Solvent transport dynamics and its effect on evolution of mechanical properties of nitrocellulose(NC)-based propellants under hot-air drying process

Appropriate drying process with optimized controlling of drying parameters plays a vital role in the improvement of the quality and performance of propellant products.However,few research on solvent transport dynamics within NC-based propellants was reported,and its effect on the evolution of mechanical properties was not interpreted yet.This study is conducted to gain a comprehensive understanding of hot-air drying for NC-based propellants and clarify the effect of temperature on solvent transport behavior and further the change of mechanical properties during drying.The drying kinetic curves show the drying time required is decreased but the steady solvent content is increased and the drying rate is obviously increased with the increase of hot-air temperatures,indicating hot-air temperatures have a significant effect on drying kinetics.A modified drying model was established,and results show it is more appropriate to describe solvent transport behavior within NC-based propellants.Moreover,two linear equations were established to exhibit the relationship between solvent content and its effect on the change of tensile properties,and the decrease of residual solvent content causes an obvious increase of tensile strength and tensile modulus of propellant products,indicating its mechanical properties can be partly improved by adjustment of residual solvent content.The outcomes can be used to clarify solvent transport mechanisms and optimize drying process parameters of double-based gun propellants.

Modeling and simulation of solvent behavior and temperature distribution within long stick propellants with large web thickness undergoing drying

Drying is a complicated physical process which involves simultaneous heat and mass transfer in the removal of solvents inside propellants.Inappropriate drying techniques may result in the formation of a hard skin layer near the surface to block the free access of most solvent through for long stick propellants with large web thickness,which lead to lower drying efficiency and worse drying quality.This study aims to gain a comprehensive understanding of drying process and clarify the mechanism of the blocked layer near the propellant surface.A new three-dimensional coupled heat and mass transfer(3D-CHMT)model was successfully developed under transient conditions.The drying experiment results show that the 3DCHMT model could be applied to describe the drying process well since the relative error of the content of solvent between simulation and experiment values is only 5.5%.The solvent behavior simulation demonstrates that the mass transfer process can be divided into super-fast(SF)and subsequent minorfast(MF)stages,and the SF stage is vital to the prevention of the blocked layer against the free access for solvent molecules inside propellant grains.The effective solvent diffusion coefficient(Deff)of the propellant surface initially increases from 3.4×10^(-6)to 5.3×10^(-6)m^(2)/s as the temperature increases,and then decreases to 4.1×10^(-8)m^(2)/s at 60-100 min.The value of Deffof surface between 0-1.4 mm has a unique trend of change compared with other regions,and it is much lower than that of the internal at100 min under simulation conditions.Meanwhile,the temperature of the propellant surface increases rapidly at the SF stage(0-100 min)and then very slowly thereafter.Both the evolution of Deffand temperature distribution demonstrate that the blocked layer near the propellant surface has been formed in the time period of approximately 0-100 min and its thickness is about 1.4 mm.To mitigate the formation of blocked layer and improve its drying quality of finial propellant products effectively,it should be initially dried at lower drying temperature(30-40℃)in 0-100 min and then dried at higher drying temperature(50-60℃)to reduce drying time for later drying process in double base gun propellants.The present results can provide theoretical guidance for drying process and optimization of drying parameters for long stick propellants with large web thickness.

Spontaneous isospin polarization and quantum Hall ferromagnetism in a rhombohedral trilayer graphene superlattice

Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and nontrivial topological properties. To gain a deep understanding of such exotic properties, it is essential to clarify the broken symmetry between spin and valley flavors which universally exists in these ground states. Here in a rhombohedral trilayer graphene crystallographically aligned with a hexagonal boron nitride, we report various kinds of symmetry-breaking transition tuned by displacement fields(D) and magnetic fields:(ⅰ) While it is well known that a finite D can enhance correlation to result in correlated insulators at fractional fillings of a flat band, we find the correlation gap emerges before the flavor is fully filled at a positive D, but the sequence is reversed at a negative D.(ⅱ) Around zero D, electronic correlation can be invoked by narrow Landau levels, leading to quantum Hall ferromagnetism that lifts all the degeneracies including not only spin and valley but also orbital degrees of freedom. Our result unveils the complication of transitions between symmetry-breaking phases, shedding light on the mechanisms of various exotic phenomena in strongly correlated systems.

Correlated states in alternating twisted bilayer–monolayer–monolayer graphene heterostructure

Highly controlled electronic correlation in twisted graphene heterostructures has gained enormous research interests recently,encouraging exploration in a wide range of moirésuperlattices beyond the celebrated twisted bilayer graphene.Here we characterize correlated states in an alternating twisted Bernal bilayer–monolayer–monolayer graphene of~1.74°,and find that both van Hove singularities and multiple correlated states are asymmetrically tuned by displacement fields.In particular,when one electron per moiréunit cell is occupied in the electron-side flat band,or the hole-side flat band(i.e.,three holes per moiréunit cell),the correlated peaks are found to counterintuitively grow with heating and maximize around 20 K–a signature of Pomeranchuk effect.Our multilayer heterostructure opens more opportunities to engineer complicated systems for investigating correlated phenomena.

Tunable correlation in twisted monolayer–trilayer graphene

Flat-band physics of moirésuperlattices,originally discovered in the celebrated twisted bilayer graphene,have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field.In this work,we experimentally find the evidence of correlated insulators at half filling of the electron moiréband of twisted monolayer–trilayer graphene with a twist angle around 1.2°.Van Hove singularity(VHS),manifested as enhanced resistance and zero Hall voltage,is observed to be distinct in conduction and valence flat bands.It also depends on the direction and magnitude of the displacement fields,consistent with the asymmetric crystal structure.While the resistance ridges at VHS can be enhanced by magnetic fields,when they cross commensurate fillings of the moirésuperlattice in the conduction band,the enhancement is so strong that signatures of correlated insulator appear,which may further develop into an energy gap depending on the correlation strength.At last,Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields.It is found that electronic correlation has a negative dependence on the Fermi velocity,which in turn could be used to quantify the correlation strength.

NF-kB Inhibitor Parthenolide Promotes Renal Tubules Albumin Uptake in Type 2 Diabetic Nephropathy

Objective Injured tubular reabsorption is highlighted as one of the causes of increased albuminuria in the early stage of diabetic nephropathy;however,the underlying mechanism has not been fiilly elucidated.In this study,we aimed to explore whether reducing inflammation and remodeling the insulin signaling pathway could improve albumin uptake of renal tubules.Methods 8-week-old male db/db mice(n=8),a type 2 diabetic nephropathy model,administered with nuclear factor kappa-B(NF-kB)inhibitor parthenolide(PTN,1 mg/kg)intraperitoneally every other day for 8 weeks,were as the treatment group.Meanwhile,the age-matched male db/m mice(n=S)and db/db mice(n=8)were treated with saline as the control group and type 2 diabetic nephropathy group.When the mice were sacrificed,blood and urine were collected to examine homeostasis model assessment of insulin resistance(HOMA-IR)and urine albumin creatinine ratio,and kidney samples were used to analyze histopathologic changes with periodic acid-Schiff(PAS)staining,NF-kB p65,phosphorylation of AKT(p-AKT),amnionless and cubilin expressions with immunohistochemistry as well as western blot,and the albumin uptake of renal tubules by using immunofluorescence.In addition,HKC cells were divided into the insulin group treated with insulin alone,the TNF-a group treated with insulin and tumor necrosis factor(TNF-a),and the TNF-a+PTN group exposed to PTN,insulin and TNF-a.The levels of albumin uptake and expression levels of NF-kB p65,p-IRS-l/IRS-1,p-AKT/AKT,amnionless and cubilin in HKC cells were measured.Results Compared with the db/db group,the db/db+PTN group demonstrated decreased levels of HOMA-IR(36.83±14.09 vs.31.07+28.05)and urine albumin creatinine ratio(190.3±7.3 vs.143.0±97.6 mg/mmol);however,the differences were not statistically significant(P>0.05).Periodic acid-Schiff staining showed PTN could alleviate the glomerular hypertrophy and reduce the matrix in mesangial areas of db/db mice.The renal expression of NF-kB p65 was increased and p-AKT(s473)decreased in the db/db group compared with the db/m group(P<0.05).PTN significantly reduced the renal expression of NF-kB p65 and ameliorated the decline of p-AKT(s473)compared with the db/db group(P<0.05).Compared with the db/m group,the expression of amnionless and cubilin decreased and albumin uptake in tubules were reduced in the db/db group(P<0.05),and PTN could significantly increase the expression of cubilin(P<0.05),and improve albumin uptake in tubules.Insulin promoted albumin uptake and the expression of amnionless and cubilin in HKC cells(P<0.05).TNF-a stimulated the expression of NF-kB p65,increased p-IRS-1(s307)and reduced p-AKT(s473)in HKC cells(PV 0.05).In theTNF-a+PTN group,the expression of NF-kB p65 declined and p-IRS-1(s307)and p-AKT(s473)were restored,compared with theTNF-a group(P<0.05).The expression of amnionless and cubilin decreased in theTNF-a group(P<0.05),and PTN could significantly increase the expression of cubilin(P<0.05).Conclusions Inflammation caused damage to insulin signaling,which reduced amnionless-cubilin expression and albumin uptake.PTN could reduce inflammation and remodel the impaired insulin signaling pathway,which promoted the expression of cubilin and albumin uptake.Our study can shed light on the role of inflammation in the reduction of albumin uptake of renal tubules in type 2 diabetic nephropathy.