A comparison between different PMD compensation techniques

We quantify the benefits of using different techniques for compensation of polarization mode dispersion (PMD) in fiber-optic communication systems by means of numerical simulations. This is done both with respect to PMD-induced pulse broadening and in terms of system outage probability for different data formats [nonreturn-to-zero (NRZ) and return-to-zero (RZ)]. Attention is focused on simple and relevant single- and double-stage post-transmission compensators with a few degrees of freedom (DOF). It is generally believed that a PMD compensator with a polarization controller and a variable delay line can only compensate the PMD to the first order. We show, from analytical results, the counterintuitive fact that this scheme can also partially compensate for higher order PMD. We also investigate the benefit of using a polarizer as compensation element where the optical average power can be used as a feedback signal     

Tensile,creep, and low-cycle fatigue behavior of a cast γ-TiAl-based alloy for gas turbine applications

The influence of chemical composition on the microstructure of the γ-titanium aluminide alloy Ti-48Al-2W-0.5Si (at. pct) and the accompanying tensile, low-cycle fatigue, and creep properties has been evaluated. The study showed that small variations in chemical composition and casting procedures resulted in considerable variations in the microstructure, yielding vastly different mechanical properties. Low contents of aluminum and tungsten led to a coarse-grained lamellar (γ/α ₂) microstructure with high creep resistance. A composition close to the nominal one produced a duplex (γ+γ/α ₂) structure with favorable strength, ductility, and low-cycle fatigue properties. By controlling the solidification and cooling rates at casting, a pseudoduplex (PS-DP) microstructure with a unique combination of high strength and high fatigue and creep resistance can be obtained. These unique properties can be explained by the diffuse boundaries between the relatively small γ grains and the neighboring lamellar colonies, combined with semicoherent interfaces between the γ and α ₂ phases. At tensile and low-cycle fatigue loading, these boundaries act like high-angle boundaries, producing a virtually fine-grained material promoting strength, whereas at creep loading, grain-boundary sliding is hindered in the semicoherent interfaces leading to high creep resistance.     

Optimization of metal-based multilayers for transparent heat mirrors

Multilayer calculations by conventional matrix methods for dielectricum/noble metal/dielectricum systems on glass have been performed. The aim has been to maximize the integrated parameters for solar transmission, T_sol, and transmission of visible light, T_eye We have found that Ag is superior for maximizing the transmittance over the narrow visible wavelength range owing to the low internal absorptance. When solar energy transmission is considered multilayers based on Au are the best choice for metal film thicknesses above 15 nm. For thinner films, Ag is still to be preferred.     

Effects of quinine on the mechanical frequency response of the cupula in the fish lateral line

Quinine induces changes in the motion of the cupula in the lateral line canal of the African knife-fish in response to sinusoidal water movements. Two different phases in the action of quinine on the cupular frequency response can be discerned. In the first phase the best frequency, i.e., the frequency at which the cupular vibratory displacement is maximal in response to constant-amplitude sinusoidal canal fluid displacement, shifts toward higher frequencies. During this phase, lasting about 70-100 min, the best frequency increases by a factor between 1.3 and 1.5. In the second phase, during roughly the following 90 min, the best frequency decreases gradually to a value 0.3-0.5 times that observed before the application of quinine.     

Pressure pain thresholds in patients with craniomandibular disorders before and after treatment with acupuncture and occlusal splint therapy: a controlled clinical study

Fifty-five patients (46 women and 9 men) with craniomandibular disorders and a history of pain of at least 6 months' duration participated in this trial. The patients were randomly assigned to three groups: one group to receive acupuncture; one group to receive occlusal splint therapy; and one group to act as controls. Pressure pain threshold, clinical dysfunction score, and visual analog scale measures were used to evaluate patients before, immediately after, and 6 months after treatment. A moderate, but statistically significant, correlation was found between pressure pain threshold and the number of tender spots in the masticatory muscles (tau = -.43; P < .001), degree of tenderness in the masticatory muscles (tau = -.43; P < .001), clinical dysfunction score (tau = .32; P < .001), and the visual analog scale (tau = -.25; P < .01). The short-term results showed a statistically significant improvement in all evaluations for both treatment groups. No significant differences were found in the control group. The improvements resulted in significant differences between the control and each treatment group immediately after treatment. At the 6-month follow-up, no significant differences in pressure pain threshold or clinical dysfunction score were found in the two treatment groups compared with the short-term results.     

Fatigue anisotropy in cross-rolled, hardened medium carbon steel resulting from MnS inclusions

Anisotropy of forged steel components is especially adverse when it concerns rotationally symmetric components. Manganese sulfides (MnS) in steels may be desired for their improvement of machining properties; however, they also deteriorate fatigue behavior. A quantification of the effect of MnS on anisotropy is necessary to find an optimum for component dimensioning. To isolate the influence of MnS on anisotropy only, high cleanness of the test material is required. The test material in the current investigation was molten in a vacuum furnace to high-cleanness composition. Materials with two different S levels were produced to detect variations in anisotropy according to amount, shape, and distribution of the MnS inclusions. The two batches were cross-rolled to plates with a deformation ratio of 4.5. The MnS phase constitutes, upon forging or rolling, pancake-shaped inclusions. In the case of cross-rolling, an in-plane rotational symmetry of the inclusions could be created. The shape and size of these inclusions are essential for the mechanical behavior of the material. Push-pull fatigue testing was performed in longitudinal (in plane) and short transversal directions relative to the rolling plane. The results showed strong anisotropy of the fatigue behavior with inferior performance in short transverse directions where the principal stress is perpendicular to the flattened inclusions. The anisotropy was somewhat more pronounced for the high-S material, resulting from a different fatigue crack growth mechanism.     

Test procedures for verification of an electron pencil beam algorithm implemented for treatment planning

The calculation of an electron dose distribution in a patient is a difficult problem because of the presence of tissue and surface inhomogeneities. Verification of the dose planning system is therefore essential. In this investigation, a novel method is used to evaluate a commercially available system (Helax-TMS), at electron energies between 10 and 50 MeV, both for a conventional treatment unit and an MLC-collimated scanned beam unit with a helium-filled treatment head. First, the experiments were designed to verify the local beam database and some fundamental characteristics of the electron beam calculations. Secondly, a number of generalised situations that would be encountered in the clinical treatment planning were evaluated oblique incidence, field shaping with multi-leaf collimator, bolus edges, and air cavities. Dose distributions in two generalised anatomical phantoms simulating a neck and a nose were also analysed. The results have, when so possible, been presented as the dose ratio within the 'flattened area' for dose profiles and down to the 'treatment depth' (80% dose level) for depth doses. In the penumbra region and in the dose fall-off region, the comparison has been represented by the distance deviation between calculated and measured dose profiles or depth doses. A new tool, 'volume integration', was used to evaluate the deviations from a more clinical point of view. Most results were within +/- 2% in dose for volumes larger than a sphere with a diameter of 15 mm, or +/- 2 mm in position. Dose deviations were generally found for oblique incidences and below heterogeneities such as small air cavities and bolus edges in limited volumes.     

Extraction technique for the determination of oxygen-18 in water using preevacuated glass vials

The need for a rapid, inexpensive technique for routine 18O/16O extraction from water has arisen recently through applications in the medical sciences and in hydrology. The traditional experimental technique for determining the oxygen isotope composition of water, the CO2-H2O equilibration method, is tedious, time consuming, and involves the use of custom-made glass apparatus. Furthermore, because of potential memory effects from one sample to the next, the glassware needs to be thoroughly cleaned between runs. A few attempts have been made to improve upon the method. Attempts to analyze water directly in the source of the mass spectrometer produced large memory effects and questionable results. Commercially available apparatus for automated extraction of 18O/16O from water is generally prohibitively expensive and often is designed to interface only with the manufacturer's own mass spectrometer. The method described in this paper utilizes inexpensive, off-the-shelf, preevacuated, glass vials. Preevacuated vials have been used by others for the isotopic analysis of breath CO2 and are well tested. The vials can be purchased in bulk from scientific apparatus suppliers at a relatively low cost. These are coupled with a simplified extraction line consisting of a stainless steel syringe needle and a glass cold trap. Vials are filled with CO2 and H2O and shaken in a constant-temperature water bath for at least 90 min. Since the vials are discarded after use, no cleaning is necessary, essentially eliminating any memory effect. Reproducibility is generally better than +/- 0.05%. The only reagents required are gaseous CO2 for equilibration, a dry ice/alcohol mixture for trapping water, and liquid nitrogen for transferring the CO2.