Spot activity of the RS CVn star {\sigma} Geminorum

We model the photometry of RS CVn star $\sigma$ Geminorum to obtain new information on the changes of the surface starspot distribution, i.e., activity cycles, differential rotation and active longitudes. We use the previously published Continuous Periods Search-method (CPS) to analyse V-band differential photometry obtained between the years 1987 and 2010 with the T3 0.4 m Automated Telescope at the Fairborn Observatory. The CPS-method divides data into short subsets and then models the light curves with Fourier-models of variable orders and provides estimates of the mean magnitude, amplitude, period and light curve minima. These light curve parameters are then analysed for signs of activity cycles, differential rotation and active longitudes. We confirm the presence of two previously found stable active longitudes, synchronised with the orbital period $P_{\rm{orb}}=19.60$d and find eight events where the active longitudes are disrupted. The epochs of the primary light curve minima rotate with a shorter period $P_{\rm{min,1}}=19.47$d than the orbital motion. If the variations in the photometric rotation period were to be caused by differential rotation, this would give a differential rotation coefficient of $\alpha \ge 0.103$. The presence of two slightly different periods of active regions may indicate a superposition of two dynamo modes, one stationary in the orbital frame and the other one propagating in the azimuthal direction. Our estimate of the differential rotation is much higher than previous results. However, simulations show that this can be caused by insufficient sampling in our data.Comment: 10 pages, 6 figures. Submitted to A&

Schwarzchild Black Holes in Matrix Theory II

We present a crude Matrix Theory model for Schwarzchild black holes in uncompactified dimension greater than $5$. The model accounts for the size, entropy, and long range state interactions of black holes. The key feature of the model is a Boltzmann gas of D0 branes, a concept which depends on certain qualitative features of Matrix Theory which have not previously been utilized in studies of black holes.Comment: 20 pages,harvmac,big, Some Typos corrected, 1 reference adde

Discovery of Griffiths phase in itinerant magnetic semiconductor Fe_{1-x}Co_xS_2

Critical points that can be suppressed to zero temperature are interesting because quantum fluctuations have been shown to dramatically alter electron gas properties. Here, the metal formed by Co doping the paramagnetic insulator FeS$_2$, Fe$_{1-x}$Co$_x$S$_2$, is demonstrated to order ferromagnetically at $x>x_c=0.01\pm0.005$ where we observe unusual transport, magnetic, and thermodynamic properties. We show that this magnetic semiconductor undergoes a percolative magnetic transition with distinct similarities to the Griffiths phase, including singular behavior at $x_c$ and zero temperature.Comment: 10 pages, 4 figure

Lensing Effects on the Protogalaxy Candidate cB58 and their Implications for the Cosmological Constant

The amplification of the protogalaxy candidate cB58 due to gravitational lensing by the foreground cluster of galaxies MS1512.4+3647 is quantified based on recent ROSAT and ASCA X-ray observations. It is found that the amplification is at most 25 for any reasonable cosmological model with or without cosmological constant. It is also argued that the system may be used to place new constraints on the value of the cosmological constant. The gas mass fraction for this cluster is found to be about 0.2.Comment: LaTex, 9 pages, 9 figures, uses aas2pp4.sty, Accepted for publication in Ap

Quantum Monte Carlo method using phase-free random walks with Slater determinants

We develop a quantum Monte Carlo method for many fermions that allows the use of any one-particle basis. It projects out the ground state by random walks in the space of Slater determinants. An approximate approach is formulated to control the phase problem with a trial wave function $|\Psi_T>$. Using plane-wave basis and non-local pseudopotentials, we apply the method to Si atom, dimer, and 2, 16, 54 atom (216 electrons) bulk supercells. Single Slater determinant wave functions from density functional theory calculations were used as $|\Psi_T>$ with no additional optimization. The calculated binding energy of Si2 and cohesive energy of bulk Si are in excellent agreement with experiments and are comparable to the best existing theoretical results.Comment: 5 pages, Latex, with 1 fi

The LyAlpha Line Profiles of Ultraluminous Infrared Galaxies: Fast Winds and Lyman Continuum Leakage

We present new Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet (far-UV) spectroscopy and Keck Echellete optical spectroscopy of 11 ultraluminous infrared galaxies (ULIRGs), a rare population of local galaxies experiencing massive gas inflows, extreme starbursts, and prominent outflows. We detect H Lyman alpha emission from 8 ULIRGs and the companion to IRAS09583+4714. In contrast to the P Cygni profiles often seen in galaxy spectra, the H Lyman alpha profiles exhibit prominent, blueshifted emission out to Doppler shifts exceeding -1000 km/s in three HII-dominated and two AGN-dominated ULIRGs. To better understand the role of resonance scattering in shaping the H Lyman alpha line profiles, we directly compare them to non-resonant emission lines in optical spectra. We find that the line wings are already present in the intrinsic nebular spectra, and scattering merely enhances the wings relative to the line core. The H Lyman alpha attenuation (as measured in the COS aperture) ranges from that of the far-UV continuum to over 100 times more. A simple radiative transfer model suggests the H Lyman alpha photons escape through cavities which have low column densities of neutral hydrogen and become optically thin to the Lyman continuum in the most advanced mergers. We show that the properties of the highly blueshifted line wings on the H Lyman alpha and optical emission-line profiles are consistent with emission from clumps of gas condensing out of a fast, hot wind. The luminosity of the H Lyman alpha emission increases non-linearly with the ULIRG bolometric luminosity and represents about 0.1 to 1% of the radiative cooling from the hot winds in the HII-dominated ULIRGs.Comment: Submitted to Ap

Investigation of DC-8 nacelle modifications to reduce fan-compressor noise in airport communities. Part 2 - Design studies and duct-lining investigations, May 1967 - October 1969

Modifications to reduce fan-compressor noise level of DC-8 aircraft - Part