Search

Mathematical modeling of di-ethyl-hexyl-sebacate (DEHS) nanoparticle formation due to homogeneous nucleation, condensation and coagulation in a hot free turbulent jet issuing into a colder environment is performed. The Reynolds-averaged Navier–Stokes equations are used to describe the fluid flow. The aerosol dynamics is treated by transforming the general dynamic equation into moment equations which are closed by assuming a lognormal shape of the particle size distribution. The contribution of condensation and coagulation to particle formation in the case of high saturation ratios and nucleation rates is studied. The sensitivity of the model to existing approximations of the vapor saturation pressure curve and the ambient temperatures is analyzed. The influence of the main control parameters of the system, such as vapor saturation temperature and nozzle exit velocity, on the aerosol characteristics formed in the turbulent jet is investigated. [ABSTRACT FROM AUTHOR]

Abstract: In an attempt to develop a reference generator for the number size distribution function in the submicron size range we carried out a theoretical and experimental analysis of Brownian coagulation of liquid droplets in a continuously fed well stirred tank reactor operated in the steady state regime where the particle collision time scale is small compared to the mean residence time of the aerosol in the reactor. The feed aerosol, characterised by the flow of total particle volume (mass flow) and average particle size, is generated in a turbulent jet of finite length inside the reactor by homogeneous nucleation of a saturated stream of an organic vapour and coagulation growth. In a time scale large compared to the typical collision time the aerosol size distribution has reached a steady state. The steady state population balance equation taking into account size dependent Brownian coagulation and particle removal was solved numerically. It was found that for the conditions realized in the experimental system the asymptotic form of the size distribution function for large particle volumes can be approximated by a single function determined by two scaling groups formed of the process parameters. The relevant process parameters are the inflowing aerosol volume, the residence time and the reactor volume. In the size range between 70nm and 250nm coagulation is the only relevant mechanism controlling the distribution function. The experimental data are in good agreement with these theoretical findings. This section of the steady state size distribution could serve as a reference for the number size distribution of submicron particles. [Copyright &y& Elsevier]

Abstract: A system for delivering a reference number concentration (calibration source) is proposed as an alternative to using reference methods for calibrating instrumentation of ultrafine particle number concentration. The underlying physical principle is the asymptotic behaviour of Brownian coagulation of liquid particles. We describe and characterize a simple set-up based on aerosol formation by homogeneous nucleation of an organic vapour and subsequent growth by Brownian coagulation in a closed chamber. Controlling parameters are the coagulation time and, to a much lesser extent, the volume fraction of the condensed aerosol. The system can be used in a time window starting from 100s, the time required to reach the asymptotic state, and ending at 1000s after initiation of the nucleation process, beyond which wall losses become significant. In this regime, the temporal development of the number concentration in the coagulation vessel is exclusively determined by the physical process of Brownian coagulation. The system delivers predictable reference concentrations in the range between and . [Copyright &y& Elsevier]

Single-nucleotide polymorphism (SNP) genotyping is a fundamental tool in the rapidly growing area of complex diseases and pharmacogenomics. SNP patterns that correlate with disease or response to treatment, respectively, are identified using bioinformatic techniques. We present an integrated laboratory information and management system (LIMS) for our high-throughput TaqMan™–based SNP genotyping platform. Three new client tools (ProjectManager, AssayManager, OrderTool) for our LIMS improve quality control and workflow management. The programs support organizing multiple genotyping experiments as projects, managing reagents with barcodes, and automation of assay ordering. The tools are freely available at our homepage. [Copyright &y& Elsevier]

Objectives: We tested the hypothesis that patients with the DD genotype of the angiotensin I-converting enzyme (ACE) gene who are treated with ACE inhibitors are at a higher risk of restenosis after coronary stent placement than patients who do not receive ACE inhibitors.Background: Two recent studies with a limited series of patients carrying the DD genotype suggested an unfavorable impact of the use of ACE inhibitors on the restenotic process after implantation of stents in coronary arteries. Because these findings may question the use of ACE inhibitors after coronary stenting, we examined this important issue in a large series of patients.Methods: We determined the ACE gene I/D genotype of 2,222 consecutive patients with symptomatic coronary artery disease who underwent stent implantation. The patients with the DD genotype (n = 612) constituted the study population. The primary end point was in-stent restenosis, which was assessed as angiographic restenosis (> or =50% diameter stenosis at six-month follow-up) and clinical restenosis (need for target vessel revascularization due to symptoms or signs of ischemia in the presence of angiographic restenosis over one year after the intervention).Results: Of the 612 patients with the DD genotype, 403 (65.8%) were treated with ACE inhibitors and 209 (34.2%) did not receive ACE inhibitors. The angiographic and clinical restenosis rates were not significantly different between the group treated with ACE inhibitors and the group not receiving ACE inhibitors (p = 0.55). Continuous measures of restenosis, minimal lumen diameter, diameter stenosis, late lumen loss, and loss index were also similar in both groups (p > or = 0.55). In addition, one-year survival free of myocardial infarction was not significantly different between the two groups (p = 0.27).Conclusions: In contrast to previous reports, our study provides evidence that patients carrying the DD genotype are not exposed to an increased risk of restenosis after stent placement when treated with ACE inhibitors. [ABSTRACT FROM AUTHOR]

Ozone (O3) flux into Norway spruce (Picea abies) and cembran pine (Pinus cembra) needles was estimated under ambient conditions at six rural sites between 580 and 1950 m a.s.l. We also assessed age-related differences in O3 flux by examining changes in leaf conductance across the life span of Norway spruce. At the leaf level O3 flux into the needles was effectively controlled by stomatal conductance and, hence by factors such as temperature, irradiance and humidity, which control stomatal conductance. Seasonal variations in O3 flux were mainly attributed to the course of the prevailing temperature. During the growing season, however, data have emphasized leaf-air vapour pressure difference as the environmental factor most likely to control stomatal conductance and O3 flux into the needles. In the sun crown stomatal conductance averaged over the growing season decreased with increasing tree age from 42.0+/-3.5 mmol O3 m-2 s-1 in 17-year-old trees to 7.1+/-1.0 mmol O3 m-2 s-1 in 216-year-old trees, indicating that O3 concentration in the substomatal cavities is higher in young than in old trees. Independent from tree age stomatal conductance and O3 flux were approximately 50% lower in shade needles as compared to sun-exposed needles. Stomatal conductance was also greater in the current flush (24+/-5.6 mmol O3 m-2 s-1) and in 1-year old needles (16+/-4 mmol O3 m-2 s-1)than in older needle age classes (12+/-1 mmol O3 m-2 s-1, averaged across the four older needle age classes). In trees similar in age (60-65 years old) average O3flux into sun needles increased from 0.5510.36 nmol m-2 s-1 at the valley floor to 0.9 nmol m-2 s-1 in 1950 m a.s.l. Cumulative O3 uptake during the vege [ABSTRACT FROM AUTHOR]

Highly concentrated submicron condensation aerosols are formed in electronic cigarettes. They consist primarily of the carrier substances glycerol, propylene glycol and water. The purpose of this paper is to introduce a three wavelength light extinction method in the near and mid-infrared wavelength regime enabling transient measurements of the mass concentration and the mean particle size of the mainstream, undiluted aerosol. The measuring device uses the strong absorption bands at wavelengths of 3.4 and 2.9 µm caused by the excitation of CH- and OH-vibrations of the dominating aerosol components. The absorption allows for a direct measurement of the mass concentration. Two further light attenuation signals at non-absorbing (or negligibly absorbing) wavelengths of 1.65 and 2.01 µm reveal information on the mean particle size. The data evaluation scheme is based on a set of correlations between light attenuation and size distribution parameters derived from Mie calculations using a lognormal approximation of the mass size distribution. The development of a simple sensor is facilitated due to the availability of light emitting diodes in the mid infrared wavelength range. Extinction path lengths of the order of 0.5 cm are sufficient to measure concentrations larger than several milligrams per liter, typical for the mainstream aerosol of e-cigarettes. The aerosol quantities were measured for a wide range of operating parameters of the e-cigarette. Time integrated signals were compared with results of filter (mass generation) and impactor samples (mean particle size and standard deviation). The sensor’s concentration signal is directly proportional to the concentration measured gravimetrically, independent of the relative composition of the condensate in view of glycerol, propylene glycol and water. The mass median droplet diameters determined by the extinction method agree fairly well with cascade impactor measurements. The method, presented here, does not deliver information on the geometric standard deviation of the aerosol mass distribution as it is insensitive to this distribution parameter for values in the range between 1.3 and 2.0, typical for condensation aerosols. [ABSTRACT FROM AUTHOR]