Thermal sensitivity of Ehrlich ascites cancer cells forming colonies in agar cultures in diffusion chambers

Thermosensitivity of clonogenic ascites Ehrlich carcinoma cells (AEC), forming colonies in agar cultures in diffusion chambers was studied when heating them in vitro at 41-44 degrees C. The clonogenic cells of AEC are shown not to essentially differ both in the colony-forming efficiency (CFE) and in the proliferative status on the 3rd and 7th days. No essential differences are revealed in thermosensitivity of such cells. The heating time-survival curves are exponential or S-shaped with a small "shoulder". The temperature increase by 1 degree C resulted in a 2-2.5-fold decrease in the time of effective hyperthermia treatment. The values of D0 for cells treated with 42 degrees C in different experiments varied from 20.1 min to 24.6 min. Only one type of thermal damage reaction with the energy of inactivation about 150 kcal/M was observed in AEC cells in the temperature range studied.     

Rapid electromagnetic warming of cells and tissues

We describe a system for thawing frozen cell suspensions and tissues by electromagnetic absorption. A 25-ml sample is heated in a cylindrical resonant cavity, which is excited in three modes all close to 434 MHz. Maximum warming rates are over 10 degrees C/s (600 C/min), and a frozen sample may be brought from -65 degrees C to room temperature in < 30 s, with final spatial differences of < 20 degrees C. Samples may be frozen externally, or cooled within the cavity at typically 1 degree C/min. We have also used the resonant cavity to measure the permittivity and conductivity of the sample at temperatures from -83 degrees C to +8 degrees C. By measuring the heat capacity of the sample, we have calculated the power deposited in it as a function of its temperature. The system is currently being used to investigate the effect of warming rate on cell survival.     

Temperature-tunable 3.5 mu m fibre laser

Use of a Peltier element permits adjustment of fibre temperature over the range 5-41 degrees C, providing a tuning range of 30 nm for the 3.5 mu m laser. In this temperature range the laser emits nearly 1 mW at 130 mW pump power.<>     

Changes in birefringence as markers of thermal damage in tissues

Light microscopy using polarized transmission illumination of routinely stained histologic sections shows changes of the native birefringence of certain tissue constituents when heated by laser irradiation or electrosurgical current. The naturally occurring birefringence of cardiac muscle disappears permanently when the muscle is frozen, thawed, and heated to temperatures in excess of 42 degrees C in vitro. This loss of birefringence is produced with temperatures at which other morphologic thermal changes are hard to detect; thus, it is a low-temperature tissue marker which can be used to observe the extent of thermal damage in tissues. Partial loss of the native birefringence of collagen occurs in canine urinary bladder coagulated by laser irradiation and pericardium heated with electrodes. In addition, thermally coagulated collagens have variable birefringence color shifts when compared to the adjacent unaffected collagens in stained histologic sections. The gradual birefringence color changes are seen at tissue temperatures higher than those at which the thermally induced hyalinization (coagulation) of collagen usually occurs (about 60-70 degrees C), but below those at which carbonization is seen (200+ degrees C). Birefringence changes can be measured to test mathematical models of thermal damage necessary for development of dosimetry models in medical applications of laser irradiation.     

Titanium silicide contacts on semiconducting diamond substrates

Titanium silicide contacts have been deposited on semiconducting (p-type) natural diamond substrates by the codeposition of silicon and titanium by electron-beam evaporation. Current-voltage (I-V) measurements conducted at room temperature have demonstrated rectifying characteristics. Consistent with the observed small turn-on voltage, the corresponding I-V measurements recorded at 400 degrees C exhibit ohmic-like behaviour. However, on subsequent annealing of the titanium silicide contacts at 1100 degrees C in a vacuum of approximately 10/sup -6/ Torr for 30 min, stable rectifying I-V characteristics were observed in the 25-400 degrees C temperature range.<>     

High frequency electromagnetism, heat transfer and fluid flow coupling in ANSYS multiphysics.

The goal of this study was to numerically predict the temperature of a liquid product heated in a continuous-flow focused microwave system by coupling high frequency electromagnetism, heat transfer, and fluid flow in ANSYS Multiphysics. The developed model was used to determine the temperature change in water processed in a 915 MHz microwave unit, under steady-state conditions. The influence of the flow rates on the temperature distribution in the liquid was assessed. Results showed that the average temperature of water increased from 25 degrees C to 34 degrees C at 2 l/min, and to 42 degrees C at 1 l/min. The highest temperature regions were found in the liquid near the center of the tube, followed by progressively lower temperature regions as the radial distance from the center increased, and finally followed by a slightly higher temperature region near the tube's wall corresponding to the energy distribution given by the Mathieu function. The energy distribution resulted in a similar temperature pattern, with the highest temperatures close to the center of the tube and lower at the walls. The presented ANSYS Multiphysics model can be easily improved to account for complex boundary conditions, phase change, temperature dependent properties, and non-Newtonian flows, which makes for an objective of future studies.     

Thermal elevation in the human eye and head due to the operation of a retinal prosthesis

An explicit finite-difference time-domain formulation of the bio-heat equation is employed with a three-dimensional head eye model to evaluate the temperature increase in the eye and surrounding head tissues due to the operation of the implanted stimulator IC chip of a retinal prosthesis designed to restore partial vision to the blind. As a first step, a validation of the thermal model and method used is carried out by comparison with in vivo measurements of intraocular heating performed in the eyes of dogs. Induced temperature increase in the eye and surrounding tissues is then estimated for several different operational conditions of the implanted chip. In the vitreous cavity, temperature elevation of 0.26 degrees C is observed after 26 min for a chip dissipating 12.4 mW when positioned in the mid-vitreous cavity while it is 0.16 degrees C when the chip is positioned in the anterior portion between the eye's ciliary muscles. Corresponding temperature rises observed on chip are 0.82 degrees C for both the positions of the chip. A comprehensive account of temperature elevations in different tissues under different operational conditions is presented.     

Hepatic radiofrequency ablation with internally cooled probes: effect of coolant temperature on lesion size

Radiofrequency (RF) ablation is a minimally invasive method for treatment of primary and metastatic liver tumors. One of the currently commercially available devices employs an internally cooled 17-gauge needle probe. Within the probe, cool water is circulated during ablation, which cools tissue close to the probe resulting in larger lesions. We evaluated the effect of different cooling water temperatures on lesion size. We created a finite-element method model, simulated 12 min impedance-controlled ablation and determined temperature distribution for three water temperatures. Lesion diameters in the model were 33.8, 33.4, and 32.8 mm for water temperatures of 5 degrees C, 15 degrees C, and 25 degrees C, respectively. We solved a simplified model geometry analytically and present dependence of lesion diameter on cooling temperature. We further performed ex vivo experiments in fresh bovine liver. We created four lesions for each water temperature, with the same water temperatures as used in the finite-element method (FEM) model. Average lesion diameters were 28.3, 30, and 29.5 mm for water temperatures of 5 degrees C, 15 degrees C, and 25 degrees C, respectively. Water temperature did not have a significant effect on lesion size in the ex vivo experiments (p = 0.76), the FEM model, and the analytical solution.     

Implication of blood flow in hyperthermic treatment of tumors

Tumor blood flow varies significantly depending on the type, age, and size of tumors. Furthermore, the distribution of blood perfusion in tumors is quite heterogeneous. Blood flow in tumors may or may not be greater than that in the surrounding normal tissues at normothermic conditions. When heated at 41-430C, tumor blood flow either remains unchanged or increases slightly, usually by a factor of less than 2. The newly formed tumor vessels appear to be so vulnerable to heat that the blood flow decreases at 42-43' C in most of the animal tumors studied so far. By contrast, the blood flow in normal tissues, e. g., skin and muscle, increases by a factor of 3-20 upon heating at 42-450C. Consequently, the heat dissipation by blood flow becomes greater in normal tissues than in tumors during heating, and thereby a greater temperature rise in tumors may occur, resulting in greater damage in tumor relative to normal tissues. The intrinsically acidic intratumor environment becomes further acidic upon heating and accentuates the thermal damage on the tumor cells. Blood perfusion appears to be implicated in such a heat-induced increase in the intratumor acidity.     

Continuous wave visible InGaP/InGaAlP quantum well surface emitting laser diodes

Vertical cavity top surface emitting lasers in the 0.66 mu m visible spectral region were fabricated by the metal-organic chemical vapour deposition technique. The continuous wave threshold currents I/sub th/ are 3.9 and 4.6 mA at -75 and -25 degrees C, respectively, for 15 mu m diameter devices. The lasers can also be operated at room temperature, but only in a pulsed mode with an I/sub th/ of 12 mA at 25 degrees C.<>     

Infrared fibers for radiometer thermometry in hypothermia andhyperthermia treatment

Hypothermia is a condition which results from prolonged exposure to a cold environment. Rapid and efficient heating is needed to rewarm the patient from 32-35 degrees C to normal body temperature. Hyperthermia in cancer treatment involves heating malignant tumors to 42.5-43.0 degrees C for an extended period (e.g., 30 min) in an attempt to obtain remission. Microwave or radio frequency heating is often used for rewarming in hypothermia or for temperature elevation in hyperthermia treatment. One severe problem with such heating is the accurate measurement and control of temperature in the presence of a strong electromagnetic field. For this purpose, we have developed a fiberoptic radiometer system which is based on a nonmetallic, infrared fiber probe, which can operate either in contact or noncontact mode. In preliminary investigations, the radiometer worked well in a strong microwave or radiofrequency field, with an accuracy of +/- 0.5 degrees C. This fiberoptic thermometer was used to control the surface temperature of objects within +/- 2 degrees C.     

Microstructural characterization of damage in thermomechanically fatigued Sn-Ag based solder joints

Sn-Ag based solder joints of 100-μm thickness were thermomechanically fatigued between −15°C and +150°C with a ramp rate of 25°C/min for the heating segment and 7°C/min for the cooling segment. The hold times were 20 min at high temperature extreme and 300 min at the low temperature extreme. Surface damage accumulation predominantly consisted of shear banding, surface relief due to Sn-grain extrusion, grain boundary sliding, and grain decohesion usually near the solder/substrate interface. Small alloy additions were found to affect the extent of this surface damage accumulation.     

SEM observation of the insect prepared by microwave irradiation

The ptilinum of the fly and the compound eye are among the most fragile organs encountered during conventional procedures of morphological sample fixation. In order to identify a fixative suitable for preparing such samples for scanning electron microscopy, we examined various fixation conditions using microwave irradiation (MWI). The conditions examined were: (i) fixatives; (ii) temperature; (iii) concentration; (iv) duration; (v) dehydration; and (vi) substitution. The identified optimal conditions were 5% glutaraldehyde with MWI (350 W, 5 min). The MWI was continued until the maximal temperature of 75 degrees C was attained, followed by intermittent irradiation to maintain a temperature of 75 degrees C. After irradiation, the sample was left at room temperature for 24 h in the fixative and then dehydrated in increasing concentrations of ethanol. Each step in the ethanol series lasted for 24 h. The final absolute ethanol step included three solution changes, with each incubation lasting 1 h. A subsequent stepwise substitution of t-butyl alcohol for ethanol was conducted by reducing the ratio of 100% ethanol to t-butyl alcohol from 2:1 to 1:1 and then 1:2 (24 h each). The substitution was completed by three solution changes using 100% t-butyl alcohol, 30 min each. The best results were obtained by freeze-drying samples using t-butyl alcohol. The use of MWI improved fixative permeation, which occurred at a uniform rate throughout the sample. Comparison with temperature in a water bath at 75 degrees C indicated that the fixation effect of MWI was due to its heat generation in addition to some unknown mechanism.     

Recrystallization by annealing in SiC amorphized with Ne irradiation

Alpha-silicon carbide was irradiated with Ne+ ions at room temperature to various fluences up to 7.5 x 10(20) Ne+ m(-2) and then isochronally annealed under observation with a transmission electron microscope. In all cases, thin regions were completely amorphized by irradiation and epitaxial growth occurred from the residual crystalline region by subsequent annealing. Crystal nucleation occurred with annealing at 1000 degrees C in the cases of 3.8 x 10(20) and 7.5 x 10(20) Ne+ m(-2) irradiation, and at 1100 degrees C in the cases of 1.3 x 10(20) and 2.3 x 10(20) Ne+ m(-2) irradiation. Growth or formation of bubbles was observed with annealing at 1000 degrees C after 1.3 x 10(20), 2.3 x 10(20), and 3.8 x 10(20) Ne+ m(-2) irradiation.     

In situ SEM imaging at temperatures as high as 1450 degrees C

Modifications to a scanning electron microscope (SEM) and a commercially available heating stage permits in situ imaging at temperatures as high as 1450 degrees C. Here we report on the technical modifications necessary to allow such high-temperature in situ imaging. In addition, in order to underline the potential of this technique in the field of materials science, three heating-stage experiments are presented, which reveal microstructural changes occurring at high temperature. The respective in situ experiments are: (i) surface crystallization of a cordierite glass at 1050 degrees C; (ii) thermal recovery of asbestos (chrysotile) fibers at 1250 degrees C; and (iii) residual pore-structure evolution of tricalcium phosphate during sintering at 1450 degrees C.     

Hollow sapphire waveguides for remote radiometric temperature measurements

Hollow sapphire waveguide have been successfully employed for remote radiometric temperature measurements over an extended temperature range (30 degrees C to 1650 degrees C). These waveguides not only exhibit an infrared transmission window from 10 to 17 mu m, which permits low temperature blackbody detection, but the sapphire also possesses an intrinsic melting point of 2053 degrees C, enabling their operation in high temperature environments.<>     

Structure,Surface Morphology,and Optical and Electronic Properties of Annealed SnS Thin Films Obtained by CBD

SnS thin films were initially coated onto Pyrex substrates by the chemical bath deposition (CBD) method and annealed at various temperatures ranging from 200°C to 600°C for 30 min in nitrogen gas. X-ray diffraction (XRD) analysis revealed that a structural transition from face-centered cubic to orthorhombic occurs when the annealing temperature is over 500°C. The surface morphology of all thin layers was investigated by means of scanning electron microscopy and atomic force microscopy. The elemental composition of Sn and S, as measured by energy dispersive spectroscopy, is near the stoichiometric ratio. Optical properties studied by means of transmission and reflection measurements show an increase in the absorption coefficient with increasing annealing temperatures. The band gap energy is close to 1.5 eV, which corresponds to the optimum for photovoltaic applications. Last, the thermally stimulated current measurements show that the electrically active traps located in the band gap disappear after annealing at 500°C. These results suggest that, once again, annealing as a post-deposition treatment may be useful for improving the physical properties of the SnS layers included in photovoltaic applications. Moreover, the thermo-stimulated current method may be of practical relevance to explore the electronic properties of more conventional industrial methods, such as sputtering and chemical vapor deposition.     

Tissue cooling and its effect on brightness temperatures by contact-type microwave applicators

Contact of an applicator on the skin surface may cool the tissues so that the resulting brightness temperature measured by the applicator is varied. The tissue cooling effect on the brightness temperature was quantitatively evaluated. From the experimental results, it was concluded that an accurate temperature control was needed in order to reduce the errors in the brightness temperature. A new method of temperature control which permits continuous measurement of the thermal responses of a human body was attempted, and advantages and disadvantages of the method are discussed. The research results may be practical and useful for the accurate measurement of brightness temperature.     

Investigation of polycrystalline silicon layers by electron microscopy and x-ray diffraction

The structure of polycrystalline Si layers deposited by pyrolysis of silane in a hydrogen ambient has been investigated by replica electron microscopy and X-ray diffraction. When the gas flow ratio (SiH₄/H₂) is 3·64 × 10⁻⁴ the temperature region below 900°C is a surface reaction control region and the activation energy of the chemical surface reaction rate is 1·6 eV. The temperature range above 900°C is a mass transfer region and the deposition rate is about 500 Å/min. The grains become larger and the texture of the surface of the poly Si layers becomes coarser with the deposition temperature. Some phase change was found to occur around 900°C by replica electron microscopy. The X-ray diffraction experiments show that there exist three preferred orientations of (220), (111) and (311) in the poly Si layers. The decrease of the relative intensity of the (311) orientation might have a relation to the phase change around 900°C.     

An implantable power supply with an optically rechargeable lithiumbattery

A novel power supply for medical implants has been developed. A wireless near-infrared power transmission recharges a lithium secondary battery in the power supply. A photovoltaic cell array embedded under skin receives near-infrared light through the skin and charges the battery directly powering an implanted device. We have shown that, for a photodiode area of 2.1 cm2, 17 min of near-infrared irradiation at a 810-nm wavelength with a power density of 22 mW/cm2 can send enough energy to allow regular commercial cardiac pacemakers to run for 24 h. The temperature rise of the skin during the light irradiation was 1.4 degrees C.