The effects of the model errors generated by discretization of "on-off'' processes on VDA

International audienceThrough an idealized model of a partial differential equation with discontinuous "on-off'' switches in the forcing term, we investigate the effect of the model error generated by the traditional discretization of discontinuous physical "on-off'' processes on the variational data assimilation (VDA) in detail. Meanwhile, the validity of the adjoint approach in the VDA with "on-off'' switches is also examined. The theoretical analyses illustrate that in the analytic case, the gradient of the associated cost function (CF) with respect to an initial condition (IC) exists provided that the IC does not trigger the threshold condition. But in the discrete case, if the on switches (or off switches) in the forward model are straightforwardly assigned the nearest time level after the threshold condition is (or is not) exceeded as the usual treatment, the discrete CF gradients (even the one-sided gradient of CF) with respect to some ICs do not exist due to the model error, which is the difference between the analytic and numerical solutions to the governing equation. Besides, the solution of the corresponding tangent linear model (TLM) obtained by the conventional approach would not be a good first-order linear approximation to the nonlinear perturbation solution of the governing equation. Consequently, the validity of the adjoint approach in VDA with parameterized physical processes could not be guaranteed. Identical twin numerical experiments are conducted to illustrate the influences of these problems on VDA when using adjoint method. The results show that the VDA outcome is quite sensitive to the first guess of the IC, and the minimization processes in the optimization algorithm often fail to converge and poor optimization retrievals would be generated as well. Furthermore, the intermediate interpolation treatment at the switch times of the forward model, which reduces greatly the model error brought by the traditional discretization of "on-off'' processes, is employed in this study to demonstrate that when the "on-off'' switches in governing equations are properly numerically treated, the validity of the adjoint approach in VDA with discontinuous physical "on-off'' processes can still be guaranteed

Macroscopical Entangled Coherent State Generator in V configuration atom system

In this paper, we propose a scheme to produce pure and macroscopical entangled coherent state. When a three-level ''V'' configuration atom interacts with a doubly reasonant cavity, under the strong classical driven condition, entangled coherent state can be generated from vacuum fields. An analytical solution for this system under the presence of cavity losses is also given

Mechanism of cellular uptake of genotoxic silica nanoparticles.

Mechanisms for cellular uptake of nanoparticles have important implications for nanoparticulate drug delivery and toxicity. We have explored the mechanism of uptake of amorphous silica nanoparticles of 14 nm diameter, which agglomerate in culture medium to hydrodynamic diameters around 500 nm. In HT29, HaCat and A549 cells, cytotoxicity was observed at nanoparticle concentrations ≥ 1 μg/ml, but DNA damage was evident at 0.1 μg/ml and above. Transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy confirmed entry of the silica particles into A549 cells exposed to 10 μg/ml of nanoparticles. The particles were observed in the cytoplasm but not within membrane bound vesicles or in the nucleus. TEM of cells exposed to nanoparticles at 4°C for 30 minutes showed particles enter cells when activity is low, suggesting a passive mode of entry. Plasma lipid membrane models identified physical interactions between the membrane and the silica NPs. Quartz crystal microbalance experiments on tethered bilayer lipid membrane systems show that the nanoparticles strongly bind to lipid membranes, forming an adherent monolayer on the membrane. Leakage assays on large unilamellar vesicles (400 nm diameter) indicate that binding of the silica NPs transiently disrupts the vesicles which rapidly self-seal. We suggest that an adhesive interaction between silica nanoparticles and lipid membranes could cause passive cellular uptake of the particles

The effects of the model errors generated by discretization of 'on-off'' processes on VDA

Through an idealized model of a partial differential equation with discontinuous 'on-off'' switches in the forcing term, we investigate the effect of the model error generated by the traditional discretization of discontinuous physical 'on-off'' processes on the variational data assimilation (VDA) in detail. Meanwhile, the validity of the adjoint approach in the VDA with 'on-off'' switches is also examined. The theoretical analyses illustrate that in the analytic case, the gradient of the associated cost function (CF) with respect to an initial condition (IC) exists provided that the IC does not trigger the threshold condition. But in the discrete case, if the on switches (or off switches) in the forward model are straightforwardly assigned the nearest time level after the threshold condition is (or is not) exceeded as the usual treatment, the discrete CF gradients (even the one-sided gradient of CF) with respect to some ICs do not exist due to the model error, which is the difference between the analytic and numerical solutions to the governing equation. Besides, the solution of the corresponding tangent linear model (TLM) obtained by the conventional approach would not be a good first-order linear approximation to the nonlinear perturbation solution of the governing equation. Consequently, the validity of the adjoint approach in VDA with parameterized physical processes could not be guaranteed. Identical twin numerical experiments are conducted to illustrate the influences of these problems on VDA when using adjoint method. The results show that the VDA outcome is quite sensitive to the first guess of the IC, and the minimization processes in the optimization algorithm often fail to converge and poor optimization retrievals would be generated as well. Furthermore, the intermediate interpolation treatment at the switch times of the forward model, which reduces greatly the model error brought by the traditional discretization of 'on-off'' processes, is employed in this study to demonstrate that when the 'on-off'' switches in governing equations are properly numerically treated, the validity of the adjoint approach in VDA with discontinuous physical 'on-off'' processes can still be guaranteed

Офорт Олени Кульчицької “За море” і тема еміграції

Illustrators of the Ukrainian press at the 2nd half ХІХ to еarly XX c. and an artist Olena Kul’chitska is known consider the theme of еmigration and expressed it in the form of social satire

Superconductivity in half-Heusler compound TbPdBi

We have studied the half-Heusler compound TbPdBi through resistivity, magnetization, Hall effect and heat capacity measurements. A semimetal behavior is observed in its normal state transport properties, which is characterized by a large negative magnetoresistance below 100 K. Notably, we find the coexistence of superconductivity and antiferromagnetism in this compound. The superconducting transition appears at 1.7 K, while the antiferromagnetic phase transition takes place at 5.5 K. The upper critical field $H_{c2}$ shows an unusual linear temperature dependence, implying unconventional superconductivity. Moreover, when the superconductivity is suppressed by magnetic field, its resistivity shows plateau behavior, a signature often seen in topological insulators/semimetals. These findings establish TbPdBi as a platform for study of the interplay between superconductivity, magnetism and non-trivial band topology.Comment: 5 pages, 4 figure

Hawking Radiation of an Arbitrarily Accelerating Kinnersley Black Hole: Spin-Acceleration Coupling Effect

The Hawking radiation of Weyl neutrinos in an arbitrarily accelerating Kinnersley black hole is investigated by using a method of the generalized tortoise coordinate transformation. Both the location and temperature of the event horizon depend on the time and on the angles. They coincide with previous results, but the thermal radiation spectrum of massless spinor particles displays a kind of spin-acceleration coupling effect.Comment: 8 pages, no figure, revtex 4.0, revisted version with typesetting errors and misprint correcte

Off the Beaten Path: Let's Replace Term-Based Retrieval with k-NN Search

Retrieval pipelines commonly rely on a term-based search to obtain candidate records, which are subsequently re-ranked. Some candidates are missed by this approach, e.g., due to a vocabulary mismatch. We address this issue by replacing the term-based search with a generic k-NN retrieval algorithm, where a similarity function can take into account subtle term associations. While an exact brute-force k-NN search using this similarity function is slow, we demonstrate that an approximate algorithm can be nearly two orders of magnitude faster at the expense of only a small loss in accuracy. A retrieval pipeline using an approximate k-NN search can be more effective and efficient than the term-based pipeline. This opens up new possibilities for designing effective retrieval pipelines. Our software (including data-generating code) and derivative data based on the Stack Overflow collection is available online

Variation of the Fine-Structure Constant from the de Sitter Invariant Special Relativity

There are obvious discrepancies among various experimental constraints on the variation of the fine-structure constant, $\alpha$. We attempt to discuss the issue in the framework of de Sitter invariant Special Relativity (${\cal SR}_{c,R}$) and to present a possible solution to the disagreement. In addition, on the basis of the observational data and the discussions presented in this Letter, we derive a rough theoretical estimate of the radius of the Universe.Comment: 8 pages, no figure