On the time required for aerosols to reach electrical equilibrium

Summary Natural aerosols over the ocean are usually in electrical equilibrium. Aerosols in cities are hardly ever in electrical equilibrium. Aerosols over land are frequently not in equilibrium even though distant from any obvious source of contamination.Calculations are given of the time required to reach equilibrium which would lead one to expect the conditions encountered over the ocean and in cities. Some speculations are made on the lack of equilibrium over land.

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Zusammenfassung Natürliche Aerosole über dem Ozean sind gewöhnlich in elektrischem Gleichgewicht. Aerosole in Städten sink kaum jemals im elektrischen Gleichgewicht. Aerosole über Land sind häufig nicht im Gleichgewicht, selbst wenn sie weit weg von irgendwelchen offenkundigen Quellen der Verunreinigung sind.Es werden Berechnungen der Zeit, welche für die Erreichung des Gleichgewichtes erforderlich ist, gegeben. Einige überlegungen über das Nichtvorhandensein elektrischen Gleichgewichtes über Land werden mitgeteilt.

     

A continuous recorder for condensation nuclei

Summary A continuous recorder of condensation nuclei with multiple ranges that are substantially linear over the range of 500 to 50,000 nuclei per ml full scale is described. The range can be extended but the scale law becomes proportional to the cube root of the nuclei concentration. The sampling rate is 100 ml/sec and the response time is less than 2 seconds.The unit works on fog-scattered light with dark-field illumination. The expansion ratio is adjustable (at the expense of recalibration) and can be made high enough to respond to a radium source. The electronics are simple and sturdy; the unit has been used on a truck in motion.     

Timeline analysis and wavelet multiscale analysis of the AKARI All-Sky Survey at 90 μm

We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-μm band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS ( Infrared Astronomy Satellite ) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-μm flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio  (S/N) > 5  for a single detector row is  1.1 ± 0.1 Jy  which corresponds to a point-source detection limit of the survey of ∼0.4 Jy.
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds.     

Suspended sediment transport and deposition over a dune: Río Paraná, Argentina

Field data from the Rio Paraná, Argentina, are used to examine patterns of suspended sediment transport over a sand dune. Measurements of three‐dimensional velocity are made with an acoustic Doppler current profiler whilst suspended sediment concentration and particle size have been quantified using a laser in situ sediment scattering transmissometer. Suspended sediment concentration and streamwise and vertical sediment flux are highest close to the bed, with an upward vertical flux over the stoss side of the dune and downward flux over the lee side. Suspended sediment concentrations are higher over the crest compared with the trough and suspended sediment is coarsest near the bed. About 17% of the suspended‐load transported over the crest is deposited in the lee side before it reaches the trough. Most of this deposited sand is coarser sediment that originates close to the bed over the crest, a result consistent with simulations based on the model of Mohrig and Smith (Water Resources Research 1996; 32: 3207–3217) for the excursion lengths of sediment dispersed in the lee side of a dune. Copyright © 2009 John Wiley & Sons, Ltd.     

Cosmological information from wimp experiments

We discuss the information that can be obtained from direct and indirect detection experiments of wimp dark matter. While individual experiments yield little information about wimp cross sections or galactic abundances, we consider the possibility that data from direct and indirect experiments can be combined to give a measurement of the low-energy wimp annihilation cross section. This turns out to be possible if the wimp annihilation rate in the Earth is not balanced by the capture rate. The derived low-energy annihilation cross section can be used to constrain the cosmological density of wimps.