Local Thermal Processes Research Articles

Conditions of Gravitational Instability in Protoplanetary Disks

Abstract Gravitational instability is one of the considerable mechanisms to explain the formation of giant planets. We have studied the gravitational stability in protoplanetary disks around a protostar. The temperature and Toomre's $ Q$ value were calculated by assuming local equilibrium between viscous heating and radiative cooling (local thermal equilibrium). We assumed a constant $ \alpha$ viscosity and used a cooling function with realistic opacity. Then, we derived the critical surface density, $ \Sigma_{\rm {c}}$ , that is needed in order for a disk to become gravitationally unstable as a function of $ r$ . This critical surface density, $ \Sigma _{\rm c}$ , is strongly affected by the temperature dependence of the opacity. At a radius of $ r_{\rm c}$$ \sim$ 20 AU, where ices form, the value of $ \Sigma _{\rm c}$ changes discontinuously by one order of magnitude. This $ \Sigma _{\rm c}$ is determined only by a local thermal process and the criterion of gravitational instability. By comparing a given surface density profile with $ \Sigma _{\rm c}$ , one can discuss the gravitational instability of protoplanetary disks. As an example, we discuss the gravitational instability of two semianalytic models for protoplanetary disks. One is a steady state accretion disk, which is realized after viscous evolution. The other is a disk that has the same angular-momentum distribution as its parent cloud core, which corresponds to the disk that has just formed. As a result, it is found that the disk tends to become gravitationally unstable for $ r$$ \ge$$ r_{\rm c}$ because ices make the disk temperature low. In a region closer to the protostar than $ r_{\rm c}$ , it is difficult for a typical protoplanetary disk to fragment because of the high temperature and the large Coriolis force. Based on this result, we conclude that fragmentation near the central star is possible, but difficult.

Study on Microstructure and Performance of Heat Affected Zone about Friction Forming Hole

With equipment renewal of machining and people's demand on the green environmental protection sustainable development, green processing technology of mechanical processing process in mechanical field is becoming a development direction. The traditional method of processing hole removes a part of the general hole sheet metal, so that the depth of the hole is equal with the thickness of the board. In this paper, the new technological process to form deep hole on relative thin panel by friction heat not only saves material, but also saves man-hours, and the workpiece has a good piece of assembly. Because the processing technic is belong to local thermal processing, the microstructure and property (hardness) of heat affected zone are studied in this paper. The study results are useful to look for more appropriate machining parameters, and laid a foundation for further research on forming deep holes process on thin sheet metal by friction heat.

Direct simulation Monte Carlo on thermal distribution of rarefied gas under heated atomic force microscope nanoprobe

Heated atomic force microscope (AFM) nanoprobe is an attractive instrument for highly local thermal processing. The gases between the nanoprobe and the sample surface exhibit different behaviors from the macroscopic gases due to the nanoscale probe-sample distance. In this paper, the thermal conduction of rarefied gases heated by an AFM nanoprobe is investigated by means of the direct simulation Monte Carlo method. The heat reservoir of AFM nanoprobe consists of a heater platform and a nanotip. The effects of heater platform and nanotip on the gas heat transfer are analyzed. It is found that both the size of heater platform and the geometry of nanotip have noticeable influence on the heat flux density distribution and the spatial resolution on the sample surface. The results show that a spatial resolution of a few tens of nanometers can be achieved by the hot AFM nanoprobe and the power provided to the spatial scale can be at an order of 10−8 W. It is also found that a sample surface can be efficiently heated locally without the contact of the nanoprobe and sample, thus alleviating the wear between them and improving the system reliability. The work provides an insight for rational design and optimization of the heated nanoprobe/surface configuration-based systems for topography applications.

VLT-ISAAC 3–5 μm spectroscopy of embedded young low-mass stars

Aims.We study in this paper the ice composition in the envelope around intermediate-mass class I Young Stellar Objects (YSOs).Methods.We performed a spectroscopic survey toward five intermediate-mass class I YSOs located in the Southern Vela molecular cloud in the L (2.85–4.0 μm) and M (4.55–4.8 μm) bands at resolving powers –800 up to 10 000, using the Infrared Spectrometer and Array Camera mounted on the Very Large Telescope-ANTU. Lower mass companion objects were observed simultaneously in both bands.Results.Solid HO at 3 μm is detected in all sources, including the companion objects. CO ice at 4.67 μm is detected in a few main targets and one companion object. One object (LLN 19) shows little CO ice but strong gas-phase CO ro-vibrational lines in absorption. The CO ice profiles are different from source to source. The amount of water ice and CO ice trapped in a water-rich mantle may correlate with the flux ratio at 12 and 25 μm. The abundance of H2O-rich CO likely correlates with that of water ice. A weak feature at 3.54 μm attributed to solid CHOH and a broad feature near 4.62 μm are observed toward LLN 17, but not toward the other sources. The derived abundances of solid CHOH and OCN- are ~% and ~% of the HO ice abundance respectively. The HO optical depths do not show an increase with envelope mass, nor do they show lower values for the companion objects compared with the main protostar. The line-of-sight CO ice abundance does not correlate with the source bolometric luminosity.Conclusions.Comparison of the solid CO profile toward LLN 17, which shows an extremely broad CO ice feature, and that of its lower mass companion at a few thousand AU, which exhibits a narrow profile, together with the detection of OCN- toward LLN 17 provide direct evidences for local thermal processing of the ice.

Discrimination study on fluid-rock interaction between metallogenic and non-metallogenic sections in a shear zone

Discriminations in a local chemical, fluidal, mechanical and thermal processes in a shear zone will lead to metallogenic differentiation in a local section. This paper, based on the general geological setting of the Shibangou gold deposit in Xixia, Henan, deals with petrological and petrochemical samples of altered rocks in the metallogenic section and of mylonites in the non-metallogenic section of a selected shear zone. The discriminations in fluid-rock interaction and petrological mass balance between altered rocks near the orebody and mylonites in the shear zone are discussed as well. The results show that the petrological volume of altered rocks in the metallogenic section of the shear zone is almost always dilatant and the mylonite volume in the non-metallogenic section is almost always lost. Major elements in altered rocks from the metallogenic section and in mylonites from the non-metallogenic section always show a tendency of being enriched and depleted, respectively. Fluid-rock ratios in the mylonites (Nu=93.68−468.40) are larger than those of the altered rocks (Nc (IV) 3 =36.11−216.67). The gain and loss of major and trace elements from the altered rocks and mylonites in the shear zone are a composite process to be imported and exported by percolating fluids as well as of the loss and dilatancy of rock volume.

Bleaching of bacteriorhodopsin by continuous light

A new two step photobleaching process is observed under continuous illumination of bacteriorhodopsin. This photobleaching is considerable even at physiological temperatures and becomes large at 50–60°C. The photobleaching also increases with increasing pH from 7 to 10. We suggest that the bleaching at its final stage could be due to the dissociation of the retinal and a local thermal denaturation-like process. These facts may question the generally held belief that BR is a stable protein in vivo for a long period of time. Our results may have relevance also to practical applications of bacteriorhodopsin where the stability of bacteriorhodopsin is a key issue. In certain instances, the use of bacteriorhodopsin may require cooled conditions. Here, we defined the conditions under which bacteriorhodopsin is stable. The permanent photobleaching offers a new way of picture imaging and information input for bacteriorhodopsin-based optical devices.

The impact of the Black Sea on the local thermal and baric processes in the atmosphere

Relying on Shuleikin’s theory, defining the relationship between the elements of the temperature and air pressure fields, the paper provides numerical characteristics of the cyclone evolving into a hurricane on 15 November 1992. Calculated is the trade wind-induced circulation component for the western section of the Black Sea during the period of autumn-winter-time cooling of waters. The paper examines specific features of the north-west storms, Crimean bora, and breeze-induced circulation in the region.

The growth of density perturbations in radiative shocks

The paper presents a new investigation of the growth of thermal instabilities behind radiative shocks. The analytic and numerical results disagree with McCray, Stein, and Kafatos, who were attempting to explain the filamentary structure commonly seen in supernova remnants, and proposed that the growth of density perturbations would lead to gross condensations in the postshock cooling region. Hydrodynamical simulations are generated which corroborate arguments in favor of no growth in the long-wavelength limit. These simulations also agree with a renewed analytic approach in the short-wavelength limit, and show that the region of rapid growth will remain inconspicuous in the overall density rise toward the back of the shock. It is noted that these calculations are in accord with some recent observations of supernova remnants where the observed filaments do not seem to have been produced by any local thermal instability process.

Grain growth within a contracting interstellar cloud

The contraction of an initially isothermal interstellar cloud of about 700−3M⊚ at a temperature of 20 K and a central density of 103 atoms.cm was followed for about 106 years taking into consideration: (i) local thermal processes, (ii) molecular hydrogen formation on grain surfaces, and (iii) grain growth for the three grain models; ice, graphite and silicates of initial grain radius 0.15μ.

Unstable and Damped Equatorial Modes in Simple Coupled Ocean-Atmosphere Models

Abstract Free equatorial modes for several simple coupled ocean-atmosphere models are determined. They are found to include unstable and damped modes of large zonal scale and long period. The influence of ocean thermo-dynamics on unstable modal behavior is systematically explored. The Model I ocean features a local thermal equilibrium. In Model II, linearized temperature advection is the sole ocean thermal process. The Model III ocean features both advective and local thermal processes, while that of Model IV features only local thermal processes. The ocean and atmosphere are each represented by linear shallow water equations on the equatorial β-plane, and are linked by traditional couplings. A finite difference method with variable resolution is used to find eigenvalues and eigenvectors of the coupled systems. Key results are checked via a series method. Ocean modes are influenced most strongly by coupling, and are damped or destabilized depending on the configuration of induced atmospheric motion relati...

Plasma measurements in the Venus near wake

A study of the plasma measurements conducted with the Mariner 5, Venera 9 and 10, and the Pioneer Venus spacecraft in the Venus ionosheath and near wake is presented. The data available indicate that in the inner ionosheath, downstream from the terminator, the density and the velocity of the plasma are significantly smaller than those measured further outside. The slower particle fluxes detected near the ionopause also exhibit higher plasma temperatures and show a tendency to move towards the nightside hemisphere. The observation of high plasma temperatures in the inner ionosheath indicates that the interaction of the solar wind with the Venus ionospheric/exospheric material is dominated by dissipative phenomena, and that its entry into the wake is due to local thermal expansion processes.