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[en] In 1975, E. R. Robinson conducted the hallmark study of the behavior of classical nova light curves before eruption, and this work has now become part of the standard knowledge of novae. He made three points: 5 out of 11 novae showed pre-eruption rises in the years before eruption, one nova (V446 Her) showed drastic changes in the variability across eruptions, and all but one of the novae (excepting BT Mon) have the same quiescent magnitudes before and after the outburst. This work has not been tested since it came out. We have now tested these results by going back to the original archival photographic plates and measuring large numbers of pre-eruption magnitudes for many novae using comparison stars on a modern magnitude scale. We find in particular that four out of five claimed pre-eruption rises are due to simple mistakes in the old literature, that V446 Her has the same amplitude of variations across its 1960 eruption, and that BT Mon has essentially unchanged brightness across its 1939 eruption. Out of 22 nova eruptions, we find two confirmed cases of significant pre-eruption rises (for V533 Her and V1500 Cyg), while T CrB has a deep pre-eruption dip. These events are a challenge to theorists. We find no significant cases of changes in variability across 27 nova eruptions beyond what is expected due to the usual fluctuations seen in novae away from eruptions. For 30 classical novae plus 19 eruptions from 6 recurrent novae, we find that the average change in magnitude from before the eruption to long after the eruption is 0.0 mag. However, we do find five novae (V723 Cas, V1500 Cyg, V1974 Cyg, V4633 Sgr, and RW UMi) that have significantly large changes, in that the post-eruption quiescent brightness level is over ten times brighter than the pre-eruption level. These large post-eruption brightenings are another challenge to theorists.
[en] We present nulling interferometric observations of six nearby main-sequence stars (α CrB, α Lyr, β Leo, γ Ser, ε Eri, and ζ Lep). None of the stars show evidence for a positive detection of warm debris in the habitable zone of the systems. Using a scaled up model of solar zodiacal emission, the 3σ upper limits on dust density range from 220 to 104 Zody (1 Zody = the density of our own solar zodiacal cloud) depending on the particular star, corresponding to mass limits of 10-7 to 10-5 M + of micron-sized dust. These limits contrast with the presence of dust at greater separations from the star, implying a clearing in dust in the inner system. This suggests that the inner circumstellar environment around nearby intermediate-mass main-sequence stars more than several tens of millions of years old are generally cleared of dusty debris. Finally, the well studied nature of the debris disks around Vega, ε Eridani, and ζ Leporis allows us to place these 10 μm nulling observations in the context of previous studies to determine the physical processes responsible for shaping the debris disk in these particular systems.
[en] Properties of CrB2 thin diffusion layers sputtered in Mo/Si multilayer structures and their effect on the x-ray/EUV reflectance are reported. A special attention is paid to determine a critical thickness t* for barrier layers where they isolate parent layers of Mo and Si completely and to reveal the degree of interaction of the barrier material with parent materials. A dependence of t* on the deposition rate of CrB2 is found. CrSi2 and B3Si are established as the most probable phases formed in the barrier layers. The diffusion coefficients and temperature during formation of CrB2 are estimated. The use of thin CrB2 barriers is shown to be profitable in a fabrication of the EUV mirrors with enhanced reflectivity. (paper)
[en] Energy bands of CrB2 were calculated using the Korringa--Kohn--Rostoker method in the muffin-tin-potential approximation. The bands near the Fermi level have mostly Cr d character, and one of the bands gives rise to a very flat piece of Fermi surface perpendicular to the hexagonal axis. It is proposed that this piece of Fermi surface stabilizes a spin-density-wave state which manifests itself as antiferromagnetic ordering of the compound below 850K. The excess specific heat and electronic-spin susceptibility is also interpreted as due to exchange enhancement. (9 figures)
[en] Embedded aluminum-steel composite sheet was produced by cold roll bonding (CRB), and the interface formation process and the bonding mechanism in the CRBed deformation zone of the composite sheet were studied. The interface microstructure evolution in the deformation zone of the composite sheet produced under a typical experiment condition (0.5 mm thick aluminum sheet, 3.75 mm thick steel sheet and a rolling reduction of 65%) was analyzed. When the deformation amount in the deformation zone was less than 35%, the aluminum layer and the steel layer were combined mainly by mechanical bonding and a wavy interface formed. When the deformation amount increased to 50%, a dozen nanometers thick diffusion layer of Al and Fe atoms which contained ~ 2 nm thick amorphous layer formed at the interface, indicating that a certain extent of metallurgical bonding at the interface was achieved. Instead of deformation-induced heat, severe shear deformation at the interface generated during CRB was mainly responsible for forming amorphous layer and achieving metallurgical bonding at the aluminum/steel interface. When the thickness of the aluminum sheet reduced from 1.0 to 0.10 mm, the reduction required for achieving preliminary metallurgical bonding decreased from 60% to 40%. Decreasing the thickness of aluminum sheet can induce the increase of interfacial shear deformation, which was favorable for improving the metallurgical bonding of the composite sheet.
[en] Interaction of LaB6 with CrB2 was stUdied within a wide range of temperatures and concentrations. An eutectic phase diagram of the LaB6-CrB2 system characteriszed by the absence of mutual component solubility is plotted coming from the data of X-ray, metallographic analyses, determination of the temperature of alloy melting start, microhardness of phase constituents. Eutectic transformation temperature is 2150+-30 deg C, eutectic composition corresponds to the alloy with 50% CrB2
[en] Chromium diboride thin films possess desirable combinations of properties (such as high hardness, wear resistance, chemical inertness, high thermal and electrical conductivity), which are attractive for a wide range of potential industrial applications. However, these properties depend strongly on the deposition process and parameters. Investigation of the resultant coating structures could explain certain differences between them, giving important information about the characteristics of the deposition process (which in this particular case is a recently developed method involving magnetron sputtering of loosely packed blended powder targets) and pointing out directions for improvement. In this paper, Cr-B coatings deposited by direct current (DC) and DC-pulse magnetron sputtering of loosely packed blended powder targets are characterised by transmission electron microscopy (TEM) techniques (electron diffraction and bright-field/dark-field imaging). The structures of the coatings deposited with different parameters are investigated and compared, and the effect of oxygen contamination on the structure is discussed. Coatings with an extremely fine, nanocolumnar structure were observed. DC sputter deposited (and generally non-stoichiometric) Cr-B coatings exhibit a short range ordered 'zone T' microstructure, while DC-pulse deposited stoichiometric CrB2 coatings are dense and defect-free, crystalline and show strong preferred orientation. A small amount of contamination by oxygen of the interfacial sub-layers (due to the target material being a powder) of the DC-pulse magnetron sputter deposited stoichiometric CrB2 (and near-stoichiometric CrB) coatings was found to affect the structure by suppressing nanocolumnar growth and promoting equiaxed, nanometer-sized grains, close to the coating/substrate interface. The majority of the coating however remained nanocolumnar