Monica Pozzo - Academia.edu (original) (raw)

Papers by Monica Pozzo

Scientific Reports

In this work, the melting line of calcium has been characterized both experimentally, using synch... more In this work, the melting line of calcium has been characterized both experimentally, using synchrotron X-ray diffraction in laser-heated diamond-anvil cells, and theoretically, using first-principles calculations. In the investigated pressure and temperature range (pressure between 10 and 40 GPa and temperature between 300 and 3000 K) it was possible to observe the face-centred phase of calcium and to confirm (and characterize for the first time at these conditions) the presence of the body-centred cubic and the simple cubic phase of calcium. The melting points obtained with the two techniques are in excellent agreement. Furthermore, the present results agree with the only existing melting line of calcium obtained in laser-heated diamond anvil cells, using the speckle method as melting detection technique. They also confirm a flat slope of the melting line in the pressure range between 10 and 30 GPa. The flat melting curve is associated with the presence of the solid high-temperatu...

Nature Geoscience, 2015

The Earth's magnetic field is powered from energy supplied by slow cooling and freezing of the li... more The Earth's magnetic field is powered from energy supplied by slow cooling and freezing of the liquid iron core. Core thermal history calculations have been hindered in the past by poor knowledge of the properties of iron alloys at the extreme pressures and temperatures pertaining in the core. This obstacle is now being overcome by developments in high pressure experiments and computational mineral physics. Here we review the relevant properties of iron alloys at core conditions and discuss their uncertainty and geophysical implications. Powerful constraints on core evolution are now possible, due partly to recent factor 2-3 upward revision of the all-important electrical and thermal conductivities. This has dramatic implications for the thermal history of the entire Earth, not just the core: the inner core is very young, the core is cooling quickly, and was so hot in the past that the lowermost mantle

Physical Review Letters, 2009

By combining high-resolution photoelectron spectroscopy and ab initio calculations, we show that ... more By combining high-resolution photoelectron spectroscopy and ab initio calculations, we show that carbon nanoislands formed during the growth of a long-range ordered graphene layer on Ir(111) assume a peculiar domelike shape. The understanding of the unusual growth mechanism of these C clusters, which represent an intermediate phase between the strongly coupled carbidic carbon and a quasi-free-standing graphene layer, can provide information for a rational design of graphenelike systems at the nanoscale.

The catalogues have been created using the optimal photometry algorithm described in Naylor (1998... more The catalogues have been created using the optimal photometry algorithm described in Naylor (1998MNRAS.296..339N) and Naylor et al. (2002MNRAS.335..291N, this paper). Further information is also available from Tim Naylor&amp;amp;#39;s optimal photometry page ( http://www.astro.ex.ac.uk/people/timn/Photometry/description.html ). The catalogues are primarily in what is called cluster format, though there are occasional variations where they are needed. There is a deep survey (Table

... Authors: Pozzo, M.; Naylor, T.; Jeffries, RD; Drew, JE. ... The UBVI CCD images were taken on... more ... Authors: Pozzo, M.; Naylor, T.; Jeffries, RD; Drew, JE. ... The UBVI CCD images were taken on the nights of 1997 August 10/11 and 11/12, with the 2.5-m Isaac Newton Telescope (INT), La Palma, Canary Islands, Spain, equipped with the Wide Field Camera (WFC) and an array of ...

ABSTRACT A photometric survey of an area around gamma Vel was performed at the Cerro Tololo Inter... more ABSTRACT A photometric survey of an area around gamma Vel was performed at the Cerro Tololo Interamerican Observatory (CTIO) 0.9-m telescope. The survey was done in two parts in different years, but using the same instrumentation and filters, namely a Tek 2048x2048 CCD with a 13.5x13.5 arcmin2 field of view, the Harris B and V filters and a Kron-Cousins I filter. The first set of observations, described in Pozzo et al. (2000MNRAS.313L..23P), consisted of eight overlapping fields surveyed on the night beginning 1999 February 8. The second set of observations consisted of 20 fields which were surveyed on the nights beginning 2002 February 8, 10 and 11. (4 data files).

Monthly Notices of the Royal Astronomical Society, 2002

We have developed the techniques required to use the optimal photometry algorithm of Naylor (1998... more We have developed the techniques required to use the optimal photometry algorithm of Naylor (1998) to create colour-magnitude diagrams with well defined completeness functions. To achieve this we first demonstrate that the optimal extraction is insensitive to uncertainties in the star's measured position. We then show how to correct the optimally extracted fluxes such that they correspond to those measured in a large aperture, so aperture photometry of standard stars can be used to place the measurements on a standard system. The technique simultaneously removes the effects of a position dependent point-spread function. Finally we develop a method called "ghosting", which calculates the completeness corrections in the absence of an accurate description of the point spread function.

Monthly Notices of the Royal Astronomical Society, 2000

We report the serendipitous discovery of a population of low mass, pre-main sequence stars (PMS) ... more We report the serendipitous discovery of a population of low mass, pre-main sequence stars (PMS) in the direction of the Wolf-Rayet/O-star binary system γ 2 Vel and the Vela OB2 association. We argue that γ 2 Vel and the low mass stars are truly associated, are approximately coeval and that both are at distances between 360-490 pc, disagreeing at the 2σ level with the recent Hipparcos parallax of γ 2 Vel, but consistent with older distance estimates. Our results clearly have implications for the physical parameters of the γ 2 Vel system, but also offer an exciting opportunity to investigate the influence of high mass stars on the mass function and circumstellar disc lifetimes of their lower mass PMS siblings.

Monthly Notices of the Royal Astronomical Society, 2003

We report the discovery of a low-mass pre-main-sequence (PMS) stellar population in the younger s... more We report the discovery of a low-mass pre-main-sequence (PMS) stellar population in the younger subgroup of the Cepheus OB3 association, Cep OB3b, using UBVI CCD photometry and follow-up spectroscopy. The optical survey covers about 1300 square arcmin on the sky and gives a global photometric and astrometric catalogue for more than 7000 objects. The location of a PMS is well defined in a V versus (V-I) colour-magnitude diagram (CMD).

SpringerPlus, 2016

We report on the temperature dependence of the electrical resistivity of solid iron at high press... more We report on the temperature dependence of the electrical resistivity of solid iron at high pressure, up to and including conditions likely to be found at the centre of the Earth. We have extended some of the calculations of the resistivities of pure solid iron we recently performed at Earth's core conditions (Pozzo et al. in Earth Planet Sci Lett 393:159-164, 2014) to lower temperature. We show that at low temperature the resistivity increases linearly with temperature, and saturates at high temperature. This saturation effect is well known as the Mott-Ioffe-Regel limit in metals, but has been largely ignored to estimate the resistivity of iron at Earth's core conditions. Recent experiments (Gomi et al. in Phys Earth Planet Int 224:88-103, 2013) coupled new high pressure data and saturation to predict the resitivity of iron and iron alloys at Earth's core conditions, and reported values up to three times lower than previous estimates, confirming recent first principles calculations (de Koker et al. in Proc Natl Acad Sci 109:4070-4073, 2012; Pozzo et al. in Nature 485:355-358, 2012, Phys Rev B 87:014110-10, 2013, Earth Planet Sci Lett 393:159-164, 2014; Davies et al. in Nat Geosci 8:678-685, 2015). The present results support the saturation effect idea.

Physical Review B 87 Article 014110, Jan 22, 2013

We report on the thermal and electrical conductivities of two liquid silicon-oxygen-iron mixtures... more We report on the thermal and electrical conductivities of two liquid silicon-oxygen-iron mixtures (Fe0.82Si0.10O0.08 and Fe0.79Si0.08O0.13), representative of the composition of the Earth's outer core at the relevant pressure-temperature conditions, obtained from density functional theory calculations with the Kubo-Greenwood formulation. We find thermal conductivities k =100 (160) W m −1 K −1 , and electrical conductivities σ = 1.1(1.3) × 10 6 Ω −1 m −1 at the top (bottom) of the outer core.

Journal of the American Chemical Society, 2016

The atomistic understanding of the dissociation mechanisms for large molecules adsorbed on surfac... more The atomistic understanding of the dissociation mechanisms for large molecules adsorbed on surfaces is still a challenge in heterogeneous catalysis. This is especially true for polycyclic aromatic hydrocarbons, which represent an important class of organic compounds used to produce novel graphene-based architectures. Here, we show that coronene molecules adsorbed on Ir(111) undergo major conformational changes during dissociation. They first tilt upward with respect to the surface, still keeping their planar configuration, and subsequently experience a rotation, which changes the molecular axis orientation. Upon lifting, the internal C-C strain is initially relieved; as the dehydrogenation proceeds, the molecules experience a progressive increase in the average interatomic distance and gradually settle to form dome-shaped nanographene flakes. Our results provide important insight into the complex mechanism of molecular breakup, which could have implications in the synthesis of new carbon-based nanostructured materials.