Simulations of decomposition kinetics of Fe-Cr solid solutions during thermal aging

The decomposition of Fe-Cr solid solutions during thermal aging is modeled by Atomistic Kinetic Monte Carlo (AKMC) simulations, using a rigid lattice approximation with composition dependant pair interactions that can reproduce the change of sign of the mixing energy with the alloy composition. The interactions are fitted on ab initio mixing energies and on the experimental phase diagram, as well as on the migration barriers in iron and chromium rich phases. Simulated kinetics is compared with 3D atom probe and neutron scattering experiments.Comment: 6 pages, 5 figures, PTM 201

Red Supergiants in the Andromeda Galaxy (M31)

Red supergiants are a short-lived stage in the evolution of moderately massive stars (10-25Mo), and as such their location in the H-R diagram provides an exacting test of stellar evolutionary models. Since massive star evolution is strongly affected by the amount of mass-loss a star suffers, and since the mass-loss rates depend upon metallicity, it is highly desirable to study the physical properties of these stars in galaxies of various metallicities. Here we identify a sample of red supergiants in M31 (the most metal-rich of the Local Group galaxies) and derive their physical properties by fitting MARCS atmosphere models to moderate resolution optical spectroscopy, and from V-K photometry.Comment: Accepted for publication in the Astrophysical Journa

Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

We analyze far-ultraviolet spectra and ancillary data of the super star cluster SSC-N and its surrounding H II region in the nearby dwarf galaxy II Zw 40. From the ultraviolet spectrum, we derive a low internal reddening of E(B-V) = 0.07 +/- 0.03, a mass of (9.1 +/- 1.0) x 10^5 Lsol, a bolometric luminosity of (1.1 +/- 0.1) x 10^9 Lsol, a number of ionizing photons of (6 +/- 2) x 10^52 s^-1, and an age of (2.8 +/- 0.1) Myr. These parameters agree with the values derived from optical and radio data, indicating no significant obscured star formation, absorption of photons by dust, or photon leakage. SSC-N and its nebulosity are an order of magnitude more massive and luminous than 30 Doradus and its ionizing cluster. Photoionization modeling suggests a high ionization parameter and a C/O ratio where C is between primary and secondary. We calculate diagnostic emission-line ratios and compare SSC-N to local star-forming galaxies. The SSC-N nebula does not coincide with the locus defined by local galaxies. Rather, it coincides with the location of "Green Pea" galaxies, objects which are often considered nearby analogs of the galaxies reionizing the universe. Most stellar features are well-reproduced by synthetic spectra. However, the SSC-N cluster has strong, broad, stellar He II 1640 emission that cannot be reproduced, suggesting a deficit of He-enhanced stars with massive winds in the models. We discuss possible sources for the broad He II emission, including very massive stars and/or enhanced mixing processes.Comment: The Astrophysical Journal, accepte

Late-Type Red Supergiants: Too Cool for the Magellanic Clouds?

We have identified seven red supergiants (RSGs) in the Large Magellanic Cloud (LMC) and four RSGs in the Small Magellanic Cloud (SMC), all of which have spectral types that are considerably later than the average type observed in their parent galaxy. Using moderate-resolution optical spectrophotometry and the MARCS stellar atmosphere models, we determine their physical properties and place them on the H-R diagram for comparison with the predictions of current stellar evolutionary tracks. The radial velocities of these stars suggest that they are likely all members of the Clouds rather than foreground dwarfs or halo giants. Their locations in the H-R diagram also show us that those stars are cooler than the current evolutionary tracks allow, appearing to the right of the Hayashi limit, a region in which stars are no longer in hydrodynamic equilibrium. These stars exhibit considerable variability in their V magnitudes, and three of these stars also show changes in their effective temperatures (and spectral types) on the time-scales of months. One of these stars, [M2002] SMC 055188, was caught in an M4.5 I state, as late as that seen in HV 11423 at its recent extreme: considerable later, and cooler, than any other supergiant in the SMC. In addition, we find evidence of variable extinction due to circumstellar dust and changes in the stars' luminosities, also consistent with our recent findings for HV 11423 - when these stars are hotter they are also dustier and more luminous. We suggest that these stars have unusual properties because they are in an unstable (and short-lived) evolutionary phase.Comment: 26 pages, 6 figures; submitted to the Astrophysical Journa

Spin polarized liquid 3He

We have employed the constrained variational method to study the influence of spin polarization on the ground state properties of liquid $^3{\rm He}$. The spin polarized phase, we have found, has stronger correlation with respect to the unpolarized phase. It is shown that the internal energy of liquid $^3{\rm He}$ increases by increasing polarization with no crossing point between polarized and unpolarized energy curves over the liquid density range. The obtained internal energy curves show a bound state, even in the case of fully spin polarized matter. We have also investigated the validity of using a parabolic formula for calculating the energy of spin polarized liquid $^3{\rm He}$. Finally, we have compared our results with other calculations.Comment: 16 pages, 6 figure

Hypernetted-chain study of broken rotational symmetry states for the ν\bm{\nu} = 1/3 fractional quantum Hall effect and other fractionally filled Landau levels

We investigate broken rotational symmetry (BRS) states for the fractional quantum Hall effect (FQHE) at 1/3-filling of the valence Landau level (LL). Recent Monte Carlo calculations by Musaelian and Joynt [J. Phys.: Condens.\ Matter {\bf 8}, L105 (1996)] suggest that Laughlin's state becomes unstable to a BRS state for some critical finite thickness value. We study in detail the properties of such state by performing a hypernetted-chain calculation that gives results in the thermodynamic limit, complementing other methods which are limited to a finite number of particles. Our results indicate that while Laughlin's state is stable in the lowest LL, in higher LLs a BRS instability occurs, perhaps indicating the absence of FQHE at partial fillings of higher LLs. Possible connections to the newly discovered liquid crystalline phases in higher LLs are also discussed.Comment: 7 pages including 3 eps figure

MIcrogreens: Functional food with antiproliferative cancer properties influenced by light

The anti-proliferative/pro-oxidant efficacy of green pea, soybean, radish, Red Rambo radish, and rocket microgreens, cultivated under either fluorescent lighting (predominant spectral peaks in green and orange) or combination light-emitting diode (LED, predominant spectral peak in blue) was investigated using Ewing sarcoma lines, RD-ES and A673, respectively. All aqueous microgreen extracts significantly reduced cell proliferation (cancer prevention effect) to varying extents in two-dimensional sarcoma cell cultures. The effect of the polyphenol fraction in the aqueous food matrix was unrelated to total polyphenol content, which differed between species and light treatment. Only Pisum sativum (LED-grown) extracts exercised anti-proliferative and pro-apoptotic effects in both three-dimensional RD-ES and A673 spheroids (early tumor progression prevention), without cytotoxic effects on healthy L929 fibroblasts. A similar anti-tumor effect of Red Rambo radish (LED and fluorescent-grown) was evident only in the RD-ES spheroids. Aside from the promising anti-tumor potential of the polyphenol fraction of green pea microgreens, the latter also displayed favorable growth quality parameters, along with radish, under both light treatments over the 10 day cultivation period

Monte Carlo simulation method for Laughlin-like states in a disk geometry

We discuss an alternative accurate Monte Carlo method to calculate the ground-state energy and related quantities for Laughlin states of the fractional quantum Hall effect in a disk geometry. This alternative approach allows us to obtain accurate bulk regime (thermodynamic limit) values for various quantities from Monte Carlo simulations with a small number of particles (much smaller than that needed with standard Monte Carlo approaches).Comment: 13 pages, 6 figures, 2 table