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A New Twist on Fiber Optics

By twisting fiber optic strands into helical shapes, researchers have created unique structures that can precisely filter, polarize or scatter light. Compatible with standard fiber optic lines, these hair-like structures may replace bulky components in sensors, gyroscopes and other devices. While researchers are still probing the unusual properties ...

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ANewTwistonFiberOptics
Mathematics

How To Calculate The Area Of A Cylinder

Understanding how to find the area of a cylinder is easy if one first visualizes the cylinder and breaks its surface down into component pieces. To do this, first take a good look at the most common ... Continue reading

AreaOfACylinder
Chemistry

What Is A Half-life?

When isotopes break down, or decay, they usually split apart into two smaller atoms. Excess neutrons and protons are often sent flying off through space, taking the excess energy of the atoms with ... Continue reading

WhatIsAHalflife
Geology

How Much Water in an Inch of Snow?

If the snowfall amounts were translated into equivalent volumes of water - then how much water would that be? Using a rule of thumb that each 10 inches of snow, if melted, would produce one inch of ... Continue reading

HowMuchWaterinanInchofSnow
Biology

Batesian Mimicry

If you ever got stung by a wasp you would probably avoid all flying insects which resemble the brightly-colored yellow and black wasp. If you were a bird and certain types of butterflies gave you a ... Continue reading

BatesianMimicry

Why Is Blood Pressure Two Numbers?

WhyIsBloodPressureTwoNumbersBlood pressure might better be called heart pressure, for the heart's pumping action creates it. To measure blood pressure, health workers determine how hard the blood is pushing at two different times: when the heart contracts, called systole; and when the heart relaxes, called diastole. The contraction of the ventricles during systole gives the blood a strong push, like the rush of water through a hose when the spigot is turned on. The force propels the blood through the arteries; it also pushes against artery walls. The first number in a blood pressure reading is the systole number. It is a larger number because the pressure of blood against artery walls is greater with the push of the heart's contraction behind it. Diastole is the relaxation phase of heartbeat. Pressure diminishes within the relaxing ventricles. The pressure that blood exerts on artery walls decreases, too. This is the second number in a blood pressure measurement. It is always smaller than the first.

Blood pressure is not the same in all parts of the body, so to make comparisons meaningful, blood pressure is usually measured in the main artery of the upper arm. Also, blood pressure increases with exercise, stress, or exertion, so its readings are most accurate when the subject is lying down and relaxed. Other factors besides position and exercise can affect blood pressure. The amount of blood in the system, the strength of the heart's flexing, and the pliancy of artery walls all play a part. Emotions such as fright, excitement, or worry increase blood pressure. Blood pressure can fall in people who are depressed, lonely, or grieving.

Blood pressure is measured in millimeters of mercury. A blood pressure of less than 120 mm. over 80 mm. is considered a normal reading for adults. Until recently, pressures below 140/90 were thought acceptable. Now, new guidelines for physicians define pressure that stays between 120-139 systolic or 80-89 diastolic as 'prehypertension.' For people with pressures in that range, the risk of developing hypertension, or blood pressure high enough to require treatment, is elevated.