Uniaxial pressure dependence of magnetic order in MnSi

We report comprehensive small angle neutron scattering (SANS) measurements complemented by ac susceptibility data of the helical order, conical phase and skyrmion lattice phase (SLP) in MnSi under uniaxial pressures. For all crystallographic orientations uniaxial pressure favours the phase for which a spatial modulation of the magnetization is closest to the pressure axis. Uniaxial pressures as low as 1kbar applied perpendicular to the magnetic field axis enhance the skyrmion lattice phase substantially, whereas the skyrmion lattice phase is suppressed for pressure parallel to the field. Taken together we present quantitative microscopic information how strain couples to magnetic order in the chiral magnet MnSi.Comment: 23 pages, includes supplemen

Wavelength calibration of the JWST-MIRI medium resolution spectrometer

We present the wavelength and spectral resolution characterisation of the Integral Field Unit (IFU) Medium Resolution Spectrometer for the Mid-InfraRed Instrument (MIRI), to fly onboard the James Webb Space Telescope in 2014. We use data collected using the Verification Model of the instrument and develop an empirical method to calibrate properties such as wavelength range and resolving power in a portion of the spectrometer's full spectral range (5-28 microns). We test our results against optical models to verify the system requirements and combine them with a study of the fringing pattern in the instrument's detector to provide a more accurate calibration. We show that MIRI's IFU spectrometer will be able to produce spectra with a resolving power above R=2800 in the wavelength range 6.46-7.70 microns, and that the unresolved spectral lines are well fitted by a Gaussian profile.Comment: 12 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wav

EVALUATING PEN-DAY INTERACTIONS IN BODY TEMPERATURE BILOGISTIC MIXED MODEL FOR HANDLING OF FEEDLOT HEIFERS DURING HEAT STRESS

Daily activities consume the energy of heifers, subsequently causing an elevation of body temperature, depending on the ambient conditions. A better understanding of the dynamics of body temperature (Tb) would be helpful when deciding how to process and handle heifers. It would also lead to specific recommendations on moving heifers under different ambient conditions, especially during the summer. In this study, a bilogistic mixed model is used to describe the dynamics of Tb during the moving event. Data was taken from heifers in pens located at different distances from the heifer work station on four separate summer days under hot conditions. This bilogistic model has seven biological parameters: initial body temperature, heat challenge rate constant, upper asymptote body temperature, challenge inflection point, baseline body temperature for recovery, recovery rate constant, and recovery inflection point. Pen and day were used as treatment factors in the model. Significant interactions between the factors were found for several parameters, indicating distance moved during the handling event influences the way an animal responds to a thermal challenge. The objectives of this study are to fit a bilogistic mixed model for Tb with the above seven parameters, and to examine fixed and random effects. The main focus is to estimate and interpret the interactions between pens and days for the significant parameters to aid in management decisions involving when to work cattle

USING FUNCTIONAL DATA ANALYSIS TO EVALUATE EFFECT OF SHADE ON BODY TEMPERATURE OF FEEDLOT HEIFERS DURING ENVIRONMENTAL HEAT STRESS

Heat stress can be a serious problem for cattle. Body temperature (Tb) is a good measure of an animal’s thermo-regulatory response to an environmental thermal challenge. Previous studies found that Tb increases in response to increasing ambient temperature in a controlled chamber. However, when animals are in an uncontrolled environment, Tb is subject to many uncontrolled environmental factors, such as sunshade, wind, and humidity, that increase variation in the data. Hence, functional data analysis (FDA) was applied to analyze the data with uncontrolled environmental factors as curves in the whole series of days in this study. Breed (Angus, MARCIII, MARC-I, Charolais) and availability of shade (access versus no access to sunshade) were included as treatment factors in the statistical model. This study illustrates the potential of FDA to retain all information in the curves. The specific objectives are to use FDA to smooth Tb with large noise, to detect treatment effects on Tb, and to assess the interactions between breed and availability of shade with functional regression coefficients. The results show that FDA can be used to detect significant treatment interactions that may otherwise remain undetected using regular linear or nonlinear models. Significant interactions were found, indicating that access to sun-shade influences the way animals respond to a thermal challenge. Overall, it was found that breeds of cattle with dark-hides were more affected by temperature changes and peak temperatures than breeds of cattle with light-hides. Angus cattle (black) had the highest body temperatures in both shade and no shade areas, while Charolais (white) had the lowest body temperatures in the no shade area. However, MARC III (dark red) experienced the largest temperature differential between shade and no shade. Therefore, breed and availability of shade interactions are important considerations when making predictions to aid in management decisions involving feedlot cattle

A First Estimate Of The X-Ray Binary Frequency As A Function Of Star Cluster Mass In A Single Galactic System

We use the previously-identified 15 infrared star-cluster counterparts to X-ray point sources in the interacting galaxies NGC 4038/4039 (the Antennae) to study the relationship between total cluster mass and X-ray binary number. This significant population of X-Ray/IR associations allows us to perform, for the first time, a statistical study of X-ray point sources and their environments. We define a quantity, \eta, relating the fraction of X-ray sources per unit mass as a function of cluster mass in the Antennae. We compute cluster mass by fitting spectral evolutionary models to K_s luminosity. Considering that this method depends on cluster age, we use four different age distributions to explore the effects of cluster age on the value of \eta and find it varies by less than a factor of four. We find a mean value of \eta for these different distributions of \eta = 1.7 x 10^-8 M_\sun^-1 with \sigma_\eta = 1.2 x 10^-8 M_\sun^-1. Performing a \chi^2 test, we demonstrate \eta could exhibit a positive slope, but that it depends on the assumed distribution in cluster ages. While the estimated uncertainties in \eta are factors of a few, we believe this is the first estimate made of this quantity to ``order of magnitude'' accuracy. We also compare our findings to theoretical models of open and globular cluster evolution, incorporating the X-ray binary fraction per cluster.Comment: 20 pages, 6 figures, accepted by Ap

Observed Limits on Charge Exchange Contributions to the Diffuse X-ray Background

We present a high resolution spectrum of the diffuse X-ray background from 0.1 to 1 keV for a ~1 region of the sky centered at l=90, b=+60 using a 36-pixel array of microcalorimeters flown on a sounding rocket. With an energy resolution of 11 eV FWHM below 1 keV, the spectrum's observed line ratios help separate charge exchange contributions originating within the heliosphere from thermal emission of hot gas in the interstellar medium. The X-ray sensitivity below 1 keV was reduced by about a factor of four from contamination that occurred early in the flight, limiting the significance of the results. The observed centroid of helium-like O VII is 568+2-3 eV at 90% confidence. Since the centroid expected for thermal emission is 568.4 eV while for charge exchange is 564.2 eV, thermal emission appears to dominate for this line complex, consistent with much of the high-latitude O VII emission originating in 2-3 x 10^6 K gas in the Galactic halo. On the other hand, the observed ratio of C VI Ly gamma to Ly alpha is 0.3+-0.2. The expected ratios are 0.04 for thermal emission and 0.24 for charge exchange, indicating that charge exchange must contribute strongly to this line and therefore potentially to the rest of the ROSAT R12 band usually associated with 10^6 K emission from the Local Hot Bubble. The limited statistics of this experiment and systematic uncertainties due to the contamination require only >32% thermal emission for O VII and >20% from charge exchange for C VI at the 90% confidence level. An experimental gold coating on the silicon substrate of the array greatly reduced extraneous signals induced on nearby pixels from cosmic rays passing through the substrate, reducing the triggered event rate by a factor of 15 from a previous flight of the instrument.Comment: 14 pages, 7 figures, to be published in Ap

HST/WFPC2 and VLT/ISAAC observations of PROPLYDS in the giant HII region NGC 3603

We report the discovery of three proplyd-like structures in the giant HII region NGC 3603. The emission nebulae are clearly resolved in narrow-band and broad-band HST/WFPC2 observations in the optical and broad-band VLT/ISAAC observations in the near-infrared. All three nebulae are tadpole shaped, with the bright ionization front at the head facing the central cluster and a fainter ionization front around the tail pointing away from the cluster. Typical sizes are 6,000 A.U. x 20,000 A.U. The nebulae share the overall morphology of the proplyds (``PROto PLanetarY DiskS'') in Orion, but are 20 to 30 times larger in size. Additional faint filaments located between the nebulae and the central ionizing cluster can be interpreted as bow shocks resulting from the interaction of the fast winds from the high-mass stars in the cluster with the evaporation flow from the proplyds. The striking similarity of the tadpole shaped emission nebulae in NGC 3603 to the proplyds in Orion suggests that the physical structure of both types of objects might be the same. We present 2D radiation hydrodynamical simulations of an externally illuminated star-disk-envelope system, which was still in its main accretion phase when first exposed to ionizing radiation from the central cluster. The simulations reproduce the overall morphology of the proplyds in NGC 3603 very well, but also indicate that mass-loss rates of up to 10^-5 Mo/yr are required in order to explain the size of the proplyds. (abbreviated)Comment: 10 pages, 4 Postscript figures, uses emulateapj.sty and psfig.tex. Astronomical Journal, in press (January 2000 issue

The Luminosity & Mass Function of the Trapezium Cluster: From B stars to the Deuterium Burning Limit

We use the results of a new, multi-epoch, multi-wavelength, near-infrared census of the Trapezium Cluster in Orion to construct and to analyze the structure of its infrared (K band) luminosity function. Specifically, we employ an improved set of model luminosity functions to derive this cluster's underlying Initial Mass Function (IMF) across the entire range of mass from OB stars to sub-stellar objects down to near the deuterium burning limit. We derive an IMF for the Trapezium Cluster that rises with decreasing mass, having a Salpeter-like IMF slope until near ~0.6 M_sun where the IMF flattens and forms a broad peak extending to the hydrogen burning limit, below which the IMF declines into the sub-stellar regime. Independent of the details, we find that sub-stellar objects account for no more than ~22% of the total number of likely cluster members. Further, the sub-stellar Trapezium IMF breaks from a steady power-law decline and forms a significant secondary peak at the lowest masses (10-20 times the mass of Jupiter). This secondary peak may contain as many as \~30% of the sub-stellar objects in the cluster. Below this sub-stellar IMF peak, our KLF modeling requires a subsequent sharp decline toward the planetary mass regime. Lastly, we investigate the robustness of pre-main sequence luminosity evolution as predicted by current evolutionary models, and we discuss possible origins for the IMF of brown dwarfs.Comment: 74 pages, 30 figures, AASTeX5.0. To be published in the 01 July 2002 ApJ. For color version of figure 1 and online data table see http://www.astro.ufl.edu/~muench/PUB/publications.htm

Core Formation by a Population of Massive Remnants

Core radii of globular clusters in the Large and Small Magellanic Clouds show an increasing trend with age. We propose that this trend is a dynamical effect resulting from the accumulation of massive stars and stellar-mass black holes at the cluster centers. The black holes are remnants of stars with initial masses exceeding 20-25 solar masses; as their orbits decay by dynamical friction, they heat the stellar background and create a core. Using analytical estimates and N-body experiments, we show that the sizes of the cores so produced and their growth rates are consistent with what is observed. We propose that this mechanism is responsible for the formation of cores in all globular clusters and possibly in other systems as well.Comment: 5 page