New Probe of Departures from General Relativity Using Minkowski Functionals.

The morphological properties of the large scale structure of the Universe can be fully described by four Minkowski functionals (MFs), which provide important complementary information to other statistical observables such as the widely used 2-point statistics in configuration and Fourier spaces. In this work, for the first time, we present the differences in the morphology of the large scale structure caused by modifications to general relativity (to address the cosmic acceleration problem), by measuring the MFs from N-body simulations of modified gravity and general relativity. We find strong statistical power when using the MFs to constrain modified theories of gravity: with a galaxy survey that has survey volume ∼0.125(h^{-1} Gpc)^{3} and galaxy number density ∼1/(h^{-1} Mpc)^{3}, the two normal-branch Dvali-Gabadadze-Porrati models and the F5 f(R) model that we simulated can be discriminated from the ΛCDM model at a significance level ≳5σ with an individual MF measurement. Therefore, the MF of the large scale structure is potentially a powerful probe of gravity, and its application to real data deserves active exploration.

Subhalo Abundance Matching in f(R) Gravity.

Using the liminality N-body simulations of Shi et al., we present the first predictions for galaxy clustering in f(R) gravity using subhalo abundance matching. We find that, for a given galaxy density, even for an f(R) model with f_{R0}=-10^{-6}, for which the cold dark matter clustering is very similar to the cold dark matter model with a cosmological constant (ΛCDM), the predicted clustering of galaxies in the f(R) model is very different from ΛCDM. The deviation can be as large as 40% for samples with mean densities close to that of L_{*} galaxies. This large deviation is testable given the accuracy that future large-scale galaxy surveys aim to achieve. Our result demonstrates that galaxy surveys can provide a stringent test of general relativity on cosmological scales, which is comparable to the tests from local astrophysical observations.

Constraining f(R) Gravity Theory Using Weak Lensing Peak Statistics from the Canada-France-Hawaii-Telescope Lensing Survey.

In this Letter, we report the observational constraints on the Hu-Sawicki f(R) theory derived from weak lensing peak abundances, which are closely related to the mass function of massive halos. In comparison with studies using optical or x-ray clusters of galaxies, weak lensing peak analyses have the advantages of not relying on mass-baryonic observable calibrations. With observations from the Canada-France-Hawaii-Telescope Lensing Survey, our peak analyses give rise to a tight constraint on the model parameter |f_{R0}| for n=1. The 95% C.L. is log_{10}|f_{R0}|<-4.82 given WMAP9 priors on (Ω_{m}, A_{s}). With Planck15 priors, the corresponding result is log_{10}|f_{R0}|<-5.16.

Dua-energy virtual noncontrast imaging in diagnosis of cervical metastasis lymph nodes.

OBJECTIVE: The aim of this study was to evaluate the clinical value of dua-energy virtual noncontrast imaging (DVNCT) in the diagnosis of cervical metastasis lymph nodes. MATERIALS AND METHODS: From February 2014 to January 2015, 41 patients with 98 enlarged cervical lymph nodes were recruited in this study. All the enlarged lymph nodes were pathology confirmed. The patients received DVNCT and conventional noncontrast scan. The difference of average computed tomography (CT) value, signal to noise ratio, a contrast to noise ratio, image subjective assessment, and lesion detectability between virtual noncontrast imaging and conventional noncontrast scan were compared. The radiation dose of virtual noncontrast imaging and real noncontrast imaging of cervical lymph node were also compared. The diagnostic sensitivity and specificity for DVNCT was also evaluated. RESULTS: No statistical difference of average CT value, signal to noise ratio, a contrast to noise ratio, image subjective assessment, and radiation dosage between virtual noncontrast imaging and conventional noncontrast scan were found. However, the radiation dosage of DVNCT was significant lower than that of conventional noncontrast scan (P < 0.05). The diagnostic sensitivity and specificity for malignant metastasis lymph node were 88.6% and 70.3% by DVNCT. CONCLUSION: DVNCT combined with contrast imaging can provide clear images in the diagnosis of enlarged cervical lymph nodes and reduce radiation dosage.

Effective Dark Matter Halo Catalog in f(R) Gravity.

We introduce the idea of an effective dark matter halo catalog in f(R) gravity, which is built using the effective density field. Using a suite of high resolution N-body simulations, we find that the dynamical properties of halos, such as the distribution of density, velocity dispersion, specific angular momentum and spin, in the effective catalog of f(R) gravity closely mimic those in the cold dark matter model with a cosmological constant (ΛCDM). Thus, when using effective halos, an f(R) model can be viewed as a ΛCDM model. This effective catalog therefore provides a convenient way for studying the baryonic physics, the galaxy halo occupation distribution and even semianalytical galaxy formation in f(R) cosmologies.

Clear and measurable signature of modified gravity in the galaxy velocity field.

The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution v_{12} are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion σ_{12}(r) is very sensitive to the presence of modified gravity. Using a set of high-resolution N-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon f(R) gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the (5-10)σ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a "smoking gun" for modified gravity.

Testing gravity using the environmental dependence of dark matter halos.

In this Letter, we investigate the environmental dependence of dark matter halos in theories which attempt to explain the accelerated expansion of the Universe by modifying general relativity (GR). Using high-resolution N-body simulations in f(R) gravity models which recover GR in dense environments by virtue of the chameleon mechanism, we find a significant difference, which depends on the environment, between the lensing and dynamical masses of dark matter halos. This environmental dependence of the halo properties can be used as a smoking gun to test GR observationally.

The anatomical study of left atrium diverticulum by multi-detector row CT.

The purpose of this study was to describe radiologic anatomy of the left atrium diverticulum. There were 20 patients with 27 left atrium diverticulums in 120 consecutive patients who underwent CT of coronary angiography. The presence probability of left atrium diverticulum was 16.7%, male of it was 13.0%, female was 17.6%. There was no difference on gender (P > 0.05). There were four patients accompanying with variation of pulmonary vein at one time. The diverticulum might be single or multiple, cystiform or tubiform. It could locate anterior wall or posterior wall or superior wall of left atrium. Left atrium diverticulums which was single, cystiform, and located in anterior wall were common. The cervix width of diverticulum was 4.9 +/- 3.2 mm, the body height of them was 5.4 +/- 2.0 mm. The ratio of body height to cervix width was from 0.47 to 4.08 (median 1.16). Ten patients of them undertook cardiac ultrasound examination at same time. There were five patients who left atrial diastolic function decreased, four patients who left ventricular systolic function decreased. Three of them both existed left atrial diastolic function decreasing and left ventricular systolic function decreasing, accompanied with mitral or aortic regurgitation. No patient was found that left atrium pressure or left ventricle diastolic pressure was increasing. The left atrium diverticulums of ten patients were probably congenital because their hemodynamical status cannot lead to diverticulum formation. It can be proved by reexamination after therapy or autopsy at last. In conclusion, multi-detector row computed tomography could provide anatomy details of left atrium diverticulum to help to finish heart and chest surgery successfully.