477 research outputs found
Laser Shock Microforming of Thin Metal Sheets
Continuous and long-pulse lasers have been used for the forming of metal sheets in macroscopic mechanical applications. However, for the manufacturing of micro-electromechanical systems (MEMS), the applicability of such type of lasers is limited by the long-relaxation-time of the thermal fields responsible for the forming phenomena. As a consequence of such slow relaxation, the final sheet deformation state is attained only after a certain time, what makes the generated internal residual stress fields more dependent on ambient conditions and might make difficult the subsequent assembly process from the point of view of residual stresses due to adjustment. The use of ns laser pulses provides a suitable parameter matching for the laser forming of an important range of sheet components used in MEMS that, preserving the short interaction time scale required for the predominantly mechanic (shock) induction of deformation residual stresses, allows for the successful processing of components in a medium range of miniaturization, particularly important according to its frequent use in such systems. In the present paper, a discussion is presented on the physics of laser shock microforming and the influence of the different effects on the net bending angle. The experimental setup used for the experiments, sample fabrication and experimental results of influence of number of laser pulses on the net bending angle are also presented
Laser Shock Microformingof Thin Metal Sheets with ns Lasers
Continuous and long-pulse lasers have been used for the forming of metal sheets in macroscopic mechanical applications. However, for the manufacturing of micro-electromechanical systems (MEMS), the use of ns laser pulses provides a suitable parameter matching over an important range of sheet components that, preserving the short interaction time scale required for the predominantly mechanical (shock) induction of deformation residual stresses, allows for the successful processing of components in a medium range of miniaturization without appreciable thermal deformation.. In the present paper, the physics of laser shock microforming and the influence of the different experimental parameters on the net bending angle are presented
Hecke algebras of finite type are cellular
Let \cH be the one-parameter Hecke algebra associated to a finite Weyl
group , defined over a ground ring in which ``bad'' primes for are
invertible. Using deep properties of the Kazhdan--Lusztig basis of \cH and
Lusztig's \ba-function, we show that \cH has a natural cellular structure
in the sense of Graham and Lehrer. Thus, we obtain a general theory of ``Specht
modules'' for Hecke algebras of finite type. Previously, a general cellular
structure was only known to exist in types and .Comment: 14 pages; added reference
Observation of the Smectic C -- Smectic I Critical Point
We report the first observation of the smectic C--smectic I (C--I) critical
point by Xray diffraction studies on a binary system. This is in confirmity
with the theoretical idea of Nelson and Halperin that coupling to the molecular
tilt should induce hexatic order even in the C phase and as such both C and I
(a tilted hexatic phase) should have the same symmetry. The results provide
evidence in support of the recent theory of Defontaines and Prost proposing a
new universality class for critical points in layered systems.Comment: 9 pages Latex and 5 postscript figures available from
[email protected] on request, Phys.Rev.Lett. (in press
Experimental determination of the eutectic temperature in air of the CuO-TiO2 pseudobinary system
Eutectic temperature and composition in the CuO–TiO2 pseudobinary system have been experimentally determined in air by means differential thermal analysis (DTA), thermogravimetry (TG) and hot-stage microscopy (HSM). Samples of the new eutectic composition treated at different temperatures have been characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structural spectroscopy (XANES) to identify phases and to determine the Cu valence state, respectively. The results show that the eutectic temperature in air is higher by 100 °C (∼1000 °C) for a Ti-richer composition (XTiO2=25 mol%) than the one calculated in the literature. The reduction of Cu2+ to Cu+ takes places at about 1030 °C. The existence of Cu2TiO3 and Cu3TiO4 has been confirmed by XRD in the temperature range between 1045 and 1200 °C
Photoemission and x-ray absorption spectroscopy study of electron-doped colossal magnetoresistance manganite: La0.7Ce0.3MnO3 film
The electronic structure of La0.7Ce0.3MnO3 (LCeMO) thin film has been
investigated using photoemission spectroscopy (PES) and x-ray absorption
spectroscopy (XAS). The Ce 3d core-level PES and XAS spectra of LCeMO are very
similar to those of CeO2, indicating that Ce ions are far from being trivalent.
A very weak 4f resonance is observed around the Ce 4d 4f absorption edge,
suggesting that the localized Ce 4f states are almost empty in the ground
state. The Mn 2p XAS spectrum reveals the existence of the Mn(2+) multiplet
feature, confirming the Mn(2+)-Mn(3+) mixed-valent states of Mn ions in LCeMO.
The measured Mn 3d PES/XAS spectra for LCeMO agrees reasonably well with the
calculated Mn 3d PDOS using the LSDA+U method. The LSDA+U calculation predicts
a half-metallic ground state for LCeMO.Comment: 7 pages, 7 figure
Effects and Detectability of Quasi-Single Field Inflation in the Large-Scale Structure and Cosmic Microwave Background
Quasi-single field inflation predicts a peculiar momentum dependence in the
squeezed limit of the primordial bispectrum which smoothly interpolates between
the local and equilateral models. This dependence is directly related to the
mass of the isocurvatons in the theory which is determined by the
supersymmetry. Therefore, in the event of detection of a non-zero primordial
bispectrum, additional constraints on the parameter controlling the
momentum-dependence in the squeezed limit becomes an important question. We
explore the effects of these non-Gaussian initial conditions on large-scale
structure and the cosmic microwave background, with particular attention to the
galaxy power spectrum at large scales and scale-dependence corrections to
galaxy bias. We determine the simultaneous constraints on the two parameters
describing the QSF bispectrum that we can expect from upcoming large-scale
structure and cosmic microwave background observations. We find that for
relatively large values of the non-Gaussian amplitude parameters, but still
well within current uncertainties, galaxy power spectrum measurements will be
able to distinguish the QSF scenario from the predictions of the local model. A
CMB likelihood analysis, as well as Fisher matrix analysis, shows that there is
also a range of parameter values for which Planck data may be able distinguish
between QSF models and the related local and equilateral shapes. Given the
different observational weightings of the CMB and LSS results, degeneracies can
be significantly reduced in a joint analysis.Comment: 27 pages, 14 figure
SRAO CO Observation of 11 Supernova Remnants in l = 70 to 190 deg
We present the results of 12CO J = 1-0 line observations of eleven Galactic
supernova remnants (SNRs) obtained using the Seoul Radio Astronomy Observatory
(SRAO) 6-m radio telescope. The observation was made as a part of the SRAO CO
survey of SNRs between l = 70 and 190 deg, which is intended to identify SNRs
interacting with molecular clouds. The mapping areas for the individual SNRs
are determined to cover their full extent in the radio continuum. We used
halfbeam grid spacing (60") for 9 SNRs and full-beam grid spacing (120") for
the rest. We detected CO emission towards most of the remnants. In six SNRs,
molecular clouds showed a good spatial relation with their radio morphology,
although no direct evidence for the interaction was detected. Two SNRs are
particularly interesting: G85.4+0.7, where there is a filamentary molecular
cloud along the radio shell, and 3C434.1, where a large molecular cloud appears
to block the western half of the remnant. We briefly summarize the results
obtained for individual SNRs.Comment: Accepted for publication in Astrophysics & Space Science. 12 pages,
12 figures, and 3 table
Electric current circuits in astrophysics
Cosmic magnetic structures have in common that they are anchored
in a dynamo, that an external driver converts kinetic energy into internal
magnetic energy, that this magnetic energy is transported as Poynting fl ux across the magnetically dominated structure, and that the magnetic energy
is released in the form of particle acceleration, heating, bulk motion,
MHD waves, and radiation. The investigation of the electric current system is
particularly illuminating as to the course of events and the physics involved.
We demonstrate this for the radio pulsar wind, the solar flare, and terrestrial
magnetic storms
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