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The Influence of Natural Convection and Radiation Heat Transfer on Sintering of Polycarbonate Powders
The influence ofsurface radiation and natural convection on sintering of
polycarbonate powders processed under non-isothermal conditions is investigated. These
modes of heat transfer affect local powder temperatures and thus local sintering rates which
in turn influence part growth (uncontrolled sintering). This paper presents a 2-dimensional
sintering simulation of powder whose free surface exchanges energy with the surrounding
enclosure surfaces. Modeling is accomplished using a commercial finite element code
(FIDAP) in conjunction with a model for viscous sintering.Mechanical Engineerin
HD101584: Circumstellar characteristics and evolutionary status
We have performed a study of the characteristics of the circumstellar
environment of the binary object HD101584, that provides information on a
likely evolutionary scenario. We have obtained and analysed ALMA observations,
complemented with observations using APEX, of a large number of molecular
lines. An analysis of the spectral energy distribution has also been performed.
Emissions from 12 molecular species (not counting isotopologues) have been
observed, and most of them mapped with angular resolutions in the range 0.1" to
0.6". Four circumstellar components are identified: i) a central compact source
of size 0.15", ii) an expanding equatorial density enhancement (a flattened
density distribution in the plane of the orbit) of size 3", iii) a bipolar
high-velocity outflow (150 km/s), and iv) an hourglass structure. The outflow
is directed almost along the line of sight. There is evidence of a second
bipolar outflow. The mass of the circumstellar gas is 0.5[D/1 kpc]^2 Msun,
about half of it lies in the equatorial density enhancement. The dust mass is
0.01[D/1 kpc]^2 Msun, and a substantial fraction of this is in the form of
large-sized, up to 1 mm, grains. The estimated kinetic age of the outflow is
770[D/1 kpc] yr. The kinetic energy and the scalar momentum of the accelerated
gas are estimated to be 7x10^(45)[D/1 kpc]^2 erg and 10^(39)[D/1 kpc]^2 g cm/s,
respectively. We provide good evidence that the binary system HD101584 is in a
post-common-envelope-evolution phase, that ended before a stellar merger.
Isotope ratios combined with stellar mass estimates suggest that the primary
star's evolution was terminated already on the first red giant branch (RGB).
Most of the energy required to drive the outflowing gas was probably released
when material fell towards the companion.Comment: Accepted for publication in A&
ELVIS - ELectromagnetic Vector Information Sensor
The ELVIS instrument was recently proposed by the authors for the Indian
Chandrayaan-1 mission to the Moon and is presently under consideration by the
Indian Space Research Organisation (ISRO). The scientific objective of ELVIS is
to explore the electromagnetic environment of the moon. ELVIS samples the full
three-dimensional (3D) electric field vector, E(x,t), up to 18 MHz, with
selective Nyqvist frequency bandwidths down to 5 kHz, and one component of the
magnetic field vector, B(x,t), from a few Hz up to 100 kHz.As a transient
detector, ELVIS is capable of detecting pulses with a minimum pulse width of 5
ns. The instrument comprises three orthogonal electric dipole antennas, one
magnetic search coil antenna and a four-channel digital sampling system,
utilising flexible digital down conversion and filtering together with
state-of-the-art onboard digital signal processing.Comment: 8 pages, 3 figures. Submitted to the DGLR Int. Symposium "To Moon and
Beyond", Bremen, Germany, 2005. Companion paper to arXiv:astro-ph/050921
Prospects for Lunar Satellite Detection of Radio Pulses from Ultrahigh Energy Neutrinos Interacting with the Moon
The Moon provides a huge effective detector volume for ultrahigh energy
cosmic neutrinos, which generate coherent radio pulses in the lunar surface
layer due to the Askaryan effect. In light of presently considered lunar
missions, we propose radio measurements from a Moon-orbiting satellite. First
systematic Monte Carlo simulations demonstrate the detectability of Askaryan
pulses from neutrinos with energies above 10^{20} eV, i.e. near and above the
interesting GZK limit, at the very low fluxes predicted in different scenarios.Comment: RevTeX (4 pages, 2 figures). v2 includes updated results and extended
discussio
Transport through a disordered topological-metal strip
Features of a topological phase, and edge states in particular, may be obscured by overlapping in energy with a trivial conduction band. The topological nature of such a conductor, however, is revealed in its transport properties, especially in the presence of disorder. In this work, we explore the conductance behavior of such a system with disorder present, and contrast it with the quantized conductance in an ideal two-dimensional topological insulator. Our analysis relies on numerics on a lattice system and analytics on a simple toy model. Interestingly, we find that as disorder is increased from zero, the edge conductivity initially falls from its quantized value; yet, as disorder continues to increase, the conductivity recovers, and saturates at a value slightly below the quantized value of the clean system. We discuss how this effect can be understood from the tendency of the bulk states to localize, while the edge states remain delocalized
Statistical properties of ionospheric stimulated electromagnetic emissions
We have analysed the statistical properties of the stimulated electromagnetic emissions (SEE) spectral features in the steady state, reached after a long period of continuous HF pumping of the ionosphere in experiments performed at the Sura ionospheric radio research facility in Russia. Using a digital filter bank method, we have been able to analyse complex valued signals within narrow frequency bands. Each of the SEE spectral features are thereby separated into a number of narrow spectral components. Statistical tests were performed for all these spectral components and the distributions of the spectral amplitudes and phases were evaluated. Also, a test for sinusoidal components was performed. These tests showed that all observed SEE features were indistinguishable from coloured Gaussian noise. The test results exclude that the SEE features can be the result of a single isolated coherent process, but does not rule out that there could be many statistically independent parametric wave-wave processes taking place simultaneously at various parts of the HF-pumped ionosphere, as long as the superposition from all these is incoherent. Furthermore, from the test results, we cannot exclude the possibility that the waveforms of some, or all, of the SEE features may be chaotic
Effects of Disorder in a Dilute Bose Gas
We discuss the effects of a weak random external potential on the properties
of the dilute Bose gas at zero temperature. The results recently obtained by
Huang and Meng for the depletion of the condensate and of the superfluid
density are recovered. Results for the shift of the velocity of sound as well
as for its damping due to collisions with the external field are presented. The
damping of phonons is calculated also for dense superfluids. (submitted to
Phys.Rev.B)Comment: 21 pages, Plain Tex, 2 figures available upon request, preprint UTF
31
All-fibre source of amplitude-squeezed light pulses
An all-fibre source of amplitude squeezed solitons utilizing the self-phase
modulation in an asymmetric Sagnac interferometer is experimentally
demonstrated. The asymmetry of the interferometer is passively controlled by an
integrated fibre coupler, allowing for the optimisation of the noise reduction.
We have carefully studied the dependence of the amplitude noise on the
asymmetry and the power launched into the Sagnac interferometer. Qualitatively,
we find good agreement between the experimental results, a semi-classical
theory and earlier numerical calculations [Schmitt etl.al., PRL Vol. 81,
p.2446, (1998)]. The stability and flexibility of this all-fibre source makes
it particularly well suited to applications in quantum information science
Consideration of soil temperature in the modelling of early-age mass concrete slab
Modeling the structural behavior of concrete at early ages is one of the most
challenging, yet fundamental, tasks for civil engineers working on mass concrete. To obtain
a reasonably accurate model, a number of factors should be taken into account. Considerations
should include both external influences as well as the changes occurring in the complex
structure itself. The modeling of an early-age concrete massive slab requires the proper
assignment of initial conditions, including the initial temperature of the analyzed element and
the adjacent structures. The temperature distribution in the subsoil is the factor analyzed in this
paper. The aim of the study is the determination of the temperature distribution in the ground,
which is useful in the process related to the acquisition of the most accurate model of the
analyzed structure and reflects the actual conditions in the numerical model. For this purpose,
the analytical method described in the literature was applied and subsequently evaluated on the
basis of the numerical calculation. The performed calculations allow the estimation of the
depth representing the range of the influence of the temperature in the ground and the values of
the temperatures corresponding to the successive layers of the subsoil. Moreover, aiming the
optimization of the numerical analysis of the massive foundation slab, the legitimacy of such
detailed consideration of the temperature development in the underlying subsoil was evaluated
by the comparison with the temperature distribution in the slab obtained with simplified
consideration of the constant soil temperature.The publication is financed by BKM-547/RB6/2018 resources. Funding provided by the Portuguese
Foundation for Science and Technology (FCT) to the Research Project IntegraCrete PTDC/ECM EST/1056/2014 (POCI-01-0145-FEDER-016841), as well to the Research Unit ISISE (POCI-01-
0145-FEDER-007633) is also gratefully acknowledged
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