Structure and stability of a high-coverage (1x1) oxygen phase on Ru(0001)

The formation of chemisorbed O-phases on Ru(0001) by exposure to O_2 at low pressures is apparently limited to coverages Theta <= 0.5. Using low-energy electron diffraction and density functional theory we show that this restriction is caused by kinetic hindering and that a dense O overlayer (Theta = 1) can be formed with a (1x1) periodicity. The structural and energetic properties of this new adsorbate phase are analyzed and discussed in view of attempts to bridge the so-called "pressure gap" in heterogeneous catalysis. It is argued that the identified system actuates the unusually high rate of oxidizing reactions at Ru surfaces under high oxygen pressure conditions.Comment: RevTeX, 6 pages, 3 figures, to appear in Phys. Rev. Let

Complex surface structures studied by low-energy electron diffraction

Structural results of complex surface structures determined by employing the method of low-energy electron diffraction (LEED) are reviewed. LEED is the prime crystallographic technique in surface science, and its ranking among the surface crystallographic methods is comparable to x-ray diffraction for determining the structure of bulk materials. Various kinds of complexity are considered, starting with the atomic geometries of semiconductor surfaces which are heavily reconstructed exhibiting farreaching relaxations down to deeper layers. A next class of systems are coadsorbate phases on metal surfaces whose complexity comes from the presence of various species. In this section also the structure of larger molecules on metal surfaces is discussed. In the last two chapters we concentrate on surfaces violating the two-dimensional translational symmetry. The simplest systems are incommensurate overlayers on metal surfaces. Each layer possesses translational symmetry, but the compound system breaks it. In a next step we also disregard the translational symmetry of each layer and focus on the structure of quasicrystal surfaces

Creating a web-scale video collection for research

This paper begins by considering a number of important design questions for a web-scale, widely available, multimedia test collection intended to support long-term scientific evaluation and comparison of content-based video analysis and exploitation systems. Such exploitation systems would include the kinds of functionality already explored within the annual TRECVid benchmarking activity such as search, semantic concept detection, and automatic summarisation. We then report on our progress in creating such a multimedia collection which we believe to be web scale and which will support a next generation of benchmarking activities for content-based video operations, and we report on our plans for how we intend to put this collection, the IACC.1 collection, to use

Impregnated nets cannot fully substitute for DDT : field effectiveness of Malaria prevention in Solomon Islands

The incidence of malaria in Solomon Islands has been declining since 1992, but there is a large geographical variation between areas in the incidence level and the rate of decline. The authors used a mix of control interventions, including DDT residual house spraying and insecticide-treated mosquito nets. Data on monthly incidence and control activities performed from January 1993 to August 1999 were gathered for 41 out of the 110 malaria zones in the country. Monthly reports on the number of fevers seen at outpatient health clinics in the same zones over the same period were also extracted from the clinical health information system. The authors used multivariate random effects regression, including calendar month as an instrumental variable, to investigate the relationship between the number of malaria or fever cases and the control measures applied by month and zone, while adjusting for rainfall and proximity to water. The results showed that DDT house spraying, insecticide treatment of nets, and education about malaria were all independently associated with reduction in incident cases of malaria or fever, while larviciding with temephos was not. This was true for confirmed malaria cases even when a variable representing the passage of time was included in the models. The results show how much each method used was contributing to malaria control in Solomon Islands and how it can be used to design the most cost-effective package of interventions. The evidence suggests that impregnated bednets cannot easily replace DDT spraying without substantial increase in incidence, but impregnated nets do permit a substantial reduction in the amount of DDT spraying.Health Monitoring&Evaluation,Public Health Promotion,Climate Change,Disease Control&Prevention,Early Child and Children's Health,Health Monitoring&Evaluation,Climate Change,Malaria,Early Child and Children's Health,Health Indicators

Using Sensor Metadata Streams to Identify Topics of Local Events in the City

In this paper, we study the emerging Information Retrieval (IR) task of local event retrieval using sensor metadata streams. Sensor metadata streams include information such as the crowd density from video processing, audio classifications, and social media activity. We propose to use these metadata streams to identify the topics of local events within a city, where each event topic corresponds to a set of terms representing a type of events such as a concert or a protest. We develop a supervised approach that is capable of mapping sensor metadata observations to an event topic. In addition to using a variety of sensor metadata observations about the current status of the environment as learning features, our approach incorporates additional background features to model cyclic event patterns. Through experimentation with data collected from two locations in a major Spanish city, we show that our approach markedly outperforms an alternative baseline. We also show that modelling background information improves event topic identification

TRECVID 2008 - goals, tasks, data, evaluation mechanisms and metrics

The TREC Video Retrieval Evaluation (TRECVID) 2008 is a TREC-style video analysis and retrieval evaluation, the goal of which remains to promote progress in content-based exploitation of digital video via open, metrics-based evaluation. Over the last 7 years this effort has yielded a better understanding of how systems can effectively accomplish such processing and how one can reliably benchmark their performance. In 2008, 77 teams (see Table 1) from various research organizations --- 24 from Asia, 39 from Europe, 13 from North America, and 1 from Australia --- participated in one or more of five tasks: high-level feature extraction, search (fully automatic, manually assisted, or interactive), pre-production video (rushes) summarization, copy detection, or surveillance event detection. The copy detection and surveillance event detection tasks are being run for the first time in TRECVID. This paper presents an overview of TRECVid in 2008

The structure ofAl(111)-K−(√3 × √3)R30° determined by LEED: stable and metastable adsorption sites

It is found that the adsorption of potassium on Al(111) at 90 K and at 300 K both result in a (√3 × √3)R0° structure. Through a detailed LEED analysis it is revealed that at 300 K the adatoms occupy substitutional sites and at 90 K the adatoms occupy on-top sites; both geometries have hitherto been considered as very unusual. The relationship between bond length and coordination is discussed with respect to the present results, and with respect to other quantitative studies of alkali-metal/metal adsorption systems

Oxygen adsorption on the Ru (10 bar 1 0) surface: Anomalous coverage dependence

Oxygen adsorption onto Ru (10 bar 1 0) results in the formation of two ordered overlayers, i.e. a c(2 times 4)-2O and a (2 times 1)pg-2O phase, which were analyzed by low-energy electron diffraction (LEED) and density functional theory (DFT) calculation. In addition, the vibrational properties of these overlayers were studied by high-resolution electron loss spectroscopy. In both phases, oxygen occupies the threefold coordinated hcp site along the densely packed rows on an otherwise unreconstructed surface, i.e. the O atoms are attached to two atoms in the first Ru layer Ru(1) and to one Ru atom in the second layer Ru(2), forming zigzag chains along the troughs. While in the low-coverage c(2 times 4)-O phase, the bond lengths of O to Ru(1) and Ru(2) are 2.08 A and 2.03 A, respectively, corresponding bond lengths in the high-coverage (2 times 1)-2O phase are 2.01 A and 2.04 A (LEED). Although the adsorption energy decreases by 220 meV with O coverage (DFT calculations), we observe experimentally a shortening of the Ru(1)-O bond length with O coverage. This effect could not be reconciled with the present DFT-GGA calculations. The nu(Ru-O) stretch mode is found at 67 meV [c(2 times 4)-2O] and 64 meV [(2 times 1)pg-2O].Comment: 10 pages, figures are available as hardcopies on request by mailing [email protected], submitted to Phys. Rev. B (8. Aug. 97), other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm