Low gravity phase separator

An apparatus is described for phase separating a gas-liquid mixture as might exist in a subcritical cryogenic helium vessel for cooling a superconducting magnet at low gravity such as in planetary orbit, permitting conservation of the liquid and extended service life of the superconducting magnet

Cosmology today-A brief review

This is a brief review of the standard model of cosmology. We first introduce the FRW models and their flat solutions for energy fluids playing an important role in the dynamics at different epochs. We then introduce different cosmological lengths and some of their applications. The later part is dedicated to the physical processes and concepts necessary to understand the early and very early Universe and observations of it.Comment: 25 pages, 2 figures, v2: a typo correcte

Phloem anatomy of the Carboniferous pteridosperm Medullosa and evolutionary trends in gymnosperm phloem

This is the published version.Secondary phloem anatomy is detailed for four species of Medullosa from various coal ball localities in North America, ranging from Lower-Middle to Upper Pennsylvanian. The zone of secondary phloem can be up to 3.7 mm wide and consists of alternating, tangential bands of sieve cells, phloem fibers, and axial parenchyma separated by parenchymatous rays. Fibers are up to 4.2 mm long, thick walled, and in bands up to five cells wide radially and two to three cells tangentially. Phloem parenchyma cells are generally much smaller in diameter than either the sieve elements or the fibers and occur in bands as wide as 12 cell layers. Sieve cells are up to 4.2 mm long, with circular-oval sieve areas on the radial walls. The sieve areas are relatively uncrowded and contain a number of dark spots interpreted as callose deposits. Some deposits completely cover individual sieve pores, while others appear to line the sieve pores. Phloem anatomy in Medullosa is compared with that in other genera of Paleozoic seed fems and extant gymnosperms

Secondary phloem anatomy in Callistophyton boyssetii (Renault) Rothwell and histological changes in the outer phloem

This is the published version.Specimens with well-preserved phloem tissues of the pteridosperm Callistophyton boyssetii from coal balls in the Herrin no. 6 Coal of Illinois and the Bevier Coal of Kansas are described. The secondary phloem consists of alternating tangential bands of sieve cells and parenchyma, separated by vascular rays. Secretory cells are scattered throughout the secondary phloem, and bundles of presumed primary phloem are evenly distributed in the cortex. Histological differences between the inner (presumably functional) and the outer (presumably nonfunctional) phloem are described: changes in cell shape, thickening of cell walls, and deposition of dark-colored cell contents. In contrast to living plants, both parenchyma cells and conducting elements appear to undergo these changes. Phloem anatomy and developmental changes in the outer phloem in Callistophyton are compared with those in other Carboniferous seed ferns and extant gymnosperms

Angular Power Spectrum of the Microwave Background Anisotropy seen by the COBE Differential Microwave Radiometer

The angular power spectrum estimator developed by Peebles (1973) and Hauser & Peebles (1973) has been modified and applied to the 2 year maps produced by the COBE DMR. The power spectrum of the real sky has been compared to the power spectra of a large number of simulated random skies produced with noise equal to the observed noise and primordial density fluctuation power spectra of power law form, with $P(k) \propto k^n$. Within the limited range of spatial scales covered by the COBE DMR, corresponding to spherical harmonic indices 3 \leq \ell \lsim 30, the best fitting value of the spectral index is $n = 1.25^{+0.4}_{-0.45}$ with the Harrison-Zeldovich value $n = 1$ approximately 0.5$\sigma$ below the best fit. For 3 \leq \ell \lsim 19, the best fit is $n = 1.46^{+0.39}_{-0.44}$. Comparing the COBE DMR $\Delta T/T$ at small $\ell$ to the $\Delta T/T$ at $\ell \approx 50$ from degree scale anisotropy experiments gives a smaller range of acceptable spectral indices which includes $n = 1$.Comment: 22 pages of LaTex using aaspp.sty and epsf.sty with appended Postscript figures, COBE Preprint 94-0

Contribution of Extragalactic Infrared Sources to CMB Foreground Anisotropy

We estimate the level of confusion to Cosmic Microwave Background anisotropy measurements caused by extragalactic infrared sources. CMB anisotropy observations at high resolution and high frequencies are especially sensitive to this foreground. We use data from the COBE satellite to generate a Galactic emission spectrum covering mm and sub-mm wavelengths. Using this spectrum as a template, we predict the microwave emission of the 5319 brightest infrared galaxies seen by IRAS. We simulate skymaps over the relevant range of frequencies (30-900 GHz) and instrument resolutions (10'-10 degrees Full Width Half Max). Analysis of the temperature anisotropy of these skymaps shows that a reasonable observational window is available for CMB anisotropy measurements.Comment: 14 pages (LaTex source), 3 PostScript figures. Final version, to appear in ApJLetters May 1. Expanded discussion of systematic error

The Dipole Observed in the COBE DMR Four-Year Data

The largest anisotropy in the cosmic microwave background (CMB) is the $\approx 3$ mK dipole assumed to be due to our velocity with respect to the CMB. Using the four year data set from all six channels of the COBE Differential Microwave Radiometers (DMR), we obtain a best-fit dipole amplitude $3.358 \pm 0.001 \pm 0.023$ mK in the direction $(l,b)=(264\deg.31 \pm 0\deg.04 \pm 0\deg.16, +48\deg.05 \pm 0\deg.02 \pm 0\deg.09)$, where the first uncertainties are statistical and the second include calibration and combined systematic uncertainties. This measurement is consistent with previous DMR and FIRAS resultsComment: New and improved version; to be published in ApJ next mont

Search For Unresolved Sources In The COBE-DMR Two-Year Sky Maps

We have searched the temperature maps from the COBE Differential Microwave Radiometers (DMR) first two years of data for evidence of unresolved sources. The high-latitude sky (|b| > 30\deg) contains no sources brighter than 192 uK thermodynamic temperature (322 Jy at 53 GHz). The cumulative count of sources brighter than threshold T, N(> T), is consistent with a superposition of instrument noise plus a scale-invariant spectrum of cosmic temperature fluctuations normalized to Qrms-PS = 17 uK. We examine the temperature maps toward nearby clusters and find no evidence for any Sunyaev-Zel'dovich effect, \Delta y < 7.3 x 10^{-6} (95% CL) averaged over the DMR beam. We examine the temperature maps near the brightest expected radio sources and detect no evidence of significant emission. The lack of bright unresolved sources in the DMR maps, taken with anisotropy measurements on smaller angular scales, places a weak constraint on the integral number density of any unresolved Planck-spectrum sources brighter than flux density S, n(> S) < 2 x 10^4 (S/1 Jy)^{-2} sr^{-1}.Comment: 16 pages including 2 figures, uuencoded PostScript, COBE preprint 94-0