2,472 research outputs found
Motion of the ablation cloud in torus plasmas
The motion of an ablation cloud is investigated in a tokamak by using ideal magnetohydrodynamic equations with ablation processes. The cloud quickly expands along the magnetic field and simultaneously drifts to the lower field side due to a tire tube force and 1/R force. It is found that the acceleration of the cloud increases and subsequently decreases due to the energy deposit from the bulk plasma and, finally, the cloud is stopped due to the poloidal field
Two-dimensional simulation of pellet ablation with atomic processes
A two-dimensional hydrodynamic simulation code CAP has been developed in order to investigate the dynamics of hydrogenic pellet ablation in magnetized plasmas throughout their temporal evolution. One of the properties of the code is that it treats the solid-to-gas phase change at the pellet surface without imposing artificial boundary conditions there, as done in previous ablation models. The simulation includes multispecies atomic processes, mainly molecular dissociation and thermal ionization in the ablation flow beyond the pellet, with a kinetic heat flux model. It was found that ionization causes the formation of a quasistationary shock front in the supersonic region of the ablation flow, followed by a "second" sonic surface farther out. Anisotropic heating, due to the directionality of the magnetic field, contributes to a nonuniform ablation (recoil) pressure distribution over the pellet surface. Since the shear stress can exceed the yield strength of the solid for a sufficiently high heat flux, the solid pellet can be fluidized and flattened into a "pancake" shape while the pellet is ablating and losing mass. The effect of pellet deformation can shorten the pellet lifetime almost 3Ă— from that assuming the pellet remains rigid and stationary during ablation
Spatial propagation of excitonic coherence enables ratcheted energy transfer
Experimental evidence shows that a variety of photosynthetic systems can
preserve quantum beats in the process of electronic energy transfer, even at
room temperature. However, whether this quantum coherence arises in vivo and
whether it has any biological function have remained unclear. Here we present a
theoretical model that suggests that the creation and recreation of coherence
under natural conditions is ubiquitous. Our model allows us to theoretically
demonstrate a mechanism for a ratchet effect enabled by quantum coherence, in a
design inspired by an energy transfer pathway in the Fenna-Matthews-Olson
complex of the green sulfur bacteria. This suggests a possible biological role
for coherent oscillations in spatially directing energy transfer. Our results
emphasize the importance of analyzing long-range energy transfer in terms of
transfer between inter-complex coupling (ICC) states rather than between site
or exciton states.Comment: Accepted version for Phys. Rev. E. 14 pages, 7 figure
Quantum entanglement in photosynthetic light harvesting complexes
Light harvesting components of photosynthetic organisms are complex, coupled,
many-body quantum systems, in which electronic coherence has recently been
shown to survive for relatively long time scales despite the decohering effects
of their environments. Within this context, we analyze entanglement in
multi-chromophoric light harvesting complexes, and establish methods for
quantification of entanglement by presenting necessary and sufficient
conditions for entanglement and by deriving a measure of global entanglement.
These methods are then applied to the Fenna-Matthews-Olson (FMO) protein to
extract the initial state and temperature dependencies of entanglement. We show
that while FMO in natural conditions largely contains bipartite entanglement
between dimerized chromophores, a small amount of long-range and multipartite
entanglement exists even at physiological temperatures. This constitutes the
first rigorous quantification of entanglement in a biological system. Finally,
we discuss the practical utilization of entanglement in densely packed
molecular aggregates such as light harvesting complexes.Comment: 14 pages, 7 figures. Improved presentation, published versio
The origin of correlation between mass and angle in quasi-fission
Mass-angle distribution (MAD) measurement of heavy and superheavy element
fragmentation reactions is one of the powerful tools for investigating the
mechanism of fission and fusion process. MAD shows a strong correlation between
mass and angle when the quasi-fission event is dominant. It has characteristic
that appears diagonal correlation as long as the quasi-fission event is
dominant. This diagonal correlation could not be reproduced in previous our
model before the introduction of the parameters. In this study, we
systematically evaluate the unknown model parameters contained in our model and
clarify those model parameters to reproduce the diagonal correlation that
appears in MAD. Using a dynamical model based on the fluctuation dissipation
theorem that employs Langevin equations, we calculate MADs of two reaction
systems Ti+W and S+Th which are dominated by
quasi-fission. We were able to clarify the effects of unknown model parameters
on the MAD. In addition, we identified the values of model parameters that can
reproduce the correlation between mass and angle. As a result, it was found
that the balance of tangential friction and moment of inertia values is
important for the correlation between mass and angle.Comment: 5 pages, 2 figures, SND2020. arXiv admin note: text overlap with
arXiv:2309.11095, arXiv:2310.02547, arXiv:2310.0721
Molecular Response in One-Photon Absorption via Natural Thermal Light vs Pulsed Laser Excitation
Photoinduced biological processes occur via one photon absorption in natural
light, which is weak, CW and incoherent, but are often studied in the
laboratory using pulsed coherent light. Here we compare the response of a
molecule to these two very different sources within a quantized radiation field
picture. The latter is shown to induce coherent time evolution in the molecule,
whereas the former does not. As a result, the coherent time dependence observed
in the laboratory experiments will not be relevant to the natural biological
process. Emphasis is placed on resolving confusions regarding this issue that
are shown to arise from aspects of quantum measurement and from a lack of
appreciation of the proper description of the absorbed photon.Comment: Revised (now published) manuscript: Replaces ArXiv:1109.002
Pattern scaling using ClimGen: monthly-resolution future climate scenarios including changes in the variability of precipitation
Development, testing and example applications of the pattern-scaling approach for generating future climate change projections are reported here, with a focus on a particular software application called “ClimGen”. A number of innovations have been implemented, including using exponential and logistic functions of global-mean temperature to represent changes in local precipitation and cloud cover, and interpolation from climate model grids to a finer grid while taking into account land-sea contrasts in the climate change patterns. Of particular significance is a new approach for incorporating changes in the inter-annual variability of monthly precipitation simulated by climate models. This is achieved by diagnosing simulated changes in the shape of the gamma distribution of monthly precipitation totals, applying the pattern-scaling approach to estimate changes in the shape parameter under a future scenario, and then perturbing sequences of observed precipitation anomalies so that their distribution changes according to the projected change in the shape parameter. The approach cannot represent changes to the structure of climate timeseries (e.g. changed autocorrelation or teleconnection patterns) were they to occur, but is shown here to be more successful at representing changes in low precipitation extremes than previous pattern-scaling methods
- …