Longitudinal Shrinkage Research Articles

Variation in specific gravity and shrinkage of tapped rubberwood

Hevea brasiliensis (rubber tree), a major source of natural rubber, could also be an important source of lumber as senescence occurs. However, latex collection is known to affect Hevea brasiliensis (rubber tree) wood formation and consequently, wood properties. The impact tapping (cutting made in the bark of the tree for latex harvest) has on the tree and the way the tree responds after tapping is often overlooked. Knowledge on wood properties of tapped rubber trees in Nigeria would enhance its sustainable utilization which is especially important in developing countries where lumber is limited. Variation in specific gravity and shrinkage of rubberwood wood due to tapping duration was examined. Tapping duration had significant effect in specific gravity and longitudinal shrinkage of rubberwood but had no effect on tangential and radial shrinkage. The specific gravity (SG) of rubberwood ranged from 0,55 - 0,59. Longitudinal shrinkage (average 1,42 %) was higher than typically observed for mature wood. Average tangential shrinkage for rubberwood of all the ages was 5,37 % while radial shrinkage ranged from 2,87 % to 3,84 %. decrease in SG observed in trees tapped for 20 years may indicate the initiation of senescence. Tapped rubberwood could be used in areas not exposed to high moisture as well as in other wood composites.

Influence of polymer flow rate, mold cavity volume and injection speed on selected properties of polypropylene molded parts

Influence of the height of the molding cavity and the injection speed for three PP grades with different mass melt flow rate (MFR) on the molded parts mass and longitudinal shrinkage, before and after UV aging, was investigated. It was shown that the mass of the molded parts depends on the flow rate of the material and the volume of the molding cavity, while shrinkage depends only on the volume of the mold cavity and is greater after aging.

The Effect of Adding the Mishraq Sulfur Ore on the Physical and Chemical Properties of Al-Angor and Al-Nahrawan Clays to Producing Lightweight Bricks

This paper aims to examine the possibility of producing lightweight laboratory clay Bricks by adding sulfur ore powder in different weight ratios ranging from 0, 10, 20, 30, 40, to 50% as supplementary materials to two types of clays taken from two different sites, which is the Al-Angor clay region near the city of Ramadi and the Al-Nahrawan clay region. The bricks burned at temperatures of 950 and 1050 C°٬ and the longitudinal Shrinkage tests, bulk density, water absorption, compression strength, and efflorescence were measured. The X-ray diffraction analysis was executed to determine the formed metal phases. The results of the tests showed a direct proportion between longitudinal contraction and water absorption ratio with the addition of sulfur ore and high burning temperature. While bulk density and compression strength are inversely proportional to the sulfur ratio and high burning temperature. Efflorescence tests showed a decrease in the efflorescence rate with an increase in the proportion of sulfur ore.

The effects of ACR/MAH ionic cross-linking on the cell morphology, mechanical properties, and dimensional stability of PVC foams

This study details a novel approach to enhance the dimensional stability of foamed polyvinyl chloride (PVC) materials through the introduction of a reversible cross-linking network. This is achieved via the carboxylation of acrylate polymers (ACR) utilizing the hydrolysis reaction of maleic anhydride (MAH) during the extrusion of PVC foam sheets. Subsequently, an ionic cross-linking network is formed using calcium-zinc (Ca-Zn) stabilizers. This paper elucidates the process of cell formation and the mechanisms underpinning the ACR/MAH ion network formation. Cell morphology of the foamed PVC was characterized using SEM, and the effects of ionic cross-linking on the plasticizing time, dimensional stability, and mechanical properties were analyzed through cell diameter distribution measurements and rheometry. The longitudinal and transverse dimensional shrinkage of PVC-F/MAH1 was reduced by 28.0 % and 28.9 %, respectively. The construction of the ACR/MAH ion cross-linking network not only augments the mechanical properties but also substantially enhances the dimensional stability of the material. This approach underscores the viability of ion cross-linking networks in advancing the performance parameters of PVC foams, suggesting a promising avenue for future research and development in polymer processing technology, and potentially expanding their application spectrum.

Effect of spatial setting angle on vibration of elastically restrained rotating beams

For a fully articulated rotor system, there may exist a spatial setting angle and elastically restrained root for each individual blade in rotation procedure due to flapping, drag and pitch hinges. Most of previous studies on rotating blades or beams focused on pitch angle and clamped root. In this paper, a three-dimensional dynamic model is proposed for elastically restrained rotating beams with spatial setting angle. The elastic deformation of the beam is expressed by three scalar variables in three-dimensional space including stretch deformation instead of the conventional axial deformation. The longitudinal shrinkage is considered to capture centrifugal forces. The penalty method is adopted to deal with the elastic constraints, which greatly simplifies the construction of admissible functions. A unified formulation is derived by a variational principle combined with Chebyshev orthogonal polynomials. One of the advantages of the present method is that any linearly independent and complete basis functions can be used as admissible function regardless of boundary conditions, and another advantage is that the present method is capable of handling arbitrary boundary conditions by only adjusting the values of penalty factor. The convergence and accuracy of the present method are validated by comparison, and the effects of boundary conditions, angular velocity and spatial setting angle on vibration characteristics are discussed in detail. The results show that natural frequencies increase as the spring stiffness rises in a certain range and the spatial setting angle plays a more significant role on dynamic characteristics for rotating beams.

Preparation and properties of in situ TiC/corundum–mullite electrically conductive ceramic

AbstractIn situ TiC/corundum–mullite electrically conductive ceramics were prepared by carbon‐bed sintering method using bauxite, clay and Ti3SiC2 powders as raw materials. The phase composition, microstructure, shrinkage, apparent porosity, bulk density, compressive strength, and resistivity of samples were investigated. The X‐ray diffraction results indicate that the TiC is completely generated by desilicidation reaction of the Ti3SiC2 at 1 300°C. When the sintering temperature is 1 300°C and Ti3SiC2 powder addition is 22 wt.%, the properties of the sample are optimum, with a longitudinal shrinkage of 2.04%, a radial shrinkage of 2.56%, an apparent porosity of 19.01%, a bulk density of 2.53 g/cm3, a compressive strength of 181 MPa, and a resistivity of 267 Ω·cm. The electrically conductive phase TiC is connected into a complete electrically conductive network. The shrinkages of samples decrease with increasing sintering temperature, which indicates that the samples expand due to secondary mullitization. The continuous electrically conductive network of TiC is destroyed. As the Ti3SiC2 powder addition increases from 14 to 20 wt.%, the resistivity of the samples decreases significantly, but the further increase in the Ti3SiC2 powder addition has no significant effect on the resistivity.

Effect of different sous-vide cooking temperature-time combinations on the functional and sensory properties of goose meat

The effect of goose meat sous-vide (SV) cooking at 6 combinations of temperature (60°C, 80°C) and time (4, 6, 12h) on selected functional properties was investigated. The study conducted an assessment of cooking loss (CL), moisture content, pH, longitudinal (LS), and transverse (TS) shrinkage, shear force (SF), texture profile analysis (TPA), color parameters (L*, a*, b*, C, h°), ΔE and carried out sensory evaluation. A total of 168 breast muscles (BM with and without skin) from 17-wk-old "Polish oat geese" were utilized. The CL was affected by both cooking temperature and time. The CL for meat with skin was higher than for without ones, and it was lower for both kinds of meat cooked at 60°C than at 80°C for all cooking times. The LS was higher than the TS. The higher shrinkage was stated for meat cooked at 80°C. There was a reduction in moisture content and slightly increasing pH by increasing temperature and prolonging cooking time. For both kinds of meat, the highest moisture retention was stated at 60°C/4h, and the lowest in samples heated at 80°C/12h. The samples cooked at 60°C were characterized by a higher L* value than those at 80°C. The a* values were higher for samples cooked at 60°C than those at 80°C, whereas b* were higher for meat cooked at 80°C. The SF exhibited a trend of lower values at 60°C compared to samples cooked at 80°C and it increased with prolonged cooking time. The value of hardness, cohesiveness, springiness, gumminess, and chewiness for meat cooked at 60°C increased, and for samples cooked at 80°C decreased with increasing cooking time. It was no significant differences in sensory scores for overall palatability for both kinds of meat cooked at 60°C and 80°C. Goose meat cooked at different time and temperature combinations showed extremely desirable overall palatability. Taking into account all discussed parameters, the optimal combination seems to be 60°C/4h.

ИССЛЕДОВАНИЕ ПОЛЗУЧЕСТИ СТАЛЕЖЕЛЕЗОБЕТОННЫХ ОБРАЗЦОВ

The paper presents the results of investigation of creep and shrinkage of steel-reinforced concrete specimens. For this purpose, parallel tests of specimens made of the same class of concrete but with different reinforcement were carried out. Concrete specimens, specimens reinforced with bar reinforcement frames and steel reinforced concrete specimens with external sheet reinforcement were investigated. The tests were carried out in climatic rooms using spring setups to maintain a constant load acting on the specimens over time. The load on the specimens was selected based on the equality of stresses in the concrete in all series of specimens. The specimens were tested both waterproofed and non-waterproofed, and the effect of waterproofing coating on shrinkage and creep strains was evaluated for different series of specimens. A system was developed to capture information. which allows, in addition to longitudinal shrinkage and creep deformations, to determine transverse deformations, longitudinal deformations along the faces of the specimen to determine the influence of reinforcement and steel of the outer plate, to evaluate the change in longitudinal deformations from the center of the specimen to its edges, to evaluate separately the deformations of concrete and steel plate in steel-reinforced concrete specimens. The analysis of the results allowed a comparative assessment of the influence of conventional bar reinforcement as well as steel sheet of steel-reinforced concrete specimens on creep and shrinkage deformations; the influence of waterproofing coating on the test results in different series was also assessed. Based on the results of this work, extended requirements for experimental and theoretical studies of steel-reinforced concrete specimens with external sheet reinforcement to determine their design stiffnesses were formulated.

The Effect of TIG Welding Heat Input on the Deformation of a Thin Bending Plate and Its Weld Zone

Heat input is a crucial parameter in the process of welding thin plates. It has a direct impact on the quality of the weld and the degree of deformation caused during welding. This study investigates the impact of heat input on the deformation of a thin bending plate and its weld zone using the thermoelastic–plastic finite element method. The accuracy of the model is ascertained using the non-contact inspection method utilizing digital image correlation technology. The welding deformation patterns of thin bending plates with a radius of 500 mm were analyzed at various welding heat inputs ranging from 173 J/mm to 435 J/mm. The results indicate that the finite element prediction model proposed in this paper is highly accurate. It has been observed that, under this range of thermal input, the thin bent plates undergo saddle deformation. By examining the correlation between heat input and the maximum deformation outside of the plane, it has been determined that a heat input of at least 50 J/mm is required for the thin bending plate to experience out-of-plane deformation. Additionally, as the level of heat input increases, so too does the out-of-plane deformation of the thin bending plate. After the completion of the welding cooling process, the transverse shrinkage at the weld seam of the thin bend plate is twice that of the longitudinal shrinkage. However, the transverse deformation of the bend plate is not significantly different from the longitudinal deformation.

SIFAT FISIS BAMBU SEPANJANG BATANG PADA BAMBU SERO (Schizostachyum brachycladum Kurz.)

SIFAT FISIS BAMBU SEPANJANG BATANG PADA BAMBU SERO (Schizostachyum brachycladum Kurz.)

Properties of alkali-activated slag mortar and prediction of its compressive strength

An investigation was carried out on alkali-activated slag AAS mortar mixtures cast with three different water-to-binder ratios W/B; 0.35, 0.40, and 0.45, eight different silica modulus Ms, wide range of Na2O%, activated using a mixture of two different activators; waterglass and sodium hydroxide, and cured with two different curing methodologies; sealing and full immersion in water. The standard 70.6 mm mortar cubes were tested under compression at the age of 3 days and 7 days. Furthermore, their flow, setting time, and longitudinal shrinkage were measured. The results showed that not only the percentage of Na2O is important; but, its source. Additionally, curing methodology affected the compressive strength at both ages where the full immersion in water may cause early development of strength, with no later strength gain. Also, flow test results showed that although increasing the W/B ratio can cause an increase in the flow, however, the strength may be affected negatively at the highest W/B ratio. Drying Shrinkage of AAS mortar mixtures was also found to be very sensitive to the W/B ratio. Furthermore, four mathematical models were used to generate prediction equations of the compressive strength of AAS mortar based on the experimental data, and for both curing methods. A comparison between predictions of different mathematical models was made based on the highest coefficient of determination R2, score, and standard error. The models were verified using four AAS mortar mixtures that were casted and tested at the age of 7 days under compression. The results showed that two models closely predicted the actual strengths, except at compressive strength higher than 60 MPa, where the models were significantly conservative.

Two-photon polymerization of silica glass diffractive micro-optics with minimal lateral shrinkage.

Three-dimensional printing enables the fabrication of silica glass optics with complex structures. However, shrinkage remains a significant obstacle to high-precision 3D printing of glass optics. Here we 3D-printed Dammann gratings (DGs) with low lateral shrinkage (<4%) using a two-photon polymerization (2PP) technique. The process consists of two steps: patterning two-photon polymerizable glass slurry with a 515 nm femtosecond laser to form desired structures and debinding/sintering the structures into transparent and dense silica glass. The sintered structures exhibited distinct shrinkage rates in the lateral against longitudinal directions. As the aspect ratio of the structures increased, the lateral shrinkage decreased, while the longitudinal shrinkage increased. Specifically, the structure with an aspect ratio of approximately 60 achieved a minimal lateral shrinkage of 1.1%, the corresponding longitudinal shrinkage was 61.7%. The printed DGs with a surface roughness below 20 nm demonstrated good beam-shaping performance. The presented technique opens up possibilities for rapid prototyping of silica diffractive optical elements.

Physical and Chemical Properties of Highland Bamboo (Yushania alpina) Culms Grown in Ethiopia

Bamboo is the fastest growing plant currently known on earth, a property that enables it to be the best alternative as a future source of wood fi ber. This study investigated the effect of site and culm height on the physical and chemical properties of Yushania alpina culms grown in Ethiopia. Matured Yushania alpina 3 to 5-year-old samples were harvested from Hagere-Selam and Rebu-Gebeya sites. The culms were subdivided into three equal lengths (bottom, middle, and top), and the variations in physical and chemical properties between the two sites and the culm heights of Yushania alpina were investigated. The results showed that the average values of MC, basic density, tangential and longitudinal shrinkage of Yushania alpina culms for Hagere-Selam and Rebu-Gebeya sites were (91.78 and 80.32 %), (0.65 and 0.63 g/cm3), (6.63 and 5.84 %) and (0.63 and 0.56 %), respectively. The average values of cellulose, lignin, extractive and ash contents in the culms for Hagere-Selam and Rebu-Gebeya sites were (52.84 and 50.71 %), (26.55, and 26.04 %), (8.41 and 8.02 %) and (1.95 and 2.17 %), respectively. The results revealed that the site affected the MC, basic density, cellulose, lignin, extractive, and ash contents of Yushania alpina culms but not the tangential and longitudinal shrinkage. The culm height of Yushania alpina affected MC, basic density, tangential shrinkage, longitudinal shrinkage, cellulose, lignin, extractive, and ash contents. In the case of both sites, the highest percentages of MC, tangential and longitudinal shrinkage, and ash content were observed at the base and lowest at the top of the culms. On the contrary, both sites observed thehighest magnitude of basic density, cellulose and extractive at the top and lowest at the base of the culms. The variations in physical and chemical properties at different sites and culm heights infl uence the utilization of Yushania alpina culms for industries and end products.

Assessment of the drying behaviour of young and mature Bambusa vulgaris from Ghana

This study assessed the drying behaviour of young and mature Bambusa vulgaris culms and evaluated their utilisation potential. Two and four-year old Bambusa vulgaris culms were harvested and prepared to the required length of 21 internodes. The first seven internodes were taken as the bottom, the second seven were taken as middle and the last seven internodes were taken as the top. The study used samples from the bottom and top. Physical properties, including basic density and moisture content, were determined in accordance with ISO 13061–2 (ISO 2014) and EN 13183–1 (EN 2002), respectively, while shrinkage properties (radial, tangential, longitudinal and volumetric) were determined following established procedures. For the bottom and top portions of the mature bamboo after 18 days of drying, radial shrinkage values were 3.31% and 5.01%, tangential values were 4.95% and 5.78%, and longitudinal values were 0.28% and 0.35%, respectively. For the bottom and top portion of two-year-old culms, the values were 15.0% and 18.6% for radial shrinkage, 20.5% and 25.8% for tangential shrinkage and 0.46% and 0.47% for longitudinal shrinkage, respectively. The tangential shrinkage values were higher than the radial and longitudinal shrinkage values. The moisture content of the bottom part of the mature bamboo culm after 3 and 18 days of drying were 31.4% and 12.2%, while the young culms had values of 53.5% and 27.8%, respectively. Mature bamboo culms had better drying behaviour than young culms. Consequently, mature bamboo culms are more suitable for use in engineered composite materials.

Microscopic computed tomography aided finite element modelling as a methodology to estimate hygroexpansion coefficients of wood: a case study on opposite and compression wood in softwood branches

Abstract Microscopic X-ray computed tomography (XµCT) aided finite element (FE) modelling is a popular method in material science to relate material properties to heterogeneous microstructures. Recently, a methodology was developed for the XµCT aided FE modelling of wood, which characterises the process from specimen preparation to estimation of material properties. In the current research, this methodology is tested on branches of Norway spruce (Picea abies (L.) Karst.) to estimate the hygroexpansion coefficients of opposite (OW) and compression wood (CW). These properties are largely unknown and have engineering implications. The study is complemented by measurements of density, moisture content (MC) and elastic moduli. Results showed that the methodology assisted in the design of an integrated process and the identification of bottlenecks. It was seen that the level of detail of the numerical model had a strong influence on the obtained hygroexpansion properties. CW from branches showed higher density and longitudinal shrinkage coefficients, and elastic moduli less affected by MC. These differences are unlikely caused by MC, but more likely by the characteristics of the microstructure.

Comparative Study on the Impact of Sand and Lime on the Physical and Mechanical Characteristics of Unfired and Fired Earth Bricks

Earth bricks represent one of the most important and widely used building materials in current era, due to its unique physical and mechanical properties compared to other materials. Earth bricks are available in two main types: raw earth bricks and fired bricks. The physical and mechanical properties differ for each type, which affects their performance in various applications and their long-term durability. Several studies have been conducted to improve the properties of raw and fired bricks and address their weaknesses. In this research, we aim to investigate the effects of adding dune sand and lime on the physical and mechanical properties of raw earth and fired bricks, and compare the results. Sand was added by 25%, while lime was added by 0, 6, 8, 10, and 12% of the soil matrix weight. Initially, we determined the properties of the raw materials used. After creating the samples, they underwent tests for bulk density, longitudinal shrinkage, compressive strength, and flexural strength. The study revealed the positive impact of adding sand on the physical and mechanical properties of raw and fired bricks. It contributed to reducing the bulk density and longitudinal shrinkage of the samples, while increasing their compressive and flexural strength to varying extents. The results also showed the positive effect of lime on the physical and mechanical properties of raw bricks, as long as it was added at a ratio not exceeding 10%. However, the addition of lime to fired bricks affected the physical properties positively but it has a negative effect on the mechanical properties.

Selection history affects very early expression of wood properties in Pinus radiata

Trees in breeding programmes are often selected at 1/4–1/3 of rotation, called ‘early selection’, which is typically between 8 and 10 years in radiata pine. However, differences between populations and genotypes selected for either basic density or wood stiffness are already apparent at age 2. We report the application of very early screening techniques for wood properties in the New Zealand Radiata Pine Breeding Programme deployment populations. Approximately 3000 trees representing three populations with 92 families and 10 clones were grown in a common garden trial, leaning for 21 months to separate compression and opposite wood. The trees were harvested and analysis carried out separately by wood type. The trial showed the existence of large variability in wood properties at early age, in some cases similar to variability near rotation age, and moderate to high degree of genetic control (0.35≤h2≤0.71\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.35 \\le h^2 \\le 0.71$$\\end{document}). The genetic association between traits was strong, particularly between wood stiffness and longitudinal shrinkage (-0.69\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\,0.69$$\\end{document}) and between longitudinal and volumetric shrinkage (0.83), suggesting that improving stiffness would also have a strong effect on improving dimensional stability. Basic density was also associated with stiffness and shrinkage, but with lower predictive capacity. These results can be used for roguing deployment populations-which already contain superior growing trees-and quickly upgrade the wood quality of seeds and clones currently available to New Zealand forest growers. We discuss necessary modifications to turn this research work into operation to screen any new material before commercial release.

Sifat Fisika dan Mekanika Kayu Acacia aulacocarpa dari KHDTK Wanagama

This study aims to determinethe physical properties and mechanical properties at axial (base, middle, and top) and radial (near the pith, middle, and near the bark) positions, as well as the relationship between the specific gravity and mechanical properties of Acacia aulacocarpa wood. Three 27-year-old trees planted at KHDTK Wanagama wereused. Wood physical and mechanical propertieswere tested per British Standard 373:1957. The statistical analysis used was a two-way ANOVA and a follow-up test of Tukey HSD. The results showed that the average moisture content was 98.95%; the green and air-dry sepesific gravity were 0.58 and 0.61. Radial, tangential, and longitudinal shrinkage from green to oven-dry conditions (total shrinkage) were 2.02%, 5.09%, and 0.33%. The tangential/radial (T/R) ratio was 2.80%. The static bending strength of stress at proportion limit, MoE, and MoR were 498.13 kg/cm2, 116.16x1000 kg/cm2, and 1043.68 kg/cm2, respectively. The compressive strength parallel to the grain and perpendicular to the grain were 596.05 kg/cm2 and 227.25 kg/cm2, respectively. The results of the variance analysis showed that the radial position factor has a significant effect on green moisture content, green and air-dry specificgravity, total radial shrinkage, T/R ratio, static bending strength at stress of proportion limit, MoE, MoR, compressive strength parallel to the grain, and compressive strength perpendicular to the grain. However, the axial position factor did not show any significant differences in the physical and mechanical properties of the wood. Furthermore, air-dry specific gravity has a significant moderate to high positive correlation with all mechanical properties.&#x0D; Keywords: Acacia aulacocarpa, physical properties, mechanical properties, axial position, radial position

Study on welding buckling evaluation method based on inherent strain theory and eigenvalue buckling analysis

Welding buckling deformation is one of the foremost failure modes of thin plate welded structures. It is important to estimate welding buckling for structural design and process optimization. Inherent strain-based welding buckling evaluation methods have been proved to be valid, but the existing methods have low efficiency due to requiring multiple inherent forces. In this study, a novel welding buckling evaluation method based on longitudinal shrinkage force was established. The effectiveness of the proposed method was validated using a butt welded joint. In addition, this method was applied in a large-scale thin plate structure for evaluating the structural stability, the effects of heat input, welding manner, and external constraints on welding deformation and buckling were also discussed. The results reveal that the proposed inherent strain-based welding buckling evaluation method can be used to judge whether welded structures are buckled. The reduction of welding heat input and the use of single-sided welding can mitigate welding deformation. Increasing external constraints can not only reduce the welding deformation, but also improve the welding critical buckling load for preventing welding buckling.

Effect of Asphalt Pavement Base Layers on Transverse Shrinkage Cracking Characteristics

Transverse shrinkage cracking is considered to be one of the main factors leading to the degradation of sustainable service performance for asphalt pavement, but the effect of base layers on it is rarely studied. To investigate the effect of asphalt pavement base layers on transverse shrinkage cracking characteristics, this study analyzed and evaluated it through the test section data. The transverse shrinkage cracking test section data of four different asphalt pavement base layers were compared, and the variation characteristics of transverse shrinkage cracking under the influence of the base layer types and temperature were analyzed. Based on the conventional characteristics, the concept and calculation method of cracking area ratio (CAR) was proposed, and its rationality and accuracy were proved by calculation. It has been found that the CAR can reflect the longitudinal shrinkage performance of asphalt pavement. The shrinkage rate of a semi-rigid base is larger, while the shrinkage performance of a flexible base is better, and the shrinkage performance of the whole pavement is not affected by a small amount of cement. The research provides a practical basis for improving the anti-cracking performance of asphalt pavement and helps to enhance its sustainable service performance.