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. N

    Thermodynamic Cycle Question

    Homework Statement Im given a table with values for Delta(Internal energy), Delta(KE), Delta(PE), Delta(E), Q, and W. For certain ones, certain values are missing and I have to fill in the blanks. Specifically- D()= Delta Process 1-2) D(U) =72, D(KE)= =5 , D(PE)= -6, D(E) = ? ...
  2. D

    Reversible cycle and adiabatic expansion

    Homework Statement One mole of a monatomic ideal gas is taken through the reversible cycle shown below. Process bc is an adiabatic expansion, with Pb = 10.0 atm and Vb = 1.00 x 10-3 m3. Find (a) the energy added to the gas as heat (b) the energy leaving the gas as heat, (c) the net work done...
  3. Helios

    Stargazing What is the Wells cycle and how long does it last?

    I discovered an eclipse cycle. It will be called the Wells cycle ( Garrick Wells ). It is simply a cycle of 51649 days. I believe that if you see an eclipse, then 51649 days later, another will likely be seen from your same location. I've have indeed found an example of this while probing the...
  4. B

    Power cycle efficiency problem

    Homework Statement A power cycle has a thermal efficiency of 40% and generates electricity at a rate of 100 MW. The electricity is valued at $0.08 per kW * h. Based on the cost of fuel, the cost to supply Qin is $4.50 per GJ. For 8000 hours of operation annually, determine, in $. a. The...
  5. S

    Sloan Deep Carbon Cycle Workshop

    I have been interested in atmospheric CO2 variance on geological time scales for sometime. There are multiple paradoxes associated with trying to explain what could cause massive cyclic rapid CO2 changes in the atmosphere. There appears to be multiple fundamental errors in terms of what is the...
  6. D

    A three step cycle problem check

    THE PROBLEM: A three step-cycle of an ideal monoatomic gas (3.40 mol) undergoes an (1) increase in temperature from 200 to 500K at a constant volume, is then (2) adiabatically expanded back to it's original pressure, then is (3) contracted at a constant pressure back to it's original volume...
  7. S

    Upright Washing Machine - Why no shaking during final spin cycle?

    Hello all As anyone with a front-loading washing machine knows, watching them in action can be great entertainment. Well, I was bored tonight and did just that. During the final spin cycle, the drum spins really, really fast (not too sure how many rpm) to wring most of the water out of the...
  8. H

    Cell Cycle & Cancer - Cyclin/Cdks

    Homework Statement General questions about how cancer affects the cell cycle... 1) Does cancer actually speed up the individual phases of mitosis (prophase, metaphase, anaphase, telophase) ... ie metaphase occurs 100x sooner following prophase in a cancer cell compared to a normal cell...
  9. S

    Adiabatic process in carnot cycle

    Hey. I'm supposed to calculate the work done in an adiabatic process, B-C, and I only know the values of the temperatures and the volume in the first point (point B). It is not known if it is a mono or diatomic gas, therefore i don't know the value of gamma. I've tried T*V^(gamma-1)=K and the...
  10. H

    Is the Otto Cycle Reversible with Ideal Gas Assumptions?

    Theoretically, we can have reversible isochoric expansion and isochoric compression. Is Otto Cycle reversible then? I read that the efficiency of all reversible engine between two heat reservoir would have the same efficiency. However, since the efficiency of an Otto Cycle is lower than...
  11. S

    The mud flies off the tyre of a moving motor cycle in the direction:

    the mud flies off the tyre of a moving motor cycle in the direction: -------------------------------------------------------------------------------- 1)towards the center of the wheel 2)towards the circular motion of the wheel 3)along the tangent to the wheel 4)away from the radius of...
  12. A

    If x is a cycle of length n, x^n is the identity.

    Is it true that if \sigma \in S_n is a cycle of length k \leq n, then \sigma^k = \varepsilon, where \varepsilon is the identity permutation, and that k is the least nonzero integer having this property?
  13. C

    Siren schematic: What controls the cycle speed?

    I found http://www.uoguelph.ca/~antoon/circ/wailing.htm" schematic for creating a siren sound, but I can't figure out which component could be altered to change the cycle time of 6 seconds. If I had to guess, I'd say either C1 or C4, but I'm really lost as to how this schematic works, so I...
  14. B

    Finding Enthalpies in a Brayton Cycle with Given Temperatures

    When looking at a brayton cycle, how do you find enthalpies when your only given temperatures? This is not a homework question, just reading through the textbook and cannot see where got the value from? Thanks
  15. B

    Increase the duty cycle of a pwm?

    I need to know how can I increase the duty cycle of a pwm. Thank you very much :)
  16. L

    Question about the refrigeration cycle

    A practical question about that cycle: I've just bought a new fridge and looked at the refrigeration cycle for the first time in 5 or so years. Now, i feel that the condenser at the back is quite warm (as it should be) and is being cooled by my room. All good and well. But how does the...
  17. A

    Solve Ideal Rankine Cycle Homework: Find Min Turbine Inlet Temp

    Homework Statement A steam power plant operates on a ideal rankine cycle between the pressure limits of 9 Mpa and 10 kPa. The mass flow rate through the cycle is 25kg/s. The moisture content of the steam at the turbing exit is not to exceed 10%. Determine the minimum turbine inlet temperature...
  18. A

    HELP NEED Engine cycle Question

    URGENT HELP NEED ! Engine cycle Question ! Q: Data on an engine cycle is presented.if the gas has a compression/expansion index of 1.4, determine the work done(KJ) in the cycle by theoratical and graphical means. compare your results. Given: Pressure in (Pa) p1= 1 X 105 p2= 11.764 X...
  19. M

    Refrigeration cycle with two compressors

    Homework Statement Here is the cycle: I am to assume cold-air standard applies. I need to: a)Draw a T-s diagram b)Find where heat is transferred and work is done c)Calculate the coefficient of performanceHomework Equations COP = 1 / (TH/TL - 1) The Attempt at a Solution For the T-s...
  20. A

    Reversible processes and carnot cycle

    i want to ask why heat transfer is considered ti be an irreversibility and why in carnot carnot cycle heat addititon is at constant temperature to make this process reversible
  21. C

    The Cardiac Cycle of the heart

    Hey guys, can someone make things clear for me? Does the heart goes atrial systole followed by ventricle systole then followed by both the atrial and ventricle diastole (at once) or atrial systole, ventricle systole (at the same time atrial diastole) then only ventricle systole?
  22. P

    Where Does Phosphate for ATP Cycle Come From?

    I am wondering where the phosphate needed to carry out the ATP cycle is derived from. Is it produced by our bodies, to we get it from the food we eat, or is eat based on a particular chemical reaction?
  23. C

    Thermal efficiency in a reversible cycle for an ideal gas pV diagram

    Homework Statement A heat engine takes 4.0 moles of an ideal gas through the reversible cycle abca, on the pV diagram, as shown. The path bc is an isothermal process. The temperature at c is 600 K and the volumes at a and c are 0.04 m^3 and 0.10m^3, respectively. The molar heat capacity at...
  24. A

    How Does the Otto Cycle Work in a Cold Environment?

    Homework Statement Analyze an air-standard Otto cycle assuming it is a cold cycle with properties evaluated at 300 K. Air intake and exhaust are at 300 K, 1 bar. After the combustion (heat in) process, the temperature is 2500K. The compression ratio is 9. The volume at bottom dead center...
  25. K

    Cycle time of different methods of metal manufacturing

    Hi all, Currently I am in my internship, so I don't have any real experience in metal manufacturing. I have a difficulty of calculating the cycle time of producing a product. The product is a waterpipe fitting. The Fitting itself has 3 different types (Straight, 90-degrees elbow, and...
  26. A

    Average value of AC over a complete cycle is always zero

    Homework Statement Statement 1: Average value of AC over a complete cycle is always zero. Statement 2: Average value of AC is always defined over half cycle. We need to tell whether these two statements are right, and if 1 is right then whether 2 is its explanation. Homework...
  27. N

    What is the PDF of a Sine Wave Cycle?

    Does anybody know what the pdf of a sine wave cycle is? Or perhaps how to derive it? The problem can be done numerically, but surely there is an analytic expression for this function? There is a numerical solution available at...
  28. S

    Is an Ideal Cycle Possible? Examining Enthalpy Values in a Lab Experiment

    Is an ideal cycle possible? In a lab experiment that I have carried out, my enthalpy values for the cycle and the cycle assuming isentropic compression look like they are the same. I thought this was impossible but I am doubting myself now? Thanks Will
  29. S

    Thermodynamic cycle, work, energy heat input solving

    Homework Statement An ideal diatomic gas, in a cylinder with a moveable piston undergoes the rectangular cyclic process shown below. Assume that the temperature is always such that the translational and rotational degrees of freedom are active but the vibrational modes are "frozen out". Also...
  30. M

    What Is The Cause Of The Millennial Cycle?

    The 1-2 ky climate cycle is clearly evident in the paleoclimate records and is of primary importance in future predictions. But what actually is the driving mechanism of this cycle? http://www.sciencemag.org/cgi/content/abstract/278/5341/1257
  31. M

    A Simple The 100-Kyr Tidal Cycle?

    I was slightly exasperated with this http://www.sciencemag.org/cgi/content/abstract/289/5486/1897 report: "It is difficult to explain this predominant cycle in terms of orbital eccentricity because the 100,000-year radiation cycle (arising from eccentricity variations) is much too small in...
  32. B

    Steam power plant cycle design, Mollier Diagram help

    Hi posted the question/cry for help in a regular thread but thought it might fit in here as well. Hello All, I am currently trying to optimize a steam power plant cycle and I am stuck... What I am unable to figure out is how to use a Mollier chart/diagram in order to determine the amount of...
  33. K

    What is the Efficiency of a Carnot Refrigerator?

    In the textbook, it reads: the reverse of carnot cycle is just a refrigerator or heat pump. In this sense, except for the direction of carnot cycle is reverse, could I say the way to calculate the efficiency of the carnot refrigerator is the same? That is, could be still use \eta = 1 -...
  34. F

    Non-Isentropic Diesel Cycle (with variable specific heat)

    Homework Statement I must find temperature at each state, for starters. This is a Diesel cycle with a non-isentropic compression process, but standard the rest of the way. The specific heat is variable with temperature. Fluid is air Givens: compression efficiency (\eta_{c}), initial...
  35. J

    ATP in Fatty acid oxidation and citric acid cycle

    At what point in either beta-oxidation or citric acid cycle is ATP used? I see where ATP is produced in citric acid cycle (originally as GTP) as when succinyl CoA is converted to Succinate, but I can't find any part where ATP is required. Apparently according to my lecture notes, it is...
  36. J

    Where Does the Second Water Come From in the Glyoxylate Cycle?

    Where does the second water come from ? I get that the first one comes in the conversion of citrate to isocitrate, but where does 2nd one come in? thanks
  37. J

    Citric Acid Cycle -matching carbons

    Citric Acid Cycle --matching carbons Which glucose carbons are pyruvate carbons from? I've been trying to get this for hours. please help.. Also how do you trace carbons along the ciric acid cycle?
  38. D

    How Does the Otto Cycle Affect Internal Energy Change?

    The idealized cycle shown is known as the Otto cycle. (Intro 1 figure) Suppose an engine is executing this Otto cycle, using a gas (not necessarily ideal) as its working substance. From state A to state B, the gas is allowed to expand adiabatically. (An adiabatic process is one in which no...
  39. J

    Bridging Step of Krebs Cycle oxidatiion or reduction?

    Bridging Step of Krebs Cycle...oxidatiion or reduction? I am told that the following reaction is a oxidative decarboxylation: pyruvate +CoA + NAD+ ---> acetyl CoA + CO2 + NADH but NAD+ is reduced to form NADH... Do we call it an oxidation because we are interested in what...
  40. V

    Setup Thermodynamic Cycle for Enthalpy of Hydration of Mg2+ Ions

    Homework Statement Set up thermodynamic cycle for determining the enthalpy of hydration of Mg2+ ions The following enthalpies are given Sublimation of Mg ionization energies of Mg dissociation enthalpy of Cl2 electron gain enthalpy of Cl enthalpy of solution of MgCl2(s) enhalpy of...
  41. R

    Understanding He Closed Cycle Cryos and Vibration Damping

    Hi All, I need some basic info of He closed cycle cryos..(like working principle, etc).. I have a compressor, which compress He gas and passed into a cryo's coldhead. So He gas expands in side the coldhead and cools the coldhead..then it again passes into compressor..so the cycle repeats.. I...
  42. C

    How Much Energy is Released in the First Step of the CNO Cycle?

    Homework Statement The first step of the CNO cycle is p \rightarrow C_{6}^{12} \rightarrow N_{7}^{14} + \gamma Estimate the energy of the CNO cycle, state any assumptions. Homework Equations - The Attempt at a Solution I was looking at mass difference, (1.00728u...
  43. T

    Cycle decomposition of n-cycle's power

    Homework Statement let a=(b_1,...,b_n) n-cycle in the permutation group S_n . prove that the cycle decomposition of a^k consist of gcd(n,k) cycles of n/gcd(n,k) size. The Attempt at a Solution I know that a^k(b_i)=b_{i+k (mod n)} how can it help me ?
  44. C

    Engine cycle analysis pls help

    A twin- spool turbojet powered aircraft flies at 600(ms-1) at an altitude where the temperature and pressure are 0.116bar and 216K. The air mass flow rate into the engine intake is 20kgs-1. The isentropic efficiences of the components are: intake (diffuser) 0.95; low pressure compressor: 0.92...
  45. E

    Designing a High-Efficiency Steam Power Cycle: Tips and Cost Considerations

    I am trying to come up with a design for a steam power cycle with a 40% thermal efficiency under the conditions that all turbines have isentropic efficiencies of 85% and all pumps have isentropic efficiencies of 60%. I have tried superheat, reheat, playing around with pressures/temperatures...
  46. U

    Circular Limit Cycle Homework: Find Fixed Points, Amplitude & Period

    Homework Statement Consider the system x''+ax'(x2+x'2-1)+x = 0, where a>0. a)Find and classify all the fixed points. b)Show that the system has a circular limit cycle, and find its amplitude and period. c)Determine the stability of the limit cycle.Homework Equations y = x' For fixed points...
  47. E

    Design Rankine Cycle: $40K Budget, Calculate Payback Time

    Homework Statement I have a project for a class of mine that asks me to design a rankine cycle to produce electricity from a lake using temperature differences between the water and the atmosphere. I have a budget that I must stick with ($40,000), a defined effeciency for the pump (50%)...
  48. H

    Problems with a motor cycle battery

    Hi, Apologies in advance if this is not an academic enough question for you, I have a lawn mower that needs a motorcycle battery to start it. The battery has to sit flat on its side. The battery I have bought has a vent on the side and when I leave it on its side the battery acid leaks...
  49. A

    Nitrogen Biogeochemical Cycle (kinda)

    Homework Statement Is this following statement true? Extensive fertilization results in a shift in the the coupled equilibria of the Nitrogen Biogeochemical Cycle, driving into run off rivers, lakes, and oceans. This is a major factor behind the plume of algae growth, in the Gulf of...
  50. thenewmans

    Binary cycle power plants – One small part I don’t get

    I don’t get how a http://www1.eere.energy.gov/geothermal/powerplants.html#binarycycle" keeps the fluid flowing in one direction. My guess is it has something to do (1) with the condenser and (2) with a pump thrown in. The problem with a pump is that it must use up as much energy as the heat puts...
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