Moduli Stabilization Research Articles

Effect of shot peening pretreatment on the high-temperature tribological behaviours of a TaN coating prepared via double-cathode glow plasma alloying

Gradient coatings with excellent physical and mechanical properties show great potential for use in engineering applications. In this study, a TaN gradient-modified layer was prepared on TA15 titanium alloy by double-cathode glow plasma alloying (DGPA) with a gradient structure pretreated by rotationally accelerated shot peening (RASP). The effects of the RASP pretreatment at different speeds on the mechanical and tribological properties and microstructure of the TaN coatings were investigated. The results indicated that the crystal size was refined to the nanometre scale (41.8–71.4 nm) by RASP pretreatment, and a gradient structure layer (30–55 μm) formed, which facilitated the adsorption and inward diffusion of Ta and N atoms. The pretreated TaN-modified layer contained an interdiffusion layer with a thin deposition layer consisting of Ta 2 N and TaN. Furthermore, the pretreated TaN-modified layer maintained good wear resistance in ball-on-disc testing at 700 K, and the wear rate was only 36.9% of that without pretreatment, which can be attributed to the high hardness, elastic modulus , toughness and thermal stability of the modified layer. This work provides insights relevant to the development of a mechanical-diffusion composite process to produce titanium alloy coatings with enhanced mechanical properties and wear resistance at elevated temperature. • TaN modified layer with a gradient change of composition was prepared on titanium alloy using RASP and DGPA. • The refined surface promotes the adsorption and diffusion of Ta and N atoms to obtain a thicker gradient-modified layer. • RASP pretreatment can improve the wear resistance of TaN modified layers at high temperatures.

Flexible and stretchable polymer optical fibers for chronic brain and vagus nerve optogenetic stimulations in free-behaving animals

BackgroundAlthough electrical stimulation of the peripheral and central nervous systems has attracted much attention owing to its potential therapeutic effects on neuropsychiatric diseases, its non-cell-type-specific activation characteristics may hinder its wide clinical application. Unlike electrical methodologies, optogenetics has more recently been applied as a cell-specific approach for precise modulation of neural functions in vivo, for instance on the vagus nerve. The commonly used implantable optical waveguides are silica optical fibers, which for brain optogenetic stimulation (BOS) are usually fixed on the skull bone. However, due to the huge mismatch of mechanical properties between the stiff optical implants and deformable vagal tissues, vagus nerve optogenetic stimulation (VNOS) in free-behaving animals continues to be a great challenge.ResultsTo resolve this issue, we developed a simplified method for the fabrication of flexible and stretchable polymer optical fibers (POFs), which show significantly improved characteristics for in vivo optogenetic applications, specifically a low Young’s modulus, high stretchability, improved biocompatibility, and long-term stability. We implanted the POFs into the primary motor cortex of C57 mice after the expression of CaMKIIα-ChR2-mCherry detected frequency-dependent neuronal activity and the behavioral changes during light delivery. The viability of POFs as implantable waveguides for VNOS was verified by the increased firing rate of the fast-spiking GABAergic interneurons recorded in the left vagus nerve of VGAT-ChR2 transgenic mice. Furthermore, VNOS was carried out in free-moving rodents via chronically implanted POFs, and an inhibitory influence on the cardiac system and an anxiolytic effect on behaviors was shown.ConclusionOur results demonstrate the feasibility and advantages of the use of POFs in chronic optogenetic modulations in both of the central and peripheral nervous systems, providing new information for the development of novel therapeutic strategies for the treatment of neuropsychiatric disorders.

Study on the Optimum Steel Slag Content of SMA-13 Asphalt Mixes Based on Road Performance

To reduce the use of aggregates such as limestone and basalt, this paper used steel slag to replace some of the limestone aggregates in the production of SMA-13 asphalt mixes. The optimum content of steel slag in the SMA-13 asphalt mixes was investigated, and the performance of these mixes was evaluated. Five SMA-13 asphalt mixes with varying steel slag content (0%, 25%, 50%, 75%, and 100%) were designed and prepared experimentally. The high-temperature stability, low-temperature crack resistance, water stability, dynamic modulus, shear resistance, and volumetric stability of the mixes were investigated using the wheel tracking, Hamburg wheel tracking, three-point bending, freeze–thaw splitting, dynamic modulus, uniaxial penetration, and asphalt mix expansion tests. The results showed that compared to normal SMA-13 asphalt mixes, the high-temperature stability, water stability, and shear resistance of the SMA-13 asphalt mixes increased and then decreased as the steel slag content increased. All three performance indicators peaked at 75% steel slag content, and the dynamic stability, freeze–thaw splitting ratio, and uniaxial penetration strength increased by 90.48%, 7.39%, and 88.08%, respectively; however, the maximum bending tensile strain, which represents the low-temperature crack resistance of the asphalt mix, decreased by 5.98%. The dynamic modulus of the SMA-13 asphalt mixes increased with increasing steel slag content, but the volume expansion at a 75% steel slag content was 0.446% higher than at a 0% steel slag content. Based on the experimental results, the optimum content of steel slag for SMA-13 asphalt mixes was determined to be 75%.

Significantly reinforced and long serviceable acrylonitrile butadiene rubber/graphitic carbon nitride composites for future industrial applications

The application of graphitic carbon nitride (g-C3N4) as non-black reinforcing filler is very little-known part in rubber technology. In the present study, g-C3N4 filled acrylonitrile butadiene rubber (NBR) composites were prepared by conventional two-roll milling process to investigate the influence of g-C3N4 on the mechanical and thermal performances of NBR formulations. NBR composite with 3 phr (parts per hundred parts of rubber) g-C3N4 presents considerably higher cure rate index, hardness, tensile strength, storage modulus and thermal stability than unfilled NBR composite. Also, the addition of g-C3N4 successfully enhances the thermal oxidative aging resistance and fuel consumption efficiency of NBR composites. Thus, g-C3N4 can be used in the near future as interesting filler for developing long serviceable NBR composites with good mechanical properties.

Tensile, thermal and optical properties of poly(lactic acid)/poly(2-ethyl-2-oxazoline)/corn cob nanocellulose nanocomposite film

ABSTRACT In this study, the nanocellulose was extracted from corn cob (CCNC). The poly(lactic acid) (PLA)/CCNC and PLA/poly(2-ethyl-2-oxazoline) (PEOx)/CCNC nanocomposite films were prepared using the solvent casting method. The tensile, thermal, and optical properties of the PLA/CCNC nanocomposites were characterized. The CCNC improved the tensile modulus, tensile strength, and thermal stability of both PLA and PLA/PEOx blends. The combination of PEOx and CCNC is a viable strategy to modify the properties of PLA. PEOx induces the β-crystals formation while CCNC promotes the α-crystals. PEOx can be used to make PLA nanocomposites with higher transparency, which is suitable for packaging applications.

Improvement of low-acyl gellan gum on gelation and microstructural properties of protein hydrolysates from male gonad of scallop (Patinopecten yessoensis)

This study aimed to examine the gelation and microstructural properties of scallop male gonad hydrolysates (SMGHs) in the presence of low-acyl gellan gum (GG) at different mass ratios. The rheological results showed that both elastic modulus and thermal stability of SMGHs were significantly improved by the addition of GG. Meanwhile, the relaxation time T23 was significantly reduced in SMGHs/GG by low-field nuclear magnetic resonance, indicating a strong interaction between SMGHs and GG. Fourier transform infrared spectroscopy indicated the blueshift of amide I and II peaks in SMGHs/GG further demonstrated the electrostatic interaction between SMGHs and GG. The network structure of SMGHs/GG binary complexes was more compact and the surface was smoother than that of SMGHs by cryo-scanning electron microscopy. Furthermore, increasing the content of GG in the SMGHs/GG binary complex significantly reinforced the gel strength and promoted the gelation process.

Moduli and graviton production during moduli stabilization

In theories beyond the Standard Model, in particular in theories with extra spatial dimensions such as superstring theory, there are a large number of scalar fields which appear in the low energy effective action. These moduli fields must be stabilized. Often, moduli stabilization involves a stage during which the moduli fields oscillate coherently about their ground state value. Here, we study moduli and graviton production during the period during which the background modulus field is oscillating, assuming that this period takes place in the radiation phase. We find a resonant production of moduli fluctuations, and a tachyonic instability to the generation of long wavelength gravitational waves. As a consequence, the period of moduli stabilization is short on a Hubble time scale.

Addendum to: Moduli stabilisation and the statistics of SUSY breaking in the landscape

Addendum to: Moduli stabilisation and the statistics of SUSY breaking in the landscape

Starch other than gluten may make a dominant contribution to wheat dough mixing properties: A case study on two near-isogenic lines

Protein and starch are the two most abundant components in wheat flour that co-influence dough processing quality. Studies have demonstrated that protein content and composition play a decisive role in wheat dough development. Additionally, starch has a significant effect on dough behaviour. The physicochemical and mixing properties of two wheat near-isogenic lines (NILs; NILZX1 and NILZX2) with different high-molecular-weight glutenin subunits (HMW-GS) were analyzed to shed light on the role of starch and protein in the dough mixing process. The NILZX1 dough with superior HMW-GS combination had higher protein content than NILZX2 dough. Whereas NILZX1 had a lower storage modulus and shorter dough stability time than NILZX2. During the mixing process, the torque of NILZX1 dough was lower than that of NILZX2; the microstructure of NILZX1 dough was greatly destroyed in the starch-dominant phase, leading to inferior dough quality. NILZX2 with higher B-type starch content, relative crystallinity, and viscosity showed greater dough quality. Taken together, physicochemically, starch had a more substantial effect on the dough mixing properties than protein in the two NILs. The findings provide a foundation for exploring the contribution of starch to dough properties.

Optimization of graphene nanoplatelets dispersion and nano-filler loading in bio-based polymer nanocomposites based on tensile and thermogravimetry analysis

The incorporation of graphene nanoplatelets (GNPs) has attracted massive attention in polymer nanocomposite production. In this work, GNPs reinforced nanocomposites of liquid natural rubber (LNR) toughened poly (lactic acid) (PLA)/poly (aniline) (PANi) were fabricated through melt-mixing using internal mixer. The effects of ultrasonic treatment period, mixing rotor speed and GNPs loadings in PLA-LNR/PANi was investigated. A premix ultrasonication of LNR/PANi with GNPs for 1 h was found to be the most effective period as compared to the longer sonication time. The best melt-mixing of the materials was achieved at 100 rpm, in accordance to the tensile properties as well as homogeneous dispersion and distribution of nano-filler as shown in thermogravimetry analysis. Results revealed that the optimum loading was found at 0.4 wt.% of GNPs with excellent enhancement in tensile strength (25 MPa), tensile modulus (1188.9 MPa) and thermal stability of the nanocomposite, as proven by ANOVA statistical analysis.

Application of Polymer Based Nanocomposites for Water Shutoff—A Review

One highly undesirable characteristic of mature assets that inhibits oil recovery is high water production. Polymer gel treatment is a popular conformance improvement technique applied in this regard due to its cost effectiveness and proved efficiency. Despite this popularity, optimum performance of polymer hydrogels in water shut off is inhibited by excessive aggregation, difficulty in controlling gelation, and their instability at high temperature and high salinity reservoir conditions. To address these shortcomings, research on the application of nanoparticles (NPs) in polymer hydrogels to manage thermal stability and salinity sensitivity has significantly increased in the recent past. By incorporating metal-based NPs, silica or graphene at nanoscale; the gel strength, storage modulus, salinity tolerance and thermal stability of commonly used polymers have been greatly enhanced. In this paper, the advances in experimental studies on polymer-based nanocomposites are discussed and field experiences from adoption of polymer composites reviewed.

Macromolecular Engineering and Additive Manufacturing of Poly(styrene-b-isobutylene-b-styrene)

Although polyisobutylene (PIB)-based thermoplastic elastomers (TPEs) possess a combination of unique properties (i.e., low permeability, high environmental and chemical stability, and excellent biocompatibility), they have not been explored for 3D printing. Poly(styrene-b-isobutylene-b-styrene) (SIBS) is one of the most important PIB-based TPEs used in biomedical applications. Herein, we report, for the first time, the development of an efficient and low-cost 3D printing strategy of SIBS by fine-tuning its microstructure and properties. We discovered that blending the polystyrene (PS) homopolymer with SIBS leads to significant changes in its microphase-separated structure. The amount and molecular weight of the added PS significantly affect the micromorphology and 3D printability of SIBS/PS blends. In particular, SIBS/PS blends with high molecular weight PS at relatively high weight fractions show a unique hierarchical salami micromorphology with appropriate properties (improved hardness, modulus, and thermal stability) for 3D printing by fused filament fabrication. SIBS/PS blends with PS molecular weight close to or higher than that of SIBS show better printability than blends with low molecular weight PS. Blending the PIB block copolymer with the homopolymer of its hard block is an efficient and cost-effective strategy for additive manufacturing of PIB-based elastomers with widely tunable properties.

Removal of methylene blue from wastewater using ternary nanocomposite aerogel systems: Carboxymethyl cellulose grafted by polyacrylic acid and decorated with graphene oxide

In this study, environmentally-friendly nanocomposite hydrogels were fabricated. These hydrogels consisted of semi-interpenetrating networks of carboxymethyl cellulose (CMC) molecules grafted to polyacrylic acid (PAA), as an eco-friendly and non-toxic polymer with numerous carboxyl and hydroxyl functional groups, which were reinforced with different levels of graphene oxide particles (0.5, 1.5 or 3% wt). Field-emission electron scanning microscopy (FESEM) images indicated that the pore size of the nanocomposites decreased with increasing graphic oxide concentration. The presence of the graphic oxide increased the storage modulus and thermal stability of the nanocomposite hydrogels. The hydrogels had an adsorption capacity of 138 mg/g of a model cationic dye pollutant (methylene blue) after 250 min. Moreover, a reusability test showed that the adsorption capacity remained at around 90% after 9 cycles. Density functional theory (DFT) simulations suggested that the adsorption of methylene blue was mainly a result of π-π bonds, hydrogen bonds, and electrostatic interactions with graphene oxide. Our results indicated that the nanocomposite hydrogels fabricated in this study may be eco-friendly, stable, efficient, and reusable adsorbents for ionic pollutants in wastewater treatment.

Stabilization and modelling of tensile properties of braided synthetic fibre rope for dynamic loading

This article discusses the stabilization in longitudinal elastic modulus of braided high modulus polyethylene rope for dynamic loading in tendon-driven robot by mean of preload treatment. Dynamic loading was presented by impact loading which expressed in term of number of drops applied on the rope. Different preload levels were applied on the ropes before they were tested in five consecutive impact loadings to investigate the stability of rope modulus. The stabilization of rope modulus was performed based on experimental data of impact loading of the preloaded ropes and the proposed empirical equation which takes number of drop and preload level into account. Furthermore, spring-dashpot model was used in order to estimate tensile properties and study strain of the rope under impact loading. Results from spring-dashpot model and experimental data are in very good agreement. By using this model, the delayed time between the input (stress) and output (strain) could be estimated.

Comprehensive characterization of raw and alkali (NaOH) treated natural fibers from Symphirema involucratum stem

The present study investigated the effect of alkali treatment on the enhancement of Physico-chemical, tensile, thermal and surface properties of Symphirema involucratum stem fiber (SISF). The investigation of chemical constituents of optimally alkalized SISF revealed that ideal increment of cellulose content (68.69 wt%) and desired modification of other chemical components was accomplished through 60 min immersion period. An increase in the crystallinity index to 33.33% and small crystallite size to 3.21 nm was noted by X-ray diffraction analysis. Moreover, the treated fiber was found suitable for light-weight applications since physical analysis acknowledges that the density of the fiber augmented to 1424 kg/m3after surface treatment that reduces total weight percentage. The enhancements in tensile strength (471.2 ± 19.8 MPa), tensile modulus (5.82 ± 0.77 GPa) and thermal stability (371 °C) were noted that ensures the treated fiber has good mechanical and thermal properties required for composite preparation. These findings validated that the optimally surface-modified SISF is a suitable material for lightweight composite structures, for the time being.

How a four-dimensional de Sitter solution remains outside the swampland

We argue that, in the presence of time-dependent fluxes and quantum corrections, four-dimensional de Sitter solutions should appear in the type IIB string landscape and not in the swampland. Our construction considers generic choices of local and non-local quantum terms and satisfies the no-go and the swampland criteria, the latter being recently upgraded using the trans-Planckian cosmic censorship. Interestingly, both time-independent Newton constant and moduli stabilization may be achieved in such backgrounds even in the presence of time-dependent fluxes and internal spaces. However, once the time-dependence is switched off, any four-dimensional solution with de Sitter isometries appears to have no simple effective field theory descriptions and is back in the swampland.

Thermo‐mechanical, rheological and morphology properties of polypropylene composites: Residual CaCO3 as a sustainable by‐product

AbstractThis research looked into the possibility of using residual calcium carbonate (CaCO3) as a by‐product of the cane sugar production process combined with polypropylene (PP) to replace commercial CaCO3. Using a co‐rotating twin‐screw extruder, the CaCO3/PP composites were made in the following ratios: 10:90, 20:80, 30:70, 40:60, and 50:50, with the addition of maleic anhydride polypropylene at 5 wt% of CaCO3. In terms of mechanical properties, thermal properties, rheological properties, and morphology, the effect of the residual CaCO3 filler reinforced in PP matrix was compared to commercial CaCO3/PP composites. The findings showed that residual CaCO3 from the sugar production process can replace the use of industrial CaCO3 mixing in plastic and can add value to the residual CaCO3. The residual CaCO3/PP composites had better tensile modulus, flexural strength, flexural modulus, impact resistance, and thermal stability than commercial CaCO3/PP composites, according to the findings. The composites' tensile modulus, flexural modulus, hardness, thermal stability, and rheological properties improved as the CaCO3 loading increased.

Dilaton stabilization in KKLT revisited

We study the condition for the dilaton stabilization in Type IIB flux compactifications consistent with the KKLT scenario. Since the Gukov-Vafa-Witten superpotential depends linearly on the dilaton, the dilaton mass squared is given by a sum of the gravitino mass squared and additional terms determined by the complex structure moduli stabilization. If the dilaton mass is not much enhanced from the gravitino mass, the mass mixing with the Kähler modulus in the presence of the non-perturbative effect generates the saddle point at the supersymmetric field values, hence the potential becomes unstable. When the complex structure moduli other than the conifold modulus are neglected, the saddle point problem arises over the controllable parameter space. We also point out that the dilaton stabilization condition is equivalent to the condition on the NS 3-form fluxes, |H(1,2)|>|H(0,3)|.

Investigation of the Coarse Aggregate Texture Property Using an Improved Laplacian Smoothing Algorithm

Abstract Surface texture is one of the most important morphology properties of coarse aggregates. It has an important effect on the performances of asphalt mixtures, such as the stiffness modulus and high temperature stability. Accurate characterization of the coarse aggregate texture is important for the quality control of coarse aggregates and the design of asphalt mixtures. The two-dimensional (2-D) image analysis method has been used to study the texture property of coarse aggregates in the past two decades. Because of the spatial and mesoscopic properties of the surface texture of coarse aggregates, the traditional 2-D image analysis method is not accurate enough to characterize the texture. In this study, a three-dimensional (3-D) image analysis method (Laplacian smoothing algorithm) was employed to study the coarse aggregate texture property based on the high-precision 3-D image. A minor improvement was added into the Laplacian smoothing algorithm to determine the smoothing scale. Three parameters (deviation limit, iteration number, and smoothness level) are used in the improved Laplacian smoothing algorithm to control the final smoothing result. The 3-D images with the precision of 0.05 mm and 0.1 mm of two sizes of limestone aggregates and two sizes of basalt aggregates were used to study the effect of the three parameters on the smoothing results. The optimal combination of the three parameters was determined based on the parameter study. The results indicate that the deviation limit should be set to 3%, the iteration number should be set to 1, and the smoothness level should be set to 1. A preliminary discussion on the scanning precision was presented based on the 3-D aggregate images with the precision of 0.05, 0.1, 0.2, and 0.5 mm. The results indicate that the 3-D images with average point spacing greater than or equal to 0.2 mm cannot provide sufficient texture details for the evaluation.

Three-dimensional flux vacua from IIB on co-calibrated G2 orientifolds

We derive the 3D N = 1 superpotential for the closed string sector of type IIB supergravity on toroidal O5 orientifolds with co-calibrated G2 structure and RR background flux. We find that such compactifications can provide full closed string moduli stabilization on supersymmetric hbox {AdS}_3 vacua, and once we include brane-supersymmetry-breaking we also find indication for the existence of classical 3D de Sitter solutions. The latter however are rather difficult to reconcile with the “shape” moduli stabilization and flux quantization. We also discuss the possibility of achieving scale separation in hbox {AdS}_3 and hbox {dS}_3 vacua, but such effects seem to be hindered by the geometric flux quantization.