Wikipedia:Reference desk/Archives/Science/2020 May 6

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May 6

Naegleriasis

I am looking for information on the infection rates of naegleriasis in different countries, which occurs when naegleria fowleri consumes a host's brain. It looks as if most cases are found in the United States, but I question the accuracy of these findings. Medical evidence implies that Americans should have a biological immunity to this parasite, but the infection data does not reflect this. Has the data ever shown the infection rates for Americans with pre-existing conditions, such as heart disease or morbid obesity? Thank you CombustibleTaco (talk) 02:36, 6 May 2020 (UTC)

Which evidence does indicate that Americans have a biological immunity? Ruslik_Zero 07:54, 6 May 2020 (UTC)

Naegleria fowleri is a free living organism which is referred to in the article as a "human parasite". Developing an immunity to a parasite usually takes a very long time. Richard Avery (talk) 13:26, 6 May 2020 (UTC)

What are "ferrallitic" and "fersiallitic" soils?

I'm looking for info on mineral composition and pH of Bushveld soils, to understand what are the macro- and micronutrient requirements of the plants native to the Bushveld region. I'm looking at this map: [1] but I cannot find any good explanation as to what "ferrallitic" and "fersiallitic" soils are. What are they? And what is a good source of info on the macro- and micronutrient requirements of the plants native to the Bushveld region? Thanks in advance! Dr Dima (talk) 03:33, 6 May 2020 (UTC)

An explanation of "ferrallitic" can be found at Ferrallitisation. Fersiallitic is proving harder to find. A Bing search for "siallitic" turns up this paper which you might find interesting: [2] My McGraw-Hill Dictionary of Earth Science does not contain either term or likely derivatives. A lot of help that turned out to be.--Wikimedes (talk) 04:30, 6 May 2020 (UTC)

Given the meaning of Sial, it's not too much of a stretch to think that "fersiallitic soil" is a soil composed of iron, silicon, and aluminum compounds. With any luck, someone will come along who actually knows.--Wikimedes (talk) 04:58, 6 May 2020 (UTC)

This google books extract, from a book on pedology, provides a fairly good explanation. It seems that basically the terms ferralitic/ferrallitisation and fersiallitic/fersiallitisation refer to the degree of geochemical weathering of sesquioxide-rich soils (there is also description of a third, intermediate, process, called ferrugination). Scroll up to the start of chapter 12 on p373 of the link. PaleCloudedWhite (talk) 09:01, 6 May 2020 (UTC)

Inductors/transformers and flyback converters

When, after a current has been flowing through a inductor, or the primary coil of a transformer, and a magnetic field/flux has been built up, that current is discontinued, does the resulting current induced by the collapsing field flow in the same direction as the original current, or in reverse?

The article on flyback converters seems to me to be saying that if the initial current is flowing one way ("negative" voltage on the secondary), the current induced by the collapsing field will be in reverse ("positive" voltage on the secondary). Is that correct? ZFT (talk) 04:41, 6 May 2020 (UTC)

The current keeps going in the same direction. But for the voltage, it is proportional to the rate of change of current. If the current is increasing then the voltage drop will be positive. But if you try to stop the current, then the rate of increase is negative and the potential difference over the inductor becomes negative. You can't stop it in 0 time, else you get infinite voltage. Instead you might get 10,000 volts and a spark. Graeme Bartlett (talk) 06:27, 6 May 2020 (UTC)

In this context, what is meant by "positive" and "negative"? ZFT (talk) 01:50, 7 May 2020 (UTC)

In the hydraulic analogy, an inductor gives the current inertia. You have to apply a pressure (voltage) and do work, to get the current moving through the inductor. Once the current is moving, the inertia (inductance) will tend to keep it moving (in the same direction). Stopping the current through the inductor entails applying a reverse pressure (voltage), against the flow of the current. In stopping the current, its momentum (the magnetic field), does work against whatever is trying to stop it. If you try to stop the current very abruptly, by closing a valve (opening a switch), then the resulting pressure (voltage) spike may be very high, and may rupture the valve (create an arc across the switch). catslash (talk) 13:21, 7 May 2020 (UTC)

That doesn't answer the question: what does "positive" and "negative" mean in this context? Since an electric current is the flow of electric charges between areas of opposite polarity, it is unclear to me what the article on flyback converters means by saying that "[t]he voltage induced in the secondary winding is negative..." or "[t]he secondary voltage is positive...". ZFT (talk) 01:32, 10 May 2020 (UTC)

It seems I made the basic error of not reading the question properly. Sorry.

The flux in the core depends on the net total amp-turns linking it -- it makes no difference to the flux whether the current flow is in one winding or in the other. The inductance acts to oppose any change in the net total amp-turns. The dot convention indicates current directions which for different windings magnetize the core in the same direction. Therefore, reducing the current into the dotted end of one winding will tend to increase the current into the dotted end of all other windings, so as to maintain the net total amp-turns (or in other circumstances, reduce the current out of the dotted ends of other windings).

In the flyback converter after the switch has been closed for some time, there is a net current into the dotted ends (all of it in the primary). When the switch is opened, the transformer will generate e.m.f.s in all/both windings which tend to draw current into the dotted ends. The current will actually all flow in the secondary, since the primary circuit is broken, and since the diode in secondary allows current in that direction. catslash (talk) 23:19, 10 May 2020 (UTC)

The positive and negative in the flyback converter article, is most likely intended to refer to the potential of the line along the top of the diagram relative to the line along the bottom. It is a common convention to draw a common ground rail along the bottom. catslash (talk) 08:36, 11 May 2020 (UTC)

Voice amplification in a half mask respirator

As an NYS EMT-B working in NYC I am not provided sufficient PPE by my employer and sourcing our own PPE on our own time / out of pocket is commonplace. I have a 3M 7502 respirator I would like use on the job, because reusing my worn N95 given by my employer tends to break the seal during physical exertion (e.g. when delivering compressions) in a very inconvenient way. I would love to use my 3M 7502 regularly (with appropriate cartridges) but the number one issue is being understood. What are the ways I can amplify my voice in a half mask respirator, interview patients, talk on the radio, and deliver patient care while maintaining a strict seal? 2604:2000:1000:59A:99F9:778:BCC2:DD3D (talk) 19:47, 6 May 2020 (UTC)

There are communication devices for such things (but I don't know about your specific respirator) e.g. 107.15.157.44 (talk) 20:13, 6 May 2020 (UTC)

No luck finding anything specific -- they're expensive, anyway. A throat microphone would work universally, but are made to plug into radio devices. There are such things as Personal Throat Mic Voice Amplifier For Teachers. 107.15.157.44 (talk) 00:07, 7 May 2020 (UTC)

There are bone conduction microphones I've seen designed for tactical situations. Our WP article only talks about getting sound into the inner ear via bone from outside, but googling "bone conduction microphone" and "ear bone microphone" find several products that have a transducer that picks up sound from the bones in the vicinity of the ear. DMacks (talk) 04:14, 7 May 2020 (UTC)

Nebula density

Is there a nebula out in space that's thick enough for conduction to play the major role in heat transfer? 93.136.18.189 (talk) 21:16, 6 May 2020 (UTC)

Some of the thickest are Bok globules. But these are probably opaque due to dust. If it is conducting heat, the pressure would be high, so either it would be exploding or collapsing if there was enough force to overcome the pressure. Even in Earth's atmosphere conduction would not be most important. In stars it would be mostly convection and radiation too moving heat. So I think your chance of finding one is small. Graeme Bartlett (talk) 23:07, 6 May 2020 (UTC)

Oh, right, forgot about the pressure, that makes sense. Mainly I was wondering if there could exist a pocket of space somewhere dense enough with dust and gas that a planet like Earth could maintain its temperature without the Sun's level of incoming heat radiation, or would it just radiate all its heat down towards 2.7 K (if it didn't have an internal heating mechanism). 93.136.18.189 (talk) 00:10, 7 May 2020 (UTC)

I will object to your statement that conduction plays no role in Earth atmosphere. In fact, in thermosphere it is the primary mode of heat transfer. This is easily explained if you remember that the heat equation contains only one parameter - thermal diffusivity, which is inversely proportional to the density of medium. So, in rarefied gases, e.g. in the interstellar space, the heat conduction is important. Ruslik_Zero 13:13, 7 May 2020 (UTC)