Het "kleine wetenschappelijke vragen" topic #4

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Op maandag 4 september 2006 21:03 schreef speknek het volgende:

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Een hypothese stelt zelfs dat er bijkans ontelbaar veel zwarte gaten zijn. Ze weten namelijk nog niet wat ongeveer 80% van de materie in het heelal is. Ze weten wel dat het heelal een bepaalde massa heeft, want het effect daarvan kunnen ze meten met de relativiteitstheorie, maar niet wat die materie inhoudt, omdat het donker is, ze kunnen het dus niet zien.
Een van de hypotheses is nu dat de reden dat ze het niet kunnen zien is, dat het allemaal hele kleine zwarte gaten zijn -denk aan de grootte van micrometers tot enkele centimeters-, maar het effect daarvan is bekend..

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Op donderdag 7 september 2006 20:00 schreef Secretus het volgende:
Kan je eigenlijk, zonder dat je een oogafwijking hebt, het ene oog onafhankelijk van het andere bewegen ?

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Op donderdag 28 september 2006 20:19 schreef ThinkTank het volgende:
Hoe lang zou een mens het luchtledige kunnen overleven? In enkele SF verhalen (oa van Arthur C. Clarke dacht ik) worden reddingsacties beschreven waarin men zonder ruimtepak (of luchtsluis) van het ene ruimteschip naar het andere overstapt. In hoeverre is dit realistisch?

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Op donderdag 28 september 2006 20:19 schreef ThinkTank het volgende:
Hoe lang zou een mens het luchtledige kunnen overleven? In enkele SF verhalen (oa van Arthur C. Clarke dacht ik) worden reddingsacties beschreven waarin men zonder ruimtepak (of luchtsluis) van het ene ruimteschip naar het andere overstapt. In hoeverre is dit realistisch?

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The best data I have comes from the chapter on the effects of Barometric pressure in Bioastronautics Data Book, Second edition, NASA SP-3006. This chapter discusses animal studies of decompression to vacuum. It does not mention any human studies.

page 5, (following a general discussion of low pressures and ebullism), the author gives an account of what is to be the expected result of vacuum exposure:
"Some degree of consciousness will probably be retained for 9 to 11 seconds (see chapter 2 under Hypoxia). In rapid sequence thereafter, paralysis will be followed by generalized convulsions and paralysis once again. During this time, water vapor will form rapidly in the soft tissues and somewhat less rapidly in the venous blood. This evolution of water vapor will cause marked swelling of the body to perhaps twice its normal volume unless it is restrained by a pressure suit. (It has been demonstrated that a properly fitted elastic garment can entirely prevent ebullism at pressures as low as 15 mm Hg absolute [Webb, 1969, 1970].) Heart rate may rise initially, but will fall rapidly thereafter. Arterial blood pressure will also fall over a period of 30 to 60 seconds, while venous pressure rises due to distention of the venous system by gas and vapor. Venous pressure will meet or exceed arterial pressure within one minute. There will be virtually no effective circulation of blood. After an initial rush of gas from the lungs during decompression, gas and water vapor will continue to flow outward through the airways. This continual evaporation of water will cool the mouth and nose to near-freezing temperatures; the remainder of the body will also become cooled, but more slowly.

"Cook and Bancroft (1966) reported occasional deaths of animals due to fibrillation of the heart during the first minute of exposure to near vacuum conditions. Ordinarily, however, survival was the rule if recompression occurred within about 90 seconds. ... Once heart action ceased, death was inevitable, despite attempts at resuscitation....

[on recompression] "Breathing usually began spontaneously... Neurological problems, including blindness and other defects in vision, were common after exposures (see problems due to evolved gas), but usually disappeared fairly rapidly.

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The Bioastronautics Data Book answers this question: "Some degree of consciousness will probably be retained for 9 to 11 seconds.... It is very unlikely that a human suddenly exposed to a vacuum would have more than 5 to 10 seconds to help himself."

A larger body of information about how long you would remain conscious comes from aviation medicine. Aviation medicine defines the "time of useful consciousness", that is, how long after a decompression incident pilots will be awake and be sufficiently aware to take active measures to save their lives. Above 40,000 feet (12 km), the time of useful consciousness is 12 to 25 seconds. (The shorter figure is for a person actively moving; the longer figure is for a person sitting quietly.) For complete vacuum, this will be slightly less; 9 to 11 seconds quoted by the Bioastronautics data book, 9 to 12 seconds quoted by Fischer.

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Your blood is at a higher pressure than the outside environment. A typical blood pressure might be 75/120. The "75" part of this means that between heartbeats, the blood is at a pressure of 75 Torr (equal to about 100 mbar) above the external pressure. If the external pressure drops to zero, at a blood pressure of 75 Torr the boiling point of water is 46 degrees Celsius (115 F). This is well above body temperature of 37 C (98.6 F). Blood won't boil, because the elastic pressure of the blood vessels keeps it it a pressure high enough that the body temperature is below the boiling point-- at least, until the heart stops beating (at which point you have other things to worry about!). (To be more pedantic, blood pressure varies depending on where in the body it is measured, so the above statement should be understood as a generalization. However, the effect of small pockets of localized vapor is to increase the pressure. In places where the blood pressure is lowest, the vapor pressure will rise until equilibrium is reached. The net result is the same.)

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On a page on human survival in vacuum formerly posted to the /medlib server at NASA JSC, further details are given about the vacuum-exposure accident mentioned by Roth in NASA CR-1223:

"At NASA's Manned Spacecraft Center (now renamed Johnson Space Center) we had a test subject accidentally exposed to a near vacuum (less than 1 psi) in an incident involving a leaking space suit in a vacuum chamber back in '65. He remained concious for about 14 seconds, which is about the time it takes for O2 deprived blood to go from the lungs to the brain. The suit probably did not reach a hard vacuum, and we began repressurizing the chamber within 15 seconds. The subject regained conciousness at around 15,000 feet equivalent altitude. The subject later reported that he could feel and hear the air leaking out, and his last conscious memory was of the water on his tongue beginning to boil." .

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"Immediately following rapid decompression, it was noted that he began to cough moderately. Very shortly after this he was seen to lose consciousness, and the picture described by the physicians on duty was that the patient remained deeply cyanotic, totally unresponsive and flaccid during the 2-3 minutes [to repressurise the altitude chamber] down to ground level.
... "Manual artificial respiration was begun immediately... The patient at no time breathed spontaneously; however, at the moment ground level was reached he was seen to give a few gasps. These were very irregular and only two or three in number.
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"The conclusion of the [autopsy] report was as follows: "The major pathologic changes as outlined above are consistent with asphyxia. It is felt that the underlying cause of death in this case may be attributed to acute cardio-respiratory failure, secondary to bilateral pneumothorax..." "

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Many other cases of death following decompression are noted in the aviation literature, including one spaceflight incident, the Soyuz-11 decompression accident, in 1971. A recent analysis of this accident can be found in D. J. Shayler, Disasters and Accidents in Manned Spaceflight.

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In 1960, during a high-altitude balloon parachute-jump, a partial-body vacuum exposure incident occurred when Joe Kittinger, Jr. lost pressurization in his right glove during an ascent to 103,000 ft (19.5 miles) in an unpressurized balloon gondola, Despite the depressurization, he continued the mission, and although the hand became painful and useless, after he returned to the ground, his hand returned to normal. Kittinger wrote in National Geographic (November 1960):
"At 43,000 feet I find out [what can go wrong]. My right hand does not feel normal. I examine the pressure glove; its air bladder is not inflating. The prospect of exposing the hand to the near-vacuum of peak altitude causes me some concern. From my previous experiences, I know that the hand will swell, lose most of its circulation, and cause extreme pain.... I decide to continue the ascent, without notifying ground control of my difficulty."
at 103,000 feet, he writes:
"Circulation has almost stopped in my unpressurized right hand, which feels stiff and painful."
But at the landing:
"Dick looks at the swollen hand with concern. Three hours later the swelling will have disappeared with no ill effect."

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One of the potential dangers during a rapid decompression is the expansion of gases within body cavities. The abdominal distress during rapid decompression is usually no more severe than that which might occur during slower decompression. Nevertheless, abdominal distention, when it does occur, may have several important effects. The diaphragm is displaced upward by the expansion of trapped gas in the stomach, which can retard respiratory movements. Distention of these abdominal organs may also stimulate the abdominal branches of the vagus nerve, resulting in cardiovascular depression, and if severe enough, cause a reduction in blood pressure, unconsciousness, and shock.

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Usually, abdominal distress can be relieved after a rapid decompression by the passage of excess gas.

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Whenever a rapid decompression is faster than the inherent capability of the lungs to decompress (vent), a transient positive pressure will temporarily build up in the lungs. If the escape of air from the lungs is blocked or seriously impeded during a sudden drop in the cabin pressure, it is possible for a dangerously high pressure to build up and to overdistend the lungs and thorax. No serious injuries have resulted from rapid decompressions with open airways, even while wearing an oxygen mask, but disastrous, or fatal, consequences can result if the pulmonary passages are blocked, such as forceful breath-holding with the lungs full of air. Under this condition, when none of the air in the lungs can escape during a decompression, the lungs and thorax becomes over-expanded by the excessively high intrapulmonic pressure, causing actual tearing and rupture of the lung tissues and capillaries. The trapped air is forced through the lungs into the thoracic cage, and air can be injected directly into the general circulation by way of the ruptured blood vessels, with massive air bubbles moving throughout the body and lodging in vital organs such as the heart and brain.

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Op vrijdag 27 oktober 2006 19:50 schreef densmee het volgende:
ik denk minder dan een seconde luchtledig dus een vacuum
je zult zeer snel exploderen

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Op dinsdag 31 oktober 2006 14:25 schreef Catbert het volgende:

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Euh, nee, dat is dus complete onzin. Je explodeert absoluut niet. Je kunt het best even uithouden. Je gaat eerder dood aan verstikking dan aan iets anders. Op den duur zal je lijk gevriesdroogt worden, maar je bloed gaat niet koken ofzo, dat zijn hollywood fabeltjes.

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Would Your Blood Boil?
No.

Your blood is at a higher pressure than the outside environment. A typical blood pressure might be 75/120. The "75" part of this means that between heartbeats, the blood is at a pressure of 75 Torr (equal to about 100 mbar) above the external pressure. If the external pressure drops to zero, at a blood pressure of 75 Torr the boiling point of water is 46 degrees Celsius (115 F). This is well above body temperature of 37 C (98.6 F). Blood won't boil, because the elastic pressure of the blood vessels keeps it it a pressure high enough that the body temperature is below the boiling point-- at least, until the heart stops beating (at which point you have other things to worry about!). (To be more pedantic, blood pressure varies depending on where in the body it is measured, so the above statement should be understood as a generalization. However, the effect of small pockets of localized vapor is to increase the pressure. In places where the blood pressure is lowest, the vapor pressure will rise until equilibrium is reached. The net result is the same.)

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Op vrijdag 23 februari 2007 00:03 schreef Mirri het volgende:
Ah, is dit topic voor als je vraag niet wordt beantwoord door de Quest?

Toevallig een wiskundige/natuurkundige in de buurt?
Kan iemand me de padintegraalmethode uitleggen?

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Op vrijdag 23 februari 2007 11:13 schreef Haushofer het volgende:

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Ja, dat kan ik wel Wat moet je precies erover weten, en voor welke toepassing ?