2017

This is no more a new outbrake in the world of science has there is a very vast growth and improvement in the human knowledge, especially in the science world.
Now is the great and mind blowing quest of the human head exchange which is been insinuated by the Italian neuroscientist Sergio Canavero.

A head transplant is an experimental surgical operation involving the grafting of one organism's head onto the body of another.

To have a better grasp of what the human head consist of, we need to go into details of the head and neck anatomy, for a better view of its complexity.
the human head and neck of any animal comprises the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat, imagine all of these things to be joined together by human knowledge.
History as in its record that head transplant has been on the slate of neuroscience for a very long time that Alexis Carrel was a French surgeon who had developed improved surgical methods to connect blood vessels in the context of organ transplantation and In 1908 he collaborated with the American Charles Claude Guthrie to attempt to graft the head of one dog on an intact second dog; the grafted head showed some reflexes early on but deteriorated quickly and the animal was killed after a few hours. Carrel's work on organ transplantation later earned a Nobel Prize; Gurthrie was probably excluded because of this controversial work on head transplantation.

In 1954, Vladimir Demikhov, a Soviet surgeon who had done important work to improve coronary bypass surgery, performed an experiment in which he grafted the head and upper body including the front legs, onto another dog; the effort was focused on how to provide blood supply to the donor head and upper body and not on grafting the nervous systems. The dogs generally survived a few days; one survived 29 days. The grafted body parts were able to move and react to stimulus. The animals died due to transplant rejection.

In the 1950s and '60s immunosuppressive drugs were developed and organ transplantation techniques were developed that eventually made transplantation of kidneys, livers, and other organs standard medical procedures.

In 1965 Robert J. White did a series of experiments in which he attempted to graft only the vascular system of isolated dog brains onto existing dogs, to learn how to manage this challenge. He monitored brain activity with EEG and also monitored metabolism, and showed that he could maintain high levels of brain activity and metabolism by avoiding any break in the blood supply. The animals survived between 6 hours and 2 days. In 1970 he did four experiments in which he cut the head off of a monkey and connected the blood vessels of another monkey head to it; he did not attempt to connect the nervous systems. White used deep hypothermia to protect the brains during the times when they were cut off from blood during procedure. The recipient bodies had to be kept alive with mechanical ventilation and drugs to stimulate the heart. The grafted heads were able to function - the eyes tracked moving objections and it could chew and swallow. There were problems with the grafting of blood vessels that led to blood clots forming, and White used high doses of immunosuppressive drugs that had severe side effects; the animals died between 6 hours and 3 days after the heads were en-grafted. These experiments were reported and criticized in the media and were considered barbaric by animal rights activists. There were few animal experiments on head transplantation for many years after this.

In 2012 Xiaoping Ren published work in which he grafted the head of a mouse onto another mouse's body; again the focus was on how to avoid harm from the loss of blood supply; with his protocol the grafted heads survived up to six months.

In 2013 Sergio Canavero published a protocol that he said would make human head transplantation possible.

In 2015 Ren published work in which he cut off the heads of mice but left the brain stem in place, and then connected the vasculature of the donor head to the recipient body; this work was an effort to address whether it was possible to keep the body of the recipient animal alive without life support. All prior experimental work that involved removing the recipient body's head had cut the head off lower down, just below the second bone in the spinal column. Ren also used moderate hypothermia to protect the brains during the procedure.

In 2016 Ren and Canavero published a review of attempted as well as possible neuroprotection strategies that they said should be researched for potential use in a head transplantation procedure; they discussed various protocols for connecting the vasculature, the use of various levels of hypothermia, the use of blood substitutes, and the possibility of using hydrogen sulfide as a neuroprotective agent but its insignificant successes kept it swept under the carpet, and now December 2017 marks it all, when the first human head transplant will take place,and this would be done on a 30-year-old Russian man, Valery Spiridonov, volunteered for the procedure in the hope of living a more normal life. The computer scientist suffers from a rare motor neuron disease known as Werdnig-Hoffmann Disease. The disease causes motor neurons – the nerve cells responsible for sending signals from the central nervous system to your muscles – to deteriorate, which leads to muscle atrophy and in severe cases, difficulty swallowing and breathing. Currently there is no treatment for this disease.

“When I realized that I could participate in something really big and important, I had no doubt left in my mind and started to work in this direction,” Spiridonov, a Russian computer scientist, told Central European News (CEN). “The only thing I feel is the sense of pleasant impatience, like I have been preparing for something important all my life and it is starting to happen.”

watch video here .

Human Head Transplant

Unknown Wednesday, 25 October 2017

X -RAYS

Discovery of X-rays

Discovered in late 1895 by a German physicist, W. C. Roentgen was working with a cathode ray tube in his laboratory. Production of X-rays

An X-ray tube is a vacuum tube designed to produce X-ray photons. The Crookes tube is also called a discharge tube or cold cathode tube. A schematic x-ray tube is shown below.

The glass tube is evacuated to a pressure of air, of about 100 pascals, recall that atmospheric pressure is 106 pascals. The anode is a thick metallic target; it is so made in order to quickly dissipate thermal energy that results from bombardment with the cathode rays. A high voltage, between 30 to 150 kV, is applied between the electrodes; this induces an ionization of the residual air, and thus a beam of electrons from the cathode to the anode ensues. When these electrons hit the target, they are slowed down, producing the X-rays. The X-ray photongenerating effect is generally called the Bremsstrahlung effect, a contraction of the German “brems” for braking, and “strahlung” for radiation. The radiation energy from an X-ray tube consists of discrete energies constituting a line spectrum and a continuous spectrum providing the background to the line spectrum.

Properties of X-rays
i. X-rays travel in straight lines.
ii. X-rays cannot be deflected by electric field or magnetic field.
iii. X-rays have a high penetrating power.
iv. Photographic film is blackened by X-rays.
v. Fluorescent materials glow when X-rays are directed at them.
vi. Photoelectric emission can be produced by X-rays.
vii. Ionization of a gas results when an X-ray beam is passed through it.

Continuous Spectrum

When the accelerated electrons (cathode rays) strike the metal target, they collide with electrons in the target. In such a collision part of the momentum of the incident electron is transferred to the atom of the target material, thereby losing some of its kinetic energy, ∆K. This interaction gives rise to heating of the target. The projectile electron may avoid the orbital electrons of the target element but may come sufficiently close to the nucleus of the atom and come under its influence. The loss in kinetic energy reappears as an x-ray photon. During deceleration, the electron radiates an X-ray photon of energy.

, The resulting spectrum is continuous but with a sharp cut-off wavelength. The minimum wavelength corresponds to an incident electron losing all of its energy in a single collision and radiating it away as a single photon. If K is the kinetic energy of the incident electron, then

Because of the large accelerating voltage, the incident electrons can

(i) Excite electrons in the atoms of the target.

(ii) Eject tightly bound electrons from the cores of the atoms.

Characteristic X-Ray Spectrum

Excitation of electrons will give rise to emission of photons in the optical region of the electromagnetic spectrum. However when core electrons are ejected, the subsequent filling of vacant states gives rise to emitted radiation in the x-ray region of the electromagnetic spectrum. The core electrons could be from the K-, L- or M- shell. If Kshell (n=1) electrons are removed, electrons from higher energy states falling into the vacant K-shell states, produce a series of lines denoted as Kα, Kβ ,... as shown in the Figure below. Transitions to the L shell result in the L series and those to the M shell give rise to the M series, and so on. Since orbital electrons have definite energy levels, the emitted X-ray photons also have well defined energies. The emission spectrum therefore has sharp lines characteristic of the target element.

X–Ray Transitions

The graph shows the following features:

A continuous background of X-radiation in which the intensity varies smoothly with wavelength. The background intensity reaches a maximum value as the wavelength increases, and then the intensity falls at greater wavelengths. The minimum wavelength depends on the tube voltage. The higher the voltage the smaller the value of the minimum wavelength. The sharp peaks of the intensity distribution occur at wavelengths that is independent of the change in the tube voltage. X-Ray Diffraction A plane of atoms in a crystal, also called a Bragg plane, reflects X-ray radiation in exactly the same manner that light is reflected from a plane mirror.

Reflection from successive planes can interfere constructively if the path difference between two rays is equal to an integral number of wavelengths. (This statement is called Bragg‟s law).

Thus, the condition for constructive interference to occur is

nλ = 2a

but, from trigonometry, we can figure out what the distance 2a is in terms of the spacing, d, between the atomic planes.

a = d sin θ

or 2a = 2 d sin θ

thus, nλ = 2d sin θ

This is known as Bragg's Law for X-ray diffraction.

What it says is that if we know the wavelength ,λ , of the X-rays going in to the crystal, and we can measure the angle θ of the diffracted X-rays coming out of the crystal, then we know the spacing (referred to as d-spacing) between the atomic planes.

d = nλ /2 sin θ

Again it is important to point out that this diffraction will only occur if the rays are in phase when they emerge, and this will only occur at the appropriate value of n (1, 2, 3, etc.) and θ.

In theory, then we could re-orient the crystal so that another atomic plane is exposed and measure the d-spacing between all atomic planes in the crystal, eventually leading us to determine the crystal structure and the size of the unit cell.

Moseley’s Experiment

The high intensity penetrating radiation emitted by X-ray tubes, characteristic of the metal from which the target anode is made, was first discovered by Barkla. Changing the metal or element from which the target anode in the X-ray tube is made alters the wavelengths at which the high intensity peaks occur. The most penetrating series in an element‟s characteristic X-ray spectrum is called the K series; the second is called the L series; the third the M series and so on. Moseley carried out a systematic examination of the characteristic radiation of as many elements as possible. Moseley discovered a simple empirical relationship between the frequencies, (ν) of the lines in each series and the ordinal number, Z, of the element‟s position in the periodic table (starting from hydrogen):

v = frequency of characteristic radiation
b = constant which is different for different series
a = constant known as screening constant and is different for different series,

and

are principal quantum numbers
For Kx line, b was found to be equal to (¾)R, where R is Rydberg constant and „a‟ was found to be practically a = 1, hence for Kα line

Equation (1) is known as Moseley law or Moseley equation.

The exact form of Moseley law is

where

is a correction factor and

and

are the principal quantum numbers of the energy levels between which the transition occur.

The square root

of the frequency of an element‟s K line as a function of the ordinal number, N, of its position in the periodic table.

Moseley formed the opinion that some physical attribute of the atom must increase by (a) regular fixed amount, from one element to the next, rising through the periodic table. He postulated that this could only be the atom‟s nuclear charge. According to this hypothesis, the number N, that is the element‟s ordinal position in the periodic table, is equal to the number of natural units of positive electricity carried by the nuclei of the element, i.e., N=Z . The number Z is now called the atomic number of the element; it is equal to the number of protons in the element‟s nuclei. Prior to Moseley‟s investigation, the elements were arranged in the periodic table in the ascending order of their atomic weights and on the basis of their chemical properties. As a result of Moseley‟s researches, which provided the first direct means of determining an element‟s atomic number, inaccuracies in the periodic table were discovered and corrected.

Example 1

Find the minimum wavelength of X-rays produced by an X-ray tube operated at 1000 kV. If

Example 2

If the potential difference applied across an X-ray tube is 5kV and the current flowing through it is
2 mA, calculate
i. The number of electrons striking the target per second
ii. The speed at which they strike

Solution
i.

, where n is the number of electrons striking the anode per second.

ii. If ν is the velocity of striking electrons

Example 3

The spacing between the principal planes of a NaCl crystal is 2.82 Å. It is found that the first order Bragg reflection occur at an angle of 10˚. Calculate the wavelength of X-rays.

Solution:
According to Bragg”s law

X -RAYS

Unknown Saturday, 23 September 2017