12,369 research outputs found
Optimal traps in graphene
We transform the two-dimensional Dirac-Weyl equation, which governs the
charge carriers in graphene, into a non-linear first-order differential
equation for scattering phase shift, using the so-called variable phase method.
This allows us to utilize the Levinson Theorem to find zero-energy bound states
created electrostatically in realistic structures. These confined states are
formed at critical potential strengths, which leads to us posit the use of
`optimal traps' to combat the chiral tunneling found in graphene, which could
be explored experimentally with an artificial network of point charges held
above the graphene layer. We also discuss scattering on these states and find
the zero angular momentum states create a dominant peak in scattering
cross-section as energy tends towards the Dirac point energy, suggesting a
dominant contribution to resistivity.Comment: 11 pages, 5 figure
Fundamental Limits of Classical and Quantum Imaging
Quantum imaging promises increased imaging performance over classical
protocols. However, there are a number of aspects of quantum imaging that are
not well understood. In particular, it has so far been unknown how to compare
classical and quantum imaging procedures. Here, we consider classical and
quantum imaging in a single theoretical framework and present general
fundamental limits on the resolution and the deposition rate for classical and
quantum imaging. The resolution can be estimated from the image itself. We
present a utility function that allows us to compare imaging protocols in a
wide range of applications.Comment: 4 pages, 3 figures; accepted for Physical Review Letters, with
updated title and fixed typo
Geodynamic setting and origin of the Oman/UAE ophiolite
The ~500km-long mid-Cretaceous Semail nappe of the Sultanate of Oman and UAE (henceforth referred to as the Oman ophiolite) is the largest and best-preserved ophiolite complex known. It is of particular importance because it is generally believed to have an internal structure and composition closely comparable to that of crust formed at the present-day East Pacific Rise (EPR), making it our only known on-land analogue for ocean lithosphere formed at a fast spreading rate. On the basis of this assumption Oman has long played a pivotal role in guiding our conceptual understanding of fast-spreading ridge processes, as modern fast-spread ocean crust is largely inaccessible
VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics
Cluster mergers leave distinct signatures in the ICM in the form of shocks
and diffuse cluster radio sources that provide evidence for the acceleration of
relativistic particles. However, the physics of particle acceleration in the
ICM is still not fully understood. Here we present new 1-4 GHz Jansky Very
Large Array (VLA) and archival Chandra observations of the HST Frontier Fields
Cluster Abell 2744. In our new VLA images, we detect the previously known
Mpc radio halo and Mpc radio relic. We carry out a radio
spectral analysis from which we determine the relic's injection spectral index
to be . This corresponds to a shock Mach
number of = 2.05 under the assumption of
diffusive shock acceleration. We also find evidence for spectral steepening in
the post-shock region. We do not find evidence for a significant correlation
between the radio halo's spectral index and ICM temperature. In addition, we
observe three new polarized diffuse sources and determine two of these to be
newly discovered giant radio relics. These two relics are located in the
southeastern and northwestern outskirts of the cluster. The corresponding
integrated spectral indices measure and for
the SE and NW relics, respectively. From an X-ray surface brightness profile we
also detect a possible density jump of co-located with
the newly discovered SE relic. This density jump would correspond to a shock
front Mach number of .Comment: accepted for publication in Ap
Consistent description of NN and pi-N interactions using the solitary boson exchange potential
A unified description of NN and pi-N elastic scattering is presented in the
framework of the one solitary boson exchange potential (OSBEP). This model
already successfully applied to analyze NN scattering is now extended to
describe pi-N scattering while also improving its accuracy in the NN domain. We
demonstrate the importance of regularization of pi-N scattering amplitudes
involving Delta isobars and derivative meson-nucleon couplings, as this model
always yields finite amplitudes without recourse to phenomenological form
factors. We find an empirical scaling relation of the meson self interaction
coupling constants consistent with that previously found in the study of NN
scattering. Finally, we demonstrate that the OSBEP model does not contradict
the soft-pion theorems of pi-N scattering.Comment: 29 pages RevTeX, submitted to Phys. Rev. C, further information at
http://i04ktha.desy.d
IL-33 expression in response to SARS-CoV-2 correlates with seropositivity in COVID-19 convalescent individuals
Our understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still developing. We perform an observational study to investigate seroprevalence and immune responses in subjects professionally exposed to SARS-CoV-2 and their family members (155 individuals; ages 5-79 years). Seropositivity for SARS-CoV-2 Spike glycoprotein aligns with PCR results that confirm the previous infection. Anti-Spike IgG/IgM titers remain high 60 days post-infection and do not strongly associate with symptoms, except for fever. We analyze PBMCs from a subset of seropositive and seronegative adults. TLR7 agonist-activation reveals an increased population of IL-6+TNF-IL-1β+ monocytes, while SARS-CoV-2 peptide stimulation elicits IL-33, IL-6, IFNa2, and IL-23 expression in seropositive individuals. IL-33 correlates with CD4+ T cell activation in PBMCs from convalescent subjects and is likely due to T cell-mediated effects on IL-33-producing cells. IL-33 is associated with pulmonary infection and chronic diseases like asthma and COPD, but its role in COVID-19 is unknown. Analysis of published scRNAseq data of bronchoalveolar lavage fluid (BALF) from patients with mild to severe COVID-19 reveals a population of IL-33-producing cells that increases with the disease. Together these findings show that IL-33 production is linked to SARS-CoV-2 infection and warrant further investigation of IL-33 in COVID-19 pathogenesis and immunity
Using legume-based mixtures to enhance the nitrogen use efficiency and economic viability of cropping systems - Final report (LK09106/HGCA3447)
As costs for mineral fertilisers rise, legume-based leys are recognised as a potential alternative nitrogen source for crops. Here we demonstrate that including species-rich legume-based leys in rotations helps to maximise synergies between agricultural productivity and other ecosystem services. By using functionally diverse plant species mixtures, these services can be optimised and fine-tuned to regional and farm-specific needs. Replicated field experiments were conducted over three years at multiple locations, testing the performance of 12 legume species and 4 grass species sown in monocultures, as well as in a mixture of 10 of the legumes and all 4 grasses (called the All Species Mix, ASM). In addition, we compared this complex mixture to farmer-chosen ley mixtures on 34 sites across the UK.
The trials showed that there is a large degree of functional complementarity among the legume species. No single species scored high on all evaluation criteria. In particular, the currently most frequently used species, white clover, is outscored by other legume species on a number of parameters such as early development and resistance to decomposition. Further complementarity emerged from the different responses of legume species to environmental variables, with soil pH and grazing or cutting regime being among the more important factors. For example, while large birdsfoot trefoil showed better performance on more acidic soils, the opposite was true for sainfoin, lucerne and black medic. In comparison with the monocultures, the ASM showed increased ground cover, increased above-ground biomass and reduced weed biomass. Benefits of mixing species with regard to productivity increased over time. In addition, the stability of biomass production across sites was greater in the ASM than in the legume monocultures. Within the on-farm trials, we further found that on soils low in organic matter the biomass advantage of the ASM over the Control ley was more marked than on the soils with higher organic matter content. Ecological modelling revealed that the three best multifunctional mixtures all contained black medic, lucerne and red clover.
Within the long term New Farming Systems (NFS) rotational study, the use of a clover bi-crop showed improvement to soil characteristics compared to current practice (e.g. bulk density and water infiltration rate). Improvements in wheat yield were also noted with respect to the inclusion of a clover bi-crop in 2010, but there was evidence of a decline in response as the N dose was increased. Cumulatively, over both the wheat crop and the spring oilseed rape crop, the clover bi-crop improved margin over N. The highest average yield response (~9%) was associated with the ASM legume species mix cover cropping approach
On an inverse to the Hölder inequality
An extension is given for the inverse to Hölder's inequality obtained recently
by Zhuang
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