Temperature beneath continents as a function of continental cover and convective wavelength

International audienceGeodynamic modeling studies have demonstrated that mantle global warming can occur in response to continental aggregation, possibly leading to large-scale melting and associated continental breakup. Such feedback calls for a recipe describing how continents help to regulate the thermal evolution of the mantle. Here we use spherical mantle convection models with continents to quantify variations in subcontinental temperature as a function of continent size and distribution and convective wavelength. Through comparison to a simple analytical boundary layer model, we show that larger continents beget warming of the underlying mantle, with heating sometimes compounded by the formation of broader convection cells associated with the biggest continents. Our results hold well for purely internally heated and partially core heated models with Rayleigh numbers of 10(5) to 10(7) containing continents with sizes ranging from that of Antarctica to Pangea. Results from a time-dependent model with three mobile continents of various sizes suggests that the tendency for temperatures to rise with continent size persists on average over timescales of billions of years

It\u27s Not Love, But It\u27s Not Bad: A Response to Critics of Prepaid College Tuition Plans

Two years ago one of the authors published an article surveying the tax ramifications of prepaid college tuition plans, with a focus on the Michigan plan - the Michigan Education Trust ( MET ). That article took a generally positive view of such plans in general and of MET in particular. It discussed three basic themes: 1) the uncertainty of existing tax law with respect to prepaid tuition plans requires clarifying congressional legislation; 2) the position of the Internal Revenue Service ( Service ) with respect to prepaid tuition plans, as enunciated in a private letter ruling addressed to MET, is flawed; and 3) the position that prepaid tuition plans are basically a good idea, that deserve tax-favored treatment in any clarifying congressional legislation in order to be successful. Commentary by other authors undoubtedly bears out the first theme. The novelty of prepaid tuition plans and their sheer lack of fit with existing Internal Revenue Code provisions make predicting the tax consequences of such plans more an exercise in speculation than in legal analysis. Perhaps one could do as well by casting lots or throwing darts as with the Code and regulations. Moreover, the commentators have generally agreed that the Service\u27s position is flawed, although for widely varying reasons

N, P and K budgets for crop rotations on nine organic farms in the UK

On organic farms, where the importation of materials to build/maintain soil fertility is restricted, it is important that a balance between inputs and outputs of nutrients is achieved to ensure both short-term productivity and long-term sustainability. This paper considers different approaches to nutrient budgeting on organic farms and evaluates the sources of bias in the measurements and/or estimates of the nutrient inputs and outputs. The paper collates 88 nutrient budgets compiled at the farm scale in 9 temperate countries. All the nitrogen (N) budgets showed an N surplus (average 83.2 kg N ha-1 year-1). The efficiency of N use, defined as outputs/inputs, was highest (0.9) and lowest (0.2) in arable and beef systems respectively. The phosphorus (P) and potassium (K) budgets showed both surpluses and deficits (average 3.6 kg P ha-1 year-1, 14.2 kg K ha-1 year-1) with horticultural systems showing large surpluses resulting from purchased manure. The estimation of N fixation and quantities of nutrients in purchased manures may introduce significant errors in nutrient budgets. Overall, the data illustrate the diversity of management systems in place on organic farms, and suggest that used together with soil analysis, nutrient budgets are a useful tool for improving the long-term sustainability of organic systems

The Organic Research Centre; Elm Farm Bulletin 84 July 2006

Regular bulletin with technical updates of the Organic Advisory Service Issue contains: Battling on for Avian Flu preventive vaccination; Organic Colombian Blacktail eggs; UK Co-existence - GMOand non-GMO crops; Aspects of Poultry Behaviour; CAP in the service of biodiversity; Seeing the Wood, the Trees and the Catch 22; Beware of organic market "statistics"; A central role in energy review

Elm Farm Organic Research Centre Bulletin 83 April 2006

Regular bulleting with technical updates from Organic Advisory Service Issue contains: Testing for Tolerance - a pragmatic view GM Debate Vaccination nation - to jab or not to jab Future shape of OCIS Evolutionary wheat makes the grade? NIAB tracks health of organic cereal seed Stopping erosion of soil quality - the organic way Care needed to halt butterfly collapse Aspects of poultry behaviour: How free range is free range? On choosing an organic wheat A local education challenge New Wakelyns Science Building Organic vegetable market growt

Diversifikationsstrategien für das Management der Kraut-und Knollenfäule der Kartoffel

Fazit: Die bisherigen Ergebnisse deuten auf eine extreme Sortenabhängigkeit in den epidemiologischen Effekten von Diversifikationsstrategien hin. Außerdem spielt die Variabilität des Befallsdruckes selbst innerhalb eines Feldes eine kritische Rolle. Für die Auswertung von Daten muß deshalb die räumliche Verteilung des Befalles viel stärker mit entsprechenden statistischen Modellen in Betracht gezogen werden. Die Ergebnisse aus den Streifenexperimenten sind analog den Ergebnissen aus den Sortenmischungen und deuten darauf hin, daß Kartoffeln extrem empfindlich auf Konkurrenz sowohl verschiedener Sorten als auch Arten reagieren. Um Diversifikationsstrategien sinnvoll einsetzen zu können, sollten als erstes die Reaktionen von Sorten auf andere Sorten und Arten quantifiziert werden, um geeignete Sorten zu identifizieren. Es könnte auch ein Zuchtziel für die ökologische Landwirtschaft werden, die Konkurrenzfähigkeit mehr in den Vordergrund zu stellen. Dies wäre auch in Bezug auf Unkrautunterdrückung unter Umständen von Interesse. Um ein Streifenexperiment sinnvoll auszuwerten, muß der Ertrag und Befall der Außen- und Innenreihen von Parzellen getrennt erfaßt werden. Für die Beurteilung des Gesamtergebnisses kann dann nicht einfach auf Hektarerträge hochgerechnet werden sondern es muß das Gesamtsystem in Betracht gezogen werden. Insgesamt können Diversifikationsstrategien den Krankheitsdruck reduzieren. Dies belegen auch Beobachtungen aus China, wo der Streifenanbau von Kartoffeln und Mais zu bis zu 40% Reduktion im Befall mit P. infestans und damit zu einer Reduktion im Fungizideinsatz geführt hat (Z. Youyong, 2002, pers. Mitteilung)

Group theoretical approach to quantum fields in de Sitter space I. The principal series

Using unitary irreducible representations of the de Sitter group, we construct the Fock space of a massive free scalar field. In this approach, the vacuum is the unique dS invariant state. The quantum field is a posteriori defined by an operator subject to covariant transformations under the dS isometry group. This insures that it obeys canonical commutation relations, up to an overall factor which should not vanish as it fixes the value of hbar. However, contrary to what is obtained for the Poincare group, the covariance condition leaves an arbitrariness in the definition of the field. This arbitrariness allows to recover the amplitudes governing spontaneous pair creation processes, as well as the class of alpha vacua obtained in the usual field theoretical approach. The two approaches can be formally related by introducing a squeezing operator which acts on the state in the field theoretical description and on the operator in the present treatment. The choice of the different dS invariant schemes (different alpha vacua) is here posed in very simple terms: it is related to a first order differential equation which is singular on the horizon and whose general solution is therefore characterized by the amplitude on either side of the horizon. Our algebraic approach offers a new method to define quantum field theory on some deformations of dS space.Comment: 35 pages, 2 figures ; Corrected typo, Changed referenc