Ion-induced nucleation in polar one-component fluids

We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase of polar one-component fluids, where a liquid droplet grows with an ion at its center. By calculating the density profile around an ion, we show that the solvation free energy is larger in gas than in liquid at the same temperature on the coexistence curve. This difference much reduces the nucleation barrier in a metastable gas.Comment: 9 pagers, 9 figures, to be published in J. Chem. Phy

Resolved stellar populations: watching galaxy evolution in real time

One of the main issues in astrophysics is to understand how galaxies form and evolve. Deep photometric studies help the investigation of the evolution of resolved stellar contents of nearby systems. Hence the properties of these regions represent an archaeological record of the processes that shape a galaxy over cosmic time. So one can interpret from the star formation history the evolution of the star formation rate throughout the galaxy and the evolution of the mass and metallicity distributions. The system that has been studied in this project is the nearby galaxy M33, located in the Local Group. The photometric data was taken in the Canada-France-Hawaii Telescope with the MegaPrime/MegaCam wide-field mosaic imager and it is available for the filters g’, r’ and i’. The data analysis is presented in this work with the purpose of recovering its star formation history. Over one million point sources were identified in each filter. The program chosen for this process is DAOPHOT (Stetson, 1987). PSF-fitting photometry was performed using a few hundreds of point sources, selected from non-crowed areas, to fit the point-spread functions. This process, however, was repeated a couple of times in order to get a well adjusted point-spread function with the least residuals possible. The instrumental magnitude was then determined. A selection cut enabled spurious sources to be discarded based on the photometric errors (σ), residuals scatter (Χ²) and image quality (sharpness). Aperture and offset corrections were applied in the magnitudes before the transformation to the standard photometric system. A completeness test to examine the effects of crowding in the images was conducted in each photometric filter. The bias in the observed magnitudes and in the stellar counts due to high stellar density affects the final star formation history, resulting in the miss-assumption of the stellar age, metallicity and initial mass function. The artificial stars test (Williams et al., 2009) is a standard technique used to that end and consists of inserting synthetic stars in the images, with the routine ADDSTAR (Stetson, 1987), and performing again the photometric reductions in those synthetic images to compare the known inserted brightness with the recovered ones. The completeness is given by the ratio of the number of retrieved artificial stars over the number of added ones. Stars of all evolutionary stages lose mass and the mass recycled in the interstellar medium will be part of the next generation of stars and planets. The study of mass loss is quite well understood for metal-rich stars populating the asymptotic giant branch, though there is still a lot to be understood about the metal-poor stars losing mass during the red giant phase. The understanding of the mass loss process that happens in red giant stars of globular clusters might help us to better estimate the post-main sequence stellar evolutionary stages and the intra-cluster gas enrichment. Since the 70’s it has been known that the Galactic globular cluster ω Centauri shows an extremely complex stellar chemistry, with a wide variation in metallicity, [Fe/H] ≈ -2 to [Fe/H] ≈ -0.6, and light elements (like He, C, N...). Indeed, the properties of ω Cen favours the hypothesis that this is a remnant of a dwarf galaxy orbiting the Milky Way and tidal interactions partially disrupted it. With observations from the Infra-Red Array Camera aboard of the Spitzer telescope, investigations on red giant stars in ω Centauri are carried out to identify infrared colour excess originating from the emission of a circumstellar envelope surrounding the stars (e.g. Frogel & Elias, 1988; Origlia et al., 1996). This study is based on a proper combination of ground-based and original Spitzer photometric data as well as results from previous spectroscopic surveys. Prior to the selection of the dust excess stars, the magnitudes from the SDSS photometric system are converted to the TCS system based on the colour relations of Carpenter (2001) and Alonso et al. (1998) as the colour-temperature equations used to calculate the effective temperature are in different photometric filter systems. Bolometric corrections and the effective temperature are needed for comparisons between observations and theory and both parameters were derived according to Alonso et al. (1999). After selection, 34 giant stars presented colour excess in (K - 8) with metallicities ranging from -1.9 < [Fe=H] < -0.7; metallicities that were interpolated from PARSEC isochrones (Bressan et al., 2012). Field stars were rejected based on the proper motions from GAIA, which reduced to 18 the number of mass-losing candidates. The large amount of field stars excluded from the sample is due to the difference in spatial coverage from GAIA and Spitzer. The stellar synthetic spectral distribution of those stars is modelled and used to calculate its mass loss rate, using a modified version (Origlia et al., 2007) of the radiative transfer code DUSTY (Ivezic et al., 1999; Elitzur & Ivezic, 2001). The mass loss rates derived from our sample are in the range of 10⁻⁸ to 10⁻⁷ M yr⁻¹, which is slightly off the values proposed by Origlia et al. (2002) and Boyer et al. (2008). The mass loss rates seem to increase with increasing luminosities and its dependency with metallicity is minimal. Only a fraction of red giant stars are losing mass indicating an episodic mass loss

Semiconductor effective charges from tight-binding theory

We calculate the transverse effective charges of zincblende compound semiconductors using Harrison's tight-binding model to describe the electronic structure. Our results, which are essentially exact within the model, are found to be in much better agreement with experiment than previous perturbation-theory estimates. Efforts to improve the results by using more sophisticated variants of the tight-binding model were actually less successful. The results underline the importance of including quantities that are sensitive to the electronic wavefunctions, such as the effective charges, in the fitting of tight-binding models.Comment: 4 pages, two-column style with 2 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#jb_t

CubeHarmonic: A new interface from a magnetic 3D motion tracking system to music performance

We developed a new musical interface, CubeHarmonic, with the magnetic 3D motion tracking system IM3D. This sys- tem precisely tracks positions of tiny, wireless, battery-less, and identifiable markers (LC coils) in real time. The Cube- Harmonic is a musical application of the Rubik’s cube, with notes on each little piece. Scrambling the cube, we get dif- ferent chords and chord sequences. Positions of the pieces which contain LC coils are detected through IM3D, and transmitted to the computer to recognize the status of the Rubik’s cube, that plays sounds. The central position of the cube is also measured by the LC coils located into the corners of Rubik’s cube, and, depending on the position, we can manipulate overall loudness and pitch changes, as in theremin playing. This new instrument, whose first idea comes from mathematical theory of music, can be used as a teaching tool both for math (group theory) and music (music theory, mathematical music theory), as well as a composition device, a new instrument for avant-garde per- formances, and a recreational tool

Entorhinal–hippocampal neuronal circuits bridge temporally discontiguous events

The entorhinal cortex (EC)–hippocampal (HPC) network plays an essential role for episodic memory, which preserves spatial and temporal information about the occurrence of past events. Although there has been significant progress toward understanding the neural circuits underlying the spatial dimension of episodic memory, the relevant circuits subserving the temporal dimension are just beginning to be understood. In this review, we examine the evidence concerning the role of the EC in associating events separated by time—or temporal associative learning—with emphasis on the function of persistent activity in the medial entorhinal cortex layer III (MECIII) and their direct inputs into the CA1 region of HPC. We also discuss the unique role of Island cells in the medial entorhinal cortex layer II (MECII), which is a newly discovered direct feedforward inhibitory circuit to CA1. Finally, we relate the function of these entorhinal cortical circuits to recent findings concerning hippocampal time cells, which may collectively activate in sequence to bridge temporal gaps between discontiguous events in an episode.RIKEN Brain Science InstituteHoward Hughes Medical InstituteJPB Foundatio

Single scalar top production with polarized beams in ep collisions at HERA

From the point of view of the R-parity breaking supersymmetric model, we propose a scalar top (stop) search with longitudinally polarized electron (e-) and positron(e+) beams which will soon be available at the upgraded HERA. Fully polarized e- or e+ beams could produce the stop two times as much as unpolarized beams, while they increase background events due to the process of the standard model by about 30% in comparison with unpolarized ones. We show that right-handed e+ beams at HERA is efficient to produce the stop in the model. With 1 fb**(-1) of integrated luminosity we estimate reach in the coupling constant lambda'(131) for masses of the stop in the range 160-400 GeV. We can set a 95% confidence-level exclusion limit for lambda'(131) > 0.01-0.05 in the stop mass range of 240-280 GeV if no singal of the stop is observed. We also point out that y(=Q**2/sx) distributions of e+ coming from the stop shows the different behavior from those of the standard model.Comment: 12 pages, 6 eps figure

Considerações biológicas e econômicas sobre um sistema de produção silvo-agrícola rotativo na região do Tapajós.

bitstream/item/31918/1/CPATU-BP50.pd

Integrated Land Use-Transport Model System with Dynamic Time-Dependent Activity-Travel Microsimulation

The development of integrated land use-transport model systems has long been of interest because of the complex interrelationships between land use, transport demand, and network supply. This paper describes the design and prototype implementation of an integrated model system that involves the microsimulation of location choices in the land use domain, activity-travel choices in the travel demand domain, and individual vehicles on networks in the network supply modeling domain. Although many previous applications of integrated transport demand-supply models have relied on a sequential coupling of the models, the system presented in this paper involves a dynamic integration of the activity-travel demand model and the dynamic traffic assignment and simulation model with appropriate feedback to the land use model system. The system has been fully implemented, and initial results of model system runs in a case study test application suggest that the proposed model design provides a robust behavioral framework for simulation of human activity-travel behavior in space, time, and networks. The paper provides a detailed description of the design, together with results from initial test runs

On the Selection of Photometric Planetary Transits

We present a new method for differentiating between planetary transits and eclipsing binaries based on the presence of the ellipsoidal light variations. These variations can be used to detect stellar secondaries with masses ~0.2 M_sun orbiting sun-like stars at a photometric accuracy level which has already been achieved in transit surveys. By removing candidates exhibiting this effect it is possible to greatly reduce the number of objects requiring spectroscopic follow up with large telescopes. Unlike the usual candidate selection method, which are primarily based on the estimated radius of the orbiting object, this technique is not biased against bona-fide planets and brown dwarfs with large radii, because the amplitude of the effect depends on the transiting object's mass and orbital distance. In many binary systems, where a candidate planetary transit is actually due to the partial eclipse of two normal stars, the presence of flux variations due to the gravity darkening effect will show the true nature of these systems. We show that many of the recent OGLE-III photometric transit candidates exhibit the presence of significant variations in their light curves and are likely to be due to stellar secondaries. We find that the light curves of white dwarf transits will generally not mimic those of small planets because of significant gravitationally induced flux variations. We discuss the relative merits of methods used to detect transit candidates which are due to stellar blends rather than planets. We outline how photometric observations taken in two bands can be used to detect the presence of stellar blends.Comment: ApJ, 11 pages, 2 figures, 1 table, replaced with accepted versio

Polymerisable octahedral rhenium cluster complexes as precursors for photo/electroluminescent polymers

New polymerisable photoluminescent octahedral rhenium cluster complexes trans-[{Re₆Q₈}(TBP)₄VB)₂] (Q = S or Se; TBP – p-tert-butylpyridine; VB – vinyl benzoate) have been synthesised, characterised and used to construct rhe-nium cluster-organic polymer hybrid materials. These novel polymer systems are solution-processable and the rhenium clusters retain their photoluminescent properties within the polymer environment. Notably, when the rhenium cluster complexes are incorporated into the matrix of the electroluminescent polymer poly(N-vinylcarbazole), the resultant cluster polymer hybrid combined properties of both components and was used successfully in the construc-tion of a polymer light emitting diode (PLED). These prototype devices are the first PLEDs to incorporate octahedral rhenium clusters and provide the first direct evidence of the electroluminescent properties of rhenium clusters and indeed, to the best of our knowledge, of any member of the family of 24-electron hexanuclear cluster complexes of molybdenum, tungsten or rhenium