6,671 research outputs found
Emergence of stability in a stochastically driven pendulum: beyond the Kapitsa effect
We consider a prototypical nonlinear system which can be stabilized by
multiplicative noise: an underdamped non-linear pendulum with a stochastically
vibrating pivot. A numerical solution of the pertinent Fokker-Planck equation
shows that the upper equilibrium point of the pendulum can become stable even
when the noise is white, and the "Kapitsa pendulum" effect is not at work. The
stabilization occurs in a strong-noise regime where WKB approximation does not
hold.Comment: 4 pages, 7 figure
Ising Deconfinement Transition Between Feshbach-Resonant Superfluids
We investigate the phase diagram of bosons interacting via Feshbach-resonant
pairing interactions in a one-dimensional lattice. Using large scale density
matrix renormalization group (DMRG) and field theory techniques we explore the
atomic and molecular correlations in this low-dimensional setting. We provide
compelling evidence for an Ising deconfinement transition occurring between
distinct superfluids and extract the Ising order parameter and correlation
length of this unusual superfluid transition. This is supported by results for
the entanglement entropy which reveal both the location of the transition and
critical Ising degrees of freedom on the phase boundary.Comment: 4 pages, 4 figure
Use of a mass spectrometer to determine the composition of the undisturbed Martian atmosphere from a hypersonic entry vehicle Final report
Mass spectrometer aboard hypersonic entry vehicle for chemical composition study of Martian atmospher
JWalk: a tool for lazy, systematic testing of java classes by design introspection and user interaction
Popular software testing tools, such as JUnit, allow frequent retesting of modified code; yet the manually created test scripts are often seriously incomplete. A unit-testing tool called JWalk has therefore been developed to address the need for systematic unit testing within the context of agile methods. The tool operates directly on the compiled code for Java classes and uses a new lazy method for inducing the changing design of a class on the fly. This is achieved partly through introspection, using Java’s reflection capability, and partly through interaction with the user, constructing and saving test oracles on the fly. Predictive rules reduce the number of oracle values that must be confirmed by the tester. Without human intervention, JWalk performs bounded exhaustive exploration of the class’s method protocols and may be directed to explore the space of algebraic constructions, or the intended design state-space of the tested class. With some human interaction, JWalk performs up to the equivalent of fully automated state-based testing, from a specification that was acquired incrementally
Characterization of a CCD array for Bragg spectroscopy
The average pixel distance as well as the relative orientation of an array of
6 CCD detectors have been measured with accuracies of about 0.5 nm and 50
rad, respectively. Such a precision satisfies the needs of modern crystal
spectroscopy experiments in the field of exotic atoms and highly charged ions.
Two different measurements have been performed by illuminating masks in front
of the detector array by remote sources of radiation. In one case, an aluminum
mask was irradiated with X-rays and in a second attempt, a nanometric quartz
wafer was illuminated by a light bulb. Both methods gave consistent results
with a smaller error for the optical method. In addition, the thermal expansion
of the CCD detectors was characterized between -105 C and -40 C.Comment: Submitted to Review of Scientific Instrument
Particle dynamics of a cartoon dune
The spatio-temporal evolution of a downsized model for a desert dune is
observed experimentally in a narrow water flow channel. A particle tracking
method reveals that the migration speed of the model dune is one order of
magnitude smaller than that of individual grains. In particular, the erosion
rate consists of comparable contributions from creeping (low energy) and
saltating (high energy) particles. The saltation flow rate is slightly larger,
whereas the number of saltating particles is one order of magnitude lower than
that of the creeping ones. The velocity field of the saltating particles is
comparable to the velocity field of the driving fluid. It can be observed that
the spatial profile of the shear stress reaches its maximum value upstream of
the crest, while its minimum lies at the downstream foot of the dune. The
particle tracking method reveals that the deposition of entrained particles
occurs primarily in the region between these two extrema of the shear stress.
Moreover, it is demonstrated that the initial triangular heap evolves to a
steady state with constant mass, shape, velocity, and packing fraction after
one turnover time has elapsed. Within that time the mean distance between
particles initially in contact reaches a value of approximately one quarter of
the dune basis length
Correlations and fluctuations of a confined electron gas
The grand potential and the response of a phase-coherent confined noninteracting electron gas depend
sensitively on chemical potential or external parameter . We compute
their autocorrelation as a function of , and temperature. The result
is related to the short-time dynamics of the corresponding classical system,
implying in general the absence of a universal regime. Chaotic, diffusive and
integrable motions are investigated, and illustrated numerically. The
autocorrelation of the persistent current of a disordered mesoscopic ring is
also computed.Comment: 12 pages, 1 figure, to appear in Phys. Rev.
Quantitative assessment of cardiac load-responsiveness during extracorporeal life support: case and rationale
We describe a case of a patient assisted by extracorporeal life support, in which we obtained the dynamic filling index, a measure for venous volume during extracorporeal life support, and used this index to assess cardiac load-responsiveness during acute reloading. While reloading, the obtained findings on cardiac pump function by the dynamic filling index were supported by trans-esophageal echocardiography and standard pressure measurement. This suggests that the dynamic filling index can be used to assess cardiac load-responsiveness during extracorporeal life support
A Brownian Motion Model of Parametric Correlations in Ballistic Cavities
A Brownian motion model is proposed to study parametric correlations in the
transmission eigenvalues of open ballistic cavities. We find interesting
universal properties when the eigenvalues are rescaled at the hard edge of the
spectrum. We derive a formula for the power spectrum of the fluctuations of
transport observables as a response to an external adiabatic perturbation. Our
formula correctly recovers the Lorentzian-squared behaviour obtained by
semiclassical approaches for the correlation function of conductance
fluctuations.Comment: 19 pages, written in RevTe
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