INTRODUCTION:
It was invented by the German physicist Hans Geiger (co-discoverer of the atom nucleus) and later improved by his student Walther Muller, therefore the name Geiger-Muller counter.

GEIGER MULLER COUNTER:
A Geiger counter is an avalanche detector and is used to measure and detect forms of ionizing radiation (which includes alpha α particles, beta β particles and gamma γ rays)

PRINCIPLE:
It relys on runaway multiplication of electrons.

CONSTRUCTION:
Geiger-Muller tube, is basically a chamber filled with low pressure gas(inert gas or a mix of organic vapor and halogens.)The tube contains two electrodes, the anode and the cathode, which are usually coated with graphite. The anode is represented by a wire in the center of the cylindrical chamber while the cathode forms the lateral area. One end of the cylinder, through which the radiation enters the chamber, is sealed by a mica window.
A potential difference of +1,000 volts relative to the tube is maintained between the electrodes, therefore creating a strong electric field near the wire.

WORKING:

• Ionization in the gas is caused by the entry of photon or a particular radiation coming through the mica window. 
• The positively charged ions are attracted to their appropriate electrode (i.e. cation to cathode, anion to anode) and they gain sufficient energy to eject electrons from the gas atoms as they pass through the gas. This causes more atoms to ionize. 
• Therefore electrons are produced continuously by this process and rapid gas multiplication takes place.
• The effect of "gas multiplication" is that more than one million electrons are collected by the central electrode for every ion produced in the primary absorption process.When this happens an electrical current is established between the two electrodes.

This current can then be easily collected, amplified and measured or counted and played in the form of an acoustic signal made out of clicks each of which should correspond to the detection of a single ion.

Therefore a Geiger counter is able to detect low-energy radiation because even one ionized particle produces a full pulse on the central wire.

REGENERATION:
Regeneration is the process of renewal, restoration, and growth of lost body parts.

ABILITY OF REGENERATION:
Depends on :

• Differentiation and Complexity

The more complex an organism the more will its cells be differentiated and lesser the power of regeneration.

PROCESS:

Some organisms are capable of dedifferentiation, in which specialized cells become more basic.
This process is involved in the regeneration of limbs in animals which are capable of this feat, with the basic cells differentiating again to construct the needed tissues, bones, and other types of cells for the replacement.

A small molecule dubbed reversine, has been discovered that has proven to induce dedifferentiation in myotubes. These dedifferentiated cells could then redifferentiate into osteoblasts and adipocytes.

EXAMPLES:
SPONGES:small parts can regenerate whole colonies.
HYDRA OR STARFISH:chopped parts can form new animal.

ARTHROPODS:can regenerate lost appendages.
SALAMANDERS AND LIZARDS:can regenerate lost tails.

BIRDS AND MAMMALS:new cells can form at points of wounds.

CELL DIFFERENTIATION AND STEM CELLS:

The process during which young, immature (unspecialized) cells take on individual characteristics and reach their mature (specialized) form and function.

EXAMPLES:
Embryonic stem cells Fetal stem cells Cord blood stem cells and some adult stem cells are capable of performing this process.

Totipotent : Toti, meaning total, the zygote and the embryo during early stages of development have the potential to become any type of cell and can produce a whole human being.

Pluripotent: Cells which can differentiate into several different cell types,except placenta, are considered to be pluripotent

EMBRYONIC STEM CELLS:
Cells that form the inner mass of a blastocyst during embryological phase of growth (lasting 8 weeks)are called embryonic stem cells.Like all stem cells they can proliferate and give rise to specialized cells.

CULTURE OF EMBRYONIC STEM CELLS
Credit: The National Academy of Sciences has kindly allowed the images to be reprinted on the weird science blog. Check out the original link called Understanding Stem Cells, courtesy of the National Academies Press in Washington, D.C.

FETAL STEM CELLS:
The cells taken from a fetus (after 8 weeks of development an embryo is termed as such) are called fetal stem cells.

ADULT STEM CELLS:
These are undifferentiated cells found throughout the body that are involved in refurbishing the body with new cells to replace worn out ones.
Examples of stem cells in an adult:
Hematopoietic stem cells
Neural stem cells
intestinal stem cells

CORD BLOOD STEM CELLS:
The cells of the umbilical cord and placenta are unspecialized stem cells and can be cultured.

CAUSE:
Specific groups of genes are expressed in each cell type which leads to production of specific proteins (the other unneeded genes are turned off)
Proteins (coded for by the DNA) are the keys to differentiation in animal cells

The particular combination of genes that are turned on (expressed) or turned off (repressed) dictates cellular morphology (shape) and function. This process of gene expression is regulated by cues from both within and outside cells and lead to differentiation.

CHEMICAL COMPOSITION OF CHROMOSOMES:

The major chemical components of chromosomes are DNA, RNA, histone proteins and non-histone proteins. Calcium is also present in addition to these constituents.

DNA -Deoxyribonucleic Acid:
DNA is the most important of chemical components of chromatin, since it plays the central role of controlling heredity.

Histone proteins:
These are Lysine And Arginine rich, basic and stable proteins in chromosomes.
They are classified into five types called HI, H2A, H2B, H3 and H4. 

Non-histone proteins:
Non-histone proteins provide the scaffolding structure.

DNA PACKAGING:

The diploid human genome contains 6 billion base pairs of DNA per cell.This is enough to make some very lengthy journeys like, to the sun and back.300 times.In order for this massive amount of DNA to exist in a cell ,it has to be made very compact.In short, it needs to be packaged into a very small surface area to volume ratio.
Patterns of packaging are facilitated by associated proteins, which in eukaryotes, could be histones or non-histones.

The unit of compaction is nucleosome consisting of a segment of DNA wound in sequence around four histone protein cores.

• Histone proteins provide the spools about which DNA winds thus compressing 1.8 meters of dna into 90 mm.The negatively charged coil of polynucleotide (due to phosphate) is strongly attracted by the positively charged histone protein which helps in compaction.

• The nucleosomes are linked together by the long strand of DNA called linker DNA. 

• The beads-on-string structure in chromatin is packaged to form chromatin fibres which then fold together into large looped domain.that are further coiled and condensed at metaphase stage of cell division to form chromosomes.

• The packaging at higher level requires non-histone proteins. 

HETEROCHROMATIN AND EUCHROMATIN:

In a typical nucleus, some region of chromatin are loosely packed (and stains light) and are referred to as euchromatin.Euchromatin is said to be transcriptionally active
The chromatin that is more densely packed and stains dark is called as heterochromatin. Heterochromatin is transcriptionally inactive.

NERVE IMPULSE

Neurons send messages electrochemically i.e chemicals(ions) cause an electric impulse.Neurons and muscle cells are electrically excitable and can transmit electrical nerve impulses.

SODIUM-POTASSIUM PUMP & ION CHANNELS:

A transport protein embedded in the cell membrane acts as "Sodium/potassium/ATPase".

It works to release the Na+ ions outside and K+ ions inside using ATP.

To check the function of Sodium-Potassium pump,there are also Na+ K+ ion channels in the membrane which when closed still leak allowing sodium inside and potassium outside down their concentration gradient.

THE RESTING MEMBRANE POTENTIAL:

The combination of Sodium Potassium pump and ion channels causes a stable imbalance of ions across the membrane.This imbalance of ions creates a potential difference between the inside of the neuronal membrane and its surroundings called the RESTING MEMBRANE POTENTIAL.

It is always negative inside the cell membrane and positive outside due to the presence of -vely charged proteins and +vely charged Na+ respectively.

In humans it is -70 mV.

ACTION POTENTIAL:

"WHEN A STIMULUS IS APPLIED, A BRIEF REVERSAL OF THE MEMBRANE POTENTIAL LASTING FOR ABOUT A MILLISECOND OCCURS.THIS IS CALLED THE ACTION POTENTIAL" 

ALL OR NOTHING LAW:

The action potential only occurs if the stimulus causes enough sodium ions to cross the membrane to change the membrane potential to a certain threshold (-30 mV) in humans.At this point Na+ rush inside.If depolarization is not strong enough to reach the threshold then no action potential is generated.

DEPOLARIZATION:

When stimulated past threshold,sodium channels open and Na+ ions rush inside creating a region of positive charge within.This is called depolarization.

The region of positive charge causes the nearby voltage gated sodium channels to close.

REPOLARIZATION:

Just after the Na+ channels close,the K+ channels open wide and K+ ions enter the cell bringing the charge across the membrane back to normal.This is called REPOLARIZATION.

                                                                                                                 

PROPAGATION OF IMPULSE:

The process continues as a chain reaction along the axon membrane.The influx of Na+ depolarizes and outflow of K+ repolarizes the membrane.

REFRACTORY PERIOD:

The time period within which the sodium and potassium are returned to their rightful places on either side of the membrane through the ATP pump is called refractory period.

While the neuron is in this period ,it doesn't respond to any stimulus.

SYNAPSE:

The region where the impulse moves from one neuron to another is called synapse.

It consists of :

PRE-SYNAPTIC MEMBRANE:The axon terminals.

POST-SYNAPTIC MEMBRANE:The dendrite of the other neuron or in some cases the cell membrane of the muscle,this synapse is called motor-end plate.

TRANSMISSION OF IMPULSE:

• The pre-synaptic membrane,axon terminals contain many vesicles filled with neurotransmitters such as acetylcholine ,gab,serotonin,glycine ,nor-epinephrine etc.

• As the impulse is propagated to the axon terminals,calcium channels present there open and allow diffusion of Ca++ ions from synaptic cleft to synaptic membrane.

• This causes the vesicles to release the neurotransmitter into synaptic cleft.

• The neurotransmitters bind to specific receptors on the post-synaptic membrane to generate action potential in the cell.

• Neurotransmitters are then reabsorbed by the axon terminals.Ca++ ions move out.

COLORS OF THE SKY

The atmosphere around us contains dust particles,water droplets and gas molecules.the white light coming from the sun passes through most of the gas and water droplets but the gas molecules are way larger than the wavelengths of light ,thus these molecules absorb the low level wavelengths(mostly blue but also violets and green)and afterwards they radiate the same color light out.in this way the blue light gets absorbed and radiated making the overhead blue .the remaining colors the yellows and reds make up the color of the sunlight thus the sun appears yellow.

During sunset the light reaches us from over a larger distance(we are moving away from the sun) thus more of it (the blues) are scattered and the yellows and reds more visible.The most spectacular shows occur when the air contains many small particles of dust or water. These particles reflect light in all directions. Then, as some of the light heads towards you, different amounts of the shorter wavelength colors are scattered out. You see the longer wavelengths, and the sky appears red, pink or orange.

I Was Afraid of Rhett Butler

By Clark Gable

Liberty magazine, February 1940

THE LEGENDARY CAPTAIN RHETT BUTLER

Rhett Butler really put me on a spot, a hot one. Or rather Margaret Mitchell did when she created Rhett. I hope some day to have the privilege of meeting Miss Mitchell. This is partly curiosity. When a lady puts you on a spot it is only human to want to meet her. More than that, I feel we have a lot in common. Misery loves company. I can understand perfectly why she built a wall around her home. Haven’t I wanted to do the same thing during the past year? Rhett put us both on a spot. We are his innocent victims. I am certain I can speak for Miss Mitchell as well as for myself in saying that neither of us had any idea of the dent he was going to make in our lives.

Frankly I was one of the last few millions to read Gone with the Wind. When people first started talking about the book and Rhett, I wasn’t impressed. Everybody in Hollywood has the greatest story ever written. I am constantly asked to read novels, plays and originals that will make screen epics. Besides, I wasn’t interested in playing a character named “Red” Butler. It would mean dyeing my hair or wearing a wig and that’s too much to ask, even of art. Later I learned in a rather embarrassing discussion that it was Rhett, not “Red,” which punctured a good defense. What aroused my interest was a puzzling flood of letters, urging me to play Rhett, “because he was obviously written for me,” and those many friends who told me emphatically I was Rhett, and that fifty million Americans couldn’t be wrong. I read Gone with the Wind. My reaction was enthusiastic and immediate. “What a part for Ronald Colman,” I said. I was sincere.

Right here I would like to clear up a misunderstanding. The tremendous popularity of the book inspired many myths. One of these, frequently repeated, contends that Miss Mitchell had me in mind to play Rhett on the screen when she wrote her book. This is not true. She got her idea for the book and was writing it while I was a four-dollar-a-day laborer in the Oklahoma oil fields. I could have been an inspiration to no one, except possibly a soap salesman.

I cannot honestly say that I didn’t want to play Rhett, I did. But there certainly was a rub. Miss Mitchell hadn’t missed a thing. She left nothing to the imagination. Rhett was as real as life. That’s one of the things I have a desire to ask Miss Mitchell. Where did a quiet and gentle lady meet a man like Rhett Butler? Take it from me, there was a Rhett Butler and he wasn’t Clark Gable. In my travels I’ve known men like him. There was a gambler in Bigheart, Oklahoma, with long slender white fingers, who could deal faro like nobody else. He dressed and talked like a Virginia gentleman, killed a man one night, and every woman in town—but that’s another story.

Rhett was too popular, had fired the imaginations of too many people. Literally millions of people knew Rhett better than they knew George Washington. Everyone couldn’t be pleased, not even the majority. I knew that.

I might have saved myself my worrying. When the time came for the decision, I had little to do about it. David O. Selznick had purchased the screen rights and Dave was interested in making a separate deal with me, providing my studio would give me time off to make the picture for him. It was with considerable pleasure that I informed David my contract with Metro-Goldwyn-Mayer was about as iron-clad as smart lawyers could make it. And as a minor additional point, I didn’t want the part for money, marbles or chalk.

David was fair, but firm. He wanted me to know that he was going to try for a deal with MGM anyhow. I could see myself being sold down the river.

 I didn’t ask the studio not to loan me. I said nothing. My contract states that I have no choice of roles. News that the deal had been agreed upon reached me during the making of Idiot’s Delight. I read it in the paper. The guillotine, I thought. I was farmed out for a percentage of the profits to Metro-Goldwyn-Mayer.

Then I lost my fear of Rhett. There were too many other things to think about. I started out with the idea of knowing Rhett as well as I know myself. I lived with him day after day, reading and rereading Gone with the Wind, underlining each sentence that revealed a facet of his many-sided character. Making the picture was comparatively easy and a pleasure. The hard work was during months of unrelenting preparation.I felt that it was essential to have Rhett so minutely pegged in my mind that it would not be necessary to think consciously about him, a direct person, extremely confident, sure of himself in any situation. A man of unrelenting will, unchangeable once he had made up his mind, polished, a gentleman, yet his own worst enemy, a mellow blending of good and bad, with a saving sense of humor.

I had no difficulty visualizing Miss Leigh as Scarlett. My thanks here are publicly expressed to Miss Leigh for making it a pleasure to believe the part of Rhett.

Scenes were not filmed in sequence, since this is not practical because of technical problems, but the book was religiously followed in its essentials. If a favorite scene is missing, you can blame the restrictions of censorship. Tut, tut, Miss Mitchell. Some dialogue and certain situations were thus eliminated but ninety per cent of the dialogue used was taken directly from the book.

Rhett always will remain among the most memorable roles I have played on the screen, although I sincerely believe that Fletcher Christian in Mutiny on the Bounty was a part of equal caliber. It was the unprecedented public interest in Rhett that made him a difficult and frightening role to tackle. Gone with the Wind belongs to the public, not Hollywood. Anyhow I’m glad it’s over. Now I can get a haircut. And I’ve got my fingers crossed.

A YOUNGER PICTURE WITH THE HAIR NOT-SO-SLICKED BACK IN THAT HORRID STYLE.

FROM THE ARCHIVES OF http://dearmrgable.com/