591 research outputs found

    Estimating the Heritability of Plasticity of Thermal Tolerance and its Application in the Restoration of Endangered Caribbean Coral

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    Abstract Over the last two centuries anthropogenic activity has elevated atmospheric CO2, creating a greenhouse effect that is predicted to elevate global temperatures 1-4o C within the century. Increases in surface temperature pose a threat to the world’s coral reefs and have been the cause of many mass bleaching events. To combat this new threat, corals must migrate, acclimate, or evolve to rising temperatures. Phenotypic plasticity, or the ability of an individual to express different phenotypes to survive in different environments, is crucial for sessile organisms since it can increase survivability in species incapable of moving to better conditions. This project investigated the utility of plasticity with three questions: 1) Does phenotypic plasticity of thermal tolerance exist among endangered Caribbean corals? 2) To what extent are differences in the amount of phenotypic plasticity of thermal tolerance due to differences in coral genotype? 3) Can plasticity be utilized by managers to restore vulnerable reef zones? This study was conducted in two phases. The first utilized a raceway experiment to identify the presence of plasticity of thermal tolerance, as well as estimate Broad (H2) and Narrow-sense (h2) heritability of plasticity of thermal tolerance among Acropora cervicornis. The second phase incorporated the transplant of ambient and heat-treated Acropora cervicornis, Acropora palmata, and Orbicella faveolata fragments among shallow and deep reef zones in the Florida Keys. While a moderate degree of H2 was measured, h2was calculated as virtually non-existent among A. cervicornis fragments. The transplant study suggests depth has a more significant effect upon coral growth and viability than previous heat exposure, but thermal conditioning may still be useful for seasonal warming events. These findings have furthered the current understanding of phenotypic plasticity among and corals and may be useful to managers for future restoration efforts

    Capabilities of GRO/OSSE for observing solar flares

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    The launch of the Gamma Ray Observatory (GRO) near solar maximum makes solar flare studies early in the mission particularly advantageous. The Oriented Scintillation Spectrometer Experiment (OSSE) on GRO, covering the energy range 0.05 to 150 MeV, has some significant advantages over the previous generation of satellite-borne gamma-ray detectors for solar observations. The OSSE detectors will have about 10 times the effective area of the Gamma-Ray Spectrometer (GRS) on Solar Maximum Mission (SMM) for both photons and high-energy neutrons. The OSSE also has the added capability of distinguishing between high-energy neutrons and photons directly. The OSSE spectral accumulation time (approx. 4s) is four times faster than that of the SMM/GRS; much better time resolution is available in selected energy ranges. These characteristics will allow the investigation of particle acceleration in flares based on the evolution of the continuum and nuclear line components of flare spectra, nuclear emission in small flares, the anisotropy of continuum emission in small flares, and the relative intensities of different nuclear lines. The OSSE observational program will be devoted primarily to non-solar sources. Therefore, solar observations require planning and special configurations. The instrumental and operational characteristics of OSSE are discussed in the context of undertaking solar observations. The opportunities for guest investigators to participate in solar flare studies with OSSE is also presented

    Multipliers for p-Bessel sequences in Banach spaces

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    Multipliers have been recently introduced as operators for Bessel sequences and frames in Hilbert spaces. These operators are defined by a fixed multiplication pattern (the symbol) which is inserted between the analysis and synthesis operators. In this paper, we will generalize the concept of Bessel multipliers for p-Bessel and p-Riesz sequences in Banach spaces. It will be shown that bounded symbols lead to bounded operators. Symbols converging to zero induce compact operators. Furthermore, we will give sufficient conditions for multipliers to be nuclear operators. Finally, we will show the continuous dependency of the multipliers on their parameters.Comment: 17 page

    Encouraging versatile thinking in algebra using the computer

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    In this article we formulate and analyse some of the obstacles to understanding the notion of a variable, and the use and meaning of algebraic notation, and report empirical evidence to support the hypothesis that an approach using the computer will be more successful in overcoming these obstacles. The computer approach is formulated within a wider framework ofversatile thinking in which global, holistic processing complements local, sequential processing. This is done through a combination of programming in BASIC, physical activities which simulate computer storage and manipulation of variables, and specific software which evaluates expressions in standard mathematical notation. The software is designed to enable the user to explore examples and non-examples of a concept, in this case equivalent and non-equivalent expressions. We call such a piece of software ageneric organizer because if offers examples and non-examples which may be seen not just in specific terms, but as typical, or generic, examples of the algebraic processes, assisting the pupil in the difficult task of abstracting the more general concept which they represent. Empirical evidence from several related studies shows that such an approach significantly improves the understanding of higher order concepts in algebra, and that any initial loss in manipulative facility through lack of practice is more than made up at a later stage

    A One-sided, Highly Relativistic Jet from Cygnus X-3

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    Very Long Baseline Array images of the X-ray binary, Cygnus X-3, were obtained 2, 4 and 7 days after the peak of a 10 Jy flare on 4 February 1997. The first two images show a curved one-sided jet, the third a scatter-broadened disc, presumably at the position of the core. The jet curvature changes from the first to the second epoch, which strongly suggests a precessing jet. The ratio of the flux density in the approaching to that in the (undetected) receding jet is > 330; if this asymmetry is due to Doppler boosting, the implied jet speed is > 0.81c. Precessing jet model fits, together with the assumptions that the jet is intrinsically symmetric and was ejected during or after the major flare, yield the following constraints: the jet inclination to the line of sight must be < 14 degrees; the cone opening angle must be < 12 degrees; and the precession period must be > 60 days.Comment: 12 pages 7 figures, accepted by Ap

    Process development for manufacturing of cellular structures with controlled geometry and properties

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    This study presents experimental results on the behaviour of aluminium alloy metal structures and foams manufactured by lost-wax casting and using 3D printed components for internal structure definition. Results for tensile tests, metallurgical properties, surface quality and geometry tolerances were obtained and discussed. The analysis focused on development geometries, used for adjusting manufacturing parameters and prototype geometries intended for geometrical and mechanical validation. The results are indicative of the viability of the method for producing foam structures suitable for mechanical loading.The authors are grateful to the Portuguese Foundation for Science and Technology (FCT) who financially supported this work, through the project PTDC/EME-PME/115668/2009.info:eu-repo/semantics/publishedVersio

    Observations of GRB 990123 by the Compton Gamma-Ray Observatory

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    GRB 990123 was the first burst from which simultaneous optical, X-ray and gamma-ray emission was detected; its afterglow has been followed by an extensive set of radio, optical and X-ray observations. We have studied the gamma-ray burst itself as observed by the CGRO detectors. We find that gamma-ray fluxes are not correlated with the simultaneous optical observations, and the gamma-ray spectra cannot be extrapolated simply to the optical fluxes. The burst is well fit by the standard four-parameter GRB function, with the exception that excess emission compared to this function is observed below ~15 keV during some time intervals. The burst is characterized by the typical hard-to-soft and hardness-intensity correlation spectral evolution patterns. The energy of the peak of the nu f_nu spectrum, E_p, reaches an unusually high value during the first intensity spike, 1470 +/- 110 keV, and then falls to \~300 keV during the tail of the burst. The high-energy spectrum above ~MeV is consistent with a power law with a photon index of about -3. By fluence, GRB 990123 is brighter than all but 0.4% of the GRBs observed with BATSE, clearly placing it on the -3/2 power-law portion of the intensity distribution. However, the redshift measured for the afterglow is inconsistent with the Euclidean interpretation of the -3/2 power-law. Using the redshift value of >= 1.61 and assuming isotropic emission, the gamma-ray fluence exceeds 10E54 ergs.Comment: Submitted to The Astrophysical Journal. 16 pages including 4 figure

    A member of the tryptophan-rich protein family is required for efficient sequestration of Plasmodium berghei schizonts

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    Protein export and host membrane remodeling are crucial for multiple Plasmodium species to establish a niche in infected hosts. To better understand the contribution of these processes to successful parasite infection in vivo, we sought to find and characterize protein components of the intraerythrocytic Plasmodium berghei-induced membrane structures (IBIS) that form in the cytoplasm of infected erythrocytes. We identified proteins that immunoprecipitate with IBIS1, a signature member of the IBIS in P. berghei-infected erythrocytes. In parallel, we also report our data describing proteins that co-precipitate with the PTEX (Plasmodium translocon of exported proteins) component EXP2. To validate our findings, we examined the location of three candidate IBIS1-interactors that are conserved across multiple Plasmodium species, and we found they localized to IBIS in infected red blood cells and two further colocalized with IBIS1 in the liver-stage parasitophorous vacuole membrane. Successful gene deletion revealed that these two tryptophan-rich domain-containing proteins, termed here IPIS2 and IPIS3 (for intraerythrocytic Plasmodium-induced membrane structures), are required for efficient blood-stage growth. Erythrocytes infected with IPIS2-deficient schizonts in particular fail to bind CD36 as efficiently as wild-type P. berghei-infected cells and therefore fail to effectively sequester out of the circulating blood. Our findings support the idea that intra-erythrocytic membrane compartments are required across species for alterations of the host erythrocyte that facilitate interactions of infected cells with host tissues
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