Biomedical subjects

R Kosloff

Publications and source records attributed to R Kosloff.

15 recordsLinked to original sources

PubMed2001

Quantum thermodynamic cooling cycle.

The quantum-mechanical and thermodynamic properties of a three-level molecular cooling cycle are derived. An inadequacy of earlier models is rectified in accounting for the spontaneous emission and absorption associated with the coupling to the coherent driving field via an environmental reservoir. This additional coupling need not be dissipative, and can provide a thermal driving force-the quantum analog of classical absorption chillers. The dependence of the maximum attainable cooling rate on temperature, at ultralow temperatures, is determined and shown to respect the recently established fundamental bound based on the second and third laws of thermodynamics.

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PubMed2001

Three-dimensional ab initio quantum dynamics of the photodesorption of CO from Cr(2)O(3)(0001): stereodynamic effects.

Having performed the first three-dimensional ab initio quantum dynamical study of photodesorption from solid surfaces, we gained mechanistic understanding of the rotational alignment observed in the CO/Cr(2)O(3)(0001) system. Our study is based on potential energy surfaces obtained by embedded cluster calculations for both the electronic ground and excited state of the adsorbate substrate complex. Stochastic wave packet calculations demonstrate the importance of the angular degrees of freedom for the microscopic picture of the desorption process in addition to the desorption coordinate.

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PubMed2000

Dynamics of charge transfer states on metal surfaces: the competition between reactivity and quenching.

The dynamics of excited states of adsorbates on surfaces caused by charge transfer is studied. Both negative and positive charge transfer processes are possible. In particular we are interested in positive charge transfer from a metal surface to molecular or atomic oxygen adsorbed on the surface. Once the negatively charged oxygen on the surface loses an electron it becomes chemically activated. The ability of this species to react depends on the quenching time or back transfer. The analysis of these processes is based on a set of diabatic potential energy surfaces each representing a different charged oxygen species. The dynamics is followed by solving the multichannel time-dependent Schrödinger equation or Liouville von Neumann equation. Due to the nonadiabatic character of these reactions large isotope effects are predicted.

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PubMed2000

Charge-transfer reactions in atom scattering from ionic surfaces: a time-dependent wavepacket approach.

A diabetic description of charge transfer between atoms and ionic surfaces is presented, specifically examining the F/LiF(100) and F/KI(100) systems for which experiment shows ion formation to be very efficient. Potential energy surfaces describing the energetics for these systems have been generated with a semi-empirical scheme. At the site of charge exchange, there is a curve-crossing between the ground state and the state representing charge capture by the projectile. Quantum dynamics calculations with time-dependent wavepacket methods give an initial ion-formation probability of unity for all cases considered. At lowest energies, the ions cannot escape the surface, giving an effective threshold for negative-ion production very close to that observed in experiment. Re-neutralization by charge transfer back to the conduction band of the solid is also examined.

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PubMed2000

Performance of discrete heat engines and heat pumps in finite time

The performance in finite time of a discrete heat engine with internal friction is analyzed. The working fluid of the engine is composed of an ensemble of noninteracting two level systems. External work is applied by changing the external field and thus the internal energy levels. The friction induces a minimal cycle time. The power output of the engine is optimized with respect to time allocation between the contact time with the hot and cold baths as well as the adiabats. The engine's performance is also optimized with respect to the external fields. By reversing the cycle of operation a heat pump is constructed. The performance of the engine as a heat pump is also optimized. By varying the time allocation between the adiabats and the contact time with the reservoir a universal behavior can be identified. The optimal performance of the engine when the cold bath is approaching absolute zero is studied. It is found that the optimal cooling rate converges linearly to zero when the temperature approaches absolute zero.

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PubMed1996