93 research outputs found
Non-equilibrium diffusion limit of the compressible Navier-Stokes-Fourier-P1 approximation model at low Mach number: general initial data case
In this paper, we investigate the non-equilibrium diffusion limit of the
compressible Navier-Stokes-Fourier-P1 (NSF-P1) approximation model at low Mach
number, which arises in radiation hydrodynamics, with general initial data and
a parameter describing the intensity of scatting effect. In
previous literature, only and well-prepared initial data case to
the NSF-P1 model was considered. Here we prove that, for partial general
initial data and , this model converges to the system of low Mach
number heat-conducting viscous flows coupled with a diffusion equation as the
parameter . Compared to the classical NSF system, the
NSF-P1 model has additional new singular structures caused by the radiation
pressure. To handle these structures, we construct an equivalent pressure and
an equivalent velocity to balance the order of singularity and establish the
uniform estimates of solutions by designating appropriate weighted norms and
carrying out delicate energy analysis. We then obtain the convergence of the
pressure and velocity from the local energy decay of the equivalent pressure
and equivalent velocity. We also briefly discuss the variations of the limit
equations as the scattering intensity changes, i.e., . We
find that, with the weakening of scattering intensity, the ``diffusion
property" of radiation intensity gradually weakens. Furthermore, when the
scattering effect is sufficiently weak (), we can obtain the
singular limits of the NSF-P1 model with general initial data. To our best
knowledge, this is the first result on the influence of scattering intensity in
the non-equilibrium diffusion limit of the NSF-P1 model.Comment: 30 page
Bragg Coherent Modulation Imaging for Highly Strained Nanocrystals-A Numerical Study
Bragg coherent diffraction imaging (BCDI) is a unique and powerful method for
tracking three-dimensional strain fields non-destructively. While BCDI has been
successfully applied to many scientific research fields and receives high
demands, the reconstructed results for highly strained crystals are still
subject to big uncertainties. Here, the progress in improving the suitability
of BCDI for general samples by exploiting wavefront modulation is reported.
Extensive numerical simulations demonstrate that significant improvements over
the current method for reconstructing highly strained model nanocrystals can be
achieved. The proposed method highly suppresses the appearance of ambiguous
solutions and exhibits fast convergence and high robustness in phase retrieval.
Possible experimental difficulties in implementing this method are discussed in
detail
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Hydrological variations in central China over the past millennium and their links to the Tropic Pacific and North Atlantic Oceans
Variations of precipitation, aka the Meiyu rain, in East Asian summer monsoon (EASM) domain during the last millennium could help enlighten the hydrological response to future global warming. Here we present a precisely dated and highly resolved stalagmite δ18O record from the Yongxing Cave, central China. Our new record, combined with a previously published one from the same cave, indicates that the Meiyu rain has changed dramatically in association with the global temperature change. In particular, our record shows that the Meiyu rain has been weakened during the Medieval Climate Anomaly (MCA), but intensified during the Little Ice Age (LIA). During the Current Warm Period (CWP), our record indicates a similar weakening of the Meiyu rain. Furthermore, during the MCA and CWP, our records show that the atmospheric precipitation is similarly wet in northern China and similarly dry in central China, but relatively wet during the CWP in southern China. This spatial discrepancy indicates a complicated localized response of the regional precipitation to the anthropogenic forcing. The weakened (intensified) Meiyu rain during the MCA (LIA) matches well with the warm (cold) phases of Northern Hemisphere surface air temperature. This Meiyu rain pattern also corresponds well with the climatic conditions over the Tropical Indo-Pacific warm pool. On the other hand, our record shows a strong association with the North Atlantic climate as well. The reduced (increased) Meiyu rain correlates well with positive (negative) phases of North Atlantic Oscillation. In addition, our record links well with the strong (weak) Atlantic meridional overturning circulation during the MCA (LIA) period. All above-mentioned localized correspondences and remote teleconnections on decadal to centennial timescales indicate that the Meiyu rain is coupled closely with oceanic processes in the Tropical Pacific and North Atlantic Oceans during the MCA and LIA
High-efficiency generation of nanoscale single silicon vacancy defect array in silicon carbide
Color centers in silicon carbide have increasingly attracted attention in
recent years owing to their excellent properties such as single photon
emission, good photostability, and long spin coherence time even at room
temperature. As compared to diamond which is widely used for holding
Nitrogen-vacancy centers, SiC has the advantage in terms of large-scale,
high-quality and low cost growth, as well as advanced fabrication technique in
optoelectronics, leading to the prospects for large scale quantum engineering.
In this paper, we report experimental demonstration of the generation of
nanoscale single defect array through ion implantation without the
need of annealing. defects are generated in pre-determined locations
with resolution of tens of nanometers. This can help in integrating
defects with the photonic structures which, in turn, can improve the emission
and collection efficiency of defects when it is used in spin photonic
quantum network. On the other hand, the defects are shallow and they are
generated below the surface which can serve as critical resources
in quantum sensing application
Super-Hamiltonian Structures and Conservation Laws of a New Six-Component Super-Ablowitz-Kaup-Newell-Segur Hierarchy
A six-component super-Ablowitz-Kaup-Newell-Segur (-AKNS) hierarchy is proposed by the zero curvature equation associated with Lie superalgebras. Supertrace identity is used to furnish the super-Hamiltonian structures for the resulting nonlinear superintegrable hierarchy. Furthermore, we derive the infinite conservation laws of the first two nonlinear super-AKNS equations in the hierarchy by utilizing spectral parameter expansions. PACS: 02.30.Ik; 02.30.Jr; 02.20.Sv
Scanning phase imaging without accurate positioning system
Ptychography, a high-resolution phase imaging technique using precise
in-plane translation information, has been widely applied in modern synchrotron
radiation sources across the globe. A key requirement for successful
ptychographic reconstruction is the precise knowledge of the scanning
positions, which are typically obtained by a physical interferometric
positioning system. Whereas high-throughput positioning poses a challenge in
engineering, especially in nano or even smaller scale. In this work, we propose
a novel scanning imaging framework that does not require any prior position
information from the positioning system. Specifically, our scheme utilizes the
wavefront modulation mechanism to reconstruct the object functions at each scan
position and the shared illumination function, simultaneously. The scanning
trajectory information is extracted by our subpixel image registration
algorithm from the overlap region of reconstructed object functions. Then, a
completed object function can be obtained by assembling each part of the
reconstructed sample functions. High-quality imaging of biological sample and
position recovery with sub-pixel accuracy are demonstrated in proof-of-concept
experiment. Based on current results, we find it may have great potential
applications in high-resolution and high throughput phase imaging.Comment: 9 pages,4 figure
Karyotyping human chromosomes by optical and X-ray ptychography methods
Sorting and identifying chromosomes, a process known as karyotyping, is widely used to detect changes in chromosome shapes and gene positions. In a karyotype the chromosomes are identified by their size and therefore this process can be performed by measuring macroscopic structural variables. Chromosomes contain a specific number of base pairs that linearly correlate with their size; therefore it is possible to perform a karyotype on chromosomes using their mass as an identifying factor. Here, we obtain the first images of chromosomes using the novel imaging method of ptychography. We can use the images to measure the mass of chromosomes and perform a partial karyotype from the results. We also obtain high spatial resolution using this technique with synchrotron source X-rays
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