Rapid Local Heating Research Articles

Nitric oxide and noradrenaline contribute to the temperature threshold of the axon reflex response to gradual local heating in human skin

The initial skin blood flow response to rapid local heating is an axon reflex, which may be mediated by calcitonin gene-related peptide and substance P released from C-fibres. We investigated the role of nitric oxide (NO) and noradrenaline on the temperature threshold for the axon reflex during gradual local heating. 36 subjects participated in two studies. Using microdialysis, we examined the following interventions: NO synthase inhibition (10 mM N(G)-nitro-L-arginine methyl ester, L-NAME); low-dose NO infusion (1.0 microM sodium nitroprusside, SNP); adrenergic blockade (10 mM bretylium tosylate); and low-dose (0.1 microM) noradrenaline infusion. Laser-Doppler flowmetry was used to measure red blood cell flux. Skin was heated at a rate of 0.1 degrees C min(-1) from 33 degrees C to 40 degrees C. Compared to control skin sites, the axon reflex response was shifted to a higher temperature in 4 subjects in the L-NAME sites (control, 37.0 +/- 0.3 degrees C, n = 16; L-NAME, 39.8 +/- 0.1 degrees C, n = 4; P < 0.001) and absent in 12 subjects. The response was also absent in L-NAME plus low-dose SNP sites and not altered by low-dose SNP infusion alone. Adrenergic blockade, with and without low-dose noradrenaline infusion, also abolished the axon reflex response in all subjects. Low-dose noradrenaline infusion alone shifted the axon reflex to a significantly lower temperature threshold compared to control sites (control, 38.2 +/- 0.5 degrees C; noradrenaline, 37.7 +/- 0.4 degrees C, P < 0.05, n = 5). These results suggest that endogenous NO and noradrenaline contribute to the temperature threshold of the axon reflex response during gradual local heating of the skin.

Development and use of localized arc filament plasma actuators for high-speed flow control

The paper discusses recent results on the development of localized arc filament plasma actuators and their use in controlling high-speed and high Reynolds number jet flows. Multiple plasma actuators (up to 8) are controlled using a custom-built 8-channel high-voltage pulsed plasma generator. The plasma generator independently controls pulse repetition rate (0–200 kHz), duty cycle and phase for each individual actuator. Current and voltage measurements demonstrated the power consumption of each actuator to be quite low (20 W at 20% duty cycle). Emission spectroscopy temperature measurements in the pulsed arc filament showed rapid temperature increase over the first 10–20 µs of arc operation, from below 1000 °C to up to about 2000 °C. At longer discharge pulse durations, 20–100 µs, the plasma temperature levels off at approximately 2000 °C.Modelling calculations using an unsteady, quasi-one-dimensional arc filament model showed that rapid localized heating in the arc filament on a microsecond time scale generates strong compression waves. The results of the calculations also suggest that flow forcing is most efficient at low actuator duty cycles, with short heating periods and sufficiently long delays between the pulses to allow for convective cooling of high-temperature filaments. The model predictions are consistent with laser sheet scattering flow visualization results and particle imaging velocimetry measurements. These measurements show large-scale coherent structure formation and considerable mixing enhancement in an ideally expanded Mach 1.3 jet forced by eight repetitively pulsed plasma actuators. The effects of forcing are most significant near the jet preferred mode frequency (ν = 5 kHz). The results also show a substantial reduction in the jet potential core length and a significant increase in the jet Mach number decay rate beyond the end of potential core, especially at low actuator duty cycles.

Effect of radio wave heating on polar mesospheric clouds

Polar mesospheric clouds (PMC) are composed of dust grains (aerosols) of submicron size at altitudes within 80–90 km. The grains, formed presumably by iced particles nucleated around small meteor dust, acquire electric charges and may change significantly the properties of the ambient ionospheric plasma. The charged dust is believed to be the major cause of the polar mesosphere summer echoes (PMSE). The charge of dust particles is formed by attachment of the free electrons and ions and by photo emission. The dust charge depends on the grain sizes, plasma parameters and the dust material. Recently discovered effect of the radio wave electron heating on PMSE opens new opportunities in PMC studies. We present a dynamical model of local dust charging. Rapid local heating of electrons by the high-power radio wave results in parameter-sensitive modifications of the average dust charge and free-electron density. By monitoring the dynamics of free electron density during variable radio wave heating, parameters of dusty plasma, such parameters as mean particle size, dust density properties of material, rates of photo detachment and photo ionization/detachment can be deduced.

Quasilinear relaxation of a low-density electron beam in a plasma

The quasilinear relaxation of a low-density electron beam under the action of plasma turbulence, which is generated during the development of a beam instability, when the beam is formed due to rapid local electron heating (acceleration) is analyzed in the one-dimensional approximation. It is shown that quasilinear diffusion results in the formation of a local plateau at the top of the electron distribution function without causing any significant spread in velocities of the beam electrons and that the relaxation process proceeds primarily through the spatial expansion of electrons with different velocities.

A quantitative comparison of theory and experiments on high intensity focused ultrasound (HIFU) induced heating in a vascularized tissue phantom

High intensity focused ultrasound (HIFU) can be used to help control bleeding, both from individual blood vessels as well as from gross damage within the capillary bed. The dominant mechanism is rapid localized heating, and vascularity limits ones ability to elevate the temperature of blood vessels owing to convective heat transport. To better understand HIFU-induced heating in tissues with vascular structure, we employ a numerical scheme that couples models for ultrasound propagation, acoustic streaming, ultrasound heating, and blood cooling in Newtonian viscous media. We coordinate the theoretical effort with a series of in vitro experiments employing nonuniform flow-through tissue phantoms and designed to provide a ground truth verification of the model predictions. Calculated and measured results are compared over a range of parameter values (insonation pressure, insonation time, and flow rate). We demonstrate excellent agreement between predictions and measurements, and the simulations are extended to a study of the efficacy of HIFU in producing temperature elevations in large and small blood vessels. [Work supported by DARPA and the U.S. Army.]

Computer Predictions of Thermo-Mechanical Behavior and Residual Stresses during Induction Hardening of Notched Cylinder

This study reports computer predictions of the thermo-mechanical behavior and residual stresses during the quenching process of the notched cylinder of steel material with local rapid heating by induction method. The computer simulation is based on the metallo-thermo-mechanical theory and finite element analysis coupled temperature, phase transformation and stress/strain fields. From this research, we can know that the compression residual stresses with a large level be formed on the surface of the part by using quenching with induction heating process.

Pulsed laser recording of gratings in SiO-Cu quantum dot thin films

Interference patterns are written by two intersecting pulsed laser beams in thin films composed of Cu quantum dots in SiO glass. The rapid local optical heating of the metal clusters forming the quantum dots in the glass film results in the writing of patterns in the thin film. The high cluster temperatures attained drive the selective growth of the larger quantum dots and also result in a stress induced peeling of the film from the substrate. Estimates of the kinetics of the selective quantum dot growth agrees well with experimental observations.

Pulsed-laser induced transient phase transformations at the Si–H2O interface

Phase transformations at the Si–H2O interface, induced by nanosecond pulsed laser irradiation, were studied in real time. Si samples were irradiated using a 4 ns pulse from a Q-switched frequency-doubled Nd:YAG laser while immersed in the transparent liquid. Using time-resolved conductivity and reflectivity techniques, in combination with modeling of optical parameters and heat flow, transient processes in the Si, the H2O, and at the interface have been unraveled. In the liquid, local rapid heating occurs as a result of heat flow across the interface, and formation of a low-density steam phase occurs on a nanosecond timescale. Expansion of this phase is followed by a collapse after 200 ns. These rapid phase transformations in the water initiate a shock wave with a pressure of 0.4± 0.3 kbar. Transient phase transformations and the heat flow into the water during the laser pulse influence the energy coupling into the sample, resulting in an effective laser pulse shortening. The pulse shortening and the additional heat flow into the water during solidification result in a 30% enhancement of the solidification velocity for 270 nm deep melts. Cross-section transmission electron microscopy data reveal that the Si surface is planar after irradiation and is inert to chemical reactions during irradiation. Recent experiments described in the literature concerning pulsed-laser induced synthesis at the solid-liquid interface are reviewed and discussed in the context of the fundamental phenomena presently observed.

Adsorption and desorption of CO and H 2 on Rh(111): Laser-induced desorption

Isosteric heats of adsorption Δ H ad of CO and sticking coefficients S for CO and H 2 on Rh(111) are determined by laser-induced thermal desorption (LITD) in which a pulsed laser beam is focused onto the surface, and rapid local heating yields a desorption signal that is proportional to the adsorbate coverage θ. Δ H ad for CO falls from 32.0±2 kcal/mol at low coverage to 14 kcal/mol at saturation, and the desorption pre-exponential factor v d decreases from 10 14±0.5 to 10 10 s -1. Δ H ad, v d, and S of CO all decline sharply above θ = 0.2, corresponding to the occupation of a second binding state. Sticking coefficients for CO and hydrogen indicate precursor intermediates in adsorption.

急速加熱，冷却による硬質鋼の切断に関する研究 ＩＩＩ 急熱急冷により軸受鋼丸棒に発生する応力の弾塑性解析

The authors' method for breaking a high carbon steel rod into billets is characterized by a process in which cross-sectional cracks develop from a slight peripheral notch by rapid local heating and cooling.In the previous paper, the residual stress distribution in the notched or cracked section of SUJ-2 notched specimen was calculated by F.E.M., based on the measured residual stress distribution of the unnotched specimen caused by rapid heating and cooling. And it was shown that the length of cracks developing in actual rod breaking tests could be precisely estimated by comparing the calculated distribution of residual stress after cooling near the crack tip in the notched section of the specimen with the true fracture strength of material. However, in this rod breaking method, crack development was found to occur during cooling.In the present study, the change of stress distribution in the central cross-section of the unnotched specimen was examined with the lapse of time during heating and cooling in order to clarify the stress at crack initiation. Elastic-plastic FEM analysis was adopted for the specimens subjected to the heating and cooling conditions including the optimum one for breaking notched SUJ 2 φ 55 rods by a single heating process.The results obtained are summarized as follows.(1) The stress of specimen during heating was compressive near the surface and tensile at the core in both axial and tangential directions. During cooling, the stress at the surface layer changed to tensile, the compressive stress adjacent to the surface layer remained, and the tensile stress at the core gradually changed to compressive. The tensile stress at the surface layer of specimens under the optimum heating condition was higher in value and present in the deeper portion than those under other conditions.(2) The period when the crack started to develop in the actual rod breaking coincided with the calculated lapse of time when the stress at the surface layer reached the highest and deepest level.

急熱急冷後，丸鋼の加熱中央断面に生ずる残留応力分布 環状切欠き試料の計算結果と切断実験におけるき裂長さ

In the previous paper, the authors' method for breaking high carbon steel rod into billets was introduced, in which a cross-sectional crack was developed from a slight sharp peripheral notch of the rod by rapid local heating and cooling. Furthermore, the hardness and residual stress distributions of unnotched specimens of high carbon chromium steel (SUJ 2) were measured after they were subjected to local treatment under various heating and cooling conditions including optimum ones for breaking notched rods.In the present study, the residual stress distribution in the notched section of SUJ 2 specimens caused by local rapid heating and cooling was evaluated by FEM calculations based on the assumption that the heat-treated state is substantially the same between the unnotched and notched specimens. First, the measured residual stress distribution in the unnotched specimen was reproduced in the unnotched FEM model in which local initial strain distribution was properly given. Secondly, the same local initial strain distribution was applied to the FEM model having a notch or crack extending from the notch root.The crack lengths developed in the actual rod breaking tests were discussed in relation to the residual stress distribution calculated using the notched FEM model as well as the mechanical properties of rods.The results obtained are as follows.(1) The distribution of axial residual stress measured in the unnotched specimen was satisfactorily reproduced by giving a reasonable local initial strain distribution to FEM model.(2) The calculated residual tensile stress in the axial direction near the notch root was relatively higher and more deeply distributed under conditions causing cracks than under those not causing cracks.(3) The breaking tests of SUJ 2 rods showed that cracks propagated to the depth where the calculated axial stress at 0.1mm depth from crack tip (σeff) comes down to a value nearly equal to the net breaking strength of the rods (σt).

Analysis of Hot Tension Test Data To Obtain Stress-Strain Curves to High Strains

Abstract High strain rate hot tension tests have been carried out on AISI 1020 (Unified Numbering System [UNS] G10200) steel using a Gleeble® testing machine. Tests have been terminated at a series of strains and the specimen geometries measured. From these measurements, local areas, strains, and strain rates are derived and are used to obtain the local true stress-true strain curves. These are corrected for the change in strain rate with strain using an equation of state. The corrected curves are in good agreement with published curves on similar steels determined by compression or torsion testing. Under the present testing conditions, the maximum strain to which correction can be applied is ∼ 1.5. This is imposed by the onset of rapid local deformation heating. Up to this strain, no stress correction of the Bridgmann type for necking appears to be necessary.

Thermographic investigation of high-power ultrasonic heating in materials

Results are reported on the use of an infrared thermovision imaging system to observe the surface temperature distribution caused by the application of high-power 20 kHz ultrasound to a variety of metal specimens and one fluoroplastic. Temperature increases of the order of 200°C were found to occur 20 to 30 s after initiation of insonation in resonant specimens of fine-grained polycrystalline brass, copper, and steel. Observation of extremely rapid temperature increases localized to the points of attachment of thermocouples to the test specimens casts strong doubt on all previous thermocouple temperature measurements made during similar experiments by earlier investigators. Fatigue cracks, artificially induced defects, and grain boundaries were also found to be sites of rapid localized heating during insonation.

Physical Driving Forces and Models of Coronal Responses (Invited Paper)

The reasons for nonstationary hydrodynamic flows in solar atmospere are reviewed. It is emphasized that a rapid local heating of corona or upper chromosphere can scarcely provide a very large mass of solar plasma ejections observed in corona and interplanetary space. We suggest that coronal transients and interplanetary ejections are produced by magnetic field evolving in solar atmosphere. Magnetic reconnection in current sheets can play essential role in this process. The suitable approximation of strong magnetic field is formulated. Some solutions of MHD equations in this approximation are demonstrated. Their applications to coronal conditions are discussed.

Trans-Varestraint試験法による溶接金属の凝固割れ感受性の研究(1)

In fusion welding of constructional ferrous and non-ferrous materials solidification cracking frequently occurs in the weld metal when a great deal of distortion and shrinkage takes place in the parent and weld metals due to a local rapid weld heat cycle. The occurrence of this solidification cracking, which is a kind of hot cracking, often gives rise to serious problems for some constructional materials from a view-point of weldability.Meanwhile those constructional materials including commercially pure metals have a brittleness temperature range during solidification whose ductility is very low to cracking.The properties in the solidification brittleness range such as temperature difference, minimum ductility and shape of ductility curve depend upon the kind and amount of impurities or alloying elements in the materials. Increasing the temperature interval and decreasing the minimum ductility are considered to increase the susceptibility of solidification cracking for the material in general.Unfortunately, however, there are few reports, so far, concerning the properties in the solidification brittleness range during welding of the constructional materials in spite of their close relation to solidification cracking.In this report authors have firstly investigated the nominal susceptibility of solidification cracking during TIG arc bead-on-plate welding for various constructional materials of carbon steels, low alloy high tensile strength steels, austenitic stainless steels, aluminum and aluminum alloys and brass, using the Trans-Varestraint Tester which was modified from the original Varestraint. Secondly, utilizing the relationship between the maximum crack length occurring in the center of weld metal with the Trans-Varestraint Test and the temperature distribution during welding which was actually measured, the properties of the solidification brittleness range have been investigated for the weld metals of the materials.Lastly, authors have proposed new indices, the critical strain rate for temperature drop (CST), which reasonably evaluates the solidification crack susceptibility of material during welding and the critical strain rate to time (CSS), which is easy to measured and is substituted for (CST) under a limited condition.