TestingCPTinvariance inBd0–B¯d0and

Ping Ren

¹

,

Xing Zhang

²

Exact Solutions of Embedding the 4d Universe in a 5d Einstein Manifold

“…Despite the apparent evidence for an accelerated expansion, there is also some "neglected" but important experimental evidence against the Λ Cold Dark Matter (ΛCDM) model, which is the mainstream model in cosmology [10]. Nevertheless, given the presently popular notion, it is reasonable to study the cosmological models that can be reduced to the ΛCDM model, as in our previous works [11] and the present one.…”

A demonstration of wavefront sensing and mirror phasing from the image domain

“…in Crepp et al (2011)) and a variety of solutions have been proposed (Thomas et al 2012;N'Diaye et al 2013). Few of these, with the exception of Ren et al (2012), avoid the necessity of introducing substantial additional hardware into the beam path, with the attendant costs of time, expense and residual optical errors. Ren et al (2012) present a novel and effective algorithm for attaining a particular desired PSF, but the method demonstrated here has the advantage of producing a flat wavefront quickly, for an arbitrary pupil, without model-dependent distortions and suitable for general observing.…”

“…The DM itself can be used to introduce the known phase perturbation in order to calibrate or suppress speckles. The large number of degrees of freedom offered by a DM leads to variety of control algorithms: from random perturbations of the DM while monitoring a metric function of the PSF (Ren et al 2012); iterative speckle nulling loop compatible with coronagraphic mode (Martinache et al 2012); to a more complete determination of the wavefront with a finite number of DM modulations (Keller et al 2012). A comparable method compatible with a coronagraphic imaging mode should rely on the electric field conjugation framework (Give'on et al 2007;Thomas et al 2010;Give'On et al 2011), to construct a complex transfer matrix for the real and imaginary parts of the electric field between pupil and focal planes, for direct speckle nulling within a finite region of the field of view.…”

A high-contrast coronagraph for direct imaging of Earth-like exoplanets: design and test

“…We have firstly proposed and demonstrated that SPGD algorithm can be applied to the high-contrast coronagraph to reduce speckle noise induced by imperfection optics (Dong et al 2011). In previous paper, we used a deformable mirror (DM) to provide an optimal phase to create a dark-hole in a target region and the principle of SPGD algorithm has been discussed in details somewhere (Ren et al 2012). The DM used in his previous test has 140 effective actuators arranged in 12×12 grid.…”

“…Although the contrast can reach the level of 10 −10 , the region of the dark holes created by this two groups is not large enough to apply to space telescopes for exoplanet detecting. In our group, we have successfully used the stochastic parallel gradient descent (SPGD) algorithm to efficiently supress speckle noises according to the point spread function (PSF) on the imaging focal plane, and this algorithm is first used in our extreme adaptive optics (ExAO) for a ground-based high-contrast system, which successfully demonstrated that a small dark hole with an extra contrast gain of 65-time improvement is achievable with a DM of 140 actuators (Ren et al 2012). Recently, this approach is used in our coronagraph, and the dark hole created by our approach is much larger than that created by other groups, which we will discuss in Section 3.…”