7,598 research outputs found
Statistics of Entropy Production in Linearized Stochastic System
We consider a wide class of linear stochastic problems driven off the
equilibrium by a multiplicative asymmetric force. The force brakes detailed
balance, maintained otherwise, thus producing entropy. The large deviation
function of the entropy production in the system is calculated explicitly. The
general result is illustrated using an example of a polymer immersed in a
gradient flow and subject to thermal fluctuations.Comment: 4 pages, 1 figur
Proof Relevant Corecursive Resolution
Resolution lies at the foundation of both logic programming and type class
context reduction in functional languages. Terminating derivations by
resolution have well-defined inductive meaning, whereas some non-terminating
derivations can be understood coinductively. Cycle detection is a popular
method to capture a small subset of such derivations. We show that in fact
cycle detection is a restricted form of coinductive proof, in which the atomic
formula forming the cycle plays the role of coinductive hypothesis.
This paper introduces a heuristic method for obtaining richer coinductive
hypotheses in the form of Horn formulas. Our approach subsumes cycle detection
and gives coinductive meaning to a larger class of derivations. For this
purpose we extend resolution with Horn formula resolvents and corecursive
evidence generation. We illustrate our method on non-terminating type class
resolution problems.Comment: 23 pages, with appendices in FLOPS 201
Probing the microscopic structure of bound states in quantum point contacts
Using an approach that allows us to probe the electronic structure of
strongly pinched-off quantum point contacts (QPCs), we provide evidence for the
formation of self-consistently realized bound states (BSs) in these structures.
Our approach exploits the resonant interaction between closely-coupled QPCs,
and demonstrates that the BSs may give rise to a robust confinement of single
spins, which show clear Zeeman splitting in a magnetic field
A model for microinstability destabilization and enhanced transport in the presence of shielded 3-D magnetic perturbations
A mechanism is presented that suggests shielded 3-D magnetic perturbations
can destabilize microinstabilities and enhance the associated anomalous
transport. Using local 3-D equilibrium theory, shaped tokamak equilibria with
small 3-D deformations are constructed. In the vicinity of rational magnetic
surfaces, the infinite-n ideal MHD ballooning stability boundary is strongly
perturbed by the 3-D modulations of the local magnetic shear associated with
the presence of nearresonant Pfirsch-Schluter currents. These currents are
driven by 3-D components of the magnetic field spectrum even when there is no
resonant radial component. The infinite-n ideal ballooning stability boundary
is often used as a proxy for the onset of virulent kinetic ballooning modes
(KBM) and associated stiff transport. These results suggest that the achievable
pressure gradient may be lowered in the vicinity of low order rational surfaces
when 3-D magnetic perturbations are applied. This mechanism may provide an
explanation for the observed reduction in the peak pressure gradient at the top
of the edge pedestal during experiments where edge localized modes have been
completely suppressed by applied 3-D magnetic fields
The relationship between chaotic behavior and tunneling effect in quantum transport devices(1)Current topics of quantum chaos in nanosciences, Chaos and Nonlinear Dynamics in Quantum-Mechanical and Macroscopic Systems)
この論文は国立情報学研究所の電子図書館事業により電子化されました。狭い金属ゲート(QPC)を両端に有する開放型量子ドットについて、零磁場近傍の磁気抵抗のピーク形状が、ゲート電圧を変化させることによってローレンツ型とカスプ型が交互に現れる現象が観測された。このローレンツ型とカスプ型が交互に現れる要因としては、QPCによるトンネリング効果と量子ドットによる弱局在の両方が関係しているものではないかと推測され、考察を行った。We have studied transport properties in the low-temperature magnetoresistance through the ballistic narrow path restricted by short width metallic gates, which cause a quantum point contact(QPC) which have a saddle point potential, on the 2 dimensional electron gas(2DEG) system. An alternate and systematic variation between a Lorentzian line fitting and a cusplike line fitting in the zero-field peaks has been observed, as sweeping the gate voltage. It indicates a possibility of existence of chaotic and regular paths on the short gated ballistic/tunneling transport. We will discuss on the quantum chaos behavior on the systematic variation between the Lorentzian and the cusp-like peakshape based on the disordered path system under the short gate, and suggest a relation with level repulsion of energy spectrum
High energy cosmic-rays: puzzles, models, and giga-ton neutrino telescopes
The existence of cosmic rays of energies exceeding 10^20 eV is one of the
mysteries of high energy astrophysics. The spectrum and the high energy to
which it extends rule out almost all suggested source models. The challenges
posed by observations to models for the origin of high energy cosmic rays are
reviewed, and the implications of recent new experimental results are
discussed. Large area high energy cosmic ray detectors and large volume high
energy neutrino detectors currently under construction may resolve the high
energy cosmic ray puzzle, and shed light on the identity and physics of the
most powerful accelerators in the universe.Comment: 12 pages, 7 figures; Summary of review talk, PASCOS 03 (Mumbai,
India
Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff
The cosmic-ray energy spectrum above 10^{18.5} eV is reported using the
updated data set of the Akeno Giant Air Shower Array (AGASA) from February 1990
to October 1997. The energy spectrum extends beyond 10^{20} eV and the energy
gap between the highest energy event and the others is being filled up with
recently observed events. The spectral shape suggests the absence of the 2.7 K
cutoff in the energy spectrum or a possible presence of a new component beyond
the 2.7 K cutoff.Comment: to be published in PRL, 3 figures, REVTEX forma
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