8,089 research outputs found
On the unsteady behavior of turbulence models
Periodically forced turbulence is used as a test case to evaluate the
predictions of two-equation and multiple-scale turbulence models in unsteady
flows. The limitations of the two-equation model are shown to originate in the
basic assumption of spectral equilibrium. A multiple-scale model based on a
picture of stepwise energy cascade overcomes some of these limitations, but the
absence of nonlocal interactions proves to lead to poor predictions of the time
variation of the dissipation rate. A new multiple-scale model that includes
nonlocal interactions is proposed and shown to reproduce the main features of
the frequency response correctly
Off-Shell Electromagnetic Form Fators of the Nucleon in Chiral Perturbation Theory
We study the electromagnetic form factors of a nucleon in next-to-leading
order chiral perturbation theory (CPT) in the case where one of the nucleons is
off its mass shell. We calculate the leading nonanalytic contributions to
relevant measures for the off-shell dependence in the limited kinematical range
allowed.Comment: 3 pages LaTeX with worldsci.sty (available by mailing
[email protected] and typing "get worldsci.sty" in the subject line),
invited talk given at the International Symposium on Medium Energy Physics,
Beijing, August 199
Origin of Lagrangian Intermittency in Drift-Wave Turbulence
The Lagrangian velocity statistics of dissipative drift-wave turbulence are
investigated. For large values of the adiabaticity (or small collisionality),
the probability density function of the Lagrangian acceleration shows
exponential tails, as opposed to the stretched exponential or algebraic tails,
generally observed for the highly intermittent acceleration of Navier-Stokes
turbulence. This exponential distribution is shown to be a robust feature
independent of the Reynolds number. For small adiabaticity, algebraic tails are
observed, suggesting the strong influence of point-vortex-like dynamics on the
acceleration. A causal connection is found between the shape of the probability
density function and the autocorrelation of the norm of the acceleration
Ferromagnetism below 10 K in Mn doped BiTe
Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This
material has the BiTe structure, which is made from the stacking of two
Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure
analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an
equal amount of TeBi anti-site occupancy in the Bi2Te3 blocks. These TeBi
anti-site defects greatly enhance the Mn solubility. This is demonstrated by
comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the
solubility is limited to x = 0.067, while the latter has xmax = 0.125. The
magnetism in [Bi1-xMnx]Te changes little with x, while that for
[Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x >
0.067. Magnetic hysteresis and the anomalous Hall Effect are observed for the
ferromagnetic samples.Comment: Accepted for publication in Phys. Rev.
Persistence of the valence bond glass state in the double perovskites Ba2-xSrxYMoO6
Peer reviewedPublisher PD
Determination of buffer capacity by means of an ISFET-based coulometric sensor-actuator system with a gate-covering porous actuator
In this paper we propose a dynamic way to measure the buffer capacity of an electrolyte by means of an ISFET-based coulometric sensor-actuator system whose gate is covered with a porous actuator. A theoterical model for this measurement is presented. Experiments are carried out in nitric and acetic acid as well as in phosphoric acid solutions. A fairly good agreement has been found between the theoretical calculations and the experimental results
Spectral imbalance and the normalized dissipation rate of turbulence
The normalized turbulent dissipation rate is studied in decaying
and forced turbulence by direct numerical simulations, large-eddy simulations,
and closure calculations. A large difference in the values of is
observed for the two types of turbulence. This difference is found at moderate
Reynolds number, and it is shown that it persists at high Reynolds number,
where the value of becomes independent of the Reynolds number, but
is still not unique. This difference can be explained by the influence of the
nonlinear cascade time that introduces a spectral disequilibrium for
statistically nonstationary turbulence. Phenomenological analysis yields simple
analytical models that satisfactorily reproduce the numerical results. These
simple spectral models also reproduce and explain the increase of
at low Reynolds number that is observed in the simulations
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iPosture: The Size of Electronic Consumer Devices Affects our Behavior
We examined whether incidental body posture, prompted by working on electronic devices of different sizes, affects power-related behaviors. Grounded in research showing that adopting expansive body postures increases psychological power, we hypothesized that working on larger devices, which forces people to physically expand, causes users to behave more assertively. Participants were randomly assigned to interact with one of four electronic devices that varied in size: an iPod Touch, an iPad, a MacBook Pro (laptop computer), or an iMac (desktop computer). As hypothesized, compared to participants working on larger devices (e.g., an iMac), participants who worked on smaller devices (e.g., an iPad) behaved less assertively – waiting longer to interrupt an experimenter who had made them wait, or not interrupting at all
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