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In weak lensing by large-scale structure, the thin-lens approximation may break down, and low-density extended structures may not be well approximated by multiple thin-lens planes. In this case, the deflection can be derived by instead assuming that the gravitational potential is slowly varying everywhere (for this reason, this approximation is ...
In 1963 Yu. G. Klimov, S. Liebes, and Sjur Refsdal recognized independently that quasars are an ideal light source for the gravitational lens effect. [23] It was not until 1979 that the first gravitational lens would be discovered. It became known as the "Twin QSO" since it initially looked like two identical quasistellar objects.
Air density, like air pressure, decreases with increasing altitude. It also changes with variations in atmospheric pressure, temperature and humidity . At 101.325 kPa (abs) and 20 °C (68 °F), air has a density of approximately 1.204 kg/m 3 (0.0752 lb/cu ft), according to the International Standard Atmosphere (ISA).
Density, bulk density, or wet density, , are different names for the density of the mixture, i.e., the total mass of air, water, solids divided by the total volume of air water and solids (the mass of air is assumed to be zero for practical purposes):
Matric suction: the defining trait of unsaturated soil, this term corresponds to the pressure dry soil exerts on the surrounding material to equalise the moisture content in the overall block of soil and is defined as the difference between pore air pressure, (), and pore water pressure, (). [2]
When density and gravity are approximately constant (that is, for relatively small changes in height), simply multiplying height difference, gravity, and density will yield a good approximation of pressure difference. If the pressure at one point in a liquid with uniform density ρ is known to be P 0, then the pressure at another point is P 1:
Strong gravitational lensing is a gravitational lensing effect that is strong enough to produce multiple images, arcs, or Einstein rings. Generally, for strong lensing to occur, the projected lens mass density must be greater than the critical density, that is . For point-like background sources, there will be multiple images; for extended ...
The effects of foreground galaxy cluster mass on background galaxy shapes. The upper left panel shows (projected onto the plane of the sky) the shapes of cluster members (in yellow) and background galaxies (in white), ignoring the effects of weak lensing. The lower right panel shows this same scenario, but includes the effects of lensing.