3,178 research outputs found
The FIR-absorption of short period quantum wires and the transition from one to two dimensions
We investigate the FIR-absorption of short period parallel quantum wires in a
perpendicular quantizing magnetic field. The external time-dependent electric
field is linearly polarized along the wire modulation. The mutual Coulomb
interaction of the electrons is treated self-consistently in the ground state
and in the absorption calculation within the Hartree approximation. We consider
the effects of a metal gate grating coupler, with the same or with a different
period as the wire modulation, on the absorption. The evolution of the
magnetoplasmon in the nonlocal region where it is split into several Bernstein
modes is discussed in the transition from: narrow to broad wires, and isolated
to overlapping wires. We show that in the case of narrow and not strongly
modulated wires the absorption can be directly correlated with the underlying
electronic bandstructure.Comment: 15 pages, 9 figures, Revtex, to appear in Phys. Rev.
Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya
The sediment flux through Himalayan rivers directly impacts water quality and is important for sustaining agriculture as well as maintaining drinking-water and hydropower generation. Despite the recent increase in demand for these resources, little is known about the triggers and sources of extreme sediment flux events, which lower water quality and account for extensive hydropower reservoir filling and turbine abrasion. Here, we present a comprehensive analysis of the spatiotemporal trends in suspended sediment flux based on daily data during the past decade (2001–2009) from four sites along the Sutlej River and from four of its main tributaries. In conjunction with satellite data depicting rainfall and snow cover, air temperature and earthquake records, and field observations, we infer climatic and geologic controls of peak suspended sediment concentration (SSC) events. Our study identifies three key findings: First, peak SSC events (≥ 99th SSC percentile) coincide frequently (57–80%) with heavy rainstorms and account for about 30% of the suspended sediment flux in the semi-arid to arid interior of the orogen. Second, we observe an increase of suspended sediment flux from the Tibetan Plateau to the Himalayan Front at mean annual timescales. This sediment-flux gradient suggests that averaged, modern erosion in the western Himalaya is most pronounced at frontal regions, which are characterized by high monsoonal rainfall and thick soil cover. Third, in seven of eight catchments, we find an anticlockwise hysteresis loop of annual sediment flux variations with respect to river discharge, which appears to be related to enhanced glacial sediment evacuation during late summer. Our analysis emphasizes the importance of unconsolidated sediments in the high-elevation sector that can easily be mobilized by hydrometeorological events and higher glacial-meltwater contributions. In future climate change scenarios, including continuous glacial retreat and more frequent monsoonal rainstorms across the Himalaya, we expect an increase in peak SSC events, which will decrease the water quality and impact hydropower generation
Mechanical On-Chip Microwave Circulator
Nonreciprocal circuit elements form an integral part of modern measurement
and communication systems. Mathematically they require breaking of
time-reversal symmetry, typically achieved using magnetic materials and more
recently using the quantum Hall effect, parametric permittivity modulation or
Josephson nonlinearities. Here, we demonstrate an on-chip magnetic-free
circulator based on reservoir engineered optomechanical interactions.
Directional circulation is achieved with controlled phase-sensitive
interference of six distinct electro-mechanical signal conversion paths. The
presented circulator is compact, its silicon-on-insulator platform is
compatible with both superconducting qubits and silicon photonics, and its
noise performance is close to the quantum limit. With a high dynamic range, a
tunable bandwidth of up to 30 MHz and an in-situ reconfigurability as beam
splitter or wavelength converter, it could pave the way for superconducting
qubit processors with integrated and multiplexed on-chip signal processing and
readout.Comment: References have been update
Manifestation of the Hofstadter butterfly in far-infrared absorption
The far-infrared absorption of a two-dimensional electron gas with a
square-lattice modulation in a perpendicular constant magnetic field is
calculated self-consistently within the Hartree approximation. For strong
modulation and short period we obtain intra- and intersubband magnetoplasmon
modes reflecting the subbands of the Hofstadter butterfly in two or more Landau
bands. The character of the absorption and the correlation of the peaks to the
number of flux quanta through each unit cell of the periodic potential depends
strongly on the location of the chemical potential with respect to the
subbands, or what is the same, on the density of electrons in the system.Comment: RevTeX file + 4 postscript figures, to be published Phys. Rev. B
Rapid Com
Intake of alkylresorcinols from wheat and rye in the United Kingdom and Sweden
Alkylresorcinols, phenolic lipids present in high amounts in whole-grain wheat and rye but not present in appreciable amounts in other foods, are candidates as biomarkers of whole-grain intake from these cereals. We estimated the intake of alkylresorcinols in Sweden and the UK using two different methods: food supply data (FSD); food consumption data (FCD; based on individual and household survey data). The average per capita intake of alkylresorcinols in Sweden was 17·5 mg/d v(FSD) and 22·9 (sd 16·6) mg/d (FCD), while in the UK it was 11·9 mg/d (FSD) and 11·8 (sd 18·62) mg/d (FCD). Ninety-six per cent of all Swedes consumed some alkylresorcinols, compared with 50 % of British people surveyed. Both women and men over the age of 40 years had a higher alkylresorcinol intake than younger people. The average results from the two methods were similar, but the FCD data provided more detail about the range of alkylresorcinol intake, and indicate that because the intake of alkylresorcinols varies so widely, they may be good markers of diets rich or poor in whole-grain wheat/rye product
A full vectorial mapping of nanophotonic light fields
Light is a union of electric and magnetic fields, and nowhere is the complex relationship between these fields more evident than in the near fields of nanophotonic structures. There, complicated electric and magnetic fields varying over subwavelength scales are generally present, which results in photonic phenomena such as extraordinary optical momentum, superchiral fields, and a complex spatial evolution of optical singularities. An understanding of such phenomena requires nanoscale measurements of the complete optical field vector. Although the sensitivity of near- field scanning optical microscopy to the complete electromagnetic field was recently demonstrated, a separation of different components required a priori knowledge of the sample. Here, we introduce a robust algorithm that can disentangle all six electric and magnetic field components from a single near-field measurement without any numerical modeling of the structure. As examples, we unravel the fields of two prototypical nanophotonic structures: a photonic crystal waveguide and a plasmonic nanowire. These results pave the way for new studies of complex photonic phenomena at the nanoscale and for the design of structures that optimize their optical behavior
Exploring collaboration in challenging environments: from the car to the factory and beyond
We propose a daylong workshop at CSCW2012 on the topic collaboration in challenging and dicult environments, which are to our understanding all contexts, which go beyond traditional working/oce settings topic. Examples for these environments can be the automotive context or the context of a semiconductor factory, which show very specic contextual conditions and therefore oer special research challenges: How to address all passengers in the car, not only the driver? How to explore operator tasks in a cleanroom? How could the long-term (social) collaboration of robots and humans be investigated in privacy critical environments
Beslissingsondersteunende systemen en besluitvorming in marketing management
Nadat eerst kort de complexiteit van de marketing-beslissingssituatie is geschetst, wordt in dit
artikel een omschrijving gegeven van zogenaamde beslissingsondersteuningssystemen die een
belangrijk hulpmiddel kunnen zijn bij een analytische benadering van marketingbeslissingen. Het
artikel laat zien hoe in deze systemen marketingmodellen en marketinginformatiesystemen met
elkaar worden geintegreerd, en gaat in op diverse aspecten, zoals het onderscheid in systemen
voor strategische versus operationele beslissingen, kwantificering van modellen etc., en geeft een
indeling van bestaande modellen. Er worden een aantal concrete ervaringen met deze beslissingsondersteuningssystemen
vermeld en het artikel eindigt met een beschouwing over implementatie
en de rol die de marktonderzoeker daarin kan spelen
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