dept. of biophysics and cell biology...• a wavelength (called de broglie wavelength) can be...
TRANSCRIPT
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University of Debrecen, Faculty of Medicine
• Dept. of Biophysics and Cell Biology
director: György Panyi, M.D., PhD., professor
• Biophysics Division (1st semester)
head: Péter Nagy, M.D., PhD., professor
• Biomathematics Division (1st and 2nd semester)
head: László Mátyus, M.D., PhD., professor
• Cell Biology Division (2nd semester)
head: György Vereb, M.D., PhD., professor
General Educational manager: Enikő Nizsalóczki
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What is biophysics as a branch of science?
• An interdisciplinary science
• Provides a quantitative description of the physical principles of biology
and medicine
• What did biophysics give to medicine?
A. Understanding the operation of cells, tissues and organs at the
molecular level, e.g. functioning of the nervous system, role of ion
channels in action potential)
B. Understanding the pathomechanism of diseases, e.g. formation of
amyloid plaque in Alzheimer’s disease
C. Development of therapeutic approaches, e.g. photodynamic therapy,
ultrasound therapy)
D. Development of novel diagnostic tools: e.g. ECG, MRI, PET
A. C. D.
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Energy and force
Attraction
Kinetic energy -
motion
Machines and
instruments
Varieties of molar
motion (pertaining to a
body of matter as a
whole, as contrasted with
molecular and atomic)
What does biophysics give a medical student?
1964
Long time ago:
• physics was taught as a part of universal
science
Now:
• Science and university education got
• specialized
• practice-oriented
• student-oriented
• Biophysics teaching follows these changes
• Aims nowadays
• way of thinking: almightiness of natural
laws
• scientific rigor: be doubtful about
pseudoscience
• explanation of physiological and
pathological processes, and diagnostic
methods
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What is biophysics like? What are biophysicists like?
• Accurate, punctual (numbers have
meaning ! )
• physicist: interested in the 10th
decimal
• chemist: interested in the magnitude
• biologist: interested in whether
something increases or decreases
• Simplification, abstraction
???
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What do you get from studying biophysics?
• Introduction to natural sciences
• Medical physics (e.g. physical principles of diagnostic procedures)
• Molecular biophysics (e.g. diffusion, membrane biophysics)
• Organ biophysics (e.g. vision, hearing, circulation)
• Link to other subjects
• Physiology
• Clinical physiology
• Radiology
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• Make sense of what you learn
• How is it connected to previous
knowledge? How do you expect it to
be linked to future courses?
• Begin learning In time
• „I took a speed-reading course
and read War and Peace in
twenty minutes. It involves
Russia." - Woody Allen
This will be insufficient on
the exam
• You learn for yourself not for others, not to show off, not to put the
other one down, learning is your secret, it is all you have, it is the
only thing you can call your own. Nobody can take it away…
(Louise Bourgeois)
How to study at the university? How to study biophysics?
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Classes
GM DENT
Biophysics lectures AOBIF05T1
• lectures: 2 h. weekly, w. 1-14
• seminar, 2 h. weekly, w. 1-14
FOBIF09D1
• lectures: 2 h. weekly, w. 1-13
• seminar, 2 h. weekly, w. 1-13
Biophysics Practical AOBIF06T1
• labs, 3 h. every 2 weeks
• total of 6 labs, weeks 1-14
FOBIF10D1
• labs, 3 h. every 2 weeks
• total of 4 labs, weeks 3-14
Seminar room F102
Biophysics lab F401
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Office hours of the education manager (Dr. Enikő Nizsalóczki) from the 2nd week:
• Three times in a week, in the seminar room of the Department of Biophysics and
Cell Biology, Life Science Building, seminar room F.402
• At the same time for foreign and Hungarian students.
• Exceptions: There will be no office hours on the 1st week!
• Other exceptions and changes will be posted on the Elearning site
Monday 10:00-10:45
Thursday 15:45-16:30
Friday 14:00-14:45
Life Science Building
Ground floor
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Contacting the Manager of Education
• The primary tool for contacting the Department is the e-mail:
Advantages:
• If your problem (or question) can be solved by e-mail, you don’t need to go to the
office hours.
• Besides posting on the web site, we usually send “Neptun” messages about
important educational events (test writings, timetable changes, etc.). You will
receive them as an email as well, if you have a valid, working email address
registered in the “Neptun” system (and if you check it regularly…).
The only place and time we deal with students is seminar room
F.402 and during the office hours. Do not go to the 1st or 2nd
floor and disturb the teachers with your problems.
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Teaching material (protected content) :
https://elearning.med.unideb.hu/
• access using network ID
• one must be registered for the course
(theoretically the education department takes
care of it)
• upon login one must see the courses the
student is registered to
• These four courses run by the Biophysics
dept. must bee visible:
• Med., Dent., MB Biophysics Lecture
• Med., Dent. Biophysics Practical
• Biophysical analysis and formulas
• Med., Dent. Biostatistics
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2008
Compulsory at
• University of Debrecen
• Semmelweis University
• University of Pécs
Lecture course (theory)
Textbooks, resources
Practical courseonline lab manual
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Study-aid for the lecture material
• Being finalized now
• A quarter-page / half-page summary
to every lecture slide of every
lecture
Legend for the lecture material:
5*
!
2
,2
1mvAEAhf kinel
important material, required for
passing the exam
material required for excellent
supplementary material
only for the daredevil
equations marked by yellow are required
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Understanding biophysical equations and their application: sample
problems and exercises. Moodle e-learning module
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Minimum requirement questions
• Approx. 300 questions with the correct answers
• Summary of the most basic requirements
• Available as a PDF on the elearning site
• Not your enemy, but your friend …
• Not advisable to learn it independent of the material
Also usefulBasic terms for 1st year subjects
https://aok.unideb.hu/hu/tantargyi-alapfogalmak
• Not the same as the minimum requirement questions
• We do not explicitly ask it on the exam.
• But it is worth to know it …
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Self control tests:
Week 7, 21th October (Monday) 07:00 AM
Week 11, 18th November (Monday) 7:00 AM
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Electromagnetic waves, dual nature of light, matter waves
Why is electromagnetic radiation necessary?
• Light is the most important type of radiation. Besides its physiological aspects light has
extensive medical applications
- vision
- optical methods (microscopic techniques, endoscopy, etc.)
- therapeutic applications (photodynamic therapy, blue light therapy, photo-
chemotherapy, etc.)
• Some components of the electromagnetic spectrum (radio waves, X-rays and gamma
radiation) are also used for diagnostic and therapeutic purposes (e.g. CT, PET, MRI, etc.)
Previous knowledge (high school physics)
• Description and characterization of waves.
• Interference and deflection of (light) waves. Huygens’ principle.
• Production and propagation of electromagnetic waves.
• Work done by the electric field. Work-energy theorem.
What do we learn today?
• Dual nature of light (particle and wave)
• de Broglie hypothesis
• Thermal radiation emitted by bodies
• Heisenberg uncertainty principle
Aim: to learn …
• the experiments that prove the dual nature of light
• the energy of electromagnetic radiation is quantized
• it is physically impossible to measure simultaneously the exact position and exact linear
momentum of a particle
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The nature of light
velocity in vacuum: c = 3 108 m/s
in other materials: v = c / n, (l= c / f ) where n is the index of refraction
End of the 19th century
electromagnetic wave
transversal wave propagating with the speed of light (c), having two
components, electric and magnetic
proof for the wave nature of light: interference phenomena
Beginning of the 20th century
particle (photon)
E = hf = hc / l, where h = Planck’s constant = 6.63 10-34 Js
proof for the particle nature of light: photoelectric effect
!
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0 2 4 6 8 10
-1
-0.5
0
0.5
1
x
0 2 4 6 8 10
-2
-1
0
1
2
x
Constructive interference: waves are in phase
Destructive interference: waves are out of phase
Interference: property of waves
Two-slit experiment
Alternating bright and dark bands are
observed (interference) in accordance with
the predictions of wave theory.
Intensity distribution according to the particle
theory (one bright spot in the middle.
interfering waves
resultant wave
constructive destructive
constructive: bright
destructive: dark
interference
!
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2
,2
1mvAEAhf kinel
The photoelectric effect can be adequately explained only by the photon concept
electrode made of potassium,
2 eV needed to eject an electron
A=2 eV (A – work function, ionization energy)
l700 nm
no photoelectron
l550 nm
vel=2.96·105 m/s
l400 nm
vel=6.22·105 m/s
The kinetic energy of the
ejected photoelectrons is
analyzed with an electric
field.
+ _
eUmv 2
2
1
U
photon
energy
KE of
electron
stopping
potentialΔE
(eV)
2.25 eV 0.25 eV -0.25V 2 eV
3.1 eV 1.1 eV -1.1V 2 eV
potential difference
low intensity light
high intensity light
stopping potentials
550 nm
400 nm cu
rre
nt
• According to the wave theory the kinetic
energy of photoelectrons is proportional
to light intensity.
• Since this is not the case, the photon
theory has to be used for the
interpretation of the photoelectric effect.
E=hf=hc/ l
Ephoton=1.77 eVEphoton=2.25 eV
Ephoton=3.1 eV
!
19,
19
1V 1.6 10 1V=
=1.6 10 J 1 eV
kinetic electron electronE q C
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The wave nature of matter
• electromagnetic radiation has both wave- and matter-like properties
• Davisson and Germer succeeded in generating interference with electrons classically
regarded as a particles → electrons have wave-like properties too
• certain properties of elementary particles can only be explained by the wave model
• a wavelength (called de Broglie wavelength) can be assigned to any elementary particle:
p
hl
Planck’s constant
momentum (m x v)
The de Broglie wavelength of an electron:
nmv
mvvkg
Js 729000000729.0
101.9
1063.631
34
!
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400 nm
750 nm
The electromagnetic spectrum!
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Thermal radiation 1
Objects emit electromagnetic radiation whose spectrum depends on their temperature only, and is
independent of the material of the object. This radiation is called thermal radiation.
Kirchhoff’s law of thermal radiation:
j
j
i
iMM
,
,
,
,
l
l
l
l
Ml,i - the intensity of radiation emitted by object ‘i’ at wavelength l
l,i – the absorption coefficient of object ‘i’ (the ratio of the absorbed
radiation to the total radiation the body is exposed to)
If the emission of an object at a given wavelength is higher, it absorbs more efficiently at that wavelength.
The object whose absorption coefficient () is 1, i.e. it absorbs all the radiation it is exposed to), is
called black-body.
black
black
black
black
i
iM
MMM,
,
,
,
,
,
1l
l
l
l
l
l
Therefore the spectrum of thermal radiation emitted by any object can be determined with the
knowledge of the spectrum of a black body radiation and the absorption coefficient.
Textbook: page 123.
!
5*
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) 4TTMblack
Stefan-Boltzmann law:
Thermal radiation 2
Wien’s law:
KmconstantT 3
max 109.2l
Frequency
0 1014 2x1014 3x1014 4x1014
Inte
nsity
0
2x10-17
4x10-17
6x10-17
1000K
2000K
Frequency
0 1014 2x1014 3x1014
Inte
nsity
0
5x10-18
10-17
2x10-17
2x10-17
Planck
Rayleigh-Jeans
Explanation of the spectrum:
e-
Thermal radiation is generated by
oscillating electrons in the body.
Electrons (charged particles) oscillate
at non-zero absolute temperature.
There are two counteracting principles in action:
1. ► as the frequency increases, the number
of the states (modes) of the oscillator
increases
► each mode of oscillation has the same
(kT) amount of energy (equipartition
theorem)
Rayleigh-Jeans law:
intensity increases
with the frequency
1+2 → Planck’s law
2. ► the energy of an oscillator can only change by
integer multiples of hf
► the higher the energy of an oscillator is,
the lower its occupancy is (Boltzmann distribution)
f1
e-
f2
Textbook: page 124.
!
5*
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The Heisenberg uncertainty principle
The position (x) and the impulse (px) of an elementary particle can be
determined with limited accuracy at the same time:
hpx x
A similar relation holds for the energy-time pair: the energy and lifetime of
a state cannot be determined with infinite accuracy at the same time.
htE
Error sources in the experimental determination of a parameter:
1. Heisenberg uncertainty principle
2. the measurement itself alters the examined system
3. inaccuracy of the measurement
Werner Heisenberg (1901 - 1976)
I=?A Since the current meter has non-zero resistance, the measured
current will not be identical to what existed before the
measurement.
A consequence of the Heisenberg uncertainty principle is that the quantum world does not exist in
a deterministic form, but rather as a collection of probabilities (e.g. an interference pattern can be
predicted accurately, but the exact path of photons cannot.). This so-called Copenhagen
interpretation of quantum mechanics was disputed by Einstein („I cannot believe that God would
choose to play dice with the universe”).
The Heisenberg uncertainty principle is the consequence of the wave
(quantum)-nature of particles.
Measurement error. These have
nothing to do with the
Heisenberg uncertainty principle.
ad. 2
Textbook: page 29.
5*
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Take-home message
• The dual nature of light can be demonstrated experimentally.
• According to de Broglie, electrons, just like light, have a dual particle-wave nature,
thus duality is a general characteristic of matter.
• A de Broglie wavelength can be defined for particles having a mass of m and
moving at a speed of v.
• Light consists of tiny particles called photons whose energy is proportional to the
frequency of the electromagnetic wave associated with it.
• As an MD
• The medical application of light is widespread in both diagnostics and therapy
• The wave nature of an electron is used in electron microscopy to produce
high-resolution microscopic images that opens up the possibility of imaging
sub-cellular details.