Small Shrinkage Research Articles

Effects of flowable liners on the shrinkage vectors of bulk-fill composites

ObjectivesThis investigation evaluated the effect of flowable liners beneath a composite restoration applied via different methods on the pattern of shrinkage vectors.MethodsForty molars were divided into five groups (n = 8), and cylindrical cavities were prepared and bonded with a self-etch adhesive (AdheSe). Tetric EvoCeram Bulk Fill (TBF) was used as the filling material in all cavities. The flowable liners Tetric EvoFlow Bulk Fill (TEF) and SDR were used to line the cavity floor. In gp1-TBF, the flowable composite was not used. TEF was applied in a thin layer in gp2-fl/TEF + TBF and gp3-fl/TEF + TBFincremental. Two flowable composites with a layer thickness of 2 mm were compared in gp4-fl/TEF + TBF and gp5-fl/SDR + TBF. TEF and SDR were mixed with radiolucent glass beads, while air bubbles inherently present in TBF served as markers. Each material application was scanned twice by micro-computed tomography before and after light curing. Scans were subjected to image segmentation for calculation of the shrinkage vectors.ResultsThe absence of a flowable liner resulted in the greatest shrinkage vectors. A thin flowable liner (gp2-fl/TEF + TBFbulk) resulted in larger overall shrinkage vectors for the whole restoration than a thick flowable liner (gp4-fl/TEF + TBF). A thin flowable liner and incremental application (gp3-fl/TEF + TBFincremental) yielded the smallest shrinkage vectors. SDR yielded slightly smaller shrinkage vectors for the whole restoration than that observed in gp4-fl/TEF + TBF.ConclusionsThick flowable liner layers had a more pronounced stress-relieving effect than thin layers regardless of the flowable liner type.Clinical relevanceIt is recommended to apply a flowable liner (thin or thick) beneath bulk-fill composites, preferably incrementally.

Measurement and analysis of welding deformation in arc welded lap joints of thin steel sheets with different material properties

Welding deformation in arc welded lap joints of thin steel plates with different strengths were quantitatively investigated by experimental measurement and numerical simulation. Four welding deformation components were discussed in detail. There is a relatively uniform distribution of transverse shrinkage along the welding direction and a largest angular distortion in the middle transverse section. The bottom plate of the lap joint presents larger longitudinal shrinkage and deflection obviously in comparison with top plate. Two lap joints with different strength were discussed comparatively. It is observed that the DP590 lap joint with higher strength has larger angular distortion and smaller shrinkage and deflection in the longitudinal direction, and no obvious variation in transverse shrinkage. Correlation between material properties and welding deformation of arc welded lap joints were investigated by parametrical numerical simulations. The results show that the welding deformation varies considerably among various steels with different yield strength (YS) and coefficient of thermal expansion (CTE) although they have the same heat input.

Preparation and properties of high-porosity ZrB2-SiC ceramics by water-based freeze casting

The development of novel cermet composites based on porous ceramics with high porosity, interconnected pore structure and good mechanical property has attracted considerable attention in engineering application. In this work, water-based freeze casting process was employed to fabricate ZrB2-SiC porous ceramic with aligned lamellar-channels structure using PAA-NH4 as the dispersant. The results revealed that the well-dispersed suspension with best rheological behavior was obtained using 1.0 wt% PAA-NH4 at pH 9. The crack-free porous ceramic exhibited small volume shrinkage ranging from 2.59 % to 1.87 %. By varying the solid loading, the fabricated samples displayed a tailored porosity ranging from 76.12% to 59.37% and an excellent compressive strength of 7 MPa to 78 MPa. After oxidation, the samples displayed a decreased porosity and an increased compressive strength. The ZrB2­SiC porous ceramic fabricated in this work will be a promising candidate for the framework of cermet composite.

Microencapsulated phase change materials composited Al2O3–SiO2 aerogel and the thermal regulation properties

Phase change materials (PCMs) are effective energy storage application, which can be combined with aerogels to improve heat conversion rate in building insulation materials. A low-cost microencapsulated PCMs (MEPCM) composited Al2O3–SiO2 aerogels (MEPCM/ASA) have been successfully prepared by in situ sol–gel method following by ambient pressure drying (APD). The aerogels and the phase change microcapsules were well bonded without destroying the aerogels network structure. The morphology, microstructure, thermal conductivity, energy storage efficiency, and thermal stability of the MEPCM/ASA composite were comprehensively investigated. The experimental results showed that the composite revealed small shrinkage (4.1 wt%), high specific surface area (380.22 m2/g), and low thermal conductivity (0.0507 W/(m K)) at room temperature. The latent heat of the composites containing 50 wt% MEPCM reached 28.91 J/g around 26.7 °C. The MEPCM/ASA possessed good phase change behavior, low undercooling, and excellent thermal cycling stability. It was anticipated to provide a new path to achieve simultaneous enhancement of thermal insulation and thermal storage, and the application in building materials were of great importance for energy saving.

Impact of gliding arc plasma pretreatment on drying efficiency and physicochemical properties of grape

The effect of cold plasma pretreatment with different durations 10, 20, 30, 40, 50, and 60 s on the mass transfer rate and quality of grape fruit during hot-air drying at 60 °C and 1.5 m/s were studied. It was found that cold plasma pretreatment significantly increased effective moisture diffusivity, reducing the drying time and energy consumption by up to 26.27% and 26.30%, respectively. Longer exposure resulted in smaller shrinkage and higher rehydration ratio. Furthermore, plasma pretreatment resulted in improved quality of dried grapes, in particular higher total phenolic content, antioxidant activity, and vitamin C retention by up to 3.06–30.53%, 7.31–62.29%, and 17.87–168.73%, as compared to the untreated ones. Among all pretreatments, 50 s exposure was preferred due to the minimal energy consumption and the least effect on the samples color.

Regression shrinkage methods for clinical prediction models do not guarantee improved performance: Simulation study.

When developing risk prediction models on datasets with limited sample size, shrinkage methods are recommended. Earlier studies showed that shrinkage results in better predictive performance on average. This simulation study aimed to investigate the variability of regression shrinkage on predictive performance for a binary outcome. We compared standard maximum likelihood with the following shrinkage methods: uniform shrinkage (likelihood-based and bootstrap-based), penalized maximum likelihood (ridge) methods, LASSO logistic regression, adaptive LASSO, and Firth's correction. In the simulation study, we varied the number of predictors and their strength, the correlation between predictors, the event rate of the outcome, and the events per variable. In terms of results, we focused on the calibration slope. The slope indicates whether risk predictions are too extreme (slope < 1) or not extreme enough (slope > 1). The results can be summarized into three main findings. First, shrinkage improved calibration slopes on average. Second, the between-sample variability of calibration slopes was often increased relative to maximum likelihood. In contrast to other shrinkage approaches, Firth's correction had a small shrinkage effect but showed low variability. Third, the correlation between the estimated shrinkage and the optimal shrinkage to remove overfitting was typically negative, with Firth's correction as the exception. We conclude that, despite improved performance on average, shrinkage often worked poorly in individual datasets, in particular when it was most needed. The results imply that shrinkage methods do not solve problems associated with small sample size or low number of events per variable.

Manufactory and Properties of Poly(&lt;i&gt;p&lt;/i&gt;-Phenylenebenzobisoxazole) Aerogels Prepared by a Simple Freeze-Drying Procedure

Aerogels based on organic high performance fibers have been attracted great attention due to its excellent thermal and mechanical properties. Here, PBO nanofiber aerogel were prepared from the super-fiber PBO through a top-down process with a sol-gel process and a simple freeze-drying process, followed by thermal cross-linking. The prepared aerogel has a small volume shrinkage, a high specific surface area of 168.9 m2 /g and a small pore diameter of 1.356 nm. Because of its 3D porous structure, it results in a low density of 6 to 30 mg/cm3 and a high porosity (98%). The aerogel retains the molecular structure of PBO at the same time, which gives it initial thermal decomposition temperature up to 500 °C and a superior fire-retardant capability. PBO aerogel possesses good compressive properties with a yield stress of 0.44MPa at 80% strain and an elasticity modulus of 1.98 MPa which is higher than SiO2 and cellulose aerogel reported.

Small towns shrinkage in the Jilin Province: A comparison between China and developed countries.

Urban shrinkage is currently spreading at global level. At the same time, the scale of urban shrinkage is not limited to urban agglomerations, metropolitan areas, or big cities, but begins to expand to a vast number of small towns. Over the years, the characteristics, models, and mechanisms of shrinkage in large cities have attracted the attention of scholars; however, the problem of shrinkage in small towns has not been fully discussed. In China, small towns are located at the margins of cities and are the first part of the countryside; hence, they are the link and the bridge between urban and rural areas, and a space carrier to solve the diseases of big cities and for rural rejuvenation as a whole. However, in the process of rapid urbanization, some small towns have experienced urban shrinkage, mainly through a decline in township enterprises and the deterioration of the living environment, which has restricted their role in coordinating the spatial support of urban and rural development. Therefore, a correct understanding of the shrinkage of small towns has considerable theoretical and practical guiding significance. We focused on the towns of the Jilin Province as the research unit, and combined township population, economy, land use, and employment indices to establish an urban shrinkage index, identifying the status, spatial distribution, and influencing factors of small towns shrinkage in the Jilin Province. Moreover, we analyzed the similarities and differences of small towns shrinkage between the Jilin Province and developed countries. The results show that small towns shrinkage in the Jilin Province shares similar characteristics with developed countries, as well as important differences in aspects such as population migration, low-level industrial structure, and administrative division adjustments.

An innovative equivalent width supporting technology for sustaining large-cross section roadway in thick coal seam

As energy structures have been adjusted in China, the coal industry has begun to develop large and highly productive coal bases. Along with the problems associated with high intensity mining, support for large cross-section roadways has become a major issue. To enhance the stability of surrounding rock masses of roadways with large cross-sections and to reduce support costs, an innovative supporting technological tool referred to as equivalent width supporting (EWS) technology is studied and applied. The premise of EWS technology is to transform large cross-sections into common roadway cross-sections by using support materials of high-yielding load capacities. The basis of this technology concerns how to measure pressure levels of the equivalent part and how to find high-yielding load capacity supporting materials. In this study, computational formulas for supporting stress of the equivalent part are presented. In turn, a new supporting material called high-yielding load prop is developed. Structural and load-deformation characteristics of this prop are studied, and results show that this prop could provide stable loads ranging from 400 to 800 kN over a small shrinkage distance of less than 10 mm. The load capacity of the prop can be adjusted with a small change made to its geometry. It is shown that EWS technology perform well in field applications of the Ta Shan coal mine in China. The onsite experiment results show that EWS technology employing high-yielding load props can enhance the stability of surrounding rock and can resist dynamic pressures generated by excavation. In addition, relative to original supporting costs, EWS technology can reduce overall supporting costs by 63.8%.

Fabrication, microstructure and physico-mechanical properties of highly porous acicular mullite ceramic foams by freeze casting method

In this article, highly porous mullite ceramics with whisker-interlocked microstructure were successfully prepared by freeze casting method. The ceramics possessed very high porosity (up to 94%) and high compressive strength (up to 3.65 MPa). It was found that polyvinyl alcohol (PVA) using as a binder could also affect the microstructure of ceramics significantly. Whisker-interlocked structure could be obtained when PVA concentration was high (4 wt%), while low PVA concentration (1%) led to the aligned lamellar pore structure. Moreover, the ceramic samples had small shrinkages of less than 3%, and solid loading in slurry was found to influence the porosity and compressive strength of the ceramics greatly.

Three-dimensional flow simulations for polymer extrudate swell out of slit dies from low to high aspect ratios

The impact of the slit die geometry and the polymer melt flow characteristics on the extrudate swell behavior, which is a key extrusion operating parameter, is highlighted. Three-dimensional (3D) numerical simulations based on the finite element method are compared with their conventional two-dimensional (2D) counterparts at the same apparent shear rates using ANSYS Polyflow software. The rheological behavior is described by the differential multimode Phan-Thien-Tanner constitutive model, with polypropylene as a reference. It is shown that increasing the aspect ratio of the die geometry (width/height ratio variation from 1 to 20) contributes to a significant change in the 3D extrudate deformation (relative changes of 10% in several directions; absolute changes up to 30%) and delays the equilibrium axial position (up to a factor 10). High aspect ratios induce a switch to contract flow (swell ratio &amp;lt;1) for the edge height swell. The 3D extrudate swell strongly deviates from the 2D simplified case due to the die effect near the wall, even for higher aspect ratios. Also a different relation with the material parameters is recorded. The initially large swell behavior is followed by a small shrinkage flow in the middle height direction which cannot be captured by the 2D counterpart. The findings are supported by a comprehensive analysis of the velocity and stress fields in and out of the slit dies.

A Review of Carbonate Minerals as an Additive to Geopolymer Materials

In Malaysia, several geopolymer materials were mainly from fly ashes, kaolin, metakaolin, and boiler ash which were mainly used to prosper sustainable development especially in the building and construction sector. Geopolymers can be classified as inorganic materials that were formed with the reaction between alminosilicate materials and alkaline solutions. This reaction causing a crystalline compounds mixture to form that toughen to become a novel compound through a process called geopolymerization process. These geopolymer materials have many admirable advantages, including high strength, small shrinkage, decent thermal resistance and good chemical resistance. Although they were used as a stand-alone material with great properties, combination with another material might be another way to improve their properties. A few studies had shown that the geopolymer material can achieve better properties with the addition of moderate amount of calcium-containing material to a geopolymer. The addition of carbonate materials can have insignificant effect on the geopolymer configuration and properties. Thus, this paper review the usage of carbonate materials for example Dolomite (CaMg(CO3)2) and Calcite (CaCO3) as an addition into these geopolymer material.

Stability of the pipe-liner system with a grouting void surrounded by the saturated soil

The rehabilitation of the deteriorated pipe is most commonly undertaken by installing a thin-walled close-fitting cured-in-place pipe (CIPP) polymer liner. The lining procedure results in a small shrinkage gap between the liner and its surrounding pipe. Such a small gap is expected to be eliminated by the grouting technique. However, a small crown grouting void is inevitable between the liner and its host pipe due to the bubbles in the grout and the gravity effect. This grouting void may result in different buckling behavior from the perfectly-confined liner. Therefore, this paper studies the confined liner with a grouting void under water pressure. Firstly, the analytical solutions are derived to predict the buckling pressure of the confined liner with a grouting void. Then, a two-dimensional (2D) simulated model is developed to trace the buckling and post-buckling pressure-displacement equilibrium path, from which the maximum pressure (critical buckling pressure) is obtained. After that, the numerical buckling pressure is compared and shows excellent agreement with the analytical solution, as well as other available experimental data. Finally, the parametric study indicates that the grouting void reduces the pressure capacity dramatically and should be avoided in engineering applications.

Monoliths with MFI zeolite layers prepared with the assistance of 3D printing: Characterization and performance in the gas phase isomerization of α-pinene

Three-dimensional (3D) printing represents a promising technology of solid catalysts/reactors preparation with almost unlimited architecture. A casting route applied in this work for preparation of catalysts with the assistance of a 3D-printed template using the high-resolution Digital Light Processing (DLP) technology renders a possibility to control at the micron-scale macroporosity of the monolithic catalysts, their shape and size, with a very small shrinkage occurring during thermal treatment. We have demonstrated that the monoliths prepared with the assistance of 3D printing templates could be readily functionalized by deposition of ZSM-5 type zeolite (MFI) layers. The one-step hydrothermal process of a preparation and deposition was developed to control the Si/Al ratio and thickness (20–50 μm) of the zeolite layer. In all the cases, the phase composition (X-ray diffraction), porosity (low-temperature sorption of nitrogen), morphology and the Si/Al molar ratio in the layers (SEM/EDS), were studied. Moreover, the status of silicon and aluminium nuclei was followed by solid-state 29Si and 27Al MAS NMR, while the acidity of the zeolite layers was estimated using thermodesorption of ammonia. The catalytic performance of the monoliths was tested in the gas-phase isomerization of α-pinene. It was shown that the acidity and catalytic performance could be conveniently controlled by adjusting the Si/Al ratio in a starting gel. Over the sample with the lowest Si/Al ratio in MFI layer (Si/Al = 30), during 4 h on stream, the conversion of α-pinene changed between 97-79%, while the selectivity to limonene and camphene varied between 7–27 % and 31–39 %, respectively. Moreover, it was found that the monolithic catalyst can be regenerated by short treatment with air at 700 °C.

A lithium aluminium borate composite microwave dielectric ceramic with low permittivity, near-zero shrinkage, and low sintering temperature

A low temperature co-fired dielectric material with low shrinkage during the sintering process can enhance the circuit design of electronic devices. Lithium aluminium borate composite ceramic with a composition of Li2O:Al2O3:B2O3 = 1:1:2 (abbreviated: LAB) was prepared by a traditional solid-state reaction method. These ceramics have a low sintering temperature (675–750 °C), low permittivity, and near-zero shrinkage. When the sintering temperature was 725 °C, the LAB ceramics exhibited a small shrinkage of ˜2.4% and the best microwave dielectric properties with εr = 3.9, Q × f = 35 500 GHz, and τƒ= −64 ppm/°C. The LAB ceramics sintered at 700 °C have near-zero shrinkage of ˜ 0.4% and good microwave dielectric properties. The ceramics transformed from (Li2B4O7 and Al2O3) to (Li2Al2B4O10 and Li4Al4B6O17) phases with increasing the sintering temperature, which may be the reason why they show marginal shrinkage. In addition, the ceramics could be co-fired with Ag, indicating that this material is a good candidate for low-temperature co-fired ceramic devices.

Performance of Oxygen Carriers with Different Porosities in Chemical Looping Water‐Splitting

AbstractChemical looping is a novel process for clean energy conversion with CO2 capture. However, sintering of oxygen carriers is one of the important issues that hinders the development of chemical looping technology. Here we applied an air‐liquid foam templated sol‐gel method to produce anti‐sintering materials. By virtue of tunable sol precursors, we obtained a series of materials with different porous characteristics and found these initial textures could significantly affect the activity and stability of the materials in chemical looping. In the first cycle, materials with larger exposed surface had better reactivity. However, small pore closure and particle shrinkage occurred in the subsequent cycles. All of these factors contributed to the unstable nature of the materials, and the results suggested materials derived from templated sol solutions with more large pores were more robust during chemical looping. For other clean energy applications, we also hope the explored method can be extended to produce more materials with high reactivity and stability.

Role of second high-intensity focused ultrasound (HIFU) treatment for unsatisfactory benign thyroid nodules after first treatment.

We aimed to assess the efficacy and safety of second high-intensity focused ultrasound (HIFU) ablation treatment in benign thyroid nodules that had failed to shrink by > 50% 6 months after the first treatment. Twenty-eight patients who did not achieve 50% volume reduction at 6 months after the first HIFU treatment underwent a second HIFU treatment. Nodule volume was measured on ultrasound at baseline, 3 months and 6 months. Extent of nodule shrinkage (by volume reduction ratio) (VRR) = [Baseline volume - volume at 6 months]/[Baseline volume] * 100. Treatment success was defined as VRR > 50%. Obstructive symptom score (by 0-10 visual analogue scale, VAS) was evaluated for 6 months after treatment. No complications occurred after the second treatment. The mean 6-month VRR was 21.78 ± 16.87% with a median (range) of 16.16 (1.63-54.07)%. At 6 months, only two (7.1%) patients achieved treatment success, while nine (32.1%) patients had VRR < 10%. However, relative to baseline (3.96 ± 1.04), the mean VAS significantly improved at 3 and 6 months (2.96 ± 1.43, p<0.001 and 2.58 ± 1.39, p<0.001, respectively). There was a significant correlation between VRR and improvement in VAS score at 6 months (ρ=0.438, p=0.025). Greater nodule volume before the second treatment (OR=1.169, 95% CI=1.004-1.361, p=0.045) was a significant factor for greater VRR after the second treatment. Although subjective obstructive symptoms continued to improve after the second treatment, the actual extent of nodule shrinkage was small. Larger-volume nodules tended to shrink more significantly than smaller-volume nodules in the second treatment. • Second treatment resulted in small shrinkage in unsatisfactory nodules after first treatment. • Obstructive symptoms tended to continue to improve after second treatment. • Larger-size nodules tended to respond better in the second treatment.

Effect of Sintering Temperature on Properties of YAG Porous Ceramics via Atmospheric Sintering Method

YAG materials have a number of unique properties, the application is very extensive, the burn is due to the temperature is too high or the residence time at high temperatures is caused. The undercurrent is the sintering temperature is too low or the holding time is not enough, resulting in product performance is too low or too small shrinkage. In this paper, the effect of sintering temperature on properties of YAG porous ceramics was investigated. The results showed that the firing temperature of the ingredients will be different and cause the same sintering process and sintering additives content of different samples burned. The increase in the content of SiO2 in the furnish with the sintering aid tends to occur. the effect of temperature on the mechanical properties of the samples after sintering was significant, so the raw materials include 60wt%YAG, 10wt% CaO, 10wt% SiO2 and 20wt% soluble starch, the molding process in 20MPa pressure 10min, the sintering at 1500°C for 2h, the sample porosity is 42.2%, the compressive strength is 5.8MPa, the outside shape is keep intact and the better pore microstructure is shown.

Modeling of Novel Compound Tendon-Sheath Artificial Muscle Inspired by Hill Muscle Model

Various types of artificial muscles have been developed in recent years. Nevertheless, they are not well suited to robot applications due to the defects of their mechanical properties, such as small output, limited shrinkage, and slow response. Moreover, portable designs are difficult to realize because of the special power-source requirement. For the shortcomings above, the paper presents a motor-driven tendon-sheath artificial muscle inspired by Hill muscle model. The series and parallel elastic elements both made up of linear springs are applied on the tendon-sheath actuation system. Consequently, the tendon-sheath artificial muscle is created with a compliant structure, variable elasticity, and high power transmission capacity. Next, a compound tendon-sheath artificial muscle transmission system similar to the form of antagonist muscles is modeled based on the static Coulomb friction model. The transmission model with a sinusoidal input is simulated and analyzed in detail. And experiments are performed to validate our transmission model. The model shows high accuracy in predicting the system output. At the frequency of 1 Hz, the fidelity of output torque is 92.3% and the output displacement is 94.2%. Moreover, the maximum output force of the tendon-sheath artificial muscle with 0.8 mm tendon (under the safety factor of 4) can reach 80 N.

Two-year efficacy of single-session high-intensity focused ultrasound (HIFU) ablation of benign thyroid nodules.

Assessing the efficacy of single high-intensity focused ultrasound (HIFU) ablation in benign thyroid nodules beyond 12 months. One hundred and eight patients underwent single HIFU treatment. Extent of nodule shrinkage [by volume reduction ratio (VRR)] and obstructive symptom score [by 0-10 visual analogue scale (VAS)] were evaluated for 24 months after treatment. VRR (%) was calculated based on the formula: [baseline volume - volume at visit] / [baseline volume] × 100. Binary logistic regression was performed to evaluate factors associated with 24-month treatment success (VRR ≥ 50%). After treatment, the mean (± SD) VRR at 3, 6, 12 ,18 and 24 months were 51.32 ± 20.71%, 62.99 ± 22.05%, 68.66 ± 18.48%, 69.76 ± 17.88% and 70.41 ± 17.39%, respectively, while the median (IQR) VAS at baseline, 6, 12 and 24 months was gradually lowered from 4.0 (2.0), 2.0 (1.0), 2.0 (1.0) to 1.0 (2.0), respectively. Sixty-three (58.3%) nodules had a further volume reduction (i.e. > 4.5%) from 12 to 24 months, while 22 (20.4%) nodules had a volume increase of > 4.5% from 12 to 24 months. Small pre-ablation nodule volume was a significant determinant for treatment success at 24 months (OR=1.045, 95% CI=1.021-1.092, p = 0.038). A majority of nodules had further volume reduction beyond 12 months after single HIFU ablation, but since one-fifth of nodules had a notable volume increase beyond 12 months, a longer period of surveillance would be necessary. Small pre-ablation nodule volume was a significant factor determining 24-month treatment success. • Small but significant nodule shrinkage continues beyond 12 months after single treatment. • Obstructive symptom continues to improve beyond 12 months after single treatment • Smaller-sized nodules have a greater chance of treatment success at 24 months.