Cross-sectional Width Research Articles

Fire resistance assessment of RC columns with advanced calculation methods

This paper contains the results of fire resistance calculation of reinforced concrete columns with advanced calculation methods.
 For columns that are tested unloaded, determine the cross-sectional temperature distribution and values of temperature in reinforcement. The fire resistance of columns that have been tested without load is determined according to temperature measurements, with calculation methods according to the requirements of DBN B.1.1-7 andDBN B.1.2-7.
 According to the tabulated method, the fire resistance of reinforced concrete columns is determined by geometric parameters such as cross-section width, axis distance of the reinforcement, amount of reinforcement, length or height of the element, load level during the fire exposure, heating conditions during the fire exposure (number of fire exposed sides).
 Accidental combination of actions during the fire situation consists of characteristic values of permanent and variable long-term actions taking into account the safety factor for the consequence class of the object (CC2) and the type of design situation (accidental).
 Thermal analysis of the column was performed under conditions of the standard fire exposure. In such conditions it was assumed that the column is exposed to fire with four sides for 120 minutes that corresponds to the required fire resistance class R120.
 The thermal state of the column was determined using transient thermal models that take into account radiation-convective heat transfer in the ambient from the heat source to the structural surface, convective heat transfer in the structure, radiation-convective heat exchange from the structure to the ambient environment.
 The residual load-bearing capacity of the reinforced concrete column after the fire exposure was calculated with the reduced cross-section determined using zone method in accordance with the requirements of DSTU-N B B.2.6-197 and DSTU-N B EN 1992-1-2.
 The fire resistance period of columns for the load-bearing criterion was determined on the basis of the results of of thermal and static analysis.

Buckling and Prestressed Vibrations of Periodic Nonprismatic Beams Using Integral Equation Approach

This paper presents the use of Fredholm–Volterra integro-differential equation approach for determining the critical buckling load and natural frequencies of periodically supported nonprismatic Euler–Bernoulli beams. Neumann series solution is used to solve the integro-differential equation by using the orthogonal Chebyshev polynomials, to avoid ill-conditioning. Gauss quadrature is used to perform various needed integrals. Critical buckling load, natural frequencies, and the corresponding mode shapes are compared with those available in the literature, those obtained using the principle of virtual work, and the ones obtained using NASTRAN®. The effect of variation of taper ratio, both in width and height of a rectangular cross section, on the nondimensional critical buckling load and the nondimensional natural frequency, is also investigated. A singularity is observed near the taper ratio of unity, which impacts the accuracy of both the finite element and the principle of virtual work results. The integral equation approach converges with a lesser number of terms than the principle of virtual work, especially for higher modes for beams approaching the taper ratio of unity. Benchmark examples for free vibration of a multiple-bay beam and of inflated tube are also studied, and the results are compared with those presented in the literature.

Behavior and flexural strength of fire-damaged high-strength reinforced rectangular concrete beams with tension or compression zones exposed to fire repaired with CFRP sheets

Motivated by the fact that fire is one of the most dangerous threats to buildings and structures, the main goal of this research is to determine the residual flexural capacity of high-strength simply supported reinforced concrete beams after exposing the tension and compression zones to various fire exposure intervals, as well as the effect of strengthening using carbon fiber reinforced polymer CFRP laminates. Ten simply supported high-strength reinforced concrete beams 2000 mm in length, with a cross-section width 200 mm and height of 250 mm, were tested to failure after exposure to standard fire ISO-834 or ASTM E-119 for 45, 90,120 min and strengthened with CFRP sheets. The beams were classified into three groups. A series of nine beams were exposed to standard fire for various exposure times, in addition to the control beams. Following that, carbon fiber reinforced polymer at the soffit were used to strengthen three fire damaged beams. And, the compression faces of three beams were exposed to fire. All specimens failed in a flexural mode, with minor spalling, according to the test findings. The beam subjected to fire for two hours lost 12% of its strength without exploding, although the deflection at failure was almost identical to the control beam. It has been noticed that using EB-CFRP to reinforce fire-damaged beams considerably reduces the impacts of fire exposure. It was also enough to restore the majority of the stiffness that had been lost. The reduction in ultimate flexural-bearing capacity for beams with compression faces exposed to fire was greater than the drop for beams with tensile faces exposed to fire. The beam subjected to fire for two hours had a 35% reduction in ultimate load. When exposed to fire for 90 and 120 min, the ductility of the compression zone exposed to fire beams was reduced by roughly half. The behaviour of the fire-damaged specimens was properly predicted using simple plane section analysis and the assumptions of the 500 °C isotherm method stated in EN-1992–1–2 (2004).

Dimensional Analysis of Compound Section in The Regulate Section Channel Model for Maintenance Main Channel

A dimensionless number is used to express the relationship between parameters and is used to describe the research results. Commonly used dimensional analysis methods are the Basic Echelon method, the Buckingham method, the Rayleight method, the Stepwise method and the Langhaar method. The compound section in the regulated section channel model aims to make the section convenient to the flow existing discharge at tidal conditions, in sediment flushing. In this study using the Buckingham’s method of dimensional analysis to determine the weight equation for the flushing sediment (w) and the variables that have been scaled on the flume, W = • (B, B*, h, h*, ⊗h, t, V, Q, g, W,)w,)S), where B is the width of the river (cm), B* is the width of the Flushing section (cm), h is the height of the water level (cm), h* is the height of the flushing section (cm), ®h is the difference in water level (cm), t is the tidal time period (s), V is the flow velocity (cm/s), Q is the water discharge (cm3/s), g is the gravity (cm/s2), )S is the mass density of the sediment (gr/cm3), )w is the density of the water mass (gr/cm3). From the analysis results obtained equations = . Where w is the weight of the flushing sediment (gr), is the ratio of the design cross-sectional width to the width of the estuary, is the ratio of the flushing cross-sectional height to the water level, is the ratio of the height water level to water depth, is the velocity of falling sediment, is the discharge of sediment flushing, ρ s h 3 is the hydrostatic pressure.

RISK PREDICTION AND DIAGNOSIS OF WATER SEEPAGE IN OPERATIONAL SHIELD TUNNELS BASED ON RANDOM FOREST

Water seepage (WS) is a paramount defect during tunnel operation and directly affects the operational safety of tunnels. Effectively predicting and diagnosing WS are problems that urgently need to be solved. This paper presents a standard and an evaluation index system for WS grades and constructs a sample dataset from monitoring recoreds for demonstration purposes. First, we use bootstrap resampling to build a random forest (RF) seepage risk prediction model. Second, the optimal branch and parameters are selected by the 5-fold cross-validation method to establish the RF prediction training model. Additionally, to illustrate the effectiveness of the method, the operational stage of Wuhan Metro Line 3 in China is taken as a case study. The results conclude that the segment spalling area, crack width, and loss rate of the rebar cross-section have a strong influence on WS. Finally, the test data are predicted, and the prediction result error index is calculated. Compared with the predictions of some traditional machine learning methods, such as support vector machines and artificial neural networks, RF prediction has the highest accuracy and is the closest to the true value, which demonstrates the accuracy of the model and its application potential.

The Effect of Sediment Supply from Land on Changes in Bathymetry in the Waters of the Rupat Strait, Dumai City, Riau Province

This research was conducted in February 2021 at the mouth of the Dumai River, Rupat Strait. The purpose of this study was to determine the effect of sediment supply from land on changes in bathymetry in the waters of the Rupat Strait based on the analysis of suspended sediment (SSC) and suspended solids (TSS) divided by the area of the study. The method used is a survey method. The results showed that as much as 26,94 tons/year of sediment entered the Rupat Strait and was distributed in the research area. Each part of the research area has a different bathymetric change value. This is presumably due to oceanographic factors in the waters of the Rupat Strait such as strong and weak river currents when entering the sea, the distance between the research area and the sediment supply source, human activities in each part of the study area, erosion along the river and abrasion at the river mouth. the presence of mangrove forests, dominant sediment types, sloping water topography, the cross-sectional width of the river as a sediment supplier, and suspended solids

Evaluation of the ultimate eccentric load of rectangular CFSTs using advanced neural network modeling

In this paper an Artificial Neural Network (ANN) model is developed for the prediction of the ultimate compressive load of rectangular Concrete Filled Steel Tube (CFST) columns, taking into account load eccentricity. To this end, an experimental database of CFST specimens from the literature has been compiled, totaling 1224 individual tests, both under concentric and under eccentric loading. Except for eccentricity, other parameters taken into consideration include the cross section width, height and thickness, the steel yield limit, the concrete strength and the column length. Both short and long specimens were evaluated. The architecture of the proposed ANN model was optimally selected, according to predefined performance metrics. The developed model was then compared against available design codes. It was found that its accuracy was significantly improved while maintaining a stable numerical behavior. The explicit equation that describes mathematically the ANN is offered in the paper, for easier implementation and evaluation purposes.

Protection of Kapton from atomic oxygen attack by SiOx/NiCr coating

SiOx/NiCr coatings with different SiOx thicknesses were deposited by the combination of ion implantation (IIP), filter cathode vacuum arc (FCVA), and electron beam (E-beam) evaporation methods to protect flexible Kapton from atomic oxygen (AO) attack. Due to the ion stitching effect and mechanical interlocking of implanted Ni+, the ductility and supporting effect of the fcc γ (Ni-Cr) alloy layer, and the low growth stress of the SiOx, the SiOx/NiCr coatings showed high adhesion and toughness. Exposure tests indicated that the AO erosion yield of the 1 μm-thick SiOx/NiCr-coated Kapton was 5.6 × 10−26 cm3 atom−1, which was attributed to the formation of a compact and continuous thin SiO2 layer. In addition, the inherent kinetic energy and oxidation performance dissipation of AO on the thick inner walls of cracks helped to reduce the cavity cross-sectional area and maximum width in the matrix.

3D crystal size distributions of pyroxene nanolites from nano X-ray computed tomography: Improved correction of crystal size distributions from CSDCorrections for magma ascent dynamics in conduits

Abstract Groundmass crystals indicate syneruptive magmatic conditions, and thus their crystal size distributions (CSDs) are used to infer magma ascent histories. Three-dimensional (3D) CSDs are most commonly estimated from two-dimensional (2D) observations and plotted against long-axis length, L (hereafter referred to as “L-plot CSDs”). However, L-plot CSDs have two significant problems: the error because of the conversion from 2D to 3D and a lowered sensitivity to changes in the degree of effective undercooling (ΔTeff), which arises because a crystal’s growth rate varies with ΔTeff most strongly along its long dimension. Although these problems can result in false interpretations of magma ascent dynamics, there has been little discussion of the influence of the size criteria on CSDs. In this study, we investigated which 3D size criterion [i.e., long (L), intermediate (I), or short (S) axis length] is optimum for 2D-estimated CSDs of groundmass crystals from two perspectives: (1) conformity with the actual distributions, and (2) the sensitivity of CSD slopes to the magma ascent conditions in the conduit. We observed groundmass pyroxene crystals in pumice clasts from sub-Plinian and Vulcanian eruptive phases during the 2011 eruption of Shinmoedake (andesitic volcano, Japan) by using synchrotron radiation-based X-ray computed nanotomography (SR-XCT) and field-emission scanning electron microscopy (FE-SEM) and rein-vestigated the crystallization kinetics of pyroxene nanolites ranging in width from a few hundred nanometers to 1 µm. The SR-XCT observations provided the detailed 3D shapes and 3D CSDs (CT-CSDs) of these nanolites directly. The FE-SEM observations allowed us to estimate 3D aspect ratios (S:I:L) and CSDs (SEM-CSDs). L-plot SEM-CSDs, acquired using the program CSDCorrections, were used to calculate S-plot SEM-CSDs and I-plot SEM-CSDs. We compared the data from FE-SEM with those from SR-XCT to evaluate the accuracy of 3D aspect ratios and CSDs estimated from 2D data. The L-plot SEM-CSDs from the sub-Plinian pumice sample showed significant inconsistencies with the CTCSD, a result of the difficulty in estimating representative 3D aspect ratios from 2D observations for elongated groundmass crystals. In contrast, the S- and I-plot SEM-CSDs kept the effect of aspect ratio to a minimum and preserved their actual slopes, except for a vertical discrepancy between the CSDs. Moreover, the slopes of S- and I-plot CSDs of the nanolites differed more markedly between the two eruptive styles (by ~20% more) than those of L-plot CSDs. For estimating magma ascent dynamics, we propose that the optimum method for acquiring SEM-CSDs is to measure the cross-sectional widths of crystals and convert the resulting 2D data set into S-plot CSDs. Our new finding that the 3D shapes and CSDs of pyroxene nanolites differ according to eruptive style means that nanolites indicate distinct differences in ascent histories at the shallow conduit: increasing ΔTeff just before sub-Plinian eruptions and decreasing ΔTeff before Vulcanian eruptions. Given the similarity in CSDs of micro-lites, our results suggest that eruptive style was determined in the shallow conduit. Monitoring the condition of the shallow conduit may contribute to predicting the time evolution of eruptive activity.

Comparative Study on Structural Behavior of Reinforced Concrete Straight Beam and Beams with out of Plane Parts

This paper aims to experimentally investigate and compare the structural behavior of reinforced concrete straight beam and other beams there made with one, two, and three out of plane parts. The study focused on the effect of the number and location of the out plane parts on the beams mid span deflection, and rotation, as well as the ductility index, cracking loads, and failure modes. Four beams were manufactured with a cross-sectional width of 150 mm and a depth of 200 mm, and 2000 mm in length. All the beams were made with normal strength concrete and constant longitudinal reinforcement ratio 0.011 for negative and positive moment. All the beam specimens were clamped by a special steel fixed ends and subjected to the two-point load up to their failure. The obtained results presented that the load bearing capacity of straight beam was higher than the beams with out of plane parts. Furthermore, the beam with two out of plane parts has capacity higher than the beams with one and three out of plane part by 5.86%, and 55.07%. In addition, the results showed that the ductility increased with increasing number of out of plane parts by 5.52%, and 32.71% as copared with the beam with one out of plane part.

THE INFLUENCE OF CHEMICAL COMPOSITION AND HEAT TREATMENT ON THE MECHANICAL PROPERTIES AND WORKABILITY OF THE ALUMINIUM ALLOY EN AW 5454

The influence of chemical composition and heat treatment on the mechanical properties and formability of the selected commercial aluminium alloy EN AW 5454 was investigated. The main properties of alloy 5454 from the AA 5xxx series are very good corrosion resistant and has good formability. From the cast slab a 50 mm thick slice was taken in the width cross section in the slab centre. One half of the slice was homogenised for 10 hours at a temperature of 530 °C. The cast and homogenised samples were investigated using light and scanning electron microscopy. For the study of the influence of the heat treatment, samples in the as-cast state were annealed in the laboratory furnace at a temperature of 530 °C for 4, 6, 8, 10 and 12 hours. To study the influence of chemical composition, four different samples were prepared: the first without additions, the second with an addition of 1 wt% Mn, the third with 3 wt% Mg and the fourth with an addition of both elements, Mn and Mg. The XRF analyses confirmed the desired chemical composition of all four produced alloys. Half of each alloy’s sample was homogenised at the same temperature and time as the base alloy in the as-cast state. The hot deformation behaviour of the different alloys was investigated using cylindrical hot compression tests performed on a Gleeble 1500D thermo-mechanical simulator. By comparing flow curves a high influence of the thermo-mechanical parameters on the alloy formability can be seen. The alloy has good workability and with the addition of Mn and Mg, the stress values are higher than those of the base alloy.

Preoperative Visualized Ultrasound Assessment of the Recurrent Laryngeal Nerve in Thyroid Cancer Surgery: Reliability and Risk Features by Imaging

BackgroundPreoperative identification and visualization of tumor infiltration of the recurrent laryngeal nerve (RLN) in patients with thyroid cancer is important. The purpose of our study was to evaluate the reliability and feasibility of preoperative assessment by ultrasound and to identify ultrasound imaging features potentially associated with tumor infiltration of the RLN.MethodsIn this prospective study, patients undergoing thyroid cancer surgery at our institution between August 2020 and January 2021 were included, and preoperative ultrasound visualization of the RLN and thyroid lesions was performed. RLN infiltration was also confirmed surgically in all cases. Five patients with enlarged lymph nodes were selected to undergo injection of carbon nanoparticles to confirm the correctness of RLN identification by preoperative ultrasound. The repeatability of RLN assessment by ultrasound was evaluated by comparing the correlation between pre- and intraoperative, intra- and inter-group assessments. Parameters of normal RLNs according to age, sex, and body mass index were established. Finally, ultrasound imaging features of patients with RLN tumor infiltration were analyzed to identify potential risk predictors.ResultsAccording to the ultrasonic assessment, RLNs of 70 patients appeared normal, while 14 of those patients appeared to be infiltrated by tumors. During surgery, the 70 cases of normal RLNs were confirmed, but only 8 of the 14 suspected cases of infiltration were confirmed. In all five patients injected with carbon nanoparticles, the location of RLNs adjacent to the marked lymph nodes observed by surgeons corresponded to the RLN location identified by preoperative ultrasound. The repeatability of RLN estimation varied from moderate to excellent. There were no significant differences in cross-sectional area, width, or thickness of normal RLNs according to age, sex, or body mass index. Indistinct margin with tumor, incontinuous shape as ultrasound features by the analysis of patients with surgically confirmed RLN infiltration were associated with tumor invasion.ConclusionWe show that preoperative ultrasound can be applied to visualize the RLN and may help predict tumor infiltration of the RLN.

Elucidation of thermo-mechanical properties of silicon nanowires from a molecular dynamics perspective

The thermo-mechanical properties of silicon nanowires are of great importance in the state of the art silicon technologies. Herein, thermal and mechanical properties of silicon nanowires along [110] direction are illustrated by a molecular dynamics approach using Tersoff potential. Different lengths ranging from 10 to 45 nm and cross section widths from 2.2 nm to 6.5 nm as well as different temperatures from 200 to 500 K were studied. In all the cases, the corresponding thermal conductivities of silicon nanowires were found to be much smaller than the bulk silicon counterpart, in the range of ~1–5 W/(m.K), and strongly dependent on size while less sensitive to temperature. The elastic modulus, fractural strain and stress were also investigated upon various size and temperatures indicating dramatically lower properties at higher temperature and as a result of nano-scaling. The presented findings on <110> silicon nanowires sheds further lights on the current understandings on thermo-mechanical behavior of silicon nanowires for applications such as in Li-ion batteries and provide complementary information for the relevant data bank.

Hydrothermal performances of symmetric and asymmetric divergent-convergent microchannel heat sinks

The present work numerically studied the hydrothermal performance of symmetric and asymmetric divergent-convergent microchannel heat sink (DCMCHS) with the rectangular cross-section. Three different DCMCHS with fixed total channel volume were designed, the symmetric DCMCHS, the width-asymmetric DCMCHS with the fixed inlet-to-middle cross-sectional width ratio, and the width-asymmetric DCMCHS with the fixed middle cross-sectional width. Effects of the inlet-to-middle cross-sectional width ratio and channel height of the symmetric DCMCHS, and the outlet-to-inlet width ratio, the middle cross-sectional width and the channel height of the width-asymmetric DCMCHSs on the maximum temperature, overall thermal resistance, pressure drop, and the coefficient of performance (COP) of the DCMCHSs were analyzed. It was found that the symmetric DCMCHS with smaller inlet-to-middle width ratio has smaller thermal resistance but larger pressure drop. Moreover, the decreasing outlet-to-inlet width ratio can improve the thermal performance of the two width-asymmetric DCMCHSs and increase the pressure drop. The increasing middle cross-sectional width can reduce the thermal resistance of width-asymmetric DCMCHS with fixed channel height and fixed outlet-to-inlet width ratio by consuming more pressure drop. For the COP, all the proposed DCMCHSs in the present work have smaller COP compared with the conventional parallel MCHS.

Experimental and numerical investigations on pre-twisted steel box-section columns

Experimental and numerical investigations on pre-twisted steel box-section columns are presented in this paper. A series of tests was conducted to investigate the effects of pre-twisted angle ratio on the compressive behaviour of steel box-section columns. The pre-twisted angle ratios of 3°/m and 15°/m were considered in the design of column specimens. The column specimens had effective lengths of 1.5 m and 4.0 m, and cross-section dimensions of 280 × 100 (depth × width) mm and 350 × 120 mm. A non-linear finite element model (FEM) considering geometric imperfections was developed. The results from the finite element analysis were compared with those from the column tests in terms of ultimate loads, failure modes and load-deformation curves. After successful verification, the FEM was employed to conduct an extensive parametric study on the structural behaviour of pre-twisted steel box-section columns. The key parameters in the parametric study included the pre-twisted angle ratios, ratios of depth to width in cross section, effective column lengths and end boundary conditions. It was shown that the pre-twisted angle ratios had little effect on the axial capacity, initial stiffness and lateral deformation capacity of shorter columns that failed by plastic yielding; however, more significant effects were found for the longer columns that failed by elastic flexural buckling. Theoretical analysis on the elastic buckling of pre-twisted steel box-section columns was conducted. Based on which, the formula for the buckling coefficient (reduction factor) was proposed that was suitable for the prediction of ultimate strength of pre-twisted steel box-section column.

An Automated Measurement Method for the Endodontic Working Width of Lower Molars by Means of Parametric Models Using Cone-beam Computed Tomographcy and Micro–Computed Tomography

IntroductionA new method for the approximation of the root canal's cross-sectional shape and its working width using cone-beam computed tomographic (CBCT) or micro–computed tomographic (micro-CT) imaging was introduced. MethodsScanned data from 29 extracted human mandibular first and second molar distal root canals without instrumentation were reconstructed and analyzed with a self-developed measurement algorithm. The 3-dimensional volume models were sliced perpendicular to the vertical axis. Using different 2-dimensional parametric models, the contour of each root canal slice was approximated and used to determine the canal's cross-sectional dimensions. The measurements of minor width, major width, and the root canal's conicity were statistically analyzed using analysis of variance. ResultsThe measured minor and major widths of the investigated root canals were significantly higher (probability value P < .05) when evaluated by CBCT images than the results obtained from micro-CT data. Both dimensions increased starting from the apical foramen (P < .01). The narrowest measured canal widths were 0.19–0.24 mm for CBCT imaging and 0.09–0.21 mm for micro-CT imaging in the apical part. The maximum values for conicity were between 13% and 17% in the cervical third. ConclusionsThe 3-dimensional imaging data from CBCT and micro-CT imaging enabled a valuable anatomic assessment of the root canal's cross-sectional working width along the canal up to the physiological foramen in order to determine an adequate apical diameter as well as the correct measured taper in the cervical and medial part.

Analysis of nasal airway symmetry and upper airway changes after rapid maxillary expansion

The objectives of this study were to assess the changes in right vs left nasal cavity volumes and minimum cross-sectional width, nasopharyngeal, and oropharyngeal volumes of the upper airway in response to rapid maxillary expansion (RME). Pretreatment and posttreatment cone-beam computed tomography scans of 28 patients with a mean age of 9.86±2.43years and 20 age- and sex-matched controls were digitized and linear, angular, and volumetric measurements were obtained. Nasopharyngeal volume, right, and left nasal cavity volumes, and minimum cross-sectional widths increased significantly 2years post RME (P<0.05). These measurements did not show any significant increase in the control group (P>0.05), whereas the oropharyngeal volume increase for both groups was comparable (P=0.92). In the experimental group, the right and left nasal cavity volumes were not significantly different at baseline or posttreatment. However, the change that occurred was significantly larger for the left nasal cavity. This change for the control group was more significant for the right nasal cavity. Maxillary right and left molar inclinations were positively correlated to the nasal cavity volume, showing that the more buccally inclined the maxillary molars were, the smaller the nasal cavity volume. Nasopharyngeal and right and left nasal cavity volumes and minimum cross-sectional widths increase significantly after RME in young children. Expansion decreases the degree of difference in volume between the right and left nasal cavities. The buccal inclination of maxillary molars is correlated with nasal cavity volume.

Progression of non-carious cervical lesions: 3D morphological analysis.

This longitudinal study aimed to investigate morphologically and quantitatively the progression of non-carious cervical lesions (NCCLs) using a confocal laser scanning microscope (CLSM) and replica models. The samples examined comprised sets of replicas annually obtained from 83 lesions in 16 participants over 3 to 5years. All lesions were visually categorized as wedge-shaped, saucer-shaped, or mixed-shaped lesions. CLSM images of the replicas were analyzed in terms of axial depth, occlusogingival width (height) in the buccolingual cross-section, and estimated volume using a custom code of the image analysis software to estimate the progression of the NCCLs over time. The morphological characteristics of the NCCLs were also objectively divided into three groups according to the depth to height ratio (D/H ratio). Fisher's exact test and the Cochran-Armitage trend test were used for statistical analysis. Saucer-shaped lesions progressed mainly in height, whereas wedge-shaped lesions increased both in height and depth. Annual progression in depth and volume significantly increased as the D/H ratio increased. More than half of the NCCLs with a small D/H ratio progressed 50μm or more in height, whereas none of them progressed more than 50μm in depth. Annual progression in depth significantly increased as the lesion depth at baseline increased. Progression patterns significantly differed between NCCLs of different shapes. Most NCCLs progressed slowly in depth regardless of their shape. Moreover, NCCLs may progress through active and inactive stages.

Transport Diffusion of Linear Alkanes (C5-C16) through Thin Films of ZIF-8 as Assessed by Quartz Crystal Microgravimetry.

We report uptake capacities and transport diffusivities, D, for each of eight linear alkanes (ranging from C5 to C16) in quartz crystal-supported films of solvent-evacuated ZIF-8. Analyses of the alkane uptake profiles revealed that the transport dynamics are governed by guest diffusion through metal-organic framework (MOF) (ZIF-8) crystallites rather than by rates of entry into films at the MOF/vapor interface. The obtained diffusivities range from just over 10-18 m2/s to just under 10-14 m2/s. Notably, minimum cross-sectional widths for all guests exceed the crystallographically measured width of ZIF-8's largest apertures and imply consistently with previous experimental and computational studies that apertures expand to accommodate guest uptake. On average, each additional carbon decreases the transport diffusivity of an alkane by twofold. Closer examination, however, reveals an odd-even effect such that linear alkanes having even numbers of carbons diffuse more rapidly than alkanes featuring one more or one less carbon atom. Thus, ZIF-8's differentiation of transport diffusivities for pairs of alkanes differing in length by only one carbon atom can be significantly greater than the aforementioned factor of 2. Elucidation of the microscopic basis for the odd-even behavior, however, awaits the outcome of molecular dynamics calculations that are beyond the scope of the present study. For compact, solvothermally prepared films, guest transport is dominated by 1D diffusion from the film/vapor interface and toward the underlying quartz crystal. For much lower density, electrophoretically deposited (EPD) films, crystallites behave nearly independently, and guest transport can be adequately modeled by assuming rapid permeation of macroscopic voids between crystallites, followed by entry and rate-limiting radial diffusion into isolated crystallites. One consequence is that EPD films can be much more rapidly infiltrated by molecular guests than can compact, solvothermally grown films. The combined results have potentially favorable implications for the development of kinetic separation schemes for closely related analytes.

Evaluation of code provisions predicting the concrete shear strength of FRP-reinforced members without shear reinforcement

Concrete shear strength for elements without shear reinforcement and longitudinally reinforced with Fiber-Reinforced Polymer (FRP) bars is considered one of the critical issues that has been enormously estimated by many researchers as well as different code provisions. The implementation of various design codes for the estimation using similar input parameters observes the broad predictive spectrum of shear strength for FRP-reinforced members without stirrups. The element cross-section width and effective depth, the ratio of shear span to effective depth, concrete compressive strength, FRP-reinforcement ratio, and FRP-modulus of elasticity are mostly used as input parameters in various standards to predict the shear strength. This paper focuses on evaluating the efficiency of predicting equations used in different code provisions to estimate the shear strength compared to the nominal shear test-results of 501 tested samples collected from different literatures. An analytical study was conducted to determine the influence of each input parameter on the shear capacity as a pre-step to improve the efficiency of different code provisions when used at specific range of input parameters to predict the shear strength of members reinforced with longitudinal FRP bars. An optimized model was proposed based on refining of the Canadian Standard Association (CSAS806-12) formula and numerical analysis. The study concluded that the CSAS806-12 formula has high efficiency for predicting shear strength of FRP-reinforced members without stirrups. While both the American Concrete Institute (ACI440.1R-15) and the American Association of State and Highway Transportation Officials’ (AASHTOLRFD-17) are significantly conservative in predicting shear capacity for these members. The proposed model's performance was found to be considerably higher as compared to the CSAS806-12 formula and other studied code provisions.