Wikipedia:Reference desk/Archives/Science/2023 February 10

= February 10 =

Which one of those 2 analogies represent how depression works?
I dont have depression and this question is not about someone I know, its just a general question about how depression works.

Lets imagine an analogy, imagine everything you do has a happiness value if something has a value of 100 or higher you will think this thing is fun to you with higher values being more fun, values less than 100 means it will be boring for you and even smaller values will be even more boring.

Using an analogy, does depression get the happines value of things and divide that value by X, or it get the happiness value of stuff and set to a low value Y that is below 100.?177.63.92.219 (talk) 00:01, 10 February 2023 (UTC)
 * You need to read about Depression (mood) before heading off in the direction you're going. ←Baseball Bugs What's up, Doc? carrots→ 01:57, 10 February 2023 (UTC)
 * Probably a good idea to look at happiness too. It sounds like you ar equating it with hedonism which is quite a different thing. NadVolum (talk) 11:52, 10 February 2023 (UTC)
 * Next to the sense of a temporary low mood, often ascribable to a recent loss, the term depression is commonly used in colloquial speech for what in medical terminology is called clinical depression or major depressive disorder (MDD), a debilitating illness. There is also dysthymia or persistent depressive disorder (PDD). The major symptom is not the inability to experience happiness, but the inability to experience pleasure . But this is merely a symptom and cannot be "how it works"; people who suffer from depression often also experience the feeling that everything is meaningless. As with many disorders, the mechanisms involved are not understood, and neither is it clear how "ordinary" depression, MDD and PPD are related.  --Lambiam 21:25, 10 February 2023 (UTC)
 * The OP seems to be under the impression that people who are suffering from depression find everything "boring". Having suffered from depression myself, and having been to two funerals where the cause of death was depression related suicide (I avoided a third because I found it too depressing), I'd just like to add that people don't kill themselves out of boredom, and trying to sum depression up with a simple equation is utterly ridiculous. nagualdesign 01:52, 11 February 2023 (UTC)
 * OP. What people like and think is limited by what they know, their favorite band is not really their favorite band but the best band between the ones they know and problably (specially if the person know just few bands by only watching tv and radio stations and not searching internet) there are bands that would make his current favorite band looks like shit. The difference between the first and the second analogy, is that at the first analogy the depression makes even his current most favorite hobby, something he doenst want to do and wont bring him joy but thats only his current most favorite hobby if he find something he currently doenst know that exist but its way better than his current favorite hobby/action it would be able to beat depression and he would still have fun and want to do this hobby (but he will have less joy doing it than if he didnt had depression), with the second analogy, finding a hobby/action that is even better than the hobby his find to be his currently most pleasurable hobby will do nothing, he will still now have willpower to do it or have joy doing it.177.63.92.219 (talk) 15:27, 11 February 2023 (UTC)
 * Lambian hit the nail on the head, and I want to rephrase this for emphasis: they mentioned pleasure, and as I understand it, depression makes anything one does seem pointless. --Ouro (blah blah) 14:54, 12 February 2023 (UTC)
 * "and as I understand it, depression makes anything one does seem pointless." Op here, this means the second analogy is the real one or closer to real one. I guess beating dunning krueger effect is not a way to try to win against depression.177.63.92.219 (talk) 15:49, 12 February 2023 (UTC)
 * Don't know anything about that, but I recommend talking to real people instead of us faraway RDers. I don't believe this counts as medical advice. --Ouro (blah blah) 12:16, 13 February 2023 (UTC)
 * No. Depression is an acttual mood or mental state rather than just the absence of something. People who think nothing much is happening in their lives and things aren't pleasurable don't automatically have the black mood of depression or go and try and kill themselves. NadVolum (talk) 15:33, 13 February 2023 (UTC)

Evolution of bridges


Recently I've been doing some work on bridges on Commons (adding wikidata infoboxes to categories, etc).

I was struck by the difference between eg the tied-arch bridge at Haggerston (c:Category:Haggerston railway bridge) installed in 2006, compared to the bowstring truss bridge at Mitre Bridge (c:Category:Mitre Bridge (London)), said to have been 'reconstructed' (, p.31 -- ie completely rebuilt?) when a tram line was routed along the road in 1905.

To my untutored eye, both look like a steel arch supporting a flat deck; and I think they are both about the same length. But the 1905 bridge contains a massive amount of cross-bracing -- to build up a truss structure within the arch, and between one arch and the other.

So my question is: what is it about the 2006 bridge, even though it is still apparently said to weigh a quite substantial 350 tonnes, that means it can apparently do without any of this cross-bracing? Will it be any less rigid? Is it any closer to its design envelope than the 1905 bridge, if any of the metalwork starts to corrode? What is it that apparently lets us build a bridge with so much less apparent 'structure' in 2006 compared to 1905 ? Thanks, Jheald (talk) 17:47, 10 February 2023 (UTC)
 * In a truss bridge the sides form an open work beam. The diagonal members form the truss into a series of triangles which may be in compression or tension, but never bending.  The two thin "beams" are further stabilised against lateral forces by cross members above, below or in the deck.  A beam sits on its end supports with a downwards force.  The tied arch on the other hand forms a load bearing arch, and like all arches has a significant outwards thrust.  This thrust is absorbed by the deck which is in tension and stops the arch from springing.  If the deck was not there then massive abutments or else another equal arch would be needed.
 * Have a look at beam bridge which shows both a foot bridge and a rail bridge, in the latter the plated girder beam performs the same function as the timber beam or a truss. Then look at arch where you can see some bridges where spans provide balancing support or the Tyne Bridge where the arch is brought right down to ground level where massive masonry absorbs the outward thrust. Martin of Sheffield (talk) 18:54, 10 February 2023 (UTC)


 * Thanks, Martin. Though looking at this side view of the 1905 bridge, does it too not seem more of an arch bridge than a truss bridge?  The 'arch' part (and the base) seems to be built much more heavily that the 'truss' part.  Jheald (talk) 20:43, 10 February 2023 (UTC)


 * Meccano-Pears-Advert-1920.jpg 19th century bridge architect was essentially a manual draughtsman who drew components to be assembled. The component material(s) might be unfamiliar and his choices would by preference be standard parts from a catalogue that were readily available and priced. A prototype would likely resemble a boy's Meccano construction where liberal application of cross-bracing seems to assure rigidity under load, at least to the eye of a contractor. However our List_of_bridge_failures contains hard-won lessons such as:
 * Peak load on a bridge occured unexpectedly when soldiers marched in tact causing Failure of Broughton Suspension Bridge in 1831. That led to the order to British troops to "break step" when crossing a bridge.
 * The spectacular collapse of the Tacoma Narrows Bridge (1940) whose unexpected aeroelasticity allowed it to self-destroy in a light wind. Since that event, bridge designs are tested in wind tunnels.
 * Modern bridge designers take a multidisciplinary approach where only well-characterized materials and building codes are applied, and computed Finite element method is used to explore stability and stress limits of the adopted design before any actual construction. Even without seeing the computed data, we have become familiar with the smooth "look" of an optimized design and it is no longer architectually stylish to have dominant industrial details visible such as nuts, bolts and braces. Philvoids (talk) 20:22, 10 February 2023 (UTC)
 * No, both the foreground and mid-distance bridges are truss. The diagonal members should be under tension and can therefore be slimmer (assuming steel or wrought iron).   is quite right about modern bridges, many of which are a pair of cantilevers just touching in the middle.  An excellent example of this was the collapse of the M20 footbridge in Southern England.picture here.  One half was struck and collapsed, the other half was left standing for a month with traffic passing under it. Martin of Sheffield (talk) 23:20, 10 February 2023 (UTC)


 * See bowstring truss. It's somewhere between the typical truss bridge, which has horizontal top and bottom beams, and the tied-arch arch bridge, which has no diagonal members. Like in the tied-arch bridge, the vertical members only carry the weight of the part of the road directly underneath plus any traffic moving over the bridge, the diagonal members only carry some of the traffic. In other truss designs, all vertical/diagonal members carry the weight of the bridge between its location and the midpoint. Unlike in a tied-arch bridge, in a bowstring truss the traffic moving over the bridge causes tension forces in the diagonal members, not bending forces in the arch.
 * I can't see from the pictures whether the 2006 Haggerston Bridge is steel or something else. The vertical members look like steel, but the arch could be (prestressed?) concrete. It also appears to be a bit shorter than the 1905 bridge, which has a flatter arch (lower compared to its length). Further, steel quality has improved, and so have calculation methods, so smaller safety margins can be used. And painters have become more expensive. PiusImpavidus (talk) 11:42, 12 February 2023 (UTC)
 * I'm impressed by Meccano showing a girl as well as a boy in 1920 in their ad. Their later pictures didn't show girls, and I read some years ago that they tried having girls again and it lost them money because the boys didn't want something girls played with - and the girls that played with Meccano wanted something the boys played with! NadVolum (talk) 12:37, 12 February 2023 (UTC)