Coupling a branching process to an infinite dimensional epidemic process

Branching process approximation to the initial stages of an epidemic process has been used since the 1950's as a technique for providing stochastic counterparts to deterministic epidemic threshold theorems. One way of describing the approximation is to construct both branching and epidemic processes on the same probability space, in such a way that their paths coincide for as long as possible. In this paper, it is shown, in the context of a Markovian model of parasitic infection, that coincidence can be achieved with asymptotically high probability until o(N^{2/3}) infections have occurred, where N denotes the total number of hosts.Comment: 16 page

History of vascular disease and mild parkinsonian signs in community-dwelling elderly individuals

Background: Mild parkinsonian signs (MPS) are commonly found during the clinical examination of older people. These signs could reflect the accumulation of vascular pathological changes in the brain. If the etiology were vascular, one could hypothesize that individuals with MPS would be more likely to have systemic vascular disease than would their counterparts without these signs. Objectives: To examine whether MPS are associated with a history of vascular disease and whether certain MPS (rigidity, changes in axial function) are more strongly associated with a history of vascular disease than are other MPS (tremor). Methods: Evaluation of older people without dementia in Washington Heights-Inwood, northern Manhattan, NY. The presence of vascular diseases was assessed with a structured health interview. Results: Mild parkinsonian signs were present in 375 (16.4%) of 2286 participants without dementia. Diabetes mellitus, heart disease, peripheral vascular disease, and stroke were more prevalent in participants with MPS than without MPS, whereas nonvascular diseases (cancer, thyroid disease) were not. In a logistic regression analysis that adjusted for age, sex, education, and depressive symptoms, the number of vascular diseases was associated with MPS (odds ratio, 1.31 [95% confidence interval, 1.18-1.46]; P<.001). The combination of diabetes mellitus and heart disease increased the odds of MPS by 70% and the combination of these with stroke increased the odds by 332%. Conclusions: The presence of MPS in elderly individuals might reflect, in part, the accumulation of vascular pathological changes in the basal ganglia or white matter regions caused by preventable vascular diseases. Prospective and pathological studies are needed to further explore this finding

A law of large numbers approximation for Markov population processes with countably many types

When modelling metapopulation dynamics, the influence of a single patch on the metapopulation depends on the number of individuals in the patch. Since the population size has no natural upper limit, this leads to systems in which there are countably infinitely many possible types of individual. Analogous considerations apply in the transmission of parasitic diseases. In this paper, we prove a law of large numbers for rather general systems of this kind, together with a rather sharp bound on the rate of convergence in an appropriately chosen weighted $\ell_1$ norm.Comment: revised version in response to referee comments, 34 page

Mild parkinsonian signs and plasma homocysteine concentration in community-dwelling elderly individuals

Objective: To determine whether plasma homocysteine (Hcy) concentration is associated with mild parkinsonian signs (MPS) in community-dwelling elderly individuals. Design: Cross-sectional analyses of a population-based cohort study. Setting: Washington Heights–Inwood, New York. Patients: Persons without dementia 65 years and older. Main Outcome: Measure Participants underwent an abbreviated motor portion of the Unified Parkinson's Disease Rating Scale. Each participant was assigned an MPS score (range, 0-40). The Hcy concentration was measured from plasma. All analyses were cross-sectional. Results: There were 369 participants (mean ± SD age, 77.8 ± 6.0 years; mean ± SD MPS score, 1.51 ± 2.55; mean ± SD plasma Hcy concentration, 17.3 ± 6.5 μmol/L). Mean ± SD MPS scores in plasma Hcy concentration quintiles were as follows: lowest quintile, 1.15 ± 1.77; second quintile, 1.18 ± 1.88; third quintile, 1.64 ± 2.93; fourth quintile, 1.45 ± 2.17; and highest quintile, 2.12 ± 3.49 (84.3% higher than 1.15) (P = .02). In an unadjusted linear regression model, plasma Hcy concentration was associated with log MPS score (dependent variable) (P = .008). In a linear regression model that adjusted for confounding variables, plasma Hcy concentration was associated with log MPS score (P = .04). Conclusions: These data indicate that MPS are associated with higher plasma Hcy concentrations. Prospective neuroimaging as well as clinical-pathological studies would further our understanding of several mechanisms that could underlie the observed association

Energetics of rocked inhomogeneous ratchets

We study the efficiency of frictional thermal ratchets driven by finite frequency driving force and in contact with a heat bath. The efficiency exhibits varied behavior with driving frequency. Both nonmonotonic and monotonic behavior have been observed. In particular the magnitude of efficiency in finite frequency regime may be more than the efficiency in the adiabatic regime. This is our central result for rocked ratchets. We also show that for the simple potential we have chosen, the presence of only spatial asymmetry (homogeneous system) or only frictional ratchet (symmetric potential profile), the adiabatic efficiency is always more than in the nonadiabatic case.Comment: 5 figure

Distinct Biochemical Pools of Golgi Phosphoprotein 3 in the Human Breast Cancer Cell Lines MCF7 and MDA-MB-231

Golgi phosphoprotein 3 (GOLPH3) has been implicated in the development of carcinomas in many human tissues, and is currently considered a bona fide oncoprotein. Importantly, several tumor types show overexpression of GOLPH3, which is associated with tumor progress and poor prognosis. However, the underlying molecular mechanisms that connect GOLPH3 function with tumorigenicity are poorly understood. Experimental evidence shows that depletion of GOLPH3 abolishes transformation and proliferation of tumor cells in GOLPH3-overexpressing cell lines. Conversely, GOLPH3 overexpression drives transformation of primary cell lines and enhances mouse xenograft tumor growth in vivo. This evidence suggests that overexpression of GOLPH3 could result in distinct features of GOLPH3 in tumor cells compared to that of non-tumorigenic cells. GOLPH3 is a peripheral membrane protein mostly localized at the trans-Golgi network, and its association with Golgi membranes depends on binding to phosphatidylinositol-4-phosphate. GOLPH3 is also contained in a large cytosolic pool that rapidly exchanges with Golgi-associated pools. GOLPH3 has also been observed associated with vesicles and tubules arising from the Golgi, as well as other cellular compartments, and hence it has been implicated in several membrane trafficking events. Whether these and other features are typical to all different types of cells is unknown. Moreover, it remains undetermined how GOLPH3 acts as an oncoprotein at the Golgi. Therefore, to better understand the roles of GOLPH3 in cancer cells, we sought to compare some of its biochemical and cellular properties in the human breast cancer cell lines MCF7 and MDA-MB-231 with that of the non-tumorigenic breast human cell line MCF 10A. We found unexpected differences that support the notion that in different cancer cells, overexpression of GOLPH3 functions in diverse fashions, which may influence specific tumorigenic phenotypes

Effect of multivitamin and multimineral supplementation on cognitive function in men and women aged 65 years and over : a randomised controlled trial

Background: Observational studies have frequently reported an association between cognitive function and nutrition in later life but randomised trials of B vitamins and antioxidant supplements have mostly found no beneficial effect. We examined the effect of daily supplementation with 11 vitamins and 5 minerals on cognitive function in older adults to assess the possibility that this could help to prevent cognitive decline. Methods: The study was carried out as part of a randomised double blind placebo controlled trial of micronutrient supplementation based in six primary care health centres in North East Scotland. 910 men and women aged 65 years and over living in the community were recruited and randomised: 456 to active treatment and 454 to placebo. The active treatment consisted of a single tablet containing eleven vitamins and five minerals in amounts ranging from 50–210 % of the UK Reference Nutrient Intake or matching placebo tablet taken daily for 12 months. Digit span forward and verbal fluency tests, which assess immediate memory and executive functioning respectively, were conducted at the start and end of the intervention period. Risk of micronutrient deficiency at baseline was assessed by a simple risk questionnaire. Results: For digit span forward there was no evidence of an effect of supplements in all participants or in sub-groups defined by age or risk of deficiency. For verbal fluency there was no evidence of a beneficial effect in the whole study population but there was weak evidence for a beneficial effect of supplementation in the two pre-specified subgroups: in those aged 75 years and over (n 290; mean difference between supplemented and placebo groups 2.8 (95% CI -0.6, 6.2) units) and in those at increased risk of micronutrient deficiency assessed by the risk questionnaire (n 260; mean difference between supplemented and placebo groups 2.5 (95% CI -1.0, 6.1) units). Conclusion: The results provide no evidence for a beneficial effect of daily multivitamin and multimineral supplements on these domains of cognitive function in community-living people over 65 years. However, the possibility of beneficial effects in older people and those at greater risk of nutritional deficiency deserves further attention.Peer reviewedPublisher PD

Muonium as a hydrogen analogue in silicon and germanium; quantum effects and hyperfine parameters

We report a first-principles theoretical study of hyperfine interactions, zero-point effects and defect energetics of muonium and hydrogen impurities in silicon and germanium. The spin-polarized density functional method is used, with the crystalline orbitals expanded in all-electron Gaussian basis sets. The behaviour of hydrogen and muonium impurities at both the tetrahedral and bond-centred sites is investigated within a supercell approximation. To describe the zero-point motion of the impurities, a double adiabatic approximation is employed in which the electron, muon/proton and host lattice degrees of freedom are decoupled. Within this approximation the relaxation of the atoms of the host lattice may differ for the muon and proton, although in practice the difference is found to be slight. With the inclusion of zero-point motion the tetrahedral site is energetically preferred over the bond-centred site in both silicon and germanium. The hyperfine and superhyperfine parameters, calculated as averages over the motion of the muon, agree reasonably well with the available data from muon spin resonance experiments.Comment: 20 pages, including 9 figures. To appear in Phys. Rev.