In MRI we’re really looking at hydrogen atoms in the body, and fortunately we have a lot of hydrogen atoms in our body, we’re made up of a lot of water and the way MRI works is with a combination of magnetic fields and sending in radio waves. So this is kind of different from x-ray imaging where you’re using very high energy x-rays, radio waves are much less damaging. We call them non-ionising radiation. These radio waves, the photons don’t have enough energy to cause any chemical changes, so that’s why we believe that MRI is completely safe. The MRI scan uses the magnetic field to align these hydrogen atoms so instead of them being just in a random arrangement, the magnetic field tries to pull them into alignment like a whole set of compass needles.

Rocket aerodynamics is the study of how air flows over a rocket and how this affects drag and stability.

The nose cone and fins of a rocket are designed to minimise drag (air resistance) and to provide stability and control (keep it pointing in the right direction without wobbling).

Nose cone and rocket diameter affect drag

The amount of air resistance that opposes a rocket’s motion depends mainly on the shape of the nose cone, the diameter of the rocket and the speed of the rocket.

The first point that meets the air is the nose cone at the front end of the rocket. If the speed of a rocket is less than the speed of sound (1,200 km/h in air at sea level), the best shape of a nose cone is a rounded curve. At supersonic speeds (faster than the speed of sound), the best shape is a narrower and sharper point.

Rockets with a larger diameter have more drag because there is more air being pushed out of the way. Drag depends on the cross-sectional area of the object pushing through the air. Making a rocket as narrow as possible is the best way to reduce drag.

The speed of a rocket through the air similarly increases drag. As speed doubles, drag increases four times as much.

https://youtu.be/oAh4_bDFHls

Fins control direction and stability

The stability of a rocket is its ability to keep flying through the air pointing in the right direction without wobbling or tumbling.

Fins are used on smaller rockets to provide this stability and control direction. It works in the same way as placing feathers at the tail of an arrow. The greater drag on the feathers keeps the tail of the arrow at the back so that the point of the arrow travels straight into the wind.

To understand how to place fins and how large to make them, it is important to understand about centre of mass and centre of pressure.

Centre of mass

The centre of mass of an object is the point at which all of the mass of an object can be thought to be concentrated.

To find the centre of mass of a rigid object such as a water bottle rocket, balance the rocket on your finger so that the rocket is horizontal. The centre of mass is a point directly above your finger.

The centre of mass can be moved closer to the nose cone end of a rocket by adding some mass near the nose cone. This will increase stability.

Centre of pressure

The single point at which all of the aerodynamic forces are concentrated is called the centre of pressure.

To find the approximate position of the centre of pressure, draw an outline of the rocket on a piece of paper. The centre of the area of the outline shape is approximately the centre of pressure.

Centre of pressure

This stable model rocket shows the centre of gravity (cg) (also known as the centre of mass) closer to the front end of the rocket than the centre of pressure (cp).

For a rocket to be stable, the centre of pressure needs to be closer to the tail end than the centre of mass. If the centre of pressure is at the same position as the centre of mass, the rocket will tumble. Stability increases as the distance between the centre of mass and the centre of pressure increases.

https://youtu.be/oAh4_bDFHls

Placing fins at the tail end of a rocket moves the centre of pressure closer towards the tail end and increases stability. However, this also increases drag, so there is an optimal size for fins so that the rocket has enough stability without having too much drag.

For a plane or bird to fly, its wings must produce enough lift to equal its weight. Most wings used in flight are a special shape – called aerofoils (or airfoils). This shape is needed to help generate lift.

The explanation for lift has been traditionally attributed to a Swiss mathematician named Daniel Bernoulli (pronounced Ber-noo-lee). However, recently, many scientists have debated whether the use of the Bernoulli principle to explain how wings work is, in fact, correct.

Many feel that using the Bernoulli principle, commonly taught in schools, is either incorrect or should not be used as a single explanation for lift. This is an interesting example of how science ideas are constantly being challenged. Many people now argue that angle of attack, based on Newton’s third law of motion, is a more effective explanation for lift.

It appears there are actually a number of explanations for lift that include the angle of attack and the Bernoulli principle and that these explanations work together to explain how lift is produced.

The angle of attack – Newton’s third law

Newton’s third law of motion states that, for every action, there is an equal and opposite reaction. Based on this law, wings are forced upwards because they are tilted, pushing air downwards so the wings get pushed upwards. This is the angle of attack or the angle at which the wing meets the airflow.

As air flows over the surface of a wing, it sticks slightly to the surface it is flowing past and follows the shape. If the wing is angled correctly, the air is deflected downwards.

The action of the wing on the air is to force the air downwards while the reaction is the air pushing the wing upwards. A wing’s trailing edge must be sharp, and it must be aimed diagonally downwards to create lift. Both the upper and lower surfaces of the wing act to deflect the air.

The amount of lift depends on the speed of the air around the wing and the density of the air. To produce more lift, the object must speed up and/or increase the angle of attack of the wing (by pushing the aircraft’s tail downwards).

Speeding up means the wings force more air downwards so lift is increased. Increasing the angle of attack means the air flowing over the top is turned downwards even more and the air meeting the lower surface is also deflected downwards more, increasing lift.

There is a limit to how large the angle of attack may be. If it is too great, the flow of air over the top of the wing will no longer be smooth and the lift suddenly decreases.

Birds and planes change their angle of attack as they slow to land. Their angle of attack is increased to ensure their lift continues to support their weight as they slow down. Wings and tails need to be movable so that their shapes can be changed to control their flight.

The Bernoulli principle

To understand this principle, we need to understand air pressure. Air is composed of several invisible gases that have mass. This mass is made up of molecules, moving in rapid random motion, and exerts a force called air pressure. We are unaware of this pressure because it is evenly pressing all around us. If the air pressure is not even, the greater pressure pushes an object in the direction of the weaker (or lower) pressure.

In 1738, Bernoulli found that, when a gas (like air) moves, it exerts less pressure. According to Bernoulli’s principle, the faster air moves, the less air pressure it exerts (this is not the same as the force exerted by a wind), because the molecules in the air become more spread out.

Normally, air moves along smoothly in streams, but airflow is disturbed when a wing moves through it, and the air divides and flows around the wing. The top surface of the wing is curved (aerofoil shape). The air moving across the top of the wing goes faster than the air travelling under the bottom. Because it’s moving faster, the air on top of the wing has less air pressure on the wing than the air below the wing. In other words, air below the wing pushes on the wing more than air above the wing.

The Bernoulli Principle

When the air splits to go around the wing, the air that is forced over the wing travels farther and the distance between the air molecules increases, making the air above the wing less dense, or lower pressure. The pressure difference between higher pressure air below the wing and lower pressure air above the wing causes lift.

This difference in pressure combines with the lift from the angle of attack to give even more lift.

It used to be claimed that the air travelling over the top of the wing took the same time to reach the back of the wing as the air travelling along the bottom. This has been shown to be incorrect, but it has been shown that the speed of the air over the top is faster than the speed of the air under the bottom.

The shape of the aerofoil is different for different aircraft. It is designed to give the best trade-off between lift and drag for each aircraft. On many aeroplanes, the bottom of the wing will curve downwards slightly instead of being flat. On other aircraft, such as gliders, it will curve upwards. On a stunt plane, which is just as likely to fly upside down as it is to fly the right way up, the curve on the bottom of the wing will be the same as it is on the top.

Airplane (Product Category),airplane flying,rolling,yawing,fligh navigation,the first flight,Wright Flyer,Cockpit controls,Flap,Slat,Aileron,Rudder,Flying,airfoil,wing working,lift,jet engine

,airplane,reverse thrust,flight controls,take off,landing,airfoil

A Mysterious, Giant 'Blinking' Object Has Been Detected Near Our Galaxy's Center

There's something strange near the galactic center.

Some 25,000 light-years from Earth, astronomers have found a weird star that almost blinked out of existence for several months before reappearing.

Astronomers believe the star, named VVV-WIT-08, could belong to a new class of star - giant beasts over 100 times the Sun that are eclipsed by a mysterious orbiting body once every few decades.

Stars with peculiar dimming signatures are an endless fascination. Although space is mostly relatively empty, it stands to reason that, with all the stuff out there, some of it will line up in such a way that stars are dimmed from our terrestrial perspective from time to time.

It's not always easy to tell what that stuff is, though. A giant planet? Space dust? Debris from a disrupted object? A cosmic dragon?

The case of VVV-WIT-08 is a doozy. Although other stars have exhibited similar dips in light, none have been so deep. The culprit, astronomers think, could be another star or planet, surrounded by a thick, opaque disk of dust on a long orbit around VVV-WIT-08, that covers the star completely when it passes in front of our view.

"It's amazing that we just observed a dark, large and elongated object pass between us and the distant star and we can only speculate what its origin is," said astronomer Sergey Koposov from the University of Edinburgh in Scotland.

The model of an orbital companion with a giant disk isn't without precedent. One famous, well-known example is Epsilon Aurigae, a supergiant star and with a disk-shrouded companion on a 27-year orbit that dims the star by about 50 percent for up to 730 days.

Then there's the system TYC 2505-672-1, a red giant star with a dusty companion on a 69-year orbit that eclipses the star for a period of 3.5 years.

The survey that picked up VVV-WIT-08 (the "WIT" stands for "what is this?" because astronomers are great like that), the VISTA Variables in the Via Lactea (VVV) survey, picked up a couple of other candidates that seemed to exhibit the same behavior. Because the data on those stars aren't as complete as the data for VVV-WIT-08, they are yet to be described.

We know the star's peculiarity isn't an error, though. The dimming was also observed by the Optical Gravitational Lensing Experiment using the Warsaw Telescope in Chile, which means it wasn't a glitch (although it would have to be a very strange sort of glitch).

The data show that the dimming event lasted for approximately 200 days, with a nearly symmetrical light curve, quenching the star's light by up to 97 percent. The density of objects required in that region of space for the chance alignment of two random bodies is much higher than observed, so the team believes the two objects are gravitationally bound.

The orbital period is unknown, but it has to be at least a few decades, according to mathematical modelling.

And the discovery suggests such systems may not be all that uncommon.

"There are certainly more to be found, but the challenge now is in figuring out what the hidden companions are, and how they came to be surrounded by discs, despite orbiting so far from the giant star," said astronomer Leigh Smith of the University of Cambridge.

"In doing so, we might learn something new about how these kinds of systems evolve."

The LiveWire One, Harley-latest Davidson's battery-powered vehicle, is reviving the company's effort into electric motorcycles. While the new bike will have similar specifications to the company's initial LiveWire motorcycle, it will be more affordably priced in order to attract more customers.

The LiveWire One will be priced at $21,999 before any federal, state, or local tax incentives are applied. (Any electric motorcycle capable of travelling at least 45 miles per hour is eligible for a federal tax credit of up to $2,500.) When these credits are factored in, Harley-Davidson claims that the price will fall below $20,000 for the majority of consumers.

HARLEY-DAVIDSON SAID THE PRICE WILL ACTUALLY FALL BELOW $20,000 FOR MOST CUSTOMERS

Customers in only three states will be able to purchase the LiveWire One at first: California, New York, and Texas. The business is embracing a "hybrid" approach to retail, allowing customers to complete the majority of their buying online before picking up their bike at a local Harley-Davidson dealership. The LiveWire One will be sold by 12 dealerships at first, but the business expects that number to rise next year.

The LiveWire One will be able to travel 146 city miles on a single charge, according to Harley-Davidson, although it is unclear how that would translate on the highway. (This is presumably due to the fact that the range decreases as you speed up.) Even so, it's only a smidgeon.

There are a few additional significant variations, albeit Harley-Davidson did not provide a spec sheet at the time of publication. The LiveWire One's battery will charge from 0 to 100% in 60 minutes or 0 to 80% in 45 minutes when plugged into a DC fast charger. This new bike will incorporate a six-axis IMU (inertial measuring unit) for traction control and anti-lock braking, similar to the original LiveWire.

In an interview, Harley-Davidson CEO Jochen Zeitz noted, "It's a very different riding experience." “It's exhilarating because it's such a quick and nimble motorcycle... you can go from 0 to 100 [mph] in no time.”

A comparison of the two LiveWire motorcycles, as well as other electric two-wheelers, will show more about the new brand's ability to attract new customers. We'll have to wait until July 18th, when Harley-Davidson plans to reveal the LiveWire One at the Northern California International Motorcycle Show. If you can't wait that long, you can place an order at LiveWire.com.

While the first LiveWire was commended for being well-made and enjoyable to ride, it was frequently chastised for being too expensive, with a starting price of $29,799. Within the company's lineup, there was also an apparent dearth of options. If you truly desired to purchase an electric vehicle,

It put Harley-Davidson at a disadvantage in the developing electric motorbike market, where businesses like Zero Motorcycles are selling a variety of models for $10,000 to $16,000.

However, whereas the initial LiveWire was intended to show what Harley-Davidson could achieve with an electric motor, the LiveWire One is intended to be a more serious attempt to acquire those city-dwelling customers that the firm sees as critical to its long-term survival. The question is if this market niche exists at all.

“This is not a product sold through a regular dealer network,” Zeitz explained. “It's a new brand,” says the narrator. It's a different way of approaching the market.”

Zeitz disputed the notion that the company's main customers, the ageing "boomers," were a problem unique to Harley-Davidson. “Isn't it true that the world's population is ageing?” he joked. “So this isn't just a Harley issue.”

“IT’S A NEW BRAND. IT’S A NEW GO-TO-MARKET APPROACH.”

However, he admitted that the idea with LiveWire is to appeal to a new generation of moviegoers who didn't grow up seeing classics like Easy Rider. “Every brand needs to innovate... and excite the next generation about your product and the experience you deliver,” Zeitz said, citing the 2020 television series Long Way Up as an example of the appeal of electric motorcycles, in which actor Ewan McGregor and TV presenter Charley Boorman ride LiveWires from Argentina to Los Angeles.

With the LiveWire One, the company is recommitting itself to the electrification of an entire product line. Earlier this year, Harley-Davidson decided to spin off LiveWire into its own brand, with the goal of launching multiple electric motorcycles under that nameplate. LiveWire One is the first product of that effort, and there will be more to come.

The company telegraphed this move in its Hardwire strategic plan to reinvigorate its flagging sales over the next five years. This dedicated division would be “focused exclusively on leading the future of electric motorcycles,” the company said in its plan.

But while LiveWire will certainly play a significant role in Harley-Davidson’s future, the company is not planning to phase out gas-powered vehicles anytime soon. That’s not the case in the auto industry, with giants like Ford, General Motors, Volkswagen, Honda, Volvo, and others promising to go EV-only within the next decade. Meanwhile, California has said it would ban the sale of gas-powered vehicles by 2035. Other states are sure to follow.

A LOT OF FACTORS HOLD HARLEY-DAVIDSON BACK FROM GOING WHOLE HOG (PUN INTENDED) ON ELECTRIFICATION

There are a number of obstacles preventing Harley-Davidson from going all-in on electrification. For one thing, there is less space on a motorcycle than in a car, therefore the battery must be more compact. This reduces the bike's range, making it more difficult to sell to consumers interested in cross-country or touring journeys. And those individuals make up a sizable chunk of the company's clientele. Furthermore, the EV charging infrastructure in the United States is fragmented, unreliable, and frankly, a shambles.

“There is no path to electrifying a touring bike and giving it the three or four hundred miles that you would want,” Zeitz said. “And also bearing in mind that fast charging infrastructure is not common yet outside of the city. And even within the city, it’s not always available.”

Zeitz, who joined Harley-Davidson in 2020 after 18 years as CEO of Puma, said that “synthetic fuels are not something that you can fully disregard,” and that he was hoping for a “major revolution in that space” to help the company navigate the post-fossil fuel future.

“However, electrification will play a huge role,” he continued. “On the other hand, only time will tell. We will undoubtedly be prepared for both as a company.”

Hubble's issues began in June, when the payload computer that controls the orbiting telescope's scientific instruments went offline. When this happened, all of the instruments went into safe mode, which means they are still healthy and working, but they aren't gathering data at the moment.

The NASA team on the ground went through numerous rounds of troubleshooting to figure out what was causing the issue. According to the most recent NASA report, the fault is in a unit called Science Instrument Command and Data Handling (SI C&DH), which contains numerous pieces of hardware that could be the cause of the malfunction.

In an update, NASA outlines the next steps: “The Command Unit/Science Data Formatter (CU/SDF), which communicates and formats commands and data, is now under investigation by the team. They're also looking at a power regulator in the Power Control Unit, which is designed to keep the payload computer's hardware at a constant voltage.”

If one of these systems proves to be the source of the problem, the solution is to switch from the current units to the backups. Most Hubble hardware has both primary and backup versions, allowing the team to move from one to the other if something goes wrong with one. Switching to backup units, on the other hand, might be a difficult operation. Several pieces of hardware must be turned off before the backup CU/SDF or power regulator can be switched on due to the way the systems are coupled.

The team is ready to transfer to backup hardware this week, including utilising a simulator to test the operation. The good news is that this isn't the first time something like this has been done. “A similar swap was done in 2008, allowing Hubble to resume normal science operations when a CU/SDF module failed,” NASA noted. “In 2009, a servicing mission replaced the entire SI C&DH unit, including the malfunctioning CU/SDF module, with the current SI C&DH unit.”

History

No diamonds have survived from the ancient world, but evidence of their use in ancient times can be found. According to the American Museum of Natural History, "Beads from sites in Sri Lanka, India, Thailand, Yemen and Egypt show the marks of diamond drills prior to 700 CE and as early as the 4th century BCE in Yemen." Much later on, In the 1870s, major diamond deposits were discovered in South Africa. After these deposits were discovered, diamond prices dropped considerably.

Properties

Diamond is the hardest natural substance. It is four times harder than corundum, the second-hardest substance. Diamonds have four points of weakness, known as "directions of cleavage." A sharp impact at these points causes a split to occur. Diamonds are highly transparent with better thermal conductivity than any other substance. They also have the highest melting point of any natural material.

Sources

About 35 countries have had diamond mines. For gem quality stones, the most prominent mines are in Botswana, Russia and South Africa. Australia is a major source of diamonds for industrial purposes. Wyoming, Arkansas and Colorado are the only U.S. sources of diamonds. The most common mineral host of diamonds is a blue rock called kimberlite. Diamonds are located mostly in areas that have had volcanic activity or erosion. Past glacial activity has also moved diamond deposits.

Uses

Diamonds with exceptional clarity and color are suitable for cutting and use as jewelry. Diamonds are embedded in some saw blades to increase tool effectiveness. Other industrial uses include drilling, grinding and polishing. Diamonds can be crushed to produce abrasive powders. This hard gemstone is also used in thin windows for vacuum chambers and laser devices. Diamonds are valuable when incorporated in various mechanical parts where low friction or wear resistance is important.