Effect Of Thermal Damage Research Articles

Experimental Investigations of Thermal Damage for Rocks

As the rocks were composed of many minerals, high temperature might lead to the non-consistent deformation among these components. That was the mechanism of thermal damage. In the present paper, the thermal damage of rocks was investigated under a much broader temperature range until minerals phase transition. The experimental techniques of AE and the internal friction were proven to be the most useful tools to reveal the thermal damage. The affection of thermal damage to Kaiser Effect of temperature and the coupled effects of thermal and mechanical damage were also discussed.

Biomechanical Comparison of Anatomic Trajectory Pedicle Screw versus Injectable Calcium Sulfate Graft-Augmented Pedicle Screw for Salvage in Cadaveric Thoracic Bone

Many salvage options for failed thoracic pedicle screws exist including the use of a different trajectory or the augmentation of the screw with polymethylmethacrylate cement. Although polymethylmethacrylate immediately increases the construct stiffness and the pull-out strength, it may cause bone necrosis, toxin relaxation, and/or neural injury. On the other hand, calcium sulfate bone grafts have a high potential for biologic incorporation and no thermal damage effect. In the current study, polyaxial pedicle screws were first inserted with a straightforward approach on both sides in 17 fresh human cadaveric thoracic vertebrae. The maximal insertion torque for each screw was measured and then the pull-out strengths were recorded. Afterward, these pedicle screws were randomly assigned to be replaced either by graft augmentation or by anatomic trajectory technique for salvage. The graft-augmented screws were placed using the previous holes. The maximum insertional torque for each anatomic trajectory screw was measured. Finally, the pull-out strengths of the revision screws were recorded. The mean maximum insertional torque decreased with the anatomic trajectory salvage technique when compared with the straightforward approach, 0.23 versus 0.38 Nm, respectively (P=0.003). The anatomic trajectory revision resulted in decreased pull-out strength when compared with the pull-out strength of the straightforward technique, 297 versus 469 N, respectively (P=0.003). The calcium sulfate graft augmentation increased the pull-out strength when compared with the pull-out strength of the straightforward technique, 680 versus 477 N, respectively (P=0.017). The mean pull-out strength ratio of revised screw to original was 0.71 for anatomic trajectory and 1.8 for graft-augmented screws, a statistically significant difference (P=0.002).

IN VITRO EXPERIMENT STUDY ON ABLATION PARAMETERS IN FEMTOSECOND LASER-OCULAR TISSUE INTERACTION

In order to apply femtosecond laser technology in ophthalmology, especially in glaucoma treatment, femtosecond laser-ocular tissue interaction research was conducted. Focusing angle, output power, irradiance duration are three important laser parameters for ophthalmic microsurgery. In our work, the relationship of the three different laser parameter versus cutting effect was investigated respectively by an in-vitro experiment using an 800 nm-wavelength 150 fs-pulse-length laser system. This experiment aims to minimize the effects of thermal damage, while at the same time maximizing the speed or quality of the tissue ablation process. The experiment result shows that there is a great potential to optimize the surgical effects using femtosecond laser compared to that using a longer pulse laser.

Effect of thermal damage on optical and structural properties of In 0.08Ga 0.92N/In 0.02Ga 0.98N multi-quantum wells grown by MOCVD

Effects of thermal damage on the optical and structural properties of InGaN/InGaN multi-quantum wells (MQWs) were investigated by using photoluminescence (PL), high-resolution X-ray diffraction (HRXRD), and atomic force microscopy (AFM). The five-period In 0.08Ga 0.92N/In 0.02Ga 0.98N MQWs were grown on sapphire using metalorganic chemical vapor deposition (MOCVD). To investigate the influence of thermal damage on InGaN MQWs, the MQW sample was heated to the high-temperature for p-type GaN layer growth and cooled down and its structural and optical properties were compared with the MQW sample cooled down without high-temperature thermal treatment. The surface morphology of InGaN MQWs changes from a spiral to a step structure after the high-temperature treatment, which is induced by the desorption and the surface migration of In and Ga adatoms during the high-temperature treatment. In HRXRD (0 0 0 4) ω / 2 θ scan, the intensity fringes between high-order satellite peaks disappear, which suggests that the interface quality of InGaN MQWs be also deteriorated by high-temperature treatment. Temperature dependence of PL measurement shows that InGaN MQWs without high-temperature thermal treatment had higher internal quantum efficiency and lower localization effect.

Effect of thermal damage on the in vitro optical and fluorescence characteristics of liver tissues

Thermal energy generated by radio-frequency current or other means may be employed in treating liver tumors by means of thermal coagulation when conventional resection is impossible. Currently, these thermal energy-based therapeutic procedures suffer from the lack of an adequate feedback control system, making it difficult to determine the optimal therapeutic endpoint. In this study, the potential of optical spectroscopy to provide such an objective endpoint for these procedures is presented. Freshly harvested canine liver samples were exposed to 50/spl deg/C, 60/spl deg/C, and 70/spl deg/C water baths for times ranging from 0 to 60 min. Transmission and reflectance were measured from each sample using an integrating sphere and the optical properties of each sample were accordingly derived. Excitation-emission matrices were recorded from the samples using a spectrofluorometer to identify the intrinsic fluorescence characteristics of native and thermally coagulated liver tissues. In addition, fluorescence and diffuse reflectance spectra were separately obtained from the samples prepared using a portable spectroscopic system. Results of this study show that fluorescence and optical properties of liver tissues exhibit clear and consistent changes through the thermal coagulation process. Specifically, the primary peak in the fluorescence spectra from liver tissues shifts from 480 nm in the native state to 510 nm in the fully coagulated state. In addition, a three- to fourfold increase in the absolute intensity of the diffuse reflectance spectra is observed upon complete coagulation of liver tissues. These dynamic spectral features indicate that fluorescence and diffuse reflectance spectroscopy may provide a direct measure of the biochemical and structural changes associated with tissue thermal damage in the liver.

Mechanical properties of GRP composites with localised thermal damage

The effect of thermal damage on the mechanical properties of glass-reinforced polyester (GRP) composites is investigated. GRP panels underwent surface heating to high temperature (750-800° C) in a cone calorimeter to create localised regions of thermal damage having a circular, oval, square, diamond or irregular shape. The size of the heat-affected region ranged from 10% to 100% of the panel width. The heat damage consisted mostly of char from combustion of the polyester matrix and delamination cracks. After heating in the cone calorimeter, the GRP was cooled to room temperature and then the residual tension and compression properties were determined. Increasing the size and depth of the fire damage zone caused reductions to the stiffness and strength of the GRP. It was found that the shape of the heat-damaged region did not affect the mechanical properties. A model is presented for accurately determining the tension and compression properties of composites with localised heat damage of any shape.

TLD-100 glow-curve deconvolution for the evaluation of the thermal stress and radiation damage effects

In this work, the dose response of TLD-100 dosimeters has been studied in a 62 MeV clinical proton beams. The signal versus dose curve has been compared with the one measured in a 60Co beam. Different experiments have been performed in order to observe the thermal stress and the radiation damage effects on the detector sensitivity. A LET dependence of the TL response has been observed. In order to get a physical interpretation of these effects, a computerised glow-curve deconvolution has been employed. The results of all the performed experiments and deconvolutions are extensively reported, and the TLD-100 possible fields of application in the clinical proton dosimetry are discussed.

Migration behaviour of iodine in nuclear fuel

A novel out-reactor method has been further developed for investigating the migration behaviour of fission products in UO 2 nuclear fuel, which allows the effects of thermal diffusion, radiation damage and local segregation to be independently assessed. Tailored concentration profiles of any desired species are first created in the near-surface region of polished samples by ion implantation. The impact of either thermal annealing or simulated fission is then precisely determined by depth profiling with high-performance secondary ion mass spectrometry (SIMS). Comparison of iodine migration in UO 2 wafers that had been ion-implanted to fluences spanning five orders of magnitude has revealed subtle radiation-damage effects and a pronounced concentration dependence for thermal diffusion. At concentrations above ∼ 10 16 atoms/cm 3 much of the iodine became trapped, likely in microscopic bubbles. True thermal diffusion coefficients for iodine in polycrystalline UO 2 have been derived by modelling the low-fluence data.

The “Chunnel” Fire. I: Chemoplastic Softening in Rapidly Heated Concrete

This paper and its companion paper present the main results of an assessment of the fire in the Channel Tunel (the “Chunnel”), which destroyed a part of the concrete tunnel rings by thermal spalling. The study seeks (1) to evaluate the effect of thermal damage (loss of elastic stiffness) and thermal decohesion (loss of material strength) upon the stress state and cracking at a structural level; and (2) to check whether restrained thermal dilatation can explain the thermal spalling observed during the fire. In the present paper, a macroscopic material model for rapidly heated concrete is developed. It accounts explicitly for the dehydration of concrete and its cross-effects with deformation (chemomechanical couplings) and temperature (chemothermal couplings). The thermal decohesion is considered as chemoplastic softening within the theoretical framework of chemoplasticity. Furthermore, kinetics of dehydration, dimensional analysis, and thermodynamic equilibrium considerations show that a unique thermal dehydration function exists that relates the hydration degree to the temperature rise, provided that the characteristic time of dehydration is much inferior to the characteristic time of structural heat conduction. The experimental determination of the thermal dehydration function from in-situ measurements of the elastic modulus versus furnace temperature rise is shown from experimental data available from the chunnel concrete. Finally, by way of an example, the proposed constitutive model for rapidly heated concrete is combined with the three-parameter William-Warnke criterion extended to isotropic chemoplastic softening.

Nonlinearities in the bioeffects of ultrasound

Biological effects of ultrasound involve nonlinear phenomena (1) in the propagation of sound itself, (2) in the generation of acoustic cavitation, and (3) in the biochemistry, physiology, and pathology of the biological system. Most nonthermal bioeffects of interest to users of diagnostic ultrasound require acoustic pressures great enough that the wave can become distorted by nonlinear propagation. Under limiting conditions this process can increase the absorption parameter of weakly absorbing media by orders of magnitude and make the absorption parameter of a material such as water as great as the linear absorption coefficient of liver tissue. At low amplitudes the response of the bubbles is dominated by the acoustic pressure. At a critical acoustic pressure, however, the inertia of the surrounding medium becomes controlling. At this threshold of acoustic pressure a 10% or 20% increase in acoustic pressure leads to an increase in the collapse pressure in the bubble by orders of magnitude. The rates of biochemical processes, including denaturation of biological macromolecules, are exponential functions of the temperature. Whether the physical process of heating by ultrasound is linear or nonlinear, this leads to a very strong nonlinear dependence of thermal tissue damage and teratological effects upon the levels of ultrasound.

Light distributions in a port wine stain model containing multiple cylindrical and curved blood vessels.

Knowledge of the light distribution in skin tissue is important for the understanding, prediction, and improvement of the clinical results in laser treatment of port wine stains (PWS). The objective of this study is to improve modelling of PWS treated by laser using an improved and more realistic PWS model. Light distributions are calculated by the Monte Carlo method for various PWS blood vessel configurations, such as single and multiple vessels oriented horizontally, curved vessels, and "vertically" oriented vessels. Various vessel sizes and wavelengths are used. Our modelling confirms the concept of selective photothermolysis; 577nm laser light gives maximal deposited energy at the top side of the blood vessels closest to the skin surface and 585nm gives a more uniform energy distribution in the vessel. In the distribution of deposited energy multiple vessels mutually influence each other, because of "shadowing" of diffuse light. Modelling PWS laser treatments with multiple vessels confirms the need for successive treatments of vessels layer by layer. The use of different wavelengths affects the local deposited energy profiles in the blood vessels. It predicts that the significance of 585nm laser light lies in the uniform energy distribution in the vessels rather than in gain in energy deposition with depth. The calculated light distributions provide a more realistic input for modelling thermal damage effects in PWS laser treatment and modelling of the epidermal response in thermal imaging of the PWS blood vessel structure.

Actively stabilised electro-optic phase modulator

The authors show that a simple undoped LiNbO3 monocrystal may be used as a highly performing electro-optic phase modulator in an actively stabilised holographic recording setup regardless of thermal and optical damage effects. The performance of this modulator in a typical time-averaged holographic interferometry experiment is described.

Dynamics of graphite/epoxy composite under delamination fracture and environmental effects

The purpose of this work was to investigate the dynamics of a graphite/epoxy composite material with delamination fracture under various environmental conditions. Modal testing is proposed as a nondestructive method to evaluate the effects of a delamination crack on the natural frequency and damping ratio. The effects of both thermal damage and moisture content on the graphite/ epoxy composite material were studied. The experimental impulse responses were compared with simulated values. The results show that the fundamental mode dominates the dynamic characteristics and that the delamination crack may decrease the natural frequency, but increase the damping ratio of the specimen. After the specimen was exposed to high temperatures, the stiffness and hence the natural frequency were increased. The damping ratio was decreased significantly after the specimen was subjected to prolonged exposure to a humid environment. From correlation between modal parameters and delamination cracks, it was found that the method of modal analysis was suitable for nondestructive evaluation of composite materials.

Light dosimetry: effects of dehydration and thermal damage on the optical properties of the human aorta: errata

Light dosimetry: effects of dehydration and thermal damage on the optical properties of the human aorta: errata

Light dosimetry: effects of dehydration and thermal damage on the optical properties of the human aorta

The influences of dehydration and thermal damage on in vitro optical properties of human aorta were studied. The absorption coefficient increased by 20-50%, especially in the visible range when at least 40% of total tissue weight was lost as a result of dehydration. The reduced scattering coefficient increased by 10-45% in the visible and 30% to over 150% in the near IR after the tissue samples were heated in a constant temperature water bath at 100 degrees C for 300 +/- 10 s. This study implies that dehydration and protein coagulation during photothermal treatment of tissue are important factors altering optical properties of tissue.

Effect of CO2 laser conization of the uterine cervix on pathologic interpretation of cervical intraepithelial neoplasia

The CO2 laser has become a valuable tool for the treatment of lower genital tract neoplasia. The records of 52 women who underwent CO2 laser cervical conization were analyzed retrospectively to evaluate the effect of tissue thermal damage on histopathologic interpretation. Lesion evaluability, defined by the ability to diagnose neoplasia accurately in the specimen, was satisfactory in only 26 cases; in the other 26, thermal damage was severe enough to preclude accurate diagnosis. A postoperative diagnosis of cervical intraepithelial neoplasia III was made in 17 instances, and microinvasion was suspected but unverifiable in two of these. Two patients had frankly invasive cancer, but vascular space involvement in one could not be evaluated accurately because of thermal damage. Tissue thermal damage sufficient to interfere with accurate histologic evaluation was noted in the majority of laser conization specimens. The value of a conization is both diagnostic and therapeutic. The potential impact of a diagnosis compromised by thermal damage is serious.

Single-mode tapers as ‘fibre fuse’ damage circuit-breakers

The ‘fibre fuse’ thermal damage effect can destroy kilometres of fibre at relatively modest laser powers. A low-loss tapered region strategically placed in a single-mode fibre can act as a thermal circuit breaker, thereby halting the damage propagation and protecting the fibre ‘upstream’ from the taper.

Thermal damage effects on delamination toughness of a graphite/epoxy composite

The effects of overheating AS/3501-6 graphite/epoxy composite material have been examined after exposures in air up to 350°C. Degradation was assessed from measurements of the interlaminar fracture toughness in both Mode I tension and Mode II shear as well as the interlaminar shear strength and hardness. Exposures up to 30 minutes at 225°C and up to 15 minutes at 300°C did not significantly reduce the interlaminar toughness. However, longer exposure at 300°C and short exposures at 350°C produced catastrophic decreases in toughness values, shear strength and hardness. The primary origin of embrittlement was attributed to deterioration of the epoxy as opposed to any fibre or fibre-matrix interfacial weakening.

CO<SUB>2</SUB>レーザーメスと電気メスの比較

The most useful advantage of CO2 Laser scalpel is its hemostatic effect which may enable the dry field operation, therefore, comparison with electroscalpel is quite interesting, while their adverse effect of thermal damage against surrounding tissues cannot be ignored.We performed the comparative study of thermal damage of rat liver minovasculature after cutting with these two instruments by means of total replacement of blood with India ink.

Effect of the Thermal Damage Introduced to GaAs Substrate during the GaAs, (AlGa)As LPE Process

The effect of thermal damage introduced to the substrate surface during the LPE process was studied by photoluminescence (PL) observation at each step of the progressive etching of the epitaxial layers. There were many dark spots and dark regions on the substrate caused by the thermal damages. Most of them were not correlated with dark spots on the epitaxial layers. However, some of them were correlated with those on the epitaxial layers. The experimental result suggests that some threading dislocations of the epitaxial layers are originated at the damaged substrate surface.