Observation of many-body long-range tunneling after a quantum quench

Quantum tunneling constitutes one of the most fundamental processes in nature. We observe resonantly-enhanced long-range quantum tunneling in one-dimensional Mott-insulating Hubbard chains that are suddenly quenched into a tilted configuration. Higher-order many-body tunneling processes occur over up to five lattice sites when the tilt per site is tuned to integer fractions of the Mott gap. Starting from a one-atom-per-site Mott state the response of the many-body quantum system is observed as resonances in the number of doubly occupied sites and in the emerging coherence in momentum space. Second- and third-order tunneling shows up in the transient response after the tilt, from which we extract the characteristic scaling in accordance with perturbation theory and numerical simulations.Comment: 22 pages, 7 figure

Mechanical and Vacuum Stability Design Criteria for the LHC Experimental Vacuum Chambers

Four colliding beam experiments are planned for the Large Hadron Collider (LHC) requiring experimental vacuum chambers in the interaction region. The beam pipe should be as transparent as possible to scattered particles and detectors should be as close as possible to the interaction point, resulting in small diameter beam pipes. This, together with the bunched beam structure, makes ion induced pre ssure bump instability, well known from the Intersecting Storage Rings (ISR) at CERN, a potential problem. Adequate conductance, cleanliness of the beam pipes and efficient pumping are required to avo id this instability. Suppression of electron multipacting requires appropriate surface coatings and cleaning procedures. Small beam pipe diameters must provide the required beam stay clear and still a llow margin for alignment and stability inside detectors. Design criteria to ensure both local and global stability under static and dynamic mechanical loads are defined

Algorithms for zero-dimensional ideals using linear recurrent sequences

Inspired by Faug\`ere and Mou's sparse FGLM algorithm, we show how using linear recurrent multi-dimensional sequences can allow one to perform operations such as the primary decomposition of an ideal, by computing the annihilator of one or several such sequences.Comment: LNCS, Computer Algebra in Scientific Computing CASC 201

The Secondary Electron Yield of Technical Materials and its Variation with Surface Treatments

Secondary electron emission of surfaces exposed to oscillating electromagnetic field is at the origin of the multipacting effect that could severely perturb the operation of particle accelerators. This contribution tries to illustrate by measurement results, the origin of the secondary electron emission as well as the main reasons for the discrepancies between technical materials and pure metals. The variation of the secondary electron yield with the incident electron energy will be discussed for various types of technical surfaces. The influence of a gas condensation on these surfaces will also be addressed in the context of the LHC accelerator. Various treatments aiming at a permanent reduction of the secondary electron yield will be presented. A special attention will be paid to the decrease of the secondary electron yield under electron or photon impact and to its possible beneficial consequences for the processing of devices prone to multipacting

The LEP Vacuum System: A Summary of 10 Years of Successful Operation

he LEP accelerator is now operating regularly above 100 GeV and its vacuum system is submitted to the impact of energetic photons with a critical energy approaching 1 MeV. The consequences of this high energy on the photon induced desorption will be reviewed in the light of the various photon absorption mechanisms for aluminium. A review will also be given of the ten years of operation of the LEP vacuum system concerning more especially the evolution of the dynamic pressure with the beam dose and energy, the main difficulties experienced and the actions taken to overcome them

Ground-based aerosol optical depth trends at three high-altitude sites in Switzerland and Southern Germany from 1995–2010

Ground-based aerosol optical depth (AOD) climatologies at three high-altitude sites in Switzerland (Jungfraujoch and Davos) and Southern Germany (Hohenpeissenberg) are updated and re-calibrated for the period 1995 – 2010. In addition, AOD time-series are augmented with previously unreported data, and are homogenized for the first time. Trend analysis revealed weak AOD trends (λ = 500 nm) at Jungfraujoch (JFJ; +0.007 decade-1), Davos (DAV; +0.002 decade-1) and Hohenpeissenberg (HPB; -0.011 decade-1) where the JFJ and HPB trends were statistically significant at the 95% and 90% confidence levels. However, a linear trend for the JFJ 1995 – 2005 period was found to be more appropriate than for 1995 – 2010 due to the influence of stratospheric AOD which gave a trend -0.003 decade-1 (significant at 95% level). When correcting for a recently available stratospheric AOD time-series, accounting for Pinatubo (1991) and more recent volcanic eruptions, the 1995 – 2010 AOD trends decreased slightly at DAV and HPB but remained weak at +0.000 decade-1 and -0.013 decade-1 (significant at 95% level). The JFJ 1995 – 2005 AOD time-series similarly decreased to -0.003 decade-1 (significant at 95% level). We conclude that despite a more detailed re40 analysis of these three time-series, which have been extended by five years to the end of 2010, a significant decrease in AOD at these three high-altitude sites has still not been observed

Vacuum Stability for Ion Induced Gas Desorption

Ion induced vacuum instability was first observed in the Intersecting Proton Storage Rings (ISR) at CERN and in spite of substantial vacuum improvements, it remained a limitation of the maximum beam current throughout the operation of the machine. Extensive laboratory studies and dedicated machine experiments were made during this period to understand the details of this effect and to identify ways of increasing the limit to higher beam currents. Stimulated by the recent design work for the LHC vacuum system, the interest in this problem has been revived with a new critical review of the parameters which determine the pressure run-away in a given vacuum system with high intensity beams

Cloud fraction determined by thermal infrared and visible all-sky cameras

The thermal infrared cloud camera (IRCCAM) is a prototype instrument that determines cloud fraction continuously during daytime and night-time using measurements of the absolute thermal sky radiance distributions in the 8–14&thinsp;µm wavelength range in conjunction with clear-sky radiative transfer modelling. Over a time period of 2 years, the fractional cloud coverage obtained by the IRCCAM is compared with two commercial cameras (Mobotix Q24M and Schreder VIS-J1006) sensitive in the visible spectrum, as well as with the automated partial cloud amount detection algorithm (APCADA) using pyrgeometer data. Over the 2-year period, the cloud fractions determined by the IRCCAM and the visible all-sky cameras are consistent to within 2&thinsp;oktas (0.25 cloud fraction) for 90&thinsp;% of the data set during the day, while for day- and night-time data the comparison with the APCADA algorithm yields an agreement of 80&thinsp;%. These results are independent of cloud types with the exception of thin cirrus clouds, which are not detected as consistently by the current cloud algorithm of the IRCCAM. The measured absolute sky radiance distributions also provide the potential for future applications by being combined with ancillary meteorological data from radiosondes and ceilometers.</p

Quality assurance of the Brewer UV measurements in Finland

International audienceThe quality assurance of the two Brewer spectrophotometers of the Finnish Meteorological Institute is discussed in this paper. The complete data processing chain from raw signal to high quality spectra is presented. The quality assurance includes daily maintenance, laboratory characterizations, calculation of long term spectral responsivity, data processing and quality assessment. The cosine correction of the measurements is based on a new method, and included in the data processing software. The results showed that the actual cosine correction factor of the Finnish Brewers can vary between 1.08?1.13 and 1.08?1.12, respectively, depending on the sky radiance distribution and wavelength. The temperature characterization showed a linear temperature dependence between the internal temperature and the photon counts per cycle, and a temperature correction was used for correcting the measurements. The long term spectral responsivity was calculated using time series of several lamps using two slightly different methods. The long term spectral responsivity was scaled to the irradiance scale of the Helsinki University of Technology (HUT) for the whole measurement time periods 1990?2006 and 1995?2006 for Sodankylä and Jokioinen, respectively. Both Brewers have participated in many international spectroradiometer comparisons, and have shown good stability. The differences between the Brewers and the portable reference spectroradiometer QASUME have been within 5% during 2002?2007