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From: steveu on 29 Dec 2009 22:01 >Jerry Avins <jya(a)ieee.org> writes: > >> Randy Yates wrote: >>> Jerry Avins <jya(a)ieee.org> writes: >>> >>>> Muzaffer Kal wrote: >>>>> On Tue, 29 Dec 2009 15:39:33 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>>>> >>>>>> Muzaffer Kal wrote: >>>>>>> On Tue, 29 Dec 2009 14:37:29 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>>>>>> >>>>>>>> (I repeat: why are manhole covers round?) >>>>>>> Doesn't that question assume all manhole covers are round? There are >>>>>>> plenty of mhc which are square or rectangle (and some are hexagonal, >>>>>>> star shaped etc.) >>>>>> Yes. What disadvantage do those have? Are they often found in >>>>>> street accesses? Why [not]? >>>>> I think your main reason would be that they can't fall in their own >>>>> hole no matter how hard one tries. Another reason is that they're much >>>>> easier to roll than the pointy ones which usually need to be lifted to >>>>> be carried. >>>> Right on both counts. There is a minor manufacturability advantage, >>>> especially for the receiving surface. >>> >>> Doesn't a manhole cover have to have a lip? You can make a square cover >>> that can't fall into its own hole: set >>> >>> L > ((sqrt(2) - 1) / 2) * d >>> >>> where d is the inside distance and L is the lip size. >> >> Cast iron is too brittle to allow large lips with reasonable >> thickness. > >Well what about unreasonable thicknesses? The point is, it's not really >the "can't fall through" argument, is it? The constraint is something >else, like "too heavy" or "too expensive." Any sufficiently large object is not going to fall down a small hole. I think reasonableness of size is implicit in the argument. (Yes, I know a 20m by 1m cover would generally be considered large, and could still fall down a 1.1m x 1.1m hole. However for the purposes of this argument its just not large enough to be sufficiently large). Steve
From: Randy Yates on 29 Dec 2009 22:18 "steveu" <steveu(a)coppice.org> writes: > [...] > Any sufficiently large object is not going to fall down a small hole. I > think reasonableness of size is implicit in the argument. A two-foot diameter would require a lip size of about 5 inches. Is that unreasonably large? It doesn't seem all that unreasonable to me. -- Randy Yates % "So now it's getting late, Digital Signal Labs % and those who hesitate mailto://yates(a)ieee.org % got no one..." http://www.digitalsignallabs.com % 'Waterfall', *Face The Music*, ELO
From: robert bristow-johnson on 29 Dec 2009 22:22 On Dec 29, 2:17 pm, HardySpicer <gyansor...(a)gmail.com> wrote: > > Lot of truth in that re bogus outputs. Multiple outputs of the same > thing in many cases re-worded and sometimes not even re-worded! > Yes, new journals do spring up to serve the tenure thing and so on and > so on. For all that though, the academic system - peer-reviewed > system is the best we have to date. i actually think that the academic system that preceded the present one, say ca. 1930, was better as a system. PhDs should be very rare and very special. no one should be getting a PhD unless they contribute to the body of knowledge stuff that is *novel*, *significant*, and *relevant* (besides the obvious, like accurate, honest). i have nothing against peer review. who else should do it? but there are way too many PhDs being awarded for totally unremarkable scholarship. that is degree inflation. and the response of hiring faculties to this degree inflation is totally wrong-headed (by limiting the applicant pool to only those holding these credentials of diluted meaning). > It has flaws for sure. I blame > Governments and Unis themselves. that's who i blame too. but students (and their parents, if these students come directly out of secondary school) need to start taking responsibility because the system will not reform itself. tuition will continue to rise, whether in good times or bad, at a rate 2 or 3 times that of the CPI, more faculty will ignore their teaching duties to serve the glass-bead god of (often bogus) publication, faculty will continue to demand pay that compares to MDs and high-ranking executives, non-PhDs with important knowledge and talent to contribute will continue to be ignored to the detriment of students. these students will graduate with 6 digits of debt (that cannot be eliminated with bankruptcy) and an incomplete education because they were taught solely be ivory tower academics or their grad student TAs. most other businesses would eventually fail for widespread performance like that. > Gone are the days (in many countries) > where you can publish at your leisure. Pressure is put by the > university to have outputs on a yearly basis - and promotion is based > on this. Publish nothing and you could get kicked out all together. > although the best US Unis have tenure - other countries have done away > with this and you are assessed on a yearly basis. nothing wrong with assessment of performance. tenure should exist to protect profs from politically-correct purges in academia. but tenure should not protect profs from being purged for poor performance or for discontinued scholarship. any decent prof must view themselves as lifelong students. *some* publication is appropriate and *some* requirement for such (or other evidence of continued scholarship, even if it isn't publication in the standard journals, like IEEE Transactions) is appropriate. > Of course this is the case in industry, you can't do the job > so you get kicked out - seems fair doesn't it? there is also bullshit in industry of undeserving people hanging on to their jobs at the expense of other workers, the company, the industry, and society. this is where Scott Adams (Dilbert) gets material from. > Well yes, except academics produce volumes of > bullshit to justify their job! and pointy-headed middle managers do similarly. > Look in any IEEE transactions and you > will find good papers mixed with papers on marginal extensions to > theory blown up to huge proportions. > > So it's self preservation, you have to produce academic outputs and > hence many of them will be BS since most people can only produce a > quality output every 3 years or so. (more if you have loads of Ph.D of > course). the problem is that deans and departments rely on the journals themselves to evaluate such output where they need to learn enough of the salient content of the academic's field to make some decent judgment of the level of BS of such. r b-j
From: John Monro on 29 Dec 2009 22:30 Jerry Avins wrote: > John Monro wrote: >> Muzaffer Kal wrote: >>> On Tue, 29 Dec 2009 15:39:33 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>> >>>> Muzaffer Kal wrote: >>>>> On Tue, 29 Dec 2009 14:37:29 -0500, Jerry Avins <jya(a)ieee.org> wrote: >>>>> >>>>>> (I repeat: why are manhole covers round?) >>>>> Doesn't that question assume all manhole covers are round? There are >>>>> plenty of mhc which are square or rectangle (and some are hexagonal, >>>>> star shaped etc.) >>>> Yes. What disadvantage do those have? Are they often found in street >>>> accesses? Why [not]? >>> >>> I think your main reason would be that they can't fall in their own >>> hole no matter how hard one tries. Another reason is that they're much >>> easier to roll than the pointy ones which usually need to be lifted to >>> be carried. >> >> It is a popular misconception that a round manhole cover is the only >> shape that will not fall in. In fact you can design a regular polygon >> cover with any number of sides that will not fall in. > > Only with an impractically large flange. Cast iron, the usual material > of choice. is sufficiently brittle to make large flanges unwise. > >> For example, a square cover can be used and it will not fall in if you >> make its width more than the diagonal of the hole. > > Square (or even rectangular) with width greater than diagonal? How? > >> The problem is that the cover will then have >> an area that is more than twice that of the hole opening and, more >> importantly, will weigh twice as much. > > Oh. I see. That explains round. > >> An obvious first step would be to trim off the corners to make an >> octogon, and if we repeat this process a sufficient number of times we >> end up with a circle. >> >> The advantage of the circular cover is that it only has to be slightly >> bigger than the hole opening. The circular shape minimises the area >> and weight of the cover. > > And makes it easier to move by rolling. But when the opening must > accommodate a rectangle of a given size, a rectangular cover will weigh > less than a round one. I believe that that matches Rune's electrical case. > > Jerry And of course in the electrical case you then need to forget the whole idea of designing the cover so that it can't be dropped down the hole. I wonder how important this consideration has been in fact? Maybe the deciding issue for street manholes was that the parts can be finished on a lathe, as I think you mentioned way back in the thread. An (almost) related issue comes up concernng mine shafts. In Australia we had gold rushes in the ninteenth century, with people streaming in from all over the world. Apparently, while the Europeans dug rectangular shafts the Chinese dug round ones. Local opinion is that the reason for the round shafts was that the Chinese miners believed that rectangular shafts allowed evil spirits to lurk in the corners. Another possible reason for not wanting four-sided shafts is that the number four is condidered by many Chinese to be unlucky. On the other hand, it has been observed that you need to remove less dirt and rock when digging round shafts, so there may have been this more practical reason for the Chinese to prefer them. Regards, John
From: John Monro on 29 Dec 2009 22:35
Randy Yates wrote: > "steveu" <steveu(a)coppice.org> writes: >> [...] >> Any sufficiently large object is not going to fall down a small hole. I >> think reasonableness of size is implicit in the argument. > > A two-foot diameter would require a lip size of about 5 inches. Is that > unreasonably large? It doesn't seem all that unreasonable to me. It makes the cover twice as heavy. Regards, John |