Calculating all elements of minimal index in the infinite parametric family of simplest quartic fields

summary:It is a classical problem in algebraic number theory to decide if a number field is monogeneous, that is if it admits power integral bases. It is especially interesting to consider this question in an infinite parametric family of number fields. In this paper we consider the infinite parametric family of simplest quartic fields $K$ generated by a root $\xi$ of the polynomial $P_t(x)=x^4-tx^3-6x^2+tx+1$, assuming that $t>0$, $t\neq 3$ and $t^2+16$ has no odd square factors. In addition to generators of power integral bases we also calculate the minimal index and all elements of minimal index in all fields in this family

Fertilizing Nature: A Tragedy of Excess in the Commons

Why has nitrogen fertilizer use declined in some countries while increasing in others, despite significant environmental harm? Proper crop management strategies offer environmental and economic benefits without sacrificing yields

CAD modeling, multibody system formalisms and visualization : an integrated approach

In this paper an integrated approach of CAD (Computer Aided Design) modeling, generation of equations of motion, simulation and visualization of multibody systems is described. An object-oriented data model for different multibody formalisms is integrated in a commercially available CAD-3D-system. With respect to existing CAD-interfaces, different solid model design methods and various visualization demands the datamodel allow, multi body modeling with a direct interface to a data base. Different software tools like an integrated Newton-Euler formalism are able to use immediately the parametrized multi body system data base. For multibody systems with closed kinematic loops a set of ordinary differential equations and decoupled algebraic equations is formulated automatically which can be solved with explicit multistep integration algorithms. This is achieved by a minimal set of generalized coordinates being specified during the numerical integration. A additional interface provides data for visualization from the simulation tool

Insect Pollinated Crops, Insect Pollinators and US Agriculture: Trend Analysis of Aggregate Data for the Period 1992–2009

In the US, the cultivated area (hectares) and production (tonnes) of crops that require or benefit from insect pollination (directly dependent crops: apples, almonds, blueberries, cucurbits, etc.) increased from 1992, the first year in this study, through 1999 and continued near those levels through 2009; aggregate yield (tonnes/hectare) remained unchanged. The value of directly dependent crops attributed to all insect pollination (2009 USD) decreased from $14.29 billion in 1996, the first year for value data in this study, to$10.69 billion in 2001, but increased thereafter, reaching $15.12 billion by 2009. The values attributed to honey bees and non-Apis pollinators followed similar patterns, reaching$11.68 billion and $3.44 billion, respectively, by 2009. The cultivated area of crops grown from seeds resulting from insect pollination (indirectly dependent crops: legume hays, carrots, onions, etc.) was stable from 1992 through 1999, but has since declined. Production of those crops also declined, albeit not as rapidly as the decline in cultivated area; this asymmetry was due to increases in aggregate yield. The value of indirectly dependent crops attributed to insect pollination declined from$15.45 billion in 1996 to $12.00 billion in 2004, but has since trended upward. The value of indirectly dependent crops attributed to honey bees and non-Apis pollinators, exclusive of alfalfa leafcutter bees, has declined since 1996 to$5.39 billion and $1.15 billion, respectively in 2009. The value of alfalfa hay attributed to alfalfa leafcutter bees ranged between$4.99 and $7.04 billion. Trend analysis demonstrates that US producers have a continued and significant need for insect pollinators and that a diminution in managed or wild pollinator populations could seriously threaten the continued production of insect pollinated crops and crops grown from seeds resulting from insect pollination

Agricultural Labor Data Sources: An Update

Agricultural labor data provide information for monitoring the performance of U.S. agriculture, examining the economic well-being of farmworkers, and analyzing farm labor policies and legislation. This report identifies, describes, and compares various data sources used to analyze the different components of the agricultural work force, and alerts the reader to differences in data sources that complicate comparisons. The data sources differ by population universe, degree of coverage, frequency of data collection, concepts and definitions, age criteria, employment reference period, and published versus other available data

Distribution of Employment Growth in Nine Kentucky Counties: A Case Study

Rapid employment growth between 1974 and 1979 in a nine-county study area of south central Kentucky provided job opportunities both for local residents and for persons with limited labor force experience. But, recent inmigrants held a disproportionate share of better paying executive jobs. This case study, which examines the distributional effects of rapid employment growth in a nonmetropolitan area, shows that inmigrants also held a disproportionate share of jobs in growing business establishments. Although manufacturing was the major economic force in the study area in January 1980, jobs in the private service sector increased more than in other sectors

Test examples for multibody systems

SIGLETIB Hannover: RN 7515(13) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

An object-oriented data model for multibody systems

An object-oriented data model is defined to describe parametrized multibody systems. A scheme to store the description of a multibody system on a database as well as a file format to store it on a data exchange file are directly derived from this data model. If a multibody system may be parametrized, it is e.g. possible to apply parameter optimization as a tool for synthesis and design