The attainable superconducting Tc in a model of phase coherence by percolation

The onset of macroscopic phase coherence in superconducting cuprates is considered to be determined by random percolation between mesoscopic Jahn-Teller pairs, stripes or clusters. The model is found to predict the onset of superconductivity near 6% doping, maximum Tc near 15% doping and Tc= T* at optimum doping, and accounts for the destruction of superconductivity by Zn doping near 7%. The model also predicts a relation between the pairing (pseudogap) energy and Tc in terms of experimentally measurable quantities.Comment: 3 pages + 3 postscript figure

Determination of anisotropic dipole moments in self-assembled quantum dots using Rabi oscillations

By investigating the polarization-dependent Rabi oscillations using photoluminescence spectroscopy, we determined the respective transition dipole moments of the two excited excitonic states |Ex> and |Ey> of a single self-assembled quantum dot that are nondegenerate due to shape anisotropy. We find that the ratio of the two dipole moments is close to the physical elongation ratio of the quantum dot.Comment: 11 pages, 2 figures, MS Word generated PDF fil

Temperature dependence of trapped magnetic field in MgB2 bulk superconductor

Based on DC magnetization measurements, the temperature dependencies of the trapped magnetic field have been calculated for two MgB2 samples prepared by two different techniques: the high-pressure sintering and the hot pressing. Experimentally measured trapped field values for the first sample coincide remarkably well with calculated ones in the whole temperature range. This proves, from one side, the validity of the introduced calculation approach, and demonstrates, from another side, the great prospects of the hot pressing technology for large scale superconducting applications of the MgB2.Comment: 3 pages, 3 figures, submitted to AP

Buried heterostructure vertical-cavity surface-emitting laser with semiconductor mirrors

We report a buried heterostructure vertical-cavity surface-emitting laser fabricated by epitaxial regrowth over an InGaAs quantum well gain medium. The regrowth technique enables microscale lateral confinement that preserves a high cavity quality factor (loaded $Q\approx$ 4000) and eliminates parasitic charging effects found in existing approaches. Under optimal spectral overlap between gain medium and cavity mode (achieved here at $T$ = 40 K) lasing was obtained with an incident optical power as low as $P_{\rm th}$ = 10 mW ($\lambda_{\rm p}$ = 808 nm). The laser linewidth was found to be $\approx$3 GHz at $P_{\rm p}\approx$ 5 $P_{\rm th}$

Global Facilitation of Attended Features Is Obligatory and Restricts Divided Attention

Peer reviewedPublisher PD

LSST optical beam simulator

We describe a camera beam simulator for the LSST which is capable of illuminating a 60mm field at f/1.2 with realistic astronomical scenes, enabling studies of CCD astrometric and photometric performance. The goal is to fully simulate LSST observing, in order to characterize charge transport and other features in the thick fully depleted CCDs and to probe low level systematics under realistic conditions. The automated system simulates the centrally obscured LSST beam and sky scenes, including the spectral shape of the night sky. The doubly telecentric design uses a nearly unit magnification design consisting of a spherical mirror, three BK7 lenses, and one beam-splitter window. To achieve the relatively large field the beam-splitter window is used twice. The motivation for this LSST beam test facility was driven by the need to fully characterize a new generation of thick fully-depleted CCDs, and assess their suitability for the broad range of science which is planned for LSST. Due to the fast beam illumination and the thick silicon design [each pixel is 10 microns wide and over 100 microns deep] at long wavelengths there can be effects of photon transport and charge transport in the high purity silicon. The focal surface covers a field more than sufficient for a 40x40 mm LSST CCD. Delivered optical quality meets design goals, with 50% energy within a 5 micron circle. The tests of CCD performance are briefly described.Comment: 9 pages, 9 figure

Reducing Global Warming and Adapting to Climate Change: The Potential of Organic Agriculture

Climate change mitigation is urgent and adaptation to climate change is crucial, particularly in agriculture, where food security is at stake. Agriculture, currently responsible for 20-30% of global greenhouse gas emissions counting direct and indirect agricultural emissions), can however contribute to both climate change mitigation and adaptation. The main mitigation potential lies in the capacity of agricultural soils to sequester CO2 through building organic matter. This potential can be realized by employing sustainable agricultural practices, such as those commonly found within organic farming systems. Examples of these practices are the use of organic fertilizers and crop rotations including legumes leys and cover crops. Mitigation is also achieved in organic agriculture through the avoidance of open biomass burning and the avoidance of synthetic fertilizers and the related production emissions from fossil fuels. Common organic practices also contribute to adaptation. Building soil organic matter increases water retention capacity, and creates more stabile, fertile soils, thus reducing vulnerability to drought, extreme precipitation events, floods and water logging. Adaptation is further supported by increased agro-ecosystem diversity of organic farms, due to reduced nitrogen inputs and the absence of chemical pesticides. The high diversity together with the lower input costs of organic agriculture is key in reducing production risks associated with extreme weather events. All these advantageous practices are not exclusive to organic agriculture. However, they are core parts of the organic production system, in contrast to most non-organic agriculture, where they play a minor role only. Mitigation in agriculture cannot be restricted to the agricultural sector alone, though. Consumer behaviour strongly influences agricultural production systems, and thus their mitigation potential. Significant factors are meat consumption and food wastage. Any discussion on mitigation climate change in agriculture needs to address the entire food chain and needs to be linked to general sustainable development strategies. The main challenges to climate change mitigation and adaptation in organic agriculture and agriculture in general concern a)the understanding of some of the basic processes, such as the interaction of N2O emissions and soil carbon sequestration, contributions of roots to soil carbon sequestration and the life-cycle emissions of organic fertilizers such as compost; b) approaches for emissions accounting that adequately represent agricultural production systems with multiple and diverse outputs and that also encompass ecosystem services; c) the identification and implementation of most adequate policy frameworks for supporting mitigation and adaptation in agriculture, i.e: not putting systemic approaches at a disadvantage due to difficulties in the quantification of emissions, and in their allocation to single products; d) how to assure that the current focus on mitigation does not lead to neglect of the other sustainability aspects of agriculture, such as pesticide loads, eutrophication, acidification or soil erosion and e) the question how to address consumer behaviour and how to utilize the mitigation potential of changes in consumption patterns