conditions independently of MPD supply. Such capabilities could aid in the development of novel supports and TFC structures.

Syntheses, crystal structures, and luminescence properties of three cadmium coordination polymers assembled from a semi-rigid tetracarboxylate ligand

Crystal engineering is considerably useful in the preparation of functional coordination polymers. In the present study, a new semi-rigid tetracarboxylate, 4,5-bis(4-carboxyphenoxy)phthalic acid (H4L), was designed and applied for assembling metal coordination polymers. Self-assembling process involving Cd(II) metal ions, H4L and 4,4′-bipyridine (4,4′-bpy), (E)-1,2-bis(pyridin-4-yl)ethane (bpe) or 1,4-bis(1-imidazolyl)benzene (bib) resulted into the formation of coordination polymers, including [Cd2(L)(4,4′-bpy)1.5(H2O)]n·(H2O)n (1), [Cd2(L)(bpe)1.5(H2O)]n·(H2O)3.5n (2), and [Cd2(L)(bib)1.5]n·(H2O)n (3). Through X-ray single crystal diffraction analysis, the three compounds 1–3 were found to exhibit isostructural three-dimensional polymeric structures composed of two-dimensional secondary layers pillared by different rod-like N-donor ligands. Compared with the uncoordinated H4L exhibiting a symmetric crystal structure, the molecular configurations of L4− in 1–3 were tuned due to the complexation of cadmium ion and the introduction of different N-donors. Additionally, the coordination geometries of cadmium ions and luminescence properties in compounds 1–3 were finely tuned due to the introduction of different lengths of rod-like ligands. The thermostability and luminescence properties of compounds 1–3 were determined. The present results provide further understanding of the crystal engineering of semi-rigid ligands to a certain extent.

Effect of sonic and ultrasonic irrigation on improving root canal cleanliness after post space preparation: A confocal laser scanning microscopic study

Introduction: Removing the secondary smear layer has been presumed to increase the micromechanical retention of fiber posts. The additional use of irrigation techniques is intended to improve the cleanliness of the root canal walls. The present study aimed to determine the effectiveness of sonic and ultrasonic irrigation techniques on root canal cleanliness after the post space preparation.Materials and Methods: A total of 27 extracted single-rooted premolar samples underwent root canal treatment using gutta-percha and AH Plus that was labeled with rhodamine B. Gutta-percha was removed during the post preparation. The sample was then divided into three groups (n = 9): irrigation with sonic activation, ultrasonic activation, or without activation, respectively. The teeth were subsequently cut in the middle third area of the root, and the remnant of smear layers was observed using a confocal laser scanning microscope. Cleanliness was expressed as a percentage of the angle that contained part of the red area representing the smear layer. The results were statistically analyzed with a one-way ANOVA test and post hoc Bonferroni test set at 5% significance level.Results: The sonic group had the greatest percentage of root canal wall cleanliness (89.00 ± 2.77), followed by the ultrasonic (78.33 ± 3.09) and nonactivated groups (67.77 ± 3.37). Conversely, there was no significant difference in root canal wall cleanliness between the sonic and ultrasonic groups (P = 0.067) or the ultrasonic and nonactivation groups (P = 0.071).Conclusions: Irrigation with sonic activation improved cleanliness of the root canal dentinal wall after post space preparation.

Effect of the chitosan second layer on the gelation and controlled digestion of Citrem-chitosan bilayer emulsions.

This research aimed to induce repulsive gelation in Citrem-stabilized O/W emulsions by creating a secondary layer of chitosan around the droplets. A range of chitosan concentrations (0-0.25 wt%) and degrees of deacetylation (DDA 50% and 93%) were used to establish the conditions for repulsive gelation in 36 wt% O/W emulsion. The bilayer emulsions were prepared by the electrostatic deposition of positively charged chitosan on negatively charged Citrem-stabilized droplets at pH 4. The droplet size increased from <0.5 μm for the primary emulsion to 5-10 μm at an intermediate chitosan concentration (0.05-0.15 wt%) due to bridging flocculation and again dropped to 1.7-3.6 μm at higher concentrations (0.2 and 0.25 wt%). The droplet charge changed from -48 mV for the primary emulsion to +41.4 and +54.5 mV after surface saturation by DDA 50 and DDA 93 chitosan, respectively. The strain and frequency-dependent rheology indicated that with an increase in the chitosan concentration, emulsions changed from a viscoelastic liquid for monolayer emulsions to strong attractive gel due to bridging flocculation at an intermediate chitosan concentration. At a higher concentration, repulsive gels were formed at complete coverage due to an increase in the effective oil volume fraction towards close packing resulting from the expansion of the interfacial steric barrier and charge cloud thickness. The overall lipid digestibility during in vitro digestion was 25.7% for monolayer emulsions, which decreased with increased chitosan concentration and reached the lowest at surface saturation (17.5%). It was proposed that the formation of the Citrem-chitosan bilayer controlled lipid digestibility by delaying the action of gastric and pancreatic lipases. Such bilayer emulsion gels can be utilized for structure formation in reduced-fat foods.

Зарастание вырубок разного возраста в Висимском заповеднике (Свердловская область)

The paper represents the results of structure and dynamics studies of secondary forest types shaped by forest cuts performed at different periods. The dominant canopy layer tree species is Betula pubescens Ehrh. In the areas cut in 1995, it forms a thick contiguous canopy layer with none of the conifers participating, with open gaps dominated by Deschampsia cespitosa (L.) Beauv and Calamagrostis langsdorffii (Link) Trin. In the 1980 cuts the Betula stands are sparser, have a secondary conifer tree layer, which in future will out-compete and predominate Betula.