Number Of Large Aggregates Research Articles

Impact of GAUT1 Gene Knockout on Cell Aggregation in Arabidopsis thaliana Suspension Culture.

The development of efficient producers of recombinant pharmaceuticals based on plant cell suspension cultures is a pressing challenge in modern applied science. A primary limitation of plant cell cultures is their relatively low yield of the target protein. One strategy to enhance culture productivity involves reducing cell aggregation. In order to minimize cell-to-cell adhesion in culture, we used Cas9 endonuclease to knock out the GAUT1 gene, which is a key gene of pectin biosynthesis in the genome of Arabidopsis thaliana. The resulting knockouts exhibited altered phenotypes and were unable to form viable plants. The suspension cell culture induced from seedlings bearing a homozygous deletion in the GAUT1 gene displayed darker coloration and an increased number of large aggregates compared to the control. The biomass accumulation rate showed no difference from the control, while the level of recombinant GFP protein accumulation was significantly reduced. Thus, our findings indicate that disruptions in pectin synthesis and the formation of larger aggregates in the suspension cell culture adversely affect the accumulation of the target recombinant protein. Alternative targets should be sought to reduce cell aggregation levels in plant cell cultures through genome editing.

Analyzing Amylin Aggregation Inhibition Through Quantum Dot Fluorescence Imaging.

Protein aggregation is associated with various diseases caused by protein misfolding. Among them, amylin deposition is a prominent feature of type 2 diabetes. At present, the mechanism of amylin aggregation remains unclear, and this has hindered the treatment of type 2 diabetes. In this study, we analyzed the aggregation process of amylin using the quantum dot (QD) imaging method. QD fluorescence imaging revealed that in the presence of 100 μM amylin, aggregates appeared after 12 h of incubation, while a large number of aggregates formed after 24 h of incubation, with a standard deviation (SD) value of 5.435. In contrast, 50 μM amylin did not induce the formation of aggregates after 12 h of incubation, although a large number of aggregates were observed after 24 h of incubation, with an SD value of 2.883. Confocal laser microscopy observations revealed that these aggregates were deposited in three dimensions. Transmission electron microscopy revealed that amylin existed as misfolded fibrils in vitro and that QDs were uniformly bound to the amylin fibrils. In addition, using a microliter-scale high-throughput screening (MSHTS) system, we found that rosmarinic acid, a polyphenol, inhibited amylin aggregation at a half-maximal effective concentration of 852.8 μM. These results demonstrate that the MSHTS system is a powerful tool for evaluating the inhibitory activity of amylin aggregation. Our findings will contribute to the understanding of the pathogenesis of amylin-related diseases and the discovery of compounds that may be useful in the treatment and prevention of these diseases.

Effect of nanosilica on the hydrological properties of loess and the microscopic mechanism

Loess areas, such as the Loess Plateau, are characterized by a fragile ecological environment, high soil erosion, and frequent geological disasters due to the unique hydrological properties of loess (e.g., collapsibility and permeability). Therefore, the loess must be stabilized for use in engineering construction. Traditional stabilizers (lime, cement, and fly ash) cause environmental problems, such as soil salinization and greenhouse gas emissions. Therefore, this study investigated the effect of nanosilica on the hydrological properties of loess and the microscopic mechanism. Different nanosilica contents (0.2%, 0.4%, 0.8%, 1%, and 3%) were added to loess sample, and the particle size distribution, Atterberg limits, collapsibility, and soil water characteristics were analyzed. The results revealed the following. The addition of nanosilica changed the particle size distribution, liquid limit, plastic limit, and plasticity index of loess. After the addition of nanosilica with different contents, the loess collapsibility coefficient curve shifted downward, the soil water retention curve shifted upward, and the unsaturated permeability coefficient curve shifted downward. The pores between particles were filled, and the number of large and medium pores and the pore connectivity were lower after the nanosilica addition. The surface of the coarse particles adsorbed more fine particles, and a large number of micro-aggregates or clay aggregates were present in the pores between particles. In conclusion, the environmentally friendly material nanosilica can be used to improve the hydrological properties of loess, which is applicable to alleviating soil erosion and preventing geological disasters on the Loess Plateau.

Many-body dissipative particle dynamics simulations of micellization of sodium alkyl sulfates.

We present a study of micelle formation in alkyl sulfate surfactants using the simulation method of many-body dissipative particle dynamics (MDPD). We parametrise our model by tuning the intermolecular interactions in order to reproduce experimental values for the chemical potential and density at room temperature. Using this approach, we find that our model shows good agreement with experimental values for the critical micelle concentration (CMC). Furthermore, we show that our model can accurately predict CMC trends, which result from varying properties such as surfactant tail length and the salt concentration. We apply our model to investigate the effect of aggregation number on various micellar properties, such as the shape of individual micelles and the fraction of bound counterions. We show that micelles become aspherical at large aggregation numbers, in line with experimental predictions, and that longer tail surfactants are generally more spherical at all aggregation numbers compared to those which are shorter. We find excellent agreement between our simulations and experimental values for the degree of counterion binding, a factor that is crucial to accurately studying micellar shape, but one that is typically overlooked in the existing literature.

CONCRETE ON QUARTZITE AGGREGATES

In the post-war period, Ukraine will need a large number of aggregates to repair and rebuild destroyed and damaged objects of transport infrastructure, including roads, airfields, and parking lots. To expand the raw material base of such construction, in addition to traditional high-quality aggregates from crushed granite, quartz sand and manufactured sand, it is advisable to use some types of waste and secondary products from various industries. They must meet the basic requirements for density, strength, frost resistance. These include a by-product of iron ore mining, quartzite. The use of quartzites as aggregates for cement concretes has certain difficulties due to their characteristics. This is reflected, first of all, on the strength of the concretes in which they are included. In this article, the features of the influence of quartzite aggregates on the strength of cement concretes are considered. Studies that have been carried out on mixtures of different mobility have shown that dusty particles, which are part of quartzite, have a positive effect on the structure of concrete.

Effects of straw-returning combined with application of microbial inoculants on soil aggregates and related nutrients

We analyzed the particle size distribution of soil aggregates in 0-20 and 20-40 cm soil layers of rice-wheat rotation field based on a field plot test with two treatments, conventional straw returning (CK) and straw returning with the addition of straw decomposition promoting microbial inoculants (IT). We evaluated the water stability indices of soil aggregates (the number of soil water stable large aggregates R0.25, the average weight diameter MWD, and the geometric average diameter GMD), and measured the contents of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the soil aggregates of ＜0.053, 0.053-0.25, 0.25-1, ＞1 mm. The results showed that: 1) The number of aggregates ＜0.053, 0.053-0.25, ＞0.25 mm in the 0-20 and 20-40 cm soil layers under IT decreased by 10.0% and 6.8%, increased by 3.0% and 5.7%, and 17.9% and 26.1% compared with CK, respectively. IT effectively increased R0.25, MWD, and GMD by 26.4%, 20.0%, 18.2% and 18.2%, 10.5%, 10.0% in 0-20 and 20-40 cm soil, respectively. 2) Compared to CK, the TP content of 0.25-1 mm aggregates in 0-20 and 20-40 cm soil under IT was significantly increased by 40.3% and 37.5%, respectively, without difference in TN and SOC contents. There was no significant difference in nutrient contents of the other aggregates between the treatments. The contents of SOC and TN in large aggregates (>0.25 mm) were higher than those in silty aggregates (<0.053 mm). Compared to CK, the cumulative contribution rates of SOC, TN and TP of <0.053 mm aggregates under IT were decreased in two soil layers. There was no significant difference in the nutrient cumulative contribution rates of 0.053-0.25 mm aggregates between treatments. The cumulative contribution rates of SOC, TN, and TP of large aggregates (>0.25 mm) under IT were 32.1%, 19.6%, 52.8% and 22.8%, 11.8%, 42.9% higher than those under CK in 0-20 and 20-40 cm soils, respectively. 3) The number of <0.053 mm aggregates was significantly negatively correlated with SOC and TP contents, while that of 0.053-0.25 mm aggregates was negatively correlated with nutrient content. The number of large aggregates (>0.25 mm) were significantly positively correlated with SOC, TN, and TP contents. In conclusion, straw returning with microbial-inoculant addition could promote the formation of soil macroaggregates (>0.25 mm), and improve the water stability of soil aggregates, increasing nutrient contents in soil macroaggregates, with the nutrients transferring from silty aggregates to macroaggregates.

THE EFFECT OF SEAWATER SOAKING ON THE STABILITY OF AC-WC MIXTURES USING KOYA AGGREGATE, JAYAPURA CITY

Roads are the basic infrastructure in driving the regional economy, so a good pavement structure is needed. One of the factors of road damage is standing water, for roads around the coast are likely to be inundated by sea water. Asphalt Concrete Wearing Course (AC-WC) is one of the concrete asphalt layer which is able to provide good carrying capacity and waterproof layer for road structures. Some areas in kota Jayapura such as Koya have a large number of local aggregates. This study used oil asphalt as a binder, local aggregate for hot asphalt mixture, and saw the effect of sea water immersion in the asphalt mixture. The purpose of this study is to determine the volumetric value and Marshall value of the Laston AC-WC mixture against sea water immersion and without immersion. The material used is oil asphalt from PT. Pertamina and local aggregates from the Koya area. The research carried out is an experimental test in the laboratory, where the resulting asphalt concrete mixture (AC-WC) will be treated with sea water immersion, then Marshall characteristics testing will be carried out to determine its durability value. Based on the tests carried out, the results showed that the volumetric value and the marshall value of the samples treated with immersion did not provide a significant difference in values compared to normal samples. The results of the marshall value, namely the stability of all asphalt levels meet the specifications, while for flow only the asphalt content of 5.5% and 6% both by soaking and without soaking.

Promotion of phosphate release from humic acid-iron hydroxide coprecipitates in the presence of citric acid

Phosphate (P) resources are expected to be depleted within a century. Therefore, promoting balanced phosphorus fertilizer use and understanding phosphorus dynamics in soils containing iron (III), organic acids, and iron (III)-organic molecule particulates is crucial. This study investigated the sorption of citric acid onto humic acid-iron hydr(o)xide coprecipitate (HAFHCP) and the reciprocal effects of citric acid and P sorption on HAFHCP with different C/Fe ratios. The results showed that the maximum sorption capacity (MSC) of citric acid on HAFHCP decreased with increasing C/Fe ratios in the HAFHCP. The P sorption on HAFHCP pre-sorbed with citric acids (denoted as C–P) decreased by 50% compared with that of the MSC on FH. However, citric acids could only reduce P sorption by 20% when P was pre-sorbed on HAFHCP (denoted as P–C). The results suggested that upon the formation of HAFHCP, citric acids might increase P availability, especially in the C–P system. Although citric acids initially inhibited P sorption on HAFHCP in the P–C system, P sorption increased with prolonged reaction time. The exposures of new sorption sites upon dissolution of Fe from HAFHCP by citric acids or/and the formations of Fe bridge between P and organic domains of HAFHCP might contribute to these results. Additionally, a number of large HAFHCP aggregates became smaller while sorbing P due to the increasing electric repulsion on the surfaces of FH, enabling the subsequent dissolutions of more Fe by citric acids from HAFHCP in the P–C system. By integrating these innovative and sustainable strategies, the recycling and reuse of P can be optimized, thereby minimizing the reliance on synthetic fertilizers and mitigating environmental impacts. This approach fosters the efficient utilization of phosphorus resources, improves soil fertility, and enhances the overall resilience of agricultural systems and ecosystems.

Fabrication and Tailoring the Structural and Dielectric Characteristics of GO/Sb2O3/PMMA/PC Quaternary Nanostructures For Solid State Electronics Nanodevices

In this paper, films of (PMMA-PC/Sb2O3-GO) quaternary nanostructures were prepared by casting method with different concentrations of Sb2O3/GO NPs are (0, 1.4 %, 2.8 %, 4.2 %,and 5.6 %). The structural and dielectric characteristics of nanostructures system (PMMA-PC/Sb2O3-GO) have been explored to use in different solid state electronics nanodevices applications. The morphology of (PMMA-PC/Sb2O3-GO) nanostructures films was studied using a scanning electron microscope (SEM). SEM images indicate a large number of uniform and coherent aggregates or chunks. The Fourier transform infrared spectroscopy(FTIR) analysis were studied to show the interactions between the Sb2O3/GO NPs and PMMA/PC blend. The dielectric properties of nanostructures films were investigated in the frequency range (100HZ-5MHZ). The dielectric constant, dielectric loss, and A.C electrical conductivity increase with the concentration of (Sb2O3-GO) NPs. The dielectric constant and dielectric loss were reduced, whereas electrical conductivity increased with frequency. Finally, results showed the PMMA-PC/Sb2O3-GO nanostructures may be considered as promising materials for solid state electronics nanodevices.

Nanoparticulate air pollution disrupts proteostasis in Caenorhabditis elegans.

The proteostasis network comprises the biochemical pathways that together maintain and regulate proper protein synthesis, transport, folding, and degradation. Many progressive neurodegenerative diseases, such as Huntington's disease (HD) and Alzheimer's disease (AD), are characterized by an age-dependent failure of the proteostasis network to sustain the health of the proteome, resulting in protein misfolding, aggregation, and, often, neurotoxicity. Although important advances have been made in recent years to identify genetic risk factors for neurodegenerative diseases, we still know relatively little about environmental risk factors such as air pollution. Exposure to nano-sized particulate air pollution, referred to herein as nanoparticulate matter (nPM), has been shown to trigger the accumulation of misfolded and oligomerized amyloid beta (Aβ) in mice. Likewise, air pollution is known to exacerbate symptoms of AD in people. We asked whether nPM contributes to the misfolded protein load, thereby overwhelming the proteostasis network and triggering proteostasis decline. To address this, we utilized C. elegans that express reporter proteins that are sensitive to changes in the protein folding environment and respond by misfolding and displaying readily scorable phenotypes, such as localized YFP fluorescence or paralysis. We found that nPM exacerbated protein aggregation in body wall muscle cells, increasing the number of large visible protein aggregates, the amount of high molecular weight protein species, and proteotoxicity. Taken together, the data point to nPM negatively impacting proteostasis. Therefore, it seems plausible that nPM exposure may exacerbate symptoms of AD and age-related dementia in a manner that is at least partially dependent on proteostasis decline.

An investigation into oxidation-induced fragmentation of soot aggregates by Langevin dynamics simulations

The present work proposes a novel oxidation-induced fragmentation model for soot aggregates which is implemented as a submodel in Langevin dynamics (LD) simulations. The surface growth and particle aggregation are first simulated in the LD framework to generate a large number of aggregates with sufficient geometric diversities resembling realistic soot aggregates. The fragmentation of these aggregates induced by surface oxidation through reaction with molecular oxygen at high temperatures is then modelled. The probability density function (PDF) of a newly proposed fragmentation pattern factor is obtained from the statistical analysis of the fragment sizes. The probability of forming a monomer fragment and a remaining aggregate fragment (monomer fragmentation) is found to be two orders of magnitude higher than that of forming two fragments of similar size (equal-sized fragmentation). The relative importance of various aggregate characteristic parameters affecting the fragmentation pattern, i.e., splitting size ratio, is quantified by a Random Forest regression. It is found that the standard deviation of the overlapping coefficient is the most important parameter, followed by the global average overlapping coefficient, number of primary particles, fractal prefactor, and the fractal dimension. An exponential function is fitted to the PDF of the fragmentation pattern factor. The functional form is independent of the aggregate parameters and the fitted function shows good agreements with the statistics of the fragmentation pattern factor.

Interaction between autophagy and the NLRP3 inflammasome in Alzheimer's and Parkinson's disease.

Autophagy degrades phagocytosed damaged organelles, misfolded proteins, and various pathogens through lysosomes as an essential way to maintain cellular homeostasis. Autophagy is a tightly regulated cellular self-degradation process that plays a crucial role in maintaining normal cellular function and homeostasis in the body. The NLRP3 inflammasome in neuroinflammation is a vital recognition receptor in innate cellular immunity, sensing external invading pathogens and endogenous stimuli and further triggering inflammatory responses. The NLRP3 inflammasome forms an inflammatory complex by recognizing DAMPS or PAMPS, and its activation triggers caspase-1-mediated cleavage of pro-IL-1β and pro-IL-18 to promote the inflammatory response. In recent years, it has been reported that there is a complex interaction between autophagy and neuroinflammation. Strengthening autophagy can regulate the expression of NLRP3 inflammasome to reduce neuroinflammation in neurodegenerative disease and protect neurons. However, the related mechanism is not entirely clear. The formation of protein aggregates is one of the standard features of Neurodegenerative diseases. A large number of toxic protein aggregates can induce inflammation. In theory, activation of the autophagy pathway can remove the potential toxicity of protein aggregates and delay the progression of the disease. This article aims to review recent research on the interaction of autophagy, NLRP3 inflammasome, and protein aggregates in Alzheimer’s disease (AD) and Parkinson’s disease (PD), analyze the mechanism and provide theoretical references for further research in the future.

Micromorphological Characteristics of Fallow, Pyrogenic, Arable Soils of Central Part of Yakutia

The assessment of the micromorphological characteristics of soils is a powerful tool for studying the transformation of soils under the influence of various weathering mechanisms (physical, biogenic). The central part of Yakutia is characterized by a large area of agricultural lands, some of which has become fallow land and is subject to cryogenic processes, fires and anthropogenic impact. Under the conditions of climate change, the fallow soils of Yakutia can be re-involved in the agricultural complex. To study their state, a method of micromorphological investigation of thin soil sections is proposed. Thin sections of soils were analyzed using a polarizing microscope Leica DM750P. As a result of the work, zonal, fallow, pyrogenic and agricultural soils of the central part of Yakutia were analyzed. The soils were found to be in a degraded state. Zonal soils were characterized by the presence of quartz grains, feldspar, and undecomposed plant tissue, as well as biogenically transformed humus. Fallow soils were characterized by a thick organo-mineral (A) horizon, quartz grains, feldspar, and silty-clay plasma. Pyrogenic soils have differences from natural and fallow soils; as a result of fires and active illuviation of organo-mineral substances. The Anthrosol soils were characterized by a large number of aggregates of various sizes. In their composition there were various minerals, such as quartz, feldspar and mica. The signs of soil cryogenesis were noted only in the underlying horizons (B), while the upper horizon (A) had no signs of cryogenic transformation.

Numerical investigation of hydrolysis failure of aggregates in loess

Large numbers of aggregates in loess are vital components of the skeletal structure of loess. In this study, a simulation of the water stability of aggregates using coupled computational fluid dynamics and the discrete-element method (CFD–DEM) is presented. For the simulation, the ‘fixed coarse-grid’ method of the Particle Flow Code in 3 Dimensions (PFC3D) software program was employed to simulate the particle–fluid coupling. With respect to the degradation law, a customised code was developed using Python, which transformed through the CFD–DEM model the hydrolysis of cement into the degradation process for the bond strength between particles. Under the action of different hydraulic gradients, the rate of hydrolysis of the aggregates increased rapidly with an increase in water pressure, and many piles of particles were denuded from the aggregates, thus causing the destruction of the aggregates. At the same time and under the same water pressure, the rate of hydrolysis of the multi-aggregates was always lower than that of the single aggregate. Also, the density and porosity of the aggregates would affect, to varying degrees, the water stability.

Gas barrier properties of polylactide/cellulose nanocrystals nanocomposites

The development of polylactide (PLA)/cellulose nanocrystals (CNC) nanocomposites in the aim to increase gas barrier properties has been widely studied, but gave rise to conflicting results. To better understand the underlying gas transport mechanisms, PLA/CNC nanocomposites were produced at concentrations between 5 and 50 wt%. The role of the PLA/CNC interface for the permeability was investigated using three different CNC surface grafts, namely lauric acid (slightly interacting with PLA), stearic acid (non-interacting with PLA), and poly glycidyl methacrylate bearing a reactive epoxy end-group (crosslinking with PLA). While PLA/CNC composites contained a large number of aggregates, homogenously dispersed nanocomposites were obtained with surface modified CNCs even at high concentration of CNC (up to 30 wt%). All nanocomposites had better O2 and CO2 barrier properties than PLA. Surprisingly, the nanocomposites prepared with surface grafted CNC did not perform better than the ones prepared with neat CNC. The diffusion coefficient was successfully modeled with Nielsen's law, showing the importance of the shape factor and resulting tortuosity for the barrier performance notwithstanding PLA/CNC surface compatibility. The analysis of the dual-mode O2 sorption isotherm showed the creation of a similar quantity of supplementary sorption sites in nanocomposites prepared with neat or lauric acid grafted CNC. PGMA grafts induced a higher number of sorption sites. The most important advantage of CNC surface grafts was the shielding of CNC against water vapor uptake. As a result, the O2 barrier properties could be maintained constant up to 90% relative humidity.

Structure and ablation behavior of “Z-pins like” M-MC1-x (M = Zr, Hf) gradient cermet rods prepared by carbon diffusion in situ reaction method

In this study, “Z-pins like” M-MC1-x (M = Zr, Hf) gradient cermet rods were prepared by the carbon diffusion in situ reaction method, and the effects of different heat treatment temperatures on the microstructure of MC layers in “Z-pins like” M-MC1-x gradient cermet rods and the ablation behavior of “Z-pins like” M-MC1-x gradient cermet rods were investigated. The results showed that “Z-pins like” M-MC1-x (M = Zr, Hf) gradient cermet rods formed gradient MC layer after heat treatment, and the thickness of MC layer increased with the increase of heat treatment temperature, and the in situ reaction method improved the bonding conditions of different phase interfaces. The ablation performance of “Z-pins like” M-MC1-x cermet rods was good. After ablation, the “Z-pins like” M-MC1-x cermet rods formed multilayer structure inside, from the surface oxide layer to the substrate: partially molten MO2 layer, loose MO2 skeleton, MO2 layer formed by a large number of nanoscale microcrystalline aggregates, dense MCxOy layer and unoxidized MC1-x and M-MC1-x eutectic phases.

Preparation and Characterization of the Functional Properties of Synthetic Aggregates from Silico-Manganese Slag.

A large number of natural aggregates are used in the field of construction materials, resulting in the exhaustion of natural aggregates. Therefore, looking for an alternative will slow down the consumption of natural aggregates. The sintering method not only consumes a lot of energy to prepare aggregates but also produces a lot of pollutants. In this study, silico-manganese (SM) slag was dried, ground into powder, and used as raw material. Solid and liquid alkaline activator methods were used to prepare SM slag non-burning aggregate (SMNA) by the cold bonding method. The effects of grinding time, amounts of solid and liquid alkaline activators, curing temperature, and the amount of added fly ash on aggregate properties were investigated. The aggregate microstructure was characterized by XRD, SEM, and FTIR methods, and the toxic leaching analysis of aggregate was performed. The results showed that with a fixed amount of liquid activator (16.2% wt.) and solid activator (15% wt.) and fly ash (20% wt.), respectively, and curing was performed at room temperature, the aggregate properties were optimal: the bulk density of 1236.6–1476.9 kg/m3 and the water absorption lower than 4.9–5.5%. The apparent density was 1973.1–2281.6 kg/m3, and the bulk crushing strength was 24.7–27.9 MPa. The XRD, SEM, and FTIR results indicated that amorphous gel could be formed from SM under an alkaline activator, improving the aggregate strength. The results of toxic leaching showed that the aggregate prepared from SM exhibited environmentally friendly characteristics. The SMNA was obtained via the simple and low-energy consumption production process, paving the new way toward large-scale utilization of SM.

Effect of waste glass aggregate on performance of asphalt micro-surfacing

Huge amounts of waste glass are produced every year in China, which brings great pressure on the environment. Meanwhile, a large number of natural aggregates are required for highway construction every year. In this study, it is intended to prepare asphalt micro-surfacing materials using waste glass as aggregate and evaluate their performance. The morphology of basalt and waste glass was quantitatively analyzed through aggregate image measurement system to characterize the morphological differences. In addition, the wet stripping test, wet track abrasion test, wheel load test, sand patch test and British pendulum test were used to investigate the resistance to the action of water, the wear performance, rutting resistance and skid resistance of asphalt micro-surfacing mixtures. The results indicate that the two-dimensional (2D) form of waste glass is more abundant than that of basalt, and as the content of waste glass increases, the British pendulum number (BPN) value and the texture depth (TD) value of micro-surfacing mixtures increase, which means that the addition of waste glass can improve the skid resistance ability of micro-surfacing mixtures to some extent. The abrasion loss, lateral and vertical displacement are all increased after replacing basalt with waste glass due to its brittleness and weak bonding. Considering the feasibility of mechanical properties, it is recommended that the maximum volume amount of fine waste glass and coarse waste glass should be less than 15% and 10%, respectively. The potential use of waste glass can alleviate the overconsumption of natural resources and is a good choice for applying in micro-surfacing pavement materials.

Experimental Investigation on Combustion Characteristics and Agglomeration of Al/NEPE Propellants

AbstractIn order to understand the ignition and combustion characteristics of NEPE propellants under different pressure conditions and the agglomeration behavior of aluminum particles on the burning surface, the Al/NEPE propellant was tested on a sealed high‐pressure laser ignition platform. Laser ignition experiments show that both ignition delay time and combustion time are inversely proportional to ambient pressure. With the increase of pressure, the reduction of ignition delay time and self‐sustaining combustion time is reduced. The impact of pressure on ignition and combustion is very complex. We then analyze the effect of pressure on ignition delay time using a theoretical mechanism. High‐speed microscopic images display the agglomeration of aluminum particles in propellants mainly through the following three processes: accumulation, aggregation, and agglomeration. It is also found that many aluminum particles are agglomerated on the surface, the aluminum droplet agglomerates formed on the combustion surface are separated from the combustion surface, and the agglomerates rupture and flow out of the liquid alumina during the combustion process. The phenomenon of secondary agglomeration is also observed. The microstructure and elemental composition of combustion products of aluminum particles in NEPE propellant were obtained by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The detection results confirmed some agglomeration phenomena. At 3.0 MPa, the combustion of the propellant sample is sufficient, and the aluminum particles are smooth spherical alumina particles. At 1.0 MPa, the combustion of the propellant sample is insufficient, and the aluminum particles are rough. The particle size under different pressure was analyzed by a laser particle size analyzer. The results show that increasing the pressure can reduce the average agglomeration size of aluminum particles and improve combustion efficiency. The number of large particle aggregates is more at 3 MPa. From the perspective of overall particle size results, within the same diameter interval, the percentage of particle number does not increase or decrease significantly with the increase of pressure.

Effects of freezing rate on structural changes in l-lactate dehydrogenase during the freezing process

Freezing is a common method for improving enzyme storage stability. During the freezing process, the freezing rate is an important parameter that can affect protein stability. However, there is limited information on the denaturation mechanisms and protein conformational changes associated with the freezing rate. In this study, the effects of freezing rate on activity loss and conformational changes in a model enzyme, l-lactate dehydrogenase, were evaluated. Enzyme solutions were frozen at various rates, from 0.2 to 70.6 °C/min, and ice seeding was conducted to reduce supercooling. The results demonstrated that fast freezing results in activity loss, structural changes, and aggregation. The residual activities at freezing rates of 0.2, 12.8, and 70.6 °C/min were 77.6 ± 0.9%, 64.1 ± 0.4%, and 44.8 ± 2.0%, respectively. As the freezing rate increased, the degree of dissociation and unfolding increased significantly, as determined using blue native-polyacrylamide gel electrophoresis and fluorescence spectroscopy. Moreover, a large number of amyloid aggregates were detected in samples frozen at a fast freezing rate (70.6 °C/min). The enzyme inactivation mechanism induced by fast freezing was proposed in terms of increased dehydration at the enzyme surface and an ice/unfroze solution interface, which could be helpful to establish a common understanding of enzyme inactivation during the freezing process.