Probing the phase diagram of CeRu_2Ge_2 by thermopower at high pressure

The temperature dependence of the thermoelectric power, S(T), and the electrical resistivity of the magnetically ordered CeRu_2Ge_2 (T_N=8.55 K and T_C=7.40 K) were measured for pressures p < 16 GPa in the temperature range 1.2 K < T < 300 K. Long-range magnetic order is suppressed at a p_c of approximately 6.4 GPa. Pressure drives S(T) through a sequence of temperature dependences, ranging from a behaviour characteristic for magnetically ordered heavy fermion compounds to a typical behaviour of intermediate-valent systems. At intermediate pressures a large positive maximum develops above 10 K in S(T). Its origin is attributed to the Kondo effect and its position is assumed to reflect the Kondo temperature T_K. The pressure dependence of T_K is discussed in a revised and extended (T,p) phase diagram of CeRu_2Ge_2.Comment: 7 pages, 6 figure

Modelling the EC Agricultural Sector: Problem Assessment, Policy Scenarios and Model Outline

This paper is composed of three parts: the first section describes the economic situation and past development within the nine member countries of the European Community (EC). Particular emphasis is given to resource and production structure in agriculture as well as agricultural commodity markets. The second part contains a description of the Common Agricultural Policy (CAP) which is evaluated w.r.t., it's effects on member and non-member countries. This section contains also a discussion of alternative policy scenarios conceivable for later model applications. The third part of this paper gives a brief overview over the structure of the Agricultural Sector Model. This includes a presentation of the macro model with intersectoral linkages between agriculture and the rest of the economy as well as a mathematical formulation of the farm resource and allocation model

Quasiquartet CEF ground state with possible quadrupolar ordering in the tetragonal compound YbRu2_{2}Ge2_{2}

e have investigated the magnetic properties of YbRu$_{2}$Ge$_{2}$ by means of magnetic susceptibility $\chi$(T), specific heat C(T) and electrical resistivity $\rho$(T) measurements performed on flux grown single crystals. The Curie-Weiss behavior of $\chi$(T) along the easy plane, the large magnetic entropy at low temperatures and the weak Kondo like increase in $\rho$(T) proves a stable trivalent Yb state. Anomalies in C(T), $\rho$(T) and $\chi$(T) at T$_{0}$ = 10.2 K, T$_{1}$ = 6.5 K and T$_{2}$ = 5.7 K evidence complex ordering phenomena, T$_{0}$ being larger than the highest Yb magnetic ordering temperature found up to now. The magnetic entropy just above T$_{0}$ amounts to almost Rln4, indicating that the crystal electric field (CEF) ground state is a quasiquartet instead of the expected doublet. The behavior at T$_{0}$ is rather unusual and suggest that this transition is related to quadrupolar ordering, being a consequence of the CEF quasiquartet ground state. The combination of a quasiquartet CEF ground state, a high ordering temperature, and the relevance of quadrupolar interactions makes YbRu$_{2}$Ge$_{2}$ a rather unique system among Yb based compounds.Comment: 11 pages, 5 figure, submitted to PRB rapi

The Food and Agriculture Model of the International Institute for Applied Systems Analysis

The report summarizes objectives and scope of a global system of national agricultural sector models which is currently being developed as part of the Food and Agriculture Program at IIASA. The paper starts with a very brief characterization of the recent world food situation. It is emphasized that the main efforts to overcome current and expected food scarcities will have to be made within the affected developing nations themselves. International food policies, however, will have an important role to play in supporting these efforts. Three problem domains of international relevance are briefly discussed| instability of world markets, insecurity of food aid and deterioration of international trade. The third section contains a summary of available global models insofar as they emphasize food and agriculture. No results or policy recommendations are reported here, rather the basic structural differences are discussed. This schematic comparison of models leads then to a more detailed discussion of the international food and agriculture model of IIASA. The objective of the IIASA program is to define and quantify alternative sets of international and national policies which seem appropriate to reduce world hunger within the next 5-15 years by exploiting the international interactions between developing and industrial nations and by increasing local production in developing countries. The emphasis of the program lies on international cooperation. A stepwise procedure is envisaged, where in the first phase a set of national agricultural sector models will be specified and empirically tested which will then, during the second phase, be linked through a world consistency model to simulate the global system. The national models will have some common properties to achieve operationality. They will typically consist of a disaggregated agricultural production component, an aggregated submodel for the rest of the economy as well as a consistent national expenditure system. These components define a so-called "real world bloc" which is controlled by a "policy bloc" describing goals and instruments at the government decision level