Wikipedia:Reference desk/Archives/Science/2019 May 6

Science desk
< May 5	<< Apr | May | Jun >>	May 7 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

May 6

algae and pH

Is it possible for the pH to be more affected by photosynthetic activities in a smaller body of water than a larger body of water given that both bodies of water have the same amount of algae? Again, not a homework question. There is a small drain I am looking at which has a small trickle of water coming out and has plenty of algae in it. It usually has a higher pH than normal streams I am looking at which have much more water? If pH increases are dependent on ratio of algae and other plants/volume of water, are there any sources to back it up?

Yes, in general, any fixed volume (or mass) of acid or base will be more diluted in a large body of water than a small one, and thus have less effect on pH. However, there are some caveats:

• The flow rates of water into and out of the body of water will also have an effect.

• How much turnover there is in the body of water will also matter. That is, if water on the surface of the lake is contained in a shallow layer, this will cause pH to be different than if all the water freely mixes.

• The assumption that the amount of algae doesn't vary to match the size of the lake is doubtful. In general, you could expect the volume of algae to vary with the surface area of the body of water, since it depends on sunlight. A possible exception is if algae flows from a large body of water into a smaller one. Of course, there are many other factors, too. SinisterLefty (talk) 14:11, 6 May 2019 (UTC)

Is there a food which increases the size of the eggs?

Is the non-organic egg a result of a specific ('chemical') food which increases its size or weight? For example, if we are talking about chicken meat, then it seems that the non-organic chicken growth much faster than the organic one (if I'm not mistaken it has the same size of organic 1/2 year chicken already in 30-40 days from the 1st day of life and it's ready to go to the factories around this time). But I have no idea if it is the same about the chicken who used to lay eggs every day. I'd like to get any information about it. 93.126.116.89 (talk) 03:55, 6 May 2019 (UTC)

Diet can affect egg size (among other factors), the key seems to be the amino acid methionine, according to Hy-Line International:

• "Hyline: Nutrition and Egg Weight". www.hyline.com.

—2606:A000:1126:28D:9C3C:E8AA:C8E4:28F1 (talk) 05:02, 6 May 2019 (UTC)

I believe you are mistaken. The only part of the feed generally banned in organic productions of chicken that contributes in any significant way to growth rate I'm aware of are antibiotics. But their use definitely does not normally result in the extreme difference you're suggesting, see e.g. [1] [2] which suggest a 1-10% increase in daily body weight gain. Or see e.g. [3] [4] [5] [6] [7]. (It's possible some of the growth promoters discussed in the earlier refs would also be banned in organic farming but the point is even if you compare the growth rates to the controls without such treatments, their differences are no where near as extreme as you suggest.) Note in any case, use of antibiotic in livestock, especially routine use or use as a growth promoter is controversial and is banned or severely limited in a number of places.

Somewhat separate, but many definitions of organic tend to require some level of free range or at least limit the sort of extremely intensive methods often used with modern poultry farming [8], and these may affect growth rates although probably in a complicated fashion [9], but this isn't a "feed" issue feed issue as you seemed to suggest and the effect isn't anywhere near what you suggested. (I think it's also unclear whether free range is really part and parcel of "organic" also.)

Modern practices have significantly increase growth rates, but not all of these are banned in organic farming. Notably one of the biggest factors is probably the breed but provided they aren't GMO, these aren't banned in organic farming. It doesn't matter if you irradiated the shit out of them to get what you want. (Although this is more something in crops than livestock.)

Some of the modern breeds probably don't cope so well with free range conditions, but it's clearly many are used, in addition there's no reason to think breeds intended to be best for free range or organic farming are going to be slower growing, if anything they may perform better under such conditions than current ones. Now some consumers may feel that the extremely high growth rates are unethical or whatever and choose slower growing ones [10] and probably many who do so also prefer organic growing methods, but this isn't a part of being organic.

P.S. Some of the earlier sources mention that antibiotics are also a good growth promoter for egg production.

Nil Einne (talk) 16:13, 6 May 2019 (UTC)

Bouncing between two springs in a vacuum chamber

Idealised mass, spring and dashpot in a series system

Considering an object bouncing vertically between two sensitive springs (top-bottom) in a vacuum chamber after initial push, similar to Newton's cradle. The bouncing object (possibly a cube or a sphere) has a surface to receive maximum momentum imparted by springs and is tightly constrained by walls to avoid accidental slipping, etc. Assuming that the energy of the initial push is conserved by both springs, approximately for how long it will continue to bounce off? Is friction the only force acting to stop? Thanks. 212.180.235.46 (talk) 10:57, 6 May 2019 (UTC)

Gravity will influence the bouncing object, unless you place the vacuum chamber away from all gravitational fields (some travel might be required). A real life spring will also absorb some energy when contracting and extending (damping loss), unlike the ideal spring often used in though experiments such as this. Friction between the bouncing object and the walls of the vacuum chamber will vary wildly depending on materials, lubrication and so on - and in a vacuum you'll run the risk of vacuum welding too. WegianWarrior (talk) 12:34, 6 May 2019 (UTC)

The assumption that the energy of the initial push is conserved by both springs implies that the springs obey Hooke's law which is the case if they are made of a material that is not deflected beyond its linear elastic limit. The same must apply to the material of the bouncing object. There will be energy loss if the object rubs against side walls and in any Hysteresis such as rubber parts would introduce. If these losses are eliminated and the chamber is isolated from all vibration, magnetic field and Electromagnetic radiation, the only factors to limit bouncing duration may be Brinelling wear due to microscopic uneveness of the contacting surfaces and the springs radiating heat during compression. Zero gravity condition is not required. DroneB (talk) 12:45, 6 May 2019 (UTC)

Deformation of the metal in the springs will heat the metal, causing energy losses. Collisions between the object and the spring will make a sound, generating energy losses. Calculating how much energy that is would be stupidly complex math, so actually calculating how long it takes to slow down and stop is probably beyond the scope of this desk, but yes, even in a vacuum, where the object has no air resistance, there will still be energy losses, and the object will eventually stop. --Jayron32 13:05, 6 May 2019 (UTC)

In the real world, the bouncing object will also compress and decompress each time it strikes the springs, heating it up, and then radiating that heat. This will burn off kinetic energy. SinisterLefty (talk) 14:02, 6 May 2019 (UTC)

Yes, exactly what I meant when I said "Deformation of the metal in the springs will heat the metal, causing energy losses". --Jayron32 16:13, 6 May 2019 (UTC)

Agreed, and that will happen to the bouncing object, as well. SinisterLefty (talk) 20:45, 6 May 2019 (UTC)

Assuming the usual physics lab simplifications of "light inextensible string", frictionless surfaces etc., it will continue oscillating forever.

The situation will give simple harmonic motion. There is a restoring force towards the centre. There is no friction (if you described this as "done in vacuum", I assume that you're doing that to avoid friction, so let's assume you've removed all friction). It doesn't even matter that there's gravity acting in one direction – that displaces the central position, but doesn't change the motion.

Your example can be represented by the diagram. It doesn't need two springs, we can just assume that springs are double-acting. But how your example (being in a vacuum to avoid air resistance) differs from the diagram is that your example has a ${\text{Damping Constant }}C=0$. It will only decrease the amplitude of the oscillations (and so eventually come to a halt) if $C>0$. It's drawn there as there being a 'dashpot' or shock absorber connected to it, but in typical "real world" situations, that's more a property of the materials than a separate component.

A perfect spring can retain energy and then release it, but it releases just as much as it took in – it doesn't absorb any of it. In a "real world" spring though, there is some loss of energy as heat or sound - maybe even as electricity, if you had a piezoelectric spring. That's one place where this bouncing system could lose energy, and eventually come to a halt. If there was no vacuum, then moving the mass through the air would act as a dashpot (the viscous air has to be pushed past the mass, and that involves loss of energy as heat). Andy Dingley (talk) 15:25, 6 May 2019 (UTC)

By friction I meant friction when the bouncing object hits either spring, although it's apparently negligible. 212.180.235.46 (talk) 11:15, 7 May 2019 (UTC)

Actually, even in an otherwise perfect set-up, the system would lose energy via gravitational waves. As I understand it, that is the case for every object that has mass and is accelerated. Gravity is such a weak force that we usually ignore it, but the effect is computable. --Stephan Schulz (talk) 16:00, 6 May 2019 (UTC)

But it could be argued that since the object bounces vertically (top-bottom), gravitation actually helps by amplifying the force to hit the bottom spring. 212.180.235.46 (talk) 11:15, 7 May 2019 (UTC)

No it can't (at least, not correctly). Gravity is a constant force on the mass, acting downwards. This force is constant: it acts with the mass moving downwards, but it also acts against the mass when it's moving upwards. The work done by gravity on the mass is the integral of this, over a whole cycle, and that's equal to zero: so there's no overall assistance to it. Andy Dingley (talk) 15:12, 7 May 2019 (UTC)

Desalination in a survival environment

Could you desalinize water using a hand operated pump forcing water through a membrane? That is, what options do we have for a portable desalination in an extreme situation, all without electricity and in a region with little sun (otherwise, you could construct a kind of mini-greenhouse and evaporate water). I'm having difficulties finding such products for an acceptable price, so I wonder whether the elements for desalination imply some expensive/fancy element. --Doroletho (talk) 14:28, 6 May 2019 (UTC)

Yes. For example, see:

• "Katadyn Survivor 06". www.katadyn.com.

It utilizes reverse osmosis. Not cheap, depends on what you mean by "acceptable price"; (the membrane/filter seems to "imply some expensive/fancy element"). Or, you could use a portable solar still (weather permitting), e.g.:

• "Aquamate Solar Still Emergency Water Purification Inflatable kit Singapore". Baypore Singapore.

There is a promising new technology that promises to be "affordable"; it utilizes graphene oxide & solar energy (not available yet, AFAIK):

• "Nanjing team develops graphene oxide-based solar desalination system". www.graphene-info.com.
• "Portable desalination devices: survival technology available for everyone". Pressure vessel| Protec arisawa. 27 September 2017.

And another utilizing ion concentration polarization ←(should that be a redirect?):

• "New water desalination approach could lead to portable units for disaster relief or remote locations". newatlas.com.

—2606:A000:1126:28D:9C3C:E8AA:C8E4:28F1 (talk) 17:40, 6 May 2019 (UTC)

The Katadyn product costs a couple of thousand dollars. That's certainly prohibitively expensive. A solar still would be 10x cheaper and not only desalinize, but purify in general. --Doroletho (talk) 19:28, 6 May 2019 (UTC)

Actually, that model retails under $1k, and can be found new for $715 (or less on eBay: $200 new). —

Maybe in the US, but not where I am. Anyway, I want something cheaper. And understnad the reason why reverse osmosis membranes are so expensive.--Doroletho (talk) 20:16, 6 May 2019 (UTC)

You don't need bright sunlight, just a temperature diff between day and night. Some water will then evaporate from the saltwater reservoir during day, and condense at night. Arrange for the condensate to be collected in a freshwater reservoir, and replace the saltwater regularly, and you're all set. Alternatively, since you must be near a body of saltwater, it may well be cooler than the air during the day, and that temp difference could also be used to spray on and cool the outside of the condensate collection area, to increase the condensation rate. Or, if wood is around, you could go the other way, and build a fire to get the water to evaporate more quickly. Then, of course, your apparatus would need to be able to take those temps. SinisterLefty (talk) 20:39, 6 May 2019 (UTC)

See Brine spring; some places have access to salt water despite being far from significant bodies of it. Nyttend (talk) 21:53, 8 May 2019 (UTC)

We have an article about solar stills that might help you. Hand-pumped RO desalinators exist but they are expensive and strenuous to operate. You'd use one on a lifeboat, not on land. For further advice you might try forums.equipped.org which is full of people who get off on that type of thing. 67.164.113.165 (talk) 01:36, 7 May 2019 (UTC)

Doroletho, do you have much access to energy in other forms? See Illinois Salines, where salt was produced by boiling significant quantities of salt water. I suppose you could boil significant quantities of water, using equipment as simple as cauldrons to hold the water and glass enclosures where the steam could cool, but you'd need cheap fuel for the fires that keep the water boiling. Nyttend (talk) 21:53, 8 May 2019 (UTC)

In a survival environment if there is grass or other plants growing nearby, they will usually have some dew condensed on them early in the morning. You can go out and collect it with a sponge (to wipe it off the leaves) and a container to squeeze it into. Distilling water by boiling it with fuel takes a ridiculous amount of fuel. Doroletho, how much water are you talking about? Are you trying to provide a village with water for months or years? One or two people into a rescue arrives? Or what? If it's for short term emergencies maybe you can just store some water. 1 gallon per person per day is what I hear is needed for drinking. — Preceding unsigned comment added by 67.164.113.165 (talk) 04:25, 10 May 2019 (UTC)

Capacitors

How can I evaluate the characteristic impedance Zo of my rf capacitor? 80.2.20.124 (talk) 19:33, 6 May 2019 (UTC)

Characteristic impedance is a property of the transmission line. A capacitor does have Electrical impedance though.

For your capacitor the impedance should vary with frequency:

$\ Z_{C}={\frac {1}{j\omega C}}$

To measure this with response to different frequencies, including the phase shift, you can use a network analyzer (vector network analyzer). Since you only have one port you can only measure S₁₁. The capacitor will also have some resistance, and the connection will also have some inductance, but since that is in series you will create a resonance at some high enough frequency. Graeme Bartlett (talk) 22:47, 6 May 2019 (UTC)

Capacitors do not have a characteristic impedance; that term is applied to pure resistances and transmission lines. Characteristic impedance for either of those components holds for a wide range of applied frequencies. Capacitors (and inductors) do not exhibit a constant value of "impedance" when the applied frequency is varied. They exhibit reactance, which is an attribute that is also measured in ohms. Reactance of the capacitor varies with frequency in an inverse-law relationship, as you can see at Electrical reactance. At that article, the Capacitive reactance section explains how to calculate the reactance, so long as you know the value of your capacitor. It's unclear from your post whether you're a novice and simply don't realise that good quality capacitors exhibit reactance, or whether you're highly clued-up and trying to measure the impedance of a very poor-quality capacitor at the outer fringes of a frequency range where multiple resistive and inductive effects in the capacitor also come into play, or whether you're just stringing us along with a pseudo-technical trolling question. Anyone who plays around with capacitors knows that for all intents and purposes in the normal range of capacitance and frequency, capacitors exhibit reactance, not impedance. Akld guy (talk) 01:56, 7 May 2019 (UTC)

all capacitors will have some I ductance though so they dhould have a chsracteristic impedsnce.So can I measure the inductance by measuring its Zo?80.2.21.157 (talk) 13:10, 7 May 2019 (UTC)

The behavior of a capacitor at radio frequencies depends on its equivalent circuit

                                | |             F   =        1
------VVVVVVV------((((((`------| |-------       sr    _______________
       R            L           | | C                  2 π sqr( L   C)
        eff          eff                                         eff           

where

Reff = effective series resistance
Leff = series inductance e.g. of connecting leads
C = actual capacitance = Cnominal +/- (% tolerance)

At the series resonance frequency F_sr = 1/(2 π sqr(L_effC)) the capacitor behaves as a resistor R_eff. At that frequency only it is indistinguishable from a perfect resistor or a transmission line of characteristic impedance R_eff ohms that is either infinitely long or terminated in R_eff ohms. Theoretically one could use frequency sweeping equipment such as a network analyzer as suggested to find F_sr where the return loss parameter S₁₁ shows a sharp peak and zero phase, and calculate the R_eff from that. It is not normal to call the R_eff of a capacitor a "characteristic impedance". That term is reserved for the frequency-independant behavior of transmission lines. Measuring F_sr as described and assuming knowledge of C allows one to calculate L_eff but that is not very useful unless some calibration work is done to eliminate series inductance from the test setup. In general, capacitors selected for use at rf should be mounted with short leads, ideally be in leadless chip form, and have F_sr well above (say 3-5 times) the frequency of application. Their capacitance will often be specified at low frequency and be measured by a Capacitance meter or, for precision, a Bridge circuit such as the Wien bridge. DroneB (talk) 20:15, 7 May 2019 (UTC)

So what happens if you critically damp the lc with a resistor?80.2.21.28 (talk) 23:01, 7 May 2019 (UTC)

Theory is a wonderful thing, and you are correct DroneB. But in the real world, good quality capacitors intended for use at RF (is this what the OP meant by "RF capacitor"?) have near-negligible resistance and extremely low inductance. These attributes will therefore come into play only at exceedingly high frequencies, which will probably be well outside the frequency capability of any test equipment the OP is likely to have. More so if his capacitor is a variable air-gap type with meshing plates. We're talking about lab-quality test equipment here. So why is the OP concerned about impedance effects well outside the normal range of RF applications? This implies that he's using it in some exotic application, and by extension ought to know more about the characteristics of capacitors than he has led us to believe. Akld guy (talk) 22:29, 7 May 2019 (UTC)

Well I'm really disappointed that the cream, top flite, respondents of the ref desks can't help me here on a simple lc question.

Maybe you should ask bb. It knows everything. The pedia articles pathetic and really need tightening up on these matters. Dont they?80.2.21.28 (talk) 22:52, 7 May 2019 (UTC)

However,it is just possible that the arguments here are much too difficult for the bb brain to absorb.80.2.21.28 (talk) 23:06, 7 May 2019 (UTC)

The Wikipedia article Capacitor covers many aspects of this ubiquitous electronic component and it has a list of suggested improvements. To the OP, please point in the article to the type of capacitor you are asking about. What is "bb"? This article describes critical damping of an oscillator circuit, such as an LC circuit driven to resonance. However it is probably a circuit design error if a capacitor operates at its F_sr or higher frequency (whereupon it behaves as an inductance). An illustrative example that is often seen is where the dc supply to a sensitive integrated circuit has capacitors to filter undesired noise that comprise both an Electrolytic capacitor (that has a large value, say 100µF, to pass low frequencies but is ineffective at high frequencies due to its low F_sr) and, connected in parallel, a small ceramic capacitor of 100nF that has very high F_sr and so is effective at high frequencies. See Decoupling_capacitor#Placement. DroneB (talk) 00:44, 8 May 2019 (UTC)

never mind. I don't have network analisrr, but may be could do it using a tdr setup to find the reflection coefficient. Thanks anyway.86.8.201.25 (talk) 11:09, 10 May 2019 (UTC)

A TDR (Time-domain reflectometer) is wrong for measuring a capacitor. It can only tell you how far away (in cable delay time) is connected the capacitor, which gives a display resembling a short circuit, see [11]. DroneB (talk) 18:46, 10 May 2019 (UTC)

Multiple personality disorder

I read Dissociative identity disorder and was surprised to see that it comprises at least two distinct and relatively enduring personality states. Apparently it's less multiple than I imagined: I thought it was a real Jekyll-and-Hyde situation, where the individual alternately thinks of himself in two completely distinct identities, or where he concurrently thinks of himself thus (comparable to a Nestorian christology, with two different individuals in the same body), leading to things such as speaking to himself as a means of communication between personality A and personality B, rather than as a means of intrapersonal communication.

Has the situation I described been clinically observed, and if so, what term is used to describe it? Nyttend (talk) 22:04, 6 May 2019 (UTC)

I've wondered this too. Sagittarian Milky Way (talk) 22:44, 6 May 2019 (UTC)

The term for the second item, where the two halves consider themselves as distinct entities concurrently and even communicate with each other, is discussed in Bicameralism (psychology). It is definitely not scientific mainstream, but that article and the ones it links to may be of interest to you. Matt Deres (talk) 01:09, 7 May 2019 (UTC)

I saw part of the movie Sybil (1976 film) on TV some time back. It was based on the supposedly non-fiction book Sybil (Schreiber book), but the book is apparently considered somewhat dubious. 67.164.113.165 (talk) 01:42, 7 May 2019 (UTC)