Stability of various doping species in trans-polyacetylene

Polyacetylene, a simple conjugated organic polymer, a material of strong interest if doped by various chemical species such as iodine or antimony pentafluoride : its electrical conductivity increases by more than twelve orders of magnitude. By increasing the dopant concentration one obtains a semiconductive or a metallic regime. Such properties allow us to make electronic material and then devices by convenient n or p type doping of polyacetylene. However,it is necessary to determine the thermal stability of the various dopant species. In this paper, we compared the stability of iodine, SbF₅ and CF₃SO₃H dopants by studying the mass loss and the electrical conductivity decrease at various temperatures from 20‡C up to 180‡C. It is shown that only SbF₅ is a relatively stable dopant up to 80‡C, a temperature which may be reached in some active electronic devices. Raman spectroscopy allowed us to measure the ratio of I₋₃ to I₋₅ ions during the desorption process and to propose a possible chemical reaction which produces gaseous iodine from the active dopant species.     

Vitamin B12 and folate levels and lithium administration in patients with affective disorders

BACKGROUND: It is unclear whether there is a relationship between lithium administration and vitamin B12 metabolism. METHODS: We compared serum B12, serum folate, and red blood cell folate concentrations in patients receiving and not receiving lithium at two Mood Disorders Clinics. As the two centers differed in vitamin assay methods, data were first analyzed separately and then combined. To rule out an in vitro effect of lithium on the assays, we also added varying amounts of lithium to lithium-free blood samples and measured vitamin concentrations. RESULTS: Mean serum B12 concentrations were approximately 20% lower in the lithium than in the nonlithium group at each center. This difference was statistically significant for each center and on combination (two-tailed p = .017, .021, and .0009). The parametric effect size for each center and the combined weighted mean effect size were moderate in magnitude (.605, .523, and .565). There was a nonsignificant trend toward an increased prevalence of assay-defined B12 deficiency in the lithium group at one center only, with no cases in either group at the other center and a nonsignificant combined relative risk. CONCLUSIONS: Our data may represent a lithium-associated decrease in serum B12 concentration. The clinical significance of these findings is not yet clear.     

Constructing the Lyee method with a method engineering approach

This paper proposes an Evolution driven ME approach aiming to support the evolution of an existing method (the As–Is method) in order to obtain a new method (the To–Be method) better adapted to a given engineering situation and/or satisfying new methodogical requirements. The proposed approach is used in order to evolve the existing Lyee method into a Lyee user driven method.¹     

During the initiation of fermentation overexpression of hexokinase PII in yeast transiently causes a similar deregulation of glycolysis as deletion of Tps1

In the yeast Saccharomyces cerevisiae a novel control exerted by TPS1 (GGS1FDP1BYP1CIF1GLC6TSS1)-encoded trehalose-6-phosphate synthase, is essential for restriction of glucose influx into glycolysis apparently by inhibiting hexokinase activity in vivo. We show that up to 50-fold overexpression of hexokinase does not noticeably affect growth on glucose or fructose in wild-type cells. However, it causes higher levels of glucose-6-phosphate, fructose-6-phosphate and also faster accumulation of fructose-1,6-bisphosphate during the initiation of fermentation. The levels of ATP and Pi correlated inversely with the higher sugar phosphate levels. In the first minutes after glucose addition, the metabolite pattern observed was intermediate between those of the tps1Δ mutant and the wild-type strain. Apparently, during the start-up of fermentation hexokinase is more rate-limiting in the first section of glycolysis than phosphofructokinase. We have developed a method to measure the free intracellular glucose level which is based on the simultaneous addition of d-glucose and an equal concentration of radiolabelled l-glucose. Since the latter is not transported, the free intracellular glucose level can be calculated as the difference between the total d-glucose measured (intracellular+periplasmic/extracellular) and the total l-glucose measured (periplasmic/extracellular). The intracellular glucose level rose in 5 min after addition of 100 mm-glucose to 0·5–2 mm in the wild-type strain, ±10 mm in a hxk1Δ hxk2Δ glk1Δ and 2–3 mm in a tps1Δ strain. In the strains overexpressing hexokinase PII the level of free intracellular glucose was not reduced. Overexpression of hexokinase PII never produced a strong effect on the rate of ethanol production and glucose consumption. Our results show that overexpression of hexokinase does not cause the same phenotype as deletion of Tps1. However, it mimics it transiently during the initiation of fermentation. Afterwards, the Tps1-dependent control system is apparently able to restrict properly up to 50-fold higher hexokinase activity. © 1998 John Wiley & Sons, Ltd.     

An Impulse System for 60-GHz Wireless Networks Based on Polymer Optical Fiber

A specific impulse optical fiber system has been achieved to enhance the connectivity of 60-GHz wireless networks. Using an impulse technology, this original configuration is an efficient alternative to the conventional 60-GHz radio-over-fiber systems. Baseband subnanosecond pulses first modulate the amplitude of a 60-GHz radio-frequency carrier and second the intensity of a distributed feedback laser operating at 1300 nm. Properties of the multimode plastic optical fiber based on a perfluorinated material are exploited to transmit such signals. The overall system performance has been tested experimentally in a multihop configuration; bit-error-rate measurements are better than for transmission data rates up to 200 Mb/s.     

Link-State-Based Algorithms for Dynamic Routing in All-Optical Networks with Ring Topologies

The increased usage of large bandwidth in optical networks raises the problems of efficient routing to allow these networks to deliver fast data transmission with low blocking probabilities. Due to limited optical buffering in optical switches and constraints of high switching speeds, data transmitted over optical networks must be routed without waiting queues along a path from source to destination. Moreover, in optical networks deprived of wavelength converters, it is necessary for each established path to transfer data from source to destination by using only one wavelength. To solve this NP-hard problem, many algorithms have been proposed for dynamic optical routing like Fixed-Paths Least Congested (FPLC) routing or Least Loaded Path Routing (LLR). This paper proposes two heuristic algorithms based on former algorithms to improve network throughput and reduce blocking probabilities of data transmitted in all-optical networks with regard to connection costs. We also introduce new criteria to estimate network congestion and choose better routing paths. Experimental results in ring networks show that both new algorithms achieve promising performance.     

Modeling real-time 3-d lung deformations for medical visualization.

In this paper, we propose a physics-based and physiology-based approach for modeling real-time deformations of 3-D high-resolution polygonal lung models obtained from high-resolution computed tomography (HRCT) images of normal human subjects. The physics-based deformation operator is nonsymmetric, which accounts for the heterogeneous elastic properties of the lung tissue and spatial-dynamic flow properties of the air. An iterative approach is used to estimate the deformation with the deformation operator initialized based on the regional alveolar expandability, a key physiology-based parameter. The force applied on each surface node is based on the airflow pattern inside the lungs, which is known to be based on the orientation of the human subject. The validation of lung dynamics is done by resimulating the lung deformation and comparing it with HRCT data and computing force applied on each node derived from a 4-D HRCT dataset of a normal human subject using the proposed deformation operator and verifying its gradient with the orientation.     

A 40 GHz single-ended down-conversion mixer in 0.13 /spl mu/m SiGeC BiCMOS HBT

This work presents a single-ended active mixer realized with a 0.13 /spl mu/m BiCMOS SiGeC heterojunction bipolar transistor (HBT) technology. This mixer is designed to be integrated in a superheterodyne receiver for 40 GHz wireless communication systems. Local oscillator (LO) and RF signals are directly applied to the base of the HBT through two coupled lines. The mixer provides a down-conversion from 42 GHz to 2 GHz. The mixer exhibits a power conversion gain better than 2.4 dB and a measured double-sideband noise figure less than 8.3 dB for P/sub LO/=3 dBm (power of the local oscillator) under a global power consumption lower than 9.5 mW. This architecture exhibits good linearity performance with a measured IP/sub 1dB/ of about -7 dBm and an IIP3 of +4 dBm. The linear dynamic range for a 2 GHz system bandwidth is approximately 65 dB for P/sub LO/=+2 dBm and T/sub 0/=290 K. The third order spurious free dynamic range is calculated to be better than 52 dB.     

Fast algorithm for 3-D vascular tree modeling

In this short paper, accelerated three-dimensional computer simulations of vascular trees development, preserving physiological and haemodynamic features, are reported. The new computation schemes deal: (i). with the geometrical optimization of each newly created bifurcation; and (ii). with the recalculation of blood pressures and radii of vessels in the whole tree. A significant decrease of the computation time is obtained by replacing the global optimization by the fast updating algorithm allowing more complex structure to be simulated. A comparison between the new algorithms and the previous one is illustrated through the hepatic arterial tree.     

Task-based optimization and performance assessment in optical coherence imaging

Optimization of an optical coherence imaging (OCI) system on the basis of task performance is a challenging undertaking. We present a mathematical framework based on task performance that uses statistical decision theory for the optimization and assessment of such a system. Specifically, we apply the framework to a relatively simple OCI system combined with a specimen model for a detection task and a resolution task. We consider three theoretical Gaussian sources of coherence lengths of 2, 20, and 40 microm. For each of these coherence lengths we establish a benchmark performance that specifies the smallest change in index of refraction that can be detected by the system. We also quantify the dependence of the resolution performance on the specimen model being imaged.