533 research outputs found
Productivity levels of some Iowa soils
This report presents crop yield estimates for corn, soybeans, oats, and hay on 290 selected soil types and phases. These yield estimates are believed attainable as a 5-year average with the technology available in 1971 and average weather conditions.https://lib.dr.iastate.edu/specialreports/1063/thumbnail.jp
Response of corn yields in a Planosol soil to surface drainage, cropping system and variable fertilizer treatments
The Edina soil series of southeastern Iowa and northern Missouri are areas of relatively flat topography and poor internal drainage. For these areas, where the topography and soils permit, surface drainage is the most practical method of removing excess water from the land. One method of surface drainage that has been used on the Edina soils is bedding, in which the field is divided into narrow-width plow lands with the deadfurrows running parallel to the prevailing land slope.
Little is known about the relative returns from investment in a bedding system in comparison with other surface or subsurface drainage methods. Bedding requires that some topsoil be moved to obtain the desired grade for drainage. The effect on crop yields of topsoil removal and movement in land-forming operations such as bedding, however, is not quantitatively understood. It is the general purpose of this bulletin to present and analyze 6 years of corn-yield data involving drainage (bedded versus level), cropping and fertilizer variables from a study on the Southern Iowa Experimental Farm near Bloomfield
The Nature of the Secondary Star in the Black Hole X-Ray Transient V616 Mon (=A0620-00)
We have used NIRSPEC on Keck II to obtain -band spectroscopy of the low
mass X-ray binary V616 Mon (= A062000). V616 Mon is the proto-typical soft
x-ray transient containing a black hole primary. As such it is important to
constrain the masses of the binary components. The modeling of the infrared
observations of ellipsoidal variations in this system lead to a derived mass of
11.0 M_{\sun} for the black hole. The validity of this derivation has been
called into question due to the possiblity that the secondary star's spectral
energy distribution is contaminated by accretion disk emission (acting to
dilute the variations). Our new -band spectrum of V616 Mon reveals a
late-type K dwarf secondary star, but one that has very weak CO
absorption features. Comparison of V616 Mon with SS Cyg leads us to estimate
that the accretion disk supplies only a small amount of -band flux, and the
ellipsoidal variations are not seriously contaminated. If true, the derived
orbital inclination of V616 Mon is not greatly altered, and the mass of the
black hole remains large. A preliminary stellar atmosphere model for the
-band spectrum of V616 Mon reveals that the carbon abundance is
approximately 50% of the solar value. We conclude that the secondary star in
V616 Mon has either suffered serious contamination from the accretion of
supernova ejecta that created the black hole primary, or it is the stripped
remains of a formerly more massive secondary star, one in which the CNO cycle
had been active.Comment: 20 pages, 5 figure
Multi-Wavelength Monitoring of GRS 1915+105
Since its discovery in 1992, the superluminal X-ray transient GRS 1915+105 has been extensively observed in an attempt to understand its behaviour. We present here first results from a multi-wavelength campaign undertaken from July to September 1996. This study includes X-ray data from the RXTE All Sky Monitor and BATSE, two-frequency data from the Nancay radio telescope, and infrared photometry from the 1.8m Perkins telescope at Lowell Observatory. The first long-term well-sampled IR light curve of GRS 1915+105 is presented herein and is consistent with the interpretation of this source as a long-period binary. We compare the various light curves, searching for correlations in the behaviour of the source at differing wavelengths and for possible periodicities
Optical Variability of Narrow-Line Seyfert 1 Galaxies
We present results of a broad-band photometric study of the optical
variability of six Narrow-Line Seyfert 1 (NLS1) galaxies observed at 172
epochs. We searched for microvariability on 33 nights. Strong evidence for
microvariability was found only for our lowest luminosity object, NGC 4051, on
one night. Weaker evidence suggests such variability on a few other nights for
two other objects, but the data are not as convincing. Intra-night variability
in NLS1s is thus concluded to be rare and of low amplitude. We give
illustrations of how variable image quality can produce spurious variability.
We find that for well-studied non-NLS1s there is a spread in the amplitude of
seasonal variability (i.e., in some years an AGN is more variable than in
others). We find that the means of the variability amplitudes of non-NLS1s over
several seasons vary from object to object (i.e., some AGNs are, on average,
more variable than others). NLS1s also show a spread in seasonal variabilities.
The best-studied NLS1, Ark 564, shows a range of amplitudes of variability from
season to season that is comparable to the range found in BLS1s, and in one
season Ark 564 was as variable as the most variable non-NLS1. The seasonal
amplitudes of variability for NLS1s are mostly in the lower half of the range
of non-BLS1 seasonal amplitudes, but the absence of a suitable control sample
makes a precise comparison difficult. However, on long timescales (weeks to
years), NLS1s as a class are not more variable than non-NLS1s. The extreme
variability seen in the X-rays was not seen in the optical. This has
consequences for the models of AGNs in general as well as NLS1s in particular.Comment: Astrophysical Journal in press (tentatively scheduled for Vol. 608,
June 2004 issue);47 pages; 19 figures. Electronic tables not included
(contact first author if needed
Positron Annihilation in the Galaxy
The 511 keV line from positron annihilation in the Galaxy was the first Îł-ray line detected to originate from outside our solar system. Going into the fifth decade since the discovery, the source of positrons is still unconfirmed and remains one of the enduring mysteries in Îł-ray astronomy. With a large flux of âŒ10â3 Îł/cm2/s, after 15 years in operation INTEGRAL/SPI has detected the 511 keV line at >50Ï and has performed high-resolution spectral studies which conclude that Galactic positrons predominantly annihilate at low energies in warm phases of the interstellar medium. The results from imaging are less certain, but show a spatial distribution with a strong concentration in the center of the Galaxy. The observed emission from the Galactic disk has low surface brightness and the scale height is poorly constrained, therefore, the shear number of annihilating positrons in our Galaxy is still not well know. Positrons produced in ÎČ+-decay of nucleosynthesis products, such as 26Al, can account for some of the annihilation emission in the disk, but the observed spatial distribution, in particular the excess in the Galactic bulge, remains difficult to explain. Additionally, one of the largest uncertainties in these studies is the unknown distance that positrons propagate before annihilation. In this paper, we will summarize the current knowledge base of Galactic positrons, and discuss how next-generation instruments could finally provide the answers.Non peer reviewedFinal Accepted Versio
The Concordance Cosmic Star Formation Rate: Implications from and for the Supernova Neutrino and Gamma Ray Backgrounds
We constrain the Cosmic Star Formation Rate (CSFR) by requiring that massive
stars produce the observed UV, optical, and IR light while at the same time not
overproduce the Diffuse Supernova Neutrino Background as bounded by
Super-Kamiokande. With the massive star component so constrained we then show
that a reasonable choice of stellar Initial Mass Function and other parameters
results in SNIa rates and iron yields in good agreement with data. In this way
we define a `concordance' CSFR that predicts the optical SNII rate and the SNIa
contribution to the MeV Cosmic Gamma-Ray Background. The CSFR constrained to
reproduce these and other proxies of intermediate and massive star formation is
more clearly delineated than if it were measured by any one technique and has
the following testable consequences: (1) SNIa contribute only a small fraction
of the MeV Cosmic Gamma-Ray Background, (2) massive star core-collapse is
nearly always accompanied by a successful optical SNII, and (3) the Diffuse
Supernova Neutrino Background is tantalizingly close to detectability.Comment: Improved discussion. Version accepted for publication in JCA
Autonomy of Nations and Indigenous Peoples and the Environmental Release of Genetically Engineered Animals with Gene Drives
This article contends that the environmental release of genetically engineered (GE) animals with heritable traits that are patented will present a challenge to the efforts of nations and indigenous peoples to engage in selfâdetermination. The environmental release of such animals has been proposed on the grounds that they could function as public health tools or as solutions to the problem of agricultural insect pests. This article brings into focus two politicalâeconomicâlegal problems that would arise with the environmental release of such organisms. To address those challenges, it is proposed that nations considering the environmental release of GE animals must take into account the underlying circumstances and policy failures that motivate arguments for the use of the modified animals. Moreover, countries must recognize that the UN International Covenant on Civil and Political Rights and the UN International Covenant on Economic, Social and Cultural Rights place on them an obligation to ensure that GE animals with patented heritable traits are not released without the substantive consent of the nations or indigenous peoples that could be affected
Multiwavelength observations revealing the outbursts of the two soft X-ray transients XTE J1859+226 and XTE J1118+480
We report here on multiwavelength observations of the two new soft X-ray
transients (SXTs) XTE J1859+226 and XTE J1118+480, which we observed with
HST/RXTE/UKIRT. For XTE J1118+480 we also used EUVE since it is located at a
very high galactic latitude and suffers from very low extinction. The two
sources exhibited very different behaviour. XTE J1859+226 seems quite normal
and therefore a good object for testing the accretion mechanisms in place
during the outbursts, XTE J1118+480 is much more unusual because it exhibits i)
a low X-ray to optical ratio and ii) a strong non-thermal contribution in the
radio to optical domain, which is likely to be due to synchrotron emission. We
concentrate here on the near-infrared (NIR) and optical observations of these
two systems.Comment: 4 pages, 6 figures, conference, Proceedings of the 4th INTEGRAL
Workshop (Alicante 2000), to be published in ESA-SP (2001
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