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.

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  1. B

    Working out temperatures on an ideal brayton cycle.

    Homework Statement An ideal Brayton cycle has a pressure ratio of 15 and can be analysed using air standard cycle assumptions. The gas temperature is 300K at the compressor inlet and 1500K at the turbine inlet. The compressor and turbine can be considered to be isentropic. For an...
  2. S

    Generating Clean 50% Duty Cycle Square Waves

    Hey all! I'm trying to drive 5 speakers, each at a different preset frequency. I had been using the timer in my microcontroller to drive one, but it would get very messy to drive 5 simultaneously in software using just the 1 available timer. I've decided to drive each with a...
  3. V

    Thermodynamic cycle of jet engine

    How to choose thermodynamic cycle for designing new jet engine? While designing new jet engine what parameters are important for choosing thermodynamic cycle? what other parameters are important for jet engine designing?
  4. C

    Entropy chance with a carnot cycle?

    in a carnot cycle the gas expands adiabatically from 200 degrees to 500 degrees. what is the efficecy? and what is the entropy change of the gas during the expansion? sorry - i got the efficiency to be: 38.8% however I am unsure how to work out the entropy chance? any hints?
  5. A

    Thermodynamics (Ideal Rankine Cycle)

    1. An ideal reheat Rankine cycle operates between the pressure limits of 10 KPa and 8 MPa, with reheat occurring at 4 MPa. The temperature of steam at the inlets of both turbines is 500C, and the enthalpy of steam is 3185 KJ/kg at the exit of the high-pressure turbine, and 2247 KJ/kg at the exit...
  6. P

    Carnot cycle with efficiency > 1

    Is it possible (at least theoretically) to construct engine which uses Carnot cycle and two reservoirs with temperatures T_1<0<T_2 (one of them has negative temperature which is possible e.g. in case of two-state paramagnet). Such cycle would have efficiency greater then 1. (of course the...
  7. H

    Plotting & Finding Fourier Coefficients of Waveform Cycle

    Homework Statement Given the first cycle of a waveform: f(t)=2u(t)-2u(t-1)+u(t-2)-u(t-3) -- Plot the first cycle of the wave form -- Find the Fourier Coefficients Homework Equations Given above The Attempt at a Solution No idea yet. Will appreciate any help.
  8. S

    How much ATP is produced in the Krebs cycle for each glucose molecule?

    Homework Statement What is the total yield of ATP in the Krebs cycle for each glucose molecule that enters glycolysis? Homework Equations The Attempt at a Solution Not sure if the correct answer is 2 ATP or 24 ATP due to 6 NADH (= 18 ATP) oxidative phosphorylation 2 FADH2 (= 4...
  9. D

    Efficiency of a cycle in TS diagram

    Homework Statement A working substance goes through a cycle within which the absolute temperature varies n-fold, and the shape of the cycle is , where T is the absolute temperature, and S the entropy. Find the efficiency cycle. Homework Equations \frac{\delta Q_R}{T}=dS...
  10. C

    Need help with a question involving heat engines, the carnot cycle and entropy.

    The Attempt at a Solution For a) I imagine it is easier to control the temperature of the hot reservoir because you could use a constant heat source e.g. bunsen burner. c) melting/freezing water. d) Entropy of the environment increases and the entropy of the universe always increases...
  11. J

    [Thermodynamics] Quick question about ''Cut-off ratio'' in the Diesel Cycle.

    [SOLVED] Quick question about ''Cut-off ratio'' in the Diesel Cycle. So I've been studying the Diesel Cycle, and I've come up with something called the ''cut-off ratio'', which is simply a name for the ratio of expansion r_E. But I'm getting different definitions for this ratio. For example...
  12. R

    Gas Cycle Process; Adiabatic, Isovolumetric and Isothermal

    Homework Statement A monatomic gas has V1 P1 and T1 (volume pressure and temp) at state 1 The gas then goes through the following process adiabatic expansion to stage 2 (exapands to twice its volume) isovolumetric heating so it gets back to T1; stage 3 isothermal compression back to...
  13. C

    Cycle notation for permutations?

    Homework Statement Why are the permutations (1 4 2 6)(2 3 4 5) and (1 4 5 6)(2 3) equal? It seems to me as if the first pair of 4-cycles want to permute 4->2 and 4->5, yielding a contradiction, but I suspect I've misunderstood something about composite cycles. I suspect it has something...
  14. F

    The Eternal Cycle of Life: Nature, Death and Burial

    -------------------------------------------------------------------------------- The origin of life and humans is unknown.That is to say that humans do not know how they came into being and why humans come to this world. We only know that life and humanity is the product of natural...
  15. S

    Calculating Thermal Efficiency for a 4-Process Cycle

    Homework Statement i have an mechanical engineering problem. A gas taken thru a 4-process cycle has 1-2 isothermal volume ratio rv,2-3 isobaric constant pressure,3-4 isentropic reversable adiabatic and 4-1 isochocric constant volume. How do i formulate the thermal efficiency equation for it...
  16. N

    The Cardiac Cycle in Frogs: What is the Longest Part?

    I was struggling with the following question: In a frog heart preparation that is beating spontaneously, the longest part of the cardiac cycle involves: A. Contraction of the atria B. Contraction of the ventricle C. Relaxation of the ventricle D. Electrical conduction through the...
  17. L

    Explaining Transistor Operation in a Signal Cycle

    Would someone be kind enough to explain what happens to the operation of both transistors in both the positive cycle and the negative cycle of the input signal please? I'm having a hard time understanding how this works exactly. What I know is that with no input signal, both transistors have a...
  18. E

    Thermodynamic cycle and entropy

    Alright, I'm confused about why thermodynamic cycles can never have 100% efficiency. There reversible processes right? And a reversible process has zero change in entropy, so then why can't they achieve 100% efficiency. I thought entropy was the measure of energy that cannot be used. How would...
  19. B

    Breeding Ratio of thorium fuel cycle

    Homework Statement A breeder reactor is designed to work on a thorium fuel cycle. If the reactor generates a constant thermal power of 2.5GW and a production rate of 233U is 52kg per year. Find the breeding Ratio [You may assume the capture to fission ratio of 233U is 0.09 and the energy...
  20. T

    What is a cycle in graph theory

    Homework Statement Sorry about the basic question, I haven't takena course on graph theory yet but need this for a course in computer science. The problem: Write a program whose input is an adjecancy matrix and whose output is the number of cycles of length 3 and 4. The Attempt at a...
  21. A

    Is an Ideal Combustion Cycle Possible? Feedback from Experts.

    Hey guys, I need to get some feedbacks from all of you here. Do you guys think it is possible for an engine to have a very low exhaust gas temperature and does not need any coolant radiator? The aim is simple, with lesser heat rejected through exhaust gas and radiator, there will be more...
  22. P

    Biochemistry - Calvin Cycle Question

    Homework Statement An illuminated suspension of chloroplasts is actively carrying out photosynthesis. What would happen to the levels of 3-phosphoglycerate and Ribulose 1,5-Bisphosphate if the light was suddenly switched off? Homework Equations The Attempt at a Solution I...
  23. E

    If a given permutation in S_n has a given cycle type, describe sgn(sig).

    Homework Statement 5.4: If sigma in S_n has cycle type n_1,...,n_r, what is sgn(sig)? (sgn is the sign homomorphism)Homework Equations sgn(sigma) = 1 if sigma is even. sgn(sigma) = -1 is sigma is odd cycle type is the length of the cycle type. If n_2 = 2, sigma has two 2-cycles.The Attempt at a...
  24. O

    The Everlasting Cycle of the Universe

    Alright. So I have an idea, and I'm not sure if it has been thought up yet. So, We all know what the Big Bang is. I'm going to assume that you've heard of the big "Crunch", I believe it was called. Well, What if when the Universe comes together, or "crunch's" a big bang happens. All of...
  25. G

    What Is the Maximum Work a Heat Engine Can Perform in a Cycle?

    Homework Statement 21. A heat engine operates in a cycle between temperatures 700 K and 400 K. The heat input to the engine during each cycle is 2800 J. What is the maximum possible work done by the engine in each cycle? (A) 1200 J (B) 1600 J (C) 2100 J (D) 2800 J (E) 4400 J I...
  26. B

    PV diagram full circle cycle help

    Homework Statement I'm given a PV diagram, it goes from A, B, C, D, in a full circle, counter-clock wise. A is at the top, and is at 30 Pa and 25 m^3 for volume. B is at 20 Pa and 15 m^3. C is at 10 Pa and 25 m^3, and D is at 20 Pa and 35 m^3 (It goes in a full circle with A and C having the...
  27. X

    Answer: Solving Three Step Gas Cycle Homework Problem

    Homework Statement A monatomic ideal gas has pressure p_1 and temperature T_1. It is contained in a cylinder of volume V_1 with a movable piston, so that it can do work on the outside world. Consider the following three-step transformation of the gas: 1. The gas is heated at constant volume...
  28. B

    MATLAB Using ode45 in a for Cycle: Adding Parameters to odefun

    Hi guys, I want to run a for cycle with ode45 inside. However, some parameters that I define in odefun (the differential equation in order to dy/dt, for instance) assume different values in each iteration of that cycle. I find help examples showing odefun only receiving t and y... Is...
  29. S

    How is Kreb's cycle regulated by ADP?

    My textbook says, I checked the whole citric acid cycle, and only the conversion of succinyl coA requires ADP or GDP. I don't understand how a lack of this would make NADH accumulate. Could anyone explain this. Thanks a lot :smile:
  30. N

    Circuit for producing a single-shot cycle

    Hi all, I wish to build a triggerable circuit that gives out a single-cycle, such as the one given in the pic attached (the middle one, with magenta and blue colours). While square/trapeziod/ramp cycles are good, even an exponential fall in the beginning and rise in the end would be fine (the...
  31. H

    Electric Field/Charge cycle, rotating mass problem

    An infinite line charge l is located along the z axis. A mass m that carries a charge q whose sign is opposite to that of l is in a circular orbit in the xy plane about the line charge. If m = 0.28 kg, q = 1.1 mC, l = 3.3 nC/m, and R = 0.25 m (the radius of the orbit), find the period. Help...
  32. D

    Solve Reheat Cycle Homework: Find Condenser Pressure, Output & Efficiency

    Homework Statement Given: A reheat Rankine cycle - Steams enter the high-pressure turbine at 12.5 MPa and 550C - It leaves at 2 MPa - Steam is reheated at constant pressure to 450C before it expands in the low pressure turbine - Isentropic efficiency of turbine = 85% - Isentropic...
  33. L

    Gas cycle, rankine cycle, organic rankine cycle, kalina cycle, and all that

    (maybe it fits better in this forum) Hello, I have been asked an advice about waste heat to power systems (say wh2p). The available waste heat to be considered is a (dirty) gas in a temperature range between 250°C and 450°C. The useful power that could be generated would range between...
  34. L

    Gas cycle, rankine cycle, organic rankine cycle, kalina cycle, and all that

    Hello, I have been asked an advice about waste heat to power systems (say wh2p). The available waste heat to be considered is a (dirty) gas in a temperature range between 250°C and 450°C. The useful power that could be generated would range between 2MW and 10MW. I know some examples...
  35. Astronuc

    Why is Solar Cycle 24 Starting So Slowly?

    The fingerprint of the new solar cycle http://sidc.oma.be/news/119/welcome.html A Long Filament Erupts (December 14, 2009) http://soho.nascom.nasa.gov/pickoftheweek/old/11dec2009/ Solar Cycle 24 is off to a slow start...
  36. A

    Properties of adjacency matrix of graph with cycle

    Let A be the adjacency matrix of some graph G. I am aware that A^n counts paths of length n between vertices of G, and that for graphs without cycles and non-singular A, (I-A)^-1 counts the total number of paths between vertices of G (correct me if any of this is wrong).This is a very...
  37. D

    Arbitrary cycle of digits in rational number?

    Hello all, I have recently been wondering whether there is a way to determine a fraction for which the decimal expansion is a cycle of n numbers? I would like to be able to work this out myself, but I can't wait until I start my mathematics degree. So any help would be greatly appreciated...
  38. J

    Efficiency of Rankine Cycle Using R141b - Confirmation Needed

    I've just completed a lab session on the Rankine Cycle using R141b as the working fluid and have obtained some values for the different effciencies in the cycle. I have that; ηTheoretical =13.01% ηPractical =12.07% ηIsentropic =5.90% I'm pretty sure I've followed the lab sheet correctly...
  39. C

    Brayton cycle solar generation.

    I've been trying to wrap my head around this one for a while. What are the drawbacks to using a brayton cycle solar generation setup? Here's the setup. It seems a car turbo is the cheapest and best suited so that's what I'll prototype if the idea gets that far. Atmosphere => Compressor =>...
  40. fluidistic

    Efficiency of an Ideal Gas Cycle: Monoatomic or Polyatomic?

    Homework Statement One mole of an ideal gas is used as the working substance of an engine that operates on the cycle shown in the figure. B-C and D-A are reversible adiabatic processes. 1) Is the gas monoatomic or polyatomic? 2)What is the efficiency of the engine? Homework Equations None...
  41. K

    Question about Otto Cycle: Why Does Compression Increase Temperature?

    I have a general question about otto cycle. If we heat a gas with constant volume its temperature rise according to PV=mRT. However during Isentropic compression(delta Q and delta S is zero), the volume is becoming less and pressure is increasing but i don't know why the temperature should...
  42. fluidistic

    Ideal Gas PV=nRT Cycle: Heat Exchange & Entropy

    Homework Statement Consider an ideal gas whose volume is initially V_0=1cm^3 that is initially at P_0=1 atmosphere. It goes through a cycle a-b-c-a where b-c is at constant temperature. 1)According to the sketch, does the system absorb or release heat? 2)Calculate the heat exchange in a...
  43. J

    Are Stages 2-3 and 1-4 in the OTTO Cycle Adiabatic?

    hey guys, just wanted to know, in the graph of the OTTO cycle in the link http://www.qrg.northwestern.edu/ther...Pv-diagram.gif are stage (2-3) and (1-4) adiabatic or not, if so why are they the reason i ask is that i have a graph showing that these stages are adiabatic, however...
  44. J

    Are stages 2-3 and 1-4 adiabatic in the OTTO cycle?

    hey guys, just wanted to know, in the graph of the OTTO cycle in the link http://www.qrg.northwestern.edu/thermo/design-library/otto/Otto-Pv-diagram.gif are stage (2-3) and (1-4) adiabatic or not, if so why are they the reason i ask is that i have a graph showing that these stages are...
  45. L

    Inverse relationship - neutron flux density with sunspot cycle

    Just over half-way down this page:- http://www.embedded.com/columns/technicalinsights/220301380?cid=RSSfeed_embedded_news it says:- "These sunspot counts show variation on a cycle of roughly 11 years. By overlaying Oulu neutron measurements with sunspot count data since 1964, we see that...
  46. T

    Ericsson cycle - calculating heat added/extracted from working substance

    The Ericsson cycle is as follows: 1) Isobaric expansion: temperature T2 goes to higher T1 at pressure P. 2) Isothermal expansion:pressure P1 goes to lower pressure P2 at constant T1 3) Isobaric compression: temperature T1 goes to lower T2 at pressure P2 4) Isothermal compression: pressure P2...
  47. T

    Ericsson cycle- question concerning entropy

    Hi! I have trouble with the following: 1) Consider an ericsson cycle. It is easy to calculate the change of entropy of the working substance during the isothermal parts. But assuming that all the heat transferred/removed from the working substance during the isobaric processes is done by...
  48. G

    Cycle decompositions of the rigid motions of the cube

    Homework Statement Write down cycle decompositions of all 24 of the rigid motions of the cube by regarding each rigid motion as a permutation of the 6 faces. Then, this is a subgroup of S_{6}, called S_{CUBE}. Prove or disprove that S_{CUBE} is a subgroup of A_{6} Homework Equations...
  49. S

    Superheated Vacuum Steam Cycle

    Ok bear with me as this sounds a bit bizarre, especially for a first post. For a while I have been thinking of how to take advantage of the fact that a black passive solar collector can collect low temp BTU's at low costs, but due to the low temperature it can not be utilized in a steam cycle...
  50. D

    Cycle Length of the Positive Powers of Two Mod Powers of Ten

    The positive powers of 2 mod 5^m cycle with period 4*5^(m-1), which you can prove by showing that 2 is a primitive root mod powers of 5. I want to prove that the positive powers of two, mod 10^m, also cycle with this same period. How do I go from this powers of 5 result to powers of 10...
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