2 research outputs found
The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of the Warm and Cold Neutral Media
We use the Gaussian-fit results of Paper I to investigate the properties of
interstellar HI in the Solar neighborhood. The Warm and Cold Neutral Media (WNM
and CNM) are physically distinct components. The CNM spin temperature histogram
peaks at about 40 K. About 60% of all HI is WNM. At z=0, we derive a volume
filling fraction of about 0.50 for the WNM; this value is very rough. The
upper-limit WNM temperatures determined from line width range upward from about
500 K; a minimum of about 48% of the WNM lies in the thermally unstable region
500 to 5000 K. The WNM is a prominent constituent of the interstellar medium
and its properties depend on many factors, requiring global models that include
all relevant energy sources, of which there are many. We use Principal
Components Analysis, together with a form of least squares fitting that
accounts for errors in both the independent and dependent parameters, to
discuss the relationships among the four CNM Gaussian parameters. The spin
temperature T_s and column density N(HI) are, approximately, the two most
important eigenvectors; as such, they are sufficient, convenient, and
physically meaningful primary parameters for describing CNM clouds. The Mach
number of internal macroscopic motions for CNM clouds is typically 2.5, but
there are wide variations. We discuss the historical tau-T_s relationship in
some detail and show that it has little physical meaning. We discuss CNM
morphology using the CNM pressure known from UV stellar absorption lines.
Knowing the pressure allows us to show that CNM structures cannot be isotropic
but instead are sheetlike, with length-to-thickness aspect ratios ranging up to
about 280. We present large-scale maps of two regions where CNM lies in very
large ``blobby sheets''.Comment: Revised submission to Ap.J. Changes include: (1) correction of
turbulent Mach number in equation 16 and figure 12; the new typical value is
1.3 versus the old, incorrect value 2.5. (2) smaller typeface for the
astro-ph version to conserve paper. 60 pages, 16 figure
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The overall objective of this project is the three-phase development of an Early Entrance Coproduction Plant (EECP) that produces at least one product from at least two of the following three categories: Electric power (or heat); Fuels; and Chemicals. The objective is to have these products produced by technologies capable of using synthesis gas derived from coal and/or some other carbonaceous feedstock, such as petroleum coke. The objective of Phase I was to determine the feasibility and define the concept for the EECP located at a specific site and to develop a Research, Development, and Testing (RD and T) Plan for implementation in Phase II. This objective has now been accomplished. A specific site, Motiva Refinery in Port Arthur, Texas, has been selected as the location best suited for the EECP. The accomplishments of Phase I are discussed in detail in this Phase I Concept Report. A RD and T Plan and a preliminary project financing plan have been developed and are submitted separately from this report