154,781 research outputs found
Multiple H-Rearrangements in 10-Benzylthio-dithranol Radical Cations
10-Alkylthio- and 10-arylthio-derivatives of dithranol (anthralin;
1,8-dihydroxy-9-anthrone) are of interest in search for new anti-psoriatic
agents2 , 3 ). By working out ms procedures for unequivocal identification of
trace amounts of these compounds4 ) it was established that in case of
10-phenylthio-dithranol putative by-products, especially one giving rise to
ions at m/z = 226 (dithranol), are artefacts of thermal reaction in the mass
spectrometer1). In the EI-MS of those 10-substituted dithranols containing
a S-CH2R chain, however, these ions (m/z = 226) arise from M + * as well.
Scope and mechanism of their formation was examined by analyzing
compound 1 and its D-labelled derivatives 2 and 3
Calibrating dipolar interaction in an atomic condensate
We revisit the topic of a dipolar condensate with the recently derived more
rigorous pseudo-potential for dipole-dipole interaction [A. Derevianko, Phys.
Rev. A {\bf 67}, 033607 (2003)]. Based on the highly successful variational
technique, we find that all dipolar effects estimated before (using the bare
dipole-dipole interaction) become significantly larger, i.e. are amplified by
the new velocity-dependent pseudo-potential, especially in the limit of large
or small trap aspect ratios. This result points to a promising prospect for
detecting dipolar effects inside an atomic condensate.Comment: 5 figures, to be publishe
Fluidization of granular media wetted by liquid He
We explore experimentally the fluidization of vertically agitated PMMA
spheres wetted by liquid He. By controlling the temperature around the
point we change the properties of the wetting liquid from a normal
fluid (helium I) to a superfluid (helium II). For wetting by helium I, the
critical acceleration for fluidization () shows a steep increase
close to the saturation of the vapor pressure in the sample cell. For helium II
wetting, starts to increase at about 75% saturation, indicating that
capillary bridges are enhanced by the superflow of unsaturated helium film.
Above saturation, enters a plateau regime where the capillary force
between particles is independent of the bridge volume. The plateau value is
found to vary with temperature and shows a peak at 2.1 K, which we attribute to
the influence of the specific heat of liquid helium.Comment: 4 pages, 3 figures, Accepted by Phys. Rev. E as a rapid communicatio
GRB afterglows: deep Newtonian phase and its application
Gamma-ray burst afterglows have been observed for months or even years in a
few cases. It deserves noting that at such late stages, the remnants should
have entered the deep Newtonian phase, during which the majority of
shock-accelerated electrons will no longer be highly relativistic. To calculate
the afterglows, we must assume that the electrons obey a power-law distribution
according to their kinetic energy, not simply the Lorentz factor.Comment: Poster at the 4th workshop "Gamma-Ray Bursts in the Afterglow Era"
(Rome, 2004), accepted for publication in the proceedings. 4 pages, with 3
figures inserte
Stress-Induced Delamination Of Through Silicon Via Structures
Continuous scaling of on-chip wiring structures has brought significant challenges for materials and processes beyond the 32 nm technology node in microelectronics. Recently three-dimensional (3-D) integration with through-silicon-vias (TSVs) has emerged as an effective solution to meet the future interconnect requirement. Thermo-mechanical reliability is a key concern for the development of TSV structures used in die stacking as 3-D interconnects. This paper examines the effect of thermal stresses on interfacial reliability of TSV structures. First, the three-dimensional distribution of the thermal stress near the TSV and the wafer surface is analyzed. Using a linear superposition method, a semi-analytic solution is developed for a simplified structure consisting of a single TSV embedded in a silicon (Si) wafer. The solution is verified for relatively thick wafers by comparing to numerical results obtained by finite element analysis (FEA). Results from the stress analysis suggest interfacial delamination as a potential failure mechanism for the TSV structure. Analytical solutions for various TSV designs are then obtained for the steady-state energy release rate as an upper bound for the interfacial fracture driving force, while the effect of crack length is evaluated numerically by FEA. Based on these results, the effects of TSV designs and via material properties on the interfacial reliability are elucidated. Finally, potential failure mechanisms for TSV pop-up due to interfacial fracture are discussed.Aerospace Engineerin
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