3,539 research outputs found
Intelligent tutoring systems for space applications
Artificial Intelligence has been used in many space applications. Intelligent tutoring systems (ITSs) have only recently been developed for assisting training of space operations and skills. An ITS at Southwest Research Institute is described as an example of an ITS application for space operations, specifically, training console operations at mission control. A distinction is made between critical skills and knowledge versus routine skills. Other ITSs for space are also discussed and future training requirements and potential ITS solutions are described
Cavity QED in superconducting circuits: susceptibility at elevated temperatures
We study the properties of superconducting electrical circuits, realizing
cavity QED. In particular we explore the limit of strong coupling, low
dissipation, and elevated temperatures relevant for current and future
experiments. We concentrate on the cavity susceptibility as it can be directly
experimentally addressed, i.e., as the impedance or the reflection coefficient
of the cavity. To this end we investigate the dissipative Jaynes-Cummings model
in the strong coupling regime at high temperatures. The dynamics is
investigated within the Bloch-Redfield formalism. At low temperatures, when
only the few lowest levels are occupied the susceptibility can be presented as
a sum of contributions from independent level-to-level transitions. This
corresponds to the secular (random phase) approximation in the Bloch-Redfield
formalism. At temperatures comparable to and higher than the oscillator
frequency, many transitions become important and a multiple-peak structure
appears. We show that in this regime the secular approximation breaks down, as
soon as the peaks start to overlap. In other words, the susceptibility is no
longer a sum of contributions from independent transitions. We treat the
dynamics of the system numerically by exact diagonalization of the Hamiltonian
of the qubit plus up to 200 states of the oscillator. We compare the results
obtained with and without the secular approximation and find a qualitative
discrepancy already at moderate temperatures.Comment: 7 pages, 6 figure
Time-convolutionless master equation for quantum dots: Perturbative expansion to arbitrary order
The master equation describing the non-equilibrium dynamics of a quantum dot
coupled to metallic leads is considered. Employing a superoperator approach, we
derive an exact time-convolutionless master equation for the probabilities of
dot states, i.e., a time-convolutionless Pauli master equation. The generator
of this master equation is derived order by order in the hybridization between
dot and leads. Although the generator turns out to be closely related to the
T-matrix expressions for the transition rates, which are plagued by
divergences, in the time-convolutionless generator all divergences cancel order
by order. The time-convolutionless and T-matrix master equations are contrasted
to the Nakajima-Zwanzig version. The absence of divergences in the
Nakajima-Zwanzig master equation due to the nonexistence of secular reducible
contributions becomes rather transparent in our approach, which explicitly
projects out these contributions. We also show that the time-convolutionless
generator contains the generator of the Nakajima-Zwanzig master equation in the
Markov approximation plus corrections, which we make explicit. Furthermore, it
is shown that the stationary solutions of the time-convolutionless and the
Nakajima-Zwanzig master equations are identical. However, this identity neither
extends to perturbative expansions truncated at finite order nor to dynamical
solutions. We discuss the conditions under which the Nakajima-Zwanzig-Markov
master equation nevertheless yields good results.Comment: 13 pages + appendice
Report of Federal Legislative Committee
There has been no occasion to call the Committee into actual session. Such business as was transacted was accomplished by correspondence. The only matter referred to tins Committee had to do with a proposal to make uniform the rules relating to admission of practitioners to the bar of the federal courts. A voluminous file was transmitted to the Chairman, containing recommendations as to this matter which were mainly negative. The view expressed therein was that there was so much difference in circumstances among federal courts in various parts of the country that it would be wisest not to attempt any uniform rules which should apply to all, but to leave the matter as it now is, under the control of the judges presiding m the respective districts
Nonadiabatic Dynamics in Open Quantum-Classical Systems: Forward-Backward Trajectory Solution
A new approximate solution to the quantum-classical Liouville equation is
derived starting from the formal solution of this equation in forward-backward
form. The time evolution of a mixed quantum-classical system described by this
equation is obtained in a coherent state basis using the mapping
representation, which expresses quantum degrees of freedom in a
2N-dimensional phase space. The solution yields a simple non-Hamiltonian
dynamics in which a set of coherent state coordinates evolve in forward and
backward trajectories while the bath coordinates evolve under the influence of
the mean potential that depends on these forward and backward trajectories. It
is shown that the solution satisfies the differential form of the
quantum-classical Liouville equation exactly. Relations to other mixed
quantum-classical and semi-classical schemes are discussed.Comment: 28 pages, 1 figur
A spin-boson thermal rectifier
Rectification of heat transfer in nanodevices can be realized by combining
the system inherent anharmonicity with structural asymmetry. we analyze this
phenomenon within the simplest anharmonic system -a spin-boson nanojunction
model. We consider two variants of the model that yield, for the first time,
analytical solutions: a linear separable model in which the heat reservoirs
contribute additively, and a non-separable model suitable for a stronger
system-bath interaction. Both models show asymmetric (rectifying) heat
conduction when the couplings to the heat reservoirs are different.Comment: 5 pages, 3 figures, RevTeX
Cooking the Books: the Golem and the Ethics of Biotechnology
This working paper has three modest aims: (1) To present, in a succinct and accessible but not distorted fashion, ancient religious Jewish sources about a human-like entity called the golem and some of their later interpretations; (2) To distinguish our sources from the popular modern representation of the golem in Ashkenazi Jewish fiction and folktales, which has played a greater role in recent Jewish contributions to bioethics; (3) To suggest why our ancient sources on the golem, if we try to locate them in their own interpretive contexts, have a new relevance to anyone who is curious about the ethical significance of humanity’s rapidly increasing ability to intervene in biological creation.
The paper is organized in three parts. The introduction offers a critical synopsis of dominant ways that experts in Jewish bioethics have recently invoked the golem. As will be shown, these experts have a high degree of consensus about the golem’s significance, they refer to a narrow range of sources, and they use a similar interpretive procedure to determine the meaning of their sources. These facts are related. They result in an interpretation of the golem that equates one nineteenth-century Eastern European legend with an image spanning millennia, scores of texts, and much of the Western world. Key variables, with divergent implications, have been lost in this equation. Therefore, in the second section, a broader picture of the golem is provided. Beginning with the noun’s sole appearance in the Bible (Psalm 139) and looking at a few rabbinic and Jewish mystical writings, we will use the work of scholars and close readings of canonical sources to reveal several neglected ways that Jewish sources have used the golem image in order to reflect upon the ethics of creation. In our conclusion, we will summarize the empirical and methodological consequences of these readings. Rather than pronounce on what the golem tells scientists (not) to do with biology, we will synthesize new ways that this image might help them, or any open-minded reader, to think about this vital issue
Excitation energy transfer: Study with non-Markovian dynamics
In this paper, we investigate the non-Markovian dynamics of a model to mimic
the excitation energy transfer (EET) between chromophores in photosynthesis
systems. The numerical path integral method is used. This method includes the
non-Markovian effects of the environmental affects and it does not need the
perturbation approximation in solving the dynamics of systems of interest. It
implies that the coherence helps the EET between chromophores through lasting
the transfer time rather than enhances the transfer rate of the EET. In
particular, the non-Markovian environment greatly increase the efficiency of
the EET in the photosynthesis systems.Comment: 5 pages, 5 figure
Decoherence in a superconducting flux qubit with a pi-junction
We consider the use of a pi-junction for flux qubits to realize degenerate
quantum levels without external magnetic field. On the basis of the
Caldeira-Leggett model, we derive an effective spin-Boson model, and study
decoherece of this type of qubits. We estimate the dephasing time by using
parameters from recent experiments of SIFS junctions, and show that high
critical current and large subgap resistance are required for the pi-junction
to realize a long coherent time.Comment: 5 pages, 2 figure
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