Exploring Exact Effects of Various Factors on Chloride Diffusion in Cracked Concrete: ABAQUS-Based Mesoscale Simulations.

Chloride ion attack is a major cause of concrete durability problems, and existing studies have rarely addressed the effects of damage zones. In this paper, an improved mesoscale model including five phases was constructed using the finite element software ABAQUS to study the diffusivity of chloride ions in cracked concrete. It was found that the damage zone is negligible when the crack width is less than 50 µm, while the width and depth of the damage zone are about 15 times the crack width and 15% of the crack depth when the crack is greater than 50 µm. The results show that the diffusion of chloride is greatly influenced by the crack width, while it is little-influenced by the crack shape. Low water-cement ratio and adequate hydration of the concrete are also key factors affecting chloride diffusion. In contrast, regular rounded aggregates have a positive effect on reducing chloride diffusion compared to irregularly shaped aggregates, and this effect becomes weaker with increasing service time. In addition, the protective layer can effectively prevent the diffusion of chloride in concrete. Therefore, when designing marine concrete, efforts should be made to ensure that the concrete has a low water-cement ratio, adequate hydration, less cracking and a protective layer.

Nucleation of naturally occurring calcic amphibole asbestos.

This article proposes an initial model of natural asbestiform minerals growing in four stages. Structures dating from the early stages of the development were observed in the damaged zone surrounding meso-fractures, more particularly in microfractures, microcavities and microcracks that lie in front of and along mesofractures. This study is limited to calcium amphiboles cross-fibers, which develop from altered calcium amphiboles. The observations were made using PLM, with some using TEM. The samples are amphibolites, dolerites and skarns from France. All these rocks have in common that they have been exposed to hydrothermal circulation which gives them a propylite character. The earliest phenomenon was the development of metasomatic veins. In these veins, actinolite form pseudomorphs after hornblendes. The new amphiboles preserve the original morphology of hornblende, in particular the appearance of the cleavages. In the second stage, hydrothermal Fluid circulation promotes the development of subgrains (DSG) with boundaries generally parallel to the cleavage. Some sub-grains become thinner and more and more individualized due to dissolution by the hydrothermal fluid. The third stage is fracturing. The irregular ends of DSGs and amphibole debris can form the substrate of asbestiform mineral nuclei. Further dissolution of DSGs can also lead to the creation of substrates. The last stage is the nucleation and growth. The nuclei have a conical shape and variable widths, from a few microns to about ten microns. The basal parts of the asbestos minerals (BPAMs) extend the DSGs along the c axis. BPAMs have variable widths and can divide during their development at the level of transverse microcracks. BPAMs when not dividing have a morphology comparable to that of whisker nanocrystals synthesized using the vapor-liquid-crystal mechanism. The shape of the fragments from BPMAs is close to that of DSGs as both have variable widths and both have lengths controlled by microcracks.

Impact of Brittle Creep Failure on Time-Delayed Characteristics of Rockburst.

In this research, the combination of theoretical approach and numerical simulation was employed to comprehensively understand the initiation mechanism of time-delayed rockburst and analyze the time-delayed failure laws for surrounding rock after excavation unloading without prompt support. The investigations are principally at the angle of time and space, which refers to the creep property and damaged scope for surrounding rock. For the theoretical method, the analytical elastic and elastoplastic models for deep tunnel cross section and the creep model for brittle rock material from a microscopic view were combined. It was found that the time-delayed failure for surrounding rock resulted from the damage accumulation with crack development during the creep process. The surrounding rock with the elastic state was more stable than that in the plastic zone and the creep duration increased with growing distance from the center of tunnel section. Based on the theoretical creep model, the numerical simulation ulteriorly analyzed the brittle creep duration on the key positions. The surrounding rock tended to fail more in the strong excavation damage zone (SEDZ) than that in the weakly damaged zone (WEDZ), and brittle creep failure mainly occurred on the excavation border (EB) in a short space of time. In addition, the increase in the radius for tunnel cross section and the higher in situ stress distribution around the opening led to the acceleration of the creep process for surrounding rock, and the irregular cross-section shape of the tunnel caused the local damaged range extension and decreased the duration for time-delayed failure.

Local Effects of a 1940 nm Thulium-Doped Fiber Laser and a 1470 nm Diode Laser on the Pulmonary Parenchyma: An Experimental Study in a Pig Model.

The lungs are a common site of metastases from malignant tumors. Their removal with a minimal but safe tissue margin is essential for the long-term survival of patients. The aim of this study was to evaluate the usefulness of a 1940 nm thulium-doped fiber laser (TDFL) and a 1470 nm diode laser (DL) in a pig model of lung surgery that involved the incision and excision of lung tissue. Histopathological analysis was performed on days 0 and 7 after surgery. Neither TDFL nor DL caused significant perioperative or postoperative bleeding. Histological analysis revealed the presence of carbonized necrotic tissue, mixed fibrin-cellular exudate in the superficial zone of thermal damage and bands of deeper thermal changes. The mean total width of thermal damage on day 0 was 499.46 ± 61.44 and 937.39 ± 109.65 µm for TDFL and DL, respectively. On day 7, cell activation and repair processes were visible. The total width of thermal damage was 2615.74 ± 487.17 µm for TDFL vs. 6500.34 ±1118.02 µm for DL. The superficial zone of thermal damage was narrower for TDFL on both days 0 and 7. The results confirm the effectiveness of both types of laser in cutting and providing hemostasis in the lungs. TDFL caused less thermal damage to the lung parenchyma than DL.

Origin of the Co-Seismic Variations of Elastic Properties in the Crust: Insight From the Laboratory.

Seismological observations highlighted that earthquakes are often followed by changes in elastic properties around the fault zone. Here, we studied the origin of these variations using stick-slip experiments on saw-cut granite samples presenting different degrees of bulk damage (i.e., microcracks). Stick-slip events were induced under triaxial compression configuration with continuous active ultrasonic measurements at confining pressures representative of upper crustal conditions (15-120 MPa). Both the P-wave velocity ( V P ) and amplitude ( A P ) showed drops, concurrently with stress drops, and had a non-monotonic dependence toward the fault's stress state. Our experimental results suggest that co-seismic changes in V P were mostly controlled by the elastic re-opening of microcracks in the bulk, rather than by co-seismic damage or the formation of fault gouge. Co-seismic changes in A P were controlled by a combination of elastic re-opening of microcracks in the bulk and inelastic processes (i.e., co-seismic damage and gouge formation and dilation).

Usefulness of Thulium-Doped Fiber Laser and Diode Laser in Zero Ischemia Kidney Surgery-Comparative Study in Pig Model.

BACKGROUND: The aim of this study was to evaluate the usefulness of a thulium-doped fiber laser and a diode laser in zero ischemia kidney surgery, by carrying out a comparative study in a pig model. MATERIAL AND METHODS: Research was carried out on 12 pigs weighing 30 kg each. A thulium-doped fiber laser (TDFL) and a diode laser (DL) operating at wavelengths of 1940 and 1470 nm, respectively, were used. The cut sites were assessed both macroscopically and microscopically. The zone of thermal damage visible in the histopathological preparations was divided into superficial and total areas. RESULTS: During partial nephrectomy, moderate to minimal bleeding was observed, which did not require additional hemostatic measures. All animals survived the procedure. On day 0, the total thermal damage depth was 837.8 µm for the TDFL and 1175.0 µm for the DL. On day 7, the depths were 1556.2 and 2301.7 µm, respectively. On day 14, the overall thermal damage depth for the DL was the greatest (6800 µm). The width of the superficial zone was significantly reduced on days 7 and 14 after TDFL application. CONCLUSION: Both lasers are suitable for partial wedge nephrectomy without ischemia in pigs. The TDFL produced similar or better hemostasis than the DL, with a smaller zone of thermal damage and, therefore, seems more suitable for application in human medicine.

Scattering on a square lattice from a crack with a damage zone.

A semi-infinite crack in an infinite square lattice is subjected to a wave coming from infinity, thereby leading to its scattering by the crack surfaces. A partially damaged zone ahead of the crack tip is modelled by an arbitrarily distributed stiffness of the damaged links. While an open crack, with an atomically sharp crack tip, in the lattice has been solved in closed form with the help of the scalar Wiener-Hopf formulation (Sharma 2015 SIAM J. Appl. Math., 75, 1171-1192 (doi:10.1137/140985093); Sharma 2015 SIAM J. Appl. Math. 75, 1915-1940. (doi:10.1137/15M1010646)), the problem considered here becomes very intricate depending on the nature of the damaged links. For instance, in the case of a partially bridged finite zone it involves a 2 × 2 matrix kernel of formidable class. But using an original technique, the problem, including the general case of arbitrarily damaged links, is reduced to a scalar one with the exception that it involves solving an auxiliary linear system of N × N equations, where N defines the length of the damage zone. The proposed method does allow, effectively, the construction of an exact solution. Numerical examples and the asymptotic approximation of the scattered field far away from the crack tip are also presented.

Comparison of A 1940 nm Thulium-Doped Fiber Laser and A 1470 nm Diode Laser for Cutting Efficacy and Hemostasis in A Pig Model of Spleen Surgery.

Partial and total splenectomies are associated with a high risk of substantial blood loss. Lasers operating at wavelengths strongly absorbed by water have the potential to improve hemostasis and cut while providing a narrow zone of thermal damage. The aim of this study is to compare a thulium-doped fiber laser (TDFL) emitting a wavelength of 1940 nm and a diode laser (DL) operating at 1470 nm for spleen surgery in a pig model. A partial splenectomy and spleen incisions were made in 12 animals using the two laser devices. The hemostasis was evaluated visually during surgeries. Post-mortem and histopathological evaluations were done on days 0, 7, and 14 following surgery. Neither TDFL nor DL caused bleeding on day 0 or delayed bleeding. On day 14, pale streaks at the site of incision were slightly wider after cutting with DL than with TDFL. Histological analysis revealed a carbonized zone with exudation and a deeper zone of thermal tissue damage on day 0. The width of the thermal changes was 655.26 ± 107.70 µm for TDFL and 1413.37 ± 111.85 µm for DL. On day 7, a proliferation of fibroblasts and splenocytes was visible, as well as a formation of multinucleated giant cells adjacent to the residues of carbonization. The zone of thermal damage was broader for DL (1157.5 ± 262.77 µm) than for TDFL (682.22 ± 116.58 µm). On day 14, cutting sites were filled with connective and granulation tissues with the residues of carbonization. The zone of thermal damage was narrower for TDFL (761.65 ± 34.3 µm) than for DL (1609.82 ± 202.22 µm). Thus, both lasers are efficient in spleen surgery, providing good hemostasis. However, TDFL produces a narrower zone of thermal damage, which suggests its better efficiency for spleen surgery, especially when performing more precise procedures.

Palaeopermeability anisotropy and geometrical properties of sealed-microfractures from micro-CT analyses: An open-source implementation.

Fault zone permeability and the real 3D-spatial distribution of the fault-related fracture networks are critical in the assessment of fault zones behavior for fluids. The study of the real 3D-spatial distribution of the microfracture network, using X-ray micro-computed tomography, is a crucial factor to unravel the real structural permeability conditions of a fault-zone. Despite the availability of several commercial software for rock properties estimation from X-ray micro-computed tomography scanning, their high cost and lack of programmability encourage the use of open-source data treatment. This work presents the implementation of a methodology flow for the quantification of both structural and geometrical parameters (fractures density, fractures aperture, fractures porosity, and fractures surface area), and the modeling of palaeopermeability of fault-related fractured samples, with focus in the proper spatial orientation of both the sample and the results. This is performed with an easy to follow step-by-step implementation, by a combination of open-source software, newly implemented codes, and numerical methods. This approach keeps track of the sample's spatial orientation from the physical to the virtual world, thus assessing any fault-related palaeopermeability anisotropy.

A randomized controlled clinical and histopathological trial comparing excisional biopsies of oral fibrous hyperplasias using CO2 and Er:YAG laser.

This study was conducted in order to compare clinical and histopathological outcomes for excisional biopsies when using pulsed CO2 laser versus Er:YAG laser. Patients (n = 32) with a fibrous hyperplasia in the buccal mucosa were randomly allocated to the CO2 (140 Hz, 400 µs, 33 mJ) or the Er:YAG laser (35 Hz, 297 µs, 200 mJ) group. The duration of excision, intraoperative bleeding and methods to stop the bleeding, postoperative pain (VAS; ranging 0-100), the use of analgesics, and the width of the thermal damage zone (µm) were recorded and compared between the two groups. The median duration of the intervention was 209 s, and there was no significant difference between the two methods. Intraoperative bleeding occurred in 100% of the excisions with Er:YAG and 56% with CO2 laser (p = 0.007). The median thermal damage zone was 74.9 µm for CO2 and 34.0 µm for Er:YAG laser (p < 0.0001). The median VAS score on the evening after surgery was 5 for the CO2 laser and 3 for the Er:YAG group. To excise oral soft tissue lesions, CO2 and Er:YAG lasers are both valuable tools with a short time of intervention and postoperative low pain. More bleeding occurs with the Er:YAG than CO2 laser, but the lower thermal effect of Er:YAG laser seems advantageous for histopathological evaluation.

A theoretical and computational framework for studying creep crack growth.

In this study, crack growth under steady state creep conditions is analysed. A theoretical framework is introduced in which the constitutive behaviour of the bulk material is described by power-law creep. A new class of damage zone models is proposed to model the fracture process ahead of a crack tip, such that the constitutive relation is described by a traction-separation rate law. In particular, simple critical displacement, empirical Kachanov type damage and micromechanical based interface models are used. Using the path independency property of the C ∗ -integral and dimensional analysis, analytical models are developed for pure mode-I steady-state crack growth in a double cantilever beam specimen (DCB) subjected to constant pure bending moment. A computational framework is then implemented using the Finite Element method. The analytical models are calibrated against detailed Finite Element models. The theoretical framework gives the fundamental form of the model and only a single quantity C ^ k needs to be determined from the Finite Element analysis in terms of a dimensionless quantity ϕ 0 , which is the ratio of geometric and material length scales. Further, the validity of the framework is examined by investigating the crack growth response in the limits of small and large ϕ 0 , for which analytical expression can be obtained. We also demonstrate how parameters within the models can be obtained from creep deformation, creep rupture and crack growth experiments.

Pulsed versus continuous wave CO2 laser excisions of 100 oral fibrous hyperplasias: a randomized controlled clinical and histopathological study.

BACKGROUND: In experimental animal studies, pulsing the CO2 laser beam has been shown to reduce the thermal damage zone of excised oral mucosal tissue. However, there is still controversy over whether this is borne out under clinical conditions. OBJECTIVE: To compare the outcome following excisional biopsies of fibrous hyperplasias using a pulsed (cf) versus a continuous wave (cw) CO2 laser mode regarding the thermal damage zone, duration of surgeries, intra- and postoperative complications, postoperative pain sensation, scarring and/or relapse during the initial 6 months. MATERIALS AND METHODS: One hundred Swiss-resident patients with a fibrous hyperplasia in their buccal mucosa were randomly assigned to the cw mode (5 W) or the cf mode (140 Hz, 400 microseconds, 33 mJ, 4.62 W) group. All excisions were performed by one single oral surgeon. Postoperative pain (2 weeks) was recorded by visual analogue scale (VAS; ranging from 0 to 100). Intake of analgesics and postoperative complications were recorded in a standardized study form. The maximum width of the collateral thermal damage zone was measured (µm) in excision specimens by one pathologist. Intraoral photographs at 6-month follow-up examinations were evaluated regarding scarring (yes/no). RESULTS: Median duration of the excision was 65 seconds in the cw and 81 seconds in the cf group (P = 0.13). Intraoperative bleeding occurred in 16.3% of the patients in the cw and 17.7% of the cf group. The median value of the thermal damage zone was 161(±228) µm in the cw and 152(± 105) µm in the cf group (P = 0.68). The reported postoperative complications included swelling in 19% and minor bleeding in 6% without significant differences between the two laser modes. When comparing each day separately or the combined mean VAS scores of both groups between Days 1-3, 1-7, and 1-15, there were no significant differences. However, more patients of the cw group (25%) took analgesics than patients of the cf group (9.8%) resulting in a borderline significance (P = 0.04). Scarring at the excision site was found in 50.6% of 77 patients after 6 months, and more scars were identified in cases treated with the cf mode (P = 0.03). CONCLUSIONS: Excision of fibrous hyperplasias performed with a CO2 laser demonstrated a good clinical outcome and long-term predictability with a low risk of recurrence regardless of the laser mode (cf or cw) used. Scarring after 6 months was only seen in 50.6% of the cases and was slightly more frequent in the cf mode group. Based on the findings of the present study, a safety border of 1 mm appears sufficient for both laser modes especially when performing a biopsy of a suspicious soft tissue lesion to ensure a proper histopathological examination.

A novel tool in laryngeal surgery: preliminary results of the picosecond infrared laser.

OBJECTIVES/HYPOTHESIS: Conventional lasers ablate tissue through photothermal, photomechanical, and/or photoionizing effects, which may result in collateral tissue damage. The novel nonionizing picosecond infrared laser (PIRL) selectively energizes tissue water molecules using ultrafast pulses to drive ablation on timescales faster than energy transport to minimize collateral damage to adjacent cells. STUDY DESIGN: Animal cadaver study. METHODS: Cuts in porcine laryngeal epithelium, lamina propria, and cartilage were made using PIRL and carbon dioxide (CO2) laser. Lateral damage zones and cutting gaps were histologically compared. RESULTS: The mean widths of epithelial (8.5 µm), subepithelial (10.9 µm), and cartilage damage zones (8.1 µm) were significantly lower for cuts made by PIRL compared with CO2 laser (p < 0.001). Mean cutting gaps in vocal fold (174.7 µm) and epiglottic cartilage (56.3 µm) were significantly narrower for cuts made by PIRL compared with CO2 laser (P < 0.01, P < 0.05). CONCLUSION: PIRL ablation demonstrates superiority over CO2 laser in cutting precision with less collateral tissue damage.