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The micro-mixing combustion concept offers an elegant compromise between premixed and non-premixed combustion. By mixing the fuel and air at the smallest scale possible, one can achieve NOx emissions comparable to premixed combustion while minimizing the risks of autoignition and flashback, making this approach particularly well suited to high inlet temperature applications such as sub-MW recuperated gas turbines used in aerospace applications. This paper seeks to bridge the gap between current micro-mixing literature, limited to inlet temperatures < 800 K and hydrogen or hydrogen-rich fuels, with the design requirements of highly recuperated gas turbines, which operate on hydrocarbons at inlet temperatures > 950 K. Micro-mixing fuel nozzles are additively manufactured in Inconel 625, having up to hundreds of fuel injection holes as small as 250 μm. In addition to hydrogen, these nozzles are tested with hydrocarbon-based fuels such as propane, natural gas, and Jet A-1. An axial swirler is used to induce recirculation of the products behind the nozzle, which helps stabilize combustion with hydrocarbons due to their longer reaction times and slower flame speeds. Experimental results show that NOx emissions can be decreased down to premixed levels if the jet Damköhler number is kept under a critical value, which requires increasingly smaller holes or higher jet velocities as the inlet temperature increases. Combustion instabilities are observed at low inlet temperatures with hydrocarbons, which are also correlated to the jet Damköhler number. There is a window in which both low NOx and stable combustion is possible, which resulted in corrected NOx emissions of < 10 ppm for all the fuels tested at highly recuperated gas turbines conditions, specifically combustor inlet temperature of 950 K and flame temperature of 1550 K. The high inlet temperature also allowed to fully vaporize liquid fuels within the injector, leading to potential reductions in smoke emissions due to the absence of fuel droplets in the combustion zone.

The aerospace industry is gradually moving toward “more electric aircraft” to reduce its environmental footprint. Developing all-electric actuators brings a reliability challenge because conventional geared-motor actuators are susceptible to jamming failures from their metal-to-metal gear contacts. Magnetorheological clutch actuators solve this challenge using a layer of fluid to transmit torque and are not exposed to potential jam failures, making them particularly attractive for high reliability applications such as primary flight controls. A key challenge that must be addressed for a widespread deployment of the magnetorheological fluid technology in aerospace is the ability to monitor magnetorheological fluid condition while it degrades in operation. To date, no such efforts have been reported in the literature. Recent studies on magnetorheological fluid durability have shown that mixing the magnetorheological fluid using a magnetic screw pump principle can significantly increase the life of the fluid by up to 50%. This article presents the design, prototyping, and testing of a proof-of-concept magnetorheological fluid condition monitoring sensor, capitalizing on the flow-recirculating properties of magnetic screw magnetorheological clutches to continuously provide a well-mixed and homogeneous fluid sample to the sensor. The proposed sensing principle uses optical red green blue sensor placed in the fluid circulation path to measure the fluid color during degradation. The sensor has been tested up to fluid failure on a high-torque (60 N m) magnetorheological clutch mounted on a fully instrumented durability test bench. Tests have been performed with two types of fluid: a commercially available fluid, the Lord 140CG, and a homemade fluid based on perfluoropolyether oil, the GPL-103. Results with the Lord fluid demonstrate a strong correlation between the decrease in torque-to-current performance with fluid brightness. The average of three aging tests on Lord 140CG fluid show a 12% ± 1% decrease in brightness at end-of-life regardless of operating conditions such as torque, shear rate, and dissipated power. These results suggest that, for the Lord 140CG fluid, brightness is directly linked to the fluid degradation state and independent of operating conditions, which makes it a more accurate metric to quantify durability than life dissipated energy since the latter can vary significantly depending on operating conditions. Tests made with the GPL-103 based fluid did not show such a strong correlation, which means that optical sensing of magnetorheological fluid condition must be carefully calibrated for each individual fluid and clutch design. Results from this study suggest that optical sensing is a relevant method to measure the magnetorheological fluid condition in flow-recirculating clutches.

Magnetorheological clutches have great potential for demanding applications such as powertrains and aircraft primary flight controls. However, in such high-power applications (>1 kW), durability is a challenge because of the continuous slippage at the clutch shear interface. To improve durability, this research studies the potential of using a magnetic screw pump to promote fluid mixing within a magnetorheological clutch. The screw flights are made of magnetorheological fluid formed by the concentration of the magnetic field lines around helical grooves machined into the shear interface (drum) of the clutch. While the magnetic pump does not display a typical screw pump behavior, a semi-empirical yield screw pump model is proposed to better understand the macroscopic behavior. Experimental flow characterization results show that the pressure–flow relation is significantly affected by the number of grooves, magnetic field intensity, and rotational speed. For a clutch containing 50 mL of magnetorheological fluid, maximum flow rates of up to 25 mL/min and a maximum pressure of 150 kPa are achieved. Finally, durability test results show that the magnetic screw pump can increase durability by up to 42% when compared to a standard magnetorheological clutch, confirming that such a device is a viable solution for promoting durability.

The Inside-out ceramic turbine (ICT), a novel microturbine rotor architecture, has an air-cooled ring which keeps its composite rotating structural shroud within operating temperature. The cooling ring must achieve a significant radial temperature gradient with a minimal amount of cooling. The cooling ring is made through additive manufacturing, which opens the design space to tailored cooling geometries. Additively manufactured pin fin heat transfer enhancers are explored in this work to assess whether they hold any significant performance benefit over current rectangular cross-section open channels. Experimental friction factors and Nusselt numbers were determined for small, densely-packed pin fins over an asymmetrical thermal load. Results indicate that pressure loss is similar to what can be expected for additively manufactured pin fins, whereas heat transfer is lower due to the extremely tight streamwise pin spacing, in both in-line and staggered pin configurations. A design study presented in this paper suggests that pin fins are beneficial to an ICT for reducing cooling mass flow rate up to 40%, against an increase in cooling ring mass of roughly 50%.

We study the effect of gravity on neutrino flavor oscillations when each mass eigenstate is described by a wave packet instead of a plane wave. Two different approaches for implementing the wave packet formalism in the study of neutrino flavor oscillations in curved spacetime are examined. We work with a general static and spherically symmetric spacetime before applying our results to a few spacetime metrics of interest. We first focus on general relativity by examining the effect of the exterior and interior Schwarzschild solutions, as well as the de Sitter-Schwarzschild metric, and then we examine selected metrics from modified gravity models., Comment: 31 pages. 1 figure

Increasing turbine inlet temperature (TIT) of recuperated gas turbines would lead to simultaneously high efficiency and power density, making them prime candidates for low-emission aeronautics applications, such as hybrid-electric aircraft. The inside-out ceramic turbine (ICT) architecture achieves high TIT by using compression-loaded monolithic ceramics. To resist inertial forces due to blade tip speed exceeding 450 m/s, the shroud of the ICT is made of carbon-polymer composite, wound around a metallic cooling ring. This paper demonstrates that it is beneficial to use a titanium alloy cooling ring with a thermal barrier coating (TBC), rather than nickel superalloys, for the interstitial cooling ring protecting the carbon-polymer from the hot combustion gases. A numerical design of experiments (DOE) analysis shows the design tradeoffs between the minimum safety factor and the required cooling power for multiple geometries. An optimized high-pressure first turbine stage of a 500 kW microturbine concept using ceramic blades and a titanium cooling ring in an ICT configuration is presented. Its structural performance (minimum safety factor of 1.4), as well as its cooling losses, (2% of turbine stage power) are evaluated. Finally, a 20 kW-scale prototype is tested at 300 m/s and a TIT of 1375 K during 4 h to demonstrate the viability of the concept. Experiments show that the polymer composite was kept below its maximum safe operating temperature and components show no early signs of degradation.

We investigate the gravitational effect on Landau levels. We show that the familiar infinite Landau degeneracy of the energy levels of a quantum particle moving inside a uniform and constant magnetic field is removed by the interaction of the particle with a gravitational field. Two independent approaches are used to solve the relevant Schr\"odinger equation within the Newtonian approximation. It is found that both approaches yield qualitatively similar results within their respective approximations. With the goal of clarifying some results found in the literature concerning the use of a third independent approach for extracting the quantization condition based on a similar differential equation, we show that such an approach cannot yield a general and yet consistent result. We point out to the more accurate, but impractical, way to use such an approach; a way which does in principle yield a consistent quantization condition. We discuss how our results could be used to contribute in a novel way to the existing methods for testing gravity at the tabletop experiments level as well as at the astrophysical observational level by deriving the corrections brought by Yukawa-like and power-law deviations from the inverse-square law. The full relativistic regime is also examined in detail., Comment: 37 pages, no figures, matches the published version

In order to reach 40% efficiency, sub-MW turbines must operate in a recuperated gas Brayton cycle at a turbine inlet temperature (TIT) above 1300°C. Current sub-MW turbines have material-related operating temperature limits. Still to this day, there is no cost-effective rotor design which operates at such high temperatures. This paper introduces a novel, sliding-blade, inside-out ceramic turbine (ICT) wheel configuration, which could enable high-efficiency sub-MW recuperated engines to be achieved with cheap monolithic ceramic blades. The inside-out configuration uses a rotating structural hoop, or shroud, to convert centrifugal forces into compressive blade loading. The sliding-blade architecture uses a hub with angled planes on which ceramic blades slide up and down, allowing to match the radial expansion of the structural shroud. This configuration generates low stress values in both ceramic and metallic components and can achieve high tip speeds. A prototype is designed and its reliability is calculated using CARES software. The result is a design which has a single blade probability of failure (Pf) of 0.1% for 1000 h of steady operation. Analyses also demonstrate that reliability is greatly dependent on friction at ceramic-to-metal interfaces. Low friction could lead to acceptable reliability levels for engine applications. The prototype was successfully tested in a laboratory turbine environment at a tip speed of 350 m/s and a TIT of 1100 °C without any damage. These achievements demonstrate the robustness of the sliding-blade ICT configuration. Further research and development will focus on increasing tip speed and TIT to higher values.

Wavelength and polarization-dependent phase shifts on light interacting with a phase change material can lead to coloration shifts. By exploiting polarization selective effects, the range of attainable colors during switching of a phase-change layer is widened. Theoretical and experimental results are shown for the case of VO2, a reversible phase change material that can be excited thermally, electrically or optically.

We study the quantum Hall effect inside a gravitational field. First, we review the influence of the gravitational field of the Earth on the quantum Hall effect. Taking the gravitational field of the Earth to be uniform along the vertical direction, we compute the affected quantized Hall resistivity. Then, we investigate how the gravitational field modifies the Landau levels of a particle moving between two massive hemispheres in the presence of a constant and uniform magnetic field perpendicular to the plane of motion. We find that the familiar degeneracy of the Landau levels is removed and the spacing between the latter becomes dependent on the mass density of the hemispheres and on the gravitational constant $G$. We use this result to show that the quantum Hall effect in a thin conductor, sandwiched between two massive hemispheres, should yield a slightly different variation of the Hall resistivity with the applied magnetic field. We then argue that the well-known problem of the gravitationally induced electric field, that might a priori be thought to hinder the effect of gravity, has actually a beneficial role as it amplifies the latter. We finally discuss whether there is a possibility of using the quantum Hall effect to probe the inverse-square law of gravity., Comment: 35 pages, 3 figures, references updated

We have recently found that the gravitational field of a static spherical mass removes the Landau degeneracy of the energy levels of a particle moving around the mass inside a magnetic field by splitting the energy of the Landau orbitals. In this paper we present the second part of our investigation of the effect of gravity on Landau levels. We examine the effect of the gravitational fields created by an infinitely long massive cylinder and a rotating spherical mass. In both cases, we show that the degeneracy is again removed thanks to the splitting of the particle's orbitals. The first case would constitute an experimental test - which is quantum mechanical in nature - of the gravitational field of a cylinder. The approach relies on the Newtonian approximation of the gravitational potential created by a cylinder but, in view of self-consistency and for future higher-order approximations, the formalism is based on the full Levi-Civita metric. The second case opens up the possibility for a novel quantum mechanical test of the well-known rotational frame-dragging effect of general relativity., 35 Pages. References, corrections and improvements added. Accepted version for publication in EPJP

The Inside-Out Ceramic Turbine (ICT) is a promising microturbine for aeronautics applications. To increase the cycle efficiency and reduce fuel consumption, microturbines must operate under the recuperated Brayton cycle. The addition of a heat exchanger (HEx) increases the weight of the engine and cancels out any fuel savings as compared to a non-recuperated turbine. For this reason, the requirements applied to HEx for aeronautic gas turbines are: low weight and volume, high effectiveness with a low pressure drop, capabilities to endure high pressure and temperature, and low cost. The Laser powder bed fusion (LPBF) opens a new design space for geometries that cannot be realized by conventional methods, but induces high surface roughness. This paper presents experimental and analytical studies of the influence of surface roughness on the performances of a 3D-printed, counterflow, mini-channel HEx, with 1% of the total mass flow rate of the ICT. Results showed that the friction and heat transfer are both increased in the the regime typically defined as laminar compared to the analytical results. The experimental results are in agreement with a 1D heat transfer model when using correlations for high-roughness values from the literature. LPBF is a promising method to manufacture gas turbine parts, but it is crucial to model and incorporate its manufacturing capacities in terms of precision and surface finish to enhance HEx heat transfer and potentially reduce mass.

We examine a simple tabletop experimental setup for probing the inverse-square law of gravity and detecting eventual deviations therefrom. The nature of the setup allows indeed to effectively reach for shorter distances compared to what is allowed by other methods. Furthermore, we show that the same setup could also in principle be used to probe the interaction between gravitomagnetism and the intrinsic angular spin of quantum particles. Moreover, we show that the setup allows to have a gravitationally induced harmonic oscillator, introducing thus the possibility of studying in a novel way the interaction between gravity and quantum particles., Comment: 44 pages, 1 figure. Matches the accepted version in Int.J.Mod.Phys.D

A simple tabletop setup based on a superconducting quantum interference device is proposed for testing the gravitational interaction. A D-shaped superconducting loop has the straight segment immersed inside a massive sphere while the half-circle segment is wrapped around the sphere. The superconducting condensate within the straight arm of the loop thus bathes inside a gravitational simple harmonic oscillator potential while the condensate in the half-circle arm bathes in the constant gravitational potential around the sphere. The resulting phase difference at the Josephson junctions on both sides of the straight arm induces a sinusoidal electric current that has a frequency determined by the precise gravitational potential due to the massive sphere., 20 pages, 1 figure, references updated, title slightly improved

Thin layers of phase change materials are investigated theoretically and experimentally as way to modulate the properties of light interacting with silicon at a planar interface. By inducing a phase transition in vanadium dioxide films, the resulting changes in refractive index modulate the injection of light into silicon and the ejection out of it. Internal reflection of light propagating inside silicon causes the polarization state to be altered during the phase transition. Possible applications to silicon photonics are discussed.

The use of ceramics in gas turbines potentially allows for very high cycle efficiency and power density, by increasing operating temperatures. This is especially relevant for sub-megawatt gas turbines, where the integration of complex blade cooling greatly affects machine capital cost. However, ceramics are brittle and prone to fragile, catastrophic failure, making their current use limited to static and low-stress parts. Using the inside-out ceramic turbine (ICT) configuration solves this issue by converting the centrifugal blade loading to compressive stress, by using an external high-strength carbon-polymer composite rim. This paper presents a superalloy cooling system designed to protect the composite rim and allow it to withstand operating temperatures up to 1600 K. The cooling system was designed using one-dimensional (1D) models, developed to predict flow conditions as well as the temperatures of its critical components. These models were subsequently supported with computational fluid dynamics and used to conduct a power scalability study on a single stage ICT. Results suggest that the ICT configuration should achieve a turbine inlet temperature (TIT) of 1600 K with a composite rim cooling-to-main mass flow rate ratio under 5.2% for power levels above 350 kW. A proof of concept was performed by experimental validation of a small-scale 15 kW prototype, using a commercially available bismaleimide-carbon (BMI-carbon) composite rim and Inconel® 718 nickel-based alloy. The combination of numerical and experimental results show that the ICT can operate at a TIT of 1100 K without damage to the composite rim.

Ceramic turbines can reduce fuel consumption by increasing turbine inlet temperatures (TIT). The need for heat-resistant materials like ceramics is particularly acute for small turbomachines for which efficiencies are limited by the use of uncooled metal turbine as complex cooling schemes are impractical and costly. Efforts to introduce ceramics in the turbine rotor were made between the 1960s and the 1990s by gas turbines and automotive manufacturers in the U.S., Europe, and Japan. While significant progress was made, a suitable level of reliability still cannot be achieved as the brittleness of ceramics leads to crack propagation in the blades loaded in tension and catastrophic failure. The inside-out ceramic turbine (ICT) is a design alternative specific to ceramics that loads the blades in compression by using an outer, air-cooled composite rim that sustains the centrifugal loads. This paper provides an analytical model based on the Brayton cycle to compute the system-level performance of microturbines using an ICT. Loss submodels specific to ICT architectures are developed to account for: (1) composite rim drag, (2) composite rim cooling, (3) leakage through rotating seals, and (4) expansion heat losses. The thermodynamic core model is validated against three state-of-the-art, non-inside-out, microturbines. Based on a Monte Carlo simulation that takes into account the modeling uncertainties, the model predicts a cycle efficiency of 45±1% for a 240 kW ICT-based microturbine, leading to a predicted reduction in fuel consumption of 20% over current all-metal microturbines.

The durability of magnetorheological (MR) fluid is a fundamental aspect of any MR device, as MR fluid is submitted to shear stresses that cause its degradation. While various studies have identified MR-fluid degradation behaviours and proposed improvements, there exists no generalized failure theory to help understand the in-use degradation of MR fluids. In this regard, this study suggests that a relation exists between the Mason number and the maximum achievable lifetime dissipated energy (LDE) of magnetorheological (MR) fluids. To validate this hypothesis, custom (perfluoropolyether) and commercial (hydrocarbon) MR fluids are aged in various Mason number conditions using a clutch-type durability device. Experimental results show that under a critical Mason number of ~ 1, lifetime dissipated energy of the MR fluids can be related to the Mason Number using an analogy to metal fatigue failure. Above this critical Mason number, the fundamental degradation mechanism appears to change from a dominant mechanical wear of the particles (i.e. particle-limited) to another mechanism (i.e. fluid-limited) which is not yet fully understood. Since MR generally operate well below the critical Mason number of ~1, the relation between the Mason number and the particle-limited regime durability of MR fluids can be very useful to design novel MR fluids or MR devices, as it provides a way to estimate the impact of various design strategies on the total expected life of the device.

Objectifs: Le but de l'etude etait de comparer le resultat d'un test de depistage d'une minute au resultat d'un test de depistage valide de dix minutes pour le deficit cognitif leger (DCL) pour identifier les patients atteints d'un deficit cognitif (DC), chez des individus âges de 65 ans ou plus qui presentent deux facteurs de risque vasculaires (FRV) ou plus. Methodes: Des patients (n = 1 523) âges de 65 ans ou plus, sans symptome de DC etabli ou de demence mais qui presentaient deux FRV ou plus, ont participe a cette etude effectuee dans le contexte de soins de premiere ligne au Canada. Les donnees initiales etaient recueillies et l'Animal Fluency Test (AF) d'une minute et le Montreal Cognitive Assessment test (MoCA) de dix minutes etaient ensuite administres. Les medecins (n = 122) completaient le cahier d'observation pendant l'entrevue avec le patient et rapportaient leur impression diagnostique. La sensibilite du test AF, sa specificite et son exactitude pour predire un MoCa positif ont ete evaluees. Resultats: L'âge moyen des sujets etait de 79,7 ans, 55% etaient des femmes, 97,6% etaient des caucasiens et 75% avaient 12 ans ou moins de scolarite. Le test AF et le test MoCA ont detecte une DC chez 52% et 56% des sujets etudies respectivement. La sensibilite du test AF, la specificite et l'exactitude a predire un test MoCA positif etaient toutes deux de 67%. Selon l'impression diagnostique du medecin il s'agissait d'une DCL chez 37% des patients et d'une demence chez 6%. Conclusion: Dans une population âgee presentant au moins deux FRV, l'AF peut etre utile pour detecter les symptomes d'un DC ou d'une demence jusque la non reconnus. Le depistage d'un DC chez cette population a haut risque est justifie pour aider les medecins a identifier le debut d'un DC. Le peu de temps requis pour completer l'AF facilite son integration en pratique clinique.

There is general agreement that the current European gene pool is mainly derived from Palaeolithic hunting–gathering and Neolithic farming ancestors, but different studies disagree on the relative weight of these contributions. We estimated admixture rates in European populations from data on 377 autosomal microsatellite loci in 235 individuals, using five different numerical methods. On average, the Near Eastern (and presumably Neolithic) contribution was between 46 and 66%, and admixture estimates showed, with all methods, a strong and significant negative correlation with distance from the Near East. If the assumptions of the model are approximately correct, i.e. if the Basques' and Near Easterners' genomes represent a good approximation to the Palaeolithic and Neolithic settlers of Europe, respectively, these results imply that half or more of the Europeans' genes are descended from Near Eastern ancestors who immigrated in Europe 10 000 years ago. If these assumptions are incorrect, our results show anyway that clinal variation is the rule in the Europeans' genomes and that lower estimates of Near Eastern admixture obtained from the analysis of single markers do not reflect the patterns observed at the genomic level.

By simulating all possible offspring genotypic combinations based on pair-wise matings in three vulnerable or endangered populations of salmonids (two Atlantic salmon Salmo salar and one Arctic charr Salvelinus alpinus), family level estimates of potential offspring genetic diversity were calculated using several commonly used genetic diversity estimators (d 2 EST, d 2 scaled-EST and H EST ). By using this approach. the genetic variability of offspring could be predicted accurately based solely on parental genotype data. In addition, significant associations between offspring genetic variability and fitness-related traits were observed in the two Atlantic salmon populations and these associations were consistent between fitness measures and either estimated or observed genetic diversity. This indicates that associations with offspring fitness measures can be predicted without genetic analysis of the offspring themselves.

International audience; Craniometric measurements represent a useful tool for studying the differentiation of mammal populations. However, the fragility of skulls often leads to incomplete data matrices. Damaged specimens or incomplete sets of measurements are usually discarded prior to statistical analysis. We assessed the performance of two strategies that avoid elimination of observations: (1) pairwise deletion of missing cells, and (2) estimation of missing data using available measurements. The effect of these distinct approaches on the computation of inter-individual distances and population differentiation analyses were evaluated using craniometric measurements obtained from insular populations of deer mice Peromyscus maniculatus (Wagner, 1845). In our simulations, Euclidean distances were greatly altered by pairwise deletion, whereas Gower's distance coefficient corrected for missing data provided accurate results. Among the different estimation methods compared in this paper, the regression-based approximations weighted by coefficients of determination (r(2)) outperformed the competing approaches. We further show that incomplete sets of craniometric measurements can be used to compute distance matrices, provided that an appropriate coefficient is selected. However, the application of estimation procedures provides a flexible approach that allows researchers to analyse incomplete data sets.

Within-population genetic variability of twelve insular and four mainland populations of deer mice (Peromyscus maniculatus) was assessed using craniometric characters, and compared to results previously obtained from RAPD data. An index of Craniometric Variance (CVar) was computed from pairwise distances among all specimens. Variations in CVar measures were then compared to landscape variables using a linear regression approach. Our results suggest that CVar decreases in presence of large number of a competitive species (the boreal redback vole, Clethrionomys gapperi; r = -0.527, p < 0.037) in deer mouse populations. Island remoteness (r = -0.251, p < 0.220) and the geometry of the bank opposite to each island (r = - 0.459, p < 0.067) were marginally correlated with CVar, but the linear combination of these two variables, forming a composite isolation index, represented the major factor explaining the observed CVar (r = - 0.648, p < 0.011). Using a multiple regression model, 76.3% of the CVar was explained by a combination of this isolation index and the competitors' abundance. These results suggest that taking into account landscape barriers as well as the dispersal behavior of small mammals might provide sounder ecological variables than geographical distances alone for predicting within-population genetic variability in a network of habitat patches.

A survey of the genetic variability in deer mouse populations was performed using specimens collected from six different islands on a lake covering approximately 50 km2. Random amplified polymorphic DNA (RAPD) was used to measure the extent of the genetic differences in this insular system. An analysis of molecular variance (AMOVA) revealed that populations are clearly separated at this microgeographic scale (F st = 0.13863; P < 0.001). The homogeneity of molecular variance test (HOMOVA) indicated that within-population levels vary greatly (B p = 0.76831; P < 0.001). The within-population molecular variance was found to be mainly correlated with the accessibility of the islands, computed as the inverse of the geographic distance separating an island from the lakeshore (r = 0.916; P < 0.003).

This paper is intended to clarify some of the questions related with the application of RAPD for phylogenetic reconstruction purposes. Using different specimens of mammals selected across various taxonomic levels, we assessed the validity of RAPD to recover a known phylogeny, using four distance coefficients (simple matching, Russell & Rao, Jaccard, and Dice). We assessed the minimum number of primers required in the computations to obtain stable results in terms of distance estimates and/or topologies of the derived trees. These results based on distance methods were compared with those obtained with parsimony analyses of RAPD markers. Both approaches have shown to be equally problematic for comparing taxa above the family level. On the basis of these comparisons among various indices and methods, we recommend the use of Jaccard or Dice coefficients, with no less than twelve primers. We also suggest validation of any phylogeny based on RAPD data with a resampling procedure (i.e. the bootstrap or the jackknife) before any sound conclusion can be drawn.

Fibromyalgia syndrome (FMS) is a chronic disorder defined by widespread muscle pain and multiple tender points. The objectives of this study were to estimate prevalence of comorbidities, healthcare resources utilization, and costs associated with FMS.A retrospective cohort study was conducted using data from the Quebec provincial health plans (RAMQ) for a random sample of patients with diagnoses of FMS and a control cohort of patients without FMS, matched for age and gender. Prevalence of comorbidities was estimated. Healthcare resources consumed by FMS and non-FMS patients were identified in terms of visits to physicians, physician's interventions, pain-related medications, nonpain-related medications, and hospitalizations.A total of 16,010 patients with 2 diagnoses of FMS were identified, and control patients were randomly selected with a ratio of 1:1. Incidence of most comorbidities was significantly higher in the FMS group and the chronic disease score (3.8 vs. 2.8; ANOVA P0.001). The proportion of patients with at least 1 comorbidity was 87.4% in the FMS group and 60.1% in the control group (chiP0.001). The annual number of visits to physician and physician's interventions was 25.1 for FMS and 14.8 for non-FMS patients. The amount paid by the RAMQ was significantly higher for patients with FMS ($4065) compared with patients without FMS ($2766) (ANOVA P0.001).Results of this analysis of the RAMQ database illustrate the high prevalence of comorbidities among patients with a diagnosis of FMS and strongly indicate that the economic burden of FMS is substantial.

One of the key issues concerning the application of microsatellite DNA data in evolutionary studies is how the number of loci applied may influence the stability of genetic distances and corresponding phylograms. While computer simulations have suggested that over 30 microsatellites are required for accurate evolutionary inference, we show that a median of only six loci have been generally applied in studies of wild populations. Factors contributing to this contrast include: i) uncertainty regarding the potential benefits that can be gained from a realistic increase in the number of loci used; and ii) the lack of empirical studies assessing the influence of the number of microsatellites on the reliability of genetic distance estimation and phylogeny construction. In order to address these issues, we applied resampling techniques to microsatellite data in widely distributed populations of European grayling (Thymallus thymallus, Salmonidae). In agreement with expectations based on simulated data, we demonstrate empirically that the stability of commonly used genetic distances (DCE, DA and (deltamu)2) and the corresponding neighbor-joining phylograms is positively associated with the number of microsatellites utilized. For instance, increasing the number of loci from six to 17 resulted in a striking 75% increase in the proportion of DCE phylogram nodes supported by a bootstrap estimate of over 70%. Our results demonstrate that even moderately increasing the number of loci can be very beneficial--a finding extremely relevant for studies of natural populations for which optimally high microsatellite numbers are out of reach. Furthermore, the number of loci most commonly used to date may lead to erroneous inference of the evolutionary relationships between populations.

Numerous studies have relied on microsatellite DNA data to assess the relationships among populations in a phylogenetic framework, converting microsatellite allelic composition of populations into evolutionary distances. Among other coefficients, (δμ)2 and Rst are often employed because they make use of the differences in allele sizes on the basis of the stepwise mutation model. While it has been recognized that some microsatellites can yield disproportionate interpopulation distance estimates, no formal investigation has been conducted to evaluate to what extent such loci could affect the topology of the corresponding dendrograms. Here we show that single loci, displaying extremely large among-population variance, can greatly bias the topology of the phylogenetic tree, using data from European grayling (Thymallus thymallus, Salmonidae) populations. Importantly, we also demonstrate that the inclusion of a single disproportionate locus will lead to an overestimation of the stability of trees assessed using bootstrapping. To avoid this bias, we introduce a simple statistical test for detecting loci with significantly disproportionate variance prior to phylogenetic analyses and further show that exclusion of offending loci eliminates the false increase in phylogram stability.

In the present paper, we compare two methods (TRIANGLE and MW) for estimating trees from incomplete distances matrices through simulations. Our results illustrate that MW performs better for recovering path-length distances whereas TRIANGLE is superior in terms of topological recovery. Recommendations are provided as to which method should be used with real experimental data