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SEMMELWEIS UNIVERSITY, Medical Biophysics II. Final - Practice topics ONLY Questions and Answers
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SEMMELWEIS UNIVERSITY, Medical Biophysics II. Final - Practice topics ONLY
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SEMMELWEIS UNIVERSITY, MedicalBiophysics II. Final - Practice topics
ONLY
Coulter principle. - Correct Answers -The ability to count and measure the size of
particles using an electric circuit. Particles are moved through a small aperture, their
presence causes a narrowing of the aperture, which leads to an increase in
resistance.By using constant I, According to Ohms law (U= I * R), when R increases, U
increases and pulse is generated.
Parts and functions of the Coulter-counter - Correct Answers -- Two spaces with a small
aperture in between, capillary (contains the electrolyte solution with the cells)
- Measuring electrode, one in each of the spaces (closing the circuit and measuring
voltage between the two spaces)
- Pump (draws the solution into the smaller space, and out
again, through the capillary)
- Auxiliary electrode (signals when certain volume is
reached, to initiate pumping out of the solution)
- Integral Discriminator (filter out noise)
- Differential Discriminator (mapped of the size distribution
of the particles)
How does the voltage pulse amplitude depend on particle size in the Coulter-counter? -
Correct Answers -Its proportional, bigger particle will form higher resistance, higher
voltage pulse.
How do you separate the red-blood-cell versus white-blood-cell signals in a Coulter-
counter? - Correct Answers -when you want to measure RBC, it's not necessary to
separate them from the RBC b.c. the number of WBC is negligible (less than error of the
measurement)
By hemolyze RBC and measured them separately photochemically and subtracted the
result from the coulter-counting measurement
How do you separate the red-blood-cell versus platelet signals in a Coulter-counter? -
Correct Answers -By integral discrimination (the size of the platelets is much
smaller)
, What is the role of differential discriminator in Coulter-counting? - Correct Answers -
Mapping the size distribution of the particle
Why is dilution of blood is necessary in Coulter-counting? - Correct Answers -Because
the cells themselves do not conduct well, and so we dilute them with an electrolyte
solution so changes in resistivity are noticed. Also, for practical reasons (e.g. we don't
want the solution to dry up.)
What solution is used for blood dilution in Coulter-counting? - Correct Answers -Saline
solution, for optimal osmotic pressure (keep the RBCs in their natural size) and for good
conduction (NaCl)
How does the matter flow density (flux) change if the concentration gradient is doubled?
- Correct Answers -It doubles, due to flicks first law: Jv=-Dxdeltac/deltax
Name the parameters influencing the value of diffusion coefficient. - Correct Answers -
Size and shape of the particle as well as the temperature and viscosity of the medium.
Can be calculated for spherical particles: D=kT/6 pi n r
What diffuses faster: a potassium ion or a virus particle? - Correct Answers -K+ ion due
to smaller diffusion coefficient (smaller size)
How does the average distance travelled by a diffusing particle depend on time? -
Correct Answers -Square root function (Distance average ^2 =6 * D * t)
On what length scale is diffusion an effective transport process? - Correct Answers -On
a small scale
How does the minimum wavelength of the x-ray spectrum change with increasing anode
voltage? - Correct Answers -Decreases (higher voltage higher kinetic energy higher
frequency spectrum) - Duane-hunt law
How does the minimum wavelength of the x-ray spectrum change with increasing anode
current? - Correct Answers -Does not change
What is the maximum x-ray photon energy at 50 kV anode voltage? - Correct Answers -
50 keV
What elements are suitable as x-ray-tube anode material? - Correct Answers -High
melting point and high atomic number materials molybdenum
(more common in medical diagnosis) and tungsten.
What are the x-ray spectral lines characteristic of? - Correct Answers -Anode material
Why do we need to cool the x-ray-tube anode? - Correct Answers -Because it heats up
due to low efficiency in the conversion of high
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