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1.
A model for an anisotropic Bianchi type VI universe in a Scale Covariant theory of gravitation (Canuto et al. in Phys. Rev. D 16:6, 1977a; Phys. Rev. Lett. 39:8, 1977b) is analyzed. Exact solutions to the corresponding field equations are found under some specific assumptions. A finite singularity is found in the model at the initial time t=0. All the physical parameters are studied and thoroughly discussed. The model behaves like a big bang singular model o f the universe. 相似文献
2.
An axially symmetric non-static space-time is considered in the presence of thick domain walls in the scalar–tensor theories
formulated by Brans and Dicke (Phys. Rev. 124:925, 1961) and Saez and Ballester (Phys. Lett. A 113:467, 1985). Exact cosmological models, in both the theories, are presented with the help of special law of variation proposed by Berman
(Nuovo Cim. B 74:182, 1983), for Hubble’s parameter. Some physical and kinematical properties of the models are discussed.
相似文献
3.
S. Vargas Domínguez D. MacTaggart L. Green L. van Driel-Gesztelyi A. W. Hood 《Solar physics》2012,278(1):33-45
Recent studies of NOAA active region 10953, by Okamoto et al. (Astrophys. J. Lett.
673, 215, 2008; Astrophys. J.
697, 913, 2009), have interpreted photospheric observations of changing widths of the polarities and reversal of the horizontal magnetic
field component as signatures of the emergence of a twisted flux tube within the active region and along its internal polarity
inversion line (PIL). A filament is observed along the PIL and the active region is assumed to have an arcade structure. To
investigate this scenario, MacTaggart and Hood (Astrophys. J. Lett.
716, 219, 2010) constructed a dynamic flux emergence model of a twisted cylinder emerging into an overlying arcade. The photospheric signatures
observed by Okamoto et al. (2008, 2009) are present in the model although their underlying physical mechanisms differ. The model also produces two additional signatures
that can be verified by the observations. The first is an increase in the unsigned magnetic flux in the photosphere at either
side of the PIL. The second is the behaviour of characteristic photospheric flow profiles associated with twisted flux tube
emergence. We look for these two signatures in AR 10953 and find negative results for the emergence of a twisted flux tube
along the PIL. Instead, we interpret the photospheric behaviour along the PIL to be indicative of photospheric magnetic cancellation
driven by flows from the dominant sunspot. Although we argue against flux emergence within this particular region, the work
demonstrates the important relationship between theory and observations for the successful discovery and interpretation of
signatures of flux emergence. 相似文献
4.
Marcelo Samuel Berman 《Astrophysics and Space Science》2012,337(1):477-481
In a previous paper (Berman, in Astrophys. Space Sci., 2011), we showed how to prove the two Pioneers Anomalies, and now we add the fly-bys, by means of a rotating Universe. We discuss
Einstein’s Machian program, which we find as being fullfilled. Godlowski et al. (Los Alamos Archives, 2003) idea for a rotating General Relativistic Universe, led us to the adopted model. Updated evidence on rotation is cited (Godlowski,
in Los Alamos Archives, 2011; Ni in Phys. Rev. Lett. 107(5):051103, 2011). We conclude that a rotating and expanding Universe may be the unique solution to the apparent divergences between Einstein
and Mach. This is cosmologically important. 相似文献
5.
LRS Bianchi type-I dark energy model with variable equation of state (EoS) parameter is presented in the scalar-tensor theory
of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). To get a determinate solution of the field equations we take the help of special law of variation for Hubble’s parameter
presented by Bermann (Nuovo Cimento B 74:182, 1983) which yields a cosmological model with negative constant deceleration parameter. Some physical and kinematical properties
of the model are also discussed. 相似文献
6.
A wide variety of transient events in the solar corona seem to require explanations that invoke fast reconnection. Theoretical
models explaining fast reconnection often rely on enhanced resistivity. We start with data derived from observed reconnection
rates in solar flares and seek to reconcile them with the chaos-induced resistivity model of Numata and Yoshida (Phys. Rev. Lett.
88, 045003, 2002) and with resistivity arising out of the kinetic Alfvén wave (KAW) instability. We find that the resistivities arising from
either of these mechanisms, when localized over length scales of the order of an ion skin depth, are capable of explaining
the observationally mandated Lundquist numbers. 相似文献
7.
A Staged Z-pinch (H.U. Rahman, F.J. Wessel, N. Rostoker, Phys. Rev. Lett. 74:714, 1995), configured for a 100 ns, 2 MJ implosion accelerator, is studied using the 2-1/2 D, radiation-MHD code, MACH2. The Z-pinch
is configured as a cylindrical, high-atomic number plasma shell that implodes radially onto a co-axial, plasma target, for
example: Xenon onto a 50:50 mixture of Deuterium-Tritium. During implosion a shock develops in the plasma liner, producing
a conduction channel at the Xe/DT interface as the mass Xe accumulates, and preheating the DT target. During subsequent acceleration
and compression the Xe/DT interface remains stable, even as the outer surface of the Xe shell develops RT instabilities. At
peak implosion the simulated fusion-energy yield is 7.6 MJ, producing an energy gain of 3.8. 相似文献
8.
A locally rotationally symmetric Bianchi type-II (LRS B-II) space-time with variable equation of state (EoS) parameter and
constant deceleration parameter have been investigated in the scalar-tensor theory proposed by Saez and Ballester (Phys. Lett.
A 113:467, 1986). The scalar-tensor field equations have been solved by applying variation law for generalized Hubble’s parameter given by
Bermann (Nuovo Cimento 74:182, 1983). The physical and kinematical properties of the model are also discussed. 相似文献
9.
Farook Rahaman Mubasher Jamil Kaushik Chakraborty 《Astrophysics and Space Science》2011,331(1):191-197
Motivated by earlier studies (Tiwari et al. in Astrophys. Space Sci. 182:105, 1984; Herrera and Varela in Phys. Lett. 189:11, 1994), we model electron as a spherically symmetric charged perfect fluid distribution of matter. The existing model is extended
assuming a matter source that is characterized by quadratic equation of state in the context of general theory of relativity.
For the suitable choices of the parameters, our charged fluid models almost satisfy the physical properties of electron. 相似文献
10.
Valentí Bosch-Ramon 《Astrophysics and Space Science》2007,309(1-4):321-331
Microquasar (MQ) jets are sites of particle acceleration and synchrotron emission. Such synchrotron radiation has been detected
coming from jet regions of different spatial scales, which for the instruments at work nowadays appear as compact radio cores,
slightly resolvedradio jets, or (very) extended structures (e.g. Mirabel and Rodríguez, 1999; Fender, 2001; Corbel et al., 2002). Because of the presence of relativistic particles and dense photon, magnetic and matter fields, these outflows are also
the best candidates to generate the very high-energy (VHE) gamma-rays detected coming from two of these objects, LS 5039 and
LS I +61 303 (Aharonian, 2005; Aharonian et al., 2006a; and Albert, 2006, respectively), and may be contributing significantly to the X-rays emitted from the MQ core (e.g. Markoff et al., 2001; Bosch-Ramon et al., 2005a). In addition, beside electromagnetic radiation, jets at different scales are producing some amount of leptonic and hadronic
cosmic rays (CR), and evidences of neutrino production in these objects may be eventually found. In this work, we review on
the different physical processes that may be at work in or related to MQ jets. The jet regions capable to produce significant
amounts of emission at different wavelengths have been reduced to the jet base, the jet at scales of the order of the size
of the system orbital semi-major axis, the jet middle scales (the resolved radio jets), and the jet termination point. The
surroundings of the jet could be sites of multiwavelength emission as well, deserving also an insight. We focus on those scenarios,
either hadronic or leptonic, in which it seems more plausible to generate both photons from radio to VHE and high-energy neutrinos.
We briefly comment as well on the relevance of MQ as possible contributors to the galactic CR in the GeV–PeV range. 相似文献
11.
An exact Bianchi type-V cosmological model is obtained in a scalar-tensor theory of gravitation proposed by Saez and Ballester
(Phys. Lett. A 113:467, 1986) in case of perfect fluid distribution. Some physical properties of the model are also discussed. 相似文献
12.
A five dimensional Kaluza-Klein dark energy model with variable equation of state (EoS) parameter and a constant deceleration
parameter is presented in Saez and Ballester (Phys. Lett. A 113:467, 1986) scalar-tensor theory of gravitation. Some physical and kinematical properties of the model are also discussed. 相似文献
13.
A spatially homogeneous and anisotropic Bianchi type-II cosmological model is obtained in a scalar tensor theory of gravitation
proposed by Saez and Ballester (Phys. Lett. A 130:467, 1986) when the source for energy momentum tensor is a bulk viscous fluid containing one-dimensional cosmic strings. Some physical
and kinematical properties of the model are also discussed. 相似文献
14.
Using nine years of solar wind plasma and magnetic field data from the Wind mission, we investigated the characteristics of both magnetic clouds (MCs) and magnetic cloud-like structures (MCLs) during
1995 – 2003. A MCL structure is an event that is identified by an automatic scheme (Lepping, Wu, and Berdichevsky, Ann. Geophys.
23, 2687, 2005) with the same criteria as for a MC, but it is not usually identifiable as a flux rope by using the MC (Burlaga et al., J. Geophys. Res.
86, 6673, 1981) fitting model developed by Lepping, Jones, and Burlaga (Geophys. Res. Lett.
95(11), 957, 1990). The average occurrence rate is 9.5 for MCs and 13.6 for MCLs per year for the overall period of interest, and there were
82 MCs and 122 MCLs identified during this period. The characteristics of MCs and MCL structures are as follows: (1) The average
duration, Δt, of MCs is 21.1 h, which is 40% longer than that for MCLs (Δt=15 h); (2) the average
(minimum B
z
found in MC/MCL measured in geocentric solar ecliptic coordinates) is −10.2 nT for MCs and −6 nT for MCLs; (3) the average
Dstmin (minimum Dst caused by MCs/MCLs) is −82 nT for MCs and −37 nT for MCLs; (4) the average solar wind velocity is 453 km s−1 for MCs and 413 km s−1 for MCLs; (5) the average thermal speed is 24.6 km s−1 for MCs and 27.7 km s−1 for MCLs; (6) the average magnetic field intensity is 12.7 nT for MCs and 9.8 nT for MCLs; (7) the average solar wind density
is 9.4 cm−3 for MCs and 6.3 cm−3 for MCLs; and (8) a MC is one of the most important interplanetary structures capable of causing severe geomagnetic storms.
The longer duration, more intense magnetic field and higher solar wind speed of MCs, compared to those properties of the MCLs,
are very likely the major reasons for MCs generally causing more severe geomagnetic storms than MCLs. But the fact that a
MC is an important interplanetary structure with respect to geomagnetic storms is not new (e.g., Zhang and Burlaga, J. Geophys. Res.
93, 2511, 1988; Bothmer, ESA SP-535, 419, 2003). 相似文献
15.
Naveen Bijalwan 《Astrophysics and Space Science》2012,337(1):161-167
We show in this article that charged fluid with pressure derived by Bijalwan (Astrophys. Space. Sci. doi:, 2011a) can be used to model classical electron, quark, neutron stars and pulsar with charge matter, quasi black hole, white dwarf,
super-dense star etc. Recent analysis by Bijalwan (Astrophys. Space. Sci., 2011d) that all charged fluid solutions in terms of pressure mimic the classical electron model are partially correct because solutions
by Bijalwan (Astrophys. Space. Sci. doi:, 2011a) may possess a neutral counterpart. In this paper we characterized solutions in terms of pressure for charged fluids that
have and do not have a well behaved neutral counter part considering same spatial component of metric e
λ
for neutral and charged fluids. We discussed solution by Gupta and Maurya (Astrophys. Space Sci. 331(1):135–144, 2010a) and solutions by Bijalwan (Astrophys. Space Sci. doi:, 2011b; Astrophys. Space Sci. doi:, 2011c; Astrophys. Space Sci., 2011d) such that charged fluids possess and do not possess a neutral counterpart as special cases, respectively. For brevity, we
only present some analytical results in this paper. 相似文献
16.
D. R. K. Reddy R. L. Naidu T. Ramprasd K. V. Ramana 《Astrophysics and Space Science》2013,348(1):241-245
A locally rotationally symmetric(LRS) Bianchi type-II space-time is considered in the frame work of a modified theory of gravitation proposed by Canuto et al. (Phys. Rev. Lett. 39:429, 1977) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. A special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983) is used to obtain determinate solution of the field equations. We have also used the barotropic equation of state and the bulk viscous pressure is assumed to be proportional to the energy density. The physical and kinematical properties of the model are also discussed. 相似文献
17.
<Emphasis Type="Italic">N</Emphasis>-dimensional Bianchi type-I universe in creation-field cosmology
K. S. Adhav S. D. Katore P. S. Gadodia A. S. Bansod 《Astrophysics and Space Science》2010,327(1):125-130
We have studied the Hoyle-Narlikar C-field cosmology with Bianchi type-I space–time in N dimensions. Using methods of Narlikar and Padmanabham (Phys. Rev. D 32:1928, 1985), the solutions have been studied when the creation field C is a function of time t only. The geometrical and physical aspects for the model are also studied. 相似文献
18.
A spatially homogeneous Bianchi type-III space-time is considered in the presence of perfect fluid source in the frame work of f(R,T) gravity (Harko et al. in Phys. Rev. D 84:024020, 2011) with the help of a special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983). A cosmological model with an appropriate choice of the function f(T) has been constructed. The physical behavior of the model is studied. 相似文献
19.
A spatially homogeneous and anisotropic Bianchi type-I cosmological model is examined with N-dimensions in Brans–Dicke (Phys. Rev. 124, 925, 1961) scalar-tensor theory of gravitation. Some properties of the model are also studied.
相似文献
20.
Axially symmetric string cosmological models are obtained in a scalar- tensor theory of gravitation proposed by Brans and
Dicke (Phys. Rev. 124:925, 1961). Some physical and geometrical properties of the models are also discussed. The models are anisotropic and free from singularities. 相似文献