Mie scattering from a sonoluminescing air bubble in water

Applied Optics, Volume 34, No. 15, pp. 2648-2654 (20 May 1995)A single bubble of air in water can emit pulses of blue-white light that have durations of less than 50 ps while it is oscillating in an acoustic standing wave. The emission is called sonoluminescence. A knowledge of the bubble diameter throughout the cycle, and in particular near the time of sonoluminescence emission, can provide important information about the phenomenon. A new Mie scattering technique is developed to determine the size of the bubble through its expansion and collapse during the acoustic cycle. The technique does not rely on an independent means of calibration or on accurate measurements of the scattered intensity.This work was supported in part by the Naval Postgraduate School Research Program and the Office of Naval Research

Polyacrylamide in agriculture and environmental land management

Anionic polyacrylamide (PAM) has been sold since 1995 to reduce irrigation-induced erosion and enhance infiltration. Its soil stabilizing and flocculating properties improve runoff water quality by reducing sediments, N, dissolved reactive phosphorus (DRP) and total P, chemical oxygen demand (COD), pesticides, weed seeds, and microorganisms in runoff. PAM used for erosion control is a large (12-15 Mg mol -1) water-soluble (non-cross-linked) anionic molecule, containing <0.05% acrylamide monomer. In a series of field studies, PAM eliminated 80-99% (94% avg.) of sediment in runoff from furrow irrigation, with a 15-50% infiltration increase compared to controls on medium to fine-textured soils. Similar but less dramatic results occur with sprinkler irrigation. In sandy soils infiltration is often unchanged by PAM or can be slightly reduced. Typical seasonal application totals in furrow irrigation vary from 3 to 7 kg ha -1 . Research has shown little or no consistent adverse effect on soil microbial populations. Some evidence exists for PAM-related yield increases where infiltration was crop-limiting, especially in field portions having irregular slopes, where erosion prevention eliminated deep furrow cutting that deprives shallow roots of adequate water delivery. Modified water management with PAM shows great promise for water conservation. High effectiveness and low cost of PAM for erosion control and infiltration management, coupled with easier implementation than traditional conservation measures, has resulted in rapid adoption. About 800,000 ha of US irrigated land use PAM for erosion and/or infiltration management. In recent years, PAM has been deployed for uses beyond agricultural erosion control, including construction site erosion control, use in storm water runoff ponds to accelerate water clarification, soil stabilization and dust prevention in helicopter-landing zones, and various other high-traffic military situations. Among the newest topics being researched is the use of PAM to reduce ditch, canal, and pond seepage, using specific application protocols that take advantage of its increase of water viscosity at higher concentrations

An Alternative Method to Deduce Bubble Dynamics in Single Bubble Sonoluminescence Experiments

In this paper we present an experimental approach that allows to deduce the important dynamical parameters of single sonoluminescing bubbles (pressure amplitude, ambient radius, radius-time curve) The technique is based on a few previously confirmed theoretical assumptions and requires the knowledge of quantities such as the amplitude of the electric excitation and the phase of the flashes in the acoustic period. These quantities are easily measurable by a digital oscilloscope, avoiding the cost of expensive lasers, or ultrafast cameras of previous methods. We show the technique on a particular example and compare the results with conventional Mie scattering. We find that within the experimental uncertainties these two techniques provide similar results.Comment: 8 pages, 5 figures, submitted to Phys. Rev.

Irrigating with polyacrylamide (PAM) - Nine years and a million acres of experience

Polyacrylamide (PAM) has been available commercially since 1995 for reducing irrigation-induced erosion and enhancing infiltration. The first series of practical field tests was conducted in 1991. PAM used for erosion control is a large water soluble (non-crosslinked) anionic molecule (12-15 megagrams per mole) containing < 0.05% acrylamide monomer. In controlled field studies PAM eliminated, on average, 94% (80-99% range) of sediment loss in field runoff from furrow irrigation, with a typical 15-50% relative infiltration increase on medium to fine textured soils compared to untreated controls. Similar but less dramatic results have been seen with sprinkler irrigation. Under some conditions infiltration is unchanged or can even be slightly reduced, e.g. in sandy soils or where PAM application rates are very high. Results are achieved with per irrigation field application rates of about 1 kg per hectare, for furrow irrigation, and 2 to 4 kg per hectare for sprinkler irrigation. Cost of PAM is $7 to$13 per kg. Seasonal application totals vary from 3 to 7 kg per hectare. Farmer field sediment control has been around 80% of test plot results. Substantial runoff reductions have been documented for nutrients, pesticides, microorganisms, BOD, and weed seed. No adverse effects have been seen for soil microbial populations. Crop yields have not been widely documented, though evidence exists for yield increases related to infiltration improvement. High effectiveness, low cost, and ease of application, compared to traditional conservation measures, has resulted in rapid technology acceptance in the US and internationally. PAM-use for runoff water quality protection is one of the most potent new irrigation environmental technologies in the market place. New uses in construction and dryland erosion control are being developed rapidly. This paper discusses new insights and understanding of PAM-use and potential for future development

Boundary work: becoming middle class in suburban Dar es Salaam

Suburban space provides a useful window onto contemporary class practices in Africa, where it is difficult to identify social classes on the basis of income or occupation. In this article I argue that the middle classes and the suburbs are mutually constitutive in the Tanzanian city of Dar es Salaam. Using interviews with residents and local government officials in the city's northern suburbs, I discuss the material and representational practices of middle-class boundary work in relation to land and landscape. If the middle classes do not presently constitute a coherent political-economic force, they are nevertheless transforming the city's former northern peri-urban zones into desirable suburban residential neighbourhoods

Bounds on the possible evolution of the Gravitational Constant from Cosmological Type-Ia Supernovae

Recent high-redshift Type Ia supernovae results can be used to set new bounds on a possible variation of the gravitational constant $G$. If the local value of $G$ at the space-time location of distant supernovae is different, it would change both the kinetic energy release and the amount of $^{56}$Ni synthesized in the supernova outburst. Both effects are related to a change in the Chandrasekhar mass $M_{Ch} \propto G^{-3/2}$. In addition, the integrated variation of $G$ with time would also affect the cosmic evolution and therefore the luminosity distance relation. We show that the later effect in the magnitudes of Type Ia supernovae is typically several times smaller than the change produced by the corresponding variation of the Chandrasekhar mass. We investigate in a consistent way how a varying $G$ could modify the Hubble diagram of Type Ia supernovae and how these results can be used to set upper bounds to a hypothetical variation of $G$. We find G/G_0 \la 1.1 and G'/G \la 10^{-11} yr^{-1} at redshifts $z\simeq 0.5$. These new bounds extend the currently available constrains on the evolution of $G$ all the way from solar and stellar distances to typical scales of Gpc/Gyr, i.e. by more than 15 orders of magnitudes in time and distance.Comment: 9 pages, 4 figures, Phys. Rev. D. in pres

Unmanned Aircraft Navigation for Shipboard Landing using Infrared Vision

IEEE Transactions on Aerospace and Electronic Systems, October 2002, vol. 38 no. 4, pp. 1181-1200This paper addresses the problem of determining the relative position and orientation of an unmanned air vehicle with respect to a ship using three visible points of known separation. The images of the points are obtained from an onboard infrared camera. The paper develops a numerical solution to this problem. Both simulation and flight test results are presented

Polyacrylamide in agriculture and environmental land management

Anionic polyacrylamide (PAM) has been sold since 1995 to reduce irrigation-induced erosion and enhance infiltration. Its soil stabilizing and flocculating properties improve runoff water quality by reducing sediments, N, dissolved reactive phosphorus (DRP) and total P, chemical oxygen demand (COD), pesticides, weed seeds, and microorganisms in runoff. PAM used for erosion control is a large (12-15 Mg mol -1) water-soluble (non-cross-linked) anionic molecule, containing <0.05% acrylamide monomer. In a series of field studies, PAM eliminated 80-99% (94% avg.) of sediment in runoff from furrow irrigation, with a 15-50% infiltration increase compared to controls on medium to fine-textured soils. Similar but less dramatic results occur with sprinkler irrigation. In sandy soils infiltration is often unchanged by PAM or can be slightly reduced. Typical seasonal application totals in furrow irrigation vary from 3 to 7 kg ha -1 . Research has shown little or no consistent adverse effect on soil microbial populations. Some evidence exists for PAM-related yield increases where infiltration was crop-limiting, especially in field portions having irregular slopes, where erosion prevention eliminated deep furrow cutting that deprives shallow roots of adequate water delivery. Modified water management with PAM shows great promise for water conservation. High effectiveness and low cost of PAM for erosion control and infiltration management, coupled with easier implementation than traditional conservation measures, has resulted in rapid adoption. About 800,000 ha of US irrigated land use PAM for erosion and/or infiltration management. In recent years, PAM has been deployed for uses beyond agricultural erosion control, including construction site erosion control, use in storm water runoff ponds to accelerate water clarification, soil stabilization and dust prevention in helicopter-landing zones, and various other high-traffic military situations. Among the newest topics being researched is the use of PAM to reduce ditch, canal, and pond seepage, using specific application protocols that take advantage of its increase of water viscosity at higher concentrations