1,487 research outputs found
Influence of Time-Dependent Power Dissipations on the Ageing Behavior of Thick-Film Resistors
Reliability experiments on hybrid circuits are usually carried out by accelerated ageing test. The circuits
or the components under test are stored at an elevated ambient temperature and the change of their
electric properties is controlled at regular times. The situation becomes entirely different if the temperature
rise is due to the power dissipation in the component under test and not caused by external
means. In electronic circuits, power dissipations are expressed by a mean value, whereas the actual
situation is generally a time-dependent function. The temperature will then also be time dependent.
Therefore, ageing tests on thick film resistors will be presented in this contribution. Resistors are
submitted to a DC power source and a pulse shaped one. Different ageing characteristics are observed
Dynamic Thermal Analysis of a Power Amplifier
This paper presents dynamic thermal analyses of a power amplifier. All the
investigations are based on the transient junction temperature measurements
performed during the circuit cooling process. The presented results include the
cooling curves, the structure functions, the thermal time constant distribution
and the Nyquist plot of the thermal impedance. The experiments carried out
demonstrated the influence of the contact resistance and the position of the
entire cooling assembly on the obtained results.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Application of Structure Functions for the Investigation of Forced Air Cooling
This paper presents thermal analyses of a power amplifier placed in a wind
tunnel. All the investigations are based on the transient temperature
measurements performed during the circuit cooling process. The measured cooling
curves were used to compute the cumulative and differential structure functions
for the circuit with a heat sink. These functions helped to determine the
optimal values of circuit model parameters necessary for numerical thermal
simulations. The experiments demonstrated the influence of the wind speed on
the value of the heat transfer coefficient and consequently on the temperature
of the entire structure.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
The future of metabolic engineering and synthetic biology: Towards a systematic practice
Industrial biotechnology promises to revolutionize conventional chemical manufacturing in the years ahead, largely owing to the excellent progress in our ability to re-engineer cellular metabolism. However, most successes of metabolic engineering have been confined to over-producing natively synthesized metabolites in E. coli and S. cerevisiae. A major reason for this development has been the descent of metabolic engineering, particularly secondary metabolic engineering, to a collection of demonstrations rather than a systematic practice with generalizable tools. Synthetic biology, a more recent development, faces similar criticisms. Herein, we attempt to lay down a framework around which bioreaction engineering can systematize itself just like chemical reaction engineering. Central to this undertaking is a new approach to engineering secondary metabolism known as ‘multivariate modular metabolic engineering’ (MMME), whose novelty lies in its assessment and elimination of regulatory and pathway bottlenecks by re-defining the metabolic network as a collection of distinct modules. After introducing the core principles of MMME, we shall then present a number of recent developments in secondary metabolic engineering that could potentially serve as its facilitators. It is hoped that the ever-declining costs of de novo gene synthesis; the improved use of bioinformatic tools to mine, sort and analyze biological data; and the increasing sensitivity and sophistication of investigational tools will make the maturation of microbial metabolic engineering an autocatalytic process. Encouraged by these advances, research groups across the world would take up the challenge of secondary metabolite production in simple hosts with renewed vigor, thereby adding to the range of products synthesized using metabolic engineering.National Institutes of Health (U.S.) (1-R01-GM085323-01A1)Special Research Funds BOF (BOF08/PDO/014)Research Foundation Flanders (FWO-Vlaandern V.4.174.10.N.01
Variational assimilation of Lagrangian data in oceanography
We consider the assimilation of Lagrangian data into a primitive equations
circulation model of the ocean at basin scale. The Lagrangian data are
positions of floats drifting at fixed depth. We aim at reconstructing the
four-dimensional space-time circulation of the ocean. This problem is solved
using the four-dimensional variational technique and the adjoint method. In
this problem the control vector is chosen as being the initial state of the
dynamical system. The observed variables, namely the positions of the floats,
are expressed as a function of the control vector via a nonlinear observation
operator. This method has been implemented and has the ability to reconstruct
the main patterns of the oceanic circulation. Moreover it is very robust with
respect to increase of time-sampling period of observations. We have run many
twin experiments in order to analyze the sensitivity of our method to the
number of floats, the time-sampling period and the vertical drift level. We
compare also the performances of the Lagrangian method to that of the classical
Eulerian one. Finally we study the impact of errors on observations.Comment: 31 page
Clinical infections and nonsurgical treatment of parapharyngeal space infections complicating throat infection
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