1,948 research outputs found

    Have historical land use/land cover changes triggered a fire regime shift in central Spain?

    Get PDF
    Fire is one of the main disturbance factors shaping the landscape, and landscape is a key driver of fire behavior. Considering the role played by land use and land cover (LULC) changes as the main driver of landscape dynamics, the aim of this study was to calculate and analyze (i) the real impact of fire on LULC changes and (ii) how these LULC changes were influencing the fire regime. We used methods of historical geography and socio-spatial systemic analysis for reconstructing and assessing the LULC change and fire history in six case studies in the Central Mountain System (Spain) from archival documentary sources and historical cartography. The main result is an accurate dataset of fire records from 1497 to 2013 and a set of LULC maps for three time points (1890s–1930s, 1956–1957, and the 2000s). We have shown the nonlinear evolution of the fire regime and the importance of the local scale when assessing the interaction of landscape dynamics and fire regime variation. Our findings suggest that LULC trends have been the main influencing factor of fire regime variation in Central Spain since the mid-19th centuryinfo:eu-repo/semantics/publishedVersio

    Light emission from a scanning tunneling microscope: Fully retarded calculation

    Full text link
    The light emission rate from a scanning tunneling microscope (STM) scanning a noble metal surface is calculated taking retardation effects into account. As in our previous, non-retarded theory [Johansson, Monreal, and Apell, Phys. Rev. B 42, 9210 (1990)], the STM tip is modeled by a sphere, and the dielectric properties of tip and sample are described by experimentally measured dielectric functions. The calculations are based on exact diffraction theory through the vector equivalent of the Kirchoff integral. The present results are qualitatively similar to those of the non-retarded calculations. The light emission spectra have pronounced resonance peaks due to the formation of a tip-induced plasmon mode localized to the cavity between the tip and the sample. At a quantitative level, the effects of retardation are rather small as long as the sample material is Au or Cu, and the tip consists of W or Ir. However, for Ag samples, in which the resistive losses are smaller, the inclusion of retardation effects in the calculation leads to larger changes: the resonance energy decreases by 0.2-0.3 eV, and the resonance broadens. These changes improve the agreement with experiment. For a Ag sample and an Ir tip, the quantum efficiency is ≈\approx 10−4^{-4} emitted photons in the visible frequency range per tunneling electron. A study of the energy dissipation into the tip and sample shows that in total about 1 % of the electrons undergo inelastic processes while tunneling.Comment: 16 pages, 10 figures (1 ps, 9 tex, automatically included); To appear in Phys. Rev. B (15 October 1998

    Crime, Institutions and Sector-Specific FDI in Latin America

    Get PDF
    In this article, we explore how crime and institutions affect the flow of capital in the form of foreign direct investment (FDI) to Latin American and Caribbean countries in the primary, secondary and tertiary sectors during the 1996-2010 period. We use three different variables related to violent crime: homicides, crime victimization, and an index of organized crime. We find that there is a correlation between the institutional and crime variables, where the significance of institutional variables tends to disappear when the crime variables are added to the model. We find that higher crime victimization and organized crime are associated with lower FDI in the tertiary sector. We do not find that crime affects FDI inflows to Latin America in the primary and secondary sector

    Electrodynamics in complex systems: Application to near-field probing of optical microresonators

    Full text link
    This paper discusses recent theoretical efforts to develop a general and flexible method for the calculation of the field distributions around and inside complex optical systems involving both dielectric and metallic materials. Starting from the usual light-matter coupling Hamiltonian, we derive a self-consistent equation for the optical field in arbitrary optical systems composed of N different subdomains. We show that an appropriate solving procedure based on the real-space discretization of each subdomain raises the present approach to the rank of an accurate predictive numerical scheme. In order to illustrate its applicability, we use this formalism to address challenging problems related to nonradiative energy transfers in near-field optics. In particular, we investigate in detail the detuning of a microresonator probed by a near-field optical probe.</p

    Measurement of Energy Correlators inside Jets and Determination of the Strong Coupling Formula Presented

    Get PDF
    Energy correlators that describe energy-weighted distances between two or three particles in a hadronic jet are measured using an event sample of s\sqrt{s}=13 TeV proton-proton collisions collected by the CMS experiment and corresponding to an integrated luminosity of 36.3 fb−1^{−1}. The measured distributions are consistent with the trends in the simulation that reveal two key features of the strong interaction: confinement and asymptotic freedom. By comparing the ratio of the measured three- and two-particle energy correlator distributions with theoretical calculations that resum collinear emissions at approximate next-to-next-to-leading-logarithmic accuracy matched to a next-to-leading-order calculation, the strong coupling is determined at the Z boson mass: αS_S (mZ_Z)=0.1229 0.0040−0.0050\frac{0.0040}{-0.0050} , the most precise αS_SmZ_Z value obtained using jet substructure observable

    Measurement of the polarizations of prompt and non-prompt J/ψ and ψ (2S) mesons produced in pp collisions at s\sqrt{s} = 13 TeV

    Get PDF
    The polarizations of prompt and non-prompt J∕ψ and ψ(2S) mesons are measured in proton-proton collisions at √ = 13 TeV, using data samples collected by the CMS experiment in 2017 and 2018, corresponding to a total integrated luminosity of 103.3 fb−1^{−1}. Based on the analysis of the dimuon decay angular distributions in the helicity frame, the polar anisotropy, , is measured as a function of the transverse momentum, T_T, of the charmonium states, in the 25–120 and 20–100 GeV ranges for the J∕ψ and ψ(2S), respectively. The non-prompt polarizations agree with predictions based on the hypothesis that, for T ≳ 25 GeV, the non-prompt J∕ψ and ψ(2S) are predominantly produced in two-body B meson decays. The prompt results clearly exclude strong transverse polarizations, even for T_T exceeding 30 times the J∕ψ mass, where tends to an asymptotic value around 0.3. Taken together with previous measurements, by CMS and LHCb at √ = 7 TeV, the prompt polarizations show a significant variation with T_T, at low T_T

    Search for heavy neutral leptons in final states with electrons, muons, and hadronically decaying tau leptons in proton-proton collisions at s \sqrt{s} = 13 TeV

    Get PDF
    A search for heavy neutral leptons (HNLs) of Majorana or Dirac type using proton-proton collision data at = 13 TeV is presented. The data were collected by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 138 fb−1. Events with three charged leptons (electrons, muons, and hadronically decaying tau leptons) are selected, corresponding to HNL production in association with a charged lepton and decay of the HNL to two charged leptons and a standard model (SM) neutrino. The search is performed for HNL masses between 10 GeV and 1.5 TeV. No evidence for an HNL signal is observed in data. Upper limits at 95% confidence level are found for the squared coupling strength of the HNL to SM neutrinos, considering exclusive coupling of the HNL to a single SM neutrino generation, for both Majorana and Dirac HNLs. The limits exceed previously achieved experimental constraints for a wide range of HNL masses, and the limits on tau neutrino coupling scenarios with HNL masses above the W boson mass are presented for the first time

    Search for new physics in high-mass diphoton events from proton-proton collisions at √s = 13 TeV

    Get PDF
    Results are presented from a search for new physics in high-mass diphoton events from proton-proton collisions at sqrt(s) = 13 TeV. The data set was collected in 2016–2018 with the CMS detector at the LHC and corresponds to an integrated luminosity of 138 fb−1 . Events with a diphoton invariant mass greater than 500 GeV are considered. Two diferent techniques are used to predict the standard model backgrounds: parametric fts to the smoothly-falling background and a frst-principles calculation of the standard model diphoton spectrum at next-to-next-to-leading order in perturbative quantum chromodynamics calculations. The frst technique is sensitive to resonant excesses while the second technique can identify broad diferences in the invariant mass shape. The data are used to constrain the production of heavy Higgs bosons, Randall-Sundrum gravitons, the large extra dimensions model of Arkani-Hamed, Dimopoulos, and Dvali (ADD), and the continuum clockwork mechanism. No statistically signifcant excess is observed. The present results are the strongest limits to date on ADD extra dimensions and RS gravitons with a coupling parameter greater than 0.1

    Search for a vector-like quark Tâ€Č → tH via the diphoton decay mode of the Higgs boson in proton-proton collisions at s \sqrt{s} = 13 TeV

    Get PDF
    A search for the electroweak production of a vector-like quark Tâ€Č, decaying to a top quark and a Higgs boson is presented. The search is based on a sample of proton-proton collision events recorded at the LHC at = 13 TeV, corresponding to an integrated luminosity of 138 fb−1. This is the first Tâ€Č search that exploits the Higgs boson decay to a pair of photons. For narrow isospin singlet Tâ€Č states with masses up to 1.1 TeV, the excellent diphoton invariant mass resolution of 1–2% results in an increased sensitivity compared to previous searches based on the same production mechanism. The electroweak production of a Tâ€Č quark with mass up to 960 GeV is excluded at 95% confidence level, assuming a coupling strength ÎșT = 0.25 and a relative decay width Γ/MTâ€Č < 5%
    • 

    corecore