Gain temperature dependence of erbium-doped silica and fluoridefiber amplifiers in multichannel wavelength-multiplexed transmissionsystems

The temperature dependence of the gain of aluminosilica and fluoride based erbium-doped fiber amplifiers are theoretically and experimentally examined and compared. As expected from the larger temperature dependence of erbium-doped fluoride fibers (EDFB) cross sections, the single channel gain of EDFF amplifiers presents larger wavelength-dependent temperature sensitivity. The implications of this large and nonuniform temperature dependence of the gain on wavelength-division multiplexing (WDM) are theoretically analyzed and discussed     

Efficient Implementation Methodology of Fast FIR Filtering Algorithms on DSP

A class of Finite Impulse Response (FIR) filtering algorithms based either on short Fast Fourier Transforms (FFT) or on short length FIR filtering algorithms was recently proposed. Besides the significant reduction of the arithmetic complexity, these algorithms present some characteristics which make them useful in many applications, namely a small delay processing (independent on the FIR filter length) as well as a multiply-add based computational structure. These algorithms are presented in a unified framework, thus allowing an easy combination of any of them. However, a remaining difficulty concerns the implementation of the fast algorithms on Digital Signal Processors (DSP), given the DSP finite resources (number of pointers, registers and memory), while keeping as much as possible the improvement brought by the reduction of the arithmetic complexity. This paper provides an efficient implementation methodology, by organizing the algorithm in such a way that the memory data access is optimized on a DSP. As a result, our implementation requires a constant number of pointers whatever the algorithm combination. This knowledge is used in a DSP code generator which is able to select the appropriate algorithm meeting the application constraints, as well as to generate automatically an optimized assembly code, using macro-instructions available in a DSP-dependent library. An improvement of more than 50% in terms of throughput (number of machine cycles per point) compared to the implementation of the direct convolution is generally achieved.     

On the methods for solving Yule-Walker equations

The three well-known fast algorithms for the solution of Yule-Walker equations-the Levinson, Euclidean, and Berlekamp-Massey algorithms-are reviewed, and the relationship between each of them and the Pade approximation problem is shown. The algorithms are classified with reference to three criteria, namely: (1) the path they follow in the Pade table; (2) the organization of the computations (one-pass or two-pass); and (3) the auxiliary variables used. This classification shows that the set of known classical algorithms is not complete, and the missing variants are proposed. With these variants of the Berlekamp-Massey and Euclid algorithms, both forward and backward predictors can be obtained without additional cost. A unified representation of the two-pass algorithms is given in such a way that the application of the divide and conquer strategy becomes straightforward. A general doubling algorithm which represents all the associated doubling algorithms in an exhaustive way is provided     

Apropos of a case of neuromeningeal viral infection in pediatrics]

The effect of the immunomodulator 2-methyl-4-amino-6-oxypyrimidine (MAOP)on delayed hypersensitivity was studied in experiments on mongrel mice and in C57Bl and CBA mice. The effect of MAOP and that of oxymethyluracil on delayed hypersensitivity to sheep erythrocytes and dinitrofluorobenzene were compared. Immunosuppression of mice was induced by hydrocortisone in a dose of 50 mg/kg.     

Pharmacokinetics of fusidic acid after a single dose of a new paediatric suspension

Cell proliferation in response to growth factors is mediated by specific high affinity receptors. Ligand-binding by receptors of the protein tyrosine kinase family results in the stimulation of several intracellular signal transduction pathways. Key signalling enzymes are recruited to the plasma membrane through the formation of stable complexes with activated receptors. These interactions are mediated by the conserved, non-catalytic SH2 domains present in the signalling molecules, which bind with high affinity and specificity to tyrosine-phosphorylated sequences on the receptors. The assembly of enzyme complexes is emerging as a major mechanism of signal transduction and may regulate the pleiotropic effects of growth factors.     

Joint source-channel coding using real BCH codes for robust image transmission.

In this paper, a new still image coding scheme is presented. In contrast with standard tandem coding schemes, where the redundancy is introduced after source coding, it is introduced before source coding using real BCH codes. A joint channel model is first presented. The model corresponds to a memoryless mixture of Gaussian and Bernoulli-Gaussian noise. It may represent the source coder, the channel coder, the physical channel, and their corresponding decoder. Decoding algorithms are derived from this channel model and compared to a state-of-art real BCH decoding scheme. A further comparison with two reference tandem coding schemes and the proposed joint coding scheme for the robust transmission of still images has been presented. When the tandem scheme is not accurately tuned, the joint coding scheme outperforms the tandem scheme in all situations. Compared to a tandem scheme well tuned for a given channel situation, the joint coding scheme shows an increased robustness as the channel conditions worsen. The soft performance degradation observed when the channel worsens gives an additional advantage to the joint source-channel coding scheme for fading channels, since a reconstruction with moderate quality may be still possible, even if the channel is in a deep fade.     

A new quantization optimization algorithm for the MPEG advanced audio coder using a statistical subband model of the quantization noise

In this paper, an improvement of the quantization optimization algorithm for the MPEG Advanced Audio Coder (AAC) is presented. This algorithm, given a bit-rate constraint, minimizes the perceived distortion generated by the signal compression. The distortion can be related to the quantization error level over frequency subbands through an auditory model. Thus, optimizing the quantization requires knowledge of the rate-distortion function for each subband. When this function can be modeled in a simple way, the algorithm can take a one-loop recursive structure. However, in the MPEG AAC, the rate-distortion function is hard to characterize, since AAC makes use of nonlinear quantizers and variable length entropy coders. As a result, the standard algorithm makes use of two nested loops with a local decoder, in order to measure the error level rather than predicting its value. We first describe a partial subband modeling of the rate-distortion function of interest in the MPEG AAC. Then, using a statistical approach, we find a relationship between the error level and the so-called quantization "scale-factor" and propose a new algorithm that is basically similar to a classical one loop "bit allocation" process. Finally, we describe the complete algorithm and show that it is more efficient than the standard one.     

In vivo mouse spinal cord imaging using echo-planar imaging at 11.75 T

Object To evaluate the feasibility of mouse spinal cord MR imaging using echo-planar imaging (EPI). Materials and methods Optimized multi-shot spin-echo-EPI sequences were compared to conventional spin-echo (c-SE) at 11.75 T and used for high-spatially resolved acquisitions and relaxation-time measurements. Results Good quality images were obtained, with clear delineation of gray and white matter. Acquisition-time gain factor was up to 6 (vs. c-SE) and resolution up to 74 × 94 μm² was achieved. T ₁ and T ₂ relaxation times were reliably measured. Conclusion High-temporally and spatially resolved mouse spinal cord EPI imaging is feasible. This technique should greatly benefit to long acquisition-time experiments (diffusion imaging) and imaging of rapidly-evolving pathologies. V. Callot and G. Duhamel equally contributed to this work.     

Variable neighborhood descent with iterated local search for routing and wavelength assignment

In this work we treat the Routing and Wavelength Assignment (RWA) with focus on minimizing the number of wavelengths to route demand requests. Lightpaths are used to carry the traffic optically between origin-destination pairs. The RWA is subjected to wavelength continuity constraints, and a particular wavelength cannot be assigned to two different lightpaths sharing a common physical link. We develop a Variable Neighborhood Descent (VND) with Iterated Local Search (ILS) for the problem. In a VND phase we try to rearrange requests between subgraphs associated to subsets of a partition of the set of lightpath requests. In a feasible solution, lightpaths belonging to a subset can be routed with the same wavelength. Thus, the purpose is to eliminate one subset of the partition. When VND fails, we perform a ILS phase to disturb the requests distribution among the subsets of the partition. An iteration of the algorithm alternates between a VND phase and a ILS phase. We report computational experiments that show VND-ILS was able to improve results upon powerful methods proposed in the literature.