7,162 research outputs found
Structural relaxation in a system of dumbbell molecules
The interaction-site-density-fluctuation correlators, the dipole-relaxation
functions, and the mean-squared displacements of a system of symmetric
dumbbells of fused hard spheres are calculated for two representative
elongations of the molecules within the mode-coupling theory for the evolution
of glassy dynamics. For large elongations, universal relaxation laws for states
near the glass transition are valid for parameters and time intervals similar
to the ones found for the hard-sphere system. Rotation-translation coupling
leads to an enlarged crossover interval for the mean-squared displacement of
the constituent atoms between the end of the von Schweidler regime and the
beginning of the diffusion process. For small elongations, the superposition
principle for the reorientational -process is violated for parameters
and time intervals of interest for data analysis, and there is a strong
breaking of the coupling of the -relaxation scale for the diffusion
process with that for representative density fluctuations and for dipole
reorientations.Comment: 15 pages, 14 figures, Phys. Rev. E in pres
Structural relaxation in a supercooled molecular liquid
We perform molecular-dynamics simulations of a molecular system in
supercooled states for different values of inertia parameters to provide
evidence that the long-time dynamics depends only on the equilibrium structure.
This observation is consistent with the prediction of the mode-coupling theory
for the glass transition and with the hypothesis that the potential
energy-landscape controls the slow dynamics. We also find that dynamical
properties at intermediate wavenumber depend on the spatial correlation of the
molecule's geometrical center.Comment: 7 pages, 4 figures, Europhys. Lett. in pres
Emission Optics of the Steigerwald Type Electron Gun
The emission optics of a Steigerwald type electron gun is re-examined. The
virtual and real points of divergence, divergence angles and beam-widths of the
electron beams at different telefocusing strength are measured in detail for
first time . Two different Wehnelt cylinders are used to establish a
contrasting viewpoint. The original `focusing' curves measured by Braucks are
reconstructed and will be explained only through a `new' interpretation which
is different from the conventional views. While the image of the emitting
surface in front of the filament is indeed telefocused beyond the anode, the
envelope of the beam does not `focus' as expected. A new model for the emission
mechanism is established based on our results.Comment: 14 pages, 10 figure
Pulse generation without gain-bandwidth limitation in a laser with self-similar evolution
With existing techniques for mode-locking, the bandwidth of ultrashort pulses from a laser is determined primarily by the spectrum of the gain medium. Lasers with self-similar evolution of the pulse in the gain medium can tolerate strong spectral breathing, which is stabilized by nonlinear attraction to the parabolic self-similar pulse. Here we show that this property can be exploited in a fiber laser to eliminate the gain-bandwidth limitation to the pulse duration. Broad (Ì200 nm) spectra are generated through passive nonlinear propagation in a normal-dispersion laser, and these can be dechirped to Ì20-fs duration
Characterization of carbon nanotubes synthesized from hydrocarbon-rich flame
The present study focuses on the characterization of carbon nanotubes (CNTs) synthesized from flame under an atmospheric condition. A laminar flame burner was utilized to establish a rich premixed propane/air flame at the equivalence ratio Ί = 1.8-2.2. The flame was impinged on a stainless steel wire mesh coated with nickel (Ni) catalyst to grow CNTs. Distribution and yield of the CNTs on the substrate were quantified. Carbon nanotubes formed on the substrate were harvested and characterized using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and thermogravimetric analysis (TGA). The FESEM micrograph showed that the CNTs produced were in disarray. The synthesized CNTs were an average of 50-60 nm in diameter while the length of the tubes was in the order of microns. TGA analysis showed that 75% of CNTs were present in the sample and the oxidation temperature was 510°C
A mode-coupling theory for the glassy dynamics of a diatomic probe molecule immersed in a simple liquid
Generalizing the mode-coupling theory for ideal liquid-glass transitions,
equations of motion are derived for the correlation functions describing the
glassy dynamics of a diatomic probe molecule immersed in a simple glass-forming
system. The molecule is described in the interaction-site representation and
the equations are solved for a dumbbell molecule consisting of two fused hard
spheres in a hard-sphere system. The results for the molecule's arrested
position in the glass state and the reorientational correlators for
angular-momentum index and near the glass transition are
compared with those obtained previously within a theory based on a
tensor-density description of the molecule in order to demonstrate that the two
approaches yield equivalent results. For strongly hindered reorientational
motion, the dipole-relaxation spectra for the -process can be mapped on
the dielectric-loss spectra of glycerol if a rescaling is performed according
to a suggestion by Dixon et al. [Phys. Rev. Lett. {\bf 65}, 1108 (1990)]. It is
demonstrated that the glassy dynamics is independent of the molecule's inertia
parameters.Comment: 19 pages, 10 figures, Phys. Rev. E, in prin
Multiscale Technicolor and the Zbb-bar Vertex
We estimate the correction to the Zbb-bar vertex arising from the exchanges
of the sideways extended technicolor (ETC) boson and the flavor-diagonal ETC
boson in the multiscale walking technicolor model. The obtained result is too
large to explain the present data. However, if we introduce a new self-
interaction for the top quark to induce the top quark condensate serving as the
origin of the large top quark mass, the corrected R_b=Gamma_b/Gamma_h can be
consistent with the recent LEP data. The corresponding correction to
R_c=Gamma_c/Gamma_h is shown to be negligibly small.Comment: 9-page LaTex fil
Behavioral Factors in Strategic Alliances
Recently, there has been a growing trend among information technology (IT) organizations to form strategic alliances to increase competitive advantages in the marketplace. For an organization to exploit the benefits of alliances, human factors and IT factors must be among the basic components of any strategic plan (Kemeny & Yanowitz, 2000). Despite the obvious need to consider human and IT factors when developing a long-term plan, many strategic plans developed in the past that led to alliances have failed to consider human aspects. Examples of failure in the implementation of IT systems due to the lack of consideration of human factors have come to light in recent years, but a comprehensive study of the consideration of human factors in the development of strategic alliances resulting in a major IT system alignment for a firm, is still rare in IT literature
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