1

General Science / Re: Is zero an even number, odd number, or neither?

« on: Today at 03:40:30 »

0/1, and the related infinity

I think you mean "1/0, and the related infinity".

A lot of mathematicians survived over the centuries without accepting that zero was a real number, even if they accepted "0" as a placeholder in Indian/Arabic numerals.

2

General Science / Re: How does soap make us more clean than just water does?

« on: Today at 03:35:54 »

I know soap removes oil and that soap is hydrophobic.

The hydrophobic part is only half of the story.

In fact, soap has a hydrophobic (water-avoiding/non-polar) end, and a hydrophilic (water-loving/polar) end.
- Oils tend to be water-avoiding.

This means that the soap grabs the oils (hydrophobic end), and also grabs the water (hydrophilic end), and gets them together, so that water is able to break down oil films and wash away the oils, instead of the oils staying stubbornly in place.

Soap will help water wash away some bacteria too, but the main thing here is to scrub under running water.
See: https://en.wikipedia.org/wiki/Detergent

In reality, natural oils are helpful to our skin and hair, and overuse of soap and detergents can remove these helpful oils.

But in a hospital setting, presence of drug-resistant bacteria (eg Staphylococcus aureus) and fungi (eg Candida auris) around people with weakened immune systems means that you can't have too much hand-washing.

3

Physics, Astronomy & Cosmology / Re: Star Explosion Expected in 2022

« on: Yesterday at 03:24:40 »

Looking at the previously best-studied example of a "red nova" (V1309 Scorpii), it increased in brightness by 10 (astronomical) magnitudes, or by about a factor of 10,000 at the time of merger. The brightness then declined over a period of a month or so.

Similar behavior would take KIC 9832227 from magnitude 12 to magnitude 2, which would be very visible to the naked eye (provided it didn't happen while Earth was on the other side of the Sun).

The decreasing distance is due to tidal effects transferring angular momentum from the smaller star to the atmosphere of the larger star (gravitational waves have significant effects only on compact objects like neutron stars and black holes).
See: https://en.wikipedia.org/wiki/V1309_Scorpii
See the light curve at: http://inspirehep.net/record/1242804/plots
(Second graph on the page; the horizontal axis tick marks represent 10 days each.)

4

General Science / Re: Is zero an even number, odd number, or neither?

« on: Yesterday at 01:50:55 »

A binary computer-oriented explanation:
- If you represent any number as a binary number (if you want to include negative numbers, use the 2's complement scheme)
- You can decide if it is odd or even just by looking at the least-significant bit: If it is zero, the number is even
- The binary representation of 0 is all zeroes.
- In particular, the least-significant bit of 0 is zero, so it is even
See: https://en.wikipedia.org/wiki/Two%27s_complement

You can apply this to the decimal representation of numbers: Any decimal number ending in 2, 4, 6, 8 or 0 is even
- So 0 is even.

5

Chemistry / Re: What is the difference between cationic and anionic water?

« on: 19/07/2018 22:55:07 »

salty water is simultaneously cationic and anionic water

No, the water is still not ionic.

I am puzzled by this response.
Can you please elaborate about why salty water doesn't contain cations & anions?

6

Physics, Astronomy & Cosmology / Re: Why does my car accelerate uphill?

« on: 19/07/2018 22:38:55 »

When I drive with a vehicle up a steep hill...why does the vehicle start to accelerate by itself

If Rudolph were driving a car with cruise control enabled, the described behavior can be caused by the
 Proportional/Integral/Differential (PID) controller inside the cruise control.

This means that the amount of fuel going into the engine is controlled by several factors:
- The Preset speed, when cruise control was engaged
- Proportional component: determined by the difference in desired & actual speeds
- Integral component: determined by how long the desired & actual speeds have been different
- Differential component: determined by how quickly the desired & actual speeds are diverging

It is the Integral component that can produce the described behavior:
- The Proportional and Differential components merely try to get you back to the Preset speed, but always lag behind where you would be if you had kept a constant speed
- The Integral component tries to eliminate this lag, and will result in acceleration as you go up the hill (if your engine has enough power)
- Often coinciding with the hill levelling out at the top
- So you break the speed limit as you come over the crest of the hill
- Some more modern vehicles claim to be able to sense changes in road gradient, so they start increasing fuel flow before the hill starts, and reduce fuel flow before reaching the top of the hill. This must be quite economical with mass-produced smartphone accelerometers and barometric pressure sensors.

See: https://en.wikipedia.org/wiki/PID_controller

7

Chemistry / Re: What is the difference between cationic and anionic water?

« on: 19/07/2018 11:35:20 »

What is the difference between cationic and anionic water?

If you add salt (NaCl) to water, it dissolves to form a solution of Na⁺ and Cl^- ions.

If you put some electrodes in the water, and apply a DC voltage, the Na⁺ will migrate towards the negative electrode, traditionally called the "cathode". This makes Na⁺ a cation.

SImilarly, Cl^- will migrate towards the positive electrode, traditionally called the "anode". This makes Cl^- an anion.

So salty water is simultaneously cationic and anionic water.

See: https://en.wikipedia.org/wiki/Ion#Anions_and_cations
https://en.wikipedia.org/wiki/Cathode

Footnote: In the case of rechargeable batteries, the anode and cathode can change polarity depending on whether the battery is charging or discharging...

8

Technology / Re: How do batteries work?

« on: 15/07/2018 23:38:19 »

I just saw this PBS documentary on batteries on Netflix.
It focuses on lithium-ion batteries, but it does explain the general principles of batteries too, showing the flow of ions within the battery, and flow of electrons outside the battery.

It also shows what happens when there is a flow of electrons within the battery, with lots of spectacular explosions.

9

Physics, Astronomy & Cosmology / Re: What is the neutrino discovery announced today?

« on: 13/07/2018 12:20:19 »

Thanks for the references.

their poor interaction with other entities means that they travel vast distances unfettered

I agree with that: neutrinos can peer into times and places that are inaccessible to other astronomical tools.

Astronomers are still excited by the cosmic microwave background radiation, which was emitted about 300,000 years after the Big Bang.

If one day we are able to detect the cosmic neutrino background radiation, we will be able to see events that happened  perhaps 1 second after the Big Bang.
See: https://en.wikipedia.org/wiki/Cosmic_neutrino_background

Is there sufficient resolution in the limited number of daily detections to determine much of use?

Nuclear weapons tests are also infrequent, high-energy events, which are (fortunately) rare enough that weapons control experts are very excited to learn everything possible about every individual event.

Similarly, astronomers get very excited about one big neutrino detection, or one gravitational wave event; it's like winning the lottery! Even with this sparse data, they are able to tell a lot about fundamental physics and the statistical distribution of energetic events in the universe.

The first successful solar neutrino detector was a large vat of dry-cleaning fluid. As I recall, they flushed the tank about every 3 months, and managed to find 2 or 3 atoms that had interacted with a neutrino. But even this was enough to hint at new physics: that neutrinos have mass.
See: https://en.wikipedia.org/wiki/Solar_neutrino_problem

The main benefit of these rare detections is that astronomers and research sponsors are willing to fund bigger detectors. These can change sparse events into a flood of events that starts to produce a more coherent picture.

Ice Cube is an example of this - with a cubic kilometer of ice as the detector, it is extremely sensitive, picking up almost 20,000 neutrinos per year (unfortunately, many of them are "local", produced in Earth's atmosphere by cosmic rays).

The number of supernovas expected to occur in our galaxy every century is far higher than the number that humans have actually observed. Perhaps they are hidden behind dust clouds in the plane of the galactic disk, or they collapse into a black hole before they emit the telltale flash? But I expect that we will have a clear detection of the next supernova that happens in our galaxy, even if we can't see it with the naked eye.

could mark the founding event of neutrino astronomy

I think that this title has already been snaffled, by the detection of a supernova in the Large Magellanic Cloud in 1987, which was observed simultaneously by 3 neutrino observatories, counting a total of 25 neutrinos.

With 25 neutrinos from a single event, that is enough to point a finger right at the source.
See: https://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions

10

Physics, Astronomy & Cosmology / Re: What is the neutrino discovery announced today?

« on: 12/07/2018 23:14:22 »

I can't find the article you mentioned, but this event might be like the "Big Bird"* event, at the Ice Cube detector at the South Pole.

1) How do they know where it came from?
Modern neutrino detectors are able to estimate the original path of the neutrino from the the Cherenkov radiation emitted by the debris (in the unlikely event that a neutrino interacts with an atomic nucleus in the detector).

They can use optical and radio telescopes to look where this neutrino came from, and sometimes manage to tie it to some observable event in the sky.
https://www.skyandtelescope.com/astronomy-news/where-big-bird-neutrino-may-come-from-0505201623/

2) How do they know how old it is?
If they can pin it to an outburst in a galactic black hole, they can measure the galactic redshift, and estimate the distance.

3) Why is this important?
Massively energetic neutrinos must originate in spectacularly energetic events. Some of these events are so energetic that astronomers are baffled about where the energy is coming from.

Neutrinos can escape from the center of imploding stars, and escape from the vicinity of a black hole shrouded by dust clouds in the center of a galaxy, telling us of events that would otherwise be invisible to astronomers.

They can travel farther across the galaxy than gamma rays, since gamma rays interact with the intergalactic medium, and slowly lose energy.
See: https://www.scientificamerican.com/video/big-bird-neutrino-is-linked-to-bright-blazar/
https://en.wikipedia.org/wiki/IceCube_Neutrino_Observatory#Results

*Apparently, they are naming spectacular events after Sesame Street characters....

11

Physiology & Medicine / Re: Is neuronal activity a form of extracellular life?

« on: 12/07/2018 11:55:08 »

Lack of neuronal activity is a sign of intracellular death....

12

Cells, Microbes & Viruses / Re: Why you dont get reinfected on the same season by cold virii?

« on: 08/07/2018 23:14:04 »

why haven't you managed to be immunised for all strains by your 30s when you would have get 120 colds in total?

Immunity does improve with time - that is one reason that adults get fewer colds than children (another reason is that adults are more disciplined about washing hands and sneezing into a tissue).

But the rate of cold infection does not drop to zero as you get older - this is because viruses continually mutate (another reason is that our immune systems get weaker as we age). Viruses don't have the complex error checking and correction mechanisms that more complex organisms require, so mutations are fairly common.

Mutations that are different enough to hide from the immune system will then spread through the population, causing another wave of cold infections.
See: https://en.wikipedia.org/wiki/Virus#Genetic_mutation

Why some People never get a cold for years?

I thin if you checked their immune system for sensitivity to various viruses, you would find that they had been exposed, but they showed few symptoms of the infection.

Ironically, most of the classic cold symptoms (runny nose, fever, headache) are not caused by the virus itself, but by your body's immune response to the virus.

If you have a weak immune system, you may not get symptoms of a virus infection - but a cold could kill you.

13

The Environment / Re: Do hot dry summers occur in a 14 year cycle?

« on: 03/07/2018 12:57:41 »

In the 19th century, an economist suggested that sunspot cycles might affect the economy.

Subsequent studies have found no link, and economists now contemptuously use the term "sunspot" to refer to any random and unpredictable variable that may affect the economy.
https://en.wikipedia.org/wiki/Sunspots_(economics)

Of course, with what we now know about the Maunder minimum, we could suggest that perhaps the economists were looking on too short a timescale, and using the wrong metric? Extended periods with little or no sunspot activity have been associated with lower-than average temperatures in Europe - including the Thames River freezing over.
But this is an association, without a proven causation.
https://en.wikipedia.org/wiki/Maunder_Minimum#Little_Ice_Age

14

General Science / Re: How long will a boiled egg last?

« on: 03/07/2018 12:36:57 »

If you hard-boiled eggs as soon as you got them home, and then kept them in the fridge, I am sure they would remain safe to eat for much longer than if you left them in the kitchen at room temperature.

Salmonella bacteria is often found on or in hens eggs, and hard-boiling will kill most bacteria.
- However, you need to ensure that the eggs aren't cracked, and they are kept away from other products which may harbor bacteria, as bacteria find cooked eggs almost as tasty as raw eggs.
- Few bacteria can grow well in the low temperatures of a refrigerator (typically 4C), and this will preserve the eggs.
- Even fewer bacteria can grow in the freezer (typically -15C), so the eggs will last even longer there

But I suggest that you don't buy more eggs than you can consume within a week...

See: https://en.wikipedia.org/wiki/Salmonellosis_in_the_United_States

15

General Science / Re: How does temperature affect the colour of metals?

« on: 02/07/2018 11:43:28 »

Part of the color change is black-body radiation - as an object gets hotter, it tends to emit more energy at higher frequencies, so a yellow glowing piece of metal is hotter than the same piece of metal glowing a dull red.
But this color change goes away after the metal cools down.
See: https://en.wikipedia.org/wiki/Red_heat

Part of the color change is chemical. At higher temperatures, chemical reactions like oxidation (or "rusting") to occur much more quickly. Heating steel wool in a flame can can quickly produce a discolored layer of rust on the surface.
This color change remains after the metal cools down.

Titanium naturally forms a thin, clear protective oxide layer that inhibits further oxidation.

However, under that protective layer, titanium is still a very reactive metal - it is even able to react with nitrogen at high temperatures; we normally consider nitrogen to be a fairly inert gas.

Maybe the color change you see is the reaction product with some other substance at high temperatures?
See: https://en.wikipedia.org/wiki/Titanium#Chemical_properties

16

Physics, Astronomy & Cosmology / Re: How can we reach temperatures sufficient for fusion without melting everything?

« on: 02/07/2018 11:13:09 »

How can we reach temperatures sufficient for fusion without melting everything?

In addition to the magnetic fields keeping the plasma away from the walls (as mentioned by ChialSPO):
- They ensure the plasma is very pure (hydrogen+a tiny amount of helium), so that it doesn't emit much visible light
- The walls are often made of a highly reflective material, so visible radiation is reflected back into the plasma
- The walls have internal pipes for cooling water, and (hopefully, some time in the future), drive turbines to produce electricity.
- To make the challenge worse, the magnetic containment fields are produced by superconducting magnets, which must be cooled to almost -200C, in very close proximity to the seething hot bath of plasma.

I don't know how they measure the temperatures (of millions of degrees).

- A plasma emits black-body radiation; for temperatures in the millions of degrees, radiation would occur into the X-Ray part of the spectrum.
- When fusion starts, neutrons are emitted by the plasma. This gives an idea of how close the conditions have approached the onset of fusion.

See: https://en.wikipedia.org/wiki/ITER#Cooling_systems

17

Science Experiments / Re: Resonant effects & few questions, if you hv facility pls do these experiments...

« on: 01/07/2018 12:17:13 »

You can break the glass with very tiny power

It is true that they shattered the glass, and made it useless to hold water.

But it is a considerable step to say that you could "shatter" water molecules into hydrogen and oxygen.

In fact, they didn't shatter very much of the glass. A back-of the envelope calculation:
- The glass looked to be about 4cm diameter and 4cm high
- The area of glass would be about 50 sq cm
- When it shattered, the amount of full-depth break looked to be about 20cm in length
- The Si-O bond length is around 150pm (150x10^-12)
- So the area that was actually shattered was about 3x10^-9 sq cm
- The sound managed to shatter about 1 in 10^10 atomic bonds in the glass
- This is moderately easy in glass, since it suffers brittle fracture

However:
- Liquid water does not suffer brittle fracture
- Solid water (ice) does suffer brittle fracture, but it will break apart at the relatively weak "Hydrogen bonds" (ie between different H₂O molecules), not the much stronger Oxygen-Hydrogen covalent bonds within a single H₂O molecule.

So acoustic or electromagnetic resonance won't break apart a significant number of water molecules. To break apart water molecules, you need temperatures of several thousand degrees.

It is possible to reach these temperatures by discharging an electric spark in water, or by applying high power ultrasound power. But these are "brute force" approaches, rather than a resonance effect.
See: https://en.wikipedia.org/wiki/Sonoluminescence

18

Science Experiments / Re: Resonant effects & few questions, if you hv facility pls do these experiments...

« on: 01/07/2018 00:39:46 »

I think after watching of these videos, you may know what types of resonance effect, am talking about…

I think you may be confusing the narrow resonance of high-quality glass with the broad resonance of liquid water.

In the second video, they needed a sound pressure level of over 100dBA to shatter the glass. That is a fair bit of sound energy.
- Good-quality glass is a "high-Q" resonator, which means that the vibrations will build up over time. This is illustrated by the few, very narrow frequencies that will resonate
- Glass has some inherent manufacturing stress, which makes it easier to shatter

In contrast:
- In liquid water, the energy of one molecule is distributed through the body of water via hydrogen bonds, so it is a low-Q resonator, as indicated by the very wide band of frequencies it absorbs.
- When water is formed from Hydrogen and Oxygen, a lot of energy is released, producing a very stable water molecule. You have to pump in at least this much energy to separate them again. The water molecule won't "shatter" like glass does.

So I'm afraid that you can't get energy from nothing by shattering water with just the right resonant frequency.
See: https://en.wikipedia.org/wiki/Q_factor

19

General Science / Re: Could we run out of musical notes?

« on: 30/06/2018 05:48:11 »

Could we run out of musical notes?

Since you don't "use up" a note by playing it, no, you can't run out of them.

They are infinitely recyclable.

20

Plant Sciences, Zoology & Evolution / Re: Is terpenoids biosynthesis temperature-dependent?

« on: 28/06/2018 11:08:42 »

I would like to know if aromatic terpenoids biosynthesis is temperature-dependent?

All biosynthesis is temperature-dependent.

Not much biosynthesis occurs below about -10C, as most living things have frozen solid.
And not much biosynthesis occurs above about 100C, as most living things have all their proteins denatured. 

In animals and birds, all biological processes operate within a fairly narrow range of temperatures - if your core temperature moves more than 5C away from 37C you are likely to die without intensive medical intervention.

However, bacteria, insects, fish, trees and reptiles have a wider operating range of temperatures, since they can't maintain their own temperature at a constant temperature. But even then, there is a preferred range.

...there are exceptions to every rule: https://en.wikipedia.org/wiki/Extremophile