43 research outputs found
Skipping orbits and enhanced resistivity in large-diameter InAs/GaSb antidot lattices
We investigated the magnetotransport properties of high-mobility InAs/GaSb
antidot lattices. In addition to the usual commensurability features at low
magnetic field we found a broad maximum of classical origin around 2.5 T. The
latter can be ascribed to a class of rosetta type orbits encircling a single
antidot. This is shown by both a simple transport calculation based on a
classical Kubo formula and an analysis of the Poincare surface of section at
different magnetic field values. At low temperatures we observe weak
1/B-periodic oscillations superimposed on the classical maximum.Comment: 4 pages, 4 Postscript figures, REVTeX, submitted to Phys Rev
Estimating COâ‚‚ emissions for 108000 European cities
City-level COâ‚‚ emissions inventories are foundational for supporting the EU's decarbonization goals. Inventories are essential for priority setting and for estimating impacts from the decarbonization transition. Here we present a new COâ‚‚ emissions inventory for all 116572 municipal and local-government units in Europe, containing 108000 cities at the smallest scale used. The inventory spatially disaggregates the national reported emissions, using nine spatialization methods to distribute the 167 line items detailed in the National Inventory Reports (NIRs) using the UNFCCC (United Nations Framework Convention on Climate Change) Common Reporting Framework (CRF). The novel contribution of this model is that results are provided per administrative jurisdiction at multiple administrative levels, following the region boundaries defined OpenStreetMap, using a new spatialization approach
Future changes in consumption: The income effect on greenhouse gas emissions
The scale and patterns of household consumption are important determinants of environmental impacts. Whilst affluence has been shown to have a strong correlation with environmental impact, they do not necessarily grow at the same rate. Given the apparent contradiction between the sustainable development goals of economic growth and environmental protection, it is important to understand the effect of rising affluence and concurrent changing consumption patterns on future environmental impacts. Here we develop an econometric demand model based on the data available from a global multiregional input-output dataset. We model future household consumption following scenarios of population and GDP growth for 49 individual regions. The greenhouse gas (GHG) emissions resulting from the future household demand is then explored both with and without consideration of the change in expenditure over time on different consumption categories. Compared to a baseline scenario where final demand grows in line with the 2011 average consumption pattern up until 2030, we find that changing consumer preferences with increasing affluence has a small negative effect on global cumulative GHG emissions. The differences are more profound on both a regional and a product level. For the demand model scenario, we find the largest decrease in GHG emissions for the BRICS and other developing countries, while emissions in North America and the EU remain unchanged. Decreased spending and resulting emissions on food are cancelled out by increased spending and emissions on transportation. Despite relatively small global differences between the scenarios, the regional and sectoral wedges indicate that there is a large untapped potential in environmental policies and lifestyle changes that can complement the technological transition towards a low-emitting society
Screening Breakdown on the Route toward the Metal-Insulator Transition in Modulation Doped Si/SiGe Quantum Wells
Exploiting the spin resonance of two-dimensional (2D) electrons in SiGe/Si
quantum wells we determine the carrier-density-dependence of the magnetic
susceptibility. Assuming weak interaction we evaluate the density of states at
the Fermi level D(E_F), and the screening wave vector, q_TF. Both are constant
at higher carrier densities n, as for an ideal 2D carrier gas. For n < 3e11
cm-2, they decrease and extrapolate to zero at n = 7e10 cm-2. Calculating the
mobility from q_TF yields good agreement with experimental values justifying
the approach. The decrease in D(E_F) is explained by potential fluctuations
which lead to tail states that make screening less efficient and - in a
positive feedback - cause an increase of the potential fluctuations. Even in
our high mobility samples the fluctuations exceed the electron-electron
interaction leading to the formation of puddles of mobile carriers with at
least 1 micrometer diameter.Comment: 4 pages, 3 figure
Edge-Magnetoplasmon Wave-Packet Revivals in the Quantum Hall Effect
The quantum Hall effect is necessarily accompanied by low-energy excitations
localized at the edge of a two-dimensional electron system. For the case of
electrons interacting via the long-range Coulomb interaction, these excitations
are edge magnetoplasmons. We address the time evolution of localized
edge-magnetoplasmon wave packets. On short times the wave packets move along
the edge with classical E cross B drift. We show that on longer times the wave
packets can have properties similar to those of the Rydberg wave packets that
are produced in atoms using short-pulsed lasers. In particular, we show that
edge-magnetoplasmon wave packets can exhibit periodic revivals in which a
dispersed wave packet reassembles into a localized one. We propose the study of
edge-magnetoplasmon wave packets as a tool to investigate dynamical properties
of integer and fractional quantum-Hall edges. Various scenarios are discussed
for preparing the initial wave packet and for detecting it at a later time. We
comment on the importance of magnetoplasmon-phonon coupling and on quantum and
thermal fluctuations.Comment: 18 pages, RevTex, 7 figures and 2 tables included, Fig. 5 was
originally 3Mbyte and had to be bitmapped for submission to archive; in the
process it acquired distracting artifacts, to upload the better version, see
http://physics.indiana.edu/~uli/publ/projects.htm
Valley splitting in a Si/SiGe quantum point contact
We present the theory and measurement of valley splitting in a quantum point
contact (QPC) in a modulation doped Si/SiGe heterostructure. Our measurements
are performed on a submicron Schottky-gated device. An effective mass theory is
developed for a QPC formed in a quantum well, grown on a miscut substrate. Both
theory and experiments include a perpendicular magnetic field. Our results
indicate that both QPC and magnetic confinement can enhance the valley
splitting by reducing the spatial extent of the electronic wavefunction.
Consequently, the valley splitting can be much larger than the spin splitting
for small magnetic fields. We also observe different valley splittings for
different transverse modes in the QPC, supporting the notion that when steps
are present at the quantum well interface, the spatial extent of the
wavefunction plays a dominant role in determining the valley splitting.Comment: 23 pages, 14 figure
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Integrating Life Cycle and Impact Assessments to Map Food's Cumulative Environmental Footprint
Producing food exerts pressures on the environment. Understanding the location and magnitude of food production is key to reducing the impacts of these pressures on nature and people. In this Perspective, Kuempel et al. outline an approach for integrating life cycle assessment and cumulative impact mapping data and methodologies to map the cumulative environmental pressure of food systems. The approach enables quantification of current and potential future environmental pressures, which are needed to reduce the net impact of feeding humanity. © 2020 The AuthorsFeeding a growing, increasingly affluent population while limiting environmental pressures of food production is a central challenge for society. Understanding the location and magnitude of food production is key to addressing this challenge because pressures vary substantially across food production types. Applying data and models from life cycle assessment with the methodologies for mapping cumulative environmental impacts of human activities (hereafter cumulative impact mapping) provides a powerful approach to spatially map the cumulative environmental pressure of food production in a way that is consistent and comprehensive across food types. However, these methodologies have yet to be combined. By synthesizing life cycle assessment and cumulative impact mapping methodologies, we provide guidance for comprehensively and cumulatively mapping the environmental pressures (e.g., greenhouse gas emissions, spatial occupancy, and freshwater use) associated with food production systems. This spatial approach enables quantification of current and potential future environmental pressures, which is needed for decision makers to create more sustainable food policies and practices. © 2020 The Author
Negotiating Free Will: Hypnosis and Crime in Early Twentieth-Century Germany
The history of free will has yet to be written. With few exceptions, the literature on the subject is dominated by legal and philosophical works, most of which recount the ideas of prominent thinkers or discuss hypothetical questions far removed from specific historical contexts. The following article seeks to redress the balance by tracing the debate on hypnosis in Germany from 1894 to 1936. Examining responses to hypnosis is tantamount to recording common understandings of autonomy and heteronomy, self-control and mind control, free will and automaticity. More specifically, it is possible to identify distinct philosophical positions related to the question as to whether hypnosis could surmount free will or not. The article demonstrates that the discourse often centred on the perceived struggle, located within a particular personality', between an individual's character' or soul' and the infiltration by a foreign or hostile force. While one group (compatibilists) emphasized the resilience of the moral inhibitions', another group (determinists) doubted that these were sufficient to withstand hypnosis