Thermal pulse

Test Method for Thermal Diffusivity of Carbon and Graphite by a Thermal Pulse Method... 

A thermal pulse cycle is a means of conserving thermal energy in... 

All bodies traveling in a fluid experience dynamic heating, the magnitude of which depends upon the body characteristics and the environmental parameters. Modern supersonic aircraft, for example, experience appreciable heating. This incident flux is accommodated by the use of an insulated metallic structure, which provides a near balance between the incident thermal pulse and the heat dissipated by surface radiation. Hence, only a small amount of heat has to be absorbed by mechanisms other than radiation. 

AGB stars constitute excellent laboratories to test the theory of stellar evolution and nucleosynthesis. Their particular internal structure allows two important processes to occur in them. First is the so-called 3(,ldredge-up (3DUP), a mixing mechanism in which the convective envelope penetrates the interior of the star after each thermal instability in the He-shell (thermal pulse, TP). The other is the activation of the s-process synthesis from alpha captures on 13C or/and 22Ne nuclei that generate the necessary neutrons which are subsequently captured by iron-peak nuclei. The repeated operation of TPs and the 3DUP episodes enriches the stellar envelope in newly synthesized elements and transforms the star into a carbon star, if the quantity of carbon added into the envelope is sufficient to increase the C/O ratio above unity. In that way, the atmosphere becomes enriched with the ashes of the above nucleosynthesis processes which can then be detected spectroscopically. 

Finally we present a comparison of the final surface composition of our model (after ten thermal pulses) and the abundances of LP 625-44 [6] and LP 625-44 [7]. Model abundances are normalized to Ba. 

Fig. 5.19. Evolutionary track in the HR diagram of an AGB model of total mass 0.6 Mq, initial composition (Y, Z) = (0.25, 0.001 Z /20). Heavy dots marked 2 to 11 indicate the start of a series of thermal pulses (see Fig. 5.20), which lead to excursions along the steep diagonal lines. Numbers along the horizontal and descending track indicate times in years relative to the moment when an ionized planetary nebula appears and (in parentheses) the mass of the envelope in units of Mq. R = 0.0285 indicates a line of constant radius (R in solar units) corresponding to the white-dwarf sequence. Shaded areas represent earlier evolutionary stages for stars with initial masses 3,5 and 7 Mq and the steep broken line marks the high-temperature boundary of the instability strip in which stars pulsate in their fundamental mode. The y-axis gives log L/Lq. Adapted from Iben and Renzini (1983).

Fig. 6.4. Schematic view of ingestion during and after a thermal pulse in an AGB star. Pulses appear on an expanded scale owing to their short duration ( ...

Fig. 6.5. Development of the convective region, neutron density from 13C and 22Ne sources and maximum temperature as functions of time during a thermal pulse in a low-mass star with Z Z0/3, which seems to give the best fit to Solar-System abundances from the main s-process. However, more recent models imply that 13C is all used up in the radiative phases. After Kappeler et al. (1990). Courtesy Maurizio Busso and Claudia Raiteri.

Thus the 13 C neutron source (with a little assistance from 22Ne) in thermally pulsing low- and intermediate-mass stars is well established as the chief source of the main component of s-process nuclides in the Solar System. It is not quite clear, however, whether the r0 parameter is something unique, or just the average over a more-or-less broad distribution of values nor is it clear why a similar s-process pattern is seen in stars that are metal-deficient by factors of up to 100 (see Pagel Tautvaisiene 1997). 

The Galactic chemical evolution of heavy neutron-capture elements was studied by Travaglio et al. (1999, 2001) on the assumption that a small pocket of 13C is mixed into the inter-shell zone after the decay of each thermal pulse and generates neutrons supplemented by a small contribution from 22Ne during the next pulse see... 

All stellar evolution can be summed up by a simple rule the star tries to make itself as small as possible. Its life story is one of contraction, but in a discontinuous manner, with sometimes long pauses during which it maintains its size. There are phases when the outer layers are driven off by radiation pressure (stellar winds, ejection of the envelope) and brief periods when the star violently readjusts itself, but without breaking apart (helium flash, thermal pulses). 

Each time the downstream thermistor detects the thermal pulse, it triggers another pulse upstream and the cycle repeats as long as flow continues. Therefore, it monitors the flow rate continuously. In our system, the flow rate was determined to be 0.93 ml/rain when the nominal flow rate was set at 1.0 ml/min with THE as mobile phase operating at 40°C. 

Thermal pulses of the He shell drive the convective mixing of third dredge-up... 

Smith, V. V. and Lambert, D. L. (1990) The chemical composition of red giants. III. Further CNO isotopic and -process abundances in thermally pulsing asymptotic giant branch stars. Astrophysical Journal Supplement, 72, 387—416. 

The recent report by the National Research Council of the National Academy of Sciences entitled "Limitations of Rock Mechanics in Energy Resource Recovery and Development", highlighted some of the problems which must be addressed. The rock strength and other mechanical properties of the media must be understood both under the impact of the thermal pulse represented by the release of heat from decaying radioactive waste materials and the perturbation represented by construction of the mine. The resulting thermal stresses must be understood in developing the layout and the allowable rate of heat generation from the individual canisters. 

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