Gravitational collapse of a magnetized fermion gas with finite temperature

We examine the dynamics of a self--gravitating magnetized electron gas at finite temperature near the collapsing singularity of a Bianchi-I spacetime. Considering a general and appropriate and physically motivated initial conditions, we transform Einstein--Maxwell field equations into a complete and self--consistent dynamical system amenable for numerical work. The resulting numerical solutions reveal the gas collapsing into both, isotropic ("point-like") and anisotropic ("cigar-like") singularities, depending on the initial intensity of the magnetic field. We provide a thorough study of the near collapse behavior and interplay of all relevant state and kinematic variables: temperature, expansion scalar, shear scalar, magnetic field, magnetization and energy density. A significant qualitative difference in the behavior of the gas emerges in the temperature range $\hbox{T} sim10^{4}\hbox{K}$ and $\hbox{T}\sim 10^{7}\hbox{K}$.Comment: 9 pages, 7 figures. arXiv admin note: substantial text overlap with arXiv:1211.598

Texture Evolution of AZ31 Magnesium Alloy Sheet at High Strain Rates

In the current contribution the mechanical behaviour at high strain rates of AZ31 magnesium alloy sheet is studied. Uniaxial deformation properties were studied by means of tensile split Hopkinson pressure bar (SHPB) at different temperatures. The influence of the strain rate and temperature on the deformation mechanisms was investigated by means of electron backscatter diffraction (EBSD) and neutron diffraction. It is shown that twinning plays an important role on high strain rate deformation of this alloy, even at elevated temperatures. Significant evidence of prismatic slip as a deformation mechanism is observed, also at warm temperatures, leading to the alignment of directions with the tensile axis and to a spread of the intensities of the basal pole figure towards the in-plane direction perpendicular to the tensile axis. The rate of decrease of the CRSS of non-basal systems is observed to be slower than at quasi-static rates. Secondary twinning and pyramidal slip were also outlined for some conditions. At warm temperatures, in contrast to quasi-static range, a generalized dynamic recrystallization is not observed. Moreover, the activation of rotational recrystallization mechanisms is reporte

Twinning and grain subdivision during dynamic deformation of a Mg AZ31 sheet alloy at room temperature

The microstructural evolution of an AZ31 rolled sheet during dynamic deformation at strain rates of ∼103 s−1 has been investigated by electron backscatter diffraction, X-ray and neutron diffraction. The influence of orientation on the predominant deformation mechanisms and on the recovery processes taking place during deformation has been systematically examined. The results have been compared with those corresponding to the same alloy tested quasi-statically under equivalent conditions. It has been found that strain rate enhances the activation of extension twinning dramatically, while contraction and secondary twinning are not significantly influenced. The polarity of extension twinning is even reversed in some grains under selected testing conditions. Significant grain subdivision by the formation of geometrically necessary boundaries (GNBs) takes place during both quasi-static and dynamic deformation of this AZ31 alloy. It is remarkable that GNBs of high misorientations form even at the highest strain rates. The phenomenon of recovery has been found to be orientation dependen

Warm Electromagnetic Forming of AZ31B Magnesium Alloy Sheet

Historically, electromagnetic forming technology has mainly been used to form parts from aluminium and copper alloys due to their excellent electrical conductivity and limited formability by conventional methods. However, little research has been carried out in high strain rate forming of magnesium alloy sheets. Therefore, in the current contribution electromagnetic forming experiments are performed for rolled AZ31B magnesium alloy sheet at different temperatures up to 250°C. Two forming operations are studied in this paper, i.e. drawing and bending operations. The final deformations achieved for the different conditions were measured and the effect of both temperature and discharged energy on deformation is shown. Bending experiments at room temperature were recorded by means of a high speed camera and the springback behaviour at high strain rates is evaluated. In one hand, increasing the forming temperature the yield strength of the material decreases while on the other hand, the electrical conductivity and thus the induced forces are also decreased. It is observed that increasing the forming temperature, for a given discharged energy, the maximum height of the deformed part is decreased. However, increasing the discharged energy at warm temperatures, higher deformation values are achieved without failure. Additionally, bending experiments show that springback effect is also decreased at warm conditions. It is concluded that warm electromagnetic forming is a suitable procedure to manufacture magnesium parts

Influence of texture on the recrystallization mechanisms in an AZ31 Mg sheet alloy at dynamic rates

An AZ31 rolled sheet alloy has been tested at dynamic strain rates View the MathML source at 250 °C up to various intermediate strains before failure in order to investigate the predominant deformation and restoration mechanisms. In particular, tests have been carried out in compression along the rolling direction (RD), in tension along the RD and in compression along the normal direction (ND). It has been found that dynamic recrystallization (DRX) takes place despite the limited diffusion taking place under the high strain rates investigated. The DRX mechanisms and kinetics depend on the operative deformation mechanisms and thus vary for different loading modes (tension, compression) as well as for different relative orientations between the loading axis and the c-axes of the grains. In particular, DRX is enhanced by the operation of 〈c + a〉 slip, since cross-slip and climb take place more readily than for other slip systems, and thus the formation of high angle boundaries is easier. DRX is also clearly promoted by twinning

Engineering a light-driven cyanine based molecular rotor to enhance the sensitivity towards a viscous medium.

This article describes the enhanced sensitivity to a viscous medium by a molecular rotor based fluorophore (RBF), TPSI I. The TPSI I molecule is designed in such a way that it consists of a rotor and a fluorophore with a p-rich bridge between them. TPSI I is a light-responsive material in solution as well as in the solid state. The structural design of the molecule allows flexible rotation and photo-induced cis-trans isomerization both in the solid state as well as in solution. These combined attributes of TPSI I are responsible for the ultrasensitive viscosity response of the new material, which was verified through the Fo ̈rster-Hoffmann equation. According to this equation, the derived 'x' value is 1.02 (x is related to the sensitivity) which is the highest among the contemporary reports for RBFs. The facts were evidenced both by experimental as well as theoretical data. The ultrasensitivity towards viscosity was further analyzed in in vitro studies by detecting the subtle changes in the alteration of intracellular viscosity in normal and cancerous cells. An alteration of intracellular viscosity in cells treated with viscosity modula- tors was also confirmed using a previously well-established viscosity measurement technique, dynamic measurement through the piezoelectric patch. Our research offers a detailed mechanism to improve viscosity sensors and an efficient probe for detecting minute changes in intracellular viscosity

Dynamics of a self-gravitating neutron source

We examine the dynamics of a self--gravitating magnetized neutron gas as a source of a Bianchi I spacetime described by the Kasner metric. The set of Einstein-Maxwell field equations can be expressed as a dynamical system in a 4-dimensional phase space. Numerical solutions of this system reveal the emergence of a point--like singularity as the final evolution state for a large class of physically motivated initial conditions. Besides the theoretical interest of studying this source in a fully general relativistic context, the resulting idealized model could be helpful in understanding the collapse of local volume elements of a neutron gas in the critical conditions that would prevail in the center of a compact object.Comment: 17 pages, 6 figures, JHEP style, published versio

A Trapezoidal Octacyanoquinoid Acceptor Forms Solution and Surface Products by Antiparallel Shape Fitting with Conformational Dipole Momentum Switch

A new compound (1) formed by two antiparallelly disposed tetracyano thienoquinoidal units has been synthesized and studied by electrochemistry, UV/Vis-NIR, IR, EPR, and transient spectroscopy. Self-assembly of 1 on a Au(111) surface has been investigated by scanning tunneling microscopy. Experiments have been rationalized by quantum chemical calculations. 1 exhibits a unique charge distribution in its anionic form, with a gradient of charge yielding a neat molecular in-plane electric dipole momentum, which transforms out-of-plane after surface deposition due to twisted! folded conformational change and to partial charge transfer from Au(111). Intermolecular van der Waals interactions and antiparallel trapezoidal shape fitting lead to the formation of an optimal dense on Au(111) two-dimensional assembly of 1. The realization of novel properties emerging upon electronic covalent coupling between chromophores (i.e., bichromophoric systems) is a critical issue for the development of photo- and electrically active systems.[1–3] In this regard, the relative topology and orientation of the p-subchromophores, such as in A + B type p-systems in Figure 1, with 1D linear conjugation, 2D parallel conjugation,[4] 3D orthogonal spiroconjugation[5] or 3D conjugation[6] are key factors. On the other hand, studies of the distribution of the excess of charge in p-conjugated moieties in post-electron transfer events are central issues in photophysics and photochemistry, in energy storage[7] and in organic electronics.[8] In addition to this electronic provision, its embedment in different molecular forms is of relevance as these can define unique ways of shape fitting in supramolecular and surface assemblies. Joint electronic and molecular shape designs thus allow to build molecular-based synthons in a tailored manner towards new bulk and nano organized materials. (...)Funding for open access charge: Universidad de Málaga / CBUA. The authors thank the Spanish Ministry of Science, Innovation and Universities MCIU (projects CTQ2017-83531-R, RED2018-102815-T, MAT2017-85089-C2-1-R), Centro de Excelencia Severo Ochoa grants (SEV-2016-0686, SEV2015-0496 and FUNFUTURE CEX2019-000917-S) and the CAM (QUIMTRONIC-CM project Y2018/NMT-4783). We thank MINECO/FEDER of the Spanish Government (projects PGC2018-098533-B-100 and PID2019-109555GB-I00), the Eusko Jaurlaritza (Basque Government, project PIBA19-0004) and the Junta de Andalucía, Spain (UMA18FEDERJA057). We also thank the Research Central Services (SCAI) of the University of Málaga and the Donostia International Physics Center (DIPC) Computer Center. We thank Dr. Juwon Oh and Prof. Donhgo Kim from the Spectroscopy Laboratory for Functional p-electronic Systems and Department of Chemistry, Yonsei University in Korea for the generous gift of the TRIR and UV/Vis transient absorption spectroscopy data

A Trapezoidal Octacyanoquinoid Acceptor Forms Solution and Surface Products by Antiparallel Shape Fitting with Conformational Dipole Momentum Switch

A new compound (1) formed by two antiparallelly disposed tetracyano thienoquinoidal units has been synthesized and studied by electrochemistry, UV/Vis-NIR, IR, EPR, and transient spectroscopy. Self-assembly of 1 on a Au(111) surface has been investigated by scanning tunneling microscopy. Experiments have been rationalized by quantum chemical calculations. 1 exhibits a unique charge distribution in its anionic form, with a gradient of charge yielding a neat molecular in-plane electric dipole momentum, which transforms out-of-plane after surface deposition due to twisted→folded conformational change and to partial charge transfer from Au(111). Intermolecular van der Waals interactions and antiparallel trapezoidal shape fitting lead to the formation of an optimal dense on Au(111) two-dimensional assembly of 1.The authors thank the Spanish Ministry of Science, Innovation and Universities MCIU (projects CTQ2017-83531-R, RED2018-102815-T, MAT2017-85089-C2-1-R), Centro de Excelencia Severo Ochoa grants (SEV-2016-0686, SEV-2015-0496 and FUNFUTURE CEX2019-000917-S) and the CAM (QUIMTRONIC-CM project Y2018/NMT-4783). We thank MINECO/FEDER of the Spanish Government (projects PGC2018-098533-B-100 and PID2019-109555GB-I00), the Eusko Jaurlaritza (Basque Government, project PIBA19-0004) and the Junta de Andalucía, Spain (UMA18FEDERJA057). We also thank the Research Central Services (SCAI) of the University of Málaga and the Donostia International Physics Center (DIPC) Computer Center. We thank Dr. Juwon Oh and Prof. Donhgo Kim from the Spectroscopy Laboratory for Functional π-electronic Systems and Department of Chemistry, Yonsei University in Korea for the generous gift of the TRIR and UV/Vis transient absorption spectroscopy data.Peer reviewe