9,522 research outputs found
Attenuation of species abundance distributions by sampling
Quantifying biodiversity aspects such as species presence/ absence, richness and abundance is an important challenge to answer scientific and resource management questions. In practice, biodiversity can only be assessed from biological material taken by surveys, a difficult task given limited time and resources. A type of random sampling, or often called sub-sampling, is a commonly used technique to reduce the amount of time and effort for investigating large quantities of biological samples. However, it is not immediately clear how (sub-)sampling affects the estimate of biodiversity aspects from a quantitative perspective. This paper specifies the effect of (sub-)sampling as attenuation of the species abundance distribution (SAD), and articulates how the sampling bias is induced to the SAD by random sampling. The framework presented also reveals some confusion in previous theoretical studies.Publisher PDFPeer reviewe
Iowa Land Value Survey, 2008
Iowa land values increased 114 percent for the year. Average value was $4,468 per acre.
Farmland Ownership and Tenure in Iowa, 2007
This paper presents the results of the 2007 Iowa Farmland Ownership survey
Cross correlations of Frank sequences and Chu Sequences.
Sets of Frank sequences and Chu sequences are two classes of polyphase sequence with ideal periodic autocorrelation functions, which at the same time have optimum crosscorrelation functions. The authors consider the crosscorrelations of sets of combined Frank/Chu sequences, which contain a larger number of sequences than either of the two constituent sets. It is shown analytically that the crosscorrelations are similar to those of the original sets with one exception, while the autocorrelations remain perfectly impulsiv
Cash Rental Rates for Iowa -- 2004 Survey
Typical cash rental rates for cropland in each Iowa county are presented.
Electrophoretic Demonstration of the Hybrid Origin of the Gynogenetic Teleost \u3cem\u3ePoecilia formosa\u3c/em\u3e
Exothermic furnace module development
An exothermic furnace module was developed to rapidly heat and cool a 0.820-in. (2.1 cm) diameter by 2.75-in. (7.0 cm) long TZM molybdenum alloy crucible. The crucible contains copper, oxygen, and carbon for processing in a low-g environment. Peak temperatures of 1270 C were obtainable 3.5 min after start of ignition, and cooling below 950 C some 4.5 min later. These time-temperature relationships were conditioned for a foam-copper experiment, Space Processing Applications Rocket experiment 77-9, in a sounding rocket having a low-g period of 5 min
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