Wednesday 8 November 2017
Tuesday 26 May 2015
HOW BIG IS OUR UNIVERSE
As technology has evolved, astronomers are able to look back in time to the moments just after the Big Bang. This might seem to imply that the entire universe lies within our view. But the size of the universe depends on a number of things, including its shape and expansion. Just how big is the universe? The truth is, scientists can't put a number on it.
The observable universe
Astronomers have measured the age of the universe to be approximately 13.8 billion years old. Because of the connection between distance and the speed of light, this means they can look at a region of space that lies 13.8 billion light-years away. Like a ship in the empty ocean, astronomers on Earth can turn their telescopes to peer 13.8 billion light-years in every direction, which puts Earth inside of an observable sphere with a radius of 13.8 billion light-years. The word "observable" is key; the sphere limits what scientists can see but not what is there.
But though the sphere appears almost 28 billion light-years in diameter, it is far larger. Scientists know that the universe is expanding. Thus, while scientists might see a spot that lay 13.8 billion light-years from Earth at the time of the Big Bang, the universe has continued to expand over its lifetime. Today, that same spot is 46 billion light-years away, making the diameter of the observable universe a sphere around 92 billion light-years.
The observable universe
Astronomers have measured the age of the universe to be approximately 13.8 billion years old. Because of the connection between distance and the speed of light, this means they can look at a region of space that lies 13.8 billion light-years away. Like a ship in the empty ocean, astronomers on Earth can turn their telescopes to peer 13.8 billion light-years in every direction, which puts Earth inside of an observable sphere with a radius of 13.8 billion light-years. The word "observable" is key; the sphere limits what scientists can see but not what is there.
But though the sphere appears almost 28 billion light-years in diameter, it is far larger. Scientists know that the universe is expanding. Thus, while scientists might see a spot that lay 13.8 billion light-years from Earth at the time of the Big Bang, the universe has continued to expand over its lifetime. Today, that same spot is 46 billion light-years away, making the diameter of the observable universe a sphere around 92 billion light-years.
Thursday 21 May 2015
Ways to improve eye sight.
During the second world war, British propagandists circulated rumours that RAF pilots were such good night fliers because all the carrots they ate helped them to see in the dark. In reality the British were trying to keep their use of radar secret.
Yet it turns out that there is some truth to the idea that diet can affect our eyes. Retinal cells contain three yellow pigments – lutein, zeaxanthin and meso-zeaxanthin – which absorb near-ultraviolet light, protecting the eye from its damaging effects and reducing glare. These pigments are concentrated in the centre of the retina that produces the sharp central area of our vision, the macula. "It's like wearing internal sunglasses," says Billy Hammond of the University of Georgia in Athens. "It reduces the light intensity and absorbs scatter."
PHONE FOCOSSING FOR YOUR EYES
The lenses in our eyes get stiffer as we age, making it harder to focus on things that are close up. This is why people start to need reading glasses from their 40s onwards. Eventually, nearly everyone will own a pair. But it can be a pain putting on your glasses every time you look at your phone, for instance, assuming you can remember where you put them.
Glasses work by partly focusing light before it hits the eye – so if you are looking at a screen, why not make it do the focusing for you? A team at the Massachusetts Institute of Technology has shown that plastic screen covers can correct for all kinds of vision problems – effectively, the screen wears the glasses. But rather than making plastic covers tailored to individuals' eyes, the team want to exploit the ability of
Yet it turns out that there is some truth to the idea that diet can affect our eyes. Retinal cells contain three yellow pigments – lutein, zeaxanthin and meso-zeaxanthin – which absorb near-ultraviolet light, protecting the eye from its damaging effects and reducing glare. These pigments are concentrated in the centre of the retina that produces the sharp central area of our vision, the macula. "It's like wearing internal sunglasses," says Billy Hammond of the University of Georgia in Athens. "It reduces the light intensity and absorbs scatter."
PHONE FOCOSSING FOR YOUR EYES
The lenses in our eyes get stiffer as we age, making it harder to focus on things that are close up. This is why people start to need reading glasses from their 40s onwards. Eventually, nearly everyone will own a pair. But it can be a pain putting on your glasses every time you look at your phone, for instance, assuming you can remember where you put them.
Glasses work by partly focusing light before it hits the eye – so if you are looking at a screen, why not make it do the focusing for you? A team at the Massachusetts Institute of Technology has shown that plastic screen covers can correct for all kinds of vision problems – effectively, the screen wears the glasses. But rather than making plastic covers tailored to individuals' eyes, the team want to exploit the ability of
CONJUGATE BEAM METHOD(SLOPES ANDDEFLECTIONS)
2.The load on the conjugate beam is the M/EI diagram of the loads on the actual beam.
3.A simple support for the real beam remains simple support for the conjugate beam.
4.A fixed end for the real beam becomes free end for the conjugate beam.
5.The point of zero shear for the conjugate beam corresponds to a point of zero slope for the real beam.
6.The point of maximum moment for the conjugate beam corresponds to a point of maximum deflection for the real beam.
Supports of Conjugate Beam
Knowing that the slope on the real beam is equal to the shear on conjugate beam and the deflection on real beam is equal to the moment on conjugate beam, the shear and bending moment at any point on the conjugate beam must be consistent with the slope and deflection at that point of the real beam. Take for example a real beam with fixed support; at the point of fixed support there is neither slope nor deflection, thus, the shear and moment of the corresponding conjugate beam at that point must be zero. Therefore, the conjugate of fixed support is free end.
Real beam support and its corresponding conjugate beam support
Examples of Beam and its Conjugate
The following are some examples of beams and its conjugate. Loadings are omitted.
Wednesday 20 May 2015
TURBINES.
Spillways
Generating station construction and refurbishment
Turbines
Turbine type according to available head
Propeller up to 15 metres
Kaplan up to 30 metres
Francis 10 to 300 metres
Pelton 300 metres and over
Francis turbine
The Kaplan turbine is similar to the propeller turbine except that its blades are adjustable.
Pelton turbine
Turbines convert the energy of rushing water, steam or wind into mechanical energy to drive a generator. The generator then converts the mechanical energy into electrical energy. In hydroelectric facilities, this combination is called a generating unit.
Francis turbine
The most commonly used turbine in Hydro-Québec's power system. Water strikes the edge of the runner, pushes the blades and then flows toward the axis of the turbine. It escapes through the draft tube located under the turbine. It was named after James Bicheno Francis (1815-1892), the American engineer who invented the apparatus in 1849.
Kaplan turbine
Austrian engineer Viktor Kaplan (1876-1934) invented this turbine. It's similar to the propeller turbine, except that its blades are adjustable; their position can be set according to the available flow. This turbine is therefore suitable for certain run-of-river generating stations where the river flow varies considerably.
Each Kaplan turbine at Brisay generating station weighs 300 tonnes... That's the weight of 50 African elephants.
Propeller turbine
Since they can reach very high rotation speeds, propeller turbines are effective for low heads. Consequently, this type of turbine is suitable for run-of-river power stations.
Pelton turbine
Named after its American inventor, Lester Pelton (1829-1908), this turbine uses spoon-shaped buckets to harness the energy of falling
STRING THEORY
In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings.[1] String theory aims to explain all types of observed elementary particles using quantum states of these strings. In addition to the particles postulated by the standard model of particle physics, string theory naturally incorporates gravity and so is a candidate for a theory of everything, a self-contained mathematical model that describes all fundamental forces and forms of matter. Besides this potential role, string theory is now widely used as a theoretical tool and has shed light on many aspects of quantum field theory and quantum gravity.[2]
The earliest version of string theory, bosonic string theory, incorporated only the class of particles known as bosons. It was then developed into superstring theory, which posits that a connection – a "supersymmetry" – exists between bosons and the class of particles called fermions. String theory requires the existence of extra spatial dimensions for its mathematical consistency. In realistic physical models constructed from string theory, these extra dimensions are typically compactified to extremely small scales.
String theory was first studied in the late 1960s[3] as a theory of the strong nuclear force before being abandoned in favor of the theory of quantum chromodynamics. Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it a promising candidate for a quantum theory of gravity. Five consistent versions of string theory were developed until it was realized in the mid-1990s that they were different limits of a conjectured single 11-dimensional theory now known as M-theory.[4]
Many theoretical physicists, including Stephen Hawking, Edward Witten and Juan Maldacena, believe that string theory is a step towards the correct fundamental description of nature: it accommodates a consistent combination of quantum field theory and general relativity, agrees with insights in quantum gravity (such as the holographic principle and black hole thermodynamics) and has passed many non-trivial checks of its internal consistency.[citation needed] According to Hawking, "M-theory is the only candidate for a complete theory of the universe."[5] Other physicists, such as Richard Feynman,[6][7] Roger Penrose[8] and Sheldon Lee Glashow,[9] have criticized string theory for not providing novel experimental predictions at accessible energy scales.
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