| 1. |
- Abdo, A. A., et al.
(author)
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FERMI/LARGE AREA TELESCOPE BRIGHT GAMMA-RAY SOURCE LIST
- 2009
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In: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 183:1, s. 46-66
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Journal article (peer-reviewed)abstract
- Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the gamma-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than similar to 10 sigma) gamma-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) gamma-ray sources in the early mission data.
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| 2. |
- Abdo, A. A., et al.
(author)
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PULSED GAMMA-RAYS FROM PSR J2021+3651 WITH THE FERMI LARGE AREA TELESCOPE
- 2009
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 700:2, s. 1059-1066
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Journal article (peer-reviewed)abstract
- We report the detection of pulsed gamma-rays from the young, spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The light curve consists of two narrow peaks of similar amplitude separated by 0.468 +/- 0.002 in phase. The first peak lags the maximum of the 2 GHz radio pulse by 0.162 +/- 0.004 +/- 0.01 in phase. The integral gamma-ray photon flux above 100 MeV is (56 +/- 3 +/- 11) x 10(-8) cm(-2) s(-1). The photon spectrum is well described by an exponentially cut-off power law of the form dF/dE = kE(-Gamma)e((-E/Ec)), where the energy E is expressed in GeV. The photon index is Gamma = 1.5 +/- 0.1 +/- 0.1 and the exponential cut-off is E-c = 2.4 +/- 0.3 +/- 0.5 GeV. The first uncertainty is statistical and the second is systematic. The integral photon flux of the bridge is approximately 10% of the pulsed emission, and the upper limit on off-pulse gamma-ray emission from a putative pulsar wind nebula is < 10% of the pulsed emission at the 95% confidence level. Radio polarization measurements yield a rotation measure of RM = 524 +/- 4 rad m(-2) but a poorly constrained magnetic geometry. Re-analysis of Chandra X-ray Observatory data enhanced the significance of the weak X-ray pulsations, and the first peak is roughly phase aligned with the first gamma-ray peak. We discuss the emission region and beaming geometry based on the shape and spectrum of the gamma-ray light curve combined with radio and X-ray measurements, and the implications for the pulsar distance. Gamma-ray emission from the polar cap region seems unlikely for this pulsar.
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| 3. |
- Abdo, A. A., et al.
(author)
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A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope
- 2009
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 325:5942, s. 848-852
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Journal article (peer-reviewed)abstract
- Pulsars are born with subsecond spin periods and slow by electromagnetic braking for several tens of millions of years, when detectable radiation ceases. A second life can occur for neutron stars in binary systems. They can acquire mass and angular momentum from their companions, to be spun up to millisecond periods and begin radiating again. We searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars (MSPs) outside of globular clusters, using rotation parameters from radio telescopes. Strong gamma-ray pulsations were detected for eight MSPs. The gamma-ray pulse profiles and spectral properties resemble those of young gamma-ray pulsars. The basic emission mechanism seems to be the same for MSPs and young pulsars, with the emission originating in regions far from the neutron star surface.
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| 4. |
- Abdo, A. A., et al.
(author)
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Fermi LAT Observations of LS I +61°303 : First Detection of an Orbital Modulation in GeV Gamma Rays
- 2009
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In: Astrophysical Journal Letters. - 2041-8205. ; 701:2, s. L123-L128
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Journal article (peer-reviewed)abstract
- This Letter presents the first results from the observations of LS I +61°303 using Large Area Telescope data from the Fermi Gamma-Ray Space Telescope between 2008 August and 2009 March. Our results indicate variability that is consistent with the binary period, with the emission being modulated at 26.6 ± 0.5 days. This constitutes the first detection of orbital periodicity in high-energy gamma rays (20 MeV-100 GeV, HE). The light curve is characterized by a broad peak after periastron, as well as a smaller peak just before apastron. The spectrum is best represented by a power law with an exponential cutoff, yielding an overall flux above 100 MeV of 0.82 ± 0.03(stat) ± 0.07(syst) 10-6 ph cm-2 s-1, with a cutoff at 6.3 ± 1.1(stat) ± 0.4(syst) GeV and photon index Γ = 2.21 ± 0.04(stat) ± 0.06(syst). There is no significant spectral change with orbital phase. The phase of maximum emission, close to periastron, hints at inverse Compton scattering as the main radiation mechanism. However, previous very high-energy gamma ray (>100 GeV, VHE) observations by MAGIC and VERITAS show peak emission close to apastron. This and the energy cutoff seen with Fermi suggest that the link between HE and VHE gamma rays is nontrivial.
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| 5. |
- Abdo, A. A., et al.
(author)
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Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT
- 2009
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 325:5942, s. 840-844
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Journal article (peer-reviewed)abstract
- Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants.
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| 6. |
- Scandale, Walter, et al.
(author)
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Apparatus to study crystal channeling and volume reflection phenomena at the SPS H8 beamline
- 2008
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 79:2
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Journal article (peer-reviewed)abstract
- A high performance apparatus has been designed and built by the H8-RD22 collaboration for the study of channeling and volume reflection phenomena in the interaction of 400 GeVc protons with bent silicon crystals, during the 2006 data taking in the external beamline H8 of the CERN SPS. High-quality silicon short crystals were bent by either anticlastic or quasimosaic effects. Alignment with the highly parallel (8 μrad divergence) proton beam was guaranteed through a submicroradian goniometric system equipped with both rotational and translational stages. Particle tracking was possible by a series of silicon microstrip detectors with high-resolution and a parallel plate gas chamber, triggered by various scintillating detectors located along the beamline. Experimental observation of volume reflection with 400 GeVc protons proved true with a deflection angle of (10.4±0.5) μrad with respect to the unperturbed beam, with a silicon crystal whose (111) planes were parallel to the beam. © 2008 American Institute of Physics.
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| 7. |
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| 8. |
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| 9. |
- Scandale, Walter, et al.
(author)
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Deflection of 400GeV/c proton beam with bent silicon crystals at the CERN Super Proton Synchrotron
- 2008
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In: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 11:6
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Journal article (peer-reviewed)abstract
- This paper presents a detailed study of the deflection phenomena of a 400GeV/c proton beam impinging on a new generation of bent silicon crystals; the tests have been performed at the CERN Super Proton Synchrotron H8 beam line. Channeling and volume reflection angles are measured with an extremely precise goniometer and with high resolution silicon microstrip detectors. Volume reflection has been observed and measured for the first time at this energy, with a single-pass efficiency as large as 98%, in good agreement with the simulation results. This efficiency makes volume reflection a possible candidate for collimation with bent crystals at the CERN Large Hadron Collider. © 2008 The American Physical Society.
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| 10. |
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| 11. |
- Aceto, Luca, et al.
(author)
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Algebraic properties for free!
- 2009
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In: Bulletin of the European Association for Theoretical Computer Science. - : European Association for Theoretical Computer Science. - 0252-9742. ; 99, s. 81-103
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Journal article (peer-reviewed)abstract
- Algebraic properties specify some natural properties of programming and specification constructs. This paper provides an overview of techniques to guarantee or generate algebraic properties of language constructs by investigating the syntactic shape of the deduction rules defining their operational semantics.
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| 12. |
- Afanasiev, Sergey V., et al.
(author)
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Experimental apparatus to study crystal channeling in an external SPS beamline
- 2007
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In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6634
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Journal article (peer-reviewed)abstract
- For the new generation of high intensity hadronic machines as, for instance, LHC, halo collimation is a necessary issue for the accelerator to operate at the highest possible luminosity and to prevent the damage of superconductor magnets.1 We propose an experiment aimed to systematic study of the channeling phenomenology and of the newly observed "volume reflection" effect. This experiment will be performed for an external SPS beamline and will make use of a primary proton beam with 400 GeV/c momentum and very small (∼ 3 μrad) divergence. The advantage of a proposed experiment is precise tracking of particles that interacted with a crystal, so that to determine the single-pass efficiency for all the processes involved. For this purpose, a telescope equipped with high-resolution silicon microstrip detectors will be used. New generation silicon crystals and an extra-precise goniometer are mandatory issues. Main goal of the experiment is to get the precise information on channeling of relativistic particles and, ultimately, on the feasibility of such technique for halo collimation at LHC. In this contribution we review the status of the setting-up of experimental apparatus and its future development in sight of the planned run in September 2006.
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| 13. |
- Balgobind, Brian V, et al.
(author)
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Novel prognostic subgroups in childhood 11q23/MLL-rearranged acute myeloid leukemia : results of an international retrospective study.
- 2009
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In: Blood. - : American Society of Hematology. - 0006-4971 .- 1528-0020. ; 114:12, s. 2489-2496
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Journal article (peer-reviewed)abstract
- Translocations involving chromosome 11q23 frequently occur in pediatric acute myeloid leukemia (AML) and are associated with poor prognosis. In most cases, the MLL gene is involved, and more than 50 translocation partners have been described. Clinical outcome data of the 11q23-rearranged subgroups are scarce because most 11q23 series are too small for meaningful analysis of subgroups, although some studies suggest that patients with t(9;11)(p22;q23) have a more favorable prognosis. We retrospectively collected outcome data of 756 children with 11q23- or MLL-rearranged AML from 11 collaborative groups to identify differences in outcome based on translocation partners. All karyotypes were centrally reviewed before assigning patients to subgroups. The event-free survival of 11q23/MLL-rearranged pediatric AML at 5 years from diagnosis was 44% (+/- 5%), with large differences across subgroups (11% +/- 5% to 92% +/- 5%). Multivariate analysis identified the following subgroups as independent prognostic predictors: t(1;11)(q21;q23) (hazard ratio [HR] = 0.1, P = .004); t(6;11)(q27;q23) (HR = 2.2, P < .001); t(10;11)(p12;q23) (HR = 1.5, P = .005); and t(10;11)(p11.2;q23) (HR = 2.5, P = .005). We could not confirm the favorable prognosis of the t(9;11)(p22;q23) subgroup. We identified large differences in outcome within 11q23/MLL-rearranged pediatric AML and novel subgroups based on translocation partners that independently predict clinical outcome. Screening for these translocation partners is needed for accurate treatment stratification at diagnosis.
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| 14. |
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| 15. |
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| 16. |
- Aceto, Luca, et al.
(author)
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A Rule Format for Unit Elements
- 2009
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Reports (other academic/artistic)abstract
- This paper offers a meta-theorem for languages with a Structural Operational Semantics (SOS) in the style of Plotkin. Namely, it proposes a generic rule format for SOS guaranteeing that certain constants act as left- or right-unit elements for a set of binary operators. We show the generality of our format by applying it to a wide range of operators from the literature on process calculi.
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Corino, Valentina D. A., et al.
(author)
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Improved Time-Frequency Analysis of Atrial Fibrillation Signals Using Spectral Modeling
- 2008
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In: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 55:12, s. 2723-2730
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Journal article (peer-reviewed)abstract
- In patients with atrial fibrillation (AF), the fibrillatory frequency trend and the time-dependent spectral characteristics can be investigated using a spectral profile technique. The spectral profile is updated by fitting each short-time spectrum. The aim of this study is to develop model-based means for stricter control on the update of the spectral profile. A spectral model defined by a superposition of Gaussian functions is suggested for describing the fundamental and harmonics of the atrial waves during AF, thereby accounting for basic characteristics of the typical AF spectrum. The model parameters are obtained from weighted least squares fitting of the model to the observed spectrum. The method was tested on simulated signals as well as on 48 ECG recordings from 15 patients with persistent AF. Using simulated signals, we assessed the accuracy in terms of magnitude and width or the spectral peaks. For SNR = 0 dB, the maximum normalized error was less than 0.2 when estimating magnitude of both the fundamental and the harmonics, whereas it was less than 0.15 for the fundamental and 0.7 for the harmonics with respect to the estimation of the width. We observed a marked Improvement while tracking the main fibrillatory frequency as the error was reduced by more than 50% In comparison with the original method. Analyzing ECGs, reliable spectral profiles were obtained In all recordings, even In those cases (5/48) that were not well characterized by the original method.
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| 21. |
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| 22. |
- Coto, PB, et al.
(author)
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Characterization of the conical intersection of the visual pigment rhodopsin at the CASPT2//CASSCF/AMBER level of theory
- 2006
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In: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 104:5-7, s. 983-991
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Journal article (peer-reviewed)abstract
- The branching plane associated with the conical intersection controlling the photochemical Z -> E isomerization reaction of rhodopsin has been mapped using a CASPT2//CASSCF/ AMBER quantum mechanics-molecular mechanics method. The nature of the derivative coupling and gradient difference vectors spanning the branching plane has been investigated, showing that the conical intersection is not only associated with the isomerization process but also to a charge transfer along the retinal backbone. Using a simple Landau-Zener model, the paper discusses the possible effects of the documented conical intersection topologies on the efficiency of the reactive process. It is argued that the peculiar shape of the conical intersection favours decay at structures that are geometrically displaced towards the photoproduct bathorhodopsin.
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| 23. |
- De Luca, L., et al.
(author)
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Acute heart failure syndromes: clinical scenarios and pathophysiologic targets for therapy
- 2007
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In: Heart Fail Rev. - : Springer Science and Business Media LLC. - 1382-4147 .- 1573-7322. ; 12:2, s. 97-104
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Research review (peer-reviewed)abstract
- Acute heart failure syndromes (AHFS) represent the most common discharge diagnosis in patients over age 65 years, with an exceptionally high mortality and readmission rates at 60-90 days. Recent surveys and registries have generated important information concerning the clinical characteristics of patients with AHFS and their prognosis. Most patients with AHFS present either with normal systolic blood pressure or elevated blood pressure. Patients who present with elevated systolic blood pressure usually have pulmonary congestion, a relatively preserved left ventricular ejection fraction (LVEF), are often elderly women, and their symptoms develop typically and abruptly. Patients with normal systolic blood pressure present with systemic congestion, reduced LVEF, are usually younger with a history of chronic HF, and have symptoms that develop gradually over days or weeks. In addition to the abnormal hemodynamics (increase in pulmonary capillary wedge pressure and/or decrease in cardiac output) that characterize patients with AHFS, myocardial injury, which may be related to a decrease in coronary perfusion and/or further activation of neurohormones and renal dysfunction, probably contributes to short-term and post-discharge cardiac events. Patients with AHFS also have significant cardiac and noncardiac underlying conditions that contribute to the pathogenesis of AHFS, including coronary artery disease (ischemia, hibernating myocardium, and endothelial dysfunction), hypertension, atrial fibrillation, and type 2 diabetes mellitus. Therefore, the targets of therapy for AHFS should be not only to improve symptoms and hemodynamics but also to preserve or improve renal function, prevent myocardial damage, modulate neurohumoral and inflammatory activation, and to manage other comorbidities that may cause and/or contribute to the progression of this syndrome.
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| 24. |
- De Luca, L., et al.
(author)
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Early pharmacological treatment of acute heart failure syndromes: A systematic review of clinical trials
- 2007
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In: Acute cardiac care. - 1748-2941. ; 9:1, s. 10-21
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Journal article (peer-reviewed)abstract
- Context: Acute Heart Failure Syndromes (AHFS) is a common admission diagnosis associated with high mortality and hospital readmissions. Given the mixed results of recent clinical trials, the early management of AHFS remains controversial. Objective: To review the recent evidence regarding current and investigational therapies for the early management of AHFS. Data Sources: A systematic search of peer-reviewed publications was performed on MEDLINE and EMBASE from January 1990 to August 2006. The results of unpublished or ongoing trials were obtained from presentations at national and international meetings and pharmaceutical industry releases. Bibliographies from these references were also reviewed, as were additional articles identified by content experts. Study Selection and Data Extraction: Criteria used for study selection were controlled study design, relevance to clinicians and validity based on venue of publication and power analysis. Data Synthesis: Although all current intravenous therapies for the early management of AHFS appear to improve hemodynamics, this may not always translate into short-term clinical benefit. Conclusion: The results of the trials conducted to date in AHFS have generally been disappointing. There is, therefore, an unmet need for new therapeutic approaches for the early management of AHFS that may improve the short-term and long-term outcomes.
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| 25. |
- Fransson, Jens H. M., et al.
(author)
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Delaying transition to turbulence by a passive mechanism
- 2006
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 96:6
-
Journal article (peer-reviewed)abstract
- Reducing skin friction is important in nature and in many technological applications. This reduction may be achieved by reducing stresses in turbulent boundary layers, for instance tailoring biomimetic rough skins. Here we take a second approach consisting of keeping the boundary layer laminar as long as possible by forcing small optimal perturbations. Because of the highly non-normal nature of the underlying linearized operator, these perturbations are highly amplified and able to modify the mean velocity profiles at leading order. We report results of wind-tunnel experiments in which we implement this concept by using suitably designed roughness elements placed on the skin to enforce nearly optimal perturbations. We show that by using this passive control technique it is possible to sensibly delay transition to turbulence.
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| 26. |
- Fransson, Jens H. M., 1973-, et al.
(author)
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Experimental analysis of transition delay by means of roughness elements
- 2006
-
In: Collection of Technical Papers. - 1563478102 - 9781563478109 ; , s. 1464-1478
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Conference paper (peer-reviewed)abstract
- An experimental activity aimed at the development of a passive method for viscous drag reduction in an aerodynamic body is presented. The reduction is achieved by delaying the laminar-turbulent transition of the boundary layer. The research is motivated by previous linear stability analysis where it was demonstrated that stable streaks in a boundary layer are capable to stabilize the growth of Tollmien-Schlichting waves. In this paper the results of a series of experiments on a flat plate are presented. Firstly, it is shown that by means of suitable roughness elements it is possible to generate stable steady streaks of amplitudes up to 12% of the free stream velocity. Secondly, it is demonstrated that the generated streaks are really effective in reducing the growth of the Tollmien-Schlichting waves as predicted by the theory. Finally, it is shown that using this passive control technique it is possible to sensibly delay transition to turbulence.
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| 27. |
- Fransson, Jens H. M., et al.
(author)
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Experimental study of the stabilization of Tollmien-Schlichting waves by finite amplitude streaks
- 2005
-
In: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 17:5
-
Journal article (peer-reviewed)abstract
- It has recently been found by using temporal and spatial numerical simulations that steady optimal streaks of moderate amplitude, i.e., sufficiently large but not exceeding the critical amplitude for the inflectional instability, are able to reduce the growth of Tollmien-Schlichting (TS) waves up to their complete suppression. This investigation aims at experimentally verifying this stabilizing effect by generating stable and symmetric, close to sinusoidal, streaks of moderate amplitudes (similar to 12% of the free-stream velocity) by means of a spanwise array of cylindrical roughness elements. The three-dimensional (3D) streaky base flow is then subjected to a secondary instability generated through a spanwise slot in the plate by means of regulated blowing and suction. In this study the stabilizing role of the streaks on TS waves is unambiguously confirmed and by increasing the height of the roughness elements, thus inducing larger amplitude streaks, we are also able to show that the stabilizing action on the TS waves increases with the streak amplitude. These results are the first to confirm the numerical predictions reported in earlier works. The full cross-stream plane has been measured at different downstream positions allowing a complete evaluation and comparison of the different amplitude measures used in previous experimental works. Furthermore, theoretical impulse response analysis and stability calculations are applied to the present experimental streaky base flow enabling a qualitative comparison of the 3D modulated TS wave distribution.
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| 28. |
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| 29. |
- Ghiringhelli, Luca M, et al.
(author)
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Competing adsorption between hydrated peptides and water onto metal surfaces : from electronic to conformational properties
- 2008
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 130:40, s. 13460-13464
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Journal article (peer-reviewed)abstract
- Inorganic-(bio)organic interfaces are of central importance in many fields of current research. Theoretical and computational tools face the difficult problem of the different time and length scales that are involved and linked in a nontrivial way. In this work, a recently proposed hierarchical quantum-classical scale-bridging approach is further developed to study large flexible molecules. The approach is then applied to study the adsorption of oligopeptides on a hydrophilic Pt(111) surface under complete wetting conditions. We examine histidine sequences, which are well known for their binding affinity to metal surfaces. Based on a comparison with phenylalanine, which binds as strong as histidine under high vacuum conditions but, as we show, has no surface affinity under wet conditions, we illustrate the mediating effects of near-surface water molecules. These contribute significantly to the mechanism and strength of peptide binding. In addition to providing physical-chemical insights in the mechanism of surface binding, our computational approach provides future opportunities for surface-specific sequence design.
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| 30. |
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| 31. |
- Husser, Oliver, et al.
(author)
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Exercise testing for non-invasive assessment of atrial electrophysiological properties in patients with persistent atrial fibrillation
- 2007
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In: Europace. - : Oxford University Press (OUP). - 1532-2092. ; 9:8, s. 627-632
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Journal article (peer-reviewed)abstract
- Aims Experimental studies suggest that the autonomic nervous system modulates atrial refractoriness and conduction velocity in atrial. fibrillation (AF). These modulatory effects are, however, difficult to assess in the clinical setting. This study sought to non-invasively characterize in patients with persistent AF, the influence of autonomic modulation induced by exercise on atrial fibrillatory rate as marker of atrial refractoriness and to identify clinical and electrocardiographic predictors of atrial rate response. Methods and results In 24 patients (16 mates, mean age 60 +/- 13 years) with persistent AF (16 +/- 25 months), continuous ECGs were recorded during bicycle exercise testing. Fibrillatory rate (in fibrillations per minute, fpm) was assessed at baseline and immediately after termination of exercise with spatiotemporal QRST cancellation and time-frequency analysis. Ventricular response was characterized by time-domain HRV indices. Exercise had no influence on mean fibrillatory rate (409 +/- 42 vs. 414 +/- 43 fpm, P = NS). Seven patients responded to exercise with an increase in fibrillatory rate (26 10 fpm, P < 0.001 and three with a decrease (-21 +/- 8 fpm, P < 0.001), while the remaining 14 patients did not show a response. Responders' HRV indices changed in response to exercise similarly to that of non-responders. Their baseline fibrillatory rate was, however, lower than that of non-responders (387 +/- 18 vs. 425 +/- 48 fpm, P = 0.028). No other clinical or echocardiographic variable was associated with fibrillatory rate response. Twelve weeks after cardioverson, responders were more likely to remain in sinus rhythm than non-responders (88 vs. 46 %, P = 0.04). Conclusions Exercise-induced autonomic activation produces changes in atrial. etectrophysiological properties that can be detected by time-frequency analysis. Higher baseline fibrillatory rates are associated with an impaired atrial response to exercise that suggests advanced electrical remodelling and reduced sensitivity to autonomic stimuli.
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| 32. |
- Macovez, Roberto, et al.
(author)
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Reversible Phase Transformation and Doubly Charged Anions at the Surface of Simple Cubic RbC60
- 2008
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 101:23, s. 236403-
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Journal article (peer-reviewed)abstract
- The simple cubic phase of a RbC60 thin film has been studied using photoelectron spectroscopy. The simple cubic-to-dimer transition is found to be reversible at the film surface. A sharp Fermi edge is observed and a lower limit of 0.5 eV is found for the surface Hubbard U, pointing to a strongly correlated metallic character of thin-film simple cubic RbC60. A molecular charge state is identified in the valence band and core-level photoemission spectra which arises from C-60(2-) anions and contributes to the spectral intensity at the Fermi level.
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| 33. |
- Rossis, M., et al.
(author)
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SYNAPSE : A network reprogramming protocol for wireless sensor networks using fountain codes
- 2008
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In: 2008 5th Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks, SECON. - 9781424417773 ; , s. 188-196
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Conference paper (peer-reviewed)abstract
- Wireless reprogramming is a key functionality in Wireless Sensor Networks (WSNs). In fact, the requirements for the network may change in time, or new parameters might have to be loaded to change the behavior of a given protocol. In large scale WSNs it makes economical as well as practical sense to upload the code with the needed functionalities without human intervention, i.e., by means of efficient over the air reprogramming. This poses several challenges as wireless links are affected by errors, data dissemination has to be 100% reliable, and data transmission and recovery schemes are often called to work with a large number of receivers. State-of-the-art protocols, such as Deluge, implement error recovery through the adaptation of standard Automatic Repeat reQuest (ARQ) techniques. These, however, do not scale well in the presence of channel errors and multiple receivers. In this paper, we present an original reprogramming system for WSNs called SYNAPSE, which we designed to improve the efficiency of the error recovery phase. SYNAPSE features a hybrid ARQ (HARQ) solution where data are encoded prior to transmission and incremental redundancy is used to recover from losses, thus considerably reducing the transmission overhead. For the coding, digital Fountain Codes were selected as they are rateless and allow for lightweight implementations. In this paper, we design special Fountain Codes and use them at the heart of SYNAPSE to provide high performance while meeting the requirements of WSNs. Moreover, we present our implementation of SYNAPSE for the Tmote Sky sensor platform and show experimental results, where we compare the performance of SYNAPSE with that of state of the art protocols.
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| 34. |
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