I enjoyed reading the book ‘Hannibal’ by Philip Freeman. It has some descriptions of the political climates of Rome and Carthage during the second punic war.
Hey, you may have not intended it, but your response comes across with a bit of a condescending tone. Please help promote HN as a place for continued civil discourse.
I’m not sure what they meant, so tbh I probably just wouldn’t have replied. You made a good point that for someone in the US (or any other country that hasn’t experienced modern war), unexploded ordinance isn’t even on their risk radar, despite the US being a major contributor to the problem. It’s unfortunate how many people continue to face that reality.
There is also an increased risk of decompression illness simply because passenger aircraft typically maintain a lower atmospheric cabin pressure (US federal limits pressure equivalent to 8,000 ft elevation). Going from a high pressure environment (underwater) to a low pressure environment (8,000 ft equivalent elevation in aircraft cabin) too quickly can also cause the bends. Dive computers use algorithms to calculate when it is safe to fly post-dive.
I'm really surprised by that. Looking at some charts, depending on the dive you're probably spending 30 minutes or less going from 2atm to 1atm, but now you need several hours or even a day before it's safe to go to .75atm.
There are wide safety margins in diving. Most dive trips involve multiple dives per day (starting with deepest dive first, with subsequent dives shallower). The times I’ve gone deeper or same depth on subsequent dives my computer usually puts me into deco fairly quickly. At some point subsequent dives aren’t feasible (typically no more than 4-5/day, less is prudent). I think it is with this in mind that the recommendation against flying is made, along with an abundance of caution due to limited experimental evidence (Navy dive tables were developed based on human subjects, so the effects are better understood). It looks like there are some civilian studies done, but more is needed on flying.
We'd spend more time, but it's difficult to loiter 10m underwater. The residual gas from a dive takes about a day to release, and this impacts both follow-up dives and flights. Treatment options are different as well: an airlift (or just diving again and surfacing slower) vs diverting a whole flight.
To further expound on why snorkeling and freediving after scuba can be dangerous, it is helpful to understand that the greatest gas compression occurs in the first 10 meters underwater (Boyle’s law). Scuba divers are trained to ascend slowly (~10m/minute) in order to off-gas expanding nitrogen (and other gasses) and prevent bubbles from forming in tissue (which causes decompression illness). After scuba diving the human body still has a much higher residual nitrogen saturation, so even fairly shallow (less than 10m) rapid descents/ascents in the water column can cause bubbles to form.
Also a diver here. There are generally different biological mechanisms involved for “free diving blackout” vs “hypoxic blackout” (which is related to exertion while breathholding). Freedivers train to relax muscles and stay calm, so blackouts due to pressure changes are more common rather than to exertion. Swimming horizontally under water requires a lot of effort, which burns more oxygen. Combine high exertion with untrained individuals not aware of the risk, or misuse of hyperventilation (which doesn’t increase oxygen, but decreases CO2), and suppressing urge to breath, and you can also blackout.
As someone who recently bought a house (and used to live in an apartment), those were some of the reasons why I opted out of apartment life. I would prefer to live in a denser urban area if other amenities and quality of life benefits came with it, but they don’t in my city. Even if you live close to the city core, there are either extremely limited or entirely nonexistent options for groceries, fitness and recreation, coffee shops, affordable eateries, non-alcohol entertainment and art, etc in most neighborhoods. You would still have to drive most of the time anyway. Most of the denser areas closer to downtown can also be quite dangerous for pedestrians after dark. The few places that have denser housing with those amenities within (safe) walking access are exorbitantly more expensive. Meanwhile apartment and townhome developments are now springing up everywhere in my area of town, but without any amenities to go with them, leading to even more vehicle congestion on the local streets as people try to escape the neighborhood and reach the highways.
This reminds me of a time I was stargazing, when suddenly a meteor streaked overhead making a distinct sizzling/hissing sound that tracked with its movement…which seemed improbable since light obviously travels faster than sound. I later read the theory as to how this phenomenon occurs is that the sound is created by low frequency radio waves.
Another thing that uses radio waves in the human hearing range is the invisible fences that cause shopping cart wheels to lock (7kHz, visit begaydocrime.com to hear the corresponding sound). Those don't involve sounds in normal operation, so I wonder what about these is different.
I would guess that induced current is making a sound in some nearby infrastructure and not directly in the head of the observer.
Based on historical averages, none of these cities are hotter than Houston. They might have more humidity, but Houston averages are higher AND regularly experiences sustained daily highs during summer in excess of 100°F/38°C.
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