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Physiology & Medicine / Re: Why Are Some People Short-sighted and others Long Sighted ?

« on: 21/10/2018 15:56:56 »

Sorry, did not phrase that very well.
Dog was not a Pitbull.
It was docile and friendly. Just tapped gently forward into my eye. I did not see it coming.
Nothing like as serious as your expeience.

Cat (Catastrophe)

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Physiology & Medicine / Re: Why Are Some People Short-sighted and others Long Sighted ?

« on: 21/10/2018 13:11:55 »

This is strange:

I am also short sighted to the tune of about 16 cm, but have monovision due to a late realignment in my childhood. I have a strong preference for my right eye and only read by that one. Negligible depth perception.
Due to complications of a friendly pitbull attack, I developed cataracts, most severely in my right side.  So I was given a choice for near or far, and chose to keep the short-sightedness.  But I focus at 50cm now, about exactly where the screen is, so I actually spend most of my day without glasses, wearing them only to drive.

Bold applies to me also. Underline is what I wanted but was given no prior choice which I should have been.
The dog 'attack is some coincidence. Fortunately the claw went straight in and out of my eye so no damage was done. It was a long time ago (about 50 years ago I think. I am 79 now).
Are you in UK?
Surgeon finally admitted I should have had a choice. I wanted to keep right eye shortsighted and have left made to match. After he had made right eye 'normal' he really did not want to make my left (longsighted) eye shortsighted giving me monovision the opposite way around to all my previous life.

Catastrophe (averted)

PS I use Catastrophe as my handle because I am interested in asteroids etc..

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Physics, Astronomy & Cosmology / Re: How adsorption and desorption work?

« on: 20/10/2018 16:21:00 »

Sorry for the delay in replying. I am new around here and got lost.

What are the desorption mechanisms please?
How selective can adsorbent
be?

Let me start with the second. This seems quite straightforward. Adsorption, in theory, relates directly to the chemical nature of the two items. Substance A should adsorb more selectively onto Substance A than onto Substance B.
I am hanging on here by my shirt tails so someone more qualified may well have a better knowledge of this area.
For the record I have B.Sc. (Hons) Chemical Engineering (B'ham) so my approach is very practical and lacking theoretical foundations. After the above about 40 years experience in surfactants.

I am thinking here of silicon chemistry (in which I have developed a passing interest after my retitement) where you have the substitution of other elements of the same or similar size. There are also electrical considerations.
It really comes back to the old aphorism 'like dissolves like'.  I suppose I am postulating 'like adsorbs onto like.
Certainly the opposite should be true. I know from many years or experience that the hydrophobes (e.g., fatty) tails of surfactants adsorb readily onto hydrophobic surfaces rather than the opposite.

As far as desorption mechanisms are concerned, can only suggest that the reverse applies. Substance A should be more readily desorbed from Substance B with which it has less afinity than Substance A.

Hope that provokes some thought,

Catastrophe

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Physics, Astronomy & Cosmology / Re: Are there planet-sized bodies in interstellar space?

« on: 20/10/2018 15:39:09 »

In answer to your question: How do scientists know there aren't any planet-sized bodies in interstellar space? i.e. are they too far from the nearest star to be illuminated?
here is an example of one believed to be roughly the size of Mars approximately 4.3 billion years ago which hit our poor little planet and created our Moon.
Luckily for us the formerly interstellar visitor has not yet brought any relatives to repeat the experience.

To be serious, whilst the basis of this reply is believed to be correct, there were many more large planetary-sized objects around at that time so the background scenario is not very similar to that of today, and you are correct in your proposition that any planet, by definition, would need to be illuminated. BUT WAIT just because we normally respond to electromagnetic waves of a limited range (what we call light) even we are starting to use apparati which respond to other wavelengths such as infrared or Xrays.

Let us hope that the crashing of sound vibrations as a long lost relative arrives searching for his or her distant relative, having arrived unseen from the direction of our star too quickly to be detected by our electromagnetic apparati
(Sorry if you don't like 'apparati' but I do prefer it to apparatuses)

Catastrophe

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Physiology & Medicine / Re: Why Are Some People Short-sighted and others Long Sighted ?

« on: 20/10/2018 14:57:31 »

OR BOTH?

For most of my nearly 80 years I have been extremely longsighted in my left eye and shortsighted in my right eye.

For as long as I could read I used only my right eye. This is called monovision.

In May I was diagnosed with cataracts. It was decided to remove both my cataracts but I was given no guidance or discussion on the replacement lens. The NHS, in all its wisdom, decided to operate on the right eye first.
So what? You ask. Read the second line again. I could only read with my right eye.

Hence after more than 79 years I could only read with a magnifying glass.

I won't bother you with the rest of the story ... you can probably guess it for yourselves.

Catastrophe

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Chemistry / Re: How do you make a mirror?

« on: 20/10/2018 13:47:44 »

You ask about wetting agent (surfactant). Surfactant is short for surface active agent which (surprisingly) means an agent which is active at surfaces. The important characteristic of surfactants is that they contain both a water soluble (insoluble in oil) group and an oil soluble (insoluble in water) group.
Take a shampoo as an example. The most common surfactant used in shampoos is sodium lauryl ether (2-3 mole) sulphate. The ether is an alcohol ethoxylated with between 2 and 3 moles ethylene oxide. The layryl ether is then sulphated. The oil soluble part is the lauryl C₁₂ which may be petroleum derived or it may be deruved from fatty acids such as coconut fatty acid. The water-souble part is the sulphate group.

In detergent/cleaning applications the oil-soluble part acts at the oil/water surface where it dissolves in the oily impurities you want to remove. The water/soluble part then helps to lift them into the water solution. In a shampoo the surfactant helps to remove natural oils and greases from the hair.

There is a lot more to formulating shampoos. Other surfactants, especially amphoteric surfactants, are used to reduce eye irritation. If you want to know more about this, WHICH I AM SURE YOU DO NOT, you could refer to my book "Amphoteric Surfactants" in the Marcel Dekker Surfactant Science Series

Backtracking for a moment, there are 4 types of surfatant: anionic, cationic, nonionic and amphoteric surfactants. In anionic surfactants the water soluble group is anionic (mostly sulphate, sulphonate or carboxylate -COONa), in cationic surfactants the water soluble group is (wait for it) ... cationic. In nonionic surfactants the water soluble group is an ethylene oxide chain or sometimes an ester group.  Amphoteric surfactants contain both anionic and surfactants.

Getting back to your question, most surfaces in nature are negatively charged so it follows that most surfactants are anionics.  The negative charge in anionics is used to repel the negative surface charge to provide detergency. Cationics are used to convert negative surfaces to oily surfaces, for example in corrosion inhibitors.

Chances are you will need an anionic surfactant to improve wetting but you wll have to check that it does not interact with other chemicals in your system. If you need such an anionic then 'washing up liquid' is the easily obtainable source. For specific surfaces such as plastics you need a wetting agent (surfactant) compatible with the plastic surface.

I hope this has been helpful, but I am here if you need any clarification.

Catastrophe

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Physics, Astronomy & Cosmology / Re: Could probes affect an asteroid's orbit?

« on: 17/10/2018 15:47:00 »

Depends, of course, on the relative sizes. From suggested origin of the Moon ('asteroid' the size of Mars hitting  Earth) there is" not much " you can do about it !

A small probe landing on a large asteroid will not have much effect.

Also take into account kinetic energy. Some of these asteroids are moving at quite a pace.


Catastrophe (to be avoided) 

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Physics, Astronomy & Cosmology / Re: How adsorption and desorption work?

« on: 07/09/2018 14:22:03 »

My knowledge of this comes from my lifelong involvement with surfactants.
For example, I edited "Amphoteric Surfactants" in the Marcel Dekker Surfactant Science Series.
Surfactants work by adsorption. Their hydrophobes can absorb onto hydrophobic surfaces, making them hydrophilic, thus wettable by water. Ionic surfactants can adsorb onto ionic surfaces (charged) making them hydrophobic.
For difficult surfaces, fluorocarbon surfactants may be useful.
If you can detail  the problem I may be able to offer more suggestions. In short, surfactants can adsorb onto most surfaces to change their nature, hydrophilic or hydrophobic.