IFT POSTEN - DATO

IFT POSTEN – 23.05.2008

Fra Instituttledelsen

Ukens nummer domineres av 12 publikasjoner hvor Alex Hoffmann et al har bidratt med hele tre stykker som rapporterer målinger av flerfasestrømning i sykloner og nanopartikkelproduksjon. Våre to BFS personer Førre og Holst leverer forteller om Rydbergdynamikk og feltionisasjon av Helium og Stamnes et al beskriver lysspreding på ispartikler. På den subatomære siden skrives der bl.a. om hva vi kan forvente på ALICE eksperimentene de nærmeste årene.

Jan Petter

Nyheter og generell informasjon

HUSK: Eksplosivt fellesseminar i dag!

Kl. 14.15 aud B, http://web.ift.uib.no/fsem/Wingerden.html

Fagutvalget feiret nasjonaldagen

Tradisjonen tro arrangerte Fagutvalget ved IFT frokost på instituttet 17. mai. Deretter gikk turen til Muséplass der Universets studenter og ansatte samlet seg under Universitetets fane, før oppstilling til Hovedprosesjonen på Torgallmenningen.

Fagutvalget – ulastelig antrukket - marsjerer fra Muséplass

Eldre tidsskrift

Overflødige hefter av en del tidsskrifter er lagt på et bord i tidsskriftrommet for henting av evt interesserte. Kan avhentes for samlere uten vederlag og først til mølla seinest 1. Juni. De tidsskriftene det gjelder, er: Science, Scientific American, Ottar, Naturen

Forskning och Framsteg.

Nordic Infrastructure conference

During the conference, the participants are invited to take part in one of the following thematic workshops: Climate, Energy and Environment, Welfare and Health,

Future technologies in eScience or National Strategies and Solutions Related to Research Infrastructures.

Date and venue: November 12-13th 2008 at Clarion Hotel, Stockholm, Sweden.

Please register before October 13th.

Read more about the conference, see preliminary programme and register at: http://www.vr.se/nordicinfra.

Studiesaker

Mastereksamener ved IFT

Onsdag 28. mai 2008 avlegger Knut Solvåg sin mastereksamen i Fysikk – Mikroelektronikk

Tittel på oppgaven:

”Design and Testing of n-XYTER: The First Dedicated Neutron Detector Readout ASIC”

Presentasjon av oppgaven skjer kl. 10:00 på rom 366, IFT.

Torsdag 29. mai 2008 avlegger Ilker Meric sin mastereksamen i Fysikk – Industriell instrumentering.

Tittel på oppgaven:

”Monte Carlo modeling of the intrinsic stopping efficiency in Geiger-Müller detectors”

Presentasjon av oppgaven skjer kl. 13:30 på rom 292, IFT.

Alle interesserte er velkommen!

Formidling

Amnytt.no
Artikkel med Julie Katrine Berg, CIPR
Tittel: Drømmereise venter årets teknologistudent
Den harde kampen om teknologistudentene gjør at FMC Technologies på Kongsberg går nye veier for å få tak i de beste ingeniørhodene. Flere studenter har kjempet om å bli Årets Teknologistudent og få mulighet til å reise til Singapore for å besøke FMC Technologies virksomhet der. Den som trakk det lengste strået i år er finnmarkingen og Bergens-studenten Julie Katrine Berg.
http://www.amnytt.no/xp/pub/venstre/hovedside/307198

Publikasjoner (siste 4 uker fra ISI Web of Knowledge, http://apps.isiknowledge.com)

Impact of ice particle shape on short-wave radiative forcing: A case study for an arctic ice cloud
Author(s): Kahnert M, Sandvik AD, Biryulina M, et al.
Source: JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER Volume: 109 Issue: 7 Pages: 1196-1218 Published: MAY 2008¨

Abstract: We used four different non-spherical particle models to compute optical properties of an arctic ice cloud and to simulate corresponding cloud radiative forcings and fluxes. One important finding is that differences in cloud forcing, downward flux at the surface, and absorbed flux in the atmosphere resulting from the use of the four different ice cloud particle models are comparable to differences in these quantities resulting from changing the surface albedo from 0.4 to 0.8, or by varying the ice water content (IWC) by a factor of 2. These findings show that the use of a suitable non-spherical ice cloud particle model is very important for a realistic assessment of the radiative impact of arctic ice clouds. The differences in radiative broadband fluxes predicted by the four different particle models were found to be caused mainly by differences in the optical depth and the asymmetry parameter. These two parameters were found to have nearly the same impact on the predicted cloud forcing. Computations were performed first by assuming a given vertical profile of the particle number density, then by assuming a given profile of the IWC. In both cases, the differences between the cloud radiative forcings computed with the four different non-spherical particle models were found to be of comparable magnitude. This finding shows that precise knowledge of ice particle number density or particle mass is not sufficient for accurate prediction of ice cloud radiative forcing. It is equally important to employ a non-spherical shape model that accurately reproduces the ice particle's dimension-to-volume ratio and its asymmetry parameter. The hexagonal column/plate model with air-bubble inclusions seems to offer the highest degree of flexibility. (c) 2007 Elsevier Ltd. All rights reserved.

Transient intrashell resonances in Rydberg atoms
Author(s): Fregenal D, Forre M, Horsdal E, et al.
Source: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Volume: 41 Issue: 10 Article Number: 105003 Published: MAY 28 2008

Abstract: Rydberg atoms of principal quantum number n in a superposition of a harmonic and a slowly varying field pass through several resonances with the harmonic field of frequency Omega as the splitting omega of the shell by the slow field varies. These transient resonances which are met when omega similar or equal to N Omega, where N is an integer, have been studied for the n = 25 shell of Li. Coherent elliptic states were prepared and used as initial states, and the dynamics was probed by the probability P-a for the atom to remain in the initial state. The harmonic field (E) over right arrow (Omega) was circularly polarized and had constant amplitude, and the slow field varied such that omega at first decreased, then went through a minimum and finally increased to bring the atoms into resonance at two different times. This led to interference patterns in P-a(omega(0)), where omega(0) is the minimum splitting. These were quite regular for coherent elliptic states of low eccentricity e and for strong fields (E) over right arrow (Omega), but less regular for large e and weak (E) over right arrow (Omega). A few states of Li(n = 25) are not hydrogenic due to quantum defects from the (1s)(2) core. Without quantum defects the dynamics can be reduced to that of two spin-1/2 particles and this reproduces the regular patterns quite well. A full quantal treatment, which is required if quantum defects are important, shows that the more irregular patterns are the result of quite complex dynamics involving non-hydrogenic quasi-eigenstates.

Field ionization of free helium atoms: Correlation between the kinetic energy of ionized atoms and probability of their field ionization
Author(s): Piskur J, Borg L, Stupnik A, et al.
Source: APPLIED SURFACE SCIENCE Volume: 254 Issue: 14 Pages: 4365-4369 Published: MAY 15 2008

Abstract: In this paper the correlation between the kinetic energy of helium atoms and the probability of field ionization is investigated by exploiting the narrow velocity distribution of supersonic molecular beams. Field ionization measurements were carried out on supersonic helium beams at 298 K and 95 K corresponding to energies of about 65 meV and 20 meV, respectively, for the individual atoms. The field ionization was performed with a tungsten tip, radius of curvature 12 nm, kept at room temperature. The ionization probability was found to increase by about a factor 10 when the beam was cooled from 298 K to 95 K. The results presented in this paper are of importance for improving the understanding of field ionization and for the development of a new detector for helium and other molecular beams. (C) 2007 Elsevier B. V. All rights reserved.

An experimental investigation of scrubber internals at conditions of low pressure
Author(s): Austrheim T, Gjertsen LH, Hoffmann AC
Source: CHEMICAL ENGINEERING JOURNAL Volume: 138 Issue: 1-3 Pages: 95-102 Published: MAY 1 2008

Abstract: This paper reports experimental results for the performance of natural gas demisting equipment (natural gas scrubbers), and on basis of this discusses possible improvements in the design of gas scrubbers. The separation efficiency and pressure drop of gas scrubber internals: a vane-type inlet, a mist mat and a cyclone deck, for two gas-liquid systems: air-water and air-Exxsol were determined at a range of gas and liquid flows. To interpret results, a model for the cut size of an axial flow cyclone is given. The results show that when reentrainment limits the separation performance of the scrubber the separation performance varies with the nature of the liquid injected, so that design on basis of an air-water system has to be done with caution. The results and the analysis presented further indicate that the K-value, although generally a good evaluation parameter, does not take into account some significant effects, such as the nature of the fluids, changes in the free area for flow, e.g. in the mist mat, and the action of scrubber internals in general. The separation efficiency is shown to be dominated by reentrainment from the cyclone deck at the liquid loadings and gas flows used, loadings and flows which are typical for an industrial scrubber. (C) 2007 Elsevier B.V. All rights reserved.

Effect of calcination conditions and precursor proportions on the properties of YSZ nanoparticles obtained by modified sol-gel route
Author(s): Suciu C, Hoffmann AC, Vik A, et al.
Source: CHEMICAL ENGINEERING JOURNAL Volume: 138 Issue: 1-3 Pages: 608-615 Published: MAY 1 2008

Abstract: The effect is studied of some crucial process parameters on the properties of YSZ nanoparticles produced for solid oxide fuel cell (SOFC) components by a sol-gel method using sucrose and pectin as precursors. The role of the new organic precursors in the chemical process is also discussed. The produced particles are characterized in various ways: by differential thermal analysis (DTA), by nitrogen adsorption using the BET isotherm, by X-ray diffraction (XRD), and by transmission electron microscopy (TEM). The DTA profiles of the gel are compared with those of pure sucrose in the same temperature interval, and substantial differences are seen. The XRD signature from the nanoparticles is one of cubic YSZ and no other crystalline phases. The analyses indicate a significant influence of calcination temperature on the particle size, which increases with increasing calcination temperature. The mean particle size calculated from the BET analyses, on the one hand, and the mean crystallite size from the XRD analyses calculated using the Scherrer formula, on the other, agree in terms of both order-of-magnitude and trend. (C) 2007 Elsevier B.V. All rights reserved.

Experimental investigation of the performance of a large-scale scrubber operating at elevated pressure on live natural gas
Author(s): Austrheim T, Gjertsen LH, Hoffmann AC
Source: FUEL Volume: 87 Issue: 7 Pages: 1281-1288 Published: JUN 2008

Abstract: Experimental results for the performance of a near-full-scale natural gas scrubber operating on a live natural gas system at high pressure are given in this article. The scrubber configuration has three types of internals in series: an inlet vane, a mist-mat and an axial cyclone bank. The variations with pressure of the fluid properties of the natural gas system are calculated and given, and the performances of the over-all scrubber and of the individual internals at a range of gas and liquid flows and at three different pressures up to 113 barg are shown. The results show that beyond a Souders-Brown K-value of 0.15 m/s, the primary separation efficiency breaks down and that beyond this value of K, the scrubber relies on the cyclones for satisfactory separation. However, at a K-value of 0.26 m/s, the cyclone separation efficiency was poor at high pressure and decreased with increasing pressure. The liquid distribution to the cyclones was highly non-uniform, the outer cyclones receiving much more liquid than the inner ones. (c) 2007 Elsevier Ltd. All rights reserved.

Subatomic large collaborations:

Measurements of partial branching fractions for (B)over-bar -> X(u)l(nu)over-bar and determination of vertical bar V-ub vertical bar
Author(s): Aubert B, Bona M, Boutigny D, et al.
Source: PHYSICAL REVIEW LETTERS Volume: 100 Issue: 17 Article Number: 171802 Published: MAY 2 2008

Abstract: We present partial branching fractions for inclusive charmless semileptonic B decays (B) over bar -> X(u)l (nu) over bar, and the determination of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-ub vertical bar. The analysis is based on a sample of 383 x 10(6) gamma(4S) decays into B (B) over bar pairs collected with the BABAR detector at the SLAC PEP-II e(+)e(-) storage rings. We select events using the invariant mass M-X of the hadronic system, the invariant mass squared, q(2), of the lepton and neutrino pair, the kinematic variable P+, or one of their combinations. We then determine partial branching fractions in limited regions of phase space: Delta B = (1.18 +/- 0.09(stat) +/- 0.07(syst) +/- 0.01(theor)) x 10(-3) (M-X < 1.55 GeV/c(2)), Delta B = (0.95 +/- 0.10(stat) +/- 0.08(syst) +/- 0.01(theor)) x 10(-3) (P+ < 0.66 GeV/c), and Delta B = (0.81 +/- 0.08(stat) +/- 0.07(syst) +/- 0.02(theor)) x 10(-3) (M-X < 1.7 GeV/c(2), q(2) > 8 GeV2/c(4)). Corresponding values of vertical bar V-ub vertical bar are extracted using several theoretical calculations.

Observation of tree-level B decays with s(s)over-bar production from gluon radiation
Author(s): Aubert B, Bona M, Boutigny D, et al.
Source: PHYSICAL REVIEW LETTERS Volume: 100 Issue: 17 Article Number: 171803 Published: MAY 2 2008

Abstract: We report on our search for decays proceeding via a tree-level b -> c quark transition in which a gluon radiates into an s (s) over bar pair. We present observations of the decays B--> D-s(*)K-+(-) pi(-) and (B) over bar (0) -> (Ds+KS0)pi(-) and evidence for B--> D-s(+) K- K- and set upper limits on the branching fractions for (B) over bar (0) -> (Ds*+KS0) pi(-) and B- -> Ds*+K- K- using 383 x 10(6) gamma(4S)-> B (B) over bar events collected by the BABAR detector at SLAC. We present evidence that the invariant mass distributions of Ds(*)+K- pairs from B- -> D-s(*)K-+(-)pi(-) decays are inconsistent with the phase-space model, suggesting the presence of charm resonances lying below the D-s(*)(+) K- threshold.

Measurement of the branching fractions of exclusive (B)over-bar -> D-(*)(pi)l(-)(nu)over-bar(l) decays in events with a fully reconstructed b meson
Author(s): Aubert B, Bona M, Karyotakis Y, et al.
Source: PHYSICAL REVIEW LETTERS Volume: 100 Issue: 15 Article Number: 151802 Published: APR 18 2008

Abstract: We report a measurement of the branching fractions for (B) over bar -> D-(*)(pi)center dot(-)(nu) over bar (center dot) decays based on 341.1 fb(-1) of data collected at the Upsilon(4S) resonance with the BABAR detector at the SLAC PEP-II e(+)e(-) storage rings. Events are tagged by fully reconstructing one of the B mesons in a hadronic decay mode.

Time-dependent Dalitz plot analysis of B-0 ->(DK0)-K--/+pi(+/-) decays
Author(s): Aubert B, Bona M, Karyotakis Y, et al.
Source: PHYSICAL REVIEW D Volume: 77 Issue: 7 Article Number: 071102 Published: APR 2008

Abstract: We present for the first time a measurement of the weak phase 2 beta+gamma obtained from a time-dependent Dalitz plot analysis of B-0 ->(DK0)-K--/+pi(+/-) decays. Using a sample of approximately 347x10(6) B (B) over bar pairs collected by the BABAR detector at the PEP-II asymmetric-energy storage rings and assuming the ratio r of the b -> u and b -> c decay amplitudes to be 0.3, we obtain 2 beta+gamma=(83 +/- 53 +/- 20)degrees and the equivalent solution at +180 degrees. The magnitudes and phases for the resonances associated with the b -> c transitions are also extracted from the fit.

Heavy-ion collisions at the LHC-Last call for predictions
Author(s): Armesto N, Borghini N, Jeon S, et al.
Source: JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS Volume: 35 Issue: 5 Article Number: 054001 Published: MAY 2008

Abstract: This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from 14th May to 10th June 2007.

Real time global tests of the ALICE High Level Trigger data transport framework
Author(s): Becker B, Chattopadhyay S, Cicalo C, et al.
Source: IEEE TRANSACTIONS ON NUCLEAR SCIENCE Volume: 55 Issue: 2 Pages: 703-709 Published: APR 2008

Abstract: The High Level Trigger (HLT) system of the ALICE experiment is an online event filter and trigger system designed for input bandwidths of up to 25 GB/s at event rates of up to 1 kHz. The system is designed as a scalable PC cluster, implementing several hundred nodes. The transport of data in the system is handled by an object-oriented data flow framework operating on the basis of the publisher-subscriber principle, being designed fully pipelined with lowest processing overhead and communication latency in the cluster. In this paper, we report the latest measurements where this framework has been operated on five different sites over a global north-south link extending more than 10,000 km, processing a "real-time" data flow.