2,692 research outputs found

    On the theory of Gamma Ray Amplification through Stimulated Annihilation Radiation (GRASAR)

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    The theory of photon emission, absorption, and scattering in a relativistic plasma of positrons, electrons, and photon was studied. Expressions for the emissivities and absorption coefficients of pair annihilation, pair production, and Compton scattering are given and evaluated numerically. The conditions for negative absorption were investigated. In a system of photons and e(+) - e(-) pairs, an emission line at at approximately 0.43 MeV can be produced by grasar action provided that the pair chemical potential exceeds approximately 1 MeV. At a temperature of approximately 10 to the 9th power. This requires a pair density approximately 10 to the 30th power cm to the (-3) power a value much larger than the thermodynamic equilbrium pair density at this temperature. This emission line could account without a gravitational redshift for the observed lines at this energy from gamma ray bursts

    Criterion for purely elastic Taylor-Couette instability in the flows of shear-banding fluids

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    In the past twenty years, shear-banding flows have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. In micellar solutions, many of the data collected exhibit unexplained spatio-temporal fluctuations. Recently, it has been suggested that those fluctuations originate from a purely elastic instability of the flow. In cylindrical Couette geometry, the instability is reminiscent of the Taylor-like instability observed in viscoelastic polymer solutions. In this letter, we describe how the criterion for purely elastic Taylor-Couette instability should be adapted to shear-banding flows. We derive three categories of shear-banding flows with curved streamlines, depending on their stability.Comment: 6 pages, 3 figure

    Potential "ways of thinking" about the shear-banding phenomenon

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    Shear-banding is a curious but ubiquitous phenomenon occurring in soft matter. The phenomenological similarities between the shear-banding transition and phase transitions has pushed some researchers to adopt a 'thermodynamical' approach, in opposition to the more classical 'mechanical' approach to fluid flows. In this heuristic review, we describe why the apparent dichotomy between those approaches has slowly faded away over the years. To support our discussion, we give an overview of different interpretations of a single equation, the diffusive Johnson-Segalman (dJS) equation, in the context of shear-banding. We restrict ourselves to dJS, but we show that the equation can be written in various equivalent forms usually associated with opposite approaches. We first review briefly the origin of the dJS model and its initial rheological interpretation in the context of shear-banding. Then we describe the analogy between dJS and reaction-diffusion equations. In the case of anisotropic diffusion, we show how the dJS governing equations for steady shear flow are analogous to the equations of the dynamics of a particle in a quartic potential. Going beyond the existing literature, we then draw on the Lagrangian formalism to describe how the boundary conditions can have a key impact on the banding state. Finally, we reinterpret the dJS equation again and we show that a rigorous effective free energy can be constructed, in the spirit of early thermodynamic interpretations or in terms of more recent approaches exploiting the language of irreversible thermodynamics.Comment: 14 pages, 6 figures, tutorial revie

    Development of the drag coefficient of a sphere translating through a viscoelastic fluid

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    Presentation at 15th OpenFOAM Workshop, June 22-25, 2020, Arlington, VA, USA

    Use of geostatistical Bayesian updating to integrate airborne radiometrics and soil geochemistry to improve mapping for mineral exploration

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    Mineral exploration programmes around the world use data from remote sensing, geophysics, and direct sampling. On a regional scale, the combination of airborne geophysics and ground-based geochemical sampling can aid geological mapping and mineral exploration. Since airborne geophysical and traditional soil-sampling data are generated at different spatial resolutions, they are not immediately comparable due to their different sampling density. Several geostatistical techniques, including indicator cokriging and collocated cokriging, can be used to integrate different types of data into a geostatistical model. However, with increasing numbers of variables the inference of the crosscovariance model required for cokriging can be demanding in terms of effort and computational time. In this paper a Gaussian-based Bayesian updating approach is applied to integrate airborne radiometric data and ground-sampled geochemical soil data to maximize information generated from the soil survey, enabling more accurate geological interpretation for the exploration and development of natural resources. The Bayesian updating technique decomposes the collocated estimate into two models: prior and likelihood models. The prior model is built from primary information and the likelihood model is built from secondary information. The prior model is then updated with the likelihood model to build the final model. The approach allows multiple secondary variables to be simultaneously integrated into the mapping of the primary variable. The Bayesian updating approach is demonstrated using a case study from Northern Ireland. The geostatistical technique was used to improve the resolution of soil geochemistry, at a density of one sample per 2 km2, by integrating more closely measured airborne geophysical data from the GSNI Tellus Survey, measured over a footprint of 65 x 200 m. The directly measured geochemistry data were considered as primary data and the airborne radiometric data were used as secondary data. The approach produced more detailed updated maps and in particular enhanced information on the mapped distributions of zinc, copper, and lead. The enhanced delineation of an elongated northwest/southeast trending zone in the updated maps strengthened the potential for discovering stratabound base metal deposits

    Social Connectedness in Different Relationship Contexts

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    While an overwhelming majority of teens still spend time with their friends in person at least occasionally, people have become increasingly reliant on technology for communication and maintaining feelings of social connectedness. Social connectedness is a sense of belonging to an individual or group characterized by satisfaction, perceived level of support, and opportunities for self-disclosure within a particular relationship context. There is consistent evidence that online communication does not foster the same degree of closeness as offline interactions, largely due to the lack of indirect forms of communication like non-verbal cues and tone of voice (Scott et al., 2022a). Offline relationships encourage deeper self-disclosure and allow both parties to utilize indirect forms of communication like non-verbal cues to better communicate thoughts, feelings, and ideas (Scott et al., 2022a). However, there is also evidence that paired online and offline communication can facilitate even stronger relationships than one centered around one relationship context (Winstone et al., 2021). In this study, we will be surveying approximately 60 students enrolled in one of the Fall 2022 sections of Belmont University’s PSY1200 Introduction to Psychological Science course. Participants will complete the Inclusion of Others in the Self Scale (IOS) Scale to assess feelings of closeness and connection to friends in three different relationship contexts: online, in-person, and mixed-mode (both online and in-person) (Aron, et al., 1992). We hypothesize that participants will feel the highest level of connectedness in their mixed-mode platonic relationship. We are currently collecting data and results will be presented at SURS

    Low fruit and vegetable consumption is associated with low knowledge of the details of the 5-a-day fruit and vegetable message in the UK: findings from two cross-sectional questionnaire studies.

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    BACKGROUND: This project aimed to understand the details of the 5-a-day fruit and vegetable (FV) message (which foods are included, portion sizes, the need for variety, reasons for consumption) least known by UK consumers, and most associated with low FV consumption. METHODS: Study 1 assessed FV consumption, knowledge of the details of the message, and relationships between these, using a short questionnaire administered face-to-face to an opportunity sample of one large UK city. Study 2 assessed the same variables using a comprehensive postal questionnaire administered across the UK to a representative population sample. RESULTS: Five hundred and seven respondents completed Study 1 and 247 respondents completed Study 2. The majority of individuals in both studies were aware of the 5-a-day message and could recount this correctly. In both studies, however, knowledge of the details of the message was low, and lower knowledge was associated with lower FV consumption. Respondents had lowest knowledge of the details of the message related to portion sizes and the need for variety. However, FV consumption was not independently associated with knowledge of any one aspect of the message. CONCLUSIONS: These findings suggest that, although most of the UK population sampled were aware of the 5-a-day FV message and could recount this correctly, details of the 5-a-day FV message were not well known, and that FV consumption was related to this knowledge. These findings suggest that strategies to increase FV consumption will benefit from increasing UK consumers' knowledge of the details of the 5-a-day FV message

    Biplots for compositional data derived from generalized joint diagonalization methods

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    Biplots constructed from principal components of a compositional data set are an established means to explore its features. Principal Component Analysis (PCA) is also used to transform a set of spatial variables into spatially decorrelated factors. However, because no spatial structures are accounted for in the transformation the application of PCA is limited. In geostatistics and blind source separation a variety of different matrix diagonalization methods have been developed with the aim to provide spatially or temporally decorrelated factors. Just as PCA, many of these transformations are linear and so lend themselves to the construction of biplots. In this contribution we consider such biplots for a number of methods (MAF, UWEDGE and RJD transformations) and discuss how and if they can contribute to our understanding of relationships between the components of regionalized compositions. A comparison of the biplots with the PCA biplot commonly used in compositional data analysis for the case of data from the Northern Irish geochemical survey shows that the biplots from MAF and UWEDGE are comparable as are those from PCA and RJD. The biplots emphasize different aspects of the regionalized composition: for MAF and UWEDGE the focus is the spatial continuity, while for PCA and RJD it is variance explained. The results indicate that PCA and MAF combined provide adequate and complementary means for exploratory statistical analysis

    ‘Gobbling drops’: the jetting–dripping transition in flows of polymer solutions

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    This paper discusses the breakup of capillary jets of dilute polymer solutions and the dynamics associated with the transition from dripping to jetting. High-speed digital video imaging reveals a new scenario of transition and breakup via periodic growth and detachment of large terminal drops. The underlying mechanism is discussed and a basic theory for the mechanism of breakup is also presented. The dynamics of the terminal drop growth and trajectory prove to be governed primarily by mass and momentum balances involving capillary, gravity and inertial forces, whilst the drop detachment event is controlled by the kinetics of the thinning process in the viscoelastic ligaments that connect the drops. This thinning process of the ligaments that are subjected to a constant axial force is driven by surface tension and resisted by the viscoelasticity of the dissolved polymeric molecules. Analysis of this transition provides a new experimental method to probe the rheological properties of solutions when minute concentrations of macromolecules have been added.Schlumberger FoundationMIT Class of 1951 Fellowship Fun
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