Cycle Definition and 674 Threads

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. Genava

    I Variations in Sun-Earth distance with a 2000-year cycle?

    Hi, I see that a newspaper is making a claim that Zharkova identified a 2000-year cycle causing some significant variations in Sun-Earth distance with a cycle of 2000 years, seemingly because of the perturbations caused by Jupiter making the Sun orbiting a barycentre slightly eccentric. This...
  2. JD_PM

    Heat engine undergoing an elliptical cycle

    An ideal diatomic gas undergoes an elliptic cyclic process characterized by the following points in a ##PV## diagram: $$(3/2P_1, V1)$$ $$(2P_1, (V1+V2)/2)$$ $$(3/2P_1, V2)$$ $$(P_1, (V1+V2)/2)$$This system is used as a heat engine (converting the added heat into mechanical work). Evaluate the...
  3. S

    I Prove that a given graph contains a cycle using induction (Graph Theory)

    My Problem: Given a Graph G = (V,E), where the number of vertices is less than or equal to the number of edges, use induction to prove that the graph contains at least one cycle (the graph is not required to be completely connected). My attempt: For my base case, I used only one vertex with one...
  4. Z

    MHB Calculating amount left at the end of a repetetive cutting down cycle.

    Let's say I have a group of X's characters that I want to cut down. I use a tool similar to 'find-and-replace-all', which takes an amount of X's each time, deletes them, and replaces them with another, smaller amount. For example, I can state that I want an amount of 8 X's to be replaced with 5...
  5. C

    Could somebody please explain the vapor compression cycle?

    Heat is taken from food in the refrigerated space to the evaporator which has evaporated (I am assuming saturated vapor) refrigerant flowing through it. My first stumble would be, if this is true, why doesn't the temperature increase for the fluid coming out of the evaporator (unless it is...
  6. M

    Thermodynamics: Joule / Brayton Cycle - Specific Work Done Question

    Relevant Equations: Specific Work Done: w = \frac{p_2 v_2 - p_1 v_1}{1-\gamma} (1) w = \frac{R}{1-\gamma} \times (T_2 - T_1) (2) Thermal efficiency: \eta _{th} = 1- \frac{1}{r_p ^ {\frac{\gamma - 1}{\gamma}}} = \frac{w_{out} - w_{in}}{q_{in}} = \frac{q_{out} - q_{in}}{q_{in}} (3) Context...
  7. TheBigDig

    Efficiency of the Rankine Cycle

    WT, the work done by the turbines, as the difference in enthalpy from point 2 to point 3 WP, the work done by the pumps as the difference in enthalpy from point 4 to point 5 Q as the difference in enthalpy from point 3 to point 4 Taking these I get h5 = -252.3kJ/kg. However, my work ratio is...
  8. Clara Chung

    Can the Maximum Efficiency of a Thermal Cycle Be 2/5?

    Attempt: a) Leg 4 and Leg 1 W=P_0(V_1-V_0)+P_1(V_0-V_1) b) Leg 4: Q= C_v*ΔT=C_v*ΔP*V_0/nR = 3/2*(V_0*P_0-V_0*P_1) Leg 1: Q=C_p*ΔT=C_p*P_0*ΔV/nR = 5/2*(P_0*V_1-P_0*V_0) Q=3/2*(V_0*P_0-V_0*P_1)+ 5/2*(P_0*V_1-P_0*V_0) c) W/Q = [P_0(V_1-V_0)+P_1(V_0-V_1)] / [3/2*(V_0*P_0-V_0*P_1)+...
  9. EastWindBreaks

    Heat exchanger - efficiency of the cycle

    Homework Statement Homework EquationsThe Attempt at a Solution Since we want the fluid to be in liquid state before entering a boiler, and super-heated water can only reach 374°C before entering super-critical state, suppose after the expansion, the temperature at point 3 is still higher than...
  10. L

    Why Do Different Methods Yield Different Efficiencies in a Reversible Cycle?

    I just read about Carnot theorem (the highest efficiency is the one of reversible machines and all reversible machines working between two given temperatures have the same efficiency). Then I found a problem where I have a reversible cycle made of an isochoric, adiabatic and isotherm. I report...
  11. H

    Thermal efficiency of the Rankine cycle

    Homework Statement Calculate thermal efficiency of R-C cycle with saturated steam as shown in the picture. Steam has 4,5MPa when entering into HP part of the turbine (VT in the picture) and expansion on HP is finished at 0,3MPa. Moisture is then removed in the separator and steam is overheated...
  12. E

    Why does air rise in the water cycle?

    Hi there! I'm teaching about rain shadows to 6th graders, and I've reached a barrier in my content knowledge. For the water cycle to work, warm, wet air near Earth's surface has to rise. In general, warm air is less dense than cold. However, due to air pressure, air near Earth's surface is...
  13. M

    Need help in thermodynamics: Calculations for a thermal cycle

    Homework Statement how to know the maximum and minimum temperature for cycle in. Carnot thermal efficiency 60% heat transfer during isothermal expansion 40kj pressure is 5.6bar and volume is 0.3m^3 Homework Equations One kilogram of air as an ideal gas executes a Carnot power cycle having a...
  14. D

    Understanding the Cardiac Cycle: Diastole & Systole

    I am unsure about the underlined parts of the cardiac cycle. I was taught that the cardiac cycle started when the blood flowed into the atrium, but wouldn't there be a period when both artia and ventricles are at diastole simultaneously? For the second underlined part I was taught and read that...
  15. M

    Thermodynamics - water vapour cycle

    Homework Statement How to calculate the specific work done. Homework Equations Water vapor initially at 10 bar and 400 °C is contained within a piston-cylinder assembly. The water is cooled at constant volume until its temperature is 150 °C. The water is then condensed isothermally to saturated...
  16. F

    Do Carnot and Stirling Engines Have the Same Efficiency?

    Hi, I have some doubts and questions about the above thermodynamic cycles. These questions arise from some statements I find in a couple of textbooks: "Physics, 10th edition" by Cutnell et al [A], and the other is "Fundamentals of Physics" by Halliday and Resnick . Actually, I have the versions...
  17. davenn

    Stargazing What is the likelihood of another solar grand minimum occurring soon?

    greeting all Over the last 2 weeks I have noted the first sunspots of the new solar cycle 25. How do I know they are spots of the new cycle ? Because they are higher latitude and opposite magnetic polarity. Before I show an image, a little history and science. Over the many observed solar...
  18. Screwed

    How to calculate a coefficient of performance (COP)

    Homework Statement Homework Equations [/B][/B] 3. The Attempt at a Solution Here's my solution attempt: NOTE: Evolution 2 to 3 is really an isothermic process, but in the diagram shows as an politropic process. 4. Further Questions But it isn't giving me logical values of COP...
  19. karush

    MHB How about this? What is the inverse of a permutation cycle?

    $\tiny{412.5.9}$ this is under the section on Permutation Groups What cycle is $(a_1a_2\dots a_n)^{-1}$ ok thot there would be and east theorem on this but can't find
  20. T

    How to Calculate Efficiency of a Van der Waals Gas Cycle?

    Homework Statement n moles of gas, that follow van der Waals equation are to be employed as the auxiliary system in a circular cycle(parameterized using T_h and T_c as shown on the TS diagram. Calculate the efficiency of the cycle. Homework Equations , , Q = TdS The Attempt at a Solution...
  21. T

    Carnot Cycle efficiency, temperature dependency

    Hi, We know that a heat engine working on a Carnot Cycle the efficiency is: 1 - QL/QH = 1 - TL/TH where T is in Kelvin. But if we use a different absolute temperature scale whose values at TH and TL are different, then the value of efficiency also changes. I am confused about this issue...
  22. V

    Otto and Diesel Cycle: Heat Addition & Cutoff Ratios

    In case of Otto cycle we consider that heat is immediately added to air fuel mixture(i.e constant volume heat addition) but in case of diesel cycle we consider heat addition at constant pressure and we also talk of cutoff ratios.why so??
  23. H

    What is a good experiment for carnot cycle?

    im thinking of a stirling cycle but if otherwise then please tell as soon as possible
  24. Mr Davis 97

    Show that the order of a cycle is the length of the cycle

    Homework Statement Prove that if ##\sigma## is the m-cycle ##(a_1 ~a_2~ \dots ~ a_m)##, then for all ##i \in \{1,2, \dots , m \}##, ##\sigma^i (a_k) = a_{k+i}##. Deduce that ##\sigma^m (a_k) = a_k## Homework EquationsThe Attempt at a Solution I will try to do this by induction. Clearly...
  25. Benhur

    The entropy of a Carnot cycle and the efficiency equation

    I have my first question. It's about entropy in the Carnot cycle and I'll try to be direct. The equal sign in the Carnot cycle efficiency equation is related to the fact that the total entropy doesn't change at the end of the whole cycle (being related to the fact that the heat exchanges occur...
  26. Alexandre Ricardo

    Efficiency in a thermodynamic cycle

    I have to calculate the efficiency of the above cycle for an ideal gas, that goes at the order a-b-c-a: I know that the answer is 16/97 but I can't calculate the heat in the a-b stage.
  27. physea

    I Understanding the Parameters of an Ideal Refrigeration Cycle

    Hello, Can anyone tell me please the P,V,h, etc, ie all parameters for an ideal refrigeration cycle? I am not sure which points of the cycle have same pressure, temperature, etc. Thanks!
  28. Lucw

    The Carnot Cycle: Efficiency and Validity with Gases, Solids, and Liquids

    Hello The Carnot cycle has 4 stages. 1. Isothermal relaxation. The gas provides mechanical energy to the piston and receives heat. 2. Adiabatic relaxation. The gas provides mechanical energy to the piston and cools. 3. Isothermal compression. The gas receives mechanical energy from the piston...
  29. Rafe Zayed

    Second law efficiency of Rankine cycle

    Can you provide me any source from where I can learn about the overall second law efficiency calculation of a simple Rankine cycle?
  30. Jschrodes4

    Single Cycle Pressure Test for Pressure Vessel

    Homework Statement I need to design a pressure test that, in one cycle, will simulate the 8000 cycles that a given pressure vessel will undergo. I know the dimensions and material of the vessel, the number of pressure cycles it will undergo, and the max and min working pressures. Homework...
  31. Z

    Setting Up a 12V DC Test Stand w/ Controller & Cycle Count

    Setting up a test stand that will need a controller to cycles a device ON and OFF at an adjustable time interval (allows me to make the ON duration and OFF duration whatever I want). It will also need to keep a count, so I can track the cycles count and also set a limit on cycles so it will stop...
  32. Y

    Nuclear fuel cycle boc eoc boec eoec?

    Hello everyone! I have my first question in physics forum... When I read some reports I found those terms that can not be understood... 'BOC', 'EOC', 'BOEC', 'EOEC'... BOC and EOC are used frequently and I know those terms shortly but not exactly... but I can understand boec and eoec and...
  33. physea

    B Analyzing open steady flow systems with SFEE vs. Rankine cycle analysis

    Hello I have a point that I don't understand. In open steady flow systems, we use SFEE, where there's a term W in addition to a term PV, which are different things. When we analyse a cycle like Rankine, we always consider either W or PV, but not both. I also think that W=PdV always. Why that...
  34. Al_Pa_Cone

    Steam and Gas Turbines - The Rankine Cycle

    <<Moved from another forum, thus no template filled out.>> I am having some trouble trying to relate a question given in my distance learning lessons to the equivelent question in my assignment. The assignement question is: 1(a) Superheated steam at a pressure of 40 bar and a temperature of...
  35. morrobay

    Amplitude of Wave at 5pi/6 Radians in Cycle, y = Asin(kx-wt)

    Homework Statement λ = 3m T = .5 s k= 2π/λ = 2.09 radians/m ω= 2π/T = 12.56 = radians/sec v = ω/k = 6m/sec At π radians with sin wave x = 3m At 5π radians/6, x = 2.48 m t = 2.48m/6m/sec = .41 sec What is y at x,t At t0 x = t = 0 [/B]Homework Equations y = Asin(kx-ωt)[/B]The Attempt at a...
  36. L

    How Is the Enthalpy of Formation for Lithium Fluoride Calculated?

    Homework Statement calculate enthalpy of formation for lithium fluoride... LiF Homework Equations Given from the worksheet is: Lithium sublimation = 129 kj/mol Lithium first ionization = 520 kj/mol bond-dissociation energy of fluorine is 159 kj/mol F2 electron affinity for fluorine is -328...
  37. T

    Calculate minimum work input of refrigeration cycle

    Homework Statement The temperature of a 12-oz (0.354-L) can of soft drink is reduced from 20 to 5 ºC by a refrigeration cycle. The cycle receives energy by heat transfer from the soft drink and discharges energy by heat transfer at 20 ºC to the surroundings. There are no other heat transfers...
  38. F

    Proof about cycle with odd length

    Homework Statement In the following problems let ##\alpha## be a cycle of length ##s##, and say ##\alpha = (a_1a_2 . . . a_s)##. 5) If ##s## is odd, ##\alpha## is the square of some cycle of length s. (Find it. Hint: Show ##\alpha = \alpha^{s+1}##) Homework EquationsThe Attempt at a Solution...
  39. S

    I How fast do you need to cycle to simulate bicycle tire inflation

    My question comes from a moment when I was riding my bike. I had a flat tire. My question then was how fast do i need to cycle so that i don't ride on my rim's anymore. I tride calculating this with the force that i put on the tire (15kg+70kg= mass of the bike and I)*g= 833,85 N that devided by...
  40. S

    Thank you for your response AM. I appreciate it and will work through the steps.

    Homework Statement [/B] A four-stroke petrol engine with a compression ratio of 9 has a total swept volume of 2.71 litres distributed over 4 cylinders. Assume the corresponding ideal thermodynamic cycle and the following conditions to calculate the maximum amount of fuel which can be safely...
  41. J

    Pressure, Volume, and Temperature at a Point in a Thermodynamic Cycle

    Homework Statement Question: https://imgur.com/a/8rUw1 Graph: https://imgur.com/a/Z1oBO Homework Equations Answer for Q1 (Just the formula) : https://imgur.com/a/uesqN The Attempt at a Solution I have realized that from 1-2, there is an increase in pressure, decrease in volume and increase...
  42. Pushoam

    Work extracted from a general cycle

    Homework Statement In each cycle, the heat given to the system from the reservoir is dQ##_i##. So, why is the total work given by summing ##dQ_i ## over the cycle,why not only ##dQ_i##? Homework EquationsThe Attempt at a Solution
  43. S

    Energy in each cycle of transverse wave?

    Homework Statement Homework EquationsThe Attempt at a Solution a. ##{ P }_{ avg }=\frac { 1 }{ 2 } \mu v{ \omega }^{ 2 }{ A }^{ 2 }=\frac { 1 }{ 2 } 0.075\frac { 10 }{ 3 } { 0.35 }^{ 2 }{ (10\pi ) }^{ 2 }=15.1W## b. Not sure how to calculate that... I'm guessing it'd be some integral over 1...
  44. M

    Question About Duty Cycle and Average Value of a Square Wave

    Homework Statement [/B] 1. Using the Schematic of a 555 in astable mode from the Wikipedia entry on '555 Timer IC," resistor R1 = 8 kOhms and capacitor C = 3 micro-Farads. Determine the value of R2 so that the output duty cycle is D = 0.7. Note that D is not expressed as a percentage here for...
  45. C

    A question about second cycle studies

    Hello fellow science enthusiasts! I have a question about second cycle studies. I'm in my last year of high school and I wish to study applied physics. However, my choice of university doesn't offer a programme in applied physics. For a first cycle I can pick Physics, Astronomy or Physics Ed...
  46. Borek

    555 timer, 50% duty cycle astable, run from 5V

    Standard disclaimer: I know next to nothing about electronics (which doesn't stop me from having fun :wink: ) I have a buzzer here that I am trying to run from an 555 based oscillator. I need around 2700 Hz and 50% duty cycle, and it would be best to run whole thing from 5V. 50% duty cycle is...
  47. S

    Thermodynamic Cycle 2: Understanding PV^y, Cp/Cv and PV=nRT

    2. PV^y = const, y=Cp/Cv, PV=nRT, 3. I've drawn the cycle for part a) of the question, but I'm not sure how to do part b). I know I need to relate Vm and 4Vo using the PV^y = constant relation but I'm stuck as to how to do it.
  48. AGiantGolden49er

    Thermodynamics Power Cycle Energy Balance

    Homework Statement As shown in Fig. P5.39, a system undergoing a power cycle develops a net power output of 1 MW while receiving energy by heat transfer from steam condensing from saturated vapor to saturated liquid at a pressure of 100 kPa. Energy is discharged from the cycle by heat transfer...
  49. MCTachyon

    Rankine Cycle Efficiency Calculation - Superheated Steam at 40 bar and 500°C

    Homework Statement Superheated steam at a pressure of 40 bar and a temperature of 500°C is supplied to the turbine of a Rankine cycle. If the condenser pressure is 0.03 bar. Find the thermal efficiency of the cycle. (Neglect feed pump work). I used steam tables found...
  50. T

    Can hydraulic systems replace ebikes in power assisted cycle

    Instead of an electric motor, can it be substituted with an hydraulic force / power amplifying system instead? If yes, how would it work? Could chains still be used? Instead of an electric motor powering the hydraulic system, could the rider power the hydraulic system through force / power...
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