Calculated Mass Loss Research Articles

Pre-perihelion monitoring of interstellar comet 2I/Borisov

ABSTRACT The discovery of interstellar comet 2I/Borisov offered the unique opportunity to obtain a detailed analysis of an object coming from another planetary system, and leaving behind material in our interplanetary space. We continuously observed 2I/Borisov between 2019 October 3 and December 13 using the 1.52-m Telescopio Carlos Sánchez equipped with Multicolour Simultaneous Camera for studying Atmospheres of Transiting exoplanets 2 instrument, and the 2.54-m Isaac Newton Telescope with Wide Field Camera. We characterize its morphology and spectro-photometric features using the data gathered during this extended campaign. Simultaneous imaging in four bands (g, r, i, and zs) reveals a homogeneous composition and a reddish hue, resembling Solar system comets, and as well a diffuse profile exhibiting familiar cometary traits. We discern a stationary trend fluctuating around a constant activity level throughout 2019 October and November. Subsequently, a reduction in activity is observed in December. Dust production and mass-loss calculations indicate approximately an average of 4 kg s−1 before perihelion, while after perihelion the net mass-loss is about 0.6 kg s−1. Our simulations indicate the most probable size of coma dust particles should be in the range 200–250 nm, and the terminal speed around 300 m s−1. The spectrum acquired with the 4.2-m William Herschel Telescope shows the presence of a strong CN line for which we find a gas production rate of 1.2 × 1024 s−1. We also detected NH2 and OI bands. The ratio between NH2 and CN productions is log (NH2/CN) = −0.2. Overall, this observing campaign provides a new understanding of 2I/Borisov’s unique characteristics and activity patterns.

Co-disposal kinetics and characteristics of sewage sludge and municipal solid waste incineration fly ash

Sewage sludge (SS) and municipal solid waste incineration fly ash (MSWIFA) have characteristics of high yield, scattered distribution, and strong harm. Co-disposal of SS and MSWIFA in the existing cement kilns is a prospective way to deal with these two types of solid waste. In this study, the pyrolysis kinetic, thermogravimetric analysis, heat and mass transfer characteristics and pollutant release during SS and MSWIFA co-disposal were investigated through a series of experiments and simulations. In the experiment, pulverized coal (PC) was used as fuel to imitate the real environment of a cement kiln. According to the results, the interaction of the two solid wastes was observed mainly during the devolatilization and combustion periods. At an average blending ratio (60%) and 25 ℃/min heating rate, the blend actual mass loss rate has the largest difference compared to the linearly calculated mass loss rate (0.74%/min), with higher comprehensive combustion characteristic index (3.54), and the blends have better overall heat transfer, internally converging to 350 K. Meanwhile, when SS proportion in PC-SS-MSWIFA is between 20% and 30%, the emission concentration of SO2 and NO was low, and it has good environmental benefits. This research aims to offer theoretical support for the co-disposal of SS and MSWIFA.

Corrosion of carbon steel rebar in binary blended concrete with accelerated chloride transport

Samples with two different binary blended concrete mixes were prepared, one containing cement replacement of 50% slag (referred here as SL mix) and the other containing cement replacement of 20% fly ash (termed here as FA mix). The water to cementitious ratio used to produce concrete specimens was 0.41. On the top surface of each specimen, various reservoir lengths that ranged from 2.5 cm to 17.5 cm were fitted, and these reservoirs were filled with a 10% NaCl solution. Electromigration was used to accelerate the transport of chlorides, with an applied potential of 9 V at first, and subsequently reduced to 3 V after about a week. The electromigration was applied for a short period (few weeks to a couple of months). For a period of about 1100 days, the corrosion related parameters such as concrete solution resistance, rebar potential, and corrosion current were monitored via the rebar potential measurements, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements, the latter used only to obtain the solution resistance. The corrosion current values determined through experimental observations were then converted to mass loss using Faraday’s law. The readings of corrosion current values (last 7 sets of readings) as well as the calculated mass loss values were found to be larger for the rebars embedded in specimens prepared with SL mix, followed by rebars embedded in specimens prepared with FA mix. Corrosion current and calculated mass loss values in general tended to increase with increasing solution reservoir lengths. No cracks or corrosion products that reached the surface of the concrete were observed on the specimens for the duration of the reported monitored propagation period. This study offers a framework for future studies on accelerated steel corrosion in concrete.

Improving the post-fire behaviour of steel slag coarse aggregate concrete by adding GGBFS

Steel slag is a waste by-product from steelmaking industry but has potential for concrete industry due to its specific physical and chemical properties. Even though the effect of steel slag on the strength, workability and durability of concrete at ambient temperature has been investigated extensively, there were limited research on the behaivour of steel slag concrete (SSC) at and upon exposure to elevated temperatures. To understand and improve the post-fire behaviour of SSC, this paper firstly uses steel slag coarse aggregate (SSCA) to replace natural coarse aggregate (NCA) with replacement ratio of 50% and 100% by volume to make SSC. Then ground granulated blast furnace slag (GGBFS) was adopted to substitute ordinary Portland cement with different volumetric ratios (0%, 15%, 25% and 35%). Nine concrete mixes were designed and after 28-day curing, a series of experiments were conducted: heating test with target temperatures of 400, 600, 800 and 1000 °C, compressive test, mass loss calculation and surface change comparison. In addition, the chemical composition of concrete at different temperatures was tested using X-ray diffraction. Results showed that the heat resistance of concrete was enhanced for concrete mixes containing SSCA and/or GGBFS. Besides, the post-fire relative strength (post-fire residual strength to the ambient temperature strength ratio) of concrete containing steel slag reduced while adding GGBFS could mitigate this problem effectively. Lastly, EC2 Model was proved to be conservative when estimating the post-fire residual strength of SSC.

Study on Mass Erosion and Surface Temperature during High-Speed Penetration of Concrete by Projectile Considering Heat Conduction and Thermal Softening.

The mass erosion of the kinetic energy of projectiles penetrating concrete targets at high speed is an important reason for the reduction in penetration efficiency. The heat generation and heat conduction in the projectile are important parts of the theoretical calculation of mass loss. In this paper, theoretical models are established to calculate the mass erosion and heat conduction of projectile noses, including models of cutting, melting, the heat conduction of flash temperature, and the conversion of plastic work into heat. The friction cutting model is modified considering the heat softening of metal, and a model of non-adiabatic processes for the nose was established based on the heat conduction theory to calculate the surface temperature. The coupling numerical calculation of the erosion and heat conduction of the projectile nose shows that melting erosion is the main factor of mass loss at high-speed penetration, and the mass erosion ratio of melting and cutting is related to the initial velocity. Critical velocity without melting erosion and a constant ratio of melting and cutting erosion exists, and the critical velocities are closely related to the melting temperature. In the process of penetration, the thickness of the heat affected zone (HAZ) gradually increases, and the entire heat conduction zone (EHZ) is about 5~6 times the thickness of the HAZ.

Insight into the synergistic performance during ex-situ catalytic co-pyrolysis of poplar sawdust and polypropylene over Fe-Ni/ZSM-5 for the enhancement of aromatics

Hydrogen-deficient and oxygen-rich biomass result in low hydrocarbon production during pyrolysis. This work aims to enhance aromatics in bio-oil through ex-situ catalytic co-pyrolysis of poplar sawdust (PS) and polypropylene (PP) over Fe-Ni/ZSM-5 and gain an understanding of the synergistic pyrolysis performance. The results showed that adding PP improved the comprehensive pyrolysis performance of the PS and PP blends. The deviation between the experimental and calculated mass loss of the blends confirmed the interaction between PS and PP, with a more positive synergistic effect at a biomass/plastic mass ratio of 3:2. The average activation energy of PP was 211.6 kJ·mol−1, which is 28.2 % higher than that of PS. As the proportion of PP increases, the activation energy required for the blends increases. The established artificial neural network model accurately predicts the mass loss of the blends (R2 ≥ 0.999) by providing the mixing ratio, heating rate, and temperature. The addition of hydrogen-rich feedstock increased aromatic yield in the volatile products, indicating the positive synergy between PS and PP during catalytic co-pyrolysis over Fe-Ni/ZSM-5. As the targeted products among the aromatics, the total yields of benzene, toluene, and xylene ranged from 58.43 to 251.03 mg·g−1 in the PS and PP blends, respectively.

Influence of the coordination metal on the thermal properties of double selenates: Theoretical insights and experimental study

Thermal behavior of double selenates containing different coordination metal was evaluated at molecular level for the first time. It was achieved via a combined experimental (TGA, DSC) and theoretical (NBO, QTAM, RDG) study on Na2Fe(SeO4)2·2H2O (NaFeSe) and Na2Co(SeO4)2·2H2O (NaCoSe).The releasing of crystallization water is an endothermic process which continuously undergoes for NaFeSe . For comparison, NaCoSe released crystallization water in a single act. Thermal degradation of the anhydrous NaFeSe proceed with formation of the intermediates FeSeO3 and Na2SeO3. However, CoSeO3 and Na2SeO3 were not registered in the TGA and DSC of NaCoSe. Instead of this, Co3O4 was formed. Structural, NBO, QTAM and RDG shown that the thermal effects were due to different nature of the intramolecular interactions between coordinated water and metal center as well as between selenate anions and coordination metal. It is worth noting that theoretically calculated mass loss correlated well with the experimentally registered one.

Durability and Property Study of Decade Old Crumb Rubber Concrete Cored Specimens.

Crumb rubber concrete (CRC) is a concrete that contains rubber crumbs. This article presents a study of three experiments on long aged CRC specimens that were cored from a decade old CRC bridge deck in Tianjin, China. The three experimental tests conducted were: (1) the flexural stress–strain test on semi-circular disk specimens; (2) the accelerated steel-rebar corrosion test and (3) the carbonation test. In addition, the in situ carbonation test was also carried out on the CRC bridge deck. The flexural stress–strain test results showed that the CRC semi-circular disk specimens exhibited a ductile pattern and high-energy absorbing capacity with its flexural tensile strength being at 5 MPa and the flexural modulus of 10 GPa. The steel corrosion rust rate via the calculation of steel mass loss before and after the test in the accelerated steel-rebar corrosion test remained extremely low. The carbonation test results showed that in comparison with the prediction of two popular carbonation models, the carbonation in the CRC bridge deck took place at a much slower rate during the last 13 years. All of the results obtained in this study are reported for the first-time and indicate that these CRC cored specimens exhibit good mechanical properties and excellent durability characteristics after a decade in service, which may provide the technical knowledge for the possible future application of CRC in concrete constructions.

Corrosion susceptibility behavior in 12Cr–1Mo martensitic stainless steel welded by SAW process and the effect of δ-ferrite in the HAZ

Pitting corrosion in stainless steel (SS) is a punctual defect that promotes fatigue and cracks propagation. Martensitic steel of steam turbine is exposed to the thermal cycle of welding, high pressures, and corrosive environments in the heat-affected zone (HAZ). The presence of δ-ferrite in HAZ causes crystalline grain boundaries sensitization and reduces corrosion resistance. This research evaluated the corrosive effect of NaCl, NaOH, and H2SO4 in critical welding regions (BM, HAZ, FZ) by analyzing potentiodynamic curves, EIS, and mass loss calculation. The δ-ferrite in the HAZ promotes an increase in the corrosion rate in the NaCl and H2SO4 derivatives of the corrosion products formed. Furthermore, the mass loss in the HAZ was more significant than that in the BM and FZ. Despite having a lower Cr content in the FZ.

Synthesis and characterization of novel ionic liquids based on imidazolium for acid corrosion inhibition of aluminum: Experimental, spectral, and computational study

Three newly ionic liquids namely, 1-bnzyl-2-methyl-3-octyl-1H-imidazol-3-ium bromide, 1-bnzyl-3-decyl-2-methyl-1H-imidazol-3-ium bromide, and 1-bnzyl-3-dodecyl-2-methyl-1H-imidazol-3-ium bromide are synthesized and their chemical structures characterized via different spectra techniques (FT-IR, elemental analysis,and 1H NMR). The corrosion inhibition of newly ionic liquids was evaluated on aluminum alloy in 1 M HCl at varied exposure temperatures (298–318 K) and varied concentrations via various experimental and theoretical methods for example mass loss, electrochemical, spectral, and computational calculations. The results illustrate that these types of ionic liquids inhibit corrosion of aluminum in acid solution with maximum inhibition efficiency was reached 83.2 % at 298 K. The inhibition efficiency increases with the addition of zinc sulfate which has a synergistic impact which was reached to 92.7%. Also, the concentration of ionic liquids and the kind of cation have an impact on the obtained results. The existence of these inhibitors in the acidic solution improves the charge transfer resistance and lessens the double-layer capacitance. The Langmuir adsorption isotherm governs the adsorption of these inhibitors' molecules on the aluminum alloy surface, and they behave as mixed-type inhibitors. The outputs reveal that the computational calculations match the experimental data rather well.

ANU GRACE Data Analysis: Characteristics and Benefits of Using Irregularly Shaped Mascons

AbstractThe estimation of mass anomalies using Gravity Recovery and Climate Experiment (GRACE) data involves parameterizing the temporal gravity field using basis functions. In this study, we show that the use of irregularly shaped mass concentration (mascon) tiles that follow land/ocean boundaries reduces the leakage of land signals into ocean regions and vice versa. Leakage of signal from continents to oceans in mascons that cross the coastline affect the integrated mass changes at a regional scale. For example, the calculated mass loss in 2016 is ∼5% greater for Greenland when using mascons that follow coastlines. We describe efficient algorithms for computing the accelerations acting on the satellites caused by mass changes on mascons, along with the partial derivatives relating the mass changes to the inter‐satellite observations. Through simulation, we quantify the impact of different mascon geometries, spatial resolution and regularization. The variations of mass change signals within mascons, which we call “intra‐mascon variability,” contribute to errors in estimates of mass variation from GRACE data. While this can be mitigated through the regularization of the inversions, it cannot be removed entirely. The use of irregularly shaped mascons that follow land/ocean boundaries reduces the “intra‐mascon leakage” of land signals into ocean regions and vice versa. This approach can also be applied to hydrological basins for calculating integrated mass changes on catchment scales.

Upper mass-loss limits and clumping in the intermediate and outer wind regions of OB stars

Context. Mass loss is a key parameter throughout the evolution of massive stars, and it determines the feedback with the surrounding interstellar medium. The presence of inhomogeinities in stellar winds (clumping) leads to severe discrepancies not only among different mass-loss rate diagnostics, but also between empirical estimates and theoretical predictions. Aims. We aim to probe the radial clumping stratification of OB stars in the intermediate and outer wind regions (r ≳ 2 R*; radial distance to the photosphere) to derive upper limits for mass-loss rates and to compare that to current mass-loss implementation. Our sample includes 13 B supergiants, which is the largest sample of such objects in which clumping has been analysed so far. Methods. Together with archival optical to radio observations, we obtained new far-infrared continuum observations for a sample of 25 OB stars. Our new data uniquely constrain the clumping properties of the intermediate wind region. By using density-squared diagnostics, we further derived the minimum radial stratification of the clumping factor through the stellar wind, fclmin (r), and the corresponding maximum mass-loss rate, Ṁmax, normalising clumping factors to the outermost wind region (fclfar = 1). Results. We find that the clumping degree for r ≳ 2 R* decreases or stays constant with an increasing radius, regardless of the luminosity class or spectral type for 22 out of 25 sources in our sample. However, a dependence of the clumping degree on the luminosity class and spectral type at the intermediate region relative to the outer ones has been observed: O supergiants (OSGs) present, on average, a factor 2 larger clumping factors than B supergiants (BSGs). Interestingly, the clumping structure of roughly one-third of the OB supergiants in our sample is such that the maximum clumping occurs close to the wind base (r ≲ 2 R*), and then it decreases monotonically. This is in contrast to the more frequent case where the lowermost clumping increases towards a maximum and needs to be addressed by theoretical models. In addition, we find that the estimated Ṁmax for BSGs is at least one order of magnitude (before finally decreasing) lower than the values usually adopted by stellar evolution models, whereas the upper observational limits and predictions of OSGs agree within errors. This implies large reductions of mass-loss rates applied in evolution models for BSGs, independently of the actual clumping properties of these winds. However, hydrodynamical models of clumping suggest absolute clumping factors in the outermost radio-emitting wind of the order of fclfar ≈ 4–9, assuming these values would imply a reduction in mass-loss rates included in stellar evolution models by a factor 2–3 for OSGs (above Teff ~ 26 500 K) and by factors 6–200 for BSGs below the so-called first bi-stability jump (below Teff ~ 22 000 K). While such reductions agree well with new theoretical mass-loss calculations for OSGs, our empirical findings call for a thorough re-investigation of BSG mass-loss rates and their associated effects on stellar evolution.

A Laboratory-driven Multiscale Investigation of X-Ray Induced Mass Loss and Photochemical Evolution in Cosmic Carbon and Silicate Dust

Abstract We present the results of an integrated laboratory and modeling investigation into the impact of stellar X-rays on cosmic dust. Carbonaceous grains were prepared in a cooled (<200 K) supersonic expansion from aromatic molecular precursors, and were later irradiated with 970 eV X-rays. Silicate (enstatite) grains were prepared via laser ablation, thermally annealed, and later irradiated with 500 eV X-rays. Infrared spectra of the 3.4 μm band of the carbon sample prepared with benzene revealed 84% ± 5% band area loss for an X-ray dose of 5.2 ×1023 eV.cm−2. Infrared spectra of the 8–12 μm Si–O band of the silicate sample revealed band area loss up to 63% ± 5% for doses of 2.3 × 1023 eV.cm−2. A hybrid Monte Carlo particle trajectory approach was used to model the impact of X-rays and ensuing photoelectrons, Auger and collisionally ionized electrons through the bulk. As a result of X-ray ionization and ensuing Coulomb explosions on surface molecules, the calculated mass loss is 60% for the carbonaceous sample and 46% for the silicate sample, within a factor of 2 of the IR band loss, supporting an X-ray induced mass-loss mechanism. We apply the laboratory X-ray destruction rates to estimate the lifetimes of dust grains in protoplanetary disks surrounding 1 M ⊙ and 0.1 M ⊙ G and M stars. In both cases, X-ray destruction timescales are short (a few million years) at the disk surface, but are found to be much longer than typical disk lifetimes (≳10 Myr) over the disk bulk.

Structural integrity of Cs and Sr immobilized lacunar apatite phosphate simulated ceramic wasteform Na0.9Cs0.1Pb3Sr(PO4)3 under heat and aqueous flow

Lacunar apatite host, NaPb4(PO4)3was converted into a ceramic wasteform with the incorporation of Cs and Sr ions. The systematic substitution yielded the wasteform composition Na0.9Cs0.1Pb3Sr(PO4)3 with 8.52 wt% of Strontium and 1.29 wt% of caesium. The wasteform was subjected to continuous heating in the temperature range 298–973 K and aqueous flow to study the thermal stability and chemical durability respectively. The wasteforms response was studied by powder X-Ray diffraction analysis (Room temperature and High temperature), electron microscopic & elemental analysis and normalized mass loss (NLi) & leach rate (LRi) calculations. The average thermal expansion coefficient (αavg) value of 14.4 ± 1.1 × 10−6 K−1 and the leach rates of immobilised Cs, LRCs (10−6–10−8 gm−2d−1) and Sr, LRSr (10−3–10−4 gm−2d−1) demonstrate the structural integrity of the phase. The anisotropic nature of thermal expansion and the mechanistic feature of leaching are discussed.

Experimental evaluation of fire resistance performance of cement mortar with PCM/Mg(OH)2-based composite fine aggregate

When concrete structures are exposed to fire and high temperatures for an extended period of time, they become significantly less durable due to the decomposition of majorhydrationproducts and the evaporation of capillary water. A change in internal properties does not guarantee the stability of concrete structures and may reduce their life cycle. To preserve the durability and stability of concrete structures upon exposure to fire and high temperatures, fire-resistant mortar for exterior walls was developed in this work using zeolite, a phase change material (PCM), and magnesium hydroxide (MH). Zeolite was first coated with paraffin wax. Primary coated aggregates were then coated with MH, which was mixed with dissolved polyvinyl acetate to enhance adhesion on the surface of pre-coated aggregates. The physical and chemical properties of mortar mixed with different percentages of coated aggregates as a replacement for normal aggregates were evaluated by compressive strength tests, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Fire-resistant properties were investigated by residual compressive strength measurement tests, mass loss calculations, and mock-up tests to compare the internal temperature of mortar covered with normal and coated aggregate when heated in an electric furnace at 1000 °C. The residual compressive strength results showed a decrease in strength with a larger percentage of coated aggregates in the mortar. However, according to the mock-up test, control mortar covered with plain mortar took 5430 s (90.5 min) to reach a maximum temperature of 842 °C, while the mortar covered with 100% coated aggregate took 7170 s (119.5 min) to reach a maximum temperature of 735 °C. The obtained results indicate that the coated aggregate is a proper replacement for conventional aggregate in the development of fire-resistant mortar.

Synthesis and anti-corrosion characteristics of new 8-quinolinol analogs with amide-substituted on C35E steel in acidic medium: Experimental and computational ways

The inhibition ability of two synthesized 8-quinolinol analogs namely, N-((8-hydroxyquinolin-5-yl)methyl)-4-methoxybenzamide (HMB), N-((8-hydroxyquinolin-5-yl)methyl) propionamide (HPA) toward C35E steel corrosion in 1 M HCl was studied by mass loss, electrochemical measurements, and theoretical calculations. The experimental results indicated that 8-quinolinol analogs extremely enhanced the corrosion resistance of C35E steel in 1 M HCl, and the ηmax of HMB and HPA reached up to 93.5% and 89.3% at 10−3 M, respectively. Polarization studies indicated that 8-quinolinol analogs with amide-substituted work as mixed-type corrosion inhibitors. Electrochemical impedance spectroscopy (EIS) data proves that with the increase of temperature, both inhibitors keep their anti-corrosion performance. The adsorption of 8-quinolinol analogs with amide-substituted on the C35E steel surface was pursued the Langmuir isotherm. Theoretical density functional theory (DFT) calculations and molecular dynamics (MD) simulations gave corroborative results that are in agreement with experimental findings.

On thermal decomposition kinetics of poly(ethylene-alt- tetrafluoroethylene) using an autocatalytic model

The thermal decomposition of a commercial poly(ethylene-alt-tetrafluoroethylene) (ETFE) Fluon®C-88AXP, in nitrogen atmosphere has been carried out using thermogravimetric analysis (TG) with dynamic method at different heating rates. The widely used Kissinger equation, Friedman's and Ozawa analysis are used to estimate the activation energy of the degradation reaction. Method of fitting the dynamic derivative thermogram (DTG) data directly using isothermal kinetic model is adopted and the model parameters have been obtained which could not be acquired by using the conventional methods. The TG data of Fluon®C-88AXP could not be described properly using n-order kinetic model but the autocatalytic Kamal model fits the data perfectly. The standard deviations of the calculated mass loss rates from the experimental results decrease from 1.497 × 10−6 to 0.138 × 10−6, with a decrease of 91 %, when Kamal model was used instead of n-order kinetics. This indicates that the thermal decomposition of ETFE in nitrogen atmosphere obeys an autocatalytic kinetics.

The Effect of Eutypella parasitica on the Wood Decay of Three Maple Species

Eutypella parasitica R.W. Davidson & R.C. Lorenz is the causative agent of Eutypella canker of maple, a destructive disease of maples in Europe and North America. The fungus E. parasitica is known to cause wood stain and decay. However, it is not known how effectively it decomposes the wood of the most widespread maple species in Europe. Wood samples of Acer pseudoplatanus L., A. platanoides L., and A. campestre L. were exposed to four isolates of E. parasitica and nine other fungal species for comparison, according to the modified EN 113 standard. After 15 weeks of incubation, mass loss and microscopical analysis of samples showed evidence of colonization and different wood decay potentials among fungal species. A highly significant positive correlation was found between mass loss and moisture content for all fungal species. Similarly, the measured cell wall thickness correlated well with the calculated mass loss of the samples. On average, the fungal species caused the lowest mass loss in A. pseudoplatanus (10.0%) and the highest in A. campestre (12.6%) samples. Among the samples exposed to E. parasitica isolates, the highest mass loss was recorded in A. pseudoplatanus (6.6%). Statistical analysis showed significant differences in mass loss and moisture content between different E. parasitica isolates. Based on the results of staining, we discuss the type of decay caused by E. parasitica. Although E. parasitica isolates caused smaller mass loss of samples compared to other more effective decay species, we should not disregard its capability of degrading maple wood. Because E. parasitica usually infects the lower portion of the trunk, which is the largest and most valuable part of the tree, any damage can cause significant economic and resource loss.

Mass-loss in tidally stripped systems: the energy-based truncation method

ABSTRACT The ability to accurately predict the evolution of tidally stripped haloes is important for understanding galaxy formation and testing the properties of dark matter. Most studies of substructure evolution make predictions based on empirical models of tidal mass-loss that are calibrated using numerical simulations. This approach can be accurate in the cases considered, but lacks generality and does not provide a physical understanding of the processes involved. Recently, we demonstrated that truncating NFW distribution functions sharply in energy results in density profiles that resemble those of tidally stripped systems, offering a path to constructing physically motivated models of tidal mass-loss. In this work, we review calculations of mass-loss based on energy truncation alone, and then consider what secondary effects may modulate mass-loss beyond this. We find that a combination of dependence on additional orbital parameters and variations in individual particle energies over an orbit results in a less abrupt truncation in energy space as a subhalo loses mass. Combining the energy truncation approach with a simple prediction for the mass-loss rate, we construct a full model of mass-loss that can accurately predict the evolution of a subhalo in terms of a single parameter ηeff. This parameter can be fully determined from the initial orbital and halo properties, and does not require calibration with numerical simulations.

Stand age and species traits alter the effects of understory removal on litter decomposition and nutrient dynamics in subtropical Eucalyptus plantations

Litter decomposition is a crucial ecological process that regulates nutrient cycling. However, the effects of understory plants and overstory trees on litter decomposition and nutrient dynamics are still poorly understood. We conducted understory plants removal and/or overstory trees removal to examine the resulting effects on litter decomposition and nutrient mineralization in two Eucalyptus plantations with contrasting ages (8-yr-old, 29-yr-old) in subtropical China. Litter bags containing naturally senesced leaves of either overstory Eucalyptus urophylla or understory Dicranopteris dichotoma were placed in field and periodically collected for analyses of carbon (C), nitrogen (N), phosphorus (P) and calculation of mass loss. Our results showed that understory plants removal significantly reduced litter decomposition of E. urophylla in both plantations, but N and P mineralization were reduced only in the 8-yr-old plantation. In contrast, it reduced litter decomposition of D. dichotoma only in the 29-yr-old plantation, but had no effects on N and P mineralization in either plantation. In comparison, overstory tree removal did not have any effects on decomposition or mineralization of N and P of E. urophylla and D. dichotoma litters. These results indicate that the role of understory plants in mediating litter decomposition and nutrient mineralization is more important than overstory trees, and it can be altered by stand age and plant species. Our findings could facilitate the understanding of ecological processes of litter decomposition and nutrient mineralization in subtropical forest ecosystems.