Why do babies with clefts have problems with feeding?
This gives your baby extra calories, protein and vitamins. Swallowing noises and normal weight gain are signs that breast-feeding is going well. What to expect at your Craniofacial Center visit. Release of hormones then may cause more of those hormones to be released, causing a positive feedback loop. Some systems with feedback can have very complex behaviors such as chaotic behaviors in non-linear systems, while others have much more predictable behaviors, such as those that are used to make and design digital systems. An example of this is insulin oscillations. This is dangerous if one has no idea what one is doing.
Single Needle Direct Drive Lock Stitcher with Electronic Feeding System and Thread Trimmer
Cool temperatures seem to exacerbate the problem. I think I should feed when the bird is active. I have some vague hint that Cheep does better with earlier feedings, when he's more awake and energetic. I make sure the food is relatively warm but not too hot.
Cold food probably won't sit well. I don't forcefeed if the bird has just eaten its normal food. I'm guessing a good time to feed may be when Cheep has just started eating its normal food - then I KNOW he's hungry and feeling well enough to eat.
Take the bird to the vet to rule out any other causes! Our Results Several times over the past couple years, I've let handfeeding lapse and Cheep has, over the course of weeks or sometimes months, gone down to skeleton thin. Each time I have resumed handfeeding, and the results are fairly consistent though I do think he's slowly getting more lethargic every year. At 15 days, the difference becomes obvious, and he actually weighs grams more.
Yes, there's actually padding under the feathers at this point, instead of just skin and bone though I do wonder if the new padding is fat or muscle or both. I think he also feels better and starts complaining more about being forcefed. Things like sudden cold snaps combined with a reduction in feeding frequency can result in sudden weight loss, so I think consistent and frequent feeding during times of environmental stress may be a good idea.
For Cheep, a "maintenance" program might be force-feeding him, on average, once a day for 2 out of 3 days. Once every other day is not enough to promote consistent weight maintenance. During the build-up phase daily feeding, with maybe one day off in seven to let his system rest, seems to work well. Since handfeeding seems to cause him to just sit and vegetate for a while, it's hard to say that he's definitely happier for it. Another reason I think I ought to give him a "break" periodically, once he has enough reserves to handle it.
The other proof is in his energy level is when I give him a day or two's break from handfeeding. He certainly seems to be more energetic and cheerful on those days, compared to the days when he was fast becoming a skeleton with feathers. That's a good sign, even if counterproductive. I must suggest that, without handfeeding plus the lamps, the extra seed, and so on , Cheep would have died over two years ago.
He may yet pass on soon, but I've been given an extra two years with him. That's not bad, in my book. Concerns I worry that so much sugar and grease is a strain on the pancreas and liver. Simple sugars like table sugar are not generally healthy in the long run a bit of research shows the problem is twofold: And yet, he needs the sweetness and he needs the calories.
I mentioned these concerns to my vet and she looked me in the eye and said approx. Also, even the pellet mush doesn't look completely digested; vitamin supplementation may be a good idea, though I don't know how much to use who can tell, with this disease?
The powder I leave in the freezer. One hint is that the greater the surface area exposed to open air, the faster any food will go rancid. But in any case, there's a limit to how long anything this nutritious and bland can be stored in the fridge. I throw out anything over about a week old. If I make a mixture using raw fruits and vegetables instead of sugar, four days is the absolute longest I'll ever keep it.
All that said, though, I must reiterate that Cheep would've died several times over without this feeding! Syringe Tricks Technically I think one is supposed to use a new syringe for every feeding?
So I reuse the syringe - it's used only with Cheep, never with other birds. For cleaning, I've found that wet, soapy paper towel when jammed all the way into a reasonably large oral syringe with a smaller-size plunger shaft to push it in and rotate it around can reach where fingers can't. Vinegar dissolves away detergent with incredible ease. There should be no signs of oil or leftover food in the syringe. I rinse everything carefully in water after washing, and also before the next feeding.
I have found a real, dangerous problem with reused oral syringes when the rubber plunger tip starts to degrade and "stick. When this happens, I find it all too easy to push too hard to overcome the "stickiness" and then squirt way too much food out. If I did this at the wrong angle I could easily send food into Cheep's lungs, which could be fatal. This can also happen if there are lumps in the food that clog the syringe. These days I remove the degraded rubber plunger tip and encase the plunger plastic shaft itself I'm actually using a plunger shaft from a one-size-smaller syringe in a layer or two of fresh, clean plastic wrap.
I pour the liquid food into the syringe from the back end, and then insert the plastic-wrapped plunger until it's firmly pushed into the food I do hold the front tip closed so the food doesn't squirt out the front while all this is going on.
The syringe cannot be used to draw up fluid, but it can be used to push out fluid. Actually it works VERY well if not too much plastic wrap is used - there is no sticking and hence much less danger of pushing too hard.
One big drawback is, because the plastic wrap does not provide a perfect seal and the food leaks past the plunger and gets stuck all over the plastic wrap, I not only waste more food, but I have to guess as to how much food is making it into the bird. On good days Cheep himself is setting the food limits. Again, the consistency of thick cold cream works pretty well.
Warmth and Heat Sick birds need to stay warm, especially if they don't have enough caloric reserves! After some failures with trying a heating pad, I bought a grow-light and placed it near the cage.
I'm careful to keep flammable objects, including cage covers, away from it! For cooler weather I use two lamps! Cheep often huddles up near the lamp, and he often rushes to the lamp when he gets back in his cage especially after a bath , so clearly it is doing its job. As with the force-feeding, I think this one has been a lifesaver for Cheep, especially in the winter.
Remember to get an incandescent, not a fluorescent or LED, lamp. In this case, what you want is the heat, not necessarily the light! Replace all your other bulbs but don't replace your birdie heat bulb! There are also plenty of places in the cage that are NOT heated, so the bird can cool off if he needs to. The lost hearing was usually at higher frequencies. The living quarters of the ISS are the Russian Zvezda module, which is the noisiest module on the station.
NASA says the goal is for the working area to have noise levels at or below 60 decibels dB and sleep bunks to be 50dB. At their peak several years ago, noise levels reached 72 to 78dB in the working area and 65 dB in the sleep stations. Decibels are measured on a logarithmic scale, meaning, for example, that 60dB is 10 times louder than 50dB.
NASA has worked to reduce the noise and its effect on the crew. By November , noise levels had been lowered to between 62 to 69dB in the work area and 55 to 60dB in the sleep compartments. Astronauts on the ISS used to have to wear ear plugs all day but are now only wear them for 2 to 3 hours per work day. According to the US National Institutes of Health, however, noise levels below 80dB are unlikely to lead to hearing loss, even with prolonged exposure.
But while the primary cause of hearing loss in general is high noise levels, Buckey suggested in a paper in Aviation Space and Environmental Medicine that several other factors might contribute to the problem in space. Elevated intracranial pressure, higher carbon dioxide levels and atmospheric contaminants may make the inner ear more sensitive to noise, he says.
But there have been no studies yet to test these ideas. Buckey had designed a device to measure hearing loss of astronauts on the ISS, but his project was cancelled around the start of when NASA reduced funding for life sciences.
Crews have installed fan vibration isolators and mufflers on fan outlets, and acoustic padding to wall panels. The current crew, Russian cosmonaut Pavel Vinogradov and US astronaut Jeff Williams, installed a sound-insulating cover on the Russian carbon dioxide removal system. They also started adding acoustic padding near the Russian air conditioner.
Future crews will swap out 30 to 40 fans with quieter versions. Meteors are probably nothing to worry about. On average a spacecraft will have to wait for a couple of million years to be hit by a meteor larger than a grain of sand.
But if you insist, there are a couple of precautions one can take. First one can sheath the ship in a thin shell with a few inches of separation from the hull. This "meteor bumper" aka " Whipple shield " will vaporize the smaller guys.
For larger ones, use radar. It is surprisingly simple. For complicated reasons that I'm sure you can figure out for yourself, a meteor on a collision course will maintain a constant bearing it's a geometric matter of similar triangles. So if the radar sees an object whose bearing doesn't change, but whose range is decreasing, it knows that You Have A Problem. This happens on Earth as well. If you are racing a freight train to cross an intersection, and the image of the front of the train stays on one spot on your windshield, you know that you and the engine will reach the intersection simultaneously.
One can make an hard-wired link between the radar and the engines, but it might be a good idea to have it sound an alarm first. This will give the crew a second to grab a hand-hold.
You did install hand-holds on all the walls, didn't you? And require the crew to strap themselves into their bunks while sleeping. Having said that, Samuel Birchenough points out that anybody who has played the game Kerbal Space Program know that an object that is not on a fixed bearing can still hit you. If your spacecraft and the other object are in orbit around a planet, the object's bearing will be constantly changing up to the last few kilometers before the collision.
The moon, now visibly larger and almost painfully beautiful, hung in the same position in the sky, such that he had to let his gaze drop as he lay in the chair in order to return its stare. This bothered him for a moment -- how were they ever to reach the moon if the moon did not draw toward the point where they were aiming? It would not have bothered Morrie, trained as he was in a pilot's knowledge of collision bearings, interception courses, and the like. But, since it appeared to run contrary to common sense, Art worried about it until he managed to visualize the situation somewhat thus: It was a simple matter of similar triangles, easy to see with a diagram but hard to keep straight in the head.
The moon was speeding to their meeting place at about miles an hour, yet she would never change direction; she would simply grow and grow and grow until she filled the whole sky. To guard against larger stuff Captain Yancey set up a meteor-watch much tighter than is usual in most parts of space. The only condition necessary for collision is that the other object hold a steady bearing-no fancy calculation is involved.
The only action necessary then to avoid collision is to change your own speed, any direction, any amount. This is perhaps the only case where theory of piloting is simple. Commander Miller put the cadets and the sublieutenants on a continuous heel-and-toe watch, scanning the meteor-guard 'scopes. Even if the human being failed to note a steady bearing the radars would "see" it, for they were so rigged that, if a "blip" burned in at one spot on the screen, thereby showing a steady bearing, an alarm would sound- and the watch officer would cut in the jet, fast!
A more practical study of any such device shows that any extraneous object that does not change its aspect angle is necessarily on a collision course. Ergo, any target that does not move causes the alarm to ring, and the autopilot to swerve aside. If the habitat module or space suit is punctured, all the air will start rushing out. Unless you and the other occupants want to experience first-hand all the many horrible ways that space kills you , you'd better patch that hole stat!
An instrument called a Manometer will register a sudden loss of pressure and trigger an alarm. Life support will start high-pressure flood of oxygen, and release some bubbles. The bubbles will rush to the breach, pointing them out to the crew.
The crew will grab an emergency hull patch thoughtfully affixed near all external hull walls and seal the breach. The emergency hull patches are metal discs. They look like saucepan covers with a rubber flange around the edge. They will handle a breach up to fifteen centimeters in diameter. Never slap them over the breach, place it on the hull next to the breach and slide it over. Once over the breach, air pressure will hold it in place until you can make more permanent repairs.
A more advanced alternative to bubbles are "plug-ups" or "tag-alongs". These are plastic bubbles full of helium and liquid sealing plastic.
The helium is enough to give them neutral buoyancy, so they have no strong tendency to rise or sink. They fly to the breach, pop, and plug it with quick setting goo. Much to the relief of the crew caught in the same room with the breach when the automatic bulkheads slammed shut. Holden froze, watching the blood pump from Shed's neck, then whip away like smoke into an exhaust fan. The sounds of combat began to fade as the air was sucked out of the room.
His ears throbbed and then hurt like someone had put ice picks in them. As he fought with his couch restraints, he glanced over at Alex. The pilot was yelling something, but it didn't carry through the thin air. Naomi and Amos had gotten out of their couches already, kicked off, and were flying across the room to the two holes. Amos had a plastic dinner tray in one hand.
Naomi, a white three-ring binder. Holden stared at them for the half second it took to understand what they were doing. The world narrowed, his peripheral vision all stars and darkness. By the time he'd gotten free, Amos and Naomi had already covered the holes with their makeshift patches. The room was filled with a high-pitched whistle as the air tried to force its way out through the imperfect seals.
Holden's sight began to return as the air pressure started to rise. He was panting hard, gasping for breath. Someone slowly turned the room's volume knob back up and Naomi's yells for help became audible. She was pointing at a small red-and-yellow panel on the bulkhead near his crash couch.
Years of shipboard training made a path through the anoxia and depressurization. Inside were a white first aid kit marked with the ancient red-cross symbol, half a dozen oxygen masks, and a sealed bag of hardened plastic disks attached to a glue gun.
He wasn't sure if her voice sounded distant because of the thin air or because the pressure drop had blown his eardrums. Holden yanked the gun free from the bag of patches and threw it at her. She ran a bead of instant sealing glue around the edge of her three-ring binder. She tossed the gun to Amos, who caught it with an effortless backhand motion and put a seal around his dinner tray. The whistling stopped, replaced by the hiss of the atmosphere system as it labored to bring the pressure back up to normal.
Little gas-filled plastic balls swarm into the compartment. They range from golf-ball to tennis-ball size. A new man, I decide. He's heard about the Commander. He's too anxious to look good. He's concentrating too much. Doing his job one part at a time, with such thoroughness that he muffs the whole.
The plug-ups will drift aimlessly throughout the patrol, and will soon fade into the background environment. No one will think about them unless the hull is breached. Then our lives could depend on them. They'll rush to the hole, carried by the escaping atmosphere. If the breach is small, they'll break trying to get through. A quick-setting, oxygen-sensitive goo coats their insides. The cat scrambles after the nearest ball.
He bats it around. It survives his attentions. He pretends a towering indifference. He's a master of that talent of the feline breed, of adopting a regal dignity in the face of failure, just in case somebody is watching.
Breaches too big for the plug-ups probably wouldn't matter. We would be dead before we noticed them. Once a pressurized habitat module or space suit springs a leak in the vacuum of space, all the air starts howling out the hole escaping into the void. Since people generally need air to breath or they die, there is an intense interest in how long it will take the air to go bye-bye.
Veteran rocketeers, vacationing on Terra, tend to have a momentary panic if they feel the wind. Their instincts tell them there is a hull breach. You probably won't use this equation, but to calculate an approximate time it will take for all the air to totally escape:.
If you want to get fancy and take the atmospheric temperature into account, use Fliegner's Formula equation from quote below:. However, what we and the hapless people inside the breached compartment are more interested in is how long it takes the pressure to drop to the deadly level of anoxia, i. Remember if the compartment is using high pressure So if a posh passenger cabin of 15 cubic meters with high pressure has a 3 centimeter one inch diameter hole area 7.
So if it punches a perfect hole the same diameter as the bullet the hole will have a radius of 0. This will bring the 15 m 3 cabin down to anoxia in about seconds or The time will drop if the hole is more ragged or if there are multiple holes. Obviously each additional hole cuts the time in half. Somebody in a space suit doesn't have that kind of time. The space suit uses low pressure. A hole a half-centimeter in diameter has a hole area of 1. As long as the suit's air tanks can keep up the loss the pressure won't drop.
But once the tanks are empty, the pressure will drop to anoxia levels in a mere Does this mean that crewpeople in a combat spacecraft will do their fighting in space suits? Probably not, for the same reason that crewpeople in combat submarines do not do their fighting while wearing scuba gear.
The gear is bulky, confining, and tiring to wear. They will not wear it even though in both cases the vessel is surrounded by stuff you cannot breath. They may, however, wear partial-pressure suits or have emergency space suits handy. Those suits will only protect you for ten minutes or so, but in exchange you won't be hampered like you were wearing three sets of snow-suits simultaneously. Instead, the ship's pressurized inhabitable section will be divided into individual sections by bulkheads, and the connecting airtight hatches will be shut.
The air pressure might be lowered a bit. We do not see the room explosively decompress when the railgun projectile shoots through the Donnager's hull and wall. Except for the fact that air is being sucked out into "hard vacuum," everyone manages to stay in their seats.
This happens for a few reasons. The first is the hole, or constriction, is too small for all the air in the room to explosively leave the room. The second deals with the fact that air is made of atoms. Air escaping the hole in the hull to the vacuum of space leaves at approximately the speed of sound. As air molecules exit the hole, the remaining molecules have to "catch up. All cars do not move together. One car slowly inches forward and then everyone follows. This means there is no explosive decompression unless the entire wall is suddenly removed.
While the crew has some time to act, that time is very limited. Scientists and engineers have looked at the physics of constricted airflow for some time with regard to aircraft. It is a very good idea to know what happens to an aircraft if a hole forms while in flight. Fliegner was one of the first engineers to look at this problem and was able to work out how much air leaves depending on the pressure inside a cabin and the size of a hole.
We know this as Fliegner's Formula:. As we expect, the air flow depends on the hole's area, cabin pressure and temperature. Of course, Fliegner's Formula is not that accurate. As the leak progresses, the pressure in the cabin drops and this also affects air flow through the hole. Have no fear, we can use the equation and a little physics to figure out the time it takes the pressure to drop to a certain level. We have some new variables: Now that we have figured out the equation, we can model what happens inside the cabin and how much time the Canterbury crew have to act.
While you would not necessarily die, you can fall unconscious. We assume that the Canterbury crew can not help themselves and will eventually die as the cabin pressure decreases until all the air is sucked out to the vacuum. Maybe Shed is the lucky one here. While we do not have the exact dimensions of the room, we can make a few assumptions.
Based on the body sizes of the crew, I assume the room is 10 meters by 10 meters by 5 meters or cubic meters in size. If we plot the graph over time we see that the pressure drops to half its value where everyone has a little over a minute to plug up the holes.
Assuming that everything happens in real-time, from the moment Sed loses his head to the second the holes are sealed, the crew manages to do seal the holes with some seconds to spare. While the estimated size of the room may be larger than it really is, the point is The show definitely gets the science right and the urgency the crew must act to save their lives. It was just after reveille, "A" deck time, and I was standing by my bunk, making it up.
I had my Scout uniform in my hands and was about to fold it up and put it under my pillow. I still didn't wear it. None of the others had uniforms to wear to Scout meetings so I didn't wear mine. But I still kept it tucked away in my bunk. Suddenly I heard the goldarnest noise I ever heard in my life.
It sounded like a rifle going off right by my ear, it sounded like a steel door being slammed, and it sounded like a giant tearing yards and yards of cloth, all at once. Then I couldn't hear anything but a ringing in my ears and I was dazed.
I shook my head and looked down and I was staring at a raw hole in the ship, almost between my feet and nearly as big as my fist.
There was scorched insulation around it and in the middle of the hole I could see blackness—then a star whipped past and I realized that I was staring right out into space. I don't remember thinking at all. I just wadded up my uniform, squatted down, and stuffed it in the hole.
For a moment it seemed as if the suction would pull it on through the hole, then it jammed and stuck and didn't go any further. But we were still losing air. I think that was the point at which I first realized that we were losing air and that we might be suffocated in vacuum. There was somebody yelling and screaming behind me that he was killed and alarm bells were going off all over the place.
You couldn't hear yourself think. The air-tight door to our bunk room slid across automatically and settled into its gaskets and we were locked in. I know it has to be done. I know that it is better to seal off one compartment and kill the people who are in it than to let a whole ship die—but, you see, I was in that compartment, personally.
I guess I'm just not the hero type. I could feel the pressure sucking away at the plug my uniform made. With one part of my mind I was recalling that it had been advertised as "tropical weave, self ventilating" and wishing that it had been a solid plastic rain coat instead. I was afraid to stuff it in any harder, for fear it would go all the way through and leave us sitting there, chewing vacuum. I would have passed up desserts for the next ten years for just one rubber patch, the size of my hand.
It was the ordinary sort of pillow, soft foam rubber. I snatched one hand out and then the other, and then I was kneeling on it and pressing down with the heels of my hands.
It dimpled a little in the middle and I was scared we were going to have a blowout right through the pillow.
Noisy was screaming again and Captain Harkness was still asking for somebody, anybody, in compartment H to tell him what was going on. That was a popular idea. About three of them jumped to it. Noisy got clipped in the side of the neck, then somebody poked him in the pit of his stomach and they swarmed over him. If Noisy lets out a peep, slug him again. I told him and that is about all there was to it.
They took a while to get to us because—I found this out afterward—they isolated that stretch of corridor first, with the air-tight doors, and that meant they had to get everybody out of the rooms on each side of us and across the passageway. But presently two men in space suits opened the door and chased all the kids out, all but me.
Then they came back. One of them was Mr. The other man squatted down and took over holding the pillow in place. Ortega had a big metal patch under one arm. It had sticky padding on one side.
I wanted to stay and watch him put it on but he chased me out and closed the door. The corridor outside was empty but I banged on the air-tight door and they let me through to where the rest were waiting. They wanted to know what was happening but I didn't have any news for them because I had been chased out. After a while we started feeling light and Captain Harkness announced that spin would be off the ship for a short time.
Ortega and the other man came back and went on up to the control room. Spin was off entirely soon after that and I got very sick. Captain Harkness kept the ship's speaker circuits cut in on his conversations with the men who had gone outside to repair the hole, but I didn't listen. I defy anybody to be interested in anything when he is drop sick.
Then spin came back on and everything was all right and we were allowed to go back into our bunkroom. It looked just the same except that there was a plate welded over the place where the meteorite had come in. That was how I happened to go up to Captain's mast for the second time. George was there and Molly and Peggy and Dr. Archibald, the Scoutmaster of our deck, and all the fellows from my bunk room and all the ship's officers. The rest of the ship was cut in by visiplate. I wanted to wear my uniform but it was a mess—torn and covered with sticky stuff.
I finally cut off the merit badges and put it in the ship's incinerator. The First Officer shouted, "Captain's Mast for punishments and rewards! Dad shoved me forward. He said, "I will read from yesterday's log: Safety interlocks worked satisfactorily and the punctured volume, compartment H-twelve, was isolated with no serious drop in pressure elsewhere in the ship.
One of the passengers, William J. Lermer, contrived a makeshift patch with materials at hand and succeeded in holding sufficient pressure for breathing until a repair party could take over.
The Captain looked up from the log and went on, "A certified copy of this entry, along with depositions of witnesses, will be sent to Interplanetary Red Cross with recommendation for appropriate action. Another copy will be furnished you. I have no way to reward you except to say that you have my heart-felt gratitude. I know that I speak not only for the officers but for all the passengers and most especially for the parents of your bunk mates.
Recently, a discussion on ejecting people from airlocks or airplanes had inadequate math, and there's much confusion about the variables at play. It took a long time to work out the calculations correctly, but this post has the high-level intuition.
I put all the gritty derivations and analysis notes in this addendum below. If you want to change these constants, or calculate yourself, the script I wrote is here: You're in a corridor. In fact, it's in the regime where your peak acceleration into the great beyond might just kill you outright.
Area scales quadratically, which can decrease the ratio H counterintuitively. Hence, small reductions in dimension result in high reduction in area, which results in an even higher reduction in force. Consequently, even fairly large holes can produce almost negligible pulls.
Of course, if you got right up against the hole, the air pressure inside would act over your body instead something like N trying to slam you through that 10 cm hole. Initial conditions are the same as in scenario 1 as makes sense , but as the precious, life-giving air rushes away to oblivion, the force and density rapidly decrease. Therefore, the acceleration quickly drops to zero. This is still explosive decompression, but the initial jolt is basically a tenth of a second, which you might conceivably survive.
Note that your final velocity is much slower than v a. Again, quadratic scaling can be counterintuitive. In the first second, 3. Two important things to notice: As the previous scenarios might have hinted, this is therefore an explosive decompression event.
This combines with the rapid pressure drop to throw things out of the airplane. No hard numbers, but I'd estimate that either force would be sufficient to do this alone. You're in an airplane, when a small hole gets punched in the side somehow. The hole is small relative to the cabin volume.
This is therefore not an explosive decompression event. This was also apparently confirmed experimentally by Mythbusters eps. Explosive decompression is real, but it requires the area of the hole to be large relative to the volume of the chamber.
Even apparently large holes like, size of your opened hand 10 cm won't explosively decompress a typical room. The equations given above should be reasonably accurate, assuming I didn't screw up copying them from my notes and program.
You can check the math itself here and again use the program here: Here, I'll elaborate on the equations and the assumptions made in deriving them. For symbols used, please refer to the parent article.
There are extremely complex adjustments that people use in industry to improve on this, but to really do fundamentally better, we'd need to write an actual fluid simulator. You'd also have to run simulations and interpret them. Happily, all that is overkill. The drag equation works well at high fluid velocities such as we have here and gives plausible answers for the general cases under consideration.
The main practical limitation of this analysis is that additional effects mainly compressibility, adiabatic changes, and temperature are not considered. They'd only matter in scenarios 3 and 4, and in these cases the air rushes out so quickly, and the accelerations are so much greater in the initial part of the calculation where such corrections are zero, that I don't think they matter. Moreover, engineering texts are frankly so badly written as to be incomprehensible on this point, and resolving that by going for a BS in MechEng is overkill just for solving a stupid thought experiment on the Internet.
Intuitively, this is because air molecules can only flow into a vacuum as fast as they can "find out" about it. This happens at the speed of sound, because air molecules bump into each other or don't, because they've escaped to vacuum , and this is how sound is transmitted.
For more discussion, see e. For scenario 1, we simply use Newton's Second Law to find a t from the drag equation. Since the source has an infinite supply of air and the outward flow is sonic which means that, by definition, information about pressure cannot propagate "upstream" , the density in the chamber.
From here, we try to integrate to get v t. However, we run into a problem, because v r t itself depends on v t. So this is a recursive integral. But happily, we can just differentiate the whole mess to get the Riccati differential equation:. Which is the formula I presented. To get the other equations, you differentiate to get a t , and then scale by m to get f t because Newton's Second, again.
For scenario 3, we're considering the diminishing effects of the reducing pressure in the chamber. Unfortunately, their use of Bernoulli's Law is erroneous; they assume density is constant, but it isn't. In any case, the result is greater than Mach 1 for reasonable values, which is not possible. The volumetric flow rate should instead be calculated as:. The Riccardi obtained is:. Because I'm lazy, I tried solving this with WolframAlpha. Anyway, the equation is separable, so it's nearly as easy to solve by hand:.
You calculate a t and f t as before. Scenario 4 is to scenario 3 similarly as scenario 2 was to scenario 1. Here, the differential equation for M t is unchanged, because it is already parametrized on the hole area.
The first change is in the Riccardi equation, where we need to multiply v a by H in the final term, yielding a final v t of: If you'd like to tweak the numbers, or you don't want to enter in all this garbage into your calculator, the Python script I used for this analysis can be found here: This came up in a different newsgroup, and upon trying to answer it I blew it badly.
What happens to the helpless heroine? Back by Callie, the cross-sectional area is about 9 [m 2 ], so conservation of mass assuming uniform density says the airspeed by her is a gusty OK, so what did I screw up? I do take into account the increased airspeed as she gets very close to the breach closer than 2 [m] or so.
Or does Callie really fully decompress in the airlock, and gently drift out about 10 seconds later? I haven't verified your numbers, but for a quick sanity check, there's about kg of air in the lock, but only half of that is behind her—her own body weight—and most of that will escape past her.
If you really want the damsel to experience dramatic accelerations, I think you should start her closer to the opening, or have the inner door open, or maybe use a longer, thinner lock that she almost blocks with her body.
Yes, that's about right, if the door opens outward and sticks at a 10 cm gap. Though actually I'd be very surprised to see an airlock with a door that opened outward at all.
If it did open outward, and was free to swing open wider, consider that it has kPa pressure acting on the inner surface. It will accelerate open very rapidly indeed — probably on the order of tens of milliseconds. The rarefaction front will propagate inward at the speed of sound, with the air accelerated nearly instantaneously as the front passes. At worst, approximately, and assuming a heroine of only moderate size i. The heroine, being around a thousand times more dense than air, will be accelerated to about a thousandth of that, around a foot per second.
One cannot recommend, for the usual purposes, a heroine who obstructs a substantial proportion of nine square metres. The duration is much longer than that, since she is still in the path of the air escaping from further back in the airlock. Even though the static pressure is at 0 Pa, it still has significant density. So the air rushing past her from further in the airlock will exert pressure as it escapes past her.
So for a long airlock, her velocity would asymptotically approach the free outflow speed. Ah, so if I hang a sheet of tissue paper just inside the airlock of an O'Neill habitat, and open the door, it won't go anywhere, right?
Because all it will experience is an infinitesimal moment of acceleration as the transition between atmosphere and vacuum propagates past its negligible thickness? I'm thinking that's not right. I'm also thinking that a propagating transition between atmosphere and vacuum would represent a violation of the law of conservation of mass.
What actually propagates, is a transition between air at 10 5 Pa, and air at 5. And that transonic wind condition, remains even after the transition has passed — for as long as it takes for the transition wave to reach the farthest wall of the chamber behind our heroine, and as long beyond that as it takes for the wind to actually empty the chamber.
If the geometry is cylindrical, I get for a standard heroine in a standard atmosphere, a net velocity of 1. That's in the low-velocity limit; as she herself approaches transonic velocity downstream, the force will decrease and her own velocity will asymptotically approach The ability for explosive decompression to push people around is usually exaggerated.
Your results sound qualitatively like I'd expect — it'd budge her a little at first but very rapidly the ambient air pressure would drop to the point that it wouldn't have much of an effect. That's interesting, because it appears to conflict with the usual description of explosive decompression on aircraft: Is that description simply inaccurate, or is there a difference in the cases that I'm missing?
It is simply inaccurate. Yes, decompression is dangerous, and if a significant hole opens up the winds can be extreme. But they're not caused by the decompression! It should be noted that an airliner at altitude is usually moving at a significant fraction of the speed of sound through the air. The air doesn't just simply leave as it would in a vacuum, or if it were a zeppelin cabin.
From the point of view of the aircraft, the air outside has kinetic energy greater than any hurricane. If a large hole opens up, part of that can get in. It depends on how much air is in the vessel, how big the hole is, and how close the victim is to the breach.
Sure, there are some cases where the victim will likely be forced out of the breach. But probably not in the case Brian was talking about. Not that really helps her chances, since she's exposed to vacuum with no way to get back in.
How long will they last? Do they require maintenance? Can they be located outside? How low can they be discharged? How do you clean them? There are all kinds of batteries, using all kinds of materials. Battery technology is rapidly advancing to increase power density and reduce weight for everything from cell phones to electric vehicles.
Unfortunately, this usually requires more toxic materials and a much higher cost. When it comes to choosing a battery for an off-grid solar home or back-up emergency power system, we usually are not that concerned with battery size or weight. We just want a battery that can be quickly charged, then supply power slowly for one or more days, and last six or more years.
With all this battery research, it is still hard to beat the lowly deep-cycle lead-acid battery for this type of solar system performance and low cost.
Since any battery is stored chemical energy, perhaps a brief review of basic battery construction and the chemical to energy conversion process is in order. These have the sulfuric acid converted to a jelly-like consistency, or absorbed in a sponge blanket surrounding the individual lead plates, with the entire battery sealed at the factory.
They can be mounted in any direction and are used in solar applications that cannot receive regular maintenance, like solar-powered street lights and remote cell phone towers. Since sealed batteries do not need regular maintenance, they can be stacked closely together. Unfortunately, maintenance-free lead-acid batteries have a much higher price tag without gaining any more amp-hour capacity than an equal-sized open lead-acid battery.
A sealed battery is also very sensitive to charging voltage, and even a slight over-charge can release hydrogen gas and cause rapid battery heating and permanent damage. A sealed battery cannot be equalize charged, since any release of hydrogen gas through the safety pressure relief valve cannot be replaced, so the battery will soon dry out.
This usually results in a much shorter life for sealed batteries. Most off-grid solar and battery back-up systems use an open-cap deep-discharge liquid lead-acid battery. The battery bank will be a group of individual 2 or 6-volt deep cycle batteries wired together to provide a higher system voltage. It has the same base size as a golf cart battery, but is taller and much heavier. It was originally designed to power battery floor sweepers, fork trucks, and mining cars, and is very ruggedly constructed.
It is also available at most battery distributors for a reasonable price, and can have up to six-years of useful life for most solar applications.
This battery is made up of very tall 2-volt cells, pre-wired into a 12, 24, or volt configuration and housed in a metal box, like the volt tray battery pictured. With individual tray batteries weighing up to a ton, many installers prefer using individual cells and make the battery interconnects after the individual cells are moved to the job site.
The industrial tray battery will last longer than the smaller 6-volt batteries, and an 8 to year life is possible with proper maintenance. Lead-acid batteries can be divided into two basic subcategories: Since pure lead would be too soft to form the battery plates, several other materials are added to improve plate strength and charge performance.
When antimony is combined to make the lead plate stronger, it also improves how low the battery can be repeatedly discharged without damage. Since lead-antimony plates release much more hydrogen than other battery types, this battery will require more watering and have more out-gassing during the charging process.
When calcium is added to a pure lead plate, this also improves plate strength, but this battery type will have a much lower rate of water loss. A car battery is an example of a lead-calcium battery.
Both are fairly soft, and are formed into a waffle shape to increase the amount of surface area exposed to the sulfuric acid H2SO4. The plates are separated from physical contact by a porous spacer or fiberglass matt. During discharge, oxygen molecules O2 from the positive plate combine with hydrogen molecules H2 from the acid to form water H2O.
The now free sulfate molecule SO4 in the acid then combines with the lead in the positive plate to form lead sulfate PbSO4. On the nearby negative plate, the lead in the plate also combines with the free sulfate molecules SO4 to form lead sulfate PbSO4.
This discharge process causes the acid to become diluted when the battery is fully discharged, due to the chemical conversion of acid molecules into water molecules. In fact, a battery that is 75 percent discharged can freeze at no colder than 3 degrees due to this change in acid concentration. However, a fully charged liquid lead-acid battery will not freeze until 70 degrees below zero. Always try to locate a battery where it will not exceed 90 degrees, or fall below 50 degrees, with 77 degrees the ideal temperature for maximum battery performance.
Battery efficiency and length of service will drop significantly outside these temperature limits. During battery charging, a reverse chemical process takes place, as the negative lead plate, now covered with lead sulfate PbSO4 , separates back out into lead Pb , and the sulfate molecule SO4 is released back to combine with hydrogen in the water H2O to reform sulfuric acid H2SO4.
The positive lead plate recombines with the left over oxygen molecule in the water releasing hydrogen gas. This is the out-gassing of hydrogen that takes place near the end of every charging cycle, as the battery reaches its fully charged state.