Monday, 30 October 2017

How Nuclear Reactor Works "copied "

A nuclear reactor is a system that contains and controls sustained nuclear chain reactions. Reactors are used for generating electricity, moving aircraft carriers and submarines, producing medical isotopes for imaging and cancer treatment, and for conducting research.
Fuel, made up of heavy atoms that split when they absorb neutrons, is placed into the reactor vessel (basically a large tank) along with a small neutron source. The neutrons start a chain reaction where each atom that splits releases more neutrons that cause other atoms to split. Each time an atom splits, it releases large amounts of energy in the form of heat. The heat is carried out of the reactor by coolant, which is most commonly just plain water. The coolant heats up and goes off to a turbine to spin a generator or drive shaft. Nuclear reactors are just exotic heat sources.

Main components

  • The core of the reactor contains all of the nuclear fuel and generates all of the heat. It contains low-enriched uranium (<5% U-235), control systems, and structural materials. The core can contain hundreds of thousands of individual fuel pins.
  • The coolant is the material that passes through the core, transferring the heat from the fuel to a turbine. It could be water, heavy-water, liquid sodium, helium, or something else. In the US fleet of power reactors, water is the standard.
  • The turbine transfers the heat from the coolant to electricity, just like in a fossil-fuel plant.
  • The containment is the structure that separates the reactor from the environment. These are usually dome-shaped, made of high-density, steel-reinforced concrete. Chernobyl did not have a containment to speak of.
  • Cooling towers are needed by some plants to dump the excess heat that cannot be converted to energy due to the laws of thermodynamics. These are the hyperbolic icons of nuclear energy. They emit only clean water vapor.A nice animation of a nuclear reactor from the NRC.

Wednesday, 25 October 2017

Nuclear Reactor - Understanding how it works | Physics Elearnin





One of my students in grade 3 (level 12) asked me this question: "How does Nuclear reactor work ?" Thus ,as I need to know it myself I have seen that video and shared it . I hope it is the answer 

Saturday, 21 October 2017

Short story = "I Never Forget A face " > a very remarkable short story

I'LL tell you a strange thing about me - I never forget a face. The only trouble is that usually I'm quite unable to tell you the name of the person. I know what you're going to say - you suffer from the same thing yourself. Lots of people do, to some extent. But I'm not like that. When I say I never forget a face, I mean it. I can pass a fellow in the street one day and recognize him again months after, though we've never spoken to each other. My wife says sometimes that I ought to be a reporter for the newspapers and wait about at first nights at cinemas, looking for all the famous people who go to see the films. But, as I tell her, I should not be able to do very well at that. I should see the famous man or woman, but I should not be able to say which one it was. That's my trouble, as I say - names.
Of course, this trouble with names has put me in difficulties from time to time. But with a little skill one can usually get out of the difficulty in one way or another. In my work, moving round the City doing bits of business, I have to be very clever not to let a man see that I can't remember whether his name is Smith or Moses. I've annoyed people in that way and lost good business more than once. But on the whole, I think I gain more than I lose by this strange memory of mine.
    Quite often I've approached a man who didn't know me at all. I've said: "I think we've met before," and I've been able to give him some idea of where it was. I can always connect a face with a place, you see. Well, as I was saying, I can approach this fellow and remind him of a big dinner or a football match or whatever it is that his face reminds me of, and probably within five minutes we're talking about business. I can usually find out his name later on. My memory for faces helps me a lot in business.
      You can guess that there's not a man, woman or child here in Bardfield that I don't know by sight. I've lived in Bardfield ever
since the Second World War. I like the place; although it's only forty minutes from London, there's a lot of country here, village is almost a mile from the station, and that's rather troublesome. But quite a pleasant crowd of men travel up an down to the City most days, and 1 needn't tell you that I know the names of half of them, though we speak to each other cheerfully enough. My wife complains that 1 don't know the names of our neighbours in the next house, and that's true.
    Well, on this particular evening I'd been kept a bit late at the office, and it was difficult to get to the station in time to catch the train. There was quite a crowd on the train at first, but the gradually got out; and by the time we reached Ellingham - that's two stations before mine - there were only two of us left in the carriage. The other fellow wasn't one of the regular travellers but I knew he was a Bardfield man. I knew it as soon as I saw him of course. I'd smiled at him when I saw him get into the carriage
in London, and he had smiled back. But that didn't tell me his name.
      The annoying thing was that 1 couldn't remember where I knew this fellow's face from, if you understand what I mean. His face told me clearly that he was connected with Bardfield, but that was all it told me. 1 could not think where in Bardfield I had seen it. 1 guessed he must be one of those fellows who've come to live lately in the small houses by the bus-stop, but I couldn't be sure. Some of us who've lived in the place for a long time are rather unfriendly towards newcomers, but that's not my way - never has been. 1 never know where the next bit of business is going to come from, and it may come from one of them. I can't afford to neglect chances.
So when the two of us found ourselves alone in the carriage, with room to stretch our legs and be a bit comfortable, I started to talk, just as if we were old friends. But I can't say that I got much information out of him. He spoke well, with a quiet friendly manner, but he told me very little. 1 can generally find out what a man's work is in ten and a half minutes - that's the time it takes from Ellingham to Bardfield by train - but I failed this time. He looked a bit tired, I remember, as if he'd been working too hard lately, and I thought maybe that made him unwilling to talk much.
"Do you generally travel down on this train?" I asked him. That's usually a safe opening to a conversation, because either they do travel or they don't, and nine times out of ten they'll tell you why, and what hours they work, and what their work is. It's only human nature. But he just smiled and shook his head and said, "Not generally," which wasn't much help.
     Of course, I went on to talk about the train service in general, comparing this train with that, hut still he said nothing. He just
agreed with all I said, but he didn't seem to have any opinions ( his own. I told him I sometimes went up to the City by road, bit that didn't make him talk either. I didn't think it would, because you don't expect a fellow who lives in a cheap house to own a car.
Well, in the end, I had to give up. I'd told him a lot about myself! of course, so as to make things pleasant. I'd even boasted a little) about a rather nice bit of business I'd done that morning. I'\ always found that there's nothing as good as boasting to start! fellow talking. It makes him want to boast too. He seemed interested in a quiet sort of way, but it was no good. So I stopped talking and started to read my paper. And the next time I looked at him, he'd put his head back and gone off to sleep!
      We were just coming into the station then, and though the train) stopped rather suddenly, it didn't seem to wake him. Well, I'm a kind-hearted fellow and I wasn't going to let a Bardfield man be( carried on all the way to the next stop if I could help it. So I touched him sharply on the knee.
"Wake up, old fellow! We're there!" I said. He awoke at once and smiled at me. "Oh, so we are!" he said, and got out after me.
You know what the weather was like just then. When we came out of the station together it was quite dark and raining heavily. There was a wind blowing strong enough to knock you over, and it was bitterly cold. Well, what would you have done? The same as I did. I turned round and said to him:" Listen. There isn't a bus for a quarter of an hour. I've got my car in the station-yard, and if you're in one of those small houses I can take you there. It's on my way."
"Thanks very much," he said, and we walked through the water to where my old car was standing and off we went.
"This is very kind of you," he said as we started, and that was the last thing he said until we were halfway across the open country.
Then he suddenly turned round and said, "You can let me get out here."
"What, here?" I asked him. It seemed mad, because there wasn't a house within five hundred yards and, as I say, it was raining and blowing like the end of the world. But I slowed down, as anyone would.
The next thing that happened was that something hit me really hard on the back of the head. I fell forwards then everything went black. I can remember being pulled out of the and when I came to my senses aga was lying in the ditch with the rain pouring down on me with a bad headache, no car in sight and my pockets – as I found   out later - empty.
I pulled myself up at last and somehow managed to walk into Bardfield. I went straight to the police station, of course. It's the first building you reach if you come that way. And there I reported that someone had stolen my car, a new umbrella, a gold watch  and a hundred and fifty-two pounds ten shillings in notes.
   Of course, as soon as I got there I remembered who the man was; His picture was on the wall outside. I'd seen it every day for week. That's why his face reminded me of Bardfield. Under picture were some words: "Wanted for Robbery with Violence and Attempted Murder. John ———" Oh dear, I've forgotten the name again. I just can't keep names in my head. But that's the man. I tell you - I never forget a face.

Questions:
Answer the following questions : -1- What did the writer guess the traveller was ?2- How did the writer start a conversation with the stranger ?3- Why did the writer boast about a business he had done that morning ?4- How was the weather when the writer and the stranger got out of the station ?5- What did the writer do when the writer slowed down the car?



since and for


-  يأتي بعد since  نقطة زمنية تحدد بداية الحدث أما  for  يأتي بعدها مدة هذا الحدث.




ساعة12 o’clock            

a moment




شهر                   October
يوم                        Friday
فصلsummer                



two seconds / three minutes
 four hours / five days
six nights / seven weeks
Since
تاريخ              7thAugust
For
eight months/ one season

سنة2014                       

nine years

جملة ماضي بسيطI arrived  

ages

 ذلك الحين  yesterday /then

a long time

last ……………...

the last …………..