Practical Thermal Multi–Scale Analysis for Composite Materials–Mechanical-Orientated Approach

This paper describes a thermal multi-scale formulation for composite materials based on a mechanical homogenization approach. The presented formulation evaluates the effective macroscopic thermal conductivity of the composite materials and also the microscopic heat flux field by scaling down to the micro-scale level. The effective thermal conductivity of the composite materials was calculated by applying the homogenization theory over the unit cell. The uniqueness of the presented multi-scale analysis related to the elastic problems solved at the microscopic scale (unit cell). This method has the advantage of applying periodic boundary conditions and uniform macroscopic temperature gradient over the unit cell. The proposed thermal multi-scale analysis was verified and its efficiency was demonstrated on large scale problem.     

Defining the relationship between fetal Doppler indices,abdominal circumference and growth rate in severe fetal growth restriction using functional linear discriminant analysis

The relationship between Doppler measurements, size and growth rate in fetal growth restriction has not been defined. We used functional linear discriminant analysis (FLDA) to investigate these parameters taking account of the difficulties inherent in exploring relationships between repeated observations from a small number of cases. In 40 fetuses with severe growth restriction, serial abdominal circumference (AC), umbilical, middle cerebral artery (MCA) and ductus venosus Doppler pulsatility index measurements were recorded. In 11 singleton fetuses with normal growth, umbilical artery pulsatility index only was measured. Data were expressed as z-scores in relation to gestation and analysed longitudinally using FLDA. In severe growth restriction, the Spearman correlation coefficients between umbilical artery pulsatility index and AC z-score, MCA pulsatility index and AC z-score and ductus venosus pulsatility index z-score and AC z-score were, respectively: −0.36, p = 4.4 × 10⁻⁷; 0.70, p = 1.1 × 10⁻¹⁷ and −0.50, p = 8.1 × 10⁻⁴. No relationship was seen between Doppler parameters and growth rate. There was no relationship between umbilical artery pulsatility index and AC nor growth rate in normally grown fetuses. In severe fetal growth restriction, Doppler changes are related to absolute fetal AC size, not growth rate.     

Digital library information-technology infrastructures

This paper charts a research agenda on systems-oriented issues in digital libraries. It focuses on the most central and generic system issues, including system architecture, user-level functionality, and the overall operational environment. With respect to user-level functionality, in particular, it abstracts the overall information lifecycle in digital libraries to five major stages and identifies key research problems that require solution in each stage. Finally, it recommends an explicit set of activities that would help achieve the research goals outlined and identifies several dimensions along which progress of the digital library field can be evaluated.     

Modelling the dynamics of log‐domain circuits

Log‐domain filters are an intriguing form of externally linear, internally nonlinear current‐mode circuits, in which a compression stage is first used to convert the input currents to the logarithmic domain, then analogue processing is carried out on the resulting voltages, and finally input–output linearity is restored by mapping the output voltages to current form through an expansion stage. The compressing and expanding operations confer on log‐domain filters a number of desirable features, but they may be responsible for the loss of external linearity. In this paper, sufficient conditions for the external linearity of log‐domain LC‐ladders are established, and the local nature of this external linearity is highlighted. Certain log‐domain LC‐ladders employing floating capacitors may exhibit externally nonlinear behaviour even for zero input and very small initial conditions. We show how transistor parasitic capacitances are central to the emergence of this behaviour, and must be incorporated in the circuit model. Copyright © 2006 John Wiley & Sons, Ltd.     

A Microtransceiver for UHF Proximity Links Including Mars Surface-to-Orbit Applications

A low-volume low-mass low-power ultra-high-frequency radio transceiver for future planetary missions is described. The project targets a volume of less than 10 , mass of less than 50 grams, and power consumption of 50 mW on receive and 100 mW, 300 mW, or 3 W on transmit (for 10 mW, 100 mW, and 1 W output options). The transmitter design supports convolutionally coded binary phase-shift keying (BPSK), RC-BPSK, and quadrature phase-shift keying transmission from 1 to 256 kbps. Command/control instructions can be received at 2 or 8 kbps, with a sensitivity of better than 120 dBm. In addition to its low volume/mass/power features, temperature compensation to 100 C and radiation tolerance to 100 krad allow operation outside of thermally controlled, shielded enclosures, further reducing the mass and complexity of exploration vehicles. The design is described in a top-down format, beginning with system requirements and proceeding through digital modem algorithm development, discussion of the silicon-on-sapphire CMOS process used and elaboration of key blocks in the radio-frequency (RF) integrated circuit design. Techniques to address coupling between high-sensitivity RF and on-chip digital circuits are also presented, and test results are given for prototypes of all major functions. Although designed for the Martian environment, the transceiver is expected to be useful in other proximity links where a small low-power radio compatible with Prox-1 space-link protocols is desired.     

Langevin-schroedinger formulation of electronic tunneling through a molecular bridge with a dissipative acceptor

Modeling electronic tunneling through molecular bridges is desired in order to understand the mechanism of long-range electron transfer reactions in nature, as well as for the design of novel molecular electronics devices. Particularly interesting is the effect of the nuclear motion at the molecular bridge on the electron transfer mechanism and rate. In this work we study the effect of electronic nuclear coupling at the molecular bridge on a unidirectional electronic tunneling process from an electron donor into a dissipative acceptor, as may appear in controlled electron transfer reactions at biological membranes, or in heterogeneous electron transfer reactions. The model includes a collection of harmonic bath modes coupled to the dissipative acceptor site and a single mode at the molecular bridge. The parameters of the dissipative bath are tuned such that the electronic population decays from the donor to the acceptor. This process is simulated using a time-dependent nonlinear Langevin-Schroedinger equation, based on a mean-field approximation for the electronic-nuclear coupling at the acceptor site and a numerically exact treatment of the electronic-nuclear coupling at the molecular bridge. The simulations at zero temperature and weak electronic-nuclear coupling demonstrate that electronic tunneling is promoted by coupling to the nuclear mode at the bridge. This result is consistent with our previous studies of electronic tunneling oscillations in a symmetric donor-bridge-acceptor complex, and it emphasizes the importance of electronic nuclear coupling in analyzing long-range electron transfer processes through molecular bridges or wires.     

Synthesis of Zirconia Colloids from Aqueous Salt Solutions

We monitor the synthesis of ZrO₂ colloids from dissolved ZrOCl₂·8H₂O using quasi-elastic light scattering and cryo-transmission electron microscopy (cryo-TEM). We investigate the effects of both precursor salt concentration and pH on the final size distribution. We find that the initial pH plays the most important role in the final particle size and yield. These trends and cryo-TEM observations help elucidate the roles of nucleation, aggregation, and recrystallization.     

A formal perspective on the view selection problem

The view selection problem is to choose a set of views to materialize over a database schema, such that the cost of evaluating a set of workload queries is minimized and such that the views fit into a prespecified storage constraint. The two main applications of the view selection problem are materializing views in a database to speed up query processing, and selecting views to materialize in a data warehouse to answer decision support queries. In addition, view selection is a core problem for intelligent data placement over a wide-area network for data integration applications and data management for ubiquitous computing. We describe several fundamental results concerning the view selection problem. We consider the problem for views and workloads that consist of equality-selection, project and join queries, and show that the complexity of the problem depends crucially on the quality of the estimates that a query optimizer has on the size of the views it is considering to materialize. When a query optimizer has good estimates of the sizes of the views, we show a somewhat surprising result, namely, that an optimal choice of views may involve a number of views that is exponential in the size of the database schema. On the other hand, when an optimizer uses standard estimation heuristics, we show that the number of necessary views and the expression size of each view are polynomially bounded. Received: November 20, 1001 / Accepted: May 30, 2002 / Published online: September 25, 2002