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September 26

Machine from Birla Industrial & Technological Museum

Does anybody know, which motor / machine exactly is shown here? Thanks a lot.--Tostman (talk) 11:07, 26 September 2017 (UTC)[reply]

It's a small stationary steam engine, of a type with a central spindle valve, similar to a Willans engine. These were high-speed engines around 1900, mostly used for electricity generation. Andy Dingley (talk) 11:26, 26 September 2017 (UTC)[reply]

Water vapor again

[1] is a homework question. I don't understand it. If the air inside the pot counters the atmospheric pressure, then all we need for water to boil is when the water vapor cancels out the weight of the lid, which is 4*gravitational constant. Area of lid is pi/100, which gives me a needed water vapor of 1.249 kPa, which according to a water vapor pressure table is achieved when water is just 7 degrees Celsius. This doesn't make sense.

Alternatively, according to the professor, we are to solve the problem by cancelling out the atmospheric pressure and lid weight with the water vapor pressure. Then the required water vapor pressure is 102 kPa. I don't know how to find the temperature of water from this, but I assume it'll be just under 101 degrees Celsius. This number makes more sense, but I don't believe the logic. I don't see how we can ignore air inside the pot. Imagine Reason (talk) 11:50, 26 September 2017 (UTC)[reply]

Didn't we have this same homework question just a week ago?

Don't confuse absolute and gauge pressure. Andy Dingley (talk) 12:01, 26 September 2017 (UTC)[reply]

Oh, the water vapor needs to counter the air inside the pan as well. But how do I go from water vapor pressure to water temperature? I don't see such a table in my book. Imagine Reason (talk) 12:03, 26 September 2017 (UTC)[reply]

There are two ways. An engineer would look up the equilibrium temperature of steam and water for a particular pressure in a book of steam tables. A scientist would probably be expected to calculate it (which is easy, look for the Antoine equation at the heading of the table), or in an exam you might be expected to derive it, which is harder - start with Clausius–Clapeyron relation. Andy Dingley (talk) 12:44, 26 September 2017 (UTC)[reply]

Weights to compensate for weight loss

Suppose someone who's a little overweight is steadily losing weight, while maintaining a constant (and significant) level of physical activity. It seems obvious that, as weight declines, the physical activity itself becomes less strenuous, possibly making it difficult for the person to maintain the same level of strength, especially in the legs, and also reducing caloric output.

Have there been any good studies comparing different ways of compensating for this, through, say, ankle, wrist, or waist weights, worn throughout the day or at least while walking for exercise? For example, is one option more effective at maintaining leg strength or caloric output? Is one option safer than another in terms of effect on joints or tendons? --Trovatore (talk) 18:08, 26 September 2017 (UTC)[reply]

One problem you're going to have is distributing the weight evenly. You would need a full fat suit (but weighted) to do that, and this would block air flow to the skin, interfering with thermal self-regulation, etc. StuRat (talk) 18:13, 26 September 2017 (UTC)[reply]

Well now, I asked a specific question about the outcome of studies. I didn't ask whether it is possible to replicate the exact conditions that the person experienced when heavier. --Trovatore (talk) 18:16, 26 September 2017 (UTC)[reply]

It has been done (no, I don't have refs offhand) and that specific effect is negligible, because it's dwarfed by the other effect of exercise, that of converting fat to muscle mass. As is known only too well, many people don't lose weight by increasing exercise, they may even put it on - but they don't mind, because they recognise that they're still "looking better" as a result.

So the effect of "the exercise becoming easier" (as a number of Joules) is negligible, or even negative. But the body does become more efficient at carrying out this exercise, and that's the predominant effect. So yes, the overall effect you describe is there (and any trainer will increase the training schedule as the subject becomes fitter) but not for the reason you describe, and not compensated for by the simple "ballasting" you put forward.

There's also the question of why someone is training. It's probably not (in this case) to increase strength, but rather endurance. So the increase to make with improved fitness may be in duration, not load. Andy Dingley (talk) 19:02, 26 September 2017 (UTC)[reply]

Sorry, I was less than completely clear. The hypothesis I want you to assume is an active person with a stable level of activity, who has started losing weight as a result of reduced caloric intake. --Trovatore (talk) 19:18, 26 September 2017 (UTC)[reply]

In which case they're not exercising, so it doesn't matter. If they're exercising enough to count (presumably walking, step aerobics or similar, if their own body mass is so relevant) then we'd see the increased muscle effects too. Andy Dingley (talk) 20:34, 26 September 2017 (UTC)[reply]

I still don't seem to have gotten the point across. The hypothesis is that the person does significant exercise, but the same amount as before the weight loss started. --Trovatore (talk) 20:58, 26 September 2017 (UTC)[reply]

According to recent studies, changing your level of exercise has little to no effect on the number of calories your body uses [2]. Herman Pontzer found that the hunter-gatherer Hadza people, who are incredibly active compared to Westerners, have a similar daily energy expenditure to people living modern sedentary livestyles. So even if changing body weight has a slight effect on your body's energy budget, it likely has no measurable effect on caloric usage. However it may be relevant for other outcomes of exercise such as muscle strength or cardiovascular health. CodeTalker (talk) 23:19, 26 September 2017 (UTC)[reply]

This is an issue for arm strength but not for leg strength. For leg muscles this isn't an issue because to be in good physical shape you need to run at about 70% of maximum effort and as you lose weight you'll end up running faster if you exercise for the same amount of time. We're not limited to walking at a slow pace and small distances. But in case of our arms this is different. Exercises like pull-ups can get significantly less effective if you lose weight, and here a common method is to attach weights to your body to make these exercise heavier. Note here that our arm muscles are a lot weaker than our leg muscles, so much so that doing just a few push-ups is too much for many people, while a push-up is a lot less exertion than getting up from your chair. An arm muscle exercise equivalent to getting up from your chair is a handstand pushup. This is why in a gym you'll see people doing this, but you'll not see anyone running on treadmills while wearing heavy backpacks. Count Iblis (talk) 23:41, 26 September 2017 (UTC)[reply]

Based on my experience, I put on 1 or 2 kgs in the winter and pullups are harder than in the summer. Also, my hands don't work as well in the colder weather, which also makes the exercise more difficult. This results in less per set in winter and it takes longer to reach my target number (60-70 in case you're interested). It has been like that for the 33 years of going to the gym. --TrogWoolley (talk) 12:28, 27 September 2017 (UTC)[reply]

Shade balls

Why using shade balls when it's possible to just cover the reservoirs and ponds with a single large tent-like sheet from sun-screening material? Also, potentially the balls may enter some sort of weak chemical reaction with the water, unlike the large tent. Thanks. 212.180.235.46 (talk) 20:14, 26 September 2017 (UTC)[reply]

I tried keeping a large tent over my car in storage in the backyard, and it was a nightmare. No matter how I secured it, it always tore loose in high winds. And this "large tent" was 10×20 feet. With a much larger one it would be far more expensive and difficult to control. (If you meant that the tent should float on the water, then water currents, as opposed to wind, might damage it. Also, if you block oxygen from getting into the water, then anaerobic organisms could grow in it.) StuRat (talk) 20:25, 26 September 2017 (UTC)[reply]

They're cheap, simple to install and aren't visible in their height. Wide span covers are difficult to construct and expensive. An arched cover is tall (and expensive), a flat and less obvious cover is even more expensive. Andy Dingley (talk) 20:28, 26 September 2017 (UTC)[reply]

Googling "floating cover" gives some examples that come close to what 212.180 described. To illustrate the expenses and give one cost comparison, for covering the Los Angeles Reservoir (175 acres / 0.7 km²): "$250 million -- to install a floating cover" v. "At 36 cents a pop, the 96 million plastic balls covering the surface have a lifespan of 10 years and require almost no maintenance aside from occasional rotation". So, $34.456 million for the shade balls. Floating covers, however, "provide more of a complete barrier from both sunlight and airborne contaminants", and thus the title of the article containing this info is actually "Los Angeles to Replace ‘Shade Balls’ with Floating Covers". ---Sluzzelin talk 00:55, 27 September 2017 (UTC)[reply]

Whenever I hear that a system which works fine is being replaced by a new, more expensive system, I suspect that the brother-in-law of the person who decided on the replacement will get rich as a result. StuRat (talk) 04:51, 27 September 2017 (UTC) [reply]

The Future Structure article Sluzzelin cited explained that the smaller reservoirs still being left in production could be more completely protected from from avian pollution and photogenic bromide --> bromate synthesis by floating covers. The inference being that shade balls aren't an optimal solution for those reservoirs, but are the only workable one for the 175-acre Los Angeles Reservoir, which will still be protected by shade balls. loupgarous (talk) 01:14, 29 September 2017 (UTC)[reply]

Microbiology questions.

1. 10% bleach, 70% ethanol, 70% isopropanol, and 3% hydrogen peroxide, they are all better at killing gram-positive bacteria than gram-negative bacteria. What are some things that kill gram-negative bacteria better than gram-positive? I asked a microbio professor, who says "whatever kills lipid A and LPS better." So, Wikipedia shows both of those are stuff found in gram-negative bacteria. So my new question is, what's something that can destroy lipid A and LPS?

2. Can there be a bacteria that produces endospores, and be gram-negative and aerobic?

3. Are there any benefits to having obligate anaerobes in our intestines, such as Clostridium? It's beneficial to have E. coli in our intestines because E. coli prevents anaerobes like Clostridium from taking over, so.

4. We have chemicals that kill viruses and bacteria, and bacteria only. For example, O3 is a chemical that kills bacteria but does not kill viruses. But are there any chemicals that kill viruses but not bacteria?

5. This 1 I have the answer to, but I'll take feedback. There are bacteria that kill bacteria, viruses that kill other viruses, and viruses that kill bacteria. However, there isn't any bacteria that kill viruses. Is it because we haven't found any yet, or also because we don't think it's very easy for them to. Thanks. 12.239.13.143 (talk) 20:36, 26 September 2017 (UTC).[reply]

3.: "Anaerobic metabolism of peptides and proteins (putrefaction) by the microflora also produces short-chain fatty acids." And "anaerobic bacteria [in human gut flora ] outnumber aerobic bacteria by a factor of 100–1000." From here [3], a relatively recent and freely accessible scholarly review article. I'm no expert, but if the anaerobes outnumber the others by such a factor in healthy humans, I'd suppose they have some benefit. Also consider asking a question every day or two, rather than five at once. We'll be here all week, and these five questions span a lot of ground ;) SemanticMantis (talk) 21:25, 26 September 2017 (UTC)[reply]

1.: Membrane attack complexes (created inside the body from complement proteins) kill gram-negative bacteria but have no effect on gram-positive ones. 2601:646:8E01:7E0B:3805:A6E1:1618:EEB8 (talk) 11:43, 27 September 2017 (UTC)[reply]

3: Gut flora mentions several beneficial effects of some Clostridia species. Any bacterial species can become harmful if the gut flora's balance is disrupted and one species is able to "take over".

5: The thing is, it's debated whether viruses are "alive". They don't really "do anything", like move around or metabolize, on their own; they just hang around in the environment until they come into contact with a cell that they can infect. Many bacteria do have an "immune system" of sorts that acts against viruses that infect them. --47.138.161.183 (talk) 22:27, 27 September 2017 (UTC)[reply]