Physiology 3140A Lecture : Cell Signaling Lectures and slides with some extra things mentioned in class!

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16 Oct 2011

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Major obstacle to the development of multicellular organisms was the development of a means for individual cells and tissues to communicate with each other and their environment. Purpose of cell signaling (communication) is to permit the development of complex mechanisms to govern behaviour of cells for the overall benefit of the organism; single receptor on single cell can cause complex mechanism behavioural variations. Combination of signals evokes different responses (diagram on the left). Ach has completely different effects on different cells and receptors (diagrams on the right). All living things are made of cells (individual units of living matter) that share the same machinery for their most basic functions. Molecules (ion, protein, drug) molecular machine (receptor) cell . Either released by a cell (actively and passively) or expressed on the cell surface. molecule to the inside of the cell. appropriate parts of the cell.

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Consider a satellite of mass ms in a circular earth orbit. Anysatellite orbiting in the upper reaches of our atmosphere willexperience a small drag force, F_d, opposite to itsdirection of motion. This drag force will cause the satellite tospiral inward toward smaller orbital radii. In the process, theorbital velocity of the satellite actually increases! This problemwill investigate how a drag force can cause a body in orbit tospeed up.

The situation is sketched in Fig. 1. The diagram shows separateforce and velocity diagrams for the satellite. The mass of theearth is denoted me, while the mass of the satelliteis ms. The tangential velocity of the satellite isv_t and the small radial velocity is acquires because itis spiraling inwards is v_r. The size of v_r isgreatly exaggerated in the diagram, and we can take v_r<< v_t and use v_t as an adequateapproximation to the magnitude of the total velocity, v. We willcall Î¸ the âangle of de- scentâ.

Turning to the force diagram, we see that the total force actingon the satellite is the vector sum of Fâ_d andFâ_g. Again, the drag force is much weaker than thegravitational force, so F_d << F_g . Wecan use this to our advantage by just considering the effect ofF_g along the line of descent. We can see from thediagram that F_g has a component along the line ofdescent given by F_g sin(Î¸).

(a) First show how we arrive at the following two basicequations governing this system, and carefully describe thephysical meaning of the quantity m_sa_d inwords:

F_gsinÎ¸âF_d = m_sa_d (1)

F_g = (m_s*v_t²)/r= G(m_sm_e)/r²(2)

(b) We can find out more about a_d and its relation tothe various forces and velocities by powerful

use of the chain rule for differentiation:

Explain Eq. 3 in your own words. Where did vr comefrom and why is the â sign there?

a_d = dv/dt = (dv/dr)*(dr/dt) =v_r(dv/dr) â v_r(dv_t/dr) (3)

m_sa_d = (1/2)F_g sinÎ¸

Vapor cycles
5EM - Thermodynamics
September 2010
1 The T-S diagram
The temperature-entropy diagram is an alternative to the well knownpressure-
volume diagram. Before using it to analyze different vapor cycles,we need
to understand it properly.
1. Plot the following transformations for ideal gases in a T-Sdiagram
(a) Isothermal expansion
(b) Isobaric expansion
(c) Isometric heating
(d) Reversible adiabatic expansion
(e) Irreversible adiabatic expansion
2. Repeat the last question, but this time do it for a realsubstance,
starting in the compressed liquid1 region and ending in thesuperheated
region, when possible. Indicate the boundaries of eachregion.
3. We know that under certain circumstances the area under theplot
in a P-V diagram represents the work performed during theprocess.
What does it represent in this case? Under what assumptions isyour
answer true? Compare examples 6.1 and 6.2.
2 Thermal machines
We understand by thermal machine a device capable of transformingther-
mal energy (heat) into mechanical energy (work). We already knowthat
these machines have a limited efficiency which, in the two-sourcesmodel, is
obtained by Carnotâs cycle.
(Compressed liquid is sometimes also called subcooled liquid)
2.1 Carnot cycle
This cycle, although efficient, is impractical. To begin with, theextreme
temperatures of the cycle should be within the sources temperaturesfor a
finite heat flow to exist.
1. Given the temperature of the sources, draw the cycle accordingto the
named limitation.
2. Show that this leads to lower efficiency than the theoreticallimit.
3. Assume that heat flow from/to the sources is proportional to thetem-
perature difference between them and the working fluid, anddemon-
strate that a higher power output is related to a decreasedefficiency.
2.2 Rankine cycle
Out of the several practical possibilities, Rankine cycle and itsvariations is
widely used, especially for electric power generation.
1. Draw the basic cycle in a T-S diagram and explain it.
2. What does the efficiency of the cycle depend on? Comparewith
Carnotâs.
3. What are the differences between the ideal cycle and the realone?
4. Describe how it is modified by superheating and/or reheating.Explain
te benefits.
2.3 Problems
After answering the previous questions solve the followingexercises from the
book: 8.2, 8.4, 8.5, 8.13, 8.19, 8.20
3 Frigorific machines
3.1 Reverse Carnot cycle
We have already studied Carnot cycle in detail as the ideal thermalmachine.
Now we will take is as the starting point to understand thecharacteristics
of frigorific machines.
1. Draw the ideal cycle in a T-S diagram and explain it.
2. Show that this cycle has a theoretical efficiency Ã =Tcold/Thot-Tcold
3. What are the difficulties in implementing such cycle in actualdevices?
3.2 Actual refrigerators
1. Why is the turbine replaced by an expansion valve in mostcases?
2. Plot the actual cycle and explain the differences with the idealcase.
3. How do cascade and multistage systems improve the performanceof
the refrigerator?
4. What aspects are important in the choice of a refrigerant fluid?Justify
3.3 Problems
After answering the previous questions solve the followingexercises from the
book: 10.2 10.7, 10.8, 10.9, 10.22, 10.23 10.1D

19. The interstellar medium has a cool component measuredvia_________ observations and a hot component revealed by________observations.
AX-ray; optical
BX-ray; infrared
CX-ray;gamma-ray
Doptical; X-ray
Einfrared; X-ray

20. Which of the following processes will NOT cause a gas cloudtocollapse?
Aionization from youngstars
Bsupernovaexplosions
Cgalacticrotation
Dthe expansion of theUniverse

21. What is responsible for emitting photons in anemissionnebula?
Aexcitedprotons
Bexcitedneutrons
Cexcitedelectrons
Dexcitedneutrinos
Eexcitedastronomers

22. White dwarf stars are supported from collapse by
Anuclear fusionreactions in a shell around the core.
Belectron degeneracypressure.
Cnuclear fusion reactionsin their cores.
Dcentrifugal force due torapid rotation.

23. The "star" that is seen at the center of a planetarynebulais
Aa planet in theprocess of formation.
Ba small, hot, and verydense, white dwarf star.
Cthe accretion disk arounda black hole.
Dcomposed almost entirelyof neutrons, and is spinning rapidly.

24. A white dwarf star, the surviving core of a low-massstartowards the end of its life, can be found ontheHertzsprung-Russell diagram
Aat the bottom end ofthe main sequence, along which it has evolvedthroughout itslife.
Babove and to the right ofthe main sequence, since it evolved thereafter itshydrogen-burning phase.
Cbelow and to the left ofthe main sequence.
Dat the upper left end ofthe main sequence, since its surfacetemperature is extremelyhigh.

25. The mechanism which gives rise to the phenomenon of thenovais
Amaterial fallinginto a black hole and being condensed to the pointwhere athermonuclear explosion is produced.
Bthe impact and subsequentexplosion of a large comet nucleus upon astar's surface.
Cthe completedisintegration of a massive star because ofthermonuclear runawayin the star's interior.
Dmatter from a companionstar falling onto a white dwarf in a closebinary system,eventually causing a nuclear explosion on thedwarf'ssurface.

Physiology 3140A Lecture : Cell Signaling Lectures and slides with some extra things mentioned in class!

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