Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. II. Stability of operation.

In this paper, the second of a series of two presenting a detailed description of thermal diffusion cloud chamber operation, we address the operational stability of the vapor–gas mixture in a diffusion cloud chamber with respect to density profile extrema and the accompanying possibility of buoyancy-driven convective flow disturbances. We examine conditions for stable operation (no convective flow disturbances) in the central portion of the cloud chamber, as well as conditions necessary for stable operation in the vicinity of the cloud chamber wall. We find that the total density profile in the central portion of the cloud chamber can pass through a density minimum even though the density at the upper plate surface is less than the density at the lower plate surface. This local density profile inversion can result in unstable (convective) behavior that propagates through the cloud chamber. Furthermore, we find that local extrema in the total density profile near the chamber wall can lead to subtle, convective flows that are difficult to detect yet can exert a profound influence on nucleation in the central portion of the cloud chamber. We have developed a simple method to estimate the limiting total pressure in a cloud chamber that will support stable operation. From results of our investigations based upon this method, it appears that the thermal diffusion cloud chamber is best suited for experiments at higher temperatures where the accessible total pressure range is largest. Finally, we find that results of our investigation into the effects of total pressure and kind of background gas on nucleation in diffusion cloud chambers involving the low molecular weight alcohols and hydrogen and helium background gases cannot be explained on the basis of these kind of density disturbances occurring within the diffusion cloud chamber. Also, for (relatively) low vapor pressure materials, such as 1-pentanol or other high molecular weight alcohols and alkanes stability limitations may preclude nucleation measurements at low temperatures using a diffusion cloud chamber altogether

Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. I. Analysis and operations criteria.

In this paper we present results of a two-dimensional (z,r) treatment of the mass and energy transfer processes that occur during the operation of a thermal diffusion cloud chamber. The location of the wall is considered in solving the mass and energy transport equations, in addition to the vertical distance, z, between the upper and lower plate surfaces. We examine the effect of aspect (diameter to height) ratio on chamber operation; the effects of operation with either a dry or a wet interior chamber wall on temperature, supersaturation, nucleation rate, and total density profiles in the chamber; the effect of overheating the interior of the chamber wall on these conditions within the cloud chamber; and the effects associated with using different density background gases on the operation of the chamber. In a second paper, immediately following, we apply the formalism and the solutions developed in this paper to address the important problem of buoyancy-driven convection that can accompany (seemingly normal) operation of thermal diffusion cloud chambers in nearly all ranges of total pressure and temperature

Nucleation of sulfur hexafluoride

We measured the homogeneous nucleation of sulfur hexafluoride using a diffusion cloud chamber under conditions that avoid the possibility of non-diffusive modes of transport within the cloud chamber thus ensuring reliable data from our measurements. We extended the critical supersaturation measurements into the critical region for SF6 using helium as background gas

Thermal diffusion cloud chamber - new criteria for proper orientation

We report results of new nucleation experiments involving 1-pentanol with hydrogen as the background gas utilizing the high-pressure diffusion cloud chamber (HPCC). We discuss the important issue of buoyancy-driven convective motion and cloud chamber operation, and we focus on the lower total pressure limit required for stable chamber operation. We provide, for the first time, an empirical procedure for determining the lower total pressure limit

Background paper to the recommendation for routine rotavirus vaccination of infants in Germany

Two rotavirus (RV) vaccines were introduced to the European market in 2006. To support the decision-making process of the German Standing Committee on Vaccination ("Ständige Impfkommission", STIKO) regarding adoption of routine RV vaccination into the national vaccination schedule in Germany relevant scientific background was reviewed. According to STIKO’s Standard Operating Procedures for the development of evidence-based vaccination recommendations, a set of key questions was addressed and systematic reviews were performed with a focus on the efficacy, effectiveness, impact and safety of RV vaccines. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology was applied to assess the quality of available evidence. Data from 5 randomized controlled trials demonstrated a high efficacy of RV vaccines in preventing severe RV-associated gastroenteritis (91%) and hospitalization (92%) in settings comparable to Germany. Post-marketing observational studies confirmed these findings. In several countries, impact studies suggest that age groups not eligible for vaccination might also benefit from herd effects and demonstrated a decrease in the number of nosocomial RV infections after RV vaccine introduction. The vaccines were considered safe, except for a slightly increased risk of intussusception shortly after the first dose, corresponding to 1-2 additional cases per 100,000 infants vaccinated (relative risk =1.21, 95% confidence interval [CI] 0.68-2.14). RV case-fatality is extremely low in Germany. However, RV incidence among children age

Weighted needle pinprick sensory thresholds: a simple test of sensory function in diabetic peripheral neuropathy

A simple device is described, consisting of 12 weighted 23 gauge disposable needles (0.2 to 5.2 g), for testing sensation in busy diabetic clinics. The pinprick sensory threshold (PPT) is the lightest weighted needle which consistently elicits a sharp sensation. The subjects were 48 healthy controls (hospital staff), 44 diabetic patients without neuropathic symptoms, and 35 diabetic patients with chronic painful neuropathy. In the controls, the mean PPT from the right hand and foot obtained on two test occasions a week apart did not differ significantly. In diabetic patients without symptomatic neuropathy, the mean PPT in the right hand and right foot were significantly higher than in the controls. The diabetic patients with painful neuropathy had clearly increased mean PPT in the right hand and foot compared with controls. Marstock thermal limen in diabetic patients with painful neuropathy correlated significantly with PPT determinations. PPT and thermal thresholds probably give comparable information on small fibre dysfunction in diabetic patients with symptomatic neuropathy. Compared with thermal threshold determinations however, the weighted needle apparatus is inexpensive, simple, and rapid to use

The same but different: Understanding entrepreneurial behaviour in disadvantaged communities

While entrepreneurship is widely viewed as being equally accessible in all contexts, it could be questioned if potential or nascent entrepreneurs from minority and disadvantaged communities experience entrepreneurship in a similar manner to the mainstream population. This chapter examines immigrant, people with disability, youth, gay and unemployed communities to explore how their entrepreneurial behaviour might differ from the practices of mainstream entrepreneurs. What emerges is that marginalised communities can frequently find it difficult to divorce business from social living. This can have both positive and negative connotations for an entrepreneur, plus they face additional and distinctive challenges that mainstream entrepreneurs do not experience. The chapter concludes by proposing a novel ‘funnel approach’ that policymakers might adopt when seeking to introduce initiatives targeted at these disadvantaged communities