Numerical simulation and analysis of the propagation of a prefrontal squall line

Fall 1990.Also issued as author's dissertation (Ph.D.) -- Colorado State University, 1990.Includes bibliographical references.An observational and numerical study of the squall line that occurred on 17-18 June 1978 is described. This squall line was initially triggered by the strong surface convergence along a cold front, and stretched from Illinois to the Texas panhandle. The squall line was aligned with the surface front during its initial development (at 0000 UTC 18 June 1978), but then propagated faster than the front, resulting in a separation of approximately 200 km by 0300 UTC and 300-400 km by 0600 UTC. The CSU RAMS model is used to model the squall line development and propagation. Several sensitivity experiments were completed to test the sensitivity of the results to the use of the Kuo-type cumulus parameterization scheme and grid-scale microphysical processes. The simulations that included the cumulus parameterization scheme and grid scale latent heating or condensation effects accurately modelled the initial development of the squall line and its subsequent movement away from the front. The effects of the gridscale microphysical processes (versus the more simple grid-scale condensation and latent heat release) were m:nor in these simulations. A simulation to test the effects of varying the initial specification of roughness length zo, soil texture, and soil moisture was also completed. The results were very similar to the results with a non-varying specification of zo and soil texture, especially in the region of the squall line. Greater differences were found to the east of the squall line where the convection was not as strongly forced by the dynamics. The propagation of the squall line in the model is shown to be due to the propagation of a deep tropospheric internal gravity wave, in a wave-CISK-like process. The thermal and dynamic perturbations associated with the hypothesized wave are shown to be consistent with gravity wave theory, and the characteristics of the wave are compared to similar results from wave-CISK studies. The wave is forced by the heating profile associated with the convection and propagates southeastward at 18 m s-1 with a horizontal wavelength of ~200 km and a vertical wavelength of 10 km. The wave maintains its coherence and energy through the quasi-resonant effects of reflection from the stability discontinuity at the tropopause and a low-level layer in which the Scorer parameter is very small. The wave dissipates when the heating maximum associated with the wave forcing widens and rises so that the resonant effect is diminished. A critical layer also develops in the upper atmosphere at about the same time, which acts to absorb the wave energy. The propagation of the squall line as an internal gravity wave is discussed in relation to other studies. The current literature favors the mechanism o gust front convergence to explain squall line propagation, although there are a few other modelling studies that show specific instances of squall line propagation as being due to internal gravity waves. It is suggested that a spectrum of scales of forcing may exist and be responsible for squall line propagation, but many models and observations may be able to detect only the gust-front- type processes. The 17-18 June 1978 squall line probably did not propagate solely as the result of any one mechanism, but instead as the product of several active mechanisms. The dominant mechanism in these modelling simulations was an internal gravity wave, and it seems reasonable that the gravity wave was at least one of the mechanisms responsible for the actual propagation of the 17-18 June 1978 squall line.

The Phoenix Deep Survey: spectroscopic catalog

The Phoenix Deep Survey is a multi-wavelength survey based on deep 1.4 GHz radio imaging, reaching well into the sub-100 microJy level. One of the aims of this survey is to characterize the sub-mJy radio population, exploring its nature and evolution. In this paper we present the catalog and results of the spectroscopic observations aimed at characterizing the optically ``bright'' (R<~ 21.5 mag) counterparts of faint radio sources. Out of 371 sources with redshift determination, 21% have absorption lines only, 11% show AGN signatures, 32% are star-forming galaxies, 34% show narrow emission lines that do not allow detailed spectral classification (due to poor signal-to-noise ratio and/or lack of diagnostic emission lines) and the remaining 2% are identified with stars. For the star-forming galaxies with a Balmer decrement measurement we find a median extinction of A(Ha)=1.9 mag, higher than that of optically selected samples. This is a result of the radio selection, which is not biased against dusty systems. Using the available spectroscopic information, we estimate the radio luminosity function of star-forming galaxies in two independent redshift bins at z~0.1 and 0.3 respectively. We find direct evidence for strong luminosity evolution of these systems consistent with L(1.4 GHz) ~ (1+z)^(2.7).Comment: 39 pages, 12 figures. References added, and minor changes to reflect published versio

The Phoenix Deep Survey: X-ray properties of faint radio sources

In this paper we use a 50ks XMM-Newton pointing overlapping with the Phoenix Deep Survey, a homogeneous radio survey reaching muJy sensitivities, to explore the X-ray properties and the evolution of star-forming galaxies. UV, optical and NIR photometry is available and is used to estimate photometric redshifts and spectral types for radio sources brighter than R=21.5mag (total of 82). Sources with R<21.5mag and spiral galaxy SEDs (34) are grouped into two redshift bins with a median of z=0.240 and 0.455 respectively. Stacking analysis for both the 0.5-2 and 2-8keV bands is performed on these subsamples. A high confidence level signal (>3.5sigma) is detected in the 0.5-2keV band corresponding to a mean flux of ~3e-16cgs for both subsamples. This flux translates to mean luminosities of ~5e40 and 1.5e41cgs for the z=0.240 and 0.455 subsamples respectively. Only a marginally significant signal (2.6sigma) is detected in the 2-8keV band for the z=0.455 subsample. We argue that the stacked signal above is dominated by star-formation. The mean L_X/L_B ratio and the mean L_X of the two subsamples are found to be higher than optically selected spirals and similar to starbursts. We also find that the mean L_X and L_1.4 of the faint radio sources studied here are consistent with the L_X-L_1.4 correlation of local star-forming galaxies. Moreover, the X-ray emissivity of sub-mJy sources to z~0.3 is found to be elevated compared to local HII galaxies. The observed increase is consistent with L_X evolution of the form (1+z)^3. Assuming that our sample is indeed dominated by starbursts this is direct evidence for evolution of such systems at X-ray wavelengths. Using an empirical L_X to SFR conversion we estimate a global SFR density at z~0.3 of \~0.029M_o/yr/Mpc in agreement with previous studies.Comment: 12 pages, 6 figures, accepted for publication in MNRA

On the Determination of Star Formation Rates in Evolving Galaxy Populations

The redshift dependence of the luminosity density in certain wavebands (e.g. UV and H-alpha) can be used to infer the history of star formation in the populations of galaxies producing this luminosity. This history is a useful datum in studies of galaxy evolution. It is therefore important to understand the errors that attend the inference of star formation rate densities from luminosity densities. This paper explores the self-consistency of star formation rate diagnostics by reproducing commonly used observational procedures in a model with known galaxy populations, evolutionary histories and spectral emission properties. The study reveals a number of potential sources of error in the diagnostic processes arising from the differential evolution of different galaxy types. We argue that multi-wavelength observations can help to reduce these errors.Comment: 13 pages (including 5 encapsulated postscript figures), aastex, accepted for publication in Ap

BEYOND MODES: A NEW TYPOLOGY OF ISD CONTROL

This study focuses on the role of information systems development (ISD) control as a means to better understand the underlying elements of ISD methodologies. Based on Ackoff’s general systems theory, we propose a new typology of ISD control that moves beyond the de facto standard in ISD research: control modes. Through twenty-six interviews at four organizations, we find that our typology aids in distinguishing between control dimensions within structured and flexible development to a greater extent than control modes would allow. Our paper also discusses possible reasons why the benefits of agile development may become diluted in organizations where both flexible and structured methods are employed. This work contributes to the advancement of ISD control theory and provides useful insights for practitioners responsible for the governance of ISD projects

The Global Star Formation Rate from the 1.4 GHz Luminosity Function

The decimetric luminosity of many galaxies appears to be dominated by synchrotron emission excited by supernova explosions. Simple models suggest that the luminosity is directly proportional to the rate of supernova explosions of massive stars averaged over the past 30 Myr. The proportionality may be used together with models of the evolving 1.4 GHz luminosity function to estimate the global star formation rate density in the era z < 1. The local value is estimated to be 0.026 solar masses per year per cubic megaparsec, some 50% larger than the value inferred from the Halpha luminosity density. The value at z ~ 1 is found to be 0.30 solar masses per year per cubic megaparsec. The 10-fold increase in star formation rate density is consistent with the increase inferred from mm-wave, far-infrared, ultra-violet and Halpha observations.Comment: 10 pages, 2 figures, Astrophysical Journal Letters (in press); new PS version has improved figure placemen

Organogenesis: Cutting to the Chase

AbstractGonad morphogenesis in Caenorhabditis elegans requires two secreted proteases. Recent studies show that alterations of the extracellular matrix component fibulin-1 rescue gonadogenesis in the absence of these proteases. This finding is a critical step toward understanding the role of extracellular matrix in organogenesis

ANALYZING CONTRACT PERFORMANCE AT DEFENSE LOGISTICS AGENCY

The Department of Defense (DOD) has emphasized agility, the speed of learning, and operational readiness, based on the National Defense Strategy, with priority on deterring aggression from near-peer competition of China. The timely preparation of requirements, proper contracting methodology, enforcement of spare parts contracts, and contracted vendor performance are essential to ensuring stability of the DOD’s supply chain and maintaining warfighting readiness. The DOD faces challenges with on-time delivery rates, a direct impact to material readiness for operational requirements and DOD’s ability to remain relevant. This research explores potential relationships between Contract Value, Contract Quantity, and Awarding Office and their effects on the Delta in Delivery Date. Given Defense Logistics Agency’s (DLA) sphere of influence, managing 4.2 million spare parts, they were an ideal source of data to explore these potential relationships. The findings of our research suggest that there is no correlation between Contract Value and Contract Quantity and the Delta in Delivery Date. However, our research shows that there is a possible qualitative factor that was not measured, which is affecting intraoffice performance at DLA L&M and DLA Aviation. This research concludes with recommendations to improve upon the research in the area of on-time delivery at DLA.Lieutenant Commander, United States NavyLieutenant Commander, United States NavyLieutenant Commander, United States NavyApproved for public release. Distribution is unlimited

Virtual colonoscopy; real misses

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72356/1/j.1572-0241.2003.08448.x.pd