Degree of polarization degradation due to cross-phase modulation and its impact on polarization-mode dispersion compensators

A novel analytical model is proposed to predict the cross-phase modulation (XPM)-induced depolarization in a two-channel transmission system, in which the Stokes' vector of each channel rotates around a space-invariant pivot by a time-varying angle which depends on the total instantaneous optical power in the fiber, on the angle between pump and probe input Stokes' vectors, and on the walk-off between channels. The model leads to a simple formula of the probe degree of polarization (DOP) which is validated both by simulation and experiment. The model helps identify the key physical factors that determine the XPM-induced performance degradation of DOP-based first-order polarization-mode dispersion compensators, and experiments that quantify such degradation are presented.     

Imaging of mouse experimental melanoma in vivo and ex vivo by combination of confocal and nonlinear microscopy

We investigated possibilities of the combination of the one- and two-photon excitation microscopy for examination of the experimental melanoma tissue in vivo, in mice under general anesthesia, and ex vivo on freshly harvested specimens. Our aim was to obtain sufficiently informative images of unstained tumor tissues and their modifications after hyperthermia treatment. The mouse experimental melanoma structure was studied and compared with normal tissue from the same animal by using confocal and nonlinear microscopy techniques based on (i) one-photon excitation (1PE) fluorescence, (ii) 1PE reflectance, (iii) second harmonic generation imaging, and (iv) two-photon excitation autofluorescence. We checked different spectral conditions and other settings of image acquisition, as well as combinations of the above imaging modalities, to fully exploit the potential of these techniques in the evaluation of treated and untreated cancer tissue morphology. Our approach enabled to reveal the collagen fiber network in relation with the other tissues, and to identify invasive tumor cells. It also proved to be useful for the examination of interrelationships between functional and morphological aspects based on optical properties of the tissues, especially in studies of changes between the tumor and control tissue, as well as changes induced by physical treatments, e.g., delivery of microwave hyperthermia treatment. These differences were also evaluated quantitatively, when we found out that the maximum Euler–Poincaré characteristic reflects well the melanoma morphological structure. The results showed that the proposed investigative approach could be suitable also for a direct evaluation of tissue modifications induced by clinical interventions. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc.     

Dominance dimension: a common parametric formulation for integer-valued scientific impact indices

We introduce the dominance dimension principle and the parameterized family of criteria for the assessment of publication/citation profiles it generates. We show that by a suitable choice of parameters dominance dimension may specialize to the most widely known and used of those impact scores for the scientific output of authors which disallow endogenous reputation effects, including the Durfee- or h-number, the publication number and the citation number.     

Prediction of hot deformation resistance during processing of microalloyed steels in plate rolling process

Mean flow stress of microalloyed high-strength steels during plate rolling has been thoroughly studied. It has been found out by both thermomechanical tests and measurements taken in the industrial plate mill. For this purpose, log data obtained from the plate rolling mills have been converted to mean flow stress using the Sims approach. The agreement between thermomechanical tests and mill data has been tested in order to confirm that thermomechanical testing can provide an easy, convenient and very effective simulation of industrial hot rolling process. The results are analysed and compared to the predictions of some mathematical models developed in literature. Subsequently, the best performing formula, namely the Poliak's equation, has been optimised by means of genetic algorithms and the standard Gauss–Newton method. This latter has allowed a finer tuning of the models' parameters in order to fit at best the available data. The Poliak's formula optimised by genetic algorithms is shown to accurately predict the mean flow stress and therefore it provides a useful tool for the determination of the milling settings before the incoming strip enters the mill.     

Microcells in personal communications systems

Research projects involving fiber-connected microcell base units, measurements and models of propagation in urban microcells, and radio link performance in urban microcells are summarized. Developments in microcell system issues, such as channel assignments and handoff in microcells and architectures for combining microcells with traditional macrocells, are discussed. Research on both indoor radio propagation and wireless indoor systems is reviewed     

Hypoxia-ischemia induces a rapid elevation of ubiquitin conjugate levels and ubiquitin immunoreactivity in the immature rat brain

Postnatal rats at 7 and 21 days of age were subjected to unilateral hypoxia-ischemia (H/I) by right carotid artery ligation followed by 1.5 to 2 hours of hypoxia (8% oxygen). Brains were frozen at specific intervals of recovery from 0 to 24 hours. Western blots of samples of right and left forebrain were immunodeveloped with a monoclonal antibody specific for ubiquitin, RHUb1. An elevation of ubiquitin conjugate levels in the right compared with the left forebrain of 7-day-old animals was detectable immediately following H/I and increased by close to 60% of control level within 1 hour of recovery. The conjugate immunoreactivity remained at this level for 6 hours but had declined to control levels by 24 hours of recovery. No such increase was observed in response to hypoxia alone. Similar changes were observed in samples from the 21-day-old rat brain. However, the elevation of ubiquitin conjugate levels was of slower onset and persisted longer than observed for the 7-day-old animals. Immunocytochemical studies of brain fixed by immersion in formaldehyde/acetone/methanol showed that ubiquitin-like immunoreactivity was increased in the right, but not left, cerebral cortex and hippocampus of animals subjected to H/I. The data suggest that elevated ubiquitination may represent a neuroprotective response to H/I.     

A linear theory for laminates composed of coupled layers

Laminated composites are realised by the stacking of basic layers. If the Classical Laminated Plate Theory (CLPT) allows us to calculate the elastic behaviour of a laminate composed of traditional layers (mats, unidirectionals, taffetas, …), it is unable to do it when less common layers are used (satins for instance), because these layers are extension and bending coupled. The first part of this paper deals with this problem, and all the equations solving it are completely defined. In addition, another topic is touched on: a coupled layer does not present the same elastic behaviour if it is turned over. As a consequence, this effect is studied and a methodology is detailed to take it into account. Including the turn-over into the previous equations, a whole linear theory for laminates composed of coupled layers is obtained. Finally, uncoupling and quasi-homogeneity of laminates composed of orthotropic coupled layers are solved.     

Designing the elastic properties of laminates as an optimisation problem: a unified approach based on polar tensor invariants

The problem of designing the elastic properties of a laminate is considered. It is shown that a unique formulation for all the design problems with respect to elastic symmetries can be found using polar invariants of the stiffness tensors. In this way, the design of laminates having some general elastic properties is reduced to a classical optimisation problem: the search for the absolute minimum, whose value is 0, of a positive semi-definite form in the space of the polar invariants. A minimum characterisation of some important elastic properties is also given. Some numerical examples and a discussion of the results are also included in the paper.     

Statistical characterization of the Jones matrix of long fibers affected by polarization mode dispersion (PMD)

The unitary transfer matrix of a fiber affected by polarization mode dispersion (PMD) is analyzed using the Stokes representation of its eigenmodes and its retardation angle, or equivalently through its Pauli coordinates. We develop a statistical theory applied to these parameters and relate it to the extensive existing literature on the statistics of the PMD vector Dynamical equations are established for the Pauli coordinates. Assuming a standard "white Gaussian" model for the local birefringence, and using the tools of stochastic calculus, we derive the distributions of the eigenmodes, the retardation angle, the Pauli coordinates, and of the frequency derivatives of all these parameters. The evolution in space of the Pauli coordinates is also characterized as a standard Brownian motion on the unit sphere in /spl Rfr//sup 4/. An expression for the frequency autocorrelation function of the Pauli coordinates, the eigenmodes and the retardation angle is derived and their coherence bandwidth is compared to that of the PMD vector. All theoretical results are supported by simulation over an ensemble of 10000 fibers, using the standard retarder plate model.