What is Cycle: Definition and 673 Discussions

The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea (NH2)2CO from ammonia (NH3). This cycle occurs in ureotelic organisms. The urea cycle converts highly toxic ammonia to urea for excretion. This cycle was the first metabolic cycle to be discovered (Hans Krebs and Kurt Henseleit, 1932), five years before the discovery of the TCA cycle. This cycle was described in more detail later on by Ratner and Cohen. The urea cycle takes place primarily in the liver and, to a lesser extent, in the kidneys.

View More On Wikipedia.org
Recent contents Top users
  1. K

    Thermodynamics Cycle: Gas Temperature and Work Calculation | Homework Solution

    Homework Statement I.The gas is heated at constant pressure until the volume is 4.4L at point B II. The gas is cooled at constant volume until the pressure decreases to 1.2 atm III. The gas undergoes an isothermal compression back to point A a) Find the temperature at Point A,B,C b) Find the...
  2. M

    Temperature rise due to cycle test

    Hello all, I am working on a few test scripts to test the life of a hydraulic cylinder. (It is a mechanically operated cylinder and has a positive displacement) The testing will involve thousands of continuous pump and retraction operations, due to which the temperature of the piston seal and...
  3. kolleamm

    Not using a li-po battery reduces its life cycle?

    If I don't use my lithium polymer batteries for an extended period of time will that damage them? In that case how often should I charge them to prevent a such degradation? Thanks in advance
  4. Z

    Engineering Graph: difference between cycle & circuit

    Homework Statement What is the difference between a cycle & a circuit? (Definition not reqd, guidance reqd with the figure attached) Homework Equations No The Attempt at a Solution See the attached figure. According to this figure the walk AB, BC, CE, EF, FD, DA represents a cycle or not...
  5. N

    Low cycle fatigue, Coffin's law

    Homework Statement Hi, I require some assistance using coffin's law. I have the strain range and cycles to failure but need coffins slope- 'c'. C2 can then be found after the other values are known.Homework Equations Δε^pl=C2/N^c Where Δε^pl is plastic strain range, N is the cycles to failure...
  6. M

    HR-diagram: Describing the sun's life cycle

    We are asked to describe the sun's life in 4 different sequences of the HR-diagram. The second one is in main sequence, third one is in the red giant area, and the last one is in the white dwarf area. The first one is the one I cannot understand. I recreated where the numbers are on a new...
  7. I

    Gas Turbine TS Cycle: Understanding the Significance of Points 5-5b and 5b-6

    Homework Statement Homework Equations N/A The Attempt at a Solution I am confused what 5-5b and 5b-6 represent in the above TS diagram. I know that 1-2 is compression, 2-3 is cooling, 3-4 is compression and 4-5 is regeneration (since these are indicated in the block diagram) but as for 5-5b...
  8. M

    Calculating Internal Energy Change: Path 2 of Carnot Cycle Question

    Homework Statement A gas is to be expanded from initial stage i to final stage f along either path 1 or path 2 on a p-V diagram. Path 1 consists of three steps: an isothermal expansion(work is 23J in magnitude), an adiabatic expansion(work is 35J in magnitude), and another isothermal expansion...
  9. I

    Confused on a question about vapour refrigeration cycle

    Homework Statement http://photouploads.com/images/ae1d2f.png Homework Equations N/A The Attempt at a Solution In the image linked above, I have copied and pasted 4 different slides. In the last slide, I am confused how they got the expression for T2 (the working out). I know that they did...
  10. JuanC97

    What conditions are needed to get a stable limit cycle here?

    Homework Statement I want to find conditions over A,B,C,D to observe a stable limit cycle in the following system: \frac{dx}{dt} = x \; (A-B y) \hspace{1cm} \frac{dy}{dt} = -y \; (C-D x) Homework Equations Setting dx/dt=0 and dy/dt=0 you can find that (C/D , A/B) is a fixpoint. The Attempt...
  11. Ethan Godden

    An ideal gas going through a cycle

    Homework Statement The problem is attached Homework Equations ΔEint=Q+W W=-PΔV The Attempt at a Solution Attempted solution is in the attachment. The problem is I am not getting the same answer as the supposed correct answer. Thank You, Ethan
  12. I

    Ph diagram for a vapour compression cycle

    Homework Statement Homework Equations N/A The Attempt at a Solution I am trying to understand the above ph diagram (for a vapour compression cycle), In some examples, point 1 is situated as above in the image (i.e. to the right of the saturated vapour line) and at other times it's situated...
  13. jdawg

    Otto Cycle - calculate the net work per cycle in Btu

    Homework Statement A four cylinder, four stroke internal combustion engine has a bore of 3.7 in and a stroke of 3.4 in. The clearance volume is 16% of the cylinder volume at bottom dead center and the crankshaft rotates at 2400 RPM. The processes within each cylinder are modeled as an air...
  14. M

    How to Calculate Energy and Work in a Stirling Cycle?

    Homework Statement Suppose that 282 moles of a monatomic ideal gas is initially contained in a piston with a volume of 0.81 m^3 at a temperature of 574 K. The piston is connected to a hot reservoir with a temperature of 1365 K and a cold reservoir with a temperature of 574 K. The gas undergoes...
  15. R

    Carnot Cycle Use: Understand When to Apply

    I saw a problem for which I don't really understand the idea of the solution. This is what it says: The vaporization latent heat for water (at 100 deg C) under normal pressure (101325 pa) is 2,3*10^6. What is the saturated vapor pressure for water at 105 deg C? And the solution says that we have...
  16. F

    Do the Krebs cycle and electron transport chain require ATP?

    I cannot find a website that answers this question, and all diagrams I see do not show that ATP is used. Does this mean that these processes are intrinsically spontaneous? I can see how the electron transport chain is spontaneous, as the oxidation of oxygen to water is favorable (E 1/2=0.7V).
  17. P

    Find the limit cycle for this dynamical system

    Homework Statement Consider the dynamical system: $$\dot{r}=-ar^4+ar^3+r^6-r^5+r^2-r~;~~\dot{\theta}=1$$ Find all fixed points and limit cycles for: a) ##~~a=2## b)##~~a<2## c)##~~2<a<2\sqrt{2}## Homework Equations Not applicable. The Attempt at a Solution For all three values/ranges...
  18. A

    Proof that in Brayton reverse cycle heat is negative

    Homework Statement I was given the Brayton reverse cycle and asked to prove that the total heat is negative (hence the heat pump cools the system). I was to assume that all the steps are reversible. Homework Equations An ideal diatomic gas. 1st step: adiabatic compression. 2nd step...
  19. S

    Work out cardiac cycle and heart rate

    I would just like to know if i have worked out one cardiac cycle and heart rate correctly. I have attached the image of the ecg called 'after exercise' here are my workings out: 1. CARDIAC CYCLE: there are 4 cycles so: 9 (grids) x 0.05 = 0.45 9x 0.05 = 0.45 9x 0.05 = 0.45 9x 0.05 = 0.45...
  20. T

    Learning the Carnot Cycle: 4 Steps Explained

    I am learning the Carnot Cycle but I still get confused about this cycle. There are four steps in this cycle. 1)Isothermal expansion 2)Adiabatic expansion 3)Isothermal compression 4)Adiabatic compression After step one, we got the heat from heat reservoir through expansion but I don't...
  21. O

    Understanding the Carnot cycle

    This P-V diagram summarizes the Carnot cycle. Given a working fluid whose state ##(P,V,T)## is ##(P_1,V_1,T_1)## (at point 1) where ##PV=nRT##, the working fluid undergoes a cycle of four stages and again retrieve its original state of ##(P_1,V_1,T_1)##, that is it gets back again to point 1...
  22. rohitjinnu16

    Can Pascal's Law Be Applied to Enhance Cycle Rickshaw Efficiency?

    what if i use the pascals law for providing greater force,even by applying a small amount of force on the pedal.this larger force is used to drive the rear axle.shall i face any problems please suggest any difficulties even.
  23. H

    A power cycle receives heat input from solar collectors...

    I am having trouble with this problem. I have drawn the diagram , but don't know how I can attach it onto this post. But, for a I have COP= Qin/Wcycle = 650 J/m^2 s / Wcycle = 32.5 kW/Wcycle --> Wcycle = 10.15 kW. But,that is the wrong answer.[PLAIN]http://
  24. U

    How to get a linear solenoid actuator to cycle?

    Hi, I am working on a project with my daughter who is 10. We are trying to get a linear solenoid actuator (push) to continuously repeat (push/return...push/return). But all it does is push and stop. How do I get the wiring set up to enable the solenoid to automatically cycle? Thanks!
  25. JasonHathaway

    Calculating Efficiency and Work in Otto Cycle Engine

    Homework Statement An Engine works within Otto cycle where the compression ratio is 6, and 350 kJ of heat was added to it. Determine the efficiency of the cycle and the work done if Cp/Cv is 1.45Homework Equations Efficiency Otto = (1- r1-k) Efficiency (eff.) =Work (W) /Heat Transferred (Q)The...
  26. DavideGenoa

    Reversible cycle approximated by Carnot cycles

    My textbook gives the definition of a reversible transformation as a transformation that can be inverted by effectuating only infinitesimal changes in the surroundings. I admit that I have no idea of what infinitesimal means in a rigourous mathematical language, therefore the definition is quite...
  27. M

    Exploring the Potential of Gyroscopes for Motorcycle Balance

    Hi, I saw a video online of a self balancing 2 wheeled car. Basically a motorcycle with a body though has a steering wheel rather than handle bars. It uses two gyroscopes spinning in opposite directions to keep it's balance and was wondering if a similar thing could be adapted for regular...
  28. M

    MHB Solving 2 Watches with 12 Hour Cycle Problem

    Can you help me please on these problem. "I have 2 watches with a 12 hour cycle. One gains 2 minutes a day and the other loses 3 minutes a day. If I set them at the correct time, how many days will it be before they next together tell the correct time? "my idea of solving it is using LCM, bu t...
  29. S

    Work Done in Carnot Cycle: Adiabatic Compression

    1.what is the work done in an adiabatic compression process in a carnot cyclewhen we consider work done in efficiency why do we take heat exchange into account i.e.,qs-qrThe Attempt at a Solution
  30. SSGD

    Industrial Event Takt Times (production cycle times) and Probability

    Background: I am a Mechanical Engineer working as an Industrial Engineer. I have collected some data that is the amount of time that an event took to complete. I first assumed it would be normally distributed, but after plotting a histogram and a normal distribution with the data, I doubt...
  31. G

    What is good time for Earth to begin new evolutionary cycle?

    Humanity exctincted and after XXX years Earth is populated by "new" humans. How long could it take if exctinction happened in 2130?
  32. Mr Davis 97

    Understanding the Carnot cycle

    My textbook explains the Carnot cycle as follows: 1. Heat is added to the boiler, where the steam inside expands isothermally at high temperature (T(High))w(both valves closed). 2. The intake valve is opened (exhaust valve closed) and the steam expands adiabatically. The expanding steam...
  33. person_random_normal

    Engines in Cars: Exploring the Carnot Cycle

    are engines in our cars follow the carnot cycle or they work differently
  34. Kior

    Why is there a seasonal cycle of CO2？

    I am preparing my AOSS class next semester, and I found it is interesting that there is a seasonal cycle of CO2. I looked for some information on the Internet, and this seems to do with the plants. They awake in the spring and summer, absorbing a lot of CO2 by photosynthesis and die in the...
  35. Q

    Volumes at C and D in a Carnot cycle

    Homework Statement A Carnot cycle, shown in Fig. 20-7, has the following conditions: Va = 7.5 L, Vb = 15 L, TH = 470°C, and TL = 260°C. The gas used in the cycle is 0.50 mil of a diatomic gas, y = 1.4. Calculate (a) the pressures at a and b; (b) the volumes at c and d. (The rest of the...
  36. Stephanus

    Understanding the CNO Cycle: Exploring the Accuracy of a Commonly Shared Video

    Dear PF Forum, Is this picture correct? Or it is not CNO Cycle? I get that video from this Thanks for any answer
  37. U

    Period of Limit Cycle: Find B for Hopf Bifurcation

    Homework Statement I'm given this system: \dot x = Ax^2 y + 1 - (B+1)x \dot y = Bx - Ax^2 y (a) Find the value of B when hopf bifurcation occurs. (b) Estimate the period of the limit cycle in terms of ##A## and ##B##.Homework EquationsThe Attempt at a Solution I have found fixed point to be...
  38. I

    How does Carnot Cycle Expand and Compress Isentropically?

    Homework Statement I think I understand the first 3 steps of the Carnot cycle but not the 4th. Homework Equations The cycle here: http://en.wikipedia.org/wiki/Carnot_cycle#Stages The Attempt at a Solution I understand that in stage 1, the gas expands by taking in heat from the hot reservoir...
  39. N

    Reversible Carnot Cycle: Exploring Heat Dynamics & Conservation

    In a reversible carnot cycle the amount of heat added is always more than the amount of heat taken out. So why doesn't it explode? I'm wondering how heat is conserved mathematically as the area under the curve of a p-v diagram. u=q+w. If the heat during expansion is always more than the heat...
  40. Billy.Ljm

    What Makes the Carnot Cycle the Most Efficient?

    I have 2 questions, which are related, and was hoping someone could help me clear things up. First question, isn't the Otto cycle reversible and usable as a refrigerator? Referring to the diagram above & let me go part by part. AD: Assume the corresponding part of the working substance is...
  41. suraj 27

    Heat addition process in dual cycle

    why in dual cycle heat addition at constant volume process is first then after heat addition at constant pressure process is done?
  42. H

    Born-Haber Cycle: Formation of a Chlorine Atom

    Homework Statement I don't actually need help with an entire problem, I just can't seem to figure out what goes on when an atom is formed from a molecule in a Born-Haber cycle. For example: The formation of a chlorine atom from a chlorine molecule (1/2)Cl2 → Cl(g) ΔH = (1/2) x bond energy...
  43. W

    Need Help Mech. Eng. -- An ideal Rankine cycle

    MODERATOR NOTE: THIS IS A MISPLACED COURSEWORK THREAD, SO NO TEMPLATE WAS USED I need help verifying the correct answers for the following questions. 2. An ideal Rankine cycle is operated with a turbine inlet pressure of 500 psia and an inlet temperature of 600 oF. The steam is...
  44. P

    Max Duty Cycle for Undamaged Power Resistor (20V, 33ohm, 5W)

    Homework Statement Assuming I have a 20V source on a “power resistor” which can withstand powers of up to 5 Watts on average before it excessively heats and damage begins. What is the DC current that runs through a resistor of 33ohm? What is its power dissipation? What is the maximal DC current...
  45. C

    How Is Heat Calculated in a Diesel Cycle Using Volumes and Temperatures?

    1. Ideal gas cycle - diesel engine cycle. You begin at some volume V1. Perform an adiabatic compression to V2. Perform an expansion to V3 at constant pressure. Next, perform an adiabatic expansion to V4, Last, it moves back to V1 at a fixed volume, while decreasing temperature back to...
  46. I

    Carnot cycle work & efficiency

    Homework Statement The oxygen contained in a thermally insulated container will be cooled down to its boiling point (-183 C), and then condensed. Thereby one uses a reverse Carnot process operating between the oxygen gas (instantaneous) temperature and the room temperature (17 C). What is the...
  47. A

    Python: how to break two times to results

    Homework Statement I need a program, which would break and show results once a 0 is entered in input name and input grade. I figured how to do that in name, but how do I add another break? Like grade !="0"? Homework EquationsThe Attempt at a Solution students = [] grades = [] while True...
  48. Dorian Black

    Electric/Magnetic vicious cycle

    Apologies for the melodramatic title. In studying AC current distribution in cables (skin effect), one can view the AC current as producing a time varying magnetic field in phase with the current itself (Ampere's Law). This in turn creates an electromotive force 90 out of phase with the current...
  49. P

    Is the mass flow rate in a regenerative vapor power cycle constant?

    Does the mass flow rate differ depending on whether it's after the feedwater heaters or before the turbines or is it just constant throughout the entire system?
  50. E

    Brayton cycle combustion process

    Why does or how does combustion of fuel and air in a combustion chamber in a brayton cycle is idealized by a CONSTANT pressure. I remember that in a diesel cycle, it was idealized by constant pressure because as P increases by ignition but the volume increase offsets this increase. However, in...
Back
Top