Values Of Mass Loss Rate Research Articles

Decomposition behavior and kinetics of Beydili and Ihsangazi oil shale deposits (Turkiye) by TG-DTG-MS

This research mainly investigates the decomposition behavior and kinetics of Beydili and Ihsangazi oil shale deposits (Türkiye) by TG-DTG and MS techniques. In the initial stage of the research, geochemical and organic characterization (total organic carbon, rock-eval, fisher assay, x-ray fluorescence, etc.) of the oil shale samples were determined. TG-DTG-MS analyses of the oil shale samples were performed at three different heating rates in an air atmosphere. In all the oil shale samples studied, the TG-DTG curves indicated that the decomposition of oil shale samples followed two successive reaction stages in different temperature intervals, known as pyrolysis and mineral decomposition. In these two stages, reaction intervals, peak temperature, mass loss, derivative mass loss rate values, and gaseous constituent (MS analysis) of oil shale samples are all determined. At the same time, the different combustibility indices, such as the ignition index, combustion index, and reactivity of oil shale samples, are also determined. Also, for each reaction region, activation energy values were calculated using two different model-free methods known as Kissinger - Akahira – Sunose (KAS) and Ozawa - Flynn – Wall (OFW). In pyrolysis and mineral decomposition regions, the activation energy values varied between 73.9 and 186.4 kJ/mol and 103.3–297.1 kJ/mol.

Hydrodynamic disk solutions for Be stars using HDUST

Abstract. In this work, we implemented a hydrodynamical solution for fast rotating stars, which leaves high values of mass-loss rates and low terminal velocities of the wind. This 1D density distribution adopts a viscosity mimicking parameter which simulates a quasi-Keplerian motion. Then, it is converted to a volumetric density considering vertical hydrostatic equilibrium using a power-law scale height, as usual in viscous decretion disk models. We calculate the theoretical hydrogen emission lines and the spectral energy distribution utilizing the radiative transfer code HDUST. Our disk-wind structures are in agreement with viscous decretions disk models.

Thermal degradation characteristics, kinetics and thermodynamics of micron-sized PMMA in oxygenous atmosphere using thermogravimetry and deconvolution method based on Gauss function

Micron-sized poly (methyl methacrylate) (PMMA) with high flammability is widely applied in industries, constructions and transportations. Study on the thermal degradation behaviors of micron-sized PMMA in oxygenous atmosphere, which receives scarce attention to date, can provide valuable guidance for the prevention and mitigation of injuries and damages arising from the micron-sized PMMA dust explosions and fires. In the present study, the thermal degradation characteristics of micron-sized PMMA in air were investigated by thermogravimetry. Deconvolution method using Gauss function coupled with model-free and model-fitting methods was employed to conduct the kinetic modeling. The values of thermodynamic parameters (ΔH, ΔG and ΔS) were estimated. The results indicated that one peak and one shoulder occurred in the mass loss rate (MLR) variations of the micron-sized PMMA degradation in air. The values of MLR at peak and shoulder both decreased with heating rate. Besides, the average value of the MLR varied little with heating rate. The values of MLR at the peak and the average MLR of micron-sized PMMA degradation in air were both less than those of the traditional-sized PMMA degradation in air. The calculated kinetic parameters can be used to well predict the thermal degradation behaviors of micron-sized PMMA in air. Additionally, the micron-sized PMMA in air was easier to decompose than the traditional-sized PMMA in air. Non-spontaneous reactions were involved in the thermo-oxidative degradation of micron-sized PMMA. Besides, with the progressing of thermo-oxidative degradation, less energy was required and pyrolytic products with well-ordered structures may be generated.

Are Ionic Liquids Suitable for Suppressing Coal Spontaneous Combustion?

Due to the reported fact that the active functional groups in coal can be dissolved and destroyed by ionic liquids, it is expected that the spontaneous combustion of coal can be affected from a thermodynamic perspective. However, ionic liquids with different thermal stabilities have distinct influences on coal combustion. Here, the thermal stability of long-flame coal in the presence of five pure ionic liquids ([Bmim][BF4], [Bmim][Ac], [Bmim][NO3], [Hoemim][BF4], and [Pmim][BF4]) was analyzed by thermogravimetric analysis, and the flammability of the raw coal, pure ionic liquids, and coal–IL mixtures (mass ratio of 1:1) were tested using a cone calorimeter according to the indexes of the time to ignition (TTI), mass loss rate (MLR), heat release rate (HRR), total heat release rate (THR), specific extinction area (SEA), and CO production. It is shown that the TTIs of mixtures containing coal-[Bmim][BF4], coal-[Hoemim][BF4], and coal-[Pmim][BF4] are relatively long, and the MLR, HRR, THR, and SEA values are relatively low, indicating that these fluorine-containing ionic liquids have a better flame-retardant effect than the other two fluorine-free ones, which may be ascribed to their similar role to halogen inhibitors. In addition, the endothermic process of [Bmim][BF4], [Hoemim][BF4], and [Pmim][BF4] can reduce the temperature of the coal surface and delay the ignition time of coal. In contrast, the TTI of coal-[Bmim][NO3] and coal-[Bmim][Ac] mixtures is much shorter than that of coal alone, and the MLR, HRR, and THR values are larger. This may be caused by the poor thermal stability of the two nonfluorine ionic liquids that began to decompose and release heat prior to coal, providing a large amount of heat for the low-temperature oxidation of coal and thus accelerating coal oxidation and combustion. Although the F-containing ionic liquids show the ability to inhibit spontaneous combustion of coal to some extent, their organic cations are potentially combustible and release large amounts of heat, smoke, and CO under high temperatures.

Impact of Lithium Salts on the Combustion Characteristics of Electrolyte under Diverse Pressures

The electrolyte is one of the components that releases the most heat during the thermal runaway (TR) and combustion process of lithium-ion batteries (LIBs). Therefore, the thermal hazard of the electrolyte has a significant impact on the safety of LIBs. In this paper, the combustion characteristics of the electrolyte such as parameters of heat release rate (HRR), mass loss rate (MLR) and total heat release (THR) have been investigated and analyzed. In order to meet the current demand of plateau sections with low-pressure and low-oxygen areas on LIBs, an electrolyte with the most commonly used lithium salts, LiPF6, was chosen as the experimental sample. Due to the superior low-temperature performance, an electrolyte containing LiBF4 was also selected to be compared with the LiPF6 sample. Combustion experiments were conducted for electrolyte pool fire under various altitudes. According to the experimental results, both the average and peak values of MLR in the stable combustion stage of the electrolyte pool fire had positive exponential relations with the atmospheric pressure. At the relatively higher altitude, there was less THR, and the average and peak values of HRR decreased significantly, while the combustion duration increased remarkably when compared with that at the lower altitude. The average HRR of the electrolyte with LiBF4 was obviously lower than that of solution containing LiPF6 under low atmospheric pressure, which was slightly higher for LiBF4 electrolyte at standard atmospheric pressure. Because of the low molecular weight (MW) of LiBF4, the THR of the corresponding electrolyte was larger, so the addition of LiBF4 could not effectively improve the safety of the electrolyte. Moreover, the decrease of pressure tended to increase the production of harmful hydrogen fluoride (HF) gas.

Determination of Mass Loss Rate and Smoke Generated of Jordanian Hardwood Timber under Different Flaming Combustion and Limited Ventilation Environment

Natural wood has been used in structural applications for decades. Smoke from wood fires, additives and wood-protective coatings is a cause of death and serious injury in limited ventilation compartment. Ventilation restrictions in modern day designs complicate the combustion process and increase incomplete combustion products due to a reduction in the amount of oxygen available for fuel oxidation. Jordanian hardwood samples have been examined, tested and evaluated according to their mass loss rates, specific optical density, mass optical density, transmittance, and visibility using qualitative research used to realise the dynamics of fire phenomena. Four types of natural wood were tested under different heat fluxes with different Flaming combustion in a Smoke Density Chamber (SDC). The samples studied were Beech, Oak, Rhamnus, and Abies. The samples have been exposed to 25 and 50 kW/m2 heat fluxes in a limited ventilation compartment. Twelve samples were tested, each with dimensions of 75 x 75 mm and 10 mm thickness. An evaluation of the tested parameters, such as mass loss rate (MLR), specific optical density, transmittance, visibility and mass optical density (MOD have been carried out to determine their effectiveness as predictive parameters. Main results shows Beech has the lower values of specific optical density despite it has higher values of MLR% and MOD compared to other samples studied. Also, the mass loss rate (MLR %) increases with the heat flux even with different flaming conditions. In the opposite, there is a strong dependence for the mass optical density (MOD) on the heat flux and flaming conditions. Key conclusions have been drawn up that could be used in wood products and future works. The main objective of this work is to model the fire dynamic behavior in the pre-fire time. The results of this study can provide the bases for ventilation process and considerations of using natural woods in Jordan for different applications.

The Carnegie Supernova Project II

We present ultra-violet (UV) to mid-infrared (MIR) observations of the long-lasting Type IIn supernova (SN) 2013L obtained by the Carnegie Supernova Project II beginning two days after discovery and extending until +887 days (d). The SN reached a peak r-band absolute magnitude of ≈−19 mag and an even brighter UV peak, and its light curve evolution resembles that of SN 1988Z. The spectra of SN 2013L are dominated by hydrogen emission features, characterized by three components attributed to different emission regions. A unique feature of this Type IIn SN is that, apart from the first epochs, the blue shifted line profile is dominated by the macroscopic velocity of the expanding shock wave of the SN. We are therefore able to trace the evolution of the shock velocity in the dense and partially opaque circumstellar medium (CSM), from ∼4800 km s−1 at +48 d, decreasing as t−0.23 to ∼2700 km s−1 after a year. We performed spectral modeling of both the broad- and intermediate-velocity components of the Hα line profile. The high-velocity component is consistent with emission from a radially thin, spherical shell located behind the expanding shock with emission wings broadened by electron scattering. We propose that the intermediate component originates from preionized gas from the unshocked dense CSM with the same velocity as the narrow component, ∼100 km s−1, but also that it is broadened by electron scattering. These features provide direct information about the shock structure, which is consistent with model calculations. The spectra exhibit broad O I and [O I] lines that emerge at ≳+144 d and broad Ca II features. The spectral continua and the spectral energy distributions (SEDs) of SN 2013L after +132 d are well reproduced by a two-component black-body (BB) model; one component represents emitting material with a temperature between 5 × 103 and 1.5 × 104 K (hot component) and the second component is characterized by a temperature around 1–1.5 × 103 K (warm component). The warm component dominates the emission at very late epochs (≳+400 d), as is evident from both the last near infrared (NIR) spectrum and MIR observations obtained with the Spitzer Space Telescope. Using the BB fit to the SEDs, we constructed a bolometric light curve that was modeled together with the unshocked CSM velocity and the shock velocity derived from the Hα line modeling. The circumstellar-interaction model of the bolometric light curve reveals a mass-loss rate history with large values (1.7 × 10−2 − 0.15 M⊙ yr−1) over the ∼25−40 years before explosion, depending on the radiative efficiency and anisotropies in the CSM. The drop in the light curve at ∼350 days and the presence of electron scattering wings at late epochs indicate an anisotropic CSM. The mass-loss rate values and the unshocked-CSM velocity are consistent with the characteristics of a massive star, such as a luminous blue variable (LBV) undergoing strong eruptions, similar to η Carinae. Our analysis also suggests a scenario where pre-existing dust grains have a distribution that is characterized by a small covering factor.

A global view on the colliding-wind binary WR 147

ABSTRACT We present results from a global view on the colliding-wind binary WR 147. We analysed new optical spectra of WR 147 obtained with the Gran Telescopio Canarias and archive spectra from the Hubble Space Telescope by making use of modern atmosphere models accounting for optically thin clumping. We adopted a grid-modelling approach to derive some basic physical characteristics of both stellar components in WR 147. For the currently accepted distance of 630 pc to WR 147, the values of mass-loss rate derived from modelling its optical spectra are in acceptable correspondence with that from modelling its X-ray emission. However, they give a lower radio flux than observed. A plausible solution for this problem could be the volume filling factor at large distances from the star (radio-formation region) being smaller than that close to the star (optical-formation region). Adopting this, the model can match well both optical and thermal radio emission from WR 147. The global view on the colliding-wind binary WR 147 thus shows that its observational properties in different spectral domains can be explained in a self-consistent physical picture.

Experimental Study on Freezing and Thawing Cycles of Shrinkage-Compensating Concrete with Double Expansive Agents.

The freezing and thawing of construction concrete is becoming an increasingly important structural challenge. In this study, a shrinkage-compensating concrete based on a double expansive admixture was developed and its frost resistance was assessed through rapid freezing and thawing cycling. The frost resistance of the concrete was derived through the measurement and calculation of the relative dynamic modulus of elasticity (RDME) and the mass loss rate (MLR), and the freezing- and thawing-cycle microstructures and products of concretes with different expansive agents were analyzed using scanning electron microscopy (SEM). It was shown that changes in the properties of the concrete under freezing and thawing could be divided into three stages: slow-damage stage, fast-damage stage, and stable stage. Compared to concrete without an expansive agent, a single-expansive-agent concrete demonstrated excellent frost resistance during the slow-damage stage, but the frost resistance rapidly decreased during the fast-damage age. After 150 cycles (the stable-damage stage), the concrete with a U-type expansive agent (UEA): MgO expansive agent (MEA) mix proportion of 2:1 had the best frost resistance, with RDME and MLR values 17.35% higher and 25.1% lower respectively, than that of an expansive-agent-free concrete. These test results provide a basis for the study of frost resistance in large-scale hydraulic concrete structures.

Durability of reactive powder concrete under chloride-salt freeze–thaw cycling

The corrosion of reinforcements that results from chloride iron erosion and freeze–thaw damage is the key cause of concrete material failure. Indoor accelerated freeze–thaw cycling tests on reactive powder concrete are carried out in this study, and the mass-loss rate (MLR), relative dynamic-elastic modulus (RDEM), and compressive strength are measured in order to evaluate its durability. In addition, the microstructure and composition of the reactive powder concrete during the chloride-salt freeze–thaw cycles were analyzed using scanning electron microscopy, energy-dispersive spectroscopy, and mercury-intrusion porosimetry. The results show that the reactive powder concrete was durable under chloride freeze–thaw cycling. Furthermore, the values of MLR and RDEM indicated that the actual method is not suitable for reactive powder concrete and should be modified, and that ettringite-type erosion products are generated during the freeze–thaw cycles. The conclusions in this study are valid for specific reactive powder concrete mix.

Calibration of charcoal production from trees biomass for soil charcoal analyses in subalpine ecosystems

Subalpine ecosystems are mainly affected by surface fires of low to medium intensity. Charcoal production from trees is limited by the duration and the intensity of fires and, thus, by the wood combustibility. Because the combustibility properties of species differ, the functional traits that determine the wood combustibility could explain in part the taxonomic differences of charcoal abundance within the paleo-soil charcoal (pedoanthracological) assemblages. Eight subalpine broadleaf and needleleaf tree species were considered. Wood combustibility was studied by experimental burning on barked-wood samples exposed to constant heat. Two combustibility parameters are estimated (i) the rate of mass loss rate (MLR) and, (ii) the burning rate (BR). While BR describes the proportion of burned biomass per time unit assessing the potential conversion of wood biomass into charcoal, MLR reports the speed of fuel combustion that estimates the potential amount of charcoal produced. A hierarchy of species-specific potential production of charcoal by trees is developed by the use of biplot distribution of MLR and BR. Species were ranked from the worst to the best biomass for the charcoal conversion: Larix decidua, Abies alba, Pinus uncinata, Picea abies, Betula pendula, Salix caprea, Pinus cembra, Sorbus aucuparia. With thin smooth bark and dense wood, broadleaf trees are expected to produce more charcoal than needleleafs. Bark thickness and wood density explain half of combustibility variance. Thus, the production of charcoal tends to vary among species and among individuals of different diameter according to bark thickness. The amount of charcoal is a proxy of both (i) the abundance of understorey-tree (sapling) due to the high combustion susceptibility of small diameter stems (thin and smooth bark), and (ii) the abundance of woody debris on the ground produced by the canopy trees. The results are discussed in light of simulated data from Holocene soil charcoal assemblages for the western subalpine Alps. Among needleleafs, L. decidua is the least productive in terms of charcoal abundance due to its low MLR and BR values, whereas P. cembra and broadleafs should be better represented in the soil charcoal assemblages. This study provides rational elements for the quantitative calibration of soil charcoal through species-specific charcoal mass coefficients.

Self-aligned TiO 2 nanotube arrays produced by air-cathode as electrode

Air-cathodes were used to produce TiO 2 nanotube arrays. The effects of pH, voltage and degradation of air-cathode in tailoring the morphologies of TiO 2 nanotube arrays were investigated. Preliminary results show that TiO 2 nanotubes could be formed and are comparable to those produced by platinum electrodes under similar conditions. The lengths and diameters of TiO 2 nanotube arrays obtained are in the range of 1.0–2.2 μm and 40–150 nm, respectively. It is found that the rate of formation of the nanotubes is closely related to the pH of the solution. Air-cathodes are found to have relative low values of mass loss rates.

Spectroscopic study of the short-period WN5o + O8.5V binary system WR127 (HD 186943)

Combined with previous information (orbital period P = 9.5550 d and inclination i = 55°.5), new optical spectroscopic data lead to improved circular orbits for this WR + O system, with mass 13.4M ⊙ ) of the WN5o star and 23.9M⊙ of its O8.5V companion. These are normal for their spectral types. The WR/O mass ratio, q ≃ 0.56, is reasonable for such a binary. The relatively large orbital separation between the two components (~63 R ⊙ ) implies that there is currently no interaction between the two stars beyond their colliding winds. Analysis of the excess line emission and absorption arising in the wind-wind collision zone yields the following parameters: streaming velocity v strm = 1104 km s -1 , cone opening half-angle θ ≃ 59° and Coriolis angle shift δφ = 8°.1. Using probable values of mass-loss rate and terminal wind velocity for each star, a value of 0 ≃ 37° is obtained. The difference in θ is likely due to a combination of uncertainty in these parameters and radiative braking. Altogether, WR127 is a normal, detached and non-photospherically eclipsing binary system, although it does show atmospheric 'eclipses'.

Wolf–Rayet optically thick winds with Alfvén waves

The Wolf–Rayet (WR) stars are hot luminous objects which are suffering an extreme mass loss via a continuous stellar wind. The high values of mass loss rates and high terminal velocities of the WR stellar winds constitute a challenge to the theories of radiation driven winds. Several authors incorporated magnetic forces to the line driven mechanism in order to explain these characteristics of the wind. Observations indicate that the WR stellar winds may reach, at the photosphere, velocities of the order of the terminal values, which means that an important part of the wind acceleration occurs at the optically thick region. The aim of this study is to analyze a model in which the wind in a WR star begins to be accelerated in the optically thick part of the wind. We used as initial conditions stellar parameters taken from the literature and solved the energy, mass and momentum equations. We demonstrate that the acceleration only by radiative forces is prevented by the general behavior of the opacities. Combining radiative forces plus a flux of Alfvén waves, we found in the simulations a fast drop in the wind density profile which strongly reduces the extension of the optically thick region and the wind becomes optically thin too close its base. The understanding how the WR wind initiate is still an open issue.

Are luminous and metal-rich Wolf-Rayet stars inflated?

Aims. We investigate the influence of metallicity and stellar wind mass loss on the radius of Wolf-Rayet stars. Methods. We have calculated chemically homogeneous models of Wolf-Rayet stars of 10 to 200 M for two metallicities (Z = 0.02 and Z = 0.001), without mass loss, using OPAL opacities. We also constructed theoretical helium main sequences for 15, 18, 24 and 30 M with stellar wind mass loss rates of 10−5 M yr−1 and 10−4 M yr−1 and models for a 24 M star for a few intermediate values of mass loss rate. Results. We confirm the radius extension for luminous, metal-rich Wolf-Rayet stars reported previously by Ishii et al. (1999, PASJ, 51, 417), i.e. the inflation of the hydrostatic stellar radius. We also show that for small values of the stellar wind mass loss rate, an extended envelope structure is still present. However, for mass loss rates above a critical value, for which we derive an expression, Wolf-Rayet radii decrease and the stellar structure becomes compact. We briefly discuss possible evolutionary and observational consequences of an inflated envelope for a mass losing Wolf-Rayet star.

The thermonuclear production of $\mathsf{^{19}}$F by Wolf-Rayet stars revisited

New models of rotating and non-rotating stars are computed for initial masses between 25 and 120 and for metallicities , 0.008, 0.020, and 0.040 with the aim of reexamining the wind contribution of Wolf-Rayet (WR) stars to the 19F enrichment of the interstellar medium. Models with an initial rotation velocity are found to globally eject less 19F than the non-rotating models. We compare our new predictions with those of Meynet & Arnould (2000, A&A, 355, 176), and demonstrate that the 19F yields are very sensitive to the still uncertain rate and to the adopted mass loss rates. Using the recommended mass loss rate values that take into account the clumping of the WR wind and the NACRE reaction rates, when available, we obtain WR 19F yields that are significantly lower than predicted by Meynet & Arnould (2000, A&A, 355, 176) and that would make WR stars non-important contributors to the galactic 19F budget. In view, however, of the large nuclear and mass loss rate uncertainties, we consider that the question of the WR contribution to the galactic 19F remains quite open.

Time-dependent MHD shocks and line emission: the case of the DG Tau jet

The line emission from a growing number of Herbig-Haro jets can be observed and resolved at angular distances smaller than a few arcseconds from the central source. The interpretation of this emission is problematic, since the simplest model of a cooling jet cannot sustain it. It has been suggested that what one actually observes are shocked regions with a filling factor of $\sim 1%$. In this framework, up to now, comparisons with observations have been based on stationary shock models. Here we introduce for the first time the self-consistent dynamics of such shocks and we show that considering their properties at different times, i.e. locations, we can reproduce observational data of the DG Tau microjet. In particular, we can interpret the spatial behavior of the [SII]6716/6731 and [NII]/[OI]6583/6300 line intensity ratios adopting a set of physical parameters that yield values of mass loss rates and magnetic fields consistent with previous estimates. We also obtain the values of the mean ionization fraction and electron density along the jet, compare these values with the ones derived from observations using the sulfur doublet to constrain the electron density (e.g. Bacciotti et al. 1995).

NLTE models of line-driven stellar winds

New numerical models of line-driven stellar winds of late O stars are presented. Statistical equilibrium (NLTE) equations of the most abundant elements are solved. Properly obtained occupation numbers are used to calculate consistent radiative force and radiative heating terms. Wind density, velocity and temperature are calculated as a solution of model hydrodynamical equations. Contrary to other published models we account for a multicomponent wind nature and do not simplify the calculation of the radiative force (e.g. using force multipliers). We discuss the convergence behaviour of our models. The ability of our models to predict correct values of mass-loss rates and terminal velocities of selected late O stars (mainly giants and supergiants) is demonstrated. The systematic difference between predicted and observed terminal velocities reported in the literature has been removed. Moreover, we found good agreement between the theoretical wind momentum-luminosity relationship and the observed one for Cyg OB2 supergiants.