| 28241. |
- Balzarolo, Manuela, et al.
(författare)
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Ground-Based Optical Measurements at European Flux Sites: A Review of Methods, Instruments and Current Controversies
- 2011
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 11:8, s. 7954-7981
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Forskningsöversikt (refereegranskat)abstract
- This paper reviews the currently available optical sensors, their limitations and opportunities for deployment at Eddy Covariance (EC) sites in Europe. This review is based on the results obtained from an online survey designed and disseminated by the Co-cooperation in Science and Technology (COST) Action ESO903-"Spectral Sampling Tools for Vegetation Biophysical Parameters and Flux Measurements in Europe" that provided a complete view on spectral sampling activities carried out within the different research teams in European countries. The results have highlighted that a wide variety of optical sensors are in use at flux sites across Europe, and responses further demonstrated that users were not always fully aware of the key issues underpinning repeatability and the reproducibility of their spectral measurements. The key findings of this survey point towards the need for greater awareness of the need for standardisation and development of a common protocol of optical sampling at the European EC sites.
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| 28242. |
- Balzarotti, A, et al.
(författare)
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W=0 pairing in Hubbard and related models of low-dimensional superconductors
- 2004
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Ingår i: Journal of Physics: Condensed Matter. - 1361-648X. ; 16:47, s. 1387-1422
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Forskningsöversikt (refereegranskat)abstract
- Lattice Hamiltonians with on-site interaction W have W = 0 solutions, that is, many-body singlet eigenstates without double occupation. In particular, W = 0 pairs give a clue to understand the pairing force in repulsive Hubbard models. These eigenstates are found in systems with high enough symmetry, like the square, hexagonal or triangular lattices. By a general theorem, we propose a systematic way to construct all the W = 0 pairs of a given Hamiltonian. We also introduce a canonical transformation to calculate the effective interaction between the particles of such pairs. In geometries appropriate for the CuO2 planes of cuprate superconductors, armchair carbon nanotubes, or cobalt oxide planes, the dressed pair becomes a bound state in a physically relevant range of parameters. We also show that W = 0 pairs quantize the magnetic flux as superconducting pairs do. The pairing mechanism breaks down in the presence of strong distortions. The W = 0 pairs are also the building blocks for the antiferromagnetic ground state of the half-filled Hubbard model at weak coupling. Our analytical results for the 4 x 4 Hubbard square lattice, compared to available numerical data, demonstrate that the method, besides providing an intuitive grasp on pairing, also has quantitative predictive power. We also consider including phonon effects in this scenario. Preliminary calculations with small clusters indicate that vector phonons hinder pairing while half-breathing modes are synergic with the W = 0 pairing mechanism both at weak coupling and in the polaronic regime.
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| 28243. |
- Balzarotti, Francisco, et al.
(författare)
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Nanometer resolution imaging and tracking of fluorescent molecules with minimal photon fluxes
- 2017
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 355:6325, s. 606-612
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Tidskriftsartikel (refereegranskat)abstract
- We introduce MINFLUX, a concept for localizing photon emitters in space. By probing the emitter with a local intensity minimum of excitation light, MINFLUX minimizes the fluorescence photons needed for high localization precision. In our experiments, 22 times fewer fluorescence photons are required as compared to popular centroid localization. In superresolutionmicroscopy, MINFLUXattained similar to 1-nanometer precision, resolving molecules only 6 nanometers apart. MINFLUX tracking of single fluorescent proteins increased the temporal resolution and the number of localizations per trace by a factor of 100, as demonstrated with diffusing 30S ribosomal subunits in living Escherichia coli. As conceptual limits have not been reached, we expect this localization modality to break new ground for observing the dynamics, distribution, and structure of macromolecules in living cells and beyond.
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| 28244. |
- Balzer, Laura, et al.
(författare)
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Role of formation and decay of seston organic matter in the fate of methylmercury within the water column of a eutrophic lake
- 2023
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Ingår i: Biogeosciences. - 1726-4170 .- 1726-4189. ; 20:7, s. 1459-1472
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Tidskriftsartikel (refereegranskat)abstract
- Anoxic microniches in sinking particles in lakes have been identified as important water phase production zones of monomethylmercury (MeHg). However, the production and decay of MeHg during organic matter (OM) decomposition in the water column and its relation to the total Hg concentration in seston are poorly understood. We investigated total Hg and MeHg in relation to chemical changes in sinking seston and hydrochemical settings in a small and shallow (12 m deep) eutrophic lake during phytoplankton blooms from April to November 2019. The results show that MeHg proportions reach up to 22 % in seston in oxygen super saturation at the water surface and highest values (up to 26 %) at the oxic–suboxic redox boundary. MeHg concentrations were highest in May and November when algal biomass production was low and seston were dominated by zooplankton. Biodilution of MeHg concentrations could not be observed in the months of the highest algal biomass production; instead, MeHg and THg concentrations in seston were comparatively high. During suboxic OM decomposition and with decreasing redox potential (Mn and nitrate reduction), the concentration and proportion of MeHg in seston strongly decreased (<0.5 %), whereas total Hg concentrations show a 3.8- to 26-fold increase with water depth. Here, it remains unclear to which extent biodilution on the one hand and OM decomposition on the other alter the MeHg and THg concentration in seston. Changes in OM quality were most intense within or slightly below the redox transition zone (RTZ). The concentrations of MeHg and THg in seston from the RTZ were comparable to those found in the sediment trap material which integrated the changes in seston composition during the entire sampling period, suggesting that changes in the MeHg and THg content in the hypolimnion below the RTZ are comparatively small. Our study suggests that, in shallow eutrophic lakes, the water phase formation and decomposition of MeHg is intense and controlled by the decomposition of algal biomass and is, assumedly, largely disconnected from Hg methylation in sediments, similar to what has been observed in deep oligotrophic lakes.
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| 28245. |
- Bamba, Yu, et al.
(författare)
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Estimating the Strength of Single Chitin Nanofibrils via Sonication-Induced Fragmentation
- 2017
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 18:12, s. 4405-4410
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Tidskriftsartikel (refereegranskat)abstract
- We report the mechanical strength of native chitin nanofibrils. Highly crystalline alpha-chitiri nanofibrils Were purified from filaments produced by a microalgae Phaeocystis globosa, and two types of beta-chitin nariofibrils were purified from pens of a squid Loligo bleekeri and tubes of a tubeworm Lamellibrachia satsuma, with relatively low and high crystallinity, respectively. These chitin nanofibrils were fully dispersed in water. The strength of individualized nanofibrils was estimated using cavitation induced tensile fracture of nanoscale filaments in a liquid medium. Both types of beta-chitin nanofibrils exhibited similar strength values of approximately 3 GP; in contrast, the alpha-chitin nanofibrils exhibited a much lower strength value of 1.6 GPa. These strength estimates suggest that the tensile strength of chitin nanofibrils is governed by the molecular packing modes of chitin rather than their crystallinity.
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| 28246. |
- Bambah, B., et al.
(författare)
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QCD GENERATORS FOR LEP
- 1989
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Ingår i: LEP Physics Workshop Geneva, Switzerland, February 20, 1989. ; , s. 143-340
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 28247. |
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| 28248. |
- Bamberger, A, et al.
(författare)
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Higher order paraxial wave equation approximations in heterogeneous media
- 1988
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Ingår i: SIAM Journal on Applied Mathematics. - : Society for Industrial & Applied Mathematics (SIAM). - 0036-1399 .- 1095-712X. ; 48, s. 129-154
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Tidskriftsartikel (refereegranskat)abstract
- A new family of paraxial wave equation approximations is derived. These approximations are of higher order accuracy than the parabolic approximation and they can be applied to the same computational problems, e.g., in seismology, underwater acoustics and as artificial boundary conditions. The equations are written as systems which simplify computations. The support and singular support are studied; energy estimates are given which prove the well-posedness. The reflection and transmission are shown to be continuously dependent on material interfaces in heterogeneous media
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| 28249. |
- Bamberger, A, et al.
(författare)
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Parabolic wave equation approximations in heterogenous media
- 1988
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Ingår i: SIAM Journal on Applied Mathematics. - 0036-1399 .- 1095-712X. ; 48, s. 99-128
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Tidskriftsartikel (refereegranskat)abstract
- The properties of different variants of parabolic approximations of scalar wave equations are analyzed. These equations are of general form which includes those used in seismology, underwater acoustics and other applications. A new version of the parabolic approximation is derived for heterogeneous media. It has optimal properties with respect to wave reflection at material interfaces. The amplitud of the reflected and transmitted waves depend continuously on the interface. Existence, uniqueness and energy estimates are proved.
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| 28250. |
- Bambi, Cosimo, et al.
(författare)
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Testing the rotational nature of the supermassive object M87*from the circularity and size of its first image
- 2019
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 100:4
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Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) collaboration has recently released the first image of a black hole (BH), opening a new window onto tests of general relativity in the strong field regime. In this paper, we derive constraints on the nature of M87* (the supermassive object at the center of the galaxy M87), exploiting the fact that its shadow appears to be highly circular, and using measurements of its angular size. We first consider the simple case where M87* is assumed to be a Kerr BH. We find that the inferred circularity of M87* excludes Kerr BHs with observation angle theta(obs) greater than or similar to 45 degrees for dimensionless rotational parameter 0.95 less than or similar to a(*) <= 1 whereas the observation angle is unbounded for a(*) less than or similar to 0.9. We then consider the possibility that M87* might be a superspinar, i.e., an object described by the Kerr solution and spinning so fast that it violates the Kerr bound by having vertical bar a(*)vertical bar > 1. We find that, within certain regions of parameter space, the inferred circularity and size of the shadow of M87* do not exclude the possibility that this object might be a superspinar.
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