If antimatter were common starship fuel, what could prevent it from being commonly weaponized?

Question: My scenario involves a high sci-fi setting, where starships are readily available to civilians with sufficient qualifications and money. Most civilians would not be fueling ships with antimatter though, as it would primarily only be used in warp drives, which only larger capital ships or specialized exploration vessels would have. In this setting, antimatter is relatively abundant, with basically anyone with a ship that needs it being able to acquire it. The problem with antimatter, as you probably know, is its capability of creating massive explosions when it annihilates. Is there any conceivable reason that could prevent antimatter bombs from being commonplace and keep any Joe Schmo with an antimatter fuel cell from instantly obliterating a capital ship while still allowing plasma based projectiles to be viable?
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Comment: *Every time* you store or handle large amounts of energy there's the possibility of uncontrolled release of that energy; this can happen by accident or by someone voluntarily inducing such an 'accident'. The only way to prevent this is some fuel which intrinsically limits the rate of power output, somewhat like the nuclear fuel in power plants which is made such that it releases its energy over years instead of instantaneously (like a nuclear bomb).
Answer: Anti-matter is still not easily store-able but is instead made on-demand inside the ship in some kind of "charge reversal chamber" (possibly with the aid of some kind of 'unobtainium' which would then become the defacto fuel being bought and sold in place of the anti-matter it produces).
since anti-matter cannot be stored the maximum damage your ships can do is simply going to be equal to their reactors power-output rigged up to the best weapon they can find, which might still be lot but isn't necessarily nuclear Armageddon levels.
It's possible that major governments to have specialised/expensive/advanced machinery capable of storing anti-matter if you still want some form of anti-matter weaponry in your setting
Comment: The problem with this is that you still have the problem of energy storage or generation.  The singular advantage of antimatter is that it has the highest mass to energy ratio possible under current physics.  Thus the energy can be generated at some other place/facility at whatever pace is most convenient or efficient and then store it compactly for later use on your starship.  Creating it on the starship takes away the whole point of using antimatter and still begs the question of how are you going to generate enough energy to make enough antimatter to power a starship at relativistic speed?
Comment: I feel like all you're doing is altering the question to "what prevents people from using charge-reversal chambers as bombs".  It's basically the homunculus problem, except with physical matter.
Comment: but since energy is lost with each conversion there is no reason to convert to antimatter, just use whatever reaction you are using to supply energy to  make antimatter instead. If you can't store it antimatter offers no benefit.
Comment: @RBarryYoung, you don't. It's conversion, not creation. Think of it less as an antimatter system and more a system that converts any mass into energy. This is how reaction engines in Macross work.
Comment: @RBarryYoung I would like to point out that you have brought up a possible flaw - even anti-matter isn't necessarily fully converted into energy.  Unlike leptons, baryon/anti-baryon annihilation produces not only gamma rays, but also  electrons, positrons, and neutrinos through a complex process involving intermediary meson, and these carry off a substantial part of the released energy.  So perhaps for efficiency reasons, only electrons are "charge reversed".  Matter atoms can fairly easily be ionized to obtain the necessary electrons, but no anti-baryons... positron storage limited
Comment: I'm implying that from my "charge reversal chamber" bit that the anti-matter is being produced from conventional matter as-per star-trek rather than from pair-production.
Comment: It's the same problem.  Unless you intend to forfeit "conservation of matter and energy", changing matter into antimatter requires E=mc^2 energy. If you are throwing out conservation, then it's basically magic disguised as science and you can postulate any source of infinite energy you want, and again, there's no need or reason to use antimatter.
Comment: Actually I think this sort of works in such a setting, you have a magic dohicky that converts a stream of matter into antimater at a rate dependent on the amount of power you supply to it, in fact the thing could convert a stream of matter 50% to anti matter and annihilate it right there at a rate dependent on the externally applied power, it makes for a lovely mass to energy converter, but note that the limit is on the ability to supply power to drive the thing and mass to convert. You still have a reactor mass problem but warp universes tend to ignore that.
Comment: @ltmauve it literally doesn't matter what you call it, normal matter cannot be fully "converted" to energy without antimatter, and it cannot be converted to antimatter without useable energy.  And Macross isn't science it's fantasy fiction.
Comment: What if antimatter is the only fuel capable of producing enough energy at a given moment to power the warp drive? 1 ton of fuel may contain the same amount of energy as it's converted anti matter counterpart, but it takes time for fuel to burn, antimatter is the most reactive energy dense fuel we have
Comment: *"the maximum damage your ships can do is simply going to be equal to their reactors power-output"*... which is enough  create a stream of antimatter. The issue is that your "charge reversal chamber" requires at least as much energy *in* as you're getting *out*, which means your fuel has to contain enough energy to be creating antimatter at a usable rate, which means your fuel is now usable as a weapon too. No hard-science system can escape the Kzinti Lesson: any system with sufficient energy output to be useful as an interstellar drive is also useful as a weapon for the exact same reason.
Comment: @Chuu: OP's problem is founded on the fact that _storing_ sufficient quantities of antimatter given the owner the ability to do with it as he pleases. Ummdustry's answer merely make it so that antimatter _cannot be sufficiently stored_ to be unleashed as a bomb. Instead, "unobtainium", which is not a danger in and of itself is the stored fuel, whereas antimatter (a result from processing the unobtainium) is only ever available in a limited quantity (= engine production rate). This means that an antimatter bomb is tied to the engine production rate instead of the antimatter storage amount,.
Comment: @Flater The flaw there is the assertion that the "unobtanium" is not a danger. If it contains sufficient energy that you can use it to power an antimatter generator, and is sufficiently dense that you can carry it on your spacecraft and still have capacity left for crew and cargo, then it is sufficiently energy-dense to be a pretty effective bomb. If a tank of fuel lets you run your engine for a week, then it *must* contain at least as much energy as a week's worth of antimatter. Perhaps spread across more mass and volume, but not *too* much, or it wouldn't be a worthwhile fuel.
Comment: @anaximander: The gist of the answer is that you can only _release_ a given amount of energy (i.e. convert unobtainium to antimatter) in a short timespan, and you cannot store the antimatter long enough that you can meaningfully save up. This works when you assume that a large-energy "charge reversal chamber" cannot be built by anyone, and that a badly built "charge reversal chamber" will simply generate _less_ antimatter (**as opposed to** a badly built "charge reversal chamber" being unable to properly contain the otherwise abundant and volatile antimatter).
Comment: @anaximander: In short, the unobtainium is not volatile (compared to antimatter), and converting it is an arduous process which thus puts a ceiling on how much energy you can feasibly release. The unobtainium will not explode, nor need to be contained. It is effectively inert _unless_ processed correctly. Think of it like how an oil candle _could_ be used as a bomb (the oil can quickly release energy), but a wax candle cannot (it very slowly releases its energy and it is not highly flammable nor explosive in its room temperature form)
Comment: I never said that the unobtanium contained any accessible energy. The energy comes from conventional matter, the unobtanium is simply something that the charge reversal chamber needs in order to function, it could be as simple as liquid helium to cool the system which converts the matter into anti-matter. it could simply be a special isotope that the charge reversal chamber uses, there are a lot of options
Comment: The problem is that if your system is energetic enough that the only way to feed it fast enough is to give it antimatter, then you're talking about a *lot* of energy, and that energy has to be provided at a rate sufficient to produce an antimatter stream of sufficient size so your "slow burn" is still pretty fast. You're not downgrading from oil lamp to candle; you're downgrading from nuclear power to jet fuel - we can answer the question of why antimatter bombs might not be feasible, but the "fuel-air bomb" in that analogy is still a problem.
Answer: Expense of containing it
How do you contain anti-matter in a safe way? I don't know, but someone does in your story.
It may be that containing anti-matter is so energy expensive that the only way to power a long-term anti-matter storage unit is with an anti-matter reactor. In that case, only the people with the money to operate anti-matter reactors in the first place could possibly store enough anti-matter to make a weapon.
Comment: This.  "*The problem with antimatter as you probably know, is its capability of creating massive explosions when it annihilates*" completely ignores how incredibly difficult it is to store and manipulate antimatter.  By comparison, handling plutonium, ricin, Variola and chlorine trifluoride are child's play.
Comment: @RonJohn: Handling antimatter is easy as long as you don't want to handle it for more than a microsecond or two. Or handle more than a handful of particles at a time. Or deal with it anywhere with an electromagnetic field. Or even the vaguest hint of atmosphere. Other than that, piece of cake!!!
Comment: And also possibly the size of the containment limits it to the size of ships and large installations to generate it.  Far too large to be on a warhead.
Comment: @RonJohn And only a little more difficult to store and manipulate than chlorine pentaflouride!
Comment: Or flourantimonic acid (strongest acid in the world has a pH of -31.) All of the things you suggested are containable.
Comment: FWIW the way it's done in real life is usually magnetic fields.
Comment: @GarretGang Isn't that measured in H₀ instead of pH?
Comment: pH is the measure of free hydrogen in the solution (to my understanding which is generally H30+ for most acids) but in the case of flourantimonic acid it is H2F+. Both of which act as ejection strippers, but H2F+ can strip electrons from everything except Teflon (the least reactive substance in the world next to noble gasses and N2) while H30+ is more limited
Answer: Jon's Law: Any interesting space drive is a weapon of mass destruction.
Basically, you're in a setting where the average person who can pay is already in possession of a personal WMD. Adding antimatter simply makes the existing problem that much worse, so no, there really is nothing you can do about it.
Comment: Any interesting **real space** drive is a weapon of mass destruction.  Drives that impart pseudo-velocities (warp drives, or anything where the velocity goes away when you turn off the drive--the classic being the Lensman stories.  The only weaponized drive in the books is the Kzinti lesson, not Jon's law) aren't a problem, nor are drives that leave the universe (hyper drives.)
Comment: I second this. Even if you can prevent antimatter bombs from coming into existence, you could just take your antimatter engine, mount it on a small spacecraft, and ram that into your target at half the speed of light.
Comment: @LorenPechtel Technically they weaponized the drives by throwing planets at things in one of the later books....
Comment: Anti-matter isn't even necessary, an obsolete sublight drive strapped to an asteroid can do the trick if your intended target is a planet or space station.
Comment: @TimB No.  The used the drives to position planets correctly to attack but it was the planet's own velocity, not the velocity imparted by the drive, that drove it home.  The only high speed planets were those used against Ploor but in that case they found planets already moving at an insane clip.
Comment: @LorenPechtel I feel we're arguing technicalities that don't matter here.... however: The drives were used to position the planets so that they would act as weapons - without the drives the planets were not weapons therefore the drives turned the planets into weapons and hence were used as a weapon.
Comment: @LorenPechtel Even devices capable of imparting pseudovelocities can be weaponized. You just have to be creative enough. Take the hyperdrive from Star Wars: "no one did that before" audience: seriously? No one tried that before? Best rationalization: it was banned by treaty  (that the rebels....being rebels...still followed a treaty imposed by the empire...). Even real warp drive math says we need *a moon sized hunk of negative mass* to function. Just...put that anywhere...and boom.
Answer: There are really two problems you should be thinking about here, but luckily they both have reasonable solutions.
The question you asked: Use of home-made antimatter bombs against military assets.
You're thinking "how do I keep home-made antimatter bombs out of Joe Schmoe's hands, but a military ship isn't really going to be worried about that. Joe Schmoe with a home-made antimatter bomb is equivalent to the modern US Navy facing a pissed off white nationalist with a ton of fertilizer in a fishing boat. Yeah, the bomb will do a lot of damage to destroyer if you actually GET it there, but if they're paying any attention at all, Joe Schmoe and his bomb are going to get detected and destroyed long before they're close enough to be a threat to the ship.
The trickier question you didn't ask: Use of home-made antimatter bombs against CIVILIAN assets.
This is trickier because office buildings and cruise ships and hotels and things don't have point-defense weaponry. Terrorism is a much more serious threat when you've got freely available antimatter, but I think you've got a pretty simple solution: Unless your containment system is 100% perfect, you're always going to be emitting radiation as stray atoms of antimatter annihilate with stray atoms of regular matter. A 99.999999% perfect system is good enough to prevent that from causing any damage anybody cares about, but it will STILL result in your antimatter fuel cells having a detectable radiation signature.
Your solution is just to ensure that antimatter fuel cells are only freely available in places where ships are being refueled, and trying to take one anywhere ELSE is going to be immediately detected and result in a giant pile of authorities descending upon you.
Comment: I think your first paragraph is the real answer.  It shows that this question is like asking: in the early 21st century, what prevents gasoline (or fertiliser, etc) from being commonly weaponised?  In the absence of any (direct or indirect) defences, these can be easily weaponised as very destructive — but in technological and sociological context they're not a huge problem, since military targets are more than adequately defended against them, and the general rule of law means that attacks on civilian targets are —while not unknown — hardly a part of everyday life.
Answer: You could make it very difficult to contain in the correct way to weaponize it.
We have this issue with nuclear power (thankfully!).  It is much harder to get Uranium to explode with the force of a nuclear bomb than it is to get power from it.  You have to enrich it first.
One of the major unknowns with using antimatter is containment.  Good containment is tricky.  The best we have accomplished has contained antiprotons for 16 minutes.  Perhaps the only way to store antimatter for any reasonable period of time  stabilizes it so well that even if you dismantle the apparatus, it still takes time for the energy to dissipate.  Perhaps the antimatter itself is part of the containment, and the antimatter's properties are sufficient to maintain the containment for a short while.
Perhaps vortex math actually provides some useful results.  Rodin coils are popular in that community because they are believed to be ... well... I'll just say there's a lot of people who think you can violate the conservation of energy principle with them.  Here's an example of something they can actually do.
One of the neat things that happens in these experiments is that you manage to spin something up to great angular speeds, and even if you remove power, the object continues spinning (due to its angular inertia).  However, if anything from vortex math turns out to be correct, we might find that "something else" can start spinning, and that spinning stabilizes the antimatter so that it doesn't immediately annhilate.
(Note: in particle physics, we often refer to things as "spin" simply because they have rotation-like properties.  This "spinning" could be a new attribute of matter rather than actual physical spinning like the ball magnet in the video)
If this happened, it could take a minute or two for the spin to decay.  A weapon that discharges over a minute or two is much less terrifying than one which discharges over milliseconds.
Comment: @RonJohn If you find it difficult to contain (as we do now), that also means it is *very* difficult to deliver, because it bleeds out its energy while in storage.  If the only way to stabilize it enough to not bleed out doesn't support rapid de-containment, then you're set.
Comment: @RonJohn Yet.  It's a "high sci-fi setting."  Nearly everything about the question isn't *yet* possible.  Typically high sci-fi supports new scientific theories, as long as they don't directly contradict existing ones too badly.
Comment: "*You could make it very difficult to contain in the correct way to weaponize it.*" But -- as you acknowledge three sentences later -- it already is very difficult to contain.
Comment: But there's no such thing as "stabilizing antimatter".
Answer:
My scenario involves a high sci-fi setting, where starships are readily
available to civilians with sufficient qualifications and money.

So you've established that your world has some kind of certification authority (checking qualifications), a central bank (issuing money), and a military (implied in your reference to civilians). All this implies your story-line takes place during peaceful times with a functioning society and stable government.

In this setting, antimatter is relatively abundant, with basically
anyone with a ship that needs it being able to acquire it.

Anyone with a ship that needs it being able to acquire it is fine as long as they are not allowed to collect and store large quantities. The key is to contain the antimatter in approved fuel cells.

Is there any reason that could prevent antimatter bombs from being
commonplace and keep any Joe schmo with an antimatter fuel cell from
instantly obliterating a capital ship while still allowing plasma
based projectiles to be viable?

There's a lot of unrelated concepts mixed up in this question.

Preventing bombs from being common-place: Regions of space where the antimatter is abundant are all under tight government control. A fuel cell is not a bomb. Buying raw anti-matter to make a bomb is impossible.

Joe Schmo only has a government-issued antimatter fuel cell. Cells are only large enough to fulfill approved flight plans in between government checkpoints. Long journeys require refueling at checkpoints.

Capital ships, assuming these are military ships, wouldn't just let a civilian starship sneak up into blast range (further reading: Are nuclear weapons useful in space?). They'll shoot them before they get too close.

Plasma based projectiles only require microscopically small quantities of antimatter to be lethal, so yes you can still have that.
Answer: Yes and No,
The simplest way to think about it is how fertiliser is handled modern day, if you have a need for it (Farmer or in your case ship owner) you can get it. If you start to buy more than you need for your purpose they halt your purchasing and send investigators to clear you. So your security is making sure anyone who has enough to be a threat would never use it that way, it's not foolproof but that is the tradeoff between safety and usability.
Comment: A better solution that we're starting to see more of is robotic 'noses' that can tell if you're bringing a bunch of fertilizer somewhere that doesn't require it. (Like an FBI building).
Comment: The only real way to detect anti matter would be tracing the gamma ray emissions of matter-antimatter reactions, if it is porperly contained (The current method employed by CERN is magnetic suspension in a vaccume) there wouldbe no emssions ecept whatever the containment unit produces.
Answer: The smoking gun effect
Hydrogen and antihydrogen collisions are going to have some very energetic emission spectra, some of them in the ultraviolet.
Other than stars there are very few sources of high energy emissions at these wavelengths (read almost none). So mass production efforts  at equipping important terrestial areas and space lanes with cheaply built optical sensors and mesh networking would yield a detection network that would make it  possible to do forensic data analysis to say this explosion originated in this very narrow region of space.
Woe betide the poor sap who launched the anti-matter bullet when the cops get finished doing a lot of matrix manipulations on sensor data.
You can make the reasonable assumption here that anyone who is making anti-matter on a large scale either has harnessed enough energy to be further along the kardashev scale than we are. Or they have learned considerably more about physics and materials science. Or both. In any event, this makes it almost certain that they have the necessary raw materials and energy to mass produce a mesh network sensor array for multiple wavelengths at a cost scale far below todays standards.
It is a lot harder to get away with breaking the law when everyone sees you doing it.
Comment: This solves half the problem. The other half of the problem is that not everyone who wishes to cause damage minds being caught.
Comment: Since the OP asked, "Is there any conceivable reason that could prevent antimatter bombs from being commonplace" I deemed a deterrent answer was adequate. Answers that deal with guerrilla warfare or terrorism are both outside the scope of the question, and would in any event require more than a single pronged solution anyway. And seriously, how many people are going to throw a rock that will result in them being bathed with a lot of hard xrays and gamma as result of the impact? So I imagine that your perceived other half of the problem comes a lot closer to being between 0 and 1 percent.
Answer: I think the best way to prevent antimatter use as a weapon is to simply have it be incorporated into your ship, so that you have to crash your entire ship to actually have it react to anything. During normal operation it'll be locked into a stasis field or whatever is on your ship that prevents it from exploding you.
Now if someone does crash a ship, there's a good chance of an antimatter explosions happening. Perhaps most cities will have anti crash buffers in place that will magnetically control a ships decent, locking it in place if it seems to be crashing? That would at least deal with your landing sites.
Another way that comes to mind is to use quantum teleportation to control antimatter. Have your antimatter entangled with the inside of a vacuum tube with the quantum particle you're using. Then you buy that unit and download the entanglement specs onto your ships computer. Now your ship can only access a single molecule of antimatter at a time whenever you engage the entanglement function. That would at least prevent someone from having a lot of antimatter at once, so long as bein locked into the engine is the only way to prevent it from exploding the ship.
Answer: Containment is a trade secret and has safeguards
Perhaps only a single company/species knows how to create antimatter containment (or generate anitmatter at the moment of use or teleporting the antimatter to the user's location, for all we know--they are not telling) and they have specialized technology to do so.  Said technology has safeguards so that it limits the amount of antimatter that can be output at a time based on the size of the ship it was installed in.  Attempts to break into the device to reverse engineer the technology have only led to the timely deaths of those investigating and of course exercising the ruinous penalty clause (probably against the entire planetary system of the flag of the device, making each species very eager to enforce the rules) of the rental agreement.
How does the company get new customers?  Perhaps an exploratory advertising branch that puts plaques on the far side of the moon (or whatever is convenient in-system) of potential species with a little radio transmitter good for a few million years with instructions on how to build a FTL beacon that requires a certain level of technology.  Of course, for all we know maybe they seed life-bearing world to create their customer base.  A high-technology rich species with a long term outlook of millions of years.
Comment: This was my idea too.  Antimatter generation, containment tech and engines are all provided by an advanced race.  These folks do not mingle.  They provide this aspect of their tech to help the less evolved.  They provide the antimatter.   If you hack their engine, no more support.  If the antimatter provided is not accounted for by the engine, you get no more.  If you try anything, you get cut off.  There is no customer service line.  If you attack one of their stations you get to learn about the other tech they have.
Comment: @Willk "If you attack one of their stations you get to learn about the other tech they have" XD +1
Answer: You would need to create it somewhere else or you would need to use some other fuel to create it first, which would  beg the question why you wouldnt use that fuel directly. The implication of this is that you can readily store it without it detonating within your ship until you need it. If you can store it you can also prevent an anti-matter warhead from detonating on your hull, for example by using a larger version of whatever antimatter manipulation you have to prevent the antimatter touching the insides of your ship on the outside. Alternatives like using antimatter similar to a nuke (have it react with some matter in the warhead) might be easier to stop or detonate prematurely, for example with another antimatter warhead or long-range antimatter manipulation.
As another alternative: large ships are only capable of space drive travel. The assumption is that the drive needs to be big or specialized so only large ships can carry them. But what if only large ships can safely transport antimatter? This means any antimatter weapon would immediately be too small to contain the antimatter safely till it reaches the target. Launching "naked" antimatter would mean any matter fired into it would immediately disperse the antimatter and render it mostly harmless if not detonate too close to the ship firing it.
Answer: In order to keep anti-matter from being weaponized there should be multiple prohibitive layers to actually extracting energy from anti-matter.  I will outline some examples here.
Anti-Matter Creation is Prohibitively Expensive
It is currently incredibly difficult create anti-matter "on-demand", and certainly not in large quantities.  Perhaps, technological advancements have been made such that this substantial improvements have been made, but it is still extremely expensive for anyone outside of heavily funded government entities or extremely well-funded private corporations to do so easily.  This likely requires specific purchases or rare elements, that could be regulated or monitored much the same way deadly compounds are monitored today.
Anti-Matter Storage Is Prohibitively Expensive
If you are using anti-matter as an energy source you likely want to store it somehow.  Even though the technology exists, even in your world it is still difficult and expensive to safely store sufficiently large anti-matter quantities.  Once again, it likely has specific requirements in terms of items to purchase to achieve which could be monitored.
Amount of Anti-Matter Needed for a Weapon Is Prohibitively Large
For use of anti-matter as fuel, maybe you only need a small amount to be sufficient, or a small rate of production.  For a large-scale weapon, you might need a large quantity.  Even if a person is able to create and store a small amount, it is not enough to make anything more dangerous than conventional explosives, and is more expensive.
Use as Fuel Needs to Not be Too Prohibitive
I just listed off some reasons how to make anti-matter hard to use.  But how then can it be so commonly used as starship fuel?  Couldn't you just siphon some from your starship's tank?
What I propose is that starships have been able to get around some of the above restrictions by exploiting some of the differences in use-cases between fuel and weapon.
The starships engine is not an anti-matter storage container, and the fuel is not anti-matter.  The fuel is instead a rare and expensive element or compound that produces a specific rate of anti-matter particle emission through radioactive decay when combined with a small amount of another specific element or compound (let's call it a catalyst).  Otherwise it is inert.  The engine then combines the two substances within a specific chamber and immediately harvest the energy.  No storage is needed at all for the anti-matter, and the rate of anti-matter production is only suitable for a continuous relatively slow reaction (i.e. like a burning match, the reaction is too slow to cause a runaway reaction).
Now an intrepid terrorist can easily get ahold of the fuel, and the catalyst, but will not be able to store enough of the produced anti-matter to weaponize it.  Other methods to create large quantities of anti-matter in a short time are prohibitively expensive, so that is out as an option also.
BONUS: Since the engine gets around the need to store the anti-matter, have the emitted anti-particle be electrically neutral, such as an anti-neutron.  Since charged particles like a positron are orders of magnitude easier to capture and store compared to neutral particles, even though there is a continuous source of anti-matter, it is even more difficult to capture and store it.
Answer: The question could be answered by starting from a similar question:
Since flammable liquids are common vehicle fuels, what prevents them from being commonly weaponized?
Indeed, the majority of contemporary weapons don't use destructive potential of common fuels, they mostly use them as, well, fuels. Why is that? Probably because common-fuel-based weapons are not very powerful, effective and safe to use (although some are still occasionally used in guerrilla warfare, e.g. Molotov cocktail). Even VBIEDs/SVBIEDs don't use their fuel as a (primary) source of explosion.
Similar situation may arise for antimatter fuel. The fuel-based antimatter bombs could be so terribly impractical that it might be simpler to obtain more conventional weapons. For example, the fuel might be stored in a lot of hard-to-break containers with a relatively low antimatter content.
Add a common belief that antimatter fuel can't melt space station beams and your terrorists and guerrillas will use other means to try to achieve their goals.
Comment: Normal fuels require oxygen and thus have very little explosive potential.  The only way you can get a substantial boom out of any common civilian fuel is by making a fuel-air bomb--and that requires you to already possess some actual explosives.  (You use HE to disperse the fuel, then detonate the mix.  Without explosive dispersal you don't get a good mix.)
Answer: Anything can be Weaponized
The task is to keep it from irresponsible people
Antimatter can be stored as positronium hydride (a hydrogen atom bound to an atom of positronium) to keep from extreme damage when touching anything. Using this compound lowers the risk of catastrophic incidents. Anything can happen when you involve humans in anything.
Since Antimatter in your cas is mainly obtained through a spaceship, a system might have to be put in place that any interactions involving antimatter are computer controlled on a closed system. Internal specialists will have to be searched before entering and exiting the plant, and should work there no more than a week or so. This will keep internal sabotages at bay.
Then there is the case where an attack on an antimatter fueled ship could result in the annihilation of antimatter in extremely catastrophic ways, the same when an antimatter spaceship wrecks. This can be minimized through antimatter fuel cells, but again, anything can happen with humans.
The question you are trying to solve is about minimizing the risk of an antimatter attack, and preventing any antimatter fueled attacks means no use of antimatter whatsoever.
Comment: @Ummdustry You'd find plenty of comedians and visual artists prepared to vehemently disagree with you on that. (But, fortunately for you, that vehement disagreement will take the form of a pointed satirical reference or abstract drawing rather than a pointed stick to the skull.)
Comment: Anything can be weaponized, but most things aren't.  I could be wrong, but I've never heard of jet fuel or rocket fuel being weaponized.  I suspect most weaponization is a matter of convenience.  In other words, almost anything other than anti-matter is easier and more efficient to weaponize, so why bother.
Comment: @JBH Jet fuel was "weaponized" in the 9/11 attacks. After all, it's what fed most of the fires that ended up taking the buildings down. The planes themselves were just shipping containers for the weapon. As for rocket fuel, ammonium perchlorate (a common substance used for solid-state rockets) has most certainly been weaponized to power explosives.
Comment: @forest, jet fuel wasn't weaponized, passenger jets were weaponized.  BIG difference in relation to the OP's question.  The terrorists didn't steal jet fuel, they hijacked jets.  Yes, the fuel made a big boom, but I assumed the OP wasn't asking how to keep ships from being hijacked.
Comment: @JBH That's why I put weaponized in quotes. For ammonium perchlorate though, it must certainly has been weaponized on its own.
Comment: @forest, can you cite an example (aka, provide a link)?
Comment: I just seem to recall reading a news article about some IED being found with it, but unfortunately do not have the link to it. I'm just going off of memory.
Comment: Thankfully mankind has yet to weaponize peace, kittens, comedy or the visual arts.
Comment: @abamert , do you mind citing an example? (hyperlink or something)
Answer: Antimatter as a Catalyst, Not an Energy Storage
You said that antimatter was only used in warp drives. Well, warp drives are weird, let's make them use an exotic ingredient, antimatter, but only as a catalyst of sorts. Perhaps a (smallish) ring of anti-molybdenum is needed to convert neutrons from a nuclear power source into warp energy.
However, the anti-molybdenum slowly decays as the neutrons impact it, so it must be replenished after every voyage. This is an easy task due to the revolutionary Mr. Accelerator™ devices, which can produce small quantities of antimatter (maybe a milligram or so a week).
These devices are expensive, and only governments can afford to have enough to restore anti-molybdenum rings. The antimatter is immediately transported to the ships and installed on the rings. Better yet, it it made in situ.
Additionally, the antimatter is only stable in space in vacuum under a solid 10 meters of lead (or uranium, your choice). Due advances in 3D printing, a 3D printed frame of anti-neodymiun-iron-boron holds the anti-molybdenum ring in place, and is in turn secured by immense (regular matter) neodymium-iron-boron magnets. To remove the rings, you would need to some how break the laws of physics and turn of permanent magnets.
What stops people from using the Mr. Accelerator™ devices to make antimatter warheads? The ridiculously small amount of antimatter it produces per unit of energy. It just isn't economical to build trillion-dollar warheads just for most of them to miss a space ship.
And against civilian targets? Antimatter weapons are by no means small. They are also much too heavy to be much use on planets. It's just easier to use a fission (not even fusion) bomb.
Answer: If your society has spaceships and starships and antimatter fueled warp drives, it is probable that it has slower than light ships that can reach relativistic speeds, and faster than light ships that travel at multiples of the speed of light.
Space ships that can travel that fast make terrifying kinetic weapons, regardless of their power sources. The impact of such a ship with another objects is likely to cause an explosion similar to or greater than the explosion of its fuel supply without a collision would be.
So the deadly danger would be the spaceships as well as any antimatter fuel they contain.
Therefore, spaceship trajectories would be highly regulated anywhere near a solar system with inhabited planets.  Spaceships that approach the solar systems with threatening orbits, or spaceships within the solar system that suddenly deviate from their approved orbits, would be attacked, vaporized, and/or diverted first and questions asked later - if there are any survivors or intact flight recorders.
In the Star Trek: The Next Generation episode "Haven" (30 November 1987) an unidentified spaceship is approaching the star system of the planet Haven.  Valeda Innis, the First Electorine of Haven, calls the starship Enterprise which happens to be in the Haven system:

VALEDA [on viewscreen]: An incoming vessel has bypassed our stargate, violating our law. It has refused any attempt at communication.
PICARD: Are you saying you believe it to be hostile?
VALEDA [on viewscreen]: Failure to communicate is inherently hostile. We have no defensive capabilities here and our treaty with the Federation specifies your obligations in that matter.

The stargate is not described and it is uncertain what percentage of other star systems have stargates.
It is possible that the stargate is the exit point of a some sort of space warp leading to another solar system.  The voyage through that space warp bypassing many light years of space could be much shorter and faster than travelling though those light years of space, even with warp drive.
Because of the many, many, many problems and inconsistencies with speed, distance, and time in every Star Trek production starting with TOS, there is
a theory that many interstellar voyages in Star Trek involve travelling through one or more of those hypothetical space warps to vastly shorten the journey length and travel time.
So the idea that the stargate in "Haven" could be the exit of some type of space warp used for interstellar travel is very attractive.
Another possible theory is that the stargate in "Haven" is some type of vast  space fortress that all spaceships that approach the system have to match velocity with and dock with. The spaceships are inspected for contraband and alien germs and the passengers and crews checked.  Then the crews would probably be sent to the destination planet as guests/prisoners in a separate spaceship manned by a Haven crew and another Haven crew would board the ship to take it to Haven.
All Haven citizens allowed to operate spaceships in the Haven system would be psychologically profiled and selected for extreme loyalty to Haven, and their families would be held as hostages.  Whenever a spaceship deviated from its assigned course the families would be tortured and images of the torture broadcast to the spaceship until it returned to the assigned course.
Presumably a Federation starship would be exempt from the requirement to stop at the stargate.
Antimatter would also be very strictly controlled.  Antimatter would be produced in gigantic space factories far from anything that could be damaged by a gigantic, planet-devastating, explosion. The antimatter that was sold to customers for spaceship or other use would be in containers and legally considered to be "Sealed Evil in A Can".
https://tvtropes.org/pmwiki/pmwiki.php/Main/SealedEvilInACan 1
Because misusing a tiny amount of antimatter is equal to releasing Cthulhu upon an unsuspecting world.
Presumably the containers, and the spaceships and installations that used antimatter, would have complex AI programs to determine whether the antimatter is being used properly and whenever the programs suspected intent to misuse the antimatter they would unleash killer robots to kill first and ask questions later.
Thus the spaceship-using or antimatter-using characters in your story would be constantly worrying and checking that anything that they did with spaceships or antimatter was not only legal but also didn't appear to be even the least bit suspicious, since they would live in constant fear of the horrifying penalties for doing anything that seemed even the least bit suspicious with their spaceships and/or antimatter.
Comment: I know it is silly to talk about conservation of energy in the context of FTL travel, but mathematically the fuel should always contain more potential energy at first than the resulting kinetic energy when the fuel is spent. Whatever physics allow FTL probably also mean FTL collisions won't be as catastrophic as the detonation of their fuel.
Comment: @BlackThorn Speaking about kinetic energy in the context of FTL doesn't make much sense to me. We know that the kinetic energy grows without limit when approaching the speed of light, but we can't tell anything about it above it - the only [formula we have](https://en.wikipedia.org/wiki/Kinetic_energy#Relativistic_kinetic_energy_of_rigid_bodies) returns an imaginary number.
Comment: @BlackThorn  The closest thing that we have to a FTL theory is the Alcubierre drive,  What happens if a ship with a wide Alcubierre drive field passes by a planet?  The whole planet could be engulfed in the field and dragged away.  And if only part of the planet is engulfed and carried away by the field it might be left with a scar a thousand miles deep, resulting in catastrophe.  And if the drive is shut off near a planet the matter and energy released might have a devastating effect.
Answer: Antimatter Storing Crystal
If antiprotons could be stored in a special crystal, (ordinary protons can absorb/conduct in certain materials, so maybe there might be a way for antiprotons to do so), then it could be tied up this way that makes it tough to access a lot of it all at once.
---Edits---
I'm imagining a crystal with a certain central axis of symmetry.  When a small voltage is placed at a right angle to that axis, it breaks the symmetry allowing particle-antiparticle collisions, which somehow produces a current (I'm imagining the antiproton-proton pairs sitting in molecular holes (holes like in the center of a buckyball)).
A larger voltage can produce a larger current, but only up to a point of saturation.  So while these crystal store a great deal of energy, there are limits on how much power can be delivered at any particular point in time.
https://tvtropes.org/pmwiki/pmwiki.php/Main/PowerCrystal
https://en.wikipedia.org/wiki/Proton_conductor
Comment: A few old (4th doctor?) episodes of Dr. Who imply this sort of thing, where things made of anti-matter interact with normal matter without any violent explosions.
Comment: I believe Stephen Baxter used a similar description for the power/fuel source called a Kernel in his books Proxima and Ultima. In this case, the Kernels were essentially super-batteries, containing functionally limitless energy and impossible to recharge.
Answer: Antimatter Bombs are Useless
An antimatter reactor is a piece of precision hardware the likes of which humanity has never constructed before, Every second of its operation requires constant monitoring and if anything goes wrong there's an ungodly explosion. The people who work with them are serious, careful and procedure-oriented.
The hardware itself is a monolith of technology the size of a small spacecraft on its own.
If you wanted to explode such a reactor then you'd merely have to shut down its containment systems for a moment, but to do that, you'd have to get past every safeguard, security guard and the full defences of an active war-footing capital ship.
Such technology is strictly regulated and prohibitively expensive, the only non-military organisations who operate them are staggeringly wealthy interstellar corporations who operate their own private armies and can readily defend their equipment as well as any military would.
Anti-matter bombs are no different. they are unstable, requiring perfect containment for their entire operational lifespan. They are the last word in Mass Destruction. Their mere existence courts disaster and no government will tolerate anyone having access to them.
But they're also the most unwieldy weapon ever devised. A ball of sophisticated technology the size of a small building, regulated by a crew of a dozen highly educated men and women until the day comes that they set it on a timer and flee the scene.
Such devices are worthless as weapons of war. Too large, too cumbersome and far far too dangerous.
Instead, they're used to wreck moons and as statements of power.
"We can build this, what can you do?"
Answer: Econony and Effectivity is the key

Antimatter is expensive (energetically).
As there is not natural source, it must be done, from nothing, but energy. Basically it is the best energy storage you have at the time, but still it gets a lot of energy to move big interstelar ship and make it warp (or fast enought or what) and all that energy have to be stored in the form of antimatter first.
1.1. Solution:
There are not enought free resources at Earth to create enought AM for all ships. But it is not a problem - we simply have big (as in planetary size big) solar convertors in space, which give us nearly unlimited electrical energy for free (well Sun would waste it sending it to interstellar space anyway, so why not use it). (We would need it anyway in this system)
Everybody and his dog have space ship - we need so much energy for
it
Again, if nearly anybody (well anybody rich, but still a lot of people) can have spaceship, there is also need for fuel to move it in space - we use the electricity to break asteroids/comets/... to conventional fuel for in-system travel - and burn it in everyones rocket to something, which could be eventually later harvested and reprocessed again, when it get collected in some proto-asteroids on some convenient places (if terms of hundreds years, maybe)
Also the effectivity to get rocket from gravitational well is just poor today - lets use space elevators, with free electricity we can lift anybody to spaceyard and/or back to ground. In-system (personal)spaceships do not land on Earth, but on such elevator equipped spaceyards as well as personal airplanes are using common airports, not roof of house today.
Antimatter react with any normal matter
So it could be created in large enought quantities only in hard vacuum - basically means space, near of big enegetic source - the solar convertors. While it is possible for Joe Doe to have spaceship, it is not possible for him to have all the equipement needed to cr4ate and store large quantities of antimatter and also large enought power source to create and store it (it must be trapped in electromagnetic fields with large intensity and so large power consumption. Also the technology, to be able mass produce antimatter, must be of proper scale, not just some small facility. And its effects are clearly visible in space, as well as the power sources needed to just maintain it - you cannot hide it in garrage.
Antimatter is needed for interstellar travel
So it is sold only on interstellar spaceports deep in space (say around Pluto or something like that) and is not allowed inside Solar system. (Except for good known and protected routes from solar converter to interstellar ports.) Also as it is unstable, it must be protected by powerfull elmag shields all the time (which is possible to destroy (=put momentary down) with large energetical pulse from the converter, where the energy is abudant - so piracy is impossible, if you do not want explode while trying). The container with elmag shields itself is enought of normal matter to make explosion so large, that you just vapore, if you try to travel near its trace (which is strictly forbidden and ship-computers have coded safely avoidance such risky places as well as avoidance of say Sun itself - not that it could not be hacked with a lot of effort, but it could not be done by mistake, nor by normal interface).
Any approach to AM-container trajection is responded in military style as act of planetary agression (evaporate first, ask later) both by Energy company and any goverment/military in shooting range.
If somebody wants interstellar travel, he takes taxi/heli to nearest airport, plane to base of elevator, lift to spaceport, in-system rocket to interstellar port near Pluto and finally board big interstellar ship - be it (his) private, corporate or govermental (as well as the taxi/heli/in-system ship on his way)

Antimatter evaporates slowly anyway
As it is technologically easier to make antimatter in form of hydrogen/oxygen/any evaporable element (or at least it is presented by press and oficial sources), the antimatter still slowly evaporates, which makes continual reaction with its container and is also reused to power it. It also create clearly visible trace of any container with AM, so it can be tracked over whole Solar system. So "smugling" such container to a planet is impossible, without being detected days or weeks before landing and being evaporated in matter of hours after first detection, if communication is not successfull and such container would not fast change trace from Sun and planetary zone.

Which is responce to your question

Ofcourse it could be militarized by goverment or Energy Company, but being trackable and destroyable by EMP pulse much faster, than delivered to planet surface it is not much of risc, if there are two or more independent powers, which does not want have their Earth headerquarters eveporated by antimatter bomb. (And anti EMP-pulse pulse is not possible to use, as if it is not superexactly coordinated to amplitude and frequency with sub-nanosecond precision, it would explode the container by the anti-pulse power)

As stated, there is much larger risc of clasical near-light-speed ram to planet, but it is probabelly countermeasured by some energy weapons all around the space, conventionally powered inside the system, AM powered on interstellar ports and Sun converters (AM/energy for just launching projectile able to push something few miligrades from its trajectory, eventually evaporating by being hit by the fast attacker (which would do it as well), is a lot less, than energy needed to puch whole atmosphere (and magnetic fields around) and still do massive damage on surface.
Humans probabelly would create such defensive system anyway, as there may be interstellar comets, or what, which could endanger Earth, even without terrorist planning it. Also there is a risc of interstellar ship with failure on its return way - so at time of danger probably all avaiable anti-asteroid lasers on all ships in space would also coordinate to add a little energy to push harm from Earth.
Answer: Delivery impossible because containment not self-contained.
As you stated, only capital ships with warp drives have anti-matter drives -- and the facilities to contain antimatter.
Because containing the antimatter requires big facilities... as in, a sizeable percentage of capital ships is dedicated to antimatter containment. Nothing smaller can keep antimatter contained (which also rules out producing antimatter in some smaller facility). You need really big capacitors to buffer even the most minute power fluctuations. The radiation shielding alone weighs tons. Compare fusion chamber containment and scale up accordingly.
You just can't get the antimatter anywhere except from one containment facility (unmanned refuel station) to another (capital ship)... and even that is so extremely tricky that it is only done in orbit. (Also, to avoid some madman sabotaging his AM containment to create a huge explosion planetside.)
If you try to take antimatter out of containment to deliver it to a target... boom.
If you try to take the containment chamber out of the context of a capital ship (or a production / refueling facility) to deliver it to a target... boom.

This of course does not rule out using a capital ship, 9-11-style, as delivery vehicle. Then again, we are talking thousands of tons of mass at escape-speed velocities even without taking warp drives into account... at which point it does not really matter if you're delivering an antimatter payload or just pulverise the target with the kinetic energy of the impact.
Answer: How do we stop a WMD from being used? Pretty simple really. It's Cold War solutions. Even though we know the right thing to do for everyone to win is to not do the bad thing nobody expected it to really happen. That said there's more you can do if you're willing to add to the premise:

Everyone has antimatter Harder stand-off in a Cold War-like situation if the civilians have it in their cellphones.
Storage is extremely hard given how hard antimatter is to contain, might as well make the storage so durable that you'd need antimatter just to crack it open.
Education grind the thought right out of them. Possibly with some Big Brother monitoring for good measure.
Suicidal Attempting to use it as a weapon is most likely going to result in their deaths not from backlash but from backsplash. Feed this fear.
Manipulation Energy produced by a storage unit is only going to generate at a certain rate. Manipulating such a device to increase output should be impossible for someone not extremely well-versed in the science. Perhaps even then they don't have the required tools.
Regulation Even if everyone has access to a supply of it. It doesn't mean they have it all at once. A depot could resupply everyone's cellphone battery with a charge that's not too terrifying.
Comment: Blackadder wants to explain to you a small flaw in your first point: https://youtu.be/tGxAYeeyoIc?t=110... That something has (kind of) worked once does not mean that it will work always. With only two players who were supposedly directed by the best people of each country, there were [more than enough close calls](https://en.wikipedia.org/wiki/List_of_nuclear_close_calls) to think that the schema could be expanded to the general public successfully. Also https://en.wikipedia.org/wiki/Mutual_assured_destruction#The_doctrine_of_nuclear_deterrence_depends_on_several_challengeable_assumptions
Comment: For the regulation part, that does not seem feasible. The amount of energy (and power!) needed to put a spaceship in orbit is *very* terrifying in its own right.
Comment: @SJuan76, very well. By the simple math the more people factored into the statistics the more likely that some chance event occurs. But regardless the antimatter has a chance of being in a failing state (Ex: Fukushima reactor). Which implies that we can never prevent all accidents. Regulation to reduce the total amount in one place doesn't lower Risk but it does lower Threat. If you only have enough to launch a shuttle then the worst that can happen is exactly the same as if you just blew up a shuttle....
Comment: ...and yes everyone walking around with nukes may or may not hit the flight response on every person. Nature and nurture *does* affect things though and one would hope a positive feedback loop on this idea that winning is not fighting. Plus rationally weighing against all the other factors: I don't have much, so what can I really do that my plasma gun can't already?, etc.
If you weren't convinced that someone would be safe to society then that's part of regulation. It's *similar* to guns.
Comment: Also @OP theoretical material scientists already have designed materials that could survive the Sun's temperature. So it's not *too* far-fetched to have a material that you could pretty much only break by hitting it with anti-matter (clearly plasma guns are ineffective if the Sun isn't).
Answer: In two words Counter Containment.
Anti matter can only be contained by fields not matter. Trying to contain it with matter produces spectacular but useless results.
So we contain it either with a magnetic or electric bottle.
If you possess a device that can disrupt electric or magnetic fields you can cause antimatter explosive devices to detonate prematurely maybe even so prematurely that they destroy the launching vessel. This is not outside of the realms of possibility in a society that can create and store antimatter.
Answer: You are indicating that antimatter is only needed by some major star-going vessels.  Therefore, security comes from three things working together:
1)  Antimatter storage in vessels is built into the keel.  Removing an antimatter storage device from a ship basically requires dismantling it and still yields a very big object because the components are dispersed in the frame.
2)  Antimatter storage that can actually be moved around is handled akin to how we currently handle atomic bombs--perhaps a step further by providing an armed escort ship whose job is to destroy the transport container if it's misappropriated.
3)  The ships that use antimatter are not allowed anywhere near a planet or other such vulnerable location.  Your vector comes within 10 million miles of an inhabited world and the authorities shoot first, ask questions later.  Lesser vessels that don't use antimatter provide all the transport near population centers.
Comment: 1) could lead to a problem with refueling.
Comment: @SJuan76 Why?  You bring the mobile container to the main tank.  Ordinary gas station tanks are in effect built into the keel of the station, it doesn't cause a problem filling them up.
Comment: But you can take the gas (antimatter) easily for refueling, so you do not limit access to it (or at least the gas station is a bad analogy).
Comment: @SJuan76 You're trying to extend the analogy farther than it fits.  I was showing that having non-removeable fuel tanks doesn't make a big problem.
Answer: If you only deal with one electrical sign at a time, anti-matter or real-matter still obey to electromagnetic field and can be deflected, and so, contained, without having to enter in contact with "real" matter. In theory. As we hope to do for high energy plasma in order to produce controlled and sustained fusion. The size of the equipment to produce the required magnetic field is huge, at least for us with fusion, that this is not "possible" (economically) for a particular organisation to produce one, just for a "single" use (as a bomb). Could be used as a weapon (static location or on a huge movable platform) if the equipment used to generate the em field is not destroyed at each use. And some energy has to be available to supply and maintain that equipment while it has to contain the anti-matter. Such equipment won't be profitable to build with the goal to store a single positron. It would hardly be a hand-held weapon.
Neutral anti-matter won't react as well to magnetic fields, that is why one could held separated positrons and anti-protons (so they don't make an overall neutral anti-Hydrogen atom), while not dealing at all with anti-neutrons or other anti neutral particules, since they could not be so easily contained.
Comment: I have trouble understanding your answer. Can you check again the sentences and the punctuation? To me, it sounds like you are just stating what are the problem for antimatter in our world, not answering the OP's question.
Comment: Yes, it is a strong parallel with today nuclear fusion of Hydrogen to get Helium plus "tons" of energy, but channeled energy, with Tomahawk like fusion generators. The equipment is so huge that not everyone can make one, in his kitchen. So I tried to highlight the fact that it would not be "common", as a weapon, such that every Joe can't own one.
Answer: As far as creating and storing antimatter goes, there are several links below that may help. There are devices already in use, and in the process of being finalized for use in order to store, transport, and use antimatter. These videos should point one in the right direction for further answers about the subject. As for not using antimatter as a fuel source, this would probably not be plausible, which can also be explained in the Tedx video below. It would simply take too long, cost too much, etc. Which is one reason why space programs have slowed down today. Many other answers have pointed out the issues with using antimatter as a bomb, but this is not to say it wouldn't or can't be done in some circumstances such as previously mentioned civilian targets. As for differentiation between certain drives, it might make 'sense' in a way for some ships to use a warp drive (Alcubierre drive) for interstellar travel, and use something similar to current antimatter drive concepts for high velocity within a solar system. The problem with the antimatter drive is special relativity (specifically time dilation), which means using an antimatter drive to travel great distances is feasible, however don't expect to arrive or come back to the same time period.
Tedx talk about antimatter and a newly invented device:
https://www.youtube.com/watch?v=EBebWBjpWIQ&vl=en
Article about CERN transporting anti-matter, also mentions techniques used to store antimatter:
https://futurism.com/cern-transport-antimatter/
warp drive:
https://en.wikipedia.org/wiki/Alcubierre_drive
Answer: Antimatter explossions are too random to be efficient.
Ok, it is very powerful and reactive. But that is precisely what makes it very inefficient.
As soon as the antimatter is exposed to matter, its outer layer desintegrates and pushes the rest of the mass in the antimatter. While the explosion is perfectly simmetrical it is ok and the antimatter does not move much, but... what happens if one of the sides gets in contact with more matter (and thus desintegrates more and pushes more the lump) than the other?
For example, your lump hits a building, or the ground, or even crosses a zone of colder (denser) air, and your bomb gets thrown at top speeds in a random direction, probably away from your target and likely towards space. In top of it, the unequal force probably breaks your lump into several pieces, each of them pushing the others away with their explosion.
In short, maybe 90% of your hard-earned antimatter ends wandering aimlessly through the Solar System. You got a pretty decent explosion at your target, that is true, but 10% is a terrible efficiency for something so expensive, and probably there are better alternatives.
Answer: Government Does Its Job!
The containment answers, IMHO are the best, but in addition:
Anti-matter may be relatively abundant (relative to what, BTW?) but government controls all the sources. It can only be used specially licensed and trained individuals. So for government-controlled ships (e.g. military) that's fine, but for civilian ships, a government-appointed supervisor must retain control of the anti-matter reactor and its transport / storage units.
At the same time, a counter-terrorism organisation exists to root out anyone who may have the intention or attempt to get hold of some and use it.
So now it could still be used as a weapon, if there was any sort of slippage / corruption / hijack or something, but in the same way a car or an aeroplane could be used as a weapon in our time. (Most people in our world have access to a lethal weapon and yet deliberate car murders are very rare - the vast majority of people just aren't that evil)
Answer: High volatilability
It's all well and nice that anti-matter exists, but because it reacts with any and all matter - your own ship included - it's nearly impossible to effectively weaponise.
Interstellar groups have conducted tests with anti-matter bombs, only to find that if their torpedo bays get hit during a firefight, anti-matter containment breaches and a massive explosion results destroying the entire ship - just like sailing ships with gunpowder.
The amount of cost, armour plating, containment, secondary containment and failsafe systems required to prevent this occurring is prohibitively expensive, and if you're putting that much money into containing anti-matter you might as well turn it into a reactor and build a ship around it.
After all, even if the reactor wasn't anti-matter, if it got hit anyway you're pretty much dead in space.
Answer: Antimatter container are big and heavy. Lets make them 1000 tons and 10 meters in diameter. It is not a problem to put something like this on a a big ship but impossible to use it for terrorism. It is impossible to bring something like to to planet in secret. Also you can scan for 511 kev photons that every not perfect antimatter container will be emitting.
Answer: Artificial Custom-designed Normal-Space Degradable Antimatter, stored in Special Exotic Strange Field Generator Containers
An artificial custom designed form of anti matter which is unable to exist outside of the exotic strange field generator storage containers, which are also custom designed to match specific batches of the custom antimatter.
The antimatter degrades nonexplosively whenever the field ceases as it is designed to do.
The containers draw power from the internal store of antimatter, and contain numerous mechanical and computerized failsafes designed to detect any abnormality in excess or deficit of normal operation. Any exceeded or insufficient parameter cuts out the field generation, such as excess input, insufficient input, up to and including tampering or even excessive scanning of the device.
Not absolutely 100% foolproof, but pretty close.


Can an expat get a car loan in Malaysia?

Question: I have been working in Malaysia for few months now and want to buy a car for personal use. I have a monthly salary of 5000RM. Is it possible for expatriates to get a car loan in Malaysia?
Comment: Do you have an account with a bank in Malaysia and have you asked it?
Comment: I do have an account with a bank but I haven't asked them yet. I checked online but most of the websites says `Malaysian` as a requirement.
Answer: I have lived in Thailand (your neighbour to the north!) for over 13 years, and it was several years before I was able to apply for a loan to buy a car here. Even then, I needed a Thai citizen to sign as guarantor to the loan. Obviously my experience is useful for Thailand, and maybe not so much for Malaysia.
However - in general terms, before applying for any loan in any country, you will need to have a credit record in that country. Do you have any credit cards or other loans already? If you don't already have a credit card, I would recommend applying for one of those and keep it fully paid-up for a while (several months should be enough) before approaching a bank and applying for a loan for a car.
I would also imagine that the bank would want to see a valid work permit, a statement from your employer saying how much they pay you and the length of your employment contract with them, and bank statements showing your salary being paid every month. In Thailand they usually ask for 3 or 6 months of bank statements.
Additionally, a quick Google search found this link : Malaysia - Banking. There is some very useful information in there.
Answer: The applicable website ExpatFocus notes that you'll need some evidence of good credit, documents etc, but otherwise should be possible for expats:

With a valid visa and a decent credit rating, most expats are able to
  get loans from a Malaysian bank. The requirements are similar to those
  of a loan from an American institution. For an expat to apply for a
  loan, they should make sure they have these documents:

Photocopy of passport
Paycheck stubs from the previous 3 months
Latest tax return form (less than one year old)
For salaried employees: letter of appointment or confirmation letter stating salary and other income
Letter of Offer, Sale and Purchase Agreement, or Deposit or booking receipt from housing developer or private seller
Copy of land title
Bank statements going back six months

Note : if you haven't been there for more than 3-6 months yet, it is still worth bringing your bank statements etc from your previous country.
Answer: You would need a Malaysian citizen who is willing to co-sign, as too many expats skip out on loans. If the bank deals with Wells Fargo, you might get a American loan online from it, if you're an American. It charges a high interest rate on those loans, but I have met a few Americans in Asia who have done it that way.
Answer: You can easily get a bank loan if you put up more than 40% of the total capital of the item you want to buy, even without a guarantor.
Eg. You want to buy a car worth RM50K. Come up with 20K in cash and prove you can pay the monthly installment and you should be good to go.


Why are viruses considered microbes?

Question: My question is simple. Why is a virus considered a microbe? Considering a microbe is considered to be a "living" unit of life, which viruses are not.
Comment: "Life" is either a) arbitrarily defined or b) poorly defined.
Comment: Who considers a microbe to be "a living unit of life"? Do the people who use the word "microbe" use strict scientific definitions of life? In my experience, "microbe" is not a scientific term (although it may have been one once), it's a folklore word for "tiny bugs which make you sick". When a grandma tells her grandchild "cover your mouth when you sneeze, you're spreading microbes everywhere", she neither knows nor cares whether a biologist would classify the microbes as alive. Your question seems to need no biologic answer, but an epistemological one.
Comment: I think these sort of questions arise because we are generally too lazy to properly define terms. I've asked a similar question before: ["Why isn't a virus alive"](http://biology.stackexchange.com/questions/9438/why-isnt-a-virus-alive?noredirect=1&lq=1)? We need to carefully define "life" every time it's brought up: Genetic code? Membranes? Ability to replicate? High cognitive power? Each has problems & caveats, but without a measurable feature, it's a moot discussion. I'd suggest reading [The Seven Pillars of Life](http://science.sciencemag.org/content/295/5563/2215) by Koshland, 2002.
Comment: Some recently identified viruses are considered alive due to their more complex organisation such as mimiviruses. Take a look at [This](http://www.popsci.com/new-evidence-that-viruses-are-alive) it's pretty interesting.
Answer: What is a microbe?
A microbe (or microorganism) is a microscopic organism. Anything that is considered alive and that is small enough is called a microbe.
Note that this definition has two issues.

There is no universally accepted definition of life.
There is no universally accepted size threshold for being called a microbe (to my knowledge). I would go with a threshold of about $10^{-5}$ meters.

Is a virus a microbe?
A virus IS and IS NOT alive depending on the definition. Note btw, that the definition of what is alive is not a matter of Biology but a matter of Philosophy. Most of the time, viruses are considered as not being alive. It is important to understand that the definition of life has absolutely no impact on biology and is nothing but a question of nomenclature.
If you want to call a virus a living thing, then yes, viruses are microbes. As stated on the wiki article:

Some microbiologists also classify viruses (and viroids) as microorganisms, but others consider these as nonliving.

You can find a discussion of why viruses are generally considered as not being alive here.
Unit of life
The concept of "unit of life" has not much meaning in biology and, to my experience, is most often used as a nice image for teaching young students what a cell is. Most of the time that I heard of "unit of life" (mostly when I was in secondary school and eventually high school) was used to describe a single cell making up a multicellular individual such as a cell of your blood for example and not a unicellular individual.
Answer: Viruses are not alive until they are inside the body of the host organism (plant or animal). Viruses are active once they are inside the host and reproduce inside the host. They are a link between living and non-living.
Answer: Viruses are small bits of genetic code in a protective covering. Viruses are not "alive," that is, they cannot replicate, unless they are inside another organism. A virus is definitely too small to be seen without a microscope. Since viruses are so small (tinier than bacteria) they may be considered microbes. However, since they are not "alive" outside of a host organism, it is debatable whether they are really organisms at all. For convenience since they are neglected in other areas of biology, viruses are discussed in microbiology. Most viruses are known because they cause disease.
Comment: The claim `[some organisms] are not "alive," that is, they cannot replicate, unless they are inside another organism` is pretty bas IMO because following this logic, an endosymbiont cannot be a living thing. [Plasmodium](https://en.wikipedia.org/wiki/Plasmodium) wouldn't be a living thing for example. Note also that stating `Viruses are not alive` reduces the discussion to a single definition while several exist (it has the advantage to highlight the result most common definition though)
Comment: @Remi.b: My personal definition, as a theoretical ecologist, is that if you can meaningfully study its ecology and evolution, then it's alive. :) That easily includes viruses. Of course, if you define "ecology" and "evolution" broadly enough, that definition can also cover a lot of things we would *not* usually consider alive, such as languages and ideas. I'm not really sure if that's an argument for or against it.
Comment: @IlmariKaronen As a theoretical evolutionary biologist, I like your definition! However, it is not the most common definition. In any case, I think pretty much everybody agrees that excluding from the realm of living things, everything which reproduction depend on other life forms is quite a bad idea!

Why are viruses considered microbes?


How can I take an extended timelapse with my GoPro given the short battery life?

Question: I have a GoPro Hero 3 Silver edition.  Was wondering if anyone has any ideas on how to take a continuous timelapse for extended period of time (more than 4 hours) since the battery seems to deplete itself in less than two hours.
Comment: The two hours are with the additional [battery pack](http://gopro.com/hd-hero-accessories/hero3-battery-bacpac)?
Answer: I'd suggest either plugging it into the wall, a USB port or an external USB based battery.  Any of these should be able to provide more power for longer runtime.
Comment: Cam-do has a tiny custom USB cable that will fit into the water-proof housing, and you can let a thin cable out through the back door, making it mostly water-proof (if that is mandatory). Otherwise, shoot without the ext housing. the current 12Ah USB battery packs will give you 20-24h power for a single gopro camera, otherwise, a wall charger will give you infinite power.
Comment: Though you can't plug in a USB cable if using the standard waterproof housing. You can get a "skeleton housing" which has holes for plugging in cables, but it isn't waterproof.
Answer: There is a GoPro timelapse contoller available from Cam-Do.
This switches the camera off between each shot, which can give much longer battery life. So it can take hundreds of photos, spread over days or weeks.
This controller is compatible with the HD Hero, Hero 2, and Hero 3 White and Hero 3 Black, but it is not compatible with the Hero 3 Silver.
Answer: Obviously using a power point is not what you want. What I have discovered is that there are a host of portable external power packs available on Ebay which could extend battery life.
Now here's the switch - beware the claimed power capacities of these things. I recently bought an unbranded unit for a paltry $25 claiming 30,000 m/a hours. That also means 30 A/h. It is about 6 inches long by 4inches wide by 3/4 inch deep. It does a good job of charging devices but for time lapse it is a fizzer, the reason being that once you plug it into the GoPro through the side entry of the skeleton case, it begins to charge the internal battery. When the internals are fully charged however it switches off. So if you have left your camera recording a scene you will come back and find it switched off.
However, in defence if the unit it still had plenty if power left in it.
What you need is a portable power supply that does not switch off. I have ordered two Panasonic 6V sealed lead acid batteries (one as a spare). The battery comes with a carry bag and a cigarette lighter connector. Just stick your cigarette lighter to USB cable into it then plug into your GoPro and it should piggyback the internal battery and stay alive for some considerable time. I cannot say whether this will damage the GoPro batteries, but if like me you are frustrated at not being able to film a timelapse to completion it might be worth a try. The two batteries, carry bag, charger and freight stet me back $127 Australian.
I will never find this post agin so f you want to know whether it worked email Cliff at email@example.com.
Answer: The best option would be to plug in to a power source, such as a wall or external battery, if you also have enough memory. This would make for a completely continuous shot. However, since the timescale is more than 4 hours, if you are quick enough, you could replace the battery or memory if you have a spare. If sped up enough, the missing frames shouldn't be noticable. Just make sure, if you choose this route, to have the camera secured, so as to start recording again with the same shot.
Answer: i have also been using the CamDo timelapse controller with the battery eliminator arrangement. has worked well for me.
Comment: Can you elaborate?  How long does the battery last with it?
Comment: It depends on how often you are taking the shot. For me, I took a photo every 20 mins and you get a couple of weeks out of the battery. They have a [timelapse calculator](http://cam-do.com/TimeLapseCalculator.html) on the website which gives some estimates for your scenario.
Answer: I just found this battery at Best Buy by a company called "Refuel".
In particular I found what was called "Refuel 12 hour action pack". As the name suggests it gives a 12 hour charge; however, it gave me around 14 hours of lapse time.


Connecting Problem: ODBC versus ESRI Personal Geodatabase (*.mdb)

Question: I try over 2 days to connect an ESRI Personal Geodatabase with QGIS 2.8.1
Here is my testing report.
Testing environment: Windows 7 64-bit; MS Office 32-bit; QGIS 32-Bit
1. Step: Creating an ODBC-System-DSN
We have a 32-bit Office installation. We find the 32-bit ODBC-Administration-Tool under:
<code>C:\Windows\SysWOW64\odbcad32.exe
</code>

The mdb-file is an ESRI Personal Geodatabase.
2. Step: Testing the ODBC-Connecting work
With the database4.exe, which is free, I tested the new ODBC-Connecting does work.
(http://fishcodelib.com/Database.htm)

Yes, very good!

And here you can see all tables in the mdb-File.
3. Step: Open with ODBC-Connection in QGIS

Yes, very good. The ODBC is working!

Oh no, the geometry type is Unknown!!
4. Step: Open with ESRI-Personal-GeoDatabase-Connection in QGIS

Oh no, the ESRI-Personal-GeoDatabase-Connection doesn't work! Why?

Reference 1:
Should I try the QGIS 64-bit version? Like this post: https://gis.stackexchange.com/a/139716/53879
My opinion is, that in this post with drag the mdb file into your workspace is NOT an ODBC-Connection. The ESRI Personal Geodatabase will add with "Add Vector-Layer.." in File-Modus. Just try, drag a mdb-file into the workspace. It will open...
But I want to connect the ESRI Personal Geodatabase in Database-Modus.
Reference 2:
In this post: http://www.northrivergeographic.com/qgis-accessing-personal-geodatabase
the workaround work. I think here is QGIS 64-bit installed.
QUESTIONS:
-Why work the ODBC-Test and the ESRI-Personal-GeoDatabase-Test not?
-Should I try my workaround in QGIS 64-bit installation? Have anybody some experience?
PROBLEM:
I want to connect an existing ESRI-Personal-GeoDatabase (*.mdb) over ODBC and edit the data. In 32-bit installation of QGIS is this not possible??
INFORMATION:
I tryed over 4 days to connect an ESRI-Personal-GeoDatabase (*.mdb) over the Database-Radio-Button.
UNSUCCESSFUL!
I tested extra on a 64Bit PC: 64bit Windows 7 with SP1; 64Bit QGIS; 64Bit Office 2010.
I received the same error.
And it was an Original ESRI-Personal-GeoDatabase (*.mdb). I opened with ESRI-Software.
Comment: odbc need to be same as datastorage installation. This is the same problem with postgres. if esri run as 32bit you need use 32bit that is not in relation with os system
Comment: 1) Get this [database engine](http://www.microsoft.com/en-us/download/details.aspx?id=13255)  2) and test this [solution](http://www.northrivergeographic.com/qgis-accessing-personal-geodatabase)
Comment: Did you solve your problem? could you open/connect to the geodatabase and tables and relationships that may be stored?
Answer: You are using a Benutzer-DSN/User DSN.  I always use an ODBC connection that is configured on the System DSN tab.  Some software may expect to find the configuration in System tab and not the User DSN tab.  Hence, this may be the reason why the screen shots of your Benutzer-DSN/User DSN works correctly under certain circumstances.


Remove Cilantro Stems?

Question: Is it necessary to first remove the stems from fresh cilantro when chopping it for a recipe? If so, how much of the stem should be removed?
Answer: The stems are edible and flavorful, with a crunch that may or may not be desirable in your dish,  but the lower portion of them tends to be a little stringy.  I always trim off the bottom,  but as for the rest of the stem,  it depends on what I am making.
For raw dishes where it is chopped quite finely (koshimbir, pico de gallo) or even ground to a paste (chutney), or if there are other crunchy textured ingredients,  I will chop and include the stem (the middle to upper part, where there are also leaves branching off, or as much of it seems tender).
If I am cooking it (as a seasoning in a soup or dal) or if it will be wilted and steamed as it is tossed with a hot dish, then it is also fine to include it (chopped).
For other things (raw, where a crunch will be out of place), I only use the very tender parts of the stem with the leaves. Or if the leaves will be more visible as a garnish or accent,  I might strip the leaves from the stems more carefully and not use any (or much) stem.
This is generally how I treat most herbs that don't have a woody stem,  at least,  if the stem has a nice flavor like the leaves.
Answer: For most herbs, if the stems are tender, it is fine to just chop and add.  Of course it depends on the application. For example, as a garnish, sometimes stems with leaves work, sometimes not.  Then, there is also the SE Asian tradition of using stems and roots of cilantro in marinades and rubs (no leaves).  My own metric, for almost any herb, is if the stem is so dense that it will be noticed as "stem", I don't use it.  Otherwise, it gets chopped and added.
Comment: SE Asian - stems and roots are what recipes are referring too, roots very important. Many western growers trims the roots, and this not very helpful!. Leaves are mostly for garnishing
Answer: I pick the prettiest leaves off the stem to use (chopped as necessary) as garnish. Without getting nuts about removing all of the stem (or I do get nuts about it, depending on the dish), I chop up more leaves to use in the dish. What I'm left with is a few leaves and lots of stems. I chop off the root end of the stem (where the stem becomes paler), and then I throw the bright green stems and remaining leaves into the food processor and whir with a little bit of oil and vinegar. That's a no-waste cilantro dressing that I can use if the dish needs more cilantro flavor, or save in the fridge for weeks for a bit of cilantro when I want it later.
It is not necessary to remove the leaves from the stem, it's a matter of aesthetics. The stems are a bit woodier, big pieces can negatively affect the texture of the dish. However, the stems are full of flavor. What is wasteful of effort or cilantro (and many other herbs) is a bit subjective. I find the method above a pretty good balance of conservation of the ingredient and effort, and overall fussiness.
Comment: And while being frugal: No need to throw away the pale roots, they're used quite a lot in Thai cuisine (grounded down to pulp in pestle & mortar). They freeze well, so just save them up for when you're in the mood for a curry  :)
Comment: @WillemvanRumpt nice :)
Answer: When cooking I would always chop the stems to include them as seasoning while frying/cooking and leave the leafs for using them either freshly in the end over the dish or mix them into the dish right (a minute or so) before you serve it. This way you will still get flavor out of the stems (in a different way), and also they soften up and look great.

Remove Cilantro Stems?


Standing for someone who's turned seventy

Question: Must one stand up for someone who turned seventy years old since he is now a "saivo"? Does another person who is also over seventy have to stand up for him? Does the gender of either party matter?
Comment: My other 'sister' question has been edited out and can be seen on previous show all edits.
Answer: One must stand for someone who is seventy. Source: YD 244:1; see discussion.
Regarding a elderly person standing for another elderly person,the Aruch Hashulchan YD 244:9 brings the Tur who says וכתב עוד: דהכי מסתבר נמי בשני חכמים או שני זקנים, שאין אחד צריך לקום מפני חבירו, אלא יעשה לו הידור. עד כאן לשונו. one does not have to fully rise if he is also 70 but to one should  rise slightly(Hidur) .
Regarding standing for a woman, Chacham Ovadia in Yechavei Daas 3:72 brings from many sources (Sefer Chassidim,Sefer Hachinuch,Tshuvos Geonim,also seems from the Rambam sefer hamitzvos and Shu"t Bais Yehuda) that a woman over 70 one has to stand up for them and  he paskens it is a mitzvah(it seems like a safek d'orasia because other argue) to stand. If one has to stand for an elderly non Jewish woman see the footnote on page 229.
Comment: Yes! Does anyone discuss the possibility that because people live longer nowadays, the cut-off age may have advanced beyond 70?
Comment: One wonders if one has to stand up for ones wife if she is older than him when she turns seventy.
Answer: http://www.hakhel.info/SeferMitzvosHaKatzar.html

MiP'nei Seiva Takum VeHadarta P'nei Zakein--this is the Mitzvah to
  stand before one who has reached the age of 70 [some say 60] and to
  honor Talmidei Chachomim and stand before them, even if they are
  young.  If one is older [70 or 60], one must rise before him even if
  he is not a scholar and even if the one rising is a Chochom who is
  young.  In this case, one need not stand to full height, but can raise
  himself up enough to clearly demonstrate Kavod.  On the other hand,
  one must stand up for one who is actually a Chochom (whatever the age)
  to full height when he reaches within 4 amos until he passes by
  completely.  One must also give Kavod to his Rebbi, even if he has not
  gained most of his wisdom from the Rebbi.  A Rebbi, may, however,
  forgive any honor due him.  As part of this Mitzvah, we must recognize
  that it is a great sin to disgrace or disparage Chachomim or even to
  dislike them, and that one who disgraces a Chochom does not have a
  Chelek in Olam Habah.  This Mitzvah applies to men and women alike.
Answer: Halachipedia writes amongst other items:

There are some who try to justify a minhag of being lenient regarding standing for an elder and Talmid Chacham. [8]

The reference reads:

8 Shach 244:11 seems to say that the minhag is to stand only for an Av
  Bet Din or Rosh Yeshiva, but he leaves it as a tzarich iyun.
Rav Chaim Zonenfeld in Salmat Chaim YD 59-60 explains that the Shach
  doesn't mean that they uprooted a Deoraita but rather that the
  Talmidei Chachamim forgo the respect due to them. Rabbi Zonenfeld
  seems to say that this is not accepted as the Halacha but only a
  defense of the minhag. Similarly, Sh"t Yabia Omer YD 3:13 writes that
  one should certainly not rely on the assumption that Talmidei
  Chachamim are mochel.
Kavod VeHiddur p. 38 cites some who say that we assume that in general
  a Talmid Chacham is mochel. I personally heard from Rabbi Schachter
  that we assume a Talmid Chacham is mochel.
Regarding elders, Kavod VeHiddur p. 64 quotes Rav Elyashiv saying that
  the minhag has what to rely on, since we assume that elders forgo the
  respect due to them.

So, as often, things are not quite so clear.
Comment: Thanks. you give your age as seventy so I suppose this applies to you and that you are mochel!


What do I do about the whitish powdery mold on my peonies?

Question: Very early this year (starting in mid-May) my peonies' foliage was covered in whitish-gray powdery mold.  What is it and what if anything should I do about it?
Answer: There is another non chemical treatment which should work, particularly for powdery mildew - 1 part milk to 9 parts water mixed in a sprayer, spray all leaves and stems, including under the leaves. Doesn't matter whether the milk is full fat or skimmed. The 'scientific' explanation as to why it works is there's something about the lactic acid which seems to destroy the fungal spores. Increasing the ratio of milk to water doesn't make it more efficacious, though 2 parts to 8 parts water will be okay.
Answer: Without a visual, I think it sounds like powdery mildew, which is a fungus that is encouraged by dry, perhaps shaded, conditions and lack of air movement.  Depending on the host plant, leaving the infection untreated can lead to leaf loss and weakening of the plant.  To control it organically, prune out infected tissue, being sure not to shake it around as this can spread the fungal spores, and dispose of the prunings by burning them or putting them out with the rubbish rather than adding them to your compost.  If you want to treat it with fungicide, check with your local garden centre to see what's available, or investigate online.  To prevent it in the future, ensure that your peonies are well-watered and mulched, and improve air circulation around them, if necessary.  Perhaps they need dividing?
Answer:
Sclerotinia sclerotiorum can cause stem rot on peony as well as on many different herbaceous plants found in the garden. The entire plant or portion of the plant may wilt. The infected part of the stem turns a light tan color and may become dry and stringy. Fluffy white mycelium often appears under humid conditions, thus the name, white mold. Slice the stem lengthwise to help you diagnose this disease. Various sizes of irregularly shaped, hard black sclerotia may be found inside the tan area of the stem. Sclerotia are the overwintering structures for this fungus and they can survive for many years in the soil. Remove and dispose of any infected plant parts being careful to not drop the sclerotia. Sclerotinia is a soil-inhabiting fungus that is nearly impossible to remove. Replant infested areas with nonsusceptible plants. Wider spacing to improve air circulation will minimize infection by this fungus.

From the article: University of Minnesota - "Diseases of Peony"
Compare how your plants look to pictures of the disease, and you can judge if you believe that is what your plants are infected with.
Comment: Sclerotinia doesn't leave white powdery substance on leaves.  It is a very bad fungal infection and the entire plant should be removed and bagged as soon as one finds this in the stems of a plant.  To id positively, cut into the rotted stem.  You can see shiny, blackish capsules that look like rabbit pellets.  Just cutting off the infected part won't do any good.  The whole plant is infected.
Comment: The problem with your answer is that the question is about powdery mildew.
Answer: Try neem oil. My peonies get infected with powdery mildew every year and this is the only organic solution that seems to really work. It works immediately but you have to start applying it before the mildew sets in. Spray the whole plant liberally from all directions making sure to get the undersides of leaves. The powdery mildew washes right off. Follow the instructions on the bottle regarding dilution and not applying when it's very hot and sunny. A follow up treatment may be necessary a week later.
When I say liberally i mean drench the plant with spray and dig around to make sure you have every surface treated.
After that if you hose them off from time to time you'll wash away the spores that haven't attached firmly to the leaves and as mentioned previously wet conditions discourage powdery mildew as counter intuitive as that may sound.
Answer: I've found some useful information from Colorado State University:
Prevention:

Avoid late-summer applications of nitrogen fertilizer to limit the production of succulent tissue, which is more susceptible to infection.
Avoid overhead watering to help reduce the relative humidity.
Selectively prune overcrowded plant material to help increase air circulation. This helps reduce relative humidity and infection.

Control:

Remove and destroy all infected plant parts (leaves, etc.). For infected vegetables and other annuals, remove as much of the plant and its debris in the fall as possible. This decreases the ability of the fungus to survive the winter. Do not compost infected plant debris. Temperatures often are not hot enough to kill the fungus.

Also, you can kill it with:

sulfur fungicide

From here:

Sulfur is broad-spectrum with little detrimental environmental effects. Can be irritating to the eyes, ears, and nose during application. Used for the control of powdery mildew on grapes and other crops, it is effective against most species of pest mites, brown rot, rust, and scab. Often used in the dormant season.

neem oil

From here:

Neem oil is best as a preventative, or in low-disease-pressure situations, for fungus problems. Use it to control diseases such as powdery mildew, anthracnose, botrytis, rust, leaf spot, or flower blight.

copper fungicide

From here:

The strongest and most broad-spectrum (organic) fungus control... . Use only when other techniques have failed. Copper can be detrimental to plants and soil when applied in rates above the recommended amounts. Often used in the dormant season. Read the label!


Is there any way to transfer data from old phone's sim card to iPhone 4?

Question: I recently got the new iPhone 4 but it doesn't have my contacts and old text messages etc. I previously had the iPhone 3gs. When I upgraded my iphone 3gs to iphone 4 they gave me a new sim card but it was basically a replica of my old sim card (eg.same number).
Comment: Do you still have your old 3GS?
Answer: The iPhone can't actually read messages from the SIM card, you need to back it up to your machine and set the iPhone 4 up with the 3GS backup
Answer: iPhones don't use the SIM card that way. Sync the iPhone4 with iTunes and tell iTunes that it is a replacement phone. You'll then have the option of having all of the 3GS data installed on to the new phone.
Answer: You can do with your itunes for it you have to put them on your itunes.iTunes will backup everything on the iPhone.
In iTunes, with the iPhone selected on the left, click the Info tab and make sure Contact syncing is enabled.
Besides,there is a article about How to transfer contacts from iPhone to iTunes, which can help you transfer data from iPhone.
Good Luck.