320 research outputs found
Framework for human health characterization factor calculation of tio2 nanoparticles
No full textThe widespread use of engineered nanoparticles (ENPs) in various industrial applications is leading inevitably to releases of these materials into the environment, increasing like this human and environmental exposure to these substances, and is getting consequently more and more a concern regarding their potential adverse effects on both, the environment and the human health. In this context, Life Cycle Assessment (LCA) is recognized as one of the key methods for the assessment of the environmental performance of products containing such ENPs. However, so far, factors to assess releases of ENPs into the environment have been still completely missing, making all LCA studies of such materials incomplete. For this, a clear toxicological characterization of the effects is a prerequisite in order to establish trustworthy characterization factor (CFs) for release of nanoparticles into the environment. Humans could potentially be exposed to ENPs releases along the whole life cycle (i.e. during manufacture, handling, use and disposal treatment of ENPs). Therefore, this work aims to provide a methodological framework for establishing human health CFs for releases of ENPs, using titanium dioxide nanoparticles (TiO2-NPs) as an exemplary example. Starting point for this is USEtox, the internationally recognized consensus model for the assessment of toxicity within LCA studies. USEtox calculates the impact on human toxicity as product of emission, intake fractions (iF) and effect factors (EF). The intake fraction is originally defined as ratio of the mass intake by an individual over the mass released to the environment. The effect factor on the other hand contemplates the change in life time disease probability due to change in life time intake of a pollutant. Both effects, i.e. carcinogens and non-carcinogens, are taken into account in the calculation of the actual EF:
• the EF for carcinogens effects is determined based on a benchmark dose used by the National Institute for Occupational Safety and Health (NIOSH) to determinate the recommended occupational exposure limit (REL) for TiO2-NPs;
• the EF for non-carcinogens effects is calculated based on NOAEL (no-observed adverse effect level) and LOAEL (lowest observed adverse effect level) values.
Limiting the examinations here on releases to air as only investigated compartment, a one-box model using steady-state conditions and direct human exposure can be applied for the calculation of the intake fractions. Here, intake fractions for indoor and outdoor conditions have been calculated for TiO2-NPs. While indoor iF, a complete mixing for the volume and the indoor volume per workers for the Chemical industry in Switzerland have been evaluated. For the outdoor iF, the fate factor matrix has been calculated by applying the SimpleBox4Nano (SB4N) multimedia modelling developed by Meesters and co-author. Thanks to this model it is possible to obtain transport and removal rates constants for ENPs in and across air, rain, surface water, soil and sediment compartments, taking into account various input parameters (i.e. radius, mass density, aggregation and attachement efficiency of TiO2-NPs) and systemic dimensions (area, height and volume for each compartments). Again, based on the study by Mueller and Nowack, the scenario is focusing on Switzerland as geographical area
Electrical manipulation and detection of single electron spins in quantum dots
No full textKavli Institute of Nanoscience DelftApplied Science
Aerosolverhalten im Sicherheitsbehälter beim Einsatz von Rekombinatoren und nach Wasserstoffverbrennungen
No full textWährend schwerer Störfälle in Kernkraftwerken mit einem Schmelzen des Reaktorkerns können sowohl radioaktive Aerosole als auch Wasserstoff (H2) aus dem Reaktorkühlkreislauf in den Sicherheitsbehälter austreten.
Durch die hohen Temperaturen bei einer H2-Verbrennung ist eine Konversion aerosolförmigen Cäsiumjodids (CsI) in molekulares Jod (I2) möglich. Auch an den heißen Platten in passiven autokatalytischen Rekombinatoren (PAR), die zur Beseitigung von Wasserstoff in deutschen Druckwasserreaktoren eingesetzt werden, kann eine solche Konversion stattfinden.
Durch starke Atmosphärenströmungen, die in Folge einer H2-Verbrennung entstehen, können bereits aussedimentierte Aerosole erneut in die Atmosphäre eingetragen werden. Für diesen Effekt der trockenen Resuspension ist ein Modell entwickelt und in den Containment-Code COCOSYS eingebaut worden.
Rechnungen mit COCOSYS zeigen, dass beide Effekte eine Erhöhung des radioaktiven Quellterms bewirken können
Spin Echo of a Single Electron Spin in a Quantum Dot
No full textWe report a measurement of the spin-echo decay of a single electron spin confined in a semiconductor quantum dot. When we tip the spin in the transverse plane via a magnetic field burst, it dephases in 37 ns due to the Larmor precession around a random effective field from the nuclear spins in the host material. We reverse this dephasing to a large extent via a spin-echo pulse, and find a spin-echo decay time of about 0:5 µs at 70 mT. These results are in the range of theoretical predictions of the electron spin coherence time governed by the electron-nuclear dynamics.Kavli Institute of NanoscienceApplied Science
Coping with Environmental Fluctuations: Ecological and Evolutionary Perspectives
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Coping with Environmental Fluctuations: Ecological and Evolutionary Perspectives
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Voice Compression and Communications: Principles and Applications for Fixes and Wireless Channels
No full textUp-to-date, expert coverage of topics in wireless voice communications Voice communication is the most important facet of mobile radio service. Even when the predicted surge of wireless data and Internet services becomes a reality, voice will remain the most natural means of human communication. Voice Compression and Communications details issues in wireless voice communications and treats compression, channel coding, and wireless transmission as a joint subject. Part I covers background material, whereas Part II provides detailed information on both proprietary and standardized analysis-by-synthesis codecs, including the speech codecs of virtually all existing wireline-based and wireless systems. Parts III and IV discuss mainly research-based wideband, audio, as well as very low-rate schemes likely to find their way into future standards. Voice Compression and Communications describes fundamental concepts in a non-mathematical way early in the book for those with only a background knowledge of signal processing and communications. More advanced readers will find detailed discussions of theoretical principles, future concepts, and solutions to various specific wireless voice communications problems
Simultaneous Spin-Charge Relaxation in Double Quantum Dots
No full textWe investigate phonon-induced spin and charge relaxation mediated by spin-orbit and hyperfine interactions for a single electron confined within a double quantum dot. A simple toy model incorporating both direct decay to the ground state of the double dot and indirect decay via an intermediate excited state yields an electron spin relaxation rate that varies nonmonotonically with the detuning between the dots. We confirm this model with experiments performed on a GaAs double dot, demonstrating that the relaxation rate exhibits the expected detuning dependence and can be electrically tuned over several orders of magnitude. Our analysis suggests that spin-orbit mediated relaxation via phonons serves as the dominant mechanism through which the double-dot electron spin-flip rate varies with detuning.QN/Quantum NanoscienceApplied Science
Resolving Spin-Orbit- and Hyperfine-Mediated Electric Dipole Spin Resonance in a Quantum Dot
No full textWe investigate the electric manipulation of a single-electron spin in a single gate-defined quantum dot. We observe that so-far neglected differences between the hyperfine- and spin-orbit-mediated electric dipole spin resonance conditions have important consequences at high magnetic fields. In experiments using adiabatic rapid passage to invert the electron spin, we observe an unusually wide and asymmetric response as a function of the magnetic field. Simulations support the interpretation of the line shape in terms of four different resonance conditions. These findings may lead to isotope-selective control of dynamic nuclear polarization in quantum dots.QN/Quantum NanoscienceApplied Science
Dying two deaths — programmed cell death regulation in development and disease
No full textProgrammed cell death (PCD) is a fundamental cellular process that has adopted a plethora of vital functions in multicellular organisms. In plants, PCD processes are elicited as an inherent part of regular development in specific cell types or tissues, but can also be triggered by biotic and abiotic stresses. Although over the last years we have seen progress in our understanding of the molecular regulation of different plant PCD processes, it is still unclear whether a common core machinery exists that controls cell death in development and disease. In this review, we discuss recent advances in the field, comparing some aspects of the molecular regulation controlling developmental and pathogen-triggered PCD in plants
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