16,459 research outputs found
AN INVERSE PROBLEM USING GREEN’S FUNCTIONS AND TFBGF METHOD TO INDENTIFICATE A MOVING HEAT SOURCE IN 3D HEAT CONDUCTION
Moving heat source are present in numerous practical problems in engineering. For example, machining process as the Gas tungsten arc welding (GTAW), laser welding, friction stirwleing process or milding problem. Moving heat source are also present in biological heating as the metabolism or in heat thermal treatment. All these cases, the heat input identification is a complex task and represents an important factor in the process optimization. The aim of this work is to investigate both the temperature field as the heat flux delivered to a piece during a process with moving heat source
Matching LTB and FRW spacetimes through a null hypersurface
Matching of a LTB metric representing dust matter to a background FRW
universe across a null hypersurface is studied. In general, an unrestricted
matching is possible only if the background FRW is flat or open. There is in
general no gravitational impulsive wave present on the null hypersurface which
is shear-free and expanding. Special cases of the vanishing pressure or energy
density on the hypersurface is discussed. In the case of vanishing energy
momentum tensor of the null hypersurface, i.e. in the case of a null boundary,
it turns out that all possible definitions of the Hubble parameter on the null
hypersurface, being those of LTB or that of FRW, are equivalent, and that a
flat FRW can only be joined smoothly to a flat LTB.Comment: 9 page
Experimental determination of multipartite entanglement with incomplete information
Multipartite entanglement is very poorly understood despite all the
theoretical and experimental advances of the last decades. Preparation,
manipulation and identification of this resource is crucial for both practical
and fundamental reasons. However, the difficulty in the practical manipulation
and the complexity of the data generated by measurements on these systems
increase rapidly with the number of parties. Therefore, we would like to
experimentally address the problem of how much information about multipartite
entanglement we can access with incomplete measurements. In particular, it was
shown that some types of pure multipartite entangled states can be witnessed
without measuring the correlations [M. Walter et al., Science 340, 1205 (2013)]
between parties, which is strongly demanding experimentally. We explore this
method using an optical setup that permits the preparation and the complete
tomographic reconstruction of many inequivalent classes of three- and
four-partite entangled states, and compare complete versus incomplete
information. We show that the method is useful in practice, even for non-pure
states or non ideal measurement conditions.Comment: 12 pages, 7 figures. Close to published versio
Chemical abundances for the transiting planet host stars OGLE-TR-10, 56, 111, 113, 132 and TrES-1. Abundances in different galactic populations
We used the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolution
spectra of 6 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111,
113, 132 and TrES-1. The spectra are now used to derive and discuss the
chemical abundances for C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni,
Cu and Zn. Abundances were derived in LTE, using 1-D plane-parallel Kurucz
model atmospheres. For S, Zn and Cu we used a spectral synthesis procedure,
while for the remaining cases the abundances were derived from measurements of
line-equivalent widths. The resulting abundances are compared with those found
for stars in the solar neighborhood. Distances and galactic coordinates are
estimated for the stars. We conclude that besides being particularly
metal-rich, with small possible exceptions OGLE-TR-10, 56, 111, 113, 132 and
TrES-1 are chemically undistinguishable from the field (thin disk) stars
regarding their [X/Fe] abundances. This is particularly relevant for the most
distant of the targets, located at up to ~2 Kpc from the Sun. We also did not
find any correlation between the abundances and the condensation temperature of
the elements, an evidence that strong accretion of planetary-like material,
tentatively connected to planetary migration, did not occur.Comment: Accepted for publication in Astronomy & Astrophysics (June 2006
HEAT CONDUCTION IN MOVING SOLIDS USING GREEN’S FUNCTION
Thermal problems involving moving heat sources occur in various engineering applications, such as welding processes, heat treatment furnaces and other treatments. Typically, in these cases, the precise formulation of the numerical solution due to the high complexity of the heat diffusion governing equation, boundary condition, including convection terms. This work proposes a mathematical analysis, analytical solution, verification using other solutions and comparison with numerical solution of a 1D transient thermal model based on Green’n functions, considering a solid moving at a constant speed along a cartesian coordinated
Extended excitons and compact heliumlike biexcitons in type-II quantum dots.
We have used magneto-photoluminescence measurements to establish that InP/GaAs quantum dots have a type-II band (staggered) alignment. The average excitonic Bohr radius and the binding energy are estimated to be 15 nm and 1.5 meV respectively. When compared to bulk InP, the excitonic binding is weaker due to the repulsive (type-II) potential at the hetero-interface. The measurements are extended to over almost six orders of magnitude of laser excitation powers and to magnetic fields of up to 50 tesla. It is shown that the excitation power can be used to tune the average hole occupancy of the quantum dots, and hence the strength of the electron-hole binding. The diamagnetic shift coe±cient is observed to drastically reduce as the quantum dot ensemble makes a gradual transition from a regime where the emission is from (hydrogen-like) two-particle excitonic states to a regime where the emission from (helium-like) four-particle biexcitonic states also become significant
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