Detailed study of SNR G306.3-0.9 using XMM-Newton and Chandra observations

We used combined data from XMM-Newton and Chandra observatories to study the X-ray morphology of SNR G306.3-0.9. A spatially-resolved spectral analysis was used to obtain physical and geometrical parameters of different regions of the remnant. Spitzer infrared observations were also used to constrain the progenitor supernova and study the environment in which the SNR evolved. The X-ray morphology of the remnant displays a non-uniform structure of semi-circular appearance, with a bright southwest region and very weak or almost negligible X-ray emission in its northern part. These results indicate that the remnant is propagating in a non-uniform environment as the shock fronts are encountering a high-density medium, where enhanced infrared emission is detected. The X-ray spectral analysis of the selected regions shows distinct emission-line features of several metal elements, confirming the thermal origin of the emission. The X-ray spectra are well represented by a combination of two absorbed thermal plasma models: one in equilibrium ionization with a mean temperature of ~0.19 keV, and another out of equilibrium ionization at a higher temperature of ~1.1 or 1.6-1.9 keV. For regions located in the northeast, central, and southwest part of the SNR, we found elevated abundances of Si, S, Ar, Ca, and Fe, typical of ejecta material. The outer regions located northwest and south show values of the abundances above solar but lower than to those found in the central regions. This suggests that the composition of the emitting outer parts of the SNR is a combination of ejecta and shocked material of the interstellar medium. The comparison between the S/Si, Ar/Si, and Ca/Si abundances ratios (1.75, 1.27, and 2.72 in the central region, respectively), favor a Type Ia progenitor for this SNR, a result that is also supported by an independent morphological analysis using X-ray and IR data.Comment: 8 pages, 7 figures. Accepted by Astronomy and Astrophysic

Distribution of parallel vortices studied by spin-polarized neutron reflectivity and magnetization

We present the studies of non-uniformly distributed vortices in Nb/Al multilayers at applied field near parallel to film surface by using spin-polarized neutron reflectivity (SPNR) and DC magnetization measurements. We have observed peaks above the lower critical field, Hc1, in the M-H curves from the multilayers. Previous works with a model calculation of minimizing Gibbs free energy have suggested that the peaks could be ascribed to vortex line transitions for spatial commensuration in a thin film superconductor. In order to directly determine the distribution of vortices, we performed SPNR measurements on the multilayer and found that the distribution and density of vortices are different at ascending and descending fields. At ascending 2000 Oe which is just below the first peak in the M-H curve, SPNR shows that vortices are mostly localized near a middle line of the film meanwhile the vortices are distributed in broader region at the descending 2000 Oe. That is related to the observation of more vortices trapped at the descending field. As the applied field is sightly tilted (< 3.5degree), we observe another peak at a smaller field. The peak position is consistent with the parallel lower critical field (Hc1||). We discuss that the vortices run along the applied field below Hc1|| and rotate parallel to the surface at Hc1||.Comment: 17 pages, 9 figure

Evidence of non-thermal X-ray emission from HH 80

Protostellar jets appear at all stages of star formation when the accretion process is still at work. Jets travel at velocities of hundreds of km/s, creating strong shocks when interacting with interstellar medium. Several cases of jets have been detected in X-rays, typically showing soft emission. For the first time, we report evidence of hard X-ray emission possibly related to non-thermal processes not explained by previous models of the post-shock emission predicted in the jet/ambient interaction scenario. HH 80 is located at the south head of the jet associated to the massive protostar IRAS 18162-2048. It shows soft and hard X-ray emission in regions that are spatially separated, with the soft X-ray emission region situated behind the region of hard X-ray emission. We propose a scenario for HH 80 where soft X-ray emission is associated to thermal processes from the interaction of the jet with denser ambient matter and the hard X-ray emission is produced by synchrotron radiation at the front shock.Comment: Accepted for publication in ApJ

Automotive Battery Charging based on Efficient Capacitive Power Transfer

Isolated power converters find application in different fields of electric mobility, such as battery charging, where galvanic insulation between on-board storage system and electrical grid is required. Conventional isolated systems are based on the use of transformers, which have the drawback to be bulky and expensive. Nevertheless, insulation implemented by capacitances can be attractive due to the recent technological advances, contributing to increasingly compact, cheap and efficient converters. In this paper, an isolated power converter based on capactive power transfer (CPT), along with the switched capacitor concept, is proposed. GaN FETs are employed as switching power devices in order to handle high operation frequencies with limited power losses. In this work a 500 kHz switching frequency has been selected, with notable benefits brought to the overall power converter in terms of compactness. The developed prototype has been experimentally tested according to a target power level of 3 kW, to prove the proper operation of the proposed converter. The experimental tests have demonstrated a power transfer efficiency as high as 95%

The extraordinary Hall effect in coherent epitaxial tau (Mn,Ni)Al thin films on GaAs

Ultrathin coherent epitaxial films of ferromagnetic tau(Mn,Ni)0.60Al0.40 have been grown by molecular beam epitaxy on GaAs substrates. X-ray scattering and cross-sectional transmission electron microscopy measurements confirm that the c axis of the tetragonal tau unit cell is aligned normal to the (001) GaAs substrate. Measurements of the extraordinary Hall effect (EHE) show that the films are perpendicularly magnetized, exhibiting EHE resistivities saturating in the range of 3.3-7.1 muOMEGA-cm at room temperature. These values of EHE resistivity correspond to signals as large as +7 and -7 mV for the two magnetic states of the film with a measurement current of 1 mA. Switching between the two magnetic states is found to occur at distinct field values that depend on the previously applied maximum field. These observations suggest that the films are magnetically uniform. As such, tau(Mn,Ni)Al films may be an excellent medium for high-density storage of binary information

Temperature and orientation dependence of kinetic roughening during homoepitaxy: A quantitative x-ray-scattering study of Ag

URL:http://link.aps.org/doi/10.1103/PhysRevB.54.17938 DOI:10.1103/PhysRevB.54.17938Kinetic roughening during homoepitaxial growth was studied for Ag(111) and Ag(001). For Ag(111), from 150 to 500 K, the rms roughness exhibits a power law, σ∝tβ over nearly three decades in thickness. β≈1/2 at low temperatures, and there is an abrupt transition to smaller values above 300 K. In contrast, Ag(001) exhibits layer-by-layer growth with a significantly smaller β. These results are the first to establish the evolution of surface roughness quantitatively for a broad thickness and temperature range, as well as for the case where growth kinetics are dominated by a step-ledge diffusion barrier.Support is acknowledged from the University of Missouri Research Board, the NSF under Contract Nos. DMR-9202528 and DMR-9623827, and the Midwest Superconductivity Consortium ~MISCON! under DOE Grant No. DE-FG02-90ER45427. The SUNY X3 beamline is supported by the DOE under Contract No. DE-FG02-86ER45231, and the NSLS is supported by the DOE, Div. of Materials Sciences and Div. of Chemical Sciences. One of us ~W.C.E.! acknowledges support from the GAANN program of the U.S. Department of Education. We thank Ian Robinson for the Ag~111! crystal

Temperature dependence of surface roughening during homoepitaxial growth on Cu(001)

URL:http://link.aps.org/doi/10.1103/PhysRevB.64.125427 DOI:10.1103/PhysRevB.64.125427X-ray scattering has been used to study the roughening of the Cu(001) surface during homoepitaxial growth, as a function of temperature. Between 370 and 160 K, the mean-square roughness σ2, obtained from specular reflectivity data, was found to increase as a power law σ2=Θ2β for coverages Θ, ranging from 3 to 96 ML. The roughening exponent β was observed to depend on the temperature of the substrate: it monotonically increases with decreasing temperature from β≈1/3 at T=370K to β≈1/2, at T=200K. At 110 K a smoother growth re-enters in the presence of a large vacancy concentration in the deposited film.Support is acknowledged from the National Science Foundation under contracts ~P.W.S.! DMR-9202528 and~P.F.M. and C.E.B.! DMR-9623827 and the Midwest Superconductivity Consortium ~MISCON! under DOE Grant No. DH-FG02-90ER45427. The SUNY X3 beamline was supported by the DOE, under Contract No. DE-FG02-86ER45231, and the NSLS was supported by the DOE, Division of Material Sciences, and Division of Chemical Sciences. We thank Ian Robinson for the Cu crystal and for valuable discussions

Temperature-dependent vacancy formation during the growth of Cu on Cu(001)

URL:http://link.aps.org/doi/10.1103/PhysRevB.66.195413 DOI:10.1103/PhysRevB.66.195413X-ray diffraction measurements show that a large number of vacancies are incorporated in thin Cu films grown on Cu(001) at low temperatures. At any given deposition temperature between 110 and 160 K, the vacancy concentration cv, obtained from reflectivity data, does not change with the coverage Θ, for 2.5ML<~Θ<~20ML. However, cv is temperature dependent: for 15-ML-thick films, grown at different temperatures, it monotonically decreases with increasing T from cv≈2% at 110 K to zero at T=160K. A different “cv vs T” dependence is observed for films grown at 110 K and then annealed at progressively higher temperatures. Here cv≈2% persists over a broad temperature interval (between 110 and 200 K) and cv exhibits a slower decrease upon heating, reaching zero at 300 K.Support is acknowledged from the National Science Foundation under Contract Nos. ~P.W.S.! DMR-9202528 and ~P.F.M., C.E.B.! DMR-9623827 and the Midwest Superconductivity Consortium ~MISCON! under DOE Grant No. DEFG02-90ER45427. The SUNY X3 beamline is supported by the DOE, under Contract No. DE-FG02-86ER45231 and the NSLS is supported by the DOE, Division of Material Sciences and Division of Chemical Sciences