News tagged with density

Hot flashes linked to increased risk of hip fracture

Women who experience moderate to severe hot flashes and night sweats during menopause tend to have lower bone mineral density and higher rates of hip fracture than peers who do not have menopausal symptoms, according to a ...

Dec 18, 2014
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Popular cosmetic fix may threaten bone density

An off-label use of Botox has been found to be effective in relieving temporomandibular joint (TMJ) dysfunction syndrome and associated myofascial pain. But an oral radiologist at UConn Health is concerned ...

Dec 17, 2014
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Next steps uncertain for women with dense breasts

More women are learning their breasts are so dense that it's more difficult for mammograms to spot cancer. But new research suggests automatically giving them an extra test isn't necessarily the solution.

Dec 08, 2014
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Genetic testing could improve breast cancer prevention

Scientists used mathematical models to show that analysing genetic data, alongside a range of other risk factors, could substantially improve the ability to flag up women at highest risk of developing breast ...

Nov 13, 2014
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Osteoporosis, not just a woman's disease

Each year nearly two million Americans suffer osteoporosis-related fractures, and as the population ages that number is expected to increase dramatically, placing a major burden on the health care system. ...

Nov 05, 2014
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Density

The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ (the Greek letter rho). In some cases (for instance, in the United States oil and gas industry), density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight. Different materials usually have different densities, so density is an important concept regarding buoyancy, purity and packaging. Osmium and iridium are the densest known metal elements at standard conditions for temperature and pressure but not the densest materials.

Less dense fluids float on more dense fluids if they do not mix. This concept can be extended, with some care, to less dense solids floating on more dense fluids. If the average density (including any air below the waterline) of an object is less than water (1000 kg/m3) it will float in water and if it is more than water's it will sink in water.

In some cases density is expressed as the dimensionless quantities specific gravity (SG) or relative density (RD), in which case it is expressed in multiples of the density of some other standard material, usually water or air/gas. (For example, a specific gravity less than one means that the substance floats in water.)

The mass density of a material varies with temperature and pressure. (The variance is typically small for solids and liquids and much greater for gasses.) Increasing the pressure on an object decreases the volume of the object and therefore increase its density. Increasing the temperature of a substance (with some exceptions) decreases its density by increasing the volume of that substance. In most materials, heating the bottom of a fluid results in convection of the heat from bottom to top of the fluid due to the decrease of the density of the heated fluid. This causes it to rise relative to more dense unheated material.

The reciprocal of the density of a substance is called its specific volume, a representation commonly used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass.

This text uses material from Wikipedia licensed under CC BY-SA