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The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its value is exactly 299,792,458 metres per second, a figure that is exact because the length of the metre is defined from this constant and the international standard for time.[1]

The first quantitative estimate of the speed of light was made in 1676 by Rømer (see Rømer's determination of the speed of light).[83][84] From the observation that the periods of Jupiter's innermost moon Io appeared to be shorter when the Earth was approaching Jupiter than when receding from it, he concluded that light travels at a finite speed, and estimated that it takes light 22 minutes to cross the diameter of Earth's orbit. Christiaan Huygens combined this estimate with an estimate for the diameter of the Earth's orbit to obtain an estimate of speed of light of 220000 km/s, 26% lower than the actual value.[105]

Beginning in the 1880s several experiments were performed to try to detect this motion, the most famous of which is the experiment performed by Albert A. Michelson and Edward W. Morley in 1887.[128] The detected motion was always less than the observational error. Modern experiments indicate that the two-way speed of light is isotropic (the same in every direction) to within 6 nanometres per second.[129]

Imaging tests, such as ultrasound or CT scans, of your abdomen and pelvis. These tests can help determine the size, shape and structure of your ovaries. Blood test, which can detect a protein (CA 125) found on the surface of ovarian cancer cells. Surgery to remove a tissue sample and abdominal fluid to confirm a diagnosis of ovarian cancer. Minimally invasive or robotic surgery may be an option. If cancer is discovered, the surgeon may immediately begin surgery to remove as much of the cancer as possible.

Stages of ovarian cancer include: Stage I. Cancer is found in one or both ovaries. Stage II. Cancer has spread to other parts of the pelvis. Stage III. Cancer has spread to the abdomen. Stage IV. Cancer is found outside the abdomen.

Order of magnitude[edit] Rømer starts with an order of magnitude demonstration that the speed of light must be so great that it takes much less than one second to travel a distance equal to Earth's diameter. The point L on the diagram represents the second quadrature of Jupiter, when the angle between Jupiter and the Sun (as seen from Earth) is 90°.[note 6] Rømer assumes that an observer could see an emergence of Io at the second quadrature (L), and also the emergence which occurs after one orbit of Io around Jupiter (when the Earth is taken to be at point K, the diagram not being to scale), that is 42½ hours later. During those 42½ hours, the Earth has moved further away from Jupiter by the distance LK: this, according to Rømer, is 210 times the Earth's diameter.[note 7] If light travelled at a speed of one Earth-diameter per second, it would take 3½ minutes to travel the distance LK. And if the period of Io's orbit around Jupiter were taken as the time difference between the emergence at L and the emergence at K, the value would be 3½ minutes longer than the true value. Rømer then applies the same logic to observations around the first quadrature (point G), when Earth is moving towards Jupiter. The time difference between an immersion seen from point F and the next immersion seen from point G should be 3½ minutes shorter than the true orbital period of Io. Hence, there should be a difference of about 7 minutes between the periods of Io measured at the first quadrature and those measured at the second quadrature. In practice, no difference is observed at all, from which Rømer concludes that the speed of light must be very much greater than one Earth-diameter per second.[5]

However Rømer also realised that any effect of the finite speed of light would add up over a long series of observations, and it is this cumulative effect that he announced to the Royal Academy of Sciences in Paris. The effect can be illustrated with Rømer's observations from spring 1672. Jupiter was in opposition on 2 March 1672: the first observations of emergences were on 7 March (at 07:58:25) and 14 March (at 09:52:30). Between the two observations, Io had completed four orbits of Jupiter, giving an orbital period of 42 hours 28 minutes 31¼ seconds. The last emergence observed in the series was on 29 April (at 10:30:06). By this time, Io had completed thirty orbits around Jupiter since 7 March: the apparent orbital period is 42 hours 29 minutes 3 seconds. The difference seems minute – 32 seconds – but it meant that the emergence on 29 April was occurring a quarter-hour after it would have been predicted. The only alternative explanation was that the observations on 7 and 14 March were wrong by two minutes.

Beginning in February, large nonhuman subjects have received weekly injections of cancer cells into their livers, creating a consistent model in a "controlled environment." This month, the subjects will undergo MRIs to determine whether they now have liver cancer. If affirmative, the Kanzius noninvasive radio-wave cancer treatment will be administered, allowing data to be collected and analyzed. The success of these tests is mandatory to move forward in approaching the U.S. Food and Drug Administration and ultimately advancing to human trials.

relationships between cultural spaces, the image-making practices of smartphone users and social media platforms.

In addition to targeted advertising, value is created by leveraging a continuous circulation of meaning and attention

Much of the organization and mobilization occurred through the Internet, particularly on social media such as Facebook and Twitter. But social media also played a vital role as a democratic model. Its inclusive space indirectly taught lessons in democracy to a wide sector of Egyptian youth that was not necessarily politically inclined. When the right moment arrived, they were ready to join the revolt.

What happened in January 2011 in Egypt did not start in January 2011. It began at least ten years earlier, and it’s not over yet

The main catalyst for the January 25 revolution was the Internet, so it may be accurate to describe this as an Internet-based revolution. Not that the Internet was the only factor involved, or that Internet users were the only ones protesting. But the Internet was the tool that showed every dissident voice in Egypt that he or she is not alone, and is indeed joined by at least hundreds of thousands who seek change.

Pandora (which is also the name of the company) grew out of the Music Genome Project, which company founder Tim Westergren began six years ago.

He became fascinated with the way directors described the music they were looking for, which led to his wondering what made people enjoy certain types of music. He asked himself, "If people haven't found any music that they love since college, and artists are struggling to find an audience, is there a role for technology to help bridge the gap?"

Westergren started the Genome Project from the idea of creating a platform for connecting people with music that they'll love based on music they already enjoy. The project uses experts called "music analysts" to deconstruct music into its fundamental parts and capture the results into a database. Pandora has 40 professional musicians who come to the office every day and listen to one song at a time, analyzing each in anywhere from 200 to 400 dimensions. (The dimensions are somewhat different for each genre of music.)

So far as we know, everything we perceive, feel, think, know, and do are a result of neurons firing and resetting. When a cell in the brain fires, small chemical and electrical swings called the action potential may affect the firing of as many as a thousand other neurons in a process called neurotransmission. In this way signals are generated and carried through networks of neurons, the bulk electrical effect of which can be measured directly on the scalp by an EEG device. By the last decade of the 20th century, the essential knowledge of all the central features of neurotransmission had been gained.[4] These features are:

It has previously been known that ultimate control over the membrane voltage or potential of a nerve cell, and thus the firing of the cell, resides with the trans-membrane ion channels which control the membrane currents via the ions K+, Na+, and Ca++, and of lesser importance Mg++ and Cl-. The concentration differences between the inside and outside of the cell determine the membrane voltage.