John Cuthber

Long ago and far away a researcher at a well known University was told to do some lecturing and to set an exam. He didn't want to- it got in the way of his research- and he said so. They told him to do it anyway.

He taught the course- badly. Then he set the exam- an absolute bastard by all accounts but, strictly within the rules.

They never asked him to teach again.

The University quietly "adjusted" people's marks.

It depends how far it is streched away from straight. A bigger displacement will give a bigger velocity.

That makes no sense whatsoever.

The death of the fish cannot possibly depend on whether or not someone mentions pH any more than it matters if they mention the dead parrot sketch.

This is an interesting notion. It seems to rest on the idea that the reactions associated with aging are slowed down by deuteration of the molecules.

That might be true- I' don't know.

However, most of the reactions in the body are associated with living, rather than aging.

Do these reactions get slowed down too? Is the relative slowing the same for the two sorts of reactions?

Would it just be a case of live fast; die young vs live slow; die old?

If anything, the toxicity of heavy water might be because some reactions are slowed down more than others and things get out of step.

Since the so called kinetic isotope effects are reasonably well documented and are very variable this is entirely reasonable.

Looks like total rubish to me.

It seems unlikely that plants would take up enough arsenic from the soil to be toxic. However it would make sense to have the first crop of any plant tested.

I don't know a lot about cyclodextrins but I know that saturated solutions of salts are used to maintain constant humidity conditions. I guess that the air over a saturated solution of Ca nitrate has just enough water in it to be in equilibrium with the hexahydrated cyclodextrin.

Is it just me who is amused by the irony of someone practicing necromancy with a thread about cryonics?

Does the question tell you the electrode potential for the Cu/ Cu++ cell?

You can make a carbon scrubber for the air in a submarine, but in doing so you gennerate a lot more CO2 than the scrubber will ever absorb.

Similalry it's possible to reverse the burning of coal, but the energy needed is so large that it would require you to burn more coal and thus generate more CO2 than you got rid of.

If the only criterion for being a mammal were giving milk then a milk carton would be a mammal.

On the other hand, I wouldn't be. Like roughly half the human race I'm male.

Chiral means "handed" in the sense of a screw thread or a glove- nothing more and nothing less.

If I were to grow a single crystal of silicon it would (if it were perfect) be a single molecule If it were a cylinder then it wouldn't be chiral. If I then cut a spiral thread in the thing it would be chiral and it would also be a chiral molecule.

My gloves are chiral, but my socks are not (on a macroscopic scale- of course the thread has a twist to it).

Circulalry polarised ligh behaves differntly towards different enantiomers. To do this it must be, in some way, handed or it would not (if you forgive the anthropomorphism) "know" which enantiomer to photodisociate.

Whether that's a function of the spiral path of the electric vector of the em field; photon spin; political spin, or what, I don't know. But I know that there's something "left handed" about left circularly polarised light that distinguishes it from "right handed" right polarised light.

Just to be a PITA ;-)

Mercury, which is generally a molten metal in my experience, does not react all that vigorously with most acids- in fact, with a lot of acids the reaction is rather slow.

However, for the example given (iron and HCl) I wouldn't want to be there when someone tried it.

Every now and again there are explosions in metal foundries when the white hot metal comes into contact with water. The water flashes to steam and expands a couple of thousand times. In doing so it sprays molten metal everywhere.

In the circumstances, the reactivity of the metal with the water isn't the issue (and molten iron does react with steam BTW)

http://news.bbc.co.uk/1/hi/wales/south_west/4716918.stm

Adding acid would not make that any nicer.

"i'm guessing myself that the area of the cross section of the circuit wire is key to the magnitude of the current, no?"

No, the thing that determines the current is the resistance of the appliance you connect it to.

Let's make the arithmetic a bit easier and pretend that here in the UK (where I am) the voltage is 250.

I want a heater that provides heat to my room at 1000 Watts.

One of the equations you will see a lot is volts times amps = watts.

From that I need the fire to use 4 amps (so that 4*250=1000)

Ohms law tells me that I need the fire to have a resistance of 250/4 =62.5 Ohms

The equations Klaynos gave above let you do that in one stage

250^2/R =1000 works for R=62.5

If I wanted a 2000 Watt fire I would need twice the current so I would design the fire to have a resistance only half as big i.e. 31.25 Ohms.

If I wanted a 1000 Watt fire in the US (and lets pretend they use 100 volts rather than 110) it would need to draw 10 Amps and so it would need a resistance of just 10 Ohms.

If I brought that to the UK andd connected it up to the 250 volt supply the higher voltage would push 2.5 times more current through it ie 25 Amps. Not only that, but each amp of current would transfer 2.5 times more power (because the voltage is higher) and so the poor fire would end up trying to dissipate 6250 Watts. It would almost certainly overheat and burn out.

The speed of electricity is not as simple as it first seems. The speed of the electrons is not actually very big, but the energy is transfered at something near the speed of light.

The voltage is a measure of how hard the electrons are pushed; what determines how many of them flow past a point in given time (i.e. the current) is the resistance.

How fast they flow is also dependent on how many of the electrons there are available to carry the current and how thin the conductor is. I would leave this question aside until you are certain about voltage, current and resistance.

I am sure that circularly polarised light gives different rates of photochemical reactions with different enantiomers of some chemiclas. If the photons are not chiral, how can they know which molecules to decompose?

e.g this text "As part of these studies he probed the

assumption that interstellar/circumstellar asymmetric photochemistry is capable of inducing

significant enantiomeric enrichments in solid state amino acids, solid-state leucine films were

irradiated with VUV circularly polarised synchrotron radiation (CPSR). The most suitable

conditions for the enantioselective photodecomposition experiments were determined by recording

the VUV absorption and circular dichroism spectra of solid-state leucine films between 110 and 220

nm. Solid-state D,L-leucine films were then exposed to the intense and quasi-perfect r-CPSR at 6.8

eV (182 nm) emitted by the OPHELIE Undulator of the VUV SU5 beamline at the LURE, in

Orsay. After photodecomposition of 70 % of the starting material, enantioselective GC-MS analysis

showed a +2.6 % enantiomeric excess of D-leucine, i.e. an enantioselective decomposition of Lleucine,

in agreement with the (*, 1)-electronic transitions recorded by CD."

from here

http://www.cost.esf.org/typo3conf/ext/bzb_securelink/pushFile.php?cuid=253&file=fileadmin/domain_files/CHEM/Action_D27/mid-term_report/mid-term_report-D27.pdf.

Can I scale this up? Can someone make 2 macroscopic objects that interact differently with microwaves even though the objects only differ because they are left and right handed versions of one another?

It seems to me that since light (at least in the case of circulalry polarised light) interacts differently with different enantiomers it must be chiral.

You could, in principle, remove the sodium with an ion exchanger and swap it for hydrogen thereby turning the NaOH into H2O.

Teachers google sites like this too so, if you want to use that answer, be sure to explain where you found the idea.

I can only think of one way of looking at the density of individual atoms, and that's as monatomic vapours. At some high enough temperature and low enough pressure both gold and osmium would be vapours. The gas laws say that the gas with the higher atomic weight (gold in this case) is denser.

Interesting isn't it?

In general there isn't a nice well defined equation, but for potassium nitrate in water I think a plot of the log of the solubility vs temperature would be aproximately a straight line. There are a few solubility curves here.

http://www.saskschools.ca/curr_content/chem30_05/4_solutions/solution3_1.htm

Things get really complicated if you have something like sodium sulphate which has different hydrated forms.

http://en.wikipedia.org/wiki/Sodium_sulfate

I'm just hoping that H2O2 was a typo with one "2" too many. The first thing you should check a still with is water.

I should have thought of that.

 

I'm an Aussie. Our unions have too many people who celebrate May Day and go around calling each other "comrade". Does that give a hint of what the problem might be?

 

Well, I do sometimes address emails to the other reps as "Siblings", but only as a joke. Also, I do celebrate May day (though not always on May 1st) - it's a public holiday .

It's a habit I picked up as a student.

http://en.wikipedia.org/wiki/May_morning

Thanks for the data.

I think this bit "In autumn 2005 an estimated 6.39 million employees in the United

Kingdom were members of a trade union. This was a fall of

approximately 119,000 or 1.9 per cent, compared with levels recorded

in autumn 2004. Nonetheless union density increased by 0.2

percentage points, from 28.8 per cent to 29.0 per cent of employees in

autumn 2005." shows that people who are in work are generally joining unions.

If I worked in a closed shop I would know what the union membership was, it would be 100%.

Since I said I don't know the figure you can be sure its not a closed shop.

Government employees have a higher level of Union membership. The bigger the organisation you work for the more difficulty you will have making your voice heard on your own. Employers don't get bigger than governments.

I think having a communist party is a good idea- it lets you know where the communists are.

However, I think the biggest reason that many of you seem to have had bad experiences with unions is that you have had experiences with bad unions. Those in the US seem to have a rather different outlook to the one I'm in.

Here's what the Union says about itself.

http://www.prospect.org.uk/aboutus/index

Anyone able to cite a comparable site for any of the Unions you have had experience of?

Since it's also quite a common disinfectant I rather hope it's not a very good mutagen.

I think that it's down to manufacturing tolerance.

Imagine if the slight errors in making the lens meant that, at "infinity" it focussed at say 100 M. You wouldn't be able to get a clear pic of anything further away.

It makes sense to have the lens able to move a bit beyond "infinity" in order to ensure that, even if it gets a bit worn, it will still focus at infinity. You can then rely on the autofocus or your own abillity to sort it out.

The answer to the question is that, for a lens set at infinity it will fucus light that starts out parallel. Set nearer than that it will focus divergent rays.

Set slightly beyond infinity it will focus light that is slightly convergent.

I don't know how you got bismuth that was paramagnetic. The stuff that I have was cast from an old tin can in the dent in the bottom of a soft drink can (ie about as primitive a setup as you can get). It wasn't particulary pure- not least because it probably dissolved the tin from the can.

It still serves its purpose- A small magnet is suspended between two lumps of it by diamagnetic repulsion (and a big magnet above the system).

Bismuth is diamagnetic as a solid. Unless you are at some bizzare pressure so it forms a different crystal structure, it will always be diamagnetic.

I think the power from the router goes into breaking the wood.

That energy is the work of fracture and there's some data on it here.

http://www.nature.com/nature/journal/v252/n5479/abs/252116a0.html

That tells you how much energy is required to expose an given area of fresh timber (by cutting away the stuff in front of it).

If you multiply that by the rate at which fresh surface is exposed (the cros-sectional area times the velocity) you should get a power.

That should be roughly the router's power requirement.

The question then is what hapens as you change the force on the router.

Imagine you push it so hard the thing stalls.

Since nothing moves thewrok done is zero. However, because the motor is still using electricity, the efficiency falls to zero.

Another scenario is that the force pushing the router through the timber is zero. Since no wood gets cut the efficiency falls to zero again.

Somehere in between there is a "sweet spot" where the efficiency is high.

If the router is geared to give a slow RPM it will be harder to stall. But you will be able to force it through the wood harder. You will take bigger chunks of timber out and the cut will be rough.

On the other hand if the router's gear is very high it will not be able to take as big a cut- but it will do it more often so you will still be able to push the tool through the material reasonably quickly.