2,110 research outputs found
Preferred Embodiment of a Hardware-Assisted Garbage-Collection System
Hardware-assisted garbage collection combines the potential of high average-case allocation rates and memory bandwidth with fast worst-case allocation, fetch, and store times. This paper describes an architecture that allows memory fetch and store operations to execute, on the average, nearly as fast as traditional memory. It describes a feasible implementation of a garbage-collected memory module, but does not provide a thorough discussion of possible design alternatives, nor does it provide rigorous justification for choices between available design alternatives
Capillary-gravity wave resistance in ordinary and magnetic fluids
Wave resistance is the drag force associated to the emission of waves by a
moving disturbance at a fluid free surface. In the case of capillary-gravity
waves it undergoes a transition from zero to a finite value as the speed of the
disturbance is increased. For the first time an experiment is designed in order
to obtain the wave resistance as a function of speed. The effect of viscosity
is explored, and a magnetic fluid is used to extend the available range of
critical speeds. The threshold values are in good agreement with the proposed
theory. Contrary to the theoretical model, however, the measured wave
resistance reveals a non monotonic speed dependence after the threshold.Comment: 12 pages, 4 figures, 1 table, submitted to Physical Review Letter
Electric field inside a "Rossky cavity" in uniformly polarized water
Electric field produced inside a solute by a uniformly polarized liquid is
strongly affected by dipolar polarization of the liquid at the interface. We
show, by numerical simulations, that the electric "cavity" field inside a
hydrated non-polar solute does not follow the predictions of standard Maxwell's
electrostatics of dielectrics. Instead, the field inside the solute tends, with
increasing solute size, to the limit predicted by the Lorentz virtual cavity.
The standard paradigm fails because of its reliance on the surface charge
density at the dielectric interface determined by the boundary conditions of
the Maxwell dielectric. The interface of a polar liquid instead carries a
preferential in-plane orientation of the surface dipoles thus producing
virtually no surface charge. The resulting boundary conditions for
electrostatic problems differ from the traditional recipes, affecting the
microscopic and macroscopic fields based on them. We show that relatively small
differences in cavity fields propagate into significant differences in the
dielectric constant of an ideal mixture. The slope of the dielectric increment
of the mixture versus the solute concentration depends strongly on which
polarization scenario at the interface is realized. A much steeper slope found
in the case of Lorentz polarization also implies a higher free energy penalty
for polarizing such mixtures.Comment: 9 pages, 8 figure
Stratified shear flow instabilities at large Richardson numbers
Numerical simulations of stratified shear flow instabilities are performed in
two dimensions in the Boussinesq limit. The density variation length scale is
chosen to be four times smaller than the velocity variation length scale so
that Holmboe or Kelvin-Helmholtz unstable modes are present depending on the
choice of the global Richardson number Ri. Three different values of Ri were
examined Ri =0.2, 2, 20. The flows for the three examined values are all
unstable due to different modes namely: the Kelvin-Helmholtz mode for Ri=0.2,
the first Holmboe mode for Ri=2, and the second Holmboe mode for Ri=20 that has
been discovered recently and it is the first time that it is examined in the
non-linear stage. It is found that the amplitude of the velocity perturbation
of the second Holmboe mode at the non-linear stage is smaller but comparable to
first Holmboe mode. The increase of the potential energy however due to the
second Holmboe modes is greater than that of the first mode. The
Kelvin-Helmholtz mode is larger by two orders of magnitude in kinetic energy
than the Holmboe modes and about ten times larger in potential energy than the
Holmboe modes. The results in this paper suggest that although mixing is
suppressed at large Richardson numbers it is not negligible, and turbulent
mixing processes in strongly stratified environments can not be excluded.Comment: Submitted to Physics of Fluid
Onset of Wave Drag due to Generation of Capillary-Gravity Waves by a Moving Object as a Critical Phenomenon
The onset of the {\em wave resistance}, via generation of capillary gravity
waves, of a small object moving with velocity , is investigated
experimentally. Due to the existence of a minimum phase velocity for
surface waves, the problem is similar to the generation of rotons in superfluid
helium near their minimum. In both cases waves or rotons are produced at
due to {\em Cherenkov radiation}. We find that the transition to the
wave drag state is continuous: in the vicinity of the bifurcation the wave
resistance force is proportional to for various fluids.Comment: 4 pages, 7 figure
Young Adult Female Cancer Survivors\u27 Concerns About Future Children\u27s Health and Genetic Risk
Stretching Instability of Helical Spring
We show that when a gradually increasing tensile force is applied to the ends
of a helical spring with sufficiently large ratios of radius to pitch and twist
to bending rigidity, the end-to-end distance undergoes a sequence of
discontinuous stretching transitions. Subsequent decrease of the force leads to
step-like contraction and hysteresis is observed. For finite helices, the
number of these transitions increases with the number of helical turns but only
one stretching and one contraction instability survive in the limit of an
infinite helix. We calculate the critical line that separates the region of
parameters in which the deformation is continuous from that in which stretching
instabilities occur, and propose experimental tests of our predictions.Comment: 5 pages, 4 figure
Crossover between Kelvin-Helmholtz and counter-superflow instabilities in two-component Bose-Einstein condensates
Dynamical instabilities at the interface between two Bose--Einstein
condensates that are moving relative to each other are investigated using
mean-field and Bogoliubov analyses. Kelvin--Helmholtz instability is dominant
when the interface thickness is much smaller than the wavelength of the
unstable interface mode, whereas the counter-superflow instability becomes
dominant in the opposite case. These instabilities emerge not only in an
immiscible system but also in a miscible system where an interface is produced
by external potential. Dynamics caused by these instabilities are numerically
demonstrated in rotating trapped condensates.Comment: 10 pages, 9 figure
Polarizability of conducting sphere-doublets using series of images.
The classical electrostatic problem of two nonintersecting conducting spheres in a uniform incident electric field is considered. Starting from the basic Kelvin’s image principle, the two spheres are replaced with equivalent series of image sources, from which the polarizability is calculated. Explicit expressions for the axial and transversal components of the polarizability dyadic are found by solving the recurrence equations. Efficient numerical evaluation of the different series is also discussed.Peer reviewe
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