1,722,089 research outputs found
Decorporation of Radionuclides
No full textMetal radionuclides occur naturally in the environment, however, most radionuclides categorized as harmful are of anthropogenic origin, released from military, industrial, or medical processes. The uses of metal radionuclides for energy production, medicinal, industrial, and military purposes often generate waste with extensively long decay halftimes and potential for environmental pollution. Major pathways to hazardous radionuclides exposure are through inhalation, food contamination, and through occupational exposure at mining and processing sites. Accidents or low working standards at nuclear facilities can lead to contamination of employees with radionuclides due to ingestion, inhalation of gases or particulates, or contamination of skin or wounds, as well as contamination of the surroundings resulting in external γ-radiation exposure. The most frequent exposure situation is the contamination of skin or hair during work with radionuclides. Other potential sources for radionuclide exposure are terrorist actions via production of "dirty bombs" or deliberate contamination of infrastructure key facilities, for example, drinking water reservoirs, situations fortunately not realized yet but feared by authorities. Exposure can be to one main metal compound or to complicated mixtures. Due to decay of parent radionuclides, the effects of exposure are in some cases caused by combined effects of parent and daughter radionuclides. The health effects of metal radionuclides exposures are a combination of radiation increasing cancer risk in chronic exposure and toxicity of the metals. Acute health effects after extensive radiation exposure starts with nausea, vomiting, and headaches. Further exposure leads to weakness and fatigue, fever, hair loss, disorientation and dizziness, diarrhea with bloody stools, decreased blood pressure, and ultimately death. The main purpose of radionuclide decorporation is to minimize the radiation dose (eg, polonium) and chemical insult (eg, uranium) received by exposed individuals. Since some of the important metal radionuclides have very long biological half-times after deposition in bone, liver, or kidneys, rapid initiation of chelation treatment is imperative after a contamination event, to reduce uptake from skin or wounds, lungs, or gastrointestinal tract, and to promote excretion of circulating radionuclide in blood before tissue deposition. Two chelators are approved for radionuclide decorporation, diethylene triamine pentaacetic acid (DTPA), and Prussian blue. Several experimental chelators and drugs approved, for example, iron overload and Wilson's disease are being evaluated as potential actinide decorporating agents. New formulations of DTPA as prodrugs (eg, ethyl and pentyl diesters) are being developed for oral use. Chelators are being developed based on alginates, pectin, and other macromolecular compounds for wound and skin cleaning, for oral use, and for extracorporal chelation.</p
Chelation Treatment During Acute and Chronic Metal Overexposures:Experimental and Clinical Studies
No full textMetal overexposures, ranging from nonsymptomatic, elevated body levels to life threatening acute or chronic poisonings, should in general be treated by eliminating the exposure source, by various decontamination procedures, and by supportive treatment. However, in a quite extensive number of cases, various chelation treatment schedules offer an efficient way of handling the adverse effects of overexposure to metals, either by reducing the toxicity of the metal by forming a less toxic complex, by changing the toxicodynamics of the metal thereby reducing the interaction of the metal with a vulnerable target, and/or reducing its uptake and/or enhancing its excretion. The present chapter offers a systematic review of the present state-of-the-art for chelation treatment of metal overexposures. Such exposures can be due to occupational, environmental, dietary, or lifestyle factors, or iatrogenic procedures. The review is ordered alphabetically citing animal experimental studies and epidemiological and clinical studies for each metal, if available. The general experience is that the metal (Lewis acid) and the chelator (Lewis base) should have high affinity for each other (high stability constant), thus soft metals should be chelated by chelators with soft ligands (eg, C-SH), and hard metals with chelators with hard ligands (eg, COOH, CR. O, CR2. OH). Intermediate metals prefer, for example, N-containing ligands, but can be chelated by both hard and soft bases. However, the pharmacokinetics of the chelating agent is highly important also, especially whether the chelator and the metal-chelator complex formed are hydrophilic with enhanced renal excretion as result, or lipophilic with enhanced biliary excretion and/or brain deposition as a potential result. Some important questions are: Can the chelator be administered orally, and will it enhance or prevent systemic uptake of toxic metal remaining in the gastrointestinal tract? Is the chelator metabolically stable to allow extended treatment with appropriate time lag between doses According to generally accepted ethical principles in pharmacology and medicine, experimental chelating agents proven efficient in animal experiments cannot be used in humans except in special cases, where the benefit clearly outweighs the potential toxicity of the agent. Based on the experimental and clinical work, optimal chelating agents for acute poisonings with selected metals are as follows: Deferoxamine for aluminum compounds. Dimercaptosulfonate (DMPS) for arsenic compounds, deferoxamine for iron compounds, with deferiprone and deferasirox as potential alternative chelators. Dimercaptosuccinic acid (DMSA) for lead compounds, DMPS for inorganic mercury compounds including mercury vapor, DMSA may be superior for organic mercury compounds. Today new chelators are being developed as decorporating agents for all classes of metals.</p
Clinical therapy of patients contaminated with polonium or plutonium
No full textAlthough most of the harmful radionuclides are of anthropogenic origin and released from military or industrial processes, radioactive substances, such as uranium, also occur naturally in the environment. Low standards of care at nuclear facilities can lead to the contamination of employees with radionuclides due to inhalation of gases or dust or contamination of skin or wounds. Various sources for radionuclide exposure may present concerns for radioactive polonium or plutonium exposure, for instance, terrorist actions on the infrastructure, such as on drinking water basins. Early health effects after extensive radiation exposure may be vomiting, headaches, and fatigue, followed by bone marrow depression, fever, and diarrhea. The main purpose of radionuclide mobilization is to minimize the radiation dose. Since some of the important radionuclides, such as polonium and plutonium, have very long biological half-times after their deposition in bone, liver or kidneys, rapid initiation of chelation treatment is usually imperative after a contamination event. The antidote DMPS (dimercapto-propanesulfonate) is considered the drug of choice for polonium decorporation. DTPA (diethylenetriamine pentaacetate) is a potent chelator especially approved for radionuclide mobilization, including polonium and other actinides. Other chelators and drugs are under investigation as potential chelators of transuranic elements.Although most of the harmful radionuclides are of anthropogenic origin and released from military or industrial processes, radioactive substances, such as uranium, also occur naturally in the environment. Low standards of care at nuclear facilities can lead to the contamination of employees with radionuclides due to inhalation of gases or dust or contamination of skin or wounds. Various sources for radionuclide exposure may present concerns for radioactive polonium or plutonium exposure, for instance, terrorist actions on the infrastructure, such as on drinking water basins. Early health effects after extensive radiation exposure may be vomiting, headaches, and fatigue, followed by bone marrow depression, fever, and diarrhea. The main purpose of radionuclide mobilization is to minimize the radiation dose. Since some of the important radionuclides, such as polonium and plutonium, have very long biological half-times after their deposition in bone, liver or kidneys, rapid initiation of chelation treatment is usually imperative after a contamination event. The antidote DMPS (dimercapto-propanesulfonate) is considered the drug of choice for polonium decorporation. DTPA (diethylenetriamine pentaacetate) is a potent chelator especially approved for radionuclide mobilization, including polonium and other actinides. Other chelators and drugs are under investigation as potential chelators of transuranic elements.</p
Introduction
No full textThe focus on results in development agencies has led to increased focus on impact evaluation to demonstrate the effectiveness of development programmes. A range of methods are available for counterfactual analysis of infrastructure interventions, as illustrated by the variety of papers in this volume. Understanding impact means understanding the context in which an intervention takes place and the channels through which the impact on outcomes is expected to occur. Such analysis typically requires mixing both quantitative and qualitative approaches. The analysis will also anticipate heterogeneity, with conditioning for ‘selection bias’ being recognised as positive information about for whom and when an intervention works or not
On the multi-orbital band structure and itinerant magnetism of iron-based superconductors
No full text
Normal and superconducting state properties of B-doped diamond from first-principles
No full textIn this paper we give a theoretical description of the superconducting
and normal-state properties of hole-doped diamond based on ab initio
calculations. Our aim is to provide a useful reference to compare the
theoretical predictions with the experimental data. We also discuss the
advantages and drawbacks of the virtual crystal approximation (VCA),
which we adopted to model the boron doping, comparing our results with
supercell calculations. (c) 2006 NIMS and Elsevier Ltd. All rights
reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
