343 research outputs found
Reconstruction of a yeast cell from X-ray diffraction data
No full textDetails are provided of the algorithm used for the reconstruction of yeast cell images in the recent demonstration of diffraction microscopy by Shapiro, Thibault, Beetz, Elser, Howells, Jacobsen, Kirz, Lima, Miao, Nieman & Sayre [Proc. Natl Acad. Sci. USA (2005), 102, 15343-15346]. Two refinements of the iterative constraint-based scheme are developed to address the current experimental realities of this imaging technique, which include missing central data and noise. A constrained power operator is defined whose eigenmodes allow the identification of a small number of degrees of freedom in the reconstruction that are negligibly constrained as a result of the missing data. To achieve reproducibility in the algorithm's output, a special intervention is required for these modes. Weak incompatibility of the constraints caused by noise in both direct and Fourier space leads to residual phase fluctuations. This problem is addressed by supplementing the algorithm with an averaging method. The effect of averaging may be interpreted in terms of an effective modulation transfer function, as used in optics, to quantify the resolution. The reconstruction details are prefaced with simulations of wave propagation through a model yeast cell. These show that the yeast cell is a strong-phase-contrast object for the conditions in the experiment
Searching with iterated maps
No full textIn many problems that require extensive searching, the solution can be described as satisfying two competing constraints, where satisfying each independently does not pose a challenge. As an alternative to tree-based and stochastic searching, for these problems we propose using an iterated map built from the projections to the two constraint sets. Algorithms of this kind have been the method of choice in a large variety of signal-processing applications; we show here that the scope of these algorithms is surprisingly broad, with applications as diverse as protein folding and Sudoku
On the question of stability and disorder in icosahedral aluminum - transition metal alloys
No full textPT: J; CR: BANCEL PA, 1985, PHYS REV LETT, V54, P2422 BANCEL PA, 1986, PHYS REV B, V33, P7917 CHEN CH, 1986, PHYS REV B, V33, P2814 DUBOST B, 1986, NATURE, V324, P48 DUNLAP RA, 1985, PHYS STATUS SOLIDI A, V92, K11 DUNLAP RA, 1986, J PHYS F MET PHYS, V16, P11 EIBSCHUTZ M, 1987, PHYS REV LETT, V59, P2443 EIBSCHUTZ M, 1989, IN PRESS PHYS REV LE ELSER V, 1985, PHYS REV B, V32, P4892 ELSER V, 1985, PHYS REV LETT, V55, P2883 LAWTHER DW, 1989, IN PRESS J MATER SCI MACKAY AL, 1962, ACTA CRYSTALLOGR, V15, P916 OHASHI W, 1987, NATURE, V330, P555 REDFIELD AC, 1987, PHYS REV LETT, V58, P2322 SHECHTMAN D, 1984, PHYS REV LETT, V53, P1951 TSAI AP, 1987, JPN J APPL PHYS, V26, P1505 YAMANE H, 1987, MATER SCI FORUM, V22, P539; NR: 17; TC: 18; J9: CAN J PHYS; PG: 5; GA: AK758Source type: Electronic(1
The Elser nuclei sum revisited
No full textFix a finite undirected graph and a vertex of . Let
be the set of edges of . We call a subset of pandemic if each
edge of has at least one endpoint that can be connected to by an
-path (i.e., a path using edges from only). In 1984, Elser showed that
the sum of over all pandemic subsets of
is if . We give a simple proof of this result via a
sign-reversing involution, and discuss variants, generalizations and
refinements, revealing connections to abstract convexity (the notion of an
antimatroid) and discrete Morse theory
Transition metal site distributions in binary aluminum-transition metal quasicrystals: Al-V and Al-Cr
No full textPT: J; CR: BANCEL PA, 1985, PHYS REV LETT, V54, P2422 BIGOT J, 1988, MATER SCI ENG, V99, P453 CARLSON ON, 1955, T AM SOC MET, V47, P520 DINI K, 1986, J MATER SCI, V21, P1037 DUNLAP RA, 1985, PHYS STATUS SOLIDI A, V92, K11 DUNLAP RA, 1986, J PHYS F MET PHYS, V16, P11 DUNLAP RA, 1988, J PHYS F MET PHYS, V18, P1329 DUNLAP RA, 1988, PHYS REV B, V38, P3649 DUNLAP RA, 1988, UNPUB EDAGAWA K, 1987, J PHYS SOC JPN, V56, P2629 EIBSCHUTZ M, 1986, PHYS REV LETT, V56, P169 EIBSCHUTZ M, 1987, PHYS REV LETT, V59, P2443 ELSER V, 1985, PHYS REV B, V32, P4892 ELSER V, 1985, PHYS REV LETT, V55, P2883 HAUSER JJ, 1986, PHYS REV B, V33, P3577 INOUE A, 1986, METALL TRANS A, V17, P1657 INOUE A, 1987, J MATER SCI, V22, P1758 KIMURA K, 1985, J PHYS SOC JPN, V54, P3217 LAWTHER DW, 1989, CAN J PHYS, V67, P463 LIEBERMANN HH, 1983, BUTTERWORTHS MONOGRA, P26 MACKAY AL, 1962, ACTA CRYSTALLOGR, V15, P916 MCHENRY ME, 1989, PHYS REV B, V39, P3611 NISHITANI SR, 1988, MATER SCI ENG, V99, P443 SHECHTMAN D, 1984, PHYS REV LETT, V53, P1951 SKINNER DJ, 1988, MATER SCI ENG, V99, P407 SWARTZENDRUBER LJ, 1985, PHYS REV B, V32, P1383 WARREN WW, 1986, PHYS REV B, V34, P4902 ZHANG H, 1988, PHYS REV B, V37, P6220; NR: 28; TC: 4; J9: MATER SCI ENG A-STRUCT MATER; PG: 6; GA: CP677Source type: Electronic(1
Size-segregated aerosol in a hot-spot pollution urban area: Chemical composition and three-way source apportionment
No full textIn this work, a comprehensive characterisation and source apportionment of size-segregated aerosol collected using a multistage cascade impactor was performed. The samples were collected during wintertime in Milan (Italy), which is located in the Po Valley, one of the main pollution hot-spot areas in Europe. For every sampling, size-segregated mass concentration, elemental and ionic composition, and levoglucosan concentration were determined. Size-segregated data were inverted using the program MICRON to identify and quantify modal contributions of all the measured components. The detailed chemical characterisation allowed the application of a three-way (3-D) receptor model (implemented using Multilinear Engine) for size-segregated source apportionment and chemical profiles identification. It is noteworthy that - as far as we know - this is the first time that three-way source apportionment is attempted using data of aerosol collected by traditional cascade impactors. Seven factors were identified: wood burning, industry, resuspended dust, regional aerosol, construction works, traffic 1, and traffic 2. Further insights into size-segregated factor profiles suggested that the traffic 1 factor can be associated to diesel vehicles and traffic 2 to gasoline vehicles. The regional aerosol factor resulted to be the main contributor (nearly 50%) to the droplet mode (accumulation sub-mode with modal diameter in the range 0.5â1 Î1⁄4m), whereas the overall contribution from the two factors related to traffic was the most important one in the other size modes (34â41%). The results showed that applying a 3-D receptor model to size-segregated samples allows identifying factors of local and regional origin while receptor modelling on integrated PM fractions usually singles out factors characterised by primary (e.g. industry, traffic, soil dust) and secondary (e.g. ammonium sulphate and nitrate) origin. Furthermore, the results suggested that the information on size-segregated chemical composition in different size classes was exploited by the model to relate primary emissions to rapidly-formed secondary compounds
The effect of host Chlorella NC64A carbon: Phosphorus ratio on the production of Paramecium bursaria Chlorella Virus-1
No full text1. We used the freshwater alga Chlorella NC64A (Division Chlorophyta) and its virus Paramecium bursaria Chlorella virus-1 (PBCV-1) as a model system to test for potential stoichiometric constraints on a virus–host interaction. 2. Media phosphorus concentrations were manipulated to create Chlorella NC64A host cells with low (91 ± 23) or high (453 ± 246) C : P ratio. In contrast, the C : P ratio of PBCV-1, calculated from its biochemical composition, was 17 : 1. 3. Stoichiometric theory predicts that infection success and postinfection viral production should be depressed in high C : P cultures due to insufficient intracellular P for production of P-rich viral particles. 4. Consistent with this hypothesis, viral production was strongly affected by host C : P ratio. While host C : P ratio did not affect viral attachment or the percentage of new viral particles that were infectious, in the low C : P Chlorella NC64A treatment, nine times more viruses were produced per infected cell than in the high C : P treatment (158 ± 138 versus 18 ± 18), indicating that the low C : P cells were higher quality for PBCV-1 proliferation. 5. This result implies that the stoichiometric quality of algal cells can have a major effect on host–virus population dynamics. [ABSTRACT FROM AUTHOR]Peer reviewedfinal article publishedChlorella NC64Aviral ecologyphosphorusParamecium bursaria Chlorella virus‐1ecological stoichiometr
A mass closure and source apportionment study on PM1 in Milan (Italy)
No full textIt is well known that the particle size plays a major role in determining the particle penetration in the respiratory system and therefore in threatening human health.
Despite this fact, data on PM1 composition and sources are still relatively rare. This work aimed at a detailed physical and chemical characterisation of PM1 to obtain the mass closure and to perform a source apportionment study using receptor modelling. Episodes with very high PM1 pollution levels were analysed in detail to identify processes/sources affecting this fine PM fraction.
Moreover, a critical comparison to the results obtained during the previous PM1 campaigns carried out by our group at the same location about 10 years ago (Vecchi et al. 2004; Vecchi et al., 2008) will be also shown.
PM1 was sampled at an urban background station in Milan, Italy, during winter 2011-2012. Milan is the greatest urban area in the Po Valley, a well-known hot-spot pollution area in Europe, especially during wintertime. Parallel PM1 sampling was carried out during daytime and nighttime (07-16, 19-04) on PTFE and quartz fibre filters using two low-volume samplers for a total of about 300 samples. Mass concentration was determined by the gravimetric technique and all the PM1 samples were chemically characterised for elements, inorganic ions, levoglucosan, EC/OC and water soluble organic compounds. BC determination was also carried out on both PTFE and quartz fibre filters by a polar photometer (Vecchi et al., 2010; Vecchi et al., 2012). Moreover, BC concentrations in PM1 were monitored with a 5 minute resolution by a MAAP. Ancillary information on atmospheric dispersion conditions was available by 222Rn measurements and the main meteorological parameters (temperature, pressure, RH, solar radiation, wind speed and direction) were also monitored at the sampling site.
PM1 data were analysed by receptor modelling using Multilinear Engine ME-2 and 5 factors were identified. The most relevant contributions to PM1 were from ammonium nitrate and biomass burning (about 30% each) followed by ammonium sulphate (about 20%), traffic (about 15%) and industry (about 5%).
References.
Vecchi, R., et al. (2004). Atmos. Environ. 38, 4437–4446.
Vecchi, R., et al. (2008). Atmos. Environ. 42, 2240–2253.
Vecchi, R., et al. (2010). Abstract 11E2, International Aerosol Conference 2010, Helsinki, August 29 - September 3, 2010.
Vecchi, R., et al. (2012). Abstract, European Aerosol Conference 2012, Granada, 2 – 7 September, 2012
The Long Alchemy of Becoming: Aqua es Vida Film
No full textabstract: “The Long Alchemy of Becoming: Aqua es Vida” is a short, artistic film depicting the history of the Universe shown through the microcosm of the Mexican town, Cuatro Ciénegas, in the state of Coahuila. The film takes the viewer from the start of the universe to what scientists believe will be its end, via a poem written by Dr. James Elser. “The Long Alchemy of Becoming: Aqua es Vida” starts with the Big Bang, through the formation of matter, stars, planets, including Earth. From there, the viewer witnesses how life evolved illustrated via scenes in the ciénegas (‘marsh’ in Spanish) found in Cuatro Ciénegas, Coahuila, Mexico. The film explores how life expanded out from water, producing plants and animals, including humans. Then, modern life in Cuatro Ciénegas is shown, including the modern agricultural practices that are threatening to destroy the ciénegas that sustain long histories of microbial evolution. The film concludes with the end mankind and the eventual destruction of Earth by the dying sun. Cuatro Ciénegas is a biologically and ecologically significant location, because its pools and marshes are home to many endemic species, including stromatolites, which are very rare, bio-chemical living structures. This film is part of a National Science Foundation grant, and reflects the extensive scientific research efforts in and around Cuatro Ciénegas and its unique pools
Ultrafine particles and PM1 measurements in a hot-spot pollution area : size distribution, mass closure and source apportionment
No full textIn urban areas, ultrafine particles and PM1 are of great concern because can deeply enter the respiratory system strongly affecting human health.
Hot-spot pollution areas are peculiar sites where source emissions and meteorological conditions foster particulate matter accumulation and very high aerosol concentrations are often registered. The Po Valley is one of the main hot-spot pollution areas in Europe, especially during wintertime. Despite the high levels of PM registered in the area, little knowledge on PM1 and ultrafine particles composition and sources is available, apart from a couple of studies carried out by our group in 2002 and 2004 in the same area. This work aimed at a detailed physical and chemical characterisation of PM1 and ultrafine particles and at singling out major sources contributing to the high concentrations observed in the urban area. A critical comparison to the results obtained during the previous PM1 campaigns will be also shown.
PM1 was sampled at an urban background station in Milan, Italy, during winter 2011-2012. Parallel PM1 sampling was carried out twice a day (07-16, 19-04) on PTFE and quartz fibre filters using two low-volume samplers for a total of about 300 samples. Mass concentration was determined by the gravimetric technique and all the PM1 samples were chemically characterised for elements, inorganic ions, levoglucosan, EC/OC and water soluble organic compounds. BC determination was also carried out on both PTFE and quartz fibre filters by a polar photometer (Vecchi et al., 2010; Vecchi et al., 2012). Moreover, BC concentrations in PM1 were monitored with a 5 minute resolution by a MAAP.
The ultrafine fraction was characterised for number size distribution by an optical particle counter (range 0.25-32 μm in 31 size bins) and a differential mobility particle scanner (8-700 nm in 31 size bins). Moreover, parallel samplings using multistage cascade impactors (Dekati-SDI and nanoMOUDI) were collected on different substrates (polycarbonate membranes and quartz fibre filters) to gain information on the size-segregated chemical composition (elements, ions, and carbonaceous components). It is noteworthy that the detailed characterisation of size-segregated PM required the optimisation of the analytical techniques because of the small quantities of material to analyse and of the peculiarities of the PM deposits.
Ancillary information on atmospheric dispersion conditions was available by 222Rn measurements and the main meteorological parameters (temperature, pressure, RH, solar radiation, wind speed and direction) were also monitored at the sampling site.
PM1 data will be used to resolve the main sources in the area using Positive Matrix Factorization. This is important to develop suitable and efficient abatement strategies in an area heavily affected by high PM levels. Results obtained for size-segregated samples will be analysed using the MICRON inversion model aiming at the identification of the size-distribution modes for the different chemical components. These modes can track different formation processes adding useful information to the results obtained by PMF on the PM1 samples.
Figure 1: example of DMPS data (Milan, 21 Jan 2012)
Vecchi, R., Bernardoni, V., Broccoletti, S., Canepa, P., Cuccia, E., Massabò, D., Paganelli, C., Piazzalunga, A., Prati, P., and Valli, G. (2010). Abstract 11E2, International Aerosol Conference 2010, Helsinki, August 29 - September 3, 2010.
Vecchi, R., Valli, G., Bernardoni, V., Paganelli, C., and Piazzalunga, A. (2012). Abstract, European Aerosol Conference 2012, Granada, 2 – 7 September, 201
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