Wikipedia:Reference desk/Archives/Science/2020 June 8

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June 8

Dagga

Dagga is the natural form of Cannabis most often sold in Southern Africa and is not genetically modified. It is commonly known that when this is smoked it can often not have any effect at all on the first occasion. I would like to know why this is. I am not sure if this is the case with the ubiquitous European hydroponic equivalent. Why would this substance not have an effect on the subject when used for the first time? Thank you — Preceding unsigned comment added by 109.151.74.96 (talk) 10:51, 8 June 2020 (UTC)

Honestly, my guess is more that this is rumor and urban legend than any basis in fact. There is no reason that THC would be ineffective on first use. Certainly other compounds can alter the effect of THC, including other cannabinoids, but those would always be present or not in dagga, with no specific relationship to first use. More likely is that people consume it differently on first use. Perhaps, out of anxiety of trying something new, they smoke or consume a smaller amount on their first try, and just don't get enough to notice the high. Then, subsequently, they use more. --OuroborosCobra (talk) 14:44, 8 June 2020 (UTC)

Whether you're getting high or not, inhaling smoke cannot be good for your health, and that definitely qualifies as "having an effect". ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:26, 8 June 2020 (UTC)

That's a bit off topic... --OuroborosCobra (talk) 17:39, 8 June 2020 (UTC)

The OP said it first. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:05, 8 June 2020 (UTC)

The OP said nothing about the health of smoking in general. --OuroborosCobra (talk) 23:17, 9 June 2020 (UTC)

If it has little perceivable effect that's most likely because it's low-quality "ditch weed" with little-to-no psychoactive ingredients. I'm not aware of any genetically modified cannabis in cultivation outside of a lab, so I'm not sure why you mentioned that. Hydroponics is something totally different: just growing plants in water instead of soil. --47.146.63.87 (talk) 16:51, 8 June 2020 (UTC)

Depends on what one means by "genetically modified." Certainly selective breading has resulted in specific strains of cannabis with desired qualities. --OuroborosCobra (talk) 17:39, 8 June 2020 (UTC)

(EC) According to cannabis, The genus is widely accepted as being indigenous to and originating from Central Asia, with some researchers also including upper South Asia in its origin.[7][8] so anything in Southern Africa was undoubtedly introduced by humans likely after significant cultivation and domestication. As those previous articles and others like History of cannabis, Cannabis indica, Cannabis sativa, Cannabis ruderalis and Hemp mention, cannabis has been cultivated for a long time for a variety of so much so it's difficult to know whether to recognise it as one species or 3 or what. Despite most of this happening long before there was any real understanding of genetics, as with most domestications, the modern cannabis plant has undoubtedly undergone a lot of artificial selection. Because of the different uses, the artificial selection may have been in different directions in different cases. I mention this because your first sentence leads me to believe you may be under the impression that dagga is are varieties of cannabis which are largely untouched by human influence when they're almost definitely not. If I'm mistaken I apologise. As for the other issue, I agree with other respondents that this sounds like some probable combination of urban legend and low potency cannabis. Especially given that if people are expecting something, and then don't experience, they may ask or find out what to expect before the second time and people by be more cautious the first time afraid of a drastic effect. If you are comparing to some strain you encountered sold for recreational use especially in a fairly competitive market place, bear in mind that while we could do a lot before, modern understanding and testing methods has greatly increased what we can achieve. Nil Einne (talk) 17:44, 8 June 2020 (UTC)

Xylem solute composition

Is there any way to find out what the solution in a plants xylem is composed of? I would be happy about any kind of example. Greetings, 2003:C3:EF37:FB91:D4A5:6933:7A48:1CAF (talk) 22:06, 8 June 2020 (UTC)

There are lots of ways. An entire branch of chemistry, analytical chemistry, is devoted to things like identifying unknown substances and the quantitative composition of an unknown sample. --OuroborosCobra (talk) 22:28, 8 June 2020 (UTC)

Our "xylem" mentions the general categories of chemicals, and links to the "sap" article for more information. DMacks (talk) 04:07, 9 June 2020 (UTC)

Weird sound phenomenon

You have a room with people packed like sardines, all holding identical mono speakers close to their chests, as omnidirectional a small speaker design as practicable. A synchronising radio signal starts playback of the same file on the same microsecond — a simple perfect file of a sine wave which goes from zero to 80 decibels at the rate of say 10 decibels per second then the file instantly ends. How long can you make the delay between time of the volume peak at the speakers and time of the volume peak at some specific speaker holder's ears (average the ears or whatever physics model most resembles what the mind hears) with tricks like constructive or destructive interference and giving the room a very creative shape? Max crowd size 10,000 adults.Sagittarian Milky Way (talk) 23:51, 8 June 2020 (UTC)

This sounds a bit artificial. But if your sine wave frequency is low enough you could treat this a a phased array that does not end up with grating lobes. So all the speakers are in a plane, that you could approximate by a plane source n(Ie one giant flat speaker). At a far distance the sound would reinforce strongly perpendicularly to the plane - ie vertically. The ear would be in the near field, but random phase difference from speakers significantly away would cancel, and most sound at the ear could come from the closest speaker. So your delay would be due to the speed of sound from chest to ears. But you will also get a big echo off the ground. (And if in a room the ceiling too). Graeme Bartlett (talk) 05:12, 9 June 2020 (UTC)

The sound scattering and absorption by the sardines should mean that the contribution of the ground reflection to the sound experience is negligible except from the very close vicinity. The ceiling could be made to be very non-reflective, like is done when soundproofing audio recording rooms.  --Lambiam 06:44, 9 June 2020 (UTC)

What is the actual problem you are trying to solve? I for one think you are not actually planning to have a very creatively shaped venue constructed that will hold a 10,000 adult audience who will all be equipped with a chest-mounted omni-directional speaker.  --Lambiam 06:44, 9 June 2020 (UTC)

No practical implications, I had a dream that you could make a delay a large fraction of the time sound needs to cross the room and was wondering if this was bullshit. Sagittarian Milky Way (talk) 09:26, 9 June 2020 (UTC)

I don’t think you can make any significant delay. The sound waves from the speakers in a narrow concentric ring around a given ear will all be in phase when they reach the ear. As the radius of that ring expands, the number of speakers increases linearly, but the contribution of each omnidirectional speaker decreases inversely proportional to the cube of that radius. So their joint contribution goes down rapidly; even if all conspire to interfere and destruct the sound of the inner ring, which would require a very precise positioning of the sardines given a very specific sine wave frequency and work for one ear at a time only, they just don’t have the collective power for that.  --Lambiam 21:35, 9 June 2020 (UTC)

Could you get a significant secondary volume peak by making the ceiling a parabolic reflector and putting someone at the focus and not giving him a speaker and having everyone face away from him for maximum ceiling echo percentage and of course picking the frequency right? Heck the floor could be a parabolic reflector and everyone stands on a grate or sieve like one of them anechoic chambers. Sagittarian Milky Way (talk) 20:28, 11 June 2020 (UTC)