The fact that a fermion system in an external magnetic field breaks the spherical symmetry suggests that its intrinsic geometry is axisymmetric rather than spherical. In this work we analyze the impact of anisotropic ...The fact that a fermion system in an external magnetic field breaks the spherical symmetry suggests that its intrinsic geometry is axisymmetric rather than spherical. In this work we analyze the impact of anisotropic pressures, due to the presence of a magnetic field, in the structure equations of a magnetized quark star.We assume a cylindrical metric and an anisotropic energy momentum tensor for the source. We found that there is a maximum magnetic field that a strange star can sustain, closely related to the violation of the virial relations.展开更多
We revisit the problem of the maximum masses of magnetized white dwarfs (WDs). The impact of a strong magnetic field on the structure equations is addressed. The pressures become anisotropic due to the presence of t...We revisit the problem of the maximum masses of magnetized white dwarfs (WDs). The impact of a strong magnetic field on the structure equations is addressed. The pressures become anisotropic due to the presence of the magnetic field and split into parallel and perpendicular components. We first construct stable solutions of the Tolman-Oppenheimer-Volkoff equations for parallel pressures and find that physical solutions vanish for the perpendicular pressure whenB ≥ 10^13 G. This fact estab- lishes an upper bound for a magnetic field and the stability of the configurations in the (quasi) spherical approximation. Our findings also indicate that it is not possible to obtain stable magnetized WDs with super-Chandrasekhar masses because the val- ues of the magnetic field needed for them are higher than this bound. To proceed into the anisotropic regime, we can apply results for structure equations appropriate for a cylindrical metric with anisotropic pressures that were derived in our previous work. From the solutions of the structure equations in cylindrical symmetry we have con- firmed the same bound for B- 10^13 G, since beyond this value no physical solutions are possible. Our tentative conclusion is that massive WDs with masses well beyond the Chandrasekhar limit do not constitute stable solutions and should not exist.展开更多
The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields.After including quantum effects in the investigation of the structural properties of these systems,it is ...The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields.After including quantum effects in the investigation of the structural properties of these systems,it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures.Highly magnetized white dwarfs should collapse producing a supernova type Ia,while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode,too.A comparison of our results with a set of the available observational data of some compact stars is also presented,and the agreement between this theory and observations is verified.展开更多
This study presents the photoluminescence characteristics of the PZT 53/47 system doped at A and/or B sites, with Nb(PZTN), La(PLZT), and Nb–La(PLZTN) in the concentration range from 0.2 to 1.0 molar fraction. The in...This study presents the photoluminescence characteristics of the PZT 53/47 system doped at A and/or B sites, with Nb(PZTN), La(PLZT), and Nb–La(PLZTN) in the concentration range from 0.2 to 1.0 molar fraction. The intensity of the emission bands of the system PZTN is two orders higher than the intensity of the emission bands of the systems PLZT and PLZTN, and these emission bands are located at 1.73 eV(718 nm), 2.56 eV(485 nm), and 2.93 eV(424 nm). The origin of the luminescence in these systems is associated with lead and oxygen vacancies produced during the sintering process. The results from X-ray diffraction(XRD) show a mixture of rhombohedral and tetragonal phases. The system PZTN shows a higher tetragonal phase concentration, while PLZT and PLZTN systems show a higher rhombohedral phase concentration. The cell volume shows an increase with dopant concentration only in the case of the PLZTN system. The band gap energy shows a small variation in the PZTN and PLZTN cases around 3.0 eV, a close value to the band gap energy of the pure PZT 53/47 sample. The system PLZT shows an increasing behavior until 4.41 eV for the higher dopant concentration.展开更多
基金supported under the grant CB0407the ICTP Office of External Activities through NET-35+1 种基金financial support of the CNPqFAPESP Agencies (Brazil)
文摘The fact that a fermion system in an external magnetic field breaks the spherical symmetry suggests that its intrinsic geometry is axisymmetric rather than spherical. In this work we analyze the impact of anisotropic pressures, due to the presence of a magnetic field, in the structure equations of a magnetized quark star.We assume a cylindrical metric and an anisotropic energy momentum tensor for the source. We found that there is a maximum magnetic field that a strange star can sustain, closely related to the violation of the virial relations.
基金supported under the grant CB0407the ICTP Office of External Activities through NET-35+3 种基金the fellowship CLAF-ICTPIGA-USP for the hospitalitysupport given by the International Center for Relativistic Astrophysics Networkthe financial support of the CNPq and FAPESP Agencies(Brazil)
文摘We revisit the problem of the maximum masses of magnetized white dwarfs (WDs). The impact of a strong magnetic field on the structure equations is addressed. The pressures become anisotropic due to the presence of the magnetic field and split into parallel and perpendicular components. We first construct stable solutions of the Tolman-Oppenheimer-Volkoff equations for parallel pressures and find that physical solutions vanish for the perpendicular pressure whenB ≥ 10^13 G. This fact estab- lishes an upper bound for a magnetic field and the stability of the configurations in the (quasi) spherical approximation. Our findings also indicate that it is not possible to obtain stable magnetized WDs with super-Chandrasekhar masses because the val- ues of the magnetic field needed for them are higher than this bound. To proceed into the anisotropic regime, we can apply results for structure equations appropriate for a cylindrical metric with anisotropic pressures that were derived in our previous work. From the solutions of the structure equations in cylindrical symmetry we have con- firmed the same bound for B- 10^13 G, since beyond this value no physical solutions are possible. Our tentative conclusion is that massive WDs with masses well beyond the Chandrasekhar limit do not constitute stable solutions and should not exist.
基金One of us(A.P.M.)would like to thank the ICTPIAEA+5 种基金UNESCOCFIF(Lisbon,Portugal)for their financial support and hospitalityThe work of R.G.F.has been supported by Fundaçāo para a Ciência e a Tecnologia under the grant SFRH/BPD/1549/2000H.J.M.C.is a fellow of the Fundaçāo de AmparoàPesquisa do Estado do Rio de Janeiro(FAPERJ)Brazil,under the contract E-26/151.684/2002thanks OEA-ICTP for hospitality in Havana through NET-35.
文摘The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields.After including quantum effects in the investigation of the structural properties of these systems,it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures.Highly magnetized white dwarfs should collapse producing a supernova type Ia,while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode,too.A comparison of our results with a set of the available observational data of some compact stars is also presented,and the agreement between this theory and observations is verified.
基金supported by project PNCB 10/09,Cuba,the Sabbatical program and projects CB 240460 and(LIDTRA)LN2015-254119 of CONACYT Mexico
文摘This study presents the photoluminescence characteristics of the PZT 53/47 system doped at A and/or B sites, with Nb(PZTN), La(PLZT), and Nb–La(PLZTN) in the concentration range from 0.2 to 1.0 molar fraction. The intensity of the emission bands of the system PZTN is two orders higher than the intensity of the emission bands of the systems PLZT and PLZTN, and these emission bands are located at 1.73 eV(718 nm), 2.56 eV(485 nm), and 2.93 eV(424 nm). The origin of the luminescence in these systems is associated with lead and oxygen vacancies produced during the sintering process. The results from X-ray diffraction(XRD) show a mixture of rhombohedral and tetragonal phases. The system PZTN shows a higher tetragonal phase concentration, while PLZT and PLZTN systems show a higher rhombohedral phase concentration. The cell volume shows an increase with dopant concentration only in the case of the PLZTN system. The band gap energy shows a small variation in the PZTN and PLZTN cases around 3.0 eV, a close value to the band gap energy of the pure PZT 53/47 sample. The system PLZT shows an increasing behavior until 4.41 eV for the higher dopant concentration.