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. F

    Cycle Decomposition of Permutations

    Homework Statement Let α = (α1α2...αs) be a cycle, for positive integers α1α2...αs. Let π be any permutation that παπ-1 is the cycle (π(α1)πα2...π(αs)). Homework EquationsThe Attempt at a Solution I started by choosing a specific α and π, and tried finding παπ-1 to give myself some idea of...
  2. E

    Question regarding the Otto cycle

    Why is the heat rejection process in an otto cycle is at constant volume. Let us say that the exhaust and intake stages in the actual cycle are the last two strokes of the cycle. In the ideal cycle, it seems to me that they merge those two stages into one stage which is heat rejection and...
  3. M

    Rankine cycle with low pressure condenser

    Hi guys, first post on the physics forum! I am slightly confused by the information provided by the following resource, the website is as follows - http://www.learnthermo.com/T1-tutorial/ch09/lesson-B/pg09.php The point that I do not understand is - "For starters, the quality of the turbine...
  4. A

    Why the Carnot Cycle? | Understanding Efficiency in Heat Engines

    1-Is the efficiency of heat engines working in cycles other than Carnot independent of the nature of substance used? Can we still claim that maximum efficiency in converting heat to work is attained during reversible processes for such cycles? For which engines/cycles can we do this? 2- Why is...
  5. Suraj M

    Kreb's Cycle (TCA): Why H2O Needed in Isomerisation Step?

    In the isomerisation step of Krebs cycle, the second last step in regeneration. there is a change form fumaric acid to Malic acid by Fumarase. My textbook says that H2O is also added. From chemistry I know that that Malic and Fumaric acid are sterioisomers, Then why need that H2O??
  6. y2j

    Any help about ORC (organic Rankine cycle)

    Hi anyone can help me about the converting the rotary vane compressor into an expander to use in small scale organic Rankine cycle (micro combined heat and power)
  7. D

    Can a thermodynamic heat engine include all these processes?

    Homework Statement Hi, I'm a new user and got this problem. Sorry to bother, but I couldn't find any relevant information from my Physics books.. The problem states: Build a heat engine using these processes: adiabatic, isothermal, isochoric and isothermal. The work-cycle of the engine must...
  8. R

    Design of Vapour Compression Refrigeration Cycle

    Hi! For our class project, we have to design a system that freezes an amount of water as quick as possible. The refrigerant is R134a. The compressor is known. I don't really know how to get started here. How do I choose the evaporator pressure and the superheating, and equally the condensor...
  9. U

    Rankine Cycle Thermal Output Calculation for 1000 MWe

    Homework Statement The last part of my question reads: Give the equations you would use to determine reactor thermal output if the plant is to produce 1000 MWe. All expressions for work and heat transfer rate should be expressed in terms of the appropriate mass flow rate ratios. Homework...
  10. S

    Brayton Cycle Thermodynamic Analysis

    Hi! I'd appreciate some help solving the thermodynamic's problem. I am sorry if the problem statement isn't 100% clear, as I've translated it from my native language. I'd really like if you could help me check my equations/procedure/results. In the following link both my attempted solutions...
  11. A

    The second law efficiency of compressor in gas turbine cycle

    hi friends, I've used the following equation in Thermodynamics: an engineering approach(Cengel) for calculating exergy efficiency of compressor. In fact, for an adiabatic compressor with negligible kinetic and potential energies, the second-law(exergy) efficiency becomes...
  12. R

    Thermal fatigue for heat exchanger cycle test comparison

    I have a heat exchanger with water/air as medium and we test it in a facility where we cycle the water temperature between 25 to 95 degrees Celcius with a cycle time of 5 minutes for thermal fatigue. Our customer require the testing to be between 5 to 95 degrees instead with 3 minute long...
  13. A

    Some basic questions about the second law efficiency (gas turbine cycle)

    hi , will change first law efficiency proportional to second law efficiency? for example in gas turbine cycle, how change? other equation: hi , will change first law efficiency proportional to second law efficiency? for example in gas turbine cycle, how change? other equation: How is the...
  14. R

    T-S Carnot Cycle for Photon Gas

    So I have been thinking about the photon gas, and I have read several papers talking about how a Carnot cycle could be created for it. This is fantastic, and it is something I am quite comfortable with. All of the papers present the P-V diagram as the "golden" Carnot cycle for the photon gas...
  15. 22990atinesh

    Understanding Instruction Cycle?

    A basic instruction cycle consists of these 5 stages. 1. IF - Instruction Fetch 2. RD - Instruction Decode and Register Read 3. EX - Execute 4. MA - Memory Access 5. WB - Write Back I understood the meaning of all the stages accept 4th MA (Memory access), what's the significance of this stage.
  16. A

    Exergy analysis gas turbine cycle For EEs

    hi friends, I am working EES software for thermodynamic lesson,I am analyzing second law efficiency(exergy efficiency) and exergy analysis for all components of gas turbine cycle. Now I have a problem,exergy efficiency of turbine decrease with increasing before temperature,why? As you know...
  17. G

    Engine Cycle Homework: Energy Transfer & Exhaust Heat Questions

    Homework Statement Hi Guys, I did a heat engine experiment where we put a weight on a piston and moved an air cylinder in a hot water bath, then removed the weight and but the air cylinder in a cold water bath to make a heat engine cycle. I am just wondering in the simple heat engine which...
  18. T

    Carnot cycle heat engine max work done

    Homework Statement A heat engine containing an ideal gas has a reversible cycle which consists of 2 constant volume segments with V = 1ℓ and V = 3ℓ and two constant pressure segments with P = 1 atm and P = 2 atm (see figure below). The temperature at point “c” is Tc = 273 K. A) Is the path...
  19. Amr Ali 33

    Regeneration in steam cycle (feed water heaters)

    i know that regeneration is heating the feed water by the bled steam from the turbine to reduce the sensible heat addition by the boiler but doesn't that also causes a reduction in the steam turbine work because we've taken some steam from it . can anyone explain please i'may have some...
  20. B

    Calculating the order of an element in cycle notation

    Homework Statement Let ##g \in S_n## and suppose that we know the cycle notation for ##g##. How can one compute its order without repeatedly composing ##g## with itself? Homework EquationsThe Attempt at a Solution [/B] I took the group ##S_4## and tried formulating a conjecture. I composed...
  21. sunrah

    CNO Cycle: Understanding the Last Reaction and the Mystery of 16O

    The last reaction in CNO-I sees 15N + 1H --> 12C + 4He I'm interested why it doesn't produce 16O, which is also stable.
  22. C

    Thermodynamics - Rankine Cycle Reheating

    Homework Statement A Rankine cycle with reheat uses water as its working fluid. Superheated vapour enters the high-pressure turbine at 10 MPa and 440oC. The steam expands through this high-pressure turbine to 0.7 MPa and is then reheated to 400oC. The steam then expands through the low-pressure...
  23. A

    In the CNO cycle, how does Nitrogen-15 become Carbon-12 and Helium-4?

    Homework Statement I understand the rest of the cycle, the way my textbook has it, which is: 12C→13N→13C→14N→15O→15N→12C+4He The portion in bold is what I don't understand. Homework EquationsThe Attempt at a Solution I do understand that when the mass number increases (like from Carbon-13 to...
  24. R

    Number of amplitudes in one wave cycle

    Homework Statement During one complete cycle, a wave moves through ___ wavelength, ___ period, __ amplitudes Homework EquationsThe Attempt at a Solution Well I got 1 wavelength, 1 period, and 2 amplitudes But apparently the answer is 1 wavelength, 1 period, and 4 amplitudes But I don't see...
  25. B

    How do I write a Cayley table for ##D_3## using cycle notation?

    Hello everyone, The problem I am working on asks me to write a Cayley table for ##D_3## using cycle notation. However, I am having difficult with determining how to operate on a pair of "cycles." Here is my work so far: ##R_0 = e = ()## ##R_{120} = (123)## ##R_{240} = (312)## ##F_T =...
  26. C

    How would you organize arbitrary day cycle on an exoplanet?

    Assumption: -there is no serious astronomical phenomena determining that - either the planet is tidally locked, has too long day cycle, or is too far away from its star and inside bases anyway humans rely on artificial light; -there is a colony of a size of at least medium city; -post scarcity...
  27. E

    Organic Rankine Cycle efficiency issue

    hi all. just to give you a background story - i am graduate student at U of Calgary in the ECE department. My colleague, from the Mechanical department did not show up yet, because of which I have to work alone on my project, including the mechanical part at which i am no expert but have some...
  28. T

    Is CNO cycle more life friendly than H->He?

    Wiki claims in stars, heavier than 1.3 solar masses (where CNO plays major role) there is an inner convection zone near the core, but no outer convection zone. Hence, such stars should be "calmer" - no solar flares, less radiation... Am I right?
  29. J

    Solar Cycle: Current State & Update

    What is current state of the solar cycle?
  30. G

    Thermodynamic cycle p-v to T-s

    Homework Statement I have been given a description of a thermodynamic cycle that looks like this. I have two polytropic processes (n1=1.2, n2=1.9), and one isochoric. The known data are: p1 = 1 bar T1 = 15 °C p2 = 15 bar Homework Equations p v^(1.2) = 0.7958 p v^(1.9) = 0.69657 The Attempt...
  31. C

    Carnot cycle problem - Is it thermodynamically possible to do 500J of work?

    Homework Statement 2. The attempt at a solution Is it only possible when 600J of heat is exhausted and 400J of heat is converted into work? Is the 600J heat will enter the cold reservoir and available to do work again? q1/T hot + q3 / T cold = 0 q3 = 600 when T = 300K
  32. M

    Understanding the Carnot Cycle: Heat Pumps & Engines

    Greetings, Here is my thought process on the carnot cycle, regarding heat pumps and engines. I'd much appreciate it if you can clear up any misconceptions and answer my question at the very end. So my book states that there is no change in internal energy in a heat engine, but neither confirm...
  33. Chacabucogod

    Refrigerator Cycle Compressor Function

    I understand that you need certain work for the refrigerator to work, and that it comes from the compressor. Why isn't a pump used instead? Why do you have to compress and heat the air so much? Thank you
  34. I

    Partial Expansion in high pressure Turbine in a Reheat Rankine cycle

    Please help me with this, In Reheat Rankine cycle, we first Expand the steam partially in a high pressure turbine and then reheat it again . How is this partial expansion in high pressure turbine done ? in the sense, what is the procedure followed to have only partial expansion of steam...
  35. gfd43tg

    Fate of outer planets after sun ends its life cycle

    Do white dwarf planets ever die and eventually there will be no remains of the sun? What will happen to the gas giants with no sun to orbit?
  36. P

    Maximum temperature of fuel air cycle

    When Stiochiometrically correct mixture(equivalence ratio=1) is burned in air fuel cycle some of the air is still left after point 3 in P-V diagram...Theoretically the whole fuel and air should combust till point 3..Then why is some air left out there.And thus the max temp is when mixture is 6%...
  37. A

    Torque required to power an Electric cycle

    I am having a real tough time determining the torque required to power an electric motor used to drive a cycle. I have calculated the Torque as: Torque = μ X mg X r(radius of the wheel) Now I am confused as what is μ. I know it's the coefficient of friction but, not sure whether I have...
  38. L

    Device with transfer of KE-PE each cycle & losses

    I have a project which is to create a mechanical device that would transfer close to 1 J of energy from one form to another and must be able to show how you calculated the 2 energy individualy and show that the energy loss between the 2 is within a % difference. I posted on here yesterday...
  39. N

    AZING! How does the Carnot cycle affect refrigerator efficiency?

    Homework Statement The temperature in a refrigerator evaporator coil is -6oC and that in the condenser coil is 22oC. Assuming that the machine operates on the reversed Carnot cycle, calculate the COPref , the refrigerant effect per kW of input work, and the heat rejected to the condenser...
  40. E

    The total work in a Carnot cycle - checking some work

    Homework Statement Let the radiant energy in a cylinder be carried through a Carnot cycle. The cycle consists of an isothermal expansion at temperature T, an infinitesimal adiabatic expansion where the temperature drops to T-dT, ad returning to the original state via an isothermal compression...
  41. D

    Solving Carnot Cycle Problem: Struggling with b & c

    Homework Statement See attachment Im struggling with b and c. I did an attempt, but really don't know if it is correct. Homework Equations The Attempt at a Solution See attachment
  42. caters

    Cycle of blue moons from year 0

    Year 0 in some systems exists and in year 0 there is a blue moon. There are also blue moons in year 3, year 8 etc. This 4,5 I have seen so far and this timeanddate.com makes me think that it has that 4,5,3,16,17,2,9, and then repeats at 16 cycle. Sites including wikipedia say that a blue moon...
  43. A

    Why is a condenser necessary in a thermodynamic Rankine cycle?

    hi guys , I am studying thermodynamic cycles in my thermodynamic course , I have a question about the power cycles like Rankine , in these systems v use superheated steam to produce work from turbine, so y there must be condenser to cool it first and then heat it , y can't v use turbine - boiler...
  44. L

    Thermodynamics Cycle of Processes

    Homework Statement A certain fluid of mass 1kg undergoes a cycle of processes in a piston and cylinder device as follows: Process A-B: 70kJ of work done on the fluid. 35kJ of heat rejected to surroundings Process B-C: 50kJ of heat transferred to the fluid. No change in internal energy of...
  45. S

    Why does heat addition happen at constant pressure in diesel cycle ?

    Why does heat addition happen at constant pressure in diesel cycle ? what is the basic concept behind it?? please do enlighten me on this topic. thanks in advance
  46. S

    PWM Controller period and duty cycle questions

    I've carried out some testing on a PWM controller using a 555 timer IC (see attached for circuit diagram) and I am having a little trouble understanding the results. When the POT resistance is increased the duty cycle decreases. As I understand it, when the resistance is increased the voltage...
  47. Feodalherren

    Thermodynamics - reversible isothermal cycle

    Homework Statement Homework Equations The Attempt at a Solution I can do everything else except work for part one going from A to B. What I did was -∫PdV = -nRT ∫(1/v)dV = -nRT ln (Vf/Vi) I can solve for T because everything is given, T in Kelvin is 882. From PV=nRT T=(5atm)(10L)/1mol*R...
  48. Feodalherren

    Corrected.Finding the Energy and Work in a Carnot Cycle

    Homework Statement An ideal gas is taken through a Carnot cycle. The isothermal expansion occurs at 250°C, and the isothermal compression takes place at 50.0°C. The gas takes in 1 200 J of energy from the hot reservoir during the isothermal expansion. Find (a) the energy expelled to the cold...
  49. A

    Reversed Carnot Cycle: Explained for Refrigerators

    What happens in a reversed carnot cycle? I mean in refrigerators.The gas is adiabatically compressed so that it's temperature rises.Then it is isothermally compressed so that the heat is rejected to the sink.But then why it is said everywhere that the working substance absorbs heat from sink...
  50. J

    Actual rankine cycle - Work done by pump

    Hi, In what cases do I neglect the work done by the pump in an actual rankine cycle? I am reading that h5-h4 is negligible but in what circumstances do I accept this. Is this only for ideal rankine cycles? As I understand thermal efficiency is (work out + work in)/Heat in Thanks
Back
Top