The correlation between water production rates and visual magnitudes in comets

From the visual magnitudes of the International Comet Quarterly data base and the OH radio lines measured at the Nancay radio telescope, the law log Q(H2O) = 30.74 (+/-0.02) - 0.240 (+/-.003) m(sub h) is derived from a sample of 13 comets

First electron beam polarization measurements with a Compton polarimeter at Jefferson Laboratory

A Compton polarimeter has been installed in Hall A at Jefferson Laboratory. This letter reports on the first electron beam polarization measurements performed during the HAPPEX experiment at an electron energy of 3.3 GeV and an average current of 40 $\mu$A. The heart of this device is a Fabry-Perot cavity which increased the luminosity for Compton scattering in the interaction region so much that a 1.4% statistical accuracy could be obtained within one hour, with a 3.3% total error

Enhancing the mechanical features of clay surfaces by the absorption of nano-SiO2 particles in aqueous media. Case of study on Bronze Age clay objects

[EN] Nanoparticles are known to be able to enhance the performance of low dense materials, achieving the small intergranular spaces to further interact with the matrix. In this work, a consolidation treatment of an ancient clay material is reported. It is based on the use of silica nanoparticles dispersed in an aqueous medium as a more sustainable approach than those currently used in the conservation field. The effective consolidation has been determined by ensuring an appropriate mechanical surface resistance using the nanoindentation technique as non-destructive measurements. Moreover, the ability of SiO(2 )nanoparticles to fill the microstructure is studied by scanning electron microscopy. As a case report, several low-strength clay fragments dated from the Bronze Age were surface treated with a commercial aqueous suspension of SiO2 nanoparticles that were analyzed by transmission electron microscopy (TEM) displaying dimensions of about 20 nm in diameter. Field Emission Electron Microscopy (FESEM) revealed that nanoparticles filled the inter-granular spaces of the clay, leading to a nanostructured material. The nanoindentation results showed an increase in surface resistance against scratching. Meanwhile, the nanohardness and elastic modulus increased 10 times (from 15 to 150 MPa) and 8 times (from 1 to 8 GPa), respectively due to the nano-SiO2 treatment, confirming the consolidation effect of the nanoparticles.Authors acknowledge the financial support of Spanish Ministry of Economy and Competitiveness, MAT2014-59242-C2-1-R. Authors also acknowledge the support of Helena Bonet, Director of the Prehistory Museum of Valencia and Ma Jesus de Pedro, conservator of this Museum, and to the Photographic Archive Department. M.P. Arrieta wishes to thank the financial support of MINECO for a Juan de la Cierva (FJCI-2014-20630) contract.Rayón, E.; Arrieta, MP.; Pasies -Oviedo, T.; López-Martínez, J.; Jorda Moret, JL. (2018). Enhancing the mechanical features of clay surfaces by the absorption of nano-SiO2 particles in aqueous media. Case of study on Bronze Age clay objects. Cement and Concrete Composites. 93:107-117. https://doi.org/10.1016/j.cemconcomp.2018.07.005S1071179

Angular Correlations in Internal Pair Conversion of Aligned Heavy Nuclei

We calculate the spatial correlation of electrons and positrons emitted by internal pair conversion of Coulomb excited nuclei in heavy ion collisions. The alignment or polarization of the nucleus results in an anisotropic emission of the electron-positron pairs which is closely related to the anisotropic emission of $\gamma$-rays. However, the angular correlation in the case of internal pair conversion exhibits diverse patterns. This might be relevant when investigating atomic processes in heavy-ion collisions performed at the Coulomb barrier.Comment: 27 pages + 6 eps figures, uses revtex.sty and epsf.sty, tar-compressed and uuencoded with uufile

A photon calorimeter using lead tungstate crystals for the CEBAF Hall A Compton polarimeter

The performances of the calorimeter of the Jlab Hall A Compton Polarimeter have been measured using the Mainz tagged photon beam.Comment: 13 page

Dust observations of Comet 9P/Tempel 1 at the time of the Deep Impact

On 4 July 2005 at 05:52 UT, the impactor of NASA's Deep Impact (DI) mission crashed into comet 9P/Tempel 1 with a velocity of about 10 km/s. The material ejected by the impact expanded into the normal coma, produced by ordinary cometary activity. The characteristics of the non-impact coma and cloud produced by the impact were studied by observations in the visible wavelengths and in the near-IR. The scattering characteristics of the "normal" coma of solid particles were studied by comparing images in various spectral regions, from the UV to the near-IR. For the non-impact coma, a proxy of the dust production has been measured in various spectral regions. The presence of sublimating grains has been detected. Their lifetime was found to be about 11 hours. Regarding the cloud produced by the impact, the total geometric cross section multiplied by the albedo was measured as a function of the color and time. The projected velocity appeared to obey a Gaussian distribution with the average velocity of the order of 115 m/s. By comparing the observations taken about 3 hours after the impact, we have found a strong decrease in the cross section in J filter, while that in Ks remained almost constant. This is interpreted as the result of sublimation of grains dominated by particles of sizes of the order of some microns.Comment: Accepted by A&

Imaging Asteroid 4 Vesta Using the Framing Camera

The Framing Camera (FC) onboard the Dawn spacecraft serves a dual purpose. Next to its central role as a prime science instrument it is also used for the complex navigation of the ion drive spacecraft. The CCD detector with 1024 by 1024 pixels provides the stability for a multiyear mission and its high requirements of photometric accuracy over the wavelength band from 400 to 1000 nm covered by 7 band-pass filters. Vesta will be observed from 3 orbit stages with image scales of 227, 63, and 17 m/px, respectively. The mapping of Vesta s surface with medium resolution will be only completed during the exit phase when the north pole will be illuminated. A detailed pointing strategy will cover the surface at least twice at similar phase angles to provide stereo views for reconstruction of the topography. During approach the phase function of Vesta was determined over a range of angles not accessible from earth. This is the first step in deriving the photometric function of the surface. Combining the topography based on stereo tie points with the photometry in an iterative procedure will disclose details of the surface morphology at considerably smaller scales than the pixel scale. The 7 color filters are well positioned to provide information on the spectral slope in the visible, the depth of the strong pyroxene absorption band, and their variability over the surface. Cross calibration with the VIR spectrometer that extends into the near IR will provide detailed maps of Vesta s surface mineralogy and physical properties. Georeferencing all these observation will result in a coherent and unique data set. During Dawn s approach and capture FC has already demonstrated its performance. The strong variation observed by the Hubble Space Telescope can now be correlated with surface units and features. We will report on results obtained from images taken during survey mode covering the whole illuminated surface. Vesta is a planet-like differentiated body, but its surface gravity and escape velocity are comparable to those of other asteroids and hence much smaller than those of the inner planets o