A hot bubble at the centre of M81

Context. Messier 81 has the nearest active nucleus with broad H$\alpha$ emission. A detailed study of this galaxy's centre is important for understanding the innermost structure of the AGN phenomenon. Aims. Our goal is to seek previously undetected structures using additional techniques to reanalyse a data cube obtained with the GMOS-IFU installed on the Gemini North telescope (Schnorr M\"uller et al. 2011). Method. We analysed the data cube using techniques of noise reduction, spatial deconvolution, starlight subtraction, PCA tomography, and comparison with HST images. Results. We identified a hot bubble with T $>$ 43500 K that is associated with strong emission of [N II]$\lambda$5755\AA\ and a high [O I]$\lambda$6300/H$\alpha$ ratio; the bubble displays a bluish continuum, surrounded by a thin shell of H$\alpha$ + [N II] emission. We also reinterpret the outflow found by Schnorr M\"uller et al. (2011) showing that the blueshifted cone nearly coincides with the radio jet, as expected. Conclusions. We interpret the hot bubble as having been caused by post starburst events that left one or more clusters of young stars, similar to the ones found at the centre of the Milky Way, such as the Arches and the IRS 16 clusters. Shocked structures from combined young stellar winds or supernova remnants are probably the cause of this hot gas and the low ionization emission.Comment: 5 pages, 4 figures, accepted for publication in A&

Theory of the Fermi Arcs, the Pseudogap, TcT_c and the Anisotropy in k-space of Cuprate Superconductors

The appearance of the Fermi arcs or gapless regions at the nodes of the Fermi surface just above the critical temperature is described through self-consistent calculations in an electronic disordered medium. We develop a model for cuprate superconductors based on an array of Josephson junctions formed by grains of inhomogeneous electronic density derived from a phase separation transition. This approach provides physical insights to the most important properties of these materials like the pseudogap phase as forming by the onset of local (intragrain) superconducting amplitudes and the zero resistivity critical temperature $T_c$ due to phase coherence activated by Josephson coupling. The formation of the Fermi arcs and the dichotomy in k-space follows from the direction dependence of the junctions tunneling current on the d-wave symmetry on the $CuO_2$ planes. We show that this semi-phenomenological approach reproduces also the main future of the cuprates phase diagram.Comment: 5 pages 7 fig

Entropy change at the martensitic transformation in ferromagnetic shape memory alloys Ni_{2+x}Mn_{1-x}Ga

The entropy change $\Delta S$ between the high-temperature cubic phase and the low-temperature tetragonally-based martensitic phase of Ni$_{2+x}$Mn$_{1-x}$Ga ($x = 0 - 0.20$) alloys was studied. The experimental results obtained indicate that $\Delta S$ in the Ni$_{2+x}$Mn$_{1-x}$Ga alloys increases with the Ni excess $x$. The increase of $\Delta S$ is presumably accounted for by an increase of magnetic contribution to the entropy change. It is suggested that the change in modulation of the martensitic phase of Ni$_{2+x}$Mn$_{1-x}$Ga results in discontinuity of the composition dependence of $\Delta S$.Comment: presented at MMM-47, to be published in J. Appl. Phys. (May 15, 2003

Frequency combs and platicons in optical microresonators with normal GVD

We predict the existence of a novel type of the flat-top dissipative solitonic pulses, "platicons", in microresonators with normal group velocity dispersion (GVD). We propose methods to generate these platicons from cw pump. Their duration may be altered significantly by tuning the pump frequency. The transformation of a discrete energy spectrum of dark solitons of the Lugiato-Lefever equation into a quasicontinuous spectrum of platicons is demonstrated. Generation of similar structures is also possible with bi-harmonic, phase/amplitude modulated pump or via laser injection locking.Comment: 9 pages, 6 figure

Vortices on a superconducting nanoshell: phase diagram and dynamics

In superconductors, the search for special vortex states such as giant vortices focuses on laterally confined or nanopatterned thin superconducting films, disks, rings, or polygons. We examine the possibility to realize giant vortex states and states with non-uniform vorticity on a superconducting spherical nanoshell, due to the interplay of the topology and the applied magnetic field. We derive the phase diagram and identify where, as a function of the applied magnetic field, the shell thickness and the shell radius, these different vortex phases occur. Moreover, the curved geometry allows these states (or a vortex lattice) to coexist with a Meissner state, on the same curved film. We have examined the dynamics of the decay of giant vortices or states with non-uniform vorticity into a vortex lattice, when the magnetic field is adapted so that a phase boundary is crossed.Comment: 21 pages, 9 figure

Correlator of Topological Charge Densities in Instanton Model in QCD

The QCD sum rule for the correlator of topological charge densities and related to it longitudinal part of the correlator of singlet axial currents is considered in the framework of instanton model. The coupling constant of eta'-meson with the singlet axial current is determined. Its value appears to be in a good coincidence with the value determined recently from the connection of the part of proton spin, carried by u,d,s quarks, with the derivative of QCD topological susceptibility. From the same sum rule eta-eta' mixing angle is found in the framework of two mixing angles model. Its value is close to that found in the chiral effective theory. The correlator of topological charge densities at large momenta is calculated.Comment: 14 pages, 2 figure

Process for the preparation of calcium superoxide

Calcium superoxide is prepared in high yields by spreading a quantity of calcium peroxide diperoxyhydrate on the surface of a container, positioning said container in a vacuum chamber on a support structure through which a coolant fluid can be circulated, partially evacuating said vacuum chamber, allowing the temperature of the diperoxyhydrate to reach the range of about 0 to about 40 C; maintaining the temperature selected for a period of time sufficient to complete the disproproriation of the diperoxyhydrate to calcium superoxide, calcium hydroxide, oxygen, and water; constantly and systematically removing the water as it is formed by sweeping the reacting material with a current of dry inert gas and/or by condensation of said water on a cold surface; backfilling the chamber with a dry inert gas; and finally, recovering the calcium superoxide produced

Study of exclusive processes e^+ e^- \to VP

This paper is devoted to consideration of the hard exclusive processes $e^+e^- \to VP$, where $V=\rho,\phi; P=\eta,\eta'$. Experimental measurement of the cross section of the process $e^+ e^- \to \phi\eta$ at BaBar collaboration at large center mass energy $\sqrt s=10.6$ GeV and some low energy experimental data $\sqrt s \sim 2-4$ GeV give us the possibility to study the cross section in the broad energy region. As the result, we have determined the asymptotic behavior of the cross section of $e^+ e^- \to \phi\eta$ in the limit $s \to \infty$, which is in agreement with perturbative QCD prediction. Assuming that the same asymptotic behavior is valid for the other processes under consideration and using low energy experimental data we have predicted the cross sections of these processes at energies $\sqrt s=3.67,~10.6$ GeV. In addition, we have calculated the cross sections of these processes at the same energies within perturbative QCD. Our results are in agreement with available experimental data.Comment: 10 pages, 2 tables, 6 figures; minor changes; article accepted to publication is Phys. Rev.