481 research outputs found
Ichnofossils, cracks or crystals? A test for biogenicity of stick-like structures from vera rubin ridge, mars
New images from Mars rover Curiosity display millimetric, elongate stick- like structures in the fluvio-lacustrine deposits of Vera Rubin Ridge, the depositional environment of which has been previously acknowledged as habitable. Morphology, size and topology of the structures are yet incompletely known and their biogenicity remains untested. Here we provide the first quantitative description of the Vera Rubin Ridge structures, showing that ichnofossils, i.e., the product of life-substrate interactions, are among their closest morphological analogues. Crystal growth and sedimentary cracking are plausible non-biological genetic processes for the structures, although crystals, desiccation and syneresis cracks do not typically present all the morphological and topological features of the Vera Rubin Ridge structures. Morphological analogy does not necessarily imply biogenicity but, given that none of the available observations falsifies the ichnofossil hypothesis, Vera Rubin Ridge and its sedimentary features are here recognized as a privileged target for astrobiological research
Ceramic production and raw materials in the Tuscan-Ligurian region: an archaeological and petrographic approach in a diachronic perspective
This contribute focuses on the history of ceramic production of a large geographic area from the
archaeological point of view encompassing Liguria and N-W Tuscany and using a petro-archaeometrical approach ( essentially based on thin-section analyses of more than a thousand of samples)
Potential sources of particulate iron in surface and deep waters of the terra nova bay (Ross sea, antarctica)
The distribution of particulate Fe (pFe), suspended particulate matter (SPM), and other particulate trace metals were investigated in Terra Nova Bay as part of CDW Effects on glaciaL mElting and on Bulk of Fe in the Western Ross sea (CELEBeR) and Plankton biodiversity and functioning of the Ross Sea ecosystems in a changing Southern Ocean (P-ROSE) projects. Variable concentrations of SPM (0.09–97 mg L−1 ), pFe (0.51–8.70 nM) and other trace metals were found in the Antarctic Surface waters (AASW) layer, where the addition of meltwater contributed to the pool with both lithogenic and biogenic forms. The deeper layer of the water column was occupied by High Salinity Shelf Water (HSSW) and Terra Nova Bay Ice Shelf Water (TISW) encompassing glacial water as confirmed by the lightest δ18 O measured values. The concentration of pFe in TISW (11.7 ± 9.2 nM) was higher than in HSSW samples (5.55 ± 4.43 nM), suggesting that the drainage of material released from glaciers surrounding the area is relevant in terms of pFe contribution. Particulate Fe/Al and Mn/Al ratios were substantially in excess compared with the mean crustal ratios. Microscopic analyses confirmed that more labile Fe oxyhydroxides and authigenic MnO2 phases were present together with biogenic sinking material. Future expected increasing melt rates of these glaciers enlarge Fe input, thus having a greater role in supplying iron and counteracting the reductions in sea ice cover around Terra Nova Bay
Isselite, Cu6(SO4)(OH)10(H2O)4·h2O, a new mineral species from Eastern Liguria, Italy
The new mineral isselite, Cu6(SO4)(OH)10(H2O)4·H2O, has been discovered in the Lagoscuro mine, Monte Ramazzo mining complex, Genoa, Eastern Liguria, Italy. It occurs as sprays of blue acicular crystals, up to 0.1 mm long, associated with brochantite and posnjakite. Streak is light blue and the lustre is vitreous. Isselite is brittle, with irregular fracture and good cleavage on {001} and {100}. Measured density is 3.00(2) g/cm3. Isselite is optically biaxial (-), with α = 1.599(2), β = 1.633(2) and γ = 1.647(2) (determined in white light). The measured 2V is 63.6(5)°. Dispersion is moderate, with r > v. The optical orientation is X = b, Y = c and Z = a. Isselite is pleochroic, with X = light blue, Y = blue, Z = blue; X << Z < Y. Electron microprobe analyses give (wt.%): SO3 11.45(21), MgO 0.31(7), CoO 1.07(14), NiO 9.41(90), CuO 51.29(126), ZnO 1.10(20), H2Ocalc 24.21, total 98.84. The empirical formula of isselite, based on Σ(Mg,Co,Ni,Cu,Zn) = 6 atoms per formula unit, is (Cu4.80Ni0.94Co0.11Zn0.10Mg0.06)Σ6.00(S1.06O4.19)(OH)10·5H2O. Isselite is orthorhombic, space group Pmn21, with unit-cell parameters a = 6.8070(14), b = 5.8970(12), c = 20.653(4) Å, V = 829.0(3) Å3 and Z = 2. The crystal structure of isselite was refined from single-crystal X-ray diffraction data to R1 = 0.067 on the basis of 2964 reflections with Fo > 4σ(Fo). It shows a layered structure formed by zig-zag {001} layers of Cu-centred polyhedra. Sulfate groups occur in the interlayer along with one H2O group. Isselite is chemically related to redgillite and montetrisaite
Non-Gaussian bubbles in the sky
We point out a possible generation mechanism of non-Gaussian bubbles in the
sky due to bubble nucleation in the early universe. We consider a curvaton
scenario for inflation and assume that the curvaton field phi, whose energy
density is subdominant during inflation but which is responsible for the
curvature perturbation of the universe, is coupled to another field sigma which
undergoes false vacuum decay through quantum tunneling. For this model, we
compute the skewness of the curvaton fluctuations due to its interaction with
sigma during tunneling, that is, on the background of an instanton solution
that describes false vacuum decay. We find that the resulting skewness of the
curvaton can become large in the spacetime region inside the bubble. We then
compute the corresponding skewness in the statistical distribution of the
cosmic microwave background (CMB) temperature fluctuations. We find a
non-vanishing skewness in a bubble-shaped region in the sky. It can be large
enough to be detected in the near future, and if detected it will bring us
invaluable information about the physics in the early universe.Comment: 6 pages, 6 figure
Foreground influence on primordial non-Gaussianity estimates: needlet analysis of WMAP 5-year data
We constrain the amplitude of primordial non-Gaussianity in the CMB data
taking into account the presence of foreground residuals in the maps. We
generalise the needlet bispectrum estimator marginalizing over the amplitudes
of thermal dust, free-free and synchrotron templates. We apply our procedure to
WMAP 5 year data, finding fNL= 38\pm 47 (1 \sigma), while the analysis without
marginalization provides fNL= 35\pm 42. Splitting the marginalization over each
foreground separately, we found that the estimates of fNL are positively cross
correlated of 17%, 12% with the dust and synchrotron respectively, while a
negative cross correlation of about -10% is found for the free-free component.Comment: Submitted to MNRA
Map-making in small field modulated CMB polarisation experiments: approximating the maximum-likelihood method
Map-making presents a significant computational challenge to the next
generation of kilopixel CMB polarisation experiments. Years worth of time
ordered data (TOD) from thousands of detectors will need to be compressed into
maps of the T, Q and U Stokes parameters. Fundamental to the science goal of
these experiments, the observation of B-modes, is the ability to control noise
and systematics. In this paper, we consider an alternative to the
maximum-likelihood method, called destriping, where the noise is modelled as a
set of discrete offset functions and then subtracted from the time-stream. We
compare our destriping code (Descart: the DEStriping CARTographer) to a full
maximum-likelihood map-maker, applying them to 200 Monte-Carlo simulations of
time-ordered data from a ground based, partial-sky polarisation modulation
experiment. In these simulations, the noise is dominated by either detector or
atmospheric 1/f noise. Using prior information of the power spectrum of this
noise, we produce destriped maps of T, Q and U which are negligibly different
from optimal. The method does not filter the signal or bias the E or B-mode
power spectra. Depending on the length of the destriping baseline, the method
delivers between 5 and 22 times improvement in computation time over the
maximum-likelihood algorithm. We find that, for the specific case of single
detector maps, it is essential to destripe the atmospheric 1/f in order to
detect B-modes, even though the Q and U signals are modulated by a half-wave
plate spinning at 5-Hz.Comment: 18 pages, 17 figures, MNRAS accepted v2: content added (inc: table
2), typos correcte
Probing polarization states of primordial gravitational waves with CMB anisotropies
We discuss the polarization signature of primordial gravitational waves
imprinted in cosmic microwave background (CMB) anisotropies. The high-energy
physics motivated by superstring theory or M-theory generically yield parity
violating terms, which may produce a circularly polarized gravitational wave
background (GWB) during inflation. In contrast to the standard prediction of
inflation with un-polarized GWB, circularly polarized GWB generates
non-vanishing TB and EB-mode power spectra of CMB anisotropies. We evaluate the
TB and EB-mode power spectra taking into account the secondary effects and
investigate the dependence of cosmological parameters. We then discuss current
constraints on the circularly polarized GWB from large angular scales (l < 16)
of the three year WMAP data. Prospects for future CMB experiments are also
investigated based on a Monte Carlo analysis of parameter estimation, showing
that the circular polarization degree, varepsilon, which is the asymmetry of
the tensor power spectra between right- and left-handed modes normalized by the
total amplitude, can be measured down to |varepsilon| 0.35(r/0.05)^{-0.6}.Comment: 28 pages, 9 figures, Accepted for publication in JCA
The Rise of Cohabitation in the Southern Cone
This chapter analyses the increase in cohabitation in the Southern Cone (Argentina, Chile and Uruguay) and attempts to determine the extent to which consensual unions and marriages have similar traits or differ in the context of the cohabitation boom (Esteve et al. 2012). The first section of the chapter reviews the historical context of cohabitation in the Southern Cone. The second section uses census and survey data to analyse the trends in conjugal union formation in the three countries during the last 40 years. We analyse the patterns of both childbearing and union formation, as well as the differences between marriage and cohabitation based on educational attainment, labour market participation and household structure. The purpose of this analysis is to better understand whether the behaviour of married and cohabiting women with different characteristics are converging or diverging over time and tentatively, whether more egalitarian gender relationships are emerging in both types of conjugal unions
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