177 research outputs found
Quasiparticle Dynamics in the Kondo Lattice Model at Half Filling
We study spectral properties of quasiparticles in the Kondo lattice model in
one and two dimensions including the coherent quasiparticle dispersions, their
spectral weights and the full two-quasiparticle spectrum using a cluster
expansion scheme. We investigate the evolution of the quasiparticle band as
antiferromagnetic correlations are enhanced towards the RKKY limit of the
model. In both the 1D and the 2D model we find that a repulsive interaction
between quasiparticles results in a distinct antibound state above the
two-quasiparticle continuum. The repulsive interaction is correlated with the
emerging antiferromagnetic correlations and can therefore be associated with
spin fluctuations. On the square lattice, the antibound state has an extended
s-wave symmetry.Comment: 8 pages, 11 figure
Glacier naled evolution and relation to the subglacial drainage system based on water chemistry and GPR surveys (Werenskioldbreen, SW Svalbard)
Glacier naledi are extrusive ice masses that appear in front of glaciers as a consequence of refreezing of meltwater seepage during the accumulation season. These structures provide a unique opportunity to understand subglacial drainage activity during the accumulation season; however, only few detailed studies have previously focused on their characteristics. Here, we investigated glacier-derived naled assemblages in the proglacial zone of the polythermal glacier Werenskioldbreen (27.4 km2) in SW Svalbard. We determined the spatial distribution of naledi using ground penetrating radar surveys. The main subglacial drainage pattern was related to a channel under the medial moraine, and three sources are linked to a distributed subglacial drainage network. The relation between atmospherically-corrected (Ca2+ + Mg2+) and (SO4 2-) in sub-naled waters was closely related to sulphide oxidation coupled with carbonate dissolution (r = 0.99; slope = 1.6). This is consistent with the local lithology, which is dominated by schist containing carbonates. We also found high carbonate saturation indices in pale white ice layers within the naled. We conclude that sulphide oxidation coupled with carbonate dissolution is the dominant chemical weathering process in the subglacial drainage system of Werenskioldbreen during the accumulation season
The MuPix Telescope: A Thin, high Rate Tracking Telescope
The MuPix Telescope is a particle tracking telescope, optimized for tracking
low momentum particles and high rates. It is based on the novel High-Voltage
Monolithic Active Pixel Sensors (HV-MAPS), designed for the Mu3e tracking
detector. The telescope represents a first application of the HV-MAPS
technology and also serves as test bed of the Mu3e readout chain. The telescope
consists of up to eight layers of the newest prototypes, the MuPix7 sensors,
which send data self-triggered via fast serial links to FPGAs, where the data
is time-ordered and sent to the PC. A particle hit rate of 1 MHz per layer
could be processed. Online tracking is performed with a subset of the incoming
data. The general concept of the telescope, chip architecture, readout concept
and online reconstruction are described. The performance of the sensor and of
the telescope during test beam measurements are presented.Comment: Proceedings TWEPP 2016, 8 pages, 7 figure
Fully Modular Robotic Arm Architecture Utilizing Novel Multifunctional Space Interface
The current paradigm in space robotics is the design of specialized robotic manipulators to meet the requirements for a specific mission profile. This research aims to develop a novel concept of a modular robotic arm for multi-purpose and multi-mission use. The overall approach is based on a manipulator formed by serial connection of identical modules. Each module contains one rotational joint. The joints, rotation axis is tilted under an angle of 45° to the normal axis, which requires less stowage space compared to a traditional joint configuration. A manipulator can be reconfigured in orbit by adding or removing modules and end effectors, therefore modifying the degrees of freedom (DoF) as well as the workspace. Redundancies are introduced, since defect modules may be removed or replaced. This paper outlines the overall concept of modularization of a robotic arm. The development and mechanical design of a terrestrial demonstrator based on the multifunctional interface iSSI (intelligent Space System Interface) is presented, which is intended for OOS and OOA activities. Furthermore, a variant of the modular robotic system with 24 DoF is presented, which can be stowed in a Cubesat-sized environment. It can operate in spaces with limited accessibility and is dedicated for tasks like inspection and delicate repairs. Finally, an outlook to further research potential and future use cases for the modular robotic system is given.BMWi, 50RP1960A, Verbundvorhaben HOMER: Hoch-redundante modulare Robotersysteme zum flexiblen Einsatz in der Raumfahrt und der Automotive-Serienfertigung; Teilvorhaben Kinematik und RedundanzBMWi, 50RP1960B, Verbundvorhaben: HOMER - Hoch-redundante modulare Robotersysteme zum flexiblen Einsatz in der Raumfahrt und der Automotive-Serienfertigung; Teilvorhaben: modulare Robotikstrukture
Microwave Spin Control of a Tin-Vacancy Qubit in Diamond
The negatively charged tin-vacancy (SnV-) center in diamond is a promising
solid-state qubit for applications in quantum networking due to its high
quantum efficiency, strong zero phonon emission, and reduced sensitivity to
electrical noise. The SnV- has a large spin-orbit coupling, which allows for
long spin lifetimes at elevated temperatures, but unfortunately suppresses the
magnetic dipole transitions desired for quantum control. Here, by use of a
naturally strained center, we overcome this limitation and achieve
high-fidelity microwave spin control. We demonstrate a pi-pulse fidelity of up
to 99.51+/0.03%$ and a Hahn-echo coherence time of T2echo = 170.0+/-2.8
microseconds, both the highest yet reported for SnV- platform. This performance
comes without compromise to optical stability, and is demonstrated at 1.7
Kelvin where ample cooling power is available to mitigate drive induced
heating. These results pave the way for SnV- spins to be used as a building
block for future quantum technologies
The history of degenerate (bipartite) extremal graph problems
This paper is a survey on Extremal Graph Theory, primarily focusing on the
case when one of the excluded graphs is bipartite. On one hand we give an
introduction to this field and also describe many important results, methods,
problems, and constructions.Comment: 97 pages, 11 figures, many problems. This is the preliminary version
of our survey presented in Erdos 100. In this version 2 only a citation was
complete
Highlights of the 2nd International Symposium on Tribbles and Diseases: Tribbles tremble in therapeutics for immunity, metabolism, fundamental cell biology and cancer
The Tribbles (TRIB) family of pseudokinase proteins has been shown to play key roles in cell cycle, metabolic diseases, chronic inflammatory disease, and cancer development. A better understanding of the mechanisms of TRIB pseudokinases could provide new insights for disease development and help promote TRIB proteins as novel therapeutic targets for drug discovery. At the 2nd International Symposium on Tribbles and Diseases held on May 7‒9, 2018 in Beijing, China, a group of leading Tribbles scientists reported their findings and ongoing studies about the effects of the different TRIB proteins in the areas of immunity, metabolism, fundamental cell biology and cancer. Here, we summarize important and insightful overviews from 4 keynote lectures, 13 plenary lectures and 8 short talks that took place during this meeting. These findings may offer new insights for the understanding of the roles of TRIB pseudokinases in the development of various diseases
Enhanced woody biomass production in a mature temperate forest under elevated CO2
This is the final version. Available from Nature Research via the DOI in this record. Data availability:
All data are publicly available without restriction at Dryad (https://datadryad.org/stash) at https://doi.org/10.5061/dryad.z612jm6jw (ref. 54). Biological samples (leaf litter, tree cores) were collected at the BIFoR research site (52.801° N, 2.301° W) and are archived at the University of Birmingham.Code availability:
Quantitative structure models and calculation of tree volume from TLS data (QSMs) used the open-source software optQSM (https://github.com/apburt/optqsm) and TreeQSM v.2.4.1 (https://github.com/InverseTampere/TreeQSM).Enhanced CO2 assimilation by forests as atmospheric CO2 concentration rises could slow the rate of CO2 increase if the assimilated carbon is allocated to long-lived biomass. Experiments in young tree plantations support a CO2 fertilization effect as atmospheric CO2 continues to increase. Uncertainty exists, however, as to whether older, more mature forests retain the capacity to respond to elevated CO2. Here, aided by tree-ring analysis and canopy laser scanning, we show that a 180-year-old Quercus robur L. woodland in central England increased the production of woody biomass when exposed to free-air CO2 enrichment (FACE) for 7 years. Further, elevated CO2 increased exudation of carbon from fine roots into the soil with likely effects on nutrient cycles. The increase in tree growth and allocation to long-lived woody biomass demonstrated here substantiates the major role for mature temperate forests in climate change mitigation.Natural Environment Research Council (NERC)UK Research and InnovationJABBS foundationUniversity of BirminghamJohn Horseman Trus
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