Two-Electron Photon Emission From Metallic Quantum Wells

Unusual emission of visible light is observed in scanning tunneling microscopy of the quantum well system Na on Cu(111). Photons are emitted at energies exceeding the energy of the tunneling electrons. Model calculations of two-electron processes which lead to quantum well transitions reproduce the experimental fluorescence spectra, the quantum yield, and the power-law variation of the intensity with the excitation current.Comment: revised version, as published; 4 pages, 3 figure

Hot electron cascades in the scanning tunneling microscope

The nonequilibrium distribution of electrons at the junction of a scanning tunneling microscope is investigated by detecting photons with energies hv > eV, where V is the bias voltage. Electrons are found at energies exceeding the Fermi level by almost eV. While their distribution deviates from a Fermi-Dirac function it is consistent with a model of hot electrons and holes that diffuse in energy and real space

The bradykinin BK2 receptor mediates angiotensin II receptor type 2 stimulated rat duodenal mucosal alkaline secretion

BACKGROUND: This study investigates bradykinin and nitric oxide as potential mediators of AT2-receptor-stimulated duodenal mucosal alkaline secretion. Duodenal mucosal alkaline secretion was measured in methohexital- and α-chloralose-anaesthetised rats by means of in situ pH-stat titration. Immunohistochemistry and Western blot were used to identify the BK2 receptors. RESULTS: The AT2 receptor agonist CGP42112A (0.1 μg kg(-1 )min(-1)) administered intravenously increased the duodenal mucosal alkaline secretion by ~50 %. This increase was sensitive to the selective BK2 receptor blocker HOE140 (100 ng/kg iv), but not to luminal administration of the NOS blocker L-NAME (0.3 mM). Mean arterial pressure did not differ between groups during the procedures. Immunohistochemistry showed a distinct staining of the crypt epithelium and a moderate staining of basal cytoplasm in villus enterocytes. CONCLUSION: The results suggest that the AT2-receptor-stimulated alkaline secretion is mediated via BK2 receptors located in the duodenal cryptal mucosal epithelium

Light emission from a scanning tunneling microscope: Fully retarded calculation

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$^{-4}$ 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

Pseudomonas sp. strain MF30 suppresses Fusarium wilt of tomato in vivo

In a search of bacterial biological control agents, 50 bacterial isolates collected from roots of wild plants in northern Sweden were tested in vivo for suppression of wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici. Tomato plants were sown in 10-cm-diam. pots and after 21 d 7 ml of bacterial suspension (ca. 2x109 cfu ml-1) was poured into the soil around each plant. Two days later, 10 ml of pathogen suspension was soil-inoculated (106 conidia ml-1) around the same plants. After a further 20 days, disease incidence was measured. One bacterial isolate, MF30, protected plants from Fusarium wilt, even though the fungal pathogen and not MF30 actually colonized the plant. Several mechanisms may have contributed to the suppression of Fusarium wilt, including systemic induced resistance. The MF30 strain is highly similar to members of the RNA group I of the Pseudomonas fluorescens, well known for its capacity to induce systemic resistance

Applications and generalizations of Fisher-Hartwig asymptotics

Fisher-Hartwig asymptotics refers to the large $n$ form of a class of Toeplitz determinants with singular generating functions. This class of Toeplitz determinants occurs in the study of the spin-spin correlations for the two-dimensional Ising model, and the ground state density matrix of the impenetrable Bose gas, amongst other problems in mathematical physics. We give a new application of the original Fisher-Hartwig formula to the asymptotic decay of the Ising correlations above $T_c$, while the study of the Bose gas density matrix leads us to generalize the Fisher-Hartwig formula to the asymptotic form of random matrix averages over the classical groups and the Gaussian and Laguerre unitary matrix ensembles. Another viewpoint of our generalizations is that they extend to Hankel determinants the Fisher-Hartwig asymptotic form known for Toeplitz determinants.Comment: 25 page

Light scattering from disordered overlayers of metallic nanoparticles

We develop a theory for light scattering from a disordered layer of metal nanoparticles resting on a sample. Averaging over different disorder realizations is done by a coherent potential approximation. The calculational scheme takes into account effects of retardation, multipole excitations, and interactions with the sample. We apply the theory to a system similar to the one studied experimentally by Stuart and Hall [Phys. Rev. Lett. {\bf 80}, 5663 (1998)] who used a layered Si/SiO$_2$/Si sample. The calculated results agree rather well with the experimental ones. In particular we find conspicuous maxima in the scattering intensity at long wavelengths (much longer than those corresponding to plasmon resonances in the particles). We show that these maxima have their origin in interference phenomena in the layered sample.Comment: 19 pages, 12 figure

Управляемая самостоятельная работа студентов как способ его включния в активную учебную деятельность

Allt fler personer bär idag någon form av medicinska implantat. Det kan varaaktiva implantat som pacemakers eller passiva som exempelvis knä eller höftprotes.Återgång till arbetsliv är normalt inget problem, men i vissa yrken kandet kompliceras av den miljö som arbetaren vistas i. Exponering för elektromagnetiskafält, från statiska fält upp till och med mikrovågsområdet, kan påverkasåväl aktiva som passiva implantat. Felfunktion hos implantatet, elektrostimuleringav närliggande nerver och muskler och upphettning av närliggande vävnadär exempel på sådan oönskad påverkan. Det ställs idag höga krav på störtålighet hos implanterbar medicinteknisk utrustning.Trots detta finns det en rad situationer där oönskad påverkan kan ske.Individfaktorer, arbetssätt och inte minst att varje utrustning kan sägas varaunik, bidrar till svårigheten att ge generella råd. I den riskbedömning som arbetsgivaren är ålagd att utföra enligt arbetsmiljölagenska hänsyn tas till personer med speciella behov, exempelvis personermed olika typer av implantat. Vilka som är involverade i riskbedömningen och hur omfattande den bör varaberor på vilken typ av implantat och vilken typ av arbete det gäller. Väsentligtär att såväl medicinsk som teknisk kompetens bör delta i riskbedömningen. Vadgäller störtåligheten för ett specifikt implantat så är tillverkarna av implantatende som bäst kan bistå med information. Riskbedömningen bör inkludera följandemoment: Typ av implantat och dess känslighet för yttre påverkan samt medicinskakonsekvenser av felfunktion;Identifiera möjliga källor för påverkan på arbetsplatsen;Sammanställning och analys av insamlad data;Slutsatser och råd om hur arbetet lämpligast ska utformas och utföras;Uppföljande kontroll, speciellt viktigt vid ändrade arbetsuppgifter ellerinförande av nya moment