搜索结果：mass-dropping

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Solids dispersed in a drying drop will migrate to the edge of the drop and form a solid ring. This phenomenon produces ringlike stains and occurs for a wide range of surfaces, solvents, and solutes. Here we show that the migration is caused by an outward flow within the drop that is driven by the loss of solvent by evaporation and geometrical constraint that the drop maintain an equilibrium droplet shape with a fixed boundary. We describe a theory that predicts the flow velocity, the rate of growth of the ring, and the distribution of solute within the drop. These predictions are compared with our experimental results.

This review presents an overview of the dynamically developing field of mass spectrometry-based metabolomics. Metabolomics aims at the comprehensive and quantitative analysis of wide arrays of metabolites in biological samples. These numerous analytes have very diverse physico-chemical properties and occur at different abundance levels. Consequently, comprehensive metabolomics investigations are primarily a challenge for analytical chemistry and specifically mass spectrometry has vast potential as a tool for this type of investigation. Metabolomics require special approaches for sample preparation, separation, and mass spectrometric analysis. Current examples of those approaches are described in this review. It primarily focuses on metabolic fingerprinting, a technique that analyzes all detectable analytes in a given sample with subsequent classification of samples and identification of differentially expressed metabolites, which define the sample classes. To perform this complex task, data analysis tools, metabolite libraries, and databases are required. Therefore, recent advances in metabolomics bioinformatics are also discussed.

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We introduce a new jet substructure technique called "soft drop declustering", which recursively removes soft wide-angle radiation from a jet. The soft drop algorithm depends on two parameters -a soft threshold z cut and an angular exponent -with the = 0 limit corresponding roughly to the (modified) mass drop procedure. To gain an analytic understanding of soft drop and highlight the dependence, we perform resummed calculations for three observables on soft-dropped jets: the energy correlation functions, the groomed jet radius, and the energy loss due to soft drop. The = 0 limit of the energy loss is particularly interesting, since it is not only "Sudakov safe" but also largely insensitive to the value of the strong coupling constant. While our calculations are strictly accurate only to modified leading-logarithmic order, we also include a discussion of higher-order effects such as multiple emissions and (the absence of) non-global logarithms. We compare our analytic results to parton shower simulations and find good agreement, and we also estimate the impact of non-perturbative effects such as hadronization and the underlying event. Finally, we demonstrate how soft drop can be used for tagging boosted W bosons, and we speculate on the potential advantages of using soft drop for pileup mitigation.

A new mass formula for Kerr black holes is deduced, and is constrasted to the mass formula which is obtained by integrating term by term the mass differential and which consists of three terms interpreted, respectively, as the surface energy, rotational energy, and electromagnetic energy of the charged rotating black hole. A comparison is suggested between a rotating black hole and a rotating liquid drop which leads to a speculation that Kerr black holes may develop instabilities.

The amount of a sample compound extracted into a 1-μL drop of n -octane suspended in a stirred aqueous solution from the tip of a microsyringe needle is measured by gas chromatography (GC) as a function of time. The observed extraction rate curve is first order and yields the overall mass transfer coefficient for the sample compound, β o . For a given compound, β o varies linearly with stirring rate. Among the four compounds malathion, 4-methylacetophenone, 4-nitrotoluene, and progesterone, at a given stirring rate, β o is linearly proportional to the diffusion coefficient of the compound ( D aq ). This supports the film theory of convective−diffusive mass transfer, as opposed to the penetration theory. The relative standard deviation of the GC signal for 4-methylacetophenone after a 1.00 min extraction at 1500 rpm is 1.5%, which suggests that the system exhibits excellent potential as a tool for rapid analysis by solvent extraction/GC.

A bstract We present first analytic, resummed calculations of the rates at which wide-spread jet substructure tools tag QCD jets. As well as considering trimming, pruning and the mass-drop tagger, we introduce modified tools with improved analytical and phenomenological behaviours. Most taggers have double logarithmic resummed structures. The modified mass-drop tagger is special in that it involves only single logarithms, and is free from a complex class of terms known as non-global logarithms. The modification of pruning brings an improved ability to discriminate between the different colour structures that characterise signal and background. As we outline in an extensive phenomenological discussion, these results provide valuable insight into the performance of existing tools and help lay robust foundations for future substructure studies.

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The Kepler Spacecraft has discovered a large number of planets up to one-year periods and down to terrestrial sizes. While the majority of the target stars are main-sequence dwarfs of spectral type F, G, and K, Kepler covers stars with effective temperature as low as 2500 K, which corresponds to M stars. These cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around FGK stars. In this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planet radius and distance from the star, and show that they are significantly different from each other. We further identify two trends: First, the occurrence of Earth to Neptune-sized planets is successively higher toward later spectral types at all orbital periods probed by Kepler; Planets around M stars occur twice as frequently as around G stars, and thrice as frequently as around F stars. Second, a drop in planet occurrence is evident at all spectral types inward of a 10 day orbital period, with a plateau further out. By assigning to each spectral type a median stellar mass, we show that the distance from the star where this drop occurs is stellar mass dependent, and scales with semi-major axis as the cube root of stellar mass. By comparing different mechanisms of planet formation, trapping and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks. These results demonstrate the stellar-mass dependence of the planet population, both in terms of occurrence rate and of orbital distribution. The prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters.

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We model the broad-band (optical/UV and X-ray) continuum spectrum of the ‘changing-look’ active galactic nucleus (AGN) Mrk 1018, as it fades from Seyfert 1 to 1.9 in ∼ 8 years. The brightest spectrum, with Eddington ratio L/LEdd ∼ 0.08 has a typical type 1 AGN continuum, with a strong ‘soft X-ray excess’ spanning between the UV and soft X-rays. The dimmest spectrum, at L/LEdd ∼ 0.006, is very different in shape as well as luminosity, with the soft excess dropping by much more than the hard X-rays. The soft X-ray excess produces most of the ionizing photons, so its dramatic drop leads to the disappearance of the broad-line region, driving the ‘changing-look’ phenomena. This spectral hardening appears similar to the soft-to-hard state transition in black hole binaries at L/LEdd ∼ 0.02, where the inner disc evaporates into an advection dominated accretion flow, while the overall drop in luminosity appears consistent with the hydrogen ionization disc instability. None the less, both processes happen much faster in Mrk 1018 than predicted by disc theory. We critically examine scaling from Galactic binary systems and show that a major difference is that radiation pressure should be much more important in AGNs, so that the sound speed is much faster than expected from the gas temperature. Including magnetic pressure to stabilize the disc shortens the time-scales even further. We suggest that all changing-look AGNs are similarly associated with the state transition at L/LEdd ∼ a few per cent.

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The existence of a hot X-ray emitting gas phase in giant elliptical galaxies has long been recognized, but its structure and dynamics are still controversial. We explore the possibility that the gas is heated from below, causing it to convect. This leads to a two-component model in which a cooling flow feeds into an adiabatic core. The heat source for this core is taken to be the central black hole. The model is applied to the three galaxies with the best data from the Einstein observatory: NGC 4472,4636 and 4649. In our models of NGC 4636, gas flows inwards at all radii, while in NGC 4472 and 4649 the flow is directed outwards at large radii. Consequently, the adiabatic core of NGC 4636 is significantly larger and more luminous than those of NGC 4472 and 4649. The time-averaged luminosity that should be generated by accretion of the core's gas on to a central massive black hole is of the order of that required to enable the core to swell and accommodate most of the gas fed to it by the enveloping flow. However, one expects the nuclear luminosity to be intermittent, and observations suggest that the nuclei of all three galaxies are dormant at the present epoch.

This study describes a novel method for single-cell analysis and lipid profiling by combining drop-on-demand inkjet cell printing and probe electrospray ionization mass spectrometry (PESI-MS). Through inkjet sampling of a cell suspension, droplets with single cells were generated, precisely dripped onto a tungsten-made electrospray ionization needle, and immediately sprayed under a high-voltage electric field. Lipid fingerprints of single cells were obtained by a mass spectrometry (MS) detector. A homemade magnetic stirring device was applied to the cell suspension reservoir, which controlled the homogeneous distribution of cells in liquid and improved the single-cell-droplet percentage by 43.8%. Eight types of single cells were screened in our platform and further differentiated by principal component analysis based on cellular surface phospholipids. Thus, this study successfully provides a facile method for the direct MS profiling of single-cell lipids by PESI-MS.

Retrospective detection and identification of chemical warfare agents (CWAs) is important from the verification point of view of the Chemical Weapons Convention. In the present work, a novel method for determination of CWAs and their markers in water has been described. It is based on a single drop micro extraction (SDME) of analytes and gas chromatography/mass spectrometric identification. Extraction conditions, such as solvent selection, agitation, extraction time, and salt content, were found to have significant influence on SDME. The conditions optimized for extraction of CWAs were 1 microL CH2Cl2/CCl4 (3:1 v/v), 30-min extraction time, 300-rpm stirring rate, and with or without NaCl addition. Under optimized conditions, comparison of SDME, solid-phase microextraction, and liquid-liquid extraction was also made. The limit of detection by SDME ranged from 75 to 10 microg L(-1) at a signal-to-noise ratio of 10:1.