Computer display and manipulation of biological molecules

This paper describes a computer model that was designed to investigate the conformation of molecules, macromolecules and subsequent complexes. Utilizing an advanced 3-D dynamic computer display system, the model is sufficiently versatile to accommodate a large variety of molecular input and to generate data for multiple purposes such as visual representation of conformational changes, and calculation of conformation and interaction energy. Molecules can be built on the basis of several levels of information. These include the specification of atomic coordinates and connectivities and the grouping of building blocks and duplicated substructures using symmetry rules found in crystals and polymers such as proteins and nucleic acids. Called AIMS (Ames Interactive Molecular modeling System), the model is now being used to study pre-biotic molecular evolution toward life.     

Improving the large-signal models of bipolar transistors by dividing the intrinsic base into two lateral sections

In large-signal transistor models, the lateral voltage drop across the base region is usually represented by a single-lump constant base spreading resistance. The letter demonstrates, for the switching mode, that a much better approximation of the 2-dimensional transistor can already be achieved by dividing the intrinsic base into merely two sections (2-section model).     

On solving optimal control problems with free initial condition using iterative dynamic programming

For solving optimal control problems where the initial conditions of some of the state variables are not specified, a procedure based on iterative dynamic programming (IDP) is presented. In this procedure, the free initial conditions are taken to be additional control variables for the first time stage only; then the search for the optimal initial conditions and also the optimal control policy is carried out simultaneously using IDP. The procedure is straightforward, and as illustrated with two nonlinear optimal control problems, for each case the optimum performance index is readily obtained.     

High-gain transimpedance amplifier in InP-based HBT technology forthe receiver in 40-Gb/s optical-fiber TDM links

A monolithic integrated transimpedance amplifier for the receiver in a 40-Gb/s optical-fiber TDM system has been fabricated in an InP-based HBT technology. Despite its high gain (transimpedance of 2 kΩ in the limiting mode, 10 kΩ in the linear mode) the complete amplifier was realized on a single chip. Clear output eye diagrams were measured up to 43 Gb/s under realistic driving conditions. The voltage swing of 0.6 V_pp at the differential 50 Ω output does not change within the demanded input dynamic range of 6 dB. At the upper input current level even 48 Gb/s were achieved. The power consumption is approximately 600 mW at a single supply voltage of -5.5 V     

Forecasting fire growth using an inverse zone modelling approach

A new methodology to effectively forecast fire dynamics based on assimilation of sensor observations is presented and demonstrated. An inverse modelling approach with a two-zone model is used to forecast the growth of a compartment fire. Sensor observations are assimilated into the model in order to estimate invariant parameters and thus speed up simulations and recover information lost by modelling approximations. A series of cases of a compartment fire radially spreading at different growth rates (slow, medium and fast) are used to test the methodology. Spread rate, entrainment coefficient and smoke transport time are the invariant parameters estimated via a gradient-based optimization method with tangent linear differentiation. The parameters were estimated accurately within minutes after ignition and the heat release rate reproduced satisfactorily in all cases. Moreover, the temperature and the height of the hot layer are forecasted with a positive lead time between 50 and 80 s, depending on the fire growth rate. The results show that the simple mass and energy conservation equations and plume correlation of the zone model are suitable to forecast the main features of a growing fire. Positive lead times are reported here for the first time in fire dynamics. The results also suggest the existence of an optimal width for the assimilation window. The proposed methodology is subject to ongoing research and the results are an important step towards the forecast of fire dynamics to lead the emergency response.