5,533 research outputs found
Nonperturbative analysis of coupled quantum dots in a phonon bath
Transport through coupled quantum dots in a phonon bath is studied using the
recently developed real-time renormalization-group method. Thereby, the problem
can be treated beyond perturbation theory regarding the complete interaction. A
reliable solution for the stationary tunnel current is obtained for the case of
moderately strong couplings of the dots to the leads and to the phonon bath.
Any other parameter is arbitrary, and the complete electron-phonon interaction
is taken into account. Experimental results are quantitatively reproduced by
taking into account a finite extension of the wavefunctions within the dots.
Its dependence on the energy difference between the dots is derived.Comment: 8 pages, 6 figure
Supernova neutrinos: Flavor-dependent fluxes and spectra
Transporting nu_mu and nu_tau in a supernova (SN) core involves several
processes that have been neglected in traditional simulations. Based on a Monte
Carlo study we find that the flavor-dependent spectral differences are much
smaller than is often stated in the literature. A full-scale SN simulation
using a Boltzmann solver and including all relevant neutrino reactions confirms
these results. The flavor-dependent flux differences are largest during the
initial accretion phase.Comment: Proceedings NOON 03, Kanazawa, 10-14 Feb 200
Characterization and Modeling of Non-Uniform Charge Collection in CVD Diamond Pixel Detectors
A pixel detector with a CVD diamond sensor has been studied in a 180 GeV/c
pion beam. The charge collection properties of the diamond sensor were studied
as a function of the track position, which was measured with a silicon
microstrip telescope. Non-uniformities were observed on a length scale
comparable to the diamond crystallites size. In some regions of the sensor, the
charge drift appears to have a component parallel to the sensor surface (i.e.,
normal to the applied electric field) resulting in systematic residuals between
the track position and the hits position as large as 40 m. A numerical
simulation of the charge drift in polycrystalline diamond was developed to
compute the signal induced on the electrodes by the electrons and holes
released by the passing particles. The simulation takes into account the
crystallite structure, non-uniform trapping across the sensor, diffusion and
polarization effects. It is in qualitative agreement with the data. Additional
lateral electric field components result from the non-uniform trapping of
charges in the bulk. These provide a good explanation for the large residuals
observed.Comment: Accepted by Nucl. Instr. and Met
The Urbanization of Nature underneath and beyond ‘the city':Reflections on the book Turning up the Heat: Urban Political Ecology for a climate emergency
In this article we outline the impact that the field of Urban Political Ecology has on academia and policy-making; and argue that this body of scholarship is in a unique position to address some of the urgent political questions around urbanization and climate change. We outline the key epistemologies, ontologies, and methodologies of Urban Political Ecology and explore to what extent these can address the systemic disaster we call climate change. Our key aim is to show that academic research can − and should − remain relevant to the politics of a heating planet.<br/
Fish oil in infancy protects against food allergy in Iceland-Results from a birth cohort study
To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked FilesBACKGROUND: Consumption of oily fish or fish oil during pregnancy, lactation and infancy has been linked to a reduction in the development of allergic diseases in childhood. METHODS: In an observational study, Icelandic children (n = 1304) were prospectively followed from birth to 2.5 years with detailed questionnaires administered at birth and at 1 and 2 years of age, including questions about fish oil supplementation. Children with suspected food allergy were invited for physical examinations, allergic sensitization tests, and a double-blind, placebo-controlled food challenge if the allergy testing or clinical history indicated food allergy. The study investigated the development of sensitization to food and confirmed food allergy according to age and frequency of postnatal fish oil supplementation using proportional hazards modelling. RESULTS: The incidence of diagnosed food sensitization was significantly lower in children who received regular fish oil supplementation (relative risk: 0.51, 95% confidence interval: 0.32-0.82). The incidence of challenge-confirmed food allergy was also reduced, although not statistically significant (0.57, 0.30-1.12). Children who began to receive fish oil in their first half year of life were significantly more protected than those who began later (P = .045 for sensitization, P = .018 for allergy). Indicators of allergy severity decreased with increased fish oil consumption (P = .013). Adjusting for parent education and allergic family history did not change the results. CONCLUSION: Postnatal fish oil consumption is associated with decreased food sensitization and food allergies in infants and may provide an intervention strategy for allergy prevention.European Commission
Landspitali University Hospital Science Fund
GlaxoSmithKline Icelan
Extension of MAD Version 8 to include beam acceleration
In this paper, we describe modifications to MAD version 8.23 to include linear accelerator cavities and beam acceleration An additional energy variable has been added which is modified as the beam passes through LCAV elements (linear accelerator cavities) and can be used as a constraint in matching commands. The calculation of the beta functions and phase advance is consistent with that in other codes that treat acceleration such as TRANSPORT or DIMAD. These modifications allow this version of MAD to be used for the design and modeling of linacs and we present examples from the Next Linear Collider design as well as a muon acceleration complex. The code is available from CERN or SLAC
Electron Neutrino Pair Annihilation: A New Source for Muon and Tau Neutrinos in Supernovae
We show that in a supernova core the annihilation process nu_e nu_e-bar ->
nu_{mu,tau} nu_{mu,tau}-bar is always more important than the traditional
reaction e^+ e^- -> nu_{mu,tau} nu_{mu,tau}-bar as a source for muon and tau
neutrino pairs. We study the impact of the new process by means of a Monte
Carlo transport code with a static stellar background model and by means of a
self-consistent hydrodynamical simulation with Boltzmann neutrino transport.
Nucleon bremsstrahlung NN -> NN nu_{mu,tau} nu_{mu,tau}-bar is also included as
another important source term. Taking into account nu_e nu_e-bar -> nu_{mu,tau}
nu_{mu,tau}-bar increases the nu_mu and nu_tau luminosities by as much as 20%
while the spectra remain almost unaffected. In our hydrodynamical simulation
the shock was somewhat weakened. Elastic nu_{mu,tau} nu_e and nu_{mu,tau} nu_e
scattering is not negligible but less important than nu_{mu,tau} e^+ or e^-
scattering. Its influence on the nu_{mu,tau} fluxes and spectra is small after
all other processes have been included.Comment: 11 pages, 9 eps-figs, submitted to Ap
Apollo 15 rake sample microbreccias and non-mare rocks: Bulk rock, mineral and glass electron microprobe analyses
Quantitative electron microprobe data of Apollo 15 nonmare rake samples are presented. Bulk analyses of lithic fragments in the nomare rocks (expressed in oxide weight-percent) and the corresponding CIPW molecular norms are given. The mineralogy of the rocks and lithic fragments are also given; structural formulae for complete analyses and molecular end-members for all mineral analyses are included. The mineral analyses include pyroxene, olivine, plagioclase, barian K-feldspar, spinel and ilmenite, cobaltian metallic nickel-iron as well as SiO2-K2O-rich residual glass. Electron micropobe analyses (oxide weight percent) of glasses in loose fines and microbreccia samples and their CIPW molecular norms are presented along with electron microprobe data on bulk, mineral, and matrix glass from chondrules
Geometric potential and transport in photonic topological crystals
We report on the experimental realization of an optical analogue of a quantum
geometric potential for light wave packets constrained on thin dielectric
guiding layers fabricated in silica by the femtosecond laser writing
technology. We further demonstrate the optical version of a topological
crystal, with the observation of Bloch oscillations and Zener tunneling of
purely geometric nature
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