24 research outputs found
Modeling the black holes surrounded by a dark matter halo in the galactic center of M87
In this paper, the structure of a dark matter halo can be well described by
the mass model of M87 and the Einasto profile for the cold dark matter model,
i.e., (Wang et al. in Nature 585:39-42, 2020). Under
these conditions, we construct a solution of a static spherically symmetric
black hole in a dark matter halo. Then, using the Newman-janis algorithm, we
extend this static solution to the case of rotation, and obtain a solution for
the Kerr-like black hole. We prove that this solution of the Kerr-like black
hole is indeed a solution to the Einstein field equations. Finally, taking M87
as an example, we study and analyze some physical properties of this Kerr-like
black hole, and then compare them with the Kerr black hole. Particularly, from
the perspective of the black hole shadow and the fact that the Kerr-like black
hole and the Kerr black hole is distinguishable, we give the upper limit of the
shape parameter of the Einasto density profile, that is approximately
, which may provide a new method to further improve and perfect
the density profile of dark matter model. These research results for the black
hole in a dark matter halo may indirectly provide an effective method for
detecting the existence of dark matter
Echoes from black bounces surrounded by the string cloud
In the string theory, the fundamental blocks of nature are not particles but
one-dimensional strings. Therefore, a generalization of this idea is to think
of it as a cloud of strings. Rodrigues et al. embedded the black bounces
spacetime into the string cloud, which demonstrates that the existence of the
string cloud makes the Bardeen black hole singular, while the black bounces
spacetime remains regular. On the other hand, the echoes are the correction to
the late stage of the quasinormal ringing for a black hole, which is caused by
the deviation of the spacetime relative to the initial black hole spacetime
geometry in the near-horizon region. In this work, we study the gravitational
wave echoes of black bounces spacetime surrounded by a cloud of strings under
scalar field and electromagnetic field perturbation to explore what
gravitational effects near-horizon region are caused by string cloud. The
ringing of the regular black hole and traversable wormhole with string cloud
are presented. Our results demonstrate that the black bounce spacetime with
strings cloud is characterized by gravitational wave echoes as it transitions
from regular black holes to wormholes, i.e. the echoes signal will facilitate
us to distinguish between black holes and the wormholes in black bounces
surrounded by the string cloud
Probing hairy black holes caused by gravitational decoupling using quasinormal modes, and greybody bounds
Extended gravitational decoupling can add hair to the black holes in general
relativity by adding extra sources. The quasinormal modes of hairy black holes
caused by gravitational decoupling for the massless scalar field,
electromagnetic field, and axial gravitational perturbation are investigated.
The equation of effective potential for three perturbations is derived in hairy
black holes spacetime. We also study the time evolution corresponding to the
three perturbations, and the quasinormal mode frequencies are calculated using
the Prony method through the time-domain profiles. Particularly, we find that
the response of hairy black hole spacetime to axial gravitational perturbations
is completely different from scalar field and electromagnetic field
perturbations, which may be due to the fact that the gravitational radiation
produced by the perturbations of the hairy black hole metric itself is much
stronger than that of the external field. Furthermore, we have calculated the
bounds on this greybody factor and high-energy absorption cross section with
the Sinc approximation. The study reveals that the charges ( and )
generating primary hair contributes positively to the greybody bounds and
absorption cross section, whereas the tidal charge from the extra sources
does the opposite
Recent wetting trend over Taklamakan and Gobi Desert dominated by internal variability
Abstract The Taklamakan and Gobi Desert (TGD) region has experienced a pronounced increase in summer precipitation, including high-impact extreme events, over recent decades. Despite identifying large-scale circulation changes as a key driver of the wetting trend, understanding the relative contributions of internal variability and external forcings remains limited. Here, we approach this problem by using a hierarchy of numerical simulations, complemented by diverse statistical analysis tools. Our results offer strong evidence that the atmospheric internal variations primarily drive this observed trend. Specifically, recent changes in the North Atlantic Oscillation have redirected the storm track, leading to increased extratropical storms entering TGD and subsequently more precipitation. A clustering analysis further demonstrates that these linkages predominantly operate at the synoptic scale, with larger contributions from large precipitation events. Our analysis highlights the crucial role of internal variability, in addition to anthropogenic forcing, when seeking a comprehensive understanding of future precipitation trends in TGD
Quasinormal Modes and Greybody Bounds of Rotating Black Holes in a Dark Matter Halo
Quasinormal mode(QNM) is a characteristic "sound" for a black hole which can
provide us with a new method to verify black holes in our universe. This
characteristic "sound" can be represented by a complex frequency, that is,
quasinormal frequency (QNF). On the other hand, the study of greybody factors
can provide us with important clues for the quantum structure of black holes.
Based on these interesting physical background, we study quasinormal modes
(QNMs) and greybody factors (GFs) of rotating black holes in a dark matter
halo, and make comparisons with the Kerr black hole. The main results we
obtained are as follows: QNFs are directly related to the rotation parameter
of black holes. The oscillation frequencies (real part) of black holes both
in a dark matter halo and the Kerr spacetime decrease with the increasing of
rotation parameter . The decay rates (imaginary part) of QNF increase with
the increasing of the rotation parameter . On the other hand, QNFs of black
holes increase with the increasing of the angular quantum number and the
magnetic quantum number , respectively. The rotation parameters and
separation constant of black holes both in a dark matter halo and the Kerr
spacetime have a positive contribution to the greybody bounds. The value of
greybody bounds decreases with increasing of rotation parameter and
separation constant , respectively. Besides, QNFs of black holes fitted by
P{\"o}schl-Teller potential approximation and sixth-order WKB method are in
good agreement
Rapid Transient Explosive Boiling of Binary Mixture under Pulsed-Laser Irradiation
Rapid transient explosive boiling of mixed ethanol and acetone of different volume fractions were investigated experimentally. The temperature of the metal film surface irradiated by a pulse laser was measured by a fast-response measurement system with a platinum film resistor. The behaviors of bubbles, including their formation, growth, departure and floating-up, were observed and captured by a microscope camera system. It was found that bubble nucleation temperature depends strongly on the heating rate. Some special characteristics different from those of conventional boiling were revealed, and the factors affecting explosive boiling were studied
The Genome of Bacillus velezensis SC60 Provides Evidence for Its Plant Probiotic Effects
Root colonization and plant probiotic function are important traits of plant growth-promoting rhizobacteria (PGPR). Bacillus velezensis SC60, a plant endophytic strain screened from Sesbania cannabina, has a strong colonization ability on various plant roots, which indicates that SC60 has a preferable adaptability to plants. However, the probiotic function of the strain SC60 is not well-understood. Promoting plant growth and suppressing soil-borne pathogens are key to the plant probiotic functions. In this study, the genetic mechanism of plant growth-promoting and antibacterial activity of the strain SC60 was analyzed by biological and bioinformatics methods. The complete genome size of strain SC60 was 3,962,671 bp, with 4079 predicted genes and an average GC content of 46.46%. SC60 was designated as Bacillus velezensis according to the comparative analysis, including average nucleotide polymorphism (ANI), digital DNA-DNA hybridization (dDDH), and phylogenetic analysis. Genomic secondary metabolite analyses indicated two clusters encoding potential new antimicrobials. The antagonism experiments revealed that strain SC60 had the ability to inhibit the growth of a variety of plant pathogens and its closely related strains of Bacillus spp., which was crucial to the rhizospheric competitiveness and growth-promoting effect of the strain. The present results further suggest that B. velezensis SC60 could be used as a PGPR strain to develop new biocontrol agents or microbial fertilizers
An experimental investigation on air-side performances of finned tube heat exchangers for indirect air-cooling tower
A tremendous quantity of water can be saved if the air cooling system is
used, comparing with the ordinary water-cooling technology. In this study,
two kinds of finned tube heat exchangers in an indirect air-cooling tower are
experimentally studied, which are a plain finned oval-tube heat exchanger and
a wavy-finned flat-tube heat exchanger in a cross flow of air. Four different
air inlet angles (90°, 60 °, 45°, and 30°) are tested separately to obtain
the heat transfer and resistance performance. Then the air-side experimental
correlations of the Nusselt number and friction factor are acquired. The
comprehensive heat transfer performances for two finned tube heat exchangers
under four air inlet angles are compared. For the plain finned oval-tube heat
exchanger, the vertical angle (90°) has the worst performance while 45° and
30° has the best performance at small ReDc and at large ReDc, respectively.
For the wavy-finned flat-tube heat exchanger, the worst performance occurred
at 60°, while the best performance occurred at 45° and 90° at small ReDc and
at large ReDc, respectively. From the comparative results, it can be found
that the air inlet angle has completely different effects on the
comprehensive heat transfer performance for the heat exchangers with
different structures
Rock Burst Mechanism under Coupling Action of Working Face Square and Regional Tectonic Stress
With the development of faults in many coalfields, many large faults will form a relatively independent area, forming regional tectonic stress concentration. Under the influence of mining, it is easy to induce fault activation, produce mine tremor, and then induce rock burst. Through field investigation, theoretical analysis, numerical simulation, and engineering verification, the overburden movement model of No. 3504 working face square and fault activation in Liangbaosi Coal Mine was established. The stress variation and energy release law of working face advance and fault area were analyzed, and the mechanism of rock burst under the coupling action of working face square and regional tectonic stress was revealed. The results show that the regional stress adjustment and fault activation are caused by the large-scale overall movement of overburden during the working face square, and there is a peak value of elastic energy release during the fault activation, which is easy to produce large energy mine earthquake. The energy level of the daily maximum energy event is higher than that of the initial mining stage in the square period, and the location of on-site large energy microseismic event is basically consistent with the predicted fault strike. The study provides a theoretical basis for the prevention and control of rock burst during the working face square under the condition of regional tectonic stress
Wu-Mei-Wan Reduces Insulin Resistance via Inhibition of NLRP3 Inflammasome Activation in HepG2 Cells
Wu-Mei-Wan (WMW) is a Chinese herbal formula used to treat type 2 diabetes. In this study, we aimed to explore the effects and mechanisms of WMW on insulin resistance in HepG2 cells. HepG2 cells were pretreated with palmitate (0.25 mM) to impair the insulin signaling pathway. Then, they were treated with different doses of WMW-containing medicated serum and stimulated with 100 nM insulin. Results showed that palmitate could reduce the glucose consumption rate in HepG2 cells and impair insulin signaling related to phosphorylation of insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), thereby regulating the downstream signaling pathways. However, medicated serum of WMW restored impaired insulin signaling, upregulated the expression of phospho-IR (pIR), phosphatidylinositol 3-kinase p85 subunit, phosphoprotein kinase B, and glucose transporter 4, and decreased IRS serine phosphorylation. In addition, it decreased the expression of interleukin-1β and tumor necrosis factor-α, which are the key proinflammatory cytokines involved in insulin resistance; besides, it reduced the expression of NLRP3 inflammasome. These results suggested that WMW could alleviate palmitate-induced insulin resistance in HepG2 cells via inhibition of NLRP3 inflammasome and reduction of proinflammatory cytokine production