Testing gravity using cosmic voids Cai, Yan-Chuan; Padilla, Nelson; Li, Baojiu
Monthly notices of the Royal Astronomical Society,
07/2015, Volume:
451, Issue:
1
Journal Article
Peer reviewed
Open access
We explore voids in dark matter and halo fields from simulations of Λ cold dark matter and Hu–Sawicki f (R) models. In f (R) gravity, dark matter void abundances are greater than that of general ...relativity (GR). Differences for halo void abundances are much smaller, but still at the 2σ, 6σ and 14σ level for the f (R) model parameter |f
R0| = 10−6, 10−5 and 10−4. Counter-intuitively, the abundance of large voids found using haloes in f (R) gravity is lower, which suggests that voids are not necessarily emptier of galaxies in this model. We find the halo number density profiles of voids are not distinguishable from GR, but the same voids are emptier of dark matter in f (R) gravity. This can be observed by weak gravitational lensing of voids, for which the combination of a spec-z and a photo-z survey over the same sky is necessary. For a volume of 1 (Gpc h
−1)3, |f
R0| = 10−5 and 10−4 may be distinguished from GR at 4σ and 8σ using the lensing tangential shear signal around voids. Sample variance and line-of-sight projection effect sets limits for constraining |f
R0| = 10−6. This might be overcome with a larger volume. The smaller halo void abundance and the stronger lensing shear signal of voids in f (R) models may be combined to break the degeneracy between |f
R0| and σ8. The outflow of dark matter from void centres are 5, 15 and 35 per cent faster in f (R) gravity for |f
R0| = 10−6, 10−5 and 10−4. The velocity dispersions are greater than that in GR by similar amounts. Model differences in velocities imply potential powerful constraints for the model in phase space and in redshift space.
Dehydrogenative annulation reactions are among the most straightforward and efficient approach for the preparation of cyclic structures. However, the applications of this strategy for the synthesis ...of saturated heterocycles have been rare. In addition, reported dehydrogenative bond-forming reactions commonly employ stoichiometric chemical oxidants, the use of which reduces the sustainability of the synthesis and brings safety and environmental issues. Herein, we report an organocatalyzed electrochemical dehydrogenative annulation reaction of alkenes with 1,2- and 1,3-diols for the synthesis of 1,4-dioxane and 1,4-dioxepane derivatives. The combination of electrochemistry and redox catalysis using an organic catalyst allows the electrosynthesis to proceed under transition metal- and oxidizing reagent-free conditions. In addition, the electrolytic method has a broad substrate scope and is compatible with many common functional groups, providing an efficient and straightforward access to functionalized 1,4-dioxane and 1,4-dioxepane products with diverse substitution patterns.
Observations of galaxies and galaxy clusters in the local universe can account for only ∼10% of the total baryon content. Cosmological simulations predict that the “missing baryons” are spread ...throughout filamentary structures in the cosmic web, forming a low-density gas with temperatures of 105−107 K. We search for this warm-hot intergalactic medium (WHIM) by stacking the Planck Compton y-parameter map of the thermal Sunyaev-Zel’dovich (tSZ) effect for 1 002 334 pairs of CMASS galaxies from the Sloan Digital Sky Survey. We model the contribution from the galaxy halo pairs assuming spherical symmetry, finding a residual tSZ signal at the 2.9σ level from a stacked filament of length 10.5 h−1 Mpc with a Compton parameter magnitude y = (0.6 ± 0.2)×10−8. We consider possible sources of contamination and conclude that bound gas in haloes may contribute only up to 20% of the measured filamentary signal. To estimate the filament gas properties we measure the gravitational lensing signal for the same sample of galaxy pairs; in combination with the tSZ signal, this yields an inferred gas density of ρb = (5.5 ± 2.9) × ρ̄b ρ b = ( 5.5 ± 2.9 ) × ρ b ¯ $ \rho_{\mathrm{b}}=(5.5\pm 2.9)\times\bar{\rho_{\mathrm{b}}} $ with a temperature T = (2.7 ± 1.7) × 106 K. This result is consistent with the predicted WHIM properties, and overall the filamentary gas can account for 11 ± 7% of the total baryon content of the Universe. We also see evidence that the gas filament extends beyond the galaxy pair. Averaging over this longer baseline boosts the significance of the tSZ signal and increases the associated baryon content to 28 ± 12% of the global value.
Covalent organic frameworks (COFs), as a new emerging class of highly crystalline advanced porous materials with fascinating structural tunability and diversity as well as the desired semiconductor ...properties, have gained significant attention as highly promising and efficient photocatalysts or designer platforms for a variety of photocatalytic applications in recent years; thus a comprehensive review is timely to summarize the advances of this field. In this review, a background and brief timeline concerning the developments and key achievements of COFs are provided. Afterwards, a systematic overview of the potential photocatalytic applications realized to date in the fast growing field of COFs is provided with the aim of presenting a full blueprint of COFs for possible photochemical energy conversion and reactions. Finally, the challenges remaining and personal perspectives on further development of this type of material for photocatalysis are presented.
In this review, a comprehensive summary of the potential photocatalytic applications realized to date in the fast-growing field of COFs is provided with the aim to present a full blueprint of COFs for photochemical energy conversion and reactions.
The 1,2-diamine motif is widely present in natural products, pharmaceutical compounds, and catalysts used in asymmetric synthesis. The simultaneous introduction of two amino groups across an alkene ...feedstock is an appealing yet challenging approach for the synthesis of 1,2-diamines, primarily due to the inhibitory effect of the diamine products to transition metal catalysts and the difficulty in controlling reaction diastereoselectivity and regioselectivity. Herein we report a scalable electrocatalytic 1,2-diamination reaction that can be used to convert stable, easily available aryl alkenes and sulfamides to 1,2-diamines with excellent diastereoselectivity. Monosubstituted sulfamides react in a regioselective manner to afford 1,2-diamines bearing different substituents on the two amino groups. The combination of an organic redox catalyst and electricity not only obviates the use of any transition metal catalyst and oxidizing reagent, but also ensures broad reaction compatibility with a variety of electronically and sterically diverse substrates.
ABSTRACT
We use data from the DESI Legacy Survey imaging to probe the galaxy density field in tomographic slices covering the redshift range 0 < z < 0.8. After careful consideration of completeness ...corrections and galactic cuts, we obtain a sample of 4.9 × 107 galaxies covering 17 739 deg2. We derive photometric redshifts with precision σz/(1 + z) = 0.012−0.015, and compare with alternative estimates.1 Cross-correlation of the tomographic galaxy maps with Planck maps of cosmic microwave background (CMB) temperature and lensing convergence probe the growth of structure since z = 0.8. The signals are compared with a fiducial Planck ΛCDM model, and require an overall scaling in amplitude of Aκ = 0.901 ± 0.026 for the lensing cross-correlation and AISW = 0.984 ± 0.349 for the temperature cross-correlation, interpreted as the integrated Sachs–Wolfe effect. The ISW amplitude is consistent with the fiducial Λ cold dark matter (ΛCDM) prediction, but lies significantly below the prediction of the AvERA model of Rácz et al., which has been proposed as an alternative explanation for cosmic acceleration. Within ΛCDM, our low amplitude for the lensing cross-correlation requires a reduction either in fluctuation normalization or in matter density compared to the Planck results, so that $\Omega _\mathrm{ m}^{0.78}\sigma _8=0.297\pm 0.009$. In combination with the total amplitude of CMB lensing, this favours a shift mainly in density: Ωm = 0.274 ± 0.024. We discuss the consistency of this figure with alternative evidence. A conservative compromise between lensing and primary CMB constraints would require Ωm = 0.296 ± 0.006, where the 95 per cent confidence regions of both probes overlap.
This paper proposes a variable proportion coefficient based control scheme for the doubly-fed induction generator based wind turbines (DFIG-WTs) to implement frequency support by regulating rotor ...speed. To reduce the adverse impact caused by regulating DFIG-WT on the dynamic characteristic of the grid frequency, a two-stage switching control scheme is employed for the proposed method. In the first stage, the variable proportion coefficient is designed for emulating the virtual inertia of the DFIG-WT to provide inertia response. In the second stage, a fuzzy control scheme is employed to design the variable proportion coefficient for both quickly restoring the maximum power point tracking (MPPT) operation of DFIG-WTs and avoiding the secondary frequency drop to system. Case studies are undertaken based on WSCC 9-bus and IEEE 39-bus power systems, respectively. Simulation results show that the proposed control scheme can not only make grid-connected DFIG-WTs provide the friendly frequency support, but also help them to fully use the frequency regulation ability of synchronous generators for quickly restoring the MPPT operation.
By changing the charge distribution of boron vertices via introducing an amide on cage B(9), the selective B(4) arylation of o-carboranes via Suzuki-Miyaura coupling has been developed. A series of ...o-carborane derivatives decorated with diverse active groups have been synthesized with moderate to good yields, which have been proved to be further transformed to a novel kind of tri-substituted nido-carborane fused oxazole with potential application in boron neutron capture therapy, organometallic as well as coordination chemistry.
Redshift-space distortions around voids Cai, Yan-Chuan; Taylor, Andy; Peacock, John A ...
Monthly notices of the Royal Astronomical Society,
11/2016, Volume:
462, Issue:
3
Journal Article
Peer reviewed
Open access
We have derived estimators for the linear growth rate of density fluctuations using the cross-correlation function (CCF) of voids and haloes in redshift space. In linear theory, this CCF contains ...only monopole and quadrupole terms. At scales greater than the void radius, linear theory is a good match to voids traced out by haloes; small-scale random velocities are unimportant at these radii, only tending to cause small and often negligible elongation of the CCF near its origin. By extracting the monopole and quadrupole from the CCF, we measure the linear growth rate without prior knowledge of the void profile or velocity dispersion. We recover the linear growth parameter beta to 9 per cent precision from an effective volume of 3(h super( -1) Gpc) super( 3) using voids with radius >25 h super( -1) Mpc. Smaller voids are predominantly sub-voids, which may be more sensitive to the random velocity dispersion; they introduce noise and do not help to improve measurements. Adding velocity dispersion as a free parameter allows us to use information at radii as small as half of the void radius. The precision on beta is reduced to 5 per cent. Voids show diverse shapes in redshift space, and can appear either elongated or flattened along the line of sight. This can be explained by the competing amplitudes of the local density contrast, plus the radial velocity profile and its gradient. The distortion pattern is therefore determined solely by the void profile and is different for void-in-cloud and void-in-void. This diversity of redshift-space void morphology complicates measurements of the Alcock-Paczynski effect using voids.
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