On thermal resistance in concentric residential geothermal heat exchangers

Residential geothermal ground-source heat pumps have been used for nearly 30 years as a low-cost, environmentally friendly alternative to traditional fossil-fuel systems. However, the limitation on a wider range of acceptance of the technology is the cost of the installation of a piping network through which the energy is transferred between the soil and the coolant. This cost is proportional to the piping length. We formulate a new mathematical modeling framework that calculates a characteristic streamwise length based on the geometry of the system, the operating conditions, and the material properties of the system materials and effective properties of the surrounding soil using a vertical concentric geothermal heat exchanger as an example. These concentric systems consist of a core flow (from the residence), which flows from the ground surface to the base of the well, and an annular return region in which the heat exchange between the fluid and the soil is expected to take place. Two modeling scenarios are considered: steady-state temperature profiles in the annular fluid region if the radial thermal resistance between the fluid and soil is fixed; a quasi-steady fluid temperature that captures the radial heat transfer from the fluid to the soil. For the first case, we find that the characteristic length is determined by the smallest eigenvalue of the separable thermal problem, where the velocity profile is laminar and there is no thermal transport between the core and the fluid. When this core-annular heat transfer is possible, the eigenvalue problem no longer satisfies the conditions for Sturm–Liouville theory, and through direct computation we find that energy transferred from the annular flow to the core reduces the temperature change. In the second case, we find that the temperature change is reduced over time, as the soil temperature near the exchanger responds to the energy transport. In both cases, the best thermal transport takes place when the annular gap is small. The impact of these results on system design considerations is discussed.     

Fifty years of individual monitoring of ionising radiation in Switzerland: history, trends and perspectives

In the last 50 y, individual monitoring of ionising radiation in Switzerland underwent substantial development, strongly influenced by type of applications of ionising radiation, monitoring technologies, knowledge of health risks, protection philosophies and regulatory frameworks. The role of individual monitoring in the system of radiation protection moved from a passive, a posteriori control of limits towards an important and more interactive tool for optimisation. Dose trends for occupational exposures document these developments. In the future, new and emerging dose intensive applications in medicine and an increasing demand for international harmonisation, particularly in Europe, will pose new challenges in individual monitoring.     

Glass-coated beryllium mirrors for the LHCb RICH1 detector

The design, manufacture and testing of lightweight glass-coated beryllium spherical converging mirrors for the RICH1 detector of the LHCb experiment are described. The mirrors need to be lightweight to minimize the material budget and fluorocarbon-compatible to avoid degradation in the RICH1 C₄F₁₀ gas radiator. Results of the optical measurements for small-sized prototypes and for a full-sized prototype mirror are reported.     

An Open Environment for Real-Time Applications

This paper describes an open system architecture that allows independently developed hard real-time applications to run together and supports their reconfiguration at run-time. In the open system, each real-time application is executed by a server. At the lower level, the OS scheduler schedules all the servers on the EDF basis. At the upper level, the server scheduler of each server schedules the ready jobs of the application executed by the server according to the algorithm chosen for the application. The paper describes the two-level CPU scheduling scheme used by the open system and the design and implementation of a uniprocessor open system within the framework of the Windows NT operating system. The implementation consists of three key components: the two-level hierarchical kernel scheduler, common system service providers, and real-time application programming interface.     

Display Processing of Computed Tomography Images

In this paper, we review some of the possibilities for digital enhancement of Computed Tomography (CT) images. The basic hypothesis is that the array of computed x-ray absorbtion values obtained in CT contains more information than the unaided eye can generally grasp. Examples of novel contrast enhancement and noise smoothing algorithms are included to support this hypothesis. Particular attention is paid to properties of the human visual system which we consider an element of the overall information processing loop.     

Cardiovascular disease and nutrient antioxidants: Role of low‐density lipoprotein oxidation

Increasing evidence indicates that oxidative modification of low‐density lipoprotein (LDL) is causally related to atherosclerosis. Oxidatively modified LDL (oxLDL), in contrast to native LDL, is taken up avidly by macrophages, leading to formation of lipid‐laden foam cells. Foam cells are pathognomonic of the atherosclerotic fatty streak. Modified LDL may also promote atherosclerosis by many other mechanisms, such as recruitment and retention of monocyte‐macrophages, T‐lymphocytes, and smooth muscle cells in the arterial intima, and cytotoxicity toward endothelial cells and macrophage‐derived foam cells. The “oxidation hypothesis of atherosclerosis” is supported by a number of in vivo findings, such as the presence of oxLDL in atherosclerotic lesions, and increased titers of autoantibodies against modified LDL in patients with atherosclerosis.

As a corollary of the oxidation hypothesis of atherosclerosis, antioxidants that can inhibit LDL oxidation may act as antiatherogens. This conception is supported by animal studies showing that antioxidants such as probucol, butylated hydroxytoluene, and α‐tocopherol can slow the progression of atherosclerosis. Epidemiological and clinical data indicate a protective role of dietary antioxidants against cardiovascular disease, including vitamin E, β‐carotene, and vitamin C. Likewise, basic research studies on LDL oxidation have demonstrated a protective role for antioxidants, present either in the aqueous environment of LDL or associated with the lipoprotein itself. More studies are needed to establish the effectiveness and determine the required doses of specific antioxidants to prevent and possibly treat cardiovascular disease.     

Fluorogenic labeling of organophosphate pesticides with dansyl chloride. Application to residue analysis by high-pressure liquid chromatography and thin-layer chromatography

The analysis of some organophosphorus pesticides by fluorogenic labeling with dansyl chloride (5-dimethylaminonaphthalene--l-sulfonyl chloride) was investigated. The pesticides were hydrolysed in sodium hydroxide to the corresponding phenols. The reaction of dansyl chloride with the phenols was accomplished in a two-phase system. The resulting fluorescent derivatives were separated and analysed quantitatively by in situ thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC). As little as 10-25 ng/spot of pesticide was detected by both TLC and HPLC.