Looking Beyond Fossil Fuel Divestment: Combating Climate Change in Higher Education

The young fossil fuel divestment movement is altering the landscape of climate change activism on US campuses. Student-run divestment campaigns are now pushing for institutions of higher education to withdraw their investments from the top 200 public fossil fuel companies. Despite student fervor, however, divestment has remained a controversial tactic for combating climate change. The first half of this thesis examines the stated motives of a selection of institutions that have officially agreed or declined to divest, and investigates the hypothesis that pushing for divestment alone will not achieve broad success because it does not appeal to a wide enough range of motives that may persuade people to engage in environmentally beneficial behavior. A multi-pronged approach to climate change activism that advocates for many initiatives to fight climate change may see more success than a singularly divestment-centered approach because it is more flexible and inclusive. The second half of this thesis offers an index of suggested actions from which activists and institutions of higher education could craft a multi-pronged approach to fight climate change. These measures, including climate neutrality goals, environmental education initiatives, and various types of internal financial mechanisms, may go a long way in improving the chances for success in climate change activism on campuses

N=2 superconformal nets

We provide an Operator Algebraic approach to N=2 chiral Conformal Field Theory and set up the Noncommutative Geometric framework. Compared to the N=1 case, the structure here is much richer. There are naturally associated nets of spectral triples and the JLO cocycles separate the Ramond sectors. We construct the N=2 superconformal nets of von Neumann algebras in general, classify them in the discrete series c<3, and we define and study an operator algebraic version of the N=2 spectral flow. We prove the coset identification for the N=2 super-Virasoro nets with c<3, a key result whose equivalent in the vertex algebra context has seemingly not been completely proved so far. Finally, the chiral ring is discussed in terms of net representations.Comment: 42 pages. Final version to be published in Communications in Mathematical Physic

Migration, trapping, and venting of gas in a soft granular material

Gas migration through a soft granular material involves a strong coupling between the motion of the gas and the deformation of the material. This process is relevant to a variety of natural phenomena, such as gas venting from sediments and gas exsolution from magma. Here, we study this process experimentally by injecting air into a quasi-2D packing of soft particles and measuring the morphology of the air as it invades and then rises due to buoyancy. We systematically increase the confining pre-stress in the packing by compressing it with a fluid-permeable piston, leading to a gradual transition in migration regime from fluidization to pathway opening to pore invasion. We find that mixed migration regimes emerge at intermediate confinement due to the spontaneous formation of a compaction layer at the top of the flow cell. By connecting these migration mechanisms with macroscopic invasion, trapping, and venting, we show that mixed regimes enable a sharp increase in the average amount of gas trapped within the packing, as well as much larger venting events. Our results suggest that the relationship between invasion, trapping, and venting could be controlled by modulating the confining stress

Multichannel cold collisions between metastable Sr atoms

We present a multichannel scattering calculation of elastic and inelastic cold collisions between two low-field seeking, metastable ^{88}Sr [(5s5p) ^3P_2] atoms in the presence of an external magnetic field. The scattering physics is governed by strong anisotropic long-range interactions, which lead to pronounced coupling among the partial waves of relative motion. As a result, nonadiabatic transitions are shown to trigger a high rate of inelastic losses. At relatively high energies, T > 100 mkK, the total inelastic collision rate is comparable with the elastic rate. However, at lower collisional energy, the elastic rate decreases, and at T ~ 1mkK, it becomes substantially smaller than the inelastic rate. Our study suggests that magnetic trapping and evaporative cooling of ^{88}Sr [(5s5p) ^3P_2] atoms, as well as ^{40}Ca [(4s4p) ^3P_2], in low-field seeking states will prove difficult to achieve experimentally.Comment: 4 pages, Latex, Submitte

Design of a cascade refrigeration system for applications below -50°C using CO2-sublimation

Trifluoromethane (R-23) is currently the most widely used non-flammable refrigerant for applications down to about -80°C (193K). However, R-23 has an enormous global warming potential (GWP100=14800) and recent price increases lead to a loss of attractiveness in industry. As an alternative, some studies in recent years indicated the possibility of extending the application temperature of the natural refrigerant carbon dioxide (CO2) beneath its triple conditions in a refrigeration cycle. Thus there would be a great potential for CO2 to replace R-23. In present paper, the design of a cascade refrigeration machine using CO2-sublimation is introduced. R-452A is used as refrigerant for the upper stage. The lower stage can be switched between the CO2-sublimation cycle, featuring a two-stage compression with intercooling as well as an internal heat exchanger, and a conventional R-23 cycle. Both the CO2-sublimation as well as the R-23 lower stage cycles can be compared directly under the same ambient conditions. Stationary process simulations were made in order to compare the CO2 and R-23 cycles under various boundary conditions. It turned out that the overall system efficiency of the CO2-sublimation cycle could exceed the conventional R-23 cycle in many operation points. The design of this cascade refrigeration machine is currently used for building-up a demonstrator to prove the concept experimentally

An extra-heating mechanism in Doppler-cooling experiments

In this paper we experimentally and theoretically investigate laser cooling of Strontium 88 atoms in one dimensional optical molasses. In our case, since the optical cooling dipole transition involves a $J_g=0$ groundstate, no Sisyphus-type mechanisms can occur. We are thus able to test quantitatively the predictions of the Doppler-cooling theory. We have found, in agreement with other similar experiments, that the measured temperatures are systematically larger than the theoretical predictions. We quantitatively interpret this discrepancy by taking into consideration the extra-heating mechanism induced by transverse spatial intensity fluctuations of the optical molasses. Experimental data are in good agreement with Monte-Carlo simulations of our theoretical model. We thus confirm the important role played by intensity fluctuations in the dynamics of cooling and for the steady-state regime