(10.4) Evaporative cooling A cloud of atoms has a Boltzmann energy distri- bution N(E)= Ae-E, where...
Fantastic news! We've Found the answer you've been seeking!
Question:
Transcribed Image Text:
(10.4) Evaporative cooling A cloud of atoms has a Boltzmann energy distri- bution N(E)= Ae-E, where 1/3 = kBT and the normalisation constant A is found from Af -BE dE = The cloud has a total energy given by Etotal = A Ee-BE DE AS Ntotal = A 3 = NtotalkBT. Hence each atom has a mean energy E = kBT. In an evaporative cooling step all atoms with energy greater than e escape. (a) Calculate the fraction of atoms lost AN/Ntotal. (b) Calculate the fractional change in the mean energy per atom. (c) Evaluate your expressions for cuts with 3 = 3 and 6. Compare the ratio of energy lost and the number of atoms removed in the two cases and comment on the implications for evaporative cooling. (d) The collision rate between atoms in the cloud is Rcoll= nuo. Assuming that the collision cross-section is independent of the energy, show that Reoll x Ntotal/Etotal in a harmonic trapping potential. Show that the collision rate increases during evaporation in such a potential. 10.4) Initial Boltzmann distribution: N(E)= Ae-E Normalization condition: No = A fedE = A/B Total energy: E = Af Ee-dE = A/ = NokT Mean energy: E=1/3=kT For a distribution truncated at energy e N = A fedE = No (1-e) where 3= kBT E = A EedE = (1-e-c-ce-) Therefore the mean energy after truncation is: E =kBT x 3 6 Fractional changes (in terms of r= c/kBT): (a) = , (b) and (c) exp(-x) = | 16% e-6-0.25% 1.5% Bee-le 1-e-Be 6.0 Cutting less deeply is more efficient, i.e. it de- creases the temperature more for a given loss I atoms. In this example 20 small cuts with Be= 6 would give about the same loss of atoms sa single cut with e= 3, but the many small cuts reduce the energy by twice as much as the single large cut. (d) AE/F ANIN Density n~ N/4r and M = TE therefore n x N/E/2, Speed x E/2, So the collision rate Reall na x AR = AR R N EREN Write this as R=AN/E where A = constant. A (AN-EN) -45 AN AE N E N = E The collision rate increases, e.g. using the val ues from part (c), a cut with z=3 gives =-5% - (- 16 %) = +11% (10.4) Evaporative cooling A cloud of atoms has a Boltzmann energy distri- bution N(E)= Ae-E, where 1/3 = kBT and the normalisation constant A is found from Af -BE dE = The cloud has a total energy given by Etotal = A Ee-BE DE AS Ntotal = A 3 = NtotalkBT. Hence each atom has a mean energy E = kBT. In an evaporative cooling step all atoms with energy greater than e escape. (a) Calculate the fraction of atoms lost AN/Ntotal. (b) Calculate the fractional change in the mean energy per atom. (c) Evaluate your expressions for cuts with 3 = 3 and 6. Compare the ratio of energy lost and the number of atoms removed in the two cases and comment on the implications for evaporative cooling. (d) The collision rate between atoms in the cloud is Rcoll= nuo. Assuming that the collision cross-section is independent of the energy, show that Reoll x Ntotal/Etotal in a harmonic trapping potential. Show that the collision rate increases during evaporation in such a potential. 10.4) Initial Boltzmann distribution: N(E)= Ae-E Normalization condition: No = A fedE = A/B Total energy: E = Af Ee-dE = A/ = NokT Mean energy: E=1/3=kT For a distribution truncated at energy e N = A fedE = No (1-e) where 3= kBT E = A EedE = (1-e-c-ce-) Therefore the mean energy after truncation is: E =kBT x 3 6 Fractional changes (in terms of r= c/kBT): (a) = , (b) and (c) exp(-x) = | 16% e-6-0.25% 1.5% Bee-le 1-e-Be 6.0 Cutting less deeply is more efficient, i.e. it de- creases the temperature more for a given loss I atoms. In this example 20 small cuts with Be= 6 would give about the same loss of atoms sa single cut with e= 3, but the many small cuts reduce the energy by twice as much as the single large cut. (d) AE/F ANIN Density n~ N/4r and M = TE therefore n x N/E/2, Speed x E/2, So the collision rate Reall na x AR = AR R N EREN Write this as R=AN/E where A = constant. A (AN-EN) -45 AN AE N E N = E The collision rate increases, e.g. using the val ues from part (c), a cut with z=3 gives =-5% - (- 16 %) = +11%
Expert Answer:
Related Book For
Income Tax Fundamentals 2013
ISBN: 9781285586618
31st Edition
Authors: Gerald E. Whittenburg, Martha Altus Buller, Steven L Gill
Posted Date:
Students also viewed these physics questions
-
Let A, B be sets. Define: (a) the Cartesian product (A B) (b) the set of relations R between A and B (c) the identity relation A on the set A [3 marks] Suppose S, T are relations between A and B, and...
-
can someone solve this Modern workstations typically have memory systems that incorporate two or three levels of caching. Explain why they are designed like this. [4 marks] In order to investigate...
-
What is the significance of communication between managers and their subordinates, and how does it impact employee performance?
-
Bond ABC is a 6 percent coupon bond. Bond XYZ is a 11 percent coupon bond. Both bonds have 11 years to maturity, make semiannual payments, and have a YTM of 8.5 percent. If interest rates suddenly...
-
Holdaway Company is preparing financial statements for the calendar year 2012. The following totals for each account have been verified as correct: Office Supplies on Hand. . . . . . . . . . . . . ....
-
Randomly permute each row of the matrix below using R. \[\left[\begin{array}{llll}1 & 1 & 1 & 1 \\2 & 2 & 2 & 2 \\3 & 3 & 3 & 3 \\4 & 4 & 4 & 4\end{array} ight]\] You can construct the matrix below...
-
Wonderful! Not only did our salespeople do a good job in meeting the sales budget this year, but our production people did a good job in controlling costs as well, said Kim Clark, president of...
-
Calculate the angular momentum of a 265 kg motorcycle traveling at 25 m/s. traveling around a circular curve 500 m in radius
-
Q1 JE # 1 JE # 2 JE # 3 JE # 4 Business Insurance Annual Expense Coverage Period Here is the billing schedule of the insurance carrier. Invoice Schedule Invoice Amount Installment 1 Installment 2...
-
Listed below are the values of 24-hours temperature change (in F) for 14 different cities. Positive values correspond to "warmer than the day before" temperature, and negative values to "colder than...
-
Michael earns $110,000, and his tax liability for the current year is $8,000, double what it was the previous year.To avoid penalties, how much do his combined payments (withholding and credits) have...
-
Assume a stock with a volatility of 0.5 sells at $50. The risk-free rate is 6% per annum and volatility is 0.2. What is the price of a European call with a $50 strike and time to expiration 3 months?
-
What are the costs of implementing an accounting change? What are some other possible costs of changing accounting methods? Can you think of examples other than the ones provided in your reading this...
-
GAF was approached by the AAA Airline to see if it would be interested in auditing AAA. GAF was open to the notion, but disclosed to AAA that it had long audited several other airline companies....
-
A number of states have legalized marijuana possession and use up to certain levels designated in their laws. Several other states have legalized marijuana possession and use for medicinal purposes,...
-
2. Morphine is a weak base with a pk, of 5.80. a) If 25.0 mL of a 0.0700 M morphine solution is titrated with 0.100M hydrochloric acid, what will the pH of the solution be at the equivalence point?...
-
Consider a closed, rigid tank with a volume of 0.8L, filled with cold water initially at 27C. The tank is filled such that there are no voids (air pockets) within. The initial pressure within the...
-
Frank Willingham has the following transactions during the year: Sale of office equipment on March 15 that cost $20,000 when purchased on July 1, 2010. Frank has claimed $5,000 in depreciation and...
-
Joan is a self-employed attorney in New York City. Joan took a trip to San Diego, CA, primarily for business, to consult with a client and take a short vacation. On the trip, Joan incurred the...
-
Clifford Johnson has a limited partnership investment and a rental condominium. Clifford actively manages the rental condominium. During 2012, his share of the loss from the limited partnership was...
-
Nestls financial statements are presented in Appendix B. Financial statements of Delfi Limited are presented in Appendix C. Instructions Refer to the financial statements and answer the following...
-
Writing Financial statement information about four different companies is as follows. Instructions a. Determine the missing amounts. (Hint: For example, to solve for (a), Assets Liabilities = Equity...
-
The financial statements of TSMC are presented in Appendix A. The complete annual report, including the notes to the financial statements, is available at the companys website. Instructions Refer to...
Study smarter with the SolutionInn App