New Internal Stress Driven on-Chip Micromachines for Extracting Mechanical Properties of Thin Films

A new concept of micromachines has been developed for measuring the mechanical properties of thin metallic films. The actuator is a beam undergoing large internal stresses built up during the deposition process. Al thin films are deposited partly on the actuator beam and on the substrate. By etching the structure, the actuator contracts and pulls the Al film. Full stress strain curves can be generated by designing a set of micromachines with various actuator lengths. In the present study, the displacements have been measured by scanning electronic microscopy. The stress is derived from simple continuum mechanics relationships. The tensile properties of Al films of various thicknesses have been tested. A marked increase of the strength with decreasing film thickness is observed.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Renormalization Group Improved Optimized Perturbation Theory: Revisiting the Mass Gap of the O(2N) Gross-Neveu Model

We introduce an extension of a variationally optimized perturbation method, by combining it with renormalization group properties in a straightforward (perturbative) form. This leads to a very transparent and efficient procedure, with a clear improvement of the non-perturbative results with respect to previous similar variational approaches. This is illustrated here by deriving optimized results for the mass gap of the O(2N) Gross-Neveu model, compared with the exactly know results for arbitrary N. At large N, the exact result is reproduced already at the very first order of the modified perturbation using this procedure. For arbitrary values of N, using the original perturbative information only known at two-loop order, we obtain a controllable percent accuracy or less, for any N value, as compared with the exactly known result for the mass gap from the thermodynamical Bethe Ansatz. The procedure is very general and can be extended straightforwardly to any renormalizable Lagrangian model, being systematically improvable provided that a knowledge of enough perturbative orders of the relevant quantities is available.Comment: 18 pages, 1 figure, v2: Eq. (4.5) corrected, comments adde

Hard parton damping in hot QCD

The gluon and quark collisional widths in hot QCD plasmas are discussed with emphasis on temperatures near Tc, where the coupling is large. Considering the effect on the entropy, which is known from lattice calculations, it is argued that the width of the partons, which in the perturbative limit is given by gamma ~ g^2 ln(1/g) T, should be sizeable at intermediate temperatures but has to be small close to Tc. This behavior implies a substantial reduction of the radiative energy loss of jets near Tc.Comment: invitetd talk given at 'Hot Quarks 04', July 18-24 2004, Taos Valley, NM, US

Visualizing quantum entanglement and the EPR paradox during the photodissociation of a diatomic molecule using two ultrashort laser pulses

We investigate theoretically the dissociative ionization of a H2+ molecule using two ultrashort laser (pump-probe) pulses. The pump pulse prepares a dissociating nuclear wave packet on an ungerade surface of H2+. Next, an UV (or XUV) probe pulse ionizes this dissociating state at large (R = 20 - 100 bohr) internuclear distance. We calculate the momenta distributions of protons and photoelectrons which show a (two-slit-like) interference structure. A general, simple interference formula is obtained which depends on the electron and protons momenta, as well as on the pump-probe delay on the pulses durations and polarizations. This interference can be interpreted as visualization of an electron state delocalized over the two-centres. This state is an entangled state of a hydrogen atom with a momentum p and a proton with an opposite momentum. -p dissociating on the ungerade surface of H2+. This pump-probe scheme can be used to reveal the nonlocality of the electron which intuitively should be localized on just one of the protons separated by the distance R much larger than the atomic Bohr orbit

The immediate environment of the Class 0 protostar VLA1623, on scales of ~50-100 AU, observed at millimetre and centimetre wavelengths

We present high angular resolution observations, taken with the Very Large Array (VLA) and Multiple Element Radio Linked Interferometer Network (MERLIN) radio telescopes, at 7mm and 4.4cm respectively, of the prototype Class 0 protostar VLA1623. At 7mm we detect two sources (VLA1623A & B) coincident with the two previously detected components at the centre of this system. The separation between the two is 1.2arcsec, or ~170AU at an assumed distance of 139pc. The upper limit to the size of the source coincident with each component of VLA1623 is ~0.7arcsec, in agreement with previous findings. This corresponds to a diameter of ~100AU at an assumed distance of 139pc. Both components show the same general trend in their broadband continuum spectra, of a steeper dust continuum spectrum shortward of 7mm and a flatter spectrum longward of this. We estimate an upper limit to the VLA1623A disc mass of <0.13Msol and an upper limit to its radius of ~50AU. The longer wavelength data have a spectral index of \alpha~0.6+/-0.3. This is too steep to be explained by optically thin free-free emission. It is most likely due to optically thick free-free emission. Alternatively, we speculate that it might be due to the formation of larger grains or planetesimals in the circumstellar disc. We estimate the mass of VLA1623B to be <0.15M$sol. We can place a lower limit to its size of ~30x7 AU, and an upper limit to its diameter of ~100AU. The longer wavelength data of VLA1623B also have a spectral index of \alpha~0.6+/-0.3. The nature of VLA1623B remains a matter of debate. It could be a binary companion to the protostar, or a knot in the radio jet from VLA1623A.Comment: 7 pages, 3 figures, 1 table, accepted for publication in MNRA

Recent advances on IMF research

Here I discuss recent work on brown dwarfs, massive stars and the IMF in general. The stellar IMF can be well described by an invariant two-part power law in present-day star-formation events within the Local Group of galaxies. It is nearly identical in shape to the pre-stellar core mass function. The majority of brown dwarfs follow a separate IMF. Evidence from globular clusters and ultra-compact dwarf galaxies has emerged that IMFs may have been top heavy depending on the star-formation rate density. The IGIMF then ranges from bottom heavy at low galaxy-wide star formation rates to being top-heavy in galaxy-scale star bursts.Comment: 6 pages, LaTeX, to appear in The Labyrinth of Star Formation, 18-22 June 2012, Crete, (eds.) D. Stamatellos, S. Goodwin, and D. Ward-Thompson, Springer, in press; replaced version: very minor corrections plus the addition of reference Smith & Lucey (2013) on the bottom-heavy IMF in elliptical galaxie