22 research outputs found
Effects of the wind speeds on heat transfer in a street canyon with a skytrain station
No full text© 2019, The Author(s).
The street under a skytrain station can be seen in many urban cities. Due to the cavity geometry of the street canyon, natural ventilation is decreased. The reduction of the ventilation causes the heat accumulation in the street canyon. To keep the thermal climate at an acceptable level in the street canyon, controlling the air movement with proper temperature is important. In this paper, mathematical models of air flow and heat transfer in the skytrain street canyon are developed. The governing equations are the Reynolds-averaged Navier–Stokes equations and the energy equation. Finite element method is applied for the solution of the problem. The effect of wind speeds on temperature distribution in the street canyon is investigated. Three levels of wind speed including gentle, moderate, and strong wind speeds are chosen in this study. The results indicate that our model can capture the air flow and temperature distribution within a street canyon with a skytrain station
Oscillating pressure-driven slip flow and heat transfer through an elliptical microchannel
No full text© 2019, The Author(s).
This paper studies the transient slip flow and heat transfer of a fluid driven by the oscillatory pressure gradient in a microchannel of elliptic cross section. The boundary value problem for the thermal-slip flow is formulated based on the assumption that the fluid flow is fully developed. The semi-analytical solutions of velocity and temperature fields are then determined by the Ritz method. These solutions include some existing known examples as special cases. The effects of the slip length and the ratio of minor to major axis of the elliptic cross section on the velocity and temperature distribution in the microchannel are investigated
Numerical simulation of granular mixing in static mixers with different geometries
No full text© 2019, The Author(s). A static mixer is a fidelity engineered device for the continuous mixing of fluid/solid materials. To meet the requirements for mixing purpose, a proper design of the static mixer is important. In this study, we proposed various designs of static mixer based on the blade geometry. Six blade patterns including four twisted blades, four elliptical blades and other four combined geometries of two twisted blades and two elliptical blades are chosen to investigate its mixing performance. Mathematical model of the two-phase flow with fluid/solid interaction in the static mixer is presented. Numerical solution of the flow patterns of particulate solids, and the velocity and the pressure fields of the fluid in the static mixer with different blade geometries are carried out. To evaluate the quality of the mixing performance, the results obtained from six blade designs are compared via the relative standard deviation and the amount of pressure drop along the mixing path
Modeling and simulation of air pollutant distribution in street canyon area with Skytrain stations
No full text© 2019, The Author(s).
This paper focuses on effects of the wind flow velocity on the air flow and the air pollution dispersion in a street canyon with Skytrain. The governing equations of air pollutants and air flow in this study area are the convection–diffusion equations of species concentration and the Reynolds-averaged Navier–Stokes (RANS) equations of compressible turbulent flow, respectively. Finite element method is utilized for the solution of the problem. To investigate the impact of the air flow on the pattern of air pollution dispersion, three speeds of inlet wind in three different blowing directions are chosen. The results illustrate that our model can depict the airflows and dispersion patterns for different wind conditions
Elimination of Plasmodium falciparum in an area of multi-drug resistance
No full textInternational audienceBackground: Resistance to the artemisinin derivatives in Plasmodium falciparum has emerged in Cambodia and is now spreading throughout SouthEast Asia. The rapid elimination of P. falciparum seems to be the only viable option to avoid a public health disaster but this is difficult because even in low transmission settings many residents have asymptomatic parasitaemias. Methods: In response to a large number of malaria cases reported in three remote villages on the Thai-Myanmar border where malaria is endemic and the disease is seasonal, surveys were conducted using an ultra-sensitive qPCR assay (LOD 22 parasites per mL). In one of the villages where it was feasible, mass anti-malarial drug administration was proposed to the population as a potential solution, and this was adopted. Results: In the three villages 204/356 (57.3 %), 212/385 (55.1 %) and 195/286 (68.2 %) of the resident populations were positive by qPCR (approximately one-third P. falciparum and two-thirds P. vivax). Of those positive for P. falcipa-rum 62 % carried single point mutations in the P. falciparum kelch protein (a marker of artemisinin resistance). In one of the villages 217 of 674 inhabitants received at least one dose of dihydroartemisinin-piperaquine chemoprevention in June 2012, 155 (71.4 %) received two consecutive months, and 98 (45.2 %) received three treatment doses. The chemoprevention was generally well tolerated. The sub-microscopic reservoir of P. falciparum malaria was eliminated during the six-month follow-up period (prevalence fell from 7 to 0 %); P. vivax malaria persisted (prevalence fell from 35 to 8 %). From June to October 2012 (rainy season) the number of clinical episodes of P. falciparum was six times lower (46), than during the same period in the previous year (290). Conclusion: Mass drug administration with dihydroartemisinin-piperaquine may be an effective strategy to eliminate P. falciparum rapidly where multi-drug resistance is present
The numerical distributions of parasite densities in asymptomatic malaria
No full textBackground. Asymptomatic parasitemia is common even in areas of low seasonal malaria transmission, but the true proportion of the population infected has not been estimated previously because of the limited sensitivity of available detection methods. Methods. Cross-sectional malaria surveys were conducted in areas of low seasonal transmission on the Northwestern Thailand-Myanmar border and in Western Cambodia. Using an ultra- sensitive PCR DNA quantitation method (uPCR: limit of accurate detection 22 parasites/mL) parasite density distributions for Plasmodium falciparum and Plasmodium vivax were characterised and the proportions of undetected infections imputed. Results. The prevalence of asymptomatic malaria by uPCR was 19.9% (988 of 4,975 people tested). Both P. vivax and P. falciparum density distributions were unimodal and log normally distributed with modal values well within the quantifiable range. The estimated proportions of all parasitemic individuals identified by uPCR were over 70% for P. falciparum and over 85% for P. vivax. Predicted proportions overall were 83% P. vivax, 13% P. falciparum and 4% mixed. Geometric mean parasite densities were similar; P. vivax: 5,601/mL and P. falciparum: 5,158/mL. Conclusions. This uPCR method identified most infected individuals in malaria endemic areas. Malaria parasitemias persist in humans at levels which optimise the probability of generating transmissible gametocyte densities without causing illness
The epidemiology of subclinical malaria infections in South-East Asia: findings from cross-sectional surveys in Thailand-Myanmar border areas, Cambodia, and Vietnam
No full textBackroundThe importance of the submicroscopic reservoir of Plasmodium infections for malaria elimination depends on its size, which is generally considered small in low transmission settings. The precise estimation of this reservoir requires more sensitive parasite detection methods. The prevalence of asymptomatic, sub-microscopic malaria was assessed by a sensitive, high blood volume quantitative real-time polymerase chain reaction method in three countries of the Greater Mekong Sub-region. MethodsCross-sectional surveys were conducted in three villages in western Cambodia, four villages along the Thailand-Myanmar border and four villages in southwest Vietnam. Malaria parasitaemia was assessed by Plasmodium falciparum/pan malaria rapid diagnostic tests (RDTs), microscopy and a high volume ultra-sensitive real-time polymerase chain reaction (HVUSqPCR: limit of detection 22 parasites/mL). All villagers older than 6 months were invited to participate. ResultsA census before the surveys identified 7355 residents in the study villages. Parasite prevalence was 224/5008 (4 %) by RDT, 229/5111 (5 %) by microscopy, and 988/4975 (20 %) when assessed by HVUSqPCR. Of these 164 (3 %) were infected with P. falciparum, 357 (7 %) with Plasmodium vivax, 56 (1 %) with a mixed infection, and 411 (8 %) had parasite densities that were too low for species identification. A history of fever, male sex, and age of 15 years or older were independently associated with parasitaemia in a multivariate regression model stratified by site. ConclusionLight microscopy and RDTs identified only a quarter of all parasitaemic participants. The asymptomatic Plasmodium reservoir is considerable, even in low transmission settings. Novel strategies are needed to eliminate this previously under recognized reservoir of malaria transmission
MOESM6 of The epidemiology of subclinical malaria infections in South-East Asia: findings from cross-sectional surveys in ThailandâMyanmar border areas, Cambodia, and Vietnam
No full textAdditional file 6. Parasite prevalence detected by HVUSqPCR by age group
MOESM7 of The epidemiology of subclinical malaria infections in South-East Asia: findings from cross-sectional surveys in Thailand–Myanmar border areas, Cambodia, and Vietnam
No full textAdditional file 7. Adjusted odds for being HVUSqPCR positive stratified by household, random effects modelling by country. In Cambodia the initial model included resident (0/1), anemia (mild, moderate, none), fever (defined as a temperature >37.5 °C) at presentation* (0/1), history of fever (0/1), sex, age group (<6 year-old, ≥6 year-old–<15 year-old, and ≥15 year-old), height, weight, history of illness (0/1), history of malaria (0/1), previous anti-malarials (0/1), use of bednets (0/1), recent visit to forest (0/1), occupation (0/1), family (0/1) and village. In TMBA the initial model included anemia (mild, moderate, none), fever at presentation (0/1), history of fever (0/1), sex, age group <6 year-old, ≥6 year-old–<15 year-old, and ≥15 year-old), occupation (0/1), family (0/1) and village. In Vietnam the initial model included resident (0/1), anemia (mild, moderate, none), fever at presentation* (0/1), history of fever (0/1), sex, age group (<6 year-old, ≥6 year-old–<15 year-old, and ≥15 year-old), height, weight, history of illness (0/1), history of malaria (0/1), use of bednets (0/1), recent visit to forest (0/1), occupation (0/1) and village
MOESM3 of The epidemiology of subclinical malaria infections in South-East Asia: findings from cross-sectional surveys in ThailandâMyanmar border areas, Cambodia, and Vietnam
No full textAdditional file 3. Study population characteristics in the malaria surveys (disaggregated by village)
