Reduced Mass Loss Research Articles

Hydrolytic stability of unsaturated polyester networks with controlled chain ends

Four unsaturated polyester networks with chain ends modified by isocyanate or dicyclopentadiene (DCPD) were immersed in distilled water at 100 °C or exposed in humid atmosphere at 70 °C and 50 °C. The hydrolytic stabilities of these materials were determined by gravimetric analyses and infrared spectrometry. The results obtained were compared with those obtained on standard polyesters under similar conditions. For a given hydrolysis rate, the modification of chain ends by an isocyanate very clearly induces a decreasing rate of weight loss within the framework of degradations involving osmotic phenomena. The controlling of chain ends by DCPD does not reduce mass loss efficiency, but it does limit the hydrolysis rate.

Ventilation Effects On Compartment Fire Characterization

Compartment fire experiments were performed using either natural or overhead forced ventilation to assess the effect of ventilation on the compartment fire environment. The ventilation rate was varied by changing the vent size in natural ventilation tests and mechanically in forced ventilation tests. Three fuels were used: diesel fuel, wood cribs, and polyurethane slabs. For naturally ventilated fires, it was noted that the vent size and geometry had a significant impact on the vertical temperature and oxygen concentration profiles. Both the temperature and oxygen concentration measurements were representative of two-layer environments. However, in terms of oxygen concentration, forced ventilation fires resulted in a well-mixed compartment regardless of the ventilation rate. In contrast, temperature measurements showed either a two-layer or linear variation with respect to compartment height, depending on the scenario. These results defy the conventional assumption that compartment temperatures and gas concentrations have the same vertical distribution. Furthermore, these results identify the need to go beyond the classic twolayer paradigm. In addition, reduced oxygen concentrations at the flame base resulted in reduced mass loss rates. The relationship between these burning rates and the oxygen concentration at the flame base was examined, and a correlation was developed. The results show that temperature and flashover potential assessments based on furniture calorimeter data may be significantly overestimated.

Inhibition of Wind-Compressed Disk Formation by Nonradial Line Forces in Rotating Hot-Star Winds

We investigate the effects of nonradial line forces on the formation of a wind-compressed (WCD) around a rapidly rotating B star. Such nonradial forces can arise both from asymmetries in the line resonances in the rotating wind and from rotational distortion of the stellar surface. They characteristically include a latitudinal force component directed away from the equator and an azimuthal force component acting against the sense of rotation. Here we present results from radiation-hydrodynamical simulations showing that these nonradial forces can lead to an effective suppression of the equatorward flow needed to form a WCD as well as a modest (~20%) spin-down of the wind rotation. Furthermore, contrary to previous expectations that the wind mass flux should be enhanced by the reduced effective gravity near the equator, we show here that gravity darkening effects can actually lead to a reduced mass loss, and thus lower density, in the wind from the equatorial region. Overall, the results here thus imply a flow configuration that is markedly different from that derived in previous models of winds from rotating early-type stars. In particular, a major conclusion is that equatorial wind compression effects should be effectively suppressed in any radiatively driven stellar wind for which, as in the usual CAK formalism, the driving includes a significant component from optically thick lines. This presents a serious challenge to the WCD paradigm as an explanation for disk formation around Be and other rapidly rotating hot stars thought to have CAK-type, line-driven winds.

Paired Watershed Comparison of Tillage Effects on Runoff, Sediment, and Pesticide Losses

AbstractA paired watershed study was used to compare runoff, sediment, atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5 triazine), and cyanazine (2‐[[4‐chloro‐6‐(ethylamino)‐S‐triazin‐2‐yl]amino]‐2‐methyl propionitrile) losses from conventional‐tilled (CT) and reduced‐tilled (RT) corn (Zea mays L.) watersheds. During a 13‐mo calibration period both watersheds were moldboard plowed and runoff was measured in H‐flumes. Composite samples were analyzed for sediment and for atrazine and cyanazine in dissolved and sediment phases. During a 30‐mo treatment period, one watershed was moldboard plowed while the other was disk harrowed. Reduced tillage decreased runoff by 64% and sediment losses by 99% but did not change dissolved atrazine or cyanazine concentrations in runoff. Concentrations of sediment‐sorbed pesticides increased in runoff. The RT reduced mass losses of atrazine and cyanazine in runoff, primarily because of decreases in runoff volume and sediment mass. Most pesticide losses occurred within 3 wk of field application. Pesticide loss was primarily in the dissolved phase. The paired watershed approach was a useful technique for determining watershed treatment effects when differences existed between watersheds chosen for study.

The Evolution and Explosion of Massive Stars. II. Explosive Hydrodynamics and Nucleosynthesis

view Abstract Citations (3317) References (76) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Evolution and Explosion of Massive Stars. II. Explosive Hydrodynamics and Nucleosynthesis Woosley, S. E. ; Weaver, Thomas A. Abstract The nucleosynthetic yield of isotopes lighter than A = 66 (zinc) is determined for a grid of stellar masses and metallicities including stars of 11, 12, 13, 15, 18, 19, 20, 22, 25, 30, 35, and 40 Msun and metallicities Z = 0, l0-4, 0.01, 0.1, and 1 times solar (a slightly reduced mass grid is employed for nonsolar metallicities). Altogether 78 different model supernova explosions are calculated. In each case nucleosynthesis has already been determined for 200 isotopes in each of 600 to 1200 zones of the presupernova star, including the effects of time dependent convection. Here each star is exploded using a piston to give a specified final kinetic energy at infinity (typically 1.2 × 1051 ergs), and the explosive modifications to the nucleosynthesis, including the effects of neutrino irradiation, determined. A single value of the critical 12C(α,γ) 16O reaction rate corresponding to 8(300 keV) = 170 keV barns is used in all calculations. The synthesis of each isotope is discussed along with its sensitivity to model parameters. In each case, the final mass of the collapsed remnant is also determined and often found not to correspond to the location of the piston (typically the edge of the iron core), but to a "mass cut" farther out. This mass cut is sensitive not only to the explosion energy, but also to the presupernova structure, stellar mass, and the metallicity. Unless the explosion mechanism, for unknown reasons, provides a much larger characteristic energy in more massive stars, it appears likely that stars larger than about 30 Msun will experience considerable reimplosion of heavy elements following the initial launch of a successful shock. While such explosions will produce a viable, bright Type II supernova light curve, lacking perhaps the radioactive tail, they will have dramatically reduced yields of heavy elements and may leave black hole remnants of up to 10 and more solar masses. The production of black holes may be particularly favored for stars of low metallicity, both because of their more compact structure and reduced mass loss. Publication: The Astrophysical Journal Supplement Series Pub Date: November 1995 DOI: 10.1086/192237 Bibcode: 1995ApJS..101..181W Keywords: HYDRODYNAMICS; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES; STARS: EVOLUTION; STARS: INTERIORS; STARS: SUPERNOVAE: GENERAL full text sources ADS | data products SIMBAD (1)

The climatic conditions of polar-type glaciers development in china

Around the Kunlun Peak there are many huge and broad mountains lifting above the Equilibrium Line altitade (ELA). forming the largest glacier distribution centre in China. Here the ELA is very high and the glacier existence is attributed to the unfavorableness of ablation, not the favorablenesses of accumulation. In the ablation period strong evaporation-sublimation and conduction expend a large amount of heat. restraining melting. In addition. meltwater is easy to refreeze, forming superimposed ice and then reducing mass loss. Low air temperature causes low ablation rate and short ablation period. Arid and cold climate is favorable to glacier development. comparable to the polar regions. Nonuniform precipitation decreases heat income during the ablation period and increases heat loss in winter, also resulting in restraining ablation.

Mass Loss from Rotating Hot-stars: Inhibition of Wind Compressed Disks by Nonradial Line-forces

We review the dynamics of radiatively driven mass loss from rapidly rotating hot-stars. We first summarize the angular momentum conservation process that leads to formation of a Wind Compressed Disk(WCD) when material from a rapidly rotating star is driven gradually outward in the radial direction. We next describe how stellar oblateness and asymmetries in the Sobolev line-resonance generally leads to nonradialcomponents of the driving force is a line-driven wind, including an azimuthal spin-down force acting against the sense of the wind rotation, and a latitudinal force away from the equator. We summarize results from radiation-hydrodynamical simulations showing that these nonradial forces can lead to an effective suppressionof the equatorward flow needed to form a WCD, as well as a modest (∼ 25%) spin-downof the wind rotation. Furthermore, contrary to previous expectations that the wind mass flux should be enhanced by the reduced effective gravity near the equator, we show here that gravity darkening effects can actually lead to a reducedmass loss, and thus lower density, in the wind from the equatorial region. Finally, we examine the equatorial bistability model, and show that a sufficiently strong jump in wind driving parameters can, in principle, overcome the effect of reduced radiative driving flux, thus still allowing moderate enhancements in density in an equatorial, bistability zone wind.

Moderate water restriction differentially constrains reproduction in two species of dwarf hamster (Phodopus)

The dwarf hamsters Phodopus campbelli and P. sungorus are found in semi-arid areas of Siberia and northern Mongolia, but habitat and diet differences suggest species differences in water regulatory efficiency. These differences were investigated by examining the effect of moderate water restriction (50% of ad libitum consumption) on solitary dams and on their reproductive success. In response to water restriction, P. sungorus dams lost less body mass than P. campbelli dams, and despite similar litter sizes, P. sungorus produced heavier litters and pups than P. campbelli, indicating that P. sungorus pups were larger. These results suggest that P. sungorus is more tolerant of water restriction than P. campbelli. In a second experiment the possibility that paternal care may mitigate the effects of water restriction was examined by leaving the mated pair together throughout lactation. Pairing reduced mass loss by P. campbelli dams and increased the proportion of large P. campbelli pups at weaning, but had no effect on these measures in P. sungorus, eliminating interspecific differences in responses to water restriction. Results suggest that biparental care may be a facultative response to environmental stress in P. campbelli.

Decomposition of tree leaf litters grown under elevated CO2: Effect of litter quality

Ash (Fraxinus excelsior L.), birch (Betula pubescens Ehrh.), sycamore (Acer pseudoplatanus L.) and Sitka spruce (Picea sitchensis (Bong.) Carr.) leaf litters were monitored for decomposition rates and nutrient release in a laboratory microcosm experiment. Litters were derived from solar domes where plants had been exposed to two different CO2 regimes: ambient (350 μL L-1 CO2) and enriched (600 μL L-1 CO2). Elevated CO2 significantly affected some of the major litter quality parameters, with lower N, higher lignin concentrations and higher ratios of C/N and lignin/N for litters derived from enriched CO2. Respiration rates of the deciduous species were significantly decreased for litters grown under elevated CO2, and reductions in mass loss at the end of the experiment were generally observed in litters derived from the 600 ppm CO2 treatment. Nutrient mineralization, dissolved organic carbon, and pH in microcosm leachates did not differ significantly between the two CO2 treatments for any of the species studied. Litter quality parameters were examined for correlations with cumulative respiration and decomposition rates: N concentration, C/N and lignin/N ratios showed the highest correlations, with differences between litter types. The results indicate that higher C storage will occur in soil as a consequence of litter quality changes resulting from higher atmospheric concentrations of CO2.

Microbial and Faunal Interactions and Effects on Litter Nitrogen and Decomposition in Agroecosystems

We conducted field experiments to test the general hypothesis that the composition of decomposer communities and their trophic interactions can influence patterns of plant litter decomposition and nitrogen dynamics in ecosystems. Conventional (CT) and no—tillage (NT) agroecosystems were used to test this idea because of their structural simplicity and known differences in their functional properties. Biocides were applied to experimentally exclude bacteria, saprophytic fungi, and microarthropods in field exclosures. Abundances of decomposer organisms (bacteria, fungi, protozoa, nematodes, microarthropods), decomposition rates, and nitrogen fluxes were quantified in surface and buried litterbags (Secale cereale litter) placed in both NT and CT systems. Measurements of in situ soil respiration rates were made concurrently. The abundance and biomass of all microbial and faunal groups were greater on buried than surface litter. The mesofauna contributed more to the total heterotrophic C in buried litter from CT (6—22%) than in surface litter from NT (0.4—11%). Buried litter decay rates (1.4—1.7%/d) were ≈2.5 times faster than rates for surface litter (0.5—0.7%/d). Ratios of fungal to bacterial biomass and fungivore to bacterivore biomass on NT surface litter generally increased over the study period resulting in ratios that were 2.7 and 2.2 times greater, respectively, than those of CT buried litter by the end of the summer. The exclusion experiments showed that fungi had a somewhat greater influence on the decomposition of surface litter from NT while bacteria were more important in the decomposition of buried litter from CT. The fungicide and bactericide reduced decomposition rates of NT surface litter by 36 and 25% of controls, respectively, while in CT buried litter they were reduced by 21 and 35% of controls, respectively. Microarthropods were more important in mobilizing surface litter nitrogen by grazing on fungi than in contributing to litter mass loss. Where fungivorous microarthropods were experimentally excluded, there was less than a 5% reduction in mass loss from litter of both NT and CT, but fungi–fungivore interactions were important in regulating litter N dynamics in NT surface litter. As fungal densities increased following the exclusion of microarthropods on NT surface litter, there was 25% greater N retention as compared to the control after 56 d of decay. Saprophytic fungi were responsible for as much as 86% of the net N immobilized (1.81 g/m2) in surface litter by the end of the study when densities of fungivorous microarthropods were low. Although bacteria were important in regulating buried litter decomposition rates and the population dynamics of bacterivorous fauna, their influence on buried litter N dynamics remains less clear. The larger microbial biomass and greater contribution of a bacterivorous fauna on buried litter is consistent with the greater carbon losses and lower carbon assimilation in CT than NT agroecosystems. In summary, our results suggest that litter placement can strongly influence the composition of decomposer communities and that the resulting trophic relationships are important to determining the rates and timing of plant litter decomposition and N dynamics. Furthermore, cross placement studies suggest that the decomposer communities within each tillage system, while not discrete, are adapted to the native litter placements in each.

Litter Decomposition in a Chihuahuan Desert Playa

Mass loss rates were compared for several types of litter in a flooded desert ephemeral playa. Most nonwoody types of organic matter, including black grama grass, creosotebush leaves and rabbit feces decomposed rapidly. Creosotebush twigs and wood decomposed slowly. About 25% of the mass was lost due to abiotic leaching. Predator exclusion significantly increased decomposition of creosotebush leaves, but reduced mass loss rate of creosotebush twigs and black grama grass. Decomposition rates were within the range of those found in lakes, and much lower than rates typical of streams. Our data suggest that organisms have little effect on mass loss of debris transported into a desert playa.

Evaluation of plasma-deposited protective coatings for multipurpose space applications

Summary This paper reports evaluations of protective thin films applied to important polymers used on spacecraft, Kapton® polyimide and graphite-epoxy, that are attacked by atomic oxygen. These films, derived from volatile compounds through microwave glow discharge deposition, include amorphous silicon (a-Si:H) and inorganic silicon compounds (P-SiN and P-SiO 2 ). These materials are shown to provide excellent protection against atomic oxygen attack, as evidenced by the reduction in mass loss compared to unprotected specimens of the same materials after exposure to an atomic oxygen beam source. Scanning electron microscope photomicrographs are presented to confirm the lack of apparent attack of the surface. Results from high-energy (20 keV) electron beam bombardment show that these coatings reduce charge build-up which might otherwise result in electrostatic discharge phenomena. These materials provide promising candidates for coatings for exterior surfaces of spacecraft to protect the underlying materials from the deleterious effects of the space environment.

Colder specimens give a sharper impression: Prospects for higher resolution Electron Microscopy at liquid helium temperature

Designers of electron microscopes started putting liquid helium into their plans with the hopes of improving instrumental resolution. Liquid helium can be used to cool specimen stages within conventional lenses, but it can also be used to make some materials superconducting. Once started, current flows continuously in a superconducting coil because it faces negligible electrical resistance. Superconducting lenses were introduced in electron microscopy to take advantage of the high magnetic field strengths that could be generated as well as the stability of the persistent current in the superconducting coils. As time passed, it became clear that electronic regulation of power supplies could produce more than adequate current regulation to supercede the need for the persistent current maintained in a superconducting lens. Meanwhile, the realization grew that low temperatures might give another kind of advantage to electron microscopy of radiation-sensitive materials. The very low temperature might help protect sensitive specimens from damage.Several methods are available for detecting damage to specimens in electron microscopes. The loss of mass from specimens is one sign of radiation damage. A mass loss measurement with a liquid helium cooled stage seemed to show a significant reduction in mass loss; a different measurement that included a superconducting lens also indicated reduced damage. Another indicator of damage is the rate of fading of diffraction patterns of ordered specimens, and in this case it has been established that liquid helium temperature causes a moderate reduction of damage.

An investigation of rail corrugation using friction-induced vibration theory

Rolling wear tests of wheel steel were carried out on friction and wear testing machines, and the effects of pearlite content and slip ratio on the microstructure evolution and property change of wheel steel were studied. The results indicated that if the pearlite content is low, surface cracks propagate along the deformed proeutectoid ferrite and deformed pearlite after initiation, and the wear mechanism is mainly fatigue wear. With an increase in pearlite content, the surface cracks propagate along the plastic flow lines, and the wear mechanism is mainly fatigue wear and adhesive wear. The fatigue wear and adhesive wear gradually increase as the slip ratio increases, resulting in a gradual increase in mass loss. The fatigue wear degree at each slip ratio is significantly reduced as the pearlite content increases, as well as the crack length, resulting in a substantial reduction in mass loss. When the pearlite content is low, low-angle boundaries are formed first in the proeutectoid ferrite. With an increase in the degree of deformation, the cementite is bent, fractured, or even dissolved. The proportion of high-angle boundaries in the ferrite gradually increases, and the grains are refined. When the pearlite content is high, the low-angle boundaries are formed in the lamellar ferrite, which eventually transforms into high-angle boundaries, making it more refined than with low-pearlite content. The cementite is severely fragmented and dissolved on the worn surface, the ferrite is elongated or even fibrous, and the microstructure is the most severe, resulting in the maximum surface hardness. The dissolution of surface cementite and the degree of ferrite refinement increase as the pearlite content and slip ratio increase, as does the hardness.

Mass Accuracy in the STEM

The scanning transmission electron microscope (STEM) has a number of features which make it ideal for quantitative studies: 1) large acceptance angle scintillator-photomultiplier detectors for low dose dark field imaging with linear electron detection, 2) simple contrast transfer function with no oscillations, 3) cold stage for zero contamination and reduced mass loss, 4) digital scanning for accurate magnification and positioning and 5) serial readout of several signals simultaneously for direct interfacing to a computer.For the past 10 years the Brookhaven STEM has been used for mass measurements on isolated individual molecules in freeze dried biological specimens. Interpretation of dark field STEM images is straightforward because of the clean background and linearity of the entire imaging process. Mass measurements provide a quantitative link to biochemical studies. Tobacco mosaic virus (TMV) usually is included along with the specimen of interest as a measure of the quality of the freeze drying and as a check on the microscope calibration, but is not necessary for absolute mass measurements.

Selective Mass Loss, Abundance Anomalies, and Helium-rich Stars

view Abstract Citations (49) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Selective Mass Loss, Abundance Anomalies, and Helium-rich Stars Michaud, G. ; Dupuis, J. ; Fontaine, G. ; Montmerle, T. Abstract In the presence of mass loss, the He abundance in the line-forming region is modified by the chemical separation that takes place not only in the atmospheric region but also in the wind and in the envelope. Since He-rich stars of the upper main sequence appear to be a hot extension of the Ap-Bp phenomenon in which mass loss is observed to be present, we here take diffusion in the wind, the atmosphere, and the envelope simultaneously into account in order to obtain constraints on the hydrodynamics of mass loss. It is shown that to explain the He enrichment by separation in the atmosphere in stars of both Teff = 20,000 K and Teff = 25,000 K requires that the mass-loss rate decrease when Teff increases. It is also shown that the mass loss allowing separation (about 3 x 10-13 Msun yr-1 at Teff = 25,000 K) is smaller than that expected from an extrapolation of the mass-loss rates observed in O stars and of that which is observed in some He-rich stars. The magnetic field seems to be required to reduce the mass-loss rate where the separation occurs. It is suggested that most of the mass loss occurs at the poles, while the chemical separation leading to He enrichment occurs at the magnetic equator where the magnetic field reduces mass loss. This explains the observed single-wave pattern of He enrichment. It also leads to an observational test of the model: the CNO abundances should be normal. The maximum mass loss for which separation can occur in the wind is determined to be 2 x 10-12 Msun yr-1 in main-sequence stars and 10 times larger in white dwarfs. However, this is obtained using models for the wind region that maximize the effect of separation, and it is argued that separation in the wind coudl actually be much smaller. It depends in particular on the temperature in the wind region, and cold winds lead to much less separation. Separation in the atmosphere is likely to be more important than separation in the wind. Separation in the envelope leads to underabundances of helium. It is, however, shown here that for mass-loss rates leading to He overabundances by chemical separation in the atmospheric region, separation in the envelope is too slow to reduce the He abundance in the atmosphere during the main-sequence life of He-rich stars. Confirming that the separation occurs in the atmospheric region has important hydrodynamical consequences. Not only does it limit the mass-loss rate and its space distribution, but it also implies that the He convection zones do not extend into the atmosphere and that there is little, if any, overshooting into the atmosphere. Evaluations of the separation in the atmosphere and wind of white dwarfs and sdB stars are also carried out to show the dependence on gravity. Publication: The Astrophysical Journal Pub Date: November 1987 DOI: 10.1086/165726 Bibcode: 1987ApJ...322..302M Keywords: DIFFUSION; STARS: ABUNDANCES; STARS: INTERIORS; STARS: MASS LOSS; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (1)

Development of a multi-purpose solar crop dryer for arid zones

A multi purpose solar crop dryer was developed for drying various agricultural products such as fruits, vegetables, medicinal plants etc. The newly developed system consists of a small fan, a solar air heater and a tunnel dryer. The simple design allows production either by farmers themselves, using cheap and locally available materials, or by small scale industries. Due to the low investment required, the solar dryer is predestined for application on small farms in developing countries. Depending on the crop to be dried and the size of the dryer 100–1000 kg of fresh material can be dried within 1–7 days to safe storage conditions. The solar dryer was successfully tested in Greece, Yugoslavia, Egypt, Ethiopia and Saudia Arabia drying grapes, dates, onions, peppers and several medicinal plants. Compared to traditional sun drying methods, the use of the solar dryer reduces drying time significantly and prevents mass losses. Furthermore, product quality can be improved essentially. During drying, the crop is protected completely from rain, dust, insects and animals. All these features contribute to the desired high product quality. The energy cost required for operating the fan features contribute to the the additional earnings from reduced mass losses and improved quality. On-farm tests also showed that the dryer can be easily operated by farmers. However, at present the dissemination of the solar dryer is limited to electrified areas.

The Mass Loss Rate of SK 80 (07Iaf) in the Small Magellanic Cloud

The star SK 80 in the SMC is classified as 07Iaf by Walborn (1976) who notes that it is the only confirmed Of star in that Galaxy known to date. A knowledge of the mass loss properties of OB stars in the Magellanic Clouds is of interest because of the recent evidence that such stars show reduced mass loss properties than their galactic counterparts (Hutchings 1980) and for Of stars because of the possible link between such stars and Pop I transition WNL stars (Conti 1976).We have secured HIRES IUE and optical spectra of SK 80 and have attempted to derive the mass loss rate from these data.

Reflecting Ablating Heat Shields for Planetary Entry

Heat shielding for planetary entry probes of future Jovian and Venusian missions will encounter heating levels well beyond those previously experienced. These entries are typically dominated by radiative heating from the shock layer. This paper demonstrates the potential of reflecting this incident radiation diffusely from an ablating material. This technique contrasts with the absorption experienced by char-forming or graphitic ablators. Two dielectric materials, Teflon (polytetra-fluoroethylene) and boron nitride, are examined for their ablative performance, including reflection, in a combined convective- and radiative-heating environment. For Teflon, at the conditions obtained, superimposition of radiative heating upon a convective stream causes no additional increase in surface recession over the convective only results. For boron nitride, an excellent room-temperature reflector in the visible spectrum, a decrease in reflectivity from 90 to 55 percent is experienced when the surface undergoes sublimation at high temperatures. The process of reflection in each of these materials is described in terms of backscattering from crystals. The significance of a sizable reflection as a mode of energy accommodation is demonstrated for Venusian entries as a potential reduction in mass loss due to ablation.