Saturday, December 3, 2022

Weird and Wonderful: The psychedelic jelly is one of the most colorful residents of the deep sea

This jelly is one of the most colorful residents of the ocean’s midnight zone.
The remarkable coloration of this jelly tipped off scientists that they had found a previously unknown species.
It was named in honor of Claudia Mills for her dedication to studying the ocean’s delicate drifters. MBARI has observed several species of Crossota in Monterey Canyon.
Unlike many jellies, we can see obvious differences between the males and females.
The eggs in the females are large and globular, while the male gonads are shaped like sausages.
The baby medusae stay attached under the mother’s bell until they are ready to launch.
While brooding behavior is not unique to this jelly, it is always exciting to observe in the deep sea. MBARI’s robotic submersibles give us a peek at how animals thrive in the ocean’s dark depths.

Friday, December 2, 2022

World-first bathymetry of Indian Ocean marine park

During October 2022, CSIRO research vessel (RV) Investigator completed the first high resolution mapping of the new Cocos (Keeling) Islands Marine Park.
The mapping shows the Cocos (Keeling) Islands as the twin peaks of a massive seamount (underwater volcanic mountain) that lies beneath these idyllic tropical islands

For the past several weeks, scientists on board the CSIRO research vessel RV Investigator have been conducting a world-first survey of marine biodiversity in the newly established Cocos (Keeling) Islands Marine Park.

The 35-day voyage, led by the Museums Victoria Research Institute, has also enabled the team on board to capture the first high-resolution bathymetry of the new marine park, revealing in incredible detail the ancient underwater mountain that lies beneath these idyllic tropical islands.

Localization with the GeoGarage platform (AHS nautical raster chart)
Nelson Kuna, one of two hydrographic surveyors on board from CSIRO, said that very little high-resolution mapping had been done in the Marine Park prior to this voyage.
“We’ve used the full ocean depth mapping capabilities of RV Investigator to completely survey around the Cocos (Keeling) Islands, from coastal depths less than 100 metres all the way down to the abyss some 4,800 metres below,” said Nelson.
“The data set now covers a substantial area of the new marine park and shows the Cocos (Keeling) Islands as the twin peaks of a massive seamount that rises nearly 5,000 metres from the surrounding seafloor,” he said.
“We also revealed, among the many fascinating features, a smaller peak on the ridge between the north and south islands, rising to approximately 350 metres below sea level.”
“It’s truly an honour to see, for the first time, this stunning marine geomorphology revealed from the deep.”

The first high-resolution bathymetry of the new Cocos (Keeling) Islands Marine Park.
The new mapping will provide important information for Parks Australia, which manages the Cocos (Keeling) Island Marine Park, along with the newly established Christmas Island Marine Park, as part of the Australian Marine Parks network.

The 3D geospatial products were produced on board RV Investigator by combining the newly acquired CSIRO data with other existing datasets, including from the Australian Hydrographic Office (LiDAR bathymetry-elevation), GEBCO2022 (background bathymetry) and Geoscience Australia AusSeabed (background bathymetry).

The 3D products were produced using QPS Fledermaus. RV Investigator captured the bathymetry using its gondola mounted Kongsberg EM122 multibeam echosounder.
Links :

Thursday, December 1, 2022

Hy-Brasil: ghost island that has not been seen since 1878

Hy-Brasil is also known as the Irish Atlantis (Source: YouTube)

From History of Yesterday by Irena Curik

On maps, phantom island lies somewhere in the Atlantic Ocean to the west of Ireland

Irish folktales are full of ghosts, giants, pookas, demons, goblins, banshees, fairies, witches, widows, old maids, and other imaginary beings and places.
One such impossible place is a strange, eerie island on the west coast of Ireland, shrouded in thick fog and seen only once every seven years.
In the oral storytelling tradition of Ireland, the island was described as an island in a fog bank or a “floating island” that disappeared when approached.
Later, these stories appeared in printed books of Irish folklore, and you do not know which one to read first because they are all mind-blowing.
According to the 1888 book Irish Wonders by D. R. McAnally, the floating island was seen by the inhabitants of County Cork on 7 July 1878.

The number seven has already appeared three times, and this is very symbolic because seven is considered a spiritual number that indicates a strong spiritual presence behind the matter.
It can also indicate coded information, as in alchemical texts.
In any case, the strange apparition was described in Irish Wonders as follows:

“On Sunday afternoon, 7 July 1878, the inhabitants of Ballycotton in County Cork were greatly excited by the sudden appearance of an island far out to sea, which was not known to exist.
The men of Ballycotton town and island were fishermen and knew the sea as well as they knew the land.
The day before they had gone out in their boats and headed for the spot where the strange island now appeared, and they were sure it was the best fishing ground they had.
And still, they looked further, and still, their astonishment grew, for the day was clear, and the island was as plain to see as the hills to the north.
In some places it was rugged, in others thickly wooded; here and there deep shadows on the sides pointed to ravines thick with brush and grasses.
At one end it rose almost steeply from the sea, at the other it fell gradually; the dense forest of the mountainous part gave way to smaller trees, these in turn to shrubs, these in turn to green meadows, which finally merged with the sea and could no longer be distinguished from the waves.”

The island appeared on maps until at least 1873

Hy-Brasil has been featured in all sorts of legends, including giant black rabbits who lived with a sorcerer, gods hidden in the mist, lost civilizations, and, of course, UFOs.
Although it was never discovered, the phantom island was on maps from the 14th to the 19th century.
Historians believe that this is because cartographers could not check all places and locations and therefore sometimes inadvertently included persistent rumors in their maps. 
A section of a map by the Spanish cartographer Diego Gutiérrez from 1562 shows the island of Isola de Brazil, which lies southwest of Ireland and east of the sea monster
(Source: Rare maps)

An island called Bracile was first marked on a portolan chart in 1325 by the Mallorcan cartographer Angelino Dulcert.
The Venetian cartographer Andrea Bianco entered an island called Insula de Brasil on a map in 1436.
He assigned it to a group of islands in the Atlantic, and for a time the Insula de Brasil was identified with the present-day Azores island of Terceira, on which there is a volcanic mountain that is still called Monte Brasil.

On a Catalan map of 1480, there are even two islands named “Illa de brasil”, one southwest of Ireland and one south of “Illa verde” or Greenland.
The Spanish cartographer Diego Gutiérrez included Isola de Brasil in his map of 1562.
A map by Flemish cartographer Abraham Ortelius from 1570 shows an island called Brasil west of central Ireland.

A 1630 nautical chart by Portuguese cartographer João Teixeira Albernaz features the island in a circular shape divided in half by a river and called Do brasil.
A map by the British cartographer Thomas Jefferysfrom 1753 shows the island southwest of Ireland and calls it the “Imaginary Isle of O Brazil”, proving that cartographers had begun to doubt the island’s existence.

And on the map of the French cartographer Guillaume de L’Isle of 1769, the island is just a rock called Rocher de Brasil (Brasil Rock).
Brasil Island continued to appear on maps until 1873 when it was last shown on a British Admiralty chart.

Hy-Brasil has nothing to do with Brazil or reality

The origin of the names Brasil and Hy-Brasil is unknown, but in Irish tradition, they are thought to derive from the Irish Uí Breasail (“descendants (of Bresail”), one of the ancient clans in the north-east of Ireland: Í: island; bres: beauty, worth, great, powerful.
The island has changed many names, from Brasil, Brazil, Breasil, Hy-Brasil to O’Brasil.

There have been many documented expeditions to the island which, apart from their fanciful descriptions, haven’t resulted in any finds.
In 1480 and 1481, two explorers set out from Bristol to spend more than two months sailing around the Irish coast to find the mysterious island.
Although both expeditions were supposedly unsuccessful, there is a report from a Spanish diplomat in 1497 who recalls “the men from Bristol who found Brasil“.

Another account from 1629 by a French adventurer, M. de La Boullaye Le Gouz, tells how several sailors discovered the Hy Brasil.
He also mentions a letter written by a Derry man to a friend in England, describing how Captain John Nisbet and his crew were stranded on Hy-Brasil and found an old empty castle.
After they’d gone to sleep during the night, they suddenly woke up and “saw a very old, serious gentleman and ten men following him, coming bare-chested (as if they were his servants) to the shore where the ship lay“.

The mysterious gentleman gave a welcome party at which he revealed his identity.
He said the island was called O’Brasile and his ancestors had been princes, but then a great evil sorcerer had wiped them all out, leaving only a few members of the family alive behind the unbreakable castle, while he’d made the island invisible so that no one could find it.
When the captain knocked yesterday, he released the spell and the island will be visible again.
The gentleman has also distributed great gifts to the crew, who’ve happily returned home, but the island has still not become visible.

What about UFOs?

This is a strange story.
42 years ago, in late December 1980, a famous UFO encounter occurred in Rendlesham Forest, Suffolk, England, near a military base.
One of the witnesses, Sergeant Jim Penniston, said that when he touched the alien craft, information was telepathically implanted in his brain.
The next day he wrote down the information in his notebook.
It was a 16-page list with a binary code that seemed indecipherable.

Decades later, however, the code was run through sophisticated computer software and decoded as a list of very specific information matched to specific locations on Earth.
One location was the pyramids of Giza.
Another was the Nazca Lines in Peru.
And one was exactly where the ancient cartographers located Hy-Brasil!
Is this a coincidence or proof that both aliens and Hy-Brasil exist?

Wednesday, November 30, 2022

We’ve reached the end of a bizarre Atlantic hurricane season

From Ars Tecnica by Eric Berger

This was the rare year when there were no August storms.
Then things blew up.

The Atlantic hurricane season officially ends on Wednesday, bringing to a close the six-month period when the vast majority of tropical activity occurs in the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea.

Prior to the season, forecasters generally expected a busier-than-normal season.
However, six months later, overall activity this year has come in slightly below normal.
One of the more scientifically rigorous measurements of seasonal activity—based on the length and intensity of storms—is accumulated cyclone energy.
This year's value, 95, is about three-quarters of the normal value of 126.

Enlarge / Hurricane Ian, as seen from the International Space Station.
That bland statistic belies the fact that this was an odd season.
After three weak early-season storms, the Atlantic basin produced zero named storms between July 3 and August 31.
This was the first time since 1941 that the Atlantic had no named storm activity during this period.
Then, a light came on.
Four hurricanes formed in September, along with three more in November.
This brought seasonal activity to near-normal levels.

"This season was really bizarre," said Phil Klotzbach, one of the world's foremost seasonal hurricane forecasters.
"I’m giving a talk to the American Meteorological Society on Tuesday about the season, and I’m referring to it as the most abnormal 'normal' season on record."
What happened

So what caused this?
It's a question that Klotzbach and his research team at Colorado State University have been investigating since the anomalously quiet August.
The season's sputtering start was all the more surprising because this is a La Niña year, a pattern that typically leads to lower-than-average wind shear across the Atlantic.
This favors increased tropical activity.

In August, however, wind shear was higher than average in the region of the Atlantic Ocean where tropical systems commonly form.
These crosswinds at varying altitudes disrupt the circulation of rotating storms, such as tropical storms and hurricanes.
Another big factor this August was the incursion of dry air from the mid-latitudes.
Dry air, of course, saps the thunderstorms that are essential to forming a tropical cyclone.Advertisement

The shear and dry air appear to have had their origins in the mid-latitudes, the area between 30 degrees and 60 degrees north of the equator.
And this higher wind shear and increased amount of dry air may have been transported southward into the tropical Atlantic Ocean due to a phenomenon called "wave breaking," Klotzbach told Ars.

"I think a lot of the shear and dry air had mid-latitude origins and was associated with vigorous wave breaking," he said.
"Wave breaking is associated with upper-level low-pressure systems that have anomalous upper-level westerlies on their southern periphery.
These upper-level westerlies increase vertical wind shear.
Also, mid-latitude air is typically drier than tropical air, stifling thunderstorm development and effectively choking African easterly waves."

Chart showing "normal" accumulated cyclone energy (in black) versus what happened this year (in light blue).
Colorado State University

Klotzbach said he has been working with Jhordanne Jones, who graduated from his research group last year and got her Ph.D.
studying the predictability of mid-latitude wave breaking.
The goal is to better understand the predictability of this phenomenon and incorporate it into seasonal forecasting.

"The predictors that she found did hint at some increased potential for wave breaking this year, but not as much as was anticipated," Klotzbach said.
"We’ll certainly be spending more time looking at prediction of wave breaking for our forecasts in the future."

Blowing up

After the quiescent period in August, the Atlantic tropics came alive in September, beginning with the formation of Tropical Storm Danielle on September 1.
Five additional storms followed in the next three weeks, with Hurricane Ian being the strongest of them.
With maximum sustained winds of 150 mph at landfall along the southwestern coast of Florida, Ian is tied with five other hurricanes for the fifth strongest continental US hurricane landfall on record.

Another surprise came in November when the late-season Hurricane Nicole formed.
It eventually made landfall along the southeast coast of Florida as a Category 1 hurricane.

Both of these storms—Ian and Nicole—proved disruptive for NASA and its Artemis I program.
Ian's fury forced the space agency to roll the Space Launch System rocket and its Orion spacecraft back into the Vehicle Assembly Building to protect it from the storm in September.
Less than two months later, facing another hurricane, NASA opted to remain at the launch pad.

It proved a smart decision, as less than a week later, the Artemis I rocket had safely launched Orion toward the Moon.
Links :

Tuesday, November 29, 2022

The physics of scuba diving

Photograph: Lewis Mulatero/Getty Images

From Wired by Rhett Allain

A deep dive into the science of staying alive underwater.

I used to scuba dive way more than I should.
I pretty much did everything: open-water dives, technical dives, spearfishing, and cave diving.
It's a fun sport that allows you to see some incredible things, but there’s also tons of science that goes into the process of safely putting a human underwater.
So let’s discover what scuba diving can teach us about physics.


Perhaps the first thing a scuba diver thinks of when dealing with pressure is tank pressure.
Scuba tanks contain a lot of air in a relatively small volume, and the only way to do this is to compress the air, producing high pressure.
A diver can determine the amount of air left in a tank by using a pressure gauge.
Usually, a full tank has a pressure of 3,000 pounds per square inch (psi).
If you get below 200 psi, you should be out of the water.

Normal air—the stuff that blankets the Earth—is mostly nitrogen molecules, which make up about 79 percent of it.
The rest is oxygen, at around 21 percent.
We can imagine that these molecules are like super-tiny balls moving at different speeds and in different directions.
If this gas was in a container, some of the molecules would collide with the wall, bounce off of it, and change direction.
This change in motion means that each molecule exerts a small force on the wall.
(A bigger wall or container will experience more collisions and a greater overall force.)

One way we describe the motion of gas molecules is to think about the force per unit area.
This is the pressure of the gas:

Illustration: Rhett Allain

If you measure the force in pounds and the area in square inches, you get pressure in pounds per square inch, or psi.
That's the most common unit for tank pressure in the United States.

Another unit is the bar, where 1 bar is equal to 14.5 psi.
The value of 1 bar is very close to the pressure of air on Earth.
The atmospheric pressure of the air that surrounds you right now is probably 14.5 psi.
(Yes, I said "probably" because I don't want to judge you.
Maybe you are reading this from the top of Mount Everest, where the pressure is just 4.9 psi, because there is less air above you pushing down.
If so, send me a picture.) In terms of force and area, it is equal to 100,000 newtons per square meter.

Water is also made of tiny moving molecules that act like balls, and those molecules collide with underwater objects (like people), producing pressure.
Water has many more molecules than the same volume of air, which means there are more collisions to produce a greater pressure.
But just like going to the top of Mount Everest decreases the air pressure, going deeper in water increases the pressure, because gravity pulls downward on the molecules of water.
For every 10 meters of depth, the pressure increases by 1 bar, or 14.5 psi.
That means that on a dive 20 meters (around 60 feet) below sea level, there would be a water pressure of 43.5 psi, three times greater than the air pressure at Earth’s surface.

(The fact that pressure increases with depth prevents all the ocean’s water from collapsing into an infinitely thin layer.
Since the pressure is greater the deeper you go, the water underneath pushes up more than the water above it pushes down.
This difference compensates for the downward gravitational force, so the water level stays constant.)

It might sound like 43.5 psi is too much for a person to handle, but it's actually not that bad.
Human bodies are very adaptable to changes in pressure.
If you have been to the bottom of a swimming pool, you already know the answer to this pressure problem—your ears.
If the water pressure on the outside of your eardrum is greater than the pressure from the air inside your inner ear, the membrane will stretch, and it can really hurt.
But there is a nice trick to fix this: If you push air into your middle ear cavity by pinching your nose closed while attempting to blow air out of it, air will be forced into this cavity.
With more air in the inner ear, the pressure on both sides of the membrane will be equal and you will feel normal.
This is called "equalization," for hopefully obvious reasons.

There's actually another air space that you need to equalize while diving—the inside of your scuba mask.
Don't forget to add air to it as you go deeper, or that thing will awkwardly squish your face.

There is one other physics mistake a diver could make.
It's possible to create an enclosed air space in your lungs by holding your breath.
Suppose you hold your breath at a depth of 20 meters and then move up to a depth of 10 meters.
The pressure inside your lungs will stay the same during this ascent, because you have the same lung volume, and they contain the same amount of air.
However, the water pressure outside of them will decrease.
The reduced external pressure on your lungs makes it as though they are overinflated.
This can cause tears in lung tissue, or even force air into the bloodstream, which is officially bad stuff.

There's another problem to deal with when you are underwater: floating and sinking.
If you want to stay underwater, it’s useful to sink instead of float—to a point.
I don't think anyone wants to sink to such depths that they never return.
Also, it’s nice to be able to float when you’re at the surface.
Luckily, scuba divers can change their "floatiness" for different situations.
This is called buoyancy control.

Things sink when the downward-pulling gravitational force is greater than the upward-pushing buoyancy force.
If these two forces are equal, then the object will be neutrally buoyant and neither rise nor sink.
It's like hovering, but in water, and it is essentially what you want to do when scuba diving.

Water actually has neutral buoyancy.
Yes, water floats! Suppose you have a cubic volume of water that’s 1 meter on a side, and it’s in the middle of more water.
We know that this water will just stay there, which means that the upward buoyancy force and the downward gravitational force must be equal.

Now replace that cubic meter of water with a rock of the same shape and size.
Since the buoyancy force is due to the interaction between the object and the water surrounding it, this rock will have the same buoyancy as the cube of water.
However, since it has a greater mass (and therefore weight) than the water, the total force on it will be downward and it will sink.

We can expand this to any generic object to say that the buoyancy force on something is equal to the weight of the water that it displaces (some volume V).
It's useful to think about the mass per unit-volume of water.
We call this the density.
(Physicists like the symbol ρ for density.)

Illustration: Rhett Allain

Since the weight of the displaced water depends on the density of water (ρw) and the gravitational field (g), we get the following expression for buoyancy:

Illustration: Rhett Allain

The weight of an object depends on the density, too.
If the density of that object is less than water, then the buoyancy force will be greater than its own weight and it will float.
Most wood has a density lower than water, so it floats.
A metal boat can float because it's not solid metal—the air inside makes its density lower than that of water.
Also, very small rocks, a great gravy, and cider might float.
(If you don't know that quote, I won't judge you.) On the other hand, an iron nail has a density that’s greater than water’s, so it will sink.

But now we have an idea of how a scuba diver can control buoyancy.
If you increase your volume (and your mass stays the same), then your density will decrease.
This will increase your buoyancy force and you will rise.
Decreasing your volume will decrease your buoyancy force, and you will sink.
You can actually change your volume underwater just by breathing.
Inhaling from a scuba regulator will make your lungs expand, which increases your volume and your buoyancy.
Exhaling does the opposite.

Scuba divers also wear an exterior device to change their volume.
It's basically an inflatable bag that you wear on your back called (not surprisingly) a buoyancy control device.
It connects to a scuba tank so that you can add or remove air to change your buoyancy.

Thermal Conductivity

When the air has a temperature of 72 degrees Fahrenheit, it feels quite nice.
But have you ever been in water at the same temperature? Oh boy, that stuff feels super cold.
Really, the difference is not the temperature, but rather how fast thermal energy transfers from your body to something else.
That’s called thermal conductivity, or the rate that thermal energy can transfer between two objects.
(In this case, from your body to the colder water.)

Here's another example: Suppose you have a wood block and a metal block sitting at room temperature—they’re not in direct sunshine nor sitting on a heater.
If you touch both blocks, the wood will feel warmer than the metal, even though they are actually at the same temperature.
This is because metal has a higher thermal conductivity than wood.
The hand touching the metal will decrease in thermal energy faster, making that one feel colder.

The exact same thing happens with scuba diving.
Since water is a much better thermal conductor than air, the rate that thermal energy moves from your body—which is almost always warmer than the water—to the water is faster than the same process in the air.
In fact, you can lose energy so fast that it's very possible to decrease your core body temperature, which can cause problems like loss of muscle function and even respiratory and heart failure.

The most common solution to this water problem is to wear a wetsuit, which is usually made of a material like neoprene with a very low thermal conductivity.
This decreases the rate at which the human body loses thermal energy.
It's called a wetsuit because you still get wet: Exterior water gets trapped in between your skin and the tight-fitting suit, and your body warms it up.

If you don't like being exposed to water, you could get a dry suit, which has watertight seals on the wrists and neck, and built-in boots, so that water doesn't get in at all.
(OK, maybe just a few tiny leaks.) This does add an extra task for the diver, though.
As you descend to greater water pressures, the air inside the suit will decrease in volume, causing a “shrink-wrap” effect on the body, so that there is no space inside of the suit to bend your arms and legs.
You can fix this by adding air to the suit at greater depths—but you also have to let that air out when you go back up toward the surface.

Underwater Vision

I've been on some dives in murky water where I really couldn't see much.
Spoiler alert: It wasn't very fun.
The point of diving is to see cool stuff underwater.
But even in clear water, you need a mask in order to really see anything.
The mask creates an air space between your eyes and the water, which is what they need to properly focus.
Here's how the lens in your eye works when you're on land, as humans are meant to be, compared to what happens in water:

Illustration: Rhett Allain

A lens bends light based on its shape, as well as the difference in the speed of light in both the lens material and outside of it.
(We can describe the speed of light in a material with the index of refraction.) The speed of light in water is only 66.7 percent the speed of light in air.
That's a problem, as it makes the lens in your eye less able to bend the light to focus on your retina.
The result is blurry vision.

When you put on a mask, you once again have air in front of your eyes, which allows your lens to bend the light the proper amount.
But light is still traveling through the water at a slower speed than it does through air.
When light goes from one medium (like water) into another medium (like air), the light's path bends.
We call this refraction, and it can make things underwater appear closer than they actually are.

How does this work? It's important to remember that we see things because light reflects off objects and then into our eyes.
Take the example of a fish you spot on your diving trip.
Rays of light bounce off the fish, travel through the water and then into the air inside the scuba mask.
Because of the difference in the index of refraction between air and water, the light rays bend.
But our eyes and brain don't know that the light changed directions.
They just assume that it traveled in a straight line, as it does in the air.
This makes it appear that the light came from a spot that is closer than where the fish actually is.

This diagram should help:

Illustration: Rhett Allain

There's another issue with seeing fish (and especially coral) underwater: color.
Although we like to think that water is transparent, it's only sort of transparent.
If you have pure water, visible light will be absorbed as it travels through it.
After 300 meters, essentially none of the light will be left.
That means even in the clearest water, it would be as dark as night at a depth of 300 meters.
(You shouldn't be scuba diving that deep, anyway.)

The absorption of light isn't the same for all colors.
Almost all red light will be absorbed after only 5 meters of water.
As you go deeper, you will only see light that is more blue than red.
Without red light, red things, including fish and coral, will seem to be dark gray.

But you can fix this problem with a simple trick: Bring a flashlight.
The light from your flashlight doesn't have to travel as far as light from the surface before it reflects off that pretty fish, so you can still see the red parts.

Partial Pressure of Gases

Recall that air is normally a mixture of 79 percent nitrogen and 21 percent oxygen at a pressure of 1 atmosphere (1 ATM).
But we need to think about oxygen and nitrogen differently, since they interact with the body in different ways.
We can deal with gas mixtures using the idea of “partial pressure.” Air at 1 ATM (with a mixture of oxygen and nitrogen) is the same as oxygen at a pressure of 0.21 ATM (21 percent of the mixture) and nitrogen at 0.79 ATM.

Let’s look at how both of these gases impact the body.
I’m going to start with the partial pressure of oxygen, which we often just call PPO2.
People need oxygen, but not too little or too much.
Say you’re traveling in a plane at high altitude, where the air pressure is lower.
If you get to a PPO2 below about 0.17, it’s just not enough oxygen for your brain to function.
You won’t be able to think straight, and you might even pass out.
(This is why high-altitude aircraft have pressurized cabins; if they don't, people have to wear supplemental oxygen masks.
It’s also why the flight attendants in a commercial airliner go over safety procedures in the event of a decrease in cabin pressure.)

But underwater, the problem is likely to be too much pressure.
If the partial pressure of oxygen gets around 1.6 ATM, it can cause people to have convulsions.

How do you get a PPO2 that high? Consider the following case: You have a tank with pure oxygen (and no nitrogen) and you dive to a depth of 10 meters.
In order to actually breathe from a scuba regulator, the pressure delivered to your lungs must be equal to the ambient pressure, or you wouldn't be able to inhale.
That means the pure oxygen will be at 2 ATM.
(Remember, you get 1 ATM of pressure for every 10 meters of depth.) Breathing this would produce a PPO2 of 2.0—which is greater than 1.6 ATM.
So, don’t do that.

This is why scuba divers don't use pure oxygen and instead use normal air that’s only 21 percent oxygen.
Its PPO2 at that same depth would be 0.42 ATM, which is not likely to cause problems.
Also, it's much easier to just pump regular air into tanks.
Using other mixtures involves complicated stuff like compressions and the kind of oxygen tanks you see in hospitals.

Now suppose you put a custom mix of gas in your tank.
How about 40 percent oxygen and 60 percent nitrogen? (Note: This is real stuff, it's called Nitrox.) This increases the ratio of oxygen to nitrogen, above what’s in air.
If you breathe this gas at a depth of 20 meters, which is 3 ATM, the oxygen would be at PPO2 of 0.4 × 3 ATM, which equals 1.2 ATM.
This is getting close to a PPM of 1.6 ATM, so maybe you shouldn't go any deeper than that with this gas mixture.

What is the advantage of adding extra oxygen to your tank if you can't go as deep? The answer is that increasing the oxygen decreases the nitrogen.
Although your body doesn't use nitrogen gas, it does get absorbed by your tissues.
When you go to lower pressures (like when coming up to the surface), this nitrogen comes out of your tissues, which is called outgassing.
If too much nitrogen comes out too fast, it will form bubbles that get in your blood and cause serious medical problems.
This is commonly called decompression sickness, or the bends.
Using less nitrogen will mean your tissues absorb less, giving you a lower chance of decompression sickness.

You can also prevent decompression sickness by moving to shallower depths very slowly.
For recreational dives, the goal is to only absorb an amount of nitrogen that can be safely outgassed in the time it takes to swim back to the surface.

The actual calculation for the time you can stay at a certain depth is complicated, and it relies on rough estimations about the average human body.
This is why most modern scuba divers use small dive computers that constantly calculate the time they have remaining based on the depth and time.

That’s not enough physics for you to actually go on a scuba dive, but it's enough to give you a sense of what's going on.
If you’d like to try it out, a dive instructor at a scuba shop can help you learn the rest.
Just remember to bring your flashlight.

Monday, November 28, 2022

3 weeks, 15 unmanned systems: Navy launches ‘Digital Horizon’ exercise in Middle East

From Breaking Defense by Justin Katz

Various unmanned systems sit on display in Manama, Bahrain, Nov. 19, prior to exercise Digital Horizon 2022.
(U.S. Army photo by Sgt. Brandon Murphy)
The event will feature 15 unmanned systems, 10 of which will be operating with the Navy in US 5th Fleet for the first time.
The US Navy is launching today a three-week event in the Middle East focused on employing artificial intelligence and 15 different unmanned systems, many of which the service will operate in the region for the first time.
One spot for the test with the GeoGarage platform

The event, called Digital Horizon, is being hosted by Task Force 59, a group established by US 5th Fleet in September 2021 and tasked to experiment with how the service can incorporate unmanned systems into operations.
Vice Adm. Brad Cooper, the officer leading 5th Fleet and overseeing the task force, has said he aims to have 100 unmanned surface vessels operating in the region by next summer.
The exercise in its current form has taken place at least once before in December 2021.

“By harnessing these new unmanned technologies and combining them with artificial intelligence, we will enhance regional maritime security and strengthen deterrence,” Cooper said in a Navy statement about Digital Horizon.
This year’s exercise will feature 17 companies that collectively bring 15 “different types of unmanned systems, 10 of which will operate with US 5th Fleet” for the first time, according to the Navy statement.

Some of the systems participating include Aerovel’s Flexrotor and Shield AI’s V-BAT unmanned aerial vehicles as well as Elbit Systems Seagull, MARTAC’s T-38 Devil Ray and Saildrone’s Explorer unmanned surface vessels.
courtesy of Martac in Bahrein

The latter USV became a point of international contention earlier this year when Iranian military and paramilitary forces temporarily pulled some US-owned Saildrones out of the water, accusing the US Navy of abandoning the “spying” vehicles.

Following both incidents, a spokesman for the US Navy dismissed Iran’s claims, saying the Saildrones kept appropriate distances from other vessels and were unarmed and taking unclassified photos of the environment.
The service was ultimately able to recover the drones.

In addition to contributing vehicles, several companies involved in the exercise will also incorporate artificial intelligence and data analytics systems.

“Industry partners Accenture Federal Services and Big Bear AI will also employ data integration and artificial intelligence systems during the event, and Silvus Technologies will provide line-of-sight radio communications while an unmanned surface vessel from Ocius participates from off the coast of Western Australia,” according to the Navy statement.

Capt. Michael Brasseur, commander of Task Force 59, added that industry is working with the service in “one of the most difficult operational environments… I am extremely proud of the entire team, including our many partners across government, academia, and industry for their commitment to Digital Horizon, as we discover new capability together.”

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Sunday, November 27, 2022

Great Lakes extruded bathymetry

Mapbox's William B Davis has created an awesome demo map showing the bathymetry of the Great Lakes in 3D.
His Great Lakes Extruded map actually allows you to virtually dive in and out of Lake Superior, the largest freshwater lake in the world.