Wikipedia:Reference desk/Archives/Science/2016 April 5

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April 5

Nuclides undergoing nuclear fission

What nuclides beside U, Th, can undergo nuclear fission? The nuclear fission article seems not to specify a list of fissionable and fissile nuclides. Can bismuth and palladium, for instance, undergo fission?--5.2.200.163 (talk) 10:44, 5 April 2016 (UTC)

Please see Fissile material. Did you consider an internet search for "fissile elements" before asking here?--Phil Holmes (talk) 11:03, 5 April 2016 (UTC)

I find the article you mention not very informative. It mentions fissile rule and centers on actinides. Other elements beside actinides and other ways of triggering fission are not mentioned. I have considered a gogle search, again not very informative. I've read somewhere (don't remember where) about elements like bismuth and palladium fissioned by deuteron beam collision.--5.2.200.163 (talk) 11:20, 5 April 2016 (UTC)

Also nuclear fission does not specify many details about fission reaction mechanisms and triggering possibilities.--5.2.200.163 (talk) 11:20, 5 April 2016 (UTC)

You're right - that article could do much better. The topmost graph answers your question, but turning the low-res little dots into element and isotope is ... laborious. We should have a real chart that excludes the long gray band and just focuses on where there is data (if that indeed is all the data that is available, which seems odd) Wnt (talk) 14:40, 5 April 2016 (UTC)

That chart is only about fissile elements, not about fissionable ones (which might be all elements heavier than iron or lead [1]). Rmhermen (talk) 15:04, 5 April 2016 (UTC)

I would even go so far as to say every atom except Hydrogen-1 can undergo fission, although it requires bombardment with some rather high energy particles to make it happen in stable isotopes. So, I assume they meant to ask about spontaneous fission. StuRat (talk) 19:38, 5 April 2016 (UTC)

MHD and nuclear reactors coupling

What are the requirements for the coupling of nuclear reactors with MHD generators in order to convert nuclear heat directly into electricity?--5.2.200.163 (talk) 10:47, 5 April 2016 (UTC)

Big Pipes. Greglocock (talk) 19:54, 5 April 2016 (UTC)

Only that? What else? Perhaps a conducting fluid such as liquid metal put in motion by a gas like helium from the reactor core by sparging in liquid metal?--89.122.39.86 (talk) 08:30, 8 April 2016 (UTC)

Arduino: RGB LED lights and Resistors

If we want to link 5 of 5V or 3V RGB LED to Arduino, how many resistors should i get? and how many Ohm does single resistor have to be? hellllpppp — Preceding unsigned comment added by 195.94.247.199 (talk) 11:23, 5 April 2016 (UTC)

What happens when you type [ Arduino: RGB LED lights and Resistors ] in the Google search box? --Guy Macon (talk) 16:27, 5 April 2016 (UTC)

Solubility

How is the solubility of a substance, say a salt, influenced by another salt? Is the solubility the same when dissolving a salt in a saturated solution of other salt comparatively to dissolution in pure solvent(water)?--5.2.200.163 (talk) 11:32, 5 April 2016 (UTC)

What happens when you type [ How is the solubility of a salt influenced by another salt? ] in the Google search box? --Guy Macon (talk) 16:29, 5 April 2016 (UTC)

Common-ion effect may come into play, depending on the identity of the other salt. --Jayron32 16:41, 5 April 2016 (UTC)

I see this discussion and I wonder how the above said aspects can be quantitatively characterized? Is the mixture of the two solutions an ideal mixture or not?--89.122.39.86 (talk) 08:26, 8 April 2016 (UTC)

Voltage drop over fully open transistor?

I've made a [schematic for a circuit] which uses two PIR circuits to control some LEDs (either PIR sensor will activate the LEDs). A couple of resistors and a capacitor slow the opening and closing of the transistor so that the LEDs fade on and off. Can anyone advise the voltage drop over a 2N2222 transistor that is fully open? The LEDs accept 1.8-2.2 V. --78.148.105.117 (talk) 12:31, 5 April 2016 (UTC)

If by "open" you mean not passing current (when V_B = V_E = 0V), the voltage drop across the transistor collector-to-emitter is the whole 6V supply. The 2N2222 is a common NPN switching transistor with h_FE >75 @ I_C =10 mA. Datasheet here. The HC-SR501 Body Sensor Modules that you use seem to deliver maximum 3.3V outputs; that suggests an inadequate 1V approx. to the LEDs after voltage drops in the 1N4001, division by 7 k ohm resistors, and V_BE. The 470µF capacitor in your circuit diagram is an electrolytic type that should be shown with correct polarity. The power dissipated in the transistor would be maximum and equal to the power in the LEDS if its emitter could supply 3V to the LEDs. P_tot in 2N2222 must not exceed 500mW so the LEDs should draw somewhat less than 160 mA. (If by "open" you meant the fully conducting state, V_CEsat of the 2N2222 is about 0.4V ). AllBestFaith (talk) 14:26, 5 April 2016 (UTC)

Damn! I meant closed! Thanks. I'm not sure I'm using the symbol properly either. The base is where the signal goes right? The 6V is meant to be shared across the LEDs when the transistor is closed/on. The 3.3 V is meant to be delivered to the transistor to tell it to turn on. 78.148.105.117 (talk) 15:13, 5 April 2016 (UTC)

The base is ... where the base is. Refer to our article on bipolar junction transistors for an introduction. To be clear, it is possible to design a single transistor amplifier that places the input or output signal on any of the terminals of a transistor. Most commonly, though, the convention is to use the base as the input signal, because this yields the most desirable current gain. This is called the common emitter configuration, and it is popular for lots of general purpose circuits like simple audio amplifiers or simple current drivers. Not all amplifier circuits need high current gain, so other configurations exist for different applications. Nimur (talk) 15:18, 5 April 2016 (UTC)

Unfortunately the OP drew a transistor in Common collector (known as "emitter follower") arrangement where there will be no voltage gain, and V_E cannot be more positive than V_B. This seems to be a case of wanting several functions together i.e. (i) an OR-logic combination of the two sensor outputs, (ii) slow ramp switching on/off and (iii) a driver for 9 LEDs. There are better circuit solutions for these functions e.g. (i) a standard CMOS device such as MC14071, (ii) an Op amp integrator with (iii) a high-current output stage respectively. A designer would enquire why the ramp switching is wanted (reasons could be to reduce transient loading of a power supply shared with something else, or to prolong the life of incandescent bulbs but that's not necessary for LEDs) and (s)he would consider a Switched-mode power supply especially if the total LED power is large. Advantages of the more complex switched mode is that little power is dissipated by the driver since its output transistors are mostly fully on or fully off, and the ramp dimming function is easily done by varying the switching Duty cycle. AllBestFaith (talk) 19:13, 5 April 2016 (UTC)

Hi. I've rearranged the circuit a lot. The reason for the fading is to make the light look more like a flame coming on and going off. [[http://everycircuit.com/circuit/4523679919112192 This is part of the circuit - I'm trying to make the on phase switch on more slowly but I don't seem to be able without reducing the final voltage/brightness. The first switch simulates the PIR sensor coming on and the second switch is just to drain the capacitor to reset the circuit for the simulation. The problem is that I can only make the light fade-on take longer by simultaneously increasing the delay before any light shows at all. Thanks for any advice. 78.148.105.117 (talk) 21:24, 5 April 2016 (UTC)

Why is Fresh-water Fishing mostly so poor in Winter? (I'm sure there are exceptions)

Fish don't hibernate, so it has to eat and swim around same as any other season. Some fish can't even breathe unless they are on the move. Not sure if this applies to fresh-water fish, but maybe it does. Anyway, it has to eat and it has to exist same as any other season, so why is fishing so poor in winter?

2A02:FE0:C711:5C41:3155:1744:AA32:2C45 (talk) 15:28, 5 April 2016 (UTC)

Fish are cold-blooded animals, so their metabolism slows down in cold weather. Therefore fish use less energy and don't have to feed as often in winter, and thus are less likely to take the bait. - Lindert (talk) 16:09, 5 April 2016 (UTC)

(edit conflict)Doesn't it depend on what sort of fishing? Fly fishing will be more successful when there are more flies around in summer, but other fishing techniques are possibly better in winter? Freshwater fish can breathe when at rest relative to the river bed just by relying on the flow of water past their gills. Dbfirs 16:14, 5 April 2016 (UTC)

Yup, it's hard to ice fish at all come summer. Rmhermen (talk) 20:32, 5 April 2016 (UTC)

... hadn't thought of that! I was thinking of worms and spinners. Dbfirs 21:04, 5 April 2016 (UTC)

Thanks guys, for answering 2A02:FE0:C711:5C41:D448:2C0C:836:8174 (talk) 14:02, 6 April 2016 (UTC)

What happens to dissolved oxygen in the water when the lake is completely frozen over ?

I would expect the level to steadily go down, since there's no air in contact with the water at the surface to replenish the supply. Wouldn't the fish then use up the oxygen, converting it to carbon dioxide ? Or are there enough plants in freshwater lakes so that the oxygen cycle is self-sustaining ? StuRat (talk) 16:19, 5 April 2016 (UTC)

Completely frozen over as in "a layer of ice on top, with no gaps" or as in "ice down to the bottom of the lake"? --Jayron32 16:42, 5 April 2016 (UTC)

The first case. StuRat (talk) 16:44, 5 April 2016 (UTC)

[2], [3], [4], [5]. --Jayron32 17:56, 5 April 2016 (UTC)

Can it be ever so cold that a lake is frozen down to the bottom? --Scicurious (talk) 00:49, 6 April 2016 (UTC)

A shallow lake, yes. StuRat (talk) 00:53, 6 April 2016 (UTC)

A shallow lake is not a lake, but a pond. These can freeze all the way down, but I do not believe a lake can be completely frozen. Scicurious (talk) 11:01, 6 April 2016 (UTC)

Sometimes. Depends on who does the defining. --Jayron32 14:38, 6 April 2016 (UTC)

Whoever named Shallow Lake apparently disagrees. StuRat (talk) 17:45, 6 April 2016 (UTC)

Why is it that water freezes on the surface of a lake but not below it?, Why Fish don’t Freeze in a Frozen Lake and Lake Vostok. I've not come across a lake frozen to the bottom during the last 40+ years in the Arctic. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 02:37, 7 April 2016 (UTC)

Thanks guys, for answering... Ops, wrong post. Sorry. Was meant for the one above. 2A02:FE0:C711:5C41:D448:2C0C:836:8174 (talk) 14:00, 6 April 2016 (UTC)

How does lactulose cause flatulence ?

It's an indigestible sugar used to treat constipation (among other things). So, if it isn't digestible, what generates the gas ? StuRat (talk) 19:20, 5 April 2016 (UTC)

It's a stool softener. What it does is draw water into the stool, thus expanding and softening the stool and replacing the gas contained within the stool with water. All that gas gotta go somewhere... --TammyMoet (talk) 19:43, 5 April 2016 (UTC)

Lactulose is metabolized in the colon by bacterial flora, see Lactulose#Mechanism of action.Fermentation is the name of the metabolic process that converts sugar to acids, gases or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation. AllBestFaith (talk) 19:44, 5 April 2016 (UTC)

See also Flatulence#Production.2C_composition.2C_and_smell. ---- LongHairedFop (talk) 19:47, 5 April 2016 (UTC)

As others have noted, lactulose's medicinal usage (and veterinary usage; its common as a no-fuss/easy on the metabolic pathways treatment option for constipation in certain mammals) is directly a result of the fact that it is not digested or absorbed in the upper gastrointestianl tract. When it reaches the lower tract, it becomes a readily-available form of sustenance which can greatly increase the numbers of various bacterial species within your gut's microbiota. In metabolizing the sugar, these gut flora change the pH of the stool mass and, through osmotic differential, pull water across the intestinal wall, the sum result of which is fecal matter with more water content and a greater volume, both of which make stools easier to pass and also create greater stimulation of the voiding reflex. Snow ^{let's rap} 20:49, 5 April 2016 (UTC)

Gravity detector

Hi, on a TV programme I saw demonstrated a gravity detector supposedly sensitive enough to detect people moving around nearby (within a few feet). The man demonstrating it moved from side to side in front of it, and the signal from the detector appeared to oscillate in sync with his movements. Is this really feasible, or would a detector that sensitive be overwhelmed by background noise? 86.161.61.41 (talk) 20:04, 5 April 2016 (UTC)

Simple gravimeters have been known for centuries. See Cavendish experiment for one of the famous early experiments in detecting the strength of a gravitational attraction between relatively small masses. Modern gravimeters are more sensitive and transportable. --Jayron32 20:10, 5 April 2016 (UTC)

With regards to background noise, consider that a person weighing 80 kg at two feet from the sensor has about the same effect as a 8000 kg truck at 20 feet (gravity decreases with the distance squared). Hence I'd say that background noise could be a problem in some locations, but if the immediate vicinity of the sensor is not too eventful the scenario you describe is entirely feasible. - Lindert (talk) 20:22, 5 April 2016 (UTC)

What about larger terrestrial and celestial events? 86.161.61.41 (talk) 20:53, 5 April 2016 (UTC)

Even though the gravitational effects associated with those things are large compared to what the sensor is measuring (e.g. the moon has a much larger gravitational pull on the sensor than any person standing a feet away), the time scales for these events are of a completely different order. Because these larger events happen so slowly relatively speaking you can still see the immediate effects of people moving by the sensor. - Lindert (talk) 21:18, 5 April 2016 (UTC)

I see, thanks. 86.161.61.41 (talk) 22:55, 5 April 2016 (UTC)

The LIGO detectors are incredibly sensitive. Your observation about background noise is correct; Neil deGrasse Tyson talks here about the signs they have around the facilities telling you to drive slowly to reduce interference. --71.110.8.102 (talk) 23:04, 5 April 2016 (UTC)

That may be more for mechanical vibration than gravitational disturbance? 86.161.61.41 (talk) 00:04, 6 April 2016 (UTC)

Yes, LIGO is very sensitive to mechanical vibrations. I once heard a talk discussing the sources of noise that LIGO has to deal with, and it included many ridiculous problems including: tides caused by the moon, continental drift, weather patterns, and apparently tumbleweeds hitting the side of the building (so they erected fences to catch the weeds before they got too close). Dragons flight (talk) 07:03, 6 April 2016 (UTC)

Bacterial victim

Viruses notoriously infect us eukaryotes. Are prokaryotes spared this affliction? Jim.henderson (talk) 20:25, 5 April 2016 (UTC)

In fact, there is a specific word for viruses that attack bacteria: bacteriophage. Nimur (talk) 20:38, 5 April 2016 (UTC)

Ah. Thanks. And I should have phrased the question as to not invite a double negative. Jim.henderson (talk) 20:42, 5 April 2016 (UTC)

Also, you need to phrase your comment not to include a split infinitive. Only jesting!--178.101.224.162 (talk) 00:09, 6 April 2016 (UTC)

There are even virophages! Nobody gets a free pass. :) But honor among thieves means that more of them are simply satellite viruses. Wnt (talk) 11:30, 6 April 2016 (UTC)

Reaction with ice

Does sodium react with ice? What are some values of the reaction rate?--213.233.84.20 (talk) 21:03, 5 April 2016 (UTC)

It reacts quite violently with water. So if the ice melts.....--178.101.224.162 (talk) 00:29, 6 April 2016 (UTC)

If there is any reaction at all, that would melt some of the ice, which would react more, and melt more ice, in a chain reaction until all the ice was gone. And I would expect there would be some reaction at first, since ice still sublimates into water vapor even at low temperatures. StuRat (talk) 00:42, 6 April 2016 (UTC)

It would actually be an interesting experiment if you got some very cold sodium and pressed it up against some very cold ice. I don't mean like -1c, i mean like -20c or something. I'm actually not sure you could really guess what would happen from fundamentals, without actually trying the experiment... I agree water sublimates into vapor but that is VERY VERY slow at very low temperatures. A single ice cube can take a month or more to sublimate in a freezer, not sure that would be enough to really "set off" the reaction, sodium is only the 2nd alkili metal. Vespine (talk) 02:02, 6 April 2016 (UTC)

Interesting question. There must be a some values of the reaction rate. Do a thought experiment: place some ice in vacuum chamber with a clean unoxidised piece of sodium. The ice (on recsiving any heat) will sublimate. That water vapour will create a 'protective' film of hydrate on said lump of element preventing further ingress of water vapour. Decrees vacuum (ingress persure) enough and the the vapour pressure increases and penetrates the protective film. Thus creating heat – which if sufficient, will cause frozen water to change state. At temperatures of boiling helium I doubt anything will happen, perhaps not even at boiling nitrogen because too much heat is being lost to the rest of cryogenic vessel. So, the reaction must depend on temperature and pressure -with a cut off point where nothing happens. --Aspro (talk) 20:25, 6 April 2016 (UTC)

Interesting aspect suggested about a thin film of the surface of the ice formed by sublimation. I think the problem reduces to the presence or absence of a water layer on the surface of the ice. Can sublimation form such a thin layer?--89.122.39.86 (talk) 08:37, 8 April 2016 (UTC)