Final post for a few months
I am not able to devote as much time as I would like for this topic. Originally, I hoped to write on simple topics of interest in every day life but wo'nt have enough time for a few months to do the spade work. If there is no interest from others, the moderatorsmay kindly close this topic.
I end with some URLs on sustainable agriculture. The following URL contains the story of farmers' suiides in Australia with a comment and links to sites about soil improvement and water preservation:
http://www.rense.com/general66/dro.htm
Some siimilar efforts in A.P. are in:
http://www.ddsindia.com/activities.htm
http://www.ddsindia.com/publications.htm
http://search.atomz.com/search/?sp-a...n%22&submit=Go
There are similar efforts by various organizations in India, e.g. Sunita Narayanan of CSE in New Delhi.
Regards,
Swarup
Affect of parental smoking
From: http://www.newscientist.com/article.ns?id=dn7952
"Children as young as 2 years old may be influenced by their parents’ tobacco habits, many years before they even consider using cigarettes themselves, a novel study has shown."
Swarup
After being in the sun for sometime, why do we experience di
After being in the sun for sometime, why do we experience dim vision on entering a room?
The human eye contains two types of receptors for light namely cones and rods. Cones are responsible for colour vision and seeing in bright light. Rods are meant for seeing in dim light.
Cones cannot be stimulated in dim light because of their high threshold for light.
Pigments present in these photoreceptors are made of Vitamin A and a protein called opsin.
On exposure to light, these pigments (called rhodopsin in case of rods) breakdown and this degradation leads to excitation of nerve cells leading to appreciation of light (that is, seeing).
Regeneration of the pigment occurs continuously and simultaneously so that the pigment will be available for degradation leading to uninterrupted seeing.
Regeneration of the pigment occurs faster than degradation in cones. But in rods the regeneration is a slow process and degradation outweighs regeneration in day light in rods.
Rods get exhausted of their pigment when in bright light while cones continue to act.
When a person who stayed for sometime in bright light, enters into dim light, the cones can't be stimulated because of their high threshold for light.
All the pigment in the rods gets degraded. So immediately rods can't be of help to see.
This is the reason why a person after spending some time in sunlight, experiences dim vision in a room.
A more common and striking experience of this phenomenon by everyone of us is when we cannot see properly soon after entering a cinema hall.
Subsequently, as time passes on in dim light, regenerations of pigment is taking place in rods and when it is formed in sufficient quantity, then rods begin to be stimulated by dim light leading to proper vision.
In dim light, regeneration is at a higher level than degradation of pigment in rods and hence we continue to see uninterruptedly in dim vision. This phenomenon is called `dark adaptation' in the medical field.