26,243 research outputs found
Intrinsic interface exchange coupling of ferromagnetic nanodomains in a charge ordered manganite
We present a detailed magnetic study of the Pr1/3Ca2/3MnO3 manganite, where
we observe the presence of small ferromagnetic (FM) domains (diameter ~ 10A)
immersed within the charge-ordered antiferromagnetic (AFM) host. Due to the
interaction of the FM nanodroplets with a disordered AFM shell, the
low-temperature magnetization loops present exchange bias (EB) under cooling in
an applied magnetic field. Our analysis of the cooling field dependence of the
EB yields an antiferromagnetic interface exchange coupling comparable to the
bulk exchange constant of the AFM phase. We also observe training effect of the
EB, which is successfully described in terms of a preexisting relaxation model
developed for other classical EB systems. This work provides the first evidence
of intrinsic interface exchange coupling in phase separated manganites.Comment: 7 pages, 6 figure
The effect of Mach number on unstable disturbances in shock/boundary-layer interactions
The effect of Mach number on the growth of unstable disturbances in a boundary layer undergoing a strong interaction with an impinging oblique shock wave is studied by direct numerical simulation and linear stability theory (LST). To reduce the number of independent parameters, test cases are arranged so that both the interaction location Reynolds number (based on the distance from the plate leading edge to the shock impingement location for a corresponding inviscid flow) and the separation bubble length Reynolds number are held fixed. Small-amplitude disturbances are introduced via both white-noise and harmonic forcing and, after verification that the disturbances are convective in nature, linear growth rates are extracted from the simulations for comparison with parallel flow LST and solutions of the parabolized stability equations (PSE). At Mach 2.0, the oblique modes are dominant and consistent results are obtained from simulation and theory. At Mach 4.5 and Mach 6.85, the linear Navier-Stokes results show large reductions in disturbance energy at the point where the shock impinges on the top of the separated shear layer. The most unstable second mode has only weak growth over the bubble region, which instead shows significant growth of streamwise structures. The two higher Mach number cases are not well predicted by parallel flow LST, which gives frequencies and spanwise wave numbers that are significantly different from the simulations. The PSE approach leads to good qualitative predictions of the dominant frequency and wavenumber at Mach 2.0 and 4.5, but suffers from reduced accuracy in the region immediately after the shock impingement. Three-dimensional Navier-Stokes simulations are used to demonstrate that at finite amplitudes the flow structures undergo a nonlinear breakdown to turbulence. This breakdown is enhanced when the oblique-mode disturbances are supplemented with unstable Mack modes
Disks around massive young stellar objects: are they common?
We present K-band polarimetric images of several massive young stellar
objects at resolutions 0.1-0.5 arcsec. The polarization vectors around
these sources are nearly centro-symmetric, indicating they are dominating the
illumination of each field. Three out of the four sources show elongated
low-polarization structures passing through the centers, suggesting the
presence of polarization disks. These structures and their surrounding
reflection nebulae make up bipolar outflow/disk systems, supporting the
collapse/accretion scenario as their low-mass siblings. In particular, S140
IRS1 show well defined outflow cavity walls and a polarization disk which
matches the direction of previously observed equatorial disk wind, thus
confirming the polarization disk is actually the circumstellar disk. To date, a
dozen massive protostellar objects show evidence for the existence of disks;
our work add additional samples around MYSOs equivalent to early B-type stars.Comment: 9 pages, including 2 figures, 1 table, to appear on ApJ
Phase equilibrium in two orbital model under magnetic field
The phase equilibrium in manganites under magnetic field is studied using a
two orbital model, based on the equivalent chemical potential principle for the
competitive phases. We focus on the magnetic field induced melting process of
CE phase in half-doped manganites. It is predicted that the homogenous CE phase
begins to decompose into coexisting ferromagnetic phase and CE phase once the
magnetic field exceeds the threshold field. In a more quantitative way, the
volume fractions of the two competitive phases in the phase separation regime
are evaluated.Comment: 4 pages, 4 figure
Precise dispersive data analysis of the f0(600) pole
We review how the use of recent precise data on kaon decays together with
forward dispersion relations (FDR) and Roy's equations allow us to determine
the sigma resonance pole position very precisely, by using only experimental
input. In addition, we present preliminary results for a modified set of
Roy-like equations with only one subtraction, that show a remarkable
improvement in the precision around the sigma region. We also improve the
matching between the parametrizations at low and intermediate energy of the S0
wave, and show that the effect of this on the sigma pole position is
negligible.Comment: 4 pages, 1 figure. To appear in the proceedings of the Meson 2008
conference, June 6-10, Cracow, Polan
A Centimeter-Sized Quaternary Ti-Zr-Be-Ag Bulk Metallic Glass
A novel centimeter-sized Ti-based bulk metallic glass (BMG) was developed by the addition of Ag in the ternary Ti41Zr25Be34 glassy alloy. By replacing Be with Ag, the glass forming ability (GFA), the yield strength, and the supercooled liquid temperature of the quaternary Ti41Zr25Be34âxAgx (x=2, 4, 6, 8 at.%) glassy alloys have been obviously enhanced. Among the developed Ti-Zr-Be-Ag alloy systems, the Ti41Zr25Be28Ag6 alloy possesses the largest critical diameter (Dmax) of 10âmm, while the yield strength is also enhanced to 1961âMPa, which is much larger than that of Ti41Zr25Be34 (1755âMPa) alloy. The experimental results show that Ag is an effective element for improving the GFA and the yield strength of Ti-Zr-Be glassy alloy
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