In order for mechanical oscillation to occur, a system must posses two quantities: elasticity and inertia. When the system is displaced from its equilibrium position, the elasticity provides a restoring force such that the system tries to return to equilibrium. The inertia property causes the system to overshoot equilibrium. This constant play between the elastic and inertia properties is what allows oscillatory motion to occur.
The animated gif shows the simple harmonic motion of three undamped mass-spring systems, with natural frequencies (from left to right) of ωo, 2ωo, and 3ωo. All three systems are initially at rest, but displaced a distance xm from equilibrium.
Source:http://www.acs.psu.edu/drussell/Demos/SHO/mass.html
Reference:http://farside.ph.utexas.edu/teaching/315/Waves/node4.html
http://scipp.ucsc.edu/~haber/ph5B/sho09.pdf
Approaching opposition early next month, Jupiter is offering some of its best telescopic views from planet Earth. On March 17, this impressively sharp image of the solar system's ruling gas giant was taken from a remote observatory in Chile. Bounded by planet girdling winds, familiar dark belts and light zones span the giant planet spotted with rotating oval storms. The solar system's largest moon Ganymede is above and left in the frame, its shadow seen in transit across the northern Jovian cloud tops. Ganymede itself is seen in remarkable detail along with bright surface features on fellow Galilean moon Io, right of Jupiter's looming disk.
Image & info via APODhttps://apod.nasa.gov/apod/astropix.html
Image Credit & Copyright: Damian Peach, Chilescope
On Thursday, SpaceX is scheduled to launch the SES-10 communications satellite. What's unusual about the launch is that it will be the company's first relaunch of a rocket that successfully launched and landed. Just under 1 year ago, the rocket was used on a resupply mission to the International Space Station. Reusing its rockets has been SpaceX's primary goal, with the company viewing reuse as the key to drastically reducing the cost of spaceflight, so this launch is a key milestone in the company's efforts.
Article:http://www.theverge.com/2017/3/28/15071288/spacex-launch-recycled-falcon-9-rocket-landing-schedule
Some parts of the body – including the tissues of the brain and testes – have long been considered to be completely hidden from our immune system.
Last year scientists made the amazing discovery that a set of previously unseen channels connected the brain to our immune system; now, it appears we might also need to rethink the immune system's relationship with the testes, potentially explaining why some men are infertile and how some cancer vaccines fail to provide immunity.
Researchers from University of Virginia School of Medicine discovered a 'very small door' which allows the testes to expose some of its antigens to the immune system without letting it inside.
For the past four decades the testes have been regarded as having 'immune privilege', meaning they don't mount an immune response when introduced to materials the immune system considers foreign.
Together with the brain, eyes, and placenta, inflammation in these parts of the body would be seriously bad news, which could explain why they are all physically or chemically hidden from the white cells and antibodies which protect us from infection.
This 'immunity from immunity' means any sperm outside of the testes can produce an autoimmune reaction, proving that the body considers its own sperm as foreign.
At least that's the current thinking, which might need to be modified if this new research is verified.
Separating the sperm-producing tissues in the testes from the blood vessels is a layer of tissue called Sertoli cells, serving as a kind of nurse cell to the developing sperm.
Sertoli cells lock together in such a way that they effectively form what's called a 'blood-testes barrier', preventing T-cells in the blood from sniffing out the growing sperm.
The system works well, but isn't foolproof – in up to 12 percent of men with spontaneous infertility, the immune system recognizes a chemical on the surface of sperm cells called the meiotic germ cell antigen (MGCA), suggesting they've met previously and don't tolerate it as native to the body.
The immunologists hypothesized this particular autoimmune response might say more about a break-down in tolerance than a break in the blood-testes barrier, suggesting that there were reasons to suspect MGCA wasn't as hidden as previously thought.
By focusing on two types of MGCA in normal and genetically altered mice and analyzing the mouse's T-cell tolerance to the antigens, the researchers found the Sertoli cells can 'leak' some types of the antigen into the blood vessels.
"In essence, we believe the testes antigens can be divided into those which are sequestered [behind the barrier] and those that are not," said researcher Kenneth Tung.
Not only could this discovery provide insight into how infertility can arise in some men, it could also help immunologists understand how cancer cells sequester, or hide, their own antigens, explaining why certain cancer vaccines can fail.
Paper:https://www.jci.org/articles/view/89927
Read the story:http://www.sciencealert.com/it-turns-out-the-immune-system-is-connected-to-the-testes-after-all
