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# MEG Fields

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## Amatullah Mamajiwala

on 7 January 2014

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#### Transcript of MEG Fields

FIELDS
Gravitational Fields
ELECTROMAGNETIC FIELDS
Magnetic Fields
Electric Fields
A theory originated to visualize the patterns of forces surrounding an object.
A region in which an object experiences forces exerted.
A medium to transmit and explain action-at-a-distance forces.
The electric force per unit positive charge.
Vector Quantity
Michael Faraday - 1st to introduce the concept of electric fields. [19th century]
Coloumbs Law:
Fe = (K* Q* q) /d^2

• K = 9.0* (10^9) N* m^2 /C^2 (constant),
• Q = electric force of one object (C),
• q = electric force of the other object (C), and
• d = distance between the two objects (m)
Newton's Universal Law of Gravitation:
F = (G*M*m)/d^2
G = 6.67* 10^-11 N*m^2 /kg^2
M = mass of the Earth (kg)
m = mass of the object (kg)
d = distance between their centers (m)

e = Fe/q
An electric field is viewed as a quantity which exists independently, whether or not a test charge q is present. Therefore, it can be represented without a test charge q.
SI unit is Newtons /Coloumb (N/C)
The closer the adjacent field lines - stronger the electric field.
Electric Field Lines
Negative q - converge in
These lines never cross!

A test q can have only one net force acting on it (multiple are not possible), in the direction of the electric field.
When charges are unequal, line density is not an accurate representation of the field strength.
Colours are used to indicate strength of the field.
For example, red is the strongest field and blue for the weakest.
Electrophoresis: A technique that uses Electric fields to separate large charged molecules.
How it works: Targets large molecules since many of them are charged and will move in the presence of electric field. When placed in a medium under the influence of an electric field, different types of molecules separate due to their unique charges and masses.
Electrophoresis is commonly used in DNA testing. It generates separate bands which act as a fingerprint unique to a person. Blood relatives will share some similarities in the band patterns.
Before the introduction of electrophoresis, DNA fragments were separated by gravity.
Human Body and Electric Fields
The human body is a good conductor of electricity. Under the influence of an A.C (alternating current), the electric charges inside the body can move back and forth at the same frequency as the field.
Electric fields can affect a body in three different ways:

weak currents can be induced in the body
electric charges can build up on the surface of your skin and hair
body's voltage can increase
These effects are in proportion to the intensity of the field.

The average electric field in an individual's home is 5 V/m.
At 1000 V/m, the electric field can be felt. Tingling sensation caused by moving hair on the skin surface and micro-discharges when coming in contact with metal.
The heart, like the brain, generates an ELECTROMAGNETIC field. The heart generates the LARGEST electromagnetic field in the body.
Bio-Electromagnetics
Study of electromagnetic field interaction with biological entities.
Law of Electromagnetic Induction:
CERN
An electric current is induced in a conductor when subjected to fluctuations in the magnetic field in a region near the conductor.
Magnet is being moved - magnetic field is changing.
Therefore, an electric current is induced. [the amp meter records the change in the current]
Magnet is held still - v=0m/s - magnetic field is constant.
Therefore, no electric current is induced. [ the amp meter's reading is at 0 A]
ELECTROSTATIC PRECIPITATORS
Control air pollution.
Capable of removing about 99% of the tiny particles of soot, ash and dust.
Used at large industrial facilities to remove tiny particles from the emission produced by burning fossil fuels.
Relies directly of the properties of electric fields to remove soot, ash and dust from the air.
Outer view
Inner view [between the plates]
Kingdom Anamalia - Electroreception
Many animals can detect weak electric fields.
For example,
Knifefish (Electric Eels)
Platypus and Echidnas
Due to the presence of electroreceptors.
Hammerheads have cells responsive to the weak electric fields (10^-6 N/C) created by the muscles of their moving prey.
The goby fish hides beneath the sand in small holes. Its electric field extends about 25 cm above the sand, giving its presence.
The hammerheads skim the sandy ocean floors and once it detects the goby, due to its movements and breathing, the shark will swim in a figure-8 pattern to centre in on its location.
Knifefish' electric field
watch from 0.55 s to 1.33
Electric Eels produce 600V of electricity. It lives in muddy waters and has poor vision. Hence, it relies on low-level electric fields for navigation and hunting.
High levels of voltage are produced to protect itself from predators or to stun or kill prey.
Electric Potential:
The energy stored between q1 and q2.

Ee = (k*q1*q2) / r

There are many similarities between the two laws:
Both are inverse square laws that are also proportional to the product of another quantity.
The forces (action-at-a-distance) act along the line joining the two centers.
Distance is measured from the centers of the masses or charges.
This is not a coincidence, it just implies that Coloumbs law and the Universal law of Gravitation are related (intertwined) but NOT the SAME.
The
magnitude of an electric field
can be expressed in terms of potential difference per unit radius:
The
potential difference
between q1 and q2 in an electric field is:
Tumour Treating Fields : New Frontier in Cancer Therapy
The use of electric fields to disrupt cancer cells from division.
Two processes of Cell division:
Mitosis (somatic cells)
Miosis (gametes a.k.a sex cells)
Indicates Prometaphase, where the polymerization is disrupted.
Low intensity electric fields are used. Frequency depends on the type of the cell being treated.
When a cancer cell undergoes cell division (mitosis/miosis), the electric fields do not let the microtubule spindles to form. [PROMETAPHASE is not carried out properly]. Polymerization, the formation of chains of molecules, is undone and hence the cell cannot divide properly.
The artificial electric field is created around the cell, causing the microtuble spindles and the chromosomes to get ionized and aligned in columns
End result: lysis (cell death) or apoptosis (programmed cell death)
CERN - European Organization for Nuclear Research
They use the world's largest and most complex scientific instruments to study the basic constituents of matter - the fundamental particles. The particles are made to collide together at close to the speed of light.
Their main devices are particle accelerators and detectors
What are accelerators?
The accelerator complex at CERN is a succession of machines that accelerate particles to increasingly higher energies. Each machine boosts the energy of a beam of particles, before injecting the beam into the next machine in the sequence.
The accelerator is a machine that provides energetic particles to investigate the structure of the atomic nucleus.
The accelerators generates electric fields to accelerate particles and magnetic fields to steer the particles in a certain direction
Last part of the accelerator chain.
In the Booster - stage 2 of the process,
watch 1:23 to 1:55
More speed = more energy = stronger magnetic field needed to bend the beam (in circular accelerators, dipole magnets are used to keep it from travelling straight.) Electromagnets around particle detectors generate a magnetic field.
The LHC is used to separate protons and heavy lead ions
An Electric field is used to strip off the electron from an hydrogen ion.
Then the fields switch between + and - charge thus making the protons move along the accelerator.
Radiofrequency cavities are metallic chambers placed around the accelerator. Whenever a beam passes the electric field in the RF cavity, some energy from radio waves are gained by the beam thereby increasing the speed.
The area around a magnet in which magnetic forces are exerted.
Vector Quantity
Represented by
The distance between adjacent field lines indicate the strength of the field lines
16th century - Sir William Gilbert, an English physicist, first to devise a model to describe Earth's magnetic field.
Earth's magnetic field is compared to the magnetic field around a bar magnet
Angle of declination
Angle of inclination: The dip between the Earth's magnetic field and the horizontal.
Measured with a magnetic dipping needle.
Earth's magnetic field is changing at a slow rate. The angles of inclination and declination are, thus, revised periodically.
Principle of Electromagnetism: Moving electric charges produce a magnetic field.
Numerous unsuccessful attempts have been made to unify the gravitational and electromagnetic interactions into a unified, single interaction.

However, to the extent of our current knowledge, the two interactions are not related and so, must be treated by separate, distinct "laws".

Hans Christian Oersted observed movement in a magnetic compass needle by an electric current flowing threw a wire.
Right-Hand Rule for a Straight Conductor
In curled loops, the field lines inside the loops are closer - indicating a stronger magnetic field.
Electrostatic Equilibrium: the condition established by charged conductors in which the excess charge has optimally distanced itself so as to reduce the total amount of repulsive forces.
For example, If one were to add electrons to a conductor in a region with no net electric field, the excess electrons will redistribute themselves on the surface of the conductor until equilibrium is reached [no net force].
Then, none of the charges will experience a net force - The electric field inside the conductor must be zero!
The electric field is perpendicular to the surface of the conductor.
Applicable for a single loop
Magnetic Fields in Multiple Loops
Right-Hand Rule for a Solenoid
If a solenoid is grasped in the right hand, with the fingers
curled in the direction of the electric current, the thumb
points in the direction of the magnetic field lines in its core.
Right hand rules for both are consistent when pointing the thumb along or tangent to the curved wire of the coil.
Magnitude of Magnetic Fields
FM - Magnitude of the force on the moving particle, N.
q - charge on the moving particle, C
v - velocity of the moving particle, m/s
B - magnitude of field strength, T
Theta - angle between v and B, degrees
SI unit is Tesla (T); 1T =1 kg/ C*s
This equation just specifies the magnitude of the force.
For direction of the force use:
Right-Hand Rule
If the thumb points in the direction of the motion of a +q, and the extended fingers point in the direction of the magnetic field, the force is in the direction in which the right palm would push.
Note: In case of a -q, reverse the direction of the thumb. (motion of a -ve charge is equivalent to the motion of a +ve charge in the opposite direction.)
Yamato 1 -1st ship to apply the right hand principle for magnetic force
Instead of using propellers, it uses Magnetohydrodynamics propulsion
Using Newton's 3rd law, if the water is pushed out, the force exerted on the water will act on the boat in the opposite direction. Causing the boat to be propelled forward.
How it works:
2 large metal parallel plates are connected on either side of the unit, a DC electric generator creates a large potential difference across them.
Thereby creating a current through seawater, which is perpendicular to the magnetic force.
Using the right-hand rule, in the direction of the palm's push, the boat pushes seawater out from the back.
Magnetohydrodynamics (MHD)
MHD Propulsion PROS:
Inexpensive device
Low noise levels
Low maintenance costs
Branch of physics studying the interaction of electrically conducting fluids with magnetic fields, through electromagnetic forces called "Lorentz forces".
Fm is always perpendicular to v, so it acts as a deflecting force. Therefore only affecting direction, not its magnitude.
In some cases.....
when the magnetic force is the only force acting on the particle, this force = net force on the particle.
Recall, Fm is perpendicular to v, hence in an ideal situation the particle will move in uniform circular motion, as long as the field is strong enough and that the particle does not lose any energy.
Uniform Circular Motion!!!!
British Scientist - J.J. Thomson
With the use of electric and magnetic fields, Thomson concluded that cathode rays consist of fast moving negatively charged particles which travel from the cathode to the anode.
A.K.A Electrons
Case 1: A current in a coil can induce a magnetic field, which can deflect electrons along a circular path - Resulting in hitting X
B can be calculated using physical dimensions of the coil and I (current). r can be measured directly.
Case 2: With no current flowing and with a potential difference applied to both plates, the electron gets deflected to Y.
Case 3: Current and a magnetic field is present + potential difference of the plate = electric and magnetic field cancel out
Electron hits Z!
Only when FM = Fe
Charge to Mass ratio for an electron
Magnetic field effects
When electrons are not moving perpendicular to the magnetic field lines, the parallel component of the velocityto the lines remains unaffected while, the perpendicular component rotates.
spiraling motion
In case of a non-uniform magnetic field which increases in magnitude in the direction of the motion of the electron, the Fm will cause the electron to slow down. [initially parallel component is reduced] The spiraling motion can be reversed and cause a magnetic mirror.
Auroras
Charged particles from cosmic rays
Enter
's atmosphere
down, towards the poles (higher magnetic concentration)
Gets trapped in spiral orbit
Field strength is stronger at the poles, causing aurora borealis (Northern Hemisphere) and aurora australis (Southern Hemisphere)
Van Allen Belts
Earth has two major radiation belts
The intensity of the radiation in these belts is very high, making it possible to damage sensitive electronic equipment in satellites.
Outer belt - 25500 km above the surface of the Earth
Inner belt - 12500 km above the surface of the Earth
Thermonuclear fusion
Given the risk involved in generating power through nuclear reactors and the depleting reserves of radioactive elements, the scientists across the world are working towards the area of thermonuclear fusion.
Tokamak Nuclear-fusion reactors with a toroidal shape uses the magnetic fields to contain hot, highly ionized gases (plasmas) needed for a thermonuclear reaction.
In the Tokamak, 2 superimposed magnetic fields enclose the plasma: this is the toroidal field generated by external coils on the one hand and the field of a flow in the plasma on the other hand.
Magnetic fields are used for confinement since no solid material could withstand the extremely high temperature of the plasma
If the thumb points in the direction of the current (positive q) and the extended fingers point in the direction of the magnetic field, the force is in the direction which the right palm pushes.
Right-Hand rule for the Motor Principle
Calculating the force acting on a conductor:
Very similar to the magnetic force on a single point charge.
I - Current, Amps
l - length of the conductor in the magnetic field, m
B - magnitude of the strength of a magnetic field, T
theta - angle between conductor and the magnetic field lines
Electric motors involve rotating coils of wire which are driven by the
magnetic force
exerted by a
magnetic field
on an
electric current
. They transform electrical energy into mechanical energy.
Cheap
Easy to repair
Emissions-free
Low maintenance
Maglev Trains
~The flying train~
Electromagnetic force levitates the train, eliminating wheels-on-rails friction.
Superconducting electromagnets induce currents in coils beneath the train.
The currents set up magnetic fields which oppose the downward motion of the train, thus lifting it above the rails
Electromagnetic forces are used for forward and backward motion.
Energy Consumption
ICE
- InterCity Express Train in Germany
Transrapid
- Maglev
On the basis of the graph, Maglev uses considerably less energy than an ICE at both 200 kph and 300 kph. At 400 kph, a speed that an ICE cannot obtain.
CO2 Emissions
ICE
- InterCity Express Train in Germany
Transrapid
- Maglev
Results show:
At 300 kph Maglev emissions are significantly less than that of a ICE, primarily due to a lower energy usage.
At 400 kph, a speed at which ICE cannot achieve, the CO2 emissions of Maglev are high.
However this emission level is still half that of a traditional automobile, and is five and three quarters times more efficient than a short haul airliner flight.
Noise pollution
Maglev has no noise problems from friction between trolley and pantograph, nor from rolling friction. the only source of noise pollution from it is aerodynamic noise.
Financial Aspect
Construction Costs: High
[\$27 billion approx. to build]
Maintenance Costs: Low
[operation and maintenance costs are lower than traditional high-speed trains.
At the speeds of 480 kph (300mph) it generates 100 decibels of sound a distance of 24 meters
exposure to 90-95 dB of sound for a long period of time can result in hearing loss.
BUT...
MRI
Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body.
a space which surrounds an object on which the force of gravity exists.
Strength of the Gravitational Field
Closer the objects are to large masses, the stronger the force experienced.
Denser field lines indicate a stronger field
Field points inward
Expressed in terms of the mass of the central body: FG and Fg are equated
FG = Fg
The magnitude of FG strength on Mars is only 0.375 of that of Earth.
If a straight conductor carries a current of 80.0 A through a uniform 0.30-T magnetic field. The magnitude of the force on the conductor is 14.0 N and the angle between the current and the magnetic field is 76.0°. Calculate the length of the conductor.
Lenz's law
Heinrich Lenz - In attempt to find the direction of the induced current by applying the law of conservation of energy and the law of electromagnetic induction
His law states: When a current is induced in a coil by a changing magnetic field, the electric current's direction is such that its own magnetic field opposes the change that produced it.
not possible - violates the law of conservation of energy
Possible - obeys the law of conservation of energy
ABS was found to reduce the number of rear-end collisions by 1-38% and single-vehicle accidents by 10-33%
Statistics also show that induction cooking saves 20% of energy for the same amount of transferred heat
Economically friendly
Easy to clean!
Pot recognition feature - Safer Cooking
In 2012, Canadians underwent 1.7 million magnetic resonance imaging (MRI) exams
How it works:
0.25s to 1.50s
MRI's are used for detecting:
Abnormalities of the brain and spinal cord
Tumors, cysts, and other abnormalities in various parts of the body
Injuries or abnormalities of the joints
Certain types of heart problems
Diseases of the liver and other abdominal organs
Causes of pelvic pain in women (e.g. fibroids, endometriosis)
Suspected uterine abnormalities in women undergoing evaluation for infertility

Some of the risks involved
The magnet may cause implanted medical devices that contain metal to malfunction or heat up during the exam.
Any loose metal object may cause damage or injury if it gets pulled toward the magnet.
Dyes from tattoos or tattooed eyeliner can cause skin or eye irritation.
Medication patches can cause a skin burn.
Medical Application - LINAC + MRI
Watch from 0.44s onwards
Great amount of matter packed into a very small area
Has the strongest gravitational field due to which, even light cannot escape it.
BLACK HOLES
Telescopes with x-rays, light, or other forms of electromagnetic radiation
CANNOT
detect
Black Holes.
FG holds all things on Earth together. The sun's FG is one factor which keeps all planets in orbit
Waves: the moon's gravity pulls and pushes water, creating waves.
Water
Distribution of nutrients in the water, allowing marine life to thrive
Soil
When plants or parts of them die, they fall down. This allows the soil regains its nutrients.
Plants as well as animals scatter pollen to allow for germination to occur. If gravity did not exist, then all pollen would remain suspended in the atmosphere.
Essence of life
Circle of life
Importance of FG
FG =Fg
GOCE - Gravity field and steady-state Ocean Circulation Explorer
ESA's mission was launched on 17 March 2009 and ended on 11 November 2013.
The value of 'g' varies subtly from place to place (due to the rotation of Earth, the position of mountains and ocean trenches and variations in density of Earth's interior),

GOCE mapped these variations in the gravity field with extreme detail and accuracy.

This resulted in a unique model of the 'geoid', (surface of equal gravitational potential defined by the gravity field – crucial for deriving accurate measurements of ocean circulation and sea-level change, both of which are affected by climate change).
Equipped with 3 ultra sensitive accelerometers arranged in 3-dimensions to take precise reading of the gravitational field.
This allows GOCE to take six simultaneous measurements of the gravity field
Force of gravity - General Relativity
Electric Force - Quantum Mechanics
Unifying these forces has been a mystery even before Einstein's death.
String Theory : Theory that all matter at quantum level is composed of tiny vibrating strings of energy. These strings unify all the forces.
Geodesy
Studying the geoid with satellites like GOCE, will allow:
navigate satellites with much higher accuracy
scientists to much more accurately infer the Earth's internal structure and at finer resolution than was ever before possible from Space.
Ocean scientists can combine this gravity model with ocean height measurements from satellite altimeters to study global ocean circulation on a finer scale than has been previously possible.

Better understanding of the processes that drive the Earth's dynamic system (solid Earth, ocean and atmosphere), thus leading to better analysis and predictions of climate change & natural hazards (e.g., Earthquakes).
Gravitational Field effects on Human Health
Studies from NASA show:
Increased levels of bone loss
Increased risk of cancer (cosmic rays)
Low immune system
Increased levels of bone loss
Bone density remains less than normal in flights up to 84 days and the most significant bone loss occurs in the lower bones that would normally bear more weight.
Increased risk for cancer
High exposure to Cosmic rays from the sun increase the risk of cancer.
The Earth's FG protects us from the sun's cosmic rays, but as the distance from the Earth increases, the field gets weaker.
Low Immune system
The stresses of spending time in space can weaken the immune system's ability to protect itself against disease, and activate dormant viruses present in the body. Latent viruses have been linked to the development of cancer.
Just as a lack of weight-bearing exercise on Earth can add to the chances of developing osteoporosis, bone loss is a problem for astronauts spending months or years in a weight-less environment.
Vector Quantity
Test Question:
Test Question:
What is the magnitude of the surface gravitational acceleration of Planet X whose mass is 0.25 times the mass of Earth and radius is 0.95 times that of Earth. State as a multiple of Earth's surface g
Test Question:
A 8.0X10^3 kg satellite above Earth's surface experiences a FG strength of 4.5 N/kg. Determine:
Distance from the Earth's surface
Magnitude of the gravitational force on the satellite
Test Question:
The magnitude of FE between 2 small charged objects is 6.0X10^-6 N. Calculate the FE when:
d is double, while charges remain same
q1 is doubled and q2 is tripled
all above changes occur simultaneously
Cyclotron
Not all accelerators are linear. The cyclotron is a circular particle accelerator.
Watch for 2:41 seconds
Medical Physics
Magnetoencephalography
Non-invasive neurophysiological technique that measures the magnetic fields generated by neuronal activity of the brain
Has a very high temporal resolution
Has excellent spatial resolution but it is not as reliable as that of positron emission tomography (PET) or functional magnetic resonance imaging (fMRI), MEG has much higher temporal resolution.
Used for:
presurgical functional mapping of important brain functions, such as tactile sensation, motor function, and language.
localization of epileptic foci in epilepsy surgery patients.
Glioblastoma multiforme is the most deadly of all brain tumors. Standard therapy often does not provide a cure and causes side effects that diminish quality of life.
Approximately 5 out of every 100,000 Americans are diagnosed each year with glioblastoma, according to the American Brain Tumor Association.
TTF for Brain Tumors
Brain tumor cells have different electrical properties than healthy cells, the healthy cells are spared from damage
Advantage of using TTF for treating Brain Tumors:
Compiled by: Amatullah. Mamajiwala
EP-MRSI
Echo-Planer Magnetic Resonance Spectroscopic Imaging
It uses low-intensity magnetic fields to produce three-dimensional images of the brain's chemistry, which reveal various abnormalities in its nerve-cell activity. The specific timing and amplitude of the magnetic pulses induce electric fields that may match the natural electrical firing rhythm of brain cells
As the pulses travel right and left in the wires, it is thought to restore the balance between the two halves of the brain.
In January 2004, The American Journal of Psychiatry published the experimental results of EP-MRSI on 30 bipolar disorder subjects. Significant mood improvements were found.
Extension on EP-MRSI
Transcranial Magnetic Stimulation
TMS
Involves holding a figure-of-eight-shaped wand near a person's head. Two coils of wire on the wand generate a strong magnetic field that induces electric currents in brain cells.
Electric fields induced by TMS are 1-500 V/m, much stronger than EP-MRSI at 0.7 V/m.
Some patients reported feelings of discomfort after the TMS treatment.
Risks associated with TMS
Scalp discomfort at the site of stimulation
Tingling, spasms or twitching of facial muscles
Discomfort from noise during treatment
Seizures
Mania, particularly in people with bipolar disorder
Hearing loss due to inadequate ear protection during treatment
BLUE - Indicates uncommon risks
Why choose EP-MRSI or TMS?
The electric fields are better medicine than drugs. Anti-depressants can have disturbing side effects:
fatigue
anxiety
loss of libido
increased blood pressure.
They usually take weeks to work, and sometimes they don't work at all.
Electrophoresis for DNA analysis in forensic science
In gel electrophoresis, DNA strands from crime scenes, victims or suspects are applied to an agarose gel that is subjected to an electric potential.
Faster and requires less DNA.
In capillary electrophoresis, a fused silica capillary is used instead of a gel slab, more frequently used in DNA electrophoresis. Both apply the same principles of separation, however capillary electrophoresis is
more rapid and has a higher resolution
.
About 25% of violent crime cases in the U.S. since 1989, however, have in fact resulted in the exoneration of suspects because of DNA profiling procedures.
This is how the Van de graff cage works. The person inside is safe as there is no electric field present inside the cage which acts as a conductor.
LIGHT
X-RAYS
Employed to diagnose broken limbs after accidents
Benefits:
noninvasive
guides medical personnel as they insert catheters, stents, or other devices inside the body
painless
On the electromagnetic spectrum below Gamma rays
Natural and man-made electromagnetic wave (at times behaves as a particle)
Transmission of energy through a vacuum or using no medium is accomplished by electromagnetic waves, caused by the oscillation of electric and magnetic fields.

speed of light 3x108 m/s.
Therefore, they are called electromagnetic radiation, light, or photons.
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