Through a laser pulse, the scientists can coax the system to go from a ground state to an excited state in a cyclical fashion resulting in a superposition of the two states. Ho said the hydrogen molecule is an example of a two-level system because its orientation shifts between two positions, up and down and slightly horizontally tilted. “A quantum microscope that relies on probing the coherent superposition of states in a two-level system is much more sensitive than existing instruments that are not based on this quantum physics principle.” “This project represents an advance in both the measurement technique and the scientific question the approach allowed us to explore,” said co-author Wilson Ho, Donald Bren Professor of physics & astronomy and chemistry. With pulses of the laser lasting trillionths of a second, the scientists were able to excite the hydrogen molecule and detect changes in its quantum states at cryogenic temperatures and in the ultrahigh vacuum environment of the instrument, rendering atomic-scale, time-lapsed images of the sample. Today in Science, the researchers in UCI’s Department of Physics & Astronomy and Department of Chemistry describe how they positioned two bound atoms of hydrogen in between the silver tip of the STM and a sample composed of a flat copper surface arrayed with small islands of copper nitride. This new technique can also be applied to analysis of two-dimensional materials which have the potential to play a role in advanced energy systems, electronics and quantum computers. The predictions of the model have been validated further through a detailed experimental study of the effects of feed flow rate, temperature, size of catalyst charge, and cycling frequency on the instantaneous and time-average conversions during forced cycling of the feed composition.Irvine, Calif., ApPhysicists at the University of California, Irvine have demonstrated the use of a hydrogen molecule as a quantum sensor in a terahertz laser-equipped scanning tunneling microscope, a technique that can measure the chemical properties of materials at unprecedented time and spatial resolutions. This mathematical model can also quantitatively describe the complex steady-state behavior (uniqueness-multiplicity transitions) observed for this reaction. This phenomenon can be explained quantitatively by a model based on an adsorbate-induced phase change of the Pt surface combined with CO adsorption self-exclusion. Reaction rate enhancement is shown to occur, and by varying the phasing of the feed streams it is possible to achieve a global maximum in the time-average reaction rate. A novel approach to forced composition cycling was examined, in which the phase angle between the two input streams was varied. © 2010 American Institute of Chemical Engineers AIChE J, 2011Ī combined experimental and theoretical investigation of the effect of forced feed composition cycling for CO oxidation on platinum has been performed. The insight provided by these simulations will help develop operation and control protocols that circumvent or at least decrease the probability of the occurrence of the destructive melting of the DPF. We present simulations that provide insight about the dependence of the amplitude of this wrong-way temperature rise on the filtration velocity, the PM loading, dimensions of the DPF, and the amplitude of the rapid temperature decrease and when it occurs after the start of the regeneration. This unexpected behavior is similar to the well-known wrong-way behavior in packed-bed reactors, even though the axial-dependent flow through the filter in a DPF is rather different from the constant axial flow through a packed bed. Specifically, a rapid decrease in the exhaust temperature can lead to a counterintuitive large transient temperature rise above that which would exist under a higher stationary feed temperature. ![]() We propose that these temperature excursions are a dynamic effect following a rapid change in the driving mode while the DPF is being regenerated. This behavior cannot be explained by operation under stationary feed conditions. ![]() The accumulated PM is periodically removed by combustion, which sometimes leads to excessive temperature excursions that melt the ceramic filter. ![]() A diesel particulate filter (DPF) is used to remove particulate matter (PM) from the diesel engine exhaust.
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