This article considers a static and spherical black hole(BH)in f(Q)gravity.f(Q)gravity is the extension of symmetric teleparallel general relativity,where both curvature and torsion are vanishing and gravity is descri...This article considers a static and spherical black hole(BH)in f(Q)gravity.f(Q)gravity is the extension of symmetric teleparallel general relativity,where both curvature and torsion are vanishing and gravity is described by nonmetricity.In this study,we investigate the possible implications of quasinormal mode(QNM)modified Hawking spectra and deflection angles generated by the model.The Wentzel–Kramers–Brillouin method is used to solve the equations of motion for massless Dirac perturbation fields and explore the impact of the nonmetricity parameter(Q_(0)).Based on the QNM computation,we can ensure that the BH is stable against massless Dirac perturbations and as Q_(0)increases the oscillatory frequency of the mode decreases.We then discuss the weak deflection angle in the weak field limit approximation.We compute the deflection angle up to the fourth order of approximation and show how the nonmetricity parameter affects it.We find that the Q_(0)parameter reduces the deflection angle.展开更多
In this study,we examined the thermal fluctuations,deflection angle,and greybody factor of a high-dimensional Schwarzschild black hole in scalar-tensor-vector gravity(STVG).We calculated some thermodynamic quantities ...In this study,we examined the thermal fluctuations,deflection angle,and greybody factor of a high-dimensional Schwarzschild black hole in scalar-tensor-vector gravity(STVG).We calculated some thermodynamic quantities related to the correction of the black hole entropy caused by thermal fluctuations and discussed the effect of the correction parameters on these quantities.By analyzing the changes in the corrected specific heat,we found that thermal fluctuations made the small black hole more stable.It is worth noting that the STVG parameter did not affect the thermodynamic stability of this black hole.Additionally,by utilizing the Gauss-Bonnet theorem,the deflection angle was obtained in the weak field limit,and the effects of the two parameters on the results were visualized.Finally,we calculated the bounds on the greybody factor of a massless scalar field.We observed that as the STVG parameter around the black hole increased,the weak deflection angle became larger,and more scalar particles can reach infinity.However,the spacetime dimension has the opposite effect on the STVG parameter on the weak deflection angle and greybody factor.展开更多
The deflection angle of a river bend plays an important role on behaviours of the flow within it, and a clear understanding of the angle's influence is significant in both theoretical study and engineering applica...The deflection angle of a river bend plays an important role on behaviours of the flow within it, and a clear understanding of the angle's influence is significant in both theoretical study and engineering application. This paper presents a systematic numerical investigation on effects of deflection angles(30°, 60°, 90°, 120°, 150°, and 180°) on flow phenomena and their evolution in open-channel bends using a Re-Normalization Group(RNG) κ-ε model and a volume of fluid(VOF) method. The numerical results indicate that the deflection angle is a key factor for flows in bends. It is shown that the maximum transverse slope of water surface occurs at the middle cross section of a bend, and it increases with the deflection angle. Besides a major vortex, or, the primary circulation cell near the channel bottom, a secondary vortex, or, an outer bank cell, may also appear above the former and near the outer bank when the deflection angle is sufficiently large, and it will gradually migrate towards the inner bank and evolve into an inner bank cell. The strength of the secondary circulations increases with the deflection angle. The simulation demonstrates that there is alow-stress zone on the bed near the outer bank and a high-stress zone on the bed near the inner bank, and both of them increase in size with the deflection angle. The maximum of shear stress on the inner bank increases nonlinearly with the angle, and its maximums on the outer bank and on the bed take place when the deflection angle becomes 120°.展开更多
With the wide application of laser in the field of skin plastic surgery, micro laser galvanometer scanner has made great progress in this field with its portability. However, the measurement method used to measure the...With the wide application of laser in the field of skin plastic surgery, micro laser galvanometer scanner has made great progress in this field with its portability. However, the measurement method used to measure the deflection angle of laser galvanometer in the narrow space of scanner with high precision remains to be studied. In this paper, an angle measurement method based on magnetic field is proposed, and the effect of the shapes of permanent magnets(PMs) on the measurement is studied by theoretical and experimental study under the condition that the maximum available space for the PMs is a 10 mm side cube. An angle measuring experimental device is set up, and the contrast experiment is carried out with different PMs which are the same as simulation. The experimental results show that cylindrical PM is more suitable than other PMs, which is consistent with the simulation results, and the maximum nonlinearity error is 0.562%. This method has the advantages of small volume,non-contact measurement, small moment of inertia, good dynamic response and no external excitation for the PMs, so it has a broad application prospect in micro laser galvanometer scanner.展开更多
Loop Heat Pipe(LHP)is an efficient two-phase heat transfer device,which can be used in waste heat recovery,electronics cooling,aerospace and other fields.The wick,the core component of LHP,plays an important role in i...Loop Heat Pipe(LHP)is an efficient two-phase heat transfer device,which can be used in waste heat recovery,electronics cooling,aerospace and other fields.The wick,the core component of LHP,plays an important role in its start-up and operation.In this paper,the wick fabricated by 3D printing technology had uniform and interconnected pores.In the experiment,the position of the parallel vapor removal grooves was always fixed towards the vapor outlet.When the cylindrical wick was placed in the evaporator,the rotation angle relative to its central axis could be changed,thus changing the number and shape of the pores facing the vapor removal grooves.The wick deflection angle represented its change in spatial position relative to the fixed vapor removal grooves.The effect of the wick deflection angles on the heat transfer characteristics of the flat LHP was experimentally investigated.It was found that with the change of deflection angle,the number of pores in the evaporation-oriented zone would also change,which had a significant impact on the start-up process and heat transfer performance of LHP.When the deflection angle was 30°,LHP could start fastest at a low heat load of 20 W and operate stable at a high heat load of 180 W.展开更多
Previously, the gravitational lens of a wormhole was introduced by various researchers. Their treatment was focused basically on the lens signature that describes wormhole geometrical character such as the differences...Previously, the gravitational lens of a wormhole was introduced by various researchers. Their treatment was focused basically on the lens signature that describes wormhole geometrical character such as the differences from a black hole or between any various types of wormhole models. The braneworld scenario provides the idea of spacetime with underlying extra-dimensions. The inclusion of extra-dimensional terms in the lens object spacetime line element will result in some variation in the expression for its gravitational lens deflection angle. Thus in this paper we investigate such variation by deriving this deflection angle expression. As such, this paper not only shows the existence of such variation but also suggests the potential utilization of gravitational lensing to prove the existence of extra dimensions by studying the deflection angle characteristic in accordance with the spacetime expansion rate of the universe.展开更多
We investigate the light deflection in the weak field approximation from the accelerating charged AdS black hole.For this purpose,we apply the Gauss–Bonnet theorem to calculate the light deflection in the weak field ...We investigate the light deflection in the weak field approximation from the accelerating charged AdS black hole.For this purpose,we apply the Gauss–Bonnet theorem to calculate the light deflection in the weak field area and use the Gibbons–Werner approach to analyze the optical geometry of the accelerating charged AdS black hole in the non-magnetic plasma absence/presence of a non-magnetic medium.We also represent the graphical behavior of the light deflection angle w.r.t.the impact parameter.We also compute the light deflection angle using Keeton and Petters approximations under the impact of accelerating charged AdS black hole geometry.Furthermore,by using the ray-tracing approach,we determine the shadow in the nonmagnetic plasma presence and also demonstrate that graphical shadow has an impact on the gauge potential,non-magnetic plasma frequencies and charge.展开更多
The description and function characterization of a flange-on type low energy electron mi- croscope are given. In this microscope a magnetic beam separator with 10° deflection angle is used in order to facilitate ...The description and function characterization of a flange-on type low energy electron mi- croscope are given. In this microscope a magnetic beam separator with 10° deflection angle is used in order to facilitate compacting the instrument on a single 10 in. flange. Mean- while some correcting elements in the electron optical system are simplified to reduce the complexities of construction and operation. The sample is set close to ground potential, so that all the electrostatic lenses are easily to float at high voltages. The performance of the microscope in typical low energy electron microscopy, low energy electron diffraction and photoemission electron microscopy modes is demonstrated through several experiments. A lateral resolution of 51 nm is estimated for low energy electron microscopy imaging. With femtosecond laser as light source, the consequent nonlinear photoemission makes this micro-scope also suitable for the observation of optical near field phenomena and a lateral resolution of 110 nm is obtained.展开更多
To control the deflection of the gas plasma jet, a new analytical method is proposed based on the Magnetohydrodynamic(MHD) technique. Based on the typical MHD power generation model, the applied voltage is applied to ...To control the deflection of the gas plasma jet, a new analytical method is proposed based on the Magnetohydrodynamic(MHD) technique. Based on the typical MHD power generation model, the applied voltage is applied to the staggered electrodes, that is, a pair of electrodes on the same side wall are connected to generate an axial current in the channel. Under the action of the magnetic field perpendicular to the direction of the flow, the plasma is subjected to electromagnetic forces perpendicular to these two directions, and the jet is deflected. The computational model including the Navier-Stokes equations coupled with electromagnetic source terms, the electric potential equation and Ohm’s law is solved. The deflection of the gas jet under the action of an electromagnetic field is observed, and the maximum deflection angle is about 14.8°. The influences of the electric field, magnetic field, and conductivity on the jet deflection are studied. Results show that although the influences of these three factors on the deflection are similar, and the effect of increasing the electric field strength is slightly greater, priority should be given to increasing the magnetic field strength from the perspective of reducing energy consumption. The Stuart number is introduced to assess the ability of electromagnetic force to control jet deflection. When the electromagnetic parameters are constant, this solution provides better control of low-density and low-speed fluid flows. The calculation results show that using the staggered electrode method configuration is feasible in terms of controlling the deflection of a plasma jet deflection.展开更多
The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated compo...The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress-strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.展开更多
In this study,we analyze the models of the deflection angle of a new Schwarzschild-like black hole(BH)and employ the optical metric of the BH.To achieve this,we use the Gaussian curvature of the optical metric and the...In this study,we analyze the models of the deflection angle of a new Schwarzschild-like black hole(BH)and employ the optical metric of the BH.To achieve this,we use the Gaussian curvature of the optical metric and the Gauss-Bonnet theorem,known as the Gibbons-Werner technique,to determine the deflection angle.Furthermore,we examine the deflection angle in the presence of a plasma medium and the effect of the plasma medium on the deflection angle.The deflection angle of the BH solution in the gauged super-gravity is computed using the Keeton-Petters approach.Utilizing the ray-tracing technique,we investigate the shadow of the corresponding BH and analyze the plots of the deflection angle and shadow to verify the influence of the plasma and algebraic thermodynamic parameters on the deflection angle and shadow.展开更多
After comparing the mechanism of tilted plume under stack effect with that of spill plume,the tilted plume model induced by stack effect in a vertical shaft is developed simply based on the theoretical results and a s...After comparing the mechanism of tilted plume under stack effect with that of spill plume,the tilted plume model induced by stack effect in a vertical shaft is developed simply based on the theoretical results and a series of full-scale tests. It is shown that the two sides of plume are symmetrical and have an accordant regulation that the plume radius has a linear relation to the height z. The profile of fire plume under stack effect is similar to the windblown flame in wind tunnel,and the range of flame deflection angle is about from 50 to 60 degree.展开更多
This paper investigates off-equatorial plane deflections and gravitational lensing of both null signals and massive particles in Kerr spacetime in the weak deflection limit,considering the finite distance effect of th...This paper investigates off-equatorial plane deflections and gravitational lensing of both null signals and massive particles in Kerr spacetime in the weak deflection limit,considering the finite distance effect of the source and detector.This is the effect caused by both the source and detector being located at finite distances from the lens although many researchers often use the deflection angle for infinite distances from sources and detectors.The deflection in both the and directions is computed as a power series of M/r_(0) and r_(0)/rsd,where M,rs.d are the spacetime mass and source and detector radi,respectively,and r_(0) is the minimal radial coordinate of the trajectory.The coefficients of these series are simple trigonometric functions of Ge,the extreme value of the coordinate of the trajectory.A set of exact gravitational lensing equations is used to solve for ro and Ge for given deviation angles so and Sp of the source,and two lensed images are always obtained.The apparent angles and their magnifications of these images and the time delays between them are solved.Additionally,their dependences on various parameters,particularly spacetime spin a,are analyzed in depth.We find that generally two critical spacetime spin values exist that separate the case of test particles reaching the detector from different sides of the z axis from the cases in which the images appear from the same side in the celestial plane.Three potential applications of these results are discussed.展开更多
In recent years,potassium tantalum niobate(KTN)electro-optical deflection devices have gained considerable attention because of their notable advantages,such as large deflection angles,low operational voltage requirem...In recent years,potassium tantalum niobate(KTN)electro-optical deflection devices have gained considerable attention because of their notable advantages,such as large deflection angles,low operational voltage requirements,and compact dimensions.This study uses the phase-shifted interferometric optical path to characterize the influence of direct current(DC)voltage on charge density.An interferogram is acquired using the four-step phase-shifting technique,enabling the calculation of phase delays and deducing the variation in charge density.Experimental results demonstrate that the charge density near the cathode increases with an increase in DC voltage.Subsequently,we utilize the frequency dependence of the dielectric constant of the KTN crystal on the electricfield.The dielectric constant can be enhanced when the characteristic frequency of the motion of the polar nanoscale region matches the frequency of the electricfield.Thisfield-induced enhancement effect improves the beam deflection performance of the KTN crystal.Application requirements in thefield of high-speed random scanning can be realized through the mechanism of the KTN crystal co-acting with DC and alternating current electricfields.展开更多
From an astrophysical perspective,the composition of black holes(BHs),dark matter(DM),and dark energy can be an intriguing physical system.In this study,we consider Schwarzschild BHs embedded in a Dehnentype DM halo w...From an astrophysical perspective,the composition of black holes(BHs),dark matter(DM),and dark energy can be an intriguing physical system.In this study,we consider Schwarzschild BHs embedded in a Dehnentype DM halo with a quintessential field.This study examines the horizons,shadows,deflection angle,and quasinormal modes(QNMs)of the effective BH spacetime and how they are affected by the dark sector.The Schwarzschild BH embodied in a Dehnen-type DM halo with a quintessential field possesses two horizons:the event and cosmological horizons.We demonstrate that all dark sector parameters increase the event horizon while decreasing the cosmological horizon.We analyze the BH shadow and emphasize the impact of DM and quintessence parameters on the shadow.We show that the dark sector casts larger shadows than a Schwarzschild BH in a vacuum.Further,we delve into the weak gravitational lensing deflection angle using the Gauss-Bonnet theorem(GBT).We then investigate the system's QNMs using the 6th order WKB approach.To visually demonstrate the dark sector parameters,we present figures that illustrate the impact of varying the parameters of the Dehnen-type DM halo as well as the quintessence background.Our findings show that the gravitational waves emitted by BHs with a dark sector have a lower frequency and decay rate compared to those emitted by BHs in a vacuum.展开更多
In this work, we develop a general perturbative procedure to determine the off-equatorial plane deflections in the weak deflection limit in general stationary and axisymmetric spacetimes, enabling the existence of the...In this work, we develop a general perturbative procedure to determine the off-equatorial plane deflections in the weak deflection limit in general stationary and axisymmetric spacetimes, enabling the existence of the generalized Carter constant. Deflections of both null and timelike rays, with the finite distance effect of the source and detector considered, are obtained as dual series of M/r_(0) and r_(0)/r_(s,d.) These deflections enable a set of exact gravitational lensing equations from which the apparent angular positions of the images are solved. The method and general results are then applied to the Kerr-Newmann, Kerr-Sen, and rotating Simpson-Visser spacetimes to study the effect of the spin and characteristic(effective) charge of the spacetimes and the source altitude on the deflection angles and image apparent angles. We find that, generally, both the spacetime spin and charge affect only the deflections from the second non-trivial order, whereas the source altitude influences the deflection from the leading order.Because of this, measuring the effects of the spacetime spin and charge from the apparent locations of the images in gravitational lensing in realistic scenarios is difficult. We also present the off-equatorial deflections in the rotating Bardeen, Hayward, Ghosh, and Tinchev black hole spacetimes.展开更多
Dark energy is typically the principal component needed for the traversability of wormholes(WH),as it provides the negative gravity effect required to keep the throat open.However,can this be achieved without dark ene...Dark energy is typically the principal component needed for the traversability of wormholes(WH),as it provides the negative gravity effect required to keep the throat open.However,can this be achieved without dark energy?It turns out that if we couple the trace of energy-momentum with the standard Einstein-Hilbert Lagrangian and utilize a specific equation of state(EoS),dark energy may be obviated.The Casimir stress energy is known to result in the violation of the null energy condition(NEC)on the energy momentum tensor.This phenomenon makes such an EoS an ideal candidate for generating traversable WH geometries.The laboratory proven phenomenon provides a natural mechanism to sustain an open WH throat without relying on dark energy.Therefore,we generate two classes of WH solutions using this in energy-momentum trace-coupling gravity.For the specific choice of the Casimir EoS relating the energy-momentum tensor components[Kar and Sahdev:Phys.Rev.D 52,2030(1995)]and different choices of redshift functions,we determine the WH geometry completely.The obtained WH solutions violate the NECs,and all qualitative constraints demanded for physically realizable WHs are satisfied.This is demonstrated via graphical plots for a suitably chosen range of coupling parameter values.Furthermore,our study investigates the repulsive effect of gravity,revealing that its presence leads to a negative deflection angle for photons traveling along null geodesics.Notably,we observe a consistent pattern of negative values for the deflection angle across all values of r_(0) in the three scenarios considered,thus indicating the clear manifestation of the repulsive gravity effect.All of this is possible without invoking the existence of dark energy.展开更多
In this study, we investigate the properties of black holes within the framework of multi-fractional theories of gravity, focusing on the effects of q-derivatives and weighted derivatives. These modifications, which i...In this study, we investigate the properties of black holes within the framework of multi-fractional theories of gravity, focusing on the effects of q-derivatives and weighted derivatives. These modifications, which introduce scale-dependent spacetime geometries, alter black hole solutions in intriguing ways. Within these frameworks,we analyze two key observable phenomena-black hole shadows and particle deflection angle in the weak field limit-using both analytical techniques and observational data from the Event Horizon Telescope(EHT) for M87^(*) and Sgr A^(*). The study using the q-derivative formalism reveals that the multi-scale length l_(*)influences the size of the black hole shadow in two ways and modifies the weak deflection angle. Constraints on l_(*)are derived from the EHT observations, showing significant deviations from standard Schwarzschild black hole predictions, which range from 10^(9) to 10^(10)orders of magnitude. Additionally, the weak deflection angle is computed using the non-asymptotic generalization of the Gauss-Bonnet theorem(GBT) to reveal the effects of finite-distance and multi-scale parameters.Using the Sun in the Solar System test, we observe that the constraints for l_(*)range from 10^(8) to 10^(9) orders of magnitude. Results from the weighted derivative formalism generate a dS/AdS-like behavior, where smaller deviations are found in the strong field regime than in the weak field regime. The results suggest that, while these effects are subtle, they provide a potential observational signature of quantum gravity effects. The findings presented here contribute to the broader effort of testing alternative theories of gravity through black hole observations, offering a new perspective on the quantum structure of spacetime at cosmological and astrophysical scales.展开更多
In this study,the gravitational deflection angle of photons in the weak field limit(or the weak deflection angle)and shadow cast by the electrically charged and spherically symmetric static Kiselev black hole(BH)in th...In this study,the gravitational deflection angle of photons in the weak field limit(or the weak deflection angle)and shadow cast by the electrically charged and spherically symmetric static Kiselev black hole(BH)in the string cloud background are investigated.The influences of the BH charge Q,quintessence parameterγ,and string cloud parameter a on the weak deflection angle are studied using the Gauss-Bonnet theorem.in addition to studying the influences on the radius of photon spheres and size of the BH shadow in the spacetime geometry of the chargedKiselev BH in string clouds.Moreover,we study the effects of plasma(uniform and non-uniform)on the weak deflection angle and shadow cast by the charged-Kiselev BH surrounded by the clouds of strings.In the presence of a uniform/nonuniform plasma medium,an increase in the string cloud parameter a increases the deflection angleα.In contrast,a decrease in the BH charge Q decreases the deflection angle.Further,we observe that an increase in the BH charge Q causes a decrease in the size of the shadow of the BH.We notice that,with an increase in the values of the parametersγand a,the size of the BH shadow increases,and therefore,the intensity of the gravitational field around the charged-Kiselev BH in string clouds increases.Thus,the gravitational field of the charged-Kiselev BH in the string cloud background is stronger than the field produced by the pure Reissner-Nordstrom BH.Moreover,we use the data released by the Event Horizon Telescope(EHT)collaboration,for the supermassive BHs M87*and Sgr A*,to obtain constraints on the values of the parametersγand a.展开更多
In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present ...In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present the modifications in the shadow radius of the RGI BH.To this end,we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media.Importantly,owing to the plasma media,we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified.This,in turn,changes and modifies the expression for the intensity observed far away from the BH.Finally,we obtain the shadow images for the RGI BH for different plasma models.Although quantum effects change the background geometry,such effects are minimal,and practically detecting these effects using the current technology based on supermassive BH shadows is impossible.The parameterΩencodes the quantum effects,and in principle,one expects such quantum effects to play significant roles only for very small BHs.However,the effects of plasma media can play an important role in the optical appearance of BHs,as they affect and modify the equations of motion.展开更多
文摘This article considers a static and spherical black hole(BH)in f(Q)gravity.f(Q)gravity is the extension of symmetric teleparallel general relativity,where both curvature and torsion are vanishing and gravity is described by nonmetricity.In this study,we investigate the possible implications of quasinormal mode(QNM)modified Hawking spectra and deflection angles generated by the model.The Wentzel–Kramers–Brillouin method is used to solve the equations of motion for massless Dirac perturbation fields and explore the impact of the nonmetricity parameter(Q_(0)).Based on the QNM computation,we can ensure that the BH is stable against massless Dirac perturbations and as Q_(0)increases the oscillatory frequency of the mode decreases.We then discuss the weak deflection angle in the weak field limit approximation.We compute the deflection angle up to the fourth order of approximation and show how the nonmetricity parameter affects it.We find that the Q_(0)parameter reduces the deflection angle.
基金supported by the National Natural Science Foundation of China (Grant No.12065012)Yunnan Fundamental Research Projects (202301AS070029)Yunnan High-Level Talent Training Support Plan Young&Elite Talents Project (Grant No.YNWR-QNBJ-2018-360)。
文摘In this study,we examined the thermal fluctuations,deflection angle,and greybody factor of a high-dimensional Schwarzschild black hole in scalar-tensor-vector gravity(STVG).We calculated some thermodynamic quantities related to the correction of the black hole entropy caused by thermal fluctuations and discussed the effect of the correction parameters on these quantities.By analyzing the changes in the corrected specific heat,we found that thermal fluctuations made the small black hole more stable.It is worth noting that the STVG parameter did not affect the thermodynamic stability of this black hole.Additionally,by utilizing the Gauss-Bonnet theorem,the deflection angle was obtained in the weak field limit,and the effects of the two parameters on the results were visualized.Finally,we calculated the bounds on the greybody factor of a massless scalar field.We observed that as the STVG parameter around the black hole increased,the weak deflection angle became larger,and more scalar particles can reach infinity.However,the spacetime dimension has the opposite effect on the STVG parameter on the weak deflection angle and greybody factor.
基金supported by the National Natural Science Foundation of China(Grant No:51579162,51879174 and 51379137)the Open Funds of the State Key Laboratory of Hydraulics and Mountain River Engineering,Sichuan University(SKHL1301,SKHL1509)
文摘The deflection angle of a river bend plays an important role on behaviours of the flow within it, and a clear understanding of the angle's influence is significant in both theoretical study and engineering application. This paper presents a systematic numerical investigation on effects of deflection angles(30°, 60°, 90°, 120°, 150°, and 180°) on flow phenomena and their evolution in open-channel bends using a Re-Normalization Group(RNG) κ-ε model and a volume of fluid(VOF) method. The numerical results indicate that the deflection angle is a key factor for flows in bends. It is shown that the maximum transverse slope of water surface occurs at the middle cross section of a bend, and it increases with the deflection angle. Besides a major vortex, or, the primary circulation cell near the channel bottom, a secondary vortex, or, an outer bank cell, may also appear above the former and near the outer bank when the deflection angle is sufficiently large, and it will gradually migrate towards the inner bank and evolve into an inner bank cell. The strength of the secondary circulations increases with the deflection angle. The simulation demonstrates that there is alow-stress zone on the bed near the outer bank and a high-stress zone on the bed near the inner bank, and both of them increase in size with the deflection angle. The maximum of shear stress on the inner bank increases nonlinearly with the angle, and its maximums on the outer bank and on the bed take place when the deflection angle becomes 120°.
基金supported by the Aeronautical Science Foundation of China [grant numbers 20175748009]。
文摘With the wide application of laser in the field of skin plastic surgery, micro laser galvanometer scanner has made great progress in this field with its portability. However, the measurement method used to measure the deflection angle of laser galvanometer in the narrow space of scanner with high precision remains to be studied. In this paper, an angle measurement method based on magnetic field is proposed, and the effect of the shapes of permanent magnets(PMs) on the measurement is studied by theoretical and experimental study under the condition that the maximum available space for the PMs is a 10 mm side cube. An angle measuring experimental device is set up, and the contrast experiment is carried out with different PMs which are the same as simulation. The experimental results show that cylindrical PM is more suitable than other PMs, which is consistent with the simulation results, and the maximum nonlinearity error is 0.562%. This method has the advantages of small volume,non-contact measurement, small moment of inertia, good dynamic response and no external excitation for the PMs, so it has a broad application prospect in micro laser galvanometer scanner.
文摘Loop Heat Pipe(LHP)is an efficient two-phase heat transfer device,which can be used in waste heat recovery,electronics cooling,aerospace and other fields.The wick,the core component of LHP,plays an important role in its start-up and operation.In this paper,the wick fabricated by 3D printing technology had uniform and interconnected pores.In the experiment,the position of the parallel vapor removal grooves was always fixed towards the vapor outlet.When the cylindrical wick was placed in the evaporator,the rotation angle relative to its central axis could be changed,thus changing the number and shape of the pores facing the vapor removal grooves.The wick deflection angle represented its change in spatial position relative to the fixed vapor removal grooves.The effect of the wick deflection angles on the heat transfer characteristics of the flat LHP was experimentally investigated.It was found that with the change of deflection angle,the number of pores in the evaporation-oriented zone would also change,which had a significant impact on the start-up process and heat transfer performance of LHP.When the deflection angle was 30°,LHP could start fastest at a low heat load of 20 W and operate stable at a high heat load of 180 W.
基金Supported by the Short-Term Research Grant Awarded of University of Malaya
文摘Previously, the gravitational lens of a wormhole was introduced by various researchers. Their treatment was focused basically on the lens signature that describes wormhole geometrical character such as the differences from a black hole or between any various types of wormhole models. The braneworld scenario provides the idea of spacetime with underlying extra-dimensions. The inclusion of extra-dimensional terms in the lens object spacetime line element will result in some variation in the expression for its gravitational lens deflection angle. Thus in this paper we investigate such variation by deriving this deflection angle expression. As such, this paper not only shows the existence of such variation but also suggests the potential utilization of gravitational lensing to prove the existence of extra dimensions by studying the deflection angle characteristic in accordance with the spacetime expansion rate of the universe.
基金funded by the National Natural Science Foundation of China 11975145。
文摘We investigate the light deflection in the weak field approximation from the accelerating charged AdS black hole.For this purpose,we apply the Gauss–Bonnet theorem to calculate the light deflection in the weak field area and use the Gibbons–Werner approach to analyze the optical geometry of the accelerating charged AdS black hole in the non-magnetic plasma absence/presence of a non-magnetic medium.We also represent the graphical behavior of the light deflection angle w.r.t.the impact parameter.We also compute the light deflection angle using Keeton and Petters approximations under the impact of accelerating charged AdS black hole geometry.Furthermore,by using the ray-tracing approach,we determine the shadow in the nonmagnetic plasma presence and also demonstrate that graphical shadow has an impact on the gauge potential,non-magnetic plasma frequencies and charge.
文摘The description and function characterization of a flange-on type low energy electron mi- croscope are given. In this microscope a magnetic beam separator with 10° deflection angle is used in order to facilitate compacting the instrument on a single 10 in. flange. Mean- while some correcting elements in the electron optical system are simplified to reduce the complexities of construction and operation. The sample is set close to ground potential, so that all the electrostatic lenses are easily to float at high voltages. The performance of the microscope in typical low energy electron microscopy, low energy electron diffraction and photoemission electron microscopy modes is demonstrated through several experiments. A lateral resolution of 51 nm is estimated for low energy electron microscopy imaging. With femtosecond laser as light source, the consequent nonlinear photoemission makes this micro-scope also suitable for the observation of optical near field phenomena and a lateral resolution of 110 nm is obtained.
文摘To control the deflection of the gas plasma jet, a new analytical method is proposed based on the Magnetohydrodynamic(MHD) technique. Based on the typical MHD power generation model, the applied voltage is applied to the staggered electrodes, that is, a pair of electrodes on the same side wall are connected to generate an axial current in the channel. Under the action of the magnetic field perpendicular to the direction of the flow, the plasma is subjected to electromagnetic forces perpendicular to these two directions, and the jet is deflected. The computational model including the Navier-Stokes equations coupled with electromagnetic source terms, the electric potential equation and Ohm’s law is solved. The deflection of the gas jet under the action of an electromagnetic field is observed, and the maximum deflection angle is about 14.8°. The influences of the electric field, magnetic field, and conductivity on the jet deflection are studied. Results show that although the influences of these three factors on the deflection are similar, and the effect of increasing the electric field strength is slightly greater, priority should be given to increasing the magnetic field strength from the perspective of reducing energy consumption. The Stuart number is introduced to assess the ability of electromagnetic force to control jet deflection. When the electromagnetic parameters are constant, this solution provides better control of low-density and low-speed fluid flows. The calculation results show that using the staggered electrode method configuration is feasible in terms of controlling the deflection of a plasma jet deflection.
基金part of a research project supported by Korea Ministry of LandTransportation Maritime Affairs (MLTM) through Core Research Project 1 of Super Long Span Bridge R&D Centersupported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education,Science and Technology (2012R1A1A2007054)
文摘The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress-strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.
基金Supported by the National Natural Science Foundation of China(11975145)。
文摘In this study,we analyze the models of the deflection angle of a new Schwarzschild-like black hole(BH)and employ the optical metric of the BH.To achieve this,we use the Gaussian curvature of the optical metric and the Gauss-Bonnet theorem,known as the Gibbons-Werner technique,to determine the deflection angle.Furthermore,we examine the deflection angle in the presence of a plasma medium and the effect of the plasma medium on the deflection angle.The deflection angle of the BH solution in the gauged super-gravity is computed using the Keeton-Petters approach.Utilizing the ray-tracing technique,we investigate the shadow of the corresponding BH and analyze the plots of the deflection angle and shadow to verify the influence of the plasma and algebraic thermodynamic parameters on the deflection angle and shadow.
基金supported by the National Key Project of Scientific and Technical Supporting Programs Funded by Ministry of Science &Technology of China ( Grant No: 2006BAJ13B03)the RGCCERG Grant #CityU1253/04E from Hong Kong Re-search Grant Council, HKSAR
文摘After comparing the mechanism of tilted plume under stack effect with that of spill plume,the tilted plume model induced by stack effect in a vertical shaft is developed simply based on the theoretical results and a series of full-scale tests. It is shown that the two sides of plume are symmetrical and have an accordant regulation that the plume radius has a linear relation to the height z. The profile of fire plume under stack effect is similar to the windblown flame in wind tunnel,and the range of flame deflection angle is about from 50 to 60 degree.
基金Partially Supported by the Wuhan University Students Innovation and Entrepreneurship Program。
文摘This paper investigates off-equatorial plane deflections and gravitational lensing of both null signals and massive particles in Kerr spacetime in the weak deflection limit,considering the finite distance effect of the source and detector.This is the effect caused by both the source and detector being located at finite distances from the lens although many researchers often use the deflection angle for infinite distances from sources and detectors.The deflection in both the and directions is computed as a power series of M/r_(0) and r_(0)/rsd,where M,rs.d are the spacetime mass and source and detector radi,respectively,and r_(0) is the minimal radial coordinate of the trajectory.The coefficients of these series are simple trigonometric functions of Ge,the extreme value of the coordinate of the trajectory.A set of exact gravitational lensing equations is used to solve for ro and Ge for given deviation angles so and Sp of the source,and two lensed images are always obtained.The apparent angles and their magnifications of these images and the time delays between them are solved.Additionally,their dependences on various parameters,particularly spacetime spin a,are analyzed in depth.We find that generally two critical spacetime spin values exist that separate the case of test particles reaching the detector from different sides of the z axis from the cases in which the images appear from the same side in the celestial plane.Three potential applications of these results are discussed.
基金the National Natural Science Foundation of China(Grant No.62005320,52072189)the Key Research Development Plan of Shandong Province(Grant No.2018YFJH0402)and studio for the Leader of Scientific Research in Jinan(Grant No.2021GXRC089).
文摘In recent years,potassium tantalum niobate(KTN)electro-optical deflection devices have gained considerable attention because of their notable advantages,such as large deflection angles,low operational voltage requirements,and compact dimensions.This study uses the phase-shifted interferometric optical path to characterize the influence of direct current(DC)voltage on charge density.An interferogram is acquired using the four-step phase-shifting technique,enabling the calculation of phase delays and deducing the variation in charge density.Experimental results demonstrate that the charge density near the cathode increases with an increase in DC voltage.Subsequently,we utilize the frequency dependence of the dielectric constant of the KTN crystal on the electricfield.The dielectric constant can be enhanced when the characteristic frequency of the motion of the polar nanoscale region matches the frequency of the electricfield.Thisfield-induced enhancement effect improves the beam deflection performance of the KTN crystal.Application requirements in thefield of high-speed random scanning can be realized through the mechanism of the KTN crystal co-acting with DC and alternating current electricfields.
基金Supported by the National Science Foundation of China(W2433018)。
文摘From an astrophysical perspective,the composition of black holes(BHs),dark matter(DM),and dark energy can be an intriguing physical system.In this study,we consider Schwarzschild BHs embedded in a Dehnentype DM halo with a quintessential field.This study examines the horizons,shadows,deflection angle,and quasinormal modes(QNMs)of the effective BH spacetime and how they are affected by the dark sector.The Schwarzschild BH embodied in a Dehnen-type DM halo with a quintessential field possesses two horizons:the event and cosmological horizons.We demonstrate that all dark sector parameters increase the event horizon while decreasing the cosmological horizon.We analyze the BH shadow and emphasize the impact of DM and quintessence parameters on the shadow.We show that the dark sector casts larger shadows than a Schwarzschild BH in a vacuum.Further,we delve into the weak gravitational lensing deflection angle using the Gauss-Bonnet theorem(GBT).We then investigate the system's QNMs using the 6th order WKB approach.To visually demonstrate the dark sector parameters,we present figures that illustrate the impact of varying the parameters of the Dehnen-type DM halo as well as the quintessence background.Our findings show that the gravitational waves emitted by BHs with a dark sector have a lower frequency and decay rate compared to those emitted by BHs in a vacuum.
基金Supported by the National Natural Science Foundation of China。
文摘In this work, we develop a general perturbative procedure to determine the off-equatorial plane deflections in the weak deflection limit in general stationary and axisymmetric spacetimes, enabling the existence of the generalized Carter constant. Deflections of both null and timelike rays, with the finite distance effect of the source and detector considered, are obtained as dual series of M/r_(0) and r_(0)/r_(s,d.) These deflections enable a set of exact gravitational lensing equations from which the apparent angular positions of the images are solved. The method and general results are then applied to the Kerr-Newmann, Kerr-Sen, and rotating Simpson-Visser spacetimes to study the effect of the spin and characteristic(effective) charge of the spacetimes and the source altitude on the deflection angles and image apparent angles. We find that, generally, both the spacetime spin and charge affect only the deflections from the second non-trivial order, whereas the source altitude influences the deflection from the leading order.Because of this, measuring the effects of the spacetime spin and charge from the apparent locations of the images in gravitational lensing in realistic scenarios is difficult. We also present the off-equatorial deflections in the rotating Bardeen, Hayward, Ghosh, and Tinchev black hole spacetimes.
基金Sudan Hansraj is grateful to the National Research Foundation of South Africa for support through Grant 138012the National Research Foundation of South Africa for the award of a postdoctoral fellowship。
文摘Dark energy is typically the principal component needed for the traversability of wormholes(WH),as it provides the negative gravity effect required to keep the throat open.However,can this be achieved without dark energy?It turns out that if we couple the trace of energy-momentum with the standard Einstein-Hilbert Lagrangian and utilize a specific equation of state(EoS),dark energy may be obviated.The Casimir stress energy is known to result in the violation of the null energy condition(NEC)on the energy momentum tensor.This phenomenon makes such an EoS an ideal candidate for generating traversable WH geometries.The laboratory proven phenomenon provides a natural mechanism to sustain an open WH throat without relying on dark energy.Therefore,we generate two classes of WH solutions using this in energy-momentum trace-coupling gravity.For the specific choice of the Casimir EoS relating the energy-momentum tensor components[Kar and Sahdev:Phys.Rev.D 52,2030(1995)]and different choices of redshift functions,we determine the WH geometry completely.The obtained WH solutions violate the NECs,and all qualitative constraints demanded for physically realizable WHs are satisfied.This is demonstrated via graphical plots for a suitably chosen range of coupling parameter values.Furthermore,our study investigates the repulsive effect of gravity,revealing that its presence leads to a negative deflection angle for photons traveling along null geodesics.Notably,we observe a consistent pattern of negative values for the deflection angle across all values of r_(0) in the three scenarios considered,thus indicating the clear manifestation of the repulsive gravity effect.All of this is possible without invoking the existence of dark energy.
文摘In this study, we investigate the properties of black holes within the framework of multi-fractional theories of gravity, focusing on the effects of q-derivatives and weighted derivatives. These modifications, which introduce scale-dependent spacetime geometries, alter black hole solutions in intriguing ways. Within these frameworks,we analyze two key observable phenomena-black hole shadows and particle deflection angle in the weak field limit-using both analytical techniques and observational data from the Event Horizon Telescope(EHT) for M87^(*) and Sgr A^(*). The study using the q-derivative formalism reveals that the multi-scale length l_(*)influences the size of the black hole shadow in two ways and modifies the weak deflection angle. Constraints on l_(*)are derived from the EHT observations, showing significant deviations from standard Schwarzschild black hole predictions, which range from 10^(9) to 10^(10)orders of magnitude. Additionally, the weak deflection angle is computed using the non-asymptotic generalization of the Gauss-Bonnet theorem(GBT) to reveal the effects of finite-distance and multi-scale parameters.Using the Sun in the Solar System test, we observe that the constraints for l_(*)range from 10^(8) to 10^(9) orders of magnitude. Results from the weighted derivative formalism generate a dS/AdS-like behavior, where smaller deviations are found in the strong field regime than in the weak field regime. The results suggest that, while these effects are subtle, they provide a potential observational signature of quantum gravity effects. The findings presented here contribute to the broader effort of testing alternative theories of gravity through black hole observations, offering a new perspective on the quantum structure of spacetime at cosmological and astrophysical scales.
基金Partly supported by the Uzbekistan Ministry for Innovative Development(FZ-20200929344 and F-FA-2021-510)supported by Postdoctoral Fellowship of Zhejiang Normal University(ZC304022919)。
文摘In this study,the gravitational deflection angle of photons in the weak field limit(or the weak deflection angle)and shadow cast by the electrically charged and spherically symmetric static Kiselev black hole(BH)in the string cloud background are investigated.The influences of the BH charge Q,quintessence parameterγ,and string cloud parameter a on the weak deflection angle are studied using the Gauss-Bonnet theorem.in addition to studying the influences on the radius of photon spheres and size of the BH shadow in the spacetime geometry of the chargedKiselev BH in string clouds.Moreover,we study the effects of plasma(uniform and non-uniform)on the weak deflection angle and shadow cast by the charged-Kiselev BH surrounded by the clouds of strings.In the presence of a uniform/nonuniform plasma medium,an increase in the string cloud parameter a increases the deflection angleα.In contrast,a decrease in the BH charge Q decreases the deflection angle.Further,we observe that an increase in the BH charge Q causes a decrease in the size of the shadow of the BH.We notice that,with an increase in the values of the parametersγand a,the size of the BH shadow increases,and therefore,the intensity of the gravitational field around the charged-Kiselev BH in string clouds increases.Thus,the gravitational field of the charged-Kiselev BH in the string cloud background is stronger than the field produced by the pure Reissner-Nordstrom BH.Moreover,we use the data released by the Event Horizon Telescope(EHT)collaboration,for the supermassive BHs M87*and Sgr A*,to obtain constraints on the values of the parametersγand a.
基金supported by the following grants of the Uzbekistan Ministry for Innovative Development:Research Grant(FZ-20200929344 and F-FA-2021-510)。
文摘In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present the modifications in the shadow radius of the RGI BH.To this end,we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media.Importantly,owing to the plasma media,we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified.This,in turn,changes and modifies the expression for the intensity observed far away from the BH.Finally,we obtain the shadow images for the RGI BH for different plasma models.Although quantum effects change the background geometry,such effects are minimal,and practically detecting these effects using the current technology based on supermassive BH shadows is impossible.The parameterΩencodes the quantum effects,and in principle,one expects such quantum effects to play significant roles only for very small BHs.However,the effects of plasma media can play an important role in the optical appearance of BHs,as they affect and modify the equations of motion.
