We suggest that the vacuum field equation in Finsler spacetime is equivalent to the vanishing of the Ricci scalar. The Schwarzschild metric can be deduced from a solution of our field equation if the ...spacetime preserves spherical symmetry. Supposing that the spacetime preserves the symmetry of the "Finslerian sphere," we find a non-Riemannian exact solution of the Finslerian vacuum field equation. The solution is similar to the Schwarzschild metric. It reduces to the Schwarzschild metric as the Finslerian parameter epsilon vanishes. It is proven that the Finslerian covariant derivative of the geometrical part of the gravitational field equation is conserved. The interior solution is also given. We get solutions of the geodesic equation in such a Schwarzschild-like spacetime, and show that the geodesic equation returns to its counterpart in Newtonian gravity in the weak-field approximation. Celestial observations give a constraint on the Finslerian parameter epsilon < 10 super(-4), and the recent Michelson-Morley experiment requires epsilon < 10 super(-16). A counterpart of Birkhoff's theorem exists in the Finslerian vacuum. This shows that the Finslerian gravitational field with the symmetry of the "Finslerian sphere" in vacuum must be static.
B(npy)Ar2 (npy=2‐(naphthalen‐1‐yl)pyridine) compounds bearing various nonbulky aryl groups undergo a clean and sequential two‐step photoisomerization in which two aryl substituents on boron migrate ...to a carbon atom of the naphthyl moiety. The second isomerization step is the first example of a reversible photoisoermization between a borepin and a borirane. Both steric and electronic factors have been found to have a great impact on this photoreactivity. Furthermore, the borirane isomer reacts with oxygen, forming a rare oxaborepin dimer.
Double move: Boron chelate compounds undergo a two‐stage photoisomerization involving double aryl migration from a boron to carbon atom, and an unprecedented reversible phototransformation of a borepin (a) into a new boratanorcaradiene species (b).
In a recent work on rotating black hole shadows Z. Chang and Q.-H. Zhu, Phys. Rev. D 101, 084029 (2020), we proposed a new approach for calculating size and shape of the shadows in terms of ...astrometrical observables with respect to finite-distance observers. In this paper, we introduce a distortion parameter for the shadow shapes and discuss the appearance of the shadows of static spherical black holes and Kerr black holes in a uniform framework. We show that the shape of the shadow of a spherical black hole is circular in the view of arbitrary observers, and the size of the shadows tends to be shrunk in the view of a moving observer. The diameter of the shadows is contracted even in the direction perpendicular to the observers' motion. This seems not to be understood as length contraction effect in special relativity. The shape of Kerr black holes is dependent on motional status of the observers located at finite distance. In spite of this, it is found that there is not a surrounding observer who could view the shape of the Kerr black hole shadows as circularity. These results could be helpful for observation of the Sagittarius A* in the center of the Milky Way, as our Solar System is moving around the center of the black hole.
As an attractive candidate for dark matter, the primordial black holes (PBHs) in the mass range (8×1014 ∼ 1016) g could be detected via their Hawking radiation, including neutrinos and antineutrinos ...of three flavors. In this paper, we investigate the possibility to constrain the PBHs as dark matter by measuring (anti)neutrino signals at the large liquid-scintillator detector of Jiangmen Underground Neutrino Observatory (JUNO). Among six available detection channels, the inverse beta decay νe + p → e+ + n is shown to be most sensitive to the fraction fPBH of PBHs contributing to the dark matter abundance. Given the PBH mass MPBH = 1015g, we find that JUNO will be able to place an upper bound fPBH ≲ 3×10−5, which is 20 times better than the current best limit fPBH ≲ 6×10−4 from Super-Kamiokande. For heavier PBHs with a lower Hawking temperature, the (anti)neutrinos become less energetic, leading to a relatively weaker bound.
The damping effect of the free-streaming neutrinos on the second order gravitational waves is investigated in detail. We solve the Boltzmann equation and give the anisotropic stress induced by ...neutrinos to second order. The first order tensor and its coupling with scalar perturbations induced gravitational waves are considered. We give the analytic equations of the damping kernel functions and finally obtain the energy density spectrum. The results show that the free-streaming neutrinos suppress the density spectrum significantly for low frequency gravitational waves and enlarge the logarithmic slope
n
in the infrared region (
k
≪
k
∗
) of the spectrum. For the spectrum of
k
∗
∼
10
-
7
Hz
, the damping effect in the range of
k
<
k
∗
is significant. The combined effect of the first and second order could reduce the amplitude by
30
%
and make
n
jump from 1.54 to 1.63 at
k
∼
10
-
9
Hz
, which may be probed by the pulsar timing arrays (PTA) in the future.
To increase the reliability and success rate of drug discovery, efforts have been made to increase the C(sp
) fraction and avoid flat molecules. sp
-Rich enantiopure amines are most frequently ...encountered as chiral auxiliaries, synthetic intermediates for pharmaceutical agents and bioactive natural products. Streamlined construction of chiral aliphatic amines has long been regarded as a paramount challenge. Mainstream approaches, including hydrogenation of enamines and imines, C-H amination, and alkylation of imines, were applied for the synthesis of chiral amines with circumscribed skeleton structures; typically, the chiral carbon centre was adjacent to an auxiliary aryl or ester group. Herein, we report a mild and general nickel-catalysed asymmetric reductive hydroalkylation to effectively convert enamides and enecarbamates into drug-like α-branched chiral amines and derivatives. This reaction involves the regio- and stereoselective hydrometallation of an enamide or enecarbamate to generate a catalytic amount of enantioenriched alkylnickel intermediate, followed by C-C bond formation via alkyl electrophiles.
Deep–ultradeep carbonates have long been a hotspot in the field of oil and gas exploration in the Tarim Basin. The hydrocarbon source rock distribution is a key factor restricting deep–ultradeep oil ...and gas exploration, and in particular, there has been controversy over the sources of the deep oil and gas in the Tarim Basin. In addition, the black shale sediments of the Yuertusi Formation formed during the important transition period of the Precambrian/Cambrian and recorded globally significant climatic events. Research on this formation is of great scientific value for understanding the changes in the Earth's surface climate system during this major and critical transition period. Based on nine field sections, 36 wells, and 2D and 3D seismic data, this paper analyzes the sedimentary environment and hydrocarbon source rock distribution of the Yuertusi Formation in the Tarim Basin. The results show that the lower Cambrian Yuertusi Formation in the Tarim Basin can be divided into two third-order sequences (SQ1 and SQ2) and five fourth-order sequences (sq1-sq5), which experienced two primary transgressions during the deposition of sq2 and sq4. During the depositional period of sq2, hydrocarbon source rocks with the highest organic carbon content in the entire area formed under the influence of high paleoproductivity and upwelling currents. sq4 formed in the context of a second large-scale transgression, and the depositional center moved to the southwest. The organic matter content in sq4 is lower than that in sq2, but it features an extensive distribution and a large thickness. sq3 and sq5 are shallow-water deposits, primarily gray dolomite and algal dolomite with local argillaceous interlayers, that formed during marine regression phases. sq2 and sq4 of the Yuertusi Formation are primarily deep-water to shallow-water shelf sediments with stable thicknesses and are widely distributed in the slope area of the basin and on the shelf. These two sets of high-quality hydrocarbon source rocks indicate the huge hydrocarbon exploration potential of the deep Cambrian strata in the Tarim Basin. These research results can provide important scientific references for evaluating deep–ultradeep oil and gas resources in the Tarim Basin.
•The Yuertusi Formation can be subdivided into two third-order sequences and five fourth-order sequences (sq1-sq5).•The sq2 and sq4 associated with large-scale transgressions are potential source rocks.•The enrichment of organic matter in sq2 was controlled by upwelling currents and hydrothermal activity.
An efficient approach to saccharin‐fused 1,4‐DHPs has been established by using a 3+3 annulation process. The chemical event was enabled by a Et3N‐catalyzed tandem Michael/aza‐Pinner reaction of ...alkyl cyclic N‐sulfonyl ketimines as nucleophiles with α,α‐dicyanoolefins. Under mild conditions, the desired products were readily prepared in good to excellent yields and with broad functional group tolerance (up to 95 % yield, 29 examples). Notably, this practical methodology features the synthesis of pentacyclic spirooxindoles bearing a quaternary spiro‐stereocenter.
An efficient 3+3 annulation reaction of cyclic N‐sulfonyl ketimine and α,α‐dicyanoolefins has been developed via a Et3N‐catalyzed tandem Michael/aza‐Pinner process, affording a broad range of saccharine‐fused 1,4‐DHPs in good to excellent yields (up to 95 %).
Long‐term arsenic exposure is a worldwide public health problem that causes serious harm to human health. The liver is the main target organ of arsenic toxicity; arsenic induces disruption of the DNA ...damage repair pathway, but its mechanisms remain unclear. In recent years, studies have found that epigenetic mechanisms play an important role in arsenic‐induced lesions. In this study, we conducted experiments in vitro using normal human liver cells (L‐02) to explore the mechanism by which the histone demethylase JHDM2A regulates H3K9 dimethylation (me2) in response to arsenic‐induced DNA damage. Our results indicated that arsenic exposure upregulated the expression of JHDM2A, downregulated global H3K9me2 modification levels, increased the H3K9me2 levels at the promoters of base excision repair (BER) genes (N‐methylpurine‐DNA glycosylase MPG, XRCC1 and poly(ADP‐ribose)polymerase 1) and inhibited their expression levels, causing DNA damage in cells. In addition, we studied the effects of overexpression and inhibition of JHDM2A and found that JHDM2A can participate in the molecular mechanism of arsenic‐induced DNA damage via the BER pathway, which may not be involved in the BER process because H3K9me2 levels at the promoter region of the BER genes were unchanged following JHDM2A interference. These results suggest a potential mechanism by which JHDM2A can regulate the MPG and XRCC1 genes in the process of responding to DNA damage induced by arsenic exposure and can participate in the process of DNA damage repair, which provides a scientific basis for understanding the epigenetic mechanisms and treatments for endemic arsenic poisoning.
Arsenic poisoning can lead to abnormal DNA damage and repair, which is related to the regulation of histone methylation. JHDM2A is the histone demethylase that specifically removes the methyl group from histone lysine H3K9, which is overexpressed in various tumors. After inhibition of JHDM2A, it can increase the expression of H3K9me2 and inhibit the proliferation of cancer cells. Our study shows that arsenic can upregulate JHDM2A and aggravate DNA damage, and JHDM2A inhibition can reduce levels of DNA damage.
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