ALBERT

Notes: Abstract  The development of an electrochemical microanalytical system for ionometric measurements (acronym ELMAS) is described. ELMAS combines potentiometric microsensors with solid state ion sensitive membranes, plastic molded and adhesive mounted micropumps, a microchannel system for connecting all components (several sensors, the calibrating solution reservoirs, the micropumps) and microelectronic components for signal processing and system control. The development of any complex technical system requires a good understanding and asks for a specification of high quality. Very useful for this purpose are executable specifications; they can demonstrate system properties already in an early design stage and give a deep insight in the behaviour of the system. Thus the system requirements can be verified and design errors can be detected and eliminated earlier than by other approaches. So we started the development of the ELMAS microsystem with the creation of a dynamical executable specification model, based on Statecharts, performed by the STATEMATE tool. Statecharts are extended finite automata. This model has been combined with a graphical user interface. Running simulations guarantees the correct system behaviour. The graphical interface itself was used for communication between the institutes participating on the development of ELMAS. The next stage of development was characterized by substituting some simulated components by real ones. At this stage microsensors have been combined with macro pumps and conventional electronics. The model running on a workstation controls the sensor and actuator components of macro dimension. The result of this stage was a macro prototype of ELMAS. It was used for testing the new developed microsensors and analysing the system behaviour. Going from the macro to micro components and replacing the workstation by a microcontroller the step by step development of ELMAS ends up in a real microsystem for the simultaneous measurement of pNa and pH. Thus we get a closed chain from specification to realization.

Notes: The determination of high-degree geopotential models currently requires accurate terrestrial gravity information on a global basis. For the regions where such information is unavailable or poor, it is important to develop procedures for the estimation of gravity anomalies, based on existing data sources. This paper examines the possibility of combining low-degree satellite-derived geopotential models with the harmonic coefficients of the topographic-isostatic potential implied by the Airy/Heiskanen isostatic hypothesis.The compilation of a new global topographic database that provides additional information pertaining to terrain type classification, ice coverage etc., is discussed first. Then the rigorous formulation for the determination of harmonic coefficients of the topographic-isostatic potential is extended to account for the various terrain types. This formulation, and a series expansion approach are implemented to determine topographic-isostatic coefficient sets complete to degree and order 360. These coefficients are then combined with satellite-derived models (GEM-T1/T2) to estimate 1°× 1° mean gravity anomalies. Comparisons of the estimated anomalies with observed values, as well as with anomalies derived from satellite altimetry, indicated the following. (a) Optimum results are obtained when the satellite models are used to degree 36 and the topographic-isostatic coefficients from 37 onwards. For example, when GEM-T2 to degree 36 is combined with the topographic-isostatic coefficients from 37 to 180, the root mean square (rms) anomaly difference with 6237 1°× 1° terrestrial values having a standard deviation less than 10 mgals, was ±18 mgals, which should be compared to the rms value of the terrestrial anomalies which was about ±27 mgals. The use of GEM-T2 alone up to degree 36 yields an rms discrepancy with the same terrestrial values of the order of ±22 mgal. (b) The effect of ice is significant and improves the quality of the estimated anomalies in polar regions where very limited gravity material exists. (c) The overall accuracy of the estimated anomalies is about equal to the overall accuracy of existing geophysically predicted anomalies. However, the use of the satellite model for the low degrees in the current procedure, may resolve problems associated with regional biases detected in the geophysical anomalies.

Notes: The specific heat as a function of temperature of Stycast 1266 was measured in the range from 0.1 to 1 K. The results are described, within 2%, by the expression c(T)=aT+bT3+cT5, where a=2.91(6) μJ/g K2, b=15.7(5) μJ/g K4, and c=8.98(0) μJ/g K6. The linear and cubic terms were related to the model of two-level systems and to the Debye specific heat, respectively. The origin of the T5 contribution remains unexplained.

Notes: A specific heat calorimeter for the temperature range 0.07–1.3 K with a novel sample support of four commercial pencil leads is described. It is shown that this support substantially reduces the vibrational heat input to the sample assembly. The thermal shield of the calorimeter is vacuum tight to allow measurements with gas adsorbing samples. We estimate and derive expressions for the temperature dependence of the thermal conductances of the AuCu thermal link and of the pencil leads support.

Notes: The magnetic properties of the Mn12ac molecular cluster were studied by complex susceptibility and specific heat measurements. Extensive ac susceptibility measurements done under a magnetic field on good quality single crystals and zero field powder sample specific heat results indicate that the usual uniaxial Hamiltonian, as well as the recently proposed fourth order corrections, are not enough to account for all the observations. Very low temperature specific heat data indicate the presence of zero field splitting of the ground state which is much larger than expected. Finally, specific heat measurements done under a magnetic field permitted us to observe and measure the lattice spin relaxation by calorimetric methods with time constants that are in agreement with the magnetic relaxation measurements. © 1998 American Institute of Physics.