32,953 research outputs found
The Cross-correlation of KSZ Effect and 21 cm Intensity Mapping with Tidal Reconstruction
We discuss the possibility of studying diffuse baryon distributions with
kinematic Sunyaev-Zel'dovich (kSZ) effect by correlating cosmic microwave
background (CMB) temperature fluctuations with density fluctuations from 21\,cm
intensity mapping (IM). The biggest challenge for the cross-correlation is the
loss of large-scale information in IM, due to foregrounds and the zero spacing
problem of interferometers. We apply the tidal reconstruction algorithm to
restore the lost large-scale modes, which increases the correlation by more
than a factor of three. With the predicted foreground level, we expect a
detection of kSZ signal for with
CHIME and Planck, and a detection with HIRAX and Planck. The
significance can be greatly increased with next-generation facilities of higher
spatial resolutions.Comment: 8 pages, 4 figures, submit to PR
Optimized Structured Sparse Sensing Matrices for Compressive Sensing
We consider designing a robust structured sparse sensing matrix consisting of
a sparse matrix with a few non-zero entries per row and a dense base matrix for
capturing signals efficiently We design the robust structured sparse sensing
matrix through minimizing the distance between the Gram matrix of the
equivalent dictionary and the target Gram of matrix holding small mutual
coherence. Moreover, a regularization is added to enforce the robustness of the
optimized structured sparse sensing matrix to the sparse representation error
(SRE) of signals of interests. An alternating minimization algorithm with
global sequence convergence is proposed for solving the corresponding
optimization problem. Numerical experiments on synthetic data and natural
images show that the obtained structured sensing matrix results in a higher
signal reconstruction than a random dense sensing matrix.Comment: 2 tables, 10 figure
Ill-posedness for the 2D viscous shallow water equations in the critical Besov spaces
In this paper, we prove that the 2D viscous shallow water equations is
ill-posed in the critical Besov spaces \B^{\frac2p-1}_{p,1}(\R^2) with .
Our proof mainly depends on the method introduced by the paper \cite{C-M-Z4}.Comment:
Unbiased constraints on the clumpiness of universe from standard candles
We perform unbiased tests for the clumpiness of universe by confronting the
Zel'dovich-Kantowski-Dyer-Roeder luminosity distance which describes the effect
of local inhomogeneities on the propagation of light with the observational one
estimated from measurements of standard candles, i.e., type Ia supernovae (SNe
Ia) and gamma-ray bursts (GRBs). Methodologically, we first determine the
light-curve fitting parameters which account for distance estimation in SNe Ia
observations and luminosity/energy relations which are responsible for distance
estimation of GRBs in the global fit to reconstruct the Hubble diagrams in the
context of a clumpy universe. Subsequently, these Hubble diagrams allow us to
achieve unbiased constraints on the matter density parameter as well
as clumpiness parameter which quantifies the fraction of homogeneously
distributed matter within a given light cone. At 1 confidence level,
the constraints are and from
the joint analysis. The results suggest that the universe full of
Friedman-Lema\^{i}tre-Robertson-Walker fluid is favored by observations of
standard candles with very high statistical significance. On the other hand,
they may also indicate that the Zel'dovich-Kantowski-Dyer-Roeder approximation
is a sufficient accurate form to describe the effects of local homogeneity in
the expanding universe.Comment: 20 pages, 5 figures, and 2 tables. Accepted for publication in Phys.
Rev.
Non-Markovian dynamics without using quantum trajectory
Open quantum system interacting with structured environment is important and
manifests non- Markovian behavior, which was conventionally studied using
quantum trajectory stochastic method. In this paper, by dividing the effects of
the environment into two parts, we propose a deterministic method without using
quantum trajectory. This method is more efficient and accurate than stochastic
method in most Markovian and non-Markovian cases. We also extend this method to
the generalized Lindblad master equation.Comment: 4 pages, 2 figure
Nonlinear reconstruction of redshift space distortions
We apply nonlinear reconstruction to the dark matter density field in
redshift space and solve for the nonlinear mapping from the initial Lagrangian
position to the final redshift space position. The reconstructed anisotropic
field inferred from the nonlinear displacement correlates with the linear
initial conditions to much smaller scales than the redshift space density
field. The number of linear modes in the density field is improved by a factor
of 30-40 after reconstruction. We thus expect this reconstruction approach to
substantially expand the cosmological information including baryon acoustic
oscillations and redshift space distortions for dense low-redshift large scale
structure surveys including for example SDSS main sample, DESI BGS, and 21 cm
intensity mapping surveys.Comment: 18 pages, 21 figures, published version. The nonlinear reconstruction
code is available at https://github.com/ColdThunder/NR-cod
Regularity of powers of edge ideals of vertex-weighted oriented unicyclic graphs
In this paper we provide some exact formulas for the regularity of powers of
edge ideals of vertex-weighted oriented cycles and vertex-weighted unicyclic
graphs. These formulas are functions of the weight of vertices and the number
of edges. We also give some examples to show that these formulas are related to
direction selection and the weight of vertices
Projective dimension and regularity of edge ideals of some vertex-weighted oriented -partite graphs
In this paper we provide some exact formulas for the projective dimension and
the regularity of edge ideals associated to three special types of
vertex-weighted oriented -partite graphs. These formulas are functions of
the weight and number of vertices. We also give some examples to show that
these formulas are related to direction selection and the weight of vertices.Comment: arXiv admin note: substantial text overlap with arXiv:1904.03019,
arXiv:1904.02305, arXiv:1802.0631
Resistive MHD Modelling of Quasi-Single Helicity State in the KTX Regimes
The potential formation of the quasi-single-helicity (QSH) state in the Keda
Torus eXperiment (KTX) is investigated in resistive MHD simulations using the
NIMROD code. We focus on the effects of finite resistivity on the mode
structure and characteristics of the dominant linear and nonlinear resistive
tearing-mode in a finite , cylindrical configuration of reversed field
pinch model for KTX. In the typical resistive regimes of KTX where Lundquist
number , the plasma transitions to a steady QSH state after
evolving through an initial transient phase with multiple helicities. The
dominant mode of the QSH state develops from the dominant linear tearing mode
instability. In lower regime, the QSH state are intermittent and short
in duration; in higher regime, the QSH state persists for a longer time
and should be more observable in experiment.Comment: The manuscript confirms that the MHD dynamics of RFP quasi-single
helical states is based on the resistive-kink tearing modes, shows the
spontaneous emergence of a QSH state during the RFP dynamics and studies the
effect of a finite pressure on the system. The authors find that higher
plasma pressure increases the persistence of QSH state
Projective dimension and regularity of edge ideal of some weighted oriented graphs
In this paper we provide some exact formulas for the projective dimension and
the regularity of edge ideals associated to vertex weighted rooted forests and
oriented cycles. As some consequences, we give some exact formulas for the
depth of these ideals.Comment: 11 page
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