Thin-film flow of a viscoplastic material round a large horizontal stationary or rotating cylinder

We consider the steady two-dimensional thin-film flow of a viscoplastic material, modelled as a biviscosity fluid with a yield stress, round the outside of a large horizontal stationary or rotating cylinder. In both cases we determine the leading- order solution both when the ratio of the viscosities in the 'yielded' and 'unyielded' regions is of order unity and when this ratio approaches zero in the appropriate distinguished limit. When the viscosity ratio is of order unity the flow consists, in general, of a region of yielded fluid adjacent to the cylinder and a region of unyielded fluid adjacent to the free surface, separated by the yield surface. In the distinguished limit the flow consists, in general, of a region of yielded fluid adjacent to the cylinder whose stress is significantly above the yield stress and a pseudo-plug region adjacent to the free surface, in which the leading-order azimuthal component of velocity varies azimuthally but not radially, separated by the pseudo-yield surface; the pseudo-plug is itself, in general, divided by the yield surface into a region of yielded fluid whose stress is only just above the yield stress and a region of unyielded fluid adjacent to the free surface whose stress is significantly below the yield stress. The solution for a stationary cylinder represents a curtain of fluid with prescribed volume flux falling onto the top of and off at the bottom of the cylinder. If the flux is sufficiently small then the flow is unyielded everywhere, but when it exceeds a critical value there is a yielded region. In the distinguished limit the yielded region always extends all the way round the cylinder, but the unyielded region does so only when the flux is sufficiently small. For a rotating cylinder a film with finite thickness everywhere is possible only when the flux is sufficiently small. Depending on the value of the flux and the speed of rotation the flow may be unyielded everywhere, have a yielded region on the right of the cylinder only, or have yielded regions on both the right and left of the cylinder. At the critical maximum flux the maximum supportable weight of fluid on the cylinder is attained and the pseudo-yield, yield and free surfaces all have a corner. In the distinguished limit there are rigid plugs (absent in the stationary case) near the top and bottom of the cylinder

On the gravity-driven draining of a rivulet of a viscoplastic material down a slowly varying substrate

We use the lubrication approximation to investigate the steady locally unidirectional gravity-driven draining of a thin rivulet of viscoplastic material, modeled as a biviscosity fluid (or, as a special case, as a Bingham material), down a slowly varying substrate. In contrast to the earlier work on viscoplastic rivulets we consider small-scale flows, such as those found in many industrial coating and printing processes, in which surface-tension effects play a significant role. We interpret our results as describing a slowly varying rivulet draining in the azimuthal direction from the top to the bottom of a large horizontal circular cylinder. Provided that the yield stress is nonzero we find that the flow is always unyielded near the top of the cylinder (where the rivulet becomes infinitely wide in the transverse direction), and, except in the special case when the viscosity ratio is zero, near the bottom of the cylinder (where it becomes infinitely deep). For sufficiently small values of the prescribed volume flux the flow is unyielded everywhere, but for larger values of the flux the flow near the substrate in the center of the rivulet is yielded. We obtain numerically calculated values of the semiwidth of the rivulet and of the yielded region as well as of the maximum height of the rivulet and of the yielded region for a range of parameter values, and describe the asymptotic behavior of the solution in the limits of large and small yield stress, large and small flux, and small viscosity ratio. In the special case of a Bingham material the flow near the top of the cylinder consists of an infinitely wide rigid and stationary plug, while elsewhere it consists of two rigid and stationary 'levæ#169;es' at the edges of the rivulet and a central region in which the flow near the free surface is a 'pseudoplug' whose velocity does not vary normally to the substrate, separated from the 'fully plastic' flow near the substrate by a 'pseudoyield surface.' ¦#169;2002 American Institute of Physics

Restoring the sting to metric preheating

The relative growth of field and metric perturbations during preheating is sensitive to initial conditions set in the preceding inflationary phase. Recent work suggests this may protect super-Hubble metric perturbations from resonant amplification during preheating. We show that this possibility is fragile and sensitive to the specific form of the interactions between the inflaton and other fields. The suppression is naturally absent in two classes of preheating in which either (1) the vacua of the non-inflaton fields during inflation are deformed away from the origin, or (2) the effective masses of non-inflaton fields during inflation are small but during preheating are large. Unlike the simple toy model of a $g^2 \phi^2 \chi^2$ coupling, most realistic particle physics models contain these other features. Moreover, they generically lead to both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble scales. Large-scale coherent magnetic fields may also appear naturally.Comment: 6 pages, 3 ps figures, RevTex, revised discussion of backreaction and new figure. To appear Phys. Rev. D (Rapid Communication

Generating asymptotically plane wave spacetimes

In an attempt to study asymptotically plane wave spacetimes which admit an event horizon, we find solutions to vacuum Einstein's equations in arbitrary dimension which have a globally null Killing field and rotational symmetry. We show that while such solutions can be deformed to include ones which are asymptotically plane wave, they do not posses a regular event horizon. If we allow for additional matter, such as in supergravity theories, we show that it is possible to have extremal solutions with globally null Killing field, a regular horizon, and which, in addition, are asymptotically plane wave. In particular, we deform the extremal M2-brane solution in 11-dimensional supergravity so that it behaves asymptotically as a 10-dimensional vacuum plane wave times a real line.Comment: 23 pages, 1 eps figure; harvmac; v2:refs added; v3:minor comments adde

Distribution of invasive alien Tithonia (Asteraceae) species in eastern and southern Africa and the socio-ecological impacts of T. diversifolia in Zambia

Background: Many alien plant species, such as Tithonia diversifolia, T. rotundifolia and T. tubaeformis, have been introduced to areas outside of their natural distribution range to provide benefits, but have subsequently become invasive, threatening biodiversity and agricultural productivity. Objectives: The aim of this study was to determine the current distribution and dates of introduction of invasive Tithonia species in eastern and southern Africa and to document the effects of T. diversifolia on rural livelihoods in Zambia. Method: Roadside surveys, and other sources of information, were used to determine the distribution of invasive Tithonia species in eastern and southern Africa. Household interviews were conducted to gauge perceptions and understand the impacts of T. diversifolia on local livelihoods in Zambia’s Copperbelt province. Results: Tithonia diversifolia is widespread in Uganda, Kenya, Tanzania, South Africa, Malawi and parts of Zambia but less so in Zimbabwe. Tithonia rotundifolia was comparatively uncommon in eastern Africa but common in some southern African countries, while T. tubaeformis was invasive in Swaziland, South Africa, Zambia and possibly also Zimbabwe. According to the majority of respondents in Zambia, T. diversifolia has negative impacts on native vegetation, mobility or access, water availability, crop yields and animal health. Conclusion: Invasive Tithonia species are widespread and spreading throughout much of Africa. Livelihood and biodiversity costs have not been considered by those actively promoting the use and further dissemination of T. diversifolia. We therefore recommend that detailed cost–benefit studies should be undertaken to support informed decisions on the future management of these species

Approach to the semiconductor cavity QED in high-Q regimes with q-deformed boson

The high density Frenkel exciton which interacts with a single mode microcavity field is dealed with in the framework of the q-deformed boson. It is shown that the q-defomation of bosonic commutation relations is satisfied naturally by the exciton operators when the low density limit is deviated. An analytical expression of the physical spectrum for the exciton is given by using of the dressed states of the cavity field and the exciton. We also give the numerical study and compare the theoretical results with the experimental resultsComment: 6 pages, 2 figure

Closed string tachyons, flips and conifolds

Following the analysis of tachyons and orbifold flips described in hep-th/0412337, we study nonsupersymmetric analogs of the supersymmetric conifold singularity and show using their toric geometry description that they are nonsupersymmetric orbifolds of the latter. Using linear sigma models, we see that these are unstable to localized closed string tachyon condensation and exhibit flip transitions between their two small resolutions (involving 2-cycles), in the process mediating mild dynamical topology change. Our analysis shows that the structure of these nonsupersymmetric conifolds as quotients of the supersymmetric conifold obstructs the 3-cycle deformation of such singularities, suggesting that these nonsupersymmetric conifolds decay by evolving towards their stable small resolutions.Comment: Latex, 22 pgs, 2 figs. v4: matches JHEP version, 29 pgs, 3 figures, more elaborate Introduction, various clarifications adde

Somatotypes trajectories during adulthood and their association with COPD phenotypes

Rationale: Chronic obstructive pulmonary disease (COPD) comprises distinct phenotypes, all characterised by airflow limitation. Objectives: We hypothesised that somatotype changes - as a surrogate of adiposity - from early adulthood follow different trajectories to reach distinct phenotypes. Methods: Using the validated Stunkard''s Pictogram, 356 COPD patients chose the somatotype that best reflects their current body build and those at ages 18, 30, 40 and 50 years. An unbiased group-based trajectory modelling was used to determine somatotype trajectories. We then compared the current COPD-related clinical and phenotypic characteristics of subjects belonging to each trajectory. Measurements and main results: At 18 years of age, 88% of the participants described having a lean or medium somatotype (estimated body mass index (BMI) between 19 and 23 kg.m(-2)) while the other 12% a heavier somatotype (estimated BMI between 25 and 27 kg.m(-2)). From age 18 onwards, five distinct trajectories were observed. Four of them demonstrating a continuous increase in adiposity throughout adulthood with the exception of one, where the initial increase was followed by loss of adiposity after age 40. Patients with this trajectory were primarily females with low BMI and D-LCO (diffusing capacity of the lung for carbon monoxide). A persistently lean trajectory was seen in 14% of the cohort. This group had significantly lower forced expiratory volume in 1 s (FEV1), D-LCO, more emphysema and a worse BODE (BMI, airflow obstruction, dyspnoea and exercise capacity) score thus resembling the multiple organ loss of tissue (MOLT) phenotype. Conclusions: COPD patients have distinct somatotype trajectories throughout adulthood. Those with the MOLT phenotype maintain a lean trajectory throughout life. Smoking subjects with this lean phenotype in early adulthood deserve particular attention as they seem to develop more severe COPD

The role and importance of gene polymorphisms in the development of atherosclerosis

The development of atherosclerosis is a multifactorial process. The purpose of the study was to examine three genetic polymorphisms playing a role in the metabolic processes underlying the disease. We compared the data of 348 atherosclerotic non-diabetic patients with 260 atherosclerotic diabetic patients and 384 healthy controls. We analyzed the prevalence of myocardial infarction and stroke in three different groups of patients carrying different polymorphisms. It was proved that if the mutant TT eNOS Glu298ASP variant is present, a significantly higher number of myocardial infarctions can be observed than in patients carrying heterozygote GT or normal GG genotype. We proved that in the case of MTHFR 677CT heterozygote variants, the occurrence of myocardial infarction is significantly higher and the difference is also significant in case of the 677TT homozygote variant. It was verified that among patients with the mutant TNF-α AA genotype the occurrence of cardiovascular events was significantly higher. Screening the genetically high risk groups on the long run should be considered as an early detection opportunity that may give better chances for prevention and treatment. Understanding the inflammatory mechanisms of the atherosclerosis may give new therapeutical targets to pharmacologists

Somatotypes trajectories during adulthood and their association with COPD phenotypes

Rationale: Chronic obstructive pulmonary disease (COPD) comprises distinct phenotypes, all characterised by airflow limitation. Objectives: We hypothesised that somatotype changes – as a surrogate of adiposity – from early adulthood follow different trajectories to reach distinct phenotypes. Methods: Using the validated Stunkard’s Pictogram, 356 COPD patients chose the somatotype that best reflects their current body build and those at ages 18, 30, 40 and 50 years. An unbiased group-based trajectory modelling was used to determine somatotype trajectories. We then compared the current COPD-related clinical and phenotypic characteristics of subjects belonging to each trajectory. Measurements and main results: At 18 years of age, 88% of the participants described having a lean or medium somatotype (estimated body mass index (BMI) between 19 and 23 kg·m−2 ) while the other 12% a heavier somatotype (estimated BMI between 25 and 27 kg·m−2 ). From age 18 onwards, five distinct trajectories were observed. Four of them demonstrating a continuous increase in adiposity throughout adulthood with the exception of one, where the initial increase was followed by loss of adiposity after age 40. Patients with this trajectory were primarily females with low BMI and DLCO (diffusing capacity of the lung for carbon monoxide). A persistently lean trajectory was seen in 14% of the cohort. This group had significantly lower forced expiratory volume in 1 s (FEV1), DLCO, more emphysema and a worse BODE (BMI, airflow obstruction, dyspnoea and exercise capacity) score thus resembling the multiple organ loss of tissue (MOLT) phenotype. Conclusions: COPD patients have distinct somatotype trajectories throughout adulthood. Those with the MOLT phenotype maintain a lean trajectory throughout life. Smoking subjects with this lean phenotype in early adulthood deserve particular attention as they seem to develop more severe COPD