mzatanoskas

thanks

So Z in that funky font is the set of integers, but is there a specific symbol for an integer or do people use Z for that as well? Also is there a symbol or a set of the integers not including 0?

Ooops, sorry!! I forgot that the breakdown featured as part of the narrative, I was imagining I had found that out independently of the book but of course there was no wikipedia in those days!

I get the general logic for rounding numbers, I just remember being told by my Maths teacher once a long time ago that numbers were always rounded in a set way in science, according to how many digits you used; 0.5 and above would be rounded to 1 (accurate to 0 decimal places) and 0.4 would be rounded to 0. (or something like that, I don't really remember which was why I was asking) So 3.14159265 could be expressed as 3.14 or 3.142 and 23.44 could be expressed as 23, 23.4 or 23.44 etc accurate to the relevant number of decimal places. However if you can also round up to the nearest "half" a decimal place, different people could over time round a number to a completely inaccurate result. Ie 3.33 rounded to the nearest "half" a second decimal point is 3.35, round that accurate to one decimal place you get 3.4, round to a half, 3.5, then to 4, then to 5 then to 10. Thinking about it again, I guess it's probably more a linguistic thing where people prefer to talk about "twenty three and a half" rather than saying "twenty three point four." I just thought the scientists would have been more pedantic. I know I would have lost marks for that at school!

When it should be either 23 or 23.4, or 23.44 or some other appropriately rounded amount?

Fair enough, thanks.

Thanks tree, so identities and equalities are just special types of equations right? Just to check though, equalities can only feature constants? (like in the wikipedia example) or can they have a variable which has to be of a certain value ie. x + 1 = 3

I'm looking at the wikipedia page on equations. But I'm getting a little confused by the different use of the terms equality, equation and identity in different situations. Amongst other stuff they say: [math] 2 + 3 = 5[/math] The equations above are examples of an equality: a proposition which states that two constants are equal. [math]x(x - 1) = x^2 - x [/math] The equation above is an example of an identity... ... Many authors reserve the term equation for an equality which is not an identity. But they said that an equality was a proposition which states that two constants are equal? What's the relationship between the three terms? Identities are a subset of Equalities which are a subset of Equations? Or Identities are subset of Equations which are a subset of Equalities? Or something else?

Sorry it seems it's an .svg file. I got it from the wikipedia page here where it is shown as a .png. But I should have looked harder earlier as I just found the main wikipedia page explaining the structure of the periodic table, which basically clarifies the color coding. The table on this page is similar to the one I had, except it doesn't predict the groups of the undiscovered ununtrium etc elements. ... And this page explains the difference between wikipedia's hybrid organisation and IUPAC approved categories. Beh, this is more complicated than I thought it would be. Why can't everything be nice and standard and simple. I guess my questions should now be: 1. Should I create a table with groupings according to IUPAC approved categories or follow the wikipedia version? 2. Which would be more helpful in the long run? Maybe it doesn't matter so much.

I am a chemistry beginner who has got it into his head to start learning all the elements of the periodic table. I'm looking at this wikipedia version which seems pretty up to date, but I'm not sure what the standard terms for all the colored groups are. Also other versions seem to group some parts of the table slightly differently. Normally I would just start reading up on the basics, but I want to put together a standard, simple, colour coded reference table for myself before I begin. As far as I can tell from left to right, top to bottom: 1. Pale Green Hydrogen (nonmetals?) 2. Red Alkali metals 3. Wheat Alkaline earth metals 4. Pink Transition metals 5. Lanthanides (Rare earth) marked on table already 6. Actinides (Rare earth) marked on table already 7. Dirty Green Metalloids? 8. Grey Poor metals? (a mini table on wikipedia includes zinc and cadmium here) 9. Pale Green Non metals? (includes Hydrogen) 10. Yellow Halogens 11. Turquoise Noble gases My questions are: 1. Is this table a standard way of grouping the elements? 2. Are the categories I've noted above correct? Thanks!

, even indie rock videos are a feminist's nightmare! I wouldn't say I have a type, but I thought the girl in pink was the most beautiful in that video. Jared Diamond mentioned some amusing correlations between specific physical characteristics such as earlobe length, breadth of nose, length of middle finger and sexual partners in his excellent book The Third Chimpanzee. I seem to remember there were a bunch of tests that suggested we chose partners based on their similarity to our parents. Some other study reported less specifically that traits such as perceived physical beauty in a potential partner were more important to children of "beautiful" parents... Diamond also speculated that the general differences between the skin colour of different ethnicities was based more on an evolutionary response to sexual preference within the groups over time rather than the common belief that it was an evolutionary response to environmental conditions such as the amount of sun.

****************** Quick summary of overlong post that follows: :-):-):-) My goal in participating in this thread is clarification of interesting ideas/principles, not attacking anyone or point scoring! Please assume my good faith in all my posts! I'll try and address the actual meat of the issues when I can find some time later. :-):-):-) ****************** No, not really, my point was just that I thought it would be constructive to have an explicitly stated "counter" claim as such to help keep the argument on track. Although the title of the thread is about game censorship in Australia, I was focusing on the OP's only statement which is: I think adults should be able to read, hear and see what they want...... unless it's something like child porn. Which I guess is a more generic statement on censorship of all media. But this was my point about stating positions or making explicit claims so that we avoid talking past each other. Being aware who is arguing about a specific claim related to the censorship of videogames in Australia or a broader statement on censorship of the media or whatever is helpful. Here we go, now we are getting closer to isolating certain sticking points around which we can better focus the argument. Would it be fair for me to rephrase this as saying the important point for you is: Whether child pornography in games can harm children? If not, then society does not have a right to legislate censorship. A quick point here to mention (I'll make other points and give details when I have time, but seeing that similar points to this have been brought up a number of times already) is a connection between demand and supply. Simply put, if child pornography in games is not censored and can legally be sold, the financial incentives as described by economic theories of demand and supply will encourage increased production of child pornography which would harm children. Now you may have any number of objections to this argument, including for example that you meant only virtual child pornography in videogames (when no real child was abused in the production of the game) should not be censored. But of course I don't know for sure until you make them. Let's not forget we are always going to end up in a "grey area" and expecting either "side" to come up with exhaustive and absolute treatises off the bat is unreasonable, probably intrinsically impossible and would definitely exceed the maximum word count for a post on any forum board. I was arguing about consumption of child pornography (real not simulated) and the demand/supply effect, not videogames, so there we were talking past each other there as so often happens in these threads. As far as whether playing videogames can have a negative effect on people's behaviour or not, that's another very important point to be addressed, but I think the debate has to be more nuanced than framing positions as starkly as "playing games ... make them want to go out and kill real people." Look I'm not saying there aren't people who do think in infuriatingly knee-jerk and simplistic ways. However in an intelligent discussion, do we have to assume that someone who seems to be disagreeing with us is so intellectually challenged?! Let's try not to argue to the lowest common denominator! This is basically what I meant re iNow and strawmen. Apologies if I phrased it too agressively or in too accusatory a manner; it's not that I think iNow is specifically taking words out of context etc, but that I'm sure he could phrase the arguments he is attacking in a stronger form. I believe there is no point setting up a weak version of an argument (ie a straw man) that I disagree with in order to knock it down. Not on an internet thread anyway because I honestly have no interest in scoring "points" here. Again as you set forth more claims we can better identify and isolate the real sticking points around which the argument revolves. So just to clarify, here you are arguing that: 1. even if some videogames cause violence in children, the blame lies solely with the parents of the children, and censorship should not be the answer. 2. something else? Again to rephrase to ensure we are on the same page, here are you arguing that: 1. even if some videogames cause violence in adults, the adults were ill already and blame lies solely with them, therefore censorship should not be the answer (because it is unecessary, ineffectual, immoral or some combination of the above). 2. even if we find evidence of adults behaving violently after playing games, this is probably not evidence of the games negative effect, but evidence of the adult's inherent behavioural problems, therefore censorship should not be the answer (because it is unecessary, ineffectual, immoral or some combination of the above). 3. something else? Ok here I think I should lay my cards on the table and make my position a little more explicit too: 1. I normally don't touch internet debate threads with a bargepole, especially "controversial" topics such as these, because they usually almost exclusively feature name-calling, point-scoring, shouting matches, where the arguers talk completely past each other and no progress is ever made whatsoever. In other words, flame wars. 2. I decided to jump in this thread therefore precisely because I thought it showed signs that people were interested in debating for the same reasons as me. 3. Why am I interested in debating this? Because I believe a measured and disciplined discussion can ideally result in: a) clarification of all our own ideas, principles, their strengths and inconsistencies etc b) clarification of all other possible ideas, principles, their strengths and inconsistencies etc c) identification of what we need to think about/analyse further d) where disagreements amongst different people really lie etc... To me the above is what an "interesting conversation" about controversial topics looks like. It's basically a rephrasing of a concept of "ideal argumentation". Ok that can sound pompous, or unrealistic, but I don't think it's that out of place on a science forum. I would never post this on a youtube thread. 4. So as I said, in order to achieve all this lofty stuff, I have to assume that the majority of other participants share a similar goal. It is not necessarily true. Indeed it is rarely true on most "argument" threads. But it is on the basis of this assumption that I encouraged the explicit statement of claims, the avoidance of strawmen, the notion of a "constructive" devil's advocate etc... 5. Why have I concentrated on one "side" as it were? Because that is another application of the concept of "ideal argumentation" to this thread. It seems to be the most constructive way to achieve the goals I have set out. But yes, I think the points I have made are valid to everyone arguing in the thread. 6. And finally I should state something a little more immediately relevant to the controversy being discussed: I would tentatively say that for a whole wadge of reasons of varying strength and clarity, I support the general notion that in the society that I currently live in (UK, 2009) some form of censorship of media is appropriate, including censorship of child pornography. Ok I have points, responses and clarifications I need to add, but will have to save for later. Just one final thing though: Amongst other things' date=' I presumed it from the forum we are in, the position you were taking, comments you made about interesting conversation and clarifying arguments etc... It was that assumption that made me decide to contribute to the thread. Of course all these words are subjective to some degree, but we can't have any conversation without making some assumptions on what they mean. Ok so very importantly: [b']are you not interested in being constructive then?[/b] I don't mean this in an aggressive way at all, but it will save me some time coming up with a response to your earlier posts if you are not.

I remember being mesmerised by the book a good, oh dear, 15 years or so ago... my how time flies. I remember really identifying with the author's concerns, attitudes and way of thinking and then getting really worried when I found out he had recently suffered a nervous breakdown and had been diagnosed with clinical depression and paranoid schizophrenia! But most depressing of all is that now I barely remember a thing about the content of the book at all... I'll have to pick it up again when I have the time.

I always find the standard forum format is really not that great for these kind of debate threads. It's a pity because there's a lot brain power to be harnessed out there and a lot of interesting debates to be had. When I have time I shall surely come up with a better system. In the mean time a few general comments: We are dealing with informal reasoning here, not formal logic. Pointing out that something is not certain or absolute or immutably true is almost a truism. So while having a devil's advocate is great, it shouldn't mean they just get to ask the questions and don't have their burden of proof/refutation to fulfill as well! We have the OP's eloquently phrased position : "I think adults should be able to read, hear and see what they want...... unless it's something like child porn." So I'd ask iNow or dudde to come up with a position in response. It would give others the chance to examine the consistency of their position and the reasoning behind it and should make the thread more disciplined and more fruitful. And now for some more specific comments for our devil advocator in general, iNow: I disagree with that characterisation. I would say that the producer directly harms the child, and the consumer indirectly harms the child.They both contribute and both have moral responsibility. (I'm sure you could split up the process even further into things such as perpertrator/facilitator/accessory etc, but it doesn't seem very helpful in this case) This is a fairly common pattern of argument though not always applied as consistently as it might. It sometimes rears its head in arguments on the so-called "war on drugs", proliferation of guns, sweat shops, child labour, human trafficking etc... At the end of the day though, it's the specifics of the case that make the difference. Again I dispute your characterisation of the fictive law. It is unreasonable to suggest that the censorship's purpose (the reasoning behind those who legislated it) was to "punish the consumers" of child pornography. I would suggest a better characterization would be that the law "seeks" to protect children, given that that is the reason which those who would implement such a law would give. because it helps protect children because it helps protect children Because consumption of child pornography encourages the manufacture of child pornography which in turn harms children. The basic tenet of demand and supply. I don't think we agree. The harm to the children comes from the whole process/industry of child pornography of which the consumer is an integral part. Establishing scientific data for such correlation and causal effects is practically and ethically problematic in the extreme in these kind of cases. How would you propose a double-blind test of the correlation between child pornography and the sexual abuse of children? Given the severity of the risk and the difficulty/impossibility of obtaining the full data, this particular claim comes down to a more pragmatic appraisal. Ie the probability of a link vs the severity of the problem if there is a link. Regardless of my previous comments, the difference in the two situations comes down to the details of course. But I feel you are coming up with unnecessarily weak analogies here. You phrased your analogy as: There are also a large number of people who eat cornflakes in the morning who go on to harm women. Well obviously a correlation of this sort is not the point of the argument here. Even if the OP hasn't phrased the argument as accurately as you might have liked, it would be more interesting/helpful for the thread if you were to point out how it could have been phrased better, where ambiguities lie. Instead of setting up strawmen. Also you don't seem to answer responses other posters have made to your points. In fact re-reading the thread, it seems that most of my rebuttals have already been made and ignored. That is a scatter-gun approach worryingly reminiscent of certain individuals of a creationist bent... ahem, poorly disguised ad hominem Anyway I absolutely agree that we should examine our assumptions and think why we draw lines where we do. We can't expect certainty though and I think that you are being slightly too trigger happy to be a really constructive devil's advocate!

I read that a telescope's three main attributes were: 1. it's light collecting power 2. it's resolving power 3. it's magnification power The magnification power can be changed independently of the light collecting power by using different eyepieces with different focal lengths. But the resolving power is dependent on the diameter of the primary mirror/lens and is basically just a function of the light collecting power, no? So you could better summarise a telescope's attributes as: 1. light collecting power (from which resolving power is derived) 2. magnification power Just trying to clarify in my head as always.

Yeah, d'uh it was an eclipse! In my defense I found a link direct to the photo w/o explanation whilst looking for stuff about lunar phases which confused me mightly.

I've been learning about the lunar phases and then came across this photograph of Mauna Kea. The photo seems to show sunrise in Hawaii throwing Mauna Kea's shadow over the atmosphere, so that we can see the moon through this shadow. What confused me is this: From the shadow of the mountain the Sun would appear to be low in the sky behind the viewer and the mountain and to the left. However from the phase of the moon (which appears to be a waxing crescent), the Sun should appear relatively near the Moon in the sky, seemingly below the horizon to the right of the picture in front of the viewer and the mountain... Can anyone set me straight? Merged post follows: Consecutive posts mergedOf course the second I post the question, I find a link explaining the photo. I won't post the explanation yet, who can work it out for themselves?

My knowledge of the subject is from a generalised scuba/freediving background rather than science so apologies if not entirely accurate... With diving the first problem caused by changing pressure is the compression and expansion. As you go deeper underwater, all the water above you pushes down more and more on your body, in other words exerts pressure. Your body is mostly water and water doesn't compress or expand very much, so no problem there. However within your body are pockets of air (lungs, inner ear and sinuses) and of course air is a gas and gases do compress or expand a lot. You will also have pockets of air in your mask. You must make sure these pockets of gas are kept at roughly the same pressure as the external environment or else there will be trouble. If you don't "equalize" the pressure for these pockets of gas, as you dive deeper and deeper, the weight of the water pushes more and more on them and they compress and get smaller and smaller. When you are scuba diving, you breathe air from a highly compressed source, something like 120 bar or so, and the Scuba system cleverly shifts that pressure down to match the ambient pressure. When you take a deep breath of air from a Scuba system 10 metres under the water, you are breathing air at 2 bar pressure. You are essentially breathing twice the amount of air in one breath than you would at the surface. Because of this your lungs don't change in size at all. A problem does arise for the pockets of air in your inner ear and sinuses. These pockets are surrounded by inflexible skull. They are actually joined to your nose and mouth cavity by very small tubes that are usually closed. You need to consciously force some extra air into these pockets by one of a number of different techniques in order to stop them from compressing too much and causing problems. You also need to force air into your mask. If you didn't the space between your mask would get smaller and smaller until the mask frame couldn't shrink anymore at which point your eyeballs would pop out of your skull into the mask! This carries on as you go deeper, but of course the difference in pressure changes slower the deeper you go, so the most difficulty is in those first 10 metres or so. Now when you want to go back up to the surface again, the opposite happens. If you are at 30 metres, you are breathing air at 4 bar. As you go up, this air expands as the pressure from the water pushing on you decreases. As for your lungs, no problem, you just breathe that air out. Usually the same applies to your inner ear and sinuses, the air just forces it's way out of the small tubes. Sometimes however if you have a cold or if you rise too quickly the tube gets blocked and you get a reverse ear/sinus squeeze. The air in the pockets expands but can't escape anywhere. This is damn painful but usually sorts itself out if you just take your time. The real danger would be if you held your breath while ascending from a scuba dive. As the pressure from the water is taken away, the air expands and if you hold your breath it has nowhere to go. What can happen is that your airway can then be forced shut and your lung ruptures instead. This is not good at all, but very rare because you just need to keep breathing to stop it happening. Freediving is when you just take a deep breath at the surface and dive on one breath. In this case you still need to worry about equalizing your inner ear and sinuses. Your lungs however are very flexible, like a balloon to a certain extent and so is your rib cage. As you dive down, the water pressure pushes on your lungs, the air inside them compresses and just get smaller and smaller. It's quite interesting to observe because you can see your diaphragm get pushed up into your rib cage when you get quite deep. Once you get to around the 40 metre or so mark, however you start reaching the smallest size your lung can get. If you go past this depth (or even at shallower depths) you can get lung squeeze, where a bit of your lung rips and blood pours into your lung to make up the pressure difference. However us mammals also have something called the Mammalian Dive Reflex where blood shifts to the lungs and the lungs kind of turn inside out a bit to fill up that ever shrinking pocket of air. With highly trained and talented divers the reflex can allow humans to dive to 200+ metres on one breath. On the way up when freediving, you also have to let the extra air out of your inner ear/sinuses/mask (usually happens automatically), but you don't have to worry about your lungs as they will just expand back to the same size as they were when you took your deep breath at the surface. Check this picture out of a freediver ascending from a dive. The air bubbles are from the expanding air in the diver's mask as the diver rises. The diver had forced that air into his mask on the way down to equalize the pressure. Freedivers don't have to worry about nitrogen narcosis or the bends either until very deep depths (around 100m or more). I'm guessing this is because although the pressure gets very high, the amount of nitrogen in the air in their lungs is no different to the surface. Also the surface area of the lung to absorb the nitrogen is going to be proportionally less as the lung gets smaller. I don't know for sure. Well I sure went off on a bit of a tangent there. Sorry for the novel, hope I didn't just confuse the matter. And just because freediving is so amazing, here's a .

Thanks swansont.

Quick question to check I'm visualising this correctly: Over the course of a day/night cycle, from any point on the Earth you actually see as much of the celestial sphere as you are ever going to during the year (ignoring precession of equinoxes etc). The only thing that stops you seeing some stars is the inconvenience of the Sun; you have to wait for it to "move along" the ecliptic and stop blinding you with pesky daylight. Is that correct?

Although don't make the mistake that I made and confuse the constancy of the speed of light in a vacuum and the speed of light through other media. Google came up with some interesting articles: Here's one about the speed of light in different media. And another about experiments that measured speed faster than the speed of light in a vacuum?! (new to me, and I didn't really understand the explanation either to be honest)

Good, good! thanks Mr Skeptic, that's a nice little summary. I'm plagued by millions of niggly little thought experiments that I'd like to straighten out in my head, but I think I should take a look at a special relativity primer first.

Well I wasn't looking for anything like this, but damm that's an interesting project there, thanks. Definitely going to play about with this too.

Thanks, that looks great akshay, I'll check it out right away.