Mathematics and Statistics

Objective The incidence of cardiovascular disease and the prevalence of risk factors have been shown to differ significantly across ethnic groups. The objective of this study was to examine the impact of ethnicity on 1-year mortality among patients with heart failure in a single payer healthcare system with universal access. Design, setting and patients Alberta residents aged 20 years or older hospitalised with heart failure between 1 April 1999 and 31 December 2005 are included. Previously validated algorithms were used to assign ethnicity based on patient surname. Patients were categorised as white, Chinese or East Indian. Main outcome measure One-year mortality after adjusting for baseline differences. Results 52 980 white, 851 Chinese, and 377 East Indian individuals were hospitalised with heart failure. Chinese patients were the oldest and had the highest rates of renal disease. East Indian patients were the youngest and had the highest rates of ischaemic heart disease and diabetes. One-year mortality rates were 31.0% among white patients, 38.7% among Chinese and 26.5% among East Indian patients (p<0.01). Adjusted HR (and 95% CI) for 1-year mortality among Chinese compared with white patients was 1.34 (1.20 to 1.49) and among East Indian compared with white patients it was 1.04 (0.85 to 1.27). These findings were consistent across various subgroups, including patients with incident heart failure. Conclusions Ethnicity appears to modulate patient outcomes in heart failure. Chinese patients have significantly higher 1-year mortality rates compared with white patients; there appear to be no differences in mortality among East Indian and white patients.

SummaryRenal stone formation due to hypercalciuria is a relatively common disorder with clear evidence for genetic predisposition, but cryptic phenotypic heterogeneity has hampered identification of candidate genes. The R990G single‐nucleotide polymorphism (SNP) of the calcium sensing receptor (CASR) gene has been associated with hypercalciuria in stone formers and shows the appropriate functional phenotype in cell culture. In our preliminary association analysis of a case‐control cohort, however, we observed significant Hardy‐Weinberg disequilibrium (HWD) for the cases (n= 223), but not controls (n= 676) at the R990G locus, pointing us toward the general disease model incorporating HWD. Because there is an adjacent CASR SNP, A986S, which is in negative linkage disequilibrium with R990G, we extended the general disease model to enable testing of a two‐site hypothesis. In our data set, there is no lack of fit (P= .345) for the single‐locus model for the R990G genotype, and likelihood...

Objective The incidence of cardiovascular disease and the prevalence of risk factors have been shown to differ significantly across ethnic groups. The objective of this study was to examine the impact of ethnicity on 1-year mortality among patients with heart failure in a single payer healthcare system with universal access. Design, setting and patients Alberta residents aged 20 years or older hospitalised with heart failure between 1 April 1999 and 31 December 2005 are included. Previously validated algorithms were used to assign ethnicity based on patient surname. Patients were categorised as white, Chinese or East Indian. Main outcome measure One-year mortality after adjusting for baseline differences. Results 52 980 white, 851 Chinese, and 377 East Indian individuals were hospitalised with heart failure. Chinese patients were the oldest and had the highest rates of renal disease. East Indian patients were the youngest and had the highest rates of ischaemic heart disease and diabetes. One-year mortality rates were 31.0% among white patients, 38.7% among Chinese and 26.5% among East Indian patients (p<0.01). Adjusted HR (and 95% CI) for 1-year mortality among Chinese compared with white patients was 1.34 (1.20 to 1.49) and among East Indian compared with white patients it was 1.04 (0.85 to 1.27). These findings were consistent across various subgroups, including patients with incident heart failure. Conclusions Ethnicity appears to modulate patient outcomes in heart failure. Chinese patients have significantly higher 1-year mortality rates compared with white patients; there appear to be no differences in mortality among East Indian and white patients.

Standard practice in obstructive sleep apnea (OSA) management requires that a positive diagnostic, overnight polysomnography (PSG) test be obtained before initiating treatment. However, long waiting times due to lack of access to PSG testing facilities may delay the initiation of definitive treatment for OSA. To evaluate the response of patients who had a high clinical suspicion for OSA and who were waiting for a PSG test to an empirical continuous positive airway pressure (CPAP) trial. A retrospective study of all patients who had been offered empirical CPAP therapy for suspected OSA was conducted. After outpatient assessment, 183 patients with a high pretest probability of having OSA began empirical CPAP testing using an arbitrary CPAP pressure. The presence of OSA, the accuracy of empirical CPAP pressure prescription, the adherence to empirical CPAP and the improvement in daytime somnolence were evaluated at the time of PSG. Of 183 patients on a CPAP trial, 91% had OSA, which was...

The behaviour of a Pólya-like urn which generates Ewens' sampling formula in population genetics is investigated. Connections are made with work of Watterson and Kingman and to the Poisson-Dirichlet distribution. The order in which novel types occur in the urn is shown to parallel the age distribution of the infinitely many alleles diffusion model and consequences of this property are explored. Finally the urn process is related to Kingman's coalescent with mutation to provide a rigorous basis for this parallel.

We present long-slit spectroscopic data which reveals extended Lyman alpha emission around the z=6.417 radio-quiet quasar CFHQS J2329-0301. The Lyman alpha emission is extended over 15 kpc and has a luminosity of > 8 x 10^36 W, comparable to the most luminous Lyman alpha halos known. The emission has complex kinematics, in part due to foreground absorption which only partly covers the extended nebula. The velocity ranges from -500 km/s to +500 km/s, with a peak remarkably close to the systemic velocity identified by broad MgII emission of the quasar. There is no evidence for infall or outflow of the halo gas. We speculate that the Lyman alpha emission mechanism is recombination after quasar photo-ionization of gas sitting within a high-mass dark matter halo. The immense Lyman alpha luminosity indicates a higher covering factor of cold gas compared to typical radio-quiet quasars at lower redshift.

We take a model for Ferromagnetic Superconductors based on a variational energy functional, and search for radially symmetric minimizers. First we define what it means for a solution to the Euler-Lagrange equations to be admissible, before relating these admissible solutions to an appropriate function space. We then use a variational approach to prove the existence of minimizers. Since it is not clear at first whether or not the energy is bounded below, the direct method of the calculus of variations does not apply. Instead, we first prove existence in a case where the energy is bounded below, namely when the Zeeman coupling constant g vanishes. We then use the implicit function theorem to prove the existence of physically relevant minimizers for small values of g.

introduced a qualitative simplification to the ADM1 model for anaerobic digestion. We obtain global results for this model by first analyzing the limiting system, a model of single species growth in the chemostat in which the response function is non-monotone and the species decay rate is included. Using a Lyapunov function argument and the theory of asymptotically autonomous systems, we prove that even in the parameter regime where there is bistability, no periodic orbits exist and every solution converges to one of the equilibrium points. We then describe two algorithms for stochastically perturbing the parameters of the model. Simulations done with these two algorithms are compared with simulations done using the Gillespie and tau-leaping algorithms. They illustrate the severe impact environmental factors may have on anaerobic digestion in the transient phase.

For the general central force equations of motion in n&gt;1 dimensions, a complete set of 2n first integrals is derived in an explicit algorithmic way without the use of dynamical symmetries or Noether&#39;s theorem. The derivation uses the polar formulation of the equations of motion and yields energy, angular momentum, a generalized Laplace-Rugge-Lenz vector, and a temporal quantity involving the time variable explicitly. A variant of the general Laplace-Rugge-Lenz vector, which generalizes Hamilton&#39;s eccentricity vector, is also obtained. The physical meaning of the general Laplace-Rugge-Lenz vector, its variant, and the temporal quantity are discussed for general central forces. Their properties are compared for precessing bounded trajectories versus non-precessing bounded trajectories, as well as unbounded trajectories, by considering an inverse-square force (Kepler problem) and a cubically perturbed inverse-square force (Newtonian revolving orbit problem).

We analyze a within-host model of virus infection with antibody and CD8 cytotoxic T lymphocyte (CTL) responses proposed by Schwartz et al. (2013). The goal of this work is to gain an overview of the stability of the biologically-relevant equilibria as a function of the model’s immune response parameters. We show that the equilibria undergo at most two forward transcritical bifurcations. The model is also explored numerically and results are applied to equine infectious anemia virus infection. In order to arrive at stability of the biologically-relevant endemic equilibrium characterized by coexistence of antibody and CTL responses, the parameters promoting CTL responses need to be boosted over parameters promoting antibody production. This result may seem counter-intuitive (in that a weaker antibody response is better) but can be understood in terms of a balance between CTL and antibody responses that is needed to permit existence of CTLs. In conclusion, an intervention such as a vac...