127 research outputs found
Reply to ``Comment on `Insulating Behavior of -DNA on the Micron Scale' "
In our experiment, we found that the resistance of vacuum-dried -DNA
exceeds at 295 K. Bechhoefer and Sen have raised a number of
objections to our conclusion. We provide counter arguments to support our
original conclusion.Comment: 1 page reply to comment, 1 figur
Kramers-Kronig, Bode, and the meaning of zero
The implications of causality, as captured by the Kramers-Kronig relations
between the real and imaginary parts of a linear response function, are
familiar parts of the physics curriculum. In 1937, Bode derived a similar
relation between the magnitude (response gain) and phase. Although the
Kramers-Kronig relations are an equality, Bode's relation is effectively an
inequality. This perhaps-surprising difference is explained using elementary
examples and ultimately traces back to delays in the flow of information within
the system formed by the physical object and measurement apparatus.Comment: 8 pages; American Journal of Physics, to appea
Secondary Instabilities of Surface Waves on Viscous Fluids in the Faraday Instability
Secondary instabilities of Faraday waves show three regimes: (1) As seen
previously, low-viscosity (nu) fluids destabilize first into squares. At higher
driving accelerations a, squares show low-frequency modulations corresponding
to the motion of phase defects, while theory predicts a stationary transverse
amplitude modulation (TAM). (2) High-nu fluids destabilize first to stripes.
Stripes then show an oscillatory TAM whose frequency is incommensurate with the
driving frequency. At higher a, the TAM undergoes a phase instability. At still
higher a, edge dislocations form and fluid droplets are ejected. (3)
Intermediate-nu fluids show a complex coexistence of squares and stripes, as
well as stationary and oscillatory TAM instabilities of the stripes.Comment: REVTEX, with 3 separate uuencoded figures, to appear in Europhys.
Let
Enhancement of Gear Fault Detection Using Narrowband Interference Cancellation
The development of enhanced fault detection ability for gearbox systems has received considerable attention in recent years. Detecting the gear fault easier is very important for maintenance action. This has driven the need in research for enhanced gear fault detection method. The goal is to extract periodic impulse signal from the very noise signal which mainly contains the narrowband signals. This can be done by enhancing the impulsive signals while suppressing the narrowband signals. This paper used a new method, Narrowband Interference Cancellation, to detect the gear fault. This method reserves the impulsive signal produced by gear fault and removes the other signals out. The methodology is demonstrated on a gearbox run-to-failure test. The results show that Narrowband Interference Cancellation can enable the gear fault detection easier
Arbitrarily slow, non-quasistatic, isothermal transformations
For an overdamped colloidal particle diffusing in a fluid in a controllable,
virtual potential, we show that arbitrarily slow transformations, produced by
smooth deformations of a double-well potential, need not be reversible. The
arbitrarily slow transformations do need to be fast compared to the barrier
crossing time, but that time can be extremely long. We consider two types of
cyclic, isothermal transformations of a double-well potential. Both start and
end in the same equilibrium state, and both use the same basic operations---but
in different order. By measuring the work for finite cycle times and
extrapolating to infinite times, we found that one transformation required no
work, while the other required a finite amount of work, no matter how slowly it
was carried out. The difference traces back to the observation that when time
is reversed, the two protocols have different outcomes, when carried out
arbitrarily slowly. A recently derived formula relating work production to the
relative entropy of forward and backward path probabilities predicts the
observed work average.Comment: 6 pages, 6 figure
Diffusion-limited loop formation of semiflexible polymers: Kramers theory and the intertwined time scales of chain relaxation and closing
We show that Kramers rate theory gives a straightforward, accurate estimate
of the closing time of a semiflexible polymer that is valid in cases
of physical interest. The calculation also reveals how the time scales of chain
relaxation and closing are intertwined, illuminating an apparent conflict
between two ways of calculating in the flexible limit.Comment: Europhys. Lett., 2003 (in press). 8 pages, 3 figures. See also,
physics/0101087 for physicist's approach to and the importance of
semiflexible polymer looping, in DNA replicatio
Formation of disclination lines near a free nematic interface
We have studied the nucleation and the physical properties of a -1/2 wedge
disclination line near the free surface of a confined nematic liquid crystal.
The position of the disclination line has been related to the material
parameters (elastic constants, anchoring energy and favored anchoring angle of
the molecules at the free surface). The use of a planar model for the structure
of the director field (whose predictions have been contrasted to those of a
fully three-dimensional model) has allowed us to relate the experimentally
observed position of the disclination line to the relevant properties of the
liquid crystals. In particular, we have been able to observe the collapse of
the disclination line due to a temperature-induced anchoring angle transition,
which has allowed us to rule out the presence of a real disclination line near
the nematic/isotropic front in directional growth experiments.
61.30.Jf,61.30.G
Theory and computation of directional nematic phase ordering
A computational study of morphological instabilities of a two-dimensional
nematic front under directional growth was performed using a Landau-de Gennes
type quadrupolar tensor order parameter model for the first-order
isotropic/nematic transition of 5CB (pentyl-cyanobiphenyl). A previously
derived energy balance, taking anisotropy into account, was utilized to account
for latent heat and an imposed morphological gradient in the time-dependent
model. Simulations were performed using an initially homeotropic
isotropic/nematic interface. Thermal instabilities in both the linear and
non-linear regimes were observed and compared to past experimental and
theoretical observations. A sharp-interface model for the study of linear
morphological instabilities, taking into account additional complexity
resulting from liquid crystalline order, was derived. Results from the
sharp-interface model were compared to those from full two-dimensional
simulation identifying the specific limitations of simplified sharp-interface
models for this liquid crystal system. In the nonlinear regime, secondary
instabilities were observed to result in the formation of defects, interfacial
heterogeneities, and bulk texture dynamics.Comment: first revisio
Non-isothermal model for the direct isotropic/smectic-A liquid crystalline transition
An extension to a high-order model for the direct isotropic/smectic-A liquid
crystalline phase transition was derived to take into account thermal effects
including anisotropic thermal diffusion and latent heat of phase-ordering.
Multi-scale multi-transport simulations of the non-isothermal model were
compared to isothermal simulation, showing that the presented model extension
corrects the standard Landau-de Gennes prediction from constant growth to
diffusion-limited growth, under shallow quench/undercooling conditions.
Non-isothermal simulations, where meta-stable nematic pre-ordering precedes
smectic-A growth, were also conducted and novel non-monotonic
phase-transformation kinetics observed.Comment: First revision: 20 pages, 7 figure
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