5,829 research outputs found

    Integral representation of the linear Boltzmann operator for granular gas dynamics with applications

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    We investigate the properties of the collision operator associated to the linear Boltzmann equation for dissipative hard-spheres arising in granular gas dynamics. We establish that, as in the case of non-dissipative interactions, the gain collision operator is an integral operator whose kernel is made explicit. One deduces from this result a complete picture of the spectrum of the collision operator in an Hilbert space setting, generalizing results from T. Carleman to granular gases. In the same way, we obtain from this integral representation of the gain operator that the semigroup in L^1(\R \times \R,\d \x \otimes \d\v) associated to the linear Boltzmann equation for dissipative hard spheres is honest generalizing known results from the first author.Comment: 19 pages, to appear in Journal of Statistical Physic

    Deposition-mode ice nucleation reexamined at temperatures below 200 K

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    The environmental chamber of a molecular beam apparatus is used to study deposition nucleation of ice on graphite, alcohols and acetic and nitric acids at temperatures between 155 and 200 K. The critical supersaturations necessary to spontaneously nucleate water ice on six different substrate materials are observed to occur at higher supersaturations than are theoretically predicted. This contradictory result motivates more careful examination of the experimental conditions and the underlying basis of the current theories. An analysis based on classical nucleation theory supports the view that at these temperatures nucleation is primarily controlled by the rarification of the vapor and the strength of water's interaction with the substrate surface. The technique enables a careful probing of the underlying processes of ice nucleation and the substrate materials of study. The findings are relevant to atmospheric nucleation processes that are intrinsically linked to cold cloud formation and lifetime

    The event generator DECAY4 for simulation of double beta processes and decay of radioactive nuclei

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    The computer code DECAY4 is developed to generate initial energy, time and angular distributions of particles emitted in radioactive decays of nuclides and nuclear (atomic) deexcitations. Data for description of nuclear and atomic decay schemes are taken from the ENSDF and EADL database libraries. The examples of use of the DECAY4 code in several underground experiments are described.Comment: 8 pages, 1 fi

    Deltagardriven forskning – VĂ€xtodlingsgruppen, resultat och utvĂ€rdering av arbetet under 1998 till 2001

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    DÄ arbetet i vÀxtodlingsgruppen pÄbörjades var förvÀntningarna pÄ deltagardriven forskning att den sammanlagda erfarenheten hos lantbrukare, forskare och rÄdgivare skulle bidra till utförandet av relevanta gÄrdsförsök. Lantbrukarna önskade dessutom strÀva efter att öka och vidarebefordra den kunskap som fanns i gruppen, samt att fÄ etablerade forskare att undersöka omrÄden som praktikerna upplever som viktiga och svÄra. Redan i initialskedet slog vÀxtodlingsgruppen fast att arbeta för att gemensamt identifiera problem och anvÀnda relevanta forskningsmetoder pÄ gÄrdsnivÄ. Syftet var att genom olika odlingsÄtgÀrder kunna förbÀttra förutsÀttningarna för ekologisk vÀxtodling. Ett mÄl var att finna effektiva metoder för optimal vÀxtnÀringstillförsel i ekologisk produktion pÄ lerjordar i MÀlardalen. För nÀrvarande saknas bra underlag för hur kvÀveleveransen varierar under sÀsongen framförallt till strÄsÀd. Detta pÄverkar i sin tur bÄde skördeutfall, proteinhalt, miljöbelastning och ekonomi. Ett annat mÄl var att kunna reglera ogrÀsförekomsten, frÀmst kvickrot och tistel, pÄ ett effektivt sÀtt i vÀxtföljden. Motivationen för lantbrukarna har under projektets gÄng varit att frÀmja det ekologiska lantbruket som helhet. Detta har möjliggjorts genom erfarenhetsutbyte pÄ grupptrÀffar kombinerat med gÄrdsbesök dÀr lantbrukarnas intressen och frÄgestÀllningar har varit drivande. VÀxtodlingsgruppen har pÄ sÄ vis initialt bidragit till ett lokalt utvecklingsarbete och en uppbyggnad av ökat kunnande inom ekologiskt vÀxtodling

    Measurement of the Slope Parameter for the eta->3pi0 Decay in the pp->pp eta Reaction

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    The CELSIUS/WASA setup is used to measure the 3pi0 decay of eta mesons produced in pp interactions with beam kinetic energies of 1.36 and 1.45 GeV. The efficiency-corrected Dalitz plot and density distributions for this decay are shown, together with a fit of the quadratic slope parameter alpha yielding alpha = -0.026 +/- 0.010(stat) +/- 0.010(syst). This value is compared to recent experimental results and theoretical predictions.Comment: 4 pages, 7 Postscript figures, uses revtex4.st

    Anisotropy in the pion angular distribution of the reaction pp -> pp pi0 at 400 MeV

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    The reaction pp -> pp pi0 was studied with the WASA detector at the CELSIUS storage ring. The center of mass angular distribution of the pi0 was obtained by detection of the gamma decay products together with the two outgoing protons, and found to be anisotropic with a negative second derivative slope, in agreement with the theoretical predictions from a microscopic calculation.Comment: Revtex 4 style, 5 pages 7 figures, PACS numbers:13.60.Le, 13.75.Cs, 21.45.+v, 25.10.+

    Organic molecular markers and signature from wood combustion particles in winter ambient aerosols: aerosol mass spectrometer (AMS) and high time-resolved GC-MS measurements in Augsburg, Germany

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    The impact of wood combustion on ambient aerosols was investigated in Augsburg, Germany during a winter measurement campaign of a six-week period. Special attention was paid to the high time resolution observations of wood combustion with different mass spectrometric methods. Here we present and compare the results from an Aerodyne aerosol mass spectrometer (AMS) and gas chromatographic &ndash; mass spectrometric (GC-MS) analysed PM<sub>1</sub> filters on an hourly basis. This includes source apportionment of the AMS derived organic matter (OM) using positive matrix factorisation (PMF) and analysis of levoglucosan as wood combustion marker, respectively. <br><br> During the measurement period nitrate and OM mass are the main contributors to the defined submicron particle mass of AMS and Aethalometer with 28% and 35%, respectively. Wood combustion organic aerosol (WCOA) contributes to OM with 23% on average and 27% in the evening and night time. Conclusively, wood combustion has a strong influence on the organic matter and overall aerosol composition. Levoglucosan accounts for 14% of WCOA mass with a higher percentage in comparison to other studies. The ratio between the mass of levoglucosan and organic carbon amounts to 0.06. <br><br> This study is unique in that it provides a one-hour time resolution comparison between the wood combustion results of the AMS and the GC-MS analysed filter method at a PM<sub>1</sub> particle size range. The comparison of the concentration variation with time of the PMF WCOA factor, levoglucosan estimated by the AMS data and the levoglucosan measured by GC-MS is highly correlated (<i>R</i><sup>2</sup> = 0.84), and a detailed discussion on the contributors to the wood combustion marker ion at mass-to-charge ratio 60 is given. At the end, both estimations, the WCOA factor and the levoglucosan concentration estimated by AMS data, allow to observe the variation with time of wood combustion emissions (gradient correlation with GC-MS levoglucosan of <i>R</i><sup>2</sup> = 0.84). In the case of WCOA, it provides the estimated magnitude of wood combustion emission. Quantitative estimation of the levoglucosan concentration from the AMS data is problematic due to its overestimation in comparison to the levoglucosan measured by the GC-MS
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