Deceleration Equation Research Articles

Photodegradation influences litter decomposition rate in a humid tropical ecosystem, Brazil

Solar radiation in general and UV radiation in particular have been recognized to stimulate plant litter decomposition through photochemical mineralization of organic molecules such as lignin and through facilitation of microbial decomposition in dryland ecosystems. However, little is known about how photodegradation may influence decomposition in other ecosystems not subject to moisture limitations and under what conditions photodegradation may be favored. Decomposition in humid tropical ecosystems is a complex process, and it can be influenced by a number of environmental factors that are distinct from arid and semi-arid ecosystems. To assess the mechanisms underlying photodegradation by ultraviolet B (UV-B) radiation in a humid tropical ecosystem, we designed a 300-day field experiment in a tropical site in Brazil with high levels of annual precipitation, compared to arid ecosystems, and exposed litter to three levels of radiation (full sun, UV-B removed, and shade) combined with a biocide treatment. Results show that after nearly one year of exposure, the microbial biomass was not affected by UV-B incidence, and this effect has not yet been fully understood for tropical ecosystems. Modeled using an exponential deceleration equation, the removal of UV-B radiation decelerated the plant litter decomposition rate for the control conditions by 21% compared to litter exposed to full sun. Interestingly, shaded litter exhibited similar mass loss compared to litter exposed to full sun. Furthermore, differences in the decay constant among radiation treatments due to the UV-B effect were independent of lignin loss. Overall, our study suggests that UV-B radiation contributed to plant litter decomposition through carbon losses but had no discernible effect on nitrogen, lignin, or cellulose loss specifically. Importantly, our results demonstrate that photodegradation occurs under humid tropical conditions, and further studies are necessary to examine the mechanisms of carbon loss.

Analytical solution of the equations of the physical theory of meteors for a single (non-fragmenting) body with mass loss in a non-isothermal (arbitrary) atmosphere with a variable ablation parameter

We have obtained an analytical solution of two simultaneous ordinary differential equations of the physical theory of meteors: the equation of motion for the center of mass of a meteoroid (deceleration equation), the thermal balance equation (ablation equation), the luminosity equation, and the ionization trail equation. The solution has been obtained by assuming a straight-line trajectory and a power-law dependence of the ablation parameter on the meteoroid velocity for an arbitrary atmosphere in the continuous flow regime.

Impact experiments of exotic dust grain capture by highly porous primitive bodies

Small primitive bodies were presumably highly porous when they formed and some still have low densities that are indicative of a high pore content. Therefore, after their formation, interplanetary dust impacting on their surface may have been captured because of their porous structure. The mechanism of dust penetration is thus of importance to understand the evolution of small bodies and the origin of their internal dust particles. Impact experiments of sintered glass-bead targets characterized by 80%, 87%, and 94% bulk porosity were conducted using metal and basalt projectiles at impact velocities ranging from 1.6 to 7.2kms−1. Track morphology and penetration processes were analyzed using both X-ray tomography and a flash X-ray system. Two types of track were observed, as previously also found in the Stardust aerogel: a thin and long track (carrot-shaped track), and a “bulb” with tails (bulb-shaped track). The track shape changed with initial dynamic pressure. We found that the transition between “carrot” and “bulb” occurred at a pressure of roughly 20 times the projectile’s tensile strength. The deceleration process of projectiles without severe deformation and fragmentation was reproduced by a drag equation composed of an inertia drag that was proportional to the square of the projectile’s velocity and a constant drag proportional to the target’s compressive strength. We applied this deceleration equation to silicate dust penetrating into hypothetical porous icy bodies which were homogeneous on much smaller scales than the impacting dust particles. The penetration depth was approximately 100 times the projectile diameter for the bodies with 90% porosity.

Dynamics and Control on Double-drum Roller Maximum Brake Deceleration

Reducing start and stop time without destroying the pavement surface is important in enhancing productivity of double-drum roller and compact quality of asphalt pavement, but it is difficult in confirming the maximum brake deceleration or start acceleration of double-drum roller. Dynamic analysis is used in studying these questions, and a mathematic model of double-drum roller is established, based on the model, the factors which will affect the maximum brake deceleration of double-drum roller is studied, such as brake force from travel hydraulic travel system, the adhesive force from compacted ground, the inertia force of drums and double-drum roller itself. And the max brake deceleration equation is obtained which consider all these factors. It indicates that drum inertia affects the max brake deceleration of double-drum roller notable, and should be taken into account during design procedure and control program. At last a maximum deceleration control method based on slip control and classic PID algorithm is advised.

Study on Double-Drum Roller Maximum Braking Deceleration

Reducing start and stop time is important in enhancing productivity of double roller and compact quality of asphalt pavement, but it is difficult in confirming the max braking deceleration or starting acceleration of double-drum roller. Dynamic analysis is used and a mathematic model of double roller is established. Based on the model, the factors which affect the max braking deceleration is studied, such as braking force from hydraulic travel system, the adhesive force from ground, the inertia force from machine itself. And the max braking deceleration equation is obtained which consider the entire factors. The result indicates that drum inertia affects the max braking deceleration of double drum roller notable, and should be taken into account during design procedure and control program.

Micrometeor Observations Using the Arecibo 430 MHz Radar: I. Determination of the Ballistic Parameter from Measured Doppler Velocity and Deceleration Results

We present a sample of radar meteors detected during the November 1997 Leonids shower period using the narrow-beam, high-power Arecibo Observatory 430-MHz radar. During this period ∼7700 events were detected over 73 h of observations that included six mornings. Near apex-crossing, 6–10 events per minute were observed in the ∼300-m diameter beam. From these events a total of 390 meteors are characterized by a clear linear deceleration as derived from the radial Doppler speed determined from the meteor-echo leading-edge (head-echo). We interpret our results in terms of the meteor ballistic parameter—the ratio of the meteoroid mass to cross-sectional area—yielding a physical characterization of these particles prior to any assumptions regarding meteoroid shape and mass density. In addition, we compare these measurements with the results of a numerical solution of the meteor deceleration equation and find them in good agreement. The size and dynamical mass of the meteoroids are estimated considering these particles to be spheres with densities of 3 g/cm 3. We also discuss atmospheric energy-loss mechanisms of these meteroids. We believe these are the first radar meteor decelerations detected since those ones reported by J. V. Evans (1966, J. Geophys. Res. 71, 171–188) and F. Verniani (1966, J. Geophys. Res. 71, 2749–2761; 1973, J. Geophys. Res. 78, 8429–8462) and the first ones for meteors of this size.

Asymmetric Hydrodynamic Impact and Dynamic Response of Vessels

Theoretical simulations are compared with drop test experiments of vessel free-fall impact on calm water, with zero and nonzero initial heel angles. The impact force and moment are predicted by using a theory described in Xu et al. (1998). The resulting motions of vessels at asymmetric impact include vertical water entry and transverse rolling. The downward deceleration equation combines the hydrostatic and hydrodynamic forces and the weight of hull, while the rolling equation takes into account the restoring moments due to asymmetry. Another simplified approach of a water entry dynamics and injury model (Gollwitzer and Peterson, 1996) is also applied to evaluate the impact acceleration for symmetric cases. The experiments were conducted at the Coastal Systems Station, Panama City, Florida, using a 2 ft × 8 ft (0.61 m × 2.44 m) prismatic hull model with 20 deg deadrise. The comparisons between the asymmetric impact theory and experiment shows varying degrees of qualitative and quantitative agreement.

Electrophysical and optophysical properties of air ionized by a short pulse of fast electrons

A method of solving the nonsteady kinetic equation of deceleration of electrons is developed in the basis of the application of the multigroup approximation. The electron distribution function in air ionized by nonsteady sources of primary electrons is determined, and the process of avalanche formation of secondary electrons in air is investigated. The time dependence of the emission intensity of air is determined, experimentally and by calculation, in two spectral intervals, one of which includes the lambda = 391.4 nm NS N/sub 2//sup +/ (O, O) band while the other includes the lambda = 337.1 nm 2 PS N/sub 2/ (O, O) band, under the action of a short electron beam with an energy E = 100 keV for different values of the gas pressure. The agreement between theoretical results and experimental data indicates the reliability of the method of solving the nonsteady kinetic equation of electron deceleration proposed in the paper.

Simple analytical solutions for spherically symmetric production and modulation of energetic solar particles

Exact analytical solutions are presented for the standard time-independent spherically symmetric convection-diffusion-adiabatic deceleration equation governing the transport of cosmic rays in the interplanetary medium for the case in which particles are produced with spherical symmetry at the sun. It is assumed that the solar-wind speed is constant and radial, and that the spatial diffusion coefficient has a power-law dependence on momentum. The Green's function describing the modulation of a monoenergetic production of particles is presented. The solutions provide a useful basis for the study of time-integrated properties of energetic solar-flare particle spectra.

Simple analytic solutions appropriate for galactic cosmic-ray modulation

view Abstract Citations (12) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Simple analytic solutions appropriate for galactic cosmic-ray modulation. Cowsik, R. ; Lee, M. A. Abstract Exact analytic solutions, for the galactic cosmic-ray density, to the standard time-independent spherically symmetric convection-diffusion-adiabatic deceleration equation governing the transport of cosmic rays in the interplanetary medium are presented. It is assumed that the solar-wind speed is constant and that the spatial diffusion coefficient is given by a power law, independent of distance from the sun, in accordance with Pioneer 10 and 11 measurements and recent calculations. One solution depicts with decreasing distance from the sun the energy loss and intensity decrease of an interstellar spectrum which is peaked in momentum. From this solution others are constructed which (1) are extremely simple analytically; (2) are sufficiently general both to yield excellent agreement with observations near earth and to demonstrate quantitatively the sensitivity of derived interstellar spectra on the forms assumed in the inner solar system, particularly at low energies; and (3) promise to replace the standard convection-diffusion solution often utilized in data analysis and modulation estimates, while providing a useful tool for future research involving cosmic-ray modulation. Publication: The Astrophysical Journal Pub Date: September 1977 DOI: 10.1086/155503 Bibcode: 1977ApJ...216..635C Keywords: Cosmic Rays; Galactic Radiation; Interplanetary Medium; Particle Diffusion; Plasma-Particle Interactions; Solar Wind; Energy Dissipation; Energy Spectra; Modulation; Particle Flux Density; Pioneer Space Probes; Space Radiation full text sources ADS |