1,361,683 research outputs found
Strong gravitational lensing by Kiselev black hole
No full textWe investigate the gravitational lensing scenario due to Schwarzschild-like black hole surrounded by quintessence (Kiselev black hole). We work for the special case of Kiselev black hole where we take the state parameter
w
q
=
−
2
3
. For the detailed derivation and analysis of the bending angle involved in the deflection of light, we discuss three special cases of Kiselev black hole: nonextreme, extreme, and naked singularity. We also calculate the approximate bending angle and compare it with the exact bending angle. We found the relation of bending angles in the decreasing order as: naked singularity, extreme Kiselev black hole, nonextreme Kiselev black hole, and Schwarzschild black hole. In the weak field approximation, we compute the position and total magnification of relativistic images as well
Reduced Kiselev black hole
No full textThe Kiselev model describes a black hole surrounded by a fluid with equations of state and respectively in radial and tangential directions. It has been extensively studied in the parameter region , then a new horizon of black hole type will emerge. This case has been mentioned in Kiselev’s pioneer work but seldom investigated in the literature. Referring to it as reduced Kiselev black hole, we revisit this case with attention to its causal structure, thermodynamics, shadow cast and weak-field limit. An alternative interpretation and extensions of the black hole are also discussed
Andrey Kiselev: the life and the legend
No full textThis article is devoted to Andrey Kiselev, probably the most well-known Russian author of mathematics textbooks. His books remained in schools for nearly one hundred years, and his name became legendary, symbolizing the “good old days” when all was supposedly well with mathematics education. Meanwhile, even in Russia, let alone abroad, many aspects of Kiselev’s life are little known. Their study facilitates a better understanding of the complicated nature of the development of Russian and Soviet mathematics education, including the connection between them and seemingly distant social-political issues. The present article undertakes such a study. The author draws on his Russian publications, materials from Russian archives, and other primary sources
Improving the novikov and kiselev user authentication scheme
No full textNovikov and Kiselev [7] proposed an authentication method of a user from a remote autonomous object. Recently, Yang et al. [12] and Awasthi [1] have pointed out that the Novikov-Kiselev scheme is insecure against the man-in-the-middle attack. In this article, we propose an improved version of the Novikov-Kiselev scheme to overcome such vulnerability
Accretion onto a charged Kiselev black hole
No full text Accretion of matter onto a compact is one of the interesting astrophysical processes. Here, we study the accretion of matter onto a charged Kiselev black hole. The problem of static and spherically symmetric accretion of a polytropic fluid is explored for the analytic solution of equations of motion. We have investigated the necessary conditions for existence of the critical flow points and the mass accretion rate. Finally, we discuss the polytropic gas accretion in detail. It has been found that in the accretion process the quintessence and charge parameters play a dominant role. </jats:p
Reduced Kiselev black hole
No full textThe Kiselev model describes a black hole surrounded by a fluid with equations
of state and respectively in radial and
tangential directions. It has been extensively studied in the parameter region
. If one rids off the black hole and turns to the region ,
i.e. , then a new horizon of black hole type will emerge. This case has
been mentioned in Kiselev's pioneer work but seldom investigated in the
literature. Referring to it as reduced Kiselev black hole, we revisit this case
with attention to its causal structure, thermodynamics, shadow cast and
weak-field limit. An alternative interpretation and extensions of the black
hole are also discussed.Comment: 8 pages, 5 figures, references adde
Microscopia de força piezoeléctrica de relaxors ferroeléctricos
No full textDoutoramento em Ciência e Engenharia de MateriaisNesta tese, ferroeléctricos relaxor (I dont know uf the order is correct) de base
Pb das familias (Pb,La)(Zr,Ti)O3 (PLZT), Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT),
Pb(Zn1/3,Nb2/3)O3-PbTiO3 (PZN-PT) foram investigados e analisados. As
propriedades ferroeléctricas e dieléctricas das amostras foram estudadas por
métodos convencionais de macro e localmente por microscopia de força
piezoeléctrica (PFM).
Nos cerâmicos PLZT 9.75/65/35 o contraste da PFM à escala nanometrica _
foi investigado em função do tamanho e orientação dos grãos. Apurou-se que
a intensidade do sinal piezoeléctrico das nanoestruturas diminui com o
aumento da temperatura e desaparece a 490 K (La mol. 8%) e 420 K (9,5%).
Os ciclos de histerese locais foram obtidos em função da temperatura. A
evolução dos parâmetros macroscópicos e locais com a temperatura de
superfície sugere um forte efeito de superfície nas transições de fase
ferroeléctricas do material investigado. A rugosidade da parede de domínio é
determinada por PFM para a estrutura de domínio natural existente neste
ferroeléctrico policristalino. Além disso, os domínios ferroeléctricos artificiais
foram criados pela aplicação de pulsos eléctricos à ponta do condutor PFM e o
tamanho de domínio in-plane foi medido em função da duração do pulso.
Todas estas experiências levaram à conclusão de que a parede de domínio
em relaxors do tipo PZT é quase uma interface unidimensional. O mecanismo
de contraste na superfície de relaxors do tipo PLZT é medido por PFMAs estruturas de domínio versus evolução da profundidade foram estudadas
em cristais PZN-4,5%PT, com diferentes orientações através da PFM. Padrões
de domínio irregulares com tamanhos típicos de 20-100 nm foram observados
nas superfícies com orientação das amostras unpoled?. Pelo contrário,
os cortes de cristal exibem domínios regulares de tamanho mícron
normal, com os limites do domínio orientados ao longo dos planos
cristalográficos permitidos. A existência de nanodomínios em cristais com
orientação está provisoriamente (wrong Word) atribuída à natureza
relaxor de PZN-PT, onde pequenos grupos polares podem formar-se em
coindições de zero-field-cooling (ZFC). Estes nanodomínios são considerados
como os núcleos do estado de polarização oposta e podem ser responsáveis
pelo menor campo coercitivo para este corte de cristal em particular. No
entanto, a histerese local piezoelétrica realizada pelo PFM à escala
nanométrica indica uma mudança de comportamento de PZN-PT semelhante
para ambas as orientações cristalográficas investigadas. A evolução das
estruturas de domínio com polimento abaixo da superfície do cristal foi
investigada. O domínio de ramificações e os efeitos de polarização de triagem
após o polimento e as medições de temperatura têm sido estudados pela PFM
e pela análise SEM. Além disso, verificou-se que a intensidade do sinal
piezoeléctrico a partir das estruturas de nanodomínio diminui com o aumento
da temperatura, acabando por desaparecer aos 430 K (orientaçáo ) e
470 K (orientação ). Esta diferença de temperatura nas transições de
fase local em cristais de diferentes orientações é explicada pelo forte efeito de
superfície na transição da fase ferroelétrica em relaxors.A comutação da polarização em relaxor ergódico e nas fases ferroeléctricas do
sistema PMN-PT foram realizadas pela combinação de três métodos,
Microscopia de Força Piezoeléctrica, medição de um único ponto de
relaxamento eletromecânico e por ultimo mapeamento de espectroscopia de
tensão. A dependência do comportamento do relaxamento na amplitude e
tempo da tensão de pulso foi encontrada para seguir um comportamento
logarítmico universal com uma inclinação quase constante. Este
comportamento é indicativo da progressiva população dos estados de
relaxamento lento, ao contrário de uma relaxação linear na presença de uma
ampla distribuição do tempo de relaxamento. O papel do comportamento de
relaxamento, da não-linearidade ferroeléctrica e da heterogeneidade espacial
do campo na ponta da sonda de AFM sobre o comportamento do ciclo de
histerese é analisada em detalhe. Os ciclos de histerese para ergódica PMN-
10%PT são mostrados como cineticamente limitados, enquanto que no PMN,
com maior teor de PT, são observados verdadeiros ciclos de histerese
ferroeléctrica com viés de baixa nucleação.In this thesis, Pb-based relaxor ferroelectrics of the (Pb,La)(Zr,Ti)O3 (PLZT),
Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT), Pb(Zn1/3,Nb2/3)O3-PbTiO3 (PZN-PT)
families were investigated and analyzed. Ferroelectric and dielectric properties
of the samples were studied by conventional macroscopic methods and locally
by piezoresponse force microscopy (PFM).
In PLZT 9.75/65/35 ceramics the nanoscale PFM contrast was investigated as
a function of grain size and grain orientation. It was found that the intensity of
piezoresponse signal from nanodomain structure decreases with temperature
and it disappears at 490 K (La mol. 8%) and 420 K (9.5%). Local hysteresis
loops were obtained as a function of temperature. The evolution of the
macroscopic and local parameters with temperature suggests strong surface
effect on ferroelectric phase transition in the investigated materials. The domain
wall roughness is determined with PFM for the natural domain structure
existing in this polycrystalline ferroelectric. Besides, artificial ferroelectric
domains were created by application of voltage pulses to the conducting PFM
tip, and the in-plane domain size was measured as a function of pulse duration.
All these experiments result in the conclusion that the domain wall in PZT-type
relaxors is quasi one-dimensional interface. The mechanism of the surface
contrast in PLZT-type relaxors is uncovered by PFM.
Domain structures vs. depth evolution was studied in PZN-4.5%PT crystals
with different orientation via PFM. Irregular domain patterns with the typical
sizes 20-100 nm were observed on the (001)-oriented surfaces of unpoled
samples. On the contrary, (111) crystal cuts exhibit normal micron-size regular
domains with the domain boundaries directed along allowed crystallographic
planes. The existence of nanodomains in (001)-oriented crystals is tentatively
attributed to the relaxor nature of PZN-PT where small polar clusters may form
under zero-field-cooling (ZFC) conditions. These nanodomains are considered
as the nuclei of the opposite polarization state and can be responsible for the
smaller coercive field for this particular crystal cut. However, local piezoelectric
hysteresis performed by PFM on the nanometer scale indicates similar
switching behavior of PZN-PT for both investigated crystallographic
orientations. Evolution of the domain structures with polishing below the crystal
surface has been investigated. The domain branching and polarization
screening effects after polishing and temperatures measurements have been
studied by PFM and SEM analysis. In addition, it was found what the intensity
of piezoresponse signal from nanodomain structures decreases with
temperature and finally disappears at 430 K ( orientation) and 470 K
( orientation). This difference of the temperature of local phase
transitions for crystals of different orientaions is explained by strong surface
effect on ferroelectric phase transition in relaxors.
Polarization switching in ergodic relaxor and ferroelectric phases in the PMNPT
system is studied using Piezoresponse Force Microscopy, single point
electromechanical relaxation measurements, and voltage spectroscopy
mapping. The dependence of relaxation behavior on voltage pulse amplitude
and time was found to follow a universal logarithmic behavior with a nearly
constant slope. This behavior is indicative of the progressive population of
slow relaxation states, as opposed to a linear relaxation in the presence of a
broad relaxation time distribution. The role of relaxation behavior,
ferroelectric non-linearity, and the spatial inhomogeneity of the tip field on
hysteresis loop behavior is analyzed in detail. The hysteresis loops for
ergodic PMN-10%PT are shown to be kinetically limited, while in PMN with
larger PT content, true ferroelectric hysteresis loops with low nucleation
biases are observed.FCT - SFRH/BD/22391/200
Equatorial light bending around a Hairy Kiselev black hole
No full textWe investigate the deflection angle of light rays confined to the equatorial plane of a Hairy Kiselev black hole. The analysis includes a thorough study of the horizon structure and critical parameters, leading to an analytic expression for the deflection angle in terms of elliptic integrals. Our results confirm that the deflection angle decreases with increasing impact parameter, in agreement with classical predictions of gravitational lensing. The influence of the scalar field, characterized by the coupling constant, shows a nontrivial effect: while moderate values of the coupling constant initially enhance light bending, further increases lead to a suppression of the deflection in the strong-field regime due to modifications in spacetime geometry. Comparative analysis among the Schwarzschild, Kiselev, and Hairy Kiselev black holes indicates that the presence of a quintessence-like field tends to enhance the deflection, whereas the scalar hair component reduces it. Further, we investigate the angular shadow radius of the Hairy Kiselev black hole for a static observer and analyze how mass-dependent variations affect the shadow features. These findings underscore the significant role of scalar fields and exotic matter distributions in shaping light propagation in a modified gravity scenario
Matlab code for a multipolar decomposition of optical forces
No full textThis dataset supplements Figure 5 from the publication "Multipolar Origin of the Unexpected Transverse
Force Resulting from Two-Wave Interference*" by Karim Achouri, Andrei Kiselev, and Olivier J. F. Martin. Here, we provide the code for the multipolar analysis of the optical force based on the vector spherical harmonic decomposition. Based on the Mie solution, electric fields can be obtained numerically in the far-field by using the software developed by Dr. Karim Achouri https://github.com/kachourim/MieScatteringPEC. This code analyzes the far-field scattered by a perfect electric conductor sphere placed in vacuum for different sphere radii. In the framework of the Maxwell stress tensor, we find the optical force acting on a sphere along the z-direction in the illumination configuration presented in Figure 1*. The use of the vector spherical decomposition allows to observe contributions from different multipolar interactions. In this code,we analyze the force appearing as a result of the interaction between electric dipole aligned along x, px, and electric quadrupole with components xz, Qexz and compare it with the total force along the z-axis appearing as a result of interaction between all multipoles supported by the sphere with given radius
Tidal forces in Kiselev black hole
No full textAbstract The aim of this paper is to examine the tidal forces occurring in a Kiselev black hole surrounded by radiation and dust fluids. It is noted that the radial and angular components of the tidal force change the sign between event and Cauchy horizons. We solve the geodesic deviation equation for radially free-falling bodies toward Kiselev black holes. We explain the geodesic deviation vector graphically and point out the location of the event and Cauchy horizons for specific values of the radiation and dust parameters
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